Fabrication of centimeter-sized Sb2S3/SiO2 monolithic mimosa pudica nanoflowers for remediation of hazardous pollutants from industrial wastewater

Abstract

Photocatalysis using ‘easy-to-separate’ metal-oxide/sulfide monoliths is a promising method to tackle the grievous issue of water pollution. Here, ‘mimosa pudica’ flower-like Sb2S3/SiO2 monoliths were prepared by impregnation of antimony chloride solution in silica monoliths followed by treatment with potassium thiocyanate, refluxing and calcination. The nanoflower-like morphology of the synthesized monoliths was verified using field emission scanning electron microscope images. The Brunauer–Emmett–Teller model for surface area analysis showed that monoliths had a high surface area of 83 m2/g with mesopore diameter of 13.61 nm. The purity/crystallinity and the elemental state of the sulfide were confirmed using X-ray diffraction analysis and X-ray photon spectroscopy whereas energy dispersive spectroscopy verified the homogeneous elemental distribution of the catalyst. The diffuse reflectance spectroscopy and photoluminescence spectroscopy confirmed that Sb2S3/SiO2 monoliths had a narrow band gap (∼1.57 eV) and low recombination rate of photoinduced charge carriers. Thermal stability of the materials was also investigated by thermogravimetric analysis. The photocatalytic performance of monoliths was examined by photodegradation of model pollutants methylene blue (MB) and thiamethoxam (TM). At optimum pH and catalyst-concentration, monoliths exhibited best efficiency (with high rate-constant) in sunlight for degradation of MB (96%; 0.018 min−1) and in UV light for degradation of TM (70%; 0.0057 min−1). The catalyst was reused for four cycles for degrading MB (∼71% efficiency). A comparative study with reported literature data confirmed the superiority of the monoliths for MB degradation. The trapping experiments indicated that superoxide anion radicals and holes had a dominant role in the MB and TM degradation, respectively. MB was mineralized almost completely exhibiting ∼99.7% removal of total organic carbon (TOC). The photocatalytic treatment of industrial wastewater revealed ∼97% TOC- removal besides ∼92% removal of chemical oxygen demand. It validated that this photocatalyst is better than physicochemical treatment done by industries. This monolithic catalyst can indeed be advantageous for the remediation of perilous contaminants from a practical viewpoint.