Reason for the loss of hydrophilicity of TiO_2 film and its photocatalytic regeneration

TiO2 film was prepared on soda-lime glass by sol-gel method. The water contact angle (θ) of the fresh TiO2 film is 0°. During storage in air, the surface of TiO2 film is gradually converted to the hydrophobic state. XPS and ITD results reveal that it is due to the adsorption of organic contaminants on TiO2 surface in air ambience. The lost hydrophilicity of TiO2 film can be regenerated by UV illumination.     

Preparation and Photocatalytic Activity of Ce,H3PW12O40 co-doped TiO2 Hollow Fibers

A series of Ce, H3PW12O40 co-doped TiO2 hollow fibers photocatalysts have been prepared by sol-gel method using ammonium ceric nitrate, H3PW12O40 and tetrabutyltitanate as precursors and cotton fibers as template, followed by calcination at 500 ℃ in N2 atmosphere for 2 h. Scanning electron microscopy, X-ray diffraction, nitrogen adsorption-desorption mea- surements, and UV-Vis spectroscopy are employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photo- catalytic performance of the samples has been studied by photodegradation phenol in water under UV and visible light irradiation. The results show that the TiO2 fiber materials have hollow structures, and the co-doped TiO2 hollow fibers exhibit higher photocatalytic activities for the degradation of phenol than un-doped, single-doped TiO2 hollow fibers under UV and visible light. In addition, the recyclability of co-doped TiO2 fibers is also confirmed that the TiO2 fiber retains ca. 90% of its activity after being used four times. It is shown that the co-doped TiO2 fibers can be activated by visible light and may be potentially applied to the treatment of water contaminated by organic pollutants. The synergistic effect of Ce and H3PW12O40 co-doping plays an important role in improving the photocatalytic activity.     

Two Photoelectrochemical Processes for TiO2 Electrode under UV Illumination

TiO2 thin film electrode was prepared by a sol-gel method on ITO substrates. Cyclic voltammetric behavior of the ITO/TiO2 electrode under ultraviolet (UV) illumination was investigated in the solution of Na2SO4.There are two photoelectrochemical processes for TiO2 electrode under UV illumination.One is a fast process,which results in the appearance of anodic photocurrent.The anodic photocurrent will appear and disappear with the light on and off.The other is a slow process,which will be responsible for the appearance of an oxidative peak. When the electrode is illuminated under UV light for a long time,a new oxidative peak can be observed.The peak current increases with the increase of UV illumination time.It is assumed that the new peak belongs to the oxidation of Ti^3 ,which formed and accumulated on the electrode surface during the UV illumination.A detailed mechanism is proposed on the base of these two photoelectrochemical processes.It is assumed that the change of hydrophilicity of TiO2 thin film may be related to the slow process while the film irradiated by UV light.     

Synthesis of TiO2 photocatalysts with abundant surface defects using a TiO2@NaCl precursor

TiO2 nanoparticles have been synthesized by using a TiO2@NaCl core-shell structure as the precursor. The surface defects were well preserved by the NaCl shell, and therefore high oxygen adsorption capacity was observed. After the NaCl shell was removed, the resulting pure TiO2 nanoparticles were of anatase phase and uniform size of around 20?24 nm. The presence of an abundance of surface defects contributes to the high photocatalytic activity of the synthesized materials, and the TiO2 materials obtained from the TiO2@NaCl precursor can be used as efficient photocatalysts for degradation of rhodamine B under UV light irradiation.     

One-step solvothermal synthesis of N-doped TiO2 nanoparticles with high photocatalytic activity in the reduction of aqueous Cr（Ⅵ）

N-doped TiO2 （N-TiO2） nanoparticles were synthesized via a one-step low temperature （180℃） solvothermal route, which adopted NH4NO3 as the nitrogen source. The structure, composition, BET specific surface area, and optical properties of the as-synthesized product were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption- desorption isotherms, and UV-vis diffuse reflectance spectroscopy. In addition, its photocatalytic properties were tested by the reduction of aqueous Cr（VI） under UV and visible light （x 〉 420 rim） irradiation. It was observed that for the reduction of aqueous Cr（VI）, the as-synthesized N-TiO2 nanoparticles not only exhibited much higher photocatalytic activity than P25 TiO2 under UV light, but also exhibited remarkably high photocatalytic activity under visible light （λ 〉 420 nm）.     

