Eco-friendly synthesis of copper sulphide nanoparticles using rice starch water and their photocatalytic application for Congo red dye degradation

Synthetic dye water pollution is an ongoing environmental issue, especially due to the extensive application and toxicity of dyes such as Congo Red. When released into water bodies such as rivers and lakes, these dyes cause severe damage to the environment and human health. This study seeks to solve this problem by investigating a low-cost and biocompatible method for the removal of Congo red dye from water using copper sulphide (CuS) nanoparticles as a photocatalyst. The CuS nanoparticles were prepared through a green method using rice starch water as a green reducing and stabilising agent. Several analytical methods—such as X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR), and UV-Vis spectroscopy—were applied to examine the structural, morphological, and optical characteristics of the nanoparticles. The findings indicated that the CuS samples consisted of a hexagonal crystal structure, and their shape and size depended on the copper to sulfur molar ratio used in the synthesis. For instance, the 1:1 Cu: S ratio sample (Sample A) produced larger, denser clusters, while those prepared using greater sulfur content—Samples B (1:4) and C (1:7)—were more porous and layered in shape. Photocatalytic activity under visible light showed that these nanoparticles were highly efficient in decomposing Congo red dye. Among the samples tested, Sample C (1:7) was the most active, decomposing about 89.49 % of the dye in 60 min. Sample B was second with a removal of 86.14 %, while Sample A registered 75.76 %. The increased activity in sulfur-rich samples is most likely due to an increased surface area and improved separation of photo-generated charge carriers. The response is focused on the possible use of CuS nanoparticles as a potent, effective, and sustainable method of environmental remediation, particularly the degradation of toxic dyes like Congo red from wastewater. The response addresses the optimisation of the synthesis conditions to create the structural and functional properties of nanoparticles to attain enhanced photocatalytic activity. • CuS nanoparticles synthesized using precipitation method with rice starch water as a natural capping agent. • A green alternative minimizes toxic chemical usage, with sustainable research practices. • Superior stability and controlled growth of CuS nanoparticles. • Suitable for applications in catalysis, sensing, and green energy solutions.