ZnO (M= Ag, Au) Heterostructured

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Fabrication of M@ CuxO/ ZnO (M= Ag, Au) heterostructured nanocomposite with enhanced photocatalytic performance under sunlight Nana L Gavade, Santosh babasaheb babar, Abhijit N Kadam, Anna Gophane, and Kalyanrao M. Garadkar Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b03168 • Publication Date (Web): 20 Nov 2017 Downloaded from http://pubs.acs.org on November 20, 2017

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Industrial & Engineering Chemistry Research

Fabrication of M@ CuxO/ ZnO (M= Ag, Au) heterostructured nanocomposite with enhanced photocatalytic performance under sunlight Nana L. Gavadea, Santosh B. Babara, Abhijit N. Kadamb, Anna D. Gophanec and Kalyanrao M. Garadkar*a a

Nanomaterials Research Laboratory, Department of Chemistry, Shivaji University, Kolhapur, Maharashtra, India-416004 b Nanoparticles Processing Laboratory, Department of Chemical and Biochemical Engineering, Gachon University, Seongnam City, South Korea-461701. c Department of Zoology, Shivaji University, Kolhapur, Maharashtra, India-416004 S- Supporting Information. *Corresponding Author. Tel.: +91 0231 2609167; fax: +91 0231 2692333. E-mail Address: [email protected]

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Abstract We report the biogenic method for the design and characterization of three different composite nanomaterials CuxO/ZnO, Ag@CuxO/ZnO and Au@CuxO/ZnO (x= I and II) with surface plasmon resonance (SPR) effect and p−n heterojunction for photocatalysis. The crystal structure of the material was scrutinized by XRD, DRS, PL, XPS, FT-IR, EDS, and TEM analysis. To make the composite efficient we have sensibly introduced plasmonic Ag and Au on CuxO/ZnO individually by using Ziziphus Jujuba leaf extract. That widen light incorporation, effectual convey of photogenerated carriers and incidence of brawny SPR effect makes the composites sensitive under visible light. The synthesized ternary composites, Ag@CuxO/ZnO and Au@CuxO/ZnO exhibit much higher photocatalytic activity than the ZnO and CuxO/ZnO for the degradation of industrial Textile Effluent and Methyl Orange under sunlight as well as UV light. By effortless comet assay practice genotoxicity of TE prior to and past photodegradation was assessed. 1. Introduction Water is often synonymous with life and is gifted with unusual physical and chemical properties which are responsible for its specificity. There has been an escalation of global warming as well as air and water pollution allied with industrialization. Consistent with the World Health Organization (WHO) over one billion community in the world are anguish from necessitate accessing the potable water1. Rapid industrialization and extensive use of chemicals and natural resources that have led to an ironic situation where the role of nanomaterials is to mitigate the damage caused due to disposal of toxic chemical and dyes in water. The protection of water recourses from population is essential and in recent years anti pollution measures are impressed by environmental


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protection agencies in a developed as well as developing countries. It is mandatory for all the chemical industries to reduce generation of hazardous waste and forced to reuse or recycle the waste after proper treatment. Photocatalysis is one of the “Green Technology” for wastewater treatment; ZnO is one of the best materials for photocatalyst2. However, it absorb only the UV section of light attributable to its large band gap (3.37 eV) and electron hole recombination confines the bustle of ZnO. To overcome this limiting factor, development of multifunctional oxide systems with p-n heterojunctions, is finest strategy3. The coupling of ZnO with additional small band gap semiconductors, for instance CdS, CuO, Cu2O Fe2O3 and WO3 have diverted more attention for the reason that of their synergetic effects on the photocatalytic performance, which not only endorse electron–hole association but also shifts the absorption towards the visible range4-8. Cu2O or CuO semiconductors (Eg ≈ 2.1 and 1.2 eV, correspondingly) which is p-type with direct band gap, ZnO (Eg ≈ 3.37 eV) is n-type semiconductor have gained more interest for the preparation of CuxO/ZnO (x = I, II oxidation state) nanomaterials5-7. Coupling of ZnO nanostructures with Cu2O nanoparticles can modify the photocatalysis reaction towards visible region. The position of conduction band (CB) of Cu2O is a superior than the CB of ZnO and the position of valance band (VB) of ZnO is worse than the VB of Cu2O, these two materials have a meticulous virtual site of the energy band9-10. Therefore the p–n heterojunction of Cu2O/ZnO has more appropriate in photocatalysis11. Though Cu2O has display to be a satisfactory visible photosensitizer for nanocomposite photocatalyst (e.g. Cu2O/ZnO), but its band gap (2.1 eV) means a substantial portion of visible light cannot be well apply for the photocatalytic application12. Therefore, longer wavelength, even up to the near-infrared (NIR) band of the solar spectrum remains vacant. The localized SPR



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outcome of metal nanoparticles (MNPs) brings huge convenience for higher plasmonic performance as a photocatalyst13-15. Among metal NPs Ag and Au have the strapping SPR consequence, and that can be absorbing lower energy16-17. Also peculiar reactivity and functionality as electron sink of MNPs supply to develop charge transport duration and material performance particularly for photocatalysis18. Based on a similar consideration, the activity of Cu2O/ZnO established photocatalyst can be further enhanced by the loading of MNPs. To date methods for the creation of hybrid nanocomposite revealed in literature are chiefly precipitation, hydrothermal and wet chemical routes. These chemical routes are not ecofriendly but also requires costly chemicals.. There is mounting claim of time to reinstate alike process by environmental kindly, clean, harmless and low cost way owing to the pessimistic impact on environment of those chemical methods. This has guide to latest awareness in exploit natural thing to practice nanomaterials. The application of biological agents to create MNPs is secure and fulfils several principles of Green Chemistry approach, as it employ renewable reagents. The current research work demonstrate the fabrication of CuxO/ZnO heterostructures by simpler thermal decomposition means. Then the CuxO/ZnO composite surface is decorated with AgNPs and AuNPs separately, to form M@CuxO/ZnO (M= Ag, Au) by simple biogenic method using leaf extract of Ziziphus Jujuba (Z. J.) acts as a stabilizing and reducing agents19. The DRS, XRD, PL, EDS, XPS, FT-IR, and TEM were used for depiction of synthesized CuxO/ZnO and M@CuxO/ZnO NRs. Besides, the photocatalytic performance of M@CuxO/ZnO NRs was ensure for the degradation of industrial Textile Effluent (TE) and Methyl Orange (MO) as a model dyes with UV and sunlight. The effects of diverse restriction for instance, content of MNPs, opening pH of the dye and scavenger have been optimized analytically for accomplish


