Polyoxometalate-stabilized Pt nanoparticles and their electrocatalytic activities

The synthesis of long-term stable polyoxometalate (POM)-stabilized Pt nanoparticles (NPs) is described here. By means of controlled bulk electrolysis, the reduced POM anions, SiW(12)O(40)(4-) (or SiW(12)) and H(2)W(12)O(40)(6-) (or H(2)W(12)), respectively, served the dual role of reductant and protecting/stabilizing ligand for the Pt NPs. Transmission electron microscopy (TEM) images confirmed the formation of 3 to 4 nm sized Pt NPs, which coincidently was in the same size range of the commercial Pt black that was used as a reference. Elemental XPS analyses showed W/Pt ratios of 0.12 for the SiW(12)- and 0.18 for the H(2)W(12)-stabilized Pt NPs, but found no evidence of the presence of Cl(-) anion in the samples. Controlled electrochemical (EC), UV-Vis, and IR data provided unambiguous evidence for the structural integrity of the POM anions on the Pt NP surface. CO stripping, methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) were used to assess their electrocatalytic activities. It was found that both SiW(12)- and H(2)W(12)-stabilized Pt NPs showed enhanced activities in MOR and ORR as compared to that of Pt black, with the latter having higher enhancement. These observations clearly demonstrated that the stabilizing POM anions have a profound influence on the electrocatalytic activity of the underlying Pt NPs.     

新型耐甲醇氧还原电催化剂——氮掺杂中空碳微球@铂纳米粒子复合材料

通过模板法制备了一种新型耐甲醇氧还原电催化剂——氮掺杂中空碳微球@铂纳米粒子复合材料(HNCMS@PtNPs)。首先,将铂纳米粒子负载于氨基化二氧化硅微球上,获得PtNPs/SiO₂复合材料。然后通过多巴胺自聚合反应在PtNPs/SiO₂复合材料上包裹聚多巴胺(PDA)膜,将其在氮气气氛中直接进行碳化处理并通过氢氟酸溶液刻蚀去除SiO₂,获得了内嵌有PtNPs的氮掺杂中空碳微球,标记为HNCMS@PtNPs复合材料。采用扫描电子显微镜、透射电子显微镜、X射线衍射仪、拉曼光谱仪、比表面积分析仪和X射线光电子能谱仪对HNCMS@PtNPs复合材料的形貌和结构进行了表征。采用循环伏安法和线性扫描伏安法研究了HNCMS@PtNPs复合材料的电催化氧还原性能。结果表明：HNCMS@PtNPs催化剂的Pt载量高达11.9%(w,质量分数),对氧还原反应具有高电催化活性、高稳定性和优良的抗甲醇性能,是一种具有应用潜力的直接甲醇燃料电池(DMFCs)阴极电催化剂。     

Facile preparation of Sb and oxide-coated Sb nanoparticles via cathodic dispersion of bulk Sb in different media

We report here a facile electrochemical method on the preparation of antimony nanoparticles (NPs) by dispersing a bulk antimony electrode under highly cathodic polarization in different media at room temperature, requiring neither precursor ions nor organic capping agents. The dispersion of bulk antimony in a tetrabutyl ammonium bromide (TBAB) acetonitrile solution involved the formation and oxidation of an unstable Zintl compound of antimony, and the as-prepared Sb NPs were readily transferred into Sb–Sb₂O₃ core–shell NPs during the post treatment and characterization because of the surface oxidation of Sb NPs by oxygen in the air. In contrast, Sb NPs prepared by dispersing the bulk antimony cathode in a blank aqueous NaOH solution were oxygen-resistant in the air because the strongly adsorbed hydroxide ions from the solution could stabilize the Sb NPs. The incorporation of sodium, the formation/oxidation of polyanions of antimony (Zintl ions), and the formation/decomposition of unstable antimony hydrides may all take effect for the cathodic dispersion of bulk antimony electrodes in the NaOH solution. Transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize these NPs.     

