Optimization of the Synthesis Procedures of Graphene and Graphite Oxide

The optimization of both the chemical vapor deposition (CVD) synthesis method to prepare graphene and the Improved Hummers method to prepare graphite oxide is reported. Copper and nickel were used as catalysts in the CVD-graphene synthesis, CH4 and H2being used as precursor gases. Synthesis variables were optimized according to a thickness value, calculated using a homemade Excel-VBA application. In the case of copper, the maximum thickness value was obtained for those samples synthesized at 1050°C, a CH4/H2 flow rate ratio of 0.07 v/v, a total flow of 60 Nml/min, and a time on stream of 10 min. In the case of nickel, a reaction temperature of 980°C, a CH4/H2 flow rate ratio of 0.07 v/v, a total flow of 80 Nml/min, and a time on stream of 1 min were required to obtain a high thickness value. On the other hand, the Improved Hummers method used in the synthesis of graphite oxide was optimized. The resultant product was similar to that reported in literature in terms of quality and characteristics but both time and cost of the synthesis procedure were considerably decreased

Bioaccessibility of heavy metals and risk assessment in urban gardens of Madrid

Human health problems and solutions. Urban gardening has spread worldwide in recent years as it enhances food security and selfsupply and promotes community integration. However urban soils are significantly enriched in trace elements relative to background levels. Exposure to the soil in urban gardens may therefore result in adverse health effects depending on the degree of contact during gardening, infant recreational activities and ingestion of vegetables grown in them. In order to evaluate this potential risk, 36 composite samples were collected from the top 20 cm of the soil of 6 urban gardens in Madrid. The aqua regia (pseudototal) and glycine-extractable (bioaccessible) concentrations of Co, Cr, Cu, Ni, Pb and Zn were determined by atomic absorption spectrophotometry. Additionally, pH, texture, Fe, Ca, and Mn concentrations, and organic matter and calcium carbonate contents were determined in all urban gardens and their influence on trace element bioaccessibility was analyzed

Hydroxyethyl cellulose/alumina-based aerogels as lightweight insulating materials with high mechanical strength

Alumina aerogels reinforced with hydroxyethyl cellulose (HEC) have been successfully synthesised using an environmentally friendly freeze-drying method. Alumina aerogels are materials with interesting properties, such as low density, high-temperature stability, high porosity and high surface area, which can be used in several industrial applications. It is necessary to add one or more supporting materials, such as carbon nanofibres and a fibrous second phase such as cellulose, to the matrix to reinforce the mechanical properties of the aerogels. In this study, the influence of the HEC-to-aluminium tri-sec-butoxide (ASB) solution mass ratio on the morphological, mechanical and thermal properties of the synthesised aerogels and its impact on the thermal insulation properties of the resulting materials were evaluated. The apparent density of the hydroxyethyl cellulose-reinforced alumina-based aerogels increased with the amount of HEC. Thus, compact structures with a small pore size were obtained when increasing HEC/ASB solution mass ratio. The incorporation of HEC into the ASB matrix led to an increase in the mechanical properties in terms of the Young’s modulus. Thermal stability of samples varied as a consequence of the HEC addition. Thus, the second decomposition stage shifted to lower temperatures with HEC incorporation. In addition, all synthesised aerogels showed low thermal conductivities. The remarkable physical characteristics of the hydroxyethyl cellulose-reinforced alumina-based aerogels prepared herein and the successful synthesis suitable for scale-up make them a good candidate for construction applications

