Fabrication of ZnS Hollow Spheres and RGO-ZnS Nanocomposite

Subscriber access provided by Eastern Michigan University | Bruce T. Halle Library

Article

Fabrication of ZnS hollow spheres and RGO-ZnS nanocomposite using Cysteamine as novel sulphur source: Photocatalytic performance on industrial dyes and effluent Suvanka Dutta, SRIPARNA CHATTERJEE, Indrani Mukherjee, Rajnarayan Saha, and Bimal P. Singh Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 05 Apr 2017 Downloaded from http://pubs.acs.org on April 5, 2017

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 free 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 accessible to all readers and 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.

Industrial & Engineering Chemistry Research 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 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

Industrial & Engineering Chemistry Research

Fabrication of ZnS hollow spheres and RGO-ZnS nanocomposite using Cysteamine as novel sulphur source: Photocatalytic performance on industrial dyes and effluent Suvanka Dutta,a Sriparna Chatterjee,b* Indrani Mukherjee,a,b Rajnarayan Sahaa,* and Bimal P Singhb a

b

Department of Chemistry, National institute of Technology, Durgapur CSIR-Institute of Minerals and Materials Technology, Acharya Vihar, Bhubaneswar, India 751 013

Corresponding e-mail address: [email protected], [email protected] Abstract: A facile one pot hydrothermal synthesis of hollow ball like ZnS nanostructures is reported using cysteamine, an ecofriendly sulphur source. Following similar protocol a heterostructure of ZnS-RGO nanocomposite have been synthesized. The as synthesized samples are structurally and optically characterized using different techniques. The photocatalytic activity of ZnS-RGO has been found to be ~ 9 % higher than that of ball like ZnS nanostructures at a dose of 0.4g/L. This result is attributed to the improved charge transport by hindering charge recombination of photo-induced excitons. One of the significant findings of this work is the model anionic dye degraded better in alkaline condition with ZnS whereas the trend is reverse for ZnS-RGO composite. The removal efficiency of both the systems is allied with structural, morphological and optical properties to understand the underlying mechanism of synthesis as well as photocatalysis process. Keywords: Zinc sulphides; Reduced graphene oxide; Heterostructure; Photocatalysis; Wastewater treatment; Effluent

1 ACS Paragon Plus Environment


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 2 of 42

Introduction: Since last decade nanostructures of semiconductors have acclaimed global recognition as photocatalysts for waste-water treatment because of their varied band gaps, high specific surface area, thermal and chemical stability etc.1, 2 Most studied photocatalysts are oxides of titanium3,4,5 and zinc6,7,8. Other than oxides, metal chalcogenides have also created impressions as photocatalyst and ZnS is an important example of this class of photocatalyst. ZnS has been tailor made in various fascinating morphologies like nanobelts,9 stacked-pyramid,10 nanocombs,11 spheres,12,13 nanoflowers14 and so on to meet the demands of high-performance applications like fungicides,15 solar cells,16 sensors17 and light emission diodes (LEDs),18 photocatalysts,19 electro optical devices20 etc. However, poor response to visible light and high recombination rate of excitons significantly confines its realistic uses. To overcome this limitation, lot of efforts have been given on coupling of ZnS with ZnO to bring about synergetic effect.21 Hu et al., reported fabrication of ZnO/ZnS core–shell nanorods via microwave- assisted in situ surface sulfidation of ZnO nanorods.22 Wang et al., studied structural and optical properties of hierarchical ZnS nanobelt/ZnO nanorod heterostructures.23 Researchers have successfully developed visible-lightactive heterostructured photocatalysts for solar fuel production.24,25 Other fascinating approach is the fabrication of composites of metal sulfides and carbon-based materials.26,27,28 Graphene is the two-dimensional (2D) magic material which has thickness of one atom, ~ 97.7% transparency, huge surface area ~2600 m2 g-1 29,30,31 and room temperature charge carrier mobility ~10000 cm2 V-1 s-1. The strong π conjugation of graphene allows excellent electronic mobility32 and the conductive mat of sp2 carbon framework helps in shuttling the electrical charges between nanaoparticles.33 Composites of graphene and metal sulphide showed promising photocatalytic activity28,34,35,36,37 by reducing the problem of electron hole pair recombination.35,38 Synthesis of 2 ACS Paragon Plus Environment

Page 3 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


metal-sulphide nanostructures as well as graphene-metal sulphide nanocomposite is always a great concern because in the field of practical applications, morphology and crystal structure play crucial role in controlling transportation properties, thermal stability and excitonic movements.Error! Bookmark not defined.5 Although ZnS is known to be synthesized in various forms using varying precursors and methods11,12,13,39,40,41 however, mostly template based synthesis method has been followed to grow hollow sphere of ZnS42. Herein, we report a facile, one-pot, template free synthesis of zinc sulphide hollow-sphere (ZnS HS) following a hydrothermal route where a novel sulphur source is used. Traditionally sulphur sources are the hazardous chemicals like Na2S, DMSO, thiourea etc.43,44,45 which poses severe risk to nature. Consequently, in recent lot of emphasis is being given on the usage of ecofriendly sulphur source for synthesizing metal sulfide nanoparticles.46 Amino acids e.g. L-cysteine is found to be effective in synthesizing various metal sulphides.38,39 In this work, first time we are reporting the synthesis of phase pure ZnS hollow spheres (ZnS HS) using cysteamine as a new in situ source of S2− ions without the use of a templating agent. Cysteamine is the degradation product of the amino acid, cysteine and having wide application in various fields of biochemistry. It is used for cysteine disorder, radiation sickness etc.47 Cysteamine can acts as a potential chelating agent as it has affinity towards soft metal centers like Zn, Cu, Pb, Sn etc. We have synthesized a zinc-cysteamine complex and further through hydrothermal treatment of the complex, ZnS hollow spheres are synthesized without using any hard template. In the next step, RGO-ZnS nanocomposite (RGOZnS NC) is also synthesized using same zinc-cysteamine complex where cysteamine also acted as a reducing agent to reduce graphene oxide to RGO. Usage of cysteamine hydrochloride renders the whole synthesis process least hazardous as compared to conventional chemical methods.43,44,45 Further, we have studied the photocatalytic efficiency of both hollow spheres of



