Water Vapor Exposure Research Articles

P-Phenylenediaminium iodide capping agent enabled self-healing perovskite solar cell

In this study, p-Phenylenediaminium iodide (PDAI) is used to in-situ growth of 2D (PDA)2PbI4 perovskite layer between (FAPbI3)0.85(MAPbBr3)0.15 3D perovskite and CuSCN as a cheap hole transport layer. The results indicate that the incorporation of 5 mg mL−1 PDAI leads to enlarged grain sizes, compact grain boundaries, reduced trap density, efficient charge extraction, and enhanced stability of perovskite film. Passivation of perovskite film with the appropriate amount of PDAI helps in achieving efficient perovskite solar cell with a PCE as high as 16.10%, a JSC of 21.45 mA cm−2, a VOC of 1.09 V, and FF of 70.21%, with negligible hysteresis and excellent moisture stability which remains 99.01% of its initial PCE value after 5 h in high relative humidity of 90 ± 5% and shows unchanged PCE after 1440 h in low relative humidity of 15 ± 5%. Most strikingly, this ultra-thin 2D passivation layer by the use of PDA cations as a bulky spacer not only passivates the defects on the surface of perovskite film but also induces self-healing properties in PSCs which can be rapidly recovered after keeping away from water vapor exposure. This study introduces the cheap and extra stable perovskite solar cells with outstanding self-healing ability towards commercialization.

Influence of strain on SrFeO3-δ oxidation, reduction, and water dissociation: Insights from ambient pressure X-ray photoelectron spectroscopy

The oxidation and reduction of metal oxides and their interaction with the environment play a critical role in their use for energy storage and conversion applications. The formation of surface adsorbates and their impact on oxide electronic structure can be challenging to probe experimentally, particularly for thin films which enable the study of epitaxial strain but have low surface areas. Here we present a detailed study using ambient pressure X-ray photoelectron spectroscopy of the reduction and oxidation of strained SrFeO3-δ, induced by changes in temperature, oxygen partial pressure, and water vapor exposure. We find that in comparison to the oxidized lattice, application of tensile strain promotes the formation of oxygen vacancies at the surface, facilitating the subsequent incorporation of oxygen into the lattice in an oxygen environment. While tensile strain does promote the formation of hydroxyls from water dissociation, the kinetics of this process appear more sluggish than on less-strained surfaces, likely due to a competitive surface interaction with oxygen or bulk absorption of hydroxyl species. These findings relating strain, oxygen vacancies, and surface reactivity yield important insight into the surface functionality of oxides for energy conversion and storage applications.

Monitoring the Progress and Healing Status of Burn Wounds Using Infrared Spectroscopy.

Burns are one of the leading causes of morbidity worldwide and the most costly traumatic injuries. A better understanding of the molecular mechanisms in wound healing is required to accelerate tissue recovery and reduce the health economic impact. However, the standard techniques used to evaluate the biological events associated to wound repair are laborious, time-consuming, and/or require multiple assays/staining. Therefore, this study aims to evaluate the feasibility of Fourier transform infrared (FT-IR) spectroscopy to monitor the progress and healing status of burn wounds. Burn injuries were induced on Wistar rats by water vapor exposure and biopsied for further histopathological and spectroscopic evaluation at four time-points (3, 7, 14, and 21 days). Spectral data were preprocessed and compared by principal component analysis. Pairwise comparison of post-burn groups to each other revealed that metabolic activity induced by thermal injury decreases as the healing progresses. Higher amounts of carbohydrates, proteins, lipids, and nucleic acids were evidenced on days 3 and 7 compared to healthy skin and reduced amounts of these molecular structural units on days 14 and 21 post-burn. FT-IR spectroscopy was used to determine the healing status of a wound based on the biochemical information retained by spectral signatures in each phase of healing. Our findings demonstrate that FT-IR spectroscopy can monitor the biological events triggered by burn trauma as well as to detect the wound status including full recovery based on the spectral changes associated to the biochemical events in each phase.

