Supporting Information
Down-conversion Photoluminescence Sensitizing Plasmonic Silver Nanoparticles
on ZnO nanorods to Generate Hydrogen by Water Splitting Photochemistry
Po-Yen Kunga, Li-Wen Huanga, Tin-Wei Shena, Wen-Lin Wanga, Yen-Hsun Sua,
Melody I. Linb
a
Department of Materials Science and Engineering, National Cheng Kung University
b
Department of Physics, University of California Berkeley, CA, USA
S1. Experimental
S1.1 Preparation of ZnO nanorods on indium tin oxide (ITO) as the anode.
The first step was to clean the ITO glass and carry out surface modifications. The
ITO glasses were thus soaked in solution (𝑁𝐻4 𝑂𝐻：𝐻2 𝑂2：𝐻2 𝑂=1：1：5) for 12 hr.
The ZnO nanorod arrays were synthesized from an aqueous growth solution by a
two-step process. First, a seed layer was added to the ITO. The seed solution was
prepared by dissolving equimolar (0.004 M) zinc acetate ( 𝑍𝑛(𝐶𝐻3 𝐶𝑂𝑂)2 and
hexamethylenetetramine (𝐶6 𝐻12 𝑁4 ) in deionized water. Zinc acetate (𝑍𝑛(𝐶𝐻3 𝐶𝑂𝑂)2 ,
0.01 M) and hexamethylenetetramine (𝐶6 𝐻12 𝑁4 , 0.01 M) were dissolved in 400 ml
of deionized water at room temperature, which was then heated to 80 °C on a hot
plate. The ITO glass was connected to the cathode. At the end of the growth period (5
hr) the sample was removed from the solution and immediately rinsed in flowing
deionized water to remove any residual salt from the surface. Finally, the samples
were annealed in air at 350 °C for 30 min.
S1.2 Preparation of silver nanoparticles and coating them on the anode.
Polyol synthesis was carried out to produce silver nanoparticles, as follows: First,
5 ml of ethylene glycol was added to the sample bottle, which was then placed in
silicone oil at 140 ℃ for 1 hour. A concentration of 0.1 M, 3 ml of silver nitrate
solution and 0.05 M, 3 ml polyvinylpyrrolidone was then added to the sample bottles.
The reaction was continued for 24 hours, resulting in a yellowish brown turbid
solution of silver nanoparticles.
S1.3 Coating the organic pigments (fluorescein, rhodamine B and copper (II)
phthalocyanine (CuPC) ) on the anode.
Three bottles were prepared, each filled with one of the following: 10−3 M of
fluorescein, 10−3 M of rhodamine B, and 10−3 M copper (II) phthalocyanine
(CuPC) in alcohol solvent. Each sample of silver nanoparticles coated in the ZnO
nanorods on ITO was then dropped into one of the solutions and quantitatively for
0.004 ml.
S1.4 Preparation of solar hydrogen generation devices.
The prepared platinum electrodes act as cathodes. The electrolytes were prepared
using 0.2 M potassium bicarbonate in DI-water : methanol = 1:1 solution. A scheme
of the solar hydrogen generation device is shown in Fig 1.
S1.5 Measurement.
The crystalline patterns were measured by X-ray diffraction (XRD). The
morphology of the ZnO nanorods on the ITO substrate was observed with a field
emission scanning electron microscope (FE-SEM). The morphology and diffraction
patterns of the silver nanoparticles were obtained by transmission electron microscopy
(TEM). The photoluminescence was measured with a spectrometer (Optics 4000) by
using 405nm wavelength excitation organic pigments. The power of the simulated
solar energy was found to be 1000 W/𝑚2 , the J–V curve and IPCE under simulated
solar radiation was recorded. Hydrogen generation was measured by gas
chromatography.