Basic concepts and recent advances in nitrophenol reduction by gold- and other transition metal nanoparticles

On the Roles of Electron Transfer in Catalysis by Nanoclusters and Nanoparticles

Electron transfer plays a major role in chemical reactions and processes, and this is particularly true of catalysis by nanomaterials. The advent of metal nanoparticle (NP) catalysts, recently including atomically precise nanoclusters (NCs) as parts of nanocatalyst devices has brought increased control of the relationship between NP and NC structures and their catalytic functions. Consequently, the molecular definition of these new nanocatalysts has allowed a better understanding and management of various kinds of electron transfer involved in the catalytic processes. This Minireview brings a chemist's view of several major aspects of electron-transfer functions concerning NPs and NCs in catalytic processes. Particular focus concerns the role of NPs and NCs as electron reservoirs and light-induced antenna in catalytic processes from H₂ generation to more complex reactions and sustainable energy production.

Preparation and Application of a Hydrochar-Based Palladium Nanocatalyst for the Reduction of Nitroarenes

In the present study, a novel heterogeneous catalyst was successfully fabricated through the decoration of palladium nanoparticles on the surface of designed Fe3O4-coffee waste composite (Pd-Fe3O4-CWH) for the catalytic reduction of nitroarenes. Various characterization techniques such as XRD, FE-SEM and EDS were used to establish its nano-sized chemical structure. It was determined that Pd-Fe3O4-CWH is a useful nanocatalyst, which can efficiently reduce various nitroarenes, including 4-nitrobenzoic acid (4-NBA), 4-nitroaniline (4-NA), 4-nitro-o-phenylenediamine (4-NPD), 2-nitroaniline (2-NA) and 3-nitroanisole (3-NAS), using NaBH4 in aqueous media and ambient conditions. Catalytic reactions were monitored with the help of high-performance liquid chromatography. Additionally, Pd-Fe3O4-CWH was proved to be a reusable catalyst by maintaining its catalytic activity through six successive runs. Moreover, the nanocatalyst displayed a superior catalytic performance compared to other catalysts by providing a shorter reaction time to complete the reduction in nitroarenes.

Nanocatalysis under Nanoconfinement: A Metal-Free Hybrid Coacervate Nanodroplet as a Catalytic Nanoreactor for Efficient Redox and Photocatalytic Reactions

Nature utilizes cellular and subcellular compartmentalization to efficiently drive various complex enzymatic transformations via spatiotemporal control. In this context, designing of artificial nanoreactors for efficient catalytic transformations finds tremendous importance in recent times. One key challenge remains the design of multiple catalytic centers within the confined space of a nanoreactor without unwanted agglomeration and accessibility barrier for reactants. Herein, we report a unique blend of nanoscience and chemical catalysis using a metal-free hybrid synthetic protocell as a catalytic nanoreactor for redox and photocatalytic transformations, which are otherwise incompatible in bulk aqueous medium. Hybrid coacervate nanodroplets (NDs) fabricated from 2.5 nm-sized carbon dots (CDs) and poly(diallyldimethyl)ammonium chloride have been utilized toward reductive hydrogenation of nitroarenes in the presence of sodium borohydride (NaBH₄). It has been found that the reduction mechanism follows the classical Langmuir-Hinshelwood (LH) model at the surface of embedded CDs inside the NDs via the generation of reactive surface hydroxyl groups. These NDs show excellent recyclability without any compromise on reaction kinetics and conversion yield. Importantly, spatiotemporal control over the hydrogenation reaction has been achieved using two mixed populations of coacervates. Moreover, efficient visible light-induced photoredox conversion of ferricyanide to ferrocyanide and artificial peroxidase-like activity have also been demonstrated inside these catalytic NDs. Our findings indicate that the individual polymer-bound CD inside the NDs acts as the catalytic center for both the redox and photocatalytic reactions. The present study highlights the unprecedented catalytic activity of the metal-free CD-based coacervate NDs and paves the way for next-generation catalytic nanoreactors for a wide range of chemical and enzymatic transformations.

Rhenium Nanostructures Loaded into Amino-Functionalized Resin as a Nanocomposite Catalyst for Hydrogenation of 4-Nitrophenol and 4-Nitroaniline

The present work presents a new nanocomposite catalyst with rhenium nanostructures (ReNSs) for the catalytic hydrogenation of 4-nitrophenol and 4-nitroaniline. The catalyst, based on an anion exchange resin with functionality derived from 1,1'-carboimidazole, was obtained in the process involving anion exchange of ReO4- ions followed by their reduction with NaBH4. The amino functionality present in the resin played a primary role in the stabilization of the resultant ReNSs, consisting of ≈1% (w/w) Re in the polymer mass. The synthesized and capped ReNSs were amorphous and had the average size of 3.45 ± 1.85 nm. Then, the obtained catalyst was used in a catalytic reduction of 4-nitrophenol (4-NP) and 4-nitroaniline (4-NA). Following the pseudo-first-order kinetics, 5 mg of the catalyst led to a 90% conversion of 4-NP with the mass-normalized rate constant (km1) of 6.94 × 10-3 min-1 mg-1, while the corresponding value acquired for 4-NA was 7.2 × 10-3 min-1 mg-1, despite the trace amount of Re in the heterogenous catalyst. The obtained material was also conveniently reused.

