Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

Nanoparticle (NP) size and proximity are two physical descriptors applicable to practically all NP-supported catalysts. However, with conventional catalyst design, independent variation of these descriptors to investigate their individual effects on thermocatalysis remains challenging. Using a raspberry-colloid-templating approach, we synthesized a well-defined catalyst series comprising Pd12Au88 alloy NPs of three distinct sizes and at two different interparticle distances. We show that NP size and interparticle distance independently control activity and selectivity, respectively, in the hydrogenation of benzaldehyde to benzyl alcohol and toluene. Surface-sensitive spectroscopic analysis indicates that the surfaces of smaller NPs expose a greater fraction of reactive Pd dimers, compared to inactive Pd single atoms, thereby increasing intrinsic catalytic activity. Computational simulations reveal how a larger interparticle distance improves catalytic selectivity by diminishing the local benzyl alcohol concentration profile between NPs, thus suppressing its readsorption and consequently, undesired formation of toluene. Accordingly, benzyl alcohol yield is maximized using catalysts with smaller NPs separated by larger interparticle distances, overcoming activity-selectivity trade-offs. This work exemplifies the high suitability of the modular raspberry-colloid-templating method as a model catalyst platform to isolate individual descriptors and establish clear structure-property relationships, thereby bridging the materials gap between surface science and technical catalysts.

In situ visualizing reveals potential drive of lattice expansion on defective support toward efficient removal of nitrogen oxides

As a sustainable and promising approach of removing of nitrogen oxides (NOx), catalytic reduction of NOx with H2 is highly desirable with a precise understanding to the structure-activity relationship of supported catalysts. In particular, the dynamic evolution of support at microscopic scale may play a critical role in heterogeneous catalysis, however, identifying the in situ structural change of support under working condition with atomic precision and revealing its role in catalysis is still a grand challenge. Herein, we visually capture the surface lattice expansion of WO3-x support in Pt-WO3-x catalyst induced by NO in the exemplified reduction of NO with H2 using in situ transmission electron microscopy and first reveal its important role in enhancing catalysis. We find that NO can adsorb on the oxygen vacancy sites of WO3-x and favorably induce the reversible stretching of W-O-W bonds during the reaction, which can reduce the adsorption energy of NO on Pt4 centers and the energy barrier of the rate-determining step. The comprehensive studies reveal that lattice expansion of WO3-x support can tune the catalytic performance of Pt-WO3-x catalyst, leading to 20% catalytic activity enhancement for the exemplified reduction of NO with H2. This work reveals that the lattice expansion of defective support can tune and optimize the catalytic performance at the atomic scale.

Ultra-Dense Supported Ruthenium Oxide Clusters via Directed Ion Exchange for Efficient Valorization of 5-Hydroxymethylfurfural

Maximizing the loadings of active centers without aggregation for a supported catalyst is a grand challenge but essential for achieving high gravimetric catalytic activity, especially toward multi-step reactions. The oxidation of 5-hydroxymethylfurfural (HMF), a key biomass-derived platform molecule, into 2,5-furandicarboxylic acid (FDCA), a promising alternative to polyester monomer, is such a multi-step reaction that involves 6 proton and electron transfers. This process often demands strong alkaline environment but also suffers from the alkali-driven polymerization side-reaction. Meanwhile, neutral media ameliorates the polymerization, but lacks efficient catalyst toward deep oxidation. Herein, we devised a strategy of creating ultra-dense supported Ru oxide clusters via directed ion exchange in a Co hydroxyanion (CoHA) support material. Pyrimidine ligands were first incorporated into the CoHA interlayers, and the subsequent evacuation of pyrimidines created porous channels for the directed ion exchange with the built-in anions in CoHA, which allowed the dense and mono-disperse functionalization of RuCl6 2- anions and their resulting Ru oxide clusters. These ultra-dense Ru oxide clusters not only enable high HMF electrooxidation currents under neutral conditions but also create microscopic channels in-between the clusters for the expedited re-adsorption and oxidation of intermediates toward highly oxidized product, such as 5-formyl-2-furoic acid (FFCA) and FDCA. A two-stage HMF oxidation process, consisting of ambient conversion of HMF into FFCA and FFCA oxidation into FDCA under 60 °C, was eventually developed to first achieve a high FDCA yield of 92.1 % under neutral media with significantly reduced polymerization.

Understanding and controlling the formation of single-atom site from supported Cu10 cluster by tuning CeO2 reducibility: Theoretical insight into the Gd-doping effect on electronic metal-support interaction

Controlling the formation of single-atom (SA) sites from supported metal clusters is an important and interesting issue to effectively improve the catalytic performance of heterogeneous catalysts. For extensively studied CO oxidation over metal/CeO2 systems, the SA formation and stabilization under reaction conditions is generally attributed to CO adsorption, however, the pivotal role played by the reducible CeO2 support and the underlying electronic metal-support interaction (EMSI) are not yet fully understood. Based on a ceria-supported Cu10 catalyst model, we performed density functional theory calculations to investigate the intrinsic SA formation mechanism and discussed the synergistic effect of Gd-doped CeO2 and CO adsorption on the SA formation. The CeO2 reducibility is tuned with doped Gd content ranging from 12.5 % ∼ 25 %. Based on ab initio thermodynamic and ab initio molecular dynamics, the critical condition for SA formation was identified as 21.875 % Gd-doped CeO2 with CO-saturated adsorption on Cu10. Electronic analysis revealed that the open-shell lattice Oδ- (δ < 2) generated by Gd doping facilitates the charge transfer from the bottom-corner Cu (Cubc) to CeO2. The CO-saturated adsorption further promotes this charge transfer process and enhances the EMSI between Cubc and CeO2, leading to the disintegration of Cubc from Cu10 and subsequent formation of the active SA site.

