Crystallinity swayed phase transformation and oxygen vacancy formation in TiO2 aerogel photocatalysts.

The lack of crystallinity of the aerogel materials has limited their significance which otherwise have found huge potential in wide variety of applications. In current work, we have developed TiO2 aerogels by solid-state gelation method using commercially available P25 and ST-01 (commercial Ishihara TiO2 Powder). The lack of crystallinity in the aerogel framework was resolved via utilizing crystalline TiO2 nanoparticles and the phase transformation was assessed as a function of phase composition. Via controlled solid-state gelation, surface area retention of 88.7% was achieved whereas the rutile-to-anatase weight fraction (WR) was considerably enhanced to 0.50. Interestingly, the phase transformation occurred only in P25, which suggests the mixed phase (anatase + rutile) composition as prerequisite for successful phase transformation. Favorably, TiO2 aerogels imbibe high degree of oxygen vacancies (Vo) responsible for photocatalytic applications. Interestingly, Vo induction is higher for the TiO2 with anatase phase composition (ST-01) followed by the sample with mixed phase composition (P25). The developed TiO2 aerogel photocatalysts were employed to dye degradation of Rhodamine B (RhB) and Methylene Blue (MB). The samples attained 94.8% and 96.8% degradation efficiency within 15 min for RhB and MB with nearly 2-fold improvement in the photocatalytic efficiency compared to parent P25 TiO2 respectively.

Recent Developments on the Catalytic and Biosensing Applications of Porous Nanomaterials.

Nanoscopic materials have demonstrated a versatile role in almost every emerging field of research. Nanomaterials have come to be one of the most important fields of advanced research today due to its controllable particle size in the nanoscale range, capacity to adopt diverse forms and morphologies, high surface area, and involvement of transition and non-transition metals. With the introduction of porosity, nanomaterials have become a more promising candidate than their bulk counterparts in catalysis, biomedicine, drug delivery, and other areas. This review intends to compile a self-contained set of papers related to new synthesis methods and versatile applications of porous nanomaterials that can give a realistic picture of current state-of-the-art research, especially for catalysis and sensor area. Especially, we cover various surface functionalization strategies by improving accessibility and mass transfer limitation of catalytic applications for wide variety of materials, including organic and inorganic materials (metals/metal oxides) with covalent porous organic (COFs) and inorganic (silica/carbon) frameworks, constituting solid backgrounds on porous materials.

Theoretical investigation of selective CO2 capture and desorption controlled by an electric field.

Low-cost carbon dioxide (CO2) capture technologies have been studied widely. Among such technologies, the control of CO2 adsorption by the application of an electric field to solid materials has been shown to be a promising technology that can combine high CO2 adsorption with low energy consumption. Suitable materials must be found for electric field-assisted CO2 adsorption. For this study, the CO2 adsorption energies of CeO2 partially substituted with hetero-cations were investigated using theoretical calculations. The differences in adsorption performance attributable to the application of an electric field were clarified for different doped cations. The results show that the amount of change in the CO2 adsorption energy by the application of an electric field depended on the different doped cations. Furthermore, it is found that this difference in cations is related to the electronegativity of the doped cations. These results suggest a tuning strategy for the material properties necessary for CO2 capture and separation using an electric field.

Enhanced Hydrogenation of Levulinic Acid over Ordered Mesoporous Alumina-Supported Catalysts: Elucidating the Effect of Fabrication Strategy.

In this work, three types of alumina-supported bimetallic Ni-Cu catalysts [Ni-Cu/commercial non-ordered mesoporous alumina (CMA), Ni-Cu/ordered MA (OMA), and Ni-Cu-OMA] were prepared via different fabrication strategies and investigated in the conversion of levulinic acid (LA) into γ-valerolactone and 2-methyltetrahydrofuran (2-MTHF). This study employed characterization techniques and reactions to reveal the effects of the fabrication strategy on the activities of the catalysts. It was observed that the catalysts constructed on OM supports (Ni-Cu/OMA and Ni-Cu-OMA) displayed superior catalytic performance compared to those constructed on CM supports (Ni-Cu/CMA). Specifically, Ni-Cu-OMA, which was fabricated via the one-pot evaporation-induced self-assembly strategy, exhibited the best catalytic performance, achieving a complete conversion of LA and a high selectivity of 73.0 % toward 2-MTHF in a solvent-free reaction environment. The promising activity of Ni-Cu-OMA was ascribed to the well-dispersed active sites within the framework of the support, the enhanced metal-support interaction, and the highly efficient exploitation of the synergistic effect between Ni and Cu. Detailed post-characterization techniques were also employed to highlight the outstanding stability of Ni-Cu-OMA.

Characterisation of bacterial nanocellulose and nanostructured carbon produced from crude glycerol by Komagataeibacter sucrofermentans.

