Search

Silica aerogels are interesting porous materials with extremely low density and high surface area, making them advantageous for a number of aerospace and catalysis applications. Here, we report the preparation of polydopamine (PDA)-functionalized silica aerogels using an in situ coating method, wherein the dopamine monomer was allowed to diffuse through the underlying structure of the gels in the absence of any external base and polymerize on the surface of the gel. The use of a siloxane precursor with an amine functionality decorates the silica backbone, allowing for a superior PDA coating, as evident in the darker color of PDA-coated amine-functionalized silica gels than PDA-coated silica-only gels and the X-ray photoelectron spectroscopy results. Furthermore, by varying the coating time, a series of aerogels with increasing optical absorption are prepared. Analyses using Brunauer-Emmett-Teller, scanning electron microscopy, and pycnometry show that the in situ PDA coating does not affect the inherent properties of the silica aerogels as opposed to PDA coatings deposited using an external base. Aerogels coated for 12 h and 24 h offer a surface area of 614 ± 35 and 658 ± 15 m2/g along with a porosity of 92.6 ± 0.9 and 92.4 ± 0.7%, respectively, properties similar to the native silica aerogels. PDA-coated aerogels have the potential to serve as UV ray mitigating materials due to the tortuosity of the underlying structure and the unique chemical properties of the PDA coating.

The design of new remediation strategies and materials for treating saline-alkaline soils is of fundamental and practical importantance for many applications. Conventional soil remediation strategies mainly focus on the development of fertilizers or additives for water, nutrient, and heavy metal managements in soils, but they often overlook a soil sensing function for early detection of salinization/alkalization levels toward optimal and timely soil remediation. Here, new smart soils, structurally consisting of the upper signal soil and the bottom hygroscopic bed and chemically including zwitterionic, thermo-responsive poly(NIPAM-co-VPES) and poly(NIPAM-co-SBAA) aerogels in each soil layer are formulated. Upon salinization, the resultant smart soils exhibit multiple superior capacities for reducing the soil salinity and alkalinity through ion exchange, controlling the water cycling, modulating the degradation of pyridine-base ligands into water-soluble, nitrogenous salts-rich ingredients for soil fertility, and real-time monitoring salinized soils via pH-induced allochroic color changes. Further studies of plant growth in smart soils with or without salinization treatments confirm a synergy effect of soil remediation and soil sensing on facilitating the growth of plants and increasing the saline-alkaline tolerance of plants. The esign concept of smart soils can be further expanded for soil remediation and assessment.

International audience; Hydrogels are deployed widely in all areas of regenerative medicine, including bioprinting. The transport and mechanical properties exhibited by hydrogel assemblies are controlled by their organization and hierarchical assembly. This paper points out the role of the nanoscale size and ordering of hydrophobic cross-linked domains on the mechanical and degradation properties of three-dimensional (3D) printed amphiphilic hydrogels. A series of six poly(propylene fumarate)-block-poly(ethylene glycol)-block-poly(propylene fumarate) (PPF-b-PEG-b-PPF) ABA triblock copolymers were synthesized by varying both the water-soluble PEG block and the cross-linkable hydrophobic terminal PPF block lengths. Self-assembled hydrogels were formed by dissolving these amphiphilic PPF-b-PEG-b-PPF copolymers in water and covalently cross-linking the PPF units via digital light processing (DLP) additive manufacturing. Differential scanning calorimetry (DSC), in situ diffuse reflectance infrared spectroscopy (DRIFTS-IR) measurements, small-angle neutron scattering (SANS), and compressive measurements highlight how structural properties correlate with mechanical properties within this hydrogel system. Finally, swelling and in vitro degradation tests showed the influence of the nanoscale ordering on the degradation timescale.

The accurate distribution of countercations (Rb+ and Sr2+ ) around a rigid, spherical, 2.9-nm size polyoxometalate cluster, {Mo132 }42- , is determined by anomalous small-angle X-ray scattering. Both Rb+ and Sr2+ ions lead to shorter diffuse lengths for {Mo132 } than prediction. Most Rb+ ions are closely associated with {Mo132 } by staying near the skeleton of {Mo132 } or in the Stern layer, whereas more Sr2+ ions loosely associate with {Mo132 } in the diffuse layer. The stronger affinity of Rb+ ions towards {Mo132 } than that of Sr2+ ions explains the anomalous lower critical coagulation concentration of {Mo132 } with Rb+ compared to Sr2+ . The anomalous behavior of {Mo132 } can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion-cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion-{Mo132 } interaction.

One critical issue in the design of amine-based sorbents and solvents for next-generation CO2 capture technology is the effect of H2O on the behavior of adsorbed CO2. To gain an insight into the ef...

