Quick cold preparation of TiO2 nanolayers on gold from P25 suspensions – film structure, voltammetric behavior and photocatalytic performance for the oxidation of EDTA under UVA-LED irradiation

Abstract

Time consuming thermal treatments are a common place in the preparation of photocatalysts and their immobilization on substrates. In this work nanolayers of TiO2 were applied at room temperature on gold surfaces by simply exposing the metal during a minute to an acidic aqueous suspension of P25 TiO2 (10gL−1 in 0.1molL−1 HCl). Repulverization of the commercial semiconductor by dry grinding in a mortar increased the stability of the suspension and more than doubled the photoelectrocatalytic activity of the TiO2 nanolayer. While the average TiO2 particle size in the suspension was of 103±3nm (obtained by DLS), the less than 100nm thick TiO2 nanolayer on the gold surface was dominated by particles with diameters ranging from 20nm (anatase) to 30nm (rutile) (observed by SEM, TEM and EDS). Photooxidation experiments with EDTA −an emerging organic pollutant– revealed a linear relationship between the photocurrent and the potential applied to the TiO2 modified electrode until the saturation photocurrent was attained. For a 1.0mmolL−1 EDTA solution the integrated saturation photocurrent resulted in a net charge, repeatable from one electrode modification to another, of 38±3CLmol−1cm−2 (conditions: 100s irradiation with an UV-LED at 365nm, 91mWcm−2; 0.5V vs. Ag/AgCl applied potential). A micrometric TiO2 layer applied on gold by drop casting enhances this net charge by just 50%. Cyclic voltammograms of the ferrocyanide/ferricyanide redox probe on gold remained undisturbed (in the dark) after the application of the TiO2 nanolayer, but they became distorted with the drop-cast micrometric layer. The photoactivity of the TiO2 nanolayer lasts with little decay for many days of photoelectrocatalytic treatment of EDTA. The simple and quick modification process at room temperature can be easily scaled-up to large areas.