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The use of low-cost photocatalysts to split water into H2 fuel via solar energy is highly desirable for the production of clean energy and a sustainable society. Here three-dimensional graphene oxide (3DG) porous materials were prepared by cross-linking graphene oxide (GO) sheets using aromatic diamines (benzidine, 2,2′-dimethyl-4,4′-biphenyldiamine, 4,4′-diaminodiphenylmethane) that reacted with the carboxyl groups of the GO sheets at room temperature. The prepared 3DG porous materials were used as efficient metal-free photocatalysts for the production of H2 via water splitting under full-spectrum light, where the photocatalytic activity was highly dependent on the cross-linker and the 3DG reduction level. It was also found that the 3DG prepared with benzidine as the linker demonstrated a significantly higher H2 evolution rate than the 3DGs prepared using 2,2′-dimethyl-4,4′-biphenyldiamine and 4,4′-diaminodiphenylmethane as the cross-linkers. The photoactivity was further tuned by varying the mass ratio of GO to benzidine. Among the prepared 3DG materials, 3DG-3, with an intermediate C/O ratio of 1.84, exhibited the highest H2 production rate (690 μmol g−1 h−1), which was significantly higher than the two-dimensional GO (45 μmol g−1 h−1) and the noncovalent 3DG synthesized by a hydrothermal method (128 μmol g−1 h−1). Moreover, this study revealed that the 3DG photocatalytic performance was favored by effective charge separation, while it could be further tuned by changing the reduction level. In addition, these results could prompt the preparation of other 3D materials and the application of new types of photocatalysts for H2 evolution.

The photocatalytic conversion of CO2 to fuels by light is of research interest owing to its relevance to environment and energy concerns. In this work, a hybrid H-TiO2–rGO–Re(bpy)(CO)3Cl composite consisting of a rhenium 2,2′-bipyridine compound, Re(bpy)(CO)3Cl, which was covalently grafted on reduced graphene oxide (rGO) and hydrogenated TiO2 (H-TiO2) was prepared. H-TiO2–rGO–Re(bpy)(CO)3Cl demonstrated high efficiency for visible light photo-conversion of CO2 into CO in triethanolamine/N,N-dimethylformamide (V:V = 1:9) solution with total turnover numbers larger than 580. In addition, the composite showed high stability with no leveling-off tendency after four catalytic experimental runs. The experimental results indicate that the suitable assembly of the Re(bpy)(CO)3Cl, rGO, and H-TiO2 components in the H-TiO2–rGO–Re(bpy)(CO)3Cl composite is necessary for the observed high performance of the catalyst for CO2 reduction under visible light irradiation.

In this work, two new D-A-π-A perylene dyes featuring with cyanoacrylic acid and 2-(1,1-dicyanomethylene) rhodamine (DCRD) as the electron acceptor/anchoring group, respectively, in combination with a N-annulated perylene electron donor and a quinoxaline auxiliary acceptor were investigated for application in dye-sensitized solar cells (DSCs) and dye-sensitized photocatalytic hydrogen production. The results showed that the sensitizer with cyanoacrylic acid ( YFT-1 ) based DSCs showed a higher conversion efficiency of 7.58% under AM1.5 solar conditions. However, it was interesting that the sensitizer with DCRD ( YFT-2 ) sensitized Pt/TiO 2 photocatalysts displayed a higher rate of H 2 evolution of 83.5 μmol h −1 under visible-light irradiation with wavelength between 420 nm and 780 nm. This may be ascribed to less interface charge recombination and more effective interfacial electron transfer between photo-excited YFT-2 and TiO 2 in aqueous solution. This study demonstrates that YFT-2 containing DCRD anchoring group is a promising candidate to achieve high and stable activity of H 2 production.

