Rapid Photocatalytic Decolorization of Methyl Orange under Visible

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Rapid Photocatalytic Decolorization of Methyl Orange under Visible Light Using VS4/Carbon Powder Nanocomposites Ruquan Cai, Baogang Zhang, Jiaxin Shi, Min Li, and Zhen He ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.7b01137 • Publication Date (Web): 21 Jul 2017 Downloaded from http://pubs.acs.org on July 24, 2017

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ACS Sustainable Chemistry & Engineering

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Rapid Photocatalytic Decolorization of Methyl Orange under Visible Light

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Using VS4/Carbon Powder Nanocomposites

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Ruquan Caia, Baogang Zhanga,*, Jiaxin Shia, Min Lia, Zhen Heb,*

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a

School of Water Resources and Environment, China University of Geosciences Beijing, Key

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Laboratory of Groundwater Circulation and Evolution (China University of Geosciences

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Beijing), Ministry of Education, Beijing 100083, China b

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Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and

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State University, Blacksburg, VA 24061, USA

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10

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Intended for: ACS Sustainable Chemistry & Engineering

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Type of Contribution: Research Article

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*

Corresponding authors. Tel.: +86 10 8232 2281; fax: +86 10 8232 1081. E-mail: [email protected], [email protected] (B. Zhang); [email protected] (Z.

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He).

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Other authors’ mailing addresses,

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Ruquan Cai, [email protected];

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Jiaxin Shi, [email protected];

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Min Li, [email protected].

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Address for Ruquan Cai, Baogang Zhang, Jiaxin Shi and Min Li,

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303# Jiaoyi Building, 29# Xueyuan Road, Haidian District, Beijing, 100083, China.

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Address for Zhen He,

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403 Durham Hall, Blacksburg, VA 24061, USA.

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ACS Paragon Plus Environment


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Abstract

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Photocatalytic decolorization of the dye compounds represents a promising approach for

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textile wastewater treatment and thus, development of new photocatalysts will be of strong

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interest. Herein, a novel photocatalyst based on transition metal chalcogenides Vanadium

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Tetrasulfide (VS4) was prepared via a simple one-step hydrothermal synthesis and the

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synthesized VS4/carbon powder nanocomposites exhibited excellent photocatalytic

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decolorization efficiency under visible light irradiation. Significantly higher methyl orange

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(MO) decolorization rate of 13.4 - 19.8 mg L-1 h-1 was achieved. Reactive species such

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as ·O2−, h+ and e− generated through this photocatalytic process have played the key roles in

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the decolorization with phthalic acid as a product. The optimal catalyst dosage was

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determined to be 1.0 g L-1. The decolorization rate was enhanced with the increase of initial

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MO concentration and an acidic condition favored the degradation. The VS4/carbon powder

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nanocomposites could maintain the MO decolorization efficiency above 90% in four

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consecutive reused cycles. The results of this study have collectively demonstrated a

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promising photocatalyst that encourages further investigation and development for dye

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decolorization in textile wastewater.

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Keywords: Vanadium Tetrasulfide (VS4); Photocatalytic decolorization; Methyl Orange

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(MO); Nanocomposites; Visible light

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Introduction Wastewater generated by the textile industries is known to contain a considerable

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amount of untreated dyes.1 Some dyes are highly toxic, carcinogenic and mutagenic, and can

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be bio-accumulated along the food chain.2,3 Thus, removing dyes before discharging those

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textile wastewaters is critically important to protecting natural water bodies and our

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environment. Dye wastewater can be treated via biochemical and/or physico-chemical

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methods.4 Although biological treatment is usually cost-effective, the treatment efficiency

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and removal rate is generally low, likely due to the recalcitrant characteristics of dye

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compounds to microbial degradation.5 Physico-chemical treatments, such as advanced

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oxidation processes (AOPs),6 are more powerful and faster.7 AOPs are an effective method to remove bio-refractory organics from wastewaters and

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have been applied to treat dye compounds in wastewater.8 In general, there are three major

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types of AOPs applied to treat dye compounds, Fenton (H2O2/Fe2+) processes, Fenton-like

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processes, and photocatalytic processes.9 Fenton processes use chain reactions of H2O2 and

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Fe2+ to generate hydroxyl radicals (·OH) that have a strong oxidizing ability and can break

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down dye compounds. Despite the advantages such as low cost, high dye degradation

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efficiency, and relatively simple operation, Fenton processes have major drawbacks of

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requirement of low pH range, generation of a large amount of iron sludge, and rapid decay of

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catalyst.10 To assist or improve Fenton processes, Fenton-like processes have been developed

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by incorporating UV, O3 and/or photoelectric effects, for example forming a photo-Fenton

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(H2O2/Fe2+/UV) process. The dye degradation efficiency of the photo-Fenton process can be

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increased by the Fe3+ photo-reduction that generates new ·OH and regenerates Fe2+ ions 3



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under UV light, and Fe2+ ions can further react with H2O2.11 Photocatalytic processes use

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light energy to drive chemical reactions via photocatalysis; in this process, O2 is adsorbed on

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the surface of pholocatalysts by accepting electrons, converted to ·O2−, and may later interact

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with H2O to generate ·OH.12,13

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Among the various AOP technologies, semiconductor photocatalysis has emerged as a

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promising technology because of potential energy advantages by using either natural sunlight

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or artificial indoor illumination to drive oxidation.14 Numerous photocatalytic materials have

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been discovered and developed, such as titanium dioxide (TiO2) and zinc oxide (ZnO), tin

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oxide (SnO2), cubic zirconia (ZrO2), cadmium sulfide (CdS) and other oxide sulfide

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semiconductor.15 Despite good decolorization effects, those catalysts have a relatively low

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catalytic efficiency or rate, resulting in the demand for a large amount of catalysts to achieve

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desired results. In addition, some of them can only be used under UV light irradiation, and

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this will affect application prospect of those catalysts. Vanadium ion doping is one of the best

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alternatives to enhance the separation efficiency of electron-hole pairs and the visible

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light-driven photoactivity,16 suggesting that vanadium can function as an essential element in

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photocatalysts. To develop photocatalysts towards practical applications especially under

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visible light irradiation, metal chalcogenides were studied.17 Those materials have been used

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in Li-ion batteries, optics, photocatalysis, energy storage and conversion.18

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Vanadium Tetrasulfide (VS4) is a metal chalcogenide that has received relatively little

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attention from the scientific community. The past research of VS4 focused on its applications

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as an anode material for Li batteries, which can have a high charge capacity after 100 cycles

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(e.g., initial: 1105 mA h g-1; 100 cycles: 954 mA h g-1).18 VS4 has also been studied for 4


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visible-light-driven photocatalytic water splitting with effective hydrogen production.17

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Although VS4 exhibits catalytic abilities for different applications, there have not been any

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studies exploring its photocatalytic decolorization of dyes under visible light. Furthermore,

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the synthesis of pure VS4 has not been clearly demonstrated because of experimental

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difficulties and the existence of nonstoichiometric phases.18 Carbonaceous materials with

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π-electron conjugative structures can be utilized as templates to form hybrids to enhance the

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absorption in the visible spectrum region during VS4 preparation,17-19 while these

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conjunctions and benefits for VS4 have not been fully revealed. In this study, we used a

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simple one-step hydrothermal method to synthesize VS4/carbon powder (VS4/CP)

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nanocomposites, and experimentally investigated the feasibility of the synthesized VS4/CP

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nanocomposites for photocatalytic decolorization of Methyl Orange (MO) under visible light

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irradiation. The key factors that could affect the dyes decolorization including pH, catalyst

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dosage, and dye concentration were systematically investigated.20 To examine the stability of

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the photocatalysts, the VS4/CP nanocomposites photocatalytic decolorization process was

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repeated for at least four consecutive cycles. A scavenger study and detection of reactive

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species generation was performed to determine the photocatalytic decolorization mechanism

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of the developed photocatalyst.