The evergrowing plastic production and the caused concerns of plastic waste accumulation have stimulated the need for waste plastic chemical recycling/valorization. Current methods suffer from harsh reaction conditions and long reaction time. Herein we demonstrate a non-thermal plasma-assisted method for rapid hydrogenolysis of polystyrene (PS) at ambient temperature and atmospheric pressure, generating high yield (>40 wt%) of C1–C3 hydrocarbons and ethylene being the dominant gas product (Selectivity of ethylene, SC2H4 > 70%) within ~10 min. The fast reaction kinetics is attributed to highly active hydrogen plasma, which can effectively break bonds in polymer and initiate hydrogenolysis under mild condition. Efficient hydrogenolysis of post-consumer PS materials using this method is also demonstrated, suggesting a promising approach for fast retrieval of small molecular hydrocarbon modules from plastic materials as well as a good capability to process waste plastics in complicated conditions.

Reaction intermediates on catalyst surfaces have often been elucidated on the basis of ex situ observation of adsorbed species and theoretical computations because of the difficulty in carrying out in situ studies, and the elusive nature of the intermediates under reaction conditions. In the past few decades, we have developed an in situ infrared spectroscopic method coupled with mass spectrometry (IR/MS setup) for investigating reaction intermediates for a number of catalytic reactions: CO/H2, CO/H2/C2H4, NO/CO, NO decomposition, CO2/CH3OH, and photocatalytic reactions. This review presents the key features of using an IR/MS experimental setup to perform transient studies. Transient studies involve perturbing the reaction system and monitoring the responses. This review highlights the usefulness of transient response data to unravel the reaction intermediates and pathways.

Upcycling is an attractive approach for valorization of waste plastics to valuable chemicals. Here we report the first case study of non-thermal plasma-assisted hydrogenolysis of high-density polyethylene (HDPE) to C1-C3 hydrocarbons. Light alkanes, predominately CH4, C2H6 and C3H8 with >95% selectivity, were obtained under ambient condition as result of favorable thermodynamics and fast reaction kinetics. The findings demonstrated that hydrogenolysis that typically demands above 300 °C with thermal catalysis can occur at room temperature in assistance of non-thermal plasma. This proof-of-concept study showcases a novel strategy for upcycling of plastics to valuable hydrocarbons under ambient condition.

The effect of pH, concentration, and membrane thickness on the performance of a photoelectrochemical (PEC) cell using kraft lignin as a reactant was studied at 25 °C. Kraft lignin served as an electron donor which consumed photogenerated holes on the TiO2 anode, while photogenerated electrons reduced protons to hydrogen gas at the Pt cathode. Saturated photocurrent increased linearly with UV intensity. High concentrations of kraft lignin reduced the photo-current of the cell. A high pH differential across the membrane could degrade a thin perfluorosulfonic acid (PFSA) membrane. This study demonstrated the potential of kraft lignin as an electron donor.

A micropore-rich mesoporous carbon (MMC) derived from ordered mesoporous carbon (OMC) is fabricated as support to prepare a highly active nano Cu2O catalyst for methanol oxidation carbonylation. The well-dispersed ~3.3 nm Cu nanoparticles with ca. 90% purity of Cu2O are obtained. The space-time yield and turnover frequency of DMC are significantly enhanced to 34.2 g g Cu − 1 h − 1 and 89.1 h−1, both of which are greater than that over the mesoporous-only Cu/OMC catalyst. It is found that plentiful under-coordinated carbon atoms are formed in the introduced micropores, which serve as binding sites to immobilize Cu precursors to form the well-dispersed Cu nanoparticles. A large number of these atoms are favorable to accelerate auto-reduction of CuO to Cu2O in kinetics and further promote to form high-purity Cu2O. Besides, the electrons of Cu2O are forced to transfer to the micropore surrounding, forming an electron-deficient Cu+ site in favor of intrinsic activity enhancement.

In situ infrared spectroscopy (IR) allows direct observation of the evolution of adsorbed species as well as photogenerated conduction/trapped electrons on TiO2 under reaction environment in transmission, diffuse reflectance, and attenuated total reflectance modes. This chapter will cover the design of in situ IR cells for mechanistic investigation of gas–solid photocatalytic reactions using photocatalytic oxidation of ethanol as an example. We will discuss the approaches for in situ IR studies, analysis of IR data, and elucidation of reaction pathways involved with photogenerated electrons. The approaches described in this chapter can be extended for investigating mechanisms of a wide range of gas–solid catalytic reactions.

A one-step photocatalytic synthesis of l-pipecolic acid (l-PCA) from l-lysine (l-Lys) has been investigated by in situ infrared (IR), circular dichroism, and 1H NMR spectroscopy. Chiral selectivity toward l-Lys was found to be governed by the structure of adsorbed l-Lys and the structure of TiO2. Both anatase and rutile were not able to catalyze the reaction in a solvent-free environment. In situ IR studies revealed that l-Lys adsorbed on these TiO2 in a dicationic form of which the positive −NH3+ functional groups are not able to interact with photogenerated holes. Interestingly, P-25 TiO2, which contains 80 wt % anatase and 20 wt % rutile, adsorbs l-Lys in a zwitterionic form, allowing its hydrogen in the α-amino group to be abstracted by the photogenerated hole, producing racemic PCA. The addition of H2O as a solvent allowed l-Lys to be adsorbed on P-25 in an anionic form, producing l-PCA as a major product. This study demonstrates that the reaction environment has a direct impact on the structure of a...

