Characterization and adsorption of malachite green dye from aqueous solution onto Salix alba L. (Willow tree) leaves powder and its respective biochar

NOVELTY STATEMENT This study reports for the first time the use of Salix alba L. (Willow tree) leaves and its biochar as the adsorbents for the removal of malachite green dye from its aqueous solution. Both the adsorbents namely willow leaves powder (WLP) and willow leaves biochar (WLB) are rapid and highly efficient for MG dye removal having percentage removal more than 92.5%. For WLB adsorbent the percentage removal crosses 98.5% by the addition of 0.2 g KCl and by increasing 40 degrees C temperatures. The adsorbents used in this research work are comparable with the highly efficient low-cost adsorbents used for MG dye like rice husk, water hyacinth, seaweed, etc. found in the literature. The adsorbents (WLP and WLB) were used without chemical treatment having good removal efficiency, cheap, easy available, and their mode of preparation is simple. In the present study, the use of low-cost, highly efficient, eco-friendly, and abundantly available (in Kashmir region, J&K India) willow leaves from which adsorbents like willow leaves powder (WLP) and willow leaves biochar (WLB) were prepared, have been found to be efficient for malachite green (MG) dye removal and can be used as an alternative to the current expensive methods of removing the same dye from an aqueous solution. The techniques like Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and carbon, hydrogen, nitrogen, sulphur (CHNS) analyser were used to characterize the samples without any chemical treatment. SEM of the adsorbents shows the presence of different sized pores, cracks, and crevices. FTIR and CHNS show functional groups and elemental concentration, respectively. The effects of various experimental parameters such as contact time, adsorbent dosage, initial dye concentration, salt treatment, and pH were investigated and optimal experimental conditions were obtained. It has been found that Langmuir, Freundlich, and Temkin isotherms were useful for describing the equilibrium of adsorption system. The equilibrium adsorption data in this research work was found to follow both Langmuir and Freundlich isotherm models and maximum monolayer capacity of WLP and WLB were found to be 10.014 and 21.244 mg/g, respectively. The experimental data for both WLP and WLB followed pseudo-second-order kinetic model with R-2= 0.999. Intraparticle diffusion model reveals that more than one mechanism influenced the adsorption process. Thermodynamic study concluded that the adsorption is spontaneous for both adsorbents but exothermic for WLP and is endothermic in nature for WLB. Present exploration and comparison with other reported adsorbents concluded that, WLP and WLB may be useful as low-cost attractive option for the removal of MG dye from aqueous solution and therefore, also from wastewater containing MG dye.