Graphene-based materials behaviour for dyes adsorption

Due to the environmental damage caused by dye dumping, the scientific community has been researching into different adsorbents in order to mitigate this impact. In this respect, different graphene-based materials with a high adsorption capacity were studied (graphite and graphene oxide and two different types of reduced graphene oxide). In this work, four graphene-based materials with different properties and structures were evaluated. All materials were those obtained at each step in the pathway of oxidation, exfoliation, and reduction of graphite for conversion into reduced graphene. These four materials were characterized in depth by different methods (RAMAN, XRD, EDX, SEM, FTIR). Adsorption variables were researched to demonstrate their great adsorptive rate, which reached in some cases values of over 300 mg/g of adsorbed dye. Therefore, this study established a relationship between the physicochemical properties of the materials and their adsorption capacity. Furthermore, the effect of different variables on the process was studied: temperature, contact time and amount of adsorbent.This study creates new adsorbent materials with a long lifespan, reducing the environmental impact of industry on nature.Debido al daño ambiental causado por el vertido de colorantes, la comunidad científica ha estado investigando diferentes adsorbentes para mitigar este impacto. En este sentido, se estudiaron diferentes materiales a base de grafeno con una alta capacidad de adsorción (grafito y óxido de grafenoy dos tipos diferentes de óxido de grafeno reducido). En este trabajo se evaluaron cuatro materiales a base de grafeno con diferentes propiedades y estructuras. Todos los materiales fueron los obtenidos en cada paso del proceso de oxidación, exfoliación y reducción del grafito para convertirlo en grafeno reducido. Estos cuatro materiales se caracterizaron en profundidad por diferentes métodos (RAMAN, XRD, EDX, SEM, FTIR). Se investigaron variables de adsorción para demostrar su gran tasa de adsorción, que alcanzó en algunos casos valores superiores a 300 mg/g de colorante adsorbido. Por lo tanto, este estudio estableció una relación entre las propiedades fisicoquímicas de los materiales y su capacidad de adsorción. Además, se estudió el efecto de diferentes variables en el proceso: temperatura, tiempo de contacto y cantidad de adsorbente

Solvent-Based Exfoliation via Sonication of Graphitic Materials for Graphene Manufacture

Graphene, a new 2D material, is gaining a lot of attention because of its remarkable mechanical, electrical, chemical, thermal, and optical properties. Graphene synthesis procedures can follow two different strategies named as “bottom up” and “top down”. In the first one, a carbonaceous carbon material is used to deposite graphene over a substrate and, in the second one, graphite is used as raw material to obtain graphene using different methods. Inside the top down strategy, exfoliation of carbon nanomaterials, both graphite and graphene oxide, is considered as a cheap and simple method to synthesize graphene. Graphite exfoliation can be conducted with both aqueous and organic methods. On the other hand, different alternatives to produce graphene using graphene oxide as the raw material can be followed, which are based on either the presonication of graphite, as a previous step for manufacturing graphene, or the sonication of the synthesized graphite oxide, leading to graphene oxide.El grafeno, un nuevo material 2D, está ganando mucha atención debido a sus notables propiedades mecánicas, eléctricas, químicas, térmicas y ópticas. Los procedimientos de síntesis de grafeno pueden seguir dos estrategias diferentes denominadas "de abajo hacia arriba" y "de arriba hacia abajo". En el primero, se utiliza un material de carbono carbonoso para depositar grafeno sobre un sustrato y, en el segundo, se utiliza grafito como materia prima para obtener grafeno por diferentes métodos. Dentro de la estrategia top down, la exfoliación de nanomateriales de carbono, tanto de grafito como de óxido de grafeno, se considera un método económico y sencillo para sintetizar grafeno. La exfoliación de grafito se puede realizar con métodos acuosos y orgánicos. Por otro lado, se pueden seguir diferentes alternativas para producir grafeno utilizando óxido de grafeno como materia prim

