A Study of Photocatalytic Activity Towards the Degradation of Organic Pollutants Under Visible Light Irradiation

Nanocomposites are composite materials made up of two or more nanoscale materials, each with its own unique physical, chemical, and mechanical characteristics. In recent years, nano-composites' potential uses in photocatalysis—the use of light energy to kickstart chemical reactions—have been the subject of intense research. Due to its great efficiency and lack of environmental impact, photocatalysis has been extensively employed for the elimination of organic contaminants in water and air. When synthesizing nanocomposites for photocatalysis, one material is combined with another that can boost its photocatalytic properties. Among them is graphene oxide (GO), which excels at electron transport despite its small size and enormous surface area. Nanocomposites of GO and photocatalytic materials like titanium dioxide (TiO2) are simple to create by functionalization. TiO2/GO nanocomposites are synthesized using the hydrothermal approach, which requires the application of both heat and pressure during the synthesis process. Methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-vis) are then used to describe the nanocomposites and verify their structure, morphology, and optical characteristics. Degradation of organic contaminants in the presence of visible light is used to assess the photocatalytic efficacy of TiO2/GO nanocomposites. The findings demonstrate that the synergistic impact of GO and TiO2 leads in greater photocatalytic activity in the TiO2/GO nanocomposites compared to pure TiO2. Water and air purification are only two potential uses since the nanocomposites are so durable and versatile. [8] For the photocatalytic destruction of organic pollutants using visible light, nanocomposites have emerged as a potential material. Two or more of these components work together to improve the material's overall performance. Titanium dioxide (TiO2) and carbon-based materials like graphene or carbon nanotubes are one example of such a nanocomposite. By absorbing visible light and transmitting that energy to TiO2, the carbon-based substance functions as a sensitizer, causing the latter to produce reactive oxygen species that may degrade organic pollutants. Nanocomposites of silver and zinc oxide (ZnO) provide still another example. By absorbing visible light and producing localized surface plasmon resonance (LSPR), silver functions as a plasmonic material that boosts the photocatalytic activity of zinc oxide. This is because the LSPR is strongly coupled to the ZnO semiconductor, resulting in enhanced electron-hole separation and greater efficiency.[9] grapheme oxide as raw materials, a ZnO-Reduced graphene hybrid was synthesized using a hydrothermal technique at a pH=11 condition. The shape of ZnO nanostructures such nanoparticles and nanorods was drastically affected by the different mass ratios of zinc nitrate hexahydrate to GO employed to create ZnO-RGO. When exposed to UV light, ZnO-RGO photocatalytically degrades Methylene Blue at a high rate.. Huo et al. [2] revealed a scalable method for making microspheres of ZnO/ZnAl2O4 from the ZnAl-LDH precursor. The ZnO/ZnAl2O4 microspheres have much better photodegradation capability to methylene blue (MB) than the commercial ZnO powder, as shown by photocatalytic assessment under UV irradiation.. Yi et al. [3] nanoflowers of ZnO and Fe/ZnO were produced using a straightforward hydrothermal method. Characterization of the synthesized samples included XRD, XPS, UV-DRS, and scanning electron microscopy. Dopant ions were discovered to coexist with Fe3+ and Fe2+ ions, and to have replaced part of the zinc ions in the crystal lattice. Rhodamine B degradation in aqueous solutions was used to evaluate the photocatalytic activity of the catalysts in both UV and visible light. Photocatalytic activity was found to be greatest in all Fe/ZnO samples when exposed to visible light rather than UV light.. Li et al. [4] reduced graphene oxide (RGO) nanocomposites (ZnO-RGO) were created by reacting zinc chloride (ZnCl2) with graphene oxide (GO) in a single hydrothermal process. Rhodamine B (RhB) was used to measure the photocatalytic activity of the synthetic samples when exposed to artificial sun radiation. The RGO sheets were covered in a homogeneous layer of ZnO nanorods, each having an average diameter of 150 nm. The incorporation of RGO into ZnO nanorods increased light absorption, lowered ZnO size, enhanced the degree of crysatllinity, and stopped ZnO particles from self-aggregating. The nanocomposites had greater photocatalytic effectiveness for RhB degradation than ZnO. Lam et al. [5] WO3/ZnO nanorods were successfully produced using hydrothermal-deposition, it was reported. They looked examined 2,4-dichlorophenoxyacetic acid (2,4-D)'s photocatalytic breakdown in sunlight. The photocatalytic activity of WO3/ZnO nanorods for 2, 4-D degradation in sunshine was very high. The chemical intermediates and breakdown routes of 2, 4-D were investigated using an HPLC technique, and the appropriate WO3 loading and calcination temperature were determined. Total organic carbon (TOC) and ion chromatography (IC) studies were also performed to evaluate the level of mineralization that occurred during the 2, 4-D degradation. nanocomposite. In comparison to binary ZnO/Ag and ZnO/CdO nanocomposites, the ZnO/Ag/CdO nanocomposite showed higher photocatalytic activity under visible light irradiation for the destruction of methyl orange and methylene blue. Under visible light irradiation, the ZnO/Ag/CdO nanocomposite decomposed more than 90% of the industrial textile effluent (actual sample analysis) in 210 minutes. Bhukal et al. [7] examined the structural, magnetic, electrical, and catalytic characteristics of cobalt zinc ferrites (Co0.6Zn0.4MnxFe2-xO4 (0.2, 0.4, 0.6, 0.8, and 1.0) when Fe3+ ions were replaced by Mn3+ ions. It was discovered that when the concentration of Mn3+ ions increased, the saturation magnetization decreased. It was discovered that, due to the semiconductor nature of nanoferrites, the drift mobility of all compositions decreased with increasing temperature. All of the nanoferrites were tested for their photo-catalytic activity by breaking down methyl orange dye, and it was found that when the quantity of Mn3+ ions was raised from 0.2 to 1.0, the nanoparticles' ability to break down the dye improved. This might be because manganese ions have a larger redox potential and a stronger predilection for octahedral sites than iron ions do.

