Wettability conversion on the liquid flame spray generated superhydrophobic TiO2 nanoparticle coating on paper and board by photocatalytic decomposition of spontaneously accumulated carbonaceous overlayer

Titanium dioxide (TiO₂) is a photoactive material with various interesting and useful properties. One of those is the perfect wettability of TiO₂ surface after ultraviolet (UV) illumination. Wettability of a solid surface plays an important role in the field of printing, coating, and adhesion among others. Here we report on a superhydrophobic and photoactive liquid flame spray (LFS) generated TiO₂ nanoparticle coating that can be applied on web-like materials such as paper and board in one-step roll-to-roll process. The LFS TiO₂ nanoparticle coated paper and board were superhydrophobic instantly after the coating procedure because of spontaneously accumulated carbonaceous overlayer on TiO₂, and thus there was no need for any type of separate hydrophobization treatment. The highly photoactive LFS TiO₂ nanoparticle coating could be converted steplessly from superhydrophobic to superhydrophilic by UV-illumination, and the coating gave strong response to natural daylight illumination even in the shade. The superhydrophobic LFS TiO₂ coated surface can be used as an intelligent substrate, where photo-generated hydrophilic patterns guide the fluid setting and figure formation. Our study reveals that the wettability changes on the LFS TiO₂ surface were primarily caused by the photocatalytic removal of the carbonaceous material from TiO₂ during the UV-illumination and spontaneous accumulation of the carbonaceous material on the surface of the metal oxide during storage in the dark. The latter mechanism was found to be a temperature activated process which could be significantly speeded up by heat treatment. If other mechanisms such as surface oxidization, increment of hydroxyl groups, or charge separation played a role in the wetting phenomena on TiO₂, their effect was rather secondary as the removal and accumulation of the carbonaceous material dominated the wettability changes on the surface. Our study gives valuable information on the complex issue of photo-induced wettability changes on TiO₂.     

Switchable solvent based liquid phase microextraction of palladium coupled with determination by flame atomic absorption spectrometry

A switchable solvent-based micro-extraction method for pre-concentration and separation of ultratrace palladium was developed prior to its flame atomic absorption spectrometric detection. Reverse change of hydrophilicity of N,N-dimethylcyclohexylamine (DMA) was achieved by reaction with carbonated water. The hydrophilic bicarbonate salt of the protonated DMA was used as extractant for palladium complexed with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). Formation of the hydrophobic form of switchable solvent from hydrophilic form of switchable solvent phase was achieved by addition of sodium hydroxide into the extractant-sample solution. The effect of key parameters affected extraction recovery was studied and optimised by using Plackett–Burman design, central composite design and three dimension (3D) surfaces response. The calibration plot was linear in the range 0.015–1.6 mg L^?1 of palladium with a correlation coefficient of 0.999. The limit of detections values of palladium for liquid and solid samples were 4.28 μg L^?1 and 0.54 µg g^?1, respectively. The pre-concentration factor was 37.5. The accuracy was confirmed by determination of palladium in certified reference material. The procedure was also applied for determination of palladium content of real samples as automotive catalytic converter, roadside dust, sea water and river water.     

Polymeric coacervate coating for flame retardant paper

Cellulose - Cellulosic paper (from wood fibers) is a highly flammable material that is used in corrugated carboard, packaging, printing, and construction. While there is significant work focused on...     

X-ray absorption spectroscopy measurements of liquid water

Recent studies, based on X-ray absorption spectroscopy (XAS) and X-ray Raman scattering (XRS), have shown that the hydrogen bond network in liquid water consists mainly of water molecules with only two strong hydrogen bonds. Since this result is controversial, it is important to demonstrate the reliability of the experimental data, which is the purpose of this paper. Here we compare X-ray absorption spectra of liquid water recorded with five very different techniques sensitive to the local environment of the absorbing molecule. Overall, the spectra obtained with photon detection show a very close similarity and even the observable minor differences can be understood. The comparison demonstrates that XAS and XRS can indeed be applied reliably to study the local bonding of the water molecule and thus to reveal the hydrogen bond situation in bulk water.     

