Development of micro-mesoporous carbons from several seed hulls under varying conditions of activation

Abstract

Seed hulls (or coats) of peanut, soybean, cottonseed, lupine, broad beans, and sunflower seeds, were subjected to various treatments in order to get adsorbing carbons. Characterization of porosity was determined by N 2/77 K adsorption isotherms. Simple pyrolysis at 500 °C yields low adsorbing carbons of meso-/macroporous character, whereas steam activation of these chars at 850 °C enhances porosity, in micropores, to a limited extent. Chemical activation with H 3PO 4 at 500 °C exerts the best recommending influence in producing high adsorbing carbons with evenly distributed porosity within micro-mesopore ranges. It was found that phosphoric acid activation of the studied precursors enhanced the yield, surface area and pore volume; 32–46%, 437–1022 m 2/g and 0.444–0.809, respectively, as compared to other treatments. The capacity to remove methylene blue, in single bottle experiments, complements the state of porosity deduced from the gas phase adsorption of N 2. Peanut shells proved the best feasible raw material under all treatment processes, whereas lupine seeds and sunflower seed hulls show relatively the least affected. Dye removal capacity was enhanced by carbon mesoporosity, whereas adversely affected by its increased surface pH and ash content was observed. Low-cost by-products of oil producing industry seem, thus, to be promising precursors for the production of highly valuable adsorbing carbons.