[Show abstract][Hide abstract] ABSTRACT: Immobilized TiO2 nanotube (NT) arrays containing anatase phases were synthesized through electrochemical oxidation of TiO2 foil. At ultrasonic (US) frequencies of 28 and 1000 kHz, the feasibility of the use of TiO2 NTs was investigated in terms of the production of H2O2 and the degradation of acetaminophen (AAP) and naproxen (NPX), which are pharmaceuticals (PhACs) used for pain relief and which persist despite wastewater treatment. The degradation efficiencies of the PhACs, as well as the production of H2O2, were enhanced in the presence of TiO2 NTs. Furthermore, the reduction of TiO2 slurries after the reaction was achieved at 1000 kHz. The feasibility of the TiO2 NTs was clearly shown in US/Fenton/TiO2 NT process, exhibiting the highest degradation (85.3% for AAP and 96.0% for NPX) at low Fe2+:H2O2 ratio of 20:4 ratio at 1000 kHz. These results could be attributed to the accelerated cycling of Fe2+-Fe3+, assisted by electrons in the presence of TiO2 NTs under US irradiation. In the US/CCl4 process, the degradation rates of both PhACs were improved with an increased concentration of CCl4, implying that the scavenging H leads to high concentrations of OH and the accumulation of reactive chlorine species, while t-BuOH notably inhibited the degradation of the PhACs. In acidic conditions, high degradation efficiencies were observed because of the hydrophobicity of the PhACs, high OH activity, and high HOCl/OCl− ratio. Finally, we suggest possible process mechanisms of the US/Fenton/TiO2 NT and US/CCl4 processes.
Separation and Purification Technology 02/2015; 141:1-9. · 3.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, a self-rotating photocatalytic system is applied to reduce toxic Cr(VI) to non-toxic Cr(III) in aqueous solution under UV irradiation. To overcome the limitation of powdery photocatalysis, a novel approach towards a photocatalytic system for aqueous Cr(VI) reduction including self-rotating TiO2 nanotubes on a Ti substrate (mesh type) was established.For the preparation of TiO2 nanotubes on the Ti substrate, Ti mesh (10 cm × 10 cm) was anodized at 50 V to 25 °C for 25 min with mixed electrolytes (NH4F–H2O–C2H6O2), and then annealed at 450 °C for 2 h in ambient oxygen at a flow rate of 400 mL min−1. The fabricated TiO2 nanotube arrays were uniformly grown on Ti mesh and surface characterizations was performed through the measurements of SEM, XRD, and zeta potential.The HRT (Hydraulic retention time) and rotating speeds were significantly affected by inlet flowrate in this reactor being decreased and increased, respectively, with increasing inlet flowrate. Hence, the efficiency of photocatalytic Cr(VI) reduction was observed to be highest up to 95% at the 90 rpm. In addition, the rate of Cr(VI) reduction was increased by increasing the number of TiO2/Ti meshes.
Chemical Engineering Journal 08/2013; 229:66–71. · 4.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ultrasonic (US) and single-walled carbon nanotube (SWNT)-catalyzed ultrasonic (US/SWNT) degradation of a pharmaceutical (PhAC) mixture of acetaminophen (AAP) and naproxen (NPX) used as analgesics was carried out in water. In the absence of SWNTs, maximum degradations of AAP and NPX occurred at a high frequency (1000kHz) and under acidic conditions (pH 3) and different solution temperatures (25°C at 28kHz and 35°C at 1000kHz) during US reactions. Rapid degradation of PhACs occurred within 10min at 28kHz (44.5% for AAP; 90.3% for NPX) and 1000kHz (39.2% for AAP; 74.8% for NPX) at a SWNT concentration of 45mgL(-1) under US/SWNT process, compared with 28kHz (5.2% for AAP; 10.6% for NPX) and 1000kHz (29.1% for AAP; 46.2% for NPX) under US process. Degradation was associated with the dispersion of SWNTs; small particles acted as nuclei during US reactions, enhancing the H2O2 production yield. NPX removal was greater than AAP removal under all US-induced reaction and SWNT adsorption conditions, which is governed by the chemical properties of PhACs. Based on the results, the optimal treatment performance was observed at 28kHz with 45mgL(-1) SWNTs (US/SWNT) within 10min.
