N-doped Na₂Ti₆O₁₃@TiO₂ (denoted as N-NTO@TiO₂) composites are successfully synthesized using a simple two-step process: 1) ball-milling of TiO₂ with Na₂CO₃ followed by heat treatment at 900°C; 2) mixing of the prepared Na₂Ti₆O₁₃ with titanium isopropoxide and calcining with urea at 500°C. The prepared composites are characterized using XRD, SEM, TEM, FTIR, and BET. The N-NTO@TiO₂ composites exhibit well-defined crystalline and anatase TiO₂ with exposed {101} facets on the external surface. Moreover, dopant N atoms are uniformly distributed over a relatively large area in the lattice of the composites. Under visible light irradiation, ~51% of the aqueous methylene blue is photodegraded by N-NTO@TiO₂ composites, which is higher than the values shown by other samples because of the coupling effects of the hybridization of NTO and TiO₂, N-doping, and presence of anatase TiO₂ with exposed {101} facets.

In this work, TiO₂ 3D nanostructures (TF30) were prepared via a facile wet chemical process using ammonium hexafluorotitanate. The synthesized 3D TiO₂ nanostructures exhibited well-defined crystalline and hierarchical structures assembled from TiO₂ nanorods with different thicknesses and diameters, which comprised numerous small beads. Moreover, the maximum specific surface area of TiO₂ 3D nanostructures was observed to be 191 m²g^-1, with concentration of F ions on the surface being 2 at%. The TiO₂ 3D nanostructures were tested as photocatalysts under UV irradiation using Rhodamine B solution in order to determine their photocatalytic performance. The TiO₂ 3D nanostructures showed a higher photocatalytic activity than that of the other TiO₂ samples, which was likely associated with the combined effects of a high crystallinity, unique features of the hierarchical structure, a high specific surface area, and the advantage of adsorbing F ions.

It is necessary to fabricate uniformly dispersed nanoscale catalyst materials with high activity and long-term stability for polymer electrolyte membrane fuel cells with excellent electrochemical characteristics of the oxygen reduction reaction and hydrogen oxidation reaction. Platinum is known as the best noble metal catalyst for polymer electrolyte membrane fuel cells because of its excellent catalytic activity. However, given that Pt is expensive, considerable efforts have been made to reduce the amount of Pt loading for both anode and cathode catalysts. Meanwhile, the atomic layer deposition (ALD) method shows excellent uniformity and precise particle size controllability over the three-dimensional structure. The research progress on noble metal ALD, such as Pt, Ru, Pd, and various metal alloys, is presented in this review. ALD technology enables the development of polymer electrolyte membrane fuel cells with excellent reactivity and durability.

The coupling of two semiconducting materials is an efficient method to improve photocatalytic activity via the suppression of recombination of electron-hole pairs. In particular, the coupling between two different phases of TiO₂, i.e., anatase and rutile, is particularly attractive for photocatalytic activity improvement of rutile TiO₂ because these coupled TiO₂ powders can retain the benefits of TiO₂, one of the best photocatalysts. In this study, anatase TiO₂ nanoparticles are synthesized and coupled on the surface of rutile TiO₂ powders using a microemulsion method and heat treatment. Triton X-100, as a surfactant, is used to suppress the aggregation of anatase TiO₂ nanoparticles and disperse anatase TiO₂ nanoparticles uniformly on the surface of rutile TiO₂ powders. Rutile TiO₂ powders coupled with anatase TiO₂ nanoparticles are successfully prepared. Additionally, we compare the photocatalytic activity of these rutile-anatase coupled TiO₂ powders under ultraviolet (UV) light and demonstrate that the reason for the improvement of photocatalytic activity is microstructural.

Citations

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• Refractory Metal Oxide–Doped Titanate Nanotubes: Synthesis and Photocatalytic Activity under UV/Visible Light Range
  Min-Sang Kim, Hyun-Joo Choi, Tohru Sekino, Young-Do Kim, Se-Hoon Kim
  Catalysts.2021; 11(8): 987.     CrossRef
• Effect of Surfactant on the Dispersion Stability of Slurry for Semiconductor Silicon CMP
  Hye Won Yun, Doyeon Kim, Do Hyung Han, Dong Wan Kim, Woo-Byoung Kim
  Journal of Korean Powder Metallurgy Institute.2018; 25(5): 395.     CrossRef

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 450°C, 550°C and 650°C 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 650°C, 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.

10 wt.% and 20 wt.%Li-TiO₂ composite powders are synthesized by a sol-gel method using titanium isopropoxide and Li₂CO₃ as precursors. The as-received amorphous 10 wt.%Li-TiO₂ composite powders crystallize into the anatase-type crystal structure upon calcination at 450°C, which then changes to the rutile phase at 750°C. The asreceived 20 wt%Li-TiO₂ composite powders, on the other hand, crystallize into the anatase-type structure. As the calcination temperature increases, the anatase TiO₂ phase gets transformed to the LiTiO₂ phase. The peaks for the samples obtained after calcination at 900°C mainly exhibit the LiTiO₂ and Li₂TiO₃ phases. For a comparison of the photocatalytic activity, 10 wt.% and 20 wt.% Li-TiO₂ composite powders calcined at 450°C, 600°C, and 750°C are used. The 20 wt.%Li-TiO₂ composite powders calcined at 600°C show excellent efficiency for the removal of methylorange.

Citations

Citations to this article as recorded by  

• Refractory Metal Oxide–Doped Titanate Nanotubes: Synthesis and Photocatalytic Activity under UV/Visible Light Range
  Min-Sang Kim, Hyun-Joo Choi, Tohru Sekino, Young-Do Kim, Se-Hoon Kim
  Catalysts.2021; 11(8): 987.     CrossRef
• Photocatalytic activity of rutile TiO2 powders coupled with anatase TiO2 nanoparticles using surfactant
  Jong Min Byun, Chun Woong Park, Young In Kim, Young Do Kim
  journal of Korean Powder Metallurgy Institute.2018; 25(3): 257.     CrossRef
• Synthesis and characterization of nitrogen-doped TiO 2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity
  Yifan Zhang, Hye Mee Yang, Soo-Jin Park
  Current Applied Physics.2018; 18(2): 163.     CrossRef