Sonochemical preparation of powerful S-scheme Zr(HPO4)2/g-C3N4 heterojunction for photocatalytic degradation of rhodamine B under natural solar radiations

An effective Zr(HPO₄)₂/g-C₃N₄ S-scheme heterojunction was synthesized by sonochemical coupling of Zr(HPO₄)₂ nanoparticles as an oxidative photocatalyst [E_VB = +3.0 eV] with g-C₃N₄ nanosheets as an effective reductive photocatalyst [E_CB = −1.25 eV] for photocatalytic degradation of rhodamine B dye under natural solar radiation of 1000 W power. The physicochemical properties of the as-synthesized heterojunctions were investigated by X-ray diffraction [XRD], N₂-adsorption-desorption isotherm, diffuse reflectance spectrum [DRS], photoluminescence [PL], scanning electron microscope [SEM], X-ray photoelectron spectroscope [XPS], and high resolution transmission electron microscope [HRTEM]. The experimental results implied the agglomeration of Zr(HPO₄)₂ nanoparticles on g-C₃N₄ sheets which reduced the specific surface area of the solid specimen from 88 to 21 m²/g. The significant increase in the photocatalytic degradation rate of RhB dye with introducing Zr(HPO₄)₂ nanoparticles implied that Zr(HPO₄)₂ plays a crucial role in reducing the band gap energy and remarkable increasing in the rate of electron-hole separation. The photocatalytic experiments implied that incorporation of 5 wt% Zr(HPO₄)₂ on g-C₃N₄ sheets destroyed 98 % of RhB dye during 3 h of light illumination with pseudo-first-order rate of 0.048 min⁻¹. The remarkable enhancement in the photocatalytic performance of Zr(HPO₄)₂/g-C₃N₄ heterojunctions was ascribed to successful generation of an effective S-scheme heterojunction with strong redox power, utilizing of both hydroxyl and superoxide radicals in the degradation process and limiting the electron-hole recombination rate. Based on scavenger experiments and terephthalic acid PL analysis, the S-scheme pathway was chosen as the proposed mechanism for photocatalytic charge transfer. The as-synthesized Zr(HPO₄)₂/g-C₃N₄ heterojunction with exceptional redox power is considered a novel candidate for destructing organic pollutants that exist in industrial wastewater.