Mg/Ca decorated on carbon-doped boron nitride sheet: Application for gas adsorption

Through first-principles calculations, we investigate the adsorption of alkaline-earth(AE) metal (Mg/Ca) on carbon doped hexagonal boron nitride (h-BN) sheet, as well as its potential application as a sensor for gas molecules H₂, H₂O, CO, CO₂, O₂, and NO. With carbon substitution of nitrogen, Mg and Ca were energetically favorable to doped on the BN sheet with binding energies of 1.464 and 2.047 eV, respectively, due to the strong binding between AE atoms and substrate. With the Mg/Ca dopant, the binding interaction between gas molecules and the moderated BN sheet becomes stronger. For all the studied gases, the overall process of adsorption was found to be exothermic, moreover, NO, H₂O, and O₂ are chemisorbed while CO, H₂, and CO₂ are physisorbed. After adsorption, the electronic structures of systems are also affected judging from the electronic density of the state calculation.     

掺杂和修饰的石墨烯对半胱氨酸吸附性能的密度泛函理论研究

使用密度泛函理论计算了掺杂或修饰Al或Mn原子的石墨烯对半胱氨酸的吸附性能。计算结果表明,掺杂或修饰Al或Mn原子后,Graphene与半胱氨酸之间结合稳定,具有较大的结合能。其中掺杂或修饰Mn原子的体系的吸附能整体高于掺杂或修饰Al原子的体系。石墨烯上修饰或掺杂Al或Mn原子,增加了石墨烯基底与半胱氨酸之间的电荷转移,特别是修饰方式显著改变了费米能级附近的性质,同时改变了Graphene的电导性质。Al或Mn原子修饰或者掺杂的Graphene除了增加对半胱氨酸吸附能力外,也是一种潜在的检测半胱氨酸的传感器材料,进而在生物领域得到更广泛的应用,比如用来检测富含半胱氨酸的金属硫蛋白。     

Microwave-assisted synthesis of Bi2Se3 /reduced graphene oxide nanocomposite as efficient catalytic counter electrodefordye-sensitized solar cell

Bi₂Se₃/reduced graphene oxide (rGO) composite was successfully synthesized by a facile microwave-assisted hydrothermal method and applied as a counter electrode for efficient dye-sensitized solar cells. By this means, the size and distribution of the formed Bi₂Se₃ nanoparticles onto a flexible graphene sheet were effectively controlled, which is crucial for achieving high electrocatalytic activity on I₃^? reduction. Mainly due to the homogeneous single-layer immobilization of Bi₂Se₃ nanoparticles on a graphene sheet with high density, BiG2 exhibited the highest catalytic activity and the lowest electrolyte diffusion resistance. Adye-sensitized solar cell with BiG2 as a counter electrode can yield 7.09% photoelectric conversion efficiency, which is comparable to that of the cell with a Pt-film counter electrode (6.23), exhibiting the application potential of BiG2 as a low cost non-Pt CE materials for DSSC.     

H+ ions on graphene electrode as hydrogen storage reservoirs

A new idea for hydrogen storage is proposed in which H⁺ ions are adsorbed chemically on graphene sheet and it is possible to overcome the fundamental problem of current methods that hydrogen is not able to reversibly adsorbed/desorbed in appropriate temperature and under moderate pressure. As the top priority to test the feasibility, H⁺ ions storing capacity is studied by theoretical calculations. And the bonding and structural properties of H⁺/graphene complexes are investigated thoroughly. Our data yield promising results. The graphene fragment C₆₂H₂₀, in a quasi one-dimensional arch-like tunnel geometry, can absorb up to 54 H⁺ ions on the same side (6.6 wt.% H₂) while maintaining its conductivity because of the sp²-rich structure. The feasibility of the new idea is proved from a viewpoint of hydrogen storing capacity. Additional calculation using an infinite graphene sheet model gives credibility to our conclusions. Considering the successful development of synthesis techniques in mass-producing atom-thick graphene sheets, it is really worth expecting a hydrogen-based energy economy can be realized by hydrogen-ion storage graphene electrodes.     

