Unveiling the highly efficient binary NH2-MIL-125 (Ti) MOF/CuS photocatalyst with Z-scheme for efficient removal of enrofloxacin and Cr(VI): DFT, toxicity and mechanism insight

Abstract

Antibiotics and heavy metal ions removal from contaminated water is a demanding environmental concern. The present study reports a novel Z-scheme heterostructure NH₂-MIL-125(Ti)/CuS (NMT/CuS) nano-photocatalyst for the removal of enrofloxacin (ENR) and hexavalent chromium (Cr(VI)) contaminants under visible-light illumination (300 W-Xe). Based on the structural and optical study findings, it was found that the uniform distribution of CuS nanoflakes on Ti-MOF nanorods led to the construction of p-n heterojunctions having large surface area, which avoided agglomeration-induced inactivation and enhanced the spectral response by facilitating the separation and utilization of charge carriers. To achieve higher Cr(VI) reduction and ENR degradation efficiencies, various physiochemical properties were studied and optimized. Based on the kinetic studies and the resulting Z-Scheme mechanism pathway, it was found that NMT/CuS heterojunction showed 97.5 % removal efficiency for ENR (pH-5.0, dosage-20 ppm) and 95.5 % Cr(VI) reduction efficiency (pH-3.0, dosage-50 ppm) within 120.0 min of reaction, leading to a higher removal rate than pristine materials. A deeper understanding of the electronic properties of NH₂-MIL-125(Ti) and CuS materials was calculated through DFT calculations. By using LC-ESI/MS and DFT Fukui Index calculations, the degradation pathway of ENR were monitored. Moreover, the results obtained from toxicity study (TEST) of the identified photoproducts shows that most of the degraded products display less toxic characteristics than ENR. Additionally, the composite is highly reusable and can be recycled six times. This study sheds light on the potential of MOF-based composite photocatalysts offering an efficient and sustainable method of addressing complex water pollution problems.