Search

Solid-supported amines are effective CO 2 adsorbents capable of capturing CO 2 from flue gas streams (10-15 vol % CO 2 ) and from ultradilute streams, such as ambient air (∼400 ppm CO 2 ). Amine sorbents have demonstrated promising performance (e.g., high CO 2 uptake and uptake rates) with stable characteristics under repeated, idealized thermal swing conditions, enabling multicycle application. Literature studies suggest that solid-supported amines such as PEI/SBA-15 generally exhibit slowly reducing CO 2 uptake rates or capacities over repeated thermal swing capture-regeneration cycles under simulated DAC conditions. While there are experimental reports describing changes in supported amine mass, degradation of amine sites, and changes in support structures over cycling, there is limited knowledge about the structure and mobility of the amine domains in the support pores over extended use. Furthermore, little is known about the effects of H 2 O on cyclic applications of PEI/SBA-15 despite the inevitable presence of H 2 O in ambient air. Here, we present a series of neutron scattering studies exploring the distribution and mobility of PEI in mesoporous silica SBA-15 as a function of thermal cycling and cyclic conditions. Small-angle neutron scattering (SANS) and quasielastic neutron scattering (QENS) are used to study the amine and H 2 O distributions and amine mobility, respectively. Applying repeated thermal swings under dry conditions leads to the thorough removal of water from the sorbent, causing thinner and more rigid wall-coating PEI layers that eventually lead to slower CO 2 uptake rates. On the other hand, wet cyclic conditions led to the sorption of atmospheric water at the wall-PEI interfaces. When PEI remains hydrated, the amine distribution (i.e., wall-coating PEI layer thickness) is retained over cycling, while lubrication effects of water yield improved PEI mobility, in turn leading to faster CO 2 uptake rates., Competing Interests: The authors declare the following competing financial interest(s): C.W.J. has a financial interest in several companies that seek to commercialize CO2 capture from air. C.W.J. has a conflict-of-interest management plan in place at Georgia Tech., (© 2024 The Authors. Published by American Chemical Society.)

Solid-supported amines having low molecular weight branched poly(ethylenimine) (PEI) physically impregnated into porous solid supports are promising adsorbents for CO 2 capture. Co-impregnating short-chain poly(ethylene glycol) (PEG) together with PEI alters the performance of the adsorbent, delivering improved amine efficiency (AE, mol CO 2 sorbed/mol N) and faster CO 2 uptake rates. To uncover the physical basis for this improved gas capture performance, we probe the distribution and mobility of the polymers in the pores via small angle neutron scattering (SANS), solid-state NMR, and molecular dynamic (MD) simulation studies. SANS and MD simulations reveal that PEG displaces wall-bound PEI, making amines more accessible for CO 2 sorption. Solid-state NMR and MD simulation suggest intercalation of PEG into PEI domains, separating PEI domains and reducing amine-amine interactions, providing potential PEG-rich and amine-poor interfacial domains that bind CO 2 weakly via physisorption while providing facile pathways for CO 2 diffusion. Contrary to a prior literature hypothesis, no evidence is obtained for PEG facilitating PEI mobility in solid supports. Instead, the data suggest that PEG chains coordinate to PEI, forming larger bodies with reduced mobility compared to PEI alone. We also demonstrate promising CO 2 uptake and desorption kinetics at varied temperatures, facilitated by favorable amine distribution., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Intensified reactors for conversion of CO 2 to methanol (via hydrogenation) using metal oxide catalysts coupled with methanol conversion to aromatics in the presence of zeolites (e.g., H-ZSM-5) in a single step are investigated. Brønsted acid sites (BAS) in H-ZSM-5 are important sites in methanol aromatization reactions, and correlations of the reactivity with zeolite acid properties can guide reaction optimization. A classical way of tuning the acidity of zeolites is via the effect of the isomorphous substitution of the heteroatom in the framework. In this work, H-[Al/Ga/Fe]-ZSM-5 zeolites are synthesized with Si/ T ratios = 80, 300, affecting the acid site strength as well as distribution of Brønsted and Lewis acid sites. On catalytic testing of the H-[Al/Ga/Fe]-ZSM-5/ZnO-ZrO 2 samples for tandem CO 2 hydrogenation and methanol conversion, the presence of weaker Brønsted acid sites improves the aromatics selectivity (CO 2 to aromatics selectivity ranging from 13 to 47%); however, this effect of acid strength was not observed at low T atom content. Catalytic testing of H-[B]-ZSM-5/ZnO-ZrO 2 provides no conversion of CO 2 to hydrocarbons, showing that there is a minimum acid site strength needed for measurable aromatization reactivity. The H-[Fe]-ZSM-5-80/ZnO-ZrO 2 catalyst shows the best catalytic activity with a CO 2 conversion of ∼10% with a CO 2 to aromatics selectivity of ∼51%. The catalyst is shown to provide stable activity and selectivity over more than 250 h on stream., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Direct air capture (DAC) processes for extraction of CO 2 from ambient air are unique among chemical processes in that they operate outdoors with minimal feed pretreatments. Here, the impact of humidity on the oxidative degradation of a prototypical solid supported amine sorbent, poly(ethylenimine) (PEI) supported on Al 2 O 3 , is explored in detail. By combining CO 2 adsorption measurements, oxidative degradation rates, elemental analyses, solid-state NMR and in situ IR spectroscopic analysis in conjunction with 18 O labeling of water, a comprehensive picture of sorbent oxidation is achieved under accelerated conditions. We demonstrated that the presence of water vapor can play an important role in accelerating the degradation reactions. From the study we inferred the identity and kinetics of formation of the major oxidative products, and the role(s) of humidity. Our data are consistent with a radical mediated autooxidative degradation mechanism., (© 2023 Wiley-VCH GmbH.)