Effect of gas type,pressure and temperature on the electrical characteristics of Al-doped SnO2 thin films deposited by RGTO method for gas sensor application

In this paper, we present the experimental results of Al-doped SnO₂ thin films obtained by Rheotaxial Growth and Thermal Oxidation (RGTO) method. The effect of gas type (synthetic air, CO, NO₂ and H₂), pressure (10⁻⁴, 1 and 100 mbar) and temperature (in the range 300–650 K), on the electrical properties of Al-doped SnO₂ thin films were considered. The change of the work function of Al-doped SnO₂ thin films as a function of exposure time to synthetic air, CO (150 ppm), H₂ (1000 ppm) and NO₂ (80 ppm) was discussed under different pressures of 10⁻⁴, 1 and 100 mbar. The effect of ambient temperature at 303,373 and 433 K on the work function difference was investigated. The results reveal that the sensitivity of reaction to the gases was improved to high ambient temperature. The time and temperature dependent of electrical properties of the Al-doped SnO₂ films were studied using four probe method. The Al-doped SnO₂ films demonstrate negative temperature coefficient (NTC) characteristics of resistance in the higher temperature range as well as positive temperature coefficient (PTC) characteristics of resistance in the lower temperature range. The best sensitivity and the optimum work temperature were also considered.     

Highly Conductive and Transparent Large‐Area Bilayer Graphene Realized by MoCl5 Intercalation

Bilayer graphene (BLG) comprises a 2D nanospace sandwiched by two parallel graphene sheets that can be used to intercalate molecules or ions for attaining novel functionalities. However, intercalation is mostly demonstrated with small, exfoliated graphene flakes. This study demonstrates intercalation of molybdenum chloride (MoCl₅) into a large‐area, uniform BLG sheet, which is grown by chemical vapor deposition (CVD). This study reveals that the degree of MoCl₅ intercalation strongly depends on the stacking order of the graphene; twist‐stacked graphene shows a much higher degree of intercalation than AB‐stacked. Density functional theory calculations suggest that weak interlayer coupling in the twist‐stacked graphene contributes to the effective intercalation. By selectively synthesizing twist‐rich BLG films through control of the CVD conditions, low sheet resistance (83 Ω ?^?1) is realized after MoCl₅ intercalation, while maintaining high optical transmittance (≈95%). The low sheet resistance state is relatively stable in air for more than three months. Furthermore, the intercalated BLG film is applied to organic solar cells, realizing a high power conversion efficiency.     

An Atomistic Tomographic Study of Oxygen and Hydrogen Atoms and their Molecules in CVD Grown Graphene

The properties and growth processes of graphene are greatly influenced by the elemental distributions of impurity atoms and their functional groups within or on the hexagonal carbon lattice. Oxygen and hydrogen atoms and their functional molecules (OH, CO, and CO₂) positions' and chemical identities are tomographically mapped in three dimensions in a graphene monolayer film grown on a copper substrate, at the atomic part‐per‐million (atomic ppm) detection level, employing laser assisted atom‐probe tomography. The atomistic plan and cross‐sectional views of graphene indicate that oxygen, hydrogen, and their co‐functionalities, OH, CO, and CO₂, which are locally clustered under or within the graphene lattice. The experimental 3D atomistic portrait of the chemistry is combined with computational density‐functional theory (DFT) calculations to enhance the understanding of the surface state of graphene, the positions of the chemical functional groups, their interactions with the underlying Cu substrate, and their influences on the growth of graphene.     

Ab initio study of hydrogen binding on Ca-inserted porphyrin

To study the binding of hydrogen molecules on Ca-inserted porphyrin, we perform ab initio pseudopotential calculations within the local density approximation (LDA). One Ca atom is inserted in the central N₄ cavity formed by the removal of two hydrogen atoms of porphin. By increasing the number of hydrogen molecules, we investigate hydrogen binding on Ca-inserted porphyrin for hydrogen storage. We find that the binding energy of H₂ molecules to the Ca atom is ∼0.25 eV/H₂ up to four hydrogen molecules. When the fifth or sixth H₂ molecule is adsorbed on the Ca atom, the molecule is adsorbed onto Ca-porphyrin with the average binding energy of ∼0.2 eV/H₂. Examining the projected density of states, we study orbital hybridization between the Ca atom and hydrogen molecule. Finally, the possibility of Ca-porphyrin as a hydrogen storage material is discussed.     

