Adsorption Of Gas Molecules Research Articles

Spectroscopic determination of the role of vanadyl oxygen in room temperature NH3 sensing by V2O5 nanoparticles

In the present study, a multi-modal approach consisting of in-situ photoluminescence, Raman, and UV-Vis absorption spectroscopic studies is carried out along with chemiresistive sensing to unveil the mechanism of NH3 gas sensing by V2O5 nanoparticles in ambient air. V2O5 nanoparticles with an average size of 49 nm show a superior sensor response of 17 ± 1.5 % towards 1 ppm of NH3 gas with a response and recovery time of 96 s and 45 s, respectively. The photoluminescence and UV-Vis absorption studies in the presence of NH3 reveal electron doping to a new energy level at 1.84 eV, resulting in conduction band filling and increase in the optical band gap. The intensity of the photoluminescence spectrum shows an increase in the presence of NH3 gas as a result of this electron doping. The sensor response from the optical sensing carried out by in-situ photoluminescence study is 43 % for 40 ppm of NH3 gas. The vanadyl oxygen site is the most active in the sensing process, as evident by a selective enhancement in the intensity of V–O (vanadyl) bond vibration. This study gives an experimental evidence for the changes in optical and electronic properties of V2O5 on the adsorption of NH3 gas molecules.

Methane enrichment of biogas using carbon capture materials

An important percentage of biogas is made of CO2, which decreases its heating value. If CO2 is adsorbed two advantages can be achieved: CO2 capture and the increase of biogas heating value. Biomethane is a renewable fuel, which can provide energy autonomy and a reduction of greenhouse gases emissions. CO2 capture from power plants by using solid adsorbents is an effective method for the reduction of CO2 emission and an excellent solution for methane enrichment of biogas. This work evaluates the CO2 removal and methane enrichment of biogas by adsorption of gas molecules to solid surfaces of sorbents in a pilot-scale biogas upgrading system. The materials selected to remove CO2 from gases were three: calcium hydroxide, commercial activated carbon and solid amine adsorbent, loaded on commercial activated carbon. The amine adsorbent used in this work was polyethylenimine (PEI). The adsorbents were characterized by thermal stability through thermogravimetric analyzer (TGA), X-ray diffraction analysis (XRD), specific area, pore size distribution and particle size distribution. The CO2 adsorption capacities of the sorbents were measured using a thermogravimetric analyzer with pure CO2 at atmospheric pressure. The CO2 adsorption capacity test was 0.00653 mol/g for calcium hydroxide, 0.00219 mol/g for commercial activated carbon with 0,1 wt% of amine and 0.00168 mol/g for commercial activated carbon. The effect of adsorbent dosage as a function of time was also investigated. The result showed that the CO2 adsorption of the sorbents increases with adsorbent dosage. The results obtained from the upgrading tests conducted in the lab-scale system showed that a purity of 99.9 % methane was obtained using 15 g of calcium hydroxide, a purity of methane of 87 % was obtained using 30 g of commercial activated carbon with 0.1 wt% amine and a purity around 86 % methane was obtained using 30 g of commercial activated carbon.

Adsorption of gas molecules (CO, CO$${_{2}}$$, NO, NO$${_{2}}$$, and CH$${_{4}}$$) on undoped and Ag-doped bismuth ferrite oxide (BFO) by DFT investigation

Adsorption of gas molecules (CO, CO$${_{2}}$$, NO, NO$${_{2}}$$, and CH$${_{4}}$$) on undoped and Ag-doped bismuth ferrite oxide (BFO) by DFT investigation

Triptycene based fluorinated polymers with improved carbon dioxide capture and hydrogen/methane storage