Preparation of TiO2 Nanocrystals/Graphene Composite and Its Photocatalytic Performance

TiO2 nanocrystals/graphene （TiO2/GR） composite are prepared by combining flocculation and hydrothermal reduction technology using graphite oxide and TiO2 colloid as precursors. The obtained materials are examined by scanning electron microscopy, transition electron microscopy, X-ray diffraction, N2 adsorption desorption, and ultraviolet-visible diffuse spectroscopy. The results suggest that the presence of TiO2 nanocrystals with diameter of about 15 nm prevents GR nanosheets from agglomeration. Owing to the uniform distribution of TiO2 nanocrystals on the GR nanosheets, TiO2/GR composite exhibits stronger light absorption in the visible region, higher adsorption capacity to methylene blue and higher efficiency of charge separation and transportation compared with pure TiO2. Moreover, the TiO2/GR composite with a GR content of 30% shows higher photocatalytic removal efficiency of MB from water than that of pure TiO2 and commercial P25 under both UV and sunlight irradiation.     

Comparative Study of Hypophosphite H2PO2^- Adsorption on Ni（111） and Ag（111） Surfaces by DFT

Surface structures and electronic properties of hypophosphite H2PO2^- on Ni（111） and Ag（111） surfaces were investigated by means of density functional theory at B3LYP/6-31 ＋ ＋G（d,p） level. The most stable structure was that in which the H2PO2^- adsorbs with its two P--O bonds faced to the substrate surface. The results of the Mulliken population analysis showed that because of the subtle difference of electron configuration, the adsorption energy was larger on the Ni surface than on the Ag surface, and the amounts of both donation and back donation were larger on the Ni（111） surface than on the Ag（111） surface. There were more negative Mulliken charge transfer from H2PO2^- to substrate clusters on Ni surface than on Ag surface and more positive Mulliken charges on P atom in Ni4H2PO2^- than in Ag4H2PO2^-, which means that P atom in Ni4H2PO2^- is easily attacked by a nucleophile such as OH . Thus, H2PO2^- is more easily oxidated on Ni（111） surface than on Ag（111） suface. These results indicated that the silver surface is inactive for the oxidation reaction of the hypophosphite anion.     

Density Functional Theory Studies on the Adsorption of CO2 on Different CaO Surfaces

Carbon dioxide adsorbed on different kinds of CaO surfaces has been investigated with the help of the first principle density functional theory plane wave calculations. Various possible configurations have been considered and the calculated results showed that CO2 was strongly adsorbed by C atom bonded with the CaO （001） and （110） surfaces with adsorption energies of 1.38 and 3.22 eV, respectively. The adsorption of CO2 molecule on defect surfaces is complicated compared with that on the pristine surfaces. The adsorption energy of CO2 absorbed on the CaO（110） surface is larger than that of CaO（001） surface when the type of defect surface is the same.     

Defect-enhanced Photocatalytic Activity of ZnO Micro/nanostructures

ZnO micro/nanocrystals with controlled oxygen defects are successfully prepared through annealing precursors obtained via a simple solvothermal method. The size and surface defects of the as-synthesized ZnO mi- cro/nanocrystals increase with the solvent volume ratio of water/ethanol increasing; the BET surface areas of the corresponding samples decrease during these processes; photoluminescence reveals that the type and concentration of surface defects （oxygen vacancy and interstitial oxygen） are quite different for the samples prepared via different solvent volume ratio of water/ethanol. In addition, it is found that the photocatalytic activity of the synthesized ZnO nanocrystals is mainly dependent on the concentration of surface defects. The sample with more surface defects ex- hibits higher photocatalytic activity toward the degradation of methylene blue （MB）. The possible photocatalytic mechanism is discussed in detail.     