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ceiling photodegradation. The genotoxicity of TE before and after photodegradation was also carried out by comet assay technique. 2. Experimental Details 2.1. Chemicals Leaves of Z. J. were composed from Kolhapur (India). From (s d fine-chemical Ltd.), the [Zn(CH3COO)2]2H2O and [Cu(CH3COO)2]H2O were acquired. NaOH, Methyl Orange and HCl were inward from Spectrochem Pvt. Ltd., AgNO3 and HAuCl4 were attained from Sigma Aldrich Chemicals Pvt. Ltd. Mumbai (India). Every chemicals were of analytical grade and tatty as straight and solutions be set in Millipore water. 2.2. Synthesis of CuxO/ZnO NRs For the design of CuxO/ZnO NRs, we beached the combination of 6.0 g of [Zn (CH3COO)2]2H2O and deliberate quantity of [Cu(CH3COO)2]H2O for 1 h by mortar and pestle. Subsequently via temperature proscribed muffle furnace the beached powder was calcined for 3 hrs at 400˚C. 2.3. Synthesis of M@CuxO/ZnO NRs To facilitate Ag@CuxO/ZnO and Au@CuxO/ZnO NRs, as equipped CuxO/ZnO NRs strewn in the AgNO3 and HAuCl4 solution correspondingly, with stirring for 3 hrs. Later to reduce Au3+ and Ag+ ions, leaf extract of Z. J. comprise into the above dispersion dropwise19, 20. The blended M@CuxO/ZnO NRs were centrifuged and many times with distilled water followed by dried up in hot air oven at 45˚C after 3 hrs.



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2.4. Characterization of M@CuxO/ZnO NRs The morphology of the nanomaterials was achieved from TEM (JEM2100). By Panalytical Diffractometer with CuKa radiation XRD patterns of nanocomposites were scanned. EDS were recorded using FE-SEM connected with EDS (x-act with INCA and Aztec EDS). Via UV-Vis. Spectrophotometer (LABINDIA Analytical UV-3092) DRS were

achieved.

Using

spectrofluorometer

(JASCO,

Model

FP.750,

Japan).

Photoluminescence (PL) spectra were recorded. FT-IR spectra were engaged via a Perkin–Elmer spectrometer (Spectrum BX-II). X-ray Photoelectron Spectra (XPS) were recorded by X-ray photoelectron spectroscopy (220I)-VG ESCALAB 220i. 2.5. Photocatalytic Activity of M@CuxO/ZnO NRs Via UV (365 nm) and sunlight the photocatalytic performance was investigated by supervising the degradation of dyes. The control of pH of solution from 3 to 9 by HCl and NaOH solutions

seen the pH effect. The extent of catalyst in the dye solution content of

catalyst used from 0.5 to 2.0 g/dm3 to search the finest performance and 1.5 g/dm3 was originate to be best possible amount. The photoreactor was set aside disclosed to catch adequate magnitude of oxygen for to photooxidation. Characteristically, 1.5 g/dm3 of catalyst was included in photoreactor enclosing dye (100 mL, 20 ppm). Prior to elucidation of light, the dye solution be motivated for 30 min. in dark to certify adsorption–desorption equilibrium, then uncovered to light21. The duration of light was within 11 am to 2 pm through the shiny day. At meticulous time aliquots were procured and the catalyst was collected from the solution by centrifugation process. The dye solutions were applied to monitor the concentration by UV–Vis. spectrophotometer. The % degradation was determined by following equation. Degradatio n(%) =

C0 − Ct × 100 C0


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Where, C0 and Ct are the dye concentration at initial and after time t respectively. The absorbance at time 0 (A0) and time t (At) is comparable to concentration at time 0 (C0) and time t (C t) correspondingly.

2.6. Determination of hydroxyl radicals (˙OH) Hydroxyl radicals (˙OH) are most significant oxidative agent in photocatalytic reactions. Therefore, the ˙OH produced under sunlight illumination were examined by fluorometric method via terephthalic acid (TA) as a probe molecule. Photocatalyst (50 mg) were poised in aqueous solution (100 mL) including TA (6 mM) and NaOH (20 mM) to quantify the level of ˙OH. Prior to light exposure the solution was motivated in dark for 30 min. Following illumination, the suspension was centrifuged, and the supernatant was sampled for investigation by demo the fluorescence signal of the engender 2-hydroxyterephthalic acid (TAOH) via a spectroflorometer with 315 nm excitation wavelength. This manner relies on the fluorescence indication at 427 nm of the hydroxylation of TA with ˙OH engender at the photocatalyst interface22.

2.7. Genotoxicity of Textile Effluent and its Photodegradation product Genotoxicity of TE from the textile industries were experienced on freshwater common carp, Cyprinus carpio (acquire from Govt. Fish Farm, Dhom, Satara, Maharashtra, India). The fishes were allowed to acclimatize for 72 hrs in laboratory. Then 10 fingerlings of 6±1g and 5.5±1 x 2.8±1cm size were transferred in each tank (1 L) for testing. The tank were filled with 10% effluent in tap water (pH= 6.8, temperature 26 ± 10C). Tap water containing and 0.2 mg/L MMS containing set considered as the negative and positive control correspondingly. 12 hrs photoperiod was sustained during the experiment. By deflating heart of fish the blood samples were gain with sterile heparinized insulin syringe and diluted with an equivalent quantity of Hank’s balanced salt solution (HBSS). For appraisal of effluent genotoxicity the alkaline



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(pH>13) comet assay was conducted23-24. From diverse experimental group 10 µL of blood samples were assorted with 180 µL of liquefy 0.5% agarose and swell over the pre-coated (with 1.5% normal agarose) slide. The slide was kept in lysis buffer for 1 h at 4 0C. Then the gel electrophoresis was performed for 20 min at 25 V and 300 mA (1.6 V/cm) afterword neutralization, fixing and staining by means of 0.002 mg/mL Ethidium Bromide was carried out. The cells were scrutinized with the fluorescence microscope (Nikon TS100-F) at 400 X, at 420 nm and 520 nm excitation and emission filter respectively. The snap of pragmatic cells were taken for the DNA investigation. Images were evaluated with software Open Comet (v1.3) to verify the % of DNA in the comet tail25-26. The data obtained were processed for standard deviation and ANOVA in excel to analyze difference between DNA damage before and after degradation of TE.

