Adsorption and electrosorption of paraquat, diquat and difenzoquat from aqueous solutions onto activated carbon cloth as monitored by in-situ uv–visible spectroscopy

Abstract Removal of high polarity herbicides, paraquat (PQ), diquat (DQ) and difenzoquat (DFQ) from their aqueous solutions was investigated by adsorption and electrosorption onto activated carbon cloth (ACC). Adsorption and electrosorption processes were followed on-line by in- situ uv–visible spectroscopy. Kinetics of adsorption and electrosorption was found to follow pseudo-second order model in a better way than pseudo-first order model. Excellent open circuit (OC) adsorption efficiency (99.9%) was achieved for DFQ. Lower OC adsorption efficiencies of PQ (47.1%) and DQ (45.9%) were increased by the application of electrosorption (over 98%). Adsorption and electrosorption behaviors of the herbicides under study were explained based on herbicide-ACC surface interactions. Adsorption isotherms were derived and examined according to Langmuir and Freundlich models. Adsorption isotherm data fitted to Freundlich isotherm model better than Langmuir isotherm model. Parameters of these models were determined. Application of electrodesorption caused the removal of mainly electrosorbed herbicides.