Activation Energy For Dissociation Research Articles

Adsorption and dissociation of NO on gold-palladium alloy clusters: A density functional theory study

Alloy nanoclusters often exhibit distinctive and exceptional performance, making them especially appealing as catalysts. In this study, the adsorption and dissociation of NO on AumPdn (m + n = 8) clusters was studied using density functional theory (DFT). The most stable structures of AumPdn (m + n = 8) clusters were reported by the CALYPSO search screening program and DFT geometric optimization. The binding energy and bond critical point (BCP) analysis show that alloying could lead to a more compact structure and relatively stronger stability. Molecular electrostatic potential (MESP) analysis revealed that the optimal site for the adsorption of the NO molecule on AumPdn (m + n = 8) clusters was at the top site, with Pd atoms being the preferred choice. Projected density of states (PDOS) calculations demonstrate that the d-band center of the Au5Pd3 cluster was closest to the Fermi level, enhancing the interaction between the cluster surface and adsorbed molecules. The activation energy of NO dissociation on the Au5Pd3 suserface is the lowest at 0.48 eV. These findings indicate that the Au5Pd3 nano-alloy cluster shows promise as an effective catalyst in the direct transformation of NO into non-toxic substances.

Cost-efficient sunlight-driven thermoelectric electrolysis over Mo-doped Ni5P4 nanosheets for highly efficient alkaline water/seawater splitting

Thermoelectric water spitting to hydrogen systems has great potential in the production of environment-friendly fuel using renewable solar energy in the future. In this work, we prepared porous nanosheet Mo doping Ni5P4 catalysts on nickel foam with efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in alkaline media. Density Functional Theory (DFT) calculations and experimental studies have shown that Mo doping deadeneds the interaction between H and O atomic orbitals of transition state water molecules, effectively weakening the activation energy of H2O dissociation. Therefore, Mo doping is favorable for enhancing HER activity with overpotential at 10 mA cm–2 of 93 mV and Tafel slope of 40.1 mV dec–1 in 1 M KOH. Besides, it exhibits high alkaline OER activity with an ultra-low overpotential of 200 mV at 10 mA cm–2. Moreover, this catalyst only needs 1.537 V in a dual-electrode configuration of the electrolytic cell, which is much lower than the commercial Pt/C-RuO2 couple (1.614 V). In addition, we have developed and constructed a solar thermoelectric generator (TEG) that is capable of floating on water. This TEG has a continuous power output and an exceptionally long lifespan, providing a stable power supply to the synthesized catalyst electrolyzer. It can produce a maximum power output of over 90 mW, meeting the requirement of converting solar radiation heat into usable electricity. As a result, the system achieves productivity of 0.11 mL min–1 H2. This solar thermal energy conversion technology shows the possibility of large-scale industrial production of H2 and provides a new idea for exploring heat source utilization.

Direct investigations of interactions between nucleolins and aptamers on pancreatic cancer and normal cells by atomic force microscopy

Nucleolin is overexpressed on the surface of pancreatic cancer cells and are regarded as the remarkable therapeutic target. Aptamers are capable of binding the external domain of nucleolin on the cell surface with high affinity and specificity. But nucleolin has not been localized on pancreatic cancer cells at very high spatial resolution, and the interactions between nucleolin and aptamers have not been investigated at very high force resolution level. In this work, nucleolin was localized on pancreatic cancer and normal cells by aptamers (9FU-AS1411-NH2, AS1411-NH2 and CRONH2) in Single Molecule Recognition Imaging mode of Atomic Force Microscopy. There are plenty of nucleolin on the surfaces of pancreatic cancer cells (area percentage about 5 %), while there are little nucleolin on the surfaces of normal cells. The interactions between three types of aptamers and nucleolins on the surfaces of pancreatic cancer cells were investigated by Single Molecule Force Spectroscopy. The unbinding forces of nucleolins-(9FU-AS1411-NH2) are larger than nucleolins-(AS1411-NH2). The dissociation activation energy on nucleolin-(9FU-AS1411-NH2) is higher than nucleolin-(AS1411-NH2), which indicates that the former complex is more stable and harder to dissociate than the later complex. There are no unbinding forces between nucleolin and CRONH2. All these demonstrate that nucleolin was localized on pancreatic cancer and normal cells at single molecule level quantitatively, and the interactions (unbinding forces and kinetics) between nucleolin and aptamers were studied at picoNewton level. The approaches and results of this work will pave new ways in the investigations of nucleolin and aptamers, and will also be useful in the studies on other proteins and their corresponding aptamers.

