Fabrication, annealing, and electrocatalytic properties of platinum nanoparticles supported on self-organized TiO_2 nanotubes

The platinum nanoparticles supported on self-organized TiO2 nanotubes （Pt-TiO2/Ti） were prepared using electrochemical anodic oxidation followed by cathodic reduction. The structure and chemical nature of the Pt-TiO2/Ti electrocatalyst were investigated by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Both XRD and SEM results indicate the presence of platinum on nanotubular TiO2. The stability of the Pt deposits was also investigated in 0.5 mol/L H2SO4 solution by cyclic voltammetry. The electrocatalytic activity of the Pt-TiO2/Ti catalyst exhibits enhancement effect during electro-oxidation of methanol when annealed to anatase. Successive cyclic voltam- mograms of methanol oxidation on the Pt-TiO2/Ti electrocatalyst shows unique electrocatalytic characteristics when compared to methanol oxidation on the bulk Pt catalyst. This is because of further quick oxidation of adsorbed CO by Pt （111） facets of Pt particles on self-organized TiO2 nanotubes when the formation of an electroactive film onto the working catalyst surface occurs.

One-pot Synthesis of TiO2 Nanoparticles in Suspensions for Quantification of Titanium Debris Release in Biological Liquids

In this work we have developed an analytical method to measure potential titanium debris released from TiO2 nanotube layers devices immersed in biological fluids. This quantitative study is highly required to ensure both the security and non toxicity of the nanostructured surfaces used as future implantable medical devices in the living. A one-pot synthesis process is developed to produce high quality standard solutions of titanium dioxide nanoparticles in aqueous medium. The elaborated dispersion is then used to fabricate standard solutions in both aqueous and human blood plasma media. The synthesized nanoparticles dispersion was characterized by granulometry. The nanoparticles structure and morphology were then observed using Transmission Electron Microscopy (TEM). Thermogravimetric Analysis (TGA) was used to evaluate the concentration of TiO2 in the suspension. A quantitative routine by the use of Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) is developed. The quantification threshold of titanium species is found to be in the 30 - 40 ppb range. None interference is detected between the particles and the human blood plasma. Using the established quantitative routine, the titanium species release from titania nanotube layers in human blood plasma is evaluated.

Enhanced electrocatalytic activity of Co@N-doped carbon nanotubes by ultrasmall defect-rich TiO2 nanoparticles for hydrogen evolution reaction

Despite being technically possible, splitting water to generate hydrogen is practically unfeasible, mainly because of the lack of sustainable and efficient earth-abundant catalysts for the hydrogen-evolution reaction （HER）. Herein, we report a durable and highly active electrochemical HER catalyst based on defect-rich TiO2 nanoparticles loaded on Co nanoparticles@N-doped carbon nanotubes （D-TiOdCo@NCT） synthesized by electrostatic spinning and a subsequent calcining process. The ultrasmall TiO2 nanoparticles are 1.5-2 nm in size and have a defect-rich structure of oxygen vacancies. D-TiO2/Co@NCT exhibits excellent HER catalytic activity in an acidic electrolyte （0.5 M H2SO4）, with a low onset potential of -57.5 mV （1 mA·cm^-2）, a small Tafel slope of 73.5 mV·dec^-1, and extraordinary long-term durability. X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and theoretical calculations confirm that the Ti3. defect-rich structure can effectively regulate the catalytic activity for electrochemical water splitting.

Transient competition between photocatalysis and carrier recombination in TiO_2 nanotube film loaded with Au nanoparticles

Highly ordered TiO2 nanotube array （TNA） films are fabricated by using an anodic oxidation method. Au nanoparticles （NPs） films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C （UVC, 266 nm） light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence （PL） spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence （NTRT-PL） spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au-TNA composite are evaluated through photo-degradation of methyl orange （MO） in an aqueous solution with ultraviolet-visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.

Analysis of the factors controlling performances of Au-modified TiO2 nanotube array based photoanode in photo-electrocatalytic(PECa)cells

The efficiency of photo-electrocatalytic（PECa） devices for the production of solar fuels depends on several limiting factors such as light harvesting, charge recombination and mass transport diffusion. We analyse here how they influence the performances in PECa cells having a photo-anode based on Au-modified TiOnanotube（TNT） arrays, with the aim of developing design criteria to optimize the photo-anode and the PECa cell configuration for water photo-electrolysis（splitting） and ethanol photo-reforming processes.The TNT samples were prepared by controlled anodic oxidation of Ti foils and then decorated with gold nanoparticles using different techniques to enhance the visible light response through heterojunction and plasmonic effects. The activity tests were made in a gas-phase reactor, as well as in a PECa cell without applied bias. Results were analysed in terms of photo-generated current, Hproduction rate and photoconversion efficiency. Particularly, a solar-to-hydrogen efficiency of 0.83% and a Faradaic efficiency of 91%were obtained without adding sacrificial reagents.