CO sensing with SnO2 thick film sensors: role of oxygen and water vapour

The paper investigates the gas response of nanocrystalline SnO₂ based thick film sensors upon exposure to carbon monoxide (CO) in changing water vapour (H₂O) and oxygen (O₂) backgrounds. The sensing materials were undoped, Pt- and Pd-doped SnO₂. We found that in the absence of oxygen, the sensor signal (defined as the ratio between the resistance in the background gas, R₀ and the resistance in the presence of the target gases, R, namely R₀/R) have the highest values. These values are higher for doped materials than for the undoped ones. The presence of humidity increases dramatically the sensor signal of the doped materials. In the presence of oxygen, the sensor signal decreases significantly for all sensor materials. The results indicate that there is a competitive adsorption between O₂ and H₂O related surface species and, as a result, different sensing mechanisms can be observed for CO.     

Synthesis and characterization of CdO-doped nanocrystalline ZnO:TiO2-based H2S gas sensor

This paper reports the preparation and gas-sensing characteristic of ZnO:TiO₂-based hydrogen sulfide (H₂S) gas sensor with different mol% of CdO by polymerized complex method. The structural and gas-sensing properties of ZnO:TiO₂ materials have been characterized using X-ray diffraction and gas-sensing measurement. The electrical resistance response of the sensor based on the materials was investigated at different operating temperatures and different gas concentrations. The sensor with 10 mol% CdO-doped ZnO:TiO₂ shows excellent electrical resistance response toward H₂S gas. The cross sensitivity was also checked for reducing gases like CH₄, CO and H₂ gas. The selectivity and sensitivity of ZnO:TiO₂-based H₂S gas sensor were improved by the addition of 10 mol% of CdO at an operating temperature of 250 °C.     

Computational investigations of Cu-embedded MoS<Subscript>2</Subscript> sheet for CO oxidation catalysis

Elevated amount of CO levels in the atmosphere poses serious health and environmental hazards. Oxidation of CO using suitable catalysts is one of the methods to control it. By means of DFT calculations, single Cu atom doped in S vacancy of MoS₂ nanosheet is studied for CO oxidation catalysis. Cu atom is strongly confined at the S-defective site of the MoS₂ sheet, possessing high energy barrier for the diffusion to its neighboring sites. Adsorption energy, charge transfer and orbital hybridization of CO and O₂ molecules adsorbed Cu-doped MoS₂ sheet reveal that O₂ is relatively more strongly adsorbed than CO. High adsorption energy of O₂ (??2.115 eV) and large charge transfer between O₂ and Cu–MoS₂ sheet (0.493e), compared to CO, make O₂ adsorption more favorable, which extenuates CO poisoning and hence helps in the efficient CO oxidation process. The complete oxidation of CO takes place in two steps: \( {\text{CO}} + {\text{O}}_{2} \to {\text{OOCO}} \) with activation energy of 0.201 eV, succeeded by \( {\text{OOCO}} + {\text{CO}} \to 2{\text{CO}}_{2} \) without any energy barrier. Our results show that the basal plane of MoS₂ sheet gets activated by embedding it with Cu metal, which can catalyze CO oxidation reaction effectively and without poisoning issues. The high activity, stability and low cost features can possibly encourage fabricating MoS₂-based catalysts for CO oxidation reaction.     

Synthesis, FTIR studies and sensor properties of WO3 powders

Several synthetic approaches were used to obtain nano-sized porous and nonporous monoclinic WO₃ (m-WO₃) powders. All of these methods begin with a standard preparative method where H₂WO₄ is first generated by passing a Na₂WO₄ solution through a cation-exchange resin. It is shown that high surface area particles are produced by dripping the H₂WO₄ exiting from the ion-exchange column into a solution containing oxalate and acetate exchange ligands or alternatively, into a water-in-oil (W/O)-based emulsion. Porous materials are produced using surfactant-templating architectures. The surface properties were investigated by IR spectroscopic studies during thermal evacuation and the use of chemical probes. The nature of the surface depends on the initial evacuation temperature of the WO₃ surface as this alters the relative number of the Lewis and Brønsted acid sites along with the amount of adsorbed water. Infrared studies of the adsorption of various molecules on the powders led to a new size-selective approach to improve selectivity in semiconducting metal oxide (SMO) sensors. The key for achieving high selectivity is based on using a dual sensor configuration where the response on a porous WO₃ powder sensor was compared to the response on a nonporous WO₃ powder sensor. Detection selectivity between methanol and dimethyl methylphosphonate (DMMP) is obtained because the access of a gas molecule in the interior pore structure of WO₃ is size-dependent leading to a size-dependent magnitude change in the conductivity of the SMO sensor.     

