Jeffrey C.S. Wu

Artificial Photosynthesis over Crystalline TiO2-Based Catalysts: Fact or Fiction?

The mechanism of photocatalytic conversion of CO(2) and H(2)O over copper oxide promoted titania, Cu(I)/TiO(2), was investigated by means of in situ DRIFT spectroscopy in combination with isotopically labeled (13)CO(2). In addition to small amounts of (13)CO, (12)CO was demonstrated to be the primary product of the reaction by the 2115 cm(-1) Cu(I)-CO signature, indicating that carbon residues on the catalyst surface are involved in reactions with predominantly photocatalytically activated surface adsorbed water. This was confirmed by prolonged exposure of the catalyst to light and water vapor, which significantly reduced the amount of CO formed in a subsequent experiment in the DRIFT cell. In addition, formation of carboxylates and (bi)carbonates was observed by exposure of the Cu(I)/TiO(2) surface to CO(2) in the dark. These carboxylates and (bi)carbonates decompose upon light irradiation, yielding predominantly CO(2). At the same time a novel carbonate species is produced (having a main absorption at approximately 1395 cm(-1)) by adsorption of photocatalytically produced CO on the Cu(I)/TiO(2) surface, most likely through a reverse Boudouard reaction of photocatalytically activated CO(2) with carbon residues. The finding that carbon residues are involved in photocatalytic water activation and CO(2) reduction might have important implications for the rates of artificial photosynthesis reported in many studies in the literature, in particular those using photoactive materials synthesized with carbon containing precursors.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis.

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+–[WO4]2−–[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

Vitalizing fuel cells with vitamins: pyrolyzed vitamin B12 as a non-precious catalyst for enhanced oxygen reduction reaction of polymer electrolyte fuel cells

The limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H2–O2fuel cell using py-B12/C provides a maximum power density of 370 mW cm−2 and a current density of 0.720 A cm−2 at 0.5 V at 70 °C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.

Photocatalytic CO2 reduction using an internally illuminated monolith photoreactor

One of the promising solutions to both global climate warming and increasing energy demands is artificial photosynthesis, which can be implemented via the photoreduction of CO2 to produce fuel. A monolith photoreactor was used to increase the amount of catalyst loading due to its multiple channels. The photocatalyst was dip coated using NiO/InTaO4 sol and then calcined at 1100 °C. A uniform NiO/InTaO4 layer was obtained on the top of pre-coated SiO2 sublayer on the internal channels of the monolith. The polymethylmethacrylate (PMMA) optical fibers, after being carved on their surface, could transmit and scatter light to effectively illuminate the catalyst inside the channels of the monolith. Vapor-phase CO2 with H2O was photocatalytically reduced to hydrocarbons by UV or visible-light in a steady-state flow mode. The maximum methanol conversion rate achieved was 0.16 µmol g−1 h−1 with visible-light of 290 klx at 25 °C. The highest rate of acetaldehyde was 0.3 µmol g−1 h−1 which was obtained with a loading of 2.6% NiO by simulated sunlight AM1.5G at 70 °C. More importantly, the quantum efficiency was significantly improved indicating that photon energy was effectively utilized in the monolith reactor, compared with previous optical-fiber reactor.

Photo reduction of CO2 to methanol via TiO2 photocatalyst

Greenhouse gas such as CO2 is the primary cause of global warming. Alternative energy source should be provided without producing more CO2, such as solar energy. One of the best routes to remedy CO2 is to transform it to hydrocarbons using photo reduction. In our study, CO2 was photocatalytically reduced to produce methanol using a Hg lamp with wavelength 365 nm in a steady-state optical-fiber photo reactor. The optical-fiber photo reactor, comprised of near 120 Cu/TiO2-coated fibers, was designed and assembled to transmit and spread light uniformly inside reactor. TiO2 film was coated on optical fiber using dip-coating method. Titania and Cu-loaded solutions were prepared by a thermal hydrolysis method. The thickness of Cu/TiO2 film was 53 nm and consisted of very fine spherical particle with diameter of near 14 nm. The XRD spectra indicated the anatase phase of all TiO2 and Cu/TiO2 films. The wavelength of absorption edge was on 367 nm, equivalent to near 3.3 eV. Most active Cu species on TiO2 surface were Cu2O clusters, and played an important role for the formation of methanol. The methanol yield increased with UV irradiative intensity. Photo activity increased with increasing Cu loadings. Maximum methanol rate was 0.45 μmole/g-cat•hr using 1.2 wt%-Cu/TiO2 catalyst under 16 W / cm2 irradiation, 1.3 bar pressure of CO2, and 5000 seconds mean residence time. Higher than 1.2 wt% Cu loading gave less rate of methanol yield because of the masking effect of Cu2O clusters on the surface of TiO2.

Separation of oil from oily sludge by freezing and thawing

Abstract This communication reports for the first time the feasibility of employing freeze/thaw method to separate oil from an oily sludge. The freeze/thawed sludge comprises three distinct layers, an oil layer at the top, a sediment layer at the bottom and a water layer locating in between, whose compositions were identified with the help of GC–MS. Freezing and thawing can separate over 50% of its oil content. However, ultra-fast freezing is not beneficial for oil separation.