CO2 capture properties of Li4SiO4 after aging in air at room temperature

In this study, we evaluated the physicochemical stability of lithium orthosilicate (Li4SiO4) powders after aging in air. Thermogravimetric (TG) analysis in CO2 flow evidences that as-milled Li4SiO4 stored in a closed plastic container in air at Room Temperature (RT) suffers a time progressive CO2 absorption. This carbonation is clearly noticed in the samples with greater specific surface area and depends on two factors: the time of air exposure and the renewal of the air atmosphere in the plastic container, both of them modifying the CO2 capture capacity and kinetics of the material. Specific experiments to analyze the effect of water vapor and carbon dioxide atmospheres on the CO2 capture properties of Li4SiO4 were designed. TG, X-ray diffraction and spectroscopic studies demonstrate that the reaction between as-milled Li4SiO4 and CO2 present in air was promoted by exposure to humidity. In fact, LiOH and LiOH.H2O were formed at the surface of Li4SiO4 during water vapor exposure. These phases enhance the reaction with CO2 from the air to form Li2CO3 at RT before the first carbonation cycle. As a consequence, the CO2 capture capacity of Li4SiO4 in the first carbonation cycle was smaller than the one of Li4SiO4 without water vapor exposure. In opposition, negligible CO2 absorption occurred at RT under CO2 atmosphere. The original properties of Li4SiO4 powders with high specific surface area could be regenerated by heating at 700 °C. Consequently, the storage conditions of Li4SiO4 powders should be considered for their use in different applications.

Water vapor-induced structure modification of vertically-aligned carbon nanotube arrays and successive thin film coating for enhanced field emission properties

Vertically-aligned carbon nanotubes (VCNTs) are used as electron source in various field emission applications owing to its high aspect ratio, chemical inertness, mechanical strength and electrical conductivity. Here, we demonstrate that surface structure modification along with thin film coating enhances the field emission performance, such as turn-on voltage, emission site density, and stability. In the present study, VCNTs with different heights were grown on silicon wafers by thermal chemical vapor deposition followed by the structure modification of VCNTs using capillarity-driven water vapor condensation. We obtained various surface morphologies by varying the water vapor exposure time and heating temperature. In addition, the structure-modified VCNTs surfaces were coated with W and SiO2 thin films using electron-beam evaporation. It was observed that W-coated VCNTs with modified surface morphology results in the best field emission performance.

Stability of the Y2O3–SiO2 system in high‐temperature, high‐velocity water vapor

AbstractHigh‐temperature, high‐velocity water vapor (steam‐jet) exposures were conducted on Y2O3, Y2SiO5, Y2Si2O7, and SiO2 for 60 hours at 1400°C. Volatility of Y2O3 was not observed. Phase‐pure Y2SiO5 exhibited SiO2 loss forming Y2O3 and porosity. A mixed porous and dense Y2SiO5 layer formed on the surface of Y2Si2O7 due to SiO2 depletion. The mechanisms and kinetics of the reaction between SiO2 and H2O(g) to form Si(OH)4(g) from Y2SiO5, Y2Si2O7, and SiO2 are discussed.

Devising Chemically Robust and Cationic Ni(II)-MOF with Nitrogen-Rich Micropores for Moisture-Tolerant CO2 Capture: Highly Regenerative and Ultrafast Colorimetric Sensor for TNP and Multiple Oxo-Anions in Water with Theoretical Revelation.

Metal-organic frameworks (MOFs) show distinctive superiority for carbon dioxide (CO2) capture and luminescent sensing of toxic pollutants over other materials, where combination of both of these properties together with improvement of hydrolytic stability and pore functionality is critical to environmental remediation applications. The Ni(II) framework [Ni2(μ2-OH)(azdc)(tpim)](NO3)·6DMA·6MeOH (CSMCRI-3) (tpim = 4,4',4″-(1H-imidazole-2,4,5-triyl)tripyridine, H2azdc = azobenzene-4,4'-dicarboxylic acid, DMA = dimethylacetamide, CSMCRI = Central Salt & Marine Chemicals Research Institute), encompassing cationic [Ni2(μ2-OH)(CO2)2] SBUs, is solvothermally synthesized from nitrogen-rich and highly fluorescent organic struts. The noninterpenetrated structure, containing free nitrogen atom affixed microporous channels, is stable in diverse organic solvents and weakly basic and acidic aqueous solutions. The activated MOF (3a) exhibits strong CO2-framework interaction and extremely selective CO2 adsorption over N2 (292.5) and CH4 (11.7). Importantly, water vapor exposure does not affect the surface area and/or multiple CO2 uptake-release cycles, signifying potential of the porous structure for long-term use under humid conditions. Aqueous-phase sensing studies illustrate extremely specific and ultrafast detection of explosive 2,4,6-trinitrophenol (TNP) via remarkable fluorescence quenching (KSV = 1.3 × 105 M-1), with a 0.25 ppm limit of detection (LOD). Furthermore, 3a serves as unique luminescent probe for highly discriminative and quick responsive detection of three noxious oxo-anions (Cr2O72-, CrO42-, MnO4-) in water via noteworthy turn-off responses and extreme low LODs (Cr2O72- 0.9; CrO42- 0.29; MnO4- 0.25 ppm). It is imperative to stress the outstanding reusability of the MOF toward multicyclic sensing of all four major water contaminants, alongside visible colorimetric changes upon individual analyte detection. Mechanistic insights in light of the electron transfer route together with density functional theory calculations portray the influence of pore functionalization in framework-analyte interactions, including alternation in energy levels, where varying degrees of contribution of energy transfer explicitly authenticates high quenching of the material.

