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Nanomaterials are materials with one or more nanoscale dimensions (internal or external) (i.e., 1 to 100 nm). The nanomaterial shape, size, porosity, surface chemistry, and composition are controlled at the nanoscale, and this offers interesting properties compared with bulk materials. This review describes how nanomaterials are classified, their fabrication, functionalization techniques, and growth-controlled mechanisms. First, the history of nanomaterials is summarized and then the different classification methods, based on their dimensionality (0–3D), composition (carbon, inorganic, organic, and hybrids), origin (natural, incidental, engineered, bioinspired), crystal phase (single phase, multiphase), and dispersion state (dispersed or aggregated), are presented. Then, the synthesis methods are discussed and classified in function of the starting material (bottom-up and top-down), reaction phase (gas, plasma, liquid, and solid), and nature of the dispersing forces (mechanical, physical, chemical, physicochemical, and biological). Finally, the challenges in synthesizing nanomaterials for research and commercial use are highlighted.

The mobility of heavy metals in aquatic environments, impacted by discharges from mining waste, is one of the major processes causing metal pollution mainly by arsenic (As), cadmium (Cd), lead (Pb), zinc (Zn) and iron (Fe), which could be risky for biota and human health. The heavy metals contained in mining waste constituted by large amounts of sulfides can reach the aquatic compartments by acid mine drainage and runoff and eventually become deposited in sediments and associated with colloidal material, being this one of the main reservoirs and ways of transport. However, the mobility of heavy metal is influenced by their specific chemical properties and undergo several physicochemical phenomena as sorption, oxidation–reduction, hydrolysis and this can be influenced by water flow, the size and composition of geological material. Hence, this work aims to review the processes and mechanism involved in the fate and transport of heavy metals from mining-waste to aquatic compartments and the methods used for identification of the specific chemical species associated with their mobility and ecological risk.

A nanostructure is a system in which at least one external dimension is in the nanoscale, it means a length range smaller than 100 nm. Nanostructures can be natural or synthetic and determine the physicochemical properties of bulk materials. Due to their high surface area and surface reactivity, they can be an efficient alternative to remove contaminants from the environment, including heavy metals from water. Heavy metals like mercury (Hg), cadmium (Cd), arsenic (As), lead (Pb), and chromium (Cr) are highly poisonous and hazardous to human health due to their non-biodegradability and highly toxic properties, even at trace levels. Thus, efficient, low-cost, and environmentally friendly methodologies of removal are needed. These needs for removal require fast detection, quantification, and remediation to have heavy metal-free water. Nanostructures emerged as a powerful tool capable to detect, quantify, and remove these contaminants. This book chapter summarizes some examples of nanostructures that have been used on the detection, quantification, and remediation of heavy metals in water.

Removal and photodegradation of methylene blue on the surface of three distinct carbonaceous materials, pure and nitrogen-doped multi-walled carbon nanotubes, and graphitic nanoribbons, were examined. Carbon nanostructures were characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption/desorption isotherms. Removal and photocatalytic activity were evaluated by static adsorption under UV irradiation. Photocatalytic activity on carbon nanostructure exhibited a pseudo-first-order kinetic model. The adsorption capacity and photocatalytic activity of carbon nanostructures were mainly attributed to their defective and reactive surface. Nitrogen-doped multi-walled carbon nanotubes showed the best adsorption capacity and photocatalytic activity, which can be attributed to the highly reactive sites due to nitrogen doping, also by π–π electron donor-acceptor interaction between sp2 lattice of carbon nanostructure surface and negatively charged sites at methylene blue molecules.

We investigated the effects of long-time thermal oxidation (LTO) of nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) at 330 °C in air. By scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, Raman spectroscopy and cyclic voltammetry we characterize the oxidized N-MWCNTs (Ox-NMWCNTs). SEM and TEM characterizations revealed that LTO promoted structural damages driven by Fe-based nanoparticles, producing holey N-MWCNTs. The XRD patterns showed that short times of oxidation process, encapsulated Fe3C, and α-Fe nanoparticles in N-MWCNTs cut or perforate their graphite layers. For LTO (>300 h), Fe3C and α-Fe nanoparticles are transformed into Fe3O2 (hematite structure). Deconvolution analysis of the (0 0 2) crystallographic planes allows us to monitor the graphitization evolution of the Ox-NMWCNTs. XPS characterization demonstrated that the surface composition of Ox-N-MWCNTs is influenced by the LTO, while carbon and nitrogen decrease in percentage, the oxygen increases. We have found that LTO favored the formation of pyrrolic nitrogen doping. The holey N-MWCNTs are a porous material with a moderate surface area. According to the voltammetry studies, when the Ox-N-MWCNTs are acid-treated, the surface area is doubled and presents a double layer capacitance that could be advantageous for energy applications.

