A non-template hydrothermal route to uniform 3D macroporous films with switchable optical properties

Here we report the direct synthesis of long-range uniform 3D macroporous film on the surface of glass via a non-template strategy by reacting silica with a mixture solution of HCl and H2O2 under hydrothermal conditions. The size of macropores can be tuned from 1 μm to 7 μm by changing the hydrothermal temperature. Followed by the impregnation or release of water, the 3D porous films showed a high-contrast optical switchable property. The maximum optical transmittance modulation of these 3D porous films was up to 50% over the visible and near IR wavelength range. Furthermore, liquid-induced optical switching device were designed as a sandwich structure. The average transmittance of the device was varied between 62.3% (from 350 to 1100 nm) at the transparent state and 13.2% (from 350 to 1100 nm) at the opaque state, respectively. Such a wide modulation range of optical transmittance is suitable for application of this porous film to energy saving smart windows.