Kinetics and equilibrium study of 2-nitrophenol adsorption onto polyurethane cross-linked pine cone biomass

Abstract

Abstract Diisocyanate cross-linked biomaterials are gaining interest as alternatives for the adsorption of organic materials from aqueous solution. Several biomaterials have been applied as substrate onto which diisocyanates are reacted, most of which lack mechanical strength or are expensive to extract from natural source. In this study pine cone powder was cross-linked with hexamethylene diisocyanates (HMDI) and applied as adsorbent for an organic micropollutant, 2-nitrophenols from aqueous solution. Pine cone powder was pre-treated with Fenton reagent to improve surface area, porosity of the adsorbent and to add carboxylic acid sites for cross-linking. The raw, Fenton pre-treated and Fenton pre-treated cross-linked pine were characterized using Fourier Transform Infrared spectroscopy, thermogravimetric analysis, X-ray diffractometry, scanning electron microscopy, nitrogen adsorption surface area analysis and the acid functional groups and pHPZC were also determined to confirm HMDI cross-linking. The adsorption kinetics of 2-nitrophenol in the concentration range of 100–400 mg/dm3 was best described by the pseudo second order kinetics while the Langmuir maximum capacities for Raw, Fenton pre-treated and Fenton pre-treated cross-linked samples were 41.17, 65.75 and 78.05 mg/g. An increase in surface area and carbonyl function increased the external mass transfer of 2-nitrophenol. Film diffusion was observed to be higher in magnitude for the raw pine while pore diffusion was faster for Fenton pre-treated and Fenton pre-treated cross-linked pine. Redlich-Peterson isotherm best described the adsorption process and the Fenton pre-treated pine showed stronger affinity for the adsorbate. The adsorption was spontaneous at all temperatures for all samples but spontaneity reduced with temperature and the adsorption process were all exothermic in nature. Adsorption mechanism for the cross-linked adsorption was found to be via π-π, polar and hydrophobic interaction.