A density functional theory research on the interaction of H2X molecules with the Al2C nanosheet (X = O, S, Se, Te)

The potential application of the 2D material Al2C, as catalysts and as sensor of the hazardous molecules H2S, H2Se and H2Te, is studied using theoretical methods. Density functional theory (DFT) has been applied to study the interaction between the pristine Al2C nanosheet and small molecules, such as H2O, H2S, H2Se and H2Te. Results show the Al2C nanosheet is a promising material to dissociate the studied molecules as well as its potential use as sensor of these molecules in molecular or dissociated state. Molecular interactions are weak even considering the London dispersion forces. Partial dissociative adsorption is strongly preferred to molecular adsorption for all four molecules. Applying the climbing image NEB method, the activation energy for H2O dissociation to OH-H is calculated in ≈ 0.1 eV whereas it is just a few meV for H2S, H2Se and H2Te partial dissociation. The calculated energy gap for the clean Al2C nanosheet is 1.078 eV whereas it is increased to 1.371, 1.338, 1.379 and 1.416 eV for molecular adsorption and to 1.209, 1.363, 1.370 and 1.388 eV for partial dissociative adsorption.

Oxygen vacancy-rich CoMoO4/Carbon nitride S-scheme heterojunction for boosted photocatalytic H2 production: Microstructure regulation and charge transfer mechanism

Developing highly efficient S-scheme photocatalysts is a subject of immense interest for harnessing solar energy towards sustainable hydrogen production. Herein, a novel S-scheme heterojunction of oxygen vacancy-rich CoMoO4/CN (CMO/CN) photocatalyst was rationally constructed through loading CoMoO4 nanorods on carbon nitride (CN) nanosheets via a direct one-pot calcination method. The CMO/CN S-scheme heterojunction exhibited enhanced surface area, fine CN dispersion, rich oxygen vacancies, and accelerated charge separation/transfer efficiency, which were conducive to improving photocatalytic H2 evolution performance. Of note, the optimal 3 %CMO/CN sample displayed the highest H2 production rate of 8.35 mmol g−1 h−1, which is 4.6 folds that of pristine CN. In situ irradiated X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) characterizations confirmed the S-scheme charge transfer path between CN and CMO, which greatly promoted spatial charge separation. Density functional theory (DFT) calculations together with contact angle tests revealed the reduced activation energies for H2O dissociation and enhanced hydrophilicity of the CMO/CN. The CMO/CN photocatalysts also presented high stability and fine reusability. This work may provide insights into the combination of defect engineering and heterojunction designing for high-efficiency solar-to-chemical energy conversion.

Experimental and Simulation Studies of Acetone Detection By Pt-Au Nanofilm Sensors