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Methods and Materials

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Synthesis of VS4/CP nanocomposites

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To synthesize the catalyst, 0.448 g of carbon powder was dispersed in 30 mL of 5



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deionized (DI) water using ultrasonic oscillation for about 0.5 h to form a homogenous

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solution. Then, 0.9 g of sodium orthovanadate and 2.5 g of thioacetamide were added

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gradually to the above solution; after continuous stirring for 30 min, the solution was

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transferred to a 50-mL Teflon-lined stainless steel autoclave, heated up to 170 °C for 12 h.

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Once the autoclave was sufficiently cooled, the nanocomposite products were centrifuged (at

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4000 rpm), washed with DI water and ethyl alcohol several times to remove water-soluble

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ions, and then dried in a vacuum drying oven at 60 °C for 6 h. The obtained nanocomposite

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product was black VS4 powder containing 5 wt % carbon.18 Synthesis was also performed in

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the same way with the same kinds and amounts of reagents except the addition of carbon

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powders to prepare vanadium chalcogenide (VSx). Its physical-chemical characteristics and

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photocatalytic performance were also comparatively studied to confirm the function of the

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added carbon powders in the VS4/CP nanocomposites.

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Characterization

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Compositions of the VS4/CP nanocomposites and VSx were analyzed by energy

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dispersive X-ray (EDX) on a JEOL JAX-840 scanning electron microscope (SEM) operating

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at 20 KV (JEOL JAX-840, Hitachi Limited, Japan). Zeta potentials were measured by zeta

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potential instrument (Zetasizer Nano ZS, Malvern, UK). X-ray diffraction (XRD)

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measurements were performed using a Rigaku-D/MAX-PC 2500 X-ray diffractometer with a

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Cu Kα (λ=1.5405 Å) as radiation source operating at 40 Kv and 200 mA

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(Rigaku-D/MAX-PC 2500, Rigaku, Japan). The XRD patterns were analyzed by using Jade 6

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software. The transmission electron microscope (TEM) images were obtained on a JEOL

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TEM system operating at 200kV (JEM-2100, Hitachi Limited, Japan). X-ray photoelectron 6


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spectroscopy (XPS) measurements were carried out using a Kratos XSAM-800 spectrometer

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with an Mg Kα radiator (XSAM-800, Kratos, UK).

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Photocatalytic test

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The photocatalytic performance of the synthesized photocatalysts was examined by the

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photocatalytic decolorization of MO in an aqueous solution. In the experiment, 0.05 g of the

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VS4/CP nanocomposites was added to a 50-mL MO aqueous solution with an initial MO

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concentration of 10 mg L-1 and pH of 5. Prior to irradiation, the suspension was mixed with a

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magnetic stirrer in a dark box for 1 h to obtain the adsorption/desorption equilibration for the

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photocatalysts. The mixing by stir was also continuously applied throughout the

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photocatalytic decolorization process. The solution was irradiated by a 300 W xenon lamp

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(CEL-HXF300E, CEAULIGHT, China) passing through a 420 nm cut-off filter, which was

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used as a visible illuminant of the photocatalytic reaction. A circulating cooling water bath

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was employed to eliminate the thermal effect derived from the light, and the temperature of

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the MO solution was maintained at 25.0 °C. Every 5 min, 4 mL of the solution was collected

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and then filtered using a 0.22 µm millipore membrane to remove the VS4/CP nanocomposites

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particles for MO measurement, and a typical cycle lasted 0.5 h. Photocatalytic tests were also

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conducted with phenol (40 mg·L−1) as the target in 4-h operation with the same initial

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condition as a previous study.21

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Several factors affecting MO decolorization such as pH, catalyst dosage, dye

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concentration and irradiation condition were evaluated for the VS4/CP nanocomposites. The

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pH of the MO solution was adjusted to 3, 5, 7, and 9, respectively, by adding sulphuric acid

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or sodium hydroxide, and monitored by using a pH Meter (S500, METTLER TOLEDO, 7



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USA). The synthesized photocatalysts were also submerged in the target solution under the

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selected pH for 1 h, after which they were used for photocatalytic decolorization with an

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initial MO concentration of 10 mg L-1 and pH of 5 to examine the stability of the developed

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photocatalysts at different pH values. The catalyst dosage was adjusted to 0.5, 1.0, 1.5 and

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2.0 g L-1, respectively. The dye concentration was varied at 5, 10, 15 and 20 mg L-1,

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respectively. Three light sources were used as the irradiation conditions for the VS4/CP

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nanocomposites, namely visible light, UV light, and sunlight (natural light that was directly

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obtained in the sunshine from 1 pm to 4 pm). Visible light (artificial light source) was

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provided by xenon lamp with UV cut-off filter (UVIRCUT420, CEAULIGHT, China) while

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the UV was supplied from xenon lamp by using UV reflection sheet (UVREF, CEAULIGHT,

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China).

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Functional scavenger compounds were added to the MO solution respectively to remove

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the corresponding reactive species during the photocatalytic decolorization process with

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catalyst dosage of 1.0 g L-1, an initial MO concentration of 10 mg L-1 and pH of 5 under

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visible light irradiation:22 Fe(II)-EDTA of 0.1 mM was used to remove H2O2,23 sodium

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oxalate (Na2C2O4) with a concentration of 0.5 mM was employed to remove h+, Cr(VI) of

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0.05 mM was used to remove e-,24 isopropanol of 5 mM was used to remove ·OH, and

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4-hydroxy-2,2,6,6- tetramethyl-piperidinyloxy (TEMPOL) of 2 mM was used for ·O2-

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removal.25 Variations of MO decolorization under each condition were used to understand the

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mechanisms of photodegradation.

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In the stability test, four consecutive cycles were performed and the corresponding

22

decolorization efficiencies were recorded to examine the stability and reusability of the 8


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VS4/CP nanocomposites with a catalyst dosage of 1.0 g L-1, an initial MO concentration of 10

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mg L-1 and pH of 5 under visible light irradiation; the result was compared with that of the

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prepared VSx. Each test during the whole photocatalytic process was repeated three times and

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the mean results were reported.

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Analytical methods

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The concentration of MO was measured by an UV-visible spectrophotometer at 464 nm

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(DR 5000, HACH, USA).26 Total oxidation ability was determined by spectrophotometry as

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previously reported.26 The MO solution sample was added to the mixture of potassium iodide

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(KI) and ammonium molybdate, shaken quickly and monitored by an UV-visible

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spectrophotometer (DR 5000, HACH, USA) at 352 nm for H2O2 determination. Hydroxyl

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radical was determined by using the dimethyl sulfoxide (DMSO) method.27,28 To investigate

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the changes of the molecule and structural characteristics of MO with photocatalytic

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decolorization, the full-wavelength scan was monitored by a UV-visible spectrophotometer

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(DR 5000, HACH, USA).29 To determine the decolorization products, gas

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chromatography/mass spectrometry (GC/MS, Trace GC-DSQ, Thermo Fisher, TR-35MS,

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30 m × 0.25 mm × 0.25 µm) analysis was performed.26 In the GC/MS measurement, 100-mL

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treated samples were extracted by 20 mL methylene dichloride (chromatogram grade) and the

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extraction solutions without water were confirmed by anhydrous sodium sulfate dehydrated;

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then the samples were used in Termovap Sample Concentrator (HGC-24A, Hengao, CHN ) to

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blow-dry. According to the previous studies,30 ultrapure helium was used as the carrier gas

21

with a constant flow rate of 1.0 mL min-1. The oven temperature was programmed from

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50 °C for 4 min, then increased at a ramp of 15 °C min-1 to 280 °C and held for 3 min. MS 9



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was operated under the following conditions: transfer line, 220 °C; ion source, 220 °C, and

2

electron energy, 70 eV.

