**2.1 Iron oxide nanoparticles**

*Novel Nanomaterials*

**Figure 1.**

**Solid Phase Typical size** 

Goethite A few nm to

Hematite A few nm to

Glauconite A few nm to

**(nm)**

Ferrihydrite 2–10 Irregular and

micrometer

micrometer

100 nm

A few to hundreds nm

*Examples of naturally occurring nanoparticles in various environments.*

< 200 nm Rounded or

with various environmental constituents and by comparing those results of the nanoparticles to that of microparticles to elucidate the role of nanoparticles in the environment. A wide range of nanoparticle phases has been reported in various environmental conditions as shown in **Table 1**. Of particular, the dependence of aquatic chemical reactivity of iron oxides on particle size is important because iron oxide plays a key role in the geocycling of elements, rock weathering and soil formation, as well as in the transport of aqueous metal species and contaminants. Iron oxide clusters are also found in living organisms (e.g., plants, bacteria, molluscs, fish, birds, and humans). They are also applied to (nano)technologies, including alternative energy, catalysis, electronics, optoelectronics, memory devices, corrosion protection, cleaning of waters and control of acid mine drainage, radioactive waste storage and disposal, flotation, pigments, magnetocaloric refrigeration, colour imaging, biochemical engineering, sensors, and other surface-based

spherical

Rounded or platy

Magnetite Several nm Octahedron Anoxic soils and sediments [28]

Gold < 200 nm Platy Groundwater, mining pits [31]

platy

Rounded or platy

**Shape Environments Reference**

Oxic surface water and soils, bacterial surfaces

> Oxic water, bacterial surfaces

bacterial surfaces

Bacterial surfaces, anoxic soil and water

Acicular Soils, water [28]

Acicular Anoxic soils and sediments,

[28]

[28, 29]

[28, 30]

[32]

[33, 34]

*A nanoparticle of 5 nm core diameter with different organic molecules drawn to scale.*

**334**

**Table 1.**

Aluminum Oxide

Manganese Oxide

Hematite (α-Fe2O3) is one of the most naturally abundant iron oxide mineral phases [12, 22–24, 28]. It is also a commonly present in a nanoparticle form, occurring in soils, acid mine drainage effluent, and on bacterial surfaces as well as in atmospheric dusts (**Figure 2**). Iron is one of the essential element in governing the biogeochemical cycling of nutrients in marines and sedimentary environments. During the iron cycling process in those environment, various nanostructures of iron oxides and oxyhydroxides form and persist under certain conditions, especially at redox and pH interfaces [29]. Recent surveys on the global budget of naturally occurring iron oxide nanostructures suggest 105 Tg (teragram) of iron oxide including hematite phase is introduced annually in soil by mass [30]. The ubiquitous existence of hematite nanoparticles has a significant implication on fate on toxic heavy metal contaminants. For example, heavy metals such as Cr and U that are introduced to environments by anthropogenic activities such as mining and spills can be effectively sequestered by iron oxide nanostructures through sorption and precipitation reactions due to the thermodynamically active nanomorphologies and crystallinity of the nanparticulate phase. It has been shown that the adsorption capacities of Cr and U by ferrihydrite decrease remarkably with either increasing

#### **Figure 2.**

*(A) Powder X-ray diffraction pattern of hematite microparticles (HM) compared with the reference XRD pattern of hematite46 and the TEM image of HM; (B) Powder X-ray diffraction pattern of hematite nanoparticles (HN) compared with the reference XRD pattern of hematite.*

crystallinity or transformation to more crystalline phases (such as goethite or hematite) further confirming the effectiveness of the nanoparticle phases in contaminant removal [31–33].

Moreover, hematite nanoparticles recently has received much attention from industry for different applications due to their unique properties, such as extremely small size, high surface-area-to-volume ratio, surface modifiability, excellent magnetic properties and great biocompatibility. A range of environmental clean-up technologies have been proposed in wastewater treatment which applied iron oxide nanomaterials as nanosorbents and photocatalysts [34]. Nanoscale zero-valent iron (nZVI) is an example of extensively applied iron nanomaterials for groundwater and hazardous waste treatment. Over the past decade, nZVI synthesis and application have been comprehensively investigated for its remediation applications focusing on enhanced sequestration of a wide spectrum of contaminants in addition to the well-documented chlorinated solvents both in the laboratory and field experiments [25, 32, 35–37]. At least 50 successful field applications of nZVI for in-situ groundwater and soil cleanup worldwide were reported by recent reviews by Karn et al. [38] and Mueller et al. [39]. As the application of the nZVI gained more attention, colloidal stability and transport properties of nZVI in porous media, and the effects of nZVI amendment on the biogeochemical environment were also studied in order to understand the impacts of the nZVI in the environment once released [25, 35, 40]. Dong et al. [40] observed the presence of humic acid increases the stability of nZVI in the aqueous phase due to enhanced the electrosteric repulsion effect but it can also cause coagulation among nZVI particules via bridging effect if too much humic acid is present. Hence, the nanoparticle stability and transport behavior depends on the concentrations of other environmental constituents, especially organic acids, both in aqueous and soil environments. Further studies are needed to enhance the colloidal stability and transport properties of nZVI in porous media to fully understand effects of nZVI on the biogeochemical environment.