3. Result and Discussion 3.1. XRD Analysis To understand the phase purity and crystallinity of the as synthesized composite nanomaterials, X-ray diffraction (XRD) experiments were made and the patterns are exhibit in Figure 1. The XRD pattern of ZnO illustrate in Figure 1a that exhibits peaks at 2θ = 31.80˚,

34.40˚, 36.29˚, 47.52˚, 56.63˚, 63.01˚, 66.44˚, 67.98˚, 69.16˚, 72.59˚ and 77.08˚were indexed to the (100), (002), (101), (102), (110), (103), (200), (112), (201), (004) and (202) planes respectively, that are diffractions of ZnO crystal with a hexagonal wurtzite structure, accordingly (JCPDS Card No. 36-1451). The XRD pattern of CuxO illustrates in Figure 1b, the diffraction peaks at 2θ = 32.50˚, 35.54˚, 38.70˚, 46.26˚, 48.71˚, 51.34˚, 53.48˚, −

−

−

58.26˚, 66.22˚, 68.12˚, 72.37˚, and 75.24˚, which represent the (110), (11 1 ), (111), (11 2 ), (20 2 −

−

), (112), (020), (202), (31 1 ), (220), (311), and (22 2 ) crystal planes corresponding to monoclinic 8 ACS Paragon Plus Environment

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structure of CuO matches with JCPDS Card No. 048-1548. The peaks at 2θ = 29.58˚, 36.44˚, 42.32˚, 52.48˚, 61.40˚, 65.58˚, 73.55˚ and 77.41˚ which corresponds to (110), (111), (200), (211), (220), (221), (311) and (222) respectively with cubic structure of Cu2O planes matches with JCPDS Card No. 078-2076. The consequence proposes that, the sample have a mixture of Cu2O and CuO phases, which is reliable with the outcome described in the literature27. The Figure 1c indicates the XRD pattern of CuxO/ZnO and Figure 1d represents the XRD pattern of Ag@CuxO/ZnO and Au@CuxO/ZnO. The peaks allied with Cu2O and CuO, were not pragmatic in the XRD patterns of CuxO/ZnO in Figure 1c and peaks related to Ag and Au also does not observed in Figure 1d likely due to the low content of CuxO (0.75 wt%), Ag (0.5 wt%), Au (0.1 wt%) and high dispersion. Qiu et al reported that, when the amount of Cu was below 1%, peaks associated with Cu2O and CuO, were not detected in the XRD patterns of the hybrid CuxO/TiO2 nanocomposites28. According to Rietveld refinement Full Proof software CuO is 68.23% and Cu2O is 31.77% in a mixed phase CuxO. Figure 2 shows structure of, a) CuO monoclinic, b) Cu2O cubic and c) mixed structure of CuO and Cu2O. Figure 2d shows the XRD pattern of refinement that indicates the experimental and calculated pattern closely matched. The average crystallite size of ZnO NRs was found to be 20 nm, which is premeditated by Scherrer’s formula.

D=

0.9λ β cosθ

Where, θ, β, λ and D are correspondingly, scattering angle in degree, full width at half maximum [FWHM] in radian, wavelength of X-ray in Å and the crystallite size.

3.2. UV-Vis. Diffuse Reflectance Spectra To observe the photoabsorption nature of ZnO, CuxO, CuxO/ZnO, Ag@CuxO/ZnO and Au@CuxO/ZnO photocatalyst, recorded the comparative DRS spectra revealed in Figure 3. The absorption peak of pure ZnO NRs at around 385 nm (3.22 eV) could be attributed to the well9 ACS Paragon Plus Environment


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defined ground excitonic peak of ZnO NRs, which can hardly absorb visible light29. The absorption peak of pure CuxO indicates broad absorption peak in the sort of 400-800 nm. The broad absorbance peak of CuxO in visible window is crucial for complete use of solar spectrum. Owing to the involvement of the fine band gap semiconductor CuxO, the sample CuxO/ZnO display incessant light absorption in the span of 400-800 nm. The emergence of a peak fluctuation at wavelength inferior than 590 nm due to the absorption of Cu2O demonstrating the successful formation of composite of ZnO and CuxO28. Spectrum of sample containing Ag@CuxO/ZnO and Au@CuxO/ZnO NRs shows big hump with upper intensity in the visible section because the SPR of Ag and AuNPs that further enhances the absorption capacity in visible light region30. In addition, this ternary nanostructure also harvest more light via enhanced light scattering over greater scales. Furthermore, the MNPs also harvest the incident photons with certain energy and arouse the plasmonic “hot” spots and “hot” electrons in the SPR excitation process31. This plasmon oscillation can promote further the photon absorption as well as the generation and separation of photogenerated carriers in semiconductors, which is expected to augment the photocatalytic bustle. The SPR of MNPs further stretches the absorption series of CuxO/ZnO in the visible area of the spectrum and plays pivotal job in upgrading the photocatalytic bustle of the CuxO/ZnO. The band gap of semiconductors could be engineered for achieving desired physical properties. In hybrid semiconductor−plasmonic MNPs, the photoinduced charge carriers are trapped by the metallic counterparts and become able to promote the interfacial charge−transfer processes32-33.

