Immobilization of chitosan-templated MnO2 nanoparticles onto filter paper by redox method as a retrievable Fenton-like dip catalyst

Abstract

By exploiting the hydrophilicity of cellulose filter paper (FP) and the excellent chelating property of chitosan (CH) for Mn²⁺, we have designed an efficient and retrievable dip catalyst MnO₂/CH-FP for Fenton-like degradation of methylene blue (MB) over a wide pH range from 2.8 to 11.2. The MnO₂ nanoparticles were uniformly immobilized in the CH-FP matrix by in-situ redox precipitation method where Mn(NO₃)₂ was treated with KMnO₄ at mild conditions. A series of MnO₂/CH-FP hybrids with different MnO₂ loading were fabricated via varying concentration of Mn(NO₃)₂ solution, and their structure-function relationships were discussed based on detailed characterization. The optimal catalyst 1.0MnO₂/CH-FP could cooperate with multiple low-concentration dosages of H₂O₂ to efficiently degrade 95.6% MB in 90 min (50 mg L^-1 MB, 1 g L^-1 catalyst, 30 mg L^-1 H₂O₂, pH 7). It is also shown that 1.0MnO₂/CH-FP could still keep 83.3% degradation efficiency of MB after six cycles. Moreover, the activity of this composite greatly surpassed that of bare MnO₂ for nearly 50%, owing to its larger surface area and more accessible active sites. This method for preparing MnO₂/CH-FP could effectively avoid the agglomeration of MnO₂ nanoparticles and make the reaction turn on/off almost instantaneously by mere insertion/removal.

Keywords: Biopolymer; Dip catalyst; Fenton-like; Manganese dioxide; Redox precipitation.