CO2 absorption and sequestration as various polymorphs of CaCO3 using sterically hindered amine

Composite Porous Liquid for Recyclable Sequestration, Storage and In Situ Catalytic Conversion of Carbon Dioxide at Room Temperature

Permanent pores combined with fluidity renders flow processability to porous liquids otherwise not seen in porous solids. Although porous liquids have been utilized for sequestration of different gases and their separation, there is still a dearth of studies for deploying in situ chemical reactions to convert adsorbed gases into utility chemicals. Here, we show the design and development of a new type of solvent-less and hybrid (meso-)porous liquid composite, which, as demonstrated for the first time, can be used for in situ carbon mineralization of adsorbed CO₂ . The recyclable porous liquid composite comprising polymer-surfactant modified hollow silica nanorods and carbonic anhydrase enzyme not only sequesters (5.5 cm³  g^-1 at 273 K and 1 atm) and stores CO₂ but is also capable of driving an in situ enzymatic reaction for hydration of CO₂ to HCO₃ ^- ion, subsequently converting it to CaCO₃ due to reaction with pre-dissolved Ca²⁺ . Light and electron microscopy combined with X-ray diffraction reveals the nucleation and growth of calcite and aragonite crystals. Moreover, the liquid-like property of the porous composite material can be harnessed by executing the same reaction via diffusion of complimentary Ca²⁺ and HCO₃ ^- ions through different compartments separated by an interfacial channel. These studies provide a proof of concept of deploying chemical reactions within porous liquids for developing utility chemical from adsorbed molecules.

Enzymes for Efficient CO2 Conversion

The accumulation of carbon dioxide in the atmosphere as a result of human activities has caused a number of adverse circumstances in the world. For this reason, the proposed solutions lie within the aim of reducing carbon dioxide emissions have been quite valuable. However, as the human activity continues to increase on this planet, the possibility of reducing carbon dioxide emissions decreases with the use of conventional methods. The emergence of compounds than can be used in different fields by converting the released carbon dioxide into different chemicals will construct a fundamental solution to the problem. Although electro-catalysis or photolithography methods have emerged for this purpose, they have not been able to achieve successful results. Alternatively, another proposed solution are enzyme based systems. Among the enzyme-based systems, pyruvate decarboxylase, carbonic anhydrase and dehydrogenases have been the most studied enzymes. Pyruvate dehydrogenase and carbonic anhydrase have either been an expensive method or were incapable of producing the desired result due to the reaction cascade they catalyze. However, the studies reporting the production of industrial chemicals from carbon dioxide using dehydrogenases and in particular, the formate dehydrogenase enzyme, have been remarkable. Moreover, reported studies have shown the existence of more active and stable enzymes, especially the dehydrogenase family that can be identified from the biome. In addition to this, their redesign through protein engineering can have an immense contribution to the increased use of enzyme-based methods in CO₂ reduction, resulting in an enormous expansion of the industrial capacity.

Metal Organic Framework - Based Mixed Matrix Membranes for Carbon Dioxide Separation: Recent Advances and Future Directions

Gas separation and purification using polymeric membranes is a promising technology that constitutes an energy-efficient and eco-friendly process for large scale integration. However, pristine polymeric membranes typically suffer from the trade-off between permeability and selectivity represented by the Robeson's upper bound. Mixed matrix membranes (MMMs) synthesized by the addition of porous nano-fillers into polymer matrices, can enable a simultaneous increase in selectivity and permeability. Among the various porous fillers, metal-organic frameworks (MOFs) are recognized in recent days as a promising filler material for the fabrication of MMMs. In this article, we review representative examples of MMMs prepared by dispersion of MOFs into polymer matrices or by deposition on the surface of polymeric membranes. Addition of MOFs into other continuous phases, such as ionic liquids, are also included. CO2 separation from hydrocarbons, H2, N2, and the like is emphasized. Hybrid fillers based on composites of MOFs with other nanomaterials, e.g., of MOF/GO, MOF/CNTs, and functionalized MOFs, are also presented and discussed. Synergetic effects and the result of interactions between filler/matrix and filler/filler are reviewed, and the impact of filler and matrix types and compositions, filler loading, surface area, porosity, pore sizes, and surface functionalities on tuning permeability are discoursed. Finally, selectivity, thermal, chemical, and mechanical stability of the resulting MMMs are analyzed. The review concludes with a perspective of up-scaling of such systems for CO2 separation, including an overview of the most promising MMM systems.

