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Alpha-NiS/Bi2O3 Nanocomposites for Enhanced Photocatalytic Degradation of Tramadol Dibyananda Majhi, Pankaj kumar Samal, Krishnendu Das, Somesh K Gouda, Yagna P Bhoi, and Braja Gopal Mishra ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01974 • Publication Date (Web): 27 Dec 2018 Downloaded from http://pubs.acs.org on January 2, 2019

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ACS Applied Nano Materials

Alpha-NiS/Bi2O3 Nanocomposites for Enhanced Photocatalytic Degradation of Tramadol Dibyananda Majhi, Pankaj K. Samal, Krishnendu Das, Somesh K. Gouda, Y.P. Bhoi, B.G. Mishra* Department of Chemistry, National Institute of Technology, Rourkela-769008, Odisha, India ABSTRACT: In this study, a series of αNiS/Bi2O3 composite nanomaterials were prepared

and

evaluated

as

efficient

photocatalyst for degradation of tramadol under visible light. Two polymorphs of Bi2O3 namely α- (monoclinic) and - (tetragonal) were prepared by using combustion method and bismuth subcarbonate decomposition route, respectively. A facile method was also developed for synthesis of ultrathin α-NiS nanosheets under mild conditions using hexamethylenetetramine as hydrolyzing agent and Na2S2O3 as sulfur source. The NiS/α-Bi2O3 and NiS/-Bi2O3 composite materials were thoroughly characterized using a variety of techniques to understand their structural, optical, electrochemical, microstructural and morphological attributes. The αNiS/Bi2O3 materials exhibited improved visible light absorption, enhanced charge carrier separation and photo-electrochemical properties. The microscopic close contact between the two semiconductor phases is established from the morphological studies. The α-NiS/Bi2O3 materials exhibited excellent photocatalytic activity for aqueous phase degradation of tramadol under visible light irradiation. Particularly, the α-NiS/-Bi2O3 system is highly active achieving 94% degradation in 3 h. The mechanism of photocatalytic action involves a z-scheme electron transfer from the CB of Bi2O3 to the VB of NiS which is responsible for efficient space separation of charge carriers and their increased reactivity. The OH radicals and h+ species have been identified as the major transient species responsible for tramadol oxidation. The photocatalytic method developed in this study can be a viable alternative for TiO2 based UV active photocatalyst studied so far for tramadol degradation. KEYWORDS: α-NiS, Bi2O3, Z-scheme, Tramadol, Photocatalysis

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1. INTRODUCTION Bismuth-based photocatalysts particularly, Bi-based oxides have been extensively studied in the past few years due to their unique electronic structure, various polymorphic forms and excellent photocatalytic properties for waste water remediation.1-5 The bismuth oxide exists in several stoichiometric crystalline phases such as BiO, BiO2, Bi2O3, Bi2O5, Bi2O4, Bi4O7 and Bi8O11 with different photonic excitation energy.6,7 Out of these Bi2O3 is of special importance due to its narrow band gap, non-toxicity and wide applications in the field of photocatalysis. Recent studies reveal that Bi2O3 semiconductor exhibits several polymorphic forms, among which αand -phase has been widely studied as photocatalysts due to their efficient visible light absorption property.8-10 Further, the metastable -Bi2O3 shows superior photocatalytic property than α-phase due to its lower band gap energy (2.4 eV).11 However, the rapid recombination of electron-hole pairs and the larger grain size of Bi2O3 are the major disadvantages which limit its photocatalytic potential. To improve the charge carrier separation and photocatalytic activity, Bi2O3 has been modified recently by supporting Au and forming heterostructure photocatalytic systems with BiOCl , g-C3N4, TiO2, C/Bi, TiO2−xBx, SrFe12O19 and ZnO.10,12-18 These modified systems exhibit efficient photocatalytic activity for degradation of salicylic acid, Rhodamine B, ofloxacine, 2,4-dichlorophenol, pentachlorophenol and methylene blue under visible light irradiation. Recently, Bi2O3/Bi2SiO5 p-n heterojunction material has been synthesized by a single step calcination method using bismuth nitrate and SiO2 nanoparticles as precursors. The presence of SiO2 selectively stabilizes the -Bi2O3 phase. The heterojunction system shows excellent photocatalytic activity for degradation of chlorophenols under simulated sunlight irradiation.19 Although there are reports on the photocatalytic application of Bi2O3 based heterostructure materials, most of the studies are confined to degradation of dyes and various organic effluents.12-18 So far there are very few studies which deal with the application of this important class of photocatalyst towards degradation of emerging pharmaceutical contaminants.14 Moreover, synthesis and photocatalytic application of Bi2O3 based heterostructure photocatalytic systems with low band gap nickel sulfide nanoparticles is yet to be explored. Nickel sulfide (NiS) is a narrow band gap, p-type semiconductor which has been extensively studied for photocatalytic hydrogen evolution and organic dye degradation.20-25 Literature reports revealed that mostly hydrothermal method has been used for the synthesis of NiS nanoparticles. In most of the studies multi-steps precursor route and high temperature condition have been adopted for 2 ACS Paragon Plus Environment

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selective stabilization of -NiS phase.26-28 In this work, we have prepared α- and -phase of Bi2O3 by using combustion synthesis and carbonate precursor route, respectively. In a novel approach, we have also devised a low temperature, single-step reflux method for phase control synthesis of -NiS nanosheets. The two polymorphic forms of Bi2O3 were subsequently modified with -NiS to prepare -NiS/Bi2O3 composite system. The photocatalytic application of -NiS/Bi2O3 has been studied for visible light assisted photocatalytic degradation of tramadol. Several pharmaceutical compounds including non-steroidal anti-inflammatory drugs (NASIDs), antibiotics and steroidal hormones e.g. tramadol, tetracycline, salbutamol, 17α-ethinylestradiol, 17-estradiol, estrone etc. have been identified recently as emerging contaminants.29-32 These contaminants are highly persistent in aquatic ecosystems, extremely resistant to biological degradation processes and are capable of escaping intact from conventional treatment plants.29-32 Tramadol (TRA) is an instance of such pharmaceutical compound being used as an analgesic for relief of moderate to severe acute and chronic pain. Up to 30% of consumed tramadol is excreted via urine as a pure compound which undergoes extensive metabolism in the environment resulting in the formation of N-desmethyl-(N-DES) and O-desmethyl-(O-DES) tramadol.33,34 A European-wide monitoring study on occurrence of organic micropollutants in waste water treatment plant depicts TRA as most frequently detected contaminant.33,34 In recent past, biotic, abiotic and electrochemical degradation methods have been developed for TRA degradation.35-37 Biotic processes employ natural microorganisms for transforming pharmaceutical compounds and allied metabolites into smaller fragments whereas abiotic processes include degradation of these compounds through direct/indirect photo-degradation. Among the advanced oxidation processes (AOPs), the heterogeneous photocatalysis, is a promising technology for pharmaceutical compound eradication from aqueous media.38 The photocatalytic method is economic, environment friendly and a sustainable method for waste water treatment. Till date TiO2 and photosensitized TiO2 are the only photocatalytic systems studied for TRA degradation.38,39 The high band gap of TiO2 (3.2 eV) limits its practical applicability due to high energy UV light requirement and poor quantum yield owing to fast electron hole recombination. Hence, it is desirable to develop novel photocatalytic systems which can efficiently catalyze the degradation of tramadol from aqueous media under visible light irradiation. In the recent past, we have studied a series of Bi based heterostructure photocatalytic materials towards visible light 3 ACS Paragon Plus Environment


assisted degradation of persistent organic pollutants.40-42 In continuation of our interest to develop novel visible light responsive heterostructure materials for waste water remediation, here in we have studied the photocatalytic application of α-NiS/Bi2O3 composite photocatalyst for TRA degradation. 2.

