In-situ evaluation of dye adsorption on TiO₂ using QCM

¹ KTH Royal Institute of Technology, Dept. of Chemistry, Division of Surface and Corrosion Science, 100 44 Stockholm, Sweden
² KTH Royal Institute of Technology, Material Physics, ICT, 164 40 Stockholm, Sweden
³ Institute for Advanced Studies, IMDEA Nanociencia, c/o Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
⁴ Uppsala University, Dept. of Chemistry, Physical Chemistry, Box 523, 751 20 Uppsala, Sweden
⁵ KTH Royal Institute of Technology, Dept. of Chemistry, Fiber and Polymer Technology, 10044 Stockholm, Sweden

^a e-mail: besharat@kth.se

Received: 4 October 2016
Accepted: 24 January 2017
Published online: 13 March 2017

Abstract

We measured the adsorption characteristics of two organic dyes; triphenylamine-cyanoacrylic acid (TPA-C) and phenoxazine (MP13), on TiO₂, directly in a solution based on quartz crystal microbalance (QCM). Monitoring the adsorbed amount as a function of dye concentration and during rinsing allows determination of the equilibrium constant and distinction between chemisorbed and physisorbed dye. The measured equilibrium constants are 0.8 mM^-1 for TPA-C and 2.4 mM^-1 for MP13. X-ray photoelectron spectroscopy was used to compare dried chemisorbed layers of TPA-C prepared in solution with TPA-C layers prepared via vacuum sublimation; the two preparation methods render similar spectra except a small contribution of water residues (OH) on the solution prepared samples. Quantitative Nanomechanical Mapping Atomic Force Microscopy (QNM-AFM) shows that physisorbed TPA-C layers are easily removed by scanning the tip across the surface. Although not obvious in height images, adhesion images clearly demonstrate removal of the dye.