Lastly, iron oxide nanoparticles have received a great attention recently in biomedical applications due to their non-toxic role in the biological systems [41–43]. Iron oxide nanoparticles have both magnetic behavior and semiconductor property, which lead to multifunctional biomedical imaging applications. According to Chen et al. [41] gold coated nanoparticle of iron oxide has enhanced magnetic properties compared to the same phase of larger particles. Cheong et al. [43] similarly reported greater cellular MRI contrast enhancement of nanoparticles compared to iron oxides of a bigger size without increase in cytotoxicity. Iron oxide nanoparticles also became popular for its application in biomedical fields as antibacterial, antifungal and anticancer agents as well as bone marrow treatments and cell labelling activities for its unique biocompatibility, biodegradability, ease of synthesis and different magnetic behaviors [44].

In addition to the above reported laboratory synthesized nanoparticles, iron oxide nanoparticles exist in nature at low-temperature environmental conditions and places that have high degrees of supersaturation. The supersaturation condition is typically created by changing the physical and chemical conditions, such as influx of Fe(II)-rich hydrothermal vent fluids, mixing of highly acidic solutions with neutral pH water, and the evaporation of soil solutions [12, 22–24, 45, 46]. Once formed, iron oxide and oxyhydroxide nanoparticles are redistributed by rivers, glaciers, winds, and ocean currents into various ecosystems, where they can undergo continuous phase transformations, dissolution, and morphology changes. One potentially important role played by naturally occurring hematite nanoparticles is their interaction with various types of organic acids. In many natural environmental settings, ubiquitous presence of naturally occurring low-molecular weight (LMW) organic compounds and nanoparticles often controls the fate and transport

**337**

**Figure 3.**

*Novel Applications of Nanoparticles in Nature and Building Materials*

behavior of many heavy metal contaminants by sorption and/or co-precipitation processes. For example, mobile nanoparticles can serve as carriers for strongly sorbed contaminants and thereby facilitate contaminant transport in soils, groundwater aquifers, and fractured rocks [21, 25]. The colloidal stability of nanoparticles is greatly influenced by the presence of adsorbed natural organic matter. Recent studies have suggested that sorption of organic acids can dramatically enhance the particle-based transport of heavy metal contaminants by physically stabilizing contaminant-containing nanoparticles in aquatic environments [47, 48]. In addition, the organic matters typically bind strongly to common iron- and aluminum- (oxy)hydroxide minerals as well as to heavy metal contaminants (e.g., Pb, Hg, Cr, and Zn) under circumneutral to moderately acidic pH conditions [47, 49, 50]. Therefore, the nature of bonding between organic species and nanoparticle surfaces can substantially alter the properties of mineral nanoparticle-water interfaces and

Ha et al. [51] studied the interaction of the L-lactate ion (L-CH3CH(OH)COO<sup>−</sup>

Lact−1) with hematite (α-Fe2O3) nanoparticles (average diameter 11 nm) in the presence of bulk water at pH 5. Their combined dissolution and ATR-FTIR spectroscopy data suggested different hydrogen bonding environments was found as Lact−1 surface coverage on hematite nanoparticle surfaces increases which resulted in a concomitant increase in Fe(III) dissolution from the hematite nanoparticles due

*(Left) Fit of ATR-FTIR spectra of aqueous deprotonated lactate species, aqueous Fe(III)-lactate complex, and Lact-1 species at the hematite/water interface at 25oC, pH 5.0 and 0.01 M and 0.5M of NaCl for different Lact-1 surface coverages.(Top Right) Molecular model for Lact-1 sorption on monomer and dimetric Fe cluster unit. (Bottom Right) Fit of ATR-FTIR spectra of aqueous deprotonated lactate species, aqueous Fe(III)-lactate complex, and Lact-1 species at the hematite/water interface at 25oC, pH 5.0 and 0.01 M and 0.5M of NaCl for* 

*different Lact-1 surface coverages demonstrating different surface complexation*

,

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

thereby affect the geochemical cycling of metals.

to the inner-sphere complex formation as shown in **Figure 3**.

