Photoelectrochemical Sensors Based On PTh/Pd/TiO₂ Nano-Functional Composite Materials

Photoelectrochemical (PEC) sensor is a promising analytical tool of high sensitivity, excellent selectivity and rapid response, which is used to detect the concentration of a substance based on photoelectrochemical conversion characteristics. Titanium dioxide is always used as PEC sensor photoelectrode modified material, because of their stable chemical properties, and unique optical, electrical, photoelectric conversion characteristics. Pd can effectively retard the recombination between photogenerated electron and hole pairs at TiO2 surface and PTh has enhancing light absorption and improving charge tranaport. In this paper, we focus on the PEC sensor performance based on TiO2-composites. The major contents are as follows:(1) Different molar composition ratio of polythiophene/titania (PTh/TiO2) nanocomposites were synthesized by oxidative polymerization of thiophene using FeCl3 as oxidant on the surface of TiO2. This series of nanocomposites were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectra (FTIR), Thermal gravimetric analysis (TGA) and UV-Vis absorption spectroscopy. The results indicated that the TiO2 anatase nanocrystalline structure has not been changed by the coating thin layer of PTh, but it could enhance the absorption in the visible range. The photoelectrochemical properties of photoelectrodes were prepared by modifying FTO conductive glass using PTh/TiO2 composites were investigated by transient photocurrent response test and amperometric response test. The test results showed that the photocurrent response of composite was improved. In addition, The largest current response was obtained when the molar composition ratio was 0.04, while the most obvious amperometric step appeared at 0.5V. The PEC senor was assembled by photoelectrode was used to detect the content of L-cysteine. The results demonstrated that the senor successfully detected the concentration of L-cysteine, the linear regression equation between the photocurrent response and L-cysteine concentration was Y=35.60X+6.37 and the detection limit of L-cysteine was 12.6μM.(2) TiO2 microsphere was synthesized by polyol method and PTh/Pd layer decorated onto TiO2 microsphere were prepared by reduction of Pd salts and polymerization of thiophene. These composites were characterized by TEM, scanning electron microscope (SEM), XRD, FTIR, TGA, X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherm (BET) and photoluminescence spectra (PL). The results showed that Pd species consisted of metallic and oxidized Pd and PTh were successfully prepared and a PTh/Pd layer formed on the surface of TiO2. The PTh/Pd/TiO2 composite microsphere was a mesoporous structure, which could make contribution to the diffusion of analyte. The properties of photoelectrodes were prepared by modifying FTO conductive glass using PTh/Pd/TiO2 composite were investigated by electrochemical impedance spectroscopy, transient photocurrent response test and amperometric response test. The test results demonstrated that the photocurrent response of ternary composite material was stronger than that of other electrodes and the recombination rate of photogenerated electrons of PTh/Pd/TiO2 composite was lower than Pd/TiO2 and TiO2. The most obvious amperometric step appeared when applied voltage was 0.5 V. The PEC senor was assembled by photoelectrode was used to detect the content of L-cysteine. The results demonstrated that the senor successfully detected the concentration of L-cysteine, the linear regression equation between the photocurrent response and L-cysteine concentration was Y=35.05X+7.33 and the detection limit of L-cysteine was 9.24 μM.