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

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 N2/77 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 H3PO4 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 m2/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 N2. 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.

Figure shows the nitrogen adsorption isotherms of some selected carbons and displays type II isotherms, indicating that the prepared carbons with a mixed porosity character (micro-/mesoporous).Figure optionsDownload as PowerPoint slideResearch highlights
► Our current research aimed at preparation and characterization of micro-mesoporous carbons from local and renewable seed hulls such as peanut, lupine, sunflower, cotton seed, soy bean, etc.
► Various treatment schemes were applied as simple pyrolysis, steam activation and phosphoric acid activation.
► The findings were shown that chemical activation with H3PO4 at 500 °C proved to be the most recommending procedure as it leads to low ash, high yield and good quality adsorbing carbons with mixed micro-/mesopores.