Bimetallic nanocomposite (Ag-Au, Ag-Pd, Au-Pd) synthesis using gum kondagogu a natural biopolymer and their catalytic potentials in the degradation of 4-nitrophenol

Bimetallic nanoparticles (BNPs) constitute two different metal elements and exhibit relatively superior mechanistic and catalytic efficacies owing to their synergistic functions over monometallic nanoparticles. In the present study various bimetallic Ag-Au, Ag-Pd, Au-Pd nanoparticles were synthesized using a natural biopolymer gum kondagogu (GK) as a reducing and capping agent, by a simple and cost-effective method. The synthesized BNPs when characterized using UV-vis spectroscopy revealed a specific surface plasmon resonance band (SPR) of each nanocomposite. The average particle size of Ag-Au, Ag-Pd, and Au-Pd BNPs was found to be 23 ± 10.3, 21 ± 7.6, and 23 ± 9.4 nm respectively based on transmission electron microscopy analysis. Surface morphology and functional groups on the gum matrix of GK-BNPs were analyzed by XRD and FT-IR respectively. The bimetallic nanocomposites were evaluated for their catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol in the presence of NaBH₄. The kinetic studies performed, depicted rate constants for Ag-Au, Ag-Pd, and Au-PdNPs as 0.31, 0.39, and 0.28 min^-1 respectively. The catalytic efficiencies of three bimetallic nanocomposites were of the following order Ag-Pd > Ag-Au > Au-Pd. This study establishes the catalytic potentials of the three different bimetallic nanocomposites in the reduction of 4-NP an environmental pollutant, and the impact of their synergistic property.

Superhydrophilic three-dimensional porous spent coffee ground reduced palladium nanoparticles for efficient catalytic reduction

The use of functional biodegradable wastes to treat environmental problems would create minimal extra burden to our environment. In this paper, we propose a sustainable and practical strategy to turn spent coffee ground (SCG) into a multifunctional palladium-loaded catalyst for water treatment instead of going into landfill as solid waste. Bleached delignified coffee ground (D-SCG) has a porous structure and a good capability to reduce Pd (II) to Pd (0). A large amount of nanocellulose is formed on the surface of SCG after bleaching by H₂O₂, which anchors and disperses the palladium nanoparticles (Pd NPs). The D-SCG loaded with Pd NPs (Pd-D-SCG) is superhydrophilic, which facilitates water transport and thus promotes efficient removal of organic pollutants dissolved in water. Pd-D-SCG exhibits excellent room temperature catalytic activity for the removal of 4-nitrophenol (4-NP) and methylene blue (MB) in water and shows good chemical stability and recyclability in water, with no obvious decrease even after five repeated cycles.

Copper Nanoparticles as Growth Promoter, Antioxidant and Anti-Bacterial Agents in Poultry Nutrition: Prospects and Future Implications

Copper (Cu) is a vital trace mineral involved in many physiological functions of the body. In the poultry industry, copper sulfate is being used as a major source of Cu. Copper in the bulk form is less available in the body, and much of its amount excreted out with feces causing environmental pollution and economic loss. The application of nanotechnology offers promise to address these issues by making nanoparticles. Copper nanoparticles (Cu-NP) are relatively more bioavailable due to their small size and high surface to volume ratio. Although, there is limited research on the use of Cu-NP in the poultry industry. Some researchers have pointed out the importance of Cu-NP as an effective alternative of chemical, anti-bacterial agents, and growth promoters. The effect of Cu-NP depends on their size, dose rate and the synthesis method. Apart from there, high bioavailability Cu-NP exhibited positive effects on the immunity of the birds. However, some toxic effects of Cu-NP have also been reported. Further investigations are essentially required to provide mechanistic insights into the role of Cu-NP in the avian physiology and their toxicological properties. This review aims to highlight the potential effects of Cu-NP on growth, immune system, antioxidant status, nutrient digestibility, and feed conversion ratio in poultry. Moreover, we have also discussed the future implications of Cu-NP as a growth promoter and alternative anti-bacterial agents in the poultry industry.

Ferrocenyl-terminated polyphenylene-type "click" dendrimers as supports for efficient gold and palladium nanocatalysis

Although dendrimer supports have been known as key parts of nanocatalysts, the capability of rigid dendrimers for this function has not yet been reported. Here, the study is focused on ferrocenylmethylenetriazolyl-terminated dendrimers (FcMTPD) as supports of remarkably efficient nanogold and nanopalladium catalysts. A biphasic system is elaborated to evaluate the catalytic activity of FcMTPD-supported Au and Pd nanoparticles (NPs) for the reduction of 4-nitrophenol to 4-aminophenol by NaBH₄ at 20 °C, and FcMTPD-supported PdNPs are found to be the best nanocatalysts with a rate constant k_app = 7.8 × 10^-2 s^-1. Excellent catalytic results are also obtained in this reaction for FcMTPD-supported AuNPs with a rate constant k_app = 5.6 × 10^-2 s^-1. For both Pd NPs and AuNPs, the kinetic results are shown to strongly depend on the method of preparation of these NPs that influences the NP size and thus their catalytic efficiency. The FcMTPD-stabilized PdNPs are easily recovered and reused at least 13 times, and their catalytic performance displays only a slight decrease during the first seven runs.

