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The development of highly selective, stable, and sensitive materials for the various gas emissions is a challenging task concerning the numerous applications: environmental control, security systems, energy, and, more recently, biological monitoring. One of the major challenges to reach this activity's requirements is developing nanostructured functional and smart materials that can selectively detect and monitor the gases at high temperatures. The semiconductor materials based on metallic oxides have gained increasing attention within this scenario, especially titanium dioxide (TiO2), due to their excellent properties. The literature presents multiple sensors based on TiO2 nanoparticles to detect various gases: CO, ethanol, benzene, toluene, NO2, O2, CO, SO2, NOx, NH3, Cl2, H2S, alkanes, among others. This review initially explores some aspects of TiO2 and its properties regarding the sensor sensitivity's influence. Then, the insertion of noble metals (Ag, Pt, Au, and Ru) and carbon structures (graphene, carbon nanotube, and other carbon forms) was also explored in the search to improve the TiO2 capacity as a gas sensor. This review focuses on the most significant achievements related to TiO2 and TiO2 combined with carbon structures or noble metals for gas sensor applications. Several studies were presented, highlighting the synthesis methods employed, the sensor response/recovery times, and some detection mechanisms after the carbon and noble metal insertion. Finally, the influence of a triple combination between TiO2-carbon-metal was also explored.

Homogeneous dispersion of carbon nanotubes (CNTs) in polymers has significantly improved their processing and application as nanomaterials. Generally, CNTs tend to agglomerate due to their high aspect ratios and strong van der Waals interaction. Surface functionalization appears to be a solution to this problem. This study presents a controlled dispersion of carbon nanotubes in polyethylene through surface modification using a mixture of concentrated acid and octadecylamine (ODA). CNTs were characterized by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, and transmission electron microscopy. The results confirmed that carboxyl and alkane groups were successfully introduced on CNT surfaces. The acid- and amine-functionalized carbon nanotubes were dispersed in four solvents with different polarities (water, ethanol, acetone, and xylene) to correlate the degree of dispersion of CNT with their polarity. The results showed that CNT dispersion stability strongly depends on solvent and carbon nanotube polarities after the functionalization step. The nanohardness and tensile tests showed that the addition of CNTs, especially the functionalized with ODA, leaded the polymer harder, increasing its Young’s modulus and tensile strength. However, its toughness and deformation capacity were reduced. The potential applications of CNT-based polymer nanocomposites broaden considerably due to the surface engineering of carbon nanotubes.

The effects of amine-modified graphene oxide on dispersion and micro-hardness of epoxy based nanocomposites are reported. Graphene oxide was prepared by the modified Hummers method followed by hexamethylenediamine functionalization. Analysis conducted through Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy-based infrared spectroscopy show that the functionalization process effectively promoted a replacement of oxygen with amine groups while simultaneously creating defects in the graphitic structure. An increase in hardness was observed for the developed nanocomposites.

The surface modification of carbon-based nanomaterials, including carbon nanotubes (CNTs) and graphene oxide (GO), is advantageous for tailoring their dispersion in different solvents, as well as polymer matrices. Although the surface modification methodology of such nanomaterials is well established, the relationship between functionalization and interaction with the surrounding environment (solvents or polymers) – particularly repulsion/attraction forces that govern the clusters’ formation – is still not well understood to date. Herein, the dispersion of pristine and oxygenated/amino-functionalized CNTs and GO in different solvents were studied qualitatively (by optical microscopy and visual observations of dispersion tests) and quantitatively (by UV–Vis spectroscopy), and the repulsion/attraction process was explained based on π-π* transitions between CNT or GO and solvents. We found that both CNT and GO can have good dispersion in water, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DMF), and the key to this behavior is the precise functionalization control, including orientation and type of functional group. In this sense, the introduction of functional groups improves the interaction quality of CNT and GO due to nanoscale attraction, and at the same time, enhances their orientation due to steric effect. The present study is expected to contribute to carbon-based nanomaterials’ surface engineering, which may be useful for researchers from different fields, such as carbon nanostructures, materials chemistry, and polymer nanocomposites.

Due to its high efficiency, low cost and a simple operation, the adsorption process is an important and widely used technique for industrial wastewater treatment. Recent studies on the removal of artificial dyes by adsorption include a large number of adsorbents, such as: activated carbon, silicates, carbon nanotube, graphene, fibers, titanates and doped titanates. The carbon insertion in the TiO 2 structure promotes a synergistic effect on the adsorbent composite, improving the adsorption and the charge-transfer efficiency rates. However, there are few studies regarding the adsorption capacity of TiO 2 /Carbon composites with the carbon concentration. This study evaluates the effect of carbon (resorcinol/formaldehyde) insertion on TiO 2 structure through the adsorption process. Adsorbents were prepared by varying the carbon weight percentages using the sol-gel method. The physicochemical properties of the catalysts prepared, such as crystallinity, particle size, surface morphology, specific surface area and pore volume were investigated. The kinetic study, adsorption isotherm, pH effect and thermodynamic study were examined in batch experiments using methylene blue as organic molecule. In addition, the effect of carbon phase on the adsorption capacity of TiO 2 -carbon composite was deeply investigated. SEM micrographs showed that TiO 2 phase grows along the carbon phase and FT-IR results showed the presence of Ti O C chemical bonding. The experiments indicate that the carbon phase acted as a nucleation agent for the growth of TiO 2 during the sol-gel step, with a TiO 2 structure suitable for blue methylene adsorption, resulting in a material with large surface area and slit-like or wedge-shaped pores. Further experiments will show the best carbon concentration for methylene blue adsorption using a TiO 2 based material.

