Vishwanath Hiremath

Fine-Tuning of the Carbon Dioxide Capture Capability of Diamine-Grafted Metal-Organic Framework Adsorbents Through Amine Functionalization.

A combined sonication and microwave irradiation procedure provides the most effective functionalization of ethylenediamine (en) and branched primary diamines of 1-methylethylenediamine (men) and 1,1-dimethylethylenediamine (den) onto the open metal sites of Mg2 (dobpdc) (1). The CO2 capacities of the advanced adsorbents 1-en and 1-men under simulated flue gas conditions are 19 wt % and 17.4 wt %, respectively, which are the highest values reported among amine-functionalized metal-organic frameworks (MOFs) to date. Moreover, 1-den exhibits both a significant working capacity (12.2 wt %) and superb CO2 uptake (11 wt %) at 3 % CO2 . Additionally, this framework showcases the superior recyclability; ultrahigh stability after exposure to O2 , moisture, and SO2 ; and exceptional CO2 adsorption capacity under humid conditions, which are unprecedented among MOFs. We also elucidate that the performance of CO2 adsorption can be controlled by the structure of the diamine ligands grafted such as the number of amine end groups or the presence of side groups, which provides the first systematic and comprehensive demonstration of fine-tuning of CO2 uptake capability using different amines.

Mesoporous magnesium oxide nanoparticles derived via complexation-combustion for enhanced performance in carbon dioxide capture

Magnesium oxide (MgO) is a promising candidate for carbon dioxide (CO2) capture at high temperature applicable to pre-combustion capture in an integrated gasification combined cycle (IGCC) scheme. In this work, mesoporous MgO nanoparticles were synthesized via simple complexation-combustion method by using glycine (G) and urea (U) as fuels (F). The obtained sorbents were thoroughly characterized in terms of the crystalline structure, morphology, nature of the fuel, F/O ratio, and their consequent effects on CO2 sorption. It was observed that due to the complexation followed by combustion in the presence of glycine, MgO with crystallite size as small as∼8nm could be derived. The synthesized MgO nanoparticles exhibited exceptionally high CO2 sorption at elevated temperatures. Furthermore, CO2 sorption isotherms in assistance with FT-IR and DSC experiments demonstrated that the low CO2 uptake at ambient temperature (25-100°C) may be due to the formation of monodentate carbonates, whereas predominant bicarbonates enhance the CO2 uptake at elevated temperatures (100-300°C). MgO-1.5(G) obtained the highest sorption corresponding to 1.34mmol/g at 200°C.

Synergistic activating effect of promoter and oxidant in single step conversion of methane into methanol over a tailored polymer-Ag coordination complex

Single-step conversion of methane to its oxygenated derivatives, such as methanol, is a challenging topic in C1 chemistry. The presence of Bronsted-acidic sites, N- and O-type chelating ligands, and noble metals are demonstrated to be essential criteria for effective catalysis of this reaction. Considering these criteria, a catalytic complex was tailored herein. Poly-D-glucosamine (Ch) was used as chelating ligand for Ag, to incorporate the robust redox properties of Ag(I). The prepared AgCh complex was characterized by techniques including solid-state 1H-NMR, FE-TEM, XANES, and XPS. Besides highlighting the utility of chelate complexation for providing new materials, this study elucidates the effects of the oxidant and promoters on the methane oxidation. The catalytic activity was tested for different oxidant combinations, including hydrogen peroxide, oxygen, and carbon dioxide. Of all of them, a mixture of hydrogen peroxide and oxygen showed the highest selectivity for oxidation of methane to methanol. Further, it was observed that the addition of 1-butyl-3-methylimidazolium chloride [BMIM]+Cl− as a promoter to the hydrogen peroxide and oxygen-containing AgCh system could enhance methanol production. The methanol yield reached up to 3166 μmol, representing an 18-fold yield increase and an 8-fold methane conversion increase when compared to the results (175 μmol) without a promoter.

