Spontaneously formed porous and composite materials

In recent years, a number of routes to porous materials have been developed which do not involve the use of pre-formed templates or structure-directing agents. These routes are usually spontaneous, meaning they are thermodynamically downhill. Kinetic control, deriving from slow diffusion of certain species in the solid state, allows metastable porous morphologies rather than dense materials to be obtained. While the porous structures so formed are random, the average architectural features can be well-defined, and the porosity is usually highly interconnected. The routes are applicable to a broad range of functional inorganic materials. Consequently, the porous architectures have uses in energy transduction and storage, chemical sensing, catalysis, and photoelectrochemistry. This is in addition to more straightforward uses deriving from the pore structure, such as in filtration, as a structural material, or as a cell-growth scaffold. In this feature article, some of the methods for the creation of porous materials are described, including shape-conserving routes that lead to hierarchical macro/mesoporous architectures. In some of the preparations, the resulting mesopores are aligned locally with certain crystallographic directions. The coupling between morphology and crystallography provides a macroscopic handle on nanoscale structure. Extension of these routes to create biphasic composite materials are also described

Porous Single-Crystal-Based Inorganic Semiconductor Photocatalysts for Energy Production and Environmental Remediation: Preparation, Modification, and Applications

This is the peer reviewed version of the following article: Niu, J., Albero, J., Atienzar, P., García, H., Porous Single-Crystal-Based Inorganic Semiconductor Photocatalysts for Energy Production and Environmental Remediation: Preparation, Modification, and Applications. Adv. Funct. Mater. 2020, 30, 1908984, which has been published in final form at https://doi.org/10.1002/adfm.201908984. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] Semiconductor photocatalytic and photovoltaic performance depends on crystallinity and surface area to a large extent. One strategy that has recently emergyed to improve semiconductor photoresponse efficiency is their synthesis as porous single crystals (PSCs), therefore providing simultaneously high crystallinity, minimization of grain boundaries, and large specific surface area. Other factors, such as high density of active sites, and enhanced light absorption, also contribute to increased PSC photoresponse with respect to analogous bulk or amorphous materials. This review initially presents the concept and main properties of PSCs. Then, the synthetic routes and the applications as photocatalysts and as photovoltaic devices, mainly in sunlight applications, are summarized. The synthetic procedures have been classified according to the mechanism of pore generation. Applications cover photocatalysis for environmental remediation, solar fuels production, selective photooxidation of organic compounds, and photovoltaic devices. Finally, a summary and views on future developments are provided. The purpose of this review is to show how the use of PSCs is a powerful general methodology applicable beyond metal oxides and can ultimately lead to sufficient photoresponse efficiency, bringing these processes close to commercial application.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV2016-0683 and RTI2018-89023-CO2-R1) and by the Generalitat Valenciana (Prometeo 2017-083) is gratefully acknowledged. J.N. also gratefully acknowledges financial support from the Fundamental Research Funds for the Central Universities (2019XKQYMS76).Niu, J.; Albero-Sancho, J.; Atienzar Corvillo, PE.; García Gómez, H. (2020). Porous Single-Crystal-Based Inorganic Semiconductor Photocatalysts for Energy Production and Environmental Remediation: Preparation, Modification, and Applications. Advanced Functional Materials. 30(15):1-51. https://doi.org/10.1002/adfm.2019089841513015Lee, B., Yamashita, T., Lu, D., Kondo, J. N., & Domen, K. (2002). Single-Crystal Particles of Mesoporous Niobium−Tantalum Mixed Oxide. Chemistry of Materials, 14(2), 867-875. doi:10.1021/cm010775mCrossland, E. J. W., Noel, N., Sivaram, V., Leijtens, T., Alexander-Webber, J. A., & Snaith, H. J. (2013). Mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance. Nature, 495(7440), 215-219. doi:10.1038/nature11936Liu, G., Yang, H. G., Pan, J., Yang, Y. Q., Lu, G. Q. (Max), & Cheng, H.