EXPERIMENTAL SECTION 2.1. Materials. All the chemicals and reagents were purchased from Merck Specialities

Pvt. Ltd. and Hi Media Laboratories Pvt. Ltd, India. All the chemical reagents were of analytical grade and they were used directly without further purification. The deionized water prepared in our laboratory was used in all synthesis process. 2.2. Synthesis of -Bi2O3 material (BBO). The tetragonal phase of Bi2O3 (β-Bi2O3) was synthesized by thermal decomposition of bismuth subcarbonate (Bi2O2CO3). Initially, tetragonal phase of Bi2O2CO3 was prepared by a facile hydrothermal method using bismuth nitrate as salt precursor, urea as hydrolyzing agent and KBr as additive at a molar ratio of 1:5:1, respectively. In a typical synthesis, required amount of bismuth nitrate, urea and KBr were dissolved in 150 ml of water and stirred for 1 h. The aqueous mixture was then transferred to a teflon lined autoclave and treated under autogenous pressure at 160oC for 24 h. After completion of the reaction, the autoclave was cooled to room temperature and the solid residue was filtered, washed several times with water and ethanol to eliminate byproducts. The obtained white solid residue was kept in hot air oven at 80oC for 12 h to yield the Bi2O2CO3 material and labeled as BSC-K. The BSC material was also synthesized by the urea hydrolysis method in absence of KBr, which is labeled as BSC-U. The as synthesized BSC-K material was calcined at 400oC for 2 h to prepare β-Bi2O3 (BBO) material. 2.3. Synthesis of α-Bi2O3 material (ABO). The monoclinic Bi2O3 (-Bi2O3) phase was prepared by combustion route by taking bismuth nitrate as salt precursor and urea as fuel. Bismuth nitrate and urea was taken in 1:5 molar ratios to make a gel with minimum amount of water and heated at 400oC for 30 min to prepare a precursor. This precursor was calcined in the temperature range of 500-650oC for 2 h to synthesize the ABO material. 2.4. Synthesis of α-NiS/Bi2O3 composite nanomaterials. The α-NiS/Bi2O3 composite was synthesized using a facile reflux method. In a typical synthesis procedure, 200 mg of as synthesized Bi2O3 material was dispersed in 70 ml water by ultrasonic treatment. To the above 4 ACS Paragon Plus Environment

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suspension required amount of nickel nitrate and hexamethylenetetramine (HMTA) was added in 1:1 molar ratio and stirred for 30 min. Subsequently, 1 molar equivalent of sodium thiosulfate was added and stirred for 1 h. The resulting suspension was refluxed for 6 h under continuous stirring condition. The reaction mixture was subsequently cooled to RT and the solid products are separated by centrifugation. The solid residue was washed several times with water and ethanol and kept under vacuum drying at 80oC for 12 h. Both the ABO and BBO materials were modified with 5, 10, 15 and 25 wt% of NiS using the above route to prepare their respective composite photocatalytic systems. The composite materials are labeled as NiSxABO and NiSxBBO, respectively (x=5, 10, 15 and 25). Pure -NiS was also prepared by using similar experimental procedure. 2.5. Characterization techniques. The crystalline phases in the samples were identified by X-ray powder diffraction using a Rigaku Ultima-IV diffractometer fitted with Ni filtered CuKα (λ= 1.5418 Å) radiation as X-ray source. The XRD measurements were carried out in the 2θ range of 20-60o with a scan speed of 2o per minute using the Brag-Brentano configuration. The TGA-DTA analysis of the BSC-K material was carried out from RT to 600oC in air atmosphere using a Perkin-Elmer TGA-7 apparatus. The FESEM images were taken by using a Nova Nano SEM/FEI microscope. HRTEM study was performed by using a TECNAI 300 kV instrument using carbon coated copper grid as substrate. The specific surface areas of the materials were determined by BET method using a Quantachorme AUTOSORB 1 instrument. The samples were degassed at 120oC for 5 h prior to BET analysis. The confocal micro-Raman spectra were obtained using a WITec alpha 300R spectrometer using a laser light source with excitation wavelength of 532 nm. The FTIR spectra of the samples were recorded as KBr pellet using a Perkin–Elmer infrared spectrometer in the range of 400–1200 cm-1. The UV-Vis diffuse reflectance spectra of the powder samples were recorded using a Jasco V-650 spectrometer fitted with a BaSO4 integration sphere. The solid state photoluminescence (PL) spectra of the heterojunction materials were recorded using a Horiba Scientific Fluoromax-4 spectrometer at an excitation wavelength of 320 nm. The XPS spectra of NiS15BBO material was recorded using a SPECS spectrophotometer (Germany) fitted with a 150 mm hemispherical electron energy analyzer operating at a band pass energy of 12 eV. The monochromatic Al Kα radiation (1486.74 eV) was used as X-ray source for XPS study. The photoconductivity measurement for BBO and NiS15BBO materials was carried out using a Keithley 2400 sourcemeter integrated with AM 5 ACS Paragon Plus Environment


1.5G filter fitted solar simulator. The photelectrodes were prepared by depositing the slurry of the materials over the ITO substrate. The electrochemical impedance measurements were carried out using a HIOKI IM-3570 impedance analyzer. The H2-TPR experiments were performed using a Chembec 3000, Quantachrome instrument fitted with a TCD detector. Prior to TPR experiment the samples were degassed at 200oC under He flow and cooled to 50oC. The TPR tests were carried out in the temperature range of 50-800oC using 5% H2 in Ar at flow rate of 50 cm3/min and linear heating rate of 10oC/min. 2.6. Photocatalytic activity test. The photocatalytic activity of the NiSxABO and NiSxBBO composite materials was evaluated for aqueous phase degradation of tramadol under visible light irradiation. The photocatalytic degradation reaction was carried out using an immersion well quartz photoreactor fitted with a 250 W Xe lamp (> 400 nm) as visible light source. Typically, 20 mg of NiSxBBO photocatalyst was dispersed in 100 mL of 10 ppm TRA aqueous solutions and stirred for 1 h under dark condition to reach the adsorption–desorption equilibrium. The aqueous suspension was exposed to the light source under continuous stirring. At regular interval of time, 2 ml of reaction mixture was taken out and analyzed for TRA concentration using a HPLC [Agilent semi preparative HPLC, G1322A, C-18 column] by literature reported method.39 The total organic carbon (TOC) content in the reaction mixture at different time was analyzed using a TOC analyser (Analytik Jena/multi N/C 3100, TOC analyzer). The concentration of ammonium and nitrate ions was measured by spectrophotometric method using the literature reported procedure.41 3.

RESULTS AND DISCUSSION 3.1. Characterization of the NiSxABO and NiSxBBO composite materials. In this

study, the -Bi2O3 (BBO) is prepared by thermal decomposition of bismuth subcarbonate (BSC) precursor. The BBO material is subsequently modified with α-NiS prepared by a facile reflux route to prepare the NiSxBBO composite photocatalytic systems. The scheme for synthesis of BBO and the NiSxBBO composite material is presented in Fig 1. For comparison purpose, phase pure α-Bi2O3 (ABO) is prepared by combustion route using urea as fuel. The ABO material is subsequently modified with α-NiS to prepare NiSxABO heterostructure material. The detailed


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characterization study of ABO and BBO materials are presented in the supporting information file (Fig S1-S4).

