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.     

Nanocrystalline chemically modified CdIn2O4 thick films for H2S gas sensor

CdIn₂O₄ sensor with high sensitivity and excellent selectivity for H₂S gas was synthesized by using sol-gel technique. Structural, electrical and gas sensing properties of doped and undoped CdIn₂O₄ thick films were studied. XRD revealed the single-phase polycrystalline nature of the synthesized CdIn₂O₄ nanomaterials. Since the resistance change of a sensing material is the measure of its response, selectivity and sensitivity was found to be enhanced by doping different concentrations of cobalt in CdIn₂O₄ thick films. The sensor exhibits high response and selectivity toward H₂S for 10 wt.% Co doped CdIn₂O₄ thick films. The current-voltage characteristics of 10 wt.% Co doped CdIn₂O₄ calcined at 650 °C shows one order increase in current with change in the bias voltage at an operating temperature of 200 °C for 1000 ppm H₂S gas.     

Synthesis of CdS nanorods by reacting CdCl2 nanorods with H2S at room temperature

We report the synthesis of CdS nanorods by reacting CdCl₂ nanorods with H₂S at room temperature. The preparation method was based on CdCl₂ nanorods employed as chemical template. The length and the diameter of the obtained CdS nanorods are about tens micron and 120−300 nm, respectively. The phase and the crystallographic structure of the products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The composition of the products was investigated by X-ray photoelectron spectroscopy (XPS).     

硫化镉和硫化银与多壁碳纳米管复合材料合成的研究

本文以硝酸镉和硫脲为镉源和硫源,用溶剂热技术在乙二胺和水的混合溶剂中合成CdS/MWNTs复合材料;再以硝酸银和硫化钠为银源和硫源,十二烷基磺酸钠(SDS)为表面活性剂,以水为溶剂在室温下合成Ag2S/MWNTs复合材料并采用TEM、XRD对复合材料进行表征,结果表明:CdS纳米晶和Ag2S纳米粒子成功长到了多壁碳纳米...     

H2S sensing properties of La-doped nanocrystalline In2O3

The nanocrystalline powders of pure and La³⁺-doped In₂O₃ with cubic structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution in the concentration of doping investigated. Gas-sensing properties of the sensor elements were tested by mixing a gas in air at static state, as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure In₂O₃ exhibited high response towards H₂S gas at an operating temperature 150 °C. Doping of In₂O₃ with La³⁺ increases its response towards H₂S and La³⁺ (5.0 wt.% La₂O₃)-doped In₂O₃ showed the maximum response at 125 °C. The selectivity of the sensor elements for H₂S against different reducing gases was studied. The results on response and recovery time were also discussed.     

Comparative study of alumina sulfation from H2S and SO2 oxidation

Alumina sulfation was studied under static conditions from H₂S or SO₂ oxidation, using infrared spectroscopy to determine the amounts of SO₄^2? formed. On heating without O₂ traces, no sulfate appears. With a large excess of O₂, some H₂S sulfation occurs even at room temperature. It does not depend on the alumina hydroxyl content and increases with the oxidation temperature, T_ox. It reaches a limit value, ~ 2.2 μmol m^?2, when T_ox ? 723 K. SO₂ sulfation is more difficult as it occurs at higher oxidation temperatures than the H₂S reaction. Water and hydroxyl groups promote it. It reaches the same limit value as the H₂S reaction when T_ox ? 723 K.Two mechanisms are proposed to explain H₂S sulfation. When t_ox < 473 K, there is direct sulfation, involving an H₂S chemisorbed species. Radicals are certainly an intermediate species. For higher T_ox values, H₂S is first transformed into SO₂; this explains why the SO₄^2? amounts then formed do not depend on the starting compound, H₂S or SO₂. A mechanism involving in the first step formation of hydrogen sulfite species accounts well for the results obtained on SO₂ sulfation.     

