Fundamental aspects and actual developments of selective CO2 capture from relevant sources (flue gas or air) by reversible physisorption are critically reviewed. Thermodynamic as well as kinetic principles of CO2 adsorption in the presence of other gases are linked to current approaches of materials development. Whilst hundreds or even thousands of porous materials have been evaluated for CO2 capture, research in this field is still full of challenges, as for instance a feasible physical adsorbent for CO2 capture for direct capture from air has still not been found. Current attempts towards the optimization of materials in terms of CO2 uptake/selectivity, regenerability, tolerance against water, and cost most often exclude each other. The aim of this article is not to summarize all recent attempts towards tailoring of materials for selective CO2 capture but to discuss the most fundamental aspects of adsorptive CO2 separation in order to illuminate the “sweet spot” to be explored when electronic structure, polarity, and pore size/geometry are rationally balanced and optimized – just like nature does when exerting selective binding of gases.

/pdf/a-search-for-selectivity-to-enable-co2-capture-with-porous-3ot3t7vwi6.pdf

A search for selectivity to enable CO2 capture with porous adsorbents

Carbon dioxide (CO2) is the main anthropogenic greenhouse gas contributing to global warming, causing tremendous impacts on the global ecosystem. Fossil fuel combustion is the main anthropogenic source of CO2 emissions. Biochar, a porous carbonaceous material produced through the thermochemical conversion of organic materials in oxygen-depleted conditions, is emerging as a cost-effective green sorbent to maintain environmental quality by capturing CO2. Currently, the modification of biochar using different physico-chemical processes, as well as the synthesis of biochar composites to enhance the contaminant sorption capacity, has drawn significant interest from the scientific community, which could also be used for capturing CO2. This review summarizes and evaluates the potential of using pristine and engineered biochar as CO2 capturing media, as well as the factors influencing the CO2 adsorption capacity of biochar and issues related to the synthesis of biochar-based CO2 adsorbents. The CO2 adsorption capacity of biochar is greatly governed by physico-chemical properties of biochar such as specific surface area, microporosity, aromaticity, hydrophobicity and the presence of basic functional groups which are influenced by feedstock type and production conditions of biochar. Micropore area (R2 = 0.9032, n = 32) and micropore volume (R2 = 0.8793, n = 32) showed a significant positive relationship with CO2 adsorption capacity of biochar. These properties of biochar are closely related to the type of feedstock and the thermochemical conditions of biochar production. Engineered biochar significantly increases CO2 adsorption capacity of pristine biochar due to modification of surface properties. Despite the progress in biochar development, further studies should be conducted to develop cost-effective, sustainable biochar-based composites for use in large-scale CO2 capture.

/pdf/biochar-based-adsorbents-for-carbon-dioxide-capture-a-bjyufk8sfw.pdf

Biochar-based adsorbents for carbon dioxide capture: A critical review

A recent report from the United Nations has warned about the excessive CO2 emissions and the necessity of making efforts to keep the increase in global temperature below 2 °C. Current CO2 capture t...

Trends in Solid Adsorbent Materials Development for CO2 Capture

Adsorption of CO2 from flue gas by novel seaweed-based KOH-activated porous biochars

Chemical doping of graphene is necessary to generate a band gap that is valuable for a range of applications. Chemical doping of graphene with elements like nitrogen and boron gives rise to useful ...

Borocarbonitrides, BxCyNz, 2D Nanocomposites with Novel Properties

Carbon capture and storage is a crucial technology for reducing atmospheric CO 2 emissions from power plants and other industrial facilities. While many technologies have been developed, the high cost and energy requirements of current CO 2 capture methods still are the primary barriers. Adsorption is one of the cost-effective options for CO 2 capture because of its low energy requirement, cost advantage, and ease of applicability over a relatively wide range of temperature and pressure. However, the success of adsorption methods depends on the development of the adsorbents with high CO 2 selectivity and capacity and easy regeneration. Although some adsorbents exhibited good CO 2 adsorption capacity, their adsorption for water vapor is an important issue for this purpose because water usually exists in flue gas streams. Activated carbons are proposed as suitable candidates for CO 2 capture: they do not require moisture removal, present a high CO 2 capacity at ambient pressures, and are easy to regenerate. However, the low selectivity to CO 2 for activated carbons is the restriction. This article reviews recent advances in surface microstructure or chemistry of carbonaceous materials as CO 2 adsorbents with emphasis on the reactions of surface functionalization, CO 2 adsorption performance and mechanism on the carbons with different features.

