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

Abstract

We fabricated a novel adsorbent to remove glyphosate (PMG) in solution by in situ growing of NH2-MIL-101 metal-organic framework on biochar derived by the calcination of waste rice husk (hereafter NMBC61 formulated as NH2-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 NMBC61 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 NMBC61 at 323 K for PMG is 186.71 mg g−1. The PMG adsorption did not significantly interfere with NO3−, Cl−, HCOO−, and citric acid in the solution matrix; SO42− show an intermediate interfering behavior. However, PMG adsorption interferes significantly in the presence of H2PO42− and citric acid. The contrasting interfering patterns show the nature of surface bonding in PMG adsorption on NBMC61. The subtilties arisen between surface –NH2 and –OH sites on PMG adsorption were resolved by IR and XPS spectral data. The PMG adsorbed on NBMC61 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. NBMC61 shows over 83% PMG removal efficiency at the end of three cycles. The NMBC61 show optimal PMG adsorption between pH 2 and 6 with minimal interference from the solution matrix. Therefore, NBMC61 has the potential in treating organic pollutants found in natural and wastewaters efficiently with minimal pre-treatment steps.