Cyanometallate framework templated synthesis of hierarchically porous La (OH)3 for High-Efficient and stable phosphorus removal from tailwater

Lanthanum (La)-based hydroxides have been recognized as promising candidates for dephosphorization due to their high affinity and selectivity for phosphate adsorption. However, the development of porous La(OH)3 ma-terials with enriching active sites and high structural stability remains a challenge in tailwater treatment. Here we developed a novel self-templating method based on an ion-exchange mechanism to construct hierarchically porous La(OH)3, where the OH- of an alkali conversion reagent replaces the [Fe(CN)6]4-cluster within the LaFe cyanometalate (CM) precursor, simultaneously completing the hydroxide conversion and pore-creating pro-cesses. The obtained hierarchically porous La(OH)3 shows excellent structural stability with no ion leaching and can maintain its primary microsphere structure and secondary nanoneedle morphology after multiple cycles of application. Due to the abundant micropores/mesopores, there are fully exposed active sites inside and outside the porous La(OH)3 microsphere, giving it an excellent phosphate adsorption capacity (maximum capacity of 163.6 mg P/g). Its high selectivity and environmental adaptability make it a favorable adsorbent for aquaculture tailwater treatment that can rapidly reduce the dissolved inorganic phosphorus level to below 0.05 mg P/L to meet the mariculture tailwater discharge standard in a wide range of salinities and temperatures. The infor-mation gleaned in this study provides valuable guidance for the materials design of porous La-based hydroxides for phosphorus removal.

Automated summary

In this study, a self-templating method was developed to fabricate hierarchically porous La(OH)3 materials with excellent structural stability and phosphate adsorption capacity. These materials are suitable for tailwater treatment in aquaculture.