Journal of hazardous materials 04/2013; 254-255C:284-292. · 4.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to develop effective cathodes to increase the production of hydrogen and use the seawater, an abundant resource in the earth as the electrolyte in photoelectrochemical systems. In order to fabricate the Pt/TiO2 cathodes, various contents of the Pt precursor (0–0.4wt%) deposited by the electrodeposition method were used. On the basis of the hydrogen evolution rate, 0.2wt% Pt/TiO2 was observed to exhibit the best performance among the various Pt/TiO2 cathodes with the natural seawater and two concentrated seawater electrolytes obtained from single (nanofiltration) and combined membrane (nanofiltration and reverse osmosis) processes.The surface characterizations exhibited that crystal structures and morphological properties of Pt and TiO2 found the results of XRD pattern and SEM/TEM images, respectively.
Journal of Solid State Chemistry 11/2011; 184(11):2920-2924. · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Water shortages are anticipated to occur all over the world and are likely to have a significant effect on the availability of water for processes such as photocatalysis and electrolysis, as well as for drinking and industrial water. To overcome this problem, it has been suggested that seawater could be used as an alternative resource for the various water industries, such as hydrogen production, industrial and drinking water. Seawater contains a large amount of dissolved ion components, thus allowing it to be utilized as an electrolyte in photoelectrochemical system for producing hydrogen. Especially, the concentrated shows higher salinity (total dissolved solids, TDS) than the general seawater fed to the membrane process, because the permeate has a lower salinity and the retentate is more concentrated than the original seawater. For these reasons, the hydrogen evolution rate was investigated in a photoelectrochemical system, including anodized tubular TiO2 and platinum as the photoanode and cathode, an external bias (solar cell) and the use of various types of seawater prepared by the nanofiltration membrane process as the electrolyte in the photoelectrochemical system.The results showed that the rate of hydrogen evolution obtained using the relatively tight nanofiltration membrane, NF90, operated at 20 MPa in the photoelectrochemical system is ca. 270 μmol/cm2 h, showing that the retentate with a higher TDS than the general TDS of seawater acts as a more effective seawater electrolyte for hydrogen production.Highlights► Seawater is an alternative resource for H2 production against future water shortage. ► High concentrated ions dissolved in seawater are useful for PEC H2 production. ► PEC is composed of anodized TiO2 anode, Pt cathode, and solar cell as ext. bias. ► H2 shows 215 μmol/cm2 h with natural seawater. ► H2 increases 270 μmol/cm2 h with concentrated seawater by NF membrane at 20 MPa.
Solar Energy 09/2011; 85(9):2256-2263. · 3.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A series of experiments were conducted to compare the effectiveness of various catalysts in the production of H2O2 and in the degradation of endocrine disrupting compounds (EDCs), including bisphenol A (BPA) and 17α-ethinyl estradiol (EE2), in water by sonocatalysis using ultrasonication at 28 kHz with a contact time of 60 min. The catalysts included a stainless steel wire mesh (SSWM), glass beads (GB), TiO2 powder, a Ti-wire mesh (Ti-WM), and an oxidized Ti-wire mesh (TiO2-WM). The most effective catalyst combination for the production of 215.7 μM of H2O2, was the use of SSWM with TiO2 as the cocatalyst. A significantly lower sonochemical reactivity was observed when there was no added catalyst (18.5 μM), SSWM (61.3 μM), and TiO2 alone (134.1 μM). For the given contact time and frequency, sonochemical reactivity was determined from the rate constants for H2O2 production. EDC sonodegradation occurred in the following order: SSWM + TiO2 (powder) > GB > TiO2 (powder) > SSWM + GB > TiO2-WM > Ti-WM > SSWM > no catalyst, although the catalyst type, surface area, and amount were varied. Our findings suggest that TiO2-WM can be continuously reused for the catalysis of H2O2 production and the degradation of EDC.
