ZnO thin film nanostructures for hydrogen gas sensing applications

A ZnO thin film-based gas sensor was fabricated using a SiO₂/Si substrate with a platinum comb-like integrated electrode and heating element. The structural characteristics, morphology, and surface roughness of the as-grown ZnO nanostructure were investigated. The film revealed the presence of a c-axis oriented (002) phase with a grain size of 20.8 nm. The sensor response was tested for hydrogen concentrations of 50, 70, 100, 200, 400, and 500 ppm at the optimum operating temperature of 350 °C. The sensitivities towards 50 and 200 ppm of hydrogen gas at 350 °C were approximately 78% and 98%, respectively. A linear response was observed for hydrogen concentrations within the range of 50 ppm–200 ppm. These results demonstrated the potential application of the ZnO nanostructure for the fabrication of cost-effective and high-performance gas sensors.     

Photoacoustic effect of piezoelectric ZnO thin films

This paper describes the photoacoustic (PA) effect of piezoelectric ZnO thin films. The one-dimensional theory of the PA-effect was derived. The relationships between PA-signals and modulation frequency, thin film properties such as piezoelectric coefficients, dielectric constant, specific heat and thermal conductivity coefficient were obtained. The experimental results on the PA-effect of sputter-deposited ZnO thin films exhibited good agreement with the theoretical analysis. The piezoelectric stress coefficients, e₃₃ and e₃₁, of some ZnO films were determined from the PA-signals, typical values of which are 0.82 C/m² and -0.43 C/m², respectively.     

Improved photoluminescence emission and gas sensor properties of ZnO thin films

In this article, we report a comparative study of the influence of pressure-assisted (1.72 MPa) versus ambient pressure thermal annealing on both ZnO thin films treated at 330 °C for 32 h. The effects of pressure on the structural, morphological, optical, and gas sensor properties of these thin films were investigated. The results show that partial preferential orientation of the wurtzite-structure ZnO thin films in the [002] or [101] planes is induced based on the thermal annealing conditions used (i.e., pressure assisted or ambient pressure). UV–vis absorption measurements revealed a negligible variation in the optical -band gap values for the both ZnO thin films. Consequently, it is deduced that the ZnO thin films exhibit different distortions of the tetrahedral [ZnO₄] clusters, corresponding to different concentrations of deep and shallow level defects in both samples. This difference induced a variation of the interface/bulk-surface, which might be responsible for the enhanced optical and gas sensor properties of the pressure-assisted thermally annealed film. Additionally, pressure-assisted thermal annealing of the ZnO films improved the H₂ sensitivity by a factor of two.     

纳米氧化锌脱硫剂在硫化氢去除中的潜在应用

采用两种不同路线合成了纳米氧化锌改性SBA-15的复合介孔材料,并在材料上进行了含有0.1%硫化氢气体的脱硫实验。使用氮吸附、X射线衍射、X射线能谱、透射电子显微镜和电感耦合等离子体原子发射光谱方法对实验前后的材料进行了表征。不同路线合成材料的结构、硫化氢捕集能力有较大区别。两种合成途径制备的材料(S/Z、SZ)分别较商用氧化锌脱硫剂的穿透硫容高出336%和77.3%,其中超声波辅助浸渍法制备的介孔脱硫剂的脱硫性能最佳。高效的脱硫活性源自介孔材料的高比表面积和纳米颗粒的高反应活性的共同作用。     

Nanostructured hybrid ZnO thin films for energy conversion

We report on hybrid films based on ZnO/organic dye prepared by electrodeposition using tetrasulfonated copper phthalocyanines (TS-CuPc) and Eosin-Y (EoY). Both the morphology and porosity of hybrid ZnO films are highly dependent on the type of dyes used in the synthesis. High photosensitivity was observed for ZnO/EoY films, while a very weak photoresponse was obtained for ZnO/TS-CuPc films. Despite a higher absorption coefficient of TS-CuPc than EoY, in ZnO/EoY hybrid films, the excited photoelectrons between the EoY levels can be extracted through ZnO, and the porosity of ZnO/EoY can also be controlled.     