Control of the water adhesion on hydrophobic micropillars by spray coating technique

We present an alternative approach for controlling the water adhesion on solid superhydrophobic surfaces by varying their coverage with a spray coating technique. In particular, micro-, submicro-, and nanorough surfaces were developed starting from photolithographically tailored SU-8 micropillars that were used as substrates for spraying first poly(tetrafluoroethylene) submicrometer particles and subsequently iron oxide nanoparticles. The sprayed particles serve to induce surface submicrometer and nanoscale roughness, rendering the SU-8 patterns superhydrophobic (apparent contact angle values of more than 150°), and also to tune the water adhesion between extreme states, turning the surfaces from “non-sticky” to “sticky” while preserving their superhydrophobicity. The influence of the chemical properties and of the geometrical characteristics of the functionalized surfaces on the wetting properties is discussed within the frame of the theory. This simple method can find various applications in the fabrication of microfluidic devices, smart surfaces, and biotechnological and antifouling materials.     

Indirect flame atomic absorption detection for the liquid chromatographic separation of alkaline metals

Alkaline metals and ammonium ion are separated by cationic exchange liquid chromatography using a 60 g ml^–1 aqueous copper solution as the mobile phase at 1.5 ml min^–1. Detection is carried out by measuring copper with an atomic absorption spectrometer directly interfaced to the chromatograph. A simple T-piece is used to compensate the difference between the nebulizer uptake rate and the chromatographic flow-rate with air. The method is applicable to the analysis of alkaline metals and ammonium in waters. Average recovery (n = 16) was 100.3 ± 4.0%.     

Switchable mirrors of chiral liquid crystal gels

Chiral nematic liquid crystal compositions containing mono- and di-acrylates in mixtures with non-reactive liquid crystal molecules were produced. Defect-free planar macroscopic alignment of the molecules was induced between uniaxially rubbed substrates. Polymerization of the acrylate groups was initiated photochemically leading to the formation of a new class of chiral gels consisting of a lightly cross-linked network containing non-reactive molecules. In this way, the chiral pitch and, hence, the reflection colour became permanently fixed. Under the influence of an electric field the gels could be switched to the homeotropic state and reverted to the planar defect-free state upon removal of the electric field. Depending on the composition of the gel, either the position of the reflection band remained the same while its magnitude and/or width decreased, or its position shifted to smaller wavelengths with increasing electric field. Some of the gels showed sharp switching characteristics with a hysteresis making them suitable for passive matrix addressing with a high degree of multiplexability. The gels also showed fast switching times as they reverted to the defect-free optical state upon removal of the electric field. The phase structure of the gels was studied using dielectric spectroscopy which showed that the gels have an inhomogeneous structure.     

Indirect flame atomic absorption detection for the liquid chromatographic separation of alkaline metals

Alkaline metals and ammonium ion are separated by cationic exchange liquid chromatography using a 60 microg ml(-1) aqueous copper solution as the mobile phase at 1.5 ml min(-1). Detection is carried out by measuring copper with an atomic absorption spectrometer directly interfaced to the chromatograph. A simple T-piece is used to compensate the difference between the nebulizer uptake rate and the chromatographic flow-rate with air. The method is applicable to the analysis of alkaline metals and ammonium in waters. Average recovery ( n = 16) was 100.3 +/- 4.0%.     

Use of paper capsules for cadmium determination in biological samples by solid sampling flame atomic absorption spectrometry

In this study, a new device was applied for direct solid sampling flame atomic absorption spectrometry. It was used for trace determination of cadmium in biological samples (bovine and chicken liver). Test samples (0.5 to 7 mg) were weighed into small paper capsules, which were introduced into a quartz cell heated by an air-acetylene flame. Operational conditions for the proposed system were evaluated. There was no significant difference between the results obtained with the proposed system and those obtained after digestion and determination by conventional graphite furnace atomic absorption spectrometry. Good agreement was also obtained with the certified values of two reference materials. Background signals were always low. The characteristic mass was 0.34 ng and relative standard deviation was less than 8%. The limit of detection for the proposed procedure was 1.6 ng or 0.23 μg g^− 1 if a sample mass of 7 mg was used. Excluding the steps for sample preparation (drying, milling and weighing), the proposed system allows the determination of 40 test samples per hour and it can be easily adapted to conventional flame atomic absorption spectrometers.     