Nitrogen-doped multiwalled carbon nanotube (CNT) bundles exhibiting pine-tree-like morphologies were synthesized on silicon–silicon oxide (Si/SiO2) substrates using a pressure-controlled chemical vapor deposition process. Electron field emission (FE) measurements showed a notable emission improvement at low turn-on voltages for the CNT pine-like morphologies (e.g., 0.59 V/µm) in comparison with standard aligned N-doped CNTs (>1.5 V/µm). We envisage that these pine-tree-like structures could be potentially useful in the fabrication of efficient FE and photonic devices.

Nitrogen-doped multi-walled carbon nanotubes (CNxMWNTs) with multiple morphological defects were produced using a modified chemical vapor deposition (CVD) method. In a typical CNxMWNTs synthesis by CVD, an acetone trap is used to catch organic by-products from pyrolysis. In the present work, an aqueous solution of NaCl (26.82 wt%) was used in the trap, instead of acetone. Carbon nanotubes with sharp tips and lumps were found in the products. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy showed the formation of nanoparticles of different shapes inside the nanotubes. The electronic and magnetic properties were studied using a physical properties measurement Evercool system (PPMS). With this simple change in the CVD-trap, it is possible to control the morphology of carbon nanotubes and metallic nanoparticles. Differences in gas flow are proposed as a possible mechanism to produce these changes in both nanoparticles and CNxMWNTs.

In this study, two hormones 17&beta, estradiol (E2) and 17&alpha, ethynylestradiol (EE2), and three phenolic compounds, bisphenol A (BPA), 4-N-nonylphenol (4-NP) and 4-tert-octylphenol (4-t-OP), were determined in surface water in the Cuautla River at the State of Morelos during the dry-season in Mexico. The endocrine disrupting compounds (EDCs) were extracted from water samples using solid-phase extraction (SPE) with end-capped C18, and then the extracts were chemically derivatized to TMS (trimethylsylane)-compounds and analyzed by gas chromatography coupled to mass spectrometry (GCMS). The most abundant compound was BPA (22.46 &plusmn, 30.17 ng L&minus, 1), followed by 4-t-OP (11.24 &plusmn, 11.76 ng L&minus, 1), 4-NP (7.53 &plusmn, 14.88 ng L&minus, 1), EE2 (2.37 &plusmn, 4.36 ng L&minus, 1) and E2 (0.97 &plusmn, 1.82 ng L&minus, 1). The residual amounts of target compounds could either reach stream surface water from direct domestic wastewater discharges, conventional wastewater treatment plant or can be a result from the use of agrochemicals in crop areas. The EDCs in Cuautla River exerted a high pressure on the aquatic ecosystem because their presences in surface water caused medium and high potential ecological risk. Besides, it was found that aquatic organisms were exposed to estrogenic activity.

We report the preparation of hybrid paperlike films consisting of alternating layers of graphene (or graphene oxide) and different types of multiwalled carbon nanotubes (N-doped MWNTs, B-doped MWNTs, and pristine MWNTs). We used an efficient self-assembly method in which nanotubes were functionalized with cationic polyelectrolytes in order to make them dispersible in water, and subsequently these suspensions were mixed with graphene oxide (GO) suspensions, and the films were formed by casting/evaporation processes. The electronic properties of these films (as produced and thermally reduced) were characterized, and we found electrical resistivities as low as 3 × 10(-4) Ω cm. Furthermore, we observed that these films could be used as electron field emission sources with extraordinary efficiencies; threshold electric field of ca. 0.55 V/μm, β factor as high as of 15.19 × 10(3), and operating currents up to 220 μA. These values are significantly enhanced when compared to previous reports in the literature for other carbon nanostructured filmlike materials. We believe these hybrid foils could find other applications as scaffolds for tissue regeneration, thermal and conducting papers, and laminate composites with epoxy resins.

We report on the fabrication of sapphire samples containing platinum nanoparticles (Pt-NPs) and platinum ions (Pt-ions) and the investigation of their third-order nonlinear (NL) optical properties. The presence of Pt-NPs was confirmed by electronic microscopy and by the linear absorption spectrum that shows a localized surface plasmon band centered at 290 nm. A sample without NPs but containing Pt-ions was also studied. The absorptive and refractive contributions to the nonlinearity were studied using the z-scan technique with 100 fs pulses at 800nm. The experiments revealed a NL refractive index, +3.8×10sup-13/supnsub2/sub+1.3×10sup-12/supcmsup2/sup/W and NL absorption coefficient (β9.3 cm/GW). The results show enhancement of about five orders of magnitude with respect to the NL refractive index of sapphire.

