View Article Online View Journal
ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Zhou, Z. zou, X. Y. Wang, M. Xiao, Q. F. Xu, W. Tu, S. Feng and P. Li, Chem. Commun., 2015, DOI: 10.1039/C5CC03905C.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/chemcomm
Please do not adjust margins ChemComm
Page 1 of 5
View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
Hollow spheres consisting of Ti0.91O2/CdS nanohybrids for CO2 photofixation † Received 00th January 20xx, Accepted 00th January 20xx DOI: 10.1039/x0xx00000x
Wenguang Tu,a, b, c Yong Zhou,*, a, b, c Shichao Feng,a, b, c Qinfeng Xu,b, d Peng Li,e,f Xiaoyong Wang,b Min Xiao,b and Zhigang Zou*, b, c
www.rsc.org/
Here we report multilayer hollow spheres consisting of alternating ultrathin Ti0.91O2 nanosheets and CdS nanoparticles via exquisite layer-by-layer self-assembly to achieve all solid-state Z-scheme system with 7–times enhancement of CH4-production rate relative to pure Ti0.91O2 hollow spheres, due to greatly prolonged lifetime of charge carriers. Photocatalytic reduction of CO2 into hydrocarbon fuels using solar energy, an idea of mimicking natural photosynthetic cycle of chemical conversion of CO2 into carbohydrates, has been consistently gaining attention for more than 30 years, because it is like killing two birds with one stone in terms of mitigating global warming and consumption of fossil fuels.1 Natural photosynthesis uses a sophisticated Z-scheme system to harvest two photons through two photosystems connected in series with an electron transfer chain to drive chemical reactions involved in water oxidation and reduction of coenzyme NADP on two photosystems individually, which can ensure the charge separation quantum efficiency is close to 100% under optimal conditions.2 The artificial Z-scheme system has been successfully applied to split water into H2 and O2 using two different semiconductor photocatalysts with redox mediators driven by a two-step photoexcitation.3 However, the reaction efficiency of this system is limited by electron transfer from O2-evolution photocatalyst to H2-evolution photocatalyst, which is mainly determined by redox mediators that causes undesirable backward reactions involving redox mediators, such as competitive oxidation of I− by holes on O2-evolution photocatalyst when using IO3−/I− as redox mediator.4 Relative to solution-based a.
Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, School of Physics, Nanjing University, Nanjing 210093, P. R. China; E-mail: [email protected] b. National Laboratory of Solid State Microstructures, Department of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China; E-mail: [email protected] c. Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China d. Department of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, P. R. China e. Environmental Remediation Materials Unit and International Center for Materials Nanoarchitectonics (WPI-MANA), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. † Electronic Supplementary Information (ESI) available: [experimental section, UVVis, SEM, photoactivity and so on]. See DOI: 10.1039/x0xx00000x
- -
3+
2+
systems such as IO3 /I and Fe /Fe redox couples, solid electron 5, 6 7 mediators such as Au and graphene are more favorable in terms of ensuring a continuous flow of electrons between the source and target photocatalysts because of the close photocatalyst8 mediator−photocatalyst contact. In a typical all-solid-state Z5 scheme of CdS/Au/TiO2, photoexcited electrons in conduction band (CB) of TiO2 under ultraviolet (UV) irradiation transferred to Au and then to the valence band (VB) of CdS, and subsequently recombined with photogenerated holes in CdS. Simultaneously, photogenerated electrons in the CB of CdS and holes in VB the of TiO2 exhibited strong reduction power and oxidation power respectively, leading to high photocatalytic reduction of 2+ methylviologen (MV ). Moreover, recombination of photoexcited holes in the VB of CdS with electrons from TiO2 results in the improvement of photostability of CdS. Despite of the well developed TiO2-Au-CdS system, however, Au electron mediator strongly absorb part of the visible light, reducing the light absorption of semiconductor photocatalysts. Therefore a Z-scheme system without an electron mediator is highly desirable for eliminating this limitation. Ultrathin highly crystalline Ti0.91O2 nanosheets exfoliated from protonic titanate exhibit very high 2D anisotropy with a thickness of 0.75 nm and lateral dimensions of up to several tens of micrometers.9 Layer-by-layer (LBL) self-assembly offers opportunity to use ultrathin Ti0.91O2 nanosheets as one of building blocks to form well-defined multilayer films or hollow spheres stacked with complementary interaction (such as electrostatic attraction, and covalent bonding), due to its simplicity and excellent size control.1012 Such ultrathin multilayer stacked films or hollow spheres at the molecular scale possess novel physicochemical properties, such as high dielectric constant,10 ultrafast electron transfer,11 and indirect optical transition (IOT) effect.12 IOT effect observed in ultrathin hollow spheres consisting of alternating Ti0.91O2 nanosheets and graphene oxide results from optical recombination of electrons in the CB of TiO2 and holes in the O 2p levels of graphene oxide,12 which is similar to the basic process of artificial Z-scheme system that electrons in the CB of O2-evolution photocatalyst migrate to the holes in VB of H2-evolution photocatalyst. IOT effect has also
J. Name., 2013, 00, 1-3 | 1
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
COMMUNICATION
Please do not adjust margins ChemComm
Page 2 of 5 View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
13
been observed in the multiple GaAs/A1GaAs quantum wells or 14 coupled InAs quantum dots (QDs). Herein we design ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs via exquisite LBL selfassembly to realize a redox mediator-free artificial Z-Scheme system based on the carrier transfer of IOT effect. The photoluminescence (PL) spectra and transient time-resolved PL decay measurements prove that excited electrons in the CB of Ti0.91O2 nanaosheets recombine with holes in the VB of CdS NPs through d-p conjugation, totally different from traditional TiO2-CdS 15, 16 system. Multilayer Ti0.91O2/CdS hollow spheres exhibited 7– times enhancement of photocatalytic activity for photoreduction of CO2, relative to pure Ti0.91O2 hollow spheres, due to greatly prolonged lifetime of charge carriers through construction of artificial Z-scheme system. Our work may provide a new viewpoint for tailoring and constructing hybrid nanostructure of semiconductors for photocatalysis.17
Fig. 1 Schematic llustration of procedure for constrution of ultrathin multilayer Ti0.91O2/CdS hollow spheres for CO2 photoreduction.
