Direct and indirect Z-scheme heterostructure-coupled photosystem enabling cooperation of CO2 reduction and H2O oxidation.

The stoichiometric photocatalytic reaction of CO2 with H2O is one of the great challenges in photocatalysis. Here, we construct a Cu2O-Pt/SiC/IrOx composite by a controlled photodeposition and then an artificial photosynthetic system with Nafion membrane as diaphragm separating reduction and oxidation half-reactions. The artificial system exhibits excellent photocatalytic performance for CO2 reduction to HCOOH and H2O oxidation to O2 under visible light irradiation. The yields of HCOOH and O2 meet almost stoichiometric ratio and are as high as 896.7 and 440.7 µmol g-1 h-1, respectively. The high efficiencies of CO2 reduction and H2O oxidation in the artificial system are attributed to both the direct Z-scheme electronic structure of Cu2O-Pt/SiC/IrOx and the indirect Z-scheme spatially separated reduction and oxidation units, which greatly prolong lifetime of photogenerated electrons and holes and prevent the backward reaction of products. This work provides an effective and feasible strategy to increase the efficiency of artificial photosynthesis.

Moderate-temperature catalytic incineration of cooking oil fumes using hydrophobic honeycomb supported Pt/CNT catalyst.

Catalytic incineration is one of the cost-effective technologies to deal with odor cooking oil fumes (COFs). Hydrophobic carbon nanotubes (CNT) supported Pt catalysts were prepared by incipient wetness impregnation method. The 2.0 wt.%Pt/CNT catalyst gave the highest activity with the lowest light-off temperature near 200 °C. The catalyst was further coated on the carbonized honeycomb which offered low-pressure drop and high surface area per unit volume. Toward feasibility application, hydrophobic honeycomb supported Pt/CNT catalyst achieved an excellent catalytic performance with the conversion of 88.0-91.3 % in gas hourly space velocity (GHSV) ranging from 5,700 to 17,200 h-1 at 300 °C. Importantly, the honeycomb supported Pt/CNT catalyst could remove COFs substantially under simulated cooking conditions. Only a slight amount of heptane remained after catalytic incineration. In addition, the honeycomb support used much less Pt/CNT catalyst by maintaining the same performance, compared with powder catalyst. Our research outcome provides an excellent opportunity to apply the honeycomb supported Pt/CNT catalyst for moderate-temperature catalytic incineration of odor exhaust from kitchen hood.

Defect engineering of metal-oxide interface for proximity of photooxidation and photoreduction.

Close proximity between different catalytic sites is crucial for accelerating or even enabling many important catalytic reactions. Photooxidation and photoreduction in photocatalysis are generally separated from each other, which arises from the hole-electron separation on photocatalyst surface. Here, we show with widely studied photocatalyst Pt/[Formula: see text] as a model, that concentrating abundant oxygen vacancies only at the metal-oxide interface can locate hole-driven oxidation sites in proximity to electron-driven reduction sites for triggering unusual reactions. Solar hydrogen production from aqueous-phase alcohols, whose hydrogen yield per photon is theoretically limited below 0.5 through conventional reactions, achieves an ultrahigh hydrogen yield per photon of 1.28 through the unusual reactions. We demonstrated that such defect engineering enables hole-driven CO oxidation at the Pt-[Formula: see text] interface to occur, which opens up room-temperature alcohol decomposition on Pt nanoparticles to [Formula: see text] and adsorbed CO, accompanying with electron-driven proton reduction on Pt to [Formula: see text].

Visible-Light Driven Overall Conversion of CO2 and H2O to CH4 and O2 on 3D-SiC@2D-MoS2 Heterostructure.

A marigold-like SiC@MoS2 nanoflower with a unique Z-scheme structure efficiently achieves the overall conversion of gas phase CO2 with H2O (CO2 (g) + 2H2O (g) = CH4 + 2O2) without any sacrificial reagents under visible light (λ ≥ 420 nm) irradiation. The CH4 and O2 evolution are 323 and 621 µL·g-1·h-1, and stable throughout 5 cycle reactions of total 40 h. This work demonstrates a breakthrough in artificial photosynthesis with the Z-scheme 1D heterojunction constructed by combining 2D semiconductor and 3D semiconductor based on the transfer balance of photogenerated electron and hole.

Degradation and Mineralization of Carbamazepine Using an Electro-Fenton Reaction Catalyzed by Magnetite Nanoparticles Fixed on an Electrocatalytic Carbon Fiber Textile Cathode.

Pharmaceutical wastes are considered to be important pollutants even at low concentrations. In this regard, carbamazepine has received significant attention due to its negative effect on both ecosystem and human health. However, the need for acidic conditions severely hinders the use of conventional Fenton reagent reactions for the control and elimination of carbamazepine in wastewater effluents and drinking water influents. Herein, we report of the synthesis and use of flexible bifunctional nanoelectrocatalytic textile materials, Fe3O4-NP@CNF, for the effective degradation and complete mineralization of carbamazepine in water. The nonwoven porous structure of the composite binder-free Fe3O4-NP@CNF textile is used to generate H2O2 on the carbon nanofiber (CNF) substrate by O2 reduction. In addition, ·OH radical is generated on the surface of the bonded Fe3O4 nanoparticles (NPs) at low applied potentials (-0.345 V). The Fe3O4-NPs are covalently bonded to the CNF textile support with a high degree of dispersion throughout the fiber matrix. The dispersion of the nanosized catalysts results in a higher catalytic reactivity than existing electro-Fenton systems. For example, the newly synthesized Fe3O4-NPs system uses an Fe loading that is 2 orders of magnitude less than existing electro-Fenton systems, coupled with a current efficiency that is higher than electrolysis using a boron-doped diamond electrode. Our test results show that this process can remove carbamazepine with high pseudo-first-order rate constants (e.g., 6.85 h-1) and minimal energy consumption (0.239 kW·h/g carbamazepine). This combination leads to an efficient and sustainable electro-Fenton process.