-M. (2014). Titanium Dioxide Crystals with Tailored Facets. Chemical Reviews, 114(19), 9559-9612. doi:10.1021/cr400621zZheng, X., Lv, Y., Kuang, Q., Zhu, Z., Long, X., & Yang, S. (2014). Close-Packed Colloidal SiO2 as a Nanoreactor: Generalized Synthesis of Metal Oxide Mesoporous Single Crystals and Mesocrystals. Chemistry of Materials, 26(19), 5700-5709. doi:10.1021/cm5025475Jiao, W., Xie, Y., Chen, R., Zhen, C., Liu, G., Ma, X., & Cheng, H.-M. (2013). Synthesis of mesoporous single crystal rutile TiO2 with improved photocatalytic and photoelectrochemical activities. Chemical Communications, 49(100), 11770. doi:10.1039/c3cc46527fFang, W. Q., Huo, Z., Liu, P., Wang, X. L., Zhang, M., Jia, Y., … Yao, X. (2014). Fluorine-Doped Porous Single-Crystal Rutile TiO2Nanorods for Enhancing Photoelectrochemical Water Splitting. Chemistry - A European Journal, 20(36), 11439-11444. doi:10.1002/chem.201402914Bian, Z., Zhu, J., Wen, J., Cao, F., Huo, Y., Qian, X., … Lu, Y. (2010). Single-Crystal-like Titania Mesocages. Angewandte Chemie International Edition, 50(5), 1105-1108. doi:10.1002/anie.201004972Cho, S., Kim, S., Jung, D.-W., & Lee, K.-H. (2011). Formation of quasi-single crystalline porous ZnO nanostructures with a single large cavity. Nanoscale, 3(9), 3841. doi:10.1039/c1nr10609kXu, G., Deng, S., Zhang, Y., Wei, X., Yang, X., Liu, Y., … Han, G. (2014). Mesoporous-structure-tailored hydrothermal synthesis and mechanism of the SrTiO3 mesoporous spheres by controlling the silicate semipermeable membranes with the KOH concentrations. CrystEngComm, 16(10), 2025. doi:10.1039/c3ce41809jWei, L., Yang, Z., Ren, H., & Chen, X. (2010). Phase Transitional Behavior and Electrical Properties of Sr2K0.1Na0.9Nb5−xTaxO15 Ceramics. Journal of the American Ceramic Society, 93(12), 3986-3989. doi:10.1111/j.1551-2916.2010.04177.xHong, Z., Zhou, K., Huang, Z., & Wei, M. (2015). Iso-Oriented Anatase TiO2 Mesocages as a High Performance Anode Material for Sodium-Ion Storage. Scientific Reports, 5(1). doi:10.1038/srep11960Song, R.-Q., & Cölfen, H. (2009). Mesocrystals-Ordered Nanoparticle Superstructures. Advanced Materials, 22(12), 1301-1330. doi:10.1002/adma.200901365Weckhuysen, B. M., & Yu, J. (2015). Recent advances in zeolite chemistry and catalysis. Chemical Society Reviews, 44(20), 7022-7024. doi:10.1039/c5cs90100fRangnekar, N., Mittal, N., Elyassi, B., Caro, J., & Tsapatsis, M. (2015). Zeolite membranes – a review and comparison with MOFs. Chemical Society Reviews, 44(20), 7128-7154. doi:10.1039/c5cs00292cWang, C. W., Yang, S., Fang, W. Q., Liu, P., Zhao, H., & Yang, H. G. (2015). Engineered Hematite Mesoporous Single Crystals Drive Drastic Enhancement in Solar Water Splitting. Nano Letters, 16(1), 427-433. doi:10.1021/acs.nanolett.5b04059Wu, Q., Bao, S., Tian, B., Xiao, Y., & Zhang, J. (2016). Double-diffusion-based synthesis of BiVO4 mesoporous single crystals with enhanced photocatalytic activity for oxygen evolution. Chemical Communications, 52(47), 7478-7481. doi:10.1039/c6cc02737gNiu, J., Shen, S., Zhou, L., Liu, Z., Feng, P., Ou, X., & Qiang, Y. (2016). Synthesis and hydrogenation of anatase TiO2 microspheres composed of porous single crystals for significantly improved photocatalytic activity. RSC Advances, 6(67), 62907-62910. doi:10.1039/c6ra12053aLu, D., Ouyang, S., Xu, H., Li, D., Zhang, X., Li, Y., & Ye, J. (2016). Designing Au Surface-Modified Nanoporous-Single-Crystalline SrTiO3 to Optimize Diffusion of Surface Plasmon Resonance-Induce Photoelectron toward Enhanced Visible-Light Photoactivity. ACS Applied Materials & Interfaces, 8(14), 9506-9513. doi:10.1021/acsami.6b00889Jiang, S., Zhang, J., Qi, X., He, M., & Li, J. (2013). Large-area synthesis of diameter-controllable porous single crystal gallium nitride micro/nanotube arrays. CrystEngComm, 15(46), 9837. doi:10.1039/c3ce41803kLiu, H., Chen, X., Yan, S., Li, Z., & Zou, Z. (2014). Basic Molten Salt Route to Prepare Porous SrTiO3Nanocrystals for Efficient Photocatalytic Hydrogen Production. European Journal of Inorganic Chemistry, 2014(23), 3731-3735. doi:10.1002/ejic.201402280Li, C., Chen, G., Sun, J., Rao, J., Han, Z., Hu, Y., & Zhou, Y. (2015). A Novel Mesoporous Single-Crystal-Like Bi2WO6 with Enhanced Photocatalytic Activity for Pollutants Degradation and Oxygen Production. ACS Applied Materials & Interfaces, 7(46), 25716-25724. doi:10.1021/acsami.5b06995Choi, J., Song, S., Hörantner, M. T., Snaith, H. J., & Park, T. (2016). Well-Defined Nanostructured, Single-Crystalline TiO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells. ACS Nano, 10(6), 6029-6036. doi:10.1021/acsnano.6b01575Yu, Y., Zhang, J., Wu, X., Zhao, W., & Zhang, B. (2011). Nanoporous Single-Crystal-Like CdxZn1−xS Nanosheets Fabricated by the Cation-Exchange Reaction of Inorganic-Organic Hybrid ZnS-Amine with Cadmium Ions. Angewandte Chemie International Edition, 51(4), 897-900. doi:10.1002/anie.201105786Zhao, W., Liu, C., Cao, L., Yin, X., Xu, H., & Zhang, B. (2013). Porous single-crystalline CdS nanosheets as efficient visible light catalysts for aerobic oxidative coupling of amines to imines. RSC Advances, 3(45), 22944. doi:10.1039/c3ra43929aLiu, J., Hu, Z.