Green Synthesis of AgâTiO2 Supported on Porous Glass with

Subscriber access provided by Kaohsiung Medical University

Article

Green Synthesis of Ag–TiO2 Supported on Porous Glass with Enhanced Photocatalytic Performance for Oxidative Desulfurization and Removal of Dyes under Visible Light Yuqing Chen, Chun Shen, Jie Wang, Gang Xiao, and Guangsheng Luo ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02860 • Publication Date (Web): 05 Sep 2018 Downloaded from http://pubs.acs.org on September 5, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 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

ACS Sustainable Chemistry & Engineering

Green Synthesis of Ag–TiO2 Supported on Porous Glass with Enhanced

Photocatalytic

Performance

for

Oxidative

Desulfurization and Removal of Dyes under Visible Light

Yuqing Chen†, Chun Shen†,‡*, Jie Wang†, Gang Xiao†, and Guangsheng Luo‡,*

†Beijing Key Laboratory of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, No. 15 of North Three-Ring East Road, Chaoyang District, Beijing 100029, P. R. China. ‡The State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China.

Corresponding authors: Email address: [email protected] (Chun Shen), [email protected] (Guangsheng Luo).

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

ABSTRACT: As the energy shortage and environmental problem become the worldwide concern, the green synthesis of catalysts and their green applications has long been pursued. Here we proposed a facile catalyst synthesis approach in which Ag–TiO2 composites was prepared through an in-situ reduction at room temperature without severe conditions or hydrogen atmosphere. Porous glass (PG) was chosen as the support, and the as-prepared Ag–TiO2/PG was equipped with the remarkable merits of intense visible light absorbance, effective separation of electron–hole pairs, high surface areas for adsorption, and abundant reactive sites for the photocatalytic oxidation. Conversions of 95.2% and 92.1% for dibenzothiophene (DBT) and benzothiophene (BT), respectively, were realized under irradiation of energy-saving visible-light emitting diodes (LED), complying with the principles of ‘green chemistry’. Moreover, none of external oxidants, such as H2O2 or O2, was introduced, greatly increasing the viability of industrial applications. Ag– TiO2/PG also showed remarkable activity for removing rhodamine B (RhB), methylene blue (MB), and methylene orange (MO) with the rate constant of 0.14, 0.18, and 0.055 min–1, respectively. The mechanism study revealed that the immobilized Ag acted as the role of “killing two birds with one stone”: enhancing the absorption of visible light, suppressing the recombination of photoinduced electron–hole pairs via trapping electrons, and contributing to the generation of ·O2–. In addition, oxygen vacancies, ·OH and h+ also took part in the photocatalytic oxidation. This work explored the green synthesis of Ag–TiO2/PG and characterized their excellent photocatalytic activity for photocatalytic desulfurization and degradation of organic dyes, opening up new possibilities for low-energy consumption photocatalysis and sustainable chemistry.

Keywords: Ag–TiO2/porous glass; Visible light irradiation; Photocatalytic desulfurization; Photodegradation of organic dyes; Enhanced photocatalytic activity


Page 2 of 39

Page 3 of 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


INTRODUTION The environmental contamination caused by aromatic sulfur-containing compounds and

organic dyes has become one of the most serious problems in the last decades.1–3 The toxic SOx released during diesel combustion causes air pollution issues, such as acid rain and atmospheric haze, and organic dyes discharged into the water bodies pose a major threat to human health due to their carcinogenicity.4–7 Therefore, decomposing organic compounds in a green and energy-efficient way is highly desired. Recently, photocatalysis has become the research hotspot in the field of removing aromatic sulfur-containing compounds and degrading organic dyes, as it provides a green alternative to transform organic pollutants to environmental friendly substances with the aid of light. For instance, Zhou et al. 8 reported a novel visible-light-driven photocatalyst AgI/Bismuth oxychloride hybrid for efficient degradation of sulfamethazine. So far, TiO2 has been proved to be the most suitable photocatalyst on account of its abundance, chemical stability, nontoxicity, and low cost.9 Nevertheless, TiO2 can only harvest UV light which occupies a small fraction of solar spectrum (about 4%) because of its wide band gap (3.2 eV for anatase). In addition, it also involves the high recombination rate of electron–hole pairs leading to low photocatalytic efficiency.10 The key issue for TiO2-based photocatalyst is to tune its photoactive range towards the visible light region (λ > 400 nm).11 To date, coupling of a semiconductor with plasmon resonance nanoparticles has emerged as a breakthrough since the shape-dependent optical properties of metallic nanostructures retrieve the quantum efficiency.12,13 As reported by Gong et al.,14 the integration of plasmonic noble metals (such as Au and Ag) with photocatalysts was regarded as an effective method by taking advantage of the plasmonic effect to



enhance the absorbance of visible light and trapping the photogenerated electrons to decrease the charge carrier recombination rate. The noble metal/TiO2 composites have been used as photocatalysts in degrading organic pollutants, such as aromatic sulfur-containing compounds and dyes.15 As reported by Khayyat,16 the photocatalytic oxidation of benzothiophene (BT) and dibenzothiophene (DBT) over Au/TiO2 catalyst was conducted under UV radiation using H2O2 as the oxidant. The aromatic sulfur-containing compounds could be photooxidized to highly polar sulfoxide or sulfone species and then extracted by solvents. Similarly, other oxidants such as molecular oxygen (O2) was often used as well.17 However, introducing external oxidants such as O2 or H2O2 to fuels greatly increases the risk of explosion, besides, photocatalytic desulfurization was still conducted under UV light in most works, suffering from the rather low utilization of solar energy. Therefore, it is reasonable to predict that development of visible-light sensitive photocatalysts which own abundant self-generated electron–hole pairs to yield reactive oxygen species without external oxidants would be a more promising option for photocatalytic desulfurization. In the field of water purification, intensive studies have shown that Ag/TiO2 composites are specialized in photodegrading dyes such as rhodamine B (RhB) and methylene orange (MO). As reported by Jafari et al.,18 silver nanoparticles were loaded on the surface of TiO2 nanoparticles by a photocatalytic reduction and solvothermal method in which Ag+ ions were reduced under UV irradiation. The obtained Ag nanocrystals were in the size range of 5–10 nm and the rate constant was 0.032 min–1 for the photocatalytic degradation of RhB. Yang et al. reported the preparation of Ag/TiO2-N hybrids with Ag diameter of about 15 nm through a solvothermal process.19 Similarly, Alsharaeh et al. reported a sol–gel method to prepare Ag/TiO2 nanocomposites with the Ag


Page 4 of 39

Page 5 of 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


nanoparticle (NP) size of 10–13 nm.20 As a matter of fact, the size of Ag nanoparticles significantly affects the efficiency of electron–hole separation and the localized surface plasmon resonance (LSPR). Meanwhile, the synthetic routes of Ag–TiO2 hybrids mentioned above are relatively complex, involving tedious process with rigorous experimental conditions. Therefore, from the standpoint of green and sustainable chemistry, development of novel methods, in which Ag–TiO2 catalysts with a high photocatalytic activity under visible light emitting diode (LED) irradiation could be controllably and facilely prepared, is still in urgent need. In our previous work, Pd and Ag nanoparticles have been successfully prepared at room temperature by coupling the ion exchange and reduction process in one step using alcohols both as the solvent and reducing agent. Meanwhile, we also prepared TiO2/porous glass (PG) catalysts with the mean size of 2.1 nm for TiO2 nanoparticles, and the as-prepared catalysts exhibited excellent catalytic activities for oxidation desulfurization and photodegradation of organic dyes under UV light.21,22 On the basis of these works, we explore the feasibility of preparing Ag–TiO2 nanoparticles supported on porous glass by in-situ reduction at room temperature, and the catalyst is denoted as Ag–TiO2/PG. As far as we know, neither the facile preparation of Ag–TiO2/PG nor its photocatalytic performance for sulfur-containing compounds such as DBT and BT and organic dyes under visible light has been reported yet. There may be four possible advantages for choosing Ag–TiO2/PG as the photocatalyst: first, because of the ion-exchange property of porous glass, it is readily to obtain TiO2 nanoparticles with small particle sizes, which is benefit for their photocatalytic activity; second, the support, namely porous glass, makes the in-situ reduction of



