Jeremiah S. Duncan

Competition for Water

Publisher Summary This chapter explores the issues and considers ways that advances in nanotechnology might help. Water is used in virtually every aspect of human activity, from food production and personal hygiene to economic development and, as such, has deep-seated connections to social, cultural, and religious customs. It may seem there is an abundance of water, especially to anybody living in a developed nation where water flows freely and cleanly from the kitchen tap, but scarcity is already a challenge in many areas of the world. Further, it is predicted to become increasingly worse as the world population grows and climate change affects natural precipitation and evaporation patterns. Indeed, over the next 20 years, the available freshwater resources are likely to dwindle by 30 percent.

[Fe4S4]q Cubane Clusters (q = 4+, 3+, 2+) with Terminal Amide Ligands

Bis(trimethylsilyl)amide-ligated iron-sulfur cubane clusters [Fe(4)(mu(3)-S)(4)(N{SiMe(3)}(2))(4)](z) (z = 0, 1-, 2-) are accessible by the reaction of FeCl(N{SiMe(3)}(2))(2)(THF) (1) with 1 equiv of NaSH (z = 0), followed by reduction with either 0.25 (z = 1-) or 1 equiv (z = 2-) of Na(2)S as needed. The anionic clusters are obtained as the sodium salts [Na(THF)(2)][Fe(4)S(4)(N{SiMe(3)}(2))(4)] and [Na(THF)(2)](2)[Fe(4)S(4)(N{SiMe(3)}(2))(4)]; in the solid state, these two clusters both possess a unique contact ion pair motif in which individual sodium ions each coordinate to a cluster core sulfide, an adjacent amide nitrogen, and two THF donors. The monoanionic cluster can also be prepared as the lithium salt [Li(THF)(4)][Fe(4)S(4)(N{SiMe(3)}(2))(4)] by the reaction of 1 with 1:0.5 LiCl/Li(2)S. The characterization of the three-membered redox series allows an analysis of redox trends, as well as a study of the effects of the amide donor environment on the [Fe(4)S(4)] core. Bis(trimethylsilyl)amide terminal ligation significantly stabilizes oxidized cluster redox states, permitting isolation of the uncommon [Fe(4)S(4)](3+) and unprecedented [Fe(4)S(4)](4+) weak-field cores.

Selective Syntheses of Iron−Imide−Sulfide Cubanes, Including a Partial Representation of the Fe−S−X Environment in the FeMo Cofactor

The dinuclear precursors Fe(2)(N(t)Bu)(2)Cl(2)(NH(2)(t)Bu)(2), [Fe(2)(N(t)Bu)(S)Cl(4)](2-), and Fe(2)(NH(t)Bu)(2)(S)(N{SiMe(3)}(2))(2) allowed the selective syntheses of the cubane clusters [Fe(4)(N(t)Bu)(n)(S)(4-n)Cl(4)](z) with [n, z] = [3, 1-], [2, 2-], [1, 2-]. Weak-field iron-sulfur clusters with heteroleptic, nitrogen-containing cores are of interest with respect to observed or conjectured environments in the iron-molybdenum cofactor of nitrogenase. In this context, the present iron-imide-sulfide clusters constitute a new class of compounds for study, with the Fe(4)NS(3) core of the [1, 2-] cluster affording the first synthetic representation of the corresponding heteroligated Fe(4)S(3)X subunit in the cofactor.

Iron–Amide–Sulfide and Iron–Imide–Sulfide Clusters: Heteroligated Core Environments Relevant to the Nitrogenase FeMo Cofactor

Heteroligated cluster cores consisting of weak-field iron, strongly basic nitrogen anions, and sulfide are of interest with respect to observed and conjectured environments in the FeMo cofactor of nitrogenase. Selective syntheses have been developed to achieve such environments with tert-butyl-substituted amide and imide core ligands. A number of different routes were employed, including nominal ligand substitution and oxidative addition reactions, as well as novel transformations involving the combination of different cluster precursors. New cluster products include precursor Fe(2)(μ-NH(t)Bu)(2)[N(SiMe(3))(2)](2) (6), Fe(2)(μ-NH(t)Bu)(2)(μ-S)[N(SiMe(3))(2)](2) (7), which has a rare confacial bitetrahedral geometry previously unknown in iron chemistry, [Fe(2)(μ-N(t)Bu)(μ-S)Cl(4)](2-) (2), and cuboidal [Fe(4)(μ(3)-N(t)Bu)(3)(μ(3)-S)Cl(4)](-) (8), [Fe(4)(μ(3)-N(t)Bu)(2)(μ(3)-S)(2)Cl(4)](2-) (9), and [Fe(4)(μ(3)-N(t)Bu)(μ(3)-S)(3)Cl(4)](2-) (10), as well as selenide-substituted derivatives Fe(2)(μ-NH(t)Bu)(2)(μ-Se)[N(SiMe(3))(2)](2) (7-Se) and [Fe(4)(μ(3)-N(t)Bu)(μ(3)-Se)(3)Cl(4)](2-) (10-Se). The imide-sulfide clusters complete the compositional sets [Fe(2)(μ-N(t)Bu)(n)(μ-S)(2-n)Cl(4)](2-) (n = 0-2) and [Fe(4)(μ(3)-N(t)Bu)(n)(μ(3)-S)(4-n)Cl(4)](z) (n = 0-4), represented previously only by the all-imide and all-sulfide core congeners, and they share chemical and physical properties with the parent homoleptic core species. All imide-sulfide cores are compositionally stable and show no evidence of core ligand exchange over days in solution. Beyond structural differences, the impact of mixed core ligation is most evident in redox potentials, which show progressive decreases of -435 (for z = 1-/2-) or -385 mV (for z = 2-/3-) for each replacement of sulfide by the more potent imide donor, and a corresponding effect may be expected for the interstitial heteroligand in the FeMo cofactor. Cluster 10 presents an [Fe(4)NS(3)] core framework virtually isometric with the isostructural [Fe(4)S(3)X] subunit of the FeMo cofactor, thus providing a synthetic structural representation for this portion of the cofactor core.

