Practical applications of total internal reflection fluorescence microscopy for nanocatalysis

Fluorescence microscopy has evolved from a purely biological tool to a powerful chemical instrument for imaging and kinetics research into nanocatalysis.And the demand for high signal-to-noise ratio and temporal–spatial resolution detection has encouraged rapid growth in total internal reflection fluorescence microscopy(TIRFM).By producing an evanescent wave on the glass–water interface,excitation can be limited to a thin plane to ensure the measured accuracy of kinetics and image contrast of TIRFM.Thus,this unique physical principle of TIRFM makes it suitable for chemical research.This review outlines applications of TIRFM in the field of chemistry,including imaging and kinetics research.Hence,this review could provide guidance for beginners employing TIRFM to solve current challenges creatively in chemistry.

Morphology-dependent nanocatalysis on metal oxides

The design and fabrication of solid nanomaterials are the key issues in heterogeneous catalysis to achieve desired performance. Traditionally, the main theme is to reduce the size of the catalyst particles as small as possible for maximizing the number of active sites. In recent years, the rapid advancement in materials science has enabled us to fabricate catalyst particles with tuna- ble morphology. Consequently, both size modulation and morphology control of the catalyst particles can be achieved inde- pendently or synergistically to optimize their catalytic properties. In particular, morphology control of solid catalyst particles at the nanometer level can selectively expose the reactive crystal facets, and thus drastically promote their catalytic performance. In this review, we summarize our recent work on the morphology impact of Co304, CeO2 and Fe203 nanomaterials in catalytic reactions, together with related literature on morphology-dependent nanocatalysis of metal oxides, to demonstrate the importance of tuning the shape of oxide-nanocatalysts for prompting their activity, selectivity and stability, which is a rapidly growing topic in heterogeneous catalysis. The fundamental understanding of the active sites in morphology-tunable oxides that are enclosed by reactive crystal facets is expected to direct the development of highly efficient nanocatalysts.

Recent progress on single-molecule nanocatalysis based on single-molecule fluorescence microscopy

Understanding the heterogeneous catalytic properties of nanoparticles is of great significance for the development of high efficient nanocatalysts, but the intrinsic heterogeneities of nanocatalysts were always covered in traditional ensemble studies. This issue can be overcome if one can follow the catalysis of individual nanoparticles in real time. This paper mainly summarizes recent developments in single- molecule nanocatalysis at single particle level in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. These developments include the revealing of catalytic kinetics of different types （plane ＆ edge） of surface atoms on individual Pd nanocubes, the observing of in situ deactivation of indi- vidual carbon-supported Pt nanoparticles during the electrocatalytic hydrogen-oxidation reaction, and the measurement of catalytic activation energies on single nanocatalysts for both product formation process and dissociation process, etc. These studies further indicate the advantages or unique abilities of single-molecule methods in the studies of nanocatalvsis or even chemical reactions.

Recent progress in single-molecule fluorescence technology in nanocatalysis

Nanoparticles(NPs)play a vital role in the energy catalysis process,so understanding the heterogeneous catalytic properties of nanocatalysts is of great significance for rationally guiding the design of catalysts.However,the traditional method obtains the average information based on the whole and cannot study the catalytic activity of a single nanoparticle.It is critical to investigate the catalytic activity of individual nanoparticles using in situ techniques.This review summarizes some of Prof.Xu's recent accomplishments in studying the catalytic behavior of nanoparticles at the single-particle level using single-molecule fluorescence microscopy(SMFM).These achievements include revealing the effect of size,shape,and surface atoms of Pd nanoparticles on catalytic kinetics and dynamics as well as obtaining the activation energy of single Au nanoparticles for catalytic reactions by single-molecule methods.It is the first time to study the kinetics and dynamics of single-atom Pt catalysts.Furthermore,the method was extended to study the Pt deactivation process for hydrogen oxidation reactions as well as the catalytic kinetics of two-electron oxygen reduction reactions of individual Fe3O4 nanoparticles in electrocatalysis.Finally,single-molecule super-resolution techniques were used to observe the evolution of the activity of single Sb doped TiO2 nanorod domains.These studies are of guiding significance for in-depth understanding and realization of rational design of optimal catalysts.

Optical approaches in study of nanocatalysis with single-molecule and single-particle resolution

Studying the activity of individual nanocata- lysts, especially with high spatiotemporal resolution of single-molecule and single-turnover scale, is essential for the understanding of catalytic mechanism and the designing of effective catalysts. Several approaches have been developed to monitor the catalytic reaction on single catalysts. In this review, we summarized the updated progresses of several new spectroscopic and microscopic approaches, including single-molecule fluorescence microscopy, surface-enhanced Raman spectroscopy, surface plasmon resonance microscopy and X-ray microscopy, for the study of single-molecule and single-particle catalysis.

