Potassium and Zeolitic Structure Modified Ultra-microporous Adsorbent Materials from a Renewable Feedstock with Favorable Surface Chemistry for CO2 Capture

Biomass-based adsorbents for post-combustion CO2 capture: Preparation, performances, modeling, and assessment

The adsorbents are critical carriers in the process of adsorption-based post-combustion CO₂ capture. Biomass-based adsorbents (BAs) are considered to have great potential because of their high efficiency, low cost, and good sustainability. To understand the methods, theories, and technologies of BAs-based CO₂ capture, this work analyzes their preparation and activation/modification, influencing factors, mechanisms, thermodynamics/kinetics, regeneration and cycle performances, and the pathway to application. It is found that BAs prepared by pyrolysis, chemical activation, and modification with dual heteroatoms are more conducive to improving adsorption sites. CO₂ adsorption capacity positively correlates with elemental C and fixed carbon of feedstocks, but negatively with moisture. The BAs prepared at 550-600 °C have high performance. The specific surface area (SSA) increases as the preparation time increases by 9.4%-93.4%. The adsorption capacity is positively correlated to the SSA (R = 0.880) and microporous volume (R = 0.773). Moreover, it decreases linearly with increasing operating temperature with the slope of -0.6 mmol/(g·°C) but increases exponentially with increasing operating pressure and CO₂ concentration with the power of 0.824. The adsorption process includes physical and/or physicochemical adsorption. Freundlich isotherm equation and pseudo-second-order model characterize the adsorption thermodynamics and kinetics more effectively with R² = 0.985-1.000 and R² = 0.894-1.000. The quantum chemistry indicates that most BAs modified with non-metallic belong to physisorption. The regeneration of BAs has low energy consumption (<3.44 MJ/kg CO₂) and loss rate (<8%). Furthermore, the technical pathway is proposed for application. Finally, the challenges are also presented to facilitate the development of BAs-CO₂ capture.

From polyvinyl chloride waste to activated carbons: the role of occurring additives on porosity development and gas adsorption properties

Conversion of waste plastic to carbon materials has been considered as a potential approach for plastic recycling. In this study, polyvinyl chloride (PVC) plastic, one of the most widely used polymers, was used as a single precursor to prepare porous carbons via chemical activation process. The results showed that KOH activation followed by acid washing was an effective strategy to recover all calcium- and up to 92% of titanium-based compounds, the main metal additives in PVC, in the form of soluble salt. Those metal additives in PVC acted as a type of hard template, which benefit the development of microporosity and carbon dioxide (CO₂) adsorption. Textural characterization demonstrated that the prepared carbons possessed high surface area and pore volume of up to 2507 m²/g and 1.11 cm³/g, respectively. At 0 °C and 100 kPa, the PVC-derived carbon, PH_73, which has highest ultra-micropore volume among all samples, exhibited excellent CO₂ adsorption capacity of 6.90 mmol/g and high CO₂/N₂ selectivity. Converting the non-degradable PVC into high-quality porous carbon materials could be considered as a potential strategy for plastic waste recycling.

Hierarchical TiO2:Cu2O Nanostructures for Gas/Vapor Sensing and CO2 Sequestration

We investigate the effect of high-surface-area self-assembled TiO₂:Cu₂O nanostructures for CO₂ and relative humidity gravimetric detection using polyethylenimine (PEI), 1-ethyl-3-methylimidazolium (EMIM), and polyacrylamide (PAAm). Introduction of hierarchical TiO₂:Cu₂O nanostructures on the surface of quartz crystal microbalance sensors is found to significantly improve sensitivity to CO₂ and to H₂O vapor. The response of EMIM to CO₂ increases fivefold for 100 nm-thick TiO₂:Cu₂O as compared to gold. At ambient CO₂ concentrations, the hierarchical assembly operates as a sensor with excellent reversibility, while at higher pressures, the CO₂ desorption rate decreases, suggesting possible application for CO₂ sequestration under these conditions. The gravimetric response of PEI to CO₂ increases by a factor of 3 upon introduction of a 50 nm TiO₂:Cu₂O layer. The PAAm gravimetric response to water vapor also increases by a factor of 3 and displays improved reversibility with the addition of 50 nm TiO₂:Cu₂O structures. We found that TiO₂:Cu₂O can be used to lower the detection limits for CO₂ sensing with EMIM and PEI and lower the detection limits for H₂O sensing with PAAm by over a factor of 2. Coarse-grained and all-atom molecular dynamics simulations indicate the dissociative character of ionic liquid assembly on TiO₂:Cu₂O interfaces and different distributions of CO₂ and H₂O molecules on bare and ionic liquid-coated surfaces, confirming experimental observations. Overall, our results show high potential of hierarchical assemblies of TiO₂:Cu₂O/room temperature ionic liquid and polymer films for sensors and CO₂ sequestration.