3

4

Results and Discussion

5

Characterization of the VS4/CP nanocomposites

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The synthesized composites were characterized for structure and composition. The

7

uniformly distributed nanoparticles were observed on the carbon powder matrix with size of

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50-100 nm as shown in the TEM images (Fig. 1A and B). Their lattice spacing was about

9

0.56 nm, well consistent with the VS4 nanostructures reported previously.18 Elemental

10

mapping of the composites revealed higher element counts of vanadium, sulfur and carbon in

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the deeper color region, combined with elemental carbon (Fig. 1C), and the Stoichiometric

12

ratio of S to V was determined as 22:5.4 (or 4.07:1). The EDX results of the developed

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composites suggested the components of C, V, and S, with a S/V ratio of 4; Si element could

14

be derived from the immersible silicon lithium-drift detector (Fig. 2A, Fig. S1, Supporting

15

Information). The XRD pattern of the VS4/CP nanocomposites showed the diffraction peak

16

corresponding to the (110) plane at 15.8° [JCPDS No. 072-1294] (Fig. 2B), demonstrating

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the monoclinic phase of nano-particles,31 while the peak of carbon at 16.7° and peak of sulfur

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at 22.8° were assigned to the (020) and (101) diffraction, respectively [JCPDS No.

19

024-1206],18 compared with the XRD pattern of VSx (Fig. S2A, Supporting Information).

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XPS was employed to probe the electronic structures of the VS4/CP nanocomposites (Fig. 2C,

21

D and E). The overall XPS spectra of VS4/CP nanocomposites showed the detected

10


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characteristic peaks of S, C, and V elements, suggesting the successful removal of

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water-souble ions after hydrothermal synthesis (Fig. S3). The highest C 1s peak centered at

3

284.4 eV was correspond to C-C bond, and the fitted peak observed at 287.8 eV indicated the

4

presence of a trace amount of oxygen-containing functional groups, suggesting that the

5

hydrothermal method was efficient to remove these kinds of functional groups.18 The S 2p

6

core level analysis confirmed the existence of the S22− species,17 as the peaks at 162.7 eV and

7

163.9 eV can be indexed to S 2p3/2 and S 2p1/2, respectively, for the S22− dimer. The shift of

8

these two peaks (about 0.4 eV) to the higher binding energy direction could be explained by

9

the formation of C-S bond,17,32 indicating that the chemical interaction between VS4 and

10

carbon powders, compared with the S 2p spectrum of VSx (Fig. S2B, Supporting

11

Information). The V 2p peak located at about 515.7 eV and 523.1 eV could be ascribed to

12

binding energies of V 2p3/2 and V 2p1/2, respectively, suggesting that V 2p was the

13

characteristic of V4+.18 The shift of V 2p to the lower binding energy direction referring to V

14

2p spectrum of prepared VSx (Fig. S2C, Supporting Information) indicated that V received

15

some electrons from the neighbors through electronic effect, which would promote electron

16

transfers during photocatalytic process. XPS analysis of VSx showed that the component of

17

prepared vanadium chalcogenide was the mixture of VS4 and VSx (x = 2~4) (Fig. S2B and

18

S2C, Supporting Information).33 All these results confirmed the successful synthesis of VS4

19

with the benefits of adding carbon powders in the VS4/CP nanocomposites.

20

Photocatalytic MO decolorization by the VS4/CP nanocomposites

21 22

The photocatalytic test was performed by the photocatalytic decolorization of a MO aqueous solution.34 Clearly, the addition of the VS4/CP nanocomposites under visible light 11



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irradiation led to significant decolorization of MO dye (98.8 ± 0.9%) in 30 min, while the

2

MO solution without the VS4/CP nanocomposites had decolorization efficiency of 3.8 ± 1.2%

3

(Fig. 3). This demonstrated that the prepared VS4/CP nanocomposites were an effective

4

photocatalyst for photocatalytic decolorization of MO dye. In the absence of illumination

5

(dark condition), the VS4/CP nanocomposites resulted in 16.3 ± 2.2% of MO decolorization,

6

indicating that adsorption reaction occurred. When a different light source - UV light,

7

replaced visible light, the decolorization efficiency of MO decreased to 67.0 ± 3.9%, due to a

8

relatively narrow bandgap of 1.0 eV for VS4 according to density functional theory (DET).18

9

This exhibited the advantage of the VS4/CP nanocomposites because visible light has more

10

application prospect than UV light. Even under sunlight, the VS4/CP nanocomposites

11

achieved 70.1 ± 3.3% decolorization efficiency of MO. The VSx under visible light

12

irradiation resulted in only 44.0 ± 1.4% of MO decolorization, demonstrating that vanadium

13

could realize separation of electron-hole pairs while carbon material playing a role in the

14

nucleation to promote photocatalytic activity. The added carbon powders increased MO

15

decolorization efficiencies through strengthening visible light absorption by reducing the

16

bandgap of VS4 and weakening the recombination of photo-generated holes and electrons,35

17

thereby improving the dispersibility of VS4. Additionally, the VS4/CP nanocomposites also

18

exhibited satisfactory performance of photocatalytic degradation of phenol (Fig. S4,

19

Supporting Information), with removal efficiency of 49.7 ± 1.2% within 4 h; this was

20

comparable with the results using FeWO4@ZnWO4/ZnO photocatalyst21 and thus further

21

confirmed the excellent photocatalytic activities of the VS4/CP nanocomposites in pollutants

22

degradation. 12


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Compare to other photocatalysts for decolorization of MO in aqueous solutions under

2

visible light such as graphene oxide/TiO2 composites and CdS/TiO2, the VS4/CP

3

nanocomposites catalysts achieved comparable decolorization efficiency but had significant

4

advantages in short reaction time, low catalyst dosage, and high MO decolorization rate, as

5

shown in Table 1, where the data were normalized based on previous studies.36 For example,

6

to achieve 88% decolorization for MO, only 0.5 h was required for the VS4/CP

7

nanocomposites, much shorter than 2 h using CdS/TiO2 and 2.7 h using CuFe2O4/AgBr under

8

visible light in the similar glass beaker with a cooling-water-cycle system.37 Particularly, the

9

calculated MO decolorization rate was 19.8 mg L-1 h-1 for the VS4/CP nanocomposites,

10

significantly higher than 4.8 mg L-1 h-1 for CdS/TiO2, 1.4 mg L-1 h-1 for graphene oxide/TiO2

11

composites and 6.5 mg L-1 h-1 for CuFe2O4/AgBr.37-39 Although the VS4/CP nanocomposites

12

had lower decolorization efficiency of MO than Cu/ZnO, Co2TiO4 nanoparticles or Se-ZnS

13

nanocomposites under UV light in glass beakers,40-42 its MO decolorization rate of 13.4 mg

14

L-1 h-1 was much higher than that of those photocatalysts, with 4.4 mg L-1 h-1 for Cu/ZnO, 7.1

15

mg L-1 h-1 for Co2TiO4 nanoparticles and 4.6 mg L-1 h-1 for Se-ZnS nanocomposites,

16

respectively. Likewise, despite a lower MO decolorization efficiency under sunlight, the

17

VS4/CP nanocomposites had a significantly higher decolorization rate of 14.0 mg L-1 h-1 than

18

the reported ZnO of 3.2 mg L-1 h-1, g-C3N4/graphene oxide aerogel of 4.6 mg L-1 h-1 and TiO2

19

of 5.0 mg L-1 h-1 in a beaker with a circulating water jacket or quartz conical flask,

20

respectively.43-45 The photoreactor setup can affect the decolorization efficiency (Table 1), so

21

the common photoreactor (beaker with a circulating cooling water bath) have used in

22

photocatalytic reactions. Those results have demonstrated the effective and efficient 13



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Page 14 of 42

1

photocatalytic MO decolorization by the VS4/CP nanocomposites with a high photocatalytic

2

decolorization rate.