The overall fabrication procedure of ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs is schematically illustrated in the Fig. 1. Poly (methyl methacrylate) (PMMA) beads were successively modified with a protonic polyethylenimine (PEI) aqueous solution (Fig. 1a), a colloidal suspension of negatively charged Ti0.91O2 nanosheets (Fig. 1b), a protonic PEI aqueous solution (Fig. 1c), and a negatively charged CdS NPs suspension (Fig. 1d) via LBL self-assembly procedures. After repeating the dipping cycles five times, yellow composites with 5 layers of (PEI/ Ti0.91O2/PEI/CdS)5 were obtained (Fig. S1). The UVvisible spectra confirm the successful loading of (PEI/Ti0.91O2)5 and (PEI/Ti0.91O2/PEI/CdS)5 shells onto the PMMA beads (Fig. S2 and Fig. S4). A strong absorption band centering at around 220 nm is diagnostic of PMMA polymers. The spectrum of (PEI/Ti0.91O2)5 shells on the PMMA bead shows a characteristic absorption peak of molecular Ti0.91O2 nanosheet at 265 nm and an absorption edge at about 326 nm (Fig. S2a), displaying a bandgap of 3.8 eV which is exactly consistent with the band gap energy of the Ti0.91O2 18 nanosheet. Pure CdS NPs shows an absorption edge at around 500 nm corresponding to the band gap energy of ~2.48 eV (Fig. S2b and Fig. S3), indicating the effective light-response in the visible light region. Compared to (PEI/Ti0.91O2)5 shells on PMMA and (PEI/CdS)5 shells on PMMA, (PEI/Ti0.91O2/PEI/CdS)5 shells on PMMA show
extended light absorption range assigned to pure (PEI/Ti0.91O2)5 on PMMA and (PEI/CdS)5 on PMMA (Fig. S2c). The field emission scanning electron microscopy (FE-SEM) images (Fig. S4b) show the noteworthy crinkled and rough textures of PMMA spheres with (PEI/Ti0.91O2/PEI/CdS)5 shells associated with the presence of flexible and ultrathin Ti0.91O2 sheets, distinguishing from smooth surface of bare PMMA sphere (Fig. S4a). Partial Ti0.91O2 sheets patch peeling off from the core surfaces and corrugation can clearly be observed, proving that the block sheets have indeed been suceessfully coated onto PMMA. Hollow spheres with (Ti0.91O2/CdS)5 shell were obtained by removing PMMA templates and PEI moiety with the assistance of microwave irradiation. For comparion, hollow spheres with (CdS)5 shell and (Ti0.91O2)5 shell were also prepared by the analogous procedure above.
Fig. 2 (a) SEM, (b) TEM, and (c, d) high-resolution TEM images of Ti0.91O2/CdS hollow spheres. Scale bare of the inset (b) is 200 nm.
After rapid decomposition of the PMMA core into exhaust gas resulted from local high temperature with the assistance of microwave irradiation, Ti0.91O2/CdS hollow spheres were formed (Fig. 2 and Fig. S5). Some occasional holes and traces of rupture prove the production of hollow structure, as shown in Fig. 2a, b. The well preserved spherical configuration demonstrates the robust virtue of Ti0.91O2/CdS hollow spheres. The dried hollow spheres are prone to aggregate together. TEM image (Fig. 2b) also clearly shows ultrathin hollow nanostructure. High-resolution TEM observation reveals intactness of multilayer stacking structures of alternating ultrathin Ti0.91O2 nanosheets and CdS NPs of 5-6 nm in size (Fig. 2c, d), resembling hybrid of lamellar fringes separated with small dark dots. HRTEM reveals the well-defined lattice fringes of CdS NPs, corresponding to (101) plane of cubic CdS. Ti0.91O2 and Ti0.91O2/CdS hollow spheres were used as photocatalysts to reduce CO2 into hydrocarbon fuels in the presence of water vapor (Fig. 3). The CH4 production rate of -1 Ti0.91O2/CdS hollow spheres (0.1 μmol h CH4) is about 7-times -1 higher than that of Ti0.91O2 hollow spheres (0.014 μmol h CH4) under UV-visible light irradiation. While only CH4 was detected in our case, the other species may also be produced, however, concentration of which is perhaps beyond the minimum detection limitation of our gas chromatograph. The deactivation of photocatalysts after long time illumination could possibly be caused
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
COMMUNICATION
Please do not adjust margins ChemComm
Page 3 of 5
View Article Online
DOI: 10.1039/C5CC03905C
COMMUNICATION
Fig. 3 (a) Photocatalytic CH4 evolution amounts and (b) Comparison of photocatalytic activity over hollow spheres with (CdS NPs)5, (Ti0.91O2)5, and (Ti0.91O2/CdS)5 shells. Samples: 0.01 g
by the surface coverage of products or intermediate products. The generation rate ratio of O2 to CH4 over Ti0.91O2/CdS is 1.8: 1, close to the theoretical mole ratio of 2:1 (CO2 + 2H2O → CH4 + 2O2) (Fig. 3b and Fig. S6). The isotope experiment using 13CO2 as carbon source leads to the formation of 13CH4, demonstrating that the carbon moiety of photoreduction products truly comes from applied CO2 (Figure S7). A CO2 reduction experiment performed in the dark or in the absence of the both Ti0.91O2 and Ti0.91O2/CdS hollow spheres showed no appearance of productions (CH4), proving that the CO2 reduction reaction is driven by light with the photocatalysts. CdS NPs shows no photoactivity toward CO2 photoreduction under both UV and UV-visible light irradiation (Table S1), i.e. no any products was detected, which is possibly due to quick recommendation of photogenerated electrons and holes or the consumption of photogenerated holes for photocorrosion of CdS. As we known, it is difficult for CdS to induce direct splitting of H2O into O2 and H2 under light irradiation. One main reason is the consumption of + photogenerated holes for photocorrosion of CdS (CdS+2h → 2+ 19 Cd +S). A hole scavenger is needed when CdS is used for H2 evolution or CO2 reduction with H2O under light irradiation. The CO2+ H2O photoreduction generally involves two halfreactions: photogenerated holes on the VB top of photocatalyst + − ° induce the water oxidation of 2H2O → O2 + 4H + 4e CB (E = 0.82 V vs NHE) and photogenerated electrons on the bottom of the CB of the photocatalyst drive the reduction of CO2 into hydrocarbon fuels − + ° such as CH4 by the reaction of CO2 + 8e + 8H → CH4 + 2H2O (E = 0.24 V vs NHE). H2O that serves as the reducing agent is oxidized to + provide H and e for inducing phtotoreduction of CO2 into hydrocarbons. This means that both CO2 photoreduction as well as H2O oxidation have to occur simultaneously in a photoreactor. Moreover, hole scavenger is not existed in our system, so CdS NPs shows no photoactivity toward CO2 photoreduction under light irradiation. The CB and VB edge levels of Ti0.91O2 nanosheets are -0.39 eV and 18, 20 +3.41 eV (vs. NHE) respectively, and the CB and VB edge levels 20 of CdS NPs are -0.52 eV and +1.96 eV (vs. NHE) respectively. In the traditional type-II TiO2-CdS heterostructure, simultaneous light activation of anatase TiO2 and CdS will transfer photogenerated
Fig. 4 (a) PL decay traces of Ti0.91O2 hollow spheres (blue), CdS hollow spheres (green) and Ti0.91O2/CdS hollow spheres (red). The inset is the PL emission spectra of Ti0.91O2 hollow spheres (blue) and Ti0.91O2/CdS hollow spheres (red). (b) Schematic illustration of traditional TiO2-CdS system (route 1) and artificial Zscheme system (route 2).
