Synthesis of Monolithic Graphene Oxide-based Adsorbents for CO2 Capture

Abstract

A high surface area of physically activated oxygen-enriched monolithic graphene oxide was developed by a self-assembly reduction process of graphene oxide at 90 °C. The as-synthesized monoliths were physically activated (UV treatment) within different periods (2.5, 5, 10, and 15 h) and observed the CO2 adsorption effect in various conditions (temperature and concentration of CO2 flow). The synthesized monolithic properties explored the CO2 adsorption effect under dynamic conditions and revealed the CO2 capture performance. The variation in morphology, specific surface area, crystal defects, functionality detection, and CO2 capture performance were analyzed by SEM, BET, XRD/Raman, FTIR, and TGA, respectively. The optimized adsorbent reveals an excellent dynamic CO2 capture capacity of 1.65 mmol g-1 at 25 °C, owing to its elevated BET surface area of 577.3 m2 g-1. Considering the desorption step with a constant volume flow rate, it becomes evident that the pressure drop results in excessive consumption of desorbing gas (N2), approximately 50 % of the regeneration process. Several studies were investigated; the regenerability of 98.8 %, an excellent CO2/N2 selectivity, fast kinetics, the pseudo-second-order kinetic model and Freundlich isotherm model were best fitted. Thermodynamic studies reveal the heterogeneity of the adsorption site and the adsorption process endothermic nature, as indicated by ΔH° value of +13.1154139 KJ mol-1, underscoring the distinctive characteristic property of chemisorption. High surface area chemically activated carbon-enriched monolithic reduced Graphene Oxide was synthesized by self-assembly reduction process of graphene oxide at 90 °C with different weight ratios of oxalic acid (1:1, 1:0.500, and 1:0.250). The as-synthesized monoliths were carbonized (at 600 °C) and chemically activated with varying proportions of NaOH (1:1, 1:2, and 1:3). These materials offer the CO2 adsorption effect under dynamic conditions, fast mass transfer, easy handling, and outstanding stability throughout the adsorption-desorption cycle. FE-SEM and HR-TEM analyses confirmed the porous nature and shape of the adsorbents. At the same time, XPS examination revealed the presence of distinct functional groups on the surface of the monolith. By increasing the mass ratios (MGO:NaOH) from 1:1 to 1:2, the surface areas increased by approximately 2.6 times, ranging from 520.8 to 753.9 m² g⁻¹ (surface area of the untreated MGO was 289.2 m² g⁻¹). Consequently, this resulted in a notable enhancement of 2.10 mmol g⁻¹ in dynamic CO2 capture capacity. The assessment encompassed the evaluation of production yield, selectivity, regenerability, kinetics, equilibrium isotherm, and isosteric temperatures of adsorption (Qst). The decrease in CO2 capture effectiveness with rising adsorption temperature indicated an exothermic and physisorption process. The regenerability of 99.1 % at 100 °C and excellent cyclic stability with efficient CO2 adsorption make this monolithic adsorbent appropriate for post-combustion CO2 capture. The significant Qst supports the heterogeneity of the adsorbent's surface, and the pseudo-second-order kinetic model,andh the Freundlich isotherm model emerged as the most fitting. Therefore, the current investigation shows that the carbon-enriched adsorbents enhance the CO2 adsorption capacity. It may be used as a low-cost pretreatment method on an industrial scale before carbon capture. Innovating Monolithic Graphene Oxide Frameworks were prepared through the utilization of innovative porous crystalline structures established via KOH-treated monolithic graphene oxide frameworks. These materials exhibit remarkable and versatile characteristics for both functional exploration and applications within the realm of CO2 capture. In this comprehensive study, we have synthesized monolithic reduced graphene oxide-based adsorbents through a meticulous self-assembly process involving different mass ratios of GO/malic acid (MaA) (1:0.250, 1:0.500, and 1:1 by weight). Building upon this foundation, we further modified MGO 0.250 through KOH treatment by chloroacetic acid method, leading to the creation of MGO 0.250_KOH, which was subjected to CO2 capture assessments. The comprehensive investigation encompassed an array of parameters, including morphology, specific surface area, crystal defects, functional group identification, and CO2 capture efficiency. Employing a combination of FT-IR, XRD, Raman, BET, SEM, HR-TEM, and XPS techniques, the study revealed profound insights. Particularly notable was the observation that the MGO 0.250_KOH adsorbent exhibited an exceptional CO2 capture performance, leading to a significant enhancement of the CO2 capture capacity from 1.69 mmol g-1 to 2.35 mmol g-1 at standard conditions of 25 °C and 1 bar pressure. This performance enhancement was concomitant with an augmentation in surface area, elevating from 287.93 to 419.75 m2 g-1 (a nearly 1.5-fold increase compared to MGO 1.000 with a surface area of 287.93 m2 g-1). The monolithic adsorbent demonstrated a commendable production yield of 82.92%, along with an impressive regenerability of 98.80% at 100 °C. Additionally, adsorbent's proficiency in CO2 adsorption renders it a promising candidate for post-combustion CO2 capture applications. These findings collectively underscore the capacity of adsorbents to significantly amplify CO2 capture capabilities. The viability of employing this strategy as an uncomplicated pre-treatment technique in various industrial sectors is a plausible prospect, given the study's outcomes.