3

Catalytic mechanisms by the VS4/CP nanocomposites

4

Photocatalytic process can generate reactive species such as ·OH, H2O2, ·O2−, e−, and h+

5

through Eqs. (1)-(4), and some of them may be responsible for the MO decolorization on the

6

VS4/CP nanocomposites.46

7

O2 + e− → ·O2−

(1)

8

·O2− + H+ → ·OOH

(2)

9

·OOH + e− + H+ → H2O2

(3)

10

·O2− + H2O2 → ·OH + OH- + O2

(4)

11

The measured total oxidation ability in the photocatalytic decolorization system

12

performed by the VS4/CP nanocomposites was about 3.3 ± 0.3 mg L-1, higher than that

13

obtained from VS4 (1.5 ± 0.2 mg L-1), and it also had a much higher level of H2O2 (11.0 ± 0.2

14

µM) and slight increase of ·OH (1.88 ± 0.2 µM) than those obtained for VSx (3.5 ± 0.3 mg L-1

15

of H2O2 and 1.8 ± 0.2 µM of ·OH). To further examine the mechanism of photocatalytic MO

16

decolorization by the VS4/CP nanocomposites, several scavenger compounds were added to

17

the MO aqueous solution respectively to remove the corresponding reactive species,

18

compared with the photocatalytic reaction without scavengers (Fig. 4). Addition of TEMPOL,

19

sodium oxalate and Cr(VI) significantly inhibited the photocatalytic decolorization by the

20

VS4/CP nanocomposites with MO decolorization efficiency decreased to 18.4 ± 2.3%, 53.4 ±

21

2.8% and 21.2 ± 3.1%, respectively, suggesting that ·O2−, h+ and e− could have played

22

important roles in the photocatalytic decolorization of MO. Functions of ·O2− and e− were 14


Page 15 of 42

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1

crucial to this process with some auxiliary effects from h+ as MO decolorization might

2

happen through both oxidation by active oxidants and reduction by electrons. 47,48 Similar

3

observations were also obtained in the photocatalytic disinfection experiments with the main

4

contribution from ·O2− and the complementary role of h+.22 The addition of Fe(II)-EDTA and

5

Isopropanol hardly inhibited the MO decolorization (Fig. 4), with MO decolorization

6

efficiencies of 95.2 ± 1.3% and 99.0 ± 2.9%, respectively. Thus, the roles of H2O2 and ·OH in

7

the photocatalytic decolorization of MO by the VS4/CP nanocomposites could be minor,

8

consistent with the findings in a previous study of photocatalytic disinfection.22

9

The change of MO molecule during photocatalytic decolorization by the VS4/CP

10

nanocomposites was also monitored. The azo group of MO was destroyed gradually as the

11

peak at 464 nm showing the n-π* transition of the azo group weakened over time and

12

eventually disappeared through the photooxidation, confirming the achievement of color

13

removal (Fig. 5). Another peak at 270 nm from the π-π* transition of benzene rings

14

disappeared quickly, while a new peak at 248 nm appeared accordingly, indicating that the

15

relevant structures had been progressively destroyed with the generation of new compounds.

16

The newly appeared peaks also became weaker during the operation, implying the gradual

17

mineralization of MO.49 GC/MS results revealed the changes of the molecule and structural

18

characteristics of MO (Table 2). The compounds in the original samples were similar to the

19

results obtained in our previous MO study.26 Organics reflected by appeared peaks in GC/MS

20

scheme were also listed as cracking reaction and recombination could take place during the

21

detection process at a high temperature, consistent with the results of the previous MO

22

study.50 The dye molecules were broken down into the compounds with smaller molecular 15



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Page 16 of 42

1

weights after 30 min operation, for example indole. Some derivatives of benzene, such as

2

phthalic acid, were also detected. This confirmed the destruction of MO molecule and the

3

generation of the intermediates.26 Additionally, the species of intermediates detected here

4

were more complex than results obtained by Li et al.,51 probably due to the effective destroy

5

of MO as well as the bonding between the intermediates.

6

Effects of operating factors

7

In order to evaluate the effects of catalyst dosage, the experiment was conducted by

8

varying the VS4/CP nanocomposites catalyst dosage from 0.5 to 2.0 g L-1, with the initial MO

9

of 10 mg L-1 and pH of 5 under visible light irradiation. As shown in Fig. 6A, the

10

decolorization efficiency of MO increased from 82.1 ± 2.1% to 98.8 ± 0.9% with increasing

11

the catalyst dosage from 0.5 to 1.0 g L-1. However, further increase of the catalyst dosage to

12

1.5 and 2.0 g L-1 did not result in further enhancement of the decolorization efficiency (97.3 ±

13

1.7% at 1.5 g L-1 and 95.7 ± 1.3% at 2.0 g L-1). The improved removal efficiency with more

14

catalysts was likely due to the increased number of active sites that caused an increase in the

15

number of reactive species, benefiting the decolorization of MO.52 Overdose of the catalysts

16

could decrease the removal efficiency when a large amount of catalysts shield the light, and

17

then increase in turbidity of the suspension, resulting in the decrease in photoactivated

18

volume of MO solution.52,53 This light attenuation effect was established through a linear

19

correlation between kinetics constant k and catalyst dosage:

20 21 22

k = 18.52 [VS4/CP nanocomposites] - 0.307

R2 = 0.722

(5)

This assumption had also been reported previously.54 The optimized catalyst dosage of 1.0 g L-1 was selected for the following experiments. Moreover, the basis on optimum 16


Page 17 of 42

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1

catalyst dosage is found to be dependent on the initial solute concentration and 10 mg L-1 of

2

MO was frequently employed during photocatalytic decolorization.39,44,45 Thus, this selected

3

dosage was significantly less than those applied for MO decolorization by other

4

photocatalysts (Table 1), retaining the significant advantage of the VS4/CP nanocomposites

5

catalyst.

6

The initial concentration of MO dye in a given photocatalytic reaction can affect its

7

removal. This was examined by varying the initial MO concentration from 5 to 20 mg L-1,

8

with pH of 5 under visible light irradiation. As expected, the low concentrations of 5 or 10

9

mg L-1 led to great decolorization efficiency of 99.6 ± 1.9% or 98.8 ± 0.9% (Fig. 6B). The

10

MO decolorization efficiency decreased to 68.5 ± 1.8% or 66.2 ± 1.6% when the initial MO

11

concentration increased to 15 or 20 mg L-1. However, the MO decolorization rate per unit

12

mass of the VS4/CP nanocomposites catalyst increased significantly with the enhancement of

13

initial MO concentration. When the initial MO concentration was increased from 5 mg L-1 to

14

10 mg L-1, the MO decolorization rate was nearly doubled from 10.0 mg L-1 h-1 to 19.8 mg

15

L-1 h-1. Further increase of the initial MO concentration also improved the MO decolorization

16

rate to 20.6 mg L-1 h-1 (initial MO concentration of 15 mg L-1) and then to 26.5 mg L-1 h-1

17

(initial MO concentration of 20 mg L-1). Sufficient contact between MO and generated

18

reactive species could be realized under higher initial MO concentrations, making the use of

19

reactive species more effectively and thus improving MO decolorization rates. Similar

20

principles had also been observed with photocatalytic decolorization of MO by TiO2.55

21

The solution pH is another key factor to both the generation of reactive species and

22

chemical forms of MO, thereby affecting the MO decolorization. Different initial pH (3, 5, 7, 17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

9) was examined, with an initial MO concentration of 10 mg L-1 under visible light

2

irradiation. It was observed that the decolorization efficiency of MO decreased with the

3

increase of pH (Fig. 6C). An acidic condition of pH 3 or 5 led to higher MO decolorization

4

efficiency of 99.7 ± 0.2% or 98.8 ± 0.9%. Slight decrease of color removal efficiency (94.3 ±

5

2.5%) was observed under a neutral condition (pH 7), while the lowest MO decolorization

6

efficiency of 88.6 ± 1.4% was obtained under an alkaline condition (pH 9). The acidic

7

condition favored the decolorization process catalyzed by theVS4/CP nanocomposites,

8

because a high concentration of H+ would facilitate the generation of reactive species

9

according to Eqs. (2), (3) and (4). In addition, MO is likely to change into quinine form under

10

the acidic condition, which is ionized.41,43 H+ ions interact with the azo linkage which is

11

particularly susceptible to be electrophilic attacked by reactive species, decreasing the

12

electron densities at azo group.53 Oxidative powers of the photogenerated reactive species are

13

lowered with increasing the pH, and MO is in the azo form in neutral and alkaline medium.

