Efficient removal of Reactive Black from aqueous solution using polyaniline coated ligno-cellulose composite as a potential adsorbent

Polyaniline coated ligno-cellulose composite (PLC) was synthesised via in-situ polymerisation of aniline monomer and used for the removal of Reactive Black 5 (RB-5) from aqueous solutions. The adsorbent was characterised before and after adsorption to verify that the dye was indeed adsorbed. The removal occurred through the surface adsorption of RB 5 onto the PLC as identified from the Fourier transform infrared spectra, X-ray diffraction spectra and SEM image. Sorption kinetics were very fast and equilibrium was reached within 60 and 120 min of interaction for initial concentrations of 50 mg/L and 100 mg/L, respectively. Kinetic studies revealed that the pseudo-second-order model described the sorption process better than the pseudo-first-order model and intra-particle diffusion was identified as the rate-limiting step. The equilibrium adsorption isotherm studies also revealed that the Langmuir isotherm provided the best fit with monolayer adsorption capacity of 312 mg/g. The adsorption process was spontaneous and endothermic. Up to 98% desorption of the dye was also achieved using a 1:1 water:acetone mixture and this desorption efficiency could be achieved over four adsorption-desorption cycles. Single-stage batch adsorber studies confirmed that the maximum quantity of adsorbent required to achieve 95% removal of the dye was 20.41 kg.