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Theory of nitride oxide adsorption on transition metal (111) surfaces: a first-principles investigation

ZENG, Zhen-Hua; SILVA, Juarez L. F. Da; LI, Wei-Xue
Fonte: ROYAL SOC CHEMISTRY Publicador: ROYAL SOC CHEMISTRY
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.9%
In this work, we report a density functional theory study of nitric oxide (NO) adsorption on close-packed transition metal (TM) Rh(111), Ir(111), Pd(111) and Pt(111) surfaces in terms of adsorption sites, binding mechanism and charge transfer at a coverage of Theta(NO) = 0.25, 0.50, 0.75 monolayer (ML). Based on our study, an unified picture for the interaction between NO and TM(111) and site preference is established, and valuable insights are obtained. At low coverage (0.25 ML), we find that the interaction of NO/TM(111) is determined by an electron donation and back-donation process via the interplay between NO 5 sigma/2 pi* and TM d-bands. The extent of the donation and back-donation depends critically on the coordination number (adsorption sites) and TM d-band filling, and plays an essential role for NO adsorption on TM surfaces. DFT calculations shows that for TMs with high d-band filling such as Pd and Pt, hollow-site NO is energetically the most favorable, and top-site NO prefers to tilt away from the normal direction. While for TMs with low d-band filling (Rh and Ir), top-site NO perpendicular to the surfaces is energetically most favorable. Electronic structure analysis show that irrespective of the TM and adsorption site...

Nickel adsorption in two Oxisols and an Alfisol as affected by pH, nature of the electrolyte, and ionic strength of soil solution

MOREIRA, Cindy Silva; CASAGRANDE, Jose Carlos; ALLEONI, Luis Reynaldo Ferracciu; CAMARGO, Otavio Antonio de; BERTON, Ronaldo Severiano
Fonte: SPRINGER HEIDELBERG Publicador: SPRINGER HEIDELBERG
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.92%
Background, aim, and scope The retention of potentially toxic metals in highly weathered soils can follow different pathways that variably affect their mobility and availability in the soil-water-plant system. This study aimed to evaluate the effects of pH, nature of electrolyte, and ionic strength of the solution on nickel (Ni) adsorption by two acric Oxisols and a less weathered Alfisol. Materials and methods The effect of pH on Ni adsorption was evaluated in surface and subsurface samples from a clayey textured Anionic `Rhodic` Acrudox ( RA), a sandy-clayey textured Anionic `Xantic` Acrudox (XA), and a heavy clayey textured Rhodic Kandiudalf (RK). All soil samples were equilibrated with the same concentration of Ni solution (5.0 mg L(-1)) and two electrolyte solutions (CaCl(2) or NaCl) with different ionic strengths (IS) (1.0, 0.1 and 0.01 mol L(-1)). The pH of each sample set varied from 3 to 10 in order to obtain sorption envelopes. Results and discussion Ni adsorption increased as the pH increased, reaching its maximum of nearly pH 6. The adsorption was highest in Alfisol, followed by RA and XA. Competition between Ni(2+) and Ca(2+) was higher than that between Ni(2+) and Na(+) in all soil samples, as shown by the higher percentage of Ni adsorption at pH 5. At pH values below the intersection point of the three ionic strength curves (zero point of salt effect)...

Adsorption of NO on the Rh-13, Pd-13, Ir-13, and Pt-13 Clusters: A Density Functional Theory Investigation

Piotrowski, Mauricio J.; Piquini, Paulo; Zeng, Zhenhua; Silva, Juarez Lopes Ferreira da
Fonte: AMER CHEMICAL SOC; WASHINGTON Publicador: AMER CHEMICAL SOC; WASHINGTON
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.9%
The adsorption of NO on transition-metal (TM) surfaces has been widely studied by experimental and theoretical techniques; however, our atomistic understanding of the interaction of nitrogen monoxide (NO) with small TM clusters is far from satisfactory, which compromises a deep understanding of real catalyst devices. In this study, we report a density functional theory study of the adsorption properties of NO on the TM13 (TM = Rh, Pd, Ir, Pt) clusters employing the projected augmented wave method. We found that the interaction of NO with TM13 is much more complex than that for NO/TM(111). In particular, for low symmetry TM13 clusters, there is a strong rearrangement of the electronic charge density upon NO adsorption and, as a consequence, the adsorption energy shows a very complex dependence even for adsorption sites with the same local effective coordination. We found a strong enhancement of the binding energy of NO to the TM13 clusters compared with the TM(111) surfaces, as the antibonding NO states are not occupied for NO/TM13, and the general relationship based on the d-band model between adsorption energy and the center of gravity of the occupied d-states does not hold for the studied TM13 clusters, in particular, for clusters with low symmetry. In contrast with the adsorption energy trends...