The synthesis of dimethyl carbonate (DMC) from CO2 and methanol by Zr-doped CeO2 nanorods with different ratios of Zr/Ce has been studied at 6.8 MPa and 140 °C. The catalysts were characterized ext...

A series of titania-supported transition metal oxide catalysts were evaluated for NO reduction with CO as reductant at low temperature (200 °C) in the presence of excess oxygen. Among the investigated systems, MnOx/TiO2 has been found to be the preeminent catalyst. In situ FT-IR and transient studies were carried out in order to identify the chemisorbed species which could act as catalytic intermediates, and in consequence to propose the low temperature reduction of NO pathway over the Mn/TiO2. The NO adsorption and NO + O2 co-adsorption of in situ FT-IR experiments revealed the formation of surface reaction intermediate N2O species along with the formation of monodentate and bidentate nitrates, whereas CO adsorption on the catalyst leads to the formation of carbonate species. Interestingly, in the case of NO and CO co-adsorption over MnOx/TiO2, the formation of CO2 (CO oxidation with gas phase oxygen) is inhibited due to the surface reaction competition between NO and CO. The formation of N2O as an intermediate was evident from the occurrence of peaks at 1286 and 1335 cm−1 region. There is no formation of NO2 as a surface intermediate or gas phase stable product in the present in situ Fourier transform infrared spectroscopy (FT-IR) and transient mass spectroscopic studies, respectively. Remarkably, a neat absorption peak at 2178 cm−1 ascribed to the isocyanate (–NCO) species was not observed during in situ infrared spectroscopic studies of NO + CO and CO + NO co-adsorptions. Based upon this evidence it is proposed that the formation of NCO− species from the reaction between CO and Nads is completely forbidden over the Mn/TiO2 catalysts. These results indicate that the reaction mechanism follows a different pathway for our catalyst, from that of the other metal based catalysts. The role of lattice oxygen in the reaction mechanism is substantiated by isotopic labeling and transient analysis studies. Lewis acid sites act as the active sites for the reaction.

Water, a component in flue gas, plays a significant role in CO2 capture through a complex interaction between water molecules and adsorbed CO2 on amine sorbents. To determine how the H2O–CO2–amine interactions affect amine efficiency and the binding energy of adsorbed CO2, we used in situ infrared spectroscopy (IR) to determine the structure of adsorbed CO2 and H2O as well as their relations to adsorption/desorption kinetics and CO2 capture capacity on tetraethylenepentamine (TEPA) films and Class I amine (i.e., impregnated) sorbents. H2O enhanced amine efficiency of TEPA films and sorbents by increasing the accessibility of secondary amine sites to CO2 and promoting the formation of hydronium carbamate and carbamic acid. CO2 adsorbed on the surface of the TEPA film as a weakly adsorbed CO2 in the form of hydronium and ammonium–carbamate with a low IR intensity of hydrogen bonding (−OH···–OOC or −NH···–OOC) between hydronium/ammonium ions and carbamate ions. CO2 adsorbed on the middle layers (i.e., 0.2–0....

Novel pigments isoepindolidiones (isoEpi) and di-tert-butyl quinolino[8,7-h]quinoline-1,7-diyl bis(carbonate) (isoEpi-Boc) were synthesized and characterized. The spectroscopic characterizations indicated that the tert-butyloxycarbonyl (t-Boc) units could be removed from soluble isoEpi-Boc by thermal annealing, forming insoluble isoEpi with hydrogen bonding. A solid-state isoEpi-Boc crystal to isoEpi crystal transition was observed during the annealing process and the molecular packing was significantly changed. With the emergence of hydrogen bonds, the isoEpi molecules were arranged into a brick-in-wall structure with π-stacking along the crystal growth axis, leading to a significant enhancement of charge mobility along the crystal growth direction (the hole mobility from 3.4 × 10–4 to 0.32 cm2/(V·s), and the electron mobility from nondetectable to 5.6 × 10–3 cm2/(V·s)). The results indicate that isoEpi is a promising chromophore for organic field-effect transistor (OFET). The crystal-to-crystal transiti...

Charge transfer between adsorbed dyes and the TiO2 surface plays a key role in controlling the efficiency of dye-sensitized solar cells (DSSCs). The lack of understanding of charge transfer steps has hindered further development of DSSCs and many solar energy conversion devices/processes. In this study, we used in situ infrared spectroscopy to investigate electron transfer and photo-electric energy conversion processes at the interface, i.e., surface hydroxyls, adsorbed species, as well as the dynamics of photo-generated electrons in TiO2 and N-TiO2 in DSSCs. Nitrogen (N-) doping of TiO2 blocked linear OH, giving more hydrophobic surface characteristics than undoped TiO2. N-Doping further increased the electron–hole separation caused by solar light on the working electrode and the current density in the DSSC. In situ infrared (IR) studies revealed that N-doping facilitated the electron transfer from the N719 dye (di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4-dicarboxylato)ruthenium(II)) to the conduction band in TiO2, reducing the impedance in the DSSC. Probing N-TiO2 with adsorbed ethanol showed that shallow traps in N-TiO2 can be accessed by electrons from adsorbed ethanol. Electron transfer from the N719 dye is significantly faster than that from adsorbed ethanol which involves C–H bond breaking.

