Highly dispersed La on biochar-based self-support framework for rapid and selective phosphate removal: Performance and mechanism.

Metal-doped biochar is a promising phosphate adsorbent for mitigating phosphate-driven eutrophication and valorizing biomass, but its adsorption performance, selectivity and stability are strongly governed by the biochar-metal structure. Herein, the biochar was embedded into carbon nanofiber' networks to construct a self-supporting biochar-carbon nanofiber framework (C-ACF). The C-ACF was first functionalized with an amine-rich HCCP-PEI polymer layer to obtain PCP@C-ACF, which was then used to anchor highly dispersed La species, yielding the performant La-loaded adsorbent PCP-La@C-ACF. Expectantly, PCP-La@C-ACF exhibited outstanding phosphate adsorption kinetics and selectivity, achieving phosphate uptake of 63.5 mg P·g-1 within 1 min (9.3-fold that of La(OH)3) and an equilibrium capacity of 93.9 mg P·g-1, along with broad pH tolerance and marked reusability. Under fixed-bed operation, PCP-La@C-ACF maintained the effluent phosphate concentration below 0.2 mg P·L-1 (removal rate > 99.4%). Owing to the loaded La species, markedly improved phosphate selectivity under high concentrations of Cl-, NO3-, and SO42- was achieved, with selectivity coefficients against NO3- and SO42- being 14- and 32-fold higher than La-free PCP@C-ACF. Molecular dynamics simulations rationalize that such dispersed La species enhance adsorption selectivity/rate by promoting phosphate dehydration and improving interfacial diffusion efficiency.