Absorbed Water Molecules Research Articles

Crystallographic Facet-Induced Toxicological Responses by Faceted Titanium Dioxide Nanocrystals.

Toxicological responses of nanomaterials have been closely correlated to their physicochemical properties, and establishment of a property-activity relationship of nanomaterials is favorable for a deep understanding of the nanomaterials' toxicity mechanism, prospectively predicting nanomaterials' potential hazards and rationally designing safer nanomaterials. Faceted nanomaterials usually exhibit more versatile and effective performance than spherical nanomaterials due to their selectively exposed crystallographic facets with high densities of unsaturated atoms. These facets have high surface reactivity, capable of eliciting strong interactions with biological systems. Few studies paid attention to the toxic behaviors of faceted nanomaterials in terms of their distinctive facets. In the present study, the toxicological role of the crystallographic facets of TiO2 nanomaterials was investigated, and the precise property-activity relationship was exploited to clearly understand the toxicity of faceted nanomaterials. A series of faceted TiO2 nanocrystals with the morphology of truncated octahedral bipyramids were prepared to expose different percentages of {101} and {001} facets on the surface. Density functional theory calculation revealed that {101} facets could only molecularly absorb water molecules while {001} facets due to their surface-unsaturated Ti atoms could dissociate the absorbed water molecules to generate hydroxyl radicals. Biophysical assessments corroborated the increased production of hydroxyl radicals on the {001} facets compared to {101} facets, which endowed {001} facets with strong hemolytic activity and elicited severe toxicities. A series of increased oxidative stress toxicological responses, including cellular ROS production, heme oxygenase-1 expression, cellular GSH depletion, and mitochondrial dysfunctions, were triggered by faceted TiO2 nanocrystals with progressively increased {001} percentages, demonstrating the toxicological roles of {001} facets.

Structural Changes of Gluten/Glycerol Plastics under Dry and Moist Conditions and during Tensile Tests

The structures of wheat gluten-based materials are greatly influenced by plasticizer content, moisture content, and external mechanical loading. In this study, the effects of moisture on the structure of wheat gluten (WG) plasticized by glycerol were investigated by using in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS), mechanical tensile testing, and thermal analyses. The materials were processed with additives of ammonium hydroxide/salicylic acid or urea and conditioned at 0, 50, and 100% relative humidity (RH). In general, water showed similar effects on the WG structure and mechanical properties regardless of the type of additive. It was observed that the known hexagonal close-packed (HCP) structure in WG was present mainly under moist conditions and swelled with an increase in water content. The absorbed water molecules hydrated the protein chains at 50% RH and further led to the formation of a separate water/glycerol phase at 100% RH. An interesting feature was observed by in situ SAXS during tensile deformation; both the HCP structure and other protein aggregates packed more densely in both the tensile and transverse directions. It is interpreted as follows: “randomly oriented” chains were drawn out and stretched in the tensile direction, which squeezes the self-assembled structures together, similar to “tightening a knot”.

Investigation of Traps at MoS2/Al2O3Interface in nMOSFETs by Low-Frequency Noise

A new method is proposed to distinguish the contributions of the low-frequency noise (LFN) from the channel and the source/drain Schottky contacts in MOS devices. The method is applied to back-gated nMOSFETs with MoS2 channel and Al2O3 gate dielectric. To avoid a possible noise signal contamination from the top MoS2 surface by oxygen or water molecules absorption, the nMOSFETs with multilayer MoS2 are fabricated, and the measurements are carried out in the vacuum. The trap density Not at the MoS2/Al2O3 interface is derived for the first time using the proposed method. It is found that the Not responsible to LFN depends strongly on the surface potential, ranging from $4\times 10^{10}$ cm $^{\mathrm {-2}}$ in the weak over-drive region to $5\times 10^{11}$ cm $^{\mathrm {-2}}$ in the strong over-drive region.

Heating of Nanosized Liquid Water in High-Intensity Terahertz Pulses**Supported by the National Natural Science Foundation of China under Grant Nos 10975033, 11404070 and 11275048, the Science Foundation for Youths of Guangxi Province under Grant No 2014GXNSFBA118022, and the Scientific Research Foundation of Guangxi Education Department under Grant No 2013ZD039.

