Polyethylenimine as a Versatile Simultaneous Reducing and Stabilizing Agent Enabling One-Pot Synthesis of Transition-Metal Nanoparticles: Fundamental Aspects and Practical Implications

The large surface area of metallic nanoparticles provides them with particular optical, chemical, and biological properties, accordingly enabling their use in a wide array of applications. In this regard, facile and fast synthetic approaches are desirable for ready-to-use functional materials. Following early investigations focused on the direct synthesis of polymer-coated gold nanoparticles, we herein demonstrate that such a strategy can be used to manufacture different types of d-block transition-metal nanoparticles via a one-pot method in aqueous media and mild temperature conditions. Gold (Au3+), palladium (Pd2+), and silver (Ag+) ions could be reduced using only polyethylenimine (PEI) or PEI derivatives acting simultaneously as a reducing and stabilizing agent and without the aid of any other external agent. The process gave rise, for instance, to Pd urchin-like nanostructures with a large surface area which confers to them outstanding catalytic performance compared to AuNPs and AgNPs produced using the same strategy. The polymer-stabilized AgNPs were demonstrated to be biocide against a variety of microorganisms, although AuNPs and PdNPs do not hold such an attribute at least in the probed concentration range. These findings may provide significant advances toward the practical, facile, and ready-to-use manufacturing of transition-metal nanoparticles for a myriad of applications.

Precision nanoengineering for functional self-assemblies across length scales

As nanotechnology continues to push the boundaries across disciplines, there is an increasing need for engineering nanomaterials with atomic-level precision for self-assembly across length scales, i.e., from the nanoscale to the macroscale. Although molecular self-assembly allows atomic precision, extending it beyond certain length scales presents a challenge. Therefore, the attention has turned to size and shape-controlled metal nanoparticles as building blocks for multifunctional colloidal self-assemblies. However, traditionally, metal nanoparticles suffer from polydispersity, uncontrolled aggregation, and inhomogeneous ligand distribution, resulting in heterogeneous end products. In this feature article, I will discuss how virus capsids provide clues for designing subunit-based, precise, efficient, and error-free self-assembly of colloidal molecules. The atomically precise nanoscale proteinic subunits of capsids display rigidity (conformational and structural) and patchy distribution of interacting sites. Recent experimental evidence suggests that atomically precise noble metal nanoclusters display an anisotropic distribution of ligands and patchy ligand bundles. This enables symmetry breaking, consequently offering a facile route for two-dimensional colloidal crystals, bilayers, and elastic monolayer membranes. Furthermore, inter-nanocluster interactions mediated via the ligand functional groups are versatile, offering routes for discrete supracolloidal capsids, composite cages, toroids, and macroscopic hierarchically porous frameworks. Therefore, engineered nanoparticles with atomically precise structures have the potential to overcome the limitations of molecular self-assembly and large colloidal particles. Self-assembly allows the emergence of new optical properties, mechanical strength, photothermal stability, catalytic efficiency, quantum yield, and biological properties. The self-assembled structures allow reproducible optoelectronic properties, mechanical performance, and accurate sensing. More importantly, the intrinsic properties of individual nanoclusters are retained across length scales. The atomically precise nanoparticles offer enormous potential for next-generation functional materials, optoelectronics, precision sensors, and photonic devices.

