Polyoxometalate Derived Materials as Laccase-Mimic Nanozyme and Reduction Catalyst for p-Nitrophenol Remediation in Water

p-Nitrophenol (PNP), a highly toxic water pollutant, poses significant risks to human health and the environment. For detecting PNP, a colorimetric method utilizing a nanozyme that mimics laccase activity presents a viable approach. In this study, PV₁₄@MIL-88A, a robust nanozyme with superior laccase-mimic capabilities, was synthesized by incorporating Na₇H₂[PV₁₄O₄₂] (PV₁₄) into MIL-88A, a metal-organic framework (MOF). This nanozyme demonstrates optimal laccase-mimicking activity, enabling effective PNP detection via colorimetry and digital image colorimetry using smartphones. Theoretical analyses suggest that the outstanding laccase-mimic activity of PV₁₄@MIL-88A is derived from the optimized d-band center in PV₁₄. Upon calcination with dicyandiamide (DCDA), PV₁₄@MIL-88A transforms into Fe₂O₃/VO₂@NCNF. In the presence of NaBH₄, Fe₂O₃/VO₂@NCNF facilitates the conversion of PNP to p-aminophenol (PAP), an essential precursor in paracetamol synthesis. The interaction between Fe₂O₃ and VO₂ in Fe₂O₃/VO₂@NCNF enhances adsorption and subsequent reduction of PNP. The saturation magnetization of Fe₂O₃/VO₂@NCNF reaches 25 emu g⁻¹, which supports efficient magnetic separation in the reduction process. This study not only advances an effective method for PNP detection but also facilitates its transformation from a hazardous pollutant into a valuable chemical precursor.