One-Pot Synthesis of Noble Metal/Zinc Oxide Composites with Controllable Morphology and High Catalytic Performance

Atomically dispersed ternary FeCoNb active sites anchored on N-doped honeycomb-like mesoporous carbon for highly catalytic degradation of 4-nitrophenol

In the last decades, 4-nitrophenol is regarded as one of highly toxic organic pollutants in industrial wastewater, which attracts great concern to earth sustainability. Herein, atomically dispersed ternary FeCoNb active sites were incorporated into nitrogen-doped honeycomb-like mesoporous carbon (termed FeCoNb/NHC) by a two-step pyrolysis strategy, whose morphology, structure and size were characterized by a set of techniques. Further, the catalytic activity and reusability of the as-prepared FeCoNb/NHC were rigorously examined by using 4-NP catalytic hydrogenation as a proof-of-concept model. The influence of the secondary pyrolysis temperature on the catalytic performance was investigated, combined by illuminating the catalytic mechanism. The resultant catalyst exhibited significantly enhanced catalytic features with a normalized rate constant (kapp) of 1.2 × 104 min-1g-1 and superior stability, surpassing the home-made catalysts in the control groups and earlier research. This study provides some constructive insights for preparation of high-efficiency and cost-effectiveness single-atom nanocatalysts in organic pollutants environmental remediation.

Engineering Asymmetric Strain within C-Shaped CeO2 Nanofibers for Stabilizing Sub-3 nm Pt Clusters against Sintering

Ultrafine noble metals have emerged as advanced nanocatalysts in modern society but still suffer from unavoidable sintering at temperatures above 250 °C (e.g., Pt). In this work, closely packed CeO2 grains were confined elegantly in fibrous nanostructures and served as a porous support for stabilizing sub-3 nm Pt clusters. Through precisely manipulating the asymmetry of obtained nanofibers, uneven strain was induced within C-shaped CeO2 nanofibers with tensile strain at the outer side and compressive strain at the inner side. As a result, the enriched oxygen vacancies significantly improved adhesion of Pt to CeO2, thereby boosting the sinter-resistance of ultraclose sub-3 nm Pt clusters. Notably, no aggregation was observed even after exposure to humid air at 750 °C for 12 h, which is far beyond their Tammann temperature (sintering onset temperature, below 250 °C). In situ HAADF-STEM observation revealed a unique sintering mechanism, wherein Pt clusters initially migrate toward the grain boundaries with concentrated stain and undergo slight coalescence, followed by subsequent Ostwald ripening at higher temperatures. Moreover, the sinter-resistant Pt/C-shaped CeO2 effectively catalyzed soot combustion (over 700 °C) in a durable manner. This work provides a new insight for developing sinter-resistant catalysts from the perspective of strain engineering within nano-oxides.

Facile Controlled Synthesis of Pd-ZnO Nanostructures for Nitrite Detection

The electrocatalytic characteristics of nanostructures are significantly affected by surface structure. The strict regulation of structural characteristics is highly beneficial for the creation of novel nanocatalysts with enhanced electrocatalytic performance. This work reports a nitrite electrochemical sensor based on novel flower-like Pd-ZnO nanostructures. The Pd-ZnO nanocatalysts were synthesized through a simple hydrothermal method, and their morphology and structure were characterized via field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Their electrocatalytical performance in the nitrite oxidation reaction was studied via cyclic voltammetry (CV) and the amperometric technique. Compared to pure ZnO and Pd nanoparticles, the Pd-ZnO nanostructures exhibited enhanced electrochemical performance in the nitrite oxidation reaction. In order to investigate the relationships between the structures of Pd-ZnO nanocatalysts and the corresponding electrocatalytic performances, different surface morphologies of Pd-ZnO nanocatalysts were fabricated by altering the solution pH. It was found that the flower-like Pd-ZnO nanostructures possessed larger effective surface areas and faster electron transfer rates, resulting in the highest electrocatalytic performance in the nitrite oxidation reaction. The designed nitrite sensor based on flower-like Pd-ZnO displayed a wide concentration linear range of 1 μM-2350 μM, a low detection limit of 0.2 μM (S/N of 3), and high sensitivity of 151.9 μA mM^-1 cm^-2. Furthermore, the proposed sensor exhibited perfect selectivity, excellent reproducibility, and long-time stability, as well as good performance in real sample detection.