Charge State of Au25(SG)18 Nanoclusters Induced by Interaction with a Metal Organic Framework Support and Its Effect on Catalytic Performance

We investigated the charge transfer between Au₂₅(SG)₁₈ nanoclusters and metal-organic framework (MOF) supports including Mil-101-Cr, Mil-125-Ti, and ZIF-8 by an X-ray photoemission technique and discussed the influence of resulted charge states of supported Au₂₅(SG)₁₈ nanoclusters on the 4-nitrophenol reduction reaction. Charge transfer from Au₂₅(SG)₁₈ to Mil-101-Cr induces positive charge Au^δ+ (0 < δ < 1) while charge transfer from ZIF-8 to Au₂₅(SG)₁₈ generates negative charge Au^δ- due to different metal-support interactions. Au₂₅(SG)₁₈ on Mil-125 shows metallic Au⁰, similar to unsupported Au₂₅(SG)₁₈, due to negligible charge transfer. The resulted charge state of Au^δ- inhibits the formation of adsorbed hydride (H^-) species because of electrostatic repulsion, while Au^δ+ impairs the reductive ability of adsorbed hydride (H^-) species due to strong affinity between them. In comparison, metallic Au⁰ in Au₂₅(SG)₁₈/Mil-125 and unsupported Au₂₅(SG)₁₈ presents the optimum catalytic activity. The current work provides guidelines to design effective metal nanoclusters in heterogeneous catalysis through metal-support interaction exerted by metal-oxo/nitric clusters within MOFs.

Size-Dependent Catalytic Activity of PVA-Stabilized Palladium Nanoparticles in p-Nitrophenol Reduction: Using a Thermoresponsive Nanoreactor

Palladium nanoparticles (Pd NPs) of various average global diameters (2.1-7.1 nm) encapsulated with hydrophilic polymer polyvinyl alcohol (PVA) have been synthesized and used as catalysts for sodium borohydride assisted reduction of p-nitrophenol to p-aminophenol. The synthesized catalysts exhibit excellent and typical size-dependent catalytic activity in the green protocol. UV-visible absorption spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were employed to characterize the prepared Pd NPs. The kinetics of this reaction was easily monitored by a UV-visible absorption spectrophotometer. The mechanism of the reaction is explained by the Langmuir-Hinshelwood model. The catalytic performance increases with decreasing size of the synthesized nanoparticles. The apparent rate constants (k app × 103/s-1) of the catalytic reduction in the presence of Pd NPs of average diameters of 2.1, 3.35, 6.2, and 7.1 nm are determined as 8.57, 7.67, 6.16, and 5.04, respectively, at 298 K by using 2.91 mol % palladium nanocatalyst in each case. Moreover, the estimated activation energy of 22.2 kJ mol-1 obtained for Pd NPs with the smallest average diameter of 2.1 nm is very low as reported in the literature for the reduction. The influences of catalyst dose and concentration of p-nitrophenol on catalytic reduction are fully investigated. The catalyst with the largest diameter shows a temperature-sensitive property that might be due to the presence of a very low amount of rapped PVA used as stabilizer during the fabrication process. Thus, the synthetic protocol provides a unique fabrication process of a catalytically active thermoresponsive nanoreactor consisting of Pd NPs encapsulated into a PVA stabilizing agent.

Simple borophosphate glasses for on-demand growth of self-supported copper nanoparticles in the reduction of 4-nitrophenol

Herein, we demonstrate a single-step synthesis of simple copper-doped borophosphate glasses and their unusual use for catalytic reduction of nitro groups from the aromatic nitro compounds. The copper-doped glasses were evaluated as an affordable heterogeneous catalytic glass-based material for the reduction of 4-nitrophenol by sodium borohydride. The glass matrix acts as a host and support material for in situ self-growth of zero-valent copper (Cu) nanoparticles (NPs) on the glass surface. Thus, zero-valent CuNPs are produced in situ on the glass surface that is accomplished by the interaction of copper ions with hydride ions. Using an intrinsic reaction kinetic constant, we find a catalytic activity of 0.144 L s^-1 g^-1 for a glass-based catalyst doped with a non-noble metal, which is an order of magnitude higher when compared to the values observed elsewhere. Furthermore, the reuse of glass catalyst after six successive cycles demonstrates an outstanding performance compared to that of the parent material. A mathematical model based on the Langmuir-Hinshelwood mechanism related to an empirical growth rate of the zero-valent CuNPs was proposed to describe the kinetic of the 4-nitrophenol catalytic hydrogenation.

In Situ Preparation of Composite Redox-Active Micelles Bearing Pd Nanoparticles for the Reduction of 4-Nitrophenol

Owing to the redox activity of the poly(ferrocenylsilane)-based polymer, several noble metal nanoparticles can be successfully prepared. As reported herein, the in situ preparation of Pd nanoparticles was performed using a redox-active platform of poly(ferrocenylmethylethylthiocarboxylpropylsilane) (PFC) micelles. PFC/Pd nanocomposites (NCs) with Pd nanoparticles uniformly dispersed at the surface of PFC nanospheres were obtained. The morphology of PFC/Pd NCs was further confirmed via high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Taking advantage of Pd nanoparticles, the PFC/Pd NCs showed significant catalytic activity during the reduction process of 4-nitrophenol by sodium borohydride. Although PFC micelles themselves showed no catalytic activity, they promoted the catalytic behavior of Pd nanoparticles obviously by anchoring the Pd nanoparticles at their surface to avoid the aggregation and leaching of Pd nanoparticles. In all, PFC/Pd NCs exhibited great potential as a composite nanocatalyst. Moreover, the PFC micelle was found to be a desired platform for nanocatalysts.

