Mesoporous Polyacrylonitrile with Ultrahigh Loading of Well-dispersed Fe2O3 Nanoparticles: A Powerful Phosphate Scavenger for Inhibition of Microbial Regrowth

ABSTRACT Microbial regrowth occurs frequently even in sanitized water, and phosphorus is an essential nutrient for all microorganisms. Ultrafiltration membranes containing nano-adsorbents can realize size-exclusive removal of bacteria and adsorptive removal of phosphorus simultaneously, thus enabling long-term inhibition of microbial regrowth without the formation of disinfection by-products. However, nanocomposite membranes suffer from issues associated with nanoparticle (NP) loading, accessible sites, and ultrafiltration performance. Low NP loadings lead to unsatisfactory adsorption performance, while high loadings (e.g., > 6 wt%) often cause evident macro-phase separation of the polymer/NP blend and severe NP aggregation, which greatly decrease the separation efficiency. Herein, we prepare a novel polymer nanocomposite Fe2O3@PAN through flash freezing of a polyacrylonitrile (PAN)/Fe2O3 (∼3 nm) casting solution. Micro-phase separation is utilized to prevent NP aggregation and to generate abundant mesopores with sizes of 7.8–11.9 nm. The Fe2O3@PAN membranes contain up to 52.7 wt% Fe2O3 NPs and have a mesoporous volume of 0.31–0.51 cm3/g. With Fe2O3@PAN, we successively generated 670–800 L/m2 of sterile water containing less than 20 μg/L phosphorus, which is unsuitable for microbial (re-)growth. The exhausted Fe2O3@PAN can be continuously refreshed with 10 mM NaOH for repeated use without loss of adsorption performance. This work may stimulate more studies aimed at the rational design of highly efficient nanocomposite membranes.