A flexible Ag2S QD sensitized TiO2 Janus photocatalytic nanofiber membrane for visible light organic pollutant degradation and COD removal

Abstract

This study aims to develop a reusable, self-supporting Ag₂S/TiO₂ photocatalyst for the degradation of tetracycline hydrochloride (TCH) and chemical oxygen demand (COD) removal under visible light irradiation. The flexible Ag₂S/TiO₂ nanofibrous membranes (NFMs) were prepared by electrospinning and subsequent calcination followed by the deposition of Ag₂S quantum dots (QDs) on TiO₂ nanofibers by the successive ionic layer adsorption and reaction (SILAR) method. The precise deposition of Ag₂S QDs preserved the self-standing properties of TiO₂ NFM, and the amount of Ag₂S QDs was regulated by altering precursor concentration while keeping the SILAR cycles constant. The SEM-EDX, XPS, TEM, and PL measurements confirmed the formation of an Ag₂S/TiO₂ heterojunction, which lowered the band gap energy to 2.68 eV. This band gap engineering reduced the electron-hole pair recombination and accelerated TCH degradation and COD removal under visible light. The photocatalytic degradation of TCH obeyed pseudo-first-order reaction dynamics, showing a strong influence of the Ag₂S amount and the pH of the TCH solution on degradation. The Ag₂S/TiO₂ heterojunction exhibited superior photocatalytic degradation, achieving up to 85.6 % in 90 min, compared to 66.6 % for TiO₂ NFM. The TCH degradation rate significantly increased from 0.012 min⁻¹ for TiO₂ NFM to 0.029 min⁻¹ for Ag₂S/TiO₂ NFM, marking a 2.4-fold improvement. Furthermore, the optimal TCH degradation occurred at neutral pH 7, while COD removal (94.2 %) from pharmaceutical samples was most effective at acidic pH 5, demonstrating the significant influence of pH on photocatalytic pollutant removal. The as-prepared Ag₂S/TiO₂ NFM demonstrated strong recyclability, retaining high efficiency after five cycles of use, while maintaining its self-supporting properties, allowing for easy separation after application.