Enhanced CH4 yield by photocatalytic CO2 reduction using TiO2 nanotube arrays grafted with Au, Ru, and ZnPd nanoparticles

Metal nanoparticle （NP） co-catalysts on metal oxide semiconductor supports are attracting attention as photocatalysts for a variety of chemical reactions. Related efforts seek to make and use Pt-free catalysts. In this regard, we report here enhanced CH4 formation rates of 25 and 60 μmol·g^-1·h^-1 by photocatalytic CO2 reduction using hitherto unused ZnPd NPs as well as Au and Ru NPs. The NPs are formed by colloidal synthesis and grafted onto short n-type anatase TiO2 nanotube arrays （TNAs）, grown anodically on transparent glass substrates. The interfacial electric fields in the NP-grafted TiO2 nanotubes were probed by ultraviolet photoelectron spectroscopy （UPS）. Au NP-grafted TiO2 nanotubes （Au-TNAs） showed no band bending, but a depletion region was detected in Ru NP-grafted TNAs （Ru-TNAs） and an accumulation layer was observed in ZnPd NP-grafted TNAs （ZnPd-TNAs）. Temperature programmed desorption （TPD） experiments showed significantly greater CO2 adsorption on NP-grafted TNAs. TNAs with grafted NPs exhibit broader and more intense UV-visible absorption bands than bare TNAs. We found that CO2 photoreduction by nanoparticle-grafted TNAs was driven not only by ultraviolet photons with energies greater than the TiO2 band gap, but also by blue photons close to and below the anatase band edge. The enhanced rate of CO2 reduction is attributed to superior use of blue photons in the solar spectrum, excellent reactant adsorption, efficient charge transfer to adsorbates, and low recombination losses.

Fabrication, modification and environmental applications of TiO2 nanotube arrays （TNTAs） and nanoparticles

Among the semiconductors, titanium dioxide has been identified as an effective photocatalyst due to its abundance, low cost, stability, and superior electronic energy band structure. Highly ordered nanotube arrays of titania were produced by anodization and mild sonication. The band gap energy of the titania nanotube arrays was reduced to 2.6 eV by co-doping with Fe, C, N atoms using an electrolyte solution containing K3Fe（CN）6. The photo- conversion of phenol in a batch photoreactor increased to more than 18% based on the initial concentration of phenol by using a composite nanomaterial consisting of titania nanotube arrays and Pt/ZIF-8 nanoparticles. A layer-by- layer assembly technique for the deposition of titania nanoparticles was developed to fabricate air filters for the degradation of trace amounts of toluene in the air and preparation of superhyrophobic surfaces for oil-water separation and anti-corrosion surfaces.

Synergetic effect of graphene and Co(OH)2 as cocatalysts of TiO2 nanotubes for enhanced photogenerated cathodic protection

A layer of graphene(GR)particles was successfully deposited at the interface between Co(OH)2 nanoparticles and TiO2 nanotubes,aiming to improve the photoelectrochemical performance of the large-bandgap semiconductor TiO2.The obtained Co(OH)2/GR/TiO2 was extensively characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),UV–vis absorption spectra and photoluminescence(PL)emission spectra.Electrochemical impedance spectra,photogenerated potential-time(E-t),photocurrent density-time(i-t)and i-E curves and open circuit potential(OCP)curves were measured to investigate the photoelectrochemical activities and photogenerated cathodic protection properties.The results revealed that Co(OH)2/GR/TiO2 exhibits excellent photoelectrochemical and photogenerated cathodic performance due to synergistic effect between Co(OH)2 and graphene.Co(OH)2 and graphene co-modified TiO2 photoanode could provide an effective protection for 304 stainless steel(304 SS)in 3.5 wt%Na Cl solution for 12 h,which would be promising for future practical applications in the field of marine corrosion protection.