Carbon Dioxide Promotes Dehydrogenation in the Equimolar C2H2‐CO2 Reaction to Synthesize Carbon Nanotubes

The equimolar C₂H₂‐CO₂ reaction has shown promise for carbon nanotube (CNT) production at low temperatures and on diverse functional substrate materials; however, the electron‐pushing mechanism of this reaction is not well demonstrated. Here, the role of CO₂ is explored experimentally and theoretically. In particular, ¹³C labeling of CO₂ demonstrates that CO₂ is not an important C source in CNT growth by thermal catalytic chemical vapor deposition. Consistent with this experimental finding, the adsorption behaviors of C₂H₂ and CO₂ on a graphene‐like lattice via density functional theory calculations reveal that the binding energies of C₂H₂ are markedly higher than that of CO₂, suggesting the former is more likely to incorporate into CNT structure. Further, H‐abstraction by CO₂ from the active CNT growth edge would be favored, ultimately forming CO and H₂O. These results support that the commonly observed, promoting role of CO₂ in CNT growth is due to a CO₂‐assisted dehydrogenation mechanism.     

Structural and gas sensing behavior of nanocrystalline BaTiO3 based liquid petroleum gas sensors

In this paper nanosized BaTiO₃ thick films based gas sensor has been fabricated for liquid petroleum gas (LPG). Doping with different concentrations of metal oxides influenced the sensitivity of BaTiO₃ thick films for LPG sensor. We present the characterization of both their structural properties by means of X-ray powder diffraction (XRD) and the electrical characteristics by using gas-sensing properties. X-ray powder diffraction analyses revealed the persistence of cubic phase with grain growth 65 nm. The LPG-sensing properties of BaTiO₃ thick films doped with CuO and CdO are investigated. It was found that 10 wt.% CuO: 10 wt.% CdO doped BaTiO₃ based LPG sensor shows better sensitivity and selectivity at an operating temperature 250 °C which is an important commercial range for LPG alarm development. Incorporation of 0.3 wt.% Pd doped CuO:CdO:BaTiO₃ element shows maximum sensitivity with high cross selectivity to the other gases including CO, H₂ and H₂S at an operating temperature 225 °C for low concentrations of LPG sensor.     

Novel Mg- and Ga-doped ZnO/Li-Doped Graphene Oxide Transparent Electrode/Electron-Transporting Layer Combinations for High-Performance Thin-Film Solar Cells (Small 22/2023)

Herein, a novel combination of Mg- and Ga-co-doped ZnO (MGZO)/Li-doped graphene oxide (LGO) transparent electrode (TE)/electron-transporting layer (ETL) has been applied for the first time in Cu₂ZnSn(S,Se)₄ (CZTSSe) thin-film solar cells (TFSCs). MGZO has a wide optical spectrum with high transmittance compared to that with conventional Al-doped ZnO (AZO), enabling additional photon harvesting, and has a low electrical resistance that increases electron collection rate. These excellent optoelectronic properties significantly improved the short-circuit current density and fill factor of the TFSCs. Additionally, the solution-processable alternative LGO ETL prevented plasma-induced damage to chemical bath deposited cadmium sulfide (CdS) buffer, thereby enabling the maintenance of high-quality junctions using a thin CdS buffer layer (≈30 nm). Interfacial engineering with LGO improved the V_oc of the CZTSSe TFSCs from 466 to 502 mV. Furthermore, the tunable work function obtained through Li doping generated a more favorable band offset in CdS/LGO/MGZO interfaces, thereby, improving the electron collection. The MGZO/LGO TE/ETL combination achieved a power conversion efficiency of 10.67%, which is considerably higher than that of conventional AZO/intrinsic ZnO (8.33%).     

Novel synthesis of quaternary nanocomposites based on chemical vapor grown graphene for photocatalytic hydrogen evolution

Pd-Pt/graphene-TiO₂ nanocomposites were synthesized via a facile ultrasonic and hydrothermal method. For the functionalization of graphene, large area graphene obtained by chemical vapor deposition method was oxidized by 3-chloroperoxybenzoic acid. The functionalized graphene oxide was decorated with TiO₂. And then, Pt and Pd nanoparticles were dispersed on graphene surface, simultaneously. The characterizations of “as-prepared” samples were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), Raman, specific surface area (BET) and with energy dispersive X-ray (EDX). The photocatalytic activity of the Pd-Pt/graphene-TiO₂ nanocomposite catalyst was evaluated by H₂ evolution under UV light. Pd-Pt/graphene-TiO₂ (Pd-Pt/G-TiO₂) exhibited higher photocatalytic activities than control experimental group samples (TiO₂, G-TiO₂, Pd/G-TiO₂ and Pt/G-TiO₂) under UV light irradiation.     