Nanopatterned evanescent-field fiber-optic interferometer as a versatile platform for gas sensing

We introduced a nanopatterned fiber-optic interferometer (FOI) based on an optical fiber line embedded with a short capillary which excites the evanescent field by total reflection of light in the wall waveguide interacting with the fluid and causing the optical signal change. As modal interference was generated with near-infrared light in the tube wall, we detected a reversible wavelength shifts of the proposed FOI in the interference fringe upon water vapor exposure by using an optical fiber interrogator. We also deposited a patterned palladium (Pd) nanoparticle film on the outer surface of the FOI by using self-assembly microspheres as a template and detected the reaction of the Pd membrane with hydrogen through monitoring the wavelength shifts of interference fringes. The Pd nanoparticle restrained the fiber stress response caused by hydrogen-induced expansion of the Pd film, and theoretically helped to improve the evaluation accuracy of the Pd permittivity in hydrogen. In addition, the nanoparticle-coated FOI with asymmetric structure could serve as a Mach-Zehnder interferometer (MZI) for fast hydrogen sensing and air refractive index measurement. Considering sensitivity and detector parameters, the FOI could provide a high resolution up to 7.57 × 10−7 RIU.

Compositional and Morphological Changes in Water-Induced Early-Stage Degradation in Lead Halide Perovskites

With tremendous improvements in lead halide perovskite-based optoelectronic devices ranging from photovoltaics to light-emitting diodes, the instability problem stands as the primary challenge in their development. Among all factors, water is considered as one of the major culprits to the degradation of halide perovskite materials. For example, CH3NH3PbI3 (MAPbI3) and CH(NH2)2PbI3 (FAPbI3) decompose into PbI2 in days under ambient conditions. However, the intermediate changes of this degradation process are still not fully understood, especially the changes in early stage. Here we perform an in-situ investigation of the early-stage MAPbI3 and FAPbI3 degradation under high water vapor pressure. By probing the surface and bulk of perovskite samples using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and XRD, our findings clearly show that PbI2 formation surprisingly initiates below the top surface or at grain boundaries, thus offering no protection as a water-blocking layer on surface or grain boundaries to slow down the degradation process. Meanwhile, significant morphological changes are observed in both samples after water vapor exposure. In comparison, the integrity of MAPbI3 film degrades much faster than the FAPbI3 film against water vapor. Pinholes and large voids are found in MAPbI3 film while only small number of pinholes can be found in FAPbI3 film. However, the FAPbI3 film suffers from its phase instability, showing a fast α-to-δ phase transition. Our results highlight the importance of the compositional and morphological changes in the early stage degradation in perovskite materials.

