Methylene Blue Removal by Biochar-Hydrochar from Date Palm Seeds and its Binding Interaction Analysis

Large volumes of polluted industrial wastewater discharges had made it imperative to continue on the development of adsorbent materials with improved adsorptive properties yet economically feasible. Agricultural waste such as date palm biomass offers an interesting solution as raw material due to its abundance and availability throughout the year. Biochar and hydrochar produced from date palm biomass were reported as a potent adsorbent to remove pollutants such as dyes from aqueous environment. However, very few studies had reported on the mechanism of dye removal by these types of adsorbents. Therefore, this study aimed to evaluate the methylene blue (MB) removal capacity of biochar (DPSB) and hydrochar (DPSH) produced from date palm seeds (DPS). This was followed by molecular dynamics studies (density functional theory, DFT) which was targeted to propose the geometry of the adsorbents as well as the interaction between MB and functional groups present on DPSB and DPSH. Finding from this molecular dynamics studies acted as the direct contribution of new knowledge for the interaction between DSP-based adsorbents and MB. DPSB and DPSH were produced from DPS samples that were collected from the Kingdom of Saudi Arabia's Hail region. FTIR analysis showed the presence of C = C, C = O, CO, and OH on both DPSB and DPSH while SEM micrographs reveal a highly porous structure with open pores and sharp edges in both samples. Thermogravimetric analysis (TGA) revealed a total weight loss of 20.79% for both samples. The maximum methylene blue (MB) removal of 85.6% (DPSB) and 89.4% (DPSH) was achieved at initial MB concentration of 10 mg L⁻¹, 2 g of adsorbent and equilibrium time of 45 min. Kinetic parameters (pseudo-first order and pseudo-second order interaction) were also used to evaluate the MB removal capacity. From the Density Functional Theory (DFT) analysis, all of the DPSH peaks exhibited an increase in intensity in the Band Gap of the hydrochar spectrum (-0.02102), indicating its resistant to chemicals and environmental degradation. To conclude, DPS were successfully demonstrated to be a useful alternative as raw material to produce biochar and hydrochar with good pollutant (MB) removal capacity. Nevertheless, more studies need to be carried out to ensure smooth transition of this type of adsorbent prior to any attempts for actual on-site application.