Cu
2+ ion removal from aqueous streams by poly(acrylic acid-co-acrylamide) hydrogels is discussed. The monomer ratio has a significant effect on Cu
2+ removal. XPS and FTIR results suggest the ...formation of a tetradentate copper complex.
The adsorption of Cu(II) ions from aqueous solutions onto poly(acrylic acid-co-acrylamide) hydrogels was investigated. The hydrogels were prepared via free-radical solution polymerization using Irgacure 754 as a photoinitiator and ethylene glycol dimethacrylate as a cross-linking agent. Loading of acrylamide/acrylic acid moieties on the surfaces of hydrogels and the amount of cross-linking agent were varied to determine the maximum metal uptake. Polymerization kinetics was investigated by
1H NMR. The physicochemical properties of hydrogels were investigated by nitrogen sorption measurements, elemental analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The
1H NMR results demonstrated that the polymerization reaction was carried out almost to completion and confirmed the absence of residual monomers. Swelling results indicated that, by appropriate selection of cross-linking agent amount and monomer ratio, hydrogels can be swollen up to 70,000%. Further characterization of the hydrogels showed rapid adsorption kinetics and equilibrium Cu(II) adsorption capacities of 121
mg
g
−1. Cu(II) adsorption kinetic data followed pseudo-first-order kinetics. Adsorption equilibrium data were better fitted by a Langmuir isotherm. FTIR and XPS results indicated the presence of a tetradentate copper complex on the surfaces of hydrogels. The copper uptake achieved suggests the potential use of hydrogels to extract toxic metals from industrial aqueous streams.
Oxidized multiwalled carbon nanotubes (MWCNTs) were employed as sorbent to study the sorption characteristic of Pb(II) from aqueous solution as a function of contact time, pH, ionic strength, foreign ...ions, and oxidized MWCNTs’ contents under ambient conditions using batch technique. The results indicate that sorption of Pb(II) on oxidized MWCNTs is strongly dependent on pH values, and independent of ionic strength and the type of foreign ions. The removal of Pb(II) to oxidized MWCNTs is rather quickly and the kinetic sorption can be described by a pseudo-second-order model very well. Sorption of Pb(II) is mainly dominated by surface complexation rather than ion exchange. The efficient removal of Pb(II) from aqueous solution is limited at pH 7–10. X-ray photoelectron spectroscopy (XPS) is performed to study the sorption mechanism at a molecular level and thereby to identify the species of the sorption processes. The 3-D relationship of pH,
C
eq and
q indicates that all the data of
C
eq
−
q lie in a straight line with slope −
V/
m and intercept
C
0
V/
m for the same initial concentration of Pb(II) and same content of oxidized MWCNTs of each experimental data.
A Natureza e os processos que envolvem partículas carregadas, como elétrons e prótons, são bastante estudados por alunos de ensino médio e em cursos de graduação. A técnica de Espectroscopia de ...Fotoelétrons por Raios X, por exemplo, é desenvolvida a partir de fenômenos físicos de interação de fótons e a matéria. Esta técnica analítica é cada vez mais utilizada na caracterização de rochas terrestres, em missões espaciais à Marte, tal como em análises de meteoritos. Dessa maneira, o objetivo deste trabalho é apresentar de forma sintetizada e simples os conceitos da Espectroscopia de Fotoelétrons por Raios X. Assim, não faz parte da proposta ter um aprofundamento detalhado da técnica, sendo que para maiores especificidades, os leitores poderão obter através de materiais complementares e com assistências de técnicos mais especializados no equipamento que for de seu interesse. Por fim, será apresentado alguns espectros obtidos através da utilização da técnica em um meteorito marciano e explicado de forma sucinta os resultados. Espera-se com isto, que este venha servir de material inicial e de apoio para estudantes que estejam começando a desenvolver interesses científicos e estejam procurando técnicas alternativas para suas pesquisas, tal como a conexão entre conceitos físicos e sua aplicabilidade.
Nature and processes involving charged particles, such as electrons and protons, are extensively studied by high school students and in undergraduate courses. The X-Ray Photoelectron Spectroscopy technique, for example, is developed from physical phenomena of photon and matter interaction. This analytical technique is increasingly used in the characterization of terrestrial rocks, in space missions to Mars, as well as in meteorite analysis. Thus, the objective of this work is to present in a synthesized and simple way the concepts of X-ray Photoelectron Spectroscopy. Thus, it is not part of the proposal to have a detailed deepening of the technique, and for greater specificities, readers will be able to obtain through complementary materials and with the assistance of more specialized technicians in the equipment of interest. Finally, some spectra obtained through the use of the technique on a Martian meteorite will be presented and the results briefly explained. It is hoped that this will serve as initial and support material for students who are beginning to develop scientific interests and are looking for alternative techniques for their research, such as the connection between physical concepts and their applicability.
