2S Concentrations Research Articles

Compact microstructured Cu2ZnSnS4 thin films with enhanced optoelectronic properties via (NH4)2S tunable hybrid colloidal ink coating and transformation

Kesterite Cu2ZnSnS4 (CZTS) is a quaternary semiconductor material composed of earth-abundant elements that is a promising material for sustainable thin film photovoltaics and other optoelectronic applications. In this work, CZTS thin films are deposited using aqueous colloidal suspensions of binary sulfides (Cu and Zn) and thiostannate complexes formed by in situ reaction of SnS2 with (NH4)2S. In a departure from previous works that used only dissolved thiostannate complexes, we utilize a hybrid state of tin sulfide as both nanoparticles and thiostannate complexes to improve thin film quality. This finding was made by adjusting the (NH4)2S concentration in our aqueous inks, which modified the relative abundance of thiostannate complexes vis-à-vis the amount of SnS2 nanoparticles. In the absence of (NH4)2S, the unstable ink yields nonuniform, partially oxidized thin films. Meanwhile, thiostannate complex formation with the use of (NH4)2S (2–10 vol%) can suppress the presence of secondary phases such as CuxS in the absorber layer and protects against oxidation (avoiding undesirable SnO2 formation). Lowering the aqueous (NH4)2S concentration to 2 vol% yielded the most stable ink formulation, featuring a hybrid state of tin sulfide as both colloidal particles and dissolved thiostannate complexes. The hybrid tin sulfide ink produced compact thin films and reduced the level of Cu-Zn antisite defects in the kesterite crystal structure. We attribute the compact microstructure attained with the hybrid tin sulfide formulation to thiostannate complexes acting as linkers among the three binary sulfides (Cu, Zn, and Sn), enabling their orderly packing into an amorphous, quaternary initial state which is then annealed to grow crystalline kesterite CZTS. UV-Vis absorption characterization shows the Tauc bandgap for 2 vol% hybrid ink coated films to be 1.40 eV with reduced absorption tails based on Urbach energy measurements, while photoluminescence studies showed significantly enhanced emission.

Evaluation of Integrated Management Approaches against Citrus Nematode (Tylenchulus semipenetrans) in Pakistan

Present study was conducted to explore the nematicidal potential of different synthetic chemicals, biopesticides and antagonists against citrus decline. Effect of eleven chemicals, seven biopesticides and two antagonists on juvenile mortality was evaluated in vitro. Four concentrations (2S, S, S/2 and S/4) of each chemical were prepared on the basis of recommended dose for each chemical. Juvenile mortality of citrus nematodes was calculated after 24, 48 and 72 hour of exposure to chemicals. Rugby expressed maximum percentage of juvenile mortality at 2S, S, S/2 and S/4 concentration. Mortality percentage observed by Rugby, Furadan, Match and Cartap after 72 h at 2S concentration was (100, 100, 95.44, 88.23%) whereas at S/4 concentration mortality percentage was (76.32, 81.18, 62.15, 55.28%) respectively. Among biopesticides maximum percentage mortality observed by Proclaim and Cure after 72 hours at 2S concentration was (83.87, 80.44%) while at S/4 concentration it was (59.87, 57.38%) respectively. Cultural filtrates of two antagonist Trichoderma harzianum and Trichoderma viridi were evaluated at S, S/2 and S/4 concentration under lab conditions. Maximum mortality (88.42%) was observed when both antagonists were applied in combined treatment at S concentration after 72 hours of exposure. Two best performing chemicals, one biopesticide and one antagonist were evaluated under greenhouse against T. semipenetrans on Citrus jambhiri Lush (rough lemon) and their effect on plant growth and nutrient uptake was measured. Nitrogen uptake was measured by following micro Kjeldahl method. For phosphorus and potassium uptake absorbance of samples at 720 nm was measured with the help of spectrophotometer. Phosphorus was calculated by comparing standard curve already prepared while potassium uptake was assessed by flame photometer method after digestion. All the treatments were found significantly effective against citrus nematode but maximum plant height, stem diameter, number of leaves, root length, root weight, shoot weight, and number of feeder roots (90 cm, 2.4 cm, 102, 48.3 g, 12.1 g, 48.8 g and 70) as compared to control when Rugby, Furadan, Proclaim and T. harzianum were applied in combination. Similarly maximum uptake of Nitrogen (3.14) Phosphorous (2.44%) and Potassium (1.95%) was observed when all the treatments were applied in combination. The results of present study will be helpful in selecting the suitable chemicals for growers having problems of citrus nematodes in orchards.