Effect of H2S on Fe corrosion in CO2-saturated brine

The effect of H₂S at ppm level concentrations on iron corrosion in 3 wt% NaCl solutions saturated with CO₂ in the temperature range of 25–85 °C is examined using electrochemical and surface science techniques. Small H₂S concentrations (5 ppm) have an inhibiting effect on corrosion in the presence of CO₂ at temperatures from 25 to 55 °C. At 85 °C, however, 50 ppm H₂S is needed to provide significant corrosion inhibition. At higher H₂S concentrations, the corrosion rate increases rapidly, while still remaining below the rate for the H₂S-free solution. Characterization of the iron surfaces after corrosion was carried out using X-ray photoelectron spectroscopy and X-ray diffraction. A sulfur peak (S2p) is observed at a binding energy of 161.8 eV in all cases, attributable to disulfide (\textS₂^2-) ({\text{S}}_{2}^{2-}) formation. Corrosion protection in the temperature range 25–55 °C can be attributed to Fe(II) bonded to S and O. At 85 °C, protection of the iron surface is most likely due to FeS₂ formation. Morphological changes on the iron surface after exposure to H₂S containing solutions were observed by SEM. A thin protective film was seen after exposure to solutions containing 5 ppm H₂S at 25 °C, while at 85 °C, with the addition of 50 ppm H₂S to CO₂-saturated brine solution, a dense protective film was formed on the iron surface.     

H2S sensors based on SnO2 films: RGTO verses RF sputtering

Gas sensing characteristics of SnO₂ thin films prepared by RF sputtering have been investigated and compared to that of RGTO (Rheotaxially Grown and Thermally Oxidized) films. Both the sensor films exhibited a highly selective response towards H₂S with RF sputtered film showing better response characteristics. RF sputtered and RGTO films exhibited a maximum response of 54 and 15 towards 10 ppm of H₂S at an optimum operating temperature of 150 and 250 °C, respectively. Sputtered films exhibited a linear response in the wide concentration range from 500 ppb to 500 ppm while RGTO films were found to saturate for concentrations above 100 ppm. XPS investigations revealed that the RGTO films are more sub–stoichiometric or oxygen deficient than the sputtered films. Raman studies further indicates that the surface of sputtered and RGTO films are characterized by the presence of oxygen deficiency attributed to the “bridging-type” and deeper “in-plane/sub-bridging” oxygen vacancies, respectively. The improved response kinetics of the RF sputtered films is attributed to the presence of bridging type oxygen vacancies that facilitates the charge transfer between the sensor surface and H₂S molecules.     

Evaporation of CuCl and CuCl2 for the fabrication of Cu2S/CdS thin film solar cells

The so-called dry method for the fabrication of Cu₂S/CdS thin film solar cells uses a thin CuCl film,in order to convert the surface layer of the CdS film into Cu₂S. Usually, the CuCl film is deposited by evaporation of freshly prepared CuCl powder. In the present paper we investigate the influence of contamination of this evaporation material by CuCl₂ and by CuCl₂·2H₂O. The experiments show that about 99% of these contaminants decompose into CuCl during the evaporation process.     

复合结构Ni-P 非晶态镀层在H2S/ CO2环境中的耐腐蚀性能

通过在同一镀液中改变温度、p H 值和施加电流完成化学镀和电镀过程, 在普通碳钢基体上得到电位差高于160 mV 的复合结构的非晶态Ni- P 合金镀层。采用SEM、电化学测试设备及专门的腐蚀环境试验箱, 研究了该复合镀层在H₂S/ CO₂ 腐蚀气氛中的耐腐蚀行为。结果表明: 所制备的复合结构Ni- P 非晶态镀层在H₂S/CO₂腐蚀环境中, 100 h 后镀层表面出现均匀的硫化物腐蚀膜, 300 h 后镀层表面出现腐蚀裂纹, 并沿着与基体表面平行的方向扩展、剥离, 在电镀层剥离处磷元素的相对含量增加。所制备的12μm 厚的复合叠加结构Ni- P 非晶态镀层的耐腐蚀性能优于25μm 厚的普通化学Ni-P 非晶态合金镀层。      

Thermophilic biofiltration of H2S and isolation of a thermophilic and heterotrophic H2S-degrading bacterium, Bacillus sp. TSO3

