Coating the surface of interconnected Cu2O nanowire arrays with HKUST-1 nanocrystals via electrochemical oxidation.

Controlling the crystallization of Metal-Organic Frameworks (MOFs) at the nanoscale is currently challenging, and this hinders their utilization for multiple applications including photo(electro)chemistry and sensors. In this work, we show a synthetic protocol that enables the preparation of highly homogeneous Cu2O@MOF nanowires standing on a conductive support with extensive control over the crystallization of the MOF nanoparticles at the surface of the Cu2O nanowires. Cu2O nanowires were first prepared via templated electrodeposition, and then partially converted into the well-known Cu-MOF HKUST-1 by pulsed electrochemical oxidation. We show that the use of PVP as a capping agent during the electrochemical oxidation of Cu2O into HKUST-1 provides control over the growth of the MOF nanocrystals on the surface of the Cu2O nanowires, and that the size of the MOF crystals obtained can be tuned by changing the concentration of PVP dissolved in the electrolyte. In addition, we propose the use of benzoic acid as an alternative to achieve control over the size of the obtained MOF nanocrystals when the use of a capping agent should be avoided.

Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications.

Long triplet lifetimes of excited photosensitizers are essential for efficient energy transfer reactions in water, given that the concentrations of dissolved oxygen and suitable acceptors in aqueous media are typically much lower than in organic solvents. Herein, we report the design, synthesis and photochemical characterization of two structurally related water-soluble ruthenium complex-based dyads decorated with a covalently attached pyrene chromophore. The triplet energy of the latter is slightly below that of the metal complex enabling a so-called triplet reservoir and excited-state lifetime extensions of up to two orders of magnitude. The diimine co-ligands, which can be modified easily, have a major impact on both the ultrafast intramolecular energy transfer (iEnT) kinetics upon excitation with visible light and the lifetime of the resulting long-lived pyrene triplet. The phenanthroline-containing dyad shows fast triplet pyrene formation (25 ps) and an exceptionally long triplet lifetime beyond 50 microseconds in neat water. The iEnT process via the Dexter mechanism is slower by a factor of two when bipyridine co-ligands are employed, which is rationalized by a poor orbital overlap. Both dyads are very efficient sensitizers for the formation of singlet oxygen in air-saturated water as well as for the bimolecular generation of anthracene triplets that are key intermediates in upconversion mechanisms. This is demonstrated by the 5-hydroxymethylfurfural oxidation, which yields completely different main products depending on the pH value of the aqueous solution, as an initial application-related experiment and by time-resolved spectroscopy. Our findings are important in the greater contexts of photocatalysis and energy conversion in the "green" solvent water.

Experimental data showing the influence of different boron nitride particles on the silica network, the butyl stearate and the porogens in shape-stabilized phase change materials.

Shape-stabilized phase change materials (ss-PCMs) based on silica and butyl stearate were thermally enhanced via the addition of different hexagonal boron nitride particles (BN) to the in situ sol-gel synthesis. The dataset is used in conjunction with the experimental data of the influence of the particle size and surface area of BN on the thermal and mechanical properties of ss-PCMs discussed in Marske et al. (2021). To study the effect of the different BN particles on the hydrolysis degree of the silica network and on the chemical nature of the porogens sodium dodecyl sulfate and poly(vinyl alcohol) used for the ss-PCM synthesis, the ss-PCM samples are measured via High Power Decoupling (HPDEC) Magic Angle Spinning (MAS) 29Si NMR and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, respectively. Additionally, data of the influence of BN on the thermal properties is presented as thermogravimetric analysis (TG). The 29Si MAS NMR spectra are referenced to tetramethylsilane and show the different silica species in ppm. The different value of wavenumber and intensity of each reference and ss-PCM sample is listed in the IR spectra. The decomposition points of the ss-PCMs are calculated from the TG data via OriginLab. The spectra and data can be used as a reference for other researchers and engineers to use in synthesizing ss-PCMs based on silica and other polymeric materials or as reference for pure BN, SDS, stabilized silica sol and PVA.

Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting.

Transition-metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co-P films were deposited by using PH3 plasma as the phosphorus source and an extra H2 plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self-limited layer-by-layer growth, and the deposited Co-P films were highly pure and smooth. The Co-P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co-P films prepared by the traditional post-phosphorization method. Moreover, the deposition of ultrathin Co-P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three-dimensional (3D) architectures.

Tuning the Size and Shape of NanoMOFs via Templated Electrodeposition and Subsequent Electrochemical Oxidation.

The control over the size and shape of nanoMOFs is essential for their exploitation in integrated devices such as sensors, membranes for gas separation, photoelectrodes, etc. Here, we demonstrate the synthesis of nanowires and three-dimensionally interconnected nanowire networks of Cu-based metal-organic frameworks (MOFs) by a combination of ion-track technology and electrochemical methods. In particular, Cu nanowires and nanowire networks were electrodeposited inside polymeric etched ion-track membranes and subsequently converted by electrochemical oxidation into different Cu-based MOFs such as the well-known Cu3(BTC)2 (also known as HKUST-1) and the lesser-known MOF Cu(INA)2. The MOFs are formed inside the template, therefore adopting the shape of the host nanochannels. The synthesized MOF nanowires exhibit tunable diameters between 80 and 260 nm. Characterization by X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy indicates that the employed electrochemical conversion includes the formation of Cu2O as an intermediate, as well as the initial formation of an amorphous MOF phase, which crystallizes upon longer reaction times.

