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SiO 2 -aerogel inverse opals were produced for the first time in supercritical carbon dioxide (scCO 2 ) with three-dimensional (3D) latex arrays as templates. The polymeric templates were reacted with tetraethyl orthosilicate in humidified scCO 2 at 40 °C and 85 bar. After calcination of the template, highly porous materials replicating the structure of the original template were obtained. Polystyrene latex particles decorated with different hydrophilic groups were organized in 3D ordered arrays and used as templates. Particles were impregnated with benzenesulfonic acid, which activates the condensation process of silica precursors. Scanning and transmission electron microscopy (SEM and TEM) images showed that the reaction in scCO 2 takes place only on the particle surface and that the octahedral and tetrahedral holes in the original fcc packing of latex spheres are empty. N 2 adsorption isotherms showed broad adsorptiondesorption loops characteristic of mesopores. Brunauer-Emmett-Teller (BET) surface areas are large and range from 270 to 594 m 2 /g, since these materials are structured aerogels produced directly in scCO 2 . Analysis of the desorption branch revealed the presence of an extremely large mesoporosity that is located in the macropore walls. The porosity of the materials obtained for each template is different. Furthermore, shrinkage of the network upon condensation in scCO 2 was small. The synthesis of inverse opals in scCO 2 overcomes some of the limitations of the liquid-phase techniques, being a faster method of synthesis and, at the same time, rendering materials of unique properties.

Then, the bands of the semiconductor particle become flat, and the flat-band condition will be established.Since the electrochemical potential of photogenerated holes is still very high at the flat-band condition, the holes more or less react with reductants faster than electrons even in the flat-band condition. Here we consider the case where further charge separation occurs from the semiconductor particle to the bulk of the solution. In such a case, true charge (electrons) further accumulate on the semiconductor particle, and, most possibly, the potential drop across the Helmholtz layer is changed to shift the band edges to the more negative, holding the bands flat. The particle potential will come into a steady state when ve = vh. If, on the contrary, another case occurs where a strong accumulation layer is formed in the semiconductor particle by holding the band edges pinned, the value of Vp still has meaning since, in any case, Vp represents the pseudo-Fermi level of electrons of the semiconductor particle under illumination.

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