3.3. Photoluminescence spectra Commencing the association of photogenerated charged species the Photoluminescence (PL) emission, consequently PL was employ to explore the partition effectiveness of the 10 ACS Paragon Plus Environment

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photogenerated

species34. Thus minium the intensity of PL specifies the

good charge

separation from CB to VB. The PL spectra at 325 nm excitation wavelength of the ZnO,

0.75 wt% CuxO/ZnO, 0.5 wt% Ag@CuxO/ZnO and 0.1 wt% Au@CuxO/ZnO NRs were deliberate and results are revealed in Figure 4. The steady-state PL spectra displayed two emission peaks, a major peak at roughly 380-400 nm is by the cause of typical ZnO radiative band-to-band emission, and a minor peak at 463 nm, derived by the alteration of excited optical interior to the valence level starting from deep level, that frequently escort by the attendance of structural defects35. These defect situations are notorious as oxygen vacancies on the ZnO NRs surface36. PL spectrum of CuxO/ZnO NRs exhibited substantially depressed PL intensity, compared with pristine ZnO at both excitonic UV and defect-related green emissions, suggesting the high efficiency of charge separation37. After forming p-n hererostructure with CuxO in CuxO/ZnO composite, the electron is transferred to CB of ZnO starting from CB of CuO hence the separation of charge carrier increases that results into decrease in PL intensity38. PL spectra of Ag@CuxO/ZnO and Au@CuxO/ZnO

NRs samples exhibited substantially depressed PL intensity, compared with pristine ZnO and CuxO/ZnO at both excitonic UV and defect-related green emissions suggesting increasingly pronounced charge separation for CuxO/ZnO sample after loading MNPs. The decrease in PL intensity indicates the M@CuxO/ZnO NRs samples have longest life time of photoexcited electron–holes than the ZnO and CuxO/ZnO, which is responsible for highest photocatalytic activity39. Viewing brawny influence of MNPs on the dynamics of charge carter, the PL emission of CuxO/ZnO NRs is quenched significantly in sample Ag@CuxO/ZnO and Au@CuxO/ZnO NRs. Contrast with emission of ZnO NRs the Ag@CuxO/ZnO and Au@CuxO/ZnO NRs exhibits significantly weaker and featureless



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emission due to the blockage of both straight and trap-related charge hauler association corridor by MNPs. This consequence advises that MNPs on the surface of CuxO/ZnO are capable to dig out electrons from the CB of ZnO that thwart charge transporter recombination within the ZnO NRs40. The MNPs prolong the lifetime of photogenerated electrons and holes indicated in decreased PL intensity41. M@CuxO/ZnO NRs have longest life time of photoexcited electron–holes than the ZnO and CuxO/ZnO NRs, which is responsible for highest photocatalytic activity.

3.4. XPS Spectra Figure 5 represents the XPS result of sample CuxO/ZnO (0.75 wt% Cu). The survey spectrum of sample CuxO/ZnO is shown in Figure 5a. The high resolution scan of Zn 2p spectrum (Figure 5b) shows spin orbital doublets with at binding energy 1044.1 and 1021.1 eV can be assigned to the Zn 2p1/2 and Zn 2p3/2 lines, correspondingly and splitting energy 23 eV which confirms Zn2+ oxidation state42. However it is very firm to doggedness CuO and Cu2O by this deconvolution due to marginal gap of binding energy between Cu2+ and Cu+. The fitting Cu 2p spectrum (Figure 5c) shows the peaks at 932.5 eV and 952.5 eV, which are endorsed to the Cu 2p3/2 and Cu 2p1/2 of the Cu2O respectively43-44, while the peak at 953.7 eV can be credited to CuO, the appearance of CuO is also inveterate by the satellite peak at 941.6 eV45. The O 1s core spectrum (Figure 5d) is asymmetric and can be deconvoluted into two peaks located at 529.78 and 531.37 eV. The first peak due to the lattice oxygen of ZnO and second is due to adsorbed oxygen from surface hydroxyl groups that indicates the oxygen deficiency which improves photocatalytic activity of the catalyst46. The XPS results shows the presence of Zn2+, Cu1+ and Cu2+, the oxidation state of Cu also confirmed from XRD results. The XPS analysis of sample 0.5 wt% Ag@CuxO/ZnO shown in Figure S1 in supporting information and results clues the 12 ACS Paragon Plus Environment

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presence of Zn2+, Cu1+, Cu2+ and Ag0 also the XPS analysis result of the 0.1 wt% Au@CuxO/ZnO sample indicates presence of Zn2+, Cu1+, Cu2+ and Au0 as revealed in Figure S2 in supporting information.

3.5. FT-IR spectra The FT-IR spectra of the ZnO and M@CuxO/ZnO NRs in the sort of 4000–400 cm-1 are exposed in Figure S3 in supporting information. The spectrum of ZnO NRs shows the feature absorption band for the Zn–O stretching vibration at 530 cm−1 and the peak at 624 cm-1 harmonizes to the Cu–O bond47. The three bands happening in the zone of 1000700 cm−1 and one at 1380 cm−1 are corresponds to the disparate posture of CO32vibrations48. The band at ∼2900 cm−1, corresponds to

C-H species. The broad peaks at

1661 and 3000–3500 cm−1 are ascribed respectively to the O–H bending and stretching vibrations of water molecules adsorbed on catalyst surface49. 3.6. EDS Analysis

The EDS examination was worn to probe the elements present in the Ag@CuxO/ZnO and Au@CuxO/ZnO material as shown in Figure 6. EDS spectra of Ag@CuxO/ZnO sample shown in Figure S4a in supporting information view peaks equivalent to elemental Zn, Cu, Ag and O. Figure S4b in supporting information represents the EDS spectra of the sample Au@CuxO/ZnO that indicates the presence of peaks related to the Zn, Cu, Au and O. Further we have roughly estimated Zn, Cu, Ag, and Au content by EDS analysis. It is found that their content is closer to the amount taken during synthesis shown in Table S1 in supporting information. No supplementary peaks were recognized in EDS, which endorse that the as synthesized Ag@CuxO/ZnO and Au@CuxO/ZnO NRs are gratis from contamination.