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 4 of 42

ZnS and ZnS-RGO composite in presence of a model “azo” dye (Direct Blue 53) and then it was applied on a real textile effluent to check the actual applicability of these photocatalyst. Most toxic chemical present in a textile effluent is the dye stuff itself,48 as more than 50% of dye mass get dispersed to water during manufacturing and processing.49,50,51 RGO-ZnS composite is found to be more effective than ZnS hollow spheres in removal of textile effluent and with the help of physicochemical and photoluminescence study, we attribute this observation to efficient electron–hole separation at the interface of the two semiconducting systems. However, it is important to mention here that both of our as-synthesized materials (ZnS hollow spheres and RGO-ZnS composite) act as potential photocatalyst even at very low dose (see Table S1 and Table S2 in supporting information) as compared to earlier reports.29,34,35,36,48 In summary, we have successfully synthesized well-dispersed, uniform hollow spheres of ZnS and RGO-ZnS nanocomposites using a novel, ecofriendly sulphur source and effectively explored them for the degradation of textile effluent. We also show that even at very low scale these photocatalysts can effectively degrade high concentration of pollutant in reasonably short time (~ 60 min) with high degree of recyclability (6 cycles). 2. Experimental 2.1. Materials and Methods 2.1.1. Materials and method of synthesis of ZnS HS 20 ml of 0.5 (M) zinc nitrate (Merck India, Emplura ≥ 96%) solution is added drop wise to 60 ml of 0.18 (M) Cysteamine hydrochloride (Sigma Aldrich chemical co., ≥ 98%) solution with continuous stirring. This solution is extremely acidic and it was neutralized (pH ~7) with KOH (Merck India, Emplura, 84%) (1M and 0.1M). After 2 h of shaking at room temperature, the


Page 5 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


solution is transferred to a teflon liner of 100 ml capacity and was put in stainless steel autoclave. Autoclaving is done 160˚ C temperature for 14 hours. After the reaction vessel cools down to room temperature the whole mass and solution filtered with GF/C filter paper by a vacuum filtration system. The product is washed with 500 mL of distilled water (18 mΩ) then with 100 mL of absolute ethanol (Changshu Yangyuan Chemical China, 99%). The obtained dark yellow powder (See ESI Figure S1(a) in electronic supporting information) is vacuum dried at room temperature and stored in an amber color 15ml culture bottle in a vacuum desiccator. 2.1.2. Materials and method of synthesis of RGO-ZnS nanocomposite (RGO-ZnS NC) Graphene oxide was prepared by following the Hummer’s method52 (detailed method described in ESI). ZnS-RGO nanocomposite is synthesized following same protocol of ZnS hollow sphere synthesis. However, this time 0.36(M) cysteamine hydrochloride solution is prepared using GO solution instead of water. A black colored powder obtained at the end of the synthesis process (See ESI Figure S1(b) in supporting information). 2.2. Characterization The morphological studies were done using a field emission-scanning electron microscope (Bruker XFlash 6160 FESEM) and a high-resolution transmission electron microscope (TECHNAI TF20 ST HRTEM). A small amount of as-grown powder was evenly sprinkled on copper tape for FESEM study. For TEM study, one drop of ethanolic suspension of as-grown powder was placed on carbon coated copper grid. Crystal structure of the as-grown materials was determined using Pananalytical X’pert Pro X-ray Diffractometer. UV–Visible absorption spectra of dispersed nanoparticle solutions were recorded by a UV–Visible spectrophotometer (1601SHIMADZU). Photoluminescence spectra were recorded using a Hitachi F-2500



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 6 of 42

spectrofluorimeter at room temperature. For UV-Visible absorption spectroscopy and photoluminescence study, as-synthesized nanoparticles (0.005g) were dispersed in deionised water (10 mL).

FT-IR Spectra of the samples were recorded by Thermo Nicolet iS10

spectrometer using KBr pellets in the range 4000- 400 cm-1. pH of the dye solutions were measured using Orion star A214 Thermo Scientific pH meter. Brauner–Emmet– Teller (BET) surface

area

was

obtained

using

a

Micromeritics

ASAP

2020

surface

analyser.

Thermogravimetric analysis (TGA) was carried out in ambient atmosphere using a custom

made Okay 1200 TGA-DSC instrument equipped with Libratherm controller TGA-8001.

2.3. Photocatalysis experiment Photo-oxidation of Direct Blue 53 (DB 53; C.I.23860) dye (See ESI Figure S2) was conducted in a batch process. This experimental unit is configured with an annular cylindrical glass reactor with a quartz tube at the centre of the reactor to house UV light source of 125 W, jacket was provided for cooling purpose. Cooling media (water) was continuously circulated, throughout the reaction time to maintain the UV bulb from fusing. The reactor is provided with inlets for feeding reactants, and ports for withdrawing samples. It is open to air with a magnetic stirring bar placed at the bottom for homogenization. The reactor is covered with a wooden box to prevent loss of UV light. All the photo-induced experiments were performed in this cylindrical photo-reactor whose total volume is 500 mL. Samples were periodically withdrawn from sampling port and analysed for the residual dye concentration. Before illumination, the suspension of DB 53 dye along with the photocatalyst, were magnetically stirred in the dark for 60 min, after dispersing in an ultrasonic bath for 5 min, to ensure the establishment of an adsorption–desorption equilibrium between nanomaterial and DB 53. 6 mL of the solution was 6 ACS Paragon Plus Environment

Page 7 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


collected by filtration within a fixed time interval. The concentration of the remnant DB 53 dye in the collected solutions was monitored after the experimental time was over. Textile effluent is collected from Rishra industrial zone, West Bengal, India. All water parameters of textile effluent were measured as per the standard method of APHA, 1998.53 3. Results and discussion 3.1. Structural characteristics The x-ray diffraction pattern of as-prepared samples is shown in Figure 1(a). Both samples are found to be crystalline in nature with diffraction lines at 2θ = 28.5°, 47.5° and 56.3° that can be assigned to the (111), (220) and (311) set of planes of the cubic ZnS (ICSD reference card no. 01-073-1667) structure. No separate diffraction line for RGO is observed in the composite sample, which may be due to the low amount of RGO loading in the composite. The absence of any additional diffraction peaks other than ZnS indicates high phase purity of the as-grown samples. The mean crystallite sizes (D) of the samples are calculated using the Scherer equation (Eqn. 1), D = 0.94λ/B cos θ

Eqn. (1)

where, D is the crystallite size, λ is wavelength of X-ray used, B is the value of full width at half maximum (FWHM) and θ is the Bragg's angle. The crystallite size of ZnS (~ 28 nm) is calculated to be more than size of ZnS-RGO (~ 4 nm) composite samples (See Table 1). The thermal stabilities of the as-grown samples are shown in Figure 2. The TGA curve of the ZnS HS (black trace Figure 2) shows minimal weight loss (10%) in the entire temperature range of 35°C to 800°C which can be attributed to the loss of surface bound water. In case of 7 ACS Paragon Plus Environment


