Efficient removal of Cs ion by electrochemical adsorption and desorption reaction using NiFe Prussian blue deposited carbon nanofiber electrode.

Prussian blue (PB) analog (NiFe, CoFe, FeFe, and commercial(cPB)) decorated carbon nanofiber (CNF) electrodes were synthesized by the drop casting method in this study to investigate the interaction between PB and CNF for the electrochemical adsorption (EA) and electrochemical desorption (ED) of Cs ion (Cs+). The adhesion of PB on the electrode and the EA and ED of Cs+ were substantially higher when the CNF electrode was used, compared with the fluorine-doped tin oxide supporting electrode. The use of CNF led to the smooth occurrence of EA and ED of Cs+, where the reported efficiency was: NiFe > FeFe > cPB. The EA and ED of Cs+ on NiFe decorated CNF (C-NiFe) were strongly affected by the loading amount of NiFe. Although the strongest EA capacity was identified when 1 mg of NiFe was used, it decreased as the loading amount of NiFe increased. Thus, the EA of Cs+ occurs under the reduction of NiFe with some Fe(III) reduced to Fe(II) of NiFe, thus inducing more adsorption of Cs+. Overall, we confirmed that the C-NiFe electrode with appropriate thickness of NiFe layer is potentially an excellent adsorbent for Cs removal.

Ice-templated synthesis of tungsten oxide nanosheets and their application in arsenite oxidation.

Tungsten oxide (WO3) nanosheets were prepared as catalysts to activate hydrogen peroxide (H2O2) in arsenite (As(III)) oxidation. Ice particles were employed as templates to synthesize the WO3 nanosheets, enabling easy template removal via melting. Transmission electron microscopy and atomic force microscopy revealed that the obtained WO3 nanosheets were plate-like, with lateral sizes ranging from dozens of nanometers to hundreds of nanometers and thicknesses of <10 nm. Compared to that of the WO3 nanoparticle/H2O2 system, a higher efficiency of As(III) oxidation was observed in the WO3 nanosheet/H2O2 system. Electron spin resonance spectroscopy, radical quenching studies, and As(III) oxidation experiments under anoxic conditions suggested that the hydroperoxyl radical (HO2●) acted as the primary oxidant. The WO3 nanosheets possessed numerous surface hydroxyl groups and electrophilic metal centers, enhancing the production of HO2● via H2O2 activation. Various anions commonly present in As(III)-contaminated water exhibited little effect on As(III) oxidation in the WO3 nanosheet/H2O2 system. The high oxidation efficiency was maintained by adding H2O2 when it was depleted, suggesting that the catalytic activity of the WO3 nanosheets did not deteriorate after multiple catalytic cycles.

Simultaneous removal of radioactive cesium and strontium from seawater using a highly efficient Prussian blue-embedded alginate aerogel.

Radioactive cesium (137Cs) and strontium (90Sr) contaminants in seawater have been a serious problem since the Fukushima accident in 2011 due to their long-term health risks. For the effective and simultaneous removal of radioactive cesium (137Cs) and strontium (90Sr) from seawater, a Prussian blue (PB)-immobilized alginate aerogel (PB-alginate aerogel) was fabricated and its adsorption performance was evaluated. PB nanoparticles were homogeneously dispersed in the three-dimensional porous alginate aerogel matrix, which enabled facile contact with seawater. The PB-alginate aerogel exhibited Cs+ and Sr2+ adsorption capacities of 19.88 and 20.10 mg/g, respectively, without substantial interference because Cs+ and Sr2+ adsorption occurred at different adsorption sites on the composite. The Cs+ and Sr2+ adsorption onto the PB-alginate aerogel was completed within 3 h due to the highly porous morphology of the aerogel. The Cs+ and Sr2+ adsorption behaviors on the PB-alginate aerogel were systematically investigated under various conditions. Compared with Cs+ adsorption, Sr2+ adsorption onto the PB-alginate aerogel was more strongly influenced by competing cations (Na+, Mg2+, Ca2+, and K+) in seawater. 137Cs and 90Sr removal tests in real seawater demonstrated the practical feasibility of the PB-alginate aerogel as an adsorbent.