The adsorption of H2O molecules on metal surfaces is important to understand the early process of water corrosion. This process can be described by computational simulation using molecular dynamics and Monte Carlo. However, this simulation demands an efficient description of the surface interactions between the water molecule and the metallic surface. In this study, an effective force field to describe the iron-water surface interactions was developed and it was used in a molecular dynamics simulation. The results showed a very good agreement between the simulated vibrational-DOS spectrum and the experimental vibrational spectrum of the iron–water interface. The water density profile revealed the presence of a water double layer in the metal interface. Furthermore, the horizontal mapping combined with the angular distribution of the molecular plane allowed the analysis of the water structure above the surface, which in turn agrees with the model of the double layer on metal surfaces.

Carbon nanotube-epoxy composites were prepared using amino-functionalized CNTs and sonication as a mixing process. Different times and sonication powers were used for preparing composites in order to study how the sonication process may influence the curing reaction of both systems: neat epoxy resin and amino-CNT/epoxy composite.The curing reaction was investigated with differential scanning calorimetry and the results were associated with analysis of gel permeation chromatography. The results showed that the effect of CNTs on the cure behavior of the epoxy resin depends on the sonication power. The sonication of neat resin with a 150 W powered device led to a molar mass reduction of the resin and an increase in the cure enthalpy. The CNT addition to this system reduced the cure enthalpy. However, when neat epoxy resin was sonicated with a 200 W powered device, the molar mass did not decrease (i.e. it was increased or was not changed) and the cure enthalpy did not increase (essentially it decreased or did not change). The CNT addition to such solutions did not reduce (i.e. it was increased or did not change) the cure enthalpy, which is a contrary result from that obtained with a 150 W powered device. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

TFC was used for chromium ions (III and VI) adsorption from aqueous solution. The total chromium removal was strongly affected by pH changes and reached a maximum value at pH 1. The adsorption process was well described by the Langmuir model. The thermodynamic parameters exhibited the feasibility and the spontaneous nature of the adsorption. The optimum adsorbent dose obtained for chromium adsorption onto TFC was 0.1 g. The optimum contact time for chromium removal and treatment efficiency was 10 and 14 h, respectively. The kinetic studies showed that the adsorption process could fit into a pseudo-second-order model and the particle diffusion process was the rate-limiting step of the adsorption process. The desorbing agents studied did not show any promising result for the TFC regeneration process. The FT-IR results showed that the Cr(VI) removal onto TFC occurs through an indirect reduction mechanism. According to XPS spectrum, the majority of the adsorbed Cr is Cr(III), only a small quantity of Cr(VI) remains loaded on the TFC surface.

The main objective of this work was to evaluate nanocomposites formed by TiO2-CNT (carbon nanotube) and TiO2-C (resorcinol/formaldehyde) via a sonocatalytic process. The synthesis of composites was performed by the sol-gel method using titanium isopropoxide (Ti(OPr)4-TTIP), acetic acid and ethylene glycol as dispersing medium. Ultrasound was used as the irradiation source and methylene blue was chosen as a model substance. In addition, the adsorption capacity was studied in an attempt to achieve greater ratio degradation/adsorption. The methylene blue concentration after adsorption and sonocatalysis was investigated by UV–vis spectroscopy. It was found that adsorption was an important factor to achieve high degradation capacity. However, the sonocatalytic activity decreased when adsorption was too intense.

Mullite is an aluminosilicate widely used as a structural material for high temperature applications. This paper studies the effect of the gelation temperature on the synthesis of two mullite precursors: polymeric and colloidal silica, using both in fully-hydrolyzed silica sol, derived from sodium silicate. The gels were synthesized using aqueous silicic acid and aluminum nitrate. Ethylene glycol was added into polymeric gels. Two gelation temperatures were used: 80 and 100 °C. In the polymeric precursor, the increasing of the gelation temperature caused an increase in the silica incorporation inside the mullite crystalline lattice at 1,000 °C, and it also generated an increase in the reaction extent at all calcination temperatures. In the colloidal precursors, these effects were more intense than in the polymeric precursors in terms of yield. Colloidal samples calcined at 1,250 °C crystallized cristobalite and alpha alumina in addition to mullite when they were previously gelled at 80 °C. On the other hand, the same sample gelled at 100 °C led to only crystallized mullite. The reaction extent increased by more than 20 % for colloidal samples gelled at 100 °C compared to colloidal samples gelled at 80 °C (calcined at 1,250 °C). This increase was due to the almost total incorporation of alumina and silica in the crystalline lattice of mullite.

