Fundamentals and Advances of the Oxidant Peroxo Method (OPM) for the Synthesis of Transition Metal Oxides

The ability to produce phase pure and compositionally controlled nanomaterials at temperatures lower than the ones required by solid state reaction methods is one of the most important features in a solution-chemistry synthetic method. The sol–gel based methods usually use many of organic compounds throughout the synthetic process, which can be detrimental to certain applications, as high quantities of residual carbon can be found along the final product. The Oxidant Peroxo Method, usually known by the acronym OPM, is a solution-chemistry method based on the production of peroxo complexes with hydrogen peroxide and different transition metal ions at alkaline pH. The production of these peroxo complexes leads to an amorphous material that upon calcination produces phase pure transition metal oxides with controlled composition. One special feature of the OPM method is the total absence of the organic compounds during the synthesis, which avoids the presence of undesired pyrolyzed organic molecules mixed with the metal oxide product. Additionally, the absence of organic compounds produces an oxidizing atmosphere during the synthesis, yielding very reactive powders, facilitating the production highly dense ceramic pellets for electronic applications. The production of powders with surface containing peroxo groups, also, has been beneficial for increasing the photocatalytic activity of titanium-based compounds and for use as a precursor in the solid-state reactions, which considerably decreases the processing temperature. Since its inception and first publication, back in 2001, the OPM method has been successfully applied by different research groups worldwide to produce binary oxides, i.e. TiO2, tertiary oxides, PbTiO3, BaZrO3, and doped tertiary oxides Pb1−xLaTiO3. The variety of different metal oxides produced confirms the versatility of OPM method on yielding not only different compositions, but also different crystalline structures, like anatase, perovskite, sillenite, and spinel. Furthermore, the OPM method has yield metal oxides for many different applications, such as dielectric, optical, and photocatalytic. For instance, undoped Bi12TiO20 and Nb-doped Bi12(Ti1−xNbx)O20 were used as efficient photocatalysts for degradation of rhodamine B under ultraviolet and visible lights, presenting better activity than TiO2. In this chapter, the chemistry underlying the OPM method and the oxides most commonly prepared by this technique will be described, focusing how the method contributed to the advance of the synthetic, structural, and application aspects related to each one of these compounds. The future goals and applications of the method will be critically discussed. The authors hope this chapter can provide enough information to motivate a continuous dissemination of the OPM method, in view of its confirmed successful features and potential.