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

*Novel Nanomaterials*

removal [31–33].

crystallinity or transformation to more crystalline phases (such as goethite or hematite) further confirming the effectiveness of the nanoparticle phases in contaminant

Moreover, hematite nanoparticles recently has received much attention from industry for different applications due to their unique properties, such as extremely small size, high surface-area-to-volume ratio, surface modifiability, excellent magnetic properties and great biocompatibility. A range of environmental clean-up technologies have been proposed in wastewater treatment which applied iron oxide nanomaterials as nanosorbents and photocatalysts [34]. Nanoscale zero-valent iron (nZVI) is an example of extensively applied iron nanomaterials for groundwater and hazardous waste treatment. Over the past decade, nZVI synthesis and application have been comprehensively investigated for its remediation applications focusing on enhanced sequestration of a wide spectrum of contaminants in addition to the well-documented chlorinated solvents both in the laboratory and field experiments [25, 32, 35–37]. At least 50 successful field applications of nZVI for in-situ groundwater and soil cleanup worldwide were reported by recent reviews by Karn et al. [38] and Mueller et al. [39]. As the application of the nZVI gained more attention, colloidal stability and transport properties of nZVI in porous media, and the effects of nZVI amendment on the biogeochemical environment were also studied in order to understand the impacts of the nZVI in the environment once released [25, 35, 40]. Dong et al. [40] observed the presence of humic acid increases the stability of nZVI in the aqueous phase due to enhanced the electrosteric repulsion effect but it can also cause coagulation among nZVI particules via bridging effect if too much humic acid is present. Hence, the nanoparticle stability and transport behavior depends on the concentrations of other environmental constituents, especially organic acids, both in aqueous and soil environments. Further studies are needed to enhance the colloidal stability and transport properties of nZVI in porous media to fully understand effects of nZVI on the biogeochemical environment. Lastly, iron oxide nanoparticles have received a great attention recently in biomedical applications due to their non-toxic role in the biological systems [41–43]. Iron oxide nanoparticles have both magnetic behavior and semiconductor property, which lead to multifunctional biomedical imaging applications. According to Chen et al. [41] gold coated nanoparticle of iron oxide has enhanced magnetic properties compared to the same phase of larger particles. Cheong et al. [43] similarly reported greater cellular MRI contrast enhancement of nanoparticles compared to iron oxides of a bigger size without increase in cytotoxicity. Iron oxide nanoparticles also became popular for its application in biomedical fields as antibacterial, antifungal and anticancer agents as well as bone marrow treatments and cell labelling activities for its unique biocompatibility, biodegradability, ease of synthesis and different

In addition to the above reported laboratory synthesized nanoparticles, iron oxide nanoparticles exist in nature at low-temperature environmental conditions and places that have high degrees of supersaturation. The supersaturation condition is typically created by changing the physical and chemical conditions, such as influx of Fe(II)-rich hydrothermal vent fluids, mixing of highly acidic solutions with neutral pH water, and the evaporation of soil solutions [12, 22–24, 45, 46]. Once formed, iron oxide and oxyhydroxide nanoparticles are redistributed by rivers, glaciers, winds, and ocean currents into various ecosystems, where they can undergo continuous phase transformations, dissolution, and morphology changes. One potentially important role played by naturally occurring hematite nanoparticles is their interaction with various types of organic acids. In many natural environmental settings, ubiquitous presence of naturally occurring low-molecular weight (LMW) organic compounds and nanoparticles often controls the fate and transport

**336**

magnetic behaviors [44].

behavior of many heavy metal contaminants by sorption and/or co-precipitation processes. For example, mobile nanoparticles can serve as carriers for strongly sorbed contaminants and thereby facilitate contaminant transport in soils, groundwater aquifers, and fractured rocks [21, 25]. The colloidal stability of nanoparticles is greatly influenced by the presence of adsorbed natural organic matter. Recent studies have suggested that sorption of organic acids can dramatically enhance the particle-based transport of heavy metal contaminants by physically stabilizing contaminant-containing nanoparticles in aquatic environments [47, 48]. In addition, the organic matters typically bind strongly to common iron- and aluminum- (oxy)hydroxide minerals as well as to heavy metal contaminants (e.g., Pb, Hg, Cr, and Zn) under circumneutral to moderately acidic pH conditions [47, 49, 50]. Therefore, the nature of bonding between organic species and nanoparticle surfaces can substantially alter the properties of mineral nanoparticle-water interfaces and thereby affect the geochemical cycling of metals.

Ha et al. [51] studied the interaction of the L-lactate ion (L-CH3CH(OH)COO<sup>−</sup> , Lact−1) with hematite (α-Fe2O3) nanoparticles (average diameter 11 nm) in the presence of bulk water at pH 5. Their combined dissolution and ATR-FTIR spectroscopy data suggested different hydrogen bonding environments was found as Lact−1 surface coverage on hematite nanoparticle surfaces increases which resulted in a concomitant increase in Fe(III) dissolution from the hematite nanoparticles due to the inner-sphere complex formation as shown in **Figure 3**.