14

The generated reactive species tended to be consumed by oxygen evolution reaction in

15

photocatalytic water splitting process instead of MO decolorization through Eq. (6),56

16

2H2O + 4h+ →O2 ↑ + 4H+

17

The effects of adsorption by the VS4/CP nanocomposites under dark condition for MO

18

removal were also investigated under different pH. MO removal efficiencies increased with

19

the decrease of pH, as surfaces of VS4/CP nanocomposites were positively charged, which

20

favored the adsorption of azo dyes,57 with the point of zero charge for the VS4/CP

21

nanocomposites of 4.8 that was indicated by the measured zeta potentials. The highest

22

adsorption decolorization efficiency was less than 20%, indicating that dark adsorption of dye

(6)

18


Page 18 of 42

Page 19 of 42

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1

on the developed VS4/CP nanocomposites only showed very slight effects on MO

2

decolorization. In addition, the decolorization efficiencies obtained by the VS4/CP

3

nanocomposites and prepared VSx submerged in the target solution under the tested pH

4

showed rare differences to their performances without presoaks in the same solution as

5

presented in Fig. 3 and Fig. S5 (Supporting Information), confirming that the developed

6

photocatalysts were fairly stable in the tested pH range.58

7

Stability and reusability

8 9

The stability and reusability of the VS4/CP nanocomposites catalyst was examined with four consecutive cycles. As shown in Fig. 7, only slight decrease was observed with all the

10

MO decolorization efficiency maintained above 90%. The XRD spectra after four continuous

11

cycles with visible light irradiation were nearly identical to its zero irradiation level (Fig. S6,

12

Supporting Information), suggesting that the structure of the VS4/CP nanocomposites was

13

hardly destroyed during photocatalytic decolorization. Little leakage of vanadium in the

14

aqueous solution was detected by inductively coupled plasma mass spectroscopy (less than

15

1% of the vanadium mass loading).These have demonstrated that the VS4/CP nanocomposites

16

were stable and robust, when compared with several existing catalysts. For example, a

17

considerable reduction in photocatalytic activity of ZnO was observed, with only 52% of MO

18

being decolorized after three cycles of usage.59 Another catalyst BaTiO3@g-C3N4

19

accomplished 67-76% of the MO decolorization after three consecutive runs.60 In the VS4/CP

20

nanocomposites, the added carbon powders played an important role in the nucleation,18

21

strengthening the visible light absorption of photocatalyst and promoting photoproduction

22

carrier separation and transfer effectively.35 Presumable photocorrosion effect could also lead 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

to the declining trend in MO decolorization, but the close contact between VS4 and carbon

2

powder in the VS4/CP nanocomposites might inhibit the photocorrosion. Sulfur and carbon

3

also formed chemical bonds, thus representing long-lasting photostability. Such a structure

4

between metal and carbon was also reported for ZnO-Graphene composites in which

5

graphene exhibited a protective effect for ZnO.59

6

7

Conclusions

8

In this study, the VS4/CP nanocomposites were prepared by a simple one-step

9

hydrothermal synthesis method as a novel photocatalyst for dye decolorization. Both the

10

morphology and structure of the synthesized photocatalysts proved the formation of

11

nano-structured VS4 carbon composites. The feasibility of this photocatalyst for MO

12

decolorization had been examined with exhibiting great photocatalytic decolorization

13

efficiency under the visible light irradiation. Compared with the other photocatalysts for

14

decolorization of MO in aqueous solution, the VS4/CP nanocomposites had significant

15

advantages of short reaction time and high MO removal rate per mass of catalysts. The

16

scavenger study suggested that ·O2−, h+ and e− could have played important roles in the

17

photocatalytic decolorization of MO, while the contributions of H2O2 and ·OH were minor.

18

The tests of operating factors showed that the optimal catalyst dosage was identified as 1.0 g

19

L-1, increasing the initial MO concentration improved the MO removal rate per mass of

20

catalysts, and an acidic condition would favor MO decolorization. The VS4/CP

21

nanocomposites had a relatively stable performance in four consecutive reused cycles. This

22

work has provided a promising route to increase our understanding of VS4/CP 20


Page 20 of 42

Page 21 of 42

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1

nanocomposites towards its further development and application to dye decolorization.

2

Acknowledgements

3 4

This research work was supported by the National Natural Science Foundation of China (NSFC) (No. 41672237).

5 6

Supporting Information

7

Figure S1. TEM image of VS4/CP nanocomposites.

8

Figure S2. (A) XRD pattern; (B) and (C) XPS spectra of the VSx.

9

Figure S3. Overall XPS spectra of VS4/CP nanocomposites.

10

Figure S4. Photocatalytic activity toward the degradation of phenol under visible light

11

irradiation by VS4/CP nanocomposites.

12

Figure S5. Decolorizations of VS4/CP nanocomposites and VSx with initial MO concentration

13

of 10 mg L-1 and pH of 5.

14

Figure S6. XRD of VS4/CP nanocomposites after four consecutive cycles with visible light

15

irradiation.

16

21



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Page 22 of 42

1

References

2

(1) Lachheb, H.; Puzenat, E.; Houas, A.; Ksibi, M.; Elaloui, E.; Guillard, C.; Herrmann, J.

3

M. Photocatalytic degradation of various types of dyes (Alizarin S, Crocein Orange G,

4

Methyl Red, Congo Red, Methylene Blue) in water by UV-irradiated titania. Appl. Catal. B:

5

Environ. 2002, 39, 75-90. DOI: 10.1016/S0926-3373(02)00078-4.

6

(2) Patil, B. N.; Naik, D. B.; Shrivastava, V. S. Photocatalytic degradation of hazardous

7

Ponceau-S dye from industrial wastewater using nanosized niobium pentoxide with carbon.

8

Desalination 2011, 269, 276-283. DOI: 10.1016/j.desal.2010.11.014.

9

(3) Wei, S. T.; Hu, X. L.; Liu, H. L.; Wang, Q.; He, C. Y. Rapid degradation of Congo red by

10

molecularly imprinted polypyrrole-coated magnetic TiO2 nanoparticles in dark at ambient

11

conditions. J. Hazard. Mater. 2015, 294, 168-176. DOI: 10.1016/j.jhazmat.2015.03.067.

12

(4) Mu, Y.; Rabaey, K.; Rozendal, R. A.; Yuan, Z.G. Decolorization of azo dyes in

13

bioelectrochemical

14

10.1021/es900057f.

15

(5) Quan, X.; Zhang, X.; Xu, H. In-situ formation and immobilization of biogenic

16

nanopalladium into anaerobic granular sludge enhances azo dyes degradation. Water Res.

17

2015, 78, 74-83. DOI: 10.1016/j.watres.2015.03.024.

18

(6) Kuriechen, S. K.; Murugesanb, S.; Raj, S. P.; Maruthamuthu, P. Visible light assisted

19

photocatalytic mineralization of Reactive Red 180 usingcolloidal TiO2 and oxone. Chem.

20

Eng. J. 2011, 174, 530-538. DOI: 10.1016/j.cej.2011.09.024.

21

(7) Sapawe, N.; Jalil, A. A.; Triwahyono, S. One-pot electro-synthesis of ZrO2–ZnO/HY

22

nanocomposite for photocatalytic decolorization of various dye-contaminants. Chem. Eng. J.

systems.

Environ.

Sci.

Technol.

2009,

22


43,

5137-5143. DOI:

Page 23 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

2013, 225, 254-265.DOI: 10.1016/j.cej.2013.03.121.

2

(8) Oturan, M. A.; Aaron, J. J. Advanced Oxidation Processes in water/wastewater treatment:

3

principles and applications. A Review. Crit. Rev. Env. Sci. Tec. 2014, 44, 2577-2641. DOI:

4

10.1080/10643389.2013.829765.

5

(9) Lucas, M. S.; Peres, J. A. Decolorization of the azo dye Reactive Black 5 by Fenton and

6

photo-Fenton

7

10.1016/j.dyepig.2005.07.007.

