Abstract
ZnS and CdS nanoparticles were prepared by a simple microwave irradiation method under mild conditions. The obtained nanoparticles were characterized by XRD, TEM and EDX. The results indicated that high purity of nanosized ZnS and CdS was successfully obtained with cubic and hexagonal crystalline structures, respectively. The band gap energies of ZnS and CdS nanoparticles were estimated using UV-visible absorption spectra to be about 4.22 and 2.64 eV, respectively. Photocatalytic degradation of methylene blue was carried out using physical mixtures of ZnS and CdS nanoparticles under a 500-W halogen lamp of visible light irradiation. The residual concentration of methylene blue solution was monitored using UV-visible absorption spectrometry. From the study of the variation in composition of ZnS:CdS, a composition of 1:4 (by weight) was found to be very efficient for degradation of methylene blue. In this case the degradation efficiency of the photocatalyst nanoparticles after 6 h irradiation time was about 73% with a reaction rate of 3.61 × 10−3 min−1. Higher degradation efficiency and reaction rate were achieved by increasing the amount of photocatalyst and initial pH of the solution.
Highlights
Textile, paper and some other industrial processes discharge large amounts of colored dye wastewater which is toxic and non biodegradable in most cases and when it reaches the natural water runoff, the impending photosynthetic activity of aquatic plants seriously threatens the whole ecosystem
In this figure the peaks observed in the X-ray diffraction (XRD) patterns of ZnS nanoparticles at 2θ values of 28.5°, 33.1°, 47.4°, 56.3°, 69.4° and 76.7°, match perfectly with the (111), (200), (220), (311), (400) and (331) crystalline planes of the face centered cubic structure of ZnS reported in ICDD PDF 65-1691 with lattice parameter of 5.41 Ao and cell volume of 158.4 Ao3
This paper presented a simple method for preparation of efficient visible light photocatalytic materials, namely high purity ZnS and CdS nanoparticles, by a microwave irradiation route
Summary
Paper and some other industrial processes discharge large amounts of colored dye wastewater which is toxic and non biodegradable in most cases and when it reaches the natural water runoff, the impending photosynthetic activity of aquatic plants seriously threatens the whole ecosystem. Over the past several decades, various physical, chemical, and biological techniques for decoloration of dye effluents have been developed Conventional treatments such as coagulation, flocculation, absorption, adsorption, ultrafiltration, reverse osmosis, and membrane technologies merely concentrate or transfer organic compounds from one phase to another. Photocatalysis is a process by which a semiconductor material absorbs light of energy greater than or equal to its band gap, causing excitations of valence band electrons in the conduction band Such charge separation leads to the formation of electron-hole pairs which can further generate free radicals in the system for redox of the substrate. For efficient degradation of dyes, a photocatalyst that has a suitable band gap, flat band potential/energy levels and good adsorption properties in the visible region is needed The photocatalytic activity of the obtained nanostructures was examined using the degradation of methylene blue (MB) under visible light in air at room temperature by considering the influence of experimental parameters such as the ZnS:CdS weight ratio, the amount of catalyst used and the initial pH of the solution
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