Plasma-Enhanced Synthesis of Poly(allylamine)-Encapsulated Ruthenium Dye-Sensitized Titania Photocatalysts

Abstract

Photocatalysis for sustainable hydrogen production from water is becoming one of the core challenges for an efficient conversion of solar energy into a clean and renewable fuel, enabling the growth of a carbon-free hydrogen economy. In dye-sensitized TiO2, performances were obtained to be unstable over time due to weak covalent bonding of the molecule at the surface leading to detachment of the dye from the TiO2 surface and dye self-aggregation, with recombination of charge carriers at the dye/TiO2 interface being the second major factor for efficiency losses. Our strategy for improvement of the stability of the dye/TiO2 catalyst is the encapsulation of the assembly by a plasma-polymerized allylamine layer, providing a chemically and mechanically stable nanoconfinement of the dye in close proximity of the titania surface. The TiO2-layer was synthesized by a plasma-enhanced DC magnetron sputtering process on FTO substrates, resulting in homogeneous porous semiconductor layers. The stability of the PPAAm layer on the sputtered TiO2-layer as well as catalyst performance with regard to impairment of the charge transfer between the photoactive sites and the electrolyte was investigated; further XPS, electron microscopy, and UV/vis spectroscopy, as well as photoelectrochemical studies, were carried out for characterization of the new catalyst structure.

Photocatalytic Hydrogen Production with Copper Photosensitizer–Titanium Dioxide Composites

“…As a result, the typical absorption bands of the pure solid sensitizers around 420 nm are also present in the composites, and therefore, render them absorptive in the visible region. As previously shown, coating with polyallylamine has no influence on the absorption behavior, [12] but leads to a somewhat weaker absorbance. Additionally, the emission of 1 as powder originating from the deactivation of the MLCT excited states was detected (see Figure SI10 and 11).…”

“…The photocatalytic activity of the molecular and the immobilized sensitizers is compared. Furthermore, the influence of protecting polymer coatings, that is, plasma-polymerized allylamine (PPAAm) [12] on the stability and catalytic activity of the sensitized materials is assessed.…”

“…More details on the properties of PPAAm-coated titania nanostructures are given elsewhere. [12] The sensitization and interaction of the sulfonate linkers with the titanium dioxide support is evidenced by means of FTIR spectroscopy (see Figure 2). Characteristic asymmetric and symmetric stretching vibrations of the sulfonate groups are expected around 1180 and 1060 cm À1 , respectively.…”

“…These findings are in good agreement with those reported previously by Huang et al [11] Based on the photophysical analysis, the photosensitizers as well as their composites should be capable of producing hydrogen in the presence of visible light. Therefore, catalytic experiments were performed using [Fe 3 (CO) 12 ] as WRC and triethylamine (TEA) as sacrificial reductant (Figure 4 and Table 2).…”

Plasma‐Assisted Immobilization of a Phosphonium Salt and Its Use as a Catalyst in the Valorization of CO2

“…So far,t here are only al imited number of reports regarding the immobilization of catalysts by plasma techniques.F or example,K ruth et al encapsulated Ru dyes [11] and Ir dyes [12] with plasma polyallylamine (PPAAm) on TiO 2 .T he prepared stable TiO 2 /N 3 (Ru dye complex)/PPAAm catalysta ssemblies and encapsulated Ru sensitizer at the TiO 2 surfaces howed improved catalytic performance in visible-light-driven hydrogen evolution. Additionally,s ignificant enhancement of photoefficiency was observed with the PPAAm-encapsulatedIrdye/titania catalyst assemblies.…”