Fig 1. Schematic for synthesis of pure phase -NiS, BBO and NiSxBBO heterostructure nanocomposite. The XRD patterns of NiSxBBO materials containing different weight percentage of α-NiS are presented in Fig 2. The BBO material shows distinct XRD peaks at d values of 3.19, 2.81, 2.73, 1.96, 1.93, 1.68 and 1.65 which are indexed to (201), (002), (220), (222), (400), (203) and (421) crystallographic planes of tetragonal -Bi2O3 phase (JCPDS file No.27-0050) (Fig 2a). Pure NiS synthesized by reflux method shows broad and low intense reflections at d values of 2.96, 2.58, 1.97 and 1.71 Å characteristic of the hexagonal α-NiS phase (Fig 2f) (JCPDS No.75-0613). All the individual diffraction peaks of BBO are preserved in the composite system (Fig 2b-e). In general, a decrease in peak intensity and peak broadening is noticed for BBO phase with increase in NiS content in the NiSxBBO composite. The XRD peak due to NiS phase could not be discerned in the NiSxBBO system probably due to low crystalline character of NiS phase. The XRD patterns of NiSxABO materials are presented in Fig S5. The NiSxABO systems exhibited well defined XRD peak due to ABO phase without any assignable XRD peak due to NiS phase.



Fig 2. XRD profiles of (a) BBO, (b) NiS5BBO, (c) NiS10BBO, (d) NiS15BBO, (e) NiS25BBO and (f) α-NiS materials. The morphological features of the NiSxBBO and NiSxABO materials are studied using FESEM technique. Fig 3 shows the FESEM images of NiSxBBO materials together with pure BBO and NiS. Pure BBO material contains particles with irregular shape and size in the range of 60-120 nm (Fig 3a). Pure NiS contains sheet shaped particles present in an agglomeration state (Fig 3b). The presence of both NiS nanosheets and BBO particles are noticed for the NiSxBBO materials (Fig 3c-f). Upto 15 wt% NiS content the two phases are present in a well dispersed state. However, for NiS25BBO material the local agglomeration of both NiS and BBO particles are noticed (Fig. 3f). The elemental mapping study of NiS15BBO revealed well dispersion of both components throughout the microscopic specimen of the heterostructure material (Fig 3 gk). The morphological attributes of NiSxBBO system is further explored by HRTEM technique. The presence of ultrathin NiS nanosheets and BBO nanoparticles is clearly noticed for the pure 8 ACS Paragon Plus Environment

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materials (Fig 4 a&b). For NiS15BBO composite systems, the presence of well dispersed BBO particles in a continuous NiS matrix is confirmed from Fig 4c.The high resolution TEM image of NiS15BBO revealed close microscopic contact between the (102) plane of NiS and (220) planes of BBO leading to the heteostructure formation (Fig 4d). The FESEM images of NiSxABO materials together with pure ABO are presented in Fig S6. The presence of agglomerated ABO plates with planar dimension of 280-370 nm and thickness between 50-80 nm is observed in FESEM study (Fig S6a). The ABO plates morphologically transform to irregular shaped flake like particles in the composite materials (Fig S6b-d). The NiSxABO systems contain agglomerated particles consisting of ABO particles and NiS nanosheets.



Fig

3.

FESEM

images

of

(a)

BBO,

(b)

NiS,

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(c)

NiS5BBO,

(d)

NiS10BBO,

(e) NiS15BBO, (f) NiS25BBO materials and (g-k) Elemental mapping of NiS15BBO material. 10 ACS Paragon Plus Environment

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Fig 4. HRTEM images of (a) NiS, (b) BBO, (c,d) NiS15BBO materials. The optical property of the NiSxABO and NiSxBBO materials is studied using UV-Vis and PL techniques. The UV-Vis spectra of NiSxBBO materials together with BBO and NiS are presented in Fig 5.



Fig 5. (I) UV-Vis and (II) PL spectra of (a) BBO, (b) NiS5BBO, (c) NiS10BBO, (d) NiS15BBO and (e) NiS materials. Pure BBO shows significant visible light absorption with absorption edge commencing near 550 nm (Fig 5Ia). Pure NiS shows strong visible light absorption characteristics which extents up to the NIR region (Fig 5I inset). For NiSxBBO heterostructure system, a significant improvement in absorption feature is noticed in the spectral range of 400-800 nm (Fig 5I b-d). The UV-Vis study suggests that the NiSxBBO materials efficiently absorb visible light and hence can be used as photocatalyst under visible light irradiation. The pure ABO material shows a sharp absorption edge near 450 nm (Fig S7a). However, after composite formation, enhancement in visible light absorption property of ABO is observed (Fig S7). The optical band gap of pure ABO, BBO and NiS materials is calculated (from Tauc’s plot) to be 2.89, 2.48 and 1.40 eV, respectively (Fig S8). The calculated band gap values are in good agreement with previously reported data.11,17,25 The room temperature PL spectra of BBO and ABO together with their respective heterostructure materials acquired at an excitation wavelength of 320 nm are represented in Fig 5II and Fig S7II, respectively. The BBO material shows a series of PL bands in the range of 450-550 nm due to band edge transition as well as transition occurring from defect centers and oxygen vacancies.41 12 ACS Paragon Plus Environment

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similarly, the ABO material exhibits a strong PL band at 465 nm due to band edge transition. The intensity of these PL bands decrease drastically in the NiSxABO and NiSxBBO composite systems. The decrease in PL intensity is ascribed to a decrease in recombination rate due to efficient space separation of charge carriers. The mobility of the charge carriers and their space separation is probed further using transient photocurrent measurement and electrochemical impedance spectroscopy (Fig S9). The NiS15BBO material exhibited a significant enhancement in photocurrent density in comparison to pure ABO and BBO material (Fig S9I). Among ABO and BBO materials, a higher photocurrent density is noticed for BBO material (Fig S9I). Furthermore, the arc radius on EIS Nyquist plot of NiS15BBO material is much smaller than that of pure BBO material (Fig S9II). The improved photocurrent as well as the lower arc radius in EIS study suggests higher mobility and greater charge carrier separation efficiency in NiS15BBO heterostructure material. The vibrational spectroscopic study is employed to evaluate the microstructural properties and structural integrity of the individual components in the NiSxBBO composite system. The Raman spectra of NiS15BBO material together with ABO and BBO materials in the spectral range of 100-600 cm-1 are presented in Fig 6I. Pure ABO exhibited strong and sharp Raman bands at 123, 143, 154, 188, 215, 283, 317, 414 and 451 cm-1 (Fig 6Ia). The first five Raman bands correspond to the lattice vibrations whereas the higher frequency peaks in the range of 250-500 cm-1 can be assigned to the Bi-O stretching vibrations.8 The observed Raman bands are characteristics of the monoclinic α-Bi2O3 with high crystallinity. The BBO materials exhibit three vibrational Raman bands at 124, 310 and 472 cm-1 corresponding to different Bi-O stretches of tetragonal -Bi2O3 (Fig 6Ib).43 These characteristic Raman bands suggests formation of pure -Bi2O3 without any analogous Bi2O3 crystalline phases as impurity. For NiS15BBO heterostructure system, there is a significant change in Raman spectra (Fig 6Ic). The 124 cm-1 peak is retained whereas the intensity of the 310 cm-1 peak decreases drastically. This observation suggests a change in the microstructural property and an alteration in symmetry due to microscopic material contact with NiS phase. In addition, a weak and broad peak observed at 349 cm-1 can be assigned to Ni-S stretching. The FTIR spectra of the BBO and NiSxBBO materials in the spectral region of 400-1200 cm-1 are presented in Fig 6(II). The characteristic vibrational bands of pure BBO are observed at 847 (Bi–O–Bi), 587 and 524 cm-1 corresponding to the vibration from [BiO6] units.44 All the characteristic vibrational bands of BBO are 13 ACS Paragon Plus Environment


preserved in the NiSxBBO composite materials. In addition, a weak band observed around 634 cm-1 for NiSxBBO system is due to the Ni-S stretching vibrational modes of NiS.45

