Photocatalytic H2 production on trititanate nanotubes coupled with CdS and platinum nanoparticles under visible light: revisiting H2 production and material durability.

The photocatalytic production of molecular hydrogen (H2) on ternary composites of Pt, CdS, and sodium trititanate nanotubes (NaxH2-xTi3O7, TNTs) is examined in an aqueous 2-propanol (IPA) solution (typically 5 vol%) at a circum-neutral pH under visible light (λ > 420 nm). The H2 production rates are dependent on the Pt-loading level, and the optimum production rate in the Pt/CdS/TNTs is approximately six times higher than that in Pt/CdS/TiO2. A D2O solution containing 5 vol% IPA leads only to the production of D2 molecules, whereas increasing the IPA amount to 30 vol% leads to the production of DH molecules. This indicates that the Pt/CdS/TNTs composites enable H2 production via true water splitting under our typical experimental conditions. X-ray photoelectron spectroscopy (XPS) analyses of the as-synthesized Pt/CdS/TNTs and those used for 6 and 12 h show that metallic Pt on the CdS/TNTs is less susceptible to oxidation than Pt on CdS/TiO2. In addition, photocorrosion of CdS (i.e., sulfate formation) is significantly inhibited during the photocatalytic H2 production reactions in the Pt/CdS/TNTs because of the efficient charge transfer via the TNTs framework. The Pt/CdS/TNTs samples are thermally more stable than Pt/CdS/TiO2 and CdS/TNTs, effectively inhibiting the formation of CdO during the thermal synthesis. Detailed surface characterizations of the as-synthesized ternary composites are performed using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and XPS.

Artificial photosynthesis of C1-C3 hydrocarbons from water and CO2 on titanate nanotubes decorated with nanoparticle elemental copper and CdS quantum dots.

The conversion of CO2 and water into value-added fuels with visible light is difficult to achieve in inorganic photocatalytic systems. However, we synthesized a ternary catalyst, CdS/(Cu-TNTs), which is assembled on a core of sodium trititanate nanotubes (TNTs; NaxH2-xTi3O7) decorated with elemental copper deposits followed by an overcoat of CdS quantum dot deposits. This ternary photocatalyst is capable of catalyzing the conversion of CO2 and water into C1-C3 hydrocarbons (e.g., CH4, C2H6, C3H8, C2H4, C3H6) upon irradiation with visible light above 420 nm. With this composite photocatalyst, sacrificial electron donors are not required for the photoreduction of CO2. We have shown that water is the principal photoexcited-state electron donor, while CO2 bound to the composite surface serves as the corresponding electron acceptor. If the photochemical reaction is carried out under an atmosphere of 99.9% (13)CO2, then the product hydrocarbons are built upon a (13)C backbone. However, free molecular H2 is not observed over 5 h of visible light irradiation even though proton reduction in aqueous solution is thermodynamically favored over CO2 reduction. In terms of photocatalytic efficiency, the stoichiometric fraction of Na(+) in TNTs appears to be an important factor that influences the formation of the observed hydrocarbons. The coordination of CO2 to surface exchange sites on the ternary catalyst leads to the formation of surface-bound CO2 and related carbonate species. It appears that the bidentate binding of O═C═O to certain reactive surface sites reduces the energy barrier for conduction band electron transfer to CO2. The methyl radical (CH3(•)), an observed intermediate in the reaction, was positively identified using an ESR spin trapping probe molecule. The copper deposits on the surface of TNTs appear to play a major role in the transient trapping of methyl radical, which in turn self-reacts to produce ethane.

Microwave-assisted hydrothermal synthesis of N-doped titanate nanotubes for visible-light-responsive photocatalysis.

This study employs a rapid, energy frugal and environmental friendly method to synthesize nitrogen doped titanate nanotubes (NTNTs), and uses TEM, XRD, Raman, nitrogen adsorption-desorption isotherms analysis, and UV-vis spectroscopy to characterize the obtained NTNTs. TEM results demonstrate that the current research successfully synthesized one-dimensional NTNTs via the microwave hydrothermal (M-H) method, and show that NTNTs retain a tubular structure after sintering at a temperature of 350°C. XRD results agree well with Raman spectrum findings. Both show that the intensity of anatase crystallization increases with an increase in sintering temperature. After sintering at high temperature, above 250°C, the UV-vis absorbance edges of NTNTs significantly shift to the visible-light region, which illustrates N atom doping into nanotubes. Photocatalytic tests conclude that the NTNTs-350 shows good efficiency with visible-light response.

Selective decomposition of aqueous nitrate into nitrogen using iron deposited bimetals.

