Hydrogen peroxide modified and bismuth vanadate decorated titanium dioxide nanocomposite (BiVO4@HMT) for enhanced visible light photocatalytic growth inhibition of harmful cyanobacteria in water

Abstract

The persistence of harmful cyanobacterial algal blooms in aquatic ecosystems leads to health damage for various life forms. In this study, a photocatalyst active in the visible light range was prepared by combining BiVO₄ with hydrogen peroxide modified titanium dioxide (BiVO₄@HMT; for short), using an impregnation method. The catalyst was used to photocatalytically inhibit the growth of cyanobacteria collected from a bloom site. To infer the optimum pH for cyanobacterial growth, the effect of pH was studied. The growth of cyanobacteria was favoured in an alkaline environment at pH values in the range of 8–9.5 when analysed on the 20^th day of incubation. Structural and chemical analysis of pristine and composite nano-powders was performed using XRD, SEM, TEM and XPS, confirming the heterojunction formation, while optical and band gap analysis revealed increased visible light absorption and reduced band gap of the composite. A small strawberry seed-like assembly of BiVO₄ particles increased the light absorption in the 15%BiVO₄@HMT composite and increased the inhibition efficiency up to 2.56 times compared to pristine HMT at an exposure time of 6 h and cell concentration at 0.1 g L⁻¹ with an optimum catalyst dose of 1 g L⁻¹. The amount of chlorophyll ‘a’ decreased due to the generation of catalytically reactive species, especially holes (h⁺), which caused oxidative damage to the cell wall, cell membrane and antioxidants in algal cells. This study reports that visible light active nanocatalysts can be used as a promising method for reducing algal blooms in water bodies.