Fabrication of AgCl/Bi24O31Cl10 for Vis-Light Activated Photocatalytic Degradation of Tetracycline and Other Related Phenolic Organics in Aqueous Systems

Abstract

Photocatalysis has attracted attention as a viable technology for use in the environmental and energy generation fields. In the last couple of decades, researchers have continued to develop new photocatalysts in the area of photocatalysis for environmental remediation. In this study, a AgCl/Bi24O31Cl10 composite heterostructure was synthesized. Varying ratios of AgCl nanoparticles were immobilized onto the Bi24O31Cl10 rod-like structure. The physical and optical properties of the synthesized catalysts were characterized using a range of techniques. The photocatalytic activity of the catalysts was investigated by the degradation of 2,4-dichlorophenoxy acetic acid (2,4-D) and tetracycline (TC) under visible light irradiation. The performance of the composite photocatalysts was 18 and 3.4 times better in 2,4-D and TC photodegradation when compared to Bi24O31Cl10 alone. The improved photocatalytic performance was attributed to the surface plasmon resonance (SPR) effects of the AgCl nanoparticles deposited on the surface of the Xwt%AgCl/BOC thereby improving the separation of the electron-hole pair. The effects of the initial contaminant concentration, pH, and photocatalyst loading were investigated. Trapping experiments were also carried out to deduce the reactive species responsible for the degradation process and a preliminary mechanism of degradation was proposed. Mineralization of 2,4-D and TC at 65% and 63% efficiency was measured after 24 h and the potential for reusability of the as-synthesized photocatalyst was established.

It was also important to investigate the activity of the semi-conductor materials with real water samples. The photocatalytic activity of the photocatalyst was investigated in the secondary effluent of a wastewater treatment plant (WWTP) in Pretoria, South Africa for the degradation of phenol under visible light irradiation. The experimental design was done using the Taguchi method L16 orthogonal tray with three factors (pH, initial phenol concentration and photocatalyst dosage) and four levels. The results showed that pH was the highest-ranked significant factor influencing the degradation rate, closely followed by the initial concentration of the pollutant. The photocatalyst dosage had the least significant impact on degradation. The effects of individual anions components such as Cl-, NO3-, NO2- and SO42- and cations such as Ca2+, Mg2+, Zn2+ and K+ were investigated. While Cl- did not negatively influence the degradation rate, the results show that NO3- and SO42- inhibit the degradation of phenol. More specifically, total inhibition of the degradation process was achieved when nitrite concentration of 20 ppm or more was added. This illustrates that nitrite concentrations ≥ 20 ppm should be removed from wastewater prior to photocatalytic degradation. The cations investigated promoted the degradation of phenol. Generally, there was enhanced degradation in the water matrix when compared to DI water and the results revealed improved degradation efficiency due to the cumulative impact of various components of the wastewater. This work reports a promising photocatalyst for the visible-light-driven removal of pollutants such as phenol, tetracycline and 2,4-dichlorophenoxy acetic acid from wastewater.