Synthesis and characterization of a green and recyclable arginine-based palladium/CoFe2O4 nanomagnetic catalyst for efficient cyanation of aryl halides

The utilization of magnetic nanoparticles in the fields of science and technology has gained considerable popularity. Among their various applications, magnetic nanoparticles have been predominantly employed in catalytic processes due to their easy accessibility, recoverability, effective surface properties, thermal stability, and low cost. In this particular study, cyanuric chloride and arginine were utilized to synthesize an arginine-based oligomeric compound (ACT), which was supported on cobalt ferrite, resulting in a green catalyst with high activity and convenient recyclability for the cyanation reaction of aryl halides. The Pd/CoFe2O4@ACT nanomagnetic catalyst demonstrated excellent performance in the cyanation of various aryl iodides and bromides, yielding favorable reaction outcomes at a temperature of 90 °C within a duration of 3 hours. The synthesized nanoparticles were successfully characterized using various techniques, including FTIR, FE-SEM, EDX/MAP, XRD, TEM, TGA, BET, and ICP-OES. Moreover, the Pd/CoFe2O4@ACT catalyst exhibited remarkable catalytic activity, maintaining an 88% performance even after five consecutive runs. Analysis of the reused catalyst through SEM and TEM imaging confirmed that there were no significant changes in the morphology or dispersion of the particles. Ultimately, it was demonstrated that the Pd/CoFe2O4@ACT nanomagnetic catalyst outperformed numerous catalysts previously reported in the literature for the cyanation of aryl halides.

Metal-Sulfur Interfaces as the Primary Active Sites for Catalytic Hydrogenations

The determination of catalytically active sites is crucial for understanding the catalytic mechanism and providing guidelines for the design of more efficient catalysts. However, the complex structure of supported metal nanocatalysts (e.g., support, metal surface, and metal-support interface) still presents a big challenge. In particular, many studies have demonstrated that metal-support interfaces could also act as the primary active sites in catalytic reactions, which is well elucidated in oxide-supported metal nanocatalysts but is rarely reported in carbon-supported metal nanocatalysts. Here, we fill the above gap and demonstrate that metal-sulfur interfaces in sulfur-doped carbon-supported metal nanocatalysts are the primary active sites for several catalytic hydrogenation reactions. A series of metal nanocatalysts with similar sizes but different amounts of metal-sulfur interfaces were first constructed and characterized. Taking Ir for quinoline hydrogenation as an example, it was found that their catalytic activities were proportional to the amount of the Ir-S interface. Further experiments and density functional theory (DFT) calculations suggested that the adsorption and activation of quinoline occurred on the Ir atoms at the Ir-S interface. Similar phenomena were found in p-chloronitrobenzene hydrogenation over the Pt-S interface and benzoic acid hydrogenation over the Ru-S interface. All of these findings verify the predominant activity of metal-sulfur interfaces for catalytic hydrogenation reactions and contribute to the comprehensive understanding of metal-support interfaces in supported nanocatalysts.

H-Glass Supported Hybrid Gold Nano-Islands for Visible-Light-Driven Hydrogen Evolution

Flat panel reactors, coated with photocatalytic materials, offer a sustainable approach for the commercial production of hydrogen (H2) with zero carbon footprint. Despite this, achieving high solar-to-hydrogen (STH) conversion efficiency with these reactors is still a significant challenge due to the low utilization efficiency of solar light and rapid charge recombination. Herein, hybrid gold nano-islands (HGNIs) are developed on transparent glass support to improve the STH efficiency. Plasmonic HGNIs are grown on an in-house developed active glass sheet composed of sodium aluminum phosphosilicate oxide glass (H-glass) using the thermal dewetting method at 550 °C under an ambient atmosphere. HGNIs with various oxidation states (Au0, Au+, and Au-) and multiple interfaces are obtained due to the diffusion of the elements from the glass structure, which also facilitates the lifetime of the hot electron to be ≈2.94 ps. H-glass-supported HGNIs demonstrate significant STH conversion efficiency of 0.6%, without any sacrificial agents, via water dissociation. This study unveils the specific role of H-glass-supported HGNIs in facilitating light-driven chemical conversions, offering new avenues for the development of high-performance photocatalysts in various chemical conversion reactions for large-scale commercial applications.

Functionalisation of alkali-resistant nanoporous glass via Au nanoparticle decoration using alkaline impregnation: catalytic activity for CO removal

The concerted use of nano-metal particles with catalytic functions and nanoporous materials holds promise for effective air purification and gas sensing; however, only a few studies have used porous glasses as supports for Au nanoparticles. Furthermore, Au/nanoporous glasses with activities comparable to that of Au/TiO2, which is a typical Au catalyst, have not been reported to date. This study demonstrates that a nanoporous glass, which is highly acid- and alkali-resistant and chemically stable, can be decorated with Au nanoparticles using an alkali impregnation method. The resulting composite exhibits high catalytic activity in CO oxidation. The catalysts reported herein are as active as Au/TiO2 catalysts per active site. Further optimisation of the pore properties of the glass and sizes of the Au nanoparticles is expected to result in excellent catalytic systems for CO removal and sensing.