8

(10) Jia, Z.; Zhang, W. C.; Wang, W. M.; Habibi, D.; Zhang, L. C. Amorphous Fe78Si9B13

9

alloy: An efficient and reusable photo-enhanced Fenton-like catalyst in degradation of

10

cibacron brilliant red 3B-A dye under UV-vis light. Appl. Catal. B: Environ. 2016, 192,

11

46-56. DOI: 10.1016/j.apcatb.2016.03.048.

12

(11) Subramanian, G.; Madras, G. Introducing saccharic acid as an efficient iron chelate to

13

enhance photo-Fenton degradation of organic contaminants. Water Res. 2016, 104, 168-177.

14

DOI: 10.1016/j.watres.2016.07.070.

15

(12) Pan, D. Y.; Jiao, J. K.; Li, Z.; Guo, Y. T.; Feng, C. Q.; Liu, Y.; Wang, L.; Wu, M. H.

16

Efficient separation of electron-hole pairs in graphene quantum dots by TiO2 heterojunctions

17

for dye degradation. ACS Sustain. Chem. Eng. 2015, 3, 2405-2413. DOI: DOI:

18

10.1021/acssuschemeng.5b00771.

19

(13) Tripathy, N.; Ahmad, R.; Song, J. E.; Ko, H. A.; Hahn, Y. B.; Khang, G. Photocatalytic

20

degradation of methyl orange dye by ZnO nanoneedle under UV irradiation. Mater. Lett.

21

2014, 136, 171-174. DOI: 10.1016/j.matlet.2014.08.064.

22

(14) Gong, D. G.; Highfield, J. G.; Ng, S. Z. E.; Tang, Y. X.; Ho, W. C. J.; Tay, Q., Chen, Z.

oxidation.

Dyes

Pigments

2006,

23


71,

236-

244.

DOI:


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 42

1

Poly tri-s-triazines as visible light sensitizers in titania-based composite photocatalysts:

2

promotion of melon development from urea over acid titanates. ACS Sustain. Chem. Eng.

3

2014, 2, 149-157. DOI: 10.1021/sc400162p.

4

(15) Karunakaran, C.; Dhanalakshmi, R. Semiconductor-catalyzed degradation of phenols

5

with

6

10.1016/j.solmat.2008.05.002.

7

(16) Zhang, M.; Lu, D. D.; Zhang, Z. H.; Yang, J. J. Enhancement of visible-light-induced

8

photocurrent photocatalytic activity of V and N codoped TiO2 nanotube array films. J.

9

Electrochem. Soc. 2014, 161, H416-H421. DOI: 10.1149/2.119406jes.

sunlight.

Sol.

Energ.

Mat.

Sol.

C.

2008,

92,

1315-1321.

DOI:

10

(17) Guo, W. W.; Wu, D. F. Facile synthesis of VS4/graphene nanocomposites and their

11

visible-light-driven photocatalytic water splitting activities. Int. J. Hydrogen Energ. 2014, 39,

12

16832-16840. DOI: 10.1016/j.ijhydene.2014.08.088.

13

(18) Rout, C. S.; Kim, B. H.; Xu, X.; Yang, J.; Jeong, H. Y.; Odkhuu, D.; Park, N.; Cho, J.;

14

Shin, H. S. Synthesis and characterization of patronite form of vanadium sulfide on graphitic

15

layer. J. Am. Chem. Soc. 2013, 135, 8720-8725. DOI: 10.1021/ja403232d.

16

(19) Bao, N.; Hu, X. D.;Zhang, Q. Z.; Miao, X. H.; Jie, X. Y.; Zhou, S. Synthesis of porous

17

carbon-doped g-C3N4 nanosheets with enhanced visible-light photocatalytic activity. Appl.

18

Surf. Sci. 2017, 403, 682-690. DOI: 10.1016/j.apsusc.2017.01.256.

19

(20) Thi, D. N.; Ngoc, H. P.; Manh, H. D.; Kim, T. N. Magnetic Fe2MO4 (M:Fe, Mn)

20

activated carbons: Fabrication, characterization and heterogeneous Fenton oxidation of

21

methyl orange. J. Hazard. Mater. 2011, 185, 653-661. DOI: 10.1016/j.jhazmat.2010.09.068.

22

(21) Wang, F. Z.; Li, W. J.; Gu, S. N.; Li, H. D.; Liu, X. T.; Wang, M. Z. Fabrication of 24


Page 25 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

FeWO4@ZnWO4/ZnO heterojunction photocatalyst: synergistic effect of ZnWO4/ZnO and

2

FeWO4@ZnWO4/ZnO heterojunction structure on the enhancement of visible-Light

3

photocatalytic

4

10.1021/acssuschemeng.6b00660.

5

(22) Jiang, D. L.; Li, J.; Xing, C. S.; Zhang, Z. Y.; Meng, S. C.; Chen, M. Two-dimensional

6

CaIn2S4/g-C3N4 heterojunction nanocomposite with enhanced visible-light photocatalytic

7

activities: interfacial engineering and mechanism insight. ACS Appl. Mater. Inter. 2015, 34,

8

19234-19242. DOI: 10.1021/acsami.5b05118.

9

(23) Zhang, L. S.; Wong, K. H.; Yip, H. Y.; Hu, C.; Yu, J. C.; Chan, C. Y.; Wong, P. K.

10

Effective photocatalytic disinfection of E. coli K-12 using AgBr-Ag-Bi2WO6 nanojunction

11

system irradiated by visible light: The role of diffusing hydroxyl radicals. Environ. Sci.

12

Technol. 2010, 44, 1392-1398. DOI: 10.1021/es903087w.

13

(24) Chen, Y. X.; Yang, S. Y.; Wang, K.; Lou, L. P. Role of primary active species and TiO2

14

surface characteristic in UV-illuminated photodegradation of Acid Orange 7. J. Photoch.

15

Photobio. A. 2005, 172, 47-54. DOI: 10.1016/j.jphotochem.2004.11.006.

16

(25) Hunag, H. W.; He, Y.; Du, X.; Chu, P. K.; Zhang, Y. H. A general and facile approach to

17

heterostructured core/shell BiVO4/BiOI p-n lunction: room-temperature in situ assembly and

18

highly boosted visible-light photocatalysis. ACS Sustain. Chem. Eng. 2015, 3, 3262-3273.

19

DOI: 10.1021/acssuschemeng.5b01038.

20

(26) Wang, Z. J.; Zhang, B. G.; Borthwick, A. G. L.; Feng, C. P.; Ni, J. R. Utilization of

21

single-chamber microbial fuel cells as renewable power sources for electrochemical

22

degradation of nitrogen-containing organic compounds. Chem. Eng. J. 2015, 280, 99-105.

activity.

ACS

Sustain.

Chem.

Eng.

2016,

25


4,

6288-6298.

DOI:


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 42

1

DOI: 10.1016/j.cej.2015.06.012.

2

(27) Li, Y. L.; Zhang, B. G.; Borthwick, A.; Long, Y. L. Efficient electrochemical oxidation of

3

thallium (I) in groundwater using boron-doped diamond anode. Electrochim. Acta 2016, 222,

4

1137-1143. DOI: 10.1016/j.electacta.2016.11.085.

5

(28) Li, H. N.; Zhu, X. P.; Ni, J. R. Inactivation of Escherichia coli in Na2SO4 electrolyte

6

using boron-doped diamond anode. Electrochim. Acta 2010, 56, 448-453. DOI:

7

10.1016/j.electacta.2010.08.055.

8

(29) Jantawasu, P.; Sreethawong, T.; Chavadej, S. Photocatalytic activity of nanocrystalline

9

mesoporous-assembled TiO2 photocatalyst for degradation of methyl orange monoazo dye in

10

aqueous wastewater. Chem. Eng. J. 2009, 1155, 223-233. DOI: 10.1016/j.cej.2009.07.036.

11

(30) Zhang, C. P.; Li, M. C.; Liu, G. L.; Luo, H. P.; Zhang, R. D. Pyridine degradation in the

12

microbial

13

10.1016/j.jhazmat.2009.07.027.

