Degradation of CV dye by the as-synthesized Fe0–TiO2 supported clinoptilolite under UV and solar irradiations

Abstract

Textile industries release toxic organic dyes into wastewater, harming aquatic ecosystems and affecting photosynthesis. This study aims to synthesize a photocatalyst for the efficient degradation of crystal violet (CV) dye in aqueous media. Titanium dioxide (TiO₂) is the most preferable photo-catalyst, but its fast electron–hole recombination rate and low adsorption capacity have limited its applications on a large scale. To enhance the adsorption and degradation efficiency, a TiO₂-supported clinoptilolite (CP) and a porous composite of zerovalent iron (Fe⁰) co-doped with titanium dioxide/clinoptilolite (Fe⁰–TiO₂/CP) were synthesized using sol–gel and borohydride reduction methods, respectively. The effects of various parameters like acidity, temperature and concentration on the photo-catalytic activity, morphological and micro-structural features and surface areas of different TiO₂/CP and Fe⁰–TiO₂/CP composites were characterized by various techniques such as X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), Fourier transform infrared (FTIR) spectroscopy, UV-Visible spectroscopy, thermogravimetric (TG) and differential thermogravimetric (DTG) analyses and Brunauer–Emmett–Teller (BET) isotherm. The as-synthesized composites (TiO₂/CP and Fe⁰–TiO₂/CP) were used as photocatalysts to remove CV dye from water. The parent CP and TiO₂ achieved 51% and 58% removal efficiency of CV dye under UV radiation, respectively. The 0.25 M TiO₂/CP composite showed the highest degradation efficiency (92.3%) under UV radiation, while 0.1 M TiO₂/CP performed best under solar radiation (88.5% removal) in 120 minutes. Theoretical analysis via kinetic models revealed that the adsorption and degradation processes of CV dye followed pseudo-second-order (PSO) and pseudo-first-order (PFO) kinetic models, respectively. The TiO₂/CP composite mainly produces hydroxyl radicals (˙OH) during dye degradation, while Fe⁰–TiO₂/CP generates both ˙OH and superoxide radicals (˙O₂⁻). This ˙O₂− radical enhances the degradation efficiency of Fe⁰–TiO₂/CP due to Fe⁰'s favorable reduction potential. CV mineralization occurs through two pathways: N-de-methylation and hydroxyl radical attack on the central carbon, leading to degradation and complete mineralization. Moreover, the structure, morphology and particle size of the composite play vital roles in the extent of their photocatalytic efficiencies. Therefore, a combination of compositional and structural engineering of TiO₂-based photocatalysts is expected to give better device performance. However, further investigation is needed in the near future.