electrons from the higher CB of CdS to the lower CB of TiO2 and photogenerated holes from the lower VB of Ti0.91O2 to the higher VB of CdS, as shown Route 1 of Fig. 4b. However, experiment shows that Ti0.91O2 and Ti0.91O2/CdS hollow spheres show no photocatalytic activity under visible light irradiation (Table S1) i.e. no occurring of sensitization of CdS on TiO2. It means that the photogenerated electrons of CdS prefer to recombination with the hole of CdS rather than transfer to Ti0.91O2 nanosheets. To better study charge transfer and electronic interaction between present Ti0.91O2 nanosheets and CdS NPs, PL spectra and transient time-resolved PL decay measurements were carried out on the samples excited at 266 nm (Fig. 4a). Transient PL decay traces of CdS NPs and Ti0.91O2 hollow spheres show short PL lifetime of 0.42 ns and 0.33 ns with a single exponential decay behavior, respectively. In contrast, the ultrathin Ti0.91O2/CdS hollow spheres displays a longer PL decay lifetime of 3.6 ns with approximate one order of magnitude increase, which can be well-fitted by a biexponential decay rather than a single exponential decay. The prolonged decay lifetime observed in Ti0.91O2/CdS hollow spheres reveals that decay dynamics for Ti0.91O2/CdS hollow spheres are fundamentally 15, 16 different from traditional TiO2-CdS system. If the whole PL emission of Ti0.91O2/CdS hollow spheres still originates from luminescent CdS NPs, a faster PL decay process should be observed, due to the fluorescence quenching effect realized by an additional nonradiative decay channel for the transfer of electrons from the 16 CB of CdS NPs to the CB of TiO2 in traditional TiO2-CdS system. However, a much slower PL decay kinetics of Ti0.91O2/CdS hollow spheres implies that the transfer of electrons from the CB of CdS NPs to the CB of Ti0.91O2 nanosheets only plays a minor role in the appearance of PL emission. As shown in the inset of Fig. 4a, under the excitation of energetic energy of 266 nm, CdS NPs show an emission peak around 520 nm with energy that is smaller than the energy bandgap of CdS (2.48 eV), in which the non-radiative
J. Name., 2013, 00, 1-3 | 3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
Journal Name
Please do not adjust margins ChemComm
Page 4 of 5 View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
transition of excited electrons from the CB bottom to different subbands (or surface states) occurs first, and radiative transition from the sub-band to the VB top lead to PL emission subsequently (Fig. 21 S8). Ti0.91O2 hollow spheres just exhibit a broad emission peak around 468 nm, arising from abundant surface defects of molecular-scale Ti0.91O2 nanosheets. Compared with pure Ti0.91O2 hollow spheres, the emission peak of Ti0.91O2 –CdS hollow spheres shows a red shift to 506 nm (2.45 eV), which is nearly consist with the bandgap value between VB of CdS NPs and the CB of Ti0.91O2 nanosheets (2.35 eV). It means that an unusual charge transfer process of the recombination of electrons in the CB of Ti0.91O2 nanosheets and the holes in the VB of CdS NPs could occur, due to the reduced symmetry at the hybrid interface, thus avoiding the defect-mediated optical emission and giving rise to the red-shifted 12 emission of Ti0.91O2 –CdS hollow spheres. This type PL emission is called IOT effect, and also called type-II fluorescence, which is has been widely observed in semiconductor nanocrystals with 13, 14 To certify the intimate heterogeneous interface structures. contact between ultrathin Ti0.91O2 nanosheets and CdS NPs favorable for the efficient charge transfer, the XPS spectra reveals that a new peak at around 162-163 eV arises in the Ti0.91O2-CdS nanocomposite in comparsion with bare CdS NP and Ti0.91O2 22 nanosheet (Fig. S9), which can be ascribed to Ti-S bond. The formation of the Ti-S chemical bond may be facilitated from the surface conjugation of S atoms with unsaturated Ti atoms that allows the orbital overlap of p-orbital of CdS (S 3p forms the VB of CdS) and d orbital of Ti0.91O2 (Ti 3d forms the CB of Ti0.91O2), which is similar with the surface conjugation (d–π conjugation) of graphene nanosheets with the coordinately unsaturated Ti atoms in the 11 Ti0.91O2 nanosheets. Due to the reduced overlap of electron and hole wave functions in Ti0.91O2/CdS hollow spheres, the PL decay 12 lifetime could be increased. Therefore, a new electron transfer was proposed for the present Ti0.91O2/CdS hollow sphere system for photocatalytic reduction of CO2: the photogenerated electrons in the CB of Ti0.91O2 move to the VB of the CdS, and then recombine with photogenerated holes at the CdS, resulting in the holes in the VB of Ti0.91O2 nanosheets with a strong oxidation power and the electrons in the CB of CdS NPs with a strong reduction power (route 2 of Fig. 4b). This appropriately explains the higher photocatalytic activity for CO2 photoreduction over Ti0.91O2/CdS hollow spheres. So a redox mediator-free artificial Z-scheme system has been constructed by exquisitely fabricating ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs via LBL self-assembly. In conclusion, we demonstrated a redox mediator-free artificial Z-scheme system for photocatalytic reduction of CO2 into CH4 by constructing an ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs via exquisite LBL selfassembly. This artificial Z-scheme system achieved 7–time enhancement of CH4-production rate relative to pure Ti0.91O2 hollow spheres, due to efficient separation of photogenerated electron-hole pairs and greatly prolonged lifetime of charge carriers. The IOT effect in multilayer Ti0.91O2/CdS hollow spheres confirms successful construction of artificial Z-scheme system, where excited electrons in the CB of Ti0.91O2 recombine with holes in the VB of CdS NPs through d-p conjugation. To the best of our knowledge, this is the first introduction of the IOT effect into the
examination of the construction of artificial Z-scheme system. Our work may open a new sight to penetrate into the study of the construction of redox mediator-free artificial Z-scheme system and other photocatalytic system for both water splitting and photoreduction of CO2. This work was supported by 973 Programs (No. 2014CB239302, 2011CB933303, and 2013CB632404), National Natural Science Foundation of China (No. 21473091, 51272101, 51202005, and 61307067), National Science Foundation of Jiangsu Province (No. BK2012015 and BK 20130053).
