Layer-by-layer assembling TiO2 film from anatase TiO2 sols as the photoelectrochemical sensor for the determination of chemical oxygen demand

Anatase TiO2 sols containing ultrafine TiO2 crystallites (ca. 5 nm) were prepared by the peptization of amorphous precipitates in trifluoroacetic acid (TFA) solution. The crystallite size of TiO2 in the sols was tuned by the subsequently hydrothermal treatment. The as-prepared TiO2 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 TiO2 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 TiO2 LBL thin films were introduced to be working electrodes in three-electrode photoelectrochemical cells. The 15-layer TiO2 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.

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► The anatase TiO2 sols containing 5 nm nanocrystals were prepared by the peptization of trifluoroacetic acid for the first time.
► The anatase TiO2 sols were used to prepare TiO2 thin films, and the films were employed as a photo-electrochemical sensor for the determination of chemical oxygen demand (COD).
► The COD detection limit of 1 mg L−1 with a working range of 0–130 mg L−1 was achieved with the layer-by-layer TiO2 films.