**2.3 Spectroscopic and theoretical tools used to study nanoparticle-water interface**

Synchrotron-based [32, 54, 55, 71]. X-ray absorption spectroscopy (XAS) is one of the most structurally and chemically sensitive tools probing solid-water interface [32, 54, 55, 71]. It has been used in many different scientific research fields such as material sciences, chemistry, and environmental sciences [76–79] . Because XAS is non-destructive and element sensitive, it allows to probe the interface between the solid and liquid phases in-situ to elucidate the chemical coordination of metal ions in many different matrices. Furthermore, XAS can simultaneously characterize both the amorphous and crystalline portions of samples which makes it to be one of the most suitable tools to investigate biological and environmental samples because many samples involving nanoparticles and/or environmental matrices are often either non-crystalline or in a solution matrix [80–82]. Much advances in molecular understanding of the interactions of ions in solution with nanoparticle surfaces and the structures of complexes are made since XAS has been used as a research tool. XAS spectroscopy consists of two different complimentary techniques, extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) [76, 78, 80, 83–85]. XANES provides information on the oxidation state, three-dimensional geometry, and coordination environment of the element under investigation while EXAFS provides information on the coordination environment and nearest neighboring atoms to the atom of interest. Of particular, the Extended X-ray absorption fine structure (EXAFS) analyze the oscillatory variation of the X-ray absorption as a function of photon energy beyond an absorption edge. The absorption, normally expressed in terms of absorption coefficient (μ), can be determined from a measurement of the attenuation of X-rays upon their passage through a material. When the X-ray photon energy (E) is tuned to the binding energy of some core level of an atom in the material, an abrupt increase in the absorption coefficient, known as the absorption edge, occurs. For isolated atoms, the absorption coefficient decreases monotonically as a function of energy beyond the edge. For atoms either in a molecule or embedded in a condensed phase, the variation of absorption coefficient at energies above the absorption edge displays a complex fine structure called EXAFS. This is how EXAFS can be used to probe the molecular sorption complex of different metal ions on various surfaces.

In the last 15 years, X-ray absorption spectroscopy (XAS) has found wide application in determination of the local atomic and electronic structures of absorbing centers (atoms) in materials science, physics, chemistry, biology, and geophysics. With its elemental specificity and ability to determine the molecular-scale speciation in situ even at the parts per million concentration range, EXAFS has become a useful method for the analysis of environmentally relevant elements in natural sediment and soils, and in laboratory model system studies involving nanoparticles [83, 86–88]. Quantitative measures of interatomic distances and coordination numbers for the first and second coordination neighbors around specific elements can be obtained based on EXAFS analysis, and these information, especially of the second-shell coordination, provide the means to construct surface complex structures in which an adsorbate ion is bonded to a sorbent surfaces. Sheng et al. [89] studied nanoparticle zero-valent iron (NZVI) interaction with uranium using EXAFS. They found that reduction of highly toxic and mobile UO22+ into less toxic and mobile UO2 could be enhanced using NZVI. Their EXAFS analysis provide evidence to support the proposed detailed reaction mechanisms the iron nanoparticles sequester insoluble products like UO2, and thus more reactive sites could be used for U(VI) reduction and increase the rate and extent of the overall reductive reactions. Others also successfully characterized CuO nanoparticles and

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contaminants.