Efficient Reduction Photocatalyst of 4-Nitrophenol Based on Ag-Nanoparticles-Doped Porous ZnO Heterostructure

Oxide-supported Ag nanoparticles have been widely reported as a good approach to improve the stability and reduce the cost of photocatalysts. In this work, a Ag-nanoparticles-doped porous ZnO photocatalyst was prepared by using metal-organic frameworks as a sacrificial precursor and the catalytic activity over 4-nitrophenol was determined. The Ag-nanoparticles-doped porous ZnO heterostructure was evaluated by UV, XRD, and FETEM, and the catalytic rate constant was calculated by the change in absorbance value at 400 nm of 4-nitrophenol. The photocatalyst with a heterogeneous structure is visible, light-responsive, and beneficial to accelerating the catalytic rate. Under visible light irradiation, the heterostructure showed excellent catalytic activity over 4-nitrophenol due to the hot electrons induced by the localized surface plasmon resonance of Ag nanoparticles. Additionally, the catalytic rates of 4 nm/30 nm Ag nanoparticles and porous/nonporous ZnO were compared. We found that the as-prepared Ag-nanoparticles-doped porous ZnO heterostructure catalyst showed enhanced catalytic performance due to the synergetic effect of Ag nanoparticles and porous ZnO. This study provides a novel heterostructure photocatalyst with potential applications in solar energy and pollutant disposal.

Hierarchical-Structured Pd Nanoclusters Catalysts x-PdNCs/CoAl(O)/rGO-T by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4-Nitrophenol Reduction

Water-soluble captopril-capped atomically precise Pd nanoclusters (Pd₁₇Capt₈ NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid Co₃Al-layered double hydroxide/reduced graphene oxide (Co₃Al-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts x-PdNCs/CoAl(O)/rGO-T (x (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), T = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl(O) nanosheets. All of the x-PdNCs/CoAl(O)/rGO-T catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h^-1, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs-Co²⁺-OH(LDH)-rGO three-phase synergy, and the much improved adsorption of the substrate via π-π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants.

Yolk-shell ZnO@C-CeO2 ternary heterostructures with conductive N-doped carbon mediated electron transfer for highly efficient water splitting

Herein, carbon-incorporated yolk-shell ZnO@C-CeO₂ ternary heterostructures are employed as visible light responsive photocatalyst for highly efficient photoelectrochemical (PEC) water splitting. Compared to conventional ZnO/CeO₂ semiconductors, introduction of a thin PDA shell layer assures the generation of a conductive N-doped graphitic carbon layer after a calcination post-treatment with mesoporous hollow morphologies. The evaluation of PEC water splitting performance of ZnO@C-CeO₂ photoanodes reveals the maximum photocurrent density as 7.43 mA/cm² at 1.18 V RHE under light whereas almost no response is recorded at dark. These superior PEC H₂ evolution performance strongly implies efficient charge separation, facilitated charge transfer between photoanode and electrolyte interface as well as within the semiconductor bulk by means of rapid electron transfer ability of N-doped graphitic carbon layer and prolong life time of light inside yolk-shell structure. Furthermore, considerable depression in PL intensity of ZnO@C-CeO₂ photoanodes compared to ZnO clearly reveals a higher photon absorption due to the reflection of light in hollow region and increase in electron hole separation efficiency. Moreover, plausible Z-scheme charge transfer mechanism using ZnO@C-CeO₂ photoanodes under visible light illumination is verified using radical trapping experiments and X-ray photoelectron spectroscopy (XPS) methods, suggesting new generation of heterostructures for sufficient conversion of sunlight to H₂ fuels.

