Visible Light Photoreduction of CO2 Using CdSe ... - ACS Publications

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Visible Light Photoreduction of CO2 Using CdSe/Pt/TiO2 Heterostructured Catalysts Congjun Wang,*,†,‡,§ Robert L. Thompson,†,‡,§ John Baltrus,† and Christopher Matranga† †

National Energy Technology Laboratory, U.S. Department of Energy, 626 Cochrans Mill Road, Pittsburgh, Pennsylvania 15236, and ‡Parsons Project Services, Inc., P.O. Box 618, South Park, Pennsylvania 15219

ABSTRACT A series of CdSe quantum dot (QD)-sensitized TiO2 heterostructures have been synthesized, characterized, and tested for the photocatalytic reduction of CO2 in the presence of H2O. Our results show that these heterostructured materials are capable of catalyzing the photoreduction of CO2 using visible light illumination (λ > 420 nm) only. The effect of removing surfactant caps from the CdSe QDs by annealing and using a hydrazine chemical treatment have also been investigated. The photocatalytic reduction process is followed using infrared spectroscopy to probe the gas-phase reactants and gas chromatography to detect the products. Gas chromatographic analysis shows that the primary reaction product is CH4, with CH3OH, H2, and CO observed as secondary products. Typical yields of the gas-phase products after visible light illumination (λ > 420 nm) were 48 ppm g-1 h-1 of CH4, 3.3 ppm g-1 h-1 of CH3OH (vapor), and trace amounts of CO and H2. SECTION Surfaces, Interfaces, Catalysis

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ne quarter of the world's coal reserves are located in the United States. Coal is also the workhorse of our power industry, responsible for more than half of the electricity consumed by Americans. Even though coal is a national treasure, managing CO2 emissions from its utilization is perhaps the largest technical challenge currently faced by the fossil energy industry. Although CO2 is routinely captured from industrial processes such as ammonia production and limestone calcination, existing capture technologies are not cost-effective for use in power plants. As such, transformational new technologies are needed to help address the CO2 challenge. The photocatalytic reduction of CO2 is a promising technical solution since it uses readily available sunlight to convert CO2 into valuable chemicals, such as methanol or methane, in a carbon friendly manner.1 TiO2 is a popular catalyst for this photoreduction because it is inexpensive, has reasonable activity, and is abundant. Despite these attributes, the efficiency of TiO2 for photovoltaic and photocatalytic applications is severely limited by its large band gap (∼3.2 eV) and rapid charge carrier recombination dynamics.2 For photovoltaics applications, the band gap sensitization of TiO2 by dye molecules has improved activity and demonstrated conversion efficiencies of over 11%.3 Enhancement of activity has also been achieved by introducing impurity atoms such as N and S into TiO2.4 Despite the tremendous progress in developing more robust and efficient dyes for photovoltaic cells,3b one disadvantage of dye molecules for photoreduction applications is the potential for photo- and thermal degradation. Likewise, impurity doping has the disadvantage of creating defect states, which may inherently limit the effectiveness of this strategy.5

r 2009 American Chemical Society

Recently, there has been a growing interest in using semiconductor nanocrystal QDs to sensitize TiO2 for photovoltaic6 and photocatalytic7 applications. These QDs are thermally stable, have large absorption cross sections, and do not easily photodegrade. QDs such as CdSe form a type II band alignment with TiO2. As a result, any photoexcited electrons in the CdSe QDs can be injected into TiO2 and subsequently collected by an electrode or used to initiate a photocatalytic reaction. This type of heterostructured material can make use of visible or near-IR photons as well as facilitate charge separation to prevent recombination. Using this approach, the photocatalytic decomposition of dye molecules at wavelengths > 600 nm has been demonstrated with heterostructured PbSe QD-sensitized TiOx catalysts.7 In this Letter, we describe the use of CdSe/Pt/TiO2 heterostructured materials for the photocatalytic reduction of CO2 using visible light excitation (λ > 420 nm). We have been able to manipulate the activity of this system so that no ultraviolet light is needed and the direct excitation of the TiO2 band gap is completely avoided. To the best of our knowledge, the photocatalytic reduction of CO2 with H2O has only been demonstrated using broad-band UV irradiation or optical filters which still allow for small amounts of stray UV light to directly excite TiO2.1,8-24 Our results represent a significant new finding for the photocatalytic reuse of CO2, namely, that the lower-energy tails of the solar spectrum can be utilized for this application and that the conversion rates are comparable to previous Received Date: September 21, 2009 Accepted Date: October 20, 2009 Published on Web Date: November 05, 2009