**3. Nanoparticle applications**

*Novel Applications of Nanoparticles in Nature and Building Materials*

nanocomposites crystal structures and the detailed local electronic structures using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy [85]. Frenkel [90] also demonstrated that mono- and heteroatomic nanoparticles can be modeled using EXAFS experimental data and theory the multiple-scattering FEFF6 theory. Combined with the results of other experimental evidence such as transmission electron microscopy and electron diffraction, EXAFS analysis can be used to determine the size and shape of the nanoparticles with much higher accuracy than any other experimental tools. Synchrotron-based scanning transmission x-ray microscopy (STXM) is another powerful spectroscopic tool capable of both imaging and spectroscopic speciation for samples with ~30 nm spatial resolution under fully hydrated conditions [91–94]. The emergence of combination of microspectroscopic and fluorescence-based techniques with imaging has permitted investigations of carbon containing materials such as microorganisms at nanometer scale. Imaging of nanoparticle samples coupled with X-ray absorption near edge structure (XANES) spectroscopy provides an excellent opportunity to identify and fingerprint the fine structures of carbon and directly image micro to nanometer sized environmental samples with nanometer spatial resolution. More recently, STXM and NEXAFS spectromicroscopic analyses has been effectively employed to investigate soil carbon and mineral associations at a nanometer scale. For example, using the STXM technique, Obst et al. [92] found that cyanobacteria produced an amorphous or nanocrystalline calcium carbonate phase with a short-range structure order. STXM results provided direct evidence that the bacteria induced the formation of the nanocrystliine as part of their metabolic activity on the extracellular polymeric substances (EPS). Because of the spectral data and mapping information provided by STXM technique, they were able to discriminate the nucleation of the amorphous aragonite-like nanoparticles were taking place within the cyanobacteria cell wall structure. Lawrence et al. [95] also reported for the first time the spatial correlation between the copper nanoparticles and natural river biofilms based on the STXM experimental data. Their results of copper nanoparticles dissolved and redistributed in the biofilm lipid and polymers have significant implications on the fate and transport mechanism of the metal particulates in the natural environments. Several other studies were also carried out successfully using STXM to elucidate the nanomaterial sorption reaction with subsequent dissolution and/or re-sorption chemodynamics with bacterial surfaces [96, 97]. Leuf et al. [97] used STXM and identified iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth suggesting the aquatic food chain can be substantially altered due to the presence of the nanoparticles. Clearly, the advances in the spectroscopic and microscopic tools and techniques enhance our understanding of the nanoparticle dynamics with other environmental constituents and their roles in the ecosystem as well as the subsequent effects on the long term fate and transport of other metal

Nanomaterials have gained much attention due to their unique properties. Many engineered nanoparticles, such as nano silver (nano-Ag), nano TiO2 (nano-TiO2), nano aluminum oxide (nano-Al2O3) and carbon nanotubes (CNT), have found potential commercial applications in catalysis, biomedical researches, medicinal applications, etc. Their subsequent impending effects on the ecosystem have also raised concerns over human health and environments as evidence has suggested that engineered nanomaterials are likely to present potential risks. Numerous

*DOI: http://dx.doi.org/10.5772/intechopen.97668*

#### *Novel Applications of Nanoparticles in Nature and Building Materials DOI: http://dx.doi.org/10.5772/intechopen.97668*

*Novel Nanomaterials*

**interface**

**2.3 Spectroscopic and theoretical tools used to study nanoparticle-water** 

sorption complex of different metal ions on various surfaces.

In the last 15 years, X-ray absorption spectroscopy (XAS) has found wide application in determination of the local atomic and electronic structures of absorbing centers (atoms) in materials science, physics, chemistry, biology, and geophysics. With its elemental specificity and ability to determine the molecular-scale speciation in situ even at the parts per million concentration range, EXAFS has become a useful method for the analysis of environmentally relevant elements in natural sediment and soils, and in laboratory model system studies involving nanoparticles [83, 86–88]. Quantitative measures of interatomic distances and coordination numbers for the first and second coordination neighbors around specific elements can be obtained based on EXAFS analysis, and these information, especially of the second-shell coordination, provide the means to construct surface complex structures in which an adsorbate ion is bonded to a sorbent surfaces. Sheng et al. [89] studied nanoparticle zero-valent iron (NZVI) interaction with uranium using EXAFS. They found that reduction of highly toxic and mobile UO22+ into less toxic and mobile UO2 could be enhanced using NZVI. Their EXAFS analysis provide evidence to support the proposed detailed reaction mechanisms the iron nanoparticles sequester insoluble products like UO2, and thus more reactive sites could be used for U(VI) reduction and increase the rate and extent of the overall reductive reactions. Others also successfully characterized CuO nanoparticles and