Distinct Site Motifs Activate O2 and H2 on Supported Au Nanoparticles in Liquid Water

Au nanoparticles catalyze the activation and conversion of small molecules with rates and kinetic barriers that depend on the dimensions of the nanoparticle, composition of the support, and presence of catalytically culpable water molecules that solvate these interfaces. Here, molecular interpretations of steady-state rate measurements, kinetic isotope effects, and structural characterizations reveal how the interface of Au nanoparticles, liquid water, and metal oxide supports mediate the kinetically relevant activation of H2 and sequential reduction of O2-derived intermediates during the formation of H2O2 and H2O. Rates of H2 consumption are 10-100 fold greater on Au nanoparticles supported on metal oxides (e.g., titania) compared to more inert and hydrophobic materials (carbon, boron nitride). Similarly, Au nanoparticles on reducible and Lewis acidic supports (e.g., lanthana) bind dioxygen intermediates more strongly and present lower barriers (<22 kJ mol-1) for O-O bond dissociation than inert interfaces formed with silica (>70 kJ mol-1). Selectivities for H2O2 formation increase significantly as the diameters of the Au nanoparticles increase because differences in nanoparticle size change the relative fractions of exposed sites that exist at Au-support interfaces. In contrast, site-normalized rates and barriers for H2 activation depend weakly on the size of Au nanoparticles and the associated differences in active site motifs. These findings suggest that H2O aids the activation of H2 at sites present across all surface Au atoms when nanoparticles are solvated by water. However, molecular O2 preferentially binds and dissociates at Au-support interfaces, leading to greater structure sensitivity for barriers of O-O dissociation across different support identities and sizes of Au nanoparticles. These insights differ from prior knowledge from studies of gas-phase reactions of H2 and O2 upon Au nanoparticle catalysts within dilute vapor pressures of water (10-4 to 0.1 kPa H2O), in which catalysis occurs at the perimeter of the Au-support interface. In contrast, contacting Au catalysts with liquid water (55.5 M H2O) expands catalysis to all surface Au atoms and enables appreciable H2O2 formation.

Materials Genes of CO2 Hydrogenation on Supported Cobalt Catalysts: An Artificial Intelligence Approach Integrating Theoretical and Experimental Data

Designing materials for catalysis is challenging because the performance is governed by an intricate interplay of various multiscale phenomena, such as the chemical reactions on surfaces and the materials' restructuring during the catalytic process. In the case of supported catalysts, the role of the support material can be also crucial. Here, we address this intricacy challenge by a symbolic-regression artificial intelligence (AI) approach. We identify the key physicochemical parameters correlated with the measured performance, out of many offered candidate parameters characterizing the materials, reaction environment, and possibly relevant underlying phenomena. Importantly, these parameters are obtained by both experiments and ab initio simulations. The identified key parameters might be called "materials genes", in analogy to genes in biology: they correlate with the property or function of interest, but the explicit physical relationship is not (necessarily) known. To demonstrate the approach, we investigate the CO2 hydrogenation catalyzed by cobalt nanoparticles supported on silica. Crucially, the silica support is modified with the additive metals magnesium, calcium, titanium, aluminum, or zirconium, which results in six materials with significantly different performances. These systems mimic hydrothermal vents, which might have produced the first organic molecules on Earth. The key parameters correlated with the CH3OH selectivity reflect the reducibility of cobalt species, the adsorption strength of reaction intermediates, and the chemical nature of the additive metal. By using an AI model trained on basic elemental properties of the additive metals (e.g., ionization potential) as physicochemical parameters, new additives are suggested. The predicted CH3OH selectivity of cobalt catalysts supported on silica modified with vanadium and zinc is confirmed by new experiments.

Exfoliated MXene-AuNPs hybrid in sensing and multiple catalytic hydrogenation reactions

The increasing use of nanomaterials in consumer products is expected to lead to environmental contamination sometime soon. As water pollution is a pressing issue that threatens human survival and impedes the promotion of human health, the search for adsorbents for removing newly identified contaminants from water has become a topic of intensive research. The challenges in the recyclability of contaminated water continue to campaign the development of highly reusable catalysts. Although exfoliated 2D MXene sheets have demonstrated the capability towards water purification, a significant challenge for removing some toxic organic molecules remains a challenge due to a need for metal-based catalytic properties owing to their rapid response. In the present study, we demonstrate the formation of hybrid structure AuNPs@MXene (Mo2CTx) during the sensitive detection of Au nanoparticle through MXene sheets without any surface modification, and subsequently its applications as an efficient catalyst for the degradation of 4-nitrophenol (4-NP), methyl orange (MO), and methylene blue (MB). The hybrid structure (AuNPs@MXene) reveals remarkable reusability for up to eight consecutive cycles, with minimal reduction in catalytic efficiency and comparable apparent reaction rate constant (Kapp) values for 4-NP, MB, and MO, compared to other catalysts reported in the literature.

Ultra-stable and highly reactive colloidal gold nanoparticle catalysts protected using multi-dentate metal oxide nanoclusters

Owing to their remarkable properties, gold nanoparticles are applied in diverse fields, including catalysis, electronics, energy conversion and sensors. However, for catalytic applications of colloidal gold nanoparticles, the trade-off between their reactivity and stability is a significant concern. Here we report a universal approach for preparing stable and reactive colloidal small (~3 nm) gold nanoparticles by using multi-dentate polyoxometalates as protecting agents in non-polar solvents. These nanoparticles exhibit exceptional stability even under conditions of high concentration, long-term storage, heating and addition of bases. Moreover, they display excellent catalytic performance in various oxidation reactions of organic substrates using molecular oxygen as the sole oxidant. Our findings highlight the ability of inorganic multi-dentate ligands with structural stability and robust steric and electronic effects to confer stability and reactivity upon gold nanoparticles. This approach can be extended to prepare metal nanoparticles other than gold, enabling the design of novel nanomaterials with promising applications.