The use and implementation of renewable energies has increased worldwide in recent years as a green and sustainable alternative to fossil fuels. Among the renewable energies available, wind and solar stand as the first choice to achieve this goal. Although the use of solar and wing have multiple advantages, their availability and efficient use are limited by their intermittent nature. For this reason, there has been an urgent need to design systems that store energy when is produced in excess for further use, thus, this will be always available. Redox flow batteries (RFBs) have been recognized as one of the most suitable options among the electrochemical technologies to store energy at large scale (kW - MW) and also to facilitate the integration of solar or eolic energy to the electricity grid. Over the last three decades, different RFB chemistries have been proposed and successfully demonstrated for practical applications, for instance, the all vanadium RFB. Recently, the hybrid H₂-Br₂ system has attracted attention as possible candidate for energy storage because its high power and efficiency, low reactant cost, fast kinetics and great reversibility. The redox reactions of Br₂ and H2 at the negative and positive electrode, respectively, are responsible for the energy storage with a theoretical Ecell=1.09 V. In general, the reactions of Br2 are reversible and exhibit fast kinetics on carbon felt electrodes. At the H2 electrode, the hydrogen reactions are performed at a Pt/C electrocatalyst in order to achieve low activation overpotential and fast kinetics. However, Pt electrocatalyst is poisoned by crossover of bromine and bromide species from the positive electrode to the negative electrode through the membrane during operation. Consequently, the kinetics of the H₂ reactions is affected which decreases the efficiency and energy storage capacity of the device. Some transition materials have been investigated as alternative electrocatalysts for hydrogen reactions. For example, it has been reported that MoS2 presents good catalytic activity and low overpotentials towards the hydrogen reactions. However, it is necessary to perform a fundamental study of MoS2 as electrocatalyst for the hydrogen reactions in presence of bromine and bromide species. Additionally, new synthesis methods should be explored in order to enhance the physical, chemical and electrocatalytic properties of MoS2 for its possible use in the design of H2 electrodes for the hybrid H2-Br2 RFB. In this research, MoS2 - Pt nanoparticles are synthesized directly on carbon nanostructures by a single step microwave assisted solvothermal or hydrothermal method. Carbon Nanosponge (CNS), N2 – doped Carbon Nanotubes (N2-CNT) or Multiwall Carbon Nanotubes (MWCNT) are considered in this study. The kinetics and electrocatalytic activity of the MoS2 – Pt nanoparticles are studied by cyclic voltammetry (CV), rotating disk electrode (EDR) and electrochemical impedance spectroscopy (EIS) towards the hydrogen reactions in acidic media with additions of HBr. Scanning electron microscopy (SEM) and X-Ray diffraction (XRD) are carried out to study the distribution and particle size, morphology and crystalline phases present in the MoS2-Pt/C nanomaterials. The synthesis time of the MoS2-Pt on carbon assisted by microwave is highly reduced as compared with the conventional solvothermal or hydrothermal methods, 10 min vs. 36 h. Preliminary electrochemical studies show that MoS₂-Pt based materials exhibit stability in the presence of HBr for further use as H₂ electrodes in a H₂-Br₂ RFB. Keywords: energy storage, nanomaterials, hydrothermal synthesis, RFB

This work reports on the electron microscopy analysis of the structure and morphology of gold nanoparticles produced by ion implantation as well as their relationship to their optical properties. Metalic nanoparticles by ion implantation are usually spherical and formed beneath the surface of a dielectric matrix. In this experiment, the matrix was sapphire. After high-energy Si ion irradiation, the gold nanoparticles were elongated into prolate spheroids. Since the nanoparticles are embedded in a dielectric matrix, secondary electron imaging in a JEOL JSM-7800F at low voltage did not allow their analysis. This work proposes an analysis using backscattered electron imaging in a field emission scanning electron microscopy at higher voltages (20 kV) to explore the morphology of the embedded nanoparticles. The samples were observed by cross-sectional view as well as a top view of the surface of the sapphire matrix for exploration and recognition of their morphology, dimensions, distribution, and composition. The analysis was extended by means of Rutherford backscattering spectrometry, X-ray diffraction, and optical extinction spectroscopy. The nanoparticles exhibited structural and optical properties correlated directly to the morphology observed by microscopy. The beam interaction with the sample and the used parameters was simulated in the CASINO code, from which the depth of exploration with distinct parameters used in microscopy analysis was estimated.

Chemical vapor deposition (CVD) is a preferential method to fabricate carbon nanotubes (CNTs). Several changes have been proposed to obtain improved CNTs. In this work we have fabricated nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) by means of a CVD which has been slightly modified. Such modification consists in changing the content of the by-product trap. Instead of acetone, we have half-filled the trap with an aqueous solution of NaCl (0–26.82 wt.%). Scanning electron microscope (SEM) characterization showed morphological changes depending upon concentration of NaCl included in the trap. Using high resolution transmission electron microscopy several shape changes on the catalyst nanoparticles were also observed. According to Raman spectroscopy results N-MWCNTs fabricated using pure distillate water exhibit better crystallinity. Resistivity measurements performed on different samples by physical properties measurement Evercool system (PPMS) showed metallic to semiconducting temperature dependent transitions when high content of NaCl is used. Results of magnetic properties show a ferromagnetic response to static magnetic fields and the coercive fields were very similar for all the studied cases. However, saturation magnetization is decreased if aqueous solution of NaCl is used in the trap.