Ultra-Microporous and Stable MOFs with Zero-Linker Ligands for Gas Capture and Separation.

Zero-linker ligands have maximized the size coordination efficiency of the metal ions in MOF framework which is important in constructing ultra-microporous MOFs with high stability and density, a bridge between zeolites and traditional MOFs. This article highlighted several recently developed ultra-microporous MOFs with zero-linker ligands for gas capture and separation.

CO2 adsorption on pyrolysis char from protein-containing livestock waste: How do proteins affect?

Biogas generation through anaerobic digestion provides an interesting opportunity to valorize some types of animal waste materials whose management is increasingly complicated by legal and environmental restrictions. To successfully expand anaerobic digestion in livestock areas, operational issues such as digestate management must be addressed in an economical and environmentally sustainable way. Biogas upgrading is another necessary stage before intending it to add-value applications. The high concentration of CO2 in biogas results in a reduced caloric value, so the removal of CO2 would be beneficial for most end-users. The current work evaluates the CO2 uptake properties (thermogravimetry study) of low-cost adsorbent materials produced from the animal wastes generated in the livestock area itself, specifically via pyrolysis of poorly biodegradable materials, such as meat and bone meal, and the digestate from manure anaerobic digestion. Therefore, the new element in this study with respect to other studies found in the literature related to biochar-based CO2 adsorption performance is the presence of high content of pyrolyzed proteins in the adsorbent material. In this work, pyrolyzed chars from both meat and bone meal and co-digested manure have been proven to adsorb CO2 reversibly, and also the chars produced from their representative pure proteins (collagen and soybean protein), which were evaluated as model compounds for a better understanding of the individual performance of proteins. The ultra-microporosity developed in the protein chars during pyrolysis seems to be the main explanation for such CO2 uptake capacities, while neither the BET surface area nor N-functionalities on the char surface can properly explain the observed results. Although the CO2 adsorption capacities of these pristine chars (6-41.0 mg CO2/g char) are far away from data of commercially activated carbons (~80 mg CO2/g char), this application opens a new via to integrate and valorize these wastes in the circular economy of the primary sector.

Synergistic Effect of Nitrogen Doping and Ultra-Microporosity on the Performance of Biomass and Microalgae-Derived Activated Carbons for CO2 Capture.

We report a unique naturally derived activated carbon with optimally incorporated nitrogen functional groups and ultra-microporous structure to enable high CO2 adsorption capacity. The coprocessing of biomass (Citrus aurantium waste leaves) and microalgae (Spirulina) as the N-doping agent was investigated by probing the parameter space (biomass/microalgae weight ratio, reaction temperature, and reaction time) of hydrothermal carbonization and activation process (via the ZnCl2/CO2 activation) to generate hydrochars and activated carbons, respectively, with tunable nitrogen content and pore sizes. The central composite-based design of the experiment was applied to optimize the parameters of the prehydrothermal carbonization procedure resulting in the fabrication of N-enriched carbonaceous products with the highest possible mass yield and nitrogen content. The resulting hydrochars and activated carbon samples were characterized using elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and Brunauer-Emmett-Teller surface area analysis. We observe that while N-doping and the activation process can individually enhance the CO2 adsorption capacity to some extent, it is the combined effect of the two processes that synergistically work to greatly increase the adsorption capacity of the N-doped activated carbon by an amount which is more than the sum of individual contributions. We analyze the origins of this synergy with both physical and chemical characterization techniques. The resulting naturally derived activated carbon demonstrates one of the highest CO2 adsorption capacities (8.43 mmol/g) with rapid adsorption kinetics and good selectivity and reusability.

Adamantane-Based Micro- and Ultra-Microporous Frameworks for Efficient Small Gas and Toxic Organic Vapor Adsorption.

Microporous organic polymers and related porous materials have been applied in a wide range of practical applications such as adsorption, catalysis, adsorption, and sensing fields. However, some limitations, like wide pore size distribution, may limit their further applications, especially for adsorption. Here, micro- and ultra-microporous frameworks (HBPBA-D and TBBPA-D) were designed and synthesized via Sonogashira⁻Hagihara coupling of six/eight-arm bromophenyl adamantane-based "knots" and alkynes-type "rod" monomers. The BET surface area and pore size distribution of these frameworks were in the region of 395⁻488 m² g-1, 0.9⁻1.1 and 0.42 nm, respectively. The as-made prepared frameworks also showed good chemical ability and high thermal stability up to 350 °C, and at 800 °C only 30% mass loss was observed. Their adsorption capacities for small gas molecules such as CO2 and CH4 was 8.9⁻9.0 wt % and 1.43⁻1.63 wt % at 273 K/1 bar, and for the toxic organic vapors n-hexane and benzene, 104⁻172 mg g-1 and 144⁻272 mg g-1 at 298 K/0.8 bar, respectively. These are comparable to many porous polymers with higher BET specific surface areas or after functionalization. These properties make the resulting frameworks efficient absorbent alternatives for small gas or toxic vapor capture, especially in harsh environments.

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

Novel hierarchically structured microporous biocarbons with exceptionally high capacities for CO2 capture have been synthesized from the abundant agricultural waste of rice husk (RH), using a facile methodology that effectively integrated carbonization, activation, and potassium intercalation into a one-step process. Textural characterization demonstrates that the synthesized biocarbons exhibit exceedingly high ultra-microporosity accounting for up to 95% of total porosity mainly as a result of the naturally occurring silicon compounds within the RH molecular framework structures. With a modest surface area of up to 1035 m2/g and a total pore volume of 0.43 cm3/g, the best performing RH carbon has shown exceptionally high and fully reversible CO2 uptake capacity of 2.0 mmol/g at 25 °C and a CO2 partial pressure of 0.15 bar, which represents one of the highest uptakes ever reported for both carbon and MOF materials usually prepared from using cost-prohibitive precursor materials with cumbersome methodologies. It has been found that up to 50% of the total CO2 uptake is attributable to the unique surface chemistry of the RH carbons, which appears to be dominated by the enhanced formation of extra-framework potassium cations owing to the exceedingly high levels of ultra-microporosity and the presence of zeolitic structures incorporated within the carbon matrices. Characterizations by EDX element mapping, XPS, and heat of adsorption measurements confirm the existence of a range of zeolitic structures, which essentially transforms the RH carbons into a kind of zeolite-carbon nanocomposite material with strong surface affinity for CO2.