Preparation and adsorption performance of MnO_2/PAC composite towards aqueous glyphosate

摘要

Glyphosate (N-phosphonomethylglycine (PMG)) is the organophosphate herbicide most widely used in the world, and industrial production of PMG generates large quantities of wastewater. A manganese dioxide-coated powdered activated carbon (MnO_2/PAC) composite was synthesized and investigated for the adsorption of PMG from wastewater. The results of scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDAX) revealed that MnO_2 was formed on the surface of the carbon during the modification process. Batch adsorption results showed that the optimal pH for glyphosate adsorption on MnO_2/PAC was 3.0. In the range 0.01-1 molL~(-1), glyphosate removal by MnO_2/PAC decreased with an increase in ionic strength. Among the coexistent anions, only phosphate showed significant inhibition of PMG removal due to competitive complexation. Batch studies revealed that MnO_2/PAC could reach a maximum PMG adsorption capacity of 283 mg g~(-1). The Langmuir equilibrium model was found to be suitable for describing PMG sorption, and kinetic studies revealed that adsorption followed second-order rate kinetics. It was also proved that the adsorbed PMG could be effectively desorbed from MnO_2/PAC in 1.0mol L~(-1) NaOH. All of these results implied that the MnCO_2/PAC composite may be used as an effective adsorbent for recycling PMG from wastewater.