Hydrogen is expected to become an ideal candidate for renewable and cleaner energy carrier and to progressively replace the existing fossil fuels, at least when the issue of how it can be stored safely and cheaply is resolved. So far only few technologies for storing hydrogen fuel have been adopted by automobile factories [1], but these systems present significant disadvantages. Most recently, tremendous interest have been aroused by the discovery of the hydrogen adsorption capacity in carbon materials [2], such as nanoporous carbon or nanofibers, and particularly carbon nanotubes (CNTs) because of their unique physical/chemical properties and their potential applications. In particular, since their very low density and high porosity, they are potentially useful as a safe hydrogen storage [3], although in the literature the actual amount of hydrogen uptake in CNTs varies significantly. In this work we report about growth of carbon nanotubes, carbon fibers and nanographite obtained by thermal CVD [4] by co-evaporating of either solid or liquid carbon precursor in presence of metal catalysts, such as ferrocene. The morphology and structure of our samples, grown at different conditions, were characterized by SEM, HR-TEM and BET analyses. Furthermore spectroscopic tools were employed both in characterization of carbon nanotubes and their interaction with hydrogen atmosphere, in order to investigate the mechanism in which hydrogen is adsorbed onto different kind of nanotube samples. Physical and chemical properties were investigated by Raman, FT-IR and ESR spectroscopy.

In this study, carbon nanotubes (CNTs) were synthesized on an oil-well cement substrate using the chemical vapor deposition (CVD) method. The effect of synthesis process on cement was investigated in depth. In this regard, FE-SEM, RAMAN and X-Ray spectroscopy were used to characterize the cement before and after the synthesis process to reveal the modifications to the cementitious matrix and some unique morphological features of CNTs.

Carbon nanotubes are used to improve both the mechanical properties and electrical conductivity of cement, allowing the preparation of a strengthened and toughened cement that can be used for self-monitoring applications. Functionalization by reaction with acid is necessary to guarantee both a good dispersion in water and a strong interaction with cement. Sulfonitric acid (a solution of sulfuric acid and nitric acid) is the best oxidation treatment to decorate the surface of carbon nanotubes with polar groups. The time of treatment influences the mechanical and electrical properties of the composites, and in this work, the effect of the length of the treatment on both CNTs and composites was thoroughly analyzed. It was shown that a long-time oxidation treatment (90 min) was very effective to obtain well-dispersed carbon nanotubes that allow us to obtain cement-based composites with a large improvement of mechanical properties with respect to plain cement: 213% for flexural strength, 90% for fracture energy, and 20% for compressive strength. Furthermore, the electrical resistivity of cement-based composites was reduced to only 3% of the value of plain cement.

The past 3 decades of thorough scientific scrutiny of carbon nanotubes (CNTs) revealed that, in spite of their remarkable properties, some technological applications are adversely affected by certain difficulties in handling the CNTs, along with their tendencies, arising out of their graphitic structure, to form agglomerates and exhibit limited interaction with other materials. These issues play a crucial role when CNTs are applied as nanofillers inside matrices, in particular polar ones. In this case, unless several preliminary steps are taken, an efficient and uniform dispersion of the CNTs becomes impossible, thus the nanocomposite cannot exhibit the expected final properties. Unfortunately, a universal procedure does not exist since the problem of the dispersion of CNTs is very complex, and its solution requires an advanced understanding of the properties of the CNTs (e.g. whether the CNTs are single-or multiwalled, size, length, lattice defects etc.) as well as of the matrices used. This review aims to help the reader to select the appropriate dispersion procedure by acquiring fundamental knowledge regarding: (1) the synthesis and properties of pristine CNTs; (2) methods of chemical functionalization and properties of functionalized CNTs; and (3) methodologies for the mechanical dispersion of CNTs. A brief overview regarding chemo-physical characterization techniques is also given to enable a better evaluation of the properties of the CNTs, both before and after functionalization. (c) 2021 Elsevier Ltd. All rights reserved.