Surface modifications of carbonaceous materials for carbon dioxide adsorption: A review

Microporous activated carbon fibers (ACFs) were developed for CO2 capture based on potassium hydroxide (KOH) activation and tetraethylenepentamine (TEPA) amination. The material properties of the modified ACFs were characterized using several techniques. The adsorption breakthrough curves of CO2 were measured and the effect of relative humidity in the carrier gas was determined. The KOH activation at high temperature generated additional pore networks and the intercalation of metallic K into the carbon matrix, leading to the production of mesopore and micropore volumes and providing access to the active sites in the micropores. However, this treatment also resulted in the loss of nitrogen functionalities. The TEPA amination has successfully introduced nitrogen functionalities onto the fiber surface, but its long-chain structure blocked parts of the micropores and, thus, made the available surface area and pore volume limited. Introduction of the power of time into the Wheeler equation was required to fit the data well. The relative humidity within the studied range had almost no effects on the breakthrough curves. It was expected that the concentration of CO2 was high enough so that the impact on CO2 adsorption capacity lessened due to increased relative humidity.

Effect of Relative Humidity on Adsorption Breakthrough of CO2 on Activated Carbon Fibers

In this paper, multiscale composites formed by grafting N-doped carbon nanotubes (CNs) on the surface of polyamide (PAN)-based activated carbon fibers (ACFs) were investigated and their adsorption performance for CO2 was determined. The spaghetti-like and randomly oriented CNs were homogeneously grown onto ACFs. The pre-immersion of cobalt(II) ions for ACFs made the CNs grow above with a large pore size distribution, decreased the oxidation resistance, and exhibited different predominant N-functionalities after chemical vapor deposition processes. Specifically, the CNs grafted on ACFs with or without pre-immersion of cobalt(II) ions were characterized by the pyridine-like structures of six-member rings or pyrrolic/amine moieties, respectively. In addition, the loss of microporosity on the specific surface area and pore volume exceeded the gain from the generation of the defects from CNs. The adsorption capacity of CO2 decreased gradually with increasing temperature, implying that CO2 adsorption was exothermic. The adsorption capacities of CO2 at 25 °C and 1 atm were between 1.53 and 1.92 mmol/g and the Freundlich equation fit the adsorption data well. The isosteric enthalpy of adsorption, implying physical adsorption, indicated that the growth of CNTs on the ACFs benefit CO2 adsorption.

Enhanced CO2 Adsorption on Activated Carbon Fibers Grafted with Nitrogen-Doped Carbon Nanotubes

Due to its special electronic and ballistic transport properties, graphene has attracted much interest from researchers. In this study, platinum (Pt) nanoparticles were deposited on oxidized graphene sheets (cG). The graphene sheets were applied to overcome the corrosion problems of carbon black at operating conditions of proton exchange membrane fuel cells. To enhance the interfacial interactions between the graphene sheets and the Pt nanoparticles, the oxygen-containing functional groups were introduced onto the surface of graphene sheets. The results showed the Pt nanoparticles were uniformly dispersed on the surface of graphene sheets with a mean Pt particle size of 2.08 nm. The Pt nanoparticles deposited on graphene sheets exhibited better crystallinity and higher oxygen resistance. The metal Pt was the predominant Pt chemical state on Pt/cG (60.4%). The results from the cyclic voltammetry analysis showed the value of the electrochemical surface area (ECSA) was 88 m²/g (Pt/cG), much higher than that of Pt/C (46 m²/g). The long-term test illustrated the degradation in ECSA exhibited the order of Pt/C (33%) > Pt/cG (7%). The values of the utilization efficiency were calculated to be 64% for Pt/cG and 32% for Pt/C.

https://www.mdpi.com/1996-1944/8/9/5318/pdf

Yu-Chun Chiang

Papers

Surface modifications of carbonaceous materials for carbon dioxide adsorption: A review

Effect of Relative Humidity on Adsorption Breakthrough of CO2 on Activated Carbon Fibers

Enhanced CO2 Adsorption on Activated Carbon Fibers Grafted with Nitrogen-Doped Carbon Nanotubes

Characterization of Platinum Nanoparticles Deposited on Functionalized Graphene Sheets.

Effects of activation on the properties of electrospun carbon nanofibers and their adsorption performance for carbon dioxide