Prussian blue-embedded carboxymethyl cellulose nanofibril membranes for removing radioactive cesium from aqueous solution.

In this study, we synthesized a Prussian blue (PB)-embedded macroporous carboxymethyl cellulose nanofibril (CMCNF) membrane for facile cesium (Cs) removal. The PB was formed in situ at Fe3+ sites on a CMCNF framework cross-linked using FeCl3 as a cross-linking agent. Cubic PB particles of size 5-20 nm were observed on the macroporous CMCNF membrane surface. The PB-CMCNF membrane showed 2.5-fold greater Cs adsorption capacity (130 mg/gPB-CMCNF) than commercial PB nanoparticles, even though the PB loading of the PB-CMCNF membrane was less than 100 mg/gPB-CMCNF. The macroporous structure of the CMCNF membrane led to improved diffusion in the solution, thereby increasing the Cs adsorption capacity. The Cs adsorption behavior was systematically investigated in different solution chemistry. Finally, 137Cs removal using a semicontinuous adsorption module was demonstrated in real seawater. The results showed that the PB-CMCNF membrane is a highly effective, practical material for the removal of 137Cs from aqueous environments.

Photoreaction characteristics of ferrous oxalate recovered from wastewater.

Photoreaction with the Fe(III)-oxalate complex has been reported to play an important role in various photochemical reactions in the natural atmospheric environment, and are applicable to treat various recalcitrant compounds in wastewater. We previously showed that a Fe(II) oxalate (FeOx) crystal can be recovered from the wastewater generated from soil washing, which can then be applied to the photoreaction for degradation of recalcitrant pollutants; however, photoreactions with FeOx compounds have not been fully reported yet. Therefore, this study aims to investigate the photoreaction characteristics of FeOx recovered from wastewater, to demonstrate the feasibility of its application to wastewater treatment. The physical and chemical properties of FeOx were characterized with X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy analyses. The photoreaction of FeOx showed high methylene blue (MB) removal efficiencies similar to the reaction with TiO2, indicating that FeOx is applicable to the photoreaction for degradation of pollutants. Furthermore, the photodegradation of MB with FeOx was observed under visible light, as opposed to TiO2. MB could be removed by the photoreaction of FeOx under both basic and acidic pH conditions. Under basic pH conditions, MB could be removed by FeOx via both photoreaction and surface adsorption. The concentration of FeOx affected light penetration and Fe and oxalate levels in the solution, resulting in different MB removal kinetics. The photoreaction efficiency of FeOx could be affected by both photoreaction of Fe and oxalate in the solution and photoreaction and adsorption reaction of the FeOx surface.

In vivo removal of radioactive cesium compound using Prussian blue-deposited iron oxide nanoparticles.

Aim: To mitigate the side effects of medical treatment by Prussian blue (PB), a well-known adsorbent for radioactive cesium (Cs), PB-deposited magnetic nanoparticles (MNPs), were prepared and analyzed on the adsorbent capacity for Cs removal. Materials & methods: The PB-deposited MNPs were prepared by photo-deposition method and investigated for their Cs adsorption properties in vitro and in vivo. The distribution of the adsorbents was also evaluated in C57BL/6 mice. Results: PB-deposited MNPs provided an improved adsorbent capacity for Cs removal and reduced toxicity to blood cells compared with those of bulk PB. Conclusion: PB-deposited MNPs could be considered as an alternative of PB-based medicine to reduce the possible hazards caused by high dose of PB intake.

Photocatalytic enhancement of cesium removal by Prussian blue-deposited TiO2.

After the Fukushima nuclear accident, tremendous efforts were made to treat radiocesium, radiostrontium, and other radioactive materials. For the first time, we demonstrate that a TiO2 photocatalyst can significantly enhance Cs adsorption by Prussian blue-deposited TiO2 (PB/TiO2) under UV irradiation. In this study, we synthesized PB/TiO2 using the photodeposition method. After the Cs ions were adsorbed on the PB/TiO2 in darkness, we then exposed the PB/TiO2 to UV light irradiation. This resulted in a further increase in Cs ion adsorption of more than 10 times the amount adsorbed in darkness. This photocatalytic-enhanced adsorption of Cs ions was not observed on PB mixed with SiO2, nor under visible light irradiation. We investigated the effects of PB concentration, PB/TiO2 concentration, and gas purging on both dark and photocatalytic-enhanced adsorption of Cs ions by PB/TiO2. Based on the results, we suggest that the photocatalytic-enhanced adsorption of Cs ions on PB/TiO2 is due to photocatalytic reduction of PB, which leads to additional adsorption of Cs ions. The change in solution color before and after the reaction, and the change in solution pH in the dark and during UV irradiation strongly support this suggestion. The photocatalytic-enhanced adsorption of Cs ions was equivalent during radioactive 137Cs removal, indicating important applications for pollutant removal from contaminated water.

