Highly photocatalytic activity of metallic hydroxide/titanium dioxide nanoparticles prepared via a modified wet precipitation process

Surface modification is one important approach to increase the photocatalytic activity of TiO₂. By using a modified wet precipitation process, novel M(OH)_x/TiO₂ nanoparticles were synthesized, where M(OH)_x represents ferric or cupric hydroxide. The prepared M(OH)_x/TiO₂ powders were characterized with XRD, FT-IR, BET, UV–vis DRS, and TGA, and were observed to yield high photocatalytic ability by using methyl orange (MO) as a model compound of organic pollutants to be degraded. Due to the accelerating effects of the new photocatalyst, the half-time of MO during its photocatalytic degradation at pH 6.0 over M(OH)_x/TiO₂ was decreased from 332 min for unmodified neat TiO₂ to 63 min for Fe(OH)₃/TiO₂ and 65 min for Cu(OH)₂/TiO₂, respectively. The enhancing effects of M(OH)_x/TiO₂ was further observed in a wide composition range with various M/Ti atomic ratios in the photocatalysts and in a wide pH range of the MO solution from 3 to 7. This enhancing effect is mainly attributed to the increased trapping of the photogenerated electron by the higher valence sites (Fe(III) or Cu(II)) in the hydroxide layer near the M(OH)_x/TiO₂ interface and the enriched surface hydroxyl groups which accept photogenerated holes to yield more hydroxyl radicals.     

Comparison of efficiencies between single-drop microextraction and continuous-flow microextraction for the determination of methomyl in natural waters

Two liquid-phase microextraction (LPME) approaches, static direct-immersed single-drop microextraction (DI-SDME) and continuous-flow microextraction (CFME), were used to extract methomyl in water samples and their respective extraction efficiencies were compared. Several important parameters affecting extraction efficiency such as the type of extraction solvent, solvent drop volume, stirring speed or flow rate, extraction time and salt concentration were optimised. The optimised conditions were as follows: 3.0-µL tetrachloroethane (C₂H₂Cl₄) as the extraction solvent, 15% NaCl (w/v), 15 min extraction time and stirring speed at 600 rpm for DI-SDME; 3.5-µL C₂H₂Cl₄ as the extraction solvent, 15% NaCl (w/v), 21 min extraction time and flowing rate at 0.8 mL min^?1 for CFME. Under the previous optimal conditions, the linear range, detection limit (S/N = 3) and precision (RSD, n = 6) were 5.0-5000 ng mL^?1, 1.5 ng mL^?1, 6.9% for DI-SDME, and 4.0–10000 ng mL^?1, 2.5 ng mL^?1, 4.6% for CFME, respectively. Lake and river water samples were successfully analysed by DI-SDME and CFME. The result demonstrated that both SDME and CFME techniques are simple, low cost and amity to environment. As a result, the two approaches have tremendous potential in trace analysis of methomyl in natural waters.     

Photocatalytic activity of silver-modified titanium dioxide at solid–liquid and solid–gas interfaces

Silver-modified titania samples (Ag–TiO₂) with varying silver content (0.1–1.0 wt%) were prepared. Silver-modification of titanium dioxide was examined by TEM, XRD, XPS and DR-UV–vis spectroscopy. Ag or AgO_x particles on TiO₂ surface could not be observed by XRD and TEM investigation, however the color of the Ag–TiO₂ samples varied between light rose and purple-brown. XPS measurements revealed that silver exists mainly in oxide form. The photocatalytic activity of pure and Ag–TiO₂ samples were compared both in solid–liquid and in solid–gas interfaces. In the liquid phase the 2,2′-thiodiethanol was used as test molecule. Ethanol photodegradation was examined in gas phase at dry initial condition. It was shown that the rate of photooxidation of organic compounds significantly enhanced by silver-modification of titania.     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

Sensitive trace enrichment of environmental andiandrogen vinclozolin from natural waters and sediment samples using hollow-fiber liquid-phase microextraction