Manganese-oxide-supported gold catalyst derived from metal-organic frameworks for trace PCl3 oxidation in an organic system

Polysilicon is widely used in the field of semiconductors and solar energy. Trichlorosilane feedstocks that are used to produce polysilicon in the mainstream production process contain PCl3 impurities that have adverse effects on the quality of the polysilicon. Traditional methods for dephosphorization cannot achieve the effect of complete removal, whereas oxidizing PCl3 to POCl3 in the presence of oxygen for removal via adsorption is a promising and appealing route for establishing a dephosphorization process; it has a high phosphorous removal rate due to the strong Lewis-base property of POCl3 in comparison with PCl3. In this work, we synthesized an active catalyst with an active interface between Au nanoparticles (NPs) and a manganese-oxide support (Mn3O4) by calcination of a corresponding composite, where Au NPs were embedded uniformly in a metal-organic framework (MOF). The catalyst shows a significantly active catalytic performance for trace PCl3 oxidation in an organic system that is an imitation of a trichlorosilane system, with a 99.13% yield of POCl3 in an 80 °C and 0.6 MPa reaction environment. The structure-performance-mechanism analysis shows that the possible reaction and catalytic mechanism is PCl3 oxidation by interface lattice oxygens, which bridge the Au NPs and the support, in a Mars van Krevelen (MvK) process; this process was promoted by the interaction between the Au NPs and Mn3O4 in terms of charge transfer and chemical potential changes. This work provides an effective way to dephosphorize trichlorosilane feedstocks in the polysilicon industry and gives guidance for constructing an efficient catalyst via the study of the structure and mechanism.

Light-enhanced catalytic activity of stable and large gold nanoparticles in homocoupling reactions

Validating the direct photocatalytic activity of colloidal plasmonic nanoparticles is challenging due to their limited stability and needed support materials that can often contribute to the chemical reactions. Stable gold nanoparticles (AuNPs) with tunable sizes are prepared across porous polymer particles without any chemical bonds where the resulting composite particles exhibit intense surface plasmon resonances (SPRs) in the visible region. These composite particles are then tested as photocatalysts under a broadband solar-simulated light source to examine the contribution degree of photothermal heating and SPR coming from the incorporated AuNPs in the C-C bond forming homocoupling reaction. Generally, the thermal and photothermal heating are the main driving force to increase the reactivity of relatively smaller AuNPs (~ 44 nm in diameter) with a narrower SPR band. However, the SPR-induced catalytic activity is much greater for the composite particles containing larger AuNPs (~ 87 nm in diameter) with a broader SPR. As the polymer particle matrix does not influence the catalytic activity (e.g., inducing charge delocalization and/or separation), the unique SPR role of the colloidal AuNPs in the catalytic reaction is assessable under light irradiation. This study experimentally demonstrates the possibility of evaluating the direct contribution of SPRs to photocatalytic chemical reactions.

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).

Shape-Induced Variations in Aromatic Thiols Adsorption on Gold Nanoparticle: A Novel Method for Accurate Evaluation of Adsorbed Molecules

Nonspherical gold nanoparticles (GNPs) are increasingly used to enhance sensitivity and selectivity in analytical methods such as surface-enhanced Raman spectroscopy (SERS) for detecting trace biomarkers. However, there is limited research on the adsorption properties of aromatic thiols onto gold nanoparticles of different morphologies, where surface curvature varies significantly at the molecular level. In this study, we investigated the adsorption kinetics of 4-mercaptobenzoic acid, an aromatic molecule, on GNPs with different shapes using SERS. Our findings revealed significant differences in the adsorption behavior and binding site preferences of aromatic thiols on GNPs with distinct morphologies. While thiol molecules consider any surface site on nanospheres equally appealing, nanostars exhibit variations in curvature and surface energy, leading to initial binding with further repositioning from the tips of the nanostar after plasmon activation. To address these differences, we proposed a universal method to evaluate the quantity of tightly bound adsorbed molecules on GNPs independently of the particle size, shape, or concentration.

Constructing an oxygen vacancy- and hydroxyl-rich TiO2-supported Pd catalyst with improved Pd dispersion and catalytic stability

Surface property modification of catalyst support is a straightforward approach to optimize the performance of supported noble metal catalysts. In particular, oxygen vacancies and hydroxyl groups play significant roles in promoting noble metal dispersion on catalysts as well as catalytic stability. In this study, we developed a nanoflower-like TiO2-supported Pd catalyst that has a higher concentration of oxygen vacancies and surface hydroxyl groups compared to that of commercial anatase and P25 support. Notably, due to the distinctive structure of the nanoflower-like TiO2, our catalyst exhibited improved dispersion and stabilization of Pd species and the formation of abundant reactive oxygen species, thereby facilitating the activation of CO and O2 molecules. As a result, the catalyst showed remarkable efficiency in catalyzing the low-temperature CO oxidation reaction with a complete CO conversion at 80 °C and stability for over 100 h.

Heterogeneous catalytic oxidation of glycerol over a UiO-66-derived ZrO2@C supported Au catalyst at room temperature

The catalytic conversion of biomass-derived glycerol into high-value-added products, such as glyceric acid (GLYA), using catalyst-supported Au nanoparticles (Au NPs) at room temperature presents a significant challenge. In this study, we constructed a series of supported Au catalysts, including Au/ZrO2@C, Au/C, Au/ZrO2, and Au/ZrO2-C, and investigated their effectiveness in selectively catalytic oxidizing glycerol to GLYA at room temperature. Among these catalysts, the Au/ZrO2@C catalyst exhibited the best catalytic performance, achieving a glycerol conversion rate of 73% and a GLYA selectivity of 79% under the optimized reaction conditions (reaction conditions: 30 mL 0.1 M glycerol, glycerol/Au = 750 mol mol-1, T = 25 °C, p(O2) = 10 bar, stirring speed = 600 rpm, time = 6 h). Physical adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and other characterization methods were employed to analyze the texture properties of the catalyst. The findings indicated that the support structure, the strong metal-support interactions between Au NPs and the support, and the presence of small metallic Au NPs were the primary factors contributing to the catalyst's high activity and selectivity. Moreover, the reusability of the Au/ZrO2@C catalyst was investigated, and a probable reaction mechanism for the oxidation of glycerol was proposed.