Rapid removal of radioactive cesium by polyacrylonitrile nanofibers containing Prussian blue.

After the Fukushima Daiichi Nuclear Power Plant disaster in Japan in 2011, the demand drastically increased for efficient technology for the removal of radioactive cesium. Prussian blue (PB) nanoparticles have shown excellent adsorption ability toward Cs. In this study, we synthesized PB nanoparticles incorporated polyacrylonitrile nanofiber (PB/PAN). PB/PAN has the porous structure of nanofibers, with diameters of several hundred nanometers. PB nanoparticles can be incorporated successfully into the PAN matrix without any change to their intrinsic crystallinity and structure. The mesoporous structure of PB/PAN and the incorporation of PB nanoparticles led to an increase in the Brunauer-Emmett-Teller surface area and pore volume. In addition, PB/PAN exhibited excellent wettability with water. With simple filtering for the removal of radioactive cesium, PB/PAN showed high removal efficiency (87 ±â€¯3%) within 10 s for 10 mL of 137Cs solution (1000 Bq L-1). In addition, the 137Cs removal by PB/PAN showed high removal efficiency (70 ±â€¯2%, after 1 h), even in the actual seawater medium (1000 Bq L-1 of 137Cs). Therefore, PB-incorporated PAN nanofibers can be considered useful in the practical application of Cs removal from radioactive wastewater.

Hybrid metal-Cu2S nanostructures as efficient co-catalysts for photocatalytic hydrogen generation.

In this communication, we present a new synthesis method for the fabrication of hybrid metal-Cu2S (M = Pt, FePt) nanocrystals (HNs). The metal-Cu2S HNs were investigated in photocatalytic hydrogen generation as effective co-catalysts on TiO2. The Pt-Cu2S/TiO2 catalyst showed a higher hydrogen generation rate compared with a pure TiO2 catalyst. This enhancement is attributed to the synergistic effects between Cu2S and Pt, which significantly improve the light absorption ability and the charge separation activity.

Decrease of reactive oxygen species-related biomarkers in the tissue-mimic 3D spheroid culture of human lung cells exposed to zinc oxide nanoparticles.

Common 2-dimensional (2D) cell cultures do not adequately represent cell-cell and cell-matrix signaling and substantially different diffusion/transport pathways. To obtain tissue-mimic information on nanoparticle toxicity from in vitro cell tests, we used a 3-dimensional (3D) culture of human lung cells (A549) prepared with elastin-like peptides modified with an arginine-glycine-aspartate motif. The 3D cells showed different cellular phenotypes, gene expression profiles, and functionalities compared to the 2D cultured cells. In gene array analysis, 3D cells displayed the induced extracellular matrix (ECM)-related biological functions such as cell-to-cell signaling and interaction, cellular function and maintenance, connective tissue development and function, molecular transport, and tissue morphology. Additionally, the expression of ECM-related molecules, such as laminin, fibronectin, and insulin-like growth factor binding protein 3 (IGFBP3), was simultaneously induced at both mRNA and protein levels. When 0.08-50 microg/ml zinc oxide nanoparticles (ZnO-NPs) were administered to 2D and 3D cells, the cell proliferation was not significantly changed. The level of molecular markers for oxidative stress, such as superoxide dismutase (SOD), Bcl-2, ATP synthase, and Complex IV (cytochrome C oxidase), was significantly reduced in 2D culture when exposed to 10 microg/ml ZnO-NPs, but no significant decrease was detected in 3D culture when exposed to the same concentration of ZnO-NPs. In conclusion, the tissue-mimic phenotype and functionality of 3D cells could be achieved through the elevated expression of ECM components. The 3D cells were expected to help to better predict the nanotoxicity of ZnO-NPs at tissue-level by increased cell-cell and cell-ECM adhesion and signaling. The tissue-mimic morphology would also be useful to simulate the diffusion/transport of the nanoparticles in vitro.

