Preparation And Photocatalytic Property Of N-Fe Codoped TiO₂Thin Films On Stainless Steel

With the advantage of high photocatalytic activity, no toxicity and low cost,many practical applications of TiO2like degradation of organic pollutant,wastewater treatment, air purification and sterilization have been studied for afew decades. However, TiO2has a fatal drawback that it shows a selectiveresponse to the ultraviolet region of the solar spectrum. There is only4-6percent of ultraviolet light in the sunlight, making the low utilization of solarenergy. Therefore, narrowing the band gap of TiO2is a hot point in the researchof photocatalyst in recent years. Researches show that codoping properly withnonmetal and metal elements, such as N-Fe codoping, is an effective means tomake TiO2with visible light photocatalytic activity. In this paper, we prepared theN-Fe co-doped TiO2thin films by using a combined method of the pulsed-directcurrent electrophoretic deposition (pulsed-DC EPD) and thermal oxidation, andstudied the surface morphology, composition, structure and photoelectricproperties of the films. The main work is as following:(1) TiN film was deposited on the surface of304stainless steel (SS) bypulsed-DC EPD with two304SS plates as electrodes in5g/L aqueous TiNnanoparticle suspension. The morphology, structure, composition and formationof TiN film were studied. It turned out that the generation of bubbles from waterhydrolysis was significantly inhibited by adopting pulsed-DC voltage. Thefrequency is a key factor to influence the depositing speed and morphology ofTiN films. In the range of5-30Hz, the smooth and uniform TiN films were obtained and the deposition rate of TiN film decreased with the increasing offrequency. Oxygen and iron also existed in the TiN film because of anodeoxidation. The elements in the interface layer between the TiN film and SSsubstrate showed gradient distribution, which is benefit to the adhesion strengthof TiN film.(2) N-Fe co-doped TiO2film was formed by annealing TiN film in thetemperature range of400~700℃in air. The research showed that oxidationtemperature had important effect on crystal phase of TiO2. At450℃, anatase TiO2was formed. At500℃and600℃, the films had mixed phase structure of anataseand rutile TiO2. When the oxidation temperature reached700℃, anatase TiO2allturned into rutile phase. According to the UV-Vis absorption spectra, theabsorption edges of the N-Fe co-doped TiO2films all had obvious red-shift andthe band gaps decreased compared with that of the undoped TiO2. Furthermore,the photoelectric response and photocatalytic property of the N-Fe co-doped TiO2thin film formed by annealing at500℃was emphatically studied. Theapparently boosted photocurrent response appeared under both ultraviolet andvisible light irradiation, and the transient photocurrent densities were about7.0μA/cm2and3.8μA/cm2, respectively. The photocatalytic activity of N-Feco-doped TiO2film was evaluated by the degradation of5mg/L rhodamine Bsolution under ultraviolet and visible light irradiation for3hours and thedegradation rate was82.7%and67.5%, respectively.