Notes and references 1 2 3 4 5 6 7
8 9 10 11
12 13 14 15 16 17
18 19 20 21
22
W. G. Tu, Y. Zhou and Z. G. Zou, Adv. Mater., 2014, 26, 4607. G. D. Scholes, G. R. Fleming, A. Olaya-Castro and R. van Grondelle, Nat. Chem., 2011, 3, 763; Y. Tachibana, L. Vayssieres and J. R. Durrant, Nat. Photon., 2012, 6, 511. K. Maeda, Acs Catal., 2013, 3, 1486; P. Zhou, J. G. Yu and M. Jaroniec, Adv. Mater., 2014, 26, 4920. M. Tabata, K. Maeda, M. Higashi, D. Lu, T. Takata, R. Abe and K. Domen, Langmuir, 2010, 26, 9161. H. Tada, T. Mitsui, T. Kiyonaga, T. Akita and K. Tanaka, Nat. Mater., 2006, 5, 782. H. J. Yun, H. Lee, N. D. Kim, D. M. Lee, S. Yu and J. Yi, Acs Nano, 2011, 5, 4084. A. Iwase, Y. H. Ng, Y. Ishiguro, A. Kudo and R. Amal, J. Am. Chem. Soc., 2011, 133, 11054; P. Li, Y. Zhou, H. J. Li, Q. F. Xu, X. G. Meng, X. Y. Wang, M. Xiao and Z. G. Zou, Chem. Commun., 2015, 51, 800. A. Kudo, Mrs. Bull., 2011, 36, 32. L. Wang and T. Sasaki, Chem. Rev., 2014, 114, 9455; M. Osada, Y. Ebina, H. Funakubo, S. Yokoyama, T. Kiguchi, K. Takada and T. Sasaki, Adv. Mater., 2006, 18, 1023. K. K. Manga, Y. Zhou, Y. L. Yan and K. P. Loh, Adv. Funct. Mater., 2009, 19, 3638; W. G. Tu, Y. Zhou, Q. Liu, Z. P. Tian, J. Gao, X. Y. Chen, H. T. Zhang, J. G. Liu and Z. G. Zou, Adv. Funct. Mater., 2012, 22, 1215. S. S. Bao, Z. Hua, X. Y. Wang, Y. Zhou, C. F. Zhang, W. G. Tu, Z. G. Zou and M. Xiao, Opt. Express., 2012, 20, 28801. J. S. Weiner, G. Danan, A. Pinczuk, J. Valladares, L. N. Pfeiffer and K. West, Phys. Rev. Lett., 1989, 63, 1641. E. A. Stinaff, M. Scheibner, A. S. Bracker, I. V. Ponomarev, V. L. Korenev, M. E. Ware, M. F. Doty, T. L. Reinecke and D. Gammon, Science, 2006, 311, 636. D. R. Baker and P. V. Kamat, Adv. Funct. Mater., 2009, 19, 805. Y. Y. Zhang, Y. X. Tang, X. F. Liu, Z. L. Dong, H. H. Hng, Z. Chen, T. C. Sum and X. D. Chen, Small, 2013, 9, 996. H. X. Li, Z. F. Bian, J. Zhu, D. Q. Zhang, G. S. Li, Y. N. Huo, H. Li and Y. F. Lu, J. Am. Chem. Soc., 2007, 129, 8406; J. H. Sun, J. S. Zhang, M. W. Zhang, M. Antonietti, X. Z. Fu and X. C. Wang, Nat Commun, 2012, 3. 1139; D. D. Zheng, C. J. Huang and X. C. Wang, Nanoscale, 2015, 7, 465; D. Zheng, C. Pang, Y. Liu and X. Wang, Chem. Comm., 2015, DOI:10.1039/C5CC03143E. N. Sakai, Y. Ebina, K. Takada and T. Sasaki, J. Am. Chem. Soc., 2004, 126, 5851. A. Kudo and Y. Miseki, Chem. Soc. Rev., 2009, 38, 253. Y. Xu and M. A. A. Schoonen, Am. Mineral., 2000, 85, 543. D. Kim, M. Miyamoto, T. Mishima and M. Nakayama, J. Appl. Phys., 2005, 98; L. Q. Jing, Y. C. Qu, B. Q. Wang, S. D. Li, B. J. Jiang, L. B. Yang, W. Fu, H. G. Fu and J. Z. Sun, Sol. Energ. Mat. Sol. C., 2006, 90, 1773. T. Umebayashi, T. Yamaki, H. Itoh and K. Asai, Appl. Phys. Lett., 2002, 81, 454; Q. W. Zhang, J. Wang, S. Yin, T. Sato and F. Saito, J. Am. Ceram. Soc., 2004, 87, 1161.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
COMMUNICATION
Please do not adjust margins ChemComm
Page 5 of 5
View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
COMMUNICATION
Table of Contents
Hollow spheres consisting of Ti0.91O2/CdS nanohybrids for CO2 photofixation
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
Wenguang Tu, Yong Zhou,* Shichao Feng, Qinfeng Xu, Shicheng Yan, Xiaoyong Wang, Min Xiao, and Zhigang Zou*
Multilayer hollow spheres consisting of alternating ultrathin Ti0.91O2 nanosheets and CdS nanoparticles have achieved a redox mediator-free artificial Z-scheme for photocatalytic reduction of CO2 into CH4, which was proved by indirect optical transition effect.