Page 6 of 39

Ag+ ions available at room temperature without strong reducing agents such as NaHB4, simplifying the preparation process; third, the porous glass is composed of magnesium silicate, which has shown great potential in adsorption for organic pollutions,

23

and as improved in our

previous work, the porous glass showed high adsorptive property for aromatic sulfur-containing compounds via polar interaction.22 Heterogeneous reactions would be greatly enhanced by the remarkable adsorptive property of catalysts for reactants; and fourth, the core–shell structure of the support would facilitate mass transfer efficiently. The morphologic structures and optical properties of the Ag–TiO2/PG were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence and ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy. Degradation of aromatic sulfur-containing compounds such as DBT and BT as well as organic dyes such as MO, RhB, and methylene blue (MB) under visible LED irradiation was carried out to evaluate the catalytic activity of the as-prepared catalysts. A possible photocatalytic mechanism was proposed based on the analysis of behaviors of photoinduced electron–hole pairs and band position of photocatalysts

EXPERIMENTAL Materials. The sieved glass microbeads with an average diameter from 95 to 105 µm were

procured from Hebei Chiye Corporation. Titanium (IV) oxysulfate and silver nitrate (AgNO3) were purchased from Aladdin Chemical Co. Ltd. CTAB was supplied by Sigma-Aldrich. MO, RhB, and MB were obtained from Tianjin Fu Chen Chemical Reagents Factory (Tianjin, China). Analytical grade octane was purchased from Fuchen Chemical Plant in Tianjin, China. DBT and


Page 7 of 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


BT were purchased from Acros Organics. All chemicals used in this work were of analytical grade without further treatment. Preparation of Ag–TiO2/PG photocatalyst. TiO2/PG catalysts were prepared according to our previous work.21 To prepare Ag–TiO2/PG catalysts, AgNO3 and ethanol was firstly mixed and stirred for 30 min to form a uniform solution. Then 1 g of TiO2/PG catalyst was added to the solution containing AgNO3, and they were marked as mixture A. After that, the colloid consists of CTAB and deionized water was added to the mixture A and the final mixture was shaken for 3 h at room temperature. The obtained Ag–TiO2/PG catalysts was separated from the solution by centrifugation and washed with deionized water and ethanol for several times. The composites were dried at 373 K under vacuum conditions and the obtained catalysts were denoted as x% Ag– TiO2/PG with x representing the mass ratio of Ag/Ti in the starting materials. Characterization. The surface morphology of the catalyst was obtained using SEM (Hitachi S-4500, Japan). JEOL JEM-2011 high-resolution transmission electron microscope was used to get TEM images. Nitrogen adsorption–desorption isotherms were measured using a Micromeritics ASAP 2020 instrument. XRD was performed by a Bruker D8 X-ray diffractometer, with monochromatic Cu ‫ܭ‬డ radiation (λ = 1.5406 Å). XPS was measured by X-ray photoelectron spectrometer (Esca Lab 250Xi, USA) and the bind energies were calibrated to the C 1s peak at 284.8 eV. Contents of titanium and silver were determined using ICP-AES (Agilent ICP 700, USA). UV–vis diffuse reflectance spectra was recorded on a spectrophotometer (UV-3600, Japan) in the range of 220–800 nm. Photoluminescence (PL) spectra were recorded with a fluorescence spectrometer (F-7000 FL Spectrophotometer, Japan) using a Xe lamp as the excitation light source. Electron spin resonance (ESR) spectra were operated on a Brucker E500 spectrometer.



Photocatalytic oxidative desulfurization of DBT and BT. Typically, 5 g of model fuel (the solution of DBT or BT dissolved in octane was used as the model fuel) with the initial concentration of 50 ppm and 0.5 g of photocatalysts was added into a home-made quartz cup with water bath circulation, and then a certain amount of ethanol was also introduced. After 30 min’s stirring for adsorption–desorption equilibrium, the system was irradiated with 50 W LED (20 mW/cm2) which was placed above the solution with the distance of 3 cm. The samples were withdrawn periodically every 20 min from the upper phase and after high speed centrifugation, the reaction product was analyzed by gas chromatography (GC) 2014 with an FPD detector (Shimadzu). The detailed parameter about chromatographic column was shown in supplementary material. DBT conversion is defined in equation (1).

x=

∆nDBT (1) n0 DBT

Photocatalytic degradation of organic dyes. The reactor was composed of a 50 W LED (20 mW/cm2) with the main emission wavelength at 447 nm and a magnetic stirrer. The lamp was placed at a distance of 10 cm from the solution. Throughout the experiment, the suspension containing 10 mg catalysts and 5 mL dye solution (50 mg/L) was continuously stirred for 30 min in dark to achieve adsorption–desorption equilibrium. After that, LED was turned on starting the photocatalytic reaction. Aliquots were withdrawn from the irradiated solutions at specific intervals and analyzed by UV–vis spectroscopy (UV-1200, AOE, China) at 554 nm for RhB, 464 nm for MO, and 664 nm for MB.

RESULT AND DISCUSSION Preparation and characterization of Ag–TiO2/PG. The crystalline structure of catalysts was


Page 8 of 39

Page 9 of 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


investigated by XRD and the results are shown in Fig. 1. The TiO2/PG catalysts exhibit a strong diffraction peak corresponding to the diffraction plane (1 0 1) which demonstrates the existence of the anatase phase (JCPDS 21-1272). The typical diffraction peaks with 2θ values of 38.1° (1 1 1) and 44.4° (2 0 0) were observed in patterns of Ag/PG correlated to the standard peaks of Ag0 nanoparticles with the face-centered cubic structure (JCPDS 4-0783), indicating the successful loading of Ag onto the porous glass. After the in-situ reduction of Ag+ ions, intensity of the anatase diffraction peaks decreases, which may result from the formation of Ag on the surface of TiO2. The ICP-AES result indicates that the Ag content of the Ag–TiO2/PG samples is 1.45 wt%. The XRD patterns and ICP-AES results for 1% Ag–TiO2/PG, 3% Ag–TiO2/PG, and 5% Ag– TiO2/PG are shown in Fig. S1 and Table S1 in the supplementary material, respectively. In order to gain a deeper insight into the role of CTAB in the preparation procedures, we prepared Ag–TiO2/PG catalysts with different CTA+ amounts, denoted as I-CTAB, II-CTAB, and III-CTAB, respectively. As shown in Fig. S2, Ag nanoparticles are uniformly dispersed on the surface of Ag–TiO2/PG in all the three catalysts. However, with the increase of CTAB amount from 1.9×10-4 mol to 8.7×10-4 mol, the mean particle size of Ag nanoparticles decreases gradually from 9.0 to 3.6 nm. Therefore, CTA+ plays a key role in controlling the diameter of Ag nanoparticles by preventing particle agglomeration. Previous studies have reported that the CTA+ plays an important role in morphology and stability of Ag nanoparticles where CTA+ molecules would form bilayers, and the molecules on the inner layer are adsorbed onto silver clusters with their headgroups. 24 SEM images of the prepared samples are shown in Fig. S3. After the immobilization of TiO2 and Ag nanoparticles, the catalysts retained their sphere structure. As shown in Fig. 2a, the Ag



