Preparation Of Lanthanum Or Nitrogen Doped TiO₂/Ti Photoelectrodes And Their Photoelectrocatalytic Properties Under Visible Light

The present work aimed to prepare TiO₂/Ti photoelectrode by means of anodic oxidation to solve the problem for low efficiency to solar of TiO₂ catalyst. La doped and N-doped TiO₂/Ti photoelectrodes were prepared via incorporation of lanthanum and nitrogen, respectively, which could extend the response of TiO₂ to visible light. The present work also investigated the degradation of endocrine disrupting chemicals-alachlor.Compared to sol-gel method, anodic oxidation was simple, and the film was uniform and it is hard to detach and combined firmly with the substrate. La-doped TiO₂/Ti photoelectrodes can be prepared and optimized by anodization, in situ formation of TiO₂ film on titanium substrate in the mixed solution of H2SO4 and La(NO₃)₃ . The preparation parameters, such as the concentration of dopants and voltage, were optimized. The La(NO₃)₃ concentration of 800 mg/L and the voltage of 160 V are the optimal conditions for preparation of La-doped TiO₂/Ti photoelectrodes.With respect to the fact that doping of nitrogen and nitrogen compounds is difficult to enter directly into the TiO₂ film in the anodic oxidation process, the N-doped TiO₂/Ti photoelectrode was prepared on TiO₂/Ti photoelectrode substrate by Plasma based ion implantation(PII) method. The optimal preparation conditions were preparation voltage 160 V, implantation voltage 30 KV and the doing content 4×10¹⁵ N/cm², respectively.By using scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-vis DRS), surface photovoltage spectroscopy (SPS) and electrochemical methods and other methods, the doped and undoped TiO₂/Ti photoelectrode surface morphology, crystal structure, grain size, surface composition and chemical form, absorption spectra, surface optical properties were analyzed. The results showed that lanthanum at the surface of TiO₂ film was in the form of La₂O₃, and in the interface titanium atoms replaced lanthanum atoms in the lattice of lanthanum oxide to form Ti-O-La bonding; Three kinds of nitrogen existed in the TiO₂ lattice or molecular gap among theβ-N,γ-N, and O-Ti-N. The reposes of two modified TiO₂/Ti to visible light were superior to that of unmodified TiO₂/Ti and the degradation of Rhodamine B was better for modified TiO₂/Ti than that of unmodified TiO₂/Ti photoelectrode.N-doped TiO₂/Ti photoelectrode were used for the photocatalytic oxidation of endocrine disrupting chemicals-alachlor whose photocatalytic oxidation process was proved to be pseudo first order kinetic. The results showed that the influencing factors of alachlor degradation were in the following orders: light irradiation intensity>catalyst area> catalyst initial concentration of alachlor>external bias. The energy band structure of N-doped anatase TiO₂ was studied by first principles. The calculation revealed that impurity energy level was generated in the energy band of TiO₂ after the incorporation of nitrogen, which resulted in a narrower band gap and a red shift of the absorption spectra of TiO₂. The calculating result was in good agreement with experimental data.The electro-assisted photocatalytic efficiency for the degradation of alachlor was studied by means of potentiostatic and galvanostatic models, whose results confirmed the synergistic effect between the photocatalysis and electrocatalysis. When Na₂SO₄ electrolyte was added into the reaction solution, the SO₄^2- can be oxidized by strong valence band hole to S₂O₈^2-, which could improve the degradation efficiency of alachlor. The·OH generation in the process of TiO₂/Ti photocatalytic degradation was studied by fluorescence method, and the intermediate products were analyzed by liquid chromatography-mass line (LC-MS) in the course of alachlor degradation. Experimental results showed that a series of redox reactions including bond-breaking and ring-open of alachlor took place via hydroxylation and dealkylation under the force of hydroxyl radicals. Eventually, this kind of organic compound was decomposed into inorganic molecules such as CO₂ and H₂O.