A Rational Solid-State Synthesis of Supported Au-Ni Bimetallic Nanoparticles with Enhanced Activity for Gas-Phase Selective Oxidation of Alcohols

Self-Transformation of Atomically Precise Alloy Nanoclusters to Plasmonic Alloy Nanocrystals: Evaluating Photosensitization in Solar Water Oxidation

Atomically precise alloy nanoclusters (NCs) inherit the advantages of homometal NC counterparts such as atomic stacking fashion, quantum confinement effect, and enriched catalytic active sites and simultaneously possess the advantageous physicochemical properties such as significantly enhanced photostability, ideal photosensitization efficiency, and favorable energy band structure. Nevertheless, elucidation of the roles of alloy NCs and alloy nanocrystals (NYs) in boosting solar water oxidation has so far not yet been reported owing to the deficiency of applicable alloy NC photosystems. Herein, utilizing the generic thermal-induced self-transformation of alloy NCs to alloy NYs, we comprehensively explore the photosensitization properties of glutathione (GSH)-capped alloy NCs (AgxAu1-x@GSH and CuxAu1-x@GSH) and the corresponding alloy NY (AgAu and CuAu) counterparts in solar water oxidation reaction. The results imply that photoelectrons of alloy NCs surpass the hot electrons over plasmonic alloy NYs in stimulating the PEC water oxidation reaction. The photoelectrons of alloy NCs demonstrate lower interfacial charge-transfer resistance, longer carrier lifetime, and a more enhanced photosensitization effect with respect to the plasmonic alloy NYs, contributing to the significantly boosted photoelectrochemical water oxidation activities. Moreover, we found that our result is universal.

Efficient oxidation of benzyl alcohol into benzaldehyde catalyzed by graphene oxide and reduced graphene oxide supported bimetallic Au-Sn catalysts

A series of bimetallic and monometallic catalysts comprising Au and Sn nanoparticles loaded on graphene oxide (GO) and reduced graphene oxide (rGO) were prepared using three distinct techniques: two-step immobilization, co-immobilization, and immobilization. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and Inductively-coupled plasma optical emission spectroscopy (ICP-OES) were used to characterize the chemical and physical properties of prepared Au-Sn bimetallic and Au or Sn monometallic nanocatalysts. The catalytic performance of the prepared nanocatalysts was evaluated in the selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using O2 as an oxidizing agent under moderate conditions. To obtain the optimal BzH yield, the experimental conditions and parameters, including the effects of the reaction time, temperature, pressure, and solvent type on BzOH oxidation, were optimized. Under optimal reaction conditions, bimetallic Au-Sn nanoparticles supported on GO (AuSn/GO-TS, 49.3%) produced a greater yield of BzH than the AuSn/rGO-TS catalysts (35.5%). The Au-Sn bimetallic catalysts were more active than the monometallic catalysts. AuSn/GO-TS and AuSn/rGO-TS prepared by the two-step immobilization method were more active than AuSn/GO-CoIM and AuSn/rGO-CoIM prepared by co-immobilization. In addition, the AuSn/GO-TS and AuSn/rGO-TS catalysts were easily separated from the mixture by centrifugation and reused at least four times without reducing the yield of BzH. These properties make Au-Sn bimetallic nanoparticles supported on GO and rGO particularly attractive for the environmentally friendly synthesis of benzaldehyde.

Boosting the catalytic behavior and stability of a gold catalyst with structure regulated by ceria

In this work, a series of colloidal gold nanoparticles with controllable sizes were anchored on carbon nanotubes (CNT) for the aerobic oxidation of benzyl alcohol. The intrinsic influence of Au particles on the catalytic behavior was unraveled based on different nanoscale-gold systems. The Au/CNT-A sample with smaller Au sizes deserved a faster reaction rate, mainly resulting from the higher dispersion degree (23.5%) of Au with the available exposed sites contributed by small gold particles. However, monometallic Au/CNT samples lacked long-term stability. CeO2 was herein decorated to regulate the chemical and surface structure of the Au/CNT. An appropriate CeO2 content tuned the sizes and chemical states of Au by electron delivery with better metal dispersion. Small CeO2 crystals that were preferentially neighboring the Au particles facilitated the generation of Au-CeO2 interfaces, and benefited the continuous supplementation of oxygen species. The collaborative functions between the size effect and surface chemistry accounted for the higher benzaldehyde yield and sustainably stepped-up reaction rates by Au-Ce5/CNT with 5 wt% CeO2.