nanoparticles are monodispersed with an average diameter of 2.2 nm and the particle size distribution histogram is shown in Fig. 2b. Lattice fringes of 0.34 and 0.24 nm are observed in Fig. 2c which should be contributed to the (1 0 1) plane of anatase and (1 1 1) plane of metallic silver, respectively. Fig. 2d shows the selected area electron diffraction (SAED) pattern, which clearly displays a set of diffraction spots of Ag NPs, indicative of a monocrystalline structure. In order to take a deeper insight into the distribution of Ag and TiO2 nanoparticles, STEM-EDS elemental line scanning was performed. As depicted in Figs. 2e and 2f, an isolated light-colored dot can be regarded as a nanoparticle containing heavier element. No NPs agglomeration exists in this catalyst, which is consistent with TEM results. It could be evidently observed that the intensity of Ag element is much stronger than that of Ti and O element. More importantly, in Fig. 2g, the Ag-rich position is in the central section while Ti and O are distributed uniformly with similar steady intensity all along, further verifying the formation of metallic Ag NPs on TiO2. XPS survey spectra of Ag–TiO2/PG catalysts is shown in Fig. S4. The XPS spectra of Ti 2p and Ag 3d are shown in Fig 3. The two peaks detected at 458.8 and 464.5 eV correspond to Ti 2p3/2 and 2p1/2, respectively. As shown in Fig. 3b, two symmetrical peaks at 374.2 and 368.2 eV with a peak separation of 6.0 eV could be attributed to metallic silver (Ag0).25 It is worth noting that the Ag 3d peaks for Ag–TiO2/PG are observed at 373.9 and 367.9 eV (0.3 eV shift from metallic Ag0 368.2 eV for Ag/PG catalysts), indicating the Ag nanoparticles loaded on Ag– TiO2/PG catalyst are more negatively charged. Meanwhile, the characteristic peaks of Ti 2p have a slight shift to lower binding energy after the in-situ reduction by ethanol, suggesting the Ti species was also more negatively charged than Ti4+ and oxygen vacancies may be generated, which would promote the visible light absorbance and photoinduced charge separation efficiency.26


Page 10 of 39

Page 11 of 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


To further detect the existence of oxygen vacancies, the as-prepared photocatalysts were characterized by electron spin resonance (ESR), and the result is shown in Fig. 4. The g-value of the symmetrical signals equals 2.004, which is the characteristic signal of the surface oxygen vacancies.27,28 The observed intensity of ESR signals of Ag–TiO2/PG is much stronger than that of TiO2/PG, indicating more negatively charged Ti species appeared after the reduction with ethanol. Oxygen vacancies with visible-light response are conducive to the production of superoxide radicals because lifetime of the photoinduced electron in the oxygen vacancies is much longer than that on conduction band (CB), as reported by Sugawara.29 On the basis of the above analysis, it is reasonable to predict high photocatalytic activity of the as-prepared Ag–TiO2/PG catalysts. The N2 adsorption–desorption isotherms of photocatalysts are depicted in Fig. S5. The specific surface areas, pore size distributions, and pore volumes of the TiO2/PG and the Ag– TiO2/PG catalysts are determined by the Barret–Joyner–Halenda (BJH) method, and the results are listed in Table S2. The as-prepared Ag–TiO2/PG photocatalysts possess a high interfacial surface area of 131.2 m2 g−1 which enhances the reaction performance and adsorption of organic pollutants. Optical properties of Ag–TiO2/PG. UV–visible diffuse reflectance was carried out to ascertain the light absorption ability and the band gaps of the photocatalysts. As shown in Fig. 5a, TiO2/PG photocatalysts present poor light absorption in the visible light region from 400 to 800 nm. Compared with TiO2/PG, the synthesized Ag–TiO2/PG photocatalysts exhibit a strong visible light absorption because of the localized surface plasmon resonance (LSPR) of Ag NPs. The energy band gaps could be calculated according to the formula which has been widely adopted to relate the absorption coefficient to the energy band gap:



∂hν = A(hν − E g )

n

2

(2)

where A is the absorbance and hv is the incident photon energy.30 Fig. 5b shows plots of ( ∂hv )2 versus photon energy. The band gap energies (Eg) of TiO2/PG, 1% Ag–TiO2/PG, 3% Ag–TiO2/PG, 5% Ag–TiO2/PG, and 7% Ag–TiO2/PG are determined from the intercepts to be 3.1, 2.1, 2.3, 2.2, and 2.9 eV, respectively. The narrow band gaps could be explained by the Schottky junction formed at the interface of the Ag nanoparticles and TiO2 substrate. It would capture the photo-induced electrons, leading to the redundant electrons accumulation on Ag nanoparticles. The Fermi level thereby gets close to the conduction band of TiO2 NPs and reduces the band gap energy of the composite.31 The migration and separation efficiency of the photogenerated electron–hole pairs are regarded as the key parameters in estimating the photocatalytic performance of photocatalysts. The charge-carrier separation of the photocatalysts is often verified by photoluminescence (PL), since the PL emission was caused by the recombination of free charge carriers.32 Two emission peaks at 398 and 468 nm are observed in both of the spectra (Fig. 6), which are equivalent to 3.12 and 2.65 eV, respectively. The former is attributed to the emission of band gap transition of trititanate,33 and the latter derives from the emission caused by the charge-transfer transition from Ti3+ to oxygen anion of TiO68− complex.34 Compared with TiO2/PG, the intensity of PL signal for the Ag decorated photocatalysts are much lower, indicating that the deposition of Ag lowered the recombination rate of electrons and holes under UV and visible light irradiation. This is ascribed to the fact that the electrons excited from the valence band would transfer to silver nanoparticles where its excellent electronic conductivity restrained the recombination of electrons and holes. Therefore, we can conclude that recombination of the photogenerated charge carriers could be


Page 12 of 39

Page 13 of 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


greatly inhibited by the successful deposition of Ag NPs, which is charged for the high photocatalytic activity. To further investigate the behavior of photogenerated electron–hole pairs, the transient photocurrent responses of Ag–TiO2/PG and TiO2/PG were measured to prove the retard of the recombination of photogenerated electron–hole pairs caused by Ag deposition. The results in Fig. 7 clearly show that the photocurrents of TiO2/PG are relatively low, and the decay of the photocurrent indicates the recombination of holes with electrons.35,36 On the contrary, the photocurrent density of Ag–TiO2/PG is almost two times higher than that of TiO2/PG, demonstrating the stimulating effect of Ag NPs in trapping the photogenerated electrons and accelerating the interfacial charge transfer, which is closely consistent with the results presented by PL spectra. Moreover, the photocurrents of the Ag–TiO2/PG and TiO2/PG catalysts were repeatable for 7 on–off cycles, demonstrating high photostability of the as-prepared photocatalysts. The transient photocurrent responses of Ag–TiO2/PG with different Ag content are shown in Fig. S6. Photocatalytic desulfurization under visible light. In previous studies,37,38 molecular oxygen (O2) and hydrogen peroxide (H2O2) were conventionally used as oxidants to propel the oxidation of organic sulfur compounds. However, the coexistence of fuel and O2 (even labile H2O2) will definitely trigger the explosion accident when applied in industrial applications. In consideration of this, none of external oxidants such as O2 and H2O2 was added during the photocatalytic desulfurization conducted in this work. Alcohols such as ethanol have become one of the most competitive sustainable energy due to its high octane number and easy generation from renewable biomass.39 Besides, bio-ethanol has been used as the additive into gasoline in



