Exploring the potential of Eucalyptus citriodora biochar against direct red 31 dye and its phytotoxicity assessment

The feasibility of using Eucalyptus citriodora leaves (ECL), an abundantly available agricultural waste, for adsorption of an anionic dye, direct red 31 (DR31), adsorption from hydrous solution has been examined in the present research. The batch adsorption trials were performed to analyse the effects of pH, contact time, initial dye concentration, adsorbent dose, temperature and particle size on DR31 removal from its aqueous solution on biochar of ECL. A maximum of 97% removal of DR31 dye was observed at pH and initial adsorbate concentration of 2 and 40 mg/L by the ECL biochar, respectively. Equilibrium data were examined by Langmuir and Freundlich isotherms. Langmuir isotherm appeared as the best fit model with the highest adsorption capacity of 3.2 mg/g. The kinetic results were also examined and found pseudo-second-order to be the best fit which expressed that the adsorption rate was mainly regulated by chemisorption. ECL biochar maintained > 41.56% adsorption capacity of DR31 dye even after five adsorption–desorption consecutive cycles. Phytotoxicity studies on Vigna radiata substantiated the non-toxic nature of the treated DR31 dye-containing water. The present study reveals that the biochar of ECL can be utilized as a cost-effective adsorbent to make the dye-contaminated wastewater reusable.