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.