H₂O₂ Electrochemical Sensing And Direct Synthesis Catalyst Based On Pd Nanoparticle

With more attention to health and environment, many researches have been put into reducing the pollution from industrial production and analysis techniques. In this thesis, we combine the unique catalytic properties of palladium nanoparticles, Pd NPs with controlled size and coverage were deposited on different substrates by using gas phase cluster beam deposition for non-enzymatic hydrogen peroxide detection and heterogeneous catalysis. respectively. The main research results are as follows:1. The Pd nanoparticles (PdNPs) were fabricated on glass carbon electrodes (GCEs) by using gas phase cluster beam deposition. The Pd NPs fabricated by this method have the advantages of clean surface, good adhesion ability and nice dispersion. Pd NPs/GCEs possess high specific surface area, allow free access of analytes to the electrode surface, and enable the enhanced electron transfer reaction between H2O2 and the electrodes. To examine the effects of the coverage of the Pd NPs on the reduction of the H2O2, a series of Pd NPs with different deposition time have been fabricated. We have shown that the electrocatalytic ability of the Pd NPs/GCEs changes with the nanoparticle coverage. The coverage of 85% is the optimal coverage to achieve both the best sensitivity and linearity. With such optimal nanoparticle coverage, a high selective nonenzyme sensing platform for stable detection of H2O2 with a low detection limit (3.4×10-7M), high sensitivity (50.9μA mM-1) as well as a wide linear range (from 1.0×10-6 to 6.0×10-3M) has been demonstrated. All these features provide a favorable environment for the electrocatalytic reduction of H2O2 and allow the detection of H2O2 at a sufficient low applied potential (-0.12V), which effectively minimizes the interference. The fabricated device is promising for the development of sensor and biosensor based on nonenzymatic H2O2 detection.2. Bilayer graphene films (BGF) were synthesized by chemical vapor deposition(CVD) with copper foil as the growth substrate, the BGFs have transferred on GCE and indium tin oxide(ITO) glass to obtained graphene modified electrodes with good electrical conductivity. A series of Pd NPs with three different size distribution～6.47nm,～10.56nm,～12.21nm were prepared by gas phase cluster beam deposition. An investigation about electrocatalytic ability of the nanoparticle with different size distribution has been finished. The result shows that the size about 10nm of Pd nanoparticles is optimum for the reduction of H2O2. The nonenzye sensing platform shows wide linear range (4μM-13555μM), response time (typically less than 3 second) and high sensitivity (115.14μA mM-1). Pd NPs/BGF/GCEs were stored in air at room temperature for 1 week. The CV showed their response to 0.01M H2O2 retains 100%. This could be attributed to the Pd NPs which produced by the gas phase clusters beam deposition system can closely integrated with bilayer graphene. This structure could stabilize the nanoparticle. The PdNPs with size distribution-10.56nm were fabricated on BGF/ITO/glass. The Pd NPs/BGF/ITO/glass electrode shows enhanced electrocatalytic activity toward the reduction of H2O2 with response time (typically less than 3 second) and high sensitivity (186.11μA mM-1), The electrochemical activity surface area was confirmed by the cyclic voltammetry (CV) for 0.1M NaOH. The result shows that the active surface area was promoted by BGF, and the Pd NPs/BGF/GCE exhibited better electrochemical reduction of H2O2 than Pd NPs/GCE.3. Anodic alumina membranes and highly ordered TiO2 nanotube arrays were prepared by potentiostatic anodization method in a two-electrode electrochemical cell. The same amount of Pd NPs was fabricated on SiO2/Si, Al2O3, and TiO2 by using gas phase cluster beam deposition. The ultra high vacuum test system was builded. To understand the activities of catalysts, temperature programmed desorption (TPD) have been used for the direct synthesis of H2O2. The result shows that Pd NPs/TiO2 has strong adsorption for H2 and O2, but the Pd NPs/SiO2/Si and Pd NPs/Al2O3 do not have apparent adsorption. The temperature programmed surface reaction shows that Pd NPs/TiO2/Ti has a H2O2 desorption peak at 68℃, at 429℃ for Pd NPs/SiO2/Si and at 471℃ for Pd NPs/Al2O3. Combined with O2-TPD, H2-TPD and TPSR, we proposed a possible catalytic mechanism of the direct synthesis of H2O2 by Pd NPs/TiO2.