The use of direct arylation polymerization (DArP) as a viable strategy to obtain porous organic polymers (POPs) has not been explored to its full potential. Instead, other strategies (such as conventional cross-coupling reactions) are usually employed to yield POPs that employ expensive organometallic monomers whose syntheses require multiple steps. Herein, using DArP, three fluorinated porous organic polymers (fPOPs: TFPP1, TFPP2 and TFPP3) were obtained that represent unique examples of triptycene motif containing fluorine rich network polymers. These thermally stable polymers (Td > 400 °C with high char yields at 800 °C) are predominantly microporous with high surface areas (up to 1295 m2/g) and thus satisfy the requirement for facilitating superior adsorption of small gas molecules. The recorded CO2, CH4, and H2 uptake capacities of fPOPs are superior than several previously reported fluorinated/non-fluorinated POPs. High CO2 uptake capacities of fPOPs are due to the incorporation of ample triptycene motifs and polar C–F bonds in the polymeric backbone. Overall, the high thermal stability, surface area and sorption capacities demonstrated by these fluorinated polymers render them potential materials for the applications in capture of CO2 and storage of CH4/H2.

Adsorption of NO gas molecule on the vacancy defected and transition metal doped antimonene: A first-principles study

The adsorption behaviors of single vacancy defected and transition metal (TM) atoms (Sc, Ti) doped antimonene for NO molecule have been systematically investigated using the first-principles calculations based on the density functional theory (DFT-D2 method). The results show that the NO molecule is physisorbed on pure antimonene with the low adsorption energy. While the NO molecule is chemisorption on single vacancy defected antimonene (SV-antimonene), TM doped antimonene (Sc-antimonene, Ti-antimonene) and TM doped single vacancy defected antimonene (Sc-SV-antimonene, Ti-SV-antimonene). The introduction of vacancy defects and TM atoms can effectively enhance the interaction between the NO molecule and the antimonene by analyzing the density of states (DOS), charge density difference (CDD) and the electron localization function (ELF). In addition, the significant changes in work function (WF) after NO adsorption indicate that defected and doped antimonene are sensitive to NO molecule. The optical properties suggest that the increase in absorption coefficients of all adsorption systems can be observed in the visible region. Therefore, these results provide theoretical guidance for the design of high-sensitive gas sensors based on antimonene.

Experimental and simulation study on the delayed release of CO in the initial stage of the low-temperature oxidation of coal

To investigate the delayed release characteristics of CO gas in the initial stage of the low-temperature oxidation of coal, closed oxygen consumption experiments were conducted on coal samples taken from the Hongqingliang coal mine, and the corresponding relationship between the CO concentration and time in the initial stage of the experimental reaction was analyzed. A physical adsorption model of the macromolecules in coal for O2 and CO was established, and the difference in the competitive adsorption between the CO and O2 gas molecules on the coal surface was analyzed from a microscopic perspective using the grand canonical ensemble Monte Carlo simulation. The results showed a delayed CO release phenomenon in the initial stage of the reaction in all the experiments, and the delayed time of CO release was negatively correlated with the temperature; the relationship between the adsorption amounts of CO and O2 in the molecular structure model of coal was CO > O2. With increasing temperature, the adsorption capacity of the two gases decreased. Under the same conditions, there was competitive adsorption of the mixture of CO and O2 by coal, with the adsorption capacity of CO being much greater than that of O2. The adsorption of CO gas molecules by coal played an inhibitory role in the release of CO gas in the initial oxidation stage. The study results are expected to help understand the CO generation characteristics in the goaf of coal seam working faces and thus prevent coal mine disasters.

Adsorption of SO2 air pollutant gas molecule on the pure and Al-doped graphene nano sheet: A DFT study

The interaction of pure graphene nano sheet and Al-doped graphene nano sheet with SO2 pollutant gas molecules was examined by density functional theory (DFT). Adsorption energies and the transferred Mulliken charge were calculated. Doping Al on the graphene improved adsorption and electronic properties of graphene. Dos plots and HOMO-LUMO band gaps showed that pure graphene and Al-doped were semiconductor materials. The results revealed that sensitivity of graphene-based materials was enhanced by doping Al on the surface of pure graphene. Thus, Al-doped graphene was found to be a better detector of SO2 gas molecules.

A Novel Two-Dimensional ZnSiP2 Monolayer as an Anode Material for K-Ion Batteries and NO2 Gas Sensing.