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DOI: 10.1021/jz9000032 |J. Phys. Chem. Lett. 2010, 1, 48–53

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studies which directly excite TiO2 using UV irradiation. As such, our results demonstrate a significant step toward making more efficient photocatalysts for CO2 capture and reuse. Commercial P25 TiO2 nanoparticles and CdSe QDs were used in our experiments. In order to enhance the photoreduction activity, various metals such as Pt were incorporated by the wet impregnation methods onto the TiO2.25 Two sizes of CdSe QDs (2.5 and 6 nm diameter) were then mixed with the Pt/TiO2. One set of samples was thermally annealed in an inert atmosphere to desorb the organic capping molecules on the CdSe QDs, and these are referred to as t-CdSe/Pt/TiO2.26 Likewise, the caps were also removed using a chemical hydrazine treatment (see below) of the CdSe QDs prior to mixing with TiO2 and are referred to as c-CdSe/Pt/TiO2.27 Although composite TiO2 materials have been prepared by other methods such as single-step aerosol routes,28 our synthesis is also relatively simple and similar to approaches reported by other groups for a range of applications. Approximately 300 mg of the heterostructured photocatalyst was deposited on a glass slide and placed inside of a custom-built photocatalysis cell. In order to follow the photoconversion of CO2 by infrared (IR) spectroscopy, the reaction cell was first evacuated to a base pressure of ∼10-7 Torr and then dosed with ∼3 Torr of H2O vapor and ∼0.3 Torr of CO2. The IR spectra of the gas in the photocatalysis cell were recorded as a function of light illumination time. A second series of experiments were conducted which used gas chromatography (GC) to detect reaction products. For these experiments, the cell was purged for 15 min with CO2 which had been bubbled through H2O. A 300 W Xe arc lamp was used as the light source, and long pass filters were used to remove UV light, leaving only λ > 420 nm. A water filter and control experiments rule out the possibility of heat from the lamp bulb causing the photocatalytic process. The light intensity was e100 mW/cm2 at the sample. The BET surface area of the TiO2-based catalysts remains essentially constant (∼50 m2/g) in all of our samples, indicating that the Pt cocatalysts, CdSe QD sensitizers, thermal annealing steps, and hydrazine treatments do not lead to structural changes of the TiO2. While the conduction band of bulk CdSe is only slightly above that of TiO2, quantum confinement shifts the conduction band of CdSe QDs to higher energies, which facilitates charge injection into TiO2 (Figure 1). Redox potentials indicate that it is also energetically favorable for the injected electrons to initiate the reduction of CO2 with H2O (Figure 1). For efficient carrier separation across the CdSe and TiO2 heterojunction, the QDs should be uniformly distributed and in close/direct contact with the TiO2 nanoparticles. Figure 2 shows the scanning electron microscopy (SEM) image of a tCdSe/Pt/TiO2 sample and demonstrates a uniform distribution. The small white dots on the TiO2 surface (Figure 2a) are Pt cocatalysts, as confirmed by energy dispersive spectroscopy (EDS) analysis. Because thermal annealing leads to the sintering of CdSe QDs, it is difficult to distinguish individual CdSe QDs in the SEM images; however, EDS analysis shows that CdSe is uniformly distributed on the TiO2. X-ray photoelectron spectroscopy (XPS) indicates that the atomic concentrations of Pt and Cd in our samples are ∼0.5 and ∼1%,


Figure 1. Band alignment of bulk CdSe and 2.5 nm CdSe QDs with TiO2 and relevant redox potentials of CO2 and H2O.