PVA/nanoclay/graphene oxide aerogels with enhanced sound absorption properties

Aerogels based on a ternary system of polyvinyl alcohol (PVA), nanoclay and thermally reduced graphene oxide (trGO) have been synthesised at pilot plant scale using an environmentally friendly freeze-drying method. In the present work, the influence of the trGO addition on the physical, thermal and acoustic properties of the resulted aerogels has been evaluated. The trGO incorporation into the PVA/nanoclay matrix resulted in pore diameter decrease. In addition, trGO addition allowed to improve thermal stability of the aerogels. On the other hand, the introduction of the trGO resulted in improvements of the sound absorption coefficient of the aerogels. This process opens new opportunities to produce materials with exceptional properties as thermal insulators (resulting values of the thermal conductivities ranging from 0.0255 to 0.0289 W/m·K) with enhanced sound absorption properties.Aerogeles basados ​​en un sistema ternario de alcohol polivinílico (PVA), nanoarcilla y óxido de grafeno reducido térmicamente (trGO) se han sintetizado a escala de planta piloto utilizando un método de liofilización respetuoso con el medio ambiente. En el presente trabajo se ha evaluado la influencia de la adición de trGO sobre las propiedades físicas, térmicas y acústicas de los aerogeles resultantes. La incorporación de trGO en la matriz de PVA/nanoarcilla resultó en una disminución del diámetro de los poros. Además, la adición de trGO permitió mejorar la estabilidad térmica de los aerogeles. Por otro lado, la introducción del trGO resultó en mejoras del coeficiente de absorción de sonido de los aerogeles. Este proceso abre nuevas oportunidades para producir materiales con propiedades excepcionales como aislantes térmicos (resultando valores de las conductividades térmicas que van desde 0.0255 a 0

CVD-graphene growth on different polycrystalline transition metals

The chemical vapor deposition (CVD) graphene growth on two polycrystalline transition metals (Ni and Cu) was investigated in detail using Raman spectroscopy and optical microscopy as a way to synthesize graphene of the highest quality (i.e. uniform growth of monolayer graphene), which is considered a key issue for electronic devices. Key CVD process parameters (reaction temperature, CH4/H2flow rate ratio, total flow of gases (CH4+H2), reaction time) were optimized for both metals in order to obtain the highest graphene uniformity and quality. The conclusions previously reported in literature about the performance of low and high carbon solubility metals in the synthesis of graphene and their associated reaction mechanisms, i.e. surface depositionand precipitation on cooling, respectively, was not corroborated by the results obtained in this work. Under the optimal reaction conditions, a large percentage of monolayer graphene was obtained over the Ni foil since the carbon saturation was not complete, allowing carbon atoms to be stored in the bulk metal, which could diffuse forming high quality monolayer graphene at the surface. However, under the optimal reaction conditions, the formation of a non-uniform mixture of few layers and multilayer graphene on the Cu foil was related to the presence of an excess of active carbon atoms on the Cu surfaceEl crecimiento de grafeno por deposición química de vapor (CVD) en dos metales de transición policristalinos (Ni y Cu) se investigó en detalle utilizando espectroscopía Raman y microscopía óptica como una forma de sintetizar grafeno de la más alta calidad (es decir, crecimiento uniforme de grafeno monocapa), que es considerado un tema clave para los dispositivos electrónicos. Parámetros clave del proceso de CVD (temperatura de reacción, relación de caudal de CH 4 /H 2 , flujo total de gases (CH 4 +H 2), tiempo de reacción) se optimizaron para ambos metales con el fin de obtener la mayor uniformidad y calidad del grafeno. Las conclusiones previamente reportadas en la literatura sobre el desempeño de metales de baja y alta solubilidad en carbono en la síntesis de grafeno y sus mecanismos de reacción asociados, es decir , deposición superficial y precipitación al enfriarse ., respectivamente, no fue corroborada por los resultados obtenidos en este trabajo. Bajo las condiciones óptimas de reacción, se obtuvo un gran porcentaje de grafeno monocapa sobre la lámina de Ni ya que la saturación de carbono no fue completa, lo que permitió que los átomos de carbono se almacenaran en el metal a granel, que podría difundirse formando grafeno monocapa de alta calidad en la superficie. Sin embargo, bajo las condiciones óptimas de reacción, la formación de una mezcla no uniforme de pocas capas y grafeno multicapa sobre la lámina de Cu se relacionó con la presencia de un exceso de átomos de carbono activo en la superficie de C