14

(31) Xu, X.; Gao, Z.; Cui, Z.; Liang, Y.; Li, Z.; Zhu, S.; Yang, X.; Ma, J. Synthesis of Cu2O

15

Octadecahedron/TiO2 quantum dot heterojunctions with high visible light photocatalytic

16

activity

17

10.1021/acsami.5b06536.

18

(32) Qian, W. W.; Gao, Q. M.; Zhang, H.; Tian,W. Q.; Li, Z. Y.; Tan, Y. L. Crosslinked

19

polypyrrole grafted reduced graphene oxide-sulfur nanocomposite cathode for high

20

performance

21

10.1016/j.electacta.2017.03.063.

22

(33) Mohan, P.; Yang, J.; Jena, A.; Shin, H. S. VS2/rGO hybrid nanosheets prepared by

fuel

and

high

Li-S

cells.

J.

stability.

Battery.

Hazard.

ACS

Mater.

Appl.

Electrochim.

Mater.

Acta

Inter.

2016,

2017,

26


465-471.

172,

2009,

8,

235,

91-101.

32-41.

DOI:

DOI:

DOI:

Page 27 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

annealing

of

2

10.1016/j.jssc.2014.06.031.

3

(34) Wang, D.; Zhang, J.; Luo, Q.; Li, X.; Duan, Y.; An, J. Characterization and

4

photocatalytic activity of poly(3-hexylthiophene)-modified TiO2 for degradation of methyl

5

orange

6

10.1016/j.jhazmat.2009.03.135.

7

(35) Zhu, G.; Li, X. L.; Wang, H. Y.; Zhang, L. Microwave assisted synthesis of reduced

8

graphene oxide incorporated MOF-derived ZnO composites for photocatalytic application.

9

Catal. Commun. 2017, 88, 5-8. DOI: 10.1016/j.catcom.2016.09.024.

under

VS4/rGO.

visible

J.

light.

Solid

J.

State

Hazard.

Chem.

Mater.

2015,

2009,

224,

169,

82-87.

546-550.

DOI:

DOI:

10

(36) Huang, W. T.; Chen, J. F.; Hu, Y. Y.; Chen, J.; Sun, J.; Zhang, L. H. Enhanced

11

simultaneous decolorization of azo dye and electricity generation in microbial fuel cell (MFC)

12

with redox mediator modified anode. Int. J. Hydrogen Energ. 2017, 42, 2349-2359. DOI:

13

10.1016/j.ijhydene.2016.09.216.

14

(37) Chen, C.; Cai, W.; Long, M.; Zhou, B.; Wu, Y.; Wu, D.; Feng, Y. Synthesis of

15

visible-light responsive graphene oxide/TiO2 composites with p/n heterojunction. ACS Nano

16

2010, 4, 6425-6432. DOI: 10.1021/nn102130m.

17

(38) Yang, G.; Yang, B.; Xiao, T.; Yan, Z. One-step solvothermal synthesis of hierarchically

18

porous nanostructured CdS/TiO2 heterojunction with higher visible light photocatalytic

19

activity. Appl. Surf. Sci. 2013, 283, 402-410. DOI: 10.1016/j.apsusc.2013.06.122.

20

(39) Zhao, Y. L.; Lin, C. P.; Bi, H. J.; Liu, Y. G.; Yan, Q. S. Magnetically separable

21

CuFe2O4/AgBr composite photocatalysts: Preparation, characterization, photocatalytic

22

activity and photocatalytic mechanism under visible light. Appl. Surf. Sci. 2017, 392, 701-707. 27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 42

1

DOI: 10.1016/j.apsusc.2016.09.099.

2

(40) Fu, M.; Li, Y.; Wu, S.; Lu, P.; Liu, J.; Dong, F. Sol-gel preparation and enhanced

3

photocatalytic performance of Cu-doped ZnO nanoparticles. Appl. Surf. Sci. 2011, 258,

4

1587-1591. DOI: 10.1016/j.apsusc.2011.10.003.

5

(41) Majid, R.; Mostafa, S. H. M. Controlled synthesis, characterization, and photocatalytic

6

application of Co2TiO4 nanoparticles. J. Electron. Mater. 2017, 46, 1371-1377. DOI:

7

10.1007/s11664-016-5129-6.

8

(42) Ahluwalia, S.; Prakash, N. T.; Prakash, R.; Pal, B. Improved degradation of methyl

9

orange dye using bio-co-catalyst Se nanoparticles impregnated ZnS photocatalyst under UV

10

irradiation. Chem. Eng. J. 2016, 306, 1041-1048. DOI: 10.1016/j.cej.2016.08.028.

11

(43) Khatamian, M.; Fazayeli, M.; Divband, B. Preparation, characterization and

12

photocatalytic properties of polythiophene-sensitized zinc oxide hybrid nanocomposites. Mat.

13

Sci. Semicon. Proc. 2014, 26, 540-547. DOI: 10.1016/j.mssp.2014.04.038.

14

(44) Tong, Z.; Yang, D.; Shi, J.; Nan, Y.; Sun, Y.; Jiang, Z. Three-dimensional porous aerogel

15

constructed by g-C3N4 and graphene oxide nanosheets with excellent visible-light

16

photocatalytic performance. ACS Appl. Mater. Inter. 2015, 7, 25693-25701. DOI:

17

10.1021/acsami.5b09503.

18

(45) Ong, S. A.; Min, O. M.; Ho, L. N.; Wong, Y. S. Comparative study on photocatalytic

19

degradation of mono azo dye acid orange 7 and methyl orange under solar light irradiation.

20

Water Air Soil Poll. 2012, 223, 5483-5493. DOI: 10.1007/s11270-012-1295-1.

21

(46) Liang, J. L.; Shan, C.; Zhang, X.; Tong, M. P. Bactericidal mechanism of BiOI-AgI

22

under

visible

light

irradiation.

Chem.

Eng.

J.

2015,

28


279,

277-285.

DOI:

Page 29 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

10.1016/j.colsurfb.2015.01.013.

2

(47) Troupis, A.; Triantis, T. M.; Gkika, E.; Hiskia, A.; Papaconstantinou, E. Photocatalytic

3

reductive-oxidative degradation of Acid Orange 7 by polyoxometalates. Appl. Catal. B:

4

Environ. 2009, 86, 98-107. DOI: 10.1016/j.apcatb.2008.08.001.

5

(48) Zhang, B.; Wang, Z.; Zhou, X.; Shi, C.; Guo, H.; Feng, C. Electrochemical

6

decolorization of methyl orange powered by bioelectricity from single-chamber microbial

7

fuel cells. Bioresour. Technol. 2015, 181, 360-362. DOI: 10.1016/j.biortech.2015.01.076.

8

(49) Lu, X. F.; Ma, H. R.; Zhang, Q.; Du, K. Degradation of methyl orange by UV, O3 and

9

UV/O3 systems: analysis of the degradation effects and mineralization mechanism. Res.

10

Chem. Intermed. 2013, 39, 4189-4203. DOI: 10.1007/s11164-012-0935-9.

11

(50) Fang, Z.; Song, H. L.; Yu, R.; Li, X. A microbial fuel cell-coupled constructed wetland

12

promotes degradation of azo dye decolorization products. Ecol. Eng. 2016, 94, 455-463. DOI:

13

10.1016/j.ecoleng.2016.06.020.

14

(51) Li, S. H.; Zhao, Y.; Chu, J.; Li, W. W.; Yu, H. Q.; Liu, G. Electrochemical degradation of

15

methyl orange on Pt-Bi/C nanostructured electrode by a square-wave potential method.

16

Electrochim. Acta 2013, 92, 93-101. DOI: 10.1016/j.electacta.2013.01.012.

17

(52) Kansal, S.K.; Singh, M.; Sud, D. Studies on photodegradation of two commercial dyes in

18

aqueous phase using different photocatalysts. J. Hazard. Mater. 2007, 141, 581-590. DOI:

19

10.1016/j.jhazmat.2006.07.035.