The chemicals and reagents utilized in this research were all of the highest purity and analytical grade. The whole process relied on double-distilled water, which was produced in an all-glass apparatus (of Borosil brand). P-Nitrophenol was obtained from SISCO Chem, Rose Bengal (RB) was purchased from Merck chemical, Malachite Green (MG) was purchased from Loba Chemie, and Celestin Blue (CB) was purchased from Merck chemistry, India. The degradation experiment used them in this form.

PHOTOCATALYST CHARACTERIZATION

The following techniques were used to characterize the produced nanocomposites. BaSO4 was used as the standard for recording UV-Vis-DRS on a UV-2450 spectrophotometer (Shimadzu Corporation, Japan). Using the industry-standard KBr pellet method, we were able to describe the surface structure using an FT-IR spectrometer (JASCO-FT-IR-460 Plus). The crystallite size was calculated from the XRD pattern acquired on an X- ray diffractometer (XPERT PRO) using Cu K radiation at 25°C. We used a JSM 6701F-6701 scanning electron microscope (SEM) to take images in secondary and backscattered electron modes. Energy dispersive X-ray spectroscopy (EDX) coupled to the SEM detected the elemental analyses. Transmission electron microscopy (TEM) using a TECNAI G2 model was also used to examine the surface morphology.Average pore diameters were calculated adsorption analyzer (MICROMERITICS, ASAP 2020). At room temperature, a xenon lamp was used as the excitation light source for the fluorescence spectrophotometer (JASCO- FP-6500) that was used to detect the photoluminescence (PL) spectra. Spectra of adsorption were collected using a UV-visible spectrophotometer (JASCO-V-530). A pH meter (EUTECH) was used to check the pH level. The HEBER immersion photoreactor (HIPR-MP125) was used for the photodegradation studies. [10] Diffuse reflectance UV-Visible spectroscopic studies (DRS) When it comes to the optical characterisation of powder or crystalline materials, diffuse reflectance is a fantastic sampling method. Diffuse reflectance requires the spectrometer beam to be projected precisely into the sample, where it will be scattered, reflected, and ultimately transmitted. The accessory collects the back-reflected, diffusely dispersed light (part of which is absorbed by the sample) and guides it toward the detector optics. Diffuse reflection only applies to the fraction of the beam that is internally dispersed inside a sample and reflected back to the surface. In the range of 200 to 600 nm, using barium sulfate (BaSO4) as a standard, UV-vis diffuse reflectance spectra (DRS) of the produced powder samples were recorded using a Shimadzu UV2550 UV-vis spectrophotometer fitted with an integrating sphere attachment (IRS 2200). The sample is gently stuffed into a sample container that has a five square centimeter circular opening..