Electronic Tuning of Gold Nanoparticle Active Sites for Reduction Catalysis

Electronic tuning of active sites in heterogeneous catalysis with organic ligands remains challenging since the ligands are often bound to the most active sites on the catalysts' surfaces. In this work, gold nanoparticles, which are on average less than 2 nm in diameter, are synthesized with strongly binding thiol and phosphine ligands and have measurable quantities of accessible sites on their surfaces in both cases. Triphenylphosphine (TPP) is used as the phosphine ligand, while triphenylmethyl mercaptan (TPMT) serves as the thiol ligand. Phosphines are chosen because they are electron-donating ligands when bound to Au, and thiols are selected because they are electron-withdrawing on the Au surface. X-ray photoelectron spectroscopy (XPS) results show differences in the Au 4f binding energies between the TPP- and TPMT-bound Au nanoparticles. Fourier transform infrared spectroscopy (FTIR) measurements of bound CO indicate that the TPP-bound Au nanoparticles are more electron-rich than the TPMT-bound Au nanoparticles. The number of binding sites on the surface is quantified using 2-naphthalenethiol titration experiments. It is observed that the number of binding sites on the thiol and phosphine-bound Au nanoparticles is similar in both cases. The Au nanoparticles are used for three different reactions: resazurin reduction, CO oxidation, and benzyl alcohol oxidation. For both CO oxidation and benzyl alcohol oxidation, which are performed with the ligands attached, TPP- and TPMT-bound nanoparticles are both catalytically active. However, for resazurin reduction, the TPMT-bound Au nanoparticles are not active, while the TPP-bound Au nanoparticles are catalytically active. These results illustrate that the catalytic activity can be tuned using bound organic ligands with different electronic properties for reduction reactions using Au nanoparticle catalysts.

Formation and evolution of the nanoparticle environmental corona: The case of Au and humic acid

Studying the behaviour of nanomaterials after their release into natural water is essential to understand the risk associated to their environmental exposure. In particular, the interaction and adsorption of dissolved organic matter onto nanoparticles strongly influence the behaviour and fate of nanomaterials in natural water systems. We herein study the interaction of Au and Ag nanoparticles and humic acids, the principal component of natural dissolved organic matter. Physicochemical characterization results showed the formation of an organic matter corona, consisting of two layers: a "hard" one, firmly bound to the nanoparticle surface, and a "soft" one, in dynamic equilibrium and, consequently, highly dependent on the media organic matter concentration. The extent of the electro-steric stabilization of the so called environmental corona depends on the size of the supramolecular association of humic acid (which depends on its hydrophilic and lipophilic moieties), the nanoparticle size, the total concentration of organic matter in the media, and the ratio between them. Interestingly, environmental coronas can eventually prevent Ca²⁺ and Mg²⁺ induced aggregation at concentrations range present in most of the freshwater bodies. The humic coating formed on top of the Au or control Ag nanoparticles presented a similar profile, but the corrodibility of Ag led to a more natural detachment of the corona. These results were further confirmed by exposing the nanoparticles to a model of natural water and standard mud (LUFA 2.2 dispersion). In the latter case, after several days, nanoparticle sedimentation was observed, which was attributed to interactions with macro organic and inorganic matter (fraction larger than particulate matter).

Coarse-grained simulation of PEGylated and tethered protein devices at all experimentally accessible surface residues on β-lactamase for stability analysis and comparison

PEGylated and surface-tethered proteins are used in a variety of biotechnological applications, but traditional methods offer little control over the placement of the functionalization sites on the protein. Fortunately, recent experimental methods functionalize the protein at any location on the amino acid sequence, so the question becomes one of selecting the site that will result in the best protein function. This work shows how molecular simulation can be used to screen potential attachment sites for surface tethering or PEGylation. Previous simulation work has shown promise in this regard for a model protein, but these studies are limited to screening only a few of the surface-accessible sites or only considered surface tethering or PEGylation separately rather than their combined effects. This work is done to overcome these limitations by screening all surface-accessible functionalization sites on a protein of industrial and therapeutic importance (TEM-1) and to evaluate the effects of tethering and PEGylation simultaneously in an effort to create a more accurate screen. The results show that functionalization site effectiveness appears to be a function of super-secondary and tertiary structures rather than the primary structure, as is often currently assumed. Moreover, sites in the middle of secondary structure elements, and not only those in loops regions, are shown to be good options for functionalization-a fact not appreciated in current practice. Taken as a whole, the results show how rigorous molecular simulation can be done to identify candidate amino acids for functionalization on a protein to facilitate the rational design of protein devices.

