Vitis vinifera leaf litter for biosorptive removal of nitrophenols

Vitis vinifera (grape) leaf litter, an abundant agricultural waste in South Africa was chemically modified with H3PO4 and carbonized for use as biosorbent. Characterization and the potential application of the adsorbent in simultaneous removal of 4-nitrophenol and 2-nitrophenol from aqueous solutions were investigated. The adsorbent was characterized using FTIR, SEM and EDX elemental microanalysis. The EDX and FTIR analysis revealed the presence of surface oxygen moieties capable of binding to adsorbate molecules while the SEM micrographs showed the development of pores and cavities in the adsorbent. Batch adsorption experiments were conducted at a varying contact time, adsorbent dosage, pH and initial adsorbate concentration to investigate optimal conditions. The maximum adsorption capacity of the adsorbent was 103.09 and 103.10 mg/g for 4-nitrophenol and 2-nitrophenol, respectively. The adsorption process was best fitted into Freundlich isotherm while the adsorption kinetics followed a pseudo-second-order model. Liquid film and intra-particle diffusion contributed to the adsorption process. Thermodynamic parameters of ΔG°, ΔH° and ΔS° were evaluated. The adsorption was exothermic, feasible and spontaneous. The results suggest a possible application of grape leaf litter as a precursor for activated carbon and for cheaper wastewater treatment technologies.