Comparative study of raw and biochar-derived Ziziphus spina-christi leaves embedded in a hydrogel matrix for malachite green dye uptake

This work examines the relative adsorption capacity of raw Ziziphus spina-christi (ZSC) leaves and their biochar derivative incorporated into a polyacrylamide-based hydrogel matrix to eliminate malachite green (MG) dye from aqueous solutions. Four adsorbent systems were synthesized and characterized, namely raw ZSC leaves, ZSC-derived biochar (BC-ZSC), raw ZSC/hydrogel composite (Raw-ZSC/HG), and biochar ZSC/hydrogel composite (BC-ZSC/HG). The characterization was performed by FTIR, XRD, FESEM, TEM, BET, and zeta potential measurements. The BC-ZSC/HG composite showed a BET surface area of ۵۲.۴ m²/g, a total pore volume of ۰.۰۸۹ cm³/g, and the point of zero charge was at pH ۴.۸. Batch adsorption tests were performed to investigate the effect of solution pH, adsorbent dose, contact time, initial dye concentration, and temperature. The BC-ZSC/HG composite showed excellent adsorption performance, with the highest adsorption capacity of ۱۷۸.۴ mg/g at pH ۸, temperature ۴۵°C, and equilibrium time ۱۲۰ min. Adsorption data best matched to the Langmuir isotherm model (R² = ۰.۹۹۸۱) and pseudo-second-order kinetics (R² = ۰.۹۹۹۴). Thermodynamic analysis indicated the process to be spontaneous and endothermic. The BC-ZSC/HG composite maintained ۷۴% removal effectiveness after six cycles of adsorption-desorption. The results indicate that the use of ZSC biochar incorporated into a hydrogel matrix can significantly improve the adsorption capacity and reusability of the removal of cationic dyes.

کلیدواژه ها:

Ziziphus spina-christi ، Biochar ، Hydrogel Composite ، Malachite Green ، Adsorption