-Y., Peng, Y., Huang, H.-W., Li, Y., Wu, M., … Su, B.-L. (2016). 2D ZnO mesoporous single-crystal nanosheets with exposed {0001} polar facets for the depollution of cationic dye molecules by highly selective adsorption and photocatalytic decomposition. Applied Catalysis B: Environmental, 181, 138-145. doi:10.1016/j.apcatb.2015.07.054Niu, J., Shen, S., He, S., Liu, Z., Feng, P., Zhang, S., … Zhu, Z. (2015). Synthesis and photoactivity of anatase porous single crystals with different pore sizes. Ceramics International, 41(9), 11936-11944. doi:10.1016/j.ceramint.2015.06.005Sivaram, V., Crossland, E. J. W., Leijtens, T., Noel, N. K., Alexander-Webber, J., Docampo, P., & Snaith, H. J. (2014). Observation of Annealing-Induced Doping in TiO2 Mesoporous Single Crystals for Use in Solid State Dye Sensitized Solar Cells. The Journal of Physical Chemistry C, 118(4), 1821-1827. doi:10.1021/jp410495kKondo, J. N., Takahara, Y., Lee, B., Lu, D., & Domen, K. (2002). Topics in Catalysis, 19(2), 171-177. doi:10.1023/a:1015255906229Jiang, H., Meng, X., Dai, H., Deng, J., Liu, Y., Zhang, L., … Zhang, R. (2012). High-performance porous spherical or octapod-like single-crystalline BiVO4 photocatalysts for the removal of phenol and methylene blue under visible-light illumination. Journal of Hazardous Materials, 217-218, 92-99. doi:10.1016/j.jhazmat.2012.02.073Liu, Y., Luo, Y., Elzatahry, A. A., Luo, W., Che, R., Fan, J., … Zhao, D. (2015). Mesoporous TiO2 Mesocrystals: Remarkable Defects-Induced Crystallite-Interface Reactivity and Their in Situ Conversion to Single Crystals. ACS Central Science, 1(7), 400-408. doi:10.1021/acscentsci.5b00256Xiong, Y., Liu, Y., Lan, K., Mei, A., Sheng, Y., Zhao, D., & Han, H. (2018). Fully printable hole-conductor-free mesoscopic perovskite solar cells based on mesoporous anatase single crystals. New Journal of Chemistry, 42(4), 2669-2674. doi:10.1039/c7nj04448hGirija, K., Thirumalairajan, S., Patra, A. K., Mangalaraj, D., Ponpandian, N., & Viswanathan, C. (2013). Organic additives assisted synthesis of mesoporous β-Ga2O3 nanostructures for photocatalytic dye degradation. Semiconductor Science and Technology, 28(3), 035015. doi:10.1088/0268-1242/28/3/035015Liu, H., Luo, M., Hu, J., Zhou, T., Chen, R., & Li, J. (2013). β-Bi2O3 and Er3+ doped β-Bi2O3 single crystalline nanosheets with exposed reactive {001} facets and enhanced photocatalytic performance. Applied Catalysis B: Environmental, 140-141, 141-150. doi:10.1016/j.apcatb.2013.04.009Qiu, Y., Xu, G.-L., Kuang, Q., Sun, S.-G., & Yang, S. (2012). Hierarchical WO3 flowers comprising porous single-crystalline nanoplates show enhanced lithium storage and photocatalysis. Nano Research, 5(11), 826-832. doi:10.1007/s12274-012-0266-6Cha, H. G., Kim, S. J., Lee, K. J., Jung, M. H., & Kang, Y. S. (2011). Single-Crystalline Porous Hematite Nanorods: Photocatalytic and Magnetic Properties. The Journal of Physical Chemistry C, 115(39), 19129-19135. doi:10.1021/jp206958gBharathi, S., Nataraj, D., Mangalaraj, D., Masuda, Y., Senthil, K., & Yong, K. (2009). Highly mesoporous α-Fe2O3nanostructures: preparation, characterization and improved photocatalytic performance towards Rhodamine B (RhB). Journal of Physics D: Applied Physics, 43(1), 015501. doi:10.1088/0022-3727/43/1/015501Liao, A., He, H., Tang, L., Li, Y., Zhang, J., Chen, J., … Zou, Z. (2018). Quasi-Topotactic Transformation of FeOOH Nanorods to Robust Fe2O3 Porous Nanopillars Triggered with a Facile Rapid Dehydration Strategy for Efficient Photoelectrochemical Water Splitting. ACS Applied Materials & Interfaces, 10(12), 10141-10146. doi:10.1021/acsami.8b00367Li, L., Yu, Y., Meng, F., Tan, Y., Hamers, R. J., & Jin, S. (2012). Facile Solution Synthesis of α-FeF3·3H2O Nanowires and Their Conversion to α-Fe2O3 Nanowires for Photoelectrochemical Application. Nano Letters, 12(2), 724-731. doi:10.1021/nl2036854Xu, T., Zheng, H., Zhang, P., Lin, W., & Sekiguchi, Y. (2015). Hydrothermal preparation of nanoporous TiO2 films with exposed {001} facets and superior photocatalytic activity. Journal of Materials Chemistry A, 3(37), 19115-19122. doi:10.1039/c5ta02640gXu, T., Zheng, H., Zhang, P., & Lin, W. (2016). Photocatalytic