Polymer-derived mesoporous SiOC/ZnO nanocomposite for the purification of water contaminated with organic dyes

Polymer-derived mesoporous SiOC/ZnO nanocomposite for water decontamination was prepared by a simple mechanical incorporation of ZnO nanopowders into the commercial vinyl-functionalized polysiloxane followed by pyrolysis at 700 °C for 2 h. The as-prepared nanocomposite was characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physisorption measurement and UV–vis spectroscopy. The effects of pyrolysis temperature (700–900 °C) and ZnO content (0–20 wt.%) on the formation of SiOC/ZnO nanocomposite were investigated. The polymer-to-ceramic transformation of pure polymer resulted in the formation of an amorphous microporous SiOC ceramic (pore size <2 nm). With the incorporation of ZnO nanopowders into the polymer, the microporosity-to-mesoporosity transformation was observed for all the nanocomposites regardless of pyrolysis temperature and ZnO content. The SiOC ceramic obtained at 700 °C indicated the highest specific surface area (SBET = 398 m2/g) value with the pore size of <2 nm while the SiOC/20 wt.% ZnO nanocomposite prepared at 700 °C showed the SBET value of 220 m2/g with the pore size of ∼4 nm. The adsorption and photocatalytic properties of the as-prepared samples were evaluated by measuring the decrease in concentration of methylene blue (MB) after adsorption in the dark and photochemical reaction under UV irradiation, respectively. The lowest MB adsorption was noted for SiOC ceramic, and MB adsorption by SiOC/ZnO nanocomposite monotonically decreased with the increase in the ZnO content. The photocatalytic activity of porous SiOC ceramic for the degradation of MB is enhanced significantly by the incorporation of ZnO nanopowders into the SiOC matrix.

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► ZnO embedded in the SiOC matrix remains chemically stable up to 800 °C.
► Microporous SiOC ceramic transforms to mesoporous SiOC/ZnO nanocomposite.
► Increase in pyrolysis temperature and ZnO content decreases the SBET value.
► Microporous SiOC ceramic presents the lowest MB adsorption capacity.
► Increase in the ZnO content increases the MB decomposition rate constant.