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 8 of 42

RGO-ZnS NC sample upto 250oC, the weight loss may be related with loss of surface bound water. However, the weight loss from 250oC to 700°C can be attributed to the removal of oxygen-containing groups of RGO and the decomposition of the carbon framework in the composite. TGA analysis shows that the RGO mass ratios of the RGO-ZnS NC is ~28 wt%. 3.2. Morphological characteristics Figure 3 represents the surface morphologies of as-synthesized powder samples of ZnS. Formation of sphere-like morphology (~ 2 ± 1 µm) are seen in Figure 3(a). A closer look reveals that small sized particles are self-aggregated to form large sphere-like morphologies (Figure 3(b)) and thus the spheres are having rough, porous surface wall. Figure 3(c) represents FESEM of a single sphere of ZnS confirming that the spheres are actually hollow in nature (also see Figure 3(d) and Figure S3 in supporting information). Interestingly, TEM study of ZnS HS does not show any sphere like morphology (Figure 4a). Rather presence of small particles having diameter between 10-30 nm (ESI Figure S4a) is found. TEM samples are prepared by drop casting of dispersed powder samples on carbon grid and vigorous ultrasonication is generally used to make a uniform dispersion. It may be assumed that the hollow spheres disintegrate into cluster of particles during ultrasonication process and for this reason TEM shows presence of only particles. HRTEM of individual nanoparticle shows lattice fringes with spacing of about 0.31 nm that corresponds to (111) set of plane (Figure 4(b)). Figure 4(c) represents electron diffraction image taken over a few numbers of nanoparticles and diffraction rings from (111), (220) and (311) set of plane are seen. Figure 5(a) shows surface morphology of RGO-ZnS NC and in this case no spheres are formed. TEM image reveals that ZnS particles are uniformly distributed on RGO sheet indicating intimate interfacial interaction (Figure 5b). This interaction


Page 9 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


is essential for charge transfer or charge carrying between ZnS and RGO sheet, which in turn will facilitate processes like photocatalysis. The formation mechanism of ZnS hollow spheres is explained considering the interaction of zinc ion with novel precursor, cysteamine (as shown in scheme 1). Formation zinc-cysteamine complex occurs at neutral pH by the reaction of zinc nitrate and cysteamine hydrochloride. During autoclaving (~160 ˚C for 14 h) the complex disintegrates and controlled amount of S2ions are released upon breakage of C–S and S–H bonds of cysteamine. These S2- ions react with Zn2+ and form ZnS nuclei54 which self-aggregares to minimize the surface energy and thus forms hollow spheres (as shown in Scheme 1). The formation of hollow spheres is not observed in case of ZnS-RGO nanocomposite (Figure 5(a)) and the nanoparticles are in good interfacial contacts with graphene sheets (Figure 5(b)). The loss of spherical morphology of ZnS in presence of RGO can be discussed considering the following facts. According to Luong et al., in presence of both cysteamine hydrochloride and RGO, C-S bonds are formed and they get anchored55 on the surface of GO. Upon addition of zinc nitrate solution to it, Zn2+ coordinates with S and gets immobilized on the surface of GO. During hydrothermal condition, the positive Zn2+ binds with the negative oxygen-containing group on the surface of the RGO due to the electrostatic interaction and the surface of the graphene sheets become the ZnS nucleation sites, leading to a dispersion of nanosized ZnS nanoparticles on the graphene sheet support (scheme 2). This restrains the ZnS nanoparticles from self-aggregation that also facilitates the formation of smaller crystallite size as revealed in XRD data analysis. The dispersion of ZnS nanoparticles also complements by hindering the collapse and restacking of exfoliated sheets of graphene during the hydrothermal synthesis. 3.3. Physico-chemical properties 9 ACS Paragon Plus Environment


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 10 of 42

The BET surface area of RGO-ZnS composite is found be 81.5 m2/g whereas the same for hollow spheres is 70.6 m2/g. The N2 adsorption-desorption curve (Figure 6(a)) of hollow sphere of ZnS presents a type II isotherm56 indicating larger pore diameters than micropores with a hysterisis loop in the relative pressure range 0.45 to 1. On the other hand, ZnS-RGO composite exhibits type III isotherm56 (Figure 6 (b)). It confers that additional adsorption is occurring as the interaction of adsorbate with adsorbed layer is greater than the interaction with the adsorbent surface. Pore size calculation was done following BJH method (Barret-Joyner-Halenda method) and for hollow spheres of ZnS the pore size is found to be ~ 5.7 nm and that for composite is ~29 nm (Figure 6(b)). Higher surface area of the composite can be attributed to the presence of exfoliated RGO sheet that is expected to increase active sites of surfaces enhancing the surface adsorption process. The formation of RGO-ZnS nanocomposite is confirmed by FTIR study. FTIR spectra of samples spherical ZnS, and nanocomposite is present in Figure 7(a). The FTIR spectrum of graphene oxide (GO) is also presented to compare with RGO-ZnS nanocomposite. In Figure 7(b), the strong and broad peak at ~ 3425 cm-1 and 1716 cm-1 can be assigned to the stretching vibrations of O–H and C=O group present in GO. Peaks at 1227 cm-1 and 1076 cm-1 indicate presence of unsaturated and saturate C-OH groups. All three samples show a peak at 1631 cm-1, which may be assigned to overtone of water molecule. The intensity of absorption peaks of the oxygen-containing groups in GO dramatically decreased due to deoxygenation in case of formation of RGO-ZnS nanocomposite. The peak at 1716 cm−1 that arises from C=O stretching mode, completely disappears in RGO-ZnS composite and the peak of the unsaturated and saturate C-OH group has shifted from 1027 cm-1 to 1047 cm−1 and 1082 cm-1 to 1092 cm-1 respectively. The sharpness of the peaks may be attributed to the presence of unreacted side


Page 11 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


chain hydroxyl groups, which also indicates that the C=O functional group in GO is decomposed after the hydrothermal treatment. Peaks in the range of 400 cm-1 - 650 cm-1 are the indicator of Zn-S bond formation as this region is the fingerprint region of metal sulphide bond57. 3.4. Optical properties Cubic ZnS is a known semiconductor with a direct band gap of 3.54 eV.58 The bandgap of hollow spherical ZnS and RGO-ZnS nanocomposite are calculated using the following relation, E bandgap = hc/ λint

Eqn. (2)

where, ‘h’ refers to Plank’s constant (4.135 x 10-15 eV s), ‘c’ is the velocity of light (3 x 108 m s1