#### **Figure 3.**

*(Left) Fit of ATR-FTIR spectra of aqueous deprotonated lactate species, aqueous Fe(III)-lactate complex, and Lact-1 species at the hematite/water interface at 25oC, pH 5.0 and 0.01 M and 0.5M of NaCl for different Lact-1 surface coverages.(Top Right) Molecular model for Lact-1 sorption on monomer and dimetric Fe cluster unit. (Bottom Right) Fit of ATR-FTIR spectra of aqueous deprotonated lactate species, aqueous Fe(III)-lactate complex, and Lact-1 species at the hematite/water interface at 25oC, pH 5.0 and 0.01 M and 0.5M of NaCl for different Lact-1 surface coverages demonstrating different surface complexation*

Lenhart et al. [52] also reported the impacts of fumaric acid and maleic acid, which are naturally occurring dicarboxylic acids, on aggregation kinetics of nanosized hematite. Interestingly, they found that the structure and orientation of the adsorbed dianion at the hematite surface, not the adsorption mechanism, defined the resulting effect. Maleate, which directed both carboxyl groups to the surface in the form of inner- and outer-sphere surface complexes, enhanced colloidal stability. Fumarate, however, which bounded to the hematite surface as an outer-sphere complex with just one carboxyl group only slightly influenced particle stability. Their research outcome suggested that subtle differences in the structure of adsorbed acids produced important differences in the physicochemical behavior of particles in dilute aquatic systems. Another study by Dickson et al. [47] similarly suggested that the surface chemical reactions and dissolution of the iron oxide nanoparticles strongly depend on the presence of organic molecules. They found significantly increased aggregation and sedimentation reactions of iron oxide nanoparticles in presence of humic acids regardless of different ionic strength of the solution. Their results suggested that understanding the effects of important environmental factors on the stability of nanoparticles is key to fully and accurately be able to predict the mobility of the nanoparticles in aquatic environment.

On the contrary, Palomino and Stoll [53] identified that iron oxide nanoparticle aggregation process significantly depends on the solution pH conditions even in the presence of fulvic acids. Dispersion and stability of the nanoparticles were maintained only at pH conditions of which the surface charge of the nanoparticles remained positive regardless of the fulvic acid concentrations. Their results showed that the examined environmentally relevant range of fulvic acid concentrations were expected to promote not only the nanoparticle stabilization but also the disaggregation of nanoparticle aggregates, but only at very low concentrations of fulvic acid and specific solution pH conditions. This finding suggests that hematite nanoparticle behavior in natural aquatic environments are much more complex and dynamic that it cannot generalized or linearly predicted based on a single parameter. A recent study by Xu et al. [50] presented laboratory experimental results to simulate more environmentally relevant conditions by investigating the hematite nanoparticles coated with naturally found peat humic acid and soil humic acid. Their model system reflects the fact that hematite nanoparticles exist naturally and ubiquitously in soil, and they are always associated with soil organic matter by forming organic–inorganic complexes. In this work, the organic coated hematite nanoparticles reacted with hydrophobic organic contaminants (HOCs) to simulate the sorption processes in soil. The sorption of HOCs on organic acid coated nanoparticles were inhibited with increasing pH values of solution due to the deprotonation reaction of the organic acid functional groups within the adsorbed humic acids. Their findings further elucidated the mechanisms involved in contaminant sorption processes by organic acids coated hematite nanoparticles are complex reactions governed both by the surface complex structures formed within the mineral-water interfaces as well as the solution chemistry of the aquatic environments. Results on sorption of a commonly occurring pollutant, Zn(II), on hematite nanoparticles in presence or absence of dicarboxylate organic compound, oxalate, also identified the complexity of the nanoparticle reactions with naturally occurring constituents [54, 55]. At higher concentrations of Zn(II), formation of surface precipitates on hematite nanoparticles was observed based on comparison of the EXAFS spectra of the sorption samples with that of zinc-bearing hydrotalcite (Zn6Al2(CO3)(OH)16•4H2O), Cauchy wavelet analysis, and fitting of the Zn K-edge EXAFS data. On the contrary, no surface precipitate was observed on the bigger size hematite particles even at the same concentrations of Zn(II) suggesting enhanced dissolution of hematite nanoparticles was promoted by the divalent metal ions in

**339**

*(iv) 568.49 micromol/g; (v) 640.19 micromol/g.*

**Figure 4.**

*Novel Applications of Nanoparticles in Nature and Building Materials*

reactions of organic matter with nanoparticles in the environment.

chemical reactions on hematite nanoparticles persist.

solution (**Figure 4**). Similarly, different types of Zn(II) surface complex structures formed in the presence of oxalate on hematite nanoparticle surfaces. These studies provide a direct comparative and quantitative evidence that different surface