We used a transient kinetic technique, which involves a step-switching of the reactant flows, to identify the reaction pathways on the Ni anode catalysts of SOFCs utilizing CH 4 /CO 2 and CH 4 as fuels. Carbon deposited at the external layer of the Ni anode support in CH 4 -SOFC. The transient response revealed that carbon deposition, which occurred with CH 4 as a fuel molecule, was suppressed and dominated by the dry reforming of CH 4 /CO 2 to CO/H 2 and the electrochemical oxidization of CO/H 2 . Electricity generation from the electrochemical oxidation reactions is governed by Faraday resistance at the anode Ni catalyst interlayer.

One critical issue in the development of immobilized amine sorbents for CO2 capture is sorbent degradation, which leads to a significant increase in the overall CO2 capture cost. Here we report a novel approach for enhancing the degradation resistance of a branched polyethylenimine (PEI) by hydroxyl groups (i.e., −OH) of a porous cross-linked poly(vinyl alcohol) (PVA) support. The CO2 capture capacity of a PEI/PVA sorbent showed a 25% decrease and then leveled off. In contrast, the PEI/SiO2 sorbent exhibited more than a 3-fold decrease in CO2 capture capacity after exposure to a cyclic CO2 capture and oxidative degradation environment (15 vol % of CO2 in air at 130 °C). In situ infrared spectroscopic study revealed that the secondary amine is more liable to degrade than the primary amine on PEI/SiO2. On PEI/PVA, the PVA’s −OH groups interacted mainly with the secondary amine of branched PEI through a hydrogen bonding, which could contribute to enhancing the resistance of PEI against degradation. This new ...

The dynamic behaviors of conduction-band electrons ( $${\text{e}}_{CB}^{ - }$$ ) and shallow-trap electrons ( $${\text{e}}_{ST}^{ - }$$ ) generated from UV irradiation on ethanol-adsorbed TiO2 and N-TiO2 have been studied by in situ Fourier transform infrared spectroscopy (FTIR) in a diffuse reflectance mode at 300 K and 0.1 MPa. UV irradiation on ethanol-adsorbed TiO2 resulted in the breaking of C–H bond of ethanol, the transfer of electrons from ethanol to the photo-generated holes on TiO2 and N-TiO2, the accumulation of $${\text{e}}_{CB}^{ - }$$ and $${\text{e}}_{ST}^{ - }$$ , and the formation of acetate on TiO2 and the formation of acetate, formate, and formaldehyde on N-TiO2. Accumulated $${\text{e}}_{CB}^{ - }$$ and $${\text{e}}_{ST}^{ - }$$ are manifested by broad and featureless IR absorbance spectra, which can be fitted into two models for estimation of their relative concentrations. N-doping onto TiO2 produced a higher population of $${\text{e}}_{ST}^{ - }$$ and generated $${\text{e}}_{ST}^{ - }$$ and $${\text{e}}_{CB}^{ - }$$ at a lower rate than TiO2. The average energy level of $${\text{e}}_{ST}^{ - }$$ was determined to be 0.30 eV for TiO2 and 0.26 eV for N-TiO2 below the conduction band. Upon terminating UV irradiation, the IR intensity of accumulated $${\text{e}}_{CB}^{ - }$$ and $${\text{e}}_{ST}^{ - }$$ showed a gradual decay in a time scale of minutes. This study demonstrated that the recombination of photo-generated electrons and holes can be a slow process on TiO2 and N-TiO2 in the presence of adsorbed ethanol under ambient conditions.

A transition between two isomeric clusters involving the change of the main skeleton structure of a well-defined, rigid molecular cluster [(UO2 )24 (O2 )24 (P2 O7 )12 ]48- , {U24 Pp12 }, is achieved by simply introducing proper alkali cations into its dilute aqueous solution. While the unique structural transition can be triggered by introducing any of the Na+ /K+ /Rb+ /Cs+ alkali ions, the two isomers, Li/Na-{U24 Pp12 } and Na/K-{U24 Pp12 }, as typical macroions, can accurately choose among different alkali counter-cations based on their hydrated sizes, and the ion selectivity process clearly showed endothermic features. The preferred K+ and Rb+ ions have suitable sizes to be incorporated into the proper windows on {U24 Pp12 } nanocapsules, as supported by the transition points in both ITC studies and IR measurements.