J. Name., 2013, 00, 1-3 | 5
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Zhou, Z. zou, X. Y. Wang, M. Xiao, Q. F. Xu, W. Tu, S. Feng and P. Li, Chem. Commun., 2015, DOI: 10.1039/C5CC03905C.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/chemcomm
Please do not adjust margins ChemComm
Page 1 of 5
View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
Hollow spheres consisting of Ti0.91O2/CdS nanohybrids for CO2 photofixation † Received 00th January 20xx, Accepted 00th January 20xx DOI: 10.1039/x0xx00000x
Wenguang Tu,a, b, c Yong Zhou,*, a, b, c Shichao Feng,a, b, c Qinfeng Xu,b, d Peng Li,e,f Xiaoyong Wang,b Min Xiao,b and Zhigang Zou*, b, c
www.rsc.org/
Here we report multilayer hollow spheres consisting of alternating ultrathin Ti0.91O2 nanosheets and CdS nanoparticles via exquisite layer-by-layer self-assembly to achieve all solid-state Z-scheme system with 7–times enhancement of CH4-production rate relative to pure Ti0.91O2 hollow spheres, due to greatly prolonged lifetime of charge carriers. Photocatalytic reduction of CO2 into hydrocarbon fuels using solar energy, an idea of mimicking natural photosynthetic cycle of chemical conversion of CO2 into carbohydrates, has been consistently gaining attention for more than 30 years, because it is like killing two birds with one stone in terms of mitigating global warming and consumption of fossil fuels.1 Natural photosynthesis uses a sophisticated Z-scheme system to harvest two photons through two photosystems connected in series with an electron transfer chain to drive chemical reactions involved in water oxidation and reduction of coenzyme NADP on two photosystems individually, which can ensure the charge separation quantum efficiency is close to 100% under optimal conditions.2 The artificial Z-scheme system has been successfully applied to split water into H2 and O2 using two different semiconductor photocatalysts with redox mediators driven by a two-step photoexcitation.3 However, the reaction efficiency of this system is limited by electron transfer from O2-evolution photocatalyst to H2-evolution photocatalyst, which is mainly determined by redox mediators that causes undesirable backward reactions involving redox mediators, such as competitive oxidation of I− by holes on O2-evolution photocatalyst when using IO3−/I− as redox mediator.4 Relative to solution-based a.
Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, School of Physics, Nanjing University, Nanjing 210093, P. R. China; E-mail: [email protected] b. National Laboratory of Solid State Microstructures, Department of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China; E-mail: [email protected] c. Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China d. Department of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, P. R. China e. Environmental Remediation Materials Unit and International Center for Materials Nanoarchitectonics (WPI-MANA), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. † Electronic Supplementary Information (ESI) available: [experimental section, UVVis, SEM, photoactivity and so on]. See DOI: 10.1039/x0xx00000x
- -
3+
2+
systems such as IO3 /I and Fe /Fe redox couples, solid electron 5, 6 7 mediators such as Au and graphene are more favorable in terms of ensuring a continuous flow of electrons between the source and target photocatalysts because of the close photocatalyst8 mediator−photocatalyst contact. In a typical all-solid-state Z5 scheme of CdS/Au/TiO2, photoexcited electrons in conduction band (CB) of TiO2 under ultraviolet (UV) irradiation transferred to Au and then to the valence band (VB) of CdS, and subsequently recombined with photogenerated holes in CdS. Simultaneously, photogenerated electrons in the CB of CdS and holes in VB the of TiO2 exhibited strong reduction power and oxidation power respectively, leading to high photocatalytic reduction of 2+ methylviologen (MV ). Moreover, recombination of photoexcited holes in the VB of CdS with electrons from TiO2 results in the improvement of photostability of CdS. Despite of the well developed TiO2-Au-CdS system, however, Au electron mediator strongly absorb part of the visible light, reducing the light absorption of semiconductor photocatalysts. Therefore a Z-scheme system without an electron mediator is highly desirable for eliminating this limitation. Ultrathin highly crystalline Ti0.91O2 nanosheets exfoliated from protonic titanate exhibit very high 2D anisotropy with a thickness of 0.75 nm and lateral dimensions of up to several tens of micrometers.9 Layer-by-layer (LBL) self-assembly offers opportunity to use ultrathin Ti0.91O2 nanosheets as one of building blocks to form well-defined multilayer films or hollow spheres stacked with complementary interaction (such as electrostatic attraction, and covalent bonding), due to its simplicity and excellent size control.1012 Such ultrathin multilayer stacked films or hollow spheres at the molecular scale possess novel physicochemical properties, such as high dielectric constant,10 ultrafast electron transfer,11 and indirect optical transition (IOT) effect.12 IOT effect observed in ultrathin hollow spheres consisting of alternating Ti0.91O2 nanosheets and graphene oxide results from optical recombination of electrons in the CB of TiO2 and holes in the O 2p levels of graphene oxide,12 which is similar to the basic process of artificial Z-scheme system that electrons in the CB of O2-evolution photocatalyst migrate to the holes in VB of H2-evolution photocatalyst. IOT effect has also
J. Name., 2013, 00, 1-3 | 1
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
COMMUNICATION
Please do not adjust margins ChemComm
Page 2 of 5 View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
13
been observed in the multiple GaAs/A1GaAs quantum wells or 14 coupled InAs quantum dots (QDs). Herein we design ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs via exquisite LBL selfassembly to realize a redox mediator-free artificial Z-Scheme system based on the carrier transfer of IOT effect. The photoluminescence (PL) spectra and transient time-resolved PL decay measurements prove that excited electrons in the CB of Ti0.91O2 nanaosheets recombine with holes in the VB of CdS NPs through d-p conjugation, totally different from traditional TiO2-CdS 15, 16 system. Multilayer Ti0.91O2/CdS hollow spheres exhibited 7– times enhancement of photocatalytic activity for photoreduction of CO2, relative to pure Ti0.91O2 hollow spheres, due to greatly prolonged lifetime of charge carriers through construction of artificial Z-scheme system. Our work may provide a new viewpoint for tailoring and constructing hybrid nanostructure of semiconductors for photocatalysis.17
Fig. 1 Schematic llustration of procedure for constrution of ultrathin multilayer Ti0.91O2/CdS hollow spheres for CO2 photoreduction.
