Adsorption of malachite green by Aegle marmelos-derived activated biochar: Novelty assessment through phytotoxicity tests and economic analysis

The efficacy of chemically activated Indian bael (Aegle marmelos) shell biochar (CAIBSB) was investigated as an adsorbent. The adsorbent was used for the sequestration of the toxic dye malachite green (MG) from wastewater. The activation of biochar by sodium hydroxide introduced more pores, hence more surface area, leading to enhanced adsorption capacity. CAIBSB was characterized with XRD, FEGSEM, EDX, BET, and FTIR spectroscopy for estimating its adsorption prospects. The XRD pattern of CAIBSB displayed a diffuse peak and indicated that the biochar was amorphous. The BET and isotherms of CAIBSB revealed biochar to be mesoporous, with a favourable surface area of 70.9 m2/g. An uptake capacity of 120.45 mg/g with 95 % removal at optimum process conditions (initial dye concentration of 50 mg/L, solution pH of 8.0, and equilibrium time of 60 min) were observed. The adsorption mechanism followed pseudo-second-order kinetics and Langmuir isotherms. Over 80 % of the adsorption capacity remained intact after five cycles of use and regeneration. The fabrication cost of CAIBSB adsorbent was estimated to be only 7.79 USD/kg of adsorbent. A substantial reduction in the toxicity of MG dye was confirmed in the phytotoxicity experiments on the growth of Vigna mungo seeds. [Display omitted] •Toxic malachite green dye adsorption by inexpensive and modified biochar.•Chemical activation ensured better adsorption capacity and reusability of biochar.•Analyses of fabrication cost and phytotoxicity ensured a sustainable treatment method.•A dye removal of 95 % at an uptake capacity of 120.5 mg/g was achieved.