respectively. Pt also shows multiple oxidation states, with Pt0 accounting for ∼76% of the total Pt and ∼11 and ∼13% for Pt1þ and Pt2þ, respectively (Supporting Information, Figure S1). The charge injection rate from CdSe QDs into TiO2 depends on the size of the QDs.29 Likewise, good contact between the CdSe and TiO2 is needed to facilitate charge transfer. Since using thermal annealing to create this contact can sinter QD particles, we also investigated removing QD caps with a chemical treatment to preserve their size distribution. This was accomplished by treating the CdSe QDs with 1 M hydrazine prior to mixing with the Pt/TiO2. This approach has been reported to improve electronic coupling between PbSe QDs in thin films.30,31 The hydrazine treatment should remove capping molecules, allow for direct contact between the QDs and TiO2, and maintain the size distribution and quality of the QDs. The removal of the organic capping molecules on the QDs using the hydrazine treatment was confirmed with IR spectroscopy (Figure S2A).27,31 The size and optical properties of the CdSe QDs are preserved after the hydrazine treatment, as evidenced by the UV/vis absorption spectra of the QDs (Figure S2B, Supporting Information). Diffuse reflectance spectra of the c-CdSe/Pt/TiO2 samples exhibit clear and distinct absorption features of CdSe QDs in the visible region (Figure S3, Supporting Information). SEM and EDS data for the c-CdSe/Pt/ TiO2 sample suggest that CdSe QDs form aggregates on the surface of TiO2 due to the loss of the capping molecules (Figure 3), which limits the interfacial contact between the QDs and TiO2. The photoreduction of CO2 using the t-CdSe/Pt/TiO2 sample was studied with IR spectroscopy (Figure S4, Supporting Information). The photocatalysts were first allowed to equilibrate in the CO2/H2O atmosphere for several hours to ensure that the adsorption of gas molecules was complete. Figure 4 shows the CO2 peak area as a function of photolysis time under λ > 420 nm irradiation (Edmund Optics GG-420 long pass filter). After ∼4 h of reaction, the CO2 peak intensity was

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Figure 2. SEM image of (A) t-CdSe/Pt/TiO2 photocatalyst, scale bar 100 nm, and (B) EDS mapping of the same sample, scale bar 80 nm (Se: yellow; Cd: red; Pt: pink).

reduced by ∼10%. The reduction of the gas-phase CO2 absorption intensity indicates that the molecule is being consumed in a photoreaction. To confirm that the changes in the CO2 intensity result from a visible-light-mediated photocatalytic reaction, a series of control experiments were carried out (Figure S5, Supporting Information). When the t-CdSe/Pt/TiO2 sample in the cell was kept in the dark, no changes were observed in the CO2 absorption intensity. For Pt/TiO2 samples (no CdSe QDs present) annealed identically to the t-CdSe/Pt/TiO2 samples, no CO2 intensity changes were seen during irradiation with λ > 420 nm light. As a final control experiment, we exposed just the CdSe QDs annealed identically to the t-CdSe/Pt/TiO2 samples, to the full spectral output of the lamp, as well as to visible light only (λ > 420 nm) and observed no evidence of CO2 consumption. These experiments strongly suggest that both CdSe and Pt/TiO2 must be present to achieve photocatlytic activity during visible light (λ > 420 nm) excitation. The absence of activity when only Pt/TiO2 or CdSe QDs are irradiated also indicates that thermally mediated processes on the surfaces of these materials are not responsible for CO2 consumption. As a final note, the photocatalyst slowly deactivates over time and becomes inactive after 4-6 h of illumination (Figures 4 and S4, Supporting Information). The degradation is most likely due to the oxidation of CdSe QDs, an effect observed in similar systems. A variety of hole scavengers and caps are currently being examined to improve the lifetime of the CdSe-sensitized TiO2 photocatalysts. The IR experiments provide clear evidence that CO2 is being consumed in a photoreaction. The strong IR absorption bands of CO2 and H2O make it difficult to detect the products of the reaction with our current cell geometry. To identify these products and quantify reaction yields, gas chromatography (GC) experiments were conducted. For these experiments, the c-CdSe/Pt/TiO2 samples were used to exploit the quantum confinement effect in the CdSe QDs (sizes are preserved). Because smaller QDs have faster electron injection rates into TiO2 and larger QDs extend the visible


