Nanostructured Aggregates Research Articles

Role of nanostructured aggregation of chitosan derivatives on [5-methionine]enkephalin affinity

Affinities of quaternary ammonium-chitosan conjugates, their thiolated derivatives and corresponding nanostructured aggregates towards the hydrophilic drug [5-methionine]enkephalin were compared by Nuclear Magnetic Resonance (NMR) spectroscopic methods based on proton selective relaxation rate measurements. Nanoaggregates showed enhanced drug affinity in comparison with corresponding polymers, especially in the case of thiolated systems.

Plasmonic Nanorattles as Next‐Generation Catalysts for Surface Plasmon Resonance‐Mediated Oxidations Promoted by Activated Oxygen

AbstractNanorattles, comprised of a nanosphere inside a nanoshell, were employed as the next generation of plasmonic catalysts for oxidations promoted by activated O2. After investigating how the presence of a nanosphere inside a nanoshell affected the electric‐field enhancements in the nanorattle relative to a nanoshell and a nanosphere, the SPR‐mediated oxidation of p‐aminothiophenol (PATP) functionalized at their surface was investigated to benchmark how these different electric‐field intensities affected the performances of Au@AgAu nanorattles, AgAu nanoshells and Au nanoparticles having similar sizes. The high performance of the nanorattles enabled the visible‐light driven synthesis of azobenzene from aniline under ambient conditions. As the nanorattles allow the formation of electromagnetic hot spots without relying on the uncontrolled aggregation of nanostructures, it enables their application as catalysts in liquid phase under mild conditions using visible light as the main energy input.

Plasmonic Nanorattles as Next-Generation Catalysts for Surface Plasmon Resonance-Mediated Oxidations Promoted by Activated Oxygen.

Nanorattles, comprised of a nanosphere inside a nanoshell, were employed as the next generation of plasmonic catalysts for oxidations promoted by activated O2 . After investigating how the presence of a nanosphere inside a nanoshell affected the electric-field enhancements in the nanorattle relative to a nanoshell and a nanosphere, the SPR-mediated oxidation of p-aminothiophenol (PATP) functionalized at their surface was investigated to benchmark how these different electric-field intensities affected the performances of Au@AgAu nanorattles, AgAu nanoshells and Au nanoparticles having similar sizes. The high performance of the nanorattles enabled the visible-light driven synthesis of azobenzene from aniline under ambient conditions. As the nanorattles allow the formation of electromagnetic hot spots without relying on the uncontrolled aggregation of nanostructures, it enables their application as catalysts in liquid phase under mild conditions using visible light as the main energy input.

1,2,3‐Triazole–Diketopyrrolopyrrole Derivatives with Tunable Solubility and Intermolecular Interactions

Abstract1,2,3‐Triazole rings bearing hydrophobic aliphatic or hydrophilic oligoether chains were easily introduced at the two ends of the conjugated skeleton of bisthiophene–diketopyrrolopyrrole (TDPP) derivatives by simple click cycloaddition reactions. The combination of side chains with different structures and polarities on the triazole rings with the side chains on the N‐atoms of the lactam groups of the TDPP moiety enabled the solubility and the solid‐state spectroscopic properties of the resulting conjugated molecules to be tuned. Formation of nanostructured aggregates and dependence of their spectroscopic behavior on the substitution pattern were investigated.

Validation of an air-liquid interface toxicological set-up using Cu, Pd, and Ag well-characterized nanostructured aggregates and spheres.