Fig 6. (I) Raman spectra of (a) ABO, (b) BBO and (c) NiS15BBO and (II) FTIR spectra of (a) BBO, (b) NiS5BBO, (c) NiS10BBO and (d) NiS15BBO materials. The chemical environment and oxidation state of the constituent elements on the surface of NiS15BBO material is studied using XPS technique (Fig 7). The survey spectra indicated the presence of Bi, Ni, O and S together with adventitious carbon on the surface of the sample (Fig 7a). In the high resolution spectra, a doublet is noticed at 158.8 and 164.1 eV due to photoelectron emission from the 4f7/2 and 4f5/2 energy states of Bi (III) species (Fig 7b). The spectral doublet together with the spin-orbit splitting of 5.3 eV is characteristics of Bi(III) species in oxide environment.41 In the O core level spectra, a symmetrical broad peak observed at 530 eV corresponds to the lattice oxygen of Bi2O3 (Fig 7c ). In the Ni 2p region, two set of peaks are noticed. The intense doublet observed at 873.6 eV and 855.9 eV corresponds to the 2p1/2 and 2p3/2 energy states of Ni(II) ions of α-NiS. The low intense peaks noticed at 879.8 eV and 861.8 eV is attributed to satellite peaks of a minor amount of NiO which is probably 14 ACS Paragon Plus Environment

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generated from surface oxidation of NiS. Such peaks have been observed earlier in the XPS study of Nickel sulfide.46 In the S2S region, a broad asymmetric peak with maxima at 225.8 eV corresponds to the sulfide ions of NiS.47

Fig 7. X-ray photoelectron (a) survey spectrum and high resolution spectra of (b) Bi 4f, (c) O1s, (d) Ni2p and (e) S2s for NiS15BBO materials. The interaction between the α-NiS and BBO in the NiS15BBO composite is further studied using H2-temperature programmed reduction (H2-TPR) technique (Fig S10). Pure BBO shows a symmetric and broad reduction peak in the range of 300-650oC with maxima at 510oC. The 15 ACS Paragon Plus Environment


observed TPR profile of BBO is similar to the previous literature reports.48 α-NiS exhibits two peaks with maxima at 452oC and 540oC (Fig S10 c). The low temperature peak can be assigned to the surface reduction whereas the peak at 540oC is due to reduction of the bulk phase. The αNiS prepared in this work displays nanosheet morphology with high exposed surface which is responsible for the occurrence of the surface reduction peak. In contrast, the NiS15BBO material shows three TPR peaks at 260, 490 and 551oC (Fig S10 b). The small peak observed at 260oC can be assigned to the reduction of a minor amount of NiO present in the sample.49 The TPR peak at 490 and 550oC can be assigned to the reduction of NiS and BBO phases, respectively. The NiS phase shows a single low temperature reduction peak in the heterostructure system due to facile migration of electrons from BBO to NiS phase. This electron transfer process improves the reducibility of NiS phase. The reduction peak of BBO has shifted to higher temperature in the composite system relative to pure BBO material. This can be ascribed to the strong interaction between the NiS and BBO phases originating from the higher electron donor ability of Bi2O3.50 3.2. Formation mechanism of -NiS phase and metastable β-Bi2O3 phase. In this study, phase control synthesis of α-NiS is performed under reflux condition using HMTA as hydrolyzing agent as well as buffer. The HMTA is a weak base which undergoes slow dissociation in aqueous medium to form six molecules of formaldehyde and four molecules of ammonia.51 The liberated ammonia is hydrated to give OH- ion. This slow released hydroxyl ion combine with Ni2+ to form Ni(OH)2 intermediate. The formation of Ni(OH)2 in presence of HMTA is presented in equation 1-3. C6H12N4 + 6 H2O NH3 + H2O

6HCHO + 4 NH3 ……………. (1) NH4+ + OH- …………………….. (2)

Ni2+ + 2OH-

Ni(OH)2 ……………………... (3)

Simultaneously, the decomposition of S2O3-2 ions from sodium thiosulfate under reflux condition can be described using equation 4 and 5. Na2S2O3 S2O32- + H2O

2Na+ + S2O32- ………………………(4) H2S +SO42- ………………………(5) 16

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The insitu generated Ni(OH)2 reacts with liberated H2S to give α-NiS phase. The transformation of Ni(OH)2 (pKsp[Ni(OH)2]=15.26) to α-NiS (pKsp [-NiS]=18.5) phase in presence of sulfur source is due to the lower thermodynamic stability of Ni(OH)2.52 H2S + Ni(OH)2

NiS+ 2H2O ……………………(6)

The formation of Ni(OH)2 is evident from the reaction of aqueous solution of nickel nitrate and HMTA under reflux condition. A pale green precipitate is obtained when a solution containing nickel salt and HMTA is refluxed for 6 h. The XRD pattern of the obtained product matches the hexagonal Ni(OH)2 phase (JCPDS No.73-1520) (Fig S11I). The formation of nickel hydroxide phase is further confirmed from the characteristics peaks from FTIR (506, 629, 1383 and 1637 cm-1)53 and Raman (320 and 450 cm-1)54 study (Fig S11 II&III). The FESEM study revealed the presence of Ni(OH)2 nanosheets for this material (Fig S11 IV). In order to ascertain that HTMA is essential for selective synthesis of α-NiS, the nickel nitrate and sodium thiosulfate solution is refluxed for 6 h in absence of HTMA. Without HTMA, the formation of sulfur deficient NiS1.97 phase is noticed (JCPDS No. 83-0575) (Fig S12). This observation suggests that the selective formation of NiS phase in presence of HMTA proceeds through the formation of Ni(OH)2 as an intermediate phase. In this study, the selective synthesis of β-Bi2O3 has been accomplished through Bi2O2CO3 precursor route using KBr as an additive. The β-Bi2O3 is a metastable polymorph of Bi2O3 which is stabilized at 650oC and transform to α-phase when cooled to room temperature. The selective stabilization of β-Bi2O3 has been accomplished by low temperature calcination of bismuth carbonate.55 It has been observed that, at low calcination temperature a fraction of carbonate ions remain coordinated to the surface of Bi2O3, which reduces the surface energy and stabilizes the β-Bi2O3 phase. In the present study, the Br- ions can facilitate the insitu release of CO32- ions from urea to form tetragonal Bi2O2CO3. Moreover, the Br- ions can coordinate with the [Bi2O2]2+ layers on the surface which can reduce the surface energy leading to β-Bi2O3 formation. The formation of β-Bi2O3(BBO) is presented schematically in Fig 1. 3.3. Enhanced photocatalytic activity of NiS/Bi2O3 composite materials. The photocatalytic activity of NiSxABO and NiSxBBO composite materials is evaluated for the degradation of tramadol (TRA) under visible light irradiation. Initially, in order to establish the photocatalytic nature of the reaction, TRA degradation is carried out in presence as well as in 17 ACS Paragon Plus Environment