The overall fabrication procedure of ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs is schematically illustrated in the Fig. 1. Poly (methyl methacrylate) (PMMA) beads were successively modified with a protonic polyethylenimine (PEI) aqueous solution (Fig. 1a), a colloidal suspension of negatively charged Ti0.91O2 nanosheets (Fig. 1b), a protonic PEI aqueous solution (Fig. 1c), and a negatively charged CdS NPs suspension (Fig. 1d) via LBL self-assembly procedures. After repeating the dipping cycles five times, yellow composites with 5 layers of (PEI/ Ti0.91O2/PEI/CdS)5 were obtained (Fig. S1). The UVvisible spectra confirm the successful loading of (PEI/Ti0.91O2)5 and (PEI/Ti0.91O2/PEI/CdS)5 shells onto the PMMA beads (Fig. S2 and Fig. S4). A strong absorption band centering at around 220 nm is diagnostic of PMMA polymers. The spectrum of (PEI/Ti0.91O2)5 shells on the PMMA bead shows a characteristic absorption peak of molecular Ti0.91O2 nanosheet at 265 nm and an absorption edge at about 326 nm (Fig. S2a), displaying a bandgap of 3.8 eV which is exactly consistent with the band gap energy of the Ti0.91O2 18 nanosheet. Pure CdS NPs shows an absorption edge at around 500 nm corresponding to the band gap energy of ~2.48 eV (Fig. S2b and Fig. S3), indicating the effective light-response in the visible light region. Compared to (PEI/Ti0.91O2)5 shells on PMMA and (PEI/CdS)5 shells on PMMA, (PEI/Ti0.91O2/PEI/CdS)5 shells on PMMA show
extended light absorption range assigned to pure (PEI/Ti0.91O2)5 on PMMA and (PEI/CdS)5 on PMMA (Fig. S2c). The field emission scanning electron microscopy (FE-SEM) images (Fig. S4b) show the noteworthy crinkled and rough textures of PMMA spheres with (PEI/Ti0.91O2/PEI/CdS)5 shells associated with the presence of flexible and ultrathin Ti0.91O2 sheets, distinguishing from smooth surface of bare PMMA sphere (Fig. S4a). Partial Ti0.91O2 sheets patch peeling off from the core surfaces and corrugation can clearly be observed, proving that the block sheets have indeed been suceessfully coated onto PMMA. Hollow spheres with (Ti0.91O2/CdS)5 shell were obtained by removing PMMA templates and PEI moiety with the assistance of microwave irradiation. For comparion, hollow spheres with (CdS)5 shell and (Ti0.91O2)5 shell were also prepared by the analogous procedure above.
Fig. 2 (a) SEM, (b) TEM, and (c, d) high-resolution TEM images of Ti0.91O2/CdS hollow spheres. Scale bare of the inset (b) is 200 nm.
After rapid decomposition of the PMMA core into exhaust gas resulted from local high temperature with the assistance of microwave irradiation, Ti0.91O2/CdS hollow spheres were formed (Fig. 2 and Fig. S5). Some occasional holes and traces of rupture prove the production of hollow structure, as shown in Fig. 2a, b. The well preserved spherical configuration demonstrates the robust virtue of Ti0.91O2/CdS hollow spheres. The dried hollow spheres are prone to aggregate together. TEM image (Fig. 2b) also clearly shows ultrathin hollow nanostructure. High-resolution TEM observation reveals intactness of multilayer stacking structures of alternating ultrathin Ti0.91O2 nanosheets and CdS NPs of 5-6 nm in size (Fig. 2c, d), resembling hybrid of lamellar fringes separated with small dark dots. HRTEM reveals the well-defined lattice fringes of CdS NPs, corresponding to (101) plane of cubic CdS. Ti0.91O2 and Ti0.91O2/CdS hollow spheres were used as photocatalysts to reduce CO2 into hydrocarbon fuels in the presence of water vapor (Fig. 3). The CH4 production rate of -1 Ti0.91O2/CdS hollow spheres (0.1 μmol h CH4) is about 7-times -1 higher than that of Ti0.91O2 hollow spheres (0.014 μmol h CH4) under UV-visible light irradiation. While only CH4 was detected in our case, the other species may also be produced, however, concentration of which is perhaps beyond the minimum detection limitation of our gas chromatograph. The deactivation of photocatalysts after long time illumination could possibly be caused
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
COMMUNICATION
Please do not adjust margins ChemComm
Page 3 of 5
View Article Online
DOI: 10.1039/C5CC03905C
COMMUNICATION
Fig. 3 (a) Photocatalytic CH4 evolution amounts and (b) Comparison of photocatalytic activity over hollow spheres with (CdS NPs)5, (Ti0.91O2)5, and (Ti0.91O2/CdS)5 shells. Samples: 0.01 g
by the surface coverage of products or intermediate products. The generation rate ratio of O2 to CH4 over Ti0.91O2/CdS is 1.8: 1, close to the theoretical mole ratio of 2:1 (CO2 + 2H2O → CH4 + 2O2) (Fig. 3b and Fig. S6). The isotope experiment using 13CO2 as carbon source leads to the formation of 13CH4, demonstrating that the carbon moiety of photoreduction products truly comes from applied CO2 (Figure S7). A CO2 reduction experiment performed in the dark or in the absence of the both Ti0.91O2 and Ti0.91O2/CdS hollow spheres showed no appearance of productions (CH4), proving that the CO2 reduction reaction is driven by light with the photocatalysts. CdS NPs shows no photoactivity toward CO2 photoreduction under both UV and UV-visible light irradiation (Table S1), i.e. no any products was detected, which is possibly due to quick recommendation of photogenerated electrons and holes or the consumption of photogenerated holes for photocorrosion of CdS. As we known, it is difficult for CdS to induce direct splitting of H2O into O2 and H2 under light irradiation. One main reason is the consumption of + photogenerated holes for photocorrosion of CdS (CdS+2h → 2+ 19 Cd +S). A hole scavenger is needed when CdS is used for H2 evolution or CO2 reduction with H2O under light irradiation. The CO2+ H2O photoreduction generally involves two halfreactions: photogenerated holes on the VB top of photocatalyst + − ° induce the water oxidation of 2H2O → O2 + 4H + 4e CB (E = 0.82 V vs NHE) and photogenerated electrons on the bottom of the CB of the photocatalyst drive the reduction of CO2 into hydrocarbon fuels − + ° such as CH4 by the reaction of CO2 + 8e + 8H → CH4 + 2H2O (E = 0.24 V vs NHE). H2O that serves as the reducing agent is oxidized to + provide H and e for inducing phtotoreduction of CO2 into hydrocarbons. This means that both CO2 photoreduction as well as H2O oxidation have to occur simultaneously in a photoreactor. Moreover, hole scavenger is not existed in our system, so CdS NPs shows no photoactivity toward CO2 photoreduction under light irradiation. The CB and VB edge levels of Ti0.91O2 nanosheets are -0.39 eV and 18, 20 +3.41 eV (vs. NHE) respectively, and the CB and VB edge levels 20 of CdS NPs are -0.52 eV and +1.96 eV (vs. NHE) respectively. In the traditional type-II TiO2-CdS heterostructure, simultaneous light activation of anatase TiO2 and CdS will transfer photogenerated
Fig. 4 (a) PL decay traces of Ti0.91O2 hollow spheres (blue), CdS hollow spheres (green) and Ti0.91O2/CdS hollow spheres (red). The inset is the PL emission spectra of Ti0.91O2 hollow spheres (blue) and Ti0.91O2/CdS hollow spheres (red). (b) Schematic illustration of traditional TiO2-CdS system (route 1) and artificial Zscheme system (route 2).