Active catalytic species generated in situ in zirconia incorporated hydrogen storage material magnesium hydride

This study explores how zirconia additive interacts with MgH_(2)to improve its hydrogen storage performance.Initially it is confirmed that the zirconia added MgH_(2)powder releases hydrogen at a temperature of about 50℃below that of the additive free MgH_(2).Subsequent tests by X ray diffraction(XRD)and infrared(IR)spectroscopy techniques reveal that the ZrO_(2) mixed MgH_(2)powder contains ZrHx(2<x>1.5)and MgO secondary phases.This observation is supported by the negative Gibbs free energy values obtained for the formation of ZrH_(2)/MgO from ZrO_(2)/MgH_(2)powder samples.An X ray photoelectron spectroscopy(XPS)study reveals that apart from Zr^(4+)cations,Zr^(2+) and zero valent Zr exist in the powder.Atomic force microscopy(AFM)study reveals that the average grain size is 20 nm and the elemental line scan profiles further proves the existence of oxygen deficient Zr bearing phase(s).This study strengthens the belief that functional metal oxide additives in fact chemically interact with MgH_(2)to make active in-situ catalysts in the MgH_(2)system.

A ligand-free Heck reaction catalyzed by the in situ-generated palladium nanoparticles in PEG-400

A ligand-free Heck reaction catalyzed by in situ-generated palladium nanoparticles in PEG-400 has been developed.This catalytic system is a simple and active protocol for the Heck reaction of aryl halides under mild conditions.Comparative experiments demonstrated that the Heck reaction catalyzed by the palladium nanoparticles in situ-generated under the Heck reaction conditions was carried out much quicker than that by the in ex situ-generated ones.

Catalytic activity of recyclable resorcinarene-protected antibacterial Pd nanoparticles in C-C coupling reactions

Novel tetra-methoxy resorcinarene tetra-hydrazide（TMRTH） has been synthesized and used as a reducing agent and a capping agent for the synthesis of water-dispersible stable palladium nanoparticles（PdNPs）.The TMRTH-PdNPs were characterized by UV-Vis spectroscopy,transmission electron microscopy,energy-dispersive X-ray spectroscopy,and powder X-ray diffraction.The synthesized nanoparticles are polydispersible with a size of 5 ± 2 nm and were found to be recyclable over five cycles maintaining a catalytic activity in the Suzuki-Miyuara cross-coupling reaction.The nanocatalyst was superior in catalytic performance to conventional palladium catalysts with respect to reaction time,catalyst loading and recyclability.TMRTH-PdNPs show promise for their use in biological applications as they exhibit good antibacterial activity against gram-positive bacteria.

Single Ti atoms coupled with Ti-O clusters enable low temperature hydrogen cycling by sodium alanate

Ti-based catalysts are known to improve the hydrogen storage performance of NaAlH4by facilitating the dissociation/recombination of H-H and Al-H bonds.The catalytic activity of metallic Ti species strongly depends on its particle size and dispersity.Ti clusters and even single atoms are therefore highly desirable,but their controllable fabrication has been highly challenging.He rein,we demonstrate a novel facile sonochemical synthesis of a Ti-O clusters featuring single Ti atom catalyst at room temperature.Through reducing TiCl_(4)by MgBu_(2)with ultrasound instead of heating as driving force,numerous single Ti atoms coupled with Ti-O clusters with Ti loading on graphene(Ti_(1)/Ti-O@G)up to 22.6 wt%have been successfully obtained.The prepared Ti_(1)/Ti-O@G contributes high reactivity and superior catalytic activity,therefore enabling full dehydrogenation of NaAlH_(4)at 80℃in thermogravimetric mode and re-hydrogenation at 30℃and 10 MPa with 4.9 wt% H_(2).This fact indicates for the first time that single Ti atom catalyst with high loading is highly effective in catalyzing hydrogen cycling of NaAlH4at remarkably reduced temperatures.

Controlled Synthesis and Multifunctional Properties of FePt-Au Heterostructures

In this work FePt-Au heterostructured nanocrystals （HNCs） such as tadpole-, dumbbell-, bead-, and necklace-like nanostructures were synthesized by a facile heteroepitaxial growth of Au NCs onto FePt nanorods （NRs）. A study of the growth mechanism revealed that the morphology control of the final products can be correlated with the adsorption sites of hydrogen onto the FePt NRs, which can be manipulated by the amount of the forming gas （At/7% H2） added. Not only the optical characteristic and magnetic properties of the intrinsic materials were retained in the products, but also the FePt-Au HNCs showed the tunable multifunctional properties resulted from the interactions between Au and FePt. Moreover, for methanol oxidation, the FePt-Au HNCs exhibited enhanced catalytic activity and CO tolerance on the catalyst surface compared to commercial Pt catalysts. It is worth noting that as multifunctional units, the FePt-Au HNCs also possess a heterogeneous surface, which could potentially enable their site-specific functionalization for targeting or imaging purposes in biomedical applications. More interestingly, the catalytic properties of the FePt-Au HNCs also endow this material with application potentials in nanocatalysis.