Characterization of novel calcium hydroxide-mediated highly porous chitosan-calcium scaffolds for potential application in dentin tissue engineering

The aim of this study was to develop a highly porous calcium-containing chitosan scaffold suitable for dentin regeneration. A calcium hydroxide (Ca[OH]₂ ) suspension was used to modulate the degree of porosity and chemical composition of chitosan scaffolds. The chitosan solution concentration and freezing protocol were adjusted to optimize the porous architecture using the phase-separation technique. Scanning electron microscopy/energy-dispersive spectroscopy demonstrated the fabrication of a highly porous calcium-linked chitosan scaffold (CH-Ca), with a well-organized and interconnected porous network. Scaffolds were cross-linked on glutaraldehyde (GA) vapor. Following a 28-day incubation in water, cross-linked CH scaffold had no changes on humid mass, and CH-Ca featured a controlled degradability profile since the significant humid mass loss was observed only after 21 (26.0%) and 28 days (42.2%). Fourier-transform infrared spectroscopy indicated the establishment of Schiff base on cross-linked scaffolds, along with calcium complexation for CH-Ca. Cross-linked CH-Ca scaffold featured a sustained Ca²⁺ release up to 21 days in a humid environment. This porous and stable architecture allowed for human dental pulp cells (HDPCs) to spread throughout the scaffold, with cells exhibiting a widely stretched cytoplasm; whereas, the cells seeded onto CH scaffold were organized in clusters. HDPCs seeded onto CH-Ca featured significantly higher ALP activity, and gene expressions for ALP, Col1, DMP-1, and DSPP in comparison to CH, leading to a significant 3.5 times increase in calcium-rich matrix deposition. In sum, our findings suggest that CH-Ca scaffolds are attractive candidates for creating a highly porous and bioactive substrate for dentin tissue engineering.

Rapid CO2 capture-to-mineralisation in a scalable reactor

A CO₂ mineralisation process using brine solutions with a catalyst was investigated from experimental and modelling perspectives.

Biogenic Calcium Carbonate with Hierarchical Organic-Inorganic Composite Structure Enhancing the Removal of Pb(II) from Wastewater

Calcium carbonate from geological sources (geo-CaCO₃, e.g., calcite, aragonite) is used extensively in removing heavy metals from wastewater through replacement reaction. However, geo-CaCO₃ has an intrinsically compact crystalline structure that results in low efficiency in pollutant removal and thus its use may produce enormous sludge. In this work, biogenic calcium carbonate (bio-CaCO₃) derived from oyster shells was used to remove Pb(II) from wastewater and found to significantly outperform geo-CaCO₃ (calcite). The thermodynamics study revealed that the maximum adsorption capacity of bio-CaCO₃ for Pb(II) was three times that of geo-CaCO₃, reaching up to 1667 mg/g. The kinetics study disclosed that the dissolution kinetics and the rate of intraparticle diffusion of bio-CaCO₃ were faster than those of geo-CaCO₃. Extensive mechanism research through X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption/desorption test and mercury intrusion porosimetry showed that the hierarchical porous organic-inorganic hybrid structure of bio-CaCO₃ expedited the dissolution of CaCO₃ to provide abundant CO₃^2- active sites and facilitated the permeation and diffusion of Pb(II) into the bulk solid phases. In addition, Fourier transform infrared spectroscopy (FTIR) study, X-ray photoelectron spectroscopy (XPS) analysis, and the examination of Pb(II) removal ability of bio-CaCO₃ after calcination indicated that the organic functional groups of bio-CaCO₃ also facilitated the immobilization of Pb(II) into CaCO₃ particles, although the major contribution was from the hierarchical porous structure of bio-CaCO₃.

Ammonium-Carbamate-Rich Organogels for the Preparation of Amorphous Calcium Carbonates

Amine-CO2 chemistry is important for a range of different chemical processes, including carbon dioxide capture. Here, we studied how aspects of this chemistry could be used to prepare calcium carbonates. Chemically crosslinked organogels were first prepared by reacting hyperbranched polyethylene imine (PEI) dissolved in DMSO with carbon dioxide. The crosslinks of the organogel consisted of ammonium-carbamate ion pairs as was shown by IR spectroscopy. These carbamate-rich organogels were subsequently subjected to aqueous solutions of calcium acetate, and amorphous calcium carbonate (ACC) precipitated. The ACC did not crystalize during the mixing for up to 20 h, as was shown by a combination of IR spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal analysis. Some PEI had been included or adsorbed on the ACC particles. Traces of calcite were observed in one sample that had been subjected to water in a work-up procedure.