electrons from the higher CB of CdS to the lower CB of TiO2 and photogenerated holes from the lower VB of Ti0.91O2 to the higher VB of CdS, as shown Route 1 of Fig. 4b. However, experiment shows that Ti0.91O2 and Ti0.91O2/CdS hollow spheres show no photocatalytic activity under visible light irradiation (Table S1) i.e. no occurring of sensitization of CdS on TiO2. It means that the photogenerated electrons of CdS prefer to recombination with the hole of CdS rather than transfer to Ti0.91O2 nanosheets. To better study charge transfer and electronic interaction between present Ti0.91O2 nanosheets and CdS NPs, PL spectra and transient time-resolved PL decay measurements were carried out on the samples excited at 266 nm (Fig. 4a). Transient PL decay traces of CdS NPs and Ti0.91O2 hollow spheres show short PL lifetime of 0.42 ns and 0.33 ns with a single exponential decay behavior, respectively. In contrast, the ultrathin Ti0.91O2/CdS hollow spheres displays a longer PL decay lifetime of 3.6 ns with approximate one order of magnitude increase, which can be well-fitted by a biexponential decay rather than a single exponential decay. The prolonged decay lifetime observed in Ti0.91O2/CdS hollow spheres reveals that decay dynamics for Ti0.91O2/CdS hollow spheres are fundamentally 15, 16 different from traditional TiO2-CdS system. If the whole PL emission of Ti0.91O2/CdS hollow spheres still originates from luminescent CdS NPs, a faster PL decay process should be observed, due to the fluorescence quenching effect realized by an additional nonradiative decay channel for the transfer of electrons from the 16 CB of CdS NPs to the CB of TiO2 in traditional TiO2-CdS system. However, a much slower PL decay kinetics of Ti0.91O2/CdS hollow spheres implies that the transfer of electrons from the CB of CdS NPs to the CB of Ti0.91O2 nanosheets only plays a minor role in the appearance of PL emission. As shown in the inset of Fig. 4a, under the excitation of energetic energy of 266 nm, CdS NPs show an emission peak around 520 nm with energy that is smaller than the energy bandgap of CdS (2.48 eV), in which the non-radiative
J. Name., 2013, 00, 1-3 | 3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
Journal Name
Please do not adjust margins ChemComm
Page 4 of 5 View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
transition of excited electrons from the CB bottom to different subbands (or surface states) occurs first, and radiative transition from the sub-band to the VB top lead to PL emission subsequently (Fig. 21 S8). Ti0.91O2 hollow spheres just exhibit a broad emission peak around 468 nm, arising from abundant surface defects of molecular-scale Ti0.91O2 nanosheets. Compared with pure Ti0.91O2 hollow spheres, the emission peak of Ti0.91O2 –CdS hollow spheres shows a red shift to 506 nm (2.45 eV), which is nearly consist with the bandgap value between VB of CdS NPs and the CB of Ti0.91O2 nanosheets (2.35 eV). It means that an unusual charge transfer process of the recombination of electrons in the CB of Ti0.91O2 nanosheets and the holes in the VB of CdS NPs could occur, due to the reduced symmetry at the hybrid interface, thus avoiding the defect-mediated optical emission and giving rise to the red-shifted 12 emission of Ti0.91O2 –CdS hollow spheres. This type PL emission is called IOT effect, and also called type-II fluorescence, which is has been widely observed in semiconductor nanocrystals with 13, 14 To certify the intimate heterogeneous interface structures. contact between ultrathin Ti0.91O2 nanosheets and CdS NPs favorable for the efficient charge transfer, the XPS spectra reveals that a new peak at around 162-163 eV arises in the Ti0.91O2-CdS nanocomposite in comparsion with bare CdS NP and Ti0.91O2 22 nanosheet (Fig. S9), which can be ascribed to Ti-S bond. The formation of the Ti-S chemical bond may be facilitated from the surface conjugation of S atoms with unsaturated Ti atoms that allows the orbital overlap of p-orbital of CdS (S 3p forms the VB of CdS) and d orbital of Ti0.91O2 (Ti 3d forms the CB of Ti0.91O2), which is similar with the surface conjugation (d–π conjugation) of graphene nanosheets with the coordinately unsaturated Ti atoms in the 11 Ti0.91O2 nanosheets. Due to the reduced overlap of electron and hole wave functions in Ti0.91O2/CdS hollow spheres, the PL decay 12 lifetime could be increased. Therefore, a new electron transfer was proposed for the present Ti0.91O2/CdS hollow sphere system for photocatalytic reduction of CO2: the photogenerated electrons in the CB of Ti0.91O2 move to the VB of the CdS, and then recombine with photogenerated holes at the CdS, resulting in the holes in the VB of Ti0.91O2 nanosheets with a strong oxidation power and the electrons in the CB of CdS NPs with a strong reduction power (route 2 of Fig. 4b). This appropriately explains the higher photocatalytic activity for CO2 photoreduction over Ti0.91O2/CdS hollow spheres. So a redox mediator-free artificial Z-scheme system has been constructed by exquisitely fabricating ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs via LBL self-assembly. In conclusion, we demonstrated a redox mediator-free artificial Z-scheme system for photocatalytic reduction of CO2 into CH4 by constructing an ultrathin multilayer hollow spheres consisting of alternating Ti0.91O2 nanosheets and CdS NPs via exquisite LBL selfassembly. This artificial Z-scheme system achieved 7–time enhancement of CH4-production rate relative to pure Ti0.91O2 hollow spheres, due to efficient separation of photogenerated electron-hole pairs and greatly prolonged lifetime of charge carriers. The IOT effect in multilayer Ti0.91O2/CdS hollow spheres confirms successful construction of artificial Z-scheme system, where excited electrons in the CB of Ti0.91O2 recombine with holes in the VB of CdS NPs through d-p conjugation. To the best of our knowledge, this is the first introduction of the IOT effect into the
examination of the construction of artificial Z-scheme system. Our work may open a new sight to penetrate into the study of the construction of redox mediator-free artificial Z-scheme system and other photocatalytic system for both water splitting and photoreduction of CO2. This work was supported by 973 Programs (No. 2014CB239302, 2011CB933303, and 2013CB632404), National Natural Science Foundation of China (No. 21473091, 51272101, 51202005, and 61307067), National Science Foundation of Jiangsu Province (No. BK2012015 and BK 20130053).
