Abstract
Recently, carbon spherogels have been introduced as a novel monolithic aerogel composed of hollow spheres. This material is conveniently obtained via polystyrene (PS) sphere templating. In the present study, we apply a water-soluble titania precursor (titanium(IV) bis(ammonium lactate) to the aqueous sol-gel synthesis based on resorcinol-formaldehyde (RF) to effectively encapsulate titania. In this way, a very high mass loading of up to 59 mass% of titania can be confined strictly to the inside of the hollow carbon spheres. In the final synthesis step, carbonization at 800 °C has three simultaneous effects: Transformation of the RF coating on PS into microporous carbon, PS template removal by decomposition, and formation of titania due to precursor dissociation. A deliberate tuning of the microporous carbon shell, accessibility of the titania, titania amount, and titania's polymorph is further demonstrated by thermal treatment under a carbon dioxide atmosphere. In contrast to non-tuned or TiC-containing carbon spherogels, CO 2 activation of the composites results in a three orders of magnitude rise of their photocatalytic activity towards hydrogen evolution reaction, which we evaluate using flow and batch reactors. We further show that this effect is related to the partial etching of the carbon shell, which renders the TiO 2 surface accessible to the reactants in the solution and allows for an efficient hole scavenging. Given the simplicity of the hybrid carbon spherogel (HCS) composite fabrication, the high degree of control of their morphological characteristics, and the striking effects of CO 2-activation on performance, we believe that our results will contribute to the development of similar carbon-inorganic composites.
Originalsprache | Englisch |
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Aufsatznummer | Volume 202, Part 1 |
Seiten (von - bis) | 487-494 |
Seitenumfang | 8 |
Fachzeitschrift | Carbon |
Jahrgang | 202 |
Ausgabenummer | Volume 202, Part 1 |
DOIs | |
Publikationsstatus | Veröffentlicht - 15 Jan. 2023 |
Bibliographische Notiz
Funding Information:This research was financially supported by the Salzburg Center for Smart Materials ( P1727558-IWB01 ), which is funded by the European Funds for Regional Development ( EFRE ) and the Austrian Wirtschaftsservice ( AWS ). M.S. is grateful for receiving the DOC Fellowship of the Austrian Academy of Sciences (ÖAW). Moreover, the authors acknowledge that the JEOL JEM F200 TEM instrument was funded by Interreg Österreich-Bayern 2014–2020 Programm- AB29 “Synthese, Charakterisierung und technologische Fertigungssätze für den Leichtbau” n2m “(nano-to-macro)”. The INM author thanks Eduard Arzt for his continuing support. AC and SM acknowledge research funding by the Austrian Science Fund ( FWF ) P32801–N . Furthermore, the authors acknowledge the financial support for the DXR2 Raman microscope provided by the European Regional Development Fund and Interreg V-A Italy Austria 2014–2020 through the Interreg Italy-Austria project ITAT 1023 InCIMa “Smart Characterization of Intelligent Materials” and the Interreg Italy-Austria project ITAT1059 InCIMa4 for Science and SMEs project.
Funding Information:
In addition to the increased surface area, another important feature of the CO2 activation is the possibility of avoiding the TiO2-to-TiC transition, thus stabilizing the TiO2 phase either as anatase and/or rutile polymorph. The Raman spectra (Fig. 5D) confirmed for all HCS CO2 samples that the nature of the carbon shell is undisturbed by the CO2 processing as well as the TiO2 content as displayed by the typical coeval appearance of D-mode (∼1345 cm−1) and G-mode (∼1597 cm−1) signals, which are distinctive bands of disordered, sp2-hybridized carbon materials (Supporting Information, Table S1) [39]. All HCS CO2 samples feature a peak area ratio (AD/AG) of approximately 2.5 and thus reveal an incomplete crystalline characteristic with a large contribution of amorphous carbon, similar to other resol-based carbon aerogels [39]. Additionally, the disordered carbon structure is also marked by a broadening of the D-band and G-band, which were evaluated by cumulative fitting after deconvolution into five bands, namely D, D*, D**, G, and D’ (Supporting Information, Fig. S9) [40,41]. The overlapping of the D' peak with the G peak, and the presence of the D peak is a typical signature of disorder and defects in graphitic carbon materials. The four Raman modes in the range of 150–650 cm−1 verify the presence of titania (predominantly anatase; Supporting Information, Table S2) in all samples [30,42].This research was financially supported by the Salzburg Center for Smart Materials (P1727558-IWB01), which is funded by the European Funds for Regional Development (EFRE) and the Austrian Wirtschaftsservice (AWS). M.S. is grateful for receiving the DOC Fellowship of the Austrian Academy of Sciences (ÖAW). Moreover, the authors acknowledge that the JEOL JEM F200 TEM instrument was funded by Interreg Österreich-Bayern 2014–2020 Programm- AB29 “Synthese, Charakterisierung und technologische Fertigungssätze für den Leichtbau” n2m “(nano-to-macro)”. The INM author thanks Eduard Arzt for his continuing support. AC and SM acknowledge research funding by the Austrian Science Fund (FWF) P32801–N. Furthermore, the authors acknowledge the financial support for the DXR2 Raman microscope provided by the European Regional Development Fund and Interreg V-A Italy Austria 2014–2020 through the Interreg Italy-Austria project ITAT 1023 InCIMa “Smart Characterization of Intelligent Materials” and the Interreg Italy-Austria projectITAT1059 InCIMa4 for Science and SMEs project.
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