Query: PVP single atom

title: A new strategy for engineering a hierarchical porous carbon anchored Fe single atom electrocatalyst and the insights into its bifunctional catalysis for flexible rechargeable Zn air batteries
abstract: Single atom catalysts (SACs) provide the most efficient metal utilization for various catalytic reactions. Meanwhile, hierarchical pore structures play a decisive role in determining the catalytic activity of N doped porous carbon materials, since normally micropores provide active locations and macro/mesopores serve as mass transport channels. However, it remains challenging to engineer highly dispersed SACs with hierarchical pore structures due to the complexity in synthesizing extra templates with controlled sizes and the possible exogenous impurities from templates. Herein, we develop a facile "confined recrystallization" self template strategy to synthesize a hierarchical porous Fe SAC on N doped carbon (Fe NC SAC) with an iron mass loading of 1.5 wt% by using polyvinylpyrrolidone (PVP) ferric nitrate and melamine. In this novel strategy, the introduced PVP can restrict the recrystallization of ferric nitrate owing to its large molecular weight. The formed nano sized ferric nitrate crystals can not only serve as multifunctional self templates to produce hierarchical pores, but also form atomically dispersed Fe Nx sites through getting nitrogen from melamine. With the Fe NC SAC as the catalyst, an excellent bifunctional ORR/OER performance and long term durability superior to those of Pt/C and RuO2 are achieved in both liquid and solid Zn air battery tests. Notably, in the flexible solid Zn air battery, the Fe NC SAC showed a high discharge voltage of 1.25 V and stable charge discharge cycling at 1 mA cm 2 under different bending conditions. Further density functional theory (DFT) calculations showed that the ORR follows the association mechanism of O2 *OOH *O *OH OH while the OER goes on through the mechanism of OH *OH *O *OOH O2, with a low theoretical overpotential of 1.21 V on the Fe NC SAC. This work not only provides a novel strategy to endow SACs with a hierarchical pore structure, but also represents an example of how to effectively investigate the correlation between the structure and catalytic activity of catalysts.

title: Single atom iron containing nanozyme with peroxidase like activity and copper nanoclusters based ratio fluorescent strategy for acetylcholinesterase activity sensing
abstract: Single atom nanozymes (SAzymes) have attracted extensive interests in bio catalysis filed because of their robustness, excellent catalytic activity and unique feature of maximum atomic utilization. Herein, the peroxidase like activity of single atom iron anchored on N doped porous carbon (Fe SAs/NC) SAzyme was successfully demonstrated and a ratio fluorescence method for acetylcholinesterase (AChE) activity sensing was constructed based on Fe SAs/NC and polyvinylpyrrolidone protected copper nanoclusters (PVP CuNCs) for the first time. With H2O2 presence, Fe SAs/NC with peroxidase like activity catalyzed oxidation of nonfluorescent o phenylenediamine (OPD) to fluorescent 2,3 diaminophenazine (DAP) with maximum fluorescence emission peak at 566 nm. Meanwhile, the generated DAP efficiently quenched PVP CuNCs fluorescence at 438 nm through fluorescence resonance energy transfer (FRET) However, AChE possessed function of catalyzing the hydrolysis of acetylthiocholine (ATCh) to generate thiocholine (TCh) which can inhibit the Fe SAs/NC peroxidase like activity to block DAP generation and preserve PVP CuNCs fluorescence. Therefore, the fluorescence intensity ratio F566/F438 of the system can serve as signal output for AChE activity sensing ranging from 2 to 70 U L 1 with a detection limit of 0.56 U L 1. Moreover, Fe SAs/NC and PVP CuNCs based system was utilized for AChE determination in human serum sample.

title: Highly Active and Carbon Resistant Nickel Single Atom Catalysts for Methane Dry Reforming
abstract: The conversion of CH4 and CO2 to syngas using low cost nickel catalysts has attracted considerable interest in the clean energy and environment field. Nickel nanoparticles catalysts suffer from serious deactivation due mainly to carbon deposition. Here, we report a facile synthesis of Ni single atom and nanoparticle catalysts dispersed on hydroxyapatite (HAP) support using the strong electrostatic adsorption (SEA) method. Ni single atom catalysts exhibit excellent resistance to carbon deposition and high atom efficiency with the highest reaction rate of 1186.2 and 816.5 mol.gNi 1.h 1 for CO2 and CH4, respectively. Although Ni single atom catalysts aggregate quickly to large particles, the polyvinylpyrrolidone (PVP) assisted synthesis exhibited a significant improvement of Ni single atom stability. Characterizations of spent catalysts revealed that carbon deposition is more favorable over nickel nanoparticles. Interestingly, it was found that, separately, CH4 decomposition on nickel nanoparticle catalysts and subsequent gasification of deposit carbon with CO2 resulted in CO generation, which indicates that carbon is reacting as an intermediate species during reaction. Accordingly, the approach used in this work for the design and control of Ni single atom and nanoparticles based catalysts, for dry reforming of methane (DRM) paves the way towards the development of stable noble metals free catalysts.