Systems for studying the toxicity of metal aggregates on the airways are normally not suited for evaluating the effects of individual particle characteristics. This study validates a set-up for toxicological studies of metal aggregates using an air–liquid interface approach. The set-up used a spark discharge generator capable of generating aerosol metal aggregate particles and sintered near spheres. The set-up also contained an exposure chamber, The Nano Aerosol Chamber for In Vitro Toxicity (NACIVT). The system facilitates online characterization capabilities of mass mobility, mass concentration, and number size distribution to determine the exposure. By dilution, the desired exposure level was controlled. Primary and cancerous airway cells were exposed to copper (Cu), palladium (Pd), and silver (Ag) aggregates, 50–150 nm in median diameter. The aggregates were composed of primary particles <10 nm in diameter. For Cu and Pd, an exposure of sintered aerosol particles was also produced. The doses of the particles were expressed as particle numbers, masses, and surface areas. For the Cu, Pd, and Ag aerosol particles, a range of mass surface concentrations on the air–liquid interface of 0.4–10.7, 0.9–46.6, and 0.1–1.4 µg/cm2, respectively, were achieved. Viability was measured by WST-1 assay, cytokines (Il-6, Il-8, TNF-a, MCP) by Luminex technology. Statistically significant effects and dose response on cytokine expression were observed for SAEC cells after exposure to Cu, Pd, or Ag particles. Also, a positive dose response was observed for SAEC viability after Cu exposure. For A549 cells, statistically significant effects on viability were observed after exposure to Cu and Pd particles. The set-up produced a stable flow of aerosol particles with an exposure and dose expressed in terms of number, mass, and surface area. Exposure-related effects on the airway cellular models could be asserted.Graphical Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-016-3389-y) contains supplementary material, which is available to authorized users.

Self-assembly of alkynylplatinum(II) terpyridine amphiphiles into nanostructures via steric control and metal–metal interactions

A series of mono- and dinuclear alkynylplatinum(II) terpyridine complexes containing the hydrophilic oligo(para-phenylene ethynylene) with two 3,6,9-trioxadec-1-yloxy chains was designed and synthesized. The mononuclear alkynylplatinum(II) terpyridine complex was found to display a very strong tendency toward the formation of supramolecular structures. Interestingly, additional end-capping with another platinum(II) terpyridine moiety of various steric bulk at the terminal alkyne would lead to the formation of nanotubes or helical ribbons. These desirable nanostructures were found to be governed by the steric bulk on the platinum(II) terpyridine moieties, which modulates the directional metal-metal interactions and controls the formation of nanotubes or helical ribbons. Detailed analysis of temperature-dependent UV-visible absorption spectra of the nanostructured tubular aggregates also provided insights into the assembly mechanism and showed the role of metal-metal interactions in the cooperative supramolecular polymerization of the amphiphilic platinum(II) complexes.

Solid-State Synthesized Nanostructured Au Dendritic Aggregates Towards Surface-Enhanced Raman Spectroscopy

Micrometric Au structures, presenting a dendritic nano-structure, have been fabricated on a Si-based substrate. The fabrication method involves the deposition of a thin Au film on the substrate and a high-temperature annealing (1100°C) using fast heating and cooling ramps. The thermal process produces the growth, from the substrate, of Si micro-pillars whose top surfaces, covered by a crystalline Au layer, present a nanodendritic morphology. In addition to the micro-pillars, the sample surface presents a complex structural and chemical composition including Si3N4 regions due to the silicon–nitrogen intermixing during the heating stage. By studying the kinetic processes at the Au-Si interface during the thermal treatment, we describe the stages involved in the micro-pillars growth, in the dendritic morphology development, and in the Au atoms entrapment at the top of the dendritic surfaces. Finally, we present the analyses of the optical and surface enhanced Raman scattering properties of the Au dendritic aggregates. We show, in particular, that: (1) the Au dendrites aggregates act as effective scattering elements for the electromagnetic radiation in the infrared spectral region; and (2) the higher surface area due to the branched dendritic structure is responsible for the improvement in the sensitivity of the surface enhanced Raman scattering activity.

The removal of phosphate from aqueous solutions using two nano-structures: copper oxide and carbon tubes

The removal of phosphate from water is vital in controlling eutrophication. Adsorption is one of the most popular technologies for removing phosphate. In this study, two types of nanoparticles (NPs), namely carbon nanotubes (CNTs) and copper oxide (CuO), were used and their phosphate removal potential was investigated. The physical and chemical properties of the two NPs were systematically studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), FTIR, energy-dispersive X-ray (EDX), and BET methods. The image analyses of SEM indicated that CuO NPs and CNTs were nano-structured aggregates with mean diameters of about 85.0 and 22.2 nm, respectively. The sorption kinetic data were better described by the pseudo-second-order equation indicating its chemisorption nature. The equilibrium sorption data were well fitted into the Freundlich model for CNTs but for CuO, sorption data were better fitted into Langmuir isotherm model. The phosphate sorption capacities without the presence of competing anions were 15.4 and 23.9 mg/g (PO4 3−-P) for CNTs and CuO, respectively. Besides, the competing anions (Cl−, NO3 −, and humic acid) decreased the phosphate removal of CNTs and CuO. The negative values of the Gibbs’ free energy change (ΔG°) demonstrated the spontaneous nature of the sorption process in both sorbents, while the positive values of the enthalpy change (ΔH°) indicated that the sorption process was endothermic in nature. Overall, the results of this study suggest that CuO NPs and CNTs in a single solution have the potential to act as effective sorbents of phosphate under optimum conditions, respectively.