Using the crystal-structure search technique and first-principles calculation, we report a new two-dimensional semiconductor, ZnSiP2, which was found to be stable by phonon, molecular-dynamic, and elastic-moduli simulations. ZnSiP2 has an indirect band gap of 1.79 eV and exhibits an anisotropic character mechanically. Here, we investigated the ZnSiP2 monolayer as an anode material for K-ion batteries and gas sensing for the adsorption of CO, CO2, SO2, NO, NO2, and NH3 gas molecules. Our calculations show that the ZnSiP2 monolayer possesses a theoretical capacity of 517 mAh/g for K ions and an ultralow diffusion barrier of 0.12 eV. Importantly, the ZnSiP2 monolayer exhibits metallic behavior after the adsorption of the K-atom layer, which provides better conductivity in a period of the battery cycle. In addition, the results show that the ZnSiP2 monolayer is highly sensitive and selective to NO2 gas molecules.

Li-decorated borophene–graphene heterostructure under gas adsorption

Two-dimensional materials show great application potentials in gas sensor due to its high surface-to-volume ratio. In this regard, we investigate the adsorption energies of five gases: NH3, NO, NO2, H2S, and SO2, on borophene, with the help of the density functional theory (DFT). The results show the high adsorption capacity of borophene, but gas adsorption can lead to its structural instability with the greatest influence of nitrogen. However, the heterostructure of borophene and graphene (B/G) can inhibit the deformation and optimize the adsorption capacity of borophene. In order to enhance the adsorption of gas molecules on B/G, lithium is doped in the borophene layer, and it shows that the adsorption of sulfur gas can be significantly enhanced. In addition, the transport properties of Li-decorated B/G inhibitors are simulated by non-equilibrium Green’s function method. The graphene composite and Li doping are found to have a great impact on the gas-sensitive properties of borophene, which provides new ideas for the application of borophene in sensors.

P-Doped h-BN Monolayer: A High-Sensitivity SF6 Decomposition Gases Sensor

SF6 decomposition gas monitoring is of great significance to gas-insulated switchgear (GIS) fault detection and early warning and even the safe and stable operation of the power system. As a gas sensing material, the h-BN monolayer shows good application potential in sensing technology. Therefore, this study calculated and analyzed the gas-sensing response characteristics of P-BN monolayers to SF6 decomposition gases (SO2F2 and SOF2) based on the first-principles density functional theory, such as total density of state and sensitivity. In order to prove the selectivity of the P-BN monolayer for SO2 F2 and SOF2 gas molecules, the gas-sensitive adsorption parameters of the P-BN monolayer for H2O and CO2 gas molecules were calculated. The results show that the adsorption of SO2 F2 and SOF2 gas molecules on the P-BN monolayer is relatively strong, which is in the critical state of physical adsorption and chemical adsorption. The adsorption of H2 O and CO2 molecules is relatively weak. P-BN monolayer showed good selectivity and high sensitivity for SO2 F2 and SOF2 gas molecules. This study provides a theoretical basis for the application of P-BN monolayer in the field of SF6 decomposition gas monitoring and provides a novel way and idea for the development of other gas sensors.

High switching ratio and inorganic gas sensing performance in BeN4 based nanodevice: a first-principles study

Recently, Dirac material BeN4 has been synthesized by using laser-heated diamond anvil-groove technology (Bykov et al 2021 Phys. Rev. Lett. 126 175501). BeN4 layer, i.e. beryllonitrene, represents a qualitatively class of two-dimensional (2D) materials that can be built of a metal atom and polymeric nitrogen chains, and hosts anisotropic Dirac fermions. Enlighten by this discovered material, we study the electronic structure, anisotropic transport properties and gas sensitivity of 2D BeN4 using the density functional theory combined with non-equilibrium Green’s function method. The results manifest that the 2D BeN4 shows a typical semi-metallic property. The electronic transport properties of the intrinsic BeN4 devices show a strong anisotropic behavior since electrons transmitting along the armchair direction is much easier than that along the zigzag direction. It directly results in an obvious switching characteristic with the switching ratio up to 105. Then the adsorption characteristics indicate that H2S, CO, CO2 and H2 molecules are physisorption, while the NH3, NO, NO2, SO2 molecules are chemisorption. Among these chemisorption cases, the 2D gas sensor devices show an extremely high response for SO2 recognition, and the high anisotropy of the original 2D BeN4 device still maintains after adsorbing gas molecules. Finally, high switching ratio and inorganic gas sensing performance of BeN4 monolayer could be clearly understood with local density of states, bias-dependent spectra, scattered state distribution. In general, the results indicate that the designed BeN4 devices have potential practical application in high-ratio switching devices and high gas-sensing molecular devices.