One-dimensional ZnO micro/nanostructures: deep insight into the growth mechanism and fine control of the microscopic morphology

One-dimensional zinc oxide arrays with various finely controlled microscopic morphologies are grown on fluorine-doped tin oxide substrates by a hydrothermal method. The relationship between the microscopic morphologies and the reaction conditions are studied deeply. It is found that although all the studied reaction parameters, like reaction time, pH value, concentration of the reactants and so on, can affect the microstructures of the resultant products, what they affect, in essence, is the concentration of free Zn2+ ions of the solution. By exploring the evolution of the microstructure of the one-dimensional zinc oxide crystals, it is proved that the formation of the various microscopic morphologies is a result of the competition between the kinetic control and the thermodynamic control during the crystal growth, which in turn is mainly determined by the concentration of the free Zn2+ ions in the solution. The in-depth exploration of the growth mechanism of zinc oxide and the fine control of its microscopic morphologies is expected to provide advanced materials for current and future cutting-edge applications of zinc oxide. It is also expected that the growth mechanism reported here can provide theoretical support for achieving other oxide materials whose microstructure can be finely controlled.

Electrostatic Interaction-Controlled Formation of Pickering Emulsion for Continuous Flow Catalysis

Although noble metal or non-noble metal-catalyzed reactions are widely used, it is still difficult to apply these reactions in the large-scale synthesis of chemicals because most of the reactions are carried out by the inefficient batch reaction strategy. Herein, Pickering emulsion-based continuous flow catalysis was utilized to address this problem. Cellulose nanofibers with aldehyde groups (ACNF) were generated through oxidizing C2 and C3 hydroxyl groups of cellulose nanofibers into aldehyde groups by NaIO₄, followed by in situ depositing Ag nanoparticles on ACNF to produce Ag-decorated ACNF (ACNF@Ag) via a facile aldehyde-induced reduction method. ACNF@Ag with ∼2 wt % Ag (ACNF@Ag2) has been used to prepare the Pickering emulsion by controlling the electrostatic interaction between ACNF@Ag2 and the oil-water interface via adjusting the pH. It was found that the Pickering emulsion could be generated at a pH around 3.29 and was determined to be the oil-in-water emulsion. The reduction of organic molecules (4-nitrophenol (4-NP), methylene blue (MB), and methyl orange (MO)) was selected as a model reaction to test the reliability of the Pickering emulsion in continuous flow catalysis, which demonstrated very high conversion rates for 4-NP (>98%, 50 h), MB (>99%, 30 h), and MO (>96%, 40 h).

Metal-incorporated mesoporous oxides: Synthesis and applications

Mesoporous oxides are outstanding metal nanoparticle catalyst supports owing to their well-defined porous structures. Such mesoporous architectures not only prevent the aggregation of metal nanoparticles but also enhance their catalytic performance. Metal/metal oxide heterojunctions exhibit unique chemical and physical properties because of the surface reconstruction around the junction and electron transfer/interaction across the interface. This article reviews the methods used for synthesizing metal-supported hybrid nanostructures and their applications as catalysts for environmental remediation and sensors for detecting hazardous materials.

Green assembly of high-density and small-sized silver nanoparticles on lignosulfonate-phenolic resin spheres: Focusing on multifunction of lignosulfonate

In this work, sodium lignosulfonate (SL) was introduced in the hydrothermal preparation of phenol-formaldehyde (PF) resin sphere that was subsequently used as a green reducer and support for synthesis of Ag nanoparticles (Ag NPs). The results showed that the addition amount of SL had a remarkable effect on the size of the SL incorporated PF (SLPF) spheres and the smallest particle size was obtained when 20% of SL (based on phenol mass) was added. The addition of SL increased the surface area and negative charge of SLPF spheres, which enhanced the Ag NPs loading amount accordingly. Moreover, SL also prevented Ag NPs from aggregating effectively, resulting in the high-density loading of small size Ag NPs on the SLPF spheres. Therefore, the as-prepared Ag@SLPF composites exhibited significantly enhanced catalytic activities in the 4-nitrophenol reduction than that of SL-free Ag@PF. Besides, the Ag@SLPF catalyst demonstrated superior recyclability owing to strong anchoring between the Ag NPs and the support. Consequently, the work demonstrates the incorporation of SL enables the green formation of high-density and tunable Ag NPs on the SLPF support and then endows the composite catalyst with enhanced catalytic performance, which presents a promising value-added application of lignosulfonate for functional catalyst preparation.

