Nanoestruturas em fotocatálise: uma revisão sobre estratégias de síntese de fotocatalisadores em escala nanométrica

Advanced oxidative processes (AOPs) are based on chemical processes that can generate free radicals, such as hydroxyl radicals (.OH) which are strong, non-selective oxidant species that react with the vast majority of organic compounds. Nanostructured semiconductors, especially titanium dioxide (TiO2) in the anatase phase, are well-established photocatalysts for this process, which have proved to be useful in the degradation of dyes, pesticides and other contaminants. Research in different strategies for the synthesis of nanostructured semiconductors, with particular characteristic is currently a topic of interest in many studies. Thus, this paper presents a review about various synthesis strategies of nanostructured photocatalysts.

Eletrodos modificados por hidróxido de níquel: um estudo de revisão sobre suas propriedades estruturais e eletroquímicas visando suas aplicações em eletrocatálise, eletrocromismo e baterias secundárias

The present review paper describes the main features of nickel hydroxide modified electrodes covering its structural and electrochemical behavior and the newest advances promoted by nanostructured architectures. Important aspects such as synthetic procedures and characterization techniques such as X-Ray diffraction, Raman and Infrared spectroscopy, Electronic Microscopy and many others are detailed herein. The most important aspect concerning nickel hydroxide is related to its great versatility covering different fields in electrochemical-based devices such as batteries, electrocatalytic systems and electrochromic electrodes, the fundamental issues of these devices are also commented. Finally, some of the newest advances achieved in each field by the incorporation of nanomaterials will be shown.

Catalisadores metalocênicos suportados para a produção de poliolefinas: revisão das estratégias de imobilização

The inadequacy of strategies used for the heterogeneization of metallocene catalysts is pointed out as one of the main causes of the lack of industrial employability of such polymerization catalysts. The main problems are the necessity of large quantity of MAO (cocatalyst) and the inability to control molecular mass distribution of the polymers. Based on this background, the main strategies for the heterogeneization of metallocenes are here reviewed. The advantages and disadvantages of each strategy are presented and discussed on theoretical and practical perspective. Considering the results reported on the different researches, outcomes of heterogeneization strategies are pointed out.

Uma revisão sobre o efeito Toms: o fenômeno onde macromoléculas atenuam a turbulência em um líquido

It is very well known that the addition of polymers to a liquid increases the shear viscosity of the solution. In other words, the polymer increases the dissipation of the flow energy. Contrarily, in turbulent flow, some particular macromolecules in very low concentration are able to produce large attenuation in the turbulence and thus, decreasing the dissipation of the energy. This article present a brief revision about macroscopic and molecular models used to explain this dynamic effect. Some of the experimental techniques used to quantify the attenuation of the turbulence and the main active substances are also discussed.

A intrigante bioquímica da niacina: uma revisão crítica

Niacin (nicotinamide, nicotinic acid) interferes on homeostasis, DNA regulation, signaling and longevity. Nicotinic acid reduces synthesis of lipoproteins-apo-B and increases HDL. Its antilipemic action in liver produces: 1) inhibition of DGAT2, with decreased triacylglycerol synthesis, 2) downregulation of the b-chain of adenosine triphosphate synthase, leading to reduced HDL-apo-A-I catabolism. Nicotinic acid could increase redox potential in vascular endothelium. HM74A receptor activation in macrophages would be responsible for the release of prostaglandins, causing flushing in epidermis. HM74A agonists could assist in identifying antilipemic agents. Extended release niacin in combination with statin appears to protect cardiovascular system of patients with low HDL.

Formaldeído em escolas: uma revisão

Formaldehyde has been classified as a probable human carcinogen. Indoor air quality measurements carried out worldwide in schools indicate that levels may be of concern. This paper provides an overview of emission sources, properties and methods for quantification of formaldehyde. Quantitative information from studies performed in school environments was compiled and a comprehensive picture of the causal relationships between pollutant exposures and children's health given. Mitigation actions to reduce formaldehyde levels and its adverse impacts in school buildings are recommended.

Revisão dos tratamentos químicos da fibra natural para mistura com poliolefinas

The use of natural fibers as reinforcement in polymer composites has been a focus of interest. However, these composites exhibit lower mechanical properties than those of pure polymers because of the low interfacial interactions between the hydrophobic polymer matrix and the hydrophilic fiber. To overcome this problem, different chemical treatments applied to the fibers have been reported. One of the most used treatments is mercerization, which can improve adhesion between the fiber and polymeric matrix. Another chemical treatment involves the use of acids (stearic and oleic acids). The chemically treated fibers used in composite materials showed improved mechanical properties.

Óxidos de ferro e suas aplicações em processos catalíticos: uma revisão

A review of most of the reported studies on the use of iron oxides as catalyst in specific processes, namely Haber-Bosch reaction, Fischer-Tropsch synthesis, Fenton oxidation and photolytic molecular splitting of water to produce gaseous hydrogen, was carried out. An essential overview is thus presented, intending to address the fundamental meaning, as well as the corresponding chemical mechanisms, and perspectives on new technological potentialities of natural and synthetic iron oxides, more specifically hematite (α-Fe2O3), goethite (α-FeOOH), magnetite (Fe3O4) and maghemite (γ-Fe2O3), in heterogeneous catalysis.