There are still many open questions regarding the ability of surface reactions to alter the fate and toxicity of nanoparticles in the environment. Evidence so far suggests that surface coatings and complexation with organic acids affect nanoparticle fate and transport mechanisms hence consequently impact nanoparticle toxicity in the environment. However, as surfactant adsorption on silica nanoparticle studies revealed that such surface complexation reaction can be readily reversible so that desorption can be kinetic reactions whereas adsorption for high molecular weight polymers is essentially an irreversible process [56, 57]. Clearly, the fate of nanomaterials in the environment is highly dependent on their surface coatings and reactions, hence, it is imperative to understand the fate of these coatings and surface

Bacteria can be considered as another extension of organic compounds in the natural environment. Similar to LMW organic acids, they have been shown to exhibit a strong affinity for heavy metal contaminants and metal (oxyhydr)oxide surfaces through reactions such as sorption, bioaccumulation, and precipitation [52, 58–60]. With their estimated biomass close to the total amount of carbon in plants [61], they can potentially passivate naturally occurring mineral surfaces

*(Left) (A) Background-subtracted, normalized, and k3-weighted Zn K-edge EXAFS spectra of Zn(II) sorbed on hematite nanoparticles (HN) at different Zn surface coverages, and corresponding Fourier transforms (not phase-shift corrected) of sorption samples with following surface concentration: (i) 68.35 micromol/g; (ii) 195.80 micromol/g; (iii) 384.92 micromol/g; (iv)568.49 micromol/g; (v) 640.19 micromol/g; (B) Background-subtracted, normalized, and k3-weighted Zn K-edge EXAFS spectra of Zn sorbed on hematite microparticles (HM) at similar Zn surface coverages, and corresponding Fourier transforms (not phase-shift corrected) of sorption samples. (Right) Zn K-edge XANES spectra of Zn/HN sorption samples and four reference compounds: (i) 68.35 micromol/g; (ii) 195.80 micromol/g; (iii) 384.92 micromol/g;* 

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

**2.2 Nanoparticles and microorganisms**

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

*Novel Nanomaterials*

Lenhart et al. [52] also reported the impacts of fumaric acid and maleic acid, which are naturally occurring dicarboxylic acids, on aggregation kinetics of nanosized hematite. Interestingly, they found that the structure and orientation of the adsorbed dianion at the hematite surface, not the adsorption mechanism, defined the resulting effect. Maleate, which directed both carboxyl groups to the surface in the form of inner- and outer-sphere surface complexes, enhanced colloidal stability. Fumarate, however, which bounded to the hematite surface as an outer-sphere complex with just one carboxyl group only slightly influenced particle stability. Their research outcome suggested that subtle differences in the structure of adsorbed acids produced important differences in the physicochemical behavior of particles in dilute aquatic systems. Another study by Dickson et al. [47] similarly suggested that the surface chemical reactions and dissolution of the iron oxide nanoparticles strongly depend on the presence of organic molecules. They found significantly increased aggregation and sedimentation reactions of iron oxide nanoparticles in presence of humic acids regardless of different ionic strength of the solution. Their results suggested that understanding the effects of important environmental factors on the stability of nanoparticles is key to fully and accurately be able to predict the

On the contrary, Palomino and Stoll [53] identified that iron oxide nanoparticle aggregation process significantly depends on the solution pH conditions even in the presence of fulvic acids. Dispersion and stability of the nanoparticles were maintained only at pH conditions of which the surface charge of the nanoparticles remained positive regardless of the fulvic acid concentrations. Their results showed that the examined environmentally relevant range of fulvic acid concentrations were expected to promote not only the nanoparticle stabilization but also the disaggregation of nanoparticle aggregates, but only at very low concentrations of fulvic acid and specific solution pH conditions. This finding suggests that hematite nanoparticle behavior in natural aquatic environments are much more complex and dynamic that it cannot generalized or linearly predicted based on a single parameter. A recent study by Xu et al. [50] presented laboratory experimental results to simulate more environmentally relevant conditions by investigating the hematite nanoparticles coated with naturally found peat humic acid and soil humic acid. Their model system reflects the fact that hematite nanoparticles exist naturally and ubiquitously in soil, and they are always associated with soil organic matter by forming organic–inorganic complexes. In this work, the organic coated hematite nanoparticles reacted with hydrophobic organic contaminants (HOCs) to simulate the sorption processes in soil. The sorption of HOCs on organic acid coated nanoparticles were inhibited with increasing pH values of solution due to the deprotonation reaction of the organic acid functional groups within the adsorbed humic acids. Their findings further elucidated the mechanisms involved in contaminant sorption processes by organic acids coated hematite nanoparticles are complex reactions governed both by the surface complex structures formed within the mineral-water interfaces as well as the solution chemistry of the aquatic environments. Results on sorption of a commonly occurring pollutant, Zn(II), on hematite nanoparticles in presence or absence of dicarboxylate organic compound, oxalate, also identified the complexity of the nanoparticle reactions with naturally occurring constituents [54, 55]. At higher concentrations of Zn(II), formation of surface precipitates on hematite nanoparticles was observed based on comparison of the EXAFS spectra of the sorption samples with that of zinc-bearing hydrotalcite (Zn6Al2(CO3)(OH)16•4H2O), Cauchy wavelet analysis, and fitting of the Zn K-edge EXAFS data. On the contrary, no surface precipitate was observed on the bigger size hematite particles even at the same concentrations of Zn(II) suggesting enhanced dissolution of hematite nanoparticles was promoted by the divalent metal ions in