Titania nanofibers as a photo-antenna for dye-sensitized solar hydrogen.

Directionally grown TiO(2) nano-architectures can serve as effective platforms for photogenerated charges to flow vectorially through the architecture framework, promising an unexpectedly high efficiency. This study demonstrates that directionally aligned TiO(2) nanofibers (TNF) obtained via a simple rearrangement of randomly scattered TiO(2) nanoparticles (TNP) exhibit significantly enhanced activity in terms of hydrogen production from water under visible light (λ > 420 nm). It has been found that Eosin Y (EY)-sensitized hydrogen production with TNF is greater than those with TNP and commercial TiO(2) samples (Degussa P25 and Hombikat UV-100) by a factor of 7 and >140, respectively, in the presence of triethanolamine (TEOA) as an electron donor. The annealing of TNF at elevated temperatures reduces the amount of H(2) produced and changes various physicochemical properties. Attempts have been made to find correlation factors between hydrogen production and reaction parameters (e.g., pH-dependent EY adsorption, surface area, pore size, particle size, and anatase-to-rutile ratio), none of which have provided an apparent correlation. It was suggested that the interparticle electron transfer is facilitated when TiO(2) nanoparticles are physically interconnected, and TNF might work as a robust photo-antenna for efficiently collecting the photogenerated electrons. The photocurrent measurements in visible light-irradiated EY/TiO(2) suspensions indicate that the photocurrent of TNF is 50% higher than that of TNP, supporting the photo-antenna mechanism of TNF.

Visible light active platinum-ion-doped TiO2 photocatalyst.

Platinum-ion-doped TiO2 (Pt(ion)-TiO2) was synthesized by a sol-gel method, and its visible light photocatalytic activities were successfully demonstrated for the oxidative and reductive degradation of chlorinated organic compounds. Pt(ion)-TiO2 exhibited a yellow-brown color, and its band gap was lower than that of undoped TiO2 by about 0.2 eV. The flat band potential of Pt(ion)-TiO2 was positively shifted by 50 mV compared with that of undoped TiO2. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analyses showed that the Pt ions substituted in the TiO2 lattice were present mainly in the Pt(IV) state with some Pt(II) on the sample surface. Pt(ion)-TiO2 exhibited higher photocatalytic activities than undoped TiO2 under UV irradiation as well. The visible light activity of Pt(ion)-TiO2 was strongly affected by the calcination temperature and the concentration of Pt ion dopant, which were optimal at 673 K and 0.5 atom %, respectively. Under visible irradiation, Pt(ion)-TiO2 degraded dichloroacetate and 4-chlorophenol through an oxidative path and trichloroacetate via a reductive path. The activity of Pt(ion)-TiO2 was not reduced when used repeatedly under visible light. However, visible-light-illuminated Pt(ion)-TiO2 could not degrade substrates such as tetramethylammonium and trichloroethylene, which are degraded with UV-illuminated TiO2. The characteristics and reactivities of Pt(ion)-TiO2 as a new visible light photocatalyst were investigated in various ways and discussed in detail.

Visible-light-induced photocatalytic degradation of 4-chlorophenol and phenolic compounds in aqueous suspension of pure titania: demonstrating the existence of a surface-complex-mediated path.

