Size-Controlled Synthesis Of Anatase And Rutile TiO₂ Nanoparticles

Titania dioxide is a polymorphic compound which has three phases: rutile, anatase, and brookite, of which, rutile is the most thermodynamically stable phase. Rutile TiO₂ has been traditionally used in pigment, plastic, construction, and cosmetic fields because of its good light-scattering and light-reflecting effect, nontoxicity, and chemical inertness even in strongly acidic or basic environment. It has been found that rutile TiO₂ exhibit high photocatalytic activity for decomposition of H₂S gas, photooxidation of water with Fe³⁺ as an electron acceptor, and high dielectric constant. Nanosized Anatase TiO₂ has been found useful in diverse applications, such as environmental cleaning and purification, photovoltaics, antifogging, self-cleaning surfaces, pigment, and cosmetic sunsreen emulsion, etc.A variety of methodologies for synthesizing nanosized TiO₂ have been investigated, such as oxidation of titanium tetrachloride in a modified diffusion flame reactor,crystallization in reverse micelles or in supercritical CO₂, photoassisted sol-gel method, polymer templating method, and hydrothermal method. Organic modifiers, such as hydroxyl group-,carboxylate group-,and amine group-containing organics or polymers, are widely used in synthesis of nanosized TiO₂ to regulate their final morphology and hence their properties. The basis of such methods is the employment of organics with different types of functional groups to produce a desired product with the required shapes and interface structures by the interaction of organic modifiers with crystal surface. Amongst the modifiers are carboxylate group-containing organics widely used in the synthesis of nanosized TiO₂. An unanswered question is how the carboxylate, hydroxyl, and the nonpolar groups affect the crystal...