Photocatalytic water splitting has been considered as one of the most promising methods to produce hydrogen as a source of clean fuel. Use of co-catalysts and elemental doping in TiO2 has been extensively explored for effective photocatalysis. Here we report the synthesis of visible light responsive Pt and Co3O4 co-modified nitrogen-doped TiO2 (N–TiO2) nanocomposites for efficient photocatalytic hydrogen production. Pt–Co3O4(S)/N–TiO2 (PCNT(S)) and Pt–Co3O4(D)/N–TiO2 (PCNT(D)) composites were synthesized by one- and two-step methods, respectively. Experimental results showed that additional loading of Co3O4 onto a very low content (0.02 wt%) Pt-modified N–TiO2 nanocomposite significantly increases the efficiency of photocatalytic hydrogen production. Catalyst composites prepared by the two-step method, where close interaction occurred between the surface-loaded Co3O4 and Pt on the N–TiO2 nanoparticles, showed much higher photocatalytic activity for hydrogen production than that prepared by the one-step method, where Co3O4 is evenly dispersed in N–TiO2. The position of the co-catalyst Co3O4 in TiO2 has a significant effect on the photocatalytic properties of the prepared photocatalysts.

N–doped TiO2 effectively extends the light response range of TiO2 photocatalysts from the ultraviolet to the visible region; a p–n heterojunction would favor the separation of photogenerated electron–hole pairs, leading to high quantum efficiency, and consequently, enhanced photocatalysis. A Cu2O/N–TiO2 hybrid catalyst with p-n heterojunctions was newly prepared using a solvothermal and chemical reduction method. The hierarchical structure and valence state of copper of the Cu2O/N–TiO2 catalyst have been confirmed using X-ray diffraction, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The hybrid Cu2O/N–TiO2 catalyst demonstrated good photostability and excellent photocatalytic activity toward H2 production, with a rate of 11 μmol g−1 h−1 under visible light irradiation (>400 nm) of a methanol aqueous solution. This offers an inexpensive and facile approach for potential efficient solar photon-driven H2 production.

One of the promising solutions for decreasing atmospheric CO2 is artificial photosynthesis, in which CO2 can be photoconverted into solar fuels. In this study, a rhenium complex Re(PyBn)(CO)3 Cl (PyBn=1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole) was covalently grafted onto the surface of reduced graphene oxide (rGO). This was further combined with TiO2 to fabricate a novel catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl for CO2 photo-reduction. This hybrid composite demonstrated high selectivity conversion of CO2 into CO under xenon-lamp irradiation. Compared with the unsupported homogeneous catalyst Re(PyBn)(CO)3 Cl, the covalent immobilized catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl enhanced the turnover number six times and significantly improved catalyst stability. During the process of CO2 photo-reduction, intermediate species with lifetimes longer than hundreds of microseconds were observed and the formation of CO products was revealed using timeresolved infrared spectroscopy. A plausible mechanism for CO2 photo-reduction by the TiO2 -rGO-Re(PyBn)(CO)3 Cl catalyst composite has been suggested. The obtained results have implications for the future design of efficient catalyst composites for CO2 photo-conversion.

Metallic doping effectively extends the light response range of TiO2 photocatalysts from the ultraviolet (UV) to the visible region. We prepared Ce-doped TiO2 nanotubes (Ce-TiO2 NTs) using a sol–gel process followed by a hydrothermal treatment. The Ce-TiO2 NTs were characterized by X-ray diffraction, transmission electron microscopy, Brunauer–Emmett–Teller surface area, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), and photoluminescence (PL) spectroscopy. Given that the optical absorption was extended to wavelengths of 600 nm, the Ce-TiO2 NTs demonstrated excellent photocatalytic activity for degrading methylene blue under visible light irradiation. Ce-TiO2 NTs with various amounts of Ce doping (0.06–0.40 g of cerium nitrate hexahydrate added during preparation) were tested, and the 0.12Ce-TiO2 NTs showed the highest photocatalytic activity, 7 times higher than that of P25. For their efficient photodegrading of dyes under visible light, these Ce-TiO2 NTs may be useful for waste water treatment.

