Scaling-up of mesoporous silica films via an eco-efficient UV processing method. Part 2: Photoinduced calcination

Abstract

We describe a fast photocalcination process to prepare highly ordered silica mesoporous films through the use of a low-pressure amalgam arc (λ: 185/254 nm). Because radiant power is 2–3 times higher than conventional low-pressure UV lamps, the elimination of the PEO-b-PPO-b-PEO copolymer template in the 2D hexagonal hybrid film has been completed within 50 min, without damage to the mesostructure. The degradation kinetics are impacted by film thickness and irradiance, but hardly copolymer concentration. Compared to thermocalcination, a narrower pore size distribution and lower energy consumption have been found. Photodegradation mostly originates from a photoablation mechanism induced by radiation at 185 nm, while oxidation due to photogenerated reactive oxygen species plays a minor role. Photocalcination has been combined with an initial photoinduced mesostructuration (detailed in Part 1: Microporous Mesoporous Mater., 257 (2017) 42–50), resulting in an unprecedented “all UV” method to mesoporous silica films. The final process relies on dual wavelength photoactivation: UVB to form the hybrid copolymer/silica network, a flash intermediate thermal consolidation, and UVC to decompose the copolymer chains.