Gongxuan Lu

Photocatalytic and photoelectric properties of cubic Ag3PO4 sub-microcrystals with sharp corners and edges

Herein, we demonstrate a complex-precipitation strategy for high-yield fabrication of single-crystalline Ag(3)PO(4) sub-microcubes with sharp corners, edges, and smooth surfaces, which exhibit much higher photocatalytic activities and photoelectric conversion properties than spherical Ag(3)PO(4) particles and commercial N-doped TiO(2) under visible light irradiation.

Photocatalytic hydrogen generation and decomposition of oxalic acid over platinized TiO2

Abstract Photocatalytic hydrogen evolution using oxalic acid as electron donor has been investigated over Pt–TiO2 prepared by photodeposition. The reaction kinetics is consistent with the Langmuir model. The effects of pH, amount of deposited Pt and additives of inorganic anions on the rate of the reaction were also studied. A possible reaction mechanism was discussed.

Eosin Y-sensitized graphitic carbon nitride fabricated by heating urea for visible light photocatalytic hydrogen evolution: the effect of the pyrolysis temperature of urea

Graphitic carbon nitride (g-C3N4) was prepared by pyrolysis of urea at different temperatures (450-650 °C), and characterized by thermogravimetric and differential thermal analysis (TG-DTA), elemental analysis (C/H/N), X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), Brunauer-Emmett-Teller (BET) analysis, Fourier transform-infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The samples prepared at low temperatures (450 and 500 °C) are a mixture of g-C3N4 and impurities, whereas the samples prepared at high temperatures (550, 600 and 650 °C) should be g-C3N4 (polymeric carbon nitride). The polymerization degree of g-C3N4 for the prepared samples increases to a maximum at 600 °C with increasing pyrolysis temperature and then decreases, whereas the defect concentration changes conversely, that is, g-C3N4 prepared at 600 °C has the lowest defect concentration. Using Eosin Y (EY) and the prepared sample as the sensitizer and the matrix, respectively, the photocatalytic activity for hydrogen evolution from aqueous triethanolamine solution was investigated. The g-C3N4 prepared at 600 °C exhibits the highest sensitization activity. Under optimum conditions (1.25 × 10(-5) mol L(-1) EY and 7.0 wt% Pt), the maximal apparent quantum yield of EY-sensitized g-C3N4 prepared at 600 °C for hydrogen evolution is 18.8%. The highest activity can be attributed to the pure composition, the higher dye adsorption amount and the lowest defect concentration.

Photocatalytic degradation of dyes on a magnetically separated photocatalyst under visible and UV irradiation

A novel kind of magnetically separable photocatalyst of TiO2/SiO2/gamma-Fe2O3 (TSF) is prepared. Scanning tunnel microscope (STM) and X-ray diffractometer (XRD) were used to characterize the structure of the photocatalyst. In the TSF photocatalyst, a TiO2 shell is for photocatalysis, a gamma-Fe2O3 core as a carrier is for separation by the magnetic field and a SiO2 membrane between the TiO2 shell and the gamma-Fe2O3 core is used to weaken the adverse influence of gamma-Fe2O3 on the photocatalysis of TiO2. Three kinds of dyes, Fluoresein, Orange II and Red acid G, were used to examine the photocatalytic activity of TSF. Due to strong UV adsorption of the gamma-Fe2O3, the photocatalytic activity of TSF was lower than that of the pure TiO2. Deducting the light absorption of the gamma-Fe2O3 particles, the photocatalytic activity of TSF was found to be higher than that of the P25 under UV irradiation. On the other hand, the photocatalytic activity of TSF under visible irradiation was much lower than that of the P25 TiO2 even deducting the visible light absorption of the gamma-Fe2O3 particles. Differences in the photocatalytic mechanisms under UV and visible irradiation lead to the differences in the photodegradation characteristics of dyes on TSF. The recycled TSF exhibited a good repeatability of photocatalytic activity.

Selective growth of Ag3PO4 submicro-cubes on Ag nanowires to fabricate necklace-like heterostructures for photocatalytic applications

Selective growth of Ag3PO4 submicro-cubes on Ag nanowires to construct necklace-like hetero-photocatalysts has been demonstrated. This novel hetero-structure exhibits much higher activities than both pure Ag3PO4 cubes and Ag nanowires for degradation of organic contaminants under visible light irradiation, which may be primarily ascribed to highly efficient charge separation at the contact interfaces as well as rapid electron export through Ag nanowires.