The results regarding the effect of carbon nanotubes (CNTs) on the cure process of epoxy resin are widespread and contradictory. Therefore, this article aims to review the key studies on the effect of carbon nanotubes related to the curing process of epoxy resin, separating them according to analysis technique. Many articles have shown that nanocomposite homogeneity and medium viscosity have great influence on the cure process. Some of them have shown that heterogeneity and high viscosity slow down the epoxy resin cure, reducing the cure reaction heat. Furthermore, the presence of chemical groups such as amine and hydroxyl can catalyze this reaction, especially in the case of homogeneous composites. This review describes briefly and straightforwardly the value of using several techniques for studying and monitoring the nanocomposite cure, among them: DSC, rheometry, DMA, Raman, FT-IR, and luminescence spectroscopy. That importance is remarkably noticeable for studying a particular temporal reaction step, where a particular technique is more suitable than another. In this sense, one could say that luminescence spectroscopy is appropriate for studying the ending step of the cure reaction. Moreover, a great amount of information is also provided for supporting further research. POLYM. ENG. SCI., 54:2461–2469, 2014. © 2013 Society of Plastics Engineers

Graphene is a new member of the nanocarbon family that has revolutionized the field of materials science and has attracted much attention due to its exceptional properties. Recent progress has shown that graphene-based nanocomposites can be used in nanoelectronics, touch screens, optics, catalysis, supercapacitors, fuel cell transistors, flexible electronics, H2 storage, and polymer nanocomposites. The functionalization is a surface modification much used to reduce the cohesive force between the graphene sheets and also to manipulate the physical and chemical properties. The aim of this book was to provide a comprehensive scientific progress of graphene, containing topics such as synthesis, characterization, and application of functionalized graphene. The characterization of the functionalized graphene is extremely important for determining the physicochemical properties of the material obtained after the functionalization treatments. However, this characterization is rarely addressed in books or in review articles. Generally, the functionalization reviews are too wide-ranging, discussing the functionalization of various materials (e.g., nanomaterials) or too specific, analyzing only one functionalization agent (with some specific chemical group, for example). This book, however, proposes to discuss the functionalization of one of the most widely used nanomaterials in recent years: graphene. Thus, the reader will find information on graphene functionalization, using several functionalization agents, in the same book.

This work evaluated the potential of hydrotalcites based in Ca-Al on trasesterification of soybean oil with ethanol. The reaction was carried out at 78.5 °C with ethanol:oil molar ratio of 30 and 10 wt% of catalyst. The 2Ca-Al showed better performance than 3Ca-Al catalyst achieving conversion of 94%. The catalyst were characterized with XRD, BET and activity was evaluated on isopropanol decomposition reaction.

O biodiesel é um combustível composto por alquil ésteres de ácidos graxos com vários benefícios ambientais que o tornam um potencial substituto para os combustíveis fósseis derivados do petróleo, podendo ser usado tanto puro quanto em misturas. A rota mais tradicional utiliza a catálise homogênea no processo de transesterificação de triglicerídeos de óleos refinados para conversão à metil/etil ésteres. Esta metodologia tem demonstrado altas conversões. No entanto catalisadores heterogêneos, como as hidrotalcitas, apresentam várias vantagens, especialmente na etapa de separação dos produtos. Neste contexto, foram testados novos catalisadores no processo de transesterificação, com etanol e metanol, para avaliar o desempenho das hidrotalcitas sintetizadas, concentração do catalisador, temperatura e razão molar álcool/óleo. Também foram realizadas análises de volumetria de N2, para a determinação da área específica e volume de poros, e difratometria de raios X. As propriedades ácidas e/ou básicas dos suportes e dos catalisadores foram avaliadas através da reação de decomposição do isopropanol. As reações com metanol apresentaram conversões de até 100% a 65°C e razão molar álcool/óleo de 30 e 10% em massa de catalisador. Já a transesterificação utilizando-se etanol apresentou rendimentos de até 94%, com razão molar de 30:1(álcool/óleo) e 10% em massa de catalisador a 78°C. Biodiesel is a fuel comprised of alkyl esters of long chain fatty acids with several environmental advantages which turn it a great potential substitute to petroleum-based diesel either pure or in fuel blends. The most traditional route uses homogeneous basic catalysis in transesterification reaction of triglycerides of refined vegetable oils to produce methyl/ethyl esters. This process has demonstrated higher conversions, but heterogeneous catalysts, such as hydrotalcites, have several advantages, especially in the separation step. In this context, this work aims to study the behavior of new catalysts for transesterification process, with methanol and ethanol, using an experimental design to evaluate the performance of synthesized hydrotalcites, catalyst concentration, temperature and alcohol/oil molar ratio. It was also carried out analysis of N2 volumetry, to determine specific area and pore volume, and X-ray difratometry. The acid/basic properties of the support and catalysts were evaluated through isopropanol decomposition reaction. The reaction carried out with methanol showed high conversions (up to 100%), using 65°C, molar ratio alcohol/oil 30 and 10% of catalysts. The transesterification with ethanol showed conversions up to 94% using 78ºC, molar ratio 30:1 (alcohol/oil) and 10% of catalysts.