Synergistic Effect in Zinc Phthalocyanine—Nanoporous Gold Hybrid Materials for Enhanced Photocatalytic Oxidations

Steinebrunner Steinebrunner,Schnurpfeil Schnurpfeil,Wittstock Wittstock,Wichmann Wichmann,Wöhrle Wöhrle

doi:10.3390/catal9060555

Steinebrunner Steinebrunner, Schnurpfeil Schnurpfeil + Show 3 more

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https://doi.org/10.3390/catal9060555

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Journal: Catalysts	Publication Date: Jun 20, 2019
Citations: 11	License type: CC BY 4.0

Affiliation: University of Bremen

Abstract

Nanoporous gold (npAu) supports were prepared as disks and powders by corrosion of Au-Ag alloys. The npAu materials have pore sizes in the range of 40 nm as shown by scanning electron microscopy (SEM). The surface was modified by a self-assembled monolayer (SAM) with an azidohexylthioate and then functionalized by a zinc (II) phthalocyanine (ZnPc) derivative using “click chemistry”. By atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) the content of zinc was determined and the amount of immobilized ZnPc on npAu was calculated. Energy-dispersive X-ray (EDX) spectroscopy gave information about the spatial distribution of the ZnPc throughout the whole porous structure. NpAu and ZnPc are both absorbing light in the visible region, therefore, the heterogeneous hybrid systems were studied as photocatalysts for photooxidations using molecular oxygen. By irradiation of the hybrid system, singlet oxygen is formed, which was quantified using the photooxidation of 1,3-diphenylisobenzofuran (DPBF) as a selective singlet oxygen quencher. The illuminated surface area of the npAu-ZnPc hybrid system and the coverage of the ZnPc were optimized. The synergistic effect between the plasmon resonance of npAu and the photosensitizer ZnPc was shown by selective irradiation and excitation of only the phthalocyanine, the plasmon resonance of the npAu support and both absorption bands simultaneously, resulting in an enhanced photooxidation activity by nearly an order of magnitude.

Highlights

Plasmonic metal nanostructures exhibit a wide range of properties which are interesting for applications in optical devices, biomedicine and catalysis [1,2,3,4]
1 at %, which was confirmed by atomic absorption spectroscopy (AAS) and is in good agreement with previously reported results [24,25,26,27,28]
The pore size of a npAu disk prepared in this way is in the range of 40 nm throughout the sample measured on the surface and along the cross section of the npAu disk (Figures S1 and S2)

Summary

Introduction

Plasmonic metal nanostructures exhibit a wide range of properties which are interesting for applications in optical devices, biomedicine and catalysis [1,2,3,4]. Monolithic nanoporous gold (npAu) as a nanostructured semi-infinite thin film or disk material has recently attracted intense attention due to its unique three-dimensional bicontinuous nanostructures and unique properties such as high catalytic activity, ability as sensor and tuneable plasmonic resonance [6,7,8,9,10,11,12,13,14] Such porous nanostructures can be prepared by dealloying of a suitable Au alloy (typically Au-Ag or Au-Cu) using either concentrated nitric acid or electrochemical methods [15,16,17,18]. Localized surface plasmon resonance (LSPR) of npAu can be excited within the wavelength range of visible light with the main absorption at about λ~520 nm (Figure 1b) because the unit scale of the metal network is comparable with the mean free path of conduction electrons in the metal ligaments

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