Visible-light-driven calcium alginate hydrogel encapsulating BiOBr0.75I0.25 for efficient removal of oxytetracycline from wastewater

Abstract

Oxytetracycline (OTC), a widely used antibiotic, poses significant environmental risks due to its persistence in ecosystems. This study introduces a visible-light-driven photocatalytic hydrogel system for effectively removing OTC from wastewater. The system employs calcium alginate (CA) hydrogel beads encapsulating a BiOBr0.75I0.25 solid solution, which utilizes the synergistic effects of adsorption and visible-light-driven photocatalysis. The BiOBr0.75I0.25 solid solution photocatalyst was synthesized via a solvothermal method, while CA hydrogel beads encapsulating BiOBr0.75I0.25 were prepared through ionic gelation of sodium alginate with calcium chloride. The novel hydrogel, CA-BiOBr0.75I0.25, demonstrated rapid adsorption, capturing over 50 % of OTC within 30 min and achieving a 90.92 % degradation rate within 60 min under visible light. This performance is associated with the unique petal-like structure of BiOBr0.75I0.25 and the high surface area of the hydrogel, facilitating efficient charge separation and radical generation critical for photocatalytic activity. Additionally, the system showed excellent stability and reusability, maintaining an 83 % removal efficiency after five cycles. These findings highlight the potential of this novel hydrogel as a sustainable solution for advanced wastewater treatment technologies.