In the case of the reduction of nitrate in groundwater, the problem is how to convert nitrate [N(+V)] selectively to nontoxic dinitrogen [N(O)] and not to completely reduced ammonia [N(-III)]. Unfortunately, near 100% of the total nitrogen in nitrate is reductively converted to ammonia using naked zerovalent iron (ZVI) thus far reported. In this study, deposition of noble metals (Pt, Pd, and Au) and Cu on iron surface to offer favorable pathways for nitrate reduction was fabricated using either the complete mixing orthe successive method with spontaneous redox reactions. The prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy/energy disperse X-ray spectroscopy, and electrochemical analysis. The formation of N2 from the reduction of nitrate was confirmed by residual gas analyzer coupled to a high vacuum system. Based on the experimental results, the ZVI deposited Pd and Cu closely is suggested to promote the abstraction of oxygen from NOx by adsorbed atomic hydrogen on the Cu surface, and enhance N2 formation on the Pd surface. An optimum N2 selectivity of approximately 30% obtained in the alkaline solution containing nitrate using 0.3 wt.% Pd-0.5 wt% Cu/Fe is evident. For groundwater treatment, iron deposited Pd and Cu could facilitate the development of a process requiring neither a massive addition of chemicals nor complex equipment.

Photocatalytic oxidation of aqueous ammonia over microwave-induced titanate nanotubes.

Characterizations of microwave-induced titanate nanotubes (NaxH(2-x)Ti3O7, TNTs) were conducted by the determinations of specific surface area (S(BET)), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS), ionic coupled plasma-atomic emission spectrometry(ICP-AES), scanning electron microscopy/ energy dispersive X-ray (SEM/EDX), and high-resolution transmission electron microscopy (HR-TEM). The applied level of microwave irradiation during the fabrication process is responsible for both the intercalation intensity of Na atoms into TNTs and the type of crystallization phase within TNTs, which dominate the efficiency of photocatalytic NH3/NH4+. A pure TNT phase presents no powerful ability toward photocatalytic NH3/ NH4+, while the photocatalytic efficiency can be enhanced with the presence of a rutile phase within TNTs. In addition, the mixture of anatase and rutile phase within P25 TiO2 prefers forming NO3-, whereas TNTs yield higher NO2- amount Regarding the effect of acid-washing treatment on TNTs, the acid-treated TNTs with enhanced ion exchangeability considerably improve the NH3/NH4+ degradation and NO2-/NO3- yields. This result is likely ascribed to the easy intercalation of NH3/ NH4+ into the structure of acid-washing TNTs so that the photocatalytic oxidation of intercalated NH3/NH4+ is not limited to the shielding effect resulting from the overload of TNTs.

Photocatalysis of gaseous trichloroethylene (TCE) over TiO2: the effect of oxygen and relative humidity on the generation of dichloroacetyl chloride (DCAC) and phosgene.

Batch photocatalytic degradation of 80+/-2.5 ppm V trichloroethylene (TCE) was conducted to investigate the effect of the oxygen and relative humidity (RH) on the formation of the dichloroacetyl chloride (DCAC) and phosgene. Based on the simultaneous ordinary differential equations (ODEs), the reaction rate constants of TCE ((2.31+/-0.28) approximately (9.41+/-0.63)x10(-2) min(-1)) are generally larger than that of DCAC ((0.94+/-1.25) approximately (9.35+/-1.71)x10(-3) min(-1)) by approximate one order. The phenomenon indicates the degradation potential of TCE is superior to that of DCAC. DCAC appreciably delivers the same degradation behavior with TCE that means there exists an optimum RH and oxygen concentration for photocatalysis of TCE and DCAC. At the time the peak yield of DCAC appears, the conversion ratio based on the carbon atom from TCE to DCAC is within the range of 30-83% suggesting that the DCAC generation is significantly attributed to TCE degradation. Regarding the phosgene formation, the increasing oxygen amount leads to the inhibitory effect on the phosgene yield which fall within the range of 5-15%. The formation mechanism of phosgene was also inferred that the Cl atoms attacking the C-C bond of DCAC results to the generation of phosgene rather than directly from the TCE destruction.

Exploring the interparticle electron transfer process in the photocatalytic oxidation of 4-chlorophenol.

This work aimed to investigate the interparticle electron transfer (IPET) process within the coupled-photocatalyst systems on the basis of the degradation of 4-chlorophenol (4-CP). TiO(2), ZnO and SnO(2) are used as the model photocatalysts owing to their increasing energy levels which correspond to the IPET concept. In the single-photocatalyst tests, ZnO tests are associated with the highest degradation rate constants (0.347+/-0.083 h(-1) at pH 7 and 0.453+/-0.011 h(-1) at pH 11) and a better DOC reduction than in other single catalyst tests under given conditions. ZnO/SnO(2) coupled tests have constants of 0.612+/-0.068 and 0.948+/-0.069 h(-1) at pH 7 and 11, respectively. Additionally, the 4-CP prefers the breakdown of chloride group in TiO(2) system while proceeding hydroxylation reaction in ZnO systems. Meanwhile, a phenomenonlogical model coupled with the IPET effect was developed to explore the separation of photo-electrons and photo-holes within catalysts. Based on the model parameters, the recombination rate of photo-electrons and photo-holes in TiO(2)/SnO(2) and ZnO/SnO(2) systems is 20-45% lower than that obtained by a respective single catalyst. Thus, coupled-photocatalyst tests, TiO(2)/SnO(2) and ZnO/SnO(2) efficiently suppress the recombination, particularly for ZnO/SnO(2) tests at pH 11.