A DFT study of gas molecules adsorption on intrinsic and Cu-doped graphene gas nanosensors

In this study, first-principles calculations are performed to investigate the sensitivity of intrinsic graphene sheet (GS) and Cu-doped graphene sheet (Cu-GS) gas nanosensors for adsorbing CO, H2, and H2S gas molecules using QUANTUM ESPRESSO package. The density of states (DOS), net charge transfer, adsorption energy, partial density of states (PDOS), and the most stable adsorption configuration of these molecules on GS and Cu-GS are studied. The results show the weak physical adsorption of the three gas molecules on GS. The strength of interaction between the Cu-GS system and adsorbed gas molecules is higher due to the Cu doping. It is expected that the significant increase in charge transfer and adsorption energy leads to fundamental improvement in the electrical conductivity of the Cu-GS system. The results indicate that the introduction of Cu impurity can improve the gas sensing properties of graphene-based gas nanosensors. Therefore, Cu-GS is more appropriate for detecting gas molecules compared to pure GS. The results in this study are useful for developing the design of gas nanosensors.

Effects of O2 adsorption on secondary electron emission properties

The surface adsorption of gas molecules is a key factor limiting the secondary electron yield (SEY) of a material in many areas of applied physics. The influence of O2 adsorption on the SEY of metallic Ag is investigated in this work. To account for the particle distribution, we propose a BET theory based on multilayer O2 physisorption model. Furthermore, based on the phenomenological model of secondary electron (SE) emission and by taking into account the different scattering processes between electrons and particles in the adsorbed layer, we develop a numerical model of SEY in the adsorbed state using Monte Carlo simulations. The relationships among O2 adsorption, adsorption layer thickness, and SEY variation characteristics are then examined through a series of experiments. After 12-h exposure to O2, the clean samples increases 12%–19% of the maximum value of SEY and 2.3 nm in thickness of the adsorbed layer. Experimental results are also compared with the results from the MC model to determine whether the model is accurate.

Humidity response of single carbon nanocoil and its temperature sensor independent of humidity and strain

Carbon nanocoil (CNC) is a quasi-one dimensional material with unique helical morphology, which provides abundant sites for the adsorption of water and other gas molecules. Herein, we investigated the humidity response of CNCs, including the response mechanism and further regulation. We used several methods to modify the physical and chemical structures of CNC, including 1200 °C annealing, HCl, NH3H2O and H2O2 treatments, to regulate its humidity response and analyze response mechanism. We experimentally demonstrated the p-type conduction of CNCs and the donor characteristic of the adsorbed water molecules, which are not affected by treatment methods. It is found that NH3H2O treatment greatly suppresses the humidity response (almost no response) without affecting the temperature response of CNCs, while annealing suppresses the humidity and temperature response of CNCs simultaneously. Due to the abundant vacancies, defects and functional groups in CNCs, NH3H2O treatment introduces non-volatile water molecules into CNCs, which prevent further adsorption of water molecules and inhibit the humidity response of CNCs. By this way, we achieved an independent temperature sensor of CNCs with no response to humidity, which paves the way for the device based on single CNCs that is independent of humidity and strain.

The adsorption of NO2, SO2, and O3 molecules on the Al-doped stanene nanotube: a DFT study.

