NCNT@La-PES composite membrane activates peroxymonosulfate for the degradation of HEDP and adsorptive recycling of phosphorous

Abstract

A lanthanum-modified polyethersulfone composite membrane (La-PES) loaded with nitrogen-doped carbon nanotubes (NCNT@La-PES) was successfully fabricated in this study. The NCNT@La-PES membrane could activate PMS, which enabled the degradation of phosphonate to phosphate, while also possessing the capability for adsorptive recycling of phosphorus. During the processing of 10.31 mg/L 1-hydroxyethane-1,1-diphosphonic acid (HEDP) in the NCNT@La-PES/PMS system, the removal efficiency of HEDP achieved 100 %, and almost 78 % of total phosphate (TP) in HEDP was transformed into phosphate, which were further adsorptive recycled by the La-PES membrane. The NCNT@La-PES/PMS system demonstrated exceptional performance across a broad pH range (4–10), with complete removal of HEDP and adsorption recovery of 73 % transformed phosphate. The decrease in pH caused by catalytic reaction reduced the hindrance of the alkaline environment to phosphate adsorption. The NCNT, acting as a catalyst, facilitated the formation of surface-bound radicals upon PMS activation, playing a pivotal role in the degradation of HEDP. The adsorption of phosphate by La-PES was primarily attributed to the ligand exchange between La(OH)₃ and phosphate. Moreover, NCNT@La-PES/PMS system showed significant catalytic and adsorption performance in consecutive cyclic treatment of HEDP in actual water, indicating its potential in practical application.