Accelerated Reaction Rates within Self-Assembled Polymer Nanoreactors with Tunable Hydrophobic Microenvironments

Performing reactions in the presence of self-assembled hierarchical structures of amphiphilic macromolecules can accelerate reactions while using water as the bulk solvent due to the hydrophobic effect. We leveraged non-covalent interactions to self-assemble filled-polymer micelle nanoreactors (NR) incorporating gold nanoparticle catalysts into various amphiphilic polymer nanostructures with comparable hydrodynamic nanoreactor size and gold concentration in the nanoreactor dispersion. We systematically studied the effect of the hydrophobic co-precipitant on self-assembly and catalytic performance. We observed that co-precipitants that interact with gold are beneficial for improving incorporation efficiency of the gold nanoparticles into the nanocomposite nanoreactor during self-assembly but decrease catalytic performance. Hierarchical assemblies with co-precipitants that leverage noncovalent interactions could enhance catalytic performance. For the co-precipitants that do not interact strongly with gold, the catalytic performance was strongly affected by the hydrophobic microenvironment of the co-precipitant. Specifically, the apparent reaction rate per surface area using castor oil (CO) was over 8-fold greater than polystyrene (750 g/mol, PS 750); the turnover frequency was higher than previously reported self-assembled polymer systems. The increase in apparent catalytic performance could be attributed to differences in reactant solubility rather than differences in mass transfer or intrinsic kinetics; higher reactant solubility enhances apparent reaction rates. Full conversion of 4-nitrophenol was achieved within three minutes for at least 10 sequential reactions demonstrating that the nanoreactors could be used for multiple reactions.

Biomass-Derived Activated Carbon as a Catalyst for the Effective Degradation of Rhodamine B dye

Activated carbon (AC) was fabricated from carrot waste using ZnCl2 as the activating agent and calcined at 700 °C for 2 h in a tube furnace. The as-synthesized AC was characterized using Fourier-transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analysis; the results revealed that it exhibited a high specific surface area and high porosity. Moreover, this material displayed superior catalytic activity for the degradation of toxic Rhodamine B (RhB) dye. Rate constant for the degradation of RhB was ascertained at different experimental conditions. Lastly, we used the Arrhenius equation and determined that the activation energy for the decomposition of RhB using AC was approximately 35.9 kJ mol−1, which was very low. Hopefully it will create a great platform for the degradation of other toxic dye in near future.

Rapid Self-Assembly of Metal/Polymer Nanocomposite Particles as Nanoreactors and Their Kinetic Characterization

Self-assembled metal nanoparticle-polymer nanocomposite particles as nanoreactors are a promising approach for performing liquid phase reactions using water as a bulk solvent. In this work, we demonstrate rapid, scalable self-assembly of metal nanoparticle catalyst-polymer nanocomposite particles via Flash NanoPrecipitation. The catalyst loading and size of the nanocomposite particles can be tuned independently. Using nanocomposite particles as nanoreactors and the reduction of 4-nitrophenol as a model reaction, we study the fundamental interplay of reaction and diffusion. The induction time is affected by the sequence of reagent addition, time between additions, and reagent concentration. Combined, our experiments indicate the induction time is most influenced by diffusion of sodium borohydride. Following the induction time, scaling analysis and effective diffusivity measured using NMR indicate that the observed reaction rate are reaction- rather than diffusion-limited. Furthermore, the intrinsic kinetics are comparable to ligand-free gold nanoparticles. This result indicates that the polymer microenvironment does not de-activate or block the catalyst active sites.