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3.7. TEM Images TEM study was conceded to acquire clue regarding the range and morphology of the CuxO/ZnO and M@CuxO/ZnO NRs. TEM images of CuxO/ZnO with various magnifications are exposed in Figure 6. Figure 6a-b point out that the morphology of ZnO NRs (20-40 nm) is preserve as a rod like structure yet following the ornament of CuxO (15-30 nm). Hexagonal Cu2O and CuO are clearly differentiated from TEM images. Further TEM images demonstrate that hexagonal CuxO dispersed on ZnO surface. Figure 6c shows HRTEM image of CuxO-ZnO that indicates the d spacing of ZnO, Cu2O and CuO are 0.26, 0.24 and 0.25 nm correspondingly. Figure 6d display the SAED pattern of CuxO/ZnO, indicates the crystalline nature of synthesized nanocomposite. Figure 7a-b expo TEM similes of Ag@CuxO/ZnO at various magnifications, the inset images of Figure 7a-b clearly indicates the AgNPs dispersed on the surface of the CuxO/ZnO NRs. Figure 7c demonstrate HRTEM image of Ag@CuxO/ZnO that indicates the d spacing of

AgNPs is 0.22 nm. Figure 7d displays the SAED pattern of Ag@CuxO/ZnO sample. Figure 8a-b shows TEM similes of Au@CuxO/ZnO at various magnifications that indicate

the AuNPs dispersed on the surface of the CuxO-ZnO NRs. Figure 8c shows HRTEM image of Au@CuxO/ZnO that indicates the d spacing of Au is 0.23 nm. Figure 8d displays the SAED pattern of Au@CuxO/ZnO sample. From the TEM images it is clear that the unvarying allocation of MNPs on the surface of the CuxO/ZnO NRs. 3.8. Factors affecting the photocatalytic degradation of dyes 3.8.1. Effect of wt% of CuxO To assess the consequence of wt% of CuxO, various wt% (0.25-1.0) of CuxO are composed with ZnO. It was found that as content of CuxO increases up to 0.75 wt%,


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photocatalytic movement of CuxO/ZnO NRs continue growing and for advanced amount of CuxO (1.0 wt%) diminish the catalytic activity. The photodegradation competence of MO with pristine ZnO and CuxO/ZnO (0.75 wt%) correspondingly is 62 and 93% in 30 min beneath UV light, whereas catalytic action decline from 93 to 82% when mounting the amount of CuxO from 0.75 to 1.0 wt%, that revealed in Figure S5a in supporting information. As the content of CuxO increases up to 0.75 wt % photocatalytic activity was also increases due to the i) increased light absorption by narrow band gap material, ii) increase in the charge separation due to more active p−n heterojunctions. However, when CuxO content exceeded 0.75 wt%, the number of active sites are lock up. Also, the glut CuxO can wrap the surface of ZnO, leading to agglomeration of CuxO nanoparticles on the ZnO NRs. Between the junctions of the CuxO NPs the fashioned charges can relocate and recombine that outcome decreasing photocatalytic activity38.

In present study 0.75 wt% CuxO/ZnO NRs shows maximum efficiency and same composition is used for the degradation of TE. The photodegradation of TE carried out by

using optimized CuxO content (0.75 wt% CuxO/ZnO), the photodegradation effectiveness of TE with pristine ZnO and CuxO/ZnO (0.75 wt%) respectively beneath UV light for 60 min is 55 and 85% is shown in Figure S5b in supporting information. 3.8.2. Effect of wt% of MNPs To appraise the consequence of wt% of AgNPs, assorted wt% (0.1-0.75) of AgNPs are loaded on 0.75 wt% CuxO/ZnO NRs. It was found that as wt% of AgNPs enlarge up to 0.5 wt%, photocatalytic activity of Ag@CuxO/ZnO NRs also amplifies. For advanced content of AgNPs (0.75 wt%) photocatalytic movement of Ag@CuxO/ZnO NRs dwindles. The photodegradation competence of MO with CuxO/ZnO NRs and Ag@CuxO/ZnO (0.5 wt%) correspondingly beneath UV-light in 30 min is 93 and 99 %, 15 ACS Paragon Plus Environment


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while rising the amount of AgNPs from 0.5 to 0.75 wt%, catalytic activity decreases from 99 to 96% which is shown in Figure 9a. In case of Au@CuxO/ZnO sample, various wt% (0.05-0.2) of AuNPs are loaded on CuxO/ZnO. As the wt% of AuNPs increases up to 0.1 wt%, the photocatalytic action of Au@CuxO/ZnO NRs also increases. The catalytic activity of Au@CuxO/ZnO NRs decreases by further increasing the content of AuNPs (up to 0.2 wt%). The photodegradation efficiencies of MO with CuxO/ZnO and Au@CuxO/ZnO(0.1 wt%) correspondingly beneath UV-light for 30 min is about 93 and 98 %, while increasing the amount of AuNPs from 0.1 to 0.2 wt%, catalytic activity decreases from 98 to 95% which is shown in Figure 9b. In current work 0.5 wt% of AgNPs in Ag@CuxO/ZnO and 0.1 wt% of AuNPs in Au@CuxO/ZnO are optimum wt% of MNPs. The photodegradation of TE carried out by using optimized MNPs content. The Photodegradation of TE, underneath UV-light for 60 min is about 85, 99 and 96% for CuxO/ZnO, Ag@CuxO/ZnO (0.5 wt%) and Au@CuxO/ZnO (0.1 wt%) respectively as shown in Figure S6 in supporting information.