Adsorção competitiva de cádmio, cobre, níquel e zinco em solos.; Competitive adsorption of cadmium, copper, nickel and zinc in soils.

Moreira, Cindy Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/09/2004 PT
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Dentre os processos envolvidos no comportamento e biodisponiblidade dos metais pesados nos solos, aqueles relacionados com a adsorção são de grande importância. Tendo em vista a natureza multielementar do sistema solo-solução e a complexidade das reações envolvidas, o conhecimento dos mecanismos de adsorção em sistemas competitivos permite uma avaliação mais realista do comportamento dos metais no solo. Os objetivos desse trabalho foram (i) avaliar a adsorção competitiva de cádmio, cobre, níquel e zinco, tomadas da camada mais superficial (horizonte A) de 14 solos representativos dos do Estado de São Paulo; (ii) obter isotermas de adsorção em sistemas competitivo e não-competitivo, utilizando a equação matemática de Langmuir para simular a adsorção; (iii) estabelecer seqüências de afinidade metálica para cada solo e (iv) estabelecer a relação entre o comportamento adsortivo dos metais e alguns atributos dos solos, mediante estudos de correlações simples e regressões múltiplas. Ao correspondente a 2,0 g de terra foram adicionados 20 mL de solução 0,01 mol L-1 de NaNO3 (relação 1:10) contendo concentrações equimolares (0,017; 0,034; 0,085; 0,17; 0,255; 0,51; 0,85 e 1,275 mmol L-1) de Cu...

Estudos de adsorção e equilíbrio nos sistemas Cd(II) / SCN-/ C6H12N4 e Cd(II)/I-/SCN-. aperfeiçoamento de métodos e eletrodo; Adsorption and equilibrium studies of the systems Cd(II)/SCN-/C6N12H14 and Cd(II)/I-/SCN-. Improvement of methods and of the electrode

Angnes, Lucio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/12/1987 PT
Relevância na Pesquisa
35.91%
Na presente tese investigou-se a adsorção induzida de um cátion metálico (cádmio(II)) na presença simultânea de dois ligantes (um pseudo-haleto e uma amina ou haleto) na interface eletrodo de mercúrio/solução aquosa, com vistas a uma melhor compreensão desse processo. Os estudos de adsorção foram precedidos por estudos de equilíbrio dos compostos de coordenação formados em solução aquosa. Medidas experimentais foram feitas por potenciometria com eletrodo de amálgama, em força iônica 1,00 M, ajustada com NaCl04. Análise dos dados por programas computacionais adequados levou à quantificação das constantes de estabilidade de 7 espécies binárias e 9 espécies mistas para o sistema Cd(II)/ SCN-/C6H12N4 e de 8 espécies binárias e 6 mistas para o sistema Cd(II)/I-/SCN-, sendo todas estas espécies mononucleares. Para possibilitar um maior grau de automação das medidas cronocoulométricas de adsorção, o eletrodo de gota pendente de mercúrio, anteriormente desenvolvido no IQ-USP, teve seu sistema mecânico aperfeiçoado e passou a ser controlado por computador. O "software" se incumbe de calcular e comandar o tempo de abertura da micro-válvula do eletrodo para gerar gotas com a área solicitada. Aproveitando a possibilidade de realizar aquisição (de dados de carga durante e após a formação das gotas de mercúrio...

Adsorção de corantes aniônicos de solução aquosa em cinza leve de carvão e zeólita de cinza leve de carvão; Adsorption of anionic dyes from aqueous solutions onto coal fly ash and zeolite synthesized from coal fly ash

