Fatemeh Hashemzadeh

The single phase layered perovskite-type niobate, KCa₂Nb₃O₁₀ obtained by a solid-state reaction of the starting materials (K₂CO₃, CaCO₃ and Nb₂O₅) at 1,200 °C. Then the H⁺-exchanged form (HCa₂Nb₃O₁₀) was successfully exfoliated into colloidal porous single layers on the intercalating action of tetra (butyl) ammonium ion. The various characterization techniques such as X-ray diffraction (XRD), field-emission scanning electron microscope, N₂ absorption-desorption and DRS UV/visible gave important information on the unusual structural features of the perovskite-related niobate nanosheets. XRD analysis of the exfoliated nanosheets showed unique profile with wide peaks that represented individual molecular aspects of the nanosheets. The BET isotherm of the exfoliated coiled nanosheets showed a sharp increase in the surface area by a factor of >30 in comparison to parent layered material, that is due to exfoliation and restacking process. The nanosheets in this study were also found to act as a semiconductor with a wide band gap that is due to the quantum size effect.

Heterogeneous photocatalysis has proved to be a useful tool for the degradation of water pollutants over the past 30 years. In this work, the photocatalytic decolorization of Rhodamine B (RhB) dye as a model compound has been studied by using nano-sized Nb₂O₅ semiconductor as a photocatalyst. Structural and textural features of the Nb₂O₅ sample were characterized by X-ray diffraction, scanning electron microscope, UV–vis DRS, and Brunauer–Emmett–Teller techniques. As a result, the orthorhombic Nb₂O₅ particles displayed nearly spherical shape with the average crystalline size and the band gap energy of 43.7 nm and 2.9 eV, respectively. Different parameters of decolorization reaction like dye concentration, catalyst amount, pH, and H₂O₂ concentration have been studied. The optimum conditions for the photo treatment of the dye were initial concentration 10 mg L⁻¹ of dye, catalyst concentration 0.5 g L⁻¹, and pH 4. The optimum value of H₂O₂ concentration for the conditions used in this study was 700 mg L⁻¹. Moreover, the efficiency of photo-Fenton process either alone or in conjunction with Nb₂O₅ and a dark-Fenton process as a control experiment were evaluated. The combination of photo-Fenton and Nb₂O₅ catalysts was found to be most effective for the treatment of such type of wastewaters.

The present research deals with the development of a new heterogeneous photocatalysis and Fenton hybrid system for the removal of color from textile dyeing wastewater as Rhodamine B (RhB) solutions by using Fe²⁺/H₂O₂/Nb₂O₅ as a photocatalytic system. The application of this photocatalytic system for the decolorization of dye contaminants is not reported in the literature yet. Different parameters like dye concentration, Nb₂O₅/Fe²⁺ catalyst amount, pH, and H₂O₂ concentration have been studied. The optimum conditions for the decolorization of the dye were initial concentration of 10 mg L⁻¹ of dye, pH 4, and Nb₂O₅/Fe²⁺ catalyst concentration of 0.5 g L⁻¹/50 mg L⁻¹. The optimum value of H₂O₂ concentration for the conditions used in this study was 700 mg L⁻¹. Moreover, the efficiency of the Nb₂O₅/photo-Fenton hybrid process in comparison to photo-Fenton alone and a dark Fenton process as a control experiment to decolorize the RhB solution has been investigated. The combination of photo-Fenton and Nb₂O₅ catalysts has been proved to be the most effective for the treatment of such type of wastewaters. The results revealed that the RhB dye was decolorized in a higher percent (78 %) by the Nb₂O₅/photo-Fenton hybrid process (Fe²⁺/H₂O₂/Nb₂O₅/UV) than by the photo-Fenton process alone (37 %) and dark Fenton process (14 %) after 120 min of treatment. Moreover, the Nb₂O₅ catalyst as a heterogeneous part of the photocatalytic system was demonstrated to have good stability and reusability.

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