Effect of Titania Regular Macroporosity on the Photocatalytic Hydrogen Evolution on Cd 1x Zn x S/TiO 2 Catalysts under Visible Light Ekaterina A. Kozlova,* [a, b, c] Anna Yu. Kurenkova, [a, b, c] Victoria S. Semeykina, [a, b] Ekaterina V. Parkhomchuk, [a, b] Svetlana V. Cherepanova, [a, b, c] Evgeny Yu. Gerasimov, [a, b, c] Andrey A. Saraev, [a, b] Vasily V. Kaichev, [a, b] and Valentin N. Parmon [a, b] Introduction In view of the increasing awareness of environmental issues, the photocatalytic production of hydrogen remains a fascinat- ing challenge. [1] Titania doped with noble metals is the most widely used photocatalyst for efficient hydrogen evolution under UV-light irradiation at wavelengths shorter than that cor- responding to its bandgap energy, 3.2 eV. However, ultraviolet- light energy accounts for only about 4 % of the solar spectrum, whereas visible-light energy composes about 46 % of the irra- diation that reaches Earth. [2] Hence, the development of visi- ble-light responsive photocatalysts for hydrogen production is attracting tremendous attention. [3] Binary systems CdS/TiO 2 and Cd 1x Zn x S/TiO 2 are of great in- terest because these systems combine the good stability of ti- tania and the response of cadmium or mixed sulfides to visible light. Moreover, charge injection from the conduction band of the narrow bandgap semiconductor (CdS or Cd 1x Zn x S) to that of TiO 2 can lead to efficient and more long-living charge sepa- ration by minimizing electron–hole recombination. [4, 5] Titania- supported cadmium sulfide is widely used for the photocata- lytic water splitting that accompanies the hydrogen produc- tion. [6–10] Combining a large bandgap semiconductor (ZnS) with a relatively small bandgap semiconductor (CdS) allows bandgap tuning over a substantial range of the visible part of the spectrum. [11] The use of Cd 1x Zn x S/TiO 2 for photo-electro- chemical water splitting is preferable to the use of CdS/TiO 2 . [11] In addition to the optical properties, the enhanced porous structure is required for the increase in the efficiency of photo- catalytic processes in liquid phases. [3, 12] Recently, substantial effort has been directed toward more advanced 3D hierarchical architectures assembled based on nanoscale building blocks. [3] Polymeric colloidal crystals may serve as a hard template for producing TiO 2 with the morphology of either monodisperse- porous microbeads [12] or inverse opals with a 3D-ordered mac- roporous structure, [13] which is called a “photonic sponge”. [14] Earlier, titania-based 3D-ordered macroporous structures were successfully used for the photocatalytic oxidation of the organ- ic pollutants under UV-light irradiation. [13–15] Compared with nanocrystalline TiO 2 , the hydrogen evolution under UV light over a Pt/TiO 2 hierarchical photonic crystal can be enhanced by a factor of two. [3, 6] Different composite 3D-ordered photoca- talysts, including Cd 1x Zn x S/SBA-15, [16] CdS/ZrO 2 , [17] MoS 2 / TiO 2 , [18] and CdS-Au-WO 3 , [19] were used for the hydrogen evolu- Multiphase photocatalysts Cd 1x Zn x S/TiO 2 were synthesized through the deposition of solid solutions of cadmium and zinc sulfides on the surface of titania samples with different porous structures, including a 3D-ordered meso/macroporous struc- ture. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy combined with energy-dis- persive X-ray spectroscopy, N 2 adsorption at 77 K, X-ray photo- electron spectroscopy, and UV/VIS spectroscopy. The photoca- talytic activity was tested in a batch reactor for the H 2 evolu- tion reaction from aqueous solutions of Na 2 S/Na 2 SO 3 under visible-light irradiation (l = 450 nm). The highest achieved pho- tocatalytic activity was 1.8 mmol H 2 per gram of photocatalyst per hour. The regular porous structure of titania was demon- strated to enhance the photocatalytic activity and stability of Cd 0.4 Zn 0.6 S/TiO 2 samples. [a] Dr. E. A. Kozlova, A. Y. Kurenkova, V. S. Semeykina, Dr. E. V. Parkhomchuk, Dr. S. V. Cherepanova, Dr. E. Y. Gerasimov, A. A. Saraev, Dr. V.V. Kaichev, Prof. V. N. Parmon Laboratory of Solar Energy Conversion Boreskov Institute of Catalysis Novosibirsk State University Pr. ak. Lavrentieva, 5 Novosibirsk, 630090 (Russian Federation) E-mail : kozlova@catalysis.ru [b] Dr. E. A. Kozlova, A. Y. Kurenkova, V. S. Semeykina, Dr. E. V. Parkhomchuk, Dr. S. V. Cherepanova, Dr. E. Y. Gerasimov, A. A. Saraev, Dr. V.V. Kaichev, Prof. V. N. Parmon Novosibirsk State University Pirogova Str., 2, Novosibirsk, 630090 (Russian Federation) [c] Dr. E. A. Kozlova, A. Y. Kurenkova, Dr. S. V. Cherepanova, Dr. E. Y. Gerasimov Educational Center for Energy Efficient Catalysis Boreskov Institute of Catalysis Novosibirsk State University Pirogova Str., 2, Novosibirsk, 630090 (Russian Federation) Supporting information and ORCID(s) from the author(s) for this article are available on the WWW under http://dx.doi.org/10.1002/ cctc.201500897. ChemCatChem 2015, 7, 4108 – 4117 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4108 Full Papers DOI: 10.1002/cctc.201500897