Carvalho, Terezinha Elizabeth Mendes de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 01/06/2010 PT
Relevância na Pesquisa
35.91%
Cinza leve de carvão, resíduo gerado em usina termelétrica, foi usada para sintetizar zeólita por meio de tratamento hidrotérmico com solução de NaOH. A cinza leve (CL-2) e a zeólita sintética (ZM-2) que foi predominantemente identificada como hidroxi-sodalita foram utilizadas como adsorventes dos corantes aniônicos índigo carmina (IC) e reativo laranja 16 (RL16) de soluções aquosas. Nos processos de adsorção, os efeitos de tempo de contato, concentração inicial de corantes, pH, massa de adsorventes e temperatura foram avaliados. O estudo cinético de adsorção demonstrou que os resultados apresentaram melhor ajuste ao modelo de pseudo-segunda ordem e que adsorção de superfície e difusão intrapartícula participaram no mecanismo de adsorção. Os parâmetros termodinâmicos demonstraram que a adsorção foi espontânea em todos os processos de adsorção. Os processos de adsorção foram de natureza endotérmica para todos os sistemas, com exceção do sistema IC/ZM-2, em que foi exotérmico. Os dados de entropia mostraram a ocorrência do aumento da desordem na interface sólido/solução durante a adsorção em todos os sistemas, exceto novamente no IC/ZM-2, no qual se verificou a diminuição da desordem na interface. As isotermas de adsorção ajustaram-se à equação linear de Langmuir. As capacidades máximas de adsorção foram 1...

Adsorption of reactive dye on seawater-neutralised bauxite refinery residue

de Souza, Kelli Cristina; Antunes, Maria Lúcia Pereira; Couperthwaite, Sara Jane; da Conceição, Fabiano Tomazini; de Barros, Thalita Rangueri; Frost, Ray
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 210-214
ENG
Relevância na Pesquisa
35.91%
This investigation has demonstrated the need for thermal treatment of seawater neutralised red mud (SWRM) in order to obtain reasonable adsorption of Reactive Blue dye 19 (RB 19). Thermal treatment results in a greater surface area, which results in an increased adsorption capacity due to more available adsorption sites. Adsorption of RB 19 has been found to be best achieved in acidic conditions using SWNRM400 (heated to 400 °C) with an adsorption capacity of 416.7. mg/g compared to 250.0. mg/g for untreated SWNRM. Kinetic studies indicate a pseudosecond-order reaction mechanism is responsible for the adsorption of RB 19 using SWNRM, which indicates adsorption occurs by electrostatic interactions. © 2013 Elsevier Inc.

Produção e caracterização de quitosana imobilizada em substratos visando adsorção de ions metalicos; Production and characterization of chitosan immobilized on substrates targeting metal ions adsorption

Juliana Queiroz Albarelli
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/12/2009 PT
Relevância na Pesquisa
35.92%
A quitosana é um polímero natural muito estudado devido à sua boa capacidade adsorvente. A aplicação deste biopolímero para remoção de metais pesados tem sido estudada desde o início dos anos 1970 sendo que o número de trabalhos sobre este tema cresceu rapidamente desde então. No entanto, o uso da quitosana como adsorvente em maior escala enfrenta alguns obstáculos, devido à sua baixa resistência mecânica. Uma possível alternativa para melhorar aspectos mecânicos e que também contribui para uma melhor transferência de massa do adsorbato no adsorvente é a imobilização da quitosana em matrizes sólidas utilizando-se técnicas de recobrimento de partículas. Neste contexto, este trabalho visou investigar a imobilização da quitosana em substratos para a aplicação em sistemas de adsorção. Inicialmente foram testados como suporte para imobilização da quitosana vidro, polipropileno, borracha vulcanizada, porcelana e tecido de algodão. O substrato de vidro, utilizado na forma de esferas, apresentou melhor interação com a solução de recobrimento e características adequadas para aplicação em processos de adsorção. As esferas de vidro foram recobertas por diferentes métodos utilizando quitosana 2,5% (m/v) em solução de ácido acético 3% (v/v). O material recoberto foi utilizado em sistemas de adsorção em batelada e contínuo a fim de se analisar a capacidade de remoção de cobre pelo filme de quitosana. Dentre as diferentes técnicas de revestimento estudadas...

