Pt-decorated TiO2 Research Articles

Effect of loading of Pt-decorated TiO2 on the enhancement of aerobic photo-oxidation of benzyl alcohol

Using Pt loaded on semiconductor supports have created new opportunities for improving catalytic performance when exposed to light. This study used the photo-deposition method to create platinum loaded on TiO2, which was then examined using TEM, ICP, X-ray diffraction, BET analysis, and CO chemisorption. The effect of loading of Pt on P25 under UV light based on photocatalytic activity was assessed and compared, resulting facilitate the electron transfer from Pt to titanium element, which in turn facilitates the aerobic oxidation of C7H8O. Benzotrifluoride (BTF) was used as a solvent in the benzyl alcohol photooxidation. Different loading of Pt on P25 was investigated and the range between 1 wt.% to 3 wt.% Pt–TiO2 through photo-deposition method gave the highest photocatalytic activity (⁓5.8 gcat−1 h−1) than others because of the size of platinum, the surface area of sample and dispersion. The platinum particle size over 1 nm (less than 1nm not enough energy for electron transfer) to and less than 4 nm (over 4 nm cover semiconductor's active sites) were given the highest activity for benzyl alcohol oxidation. The surface area of the sample is increasing with increasing platinum loading before agglomeration is happening. Higher surface area caused more active sites and active species for adsorption and desorption, resulting in better activity.

Molecular-level understanding of the deactivation pathways during methanol photo-reforming on Pt-decorated TiO2

The methanol photo-reforming offers an environmentally friendly approach for hydrogen production. However, the widely studied catalyst for this reaction, Pt loaded titanium dioxide (Pt/P25), is found to suffer from the deactivation problem. Here, we employed various techniques including in situ spectroscopy characterization to probe the underlying mechanism. The formed intermediates formaldehyde and formic acid result in the decreased activity of hydrogen production over Pt/P25. Formic acid harms the Pt co-catalyst, whereas formaldehyde can inhibit both the Pt co-catalyst and P25 photocatalyst and plays a major role in the deteriorative effect on Pt/P25. In addition, rutile in P25 is identified to be the bottleneck against the poisoning of the reaction intermediate. A deactivation mechanism is developed, which helps to troubleshoot the deactivation problem; for example, a strategy based on the chemical potential difference applied to the deactivated photocatalyst enables it to recover ∼80 % of its original hydrogen production activity.

Effect of different hole scavengers on the photoelectrochemical properties and photocatalytic hydrogen evolution performance of pristine and Pt-decorated TiO2 nanotubes

TiO2 nanotubes have been investigated in photoelectrochemistry and photocatalysis for more than a decade. However, up to now, a systematic investigation of different hole scavengers is still lacking. Here we investigate the effect of the most relevant sacrificial hole scavengers on the photoelectrochemical properties and photocatalytic H2 evolution performance of pristine and Pt-decorated anodic TiO2 nanotubes. We examine methanol, isopropanol, ethylene glycol, EDTA-Na2, as well as Na2SO3 and H2O2 and find that the incident photocurrent conversion efficiency (IPCE) of the TiO2 nanotubes in 0.1 M Na2SO4 electrolytes increases by 1.8–3.1 times, depending on the used hole scavenger. The efficiency increases in the sequence H2O2 < Na2SO3 < isopropanol < methanol < ethylene glycol < EDTA-Na2. In presence of any hole scavenger, for nanotubes in the length-range of 2–10 μm, the photocurrent spectra and the IPCE magnitude are independent of the tube length. The photocurrent onset potential (optical flatband potential) is significantly affected by the different type of scavengers, in line with their red-ox potential. Under open circuit conditions (photocatalytic conditions), organic hole scavengers lead to a 10.0–28.8 times higher H2 production by TiO2 nanotubes than the scavenger-free case, with a sequence MeOH > i-PrOH > EDTA-Na2 > EG, while little or even detrimental effects of Na2SO3 and H2O2 are observed (note, this inactivity is in contrast to photoelectrochemical H2 generation). These results are compared to results obtained for TiO2 particles, and discussed in terms of various concepts in the literature.

In-situ Platinum Plasmon Resonance Effect Prompt Titanium Dioxide Nanocube Photocatalytic Hydrogen Evolution.

Herein, Pt-decorated TiO2 nanocube hierarchy structure (Pt-TNCB) was fabricated by a facile solvothermal synthesis and in-situ photodeposition strategy. The Pt-TNCB exhibits an excellent solar-driven photocatalytic hydrogen evolution rate (337.84 μmol h-1 ), which is about 37 times higher than that of TNCB (9.19 μmol h-1 ). Interestingly, its photocatalytic property is still superior to TNCB with post modification Pt (1 wt %) (208.11 μmol h-1 ). The introduction of Pt efficiently extends the photoresponse of the composite material from UV to visible light region, simultaneously boosting their solar-driven photocatalytic performance, which attribute to the porous structure, the sub size TNCB, the SPR effect of Pt NPs and strong interaction of two components. In fact, Pt NPs can enhance collective oscillations on delocalized electrons, which is conducive to capture electrons and hinder the recombination of photogenerated electron-hole pairs, leading to the longer lifetime of photogenerated charges. The fabrication of Pt-TNCB photocatalyst with SPR effect may provide a promising method to improve visible-light photocatalytic activities for traditional photocatalysts.

