Recovery of rare earth elements (Nd3+ and Dy3+) by using carbon-based adsorbents from spent tire rubber

Two samples of spent tire rubber (rubber A and rubber B) were submitted to thermochemical conversion by pyrolysis process. A450, B450 and A900, B900 chars were obtained from rubber A and rubber B at 450 °C and 900 °C, respectively. The chars were then applied as recovery agents of Nd3+ and Dy3+ from aqueous solutions in mono and bicomponent solutions, and their performance was benchmarked with a commercial activated carbon. The chars obtained at 900 °C were the most efficient adsorbents for both elements with uptake capacities around 30 mg g-1. The chars obtained at 450 °C presented uptake capacities similar to the commercial carbon (≈ 11 mg g-1). A900 and B900 chars presented a higher availability of Zn ions that favored the ion exchange mechanism. It was found that Nd3+ and Dy3+ were adsorbed as oxides after Zn was released from silicate structures (Zn2SiO4). A900 char was further selected to be tested with Nd/Dy binary mixtures and it was found a trend to adsorb a slightly higher amount of Dy3+ due to its smaller ionic radius. The uptake capacity in bicomponent solutions was generally higher than for single component solutions due to the higher driving force triggered by the higher concentration gradient.

Simultaneous Synthesis and Nitrogen Doping of Free-Standing Graphene Applying Microwave Plasma

An experimental and theoretical investigation on microwave plasma-based synthesis of free-standing N-graphene, i.e., nitrogen-doped graphene, was further extended using ethanol and nitrogen gas as precursors. The in situ assembly of N-graphene is a single-step method, based on the introduction of N-containing precursor together with carbon precursor in the reactive microwave plasma environment at atmospheric pressure conditions. A previously developed theoretical model was updated to account for the new reactor geometry and the nitrogen precursor employed. The theoretical predictions of the model are in good agreement with all experimental data and assist in deeper understanding of the complicated physical and chemical process in microwave plasma. Optical Emission Spectroscopy was used to detect the emission of plasma-generated ‘‘building units’’ and to determine the gas temperature. The outlet gas was analyzed by Fourier-Transform Infrared Spectroscopy to detect the generated gaseous by-products. The synthesized N-graphene was characterized by Scanning Electron Microscopy, Raman, and X-ray photoelectron spectroscopies.

Microwave plasma-based direct synthesis of free-standing N-graphene

Scheme of ethanol/ammonia plasma driven decomposition pathways considering injection of the nitrogen precursor in “hot” and “mild” plasma zone.

Large-scale synthesis of free-standing N-doped graphene using microwave plasma

Direct assembling of N-graphene, i.e. nitrogen doped graphene, in a controllable manner was achieved using microwave plasmas at atmospheric pressure conditions. The synthesis is accomplished via a single step using ethanol and ammonia as carbon and nitrogen precursors. Tailoring of the high-energy density plasma environment results in a selective synthesis of N-graphene (~0.4% doping level) in a narrow range of externally controlled operational conditions, i.e. precursor and background gas fluxes, plasma reactor design and microwave power. Applying infrared (IR) and ultraviolet (UV) irradiation to the flow of free-standing sheets in the post-plasma zone carries out changes in the percentage of sp², the N doping type and the oxygen functionalities. X-ray photoelectron spectroscopy (XPS) revealed the relative extension of the graphene sheets π-system and the type of nitrogen chemical functions present in the lattice structure. Scanning Electron microscopy (SEM), Transmission Electron microscopy (TEM) and Raman spectroscopy were applied to determine morphological and structural characteristics of the sheets. Optical emission and FT-IR spectroscopy were applied for characterization of the high-energy density plasma environment and outlet gas stream. Electrochemical measurements were also performed to elucidate the electrochemical behavior of NG for supercapacitor applications.

