Co3O4 Hollow Nanoparticles and Co Organic Complexes Highly Dispersed on N‐Doped Graphene: An Efficient Cathode Catalyst for Li‐O2 Batteries

Rechargeable Li‐O₂ batteries are promising candidates for electric vehicles due to their high energy density. However, the current development of Li‐O₂ batteries demands highly efficient air cathode catalysts for high capacity, good rate capability, and long cycle life. In this work, a hydrothermal‐calcination method is presented to prepare a composite of Co₃O₄ hollow nanoparticles and Co organic complexes highly dispersed on N‐doped graphene (Co–NG), which acts as a bifunctional air cathode catalyst to optimize the electrochemical performances of Li‐O₂ batteries. Co–NG exhibits an outstanding initial discharge capacity up to 19 133 mAh g^?1 at a current density of 200 mA g^?1. In addition, the batteries could sustain 71 cycles at a cutoff capacity of 1000 mAh g^?1 with low overpotentials at the current density of 200 mA g^?1. Co–NG composites are attractive as air cathode catalysts for rechargeable Li‐O₂ batteries.     

B40 fullerene: An efficient material for CO2 capture,storage and separation

Novel nanomaterials are promising for capture, storage and separation of CO₂. By density functional calculations, we find that the newly discovered B₄₀ fullerene is a suitable candidate. CO₂ forms stable chemisorptions with B₄₀ on specific sites, which is validated by the high adsorption energy, large charge transfer, and kinetic feasibility for B₄₀(CO₂) complexes. Due to the strong chemisorption, B₄₀ shows high adsorption capacity for CO₂ (up to 13.87 mmol/g). In addition, B₄₀ shows good selectivity for CO₂ and is efficient in separating it from gas mixtures like CO₂/N₂, CO₂/H₂, and CO₂/CH₄.     

Studies on ordered mesoporous materials for potential environmental and clean energy applications

Two series of ordered mesoporous materials, SBA-15 silica and CMK-3 carbon were synthesized. The ordered nanostructure of these materials was confirmed by TEM and XRD analysis. Structural parameters including the specific surface area, pore volume and pore size distribution were determined on the basis of nitrogen adsorption data at 77 K. Potential applications of these materials were explored in relation to the CO₂ sequestering, methane storage and fuel desulfurization. Initial studies of both materials showed their usefulness for environmental and clean energy applications. SBA-15 modified with triethanolamine showed a very good adsorption selectivity for CO₂ while its adsorption reversibility was retained. Also, this material after CuCl deposition was useful for removal of fuel thiophenes. However, CMK-3 was shown to be promising material for storage of natural gas. As high as 41 wt.% of methane was stored in this material in the presence of appropriate amount of water.     

A first-principles study of gas molecule adsorption on hydrogen-substituted graphdiyne

Hydrogen-substituted graphdiyne (HsGDY) is a novel alkynyl carbon material with a structure similar to that of graphene. In this paper, the adsorption of four gas molecules (NO, NO₂, NH₃, and N₂) on HsGDY and B-doped HsGDY (B-HsGDY) was studied using density functional theory. The results show that the adsorption of NO and NO₂ on HsGDY and B-HsGDY is characterized by a larger charge transfer, stronger interaction, and higher adsorption energy compared with that of NH₃ and N₂. Based on the doping with B atoms, the adsorption energies of the gas molecules on HsGDY significantly improve, especially that of NO and NO₂. The gas molecule adsorption on both HsGDY and B-HsGDY is physical adsorption and the adsorption selectivity is good and thus may be applied for gas-sensitive NO and NO₂ materials.     

New environmentally attractive separation technology for flue gas mixture

ABSTRACT

Separation of gaseous mixtures produced from any process plant can be a major issue for the industry. In comparison to other separation techniques available, hydrate formation can be an appropriate choice in terms of fuel efficiency and degree of separation. In this work, a three-stage process was designed to capture CO₂ from a hypothetical flue gas mixture (comprising 15?mol% CO_2?+?85?mol% N₂). For the hydrate based CO₂ capture process, a detailed analysis was carried out covering the material and energy balance, energy integration and economic analysis. The results show that, at steady state, 91% of the CO₂ in the flue gas can be recovered, resulting into two streams: Stream-A (94?mol% CO₂?+?6?mol% N₂) and Stream-B (1.5?mol% CO₂?+?98.5?mol% N₂). Per 100?mol of the flue gas feed, 3.9?MW of energy is required to achieve such degree of separation. This amount was reduced to 2.4?MW after energy integration was applied to the process. Overall, the process can help in reducing CO₂ emission via flue gas because of the huge difference in the carbon foot print of its energy requirement (500?g CO₂ per kWh) and the amount of CO₂ captured by the process (2190?g CO₂ per kWh).     