An in situ IR study unraveled that adsorption of CO2 on 20 μm TEPA film at 50 °C followed a zwitterion-intermediate pathway: zwitterion → ammonium carbamate. H2O in the mixed TEPA/H2O (5:1) film decreased the rate of CO2 adsorption but increased the amine efficiency. CO2 preferentially adsorbs on primary amine sites and H2O on secondary amine sites. The presence of H2O promotes the formation of carbamic acid and produces a broad IR band centered at 2535 cm–1, which can be assigned to the ν(O–H) of hydronium carbamate, −NCOO–···H–OH2+. The broadness of this 2535 cm–1 band ranging from 2100 to 2800 cm–1 persists at 120 °C. These broad components of the band can be ascribed to ν(N–H) in hydrogen-bonded ammonium carbamate, a R–NH3+/R1R2–NH2+···–NCOO– moiety. The binding strength of adsorbed species on the TEPA film increases in the order adsorbed H2O < carbamic acid < ammonium carbamate < hydrogen-bonded water/ammonium carbamate.

The structure and nature of adsorbed species on solid amine sorbent under various CO2 concentrations from ambient air (0.04 vol%) to CO2/air stream (15 vol%) have been studied by in situ infrared (IR) spectroscopy. The in situ IR study (i) provided evidence to support the zwitterion pathway for CO2 adsorption/desorption and (ii) allowed determination of the nature of adsorbed species. The IR-observable zwitterion was found to deprotonate to ammonium carbamate and carbamic acid reversibly. CO2 adsorbs on the primary amine site as strongly adsorbed species in the form of ammonium carbamate, and on the secondary amine site as weakly adsorbed species in the form of carbamic acid. Another form of weakly adsorbed species could be ammonium carbamate on the secondary amine. Raising the concentration of CO2 in the stream increased CO2 capture capacity, fractions of strongly adsorbed CO2, and binding energy of adsorbed species. 400 ppm CO2 from air competes over 0.5 % of water vapor for adsorption on class I amine sorbents.

Highly ordered N-doped mesoporous carbon/graphene frameworks (N-MCF/N-MGF) were prepared using superlattice of self-assembled Fe3O4 nanoparticles as template. The prepared N-MCF catalyst shows enhanced oxygen reduction reaction (ORR) activity compared with commercial Pt/C catalyst. The N-MGF catalyst demonstrates lower oxygen evolution reaction (OER) overpotential (324 mV at 10 mA cm−2) than most of the previously reported carbon based materials, non-noble metal oxides and their hybrids, and comparable with noble metal oxides (ruthenium/iridium oxide, RuO2 and IrO2) catalysts. The prepared N-MGF catalysts also exhibit negligible mass transfer resistance, good durability and bifunctionality in ORR and OER. The significantly improved electrocatalytic performance results from their large surface area, ordered pores, excellent internal diffusion property, and superior intrinsic conductivity. The materials show great potential for various applications in energy conversion and storage, including fuel cells, electrolyzers and metal-air batteries.

Eumelanin is a ubiquitous natural pigment that has a broad absorption across ultraviolet (UV, 100-400 nm) and visible wavelengths (400-700 nm) and can protect against radiation. Synthetic eumelanin with properties similar to natural eumelanin has been made using dopamine or dihydroxyindole. Here, we use solid-state nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy to elucidate the chemical structure of synthetic eumelanins (made from dopamine and l-3,4-dihydroxyphenylalanine precursors) and investigate how their structures change after intensive UVA (315-400 nm) exposure. We first confirm that polydopamine has indole units. Upon UV exposure, the pyrrole ring in this indole unit remains intact, and a fraction of the six-membered benzyl ring is broken and the indole potentially converted to furo[3,4-b]pyrrole. This change in the chemical structure is accompanied by a release of carbon dioxide. In addition, the sepia (natural) eumelanin used for comparison is more stable than the synthetic eumelanin. Understanding the UVA degradation mechanism of eumelanin will help reveal the role of eumelanin in skin cancer and in the design of more efficient UV stabilizers.

CO2 capture from fossil fuel (coal and natural gas) power plants has been considered a key strategy in mitigating global climate changes. One promising approach under development is the use of solid amine sorbents to bind CO2 in the form of ammonium carbamate from the flue gas of coal-fired power plants in a CO2 capture process. The CO2 capture process by solid amines consists of a number of steps: CO2 adsorption, diffusion and desorption. These steps are governed by the nature of the hydrogen bonding between the ammonium cation and the carbamate anion. This chapter discusses the sources of greenhouse gas emissions, basic principles governing the trapping of infrared energy by greenhouse gases, especially CO2, and the mechanistic step involved in the thermal swing CO2 capture process by solid amines. Infrared spectroscopy is used to illustrate the nature of hydrogen bonding in adsorbed CO2 (i.e. ammonium carbamate) and co-adsorbed CO2/H2O (i.e. hydronium carbamate). In situ infrared spectroscopy shows that hydrogen bonding interactions among these adsorbed species shift the stretching band of N–H and O–H to lower wavenumbers. The extent of hydrogen bonding is reflected in the degree of shift and broadness of the N–H and O–H stretching bands. Fine tuning solid amine (immobilized amine) sorbents for CO2 capture processes requires controlling the structure of amine sites to facilitate CO2 adsorption, diffusion and desorption.

