Few layer reduced graphene oxide : evaluation of the best experimental conditions for easy production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Chitosan nanocomposites with graphene-based filler

This study evaluates the properties of chitosan (CS) membranes modified with different percentages (0.5%, 3%, and 5% w/w) of a graphene-based material. Graphene oxide (GO) and reduced graphene oxide (RGO) were obtained by the chemical exfoliation of graphite and thermal reduction. Then, they were characterized by electrical conductivity measurements, FESEM, XRD, AFM, and Raman spectroscopy. The composites’ morphology was evaluated by FESEM. The degree of swelling over a 48 h period and mass loss behavior in phosphate-buffered saline solution for up to 70 days were also studied. The hydrophilicity of the CS and CS/graphene nanocomposites was examined by water contact angle. The graphene materials showed small stacks (6-8 sheets) with low defect density and nanoscale thickness (1.3-5.9 nm). The dispersion of the graphene material in the CS matrix significantly decreased the degree of swelling (460%) but did not modify the hydrolytic degradation process and the hydrophilicity of membranes

Reduced graphene oxide decorated with Ni-Fe-Mo permalloy obtained by sputtering

This work illustrates an effective method for obtaining hybrid nanoparticles of Ni-Fe-Mo permalloy and reduced graphene oxide (rGO). The metallic nanoparticles were spread by the sputtering technique, which allowed a good dispersion of the metallic nanoparticles onto rGO substrate powder. TEM showed permalloy nanoparticles smaller than 8 nm uniformly distributed throughout rGO. Permalloy/rGO hybrid with 10.5 wt% loading of permalloy nanoparticles was calculated by TGA. RBS experiment reveals that permalloy target and the nano-particles deposited have similar composition. The interaction between permalloy and rGO was studied by FT-IR. Ni-Fe-Mo/rGO presented an electrical conductivity of 122 Scm -¹, significantly higher than the original rGO and a magnetization hysteresis-loop coercivity of 16 Oe at room temperature. To our knowledge this is the first work in which permalloy nanoparticles are deposited onto graphene powder substrate by a physical impregnation technique

Preparation of graphene oxide and reduced graphene oxide and dispersion in biodegradable polymeric matrix

Submitted by Setor de Tratamento da Informa??o - BC/PUCRS ([email protected]) on 2016-11-29T15:45:36Z No. of bitstreams: 1 DIS_THUANY_GARCIA_MARASCHIN_COMPLETO.pdf: 3644963 bytes, checksum: fa378de0f5287d6d9eeabe72fda2aa16 (MD5)Made available in DSpace on 2016-11-29T15:45:36Z (GMT). No. of bitstreams: 1 DIS_THUANY_GARCIA_MARASCHIN_COMPLETO.pdf: 3644963 bytes, checksum: fa378de0f5287d6d9eeabe72fda2aa16 (MD5) Previous issue date: 2016-08-26Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPESThe development of methodologies able to prepare new materials, using graphene in its structure, is technological innovation that converts low-cost products in advanced materials with aggregate amount. The present work is related with the preparation of graphene oxide (GO) and reduced graphene oxide (RGO) in reasonable quantities directed to prepare nanocomposites based on biodegradable polymeric matrix. Initiating from natural graphite, Grafine, experimental conditions were investigated to obtain the GO and its reduced form, RGO, by the method of chemical exfoliation followed by thermal reduction. In order to optimize the process were evaluated oxidation time (12, 24 and 48 hours) and temperature reduction (600?C and 1000?C). The films of the nanocomposites containing different amounts of graphene (0.5; 3 and 5% w/w) dispersed in the chitosan matrix were prepared using solvent evaporation method. The characterization analyses of materials obtained were made by: Scanning Electron Microscopy, Transmission and Atomic Force, X-ray Diffraction, Thermogravimetric analysis, Elemental Analysis, Raman spectroscopy and Electric Conductivity Analysis. The 24 hours of oxidation time was sufficient for the intercalation of functional groups between the sheets of graphene and obtain GO with 29% oxygen. The reduction in temperature of 1000?C was effective in restoring graphitic network and resulted in RGO with a stack of 7-8 sheets, thermally stable and electrical conductivity of 55 S/cm. Addition of graphene in the biodegradable matrix did not modify the thermal stability and it did not change substantially the process of degradation of the prepared nanocomposites.O desenvolvimento de metodologias capazes de preparar novos materiais, que utilizem grafeno na sua estrutura, representa inova??o tecnol?gica que transforma produtos de baixo custo em materiais avan?ados com alto valor agregado. O presente trabalho est? relacionado com a prepara??o de ?xido de grafeno (OG) e ?xido de grafeno reduzido (OGR) em quantidades razo?veis visando ? prepara??o de nanocomp?sitos baseados em matriz polim?rica biodegrad?vel. Partindo do grafite natural, Grafine, foram investigadas condi??es experimentais para obten??o do OG e sua forma reduzida, OGR, pelo m?todo da esfolia??o qu?mica, seguida de redu??o t?rmica. A fim de otimizar o processo foram avaliados tempo de oxida??o (12, 24 e 48 horas) e temperatura de redu??o (600?C e 1000?C). Os filmes dos nanocomp?sitos com diferentes quantidades de grafenos (0,5; 3 e 5% m/m) dispersos na matriz de quitosana foram preparados usando a metodologia da evapora??o do solvente. A caracteriza??o dos materiais preparados deu-se por: Microscopia Eletr?nica de Varredura, de Transmiss?o e de For?a At?mica, Difra??o de Raios X, An?lise Termogravim?trica, An?lise Elementar, Espectrometria RAMAN e An?lise de condutividade el?trica. O tempo de oxida??o de 24 horas foi suficiente para a intercala??o de grupos funcionais entre as l?minas de grafeno e obten??o de OG com 29% de oxig?nio. A redu??o na temperatura de 1000?C foi eficiente na restaura??o da rede graf?tica e resultou em OGR com um empilhamento de 7-8 l?minas, est?vel termicamente e com condutividade el?trica de 55 S/cm. A adi??o dos grafenos na matriz biodegrad?vel n?o modificou a sua estabilidade t?rmica e n?o alterou significativamente o processo de perda de massa dos nanocomp?sitos preparados