), and ‘λint’ refers to wavelength (in meter) corresponding to the intersection of the extension of

the linear- part of the spectrum and the x-axis7. Figure S5(a) in supporting information shows the UV-Visible absorption spectra of ZnS and S5 (b) represents the same for RGO-ZnS sample. The 2nd derivative (inset of ESI Fig. S5(a) and (b)) of two spectra indicate that there is a 7 nm red shift of the peak in case of ZnS-RGO sample. The as-calculated band gaps are 3.77 eV and 3.69 eV for ZnS HS and nanocomposite respectively and this confirms that the absorption around 330 nm is due to excitonic transition. Room temperature photoluminence spectra of both samples are presented is Figure 8(a). The intensity of PL spectrum of ZnS-RGO composite is highly quenched as compared to PL spectrum of ZnS that indicates the facilitation of charge carrier movement due to the presence of 2D network of RGO which acts as an excellent electron collector and transporter of charge carrier and helps in shuttling photogenerated electrons from the semiconductor surface by decrementing recombination of the electron–hole pairs. The broad PL spectrum of individual sample can be deconvoluted into several sub emission peaks. Figure 8 (b) and (c) represent 11 ACS Paragon Plus Environment


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 12 of 42

individual PL spectrum of spherical ZnS and ZnS-RGO nanocomposite samples respectively. The peaks at 405.3 nm and 428.5 nm of hollow spheres of ZnS (Figure 8(b)) are the signature of band edge emission generated due to recombination of sulphur related donor and the valance band

59,60

. Peak at 455 nm may arise from presence of native defect states. The intense peak at

485.2 nm can be attributed to the trapped state emission of ZnS, related to native zinc vacancy.61,62 Likewise the peaks at 405 nm, 425 nm, 460 nm and 475 nm of ZnS-RGO composite can be related to band edge emission and defect and trapped states (Figure 8(c)). 3.4. Photocatalytic properties Both samples were examined as photocatalyst for the degradation of dyes present in industrial effluent prior to that photocatalytic efficiency of as-grown samples were studied using a model dye named Direct blue 53. Direct blue 53 is an anionic dye and it is an azo dye, which is used in physiological estimation but it is at the same time know to be carcinogenic. Therefore, we attempted for photodegradation of Direct blue 53 using ZnS hollow sphere and ZnS-RGO nanocomposite as photocatalyst. Before actual experiment, several control experiments were carried out to rule out the role of UV light and surface adsorption of catalysts in dark. It is seen that in a solution of pH ~ 6.5, the rate of dye degradation is very negligible in absence of light (Figure 9(a)). For solution of same pH, in presence of only UV irradiation the dye solution could auto-degrade to ~50% in one and half hours of time span (Figure 9(a)) although earlier studies on Direct blue 53 reveals that the dye is non-degradable under solar irradiation.63,64 Further, photocatalytic efficiencies of hollow spheres of ZnS and ZnS-RGO nanocomposite were studied in presence of UV light and both of them found to be active photocatalyst with removal efficiencies of ~94.1% and 97.4% respectively (Figure 9(a)). The reaction rates are calculated by using Langmuir-Henshelwood pseudo-first order kinetics model65 and calculated to be 0.035 12 ACS Paragon Plus Environment

Page 13 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


min-1 and 0.048 min-1 for hollow spheres of ZnS and ZnS-RGO nanocomposite (Figure 9(b)) and that for only UV irradiation with no catalyst is only 0.008 min-1. To see the effect of concentration on photodegradation ability of Direct Blue 53, 40 mg/L dye solution was treated with different sample amount (0.3g/L to 0.5g/L) of catalyst as represented in Figure 9(c). It is observed that for ZnS hollow spheres, initially removal efficiency (RE%) increases upto 0.5g/L (97.14%) and after that removal efficiency decreases on increasing the dose. Similar trend is also observed in case of ZnS-RGO nano-composite but highest removal efficiency (99.9%) is obtained for dye concentration of 0.4g/L (Figure 9(d)). With increasing catalyst concentration, the overall turbidity of the reaction medium (catalyst in dye solution) increases that hinders the UV light penetration as a result removal efficiency decreases. ZnS-RGO nanocomposite have better dispersibility than ZnS hollow sphere in water and it is comparatively darker in color, which may also hinder the penetration of light through the solution(See ESI Table S3) . pH of the reaction medium strongly influences the rate of a photocatalytic reaction66 as it controls the surface charge and oxidation potential of the photocatalysts.67 In this work, we studied the catalytic activity of both type of photocatalysts in different pH ranges varying from pH=3 to pH=11 (Figure 10 (a) and (b)). At pH= 3, the photocatalytic rate constant was calculated to be 0.027 min-1 for ZnS hollow spheres that increased to a value of 0.401 min-1 at the pH range of 11. On the other hand, a different trend is observed in case ZnS-RGO nanocomposite. At pH=5, the nanocomposite showed highest degradation efficiency (94.6%) with maximum rate constant of 0.055 min-1 and at pH=11, the degradation efficiency was least (73.21%). pH at point of zero charge (pHpzc) was determined to explore surface charge of ZnS and ZnS-RGO (See Figure S6 (a) and (b) in supporting information). The pHzpc value of ZnS hollow spheres are estimated to be 6.5 (See Figure S6 (a) in supporting information), which implies below 6.5 the surface of ZnS



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 14 of 42

hollow sphere will be positively charged and above 6.5, the surface will be negatively charged. As Direct blue 53 is an anionic dye, therefore, it is expected that in acidic medium Direct blue 53 will be readily adsorbed onto the positively charged surface68 of ZnS spheres (+vely charged) and photo-degradation of dye will be facilitated. But in our study, ZnS hollow spheres show better efficiency in alkaline medium, which may be explained taking in to account the stability issue of ZnS in acidic medium. In acidic pH, ZnS is prone to get dissolved in the reaction medium, which makes it comparatively less stable69 and therefore, degradation efficiency of ZnS hollow spheres is compromised (Figure 10(a)). On the other hand, in alkaline medium presence of large amount of OH- ions are favors the formation of OH˚ radical which in turn promotes photodegradation process. Hence, better photodegradation in presence of ZnS hollow spheres are observed in alkaline medium though degradation of anionic dye favors acidic medium. ZnSRGO nanocomposite is found to be stable above pH~ 4 but it is unstable at pH~3. For this reason, it is observed that ZnS-RGO nanocomposite shows better photodegradation ability at pH~4 than pH~3 (See Figure S7 in supporting information). The reusability of both type of photocatalysts are investigated (Figure 11) and they are found to have excellent recyclability (See Figure S8 in supporting information). The loss in removal efficiency for ZnS hollow sphere is only ̴ 2.5% after 6 cycles whereas for nanocomposite sample the loss is ~6.5%. Hollow spheres of ZnS are proved to be little better than its composite (Fig 11) counterpart. XRD of the recycled photocatalysts show no change in crystalinity (see Figure S9 in supporting information). FTIR study of recycled photocatalysts also supports absence of any significant distortion (see Figure S10 in supporting information) in structure. Small changes in FTIR spectra of nanocomposite sample may be attributed to the presence of surface absorbed dye molecules.