Introduction Acetone in exhaled breath is a biomarker of diabetes. However, since it is a very stable substance, its detection by chemical sensors has been a challenging task. Alloy nanoparticles have attracted great attention because of their great catalytic performance, and it has been reported that the response to acetone can be improved by functionalizing oxide semiconductors (In2O3) with PtAu nanoparticles [1]. However, the mechanism of better response to acetone has not been fully understood, which is partly because the effects of alloying and supporting materials cannot be separated in the composite material systems. In this study, we demonstrate that PtAu-alloy nanofilms, where the effect of supporting materials is eliminated, show a greater response to acetone than Pt nanofilms. Furthermore, the impact of alloying on sensing performance was studied by high-throughput atomistic simulation with neural network potentials. Method First, we fabricated Pt and PtAu nanofilm sensors. As the Pt and PtAu nanofilms, Pt and Pt/Au were deposited, respectively, by electron beam evaporation method. The thickness of Pt film is 3 nm, whereas Pt/Au thicknesses are 2.5 nm/0.5 nm. The electrodes consisted of 40-nm Pt and 40-nm Au layers, and they were annealed in N2 ambient for 1 hour at 300 oC. XRD measurements were performed to evaluate the alloy states for three samples: Pt (20nm), Au (20 nm), and PtAu (18 nm). The PtAu film for XRD was fabricated by repeating sequential depositions of 5-nm Pt and 1-nm Au three times. All the films were annealed for 1 hour at 300 oC in N2 ambient. The sensor responses to acetone were evaluated by measuring the resistance of Pt and PtAu at 260 oC under the following sequences.i) Dry air (15 min)ii) 1-ppm acetone in dry air (2 min)iii) Dry air (3 min)We applied DC current of 100 µA and the voltage difference between the terminals were measured. To examine the factors that contribute to the difference in sensing performance of PtAu and Pt nanofilms, we calculated the reaction pathway using the nudged elastic band method. All calculations were carried out with PFP version 2.0.0 on Matlantis [2]. DFT-D3 was used to describe the van der Waals interaction [3]. Results Pt, Au, and PtAu samples showed (111) peaks in the XRD analysis. The position of (111) peak of PtAu located between those of Pt and Au peaks, suggesting that PtAu was successfully alloyed. By applying the Vegard’s law, the composition of PtAu was determined to be 0.823:0.177, which is consistent with the thickness ratio. When acetone was exposed, the resistance of the devices decreased. The response of PtAu to acetone was greater than that of Pt. In addition, the responses of Pt and PtAu devices were proportional to the square root of the concentration of acetone. The limit of detections (LOD) determined by 3σ method were 76 ppb for Pt and 14 ppb for PtAu. Discussion We considered that H atoms introduced by CH dissociation of acetone prevent the adsorption of oxygens from the atmosphere and reduce the surface scattering of electrons, leading to a decrease in the resistance of Pt nanofilms. The Nudged Elastic Band method was used to calculate the activation energy of CH dissociation of acetone on the surface of Pt and PtAu. PtAu slab was prepared by replacing Pt atoms partly with Au atoms. The calculations showed that the activation energy for PtAu was 64-meV lower than that of Pt. In the transition state, the dissociated H atom stayed at the bridge site of Pt. When Pt atoms are substituted with Au atoms, the distance between Pt’s at the bridge site expands due to the large lattice constant of Au. As a result, the transition state became more stable on PtAu surface than on Pt surface. In fact, we confirmed that the activation energy was lowered as the Pt-Pt distance increased. Conclusion We demonstrated, for the first time, that PtAu nanofilm sensors show a greater response to acetone than Pt nanofilm. The atomic simulation demonstrated that the dehydrogenation of methyl group of acetone is the fundamental mechanism of the acetone sensing, and that the lattice expansion induced by replacing Pt with Au contributed to stabilize the transition state and to reduce the activation energy. Further optimization of the alloy composition should be essential to achieve a more highly sensitive acetone sensor.

Rational design of methane dissociation catalyst based on first principles

Based on the first principle, this paper uses the generalised gradient approximation density functional theory and slab model to investigate the dissociation of methane (CH4→CH3 + H) on the surfaces of Co group (Co, Rh, Ir) and Ni group (Ni, Pd, Pt), and investigate the influence of PtIr(100), PdRh(100) and PtPd(100) on methane decomposition. From the calculated activation energies of methane dissociation on single metal surfaces and alloy surfaces,we find that Pt and Ir are better catalysts for methane dissociation in the single metals studied. In addition, methane dissociation (CH4→CH3 + H) on PtIr(100) and PdRh(100) surfaces are easier than that on single metal surfaces(Co, Rh, Ir, Ni, Pd, Pt).