A study on the high efficiency reduction of p-nitrophenol (4-NP) by a Fe(OH)3/Fe2O3@Au composite catalyst

Precious metal nanometric catalysts are widely used in the removal of harmful substances. In the process of synthesis and catalytic reaction, it is particularly important to study green and simple synthesis methods and high catalytic efficiency. In this paper, a green one-step method was used to synthesize the Fe(OH)₃/Fe₂O₃@Au composite catalyst, in which Au was single atom-dispersed. The removal of 4-nitrophenol (4-NP), a typical dangerous chemical widely existing in factory waste gas, waste water and automobile exhaust gas, was catalysed by Fe(OH)₃/Fe₂O₃@Au. The catalytic performance of Fe(OH)₃/Fe₂O₃@Au with different synthesis conditions (different amounts of MES, NaBH₄, FeSO₄, Au and Pt) on the 4-NP reduction reaction were systematically studied. Finally, the stability and recyclability of Fe(OH)₃/Fe₂O₃@Au composite nanocatalyst were investigated thoroughly.

Metal Nanoparticles: a Promising Treatment for Viral and Arboviral Infections

Globally, viral diseases continue to pose a significant threat to public health. Recent outbreaks, such as influenza, coronavirus, Ebola, and dengue, have emphasized the urgent need for new antiviral therapeutics. Considerable efforts have focused on developing metal nanoparticles for the treatment of several pathogenic viruses. As a result of these efforts, metal nanoparticles are demonstrating promising antiviral activity against pathogenic surrogates and clinical isolates. This review summarizes the application of metal nanoparticles for the treatment of viral infections. It provides information on synthesis methods, size-related properties, nano-bio-interaction, and immunological effects of metal nanoparticles. This article also addresses critical criteria and considerations for developing clinically translatable nanosized metal particles to treat viral diseases.

Stable Mesoscale Nonwovens of Electrospun Polyacrylonitrile and Interpenetrating Supramolecular 1,3,5-Benzenetrisamide Fibers as Efficient Carriers for Gold Nanoparticles

The immobilization of metal nanoparticles without agglomeration and leaching within composite nonwovens is often challenging and of great importance, for example, for catalytic applications. In this study, we prepared composite nonwovens based on electrospun polyacrylonitrile (PAN) short fibers and supramolecular terpyridine-functionalized benzene-1,3,5-tricarboxamide (BTA1) nanofibers by a sheet-forming wet-laid process. The formation of an interpenetrating and entangled network of supramolecular BTA1 nanofibers and PAN short fibers results in mechanically stable mesoscale nonwovens. Because of the peripheral terpyridine substituents of the BTA1, nonaggregated gold nanoparticles (AuNPs) could be immobilized efficiently in the composite nonwovens. The functionality of the resulting AuNPs-loaded composite nonwovens was verified by catalytic reduction of 4-nitrophenol to 4-aminophenol as a standard model reaction. The AuNPs-loaded PAN/BTA1 composite nonwovens showed high catalytic activity, reusability, and excellent stability.

Clay nanotube-metal core/shell catalysts for hydroprocesses

Catalytic hydroprocesses play a significant role in oil refining and petrochemistry. The tailored design of new metal nanosystems and optimization of their support, composition, and structure is a prospective strategy for enhancing the efficiency of catalysts. Mesoporous support impacts the active component by binding it to the surface, which leads to the formation of tiny highly dispersed catalytic particles stabilized from aggregation and with minimized leaching. The structural and acidic properties of the support are crucial and determine the size and dispersion of the active metal phase. Currently, research efforts are shifted toward the design of nanoscale porous materials, where homogeneous catalysts are displaced by heterogeneous. Ceramic materials, such as 50 nm diameter natural halloysite nanotubes, are of special interest for this. Much attention to halloysite clay is due to its tubular structure with a hollow 10-15 nm diameter internal cavity, textural characteristics, and different chemical compositions of the outer/inner surfaces, allowing selective nanotube modification. Loading halloysite with metal particles or placing them outside the tubes provides stable and efficient mesocatalysts. The low cost of this abundant nanoclay makes it a good choice for the scaled-up architectural design of core-shell catalysts, containing active metal sites (Au, Ag, Pt, Ru, Co, Mo, Fe₂O₃, CdS, CdZnS, Cu-Ni) located inside or outside the tubular template. These alumosilicate nanotubes are environment-friendly and are available in thousands of tons. Herein, we summarized the advances of halloysite-based composite materials for hydroprocesses, focusing on the selective binding of metal particles. We analyze the tubes' morphology adjustments and size selection, the physicochemical properties of pristine and modified halloysite (e.g., acid-etched or silanized), the methods of metal clusters formation, and their localization. We indicate prospective routes for the architectural design of stable and efficient nanocatalysts based on this safe and natural clay material.

Silicone Nanofilament Support Layers in an Open-Channel System for the Fast Reduction of Para-Nitrophenol

Chemical vapor phase deposition was used to create hydrophobic nanostructured surfaces on glass slides. Subsequently, hydrophilic channels were created by sputtering a metal catalyst on the channels while masking the outside. The surface tension gradient between the hydrophilic surface in the channels and the outside hydrophobicity formed the open-channel system. The reduction of para-nitrophenol (PNP) was studied on these devices. When compared to nanostructure-free reference systems, the created nanostructures, namely, silicone nanofilaments (SNFs) and nano-bagels, had superior catalytic performance (73% and 66% conversion to 55% at 0.5 µL/s flow rate using 20 nm platinum) and wall integrity; therefore, they could be readily used multiple times. The created nanostructures were stable under the reaction conditions, as observed with scanning electron microscopy. Transition electron microscopy studies of platinum-modified SNFs revealed that the catalyst is present as nanoparticles ranging up to 13 nm in size. By changing the target in the sputter coating unit, molybdenum, gold, nickel and copper were evaluated for their catalytic efficiency. The relative order was platinum < gold = molybdenum < nickel < copper. The decomposition of sodium borohydride (NaBH₄) by platinum as a concurrent reaction to the para-nitrophenol reduction terminates the reaction before completion, despite a large excess of reducing agent. Gold had the same catalytic rate as molybdenum, while nickel was two times and copper about four times faster than gold. In all cases, there was a clear improvement in catalysis of silicone nanofilaments compared to a flat reference system.

