Enhanced adsorption and photocatalytic degradation of tetracycline antibiotics through novel I-Bi/Bi₂WO₆@MWCNTs heterostructure composite photocatalyst

Bismuth-based photocatalysts proved to have remarkable photoactivity for antibiotic degradation from water. However, the two significant challenges of bismuth-based photocatalysts are the fast charge recombination rate and higher energy band gap. This study successfully synthesized a novel I-Bi/Bi₂WO₆/MWCNTs (C-WBI) heterostructure composite photocatalysts with shorter energy band-gap and higher charge production capability through interfacial amidation linkage. The photochemical characterization of C-WBI confirms that the interfacial linkage between MWNCTs and I-Bi/Bi₂WO₆ (WBI) significantly boosted the charge production capacity and broadened visible-light harvesting (508nm), resulting in improved photocatalytic activity. As anticipated, optimized 7%C-WBI shows remarkable adsorption and photocatalytic activity for TC removal compared to pristine WBI (2.27 times) under visible light. TC removal was enhanced to 96.75% from 71.58% (WBI) at mild operating conditions of pH 8, photocatalyst loading of 20mg, and an initial TC concentration of 20 mg/l. Adsorption equilibrium was best fitted to Langmuir isotherm and pseudo-first-order kinetics with R² of 0.998 and 0.997, respectively. In contrast, the photodegradation of TC is best described by pseudo-first-order kinetics with a correlation coefficient of 0.99 and a reaction rate of k_obs of 0.0205 min^-1. The effect of co-existing ions (Cl^-, SO₄²⁻ and HCO₃⁻) reveals that the presence of Cl^- notably inhibited the photocatalytic reaction rate, reducing it to 0.0161min⁻¹. Quenching experiments identified •O₂⁻ and h⁺ radicals as key contributors to TC degradation, accounting for 63.02% and 60.8%, respectively. Furthermore, 7%C-WBI demonstrated outstanding reusability (82.05%) over 5 consecutive cycles with no obvious changes, thereby confirming the stability of the synthesised composite photocatalysts.