A new post-metallocene-ti catalyst with maltolate bidentade ligand: an investigation in heterogeneous polymerization reactions in different mesoporous supports

A new titanium catalyst easily synthesized from ethylmaltol bidentate chelator ligand was studied in homogeneous and heterogeneous ethylene polymerization. The dichlorobis(3-hydroxy-2-ethyl-4-pyrone)titanium(IV) complex was characterized by 1H and 13C NMR (nuclear magnetic resonance), UV-Vis and elemental analysis. Theoretical study by density functional theory (DFT) showed that the complex chlorines exhibit cis configuration, which is important for the activity in olefin polymerization. The complex was supported by two methods, direct impregnation or methylaluminoxane (MAO) pre-treatment, in five mesoporous supports: MCM-41 (micro and nano), SBA-15 and also the corresponding modified Al species. All the catalytic systems were active in ethylene polymerization and the catalytic activity was strongly influenced by the method of immobilization of the catalyst and the type of support.info:eu-repo/semantics/publishedVersio

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

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

New isopropylmaltol - Ti synthesis and its use as a catalyst for olefin polymerization

Este artigo mostra a síntese e caracterização do ligante isopropilmaltol obtido a partir do furfural e também um novo complexo diclorobis-(3-hidroxi-2-isopropil-4-pirona)titânio(IV) com estrutura cis. Dados de ressonância magnética nuclear de 1H, análise elementar e UV-Vis confirmam a formação do complexo. Este complexo foi estudado em reações de polimerização de etileno utilizando metilaluminoxano (MAO) como co-catalisador. A atividade catalítica deste complexo é baixa, entretanto foram obtidos polietilenos com alto peso molecular que são interessantes para diferentes aplicações.This report describes a new synthesis of isopropylmaltol from furfural. This organic compound was used as ligand to obtain a new complex, the dichlorobis-(3-hydroxy-2-isopropyl-4-pyrone) titanium(IV). 1H nuclear magnetic ressonance, elemental analysis and UV-Vis analysis confirm the complex formation. This complex was investigated in ethylene polymerization using methylaluminoxane (MAO) as cocatalyst. The catalytic activity was low, however, there were obtained very high molecular weight polyethylenes, which are interesting for various special applications

Elementary charge measurement by water electrolysis

This article presents an educational technique recommended for High School students or undergraduates on Physics or Chemistry education, which allows the measurement of the elementary charge through  water  electrolysis.  The  proposed  experiment  wraps material of easy attainment, the results have sufficient precision for the    education    purposes,    and    its    realization    promotes   interdisciplinarity, since it wraps knowledge of different areas. In addition,  this  article  presents  results  obtained  by  pupils  in laboratory classrooms

Medição da carga elementar por eletrólise da água

This article presents an educational technique recommended for High School students or undergraduates on Physics or Chemistry education, which allows the measurement of the elementary charge through  water  electrolysis.  The  proposed  experiment  wraps material of easy attainment, the results have sufficient precision for the    education    purposes,    and    its    realization    promotes   interdisciplinarity, since it wraps knowledge of different areas. In addition,  this  article  presents  results  obtained  by  pupils  in laboratory classrooms.http://dx.doi.org/10.5007/2175-7941.2009v26n2p328Este artigo apresenta uma técnica didática recomendada para o Ensino Médio ou Superior de Física ou Química, que permite a medição da carga elementar por meio da eletrólise da água. O experimento proposto envolve material de fácil obtenção, os resultados são suficientemente precisos para os fins educacionais aos quais se destinam, e sua realização promove a interdisciplinaridade, pois envolve conhecimentos de áreas distintas. São também apresentados resultados obtidos por alunos em aulas de laboratório