The presence of vinclozolin in the environment as far as the endocrine disruption effects in biota are concerned has raised interest in the environmental fate of this compound. In this respect, the present study attempts to investigate the feasibility of applying a novel quantitative method, liquid-phase microextraction (LPME), so as to determine this environmental andiandrogen in environmental samples such as water and sediment samples. The technique involved the use of a small amount (3 microL) of organic solvent impregnated in a hollow fiber membrane, which was attached to the needle of a conventional GC syringe. The extracted samples were analyzed by gas chromatography coupled with electron-capture detection. Experimental LPME conditions such as extraction solvent, stirring rate, content of NaCl and pH were tested. Once LPME was optimized, the performance of the proposed technique was evaluated for the determination of vinclozolin in different types of natural water samples. The recovery of spiked water samples was from 80 to 99%. The procedure was adequate for quantification of vinclozolin in waters at levels of 0.010 to 50 microg/L (r> 0.994) with a detection limit of 0.001 microg/L (S/N= 3). Natural sediment samples from the Aliakmonas River area (Macedonia, Greece) spiked with the target andiandrogen compound were liquid-liquid extracted and analyzed by the methodology developed in this work. No significant interferences from the samples matrix were noticed, indicating that the reported methodology is an innovative tactic for sample preparation in sediment analysis, with a considerable improvement in the achieved detection limits. The results demonstrated that apart from analyte enrichment, the proposed LPME procedure also serves as clean-up method and could be successfully performed to determine trace amounts of vinclozolin in water and sediment samples.     

Dispersive liquid-liquid microextraction followed by reversed phase HPLC for the determination of decabrominated diphenyl ether in natural water

A simple, rapid, and efficient method, dispersive liquid-liquid microextraction (DLLME), has been developed for the extraction and preconcentration of decabrominated diphenyl ether (BDE-209) in environmental water samples. The factors relevant to the microextraction efficiency, such as the kind and volume of extraction and dispersive solvent, the extraction time, and the salt effect, were optimized. Under the optimum conditions (extraction solvent: tetrachloroethane, volume, 22.0 microL; dispersive solvent: THF, volume, 1.00 mL; extraction time: below 5 s and without salt addition), the most time-consuming step is the centrifugation of the sample solution in the extraction procedure, which is about 2 min. In this method, the enrichment factor could be as high as 153 in 5.00 mL water sample, and the linear range, correlation coefficient (r(2)), detection limit (S/N = 3), and precision (RSD, n = 6) were 0.001-0.5 microg/mL, 0.9999, 0.2 ng/mL, and 2.1%, respectively. This method was successfully applied to the extraction of BDE-209 from tap, East Lake, and Yangtse River water samples; the relative recoveries were 95.8, 92.9, and 89.9% and the RSD% (n = 3) were 1.9, 2.7, and 3.5%, respectively. Comparison of this method with other methods, such as solid-phase microextraction (SPME), and single-drop microextraction (SDME), indicates that DLLME is a simple, fast, and low-cost method for the determination of BDE-209, and thus has tremendous potential in polybrominated diphenyl ethers (PBDEs) residual analysis in environmental water samples.     

Ligandless dispersive liquid-liquid microextraction for the separation of trace amounts of silver ions in water samples and flame atomic absorption spectrometry determination

In this article, a new ligandless dispersive liquid-liquid microextraction method has been developed for preconcentration of trace quantities of silver as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach, carbon tetrachloride and ethanol were used as extraction and dispersive solvents. Several factors that may be affected on the extraction process, like, extraction solvent, disperser solvent, the volume of extraction and disperser solvent, pH of the aqueous solution and extraction time were optimized. Under the optimal conditions, the calibration curve was linear in the range of 5.0 ng mL⁻¹ to 2.0 μg mL⁻¹ of silver with R² = 0.9995 (n = 9) and detection limit based on three times the standard deviation of the blank (3S_b) was 1.2 ng mL⁻¹ in original solution. The relative standard deviation for eight replicate determination of 0.5 μg mL⁻¹ silver was ±1.5%. The high efficiency of dispersive liquid-liquid microextraction to carry out the determination of silver in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of silver in standard and water samples with satisfactory results.     