China to address the environmental pollution. In this regard, ethanol was added into the model fuels instead of O2 or H2O2 in this work, and the added ethanol could serve as electron acceptor by consuming valance band holes (h+) to suppress the recombination of photogenerated electron–hole pairs.40 Furthermore, we speculated that ethanol may be conducive to the formation of hydroxyl radicals, where hydroxyl radicals are formed via the pathway as shown in Scheme. S1: firstly, with ethanol oxidized by h+, a large number of photo-induced electrons consume oxygen to yield numerous superoxide radicals (·O2-) and the quantity of ·O2- reaches the climax, and secondly, ·O2combined with H+ to form ·OH, indicating the rising of ·OH while the falling of ·O2- species. ESR spectra (Fig. S7) was especially employed to track the behavior of ·OH and ·O2- species. It can be seen that the intensity of ·O2- characteristic peak reaches maximum at the first 2 min and then decreases gradually, while the intensity of ·OH characteristic peak grows stronger over time. Photocatalytic performances of TiO2/PG and Ag–TiO2/PG are shown in Fig. 8. Under visible light irradiation, DBT conversions of 83.5% and 58.8% were realized in 80 min over Ag–TiO2/PG and TiO2/PG, respectively. Similarly, Ag–TiO2/PG exhibited a higher photocatalytic activity (BT conversion was 80.1% after 80 min) compared with TiO2/PG under LED irradiation. To further increase the conversion of the organic sulfur compounds, more experiments with higher catalyst/organic sulfur compounds mass ratio were carried out. As shown in Fig. S8, conversions of 95.2% and 92.1% were achieved for DBT and BT, respectively. The oxidative product is confirmed by IR spectrum, and the result is shown in Fig. S9. The wavenumber at 575 and 1121 cm−1 were attributed to the stretching vibration of S=O, confirming the existence of sulfone.41 Photocatalytic degradation of organic dyes under visible light. In order to investigate the individual contribution to the photocatalytic activity, Ag/PG and TiO2/PG have also been prepared,


Page 14 of 39

Page 15 of 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


and their catalytic performances are shown in Fig. S10 in the supplementary material. Compared with TiO2/PG and Ag/PG, the photocatalytic activity of Ag–TiO2/PG is higher because of the synergistic effect between Ag and TiO2 nanoparticles. As shown in Figs. 9a and 9c, porous glass shows high adsorptive abilities for cationic dyes, namely RhB and MB during the 0.5 hour’s dark adsorption, confirming the advantages of the Ag–TiO2/PG catalysts prepared in this work. The photocatalytic activities of PG and Ag–TiO2/PG photocatalysts with different mass ratios of Ag/TiO2 were evaluated by comparing the degradation efficiencies for RhB, MB, and MO under visible-light irradiation. As for the cationic dyes, the 1% Ag–TiO2/PG catalyst exhibited the highest catalytic activity. The conversion of the model dyes increased dramatically in the first 2 minutes: the RhB conversion increased from 15% to 80%, and the MB conversion varied from 55% to 95%. Afterwards, the degradation rates decreased gradually, and the complete degradation of RhB and MB was achieved within 15 min. The adsorption capability of porous glass for anionic dyes drops off obviously compared with that for cationic dyes: only 2% of MO was adsorbed by PG after 0.5 h. The difference in adsorption ability would be ascribed to the electric charges of the photocatalysts. Zeta potentials of different photocatalysts were tested and the results are shown in Fig S11 and Table S3. It reveals that the as-prepared Ag–TiO2/PG photocatalysts are negatively charged in neutral solution, suggesting the higher adsorption ability for cationic dyes than that for anionic dyes. As expected, the degradation was enhanced by better adsorptive ability. As shown in Fig. 9e, 100% degradation of MO under visible light was realized after 30 min over 7% Ag– TiO2/PG catalyst. During the degradation of organic dyes, the improvement of the catalytic activity through Ag decoration may be ascribed to the lower recombination of electron–hole pairs, higher surface area and lower band gap energy. Furthermore, UV–vis absorption spectra for



degradation of RhB, MB in the presence of 1% Ag–TiO2/PG and degradation of MO over 7% Ag– TiO2/PG are shown in Figs. 9b, 9d, and 9f, respectively. The characteristic absorbance peak intensities of RhB (~554 nm), MB (~664 nm), and MO (~464 nm) decrease dramatically as the photoreaction goes on. Additionally, the hypsochromic shifts of the absorbance peak were not observed during the photocatalytic degradation, indicating the full degradation of these dyes without the generation of intermediates.42 Degradation of RhB, MB, and MO could be described as a Langmuir−Hinshelwood first-order kinetics model.43 Accordingly, the rate constants are calculated by linear fitting of the ln(C0/C) versus time plots, where the slopes give the values of ka. As shown in Fig 10, the ln(C0/C) value increased linearly with t, and the obtained ka under visible light is 0.14, 0.18, and 0.055 min-1 for the degradation of RhB, MB and MO, respectively. Photodegradation of RhB, MB, and MO by Ag-modified TiO2 catalysts have been reported in other studies.44–51 Comparisons in photocatalytic activities for RhB, MB, and MO are listed in Table 1, 2, and 3, respectively. The Ag–TiO2/PG photocatalysts prepared in this work are highly efficient for degrading organic dyes. The Ag NPs with an average diameter of 2.2 nm cooperated well with monodispersed TiO2 NPs sized in 2.1 nm (TiO2/PG catalysts have been reported in our previous work),21 rendering the significant contribution to the outstanding photocatalytic activity. The colorless contaminant phenol has also been photodegraded in the presence of Ag–TiO2/PG, the experimental detail and result are shown in Fig. S12. The XRD pattern of spent Ag–TiO2/PG catalyst is shown in Fig. S13, which still matches with the standard card of the anatase phase (JCPDS 78-2486) and Ag0 nanoparticles with the face-centered cubic structure (JCPDS 4-0783). The TEM image and size distribution histogram of


Page 16 of 39

Page 17 of 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


the spent catalysts are shown in Fig. S14. Ag nanoparticles dispersed on TiO2 layer exhibited the average diameter of 3.7 nm, a slight increase compared to the fresh photocatalysts. There are no obvious differences in morphology between fresh photocatalysts and the spent ones. The XPS spectra of the spent catalysts with Ti 2p and Ag 3d are shown in Fig. S15. Structural properties of the used catalysts were determined by BET measurement. The specific surface area is 130.6 m² g-1, pore volume is 0.25 cm3 g-1, and the average pore diameter is 7.8 nm. Based on the results of XRD, TEM, XPS, and BET, there are no obvious differences in morphology or structure between the fresh photocatalysts and the used ones, indicating the good stability of the as-prepared photocatalysts. Possible mechanism of the photocatalytic oxidation. As reported by previous studies that active species generated from the photocatalysts upon light irradiation, such as hydroxyl radicals (·OH), superoxide radicals (·O2-) and holes (h+), are the essential active sites for the oxidization and mineralization of organic molecules.52 In order to detect the existence of radicals during the photocatalytic process over Ag–TiO2/PG and propose the possible photocatalytic mechanism, ESR measurements were performed with 5,5–dimethyl–1–pyrroline–N–oxide (DMPO) as scavenger to prove the existence of radicals in the reaction system. As shown in Fig. 11, all the experiments were operated under both dark conditions and visible light irradiation. There is no radical detected in dark conditions, while four high characteristic peaks of ·O2- and ·OH could be observed under visible light irradiation, indicating the existence of ·O2-·and ·OH. Meanwhile, the intensity of active radicals generated using Ag–TiO2/PG as the catalyst is almost twofold higher than that over TiO2/PG. Photoinduced holes (h+) were also tested by using 2,2,6,6–tetramethyl–1–piperidinyloxy (TEMPO) as probe molecular, as shown in Fig. 11c, no ESR signals of h+ were observed in dark