Semimetal graphite/ZnO Schottky diodes and their use for hydrogen sensing

A method is described for the fabrication of highly rectifying Schottky contacts on n-type ZnO (O and Zn polar face) single crystals, both bare and partially covered with Pt nanoparticles, coated with mechanically deposited colloidal graphite. A layer of Pt nanoparticles deposited by in situ pulsed electrophoretic deposition from isooctane colloid solutions is inserted between the graphite and the ZnO surface serves to dissociate hydrogen molecules in hydrogen sensing elements based on the highly rectifying Schottky barriers. The sensing elements are sensitive to gas mixtures with a low hydrogen concentration down to 10 ppm and show an extremely fast response above 1000 ppm.     

过渡金属硫化物对Claus尾气催化加氢制备硫化氢的影响

以γ-Al2O3为载体,考察了第一过渡金属亲硫元素和Cr系元素及其负载量对Claus尾气加氢生成H2S的催化活性。结果表明,经预硫化后上述负载量为10%质量分数的各元素,其催化活性按大小可以划分为4组:Ni、Co、Fe>Mo、W、Cu>Cr>Zn、Mn。针对第一组的3种元素进行物相分析表明,在反应气体积比为SO2/H2/N2=0.5/3/96.5,重量时间空速(WHSV)=6 000mL/(h.g)的强还原气氛下,Ni的催化活性相为稳定的NiS2,但Co和Fe除主晶相CoS2和FeS2外,还分别具有Co3S4和Co9S8或FeS和Fe7S8的贫硫相。     

ZnO薄膜的制备及其性能

用脉冲激光沉积(PLD)法在SiO2基片上制备了ZnO薄膜和Zn1-xMnxO薄膜。X射线衍射、原子力显微镜、紫外-可见分光光度计对ZnO薄膜的测试结果表明:薄膜具有(103)面的择优取向,表面比较平坦;SiO2基片上制备的薄膜在387nm附近存在明显的吸收边,且薄膜的吸收对基片温度变化不明显。通过对Zn1-xMnxO薄膜的吸收光谱分析得出:Mn离子的掺杂改变了ZnO薄膜的禁带宽度,随Mn离子的掺杂量的增加,薄膜禁带宽度增加;薄膜的光吸收也从直接跃迁过渡为间接跃迁过程。     

Atmospheric flame vapor deposition of WO3 thin films for hydrogen detection with enhanced sensing characteristics

Nowadays, with the increasing demand for hydrogen, sensors that can detect low concentrations of this gas are essential for its safe use. In this paper, Pd/WO₃ film hydrogen sensors are developed using a solid-feed flame vapor deposition (SF-FVD), as an atmospheric, economical, and fast film fabrication method. The crystal structure and morphology of the samples were characterized by different means. The performance of the obtained sensors was investigated for different hydrogen concentrations (1–2500 ppm) and at different operating temperatures (100–250 °C). We attempted to determine the optimum deposition conditions, including feed and substrate to flame nozzle distances. In most of the sensing conditions, the response and recovery times were measured in the order of 20 to 30 s. The layer with a more open morphology showed sensitivity at ppb hydrogen level, good stability, and selectivity. The response behavior of the samples was explained according to the power-law in the metal oxide semiconductor (MOS) gas sensors.     

Boron and nitrogen co-doped ZnO thin films for opto-electronic applications

The transparent conductive oxides such as ZnO have been widely studied due to their potential applications. As a promising wide band gap semiconductor, ZnO thin films with various dopants are important in fabricating the photonic devices to meet the various needs. In this study, boron and nitrogen co-doped ZnO thin films were fabricated at different temperatures (100–600 °C) on sapphire (0 0 1) substrates using pulsed laser deposition technique. X-ray diffractometer, atomic force microscope, spectrophotometer and spectrometer were used to characterize the structural, morphological and optical properties of the thin films. Hall measurements were also carried out to identify the electrical properties of the thin films.     

