SiO<inf>2</inf>@TiO<inf>2</inf> core@shell nanoparticles (CSNs) have recently attracted great attention due to their unique and tunable optical and photocatalytic properties and higher dispersion of the supported TiO<inf>2</inf>. Thus, development of facile, reproducible and effective methods for the synthesis of SiO<inf>2</inf>@TiO<inf>2</inf> CSNs and a fundamental understanding of their improved properties, derived from combination of different core and shell materials, is of great importance. Here we report a very facile and reproducible method for the synthesis of CSNs with a control of particle morphology, crystallinity and phase selectivity, and provide important insight into the effect of core@shell configuration on the photocatalytic and optical properties of SiO<inf>2</inf>@TiO<inf>2</inf> CSNs. For this purpose, synthesis of highly dispersed anatase nanocrystals (~5nm) of high surface area was carried out by supporting these nanocrystals on silica sub-micron spheres in the form of a porous shell of controlled thickness (10-30nm). The amorphous TiO<inf>2</inf> shell was crystallized into anatase using a low temperature (105°C) hydrothermal treatment. The resulting CSNs were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, x-ray photoelectron spectroscopy, X-ray diffraction, vibrational spectroscopy, zeta-potential measurements, BET surface area and electron paramagnetic resonance measurements. Both experimental data and theoretical simulations showed that due to the size of the complete particle (SiO<inf>2</inf>@TiO<inf>2</inf>), the general optical response of the system is regulated by Rayleigh scattering, exhibiting a red-shift of the extinction spectra as shell-thickness increases. The SiO<inf>2</inf>@TiO<inf>2</inf> configuration leads to efficient light harvesting by increasing the optical path inside the core@shell particles. An enhanced photoactivity and good recyclability of SiO<inf>2</inf>@TiO<inf>2</inf> CSNs was demonstrated compared to unsupported TiO<inf>2</inf>. Together with BET surface area measurements, direct assessment of the density of photocatalytic sites probed by electron paramagnetic resonance measurements was used to provide insight into the enhanced photocatalytic activity of CSNs, which is also understood as a consequence of Rayleigh scattering, relative enhancement of the adsorption of organic molecules on the core@shell photocatalyst surface and increased optical path inside the SiO<inf>2</inf>@TiO<inf>2</inf> particles. All these aspects are directly influenced by the core@shell configuration of SiO<inf>2</inf>@TiO<inf>2</inf> samples. © 2015 Elsevier B.V.179 333343Linsebigler, A.L., Lu, G., Yates, J.T., Yates, J.T., Photocatalysis on TiO2 Surfaces: principles, mechanisms, and selected results (1995) Chem. Rev., 95, pp. 5-758Fujishima, A., Zhang, X., Tryk, D., TiO<inf>2</inf> photocatalysis and related surface phenomena (2008) Surf. Sci. Rep., 63, pp. 515-582Pakdel, E., Daoud, W., Self-cleaning cotton functionalized with TiO<inf>2</inf>/SiO<inf>2</inf>: focus on the role of silica (2013) J. Colloid Interface Sci., 401, pp. 1-7Son, S., Hwang, S.H., Kim, C., Yun, J.Y., Jang, J., Designed synthesis of SiO<inf>2</inf>/TiO<inf>2</inf> core/shell structure as light scattering material for highly