Two organic donor-acceptor-π-acceptor (D-A-π-A) sensitizers (AQ and AP), containing quinoxaline/pyrido[3,4-b]pyrazine as the auxiliary acceptor, have been. Through fine-tuning of the auxiliary acceptor, a higher designed and synthesized photoelectric conversion efficiency of 6.02% for the AQ-based dye-sensitized solar cells under standard global AM1.5 solar conditions was achieved. Also, it was found that AQ-Pt/TiO2 photocatalysts displayed a better rate of H2 evolution under visible-light irradiation (420 nm

In this study, we investigated interfacial charge transfer dynamics in water-soluble perylenediimide (WS-PDI) dye sensitized p-type semiconductor NiO nanoparticle films to better understand how molecular interactions influence photoconversion processes involved in solar cells by means of ensemble-averaged and single-molecule spectroscopies. Transient absorption data showed that strong and weak electronic couplings coexist between WS-PDI molecules and NiO nanoparticles, resulting in fast (within several picoseconds) and slow (requiring tens of picoseconds to nanoseconds) hole transfer from the excited dye to NiO, followed by charge recombination occurring at pico- to microsecond time scales. The correlated analyses of single-molecule fluorescence intensity, lifetime, blinking, and anisotropy revealed the intrinsic distribution and temporal fluctuation of interfacial charge transfer reactivity, which are closely related to site-specific molecular interactions and dynamics. It was also found that a suitable insulating Al2O3 layer can weaken the electronic interaction between WS-PDI and NiO, thereby retarding charge recombination and significantly enhancing photoelectric conversion efficiency. The results presented here will provide a reliable basis for design of highly efficient p-type solar cells and other molecule/semiconductor systems for their use in optoelectronic and solar energy applications.

Interfacial electron transfer (ET) to and from semiconductor quantum dots (QDs) is of intense interest because of its important roles in many applications, including biosensors, light-emitting diodes, and solar cells. In this work, we have investigated the photoinduced ET between water-soluble CdTe QDs and nitrobenzene amine (NBzA) through specific cucurbit[6]uril host−guest complex interactions. The modification of cucurbit[6]uril on the QD surface with thiol linker groups significantly improved the physical and chemical stability of QDs. The steady-state and time-resolved fluorescence and absorption spectroscopies were combined to clarify the process of ET from the excited QDs to the guest NBzA molecules in the cucurbit[6]uril cavity. Furthermore, single-particle fluorescence correlation spectroscopy (FCS) experiments revealed that the blinking phenomenon in the microsecond time scale was attributed to the charge separation between the QD and the NBzA molecule.

It was found that, when the Baylis-Hillman reaction of arylaldehydes with methyl vinyl ketone was carried out at below -20 °C in the presence of boron (III) tribromide or titanium (IV) bromide using a catalytic amount of Lewis base such as amine, the brominated compounds and the Baylis-Hillman adducts could be obtained as the major products in good yields for various aryl aldehydes. But at room temperature, the elimination products were the major products. In addition, the palladium catalyzed allylic substitution reactions of the elimination products were also examined.

Charge transfer to and from semiconductor quantum dots (QDs) is of intense interest because of its important roles in QD-based devices, such as light emitting diodes and solar cells. We now report a mechanistic study of the electron transfer (ET) processes between CdTe QDs and a pyromellitimide derivative with a carboxylic acid (PI-CA) using ensemble and single-particle spectroscopies. First, to confirm whether the photochemical reactions occur by excitation of the QDs, the quenching of the QD emission by PI-CA as well as control substrates was examined using steady-state and time-resolved emission spectroscopies. It was found that the PI-CA molecules are strongly bound to the surface of the QDs and significantly quench the photoluminescence (PL) band near 675 nm. Nanosecond transient absorption measurements also revealed that PI•- was formed during the laser flash photolysis of the conjugates between CdTe QD and PI-CA in chloroform solution. The single-particle PL spectroscopy was utilized to clarify the...

The interfacial electron transfer processes between a fluorescent water-soluble perylene diimide dye (WS-PDI) and TiO 2 nanoparticles were investigated using single-molecule fluorescence spectroscopy. Based on the single-molecule fluorescence spectral measurements, it was suggested that the local environment and/or the structural conformation of single WS-PDI molecules play important roles in the efficiency of the electron injection from WS-PDI in the singlet excited state to TiO 2 . The observed single-molecule fluorescence blinking behavior was interpreted in terms of the interfacial electron-transfer dynamics between the single WS-PDI molecules and TiO 2 nanoparticles.