conditions, while the signal intensity corresponding to the characteristic peak of h+ for the Ag– TiO2/PG was significantly higher than that of TiO2/PG at the same illumination time. During the photodegradation process, the photo-induced free electrons reacted with O2 to produce ·O2-, and the holes (h+) reacted with OH− and H2O to produce ·OH. In essence, the prominent production ability of active radicals can be primarily ascribed to the coupling of Ag and TiO2 NPs. Once irradiated under visible light, the migration of photo-induced electrons from Ag to TiO2 surface took place through the heterojunctions formed at the interface, leading to the efficient reaction with dissolved O2 to yield highly oxidative species ·O2-. These results reflected that photoinduced electrons and holes both contributed to the photodegradation process over Ag–TiO2/PG photocatalysts, leading to a higher concentration of reactive species, namely ·OH, ·O2- and holes. To better understand the band position and the photocatalytic mechanism of Ag–TiO2/PG composite. The conduction band edge (ECB) and valence band edge (EVB) of TiO2 are calculated by the following equation:53,4

EVB = X + 0.5 E g − E e (3) E CB = EVB − E g (4) where the X value for TiO2 is 5.81 eV. Eg is the band gap of TiO2 (3.1 eV). Ee is the energy of free electrons on the hydrogen scale (~4.5 eV). As a result, the ECB of TiO2 is determined at -0.24 eV and the EVB is 2.86 eV. Thus, the CB of Ag–TiO2/PG is more negative than the standard redox potential of O2/·O2- (E0 (O2/·O2-) = –0.046 eV),55 while the VB levels is more positive than the standard redox potential of OH/·OH (E0 (OH/·OH) = 2.8 eV),53 meeting the demand for yield of ·OH, as shown in Scheme 1. Under visible light, oxygen vacancies doped in TiO2 act as a drawboard to facilitate the electron jump from the VB to the CB, enhancing the separation of the


Page 18 of 39

Page 19 of 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


photogenerated electron–hole pairs. Subsequently, SPR Ag plays the important role to activate the sufficient release of photoinduced electrons instead of recombination with photogenerated holes, and these electrons should be contributed to the formation of ·O2–. Combining the results with ESR signals of h+ and ·OH in the Ag–TiO2/PG containing system, it is assumed that the holes (h+) generated on the valance band of TiO2 reacted with H2O or OH– to produce ·OH. The organic molecular, dyes (RhB, MB, and MO) and sulfur organic compounds (DBT and BT) can be oxidized by the reactive radicals, ·O2–, ·OH and h+ during the photocatalytic oxidative process. The support featuring porous nanostructures with surface area of 131.2 m2 g−1 endows the as-prepared photocatalysts with high surface areas for adsorption of H2O, OH–, O2 and organic molecules, and abundant reactive sites for the photocatalytic oxidative process as well.

CONCLUSIONS In summary, the concept of ‘green chemistry’ is throughout in this work: first, the highly

active Ag–TiO2/PG photocatalyst was prepared in a facile and green method in which in-situ reduction of metallic silver was realized at room temperature instead of treatments under severe high temperatures. What’s more, ethanol was employed as the reductant and the system was clear of conventional hydrogen atmosphere. The green and low-cost fabrication of photocatalysts was achieved; second, during the photocatalytic oxidation process, energy saving visible-LED was served as light source, substituting the fragile and rigid high-pressure mercury lamps; and third, to evaluate the photocatalytic activity of as-prepared Ag–TiO2/PG photocatalyst, photocatalytic oxidation of aromatic sulfur-containing compounds and organic dyes was performed. Under visible light irradiation, a DBT conversion of 83.5% was realized in 80 min over Ag–TiO2/PG, and



BT conversion was 80.1% after 80 min. The photocatalytic oxidation of DBT and BT was driven by the reactive oxygen species which were the products of photoinduced electron–hole pairs reacted with small amount of dissolved O2 and H2O. None of external oxidants, such as H2O2 or O2, was introduced to the photocatalytic oxidation desulfurization process, effectively avoiding the explosion risk which is of significance to industrial applications. As to the photodegradation of organic dyes, Ag–TiO2/PG photocatalyst exhibited high photocatalytic activity in removal of RhB, MB and MO with the rate constant of 0.14, 0.18, and 0.055 min–1, respectively. Inspired from the feasibility of green synthesis and application of Ag–TiO2/PG, an in-depth research of credible mechanism of the photocatalytic oxidation was also proposed. Ag NPs with SPR effect deposited onto the surface of TiO2/PG acted as the role of “killing two birds with one stone”: enhancing absorption of visible light, trapping more electrons to suppress the recombination of photoinduced electron–hole pairs and contribute to high concentration of ·O2–. Moreover, oxygen vacancies, ·OH and h+ also took part in the photocatalytic oxidation process based on the analysis of ESR and band position. This work explored the green approach for fabricating Ag–TiO2 composites and investigated the green applications of Ag–TiO2/PG, providing highly promising candidates for efficient desulfurization and gradation of organic dyes.

ASSOCIATED CONTENT

Supporting information This information is available free of charge via the Internet at http://pubs.acs.org/. Detailed information about parameters of GC chromatography, XRD patterns of Ag–TiO2/PG with different Ag content, TEM images and the corresponding size distribution histograms for catalysts prepared with different amount of CTAB, SEM images of as-prepared photocatalysts, XPS survey


Page 20 of 39

Page 21 of 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


spectrum of Ag–TiO2/PG catalysts, nitrogen adsorption–desorption isotherms of Ag–TiO2/PG and the corresponding pore size distribution profiles, transient photocurrent responses of Ag–TiO2/PG with different Ag contents, DMPO spin trapping ESR spectra of the Ag–TiO2/PG photocatalysts in presence of ethanol, photocatalytic activity of the 3% Ag–TiO2/PG (1 g) for DBT and BT conversion under LED irradiation, IR spectrum of photocatalytic oxidation products of thiophene, photocatalytic performances of Ag/PG and TiO2/PG in degradation of dyes, Zeta potential results of photocatalysts, photocatalytic performances for degradation of phenol, XRD patterns of used Ag–TiO2/PG photocatalysts, TEM image and the corresponding size distribution histograms of the spent catalysts, XPS spectra of the spent catalysts, the possible pathway for the generation of hydroxyl radicals, ICP-AES results of Ag–TiO2/PG, BET results of as-prepared catalysts.

Author Information Corresponding Authors *E-mail: [email protected], [email protected] ORCID Chun Shen: 0000-0001-6993-4336 Guangsheng Luo: 0000-0002-8466-4618 Notes The authors declare no competing financial interest.

Acknowledgements We gratefully acknowledge the support of the National Nature Science Foundation of China



Page 22 of 39

(21606008), the Fundamental Research Funds for the Central Universities (buctrc201616), the State Key Laboratory of Chemical Engineering (SKL-ChE-16A01, SKL-ChE-17A02).

References (1) Liu, S. M.; Liu, Y. W.; Jiang, S. P.; Liu, S. X.; He, D. F.; Li, N.; Miao, J.; Ye, J. H. Stable visible-light photocatalytic degradation of organic pollutant by silver salt of Ti-substituted Keggin-type

polyoxotungstate.

