Insights on adsorptive and catalytic water remediation using metal chalcogenides and bismuth based nanomaterials

Abstract

Water pollution has recently garnered increased attention due to its severe negative impacts on life and the planet's ecosystem. Given the essential role of water in sustaining a healthy life, sourcing clean freshwater is one of the most pressing challenges facing modern society. The grave situation demands further advancements in sustainable water use practices and the developing of cost-effective wastewater treatment technologies. This thesis focuses on the remediation of organic and inorganic pollutants in wastewater using nanomaterials as nano-adsorbents and nano-catalysts. The primary goal is to develop nanomaterials and demonstrate their effectiveness, at the laboratory level, in adsorption and catalytic processes for water remediation. It addresses four common but toxic industrial effluents—surfactants, phosphate ions, antibiotics, and industrial dyes—using adsorptive and catalytic strategies with metal chalcogenides and Bi-based nanomaterials. We synthesized CuS nanostructures and demonstrated their effectiveness as adsorbents and catalysts for removing sodium dodecyl sulfate (SDS) from water. The efficient decomposition of SDS was achieved through adsorption and advanced oxidation processes driven by hemi-micelle enhanced adsorption and the synergistic action of H2O2. The fast catalytic decomposition of SDS resembles a Fenton-like process. This study is the first to report the use of metal chalcogenides for surfactant removal from water. We developed a dual-functional MnS nanomaterial for the removal of phosphate ions and Congo Red dye. Synthesized via a hydrothermal route, the MnS nanomaterials exhibited a phosphate adsorption capacity of 160.73 mg P/g. Adsorption studies indicated a spontaneous, exothermic process with mechanisms involving electrostatic attraction, surface complexation, and ion exchange. MnS maintained selective phosphate adsorption despite competing ions and demonstrated high sonocatalytic efficiency by degrading Congo Red dye within 10 minutes. These findings highlight MnS as a promising non-lanthanum or zirconium material for phosphate removal from wastewater and a sonocatalyst for textile dye degradation.We synthesized 𝐵𝑖𝑂𝐵𝑟( ) 𝐶𝑙 nanoplates with varied Br:Cl ratios using a co- precipitation method, showing superior visible-light-driven photocatalytic activity compared to BiOCl and BiOBr. Morphological, optical, and structural analyses revealed that halide alloying successfully tuned the optical bandgap in the samples from 3.39 eV to 2.75 eV, enhancing their light-harvesting capabilities. The 𝐵𝑖𝑂𝐵𝑟 . 𝐶𝑙 . sample achieved 89% and 99% degradation efficiency for ciprofloxacin and tetracycline hydrochloride, respectively, within 20 minutes. The high performance is due to its large surface area, suitable morphology, band gap, and effective electron-hole separation in the solid solution. The material is recyclable, stable, and adaptable to aquatic environments, making it a promising eco-friendly photocatalyst for antibiotic pollution control. We developed a heterojunction BiVO4 structure by combining distinct crystal phases to overcome limitations in traditional BiVO4 photocatalysts, such as poor charge transport and surface adsorption. A hydrothermal method was used to synthesize tetragonal, monoclinic, and monoclinic/tetragonal BiVO4 phases. The photocatalytic activity, particularly for Rhodamine B degradation, was enhanced using ultrasonic sound waves. The study revealed that the crystalline phases significantly affect photo-sono-induced charges, providing deeper insight into the mechanisms behind improved sonophotocatalytic activity. This study scientifically demonstrates, at the laboratory level, the effective removal of toxic contaminants found in industrial effluents using innovative adsorbents, photocatalysts, sonocatalysts, and sonophotocatalysis. These findings reveal the potential of these nanomaterials for scalable and energy-efficient water purification. An in-depth analysis of the mechanism and the kinetics and thermodynamics of the adsorption and catalytic processes is also reported. The research underscores the promise of metal chalcogenides and bismuth-based nanomaterials as innovative solutions for addressing water pollution challenges.