Shigehiro Kagaya

Separation of titanium dioxide photocatalyst in its aqueous suspensions by coagulation with basic aluminium chloride

Abstract A coagulation technique was applied to separate titanium dioxide photocatalyst in its aqueous suspensions after the photocatalyzed degradation of organic contaminants. When a basic aluminium chloride was used as a coagulating agent, titanium dioxide was flocculated and sedimented rapidly; the supernatant solution was practically transparent. After the coagulation with basic aluminium chloride, the titanium dioxide separated from the mother liquor could be satisfactorily reused as a photocatalyst by several simple treatments.

A sensitive and selective method for determination of gold(III) based on electrothermal atomic absorption spectrometry in combination with dispersive liquid-liquid microextraction using dicyclohexylamine.

A combined method with dispersive liquid-liquid microextraction (DLLME) and electrothermal atomic absorption spectrometry (ETAAS) has been developed for determining gold(III). Dicyclohexylamine, a new extractant for gold(III), showed excellent performance in DLLME. Acetone was indispensable to the quantitative extraction of gold(III), contributing to decrease in hydration, decrease in the difference in the dielectric constants between the supernatant phase and the sedimented phase, and dissolution of a part of chloroform as an extraction solvent to the supernatant phase as well as improvement of dipersibility. In DLLME using a mixture of 1.0mL of acetone and 100microL of chloroform containing 50mmolL(-1) of dicyclohexylamine, gold(III) could be extracted selectively and effectively from 8mL of a sample solution in the presence of iron(III), cobalt(II), nickel(II), copper(II), palladium(II), and platinum(IV) at pH 1. The extracted gold(III) was determinable by ETAAS; the detection limit was 0.002microgL(-1) (three times the standard deviation of the blank values, n=8) as a gold(III) concentration in 8mL of sample solution. The proposed method was applicable to the determination of gold in platinum metal and its alloy as well as effluent without any interference by the matrices.

A solid phase extraction using a chelate resin immobilizing carboxymethylated pentaethylenehexamine for separation and preconcentration of trace elements in water samples

A chelate resin immobilizing carboxymethylated pentaethylenehexamine (CM-PEHA resin) was prepared, and the potential for the separation and preconcentration of trace elements in water samples was evaluated through the adsorption/elution test for 62 elements. The CM-PEHA resin could quantitatively recover various elements, including Ag, Cd, Co, Cu, Fe, Ni, Pb, Ti, U, and Zn, and rare earth elements over a wide pH range, and also Mn at pH above 5 and V and Mo at pH below 7. This resin could also effectively remove major elements, such as alkali and alkaline earth elements, under acidic and neutral conditions. Solid phase extraction using the CM-PEHA resin was applicable to the determination of 10 trace elements, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, V, and Zn, in certified reference materials (EnviroMAT EU-L-1 wastewater and ES-L-1 ground water) and treated wastewater and all elements except for Mn in surface seawater using inductively coupled plasma atomic emission spectrometry. The detection limits, defined as 3 times the standard deviation for the procedural blank using 500 mL of purified water (50-fold preconcentration, n=8), ranged from 0.003 microg L(-1) (Mn) to 0.28 microg L(-1) (Zn) as the concentration in 500 mL of solution.

Selective removal of mercury(II) from wastewater using polythioamides

The potential and feasibility of polythioamides as Hg(II) sorbents were evaluated. Powdered polythioamides quantitatively sorbed Hg(II) from an aqueous solution at pH 1-8. The sorption of Hg(II) on polythioamides obeyed the Langmuir adsorption isotherm; the sorption capacity was 0.70-0.85 g-Hgg(-1). Hg(II) was selectively separated from solutions containing 500 times larger amounts of Mn(II), Fe(III), Cu(II), Zn(II), and Pb(II) at pH 1. The tertiary polythioamide (PTA1) is soluble in chloroform and can be readily coated on a commercially available polymer resin, Amberlite XAD7HP. PTA1-coated resin as well as powdered PTA1 were applicable to the selective removal of Hg(II) from real wastewater.

Comparative assessment of the efficiency of Fe-doped TiO2 prepared by two doping methods and photocatalytic degradation of phenol in domestic water suspensions

Abstract Fe-doped TiO2 particles responding to visible light were synthesized by impregnation and calcination method using TiO2 particle and Ti element, respectively. The optical and the chemical properties were characterized by measuring the X-ray diffraction (XRD) and UV–visible spectroscopy. The onset of absorption shifted to longer wavelengths on doping TiO2 by the calcination process, which showed a better response as compared to the impregnation method. The photocatalytic reactivity was evaluated by the degradation of phenol with impregnated Fe-doped (0.5% w/w in Fe) and calcined Fe-doped (FexTi1 xO2, x ¼ 0.005 (Fe/Ti molar ratio)) TiO2 separately in distilled and tap water. The characterization results have confirmed the advanced possibility of correlation between photoactivity and the special property of sulfur-containing calcined Fe-doped TiO2. In case of the coagulation of the undoped A-I and the Fe-doped B-I, the photoactivity showed a decrease due to the presence of natural electrolytes and due to the high pH of tap water, whereas in the case of the coagulation of calcined Fe-doped TiO2 prepared from sulfides (FexTiS2), the photoactivity showed an increase. In this study, highest catalytic activity was found to be strongly dependent both on catalyst structure and on the type of water used.