Non-equilibrium molecular dynamics simulations of liquid water in picosecond high-power terahertz pulses are performed by using a non-polarizable potential model. Numerical results show that the energy absorption of water molecules exhibits a pronounced resonance with THz pulses in the frequency range of 14-17 THz. With the THz pulse at resonant frequencies, the maximum temperature is about 562K by heating the water at room temperature. Further investigation indicates that the results are independent of the size of the nanoscale water box. The efficiency of energy transfer by resonant absorption is more than seven times of microwave heating. These studies show promising applications of ultrashort THz pulses.

Absorptive Properties of PA6 as Drug Delivery Container

In order to check absorptive properties of PA6 and its ability to store molecules of different size and polarity, the absorption tests were performed. Since it is well known that PA6 absorbs water molecules, it was decided to test distilled water solutions of different substances with different particle size and polarity. Distilled water was taken as reference. Solutions of glucose with neutral large molecules and salt with small ions of calcium and chloride were prepared. Gravimetrically casted PA6 specimens were submerged into the solutions for 33 days, while their mass gain was measured. Presence of the molecules inside of the material was checked by Energy dispersive X-ray (EDS) and Proton Nuclear Magnetic Resonance (NMR) methods. Results showed that chlorine and sodium ions, as well as glucose molecules penetrated into the material. This means that it absorbs molecules of various polarity and size and can be considered as drug delivery container.

Predictive Model for Tensile Properties of Carbon Fiber-Reinforced Polymers at Various Moisture Contents

A model to estimate the tensile properties of carbon fiber-reinforced polymers (CFRP) based on their moisture contents and molecular structures is formulated and studied. In the proposed model, water molecules absorbed by polymers are considered congregated near the sub-micro-cavities within the polymers. The absorbed water molecules form hydrogen bonds with the polymer molecules and cause the regions around the sub-micro-cavities to have a reduced elastic modulus. The additive group contributions for polymers are used to determine the contributions of hydrophobic and hydrophilic functional groups separately. This enables the effects of water molecules on the mechanical properties of polymers to be quantified and estimated. For CFRP laminae, an additional effect of moisture on the fiber-matrix interface is considered in the calculation of the transverse tensile strength. The tensile properties are calculated using the proposed model agreed well with the experimental values. It is expected that the time and materials required to obtain the mechanical properties of CFRP exposed to humid environments can be reduced with the help of this model.

Sequestration of carbon dioxide – influence of coal surface chemistry

The physical gas adsorption is a widely used method for the characterisation of the solids porosity. The water steam, primarilydue to its physicochemical properties and ease of use in the experiment has great potential as a sorbate. When applied to coal, water steam allows to determine the quantity of primary adsorption centers as measurement of interaction of molecules adsorbed to the surface of the adsorbent. In order to determine the adsorption capacity and the chemical nature of the coal surface, adsorption / desorption of water vapour to the selected coals was examined at 303K, using a volumetric method. The presence of water in the coal may affect on the sorption properties of other molecules. The analysis of the results show that the coals of low rank and a high content of oxygen functional groups, which are the active sites, showed a greater affinity to absorbing water molecules. Adsorption isotherms were compiled through approximating the Langmuir and BET linear equation to measurement data. Based on the adsorption equation, the amount of adsorption centers have been specified, which can potentially be involved in the adsorption of CO2 during the injection of gas into the coal seams.

Parameters of broadening of water molecule absorption lines by argon pressure using different profile models

Parameters of broadening of water molecule absorption lines by argon pressure using different profile models

Preparation of activated carbon paper by a novel method and application as high-performance supercapacitors

In this paper, the commercial carbon papers were firstly treated by potassium dichromate lotion. Their surfaces became rougher and specific surface areas were enlarged. Accordingly, their surface hydrophilicity were enhanced due to the intake of hydrophilic groups such as hydroxyl (–OH), carbonyl (>C=O), and carboxyl (–COOH), and they act as strong polar sites to absorb water molecules. Supercapacitors were then constructed with the treated carbon paper as electrode and PVA-H3PO4 gel as electrolyte, and they provided high areal capacitances, high-rate capability, long-life cycle, and low resistance due to the synergistic effect of enlarged specific surface area and enhanced surface hydrophilicity.