In this article, we described the use of an easily available polymer‐based hafnium chloride and montmorillonite KSF catalyst (HfCl4/KSF‐polyDMAP) in transamidation under relatively mild conditions. This metal catalyst can be easily recovered and reused in this reaction to give the corresponding amides in good yields.

Phenolic compounds can be nitrated with 60% nitric acid (1.2 equiv.) in the presence of catalytic amounts of a Zr or Hf oxychloride complex and montmorillonite KSF to give the corresponding nitrated products in good yields in a heterogeneous catalytic system. The co-catalyst and montmorillonite can be easily recovered and reused in the next batch of nitration. This is a practical process for the nitration of phenolic compounds in a clean way. C Wiley-VCH Verlag GmbH & Co.

The Zr(OTf)(4)-catalyzed reaction of indole, 1-methylindole or pyrrole with alpha,beta-unsaturated ketone generated the corresponding trisindolyl-, tris(1-methylindolyl-), and trispyrrolylalkanes in moderate to high yields in the mixed solvent EtOH/H2O. (C) 2004 Elsevier Ltd. All rights reserved.

Phenolic compounds can be nitrated by 65% nitric acid in the presence of catalytic amounts of montmorillonite KSF and bismuth(III) nitrate to give the corresponding nitrated products in good yields in a heterogeneous phase. The co-catalyst of KSF and Bi(NO^3)^3 can be esily recovered and reused in the next batch of nitration.

The Friedel–Crafts reaction of anisole with acetic anhydride can be carried out in the presence of perfluorinated rare earth metal catalyst without organic solvent. Perfluorodecalin (C 10 F 18 , cis - and trans -mixture) can be used as a fluorous phase solvent for this reaction. Whereas, the reaction of N , N -dimethylaniline with acetic anhydride did not give the corresponding Friedel–Crafts reaction product. On the other hand, the Friedel–Crafts reaction of N , N -dimethylaniline with ethyl glyoxylate was also examined in the presence of perfluorinated Lewis acids. Three products were in fact formed at the same time.

The Baylis–Hillman reaction of aryl aldehydes with α,β-unsaturated ketones in the presence of titanium(IV) chloride can be promoted by oxy-compounds at room temperature, although they are not as effective as amines, chalcogenides, or quaternary ammonium salts. The oxy-compounds can be simple alcohols, ethers, and ketones. For aryl aldehydes having a strong electron-withdrawing group on the phenyl ring such as nitrobenzaldehyde or p-trifluoromethylbenzaldehyde, the chlorinated compound 1 is obtained as the major product. However, for other aryl aldehydes, the elimination compound 3 was formed predominantly. We also found that TiCl4·2THF or TiCl4·2Et2O complex is very effective for this reaction to give the chlorinated products in high yields at low temperature. A plausible mechanism is proposed.

In the Baylis–Hillman reaction of aldehydes with an α,β-unsaturated ketone, the chlorinated compound 1 was obtained as the major product using tributylphosphine as a Lewis base in the presence of titanium(IV) chloride, zirconium(IV) chloride or boron trichloride in dichloromethane at

In this paper, we describe the aza-Diels–Alder reaction of Danishefsky’s diene with arylaldehydes and aromatic amines in a fluorous phase. With perfluorodecalin (C10F18, cis- and trans-mixture) as the fluorous solvent and a perfluorinated rare earth metal salt [Sc(OSO2C8F17)3] (2.0 mol %) as a catalyst, this aza-Diels–Alder reaction can be performed many times without reloading the catalyst.