Synthesis, characterization and enhanced photocatalytic CO2 reduction activity of graphene supported TiO2 nanocrystals with coexposed {001} and {101} facets.

It is known that the combination of TiO2 and graphene and the control of TiO2 crystal facets are both effective routes to improve the photocatalytic performance of TiO2. Here, we report the synthesis and the photocatalytic CO2 reduction performance of graphene supported TiO2 nanocrystals with coexposed {001} and {101} facets (G/TiO2-001/101). The combination of TiO2 and graphene enhanced the crystallinity of TiO2 single nanocrystals and obviously improved their dispersion on graphene. The "surface heterojunction" formed by the coexposed {001} and {101} facets can promote the spatial separation of photogenerated electrons and holes toward different facets and the supports of graphene can further enhance the separation through accelerated electron migration from TiO2 to graphene. The G/TiO2-001/101 exhibited high photocatalytic CO2-reduction activity with a maximum CO yield reaching 70.8 µmol g(-1) h(-1). The enhanced photocatalytic activity of the composites can be attributed to their high surface area, good dispersion of TiO2 nanoparticles, and effective separation of excited charges due to the synergy of graphene supports and the co-exposure of {001} and {101} facets.

Production of renewable fuels by the photohydrogenation of CO2: effect of the Cu species loaded onto TiO2 photocatalysts.

The efficient gas phase photocatalytic hydrogenation of CO2 into a desirable renewable fuel was achieved using a Cu-loaded TiO2 photocatalyst system. Enhancing the amount of Ti(3+) relative to Ti(4+) in a Cu-loaded TiO2 photocatalyst provided an excellent opportunity to promote the photohydrogenation of CO2. The coexistence of Cu and Cu(+) species during the photoreaction was shown to efficiently enhance the photocatalytic activity by prolonging the lifetime of the electrons. To achieve the best photoactivity, the Cu species must be maintained at an appropriately low concentration (≤1 wt%). The highest CH4 yield obtained was 28.72 µmol g(-1). This approach opens a feasible route not only to store hydrogen by converting it into a desirable renewable fuel, but also to reduce the amount of the greenhouse gas CO2 in the atmosphere.

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.

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.

Water and temperature effects on photo-selective catalytic reduction of nitric oxide on Pd-loaded TiO2 photocatalyst.

Photo-selective catalytic reduction (photo-SCR) of nitric oxide (NO) was studied in the presence of water. The incipient wetness impregnation was applied to prepare 1 wt% PdO/TiO2 photocatalyst. Steady-state photoreaction was carried out in a continuous-flow photoreactor with 0.55-1.6 v% water at 30-120 degrees C under UV-light intensity of approximately 200mW/cm(2). The C3H8/NO molar ratio in the feed ranged from 0.8 - 16.8 at a volume hourly space velocity (VHSV) from 330-1090 h(-1). The result indicates that the increase of temperature has played an important role in inhibiting NO transformation to NO2 under the humid condition. Another important factor for maximizing denitrification (reduction of nitrogen oxides, DeNOx) efficiency was C3H8/NO ratio. An increase of temperature at a suitable C3H8/NO ratio can minimize NO2 formation, which can lead to high NO removal efficiency of more than 90% at a temperature of 70-100 degrees C. In addition, the mechanism of palladium transformation during photoreaction is proposed, to explain the influence of Pd on the improvement of NO removal.

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.

Photocatalytic reduction of NO pollutant using an optical-fibre photoreactor at room temperature.

Photo-assisted catalytic reduction of nitric oxide (NO) was studied over different metal-loaded TiO2 catalysts at room temperature. The activities of metal-loaded (Pt, Ag, Cu) TiO2 photocatalysts, prepared by the sol-gel method, were compared in a batch system using CH4 as the reducing agent. The Pt/TiO2 catalyst showed the highest activity for NO reduction. Thus, Pt/TiO2 was coated on optical fibres and used in a continuous-flow optical-fibre photoreactor. The optical-fibre photoreactor provides light irradiation on the photocatalyst through the optical fibre, thus improving the efficiency ofphotoreactions. Ten per cent conversion of NO was found using CH4 as the reducing agent. The NO conversions increased to 90% in the presence of water vapour and oxygen. However, most NO was oxidized to NO2. Hydrogen had superior reducing capabilities over CH4 on Pt/TiO2 photocatalyst, and the conversion of NO reached 85%. But the conversion of NO was substantially decreased to less than 10% in the presence of water vapour and oxygen. Our research proposed an alternative way to reduce NO pollutant to N2 at room temperature using an optical-fibre photoreactor, which could possibly utilize sunlight in the future.