absorption range, a mixture of 2.5 and 6 nm CdSe QDs were used to make the c-CdSe/Pt/TiO2 samples. After illuminating the c-CdSe/Pt/TiO2 samples with visible light (λ > 420 nm), we observe methane (48 ppm g-1 h-1), methanol (3.3 ppm g-1 h-1), H2 (trace), and CO (trace) using the GC for detection (Supporting Information). We note that only vapor-phase methanol will be detected with our GC sampling and that liquid product will remain undetected. These conversion rates are consistent with the 10% intensity reduction seen in the IR experiments, once one accounts for different CO2 partial pressures, ∼0.3 Torr in the IR experiments and 760 Torr in the GC studies (Supporting Information). The composition of the products also seems to depend on the metal cocatalyst. When Fe was used in place of Pt, we primarily saw H2 production (>55 ppm g-1 h-1), suggesting that only H2O splitting was occurring. Future work will focus on evaluating the role of the metal cocatalyst. A series of control experiments were conducted to verify the origin of the photoactivity in the c-CdSe/Pt/TiO2 samples. In order to eliminate the role of residual hydrazine in the reactions, a CO2/H2O-filled photocatalysis cell with c-CdSe/Pt/ TiO2 catalyst was kept in the dark overnight, and no reaction was detected. When CdSe QDs (treated identically with hydrazine) were used without Pt/TiO2, no activity was observed during irradiation with the full lamp spectrum (white light) or with visible light only (λ > 420 nm). In addition, if only Pt/TiO2 was irradiated with λ > 420 nm (Edmond Optics GG-420), no photoconversion products were detected, illustrating that this particular filter completely removes any stray UV light that might directly excite the TiO2 band gap. A noticeable activity (CO2 conversion rate ∼ 0.8 ppm g-1 h-1) was observed when the unsensitized Pt/TiO2 was under λ >400 nm irradiation using an Edmund Optics GG-400 long pass filter instead of the GG-420 filter. This activity is most likely due to the fact that the stopband limit (λS = 340 nm) of the 400 nm GG-400 filter still allows small amounts of stray UV light to directly excite the band gap of TiO2 (∼388 nm). Our results using the λ > 420 nm filter (Edmond Optics GG-420)

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Figure 3. SEM image of c-CdSe/Pt/TiO2 photocatalyst and EDS mapping of Ti, Pt, Cd, and Se, showing the formation of CdSe QD clusters on the surface of Pt/TiO2.

reduction process to that proposed by Tanaka et al.32 and Grimes et al.1 The holes accumulated in CdSe QDs lead to the oxidation of QDs,33 as evidenced by the deactivation of the heterostructured catalyst after ∼4-6 h of continuous photoexcitation. More experiments are underway to better understand the details of the photocatalytic process and to improve the performance of these heterostructured photocatalysts.

to completely remove stray UV light and the control experiment using this filter on the unsensitized Pt/TiO2 (see above) therefore clearly demonstrate that the visible light activity of our CdSe/Pt/TiO2 samples occurs without the direct excitation of the TiO2 band gap. The charge injection from semiconductor QDs into TiO2 has been carefully studied.6c,29 On the basis of these reports, we expect that the injected electrons should follow a similar


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REFERENCES (1)

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(4) Figure 4. CO2 consumption (as measured from the reduction of CO2 absorption peak in the IR) as a function of photolysis time under λ > 420 nm light irradiation. Solid circles, t-CdSe/Pt/TiO2 photocatalyst. Triangles, Pt/TiO2 catalyst.

We have demonstrated the photocatalytic conversion of CO2 to methane and methanol in the presence of water using only visible light excitation (λ > 420 nm), where the direct photoexcitation of TiO2 can be ruled out. Our results represent a significant new finding germane to those working on photoreduction reactions for CO2 capture and reuse. We believe the activity of the CdSe-sensitized Pt/TiO2 heterostructured catalysts can be further improved by optimizing parameters such as the concentrations of CdSe QDs and Pt cocatalysts and the dispersion of CdSe QDs on the surface of the TiO2 nanoparticles and controlling the structure of CdSe/TiO2 using different growth methods. The selectivity of the heterostructured catalyst may also be enhanced by using different metal cocatalysts.