Page 15 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


3.6. Removal of Industrial effluent As collected textile effluent showed the presence of high amount of chloride, total dissolved solid (TDS) and having chemical oxygen demand (COD) (see Table S4 in ESI). Biological oxygen demand (BOD) that actually accounts for the presence of biologically degradable organic matter is found to be very low comparative to COD. Thus the ratio of BOD: COD found to be very low 0.34 which indicates that chemical treatment is required to treat them as collected filthy industrial effluent.70 As the collected sample volume was very little, therefore the effluent was diluted (9 times) before photocatalytic treatment. λmax value at time (t) = 0 is considered as initial concentration (C0) and decay of λmax in presence of photocatalysts with time is spectrophotometrically monitored (see Figure S11 in ESI). Two different doses (0.125 g/L and 0.25g/L) of each photocatalysts are used and ZnS-RGO nanocomposite shows better removal efficiency than ZnS hollow sphere (Figure 12 (a) and (b)). This can be corroborated to the instability of the ZnS in acidic pH (as described in Table S4 in ESI) as discussed in the previous section. 4. Conclusion ZnS microsphere and ZnS-RGO nanocomposite are synthesized following a one pot green synthesis protocol. Hollow spheres of ZnS dose is found to show it’s best degradation ability (97.14%) at a dosing amount of 0.5g/L for 40 mg/L dye solution. On the other hand 99.9% removal efficiency obtained with the dosing amount of 0.4 g/L for ZnS-RGO nanocomposite. This can be attributed to higher surface area, better charge carrier transportation through graphene matrix etc. ZnS hollow sphere shows better stability in alkaline medium that leads to better removal efficiency of direct blue 53 dye in alkaline medium. However, in case of ZnSRGO composite trend is reverse. A successful degradation of textile effluent is also performed with these nanomaterials that indicate practical application of the as synthesized nanomaterials. 15 ACS Paragon Plus Environment


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 16 of 42

Acknowledgement Authors are thankful to Ram Chandra Maji for FTIR analysis and Sourav Biswas and Swapnadip Roy for photoluminence analysis. Assistance for SEM study is provided by Prof. D. Mal of Chemistry Department, IIT Kharagpur and Sandip Ruidas of MME Department, NIT Durgapur. Some infrastructural help was taken from the DST project (Project No. SB/EMEQ-115/2013 dated 08.07.2013 and IFA12-CH65).

Supporting Information details: Comparative study between current study and previous reports on ZnS-HS and ZnS-RGO composite, images of as synthesized materials, chemical structure of dye, SEM of broken ZnS hollow spheres, particle size distribution, UV-Vis absorption spectra, dose dependent dye removal efficiencies, pHpzc determination, pH dependent removal efficiency, recyclability of photo-catalyst are presented in supporting information. XRD and FTIR of used photocatalysts are given in supporting information. Physico-chemical characterizations along with time dependent total scan of photocatalytic degradation of the textile effluent by using a. 0.125g/L ZnS b. 0.25g/L ZnS and c. 0.125g/L ZnS-RGO d. 0.25g/L ZnS-RGO are also presented.

References (1) Hoffmann, M.R.; Martin, S. T.; Choi, W.; Bahnemann D. W., Environmental Applications of Semiconductor Photocatalysis. Chem. Rev. 1995, 95, 69. (2) Mills, A.; Davies R. H.; Worsley D., Water purification by semiconductor photocatalysis. Chem. Soc. Rev. 1993, 22, 417. 16 ACS Paragon Plus Environment

Page 17 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


(3) Konstantinou I. K.; Albanis T. A, TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations: A review. Appl. Catal. B: Environ, 2004, 49, 1. (4) Chatterjee, S.; Bhattacharyya, K.; Ayyub, P.; Tyagi, A. K., Photocatalytic Properties of One-Dimensional Nanostructured Titanates. J. Phys. Chem. C, 2010, 114, 9424. (5) Chatterjee, S.; Tyagi A. K.; Ayyub, P., Efficient Photocatalytic Degradation of Rhodamine B Dye by Aligned Arrays of Self-Assembled Hydrogen Titanate Nanotubes. J. Nanomater., 2014, 32,8618 (6) Xu, T.; Zhang, L.; Cheng H.; Zhu, Y., Significantly enhanced photocatalytic performance of ZnO via graphene hybridization and the mechanism study. Appl. Catal. B: Environ., 2011,101, 382 (7) Thakur, I.; Chatterjee, S.; Swain, S.; Ghosh, A.; Behera S. K.; Chaudhary, Y. S., Facile synthesis of single crystalline n-/p-type ZnO nanorods by lithium substitution and their photoluminescence, electrochemical and photocatalytic properties. New J. Chem., 2015, 39, 2612

.

(8) Dutta, S.; Ghosh, A.; Kabir H.; Saha, R., Facile one pot synthesis of zinc oxide nanorods and statistical evaluation for photocatalytic degradation of a diazo dye. Water Sci. Technol., 2016, 74, 698.

(9) Shi, L.; Bao, K.; Cao J.; Qian, Y., Growth and characterization of ZnS porous nanoribbon array constructed by connected nanocrystallities. Crys. Eng. Comm., 2009, 11, 2308. (10) Chen, Z. G.; Cheng L.; Zou, J., Growth and optical properties of stacked-pyramid zinc



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 18 of 42

sulfide architectures. Crys. Eng. Comm., 2011, 13, 5885. (11) Lan, C.; Gong, J.; Jiang, Y.; Song Y.; Yang, S., Controlled synthesis of ZnS nanocombs by self-evaporation using ZnS nanobelts as source and substrates. Crys. Eng. Comm., 2012, 14, 708 (12) Li, S.; Wu, Z.; Li, W.; Liu, Y.; Zhuo, R.; Yan, D.; Jun, W.; Yan, P., One-pot synthesis of ZnS hollow spheres via a low-temperature, template-free hydrothermal route. Crys. Eng. Comm., 2013, 15, 1571. (13) Shuai, Y.; Liu, C.; Wang, J.; Cui X.; Nie, L., Pseudo-bi-enzyme glucose sensor: ZnS hollow spheres and glucose oxidase concerted catalysis glucose. Analyst, 2013, 138, 3259.

(14) Xiao, N.; Dai, Q.; Wang, Y.; Ning, J.; Liu, B.; Zou G.; Xiao, B., ZnS nanocrystals and nanoflowers

synthesized

by

a

green

chemistry

approach:

Rare

excitonic

photoluminescence achieved by the tunable molar ratio of precursors. J. Hazard. Mater., 2012, 211– 212, 62.

