Enhanced efficiency of manganese molecular sieves through K2FeO4 and KMnO4 modification: optimization and mechanistic insights

Abstract

Potassium permanganate (KMnO₄) and potassium ferrate (K₂FeO₄) were used as modifiers to modify molecular sieves, and the modification periods were 35 days (KMnO₄) and 27 days (K₂FeO₄), respectively. About 1 mol/L NaOH was used to pretreat the molecular sieves during the modification process of K₂FeO₄, and the modification period was further shortened to 22 days. After modification, modified molecular sieve (MMS) could effectively and continuously remove ammonium (NH₄⁺) and manganese ions (Mn²⁺) from water. The adsorption kinetics showed that the adsorption of NH₄⁺ and Mn²⁺ by MMS conformed to the quasi-secondary kinetic model adsorption kinetic model, and the adsorption process was mainly chemisorption. During the modification process, SEM, EDS, BET and XPS were used to investigate the structural characteristics of MMS. In the modification mechanism of molecular sieve, lattice oxygen (referred to as O_α), Mn (II), and Mn (III) accelerated the oxidation of Mn²⁺ to Mn⁴⁺ and promoted the rapid formation of active manganese oxide, which played a key role in shortening the modification period of MMS. This study contributes to a better understanding of the preparation and performance of MMS through a comprehensive analysis of the optimized molecular sieve modification process and the exploration of the accelerated formation mechanism of active manganese oxide.