Selectivity enhancement in tritium isotope separation by multiple frequency multiple photon dissociation of the CTF3/CHF3 System

Isotope separation of tritium by multiple photon dissociation process in multiple frequency fields of a TEA-CO₂ laser is reported for the first time. A ten-fold improvement in the bulk selectivity was obtained in 8.5 Torr CTF₃/CHF₃ in the presence of buffer gas at room temperature using 9R(8) to 9R(14) CO₂ laser lines compared to single frequency excitation. Investigations of various process parameters such as exciting laser frequencies, pulse energy, sample and buffer gas pressure indicate that this is a promising technique for the separation of tritium.     

CO2 adsorption on branched polyethyleneimine-impregnated mesoporous silica SBA-15

Adsorption of pure CO₂ on SBA-15 impregnated with branched polyethyleneimine (PEI) has been studied. Materials were prepared by impregnating the pore surface of SBA-15 mesoporous silica with different amounts of branched PEI (10, 30, 50 and 70 wt%). Textural properties, elemental analysis and low angle XRD measurements of the prepared samples showed a progressive pore filling of SBA-15 as PEI loading was increased. Pure CO₂ adsorption isotherms on these modified SBA-15 materials were obtained at 45 °C, showing high adsorption efficiency for CO₂ removal at 1 bar. Chemisorption of CO₂ on amino sites of the modified SBA-15 seems to be the main adsorption mechanism. PEI content of impregnated SBA-15 influences the adsorption capacity of the material, being a relevant variable for CO₂ removal by adsorption. Temperature effect on adsorption was also studied in the range 25-75 °C, showing that temperature strongly influences CO₂ adsorption capacity. Adsorption capacity was also tested after regeneration of the PEI-impregnated SBA-15 materials. Our results show that these branched PEI-impregnated materials are very efficient even at low pressure and after several adsorption-regeneration cycles.     

Sulfur dioxide adsorbed on graphene and heteroatom-doped graphene: a first-principles study

The adsorption of sulfur dioxide (SO₂) on intrinsic graphene and heteroatom-doped (B, N, Al, Si, Cr, Mn, Ag, Au, and Pt) graphene samples was theoretically studied using first-principles approach based on density functional theory to exploit their potential applications as SO₂ gas sensors. The structural and electronic properties of the graphene-molecule adsorption adducts are strongly dependent on the dopants. SO₂ molecule is adsorbed weakly on intrinsic graphene, and B-, N-doped graphene; in general, strong chemisorption is observed on Al-, Si-, Cr-, Mn-, Ag-, Au-, and Pt-doped graphene. The adsorption mechanisms are discussed from charge transfers and density of states. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO₂ can be drastically improved by introducing appropriate dopant, and Cr, as well as Mn, may be the best choices among all the dopants.     

Carbon molecular sieves from carbon cloth: Influence of the chemical impregnant on gas separation properties

Carbon materials with molecular sieve properties (CMS) were prepared by pyrolysis of cotton fabrics by chemical activation procedures. To evaluate the changes in the chemical and textural properties, the impregnants AlCl₃, ZnCl₂ and H₃PO₄ were used at 1123 K. The materials were characterized using adsorption of nitrogen and carbon dioxide, TPD, and immersion calorimetry in C₆H₆. Adsorption kinetics of O₂, N₂, CO₂, CH₄, C₃H₈ and C₃H₆ were measured in all the prepared materials to determine their behaviour as molecular sieves. The results confirm that the chemical used as impregnant has a significant effect on the resulting CMS separation properties. All materials exhibit microporosity and low oxygen surface group contents; however, the sample impregnated with zinc chloride, with an immersion enthalpy value of 66.4 J g⁻¹ in benzene, exhibits the best performance in the separation of CH₄-CO₂ and C₃H₈-C₃H₆ at 273 K.     

基于密度泛函理论研究掺杂Pd石墨烯吸附O2及CO

基于第一性原理的密度泛函理论研究了单个O₂和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O₂和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O₂后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.     