Aligned Proton‐Conducting Graphene Sheets via Block Copolymer Supramolecular Assembly and Their Application for Highly Transparent Moisture‐Sensing Conductive Coating

AbstractHere, we have demonstrated a well‐defined strategy to prepare highly sulphonated reduced graphene oxide (S‐rGO) sheets via non‐covalent modification of rGO with water soluble rod‐coil conjugated block copolymer poly(3‐hexylthiophene)‐block‐poly(4‐styrenesulfonic acid) (P3HT‐b‐PSSA) carrying a long PSSA block. S‐rGO sheets are highly water soluble and its aqueous solution can be used to fabricate highly transparent conductive thin film coating on versatile smooth substrate surfaces like glass, indium tin oxide (ITO), quartz and flexible PET. The successful anchoring of sulfonic acid group on rGO surface via non‐covalent modification by P3HT‐b‐PSSA was confirmed and analyzed by FTIR and XRD study. The bulk morphology of S‐rGO reveals sheet like morphology where individual sheets are aligned with each other in a parallel arrangement through intercalation of PSSA chains driven by block copolymer self‐ assembly. AFM image of the thin film also supports nice parallel alignment of S‐rGO sheets of average thickness ∼100 nm on substrate surface. S‐rGO sample shows very high water uptake (∼91% in comparison to its initial weight) and proton conductivity 0.5 S/cm after water vapor exposure for 1 hour. Such high proton conductivity is due to the synergy of alignment of graphene sheets with a continuous network of proton conducting nanochannels created by block copolymer microphase separation on the rGO surface. Nyquist plot with two semicircles suggested the presence of grain boundaries in the sample. I−V measurement of transparent thin film device fabricated from S‐rGO sheets shows linear behavior with systematic increase of current on increasing water vapor exposure time. The block copolymer device shows well correlated, systematic and reversible resistance change with relative humidity (RH) confirming its efficient sensing capability towards moisture. We believe that high proton conductivity and interesting, reversible moisture sensitive electrical property of this material will be useful in fabricating transparent and flexible moisture sensors, flexible electronics, moisture induced energy storage, fuel cell, biological applications and others.

Water vapor exposure chamber for constant humidity and hydrogen and oxygen stable isotope composition.

Water vapor exposure experiments have applications for studying water physisorption and chemisorption hydration and hydroxylation reactions on a wide variety of material surfaces. The stable isotopes of hydrogen and oxygen in the water molecule are useful tracers of water exchange mechanisms and/or rates in such vapor exposure experiments. We designed and built a humidity chamber system that uses membrane-mediated liquid-vapor exchange of water followed by mixing with dry air to control the relative humidity of air and its δ2 H and δ18 O isotopic composition. We tested the stability and precision of the humidity and its isotopic composition on hourly to 90-day timescales. The humidity chamber design reported here is capable of providing relative humidity control to within ±1%, and consistent δ2 H and δ18 O values of the water vapor that are similar to our cavity ringdown spectroscopy (CRDS) measurement precision (δ2 Hvap ± 0.7‰ and δ18 Ovap ± 0.24‰). We quantify the isotopic enrichment effects of Rayleigh distillation in the system and provide information on water reservoir sizes large enough to buffer isotopic enrichment effects to within measurement precision. The humidity chamber design reported here provides a means to create constant δ2 H and δ18 O values over the course of an exposure experiment. The design has applications to a wide range of studies of water sorption on material surfaces from foods and pharmaceuticals to geological materials.

Morphology and Buckling of the Oxide Scale after Fe–9Cr Steel Oxidation in Water Vapor Environment

Under water vapor exposure at 550–560 °C, Fe–9Cr ferritic–martensitic steels form a triplex oxide scale made of an outer magnetite layer surrounded by a hematite layer and an inner Fe–Cr spinel layer. Long-time oxidation tests have been performed to study scale degradation with time. It revealed that buckling and spallation of the oxide scale always occurred during isothermal oxidation or during cooling down to room temperature. The interfacial zone of delamination has been proved to be located inside the magnetite layer, where a voids belt is formed and grows. It is assumed that voids are the preponderant factor initiating delamination of the magnetite layer under compressive stresses during the oxide scale growth. A mechanism of accumulation of vacancies leading to voids formation and then to the spallation of the outer oxide scale is proposed.

