Yuexiang Li

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 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.

Nitrogen-doped TiO2 modified with NH4F for efficient photocatalytic degradation of formaldehyde under blue light-emitting diodes.

A nitrogen-doped TiO(2) (N-TiO(2)) photocatalyst was prepared by calcination of the hydrolysis precipitate of Ti(SO(4))(2) with aqueous ammonia. The prepared N-TiO(2) was treated with NH(4)F (F-N-TiO(2)) by an impregnation-calcination method. The photocatalyst (F-N-TiO(2)) was characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), UV-vis diffusive reflectance spectroscopy (DRS), BET and X-ray photoelectron spectroscopy (XPS). With blue light-emitting diode (LED) as the light source, its photocatalytic activity for the degradation of formaldehyde was investigated. NH(4)F treatment enhances markedly photocatalytic activity of N-TiO(2). The treatment increases the visible absorption of N-TiO(2), decreases its specific surface area and influences the concentration of oxygen vacancies in N-TiO(2). Photocatalytic activity of F-N-TiO(2) depends on the visible absorption, the specific surface area, and the concentration of oxygen vacancies. The preparation conditions, such as the calcination temperature and the initial molar ratio of NH(4)F to N-TiO(2), have a significant influence on the photocatalytic activity. The doping mechanism of NH(4)F was investigated.

Phosphate-assisted hydrothermal synthesis of hexagonal CdS for efficient photocatalytic hydrogen evolution

Cubic nanocrystalline CdS was hydrothermally transformed into hexagonal CdS in the presence of Na3PO4 at 180 °C for 12 h. The as-prepared CdS samples were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), BET, electrophoretic analysis, photoluminescence (PL) spectra and UV-Vis absorption spectra techniques. Effects of phosphate concentration, hydrothermal time and Pt loading content were investigated. Their photoactivity was evaluated by hydrogen evolution from aqueous solution containing formic acid as a hole scavenger under visible light (λ ≥ 420 nm) irradiation. Phosphate markedly promotes the phase transformation of CdS from cubic to hexagonal. With 0.050 mol L−1 PO43−, the formed hexagonal phase content reaches a maximum (82%). The as-prepared CdS with a high percentage of hexagonal phase displays excellent activity for photocatalytic hydrogen evolution. Pt is highly dispersed on CdS so that the Pt content for the effective hydrogen evolution is very low. The CdS loaded with 0.025 wt% Pt shows the maximum activity for the hydrogen evolution. The apparent quantum yield at 420 nm amounts to 21.4%. This work highlights a facile and low-cost method for the preparation of a highly-efficient CdS photocatalyst. The possible mechanisms were discussed.

Synergetic effect of metal nickel and graphene as a cocatalyst for enhanced photocatalytic hydrogen evolution via dye sensitization

Exploiting new, low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER) is important to resolve the energy crisis and environment pollution. In this work, graphene decorated with Ni nanoparticles (NPs) were synthesized via one-pot reduction using graphene oxide (GO, the obtained composite was denoted as GN) as a precursor. The as-prepared composite GN exhibits much better electrocatalytic and dye-sensitized HER activities than single Ni and reduced graphene oxide (RGO), namely, a great synergetic effect of RGO and Ni for HER. The coupling of metal Ni with the defect carbons of RGO plays a key role in the synergetic effect. The structure of GN composites is another key factor to the synergetic effect. The highest apparent quantum yield (AQY) for dye-sensitized photocatalytic hydrogen evolution at 470 nm reaches 30.3% under the optimal conditions.

Photosensitized reduction of water to hydrogen using novel Maya blue-like organic–inorganic hybrid material

On the basis of the understanding that membranes play an important role in the separation of the intermediate photoproducts in the photosynthetic process, a novel efficient hydrogen evolution system was constructed with Maya blue-like organic-inorganic hybrid material as a photocatalyst, in which palygorskite acts as matrix and Eosin Y as a photosensitizer. Under visible light irradiation (lambda > or = 420 nm), the highest rate of hydrogen evolution and apparent quantum yield are about 3247.2 micromol h(-1) (g Eosin Y)(-1) and 12.5%, respectively. Negatively charged palygorskite particles could control the photosensitized electron-transfer reaction by means of electrostatic interaction. Based on the activities of hydrogen generation and the experimental measurements of UV-vis absorbance and fluorescence, a probable mechanism for photosensitized hydrogen evolution was postulated.

Enhancement of photocatalytic H2 evolution of eosin Y-sensitized reduced graphene oxide through a simple photoreaction

Summary A graphene oxide (GO) solution was irradiated by a Xenon lamp to form reduced graphene oxide (RGO). After irradiation, the epoxy, the carbonyl and the hydroxy groups are gradually removed from GO, resulting in an increase of sp2 π-conjugated domains and defect carbons with holes for the formed RGO. The RGO conductivity increases due to the restoration of sp2 π-conjugated domains. The photocatalytic activity of EY-RGO/Pt for hydrogen evolution was investigated with eosin Y (EY) as a sensitizer of the RGO and Pt as a co-catalyst. When the irradiation time is increased from 0 to 24 h the activity rises, and then reaches a plateau. Under optimum conditions (pH 10.0, 5.0 × 10−4 mol L−1 EY, 10 μg mL−1 RGO), the maximal apparent quantum yield (AQY) of EY-RGO24/Pt for hydrogen evolution rises up to 12.9% under visible light irradiation (λ ≥ 420 nm), and 23.4% under monochromatic light irradiation at 520 nm. Fluorescence spectra and transient absorption decay spectra of the EY-sensitized RGO confirm that the electron transfer ability of RGO increases with increasing irradiation time. The adsorption quantity of EY on the surface of RGO enhances, too. The two factors ultimately result in an enhancement of the photocatalytic hydrogen evolution over EY-RGO/Pt with increasing irradiation time. A possible mechanism is discussed.

NaCl-assisted low temperature synthesis of layered Zn-In-S photocatalyst with high visible-light activity for hydrogen evolution

Single ZnIn2S4 or Zn-In-S composites were synthesized by a simple low temperature (80 °C) method assisted by the presence of NaCl. The products were characterized by XRD, SEM, TEM, TG/DTA, ICP-AES, BET and UV-Vis absorption spectrometry. The decomposition of thioacetamide (TAA) at low temperature was investigated by UV-Vis absorption spectrometry. The decomposition rate of TAA and NaCl concentration influenced the composition, structure, morphology and grain size of the products. The obtained samples are marigold-like microspheres consisting of nanosheets. Loading 0.10 wt% Pt on the samples by in situ photoreduction, allowed the photocatalytic activity of the prepared samples to be evaluated by hydrogen evolution from aqueous solution containing triethanolamine as the electron donor under visible light (λ ≥ 420 nm) irradiation. The activity of the sample obtained in the presence of 0.50 mol L−1 NaCl is ca. 5 times higher than samples without NaCl. Thus, a photocatalyst with layered structure is beneficial for photoactivity. A possible mechanism is discussed.