Bacterial nanocellulose (BNC), which has tunable properties, is a precursor of nanostructured energy storage materials; however, the cost of BNC production is challenging. This study uses crude glycerol from the biodiesel industry as a carbon nutrient and first-time carbonised BNC from K. sucrofermentans that is applied in energy storage. From crude glycerol in static cultivation, 6.4 g L-1 BNC was produced with a high crystallinity index (85%) and tensile properties in comparison to conventionally used pure carbon substrates. Carbon materials were derived from the BNC retained fibrous and crystalline features with disordered porous structures. The electrochemical properties of the carbon materials have a specific capacitance of 140 F g-1. This study highlights the valorisation of waste glycerol from the biodiesel industry as a substrate for efficient BNC production and the energy storage potential of carbon derived from BNC as renewable energy materials.

Interplay between electrochemical reactions and mechanical responses in silicon-graphite anodes and its impact on degradation.

Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon-graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li+ crosstalk between silicon and graphite, consequent Li+ accumulation in silicon, and capacity depression of graphite due to silicon expansion. The active material properties, i.e. silicon particle size and graphite hardness, are then modified based on these results to reduce Li+ accumulation in silicon and the subsequent degradation of the active materials in the anode. Finally, the cycling performance is tailored by designing electrodes to regulate Li+ crosstalk. The resultant full cell with an areal capacity of 6 mAh cm-2 has a cycle life of >750 cycles the volumetric energy density of 800 Wh L-1 in a commercial cell format.

Substrate Effect of Platinum-Decorated Carbon on Enhanced Hydrogen Oxidation in PEMFC.

Environmentally sustainable fuel cells with high efficiency have attracted much attention as a promising approach to resolving future energy problems. However, some obstacles must be overcome, such as corrosion, water control, and long-term degradation. Herein, we investigated the improved electrochemical performance and hydrogen oxidation reaction (HOR) mechanism of platinum loaded on carbon nanotube (Pt/CNT) catalyst by conducting experimental and theoretical studies. The Pt/CNT catalyst had a larger active area than the Pt/C (platinum loaded on carbon black) catalyst and also exhibited improved performance due to its long-term stability. In addition, the charge-transfer resistance of Pt/CNT (61.2 Ω cm2) is much smaller than that of Pt/C (90.2 Ω cm2), indicating that the CNT support offers good electron transfer. To further understand the hydrogen dissociation mechanisms of Pt/CNT and Pt/C, we investigated the adsorption characteristics and electron transfer of the catalysts with optimized geometry using the density functional theory (DFT). Pt/CNT exhibited higher adsorption energy and electron transfer than Pt/C, which leads to improved HOR. The integrated experimental and theoretical study conducted here suggests that Pt/CNT is a promising candidate for maintaining the performance of cathode catalysts in the polymer electrolyte membrane fuel cell.

Key factor for the anti-Arrhenius low-temperature heterogeneous catalysis induced by H+ migration: H+ coverage over support.

Low-temperature heterogeneous catalytic reaction in an electric field is anticipated as a novel approach for on-demand and small-scale catalytic processes. This report quantitatively reveals the important role of proton coverage on the catalyst support for catalytic ammonia synthesis in an electric field, which shows an anti-Arrhenius behaviour.

Effects of metal cation doping in CeO2 support on catalytic methane steam reforming at low temperature in an electric field.

Catalytic methane steam reforming was conducted at low temperature using a Pd catalyst supported on Ce1-x M x O2 (x = 0 or 0.1, M = Ca, Ba, La, Y or Al) oxides with or without an electric field (EF). The effects of the catalyst support on catalytic activity and surface proton hopping were investigated. Results show that Pd/Al-CeO2 (Pd/Ce0.9Al0.1O2) showed higher activity than Pd/CeO2 with EF, although their activity was identical without EF. Thermogravimetry revealed a larger amount of H2O adsorbed onto Pd/Al-CeO2 than onto Pd/CeO2, so Al doping to CeO2 contributes to greater H2O adsorption. Furthermore, electrochemical conduction measurements of Pd/Al-CeO2 revealed a larger contribution of surface proton hopping than that for Pd/CeO2. This promotes the surface proton conductivity and catalytic activity during EF application.

Support effects on catalysis of low temperature methane steam reforming.

Low temperature (<500 K) methane steam reforming in an electric field was investigated over various catalysts. To elucidate the factors governing catalytic activity, activity tests and various characterization methods were conducted over various oxides including CeO2, Nb2O5, and Ta2O5 as supports. Activities of Pd catalysts loaded on these oxides showed the order of CeO2 > Nb2O5 > Ta2O5. Surface proton conductivity has a key role for the activation of methane in an electric field. Proton hopping ability on the oxide surface was estimated using electrochemical impedance measurements. Proton transport ability on the oxide surface at 473 K was in the order of CeO2 > Nb2O5 > Ta2O5. The OH group amounts on the oxide surface were evaluated by measuring pyridine adsorption with and without H2O pretreatment. Results indicate that the surface OH group concentrations on the oxide surface were in the order of CeO2 > Nb2O5 > Ta2O5. These results demonstrate that the surface concentrations of OH groups are related to the proton hopping ability on the oxide surface. The concentrations reflect the catalytic activity of low-temperature methane steam reforming in the electric field.

