Tuning ratios of KOH and NaOH on acetic acid-mediated chitosan-based porous carbons for improving their textural features and CO2 uptakes

Abstract

We investigated an easy approach to preparing acetic acid-mediated chitosan-based highly porous carbon adsorbents through a combination of hydrothermal treatment and chemical activation, where the ratios of activating agents (KOH and NaOH) were tailored. In this protocol, the acetic acid acts as an additive and responsible for the formation of a semi-carbonized chitosan precursor (CP) for developing a texture with ultra-high porosity. The CO2 uptake properties were modified by tuning the activators ratio. By tuning the activator ratios from 1 to 3, we obtained honeycomb-structured carbons with ultra-high specific surface area (SSA) in the range 263–4168 m2 g−1 and an ultra-high micropore volume (0.914–1.386 cm3 g−1). The adsorbents fabricated with KOH ratio of 3 and NaOH ratio of 2 showed an excellent CO2 adsorption capacities of 368 and 325 mg g−1 (8.36 and 7.38 mmol g−1), respectively, at 273 K/1 bar. Moreover, CO2 adsorption capacities remained stable in four continuous adsorption experiments, demonstrating the regenerability of samples. A few of the as-synthesized porous carbons exhibited maximum isosteric heats of adsorption; 46 kJ mol−1. Furthermore, the fabricated carbons exhibited efficient CO2 selectivity over N2. Collectively, these properties indicate that the fabricated adsorbents are promising candidates for use in CO2 adsorption applications.