Simulação do processo de adsorção psa para separação da mistura etanol-água; Simulation of the adsorption process psa for separation of ethanol-water mixtures

Natalie Alexandra Amézquita Fonseca
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 04/07/2011 PT
Relevância na Pesquisa
35.91%
Um dos problemas na produção de etanol é o elevado custo energético associado a sua separação por causa do excesso de água e a existência de um azeótropo na mistura etanol - água, pelo que através da destilação convencional esta mistura só pode ser separada até um máximo de 95% em peso. Existe na atualidade um notável interesse no desenvolvimento de processos tecnológicos com o objetivo de melhorar as técnicas de separação necessárias para isolar o etanol do produto obtido na fermentação. Convencionalmente as técnicas empregadas para a purificação final na etapa posterior à destilação convencional são a destilação azeotrópica e a destilação extrativa, embora a importância relativa da adsorção tenha aumentado nos últimos anos como conseqüência do desenvolvimento dos processos de adsorção, a invenção das peneiras moleculares. Desta forma o processo PSA (Pressure Swing Adsorption) como um processo de maior eficiência térmica tornou se uma alternativa à destilação azeótropica. No entanto, o desenho e a análise de um sistema PSA é uma tarefa difícil devido ao grande número de parâmetros envolvidos na simulação numérica, pelo que é de grande importância a utilização de simuladores comerciais no estúdio deste tipo de processos. No presente trabalho foi estudada a dinâmica do processo PSA para a desidratação de etanol com zeólitas 3A mediante sua simulação no Software comercial Aspen Adsim. Foram estimados a partir de dados experimentais encontrados na literatura os parâmetros da Isoterma de Langmuir e o coeficiente de transferência de massa dado por LDF e estabelecido o ciclo de Adsorção PSA completo. As condições utilizadas foram similares as indústrias e foram estabelecidos ciclos por médio da ferramenta Cycle Organizer do simulador com 4 passos básicos assim: Adsorção...

Estudo da adsorção das enzimas do complexo celulolítico em bagaço de cana-de-açúcar submetido a diferentes pré-tratamentos e Avicel; Study of adsorption of enzymes from cellulolytic complex on Avicel and sugarcane bagasse submitted to different pretreatments

Daniele Longo Machado
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/12/2013 PT
Relevância na Pesquisa
35.94%
A hidrólise enzimática de materiais lignocelulósicos compreende uma etapa de adsorção das enzimas celulases a esse material, e as chamadas isotermas de adsorção são curvas extremamente úteis nesse estudo, pois indicam a forma como o soluto (adsorbato) adsorverá no adsorvente; dão uma estimativa da quantidade máxima de soluto que o adsorvente adsorverá, entre outras características importantes. São empregadas também para a obtenção de condições mais favoráveis e eficientes na conversão da biomassa a açúcares fermentescíveis. Assim, para melhor entendimento de como o processo da adsorção enzimática interfere nos rendimentos da hidrólise enzimática da celulose, este trabalho abordou estudos específicos, tais como, a determinação da cinética e dos parâmetros das isotermas de adsorção das enzimas do complexo celulolítico sobre diferentes biomassas. Trabalhou-se com o bagaço de cana-de-açúcar pré-tratado hidrotérmico (BH) que apresentou 31,97% de lignina em sua composição e organossolve (BO), com 4,42% de lignina, e também com Avicel e com um isolado de lignina (IL). Os experimentos de cinética e isoterma de adsorção foram realizados em duplicata com volume reacional de 15 mL contendo tãmpão citrato de sódio 50 mM pH 4.8 complementado com with 0.02% de azida sódica por grrama de substrato onde a biomassa foi adicionada. Nos ensaios de cinética...

ADSORPTION OF CHROMOPHORE CHEMICAL SPECIES PRESENT IN AN REAL INDUSTRUAL EFFLUENT USING ACTIVATED CARBONS

Nabais, Joao; Carrott, Peter; Ribeiro Carrott, Manuela; Marques, Liliana
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula Formato: 14175 bytes; application/pdf
ENG
Relevância na Pesquisa
35.91%
The use of 5 commercial activated carbons with different shapes, origins and characteristics (Norit Azo, Merck granular, DCL GDC 753 from Sutcliffe Speakman (DCL) and X2MH 6/8 from Takeda) were tested for the adsorption of the chromophore compounds present in a pulp mill effluent using batch and dynamic trials. The colour removal achieved is within the range 30-90%. The highest removal is obtained with Norit AZO and the smallest with Takeda X2MH. From the batch trials we can draw the following conclusions: - Iodine index can be used as a guide for the effluent colour removal efficiency but for this propose the methylene blue index is useless. - Acidic groups are more important than the basic groups on the adsorption mechanisms involved in the activated carbon adsorption of the chemical species that gave colour to the effluent. - The adsorption is proportional to the pzc and V0 samples values. - For small values of SBET this parameter has a significant impact on the adsorption but for sample with SBET bigger than 900m2g-1 the adsorption is apparently independent of the BET surface area. The column tests performed with X2MH, DCL and MERCK samples showed that we can obtain similar results as in batch tests, as expected. The breakthrough curves reveal that X2MH sample has a very fast saturation while DCL and MERCK sample have good efficiency with 90% colour removal when the effluent volume that passes through the column is 10 and 20 times the activated carbon volume...