Selectively coupled small Pd nanoparticles on sp2-hybridized domain of graphene-based aerogel with enhanced catalytic activity and stability

The precisely coupling of metal nanoparticles with support domain are crucial to enhance the catalytic activity and stability of supported metal nanoparticle catalysts (MNPs). Here we selectively anchor Pd nanoparticles to the sp² domain in graphene-based aerogel constructed with base-washed graphene oxide (BGO) by removing oxidative debris (OD). The effects of OD on the size and chemical composition of Pd nanoparticles in aerogels are initially unveiled. The removal of OD nanoparticles prompt selective coupling of Pd nanoparticles to the exposed sp²-hybridized domain on BGO nanosheets, and then prevent it from agglomeration. As a result, the Pd nanoparticle size of self-assembled Pd/BGA is 4.67 times smaller than that of traditional Pd/graphene oxide aerogel (Pd/GA). The optimal catalytic activity of Pd/BGA for the model catalytic reduction of 4-nitrophenol is 15 times higher than that of Pd/GA. Pd/BGA could maintain its superior catalytic activity and achieves 98.72% conversion in the fifth cycle. The superior catalytic performance could be ascribed to the small Pd nanoparticles and high percentage of Pd(0) in Pd/BGA, and the enhanced electronic conductivity of Pd/BGA. These integrated merits of Pd/BGA as heterogeneous catalysts are attributed to selectively anchor Pd nanoparticles on sp²-hybridized domain of graphene-based aerogel, and strongly coupled interaction of MNPs with support. The structure-regulated BGO nanosheets could serve as versatile building blocks for fabricating MNPs/graphene aerogels with superior performance for catalytic transformation of water pollutants.

Ag@ZnO/MWCNT ternary nanocomposite as an active and stable catalyst for the 4-nitrophenol reduction in water

The nitroaromatic compounds, known as organic pollutants, have arising attention due to their carcinogenic character, highly dangerous to human health. In this work, the Ag@ZnO/MWCNT ternary nanocomposite synthesized via conjugation of sonochemical and solvothermal treatments manifests high performance in the reduction of 4-nitrophenol in the aqueous media (TOF value of 246 min^-1μmol metal^-1). The incorporation of MWCNT onto the nanocomposite structure favored the reusing of the catalysts even after eight consecutive catalytic runs without catalysts cleaning nor product removal. Obtained samples were characterized by XRD, TEM, UV-vis, Raman and FTIR spectroscopies. It was found that ultrasonic treatment at relatively moderate conditions leads to functionalization of MWCNT, the appearance of C=C and OH groups and change of electronic properties of Ag@ZnO/MWCNT composite which provide its stable material dispersion in aqueous solution and high catalytic performance in the 4-nitrophenol reduction. This technique may be effectively applied for the functionalization of carbon including materials for their usage in an aqueous media.

A water stable Eu(III)-organic framework as a recyclable multi-responsive luminescent sensor for efficient detection of p-aminophenol in simulated urine, and MnVII and CrVI anions in aqueous solutions

A novel 3D Eu(iii) metal-organic framework (Eu-MOF-1) formulated as [Eu(L)(H2O)(DMA)] (L = 2-(2-nitro-4-carboxylphenyl)terephthalic acid) has been successfully synthesized under solvothermal conditions and characterized by structural analyses. Eu-MOF-1 displays a new 3D framework containing EuIII ions, ligand L, and coordinated DMA molecules and water molecules. The fluorescence investigations indicate that Eu-MOF-1 emits bright red luminescence, and shows relatively high water stability and outstanding chemical stability under a relatively wide range of pH conditions. It is noteworthy that Eu-MOF-1 can quantitatively detect p-aminophenol (PAP) which is a metabolite of phenylamine in human urine. More significantly, Eu-MOF-1 is the first reported multi-responsive luminescent sensor for detecting the biomarker PAP, and MnVII and CrVI anions with high selectivity, sensitivity, recyclability and relatively low detection limits in aqueous solutions. Furthermore, the possible sensing mechanisms of Eu-MOF-1 for selective sensing have also been explored in detail. Eu-MOF-1 could be an ideal candidate as a multi-responsive luminescent sensor in biological and environmental areas.

Effective reduction of nitrophenols and colorimetric detection of Pb(ii) ions by Siraitia grosvenorii fruit extract capped gold nanoparticles

This study presents a simple and green approach for the synthesis of Siraitia grosvenorii fruit extract capped gold nanoparticles (SG-AuNPs). The SG-AuNPs samples prepared under the optimized conditions were characterized by various techniques (UV-Vis, XRD, FTIR, HR-TEM, EDX, DLS). The biosynthesized nanoparticles were then studied for the reduction of 2-nitrophenol (2-NP) and 3-nitrophenols (3-NP) and for colorimetric detection of Pb2+ ions. The characterization results revealed that the crystals of SG-AuNPs were spherical with an average size of 7.5 nm. The FTIR and DLS analyses proved the presence of the biomolecule layer around AuNPs, which played an important role in stabilizing the nanoparticles. The SG-AuNPs showed excellent catalytic activity in the reduction of 3-NP and 2-NP, achieving complete conversion within 14 min. The catalytic process was endothermic and followed pseudo-first-order kinetics. The activation energy was determined to be 10.64 and 26.53 kJ mol-1 for 2-NP and 3-NP, respectively. SG-AuNPs maintained high catalytic performance after five recycles. The fabricated material was also found to be highly sensitive and selective to Pb2+ ions with the detection limit of 0.018 μM in a linear range of 0-1000 μM. The practicality of the material was validated through the analyses of Pb2+ in mimic pond water samples. The developed nanoparticles could find tremendous applications in environmental monitoring.