A Importância da determinação analítica de intermediários reativos e de seus produtos de reações com biomacromoléculas: uma mini revisão

Metabolic reactive intermediates can react with biomolecules such as DNA and proteins to produce adducts. Recently, research has shown that such adducts can act as precursors of some chronic diseases (cancer, Parkinson's, immunologic system diseases, etc.), and their determination is important because they are biomarkers of undesirable health effects. These compounds are produced at very low concentrations, but the development and dissemination of sensitive new analytical tools, especially those based on chromatography coupled to other analytical instruments, make such determinations possible. This mini review is focused on the formation of reactive intermediates, their reaction with biomolecules, and the importance of their determination.

Análise química da biomassa - uma revisão das técnicas e aplicações

Use of biomass as an alternative to nonrenewable feedstock for energy, materials, and chemicals is currently a prominent theme for industry and R Countries like Brazil, USA, and Germany are spending resources and efforts to promote a green economy based on biomass supply chains. Chemical analysis is an important tool to ensure quality, reliability, and to suggest the best potential use for the biomass, thereby enhancing its economic potential. Analytical techniques can identify chemical components, characterize their properties, and determine their concentration. This article discusses the commonly employed techniques and their application in chemical analysis of biomass and its products.

A VERSATILIDADE DOS COMPOSTOS DE COORDENAÇÃO NA PRODUÇÃO DE POLIETILENOS: UMA REVISÃO DOS SISTEMAS CATALÍTICOS

Taking into account the relevance of polyethylene for modern society and the role of catalysts for the production of this material, in the present work, we carried out a review of the main catalytic systems used in industry and academia. Most systems consist of coordination compounds, whose structural versatility allows the tuning of the characteristics of polyethylene for different applications. The structural aspects and chemical reactivity of such systems are discussed based on the existing literature and experimental data.

DEGRADAÇÃO MICROBIOLÓGICA E ENZIMÁTICA DE POLÍMEROS: UMA REVISÃO

Polymer recycling has been one of the most important trend in the petrochemical area. Among different technologies, biotechnological (enzymatic and/or microbial) degradation of polymers for the recovery of monomers and oligomers is environmentally-friendly and meet some green chemistry principles. In this work, conditions for the biotechnological degradation of some industrially-relevant polymers (e.g. poly(ethylene terephthalate) and polyethylene) were revised, and the main biocatalysts were identified. In most cases, biodegradation mechanisms are still unclear, thus being necessary more studies to unravel these promising bioprocesses. Polymer biodegradation studies also present considerable importance for other fields, including biomedical and agricultural.

METODOLOGIAS DE COLETA, PRESERVAÇÃO E ARMAZENAMENTO DE AMOSTRAS DE ÁGUA PARA ANÁLISE DE MERCÚRIO - UMA REVISÃO

Knowing the mercury levels of an environment allows a diverse array of biogeochemical studies into the mercury cycle on a local or global scale. Among matrices commonly evaluated, water remains a challenge for research because its mercury levels can be very low, requiring development of complex analytical protocols. Currently, sample preservation methods, protocols that avoid contamination, and analytical techniques with low detection limits allow analysis of mercury in pristine waters. However, different protocols suggest different methods depending on a range of factors such as the characteristics of water sampled and storage time. In remote areas, such as oceanic and Amazonian regions, sample preservation and transport to a laboratory can be difficult, requiring processing of the water during the sampling expedition and the establishment of a field laboratory. Brazilian research on mercury in water can be limited due to difficulty obtaining reagents, lack of laboratory structure, qualified personnel, and financial support. Considering this complexity for analyzing water, we reviewed methodologies for sampling, preservation, and storage of water samples for analysis of the most commonly evaluated mercury species (dissolved gaseous mercury, reactive mercury, methylmercury and total mercury).

COMUNICAÇÃO CIENTÍFICA NO ENSINO SUPERIOR DE QUÍMICA: UMA REVISÃO

The importance of teaching scientific communication skills in undergraduate chemistry courses is well recognized. This paper provides an overview of didactic activities in which students engage to improve these skills. The study was based on an extensive literature review performed on the Journal of Chemical Education and on the Journal of College Science Teaching, in the years spanning from 1991 to 2010, and on The Chemical Educator, from 1996 to 2010. The findings from the study provided an opportunity to expand the knowledge on the variety of methods and contents used to teach scientific communication skills in undergraduate chemistry education, as well as to deepen our understanding of the effects of different approaches to teaching on performance in practice.

Revisão taxonômica de algumas espécies de Ravenelia em leguminosas do Cerrado brasileiro

Oito espécies de Ravenelia descritas anteriormente foram revisadas e acrescentadas ilustrações inéditas das características morfológicas de alguns desses fungos causadores de ferrugem em Leguminosae. As espécies de Ravenelia estudadas foram: Ravenelia bezerrae sobre Enterolobium ellipticum ; R. densifera sobre Senna silvestris; R. dieteliana sobre Calliandra dysantha. var. dysantha; R. geminipora sobre Platymenia reticulata; R. lonchocarpi sobre Lonchocarpus campestris; R. mimosae-sensitivae sobre Mimosa radula var. imbricata; R. pileolarioides sobre Caesalpinia pyramydales e R. santos-costae, sobre Calliandra dysantha.