[Show abstract][Hide abstract] ABSTRACT: Water shortages are anticipated to occur all over the world and are likely to have a significant effect on the availability of water for water splitting processes, such as photocatalysis and electrolysis, as well as for drinking and industrial water. To overcome this problem, it has been suggested that seawater could be used as an alternative resource for the various water industries, including hydrogen production, industrial, and drinking water. Seawater contains a large amount of dissolved ion components, thus allowing it to be utilized as an electrolyte in PEC systems for producing hydrogen.In this study, anodized TiO2 electrodes are prepared and used as the photoanodes in a photoelectrochemical (PEC) system designed to convert natural seawater into hydrogen with the assistance of an external bias, and their electrochemical and morphological properties were characterized, and correlated with the hydrogen evolution rate and photocurrent.In order to prepare light sensitized TiO2 electrodes, titanium was anodized in single and mixed chemicals and annealed under various conditions. Based on the comparison of their electrical and physical properties and hydrogen evolution rate, the TiO2 electrode anodized in a mixture of chemicals (NH4F–H2O–C3H8O2 (ethylene glycol)) showed the best performance among the other electrodes. The experimental results showed that the hydrogen evolution rate obtained using seawater in the PEC system is ca. 215 μmol/cm2 h, thus confirming that this is an effective seawater electrolyte for hydrogen production, and the optimum external bias supplied by the solar cell is at least 3.0 V.
Solar Energy Materials and Solar Cells 10/2010; · 5.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An immobilized TiO2 electrode for photocatalytic hydrogen production is applied to reduce toxic Cr(VI) to non toxic Cr(III) in aqueous solution
under UV irradiation. To overcome the limitation of powder TiO2, a novel technique of immobilization based on anodization was applied and investigated under various experimental conditions.
The anodization was performed with three different electrolytes (single or mixed), and then the anodized samples were annealed
under an oxygen stream. Among the three kinds of anodized/annealed TiO2 on Ti foil, Sample II (anodized at 20 V in 0.5% HF for 45 min at 5 °C, and annealed at 450 °C for 5 hr in ambient oxygen
at a flow rate of 400 mL/min) was more effective for both Cr(VI) reduction than the other samples. Based on the electrolyte
compositions, nanotubular TiO2 grown on Ti meshes was fabricated for the purpose of its light-harvesting ability and efficiency, where the anodized/annealed
TiO2 on meshes were rotated in the center of the reactor and Cr(VI) could be effectively reduced at rotation speeds ranging from
0 to 64 rpm. In case of Sample II, it was found that up to 98 % of the Cr(VI) was reduced in 30 min at 64 rpm.
Key wordsCr(VI) Reduction-Immobilized TiO2
-Anodization-Rotating Mesh Type Reactor
Korean Journal of Chemical Engineering 09/2010; 26(5):1296-1300. · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Anodized tubular TiO2 electrodes (ATTEs) are prepared using an organic additive consisting of either (i) ethylene glycol (EG) or (ii) glycerol (Gly) to make various photoanodes with different length of TiO2 tubes and thereby to investigate the effect of their length on the photo-driven activity for hydrogen evolution and Cr(VI) reduction, as well as on the photocurrent. The ATTEs with EG have longer TiO2 tubes (3.42–15.6μm) than those with Gly (0.26–1.95, 6.82μm). The former samples exhibit higher photocurrent densities (22.8–32.8mAcm−2) than the latter (8.0–19.4, 20.3mAcm−2). The latter samples (tube length of less than 7μm) clearly exhibit a change of the rate-determining step from electron migration to photohole capture as the scanned applied bias increases, since the photocurrent shows a plateau for tube lengths above 2μm. Meanwhile, the samples with EG remain in the electron migration step up to a tube length of 16μm and is due to the difference of the morphology, crystal phase and crystallinity. This favourable characteristic is also applied to and well matched with the results from the reactions of Cr(VI) reduction and hydrogen evolution (up to ca. 250μmolh−1).
