Nitrogen-functionalized bone chars with developed surface area for efficient adsorption of multiple aquatic pollutants

Bone chars pyrolyzed from bone residuals exhibit impressive performances to remove heavy metals given the integration of hydroxyapatite and carbon components. Considering the complexation of functional groups with metal ions and the adsorption of molecules by porous pores, this work prepared nitrogen-functionalized bone chars (NMBCs) with developed surface area (16.99- to 6.71-fold enhancement) and favorable surface modification (maximum 6.03 at% of N) via a ball milling of pristine bone chars with the assistance of ammonia hydroxide. NMBCs presented excellent maximum adsorption capacities for Cr(VI) (339.8 mg/g), U(VI) (466.5 mg/g), and methylene blue (338.3 mg/g) (pH 5.0, T 293 K) from ideal solutions. The effects of geochemical conditions including contact time, solution pH, ionic strength, humic acid, and ambient temperature on adsorption behaviors were investigated. NMBCs favorably adsorbed Cr(VI) (221.8 mg/g at pH 2.0, 175.4 mg/g at pH 4.0) and U(VI) (202.1 mg/g) from simulated wastewater and seawater respectively. With the analysis using spectroscopic technologies, the dominant mechanisms of Cr(VI), U(VI), and methylene blue were the integration of electrostatic attraction, surface complexation, precipitation, cation exchange, cation-π coordination and π–π interaction. This work provided a promising reference for the functionalization of bone chars with enhanced performance and multifunctionality in the remediation of pollutants.