Towards large-scale in free-standing graphene and N-graphene sheets

One of the greatest challenges in the commercialization of graphene and derivatives is production of high quality material in bulk quantities at low price and in a reproducible manner. The very limited control, or even lack of, over the synthesis process is one of the main problems of conventional approaches. Herein, we present a microwave plasma-enabled scalable route for continuous, large-scale fabrication of free-standing graphene and nitrogen doped graphene sheets. The method's crucial advantage relies on harnessing unique plasma mechanisms to control the material and energy fluxes of the main building units at the atomic scale. By tailoring the high energy density plasma environment and complementarily applying in situ IR and soft UV radiation, a controllable selective synthesis of high quality graphene sheets at 2 mg/min yield with prescribed structural qualities was achieved. Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Near Edge X-ray-absorption fine-structure spectroscopy were used to probe the morphological, chemical and microstructural features of the produced material. The method described here is scalable and show a potential for controllable, large-scale fabrication of other graphene derivatives and promotes microwave plasmas as a competitive, green, and cost-effective alternative to presently used chemical methods.

Controlled growth of Cu2O nanoparticles bound to cotton fibres

A green, safe and fast procedure is presented for in situ generation of nanoparticles (NPs) of cuprous oxide (Cu2O) onto cotton fibres at room temperature using water as a solvent. The method is based on a mild surface oxidation of cellulose fibres to generate in a controlled way carboxylic groups acting as a binding site for the adsorption of Cu(2+) via electrostatic coordination. Then, the adsorbed Cu(2+) ions were readly converted into Cu2O by dipping the treated cotton fibres into a aqueous solution of a reducing agent. Field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), as well as UV-vis absorption and emission spectroscopic methods were used to analyse the size, morphology, chemical composition and the crystalline structure of the generated nanoparticles on the fabrics. The morphology of the ensuing Cu2O nanoparticles was shown to be dependent on the reduycing agent used. Antibacterial properties of the modified fibres were also investigated.

P-type Cuox thin films by rf-plasma enhanced reactive thermal evaporation: influence of rf-power density

Copper oxide is a well known p-type semiconductor material, usually obtained by thermal oxidation of copper thin-films within few minutes, at atmospheric pressure. In this paper, thin films of copper oxide that were deposited by radio-frequency plasma enhanced reactive thermal evaporation of copper at room temperature, without any post-deposition annealing treatment, are studied. The deposition of good quality p-type semiconductor oxide to be used in the fabrication of p-TFTs is the purpose of this work. The thickness of the films varies from 97 up to 160 nm. The influence of rf power density on chemical, electrical and optical properties of the films was studied. Samples present conductivity within the range of 6 x 10(-5) to 4 x 10(2) omega(-1) x cm(-1) (thermal activation energy in the interval 0.46 to 0.01 eV). The p-type conductivity of the films was confirmed by Seebeck effect in the more conductive samples. Surface composition obtained by XPS analysis was correlated with optical and electrical properties, showing that rf-power plays a main role in changes of material characteristics.

Adsorption of phenylphosphonic acid on GaAs (100) surfaces

The adsorption of phenylphosphonic acid (PPA) on GaAs (100) surfaces from solutions in acetonitrile/water mixtures was studied using Fourier transform infrared spectroscopy in attenuated total reflection in multiple internal reflections (ATR/MIR), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and atomic force microscopy (AFM). ATR/MIR in situ showed that the accumulation of PPA molecules near the GaAs surface increased with the water concentration in the solution. For water contents lower than 4%, ATR/MIR and XPS results are consistent with the formation of a low-density monolayer. A mechanism is proposed for H2O percentages lower than 4% involving the creation of interfacial bonds through a Brønsted acid-base reaction, which involves the surface hydroxyl groups most probably bound to Ga. It was found that the morphology of the final layer depended strongly on the water concentration in the adsorbing solution. For water concentrations equal to or higher than 5%, the amount of adsorbed molecules drastically increased and was accompanied by modifications in the infrared spectral region corresponding to P-O and P=O. This sudden change indicates a deprotonation of the acid. XPS studies revealed the presence of extra oxygen atoms as well as gallium species in the layer, leading to the conclusion that phosphonate and hydrogenophosphonate ions are present in the PPA layer intercalated with H3O+ and Ga3+ ions. This mechanism enables the formation of layers approximately 10 times thicker than those obtained with lower H2O percentages. HREELS indicated that the surface is composed of regions covered by PPA layers and uncovered regions, but the uncovered regions disappeared for water contents equal to or higher than 5%. XPS results are interpreted using a model consisting of a monolayer partially covering the surface and a thick layer. This model is consistent with AFM images revealing roughness on the order of 7 nm for the thick layer and 0.2-0.5 nm for the thin layer. Sonication proves to be an effective method for reducing layer thickness.