Modulation of Nanoparticle Diffusion by Surface Ligand Length and Charge: Analysis with Molecular Dynamics Simulations

To help better interpret experimental measurement of nanoparticle size, it is important to understand how their diffusion depends on the physical and chemical features of surface ligands. In this study, explicit solvent molecular dynamics simulations are used to probe the effect of ligand charge and flexibility on the diffusion of small gold nanoparticles. The results suggest that despite a high bare charge (+18 e), cationic nanoparticles studied here have reduced diffusion constants compared to a hydrophobic gold nanoparticle by merely a modest amount. Increasing the ligand length by 10 CH₂ units also has a limited impact on the diffusion constant. For the three particles studied here, the difference between estimated hydrodynamic radius and radius of gyration is on the order of one solvent layer (3-5 Å), confirming that the significant discrepancies found in the size of similar nanoparticles by recent transmission electron microscopy and dynamic light scattering measurements were due to aggregation under solution conditions. The limited impact of electrostatic friction on the diffusion of highly charged nanoparticles is found to be due to the strong anticorrelation between electrostatic and van der Waals forces between nanoparticle and environment, supporting the generality of recent observation for proteins by Matyushov and co-workers. Including the first shell of solvent molecules as part of the diffusing particle has a minor impact on the total force autocorrelation function but reduces the disparity in relaxation time between the total force and its electrostatic and van der Waals components.

Bimetallic Co/Zn zeolitic imidazolate framework ZIF-67 supported Cu nanoparticles: An excellent catalyst for reduction of synthetic dyes and nitroarenes

In this study, a sub-class of microporous crystalline metal organic frameworks (MOFs) with zeolite-like configurations, i.e., zeolitic imidazolate frameworks of single node ZIF-67 and binary nodes ZIF-Co/Zn are used as the supports to develop Cu nanoparticles based nanocatalysts. Their catalytic activities are comparatively evaluated where Cu(x)@ZIF-Co/Zn exhibits better performances than Cu(x)@ZIF-67 in the reduction of synthetic dyes and nitroarenes. For instance, the Cu(0.25)@ZIF-Co/Zn catalyst shows an excellent reaction rate of 2.088 × 10^-2 s^-1 and an outstanding activity of 104.4 s^-1g_cat^-1 for the reduction of methyl orange. The same catalyst also performs an exceptional catalytic activity in the hydrogenation of p-nitrophenol to p-aminophenol with the activity of 216.5 s^-1g_cat^-1. A synergistic role of unique electronic properties rising from the direct contact of Cu NPs with the bimetallic nodes ZIF-Co/Zn, higher surface area of support, appropriate Cu loading and maintainable microporous frameworks with higher thermal and hydrolytic stability collectively enhances the catalytic activity of Cu(x)@ZIF-Co/Zn. Moreover, this catalyst shows excellent stability and recyclability, which can retain high conversion after reuse for 10 cycles.

Effect of Polyvinyl Alcohol Ligands on Supported Gold Nano-Catalysts: Morphological and Kinetics Studies

The effect of polyvinyl alcohol (PVA) stabilizers and gold nanoparticles supported on active carbon (AuNPs/AC) was investigated in this article. Polymers with different molecular weights and hydrolysis degrees have been synthesized and used, like the stabilizing agent of Au nano-catalysts obtained by the sol-immobilization method. The reduction of 4-nitrophenol with NaBH4 has been used as a model reaction to investigate the catalytic activity of synthesized Au/AC catalysts. In addition, we report several characterization techniques such as ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) in order to correlate the properties of the polymer with the metal nanoparticle size and the catalytic activity. A volcano plot was observed linking the catalytic performance with hydrolysis degree and the maximum of the curve was identified at a value of 60%. The Au:PVA-60 weight ratio was changed in order to explain how the amount of the polymer can influence catalytic properties. The effect of nitroaromatic ring substituents on the catalytic mechanism was examined by the Hammett theory. Moreover, the reusability of the catalyst was investigated, with little to no decrease in activity observed over five catalytic cycles. Morphological and kinetic studies reported in this paper reveal the effect of the PVA polymeric stabilizer properties on the size and catalytic activity of supported gold nanoparticles.

Green Synthesis of Ag-Au Bimetallic Nanocomposites Using Waste Tea Leaves Extract for Degradation Congo Red and 4-Nitrophenol

A sustainable supply of pure water is a great challenge in most developing and third-world countries. Nanomaterial-based technology offers technological development for wastewater purification. Nanocatalysis hydrogenation of nitroarene and dye molecules is a hot model in many research fields. Herein, we report eco-friendly and facile technology to synthesize Ag-Au bimetallic nanocomposites. The synthesized nanocomposites are characterized by ultraviolet–visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The synthesized nanocomposite can efficiently degrade Congo red and 4-nitrophenol in water and in the presence of sodium borohydride. The results show that it degrades Congo red and 4-nitrophenol entirely within 6 and 7 min, respectively. These results could be useful for the green synthesis of Ag-Au bimetallic nanocomposites and help to remove organic dye molecules and nitroaromatics from wastewater.