Thermophilic biofiltration of H₂S-containing gas was studied at 60 °C using polyurethane (PU) cubes and as a packing material and compost as a source of thermophilic microorganisms. The performance of biofilter was enhanced by pH control and addition of yeast extract (YE). With YE supplement and pH control, H₂S removal efficiency remained above 95% up to an inlet concentration of 950 ppmv at a space velocity (SV) of 50 h⁻¹ (residence time = 1.2 min). H₂S removal efficiency strongly correlated with the inverse of H₂S inlet concentrations and gas flow rates. Thermophilic, sulfur-oxidizing bacteria, TSO3, were isolated from the biofilter and identified as Bacillus sp., which had high similarity value (99%) with Bacillus thermoleovorans. The isolate TSO3 was able to degrade H₂S without a lag period at 60 °C in liquid cultures as well as in the biofilter. High H₂S removal efficiencies were sustained with a periodic addition of YE. This study demonstrated that an application of thermophilic microorganism for a treatment of hot gases may be an economically attractive option since expensive pre-cooling of gases to accommodate mesophilic processes is not required.     

Photodeposition of CoOx and MoS2 on CdS as dual cocatalysts for photocatalytic H2 production

Photocatalytic H₂ production from water splitting has a promising prospect for alleviating energy and environmental issues.However,the fast recombination of photogenerated charge carriers limits the photocatalytic efficiency and its practical application.Cocatalyst engineering is an effective strategy to spatially separate photogenerated charge carriers.In this work,noble-metal-free MoS₂ and CoO_x cocatalysts are loaded on CdS nanorods by a two-step photodepositio...     

H2S sensing property of porous SnO2 sputtered films coated with various doping films

Pure SnO₂ films and Ag-, Cu-, Pt-, and Pd-doped SnO₂ films were investigated for H₂S sensing properties. SnO₂ films were deposited by DC magnetron sputtering at various substrate temperatures and discharge gas pressures. As the discharge gas pressure increased and the substrate temperature decreased, the film became porous. Doping with Cu or Ag film improved the sensitivity, and the highest sensitivity was obtained in the porous SnO₂ film coated with an Ag film 16 nm thick. According to the X-ray diffraction (XRD) pattern, Ag deposited on SnO₂ film transformed to Ag₂S upon exposure to H₂S. When the Ag-doped film sensor was operated at a low temperature, the sensitivity was extremely high, but the recovery was insufficient. By increasing the operation temperature, the recovery was improved but the sensitivity decreased.     

Room-temperature H2S gas sensing properties of carbonized silicon nanoporous pillar array

Through thermally treating silicon nanoporous pillar array (Si-NPA) in a graphite crucible in a vacuum furnace at 1100 °C, a continuous thin film composed of cubic SiC nanoparticles was prepared and its room-temperature resistive sensing properties were measured. The sensor was found to be with high sensitivity and an upper limit concentration of 1200 ppm for H₂S detection. Through carrying out the experiments of adsorption-desorption dynamic cycles and long-time air-ambient storage, the sensor was demonstrated to be with high repeatability and long-term stability. The response and recovery times were determined to be ~ 123 and ~ 114 s, respectively. The sensing mechanism was put forward through analyzing the possible adsorption modes of H₂S molecules on SiC/Si-NPA. The existence of the detecting limit concentration was attributed to the single-layer adsorption of H₂S molecules, whose quantity was restricted by the effective adsorption sites formed on SiC/Si-NPA. Our results show that SiC/Si-NPA might be an ideal sensing material for fabricating low-concentration H₂S gas sensors.     

Nanoporous TiO2 thin film based conductometric H2 sensor

Nanoporous titanium dioxide (TiO₂) based conductometric sensors have been fabricated and their sensitivity to hydrogen (H₂) gas has been investigated. A filtered cathodic vacuum arc (FCVA) system was used to deposit ultra-smooth Ti thin films on a transducer having patterned inter-digital gold electrodes (IDTs). Nanoporous TiO₂ films were obtained by anodization of the titanium (Ti) thin films using a neutral 0.5% (wt) NH₄F in ethylene glycol solution at 5 V for 1 h. After anodization, the films were annealed at 600 °C for 8 h to convert the remaining Ti into TiO₂. The scanning electron microscopy (SEM) images revealed that the average diameters of the nanopores are in the range of 20 to 25 nm. The sensor was exposed to different concentrations of H₂ in synthetic air at operating temperatures between 100 °C and 300 °C. The sensor responded with a highest sensitivity of 1.24 to 1% of H₂ gas at 225 °C.     

