Revisiting ultrasmall phosphine-stabilized rhodium-doped gold clusters AunRh (n = 5, 6, 7, 8): geometric, electronic, and vibrational properties.

Incorporation of other transition metals in Au nanoclusters has been thriving recently due to its effect on their electronic and photophysical properties. Here, the ultrasmall phosphine-stabilized Rh-doped gold clusters AunRh (n = 5, 6, 7, 8), with metal core structures represented as fragments of a rhodium-centered icosahedron, are considered. The geometric and electronic properties of these nanoclusters are revisited and analyzed using density functional theory (DFT). Moreover, infrared spectra are simulated to identify the effects of Rh doping on the clusters through vibrational properties. Peaks are assigned to breathing-like normal modes for all AuRh clusters except for Au8Rh, likely due to the presence of bound Cl ligands. Unlike their pure gold core counterparts, the % motions of both Au and Rh atoms are lower in the mixed metal clusters, suggesting more restrained metal cores by rhodium, which could result in other novel physical and chemical properties not hitherto discovered.

In Situ Incorporation of Atomically Precise Au Nanoclusters within Zeolites for Ambient Temperature CO Oxidation.

Preserving ultrasmall sizes of metal particles is a key challenge in the study of heterogeneous metal-based catalysis. Confining the ultrasmall metal clusters in a well-defined crystalline porous zeolite has emerged as a promising approach to stabilize these metal species. Successful encapsulation can be achieved by the addition of ligated metal complexes to zeolite synthesis gel before hydrothermal synthesis. However, controlling the metal particle size during post-reduction treatment remains a major challenge in this approach. Herein, an in situ incorporation strategy of pre-made atomically precise gold clusters within Na-LTA zeolite was established for the first time. With the assistance of mercaptosilane ligands, the gold clusters were successfully incorporated within the Na-LTA without premature precipitation and metal aggregation during the synthesis. We have demonstrated that the confinement of gold clusters within the zeolite framework offers high stability against sintering, leading to superior CO oxidation catalytic performance (up to 12 h at 30 °C, with a space velocity of 3000 mL g-1 h-1).

Degradation of sulfamethoxazole in water by AgNbO3 photocatalyst mediated by persulfate.

In this paper, silver niobate (AgNbO3) material was synthesized by a solid-state reaction. AgNbO3 was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) measurement. The photocatalytic activity of AgNbO3 was investigated in degradation of sulfamethoxazole (SMX) under visible light, which is a widely used antibiotic with significant threats towards health and aquatic organisms. Persulfate (PS) oxidant was found to improve the efficiency of the proposed photocatalytic removal of SMX by AgNbO3. The different operational parameters in the AgNbO3/PS/Vis system were investigated. The best photocatalytic performance was achieved with 0.5 g L-1 AgNbO3, 1.0 mM PS, and pH = 5.0 as the optimal conditions, achieving 98% of SMX degradation after 8 h of visible-light irradiation. Scavenger and electron spin resonance (ESR) experiments were carried out to identify the major reactive species in the SMX degradation and to propose the photocatalytic mechanism by the AgNbO3/PS/Vis system. The photodecomposition was found to be majorly caused by holes and ˙O2 - species, with ˙OH and SO4˙- radicals contributing to improve the photocatalytic process. The AgNbO3 catalyst was stable and reusable with efficient photocatalytic activity in three successive recycling experiments and its XRD patterns remained virtually unchanged. The reported process of PS activation by the AgNbO3 photocatalyst is promising for visible-light application in remediation of antibiotic-contaminated water.

Graphene Bridge for Photocatalytic Hydrogen Evolution with Gold Nanocluster Co-Catalysts.

Herein, the UV light photocatalytic activity of an Au101NC-AlSrTiO3-rGO nanocomposite comprising 1 wt% rGO, 0.05 wt% Au101(PPh3)21Cl5 (Au101NC), and AlSrTiO3 evaluated for H2 production. The synthesis of Au101NC-AlSrTiO3-rGO nanocomposite followed two distinct routes: (1) Au101NC was first mixed with AlSrTiO3 followed by the addition of rGO (Au101NC-AlSrTiO3:rGO) and (2) Au101NC was first mixed with rGO followed by the addition of AlSrTiO3 (Au101NC-rGO:AlSrTiO3). Both prepared samples were annealed in air at 210 °C for 15 min. Inductively coupled plasma mass spectrometry and high-resolution scanning transmission electron microscopy showed that the Au101NC adhered almost exclusively to the rGO in the nanocomposite and maintained a size less than 2 nm. Under UV light irradiation, the Au101NC-AlSrTiO3:rGO nanocomposite produced H2 at a rate 12 times greater than Au101NC-AlSrTiO3 and 64 times greater than AlSrTiO3. The enhanced photocatalytic activity is attributed to the small particle size and high loading of Au101NC, which is achieved by non-covalent binding to rGO. These results show that significant improvements can be made to AlSrTiO3-based photocatalysts that use cluster co-catalysts by the addition of rGO as an electron mediator to achieve high cluster loading and limited agglomeration of the clusters.