A highly active multi‐usable palladium pyridylfluorene film‐based catalyst for C–C cross‐coupling reactions

The two terminal pyridyl nitrogen atoms of 2,7‐bis(4‐pyridyl)fluorene (1) were coordinated to Pd(II) ions to give self‐assembled, multilayer films using the layer‐by‐layer (LbL) method. The films were prepared by alternately dipping the substrate, pre‐coated with a polyethyleneimine layer, in aqueous solutions of PdCl2 and ethanol solutions of 1. The resulting films were characterized using UV–visible absorption spectroscopy, atomic force microscopy (AFM), X‐ray photoelectron spectroscopy, scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectroscopy (ICP‐AES). UV–visible spectra and SEM images show almost uniform growth of the film in a near ideal LbL manner. AFM images show that nanostructured aggregates of Pd(II) complexes form on the surface. With an increase in the number of Pd(II)/1 bilayers, more particulate aggregates are distributed on the surface. When released from the substrate, the Pd(II) complex nanostructure shows high catalytic activity for Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions. The catalyst loading is as low as 9.1 × 10−3 mol% Pd, as measured using ICP‐AES, and high turnover numbers of up to 1.08 × 104 are obtained. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Interactions of small dendrimers with sodium dodecyl sulfate at the air-water interface.

We have determined how the bulk behavior of mixtures of small cationic poly(amidoamine) dendrimers (generation 2, PAMAM-G2) and sodium dodecyl sulfate (SDS) affects the structure and composition of the adsorbed layers at the air-water interface. The aim is to reveal how the size of a well-defined hyperbranched polyelectrolyte affects the interfacial and bulk solution behavior of mixtures with oppositely charged surfactants, when the size of the polyelectrolyte approaches that of the surfactant. A combination of electrophoretic mobility, UV-vis spectroscopy, dynamic light scattering, and small-angle X-ray scattering measurements have been employed to characterize the interactions in the bulk solution. PAMAM-G2 associates strongly with SDS in the bulk, forming large aggregates where the size and the charge depend on the bulk composition. We show that kinetically trapped aggregates can be formed at compositions outside the equilibrium two-phase region, and the positively charged aggregates are larger than the negative ones. Surface tensiometry, neutron reflectometry, and ellipsometry have been used to reveal the properties of the interfacial layers. The interfacial structures formed depend strongly on the bulk composition: structured layers are present for samples inside the two-phase region, whereas intact nanostructured aggregates adsorb for samples just outside the two-phase region. The interfacial behavior of PAMAM-G2/SDS mixtures is compared with that of small amines or multivalent ions and oppositely charged surfactants. The implications of aggregate adsorption, dissociation, and spreading processes are discussed as well as the potential of small dendrimers for applications involving the delivery of functional molecules to interfaces.

Conformational dynamics and aggregation behavior of piezoelectric diphenylalanine peptides in an external electric field

Aromatic peptides including diphenylalanine (FF) have the capacity to self-assemble into ordered, biocompatible nanostructures with piezoelectric properties relevant to a variety of biomedical applications. Electric fields are commonly applied to align FF nanotubes, yet little is known about the effect of the electric field on the assembly process. Using all-atom molecular dynamics with explicit water molecules, we examine the response of FF monomers to the application of a constant external electric field over a range of intensities. We probe the aggregation mechanism of FF peptides, and find that the presence of even relatively weak fields can accelerate ordered aggregation, primarily by facilitating the alignment of individual molecular dipole moments. This is modulated by the conformational response of individual FF peptides (e.g., backbone stretching) and by the cooperative alignment of neighboring FF and water molecules. These observations may facilitate future studies on the controlled formation of nanostructured aggregates of piezoelectric peptides and the understanding of their electro-mechanical properties.

