Algal carbon quantum dots/Bi2MoO6 S-scheme heterojunction with enhanced visible-light photocatalytic degradation for ciprofloxacin

Abstract

The formation of S-scheme heterojunctions offers a viable strategy for enhancing photocatalytic efficiency in tackling organic contaminants. However, the green, low-cost, easy-to-synthesize S-scheme heterojunction is critical to further large-scale production. In this study, we successfully developed a new, eco-friendly, and cost-effective S-scheme heterojunction photocatalyst, Carbon quantum dots prepared from Sargassum horneri / Bi₂MoO₆ (SCQDs/BMO) utilizing an in-situ hydrothermal method. Carbon quantum dots derived from marine macroalga Sargassum horneri (SCQDs) are integrated with Bi₂MoO₆ semiconductors to formulate the groundbreaking catalytic material. The results affirm that SCQDs’ incorporation generated an internal electric field (IEF) at SCQDs-BMO interfaces, significantly enhancing charge separation. Moreover, SCQDs act as electron capturers to enhance carrier separation. At the same time, during the composite process, the carbon dots can reduce Bi³⁺ to Bi⁰. The high conductivity of Bi further enhances the electron transport capability of the system, working synergistically with the internal electric field to promote the separation and migration of charge carriers. This optimization improves the interfacial charge transfer pathway between BMO and SCQDs. Thus, SCQDs/BMO exhibits superior photocatalytic degradation for ciprofloxacin (CIP) under visible light, up to 97.7 % in 180 min, whose rate constant is 2.6 times that of BMO. The primary active agents, including ·O₂⁻/·OH, produced on the surface of SCQDs/BMO are crucial in the photodegradation of CIP. The potential intermediates, degradation pathways, and underlying mechanisms have been clearly outlined. This study offers an efficient and environmentally friendly method of developing high-activity S-scheme heterojunction photocatalysts for treating antibiotics wastewater.