Synthetic strategies and application of gold-based nanocatalysts for nitroaromatics reduction

With the increasing requirement of efficient organic transformations on the basic concept of Green Sustainable Chemistry, the development of highly efficient catalytic reaction system is greatly desired. In this case, gold (Au)-based nanocatalysts are promising candidates for catalytic reaction, especially for the reduction of nitroaromatics. They have attracted wide attention and well developed in the application of nitroaromatics reduction because of the unique properties compared with that of other conventional metal-based catalysts. With this respect, this review proposes recent trends in the application of Au nanocatalysts for efficient reduction process of nitroaromatics. Some typical approaches are compared and discussed to guide the synthesis of highly efficient Au nanocatalysts. The mechanism on the use of H₂ and NaBH₄ solution as the source of hydrogen is compared, and that proposed under light irradiation is discussed. The high and unique catalytic activity of some carriers, such as oxides and carbons-based materials, based on different sizes, structures, and shapes of supported Au nanocatalysts for nitroaromatics reduction are described. The catalytic performance of Au combining with other metal nanoparticles by alloy or doping, like multi-metal nanoparticles system, is further discussed. Finally, a short discussion is introduced to compare the catalysis with other metallic nanocatalysts.

Synergistic effect of bimetallic Cu:Ni nanoparticles for the efficient catalytic conversion of 4-nitrophenol

A non-noble metal-based bimetallic Cu–Ni system for the conversion of 4-nitrophenol and effective recyclability by magnetic retrieval of the catalyst.

Synthesis of water-soluble gold–aryl nanoparticles with distinct catalytic performance in the reduction of the environmental pollutant 4-nitrophenol

In-depth kinetic insight into the catalytic reduction of nitrophenol pollutant using gold–carbon nanoparticles is described.

Capping experiments reveal multiple surface active sites in CeO2 and their cooperative catalysis

Understanding of surface active sites (SAS) of CeO₂ is crucial to its catalytic applications. In the present study, we have employed capping experiments, DFT calculations, and spectroscopic characterization to study pristine CeO₂ catalyst. We find that multiple SAS coexist on the CeO₂ surface: oxygen vacancies as redox sites and the coordinately unsaturated Ce cations near the oxygen vacancies and the neighboring oxygen ions as Lewis acid–base sites. Dimethylsulfoxide (DMSO), pyridine, and benzoic acid are utilized to cap the redox sites, Lewis acid sites, and base sites, respectively. Selective capping on the redox site does not have much effect on the acid–base catalysis, and vice versa, indicating the distinct surface proximity and independent catalysis of these SAS. We draw attention to a relationship between the well-known redox sites and the surface Lewis acid and Lewis base pairs on CeO₂ surface, which are responsible for driving various heterogeneous catalytic reactions.

Capping with pyridine, benzoic acid, and DMSO in catalytic reactions reveals the locations of surface active sites of CeO₂.

Hydride-induced ligand dynamic and structural transformation of gold nanoclusters during a catalytic reaction

Quasi-homogeneous ligand-protected gold nanoclusters (Au NCs) with atomic precision and well-defined structure offer great opportunity for exploring the catalytic nature of nanogold catalysts at a molecular level. Herein, using real-time electrospray ionization mass spectrometry (ESI-MS), we have successfully identified the desorption and re-adsorption of p-mercaptobenzoic acid (p-MBA) ligands from Au25(p-MBA)18 NC catalysts during the hydrogenation of 4-nitrophenol in solution. This ligand dynamic (desorption and re-adsorption) would initiate structural transformation of Au25(p-MBA)18 NC catalysts during the reaction, forming a mixture of smaller Au NCs (Au23(p-MBA)16 as the major species) at the beginning of catalytic reaction, which could further be transformed into larger Au NCs (Au26(p-MBA)19 as the major species). The adsorption of hydrides (from NaBH4) is identified as the determining factor that could induce the ligand dynamic and structural transformation of NC catalysts. This study provides fundamental insights into the catalytic nature of Au NCs, including catalytic mechanism, active species and stability of Au NC catalysts during a catalytic reaction.

