Lan-Cui Zhang

A Novel Carboxyethyltin Functionalized Sandwich-type Germanotungstate: Synthesis, Crystal Structure, Photosensitivity, and Application in Dye-Sensitized Solar Cells

A novel sandwich-type germanotungstate [C(NH2)3]10[Mn2{Sn(CH2)2COOH}2(B-α-GeW9O34)2]·8H2O (1) represents the first single crystalline polyoxometalate (POM) functionalized by open chain carboxyethyltin, which was designed and synthesized in aqueous solution and applied to a dye-sensitized solar cell (DSSC) for the first time. Its photosensitivity was explored through a fluorescence spectrum (FL), surface photovoltage spectrum (SPV), electrochemical method, and solid diffuse spectrum. 1 displays the primary features of sensitizers in DSSCs, and the efficiency of the solar cell is 0.22%. Delightedly, when 1 was employed to assemble a cosensitized solar cell configuration by preparing a 1-doped TiO2 electrode and additionally adsorbing N719 dyes, a considerably improved efficiency was achieved through increasing spectral absorption and accelerating electron transport, which is 19.4% higher than that of single N719 sensitization. This result opens up a new way to position different dyes on a single TiO2 film for cosensitization.

Effect of Nd3+ doping on photocatalytic activity of TiO2 nanoparticles for water decomposition to hydrogen

Abstract The undoped TiO 2 and Nd 3+ -doped TiO 2 samples were prepared by the sol–gel method and characterized by X-ray diffraction, diffuse reflectance UV-visible spectroscopy, transmission electron microscopy, and N 2 adsorption. The correlation of the photocatalytic activity for hydrogen evolution with the phase composition, BET surface area, and light absorption intensity in the UV region was investigated. For the undoped TiO 2 sample, the particle size and agglomeration increased while the BET surface area and the light absorption intensity in the UV region decreased with increasing calcination temperature. The anatase to rutile phase transformation started at 600°C and completed at 800°C. The photocatalytic activity of undoped TiO 2 decreased with increasing calcination temperature, and the sample calcined at 600°C was the best because of the coexistence of a certain proportion of rutile/anatase mixed phase. For the Nd 3+ /TiO 2 samples, Nd 3+ doping inhibited the crystal phase transformation and the rutile phase appeared at 800°C. Moreover, Nd 3+ doping restrained the growth of grain size, improved the dispersivity of the particles, and raised BET surface area. The more the doping amount, the larger the BET surface area. As the calcination temperature increased, the decreasing extent of the light absorption intensity of Nd 3+ /TiO 2 in the UV region was lower than that of undoped TiO 2 . Nd 3+ doping raised the photocatalytic activity for hydrogen generation, and the optimum amount of Nd 3+ doping was 0.1%, at which the photocatalytic activity of Nd 3+ /TiO 2 was 3.5 times that of undoped TiO 2 .

Enhanced Visible Photovoltaic Response of TiO2 Thin Film with an All-Inorganic Donor–Acceptor Type Polyoxometalate

In the field of material chemistry, it is of great significance to develop abundant and sustainable materials for solar energy harvesting and management. Herein, after evaluating the energy band characteristics of 13 kinds of polyoxometalates (POMs), the trisubstituted POM compound K6H4[α-SiW9O37Co3(H2O)3]·17H2O (SiW9Co3) was first studied due to its relatively smaller band gap (2.23 eV) and higher lowest unoccupied molecular orbital (LUMO) level (-0.63 V vs NHE). Additionally, the preliminary computational modeling indicated that SiW9Co3 exhibited the donor-acceptor (D-A) structure, in which the cobalt oxygen clusters and tungsten skeletons act as the electron donor and electron acceptor, respectively. By employing SiW9Co3 to modify the TiO2 film, the visible photovoltaic and photocurrent response were both enhanced, and the light-induced photocurrent at 420 nm was improved by 7.1 times. Moreover, the highly dispersive and small sized SiW9Co3 nanoclusters loading on TiO2 were successfully achieved by fabricating the nanocomposite film of {TiO2/SiW9Co3}3 with the layer-by-layer method, which can result in the photovoltaic performance enhancement of dye-sensitized solar cells (DSSCs), of which the overall power conversion efficiency was improved by 25.6% from 6.79% to 8.53% through the synergistic effect of POMs and Ru-complex.

A strategy for breaking the MOF template to obtain small-sized and highly dispersive polyoxometalate clusters loaded on solid films

A strategy was developed for the first time to fabricate highly dispersed and small-sized polyoxometalate nanoparticles loaded on a TiO2 film by using MIL-101 to prevent agglomeration, and calcination to break the metal–organic framework, which can result in performance improvement of quantum dot solar cells.

Two New Armtype Polyoxometalates Grafted on Titanium Dioxide Films: Towards Enhanced Photoelectrochemical Performance.

Two new carboxyethyltin-functionalized polyoxometalates (POMs) were successfully obtained and confirmed with physicochemical and spectroscopic methods including X-ray crystallography. The lowest unoccupied molecular orbitals of both compounds are higher in energy than that of TiO2 , and the optical band gaps of these compounds are smaller than that of TiO2 . Grafting them onto a TiO2 film created two kinds of novel photoanode materials that showed significantly enhanced photovoltaic and photocurrent responses, as well as improved photoelectrooxidation activities for methanol relative to that shown by a single TiO2 film. Further, P2 W15 -Co-SnR produced the largest photocurrent by exploring the photoelectric activities of a series of carboxyethyltin POM derivatives. This work provides new insight into the photoelectrochemical functionalization of POM-based organic-inorganic hybrids.

