Direct Growth of Nitrogen-Doped Carbon Quantum Dots on Co₉S₈ Passivated on Cotton Fabric as an Efficient Photoelectrode for Water Treatment

Heterogeneous growth of photocatalysts on different porous substrates is a solution to avoid secondary pollution caused by composite photocatalysts themselves. However, the heterogeneous growth of composite photocatalysts with nitrogen-doped carbon quantum dots (NCQDs) inclusions─introduced during synthesis─impedes the direct growth on the substrate. To overcome this problem, NCQDs were grown on a Co₉S₈ (NCQDs-G@Co₉S₈) layer, decorated on cotton fabric. This optimal coupling mode of NCQDs and Co₉S₈ showed 54% degradation, compared to 33% dye degradation via NCQDs-doped Co₉S₈ (NCQDs-D@Co₉S₈). The change in the crystal structure and its lower loading on fabric results in significantly lower performance of NCQDs-D@Co₉S₈. Even with the combination of both surface growth and doping (NCQDs-DG@Co₉S₈), the performance was still limited to 42%. In addition, the optimum growth concentration of NCQDs on Co₉S₈ was observed for 7.5 w/w %, resulting in 92% photocatalytic activity (PCA) in 80 min. Comparing different surface states formed in NCQDs using different solvents, water-based surface states (oxygen-rich surface) are most suitable for the dye degradation. NCQDs-G@Co₉S₈ also offers 67% Cr-VI reduction to Cr-III, showing its suitability for both inorganic and organic compounds. Better electrode performance was related to suitable charge separation of the composite, where -OH groups mainly contribute in the photocatalytic dye degradation..