Metallic and Molecular Interactions in Nanometer Layers, Pores and Particles: New Findings at the Yoctolitre Level: Volume 10 (Nanoscience & Nanotechnology Series) - Hardcover

Jurgen-Hinrich Fuhrhop

Hardcover

ISBN 10: 0854041664 ISBN 13: 9780854041664

Publisher: Royal Society of Chemistry, 2009

Synopsis

This book draws together the published material on nanochemistry from 2005-2008, choosing each important element of the periodic table, summarising relevant general properties and then detailing the findings.

About this title

About the Author

Professor Dr Jurgen Fuhrhop is at the Institute of Organic Chemistry, Freie Universitõt Berlin, Germany. He has written six books on Bioorganische Chemie (1983), Organic Synthesis (1994, 2003), Chemie f³r Mediziner (1994), Membranes and Molecular Assemblies (1995), Molecular and Supramolecular Chemistry of Natural Products and their Model Compounds (2000), Sieben Molek³le (2009) as well as more than 200 scientific papers and managed a Sonderforschungsbereich on 'Vectorial Membrane Processes'. Over the course of 35 years, he and his 126 co-workers have contributed to the development of useful models for single steps in biological photosynthesis. Typical scientific subjects were the reactivity and assembly of porphyrins and bolaamphiphiles, spherical and planar monolayer lipid membranes (MLMs), chiral bilayer effects in micellar fibers, long-distance heterodimers and most recently, yoctowells and the sorting of molecules within them. The overall keywords from this research are reversible, noncovalent synthesis or synkinesis of photo- and redox-active systems. Dr Tianyu Wang is at the Chinese Academy of Science, Beijing, China. He completed his PhD degree at the Institute of Chemistry, Chinese Academy of Science in 2001 with Professor Jinshi Ma where he was working on porphyrin synthesis. He then carried out postdoctoral research on porphyrin polymers and yoctowells made of bolaamphiphiles in the laboratory of Professor Fuhrhop at the Free University of Berlin. He has since returned to the Chinese Academy of Science where he is currently working in nanochemistry.

From the Back Cover

This book describes new developments in the nanochemistry of almost all elements of the periodic system, primarily for the period from 2006-2008. The main benefit of this book is the actualization of the interest in the elements of the periodic system. Important qualities of ultrathin assemblies, which are not common knowledge to chemists, including magnetism, luminescence, conductivity, thermoelectricity and density functional theory are explained in an introductory chapter. Carbon yoctowells and iron nanoparticles are covered in separate chapters. Other elements are discussed mostly in connection with interesting new nanocrystal and nanowire phenomena and the packing of molecules and atoms within yoctowells, containers with the volume of a few cubic nanometres. The book is written from the unique viewpoint of interesting interactions and properties which are not found in bulk materials, for example: - * silver metal nanocrystals which luminesce * glucose which becomes water-insoluble in yoctowells without any chemical reaction * the ballistic transport of electrons in thin carbon tubes without warming and their expansion and destructive power in slightly broader ones * the contraction of polymers in water upon warming from 36-40]C * the endless luminescence of metal sulphides

Excerpt. © Reprinted by permission. All rights reserved.

Metallic and Molecular Interactions in Nanometer Layers, Pores and Particles

New Findings at the Yoctolitre Level

By Jürgen Fuhrhop, Tianyu Wang

The Royal Society of Chemistry

Copyright © 2010 Jürgen Fuhrhop and Tianyu Wang
All rights reserved.

ISBN: 978-0-85404-166-4

Contents

Chapter 1 Atoms, Molecules, Electrons, Light and Heat in Nanometre Confinement, 1, 
Chapter 2 Organic Carbon, 52, 
Chapter 3 Main Group Elements, 160, 
Chapter 4 Iron, 245, 
Chapter 5 Transition Metals, 299, 
Subject Index, 403, 

CHAPTER 1

Atoms, Molecules, Electrons, Light and Heat in Nanometre Confinement

1.1 Introduction

The chemistry within yoctolitre (10-24L) holes or on the surface of particles with a yoctolitre volume is generally called "nanochemistry" because each dimension of these holes and particles measures a nanometre (nm): 1 yL = 1 nm. In volumes of up to 1000 yL, e.g. 10 × 10 × 10 nm, all distances between atoms and molecules on the particles or in the holes are within a few nanometres, which allows them to interact with each other and with ions and molecules that approach the surface. Holes left by missing single atoms, molecules or ions in yoctowell walls, and in the centres or surfaces of nano-particles or nanocrystals, can easily migrate through the whole species.