Journal of Power Sources 08/2010; 195(15):5144-5149. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rejection characteristics of chromate, arsenate, and perchlorate were examined for one reverse osmosis (RO, LFC-1), two nanofiltration (NF, ESNA, and MX07), and one ultrafiltration (UF and GM) membranes that are commercially available. A bench-scale cross-flow flat-sheet filtration system was employed to determine the toxic ion rejection and the membrane flux. Both model and natural waters were used to prepare chromate, arsenate, and perchlorate solutions (approximately 100microgL(-1) for each anion) in mixtures in the presence of other salts (KCl, K(2)SO(4), and CaCl(2)); and at varying pH conditions (4, 6, 8, and 10) and solution conductivities (30, 60, and 115mSm(-1)). The rejection of target ions by the membranes increases with increasing solution pH due to the increasingly negative membrane charge with synthetic model waters. Cr(VI), As(V), and ClO(4)(-) rejection follows the order LFC-1 (>90%) > MX07 (25-95%) congruent withESNA (30-90%)>GM (3-47%) at all pH conditions. In contrast, the rejection of target ions by the membranes decreases with increasing solution conductivity due to the decreasingly negative membrane charge. Cr(VI), As(V), and ClO(4)(-) rejection follows the order CaCl(2)<KCl congruent withK(2)SO(4) at constant pH and conductivity conditions for the NF and UF membranes tested. For natural waters the LFC-1 RO membrane with a small pore size (0.34nm) had a significantly greater rejection for those target anions (>90%) excluding NO(3)(-) (71-74%) than the ESNA NF membrane (11-56%) with a relatively large pore size (0.44nm), indicating that size exclusion is at least partially responsible for the rejection. The ratio of solute radius (r(i,s)) to effective membrane pore radius (r(p)) was employed to compare ion rejection. For all of the ions, the rejection is higher than 70% when the r(i,s)/r(p) ratio is greater than 0.4 for the LFC-1 membrane, while for di-valent ions (CrO(4)(2-), SO(4)(2-), and HAsSO(4)(2-)) the rejection (38-56%) is fairly proportional to the r(i,s)/r(p) ratio (0.32-0.62) for the ESNA membrane.
[Show abstract][Hide abstract] ABSTRACT: In the near future, potential water shortages are expected to occur all over the world and this problem will have a significant influence on the availability of water for water-splitting processes, such as photocatalysis and electrolysis, as well as for drinking water. For this reason, it has been suggested that seawater could be used as an alternative for the various water industries including hydrogen production. Seawater contains a large amount of dissolved ion components, thus allowing it to be used as an electrolyte in photoelectrochemical (PEC) systems for producing hydrogen. Especially, the concentrate (retentate) stream shows higher salinity than the seawater fed to the membrane desalination process, because purified water (fresh water) is produced as the permeate stream and the waste brine is more concentrated than the original seawater. In this study, we investigated the hydrogen evolution rate in a photoelectrochemical system, including the preparation and characterization of an anodized tubular TiO2 electrode (ATTE) as both the photoanode and the cathode with the assistance of an immobilized hydrogenase enzyme and an external bias (solar cell), and the use of various qualities of seawater produced by membrane desalination processes as the electrolyte. The results showed that the rate of hydrogen evolution obtained using the nanofiltration (NF) retentate in the PEC system is ca. 105 μmol/cm2 h, showing that this is an effective seawater electrolyte for hydrogen production, the optimum amount of enzyme immobilized on the cathode is ca. 3.66 units per geometrical unit area (1 cm×1 cm), and the optimum external external bias supplied by the solar cell is 2.0 V.
