Design of AgI/BiVO₄ heterostructures for photocatalytic antibiotic removal and antimicrobial action

Semiconductor-based photocatalysis has emerged as a promising strategy for addressing environmental pollution, particularly in water treatment. Recent advances focus on designing heterojunction nanocomposites to enhance visible-light activity and charge separation efficiency. In this study, AgI/BiVO₄ nanocomposites were prepared using a thermal-assisted co-precipitation technique. To examine their structural and optical properties, a suite of characterization methods, including energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and diffuse reflectance spectroscopy (DRS), was utilized. EDX analysis and Raman spectroscopy confirmed the incorporation of Ag, I, Bi, V, and O into the composite. TEM revealed quasi-spherical nanocomposite particles (100–200 nm), while FE-SEM showed bright AgI nanoparticles distributed on the BiVO₄ surface. XRD analysis confirmed the presence of both the scheelite-type crystalline phase of BiVO₄ and the hexagonal β-phase of AgI. The crystallite sizes of AgI were estimated to be 23.0, 31.7, and 36.3 nm for samples synthesized with 0.005, 0.02, and 0.05 mol of AgI, respectively, alongside a constant 0.05 mol of BiVO₄. These samples were labeled AgI/BV1, AgI/BV2, and AgI/BV3, respectively. An increasing AgI content led to a gradual narrowing of the bandgap from 2.4 eV for pure BiVO₄ down to 2.35, 2.0, and 1.9 eV, indicating improved charge transport and light absorption capabilities. This bandgap reduction supports more efficient separation of photogenerated electrons and holes, facilitating the production of reactive radicals such as •O₂⁻ and •OH. Under visible light, AgI/BV3 achieved the highest tetracycline degradation efficiency (81%) and the lowest MICs against P. aeruginosa and S. aureus, indicating strong antimicrobial activity. Overall, the findings underscore the effectiveness of AgI/BiVO₄ nanocomposites as photocatalysts, particularly in environmental applications. By adjusting the AgI-to-BiVO₄ ratio, their performance in degrading contaminants, especially in hospital wastewater, can be optimized.