Yoctolitre dimensions are practical for the estimation of constituent numbers and models based on them: 1 yL can contain ~100 metal atoms, 50 molecules of metal oxide (MO), 33 molecules of water or 25 molecules of metal dioxide (MO2). Nanometre concepts are more appropriate if [111] surfaces have to be compared with [100] surfaces and where vectors, angles, and tenths of an Ångström become important.

The first special property of nanochemistry in or on yoctolitre-sized wells, pores, spheres or crystals depends on the fact that a large percentage of the atoms that form the holes or particles are surface atoms. Quite often the electrons on the hole or nanoparticle surfaces do not bind anything, but represent 'dangling bonds' with special activities. The second dominating fact is the relevance of space-dependent physical properties of molecules, which play hardly any role in bulk inorganic and organic chemistry. For example, glucose becomes water-insoluble in hydrophobic yoctowells, because the molecules have a hydrophobic edge, which sticks to the wall, and metallic Ag(0) nanocrystals seem to forget about their metallic electron cloud and fluoresce like covalent molecules, for reasons yet unknown.

The translation of stereochemistry into spin interactions of electrons and different kinds of magnetism, the chemical stabilization of electron-hole pairs in order to create luminescence of all colours by the variation of electric potentials, the change in metal crystal lattices on the surface of nanocrystals that renders them catalytically active or fluorescent, and the fixation of water-soluble carbohydrate edge amphiphiles in hydrophobic, water-filled yoctowells are subjects of current research, and chemists interested in the development of new properties should become familiar with them. Research in this field requires access to modern techniques such as rapid crystallization of vapour, laser ablation under water, preparation of atomically smooth surfaces, atomic force microscopy, electron transmission microscopy and electron scanning microscopy, among others.

Subjects covered in this book are, in order of increasing complexity:

• self-cleaning surfaces of nanometre roughness

• quantum dots (QDs), which provide everlasting colours and discrete energy levels instead of bands

• soft and hard magnetic particles for computers and other engineering uses

• minimization of functional AFM tips

• localization of many different single molecules in a very small aqueous space

• decomposition of chlororganic compounds in soils

• coupling of NMR signals with magnetic field steering

• fixation of proteins, DNA and cell surfaces on nanoparticles in water

• routine interconnection of nanoscale elements by nanowiring

• photolysis of water by sunlight

• synthesis of effective catalytic corners with different elements, particularly iron

• assembly of nanoparticles to form efficient thermoelectric elements

• minimization of computer hard disks.

Today's nanochemistry offers a unique chance to have a fresh look at the periodic system of the elements. Carbon chemistry, to name a popular example, is a huge field of classical and modern chemistry, but molecular coatings of nanoparticles that shrink in water on heating, graphite tubes showing ballistic electron transport or the dominance of dangling bonds in nanodiamonds, which makes them extremely reactive, are accessible only through nanochemistry and are of interest in industry and medicine. Magnetic data storage in computer or control devices, the conversion of sunlight into electric currents and of electric currents into light and refrigeration – all these processes depend on metallic nanoparticles and help to create or replace energy sources. Working with nanocrystals, nanowires and the inner walls of nanometre-wide wells and tubules in university labs will help young scientists to find rewarding problems for work in industry, which has to engineer, optimize, produce, sell and guarantee the nanosized constituents of computers, catalysts, light bulbs, solar converters, etc.

Most of the reference citations in this book date from 2005–2009 and are from easily accessible chemical journals. They provide a starting point for learning and research. Each important element of the periodic table has its own section, where relevant general properties are summarized and the element-specific ideas behind recent publications, together with selected results, are discussed. Altogether, the book is as "hands-on" as possible, and we have tried to provide the necessary physical and material chemical background in a descriptive manner. Nanochemists should know whether the products they develop in reaction flasks or on solid surfaces contain magnetic, luminescent or conductive layers, particles or wires.

Our aim is to make readers aware of current developments, while avoiding speculations about economic perspectives. The motivation for 'going nano' should always be scientific success, the hope of finding something new and surprising.

1.2 Water, Toluene, Nanoparticles and Nanocrystals

The most useful nanoparticles have diameters between 1 and 10 nm, sometimes up to 20 nm, i.e. volumes between one and a few thousands of yoctolitres. The 1 nm species are best for structural and theoretical studies, but 10 nm guarantees relatively high stability and longevity; 5nm is the standard compromise. Furthermore, all nanosized clusters of atoms or molecules that are of interest fulfil a function. The "functionality" may be as simple as being magnetic, or separation of sodium chloride into Na+ and Cl- ions, or as complex as the recognition and removal of two proteins from the bloodstream of a living organism.