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ACKNOWLEDGMENT This technical effort was performed in support of the National Energy Technology Laboratory's ongoing research in Advanced Materials for CO2 Capture and Conversion for NETL's Carbon Sequestration Program under the RDS Contract DEAC26-04NT41817. Reference in this work to any specific commercial product is to facilitate understanding and does not necessarily imply endorsement by the U.S. Department of Energy. We thank Paul Zandhuis for technical assistance with the GC experiments.

SUPPORTING INFORMATION AVAILABLE Experimental details of the preparation and characterization of CdSe/Pt/TiO2 heterostructured catalysts and photocatalysis experiments. This material is available free of charge via the Internet at http://pubs.acs. org.

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AUTHOR INFORMATION (9)

Corresponding Author: *

To whom correspondence should be addressed. E-mail: congjun. [email protected].

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Author Contributions: §

These authors contributed equally to this work.


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Varghese, O. K.; Paulose, M.; LaTempa, T. J.; Grimes, C. A. High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels. Nano Lett. 2009, 9, 731–737. (a) Nozik, A. J. Photoelectrolysis of Water Using Semiconducting TiO2 Crystals. Nature 1975, 257, 383–386. (b) Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37–38. (a) Gr€ atzel, M. Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells. Inorg. Chem. 2005, 44, 6841–6851. (b) Chen, C.-Y.; Wang, M.; Li, J.-Y.; Pootrakulchote, N.; Alibabaei, L.; Ngoc-le, C.; Decoppet, J. -D.; Tsai, J. -H.; Gr€ atzel, C.; Wu, C. -G.; Zakeeruddin, S. M.; Gr€ atzel, M. Highly Efficient Light-Harvesting Ruthenium Sensitizer for Thin-Film Dye-Sensitized Solar Cells. ACS Nano 2009, DOI: 10.1021/nn900756s. (a) Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides. Science 2001, 293, 269–271. (b) Burda, C.; Lou, Y. B.; Chen, X. B.; Samia, A. C. S.; Stout, J.; Gole, J. L. Enhanced Nitrogen Doping in TiO2 Nanoparticles. Nano Lett. 2003, 3, 1049–1051. (c) Umebayashi, T.; Yamaki, T.; Itoh, H.; Asai, K. Band Gap Narrowing of Titanium Dioxide by Sulfur Doping. Appl. Phys. Lett. 2002, 81, 454–456. (a) Di Valentin, C.; Pacchioni, G.; Selloni, A. Origin of the Different Photoactivity of N-Doped Anatase and Rutile TiO2. Phys. Rev. B 2004, 70, 085116. (b) Lin, Z. S.; Orlov, A.; Lambert, R. M.; Payne, M. C. New Insights into the Origin of Visible Light Photocatalytic Activity of Nitrogen-Doped and Oxygen-Deficient Anatase TiO2. J. Phys. Chem. B 2005, 109, 20948–20952. (c) Lee, J. Y.; Park, J.; Cho, J. H. Electronic Properties of N- and C-Doped TiO2. Appl. Phys. Lett. 2005, 87, 011904. (d) Serpone, N. Is the Band Gap of Pristine TiO2 Narrowed by Anion- and Cation-Doping of Titanium Dioxide in Second-Generation Photocatalysts?. J. Phys. Chem. B 2006, 110, 24287–24293. (a) Lee, H. J.; Yum, J.-H.; Leventis, H. C.; Zakeeruddin, S. M.; Haque, S. A.; Chen, P.; Seok, S. I.; Gr€ atzel, M.; Nazeeruddin, M. K. CdSe Quantum Dot-Sensitized Solar Cells Exceeding Efficiency 1% at Full-Sun Intensity. J. Phys. Chem. C 2008, 112, 11600–11608. (b) Chen, J.; Song, J. L.; Sun, X. W.; Deng, W. Q.; Jiang, C. Y.; Lei, W.; Huang, J. H.; Liu, R. S. An Oleic AcidCapped CdSe Quantum-Dot Sensitized Solar Cell. Appl. Phys. Lett. 2009, 94, 153115. (c) Hyun, B.-R.; Zhong, Y.-W.; Bartnik, A. C.; Sun, L.; Abru~ na, H. D.; Wise, F. W.; Goodreau, J. D.; Matthews, J. R.; Leslie, T. M.; Borrelli, N. F. Electron Injection from Colloidal PbS Quantum Dots into Titanium Dioxide Nanoparticles. ACS Nano 2008, 2, 2206–2212. (d) Bang, J. H.; Kamat, P. V. Quantum Dot Sensitized Solar Cells. ATale of Two Semiconductor Nanocrystals: CdSe and CdTe. ACS Nano 2009, 3, 1467–1476. Wang, C.; Kwon, K.-W.; Odlyzko, M. L.; Lee, B. H.; Shim, M. PbSe Nanocrystal/TiOx Heterostructured Films: A Simple Route to Nanoscale Heterointerfaces and Photocatalysis. J. Phys. Chem. C 2007, 111, 11734–11741. Inoue, T.; Fujishima, A.; Konishi, S.; Honda, K. Photoelectrocatalytic Reduction of Carbon-Dioxide in Aqueous Suspensions of Semiconductor Powders. Nature 1979, 277, 637–638. Halmann, M.; Ulman, M.; Aurian-Blajeni, B. Photochemical Solar Collector for the Photoassisted Reduction of Aqueous Carbon Dioxide. Sol. Energy 1983, 31, 429–431. Cook, R. L.; MacDuff, R. C.; Sammells, A. F. Photoelectrochemical Carbon Dioxide Reduction to Hydrocarbons at Ambient Temperature and Pressure. J. Electrochem. Soc. 1988, 135, 3069–3070.