absence of catalyst under dark and illuminated condition. Under dark condition, the TRA degradation reaction does not occur with or without the photocatalyst. Under illuminated condition in absence of the photocatalyst, a marginal decrease of 7% TRA concentration is noticed after 6 h. However, in presence of NiS15BBO photocatalyst 94% degradation of TRA is achieved within 3 h of irradiation. The heterostructure formation between NiS and BBO seems to be crucial for the observed increase in photocatalytic activity. From the characterization studies, it has been noticed that the NiSxBBO materials exhibited improved visible light absorption, surface area and higher spatial separation and mobility of charge carriers. The microscopic close contact between the two phases in the composite system promotes the migration of charge carrier across the grain boundary resulting in their efficient separation. These factors contribute to the higher photocatalytic activity of the NiS15BBO heterostructure material compared to the pure components. Fig S13 shows a comparison of the photocatalytic activity of ABO and BBO samples together with their heterostructure systems containing 15 wt% NiS. The BBO material exhibited superior photocatalytic activity than ABO. Among the composite materials, NiS15BBO material shows higher photocatalytic activity than NiS15ABO and pure components. The photocatalytic activity of the NiS15BBO catalyst is further compared with 15 wt% NiS modified Bi2WO6 (BWO) and Bi2MoO6 (BMO) materials. Both BWO and BMO are prepared by combustion synthesis route which are subsequently modified with α-NiS to prepare NiS15BWO and NiS15BMO materials.41 The photocatalytic activity of these materials together NiS15BBO is compared in Fig. S14. Under identical reaction conditions, the NiS15BBO is more active compared to NiS15BWO and NiS15BMO materials. Based on the results described in Fig S13 and S14, the NiS15BBO heterostructure materials are selected for further photocatalytic study. Figure 8 shows a comparison of the photocatalytic activity of NiSxBBO systems containing 5-25 wt% NiS. The TRA degradation efficiency improves with NiS content in the heterostructure material. The maximum efficiency (94% in 3 h) for TRA degradation is achieved using NiS15BBO material as photocatalyst. The NiS25BBO material shows lower photocatalytic activity compared to NiS15BBO material which can be ascribed to lower surface area and segregation of both NiS and BBO component for this composition. The Kapp value for NiS15BBO is nearly 4 and 1.7 times higher than the BBO and NiS5BBO materials, respectively. The higher TRA degradation activity observed for NiS15BBO material can be ascribed to its improved visible light absorption, charge carrier separation and photoelectrochemical properties. 18 ACS Paragon Plus Environment

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Fig 8. Photocatalytic degradation of tramadol catalyzed by NiSxBBO materials. The reaction parameters are further optimized by using NiS15BBO material as photocatalyst. For a reaction mixture containing 100 ml of 10 ppm TRA solution, the catalyst dose is varied between 10-50 mg. The TRA degradation activity increases with catalyst dosage before reaching an optimum value at 20 mg NiS15BBO photocatalyst (Fig S15I). At high catalyst dose, a marginal decrease in catalytic efficiency may be due to the aggregation of photocatalyst which lead to scattering of light.40 The initial TRA concentration is varied between 2-14 ppm (Fig S15II). It is noticed that, 20 mg of NiS15BBO catalyst is quite efficient for degradation of TRA solution containing upto 10 ppm TRA. The photocatalytic degradation of TRA is studied further by analyzing the total organic carbon (TOC) and the evolved inorganic ions (NH4+, NO3-) at different irradiation time under optimized reaction condition (Fig S16). The TOC of the reaction mixture decreases rapidly with time reaching 91% removal after 3h. The rapid decrease in TOC suggests effective mineralization of TRA over the NiS15BBO photocatalyst. The TRA molecule contains one nitrogen atom which is released mainly as NH4+ and NO3- ions during the photocatalytic degradation process.39 In this study, the concentration of evolved NH4+ ions increases rapidly up to 2 h before showing a decreasing trend. The concentration of nitrate ions, on the other hand, increases linearly up to 3 h of reaction. The decrease in NH4+ ion 19 ACS Paragon Plus Environment


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concentration at higher irradiation time is due to further oxidation of NH4+ ions to NO3- ions upon prolonged exposure. The amount of nitrogen removed as NH4+ and NO3- ions after 3 h of reaction corresponds to 76% of total nitrogen present in the molecule. This incomplete nitrogen mass balance suggests that a part of the nitrogen has either escaped as innocuous N2 gas and/or still remain in the reaction mixture as organic impurity which could not be mineralized over the photocatalyst surface. Further to investigate the reusability and stability of the photocatalyst, recyclability test is performed. It is observed that the NiS15BBO photocatalyst could efficiently degrade TRA up to 4th catalytic run with minimal loss of catalytic efficiency (Fig S17). Fig S18 represents the XRD profile, FTIR spectra and FESEM image of the recovered photocatalyst after 4th catalytic cycle. No obvious change in crystallographic phase, functionality and morphology of the photocatalyst is noticed even after 4th catalytic run suggesting excellent stability of the NiS15BBO photocatalyst for TRA degradation. The possibility of NiO formation by oxidation of NiS after prolonged irradiation time is checked by comparing the intensities of Ni2p3/2 peak of fresh and used catalyst (after 4th cycle). No significant change in intensity ratio

𝐼𝑁𝑖𝑆 𝐼𝑁𝑖𝑂

is noticed

suggesting the stability of NiS phase in the composite system (Fig S18 III). 3.4. Photocatalytic mechanism. In order to investigate the active radical species involved in the photocatalytic degradation of TRA, radical scavenger experiments are performed (Fig S19). A drastic decrease in photocatalytic activity is observed when ammonium oxalate and t-butyl alcohol are used as h+ and OH radical scavengers, respectively (Fig S19). When benzoquinone is used as O2 scavenger a moderate decrease in reactivity is observed. The radical scavenger experiment suggests that h+ and OH radicals are the primary transient species responsible for TRA oxidation. The valance band (VB) and conduction band (CB) position of the semiconductor materials are calculated using the equation (7) and (8). ECB = (X –Ee) – ½Eg ……………………………….(7) EVB = (X –Ee ) + ½Eg ………………………………(8) Where Eg is the band gap energy, ECB and EVB are the conduction band and valance band edge potential (vs. SHE), X is the absolute electronegativity of the respective semiconductor material and Ee is the energy of the free electron in hydrogen scale (4.5 eV). The X value of Bi2O3 is 6.23


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eV and for NiS it is calculated to be 5.18 eV.41,56 The valance band (VB) and conduction band positions of BBO and NiS materials are depicted in Fig 9.

Fig 9. Photocatalytic mechanism for tramadol degradation over NiS15BBO heterojunction nanomaterial. After material contact between the two semiconductor materials, the band positions are realigned due to Fermi level equilibration. Upon irradiation with visible light, e--h+ pairs are generated for both BBO and NiS materials. The band alignment of both components favors facile migration of photo-generated electrons from the CB of BBO to the VB of NiS resulting in a z-scheme heterostructure system. Had it been a conventional Type-II heterostructure, the h+ population would have accumulated in the VB of NiS and the photoelectrons in the CB of BBO. Under such a scenario, the VB hole would have insufficient potential to oxidize H2O/OH- species to OH

radicals. In a z-scheme system, the h+ species would reside in the VB of BBO which can

facilitate the generation of OH radicals due to its high positive potential. The h+ species in the VB of BBO can also take part directly in the degradation TRA. The accumulated electrons in the CB of NiS can reduce dissolved oxygen to form O2 reactive species. These transient species thus formed over the photocatalyst surface can take part in the TRA degradation reaction. An indirect evidence for z-scheme formation is obtained from XPS study. Density of states (DOS) calculation suggests that the CB of -Bi2O3 is mainly Bi in character whereas the VB of α-NiS is hybrid in nature with dominant contribution from S 3p orbitals.25,57 In the present study, the Bi 4f 21 ACS Paragon Plus Environment


peak has shifted by 0.3 eV to higher energy side and S 2s peak has shifted by 0. 5 eV to energy lower side compared to the BE values of pure components reported in literature (Fig 7 b & e).10,47 This observation suggests that electron transfer occurs from CB of BBO to the VB of NiS resulting in a z-scheme heterostructure material. The formation of OH and O2 reactive species over the photocatalyst surface is further confirmed by spectroscopic method using terephthalic acid and nitroblue tetrazolium (NBT) as molecular probes, respectively.40,58 Terephthalic acid is known to trap OH radical to form the fluorescent 2- hydroxy terephthalic acid. The fluorescence intensity can thus be correlated with the OH concentration in aqueous suspension of the photocatalyst. For NiS15BBO the fluorescence intensity is found to increase with time suggesting formation of OH radical in aqueous suspension (Fig 10 I). The increase is more rapid in comparison to pure BBO photocatalyst (Fig 10 II).