The green synthesis of PdO/Pd anchored on hierarchical ZnO microflowers with a synthetic effect for the efficient catalytic reduction of 4-nitrophenol

PdO/Pd anchored on hierarchical ZnO microflowers has excellent development potential for treating dye wastewater.

g-C3N4-Mediated Synthesis of Cu2O To Obtain Porous Composites with Improved Visible Light Photocatalytic Degradation of Organic Dyes

A highly porous architecture of graphitic carbon nitride g-C3N4/Cu2O nanocomposite in the form of cubes with a side length of ≈ 1 μm, large pores of 1.5 nm, and a high surface area of 9.12 m2/g was realized by an optimized in situ synthesis protocol. The synthesis protocol involves dispersing a suitable "Cu" precursor into a highly exfoliated g-C3N4 suspension and initiating the reaction for the formation of Cu2O. Systematic optimization of the conditions and compositions resulted in a highly crystalline g-C3N4/Cu2O composite. In the absence of g-C3N4, the Cu2O particles assemble into cubes with a size of around 300 nm and are devoid of pores. Detailed structural and morphological evaluations by powder X-ray diffraction and field emission scanning electron microscopy revealed the presence of highly exfoliated g-C3N4, which is responsible for the formation of the porous architecture in the cube like assembly of the composite. The micrographs clearly reveal the porous structure of the composite that retains the cubic shape of Cu2O, and the energy-dispersive spectroscopy supports the presence of g-C3N4 within the cubic morphology. Among the different g-C3N4/Cu2O compositions, CN/Cu-5 with 10% of g-C3N4, which is also the optimum composition resulting in a porous cubic morphology, shows the best visible light photocatalytic performance. This has been supported by the ultraviolet diffuse reflectance spectroscopy (UV-DRS) studies of the composite which shows a band gap of around 2.05 eV. The improved photocatalytic performance of the composite could be attributed to the highly porous morphology along with the suitable optical band gap in the visible region of the solar spectrum. The optimized composite, CN/Cu-5, demonstrates a visible light degradation of 81% for Methylene Blue (MB) and 85.3% for Rhodamine-B (RhB) in 120 min. The decrease in the catalyst performance even after three repeated cycles is less than 5% for both MB and RhB dyes. The rate constant for MB and RhB degradation is six and eight times higher with CN/Cu-5 when compared with the pure Cu2O catalyst. To validate our claim that the dye degradation is not merely decolorization, liquid chromatography-mass spectroscopy studies were carried out, and the end products of the degraded dyes were identified.

Fast and Efficient Sun Light Photocatalytic Activity of Au_ZnO Core-Shell Nanoparticles Prepared by a One-Pot Synthesis

Gold nanostructures absorb visible light and show localized surface plasmon resonance bands in the visible region. Semiconducting ZnO nanostructures are excellent for ultraviolet detection, thanks to their wide band gap, large free exciton binding energy, and high electron mobility. Therefore, the coupling of gold and ZnO nanostructures represents the best-suited way to boost photodetection. With the above perspective, we report on the high photocatalytic activity of some Au_ZnO core-shell nanoparticles (NPs) recently prepared by a one-pot synthesis in which a [zinc citrate]^- complex acted as the ZnO precursor, a reducing agent for Au³⁺, and a capping anion for the obtained Au NPs. The overall nanostructures proved to be Au(111) NPs surrounded by a thin layer of [zinc citrate]^- that evolved to Au_ZnO core-shell nanostructures. Worthy of note, with this photocatalyst, sun light efficiently decomposes a standard methylene blue solution according to ISO 10678:2010. We rationalized photodetection, reaction rate, and quantum efficiency.

First-Principles Investigation of the Structure and Properties of Au Nanoparticles Supported on ZnO

We present a first-principles investigation of the structure, stability, and reactivity of Au nanoparticles (NPs) supported on ZnO. The morphologies of supported Au NPs are predicted using the formation energy of Au surfaces and the adhesion energy between Au and the dominant ZnO surfaces exposed on ZnO tetrapods. We show how Zn interstitials (a stable intrinsic defect in ZnO) are attracted toward the Au/ZnO interface and in the presence of oxygen can lead to the encapsulation of Au by ZnO, an effect that is observed experimentally. We find that O₂ molecules absorb preferentially at the perimeter of the NP in contact with the ZnO support. These results provide atomistic insight into the structure of ZnO-supported Au NPs with relevance to CO oxidation.

