Adsorption interactions of Di-(2-ethylhexyl) phthalate (DEHP) with cinnamon wood biochar in aqueous medium

The ubiquitous presence of di-(2-ethylhexyl) phthalate (DEHP) in wastewater is a global problem due to its toxicity. This work aims to evaluate the removal capacity of cinnamon wood biochar (CWBC) on DEHP. The dry biomass of cinnamon wood was pyrolyzed at 700 ℃. Batch sorption experiments were carried out to identify the optimum conditions and the mechanisms of DEHP removal. At the optimum pH condition (pH 3-4), both the predominant species of DEHP and the surfaces of CWBC were positively charged that revealing electrostatic interactions were not the dominant mechanism for DEHP adsorption. Kinetic experiment data showed 92% of DEHP removal within 5 hours with a maximum adsorption capacity of 22.08 mg L^-1. The batch sorption data were well fitted to the Hill isotherm model and pseudo-first-order kinetic model, suggesting the involvement of both positive cooperative binding and physisorption mechanisms for DEHP removal. Fourier-transform infrared spectroscopy (FTIR) spectra for DEHP-adsorbed CWBC indicated a new band at 1645 cm^-1 that attributes an amide formation. The amide formation between CWBC functional groups and protonated DEHP likely leads to stable H-bond formation that allows multilayer adsorption of protonated/deprotonated DEHP. Overall, the adsorption process implied chemisorption followed by a multilayer physisorption process for DEHP removal. The findings of this study suggested CWBC is a promising material for DEHP removal where the pH of wastewater greatly influences the adsorption.