Sustainable waste valorisation: Novel Areca catechu L. husk biochar for anthraquinone dye adsorption - Characterization, modelling, kinetics, and isotherm studies

Textile waste water has a great polluting potential as it consists of dyes, emulsifiers, toxic metals, organic and inorganic compounds. Agro-based biochar is an effective adsorbent for the removal of contaminants from textile wastewater. The present study aims to synthesise biochar derived from areca nut (areca catechu L.) husk agro-waste using low-rate pyrolysis and to analyse the anthraquinone cationic Rhodamine B (RhB) and anionic Alizarine red S (AZ) dye removal efficiency. Synthesised biochar was characterized. Hydroxyl, carboxyl, acid and ester functional groups and graphite structure with distorted carbon stacks in biochar were confirmed through FTIR and XRD analysis. SEM analysis confirms the presence of non-uniform pores with crosslinked-pore-tunnels which assists the physisorption process of dye adsorption. The factorial interaction and optimum conditions were identified through response surface methodology and regression models were obtained (R2adj >95 % and R2pred>95 %). The synthesised biochar delivered an adsorption efficiency of 89 % and 87 % for RhB and AZ dye removal within 40min. The adsorption follows the pseudo first order and fit with the Langmuir isotherm for both dyes with a maximum adsorption capacity of 105.43 mg/g and 109.52 mg/g for RhB and AZ dyes. This study works to meet UN Sustainable Development Goals (SDG 6,7,12,13 and 14) and provides a sustainable solution.