CO2 is a major greenhouse gas responsible for global climate changes. One potential cost-effective approach to limit CO2 emissions is the use of silica (SiO2)-based immobilized amines for capturing CO2 from the flue gas of coal-fired power plants which account for more than 40% of annual CO2 emission around the globe. This chapter discusses the approaches for preparation and fabrication of silica-based amine sorbents, their uses in fixed and fluidized bed, and issues related to scale-up and deployment of CO2 capture processes. The insight into the structure of silica and the kinetics of CO2 capture processes will be shed by examining the in situ infrared spectroscopic results. The focus will be directed toward elucidating the interactions between silica and immobilized amine as well as the bonding between CO2 and immobilized amines at a molecular level.

The reversible adsorption of CO2 on tetraethylenepentamine (TEPA) and the polyethylene glycol (PEG)-modified amine sites were investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, mass spectrometry (MS), and density functional theory (DFT). The presence of PEG at the amine site increased the rate of formation of adsorbed CO2, enhanced the formation of weakly adsorbed CO2 which can be removed from flowing inert gas at room temperature, and decreased CO2 desorption peak (i.e., sorbent regeneration) temperature. The calculated CO2 binding energy (BE) and optimized structures suggest CO2 adsorbed on TEPA primarily in the form of ammonium carbamate. The presence of PEG promoted the formation of a species which exhibited an experimental IR spectrum resembling the simulated spectrum of a low BE zwitterion species. The observation suggests PEG controlled the formation of the adsorbed intermediate species. Modeling of the transient CO2 adsorption profiles further showed PEG accelerated the...

The nature and structure of adsorbed CO2 on immobilized amine sorbent in the presence and absence of H2O vapor have been studied by in situ infrared spectroscopy. CO2 adsorbed on the primary amine as ammonium carbamate and on the secondary amine as carbamic acid. Adsorbed H2O mainly on secondary amine enhanced CO2 capture capacity by increasing accessibility of amine sites and promoting the formation of carbamic acid. The binding strength of the adsorbed species increased in the order: carbamic acid < adsorbed H2O < paired carbamic acid; ammonium carbamate < ammonium chloride. Flowing argon over the amine sorbent at 50 °C removed weakly adsorbed H2O and carbamic acid from the secondary amine sites. Raising temperature is required to completely regenerate sorbent by removing strongly adsorbed ammonium carbamate from the primary amine sites and paired carbamic acid. The results of this study clarify the role of H2O vapor in amine-sorbents for CO2 capture and provide a molecular basis for the design of the s...

Asymmetric hydrogenation reaction of dehydro-α-amino acid (i.e., α-amino ester) over cinchonidine (CD) modified Pd catalyst has been studied by an array of in situ infrared spectroscopic methods, including transmission, diffuse reflectance (DR), and attenuated total reflectance (ATR). Transmission FTIR spectra probed the hydrogenation reaction process, revealed OH–O and NH–N hydrogen bonding interactions between the adsorbed CD and during the reaction. DR and ATR spectra of the hydrogenation reaction under different conditions, which are consistent with but slightly different from the transmission spectra, evidenced the successful hydrogenation of the compound. The incorporation of DR and microfluidics flow-through design allowed us to investigate the adsorption of CD on the Pd surface efficiently. The results revealed that the N-bonded CD on Pd surface in a tilted configuration had increased abundance on the Pd surface with high coverage. These valuable insights provided an image of the reaction pathway ...

An in situ IR technique was used to study the role of Au and Ag additives on photocatalytic reaction of ethanol on TiO2 at 300 K. Au and Ag additives increased water/ethanol coverage and decreased the rate of ethanol's Csingle bondH scission, a step involving in scavenging photogenerated holes. Au and Ag promoted adsorption of ethanol as monodentate ethoxy, accelerated its conversion to formate (HCOO−ad) and acetate (CH3COO−ad). In contrast, adsorbed ethanol on TiO2 did not produce IR-observable products and exhibited a Stark effect with a decreased Csingle bondH intensity upon accumulation of photogenerated electrons.

The reversible adsorption of H2S on tetraethylenepentamine (TEPA) was investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, mass spectrometry, and density functional theory (DFT). The in situ infrared method revealed H2S ability to selectively poison the TEPA amine active site by the formation of a strongly adsorbed species in the form of (HS–) NH3+-TEPA. In addition, the H2S–amine interaction, in the presence of oxygen, resulted in the oxidative degradation of the amine, indicated by the formation of an −NO2 species. The addition of polyethylene glycol (PEG) affects the H2S-amine interactions and prevents the amine site from oxidative degradation. Both experimental IR and DFT calculations revealed that PEG affected the electronic and geometric environment around the amine binding site through hydrogen bonding and electron-donating effects. The addition of PEG decreased the (+) charge of the ammonium ion site, effectively decreasing electrostatic anion–cation interaction of the st...