Pickering Interfacial Catalysts with CO2 and Magnetic Dual Response for Fast Recovering in Biphasic Reaction

Pickering interfacial catalysis provides an excellent platform for biphasic reactions, but the separation and recycling of nanocatalysts is a challenge because of high adsorption energy of nanocatalysts at the liquid-liquid interface. In this work, we represent a new type of versatile Pickering emulsion based on magnetic and CO₂-responsive nanohybrids Fe₃O₄@SiO₂@P(TMA-DEA). The smart nanoparticles can stabilize the water-in-oil Pickering emulsion in the biphasic system and achieve the subsequent demulsification by bubbling CO₂ ascribed to their reversible switching surface. In the absence of energy barrier, the nanohybrids can be easily captured in situ by magnetic field in 2 min and showed excellent recyclability. In the Anelli system for alcohol oxidation, the nanocatalyst exhibited threefold enhancement in catalytic efficiency in comparison with an unemulsified two-phase and little loss on activity after five cycles. The conceptually novel dual-responsive system offers a green and energy-saving strategy for effective recycling of the nanocatalyst and intensification of biphasic reaction.

Encapsulation of AgNPs within Zwitterionic Hydrogels for Highly Efficient and Antifouling Catalysis in Biological Environments

Silver nanoparticles (AgNPs) have been widely used as catalysts in a variety of chemical reactions owing to their unique surface and electronic properties, but their practical applications have been hindered by severe aggregation. The immobilization of AgNPs is crucial to preventing their aggregation or precipitation as well as to improving their reusability. Herein, we developed a facile route for the reductant-free in situ synthesis of AgNPs in zwitterionic hydrogels. Via this method, the embedded AgNPs had a uniform distribution, high activity, and antibiofouling capability. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using polycarboxybetaine-AgNPs (PCB-AgNPs) could achieve >95% conversion efficiency within 5 min. Meanwhile, the normalized rate constant k_nor (10.617 s^-1mmol^-1) was higher than that of most of the reported immobilized nanocatalysts. More importantly, in a biofouling environment, PCB-AgNPs could still exhibit >97% initial catalytic activity while AgNPs in the PSB or PHEMA hydrogel lost ∼60% activity. This strategy holds great potential for the immobilization of nanoparticle catalysts, especially for applications in biological environments.

Ultra-small Mo2N on SBA-15 as a highly efficient promoter of low-loading Pd for catalytic hydrogenation

Decreasing Pd usage whilst maintaining a superior performance is promising, but remains a challenge in the catalytic field. Herein, we have demonstrated the highly efficient promotion of Mo₂N with a reduced amount of Pd for the liquid-phase hydrogenation reaction. The Mo₂N (2-3 nm) was uniformly anchored onto mesoporous SBA-15 by using PMo₁₂ as the Mo source. The small size and good dispersion of Mo₂N is favourable for allowing their effective contact with post-loading Pd. This good contact is conducive to developing a synergistic catalyst, which was verified by studying the liquid-phase hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) with NaBH₄ as the H source. The conversion ability of PNP to PAP on 1 wt% Pd-Mo₂N/SBA-15 was vastly superior to 1 wt% Pd/SBA-15 and even better than 20 wt% Pd/SBA-15. The low-Pd, highly efficient catalysis is ascribed to the transfer of the electrons from Mo₂N to Pd for the easy activation of H. The synergy can be affected by the type of support used. SBA-15 is superior to SiO₂ and the other supports, which could be related to the large surface area and the plentiful number of pores on SBA-15, which is favourable to the dispersion of Pd and Mo₂N, and the transfer/diffusion of the reactants. In particular, a highly efficient catalyst can be achieved at an even more reduced Pd loading (0.05 wt%). The current method describes the design of a highly efficient catalyst for the hydrogenation reaction using low amounts of noble metals.

