Morphology and band gap modification of flower-like BiOCl@CDs nanocomposites for photocatalysis.

Bismuth oxychloride (BiOCl) photocatalysts were synthesized using a simple, cost-effective sol-gel method and integrated with carbon dots (CDs) to form BiOCl@CDs nanocomposites. Three CD loadings (0.25, 0.75, and 1.0 wt%) were systematically investigated, and the composite containing 0.25 wt% CDs exhibited the highest photocatalytic performance. The chelating agent thiourea (CH4N2S) was used to promote porous flower-like morphologies with enlarged effective surface areas, while CDs served as photosensitizers and electron-transfer mediators to inhibit charge recombination. The experimental data confirmed that the crystalline BiOCl phase was completely retained upon CD incorporation due to the formation of interfacial Bi-C and C-O bonds between BiOCl and CDs. CH4N2S was identified as the chelating agent for tuning the morphology of BiOCl, which indirectly resulted in band gap energy (E g) narrowing from 3.39 eV to approximately 2.7-2.9 eV, thereby enabling visible-light operation. Although CD incorporation causes E g to increase slightly, the BiOCl@CDs heterostructures could be operated in the visible region and deliver superior photocatalytic performance owing to the enhanced charge separation at the BiOCl@CDs interfaces. The photocatalytic degradation of rhodamine B demonstrated that the BiOCl@CDs specimens prepared with CH4N2S achieved the highest photocatalytic reaction rate constant, confirming the suitability of these composites for treating dye-containing industrial wastewater.