Selective Phosphorus Removal from Wastewater Using Graphene Aerogel Loaded with Ferrocene-Polyaniline: Synergetic Adsorption and Electrochemically Mediated Oxidation

Abstract

Selective removal and recovery of phosphorus from wastewater is a huge challenge for water purification. In particular, phosphite is an often-neglected contaminant that is more soluble and resistant to biotransformation than phosphate. Herein, we develop an electrochemical system for phosphorus removal using nitrogen-doped graphene aerogel loaded with ferrocene-polyaniline (Fc-PANI@NGA) electrodes. The results demonstrate that this electrochemical system can selectively adsorb phosphate and phosphite in comparison to other anions and promote the oxidation of phosphite to phosphate. The high affinity of Fc-PANI@NGA to both phosphate and phosphite due to the faradic reactions and specific hydrogen-bonding interactions ensures high selectivity of P over Cl-, SO42-, and NO3-. The redox reversibility of Fc to Fc+due to its interaction with O2/H2O2led to the formation of •O2-and •OH, which are predominantly responsible for the oxidation of phosphite to phosphate. This system enables the phosphate and phosphite adsorption capacities of 29 mg PO43-g-1and 24 mg HPO32-g-1, respectively, and high phosphite conversion efficiency (99.3% at a cell voltage of ±1.6 V), exhibiting high selection efficiency and stable regeneration performance. Density functional theory calculation verifies the selective adsorption mechanism of phosphate and adsorption/oxidation of phosphite on the Fc-PANI@NGA electrode.