Thermospray nebulization for flame furnace atomic absorption spectrometry — Correlations between spray formation and cadmium analytical sensitivity

Some parameters which influence thermospray formation at low flow rate used in thermospray flame furnace atomic absorption spectrometry were systematically evaluated using spray morphology (through high-speed images acquisition) and Cd determination (used as an analytical probe). A correlation was observed between Cd sensitivity and the Sauter mean diameter of droplets of the spray introduced into the furnace. The SMD was calculated according to the empiric equation proposed by Elkotb and some physical properties of the carriers were used. Among the parameters studied, the most important is the total area of the inlets of flame gases (bottom holes of the nickel atomizer tube), since Cd sensitivity was drastically reduced when this area was increased. Another important parameter is the chemical nature of the carrier solution, which affects the pulse rate of the thermospray. The average rates measured for the different carriers were 320 ± 50, 290 ± 50 and 60 ± 20 pulses/s for water, 0.9 mmol L^− 1 Triton^® X-100 and 44% (w/w) acetonitrile, respectively. Cadmium determinations were performed in certified reference materials using different carrier solutions, and accurate determinations were attained with the use of four carrier liquids (water, 1.4 mol L^− 1 nitric acid, 0.6 mol L^− 1 hydrochloric acid, 8% (w/w) ethanol).     

Emulsification based dispersive liquid microextraction prior to flame atomic absorption spectrometry for the sensitive determination of Cd(II) in water samples

We report on the application of emulsification-based dispersive liquid microextraction (EB-DLME) to the preconcentration of Cd(II). This procedure not only possesses all the advantages of routine DLLME, but also results in a more stable cloudy state which is particularly useful when coupling it to FAAS. In EB-DLME, appropriate amounts of the extraction solvent (a solution of dithizone in chloroform) and an aqueous solution of sodium dodecyl sulfate (SDS; acting as a disperser) are injected into the samples. A stable cloudy microemulsion is formed and Cd(II) ion is extracted by chelation. After phase separation, the sedimented phase is subjected to FAAS. Under optimized conditions, the calibration curve for Cd(II) is linear in the range from 0.1 to 25 μg L^?1, the limit of detection (at S/N?=?3) is 30 pg L^?1, the relative standard deviations for seven replicate analyses (at 0.56 μg L^?1 of Cd(II)) is 4.6 %, and the enrichment factor is 151. EB-DLME in our opinion is a simple, efficient and rapid method for the preconcentration of Cd(II) (and most likely of many other ions) prior to FAAS determination.

Determination of lithium in sea water by atomic absorption and by flame emission spectrophotometry

Summary Comparison of two instrumental methods for the analysis of lithium in sea water showed that both atomic absorption and flame emission spectrophotometry can be used without pretreatment of the sample. The interference of the other constituents of sea water in the analysis has been studied. Calibrations using an artificial sea water or the standard addition method may be used.

---

Zusammenfassung Ein Vergleich der beiden Methoden hat gezeigt, daß zur Analyse von Lithium im Meerwasser sowohl die Atomabsorptionsspektrophotometrie, als auch die Flammenspektrophotometrie ohne Vorbehandlung der Probe angewendet werden können. Der Einfluß der anderen Bestandteile des Meerwassers auf die Analyse wurde untersucht. Für die Eichung des Verfahrens wurde künstliches Meerwasser sowie die Methode des Standardzusatzes verwendet.

     

Theoretical modeling and interpretation of X-ray absorption spectra of liquid water

We report extensive calculations to examine the capability of theory to explain the XAS spectra of liquid water. Several aspects that enter the theoretical model are addressed, such as the quantum mechanical methods, the statistics and the XAS model. As input into our quantum mechanical calculations we will use structural information on liquid water obtained from first principles and from classical molecular dynamics simulations. As XAS models, we will examine the full core hole and the half core hole approximations to transition state theory. The quantum mechanics is performed on the basis of density functional theory. We conclude from this study that recent experimental results are fully consistent with, and can be completely explained by, present day theory, in particular, the pre-edge peak is reproduced. We also find that the average bond coordination in liquid water is 3.1 and that the assertion in a recent paper that the hydrogen bond number is much less than that cannot be substantiated. Our calculations emphasize that further advances in our understanding of water can only be made by more sophisticated spectroscopy with significantly increased resolution.     