Synthesis of high-density polyethylene/rGO-CNT-Fe nanocomposites with outstanding magnetic and electrical properties

Semi-conducting polyethylene (PE) nanocomposites with outstanding magnetic properties at room temperature were synthesized. These exceptional properties, for a diamagnetic and insulating matrix as PE, were obtained by polymerizing ethylene in the presence of a catalytic system formed by a metallocene catalyst supported on a mixture of reduced graphene oxide (rGO) and carbon nanotubes with encapsulated iron (CNT-Fe). It was used a constant and very low amount of CNT-Fe, obtained by vapor chemical deposition using ferrocene. The percolation threshold, to achieve conductivity, was obtained using a variable amount of rGO. The nanocomposites were semiconductors with the addition of 2.8 wt % and 6.0 wt % of the filler, with electrical conductivities of 4.99 3 1026 S cm21 and 7.29 3 1024 S cm21, respectively. Very high coercivity values of 890–980 Oe at room temperature were achieved by the presence of only 0.04–0.06 wt % of iron in the nanocomposites. The novelty of this work is the production of a thermoplastic with both, magnetic and electric properties at room temperature, by the use of two fillers, that is rGO and CNT-Fe. The use of a small amount of CNT-Fe to produce the magnetic properties and variable amount of rGO to introduce the electrical conductivity in PE matrix let to balance both properties. The encapsulation strategy used to obtain Fe in CNT, protect Fe from easy oxidation and aggregation

Polyethylene/reduced graphite oxide nanocomposites with improved morphology and conductivity

Artículo de publicación ISIThe use of graphite and polyolefins as starting materials to prepare nanocomposites is convenient because both are inexpensive and have very different properties, one is conductive and the other is insulating. The formation of nanocomposites can extend the applicability of both commodities. In this work we synthesized nanocomposites of polyethylene (PE) with two types of graphites, graphite oxide (GO) and reduced graphite oxide (RGO), by in situ polymerization using a supported metallocene catalyst. The functional groups on the graphites were used to support the metallocene catalyst by a previous treatment with methylaluminoxane. The nanocomposites were obtained with good catalytic activities and presented excellent morphology and dispersion; their elastic modulus and crystallization temperatures were higher than those of neat PE. However, the nanocomposites PEGO were insulant, whereas PERGO had a conductivity of 1.1 x 10(-5) S cm(-1) with 3.1 wt% filler. This is a significant result compared to the conductivity obtained using non-supported graphite nanosheets where more than 15 wt% of graphite nanosheets are needed to obtain conductivities higher than 10(-7) S cm(-1). This improvement in the percolation threshold was attributed to the good morphology of the PERGO nanocomposites obtained due to the control of the graphitic sheets and the support methodology.CNPq 302902/2013-9 473128/2011-0 FAPERG-PRONEX 09/2009 Department of the Navy Grant N62909-11-1-7069 Millennium Nucleus of Chemical Processes and Catalysis (CPC) NC12008

Few layer reduced graphene oxide : evaluation of the best experimental conditions for easy production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Chitosan nanocomposites with graphene-based filler

This study evaluates the properties of chitosan (CS) membranes modified with different percentages (0.5%, 3%, and 5% w/w) of a graphene-based material. Graphene oxide (GO) and reduced graphene oxide (RGO) were obtained by the chemical exfoliation of graphite and thermal reduction. Then, they were characterized by electrical conductivity measurements, FESEM, XRD, AFM, and Raman spectroscopy. The composites’ morphology was evaluated by FESEM. The degree of swelling over a 48 h period and mass loss behavior in phosphate-buffered saline solution for up to 70 days were also studied. The hydrophilicity of the CS and CS/graphene nanocomposites was examined by water contact angle. The graphene materials showed small stacks (6-8 sheets) with low defect density and nanoscale thickness (1.3-5.9 nm). The dispersion of the graphene material in the CS matrix significantly decreased the degree of swelling (460%) but did not modify the hydrolytic degradation process and the hydrophilicity of membranes