Layer-by-layer assembling TiO 2 film from anatase TiO 2 sols as the photoelectrochemical sensor for the determination of chemical oxygen demand

Abstract

Anatase TiO 2 sols containing ultrafine TiO 2 crystallites (ca. 5 nm) were prepared by the peptization of amorphous precipitates in trifluoroacetic acid (TFA) solution. The crystallite size of TiO 2 in the sols was tuned by the subsequently hydrothermal treatment. The as-prepared TiO 2 nanoparticles were characterized by X-ray diffraction, Raman spectrometry, UV–vis absorption spectrometry and transmission electron microscopy. The positive charged nanoparticles in the sol with the Ti/TFA molar ratio of 1:8 and the poly(styrene sulfonic acid) sodium salt solution were used to prepare TiO 2 thin films by a layer-by-layer (LBL) self assembly method. Since the compact structure of the LBL thin films was good for the electronic transport, the TiO 2 LBL thin films were introduced to be working electrodes in three-electrode photoelectrochemical cells. The 15-layer TiO 2 thin film electrode showed a high photoelectrochemical property and it was employed as a sensor for the chemical oxygen demand. The detection limit of 1 mg L −1 with a working range of 0–130 mg L −1 was achieved. The relative standard deviation was 3.56% for 30 repetitive detections of 200 μM glucose with the theoretical COD value of 38.4 mg L −1 COD.