Pt nanohelices with highly ordered horizontal pore channels as enhanced photothermal materials

Density Functional Theory Study of Methanol Steam Reforming on Pt3Sn(111) and the Promotion Effect of a Surface Hydroxy Group

Methanol steam reforming (MSR) is studied on a Pt3Sn surface using the density functional theory (DFT). An MSR network is mapped out, including several reaction pathways. The main pathway proposed is CH3OH + OH → CH3O → CH2O → CH2O + OH → CH2OOH → CHOOH → COOH → COOH + OH → CO2 + H2O. The adsorption strengths of CH3OH, CH2O, CHOOH, H2O and CO2 are relatively weak, while other intermediates are strongly adsorbed on Pt3Sn(111). H2O decomposition to OH is the rate-determining step on Pt3Sn(111). The promotion effect of the OH group is remarkable on the conversions of CH3OH, CH2O and trans-COOH. In particular, the activation barriers of the O-H bond cleavage (e.g., CH3OH → CH3O and trans-COOH → CO2) decrease substantially by ~1 eV because of the involvement of OH. Compared with the case of MSR on Pt(111), the generation of OH from H2O decomposition is more competitive on Pt3Sn(111), and the presence of abundant OH facilitates the combination of CO with OH to generate COOH, which accounts for the improved CO tolerance of the PtSn alloy over pure Pt.

Fabrication and Elastic Properties of TiO2 Nanohelix Arrays through a Pressure-Induced Hydrothermal Method

TiO₂ nanohelices (NHs) have attracted extensive attention owing to their high aspect ratio, excellent flexibility, elasticity, and optical properties, which endow promising performances in a vast range of vital fields, such as optics, electronics, and micro/nanodevices. However, preparing rigid TiO₂ nanowires (TiO₂ NWs) into spatially anisotropic helical structures remains a challenge. Here, a pressure-induced hydrothermal strategy was designed to assemble individual TiO₂ NWs into a DNA-like helical structure, in which a Teflon block was placed in an autoclave liner to regulate system pressure and simulate a cell-rich environment. The synthesized TiO₂ NHs of 50 nm in diameter and 5-7 mm in length approximately were intertwined into nanohelix bundles (TiO₂ NHBs) with a diameter of 20 μm and then assembled into vertical TiO₂ nanohelix arrays (NHAs). Theoretical calculations further confirmed that straight TiO₂ NWs prefer to convert into helical conformations with minimal entropy (S) and free energy (F) for continuous growth in a confined space. The excellent elastic properties exhibit great potential for applications in flexible devices or buffer materials.

Facile synthesis of ultrathin single-crystalline palladium nanowires with enhanced electrocatalytic activities

Ultrathin single-crystalline palladium nanowires (PdNWs) were rapidly prepared using a facile one-step soft-template-directed method. The utilization of dioctadecyldimethylammonium chloride and an appropriate crystallization temperature determined the construction of PdNWs together. The obtained PdNWs exhibited good electrocatalytic performance toward formic acid oxidation.

Double-mesoporous core-shell nanosystems based on platinum nanoparticles functionalized with lanthanide complexes for in vivo magnetic resonance imaging and photothermal therapy

A double-mesoporous nanosystem was synthesized for treating as well as imaging cancer cells by using a simple and mild method. The mesoporous platinum (Pt) nanoparticles acting as a core show excellent photothermal effect under illumination with an 808 nm near infrared (NIR) laser. The mesoporous silica linked with a lanthanide (Gd) complex acting as a shell displays potential applications as a contrast agent for magnetic resonance imaging (MRI). The final mPt@mSiO₂-GdDTPA nanosystems exhibit good biocompatibility in vitro and in vivo, when investigated by methyl thiazolyl tetrazolium assay and histological and serum biochemistry analysis. The investigation of the photothermal effect shows that the mPt@mSiO₂-GdDTPA nanosystems exhibit an excellent photothermal therapy effect on HeLa cells and tumor-bearing mice. As theranostic agents, the nanosystems display a higher r₁ value than the medical contrast agent magnevist and were successfully applied to in vivo MRI of Kunming mice. Therefore, the first systematic study on the photothermal effect of nanosystems based on mesoporous Pt nanoparticles does encourage the potential applications of metal nanoparticles and hybrid nanocomposites for cancer bioimaging and therapy.

