# CaCO3/BiO2−x/CdS Composite with Rapid Photocatalytic Reduction of Cr(VI) Under Visible Light

## TL;DR

A new composite material was created to efficiently reduce toxic chromium under visible light, outperforming existing materials.

## Contribution

The study introduces a ternary composite with lattice distortion induced by calcium carbonate, enhancing photocatalytic performance.

## Key findings

- The CCO/BO/CS composite achieved 94.53% Cr(VI) reduction within 30 minutes under visible light.
- The composite's performance is 94.6 times higher than pure BiO2−x and 6.1 times higher than pure CdS.
- Enhanced performance is attributed to improved charge separation and lattice distortion from calcium carbonate.

## Abstract

CaCO3/BiO2−x/CdS (CCO/BO/CS) ternary composite photocatalyst was synthesized via a hydrothermal method combined with chemical precipitation, and its performance in the photocatalytic reduction of hexavalent chromium (Cr(VI)) under visible light was systematically investigated. Compared with pure BiO2−x, CdS, and binary BiO2−x/CdS composites, the CCO/BO/CS system exhibited significantly enhanced Cr(VI) reduction activity. Specifically, the CCO/BO/CS (0.75:1:2 wt) composite achieved a Cr(VI) reduction efficiency of 94.53% within 30 min of visible light irradiation—approximately 94.6 times and 6.1 times higher than those of BiO2−x (1.0%) and CdS (15.52%). Photoelectrochemical and trapping experiments revealed that the enhanced performance stems from improved charge separation, accelerated interfacial electron transfer, and the promotional role of CaCO3—likely through lattice distortion—rather than direct photocatalytic participation. This study highlights the innovation of incorporating low-cost, eco-friendly calcium carbonate into semiconductor-based photocatalysts to induce lattice distortion for enhanced charge separation, as an effective strategy for improving the reduction efficiency of Cr(VI).