Solar Energy Materials and Solar Cells 09/2009; · 5.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Anodized tubular titania (TiO2) electrodes (ATTEs) are prepared and used as both the photoanode and the cathode substrate in a photoelectrochemical system designed to split water into hydrogen with the assistance of an enzyme and an external bias of 1.5V. In particular, the ATTE used as the cathode substrate for the immobilization of the enzyme is prepared by two methods—adsorption and crosslinking. Results show that the optimized amount of enzyme is 10.98units for the slurried enzyme, 3.66units for the adsorbed one and 7.32units for the crosslinked one, and the corresponding hydrogen evolution rates are 33.04, 148.58 and 234.88μmolh−1, respectively. The immobilized enzyme, specifically the chemically crosslinked one, seems to be much superior to the slurried enzyme, due to the enhanced charge-transfer process that is caused by the lower electrical resistance between the enzyme and the ATTE. This results in a greater number of accepted electrons and a larger amount of enzymes able to deal with the electrons.
Journal of Power Sources 04/2009; 189(2):1296-1301. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, an anodized tubular TiO2 electrode (ATTE) on titanium foil was prepared and used both as a photoanode and a cathode in an enzymatic photoelectrochemical
system to split water into oxygen and hydrogen. The effect of applied voltage when anodized, thickness of the foil, electrolytes,
annealing temperature, and cathodes was investigated (optimum conditions: 20 V of applied voltage in 0.5 vol.% of hydrofluoric
acid, 0.25-mm foil thickness, and 450–650°C annealing temperature). The samples with higher activities had similar X-ray diffraction
(XRD) patterns, clearly indicating that the samples showing the highest evolution rate were composed of both anatase and rutile,
while those showing a lower evolution rate were made of either anatase or rutile. The ATTE successfully replaced the Pt mesh
cathode and the immobilization of the enzyme enhanced the H2 evolution by 50% (from ca. 66 to 99 μmol/(h × cm2)). Moreover, the use of KOH instead of Tris–HCl buffer in a cathodic compartment further increased the H2 evolution to 115 μmol/(h × cm2).
Research on Chemical Intermediates 03/2009; 35(3):287-297. · 1.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, Pt- and Ru-deposited, nitrogen-substituted TiO2 were prepared and characterized by the discoloration of MB and H2 evolution. The characteristics were evaluated in terms of methylene blue (MB) discoloration, open circuit voltage (OCV),
), and hydrogen production. First, the Pt-deposited TiON revealed comparable activity in MB discoloration, while both TiONs
resulted in somewhat less activity than P25. Second, an external bias was systematically applied to electrodes made of the
prepared samples, resulting in −0.41∼0.51 OCV, −400∼400 μA and noticeable hydrogen evolution above 300 μA in absolute value
when a bias of −1.5∼1.5 V was applied to the working electrode of P25. The electrolyte and light intensity affected the light-responsive
characteristics of the photocatalysts, confirming the relationship between OCV, I
and H2 and that metal deposition slightly inhibited the I
and H2 evolution while Ru-deposited TiON did not degrade MB effectively.
Korean Journal of Chemical Engineering 11/2008; 24(6):1031-1036. · 1.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An anodized tubular titania (TiO2) electrode (ATTE) is prepared and utilized as both a photoanode and a cathode in a photoelectrochemical system designed to split water into hydrogen (for use in fuel cells) with the assistance of a hydrogenase enzyme and an external bias of 1.5V. In particular, the cathodic ATTE acts as a substrate for the immobilization of the enzyme due to its large surface area that results from the tubular oxides. The optimum molar concentration of KOH in anode and cathode compartments is 1.0M and the optimum amount of enzyme for the cathode is ca. 3.66units per geometrical unit area (1cm×1cm) of the cathodic ATTE. After exposure to air for three weeks, the enzyme shows a hydrogen evolution rate that is 85.8% of that of an argon-purged enzyme. The rate of hydrogen evolution is increased from ca. 65 (in a slurry system) to more than 140μmolcm−2h−1, even after eliminating the electron relay (methyl viologen) and costly platinum counter electrode.