mobility of the nanoparticles in aquatic environment.

**338**

solution (**Figure 4**). Similarly, different types of Zn(II) surface complex structures formed in the presence of oxalate on hematite nanoparticle surfaces. These studies provide a direct comparative and quantitative evidence that different surface chemical reactions on hematite nanoparticles persist.

There are still many open questions regarding the ability of surface reactions to alter the fate and toxicity of nanoparticles in the environment. Evidence so far suggests that surface coatings and complexation with organic acids affect nanoparticle fate and transport mechanisms hence consequently impact nanoparticle toxicity in the environment. However, as surfactant adsorption on silica nanoparticle studies revealed that such surface complexation reaction can be readily reversible so that desorption can be kinetic reactions whereas adsorption for high molecular weight polymers is essentially an irreversible process [56, 57]. Clearly, the fate of nanomaterials in the environment is highly dependent on their surface coatings and reactions, hence, it is imperative to understand the fate of these coatings and surface reactions of organic matter with nanoparticles in the environment.

#### **2.2 Nanoparticles and microorganisms**

Bacteria can be considered as another extension of organic compounds in the natural environment. Similar to LMW organic acids, they have been shown to exhibit a strong affinity for heavy metal contaminants and metal (oxyhydr)oxide surfaces through reactions such as sorption, bioaccumulation, and precipitation [52, 58–60]. With their estimated biomass close to the total amount of carbon in plants [61], they can potentially passivate naturally occurring mineral surfaces

#### **Figure 4.**

*(Left) (A) Background-subtracted, normalized, and k3-weighted Zn K-edge EXAFS spectra of Zn(II) sorbed on hematite nanoparticles (HN) at different Zn surface coverages, and corresponding Fourier transforms (not phase-shift corrected) of sorption samples with following surface concentration: (i) 68.35 micromol/g; (ii) 195.80 micromol/g; (iii) 384.92 micromol/g; (iv)568.49 micromol/g; (v) 640.19 micromol/g; (B) Background-subtracted, normalized, and k3-weighted Zn K-edge EXAFS spectra of Zn sorbed on hematite microparticles (HM) at similar Zn surface coverages, and corresponding Fourier transforms (not phase-shift corrected) of sorption samples. (Right) Zn K-edge XANES spectra of Zn/HN sorption samples and four reference compounds: (i) 68.35 micromol/g; (ii) 195.80 micromol/g; (iii) 384.92 micromol/g; (iv) 568.49 micromol/g; (v) 640.19 micromol/g.*

either hindering or enhancing the reactivity of the underlying mineral surfaces. The resulted the cell-mineral surface interactions occurring in natural soil and water environments can retain pollutants in great extent [62, 63]. Therefore, the presence of microorganisms can result in significant modification of metal speciation or contaminant sequestration and transport, and hence, investigating the interfaces of bacteria-metal and bacteria-mineral surfaces is essential in predicting the mobility of heavy metal contaminants accurately and quantitatively.

More importantly, understanding the dynamics of the bacterial interaction with engineered and/or naturally occurring NPs have received significant attention because the fate and transport reactions and mechanisms of them in the terrestrial and aquatic environments strongly depend on the nature and extent of the bacterial sorption and reduction of the nanoparticles [64]. For example, Schwegmann et al. [65] observed iron oxide nanoparticle sorption on microorganisms (*Saccharomyces cerevisiae* and *Escherichia coli*) significantly shifted the point of zero charge for bacteria. Their results imply that overall electrostatic interaction between dissolved heavy metal contaminants and bacteria can be considerably altered due to the presence of the nanoparticles. Another study showed an enhanced removal of the heavy metals from the solution phase in conventional activated sludge wastewater treatment plants when nanoparticles were added to reactors including different types of bacteria. This study suggested that the production and transformations of the surface properties of biomass due to NP would be key factors in determining the fate of the waste toxic metals in the environment [66]. Droz et al. [67] observed biogenic MnO2 nanoparticles affected a wide range of metal fate and transport in natural and engineered systems by strongly sorbing metals ions.