20

(53) Li, H.; Lei, Z.; Liu, C.; Zhang, Z.; Lu, B. Photocatalytic degradation of lignin on

21

synthesized Ag-AgCl/ZnO nanorods under solar light and preliminary trials for methane

22

fermentation. Bioresour. Technol. 2015, 175, 494-501. DOI: 10.1016/j.biortech.2014.10.143. 29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 42

1

(54) Gong, H.; Chu, W. Photodegradation of Sulfamethoxazole with a Recyclable Catalyst.

2

Ind. Eng. Chem. Res. 2015, 54, 12763-12769. DOI: 10.1021/acs.iecr.5b03849.

3

(55) Yan, T. J.; Yuan, R. S.; Li, W. J.; You, J. M. Origin of superior photocatalytic activity in

4

rutile TiO2 hierarchical microspheres: The dominate role of “microcavity” structure. Appl.

5

Catal. A: Gen. 2014, 478, 204-210. DOI: 10.1016/j.apcata.2014.04.013.

6

(56) Montoya, J. F.; Bahnemann, D. W.; Salvador, P.; Peral, J. Catalytic role of bridging

7

oxygens in TiO2 liquid phase photocatalytic reactions: analysis of H216O photooxidation on

8

labeled Ti18O2. Catal. Sci. Technol. 2017, 7, 902-910. DOI: 10.1039/C6CY02457B.

9

(57) Sajjad, A. K. L.; Shamaila, S.; Tian, B. Z.; Chen, F.; Zhang, J. L. Comparative studies of

10

operational parameters of degradation of azo dyes in visible light by highly efficient

11

WOx/TiO2

12

10.1016/j.jhazmat.2009.12.102.

13

(58) Li, F.; Sun, S.; Jiang, Y.; Xia, M.; Sun, M.; Xue, B. Photodegradation of an azo dye

14

using immobilized nanoparticles of TiO2 supported by natural porous mineral. J. Hazard.

15

Mater. 2008, 152, 1037-1044. DOI: 10.1016/j.jhazmat.2007.07.114.

16

(59) Tayyebi, A.; Outokesh, M.; Tayebi, M.; Shafikhani, A.; Sengor, S. S. ZnO quantum

17

dots-graphene composites: Formation mechanism and enhanced photocatalytic activity for

18

degradation of methyl orange dye. J. Alloy. Compd. 2016, 663, 738-749. DOI:

19

10.1016/j.jallcom.2015.12.169.

20

(60) Xian, T.; Yang, H.; Di, L. J.; Dai, J. F. Enhanced photocatalytic activity of

21

BaTiO3@g-C3N4 for the degradation of methyl orange under simulated sunlight irradiation. J.

22

Alloy. Compd. 2015, 622, 1098-1104. DOI: 10.1016/j.jallcom.2014.11.051.

23

photocatalyst.

J.

Hazard.

Mater.

2010,

30


177,

781-791.

DOI:

Page 31 of 42

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1

Figure Captions.

2

Fig. 1. (A) and (B) TEM images, and (C) elemental mapping of the VS4/CP nanocomposites.

3

Fig. 2. (A) EDX; (B) XRD pattern; (C), (D) and (E) XPS spectra of the VS4/CP

4

nanocomposites.

5

Fig. 3. Time history of MO decolorization efficiency under different conditions within 30

6

min operation.

7

Fig. 4. MO decolorization efficiency by the VS4/CP nanocomposites in the presence of

8

different scavengers under visible light irradiation.

9

Fig. 5. UV-vis spectra evolution during the photocatalytic decolorization of MO using the

10

VS4/CP nanocomposites.

11

Fig. 6. Operating factors studies for MO decolorization by the VS4/CP nanocomposites: (A)

12

catalyst dosage; (B) MO concentration; and (C) pH.

13

Fig. 7. MO decolorization by the VS4/CP nanocomposites in four consecutive cycles with

14

visible light irradiation.

31



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Page 32 of 42

Table 1. Photocatalytic decolorization of MO in aqueous solution catalyzed by different photocatalysts.

Photocatalyst

Time (h)

MO concentration (mg L-1)

Catalyst dosage (g L-1)

Light source

Decolorization efficiency (%)

Decolorization rate (mg L-1 h-1)

Photoreactor

References

graphene oxide/TiO2 composites

3

12

1.0

visible light

36.0

1.4

glass beaker

37

CdS/TiO2

2

10

1.0

visible light

95.0

4.8

glass beaker with a cooling-water-cycle system

CuFe2O4/AgBr

2.7

20

1.0

88.2

6.5

glass beaker

VS4/CP nanocomposites

0.5

10

1.0

98.8

19.8

beaker with a circulating cooling water bath

Cu/ZnO

4

20

1.0

88.0

4.4

glass beaker

40

100

7.1

glass beaker

41

95.5

4.6

glass beaker

42

67.0

13.4

95.0

3.2

Co2TiO4 nanoparticles Se-ZnS nanocomposites VS4/CP nanocomposites

0.7

5

0.2

2.7

13.1

4

0.5

10

1.0

ZnO

3

10

2.0

visible light visible light UV light UV light UV light UV light sunlight

32


beaker with a circulating cooling water bath beaker with a circulating water jacket

38

39

This study

This study 43

Page 33 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

g-C3N4/graphen e oxide aerogel TiO2 VS4/CP nanocomposites


4

20

1.0

sunlight

92.0

4.6

quartz conical flask

44

6

50

0.6

sunlight

60.0

5.0

glass beaker

45

0.5

10

1.0

sunlight

70.1

14.0

glass beaker

This study

33



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Page 34 of 42

Table 2. Organic compounds in the original and processed solution after 30 min operation. Organic compounds

Original sample

Processed sample

Organic compounds

Original sample

Processed sample

Organic compounds

Original sample

Processed sample

Thiocarbamic acid

√a

-b

Phthalic acid

√

-

2-methylbenzoic acid

-

√

Butanoic acid

√

-

Decane

√

√

2-butanone

-

√

Cyclopentane

√

-

√

-

Ethanethioamide

-

√

3,5-Dimethylbe nzaldehyde thiocarbamoylh ydrazone

√

-

√

-

2Chloropropionic acid

-

√

2,3-dichloro-2methylPropanal

√

-

Cyclic octaatomic sulfur

-

√

2,2'-Sulfinyldieth anol

-

√

Cycloheptanone Phthalic acid Pyrazine

√ √ √

-

Methanol Indole 1,3,5-Triazine

-

√ √ √

Phthalic acid Cyclopentane 1H-Purine

-

√ √ √

a

Detected in the sample.

b

Not detected.

Heptadecanoic acid 1-(3',4'-Dichlor ophenyl)-3-phe nylimidazolidin one

34


Page 35 of 42

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Figure 1. (A) and (B) TEM images, and (C) elemental mapping of the VS4/CP nanocomposites.

35



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. (A) EDX; (B) XRD pattern; (C), (D) and (E) XPS spectra of the VS4/CP nanocomposites.

36


Page 36 of 42

Page 37 of 42

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Figure 3. Time history of MO decolorization efficiency under different conditions with 30 min operation.

37



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. MO decolorization efficiency by the VS4/CP nanocomposites in the presence of different scavengers under visible light irradiation.

38


Page 38 of 42

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Figure 5. UV-vis spectra evolution during the photocatalytic decolorization of MO using the VS4/CP nanocomposites.

39



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. Operating factors studies for MO decolorization by the VS4/CP nanocomposites: (A) catalyst dosage; (B) MO concentration; and (C) pH.

40


Page 40 of 42

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Figure 7. MO decolorization by the VS4/CP nanocomposites in four consecutive cycles with visible light irradiation.

41



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TABLE OF CONTENTS (TOC) GRAPHIC

Synopsis A novel photocatalyst-VS4/carbon powder nanocomposites is one-step hydrothermally synthesized and exhibits excellent photocatalytic decolorization efficiency for methyl orange (MO) under visible light.

42


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Rapid Photocatalytic Decolorization of Methyl Orange under Visible

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