Atomic Insights into Synergistic Nitroarene Hydrogenation over Nanodiamond-Supported Pt1 -Fe1 Dual-Single-Atom Catalyst

Fundamental understanding of the synergistic effect of bimetallic catalysts is of extreme significance in heterogeneous catalysis, but a great challenge lies in the precise construction of uniform dual-metal sites. Here, we develop a novel method for constructing Pt1 -Fe1 /ND dual-single-atom catalyst, by anchoring Pt single atoms on Fe1 -N4 sites decorating a nanodiamond (ND) surface. Using this catalyst, the synergy of nitroarenes selective hydrogenation is revealed. In detail, hydrogen is activated on the Pt1 -Fe1 dual site and the nitro group is strongly adsorbed on the Fe1 site via a vertical configuration for subsequent hydrogenation. Such synergistic effect decreases the activation energy and results in an unprecedented catalytic performance (3.1 s-1 turnover frequency, ca. 100 % selectivity, 24 types of substrates). Our findings advance the applications of dual-single-atom catalysts in selective hydrogenations and open up a new way to explore the nature of synergistic catalysis at the atomic level.

Scope of Onsite, Portable Prevention Diagnostic Strategies for Alternaria Infections in Medicinal Plants

Medicinal plants are constantly challenged by different biotic inconveniences, which not only cause yield and economic losses but also affect the quality of products derived from them. Among them, Alternaria pathogens are one of the harmful fungal pathogens in medicinal plants across the globe. Therefore, a fast and accurate detection method in the early stage is needed to avoid significant economic losses. Although traditional methods are available to detect Alternaria, they are more time-consuming and costly and need good expertise. Nevertheless, numerous biochemical- and molecular-based techniques are available for the detection of plant diseases, but their efficacy is constrained by differences in their accuracy, specificity, sensitivity, dependability, and speed in addition to being unsuitable for direct on-field studies. Considering the effect of Alternaria on medicinal plants, the development of novel and early detection measures is required to detect causal Alternaria species accurately, sensitively, and rapidly that can be further applied in fields to speed up the advancement process in detection strategies. In this regard, nanotechnology can be employed to develop portable biosensors suitable for early and correct pathogenic disease detection on the field. It also provides an efficient future scope to convert innovative nanoparticle-derived fabricated biomolecules and biosensor approaches in the diagnostics of disease-causing pathogens in important medicinal plants. In this review, we summarize the traditional methods, including immunological and molecular methods, utilized in plant-disease diagnostics. We also brief advanced automobile and efficient sensing technologies for diagnostics. Here we are proposing an idea with a focus on the development of electrochemical and/or colorimetric properties-based nano-biosensors that could be useful in the early detection of Alternaria and other plant pathogens in important medicinal plants. In addition, we discuss challenges faced during the fabrication of biosensors and new capabilities of the technology that provide information regarding disease management strategies.

Attachment of facile synthesized NaCo2O4 nanodots to SiO2 nanoflakes for sodium-rich boosted Pt-dominated ambient HCHO oxidation

Surface alkali metal ions are typically utilized as available promoters for ambient HCHO oxidation. In this study, NaCo₂O₄ nanodots with two different preferential crystallographic orientations are synthesized by facile attachment to SiO₂ nanoflakes with varying degrees of lattice defects. A unique Na-rich environment is established through interlayer Na⁺ diffusion based on the small size effect. The optimized catalyst Pt/HNaCo₂O₄/T₂ can deal with HCHO below 5 ppm in the static measurement system with a sustained release background and produces approximately 40 ppm of CO₂ in 2 h. Combining the experimental analyses with density functional theory (DFT) calculations, the possible catalytic enhancing mechanism is proposed from the support promotion perspective, and the positive synergistic effect of Na-rich, oxygen vacancies and optimized facets for Pt-dominant ambient HCHO oxidation via both kinetic and thermodynamic processes is confirmed.

Bimetallic (AuAg, AuPd and AgPd) nanoparticles supported on cellulose-based hydrogel for reusable catalysis

Biopolymer-derived hydrogels with low-cost and sustainable features have been considered as fascinating supported materials for metal nanoparticles. Cellulose, as the most abundant biopolymer, is a renewable raw material to prepare biopolymer-derived hydrogels for catalysis. Here, a cellulose-based hydrogel is designed to load bimetallic (AuAg, AuPd and AgPd) nanoparticles. 4-Nitrophenol reduction and Suzuki-Miyaura coupling reactions are selected to evaluate and compare the catalytic performance of the resulting bimetallic nanoparticle-loaded cellulose-based composite hydrogels. The bimetallic nanocomposite hydrogels are easy to be recycled over 10 times during the catalytic experiments and possess good applicability and generality for various substrates. The catalytic activity of bimetallic nanocomposite hydrogels was compared with recent literatures. In addition, the possible catalytic mechanism is also proposed. This work is expected to give a new insight for designing and preparing bimetallic nanoparticle-based cellulose hydrogels and proves its applicability and prospect in the catalytic field.