Luminescence behavior of Eu3+ activated ZnO/SnO2 nanocomposite phosphor

Eu doped ZnO/SnO2 nanocomposite powder samples with different Eu3+ concentration (0.05–1.00wt%), were synthesized by low temperature co-precipitation method. Powder X-ray diffraction pattern confirmed the presence of both hexagonal ZnO and tetragonal SnO2 simultaneously. The crystallite size was estimated, using Debye Scherrer's method and Hall–Williamson method and it was found to be in the range of 5nm to 20nm. Formation of desired compound was further confirmed by Fourier Transform Infra-red spectrometer. FTIR spectra recognized the stretching mode of ZnO and SnO with the presence of stretching and bending vibration of absorbed water molecule (OH). The FESEM images revealed the nanosphere type structure of Eu3+ doped ZnO/SnO2 nanocomposite with a dimension of 50–70nm. The room temperature photoluminescence emission spectra shows about 5 times enhancement (compared to Eu doped ZnO and Eu doped SnO2) in the peak centered at 592nm for the transition 5D0→7F1, representative of magnetic dipole transition of Eu3+ ion. Other then this several emissions peaks are observed due to zinc, tin and oxygen related defects. The study shows that the Eu3+ doped nanocomposite is more suitable material than singly Eu doped ZnO and Eu doped SnO2 with enhanced opto-electronic and luminescence properties and great applications in display devices.

Unconventional Water Splitting Platforms

Renewable hydrogen has the potential to reshape our fossil fuel based energy infrastructure as it would allow the integration of a larger share of clean energy sources. Electrolysis of water is one of the most promising pathways toward clean hydrogen production. Although high efficiency electrolyzers are commercially available, their high cost has been a major obstacle for their large scale deployment. Design simplifications of these devices are necessary in order for clean hydrogen fuel to be deployed. Here, we demonstrate two proof-of-concept devices for water splitting which differ significantly from their conventional counterparts. The first one is a membrane-less electrolyzer which by balancing fluid mechanic forces manages to keep the produced oxygen and hydrogen gas streams separated as shown in Figure 1. This allows the system to operate without commonly required ion conductive membranes, and in this way could reduce the electrolyzer’s cost and enhance its efficiency. The second device absorbs water from humid ambient air streams in a Nafion thin-film as demonstrated in Figure 2. The absorbed water molecules split into hydrogen and oxygen streams which are later collected at independent collection ports. The design simplicity of this system makes it appropriate for solar powered hydrogen production since integration of photoactive components can be easily implemented. Currently, integration of photoelectrodes into these devices is underway. Large scale implementation of the membrane-less device is another ongoing effort.

Surface activation of carbon paper with potassium dichromate lotion and application as a supercapacitor

In this paper, an effective strategy using potassium dichromate lotion to activate surfaces of commercial carbon papers leading to enhanced electrochemical capacitances was reported. It is revealed that surfaces of activated carbon papers became rougher and their specific surface areas enlarged after treatment. Further, surface hydrophilicity of the treated carbon papers enhanced due to the generation of hydrophilic groups such as hydroxyl (–OH), carbonyl (〉CO) and carboxyl (–COOH) and they act as strong polar sites to absorb water molecules. With the synergistic effect of enlarged specific surface area and enhanced surface hydrophilicity, the activated carbon papers provide high areal capacitances. In general, this strategy offers a feasible pathway to make commercial carbon paper a promising candidate for practical supercapacitors and is expected to extend to other carbon based electrode materials.

Effects of Free Surface Evaporation on Water Nanodroplet Wetting Kinetics: A Molecular Dynamics Study

The wetting kinetics of a water nanodroplet undergoing evaporation on a heated gold substrate were examined using molecular dynamics (MD) simulations. Various substrate and initial droplet temperatures were used to obtain different evaporation rates. The water molecule absorption–desorption behavior was analyzed in the vicinity of the contact line region to show the microscopic details of the spreading–evaporating droplet. Increasing substrate temperatures greatly affected the dynamic wetting process, while the initial water droplet temperature had very little effect. The effects of droplet size and substrate wettability on the droplet spreading–evaporating process were also examined. The radius versus time curves agree well with molecular kinetics theory (MKT) for spreading without evaporation but differ from MKT when the spreading induced evaporation. The enhancement of the wetting kinetics by the evaporation can be attributed to the reduction of the liquid–vapor surface tension and the increased water molecule motion in the contact line region and in the bulk droplet.