Coprecipitation with yttrium phosphate as a separation technique for iron(III), lead, and bismuth from cobalt, nickel, and copper matrices.

The coprecipitation behavior of 44 elements (47 ions because of chromium(III,VI), arsenic(III,V), and antimony(III,V)) with yttrium phosphate was investigated at various pHs. Yttrium phosphate could quantitatively coprecipitate iron(III), lead, bismuth, and indium over a wide pH range; however, 18 ions, including alkali metals and oxo anions, such as vanadium(V), chromium(VI), molybdenum(VI), tungsten(VI), germanium(IV), arsenic(III,V), selenium(IV), and tellurium(VI), were scarcely collected. In addition, 19 ions, including cobalt, nickel, and copper(II), were hardly coprecipitated at pHs below about 3. Based on these results, the separation of iron(III), lead, and bismuth from cobalt, nickel, and copper(II) matrices was investigated. Iron(III), lead, and bismuth ranging from 0.5 to 25mug could be separated effectively from a solution containing 0.5g of cobalt, nickel, or copper at pH 3.0. The separated iron(III), lead, and bismuth could be determined by inductively coupled plasma atomic emission spectrometry using internal standardization. The detection limits (3sigma, n=7) of iron(III), lead, and bismuth were 0.008, 0.137, and 0.073mug, respectively. The proposed method was applied to the analyses of metals and chlorides of cobalt, nickel, and copper.

Adsorption and aggregation of Fe(III)-hydroxy complexes during the photodegradation of phenol using the iron-added-TiO2 combined system.

The behavior of Fe(III) aquacomplexes in TiO(2) suspensions in the degradation of phenol has been investigated. The most active Fe(OH)(2+) species adsorbed on the surface of TiO(2) retards the conversion of Fe(OH)(2+) into oligomers and therefore increases the percentage of Fe(OH)(2+) with irradiation time, with a consequent enhancement in the catalytic cycle of Fe(III)/Fe(II) and excited charge traps by Fe(III) in the iron-TiO(2) system. The influence of iron addition on TiO(2) was obtained when the regeneration of [Fe(OH)(2+)] remained continuous with irradiation time. In an optimum TiO(2) suspension (0.5g/L) with the addition of 0.1mM Fe(III), the measured k(obs) values for phenol degradation were enhanced for the higher adsorption of Fe(OH)(2+) on the reactive surface of TiO(2) at a specified irradiation time.

Nitration of pyrene adsorbed on silica particles by nitrogen dioxide under simulated atmospheric conditions

Abstract Nitration of adsorbed pyrene on silica particles with nitrogen dioxide was studied under condition of room light in a simulated atmosphere. An induction period was present in the nitration process. Nitric acid formed on the silica particles acted as the catalyst, and the reaction proceeded autocatalytically. Electron donating substituents promoted the reaction, while the electron-attracting substituents diminished it. An electrophilic nitration mechanism involving HNO 2 + and HN 2 O 4 as electrophiles was proposed for the reaction

The use of a polymer inclusion membrane as a sorbent for online preconcentration in the flow injection determination of thiocyanate impurity in ammonium sulfate fertilizer

A polymer inclusion membrane (PIM) is used for the first time as a sorbent in the construction of a preconcentration column to enhance the sensitivity in flow injection analysis (FIA). The PIM-coated column is readily prepared by coating the PIM containing poly(vinyl chloride), Aliquat 336, and 1-tetradecanol onto glass beads packed in a glass tube. The determination of trace amounts of thiocyanate in ammonium sulfate fertilizer demonstrates the potential of the proposed PIM-coated column in FIA. Thiocyanate standards or samples of relatively large volume (e.g. up to 2000 µL) are injected into a nitrate carrier stream. The sample zone passes through the proposed preconcentration column where thiocyanate is concentrated in a smaller volume of a carrier solution thus resulting in up to 7.4 fold increase in sensitivity. Thiocyanate is detected spectrophotometrically after its reaction with Fe(III) downstream of the preconcentration column. The limits of detection of thiocyanate in the absence and presence of 20 g L(-1) ammonium sulfate (S/N=2) are 0.014 and 0.024 mg L(-1), respectively. Thiocyanate was successfully determined in several samples of ammonium sulfate fertilizer.

Continuous flow photocatalytic treatment integrated with separation of titanium dioxide on the removal of phenol in tap water

We studied the continuous flow photocatalytic treatment integrated with separation/reuse of titanium dioxide on the removal of phenol (20 mg l(-1)) in electrolytes containing tap water. A circulative flow tubular photoreactor and a separation tank were used, where inflow of phenol continuously flowed into a mixing tank (for titanium dioxide suspension) and treated water overflowed from the separation tank. Black light and sunlight were used by turns as the light source on the photocatalytic treatment. Photocatalytic removal of phenol was maximum at the circulative flow rate of 600 ml min(-1) and the transmittance of 0.3%. Integration of circulative photocatalytic treatment and titanium dioxide separation and continuous use of titanium dioxide could be performed effectively at low inflow of 10 ml min(-1). The titanium dioxide slurry sedimented spontaneously by standing was continuously used for at least 72 h without decreasing the efficiency of the photocatalytic treatment. The used titanium dioxide can be replaced with a fresh one by draw and fill method without interrupting the treatment.