Reduction of Nitroaromatics by Gold Nanoparticles on Porous Silicon Fabricated Using Metal-Assisted Chemical Etching

In this study, we investigated the use of porous silicon (PSi) fabricated using metal-assisted chemical etching (MACE) as a substrate for the deposition of Au nanoparticles (NPs) for the reduction of nitroaromatic compounds. PSi provides a high surface area for the deposition of Au NPs, and MACE allows for the fabrication of a well-defined porous structure in a single step. We used the reduction of p-nitroaniline as a model reaction to evaluate the catalytic activity of Au NPs on PSi. The results indicate that the Au NPs on the PSi exhibited excellent catalytic activity, which was affected by the etching time. Overall, our results highlighted the potential of PSi fabricated using MACE as a substrate for the deposition of metal NPs for catalytic applications.

L-Shaped Heterobidentate Imidazo[1,5-a]pyridin-3-ylidene (N,C)-Ligands for Oxidant-Free AuI /AuIII Catalysis

In the last decade, major advances have been made in homogeneous gold catalysis. However, Au^I /Au^III catalytic cycle remains much less explored due to the reluctance of Au^I to undergo oxidative addition and the stability of the Au^III intermediate. Herein, we report activation of aryl halides at gold(I) enabled by NHC (NHC=N-heterocyclic carbene) ligands through the development of a new class of L-shaped heterobidentate ImPy (ImPy=imidazo[1,5-a]pyridin-3-ylidene) N,C ligands that feature hemilabile character of the amino group in combination with strong σ-donation of the carbene center in a rigid conformation, imposed by the ligand architecture. Detailed characterization and control studies reveal key ligand features for Au^I /Au^III redox cycle, wherein the hemilabile nitrogen is placed at the coordinating position of a rigid framework. Given the tremendous significance of homogeneous gold catalysis, we anticipate that this ligand platform will find widespread application.

Mesoporous molecular sieve-based materials for catalytic oxidation of VOC: A review

As the main contributor of the formation of particulate matter as well as ozone, volatile organic compounds (VOCs) greatly affect human health and the environmental quality. Catalytic combustion/oxidation has been viewed as an efficient, economically feasible and environmentally friendly way for the elimination of VOCs. Supported metal catalyst is the preferred type of catalysts applied for VOCs catalytic combustion because of the synergy between active components and support as well as its flexibility in the composition. The presence of support not only plays the role of keeping the catalyst with good stability and mechanical strength, but also provides a large specific surface for the good dispersion of active components, which could effectively improve the performance of catalyst as well as decrease the usage of active components, especially the noble metal amount. Mesoporous molecular sieves, owing to their large surface area, unique porous structures, large pore size as well as uniform pore-size distribution, were viewed as superior support for dispersing active components. This review focuses on the recent development of mesoporous molecular sieve supported metal catalysts and their application in catalytic oxidation of VOCs. The effect of active component types, support structure, preparation method, precursors, etc. on the valence state, dispersion as well as the loading of active species were also discussed and summarized. Moreover, the corresponding conversion route of VOCs was also addressed. This review aims to provide some enlightment for designing the supported metal catalysts with superior activity and stability for VOCs removal.

Diverse Alkyl-Silyl Cross-Coupling via Homolysis of Unactivated C(sp3)-O Bonds with the Cooperation of Gold Nanoparticles and Amphoteric Zirconium Oxides

Since C(sp³)-O bonds are a ubiquitous chemical motif in both natural and artificial organic molecules, the universal transformation of C(sp³)-O bonds will be a key technology for achieving carbon neutrality. We report herein that gold nanoparticles supported on amphoteric metal oxides, namely, ZrO₂, efficiently generated alkyl radicals via homolysis of unactivated C(sp³)-O bonds, which consequently promoted C(sp³)-Si bond formation to give diverse organosilicon compounds. A wide array of esters and ethers, which are either commercially available or easily synthesized from alcohols participated in the heterogeneous gold-catalyzed silylation by disilanes to give diverse alkyl-, allyl-, benzyl-, and allenyl silanes in high yields. In addition, this novel reaction technology for C(sp³)-O bond transformation could be applied to the upcycling of polyesters, i.e., the degradation of polyesters and the synthesis of organosilanes were realized concurrently by the unique catalysis of supported gold nanoparticles. Mechanistic studies corroborated the notion that the generation of alkyl radicals is involved in C(sp³)-Si coupling and the cooperation of gold and an acid-base pair on ZrO₂ is responsible for the homolysis of stable C(sp³)-O bonds. The high reusability and air tolerance of the heterogeneous gold catalysts as well as a simple, scalable, and green reaction system enabled the practical synthesis of diverse organosilicon compounds.

Biodiesel Production from Waste Plant Oil over a Novel Nano-Catalyst of Li-TiO2/Feldspar

A novel Li-impregnated TiO2 catalyst loaded on feldspar mineral (Li-TiO2/feldspar) was synthesized via a wet impregnation method and was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) analysis. Using these techniques, it was possible to confirm the catalyst’s structural organization with a high crystallinity. This catalyst was used in the transesterification of five waste plant oils of Citrullus colocynthis (bitter apple), Pongamia pinnata (karanja), Sinapis arvensis (wild mustard), Ricinus communis (castor) and Carthamus oxyacantha (wild safflower). The catalytic tests were performed at temperatures ranging from 40 to 80 °C, employing a variable methanol/ester molar ratio (5:1, 10:1, 15:1, 20:1 and 25:1) and different catalyst concentrations (0.5%, 1%, 1.5%, 2% and 2.5%) relative to the total reactants mass. Conversion of 98.4% of fatty acid methyl esters (FAMEs) was achieved for Pongamia pinnata (karanja). The main fatty acids present in bitter apple, karanja, wild mustard, castor and wild safflower oils were linoleic acid (70.71%), oleic acid (51.92%), erucic acid (41.43%), ricinoleic acid (80.54%) and linoleic acid (75.17%), respectively. Li-TiO2/feldspar produced more than 96% for all the feedstocks. Fuel properties such as iodine value (AV), cetane number (CN), cloud point (CP), iodine value (IV), pour point (PP) and density were within the ranges specified in ASTM D6751.