Photocatalytic Degradation of Ethiofencarb by a Visible Light-Driven SnIn4S8 Photocatalyst.

This work reports the preparation and detailed characterization of stannum indium sulfide (SnIn4S8) semiconductor photocatalyst for degradation of ethiofencarb (toxic insecticide) under visible-light irradiation. The as-prepared SnIn4S8 showed catalytic efficiency of 98% in 24 h under optimal operating conditions (pH = 3, catalyst dosage of 0.5 g L-1). The photodegradation reaction followed pseudo-first-order kinetics. The major intermediates have been identified using gas chromatography/mass spectrometry. •O2- and •OH radicals appeared to be the primary active species in the degradation process as revealed by scavenger and electronic spin resonance studies, while photogenerated holes had a secondary role in this process. A plausible mechanism involving two routes was proposed for ethiofencarb degradation by SnIn4S8 after identifying the major intermediate species: oxidative cleavage of the CH2-S and the amide bonds of the carbamate moiety. Lastly, SnIn4S8 was found to be efficient, stable, and reusable in treating real water samples in three successive photodegradation experiments. This study demonstrates the prospect of SnIn4S8 photocatalysis in treatment of natural and contaminated water from extremely toxic organic carbamates as ethiofencarb.

Oxygen-deficient bismuth molybdate nanocatalysts: Synergistic effects in boosting photocatalytic oxidative coupling of benzylamine and mechanistic insight.

Herein, bismuth molybdate (Bi2MoO6) nanocatalysts containing oxygen vacancies (OVs) are found to considerably promote the photocatalytic performance toward oxidative coupling of benzylamine to N-benzylidenebenzylamine under visible light irradiation. The structure-activity relationship for this interesting catalyst is revealed for the first time. The oxygen-deficient Bi2MoO6 nanoplatelets (BMO-NPs) are synthesized using ethylene glycol-ethanol solvent mixture as a reaction medium in solvothermal method. A comparison with hydrothermally prepared Bi2MoO6 square-like sheets (BMO-SHs) suggests that the nanoplatelets are much smaller in size and contain higher amount of OVs. Benzylamine conversion over the BMO-NPs is ca. 4.0 times higher than that over the BMO-SHs and ca. 3.8 and ca. 34.6 times higher than that over the commercial benchmark TiO2 P25 and BiVO4 catalysts, respectively. The BMO-NPs achieve more than 80% product yield within 2 h of irradiation regardless of substituents of benzylamine derivatives. The enhanced activity of BMO-NPs is due to synergistic roles of high surface-to-volume ratio and OVs, providing enlarged active area, extended light absorption range and improved charge separation and transfer efficiency as evidenced from UV-vis DRS, BET surface area, photocurrent response, electrochemical impedance spectroscopy, and time-resolved fluorescence decay measurements. EPR-trapping and radical scavenging experiments indicate O2- as a main active species rather than 1O2 and a plausible imine formation mechanism via O2--assisted charge transfer is proposed accordingly. The work offers an alternative facile preparation method to design efficient semiconductor photocatalysts and for the first time reveals a possible benzylamine coupling mechanism over the oxygen-deficient Bi2MoO6 nanocatalyst.

Recent applications of click chemistry for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles.

Glycoscience, despite its myriad of challenges, promises to unravel the causes of, potential new detection methods for, and novel therapeutic strategies against, many disease states. In the last two decades, glyco-gold nanoparticles have emerged as one of several potential new tools for glycoscientists. Glyco-gold nanoparticles consist of the unique structural combination of a gold nanoparticle core and an outer-shell comprising multivalent presentation of carbohydrates. The combination of the distinctive physicochemical properties of the gold core and the biological function/activity of the carbohydrates makes glyco-gold nanoparticles a valuable tool in glycoscience. In this review we present recent advances made in the use of one type of click chemistry, namely the azide-alkyne Huisgen cycloaddition, for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles.

Apparatus for the investigation of high-temperature, high-pressure gas-phase heterogeneous catalytic and photo-catalytic materials.