Pd-Ni nanoparticles supported on titanium oxide as effective catalysts for Suzuki-Miyaura coupling reactions

We have successfully prepared a series of Pd- Ni/TiO2 catalysts by a one-step impregnation-reduction method. Among these catalysts with different compositions of Ni and Pd, the one with the Ni：Pd ratio of 2.95 showed the best activity. Small monodispersed Pd-Ni bimetallic nanoparticles were loaded on the surface of titanium oxide nanopowder as confirmed with TEM and EDS mapping. The XPS analysis demonstrated that Pd exists as 31% Pd（II） species and 69% Pd（0） species and all nickel is Ni（II）. The prepared Pd-Ni/TiO2 exhibited enhanced catalytic activity compared to an equal amount of Pd/TiO2 for Suzuki-Miyaura reactions together with excellent applicability and reusability.

Air-promoted selective hydrogenation of phenol to cyclohexanone at low temperature over Pd-based nanocatalysts

Attaining high activity with high selectivity at low temperature is challenging in the selective hydrogenation of phenol to cyclohexanone due to its high activation energy （Ea, 55-70 kJ/mol）. Here we report a simple and efficient strategy for phenol hydrogenation catalyzed by Pd in aqueous phase at 30 ℃ by introducing air to promote the catalysis. With the assistance of air, 〉99% conversion and 〉99% selectivity were achieved over Pd（111）/Al2O3 with an overall turnover frequency （TOF） of 621 h-1, -80 times greater than that of the state-of-art Pd catalyst at 30 ℃. Mechanism studies revealed that phenol was activated to generate phenoxyl radicals. The radicals were yielded from the reaction between phenol and hydroxyl radicals in the presence of hydrogen, oxygen and protic solvent on Pd. The phenoxyl pathway resulted in a low apparent Ea （8.2 kJ/mol） and thus high activity. More importantly, this strategy of activating substrate by air can be adapted to other Pd based catalysts, offering a new thinking for the rational design of cyclohexanone production in industry.

Resonance scattering spectral detection of ultratrace IgG using immunonanogold-HAuCl_4-NH_2OH catalytic reaction

Nanogold particles of 10 nm were used to label goat anti-human IgG (GIgG) to obtain nanogold-labeled GIgG (AuGIgG). In a citrate-HCl buffer solution of pH 2.27,AuGIgG showed a strong catalytic effect on the reaction between HAuCl4 and NH2OH to form big gold particles that exhibited a resonance scatter-ing (RS) peak at 796 nm. Under the chosen conditions,AuGIgG combined with IgG to form immuno-complex AuGIgG-IgG that can be removed by centrifuging at 16000 r/min. AuGIgG in the centrifuging solution also showed catalytic effect on the reaction. On those grounds,an immunonanogold catalytic RS assay for IgG was designed. With addition of IgG,the amount of AuGIgG in the centrifuging solution decreased; the RS intensity at 796 nm (I796 nm) decreased linearly. The decreased intensity ΔI796 nm was linear with respect to the IgG concentration in the range of 0.08-16.0 ng·mL-1 with a detection limit of 0.02 ng·mL-1. This assay was applied to analysis of IgG in sera with satisfactory sensitivity,selectivity and rapidity.

Co_3O_4 nanosheets:synthesis and catalytic application for CO oxidation at room temperature

Hexagonal β-Co(OH)2 nanosheets with edge length of 50 nm and thickness of 10 nm were hydrothermally synthesized with the aid of triethylamine.Upon calcination at 350°C in air,the β-Co(OH)2 nanosheets was converted into Co3O4 nanosheets with a similar dimension.Structural analyses during the calcination process identified that the β-Co(OH)2 precursor was initially dehydrated to HCoO2 and subsequently transferred into Co3O4.When being applied to catalyze CO oxidation at room temperature,the Co3O4 nanosheets exhibited a higher activity than the conventional spherical nanoparticles.This was perhaps related to the partial exposure of the{112}planes over the Co3O4 nanosheets.The porous structure generated during the calcination process also provided significant amounts of surface defects,which might contribute to the enhanced catalytic activity as well.