degradation of a low concentration pharmaceutical pollutant by nanoporous TiO2film with exposed {001} facets. RSC Advances, 6(98), 95818-95824. doi:10.1039/c6ra22011hLiu, Y., Shen, S., Ren, F., Chen, J., Fu, Y., Zheng, X., … Jiang, C. (2016). Fabrication of porous TiO2nanorod array photoelectrodes with enhanced photoelectrochemical water splitting by helium ion implantation. Nanoscale, 8(20), 10642-10648. doi:10.1039/c5nr05594fStein, A., Li, F., & Denny, N. R. (2007). Morphological Control in Colloidal Crystal Templating of Inverse Opals, Hierarchical Structures, and Shaped Particles. Chemistry of Materials, 20(3), 649-666. doi:10.1021/cm702107nYamamoto, E., & Kuroda, K. (2016). Colloidal Mesoporous Silica Nanoparticles. Bulletin of the Chemical Society of Japan, 89(5), 501-539. doi:10.1246/bcsj.20150420Li, J., Chang, H., Ma, L., Hao, J., & Yang, R. T. (2011). Low-temperature selective catalytic reduction of NOx with NH3 over metal oxide and zeolite catalysts—A review. Catalysis Today, 175(1), 147-156. doi:10.1016/j.cattod.2011.03.034Ilić, B., & Wettstein, S. G. (2017). A review of adsorbate and temperature-induced zeolite framework flexibility. Microporous and Mesoporous Materials, 239, 221-234. doi:10.1016/j.micromeso.2016.10.005Zheng, X., Kuang, Q., Yan, K., Qiu, Y., Qiu, J., & Yang, S. (2013). Mesoporous TiO2 Single Crystals: Facile Shape-, Size-, and Phase-Controlled Growth and Efficient Photocatalytic Performance. ACS Applied Materials & Interfaces, 5(21), 11249-11257. doi:10.1021/am403482gZhou, Y., Yi, Q., Xing, M., Shang, L., Zhang, T., & Zhang, J. (2016). Graphene modified mesoporous titania single crystals with controlled and selective photoredox surfaces. Chemical Communications, 52(8), 1689-1692. doi:10.1039/c5cc07567jDong, C., Song, H., Zhou, Y., Dong, C., Shen, B., Yang, H., … Zhang, J. (2016). Sulfur nanoparticles in situ growth on TiO2 mesoporous single crystals with enhanced solar light photocatalytic performance. RSC Advances, 6(81), 77863-77869. doi:10.1039/c6ra17884gXing, M., Zhou, Y., Dong, C., Cai, L., Zeng, L., Shen, B., … Yin, Y. (2018). Modulation of the Reduction Potential of TiO2–x by Fluorination for Efficient and Selective CH4 Generation from CO2 Photoreduction. Nano Letters, 18(6), 3384-3390. doi:10.1021/acs.nanolett.8b00197Zhu, Z., Zheng, X., Bai, Y., Zhang, T., Wang, Z., Xiao, S., & Yang, S. (2015). Mesoporous SnO2 single crystals as an effective electron collector for perovskite solar cells. Physical Chemistry Chemical Physics, 17(28), 18265-18268. doi:10.1039/c5cp01534kWang, Y., Deng, Y., Fan, L., Zhao, Y., Shen, B., Wu, D., … Zhang, J. (2017). In situ strategy to prepare PDPB/SnO2 p–n heterojunction with a high photocatalytic activity. RSC Advances, 7(39), 24064-24069. doi:10.1039/c7ra02608kLiu, G., Yu, J. C., Lu, G. Q. (Max), & Cheng, H.-M. (2011). Crystal facet engineering of semiconductor photocatalysts: motivations, advances and unique properties. Chemical Communications, 47(24), 6763. doi:10.1039/c1cc10665aChen, X., & Mao, S. S. (2007). Titanium Dioxide Nanomaterials:  Synthesis, Properties, Modifications, and Applications. Chemical Reviews, 107(7), 2891-2959. doi:10.1021/cr0500535Ong, W.-J., Tan, L.-L., Chai, S.-P., Yong, S.-T., & Mohamed, A. R. (2014). Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization. Nanoscale, 6(4), 1946. doi:10.1039/c3nr04655aYang, H. G., Sun, C. H., Qiao, S. Z., Zou, J., Liu, G., Smith, S. C., … Lu, G. Q. (2008). Anatase TiO2 single crystals with a large percentage of reactive facets. Nature, 453(7195), 638-641. doi:10.1038/nature06964Wu, T., Kang, X., Kadi, M. W., Ismail, I., Liu, G., & Cheng, H.-M. (2015). Enhanced photocatalytic hydrogen generation of mesoporous rutile TiO2 single crystal with wholly exposed {111} facets. Chinese Journal of Catalysis, 36(12), 2103-2108. doi:10.1016/s1872-2067(15)60996-2Yu, H., Wang, L., & Dargusch, M. (2016). Low-temperature templated synthesis of porous TiO2 single-crystals for solar cell applications. Solar Energy, 123, 17-22. doi:10.1016/j.solener.2015.10.044Zhen, C., Wu, T., Kadi, M. W., Ismail, I., Liu, G., & Cheng, H.-M. (2015). Design and construction of a film of mesoporous single-crystal rutile TiO2 rod arrays for photoelectrochemical water oxidation. Chinese Journal of Catalysis, 36(12), 2171-2177. doi:10.1016/s1872-2067(15)60981-0Wang, J., Bian, Z., Zhu, J., & Li, H. (2013). Ordered mesoporous TiO2with exposed (001) facets and enhanced activity in photocatalytic selective oxidation of alcohols. J. Mater. Chem. A, 1(4), 1296-1302. doi:10.1039/c2ta00035kYue, W., Randorn, C., Attidekou, P. S., Su, Z., Irvine, J. T. S., & Zhou, W. (2009). Syntheses, Li Insertion, and Photoactivity of Mesoporous Crystalline TiO2. Advanced Functional Materials, 19(17), 2826-2833. doi:10.1002/adfm.200900658Malgras, V., Ji, Q., Kamachi, Y., Mori, T., Shieh, F.