Rational design of BiOI@C-UIO-66 binary catalyst: Interfacial BiOI engineering for sustainable rhodamine B dye detoxification under low-power visible light

A series of novel metal-organic-framework (MOF)-based heterojunctions were fabricated by integrating calcinated UIO-66 (C-UIO-66) into BiOI semiconductor. The binary catalyst performance for rhodamine B (RhB) decomposition was in the order of BiOI@C-UIO-66 (8 wt.% wt.)> BiOI@C-UIO-66 (16 wt.%) > BiOI@C-UIO-66 (4 wt.%)> BiOI@C-UIO-66 (24 wt.%)> BiOI@UIO-66 >BiOI. BiOI@C-UIO-66 (8 wt.%) showed a boosted photocatalytic performance, surpassing the RhB removal by ~38% when compared to pristine BiOI. Electrochemical impedance spectroscopy revealed that BiOI@C-UiO-66 exhibited lower charge-transfer resistance, indicating enhanced electron transfer and more efficient electron-hole pair separation due to heterojunction formation. Statistical modeling for RhB degradation employed a Box-Benken method. The process reached 98.2% RhB degradation using the optimized model parameters: pH 6, illumination time of 38 min, and composite mass of 0.8 g/L. Excellent catalyst reusability was observed with minor (< 2%) loss in removal performance, where fast kinetics demonstrate the viability of BiOI@C-UIO-66 (8 wt.%) in real world scenarios. The reused material almost retained its main BiOI and C-UiO-66 phases with negligible Bi leaching, confirming good structural stability during repeated photocatalytic cycles. The radical trappers revealed the significant role of O 2 ˙ in photocatalytic dye decomposition. Germination rate and root length growth of mung bean seeds used as phytotoxicity indicators of the treated samples. The average root length and germination index for raw samples was 3.7 cm and 77.8%, which increased to 4.5 cm and 94.2% after treatment, an indicator of harmless end products. COD analysis revealed that decolorization does not necessarily correspond to complete mineralization of RhB. The mechanisms of RhB removal consists of complex radical degradation and physicochemical adsorption-interaction processes.