Modeling studies of the adsorption of Methyl Red and Acid Yellow 36 dyes by sulphonated Ulva lactuca carbon

This study investigated the adsorption of Acid Yellow 36 (AY36) and Methyl Red (MR) dyes using a novel sulfonated biochar carbon (GASC) synthesized from green algae (Ulva lactuca) via a reflux method in the presence of 80% sulfuric acid (H₂SO₄). The structural and surface characteristics of the resultant GASC were evaluated by Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). GASC exhibited a relatively low BET surface area of 6.27 m²/g, with a monolayer volume of 1.4392 cm³ (STP)/g. The total pore volume was measured as 0.0203 cm³/g, and the mean pore size was 12.971 nm. GASC's total weight loss was 46.52%, indicating higher thermal stability compared to GAUL (78.01%). FTIR spectra validated the existence of many functional groups on GASC. Adsorption experiments for AY36 and MR dyes were conducted under varying conditions, including initial dye concentrations (50-150 mg/L), contact times (5-180 min), solution pH (2-12), and GASC dosages (0.5-1.5 g/L). According to the Langmuir isotherm, the maximum adsorption capacities (Q_m​) of GASC for AY36 and MR dyes were 216.45 and 454.55 mg g^-1, respectively. Kinetic assessments indicated that the adsorption of both dyes was optimally represented by the pseudo-second order model, validating the efficacy of the synthesized GASC as an adsorbent for eliminating AY36 and MR dyes from aqueous solutions. Furthermore, response surface methodology (RSM) and Artificial neural networks (ANN) were applied to model and optimize adsorption. Optimization of the adsorption parameters using the RSM study concluded that a maximum AY-36 dye removal percentage of 96.76% could be reached when employing 147.41 mg of GASC and 56.08 mg/L of AY-36 dye solution. The most significant degradation percentage of MR dye, 99.94%, was achieved using 132.34 mg of GASC and 59.30 mg/L of MR dye solution.