Amorphous hydrogenated carbon films as barrier for gas permeation through polymer films

The influence of amorphous hydrogenated carbon (a-C:H) coatings on the gas permeation through polymer films was investigated. a-C:H films were deposited from a 13.56-MHz RF glow discharge in methane or acetylene atmosphere. Thin poly(ethylene terephthalate) and polyimide foils were used as substrates. The permeation of the gases H₂, N₂, O₂ and CO₂ was measured and the reduction of the permeability coefficient was correlated to composition and density of the a-C:H films. The stoichiometry of the layers was analyzed using ion-beam techniques on films deposited onto silicon samples. The a-C:H/PET surfaces were analyzed using optical microscopy and atomic force microscopy (AFM). Multilayer structures comprising different types of a-C:H films were also investigated. A reduction of the permeability coefficient by 80% for hard, dense and 94% for soft, polymer-like layers was found. Surprisingly, the barrier efficacy of the coating decreases with increasing a-C:H film density. This unexpected result is attributed to the appearance of a network of deep cracks spread out over the whole coating.     

Incorporation of hydrogen in diamond thin films

In this investigation, diamond thin films with grain size ranging from 50 nm to 1 µm deposited using hot filament chemical vapor deposition (HFCVD) have been analyzed by elastic recoil detection analysis (ERDA) for determining hydrogen concentration. Hydrogen concentration in diamond thin films increases with decreasing grain size. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that part of this hydrogen is bonded to carbon forming C–H bonding. Raman spectra also indicated the increase of non diamond phase with the decrease in crystallite size. Incorporation of hydrogen in the samples and increase of hydrogen content in nanocrystalline sample are discussed. Large separation between filament and substrate used for the synthesis of nanocrystalline film helped to understand the large incorporation of hydrogen in nanocrystalline diamond films during growth. The study addresses the hydrogen trapping in different samples and higher hydrogen concentration in nanocrystallites by considering the synthesis conditions, growth mechanisms for different grain sized diamond films and from the quality of CVD diamond films.     

国内硫化氢含量的检测方法浅析

本文按照分析原理,将天然气中硫化氢测定方法划分为物理法和化学法,包括碘量法、汞量法、亚甲基蓝法、色谱法、光谱法等。本文着重介绍了各种方法的分析原理,优势与缺点,以及目前国内最新的研究状况,并对未来硫化氢测定的发展前景作出展望。     

Electrochemical polishing of hydrogen sulfide from coal synthesis gas

An advanced process has been developed for the separation of H₂S from coal gasification product streams through an electrochemical membrane. This technology is developed for use in coal gasification facilities providing fuel for cogeneration coal fired electrical power facilities and molten carbonate fuel cell (MCFC) electrical power facilities. H₂S is removed from the syn-gas by reduction to the sulfide ion and hydrogen gas at the cathode. The sulfide ion migrates to the anode through a molten salt electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. The syn-gas is enriched with the hydrogen. Order of magnitude reductions in H₂S have been repeatedly recorded (100 ppm to 10 ppm H₂S) on a single pass through the cell. This process allows removal of H₂S without cooling the gas stream and with negligible pressure loss through the separator. Since there are no absorbents used, there is no absorption/regeneration step as with conventional technology. Elemental sulfur is produced as a byproduct directly, so there is no need for a Claus process for sulfur recovery. This makes the process economically attractive since it is much less equipment intensive than conventional technology.     

含硫化氢混合气处理新技术

为提高经济效益和环境效益,采用全新的物理分离的方法,将含硫化氢尾气中价值较高的组分分离出来。该分离技术的核心是根据混合气各组分的临界点,控制适当的混合气体的温度和压力,使某一种或两种组分发生相变,根据混合气组分的数量、种类、各组分含量以及所要求的分离产物的种类、浓度或纯度,采用加压、蒸馏、比重差分离、吸收等工序设计工艺流程,适当控制参数,实现含硫化氢混合气体有效组分的分离。     