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non‐porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′‐Bipy)_0.5 · DMF(H₂O)_0.5} was selected for study. We have investigated structural transformation in MOF‐508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF‐508 framework is driven by ligand conformation change and inter‐linker interactions. The presence of Raman signatures of adsorbed CO₂ and its librational mode at 149 cm⁻¹ suggests cooperative adsorption of CO₂ in the MOF‐508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of Stone–Wales defect upon adsorption of formaldehyde on graphene sheet with or without Al dopant: A first principle study

The adsorption mechanisms of formaldehyde (H₂CO) on modified graphene, including aluminum doping, Stone–Wales (SW) defects, and a combination of these two, were investigated via density functional theory (DFT). It was found that the graphene with SW defect is more sensitive than that of perfect graphene for detecting H₂CO molecules. Compared with Al-doped graphene/H₂CO complex, the binding energy for Al-doped SW defect complex can be enhanced by the introduction of a SW defect. The large values of binding energy and net charge transfer for this complex indicate a strong chemisorption and a larger affinity with H₂CO for the modified graphene. Furthermore, the density of states (DOS) of the complex shows that the effect of defect–dopant combination on adsorption mechanisms is due to the orbital hybridization between the Al atom and its adjacent C atoms. In addition, it can be expected that adsorption of H₂CO on the surface of Al-doped SW defect may occur easily, and the Al-doped SW graphene is more suitable for H₂CO gas detection.     

Facile Fabrication of Bicomponent CoO/CoFe2O4‐N‐Doped Graphene Hybrids with Ultrahigh Lithium Storage Capacity

A facile strategy is developed to fabricate bicomponent CoO/CoFe₂O₄‐N‐doped graphene hybrids (CoO/CoFe₂O₄‐NG). These hybrids are demonstrated to be potential high‐performance anodes for lithium‐ion batteries (LIBs). The CoO/CoFe₂O₄ nanoplatelets are finely dispersed on the surface of N‐doped graphene nanosheets (CoO/CoFe₂O₄‐NG). The CoO/CoFe₂O₄‐NG electrode exhibits ultrahigh specific capacity with 1172 mA h g^?1 at 500 mA g^?1 and 970 mA h g^?1 at 1000 mA g^?1 as well as excellent cycle stability due to the synergetic effects of N‐doped graphene and CoO/CoFe₂O₄ nanoplatelets. The well‐dispersed bicomponent CoO/CoFe₂O₄ is responsible for the high specific capacity. The N‐doped graphene with high specific surface area has dual roles: to provide active sites for dispersing the CoO/CoFe₂O₄ species and to function as an electrical conducting matrix for fast charge transfer. This method provides a simple and efficient way to configure the hybridized electrode materials with high lithium storage capacity.     

Dumbbell to Core–Shell Structure Transformation of Ni–Au Nanoparticle Driven by External Stimuli

Conversion of CO₂ gas to CO fuels is one of the most promising solutions for the increasing threat of global warming and energy crisis. The efficient catalyst Ni–Au dumbbell converting CO₂ into CO at elevated temperatures has high CO product selectivity; however, the accompanied atomic diffusion and subsequent surface reconstruction affect the catalytic efficiency of chemical reaction. Atomic scale characterization of structural evolution of the catalyst, which is essential to correlate the functional mechanism to active catalyst surfaces, is yet to be studied. Here, in situ transmission electron microscopy experiments and atomistic simulations are performed to characterize the structural evolution of Ni–Au dumbbell nanoparticles under two different external stimuli. In the condition of high temperature and vacuum, the Ni–Au nanostructure reveals a clear shape reconstruction from the initial dumbbell to core–shell‐like, which is induced by capillary force to minimize free surface energy of the system. The shape transformation involves two stages of processes, initial fast Au diffusion followed by slow source‐controlled diffusion. At ambient temperature, the combination of CO₂ and electron flux surprisingly induces analogous structural transformation of Ni–Au nanostructure, where the associated chemical reaction and CO absorption stimulate the Au migration on Ni surface. Such surface reconstruction can be widely present in catalytic reactions in different environmental conditions, and the results herein demonstrate the detailed processes of Ni–Au structure evolution, which provide important insights for understanding the catalyst performance.     

Graphene-based nitrogen dioxide gas sensors

In this study, we demonstrated that graphene could selectively absorb/desorb NO_x molecules at room temperature. Chemical doping with NO₂ molecules changed the conductivity of the graphene layers, which was quantified by monitoring the current–voltage characteristics at various NO₂ gas concentrations. The adsorption rate was found to be more rapid than the desorption rate, which can be attributed to the reaction occurred on the surface of the graphene layer. The sensitivity was 9% when an ambient of 100 ppm NO₂ was used. Graphene-based gas sensors showed fast response, good reversibility, selectivity and high sensitivity. Optimization of the sensor design and integration with UV-LEDs and Silicon microelectronics will open the door for the development of nano-sized gas sensors that are extremely sensitive.     

