Hideyuki Katsumata

Removal of heavy metals in rinsing wastewater from plating factory by adsorption with economical viable materials

The removal of heavy metals from plating factory wastewater with economical materials was investigated by the column method. Montmorillonite, kaolin, tobermorite, magnetite, silica gel and alumina were used as the economical adsorbents to wastewater containing Cd(II), Cr(VI), Cu(II) and Pb(II). This removal method of heavy metals proved highly effective as removal efficiency tended to increase with increasing pH and decrease with increasing metal concentration. The removal percentages by adsorption onto montmorillonite, tobermorite, magnetite, and silica gel showed high values for all metals. From the results for the heat of adsorption, the adsorption process in the present study might be chemisorption. The proposed method was successfully applied to the removal of Cd(II), Cr(VI) and Cu(II) in rinsing wastewater from plating factory in Nagoya City, Aichi Prefecture, Japan. Since the economical adsorbents used can be obtained commercially because they are easily synthesized, the wastewater treatment system developed is rapid, simple and cheap for the removal of heavy metals.

Z-scheme photocatalytic hydrogen production over WO3/g-C3N4 composite photocatalysts

WO3/g-C3N4 composite photocatalysts were prepared by a simple calcination method and H2 production activity of these composites was evaluated. The photocatalytic activity of the composites highly depended on WO3 content. The enhanced photocatalytic activity could be ascribed to the Z-scheme mechanism, which results in the efficient charge separation.

Electrochemical conversion of carbon dioxide to methane in aqueous NaHCO3 solution at less than 273 K

The electrochemical reduction of CO2 on a Cu electrode was investigated in aqueous NaHCO3 solution, at low temperature. A divided H-type cell was employed, the catholyte was 0.65 mol dm−3 NaHCO3 aqueous solution and the anolyte was 1.1 mol dm−3 KHCO3 aqueous solution. The temperature during the electrolysis of CO2 was decreased stepwise to 271 K. Methane and formic acid were obtained as the main products. The maximum Faradaic efficiency of methane was 46% at −2.0 V and 271 K. The efficiency of hydrogen formation, a competing reaction of CO2 reduction, was significantly depressed with decreasing temperature. Based on the results of this work, the proposed electrochemical method appears to be a viable means for removing CO2 from the atmosphere and converting it into more valuable chemicals. The synthesis of methane by the electrochemical method might be of practical interest for fuel production and the storage of solar energy.

Photocatalytic degradation of diuron in aqueous solution by platinized TiO2

The photocatalytic degradation of diuron, which is one of phenylurea herbicides, was carried out in the presence of platinized TiO(2) photocatalyst. Platinization was found to increase the rate of diuron degradation. When 0.2wt.% of platinum was deposited onto the surface of TiO(2), an initial diuron concentration of 10 mg L(-1) was completely degraded after 20 min. Furthermore, the first-order rate constant for diuron degradation by Pt-TiO(2) was ca. 4 times higher than P-25 TiO(2). In addition, the photocatalytic activity of Pt-TiO(2) was appeared under visible light. The decrease of TOC as a result of mineralization of diuron was observed during the photocatalytic process. The degree of diuron mineralization was about 97% under UV irradiation after 8h. The formations of chloride, nitrate and ammonium ions as end-products were observed during the photocatalytic system. The decomposition of diuron gave four kinds of intermediate products. The degradation mechanism of diuron was proposed on the base of the evidence of the identified intermediates. Based on these results, the photocatalytic reaction by Pt-TiO(2) could be useful technology for the treatment of wastewater containing diuron.

Photocatalytic activity of Ag/CuO/WO3 under visible-light irradiation

The photocatalytic activity of silver and copper oxide loaded WO3 nanocomposite (Ag/CuO/WO3) was investigated under visible-light using the decolorization of Acid Red 88 (AR 88) dye molecules in solution. The activity of WO3 nanoparticles (NPs) was significantly improved by the binary loading of Ag and CuO as cocatalysts. The photocatalytic mechanism was investigated to understand the enhanced photocatalytic activity, which was mainly attributed to the synergistic effect of the Ag and CuO binary cocatalysts loaded on the WO3 NPs. The Ag cocatalyst acted as an electron trapping center that enhanced electron/hole separation and the CuO cocatalyst significantly promoted four-electron reduction of oxygen for H2O production. The concurrent oxidation of organic dye molecules occurring on WO3 NPs was probably initiated at photogenerated holes with a high oxidation potential. To further improve the photocatalytic activity of the Ag/CuO/WO3 system, WO3 nanotubes (NTs) were synthesized and loaded with Ag and CuO. The photocatalytic activity of Ag/CuO/WO3 NTs in the decolorization of AR 88 after 180 min was approximately 1.5 and 6.4 times greater than that of Ag/CuO/WO3 NPs and N–TiO2, respectively.