efficient dye-sensitized solar cells (2013) ACS Appl. Mater. Interfaces, 5, pp. 4815-4820Li, Y., Leung, P., Yao, L., Song, Q.W., Newton, E., Antimicrobial effect of surgical masks coated with nanoparticles (2006) J. Hosp. Infect., 62, pp. 58-63Sheel, D.W., Evans, P., Photoactive and antibacterial TiO<inf>2</inf> thin films on stainless steel (2007) Surf. Coatings Technol., 201, pp. 9319-9324Saravanan, K., Ananthanarayanan, K., Balaya, P., Mesoporous TiO<inf>2</inf> with high packing density for superior lithium storage (2010) Energy Environ. Sci., 3Banerjee, S., Gopal, J., Muraleedharan, P., Tyagi, A., Raj, B., Physics and chemistry of photocatalytic titanium dioxide: visualization of bactericidal activity using atomic force microscopy (2006) Curr. Sci., 90, pp. 1378-1383Augustynski, J., The role of the surface intermediates in the photoelectrochemical behavior of anatase and rutile TiO<inf>2</inf> (1993) Electrochim. Acta, 38, pp. 43-46Mandzy, N., Grulke, E., Druffel, T., Breakage of TiO<inf>2</inf> agglomerates in electrostatically stabilized aqueous dispersions (2005) Powder Technol., 160, pp. 121-126Hanaor, D.A.H., Assadi, M.H.N., Li, S., Yu, A.B., Sorrell, C.C., Ab initio study of phase stability in doped TiO<inf>2</inf> (2012) Comput. Mech., 50, pp. 185-194Raj, K., Viswanathan, B., Effect of surface area, pore volume and particle size of P25 titania on the phase transformation of anatase to rutile (2009) Indian J. Chem., 48, pp. 1378-1382Satterfield, C.N., (1991) Heterogeneous Catalysis Industrial Practice, , McGraw-Hill, New YorkHerrmann, J., Heterogeneous photocatalysis: fundamentals and applications to the removal of various types of aqueous pollutants (1999) Catal. Today, 53, pp. 115-129Hanprasopwattana, A., Srinivasan, S., Sault, A.G., Datye, A.K., Titania coatings on monodisperse silica spheres (characterization using 2-propanol dehydration and TEM) (1996) Langmuir, 12, pp. 3173-3179Hanprasopwattana, A., Rieker, T., Sault, A., Datye, A., Morphology of titania coatings on silica gel (1997) Catal. Lett., 45, pp. 165-175Li, A., Jin, Y., Muggli, D., Pierce, D.T., Aranwela, H., Marasinghe, G.K., Nanoscale effects of silica particle supports on the formation and properties of TiO<inf>2</inf> nanocatalysts (2013) Nanoscale, 5, pp. 5854-5862Ohno, T., Numakura, K., Itoh, H., Suzuki, H., Matsuda, T., Control of the quantum size effect of TiO<inf>2</inf>-SiO<inf>2</inf> hybrid particles (2009) Mater. Lett., 63, pp. 1737-1739Joo, J.B., Lee, I., Dahl, M., Moon, G.D., Zaera, F., Yin, Y., Controllable synthesis of mesoporous TiO<inf>2</inf> hollow shells: toward an efficient photocatalyst (2013) Adv. Funct. Mater., 23, pp. 4246-4254Joo, J.B., Zhang, Q., Lee, I., Dahl, M., Zaera, F., Yin, Y., Mesoporous anatase titania hollow nanostructures though silica-protected calcination (2012) Adv. Funct. Mater., 22, pp. 166-174Wei, S., Wang, Q., Zhu, J., Sun, L., Lin, H., Guo, Z., Multifunctional composite core-shell nanoparticles (2011) Nanoscale, 3, p. 4474Zhang, Q., Lee, I., Joo, J.I.B., Zaera, F., Core-shell nanostructured catalysts (2013) Acc. Chem. Res., 46, pp. 1816-1824Li, W., Zhao, D., Extension of the stöber method to construct mesoporous SiO<inf>2</inf> and TiO<inf>2</inf> shells for uniform multifunctional core-shell structures (2013) Adv. Mater., 