Nanotechnology Solutions for Improving Water Quality

Publisher Summary This chapter reveals that nanotechnology has great potential for providing efficient, cost-effective, and environmentally acceptable solutions for improving water quality and for increasing quantities of potable water. Nanomaterials have a number of key physicochemical properties that make them particularly attractive as separation media for water purification. On a mass basis, they have much larger surface areas than bulk particles. Thus, they are ideal building blocks for developing high-capacity sorbents with the ability to be functionalized to enhance their affinity and selectivity. Nanomaterials can serve as high-capacity and recyclable ligands for cations, anions, radionuclides, and organic compounds. They provide unprecedented opportunities for developing more efficient water-purification catalysts and redox active media due to their large surface areas and their size- and shape-dependent optical and electronic properties.

Chapter 35 – Competition for Water

It is clear that in the near future the world will be facing a water crisis, and indeed, many parts of the world already are. The focus of this book has been on ways that nanotechnology may provide solutions to many of the technical problems that are or will result in scarcity and poor water quality. However, there are many potential sources of competition for water, both technical and nontechnical. Some of these, such as corruption and mismanagement, have been creating issues with water for a very long time, whereas others, such as the burgeoning biofuels industry, are only just emerging. It is important that we consider all of the many competitors for clean water and possibility for nanotechnology to address these directly and indirectly.

Nanotechnology in Water: Societal, Ethical, and Environmental Considerations

Potable water is a threatened but critical resource, the scarcity of which is devastating for the developing world. Water-related nanotechnology research has the potential to make safe drinking water inexpensive and accessible to developing countries. This technology also can improve the water infrastructure in developed nations. However, it is imperative that the technology is, first, sustainable and, second, is acceptable by the societies it will serve. This chapter discusses both these issues and addresses what should be considered by researchers and policymakers in the advent of this rapidly developing technology to ensure its responsible development and deployment. Responsible development–including the best use of resources, consideration of societal concerns, and investigation of potential environmental effects—starts in the early stages of research. As the research moves into the development stage, issues of access and parity—including patent and copyright issues and access to the technology—become controversial. Finally, public engagement is necessary to ensure overall acceptance of exotic techniques and novel treatment technologies. Public engagement demands an approach appropriate to both the society as well as the technology, and as such, a relevant case-specific strategy must be developed to coincide with the introduction of new water treatment technologies.

Chapter 33 – Introduction to Societal Issues: The Responsible Development of Nanotechnology for Water

This chapter starts with a quick overview of the subject of nanotechnology and its technical applications in water-related problems such as drinking water, already introduced in previous sections of the book. It then looks at the questions that need to be considered with regard to public acceptance of nanotechnology. Then there is a quick look at the development of nanotechnologies and the way in which experimental technology has been developed previously. Finally, the chapter very briefly introduces some of the relevant forthcoming chapters in the book.

Chapter 34 – Nanotechnology in Water: Societal, Ethical, and Environmental Considerations

Potable water is a threatened but critical resource, the scarcity of which is devastating for the developing world. Water-related nanotechnology research has the potential to make safe drinking water inexpensive and accessible to developing countries. This technology also can improve the water infrastructure in developed nations. However, it is imperative that the technology is, first, sustainable and, second, is acceptable by the societies it will serve. This chapter discusses both these issues and addresses what should be considered by researchers and policymakers in the advent of this rapidly developing technology to ensure its responsible development and deployment. Responsible development–including the best use of resources, consideration of societal concerns, and investigation of potential environmental effects—starts in the early stages of research. As the research moves into the development stage, issues of access and parity—including patent and copyright issues and access to the technology—become controversial. Finally, public engagement is necessary to ensure overall acceptance of exotic techniques and novel treatment technologies. Public engagement demands an approach appropriate to both the society as well as the technology, and as such, a relevant case-specific strategy must be developed to coincide with the introduction of new water treatment technologies.

Introduction to Societal Issues: The Responsible Development of Nanotechnology for Water

This chapter starts with a quick overview of the subject of nanotechnology and its technical applications in water-related problems such as drinking water, already introduced in previous sections of the book. It then looks at the questions that need to be considered with regard to public acceptance of nanotechnology. Then there is a quick look at the development of nanotechnologies and the way in which experimental technology has been developed previously. Finally, the chapter very briefly introduces some of the relevant forthcoming chapters in the book.