Singlet Oxygen-Engaged Selective Photo-Oxidation over Pt Nanocrystals/Porphyrinic MOF: The Roles of Photothermal Effect and Pt Electronic State

The selectivity control toward aldehyde in the aromatic alcohol oxidation remains a grand challenge using molecular oxygen under mild conditions. In this work, we designed and synthesized Pt/PCN-224(M) composites by integration of Pt nanocrystals and porphyrinic metal-organic frameworks (MOFs), PCN-224(M). The composites exhibit excellent catalytic performance in the photo-oxidation of aromatic alcohols by 1 atm O₂ at ambient temperature, based on a synergetic photothermal effect and singlet oxygen production. Additionally, in opposition to the function of the Schottky junction, injection of hot electrons from plasmonic Pt into PCN-224(M) would lower the electron density of the Pt surface, which thus is tailorable for the optimized catalytic performance via the competition between the Schottky junction and the plasmonic effect by altering the light intensity. To the best of our knowledge, this is not only an unprecedented report on singlet oxygen-engaged selective oxidation of aromatic alcohols to aldehydes but also the first report on photothermal effect of MOFs.

Facile synthesis of complex shaped Pt-Cu alloy architectures

Several intricate Pt-Cu alloy architectures have been synthesized including hexapod backbones with stretchers and caved octahedron like hexapods, as well as some other intermediates with complex structures. The mechanistic study indicates that the shape is realized via a competitive effect between etching and growth induced by different chemicals.

Methanol Oxidation on Pt3Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition

PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt3Sn(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CHxOHy, x = 1-3, y = 0-1) were strongly adsorbed and preferred decomposition rather than desorption on Pt3Sn(111). The competitive methanol decomposition started with the initial O-H bond scission followed by successive C-H bond scissions, (i.e., CH3OH → CH3O → CH2O → CHO → CO). The Brønsted-Evans-Polanyi relations and energy barrier decomposition analyses identified the C-H and O-H bond scissions as being more competitive than the C-O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt3Sn(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure.

Catalytic activities for methanol oxidation on ultrathin CuPt3 wavy nanowires with/without smart polymer

CuPt₃ nanowires are synthesized with a thermosensitive amine-terminated poly(N-isopropylacrylamide) polymer, displaying “smart” temperature-controllable electrocatalytic activity towards the methanol oxidation reaction.

Superior catalytic activity and stability for the methanol oxidation reaction of a direct methanol–air fuel cell is achieved with “clean” ultrathin CuPt₃ wavy nanowires. The nanowires are synthesized for the first time by functionalizing CuPt₃ nanoparticles with amine-terminated poly(N-isopropylacrylamide), a thermosensitive “smart” polymer having a phase transition at a liquid-electrolyte T_t (low critical solution temperature, 35 °C). Interestingly, retention of the functionalizing smart polymer on the surface of the nanowires reversibly switches the catalytic activity to lower rates above the T_t. The catalytic performance of the “clean” CuPt₃ nanowires is shown to be significantly improved over that of commercial Pt black catalyst, owing to their unique structural advantages and bimetallic synergetic effect.

CeO2 nanowires self-inserted into porous Co3O4 frameworks as high-performance "noble metal free" hetero-catalysts

Recently, mixed metal oxides have attracted tremendous interest because of their great importance for fundamental studies and practical applications in the catalytic field to replace expensive noble metals. Herein, we report the designed synthesis of novel CeO2-Co3O4 mixed metal oxides with complex nanostructures using uniform short CeO2 nanowires self-inserted into ZIF-67 nanocrystals as precursors followed by a thermal annealing treatment. Interestingly, such a synthetic strategy can be easily extended to fabricate other CeO2 nanowires inserted into metal oxide nanoframeworks such as NiCo2O4 and ZnCo2O4. Choosing the NO reduction reaction by CO as the catalytic model, the as-obtained CeO2-Co3O4 hybrids exhibited enhanced catalytic performance, which could be attributed to the strong two-phase interaction between each component.

A novel strategy to synthesize bimetallic Pt–Ag particles with tunable nanostructures and their superior electrocatalytic activities toward the oxygen reduction reaction

The ability to precisely control the nanoscale phase structure of bimetallic catalysts is required to achieve a synergistic effect between two metals for the oxygen reduction reaction (ORR).