预制铂纳米颗粒对质子交换膜燃料电池用铂纳米线阴极的结构影响

铂纳米线（Pt NWs）由于其独特的结构特点,比商业Pt/C具有更高的氧还原反应（ORR）比活性。在本工作中,我们将预先制备好的铂纳米颗粒（Pt NPs）引入到碳基体中,用于诱导生长Pt NWs,获得了均匀分布Pt NWs的阴极。通过改变Pt NP载量（0~0.015 mg·cm^-2）和Pt NP来源（不同Pt含量的Pt/C）研究了所制备阴极的结构和性能。用扫描电镜对阴极表面进行了表征,并用透射电镜和X射线衍射分析了Pt NW的形貌和晶体结构。在单电池中分别进行了极化曲线和循环伏安曲线测试。当Pt NP来源为40% Pt/C且其载量为0.005 mg·cm^-2时,制备的Pt NW阴极具有最佳的单电池性能和最大的电化学表面积（ECSA）。最后,提出了预制Pt NP影响Pt NWs分布的可能机制。     

Peroxidase-like activity of mesoporous silica encapsulated Pt nanoparticle and its application in colorimetric immunoassay

Nanomaterial-based artificial enzymes have received great attention in recent year due to their potential application in immunoassay techniques. However, such potential is usually limited by poor dispersion stability or low catalytic activity induced by the capping agent essentially required in the synthesis. In an attempt to address these challenges, here, we studied the novel Pt nanoparticles (NPs) based peroxidase-like mimic by encapsulating Pt NP in mesoporous silica (Pt@mSiO₂ NPs). Compared with other nanomaterial-based artificial enzymes, the obtained Pt@mSiO₂ NPs not only exhibit high peroxidase-like activity but also have good dispersion stability in buffer saline solution when grafted with spacer PEG. Results show that when the thickness of silica shell is about 9 nm the resulting Pt@mSiO₂ NPs exhibit the catalytic activity similar to that of Pt NPs, which is approximately 26 times higher than that of Fe₃O₄ NPs (in terms of K_cat for H₂O₂). Due to the protection of silica shell, the subsequent surface modification with antibody has little effect on their catalytic activity. The analytical performance of this system in detecting hCG shows that after 5 min incubation the limit of detection can reach 10 ng mL⁻¹ and dynamic linear working range is 5–200 ng mL⁻¹. Our findings pave the way for design and development of novel artificial enzyme labeling.     

非水体系中单分子层保护团簇在超微铂电极上的量子化充电

非水体系中单分子层保护团簇在超微铂电极上的量子化充电;单层保护团簇;量子化电容充电     

PDDA修饰的碳纳米管载铂电催化剂的合成及其在碱性条件下的氧气还原反应催化性能

采用长链聚合物聚二烯丙基二甲基氯化铵(PDDA)对多壁碳纳米管(MWCNTs)进行修饰,并将采用胶体法还原出的铂(Pt)纳米粒子通过静电作用担载于PDDA修饰的多壁碳纳米管上,从而制备出Pt/PDDA/MWCNTs复合电催化剂.透射电镜(TEM)与X射线衍射(XRD)测试结果表明, Pt纳米粒子均匀地分布在MWCNTs的表面,其平均粒径约为3.6 nm.热失重分析显示催化剂的实际负载量为36%(w).旋转圆盘电极测试结果表明, Pt/PDDA/MWCNTs催化剂对碱性条件下的氧气还原反应(ORR)具有优异的催化活性.与负载量为40%(w)的商业Pt/C催化剂相比, Pt/PDDA/MWCNTs催化剂的氧气还原反应的起始电位和半波电位均正移约30 mV,其质量比活性更大.动力学研究结果进一步证实Pt/PDDA/MWCNTs催化剂比负载量为40%(w)的商业Pt/C催化剂在碱性条件下对氧气还原反应具有更优异的催化活性.     

