This thesis focuses on the synthesis and applications of nanoscale zero valent iron (nZVI) in the environmental remediation of contaminants. The polyvalent characteristics of this nanomaterial are evaluated in this work with the study of its application in a wide range of contaminants: heavy metals and pesticides in water medium, and malodorous sulfur compounds present in air streams. Moreover, a novel method of synthesis of encapsulated nZVI from a waste material is presented, which meets the principles of green chemistry and at the same time represents a low-cost method of obtaining nZVI with improved characteristics. Chapter 1 describes the current state of the topics that will be discussed in the rest of the thesis. Specifically, the different mechanisms of contaminant remediation by nZVI are discussed, a summary of the current synthesis methods is presented and the principal modifications of nZVI to improve its characteristics are described. Finally, the limitations of the current techniques are assessed, which will be the starting point of the thesis. In Chapter 2, the application of nZVI to heavy metal removal during long time periods is explored. The contaminants studied are Zn, Cd, Ni, Cu and Cr, which are the most common heavy metals found in ground and wastewater. A delivery-effect of the heavy metal ions that had already been attached to nZVI surface is observed after long reaction times, which is a consequence of the nZVI aging and oxidation. The conditions that influence the delivery-effect are assessed and possible solutions to this detected problem are presented. In Chapter 3, nZVI is applied to the removal of sulfur-based odorous compounds in air streams. The compounds studied are hydrogen sulfide and dimethyl disulfide (DMDS), which are commonly found in wastewater treatment plants. Both nZVI loading and pH are varied to assess their influence on the process. Bimetallic nanoscale particles of Cu/Fe, Ni/Fe and Pd/Fe are synthesized in order to improve the DMDS abatement by the nZVI. The advantages of this new method for odor removal are discussed at the look of the experimental results. Lastly, a pilot scale test was performed in a wastewater treatment plant in order to test the effectiveness of the nZVI in a real application. The nZVI were applied in a scrubber to eliminate the sulfurous compounds from the pre-treatment area of the wastewater treatment plant. Chapter 4 deals with the application of nZVI to the oxidation of non-biodegradable pollutants by the Fenton reaction. Specifically, the effect of pH on the degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is studied. The advantages of using nZVI as a Fenton reagent compared to homogeneous Fenton are described. Furthermore, the addition of UV-light to the process is investigated. Finally, the main degradation intermediates of the reaction are identified and a degradation mechanism is accordingly proposed. In Chapter 5, the presence of polychlorinated dioxins and furans (PCDD/Fs) in the nZVI surface is addressed. Studies have shown that nZVI enhances the formation of such chlorinated compounds during thermal processes, but it is unclear which the origin of the compounds is. It has been suggested that nZVI could possess impurities such as PCDD/Fs in its surface. Therefore, the concentration of PCDD/Fs in both commercial and laboratory-synthesized nanoparticles is analyzed. PCDD/Fs pattern and WHO-TEQ concentrations are also obtained. As an outcome of the results obtained in this chapter, a recommendation for preventing the PCDD/Fs presence in nZVI is given. Chapter 6 is dedicated to the synthesis of carbon-encapsulated nanoparticles using hydrothermal carbonization (HTC) of an agricultural waste, particularly, olive mill wastewater (OMW). This novel method, in addition to meet the green chemistry principles, makes profit of the high polyphenol content of OMW to maximize the fraction of incorporated iron into the nZVI. Moreover, the carbon layer surrounding the nZVI protects it against oxidation and avoids its aggregation. Several HTC conditions are explored to study their implications in the characteristics of the material obtained. A deep characterization of the encapsulated nZVI is also presented in this chapter. In Chapter 7, the applications of the encapsulated nZVI synthesized in Chapter 6 are explored and compared for the same contaminants that have been studied in the previous chapters. Then, the advantages of encapsulated nZVI in comparison with common nZVI are discussed at the end of the chapter, and an estimation of the synthesis costs with this method is addressed. Lastly, in Chapter 8, the main conclusions of the thesis are summarized and suggestions for future work are presented.