Notes and references 1 2 3 4 5 6 7
8 9 10 11
12 13 14 15 16 17
18 19 20 21
22
W. G. Tu, Y. Zhou and Z. G. Zou, Adv. Mater., 2014, 26, 4607. G. D. Scholes, G. R. Fleming, A. Olaya-Castro and R. van Grondelle, Nat. Chem., 2011, 3, 763; Y. Tachibana, L. Vayssieres and J. R. Durrant, Nat. Photon., 2012, 6, 511. K. Maeda, Acs Catal., 2013, 3, 1486; P. Zhou, J. G. Yu and M. Jaroniec, Adv. Mater., 2014, 26, 4920. M. Tabata, K. Maeda, M. Higashi, D. Lu, T. Takata, R. Abe and K. Domen, Langmuir, 2010, 26, 9161. H. Tada, T. Mitsui, T. Kiyonaga, T. Akita and K. Tanaka, Nat. Mater., 2006, 5, 782. H. J. Yun, H. Lee, N. D. Kim, D. M. Lee, S. Yu and J. Yi, Acs Nano, 2011, 5, 4084. A. Iwase, Y. H. Ng, Y. Ishiguro, A. Kudo and R. Amal, J. Am. Chem. Soc., 2011, 133, 11054; P. Li, Y. Zhou, H. J. Li, Q. F. Xu, X. G. Meng, X. Y. Wang, M. Xiao and Z. G. Zou, Chem. Commun., 2015, 51, 800. A. Kudo, Mrs. Bull., 2011, 36, 32. L. Wang and T. Sasaki, Chem. Rev., 2014, 114, 9455; M. Osada, Y. Ebina, H. Funakubo, S. Yokoyama, T. Kiguchi, K. Takada and T. Sasaki, Adv. Mater., 2006, 18, 1023. K. K. Manga, Y. Zhou, Y. L. Yan and K. P. Loh, Adv. Funct. Mater., 2009, 19, 3638; W. G. Tu, Y. Zhou, Q. Liu, Z. P. Tian, J. Gao, X. Y. Chen, H. T. Zhang, J. G. Liu and Z. G. Zou, Adv. Funct. Mater., 2012, 22, 1215. S. S. Bao, Z. Hua, X. Y. Wang, Y. Zhou, C. F. Zhang, W. G. Tu, Z. G. Zou and M. Xiao, Opt. Express., 2012, 20, 28801. J. S. Weiner, G. Danan, A. Pinczuk, J. Valladares, L. N. Pfeiffer and K. West, Phys. Rev. Lett., 1989, 63, 1641. E. A. Stinaff, M. Scheibner, A. S. Bracker, I. V. Ponomarev, V. L. Korenev, M. E. Ware, M. F. Doty, T. L. Reinecke and D. Gammon, Science, 2006, 311, 636. D. R. Baker and P. V. Kamat, Adv. Funct. Mater., 2009, 19, 805. Y. Y. Zhang, Y. X. Tang, X. F. Liu, Z. L. Dong, H. H. Hng, Z. Chen, T. C. Sum and X. D. Chen, Small, 2013, 9, 996. H. X. Li, Z. F. Bian, J. Zhu, D. Q. Zhang, G. S. Li, Y. N. Huo, H. Li and Y. F. Lu, J. Am. Chem. Soc., 2007, 129, 8406; J. H. Sun, J. S. Zhang, M. W. Zhang, M. Antonietti, X. Z. Fu and X. C. Wang, Nat Commun, 2012, 3. 1139; D. D. Zheng, C. J. Huang and X. C. Wang, Nanoscale, 2015, 7, 465; D. Zheng, C. Pang, Y. Liu and X. Wang, Chem. Comm., 2015, DOI:10.1039/C5CC03143E. N. Sakai, Y. Ebina, K. Takada and T. Sasaki, J. Am. Chem. Soc., 2004, 126, 5851. A. Kudo and Y. Miseki, Chem. Soc. Rev., 2009, 38, 253. Y. Xu and M. A. A. Schoonen, Am. Mineral., 2000, 85, 543. D. Kim, M. Miyamoto, T. Mishima and M. Nakayama, J. Appl. Phys., 2005, 98; L. Q. Jing, Y. C. Qu, B. Q. Wang, S. D. Li, B. J. Jiang, L. B. Yang, W. Fu, H. G. Fu and J. Z. Sun, Sol. Energ. Mat. Sol. C., 2006, 90, 1773. T. Umebayashi, T. Yamaki, H. Itoh and K. Asai, Appl. Phys. Lett., 2002, 81, 454; Q. W. Zhang, J. Wang, S. Yin, T. Sato and F. Saito, J. Am. Ceram. Soc., 2004, 87, 1161.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
COMMUNICATION
Please do not adjust margins ChemComm
Page 5 of 5
View Article Online
DOI: 10.1039/C5CC03905C
Journal Name
COMMUNICATION
Table of Contents
Hollow spheres consisting of Ti0.91O2/CdS nanohybrids for CO2 photofixation
ChemComm Accepted Manuscript
Published on 29 June 2015. Downloaded by Carleton University on 04/07/2015 02:58:00.
Wenguang Tu, Yong Zhou,* Shichao Feng, Qinfeng Xu, Shicheng Yan, Xiaoyong Wang, Min Xiao, and Zhigang Zou*
Multilayer hollow spheres consisting of alternating ultrathin Ti0.91O2 nanosheets and CdS nanoparticles have achieved a redox mediator-free artificial Z-scheme for photocatalytic reduction of CO2 into CH4, which was proved by indirect optical transition effect.
J. Name., 2013, 00, 1-3 | 5
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