Two Keggin sandwich-type tungstophosphates modified by open-chain carboxyethyltin groups and transition metals

Two new polyoxometalates containing [PW9O34]9− (abbreviated as PW9) subunits, carboxyltin groups and transition metal ions, namely K10[Mn2{Sn(CH2)2COO}2[(B-α-PW9O34)2]·14H2O (1) and Na8K2 [Zn2{Sn(CH2)2COO}2[(B-α-PW9O34)2]·13H2O (2), were successfully assembled in aqueous solutions by a routine synthetic method, and fully characterized. They represent the first single crystal examples of open-chain carboxyethyltin group-modified Keggin sandwich-type tungstophosphates. Their important structural features are two open-chain carboxyethyltin moieties attached on the PW9 dimer, forming arm-type polyoxometalates. Furthermore, the fluorescence properties, electrocatalytic and oxidation catalytic activities were evaluated. More interestingly, the fluorescence quenching of 1/2-doped TiO2 was clearly observed, which means that the two compounds may be excellent components of photocatalytic materials.

Hydrothermal syntheses and crystal structures of crystalline catalysts based on 3-D Ln3+–pdc2− frameworks and [BW12O40]5− and their heterogeneous photocatalytic oxidation of thiophene

Five [BW12O40]5 − -containing metal-organic frameworks (MOFs), {K[Ln(H2O)4(pdc)]4}[BW12O40]·2H2O (Ln=La 1 and Ce 2, H2pdc = pyridine-2,6-dicarboxylate) and {K[Ln(H2O)3(pdc)]4}[BW12O40]·6H2O (Ln=Tb 3, Dy 4 and Er 5), are synthesized hydrothermally. Ln3+ and pdc2− are built into 3-D MOF segments containing large channels and cavities which are occupied by [BW12O40]5 − . Herein, we report MOF-containing polyoxometalates (POMs) as photocatalysts to oxidize thiophene with O2 as the oxidant. Photo-excited state species ([BW12O40]5−∗) are generated under UV irradiation and then H2O is oxidized into OH˙ radicals and O2 is reduced into O2 2−. The active oxygen species (O2 2−, OH˙) oxidize thiophene in the presence of photocatalysts and SO3, CO2, and H2O are obtained as photoproducts. ESR measurements provide evidence that OH˙ species are generated during photocatalysis.

A new boat-like tungstoarsenate functionalized by carboxyethyltin and its catalytic properties

A new polyoxometalate (POM) estertin derivative, {C(NH2)3}Na10K7[(W4O16){Sn(CH2)2COO}4(B-α-AsW9O33)2]·25H2O (1), has been synthesized from K14[As2W19O67(H2O)]·nH2O ({As2W19}) and Cl3SnCH2CH2COOCH3, which exhibits an unusual boat-like structural feature: four [Sn(CH2)2COO]2+ groups surround a center W4O16 cluster and link two [AsW9O33]9− subunits. 1 shows efficient oxidation catalytic activity and can be applied for mimicking enzyme catalysis.

Catalytic oxidation of diesel soot particulates over Ag/LaCoO3 perovskite oxides in air and NOx

Abstract Ag/LaCoO3 perovskite catalysts for soot combustion were prepared by the impregnation method. The structure and physicochemical properties of the catalysts were characterized using X-ray diffraction, N2 adsorption-desorption, H2 temperature-programmed reduction, soot temperature- programmed reduction, and X-ray photoelectron spectroscopy. The catalytic activity of the catalysts for soot oxidation was tested by temperature-programmed oxidation in air and in a NOx atmosphere. Metallic Ag particles were the main Ag species. Part of the Ag migrated from the surface to the lattice of the LaCoO3 perovskite, to form La1-xAgxCoO3. This increased the amount of oxygen vacancies in the perovskite structure during thermal treatment. Compared with unmodified LaCoO3, the maximum soot oxidation rate temperature (Tp) decreased by 50–70 °C in air when LaCoO3 was partially modified by Ag, depending on the thermal treatment temperature. The Tp of the Ag/LaCoO3 catalyst calcined at 400 °C in a NOx atmosphere decreased to about 140 °C, compared with that of LaCoO3. Ag particles and oxygen vacancies in the catalysts contributed to their high catalytic activity for soot oxidation. The stable catalytic activity of the Ag/LaCoO3 catalyst calcined at 700 °C in a NOx atmosphere was related to its stable structure.

Synthesis, spectroscopic properties and crystal structure of organophosphoryl polyoxotungstate α-[Bu4N]3H[PhCH2P(O)]2SiW11O39

Reaction of the monovacant heteropolyanions α-[SiW11O39]8− with PhCH2PO(OH)2 leads to the formation of the organophosphoryl derivative α-[Bu4N]3H[PhCH2P(O)]2SiW11O39 (1). Single-crystal X-ray diffraction analysis shows that the crystal is monoclinic with space group P21 /n and the unit cell parameters: a = 14.386 (3) Å, b = 27.015 (5) Å, c = 25.480 (5) Å, α = 90°, β = 91.44 (3)°, γ = 90°, V = 9899 (3) Å3. Z = 4, D c = 2.467 g cm−1, λ (Mo-Kα) = 0.071073 nm, R 1 = 0.0638, wR 2 = 0.1364. The hybrid anion consists of an α-[SiW11O39]8− framework on which two equivalent organophosphoryl groups are grafted through P−O−W bridges; each of the two PhCH2P(O) groups are connected to two terminal oxygen atoms belonging to a triad and a diad, respectively.