Amplified fluorescence detection and adsorption of Au3+ by the fluorescent melamine formaldehyde microspheres incorporated with N and S co-doped carbon dots

Gold is one of the potential toxic heavy metals. In the present study, Au³⁺ was detected and removed by newly-designed fluorescent microspheres (MF-CDs), i.e. melamine formaldehyde microspheres incorporated with N and S co-doped carbon dots (N,S-CDs). N,S-CDs played the role as sensing unites and melamine formaldehyde microspheres (MF) as carriers. When MF-CDs were attempted as the fluorescence probe, enhanced fluorescence sensing performance towards Au³⁺ was achieved with wider linear range (0.05-2 μM) and lower limit of detection (31 nM) compared to the N,S-CDs probe. In addition, when MF-CDs were used as the adsorbent, the adsorption capacity towards Au³⁺ reached up to 1 mmol g^-1, about ten times more than that of MF. Moreover, the Au³⁺ adsorbed on the MF-CDs could be in-situ transferred to gold nanoparticle (AuNP), forming the immobilized nanocatalyst, i.e. MF-CDs-AuNP, which could further assist the reduction of 4-nitrophenol with acceptable reusability. This study paved an avenue to design the multifunctional materials for simultaneous detection, removal and recycling of environmental concerned pollutants.

Photocatalytic degradation of p-nitrophenol using biologically synthesized ZnO nanoparticles

The present work deals with the photocatalytic degradation of p-nitrophenol as it is a United States Environmental Protection Agency-listed priority pollutant and has adverse environmental and health effects. To eradicate the detrimental environmental impact of p-nitrophenol, the biologically synthesized ZnO nanoparticles were used as a photocatalyst. The degradation of p-nitrophenol was confirmed by decreasing the absorbance value at a characteristic wavelength of 317 nm using the UV-vis spectrophotometer. Reaction parameters such as ZnO photocatalyst concentration of 0.1 g/L at pH 11 in the presence of H₂O₂ (5 mM) were found to be optimum conditions for p-nitrophenol degradation. The photocatalytic degradation was slowly enhanced in the presence of H₂O₂ as an electron acceptor. The kinetics of nitrophenol degradation was studied, which follows the pseudo-first-order reaction. The photocatalytic degradation of p-nitrophenol was characterized by using total organic carbon, chemical oxygen demand, and high-performance liquid chromatography analyses. This method is found to be effective as it is environmentally friendly, free of toxic chemicals.

One Pot Synthesis of Large Gold Nanoparticles with Triple Functional Ferrocene Ligands

In biomedical, toxicological, and optoelectronic applications, the size of nanoparticles is one of the decisive factors. Therefore, synthesis of nanoparticles with controlled sizes is required. The current methods for synthesis of larger gold nanoparticles (GNPs, ~200 nm) are complex and tedious, producing nanoparticles with a lower yield and more irregular shapes. Using ferrocene as a primary reducing agent and stabilizer, sodium citrate as a dispersant, and sodium borohydride as an accessory reducing agent, GNPs of 200 nm were synthesized in a one pot reaction. Besides the roles of reducing agent and GNP stabilizer, ferrocene also served a role of quantitative marker for ligand loading, allowing an accurate determinate of surface ligands.

How the Shape and Chemistry of Molecular Penetrants Control Responsive Hydrogel Permeability

The permeability of hydrogels for the selective transport of molecular penetrants (drugs, toxins, reactants, etc.) is a central property in the design of soft functional materials, for instance in biomedical, pharmaceutical, and nanocatalysis applications. However, the permeation of dense and hydrated polymer membranes is a complex multifaceted molecular-level phenomenon, and our understanding of the underlying physicochemical principles is still very limited. Here, we uncover the molecular principles of permeability and selectivity in hydrogel permeation. We combine the solution-diffusion model for permeability with comprehensive atomistic simulations of molecules of various shapes and polarities in a responsive hydrogel in different hydration states. We find in particular that dense collapsed states are extremely selective, owing to a delicate balance between the partitioning and diffusivity of the penetrants. These properties are sensitively tuned by the penetrant size, shape, and chemistry, leading to vast cancellation effects, which nontrivially contribute to the permeability. The gained insights enable us to formulate semiempirical rules to quantify and extrapolate the permeability categorized by classes of molecules. They can be used as approximate guiding ("rule-of-thumb") principles to optimize penetrant or membrane physicochemical properties for a desired permeability and membrane functionality.

Ultralow Loading Ruthenium on Alumina Monoliths for Facile, Highly Recyclable Reduction of p-Nitrophenol

The pervasive use of toxic nitroaromatics in industrial processes and their prevalence in industrial effluent has motivated the development of remediation strategies, among which is their catalytic reduction to the less toxic and synthetically useful aniline derivatives. While this area of research has a rich history with innumerable examples of active catalysts, the majority of systems rely on expensive precious metals and are submicron- or even a few-nanometer-sized colloidal particles. Such systems provide invaluable academic insight but are unsuitable for practical application. Herein, we report the fabrication of catalysts based on ultralow loading of the semiprecious metal ruthenium on 2–4 mm diameter spherical alumina monoliths. Ruthenium loading is achieved by atomic layer deposition (ALD) and catalytic activity is benchmarked using the ubiquitous para-nitrophenol, NaBH4 aqueous reduction protocol. Recyclability testing points to a very robust catalyst system with intrinsic ease of handling.