Development of organic aerogels reinforced with carbonaceous nanomaterials

Aerogels are currently claimed as one of the most promising materials for different applications such as aerospace, high temperature insulation, cryogenic applications, refrigeration systems, outdoor clothing and building insulation [1]. Aerogel [2,3] is a synthetic porous ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. Basically, an organic polymer aerogel is an aerogel with a framework primarily comprised of organic polymers. They are generally less crumbly and brittle than inorganic aerogels. The most common method to obtain wet gels is sol gel process [4,5]. Nevertheless, the resulting products have some disadvantages such as low porosity, low flexibility and low lightness. However, the freeze-drying method, in which the pore liquid is frozen and then sublimed in vacuum, allows the production of porous aerogels with interesting insulating behavior [6]. This method is simple, low-cost and environmentally friendly. Up to date, few works have been reported about the freeze-drying process to produce organic aerogels [7-9]. Carbonaceous nanomaterials are widely employed as reinforcements to form carbon-reinforced composites which have exhibited enhanced mechanical, electrical and functional properties compared to monolithic materials [10]. Carbon nanofibers or nanotubes (CNF, CNT), carbon nanospheres (CNS), reduced graphene oxide (RG) and, graphene oxide (GO) exhibit outstanding physical and mechanical properties, including high surface to volume area, high Young´s modulus, low coefficient of thermal expansion and an entangled structure. Therefore, the mechanical properties and the thermal and the electrical conductivity of the organic aerogels could be enhanced with the addition of these nanomaterials

Influence of the oxidizing agent in the synthesis of graphite oxide

The oxidation capacity of several procedures described in the literature which use different oxidizing agents has been exhaustively studied in order to describe the best route for oxidation of this material. The oxidation capacities of different types of materials were evaluated in the synthesis of graphite oxide in an effort to obtain a product with similar characteristics to those provided by commonly employed methods. The results obtained show that graphite oxide structures are greatly influenced by the nature of the oxidizing agent used. It was concluded that it is possible not only to establish the number of oxygenated groups attached to the structure but also, and depending on the oxidizing agent used, to know the stability of graphite oxide. The different characteristics of each graphite oxide obtained could facilitate their use in multiple applications.La capacidad de oxidación de varios procedimientos descritos en la literatura que utilizan diferentes agentes oxidantes ha sido exhaustivamente estudiada con el fin de describir la mejor ruta de oxidación de este material. Se evaluaron las capacidades de oxidación de diferentes tipos de materiales en la síntesis de óxido de grafito en un esfuerzo por obtener un producto con características similares a las proporcionadas por los métodos comúnmente empleados. Los resultados obtenidos muestran que las estructuras del óxido de grafito están muy influenciadas por la naturaleza del agente oxidante utilizado. Se concluyó que es posible no solo establecer el número de grupos oxigenados adheridos a la estructura sino también, y dependiendo del agente oxidante utilizado, conocer la estabilidad del óxido de grafito

Improvement of the mechanical and flame-retardant properties of polyetherimide membranes modified with Graphene oxide

Polyetherimide (PEI) membranes doped with different amounts (1–5 wt.%) of Graphene Oxide (GO) were prepared through a solution casting method. The effect of the Graphene Oxide incorporation on mechanical and flame-retardant properties was investigated by XDR, FTIR and SEM analyses. Results showed that the addition of 5 wt.% of GO into the membranes caused a 30% of improvement in the tensile strength and a significant increase in the glass transition temperature. Flame-retardant properties were improved when the amount of Graphene Oxide into PEI membrane was increased. These improvements in the membrane composites expand its application for aerospace and building industries.Se prepararon membranas de polieterimida (PEI) dopadas con diferentes cantidades (1–5% en peso) de óxido de grafeno (GO) mediante un método de fundición en solución. El efecto de la incorporación de óxido de grafeno sobre las propiedades mecánicas y retardantes de llama se investigó mediante análisis XDR, FTIR y SEM. Los resultados mostraron que la adición del 5% en peso de GO en las membranas provocó una mejora del 30% en la resistencia a la tracción y un aumento significativo en la temperatura de transición vítrea. Las propiedades ignífugas mejoraron cuando se incrementó la cantidad de óxido de grafeno en la membrana PEI. Estas mejoras en los compuestos de membrana amplían su aplicación para las industrias aeroespacial y de construcción