Consistent with Langmuir-Hinshelwood kinetics representation, investigational values for the degradation of MO are fixed into rate equation ln (C0/C) = kt where, k, C0 and C are rate constant, the original concentration and concentration after time t correspondingly50, Figure 10 display the ln (C0/C) versus time t plot. The photocatalytic reactions exhibit the continuous liaison that express the photodegradation of MO pursue pseudo-first order kinetics. In case of Ag@CuxO/ZnO (Figure 10a), at the beginning rising the AgNPs content in catalyst from 0 to 0.5 wt% rate constant steadily rises from 8.04 x10-2 to 18.06 x10-2 min-1 and further decline to 10.78 x


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10-2 min-1 (0.75 wt% of AgNPs). However, in case of Au@CuxO/ZnO (Figure 10b), initially sprouting the content AuNPs in catalyst from 0 to 0.1 wt% rate constant progressively inflation from 8.04 x10-2 to 11.70 x10-2 min-1 and then decline to 9.37 x 10-2 min-1 (0.2 wt% of AuNPs). The highest rate constants were established at 0.5 and 0.1 wt% of AgNPs and AuNPs respectively and this composition can be treated as optimal. Inclusion of MNPs up to optimal content boosts the photocatalytic bustle of the catalyst and over this concentration it diminishes. It is feigned that the quantity of MNPs lower than its best content execute as electron–hole division kernel. The photocatalytic activity generally depends on the concentration of hydroxyl radicals51. The PL spectral alteration of dissimilar photocatalyst in TA solution is shown in Figure 11. The OH radicals created through the photocatalytic oxidation practice revealed by apparent PL signal observed at 427 nm. Besides, Figure 11a shows the 0.5 wt% Ag@CuxO/ZnO NRs has the highest PL intensity, and Figure 11b shows the 0.1 wt% Au@CuxO/ZnO NRs has the highest PL intensity, suggesting that it has the highest rate of formation of OH radicals, that helps to enhance photocatalytic activity. When the MNPs loading are beyond its choicest, it too deeds as a charge hauler recombination hub that concurrence with the clarification of PL cram. Moreover, excessive MNPs can guard the UV light incorporation on CuxO/ZnO NRs, undermine the photon promote adaptability52-53. As a blanket outcome, the photocatalytic bustle of the catalyst is miserable, with escalating content of MNPs over its finest. In present study 0.5 wt% Ag@CuxO/ZnO and 0.1 wt% Au@CuxO/ZnO NRs shows maximum efficiency and same composition is used for the degradation of TE. Figure S7a-b in supporting information shows the UV-Vis absorption spectra of



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degradation of MO and TE, beneath UV light irradiation by adopting 0.5 wt% Ag@CuxO/ZnO. Figure S7c-d in supporting information spectacle the UV-Vis absorption spectra of degradation of MO and TE beneath UV light irradiation by adopting 0.1 wt% Au@CuxO/ZnO. 3.8.3. Effect of initial pH The pH of solution is a vital functioning factor, that can influence the photocatalytic performance of the catalyst, so obligation of pH consequence to be explored. The consequence of pH on the degradation of MO and TE were deliberate in the pH 3-9 , because of the dissolution of ZnO suspensions with extra acidic (pH< 3.0) values were not deliberate. Figure S8a-b in supporting information revealed the outcome of pH consequence on the degradation of MO and TE . The ceiling degradation effectiveness for both catalyst (Ag@CuxO/ZnO and Au@CuxO/ZnO) were attaining at pH = 7, can be elucidate by surface charge on the heterogeneous photocatalyst. The photocatalytic degradation obtained over photocatalyst surface; vary in pH influence the dissociation of dyes and surface charge assets of ZnO. The point of zero charge on the surface of ZnO is (9.0), at upper pH, the electrostatic aversion between photocatalyst and anionic dyes custom due to the net negative charge on catalyst surface. Subsequently, for the adsorption location the OH- contend with the dyes; hamper the adsorption of dye, which origin inferior degradation rate at a advanced pH value. In acidic intermediate the degradation competence was fewer due to ZnO liquefy at lower pH due to amphoteric behaviour 54.

3.8.4. Effect of Scavenger on Photocatalytic Activity When photocatalyst is exposed to light, dynamic species for instance (h+), hydroxyl radicals (˙OH) and superoxide radical anions (˙O2−) are generated during the photocatalytic


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process55. Those active species significantly influence the photocatalytic recital of degrading organic compounds. The foremost involuntary species were inspect via ensnare experiments for MO degradation over 0.5 wt% Ag@CuxO/ZnO and 0.1 wt% Au@CuxO/ZnO NRs under sunlight irradiation to elucidate the photocatalytic means as shown in Figure 12. For that purpose, different quenchers such as potassium iodide (KI) (2 mM), isopropanol (IP) (2 mM) and benzoquinone (BQ) (2 mM) were introduced in MO as scavengers for h+, ˙OH and ˙O2− respectively56. Figure 12a-b clearly shows that the maximum photocatalytic degradation of MO dye was took place without any scavenger. However, the produced active species would react with the scavengers favourably and suppress the photodegradation of MO. The photodegradation efficiency of MO was not significant decreases when KI used as scavenger. This phenomenon reveals that h+ are not more concerning the major vigorous species in the photocatalysis course. The photodegradation competence was decline considerably after addition of IP, confirming that ˙OH was an active species. Moreover, the photocatalytic performance was significantly suppressed after BQ was introduced, indicating that ˙O2− acting a crucial task in the photodegradation course. Based on scavengers test, it was found that both superoxide and hydroxyl radicals are mainly actives species involved for MO degradation. This is accordingly with the photodegradation mechanism as discussed below.

3.9. Photocatalytic activity under UV and Sunlight At favorable circumstances numerous experiments were conceded to make sure the consequence of sources of irradiation for degradation of MO and TE. Figure S9a in supporting information shows degradation results of MO under UV as well as sunlight by using CuxO/ZnO NRs. Photodegradation effectiveness of MO with no catalyst proceeds in UV and sunlight were launch 1.5 and 0 % correspondingly within 60 min. Photodegradation competence with