Controlling the enzymatic digestion of lipids using hybrid nanostructured materials.

Solid nanoparticle-lipid hybrids have been engineered by using spray drying to assemble monodisperse hydrophilic silica nanoparticles and submicron lipid (triglyceride) emulsions together into composite microparticles, which have specific activity toward enzymes. The influence of silica particle size (100-1000 nm) and emulsifier type (anionic and cationic) on the three-dimensional structure of the composite particles was investigated. The nanostructure of the hybrid particles, which is controlled by the size of the voids between the closely packed silica particles, plays a critical role in lipase action and hence lipid digestion kinetics. Confining lipid droplets within the nanostructured silica aggregates led to 2- to 15-fold enhanced rate of lipolysis in comparison with dispersed coarse oil droplets. The composite particles were tailored to enhance, retain or sustain the lipolysis kinetics of submicron lipid emulsions. The presence of repulsive nanoparticle-droplet interactions favored aqueous redispersion and fast lipolysis of the hybrid composite materials, while attractive interactions hindered redispersion and delayed lipolysis of the confined lipid droplets. Such hybrid nanomaterials can be exploited to control the gastrointestinal enzymatic action and promisingly form the basis for the next generation of foods and medicines.

Microorganism-mediated, CTAB-directed aggregation of Au nanostructures around Escherichia coli cells: Towards enhanced Au recovery through coordination of cell-CTAB–ascorbic acid

In this paper, a microorganism-mediated, cetyltrimethylammonium bromide (CTAB)-directed (MCD) aggregation of Au nanostructures around Escherichia coli cells (ECCs) for enhanced Au recovery, from aqueous HAuCl4 is demonstrated for the first time. Owing to the coordination of cell-CTAB–ascorbic acid (AA), one dimensional Au nanostructures grew around the ECCs, inducing the rapid aggregation of Au and the ECCs. The concentrations of CTAB and AA had insignificant effect on the precipitation if the ECC dosage and HAuCl4 concentration were matched. The Au recovery efficiency decreased with increasing CTAB concentration, while a minimum AA concentration was required for higher Au recovery efficiency. The ECC-binding Au ions were reduced to form Au nuclei over the cell surface that provided preferential nucleation sites. Meanwhile, the free ligand-substituted anions in the solution were reduced to Au atoms that served as Au source for growing the Au nanostructures around the ECCs. This work exemplifies a new avenue to enhance the efficiency of recovering Au through the engineering of Au nanostructures.

Synthesis and Electrochemical Performance of Olivine NaFePO4/Grahene Composite As Cathode Materials for Sodium Ion Batteries

