Biomass waste from walnut shell for pollutants removal and energy storage: a review on waste to wealth transformation

The scientific community is becoming increasingly interested in the production of activated carbon (AC) using pyrolyzed biomass wastes as potential sustainable precursors. Both chemical and physical methods may have a significant impact on the chemical and physical properties of AC, making it suitable for a variety of applications such as water pollution treatment, CO₂ capture, dye, and heavy metal (HM) removal, and energy storage. The properties of AC are significantly influenced by feedstock composition, pyrolysis conditions, and carbon activation parameters. In comparison to traditional AC, activated biochar appears to be a new potentially cost-effective, and environmentally friendly carbon material with a wide range of applications. Walnut is a well-known member of the Juglandaceae family. Walnut Shell (WS) is extremely tough and degrades very slowly, and the multiple synthesis procedures employ the shell to prepare AC. In this review article, a detailed list of products and different applications of AC from the WS is provided. The cited results explain the optimal conditions for an adsorption process, which include pH, adsorbent dosage, temperature, agitation speed, contact time, efficiency, adsorption capacity, fitting model, kinetics, and thermodynamics. In addition, it also describes the removal of a few organic compounds, and energy storage applications using parameters such as BET, different electrolytes, and specific capacitance.