Hierarchically porous ceramics with surface functionalities structured by vat photopolymerization

Abstract

Polymer-derived ceramics produced by vat photopolymerization represent a novel approach for fabricating complex monolithic structures with hierarchical porosity. In this work, preceramic polysiloxanes are combined with a secondary, sacrificial polymer compound and shaped via vat photopolymerization, during which photopolymerization-induced phase separation occurs. Through subsequent pyrolysis, ceramic SiOC materials can be obtained. As a potential use case for the hierarchically porous materials developed in this work, water purification via the removal of organic or inorganic contaminations was envisioned.By choice of polysiloxane compounds of different carbon content, pyrolysis temperature, and complexity of the monolith geometry, functionalities such as hydrophilicity, pore size, permeability, and carbon content can be manipulated. Here, the functional group present on the polysiloxane backbone polysiloxanes was varied between a phenyl-/methyl group, to manipulate the amount of carbon introduced into the system. The pyrolysis temperature was varied between 600-800 °C, whereby the polymer-to-ceramic conversion is only fully completed at the upper end of the temperature range. In terms of part geometry, both cylinders and more complex scaffold structures could be fabricated. Methylene blue was chosen as an adsorbent to observe the potential for water purification. The concentration of the dye was measured via UV-VIS spectroscopy.With increasing pyrolysis temperatures, the hydrophilicity of the surfaces, as well as overall permeability, were found to increase, while carbon content decreased. Pore size distribution was found to remain constant. By variation of different ratios of the polysiloxane derivates, carbon content in the final material could be controlled between 27 and 47 %, and the modal pore size ranged from 0.05 to 0.5 μm. At a pyrolysis temperature of 800 °C, increasing complexity, and increasing carbon content, adsorption capacity values of up to 3.85 mg·g-1 could be achieved.The system established in this work shows possibilities for future application in specific wastewater removal scenarios. However, at present, the adsorption values, not coupled with other removal techniques, do not show adequate results for standalone usage.