We start with water, the lightest natural molecule on Earth with its molecular weight of 18. Its hexameric cluster is the lightest and most dynamic sub-nanoparticle, with a molecular weight of 6 × 18 = 108 Da. All molecules that are lighter than water, in particular hydrogen (H2) and helium (He), eventually disperse into outer space after reaching the atmosphere. Water, however, forms droplets and ice crystallites in the atmosphere which could never escape the gravitational pull of the Earth, even in prebiotic times when the Earth's surface was volcanic and very hot. Our water molecules originally came here from outer space, but now they never leave the Earth, because they form nanoparticles, micrometre, and millimetre particles at heights of a few hundred metres. Liquid water is the only low-molecular-weight fluid that is stable over a 100 K temperature range. The formation of clusters and droplets has kept water on Earth for more than 4 billion years and allowed for the evolution of life here.

The oxygen atom of water is buried in the centre of a tetrahedron with two electron pairs and two protons at the corners. This polar ordering of the molecular surface dominates the behaviour of fluid and solid water. The oxygen atom holds the protons and electron pairs together, provides weight, and becomes important as molecular triplet oxygen as an end product of the water splitting in photosynthesis. Electrostatic hydrogen bridges between the electron pairs and protons of neighbouring water molecules then form a water pentamer with a molecular weight of 90, which is the unit of larger clusters and finally water droplets (Figure 1.1). But this is not all. In fluid water a sixth water molecule squeezes into the remaining empty space in the fluid pentamer clusters and forms extra hydrogen bridges, which are much less stable than the other four and correspondingly short-lived. It is this sixth molecule that accounts for the low viscosity of water. It moves so quickly from one cluster to another that it keeps them mobile.

The major effect of hydrogen bonding is not viscosity, but high surface tension and boiling point. Bulk water attracts the surface water molecules strongly with one-sided hydrogen bonds, and the air on the upper side cannot compete. We know that 18 cm3 of water contain 6 × 1023 molecules, so 1 nm3 or 1 yL of water contains 33 molecules. The hexamer nanoparticle has a volume of only one sixth of a yoctolitre. About 10 molecules of water form the inner hydration sphere of Na+ and Cl- ions, and each of the water molecules is part of a cluster. Only one or two NaCl units can thus be dissolved in a 1 yL well, and become centres of fluid water nanoparticles there.

Water is also the basis of life. More than 98% of the molecules of the human body are water, and it participates in each of the molecular actions of proteins, nucleic acids, ATP, etc. Its magical role in animal life is the formation of clusters around phosphate, K+, Na+, and H+ ions, which permits strong electric potentials in nerves, muscles, brain and stomach. The pH of human blood and cellular fluid is always 7.4, which means there is less than 0.01 mg of protons in the whole body with exception of the stomach, with a pH of 0, where there is more than a gram of protons. Enzymes, nerves and muscles for example, would not be active at pH 5.

Soft nanoparticles and nanolayers made of carbon-containing molecules in water, e.g. micelles, vesicles and bilayer lipid membranes, are described in Chapter 2. Here we discuss only a few general points about the preparation and properties of metal and metal oxide nanoparticles and nanocrystals.

Toluene (= methylbenzene, C6H5CH3) is a water-immiscible solvent. It floats on water, but both water and toluene form 1 nm long fingers, which protrude into each other at the interface for tens of picoseconds (10-12 s). Films of Au(0) NPs are formed if a hydrophobic gold(I) compound, namely triphenylphosphine gold chloride, AuPPh3Cl, is dissolved in the upper toluene phase and a water soluble reductant, formaldehyde, CH2O, in the form of the polar P(CH2OH)4Cl salt, in the water below. Irregular Au55 clusters of uniform size (1.2 nm) were then formed at the toluene-water interface and seven such clusters formed a planar heptamer at the interface: one Au(0)55 NP in the centre, six others around it. The lower side of this heptamer became hydrophilic by a water layer, the upper side was hydrophobic with a toluene solvation coat. Now came more gold particles from the water and toluene sides and three of them attach upside to the hydrophobic part, three others downside to the hydrophilic part. They occupied the gaps in the flat Auheptamer and reverted its polarity. The toluene side now had a hydrophilic surface, the water side a hydrophobic one. The polymeric metal consisted of 13 Au55 units. Growth stopped there because the short-lived, 1nm long toluene fingers in water and water fingers in toluene did not allow for longer reaction times and larger assemblies. Only one NP layer on each side and the solvent caps stabilized the heptamer in the centre. The presence of the clusters and the associated organic layer hindered the progress of the "crystallization" unless the interface was disturbed by surface pressure and/or vibrations (Figure 1.2).

