Extending the visible light absorption of -NH2-UiO-66 through diazotization reaction for photocatalytic chromium (VI) reduction

The optical properties of NH2-UiO-66 as a visible light-active metal organic framework was further enhanced through the diazotization reaction with p-conjugated 1-naphthol reagent. Diffuse reflectance UV-Vis spectrum of diazotized MOF, named as Azo-UiO-66, exhibited a significant red shift compared to unfunctionalized NH2-UiO-66 due to the formation of diazo compound. Also, Tauc calculations indicated considerable decrease in band gap energy from 2.68 to 1.7 eV, resulting in improvement of visible light harvesting. Furthermore, other physicochemical techniques, e.g., X-ray diffraction (XRD), N-2 adsorption-desorption analysis, thermogravimetric analysis (TGA), energ-dispersive X-ray (EDX), and CHN elemental analyses demonstrated the successful MOF diazotization with 1-naphthol and preservation of NH2-UiO-66 framework upon post-modification process. The reduction of hexavalent chromium, Cr(VI), as a serious contaminant in wastewater to less toxic Cr(III) was performed over prepared photocatalyst, which demonstrated the positive role of ligand functionalization and enhancement of visible light absorption on overall photocatalytic performance of Azo-UiO-66.

Automated summary

The optical properties of NH2-UiO-66 were improved through a diazotization reaction with a p-conjugated 1-naphthol reagent, resulting in the formation of Azo-UiO-66. The Azo-UiO-66 showed a significant red shift in the diffuse reflectance UV-Vis spectrum compared to unfunctionalized NH2-UiO-66. Tauc calculations indicated a decrease in band gap energy, leading to improved visible light harvesting. Various physicochemical techniques confirmed the successful diazotization of the MOF and preservation of its framework. The Azo-UiO-66 also demonstrated enhanced photocatalytic performance in the reduction of Cr(VI) to less toxic Cr(III) in wastewater.