Synthesis of ZnO/ZnS core/shell microsphere and its photocatalytic activity for methylene blue and eosin dyes degradation

Ethylenediamine-assisted solvothermal synthesis of ZnS/ZnO photocatalytic heterojunction for high-efficiency hydrogen production

Organic-inorganic hybrid materials have emerged as a class of novel materials over the last two decades, as they combine functional organic components and inorganic building blocks into unique materials through various chemical or physical interactions. In the present work, the importance of the use of ethylenediamine in sulfided materials applied to photocatalytic processes in the H2 production is demonstrated. The ZnS/ZnO heterojunction was prepared by the solvothermal synthesis in the presence and absence of ethylenediamine. The photocatalytic behavior showed that the addition of ethylenediamine increases the photocatalytic efficiency up to eight times compared to the photocatalyst without the organic agent. The materials were characterized by X-ray diffraction, scanning electron microscopy, infrared and UV-visible spectroscopies of solids, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and photoelectrochemical characterization. The ethylenediamine plays a double role: to stabilize the cubic phase of zinc sulfide and to act as a promoter molecule of charge transfer on the surface of ZnS/ZnO/en heterojunction, slowing down the rate of recombination of the electron-hole pair, which is reflected in a decrease in the resistance to transfer of charge carriers, improving the H2 production rate until 1564 µmol h-1 g-1.

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.

Facile synthesis of ZnO/ZnS hollow nanorods via Kirkendall effect with enhanced photocatalytic degradation of methylene blue

Because of the growing concerns about environmental issues, the search of proficient semiconductor catalysts for pollutants degradation from contaminated water is one of the interesting areas of research. Due to the larger surface area, hollow nanomaterials with hollow interior and outer thickness illustrate a class of significant nanostructured materials. The enhanced surface area provides remarkable applications of the hollow nanomaterials in catalysis. In Kirkendall effect, pores are formed owing to the diverse diffusion rates of two nanomaterials in a diffusion couple. Here, we have introduced the facile hydrothermal synthesis of hollow nanorods of ZnO/ZnS via Kirkendall effect using ZnO nanorods (NRs). The morphologies, optical properties, compositions, and crystal structures of the as synthesized materials are systematically studied using UV-vis, PXRD, FESEM, TEM, EDS, XPS, etc. The process of synthesis and growth mechanism of hollow NRs is suggested based on the Kirkendall effect. A hollow nanomaterial, envisaged being highly efficient for molecule adsorption on its surface, the as synthesized materials were used for the photocatalytic degradation of methylene blue (MB) dye. MB degradation efficiency of 96% within 60 min was performed over ZnO/ZnS hollow NRs, which was 2.6-fold greater than that of ZnO. The rate constant of ZnO/ZnS heterostructure was 0.045 min^-1, which was 5.5 times larger than that of bare ZnO. We have concluded our work in the directions towards the synthesis of various semiconductor hollow nanostructures for the varied catalytic reactions.

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.

Surface photosensitization of ZnO by ZnS to enhance the photodegradation efficiency for organic pollutants

It is challenging to develop a material which has low cost, high activity, good stability and recyclability under light exposure. Apart from these properties, the photocatalyst should also have good visible region absorbance and low electron-hole pair recombination rate. Keeping all this in view, we have designed a simple scalable synthesis of ZnO–ZnS heterostructures for the photocatalytic treatment of industrial waste (p-nitrophenol and methyl orange). The ZnO–ZnS heterostructures are synthesized via a solvent-free route by thermal annealing of solid-state mixture of ZnO and thiourea (a sulphur source) which results in ZnO–ZnS core shell kind of heterostructure formation. The interface formation between the ZnO–ZnS heterostructure favored the band-gap reduction in comparison to the bare ZnO and ZnS nanoparticles. Further, these ZnO–ZnS heterostructures were utilized as a photocatalyst for the degradation of toxic phenolic molecules (p-nitrophenol) and harmful organic dyes (methyl orange) present in the water under the light exposure (> 390 nm).