Capturing water vapors from humid air using microporous activated carbon derived from sunflower seed shells

Abstract

Water extraction from the atmosphere using solid desiccants is becoming an increasingly viable option for human consumption. Using sustainable raw materials is imperative to reduce the carbon footprint in the mass production of such desiccants. In this paper, we synthesized microporous activated carbon from sunflower seed shells (SSS-AC) to capture water vapors from humid or moist air. Sunflower seed shells (SSS) are an agricultural waste product that makes the final product a sustainable and environment-friendly alternative to traditional solid desiccants. Chemical activation was carried out using KOH as the activating agent, and the ratio of activating agent to carbon was 2:1. Different structural and morphological properties of synthesized microporous activated carbon (SSS-AC) were studied using FTIR, XRD, SEM, EDAX, and TGA characterization techniques. The surface area and pore distribution were characterized using N2 adsorption/desorption studies, where a steep initial uptake with a wide capillary condensation step was observed for SSS-AC. The pore distribution of SSS-AC showed high pore volume in the microporous range. The pHpzc value for the SSS-AC was measured to be 10.24 while the HI value was found to be 6.26, indicating an alkaline and hydrophobic surface. Water adsorption studies were carried out at 25, 35, and 45 °C, and the material was found to exhibit type-V isotherm, which is common for microporous activated carbons and indicates the likely occurrence of pore condensation. The SSS-AC reported a maximum adsorption capacity of 0.454 gwat/gads at 90% relative humidity and 25 °C, which is higher than some complex desiccants reported in the literature. The adsorption capacity of SSS-AC decreased with increasing temperature since, at higher temperatures, the pore-filling mechanism is hindered.