Polymer-mediated synthesis of highly dispersed Pt nanoparticles on carbon black

A new method was developed to prepare highly dispersed Pt nanoparticles on carbon black to use as proton exchange membrane (PEM) fuel cell catalysts. This method involves using a polymer, poly(vinylpyrrolidone) (PVP), to prevent particle aggregation and thereby reduce nanoparticle sizes to achieve high dispersion. It was found that Pt nanoparticles mediated by PVP are smaller than those obtained without PVP and have a narrower size distribution. Well-dispersed Pt nanoparticles with metal loadings from 5 to 35 wt % were obtained on carbon black (Vulcan XC-72R). It was found that well-dispersed Pt nanoparticles on carbon black could be synthesized at a PVP monomers-to-Pt atoms ratio of 0.1 under our experimental conditions. Larger amounts of PVP did not produce smaller nanoparticles, but rather reduced the Pt mass loading on carbon black. The morphology of the Pt nanoparticles that were supported on carbon black was characterized with transmission electron microscopy and X-ray diffraction. Their active surface areas were determined using cyclic voltammetry in a sulfuric acid solution. High Pt dispersion was obtained for the catalysts synthesized with PVP mediation, even at Pt loadings up to 35 wt %. The catalysts prepared with PVP mediation generally showed larger active specific areas than did those prepared without PVP.     

Chemoselective Transfer Hydrogenation of Cinnamaldehyde over Activated Charcoal Supported Pt/Fe3O4 Catalyst

A variety of spherical and structured activated charcoal supported Pt/Fe₃O₄ composites with an average particle size of ～100 nm have been synthesized by a self-assembly method using the difference of reduction potential between Pt (IV) and Fe (Ⅱ) precursors as driving force. The formed Fe₃O₄ nanoparticles (NPs) effectively prevent the aggregation of Pt nanocrystallites and promote the dispersion of Pt NPs on the surface of catalyst, which will be favorable for the exposure of Pt active sites for high-efficient adsorption and contact of substrate and hydrogen donor. The electron-enrichment state of Pt NPs donated by Fe₃O₄ nanocrystallites is corroborated by XPS measurement, which is responsible for promoting and activating the terminal C=O bond of adsorbed substrate via a vertical configuration. The experimental results show that the activated charcoal supported Pt/Fe₃O₄ catalyst exhibits 94.8% selectivity towards cinnamyl alcohol by the transfer hydrogenation of cinnamaldehyde with Pt loading of 2.46% under the optimum conditions of 120℃ for 6 h, and 2-propanol as a hydrogen donor. Additionally, the present study demonstrates that a high-efficient and recyclable catalyst can be rapidly separated from the mixture due to its natural magnetism upon the application of magnetic field.     

Small‐Sized Tungsten Nitride Particles Strongly Anchored on Carbon Nanotubes and their Use as Supports for Pt for Methanol Electro‐oxidation

The anchoring of small‐sized WN (tungsten nitride) nanoparticles (NPs) with good dispersion on carbon nanotubes (CNTs) offers an effective means of obtaining promising materials for use in electrocatalysis. Herein, an effective method based on grinding treatment followed by a nitridation process is proposed to realize this goal. In the synthesis, a solution containing H₄[SiO₄(W₃O₉)₄] (SiW₁₂) and CNTs modified with polyethylenimine (PEI‐CNTs) was ground to dryness. Small‐sized WN NPs were anchored onto the CNTs with good dispersion after calcination under NH₃. Under hydrothermal assembly conditions (absence of grinding), WN particles of larger size and with inferior dispersion were obtained, demonstrating the important role of the grinding process. The benefit of the small‐sized WN has been demonstrated by using WN/CNTs as a support for Pt to catalyze the methanol electro‐oxidation reaction. The mass activity of Pt‐WN/CNTs‐G‐70 (where G denotes the grinding treatment, and 70 is the loading amount (%) of WN in the WN/CNTs) was evaluated as about 817 mA mg^?1_Pt, better that those of commercial Pt/C (340 mA mg^?1_Pt) and Pt/CNTs (162 mA mg^?1_Pt). The Pt‐WN/CNTs‐G also displayed good CO tolerance. In contrast, Pt‐WN/CNTs prepared without the grinding process displayed an activity of 344 mA mg^?1_Pt, verifying the key role of grinding treatment in the preparation of WN/CNTs with good co‐catalytic effect.     