Simulations of phenol adsorption on activated carbon and carbon black

Prosenjak, Claudia; Valente Nabais, Joao; Laginhas, Carlos; Carrott, Peter; Carrott, Manuela
Fonte: Adsorption Science and Technology Publicador: Adsorption Science and Technology
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.84%
We use grand canonical Monte Carlo and molecular dynamics simulations to study the adsorption of phenol on carbon materials. Activated carbon is modelled by pore size distributions based on DFT methods; carbon black is represented by a single carbon slab with varying percentages of surface atoms removed. GCMC results for the adsorption from the corresponding gas phase gave reasonable agreement with experimental adsorption results. MD simulations, that studied the influence of the presence of water and surface roughness on the arrangement of the adsorbed phenol molecules, showed that the interaction between the adsorbed molecules is strongly influenced by the presence of water.

Characterisation of surface ionisation and adsorption of phenol and 4-nitrophenol on non-porous carbon blacks

Carrott, Peter; Carrott, Manuela; Vale, Tania; Valente Nabais, Joao; Mourao, Paulo
Fonte: Adsorption Science and Technology Publicador: Adsorption Science and Technology
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.86%
The adsorption of phenol and 4-nitrophenol from aqueous solutions by carbon blacks was studied. Particular attention was paid to the characterisation of the surface chemistry and ionisation of the carbon blacks by use of a simple carbon surface ionisation model, as well as the use of a normalised form of the Freundlich equation for the analysis of the adsorption isotherms. The results indicated that the solutes interact directly with the graphene layers and that the adsorption is sensitive to the π-electron density. Phenol has a weaker interaction and is more sensitive to the system conditions. In particular, it is more sensitive to oligomerisation under certain conditions. Comparison of the results with those previously reported for activated carbons with similar points of zero charge prepared from cork confirms the existence of a significant micropore-narrowing effect in the adsorption of organic solutes by activated carbons and which can lead to up to a doubling of the value of the Freundlich exponent, nF.

Expanded bed adsorption of bromelain (E.C. 3.4.22.33) from Ananas comosus crude extract

Silveira,E.; Souza-Jr,M. E.; Santana,J. C. C.; Chaves,A. C.; Porto,L. F.; Tambourgi,E. B
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2009 EN
Relevância na Pesquisa
35.91%
This work focuses on the adsorption of Bromelain in expanded bed conditions, such as the adsorption kinetics parameters. The adsorption kinetics parameters showed that after 40 minutes equilibrium was achieved and maximum adsorption capacity was 6.11 U per resin mL. However, the maximum adsorption capacity was only determined by measuring the adsorption isotherm. Only by the Langmuir model the maximum adsorption capacity, Qm, and dissociation constant, kd, values could be estimated as 9.18 U/mL and 0.591, respectively, at 25 ºC and 0.1 mol/L phosphate buffer pH 7.5. A column made of glass with an inner diameter of 1 cm was used for the expanded bed adsorption (EBA). The residence time was reduced 10 fold by increasing the expansion degree 2.5 times; nonetheless, the plate number (N) value was reduced only 2 fold. After adsorption, the bromelain was eluted in packed bed mode, with a downward flow. The purification factor was about 13 fold and the total protein was reduced 4 fold. EBA showed to be feasible for purification of bromelain.

Enhancing adsorption capacity of bentonite for dye removal: physiochemical modification and characterization.

Toor, Manjot Kaur
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2011
Relevância na Pesquisa
35.95%
Bentonite, enormously abundant natural clay, has been considered as a potential absorbent for removing pollutants from water and wastewater. Nonetheless, the effective application of bentonite for water treatment is limited due to small surface area and presence of net negative surface charge, leading to its low adsorption capacity. The net negative charge on the surface of bentonite is the prime factor that restricts the use of bentonite for the adsorption of cationic dyes. As a result, the focus of this research was directed towards the modification of the physical structure and the chemical properties of bentonite to maximize its adsorption capacity. To achieve this aim, the research study was carried out by two stages; (1) modification of Australian raw bentonite and (2) characterization and optimization of adsorption performance and kinetics of the modified Australian bentonite for removing recalcitrant organic dye Congo red (CR). The modification of raw bentonite was carried out by three physiochemical methods; (1) thermal activation (TA), (2) acid activation (AA) and (3) combined acid and thermal activation (ATA). The characterization of the physiochemically modified bentonite clays was carried out by Braunneur – Emmet – Teller (BET) method for surface area...