Methane dynamics in the shelf waters of the West coast of India during seasonal anoxia

Abstract The Western Continental Shelf of India experiences water-column anoxia during late summer/early autumn, thereby providing conducive conditions for methane (CH 4) accumulation. Measurements of CH4 along with other ancillary physico-chemical variables were made during the period of anoxia (September–October) in 2003, 2005 and 2009. The shelf waters experienced variable oxygen deficiency (hypoxic to anoxic) in space and time. Maximum observed accumulation of CH4 was only ~104 nmol/L although the bottom waters were strongly reducing with hydrogen sulphide (H 2S) concentration reaching up to 26.6 μmol/L. Methane showed a reasonable positive correlation with H2S. The observed CH4 accumulation over the Indian shelf was lower than previously reported from the major Eastern Boundary Upwelling systems, especially off Namibia. It is proposed that the low organic loading arising from lower productivity and consequently weak sedimentary methanogenesis may largely account for the lower CH 4 concentrations in anoxic bottom waters over the Indian shelf. Also, while anoxia may limit CH4 oxidation, sedimentary inputs are probably a more important source of water column CH4. In spite of the moderate CH4 build up in bottom waters, CH4 saturation at the sea-surface observed in the present study (89–1041%) was relatively lower than observed in 1996–1997 (~110–2521%). The sea to air flux of CH4 ranged from −0.52 to 26.56 μmol m−2 d−1, marginally higher than previously reported from the upwelling system in the western Arabian Sea.

Stability of SiGe(100) Surfaces after Ammonium Sulfide Passivation

Germanium and silicon germanium are attractive channel materials for transistors. Germanium has a smaller band gap and higher hole mobility than silicon, and varying the Ge concentration is one means of tuning the properties of SiGe alloys. Although these materials have many potential benefits, they are challenging to work with. The native oxide, GeO2, is water soluble and therefore cannot protect the surface during aqueous processes. One option is to deposit a layer that chemically passivates the surface after cleaning to protect it from reoxidation. Sulfur could passivate the surface due to its size and valency. Since the dominant cleaning technology is wet, aqueous ammonium sulfide could be a viable option. While ammonium sulfide processes deposit sub-monolayer coverages of sulfur on germanium, the surface reactions on SiGe surfaces are vastly different. Our study focuses on the treatment of Si-rich SiGe surfaces (Si1-xGex x=0.25) with aqueous (NH4)2S. We varied the concentration of (NH4)2S in solution with and without added acid and characterized the surfaces using X-ray Photoelectron Spectroscopy (XPS). Immersions in (NH4)2S alone oxidized the surface and did not deposit a sulfide layer. Instead the surface oxidized as a function of the (NH4)2S concentration. In order to remove the oxide and slow down or stop the oxidation, small volumes of HF and HCl were added to the mixture. Addition of halogen acids dropped the pH of the solution from 10 to 8 and sulfides were detected with XPS in the S 2p region. Sulfur coverage increased with increasing concentrations of HF and HCl, however oxides increased as well. The simultaneous deposition of sulfur and oxygen suggests that oxidized sulfur, such as sulfates and thiosulfates, deposited on the surface. In addition to chemical characterization of the surface, metal-insulator-semiconductor capacitors (MISCAPs) were fabricated after three different surface treatments: 1) clean and dry (control), 2) cleaning and immersion in (NH4)2S and 3) cleaning and immersion in (NH4)2S with added acid. Capacitance-voltage measurements were obtained for all three surface treatments. The density of interface defects (Dit) was calculated for each process from conductance and capacitance data. Processes that yielded the highest sulfur coverage (ammonium sulfide with added acid) showed a reduction in Dit (1.4 x 1012 cm-2 eV-1) compared to samples that were cleaned and dried only (6.4 x 1012 cm-2 eV-1) and samples treated with aqueous ammonium sulfide (4.4 x 1012 cm-2 eV-1).