25, pp. 142-149Jankiewicz, B.J., Jamiola, D., Choma, J., Jaroniec, M., Silica-metal core-shell nanostructures (2012) Adv. Colloid Interface Sci., 170, pp. 28-47Iler, R.K., (1978) The Chemistry Of Silica, , Wiley-Interscience, New YorkFink, A., Stöber, W., Bohn, E., Controlled growth of monodisperse silica spheres in the micron size range (1968) J. Colloid Interface Sci., 26, pp. 62-69Joo, J.B., Zhang, Q., Dahl, M., Zaera, F., Yin, Y., Synthesis, crystallinity control, and photocatalysis of nanostructured titanium dioxide shells (2012) J. Mater. Res., 28, pp. 2-368Periyat, P., Baiju, K.V., Mukundan, P., Pillai, P.K., Warrier, K.G.K., High temperature stable mesoporous anatase TiO<inf>2</inf> photocatalyst achieved by silica addition (2008) Appl. Catal. A Gen., 349, pp. 13-19Rasalingam, S., Peng, R., Koodali, R.T., Removal of hazardous pollutants from wastewaters: applications of TiO<inf>2</inf>-SiO<inf>2</inf> mixed oxide materials (2014) J. Nanomater., 42Anderson, C., Bard, A.J., An improved photocatalyst of TiO<inf>2</inf>/SiO<inf>2</inf> prepared by a Sol-gel synthesis (1995) J. Phys. Chem., 99, pp. 9882-9885Carp, O., Huisman, C.L., Reller, A., Photoinduced reactivity of titanium dioxide (2004) Prog. Solid State Chem., 32, pp. 33-177West, A.R., (1984) Solid State Chemistry and its Applications, , Wiley, Chichester [West Sussex] New YorkGross, T., Ramm, M., Sonntag, H., Unger, W., Weijers, H.M., Adem, E.H., An XPS analysis of different SiO<inf>2</inf> modifications employing a C 1s as well as an Au 4f7/2 static charge reference (1992) Surf. Interface Anal., 18, pp. 59-64Parks, G.A., The isoelectric points of solid oxides, solid hydroxides, and aqueous hydroxo complex systems (1965) Chem. Rev., 65, pp. 177-198Ruiz, P., Delmon, B., Koch, B., Castillo, R., Influence of preparation methods on the texture and structure of titania supported on silica (1994) J. Mater. Chem., 4, pp. 903-906Gil-Llambias, F.J., Escudey-Castro, A.M., Use of zero point charge measurements in determining the apparent surface coverage of molybdena in MoO<inf>3</inf>/(-Al<inf>2</inf>O<inf>3</inf> catalysts (1982) J. Chem. Soc. Chem. Commun., 47, pp. 8-479Ullah, S., Acuña, J.J.S., Pasa, A.A., Bilmes, S.A., Vela, M.E., Benitez, G., Photoactive layer-by-layer films of cellulose phosphate and titanium dioxide containing phosphotungstic acid (2013) Appl. Surf. Sci., 277, pp. 111-120Ewing, G., (2005) Analytical Instrumentation Handbook, , Marcel Dekker, New YorkLivage, J., Henry, M., Sanchez, C., Sol-gel chemistry of transition metal oxides (1988) Prog. Solid State Chem., 18, pp. 259-341Egerton, R.F., (2005) Physical Principles of Electron Microscopy, , Springer, US, Boston, MADjerdj, I., Tonejc, A.M., Structural investigations of nanocrystalline TiO<inf>2</inf> samples (2006) J. Alloys Compd., 413, pp. 159-174Leofanti, G., Padovan, M., Tozzola, G., Venturelli, B., Surface area and pore texture of catalysts (1998) Catal. Today, 41, pp. 207-219Regazzoni, A., Mandelbaum, P., Matsuyoshi, M., Schiller, S., Bilmes, S.A., Blesa, M., Adsorption and photooxidation of salicylic acid on titanium dioxide: a surface complexation description (1998) Langmuir, 14, p. 868Minero, C., Catozzo, F., Pelizzetti, E., Role of adsorption in photocatalyzed reactions of organic molecules in aqueous