Graphene oxide (GO) nanosheets have received a great deal of attention for a wide range of applications from optoelectronic devices to biological sensors. We now report a mechanistic study of the interfacial electron transfer (ET) processes between organic dye molecule, 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF), and nanometre-sized GO sheets using ensemble-averaged and single-molecule spectroscopies. The ET dynamics was characterized by the direct observation of the PF radical cation during the laser flash photolysis, and its reaction rate was determined to be ~10(11) s(-1). The single-molecule fluorescence spectroscopy was utilized to clarify the heterogeneous nature of the interfacial ET within individual composites. Their fluorescence lifetimes and spectra were found to vary from composite to composite, possibly due to the different local structures and molecular interactions. The autocorrelation analysis of fluorescence intensity trajectories also revealed the temporal fluctuation of the ET reactivity.

The nitration of aromatic compounds can be carried out in the presence of perfluorinated rare earth metal catalyst without halogenated organic solvent.

In the Baylis–Hillman reaction of aldehydes with an α,β-unsaturated ketone, the chlorinated compound 1 was obtained as the major product using tributylphosphine as a Lewis base in the presence of titanium(IV) chloride, zirconium(IV) chloride or boron trichloride in dichloromethane at

The Baylis–Hillman reaction of aryl aldehydes with α,β-unsaturated ketones in the presence of titanium(IV) chloride can be promoted by oxy-compounds at room temperature, although they are not as effective as amines, chalcogenides, or quaternary ammonium salts. The oxy-compounds can be simple alcohols, ethers, and ketones. For aryl aldehydes having a strong electron-withdrawing group on the phenyl ring such as nitrobenzaldehyde or p-trifluoromethylbenzaldehyde, the chlorinated compound 1 is obtained as the major product. However, for other aryl aldehydes, the elimination compound 3 was formed predominantly. We also found that TiCl4·2THF or TiCl4·2Et2O complex is very effective for this reaction to give the chlorinated products in high yields at low temperature. A plausible mechanism is proposed.

The nitration of aromatic compounds can be carried out in the presence of perfluorinated rare earth metal catalyst without halogenated organic solvent.

Airborne singlet oxygen (1O2) molecules, which are generated during the TiO2 photocatalytic reactions and diffused from the surface into air, were detected at the opposite surface using terrylenediimide (TDI) molecules at the single-molecule level. The novel 1O2 nanosensor, which has a detectable number of about 1000 1O2 molecules in 70 × 70 square micrometers, can easily detect the single 1O2 molecule at a distance of over 1000 micrometers from the place of its creation in ambient air.

In this paper, we describe a useful Mannich-type reaction in fluorous phase. By use of perfluorodecalin (C 10 F 18 , cis - and trans -mixture) as a fluorous solvent and perfluorinated rare earth metal salts such as Sc(OSO 2 C 8 F 17 ) 3 or Yb(OSO 2 C 8 F 17 ) 3 (2.0 mol%) as a catalyst, the Mannich-type reaction of arylaldehydes with aromatic amines and (1-methoxy-2-methylpropenyloxy)trimethylsilane can be performed for many times without reloading the catalyst and the fluorous solvent.

The Mannich-type reaction of imines with (1-methoxy-2-methylpropenyloxy)trimethylsilane and aza-Diels-Alder reaction of imines with Danishefsky's diene can be carried out in scCO(2) in the presence of lithium heptadecafluorooctanesulfonate which offer a way to synthesize beta-amino carbonyl compounds and nitrogen-containing six-membered ring compounds under environmentally benign conditions. (C) 2004 Elsevier Ltd. All rights reserved.

A novel mixed catalyst of LiClO4 (15% w/w), Yb(OPf)(3) (15% w/w, Pf = perfluorooctanesulfonyl), MoO3 (15% w/w) on silica gel for electrophilic aromatic nitration reaction has been explored. The nitration reactions were accomplished by this mixed catalyst and nitric acid under solvent-free conditions. Moreover, the mixed catalyst can be easily recovered from the aqueous layer by heating in an oven and reused for the next nitration reaction

In this paper, we describe a practical, useful electrophilic aromatic nitration process in fluorous phase by using perfluorodecalin (C10F18, cis- and trans-mixture) as a fluorous solvent and perfluorinated rare earth metal salt [Yb(OSO2C8F17)3] as a catalyst for the electrophilic aromatic nitration.