The visible-light-induced degradation reaction of 4-chlorophenol (4-CP) was investigated in aqueous suspension of pure TiO2. Contrary to common expectations, 4-CP could be degraded under visible illumination (lambda > 420 nm), generating chlorides and CO2 concomitantly. The observed visible reactivity was not due to the presence of trace UV light since the visible-light-induced reactions exhibited behaviors distinguished from those of UV-induced reactions. Dichloroacetate could not be degraded under visible light, whereas it degraded with a much faster rate than 4-CP under UV irradiation. The addition of tert-butyl alcohol, a common OH radical scavenger, did not affect the visible reactivity of 4-CP, which indicates that OH radicals are not involved. Other phenolic compounds such as phenol and 2,4-dichlorophenol were similarly degraded under visible light. The surface complexation between phenolic compounds and TiO2 appears to be responsible for the visible light reactivity. Diffuse reflectance UV-vis spectra showed that 4-CP adsorbed on TiO2 powder induced visible light absorption. The visible light reactivity among several TiO2 samples was apparently correlated with the surface area of TiO2. The visible-light-induced photocurrents on a TiO2 electrode could be obtained only in the presence of 4-CP. It is proposed that a direct electron transfer from surface-complexed phenol to the conduction band of TiO2 upon absorbing visible light (through ligand-to-metal charge transfer) initiates the oxidative degradation of phenolic compounds. When the surface complex formation was hindered by surface fluorination, surface platinization, and high pH, the visible-light-induced degradation of 4-CP was inhibited. The evidence of visible-light-induced reactions and the experimental conditions affecting the visible reactivity were discussed in detail.

Comparative Study of Homogeneous and Heterogeneous Photocatalytic Redox Reactions: PW(12)O(40)(3-) vs TiO(2).

Polyoxometalates (POMs) as a homogeneous photocatalyst and semiconductor oxide as a heterogeneous photocatalyst share many aspects of similarity in their operating mechanisms. This study systematically compares various photocatalytic oxidation and reduction reactions of PW12O403- (a POM) and TiO2 in water to demonstrate that the two photocatalysts are very different in many ways. Both POM and TiO2 can photooxidize various organic compounds with comparable rates, but the POM-mediated mineralization is markedly slower than the mineralization with TiO2 under the experimental conditions employed in this study. Kinetic studies using tert-butyl alcohol as an OH radical scavenger suggest that OH radicals are the sole dominant photooxidant in POM-mediated degradations regardless of the kind of substrates tested, whereas both OH radicals and direct hole transfers take part in TiO2 photocatalysis. POM immobilization on silica support and surface fluorination of TiO2 significantly modified the kinetics and intermediate distribution. POM-mediated photoreductive dechlorination of CCl4 and trichloroacetate was negligible, whereas the dechlorination with TiO2 was markedly faster. The rate of electron transfer from POM- to reducible substrates seems to be significantly slower than the rate of conduction band electron transfer on TiO2 mainly due to the strong electron affinity of POM. The effects of H2O2 addition on photocatalytic reactivity are also very different between POM and TiO2. Detailed kinetic and mechanistic comparisons between PW12O403- and TiO2 photocatalysts are presented and discussed to understand the similarities and differences.

Kinetics and mechanisms of photocatalytic degradation of (CH3)nNH(4-n)+ (0 < or = n < or = 4) in TiO2 suspension: the role of OH radicals.

The photocatalytic degradation of a series of (CH3)nNH(4-n)+ (0 < or = n < or = 4) was systematically studied in the UV-illuminated TiO2 aqueous suspensions at pH ranges of 3-11. By investigating the pH-dependent kinetics and analyzing intermediates and products, we elucidated the mechanistic pathways and the role of OH radicals in the photocatalytic oxidation. The deprotonated neutral species more rapidly degraded than their protonated counterparts for these homologous compounds because the OH radicals favorably reacted with the lone-pair electron on the nitrogen atom. Therefore, the photocatalytic degradation was highly enhanced at alkaline solutions for all substances except (CH3)4N+. The H-atom abstraction (from (CH3)4N+) by OH radicals initiated successive demethylation processes to generate tri-, di-, and monomethylammonium/amine as an intermediate and NH3/NH4+ as a final product. On the other hand, the OH-addition to the N-atom with the lone-pair electron led to NO2-/NO3- whose production was highly favored at alkaline conditions. The photocatalytic degradation rates of (CH3)4N+ were comparable at both acidic and alkaline conditions, which could not be explained by a simple electrostatic surface charge model. By using OH-scavenging tert-butyl alcohol as a diagnostic probe into the mechanism, it is suggested that the photocatalytic oxidation of (CH3)4N+ at acidic conditions proceeds through free OH radicals in the solution bulk, not on the surface of TiO2.