The nature of crystal facet effect of TiO2-supported Pd/Pt catalysts on selective hydrogenation of cinnamaldehyde: electron transfer process promoted by interfacial oxygen species.

Supported noble metal nanocatalysts typically exhibit strong crystal plane dependent catalytic behavior, but their working mechanism is still unclear. Herein, using anatase TiO2 with well-exposed crystal facets of {101}, {100} and {001} as a prototype support, Pd- and Pt-based supported TiO2 nanocatalysts (TiO2-Pd and TiO2-Pt) were prepared by chemical reduction with NaBH4 as reducer, and they showed a distinct metal-dependent crystal facet effect in the selective hydrogenation of cinamaldehyde (CAL). For Pd-based nanocatalysts, most Pd species on the {100} plane of TiO2 are present in the oxidized form with positive charges and unexpectedly show higher reactivity than the Pd species in the zero-valence state on the {101} and {001} planes. On the contrary, Pt species on all three crystal planes of TiO2 show zero-valence state, with relatively low conversion, but much better selectivity for hydrogenation of a CO bond than Pd-based catalysts. Well-designed experiments manipulating the stability and type of surface oxygen species confirmed that the essence of the crystal facet effect of the catalyst support actually creates a unique nanoconfined interface at the molecular level to construct a surface p-band intermediate state (PBIS), which provides a new alternative channel for surface electron transfer and consequently accelerates the reaction kinetics.

Structural water molecules dominated p band intermediate states as a unified model for the origin on the photoluminescence emission of noble metal nanoclusters: from monolayer protected clusters to cage confined nanoclusters.

In the past several decades, noble metal nanoclusters (NMNCs) have been developed as an emerging class of luminescent materials due to their superior photo-stability and biocompatibility, but their luminous quantum yield is relatively low and the physical origin of the bright photoluminescence (PL) of NMNCs remain elusive, which limited their practical application. As the well-defined structure and composition of NMNCs have been determined, in this mini-review, the effect of each component (metal core, ligand shell and interfacial water) on their PL properties and corresponded working mechanism were comprehensively introduced, and a model that structural water molecules dominated p band intermediate state was proposed to give a unified understanding on the PL mechanism of NMNCs and a further perspective to the future developments of NMNCs by revisiting the development of our studies on the PL mechanism of NMNCs in the past decade.

Tetraalkoxysilane-Assisted Self-Emulsification Templating for Controlled Mesostructured Silica Nanoparticles.

Although mesoporous silica nanoparticles (MSNs) have been intensively investigated, their mesostructure and formation mechanism are still a topic of debate. Here, we show that MSNS are generated at the interface of the biphasic water-surfactant-triethanolamine-tetraalkoxysilane (TAOS) quaternary system. The spontaneous microemulsification of the hydrophobic TAOS generates microdroplets and direct micelles that both determine the particle size and the pore size. We confirmed also that the dendritic morphology with conical pores is an intermediate species, which readily transforms into regular MSNs concomitantly with the collapse of the microemulsion due to the continuous consumption of TAOS. The prominent effect of the microemulsion on the mechanism growth as a primary template is thoroughly investigated and named here tetraalkoxysilane-assisted self-emulsification templating.

Activation of H2O Tailored by Interfacial Electronic States at a Nanoscale Interface for Enhanced Electrocatalytic Hydrogen Evolution.

Despite the fundamental and practical significance of the hydrogen evolution reaction (HER), the reaction kinetics at the molecular level are not well-understood, especially in basic media. Here, with ZIF-67-derived Co-based carbon frameworks (Co/NCs) as model catalysts, we systematically investigated the effects of different reaction parameters on the HER kinetics and discovered that the HER activity was directly dependent not on the type of nitrogen in the carbon framework but on the relative content of surface hydroxyl and water (OH-/H2O) adsorbed on Co active sites embedded in carbon frameworks. When the ratio of the OH-/H2O was close to 1:1, the Co/NC nanocatalyst showed the best reaction performance under the condition of high-pH electrolytes, e.g., an overpotential of only 232 mV at a current density of 10 mA cm-2 in the 1 M KOH electrolyte. We unambiguously identified that the structural water molecules (SWs) in the form of hydrous hydroxyl complexes absorbed on metal centers {OHad·H2O@M+} were catalytic active sites for the enhanced HER, where M+ could be transition or alkaline metal cations. Different from the traditional hydrogen bonding of water, the hydroxyl (hydroxide) groups and water molecules in the SWs were mainly bonded together via the spatial interaction between the p orbitals of O atoms, exhibiting features of a delocalized π-bond with a metastable state. These newly formed surface bonds or transitory states could be new weak interactions that synergistically promote both interfacial electron transfer and the activation of water (dissociation of O-H bonds) at the electrode surface, i.e., the formation of activated H adducts (H*). The capture of new surface states not only explains pH-, cation-, and transition-metal-dependent hydrogen evolution kinetics but also provides completely new insights into the understanding of other electrocatalytic reductions involving other small molecules, including CO2, CO, and N2.

Dynamic Pt-OH-·H2O-Ag species mediate coupled electron and proton transfer for catalytic hydride reduction of 4-nitrophenol at the confined nanoscale interface.

