Jute stick/stalk can be used to prepared and carboxylated to yield useful activated carbons, e.g., for removing Pb2+ from drinking water. Such activated carbons can act as an inexpensive adsorbents using agricultural waste or by-products. Carboxylation of jute stick activated carbon (JSAC) can improve its efficiency for Pb2+ removal, e.g., from aqueous solutions, even if its BET surface area is reduced. Carboxylated JSAC (JSAC-COO−) can have surface areas around 615.3±0.5, 1, 2.5, 5, 10, 15, 20, or 25 m2/g. JSAC-COO− can treat varied Pb2+ concentrations, 10, 25 mg/L, etc., pHs, e.g., 4.0, 7.0, etc., temperatures, e.g., 15° C., 27° C., etc., and contact periods, e.g., 1, 5, 10, 15, 30, 60 minutes, etc., achieving up to 99.8% Pb2+ removal within 15 minutes of contact JSAC-COO− adsorption capacity can be >25.0 mg Pb2+/g, as well as other metal ions, with potential for water and/or gas treatment.