J.

Environ.

Chem.

Eng.

2016,

4(1),

908-914.

10.1016/j.jece.2015.12.027 (2) Zhou, C.; Lai, C.; Xu, P.; Zeng, G.; Huang, D.; Li, Z.; Zhang, C.; Cheng, M.; Hu, L.; Wan, J.; Chen, F.; Xiong, W.; and Deng, R. Rational design of Carbon-doped Carbon Nitride/Bi12O17Cl2 Composites: A Promising Candidate Photocatalyst for boosting visible-light driven photocatalytic degradation of tetracycline. ACS Sustainable Chem. Eng. 2018, 6 (5), 6941–6949. 10.1021/acssuschemeng.8b00782 (3) Bahadori, E.; Vaiano, V.; Esposito, S.; Armandi, M.; Sannino, D.; Bonelli, B. Photo-activated degradation of tartrazine by H2O2 as catalyzed by both bare and Fe-doped methyl-imogolite nanotubes. Catal. Today. 2018, 304, 199–207. 10.1016/j.cattod.2017.08.003 (4) Jiang, W.; Zhu, Y.; Zhu, G.; Zhang, Z.; Chen, X. Three-dimensional photocatalysts with a network structure. J. Mater. Chem. A, 2017, 5 (12), 5661. 10.1039/c7ta00398f (5) Mokhtar, N.; Aziz, E. A.; Arisb, A.; Ishakc, W. F. W.; Ali, N. S. M. Biosorption of azo-dye using marine macro-alga of Euchema Spinosum. J. Environ. Chem. Eng. 2017, 5 (6), 5721–5731. 10.1016/j.jece.2017.10.043 (6) Hu, Liang.; Wan, Jia.; Zeng, G.; Chen, A.; Chen, G.; Huang, Z.; He, K.; Cheng, M.; Zhou, C.;


Page 23 of 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


Xiong, W.; Lai, C.; and Xu, P. Comprehensive evaluation of the cytotoxicity of CdSe/ZnS quantum dots in Phanerochaete chrysosporium by cellular uptake and oxidative stress. Environ. Sci. Nano. 2017, 4, 2018–2029. 10.1039/c7en00517b (7) Wu, M. H.; Li, L.; Xue, Y. C.; Xu, G.; Tang, L.; Liu, N.; Huang. W. Fabrication of ternary GO/g-C3N4/MoS2 flower-like heterojunctions with enhanced photocatalytic activity for water remediation. Appl. Catal. B. 2018, 228, 103–112. 10.1016/j.apcatb.2018.01.063 (8) Zhou, C.; Lai, C.; Xu, P.; Zeng, G.; Huang, D.; Zhang, C.; Cheng, M.; Hu, L.; Wan, J.; Liu, Y.; Xiong, W.; Deng, Y. and Wen, M. In Situ Grown AgI/Bi12O17Cl2 Heterojunction Photocatalysts for Visible Light Degradation of Sulfamethazine: Efficiency, Pathway, and Mechanism. ACS Sustainable Chem. Eng. 2018, 6, 4174−4184. 10.1021/acssuschemeng.7b04584 (9) Zhang, Y. Y.; Wang, L. L.; Kong, X. Y.; Jiang, H.Y.; Zhang, F.; Shi, J. S. Novel Ag–Cu bimetallic alloy decorated near-infrared responsive three-dimensional rod-like architectures for efficient photocatalytic water purification. J. Colloid Interface Sci. 2018, 522, 29–39. 10.1016/j.jcis.2018.02.005 (10) Yola, M. L.; Eren, T.; Atar, N.; Wang, S. Adsorptive and photocatalytic removal of reactive dyes by silver nanoparticle-colemanite ore waste. Chem. Eng. J. 2014, 242, 333–340. 10.1016/j.cej.2013.12.086 (11) Kleina, M.; Nadolna, J.; Gołabiewska, A.; Mazierski, P.; Klimczuk, T.; Remita, H.; Zaleska-Medynska, A. The effect of metal cluster deposition route on structure and photocatalytic activity of mono- and bimetallic nanoparticles supported on TiO2 by radiolytic method. Appl. Surf. Sci. 2016, 378, 37–48. 10.1016/j.apsusc.2016.03.191 (12) Fang, W.; Xing, M.; Zhang, J. Silver nanoparticles/graphitic carbon nitride nanosheets for



improved visible-light-driven photocatalytic performance. J Photoch Photobio C. 2017, 32, 21–39. 10.1016/j.jphotochem.2017.10.016 (13) Jiang, Z.; Zhang, X.; Yuan, Z.; Chen, J.; Huang, B.; Dionysiou, D. D.; Yang, G. Enhanced photocatalytic CO2 reduction via the synergistic effect between Ag and activated carbon in TiO2/AC-Ag ternary composite. Chem. Eng. J. 2018, 348, 592–598. 10.1016/j.cej.2018.04.180 (14) Zhang, P.; Wang, T.; Gong, J. Mechanistic Understanding of the Plasmonic Enhancement for Solar Water Splitting. Adv. Mater. 2015, 27, 5328–5342. 10.1002/adma.201500888 (15) Zhou, C.; Lai, C.; Huang, D.; Zeng, G.; Zhang, C.; Cheng, M.; Hu, L.; Wan, J.; Liu, Y.; Xiong, W.; Deng, Y.; Wen, M.; Wen, X. and Qin, L. Highly porous carbon nitride by supramolecular preassembly of monomers for photocatalytic removal of sulfamethazine under visible light driven. Appl. Catal. B 2018, 220, 202–210. 10.1016/j.apcatb.2017.08.055 (16) Khayyat, S.; Roselin, L. S. Photocatalytic degradation of benzothiophene and dibenzothiophene using supported gold nanoparticle. J. Saudi Chem. Soc. 2017, 21 (3), 349–357. 10.1016/j.jscs.2016.11.001 (17) Gao, X.; Fu, F.; Zhang, L.; Li, W. The preparation of Ag–BiVO4 metal composite oxides and its application in efficient photocatalytic oxidative thiophene. Physica B. 2013, 419 (21), 80–85. 10.1016/j.physb.2013.03.024 (18) Jafari, Z.; Mokhtarian, N.; Hosseinzadeh, G.; Farhadian, M.; Faghihi, A.; Shojaie, F. Ag/TiO2 /freeze-dried graphene nanocomposite as a high performance photocatalyst under visible light irradiation. J. Nat. Gas. Chem. 2016, 25 (3), 393–402. 10.1016/j.jechem.2016.01.013 (19) Yang, G.; Yin, H.; Liu, W.; Yang, Y.; Zou, Q.; Luo, L.; Li, H.; Huo, Y.; Li, H. Synergistic Ag/TiO2-N photocatalytic system and its enhanced antibacterial activity towards Acinetobacter