Previous research has demonstrated that amine polymers rich in primary and secondary amines supported on mesoporous substrates are effective, selective sorbent materials for removal of CO 2 from simulated flue gas and air. Common substrates used include mesoporous alumina and silica (such as SBA-15 and MCM-41). Conventional microporous materials are generally less effective, since the pores are too small to support low volatility amines. Here, we deploy our newly discovered zeolite nanotubes, a first-of-their-kind quasi-1D hierarchical zeolite, as a substrate for poly(ethylenimine) (PEI) for CO 2 capture from dilute feeds. PEI is impregnated into the zeolite at specific organic loadings. Thermogravimetric analysis and porosity measurements are obtained to determine organic loading, pore filling, and surface area of the supported PEI prior to CO 2 capture studies. MCM-41 with comparable pore size and surface area is also impregnated with PEI to provide a benchmark material that allows for insight into the role of the zeolite nanotube intrawall micropores on CO 2 uptake rates and capacities. Over a range of PEI loadings, from 20 to 70 w/w%, the zeolite allows for increased CO 2 capture capacity over the mesoporous silica by ∼25%. Additionally, uptake kinetics for nanotube-supported PEI are roughly 4 times faster than that of a comparable PEI impregnated in SBA-15. It is anticipated that this new zeolite will offer numerous opportunities for engineering additional advantaged reaction and separation processes., Competing Interests: The authors declare the following competing financial interest(s): C.W.J. has a financial interest in Global Thermostat Operations, LLC. Georgia Tech has a conflict of interest management plan in place for C.W.J., (© 2023 The Authors. Published by American Chemical Society.)

Using autogenous grafts in mucogingival surgeries is related to postoperative morbidity and limited tissue availability, and thus xenogeneic matrices are increasingly used. This in vitro study evaluated the influence of xenogeneic collagen matrix thickness on cell adhesion, morphology, viability, proliferation, and matrix degradation. Matrices were divided into three groups: SLC: single layer of Lumina Coat, as commercially available (2-mm thickness); DLC: double layer of SLC (Lumina Coat); and MG: single layer of Mucograft, as commercially available (4-mm thickness). SEM was used to evaluate the matrix surface topographies. To evaluate the cell viability, proliferation, adhesion, and morphology, human gingival fibroblasts (HGF) and stem cells from human exfoliated deciduous teeth (SHED) were used. Cell viability was evaluated through MTS colorimetric method evaluating HGF and SHED on days 1, 3, and 7. Cell proliferation was assessed by PicoGreen assay, evaluating HGF and SHED on days 3 and 7. Sample degradation was evaluated on days 1, 3, 7, 14, 21, 28, and 35. All groups were biocompatible for HGF and SHED, showing viabilities > 70% on days 1, 3, and 7. DCL promoted HGF viabilities similar to MG (P = .2828) and the highest SHED viability (P < .0001) on day 1. DLC also demonstrated HGF and SHED proliferations higher than the positive control (MG; P < .05) on day 7. SLC was completely degraded on day 14, while DLC and MG presented 48.41% and 20.52% of their initial mass, respectively, on day 35. Increasing the matrix thickness improved HGF and SHED viability and proliferation and prevented early matrix degradation. DLC demonstrated better results than SLC and MG concerning matrix degradation and HGF and SHED viability and proliferation.

Aim: This clinical technique report aimed to describe a composite resin repair technique performed in an implant-supported prosthesis., Background: Veneering ceramic fracture or chipping is one of the most frequent clinical failures in dentistry. Therefore, the use of less time- and cost-consuming ceramic repair techniques is helpful in clinical practice., Technique: Briefly, to treat the ceramic surface, the glaze was removed at the margins of the fracture area, then, air-abrasion and acid-etching were performed. To promote chemical adhesion, a silane coupling agent and adhesive system were applied over the ceramic surface, and the composite resin was applied by incremental technique. Finally, the polish was performed., Conclusion: In conclusion, the applied composite resin repair of feldspathic porcelain chipping in implant-supported prosthesis was a simple, easy, affordable, and minimally invasive treatment., Clinical Significance: The causes of veneer materials failures in metal-ceramic crowns are considered a challenge for the dentist and a problem that displeases patients. Repairs are indicated to prevent cracks from spreading and to prevent the accumulation of biofilm on the damaged surface. Therefore, different repair protocols have been proposed to enhance the esthetic, functionality, and longevity of the implant-supported prosthesis. Additionally, the success of the clinical cases depends on the capability to identify ceramic failures and the ability to indicate/perform the correct repair protocol. Since the described repair technique of the fractured screw-retained implant-supported prosthesis was a simple, easy, affordable, and minimally invasive treatment, with excellent esthetic and masticatory results, it represents an interesting clinical option.