pubs.acs.org/JPCL

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

Kanemoto, M.; Shiragami, T.; Pac, C.; Yanagida, S. Semiconductor Photocatalysis. 13. Effective Photoreduction of Carbon Dioxide Catalyzed by Zinc Sulfide Quantum Crystallites with Low Density of Surface Defects. J. Phys. Chem. 1992, 96, 3521–3526. Adachi, K; Ohta, K.; Mizuna, T. Photocatalytic Reduction of Carbon Dioxide to Hydrocarbon Using Copper-Loaded Titanium Dioxide. Sol. Energy 1994, 53, 187–190. Solymosi, F.; Tombacz, I. Photocatalytic Reaction of H2OþCO2 over Pure and Doped Rh/TiO2. Catal. Lett. 1994, 27, 61–65. Yamashita, H.; Kamada, N.; He, H.; Tanaka, K.; Ehara, S.; Anpo, M. Reduction of CO2 with H2O on TiO2(100) and TiO2(110) Single Crystals under UV-irradiation. Chem. Lett. 1994, 23, 855–858. Anpo, M.; Yamashita, H.; Ichihashi, Y.; Ehara, S. Photocatalytic Reduction of CO2 with H2O on Various Titanium Oxide Catalysts. J. Electroanal. Chem. 1995, 396, 21–26. Anpo, M.; Yamashita, H.; Ichihashi, Y.; Fujii, Y.; Honda, M. Photocatalytic Reduction of CO2 with H2O on Titanium Oxides Anchored within Micropores of Zeolites: Effects of the Structure of the Active Sites and the Addition of Pt. J. Phys. Chem. B 1997, 101, 2632–2636. Yoneyama, H. Photoreduction of Carbon Dioxide on Quantized Semiconductor Nanoparticles in Solution. Catal. Today 1997, 39, 169–175. Kaneco, S.; Shimizu, Y.; Ohta, K.; Mizuno, T. Photocatalytic Reduction of High Pressure Carbon Dioxide Using TiO2 Powders with a Positive Hole Scavenger. J. Photochem. Photobiol. A: Chem. 1998, 115, 223–226. Kaneco, S.; Kurimoto, H.; Shimizu, Y.; Ohta, K.; Mizuno, T. Photocatalytic Reduction of CO2 Using TiO2 Powders in Supercritical Fluid CO2. Energy 1999, 24, 21–30. Tseng, I.-H.; Chang, W.-C.; Wu, C. S. J. Photoreduction of CO2 Using Sol-Gel Derived Titania and Titania-Supported Copper Catalysts. Appl. Catal., B 2002, 37, 37–48. Tseng, I.-H.; Wu, J. C. S.; Chou, H. Y. Effects of Sol-Gel Procedures on the Photocatalysis of Cu/TiO2 in CO2 Photoreduction. J. Catal. 2004, 221, 432–440. Tan, S. S.; Zou, L.; Hu, E. Photocatalytic Reduction of Carbon Dioxide into Gaseous Hydrocarbon Using TiO2 Pellets. Catal. Today 2006, 115, 269–273. Xia, X.-H.; Jia, Z.-H.; Yu, Y.; Liang, Y.; Wang, Z.; Ma, L.-L. Preparation of Multi-Walled Carbon Nanotube Supported TiO2 and Its Photocatalytic Activity in the Reduction of CO2 with H2O. Carbon 2007, 45, 717–721. Lo, C.-C.; Hung, C.-H.; Yuan, C.-S.; Wu, J.-F. Photoreduction of Carbon Dioxide with H2 and H2O over TiO2 and ZrO2 in a Circulated Photocatalytic Reactor. Sol. Energy Mater. Sol. Cells 2007, 91, 1765–1774. Jang, J. S.; Choi, S. H.; Kim, H. G.; Lee, J. S. Location and State of Pt in Platinized CdS/TiO2 Photocatalysts for Hydrogen Production from Water under Visible Light. J. Phys. Chem. C 2008, 112, 17200–17205. Lee, J.-C.; Sung, Y.-M.; Kim, T. G.; Choi, H.-J. TiO2-CdSe Nanowire Arrays Showing Visible-Range Light Absorption. Appl. Phys. Lett. 2007, 91, 113104. Law, M.; Luther, J. M.; Song, Q.; Hughes, B. K.; Perkins, C. L.; Nozik, A. J. Structural, Optical, and Electrical Properties of PbSe Nanocrystal Solids Treated Thermally or with Simple Amines. J. Am. Chem. Soc. 2008, 130, 5974–5985. (a) Teoh, W. Y.; M€ adler, L.; Beydoun, D.; Pratsinis, S. E.; Amal, R. Direct (One-Step) Synthesis of TiO2 and Pt/TiO2 Nanoparticles for Photocatalytic Mineralization of Sucrose. Chem. Eng.


