BiOCl-Coated UiO-66-NH2 Metal-Organic Framework Nanoparticles for Visible-Light Photocatalytic Cr(VI) Reduction

Pollutants in wastewater, such as Cr(VI) is a continuous threat to our ecological system and human well-being because of its high noxiousness and latent carcinogenicity. Photocatalytic Cr(VI) reduction is the most suitable and eco-friendly way to convert the toxic Cr(VI) to environmentally friendly Cr(III). Porous metal-organic frameworks (MOFs) based nanocomposites are emerging green photocatalysts for Cr(VI) reduction due to their unique characteristics such as high photoconductivity, large surface area, and suitable porous structure. Herein, the preparation of ultrathin BiOCl sheets over UiO-66-NH2 is reported for the first time at room temperature via a simplistic in situ synthetic process to yield a series of UiO-66-NH2@BiOCl-UTN's heterogeneous nano composites. The activity toward Cr(VI) reduction was tested under visible-light. UiO-66-NH2@BiOCl-UTN's heterogeneous nanocomposites exhibited better performance as equated to individual BiOCl and UiO-66-NH2, particularly the composite with Bi3+ mole ratio of 5 mM surpassed other composites for photocatalytic Cr(VI) reduction. Furthermore, boosted visible-light absorption (lambda > 420 nm) was observed in the presence of -NH2 moiety on the organic linker. The excellent photocatalytic activity was attributed to the synergistic effect between BiOCl and UiO-66-NH2 for the effective separation of photogenerated electron-hole suppressing their recombination. Through active species trapping experiments, electron spin resonance measurements, and electrochemical analysis, the reliable mechanism was predicted and confirmed. Moreover, heterogeneous nanomaterial retained its structure and activity for four consecutive cycles demonstrating its superior stability.