Surface Cleaning of SiGe(100) and Passivation of Ge(100) with Aqeuous Ammonium Sulfide

The effect of standard aqueous cleans including SC-1, HCl, HF, and HCl/HF mixtures on SiGe(100) surfaces with 50, 75 and 85% Ge molar ratios was characterized with x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. HF was most effective at removing both Ge and Si oxides and reduced the carbon contamination. SC-1 selectively depleted Ge from the surface. Passivation of Ge(100) surfaces with aqueous (NH4)2S was characterized with XPS as a function of the solution concentration and with the addition of H2O2. The passivation process was independent of the (NH4)2S concentration and approximately 3 Å of S was deposited or about one layer based on XPS. Addition of H2O2 to very dilute (NH4)2S oxidized the surface while addition to higher concentrations showed similar effects as a sequential HCl/H2O2 treatment.

Chemical Passivation of In0.53Ga0.47As(100) Using Ammonium Sulfide and Thiols

III-V compound semiconductors have superior electron and hole mobilities compared to silicon, which makes them alternative materials to fabricate transistors that are faster and use less energy. Since the oxides of III-V’s contain many defects and have undesirable electrical properties, aqueous passivation chemistries are needed to incorporate these materials into existing semiconductor processing lines. This study seeks to determine whether a thin (~2-3 nm) layer of sulfur or a sulfur-containing molecule can chemically passivate clean InGaAs surfaces to prevent oxide regrowth upon ambient exposure. The goal is to devise a liquid phase process to remove carbon contamination from the surface, etch the native oxides, and deposit a thin film to prevent the diffusion of molecular oxygen and water vapor to the clean surface of the semiconductor for at least one hour. In0.53Ga0.47As(100) on InP substrates (RMS=0.18 nm by atomic force microscopy) were cleaned in dilute SC1 solutions and etched for 1 min in 0.3 M HF or 1.0 M HCl followed by immersion in dilute solutions of 1-eicosanethiol (ET, 20 carbon atoms in chain) in ethanol or ammonium sulfide ((NH4)2S) in water. The chemical composition of the passivated surfaces was analyzed by x-ray photoelectron spectroscopy (XPS). The presence of InGaAs oxides was evaluated by comparing the In 3d, Ga 2p, As 2p and O 1s region of the XPS spectra of the substrates after different processes. The analysis of InGaAs etched for 1 min in HF or HCl showed that the surface reoxidized completely after only 4 min of ambient exposure (no surface roughening occured after etching). The main oxides present on the surface after the acid etching were the As3+ and Ga3+ states. When clean substrates were etched in HF or HCl and immersed for 20 min 4 mM ET and 0.02% (NH4)2S solutions, oxides were detectable on the surface after 4 min of atmospheric exposure, but the reoxidation of InGaAs was slowed down (after 60 min of ambient exposure, less oxides were present on the surface in comparison with the substrate that was not passivated, as shown in Figure 1). Additional tests showed similar results for 0.02% (NH4)2S passivation for 1 min and for 60 min, or for 20 min in 20% (NH4)2S, suggesting that the passivation is independent of (NH4)2S concentration or deposition time. From the XPS analysis, the passivation layer is bonding to the InGaAs surface in the form of sulfide (As1+ states observed in the passivated samples only). Only when InGaAs was passivated for 20 h in ET or for 20 min in (NH4)2S under a nitrogen atmosphere in a glove box, no detectable oxygen was observed in the O 1s region after exposing to air for a short time (4 min). Oxide regrowth was observed for longer ambient exposure times. To estimate the thickness of the passivation layer deposited, spectroscopic ellipsometry was used to measure the overlayer (ET, S and InGaAs oxides) on InGaAs after the passivation processes. An overlayer thickness of 0.8 nm was measured on InGaAs after passivating for 20 min in 0.02% (NH4)2S. The thickness of the overlayer on InGaAs after passivating for 20 h in 4 mM ET was 2.6 nm (the calculated molecular length of the ET molecule is 2.7 nm). These results show that the sulfur-based chemistries are bonding to the III-V’s but the resulting layer is not thick enough to prevent oxygen or water vapor from diffusing and reacting at the surface. We are working to understand how to densify the ET layer and control the thickness of layers deposited using (NH4)2S. Figure 1. XPS spectra of In0.53Ga0.47As(100) etched in 0.3 M HF and passivated for 20 min in 0.02% (NH4)2S in a nitrogen atmosphere (glove box). A control experiment where a water rinse was done instead of the passivation, exposed for 4 min to atmosphere, is shown in a). The passivated surface was exposed to atmosphere for b) 4 min, c) 8 min, d) 20 min and e) 60 min Figure 1

