Kinetics and pseudo-isotherm studies of 4-nitrophenol adsorption onto mansonia wood sawdust

Kinetic models alone are usually applied to describe adsorption onto porous materials, but little attention is given to the fact that diffusion of pollutants especially large organic pollutant molecules may also control the reaction rates. In this investigation, the kinetics and pseudo-isotherm studies of an organic pollutant, 4-nitrophenol from aqueous solution on mansonia sawdust was examined. The intraparticle diffusion particle plots revealed three distinct sections representing sorption into external diffusion, intraparticle diffusion and diffusion to a biosorption site within the particles. The fractional removal of pollutant versus square root of time plots further revealed three sectional straight lines whose slope may represent the rates of pollutant sorption into macro-, meso- and micropores.The equilibrium capacities determined using four forms of the Ho's pseudo-second order model and the Type-1 pseudo second-order expression was also used to evaluate equilibrium concentrations and pseudo-isotherms were obtained by changing initial concentration, C0.

Graphical abstractPlot of fractional uptake of 4-nitrophenol from aqueous solution onto mansonia sawdust against square root of time.Download full-size imageResearch highlights▶ p-Nitrophenol biosorption onto mansonia sawdust is characterized by surface biosorption and intraparticle diffusion. ▶ Raw mansonia sawdust particles were observed to have iodine number (260 mg/g) comparable to activated carbon produced from rubber wood sawdust (300 mg/g). ▶ Film diffusion rate was found to be slower than the rate of pore diffusion. ▶ Pseudo-isotherms were generated by changing the initial p-nitrophenol concentrations based on the pseudo-second-order kinetic model and the Langmuir-1 isotherm provided the best fit. ▶ Four forms of the pseudo-second order model were applied to analyze the kinetic data and the Type-1 form provided the best fit to the kinetic data.