Peter W. Dunne

The Rapid Size- and Shape-Controlled Continuous Hydrothermal Synthesis of Metal Sulphide Nanomaterials

Continuous flow hydrothermal synthesis offers a cheap, green and highly scalable route for the preparation of inorganic nanomaterials which has predominantly been applied to metal oxide based materials. In this work we report the first continuous flow hydrothermal synthesis of metal sulphide nanomaterials. A wide range of binary metal sulphides, ZnS, CdS, PbS, CuS, Fe(1-x)S and Bi2S3, have been synthesised. By varying the reaction conditions two different mechanisms may be invoked; a growth dominated route which permits the formation of nanostructured sulphide materials, and a nucleation driven process which produces nanoparticles with temperature dependent size control. This offers a new and industrially viable route to a wide range of metal sulphide nanoparticles with facile size and shape control.

Planar [Ni7] discs as double-bowl, pseudo metallacalix[6]arene host cavities

We report three heptanuclear [Ni7] complexes with planar disc-like cores, akin to double-bowl metallocalix[6]arenes, which form molecular H-bonded host cavities.

A family of double-bowl pseudo metallocalix[6]arene discs

We report the synthesis and magnetic characterisation of a series of planar [M₇] (M= Ni(II), Zn(II)) disc complexes [Ni₇(OH)₆(L₁)₆](NO₃)₂ (1), [Ni₇(OH)₆(L₁)₆](NO₃)₂·2MeOH (2), [Ni₇(OH)₆(L₁)₆](NO₃)₂·3MeNO₂ (3), [Ni₇(OH)₆(L₂)₆](NO₃)₂·2MeCN (4), [Zn₇(OH)₆(L₁)₆](NO₃)₂·2MeOH·H₂O (5) and [Zn₇(OH)₆(L₁)₆](NO₃)₂·3MeNO₂ (6) (where HL₁ = 2-iminomethyl-6-methoxy-phenol, HL₂ = 2-iminomethyl-4-bromo-6-methoxy-phenol). Each member exhibits a double-bowl pseudo metallocalix[6]arene topology whereby the individual [M₇] units form molecular host cavities which are able to accommodate various guest molecules (MeCN, MeNO₂ and MeOH). Magnetic susceptibility measurements carried out on complexes 1 and 4 indicate weak exchange between the Ni(II) centres.

Towards scalable and controlled synthesis of metal–organic framework materials using continuous flow reactors

Metal–organic frameworks have emerged as one of the most diverse new families of materials in the past few years. Their hybrid structures, combinations of inorganic and organic moieties, give a wide range of complex architectures with resultant properties that are suitable for numerous important fields, including porosity for molecular sieving and sensing, heterogeneous catalysis, drug delivery, and energy storage. If applications of these materials are to be realised then scalable synthesis is required, taking laboratory batch reactions towards industrial production. Continuous flow reactors offer the most versatile method for scaling their solvothermal synthesis, with the largest range of materials accessible, in high yield, and with control over crystal form.

Continuous-flow hydrothermal synthesis for the production of inorganic nanomaterials

As nanotechnology becomes increasingly important and ubiquitous, new and scalable synthetic approaches are needed to meet the growing demand for industrially viable routes to nanomaterial production. Continuous-flow hydrothermal synthesis or supercritical water hydrothermal synthesis (scWHS) is emerging as a versatile solution to this problem. The process was initially developed to take advantage of the tunable chemical and physical properties of superheated water to produce metal oxide nanoparticles by rapid nucleation and precipitation. The development of new mixing regimes and reactor designs has been facilitated by the modelling of reactor systems. These new reactor designs further exploit the properties of supercritical water to promote faster and more uniform mixing of reagent streams. The synthetic approach has been expanded beyond the metal oxide systems for which it was conceived, and now encompasses metal sulfides, metal phosphates, metal nanoparticles and metal–organic frameworks. In many of these cases, some degree of size and shape control can be achieved through careful consideration of both chemistry and reactor design. This review briefly considers the development of scWHS reactor technology, before highlighting some of our recent work in expanding the scope of this synthetic method to include a wide range of materials.

Control of chemical state of cerium in doped anatase TiO2 by solvothermal synthesis and its application in photocatalytic water reduction

Solvothermal synthesis at 240 °C in ethanol from titanium(IV) isopropoxide and cerium(III) nitrate hexahydrate produces nanocrystalline powders of anatase-structured TiO2. At low Ce content (0.5 mol% Ti replaced by Ce) the materials contain mixtures of Ce3+ and Ce4+, seen from Ce LIII-edge X-ray absorption near-edge structure (XANES) spectroscopy, which are well dispersed in the anatase structure as evidenced from nanometre-scale electron energy loss spectroscopy maps and powder X-ray diffraction (XRD). The addition of lactic acid to the solvothermal reaction produces less crystalline samples, proved by powder XRD and Raman spectroscopy, with higher surface areas from nitrogen adsorption, and that contain a higher proportion of Ce3+. This leads to material with high activity for photocatalytic hydrogen production from water under UV irradiation in the presence of sacrificial methanol and Pt catalyst. Further in situ XANES experiments at the Ce LIII-edge recorded on heating the materials in air above 300 °C shows that oxidation to Ce4+ occurs. This process, typical of the conditions usually used in the synthesis of Ce-doped titania materials, yields materials with lower photocatalytic activity.