(29)

(30)

(31)

(32)

(33)

53

Sci. 2005, 60, 5852–5861. (b) Tiwari, V.; Jiang, J.; Sethi, V.; Biswas, P. One-Step Synthesis of Noble Metal-Titanium Dioxide Nanocomposites in a Flame Aerosol Reactor. Appl. Catal., A 2008, 345, 241–246. Robel, I.; Masaru, K.; Kamat, P. V. Size-Dependent Electron Injection from Excited CdSe Quantum Dots into TiO2 Nanoparticles. J. Am. Chem. Soc. 2007, 129, 4136–4137. Talapin, D. V.; Murray, C. B. PbSe Nanocrystal Solids for n- and p-Channel Thin Film Field-Effect Transistors. Science 2005, 310, 86–89. Williams, K. J.; Tisdale, W. A.; Leschkies, K. S.; Haugstad, G.; Norris, D. J.; Aydil, E. S.; Zhu, X.-Y. Strong Electronic Coupling in Two-Dimensional Assemblies of Colloidal PbSe Quantum Dots. ACS Nano 2009, 3, 1532–1538. Tanaka, K.; Miyahara, K.; Toyoshima, I. Adsorption of Carbon Dioxide on Titanium Dioxide and Platinum/Titanium Dioxide Studied by X-Ray Photoelectron Spectroscopy and Auger Electron Spectroscopy. J. Phys. Chem. 1984, 88, 3504–3508. (a) Spanhel, L.; Haase, M.; Weller, H.; Henglein, A. Photochemistry of Colloidal Semiconductors. 20. Surface Modification and Stability of Strong Luminescing CdS Particles. J. Am. Chem. Soc. 1987, 109, 5649–5655. (b) Wang, X.; Qu, L.; Zhang, J.; Peng, X.; Xiao, M. Surface-Related Emission in Highly Luminescent CdSe Quantum Dots. Nano Lett. 2003, 3, 1103–1106.


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