Visible-light-driven ZnO/ZnS/MnO2 ternary nanocomposite catalyst: synthesis, characterization and photocatalytic degradation of methylene blue

Visible light-driven photocatalytic activity of ZnO-MnO2/exfoliated vermiculite composite for cadmium removal

The present study delves into the efficient photocatalytic activity of ZnO-MnO2/EV composite for cadmium removal under visible light exposure, addressing the significant threat posed by high cadmium concentrations in water. An eco-friendly approach for synthesizing ZnO-MnO2 and ZnO-MnO2/exfoliated vermiculite (ZnO-MnO2/EV) composite is also discussed. Adjusting the band gap of ZnO nanomaterials is crucial in refining their optical properties. Utilizing aqueous floral extract as a reducing agent in synthesizing ZnO-MnO2 nanoparticles enhances their photocatalytic efficiency under visible light. The composite material, ZnO-MnO2/EV, is thoroughly characterized using various spectroscopic and microscopic techniques like scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Investigating different ratios of ZnO-MnO2 and exfoliated vermiculite reveals an optimal ratio of 1:2 for maximal cadmium removal. Key factors such as initial pH, contact duration, cadmium (II) ion concentration, light intensity, temperature, and photocatalyst dose are analyzed to enhance removal efficiency. Based on the collected data, a plausible mechanism for removing cadmium by ZnO-MnO2/EV is proposed. The study attains a remarkable cadmium removal efficiency of 94.5% for real wastewater under optimized conditions using visible light irradiation.

Synthesis of PVA-assisted MnO2-CuO-ZnO-g-C3N4 quaternary nanocomposite for the degradation of methylene blue from industrial wastewater

The pristine phases SS1(ZnO), SS2(MnO2), and SS3 (CuO) photocatalysts and mixed phases of ZnO-based nanocomposites were synthesized by the sol-gel method. Whereas SS4 (g-C3N4) was prepared through polymerization of urea. The synthesized photocatalysts were characterized using TGA-DTA, XRD, DRS, PL, DLS, FTIR, SEM, TEM, and HRTEM. The TGA-DTA result confirmed that the calcination temperature was attained at 400 °C to decompose PVA after assisting the sample. In this study, band-gap energy, crystallite sizes, charge separation, and surface properties of binary, ternary, and quaternary nanocomposites were modified more when compared with single-phase SS. This enhancement is probably due to the loading of SS2, SS3, and SS4 photocatalysts on the SS1 surface. The photocatalytic activities of all synthesized nanomaterials were explored under visible light radiation. The activity of SS1 photocatalysts is lower than those of all synthesized photocatalysts. The efficiency of the BQ (MnO2-CuO-ZnO-C3N4) nanocomposite is 2.2 times higher than that of SS1. This photocatalytic improvement might be ascribed to the cumulative effect of individual photocatalysts. The photocatalytic potential of BQ over Methylene blue (MB) from industrial wastewater was evaluated and its degradation efficiency was 98 % at 3 h. The reusing experiments of BQ nanocomposite were evaluated for four cycles and almost the same performance was observed. Besides, the possible photocatalytic mechanism was proposed. This could offer novel results in designing stable quaternary heterojunction nanocomposites through all single-phase photocatalysts.

Fabrication of CuWO4@MIL-101 (Fe) nanocomposite for efficient OER and photodegradation of methylene blue

The development of an efficient catalyst to meet the world's increasing energy demand and eliminate organic pollutants in water, is a concern of current researchers. In this article, a highly effective composite has been synthesized using the solvothermal approach, by incorporating CuWO4 nanoparticles into Fe-based MOF, Fe (BDC). The synthesized samples were analyzed further by some characterization techniques such as X-ray diffraction, Fourier transform infrared spectroscope (FTIR) and scanning electron microscopy. The highest catalytic activity for the oxygen evolution reaction was observed in the CuWO4@MIL-101(Fe) composite, which exhibited low overpotential 188 mV to obtained the current density of 10 mA cm-2, and a smaller Tafel slope of 40 mV dec-1. The nanocomposite CuWO4@MIL-101(Fe) material showed enhanced visible light absorption and maximum degradation of methylene blue up to 96.92 %. It has been found that this research promotes the development of an efficient MOF-based catalyst for OER and photocatalytic technology.

Novel polyvinyl alcohol-assisted MnO2-ZnO-CuO nanocomposites as an efficient photocatalyst for methylene blue degradation from wastewater

Pristine ZnO (Z), MnO2 (M), CuO (C) photocatalysts and polyvinyl alcohol (PVA)-assisted MnO2-ZnO-CuO (MZC) nanocomposites were synthesized via the sol-gel method. The synthesized samples were characterized using thermal analysis (TGA), X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM), energy dispersive X-ray (EDS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) techniques. The thermal analysis results of the prepared nanomaterial confirmed that the suitable calcination temperature for the synthesis of these nanomaterials is 420 °C. In addition to the morphological and elemental composition, the characteristic diffraction peaks of the MZC nanomaterial were found to align with those of the pristine Z, M, and C photocatalysts. The photocatalytic activities of the synthesized nanomaterials for methylene blue (MB) degradation were evaluated under optimized conditions. The degradation efficiencies of Z, M, C, and MZC were found to be 45%, 57%, 66%, and 93%, respectively, for MB in 180 minutes. The MZC nanocomposite exhibited superior photocatalytic activity compared to the pristine materials, which is attributed to the synergetic effect of the Z, M, and C photocatalysts. The effects of pH, initial dye concentration, and catalyst load were also explored to determine the optimum conditions. The best photocatalytic efficiency was observed at pH 8, with a 130 mg L-1 catalyst load, and a 10 mg L-1 initial dye concentration. The efficiency of the MZC nanocomposite in real textile wastewater was also tested, achieving 80% degradation of pollutants within 180 minutes. Recycling experiments were conducted for four consecutive cycles under optimal conditions. The photodegradation efficiency for the first, second, third, and fourth cycles was 93%, 91%, 90%, and 89%, respectively, demonstrating high consistency in photodegradation performance across the four cycles. Moreover, a Z-scheme photocatalytic mechanism was proposed as a potential mechanism for the MZC photocatalytic system.