Of particular importance, the dissimilatory microbial iron reduction is one of the important processes in determining the biogeochemical cycling of iron under anaerobic conditions and has significant influences on the aqueous geochemistry and mineralogy of sedimentary environments [68, 69]. Iron cycling has dramatic implications for trace element and heavy metal contaminant mobility, and the complex interplay of biological and chemical processes determine the extent and reaction pathways of iron cycling in the environment [69]. Past studies have identified many different chemical and biological factors controlling the microbial reduction of iron oxides, yet the role of nanoparticles in determining the extent and reaction pathways for dissimilatory iron reduction are still poorly understood. Despite the important roles of nanoparticles, current molecular-level understanding on the interaction of organic compounds, metals, and microorganisms with nanoparticle surfaces and the resulting impacts on pollutant speciation at nanoparticle-water interfaces are very limited. One of the main reasons for this limitation is lack of appropriate tools with high resolution and/or high sensitivity to molecular structural changes occurring on nanometer scales. In addition, ability to study the materials in situ, i.e., in presence of water with minimal alteration of the sample from its natural state, has been limited. For many environmental samples, especially those involving interactions at solid-water interfaces, the presence of water plays a critical role.

Due to the small size of particles, different mechanisms and processes have been observed when bacteria interacts with nanoparticles. For example, a greater bioavailability of iron was observed when iron nanoparticle reacted with *Pseudomonas mendocina* bacteria [70] because of the possible penetration of the nanoparticles through the cell membrane and proximity of the particles to the bacteria. Sulfatereducing bacteria (*Desulfovibrio desulfuricans*) also showed different metabolic responses in presence of iron oxide nanoparticles and generated biogenic pyrrhotite formation suggesting a potential impact of iron oxide nanoparticles on geomagnetic

**341**

**Figure 5.**

*and (F) Fe L-edge (709.5 eV).*

*Novel Applications of Nanoparticles in Nature and Building Materials*

field behavior of sediments. Different dissimilatory reduction of hematite nanoparticles and microparticles were also observed for *Shewanella oneidensis* bacteria [71]. Results show that proximity and encapsulation of the nanoparticles near the cell membrane allowed different iron oxide reductive mechanisms resulting in a significantly enhanced iron oxide reductive transformation rates by *Shewanella oneidensis* (**Figure 5**)*.* Clearly different reaction pathways and microbial responses toward nano-meter materials are present compared to the larger particle size even

Nanoparticles are also generated by a biogenic enzymatic process and used as engineered materials. The development of eco-friendly technologies in material synthesis has become important and widely applied. Synthesis of nanoparticles using different microorganisms, and their applications in many cutting-edge technological areas have been explored. Recent study shows that biogenically generated iron(III) (oxyhydr)oxide (Fe(OH)3) clusters by gram positive bacteria *Clostridium* could be used to create lithium storage capacity [72]. This study provides another potential use of hematite nanoparticles as a substitute for an industrial product. Other studies also have found that many microorganisms can produce different types of inorganic nanoparticles through either intracellular or extracellular routes, and such biosynthesized nanoparticles have been used in a variety of applications including drug carriers for targeted delivery, cancer treatment, gene therapy and DNA analysis, antibacterial agents, biosensors, enhancing reaction rates, separation science, and magnetic resonance imaging (MRI) [50, 73–75]. As shown, there have been tremendous developments in the field of microorganismproduced nanoparticles and their applications over the last decade. However, much work is needed to improve the synthesis efficiency and the control of particle size

*STXM images of S. oneidensis WT strain and hematite nanoparticle reacted for 98 hr under anaerobic condition at initial hematite concentration of 1mM in an aqueous suspension measured at (A) C K-edge (288.2 eV) and (D) Fe L-edge (709.5 eV). The outlined areas labeled in (A) and (D) are shown in higher magnification at (B) below C K-edge (280.0 eV), (C) C K-edge (288.2 eV), (E) below Fe L-edge (700.0 eV),* 

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

for the same mineral phases.

and morphology.

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

*Novel Nanomaterials*

metals ions.

either hindering or enhancing the reactivity of the underlying mineral surfaces. The resulted the cell-mineral surface interactions occurring in natural soil and water environments can retain pollutants in great extent [62, 63]. Therefore, the presence of microorganisms can result in significant modification of metal speciation or contaminant sequestration and transport, and hence, investigating the interfaces of bacteria-metal and bacteria-mineral surfaces is essential in predicting the mobility

