Self-Assembled Porphyrins on Modified Zinc Oxide Nanorods: Development of Model Systems for Inorganic–Organic Semiconductor Interface Studies

Abstract

Dense arrays of zinc oxide nanorods with high specific surface areas were grown by hydrothermal method and functionalized by self-assembled monolayer (SAM) of porphyrins. The growth process was optimized to obtain dense arrays of nanorods with diameter of 60–80 nm and length up to 1.5 μm. The increase in the effective surface area was monitored by comparing the absorbances of SAM deposited both on the flat and nanorod surfaces of ZnO. To alter further semiconductor-organic SAM interactions, a 2 or 5 nm thick layer of either Al2O3 or TiO2 was deposited on the ZnO nanorods. The present results show that both carboxylic acid and triethoxysilane anchors can be used to form porphyrin SAMs on the studied metal oxide substrates, and the electronic interactions between the metal oxide and porphyrin SAM are strongly modified by a thin layer of Al2O3 or TiO2. These hybrid semiconductor-organic SAM constructions present promising model systems for advanced spectroscopy studies of semiconductor-organic interfaces with high degree of control over electronic interactions and system morphology.

Porphyrins as Active Components for Electrochemical and Photoelectrochemical Devices

“…Officer 294 Galloni et al Figure 52 over TiO 2 and ZnO surfaces. 218 The electronic structure of the ZnTPP-Ipa, ZnTMP-Ipa, p-ZnTCPP and m-ZnTCPP porphyrins (see Figure 52) adsorbed both on TiO 2 (110) and ZnO(1120 ) surfaces were evaluated by using a combination of X-ray and UV photoemission spectroscopies (XPS and UPS) and inverse photoemission spectroscopy (IPS), interpreted using gas phase molecular DOS calculations.…”

“…289 ZnO micro-290 and nano-rods, [291][292][293][294] were also prepared by hydrothermal transformation of zinc salts in aqueous solutions and subsequent heating, the duration of which affected the rod length. An example is shown in Figure 78, where, starting from a seed layer, ZnO nanorods grown at 80°C are reported, after 2, 4 and 10 hours, respectively.…”

“…An example is shown in Figure 78, where, starting from a seed layer, ZnO nanorods grown at 80°C are reported, after 2, 4 and 10 hours, respectively. 294 MOCVD was also used to grow ZnO nanorods. 281 Vertically aligned ZnO nanowire arrays were fabricated on FTO glass 295 or Pt covered by polypyrrole 296 substrates by a low-temperature electrochemical method, and ZnO nanotubes were created on anodized aluminum oxide.…”

“…270 By and large, chemisorption is the most used method because of the basic character of the ZnO surface. Thus, porphyrins containing functional groups with acidic OH (carboxylic acid, 219,271,272,274,[276][277][278]281,[285][286][287]291,[293][294][295]297,298 sulfonic acid 279,283,284 and cathecol 275,282 ) were easily grafted onto ZnO 2 .…”

“…298 Finally, self-assembled monolayers of TPP-CO 2 H and 5-[3-(triethoxysilylbutanoyloxyethyloxy)phenyl]-10,15,20-tris(3,5-di-tert-butyl)phenylporphyrin (P-Si(OEt) 3 shown in Figure 84), were prepared on Zn nanorods of different lengths. 294 Porphyrins containing SO 3 H (or SO 3 − ) groups have been deposited by different strategies. Zinc 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin, ZnTPPS and the corresponding sodium sulfonate derivative were present in the solution for 279,283,284 electrodeposition of ZnO.…”