Optimization of the photocatalytic degradation of phenol using superparamagnetic iron oxide (Fe3O4) nanoparticles in aqueous solutions

The present work was carried out to remove phenol from aqueous medium using a photocatalytic process with superparamagnetic iron oxide nanoparticles (Fe3O4) called SPIONs. The photocatalytic process was optimized using a central composite design based on the response surface methodology. The effects of pH (3-7), UV/SPION nanoparticles ratio (1-3), contact time (30-90 minutes), and initial phenol concentration (20-80 mg L-1) on the photocatalytic process were investigated. The interaction of the process parameters and their optimal conditions were determined using CCD. The statistical data were analyzed using a one-way analysis of variance. We developed a quadratic model using a central composite design to indicate the photocatalyst impact on the decomposition of phenol. There was a close similarity between the empirical values gained for the phenol content and the predicted response values. Considering the design, optimum values of pH, phenol concentration, UV/SPION ratio, and contact time were determined to be 3, 80 mg L-1, 3, and 60 min, respectively; 94.9% of phenol was eliminated under the mentioned conditions. Since high values were obtained for the adjusted R2 (0.9786) and determination coefficient (R2 = 0.9875), the response surface methodology can describe the phenol removal by the use of the photocatalytic process. According to the one-way analysis of variance results, the quadratic model obtained by RSM is statistically significant for removing phenol. The recyclability of 92% after four consecutive cycles indicates the excellent stability of the photocatalyst for practical applications. Our research findings indicate that it is possible to employ response surface methodology as a helpful tool to optimize and modify process parameters for maximizing phenol removal from aqueous solutions and photocatalytic processes using SPIONs.

Fe3O4@BNPs@ZnO-ZnS as a novel, reusable and efficient photocatalyst for dye removal from synthetic and textile wastewaters

In this study, new magnetic nanocomposites with different molar ratios of zinc oxide-zinc sulfide were synthesized together with photocatalysts MNPs@BNPs@ZnO and MNPs@ BNPs@ ZnS. The photocatalytic behavior of these hybrid nanocomposites under visible light and ultraviolet light was investigated to remove methylene blue (MB), methyl orange (MO) dyes, real textile and carton effluents. After studies, the best active photocatalyst in both visible light and ultraviolet light is MNPs@BNPs@ZnO-ZnS (ZnO/ZnS: 0.75:0.25), which displayed the best performance in the ultraviolet region. According to the TEM, the average particle size for MNPs@BNPs@ZnO-ZnS (ZnO/ZnS: 0.75:0.25) is between 10 and 30 nm. Zeta potential (DLS) showed that the charge on the photocatalyst surface is negative at most pHs. PL analysis confirmed that the amount of hole-electron recombination in the optimal photocatalyst is less than MNPs@BNPs@ZnO and MNPs@BNPs@ZnS. Also, based on kinetic studies, the rate constant for removing azo dyes such as MO and MB was 0.0186 and 0.0171 min^-1, respectively. It is worth noting that in addition to the novelty of the synthesized photocatalysts, the UV and visible lamps used in this research are inexpensive, durable, and highly efficient.

A novel ZnS-CdS nanocomposite as a visible active photocatalyst for degradation of synthetic and real wastewaters

In this study, new magnetic nanocomposites with shell core structure with different molar ratios of ZnS-CdS were synthesized and their photocatalytic activity in dye removal from synthetic and real effluents in the presence of mercury high pressure lamp as a visible light source was investigated. Optimal photocatalyst with molar ratio of ZnS-CdS 0.25:0.75 showed the best performance in dye removal. Based on the particle distribution histogram of Fe₃O₄@BNPs@ZnS-CdS (ZnS/CdS: 0.25:0.75), particles with 60-100 nm have the highest abundance. According to the DRS results, hybridization of zinc sulfide with cadmium sulfide reduced the gap and as a result, light absorption was successfully extended to the visible area. The PL results confirm that the optimal photocatalyst (Fe₃O₄@BNPs@ZnS-CdS) has the lowest electron-hole recombination compared to Fe₃O₄@BNPs@ZnS and Fe₃O₄@BNPs@CdS. It should be noted that according to the DLS results, the charge on the optical photocomposite surface is negative at all acidic, alkaline and neutral pHs. One of the significant advantages in this study is the use of high-pressure mercury lamps as a light source, so that these lamps are very economical in terms of economy and also have a long life and excellent efficiency. The optimal photocatalyst not only showed excellent photocatalytic activity for the removal of methylene blue (96.6%) and methyl orange (70.9%) but also for the dye removal of textile effluents (Benton 98.5% and dark olive 100%). Introduced magnetic heterostructures are suitable options for dye removal from textile and spinning wastewaters.

Preparing a dual-function BiVO4/NiFe-LDH composite photoanode for enhanced photoelectrocatalytic wastewater treatment and simultaneous hydrogen evolution

The proposed PEC degradation over the BiVO4/NiFe-LDH photoelectrode under visible light irradiation and simultaneous hydrogen evolution at the cathode.