To improve light absorption ability in the visible light region and the efficiency of the charge transfer reaction, Pd nanoparticles decorated with reduced TiO2 nanotube photocatalyst were synthesized. The reduced TiO2 nanotube photocatalyst was fabricated by anodic oxidation of Ti plate, followed by an electrochemical reduction process using applied cathodic potential. For TiO2 photocatalyst electrochemically reduced using an applied voltage of -1.3 V for 10 min, 38% of Ti4+ ions on TiO2 surface were converted to Ti3+ ion. The formation of Ti3+ species leads to the decrease in the band gap energy, resulting in an increase in the light absorption ability in the visible range. To obtain better photocatalytic efficiency, Pd nanoparticles were decorated through photoreduction process on the surface of reduced TiO2 nanotube photocatalyst (r10-TNT). The Pd nanoparticles decorated with reduced TiO2 nanotube photocatalyst exhibited enhanced photocurrent response, and high efficiency and rate constant for aniline blue degradation; these were ascribed to the synergistic effect of the new electronic state of the TiO2 band gap energy induced by formation of Ti3+ species on TiO2, and by improvement of the charge transfer reaction.

본 연구에서는 전기분해 방법을 이용한 질산성질소(NO3 --N) 분해가 TiO2 nanotube plate 및 구리, 니켈, 스테인리스 스틸, 알루미늄, 주석, 티타늄을 환원전극으로 사용하였을 때 가능한지를 평가하였다. 전극의 전기화학적 특성 평가는 임피던스 측정을 하여 비교하였고, TiO2 nanotube plate의 표면 분석은 주사전자현미경을 통해 SEM 및 BET 분석법을 이용한 비표면적 분석을 통해 비교하였다. 질산성질소 전해실험의 경우 90분의 실험을 진행하였으며, 실험 결과 전극 표면의 부식이 수반되지 않은 TiO2 nanotube plate가 기타 금속 전극에 비해 질산성질소 환원 반응속도가 가장 뛰어난 것으로 확인되었다.

To improve photocatalytic performance, a PbS/ZnO/TiO2 nanotube catalyst was synthesized, and its surface characteristics and photocatalytic efficiency were investigated. The hybrid photocatalysts were produced by anodic oxidation and successive ionic layer adsorption and reaction(SILAR). The photocatalytic efficiency was evaluated using the dye degradation rate. The PbS/ZnO/TiO2 photocatalyst significantly enhanced the photocatalytic activity for dye degradation, which was ascribed to the synergistic effect of their better absorption of solar light and a decrease in the rate of excited electron-hole recombination.

The formation mechanism and photocatalytic properties of a multiwalled carbon nanotube (MWCNT)/TiO2- based nanotube (TNTs) composite are investigated. The CNT/TNT composite is synthesized via a solution chemical route. It is confirmed that this 1-D nanotube composite has a core-shell nanotubular structure, where the TNT surrounds the CNT core. The photocatalytic activity investigated based on the methylene blue degradation test is superior to that of with pure TNT. The CNTs play two important roles in enhancing the photocatalytic activity. One is to act as a template to form the core-shell structure while titanate nanosheets are converted into nanotubes. The other is to act as an electron reservoir that facilitates charge separation and electron transfer from the TNT, thus decreasing the electronhole recombination efficiency.

본 연구에서는 TiO2 nanotube 광촉매의 고도산화처리능을 비교하기 위해서 OH 라디칼 생성 력을 평가하고자 하였다. 자외선 조사에 따른 Probe compound인 4-Chlorobenzoic acid (pCBA)의 농 도 감소에 따라 OH radical 생성량을 산정하는 방법으로 광촉매 효율을 평가하였는데, TiO2 nanotube 표면에서의 전자의 흐름을 원활하게 하기 위하여 전기적 에너지를 주었을 시 광촉매 효율의 증가 가능 성 또한 확인하고자 자외선 조사 시 전류밀도를 인가하는 방법으로 실험을 진행하였다. 실험에 사용된 TiO2 nanotube는 전극효과를 부여하기 위해 양극산화법으로 티타늄판을 이용하여 제조하였으며, pCBA 용액에는 전도도를 부여하기 위하여 NaCl을 첨가하여 전해질로 사용하였다. 정전류 정전압 조건하에서 자외선조사 실험을 진행하였으며, 전류가 흐르는 광촉매에 자외선 조사 시 OH 라디칼 생성량은 광촉매 없이 자외선만 조사하였을 때에 비해 약 5.6배, TiO2 광촉매와 함께 자외선을 조사하였을 보다 약 2.2 배 증가하였다. 결과적으로 광촉매반응에 전기적 에너지를 부여하였을 시 시너지효과를 가져올 수 있는 가능성을 확인할 수 있었다.

