In situ growth of NH2-MIL-101 metal organic frameworks on biochar for glyphosate adsorption.

We fabricated a novel adsorbent to remove glyphosate (PMG) in solution by in situ growing of NH 2 -MIL-101 metal-organic framework on biochar derived by the calcination of waste rice husk (hereafter NMBC 61 formulated as NH 2 -MIL-101: BC = 6:1 ratio). The new adsorbent was systematically characterized by atomic, molecular spectroscopic and conventional experimental methods. The PMG adsorption efficiency on NMBC 61 was examined as a function of contact time, solution pH, temperature, matrix solutes, and substrate concentration. The modification of amino group significantly improved the adsorption performance of the material. The PMG adsorption data were modeled using Langmuir isotherm and pseudo-second-order kinetics formulations. The maximum adsorption capacities of NMBC 61 at 323 K for PMG is 186.71 mg g−1. The PMG adsorption did not significantly interfere with NO 3 −, Cl−, HCOO−, and citric acid in the solution matrix; SO 4 2− show an intermediate interfering behavior. However, PMG adsorption interferes significantly in the presence of H 2 PO 4 2− and citric acid. The contrasting interfering patterns show the nature of surface bonding in PMG adsorption on NBMC 61. The subtilties arisen between surface –NH 2 and –OH sites on PMG adsorption were resolved by IR and XPS spectral data. The PMG adsorbed on NBMC 61 via ligand exchange by inner-sphere surface complex formation. When foreign solutes show similar surface complexing, they interfere with PMG adsorption. Based on the adsorption experiments and density functional theory (DFT) calculations, the van der Waals (vdW) interactions and hydrogen bonding were assumed to be involved in the adsorption. NBMC 61 shows over 83% PMG removal efficiency at the end of three cycles. The NMBC 61 show optimal PMG adsorption between pH 2 and 6 with minimal interference from the solution matrix. Therefore, NBMC 61 has the potential in treating organic pollutants found in natural and wastewaters efficiently with minimal pre-treatment steps. [Display omitted] • NMBC 61 was synthesized by in situ growing of NH 2 -MIL-101 metal-organic framework on biochar through solvothermal method. • PMG could be efficiently removed by NMBC 61. • The PMG adsorbed on NBMC 61 via ligand exchange, electrostatic interactions and hydrogen bonding. • No by-products were produced during the adsorption of PMG by NMBC 61. [ABSTRACT FROM AUTHOR]