Integration of Gold Nanoparticles into Crosslinker-Free Polymer Particles and Their Colloidal Catalytic Property

This work demonstrates the incorporation of gold nanoparticles (AuNPs) into crosslinker-free poly(N-isopropylacrylamide), PNIPAM, particles in situ and the examination of their structural and catalytic properties. The formation process of the AuNPs across the crosslinker-free PNIPAM particles are compared to that of crosslinked PNIPAM particles. Given the relatively larger free volume across the crosslinker-free polymer network, the AuNPs formed by the in situ reduction of gold ions are detectably larger and more polydisperse, but their overall integration efficiency is slightly inferior. The structural features and stability of these composite particles are also examined in basic and alcoholic solvent environments, where the crosslinker-free PNIPAM particles still offer comparable physicochemical properties to the crosslinked PNIPAM particles. Interestingly, the crosslinker-free composite particles as a colloidal catalyst display a higher reactivity toward the homocoupling of phenylboronic acid and reveal the importance of the polymer network density. As such, the capability to prepare composite particles in a controlled polymer network and reactive metal nanoparticles, as well as understanding the structure-dependent physicochemical properties, can allow for the development of highly practical catalytic systems.

Boosted Heterogeneous Catalysis by Surface-Accumulated Excess Electrons of Non-Oxidized Bare Copper Nanoparticles on Electride Support

Engineering active sites of metal nanoparticle-based heterogeneous catalysts is one of the most prerequisite approaches for the efficient production of chemicals, but the limited active sites and undesired oxidation on the metal nanoparticles still remain as key challenges. Here, it is reported that the negatively charged surface of copper nanoparticles on the 2D [Ca₂ N]⁺ ∙e^- electride provides the unrestricted active sites for catalytic selective sulfenylation of indoles and azaindoles with diaryl disulfides. Substantial electron transfer from the electride support to copper nanoparticles via electronic metal-support interactions results in the accumulation of excess electrons at the surface of copper nanoparticles. Moreover, the surface-accumulated excess electrons prohibit the oxidation of copper nanoparticle, thereby maintaining the metallic surface in a negatively charged state and activating both (aza)indoles and disulfides under mild conditions in the absence of any further additives. This study defines the role of excess electrons on the nanoparticle-based heterogeneous catalyst that can be rationalized in versatile systems.

Atomic-Scale Engineering of CuOx-Au Interfaces over AuCu Single-Nanoparticles

A face-centered tetragonal (fct) AuCu particle with a size of 7.1 nm and an Au/Cu molar ratio of 1/1 was coated by a silica shell of 6 nm thickness. Segregation of Cu atoms from the metal particle under an oxidative atmosphere precisely mediated the CuO_x-Au interfacial structure by simply varying the temperature. As raising the temperature from 473 to 773 K, more Cu atoms emigrated from the AuCu particle and were oxidized into CuO_x layers that grew up to 0.8 nm in thickness. Simultaneously, the size of the Au-rich particle lowered moderately while the crystalline structure transformed from the fct phase into the face-centered cubic (fcc) phase. The CuO_x-Au interface shifted from the CuO_x monolayer bound to Au single-atoms to Au@CuO_x core-shell geometry, while the catalytic activity for CO oxidation at 433 K decreased dramatically. Moreover, a sharp loss in activity was observed as the crystal-phase transition occurred. This change in catalytic performance was ascribed to the geometrical configuration at the interfacial sites: the synergetic effect between the fct-AuCu particle and CuO_x monolayer contributed to the much higher activity, whereas the fcc-AuCu/Au particle weakened its interaction with the thicker CuO_x layer and thus decreased the activity.

Near Infrared Light-to-Heat Conversion for Liquid-Phase Oxidation Reactions by Antimony-Doped Tin Oxide Nanocrystals

Effective utilization of the sunlight for chemical reactions is pivotal for dealing with the growing energy and environmental issues. So far, much effort has been focused on the development of semiconductor photocatalysts responsive to UV and visible light. However, the near infrared and infrared (NIR-IR) light occupying ∼50 % of the solar energy has usually been wasted because of the low photon energy insufficient for the band gap excitation. Antimony doping into SnO₂ (ATO) induces strong absorption due to the conduction band electrons in the NIR region. The absorbed light energy is eventually converted to heat via the interaction between hot electrons and phonons. This Concept highlights the photothermal effect of ATO nanocrystals (NCs) on liquid-phase oxidation reactions through the NIR light-to-heat conversion. Under NIR illumination even at an intensity of ∼0.5 sun, the reaction field temperature on the catalyst surface is raised 20-30 K above the bulk solution temperature, while the latter is maintained near the ambient temperature. In some reactions, this photothermal local heating engenders the enhancement of not only the catalytic activity and selectivity but also the regeneration of catalytically active sites. Further, the photocatalytic activity of semiconductors can be promoted. Finally, the conclusions and possible subjects in the future are summarized.