Atomic layer deposition of ZnS via in situ production of H2S

Atomic layer deposition (ALD) of ZnS films utilizing diethylzinc and in situ generated H₂S was performed over a temperature range of 60 °C-400 °C. This method for generating H₂S in situ was developed to eliminate the need to store high pressure H₂S gas. The H₂S precursor was generated by heating thioacetamide to 150 °C in an inert atmosphere, producing acetonitrile and H₂S as confirmed with mass spectroscopy. ALD behavior was confirmed by investigation of growth behavior and saturation curves. The properties of the films were studied with X-ray diffraction, transmission electron microscopy, ellipsometry, atomic force microscopy, scanning electron microscopy, ultraviolet-visible spectroscopy, and X-ray photoelectron spectroscopy. The results show a growth rate that monotonically decreases with temperature, and films that are stoichiometric in Zn and S. The root mean square roughness of the films increases with temperature above 100 °C. A change in crystal phase begins at ∼ 300 °C. The band gap is dependent on the crystal phase and is estimated to be 3.6-4 eV.     

Selective H2S detection by CuO functionalized ZnO nanotetrapods at room temperature

ZnO nanotetrapods have been synthesized by carbothermal method. The structure, phase, morphology of the synthesized sample were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, Scanning electron microscopy, Transmission electron microscopy and Selected area electron diffraction. The gas-sensing characteristics of thick films of pure and CuO-functionalized ZnO Nanotetrapods have been compared. Pure ZnO nanotetrapod films were found to be sensitive to both H₂S and NO with similar sensitivities, at a temperature of 250–300 °C. It is demonstrated that functionalization of ZnO nanotetrapods with CuO, results in selectivity towards H₂S at a lower temperature of 50 °C.     

Reliability analysis of pipelines carrying H2S for risk based inspection of heavy water plants

Reliability analysis of pipelines containing corrosion defects due to H₂S is presented. The pipeline carrying H₂S is more susceptible to the internal corrosion thereby reducing the pipeline's load carrying capacity. The objective of this study is to obtain the pipelines' failure probabilities that are required in establishing a Risk Based Inspection (RBI) programme for heavy water plants. The reliability assessment of pipelines involves the estimation of failure pressure and evaluating the limit state function. Several failure pressure models were studied for this purpose and it was found that the modified B31G failure pressure model is most suitable for the pipeline failure pressure modeling. Due to the presence of non-linearity in the limit state function and non-normal variables, the first order reliability method has been employed for carrying out the reliability analysis. The uncertainty of the random variables on which the limit state function depends is modeled using normal and non-normal probabilistic distributions. The failure probabilities and the categories of the pipelines connected to the first pair of first stage of exchange towers are presented. In addition, a sensitivity analysis was carried out on random variables involved in the problem. The results of sensitivity analysis are also presented.     

Mild and facile synthesis of Ag2S nanowire precursor using mercaptoacetic acid as a reductant/stabilizer and its subsequent conversion to Ag2S or CdS nanowires

Silver sulfide nanowire precursor was prepared at room temperature by simple mixing of mercaptoacetic acid (MAA) and silver nitrate solutions for 10–20 min duration. The MAA concentration in the chemical reaction bath was varied from 1 to 10 mM to afford nanowire precursors ranging in length from 800 nm to 42 μm and diameters ranging from 53 to 210 nm. The chemical identity of the precursor was established as a Ag⁺–⁻SCH₂COOH complex by a variety of spectroscopic probes. It could be converted into crystalline Ag₂S nanowires (with no alteration in nanowire dimensions) by a thermal anneal at ∼300 °C. Reverse cation exchange of the Ag₂S nanowire precursor in a Cd²⁺-containing medium afforded CdS nanowires (with some alterations in morphology) whose chemical identity was confirmed by Raman spectroscopy and photoluminescence. Finally the dual role of MAA as a capping agent and reducing agent in the formation of the Ag₂S nanowire precursor complex is briefly discussed.     

高含H2S天然气集输管线氢鼓泡失效评价

针对酸性环境下硫化物造成天然气集输管线严重腐蚀开裂的失效现象,根据高含H2S天然气集输管线材质选择、力学性能、显微形貌等综合性能数据结果,对其失效行为进行深入分析和评价。结果表明,在高含H2S、CO2和水等腐蚀介质的集输管线内壁发生腐蚀失效和氢鼓泡的危险性极大,提出产生氢鼓泡现象的影响因素及其预防措施从而指导集输管线的安全运行。