-K., Wu, K. C.-W., … Yamauchi, Y. (2015). Templated Synthesis for Nanoarchitectured Porous Materials. Bulletin of the Chemical Society of Japan, 88(9), 1171-1200. doi:10.1246/bcsj.20150143Liu, Y., Lan, K., Li, S., Liu, Y., Kong, B., Wang, G., … Zhao, D. (2016). Constructing Three-Dimensional Mesoporous Bouquet-Posy-like TiO2 Superstructures with Radially Oriented Mesochannels and Single-Crystal Walls. Journal of the American Chemical Society, 139(1), 517-526. doi:10.1021/jacs.6b11641Lin, J., Zhao, L., Heo, Y.-U., Wang, L., Bijarbooneh, F. H., Mozer, A. J., … Kim, J. H. (2015). Mesoporous anatase single crystals for efficient Co(2+/3+)-based dye-sensitized solar cells. Nano Energy, 11, 557-567. doi:10.1016/j.nanoen.2014.11.017Shi, W., Zhang, X., Brillet, J., Huang, D., Li, M., Wang, M., & Shen, Y. (2016). Significant enhancement of the photoelectrochemical activity of WO3 nanoflakes by carbon quantum dots decoration. Carbon, 105, 387-393. doi:10.1016/j.carbon.2016.04.051Wang, Q., Yuan, L., Dun, M., Yang, X., Chen, H., Li, J., & Hu, J. (2016). Synthesis and characterization of visible light responsive Bi3NbO7 porous nanosheets photocatalyst. Applied Catalysis B: Environmental, 196, 127-134. doi:10.1016/j.apcatb.2016.05.026Tan, B., Zhang, X., Li, Y., Chen, H., Ye, X., Wang, Y., & Ye, J. (2017). Anatase TiO 2 Mesocrystals: Green Synthesis, In Situ Conversion to Porous Single Crystals, and Self‐Doping Ti 3+ for Enhanced Visible Light Driven Photocatalytic Removal of NO. Chemistry – A European Journal, 23(23), 5478-5487. doi:10.1002/chem.201605294Chetia, T. R., Ansari, M. S., & Qureshi, M. (2015). Ethyl Cellulose and Cetrimonium Bromide Assisted Synthesis of Mesoporous, Hexagon Shaped ZnO Nanodisks with Exposed ±{0001} Polar Facets for Enhanced Photovoltaic Performance in Quantum Dot Sensitized Solar Cells. ACS Applied Materials & Interfaces, 7(24), 13266-13279. doi:10.1021/acsami.5b01039Zhao, Y., Zhang, Y., Liu, H., Ji, H., Ma, W., Chen, C., … Zhao, J. (2013). Control of Exposed Facet and Morphology of Anatase Crystals through TiOxFy Precursor Synthesis and Impact of the Facet on Crystal Phase Transition. Chemistry of Materials, 26(2), 1014-1018. doi:10.1021/cm403054wJin, Z., Zhang, Y.-X., Meng, F.-L., Jia, Y., Luo, T., Yu, X.-Y., … Huang, X.-J. (2014). Facile synthesis of porous single crystalline ZnO nanoplates and their application in photocatalytic reduction of Cr(VI) in the presence of phenol. Journal of Hazardous Materials, 276, 400-407. doi:10.1016/j.jhazmat.2014.05.059Li, Z., Zhou, Y., Xue, G., Yu, T., Liu, J., & Zou, Z. (2012). Fabrication of hierarchically assembled microspheres consisting of nanoporous ZnO nanosheets for high-efficiency dye-sensitized solar cells. Journal of Materials Chemistry, 22(29), 14341. doi:10.1039/c2jm32823bQiu, Y., Chen, W., & Yang, S. (2010). Facile hydrothermal preparation of hierarchically assembled, porous single-crystalline ZnO nanoplates and their application in dye-sensitized solar cells. J. Mater. Chem., 20(5), 1001-1006. doi:10.1039/b917305fHosono, E., Tokunaga, T., Ueno, S., Oaki, Y., Imai, H., Zhou, H., & Fujihara, S. (2012). Crystal-Growth Process of Single-Crystal-like Mesoporous ZnO through a Competitive Reaction in Solution. Crystal Growth & Design, 12(6), 2923-2931. doi:10.1021/cg300116hDong, J.-Y., Lin, C.-H., Hsu, Y.-J., Lu, S.-Y., & Wong, D. S.-H. (2012). Single-crystalline mesoporous ZnO nanosheets prepared with a green antisolvent method exhibiting excellent photocatalytic efficiencies. CrystEngComm, 14(14), 4732. doi:10.1039/c2ce06739kLuo, Q.-P., Wang, B., & Cao, Y. (2017). Single-crystalline porous ZnO nanosheet frameworks for efficient fully flexible dye-sensitized solar cells. Journal of Alloys and Compounds, 695, 3324-3330. doi:10.1016/j.jallcom.2016.10.130Xu, Y., Wen, W., & Wu, J.-M. (2018). Titania nanowires functionalized polyester fabrics with enhanced photocatalytic and antibacterial performances. Journal of Hazardous Materials, 343, 285-297. doi:10.1016/j.jhazmat.2017.09.044Dong, Q., Yin, S., Guo, C., Wu, X., Kumada, N., Takei, T., … Sato, T. (2014). Single-crystalline porous NiO nanosheets prepared from β-Ni(OH)2 nanosheets: Magnetic property and photocatalytic activity. Applied Catalysis B: Environmental, 147, 741-747. doi:10.1016/j.apcatb.2013.10.007Ghosh, S., Roy, M., & Naskar, M. K. (2014). Template-free synthesis of mesoporous single-crystal CuO particles with dumbbell-shaped morphology. Materials Letter