In this study, we report the utilization of protonic acids to treat polyethylene glycol-triblock-polypropylene glycol (PP) modified polyethylenedioxythiophene (PEDOT) doped with tosylate (Tos−) counter-ion (PP-modified PEDOT:Tos) thin films. Investigations using absorption, Raman, electron spin resonance and X-ray photoemission spectroscopies indicate that nearly 100% enhanced electrical conductivity and over a 30% improved power factor observed from the PP-modified PEDOT:Tos thin films with protonic acid treatment are attributed to the increased densities of the polaron state and the stabilized densities of the bipolaron state. Further studies by grazing incidence wide angle X-ray scattering and atomic force microscopy reveal that the crystal structure, amorphous regions, and the size of the exchanging counter ion have great influences on the electrical conductivities, the Seebeck coefficients and the power factors. Our studies provide a facile route to realize highly electrically conductive polymers for the development of effective organic thermoelectric devices.

Charge transfer between adsorbed dyes and the TiO2 surface plays a key role in controlling the efficiency of dye-sensitized solar cells (DSSCs). The lack of understanding of charge transfer steps has hindered further development of DSSCs and many solar energy conversion devices/processes. In this study, we used in situ infrared spectroscopy to investigate electron transfer and photo-electric energy conversion processes at the interface, i.e., surface hydroxyls, adsorbed species, as well as the dynamics of photo-generated electrons in TiO2 and N-TiO2 in DSSCs. Nitrogen (N-) doping of TiO2 blocked linear OH, giving more hydrophobic surface characteristics than undoped TiO2. N-Doping further increased the electron-hole separation caused by solar light on the working electrode and the current density in the DSSC. In situ infrared (IR) studies revealed that N-doping facilitated the electron transfer from the N719 dye (di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4-dicarboxylato)ruthenium(ii)) to the conduction band in TiO2, reducing the impedance in the DSSC. Probing N-TiO2 with adsorbed ethanol showed that shallow traps in N-TiO2 can be accessed by electrons from adsorbed ethanol. Electron transfer from the N719 dye is significantly faster than that from adsorbed ethanol which involves C-H bond breaking.

A Ni/YSZ anode and a Ni/YSZ modified by Cu electroless plating were investigated for direct utilization of CH4, the major component in natural gas. The catalytic activity of the anodes toward H2 and CH4 oxidation reactions were investigated by comparing the Faraday resistance, RF, of the cells obtained from impedance spectroscopy. The RF ratio of Cu–Ni/YSZ in CH4 to H2 was greater than that of Ni/YSZ, indicating low catalytic activity of Cu–Ni/YSZ anode toward CH4 oxidation. The addition of Cu to the Ni/YSZ anode decreased the catalytic activity, but increased the long-term stability of the anode in CH4 fuel. The Cu–Ni/YSZ anode showed long-term stability of 138 h in dry CH4 at 750 °C. The Raman spectra of the fuel cell cross-section showed a change in type of carbon as a function of Cu concentration. The Cu rich surface showed more disordered carbon as opposed to graphitic carbon on Cu deficient areas in which Cu concentration gradually decreased toward the interlayer. Graphitic carbon produced on highly active Ni surface is known as a precursor to coking. Thus, optimizing the distribution of Cu in the Ni/YSZ anode will be required to develop a stable and high performance anode catalyst for direct CH4 utilization.

To simultaneously increase the electrical conductivity and Seebeck coefficient of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) was a challenge for realizing efficient organic thermoelectrics. In this study, for the first time, we report both increased electrical conductivities and Seebeck coefficients, hence, enhanced thermoelectric properties of PEDOT:PSS thin films by doped with binary secondary dopants, dimethyl sulfoxide (DMSO) and poly(ethylene oxide) (PEO). Without modifying film morphology, the molar ratios of PEDOT to PSS are tuned by PEO, resulting in increased proportions of PEDOT in the bipolaron states. Our study provides a facile route to optimizing thermoelectric properties of PEDOT:PSS thin films.

The reversible adsorption of SO2 on 1,3-phenylenediamine was investigated using the step transient response technique coupled with operando infrared spectroscopy, mass spectrometry, UV–vis spectrometry, and density functional theory (DFT). At 50 °C, the reaction of SO2 at the amine site resulted in fixation of sulfur as hydrogen-bonded SO32– (sulfite) and SO42– (sulfate) species. Simulated infrared and UV–vis spectra at the DFT B3LYP/6-31G(d,p) level were compared to the experimental results to help characterize the infrared spectra, molecular interactions, and bonding of the adsorbing species. The theoretically calculated binding energies revealed the sulfite and sulfate species bind stronger at the ammonium sites as compared to the amine site, which agrees with the infrared spectroscopic observations. Temperature-programmed desorption showed a capacity of 1.39 mol SO2/mol sorbent for pure 1,3-phenylenediamine and 2.8 mol SO2/mol sorbent for the SiO2 supported sorbent. The presence of sulfite and sulfate...