Page 24 of 39

Page 25 of 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


baumannii. Appl. Catal. B 2018, 224, 175–182. 10.1016/j.apcatb.2017.10.052 (20) Alsharaeh, E. H.; Bora, T.; Soliman, A.; Ahmed, F.; Bharath, G.; Ghoniem, M. G.; Abu-Salah, K. M.; Dutta, J. Sol-Gel-Assisted Microwave-Derived Synthesis of Anatase Ag/TiO2/GO Nanohybrids toward Efficient Visible Light Phenol Degradation. Catalysts. 2017, 7 (5), 133. 10.3390/catal7050133 (21) Shen, C.; Wang, Y. J.; Xu, J. H.; Luo, G. S. Oxidative desulfurization of DBT with H2O2 catalysed by TiO2/porous glass. Green Chem. 2016, 18 (3), 771–781. 10.1039/c5gc01653c (22) Shen, C.; Wang, Y. J.; Xu, J. H.; Luo, G. S. Synthesis of TS-1 on porous glass beads for catalytic oxidative desulfurization. Chem. Eng. J. 2015, 259, 552–561. 10.1016/j.cej.2014.08.027 (23) Gui, C. X.; Wang, Q.Q.; Hao, S. M.; Qu, J.; Huang P. P.; Cao, C. Y.; Song, W. G.; Yu, Z. Z. Sandwichlike Magnesium Silicate/Reduced Graphene Oxide Nanocomposite for Enhanced Pb2+ and Methylene Blue Adsorption. ACS Appl. Mater. Interfaces. 2014, 6, 14653–14659. 10.1021/am503997e (24) Skoglund, S.; Blomberg, E.; Odnevall Wallinder, I.; Grillo, I.; Skov Pedersen, J.; and Magnus Bergström, L. A novel explanation for the enhanced colloidal stability of silver nanoparticles in the presence of an oppositely charged surfactant. Phys. Chem. Chem. Phys. 2017, 19 (41), 28037. 10.1039/c7cp04662f (25) Kong, D.; Wang, H.; Lu, Z.; Cui, Y. CoSe2 Nanoparticles Grown on Carbon Fiber Paper: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2014, 136 (13), 4897−4900. 10.1021/ja501497n (26) Wang, L.; Wang, H.; Rice, A. E.; Zhang, W.; Li, X.; Chen, M.; Meng, X.; Lewis, J. P.; Xiao, F. S. Design and Preparation of Supported Au Catalyst with Enhanced Catalytic Activities by



Rationally Positioning Au Nanoparticles on Anatase. J. Phys. Chem. Lett. 2015, 6 (12), 2345−2349. 10.1021/acs.jpclett.5b00655 (27) Xing, M.; Fang, W.; Nasir, M.; Ma, Y.; Zhang, J.; Anpo, M. Self-doped Ti3+-enhanced TiO2 nanoparticles with a high-performance photocatalysis. J. Catal. 2013, 297, 236–243. 10.1016/j.jcat.2012.10.014 (28) Wang, D.; Shen, H.; Guo, L.; Wang, C.; Fu, F.; Liang, Y. Ag/Bi2MoO6-x with enhanced visible-light-responsive photocatalytic activities via the synergistic effect of surface oxygen vacancies and surface plasmon. Appl Surf Sci. 2018, 436, 536–547. 10.1016/j.apsusc.2017.12.002 (29) Sugawara, M. Theory of spontaneous-emission lifetime of Wannier excitons in mesoscopic semiconductor quantum disks. Phys. Rev. B Condens. Matter 1995, 51 (16), 10743–10754. 10.1103/PhysRevB.51.10743 (30) Feng, Y.; Wang, G.; Liao, J.; Li, W.; Chen, C.; Li, M.; Li, Z. Honeycomb-like ZnO Mesoporous Nanowall Arrays Modified with Ag Nanoparticles for Highly Efficient Photocatalytic Activity. SCI REP-UK. 2017, 7 (1), 11622. 10.1038/s41598-017-11100-8 (31) Lee, J. E.; Bera, S.; Choi, Y. S.; Lee, W. I. Size-dependent plasmonic effects of M and M@SiO2 (M = Au or Ag) deposited on TiO2 in photocatalytic oxidation reactions. Appl. Catal. B. 2017, 214, 15–22. 10.1016/j.apcatb.2017.05.025 (32) Liu, H.; Dong, X.; Li, G.; Su, X.; Z. Zhu. Synthesis of C, Ag co-modified TiO2 photocatalyst and its application in waste water purification. Appl. Surf. Sci. 2013, 271, 276–283. 10.1016/j.apsusc.2013.01.181 (33) Chen, F.; Liu, Z.; Liu, Y.; Fang, P.; Y. Dai. Enhanced adsorption and photocatalytic degradation of high concentration methylene blue on Ag2O-modified TiO2-based nanosheet. Chem.


Page 26 of 39

Page 27 of 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


Eng. J. 2013, 221, 283–291. 10.1016/j.cej.2013.02.019 (34) Yu, J.; Xiong, J.; Cheng, B.; Liu, S. Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity. Appl. Catal. B. 2005, 60, 211–221. 10.1016/j.apcatb.2005.03.009 (35) Wang, Y.; Wang, G.; Wang, H.; Liang, C.; Cai, W.; Zhang C. L. Chemical-Template Synthesis of Micro/Nanoscale Magnesium Silicate Hollow Spheres for Waste-Water Treatment. Chem. Eur. J. 2010, 16 (11), 3497–3503. 10.1002/chem.200902799 (36) Zhu, L.; Zheng, T.; Yu, C.; Zheng, J.; Tang, Z.; Zhang, N.; Shu, Q.; Chen, B. H. Platinum– nickel alloy nanoparticles supported on carbon for 3-pentanone hydrogenation. Appl. Surf. Sci. 2017, 409, 29–34. 10.1016/j.apsusc.2017.02.251 (37) Wang, C.; Zhu, W.; Xu, Y.; Xu, H.; Zhang, M.; Chao, Y.; Yin, S.; Li, H.; Wang, J. Preparation of TiO2/g-C3N4 composites and their application in photocatalytic oxidative desulfurization. Ceram Int. 2014, 40 (8), 11627–11635. 10.1016/j.ceramint.2014.03.156 (38) Miao, G.; Huang, D.; Ren, X.; Li, X.; Li, Z.; Xiao, J. Visible-light induced photocatalytic oxidative desulfurization using BiVO4/C3N4@SiO2 with air/cumene hydroperoxide under ambient conditions. Appl. Catal. B. 2016, 192, 72–79. 10.1016/j.apcatb.2016.03.033 (39) Kumar, S.; Cho, J. H.; Park, J.; Moon, Il. Advances in diesel–alcohol blends and their effects on the performance and emissions of diesel engines. Renew. Sust. Energy. Rev. 2013, 22, 46–72. 10.1016/j.rser.2013.01.017 (40) Ibadurrohman, M.; Hellgardt, K. Photoelectrochemical performance of graphene-modified TiO2 photoanodes in the presence of glycerol as a hole scavenger. Int J Hydrogen Energy. 2014, 39 (32), 18204–18215. 10.1016/j.ijhydene.2014.08.142



Page 28 of 39

(41) Castillo, K.; Parsons, J. G.; Chavez, D.; Chianelli, R. R. Oxidation of dibenzothiophene to dibenzothiophene-sulfone

using

silica

gel.

J.

Catal.

2009,

268

(2),

329–334.

