Plasmonic Spherical Nanoparticles Coupled with Titania Nanotube Arrays Prepared by Anodization as Substrates for Surface-Enhanced Raman Spectroscopy Applications: A Review

As surface-enhanced Raman spectroscopy (SERS) continues developing to be a powerful analytical tool for several probes, four important aspects to make it more accessible have to be addressed: low-cost, reproducibility, high sensibility, and recyclability. Titanium dioxide nanotubes (TiO2 NTs) prepared by anodization have attracted interest in this field because they can be used as safe solid supports to deposit metal nanoparticles to build SERS substrate nanoplatforms that meet these four desired aspects. TiO2 NTs can be easily prepared and, by varying different synthesis parameters, their dimensions and specific features of their morphology can be tuned allowing them to support metal nanoparticles of different sizes that can achieve a regular dispersion on their surface promoting high enhancement factors (EF) and reproducibility. Besides, the TiO2 photocatalytic properties enable the substrate’s self-cleaning property for recyclability. In this review, we discuss the different methodological strategies that have been tested to achieve a high performance of the SERS substrates based on TiO2 NTs as solid support for the three main noble metal nanoparticles mainly studied for this purpose: Ag, Au, and Pt.

Synthesis and Characterization of TiO2 Nanotubes (TiO2-NTs) Decorated with Platine Nanoparticles (Pt-NPs): Photocatalytic Performance for Simultaneous Removal of Microorganisms and Volatile Organic Compounds

This work reports on the effect of TiO2 nanotubes (TiO2-NTs), decorated wih platinum nanoparticles (Pt-NPs), on the removal of bacteria and volatile organic compounds (VOCs). The Pt-NPs were loaded onto the TiO2-NTs using the electrodeposition method at four decoration times (100, 200, 300, and 600 s). The realized Pt-NPs/TiO2-NTs nanocomposites were used for the degradation of cyclohexane, a highly toxic and carcinogenic VOC pollutant in the chemical industry. The achieved Pt-NPs/TiO2-NTs nanocomposites were characterized using X-ray diffraction (XRD), photoluminescence (PL), diffuse reflectance spectroscopy (UV–Vis), and scanning (SEM) and transmission (TEM) electron microscopy. To understand the photocatalytic and antibacterial behavior of the Pt-NPs/TiO2-NTs, simultaneous treatment of Escherichia coli and cyclohexane was conducted while varying the catalyst time decoration. We noticed a complete bacterial inactivation rate with 90% VOC removal within 60 min of visible light irradiation. Moreover, the Langmuir–Hinshelwood model correlated well with the experimental results of the photocatalytic treatment of indoor air.

RSM-Based Preparation and Photoelectrocatalytic Performance Study of RGO/TiO2 NTs Photoelectrode

In this paper, reduced graphene oxide (RGO) was prepared by a modified Hummers method and chemical reduction method, and an RGO/TiO2 NTs (RGO/TiO2 nanotubes) photoelectrode was prepared by the electrochemical deposition method. The as-prepared RGO/TiO2 NTs were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their photocatalytic activities were investigated by measuring the degradation of methylene blue (MB) under simulated solar light irradiation. The SEM and XRD results indicated that the original tubular structure of TiO2-NTs was not changed after RGO modification. The surface of the TiO2 NTs photoelectrode was covered with a non-uniform, flake-shaped reduced graphene oxide film. The thickness of the RGO/TiO2 NTs was increased to about 22.60 nm. The impedance of the RGO/TiO2 NTs was smaller than that of the TiO2 NT photoelectrode. The optimal preparation conditions of RGO/TiO2 NT photoelectrodes were investigated by using a single factor method and response surface method. The best preparation conditions were as follows: deposition potential at 1.19 V, deposition time of 10.27 min, and deposition temperature at 24.94 °C.

The Deposition of a Lectin from Oreochromis niloticus on the Surface of Titanium Dioxide Nanotubes Improve the Cell Adhesion, Proliferation, and Osteogenic Activity of Osteoblast-like Cells

Titanium and its alloys are used biomaterials for medical and dental applications, due to their mechanical and physical properties. The surface modifications of titanium with bioactive molecules can increase the osseointegration by improving the interface between the bone and implant. Titanium dioxide nanotubes (TiO2NTs) have excellent bioactivity inducing cell adhesion, spreading, growth and differentiation. In this work, TiO2NTs were functionalized with a lectin from the plasma of the fish Oreochromis niloticus aiming to favour the adhesion and proliferation of osteoblast-like cells, improving its biocompatibility. The TiO2NTs were obtained by anodization of titanium and annealed at 400 °C for 3 h. The resulting TiO2NTs were characterized by high-resolution scanning electron microscopy. The successfully incorporation of OniL on the surface of TiO2NTs by spin coating was demonstrated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIE) and attenuated total reflection-Fourier transform infrared spectrum (ATR-FTIR). Our results showed that TiO2-NTs were successfully synthesized in a regular and well-distributed way. The functionalization of TiO2-NTs with OniL favoured adhesion, proliferation, and the osteogenic activity of osteoblast-like cells, suggesting its use to improve the quality and biocompatibility of titanium-based biomaterials.

Synthesis and characterization of TiO2 nanotube Schottky diodes

Metal-semiconductor interfaces on one-dimensional (1D) nanostructures represent crucial building blocks for next-generation nanoelectronics. Over the past two decades, chemically synthesized titanium dioxide nanotubes (TiO2-NTs) have gained a considerable amount of interest due to their high specific surface areas, tunable geometries, and favorable electrical properties. Explored for a variety of applications such as solar cells, hydrogen production, memristors, and batteries, TiO2 is a transition metal oxide material that contains unique wide-bandgap semiconductor properties. This research seeks to fabricate a conformal, rectifying metal-semiconductor interface, or Schottky junction, throughout an ordered array of semiconducting nanotubes. The atomic layer deposition (ALD) technique offers a precise, conformal growth mechanism and was used to deposit a continuous platinum (Pt) Schottky contact throughout the inner walls of the TiO2-NTs. Any defects found in the nanotubes, such as cracks, led to Pt atoms reaching all areas, forming an electrical short between the anode and cathode. To address this issue, initial experiments were centered on synthesizing defect-free, ordered TiO2-NT arrays using electrochemical anodization as it offers precise geometric control over the NT growth. Fabrication parameters, such as anodization time, electrolyte concentrations, and annealing environments, were investigated until the resulting NTs were free from structural defects. Demonstrated with low vacuum annealing, oxygen vacant, nonstoichiometric TiO2 was synthesized and investigated as a diode material. By comparing the current-voltage characteristics between stoichiometric and nonstoichiometric TiO2 diodes, we find that the oxygen vacant, nonstoichiometric TiO2 diodes displayed an improved ideality factor from 3.7 to 2.4. A 350 [degrees] C post-fabrication thermal treatment, however, led to both stoichiometric and nonstoichiometric TiO2 diodes having similar ideality factors of 2.0 and similar shifts in trap concentration and depth. Nonstoichiometric TiO2 devices exhibited a unique shunt conduction regime after thermal treatment where the shunt resistance was found to be on the order of 105 [omega]. These results present valuable experimental observations into understanding the effects of oxygen vacancies in TiO2 and effectively modifying the electronic properties of a conformal Pt/TiO2 nanostructured junction using a facile post-fabrication thermal treatment.