The salt-based catalytic enhancement of CO2 absorption by a tertiary amine medium

An improved CO₂ sequestration method is proposed that uses new catalysts, specifically a series of tertiary amine nitrate salts, in an aqueous tertiary amine medium.

Carbon Dioxide Sequestration by Using a Model Carbonic Anhydrase Complex in Tertiary Amine Medium

Globally, the elevation of carbon dioxide (CO2 ) levels due to the anthropogenic effect poses a serious threat to the ecosystem. Hence, it is important to control and/or mitigate the level of CO2 in the atmosphere, which necessitates novel tools. Herein, it is proposed to improve CO2 sequestration by using model complexes based on the enzyme carbonic anhydrase (CA) in aqueous tertiary amine medium. The effect of substituents on the model CA model complexes on CO2 absorption and desorption was determined by using a stopped-flow spectrophotometer to follow pH changes through coupling to pH indicator and a continuous stirred-tank reactor (CSTR). The CO2 hydration rate constants were determined under basic conditions and compound 6, which contained a hydrophilic group, showed the highest absorption or hydration levels of CO2 (2.860×10(3)  L mol(-1)  s(-1) ). In addition, CSTR results for the absorption and desorption of CO2 suggest that simple model CA complexes could be used in post-combustion processing.

Morphology Control in the Synthesis of CaCO₃ Microspheres with a Novel CO₂Storage Material

A green and template-free method was applied to control the morphology of CaCO3 microspheres with a layered nanostructure surface and pure crystalline phase of vaterite via the hydrothermal reaction between Ca(OH)2 saturated limpid solution and a novel CO2-storage material (CO2SM). Morphologies of the as-prepared CaCO3 crystals could be tuned with CO2SM concentration, reaction temperature, or crystallization time. After the precipitation of CaCO3 crystals, the filtered solution could not only be used to absorb CO2 but also to produce CaCO3 microspheres repeatedly with the addition of Ca(OH)2 solution. Furthermore, an aggregation and self-assembly mechanism for the formation CaCO3 microspheres had been proposed. As a result, this novel synthesis strategy of CaCO3 microspheres with CO2SM again emphasized that was possible to synthesize inorganic/organic hybrid materials with exquisite morphology and offered an alternative way for comprehensive utilization of CO2.

Enzymatic conversion of carbon dioxide

With the continuous increase in fossil fuels consumption and the rapid growth of atmospheric CO2 concentration, the harmonious state between human and nature faces severe challenges. Exploring green and sustainable energy resources and devising efficient methods for CO2 capture, sequestration and utilization are urgently required. Converting CO2 into fuels/chemicals/materials as an indispensable element for CO2 capture, sequestration and utilization may offer a win-win strategy to both decrease the CO2 concentration and achieve the efficient exploitation of carbon resources. Among the current major methods (including chemical, photochemical, electrochemical and enzymatic methods), the enzymatic method, which is inspired by the CO2 metabolic process in cells, offers a green and potent alternative for efficient CO2 conversion due to its superior stereo-specificity and region/chemo-selectivity. Thus, in this tutorial review, we firstly provide a brief background about enzymatic conversion for CO2 capture, sequestration and utilization. Next, we depict six major routes of the CO2 metabolic process in cells, which are taken as the inspiration source for the construction of enzymatic systems in vitro. Next, we focus on the state-of-the-art routes for the catalytic conversion of CO2 by a single enzyme system and by a multienzyme system. Some emerging approaches and materials utilized for constructing single-enzyme/multienzyme systems to enhance the catalytic activity/stability will be highlighted. Finally, a summary about the current advances and the future perspectives of the enzymatic conversion of CO2 will be presented.

A bio-inspired nacre-like layered hybrid structure of calcium carbonate under the control of carboxyl graphene

Schematic illustration of the fabrication of GO-COOH/CaCO₃ multilayer hybrid structures: GO-COOH, the GO-COOH/CaCl₂ multilayer hybrid structure, and the GO-COOH/CaCO₃ hybrid multilayer structure (from left to right).

NMR characterization of hydrocarbon adsorption on calcite surfaces: a first principles study

The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca(2+). Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO3 (101¯4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for (43)Ca, (13)C, and (17)O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.