Double layered, one-pot hydrothermal synthesis of M-TiO2 (M = Fe3+, Ni2+, Cu2+ and Co2+) and their application in photocatalysis

A double layered,one-pot hydrothermal method was adopted in this work to prepare transition metal ions(Fe3+,Ni2+,Cu2+and Co2+)doped TiO2.The morphology and chemical properties of TiO2and the status of metal ions were characterized with XRD,TEM,BET,UV-Vis and XPS analysis.TEM images show that the obtained TiO2was very uniform with an average particle size of 10.4 nm.XPS,TEM and XRD results show that transitional metals were doped onto TiO2in the form of ions.Photocatalytic decomposition of oxalic acid under UV illumination and methylene blue degradation under visible light on these materials were conducted,respectively.The results reveal that Cu2+-TiO2and Co2+-TiO2showed a highest activity under UV and visible light illumination,respectively,and they were both more active than commercial P25 TiO2.With this special design of double layers,the hydrolysis of titanium precursor in the system with water can be easily controlled and metal ions are simply doped.This strategy can be further applied to synthesize metal ion doped TiO2using various metal precursors with controllable amounts,and thus lead to better optimization of highly active photocatalyst.     

DRIFT Study on Cr2O3-SO42-/TiO2 Catalyst for Low Temperature Selective Catalytic Reduction of NO with NH3

Chromium oxides supported on TiO2 showed good activity for the selective catalytic reduction of NO by NH3.The catalytic activity of Cr2O3-SO42-/TiO2 catalyst was greatly enhanced by the addition of SO42-into TiO2 support.The catalyst surface properties were characterized with NH3-TPD（temperature programmed desorption） and H2-TPR（temperature programmed reduction）.The sulphate on the catalyst surface could enhance the acidity and redox of the catalyst obviously.The reaction mechanism on this catalyst was researched in detail by in situ diffuse reflectance Fourier transform infrared（FTIR） spectroscope.Eley-Rideal and Langmuir-Hinshelwood mechanism existed simultaneously for selective catalytic reduction（SCR） reaction of NO over Cr2O3-SO42-/TiO2 catalyst.     

Theoretic and Experimental Studies on Titania Nanotube Doped with Ag Metal Ions

The electronic state density and energy bands of Ag-doped anatase TiO2 are studied by WIEN2k software package based on DFT. The calculation results show that the band-gap of anatase titania became bigger after doping with Ag metal ions. The band-gap transfers from 2.04 to 2.5 eV, but a new energy band appears among the forbidden band after the Ag atom substitution. The interband width of Ag-TiO2 is 0.17 eV, which is located at –0.07 eV; more excitation and jump routes are opened for the electrons. The lowest excitation energy can achieve 1.2 eV, which may allow the photons with lower energy (at longer wavelength, such as visible light) to be absorbed. Ag ions are implanted into the titania nanotube sample by MEVVA (Metal Vapor Vacuum Arc) implanter. The photo-electrochemical response and photo-degradation experiment of titania nanotube samples implanted with Ag ions are tested under UV and visible light; the results indicated that the performance of implanted titania naotubes is enhanced both under UV and visible light; it is worth mentioning that the photocurrent density can reach 0.145 mA/cm2 under visible light, which is 181 times higher than those of pure TiNT, and the k value of degradation methyl orange can obtain 0.30 h-1, which is 71 times higher than that of pure TiNT. All the experimental results are consistent well with the theoretic ones.     