titania suspensions (1992) Langmuir, 8, pp. 481-486Friesen, D.A., Morello, L., Headley, J.V., Langford, C.H., Factors influencing relative efficiency in photo-oxidations of organic molecules by Cs3PW12O40 and TiO<inf>2</inf> colloidal photocatalysts (2000) J. Photochem. Photobiol. A Chem., 133, pp. 213-220Xu, Y., Langford, C., UV-or visible-light-induced degradation of X3B on TiO<inf>2</inf> nanoparticles: the influence of adsorption (2001) Langmuir, 17, pp. 897-902Gao, X., Wachs, I.E., Titania-silica as catalysts: molecular structural characteristics and physico-chemical properties (1999) Catal. Today, 51, pp. 233-254Murashkevich, A.N., Lavitskaya, A.S., Barannikova, T.I., Zharskii, I.M., Infrared absorption spectra and structure of TiO<inf>2</inf>-SiO<inf>2</inf> composites (2008) J. Appl. Spectrosc., 75, pp. 730-734Antcliff, K.L., Murphy, D.M., Griffiths, E., Giamello, E., The interaction of H<inf>2</inf>O<inf>2</inf> with exchanged titanium oxide systems (TS-1, TiO<inf>2</inf>, [Ti]-APO-5, Ti-ZSM-5), Phys (2003) Chem. Chem. Phys., 5, pp. 4306-4316Bohren, C.F., Huffman, D.R., (1998) Absorption and Scattering of Light by Small Particles, , Wiley-VCH Verlag GmbH, Weinheim, GermanyTompkins, H., McGahan, W., (1999) Spectroscopic Ellipsometry and Reflectometry: a User's Guide, , Wiley-Interscience, New YorkDjurisic, A.B., Li, E.H., Modeling the index of refraction of insulating solids with a modified lorentz oscillator model (1998) Appl. Opt., 37, pp. 5291-5297Brus, L.E., A simple model for the ionization potential, electron affinity, and aqueous redox potentials of small semiconductor crystallites (1983) J. Chem. Phys., 79Anpo, M., Shima, T., Kodama, S., Kubokawa, Y., Photocatalytic hydrogenation of CH<inf>3</inf>CCH with H<inf>2</inf>O on samll-particle TiO<inf>2</inf>: size quantization and reaction intermediates (1987) J. Phys. Chem., 91, pp. 4305-4310Lin, H., Huang, C., Li, W., Ni, C., Shah, S., Tseng, Y., Size dependency of nanocrystalline TiO<inf>2</inf> on its optical property and photocatalytic reactivity exemplified by 2-chlorophenol (2006) Appl. Catal. B Environ., 68, pp. 1-11Shen, Z.-Y., Li, L.-Y., Li, Y., Wang, C.-C., Fabrication of hydroxyl group modified monodispersed hybrid silica particles and the h-SiO<inf>2</inf>/TiO<inf>2</inf> core/shell microspheres as high performance photocatalyst for dye degradation (2011) J. Colloid Interface Sci., 354, pp. 196-201Li, X., Wu, X., He, G., Sun, J., Xiao, W., Tan, Y., Microspheroidization treatment of macroporous TiO<inf>2</inf> to enhance its recycling and prevent membrane fouling of photocatalysis - membrane system (2014) Chem. Eng. J., 251, pp. 58-68Pagel, D., Aggergation and deaggregation in TiO<inf>2</inf> (need be corrected) (2007) J. Phys. Chem. C, 111, pp. 4458-4464Hirano, M., Ota, K., Iwata, H., Formation of anatase (TiO<inf>2</inf>)/Silica (SiO<inf>2</inf>) composite nanoparticles with high phase stability of 1300°C from acidic solution by hydrolysis under hydrothermal condition (2004) Chem. Mater., 16, pp. 3725-3732Wang, Y., Chen, E., Lai, H., Lu, B., Hu, Z., Qin, X., Enhanced light scattering and photovoltaic performance for dye-sensitized solar cells by embedding submicron SiO<inf>2</inf>/TiO<inf>2</inf> core/shell particles in photoanode (2013) Ceram. Int., 39, pp. 5407-5413