The functionalization of carbon nanotubes (CNTs) is a very important step in many applications but it is still a very complex and variable task. This work shows an efficient, easily reproducible and optimal method to introduce oxygenated functional groups to CNTs by treating them for 600 at 350 degrees C with a mixture of 2% oxygen in argon. The oxidized nanotubes were characterized through FT-IR, Raman and TGA to verify the quality of the oxidation and the lattice integrity of the treated CNTs. The results demonstrate that the treated nanotubes are not damaged even after introducing a significant number of new groups. This methodology could be easily tuned to functionalize other types of graphitic materials. (C) 2020 Elsevier B.V. All rights reserved.

In this study, cellulose fibers were chemically functionalized under mild conditions by introducing palmitate groups in order to produce a hydrophobic cellulose-based ester. The effectiveness and the degree of functionalization were evaluated by FTIR spectroscopy and thermogravimetric analysis, whereas the structural integrity was confirmed by XRD measurements. The prepared materials were tested in water remediation processes from fatty oils mixtures from both animal (cod liver oil) and vegetable (sunflower oil) sources. Experimental kinetic measurements, rationalized by means of the most common models, show that the best performances were reached toward the sunflower oil, hence proving the promising application of such green materials as a sustainable alternative tool for oil–water remediation processes.

Carbon fibers can be used to improve both mechanical properties and electrical conductivity of cement, allowing the preparation of a strengthened and toughened cement that can be used for self-monitoring applications. To guarantee both a good dispersion in water and a strong interaction with cement, surface functionalization of carbon fiber surface by reaction with acid was preferred to the use of a dispersing agent. The best oxidation conditions were chosen by using a Taguchi approach, and the samples contained the treated fibers were subjected to both mechanical and electrical tests, to determine flexural strength, toughness, compressive strength and electrical conductivity. It was shown that a not-too-strong oxidation by piranha solution was very effective to obtain well-dispersed fibers and a cement-composite with improved mechanical properties (in particular toughness) and electrical conductivity.

In order to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in aqueous media, their surface functionalization was carried out in O2-fed low-pressure plasmas. Differently from what can be found in the literature of this field, homogeneous functionalization was achieved by generating the plasma inside vials containing the nanotube powders properly stirred. Experimental parameters, such as input power, treatment time and pressure, were varied to investigate their influence on the process efficiency. A detailed characterization of the plasma treated nanotubes, dry and in aqueous suspension, was carried out with a multi-diagnostic analytical approach, to evaluate their surface chemical properties, morphology, structural integrity and stability in the colloidal state. The plasma grafting of polar ionizable (e.g. acid) groups has been proved to successfully limit the agglomeration of MWCNTs and to produce nanotubes suspensions that are stable for one month and more in water.

Recent advances in macromolecular chemistry have revolutionized the way we perceive the synthesis of polymers. Polymerization, to be modern, must be "controlled", which usually means capable of producing macromolecules of well-defined structure. The purpose of this review is to examine how the chemistry of epoxy resins, an almost century-old chemistry, is also involved in this movement.Epoxy resins are characterized by both the flexibility of implementation and the qualities of the polymers obtained. Key materials in health-, mobility- and energy related technologies, these resins are heavily present in high-performance composites, electronic boards, adhesives and coatings. Currently, a large number of resins and hardeners are available on the market or described in the literature and an interesting point is that almost any combination of the two is possible. Common to all these recipes and processes is that a liquid (or soluble) resin at some point becomes insoluble and solid. It is very important to know how to manage this transition, physically known as the gel point, as it is the point after which the shape of the object is irreversibly set. Taking into account the variety of epoxy polymerization processes - polyaddition, anionic or cationic polymerization - we detail a number of methods to program the occurrence of the gel point and how this type of control affects the structure of the growing network. (C) 2016 Elsevier Ltd. All rights reserved.

The present paper reviews the current state of the art of carbon nanotubes cement-based composites and the possible applications. The influence of carbon nanotubes additions onto cement paste mechanical and electrical properties are discussed in detail. Though promising, several challenges have still to be solved before the introduction of these new materials into the public sphere through civil infrastructures.