Understanding the strain-dependent structure of Cu nanocrystals in Ag-Cu nanoalloys

The structure of octahedral Ag-Cu nanoalloys is investigated by means of basin hopping Monte Carlo (BHMC) searches involving the optimization of shape and chemical ordering. Due to the significant size mismatch between Ag and Cu, the misfit strain plays a key role in determining the structure of Ag-Cu nanoalloys. At all the compositions, segregated chemical ordering is observed. However, the shape of the Cu nanocrystal and the associated defects are significantly different. At lower amounts of Cu (as little as 2 atom %), defects close to the surface are observed leading to a highly non-compact shape of the Cu nanocrystal which is non-trivial. The number of Cu-Cu bonds is relatively lower in the non-compact shape which is contrary to the preference of bulk Ag-Cu alloys to maximize the homo-atomic bonds. Due to the non-compact shape, {100} Ag-Cu interfaces are observed which are not expected. As the amount of Cu increases, the Cu nanocrystal undergoes a shape transition from non-compact to a compact octahedron. The associated defect structure is also modified. The structural changes due to the strain effects have been explained by calculating the atomic pressure maps and the bond length distributions. The trends relating to the structure have also been verified at larger sizes.

Engineering Pt-Bi2O3 Interface to Boost Cyclohexanone Selectivity in Oxidative Dehydrogenation of KA-Oil

Oxidative dehydrogenation of KA-oil (a mixture of cyclohexanone and cyclohexanol) is an economically attractive process to produce cyclohexanone because it provides a chance to avoid the energy-intensive alcohol-ketone separation process. The application of this process, however, is hampered by the low cyclohexanone selectivity which results from the competitive adsorption of cyclohexanol and cyclohexanone on the catalyst surface. Herein, by engineering Pt-Bi2O3 interface to tune the geometric and electronic structure of Pt, we successfully weaken the cyclohexanone adsorption without compromising the oxidation of cyclohexanol. As a result, Bi2O3-Pt/SiO2 with Bi-to-Pd ratio of 0.2 exhibits a 5 times higher cyclohexanone selectivity than Pt/SiO2 at the same conversion of KA oil. Long term test suggests that the Pt-Bi2O3 interface is stable in the oxidative dehydrogenation of KA-oil.

Phytogenic Fabrication of Ag-Fe Bimetallic Nanoparticles for Cell Cycle Arrest and Apoptosis Signaling Pathways in Candida auris by Generating Oxidative Stress

Novel green synthetic nanomedicines have been recognized as alternative therapies with the potential to be antifungal agents. Apoptosis induction, cell cycle arrest and activation of the antioxidant defense system in fungal cells have also gained attention as emerging drug targets. In this study, a facile and biodegradable synthetic route was developed to prepare Ag-Fe bimetallic nanoparticles using aqueous extract of Beta vulgaris L. Surface plasmon resonance of Beta vulgaris-assisted AgNPs nanoparticles was not observed in the UV-visible region of Ag-Fe bimetallic NPs, which confirms the formation of Ag-Fe nanoparticles. Beta vulgaris-assisted Ag-Fe NPs were characterized by FTIR spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and TGA-DTG analysis for their structural and morphological properties. The as-prepared Ag-Fe NPs were well dispersed and spherical with the average particle size of 15 nm. The antifungal activity of these Ag-Fe NPs against clinical isolates of Candida auris was determined by broth microdilution and cell viability assays. For insights into mechanisms, induction of apoptosis and triggering cell cycle arrest were studied following standard protocols. Furthermore, analysis of antioxidant defense enzymes was determined spectrophotometrically. Antifungal susceptibility results revealed high antifungal activity with MIC values ranging from 0.19 to 0.39 µg/mL. Further studies showed that Ag-Fe NPs were able to induce apoptosis, cell cycle arrest in G2/M phase and disturbances in primary and secondary antioxidant enzymes. This study presents the potential of Ag-Fe NPs to inhibit and potentially eradicate C. auris by inducing apoptosis, cell cycle arrest and increased levels of oxidative stress.