Fig 10. (I) Fluorescence spectra of 2-hydroxy terephthalic acid formed at different irradiation time in an aqueous suspension of NiS15BBO composite photocatalyst, (II) Comparison of the fluorescence intensity with time for BBO and NiS15BBO materials and (III) UV-


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Vis absorbance spectra of 5x10-5 molar nitroblue tetrazolium aqueous solution containing 200 mg/L of NiS15BBO photocatalyst. This result suggests that the VB h+ species of BBO in NiS15BBO is more efficient towards OH radical generation which is mainly ascribed to the efficient charge carrier separation in the heterostructure material. The formation of O2 radical is probed further from the selective reaction between the O2 and nitroblue tetrazolium (NBT) under illuminated condition. The superoxide radical selectively reduces the NBT molecule to formazan, which lead to a decrease in absorption intensity of NBT with irradiation time.58 The UV-Vis absorption spectra of an aqueous solution of NBT containing NiS15BBO photocatalyst is represented in Fig 10III. A noticeable decrease in the absorption intensity is observed after 2h of reaction which suggest the formation of O2 species over the catalyst surface. Based on the above discussion a plausible mechanism for photocatalytic degradation of TRA over NiSxBBO heterostructure nanomaterial is proposed in Fig 9. 4.

CONCLUSIONS

In this work, a new visible light active photocatalytic route has been developed for degradation of tramadol using the NiS/Bi2O3 composite nanomaterials as photocatalyst. Phase pure -Bi2O3 is obtained by thermal decomposition of bismuth subcarbonate in presence of KBr as a stabilizing agent. The presence of Br- controls the morphological attributes of bismuth subcarbonate as well as selectively stabilizes the -Bi2O3 phase. The combustion synthesis of Bi2O3 using urea as fuel leads to the selective formation of α-Bi2O3 phase. The calcination temperature is found to be crucial for phase purity as well as morphology of Bi2O3. A new reflux method is also developed in this work for facile synthesis of α-NiS nanosheets using HMTA as hydrolyzing agent and Na2S2O3 as sulfur source. The NiS/Bi2O3 composite materials exhibited improved optical absorption in visible region and efficient space separation of the charge carriers. Comparative study of the photocatalytic activity revealed that the NiS/-Bi2O3 composite materials are more active for photocatalytic degradation of tramadol than the NiS/αBi2O3 materials. A 94% degradation of tramadol with 90% reduction in TOC is noticed within 3 h of reaction for NiS15BBO photocatalyst. The composite materials exhibited excellent stability and recyclability for tramadol degradation. The OH radicals and h+ species have been identified as major active species responsible for TRA degradation. The photocatalytic protocol developed 23 ACS Paragon Plus Environment


in this work is advantageous in terms of the use of visible light as energy source, the minimal use of catalyst, preclusion of harmful and corrosive oxidant and shorter reaction times. 

ASSOCIATED CONTENT

Supporting information Characterization data including XRD, FESEM, TGA-DTA, UV-Vis, PL, photocurrent measurement, impedance spectroscopy, FTIR, TPR and Raman study of the BSC-K precursor, NiS and ABO pure components and their composite materials. Photocatalytic data including scavenger experiment, comparison plots and recyclability study of the composite materials. 

AUTHOR INFORMATION

Corresponding Author * Email:[email protected] Authors Contributions All authors were involved in development and designing of the experiments. D.M. and P.K.S. carried out the synthesis of photocatalyst and photocatalytic experiments. K.D. assisted with the XRD Analysis. S.K.G. and Y.P.B. assisted with the study of optical properties of the photocatalyst by PL and UV-Vis-DRS spectroscopy. D.M. and B.G.M. wrote the manuscript. All the experiments, characterization, data analysis and manuscript writing done under the supervision of B.G.M. Notes The authors declare no competing financial interest. 

ACKNOWLEDGMENTS.

Financial support from DST-WTI, New Delhi (DST/ TM/WTI/2K15/93) and CSIR, New Delhi (01(2947)/18/EMR-II), India is gratefully acknowledged. 

RFERENCES

(1)

Zhang, N.; Ciriminna, R.; Pagliaro, M.; Xu, Y. J. Nanochemistry-Derived Bi2WO6

Nanostructures: Towards Production of Sustainable Chemicals and Fuels Induced by Visible Light. Chem. Soc. Rev. 2014, 43, 5276-5287. 24 ACS Paragon Plus Environment

Page 24 of 31

Page 25 of 31 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


(2)

Jiang, H. Y.; Liu, J.; Cheng, K.; Sun, W.; Lin, J. Enhanced Visible Light Photocatalysis

of Bi2O3 upon Fluorination. J. Phys. Chem. C 2013, 117, 20029−20036. (3)

Maffeis, V.; McCourt, R. O.; Petracca, R.; Laethem, O.; Camisasca, A.; Colavita, P. E.;

Giordani, S.; Scanlan, E. M. Photocatalytic Initiation of Radical Thiol−ene Reactions Using Carbon-Bi2O3 Nanocomposites. ACS Appl. Nano Mater. 2018, 1, 4120−4126. (4)

Chen, Z.; Jiang, H.; Jin, W.; Shi, C. Enhanced Photocatalytic Performance over Bi4Ti3O12

Nanosheets with Controllable Size and Exposed {001} Facets for Rhodamine B Degradation. Appl. Catal. B: Environ. 2016, 180, 698–706. (5)

Shimodaira, Y.; Kato, H.; Kobayashi, H.; Kudo, A. Photophysical Properties and

Photocatalytic Activities of Bismuth Molybdates under Visible Light Irradiation. J. Phys. Chem. B 2006, 110, 17790-17797. (6)

Kumada, N.; Kinomura, N.; Crystal Structure of Bi2O4 with -Sb2O4-Type Structure. J.

solid state chem. 1995, 116, 281-285. (7)

Moiseev, G. K. Thermodynamic Properties and Functions of Condensed Bi8O11. Russ. J.

Phys. Chem. A 2007, 81, 308. (8)

Jalalah, M.; Faisal, M.; Bouzid, H.; Park, J. G.; Al-Sayari, S. A.; Ismail, A. A.