The atypically high modulus of pollen exine

Sporopollenin, the polymer comprising the exine (outer solid shell) of pollen, is recognized as one of the most chemically and mechanically stable naturally occurring organic substances. The elastic modulus of sporopollenin is of great importance to understanding the adhesion, transport and protective functions of pollen grains. In addition, this fundamental mechanical property is of significant interest in using pollen exine as a material for drug delivery, reinforcing fillers, sensors and adhesives. Yet, the literature reports of the elastic modulus of sporopollenin are very limited. We provide the first report of the elastic modulus of sporopollenin from direct indentation of pollen particles of three plant species: ragweed (Ambrosia artemisiifolia), pecan (Carya illinoinensis) and Kentucky bluegrass (Poa pratensis). The modulus was determined with atomic force microscopy by using direct nanomechanical mapping of the pollen shell surface. The moduli were atypically high for non-crystalline organic biomaterials, with average values of 16 ± 2.5 GPa (ragweed), 9.5 ± 2.3 GPa (pecan) and 16 ± 4.0 GPa (Kentucky bluegrass). The amorphous pollen exine has a modulus exceeding known non-crystalline biomaterials, such as lignin (6.7 GPa) and actin (1.8 GPa). In addition to native pollen, we have investigated the effects of exposure to a common preparative base-acid chemical treatment and elevated humidity on the modulus. Base-acid treatment reduced the ragweed modulus by up to 58% and water vapour exposure at 90% relative humidity reduced the modulus by 54% (pecan) and 72% (Kentucky bluegrass). These results are in agreement with recently published estimates of the modulus of base-acid-treated ragweed pollen of 8 GPa from fitting to mechanical properties of ragweed pollen-epoxy composites.

Synthesis of a Scalable Two-Dimensional Covalent Organic Framework by the Photon-Assisted Imine Condensation Reaction on the Water Surface.

An atomically thin two-dimensional (2D) covalent organic framework (COF) was successfully synthesized via the photon-assisted imine condensation reaction within 1 h from the highly uniform and homogeneous precursor solution layer floating on the water surface. The polarity optimization of the precursor solution was the key step for the successful formation of the high-quality 2D COF because only the precursor solution consisting of polarity-controlled solvents allows ideal floating on the water surface. The polarity-controlled solution not only prohibits the agglomeration of the organic precursors on the water surface but also facilitates the wafer scale and layer number-controllable synthesis of the 2D COF. The resulting 2D COF has a uniform porous structure and highly oriented layered structure along the out-of-plane direction as observed by microscopy analysis and X-ray diffraction, respectively. In addition, we successfully fabricated field effect transistor type polyimine-based COF (pi-COF) electronic devices to demonstrate the prompt electrical responses to photo-exposure and water vapor exposure, suggesting the potential applications of the pi-COF in electrical photodetector or moisture-detector devices.

Resonant Gas Sensor and Switch Operating in Air With Metal-Organic Frameworks Coating

We demonstrate a resonant gas sensor uniformly coated with a metal-organic framework (MOF) and excited near the second vibration mode for enhanced sensitivity. The possibility of realizing a smart switch triggered upon exceeding a threshold mass is demonstrated when operating the resonator near the dynamic pull-in instability. The resonator is based on an electrostatically excited clamped–clamped microbeam. The microbeam is fabricated from a polyimide layer coated from top with Cr/Au and from bottom with Cr/Au/Cr layer. The geometry of the resonator is optimized to reduce the effect of squeeze film damping, thereby allowing operation under atmospheric pressure. The electrostatic electrode is designed to enhance the excitation of the second mode of vibration with the minimum power required. Significant frequency shift in kilohertz is demonstrated for the first time upon water, acetone, and ethanol vapor exposure due to the MOF functionalization and the higher order mode excitation. The adsorption dynamics and MOF selectivity are investigated by studying the decaying time constants of the response upon gas exposure. [2017–0218]

Complete methane oxidation over Ba modified Pd/Al2O3: The effect of water vapor

The effect on complete methane (CH4) oxidation activity by an addition of up to 2 wt.% barium (Ba) promoter to alumina supported palladium (Pd/Al2O3, 2 wt.% Pd) was investigated. The catalyst samples were characterized with various techniques; temperature programmed oxidation (TPO), temperature programmed reduction with CH4 (CH4-TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). Flow reactor was used to investigate the CH4 oxidation activity in the presence and in the absence of water vapor and also to evaluate the possibility to regenerate the catalytic activity after water vapor exposure. The results from the TPO and the CH4-TPR experiments together with the XPS analysis gave no evidences for electronic promotion of the catalytic activity by addition of 0.5–2 wt.% Ba. This goes in line with the CH4 conversion in dry gas condition, which was not affected by the Ba addition. However, we observed that an addition of Ba to Pd/Al2O3 enhances the CH4 oxidation activity in the presence of water vapor, hence mitigates the effect of water deactivation. Interestingly, it was also seen that after water vapor exposure, the CH4 oxidation activity could be regenerated to greater extent for the Ba promoted samples, particularly for the regeneration temperatures of 500–600 °C. Our results clearly show that the support influences the water deactivation of the active palladium sites and that the addition of barium is beneficial for the catalyst regeneration.