Controllable synthesis of titania/reduced graphite oxide nanocomposites with various titania phase compositions and their photocatalytic performance

A facile method is presented for preparing TiO2 /reduced graphite oxide(RGO) nanocomposites with phase-controlled TiO2 nanoparticles via redox reaction between the reductive titanium(Ⅲ) precursor and graphite oxide(GO),and a series of TiO2 /RGO composites with various TiO2 phase compositions were obtained.In all the titania/RGO composites,the TiO2 nanoparticles were uniformly distributed on the surface of the RGO.The TiO2 consisted of anatase phase particles in the form of square-plates with edges less than 10 nm and the rutile phase nanorods in diameters less than 10 nm.The performances of the as-prepared TiO2 /RGO composites were investigated on catalytically degrading phenol under visible light irradiation.The TiO2 /RGO composites can effectively degrade phenol under visible light irradiation,and the phase composition of TiO2 in the composites significantly influences the activities of these catalysts.     

Effect of Binder on the Structure and Properties of Silicon Powder-supported TiO_2 Photocatalysis Material

Recoverable TiO2 photocatalysis material supported by silicon powder was prepared with sol-gel method, afterwards the silica gol and sodium silicate were used as molding binder respectively to investigate their effects （including binder type and binder addition quantity） on the crystal structure and catalysis properties of photocatalyst. In this work, the catalysis activity was defined as the degradation rate of methyl orange solution upon ultraviolet lamp irradiation, and the specific areas were determined with nitrogen desorption method. TiO2 crystal form was measured with X-ray powder diffraction and their micro-morphology was observed with SEM. Experimental results indicate that these two binders do not affect the crystal form transformation of TiO2, but silica gol can increase the specific surface area of TiO2 photocatalyst obviously and the addition of sodium silicate can decrease it. In all, silica gol is a better candidate than sodium silicate for higher catalysis property. In conclusion, 6% silica gol is the optimal addition concentration. Under this condition, the ratio of anatase to rutile TiO2 is 64：36, the specific area is 29.67 m^2/g, and as expected, the degradation rate of methyl orange could be as high as 90% after irradiation for 5 days.     

TARNISH AND PROTECTION OF SILVER DEPOSIT——MECHANISM AND METHOD

The mechanism of tarnish caused by exposure to light and Na_2S solution treatment on silver-electroplated deposit and the antitarnish effects of various antitarnish agents have been investigated in this paper. The results showed that 1-phenyl-5-mercaptotetrazole (PMTA) has excellent antitarnish effect for UV light and H_2S tests.The studies of XPS and AES and UV absorption spectra showed that PMTA can absorb effectively UV light and form a dense surface film which can prevent effectively the reactions between silver deposit with corrosive media.Antitarnish surface film could be composed of a polynuclear coordination polymeric compound with structure unit approximate to [Ag_3(PMTA)]. according to the depth dependence of percent component (C%) and sputtering time.     

Adsorption of Nin (n=1 -4) clusters on perfect and O-defective CuAl2O4 surfaces: A DFT study

The adsorption energies for single Ni atom on CuAl₂O₄(100) and (110) surfaces are 5.30 and 4.08 eV, respectively. The growth and aggregation of Ni can be effectively inhibited on the perfect CuAl₂O₄(100) surface. The adsorption of Ni on the spinel surface is accompanied by charge transfer. The interaction of Ni with CuAl₂O₄ surface is stronger than with the γ-Al₂O₃(110) surface.     

Density Functional Theory Study of C2Hx（x=4～6） Adsorption on the Fe（110） Surface

The density functional theory(DFT) and self-consistent periodic calculation were used to investigate the C2Hx(x = 4～6) species adsorption on the Fe(110) surface. The adsorption energy and equilibrium geometry of the species C2Hx(x = 4～6) on four possible sites(top,hcp,SB and LB) on the Fe(110) surface were predicted and compared. Mulliken charges and density of states analysis of the most stable site have been discussed. It is found that the species of C2H6 and C2H5 are adsorbed strongly on the Fe(110) surface with calculated adsorption energy of -80.24 and -178.89 kJ·mol-1 at the Fe-LB(long-bridge) ,respectively. However,the C2H4 is adsorbed strongly on the Fe(110) surface with calculated adsorption energies of -114.96 kJ·mol-1 at the top. The results indicate that the charge transferring process can be completed by chemisorption between Fe(110) surface and the species. Moreover,the chemical bands can be formed by chemisorptions between the Fe(110) surface and the species,too.     