10.1016/j.jcat.2009.10.002 (42) Li, Q.; Wang, F.; Hua, Y.; Luo, Y.; Liu, X.; Duan, G.; Yang, X. Deposition-precipitation preparation of Ag/Ag3PO4/WO3 nanocomposites for efficient Visible-light degradation of rhodamine B under strongly acidic/alkaline conditions. J. Colloid Interface Sci. 2017, 506, 207– 216. 10.1016/j.jcis.2017.07.018 (43) Shen, C.; Pang, K.; Du, L.; Luo, G. Green synthesis and enhanced photocatalytic activity of Ce-doped TiO2 nanoparticles supported on porous glass. Particuology. 2017, 34, 103–109. 10.1016/j.partic.2017.01.007 (44) Wang, T.; Wei, J.; Shi, H.; Zhou, M.; Zhang, Y.; Chen, Q.; Zhang, Z. Preparation of electrospun Ag/TiO2 nanotubes with enhanced photocatalytic activity based on water/oil phase separation. Physica. E. 2017, 86, 103–110. 10.1016/j.physe.2016.10.016 (45) Sui, M.; Dong, Y.; Wang, Z.; Wang, F.; You, H. A biocathode-driven photocatalytic fuel cell using an Ag-doped TiO2/Ti mesh photoanode for electricity generation and pollutant degradation. J. Photoch Photobio A. 2017, 348, 238–245. 10.1016/j.jphotochem.2017.08.047 (46) Ma, J.; Xu, S.; Chu, J.; Xue, J.; Tang, J.; Qiang, L. Effect of metal–support interaction on the structural and enhanced photocatalytic performance of mesoporous M–TiO2/SBA-16 (M = Ag and Fe). J Porous Mater. 2017, 24 (1), 45–54. 10.1007/s10934-016-0235-7 (47) Chen, S.; Xiao, Y.; Wang, Y.; Hu, Z.; Zhao H.; Xie, W. A facile approach to prepare black TiO2 with oxygen vacancy for enhancing photocatalytic activity. Nanomaterials. 2018, 8 (4), 245. 10.3390/nano8040245


Page 29 of 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


(48) Min, Y.; Zhang, K.; Zhao, W.; Zheng, F.; Chen, Y.; Zhang, Y. Enhanced chemical interaction between TiO2 and graphene oxide for photocatalytic decolorization of methylene blue. Chem. Eng. J. 2012, 193–194, 203–210. 10.1016/j.cej.2012.04.047 (49) Mesgari, Z.; Saien, J. Pollutant degradation over dye sensitized nitrogen doped titania substances in different configurations of visible light helical flow photoreactor. Sep. Purif, Technol. 2017, 185, 129–139. 10.1016/j.seppur.2017.05.032 (50) Yu, D.; Bai, J.; Liang, H.; Wang, J.; Li, C. Fabrication of a novel visible-light-driven photocatalyst Ag-AgI-TiO2 nanoparticles supported on carbon nanofibers. Appl. Surf. Sci. 2015, 349, 241-250. 10.1016/j.apsusc.2015.05.019 (51) Saqib, N.; Adnan, R.; Shah, I. Modifications of pure and Ag doped TiO2 by presulphated and calcination

temperature

treatments.

Res

Chem

Intermed.

2017,

43,

6571–6588.

10.1007/s11164-017-3005-5 (52) Liu, C.; Zhu, H.; Zhu, Y.; Dong, P.; Hou, H.; Xu, Q.; Chen, X.; Xi, X.; Hou, W. Ordered layered N-doped KTiNbO5/g-C3N4 heterojunction with enhanced visible light photocatalytic activity. Appl. Catal. B. 2019, 228, 54–63. 10.1016/j.apcatb.2018.01.074 (53) Zhang, C.; Zhou, Y.; Zhang, Y.; Zhao. S.; Fang, J.; Sheng, X. The investigation of Ag decorated double‐ wall hollow TiO2 spheres as photocatalyst. Appl. Organomet. Chem. 2018, 32, 4160. 10.1002/aoc.4160 (54) Shi, L.; Ma, J.; Yao, L.; Cui, L.; Qi, W. Enhanced photocatalytic activity of Bi12O17Cl2 nano-sheets via surface modification of carbon nanotubes as electron carriers. J. Colloid Interface Sci. 2018, 519. 10.1016/j.jcis.2018.02.056 (55) Huang, H.; Ma, C.; Zhu, Z.; Yao, X.; Liu, Y.; Liu, Z.; Li, C.; Yan, Y. Insights into enhanced



visible light photocatalytic activity of t-Se nanorods/ BiOCl ultrathin nanosheets 1D/2D heterojunctions. Chem. Eng. J. 2018, 338, 218–229. 10.1016/j.cej.2017.12.012


Page 30 of 39

Page 31 of 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


Table 1 Catalytic activities of different catalysts for RhB degradation. ka (min−1)

Light resources

References

0.14

LED, 50 W

This work

0.068

Xenon lamp, 350 W

44

0.045

Xenon lamp, 150 W

45

0.021

Xenon lamp, 300 W

46

Table 2 Catalytic activities of different catalysts for MB degradation ka (min−1)

Light resources

References

0.18

LED, 50 W

This work

0.036

Hg lamp, 500W

47

0.059

Xenon lamp, 300 W

48

0.0072

UV & LED lamp

7

Table 3 Catalytic activities of different catalysts for MO degradation ka (min−1)

Light resources

References

0.055

LED, 50 W

This work

0.039

Metal halide visible lamp

49

0.015

Xenon lamp, 300 W

50

0.011

Fluorescent light, 36W

51



Fig. 1 XRD patterns of photocatalysts: (a) PG; (b) Ag/PG; (c) TiO2/PG; (d) Ag–TiO2/PG.


Page 32 of 39

Page 33 of 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


Fig. 2 (a, c) TEM images of Ag–TiO2/PG; (b) size distribution histogram of the Ag–TiO2/PG; (d) SAED of Ag–TiO2/PG; (e) STEM images of Ag–TiO2/PG; (g) elemental scanning over this entire nanoparticle marked by the white line in (f).

Fig. 3 XPS spectra of the Ti 2p spectrum (a) and Ag 3d spectrum (b) of the TiO2/PG and Ag– TiO2/PG.



Fig. 4 ESR spectra of the Ag–TiO2/PG and TiO2/PG.

Fig. 5 (a) UV–vis spectra of TiO2/PG and Ag–TiO2/PG with different Ag content; (b) band gaps (Eg) of the photocatalysts which are acquired from the plots of ( ∂hv )2 versus hv constructed from the UV–vis spectra.

Fig. 6 Photoluminescence emission spectra of TiO2/PG and Ag–TiO2/PG with different Ag contents under UV light (320 nm).·


Page 34 of 39

Page 35 of 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


Fig. 7 Transient photocurrent responses of TiO2/PG and Ag–TiO2/PG samples.

Fig. 8 Photocatalytic activity of 3% Ag–TiO2/PG for DBT conversion (a) and BT conversion (b) under LED irradiation.



Fig. 9 (a, c, and e) photodegradation of RhB, MB, and MO in the presence of different photocatalysts; (b and d) UV–vis absorption spectra for degradation of RhB and MB under visible-light irradiation using 1% Ag–TiO2/PG sample; (f) UV–vis absorption spectra for degradation of MO under visible-light irradiation using 7% Ag–TiO2/PG catalysts.


Page 36 of 39

Page 37 of 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


Fig. 10 The degradation of (a) RhB, (b) MB with 1% Ag–TiO2/PG, and (c) MO with 7% Ag– TiO2/PG.

Fig. 11 DMPO spin trapping ESR spectra for DMPO-·O2– (a), DMPO-·OH (b) and TEMPO-h+ of the TiO2/PG and Ag–TiO2/PG materials with dark and visible light irradiation.



Scheme. 1 Schematic illustration of the possible separating and transferring behavior of charge carriers in the Ag–TiO2/PG under visible light irradiation.


Page 38 of 39

Page 39 of 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


For Table of Contents Use Only

Synopsis: Ag–TiO2 /PG was fabricated in a green and sustainable approach and are promising photocatalysts for efficient desulfurization and degradation of organic dyes.


Green Synthesis of AgâTiO2 Supported on Porous Glass with

Recommend Documents

Green Synthesis of AgâTiO2 Supported on Porous Glass with