MnO2 Nanowire-CeO2 Nanoparticle Composite Catalysts for the Selective Catalytic Reduction of NO x with NH3

MnO _x-based catalysts have been applied to the selective catalytic reduction of NO _x with ammonia (NH₃) owing to their high NO _x removal efficiency and catalytic stability. In general, the fabrication of a variety of nanomaterials in a complex structure requires complicated processes, including heat treatment and a series of cleaning steps. In addition, MnO₂ which has diverse polymorphs, exhibits different catalytic effects depending on its crystalline structure. Among them, synthesizing the ε-MnO₂ phase, which functions as a nanocatalyst, has been the most difficult and has hardly been reported. Here, we report the synthesis of heterostructured composite nanocatalysts consisting of ε-MnO₂ nanowires (NWs) and CeO₂ nanoparticles (NPs) by applying pulsed currents sequentially. This method drastically simplifies the overall process compared to the conventional techniques. Through X-ray diffraction and transmission electron microscopy, it was confirmed that 2-3 nm of CeO₂ NPs were formed on the surfaces of the ε-MnO₂ NWs. The de-NO _x efficiency of the nanocatalysts was analyzed in terms of content variation, specific surface area, and the elemental chemical state of the surface. A ceramic filter containing the nanocatalysts shows a high catalytic activity over the broad operating temperature range 100-400 °C. In the low-temperature region, ε-MnO₂ plays a major role in determining the catalytic property, which is consistent with the Brunauer-Emmett-Teller (BET), H₂ temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) results. On the other hand, in the high-temperature region, the efficiency increases gradually as the content of CeO₂ increases. The H₂ TPR, NH₃-temperature-programmed desorption, and XPS patterns reveal why the composite exhibits such superior characteristics in the temperature range mentioned above.

Redox-Responsive Polymer Template as an Advanced Multifunctional Catalyst Support for Silver Nanoparticles

Hybridization of metal nanoparticles (NPs) with redox-switchable polymer supports not only mitigates their aggregation, but also introduces interfacial electron pathways desirable for catalysis and numerous other applications. The large surface area and surface accessible atoms for noble metal nanoparticles (e.g., Ag, Au, Pt) offer promising opportunities to address challenges in catalysis and environmental remediation. Herein, AgNPs were supported onto redox-switchable polyaniline that acts as an advanced multifunctional conducting template for enhanced catalytic activity. At the initial stage of reduction of Ag⁺, leucoemeraldine is oxidized in situ to pernigraniline (PG), which acts as interfacial pathway between NPs for electron transport. With the contribution of BH₄^-, PG acts as an electron-acceptor site, which creates interfacial electron-hole pairs, serving as additional active catalytic reduction sites. The use of a redox-responsive composite system as a template enhances catalyst performance through adjustable charge injection across interfacial sites, along with catalyst reusability for the reduction of 4-nitrophenol (4-NPh). Strikingly, from X-ray photoelectron spectroscopy results it was observed that in situ reduction of Ag⁺ onto the conductive polymer alters the electronic character of the catalyst. The unique multielectronic effects of such Ag-supported NPs enrich the scope of such catalytic systems via a tunable interface, diversified catalytic activity, fast kinetics, minimization of AgNPs aggregation, and maintenance of high stability under multiple reaction cycles.

Photoinduced in Situ Deposition of Uniform and Well-Dispersed PtO2 Nanoparticles on ZnO Nanorods for Efficient Catalytic Reduction of 4-Nitrophenol

Based on the photochemical property of semiconductors, a light irradiation-assisted strategy has been designed using one-dimensional ZnO nanorods as carriers to synthesize the rod-type PtO₂/ZnO catalyst with a well-defined structure. The high crystallinity and uniform crystal structure of the ZnO matrix conduct the in situ deposition of PtO₂ nanoparticles with 1.1-2.1 nm, which are evenly and densely anchored on the surface. Those small-sized and well-dispersed PtO₂ nanoparticles endow the PtO₂/ZnO catalyst a superior catalytic performance for the reduction of 4-nitrophenol to 4-aminophenol, which can convert all the substrates within 6.25 min. It is demonstrated that the catalytic activity of the PtO₂/ZnO catalyst is 2.3 times as high as that of the sample obtained by traditional wet-oxidation method under the same reaction conditions. Moreover, the light-irradiation time has been found to greatly affect the structure and activity of PtO₂/ZnO catalysts, and the product with 30 min exhibits the best catalytic performance in this work, as well as the good stability for ten runs. In terms of the photoexcited process of ZnO and reactive species-trapped experiments, the formation mechanism of PtO₂/ZnO catalysts has been explored in detail, which will probably stimulate the design and study of other metal-supported catalysts.