Controllable Synthesis and Catalytic Performance of Gold Nanoparticles with Cucurbit[n]urils (n = 5⁻8)

A series of gold nanoparticles (AuNPs) was prepared in situ with different cucurbit[n]urils (CB[n]s) in an alkaline aqueous solution. The nanoparticle sizes can be well controlled by CB[n]s (n = 5, 6, 7, 8) with different ring sizes. The packing densities of CB[5⁻8] and free surface area on AuNPs were determined. A direct relationship was found between the ring size and packing density of CB[n]s with respect to the AuNP-catalyzed reduction of 4-nitrophenol in the presence of NaBH₄. The larger particle size and higher surface coverage of bigger CB[n]-capped AuNPs significantly decreased the catalytic activity. Furthermore, this work could lead to new applications that utilize AuNPs under an overlayer of CB[n]s for catalysis, sensing, and drug delivery.

Catalysis by Metallic Nanoparticles in Solution: Thermosensitive Microgels as Nanoreactors

Metallic nanoparticles have been used as catalysts for various reactions, and the huge literature on the subject is hard to overlook. In many applications, the nanoparticles must be affixed to a colloidal carrier for easy handling during catalysis. These “passive carriers” (e.g. dendrimers) serve for a controlled synthesis of the nanoparticles and prevent coagulation during catalysis. Recently, hybrids from nanoparticles and polymers have been developed that allow us to change the catalytic activity of the nanoparticles by external triggers. In particular, single nanoparticles embedded in a thermosensitive network made from poly(N-isopropylacrylamide) (PNIPAM) have become the most-studied examples of such hybrids: immersed in cold water, the PNIPAM network is hydrophilic and fully swollen. In this state, hydrophilic substrates can diffuse easily through the network, and react at the surface of the nanoparticles. Above the volume transition located at 32°C, the network becomes hydrophobic and shrinks. Now hydrophobic substrates will preferably diffuse through the network and react with other substrates in the reaction catalyzed by the enclosed nanoparticle. Such “active carriers”, may thus be viewed as true nanoreactors that open new ways for the use of nanoparticles in catalysis. In this review, we give a survey on recent work done on these hybrids and their application in catalysis. The aim of this review is threefold: we first review hybrid systems composed of nanoparticles and thermosensitive networks and compare these “active carriers” to other colloidal and polymeric carriers (e.g. dendrimers). In a second step we discuss the model reactions used to obtain precise kinetic data on the catalytic activity of nanoparticles in various carriers and environments. These kinetic data allow us to present a fully quantitative comparison of different nanoreactors. In a final section we shall present the salient points of recent efforts in the theoretical modeling of these nanoreactors. By accounting for the presence of a free-energy landscape for the reactants’ diffusive approach towards the catalytic nanoparticle, arising from solvent-reactant and polymeric shell-reactant interactions, these models are capable of explaining the emergence of all the important features observed so far in studies of nanoreactors. The present survey also suggests that such models may be used for the design of future carrier systems adapted to a given reaction and solvent.

Ultrasonic assisted synthesis of palladium-nickel/iron oxide core-shell nanoalloys as effective catalyst for Suzuki-Miyaura and p-nitrophenol reduction reactions

In this study, ultrasonic assisted synthesis of Pd-Ni/Fe₃O₄ core-shell nanoalloys is reported. Unique reaction condition was prepared by ultrasonic irradiation, releasing the stored energy in the collapsed bubbles and heats the bubble contents that leads to Pd(II) and Ni(II) reduction. Co-precipitation method was applied for the synthesis of Fe₃O₄ nanoparticles (NPs). Immobilized solution was produced by sonicating the aqueous mixture of Fe₃O₄ and mercaptosuccinic acid to obtain Pd-Ni alloys on Fe₃O₄ magnetic NP cores. The catalytic activity of the synthesized Pd-Ni/Fe₃O₄ core-shells was investigated in the Suzuki-Miyaura CC coupling reaction and 4-nitrophenol reduction, which exhibited a high catalytic activity in both reactions. These magnetic NPs can be separated from the reaction mixture by external magnetic field. This strategy is simple, economical and promising for industrial applications.