The ability to encapsulate linear nanoparticle (NP) chains in scrolled nanosheets is an important advance in the formation of nanocomposites.These nanopeapods (NPPs) exhibit interesting properties that may not be achieved by individual entities. Consequently, to fully exploit the potential of NPPs, the fabrication of NPPs must focus on producing composites with unique combinations of morphologically uniform nanomaterials. Various methods can produce NPPs, but expanding these methods to a wide variety of material combinations can be difficult. Recent work in our group has resulted in the in situ formation of peapod-like structures based on chains of cobalt NPs. Building on this initial success, a more versatile approach has been developed that allows for the capture of a series of preformed NPs in NPP composites. In the following chapters, various synthetic approaches for NPPs of various material combinations will be presented and the key roles of various reaction parameters will be discussed. Also, uniform hexaniobate nanoscrolls were fabricated via a solvothermal method induced by heating up a mixture of TBAOH, hexaniobate crystallites, and oleylamine in toluene. The interlayer spacing of the nanoscrolls was easily tuned by varying the relative amount and chain lengths of the primary alkylamines. To fabricate NPPs, as-synthesized NPs were treated with hexaniobate crystallite in organic mixtures via solvothermal method. During solvothermal treatment, exfoliated hexaniobate nanosheets scroll around highly ordered chains of NPs to produce the target NPP structures in high yield. Reaction mixtures were held at an aging temperature for a few hours to fabricate various new NPPs (Fe3O4@hexaniobate, Ag@hexaniobate, Au@hexaniobate, Au-Fe3O4@hexaniobate, TiO2@hexaniobate, CdS@hexaniobate, CdSe@hexaniobate, and ZnS@hexaniobate). This versatile method was first developed for the fabrication of magnetic peapod nanocomposites with preformed nanoparticles (NPs). This approach is effectively demonstrated on a series of ferrite NPs (≤ 14 nm) where Fe3O4@hexaniobate NPPs are rapidly (~ 6 h) generated in high yield. When NP samples with different sizes are reacted, clear evidence for size selectivity is seen. Magnetic dipolar interactions between ferrite NPs within the Fe3O4@hexaniobate samples leads to a significant rise in coercivity, increasing almost four-fold relative to free particles. Other magnetic ferrites NPPs, MFe2O4@hexaniobate (M = Mn, Co, Ni), can also be prepared. This synthetic approach to nanopeapods is quite versatile and should be readily extendable to other, non-ferrite NPs or NP combinations so that cooperative properties can be exploited while the integrity of the NP assemblies is maintained. Further, this approach demonstrated selectivity by encapsulating NPs according to their size. The use of polydispersed NP systems is also possible and in this case, evidence for size and shape selectivity was observed. This behavior is significant in that it could be exploited in the purification of inhomogeneous NP samples. Other composite materials containing silver and gold NPs are accessible. Partially filled Fe3O4@hexaniobate NPPs were used as templates for the in situ growth of gold to produce the bi-functional Au- Fe3O4@hexaniobate NPPs. Encapsulation of Ag and Au NP chains with a hexaniobate nanoscroll was shifted the surface plasmon resonance to higher wavelengths. In these composites NPs can be incorporated to form NPP structures, decorated on nanosheets before scrolling, or attached to the surfaces of the nanoscrolls. The importance of this advancement is the promise it holds for the design and assembly of active nanocomposites. One can create important combinations of nanomaterials for potential applications in a variety of areas including catalysis, solar conversion, thermoelectrics, and multiferroics.

Encapsulation of nanoparticles within hexaniobate nanoscrolls presents interesting advances in the formation of nanocomposites exhibiting unique multi-dimensional properties. Building upon previous successes, facile yet versatile wet-chemical and microwave-irradiation synthetic protocols for the fabrication of a series of hexaniobate composites are presented herein. Solvothermal and, more recently, microwave-assisted methods have been developed that allow for the fabrication of peapod-like structures. During solvothermal treatment, exfoliated hexaniobate nanosheets scroll around highly ordered chains of preformed nanoparticles (NPs) to produce nanopeapods (NPPs). This approach offers versatility and high yields, in addition to the potential for advanced functional device fabrication. For the characterization of these materials, advanced techniques in atomic force microscopy (AFM) were used for investigating the surface of materials at the nanometer scale. Extensive physical, dynamic, and force modulation studies were performed on novel oxide nanocomposites by implementing particular scanning techniques to determine information such as topology, stress-induced behavior at the nanoscale, magnetic behavior, and frictional forces of the nanoscale materials. These composites were then analyzed by topological intermittent contact studies in tapping and contact mode, as well as with derivative techniques of these commonly used scanning probe approaches. In addition to studying surfaces using conventional modes of AFM, the mechanical properties of these nanocomposites were measured via dynamic lateral force modulation (DLFM) and magnetic properties of functionalized magnetic nanosheets were mapped via magnetic sampling modulation (MSM). By utilizing the capabilities of the DLFM imaging mode, elastic properties such as Young’s Modulus were measured from force-distance curves. In addition to this modulation mode, MSM was used to selectively map the vibrating magnetic nanomaterials from a modulated electromagnetic field. The information obtained from these AFM techniques can be helpful in determining the relative structural behavior of these nanocomposites and gauge their use in various applications such as structural engineering of nanoarchitectures as well as studying magnetic characteristics of metal oxide nanocomposites that exhibit characteristics different from their bulk counterparts.