Carbon nanotubes (CNTs) are an allotropic form of carbon, extremely interesting for their electrical and mechanical properties[1]. Used as reinforcement in different matrices, CNTs present many problems due to their agglomeration and non-wetting surface, that can be solved by chemical functionalization[2]. In particular, when dispersion in common solvents or matrices is considered, it is necessary to have polar functional groups on the surface. Since oxygen-containing groups are easy to graft on the CNTs surface, oxidation seems to be the best way to guarantee improved surface polarity. Oxidation through acid attack has been extensively studied in literature[3], since this changes the CNTs hydrophilicity and improves their dispersion in various solvents. However, the use of acids creates numerous drawbacks such as a heavy damaging of the CNTs structure due to the aggressive environment present during the oxidation reaction. This work originates from the need to find an oxidation method able to preserve the nanotubes structure while functionalizing the surface, in order to be able to disperse them in solvents or matrices but keeping the whole advantage given from the properties of the single CNTs. The idea was to perform a very simple oxidation of carbon nanotubes (CNTs) by thermal treatment at a specific temperature in controlled atmosphere. The conditions were chosen through a thermal gravimetric analysis (TGA) screening in a low oxygen (1-5%) atmosphere. The very initial phase of the thermal degradation starts between 350 C and 450 C, hence, the thermal degradation of CNTs was tested at lower temperatures with an isothermal treatment. By choosing the right temperature, time and amount of oxygen, it was possible to perform a precise and non-destructive oxidation of the CNTs, as demonstrated by several characterization techniques. This process enable the production of oxidized CNTs, which can be easily dispersed in aqueous solutions, without damaging the structure of the nanotubes.

In this work, we report the successful development of a cement-rubber reactive composite with reversible mechanical properties. Initially, the composite behaves like rubber containing inert filler, but when exposed to water, it increases in volume and reaches a stiffness that is intermediate between that of hydrogenated nitrile butadiene rubber (HNBR) and hydrated cement, while maintaining a relatively large ductility characteristic of rubber. After drying, the modulus increases even further up to 400 MPa. Wet/drying cycles prove that the elastic modulus can reversibly change between 150 and 400 MPa. Utilizing attenuated total reflection Fourier transform infrared spectroscopy), we demonstrate that the high pH produced by the hydration of cement triggers the hydrolysis of the rubber nitrile groups into carboxylate anions. Thus, the salt bridges, generated between the carboxylate anions of the elastomer and the cations of the filler, are responsible for the reversible variations in volume and elastic modulus of the composite as a consequence of environmental moisture exposure. These results reveal that cement nanoparticles can successfully be used to accomplish a twofold task: (a) achieve an original postpolymerization modification that allows one to work with carboxylate HNBR (HXNBR) not obtained by direct copolymerization of carboxylate monomers with butadiene, and (b) synthesize a stimuli-responsive polymeric composite. This new type of material, having an ideal behavior for sealing application, could be used as an alternative to cement for oil field zonal isolation applications.

A novel approach for the chemo-mechanical characterization of cement-based materials is presented, which combines the classical grid indentation technique with elemental mapping by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). It is illustrated through application to an oil-well cement system with siliceous filler. The characteristic X-rays of major elements (silicon, calcium and aluminum) are measured over the indentation region and mapped back on the indentation points. Measured intensities together with indentation hardness and modulus are considered in a clustering analysis within the framework of Finite Mixture Models with Gaussian component density function. The method is able to successfully isolate the calcium-silica-hydrate gel at the indentation scale from its mixtures with other products of cement hydration and anhydrous phases; thus providing a convenient means to link mechanical response to the calcium-to-silicon ratio quantified independently via X-ray wavelength dispersive spectroscopy. A discussion of uncertainty quantification of the estimated chemo-mechanical properties and phase volume fractions, as well as the effect of chemical observables on phase assessment is also included.