A TiO2/CNT nanohybrid photocatalyst is synthesized via sol-gel route, with titanium (IV) isopropoxide and multi-walled carbon nanotubes (MWCNTs) as the starting materials. The microstructures and phase constitution of the nanohybrid TiO2/CNT (0.005wt%) samples after calcination at 450oC, 550oC and 650oC in air are compared with those of pure TiO2 using field-emission scanning electron microscopy and X-ray diffraction, respectively. In addition, the photocatalytic activity of the nanohybrid is compared with that of pure TiO2 with regard to the degradation of methyl orange under visible light irradiation. The TiO2/CNT composite exhibits a fast grain growth and phase transformation during calcination. The nanocomposite shows enhanced photocatalytic activity under visible light irradiation in comparison to pure TiO2 owing to not only better adsorption capability of CNT but also effective electron transfer between TiO2 and CNTs. However, the high calcination temperature of 650oC, regardless of addition of CNT, causes a decrease in photocatalytic activity because of grain growth and phase transformation to rutile. These results such as fast phase transformation to rutile and effective electron transfer are related to carbon doping into TiO2.

Excellent electron transport properties with enhanced light scattering ability for light harvesting have made well-ordered one dimensional TiO2 nanotube(TNT) arrays an alternative candidate over TiO2 nanoparticles in the area of solar energy conversion applications. The principal drawback of TNT arrays being activated only by UV light has been addressed by coupling the TNT with secondary materials which are visible light-triggered. As well as extending the absorption region of sunlight, the introduction of these foreign components is also found to influence the charge separation and electron lifetime of TNT. In this study, a novel method to fabricate the TNT-based composite photoelectrodes employing visible responsive CuInS2 (CIS) nanoparticles is presented. The developed method is a square wave pulse-assisted electrochemical deposition approach to wrap the inner and outer walls of a TNT array with CIS nanoparticles. Instead of coating as a dense compact layer of CIS by a conventional non-pulsed-electrochemical deposition method, the nanoparticles pack relatively loosely to form a rough surface which increases the surface area of the composite and results in a higher degree of light scattering within the tubular channels and hence a greater chance of absorption. The excellence coverage of CIS on the tubular TiO2 allows the construction of an effective heterojunction that exhibits enhanced photoelectrochemical performance.

Recently, nanotubes have considerably researched because of their novel application about photocatalysis, dye-sensitized solar cells (DSSCs), lithium ion battery, etc. In this work, self-standing nanotube arrays were fabricated by anodic oxidation method using pure Ti foil as a working electrode in ethylene glycole with 0.3M + . Growth behavior of nanotube arrays was compared according to temperature, voltage and time. The morphology, structure and crystalline of anodized nanotube arrays were observed by FE-SEM (field emission scanning electron microscope) and XRD (X-ray diffraction).

Self-standing TiO2 nanotube arrays were fabricated by potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as electrolytes with small addition of NH4F and H2O. The influences of anodization temperature and time on the morphology and formation of TiO2 nanotube arrays were investigated. The fabricated TiO2 nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of TiO2 nanotube show a similar value, whereas the thickness show a different trend with reaction temperature. The thickness of TiO2 nanotube arrays anodized at 20℃ and 30℃ was time-dependent, but on the other hand its at 10℃ are independent of anodization time. The conversion efficiency is low, which is due to a morphology breaking of the TiO2 nanotube arrays in manufacturing process of photoelectrode.

Titanium dioxide (TiO2) particles deposited on different quantitative Fe-treated carbon nanotube (CNT) composites with high photocatalytic activity of visible light were prepared by a modified sol-gel method using TNB as a titanium source. The composites were characterized by BET, XRD, SEM, TEM and EDX, which showed that the BET surface area was related to the adsorption capacity for each composite. From TEM images, surface and structural characterization of for the CNT surface had been carried out. The XRD results showed that the Fe-ACF/TiO2 composite mostly contained an anatase structure with a Fe-mediated compound. EDX results showed the presence of C, O, and Ti with Fe peaks in the Fe-CNT/TiO2 composites. The photocatalytic activity of the composites was examined by degradation of methylene blue (MB) in aqueous solution under visible light, which was found to depend on the amount of CNT. The highest photocatalytic activity among the different composites was related to the optimal content of CNT in the Fe-CNT/TiO2 composites. In particular, the photocatalytic activity of the Fe-CNT/TiO2 composites under visible light was better than that of the CNT/TiO2 composites due to the introduction of Fe particles.

[ ] nanotubes for photocatalytic application have been synthesized by hydrothermal method. nanotubes are formed by washing process after reaction in alkalic solution. Nanotubes with different morphology have been fabricated by changing NaOH concentration, temperature and time. nanoparticles were treated inside NaOH aqueous solution in a Teflon vessel at for 20 h, after which they were washed with HCl aqueous solution and deionized water. Nanotube with the most perfect morphology was formed from 0.1 N HCl washing treatment. nanotube was also obtained when the precursor was washed with other washing solutions such as , NaCl, , and . Therefore, it was suggested that ion combined inside the precursor compound slowly comes out from the structure, leaving nanosheet morphology of compounds, which in turn become the nanotube in the presence of hydroxyl ion. To stabilize the sheet morphology, the different type of washing treatment solution might be considered such as amine class compounds.