Insulator-to-Proton-Conductor Transition in a Dense Metal-Organic Framework.

Metal-organic frameworks (MOFs) are prone to exhibit phase transitions under stimuli such as changes in pressure, temperature, or gas sorption because of their flexible and responsive structures. Here we report that a dense MOF, ((CH3)2NH2)2[Li2Zr(C2O4)4], exhibits an abrupt increase in proton conductivity from <10(-9) to 3.9 × 10(-5) S/cm at 17 °C (activation energy, 0.64 eV) upon exposure to humidity. The conductivities were determined using single crystals, and the structures were analyzed by X-ray diffraction and X-ray pair distribution function analysis. The initial anhydrous structure transforms to another dense structure via topotactic hydration (H2O/Zr = 0.5), wherein one-fourth of the Li ions are irreversibly rearranged and coordinated by water molecules. This structure further transforms into a third crystalline structure by water uptake (H2O/Zr = 4.0). The abrupt increase in conductivity is reversible and is associated with the latter reversible structure transformation. The H2O molecules coordinated to Li ions, which are formed in the first step of the transformation, are considered to be the proton source, and the absorbed water molecules, which are formed in the second step, are considered to be proton carriers.

New Flame-Retardant Composite Separators Based on Metal Hydroxides for Lithium-Ion Batteries

In order to enhance the thermal stability of conventional polyolefin separators, we propose a novel composite separator based on metal hydroxides. In particular, metal hydroxides not only function as a thermally stable mechanical matrix like alumina (Al2O3) or silica (SiO2) but also flame retardant due to their ability to release absorbed water molecules under some accidental conditions (e.g. higher than 200 oC). The flame-retardant composite separators are prepared by coating both sides of a microporous polyethylene (PE) membrane with nano-sized metal hydroxide (Al(OH)3 and Mg(OH)2) ceramic powders and poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP binder. Their physical properties are evaluated via scanning electronic microscopy (SEM) for surface morphology, the densometer to measure Gurley number (permeability), electrochemical impedance spectroscopy for ionic conductivity, and uptake amount of liquid electrolyte for wettability. In addition, the flame retardancy of composite separator is investigated by measuring the extinction time. Furthermore, the electrochemical properties of composite separators are evaluated with lithium-ion cells composed of a graphite anode and a LiCoO2 cathode. Comparing to bare separators, the composite separators show improved flame retardancy and rate performances due to water release property and better electrolyte wettability, respectively. Acknowledgement This research was financially supported by the Ministry of Education, Science and Technology (MEST) and National Research foundation (NRF) of Korea through the Human Resource Training Project for Regional Innovation (2014066977) and This research was financially supported by Chungcheong Leading Industry Promotion Project of the Korean Ministry of Trade(R0001485).

Manufacture of Water Vapour Filter Based on Natural Pahae Zeolite Used for Hydrogen Fueled Motor Cycle

Province of North Sumatera has been well known as a territory having multi kind of industrial minerals which have not been used and maintained properly and optimally. One of which is a natural Pahae zeolite derived from Tarutung, Tapanuli Utara-Indonesia. The objective of this research is to exploit Pahae zeolite to absorb water molecules flowing into the combustion chamber of a hydrogen fueled motorcycle. The generation of water molecules was as a result of water splitting process in water to hydrogen converter of the motorcycle. The grain size of Pahae zeolite was lessened up to 60 and 200 meshes which were then chemically activated by soaking with 30% KOH solution and calcination at a temperature of 300°C for 2 hours. The test results conducted on the intake pipe of combustion chamber showed that the particle size of 200 meshes had more absorption than that of 60 meshes. It was also found that type of Pahae zeolite had better absorption compared with Cikalong zeolite.