Design of nanostructured photocatalysts for hydrogen production and environmental application

Tableau d'honneur de la Faculté des études supérieures et postdorales, 2014-2015Au cours des dernières décennies, la photocatalyse par les semiconducteurs a été intensivement étudiée pour une grande variété d'applications, y compris la production d'hydrogène à partir de la dissociation de l'eau et la décomposition des polluants dans l'air et l'eau. Actuellement, TiO2 est le matériau photocatalytique le plus largement étudié en raison de son faible coût et ses propriétés physiques et chimiques exceptionnelles. Cependant, la rapide recombinaison électron-trou et son absorption dans la région de l’ultra-violet le rendent inefficace sous la lumière du soleil. Cette thèse vise à développer des photocatalyseurs efficaces à base de TiO2 en appliquant différentes stratégies telles que le contrôle de la morphologie des nanoparticules de TiO2, le couplage du TiO2 avec des métaux et d’autres semi-conducteurs, et l'optimisation de la porosité des photocatalyseurs. Nous avons mis au point une méthode de synthèse solvo-thermique pour produire des nanocristaux de TiO2 hautement cristallins de différentes formes, tel que rhombique, sphérique, et sous forme de tige. Les nanocristaux TiO2 obtenus ont ensuite été décorés par des clusters d'Ag de taille contrôlée pour former des hybrides Ag-TiO2 ayant une performance photocatalytique supérieure à celle du photocatalyseur conventionnel Ag-TiO2-P25. Nous avons également développé une technique non-hydrolytique pour la synthèse de nanodisques uniformes de TiO2 de diamètre contrôlé entre de 12 nm et 35 nm. Ces nanodisques ont ensuite été utilisés comme blocs de construction pour la synthèse des photocatalyseurs multi-composants solubles dans l'eau à base de CdS-Titanate-Ni; ces derniers sont très actifs pour la production d'hydrogène grâce à leur absorption efficace de lumière visible et leur séparation efficace d’électrons et trous. Finalement, nous avons construit un assemblage tridimensionnel ordonné de nanosphères creuses de coquille mince de Au/TiO2, en utilisant les blocs de construction de nanodiques de titanate. Ces photocatalyseurs présentent non seulement une surface spécifique très élevée, mais aussi un comportement photonique et une diffusion multiple de la lumière, ce qui améliore significativement l'absorption de la lumière visible. Ces nanosphères creuses de structure ordonnée tridimensionnelle présentent une activité photocatalytique induite par la lumière visible, étant plusieurs fois plus élevée que celle des nanopoudres conventionnelles d’Au/TiO2.Semiconductor photocatalysis has been intensively studied over the past decades for a wide variety of applications including hydrogen production from water splitting and decomposition of pollutants in air and water. Currently, TiO2 is the most widely investigated photocatalytic material because of its low cost and outstanding physical and chemical properties. However, its fast electron-hole recombination and light absorption only in ultra-violet region make it inefficient working under sunlight. The goal of the research presented in this thesis is to design efficient TiO2 based photocatalysts by applying various strategies encompassing controlling the morphology of TiO2 particles, coupling TiO2 with metals, and other semiconductors and optimizing porosity of the photocatalysts. We have developed a solvothermal synthetic method for producing highly crystalline TiO2 nanocrystals with various shapes, such as rhombic, spherical, and bar. The obtained TiO2 nanocrystals were then decorated with size-controlled Ag clusters to form Ag-TiO2 hybrids which exhibit superior photocatalytic performance in comparison to conventional Ag-TiO2-P25 photocatalyst. We have also developed a nonhydrolytic technique for the synthesis of uniform titanate nanodisks with controlled diameter in the range of 12 nm to 35 nm. These nanodisks were then used as building blocks for the design of water-soluble CdS–Titanate–Ni multicomponent photocatalysts which are highly active for hydrogen generation due to their effective visible light absorption and efficient charge separation. Finally, we have constructed a three-dimensional ordered assembly of thin-shell Au/TiO2 hollow nanospheres from titanate nanodisk building blocks. The designed photocatalysts exhibit not only a very high specific surface area but also photonic behavior and multiple light scattering, which significantly enhances visible light absorption. As a result, Au/TiO2 hollow nanospheres with three-dimensional ordered structure exhibit a visible-light-driven photocatalytic activity that is several times higher than conventional Au/TiO2 nanopowders