The primary Au55 NPs were also formed in two steps: at first Au13 NPs were formed which attached immediately 42 more Au atoms in a second shell. Au55, a "cuboctahedron" with a diameter of 1.2 nm is formed as relatively stable gold core. In the toluene/water case this Au55 was surrounded by a non-identified 1.1 nm organic shell, possibly P(CH2OH)3/toluene, and the coated Au55 NPs again clustered to form the described cluster of 13 Au NPs of 2.3 nm diameter each, one in the centre and 12 on the surface (Figure 1.3). Such interfacial assemblies are presumably standard intermediates in the formation of very small spherical NPs. Solidification of vapours on cold surfaces, laser ablation under water or rapid precipitation in acid/base reactions in uniform solvents probably produce the same intermediates but limitation of growth is caused there by short crystallization times, rather than by "fingers" between two phases.

The major crystal lattices of metals are summarized in a general structure proposed by Hume and Rothery (Figure 1.4). The possible positions of the atoms are identified by the letters a, b, c and d. If all positions are occupied by the same kind of atoms, e.g. Fe(0), the structure is cubic close packed (ccp). The Hume–Rothery figure contains eight of these ccp units and occurs in nature in zinc blende (ZnS), gallium arsenide (page 184 ff), zinc selenate (p. 212, 215, 231), and diamond. In zinc blende the a positions on alternating corners of the cubes are occupied by zinc, the b positions appear in alternating centres of the cubes and are occupied by sulfur; c and d are unoccupied. The usual drawing of the diamond structure with cyclohexane chairs is identical, but the Hume–Rothery cube is rotated by 45°, so that the (111) axis appears perpendicular. The (111) plane unit contains one atom; this plane grows rapidly and is the largest in the real crystal. The (100) plane unit contains two atoms, grows slowly and is much smaller in surface area.

Metals crystallize in the lattice with the highest possible symmetry that is in agreement with the specific properties of the atoms. This leads mostly to simple cubic crystal lattices (with 8 neighbours) or hexagonal lattices (with 12 neighbours). Crystals of molecules are usually harder than those of amorphous materials, because the crystal is stabilized by various directed non-covalent forces, in particular crosslinking and hydrogen bonding (pages 11 and 14). Single crystals of metals behave differently: they are soft, but harden upon deformation. This is caused by sliding planes in the crystal, which are destroyed upon rearrangement. Corners are formed instead, which prevent any further movement (Figure 1.5).

The most important metal on Earth is iron (see Chapter 4). It occurs naturally as an Fe(II) or Fe(III) oxide. In laboratory simulations of stream water containing Fe(II) chloride, 87% of the Fe(II) remained unoxidized after 24 h of aeration at pH 6.5. After addition of natural organic matter or organic carbon in the form of humic and fulvic acids from plant debris, 97% of the Fe(II) was converted to Fe(III) (hydr)oxides in the form of nanoparticles, which were adsorbed and stabilized by the organic matter. The primary FeOOH nanoparticles remained < 200 nm in size and dispersed in water only in the presence of the organic matter. Their transport in stream water depended on this cooperation between phenol polymers and iron oxides. The most abundant nanoparticles in nature appear at the interface between plant debris and iron salts.

Nanocrystals of magnetite ([FORMULA NOT REPRODUCIBLE IN ASCII]), are commonly used in medicine as carriers in the bloodstream, and may be steered to damaged tissues by an external magnetic field. The magnetite nanocrystals result from an initial short burst of nucleation, when Fe(II) and Fe(III) are coprecipitated with OH- ions. Later, when the concentration of the Fe(II/III) hydroxides reaches a critical supersaturation, the diffusion of solutes allows only a slow growth of the nuclei and leads to many different crystal surfaces. Small, monodisperse magnetite nanocrystals are therefore best isolated immediately after nucleation.

In such time-dependent crystallizations, the desired size and shape of the nanocrystals can always be tailored by the conditions, such as pH, ionic strength, temperature, choice of salts (perchlorates, chlorides, sulfates, nitrates, citrates), and the experimental optimization of the absolute and relative Fe(II)/Fe(III) concentrations. Immediate microscopic control of the result and preparation according to a detailed protocol is essential. The possible addition of any other molecule for stabilization should wait until one knows how to prepare the nanocrystals. Different anions often lead to different nanocrystals; variations in size and shape are then usually traced back to more or less negative charges on the surface of the nanoparticles. For example, if increasing amounts of citrate ions are added, the diameter of the nanocrystals will decrease by a factor of ~2. Chelation of the iron ions first retards the nucleation, and a citrate coat then inhibits further growth of the nuclei.

(Continues...)

Excerpted from Metallic and Molecular Interactions in Nanometer Layers, Pores and Particles by Jürgen Fuhrhop, Tianyu Wang. Copyright © 2010 Jürgen Fuhrhop and Tianyu Wang. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2009
• Language: English
• ISBN 10: 0854041664
• ISBN 13: 9780854041664
• Binding: Hardcover
• Number of pages: 422