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CuxO/ZnO NRs was establish 99 and 78% respectively beneath UV and sunlight within 40 min. The degradation results of TE by using CuxO/ZnO NRs shown in Figure S9b in supporting information in UV as well as sunlight, Photodegradation efficiency of TE without catalyst took place under UV and sunlight were launch 1 and 0 % correspondingly within 60 min. Photodegradation effectiveness via CuxO/ZnO NRs was establish 85 and 73 % correspondingly in UV and sunlight within 60 min. Figure 13a shows degradation results of MO under UV as well as sunlight. Figure demonstrate that photodegradation competence of MO with no catalyst took place in UV and sunlight were institute to be 1.5 and 0% correspondingly within 60 min. Photodegradation efficiency of MO by using 0.5 wt% Ag@CuxO/ZnO NRs were found that 99 and 79% correspondingly beneath UV and sunlight in 30 min. Whereas photodegradation competence of MO with 0.1 wt% Au@CuxO/ZnO NRs were found that 98 and 74% correspondingly beneath UV and sunlight in 30 min. The degradation results of TE shown in Figure 13b under UV as well as sunlight, Photodegradation efficiency of TE without catalyst took place in UV and sunlight were originate to be 1 and 0 % correspondingly in 60 min. Photodegradation efficiency of TE by using 0.5 wt% Ag@CuxO/ZnO NRs was found that 99 and 87 % correspondingly beneath UV and sunlight in 60 min. Photodegradation competence of TE by using 0.1 wt% Au@CuxO/ZnO NRs was found that 96 and 77% correspondingly beneath UV and sunlight in 60 min, whereas total degradation of TE pragmatic in 100 min beneath sunlight irradiation. Besides the high photocatalytic degradation rate, the long-term stability is an additional key aspect for the photocatalytic dye degradation. The five successive cycles of photocatalytic MO degradation by using 0.5 wt% Ag@CuxO/ZnO and 0.1 wt% Au@CuxO/ZnO NRs in 30 min under UV light


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recorded as shown in Figure 14. The result indicates that the Ag@CuxO/ZnO and Au@CuxO/ZnO NRs are to be stable up to 5 runs.

3.10. Plausible Photodegradation Mechanism Figure 15 shows the schematic model for the plausible mechanism of charge creation and relocate for dye degradation imitation by light. In case of CuxO/ZnO nanocomposite, when ptype Cu2O/CuO semiconductor direct contact with n-type ZnO, that results p-n heterojunction formation at their interface57-58. The band gaps of Cu2O, CuO, and ZnO were considered to be, respectively, 2.1, 1.2, and 3.2 eV, and their CB base stages versus normal hydrogen electrode (NHE) were estimated at −1.47, −0.73, −0.31 eV59. The Cu2O, CuO, excites in the visible light but ZnO excites only in UV light irradiation. Under solar light illumination electrons of Cu2O are endorse to the CB from VB of Cu2O with generation of hole in the VB. Due to constructive band position and p−n junction across the CuxO/ZnO heterointerface, photogenerated electrons can effortlessly be migrated to CB of ZnO from CB of Cu2O, that reduce the charge recombination process60. Those electrons will be rapt by the adsorbed O2 and result in the creation of a ˙O2-. Whereas, VB holes are migrated into the VB of Cu2O from VB band of ZnO will respond to the surface bound OH- and adsorbed H2O to form, respectively ˙OH and ˙HO2. In UV exposure the electrons travel to the CB from the VB and depart positive holes in VB of ZnO. Following division of charge transporter, thinking the favourable alignment band structures of ZnO and CuO, straight convey of holes from VB of ZnO to VB of CuO thermodynamically transpire, outcomes low recombination rate of the photoinduced charges51, ˙O2- will generates by

reacting the dissolved O2 adsorbed on ZnO surface with photoinduced electrons. The OH- will be oxidized to ˙OH by photoinduced holes that are liable to degradation course. The reverse



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transport of positive and negative charge carriers retards the recombination of charges that increases activity of ZnO. In case of M@CuxO/ZnO nanostructure under solar light illumination electrons of Cu2O are excited from VB to the CB of Cu2O with instantaneous creation of hole in the VB. Photogenerated electrons can easily be relocate to CB of ZnO from CB of Cu2O, results the successfully suppress the charge recombination process in Cu2O. The photogenerated electrons in the CB of Cu2O are collected into the CB of ZnO. Along with excitation of CuxO, bouncy electrons are created through the plasmonic excitation of decorated MNPs like Ag and AuNPs by capturing the specific photons from incident light to induce the SPR effect. The SPR state photoexcited electrons injected ballistically into the CB of ZnO as well as CB of CuxO (shown by green arrow in Figure 15). Those electrons from CB of ZnO will be trapped by the adsorbed O2 and outcome ˙O2-. While, the photogenerated VB holes of Cu2O will respond to surface bound OH- and H2O to shape ˙OH and ˙HO2 correspondingly59, 61. The formed ˙O2-, ˙OH and ˙HO2 are conscientious for degradation course. The SPR-enhanced local electromagnetic field around MNPs can facilitate the photoelectron excitation and transfer dynamic, and consequently more electrons participate in the photocatalytic reduction reaction to boost photocatalytic degradation efficiency of ZnO. In case of M@CuxO/ZnO under UV irradiation the photoinduced electron–hole couple are detached from each other in ZnO. The electrons travel to the CB from the VB and depart positive holes in VB of ZnO. Following departure of electrons and holes, considering the band structures of ZnO and CuO, straight convey of photoinduced holes to VB of CuO from VB of ZnO happen thermodynamically in the CuO/ZnO NRs. Due to unequal Fermi energy level, photoexcited electrons from CB of ZnO transfer to the MNPs to equalise Fermi energy level as


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demonstrate by red arrow in Figure 15. That leads to growing the charge parting competence rate of the photoinduced electron hole pairs, the dissolved O2 adsorbed on MNPs surface respond to photoinduced electrons to shape ˙O-2. The OH- will be oxidized into ˙OH by photoinduced holes which are accountable for the degradation procedure, as stated above. The reverse transport of positive and negative charge carriers retards the electron−hole pair recombination, which enlarge the output and duration of electrons leading to short rate of recombination of the photoinduced electron-hole pairs. Therefore, the enhanced photocatalytic degradation should be accredited to the effectual charge-transfer amongst M@CuxO/ZnO NRs.

3.11. Genotoxicity of Textile effluent and its Photodegradation product The genotoxicity study on Cyprinus carpio blood showed that TE is genotoxic at low concentration also, the DNA migration shown in Figure 16. The fish exposed to TE before degradation shows 15.08±4.04 % of DNA in tail, whereas TE after degradation shows 2.68±1.009 % of DNA in tail as shown in Figure 17. There is significant decrease in the DNA damage by TE after degradation (p=0.002). So fish exposed to photodegraded TE product

demonstrate DNA migration analogous to negative control. Hence, the photodegraded TE product seems to less genotoxic to cyprinus.