Zinc Oxide Nanorods (ZnO NRs) for photovoltaic applications

Zinc oxide (ZnO) is a material that has highly attractive cost-effective features and can be grown using different methods leading to a wide range of nanostructured morphologies. In this work, zinc oxide nanorods (ZnO NRs) with various surface distribution density were sensitised using aqueous solutions based on zinc salt at 40°C85°C. Systematic investigations were carried out on the influences of zinc salt, different ZnO seed layer thickness and growth temperature (Tgrowth). The grown ZnO NRs were used in two different aspects. The first aspect was to grow the NRs on a releasable layer and here Omnicaot was used as a sacrificial layer and SU-8 photoresist as a support structural layer to reach the desired aim. Also, ZnO NRs were grown on polydimethylsiloxane (PDMS). This was used to improve the performance of different types of solar cells by mounting the full structure on top with help of optical gel. The results obtained showed that wet lift-off showed an increasing ɳ from 1.56% to 2.05% when a GaAs solar cell was used, whereas the same solar cell showed an efficiency ɳ increasing to about 2.03% when using dry peel-off nanostructures. CZTSSe (Cu2ZnSn(S,Se)4) solar cells showed an increase in ɳ from 1.3% to (1.79%, 1.65% and 2.15%) for ZnO NRs/SU-8, ZnO NRs/PDMS and flower-like/diluted PDMS, respectively. The second aspect was to fabricate extremely thin absorber solar cells. For lift-off process, the work presented herein provides a cost-effective, simple novel combination of lift-off processing with hydrothermally grown ZnO NRs on SU-8 or PDMS, in a low temperature range Tgrowth from 40°C- 85°C. This study addresses a controllable release/transfer of ZnO NRs when high growth temperature represents a barrier to carrying out an immediate growth on flexible substrates for example wearable electronics applications. The evolution of ZnO NRs with Tgrowth were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-Vis spectroscopy. The ZnO NRs/SU-8 and ZnO NRs/PDMS structures were successfully detached from the glass. The SEM images confirmed that, the ZnO NRs formed different diameters and lengths as Tgrowth increased. Transmitted/scattered light characteristics showed different trends depending on the Tgrowth and structure stack used. The findings of this study offer an easy method of lift-off ZnO NRs (and subsequent stack of layers) using the low-cost facilities and at low temperature. Current-voltage (I-V) and external quantum efficiency (EQE) measurements showed an affective influence of mounting the released ZnO NRs on CZTS and GaAs solar cells. Moreover, a study on ETA cell fabrication using CZTS is presented. The fabricated ETA cell structure was as the following: glass/ITO/ZnO seed/ZnO NRs/CdS/CZTS/P3HT/gold and the aim is for the CdS/CZTS to conformally coat the ZnO NRs, while P3HT acts as a hole transport layer which in turn helps avoiding shunting. ETA cell showed about 0.02% of efficiency (ɳ), 0.05V (Voc), 0.15mA/cm2 (Jsc), 27.46% (FF) and about 20% EQE in the 300nm-600nm spectra region. These results are clear indication of promising sight for ETA solar cells based on CZTS nanoparticles which can be more improved

Directed Synthesis and Doping of Wide Bandgap Semiconducting Oxide Nanocrystals

Wide bandgap semiconducting oxide nanocrystals are a useful class of materials with high stability and numerous useful properties. In the field of catalysis, high surface area oxides are commonly used as catalytic supports and have been found to be photocatalytically active for the production of renewable fuels. Ultra high vacuum studies of single crystals indicate that the surface structure and faceting of oxides dramatically influence their catalytic properties. For plasmonics applications, degenerately doped oxide nanocrystals may act as low-loss substitutes for metals, but little is known regarding the influence of particle shape or assembly on their optical response. With the discovery of nonaqueous surfactant assisted synthesis, methods to produce nanocrystals which provide precise control over size, shape, and crystal structure have improved dramatically. On the other hand, exploration of the influence of morphology on the properties of many materials, including wide bandgap oxide materials, is only in its infancy. Herein, improved methods are described to control both the size and shape of semiconducting oxide nanocrystals. The influence of nanocrystal shape on the photocatalytic activity for hydrogen evolution and other environmentally relevant reactions is then described, as well as the shape dependent plasmonic response and dielectric properties of conductive oxide nanocrystals

Enhanced Sensing Performance of Novel Nanostructured ZnO Gas Sensors in Ethanol Vapor Concentration Detection Applications

Sensors are devices which have been commonly used to measure the functional dependence and the variability of physical parameters like temperature, pressure, pH, voltage, current, concentration, and others. Among the numerous kinds of sensors in different areas, gas sensors have been widely used and investigated for gas monitoring. Gas sensors are of crucial importance for the detection of hazardous atmospheres, because toxic gases are frequently odorless, colorless, invisible, rapidly evaporating, and flammable, and would otherwise go unnoticed. Gas sensors have been used in a variety of applications among others for the detection of specific gas species and the detection of gas concentrations. Compared to other materials systems used in gas sensor applications, Metal Oxide Semiconductor (MOS) sensors have attracted much attention for gas detection due to their low cost, simple design and ease of production, short response time, wide detection range, and resistance to harsh working environments. Among various semiconductor materials used in MOS gas sensors, ZnO is a well-known semiconducting metal oxide material used in gas sensor applications due to its good electrical property, wide band gap of 3.37 eV, ~60 meV exciton binding energy, low cost, and high mechanical stability. ZnO has been applied for MOS gas sensor applications due to its high electrochemical stability, non-toxicity, ease of doping, and low cost. In general, gas sensors based on ZnO tend to exhibit exceptional performance for ethanol detection with respect to high sensitivity, short response time, and fast recovery time. In this dissertation, the sensing performance of novel innovative ZnO nanostructure gas sensor designs to ethanol vapor concentration detection were investigated and analyzed in terms of their sensing response, their response time, and recovery time. Currently, the shortcomings of state-of-the-art thin film ZnO gas sensors are lack of sufficient sensitivity, long response times, and long recovery times relying only on one reactive surface. My research is addressing these shortcomings by designing, fabricating and testing novel innovative 3-dimensional nanoscale ZnO sensor device architectures with increased surface-to-volume ratio using an integrated process approach combining hydrothermal growth of nanorods with Atomic Layer Deposition (ALD) wrap-around coatings. First and foremost, Aluminum doped ZnO (AZO) thin films were introduced to enhance the sensing performance of ZnO nanorod gas sensors by providing additional oxygen vacancies and extra electrons for the redox reactions using ALD technology. A roughly 100% improvement was achieved on the sensing response of ZnO nanorod gas sensors equipped with ALD AZO 3-D wrap-around coatings compared to conventional ZnO nanorod gas sensors. Secondly, the other key approach in this dissertation was to conceive a unique novel sensor architecture design to further improve the sensing performance of ZnO nanostructure gas sensors with an innovative increase of the surface-to-volume ratio. These novel nested ZnO nanorod/nanotube gas sensors exhibited a large improvement in their sensing response due to the increased surface-to-volume ratio with two additional reaction surfaces and extra reaction sites. The sensing response of ZnO gas sensors was improved up to a maximum of 150% with the novel nested coaxial nanorod/nanotube architecture compared to the sensing response of conventional ZnO nanorod gas sensors. The third approach was to investigate the sensing performance of ZnO nanotube sensors synthesized within porous templates by utilizing ALD and Al2O3 sacrificial layers. The sensing performance of these ZnO nanotube gas sensors was enhanced with increased surface-to-volume ratio by adding additional coaxial ZnO nanotubes. The enhancement can be further improved by adding additional coaxial ZnO nanotubes layers which provide each 2 additional reaction surfaces. Furthermore, ALD AZO coatings were introduced to further enhance the sensing performance of ZnO nanotube gas sensors synthesized in porous templates. With the combined benefits from approaches 1 and 2, the maximum gained enhancement reached up to 136% for the template replication case. The first two approaches established a bottom-up technology, which is subject to high variability from batch to batch hydrothermal growth. In contrast, nested ZnO nanotubes synthesized within porous templates enables a true top-down technology by using mask and photolithography patterning techniques from microelectronics to guarantee the reproducibility, which would render it ready for commercialization and to be transferred for industrial applications

