Layered double hydroxides in bioinspired nanotechnology

Layered Double Hydroxides (LDHs) are a relevant class of inorganic lamellar nanomaterials that have attracted significant interest in life science-related applications, due to their highly controllable synthesis and high biocompatibility. Under a general point of view, this class of materials might have played an important role for the origin of life on planet Earth, given their ability to adsorb and concentrate life-relevant molecules in sea environments. It has been speculated that the organic-mineral interactions could have permitted to organize the adsorbed molecules, leading to an increase in their local concentration and finally to the emergence of life. Inspired by nature, material scientists, engineers and chemists have started to leverage the ability of LDHs to absorb and concentrate molecules and biomolecules within life-like compartments, allowing to realize highly-efficient bioinspired platforms, usable for bioanalysis, therapeutics, sensors and bioremediation. This review aims at summarizing the latest evolution of LDHs in this research field under an unprecedented perspective, finally providing possible challenges and directions for future research

Transition metal chalcogenide hybrid systems as catalysts for energy conversion and biosensing

Generation of hydrogen and oxygen through catalyst-aided water splitting which has immense applications in metal air batteries, PEM fuel cells and solar to fuel energy production, has been one of the critical topics in recent times. The state of art oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) catalysts are mostly comprised of precious metals. The current challenge lies in replacing these precious metal-based catalysts with non-precious earth-abundant materials without compromising catalytic efficiency. This research explores mixed metal selenides containing Fe-Ni, Fe-Co and RhSe which were hydrothermally synthesized and/or electrodeposited and tested for OER and ORR catalytic activity in alkaline medium. This spinel class of compounds generically referred to as AB2Se4 where A and B are divalent and trivalent cations respectively. Interestingly, FeCo2Se4 and FeNi2Se4, both showed highly efficient catalytic activity with low overpotential. Increase in performance was observed when these two spinel compositions were mixed with conducting carbon matrix, which decreased the overpotential significantly and increased the stability. Finally, the metal selenides were also applied towards electrochemical bio sensing of dopamine and glucose. Electrodeposited and hydrothermally synthesized CuSe was studied towards detection of ultralow concentrations of dopamine in neutral phosphate buffer solution. The electrodeposited CuSe was also active towards detection of glucose in alkaline electrolyte. CuSe showed low detection limit, high sensitivity and selectivity towards these biomolecules --Abstract, page v

Template-Assisted Fabrication of Ferromagnetic Nanomaterials

Abstract Template assisted deposition was used to produce various nanomaterials including simple nanowires, nanorods, multi-segmented metal nanowires, core-shell nanowires, alloy and polymer wires and tubes. Anodized aluminum oxide (AAO) membranes were used as templates for the growth of the various structures using an electrochemical deposition method and also by wetting the porous templates. In the electrochemical deposition method, the pore size of the templates affects the rate of synthesis and the structures of the nanomaterials while in the wetting method, the viscosity and reaction time in the polymer solution influence the structures of the nanomaterials. A conventional two-step anodization procedure was used to synthesize thick AAO templates with porous hexagonal channels at a constant applied voltage and temperature. A maximum thickness of over 180 µm oxide layer could be fabricated using mild anodization at 60 V and 80 V. Compared to conventional mild anodization, these conditions facilitated faster growth of oxide layers with regular pore arrangement. Polyethylene glycol (PEG) containing ferromagnetic nanowires were synthesized using template assisted electrochemical deposition method. During the synthesis, simultaneous deposition of polymer and metal ions resulted nanowires coated with a uniform layer of PEG without interfering with the structure and magnetic properties of the nanowires. PEG-coated Ni nanowires were embedded in polyethylene diacrylate (PEGDA) matrix after the removal of the AAO templates. Comparison of results with and without a magnetic field during embedding showed that the presence of magnetic field supported embedding of nanowire arrays in polymer. Influence of using AAO templates with several pore diameters for the synthesis of bimetallic nanowires were studied by growing Ni-Fe and Ni-Co bi-metallic nanowires. At a constant applied current by using templates with a pore diameters of 60 nm alloy formed while with a pore diameter of 130 nm core-shell nanowires formed. Polyvinylidene fluoride (PVDF) films and nanotubes were synthesized using a solution recrystallization method that favored the formation of piezoelectric β phase thin films. Variation in the concentration of polymer in the mixture solution allowed synthesis of different types of structures such as PVDF composites, nanorods and nanocrystals with tunable morphologies. Keywords: One-dimensional structures, electrodeposition, porous alumina, ferromagnetic nanostructures, magnetic core-shell nanowires, alloys, polymer composite, stimuli-active, PEGDA, azobenzene, and PVDF

Layered Double Hydroxides

Very few materials have attracted so much attention in recent years, both from researchers and industry, as layered double hydroxides (LDHs) have. LDHs, which are also referred to as anionic clays or hydrotalcites, are a wide class of inorganic ionic lamellar clay materials consisting of alternately stacked positively charged metal hydroxide layers with intercalated charge-balancing anions in hydrated interlayer regions. Their unique properties, such as their extremely high versatility in chemical composition and intercalation ability, extraordinary tuneability in composition as well as morphology, good biocompatibility and high anion exchangeability, have triggered immense interdisciplinary interest for their use in many different fields of chemistry, biology, medicine, and physics. Indeed, the applications of LDHs are constantly growing: LDHs, in the form of aggregated lamellar clusters, exfoliated single-layer nanosheets, or hierarchical films of interconnected nanoplatelets, can be effectively used as nanoscale vehicles in drug delivery, heterogeneous catalysts and supports for molecular catalysts, ion exchangers and adsorbents, solid electrolytes or fillers in electrochemistry, for the fabrication of superhydrophobic surfaces, water treatment and purification, and the synthesis of functional thin films. This book gathers the contributions to the Special Issue “Layered Double Hydroxides” of Crystals, which includes two review articles and seven research papers

