Synthesis and characterization of biomass-derived surface-modified activated carbon for enhanced CO2 adsorption

[Display omitted] •Surface-modified ACs were prepared from corncob derived hydro-char.•Higher CO2 adsorption capacity is linked with high surface area and pore volume.•At lower temperatures and higher pressure, ACs exhibited high adsorption capacity.•AC-KOH exhibited the highest CO2 adsorption of 198 mg/g at 15 °C and 1 bar.•Thermodynamic parameters of the adsorption process were also evaluated. In this study, activated carbon (AC) based adsorbents were synthesized from biomass-derived hydro-char (HC) through modified hydrothermal carbonization (HTC) process coupled with H3PO4 (PA), ZnCl2, (ZnCl), and KOH thermochemical activation with a specific impregnation ratio of 1:3 (HC/activating agent) at 600 °C. The prepared ACs were characterized through CHN-S analyser, XRD, SEM/EDS, BET, TGA, and FTIR analysis. The modification in textural and surface morphology has been observed. Thermochemical activation results in surface modification of AC samples with a higher specific (SBET) surface area having a range of 650−1225 m2/g, large microporous volume (VμD-A, VμD–R) up to 0.624 and 0.642 cm3/g with 68–90 % micro-porosity. The CO2 adsorption capacity was examined through a high-pressure gas sorption analyser at a pressure of 0−16 bar and temperature of 15 °C, 30 °C, and 45 °C. At 15 °C of temperature, AC-PA showed the adsorption capacity of 130 and 958 mg/g, while AC-ZnCl exhibited 160 and 836 mg/g of adsorption at 1 and 16 bar of pressure respectively. Whereas AC-KOH exhibited a notable CO2 adsorption capacity of 198 and 1560 mg/g at 1 and 16 bar of pressure (15 °C). Furthermore, experimental equilibrium data of CO2 adsorption were analysed by applying Freundlich, Langmuir, Redlich-Peterson, Sips, and Toth isotherm models and validate these models by calculating the regression coefficient (R2), and standard deviation Δq (%). Finally, the thermodynamics parameters (ΔH°, ΔS°, ΔG°, and ΔHIsosteric) were evaluated and concluded that the adsorption of CO2 (adsorbate) on adsorbent is spontaneous and exothermic.