Immobilization of peroxidase-like G-quadruplex/hemin on CNTs-NH2 for efficient degradation of phenol

Abstract

The presence of phenol in coal-chemical engineering wastewater is considered a serious environmental issue. The use of enzymes to degrade phenol has received wide attention. G-quadruplex can combine with hemin to form G-quadruplex/hemin, which shows peroxidase-like activity and can be used to degrade phenol. In this work, a novel CNTs-NH₂@G-quadruplex/hemin was designed using a single-stranded DNA (ssDNA) that contained G-rich fragments and T-rich fragments. The G-rich fragments assembled with the hemin to form G-quadruplex/hemin; the pyrimidine group of the T-rich fragment could form stable chemical bonds with the amino group, which could be used for immobilization. Characterization analysis of FTIR, XRD and TEM showed that the CNTs-NH₂@G-quadruplex/hemin was successfully prepared. Meanwhile, the activity and phenol degradation ability for CNTs-NH₂@G-quadruplex/hemin were studied in detail, and the effects of pH, temperature, initial phenol concentration, H₂O₂ concentration and reusability on the degradation efficiency of phenol were also explored. The results showed that when immobilized, the CNTs-NH₂@G-quadruplex/hemin presented good activity, especially under conditions of temperature 30 °C and pH 7.0. Notably, the maximum reaction velocity of CNTs-NH₂@G-quadruplex/hemin was increased from 0.016 mM mg⁻¹ min⁻¹ (free enzyme) to 0.056 mM mg⁻¹ min⁻¹. For phenol degradation ability, it was observed that under the conditions of temperature 30 °C, pH 7.0, initial phenol concentration 40 mg L⁻¹, H₂O₂ concentration 120 mM, enzyme dose 40 mg L⁻¹, more than 90% of phenol could be degraded within 600 min. In addition, the CNTs-NH₂@G-quadruplex/hemin still maintained high activity after 10 cycles of phenol removal, demonstrating its appealing potential for practical applications.