A rapid and simple microwave-assisted digestion procedure for spectrophotometric determination of titanium dioxide photocatalyst on activated carbon

Deposition of titanium dioxide (TiO₂) on activated carbon (AC) surface has been widely utilized for the production of TiO₂/AC photocatalyst, which can be used in photo-degradation of pollutants. In this work, a fast and simple digestion procedure has been developed for the spectrophotometric quantitative analysis of TiO₂ in TiO₂/AC photocatalyst. Microwave-assisted digestion was used in the procedure. The microwave-digestion procedure was optimized using the single-variable method. Variables optimized included time of ashing, effective digestion time, volume and concentration of sulfuric acid, effect of adding a digestion catalyst, effect of sample pulverizing and on–off time cycle of the microwave. The analysis was completed spectrophotometrically after addition of hydrogen peroxide to the digested solution. Procedure precision and accuracy was tested by application to photocatalyst samples containing known amounts of TiO₂, and compared with previously published spectrophotometric procedures. The proposed microwave procedure was capable of recovering 98.4–101.1% of TiO₂ in the catalyst in less than 10 min, without the need for sample ashing. Analytical precision is 1.42–2.39% relative standard deviation (R.S.D.). In terms of accuracy and precision, the proposed microwave procedure was comparable with other procedures, but the proposed microwave procedure was superior in terms of shorter procedure duration.     

Evaluation of DGT techniques for measuring inorganic uranium species in natural waters: Interferences,deployment time and speciation

Three adsorbents (Chelex-100, manganese dioxide [MnO₂] and Metsorb), used as binding layers with the diffusive gradient in thin film (DGT) technique, were evaluated for the measurement of inorganic uranium species in synthetic and natural waters. Uranium (U) was found to be quantitatively accumulated in solution (10–100 μg L⁻¹) by all three adsorbents (uptake efficiencies of 80–99%) with elution efficiencies of 80% (Chelex-100), 84% (MnO₂) and 83% (Metsorb). Consistent uptake occurred over pH (5–9), with only MnO₂ affected by pH < 5, and ionic strength (0.001–1 mol L⁻¹ NaNO₃) ranges typical of natural waters, including seawater. DGT validation experiments (5 days) gave linear mass uptake over time (R² ≥ 0.97) for all three adsorbents in low ionic strength solution (0.01 M NaNO₃). Validation experiments in artificial sea water gave linear mass uptake for Metsorb (R² ≥ 0.9954) up to 12 h and MnO₂ (R² ≥ 0.9259) up to 24 h. Chelex-100 demonstrated no linear mass uptake in artificial sea water after 8 h. Possible interferences were investigated with SO₄²⁻ (0.02–200 mg L⁻¹) having little affect on any of the three DGT binding layers. PO₄³⁻ additions (5 μg L⁻¹–5 mg L⁻¹) interfered by forming anionic uranyl phosphate complexes that Chelex-100 was unable to accumulate, or by directly competing with the uranyl species for binding sites, as with MnO₂ and the Metsorb. HCO₃⁻ (0.1–500 mg L⁻¹) additions formed anionic species which interfered with the performance of the Chelex-100 and the MnO₂, and the Ca²⁺ (0.1–500 mg L⁻¹) had the affect of forming labile calcium uranyl species which aided uptake of U by all three resins. DGT field deployments in sea water (Southampton Water, UK) gave a linear mass uptake of U over time with Metsorb and MnO₂ (4 days). Field deployments in fresh water (River Lambourn, UK) gave linear uptake for up to 7 and 4 days for Metsorb and MnO₂ respectively. Field deployment of the Metsorb-DGT samplers with various diffusive layer thicknesses (0.015–0.175 cm) allowed accurate measurements of the diffusive boundary layer (DBL) and allowed DBL corrected concentrations to be determined. This DBL-corrected U concentration was half that determined when the effect of the DBL was not considered. The ability of the DGT devices to measure U isotopic ratios with no isotopic fractionation was shown by all three resins, thereby proving the usefulness of the technique for environmental monitoring purposes.     

