Mathematical investigation into the sequential adsorption of silver ions and brilliant green dye using biochar derived from Gracilaria Rhodophyta algae

The present work investigates the ability of robust biochar from Gracilaria Rhodophyta red weeds collected from the deep sea waters of the Bay of Bengal, for sequential removal of silver and Brilliant Green (BG) dye from contaminated water. The impacting operating parameters viz contact time, the dosage of biochar, pH, and initial Ag⁺ concentration are optimized using 2⁴ factorial central composite design (CCD)-based statistical modeling. The analysis of variance (ANOVA) projected an excellent history match of model data with experimental through high correlation coefficients. The sequential batch adsorption studies performed at a temperature of 303 K projected an uptake of 4.7 mg/g and 17.8 mg/g at the optimal operating conditions of pH 5–7 and 6, biochar dosage 1.0 and 0.5 g/100 mL, initial concentration 50 mg Ag⁺ ions and 100 mg BG dye per liter, and operating time 45 and 60 min, respectively, for Ag⁺ ions and BG dye. Further, the surface morphology, elemental compositions, functional groups, depositional, and structural characteristics of the biochar analyzed using FESEM, EDX, FTIR, BET, and XRD respectively confirmed its ability to successfully treating the contaminants. Moreover, the isothermal, thermodynamic, and kinetic analysis established the Langmuir model-based mono-layered homogeneous physisorption of Ag⁺ and BG dye with pseudo-second-order depositional characteristics at the solid-solution interface. The biochar is regenerative enough and could remove substantial amounts of Ag⁺ and BG dye from industrial contaminated water bodies. Moreover, the present work aids in promoting seaweed harvesting as an alternate occupation for littoral fisher societies.