Reduction of 2,4-dichlorophenoxy acetic acid herbicide toxicity from aqueous media by adsorption: Experimental and theoretical study using DFT method

This work studies the possibility of reducing the toxicity of water laden with 2,4-dichlorophenoxy acetic acid (2,4-D) using a commercial activated carbon (AC). Multiple structural and textural characterization techniques including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM/EDS), point of zero charge (pHzpc) determination, Boehm titration, iodine number, Methylene blue index, and BET analysis measurements were performed on the commercial AC. Various parameters affecting adsorption were studied and well-known isotherms models in their linear and non-linear forms were applied for fitting equilibrium data. The kinetic data was analyzed using intraparticle diffusion, pseudo-first and second-order kinetic models. Density functional modeling (DFT) of 2,4-dichlorophenoxyacetic acid was used to investigate the origin of the reactivity. The AC surface area was found to be 1017 m(2)& sdot;g(-1). A contact time of 30 min, an AC dose of 4 g & sdot;L-1 and a pH of 6.2 resulted in a maximum adsorption capacity of 235.55 +/- 6.43 mg & sdot;g(-1). The thermodynamic study revealed that the adsorption process was physical, spontaneous and endothermic. The adsorption process was governed by second-order kinetics and controlled by intraparticle diffusion.