Methylation of benzene with methane induced by strong adsorption of benzene on Co ion at α-position in zeolite with moderate Al−Al distance

First principles calculations are applied to find a pathway for methylation of benzene with methane into toluene and dihydrogen catalyzed by MFI type zeolite-supported Co species. On Co2+ at the α-position of MFI framework which is exposed to relatively large space, benzene is strongly adsorbed, while the adsorption on Co at the β-position is weak due to steric hindrance. Energy required for dissociation (activation) of methane was high, but the large energy evolved by adsorption of benzene on Co cancels the activation energy for the methane dissociation to suppress the energies of this step and following formation of toluene precursor. The activation energy of methane dissociation is sensitively changed by Al−Al distance also. Short distance results in difficulty of cleavage of Co–O bond, because Co is fully and strongly coordinated to basic oxygen atoms next to Al atoms, i.e., O in Al–O–Si. On the contrary, Co is partly coordinated to O in Si–O–Si with moderate Al−Al distance, and the cleavage of coordination bond is easy. Too long distance causes difficulty for hopping H+ to reach base site apart from the reaction field. At an appropriate Al−Al distance, the activation energies of the methane dissociation and toluene precursor formation are low. The latter is the rate-determining of benzene methylation with methane, and its energy, i.e., the apparent activation energy is in agreement with the experimental measurements. Experimentally, high activity at the α-position, strong dependence of activity on the framework Al content and the high activity at a moderate framework Al content were observed, supporting the theoretical conclusions. The driving force of benzene methylation with methane, a reaction between a pair of inactive reactants (methane and benzene), is thus clarified to be the strong adsorption of benzene. The origin of catalytic activity is therefore proposed to be strong electron withdrawing nature (Lewis acidity) of Co species held by the ion exchange site of zeolite.

Chemical bonding in potential PFAS products from the thermal degradation of energetic devices, a DFT analysis

This work investigates stability and chemical bonding in possible per- and polyfluoroalkyl substances (PFAS) generated through the disposal of munitions in controlled detonations and open burns. Density functional theory (DFT) calculations were used to determine bond dissociation enthalpies (BDEs), activation energies, and other chemical properties. Calculated parameters were used to determine the functional groups most likely to be present based on the level of fluorination and the position of fluorines. In compounds that form C–O bonds, the presence of α-fluorines significantly strengthens the C–O bond by ∼4–18 kcal/mol. The results of this study indicate that fluoroalkyl alcohols are a very likely product of the disposal of munitions. This work was designed to expedite the analytical process of confirming that PFAS are created from current disposal methods of energetic devices by providing insight as to of what types of compounds should be expected. The PFAS generated in such reactions are expected to contain some functional groups (i.e., nitro and nitrite) that have not been known to exist as a result of the environmental degradation of industrially relevant PFAS, therefore, they may have been overlooked before. These initial results imply that PFAS with nitro functionalities may be formed in these conditions considering the abundance of NO2 radicals expected to be present as well as the strength of the C–N bond that can form (∼40–50 kcal/mol) whereas with nitroso functionalities are not expected to be found since the bonds formed are much weaker (∼25–35 kcal/mol), and nitrosoalkanes are known to decompose under mild conditions. Although these results are promising, analytical work is needed to assess the conclusions of this study in real systems.

Co-adsorption of H2+nCO+mO2 on α-Fe (110): Effect on hydrogen adsorption, dissociation and diffusion

Hydrogen enriched compressed natural gas contains CO and O2 impurities, which have a coupling effect on hydrogen adsorption, dissociation and diffusion. First principles plane wave calculations have been used to study the co-adsorption and mutual interaction of H2+nCO + mO2 on Fe (110) plane. The results show that it’s easier for pre-adsorbed nCO + mO2 to form high surface coverage compared with pre-adsorbed nCO or mO2. The CO and O2 increased H2 dissociation barrier (Edis−b), and high coverage of nCO, mO2 and nCO + mO2 increased the hydrogen dissociation activation energy (Edis). With the coverage increased, the diffusion barrier (Edif) of H atom into Fe (110) decreased from 1.01eV to 0 by nCO and increased from 1.01eV to 2.14eV by mO2. The Edif was controlled by CO under low coverage and was controlled by O2 under high coverage when nCO + mO2 pre-adsorbed: the deformation charge density and state density analysis show that in H2+nCO + mO2 system, H atom is in an electron gain state at low coverage, which is similar to H in pre-adsorbed nCO, and H is in an electron loss state at high coverage, which is similar to H in pre-adsorbed mO2.The Edif probably related to the charge interaction of Hx− and Hy+ with Fez+.The C, O and H formant peaks from density of states show the influence of C and O on hydrogen invasion in orbital energy.