Towards the identification of the gold binding region within trypsin stabilized nanoclusters using microwave synthesis routes

Elucidating the location of stabilized nanoclusters within their protein hosts is an existing challenge towards the optimized development of functional protein-nanoclusters. While nanoclusters of various metal compositions can be readily synthesized within a wide array of protein hosts and exhibit tailorable properties, the inability to identify the cluster stabilization region prevents controllable property manipulation of both metallic and protein components. Additionally, the ability to synthesize protein-nanoclusters in a consistent and high-throughput fashion is also highly desirable. In this effort, trypsin stabilized gold nanoclusters are synthesized through standard and microwave-enabled methodologies to determine the impact of processing parameters on the materials physical and functional properties. Density functional theory simulations are employed to localize high probability regions within the trypsin enzyme for Au25 cluster stabilization, which reveal that cluster location is likely within close proximity of the trypsin active region. Trypsin activity measurements support our findings from DFT, as trypsin enzymatic activity is eliminated following cluster growth and stabilization. Moreover, studies on the reactivity of Au NCs and synchrotron characterization measurements further reveal that clusters made by microwave-based techniques exhibit slight structural differences to those made via standard methodologies, indicating that microwave-based syntheses largely maintain the native structural attributes despite the faster synthetic conditions. Overall, this work illustrates the importance of understanding the connections between synthetic conditions, atomic-scale structure, and materials properties that can be potentially used to further tune the properties of metal cluster-protein materials for future applications.

Nickel hydroxide nanoparticles decorated napthalene sulfonic acid-doped polyaniline nanotubes as efficient catalysts for nitroarene reduction

Nanosize nickel hydroxide decorated 2-napthalene sulfonic acid-doped polyaniline nanotubes nanocomposites (Ni(OH)₂@NSA-PANI NCs) were successfully developed for the catalytic reduction of aromatic nitro compounds. The Ni(OH)₂@NSA-PANI NCs were synthesised by depositing Ni(OH)₂ nanoparticles onto 2-napthalene sulfonic acid doped PANI nanotubes surface. The resulting material was characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The prepared nanocomposite showed a remarkable ability to catalytically hydrogenate aromatic nitro compounds using sodium borohydride (NaBH₄) as hydrogen source in aqueous medium at room temperature. Kinetic studies were performed using 4-nitrophenol (4-NP) as the model substrate, using the Langmuir-Hinshelwood model. The catalyst showed pseudo-first-order kinetics, with rate constants estimated between 0.08287 and 0.3649 min^-1. Catalyst recyclability without reduced activity was demonstrated over 10 successive cycles. The optimised nanocomposite catalyst demonstrated a low activation energy barrier towards 4-NP reduction.

Regulating Catalytic Activity of DNA-Templated Silver Nanoclusters Based on their Differential Interactions with DNA Structures and Stimuli-Responsive Structural Transition

This work reports exquisite engineering of catalytic activity of DNA-templated silver nanoclusters (DNA-AgNCs) based on unique adsorption phenomena of DNAs on DNA-AgNCs and reversible transition between double and triple-stranded DNAs. Four DNA homopolymers exhibit different inhibition effects on the catalytic activity of DNA-AgNCs, poly adenine (polyA) > poly guanine (polyG) > poly cytosine (polyC) > poly thymine (polyT), demonstrating that polyA strands have the strongest adsorption affinity on DNA-AgNCs. Through the formation of T-A•T triplex DNAs, catalytic activity of DNA-AgNCs is restored from the deactivated state by double or single-stranded DNAs, indicating the participation of N7 groups of adenine bases in binding to DNA-AgNCs and blocking active sites. Accordingly, reversibly regulating catalytic activity of DNA-AgNCs can be realized based on DNA input-stimulated transition between duplex and triplex structures. In the end, two low-cost and facile biosensing methods are presented, which are derived from the activity-switchable platform. It is worthy to anticipate that the DNA-AgNCs with controlled catalytic activity will inspire researchers to devise more functionalized nanocatalysts and contribute to the exploration of intelligent biomedicine in the future.

Green fabrication of hydrogel-immobilized Au@Ag nanoparticles using tannic acid and their application in catalysis

A catalytic hydrogel was obtained by immobilizing tannic acid reduced and stabilized Au@AgNPs on a PVA/TA hydrogel, used as the good solid catalyst for the degradation of environmental pollutants such as Congo red, 4-nitrophenol, -etc.

PNIPAM-immobilized gold-nanoparticles with colorimetric temperature-sensing and reusable temperature-switchable catalysis properties

The temperature-responsive core–shell hybrid nanoparticles PNIPAMs-AuNP have dual-functional applications as colorimetric temperature-sensors and reusable temperature-switchable catalysts.

Superfast flow reactor derived from the used cigarette filter for the degradation of pollutants in water

Developing high value-added products from the waste materials is highly promising from the perspective of environmental protection and resource recovery. Herein, the used cigarette filter was recycled to prepare the flow reactor via a clean and facile strategy. A continuous-flow reduction method was adopted to produce the gold nanoparticles on deacetylated cigarette filter without any extra chemical modifier, reductant or surfactant. The obtained filter was applied as a continuous-flow reactor and showed a high permeability and ultrafast flow catalytic ability. The permeability coefficient of the reactor was about 1.4 × 10^-10 m². This work provided a clean method to covert the waste cigarette filter to useful flow reactor with the relatively simple steps, and the product had a potential for the fast reduction of 4-nitrophenol and dyes including methyl blue and methylene orange.