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Theses

Electrochemical synthesis of metallic and polymeric nanoarrays through vertically oriented mesoporous silica thin films

Abstract : In this project we exploited surface modification of electrodes with vertically oriented mesoporous silica thin films, generated by electrochemically assisted self-assembly method. The silica scaffold offers narrow pores diameter around 2-3 nm and 50-150 nm film thickness, a competitive hard template material for the preparation of low dimensional metallic and organic nanopatterns on conducting surfaces. We combined the wealth of mesoporous silica thin film with electrochemistry to obtain surface nanopatterning of the underlying support. Well-adhered and mechanically stable mesoporous silica film is formed on electrodes bearing hydroxyl moieties on their surface, for example indium tin oxide (ITO). However, the adhesion and mechanical stability of mesoporous silica thin film is poor on noble metals such as gold (Au). To ensure uniform surface coverage and good adhesion of the silica film to the Au surface, it was necessary to use a (3-mercaptopropyl) trimethoxysilane (MPTMS) reagent to act as a “molecular glue” thanks to its thiol functionality, which is able to bind to the gold substrate and to its alkoxysilane moieties enabling condensation with the silica material. The MPTMS layer had, however, a significant effect on film permeability to redox probes, depending on the MPTMS treatment time. MPTMS adsorption should be long enough to ensure proper adhesion of the film but not too long to avoid surface blocking or film defects. In addition, Cu underpotential deposition (UPD) experiments revealed that the silica membrane significantly affected the UPD process, suggesting some barrier effect of the porous membrane, but the interface Au/MPTMS/silica is not sharp and allowed metal UPD between the gold substrate and the silica thin film. In the second part of the thesis, mesoporous silica thin films, with two distinct pore diameters (2.0 and 2.9 nm), covered ITO electrodes were used as hard template for the control electrochemical growth of polyaniline (PANI) nanowire arrays. To ensure proper adhesion of PANI to the underlying ITO surface, aniline moieties are first covalently attached to the bottom of mesochannels via electrografting of aminophenyl diazonium cations, serving in a second step as precursors for PANI growth by electropolymerization of aniline through the silica mesochannels. PANI wires remain attached to ITO after removal of the silica membrane, confirming the importance of initial electrografting. Both PANI inside silica template and the free PANI nanowire arrays were electroactive. Spectroelectrochemical study revealed fast electrochromic behavior and cycling stability of PANI nanowire arrays. In last part of the project, some preliminary attempts were made for the electrochemical co-deposition of bimetallic Cobalt/Platinum (CoPt) nanowire arrays onto ITO electrode covered with mesoporous silica films. The presence of Co and Pt in the deposits was confirmed from surface analysis by spectroscopic methods and electrochemical characterization.
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Theses
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https://docnum.univ-lorraine.fr/ulprive/DDOC_T_2021_0093_ULLAH.pdf
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https://hal.univ-lorraine.fr/tel-03335814
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Submitted on : Monday, September 6, 2021 - 3:15:33 PM
Last modification on : Tuesday, September 7, 2021 - 3:18:37 AM

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  • HAL Id : tel-03335814, version 1

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Wahid Ullah. Electrochemical synthesis of metallic and polymeric nanoarrays through vertically oriented mesoporous silica thin films. Chemical Sciences. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0093⟩. ⟨tel-03335814⟩

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