Pt 纳米颗粒在聚二甲基二烯丙基氯化铵功能化碳纳米管上的自发沉积及其对甲醇的电氧化性能

利用聚二甲基二烯丙基氯化铵(PDDA)非共价修饰的碳纳米管(CNTs)与PtCl₆^2-之间的自发氧化还原作用, 制备了Pt 纳米颗粒(Pt NPs)/CNTs-PDDA复合催化剂. PDDA在该催化剂中具有三种作用: (1) 作为金属前驱体PtCl₆^2-还原为Pt NPs 的还原剂; (2) 作为原位产生的Pt NPs 的稳定剂; (3) 在CNTs 表面形成保护膜抑制CNTs 在甲醇电催化氧化过程中的腐蚀. 采用傅里叶变换红外(FTIR)光谱、热重分析和拉曼光谱对CNTs-PDDA进行了表征, 表明PDDA通过π-π作用已成功覆盖在CNTs 表面, 并且修饰过程没有导致CNTs 结构的破坏. 采用透射电子显微镜(TEM)对Pt NPs/CNTs-PDDA 催化剂进行了表征, 结果表明, Pt NPs 均匀地分散在CNTs上, 平均粒径约2 nm, 且粒径分布范围窄. 用循环伏安法、计时电流法进一步考察了Pt NPs/CNTs-PDDA催化剂在酸性介质中对甲醇的电催化氧化的性能. 电化学测试结果表明, 与原始CNTs 负载的Pt NPs催化剂相比,Pt NPs/CNTs-PDDA催化剂具有更高的电化学活性表面积、电催化质量比活性和稳定性.     

One-step synthesis of Pt nanoparticles/reduced graphene oxide composite with enhanced electrochemical catalytic activity

A one-step electrochemical approach for synthesis of Pt nanoparticles/reduced graphene oxide(Pt/RGO) was demonstrated.Graphene oxide(GO) and chloroplatinic acid were reduced to RGO and Pt nanoparticles(Pt NPs) simultaneously,and Pt/RGO composite was deposited on the fluorine doped SnO 2 glass during the electrochemical reduction.The Pt/RGO composite was characterized by field emission-scanning electron microscopy,Raman spectroscopy and X-ray photoelectron spectroscopy,which confirmed the reduction of GO and chloroplatinic acid and the formation of Pt/RGO composite.In comparison with Pt NPs and RGO electrodes obtained by the same method,results of cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the composite electrode had higher catalytic activity and charge transfer rate.In addition,the composite electrode had proved to have better performance in DSSCs than the Pt NPs electrode,which showed the potential application in energy conversion.     

