Heterogeneous activation of hydrogen peroxide by cysteine intercalated layered double hydroxide for degradation of organic pollutants: Performance and mechanism

Abstract

A novel cysteine intercalated copper aluminum layered double hydroxide (CuAl-Cys-LDH) was synthesized and applied as heterogeneous catalyst for activating hydrogen peroxide (H2O2) to degrade rhodamine B (RhB) and 4-Nitrophenol (4-NP). The effects of initial pH, CuAl-Cys-LDH dosage, and H2O2 concentration on RhB and 4-NP removal were comprehensively investigated. The results indicated the intercalation of cysteine into the interlayer of LDH greatly enhanced its catalytic activity and stability. With 0.2 g/L CuAl-LDH and 50 mM H2O2, 93.7% of RhB and 80.2% of 4-NP could be removed in the CuAl-Cys-LDH activated H2O2 system. While the CuAl- LDH activated H2O2 system could only degrade 51.2% of RhB and 46.8% of 4-NP under the identical experimental conditions. Significantly, the CuAl-Cys-LDH catalyzed H2O2 system exhibited high degradation efficiency within a wide pH range from 4.0 to 10.0. Based on the electron paramagnetic resonance (EPR) tests and radical quenching experiments, it was inferred that •OH radical was the dominant species responsible for organic contaminants degradation. Mechanism study revealed that the intercalated cysteine in the interlayer of LDH strongly accelerated the rate-determining conversion of Cu(II) to Cu(I) by oxidation itself to cystine, thus enhanced the catalytic efficiency for H2O2 activation to produce •OH radicals. The findings of this work indicated that CuAl-Cys-LDH is a conveniently prepared and highly efficient and stable catalyst for the degradation of organic contaminants in environmental remediation.