Probing the local structure of liquid water by X-ray absorption spectroscopy

It was recently suggested that liquid water primarily comprises hydrogen-bonded rings and chains, as opposed to the traditionally accepted locally tetrahedral structure (Wernet et al. Science 2004, 304, 995). This controversial conclusion was primarily based on comparison between experimental and calculated X-ray absorption spectra (XAS) using computer-generated ice-like 11-molecule clusters. Here we present calculations which conclusively show that when hydrogen-bonding configurations are chosen randomly, the calculated XAS does not reproduce the experimental XAS regardless of the bonding model employed (i.e., rings and chains vs tetrahedral). Furthermore, we also present an analysis of a recently introduced asymmetric water potential (Soper, A. K. J. Phys.: Condens. Matter 2005, 17, S3273), which is representative of the rings and chains structure, and make comparisons with the standard SPC/E potential, which represents the locally tetrahedral structure. We find that the calculated XAS from both potentials is inconsistent with the experimental XAS. However, we also show the calculated electric field distribution from the rings and chains structure is strongly bimodal and highly inconsistent with the experimental Raman spectrum, thus casting serious doubt on the validity of the rings and chains model for liquid water.     

Determination of manganese in water samples by flame atomic absorption spectrometry after cloud point extraction

Cloud point extraction has been used for the preconcentration of manganese, after the formation of a complex with 1-(2-thiazolylazo)-2-naphthol (TAN), and later analysis by flame atomic absorption spectrometry using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The chemical variables affecting the separation phase and the viscosity affecting the detection process were optimized. Under the optimum conditions (i.e., pH = 9.2, [TAN] = 2.0 x 10(-5) mol l-1, [Triton X-114] = 0.05%, added methanol volume = 0.2 ml), preconcentration of 50 ml of sample solution permitted the detection of 0.28 ppb for manganese. The enhancement factor was 57.6. The proposed method has been applied to the determination of manganese in water samples.     

Supramolecular microextraction of cobalt from water samples before its microsampling flame atomic absorption spectrometric detection

The supramolecular solvent system consists of tetrahydrofuran (THF) and 1-decanol, that was used as an extraction solvent for a microextraction procedure for the preconcentration and separation of Co(II). The proposed supramolecular-based procedure was combined with microsampling flame atomic absorption spectrometry for the determination of cobalt at trace levels in water samples. N-Benzoyl-N,N-diisobutylthiourea was used to chelate Co(II) in an aqueous solution. Quantitative extraction efficiency was obtained at pH 6.5. The effects of analytical parameters including pH, amount of ligand, type, ratio and volume of supramolecular solvent, sample volume and interfering ions were investigated for optimisation of the procedure. The proposed supramolecular solvent-based microextraction procedure (Ss-ME) exhibits a limit of detection (LOD) of 1.29 µg L^?1 and a limit of quantification (LOQ) of 3.88 µg L^?1. The procedure was validated by addition/recovery tests and by applying TMDA 64.2 and TMDA 53.3 water certified reference materials. The microextraction method was successfully applied for the preconcentration and determination of cobalt in water samples.     

Determination of zinc in water samples by flame atomic absorption spectrometry after homogeneous liquid-liquid extraction

In this study, a new and simple homogeneous liquid-liquid extraction (HLLE) method based on a pH-independent phase-separation process was developed using a ternary solvent system [water-tetrabutylammonium ion (TBA ⁺)-chloroform] for the preconcentration of Zn²⁺ ions. A Schiff’s base ligand was used as the chelating agent prior to Zn²⁺ ions extraction. Flame atomic absorption spectrophotometry using acetylene-air flame was used for the quantification of analyte after preconcentration. The phase separation occurred due to ion-pair formation of TBA and perchlorate ion. The sedimented phase was then separated using a 100 μL micro-syringe and diluted to 1.0 mL with ethanol. The sample was introduced into the flame by conventional aspiration. After the optimization of complexation and extraction conditions such as pH 9.0, [ligand] = 1.0 × 10⁻⁵ M, [TBA⁺] = 2.0 × 10⁻² M, 100.0 μL of [CHCl₃] and [CLO₄⁻] = 2.0 × 10⁻² M, a preconcentration factor of 100 was achieved for only 10 mL of the sample. The relative standard deviation was 2.3% (n = 10). The limit of detection was sufficiently low and at ppb level. The proposed method was applied to the extraction and determination of Zn²⁺ in natural water samples with satisfactory results.