Journal of Power Sources 10/2008; 185(1):439-444. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study the enzymatic hydrogen production and chromium(VI) reduction with the light-sensitized photoanode were examined. The photoanodes with higher activities (450–650 °C) had similar X-ray diffraction (XRD) patterns, clearly indicating that the samples showing the highest evolution rate were composed of both anatase and rutile. Optimum thickness of Ti foil was 0.25 mm and platinum cathode could be replaced with the anodized Ti foil. Quasi-stoichiometric hydrogen and oxygen evolution was obtained from the system, recording ca. 104 μmol of H2/(h × cm2, ATTE) at 100 mW/cm2. On the other hand, the immobilized nanotubular TiO2 was also used to photocatalytically reduce toxic Cr(VI) to non-toxic Cr(III) in aqueous solution under UV irradiation. Based on the results, the Cr(VI) reduction was favorable in acidic conditions, with ∼98% of the Cr(VI) being reduced within 2 h at pH 3.
International Journal of Hydrogen Energy 10/2008; 33(19):5193-5198. · 2.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, a Pd catalyst was prepared with promoters such as CeO2, BaO and SrO in a washcoated form on a metallic monolith for autothermal reforming of methane to syngas for the Fischer-Tropsch
synthesis. A reactor was installed with an electric heater in the form of the metallic monolith as a start-up device instead
of a burner with which stable and fast start-ups (within 4 min) were achieved. Gas hourly space velocity and O2/CH4 governed, methane conversion, while H2O/CH4 controlled H2/CO ratio. A methane conversion of approx. 96%, H2+CO selectivity of approx. 85%, and H2/CO of approx. 2.6 were obtained under the conditions of gas hourly space velocity (GHSV) at 103000 h−1, O2/CH4=0.7 and H2O/CH4=0.35.
Research on Chemical Intermediates 08/2008; 34(8):803-810. · 1.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fischer-Tropsch synthesis (FTS) was carried out using Al2O3-supported Co catalyst coated on metallic monolith. Considering the liberation of a large amont of heat from the highly exothermic FTS reaction, catalytic activity of Co catalyst coated on metallic monolith was tested and compared with that of pellet-type catalysts. The reaction was carried out in a conventional tubular fixed-bed reactor and simulated distillation (SIMDIS) analysis method was used to determine the liquid products distribution. Proper control of degree of reaction, as well as the reaction temperature gave rise to a shift of products selectivity toward higher hydrocarbons, especially C13−C18 diesel range hydrocarbons.
Research on Chemical Intermediates 08/2008; 34(8-9). · 1.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, immobilized TiO(2) electrode is applied to reduce toxic Cr(VI) to non-toxic Cr(III) in aqueous solution under UV irradiation. To overcome the limitation of powder TiO(2), a novel technique of immobilization based on anodization was applied and investigated under various experimental conditions. The anodization was performed at 20V-5 degrees C for 45min with 0.5% hydrofluoric acid, and then the anodized samples were annealed under oxygen stream in the range 450-850 degrees C. Based on the results of the experiments, the photocatalytic Cr(VI) reduction was favorable in acidic conditions, with approximately 98% of the Cr(VI) being reduced within 2h at pH 3. Among the samples tested under same anodizing condition, the nanotubular TiO(2) annealed at 450 and 550 degrees C showed highest reduction efficiencies of Cr(VI). In addition, the surface characterizations (zeta potential, XRD, and SEM) of these samples proved that the Cr(VI) reduction efficiency was higher under acidic conditions and at a lower annealing temperature. From this research, it was concluded that the anodized TiO(2) has the potential to be a useful technology for environmental remediation as well as photocatalytic hydrogen production from water.
Journal of Hazardous Materials 05/2008; 161(2-3):1069-74. · 4.33 Impact Factor