ADSORPTION OF HYDROGEN SULFIDE USING PALM SHELL ACTIVATED CARBON: AN OPTIMIZATION STUDY USING STATISTICAL ANALYSIS

Removing H 2S from biogas that is produced from anaerobic diges tion of palm oil mill effluent is a crucial step in order for the biogas to be utilized as a source of energy. In this study , palm shell activated carbon (PSAC) prepared by st eam activation was used to adsorb H 2S from simulated biogas. The parameters studied wer e H 2S concentration, adsorption temperature and space v elocity. The effect of these parameters towards breakthrough ads orption capacity was studied using statistical anal ysis with Design Expert Software. H 2S concentration and space velocity were found to be significant in affecting the breakthrough adsorpti on capacity.Adsorption temperature on its own was foun d not to have significant effect on the breakthroug h adsorption capacity but its interaction with other parameters was found to be sCharacterization of fresh and spent PSA C confirmed and provided further information on the adsorption of sulfur spe cies on PSAC pore surface.

Interfacial Characteristics for LaAlO<sub>3 </sub>Gate Dielectric on S Passivated GaAs Substrate

In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide (NH4)2S concentrations in the passivation of n-type GaAs. Samples were degreased and immersed in aqueous (NH4)2S solutions of concentrations 22% and 10%for 10 min at 295 K, immediately prior to plasma enhanced atomic layer deposition of LaAlO3. The chemical bonding state of (NH4)2S treated GaAs surface were investigated by X-ray photoelectron spectroscopy (XPS), which indicate that Sulfur passivation can reduce intrerfacial GaAs-oxide formation. Transmission electron microscopy (TEM) was implemented to characterize the interface morphology. Finally, capacitance-voltage (C-V) and leakage current density-voltage (J-V) measurement were used to characterize the electrical properties of LaAlO3 films.

Optimization of the ammonium sulfide (NH4)2S passivation process on InSb(111)A

The passivation of the InSb semiconductor surface and related alloys is of interest due to their small bandgaps and high bulk mobilities, which make them favorable materials for use in quantum-well transistors and long wavelength optoelectronic devices. One of the most common passivation approaches is an ammonium sulfide ((NH4)2S) treatment; however, there are variations in the reported processing conditions for this procedure. This study represents a broad review of the different sulfur treatment parameters used as well as determining the optimal processing parameters in terms of length of time the sample is in the solution and the (NH4)2S concentration, by measuring the level of the residual native oxides, and surface roughness, by means of x-ray photoelectron spectroscopy and atomic force microscopy, respectively.

Experimental study on ozone photolytic and photocatalytic degradation of H 2S using continuous flow mode

A foam nickel support was coated with TiO 2 sols containing anatase particles. The malodorous compound, hydrogen sulfide (H 2S), was removed via photolytic and photocatalytic oxidation processes under ambient conditions using a self-made photoreactor with 185-nm ozone (O 3) lamp illumination. The reactor degraded H 2S with high removal efficiency. The effects of several factors, such as initial H 2S concentration, ultraviolet light wavelength, relative humidity (RH), oxygen content, and catalyst deactivation and regeneration, on H 2S degradation were investigated. The highest activity for H 2S destruction was achieved with 80% RH, 21% oxygen content, approximately 200 mg/m 3 initial concentration, and 185-nm O 3 lamp illumination, resulting in higher conversion. Sulfur (S 0) and sulfate ion (SO 4 2−) were detected as byproducts via the XPS technique. The catalytic activity was improved by SO 4 2− promotion, but reduced by S 0 accumulation on the photocatalyst surface. In addition, by increasing the amount of SO 4 2− generated, the yield of S 0 and catalyst poisoning could be controlled in the reaction.

