Inverse opals structures, which are also called as 3DOM materials in the catalysis science community, are the optimized photonic crystals. Since inverse opals photonic crystals have two important features, photonic band gaps and high specific surface areas, currently their applications have been extended to photo(electro)chemical processes, such as photovoltaic solar cells, DSSCs, photocatalyses, etc.The usages of inverse opals have largely improved the efficiencies of both the utilities of solar energies and the catalyses in above-metioned processes. Transition metal oxides (TMOs) are the oxide semiconductor materials with high refractive index and little light absorptions in the visible wavelength range. Therefore they are suitable candidate materials for preparing high-quality inverse opals photonic crystals. A variety of preparation methods of TMOs inverse opals, for instance, sol-gel, metal salts pyrolysis, liquid phase deposition, electrochemical deposition, electrophoresis, chemical vapor deposition (CVD), atomic layer deposition (ALD) and so on, have been developed. These synthesis processes have their unique advantages and also inherent disadvantages. No matter which technique is employed, obtaining an inverse opal material with big area, single crystal structure, and controlled layer number, would be a great challenge. This paper, from the views of preparations, properties and applications in DSSCs and photocatalyses, reviews the progress in the TMOs inverse opals.

Contents
1 Introduction
2 Characteristics of TMOs
3 Preparations of TMOs inverse opals
3.1 A brief introduction to preparation process
3.2 Liquid phase method
3.3 Vapor phase method
4 Applications of TMOs inverse opals in photo(electro)chemical processes
4.1 DSSCs
4.2 Photocatalytic degradation
4.3 Photocatalytic water splitting
5 Works of authors group in this field
6 Summary and outlook