Encapsulation of Phase-Changing Eutectic Salts in Magnesium Oxide Fibers for High-Temperature Carbon Dioxide Capture: Beyond the Capacity-Stability Tradeoff.

Eutectic mixture (EM)-promoted MgO sorbents exhibit high CO2 sorption capacities but  experience a significant decrease in uptake after multiple sorption-regeneration cycles due to EM movement and redistribution at high temperatures. Encapsulation of a pseudoliquid, phase-changing EM promoter with MgO may thus prevent the loss of active interface by confining the EM within a fixed area inside a MgO shell. In this work, we successfully embedded an EM composed of KNO3 and LiNO3 in a MgO fiber matrix via core-shell electrospinning. The synthesized sorbent achieved relatively high and steady sorption capacities, maintaining a stable uptake of ∼20 wt % after 25 sorption-regeneration cycles. The sorbent was also characterized using various techniques including in situ transmission electron microscopy (TEM) to describe its morphology, from which it was confirmed that the eutectic salt existed in distributed hollow pockets within the MgO fiber matrix and stayed confined within these fixed areas, favorably limiting its movement and redistribution when exposed to high temperatures where it exists in the liquid form. The EM may also be described as a glue that holds the fiber together, while MgO acts as a protective shell that prevents structural changes and rearrangement caused by EM movement, allowing the sorbent to retain its cyclic stability after multiple cycles and demonstrating its potential for industrial use after further improvement. Thus, the microencapsulation of a phase-changing EM material with pure MgO metal oxide was successfully achieved and might be explored for various material applications.

High-Loading Carbon Nanotubes on Polymer Nanofibers as Stand-Alone Anode Materials for Li-Ion Batteries.

To address the instability and repulsive interaction of carbon nanotubes (CNTs) in Li-ion batteries, mixed polymers (polyacrylonitrile and polyvinylpyrrolidone) were employed as matrix support to ensure that CNT particles remain in place during charge/discharge process and prevent particle migration. Various CNT-based anodes have been reported, but these require metal support that could result in contact resistance. Hence, free-standing CNT electrodes are an attractive option. A simple method of electrospinning polymers and calcination at 800 °C is presented with CNT loading as high as 50 wt % can be obtained without binder and acts as main active material rather than an additive as described in previous studies. The anode [pyrolyzed polymer (PP)-CNT] showed excellent performance with a high discharge specific capacity of 960 mA h/g at a current density of 200 mA/g. The capacity at a higher current density (1600 mA/g) remained greater than graphite (372 mA h/g) at 521 mA h/g and showed a high stability for 675 cycles without exhibiting any significant capacity loss with a Coulombic efficiency of >95%. A rate capability experiment showed the reversibility of PP-CNTs after subjecting them to an increasing current density and regaining >95% of the initial capacity at a low current density (200 mA/g). The high capacitive performance of the material is attributed to the high loading of CNTs and their containment within the bulk of the polymer matrix to prevent particle migration and agglomeration as well as the capacity of the nanofibers to preserve a tight proximity of the electrolyte-electrode interface.

Electric Field and Mobile Oxygen Promote Low-Temperature Oxidative Coupling of Methane over La1-x Ca x AlO3-δ Perovskite Catalysts.

Oxidative coupling of methane (OCM) over La1-x M x AlO3-δ (M = Ca, Sr, Ba; x = 0, 0.1, 0.2, 0.3) in an electric field at low temperature (423 K) was investigated. Among the tested catalysts, the La0.7Ca0.3AlO3-δ catalyst showed the highest performance in terms of C2H6 + C2H4 yield (11.1%). Surface mobile oxygen species (O2 2- or O-), which were considered as active oxygen species for the OCM reaction, increased with increasing Ca doping amount, and thereby the La0.7Ca0.3AlO3-δ catalyst showed the best catalytic activity.

Enhanced methane activation on diluted metal-metal ensembles under an electric field: breakthrough in alloy catalysis.

Methane activation on diluted metal ensembles is a challenging task in the field of alloy chemistry. This report describes that synergy between an electric field and Pd-Zn alloy allows improved catalytic activities in the steam reforming of methane. Because of surface protonics, Pd-Pd ensembles are no longer needed. Ligand effects facilitate methane conversion.

Mg-Ion Inversion in MgO@MgO-Al2 O3 Oxides: The Origin of Basic Sites.