Preparation and use of photocatalytically active segmented Ag|ZnO and coaxial TiO2-Ag nanowires made by templated electrodeposition.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 µm were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

MoS2 nanocube structures as catalysts for electrochemical H2 evolution from acidic aqueous solutions.

Core-shell PMMA-Au nanocube structures made by a combination of nanoimprint lithography and sidewall deposition were used as template for electrodeposition of MoS2, Ni, and Pt. Linear sweep voltammetry experiments obtained in an aqueous solution containing 0.29 M H2SO4 (pH 0.24) showed that the onset potential of the core-shell-shell PMMA-Au-MoS2 nanocube electrode for the hydrogen evolution reaction (HER) was shifted to the positive direction (i.e., requiring a lower overpotential) by 20-40 mV compared to planar MoS2 films. This indicates that the nanocube electrodes have a significantly increased HER activity, which is probably because of a higher density of catalytically active edge sites available at the nanocube surface. It was also found that the HER activity initially increased with increasing MoS2 deposition time, but decreased after deposition for 60 min because the edges of the nanocubes became rounded, thereby decreasing the number of active edge sites. By depositing Ni and Pt on top of PMMA-Au nanocubes, it was shown that this method can also be used for the synthesis of nanocube structures with varying compositions.

Ni and p-Cu2O nanocubes with a small size distribution by templated electrodeposition and their characterization by photocurrent measurement.

A method for the reproducible formation of Ni and Cu2O nanocubes with dimensions of 200-500 nm and a small size distribution is introduced. For this, the well-known templated electrodeposition technique was extended to cubic PMMA templates made by nanoimprint lithography. When making cubic templates in larger quantities, this method has the potential to become simple and cost-effective. This method was successfully used for the formation of Ni and p-Cu2O nanocubes as well as for the formation of segmented nanobars containing both phases. The lateral dimensions of the nanocubes exactly resembled the dimensions of the template, and the height could be varied by adjusting the deposition time. Nanocubes formed via this method can remain attached to the substrate or can be dispersed in solution. p-Cu2O is considered to be one of the most promising photocathode materials for solar water splitting. It is demonstrated that the activity of the p-Cu2O nanocubes for photocatalytic water splitting can be measured, and it was found that the nanocube morphology enhances the photocatalytic activity compared to thin films.

Au coated Ni nanowires with tuneable dimensions for biomedical applications.

Due to their shape anisotropy, high aspect ratio magnetic nanoparticles offer many advantages in biomedical applications. For biocompatibility, it is essential to have full control over the dimensions and surface chemistry of the particles. The aim of this study was to synthesize biocompatible nanowires with tuneable dimensions. This was achieved by electrodeposition of Ni in polycarbonate membranes. To ensure biocompatibility, a continuous gold coating was deposited onto the Ni wires by a newly developed electroless deposition method. The coating was analysed using electron microscopy and X-ray diffraction. Magnetic properties, anisotropy and Au film thickness were studied using vibrating sample magnetometry. After biofunctionalization, no significant cytotoxic effects were found in studies involving a diverse range of primary and tumour cells exposed to increasing concentrations of nanowires for up to 7 days. These nanowires may thus be used for in vivo applications such as magnetic drug delivery.

Electrodeposition in capillaries: bottom-up micro- and nanopatterning of functional materials on conductive substrates.

A cost-effective and versatile methodology for bottom-up patterned growth of inorganic and metallic materials on the micro- and nanoscale is presented. Pulsed electrodeposition was employed to deposit arbitrary patterns of Ni, ZnO, and FeO(OH) of high quality, with lateral feature sizes down to 200-290 nm. The pattern was defined by an oxygen plasma-treated patterned PDMS mold in conformal contact with a conducting substrate and immersed in an electrolyte solution, so that the solid phases were deposited from the solution in the channels of the patterned mold. It is important that the distance between the entrance of the channels, and the location where deposition is needed, is kept limited. The as-formed patterns were characterized by high resolution scanning electron microscope, energy-dispersive X-ray analysis, atomic force microscopy, and X-ray diffraction.

Nanopatterning of functional materials by gas phase pattern deposition of self-assembled molecular thin films in combination with electrodeposition.

We present a general methodology to pattern functional materials on the nanometer scale using self-assembled molecular templates on conducting substrates. A soft lithographic gas phase edge patterning process using poly(dimethylsiloxane) molds was employed to form electrically isolating organosilane patterns of a few nanometer thickness and a line width that could be tuned by varying the time of deposition. Electrodeposition was employed to deposit patterns of Ni and ZnO on these prepatterned substrates. Deposition occurred only on patches of the substrate where no organosilane monolayer was present. The process is simple, inexpensive, and scalable to large areas. We achieved formation of metallic and oxide material patterns with a lateral resolution of 80 nm.

Patterning functional materials using channel diffused plasma-etched self-assembled monolayer templates.

A simple and cost-effective methodology for large-area micrometer-scale patterning of a wide range of metallic and oxidic functional materials is presented. Self-assembled monolayers (SAM) of alkyl thiols on Au were micropatterned by channel-diffused oxygen plasma etching, a method in which selected areas of SAM were protected from plasma oxidation via a soft lithographic stamp. The patterned SAMs were used as templates for site-selective electrodeposition, electroless deposition and solution-phase deposition of functional materials such as ZnO, Ni, Ag thin films, and ZnO nanowires. The patterned SAMs and functional materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and tunneling AFM (TUNA).