Mesoporous biochar composite derived from hardwood and post-recycled plastic waste in Thailand: A case study of nickel removal in acidic solution

Uncontrolled accumulation of post-recycled plastic waste poses significant environmental and sustainability challenges due to their resistance to degradation and potential for long-term pollution. This study investigates the synthesis and application of mesoporous biochar composites derived from hardwood and post-recycled plastic waste materials through slow pyrolysis, yielding a high specific area of about 42.47 m² g-1 with a total pore volume of 0.1121 cm³ g-1 and indicating mesoporous materials of pore diameter of about 24.64 nm. Comprehensive physicochemical characterization confirmed successful carbonization, with a high carbon content indicating enhanced stability and adsorption potential. The adsorption efficiency of the mesoporous hardwood-PRPW biochar was evaluated for nickel (II) ions removal from acidic aqueous solutions via batch experiments of initial concentration (0–100 mg l-1), contact time (up to 120 min), solution pH (2–8), temperature (25 ± 1 °C), and adsorbent dosage (0.5–2 g l-1). Kinetic modelling revealed that adsorption followed General Order and Fractal-Like PSO, suggesting chemisorption as the dominant process and multilayer adsorption mechanisms. Equilibrium isotherm studies indicated that the Redlich–Peterson model provided the best fit, demonstrating a hybrid monolayer and multilayer adsorption behavior with maximum adsorption capacity was determined to be 84.76 mg g-1 based on the Toth isotherm. Thermodynamic analysis confirmed the process to be spontaneous, endothermic and entropy-driven, suggesting enhanced randomness at the solid-liquid interface, favoring metal ion uptake at higher temperatures. In addition, reusability and desorption studies demonstrated that the biochar retained 87.58 % of its adsorption capacity after the first regeneration cycle, declining to 68.81 % after four cycles, while desorption efficiency decreased from 81.65 % to 43.62 %, highlighting progressive surface fouling and structural degradation. These findings establish mesoporous hardwood-PRPW biochar as a highly efficient, cost-effective, and sustainable adsorbent for nickel removal. In conclusion, the study underscores the potential of upcycling waste materials into functional adsorbents, aligning with the ideologies of sustainable environmental management.