Although MgO-Al2 O3 is well known as having a spinel structure, the inversion of which occurs by exchange of the trivalent (Al3+ ) and divalent (Mg2+ ) cations, little analytical study of the degree of inversion has been carried out. This study concerns a simple methodology to identify the inversion by solid-state NMR spectroscopy, whereby its correlation with the CO2 capture capacity of MgO-rich MgO@MgO-Al2 O3 spinel structures is verified. Through 27 Al and 25 Mg NMR spectroscopy, temperature-programmed CO2 desorption, and thermogravimetric analysis, higher inversion is found to occur at low Mg/Al ratios and the inversion is found to decrease as the Mg/Al ratio increases. Moreover, the degree of inversion correlates with CO2 sorption, which is associated with the medium-strength basic sites induced by formation of the unsaturated O2- species. These results will open new pathways to exploit defects in complex oxides beyond spinels and their derivatives for desired applications. This demonstration of MgO-Al2 O3 for CO2 sorption can contribute to the design of future CO2 sorbents.

Irreversible catalytic methylcyclohexane dehydrogenation by surface protonics at low temperature.

Liquid organic hydrides are regarded as promising for use as hydrogen carriers via the methylcyclohexane (MCH)-toluene-hydrogen cycle. Because of the endothermic nature of MCH dehydrogenation, the reaction is usually conducted at temperatures higher than 623 K. In this work, low-temperature catalytic MCH dehydrogenation was demonstrated over 3 wt% Pt/CeO2 catalyst by application of electric field across a fixed-bed flow reactor. Results show that a high conversion of MCH beyond thermodynamic equilibrium was achieved even at 423 K. Kinetic analyses exhibited a positive correlation of hydrogen to the reaction rates and an "inverse" kinetic isotope effect (KIE), suggesting that accelerated proton hopping with the H atoms of MCH promotes the reaction. Operando analyses and DFT calculation proved that the reverse reaction (i.e. toluene hydrogenation) was suppressed by the facilitation of toluene desorption in the electric field. The electric field promoted MCH dehydrogenation by surface proton hopping, even at low temperatures with an irreversible pathway.

Low-temperature selective catalytic dehydrogenation of methylcyclohexane by surface protonics.

The methylcyclohexane (MCH)-toluene cycle is a promising liquid organic hydride system as a hydrogen carrier. Generally, MCH dehydrogenation has been conducted over Pt-supported catalysts, for which it requires temperatures higher than 623 K because of its endothermic nature. For this study, an electric field was applied to Pt/TiO2 catalyst to promote MCH dehydrogenation at low temperatures. Selective dehydrogenation was achieved with the electric field application exceeding thermodynamic equilibrium, even at 423 K. With the electric field, "inverse" kinetic isotope effect (KIE) was observed by accelerated proton collision with MCH on the Pt/TiO2 catalyst. Moreover, Pt/TiO2 catalyst showed no methane by-production and less coke formation during MCH dehydrogenation. DRIFTS and XPS measurements revealed that electron donation from TiO2 to Pt weakened the interaction between catalyst surface and π-coordination of toluene. Results show that the electric field facilitated MCH dehydrogenation without methane and coke by-production over Pt/TiO2 catalyst.

Eutectic mixture promoted CO2 sorption on MgO-TiO2 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.

Diamine-Functionalization of a Metal-Organic Framework Adsorbent for Superb Carbon Dioxide Adsorption and Desorption Properties.

For real-world postcombustion applications in the mitigation of CO2 emissions using dry sorbents, adsorption and desorption behaviors should be controlled to design and fabricate prospective materials with optimal CO2 performances. Herein, we prepared diamine-functionalized Mg2 (dobpdc) (H4 dobpdc=4,4'-dihydroxy-(1,1'-biphenyl)-3,3'-dicarboxylic acid). (1-diamine) with ethylenediamine (en), primary-secondary (N-ethylethylenediamine-een and N-isopropylethylenediamine-ipen), primary-tertiary, and secondary-secondary diamines. A slight alteration of the number of alkyl substituents on the diamines and their alkyl chain length dictates the desorption temperature (Tdes ) at 100 % CO2 , desorption characteristics, and ΔT systematically to result in the tuning of the working capacity. The existence of bulky substituents on the diamines improves the framework stability upon exposure to O2 , SO2 , and water vapor, relevant to real flue-gas conditions. Bulky substituents are also responsible for an interesting two-step behavior observed for the ipen case, as revealed by DFT calculations. Among the diamine-appended metal-organic frameworks, 1-een, which has the required adsorption and desorption properties, is a promising material for sorbent-based CO2 capture processes. Hence, CO2 performance and framework durability can be tailored by the judicial selection of the diamine structure, which enables property design at will and facilitates the development of desirable CO2 -capture materials.