Enhancing the reactivity of clean, defect-free epitaxial graphene by the substrate—Experiment and theory

Experimental and theoretical evidence is presented that a sulfur compound dissociates on clean, defect-free epitaxial graphene (Gr) in ultrahigh vacuum (UHV). Together with density functional theory calculations (DFT), experimental kinetics and spectroscopic data suggest an auto-(/self)catalytic process. The results could open a pathway to a carbocatalyst. While adsorbing H2S in UHV at low temperatures on single-layer graphene/ruthenium (Gr/Ru), H2 desorbs and sulfur remains on the surface. Vacancy and grain boundary defects, respectively, can be excluded as active sites. DFT results indicate the importance of the Ru(0001) support in facilitating a reaction pathway with small activation energy for H2S dissociation. Gr becomes reactive due to a complex interplay of structural and electronic effects, including the corrugation of the graphene layer and the hybridization of ruthenium's d orbital with antibonding states of H2S.

Annealing effect on the methane sensing performance of Pt–SnO2/ZnO double layer sensor

Low power consumption is a new emerged requirement for methane sensors long-term working in a gas supervisorycontrolsystem. Great challenges remain in development of heat free methane sensors based on metal oxide semiconductors (MOS). In this work, Pt-doped SnO2 (Pt-SnO2) grow on well aligned ZnO nanorod-array to form an inter-staggered double-layer structure on AZO glass by a two-step hydrothermal method, with the annealing temperature being systematically studied. The optimized processing parameters are 1 at% Pt doping content and 700 °C annealing temperature, offering the best sensing response of 3.36 to 800 ppm CH4 at room temperature. SnO2/ZnO without Pt doping shows linear I-V relationship, while the Pt-SnO2/ZnO shows a Schottky-like I-V curve with the Schottky barrier height decreases as increasing the CH4 concentration. The activation energy (ΔEa) for CH4 dissociation decreases with increasing the annealing temperature, and the ΔEa of the optimized Pt-SnO2/ZnO sample is only one-third of that in the SnO2/ZnO. In addition to the piezoelectric polarization electric field in ZnO, the build up Schottky-like barrier and the reduced activation energy via Pt doping and annealing are demonstrated to be efficient for enhancing the methane sensing performance at low operation temperature.

Photo-thermo catalytic hydrogen production along with pollutant degradation by cost-effective carbon materials

Photo-thermo catalysis represents one of the promising technologies for the use of solar energy to produce hydrogen while recovering chemical energy contained in wastewater. However, inefficient utilization of the whole solar spectrum, high water dissociation activation energy, and costly materials restrict its widespread applications. Herein, we propose to use non-plasmonic, metal-free, cost-effective and full-spectrum-responsive nitrogen-doped carbon materials prepared by using urea as a nitrogen source for photo-thermo catalytic hydrogen production in accompany with aqueous pollutant degradation. It is demonstrated that the used carbon materials can successfully produce hydrogen and decompose pollutants simultaneously via photo-thermo catalytic reactions upon illumination even with actual biogas slurry. Moreover, strong oxidants can be generated via photo-thermo catalysis in the presence of dissolved oxygen, which promotes hydrogen production. Particularly, due to the photothermal conversion, the redox reaction over carbon materials is enhanced and the activation energy is decreased, facilitating hydrogen production. The generated hydrogen radicals promote the regeneration of active sites for thermocatalytic hydrogen production. The synergy of photocatalysis and thermocatalysis leads to the promotion of actual biogas slurry degradation and hydrogen production. This work demonstrates a promising, efficient and cost-effective strategy for simultaneous solar hydrogen production and wastewater treatment.