Hybrid Metallic Nanostructures for Bio and Analytical Applications

Different hybrid nanoparticles (NPs), including FeM (M=Ni, Au, Pt, Pd) and Fe-biomolecules (biomolecule=glucose oxidase, p53p protein), have been synthesized by a surfactant-free, single-step electrochemical method. FeNi bimetallic NP systems have been chosen as the starting point of the present study. Shape evolution and phase transformation of FeNi NPs obtained by changing their composition is demonstrated. It has been shown that the shape evolution of NPs from concave cube to truncated sphere occurs concurrently with the phase transformation from bcc to fcc. In-situ formation of a very thin Ni-doped FeOOH outer layer and NiFe2O4 intermediate layer on the skin of the NPs is observed, the latter of which passivates the surface and dramatically enhances the air stability. Furthermore, bimetallic FeNi concave nanocubes with high Miller index planes have been obtained through controlled triggering of the different growth modes of Fe and Ni. Taking advantage of the higher activity of the high-index planes, mono-dispersed concave nanocages have been fabricated by introducing a material-independent electroleaching process. With the high-index facets exposed, these concave nanocubes and nanocages are found to be 10 and 100-fold, respectively, more active toward electrochemical detection of 4-aminophenol than cuboctahedrons which provides a label-free sensing approach to monitoring toxins in water and pharmaceutical wastes. In addition, the shape-dependent magnetic properties of a bimetallic system have been studied for FeNi NPs with well-defined concave cubic and octahedron shapes. The alloy composition was chosen to be close to that of Invar FeNi alloys (35% Ni content) but with concurrent presence of both bcc and fcc phases, in order to investigate the role of phase combination in controlling the magnetic properties. The role of the two phases in governing the magnetic properties has also been studied for both bulk and nanoalloys by large-scale density function theory (DFT) calculations using Vienna Ab-initio Simulation Package (VASP, Version 5.2), which provides a new complementary approach to understanding the magnetic properties of alloy materials. To extend the aforementioned method to other hybrid and bimetallic systems, FePt NPs with different compositions (Fe25Pt75, Fe30Pt70, Fe35Pt65) have been synthesized and their chemical sensing investigated for the electro-oxidation of vitamin C. The FePt alloy NPs are found to be superior catalysts for vitamin C electro-oxidation than Pt NPs and are significantly more selective for the detection of vitamin C against other common interference species, including dopamine, citric acid, uric acid, glucose, and NaCl. Enhancement in sensor performance can be attributed to the increase in specific surface area due to reduction of nanocrystallite size and to modification in the Pt electronic structure as a result of nanoalloying. We also synthesize bimetallic FeAu, FePd, and AuPt NPs and investigate their electrochemical properties for As(III) detection. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, Pd) than pristine noble metal NPs (without Fe alloying), with the best performance found for FePt NPs. The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), acting as the most detrimental interfering ion for As detection. The versatility of the method for hybridization of different components is demonstrated by synthesizing size-specific hybrid NPs based on Fe-biomolecules. We have chosen an anticancer peptide (p53p, MW 1.8 kDa) and an common enzyme (glucose oxidase, MW 160 kDa) as model molecules to illustrate the versatility of the method towards different types of molecules over a large size range. We show that the electrostatic interaction for complex formation of metal hydroxide ion with the partially charged side of the biomolecule in the solution is the key to hybridization of metal-biomolecule materials to form complexes as the building blocks. These hybrid NPs with controllable sizes ranging from 30 nm to 3.5 μm are found to exhibit superparamagnetic behavior, which is a big challenge for particles in this size regime. As an example of greatly improved properties and functionality of the new hybrid material, in-vitro toxicity assessment of Fe-glucose oxidase hybrid NPs shows no adverse effect, while the Fe-p53p hybrid NPs are found to selectively bind to cancer cells. The present work therefore definitely demonstrates the general applicability of the hybridization method for synthesis of metallic hybrid NPs with magnetic properties for different applications, including chemical sensing, magnetic resonance imaging contrast agents, and targeted drug delivery carriers

A NiFe Alloy Reduced on Graphene Oxide for Electrochemical Nonenzymatic Glucose Sensing

A NiFe alloy nanoparticle/graphene oxide hybrid (NiFe/GO) was prepared for electrochemical glucose sensing. The as-prepared NiFe/GO hybrid was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results indicated that NiFe alloy nanoparticles can be successfully deposited on GO. The electrochemical glucose sensing performance of the as-prepared NiFe/GO hybrid was studied by cyclic voltammetry and amperometric measurement. Results showed that the NiFe/GO-modified glassy carbon electrode had sensitivity of 173 μA mM−1 cm−2 for glucose sensing with a linear range up to 5 mM, which is superior to that of commonly used Ni nanoparticles. Furthermore, high selectivity for glucose detection could be achieved by the NiFe/GO hybrid. All the results demonstrated that the NiFe/GO hybrid has promise for application in electrochemical glucose sensing