Assembly and Deformation of Amphiphilic Copolymers and Networks at Fluid Interfaces

Surface tension generally plays a negligible role on macroscopic scales, but it is often the dominant force on nanometer to micrometer length-scales. The efforts of this dissertation are mainly focused on understanding the role that surface tension plays on sub-millimeter scale objects, especially on soft material systems, and how to utilize this phenomenon to assemble and deform objects. This dissertation addresses several phenomena of nano-and micron-sized objects at fluid interfaces. For nano-scale objects, amphiphilic block copolymer chains were used to explore interfacial behaviors due to their enhanced stability, mechanical properties, and tunability compared to other interfacially active materials such as small molecule surfactants or lipids. We investigate the tailoring of amphiphilic block copolymer assemblies through deformation at the oil/water interface by inducing interfacial instabilities to incorporate inorganic nanoparticles into micelles (chapter 2) or by controlling osmotic stresses to prepare multi-compartment emulsions and capsules (chapter 3). Next, we utilize photo-crosslinkable and temperature-responsive copolymer networks (i.e., thin hydrogel sheets) with simple to complex geometries as micro-scale soft objects. Competition between surface energy and elastic bending energy allows us to quantitatively characterize elastic properties of crosslinked thin hydrogel sheets in micron dimensions by using surface tension of liquids (chapter 4). In addition, we have found significant edge imperfections due to the finite resolution of the photo-lithographic patterning method by observation of interfacial deformations. We employ the edge imperfections to drive the buckling of narrow photo-crosslinkable hydrogel ribbons (chapter 5). Lastly, we introduce a new concept of capillary assembly of soft hydrogel sheets with various geometries. This study allows us to examine correlations between elastic properties and surface tension, as well as capillary interactions between soft materials which can be extended to more complex multi-polar interface deformation (chapter 6)

Synthesis and characterization of titanium dioxide nanomaterials for photocatalytic hydrogen production

[no abstract

Colloidal metal-organic framework particles : the pioneering case of ZIF-8

The production of metal-organic frameworks (MOFs) in the form of colloids has brought a paradigm shift in the design of new functional porous materials. Along with their intrinsic interest as porous solids, and contrary to their bulk powder counterparts, colloidal MOF particles can additionally be dispersed, shaped, functionalized, transformed and assembled in a controlled manner, conferring them further properties and applications. In this regard, zeolitic imidazolate framework-8 (ZIF-8) has become a pioneering MOF constituent of colloidal science. Today, the understanding of the role of synthetic parameters, learned after one decade of research, enables the production of monodisperse colloidal ZIF-8 particles with tunable dimensions and morphologies, offering the opportunity to develop new functional materials and composites with novel and promising functionalities. This tutorial review provides a useful guide to prepare ZIF-8 in its colloidal form, covering the published studies on the synthesis of homogeneous ZIF-8 particles with controlled size and shape. In addition, we present the most relevant advances in the development of colloidal ZIF-8 hybrid single-particles, reflecting the great potential and rapid development of this interdisciplinary research field. Finally, we highlight how formulation of ZIF-8 as colloids has led to the emergence of novel physicochemical phenomena that are useful for practical applications. This review aims at promoting the development of MOFs as colloids, taking ZIF-8 as a pioneering and successful case that clearly shows the benefits of bridging MOF chemistry and colloidal science

Design strategies for shape-controlled magnetic iron oxide nanoparticles

Ferrimagnetic iron oxide nanoparticles (magnetite or maghemite) have been the subject of an intense research, not only for fundamental research but also for their potentiality in a widespread number of practical applications. Most of these studies were focused on nanoparticles with spherical morphology but recently there is an emerging interest on anisometric nanoparticles. This review is focused on the synthesis routes for the production of uniform anisometric magnetite/maghemite nanoparticles with different morphologies like cubes, rods, disks, flowers and many others, such as hollow spheres, worms, stars or tetrapods. We critically analyzed those procedures, detected the key parameters governing the production of these nanoparticles with particular emphasis in the role of the ligands in the final nanoparticle morphology. The main structural and magnetic features as well as the nanotoxicity as a function of the nanoparticle morphology are also described. Finally, the impact of each morphology on the different biomedical applications (hyperthermia, magnetic resonance imaging and drug delivery) are analysed in detail. We would like to dedicate this work to Professor Carlos J. Serna, Instituto de Ciencia de Materiales de Madrid, ICMM/CSIC, for his outstanding contribution in the field of monodispersed colloids and iron oxide nanoparticles. We would like to express our gratitude for all these years of support and inspiration on the occasion of his retirement