4. Conclusions The present work deals with an effortless and valuable route for the synthesis of pCuxO/n-ZnO (X=1, 2) heterostructure by combining thermal decomposition method. The composites consist of monoclinic structure of CuO, cubic structure of Cu2O and hexagonal wurtzite structure of ZnO. The XPS results revels the attendance of Zn2+, Cu+ and Cu2+, in the CuxO/ZnO sample. Because of the contribution of the narrow band gap CuxO, the sample CuxO/ZnO exhibit continuous light absorption in the sort of 400-800 nm, indicating the light



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absorption range is effectively extended by the combination of ZnO and CuxO owing to development of p-n junction. Further the AgNPs and AuNPs separately decorated on the surface of CuxO/ZnO heterostructure by simple biogenic method to form M@CuxO/ZnO (M=Ag, Au). SPR of AgNPs and AuNPs extends the absorption range of CuxO/ZnO strongly in the visible region. The AgNPs and AuNPs are consistently scattered on CuxO/ZnO NRs surface.

As synthesized M@CuxO/ZnO heterostructure shows good photocatalytic activity towards the degradation MO dye and TE. Photodegradation efficiency of MO by using 0.5 wt% Ag@CuxO/ZnO NRs were found that 99 and 79% correspondingly beneath UV and sunlight in 30 min. Whereas photodegradation competence with 0.1 wt% Au@CuxO/ZnO NRs were found that 98 and 74% correspondingly beneath UV and sunlight within 30 min. The degradation results of TE by using 0.5 wt% Ag@CuxO/ZnO NRs was found that 99 and 87 % correspondingly beneath UV and sunlight in 60 min. Photodegradation competence with 0.1% Au@CuxO/ZnO NRs was found that 96 and 77 % correspondingly beneath UV and sunlight in 60 min. The enhanced photocatalytic activity of the obtained composites is due to the formation of p-n junction and SPR of AgNPs and AuNPs on CuxO/ZnO. Results shows the Ag@CuxO/ZnO and Au@CuxO/ZnO NRs have the nearly equal photocatalytic activity. This method for the synthesis of M@CuxO/ZnO NRs is totally biogenic green method, does not harm the environment and not necessitate any particular equipment. The effortlessness of the current method and considering the admirable photocatalytic performance of M@CuxO/ZnO NRs propose its budding environmental cleaning function at industrial scale. The degradation of TE prior to discharge in water bodies eliminate the water pollution and provide the clean accessible water.


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Acknowledgments Authors are thankful to Director SAIF, NEHU Shillong for providing TEM Facility

Supporting Information XPS spectra of M@CuxO/ZnO, FT-IR spectra of M@CuxO/ZnO, Table of Wt% of

elements

observed

from

EDS

analysis

of

the

samples

Ag@CuxO/ZnO

and

Au@CuxO/ZnO. Figures of effect of composition of CuxO on the degradation of dyes, UV-Vis absorption spectra of degradation of dyes and effect of initial pH of MO and TE on photo degradation efficiency of M@CuxO/ZnO NRs. Effect of light source on degradation of MO and TE by using CuxO/ZnO NRs.



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Figure Captions Figure 1: XRD pattern of a) ZnO, b) CuxO, c) CuxO/ZnO and d) Ag@CuxO/ZnO and Au@CuxO-ZnO NRs.

Figure 2: Rietveld refinement structure of a) CuO monoclinic, b) Cu2O cubic and c) mixed structure of CuO and Cu2O. d) XRD pattern of refinement CuxO.

Figure 3: DRS spectra of ZnO, 0.75 wt% CuxO-ZnO, 0.5 wt% Ag@CuxO/ZnO and 0.1 wt% Au@CuxO/ZnO NRs

Figure 4: PL spectra of ZnO, 0.75 wt% CuxO/ZnO, 0.5 wt% Ag@CuxO/ZnO and 0.1 wt% Au@CuxO/ZnO NRs.

Figure 5: XPS spectra of 0.75 wt% CuxO/ZnO sample, a) XPS survey spectra and the highresolution spectra of, b) Zn 2p, c) Cu 2p and d) O 1s.

Figure 6: a–b) TEM images at various magnification, c) HR-TEM and d) SAED pattern of 0.75 wt% CuxO/ZnO.

Figure 7: a–b) TEM images at various magnification, c) HR-TEM and d) SAED pattern of 0.5 wt% Ag@CuxO/ZnO NRs.

Figure 8: a–b) TEM images at various magnification, c) HR-TEM and d) SAED pattern of 0.1 wt% Au@CuxO/ZnO NRs.

Figure 9: Effect of composition of a) AgNPs and b) AuNPs, on the degradation of MO. Figure 10: Kinetics of MO degradation under UV light by using a) Ag@CuxO/ZnO and b) Au@CuxO/ZnO NRs.

Figure 11: PL spectral changes of different photocatalysts a) Ag@CuxO/ZnO NRs and b) Au@CuxO/ZnO NRs in TA solution.



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Figure 12: Effect of different scavengers on the MO degradation under sunlight over a) 0.5 wt% Ag@CuxO/ZnO NRs and b) 0.1 wt% Au@CuxO/ZnO NRs

Figure 13: Effect of light source on degradation of, a) MO and b) TE under UV light as well as sunlight

Figure 14: Recycling test of photocatalytic degradation of MO by using 0.5 wt%Ag@CuxO/ZnO NRs and 0.1 wt% Au@CuxO/ZnO NRs under UV light.

Figure 15: Schematic model of charge generation and transfer for organic dye degradation simulated by light.

Figure 16: Comet images showing DNA damage, a) Positive control, b) Negative control, c) Textile effluent before degradation, and d) Photodegraded product of Textile effluent.

Figure 17: Amount of DNA in comet tail in different experimental groups.


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Figure 1.

Figure 2.



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Figure 3.

Figure 4.


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Figure 5.

Figure 6. 35 ACS Paragon Plus Environment


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Figure 7.

Figure 8.


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Figure 9.

Figure 10.

Figure 11. 37 ACS Paragon Plus Environment


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Figure 12.

Figure 13.

Figure 14.


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Figure 15.

Figure 16.

Figure 17.



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ZnO (M= Ag, Au) Heterostructured

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