Generally, the catalytic transformation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at heterogeneous metal surfaces follows a Langmuir-Hinshelwood (L-H) mechanism when sodium borohydride (NaBH4) is used as the sacrificial reductant. Herein, with Pt-Ag bimetallic nanoparticles confined in dendritic mesoporous silica nanospheres (DMSNs) as a model catalyst, we demonstrated that the conversion of 4-NP did not pass through the direct hydrogen transfer route with the hydride equivalents being supplied by borohydride via the bimolecular L-H mechanism, since Fourier transform infrared (FTIR) spectroscopy with the use of isotopically labeled reactants (NaBD4 and D2O) showed that the final product of 4-AP was composed of protons (or deuterons) that originated from the solvent water (or heavy water). Combined characterization by X-ray photoelectron spectroscopy (XPS), 1H nuclear magnetic resonance (NMR) and the optical excitation and photoluminescence spectrum evidenced that the surface hydrous hydroxide complex bound to the metal surface (also called structural water molecules, SWs), due to the space overlap of p orbitals of two O atoms in SWs, could form an ensemble of dynamic interface transient states, which provided the alternative electron and proton transfer channels for selective transformation of 4-NP. The cationic Pt species in the Ag-Pt bimetallic catalyst mainly acts as a dynamic adsorption center to temporally anchor SWs and related reactants, and not as the active site for hydrogen activation.

Physical Origin of Dual-Emission of Au-Ag Bimetallic Nanoclusters.

On the origin of photoluminescence of noble metal NCs, there are always hot debates: metal-centered quantum-size confinement effect VS ligand-centered surface state mechanism. Herein, we provided solid evidence that structural water molecules (SWs) confined in the nanocavity formed by surface-protective-ligand packing on the metal NCs are the real luminescent emitters of Au-Ag bimetal NCs. The Ag cation mediated Au-Ag bimetal NCs exhibit the unique pH-dependent dual-emission characteristic with larger Stokes shift up to 200 nm, which could be used as potential ratiometric nanosensors for pH detection. Our results provide a completely new insight on the understanding of the origin of photoluminescence of metal NCs, which elucidates the abnormal PL emission phenomena, including solvent effect, pH-dependent behavior, surface ligand effect, multiple emitter centers, and large-Stoke's shift.

Caged structural water molecules emit tunable brighter colors by topological excitation.

Intrinsically, free water molecules are a colourless liquid. If it is colourful, why and how does it emit the bright colours? We provided direct evidence that when water was trapped into the sub-nanospace of zeolites, the structural water molecules (SWs) exhibited strong tunable photoluminescence (PL) emissions from blue to red colours with unprecedented ultra-long lifetimes up to the second scale at liquid nitrogen temperature. Further controlled experiments and combined characterizations by time-resolved steady-state and ultra-fast femtosecond (fs) transient optical spectroscopy showed that the singly adsorbed hydrated hydroxide complex {OH-·H2O} as SWs in the confined nanocavity is the true emitter centre, whose PL efficiency strongly depends on the type and stability of the SWs, which is dominated by H-bond interactions, such as the solvent effect, pH value and operating temperature. The emission of SWs exhibits the characteristic of topological excitations (TAs) due to the many-body quantum electron correlations in confined nanocavities, which differs from the local excitation of organic chromophores. Our model not only elucidates the origin of the PL of metal nanoclusters (NCs), but also provides a completely new insight to understand the nature of heterogeneous catalysis and interface bonding (or state) at the molecule level, beyond the metal-centred d band theory.

Surface electronic states mediate concerted electron and proton transfer at metal nanoscale interfaces for catalytic hydride reduction of -NO2 to -NH2.

Concerted electron and proton transfer is a key step for the reversible conversion of molecular hydrogen in both heterogeneous nanocatalysis and metalloenzyme catalysis. However, its activation mechanism involving electron and proton transfer kinetics remains elusive. With the most widely used catalytic hydride reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction, we evaluate the catalytic activity of noble metal nanoparticles (NPs) trapped in porous silica in aqueous NaBH4 solution. By virtue of a novel combination of catalyst design, reaction kinetics, isotope labeling, and multiple spectroscopic techniques, the real catalytic site for the conversion of -NO2 to -NH2 is identified to be the water-hydroxyl transition metal complex, which could further react with NaBH4 to form a new triangular configuration metal complex of H3B-water-hydroxyl with dynamic features. It yields an ensemble of surface electronic states (SESs) though space overlapping of p orbitals of one B and several O atoms (including the O atoms of 4-NP), which could act as an alternative channel for concerted electron and proton transfer. This work highlights the critical role of the conceptual SESs model in heterogeneous catalysis to tune the chemical reactivity and also sheds light on the intricate working of the [FeFe]-hydrogenases.

Intrarenal delivery of bFGF-loaded liposome under guiding of ultrasound-targeted microbubble destruction prevent diabetic nephropathy through inhibition of inflammation.

Basic fibroblast growth factor (bFGF) has shown great therapeutic effects for diabetic nephropathy (DN). However, its clinical applications are limited due to its short half-life, low stability and poor penetration. Herein, a bFGF-loaded liposome (bFGF-lip) was constructed and combined with ultrasound-targeted microbubble destruction (UTMD) to overcome these drawbacks. bFGF-lip exhibited spherical morphology with a diameter of 171.1 ± 14.2 nm and a negative zeta potential of -5.15 ± 2.08 mV, exhibiting a sustained-release profile of bFGF. DN rat models were successfully induced by streptozotocin. After treatment with bFGF-lip + UTMD, the concentration of bFGF in kidney of DN rats was significantly enhanced in comparison with free bFGF treatment. Additionally, the morphology and the function of the kidneys were obviously recovered after bFGF-lip + UTMD treatment as shown by ultrasonography and histological analyse. The molecular mechanism was associated with the inhibition of renal inflammation. After treatment with bFGF-lip + UTMD, the activation of NF-κB was obviously reduced in the renal tissues, and downstream inflammatory mediators including TGF-ß1, MCP-1, IL-6 and IL-1ß were also down regulated. In addition, inflammation-induced cellular apoptosis of renal tubular cells was also significantly inhibited by detecting Bax, caspase-3 and Bcl-2. Therefore, bFGF-lip in combination with UTMD might be a potential strategy to reverse the progression of early DN.