Electrochemical Fabrication of rGO-embedded Ag-TiO2 Nanoring/Nanotube Arrays for Plasmonic Solar Water Splitting

Effective utilization of hot electrons generated from the decay of surface plasmon resonance in metal nanoparticles is conductive to improve solar water splitting efficiency.Herein,Ag nanoparticles and reduced graphene oxide(rGO)co-decorated hierarchical TiO2 nanoring/nanotube arrays(TiO2 R/T)were facilely fabricated by using two-step electrochemical anodization,electrodeposition,and photoreduction methods.Comparative studies were conducted to elucidate the effects of rGO and Ag on the morphology,photoresponse,charge transfer,and photoelectric properties of TiO2.Firstly,scanning electron microscope images confirm that the Ag nanoparticles adhered on TiO2 R/T and TiO2 R/T-rGO have similar diameter of 20 nm except for TiO2 R-rGO/T.Then,the UV-Vis DRS and scatter spectra reveal that the optical property of the Ag-TiO2 R/T-rGO ternary composite is enhanced,ascribing to the visible light absorption of plasmonic Ag nanoparticles and the weakening effect of rGO on light scattering.Meanwhile,intensity-modulated photocurrent spectroscopy and photoluminescence spectra demonstrate that rGO can promote the hot electrons transfer from Ag nanoparticles to Ti substrate,reducing the photogenerated electron-hole recombination.Finally,Ag-TiO2 R/T-rGO photoanode exhibits high photocurrent density(0.98 mA cm?2)and photovoltage(0.90 V),and the stable H2 evolution rate of 413μL h?1 cm?2 within 1.5 h under AM 1.5 which exceeds by 1.30 times than that of pristine TiO2 R/T.In line with the above results,this work provides a reliable route synergizing rGO with plasmonic metal nanoparticles for photocatalysis,in which,rGO presents a broad absorption spectrum and effective photogenerated electrons transfer.

Anatase Titanium Dioxide Coated Single Wall Carbon Nanotubes Manufactured by Sonochemical-Hydrothermal Technique

A novel, cost effective, sonochemical-hydrothermal technique was used for the deposition of nanosized anatase titanium dioxide (TiO2) onto single wall carbon nanotubes (SWCNTs). This technique is described and the characterization of the synthesized TiO2-SWCNTs is reported. The characterization techniques employed include scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD). From the characterization the size and morphology of the synthesized TiO2 nanoparticles (deposited on the SWCNTs) are reported. Furthermore, it is demonstrated that the created TiO2 nanoparticles are chemically attached to the SWCNTs. Also, an important correlation between calculated TiO2 crystal size and the red shifts in the lowest Raman TiO2 (E.g.) predominate peak is reported. The synthesized TiO2-SWCNTs have potential for large scale production and application in a variety of new technologies such as clean energy power generation devices, electrical storage devices, photocatalysts, and sensors.

Removal of nanoparticles by coagulation

Nanoparticles（NPs）from anthropogenic sources have applications in several commercial products,including cosmetics,pharmaceuticals,and materials.There is evidence that during their usage and disposal,engineered nanoparticles can and will be released into wastewater（Gottschalk et al.,2013;Pasricha et al.,2012;Westerhoff et al.,2013;Zheng et al.,2015）.If water and wastewater treatment plants are inefficient or incapable of removing NPs from water,NPs will be released with the treated effluent,entering drinking water sources and natural aquatic environments,increasing exposure for plants,microorganisms,

Plasmon-enhanced Performance of Dye-sensitized Solar Cells Based on Electrodeposited Ag Nanoparticles

In the present work, pulse current deposition is used to deposit evenly distributed and uniformly sized Ag nanoparticles onto a TiO2 nanotube array as photoelectrode in dye-sensitized solar cells （DSSCs）, and the size and amount of loading Ag nanoparticles are controlled by the pulse deposition time. Due to the enhanced light absorption and electron-hole separation caused by plasmon effect, DSSCs based on Ag-modified TiO2 nanotube arrays show higher energy conversion efficiencies than those based on bare nanotubes with the same tube length. Particularly, DSSC based on nanotubes modified using pulse deposition time 1 s/3 s delivers the highest energy conversion efficiency of 1.68% and the largest short-circuit current of 4.37 mA/ cm2, while DSSC consisting of bare nanotubes exhibits efficiency of 1.20% and short-circuit current of 2.27 mA/cm2, which represents a 40% enhancement of cell efficiency in DSSC based on Ag-modified Ti02 nanotubes. It is also noted that overly long pulse deposition time will not further increase DSSC efficiency due to agglomeration of Ag particles. For example, when the pulse deposition time is increased to 2 s/6 s, DSSC based on Ag-modified nanotubes exhibits a lower efficiency of 1.42%. Moreover, high-concentration TiCI4 treatment on TiO2 nanotube arrays can further increase the energy conversion efficiencies to 3.82% and 2.61% for DSSC based on Ag-modified TiO2 nanotubes and DSSC based on bare TiO2 nanotubes, respectively, by significantly creating more surface area for dye loading.