Polypyrrole (PPy)/Fe3O4 magnetic nanocomposite as a novel adsorbent was prepared via in-situ polymerization of pyrrole (Py) monomer using FeCl3 oxidant in aqueous medium in which Fe3O4 nanoparticles ...were suspended. The adsorbent was characterized by Attenuated Total Reflectance Fourier transform infrared spectroscope (ATR-FTIR), Brunauer–Emmet–Teller (BET) method, field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectroscope (XPS) and X-ray diffraction (XRD). Magnetic property of the adsorbent was measured by electron spin resonance (ESR). Subsequently, the ability of the adsorbent to remove fluoride ions from aqueous solution was demonstrated in a batch sorption mode. Results reveal that the adsorption is rapid and that the adsorbent has high affinity for fluoride, which depends on temperature, solution pH and adsorbent dose. From equilibrium modelling, the equilibrium data is well described by Freundlich and Langmuir–Freundlich isotherms while the adsorption kinetics is described by the pseudo-second-order model. Thermodynamic parameters confirm the spontaneity and endothermic nature of the fluoride adsorption. Meanwhile, the fluoride adsorption proceeds by an ion exchange mechanism.
Recent results on solid oxide fuel cells with Ni/YSZ and Ni/GDC anodes reveal a mechanism for permanent performance degradation due to hydrogen sulfide exposure. Our results confirm the temporary ...performance decline observed by others but also reveal a mechanism for the long term permanent degradation. We find that hydrogen sulfide leads to nickel migration and depletion in the anode, thereby compromising electrical conductivity and cell performance.
Ti/PbO2 + nano-Co3O4 composite electrode materials with different compositions were prepared by anodic composite electrodeposition on Ti substrate, with a SnO2–Sb2O5 intermediate layer in Pb2+ ...plating solution containing suspended nano-Co3O4 particles. The composition, structure, and morphology of the composite materials were investigated by XRD, XPS, and SEM analyses. The composite electrodes were studied as anodes for oxygen evolution reaction (OER) in 1 mol/L NaOH solution. The activities for the OER of the composites were explained by recording linear scanning voltammograms and Tafel plots. Results indicate that the onset potential of oxygen evolution at the composite electrode was lowered by approximately 160 mV compared to the PbO2 electrode without nano-Co3O4. The catalytic activity of the composite electrode towards OER was improved significantly.
► The composition, structure, morphology and the activity for OER of the PbO2 + Nano-Co3O4 composite materials have been investigated in detail. ► The composite porosity and specific area increasing owning to the nano-Co3O4 particles were studied. ► The electrical tests indicate the Eonset of the Ti/PbO2 + Nano-Co3O4 composite electrode decreasing by approximately 160 mV because of the nano-Co3O4 particles co-catalysis.
Aço revestido com eletrodepósitos de liga ZnFe é um material de uso comum na indústria de construção civil e automotiva. O revestimento à base de zinco necessita, entretanto, ser protegido de ...ambientes corrosivos através de um tratamento de superfície que geralmente contém cromo hexavalente (Cr6+), tóxico para o meio ambiente e cancerígeno para o homem. O presente trabalho apresenta um estudo com inibidores de corrosão contendo terras raras (Ce ou La), sobre aço revestido com eletrodepósitos de liga ZnFe. Esses filmes foram avaliados através das Curvas de Polarização, da Espectroscopia de Impedância Eletroquímica (EIE), da Microscopia Eletrônica de Varredura (MEV) e Espectrometria de Energia Dispersiva (EDS). A espectroscopia fotoelétrica de emissão de raios-X (XPS) também foi utilizada para comprovar a presença desses filmes contendo óxidos sobre a superfície da liga ZnFe. Os resultados de EIE e polarização indicaram que as camadas estudadas foram eficientes contra corrosão e que seu desempenho dependia do tipo de cátion presente no sal. A amostra representada por Ce+ZnFe mostrou o melhor desempenho na proteção contra a corrosão, havendo um decréscimo de aproximadamente 10 vezes na densidade de corrente quando a liga foi medida com Ce+ ZnFe um aumento de IZI em uma ordem de grandeza.
O efeito do estiramento uniaxial na superfície de vários compósitos (misturas diluídas de copolímero polietersulfona/polidimetilsiloxano em policloropreno) foi estudado através do método de ...espectroscopia de fotoelétrons excitados por raios-X. A superfície inicial das misturas não estendida foi beneficiada pelo copolímero (75-93%). O estiramento acarretou uma queda da segregação superficial do copolímero. A comparação dos dados experimentais com o estiramento teórico, para diversos modelos de extensão da camada superficial, permitiu concluir que o copolímero com o bloco de polisulfona curto, acompanha exatamente o estiramento da matriz, ao passo que o copolímero com o bloco de polisulfona longo se atrasa um tanto e se estende um tanto menos.
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