Adsorption of crystal violet dye using Platanus orientalis (Chinar tree) leaf powder and its biochar: equilibrium, kinetics and thermodynamics study

Effluent water from dyeing industries is a challenging issue. The purpose of this study was to investigate the adsorption properties of locally available Chinar tree (Platanus orientalis) lingo cellulosic materials as adsorbents for the removal of crystal violet dye from aqueous solution. The study shows that the Chinar leaf powder and Chinar leaf biochar can be used as a potential plant by-product adsorbent for the removal of crystal violet from aqueous solution. The adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and carbon hydrogen and nitrogen analyzer (CHNS). In batch optimization studies, the maximum removal efficiency for the adsorbents was obtained at the optimum levels of contact time (30 min), adsorbent dose (2.5 g L-1), initial dye concentration 20 mgL(-1) and pH 6.52. The equilibrium adsorption data were found to follow both Langmuir and Freundlich models and maximum monolayer capacity of Chinar leaf powder and its biochar were found to be 25.88 and 30.01 mg.g(-1). Also the Langmuir and Freundlich isotherm model constants R-L(0.0425 and 0.00686 for Chinar leaf powder and Chinar leaf biochar, respectively) and n (1.3106 and 1.6103 for Chinar leaf powder and Chinar leaf biochar, respectively) suggesting favorable adsorption of crystal violet on the adsorbents. Kinetic analysis for both adsorbents revealed that adsorption experimental data was best fitted by pseudo-second-order model(R-2 = 0.999). Gibb's free energy is -2.14473 to -4.23219 for Chinar leaf powder and -7.18828 to -11.1027 for Chinar leaf biochar showing the process is spontaneous. The enthalpy changes of Chinar leaf powder and its biochar are negative (-20.6611) and positive (22.72549) indicating exothermic and endothermic processes, respectively. Uptake efficiency (>90%) recorded at an equilibrium time of 30 min shows that Chinar leaf powder and biochar were fast and effective adsorbents for the removal of crystal violet.