Synthesis of novel hybrid mesoporous gold iron oxide nanoconstructs for enhanced catalytic reduction and remediation of toxic organic pollutants

The development of highly efficient, rapid, and recyclable nanocatalysts for effective elimination of toxic environmental contaminants remains a high priority in various industrial applications. Herein, we report the preparation of hybrid mesoporous gold-iron oxide nanoparticles (Au-IO NPs) via the nanocasting "inverse hard-templated replication" approach. Dispersed Au NPs were anchored on amine-functionalized iron oxide incorporated APMS (IO@APMS-amine), followed by etching of the silica template to afford hybrid mesoporous Au-IO NPs. The obtained nanoconstructs were fully characterized using electron microscopy, N₂ physisorption, and various spectroscopic techniques. Owing to their magnetic properties, high surface areas, large pore volumes, and mesoporous nature (S _BET = 124 m² g^-1, V _pore = 0.33 cm³ g^-1, and d _pore = 4.5 nm), the resulting Au-IO mesostructures were employed for catalytic reduction of nitroarenes (i.e. nitrophenol and nitroaniline), two of the most common toxic organic pollutants. It was found that these Au-IO NPs act as highly efficient nanocatalysts showing exceptional stabilities (>3 months), enhanced catalytic efficiencies in very short times (∼100% conversions within only 25-60 s), and excellent recyclabilities (up to 8 cycles). The kinetic pseudo-first-order apparent reaction rate constants (k _app) were calculated to be equal to 8.8 × 10^-3 and 23.5 × 10^-3 s^-1 for 2-nitrophenol and 2-nitroaniline reduction, respectively. To our knowledge, this is considered one of the best and fastest Au-based nanocatalysts reported for the catalytic reduction of nitroarenes, promoted mainly by the synergistic cooperation of their high surface area, large pore volume, mesoporous nature, and enhanced Au-NP dispersions. The unique mesoporous hybrid Au-IO nanoconstructs synthesized here make them novel, stable, and approachable nanocatalyst platform for various catalytic industrial processes.

Controlling the Size of Au Nanoparticles on Reducible Oxides with the Electrochemical Potential

Controlling the size of Au nanoparticles (NPs) and their interaction with the oxide support is important for their catalytic performance in chemical reactions, such as CO oxidation and water-gas shift. It is known that the oxygen vacancies at the surface of support oxides form strong chemical bonding with the Au NPs and inhibit their coarsening and deactivation. The resulting Au/oxygen vacancy interface also acts as an active site for oxidation reactions. Hence, small Au NPs are needed to increase the density of the Au/oxide interface. A dynamic way to control the size of the Au NPs on an oxide support is desirable but has been missing in the field. Here, we demonstrate an electrochemical method to control the size of the Au NPs by controlling the surface oxygen vacancy concentration of the support oxide. Oxides with different reducibilities, La_0.8Ca_0.2MnO_3±δ and Pr_0.1Ce_0.9O_2-δ, are used as model support oxides. By applying the electrochemical potential, we achieve a wide range of effective oxygen pressures, pO₂ (10^-37-10¹⁴ atm), in the support oxides. Applying the cathodic potential creates a high concentration of oxygen vacancies and forms finely distributed Au NPs with sizes of 7-13 nm at 700-770 °C in 10 min, while the anodic potential oxidizes the surface and increases the size of the Au NPs. The onset cathodic potential required to create small Au NPs depends strongly on the reducibility of the support oxide. The Au NPs did not undergo sintering even at 700-770 °C under the cathodic potential and also were stable in catalytically relevant conditions without potential.

Sustainable Bioengineering of Gold Structured Wide-Area Supported Catalysts for Hand-Recyclable Ultra-Efficient Heterogeneous Catalysis

Metal nanoparticles grafted within inert and porous wide-area supports are emerging as recyclable, sustainable catalysts for modern industry applications. Here, we bioengineered gold nanoparticle-based supported catalysts by utilizing the innate metal binding and reductive potential of eggshell as a sustainable strategy. Variable hand-recyclable wide-area three-dimensional catalysts between ∼80 ± 7 and 0.5 ± 0.1 cm² are generated simply by controlling the size of the support. The catalyst possessed high-temperature stability (300 °C) and compatibility toward polar and nonpolar solvents, electrolytes, acids, and bases facilitating ultra-efficient catalysis of accordingly suspended substrates. Validation was done by large-volume (2.8 liters) dye detoxification, gram-scale hydrogenation of nitroarene, and the synthesis of propargylamine. Moreover, persistent recyclability, monitoring of reaction kinetics, and product intermediates are possible due to physical retrievability and interchangeability of the catalyst. Finally, the bionature of the support permits ∼76.9 ± 8% recovery of noble gold simply by immersing in a royal solution. Our naturally created, low-cost, scalable, hand-recyclable, and resilient supported mega-catalyst dwarfs most challenges for large-scale metal-based heterogeneous catalysis.

Gold nanoparticle decorated dithiocarbamate modified natural boehmite as a catalyst for the synthesis of biologically essential propargylamines

Here, we prepare an Au NP decorated dithiocarbamate functionalized boehmite (γ-AlO(OH)@C-NHCS2H·AuNPs). This stepwise synthetic method gives an efficient, cost-effective, and green heterogenous Au-based nanocatalyst for the A3-coupling preparation of the biologically essential propargylamines. Different characterization methods, including FT-IR, XRD, SEM, TEM, EDX spectra, and elemental SEM-mapping, were employed to investigate the structure of the manufactured γ-AlO(OH)@C-NHCS2H·AuNPs. Then we used the prepared composite as a heterogeneous gold-based nanocatalyst for the one-pot A3-coupling preparation of propargyl amines by reacting a variety of aldehydes, amines, and phenylacetylene which exhibited promising results.