Guanylurea phosphate-activated biochars with developed nitrogen/phosphorus groups for efficient and selective enrichment of aqueous U(VI)

Since N-/P-containing functional groups can react with aquatic U(VI) effectively, the development of adsorbents with sufficient N-/P-containing species and developed porosity is highly desirable. Herein, guanylurea phosphate-activated biochars (GPBs) with abundant surface N/P-containing groups (4.2–13.1 at.% for N and 1.7–4.6 at.% for P) and high surface area (17.2–484.6 m 2 /g, which were 2.5–16.9 times than unmodified biochars) were fabricated via the pyrolysis of waste straw at 300 °C, 500 °C, and 700 °C. By evaluating multiple hydrochemical conditions, U(VI) was adsorbed by GPBs with rapid kinetic (4 h) and excellent q max (120.4–209.6 mg/g). The mineralization of aquatic U(VI)-phosphate as hydrogen uranite enabled the superior selectivity for U(VI) uptake from simulated nuclide-containing water against interfering coexisting metals. A favorable reusability (88.2% and 85.4% of initial uptake capacity kept after six cycles) was achieved via desorbing GPBs by HCl solution and Na 2 CO 3 solution, respectively. This work provided a valuable reference for the preparation of functional biochars to efficiently and selectively capture U(VI).