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Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.
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Accessibility and Mechanical Stability of Nanoporous Zinc Oxide and Aluminum Oxide Coatings Synthesized via Infiltration of Polymer Templates
The conformal nanoporous inorganic coatings with accessible pores that are stable under applied thermal and mechanical stresses represent an important class of materials used in the design of sensors, optical coatings, and biomedical systems. Here, we synthesize porous AlOx and ZnO coatings by the sequential infiltration synthesis (SIS) of two types of polymers that enable the design of porous conformal coatings—polymers of intrinsic microporosity (PIM) and block co-polymer (BCP) templates. Using quartz crystal microbalance (QCM), we show that alumina precursors infiltrate both polymer templates four times more efficiently than zinc oxide precursors. Using the quartz crystal microbalance (QCM) technique, we provide a comprehensive study on the room temperature accessibility to water and ethanol of pores in block copolymers (BCPs) and porous polymer templates using polystyrene-block-poly-4-vinyl pyridine (PS75-b-P4VP25) and polymers of intrinsic microporosity (PIM-1), polymer templates modified by swelling, and porous inorganic coatings such as AlOx and ZnO synthesized by SIS using such templates. Importantly, we demonstrate that no structural damage occurs in inorganic nanoporous AlOx and ZnO coatings synthesized via infiltration of the polymer templates during the water freezing/melting cycling tests, suggesting excellent mechanical stability of the coatings, even though the hardness of the inorganic nanoporous coating is affected by the polymer and precursor selections. We show that the hardness of the coatings is further improved by their annealing at 900 °C for 1 h, though for all the cases except ZnO obtained using the BCP template, this annealing has a negligible effect on the porosity of the material, as is confirmed by the consistency in the optical characteristics. These findings unravel new potential for the materials being used across various environment and temperature conditions.
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- Award ID(s):
- 2045662
- PAR ID:
- 10486477
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Polymers
- Volume:
- 15
- Issue:
- 20
- ISSN:
- 2073-4360
- Page Range / eLocation ID:
- 4088
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Sequential infiltration synthesis (SIS) has emerged as a powerful technique to integrate inorganic materials into polymeric templates for fabricating functional hybrid and inorganic-only nanostructures. While several polymers, including self-assembled block copolymers (BCPs), have been widely used as templates for inorganic and hybrid oxide nanostructures, biocompatible polymers such as polycaprolactone (PCL) have not been explored for nanopatterning. In this work, we investigate SIS in polystyrene-block-polycaprolactone (PS-b-PCL) BCPs to demonstrate the feasibility of PCL as a guiding polymer for selective infiltration of Al₂O₃. Fourier transform infrared spectroscopy (FTIR) confirmed the strong interaction of TMA–H₂O precursors with the oxygen-containing functional groups of PCL, while scanning electron microscopy (SEM) revealed well-defined Al₂O₃ nanostructures after SIS and polymer removal. By varying the number of SIS cycles and processing temperatures, we observed systematic changes in the inorganic content and nanostructural fidelity, highlighting the tunability of the process. Notably, significant Al₂O₃ incorporation occurred during the first SIS cycle due to strong PCL–precursor interactions, even at temperatures as low as 60 °C, making the process both cost-effective and precise. These findings demonstrate that PCL is a promising guiding polymer for SIS, with potential to extend beyond conventional systems such as polymethylmethacrylate (PMMA). This work opens new opportunities for fabricating oxide nanostructures with applications in nanopatterning, dielectric coatings, and bio-related nanomaterials.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/polym15204088