Synchrotron-based [32, 54, 55, 71]. X-ray absorption spectroscopy (XAS) is one of the most structurally and chemically sensitive tools probing solid-water interface [32, 54, 55, 71]. It has been used in many different scientific research fields such as material sciences, chemistry, and environmental sciences [76–79] . Because XAS is non-destructive and element sensitive, it allows to probe the interface between the solid and liquid phases in-situ to elucidate the chemical coordination of metal ions in many different matrices. Furthermore, XAS can simultaneously characterize both the amorphous and crystalline portions of samples which makes it to be one of the most suitable tools to investigate biological and environmental samples because many samples involving nanoparticles and/or environmental matrices are often either non-crystalline or in a solution matrix [80–82]. Much advances in molecular understanding of the interactions of ions in solution with nanoparticle surfaces and the structures of complexes are made since XAS has been used as a research tool. XAS spectroscopy consists of two different complimentary techniques, extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) [76, 78, 80, 83–85]. XANES provides information on the oxidation state, three-dimensional geometry, and coordination environment of the element under investigation while EXAFS provides information on the coordination environment and nearest neighboring atoms to the atom of interest. Of particular, the Extended X-ray absorption fine structure (EXAFS) analyze the oscillatory variation of the X-ray absorption as a function of photon energy beyond an absorption edge. The absorption, normally expressed in terms of absorption coefficient (μ), can be determined from a measurement of the attenuation of X-rays upon their passage through a material. When the X-ray photon energy (E) is tuned to the binding energy of some core level of an atom in the material, an abrupt increase in the absorption coefficient, known as the absorption edge, occurs. For isolated atoms, the absorption coefficient decreases monotonically as a function of energy beyond the edge. For atoms either in a molecule or embedded in a condensed phase, the variation of absorption coefficient at energies above the absorption edge displays a complex fine structure called EXAFS. This is how EXAFS can be used to probe the molecular

**342**

nanocomposites crystal structures and the detailed local electronic structures using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy [85]. Frenkel [90] also demonstrated that mono- and heteroatomic nanoparticles can be modeled using EXAFS experimental data and theory the multiple-scattering FEFF6 theory. Combined with the results of other experimental evidence such as transmission electron microscopy and electron diffraction, EXAFS analysis can be used to determine the size and shape of the nanoparticles with much higher accuracy than any other experimental tools.

Synchrotron-based scanning transmission x-ray microscopy (STXM) is another powerful spectroscopic tool capable of both imaging and spectroscopic speciation for samples with ~30 nm spatial resolution under fully hydrated conditions [91–94]. The emergence of combination of microspectroscopic and fluorescence-based techniques with imaging has permitted investigations of carbon containing materials such as microorganisms at nanometer scale. Imaging of nanoparticle samples coupled with X-ray absorption near edge structure (XANES) spectroscopy provides an excellent opportunity to identify and fingerprint the fine structures of carbon and directly image micro to nanometer sized environmental samples with nanometer spatial resolution. More recently, STXM and NEXAFS spectromicroscopic analyses has been effectively employed to investigate soil carbon and mineral associations at a nanometer scale. For example, using the STXM technique, Obst et al. [92] found that cyanobacteria produced an amorphous or nanocrystalline calcium carbonate phase with a short-range structure order. STXM results provided direct evidence that the bacteria induced the formation of the nanocrystliine as part of their metabolic activity on the extracellular polymeric substances (EPS). Because of the spectral data and mapping information provided by STXM technique, they were able to discriminate the nucleation of the amorphous aragonite-like nanoparticles were taking place within the cyanobacteria cell wall structure. Lawrence et al. [95] also reported for the first time the spatial correlation between the copper nanoparticles and natural river biofilms based on the STXM experimental data. Their results of copper nanoparticles dissolved and redistributed in the biofilm lipid and polymers have significant implications on the fate and transport mechanism of the metal particulates in the natural environments. Several other studies were also carried out successfully using STXM to elucidate the nanomaterial sorption reaction with subsequent dissolution and/or re-sorption chemodynamics with bacterial surfaces [96, 97]. Leuf et al. [97] used STXM and identified iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth suggesting the aquatic food chain can be substantially altered due to the presence of the nanoparticles. Clearly, the advances in the spectroscopic and microscopic tools and techniques enhance our understanding of the nanoparticle dynamics with other environmental constituents and their roles in the ecosystem as well as the subsequent effects on the long term fate and transport of other metal contaminants.