Continuous synthesis of dispersant-coated hydroxyapatite plates

A continuous flow hydrothermal synthetic route which allows the direct “in situ” capping/coating of hydroxyapatite nanoplates with functional dispersants in a single stage is reported. The methodology induced crystallisation by rapid mixing of streams of preheated water and solutions of reagents in water, whilst the hydrophobic surface modification of the HA platelets was achieved without morphological disruption. The effect of adding the hydrocarbon either before or after the HA platelet formation point has also been assessed, proving that the presence of surfactant at the reaction site does not interfere with the formation of HA and allows for a more efficient binding and extraction of the inorganic materials. The coupling mechanisms between the surfactant and the HA surface have been proposed to be a mixture of covalent and electrostatic interactions (i.e. all forms of chemisorption). This synthesis route is fully scalable to pilot (10 tons per year) and industrial (1000 tons per year) scales.

Assessing the life cycle environmental impacts of titania nanoparticle production by continuous flow solvo/hydrothermal syntheses

Continuous-flow hydrothermal and solvothermal syntheses offer substantial advantages over conventional processes, producing high quality materials from a wide range of precursors. In this study, we evaluate the “cradle-to-gate” life cycle environmental impacts of alternative titanium dioxide (TiO2) nanoparticle production parameters, considering a range of operational conditions, precursors, material properties and production capacities. A detailed characterisation of the nano-TiO2 products allows us, for the first time, to link key nanoparticle characteristics to production parameters and environmental impacts, providing a useful foundation for future studies evaluating nano-TiO2 applications. Five different titanium precursors are considered, ranging from simple inorganic precursors, like titanium oxysulphate (TiOS), to complex organic precursors such as titanium bis(ammonium-lactato)dihydroxide (TiBALD). Synthesis at the laboratory scale is used to determine the yield, size distribution, crystallinity and phase of the nanoparticles. The specifications and operating experience of a full scale plant (>1000 t per year) are used to estimate the mass and energy inputs of industrial scale production for the life cycle assessment. Overall, higher process temperatures are linked to larger, more crystalline nanoparticles and higher conversion rates. Precursor selection also influences nano-TiO2 properties: production from TiOS results in the largest particle sizes, while TiBALD achieves the smallest particles and narrowest size distribution. Precursor selection is the main factor in determining cradle-to-gate environmental impacts (>80% in some cases), due to the production impact of complex organic precursors. Nano-TiO2 production from TiOS shows the lowest global warming potential (GWP) (<12 kg CO2-eq. per kg TiO2) and cumulative energy demand (CED) (<149 MJ kg−1 TiO2) due to the low environmental impact of the precursor, the use of water as a solvent and its high yield even at lower temperatures. Conversely, the TiBALD precursor shows the highest impact (86 kg CO2-eq. per kg TiO2 and 1952 MJ kg−1 TiO2) due to the need for additional post-synthesis steps and complexity of precursor manufacturing. The main purpose of this study is not a direct comparison of the environmental impacts of TiO2 nanoparticles manufactured utilizing various precursors under different conditions, but to provide an essential foundation for future work evaluating potential applications of nano-TiO2 and their life cycle environmental impacts.

Magnetic structuring of linear copper electrodeposits

Electrodeposition of copper is investigated in localized magnetic fields produced by linear arrays of permanent magnets. The thickness and texture of the deposits depend on the magnitude and direction of the field. The deposition rate is explained in terms of magnetic pressure on the diffusion layer. Addition of non-electroactive GdCl3 to the electrolyte inverts the structuring of the electrodeposits, producing thick dendritic growth in regions where the field is smallest.

Fluorescence study of Bovine Serum Albumin and Ti and Sn Oxide Nanoparticles Interactions.

Nanochemistry offers stimulating opportunities for a wide variety of applications in the biosciences. Understanding of the interaction of nanoparticles with biomolecules such as proteins is very important as it can help better design and fabricate nanocomposites for applications in diagnostics, drug delivery, and cell monitoring. In this work, the interaction of Bovine Serum Albumin (BSA) and two types of metal oxide nanoparticles (titanium and tin) have been studied using the intrinsic fluorescence of tryptophan residue from the proteins measured by steady state and time resolved fluorescence techniques. The nanoparticles which were fabricated using a novel synthetic process have average sizes of ∼2 nm (SnO 2 ) and ∼6 nm (estimated for TiO 2 ) and have very high solubilities in a variety of solvents. The Stem-Volmer plots indicate an effective quenching process by TiO 2 nanoparticles whereas SnO 2 nanoparticles have a lower quenching efficiency for BSA fluorescence. Static quenching is the major contribution in the overall process which may indicate a high degree of association between protein and nanoparticles. The difference in BSA fluorescence quenching efficiency between the two types of nanoparticles can be explained by the non-covalent interaction differences and the thermal stability of protein-nanoparticle associated species for both materials.