Templated 2D Polymer Heterojunctions for Improved Photocatalytic Hydrogen Production.

2D polymers have emerged as one of the most promising classes of organic photocatalysts for solar fuel production due to their tunability, charge-transport properties, and robustness. They are however difficult to process and so there are limited studies into the formation of heterojunction materials incorporating these components. In this work, a novel templating approach is used to combine an imine-based donor polymer and an acceptor polymer formed through Knoevenagel condensation.

Biocompatibility and Physiological Thiolytic Degradability of Radically Made Thioester-Functional Copolymers: Opportunities for Drug Release.

Being nondegradable, vinyl polymers have limited biomedical applicability. Unfortunately, backbone esters incorporated through conventional radical ring-opening methods do not undergo appreciable abiotic hydrolysis under physiologically relevant conditions. Here, PEG acrylate and di(ethylene glycol) acrylamide-based copolymers containing backbone thioesters were prepared through the radical ring-opening copolymerization of the thionolactone dibenzo[c,e]oxepin-5(7)-thione.

Oleylamine Aging of PtNi Nanoparticles Giving Enhanced Functionality for the Oxygen Reduction Reaction.

We report a rapid solution-phase strategy to synthesize alloyed PtNi nanoparticles which demonstrate outstanding functionality for the oxygen reduction reaction (ORR). This one-pot coreduction colloidal synthesis results in a monodisperse population of single-crystal nanoparticles of rhombic dodecahedral morphology with Pt-enriched edges and compositions close to PtNi. We use nanoscale 3D compositional analysis to reveal for the first time that oleylamine (OAm)-aging of the rhombic dodecahedral PtNi particles results in Ni leaching from surface facets, producing aged particles with concave faceting, an exceptionally high surface area, and a composition of PtNi.

Characterising porosity in platinum nanoparticles.

Accurately determining the morphology and hence the true surface areas of catalytic nanoparticles remains challenging. For many chemically synthesised nanoparticle suspensions conventional BET surface area measurements are often not feasible due to the large quantities of material required. For platinum, a paradigmatic catalyst, this issue is further complicated by the propensity of this metal to form porous aggregate structures comprised of smaller (ca.

Porosity controls the catalytic activity of platinum nanoparticles.

Dendritic/mesoporous nanoparticle structures arise naturally and result from aggregation based growth mechanisms. The resulting porous particles exhibit high total surface areas (internal and external) but determining the magnitude of the interface remains challenging. Furthermore, assessing the chemical accessibility of the catalytic interface presents an additional difficulty.

Tannic acid capped gold nanoparticles: capping agent chemistry controls the redox activity.

We report the key role of the capping agent in the detection of metal cations using tannic acid (TA) capped gold nanoparticles at both ensembles (using cyclic voltammetry) and with individual particles (using oxidative and reductive nanoimpacts). The results show that the capping agent complexes with Zn2+ and Hg2+ in a reversible and Langmuirian manner in both cases. The sensitivity of detection is determined by the amount of capping agent present on the nanoparticles with similar values seen for both oxidation and reduction reactions.

Imaging Three-Dimensional Elemental Inhomogeneity in Pt-Ni Nanoparticles Using Spectroscopic Single Particle Reconstruction.

The properties of nanoparticles are known to critically depend on their local chemistry but characterizing three-dimensional (3D) elemental segregation at the nanometer scale is highly challenging. Scanning transmission electron microscope (STEM) tomographic imaging is one of the few techniques able to measure local chemistry for inorganic nanoparticles but conventional methodologies often fail due to the high electron dose imparted. Here, we demonstrate realization of a new spectroscopic single particle reconstruction approach built on a method developed by structural biologists.

Electrochemical impacts complement light scattering techniques for in situ nanoparticle sizing.

We show that the electrochemical particle-impact technique (or 'nano-impacts') complements light scattering techniques for sizing both mono- and poly-disperse nanoparticles. It is found that established techniques - Dynamic Light Scattering (DLS) and Nanoparticle Tracking Analysis (NTA) - can accurately measure the diameters of '30 nm' silver particles assuming spherical shapes, but are unable to accurately size a smaller '20 nm' sample. In contrast, nano-impacts have a high accuracy (<5% error in effective diameters) and are able to size both individual '20 nm' and '30 nm' silver NPs in terms of the number of constituent atoms.