聚苯胺/二氧化钛纳米管固相微萃取纤维的组装及应用

以钛丝表面原位阳极氧化生成的二氧化钛纳米管为基体,通过电聚合苯胺组装得到新型聚苯胺包覆二氧化钛复合纳米管阵列固相微萃取纤维。实验讨论了无机酸介质、苯胺浓度和氧化电压对电聚合苯胺的影响,经过对纤维表面形貌和元素成分的分析,得到最佳的纤维涂层条件:电解液组成为1 mol/L的H₂SO₄-0.5 mol/L的苯胺,聚合电压10 V,氧化时间60 min。采用所制备的纤维与高效液相色谱联用萃取水样中的紫外线吸收剂并优化萃取条件,固相微萃取条件如下:萃取时间40 min,解吸时间4 min,萃取温度40℃,搅拌速率600 r/min,样品溶液中不加NaCl。同时对环境水样中的目标物分析测定,并做加标试验,目标分析物的平均回收率为78.2%～118%,相对标准偏差为4.4%～8.9%。该方法简便、灵敏、准确,适用于环境水样中紫外线吸收剂的快速测定。     

Flow injection method for the determination of silver concentration in drinking water for spacecrafts

A flow injection method has been developed for determination of silver. The method is based on a reduction reaction with sodium borohydride which leads to the formation of a colloidal species which is monitored at a wavelength of 390 nm.The reaction variables flow rate, sodium borohydride concentration and pH, which affect sensitivity, were investigated and their effects were established using a two-levels, three-factor experimental design. Further optimization of manifold variables (reaction coil and injection volume) allowed us to determine silver in the range 0.050-5.0 mg L⁻¹ with a minimum detectable concentration of 0.050 mg L⁻¹. Silver is added, as biocide, to drinking water for spacecrafts. The chemical species of silver, present in this kind of sample, were characterized by a procedure based on the selective retention of Ag⁺ onto a 2.2.2. cryptand based substrate followed by determination of the non-bound and bound (after elution) Ag⁺ by the FIA method. The method optimized was applied to a drinking water sample provided for the launch with the Automated Transfer Vehicle (ATV) module Jule Verne to the International Space Station (March 9, 2008).     

Solid phase extraction of halogenated pesticides from ground and surface waters and their determination by capillary gas chromatography

A critical study of a solid phase extraction method using C₁₈ SPE columns for the determination of 23 halogenated pesticides is presented. Type of sorbent, sorbent mass, flow rate in the extraction process, sample concentration of the different compounds, sample volume, pH, ionic strength and type of water were evaluated. Recoveries of pesticides under study yield a linear relationship, except for conazole fungicides and captan. Losses can be expected for heptachlor, aldrin, and captan. Sample volume and flow rate of extraction affect recoveries. Matrix effects from surface and groundwaters were observed. Recoveries for vinelozolin and dieldrin from groundwater were lower than those obtained from nanopure water. In river water losses of these compounds are higher. Captan and penconazole were not present and high losses were obtained for trifluralin, α-BHC, γ-BHC, tri-allate and chlorpyriphos. Impurities arising from the sorbent materials of cartridges have been detected.     