Characterization

• UV- vis DRS

Figure displayed the UV-Vis diffuse reflectance spectra of the as-prepared samples. When compared to pure Zn2SnO4 and V2O5, the absorption edges of 2%, 3%, and 5% Zn2SnO4-V2O5 nanocomposites are around 345 and 550 nm, respectively, indicating a slight red shift. Zn2SnO4-V2O5's red shift is due to the electron-hole transition between the two materials. As the semiconductor's absorption edge gets farther out into the visible spectrum, the band gap tends to get smaller. Bandgap values are shown in Fig. for Zn2SnO4,V2O5, 2% Zn2SnO4 -V2O5, 3% Zn2SnO4 -V2O5, and 5% Zn2SnO4 - V2O5, respectively, ranging from 3.6eV to 1.98eV.Since ZnSnO4, V2O5 absorbs less visible light than Zn2SnO4, a 3% mixture of the two absorbs more light.

5%Zn2SnO4-V2O5

Zn2SnO4 - V2O5 and 5% Zn2SnO4 - V2O5 According to this empirical expression, the calculated CB (ECB) and VB (EVB) edge position for Zn2SnO4 and V2O5 are listed in Table .

calculated EVB and ECBof Zn2SnO4, V2O5 FT-IR Spectrum characteristic peaks of Zn2SnO4 and V2O5 are in accordance with the reported results respectively. We can see that the three samples exhibit similar characteristics of infrared adsorption bands, which are quite similar to the Zn2SnO4 reported in previous literature . Therein, the broad absorption peaks at 3426 and 1602 cm−1 can be ascribed to the vibration of absorptive water, and the absorption peaks at ,546, 1038, and 1410 cm−1 are due to the vibration of M–O or M–O–M groups in Zn2SnO4 . Two characteristic absorption bands at 824 cm-1 and 1014 cm-1 are observed in V2O5 sample. The band at 824 cm-1 is assigned to the asymmetric stretching modes of V- O-V bond and other peak at 1014 cm-1 is attributed to the stretching vibration of V=O bond. Further, the FT-IR spectra of Zn2SnO4 - V2O5 composites represent the overlap of the Zn2SnO4 - V2O5 spectra. The FT-IR peak intensity of V2O5 is decreased with increase in the mole percent of Zn2SnO4. This indicates the coexistence of the Zn2SnO4 and V2O5in the composite.

Zn2SnO4-V2O5 X-ray diffraction The crystal structure identity and phase composition of pure Zn2SnO4, V2O5, Zn2SnO4 -V2O5 nanocomposite have been confirmed by XRD patterns and are displayed in Fig.4.4. The X-ray diffraction of Zn2SnO4 -V2O5 nanocomposite with varying Zn2SnO4 contents along with pure Zn2SnO4 and V2O5 for comparison details also investigated. The pure Zn2SnO4 sample possesses dominant diffraction peaks at 2θ with an angle of 17.7°, 23.1°, 29.1°, 34.3°, 41.7°, 51.7°, 55.1° and 60.4° representing the indices of (1 1 1), (0 1 2), (2 2 ), (3 1 25 can be noted that the main diffraction peaks detected, i.e 15.3°, 20.2°, 25.4°, 26.0°, 32.3°, 34.2°, 40.0°, 49.3° and 55.5°can be assigned to the (2 0 0), (0 0 1), (2 0 1), (1 1 0), (0 1 1), (3 1 0), (3 1 1), (1 1 2) and (0 2 1) lattice planes in the orthorhombic phase V2O5 (JCPDS no: #89-2482 card). High degrees of crystallinity are indicated by the narrowing and well-defined of the diffraction peaks of Zn2SnO4 and V2O5. Diffraction patterns of Zn2SnO4 and V2O5 samples showed no impurity-related peaks, proving their great purity. Diffraction patterns reveal that the Zn2SnO4-V2O5 nanocomposite is composed of just two phases: the orthorhombic phase of V2O5 and the cubic phase of Zn2SnO4. Since only Zn2SnO4 and V2O5 existed, the nanocomposites were denoted as such. Where D is the average crystallite size, β is the full width half maximum (FWHM) of the highest intensity peak (110 peak), k is a shape of factor of the particles (it equals to 0.89). The average crystalline sizes of Zn2SnO4, V2O5, 2% Zn2SnO4 - V2O5, 3% Zn2SnO4 - V2O5, 5% Zn2SnO4 - Scherrer equation was used to determine the atomic radii of V2O5 nanocomposite, and the resulting radii are 23.45, 24.53, 26.72, 28.45, and 30.56. The nanocomposite will be stabilized by halting the crystallization process because to the strong contact between the cubic phase of Zn2SnO4 and the orthorhombic phase of V2O5.