More importantly, understanding the dynamics of the bacterial interaction with engineered and/or naturally occurring NPs have received significant attention because the fate and transport reactions and mechanisms of them in the terrestrial and aquatic environments strongly depend on the nature and extent of the bacterial sorption and reduction of the nanoparticles [64]. For example, Schwegmann et al. [65] observed iron oxide nanoparticle sorption on microorganisms (*Saccharomyces cerevisiae* and *Escherichia coli*) significantly shifted the point of zero charge for bacteria. Their results imply that overall electrostatic interaction between dissolved heavy metal contaminants and bacteria can be considerably altered due to the presence of the nanoparticles. Another study showed an enhanced removal of the heavy metals from the solution phase in conventional activated sludge wastewater treatment plants when nanoparticles were added to reactors including different types of bacteria. This study suggested that the production and transformations of the surface properties of biomass due to NP would be key factors in determining the fate of the waste toxic metals in the environment [66]. Droz et al. [67] observed biogenic MnO2 nanoparticles affected a wide range of metal fate and transport in natural and engineered systems by strongly sorbing

Of particular importance, the dissimilatory microbial iron reduction is one of the important processes in determining the biogeochemical cycling of iron under anaerobic conditions and has significant influences on the aqueous geochemistry and mineralogy of sedimentary environments [68, 69]. Iron cycling has dramatic implications for trace element and heavy metal contaminant mobility, and the complex interplay of biological and chemical processes determine the extent and reaction pathways of iron cycling in the environment [69]. Past studies have identified many different chemical and biological factors controlling the microbial reduction of iron oxides, yet the role of nanoparticles in determining the extent and reaction pathways for dissimilatory iron reduction are still poorly understood. Despite the important roles of nanoparticles, current molecular-level understanding on the interaction of organic compounds, metals, and microorganisms with nanoparticle surfaces and the resulting impacts on pollutant speciation at nanoparticle-water interfaces are very limited. One of the main reasons for this limitation is lack of appropriate tools with high resolution and/or high sensitivity to molecular structural changes occurring on nanometer scales. In addition, ability to study the materials in situ, i.e., in presence of water with minimal alteration of the sample from its natural state, has been limited. For many environmental samples, especially those involving interactions at solid-water interfaces, the presence of

Due to the small size of particles, different mechanisms and processes have been observed when bacteria interacts with nanoparticles. For example, a greater bioavailability of iron was observed when iron nanoparticle reacted with *Pseudomonas mendocina* bacteria [70] because of the possible penetration of the nanoparticles through the cell membrane and proximity of the particles to the bacteria. Sulfatereducing bacteria (*Desulfovibrio desulfuricans*) also showed different metabolic responses in presence of iron oxide nanoparticles and generated biogenic pyrrhotite formation suggesting a potential impact of iron oxide nanoparticles on geomagnetic

of heavy metal contaminants accurately and quantitatively.

**340**

water plays a critical role.

field behavior of sediments. Different dissimilatory reduction of hematite nanoparticles and microparticles were also observed for *Shewanella oneidensis* bacteria [71]. Results show that proximity and encapsulation of the nanoparticles near the cell membrane allowed different iron oxide reductive mechanisms resulting in a significantly enhanced iron oxide reductive transformation rates by *Shewanella oneidensis* (**Figure 5**)*.* Clearly different reaction pathways and microbial responses toward nano-meter materials are present compared to the larger particle size even for the same mineral phases.

Nanoparticles are also generated by a biogenic enzymatic process and used as engineered materials. The development of eco-friendly technologies in material synthesis has become important and widely applied. Synthesis of nanoparticles using different microorganisms, and their applications in many cutting-edge technological areas have been explored. Recent study shows that biogenically generated iron(III) (oxyhydr)oxide (Fe(OH)3) clusters by gram positive bacteria *Clostridium* could be used to create lithium storage capacity [72]. This study provides another potential use of hematite nanoparticles as a substitute for an industrial product. Other studies also have found that many microorganisms can produce different types of inorganic nanoparticles through either intracellular or extracellular routes, and such biosynthesized nanoparticles have been used in a variety of applications including drug carriers for targeted delivery, cancer treatment, gene therapy and DNA analysis, antibacterial agents, biosensors, enhancing reaction rates, separation science, and magnetic resonance imaging (MRI) [50, 73–75]. As shown, there have been tremendous developments in the field of microorganismproduced nanoparticles and their applications over the last decade. However, much work is needed to improve the synthesis efficiency and the control of particle size and morphology.

#### **Figure 5.**

*STXM images of S. oneidensis WT strain and hematite nanoparticle reacted for 98 hr under anaerobic condition at initial hematite concentration of 1mM in an aqueous suspension measured at (A) C K-edge (288.2 eV) and (D) Fe L-edge (709.5 eV). The outlined areas labeled in (A) and (D) are shown in higher magnification at (B) below C K-edge (280.0 eV), (C) C K-edge (288.2 eV), (E) below Fe L-edge (700.0 eV), and (F) Fe L-edge (709.5 eV).*