Displacement-dispersive liquid-liquid microextraction coupled with graphite furnace atomic absorption spectrometry for the selective determination of trace silver in environmental and geological samples

A novel displacement-dispersive liquid-liquid microextraction method was developed for the selective determination of trace silver in complicated samples by graphite furnace atomic absorption spectrometry. This method involves two steps of dispersive liquid-liquid microextraction (DLLME). Firstly, copper ion reacted with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex and extracted with DLLME procedure using carbon tetrachloride (extraction solvent) and methanol (dispersive solvent); then, the sedimented phase was dispersed into the sample solution containing silver ion with methanol and another DLLME procedure was carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag⁺ can displace Cu²⁺ from the pre-extracted Cu-DDTC and thus the preconcentration of Ag⁺ was achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu²⁺ from Cu-DDTC complex. The tolerance limits for the co-existing ions were increased by a long way compared with conventional DLLME. Under the optimal conditions, the limit of detection was 20 ng L⁻¹ (3σ) for silver with a sample volume of 5.0 mL, and an enhancement factor of 72 was achieved. The proposed method was successfully applied to determine of trace silver in some environmental and geological samples with satisfactory results.     

Preconcentration and selective determination of traces of tin in natural waters

A combined preconcentration-photometric determination technique has been worked out for trace concentration of tin in fresh and sea waters. After refluxing the sample acidified to 1M HCl for 2 h, tin is preconcentrated by anion-exchange in the presence of thiocyanate and recovered by elution with dilute HNO₃. Tin is then generated as stannane, caught in permanganate solution, and determined spectrpphotometrically with phenylfluorone. The results are quoted on the determination of tin in several fresh and sea waters in the order of submicrogram of tin per litre. The results for tin are in good agreement with those obtained for these samples by manganese dioxide coprecipitation-hydride generation-phenylfluorone spectrophotometric method that is also newly developed.     

An improved flow system for chloride determination in natural waters exploiting solid-phase reactor and long pathlength spectrophotometry

A single and sensitive spectrophotometric method for chloride ions determination based on a commuted flow system with a 100 cm optical path flow cell and a solid-phase reactor containing immobilized silver chloranilate was proposed. This procedure exploited the AgCl formation in the solid-phase reactor leading the chloranilate ions, monitored spectrophotometrically at 530 nm. The analytical signals were 75-fold higher and the sensitivity was 12-fold than that achieved with a 1 cm flow cell, allowed a chloride determination in the 0.5-100 mg l⁻¹ range. The R.S.D. was 1.1% (n = 20) with a sample throughput of 80 h⁻¹ and a waste generated of ca. 100 ng of chloranilate ions per determination. Four samples of natural waters from São Carlos and Araraquara cities were evaluated using the proposed method. Results agreed with the obtained by a reference method at the 95% confidence level.     

Synthesis and characterisation of advanced UHMWPE/silver nanocomposites for biomedical applications

A supercritical fluid (SCF) route for facile and homogeneous introduction of silver nanoparticles into polymer hosts is described. Our focus is on ultra-high molecular weight polyethylene (UHMWPE). We demonstrate that the metallic nanoparticles have a substantial effect upon the wear and tribochemical properties of the polymer substrate.     

Hollow-fibre liquid phase microextraction for separation and preconcentration of vanadium species in natural waters and their determination by electrothermal vaporization-ICP-OES

