Synergistic Photocatalytic Degradation of Organic Dyes and Immobilization of Heavy Metals by in Situ Conversion of Cd2+ into an Active Component on Carbon Nitride

Abstract

To address the challenging issue of the co-existence of inorganic heavy metals and organic pollutants in wastewater, this study proposes a “waste-to-catalyst” strategy. In it, a novel carbon nitride (CN)/Cd(OH)₂ nanocomposite was prepared by immobilizing toxic heavy metal ions (using Cd²⁺ as a model) from water onto CN via a simple stirring process, effectively converting them into active components of the CN nanocomposite. This nanocomposite exhibited outstanding dual functionality: it not only achieved highly efficient degradation of the malachite green (MG) dye (98.58% removal within 40 min), with its performance significantly outperforming some comparative samples, but also effectively converting trace Cd²⁺ into surface-active components of CN nanocomposite. This demonstrates a “waste-to-catalyst” approach for enhancing photocatalytic performance by loading trace heavy metal. This dual functionality was visually confirmed by a phytotoxicity test using soybean growth as a marker: after treatment with CN/Cd(OH)₂, the inhibition of soybean growth caused by MG and Cd²⁺ in the wastewater can be effectively eliminated. The increased charge separation and broadened light absorption are the main reasons for its high performance. This research offers a viable new strategy for the synergistic remediation of complex wastewater contaminated with both organic dyes and heavy metals.