Methods for synthesis of zinc oxide hydrosols by peptization and condensation were developed. The basic colloid-chemical properties of the sols were determined: electrokinetic properties, size and phase composition of particles, and stability of hydrosols against introduction of electrolytes. The possibility of obtaining antibacterial and UV-protecting cosmetic preparations from the hydrosols obtained was demonstrated.Owing to the combination of diverse physical and chemical properties (high melting point and heat conductivity, ability to effectively absorb UV light, high photosensitivity, largely unique piezo-and pyroeffects, rather strong luminescence, etc.), zinc oxide ZnO is extensively used in a wide variety of industries. In particular, introduction of zinc oxide into cosmetic creams and gels makes them sunlight-protective and antibacterial [1]. The efficiency of their action largely depends not only on the concentration of the active substance, zinc oxide, but also on the size of its particles, their modification, and degree of polydispersity. In particular, the higher the dispersity of the particles, the more effective a preparation on their basis [2]. This means that the task of obtaining as fine particles of this oxide as possible is a matter of current interest.Here we demonstrate the possibility of synthesizing highly dispersed zinc oxide by the sol3gel method. This technique was chosen because it can yield nanomaterials with controlled polydispersity and prescribed particle size.We chose zinc nitrate as a precursor owing to its ready availability and nontoxicity. It should be noted that synthesis of nanodispersed ZnO by the sol3gel method has already been described in the literature [3,4], but the synthesis was performed from other materials (zinc alkoxides or organometallic compounds), whose use in cosmetology is prohibited. As for other ways to obtain zinc oxide, which are not based on the sol3gel technology, they can also be found in the literature, but are rather complicated and exotic (decomposition in an electric arc, laser evaporation of a target, etc. [5,6]). In view of the aforesaid, we suggest a rather easy procedure for preparing highly dispersed ZnO (in the form of a sol) by hydrolysis of Zn(NO 3 ) 2 .
EXPERIMENTALThe hydrosol was synthesized by two methods, peptization and condensation. The concentration of all the sols was determined gravimetrically, both in a sol itself and in the ultrafiltrate obtained from the sol. The ultrafiltration was done in a standard cell equipped with polysulfone membranes. The size of sol particles was monitored by photon-correlation spectroscopy (PCS), using the known procedure [7]. The phase composition of sol particles was determined by X-ray diffraction analysis on a DRON-3 diffractometer with CuK a radiation (1.54051 A).In the peptization method, a hydroxide freshly precipitated from a nitrate solution with ammonia was washed with distilled water and then peptized either with an electrolyte (zinc nitrate) solution or with dilute nitric acid. It should b...
