Photocatalytic Template Removal by Non-Ozone-Generating UV Irradiation for the Fabrication of Well-Defined Mesoporous Inorganic Coatings

Abstract

The processing of mesoporous inorganic coatings typically requires a high-temperature calcination step to remove organic precursors that are essential during the material assembly. Lowering the fabrication energy costs and cutting back on the necessary resources would provide a greater scope for the deployment in applications such as architectural glass, optical components, photovoltaic cells, and energy storage, as well as further compatibilize substrates with low temperature stability. Organic removal methods based on UV–ozone treatment are increasing in popularity, but concerns remain regarding large-scale ozone generation and usage of mercury-containing UV lamps. To this end, we present a method that relies on non-ozone-generating UV radiation at 254 nm (UV254) and incorporation of small amounts of photocatalytic material in the formulation, here demonstrated with TiO2 nanocrystals. At concentrations as low as 5 wt % relative to the main inorganic aluminosilicate material, the TiO2 nanocrystals catalyze a “cold combustion” of the organic components under UV254 irradiation to reveal a porous inorganic network. Using block copolymer-based co-assembly in conjunction with photocatalytic template removal, we produce well-defined mesoporous inorganic thin films with controlled porosity and refractive index values, where the required processing time is governed by the amount of TiO2 loading. This approach provides an inexpensive, flexible, and environmentally friendly alternative to traditional organic removal techniques, such as UV–ozone degradation and thermal calcination.

Fractionation of block copolymers for pore size control and reduced dispersity in mesoporous inorganic thin films

“…Inorganic sol material and mesoporous inorganic aluminosilicate films were prepared as described elsewhere. 8,25 BCP samples were first dissolved in a toluene/1-butanol azeotrope solution before mixing with the inorganic sol in an organic/inorganic ratio of 2 : 8. All samples were spin-coated at 2000 rpm for 20 seconds and immediately annealed on a programmable hot plate using a ramp rate of 1°C per min to a final temperature of 130°C for 30 minutes.…”

“…22 In a subsequent step, the hybrid composite can be transformed into an ordered inverse opal-type mesoporous structure by either thermal calcination, 22 or various physical or chemical treatments including UV-ozone degradation, 23 oxygen etching 24 or photocatalytic reactions. 25 The use of BCP as structure-directing agent offers reliable control over porosity and pore size. While porosity is commonly tuned by the mixing ratio between organic and inorganic precursor, the pore size is predominantly determined by the molecular weight of the sacrificial block forming the micelle core, 26,27 leading to final pore dimensions in the range of 5 to 50 nm.…”

Fractionation of Block Copolymers for Pore Size Control and Reduced Dispersity in Mesoporous Inorganic Thin Films

“…Inorganic sol material and mesoporous inorganic aluminosilicate films were prepared as described elsewhere. [7,22] BCP samples were first dissolved in a toluene/1-butanol azeotrope solution before mixing with the inorganic sol in an organic/inorganic ratio of 2:8. All samples were spin-coated at 2000 rpm for 20 seconds and immediately annealed on a programmable hot plate using a ramp rate of 1°C per min to a final temperature of 130 °C for 30 minutes.…”

“…[19] In a subsequent step, the hybrid composite can be transformed into an ordered inverse opal-type mesoporous structure by either thermal calcination, [19] or different physical or chemical treatments including UV-ozone degradation, [20] oxygen etching [21] or photocatalytic reactions. [22] The use of BCP as structure-directing agent offers reliable control over porosity and pore size.…”

Bio‐Inspired Silica Films Combining Block Copolymers Self‐Assembly and Soft Chemistry: Paving the Way toward Artificial Exosqueleton of Seawater Diatoms

“…Reid et al. [ 47 ] realized a photocatalytic template removal by non‐ozone‐generating UV‐irradiation to avoid the creation of ozone and the use of mercury in UV lamps due to the UVO treatment. They studied a poly(isobutylene)‐ b ‐poly(ethylene oxide) (PIB‐ b ‐PEO) copolymer as structure directing agent.…”