Removal of minor concentration of H 2S on MDEA-modified SBA-15 for gas purification

A promising adsorbent for H 2S removal of minor concentration for gas purification was prepared by synthesizing and modifying the mesoporous molecular silica of SBA-15 with methyl-diethyl-amine (MDEA). Removal performance of minor concentration of H 2S on the adsorbent was experimentally studied in a dynamic setup. The adsorbents showed good performance in removing H 2S from gas steams. The loaded amines did not change the ordered structure of SBA-15, but enhanced its removing H 2S. The adsorbents were characterized by X-ray powder diffraction (XRD) and N 2 adsorption/desorption. Effect of the R (the loading ratio) of MDEA, effect of initial H 2S concentration and effect of moisture on removal performance of H 2S were studied respectively. With increase of the R of MDEA, the H 2S removal performance of the adsorbent was improved obviously. When R of MDEA was 0.6, the removal performance was optimum. Initial H 2S concentration had a large effect on the removal performance. Both breakthrough capacity and saturation capacity increased as the initial H 2S concentration increased. In the presence of moisture, the experimental results showed the improvement in the removal performance of H 2S. In addition, not only was the adsorbent regenerable by purging with the purified gas, but also the removal performance was stable in removal adsorption cycles.

Nitrogen cycling within suboxic and anoxic sediments from the continental margin of Western North America

Here we report rates of benthic nitrogen (N) cycling and assess controls on biological NO 3 − sequestration and transport in sediments underlying oxygen deficient regions of the ocean ranging from anoxic/suboxic ([O 2] of 0–2 μM) to more oxic (57 μM [O 2]) conditions. N mass balances were constructed based on benthic fluxes (N 2, NH 4 + and NO 3 −) and pore water profiles (N 2, NO 3 −, NO 2, N 2O, Fe and HS −) at sites in the Southern California Borderland and the Mexican Margin. Fluxes across the sediment-water interface for N 2, NO 3 − and NH 4 + were determined directly by whole core incubations, and fluxes of N 2 were also determined by modeling mm-scale pore water profiles. Estimates of the N 2 flux by these two methods agree to ± 50%, thereby establishing a range of net N 2 production in these settings. The average N 2 efflux was four times larger at a site with high pore water H 2S concentrations (Soledad Basin 3.14 ± 1.10 mmol N m − 2 day − 1 ) compared to an iron-rich site (Santa Monica Basin 0.74 ± 0.21 mmol N m − 2 day − 1 ) despite both sites having comparable NO 3 − uptake fluxes (− 0.93 ± 0.14 vs. − 0.82 ± 0.08 mmol N m − 2 day − 1 respectively). Pore water profiles from both sulfidic and iron-rich sites reveal subsurface maxima in NO 3 −, NO 2 −, and N 2O that are likely caused by the presence of NO 3 − sequestered by infaunal microbiota. In Soledad Basin, the sequestered pool of microbial NO 3 − contributes to NH 4 + production via DNRA resulting in an NH 4 + efflux (2.66 ± 0.52 mmol N m − 2 day − 1 ) to the overlying water. This flux exceeds the rate of NH 4 + production by C org degradation by 10 times. At the suboxic sites, a total N balance can only be achieved if the flux of NO 3 − into sediments is composed of two components: diffusive and biologically mediated transport. The more oxic site shows no evidence of a sequestered microbial NO 3 − pool and diffusive fluxes can account for all N transformations. Core incubations do not capture the total amount of NO 3 − uptake where biological transport is important as they do not account for NO 3 − sequestered prior to the start of the incubation. Pore water N 2O concentrations of up to 500 nM in sub-surface sediments greatly exceed the background concentration (7 nM) and are likely generated by the metabolic reduction of the intracellular nitrate pool, however, there was no measurable efflux of N 2O from sediments to the overlying water. Biological NO 3 − transport is a ubiquitous process in suboxic and anoxic sediments, however the magnitude of its importance appears to be linked to the presence of dissolved iron or sulfide in the pore waters.