Comparative study on photocatalytic performances of crystalline - and -Bi2O3 nanoparticles under visible light. J. Ind. Eng. Chem. 2015, 30, 183–189. (9)

Lu, Y.; Zhao, Y.; Zhao, J.; Song, Y.; Huang, Z.; Gao, F.; Li, N.; Li, Y.; Induced Aqueous

Synthesis of Metastable β-Bi2O3 Microcrystals for Visible-Light Photocatalyst Study. Cryst. Growth Des. 2015, 15, 1031−1042. (10)

Tang, X.; Ma, C.; Liu, N.; Liu, C.; Liu, S. Visible Light β-Bi2O3/BiOCl Heterojunction

Photocatalyst with Highly Enhanced Photocatalytic Activity. Chem. Phys. Lett. 2018, 709, 82– 87. (11)

Xiao, X.; Hu, R.; Tu, S.; Zheng, C.; Zhong, H.; Zuo, X.; Nan, J. One-pot Synthesis of

Micro/Nano Structured β-Bi2O3 with Tunable Morphology for Highly Efficient Photocatalytic Degradation of Methylparaben under Visible-Light Irradiation. RSC Adv. 2015, 5, 38373– 38381. (12)

Lim, H.; Rawal, S. B. Integrated Bi2O3 Nanostructure Modified with Au Nanoparticles

for Enhanced Photocatalytic Activity under Visible Light Irradiation. Prog. Nat. Sci.: Mater. Int. 2017, 27, 289–296. 25 ACS Paragon Plus Environment


(13)

Li, Y.; Wu, S.; Huang, L.; Xu, H.; Zhang, R.; Qu, M.; Gao, Q.; Li, H. g-C3N4 Modified

Bi2O3 Composites with Enhanced Visible-Light Photocatalytic Activity. J. Phys. Chem. Solids 2015, 76, 112–119. (14)

Sood, S.; Mehta, S. K.; Sinha, A. S. K.; Kansal, S. K. Bi2O3/TiO2 Heterostructures:

Synthesis, Characterization and their Application in Solar light Mediated Photocatalyzed Degradation of an Antibiotic Ofloxacin. Chem. Eng. J. 2016, 290, 45–52. (15)

Hao, Q.; Wang, R.; Lu, H.; Xie, C.; Ao, W.; Chen, D.; Ma, C.; Yao, W.; Zhu, Y. One-pot

Synthesis of C/Bi/Bi2O3 Composite with Enhanced Photocatalytic Activity. Appl. Catal., B 2017, 219, 63–72. (16)

Su, K.; Ai, Z.; Zhang, L. Efficient Visible Light-Driven Photocatalytic Degradation of

Pentachlorophenol with Bi2O3/TiO2-xBx. J. Phys. Chem. C 2012, 116, 17118−17123. (17)

Xie, T.; Liu, C.; Xu, L.; Yang, J.; Zhou, W. Novel Heterojunction Bi2O3/SrFe12O19

Magnetic Photocatalyst with Highly Enhanced Photocatalytic Activity. J. Phys. Chem. C 2013, 117, 24601−24610. (18)

Balachandran, S.; Swaminathan, M. Facile Fabrication of Heterostructured Bi2O3−ZnO

Photocatalyst and its Enhanced Photocatalytic Activity. J. Phys. Chem. C 2012, 116, 26306−26312. (19)

Lu, H.; Hao, Q.; Chen, T.; Zhang, L.; Chen, D.; Ma, C.; Yao, W.; Zhu, Y. A High-

performance Bi2O3/Bi2SiO5 p-n Heterojunction Photocatalyst Induced by Phase Transition of Bi2O3. Appl. Catal., B 2018, 237, 59–67. (20)

Peters, A. W.; Li, Z.; Farha, O. K.; Hupp, J. T. Toward Inexpensive Photocatalytic

Hydrogen Evolution: A Nickel Sulfide Catalyst Supported on a High-Stability Metal−Organic Framework. ACS Appl. Mater. Interfaces 2016, 8, 20675−20681. (21)

Wen, J.; Li, X.; Li, H.; Ma, S.; He, K.; Xu, Y.; Fang, Y.; Liu, W.; Gao, Q. Enhanced

Visible-Light H2 evolution of g-C3N4 Photocatalysts via the Synergetic Effect of Amorphous NiS and Cheap Metal-Free Carbon Black Nanoparticles as Co-catalysts. Appl. Surf. Sci. 2015, 358, 204–212. (22)

Molla, A.; Sahu, M.; Hussain, S. Synthesis of Tunable Band Gap Semiconductor Nickel

Sulphide Nanoparticles: Rapid and Round the Clock Degradation of Organic Dyes. Scientific Reports DOI: 10.1038/srep26034.


Page 26 of 31

Page 27 of 31 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


(23)

Zhang, L.; Tian, B.; Chen, F.; Zhang, J. Nickel Sulfide as Co-catalyst on Nanostructured

TiO2 for Photocatalytic Hydrogen Evolution. Int. J. hydrogen energy 2012, 37, 170 0-17067. (24)

Li, Y.; Lin, S.; Peng, S.; Lu, G.; Li, S. Modification of ZnS1-x-0.5yOx(OH)y-ZnO

Photocatalyst with NiS for Enhanced Visible-Light Driven Hydrogen Generation from Seawater. Int. J. hydrogen energy 2013, 38, 15976-15984. (25)

Chao, J.; Duan, D.; Xing, S.; Zhao, Y.; Zhang, X.; Gao, S.; Li, X.; Fan, Q.; Yang, J.

Visible-Light-Driven Photocatalytic Properties and Electronic Structures of Nickel Sulfide Nanoflowers. Solid State Sci. 2015, 43, 59-62. (26)

Wu, D.; Wang, F.; Tan, Y.; Li, C. Facile Synthesis of NiS/CdS Nanocomposites for

Photocatalytic Degradation of Quinoline under Visible-Light Irradiation. RSC Adv. 2016, 6, 73522–73526. (27)

Yang, P.; Song, B.; Wu, R.; Zheng, Y.; Sun, Y.; Jian, J. K. Solvothermal Growth of NiS

Single-Crystalline Nanorods. J. Alloys Compd. 2009, 481, 450–454. (28)

Roffey, A.; Hollingsworth, N.; Islam, H. U.; Mercy, M.; Sankar, G.; C. Catlow, R. A.;

Hogarth, G.; de Leeuw, N. H. Phase Control During the Synthesis of Nickel Sulfide Nanoparticles from Dithiocarbamate Precursors. Nanoscale, 2016, 8, 11067–11075. (29)

Kasprzyk-Hordern, B.; Dinsdale, R. M.; Guwy, A. J. The Removal of Pharmaceuticals,

Personal care Products, Endocrine Disruptors and Illicit Drugs during Wastewater Treatment and its Impact on the Quality of Receiving Waters. Water Research 2009, 43, 363 – 380. (30)

Serpone, N.; Artemev, Y. M.; Ryabchuk, V. K.; Emeline, A. V.; Horikoshi, S. Light-

Driven Advanced Oxidation Processes in the Disposal of Emerging Pharmaceutical Contaminants in Aqueous Media: A Brief Review. Curr. Opin. Green Sustain. Chem. 2017, 6, 18–33. (31)

Ifelebuegu, A. O.; Onubogu, J.; Joyce, E.; Mason, T. Sonochemical Degradation of

Endocrine Disrupting Chemicals 17-estradiol and 17α-ethinylestradiol in Water and Wastewater. Int. J. Environ. Sci. Technol. 2014, 11, 1–8. (32)

Gmurek, M.; Olak-Kucharczyk, M.; Ledakowicz, S. Photochemical Decomposition of

Endocrine Disrupting Compounds – A review. Chem. Eng. J. 2017, 310, 437–456. (33)

Bergheim, M.; Giere, R.; Kümmerer, K. Biodegradability and Ecotoxicitiy of Tramadol,

Ranitidine, and their Photoderivatives in the Aquatic Environment. Environ. Sci. Pollut. Res. 2012, 19, 72–85. 27 ACS Paragon Plus Environment


(34)

Page 28 of 31

Rua-Gomez, P. C.; Puttmann, W. Impact of Wastewater Treatment Plant Discharge of

Lidocaine, Tramadol, and their Metabolites on the Quality of Surface Waters and Groundwater. J. Environ. Monit. 2012, 14, 1391-1399. (35)