Electrocatalytic acidic oxygen evolution reaction:From nanocrystals to single atoms

Hydrogen is the most preferred choice as an energy source to replace the nonrenewable energy resources such as fossil fuels due to its beneficial features of abundance,ecofriendly,and outstanding gravimetric energy density.Splitting water through a proton exchange membrane(PEM)electrolyzer is a well-known method of hydrogen production.But the major impediment is the sluggish kinetics of oxygen evolution reaction(OER).Currently,scientists are struggling to build out an acid-stable electrocatalyst for OER with low overpotential and excellent stability.In this review,the reaction mechanism and characterization parameters of OER are introduced,and then the improvement method of metal nanocatalysts(noble metal catalysts and noble metal-free catalysts)in acidic media is discussed.Particularly,the application of single-atom catalysts in acidic OER is summarized,which is current researching focus.At the same time,we also briefly introduced the cluster phenomenon,which is easy to occur in the preparation of single-atom catalysts.More importantly,we summarized the in situ characterization methods such as in situ X-ray absorption spectroscopy,in situ X-ray photoelectron spectroscopy,and so forth,which are conducive to further understanding of OER reaction intermediates and active sites.Finally,we put forward some opinions on the development of acidic OER.

Nanocatalytic resonance scattering spectral analysis

The resonance scattering spectral technique has been established using the synchronous scanning technique on spectrofluorometry.Because of its advantages of simplicity,rapidity and sensitivity,it has been widely applied to analyses of proteins,nucleic acids and inorganic ions.This paper summarizes the application of immunonanogold and aptamer modified nanogold(AptAu) catalytic resonance scattering spectral technique in combination with the work of our group,citing 53 references.

Catalyst-free multicomponent polymerization of sulfonyl azide,aldehyde and cyclic amino acids toward zwitterionic and amphiphilic poly(N-sulfonyl amidine)as nanocatalyst precursor

Polymers with metal coordination ability are outstanding precursors of nanocatalysts,attracting numerous attention in nanocatalysis area.It has been rarely reported for the poly(N-sulfonyl amidines)as macromolecular ligands for nanocatalysis.Herein,a catalyst-free multicomponent polymerization(MCP)strategy is developed to facilely prepare a library of amphiphilic poly(Nsulfonyl amidines)with zwitterionic properties starting from disulfonyl azide,hydrophilic dialdehyde and cyclic amino acids including proline and pipecolinic acid.Metals or additives can be thorougly avoided through this method.All the obtained polymers have well-defined structures,high yields and weight-average molecular weights(M_(w)s,up to 99,300 g/mol).The unique zwitterionic property,amphiphilicity and Cu(Ⅰ)coordination ability of the obtained poly(N-sulfonyl amidines)endow them to form the polymer-Cu(Ⅰ)complexes as nanocatalysts.Such nanocatalysts exhibit high catalytic efficiency in aqueous Cucatalyzed azide-alkyne cycloaddition(CuAAC)reaction at a low Cu(Ⅰ)loading of 50 ppm.Nanocatalysts with a high ratio of polymers to Cu(Ⅰ)have also been demonstrated with Cu(Ⅰ)stabilization ability.This work provides a“green”MCP method toward zwitterionic and amphiphilic poly(N-sulfonyl amidines),and highlights their unique potentials for nanocatalysis.

Cobalt-manganese bimetallic organic frameworks catalyzed solvent-free oxidation of benzyl C-H bonds with O_(2) as sole oxidant

The selective oxidation of hydrocarbons can be used to produce oxygen-containing functional compounds such as alcohols, aldehydes or ketones and its efficient and green conversion lies in the development of efficient catalysts that activate C-H bonds and O_(2) simultaneously. In this work, the bimetallic organic framework (CoMnBDC) material with morphology of stacked nanosheets was synthesized using terephthalic acid as ligands to coordinate with Co^(2+) and Mn^(2+) cations under solvothermal conditions. As revealed by spectroscopic characterizations, the electron transfer from Mn to Co in the CoMnBDC resulted in the reduction of the Co average oxidation state and increase of the Mn average oxidation state. The CoMnBDC nanosheets were used as catalyst in catalytic oxidation of ethylbenzene, in which the redox effect promotes the effective electron transfer, the activation of O_(2) and benzyl C-H bond. The 96.2% conversion of ethylbenzene and 98.0% selectivity towards acetophenone could be obtained with oxygen as sole oxidant and solvent-free condition. The excellent catalytic performance is related to the structure of CoMnBDC and is also the best when compared with reported results. Various types of aromatic hydrocarbons containing benzyl C-H bonds can be effectively oxidized by CoMnBDC to produce corresponding ketone products. The density functional theory (DFT) calculation revealed that the redox effect leads to the relative enrichment of electrons on Co in CoMnBDC, which is conducive to the activation of O_(2);Mn with higher oxidation state is beneficial for the adsorption of ethylbenzene and activation of C-H bonds. The CoMnBDC has a lower energy barrier for transition state, making it easier for the ethylbenzene oxidation to produce acetophenone.