Sol-gel prepared InTaO 4 and its photocatalytic characteristics

InTaO 4 is an efficient visible-light photocatalyst, which used to be synthesized by solid-state fusion at over 1100 °C. However, irregular morphology and severe agglomeration of particles were acquired due to nonuniform fusion of solid precursors. In this study, InTaO 4 was synthesized by two sol-gel routes, the thermal hydrolysis and esterification methods. The precursors were indium (III) nitrate pentahydrate [In(NO 3 ) 3 ] and tantalum(V) butoxide [Ta(OC 4 H 9 ) 5 ] dissolved in solutions. The InTaO 4 powders with a uniform grain size of 17.7 nm were successfully synthesized using the esterification method at a calcination temperature of 950 °C. A uniform InTaO 4 thin film nearly 40 nm thick formed on an optical fiber at 1100 °C using the sol prepared by the esterification method. For the first time, InTaO 4 was evaluated by the photocatalytic activity of CO 2 photo reduction, which was conducted in aqueous solution under visible light irradiation. Cocatalyst NiO was loaded on the surface of InTaO 4 to further enhance the methanol yield. The methanol yields of NiO/InTaO 4 by esterification method were significantly higher than those by solid-state fusion. The esterification method provided homogeneous mixing of Ta(OC 4 H 9 ) 5 and In(NO 3 ) 3 , resulting in nano-sized InTaO 4 with uniform crystallinity and superior photocatalytic activity.

Functionalized Fe3O4@Silica Core–Shell Nanoparticles as Microalgae Harvester and Catalyst for Biodiesel Production

Core-shell Fe3O4@silica magnetic nanoparticles functionalized with a strong base, triazabicyclodecene (TBD), were successfully synthesized for harvesting microalgae and for one-pot microalgae-to-fatty acid methyl ester (FAME, or so-called biodiesel) conversion. Three types of algae oil sources (i.e., dried algae, algae oil, and algae concentrate) were used and the reaction conditions were optimized to achieve the maximum biodiesel yield. The results obtained in this study show that our TBD-functionalized Fe3O4@silica nanoparticles could effectively convert algae oil to biodiesel with a maximum yield of 97.1 %. Additionally, TBD-Fe3O4@silica nanoparticles act as an efficient algae harvester because of their adsorption and magnetic properties. The method presented in this study demonstrates the wide scope for the use of covalently functionalized core-shell nanoparticles for the production of liquid transportation fuels from algal biomass.

SYNTHESIS OF TITANIA-SUPPORTED COPPER NANOPARTICLES VIA REFINED ALKOXIDE SOL-GEL PROCESS

Nanoparticles of titania and copper-loaded titania were synthesized by a refined sol-gel method using titanium butoxide. Unlike the conventional sol-gel procedure of adding water directly, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis-condensation process and minimize the agglomeration of titania. Following the hydrolysis, Cu/TiO2 was prepared by adding copper chloride to titania sol. The sol was dried, then calcined at 500°C to remove organics and transformed to anatase titania which was verified by XRD. Cu/TiO2 was further hydrogen-reduced at 300°C. The recovery of Ti was exceeded by an average of 95% from titanium butoxide. TEM micrographs show that the Cu/TiO2 particles are near uniform. The average crystallite sizes are 17–20 nm estimated from the peak broadening of XRD spectra. The bandgaps of TiO2 and reduced Cu/TiO2 range from 2.70 to 3.15 eV estimated from the diffusive reflective UV-Vis spectra. XPS analysis shows that Cu 2p3/2 is 933.4 eV indicating primary Cu2O form on the TiO2 supports. The binding energy of Ti does not exhibit chemical shift suggesting negligible interaction of Cu cluster and TiO2 support.

Platinum nanoparticles embedded in pyrolyzed nitrogen-containing cobalt complexes for high methanol-tolerant oxygen reduction activity

High oxygen reduction activity of methanol-tolerant catalysts was successfully reported using platinum nanoparticles embedded in cobalt-based nitrogen-containing complexes supported on carbon blacks (Pt–N-complex/C). The oxygen reduction reaction (ORR) of the Pt–N-complex/C was attributed to four-electron transfer pathway in which oxygen was directly reduced to water, yielding four electrons. In a methanol-containing solution, the platinum intrinsically favors the methanol oxidation reaction over the ORR, which is a major drawback for direct methanol fuel cells (DMFCs). In comparison, when the Pt–N-complex/C is introduced in a methanol-containing solution, not only is the methanol oxidation suppressed but also the four-electron-transfer in the ORR is maintained up to the diffusion-limiting region. Physicochemical characterization of the Pt–N-complex/C indicates that pyrrolic N-type poly-aromatic hydrocarbons were formed in a network structure around the catalysts and prevented them from the methanol oxidation reaction. In a DMFC test at elevated methanol concentrations, the one with the Pt–N-complex/C cathode showed superior stability over the one with the Pt-based cathode, which may offer a solution to the methanol crossover problem in DMFCs.