Lithium ion batteries have been attracting widespread interests over recent decades to meet the urgent needs for applications in both fully electric vehicles and hybrid electric vehicles.1, 2 However, the lithium resources are unevenly distributed and limited,3 resulting the drastically increase of the cost for lithium ion batteries in the large-scale applications. Sodium ion batteries are considered as options for large scale energy storage due to the abundance of sodium and low cost. In terms of the cathode materials for the sodium ion batteries, phosphate compounds have been paid more attentions because of the high redox potential and good structural and thermal stability. The material with highest theoretical specific capacity (154 mA h g-1) is olivine NaFePO4 among the phosphate polyanion cathode materials. However, the thermodynamically stable structure of NaFePO4 is not olivine, but maricite. The maricite shows one-dimensional, edge-sharing FeO6 octahedra and no carionic channels, giving rise to a different connectivity of the Fe and Na octahedra compared to olivine LiFePO4 which blocks Na-ion migration pathways, resulting in a structure that is not amenable to Na+ (de)insertion.4, 5 There are two methods to obtain olivine NaFePO4, chemical delithiation and then electrochemical sodiation of olivine LiFePO4, and electrochemical delithiation and sodiation of olivine LiFePO4. In terms of the chemical delithiation, the oxidizing agents are NO2BF4 in acetonitrile, and bromine in dissolved in water, which are used to obtain the olivine FePO4. For the electrochemical sodiation, the Na insertion is realized by using FePO4 as the cathode and metallic Na foil as anode. Therefore, there are few paper reported on the olivine phase NaFePO4, due to the difficulty to get it directly by standard routes.Compared to the LiFePO4, the diffusion coefficient for Na-ion in NaFePO4 is 1-2 orders of magnitude lower than that of lithium-ion in LiFePO4, and the contact and charge transfer resistance in NaFePO4 is 10 times higher than that of in LiFePO4.6 To circumvent these problems, the strategy of using nanosized structures can be applied to reduce the diffusion distance of Na ions. Moreover, introducing a conductive coating layer, decorating the nanoparticles on certain substrate and embedding the nanostructures in a conductive matrix can be used to increase the electric conductivity and prevent the nanostructures from aggregation. Due to the excellent electric conductivity and mechanical properties, graphene is widely used in the synthesis of electrode materials to hinder the growth and aggregation of nanostructures, offer easy pathways for electrons, and provide a good conductive matrix for active materials.In this work, a composite cathode material for sodium ion battery applications, olivine NaFePO4/graphene, is prepared by chemical delithiation and then electrochemical sodiation of olivine LiFePO4 nanoparticles in situ grown on graphene sheet. The nanosized LiFePO4 particles were homogeneously distributed on the graphene to inhibit the restacking of the neighbouring graphene sheets. The NaFePO4/graphene composite obtained by chemical delithiation and electrochemical Na ions insertion exhibits improved cycling performance and rate capability, indicating the important role of graphene, which not only facilitates the formation of nanosized and uniformly distributed LiFePO4 precursor, but also increases the electrical conductivity of the composite material. The electrochemical performance of this NaFePO4/graphene was evaluated and showed promising results. Acknowledgements This work is supported by an Australian Research Council (ARC) Discovery project (DP1094261).

Phosphate removal from aqueous solutions by a nano-structured Fe–Ti bimetal oxide sorbent

Phosphate removal from water is of vital importance to control eutrophication. Adsorption is one of the most popular technologies for phosphate removal. In this study, iron oxide-based sorbents with different Fe/Ti molar ratios were synthesized by coprecipitation method. Results showed that the Fe–Ti bimetal oxide prepared with a Fe/Ti molar ratio of 20:1 was the optimal sorbent for phosphate removal. Transmission electron microscopic (TEM) image analyses indicate that the Fe–Ti bimetal oxide was nano-structured aggregates. The sorption kinetic data could be described better by the pseudo-second-order equation indicating its chemisorption nature. The boundary layer (film) diffusion was the rate-limiting step of sorption process. The equilibrium sorption data were well fitted with the Langmuir and Freundlich models. The phosphate sorption capacity calculated from Langmuir equation was 35.4mg/g at pH 6.8. Thermodynamics experiments showed that the phosphate sorption was spontaneous and endothermic. The results of ionic strength effect together with zeta potential, FTIR and XPS analyses demonstrated that the main mechanism of phosphate sorption was the replacement of surface hydroxyl groups (M–OH) by phosphate via formation of inner-sphere surface complex. The spent Fe–Ti bimetal oxide could be effectively regenerated by NaOH solutions.

“Buried” nano-structure and molecular aggregation state in ordered heterojunction poly(3-hexylthiophene)-based photovoltaics

The morphology of ordered heterojunction organic photovoltaics (OHJ-OPVs) interfaces was evaluated using synchrotron radiation small angle X-ray scattering and grazing incidence X-ray diffraction. [6,6′]-phenyl C61-butyric acid methyl ester (PCBM) was deposited on the line/space patterned poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film fabricated by nano-imprinting. After deposition of the PCBM film, the P3HT thin film retained the rectangular edge features of the imprinted mold, with some Gaussian broadening due to interdiffusion and partial phase mixing at the P3HT/PCBM interface. The P3HT main chains were oriented vertically in the nano-imprinted line pattern and showed π–π stacking along the line direction. PCBM nano-crystals exist throughout the OHJ-OPV thin film.

