Inverse opal TiO₂-CdS photonic crystal beads with slow light effect for photocatalytic degradation

Photocatalytic oxidation technology using solar energy is an effective strategy to solve environmental pollution and energy shortage. To avoid angle dependence of traditional photonic crystal photocatalysts and address the limitations of high charge recombination rate and low light utilization of TiO₂, this study proposed a novel inverse opal TiO₂/CdS photonic crystal beads (IO TiO₂/CdS PCBs) photocatalyst. By leveraging the synergistic coupling of PCBs’ slow light effect and TiO₂/CdS heterojunction, the photocatalytic activity was significantly enhanced. The results revealed that the PCBs matching the blue edge with TiO₂′s electronic band gap (IO TiO₂-140 PCBs) exhibited the highest apparent rate constant of 0.01901 min⁻¹. By introducing CdS to form a heterojunction with TiO₂, the photocatalytic performance was further improved by effectively inhibiting the recombination of photogenerated carriers. The degradation rate of RhB reached 96.6 % in 60 min, outperforming that of IO TiO₂ at 65.1 %, with the rate constant increasing by 3.1 times. Electron spin resonance and trapping experiments indicated that h⁺ was the main active specie, and the possible reaction mechanism path was proposed. The combination of “extrinsic” modifications by doping CdS and “self-structural” modifications by shaping TiO₂ into periodic IO PCBs structure provided a systematic insight on the design of novel photocatalysts.