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

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 (V?D-A, V?D?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 ?q (%). Finally, the thermodynamics parameters (?H?, ?S?, ?G?, and ?HIsosteric) were evaluated and concluded that the adsorption of CO2 (adsorbate) on adsorbent is spontaneous and exothermic.

Automated summary

In this study, activated carbon based adsorbents were synthesized from hydro-char through modified hydrothermal carbonization and thermochemical activation methods, exhibiting high specific surface area and microporous volume with notable CO2 adsorption capacity. The experimental data fit various adsorption isotherm models, and the adsorption of CO2 was found to be spontaneous and exothermic on the adsorbent.