Measurement and simulation of micromechanical properties of nanostructured aggregates via nanoindentation and DEM-simulation

During the production of nanoparticles in large scale processes, usually larger aggregates are synthesized and subsequently redispersed to obtain the desired product properties. Dispersion processes are energy intense and not always predictable or even unsuccessful. The resistance of aggregates against redispersion and thus, the micromechanical properties strongly depends on the aggregate structure and the primary particle properties as well as on the binding mechanisms. The aim of this study was the investigation of the deformation and breakage behavior of aggregated structures composed of nanoparticles. This was done by comparing experimental and computational results. The larger scale simulations were based on a dimensioning of interaction forces and geometry and calibrated using experimental nanoindentation results. As a result the nature and strength of particle–particle interactions can be described. Furthermore, the distribution of normal and radial forces within the aggregates was compared to theoretical models of aggregate breakage.

Preparation of High-performance Covalently Bonded Polyaniline Nanorods/Graphene Supercapacitor Electrode Materials using Interfacial Copolymerization Approach

In this article, the polyaniline nanorods/graphene sheet composites (G-PANI) with covalent bond were synthesized through interfacial copolymerization of aniline and functionalized graphene (G-PPD) obtained by in situ reduction of graphene oxide and functionalization with para-phenylenediamine (PPD). During the interfacial polymerization, the monopolymerization of aniline and copolymerization of aniline and G-PPD are carried out simultaneously, which produce a mixture of PANI nanorods and G-PANI. Not only the homopolymer possesses one-dimensional structure, but also the graphene surface was covered evenly by the PANI nanorods. As comparison with conventional synthesis methods of PANI, the interfacial polymerization can produce large-scale one-dimensional PANI nanorods, which can form a loose crisscross aggregation. Even when it is grafted onto graphene sheet, the nanorod morphology is remained. The cyclic voltammetry (CV) and charge-discharge tests confirm that the G-PANI has higher electrochemical activity and higher capacitive properties over those of neat PANI nanorods. At the current density of 1 mAcm−2, the specific capacitance of G-PANI and PANI nanorods are 909 Fg−1 and 772 Fg−1, respectively. Especially, the specific capacitance of G-PANI has 62% enhancement over that of PANI nanorods at high current density of 50 mAcm−2. The remarkable improved capacity performance can be attributed to the enhanced mass transfer process brought from the loose nanostructure aggregation of G-PANI, as well as the reduced charge transfer resistance caused by the highly conductive graphene and strong interfacial interaction between PANI and graphene via covalent bond.

Mucoadhesivity and release properties of quaternary ammonium–chitosan conjugates and their nanoparticulate supramolecular aggregates: An NMR investigation

Selective relaxation rate measurements effectively proved the affinity of dexamethasone 21-phosphate disodium salt for quaternary ammonium-chitosan conjugates, their thiolated derivatives and the corresponding nanostructured aggregates. Affinity was also probed by dynamic dialysis. The release profile of dexamethasone loaded nanoparticles was defined by quantitative NMR and interrupted dialysis experiments, and mucoadhesivity of empty nanoparticles was effectively probed by selective relaxation rate measurements.

Antimicrobial activity of novel nanostructured Cu-SiO2 coatings prepared by chemical vapour deposition against hospital related pathogens

There is increasing recognition that the healthcare environment acts as an important reservoir for transmission of healthcare acquired infections (HCAI). One method of reducing environmental contamination would be use of antimicrobial materials. The antimicrobial activity of thin silica-copper films prepared by chemical vapour deposition was evaluated against standard strains of bacteria used for disinfectant testing and bacteria of current interest in HCAI. The structure of the coatings was determined using Scanning Electron Microscopy and their hardness and adhesion to the substrate determined. Antimicrobial activity was tested using a method based on BS ISO 22196:2007. The coatings had a pale green-brown colour and had a similar hardness to steel. SEM showed nano-structured aggregates of Cu within a silica matrix. A log10 reduction in viability of >5 could be obtained within 4 h for the disinfectant test strains and within 6 h for producing Acinetobacter baumannii, Klebsiella pneumoniae and Stenotrophomonas maltophilia. Activity against the other hospital isolates was slower but still gave log10 reduction factors of >5 for extended spectrum β-lactamase producing Escherichia coli and >3 for vancomycin resistant Enterococcus faecium, methicillin resistant Staphylococcus aureus and Pseudomonas aeruginosa within 24 h. The results demonstrate the importance of testing antimicrobial materials destined for healthcare use against isolates of current interest in hospitals as well as standard test strains. The coatings used here can also be applied to substrates such as metals and ceramics and have potential applications where reduction of microbial environmental contamination is desirable.