Facile Fabrication of Highly Active Magnetic Aminoclay Supported Palladium Nanoparticles for the Room Temperature Catalytic Reduction of Nitrophenol and Nitroanilines

Magnetically recyclable nanocatalysts with excellent performance are urgent need in heterogeneous catalysis, due to their magnetic nature, which allows for convenient and efficient separation with the help of an external magnetic field. In this research, we developed a simple and rapid method to fabricate a magnetic aminoclay (AC) based an AC@Fe₃O₄@Pd nanocatalyst by depositing palladium nanoparticles (Pd NPs) on the surface of the magnetic aminoclay nanocomposite. The microstructure and the magnetic properties of as-prepared AC@Fe₃O₄@Pd were tested using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM) analyses. The resultant AC@Fe₃O₄@Pd nanocatalyst with the magnetic Fe-based inner shell, catalytically activate the outer noble metal shell, which when combined with ultrafine Pd NPs, synergistically enhanced the catalytic activity and recyclability in organocatalysis. As the aminoclay displayed good water dispersibility, the nanocatalyst indicated satisfactory catalytic performance in the reaction of reducing nitrophenol and nitroanilines to the corresponding aminobenzene derivatives. Meanwhile, the AC@Fe₃O₄@Pd nanocatalyst exhibited excellent reusability, while still maintaining good activity after several catalytic cycles.

Gold/Periodic Mesoporous Organosilicas with Controllable Mesostructure by Using Compressed CO2

Gold nanoparticles confined into the walls of periodic mesoporous organosilicas (PMOs) with controllable morphology have been successfully fabricated through a one-pot method by using different CO₂ pressures. The synthesis can be easily conducted in a mixed aqueous solution by using HAuCl₄ as gold source and bis[3-(triethoxysilyl)propyl] tetrasulfide and tetramethoxysilane as the organosilica precursor. P123 and compressed CO₂ served as the template and catalytic/regulative agent, respectively. Transmission electron microscopy, N₂ adsorption, and X-ray diffraction were employed to characterize the structure of the obtained composite materials. To further investigate the formation mechanism, a series of ordered PMOs with one-dimensional nanotube, two-dimensional hexagonal, vesicle-like, and cellular foam structures were obtained by using different CO₂ pressures without the gold source. The mechanism for mesostructure evolution of PMOs with different CO₂ pressures was proposed and discussed in detail. The catalytic performance of Au-based PMOs was evaluated for the reduction of 4-nitrophenol (4-NP). These obtained composites with different mesostructures not only exhibit excellent catalytic activity, high conversion rate, and remarkable thermal stability, but they also exhibit morphology-dependent reaction properties in the reduction of 4-NP. The possible reaction pathway of the reactants to embedded Au active sites was proposed and schemed.

Direct one-pot synthesis of cinnamaldehyde immobilized on gold nanoparticles and their antibiofilm properties

The objective of the present study was to develop a one-pot strategy to synthesis gold nanoparticle complexes using cinnamaldehyde, a potent antibiofilm agent which in its free form, exhibits high volatility and unstable nature. Hence, we developed cinnamaldehyde gold nanoparticles (CGNPs) in a single step to overcome the limitations of free cinnamaldehyde. Furthermore, reduction abilities of cinnamaldehyde under different experimental conditions, that is, varying precursor concentrations of cinnamaldehyde and gold, metal salts, pH, temperature, and light sources, were investigated. UV-vis spectroscopy, transmission electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and dynamic light-scattering measurements revealed that heat influenced the nanoparticle formation in the presence of cinnamaldehyde, and as produced cinnamaldehyde immobilized on gold nanoparticles were spherical, monodispersed, and stable by surface charge. CGNPs containing 0.01% cinnamaldehyde by weight exhibited effective biofilm inhibition of up to >80% against Gram positive bacteria (methicillin-sensitive and -resistant strains of Staphylococcus aureus, MSSA and MRSA, respectively) and Gram negative (Escherichia coli and Pseudomonas aeruginosa) and a fungus Candida albicans. In addition, CGNPs attenuated the virulence of C. albicans by inhibiting hyphae formation. Based on observations of their antibiofilm effects and confocal microscopy findings, CGNPs caused biofilm damage by direct contact. Thus, cinnamaldehyde appears to be a promising reduction material for the eco-friendly, one-pot synthesis of CGNPs with excellent antibiofilm activity.