Linear, nonlinear rheological properties and foamability of Surlyn partially neutralized with sodium counterion

Linear viscoelasticity (LVE), elongational rheological behavior, and foamability are examined for ionomer samples based on a commercial Surlyn sample: The Surlyn sample is dialyzed back into the parent acid copolymer and partially neutralized by sodium hydroxide to different degrees. The LVE pseudo-master curves shift to the lower frequency with an increase in the molar fraction of sodium, reflecting the increased activation energy for ionic dissociation. Incorporation of this energy into the sticky-double-reptation model gives good prediction of the LVE behavior. The degree of strain hardening under the extensional flow exhibits a non-monotonous change: the transient hardening first intensifies with increasing the ion content up to ∼50 mol%, and then weakens upon further increasing the ion content. The foamability of these samples in supercritical CO2 appears to be controlled by the flowability as well as the melt strength during the elongational flow. In particular, the foaming T window widens greatly when the strain-hardening has been strengthened by the physical network based on the ionic interaction.

Analyzing characteristic and modeling of high-temperature proton exchange membrane fuel cells with CO poisoning effect

High-temperature proton exchange membrane fuel cells (HT-PEMFC) have strong resistance to CO poisoning. However, the published CO poisoning models for HT-PEMFC are based on the finite element analysis method, which are difficult to use for the performance prediction and development of system control strategies due to a large amount of calculation. In the beginning, a semi-empirical model of HT-PEMFC is deduced based on the analysis of the CO poisoning characteristics. Then the key parameters of ohmic impedance and concentration polarization advance correction factor are obtained by fitting the polarization curves, dissociation and adsorption activation energy of H2 and CO are obtained by the calculation, respectively. The slope of the straight line segment in the ohmic polarization interval of the polarization curve is linearly related to ln[H2/CO]. The change of limiting current density is the main factor for the advance of concentration polarization. The fitted ohmic impedance varies with temperature and CO concentration, but changes little above 175 °C. CO coverage depends primarily on dissociation and adsorption activation energy of CO. Subsequently, the proposed model is validated with experimental data and shows high similarity. The model can be used for studying the systematic control strategy development and performance monitoring of HT-PEMFC.

Density functional theory study of trends in water dissociation on oxygen-preadsorbed and pure transition metal surfaces

Oxygen and water are the most reactive gases of the ambient air. The adsorption of both molecules on transition metal surfaces have been studied extensively, but mostly separately. However, water and oxygen usually co-exist, and therefore realistic systems need to take into consideration both simultaneously. As these adsorption reactions are so common, state-of-the-art results are beneficial as they capture large trends as accurately as possible. A comprehensive study of oxygen and water co-adsorption and dissociation on Ag(111)-, Au(111)-, Pd(111)-, Pt(111)-, Rh(111)- and Ni(111)-surfaces have been performed using density functional theory. We present a very strong general trend, where dissociated oxygen systematically lowers the activation energy of water dissociation on transition metal surfaces. This makes the oxygen dissociation the rate-determining step of the water dissociation reaction. The effect is caused by the additional pathway that the dissociated oxygen enables for the dissociation of water molecule.

Density functional calculation of adsorption and dissociation of PbPo molecule on Pd(100), Pd(110) and Pd(111) surfaces

Radiotoxic Po are produced and mainly formed as PbPo in lead-bismuth eutectic in lead-bismuth fast reactor and accelerator-drive systems during normal operation. Part of hazardous PbPo will evaporate and accumulate in the cover gas above the lead bismuth eutectic coolant. To ensure safe handling of the reactor, suitable cover gas filter systems should be fixed but few fundamental data on the interaction between PbPo and filter materials are reported. In this work, adsorption and dissociation of PbPo molecule on candidate filter material Pd surfaces were studied with the density functional theory. It was found PbPo is strongly chemisorbed on Pd(100), Pd(110) and Pd(111) surfaces with adsorption energies in the range of -1.14 eV to -5.36 eV. The activation energies for PbPo dissociation on these tree surfaces are all very small, which are one to two order of magnitude smaller than the recombination activation energies of the reversed paths. The calculated results indicate that strong chemisorption was found between PbPo and perfect low-index Pd surfaces and PbPo molecule is highly inclined to be as Pb and Po atoms on these surfaces.