(15) Suyana, P.; Nishanth Kumar, S.; Dileep Kumar, B. S.; Nair, B.N.; Pillai, S. C.; Mohamed, A.P.; Warriera K. G. K.; Hareesh, U. S., Antifungal properties of nanosized ZnS particles synthesised by sonochemical precipitation. RSC Adv., 2014, 4, 8439. (16) Goudarzi, A.; Namghi A. D.; Ha, C.-S., Fabrication and characterization of nanostructured ZnS thin films as the buffer layers in solar cells. RSC Adv., 2014, 4, 59764. (17) Xing, R; Xue, Y.; Liu, X.; Liu, B.; Miao, B., Kang W.; Liu, S., Mesoporous ZnS hierarchical nanostructures: facile synthesis, growth mechanism and application in gas sensing. Crys. Eng. Comm., 2012, 14, 8044.


Page 19 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


(18) Kim Y.; Jang, D.-J., A facile growth mechanism of wurtzite ZnS nanostructures showing intense ultraviolet luminescence. Crys. Eng. Comm., 2014, 16, 6989. (19) Rao, H.; Lu, Z.; Liu, X.; Ge, H.; Zhang, Z.; Zou, P.; He H.; Wang, Y., Visible lightdriven photocatalytic degradation performance for methylene blue with different multimorphological features of ZnS. RSC Adv., 2016, 6, 46299. (20) Fang, X. S.; Wu L. M.; Hu, L. F., ZnS Nanostructure Arrays: A Developing Material Star. Adv. Mater., 2011, 23, 585. (21) Ahnb H. B.; Lee, J. Y.; Effects of a low-temperature sulfidation process on the microstructural properties of ZnO nanowires: ZnS formation and nanoscale Kirkendall effect. Crys. Eng. Comm., 2013, 15, 6709. (22) Hu, Y.; Qian, H.; Liu, Y.; Du, G.; Zhang, F.; Wang L.; Hu, X.; A microwave-assisted rapid route to synthesize ZnO/ZnS core–shell nanostructures via controllable surface sulfidation of ZnO nanorods. Crys. Eng. Comm., 2011, 13, 3438. (23) Wang, Z.-Q.; Liu, Z.; Gong, J.-F.; Wang S.; Yang, S.-G., Structure and optical properties of individual hierarchical ZnS nanobelt/ZnO nanorod heterostructures. Crys. Eng. Comm., 2011, 13, 6774. (24) Wang, Z.; Cao, S.-W.; Loo S. C. J.; Xue, C., Nanoparticle heterojunctions in ZnS–ZnO hybrid nanowires for visible-light-driven photocatalytic hydrogen generation Crys. Eng. Comm., 2013, 15, 5688. (25) Gao, X.X.; Wang, J.; Yu J.; Xu, H., Novel ZnO–ZnS nanowire arrays with heterostructures and enhanced photocatalytic properties. Crys. Eng. Comm. 2015, 17, 6328. (26) Roosta, M.; Ghaedi M.; Yousefi, F., Optimization of the combined ultrasonic assisted/adsorption method for the removal of malachite green by zinc sulfide nanoparticles



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 20 of 42

loaded on activated carbon: experimental design. RSC Adv., 2015, 5, 100129. (27) Fu, Y.; Zhang, Z.; Yang, X.; Gan Y.;Chen, W., ZnS nanoparticles embedded in porous carbon matrices as anode materials for lithium ion batteries. RSC Adv., 2015, 5, 86941. (28) Shi, F.; Chen, L.; Xing, C.; Jiang, D.; Li D.; Chen, M., ZnS microsphere/g-C3N4 nanocomposite photocatalyst with greatly enhanced visible light performance for hydrogen evolution: synthesis and synergistic mechanism study. RSC Adv., 2014, 4, 62223. (29) Cao, J.; Liu, Q.; Han, D.; Yang, S.; Yang, J.; Wang T.; Niu, H., Highly enhanced photocatalytic properties of ZnS nanowires–graphene nanocomposites. RSC Adv., 2014, 4, 30798. (30) Stoller, M. D.; Park, S.; Zhu, Y.; An J.; Ruoff, R. S.; Graphene-Based Ultracapacitors. Nano Lett., 2008, 8, 3498. (31) Ramachandran, R.; Saranya, M.; Kollu, P.; Kwan, S.; Andrews, J.; Grace N.; Raghupathy, B. P. C., Solvothermal synthesis of Zinc sulfide decorated Graphene (ZnS/G) nanocomposites for novel Supercapacitor electrodes. Electrochim. Acta, 2015, 178, 647. (32) Du, X.; Skachko, I.; Barker A.; Andrei, E. Y., Approaching ballistic transport in suspended graphene. Nature Nanotechnol., 2008, 3, 491. (33) Burghard, M.; Klauk H.; Kern, K., Carbon-Based Field-Effect Transistors for Nanoelectronics. Adv. Mater., 2009, 21, 2586. (34) Chen, F.-J.; Cao Y.-L.; Jia, D.-Z., A room-temperature solid-state route for the synthesis of graphene oxide–metal sulfide composites with excellent photocatalytic activity. Crys. Eng. Comm., 2013, 15, 4747. (35) Feng, Y.; Feng, N.; Zhang G.; Du, G., One-pot hydrothermal synthesis of ZnS–reduced graphene oxide composites with enhanced photocatalytic properties. Crys. Eng. Comm.,


Page 21 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


2014, 16, 214. (36) Reddy, D. A.; Choi, J.; Lee, S.; Ma R.; Kim, T. K., Self-assembled macro porous ZnS– graphene aerogels for photocatalytic degradation of contaminants in water. RSC Adv., 2015, 5, 18342. (37) Ham, S.; Kim, Y.; Park, M. J.; Hong B. H.; Jang, D.-J., Graphene quantum dotsdecorated ZnS nanobelts with highly efficient photocatalytic performances. RSC Adv., 2016, 6, 24115. (38) Zhang, Y.; Tian, J.; Rahman, A.; Al-Youbi, O.; Li, H.; Sun, X.; Wang, L.; Qin X.; Asiri, A. M., Biomolecule-Assisted, Environmentally Friendly, One-Pot Synthesis of CuS/Reduced

Graphene

Oxide

Nanocomposites

with

Enhanced

Photocatalytic

Performance. Langmuir, 2012, 28, 12893. (39) Sadollahkhani, A.; Kazeminezhad, I.; Lu, J.; Nur, O.; Hultmanc L.; Willander, M., Synthesis, structural characterization and photocatalytic application of ZnO@ZnS core– shell nanoparticles. RSC Adv., 2014, 4, 36940. (40) Shen, H.; Shang, H.; Niu, J.; Xu, W.; Wang H.; Song, L., Size- and shape-dependent growth of fluorescent ZnS nanorods and nanowires using Ag nanocrystals as seeds Nanoscale, 2012, 4, 6509. (41) Sharma, M.K.; Rohani, P.; Liu, S.; Kaus, M; Swihart, M.T., Polymer and SurfactantTemplated Synthesis of Hollow and Porous ZnS Nano- and Microspheres in a Spray Pyrolysis Reactor, Langmuir, 2015, 31, 413. (42) Rohani, P; Sharma, M.K.; Swihart, M.T., Core–satellite ZnS–Ag nanoassemblies: Synthesis, structure, and optical properties”, J. Colloid Interface Sci, 2016, 463, 207. (43) Radich, J. G.; Krenselewski, A. L.; Zhu J.; Kamat, P. V., Is Graphene a Stable Platform



