Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

In the coming decade, the ability to sense and detect the state of biological systems and living organisms optically, electrically and magnetically will be radically transformed by developments in materials physics and chemistry. The emerging ability to control the patterns of matter on the nanometer length scale can be expected to lead to entirely new types of biological sensors. These new systems will be capable of sensing at the single-molecule level in living cells, and capable of parallel integration for detection of multiple signals, enabling a diversity of simultaneous experiments, as well as better crosschecks and controls.

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The use of nanocrystals in biological detection

Hollow micro-/nanostructures are of great interest in many current and emerging areas of technology. Perhaps the best-known example of the former is the use of fly-ash hollow particles generated from coal power plants as partial replacement for Portland cement, to produce concrete with enhanced strength and durability. This review is devoted to the progress made in the last decade in synthesis and applications of hollow micro-/nanostructures. We present a comprehensive overview of synthetic strategies for hollow structures. These strategies are broadly categorized into four themes, which include well-established approaches, such as conventional hard-templating and soft-templating methods, as well as newly emerging methods based on sacrificial templating and template-free synthesis. Success in each has inspired multiple variations that continue to drive the rapid evolution of the field. The Review therefore focuses on the fundamentals of each process, pointing out advantages and disadvantages where appropriate. Strategies for generating more complex hollow structures, such as rattle-type and nonspherical hollow structures, are also discussed. Applications of hollow structures in lithium batteries, catalysis and sensing, and biomedical applications are reviewed.

Hollow Micro-/Nanostructures: Synthesis and Applications**

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Materials whose dielectric constant varies spatially with submicrometer periodicity exhibit diffractive optical properties which are potentially valuable in a number of existing and emerging applications. Here, such systems are fabricated by exploiting the spontaneous crystallization of monodisperse silica spheres into close-packed arrays. By reliance on a vertical deposition technique to pack the spherical colloids into close-packed silica−air arrays, high quality samples can be prepared with thicknesses up to 50 μm. These samples are planar and thus suitable for optical characterization. Scanning electron microscopy (SEM) of these materials illustrates the close-packed ordering of the spherical colloids in planes parallel to the substrate; cross-sectional SEM micrographs of the arrays as well as optical methods are used to measure sample thickness and uniformity. Normal-incidence transmission spectra in the visible and near-infrared regions show distinct peaks due to diffraction from the colloidal layer...

Single-Crystal Colloidal Multilayers of Controlled Thickness

We report a nanoscale “lost-wax” method for forming colloids with size distributions around 5% and their corresponding colloidal crystals. Macroporous polymer templates are first prepared from a silica colloidal crystal. We then use the uniform and interconnected voids of the porous polymer to generate a wide variety of highly monodisperse inorganic, polymeric, and metallic solid and core-shell colloids, as well as hollow colloids with controllable shell thickness, as colloidal crystals. We can also uniformly deform the polymer template to alter colloidal shape and demonstrate the formation of elliptical particles with precisely controlled aspect ratios.

https://science.sciencemag.org/content/sci/291/5503/453.full.pdf

A Lost-Wax Approach to Monodisperse Colloids and Their Crystals

The fabrication of polymeric materials with ordered submicron-sized void structures is potentially valuable for many separation technologies as well as for emerging optical applications. This paper reports the preparation of macroporous polymer membranes with regular voids and the characterization of their diffractive optical properties. These materials are made using a colloidal crystal template of silica microspheres; the air between the spheres can be replaced by monomers that can be subsequently polymerized. The use of silica microspheres as templates makes it possible to employ chemical rather than thermal methods for template removal. For this reason, polymers as diverse as polyurethane and polystyrene can be used to create free- standing macroporous films, with thickness ranging from 0.5 to 50 Im. Scanning electron microscopy of these samples indicates a well-formed porous structure consisting of voids ranging in diameter from 200 to 400 nm. These large cavities are not isolated, but rather interconnected by a network of monodisperse smaller pores (d ) 50-130 nm) whose size can be controlled by varying the polymerization temperature. These membranes exhibit striking optical properties due to the periodic arrangement of air spheres in the polymer medium. Normal-incidence transmission measurements of these samples are compared to a theoretical model based on a scalar wave approximation. This model assumes an ordered structure of close-packed, three-dimensional air spheres. The good agreement between theory and experiment provides additional evidence of the long-range order of these samples.

Template-Directed Preparation of Macroporous Polymers with Oriented and Crystalline Arrays of Voids

Template-directed syntheses have been broadly applied to the creation of both mesoand macroporous ceramics1-4 and polymers5 The extension of such methods to metals is of particular interest Monolithic metals containing large internal surface areas could be used in numerous applications, ranging from electrochemical sensors6 to catalytic converters7 Moreover, recent work on lithographically prepared metallodielectric structures suggests metals with well-ordered porous networks would exhibit interesting photonic properties8 The adaptation of template methods to the formation of porous metals has been relatively limited9-12 Lyotropic liquid crystalline12 and anodic alumina10 have been used as templates to produce mesoporous (voids 50 nm) and high void volume porous films have not yet been reported In this work we describe a strategy for extending the general methodology of template-directed synthesis to the formation of porous metals These samples are three-dimensional highly ordered, free-standing macroporous metal films with interconnected spherical voids (200-400 nm) We use as templates single-crystal colloidal multilayers made by a vertical deposition technique13 The uniform deposition of metals into colloidal arrays is challenging for several reasons Existing examples of metal deposition into lyotropic liquid crystal12 and anodic alumina10 templates exploit flat and conductive surfaces to catalyze metal formation Such surfaces are not available in the interstitial regions of colloidal crystals which are narrow and relatively inaccessible Also, these templates as made are relatively fragile and easily disrupted by agitation or gas evolution during deposition To overcome these obstacles, a metal nanocrystal catalyzed electroless deposition technique14,15 has been developed First, colloidal silica is coated with a coupling agent,16 3-mercaptopropyltrimethoxysilane (3-MPTMS), which leaves a

Jane F. Bertone

Papers

Single-Crystal Colloidal Multilayers of Controlled Thickness

A Lost-Wax Approach to Monodisperse Colloids and Their Crystals

Template-Directed Preparation of Macroporous Polymers with Oriented and Crystalline Arrays of Voids

Preparation of Macroporous Metal Films from Colloidal Crystals

Synthesis of TiO2 Nanocrystals by Nonhydrolytic Solution-Based Reactions