title: Prominent hydrogenation catalysis of a PVP stabilized Au34 superatom provided by doping a single Rh atom.
abstract: A single rhodium atom was precisely doped into a gold cluster Au34 stabilized by poly(N vinyl 2 pyrrolidone) (Au:PVP) as revealed by mass spectrometry. The Rh atom doped Au:PVP exhibited remarkable catalytic activity for hydrogenation reactions of olefins, which was much higher than that of recently reported Pd atom doped Au:PVP.

title: Doping a Single Palladium Atom into Gold Superatoms Stabilized by PVP: Emergence of Hydrogenation Catalysis
abstract: It is known that small gold clusters (average diameter: 1.2 nm) stabilized by poly(N vinyl 2 pyrrolidone) (Au:PVP) exhibit size specific catalysis in aerobic oxidation reactions. A recent matrix assisted laser desorption/ionization mass spectrometry (MALDI MS) study of Au:PVP revealed that Au clusters with the magic sizes of 34 and 43 were preferentially produced. Here, we reported how the doping of palladium (Pd) into Au:PVP affected the catalytic performance. MALDI MS analysis of Pd doped Au:PVP showed that a single Pd atom was selectively doped by co reduction of Au and Pd precursor ions and that PdAu33 and PdAu43 were produced as the dominant species. Extended X ray absorption fine structure (EXAFS) analysis indicated that a Pd atom was located at the exposed surface of the Au:PVP clusters. It was found that single Pd atom doping enhanced the catalytic activity for aerobic oxidation of benzyl alcohol and provided hydrogenation catalysis in a chemoselective manner to the C=C bonds over the C=O bonds.

title: Polyvinylpyrrolidone Coordinated Single Site Platinum Catalyst Exhibits High Activity for Hydrogen Evolution Reaction
abstract: The essence of developing a Pt based single atom catalyst (SAC) for hydrogen evolution reaction (HER) is the preparation of well defined and stable single Pt sites with desired electrocatalytic efficacy. Herein, we report a facile approach to generate uniformly dispersed Pt sites with outstanding HER performance via a photochemical reduction method using polyvinylpyrrolidone (PVP) molecules as the key additive to significantly simplify the synthesis and enhance the catalytic performance. The as prepared catalyst displays remarkable kinetic activities (20 times higher current density than the commercially available Pt/C) with excellent stability (76.3 of its initial activity after 5000 cycles) for HER. EXAFS measurements and DFT calculations demonstrate a synergetic effect, where the PVP ligands and the support together modulate the electronic structure of the Pt atoms, which optimize the hydrogen adsorption energy, resulting in a considerably improved HER activity.

title: BiOBr BiOI microsphere assembled with atom thick ultrathin nanosheets and its high photocatalytic activity
abstract: BiOBr BiOI composite microspheres assembled with atom thick ultrathin nanosheets have been synthesized via a simple solvothermal route with the surfactant polyvinylpyrrolidone (PVP) The structure was characterized with AFM, which confirmed the 0.9 nm thickness of the single layered nanosheets. The ultrathin structure with atomic thickness mainly relies on its lamellar structure and the reason for the formation of the few or even single layered structure is the strong intra layer chemical bonding and weak inter layer interaction. The 3D BiOBr BiOI exhibits excellent photocatalytic activity for BPA degradation under visible light irradiation. Nearly 80% of BPA was degraded in 2 h irradiation, and over 90% after 5 h. Based on these findings, the photodegradation mechanism was investigated and O2 was suggested to be the main active oxidant in the BPA removal processes. Our investigation showed that the electron hole pairs on ultrathin nanosheets can be separated effectively which resulted in significantly promoted solar driven photocatalytic activity for extremely low photocatalyst loading.