Passive loss of hydrogen sulfide in biological experiments

Hydrogen sulfide (H 2S) is a volatile gas of considerable interest as a physiologically relevant signaling molecule, but this volatility has typically been overlooked in the context of biological experiments. We examined volatility of 10 and 100 μM H 2S (Na 2S·9H 2O) in real time with polarographic electrodes in three commonly employed experimental apparatuses: 24-well tissue culture plates (WP), muscle myograph baths (MB), and the Langendorff perfused heart apparatus (LPH). H 2S loss from all apparatuses was rapid and exponential, with half-times ( t 1/2) of 5 min (WP), less than 4 min (MB), and less than 0.5 min (LPH). The t 1/2 for H 2S loss from MB bubbled with 100% oxygen was slightly longer than that for MB bubbled with 100% nitrogen; both were significantly shorter than stirred but unbubbled MB (>9 min). Therefore, even without tissue, H 2S rapidly disappears from buffer under a variety of experimental conditions, and this is due to volatilization, not oxidation. The inability to maintain H 2S concentration, even briefly, questions the accuracy of dose–response studies and the relevance of long-term (>10 min) exposure to a single treatment of H 2S. These results also help to explain the discrepancy between low H 2S concentrations in blood and tissues versus high concentrations of exogenous H 2S required to produce physiological responses.

Operational aspects of the desulfurization process of energy gases mimics in biotrickling filters

Biological removal of reduced sulfur compounds in energy-rich gases is an increasingly adopted alternative to conventional physicochemical processes, because of economical and environmental benefits. A lab-scale biotrickling filter reactor for the treatment of high-H 2S-loaded gases was developed and previously proven to effectively treat H 2S concentrations up to 12,000 ppm v at gas contact times between 167 and 180 s. In the present work, a detailed study on selected operational aspects affecting this system was carried out with the objective to optimize performance. The start-up phase was studied at an inlet H 2S concentration of 1000 ppm v (loading of 28 g H 2S m −3 h −1) and inoculation with sludge from a municipal wastewater treatment plant. After reactor startup, the inlet H 2S concentration was doubled and the influence of different key process parameters was tested. Results showed that there was a significant reduction of the removal efficiency at gas contact times below 120 s. Also, mass transfer was found to be the main factor limiting H 2S elimination, whereas performance was not influenced by the bacterial colonization of the packed column after the initial startup. The effect of gas supply shutdowns for up to 5 days was shown to be irrelevant on process performance if the trickling liquid recirculation was kept on. Also, the trickling liquid velocity was investigated and found to influence sulfate production through a better use of the supplied dissolved oxygen. Finally, short-term pH changes revealed that the system was quite insensitive to a pH drop, but was markedly affected by a pH increase, affecting both the biological activity and the removal of H 2S. Altogether, the results presented and discussed herein provide new insight and operational data on H 2S removal from energy gases in biotrickling filters.

Diffuse CO 2 soil degassing and CO 2 and H 2S concentrations in air and related hazards at Vulcano Island (Aeolian arc, Italy)

La Fossa crater on Vulcano Island is quiescent since 1890. Periodically it undergoes “crises” characterized by marked increase of temperature (T), gas output and concentration of magmatic components in the crater fumaroles (T may exceed 600 °C). During these crises, which so far did not lead to any eruptive reactivation, the diffuse CO 2 soil degassing also increases and in December 2005 an anomalous CO 2 flux of 1350 tons/day was estimated by 1588 measurements over a surface of 1.66 km 2 extending from La Fossa crater to the inhabited zone of Vulcano Porto. The crater area and two other anomalously degassing sites (Levante Beach and Palizzi) have been periodically investigated from December 2004 to August 2010 for diffuse CO 2 soil flux. They show a marked variation with time of the degassing rate, with synchronous maxima in December 2005. Carbon dioxide soil flux and environmental parameters have been also continuously monitored for over one year by an automatic station at Vulcano Porto. In order to assess the hazard of the endogenous gas emissions, CO 2 and H 2S air concentrations have been measured by Tunable Diode Laser profiles near the fumaroles of the crater rim and of the Levante Beach area, where also the viscous gas flux has been estimated. In addition, CO 2 air concentration has been measured both indoor and outdoor in an inhabited sector of Vulcano Porto. Results show that in some sites usually frequented by tourists there is a dangerous H 2S air concentration and CO 2 exceeds the hazardous thresholds in some Vulcano houses. These zones should be immediately monitored for gas hazard should a new crisis arise.