Construction of Pillar-Layer Metal–Organic Frameworks for CO2 Adsorption under Humid Climate: High Selectivity and Sensitive Detection of Picric Acid in Water

Adsorption of CO2 under humid conditions is important, as flue gases contain some degree of moisture, while aqueous-phase sensing of nitro-aromatic compounds is critical for environmental protection and anti-terrorism activities. However, implementing both of these aspects in metal–organic frameworks (MOFs) is rare and challenging due to their moisture instability. To this end, we prepared three isostructural, pillar-layer Zn(II) MOFs where criss-cross pillaring by the linkers tunes the pore opening and pore electronic environment that in turn modulate thermal and/or moisture stabilities. While activated 2 (2′), incorporating an azo group in the linker, exhibits excellent CO2/N2 selectivity (>200), 1′, containing a 4,4′-bipyridine linker displays superior hydrolytic stability with minimum loss in CO2 adsorption–desorption cycles up to 10 days of water vapor exposure. However, framework 3, with a bis(4-pyridyl)ethylene linker, is unstable. Importantly, aqueous-phase sensitive detection of picric acid (PA) ...

Thermal Cycling and High-Temperature Corrosion Tests of Rare Earth Silicate Environmental Barrier Coatings

Lutetium and yttrium silicates, enriched with an additional secondary zirconia phase, environmental barrier coatings were synthesized by the solution precursor plasma spraying process on silicon carbide substrates. A custom-made oven was designed for thermal cycling and water vapor corrosion testing. The oven can test four specimens simultaneously and allows to evaluate environmental barrier performances under similar corrosion kinetics compared to turbine engines. Coatings structural evolution has been observed by SEM on the polished cross sections, and phase composition has been analyzed by XRD. All coatings have been thermally cycled between 1300 °C and the ambient temperature, without spallation, due to their porosity and the presence of additional secondary phase which increases the thermal cycling resistance. During water vapor exposure at 1200 °C, rare earth disilicates showed a good stability, which is contradictory with the literature, due to impurities—such as Si- and Al-hydroxides—in the water vapor jets. The presence of vertical cracks allowed the water vapor to reach the substrate and then to corrode it. It has been observed that thin vertical cracks induced some spallation after 24 h of corrosion.

New Application of Chitosan Film as a Water Vapor Cell

This study is aimed at finding a new application of chitosan film in energy conversion material. A water vapor cell in a single chip form which consists of chitosan film on the top layer, patterned gold layer in the middle and isolator substrate in the bottom layer was manufactured and used to convert water vapor into electrical power by direct chemical interaction. When the water vapor was exposed onto chitosan film surface, the chitosan film resistance changed and as a consequence, the output voltage and current could be measured. The electrical power was significantly increased by combining several cells, namely twenty cells in series, twenty cells in parallel, twenty cells in series-parallel and twenty cells in parallel-series. It was found that twenty cells in series have the highest electrical power. Furthermore, the lifetime of a water vapor cell under water vapor exposure maintained until eight months. Therefore, chitosan film has evidenced a huge potential as energy conversion material to produce a water vapor panel in future.

Permanent water swelling effect in low temperature thermally reduced graphene oxide

We demonstrate permanent water trapping in reduced graphene oxide after high relative humidity exposure. For this purpose, we grew graphene oxide films via spin-coating on glass substrates followed by thermal reduction. The electrical resistance of the planar device was then measured. We observed that resistance is significantly increased after water vapor exposure and remains stable even after 250 days in ambient conditions. Various techniques were applied to desorb the water and decrease (recover) the material's resistance, but it was achieved only with low temperature thermal annealing (180 °C) under forming gas (H2/N2 mixture). The permanent effect of water absorption was also detected by x-ray photoelectron spectroscopy.