During the last decade, due to an increase in anthropogenic activities, a higher environmental accumulation of heavy metals has been found, which has resulted in disturbed biogeochemical balance. Many kinds of remediation techniques have been practiced to mitigate heavy metal toxicity in the aqueous phase; however, adsorption is the most commonly accepted technique for efficient heavy metal removal. In this study, conocarpus waste was pretreated with 0%, 10%, and 20% kaolinite and pyrolyzed at 600 °C for 1 h to synthesize biochars (BC, BCK10, and BCK20, respectively), while hydrothermalized at 200 °C for 6 h to synthesize hydrochars (HC, HCK10, and HCK20, respectively). After characterization, synthesized materials were employed for the removal of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) from contaminated water. Experimental data was further subjected to isotherm and kinetic models to estimate the adsorption mechanism. Among all the tested adsorbents, kaolinite-synthesized materials revealed comparatively higher adsorption compared to pristine materials. It was found that pH 7 was optimum for the maximum removal of tested heavy metals. Adsorption of tested heavy metals was well explained by Langmuir and Freundlich isotherms, while pseudo-second order and Elovich kinetics models fitted well for adsorption kinetics. The maximum adsorption capacity, as predicted by the Langmuir isotherm, was the highest for BCK20 (63.19 mg g⁻¹ for Cd, 228.05 mg g⁻¹ for Cu, 248.33 mg g⁻¹ for Pb, and 45.79 mg g⁻¹ for Zn) compared to the other tested materials, and for HCK20 (31.93 mg g⁻¹ for Cd, 181.78 mg g⁻¹ for Cu, 231.85 mg g⁻¹ for Pb, and 45.72 mg g⁻¹), it was higher than pristine HC. Isotherm and kinetics modeling data indicated that multiple mechanisms were involved in Cd, Cu, Pb, and Zn removal, such as chemisorption and electrostatic interactions. The amount of oxygen-containing surface functional groups and SiO₂ particles could be responsible for the maximum adsorption of heavy metals by BCK20 and HCK20. Our findings suggest that biochar, hydrochar, and their kaolinite-modified composites possess the excellent potential to remove heavy metals from contaminated aqueous media, and could be further applied to treat wastewater to mitigate heavy metal toxicity for a sustainable environment.

Microplastics (MPs) are emerging environmental pollutants worldwide, posing potential health risks. Moreover, MPs may act as vectors for other contaminants and affect their fate, transport, and deposition in the environment. Therefore, efficient and economical techniques are needed for the removal of contemporary MPs and contaminants from the environment. The present research study investigated the sorption of phosphorus (P) and ammonium (NH₄⁺) onto date palm waste-derived biochar (BC) from an aqueous solution in the presence of polyamide (PA) and polyethylene (PE) MPs. The BC was prepared at 600 °C, characterized for physio-chemical properties, and applied for P and NH₄⁺ removal via isotherm and kinetic sorption trials. The results of the sorption trials demonstrated the highest removal of NH₄⁺ and P was obtained at neutral pH 7. The highest P sorption (93.23 mg g⁻¹) by BC was recorded in the presence of PA, while the highest NH₄⁺ sorption (103.76 mg g⁻¹) was found with co-occurring PE in an aqueous solution. Sorption isotherm and kinetics models revealed that P and NH₄⁺ removal by MP-amended BC followed chemisorption, electrostatic interaction, precipitation, diffusion, and ion exchange mechanisms. Overall, co-existing PA enhanced the removal of P and NH₄⁺ by 66% and 7.7%, respectively, while co-existing PE increased the removal of P and NH₄⁺ by 55% and 30%, respectively, through the tested BC. Our findings suggested that converting date palm waste into BC could be used as a competent and economical approach to removing P and NH₄⁺ from contaminated water. Furthermore, microplastics such as PE and PA could assist in the removal of P and NH₄⁺ from contaminated water using BC.