A high-temperature, high-pressure, pulsed-gas sampling and detection system has been developed for testing new catalytic and photocatalytic materials for the production of solar fuels. The reactor is fitted with a sapphire window to allow the irradiation of photocatalytic samples from a lamp or solar simulator light source. The reactor has a volume of only 3.80 ml allowing for the investigation of very small quantities of a catalytic material, down to 1 mg. The stainless steel construction allows the cell to be heated to 350 °C and can withstand pressures up to 27 bar, limited only by the sapphire window. High-pressure sampling is made possible by a computer controlled pulsed valve that delivers precise gas flow, enabling catalytic reactions to be monitored across a wide range of pressures. A residual gas analyser mass spectrometer forms a part of the detection system, which is able to provide a rapid, real-time analysis of the gas composition within the photocatalytic reaction chamber. This apparatus is ideal for investigating a number of industrially relevant reactions including photocatalytic water splitting and CO2 reduction. Initial catalytic results using Pt-doped and Ru nanoparticle-doped TiO2 as benchmark experiments are presented.

Atomically resolved structure of ligand-protected Au9 clusters on TiO2 nanosheets using aberration-corrected STEM.

Triphenylphosphine ligand-protected Au9 clusters deposited onto titania nanosheets show three different atomic configurations as observed by scanning transmission electron microscopy. The configurations observed are a 3-dimensional structure, corresponding to the previously proposed Au9 core of the clusters, and two pseudo-2-dimensional (pseudo-2D) structures, newly found by this work. With the help of density functional theory (DFT) calculations, the observed pseudo-2D structures are attributed to the low energy, de-ligated structures formed through interaction with the substrate. The combination of scanning transmission electron microscopy with DFT calculations thus allows identifying whether or not the deposited Au9 clusters have been de-ligated in the deposition process.

Size-optimized galactose-capped gold nanoparticles for the colorimetric detection of heat-labile enterotoxin at nanomolar concentrations.

The development of a galactose-capped gold nanoparticle-based colorimetric sensor for the detection of the lectin heat-labile enterotoxin is reported. Heat-labile enterotoxin is one of the pathogenic agents responsible for the intestinal disease called 'traveller's diarrhoea'. By means of specific interaction between galactose moieties attached to the surface of gold nanoparticles and receptors on the B-subunit of heat-labile enterotoxin (LTB), the gold nanoparticles reported here act as an efficient colorimetric sensor, which can detect the toxin at nanomolar concentrations. The effect of gold nanoparticle size on the detection sensitivity was investigated in detail. Amongst the various sizes of gold nanoparticles studied (2, 7, 12, and 20 nm), the 12 nm sized gold nanoparticles were found to be the most efficient, with a minimum heat-labile enterotoxin detection concentration of 100 nM. The red to purple colour change of the gold nanoparticle solution occurred within two minutes, indicating rapid toxin sensing.

Gold Nanoparticles Decorated with Sialic Acid Terminated Bi-antennary N-Glycans for the Detection of Influenza Virus at Nanomolar Concentrations.

Invited for this month's cover picture is the group of Professor Antony Fairbanks and his collaborators at the University of Canterbury and University of Otago. The cover shows the isolation of complex bi-antennary oligosaccharides from hens' eggs and their conjugation to gold nanoparticles. Gold nanoparticles carrying these sugars can then bind to specific receptors (hemagglutinin) on the surface of the influenza virus, causing particle aggregation, which changes their spectroscopic properties. Upon aggregation, they undergo a red-shift in their surface plasmon resonance, as illustrated by the bound particles shining in the cover image. These changes in spectroscopic properties are the basis of a detection system capable of detecting viral hemagglutinin at nanomolar concentrations, as well as the virus itself. For more details, see the Full Paper on p. 708 ff.Read the full text of the article at 10.1002/open.201500109.

Gold Nanoparticles Decorated with Sialic Acid Terminated Bi-antennary N-Glycans for the Detection of Influenza Virus at Nanomolar Concentrations.

Gold nanoparticles decorated with full-length sialic acid terminated complex bi-antennary N-glycans, synthesized with glycans isolated from egg yolk, were used as a sensor for the detection of both recombinant hemagglutinin (HA) and whole influenza A virus particles of the H1N1 subtype. Nanoparticle aggregation was induced by interaction between the sialic acid termini of the glycans attached to gold and the multivalent sialic acid binding sites of HA. Both dynamic light scattering (DLS) and UV/Vis spectroscopy demonstrated the efficiency of the sensor, which could detect viral HA at nanomolar concentrations and revealed a linear relationship between the extent of nanoparticle aggregation and the concentration of HA. UV/Vis studies also showed that these nanoparticles can selectively detect an influenza A virus strain that preferentially binds sialic acid terminated glycans with α(2→6) linkages over a strain that prefers glycans with terminal α(2→3)-linked sialic acids.