Influence of H 2S concentration on the properties of Cu 2ZnSnS 4 thin films and solar cells prepared by sol–gel sulfurization

Cu 2ZnSnS 4 (CZTS) thin films prepared by a non-vacuum process based on the sulfurization of precursor coatings, consisting of a sol–gel solution of Cu, Zn, and Sn, under H 2S+N 2 atmosphere were investigated. The structure, microstructure, and electronic properties of the CZTS thin films as well as solar cell parameters were studied in dependence on the H 2S concentration. The sulfurization process was carried out at 500 °C for 1 h in an H 2S+N 2 mixed-gas atmosphere with H 2S concentrations of 3%, 5%, 10%, and 20%. As the H 2S concentration decreased from 20% to 5%, the S content of the CZTS thin films decreased. However, when the H 2S concentration was decreased below 3%, the S content of the films began to increase. A CZTS thin film prepared with an H 2S concentration of 3% had grains in the order of 1 μm in size, which were larger than those of films prepared at other H 2S concentrations. Furthermore, the most efficient solar cell, with a conversion efficiency of 2.23%, was obtained from a sample sulfurized at an H 2S concentration of 3%.

Oxy-fuel coal combustion—A review of the current state-of-the-art

Carbon dioxide emissions will continue being a major environmental concern due to the fact that coal will remain a major fossil-fuel energy resource for the next few decades. To meet future targets for the reduction of greenhouse gas (GHG) emissions, capture and storage of CO 2 is required. Carbon capture and storage technologies that are currently the focus of research centres and industry include: pre-combustion capture, post-combustion capture, and oxy-fuel combustion. This review deals with the oxy-fuel coal combustion process, primarily focusing on pulverised coal (PC) combustion, and its related research and development topics. In addition, research results related to oxy-fuel combustion in a circulating fluidised bed (CFB) will be briefly dealt with. During oxy-fuel combustion, a combination of oxygen, with a purity of more than 95 vol.%, and recycled flue gas (RFG) referred to as oxidant is used for combusting the fuel producing a gas consisting of mainly CO 2 and water vapour, which after purification and compression, is ready for storage. The high oxygen demand is supplied by a cryogenic air separation process, which is the only commercially available mature technology. The separation of oxygen from air as well as the purification and liquefaction of the CO 2-enriched flue gas consumes significant auxiliary power. Therefore, the overall net efficiency is expected to be decreased by 8–12% points, corresponding to a 21–35% increase in fuel consumption. Alternatively, ion transport membranes (ITMs) are proposed for oxygen separation, which might be more energy efficient. However, since ITMs are far away from becoming a mature technology, it is widely expected that cryogenic air separation will be the selected technology in the near future. Oxygen combustion is associated with higher temperatures compared with conventional air combustion. Both fuel properties as well as limitations of steam and metal temperatures of the various heat exchanger sections of the boiler require a moderation of the temperatures in the combustion zone and in the heat-transfer sections. This moderation in temperature is accomplished by means of recycled flue gas. The interdependencies between the fuel properties, the amount and temperature of the recycled flue gas, and the resulting oxygen concentration in the combustion atmosphere are reviewed. The different gas atmosphere resulting from oxy-fuel combustion gives rise to various questions related to firing, in particular, with respect to the combustion mechanism, pollutant reduction, the risk of corrosion, and the properties of the fly ash or its resulting deposits. In this review, detailed nitrogen and sulphur chemistry was investigated in a laboratory-scale facility under oxy-fuel combustion conditions. Oxidant staging succeeded in reducing NO formation with effectiveness comparable to that typically observed in conventional air combustion. With regard to sulphur, a considerable increase in the SO 2 concentration was measured, as expected. However, the H 2S concentration in the combustion atmosphere in the near-flame zone increased as well. Further results were obtained in a pilot-scale test facility, whereby acid dew points were measured and deposition probes were exposed to the combustion environment. Slagging, fouling and corrosion issues have so far been addressed via short-term exposure and require further investigation. Modelling of PC combustion processes by computational fluid dynamics (CFD) has become state-of-the-art for conventional air combustion. Nevertheless, the application of these models for oxy-fuel combustion conditions needs adaptation since the combustion chemistry and radiative heat transfer is altered due to the different combustion gas atmosphere. CFB technology can be considered mature for conventional air combustion. In addition to its inherent advantages like good environmental performance and fuel flexibility, it offers the possibility of additional heat exchanger arrangements in the solid recirculation system, i.e. the ability to control combustion temperatures despite relatively low flue gas recycle ratios even when combusting in the presence of high oxygen concentrations.