Degradation of fenitrothion by ultrasound/ferrioxalate/UV system

The sonochemical photodegradation of fenitrothion, which is one of phosphorothiate insecticides, was carried out in the presence of Fe(III) and oxalate. The degradation rate was strongly influenced by initial concentrations of Fe(III) and oxalate. An initial fenitrothion concentration of 10 mg L(-1) was completely degraded after 30 min at pH 6 under the optimum conditions. Therefore, the photo-Fenton reaction combined with sonication in the presence of oxalate was available around neutral pH. The decrease of TOC as a result of mineralization of fenitrothion was observed during ultrasound (US)/ferrioxalate/UV process. In addition, the formations of nitrite and sulfate ions as end-products were observed during this degradation system. The decomposition of fenitrothion gave two kinds of intermediate products. The degradation mechanism of fenitrothion was proposed on the base of the evidence of the identified intermediates. Based on these results, US/ferrioxalate/UV system could be useful technology for the treatment of wastewater containing fenitrothion.

Determination of simazine in water samples by HPLC after preconcentration with diatomaceous earth

A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of simazine. Simazine was preconcentrated on diatomaceous earth as an adsorbent and then determined by high-performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 2 using 100mL of validation solution containing 1.5mug of simazine and 5mL of ethanol as an eluent. Recovery of simazine was 89.0 +/- 1.6% with a relative standard deviation for seven determinations of 1.5% under optimum conditions. The maximum preconcentration factor was 100 for simazine when 500mL of sample solution volume was used. The linear range of calibration curve was 1-200ngmL(-1) with a correlation coefficient of 0.996 and the detection limit (3S/N) was 0.3ngmL(-1). The capacity of the adsorbent was also examined and found to be 1.1mgg(-1) for simazine. The proposed method was successfully applied to the determination of simazine in river water with high precision and accuracy.

Degradation of Reactive Yellow 86 with photo-Fenton process driven by solar light.

The decolorization of Reactive Yellow 86 (RY 86), one of reactive azo dyes, was investigated in the presence of Fenton reagent under solar light irradiation. The decolorization rate was strongly influenced by pH, initial concentrations of H2O2 and Fe(II), and so on. An initial concentration of 40 mg/L was decolored more than 90% after 20 min under optimum conditions. The activation energy of the solar photo-Fenton reaction was 1.50 kJ/mol for RY 86 in the temperature range of 10-60 degrees C. In the kinetic study, the rate constant of RY 86 with OH. radicals could be estimated to be 1.7 x 10(10) L/(mol.sec). The decolorization efficiency of RY 86 under solar light irradiation was comparable to the artificial light irradiation. The decrease of TOC as a result of mineralization of RY 86 was observed during photo-Fenton process. The rate of RY 86 mineralization was about 83% under UV irradiation after 24 hr. The formation of chloride, sulfate, nitrate and ammonium ions as end-products was observed during the photocatalytic process. The decomposition of RY 86 gave two kinds of intermediate products. The degradation mechanism of RY 86 was proposed on the base of the identified intermediates.

Removal of organic polyelectrolytes and their metal complexes by adsorption onto xonotlite

Natural organic polyelectrolytes (humic and fulvic acids) and their metal complexes were removed by adsorption onto xonotlite. The removal percentages of humic and fulvic acids by xonotlite were approximately 80% and 30%, respectively. Humic acid removal from solution by adsorption onto xonotlite took place more readily than fulvic acid removal. The molecular weight distributions of the humic substances remaining in solution after adsorption with the xonotlite were measured with size exclusion chromatography. A comparison of molecular weight distributions demonstrated conclusively that large molecular weight components were adsorbed preferentially, indicating that adsorption efficiency depends on the number of functional groups of humic substances. Furthermore, the surface topography of the adsorbent was observed before and after adsorption by scanning electron microscopy. The calculated heat of adsorption was of 330 kJ mol(-1) which was evaluated from the Clapeyron-Clausius equation. Therefore, the adsorption type can be considered chemical. Since xonotlite can be easily synthesized and obtained at low cost, the adsorption method of humic and fulvic acids is superior to their precipitation.

Removal of Humic Substances and Their Metal Complexes by Adsorption

The adsorption of organic polyelectrolytes (humic and fulvic acids) by bone char was characterized. The bone char was found to be a useful adsorbent for humic substances compared with an activated carbon. The present method was also successfully applied to the removal of metal-humic material complexes. The molecular weight distributions of the humic substances remaining in solution after adsorption with the bone char were measured with size-exclusion chromatography. A comparison of molecular weight distributions demonstrated conclusively that large molecular-weight components were adsorbed preferentially. Furthermore, the surface conditions of the adsorbent were observed before and after adsorption by a scanning electron microscope. From the observation, it was found that the adsorption ability of the adsorbent was closely related to its pore size. The calculated heats of adsorption were over 50 kJ mol-1, which was evaluated from the Clapeyron-Clausius equation. Therefore, the adsorption type appeared to ...