Facile synthesis of laccase mimic Cu/H3BTC MOF for efficient dye degradation and detection of phenolic pollutants

Abstract

Herein, we report an effectual method for designing a novel form of nanozyme laccase mimic namely Cu/H₃BTC, using copper ions and 1,3,5-benzene tricarboxylic acid (1,3,5-H₃BTC). This Cu-based metal-organic framework (MOF) was synthesized through a simple procedure of mixing of two usual reagents at room temperature. Amido Black 10B (AB-10B) was chosen as a model dye for degradation consequences. Results showed that Cu/H₃BTC MOF revealed significantly higher catalytic efficacy under certain conditions like high pH, extreme temperature and high salt conditions and it has long-term storage stability, which can lead to a significant decline in catalytic activity of laccase. In addition, the degradation of AB-10B was up to 60% after ten cycles, showing good recyclability of Cu/H₃BTC MOF. The UV-visible spectral changes clearly showed that Cu/H₃BTC MOF is an effective laccase mimic for the degradation of azo dye AB-10B, which was degraded more easily within the time duration of 60 min. The Cu/H₃BTC MOF also possessed fundamental activities like laccase with regard to oxidation of the phenolic compounds. Moreover, a technique for the quantitative detection of epinephrine by Cu/H₃BTC MOF was established. These findings help to understand the laccase-like reactivity and provide a basis for the future design and application of metal-based catalysts.

Fig. 1. Structure of Cu²⁺ reacting with H₃BTC to form Cu/H₃BTC MOF. Colour code: Cu (dark grey); O (red); C (light grey); H (white).

Fig. 2. (A) XRD patterns of freeze-dried Cu/H₃BTC MOF. (B) FTIR spectrum of Cu/H₃BTC MOF.

Fig. 3. (A) SEM (B) EDX spectrum (inset) percent composition. (C) Nitrogen adsorption/desorption isotherm of Cu/H₃BTC MOF to measure the specific surface area. (D) Distribution of pore size of Cu/H₃BTC MOF.

Fig. 4. (A) XPS spectrum of Cu 2p. (B) XPS fully scanned spectrum of Cu/H₃BTC MOF.

Fig. 5. Photos of MOFs prepared (A) by mixing Cu²⁺ with different nucleotides, guanosine and (C) by mixing H₃BTC with several metal ions. (B and D) Laccase-like activity by assessing 2,4-DP and 4-AP (0.1 mg mL⁻¹) with different nucleotides/metal (0.1 mg mL⁻¹) in MES buffer pH 6.8.

Fig. 6. (A) AB-10B dye degradation with Cu/H₃BTC MOF and UV-vis spectra were recorded every five minutes (till 60 min), (inset) before and after degradation. (B) percent degradation of AB-10B catalysed by Cu/H₃BTC MOF or laccase as function of time.

Fig. 7. Efficiency of Cu/H₃BTC MOF and laccase on percent degradation at different (A) pH (B) temperature (C) NaCl concentration (D) reusability of Cu/H₃BTC MOF (E) storage stability of Cu/H₃BTC MOF and laccase.

Fig. 8. (A) The chemical structures of different tested phenols. (B) Catalytic efficacy of laccase and Cu/H₃BTC MOF to oxidize substrates.

Fig. 9. (A) Sketch and photographs of oxidizing epinephrine. (B) Kinetics oxidization of epinephrine (50 μg mL⁻¹) with 0.1 mg mL⁻¹ of laccase or Cu/H₃BTC MOF. (C) Scheme of oxidizing epinephrine. (D) Linear correlations among concentration of epinephrine and absorbance in presence of laccase and Cu/H₃BTC MOF.