Effects of phosphoric acid concentration on properties of activated carbon from Strychnos spinose fruit shells

The accumulation of agricultural wastes in the environment is an emerging challenge. Their thermochemical conversion to activated carbon represents an efficient form of utilization that minimizes the secondary pollution caused by conventional treatment methods, such as incineration and landfilling. This study reports the synthesis and characterization of activated carbon from an affordable, abundant, and underutilized source of Strychnos spinosa fruit shells. The activated carbon was prepared through chemical activation using phosphoric acid of different concentrations (30%, 60%, 100%, and 150%), followed by physical activation at 500 °C for 4 h. The influence of the activating agent concentrations on the properties of activated carbon, such as yield, moisture content, ash content and iodine number, was studied. Additionally, X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller and Infrared spectroscopy techniques were used to study characteristics of activated carbon. The results showed that the yield of activated carbon increased from 25.33% to 29.2% as the concentration of phosphoric acid increased from 30% to 150%. The increased acid concentration also increased the moisture content, ash content and iodine number of the activated carbon. The highest iodine number of 999 mg/g was obtained for the activated carbon with the surface area of 507.373 m²/g impregnated with 150% phosphoric acid. Similarly, the SEM images revealed larger pore sizes for activated carbon produced using 150% phosphoric acid compared to those produced using 30%, 60% and 100% phosphoric acid. The findings demonstrate that phosphoric acid concentration influences the properties and performance of the Strychnos spinosa fruit shell activated carbon.