Phosphine-stabilised Au9 clusters interacting with titania and silica surfaces: the first evidence for the density of states signature of the support-immobilised cluster.

Chemically made, atomically precise phosphine-stabilized clusters Au9(PPh3)8(NO3)3 were deposited on titania and silica from solutions at various concentrations and the samples heated under vacuum to remove the ligands. Metastable induced electron spectroscopy was used to determine the density of states at the surface, and X-ray photoelectron spectroscopy for analysing the composition of the surface. It was found for the Au9 cluster deposited on titania that the ligands react with the titania substrate. Based on analysis using the singular value decomposition algorithm, the series of MIE spectra can be described as a linear combination of 3 base spectra that are assigned to the spectra of the substrate, the phosphine ligands on the substrate, and the Au clusters anchored to titania after removal of the ligands. On silica, the Au clusters show significant agglomeration after heat treatment and no interaction of the ligands with the substrate can be identified.

Chemically synthesised atomically precise gold clusters deposited and activated on titania. Part II.

Synchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Au(n)(PPh3)y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O2, or in O2 followed by H2 atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O2. From the position of the Au 4f(7/2) peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters.

Chemically-synthesised, atomically-precise gold clusters deposited and activated on titania.

Synchrotron XPS was used to investigate a series of chemically-synthesised, atomically-precise gold clusters Au(n)(PPh(3))(y) (n = 8, 9, 11 and 101, with y depending on cluster size) immobilized on titania nanoparticles. The gold clusters were washed with toluene at 100 °C or calcined at 200 °C to remove the organic ligand. From the position of the Au 4f(7/2) peak it is concluded that cluster size is not altered through the deposition. From the analysis of the phosphorous spectra, it can be concluded that the applied heat treatment removes the organic ligands. Washing and calcination leads to partial oxidation and partial agglomeration of the clusters. Oxidation of the clusters is most likely due to the interaction of the cluster core with the oxygen of the titania surface after removal of ligands. The position of the Au 4f(7/2) peak indicates that the size of the agglomerated clusters is still smaller than that of Au(101).

Selective oxidation with dioxygen by gold nanoparticle catalysts derived from 55-atom clusters.

Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic properties, but the origin of the catalytic activity is still not fully understood. Experimental work on gold particles supported on a titanium dioxide (110) single-crystal surface has established a striking size threshold effect associated with a metal-to-insulator transition, with gold particles catalytically active only if their diameters fall below approximately 3.5 nm. However, the remarkable catalytic behaviour might also in part arise from strong electronic interaction between the gold and the titanium dioxide support. In the case of industrially important selective oxidation reactions, explanation of the effectiveness of gold nanoparticle catalysts is complicated by the need for additives to drive the reaction, and/or the presence of strong support interactions and incomplete understanding of their possible catalytic role. Here we show that very small gold entities ( approximately 1.4 nm) derived from 55-atom gold clusters and supported on inert materials are efficient and robust catalysts for the selective oxidation of styrene by dioxygen. We find a sharp size threshold in catalytic activity, in that particles with diameters of approximately 2 nm and above are completely inactive. Our observations suggest that catalytic activity arises from the altered electronic structure intrinsic to small gold nanoparticles, and that the use of 55-atom gold clusters may prove a viable route to the synthesis of robust gold catalysts suited to practical application.

Highly efficient catalysts for the hydrogenation of nitro-substituted aromatics.

Nanoparticles of Co and NiPd, derived from colloidal precursors and supported on commercially available non-ordered mesoporous silica, are highly effective, cheap, recyclable and industrially viable catalysts for the hydrogenation of a range of nitro-substituted aromatics under mild conditions.

Production of carbon nanofibers in high yields using a sodium chloride support.

A new route for the highly convenient scalable production of carbon nanofibers on a sodium chloride support has been developed. Since the support is nontoxic and soluble in water, it can be easily removed without damage to the nanofibers and the environment. Nanofiber yields of up to 6500 wt % relative to the nickel catalyst have been achieved in a growth time of 15 min. Electron microscopy (SEM, TEM) and thermal gravimetric analysis (TGA) indicated that the catalytically grown carbon had relatively little thermal over-growth and possessed either a herringbone or a semi-ordered nanostructure, depending on the growth conditions.