氮掺杂有序介孔碳负载超小尺寸铂纳米颗粒催化硝基苯类化合物选择加氢

氮掺杂有序介孔碳材料不仅具有高的比表面积、大的孔容和均一可调的孔径等优点,其骨架中丰富的氮原子还可以对材料的物理化学性质、配位金属电荷密度等进行调控,是一类优异的催化剂载体.本文利用软模板(嵌段共聚物F127为模板),以间氨基苯酚为碳源和氮前体,制备出较高含氮量(9.58 wt%)和比表面积(417 m2/g),以及规则孔径分布的介孔碳材料.结果表明,制备的材料具有三维立方相结构.以该碳材料作为载体,使用传统浸渍氢气还原的策略负载纳米铂颗粒.发现氮掺杂的载体能够有效控制金属纳米颗粒的尺寸,可实现超小尺寸Pt纳米颗粒的有效负载(1.0±0.5 nm),且纳米颗粒均匀分布于介孔碳材料的孔道中.相比而言,使用相同负载方法的情况下,以不掺氮的介孔碳材料为载体,纳米粒子的尺寸较难控制(4.4±1.7 nm)且会发生孔道外颗粒聚集的情况.研究表明,骨架中的氮原子与金属间弱的相互作用对纳米粒子有稳定作用.这对制备超小尺寸的金属纳米粒子催化剂具有一定的指导意义.此外,由于纳米粒子的尺寸将大大影响催化剂活性中心的暴露程度,进而影响催化剂活性.因此,我们以硝基苯类化合物的氢化反应来评价该催化剂的催化性能.在室温和1 MPa H2的温和条件下,氮掺杂的介孔碳负载催化剂表现出了优异的催化性能.反应0.5 h,对氯硝基苯可完全转化,且选择性高达99%.相比而言,商业化的Pt/C催化剂上反应的转化率和选择性分别为89%和90%.其它传统催化剂的比较,如Pt/SiO2,Pt/TiO2,同样表明,氮掺杂介孔碳负载的催化剂具有更优异的催化性能.在相同反应条件下,Pt/SiO2催化剂只能得到46%的转化率和93%的选择性,而Pt/TiO2催化剂虽然能够实现完全转化,但选择性也仅为91%.由此可见,氮掺杂的负载催化剂可大大提高反应活性和选择性,能有效抑制脱氯现象的发生.这种高的催化性能可能与催化剂的介孔结构、氮功能化载体以及超小尺寸的Pt纳米粒子的稳定有关.由于氮原子和介孔孔道的限域作用,氮掺杂介孔碳负载的催化剂也具有良好的催化稳定性,循环使用10次后,催化活性和选择性几乎没有下降.结果表明,循环使用后的催化剂金属粒子尺寸变化不大,进一步表明氮掺杂介孔碳载体对金属纳米颗粒的稳定作用.     

Pt3Te4 nanoparticles from tellurium nanowires

We report the synthesis of platinum telluride nanoparticles (Pt(3)Te(4) NPs) in the solution phase at room temperature using a template-assisted method. The dendrimeric aggregates formed are composed of several small units of Pt(3)Te(4) NPs of ～4 nm diameter. Tellurium nanowires (Te NWs) are used as the template and the reducing agent in the growth of NPs which occurs due to the galvanic replacement reaction between Te NWs and PtCl(6)(2-). Surface-enhanced Raman scattering (SERS) of the dispersed Pt(3)Te(4) NPs was studied using crystal violet (CV) as the analyte. SERS sensitivity up to 10(-8) M of CV was observed. The Raman enhancement factor (EF) of adsorbed CV on NP aggregates was calculated to be 1.74 × 10(5). The catalytic ability of the as-synthesized Pt(3)Te(4) NPs for the reduction of 4-nitrophenol (4-NP) was studied.     