Effects of nanobubbles on methane hydrate dissociation: A molecular simulation study

Hydrate dissociation is often accompanied by the formation of nanobubbles. Knowledge of the effects of nanobubbles on hydrate dissociation is essential for understanding the dynamic behavior of the hydrate phase change and improving the gas production efficiency. Here, molecular dynamics simulations were performed to study the methane hydrate dissociation kinetics with and without a pre-existing methane nanobubble. The results show that the hydrate cluster in the liquid phase dissociates layer-by-layer. This process is shown to be independent of the temperature and nanobubble presence at the simulation conditions. Hydrate dissociation does not always lead to nanobubble formation because the supersaturated methane solution can be stable for a long time. A steep methane concentration gradient was observed between the hydrate cluster surface and the methane nanobubble, which can enhance the directional migration of methane and effectively minimize the methane concentration in the liquid phase, thereby increasing the driving force for the hydrate dissociation. Our findings indicate that the presence of a nanobubble near the hydrate surface does not decrease the activation energy of hydrate dissociation, but it can increase the intrinsic decomposition rate. The average hydrate dissociation rate is linearly correlated with the mass flow rate towards the nanobubble. The mass flow rate is determined by the nanobubble size and hydrate-nanobubble distance. Our findings contribute to the fundamental understanding of the dissociation mechanism of gas hydrates in the liquid phase, which is crucial for the design and optimization of efficient gas hydrate production techniques.

PBE+U-D2 study on facet selective gas adsorption and methane activation over oxygen terminated Cu2O surfaces

It has been reported that Cu2O (100) is a better surface for sensing hydrocarbons compared to Cu2O (111). In order to understand the facet selectivity in hydrocarbon sensing, density functional theory calculations were performed to obtain adsorption energies of CO2, H2O, CH4 and O2 on oxygen terminated cuprous oxide surfaces and the activation energy for C–H bond dissociation. It was observed that Cu2O (111) surface has a high affinity towards H2O and CO2. Further, it was found that the activation energy for H3C-H bond dissociation on Cu2O (100) is significantly lower than that on Cu2O (111). Increased hydrophobicity and low activation energy for CH3-H bond breaking makes Cu2O (100) a better sensing surface for hydrocarbons.

Oxygen Vacancies Engineering in Thick Semiconductor Films via Deep Ultraviolet Photoactivation for Selective and Sensitive Gas Sensing

AbstractRoom‐temperature detection of volatile organic compounds in particle‐per‐billion concentrations is critical for the development of wearable and distributed sensor networks. However, sensitivity and selectivity are limited at low operating temperatures. Here, a strategy is proposed to substantially improve the performance of semiconductor sensors. Tunable oxygen vacancies in thick 3D networks of metal oxide nanoparticles are engineered using deep ultraviolet photoactivation. High selectivity and sensitivity are achieved by optimizing the electronic structure and surface activity while preserving the 3D morphology. Cross‐sectional depth analysis reveals oxygen vacancies present at various depths (≈24% at a depth of 1.13 µm), with a uniform distribution throughout the thick films. This results in ≈58% increase in the sensitivity of ZnO to 20‐ppb ethanol at room temperature while ≈51% and 64% decrease in the response and recovery times, respectively. At an operating temperature of 150 °C, oxygen‐vacant nanostructures achieve a lower limit of detection of 2 ppb. Density functional theory analysis shows that inducing oxygen vacancies reduces activation energy for ethanol adsorption and dissociation, leading to improved sensing performance. This scalable approach has the potential for designing low‐power wearable chemical and bio‐sensors and tuning the activity and band structure of porous, thick oxide films for multiple applications.