Photocatalytic Activity for Water Decomposition to Hydrogen over Nitrogen‐doped TiO2 Nanoparticle

Nitrogen-doped TiO2 nanoparticle photocatalysts were obtained by an annealing method with gaseous ammonia and nitrogen. The influence of dopant N on the crystal structure was characterized by XRD, XPS, BET, TEM and UV-Vis spectra. The results of XRD indicate that, the crystal phase transforms from anatase to rutile structure gradually with increase of annealing temperature from 300 to 700 ℃. XPS studies indicate that the nitrogen atom enters the TiO2 lattice and occupies the position of oxygen atom. Agglomeration of particles is found in TEM images after annealing. BET results show that the specific surface areas of N-doped samples from 44.61 to 38.27 m2/g are smaller than that of Degussa TiO2. UV-Vis spectra indicate that the absorption threshold shifts gradually with increase of annealing temperature, which shows absorption in the visible region. The influence of annealing condition on the photocatalytic property has been researched over water decomposition to hydrogen, indicating that nitrogen raises the photocatalytic activity for hydrogen evolution, and the modified TiO2 annealed for 2 h at 400 ℃ under gas of NH3/N2 (V/V＝1/2) mixture shows better efficiency of hydrogen evolution. Furthermore, the N-doped TiO2 nanoparticle catalysts have obvious visible light activity, evidenced by hydrogen evolution under visible light (λ＞400 nm) irradiation. However, the catalytic activity under visible light irradiation is absent for Degussa as reference and the N-doped TiO2 annealed at 700 ℃.     

PREPRARATION OF CoPcS/TiO2/BEADS AND THEIR PHOTOCATALYTIC REACTIVITY FOR PHOTODEGRADATION OF VEGETABLE OIL FLOATING ON WATER

The paper introduces the preparation of floating TiO2/beads photocalyst attached to the hollow glass micro-beads surface by sol-gel technique using tetrabutyl titanate as material and the preparation of floating CoPcS/TiO2/beads by dip-coatig technique. The optimal factor of degradation of vegetable oil floating on water using CoPcS/TiO2/beads was studied. The result showed that the removal rate of vegetable oil floating on water can highly reach 90% at the optimal condition （acidity or neutrality, 375W medium-pressure mercury vapour lamp, illumination 2h-3h, lg CoPcS/TiO2/beads）. The photocatalytic removal efficiency causing by CoPcS/TiO2/beads was increased rapidly by adding a trace amount of H2O2.     

Influence and Characterization of Acidity on Fine Silicon Powder Immobilized Photocatalyst

TiO2 photocatalyst was supported with tetrabutyl titanate sol as precursor and fine silicon powder obtained from ferroalloys factory as carder to discuss the influence of pH value of gel precursor on microstructure and activity of photocatalyst in the process of synthesizing nano-TiO2 by using sol-gel method, the purpose of which is to provide fundamental data for the recycle of photocatalytic material. Under the irradiation of ultraviolet light, the photocatalytic degradation rate of methyl orange solution was used to characterize the photocatalytic activity of the sample. The specific surface area of the sample was tested by N2 desorption method, crystal form of TiO2 was analyzed by X-ray powder diffraction, and the microtopography of the sample was observed by scanning electron microscopy. The experimental results showed that the acidity of gel precursor could greatly affect the specific surface area and photocatalytic activity of the photocatalyst, and the optimum pH value of the precursor was determined as 2.0, and at this time the specific surface area of photocatalyst could reach 34.0 m^2/g. In the sample, the proporticn of anatase to rutile is 7：3, which makes l0 mg·L^-1 methyl orange solution fade after irradiation by 15W ultraviolet light for 24 h, and the degradation rate might be up to 98.1%.