棒状结构Pt/PbWO4微米晶的合成、表征及其高光催化性能

PbWO4是一类重要的半导体,广泛运用于高能物理领域无机闪烁晶体.它具有许多独特的物理性能,如衰减时间短(10 ns)、能量密度高(8.28 cm3)、低光产率(300 photons/MeV)、短辐射长度(0.9 cm)和高抗辐照损伤等. PbWO4纳米晶体的激子荧光、热荧光和其它光学性能主要取决PbWO4晶体的形貌和微观结构.目前已经合成了不同结构的PbWO4纳米/微米晶体,如四角双锥微米晶、微米球、纳米棒、纳米纺垂体等.近年来, PbWO4的光催化性能也引起人们的重视.研究发现, PbWO4晶体的光催化性能和其形貌、微观结构密切相关.如在不同形貌的十四面体、三维多尺度微米球和纳米颗粒中, PbWO4微米球表现了极高的光催化活性.此外, PbWO4微米球由于密度大,非常容易分离,从而有利于其回收利用,在循环使用时具有很高的稳定性.因此,合成具有特殊形貌的PbWO4纳米/微米晶体具有重要的理论和现实意义.此外,合成贵金属/半导体复合纳米结构是提高光催化性能的另一有效策略.在贵金属/半导体复合纳米结构中,光生电子(e–)和(h+)的复合可以在很大程度上得到抑制,因为光生e–可以快速地迁移至贵金属颗粒中心,从而加速e–和h+的分离.本文利用水热结合焙烧法首先合成了长度大于1μm的棒状PbWO4微米晶.然后利用光化学沉积法,在PbWO4微米晶表面沉积不同含量(0.5 wt%,1 wt%,和2 wt%)的Pt纳米粒子.利用X射线衍射(XRD)、N2物理吸附、扫描电镜(SEM)、透射电镜(TEM)、光电子能谱(XPS)、光致发光谱(PL)和紫外-可见漫反射吸收光谱(UV-Vis DRS)等手段对所制PbWO4和Pt/PbWO4进行了表征.表征结果表明,合成的PbWO4和Pt/PbWO4的比表面积很小(1.5–1.9 m2/g),沉积的Pt纳米粒子为金属态. UV-Vis DRS测试表明,沉积的Pt纳米粒子在光照下可以产生表面等离子共振,促进可见光的吸收.另外, PL的结果则证实Pt纳米粒子的存在还可抑制PbWO4晶体在光照下产生的光生e–和h+的分离.而XRD和高分辨TEM分析表明PbWO4微米棒的晶体生长方向为(–102)晶体方向.电子选区衍射表明,棒状PbWO4微米晶具有极高的结晶度.以氙灯为光源进行了光催化降解染料酸性橙II的光催化性能测试.结果表明,当沉积1–2 wt%Pt纳米粒子时,可使光催化活性提高2倍左右.另外, Pt/PbWO4微米棒的密度较大,非常容易进行离心分离催化剂及其循环使用.在第一次使用时酸性橙II的降解率为93%,而在第四次使用时酸性橙II的降解率仍维持在88%,表现出很好的光催化稳定性. Pt/PbWO4具有很高的光催化活性的原因,一方面是由于其具有很高的结晶度和独特的棒状结构,另一方面是由于沉积的Pt纳米粒子在光照下可以产生表面等离子共振,促进了可见光的吸收和光生e–与h+的分离.     

Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2O3 Catalysts

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe₂O₃ supports with a truncated hexagonal bipyramid shape (Pt/α-Fe₂O₃-O) and rod-shaped α-Fe₂O₃ supports (Pt/α-Fe₂O₃-R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe₂O₃-O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe₂O₃ support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe₂O₃-O catalyst during the cycle experiment results from the stability of Pt NPs.     

Preparation and enhanced visible-light photocatalytic H2-production activity of CdS-sensitized Pt/TiO2 nanosheets with exposed (001) facets

CdS-sensitized Pt/TiO(2) nanosheets with exposed (001) facets were prepared by hydrothermal treatment of a Ti(OC(4)H(9))(4)-HF-H(2)O mixed solution followed by photochemical reduction deposition of Pt nanoparticles (NPs) on TiO(2) nanosheets (TiO(2) NSs) and chemical bath deposition of CdS NPs on Pt/TiO(2) NSs, successively. The UV and visible-light driven photocatalytic activity of the as-prepared samples was evaluated by photocatalytic H(2) production from lactic acid aqueous solution under UV and visible-light (λ ≥ 420 nm) irradiation. It was shown that no photocatalytic H(2)-production activity was observed on the pure TiO(2) NSs under UV and/or visible-light irradiation. Deposition of CdS NPs on Pt/TiO(2) NSs caused significant enhancement of the UV and visible-light photocatalytic H(2)-production rates. The morphology of TiO(2) particles had also significant influence on the visible-light H(2)-production activity. Among TiO(2) NSs, P25 and the NPs studied, the CdS-sensitized Pt/TiO(2) NSs show the highest photocatalytic activity (13.9% apparent quantum efficiency obtained at 420 nm), exceeding that of CdS-sensitized Pt/P25 by 10.3% and that of Pt/NPs by 1.21%, which can be attributed to the combined effect of several factors including the presence of exposed (001) facets, surface fluorination and high specific surface area. After many replication experiments of the photocatalytic hydrogen production in the presence of lactic acid, the CdS-sensitized Pt/TiO(2) NSs did not show great loss in the photocatalytic activity, confirming that the CdS/Pt/TiO(2) NSs system is stable and not photocorroded.     