Parametric study of coiled carbon fibre synthesis on an in situ generated H 2S-modified Ni/Al 2O 3 catalyst

Coiled carbon fibre (CCF) synthesis on an in situ generated H 2S-modified Ni/Al 2O 3 catalyst is investigated using a high-throughput reaction system that allows real time observation of weight changes. The influence of reduction and synthesis temperatures, reduction duration, H 2 addition during synthesis, synthesis duration, C 2H 2 concentration in the synthesis gas and catalyst loading are investigated and products are analysed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. Thermodynamic equilibrium models of various experimental scenarios provide insight into the predominant species present at equilibrium. Reduction temperature and reduction duration affect H 2S concentration, a vital parameter for CCF synthesis, and CCFs form in only a narrow reduction and synthesis temperature range of 650 °C ± 50 °C with greatest coil yields observed at 650 °C and following reduction durations of between 1 and 20 min with greatest coil yields observed after a 10 min reduction. The presence of H 2 during synthesis was found to have a positive effect on CCF formation. The ratio of thick to thin carbon fibres increased with catalyst nickel loading and the greatest ratio of CCFs was produced with a 1:20 wt. Ni:Al 2O 3 catalyst.

Inhibition of hydrogen sulfide generation from disposed gypsum drywall using chemical inhibitors

Disposal of gypsum drywall in landfills has been demonstrated to elevate hydrogen sulfide (H 2S) concentrations in landfill gas, a problem with respect to odor, worker safety, and deleterious effect on gas-to-energy systems. Since H 2S production in landfills results from biological activity, the concept of inhibiting H 2S production through the application of chemical agents to drywall during disposal was studied. Three possible inhibition agents – sodium molybdate (Na 2MoO 4), ferric chloride (FeCl 3), and hydrated lime (Ca(OH) 2) – were evaluated using flask and column experiments. All three agents inhibited H 2S generation, with Na 2MoO 4 reducing H 2S generation by interrupting the biological sulfate reduction process and Ca(OH) 2 providing an unfavorable pH for biological growth. Although FeCl 3 was intended to provide an electron acceptor for a competing group of bacteria, the mechanism found responsible for inhibiting H 2S production in the column experiment was a reduction in pH. Application of both Na 2MoO 4 and FeCl 3 inhibited H 2S generation over a long period (over 180 days), but the impact of Ca(OH) 2 decreased with time as the alkalinity it contributed was neutralized by the generated H 2S. Practical application and potential environmental implications need additional exploration.

A comparative assessment of biofiltration and activated sludge diffusion for odour abatement

The deodorization performance of a biofilter and an activated sludge diffusion (AS) system was comparatively evaluated in terms of removal efficiency (RE) and process stability at empty bed residence times (EBRT) ranging from 94 to 32 s. Both bioreactors were fed with a synthetic odorous emission containing H 2S, butanone and toluene at 23.6–43.3, 4.3–6.3 and 0.4–0.6 mg m −3, respectively. While the outlet H 2S concentration was always lower than 1.4 mg m −3, the REs for butanone and toluene remained higher than 95% in both bioreactors regardless of the EBRT. The continuous supply of wastewater in the AS unit did not affect removal and appeared to be a requirement for efficient pollutant abatement. Despite the narrow carbon source spectrum treated, the AS system maintained a large bacterial diversity over time. Therefore, the results obtained confirmed the potential of AS systems as a robust and efficient biotechnology for odour treatment in WWTPs.