In Situ Synthesis of Gold Nanoparticles on Wool Powder and Their Catalytic Application

Gold nanoparticles (AuNPs) were synthesized in situ on wool powder (WP) under heating conditions. Wool powder not only reduced Au ions to AuNPs, but also provided a support for as-synthesized AuNPs. WPs were treated under different concentrations of Au ions, and corresponding optical features and morphologies of the treated WPs were investigated by UV-VIS diffuse reflectance absorption spectroscopy and scanning electron microscopy (SEM). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM) were also employed to characterize the WP treated with AuNPs. The results demonstrate that AuNPs were produced in the presence of WP and distributed over the wool particles. The porous structure led to the synthesis of AuNPs in the internal parts of WP. Acid conditions and high temperature facilitated the synthesis of AuNPs by WP in aqueous solution. The reducibility of wool was improved after being converted to powder from fibers, due to exposure of more active groups. Moreover, the obtained AuNP-WP complexes showed significant catalytic activity to accelerate the reduction reaction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH₄).

One-step catalytic reduction of 4-nitrophenol through the direct injection of metal salts into oxygen-depleted reactants

The one-step catalytic reduction of 4-nitrophenol using nanoparticles derived from the injection of metal salts leads to benchmark-setting turnover frequencies.

Investigating the role of MoS2/reduced graphene oxide as cocatalyst on Cu2O activity in catalytic and photocatalytic reactions

Synergistic effect of MoS₂/rGO as cocatalyst on Cu₂O catalytic and photocatalytic activity.

Highly efficient noble metal free copper nickel oxysulfide nanoparticles for catalytic reduction of 4-nitrophenol, methyl blue, and rhodamine-B organic pollutants

Novel and noble metal-free copper nickel oxysulfide nanoparticles have been successfully fabricated by using a simple, cost-effective, and eco-friendly solution-based approach, with copper oxysulfide as a comparative.

Catalytic Reduction of 4-Nitrophenol: A Quantitative Assessment of the Role of Dissolved Oxygen in Determining the Induction Time

The reduction of 4-nitrophenol to 4-aminophenol by borohydride is one of the foremost model catalytic reactions because it allows for a straightforward assessment of catalysts using the kinetic parameters extracted from the real-time spectroscopic monitoring of an aqueous solution. Crucial to its standing as a model reaction is a comprehensive mechanistic framework able to explain the entire time evolution of the reaction. While much of this framework is in place, there is still much debate over the cause of the induction period, an initial time interval where no reaction seemingly occurs. Here, we report on the simultaneous monitoring of the spectroscopic signal and the dissolved oxygen content within the aqueous solution. It reveals that the induction period is the time interval required for the level of dissolved oxygen to fall below a critical value that is dependent upon whether Au, Ag, or Pd nanoparticles are used as the catalyst. With this understanding, we are able to exert complete control over the induction period, being able to eliminate it, extend it indefinitely, or even induce multiple induction periods over the course of a single reaction. Moreover, we have determined that the reaction product, 4-aminophenol, in the presence of the same catalyst reacts with dissolved oxygen to form 4-nitrophenolate. The implication of these results is that the induction period relates, not to some activation of the catalyst, but to a time interval where the reaction product is being rapidly transformed back into a reactant by a side reaction.

