RSC Advances
Paper
change in pore size is coherent with a change in the specic
surface area, since smaller pore sizes result in a higher available
Conflicts of interest
surface area that has to be considered during the functionali- There are no conicts of interest to declare.
zation with the photosensitizer. The UV-Vis and EDX measure-
ments both conrmed the expected increase in immobilized Zn
content for the samples bearing smaller pores (Fig. 5b and
Acknowledgements
Table 1).
We gratefully acknowledge the experimental support of Petra
The photocatalytic experiments clearly show this trend Witte (Department of Historic Geology and Paleontology,
resulting in a higher DPBF conversion, based on a higher University of Bremen, Bremen, Germany) during the SEM and
amount of sensitized singlet oxygen, with increasing ZnPc EDX measurements as well as the lab technician trainees
coverage (Fig. S4,† Fig. 6b). Assuming a constant immobiliza- Rebecca Siemering, Jasmin Richter and Rieke Norden for their
tion fraction of the ZnPc, the increase in singlet oxygen sensi- contribution within the synthesis of compounds 1 and 2. We
tization should be proportional to the calculated specic also acknowledge the discussion of the manuscript with Prof.
surface area. The plot of the maximum DPBF conversion aer Marcus B ¨a umer (Institute of Applied and Physical Chemistry,
an irradiation time of 20 min against the specic surface area of University of Bremen, Bremen, Germany). The project was
the used hybrid material shows the linear dependency of the funded by Deutsche Forschungsgemeinscha (DFG) within the
activity to the surface area for all samples with pore sizes grants WI 4497/3-1 and WO 237/42-1.
between 14 and 50 nm. Only the sample with a pore size below
1
4 nm shows a signicant deviation from this trend, which is
References
ascribed to the diffusion limitation at small pore sizes. Except
for this one particular sample, no limitation by diffusion was
observed (Fig. 6c). In addition, the effect of higher ZnPc
immobilization completely dominates any effect of plasmonic
shi that should contrarily increase the activity for samples
with larger pores and therefore smaller surface areas. Trans-
ferring those results to the hybrid systems based on npAu
powder described in our previous study, the reduction of the
pore sizes to 15 nm could be a promising strategy for optimi-
zation of the overall activity. Those powder hybrid systems
seem to be the best solution for batch reactors, whereas the
npAu foils represent a promising material used as catalytic
coatings in ow reactors, making them also an interesting
material for industrial applications.
1 P. N. Ciesielski, A. M. Scott, C. J. Faulkner, B. J. Berron,
D. E. Cliffel and G. K. Jennings, ACS Nano, 2008, 2, 2465–
2472.
2 F. Jia, C. Yu, Z. Ai and L. Zhang, Chem. Mater., 2007, 19, 3648–
3653.
3 X. Ge, R. Wang, P. Liu and Y. Ding, Chem. Mater., 2007, 19,
5827–5829.
4 Z. Liu and P. C. Searson, J. Phys. Chem. B, 2006, 110, 4318–
4322.
5 F. Jia, C. Yu, K. Deng and L. Zhang, J. Phys. Chem. C, 2007,
111, 8424–8431.
6 J. Zhang, P. Liu, H. Ma and Y. Ding, J. Phys. Chem. C, 2007,
111, 10382–10388.
25
7
8
V. Zielasek, B. J u¨ rgens, C. Schulz, J. Biener, M. M. Biener,
A. V. Hamza and M. B ¨a umer, Angew. Chem., Int. Ed., 2006,
45, 8241–8244.
Conclusions
R. Zeis, T. Lei, K. Sieradzki, J. Snyder and J. Erlebacher, J.
Catal., 2008, 253, 132–138.
This study is, best to our knowledge, the rst example of npAu
foils functionalized with a photosensitizer and the usage of
9 C. Xu, X. Xu, J. Su and Y. Ding, J. Catal., 2007, 252, 243–248.
those new hybrid materials as photocatalytic coatings for 10 R. Zeis, A. Mathur, G. Fritz, J. Lee and J. Erlebacher, J. Power
singlet oxygen sensitization. Hybrid materials were prepared on Sources, 2007, 165, 65–72.
npAu foils with pore sizes between 9–50 nm and an increasing 11 J. Erlebacher, M. J. Aziz, A. Karma, N. Dimitrov and
amount of immobilized photosensitizer was found in both, UV- K. Sieradzki, Nature, 2001, 410, 450.
Vis and EDX spectroscopic measurements for npAu supports 12 A. Wittstock, J. Biener, J. Erlebacher and M. B ¨a umer,
with smaller pore sizes and accordingly larger specic surface
areas. The photocatalytic activity of singlet oxygen sensitization
was shown to be exclusively dominated by the amount of
Nanoporous Gold: From an Ancient Technology to a High-
Tech Material, RSC Publishing, RSC Nanoscience and
Nanotechnology, 2012.
immobilized sensitizer suppressing every indication of 13 A. Wittstock, A. Wichmann and M. B ¨a umer, ACS Catal.,
changing interaction due to the shi of the corresponding 2012, 2, 2199–2215.
surface plasmon resonance of npAu with altering pore size. In 14 A. Wittstock, A. Wichmann, J. Biener and M. B ¨a umer,
addition, the photocatalytic results clearly conrm that mass Faraday Discuss., 2011, 152, 87–98.
transport and diffusion limitation are becoming predominant 15 J. Shi, C. Mahr, M. M. Murshed, T. M. Gesing, A. Rosenauer,
for the sample with pore sizes below 14 nm. Thus, the hybrid
material on a npAu support with dened pore sizes of around
M. Baumer and A. Wittstock, Phys. Chem. Chem. Phys., 2017,
19, 8880–8888.
15 nm shows the highest singlet oxygen sensitization activity 16 A. Lackmann, C. Mahr, M. Schowalter, L. Fitzek,
due to the largest specic surface area and maximum sensitizer
coverage above the diffusion limited regime.
J. Weissm u¨ ller, A. Rosenauer and A. Wittstock, J. Catal.,
2017, 353, 99–106.
58 | RSC Adv., 2020, 10, 53–59
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