For separation and determination of vanadium(IV/V) species, a fast and sensitive method by combining hollow-fibre liquid phase microextraction (HF-LPME) with electrothermal vaporization (ETV)-ICP-OES has been developed. Two vanadium species (V(IV) and V(V)) were separated by HF-LPME with the use of ammonium pyrrolidinecarbodithioate (APDC) as chelating agent for complexing with different V species and carbon tetrachloride as the extraction solvent, and the vanadium in the post-extraction organic phase was injected into the graphite furnace for ETV-ICP-OES detection, in which APDC was acted as the chemical modifier. At pH 5.0, both V(IV)-APDC and V(V)-APDC were extracted quantitatively into CCl₄ for determination of total V. For speciation studies, 1,2-cyclohexanediaminetetraacetic acid (CDTA) was added to the sample for masking V(IV), so that only V(V)-APDC was extracted and determined. The concentration of V(IV) was calculated by subtracting the V(V) concentration from the total concentration of V. Under the optimized experimental conditions, the enrichment factor was 74 and the detection limits for V(IV) and V(V) were 86 pg mL⁻¹ and 71 pg mL⁻¹, respectively. The proposed method has been applied to the speciation of V in environmental water samples, and the recovery was in the range of 94%-107%. The results show that V(V) is the dominant existence form in oxygenic water and V(IV) could not been detected. In order to validate the developed procedure, a NIES No.8 vehicle exhaust particulates certified reference material was analyzed, and the results obtained for total vanadium are in good agreement with the certified values. The proposed method is simple, rapid, selective, and sensitive and no oxidation/reduction is required, it is applicable to the speciation of vanadium in environmental samples with the complicated matrix.     

Ultrasound-assisted emulsification microextraction using low density solvent for analysis of toxic nitrophenols in natural waters

An ultrasound-assisted emulsification microextraction (USAEME) based on low-density solvents was successfully applied for the extraction and pre-concentration of four toxic nitrophenols in water samples. The extracted analytes were analyzed by high-performance liquid chromatography-UV detection. The important parameters influencing the extraction efficiency were studied and optimized utilizing two different optimization methods: one variable at a time (OVAT) and central composite design (CCD). The results showed that the emulsification process can be completed in a few seconds using low-density solvents, but almost 10–20?min is necessary for high-density solvents. Under the optimum conditions (extraction solvent, 1-octanol; extraction solvent volume, 40?µL; sample pH, 3.0; salt concentration, 20% (w/v) NaCl; extraction temperature, 40 (±3)°C), limits of detection of the method were in the range of 0.25 to 1?µg?L^?1 and the repeatability and reproducibility of the proposed method, expressed as relative deviation, varied in the range of 2.2–4.2% and 4.7–6.9%, respectively. Linearity was found to be in the range of 1 to 200?µg?L^?1 and the preconcentration factors (PFs) were between 77 and 175. The relative recoveries of the four nitrophenols from water samples at spiking level of 10.0?µg?L^?1 were in the range of 92.0 to 115.0%.     

Headspace solvent microextraction as a simple and highly sensitive sample pretreatment technique for ultra trace determination of geosmin in aquatic media

A headspace solvent microextraction method was developed for the trace determination of geosmin, an odorant compound, in water samples. After performing the extraction by a microdrop of an organic solvent, the microdrop was introduced directly into a GC-MS injection port. One-at-the-time optimization strategy was applied to investigate and optimize some important extraction parameters such as type of solvent, drop volume, temperature, stirring rate, ionic strength, sample volume, and extraction time. The analytical data exhibited an RSD of less than 5% (n = 5), a linear calibration range of 5-900 ng/L (r2 > 0.998), and a detection limit of 0.8 and 3.3 ng/L using two different sets of selected ions. The proposed method was successfully applied to the extraction and determination of geosmin in the spiked real water sample and reasonable recovery was achieved.     

On-line preconcentration and GFAAS determination of trace metals in waters

An on-line separation preconcentration system coupled to electrothermal (graphite furnace) atomic absorption spectrometry was developed. A miniature column packed with iminodiacetic acid ethyl cellulose (IDAEC) was inserted into the loop. A peristaltic pump was used to deliver solutions. A flow of air was driven into the packed column, evacuating it between sample loading, washing and elution. The retained analyte was introduced on-line to graphite furnace using countercurrent elution with HNO₃. The system was applied for the determination of V, Co and Pb in medicinal mineral water samples, and nickel in sea water samples. The detection limits (3σ) were 0.058, 0.022, 0.067, 0.062 μg/l for Co, Pb, V, and Ni, respectively. The R.S.D. (n=5) was <5% at 0.4–1.0 μg/l concentration range.