Eutectic mixture promoted CO 2 sorption on MgO-TiO 2 composite at elevated temperature

The development of carbon dioxide (CO2) sorbents that can operate at elevated temperatures is significant for the advancement of pre-combustion capture technologies. Recently, promoter-based systems composed of alkali/alkaline earth metal nitrates and/or carbonates have been considered as next-generation solid sorbents due to their improved CO2 uptake and kinetics. However, obtaining stable MgO sorbents against temperature swing regeneration still remained challenging. Herein, we report MgO-TiO2 solid sorbents promoted by eutectic mixture (KNO3 and LiNO3) for elevated temperature CO2 sorption. The developed sorbents show improved CO2 sorption capacity, which may be attributed to the alternative CO2 sorption pathway provided by the ionization of highly dispersed MgO in the eutectic mixture. The MgO-TiO2 framework was also shown to assist in retaining the MgO configuration by constraining its interaction with CO2. Furthermore, it is demonstrated that constructing composite structures is essential to improve the CO2 sorption characteristics, mainly recyclability, at elevated temperatures. The developed promoter integrated sorbents showed exceptionally high CO2 sorption capacity of >30wt.% at an elevated temperature (300°C) with pronounced stability under temperature swing operation.

Stabilization of NaNO3-Promoted Magnesium Oxide for High-Temperature CO2 Capture

NaNO3-promoted MgO sorbents are known to achieve enhanced CO2 sorption uptake but fail to maintain their capacity after multiple sorption-regeneration cycles. In this study, commercially available hydrotalcites (Pural Mg30, Pural Mg70, and synthetic hydrotalcite) were used as stabilizers for NaNO3-impregnated MgO (MgONaNO3) sorbents to improve their cyclic stability. Results show that the Mg30-stabilized MgONaNO3 attained higher and stable overall CO2 sorption performance as compared to bare MgONaNO3 after multiple sorption cycles. XRD analyses reveal that the hydrotalcites act as templates for MgCO3 by restricting the formation of large and nonuniform product crystallites. Furthermore, CO2-TPD results show that the hydrotalcites cause a change in the basic sites of the sorbent, which may be attributed to its high interaction with both MgO and NaNO3. This interaction becomes stronger as cycles proceed due to the structural rearrangements occurring, thus contributing to the stable behavior of the sorbents. However, these characteristics were not found on MgONaNO3 and the α-Al2O3-stabilized samples, thus proving the unique ability of hydrotalcites. From these results, we then derived the formation scheme of MgCO3 on the hydrotalcite-stabilized sorbents. This study presents a simple yet effective method of improving the stability of molten salt-promoted sorbents with promising potential for industrial use.

Induced application of biological waste Escherichia coli functionalized with an amine-based polymer for CO2 capture

Carbon dioxide adsorption by solid sorbents is a promising technology to mitigate the greenhouse effect. To utilize biological waste as an alternative solid sorbent for CO2 capture, the surface of the biological waste Escherichia coli was modified through polymerization of poly(allylamine hydrochloride) with a crosslinking agent (epicholorohydrine). We found that the surface-modified PEI/E. coli showed good CO2 adsorption performance in terms of capacity (1.8 wt%) and amine efficiency (0.93 mmol CO2 per mmol N) compared with that of pristine E. coli (0.7 wt%). Furthermore, the heat of CO2 adsorption (71.67 kJ mol−1) supports the moderate interaction between CO2 and PEI/E. coli for favorable CO2 adsorption and desorption. Density functional theory calculations were carried out to investigate the PEI activity comprehensively in terms of structural deformation and binding energetics between CO2 and the PEI polymer with molecular adsorption mechanisms. This approach could open up the possibility of surface modification of biological waste and new pathways to reuse biological waste as an alternative source to reduce the concentration of various greenhouse gases, thereby conserving the environmental balance.