For the first time, a Fe–Ti–O containing pellet, a viable chemical looping particle, was used as a solid fuel for direct contact with the Ni/YSZ anode surface of a solid oxide fuel cell. A maximum power density of 97 mW cm−2, corresponding to 84% of that in the H2 fuel, was produced using Fe–Ti–O in an inert Ar gas environment at 750 °C. The Fe–Ti–O pellets were able to generate stable electricity under repeated electrochemical oxidation and hydrogen reduction cycles. Temperature-programmed oxidation–reduction coupled with infrared spectroscopic studies revealed that the oxidation of the Fe–Ti–O pellet followed a shrinking core model; the reduction followed a progressive-conversion model. The ability of the Fe–Ti–O pellet to generate electricity on the Ni/YSZ surface can be attributed to its low resistivity (

The performance of the direct carbon solid oxide fuel cell (C-SOFC) with a Ni/YSZ anode has been studied with a 50 mol% H2, 3 mol% H2, and 7 mol% H2O feed at 750 °C. The electricity generation was dominated by consumption of H2 fuel at 50 mol% H2 and by carbon at 3 mol% H2. The low (3 mol%) H2 kept the Ni/YSZ anode in reduced state, enhancing its electrochemical oxidation activities. Introducing 7 mol% H2O initiated the water reaction with carbon to produce H2 and CO that could serve as a fuel for further reactions in anode interlayer, exhibiting a decrease in the overall Faraday resistance of the C-SOFC.

A transition between two isomeric clusters involving the change of the main skeleton structure of a well-defined, rigid molecular cluster [(UO

In-situ infrared study of polyaniline (PANI) synthesis showed that the reaction initiated at pH = 1.5 produced a granule PANI microstructure via para-linked dimers of 4-aminodiphenylamine, exhibiting γ(C–H) at 802 cm−1; the reaction initiated at pH = 5.0 and 7.0 produce fiberous, and planar microstructures via ortho-linked dimers of 1,2-aminodiphenylamine and phenazine, exhibiting γ(C–H) at 738 and ν(C=N) at 1446 cm−1. The doped PANI that was produced at pH less than 5.0 showed a feature-less IR background absorption above 1600 cm−1. This absorption could correspond to π-electron delocalization as an indicative of polyaniline conductivity.

Particle loaded porous poly(vinyl alcohol) composite membranes were selected for immobilization of glucose oxidase (GOx) for their hydrophilicity and unique interactions with amino functional groups. GOx was immobilized on the membranes by adsorption at pH values between 3.5 and 7.1. The highest adsorption loading was observed at pH 7.1 and the highest catalytic activity was observed at pH 5.1. Infrared studies showed that the highest ratio of amide I to amide II at pH 5.1 is obtained for GOx immobilized on membranes loaded with amine-functionalized micro-particles, suggesting that the conformational changes of GOx on these membranes yield to higher catalytic activity than in other supports.

CO2 adsorption/desorption onto/from tetraethylenepentamine (TEPA) films of 4, 10, and 20 μm thicknesses were studied by in situ attenuated total reflectance (ATR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques under transient conditions. Molar absorption coefficients for adsorbed CO2 were used to determine the CO2 capture capacities and amine efficiencies (CO2/N) of the films in the DRIFTS system. Adsorption of CO2 onto surface and bulk NH2 groups of the 4 μm film produced weakly adsorbed CO2, which can be desorbed at 50 °C by reducing the CO2 partial pressure. These weakly adsorbed CO2 exhibit low ammonium ion intensities and could be in the form of ammonium-carbamate ion pairs and zwitterions. Increasing the film thickness enhanced the surface amine–amine interactions, resulting in strongly adsorbed ion pairs and zwitterions associated with NH and NH2 groups of neighboring amines. These adsorbed species may form an interconnected surface network, which slowed CO2 gas...

In situ Fourier transform infrared spectroscopy was used to determine the nature of adsorbed CO2 on class I (amine-impregnated) and class II (amine-grafted) sorbents with different amine densities. Adsorbed CO2 on amine sorbents exists in the form of carbamate-ammonium ion pairs, carbamate-ammonium zwitterions, and carbamic acid. The adsorbed CO2 on high-amine density sorbents showed that the formation of ammonium ions correlates with the suppression of CH stretching intensities. An HCl probing technique was used to resolve the characteristic infrared bands of ammonium ions, clarifying that the band observed around 1498 cm(-1) is a combination of the deformation vibration of ammonium ion (NH3(+)) at 1508 and 1469 cm(-1) and the deformation vibration of NH in carbamate (NHCOO(-)) at 1480 cm(-1). Carbamate and carbamic acid on sorbents with low amine density desorbed at a rate faster than those on sorbents with high amine density after switching the flow from CO2 to Ar at 55 °C. Evaluation of the desorption temperature profiles showed that the temperature required to achieve the maximal desorption of CO2 (Tmax. des) increases with amine density. The adsorbed CO2 on sorbents with high amine density is stabilized via hydrogen bonding interactions with adjacent amine sites. These sorbents require higher temperature to desorb CO2 than those with low amine density.