Spin Polarization-Induced Facile Dioxygen Activation in Boron-Doped Graphitic Carbon Nitride

Dioxygen (O₂) activation is a vital step in many oxidation reactions, and a graphitic carbon nitride (g-C₃N₄) sheet is known as a famous semiconductor catalytic material. Here, we report that the atomic boron (B)-doped g-C₃N₄ (B/g-C₃N₄) can be used as a highly efficient catalyst for O₂ activation. Our first-principles results show that O₂ can be easily chemisorbed at the B site and thus can be highly activated, featured by an elongated O-O bond (∼1.52 Å). Interestingly, the O-O cleavage is almost barrier free at room temperatures, independent of the doping concentration. It is revealed that the B atom can induce considerable spin polarization on B/g-C₃N₄, which accounts for O₂ activation. The doping concentration determines the coupling configuration of net-spin and thus the magnitude of the magnetism. However, the distribution of net-spin at the active site is independent of the doping concentration, giving rise to the doping concentration-independent catalytic capacity. The unique monolayer geometry and the existing multiple active sites may facilitate the adsorption and activation of O₂ from two sides, and the newly generated surface oxygen-containing groups can catalyze the oxidation coupling of methane to ethane. The present findings pave a new way to design g-C₃N₄-based metal-free catalysts for oxidation reactions.

High-throughput chemiluminescence immunoassay based on Co2+/hemin synergistic catalysis for sensitive detection tetrabromobisphenol A bis(2-hydroxyethyl) ether in the environments

Here, a novel chemiluminescence (CL) immunoassay was fabricated for sensitive determination of tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE), one of typical tetrabromobisphenol A derivatives. At the indirectly competitive method, the synthesized PS@hemin@Co²⁺ was labelled by secondary antibody (Ab₂) instead of common natural enzymes, which showed excellent catalysis towards the decomposition of luminol-H₂O₂ for producing CL signal. Furthermore, the CL signal was greatly amplified owing to the synergistic catalysis of hemin and Co²⁺ in the detection system. Under the optimized conditions, the established method offered (i) low detection limit (LOD, 0.9 μg/L), which was almost 5 times lower than that using a conventional ELISA with the same antibody; (ii) a good linearity (1.6-14.3 μg/L); (iii) satisfactory accuracy and precision (recoveries, 89.67-125.33%; CV, 2.75-8.37%). The proposed CL immunoassay was applied for analysis of environmental samples from various sources collected from Jiangsu and Zhejiang province, China. And the detected concentrations were ranged in 2.4-3.7 μg/L in environmental waters and 1.8-2.4 ng/g (dry weight, dw) in soil samples, indicating great potential for trace TBBPA-DHEE detection from environmental samples.

What is the effect of Sn and Mo oxides on gold catalysts for selective oxidation of benzyl alcohol?

A series of SnO_x and MoO_x promoted gold nanoparticle catalysts were used for the aerobic oxidation of benzyl alcohol.

MOF-derived CeO2/Au@SiO2 hollow nanotubes and their catalytic activity toward 4-nitrophenol reduction

A hollow CeO₂/Au@SiO₂ sandwiched nanocatalyst with enhanced catalytic activity was prepared by using Ce-MOF as a sacrificial template.

Iron oxides with a reverse spinel structure: impact of active sites on molecule adsorption

Fe₃O₄ and γ-Fe₂O₃ with the same crystal structure reflect different catalytically active sites leading to different catalyst properties.

Molecular O2 Activation over Cu(I)-Mediated C≡N Bond for Low-Temperature CO Oxidation

The activation of molecular oxygen (O₂) is extremely crucial in heterogeneous oxidations for various industrial applications. Here, a charge-transfer complex CuTCNQ nanowire (CuTCNQ NW) array grown on the copper foam was first reported to show CO catalytic oxidation activity at a temperature below 200 °C with the activated O₂ as an oxidant. The molecular O₂ was energetically activated over the Cu(I)-mediated C≡N bond with a lower energy of -1.167 eV and preferentially reduced to ^•O₂^- through one-electron transfer during the activation process by density functional theory calculations and electron paramagnetic resonance. The theoretical calculations indicated that the CO molecule was oxidized by the activated O₂ on the CuTCNQ NW surface via the Eley-Rideal mechanism, which had been further confirmed by in situ diffuse reflectance infrared Fourier transform spectra. These results indicated that the local C≡N bond electron-state engineering could effectively improve the molecular O₂ activation efficiency, which facilitates the low-temperature CO catalytic oxidation. The findings reported here enhance our understanding on the molecular oxygen activation pathway over metal-organic nanocatalysts and provide a new avenue for rational design of novel low-cost, organic-based heterogeneous catalysts.

Polyoxometalate-based Gemini ionic catalysts for selective oxidation of benzyl alcohol with hydrogen peroxide in water

Polyoxometalate-based Gemini ionic hybrids with inherent phase transfer capability are highly efficient and recyclable catalysts in the selective oxidation of alcohols with H₂O₂ in water.