Hierarchical structure and electronic effect promoted degradation of phenols over novel MnO2 nanoprisms via non-radical mechanism

Abstract

In this work, a novel 3D hierarchical cryptomelane-type manganese oxide nanocomposite (APM-OMS-2) was prepared via pre-incorporation with ammonium phosphomolybdate (APM) as an additive for the first time. The APM dosage not only transferred the material morphology from 1D to 3D, but also affected the crystal phasze, textural properties and redox ability. APM-OMS-2 displayed a unique nanoprism morphology coated by APM as the outer-sphere and consisted of a hierarchical framework. The catalytic ability of APM-OMS-2 was examined by the degradation of phenolics via peroxymonosulfate (PMS) activation in various water matrix. The optimized catalytic system gave a 95 % degradation rate and a 83 % mineralization rate of 4-chlorophenol (20 mg/L) with 200 mg/L of APM-OMS-2 and 100 mg/L of PMS within 60 min. According the first-order kinetic study of 4-chlorophenol degradation, APM-OMS-2/PMS system gave a higher initial reaction rate constant at 0.2014 min−1 and a lower activation energy at 29.2 kJ/mol than OMS-2/PMS because its hierarchical structure and textural properties were beneficial to mass transfer, diffusion and reaction between catalyst and reactants. Characterizations further suggested that PMS activation was conducted by 1O2-mediated oxidation along with MnIV/MnIII redox cycles. Moreover, electrochemical analysis indicated that mediated electron transfer contributed to the catalytic performance via the outer-sphere electronic interaction of the core/shell nanocomposite. This study provides a very simple method for the synthesis of 3D cryptomelane-type MnO2 towards oxidative degradation of aqueous contaminants.