Anodic TiO2 nanotubes decorated by Pt nanoparticles using ALD: An efficient electrocatalyst for methanol oxidation

Anodic TiO2 nanotube layers (TNTs) of different thicknesses (≈1, 5 and 20 µm) were homogeneously decorated with Pt nanoparticles using atomic layer deposition (ALD) and explored for the electrocatalytic activity in methanol oxidation reaction (MOR). Six different numbers of ALD cycles (NALD) – 24, 40, 56, 72, 88 and 104 – were used. Pt nanoparticles with diameter in the range of 1.3–4.6 nm were obtained for the first five NALD and a complete coating was achieved for the highest NALD (1 0 4). The SEM/TEM analyses revealed that Pt nanoparticles uniformly decorated exteriors and interiors of TNTs. A linear increase of the particle diameter of Pt was observed with increasing NALD. Highest electrocatalytic activities of Pt/TNTs electrodes represented by current density of 74 mA/cm2 were obtained for NALD = 88 and for thickest TNTs (20 µm). The electrooxidation performance of Pt-decorated TiO2 nanotube layers was thoroughly compared to reference substrates: Pt-decorated graphite sheets and TiO2 flat layers (on annealed Ti foils) as well as for a commercial Pt/C catalyst attached on graphite sheets. From chronoamperometric measurements it turned out that the catalytic activity of Pt-loaded nanotube layers is superior and long lasting compared to other substrates, where significant degree of catalyst poisoning takes place. The presented ALD decoration approach is an effective strategy for the homogeneous distribution of precious Pt nanoparticles on a high surface area catalyst support for high-performance electrocatalysis.

A Pt/TiO2 Nanotube Array Electrode for Glucose Detection and Its Photoelectrocatalysis Self-Cleaning Ability

A non-enzymatic amperometric glucose sensor was prepared based on Pt-decorated TiO2 nanotube array (NTA). TiO2 NTA was obtained through anodization, and Pt nanoparticles were loaded onto the TiO2 NTA by ion exchange. The prepared electrode exhibited a decent sensitivity of 1.01386 × 10−4 A mM−1 cm−2 at a very low potential and a detection limit of 0.2 mM glucose at a signal-to-noise ratio of 3. The mechanism of glucose electrocatalytic oxidation was also examined and a two-electronic decomposition reaction was observed. It was found that the electrode possessed outstanding self-cleaning ability such that it can be restored and used stably after being contaminated. Details of the self-cleaning process were further explored, and the polluted electrode proved to be able to clean itself after 50 cycles of cyclic voltammetry from –0.7 V to 1 V at 2.8 mW/cm2 light intensity at wavelength of 365 nm. The research results shed new light on glucose detection with Pt/TiO2 NTA electrode and provide a new way to renew the electrode surface by photoelectrocatalysis self-cleaning.

Pt-decorated TiO2 Electrocatalysts for PEFCs

For polymer electrolyte fuel cell (PEFC) electrocatalysts, carbon corrosion is one of the important technological issues to be solved. TiO2 is a possible alternative support material. In this study, vapor-grown carbon fiber (VGCF-H) conductive fillers are applied as the built-in electron-conductive backbone, on which Nb-doped TiO2 is coated and Pt nanoparticles are then impregnated. FESEM images of Pt/Ti0.95Nb0.05O2/VGCF-H reveal selective impregnation of Pt nanoparticles on the TiO2 grains rather than the VGCF-H conductive fillers. This conductive-filler-integrated electrocatalyst exhibits relatively higher electrochemical surface area (ECSA) and oxygen reduction reaction (ORR) activity, compared to the electrocatalysts without conductive fillers.