Adsorption of pollutant gas molecules (NO2, SO2, and O3) on the surface of the Al-doped stanene nanotube was investigated within the first principle calculations of density functional theory (DFT). Adsorption mechanisms were studied by analyzing optimized structures, band structures, projected density of states (PDOS), charge density difference (CDD), molecular orbitals, and band theory. Investigation of charge transfer by Mulliken population showed that NO2 accumulated while SO2 and O3 depleted charge density on the Al-doped nanotube. The differences in band structures before and after adsorption implied that the electronic characteristics of Al-doped nanotube changed dramatically in case of NO2 adsorption, which converted Al-doped nanotube to a semiconductor material. High adsorption energy and the significant overlap between PDOS spectra indicated that the adsorption process was chemisorption for NO2, SO2, and O3 on the doped nanotube with the obtained order of O3 > SO2 > NO2. The results showed that the adsorption of NO2, SO2, and O3 occurred on the Al-doped stanene nanotube, and that all the three gas molecules could be detected by Al-doped stanene nanotube with various detection strengths.

Adsorption mechanisms of different toxic molecular gases on intrinsic C2N and Ti-C2N-V monolayer: a DFT study.

Recently, the excessive emission of chemical toxic gases such as nitrogen trifluoride (NF3), ammonia (NH3), phosgene (COCL2), and benzene (C6H6) has caused serious environmental problems. Adsorption of these chemical toxic gas molecules is a promising method to reduce environmental pollution. In this work, density functional theory (DFT) calculations are used to investigate the adsorption properties of these chemical toxic molecules on intrinsic C2N and Ti-C2N-V monolayer. The results show that NF3, NH3, C6H6, and COCL2 can all be adsorbed to the intrinsic C2N monolayer with weak adsorption energy, while the adsorption properties of these gas molecules were greatly improved after doping Ti atom. The adsorption energy of NH3, C6H6, COCL2, and NF3 increased from - 0.585, - 0.432, - 0.633, and - 0.362eV to - 2.214, - 1.699, - 1.822, and - 0.799eV, respectively, which increased by 2 ~ 4 times compared with that before doping. Besides, the results of the electron distribution, work function, the total density of states (TDOS), and the partial density of states (PDOS) analysis indicate that the doped Ti atom can be used as a bridge to connect the adsorbed molecules with the C2N-V monolayer, strengthen their interaction, and significantly improve the adsorption capacity. Therefore, Ti-doped C2N-V (Ti-C2N-V) monolayer is a promising adsorbent for the enrichment and utilization of harmful gases.

Two-dimensional HfTe2 monolayer treated by dispersed single Pt atom for hazardous gas Detection: A First-principles study

Developing sensing materials with high response and selectivity to hazardous gases is crucial in industry, environmental area, and human life safety. In this work, the adsorption and sensing behavior of pristine and single Pt atom doped HfTe2 monolayer to six different hazardous gases (NO2, NO, CO, SO2, H2S, and NH3) were proposed theoretically. The adsorption configurations, adsorption energies, electron transfers, and the ratio of long-range interactions were compared. To discuss the response and desorption process, the work function, occupation function, and desorption time were investigated. It is found that, for pristine HfTe2, the ratio of long-range interactions is larger than 0.5 for most of hazardous gases except NO, but after the introduction of Pt, the adsorption energies increase while the ratio of long-range interactions decrease for all six hazardous gases. This phenomenon is ascribed to the conspicuous enhancement of the chemical and short-range interactions between adsorbed gas molecule and Pt atom. In addition, Pt-HfTe2 has high selectivity to CO at room temperature to about 400 K, and if CO is absent, Pt-HfTe2 shows high selectivity to NO2 at room temperature. The response of Pt-HfTe2 depends on the change of the work function. This study explored the theoretical sensing behavior of single Pt doped HfTe2 as work function-based gas sensor toward different molecules.

Humidity-Tolerant Room-Temperature Selective Dual Sensing and Discrimination of NH3 and NO Using a WS2/MWCNT Composite.

