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search.filters.applied.f.access: openAccess × Author: Hollmann, Dirk × End date: 2019 × Start date: 2010 × Type: Text × Publisher: Basel : MDPI × WGL Institute: LIKAT ×

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    Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production
    (Basel : MDPI, 2018-1-29) Sivasankaran, Ramesh P.; Rockstroh, Nils; Hollmann, Dirk; Kreyenschulte, Carsten R.; Agostini, Giovanni; Lund, Henrik; Acharjya, Amitava; Rabeah, Jabor; Bentrup, Ursula; Junge, Henrik; Thomas, Arne; Brückner, Angelika
    Solar hydrogen production from water could be a sustainable and environmentally friendly alternative to fossil energy carriers, yet so far photocatalysts active and stable enough for large-scale applications are not available, calling for advanced research efforts. In this work, H2 evolution rates of up to 1968 and 5188 μmol h−1 g−1 were obtained from aqueous solutions of triethanolamine (TEOA) and oxalic acid (OA), respectively, by irradiating composites of AgIn5S8 (AIS), mesoporous C3N4 (CN, surface area >150 m2/g) and ≤2 wt.% in-situ photodeposited Pt nanoparticles (NPs) with UV-vis (≥300 nm) and pure visible light (≥420 nm). Structural properties and electron transport in these materials were analyzed by XRD, STEM-HAADF, XPS, UV-vis-DRS, ATR-IR, photoluminescence and in situ-EPR spectroscopy. Initial H2 formation rates were highest for Pt/CN, yet with TEOA this catalyst deactivated by inclusion of Pt NPs in the matrix of CN (most pronounced at λ ≥ 300 nm) while it remained active with OA, since in this case Pt NPs were enriched on the outermost surface of CN. In Pt/AIS-CN catalysts, Pt NPs were preferentially deposited on the surface of the AIS phase which prevents them from inclusion in the CN phase but reduces simultaneously the initial H2 evolution rate. This suggests that AIS hinders transport of separated electrons from the CN conduction band to Pt NPs but retains the latter accessible by protons to produce H2.
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    Criticial Assessment of the Photocatalytic Reduction of Cr(VI) over Au/TiO2
    (Basel : MDPI, 2018-12-3) Ngo, Anh Binh; Nguyen, Hong Lien; Hollmann, Dirk
    The purification of drinking water is one of the most urgent challenges in developing countries, for which the efficient removal of traces of heavy metals, e.g., Cr(IV), represents a key technology. This can be achieved via photocatalysis. In this study, we compare the performance of Au/TiO2 to bare TiO2 P25 catalysts. Furthermore, the influence of the sacrificial reagent citric acid under UV-Vis and Vis excitation was investigated and a detailed investigation of the catalysts before and after reaction was performed. During the photocatalytic reduction of Cr(IV) under acidic conditions, both leaching of Au, as well as absorption of Cr, occur, resulting in new catalyst systems obtained in situ.