Ghalwa, N. A.; Abu-Shawish, H. M.; Zaggout, F. R.; Saadeh, S. M. Al-Dalou, A. R.;

Assi, A. A. A. Electrochemical Degradation of Tramadol Hydrochloride: Novel Use of Potentiometric Carbon Paste Electrodes as a Tracer. Arabian J. Chem. 2014, 7, 708–714. (36)

Esplugas, S.; Bila, D. M.; Krause, L. G. T.; Dezotti, M. Ozonation and Advanced

Oxidation

Technologies

to

Remove

Endocrine

Disrupting

Chemicals

(EDCs)

and

Pharmaceuticals and Personal care Products (PPCPs) in Water Effluents. J. Hazard. Mater. 2007, 149, 631–642 (37)

Klavarioti, M.; Mantzavinos, D.; Kassinos, D. Removal of Residual Pharmaceuticals

from Aqueous Systems by Advanced Oxidation Processes. Environ. Int. 2009, 35, 402–417. (38)

Antonopoulou, M.; Konstantinou, I. Photocatalytic Degradation and Mineralization of

Tramadol Pharmaceutical in Aqueous TiO2 Suspensions: Evaluation of Kinetics, Mechanisms and Ecotoxicity. Appl. Catal., A General 2016, 515, 136–143. (39)

Αntonopoulou, Μ.; Hela, D.; Konstantinou I. Photocatalytic Degradation Kinetics,

Mechanism and Ecotoxicity Assessment of Tramadol Metabolites in Aqueous TiO2 Suspensions. Sci. Total Environ. 2016, 545–546, 476–485. (40)

Majhi, D.; Bhoi, Y. P.; Samal, P. K.; Mishra, B. G. Morphology Controlled Synthesis and

Photocatalytic Study of Novel CuS-Bi2O2CO3 Heterojunction System for Chlorpyrifos Degradation under Visible Light Illumination. Appl. Surf. Sci. 2018, 455, 891–902. (41)

Bhoi, Y. P.; Behera, C.; Majhi, D.; Equeenuddin, S. M.; Mishra, B. G. Visible Light-

Assisted Photocatalytic Mineralization of Diuron Pesticide using Novel type II CuS/Bi2W2O9 Heterojunctions with a Hierarchical Microspherical Structure. New J. Chem. 2018, 42, 281-292. (42)

Bhoi, Y. P.; Mishra, B. G. Photocatalytic Degradation of Alachlor using type-II

CuS/BiFeO3 Heterojunctions as Novel Photocatalyst under Visible Light Irradiation. Chem. Eng. J. 2018, 344, 391–401. (43)

Hardcastle, F. D.; Wachs, I. E. The Molecular Structure of Bismuth Oxide by Raman

Spectroscopy. J. Solid State Chem. 1992, 97, 319-331. (44)

Liu, L.; Jiang, J.; Jin, S.; Z, X.; Tang, M. Hydrothermal Synthesis of -Bismuth Oxide

Nanowires from Particles. CrystEngComm, 2011, 13, 2529–2532. 28 ACS Paragon Plus Environment

Page 29 of 31 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


(45)

Surendran, S.; Sankar, K. V.; Berchmans, L. J.; Selvan, R. K. Polyol Synthesis of α-NiS

Particles and its Physico-chemical Properties . Mater. Sci. Semicond. Process. 2015, 33, 16–23. (46)

Luo, P.; Zhang, H.; Liu, L.; Zhang, Y.; Deng, J.; Xu, C.; Hu, N.; Wang, Yu. Targeted

Synthesis of Unique Nickel Sulfide (NiS, NiS2) Microarchitectures and the Applications for the Enhanced Water Splitting System. ACS Appl. Mater. Interfaces 2017, 9, 2500−2508. (47)

Matoba, M.; Anzai, S.; Fujimori, A. Thermal Expansion, Thermoelectric Power, and XPS

Study of the Nonmetal-Metal Transition in Ni1-xS1-ySey. J. Phys. Soc. Jpn. 1991, 60, 4230-4244. (48)

Lou, Ya.; Wang, Li.; Zhang, Y.; Zhao, Z.; Zhang, Z.; Lu, G.; Guo, Y. The Effects of

Bi2O3 on the CO Oxidation over Co3O4. Catal. Today 2011, 175, 610– 614. (49)

Lin, T. J.; Xie, H.; Meng, X.; Shi, Li. Characterization and Catalytic Application of

Bi2O3/NiO Composite Oxides in the Reppe Carbonylation to Acrylic acid. Catal. Commun. 2015, 68, 88–92. (50)

Zhu, J.; Wang, S.; Wang, J.; Zhang, D.; Li, H. Highly Active and Durable Bi2O3/TiO2

Visible Photocatalyst in Flower-like Spheres with Surface-enriched Bi2O3 Qquantum Dots. Appl. Catal. B: Environ. 2011, 102, 120–125. (51)

Nagaraju, G.; Cha, S. M.; Yu J. S. Ultrathin Nickel Hydroxide Nanosheet Arrays Grafted

Biomass-derived Honeycomb like Porous Carbon with Improved Electrochemical Performance as a Supercapacitive material. Scientific Reports DOI: 10.1038/srep45201. (52)

Wang, Y.; Zhu, Q.; Tao, L.; Su, X. Controlled-synthesis of NiS Hierarchical Hollow

Microspheres with Different Building Blocks and their Application in Lithium Batteries. J. Mater. Chem. 2011, 21, 9248–9254. (53)

Xu, Z.; Yu, J.; Liu, G.; Cheng, B.; Zhou, P.; Li, X. Microemulsion-assisted Synthesis of

Hierarchical Porous Ni(OH)2/SiO2 Composites toward Efficient Removal of Formaldehyde in air. Dalton Trans. 2013, 42, 10190–10197. (54)

Gregoire, B.; Ruby, C.; Carteret, C. Hydrolysis of Mixed Ni2+–Fe3+ and Mg2+–Fe3+

Solutions and Mechanism of Formation of Layered Double Hydroxides. Dalton Trans. 2013, 42, 15687–15698. (55)

Zhu, G.; Liu, Y.; Hojamberdiev, M.; Han, J.; Rodriguez, J.; Bilmes, S. A.; Liu, Peng.

Thermodecomposition Synthesis of Porous -Bi2O3/Bi2O2CO3 Heterostructured Photocatalyst with Improved Visible Light Photocatalytic Activity. New J. Chem. 2015, 39, 9557-9568.



(56)

Huang, Y.; Wang, W.; Zhang, Q.; Cao, J.; Huang, Ru.; Ho, W.; Lee, S. C. In situ

Fabrication of α-Bi2O3/(BiO)2CO3 Nanoplate Heterojunctions with Tunable Optical Property and Photocatalytic Activity. Scientific Reports DOI: 10.1038/srep23435. (57)

Pereira, A. L. J.; Gomis, O.; Sans, J. A.; Contreras-Garcia, J.; Manjon, F. J.; Rodriguez-

Hernandez, P.; Munoz, A.; Beltran, A. β-Bi2O3 under Compression: Optical and Elastic Properties and Electron Density Topology Analysis. Phys. Rev. B 2016, 93, 22411-22423. (58)

Obregon, S.; Ruiz-Gomez, M.A.; Hernandez-Uresti, D.B. Direct Evidence of the

Photocatalytic Generation of Reactive Oxygen Species (ROS) in a Bi2W2O9 Layered-structure. J. Colloid Interface Sci. 2017, 506, 111–119.


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