Understanding gold nanoparticle dissolution in cyanide-containing solution via impact-chemistry.

The electrochemical dissolution of citrate-capped gold nanoparticles (AuNPs) was studied in cyanide (CN-) containing solutions. It was found that the gold nanoparticles exhibited different dissolution behaviours as ensembles compared to the single particles. At the single particle level, a nearly complete oxidation of 60 nm AuNPs was achieved at concentrations greater than or equal to 35.

In Situ Atomic-Level Studies of Gd Atom Release and Migration on Graphene from a Metallofullerene Precursor.

We show how gadolinium (Gd)-based metallofullerene (GdN@C) molecules can be used to create single adatoms and nanoclusters on a graphene surface. An in situ heating holder within an aberration-corrected scanning transmission electron microscope is used to track the adhesion of endohedral metallofullerenes (MFs) to the surface of graphene, followed by Gd metal ejection and diffusion across the surface. Heating to 900 °C is used to promote adatom migration and metal nanocluster formation, enabling direct imaging of the assembly of nanoclusters of Gd.

Simultaneous activity and surface area measurements on single mesoporous nanoparticle aggregates.

The underpotential deposition of hydrogen and the hydrogen evolution reaction is studied at individual mesoporous nanoparticles. This work shows how the electroactive surface area and catalytic activity of these individual particles can be simultaneously measured.

Shape and size of non-spherical silver nanoparticles: implications for calculating nanoparticle number concentrations.

The international drive to measure accurate number concentrations of nanoparticles is impeded by the typically heterogeneous populations of non-spherical nanoparticles. The irregular shape and size of "50 nm" silver nanoparticles is studied using Electron Tomography. It is evidenced that even for highly symmetrical particles the volume can be over 20% less than that of the circumscribed sphere; more irregularly shaped particles can have volumes of over 45% less.

Coupled Optical and Electrochemical Probing of Silver Nanoparticle Destruction in a Reaction Layer.

The oxidation of silver nanoparticles is induced to occur near to, but not at, an electrode surface. This reaction at a distance from the electrode is studied through the use of dark-field microscopy, allowing individual nanoparticles and their reaction with the electrode product to be visualized. The oxidation product diffuses away from the electrode and oxidizes the nanoparticles in a reaction layer, resulting in their destruction.

A quantitative methodology for the study of particle-electrode impacts.

Herein we provide a generic framework for use in the acquisition and analysis of the electrochemical responses of individual nanoparticles, summarising aspects that must be considered to avoid mis-interpretation of data. Specifically, we threefold highlight the importance of the nanoparticle shape, the effect of the nanoparticle diffusion coefficient on the probability of it being observed and the influence of the used measurement bandwidth. Using the oxidation of silver nanoparticles as a model system, it is evidenced that when all of the above have been accounted for, the experimental data is consistent with being associated with the complete oxidation of the nanoparticles (50 nm diameter).

Multiscale Engineered Si/SiO Nanocomposite Electrodes for Lithium-Ion Batteries Using Layer-by-Layer Spray Deposition.

Si-based high-capacity materials have gained much attention as an alternative to graphite in Li-ion battery anodes. Although Si additions to graphite anodes are now commercialized, the fraction of Si that can be usefully exploited is restricted due to its poor cyclability arising from the large volume changes during charge/discharge. Si/SiO nanocomposites have also shown promising behavior, such as better capacity retention than Si alone because the amorphous SiO helps to accommodate the volume changes of the Si.

Electrochemical Hg detection at tannic acid-gold nanoparticle modified electrodes by square wave voltammetry.

We report the electrochemical sensing of Hg2+ based on tannic acid capped gold nanoparticle (AuNP@TA) complexes. At optimal conditions using square wave voltammetry, the presented analytical method exhibits a "measurable lower limit" of 100.0 fM.

Single Oxidative Collision Events of Silver Nanoparticles: Understanding the Rate-Determining Chemistry.

The oxidative dissolution of citrate-capped silver nanoparticles (AgNPs, ∼50 nm diameter) is investigated herein by two electrochemical techniques: nano-impacts and anodic stripping voltammetry. Nano-impacts or single nanoparticle-electrode collisions allow the detection of individual nanoparticles. The technique offers an advantage over surface-immobilized methods such as anodic stripping voltammetry as it eliminates the effects of particle agglomeration/aggregation.