title: Facile synthesis of SnO2 nanofibers decorated with N doped ZnO nanonodules for visible light photocatalysts using single nozzle co electrospinning
abstract: Hybrid SnO2 nanofibers, decorated with N doped ZnO nanonodules, were fabricated using a single nozzle co electrospinning process with a phase separated, mixed polymer composite solution. Core (poly(acrylonitrile) PAN) and shell (poly(vinylpyrrolidone) PVP) structured nanofibers were first fabricated, and hybrid semiconductor metal oxide (SMO) nanofibers were formed by calcination. SnO2 nanofibers were created with core structures measuring 50 nm in diameter. N doped ZnO nanonodules were grown on the surface of the SnO2 nanofibers by replacing the oxygen atom in the native oxide with a nitrogen atom. The population density and morphology of the ZnO nanonodules were precisely controlled by adjusting the precursor concentration in the PVP solution. The hybrid SMO nanofibers were applied for the degradation of organic pollutants. Rhodamine B (RB) was used in photocatalytic degradation tests with UV and visible light irradiation. The photocatalytic activity of the hybrid nanofibers was higher than that of commercial TiO2 (Degussa P 25) The photocatalytic activity increased with increasing populations of nanonodules. It was attributed to the heterostructure of the SnO2 N doped ZnO nanofiber and the resulting increased interfacial area and Brunauer Emmett Teller (BET) surface area. The synthetic methodology described herein promises to be an effective approach for fabricating hybrid core shell inorganic nanostructures for catalytic applications.

title: Synthesis and characterization of [Pb{Se2P(OiPr)2}2]n pseudo polymorphs: polymeric, single source precursor enabling preparation of shape controlled lead selenide structures.
abstract: Novel lead pseudo polymorphs supported by diselenophosphate (dsep) ligands, [Pb{Se(2)P(O(i)Pr)(2)(2)(n) (1alpha and 1beta) were synthesized and structurally characterized. The two structures differed in the binding modes of the dsep ligand. Each repeating unit in 1alpha was composed of a lead atom coordinated by two dsep ligands, one in a chelating mode and the other in a bridging dangling mode. By contrast, the dsep ligands in 1beta adopted a bimetallic biconnective (mu(1) S, mu(1) S) binding pattern. The bridging dangling mode observed in 1alpha is the first example of this mode for the dsep ligand. [Pb{Se(2)P(O(i)Pr)(2)(2)(n) could be successfully utilized as a single source precursor (SSP) for growing lead selenide (PbSe) nanostructures with different shapes via the solvothermal process. The morphologies of the as grown PbSe structures were controlled by capping agents, poly(vinyl pyrrolidone) (PVP) and ethylenediamine, both bind on the {200} plane and enhance the growth rate of the <111> direction of the PbSe crystals, resulting in the formation of cubes and eight horned rod dendrites, respectively. Raman spectroscopy was utilized to investigate the phonon vibration behaviour of the as grown eight horned rod dendrites. All peaks in the Raman spectra can be attributed to longitudinal (LO) and transverse (TO) optical phonon modes of the PbSe rod dendrites.

title: Biomineralization inspired crystallization of monodisperse a Mn2O3 octahedra and assembly of high capacity lithium ion battery anodes
abstract: Uniform colloidal building blocks enable the creation of more stable, structurally sophisticated materials. Here we describe a simple polymer mediated approach to generate grams of monodisperse, single crystal a Mn2O3 nanocrystals bound by {111} facets. The technique is inspired in part by biomineralization, where organisms use macromolecular matrices or compartments to trigger the oriented nucleation and growth of crystalline phases. Polyvinylpyrrolidone (PVP) behaves as a polymeric nano reactor by coordinating to the manganese (Mn) precursor while recruiting the NOx oxidizing agent from solution to drive the co precipitation of the manganese oxide. PVP also serves as a molecular template to guide the nucleation of trigonal bipyramids composed of Mn3O4. The porosity of the Mn3O4 particles indicates that they form non classically via oriented attachment instead of atom by atom. The particles are further oxidized and transform into single crystal a Mn2O3 octahedra. This co precipitation approach is advantageous because it can generate large amounts of monodisperse nanocrystals at low economic cost. a Mn2O3 is an alternative lithium ion battery (LIB) anode material that is earth abundant and has ~2.7 times higher capacity than conventional graphite anodes. We assembled the monodisperse a Mn2O3 octahedra into LIB anodes to examine their performance in a realistic device. The a Mn2O3 octahedra exhibit good rate performance, cycling stability, coulombic efficiency and morphology retention during extended lithiation delithiation cycles compared to previous reports for this material. We attribute the improved electrochemical performance of the a Mn2O3 octahedra to the lack of agglomeration in the uniformly distributed electrode and improved lithiation of single crystalline a Mn2O3 nanoparticles.