Formation mechanism of Pt particles by photoreduction of Pt ions in polymer solutions

The formation mechanisms of metal particles (platinum (Pt) particles) in an aqueous ethanol solution of poly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction method have been studied by transmission electron microscopy (TEM) and in situ and ex situ X-ray absorption fine structure (XAFS) analysis. The average diameter of the dilute and concentrated Pt particles in the PVP solution is estimated from TEM to be 2.0 and 2.5 nm, respectively. XAFS analysis was performed for the reduction process of Pt4+ ions to metallic Pt particles for the Pt L3 edge of the colloidal dispersions of the concentrated Pt solutions. The photoreduction process proceeds by the following steps: (1) reduction of PtCl6(2-) to PtCl4(2-), (2) dissociation of Cl from PtCl4(2-), followed by reduction of Pt2+ ionic species to Pt0, (3) formation of a Pt0-Pt0 bond and particle growth by the association of Pt0-Pt0. The reduction of PtCl4(2-) to Pt0 is a slower process, compared with the reduction of PtCl6(2-) to PtCl4(2-). There is a delay between the disappearance of PtCl4(2-) and the formation of Pt0-Pt0 clusters.     

Enhanced water photolysis with Pt metal nanoparticles on single crystal TiO2 surfaces

Two novel deposition methods were used to synthesize Pt-TiO(2) composite photoelectrodes: a tilt-target room temperature sputtering method and aerosol-chemical vapor deposition (ACVD). Pt nanoparticles (NPs) were sequentially deposited by the tilt-target room temperature sputtering method onto the as-synthesized nanostructured columnar TiO(2) films by ACVD. By varying the sputtering time of Pt deposition, the size of deposited Pt NPs on the TiO(2) film could be precisely controlled. The as-synthesized composite photoelectrodes with different sizes of Pt NPs were characterized by various methods, such as SEM, EDS, TEM, XRD, and UV-vis. The photocurrent measurements revealed that the modification of the TiO(2) surface with Pt NPs improved the photoelectrochemical properties of electrodes. Performance of the Pt-TiO(2) composite photoelectrodes with sparsely deposited 1.15 nm Pt NPs was compared to the pristine TiO(2) photoelectrode with higher saturated photocurrents (7.92 mA/cm(2) to 9.49 mA/cm(2)), enhanced photoconversion efficiency (16.2% to 21.2%), and increased fill factor (0.66 to 0.70). For larger size Pt NPs of 3.45 nm, the composite photoelectrode produced a lower photocurrent and reduced conversion efficiency compared to the pristine TiO(2) electrode. However, the surface modification by Pt NPs helped the composite electrode maintain higher fill factor values.     

Hydrogenation Size-Selective Pt/Hollow Beta Catalysts

The aim of the present work is to synthesize a zeolite-based catalyst with a hollow morphology and highly dispersed metal nanoparticles (NPs) encapsulated inside the zeolite micropores. For this purpose, we have studied a treatment using tetraalkylammonium (TAA) bromides for the selective removal of a large Pt particle from the outer surface of a hollow Beta zeolite. TEM analysis reveals that we succeeded in the synthesis of a hollow beta zeolite single crystal with encapsulated particles, with a high dispersion of 50–60 %. The molecular-sieve-type mechanism of the obtained catalysts was evaluated in the model reaction of toluene and mesitylene catalytic hydrogenation. Thanks to the high dispersion. a 10-fold activity enhancement has been obtained with respect to hollow beta zeolites with encapsulated NPs recently described in the literature.