Zn2SnO4-V2O5 microstructure and morphology of pure Zn2SnO4, V2O5, and 3% Zn2SnO4-V2O5. The morphology of pure Zn2SnO4 is shown in Fig. (a-c) to be ball-shaped aggregates, whereas that of V2O5 is shown to be aggregates of various shapes. The morphology of the 3% Zn2SnO4-V2O5 mixture, however, seems to be uniformly spherical, and the average particle size is below 26 nm. As can be seen in Fig. (d), the EDAX analysis of Zn2SnO4-V2O5 composites reveals the presence of components such as Zn, Sn, V, and O.

Zn2SnO4 - V2O5 The TEM analysis was carried out to learn more about the photocatalyst's crystalline structure. Nanocomposite of ZnSnO4 and V2O5 at a 3 percent ratio is displayed in TEM (Fig. a). The typical spherical diameter of Zn2SnO4-V2O5 is between 23 and 47 nm, as seen in the picture. The TEM micrograph reveals that V2O5 nanoparticles have been deposited on the Zn2SnO4 plates, producing a darker picture than that of pure Zn2SnO4 plates. Multiple physical and chemical changes occurred in the as-prepared composite during calcination at 80 °C. Mesoporous structures arise when water, including adsorbed, intercalated, and hydroxyl water, is removed from the structure. In Fig.(b), we see the chosen region electron diffraction pattern for the 3% Zn2SnO4-V2O5 nanocomposite. The cubic phase of Zn2SnO4 and the orthorhombic phase of V2O5 are clearly visible in the SAED pattern of the Zn2SnO4-V2O5 nanocomposite, which is in excellent agreement with the XRD pattern. Light patches correspond to the (1 1 1), (2 2 0), (3 1 1), and (4 4 0) planes of the cubic phase of 3% Zn2SnO4-V2O5, while the brighter inner ring corresponds to the orthorhombic phase of V2O5. The spots verify that the 3% Zn2SnO4-V2O5 is a single crystal. As seen by the SAED pattern, the 3%

SAED pattern of 3% Zn2SnO4 - V2O5 BET surface area analysis The surface of photocatalysts is often where the reaction occurs. The difference in subsequent photocatalytic performance can be understood by examining the isotherms depicted in Fig., which show the specific surface area and pore structure of as-prepared Zn2SnO4,V2O5, and 3% Zn2SnO4-V2O5nanocomposite at -195.609oC through the use of nitrogen adsorption-desorption. All three isotherms may be classified as type IV thanks to their mesoporous character, as defined by the International Union of Pure and Applied Chemistry. Type H3 hysteresis loops describe the hysteresis patterns.The relative pressure hysteresis loop P/P0 is between 0.6 and 1. The average pore size, pore volume, and BET surface area of as-synthesized samples are summarized in a table. Table 2: Calculated values from N2 adsorption-desorption experiments

and pore size istribution plots for sample of (a) Zn2SnO4 (b)V2O5 (c) 3% Zn2SnO4 - 2O5 Photocatalytic degradation of EY Maximum absorption in the UV-Vis range was measured over time to observe photocatalytic degradation. At a concentration of 3% the photocatalytic activity of a Zn2SnO4 -V2O5 nanocomposite was evaluated by monitoring its ability to degrade EY at pH4. It was discovered that the concentration of EY under visible light irradiation scarcely photodegraded in the absence of the photocatalytic components. Dark experiments with photocatalytic materials for 30 minutes revealed that the active sites of the synthesized photocatalysts absorbed more dye the longer they were exposed to light. The eV absorption peak at max 595 nm gradually decreased after being exposed to light for 180 minutes. The photocatalytic degradation of EY in aqueous solution with 3% Zn2SnO4 -V2O5 was 92% effective. Because no other absorption bands could be found in the visible or ultraviolet spectrum, it was assumed that the conjugated structure had been broken down. .

Using the literature on the photocatalyltic activity of nanocomposites, we propose a mechanism for the enhanced photocataltic activity of 3% Zn2SnO4-V2O5. Irradiation-induced electron transport is shown in a simplified schematic form in Fig. with visible light via 3% Zn2SnO4-V2O5. This is because when 3% Zn2SnO4-V2O5 is exposed to visible light, more electrons and holes are formed in the conduction band and valence band of Zn2SnO4 due to its small band gap. Zn2SnO4's photo-generated electrons readily enter the conduction band of V2O5, whereas V2O5-Zn2SnO4 holes go in the other way. As a result, effective electron - holes separation is obtained on the nanocomposites' surface, and the electron - holes recombination process is greatly reduced. Capturing electrons from the conduction band allows photodegradation of EY, while holes oxidize H2 to produce water.

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PhD Student, Kalinga University Raipur CG