Effect of relative humidity and temperature on the gas transport properties of 6FDA–6FpDA polyimide: Experimental study and modelling

The transport of CO2, CH4, N2 and He in films of polyimide 6FDA–6FpDA was studied at different temperatures, from 25 to 45°C, and Relative Humidity (RH) from 0% to 90%. The permeability of all gases decreases with increasing RH, by factors as high as 44% for CH4 and 35% for the other gases; moreover, the relative decrease of gas permeability with respect to the dry polymer value is constant with temperature and just weakly dependent on the gas type.Pure water vapour sorption experiments were also conducted on the polymeric films in the same RH and temperature range, showing that water solubility in 6FDA–6FpDA is almost temperature-independent. A strong correlation therefore seems to exist between gas permeability decrease and water content in the membrane, due to the fact that absorbed water molecules occupy a portion of the polymer free volume, that is no longer available for gas permeation. Based on these considerations, the humid permeation results were analysed quantitatively and modelled with a simple approach based on free volume theory.

Characterization of graphene oxide nanofilms obtained by the SAW atomization

Due to its ability to absorb water molecules, graphene oxide (GO) is considered a promising material for sensitive coatings in fast surface acoustic wave (SAW) humidity sensors. In this work, we characterize GO films obtained by the SAW atomization technique. It is shown that the atomized submicroliter droplets of aqueous suspension of GO can be deposited onto the surface of Si, LiNbO3 or quartz substrates forming discrete or continuous films of nanometer thickness. The deposited films were examined using AFM and electron microscopy. We discuss the dependence of thickness and structure of the obtained GO films on the parameters of deposition: the number of atomized droplets, a volume of the initial droplet, a distance between the atomizer and the sample, etc. To evaluate the adsorption characteristics of the obtained GO films, we used them as sensitive coatings of the SAW humidity sensors. We found that the adsorption characteristics of the GO films are determined by fast adsorption on the surface of GO sheets and slow adsorption, attributed to limited penetration of water molecules between the sheets, and depend on the number of deposited layers.

A Study of Relative Humidity Fiber-Optic Sensors

A humidity sensor made of tapered plastic optical fiber (POF) coated with agarose gel or hydroxyethylcellulose/polyvinylidenefluoride (HEC/PVDF) detects humidity from the change in the refractive index (RI) of its coating. The RI of the deposited agarose gel or HEC/PVDF coating changes when it swells after absorbing water molecules from the surrounding. Similarly, when a tapered POF seeded with ZnO nanostructure is exposed to ambient humidity, a rapid surface adsorption of water molecules into the ZnO surface occurs. Therefore, the effective RI of its coating, which consists of the thin ZnO nanostrtucture and air, changes with humidity variation. For all of these sensors, the change in the RI of the coating affects the ability of the fiber to modulate light, thereby altering the output light intensity. In this paper, the performances of the three coating materials used with tapered fibers to construct humidity sensors are investigated. The results of the experiments show that agarose gel, HEC/PVDF, and ZnO-based optical fiber sensors are both sensitive and efficient for humidity sensing.

Enhanced environmental stability induced by effective polarization of a polar dielectric layer in a trilayer dielectric system of organic field-effect transistors: a quantitative study.

We report a concept fabrication method that helps to improve the performance and stability of copper phthalocyanine (CuPc) based organic field-effect transistors (OFETs) in ambient. The devices were fabricated using a trilayer dielectric system that contains a bilayer polymer dielectrics consisting of a hydrophobic thin layer of poly(methyl methacrylate) (PMMA) on poly(vinyl alcohol) (PVA) or poly(4-vinylphenol) (PVP) or polystyrene (PS) with Al2O3 as a third layer. We have explored the peculiarities in the device performance (i.e., superior performance under ambient humidity), which are caused due to the polarization of dipoles residing in the polar dielectric material. The anomalous behavior of the bias-stress measured under vacuum has been explained successfully by a stretched exponential function modified by adding a time dependent dipole polarization term. The OFET with a dielectric layer of PVA or PVP containing hydroxyl groups has shown enhanced characteristics and remains highly stable without any degradation even after 300 days in ambient with three times enhancement in carrier mobility (0.015 cm(2)·V(-1)·s(-1)) compared to vacuum. This has been attributed to the enhanced polarization of hydroxyl groups in the presence of absorbed water molecules at the CuPc/PMMA interface. In addition, a model has been proposed based on the polarization of hydroxyl groups to explain the enhanced stability in these devices. We believe that this general method using a trilayer dielectric system can be extended to fabricate other OFETs with materials that are known to show high performances under vacuum but degrade under ambient conditions.