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 22 of 42

for Photocatalysis? Mineralization of Reduced Graphene Oxide with UV-Irradiated TiO2 Nanoparticles. Chem. Mater., 2014, 26, 4662. (44) Jiang, P.; Wang R.; Chen, Z., Thiol-based non-injection synthesis of near-infrared Ag2S/ZnS core/shell quantum dots. RSC Adv., 2015, 5, 56789. (45) Abbas, N. K.; Al- Rasoul, K. T.; Shanan, Z. J., Structural and Optical Characterization of Cu and Ni Doped ZnS Nanoparticles. Int. J. Electrochem. Sci, 2013, 8, 3049. (46) Kole, A. K.; Tiwary C. S.; Kumbhakar, P.; Ethylenediamine assisted synthesis of wurtzite zinc sulphide nanosheets and porous zinc oxide nanostructures: near white light photoluminescence emission and photocatalytic activity under visible light irradiation. Crys. Eng. Comm., 2013, 15, 5515. (47) Lukashin, B.P.; Grebeniuk, A.N., Comparative study of the radiation-protective effectiveness of low doses of cysteamine, heparin, and naphtizine in experiments on mice. Radiatsionnaia biologiia, radioecologiia, 2001, 41, 310. (48) Rajeswari, K.; Subashkumar R.; Vijayaraman, K., Biodegradation of mixed textile dyes by bacterial strains isolated from dye waste effluent. Res. J. Environ. Toxicol., 2011, 5, 97. (49) Liu, Z.; Lu, X.; Xie, S.; Zhang, J.; Liu, Z.; Tong, Y., Facile Electrochemical Synthesis of ZnO/ZnS Heterostructure Nanorod Arrays. J. Electrochem. Soc, 2011, 158, E84 (50) Dutta, S.; Saha, R.; Kalita H.; Bezbaruah, A. N., Rapid reductive degradation of azo and anthraquinone dyes by nanoscale zero-valent iron. Environ. Technol. Innov., 2016, 5, 176. (51) Dutta, S.; Ghosh, A.; Satpati S.; Saha, R., Modified synthesis of nanoscale zero-valent iron and its ultrasound-assisted reactivity study on a reactive dye and textile industry effluents, Desalin. Water Treat., 2016, 57, 19321.


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


(52) Hummers W. S.; Offeman, R. E.; Preparation of Graphitic Oxide, J. Am.Chem. Soc., 1958, 80, 1339. (53) Clesceri, L. S.; Greenberg A. E.; Eaton, A. D., Standard Methods for the Examination of Water and Wastewater, 20th ed.; American Public Health Association, Washington, DC, 1998. (54) Kaur, M.; Gupta N. K.; Nagaraja, C. M., One-pot, template-free syntheses of spherical ZnS nanocrystals using a new S2− source and their photocatalytic study.Crys. Eng. Comm., 2015,17, 2359 (55) Luong, N. D.; Sinh, L. H.; Johansson, L.-S.; Campell, J.; Sepp, J., Functional Graphene by Thiol‐ene Click Chemistry. A European J., 2015, 21, 3183 (56) Bansal, R.C.; Goyal, M., Activated Carbon adsorption. Taylor & Farncis. 2005 (57) Socrates, G., Infrared Characteristic Group Frequencies, John Wiley & Sons, New York, 1980. (58) Kasap S. O.; Capper P., Springer handbook of electronic and photonic materials. Springer. 54,327. 2006. (59) Peng, W.Q.; Cong, G.W.; Qu S.C.; Wang, Z.G., Synthesis and photoluminescence of ZnS:Cu nanoparticles. Opt. Mater., 2006, 29 ,313.

(60) Lee, S.; Song, D.; Kim, D.; Lee, J.; Kim, S.; Park I.Y.; Choi, Y.D., Effects of synthesis temperature on particle size/shape and photoluminescence characteristics of ZnS:Cu nanocrystals. Mater. Lett., 2004, 58, 342.



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

(61) Geng, B.; Ma, J.; Zhan, F., A solution phase thermal decomposition molecule precursors route to ZnS:Cu nanorods and their optical properties. Mater. Chem. Phys., 2009, 113, 534. (62) O’Neil, M.; Marohn, J.; McLendon, G., Dynamics of electron-hole pair recombination in semiconductor clusters. J. Phys. Chem., 1990, 94, 4356. (63) Sobana N.; Swaminathan, M., Combination effect of ZnO and activated carbon for solar assisted photocatalytic degradation of Direct Blue 53. Sol. Energ. Mat. Sol. Cells, 2007. 91, 727. (64) Kothari, S.; Ameta P.; Ameta, A., Photocatalytic Bleaching of Evans Blue over ZnO Particulate System. Ind. J. Chem.-Sec. A, 2007, 46A, 432. (65) Khezrianjoo S.; Revanasiddappa, H.D., Langmuir-Hinshelwood kinetic expression for the photocatalytic degradation of Metanil Yellow aqueous solutions by ZnO catalyst. Chem. Sci. J., 2012, CSJ-85, 1 (66) Khan, A.; Sajjad, L.; Shamaila, S.; Tian, B.; Chen F.; Zhang, J., Comparative studies of operational parameters of degradation of azo dyes in visible light by highly efficient WOx/TiO2 photocatalys. J. Hazard. Mater.s, 2010, 177, 781. (67) Barjasteh-Moghaddam M.; Habibi-Yangjeh, A.; Effect of Operational Parameters on Photodegradation of Methylene Blue on ZnS Nanoparticles Prepared in Presence of an Ionic Liquid as a Highly Efficient Photocatalyst. J Iranian Chem. Soc., 2011, 8, S169. (68) Hasnat, M.A.; Siddiquey I.A.; Nuruddin, A., Comparative photocatalytic studies of degradation of a cationic and an anionic dye. Dyes Pigments, 2005, 66, 185, (69) Daneshvar, N.; Aber, S.; Seyed-Dorraji, M.S.; Khataee A.R.; Rasoulifard, M.H., Photocatalytic degradation of the insecticide diazinon in the presence of prepared


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


nanocrystalline ZnO powders under irradiation of UV-C light. Sep. Purif. Technol., 2007, 58, 91. (70) Henze, M., Comeau, Y., Biological Wastewater Treatment: Principles Modelling and Design. IWA Publishing, London, UK. 2008.