Continuous detection of toxic and hazardous gases like nitric oxide (NO) and ammonia (NH3) is needed for environmental management and noninvasive diagnosis of various diseases. However, to the best of our knowledge, dual detection of these two gases has not been previously reported. To address the challenge, we demonstrate the design and fabrication of low-cost NH3 and NO dual gas sensors using tungsten disulfide/multiwall carbon nanotube (WS2/MWCNT) nanocomposites as sensing channels which maintained their performance in a humid environment. The composite-based device has shown successful dual detection at temperatures down to 18 °C and relative humidity of 90%. For 0.1 ppm ammonia, it exhibited a p-type conduction with response and recovery times of 102 and 261 s, respectively; on the other hand, with NO (10 ppb, n-type), these times were 285 and 198 s, respectively. The device with 5 mg MWCNTs possesses a superior selectivity along with a relative response of ≈7% (5 ppb) and ≈5% (0.1 ppm) for NO and NH3, respectively, at 18 °C. The response is less affected by relative humidity, and this is attributed to the presence of MWCNTs that are hydrophobic in nature. Upon simultaneous exposure to NO (5-10 ppb) and NH3 (0.1-5 ppm), the response was dominated by NO, implying clear discrimination to the simultaneous presence of these two gases. We propose a sensing mechanism based on adsorption/desportion and accompanied charge transfer between the adsorbed gas molecules and sensing surface. The results suggest that an optimized weight ratio of WS2 and MWCNTs could govern favorable sensing conditions for a particular gas molecule.

Transition metal decorated ZnO monolayer for CO and NO sensing: A DFT + U study with vdW correction

Based on density functional theory, we study the adsorption of CO and NO gas molecules on transition metal (Fe, Co, Ni, Cu) decorated ZnO monolayer (ZnO ML), with the electronic interactions taken into account by introducing Hubbard potential (U) for d-orbitals and van der Waals interactions corrected using Grimme method. From its electronic properties and adsorption energies, pristine ZnO ML shows weak physical interaction with the gas molecules with adsorption energies of −0.05 eV and −0.07 eV for CO and NO respectively. TM atoms are then placed in their most stable site (top of O atom for all TMs), with their binding energy in the range of 1.002–2.314 eV. Upon TM decoration, CO shows an adsorption energy in the range of −0.3 eV to −1.3 eV, while NO adsorption energies are in the range of −1.7 to −2 eV. Recovery time calculation shows that Fe and Co-decorated ZnO ML served as a reusable sensor for CO gas while the rest shows great application prospects in the field of industrial safety monitoring. These results showed that TM-decoration in ZnO ML is an effective way of improving its CO and NO gas sensing properties and adsorption capacities.

Noble-Nanoparticle-Decorated Ti3C2T x MXenes for Highly Sensitive Volatile Organic Compound Detection.

Two-dimensional transition-metal carbides and nitrides (MXenes) have been regarded as promising sensing materials because of their high surface-to-volume ratios and outstanding electronic, optical, and mechanical properties with versatile transition-metal and surface chemistries. However, weak gas-molecule adsorption of MXenes poses a serious limitation to their sensitivity and selectivity, particularly for trace amounts of volatile organic compounds (VOCs) at room temperature. To deal with these issues, Au-decorated MXenes are synthesized by a facile solution mixing method for room-temperature sensing of a wide variety of oxygen-based and hydrocarbon-based VOCs. Dynamic sensing experiments reveal that optimal decoration of Au nanoparticles (NPs) on Ti3C2Tx MXene significantly elevates the response and selectivity of the flexible sensors, especially in detecting formaldehyde. Au–Ti3C2Tx gas sensors exhibited an extremely low limit of detection of 92 ppb for formaldehyde at room temperature. Au–Ti3C2Tx provides reliable gas response, low noise level, ultrahigh signal-to-noise ratio, high selectivity, as well as parts per billion level of formaldehyde detection. The prominent mechanism for Au–Ti3C2Tx in sensing formaldehyde is elucidated theoretically from density functional theory simulations. The results presented here strongly suggest that decorating noble-metal NPs on MXenes is a feasible strategy for the development of next-generation ultrasensitive sensors for Internet of Things.