Fluorescence Electrochemical Microscopy: Capping Agent Effects with Ethidium Bromide/DNA Capped Silver Nanoparticles.

Fluorescence microscopy and electrochemistry were employed to examine capping agent dynamics in silver nanoparticles capped with DNA intercalated with ethidium bromide, a fluorescent molecule. The capped NPs were studied first electrochemically, demonstrating that the intercalation of the capping agent promotes oxidation of the silver core, occurring at 0.50 V (vs.

Electrochemical Detection of Ultratrace (Picomolar) Levels of Hg Using a Silver Nanoparticle-Modified Glassy Carbon Electrode.

Ultratrace levels of Hg have been quantified by undertaking linear sweep voltammetry with a silver nanoparticle-modified glassy carbon electrode (AgNP-GCE) in aqueous solutions containing Hg. This is achieved by monitoring the change in the silver stripping peak with Hg concentration resulting from the galvanic displacement of silver by mercury: Ag(np) + 1/2Hg(aq) → Ag(aq) + 1/2Hg(l). This facile and reproducible detection method exhibits an excellent linear dynamic range of 100.

Understanding nanoparticle porosity via nanoimpacts and XPS: electro-oxidation of platinum nanoparticle aggregates.

The porosity of platinum nanoparticle aggregates (PtNPs) is investigated electrochemically via particle-electrode impacts and by XPS. The mean charge per oxidative transient is measured from nanoimpacts; XPS shows the formation of PtO and PtO in relative amounts defined by the electrode potential and an average oxidation state is deduced as a function of potential. The number of platinum atoms oxidised per PtNP is calculated and compared with two models: solid and porous spheres, within which there are two cases: full and surface oxidation.

Catalytic activity of catalase-silica nanoparticle hybrids: from ensemble to individual entity activity.

We demonstrate the electrochemical detection and characterization of individual nanoparticle-enzyme hybrids. Silica nanoparticles were functionalized with catalase enzyme and investigated spectroscopically and electrochemically. The catalytic activity of the hybrids towards hydrogen peroxide decomposition was comparable to the activity of a freely diffusing enzyme in solution, exhibiting a Michaelis-Menten constant of = 74 mM and a turnover number of = 8 × 10 s per NP.

DNA capping agent control of electron transfer from silver nanoparticles.

Silver nanoparticles capped with either DNA or citrate are investigated electrochemically using stripping voltammetry and nano-impacts. Whilst the citrate capped particles are readily oxidised to silver cations at 0.7 V, the DNA capped particles undergo electron transfer from the silver core to the electrode in two distinct potential ranges -0.

Particle-impact analysis of the degree of cluster formation of rutile nanoparticles in aqueous solution.

Cluster formation can profoundly influence the bioavailability and (bio)geochemical activity of nanoparticles in natural aquatic systems. While colloidal properties of nanoparticles are commonly investigated using light-scattering techniques, the requirement to dilute samples can affect the fundamental nature and extent of the cluster size. Hence, an alternative in situ approach that can cover a much higher and wider concentration range of particles is desirable.

Quantifying Single-Carbon Nanotube-Electrode Contact via the Nanoimpact Method.

A new methodology is developed to enable the measurement of the resistance across individual carbon nanotube-electrode contacts. Carbon nanotubes (CNTs) are suspended in the solution phase and occasionally contact the electrified interface, some of which bridge a micron-sized gap between two microbands of an interdigitated gold electrode. A potential difference is applied between the contacts and the magnitude of the current increase after the arrival of the CNT gives a measure of the resistance associated with the single CNT-gold contact.

Exploring nanoparticle porosity using nano-impacts: platinum nanoparticle aggregates.

The porosity of platinum nanoparticles (PtNPs) is explored for the first time using tag-redox coulometry (TRC). This is achieved by monitoring the reduction of the 4-nitrobenzenethiol (NTP)-tagged PtNPs on carbon electrodes via both immobilisation and nanoimpacts. The average charge per impact is measured and attributed to the reduction of NTP adsorbed on individual PtNPs.