Photocatalytic production of hydrogen in single component and mixture systems of electron donors and monitoring adsorption of donors by in situ infrared spectroscopy

The photocatalytic production of hydrogen using aqueous Pt/TiO2 suspension has been investigated in single component and mixture systems of electron donors (pollutants). The reaction systems consisted of oxalic acid, formic acid and formaldehyde, respectively. The adsorption of these donors on TiO2 was also monitored by in situ attenuated total reflection infrared spectroscopy (ATRIR). In the single component systems, the efficiency order of electron donors is as follows: H2C2O4 > HCOOH > HCHO. The order is consistent with the order of adsorption affinity of the electron donors on TiO2 determined by ATRIR, which suggests a link between the strength of surface interaction and the efficiency of photocatalytic hydrogen evolution. In the binary mixture systems, competitive inhibition kinetics is observed. When a donor adsorbed strongly on TiO2 in a state of saturated adsorption in a binary system, the overall rate of the hydrogen evolution is consistent with that of decomposition of the donor, and the system can be treated as a single component system.

Photocatalytic transformation of rhodamine B and its effect on hydrogen evolution over Pt/TiO2 in the presence of electron donors

Abstract In the presence of electron donors, oxalic acid, ethanol and disodium ethylene-diamine tetraacetate (EDTA), the photocatalytic transformation of rhodamine B (Rh B) and its effect on photocatalytic hydrogen evolution over Pt/TiO2 have been examined. UV–Vis and fast atom bombardment mass spectrometry (FABMS) evidences demonstrate that two reductive reaction paths (photocatalytic hydrogenation and additive combination of Rh B with ethanol radical) take place over Pt/TiO2 in the reaction system. The adsorption behavior of Rh B on Pt/TiO2 with coexisting electron donors is a key factor for the transformation. As a result of the hydrogenation and the addition of ethanol radical, the rates of photocatalytic hydrogen generation by the donors decrease notably. A possible reaction mechanism is discussed.

Facile synthesis of tetrahedral Ag3PO4 submicro-crystals with enhanced photocatalytic properties

Tetrahedral Ag3PO4 submicro-crystals have been fabricated in high-yield by directly reacting commercial Ag foils with H2O2 and NaH2PO4 in aqueous solution at room temperature, which exhibit higher photocatalytic activities than Ag3PO4 cubes, particles, and N-doped TiO2 for the degradation of organic contaminants under visible light irradiation.

Adsorption and photo-induced reduction of Cr(VI) ion in Cr(VI)-4CP (4-chlorophenol) aqueous system in the presence of TiO2 as photocatalyst

Dark adsorption of Cr(VI) ion on TiO2 is mainly dependent on Cr(VI) concentration and the system acidity. 4-Chlorophenol (4CP) has no interference on Cr(VI) adsorption. Cr(VI) can easily be photocatalytically reduced under UV irradiation with TiO2 as catalyst. The reduction is in accord with the Langmuir-Hinshelwood (L-H) kinetic equation. Under the UV irradiation, photo-induced Cr(VI) reduction is observed in either Cr(VI)-4CP or Cr(VI)-4CP-TiO2 system. Light intensity and system acidity are two main roles influencing both reactions. The linear decrease in Cr(VI) concentration reveals the zero order of Cr(VI) reduction rate in both systems. Two different reactions are involved in Cr(VI)-4CP-TiO2 system under the experimental UV irradiation: the photo-induced homogeneous reaction between Cr(VI) and 4CP, and the photocatalytic reaction on TiO2 semiconductor photocatalyst. In the condition of excluding homogeneous reactions between Cr(VI) and 4CP, the promotive effect of 4CP on photocatalytic reduction of Cr(VI) in Cr(VI)-4CP-TiO2 system is distinguished and confirmed. Under the sunlight irradiation, no reaction is observed in Cr(VI)-4CP system. Photocatalytic reduction efficiency of Cr(VI) ion on TiO2 in Cr(VI)-4CP-TiO2 system under the sunlight irradiation is much larger than that in Cr(VI)-TiO2 system.

Direct Observation of Charge Separation on Anatase TiO2 Crystals with Selectively Etched {001} Facets.

Synchronous illumination X-ray photoelectron spectroscopy (SIXPS) was employed for the first time to directly identify the photogenerated charge separation and transfer on anatase TiO2 single-crystals with selectively etched {001} facets. More specifically, for the TiO2 crystals with intact {001} and {101} facets, most of photogenerated charge carriers rapidly recombined, and no evident electron-hole separation was detected. With selectively etching on {001} facets, high efficient charge separation via hole transfer to titanium and electron to oxygen was clearly observed. However, when the {001} facets were completely etched into a hollow structure, the recombination for photogenerated electron-hole pairs would dominate again. These demonstrations clearly reveal that the appropriate corrosion on {001} facets could facilitate more efficient electron-hole separation and transfer. As expected, the optimized TiO2 microcrystals with etched {001} facets could achieve a hydrogen generation rate of 74.3 μmol/h/g, which is nearly 7 times higher than the intact-TiO2 crystals.