Achieving Tunable Selectivity and Activity of CO2 Electroreduction to CO via Bimetallic Silver–Copper Electronic Engineering

Limited comprehension of the reaction mechanism has hindered the development of catalysts for CO₂ reduction reactions (CO₂RR). Here, the bimetallic AgCu nanocatalyst platform is employed to understand the effect of the electronic structure of catalysts on the selectivity and activity for CO₂ electroreduction to CO. The atomic arrangement and electronic state structure vary with the atomic ratio of Ag and Cu, enabling tunable d-band centers to optimize the binding strength of key intermediates. Density functional theory calculations confirm that the variation of Cu content greatly affects the free energy of *COOH, *CO (intermediate of CO), and *H (intermediates of H₂), which leads to the change of the rate-determining step. Specifically, Ag₉₆Cu₄ reduces the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction(HER), thus achieving the best CO selectivity. While Ag₇₀Cu₃₀ shows relatively low formation energy of both *COOH and *H, the compromised thermodynamic barrier and product selectivity allows Ag₇₀Cu₃₀ the best CO partial current density. This study realizes the regulation of the selectivity and activity of electrocatalytic CO₂ to CO, which provides a promising way to improve the intrinsic performance of CO₂RR on bimetallic AgCu.     

Unidentified H2 gas sensing characteristics of BaTiO3:Cu composition

A systematic evaluation of the gas sensing properties of Cu-modified BaTiO₃ pellets for CO, H₂ and LPG gases was carried out in the present investigation. The concentration of Cu in BaTiO₃ was varied systematically from 1 to 11 wt.%. The highest value of sensitivity factor (SF) of 1388 for H₂ and 557 for CO gases was obtained at considerably lower optimum operating temperatures of 180 and 250 °C respectively for 9 wt.% of Cu concentration. The sensor tends to saturate at 5.0 and 3.5% for H₂ and CO gases respectively. The XRD and SEM characterization techniques were employed to understand the possible reasons for the high performance of the sensor material with 9 wt.% of Cu. The study revealed that this sensor material shows extraordinarily promising properties for H₂ gas sensing application.     

Evaporation processes of water molecules from graphene edge: DFT and MD study

The evaporation processes of water molecules adsorbed in the edge region of graphene have been investigated by means of direct MO–MD method. A large system composed of 29 water molecules and a graphene sheet (C₉₆H₂₄) was used as a model system. The edge carbon atom of graphene was terminated by hydrogen atom. The geometry optimization showed that the water molecules interact with the hydrogen atoms in the edge region of graphene. At low temperature (300 K), the water molecules were dissociated as water clusters from the graphene. On the other hand, in addition to the dissociation of water clusters, the isolated water molecule was also found as dissociation product at high temperature (500 K). The mechanism of water evaporation was discussed on the basis of theoretical results.     

Rational Design of FeNi Bimetal Modified Covalent Organic Frameworks for Photoconversion of Anthropogenic CO2 into Widely Tunable Syngas

Direct photoconversion of low‐concentration CO₂ into a widely tunable syngas (i.e., CO/H₂ mixture) provides a feasible outlet for the high value‐added utilization of anthropogenic CO₂. However, in the low‐concentration CO₂ photoreduction system, it remains a huge challenge to screen appropriate catalysts for efficient CO and H₂ production, respectively, and provide a facile parameter to tune the CO/H₂ ratio in a wide range. Herein, by engineering the metal sites on the covalent organic frameworks matrix, low‐concentration CO₂ can be efficiently photoconverted into tunable syngas, whose CO/H₂ ratio (1:19–9:1) is obviously wider than reported systems. Experiments and density functional theory calculations indicate that Fe sites serve as the H₂ evolution sites due to the much stronger binding affinity to H₂O, while Ni sites act as the CO production sites for the higher affinity to CO₂. Notably, the widely tunable syngas can also be produced over other Fe/Ni‐based bimetal catalysts, regardless of their structures and supporting materials, confirming the significant role of the metal sites in regulating the selectivity of CO₂ photoreduction and providing a modular design strategy for syngas production.