Pt-decorated TiO2 Electrocatalysts for PEFCs

Pt nanoparticles supported on carbon black (Pt/C) are widely used as polymer electrolyte fuel cell (PEFC) electrocatalysts. However, under the high potential at the cathode, carbon corrosion can occur to decrease electrocatalyst performance. In addition, fuel starvation can also cause carbon corrosion on the anode side [1]. Therefore, alternative electrocatalyst support material is desired to be developed to replace the conventional carbon black support. Metal oxide is a promising candidate. Titanium oxide (TiO2) possesses high stability in the strongly-acidic fuel cell environment on both the anode side and the cathode side. Pt/TiO2 electrocatalyst has high durability, but the initial electrochemical activity is still much lower than Pt/C, partly due to poor electronic conductivity of TiO2 [2]. To increase the initial activity of Pt/TiO2, we dope TiO2 with a small amount of Nb ions [3], and we apply conductive fillers to further improve electrical conduction in the electrocatalysts. The aim of this study is to develop TiO2-based electrocatalysts with both high durability and high electrochemical activity. Vapor grown carbon fiber (VGCF-H) were used as conductive fillers. Ti0.95Nb0.05O2 was prepared on the VGCF-H (Ti0.95Nb0.05O2/VGCF-H) by the sol-gel process. Colloidal process and Pt(acac)2 process were applied to impregnate Pt nanoparticles to obtain the electrocatalyst, denoted as Pt/Ti0.95Nb0.05O2/VGCF-H. BET specific surface area of TiO2/VGCF-H was measured for different TiO2 loadings on the conductive fillers. We then made half-cell measurements to evaluate electrochemical activities of these electrocatalysts. Electrochemical surface area (ECSA) was measured by cyclic voltammetry (CV), and oxidation reduction reaction (ORR) activity was derived from kinetically controlled current density (ik ) in the rotating disk electrode (RDE) measurement. Figure 1 shows the BET specific surface area of TiO2/VGCF-H for different TiO2 loadings. The surface area becomes larger with increasing TiO2 loading. On the other hand, agglomeration of TiO2 particles on VGCF-H becomes obvious so that the electronic conducting passway through TiO2 becomes longer, leading to a decrease in electrochemical performance. Figure 2 shows FE-SEM images of Pt/Ti0.95Nb0.05O2/VGCF-H prepared by the colloidal process and the Pt(acac)2 process. These micrographs clearly show the selective impregnation of Pt nanoparticles on TiO2 rather than VGCF-H in the colloidal process. However, there are some Pt nanoparticles locating directly on the VGCF-H after the Pt(acac)2 process, partly because of the difference in the solvent of the inorganic colloidal process and the organic Pt(acac)2process. Details on their electrochemical activities are presented at the Symposium.

Photoelectrocatalytic/photoelectro-Fenton coupling system using a nanostructured photoanode for the oxidation of a textile dye: Kinetics study and oxidation pathway

In this study, a coupled photoelectrocatalytic/photoelectro-Fenton reactor was designed to enhance the degradation efficiency of organic pollutants and tested using the azo dye Orange G as a model compound. Pt-decorated TiO2 nanotubes were used as a photoanode with an air-diffusion polytetrafluoroethylene cathode for H2O2 generation. The sum of individual effects of coupling the photoelectrocatalytic and photoelectro-Fenton processes was evaluated as a function of the decolorization and mineralization of Orange G solutions. The dye solutions were only completely decolorized in more acidic conditions (pH 3.0). The mineralization of the Orange G solutions increased in the sequence photoelectrocatalytic<electro-Fenton<coupled photoelectrocatalytic/photoelectro-Fenton due to the gradual increase in the production of OH radicals. Total organic carbon reductions of 80% for photoelectrocatalysis, 87% for electro-Fenton and 97% for the coupled processes were obtained when using an applied electric charge per unit volume of electrolyzed solution of 200mAhL−1. The Orange G decays for all treatments followed pseudo-first-order kinetics, suggesting the attack of a constant concentration of OH radicals. Aromatics such as naphthalenic and benzenic compounds were formed as by-products and were identified using LC–MS/MS analysis. In addition, the generated aliphatic acids were identified using ion-exclusion high-performance liquid chromatography. The final by-products of oxalic and formic acid were identified as ultimate by-products and formed Fe(III) complexes that were rapidly mineralized to CO2 by UV–Vis irradiation. Then, according to the identified oxidation by-products, a plausible pathway was proposed for the degradation of Orange G dye by the coupled process.

The decoration of TiO2/reduced graphene oxide by Pd and Pt nanoparticles for hydrogen gas sensing

Abstract Reduced graphene oxide (RGO) was used to improve the hydrogen sensing properties of Pd and Pt-decorated TiO2 nanoparticles by facile production routes. The TiO2 nanoparticles were synthesized by sol–gel method and coupled on GO sheets via a photoreduction process. The Pd or Pt nanoparticles were decorated on the TiO2/RGO hybrid structures by chemical reduction. X-ray photoelectron spectroscopy demonstrated that GO reduction is done by the TiO2 nanoparticles and Ti–C bonds are formed between the TiO2 and the RGO sheets as well. Gas sensing was studied with different concentrations of hydrogen ranging from 100 to 10,000 ppm at various temperatures. High sensitivity (92%) and fast response time (less than 20 s) at 500 ppm of hydrogen were observed for the sample with low concentration of Pd (2 wt.%) decorated on the TiO2/RGO sample at a relatively low temperature (180 °C). The RGO sheets, by playing scaffold role in these hybrid structures, provide new pathways for gas diffusion and preferential channels for electrical current. Based on the proposed mechanisms, Pd/TiO2/RGO sample indicated better sensing performance compared to the Pt/TiO2/RGO. Greater rate of spill-over effect and dissociation of hydrogen molecules on Pd are considered as possible causes of the enhanced sensitivity in Pd/TiO2/RGO.