天然气脱除硫化氢的研究

用甲基二乙醇胺(MDEA)脱除天然气中的硫化氢,研究反应温度与MDEA浓度对脱硫效果的影响。甲基二乙醇胺最优工作温度为15～30℃,最佳浓度范围为40%～50%,原料气空速范围为1.5～3.5 h^(-1),脱硫剂空速范围为0.55～1.2 h(-1),脱硫剂空速范围为0.55～1.2 h^(-1)。与二乙醇胺(DEA)对比,在吸收温度20℃下,MDEA与DEA溶液浓度45%,DEA第180 h时硫含量>0.2 mg/L,超过二类气标准,MDEA在第276 h时硫含量>0.2 mg/L。10 mL硫含量大于二类气要求的时间增加53%,证明甲基二乙醇胺较二乙醇胺脱硫效果大幅增加,为采油厂工艺迭代提供了数据。     

Nucleophilic addition of hydrogen sulfide to methyl oleate,methyl linoleate,and soybean oil

Hydrogen sulfide was added to methyl oleate, methyl linoleate, and soybean oil at −70 and 25 C in the presence of boron trifluoride. Major reaction compounds were identified by gas liquid chromatography and mass spectrometry. At −70 C with a 200 molar ratio of hydrogen sulfide to ester, the reactions were complete in 4 hr. Primary reaction product from methyl oleate was methyl 9(10)-mercaptostearate. Methyl linoleate gave ca. equal amounts of methyl 9-(2-pentyl-1-thiolan-5-yl) nonanoate and methyl 8-(2-hexyl-1-thiolan-5-yl) octanoate. At 25 C, the reaction of methyl oleate and linoleate with hydrogen sulfide was less complete, and more side reactions were noted. When equimolar amounts of methyl oleate and methyl 9(10)-mercaptostearate were reacted in the presence of boron trifluoride at 25 C, a new compound was formed, bis(methyl n-octadecanoate 9[10]-yl) sulfide. The addition of liquid hydrogen sulfide to soybean oil at −70 C in the presence of boron trifluoride yields a product which, upon saponification, acidification, and methylation analyzes by gas liquid chromatography as ca. 52% thiolan, 27% mercaptostearate, 10% palmitate, 6% stearate, and 5% unidentified compounds.     

Highly responsive hydrogen gas sensing by partially reduced graphite oxide thin films at room temperature

Novel chemo-resistive gas sensors based on reduced graphite oxide (rGO) thin films have been fabricated and evaluated for hydrogen detection. The rGO materials were thermally treated at various conditions and analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy techniques to investigate the change of functional groups. The semiconductor type of the rGOs treated at different conditions were checked by flowing hydrogen gas at 20 cm³/min (sccm) under 10 Torr partial pressure. The rGOs treated at 70 °C in atmosphere (rGO070a), 200 °C in a vacuum (rGO200v), and 500 °C in a vacuum (rGO500v) exhibited n-type, ambipolar, and p-type behavior, respectively. The rGO500v was adopted as active sensing element without any rare metal decoration, and its sensing response to hydrogen was studied by using air as carrier gas. The rGO500v exhibited good sensitivity (～4.5%), response time (～20 s), and recovery time (～10 s) to 160 ppm hydrogen gas at room temperature.     

Hydrogen sulfide gas detection by Au-decorated ZnO nanotube: a computational study and comparison to experimental observations

Based on the experimental reports, Au-decoration on the ZnO nanostructures dramatically increases the electronic sensitivity to H₂S gas. In the current study, we computationally scrutinized the mechanism of Au-decoration on a ZnO nanotube (ZON) and the influence on its sensing behavior toward H₂S gas. The intrinsic ZON weakly interacted with the H₂S gas with an adsorption energy of ?11.2 kcal/mol. The interaction showed no effect on the HOMO–LUMO gap and conductivity of ZON. The predicted response of intrinsic ZON toward H₂S gas is 6.3, which increases to 78.1 by the Au-decoration at 298 K. The corresponding experimental values are about 5.0 and 80.0, indicating excellent agreement with our findings. We showed that the Au atom catalyzes the reaction 3O₂?+?2H₂S?→?2SO₂?+?2H₂O. Our calculated energy barrier (at 298 K) is about 12.3 kcal/mol for this reaction. The gap and electrical conductance Au-ZON largely changed by this reaction are attributed to the electron donation and back-donation processes. The obtained recovery time is about 1.35 ms for desorption of generated gases from the surface of the Au-ZON sensor.