Selection of Pecan Shell–Based Activated Carbons for Removal of Organic and Inorganic Impurities from Water

Activated carbons are a byproduct from pyrolysis and have value as a purifying agent. The effectiveness of activated carbons is dependent on feedstock selection and pyrolysis conditions that modify their surface properties. Therefore, pecan shell–based activated carbons (PSACs) were prepared by soaking shells in 50% (v/v) H3PO4 or 25 to 50% of KOH‐NaHCO3 followed by pyrolysis at 400 to 700°C under a N2 atmosphere. Physically activated PSACs were produced by pyrolysis at 700°C under N2 followed by activation with steam or CO2 at 700 to 900°C. Physicochemical, surface, and adsorption properties of the PSACs were compared with two commercially available activated carbons. The average mass yield of PSACs with respect to the initial mass of the biomass was about 20 and 34% for physically activated and chemically activated carbons, respectively. Acid‐activated carbons exhibited higher surface area, higher bulk density, and lower ash content compared with steam‐ or CO2–activated carbons and the two commercial products. Base activation led to the development of biochar with moderate to high surface area with surface charges suitable for adsorption of anionic species. Regardless of the activation method, PSACs had high total surface area ranging from 400 to 1000 m2 g−1, better pore size distribution, and more surface charges than commercial samples. Our results also showed that PSACs were effective in removing inorganic contaminants such as Cu2+ and NO3– as well as organic contaminants such as atrazine and metolachlor. This study showed that pyrolysis conditions and activation had a large influence on the PSAC's surface characteristics, which can limit its effectiveness as a custom sorbent for targeted water contaminants.