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

Figure and Table Captions Figure 1. X-ray diffractograms of pattern of ZnS-HS and RGO-ZnS nanocomposite; Figure 2. Thermogravimetric analysis curves of ZnS-HS and RGO-ZnS nanocomposite. Figure 3. Scanning electron micrograph of (a) ZnS Hollow Spheres; (b) Surface of ZnS HS showing porous morphology; (c) Single hollow porous ZnS sphere (d) low magnification image of broken HS. Figure 4. Transmission electron micrographs of (a) ZnS HS; (b) HR-TEM image of one particle showing lattice fringes; (c) Selected area diffraction pattern taken on a number of nanoparticles. Figure 5. (a) Scanning electron micrograph of RGO-ZnS NC showing surface morphology of the nanocomposite; (b) Transmission electron micrographs of RGO-ZnS NC showing the distribution of ZnS particle on RGO matrix. Figure 6. N2 adsorption-desorption isotherms of (a) ZnS HS and (b) RGO-ZnS NC; Insets represent corresponding pore size distribution as calculated by Barrett-Joyner-Halenda method. Figure 7. FTIR spectra of ZnS-HS, RGO-ZnS NC and graphene oxide taken in different ranges: (a) 4000 – 400 cm-1; (b) 2000 – 1000 cm-1. Figure 8. Photoluminence spectra of (a) ZnS-HS and RGO-ZnS NC. Eyeguides are given to indicate several sub-bands present in individual spectrum: (b) ZnS-HS and (c) RGO-ZnS NC. Figure 9. (a) Liquid phase photocatalytic degradation of DB 53 dye by (I) RGO-ZnS NC, (II) ZnS-HS, (III) in presence of only UV irradiation and in absence of any catalyst, (IV) RGO-ZnS NC, and (V) ZnS HS in absence of light; (b) Plot of ln(C0/C) vs. time for (I) RGO-ZnS NC, (II) ZnS-HS, (III) in presence of only UV irradiation and in absence of any catalyst. Effect of concentration variation of photocatalysts: (c) ZnS-HS and (d) RGO-ZnS NC on respective dye removal efficiencies. Figure 10. pH dependent removal efficiencies of (a) ZnS-HS and (b) RGO-ZnS NC. Insets show respective plots of ln(C0/C) vs. time. Fig 11. Reusability of the ZnS HS and RGO-ZnS NC upto 6 cycles. Fig 12. Removal efficiency of industrial textile effluent by (a) ZnS HS and (b) RGO-ZnS NC for two different catalyst concentrations, (b) Plots of ln(C0/C) vs. time for the same. Table 1: Physico-chemical property comparisons of ZnS HS and ZnS-RGO NC. Scheme 1: Formation mechanism of ZnS hollow spheres. Scheme 2: Formation mechanism of RGO-ZnS nanocomposite.


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


Figure 1. X-ray diffractograms of pattern of ZnS-HS and RGO-ZnS nanocomposite;



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

Figure 2. Thermogravimetric analysis curves of ZnS-HS and RGO-ZnS nanocomposite.


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


Figure 3. Scanning electron micrograph of (a) ZnS Hollow Spheres; (b) Surface of ZnS HS showing porous morphology; (c) Single hollow porous ZnS sphere (d) Image of bunch of broken HS



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

Figure 4. Transmission electron micrographs of (a) ZnS HS; (b) HR-TEM image of one particle showing lattice fringes; (c) Selected area diffraction pattern taken on a number of nanoparticles.


Page 31 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


(a)

(b)

Figure 5. (a) Scanning electron micrograph of RGO-ZnS NC showing surface morphology of the nanocomposite; (b) Transmission electron micrographs of RGO-ZnS NC showing the distribution of ZnS particle on RGO matrix.



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 32 of 42

Figure 6. N2 adsorption-desorption isotherms of (a) ZnS HS and (b) RGO-ZnS NC; Insets represent corresponding pore size distribution as calculated by Barrett-Joyner-Halenda method. 32 ACS Paragon Plus Environment

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 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. FTIR spectra of ZnS-HS, RGO-ZnS NC and graphene oxide taken in different ranges: (a) 4000 – 400 cm-1; (b) 2000 – 1000 cm-1.



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 34 of 42

Figure 8. Photoluminence spectra of (a) ZnS-HS and RGO-ZnS NC. Eyeguides are given to indicate several sub-bands present in individual spectrum: (b) ZnS-HS and (c) RGO-ZnS NC.


Page 35 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


Figure 9. a) Liquid phase photocatalytic degradation of DB 53 dye by (I) RGO-ZnS NC, (II) ZnS-HS, (III) in presence of only UV irradiation and in absence of any catalyst, (IV) RGO-ZnS NC, and (V) ZnS HS in absence of light; (b) Plot of ln(C0/C) vs. time for (I) RGO-ZnS NC, (II) ZnS-HS, (III) in presence of only UV irradiation and in absence of any catalyst. Effect of concentration variation of photocatalysts: (c) ZnS-HS and (d) RGO-ZnS NC on respective dye removal efficiencies.



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 36 of 42

Figure 10. pH dependent removal efficiencies of (a) ZnS-HS and (b) RGO-ZnS NC. Insets show respective plots of ln(C0/C) vs. time.


Page 37 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


Figure 11. Reusability of the ZnS HS and RGO-ZnS NC upto 6 cycles



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 38 of 42

Figure 12. Removal efficiency of industrial textile effluent by (a) ZnS HS and (b) RGO-ZnS NC for two different catalyst concentrations, (b) Plots of ln(C0/C) vs. time for the same. 38 ACS Paragon Plus Environment

Page 39 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


Sample

Crystallinity Crystallite Morphology size (nm)

ZnS HS

Cubic

~28

Hollow sphere

(RGOZnS NC)

Cubic

~4

Nanoparticle decorated grapheme matrix

Surface area (m2/g) 70.6

Bandgap (eV)

81.5

3.69

3.77

Table 1: Physico-chemical property comparisons of ZnS HS and ZnS-RGO NC.



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 40 of 42

Scheme 1: Formation mechanism of ZnS hollow spheres


Page 41 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


Scheme 2: Formation mechanism of RGO-ZnS nanocomposite



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 42 of 42

For Table of Contents only

Summary: One pot hydrothermal synthesis of hollow microspheres of ZnS and RGO-ZnS nanocomposite using a novel and ecofriendly sulphur source (cysteamine) and study of their appication in industrial effluent degradation.


Fabrication of ZnS Hollow Spheres and RGO-ZnS Nanocomposite

Recommend Documents