Multistep Coating of Thick Titania Layers on Monodisperse Silica Nanospheres

Guo, Xuan; Dong, Peng

doi:10.1021/la990220u

Cited by 85 publications

(55 citation statements)

References 5 publications

(19 reference statements)

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“…Investigation of coating titanium dioxide on silica spheres which can serve as high surface area supports has been reported [26][27][28][29][30][31][32][33]. Li et al [26] prepared monodisperse SiO 2 /TiO 2 /SiO 2 multiply coated submicrospheres with nearly monodisperse silica submicrospheres as cores, thick titania layers, and thin silica to increase the refractive index of complex submicrospheres while keeping their near monodispersity and perfect surface properties.…”

Section: Introductionmentioning

confidence: 99%

UV-Absorption and Silica/Titania Colloids Using a Core–Shell Approach

Zhou

Heinz

Soucek

et al. 2010

Silicon

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Metal-oxo-colloids have been prepared using tetraethoxysilane (TEOS) oligomers with titanium tetra-ipropoxide (TIP) or titanium (di-i-propoxide) bis(acetylacetonate) (TIA) precursors. Transmission electron microscopy (TEM), FTIR, UV-Vis, and photoluminescence spectroscopy were used to investigate the composition, the size, and optical properties of the Si/Ti core-shell colloids. The presence of hetero-bonded silicate structure (Si-O-Ti) was indicated by FTIR spectroscopy. The size of Si/TIP system ranged from 55 to 120 nm and Si/TIA system ranged from 220 to 250 nm. The TEM data indicated that the size of colloids can be controlled by the TIP or TIA content. The Si/ Ti system exhibited strong absorption in the UV-range, yet had excellent optical transmittance in the visible range. The Si/Ti systems exhibited a photoluminescence emission at 329 nm.

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Section: Introductionmentioning

confidence: 99%

UV-Absorption and Silica/Titania Colloids Using a Core–Shell Approach

Zhou

Heinz

Soucek

et al. 2010

Silicon

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“…[4,11,50±76] The inorganic coatings prepared using these approaches include silica, [4,11,50±64,67±72,74] yttrium basic carbonate, [54] titania, [65,66,73] titanium nitride, [75] and zirconia. [76] Early work focused on the coating of titania microparticles with silica layers; however, significant particle clumping and coalescence took place during silica deposition.…”

Section: Precipitation and Surface Reactionsmentioning

confidence: 99%

“…By repeating this process several times, the thickness of titania layers on silica microspheres could be increased to 46 nm. [66] In a novel two-step silica-coating process comprising a sol±gel step followed by a dense liquid coating exposure, maghemite surfaces were coated with silica, affording a magnetic nanocomposite. [67] In the aforementioned inorganic coating methods, the size and quantity of the core particles as well as the relative ratios of the reactants (e.g., alkoxide, organic solvent, and water) considerably influence the quality and thickness of the coating.…”

Section: Precipitation and Surface Reactionsmentioning

confidence: 99%

Nanoengineering of Particle Surfaces

2001

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The creation of core–shell particles is attracting a great deal of interest because of the diverse applicability of these colloidal particles; e.g., as building blocks for photonic crystals, in multi‐enzyme biocatalysis, and in drug delivery. This review presents the state‐of‐the‐art in strategies for engineering particle surfaces, such as the layer‐by‐layer deposition process (see Figure), which allows fine control over shell thickness and composition.

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“…Most sol-gel coating processes reported in the literature are batch or semibatch processes, where titania coating thickness is gradually increased in several cyclic steps involving alkoxide addition, layer growth, particle separation, washing and re-suspension. [18,22] Frequent batch-to-batch product variations adversely affect reproducibility.[23] The quality and average size of the synthesized particles in the batch process can strongly depend on factors that are difficult to control, such as local temperature and concentration fluctuations, rate of reactant addition and stirring speed. Mechanical stirring, typically used for micromixing, can cause undesired shear-induced agglomeration and shape-distortion.…”

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confidence: 99%

Microfluidic Synthesis of Titania Shells on Colloidal Silica

2007

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Core-shell colloidal materials with tailored structural, electronic, photonic and chemical properties have a wide range of applications including coatings, pigments, electronics, catalysis, separations and diagnostics.[1] Typical particle cores are polymeric (e.g., polystyrene), [2] inorganic [3] (e.g., silica) or metallic [4] (e.g., gold) in size ranges between 2 nm to 10 lm. Titania-silica core-shell particles in the sub-micron size range are of particular interest for several applications, including catalysis, [5] pigments (as whiteners) [6] and imaging materials. [7] Microfluidic synthesis schemes, when combined with segmented flow for fast mixing and well defined residence time distribution RTD), produce cores with precisely controlled and narrow size distribution. [8][9][10][11][12] Here we extend this approach to a multi-step addition microfluidic system for growth of well defined shell coatings without complications of secondary nucleation. Photolithography-based microfabrication enables microfluidic designs that provide uniform addition through periodically spaced side inlets along the length of synthesis channel. This procedure is functionally equivalent to slow dropwise addition in conventional batch synthesis with the added advantages of control and continuous processing inherent to microfluidic synthesis. We specifically demonstrate coating colloidal silica core particles with titania layers of tunable thickness in a one-step, continuous flow process through controlled hydrolysis of titanium tetraethoxide (TEOT). Several methods have been reported for titania-coated-silica synthesis, but many of these batch processes suffer from difficulties in controlling overcoat thickness, avoiding secondary nucleation and aggregation, and maintaining a narrow particle size distribution. Silica particles were coated with titania layers of varying thicknesses by aging titanyl sulfate (TiOSO 4 ) in the presence of silica particles. [6,13,14] Thick, irregular layers were obtained via a multi-step coating process that involved repeated filtration and redispersion cycles. Titanium n-butoxide hydrolysis in tetrahydrofuran yielded monolayer coatings on silica particles.[5] Thicker coatings (< 7 nm) were obtained by the hydrolysis of titanium n-butoxide in ethanol. [15,16] Titanium tetraethoxide (TEOT) was also used as a precursor to obtain thick (> 50 nm) coatings. [17,18] Other methods to synthesize titania-silica particles include the use of polyelectrolyte-coated silica spheres as templates for sol-gel reactions, [19] and the deposition of alternating coatings of cationic polyelectrolytes and anionic titania nanosheets on the surface of silica.[20]The titanium alkoxide precursors used in sol-gel coating are highly sensitive to the presence of water, readily hydrolyzing and condensing, [21] which makes it difficult to control thickness and uniformity of the coating process as well as to avoid nucleation of secondary titania particles and aggregation of cores. In order to circumvent these complications, low alkoxide and...

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Multistep Coating of Thick Titania Layers on Monodisperse Silica Nanospheres

Cited by 85 publications

References 5 publications

UV-Absorption and Silica/Titania Colloids Using a Core–Shell Approach

UV-Absorption and Silica/Titania Colloids Using a Core–Shell Approach

Nanoengineering of Particle Surfaces

Microfluidic Synthesis of Titania Shells on Colloidal Silica

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