Synthesis of graphene oxide and graphene quantum dots from miscanthus via ultrasound-assisted mechano-chemical cracking method

Whilst graphene materials have become increasingly popular in recent years, the followed synthesis strategies face sustainability, environmental and quality challenges. This study proposes an effective, sustainable and scalable ultrasound-assisted mechano-chemical cracking method to produce graphene oxide (GO). A typical energy crop, miscanthus, was used as a carbon precursor and pyrolysed at 1200 °C before subjecting to edge-carboxylation via ball-milling in a CO₂-induced environment. The resultant functionalised biochar was ultrasonically exfoliated in N-Methyl-2-pyrrolidone (NMP) and water to form GOs. The intermediate and end-products were characterised via X-ray diffraction (XRD), Raman, high-resolution transmission electron microscopy (HR-TEM) and atomic force microscopy (AFM) analyses. Results show that the proposed synthesis route can produce good quality and uniform GOs (8–10% monolayer), with up to 96% of GOs having three layers or lesser when NMP is used. Ultrasonication proved to be effective in propagating the self-repulsion of negatively-charged functional groups. Moreover, small amounts of graphene quantum dots were observed, illustrating the potential of producing various graphene materials via a single-step method. Whilst this study has only investigated utilising miscanthus, the current findings are promising and could expand the potential of producing good quality graphene materials from renewable sources via green synthesis routes.     

Enhanced gas-sensing performance of graphene by doping transition metal atoms: A first-principles study

By performing the first-principles calculations, we investigated the sensitivity and selectivity of transitional metal (TM, TMSc, Ti, V, Cr and Mn) atoms doped graphene toward NO molecule. We firstly calculated the atomic structures, electronic structures and magnetic properties of TM-doped graphene, then studied the adsorptions of NO, N₂ and O₂ molecules on the TM-doped graphene. By comparing the change of electrical conductivity and magnetic moments after the adsorption of these molecules, we found that the Sc-, Ti- and Mn-doped graphene are the potential candidates in the applications of gas sensor for detection NO molecule.     

Modeling nanoparticle uptake and intracellular distribution using stochastic process algebras

Intermolecular energy decomposition analysis (EDA) is reported for the binding of CO₂ with zeolitic imidazole frameworks (ZIF) to provide a molecular level interpretation of the recent capacity and selectivity measurements of several ZIFs and to suggest a theoretical guideline to improve their performance further, using 1?nm size of organic linker fragment of the ZIFs as a target molecule. The EDA suggests that the local electronic interaction of CO₂ and the substituent groups, mainly frozen density and polarization interactions with little charge transfer, is the primary binding interaction, but the electron correlation effects can be equally or more important depending on the binding geometry and functional groups. The present correlated calculations identify the preferred ZIF binding sites for various gases including CO₂ to be mostly near the benzene substituent groups rather than the plane of imidazole rings. We predict that the NH₂-substituted ZIF would have an enhanced capacity of CO₂ as compared to the NO₂-substituted ZIF that was recently synthesized and reported to be one of the materials with the best capacity results along with high gas selectivity. The present calculations may imply that the local functionality of the linking organics, rather than detailed framework structures, may be of primary importance in designing certain high capacity MOF or ZIF materials.     

Microcombustion of ng Amounts of Carbon in Non-Volatile Materials for isotope Ratio Evaluation

Abstract

A novel microcombustion technique for carbon isotopic analysis of nanogram amounts of carbon in non-volatile materials based on isotope ratio monitoring (irm) mass spectrometry is described. Liquid or solid samples placed in a quartz sleeve are combusted at 1000°C in a continuous stream of helium and oxygen. CO₂ removed from the carrier gas stream by cryogenic trapping is transferred onto a GC column. Following GC separation, the CO₂ is transferred via an open split to the ion source of a gas isotope ratio mass spectrometer. Reproducibility for samples >25 nmol carbon is <1‰. Problems associated with blanks from various sources and with reproducible deposition of small sample amounts led to variable accuracy, which was dependent on the compound class being analysed. Minimum sample size was in the range from 5 to 10 nmol carbon. Measurements of dissolved organic carbon (DOC) of groundwater from Germany yielded consistent values of δ¹³C = -28.8‰.