Highly effective agro-waste based functional green adsorbents for toxic chromium(VI) ion removal from wastewater

Abstract

In this investigation, two novel and economically competitive adsorbents i.e., acid treated activated biochar (ATAB) and green synthesized graphene oxide iron-nanoparticles (GS-GO@FeNPs) were synthesized from waste-tea-leaves to exterminate chromium (Cr(VI)) from the contaminated water to ensure sustainable reuse of large-scale industrially produced tea waste. The adsorbents were characterized by several instrumental techniques whereas the adsorption experiments were performed in a batch process using Diphenylcarbazide methods. The characterization profile of the adsorbents suggested substantial Cr(VI) sequestration potential. The biosorption data was found to be better fitted with a pseudo-second order (PSO) kinetic model having significant regression co-efficient and providing negligible root square mean error (RSME). Isotherm studies demonstrated Langmuir and Freundlich models perfectly matched with the experimental data for both adsorbents. The maximum adsorption capacities were found to be 369.00 and 387.59 mg/g for ATAB and GS-GO@FeNPs, respectively. The outcomes of the artificial neural network (ANN) modelling provided a good correlation (R2 = 0.999) between simulated and experimental results of the adsorption process parameters. The adsorption process was endothermic in nature and its feasibility and spontaneity were confirmed by thermodynamic models. The adsorption mechanisms of Cr(VI) can be suggested as a complex process dominated by chemisorption phenomenon owing to ion-exchange, electrostatic attraction, surface complexation formation and film or intra-particle diffusion. The substrates displayed outstanding renewal performances by means of 1.0 M HCl/H2SO4 as eluent, and the adsorbents could be reused for several cycles. In essence, the adsorbents fabricated in the present study could be a promising, eco-friendly and cheap bio-filter for the remediation of Cr(VI) from aquatic environments to safe-guard the public health.