Spectrophotometric Investigation of Polycation/TiO2 Nanoparticle Thin Films Prepared by Layer-by-Layer Self Assembly Method

Since the discovery of photocatalytic properties of TiO2, it has widely been investigated for various applications like: self cleaning, air purification, photoelectrochemical solar cells and hydrogen production. The photoelectrochemical applications usually require a porous thin film with high surface area. Layer-by-layer self assembly method (LbL) employs nanoparticles to fabricate porous thin films with precise control on thickness. LbL is based on sequential adsorption of oppositely charged materials by electrostatic attractions in aqueous solution.In literature usually UV-visible spectrophotometry method was used to qualitative monitoring of film growth during LbL [1], but for quantitative analysis, i.e. measurement of adsorbed mass and thickness, other characterization techniques like quartz crystal microbalance (QCM) and ellipsometry were employed. QCM is a very sensitive and accurate technique, but there are many factors which could change the resonance frequency of crystal (like temperature variation, viscosity of medium and etc.). An other disadvantage of QCM is that usually the substrate for film growth is the gold electrode of quartz crystal so the results are not comparable with the films formed on other substrates like quartz or glass. Although quartz crystals with varying top layers like silica layer are available, but they are usually expensive. Ellipsometry is a complicated method suitable for thickness measurement of uniform films. In this paper we introduced a quantitative method based on UV-visible spectrophotometry for determination of quantity of adsorbed nanoparticles after each dip cycle and using this technique the effect of molecular weight of polyelectrolyte and dip time determined