A ternary Cu2O-Cu-CuO nanocomposite: a catalyst with intriguing activity

In this work, the syntheses of Cu2O as well as Cu(0) nanoparticle catalysts are presented. Copper acetate monohydrate produced two distinctly different catalyst particles with varying concentrations of hydrazine hydrate at room temperature without using any surfactant or support. Then both of them were employed separately for 4-nitrophenol reduction in aqueous solution in the presence of sodium borohydride at room temperature. To our surprise, it was noticed that the catalytic activity of Cu2O was much higher than that of the metal Cu(0) nanoparticles. We have confirmed the reason for the exceptionally high catalytic activity of cuprous oxide nanoparticles over other noble metal nanoparticles for 4-nitrophenol reduction. A plausible mechanism has been reported. The unusual activity of Cu2O nanoparticles in the reduction reaction has been observed because of the in situ generated ternary nanocomposite, Cu2O-Cu-CuO, which rapidly relays electrons and acts as a better catalyst. In this ternary composite, highly active in situ generated Cu(0) is proved to be responsible for the hydride transfer reaction. The mechanism of 4-nitrophenol reduction has been established from supporting TEM studies. To further support our proposition, we have prepared a compositionally similar Cu2O-Cu-CuO nanocomposite using Cu2O and sodium borohydride which however displayed lower rate of reduction than that of the in situ produced ternary nanocomposite. The evolution of isolated Cu(0) nanoparticles for 4-nitrophenol reduction from Cu2O under surfactant-free condition has also been taken into consideration. The synthetic procedures of cuprous oxide as well as its catalytic activity in the reduction of 4-nitrophenol are very convenient, fast, cost-effective, and easily operable in aqueous medium and were followed spectrophotometrically. Additionally, the Cu2O-catalyzed 4-nitrophenol reduction methodology was extended further to the reduction of electronically diverse nitroarenes. This concise catalytic process in aqueous medium at room temperature revealed an unprecedented catalytic performance which would draw attention across the whole research community.

Plastically deformed Cu-based alloys as high-performance catalysts for the reduction of 4-nitrophenol

Plastically deformed mesoscopic structures exposed to an etching procedure are demonstrated as highly catalytic in the reduction of 4-nitrophenol.

Manipulating ligand–nanoparticle interactions and catalytic activity through organic-aqueous tunable solvent recovery

Tunable solvents are leveraged to recover dispersed, PVP-stabilized gold nanoparticles and to manipulate the amount of ligand passivating the surface thereby altering the catalytic activity.

Hyper-crosslinked β-cyclodextrin porous polymer: an adsorption-facilitated molecular catalyst support for transformation of water-soluble aromatic molecules

A hyper-crosslinked β-cyclodextrin porous polymer (BnCD-HCPP) was designed and synthesized facilely by β-cyclodextrin benzylation and subsequent crosslinking for efficient adsorption and catalysis.

A hyper-crosslinked β-cyclodextrin porous polymer (BnCD-HCPP) was designed and synthesized facilely by β-cyclodextrin benzylation and subsequent crosslinking via a Friedel–Crafts alkylation route. The BnCD-HCPP shows an extremely high BET surface area, large pore volume, and high thermal stability, making it a highly efficient adsorbent for removal of aromatic pollutants from water. The adsorption efficiency in terms of distribution coefficient, defined as the ratio of adsorption capacity to equilibrium adsorbate concentration, ranged from 10³ to 10⁶ mL g^–1 within a concentration of 0–100 ppm, one order of magnitude higher than that of other β-cyclodextrin-based adsorbents reported previously. The molar percentage of adsorbate to β-cyclodextrin exceeded 300%, suggesting that the adsorption occurred not only in the cyclodextrin cavities via a 1 : 1 complexation, but also in the nanopores of the BnCD-HCPP created during the hyper-crosslinking. The BnCD-HCPP can be further functionalized by incorporation of gold nanoparticles for catalytic transformation of adsorbed phenolic compounds such as 4-nitrophenol to 4-aminophenol.

Mycofabrication of common plasmonic colloids, theoretical considerations, mechanism and potential applications

A coupling of the plasmon on the surface of metal nanoparticles with an incident photon enhances a broad range of useful optical phenomena, such as resonant light scattering (RLS), surface plasmon resonance (SPR) or Raman scattering. Due to these unique optical properties plasmonic nanostructures of different sizes and shapes have gained increasing popularity in areas such as cancer diagnosis, photothermal therapy as well as the imaging of living cells, detection of pathogens, biomolecules, metal ions, and the catalysis of various reactions in wet chemistry. This article reviews the current trends in the synthesis of plasmonic nanoparticles, particularly gold (AuNPs) and silver (AgNPs), using fungi as well as the proposed mechanisms for their mycofabrication. We provide an overview of the theoretical concepts of plasmonic nanoparticles which are sensitive electromagnetic responses that determine these nanoparticles applications.