Development of multifunctional nanomaterials and adsorption - photocatalysis hybrid system for wastewater reclamation.

Vimonses, Vipasiri
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2011
Relevância na Pesquisa
35.92%
This thesis study aimed to develop multi-functional nano-catalyst and porous adsorbents from low-cost and locally available materials, and then implement this into an Adsorption-Photocatalysis hybrid system for wastewater reclamation. The project involves two major technological practices for wastewater treatment: adsorption and photocatalysis. For each technology, a specific functional nanomaterial has been developed and investigated regarding their removal capability for a pilot-scale water treatment process. The experimental studies include: 1) evaluation and characterisation of the natural clay minerals that deliver the most suitable properties for adsorption performance and immobilisation of titanium dioxide (TiO₂); 2) synthesis, modification, and characterisation of the clay mixtures as alternative adsorbents, and titania immobilised onto modified porous kaolin as the photocatalyst; 3) evaluation and optimisation of their removal capability, kinetics and mechanisms toward different surrogate indicators of both nanomaterials via the batch and continuous water treatment system; and 4) integration of the adsorption-photocatalysis hybrid system as a major technical outcome for the treatment and reclaimantion of wastewater. Three Australian natural clay minerals...

ADSORPTION OF POLYAMINE CHELATED COPPER IONS ONTO GANGUE MINERALS AND HIGH CAPACITY ADSORBENTS

Cushing, Alexander
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
35.92%
The effluent quality from mining & processing operations is monitored to ensure that maximum allowable limits are not exceeded. Recently, copper concentration levels in the effluent discharge flows of a copper and nickel mining company in Ontario have indicated increasing trends. A chemical particular to the problem is use of diethylenetriamine (DETA) in the process. Adsorption tests were conducted to investigate the ability of various adsorbents to remove and retain copper complexed with DETA and triethylenetetramine (TETA) in solutions. The tests were divided into two sections: gangue adsorbents (silica and pyrrhotite) and high capacity adsorbents (natural bentonite, peat, zeolite Y and zeolite ZSM-5). Pyrrhotite as a sulphide gangue had a greater adsorption capacity than silica for the concentration range studied. At 1 ppm initial concentration, over 80% of copper chelate was removed by minus 400 mesh pyrrhotite compared to 72% of the same size silica. Freundlich and Langmuir isotherm models of adsorption are applicable. However, the Langmuir adsorption isotherm was found to more closely represent the experimental data with a maximum adsorption capacity of 129.9 μg/g for copper complexed with DETA on pyrrhotite. For the high capacity adsorbents...

Adsorption of two pesticides on a clay surface: a theoretical study

Ramalho, J.P. Prates; Dordio, A. V.; Carvalho, A. J. Palace
Fonte: ISSHAC-8: Eighth International Symposium - Effects of Surface Heterogeneity in Adsorption and Catalysis on Solids Publicador: ISSHAC-8: Eighth International Symposium - Effects of Surface Heterogeneity in Adsorption and Catalysis on Solids
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.9%
The contamination of water resources with many organic xenobiotic compounds poses a challenge to environmental sciences and technologies [1]. Although in many cases these contaminants are present only in small concentrations, the large variety of such compounds (some of which are classified as priority pollutants) is a matter of concern. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many of these pollutants [2]. In this regard, the choice of adsorbent materials is crucial, which requires an understanding of the details involved in the adsorption of more or less complex organic molecules by a variety of surfaces of different types. In addition to laboratory studies, computational studies may be valuable in this study [3]. MCPA (2-methyl-4-chlorophenoxyacetic acid, a herbicide) and Clofibric acid (2-(4-chlorophenoxy)-2-methylpropanoic, the metabolite of a pharmaceutical, clofibrate, and also a herbicide) are two phenoxy acids that differ only slightly in their structures. However, a quite distinct behavior in adsorption phenomena on clay materials has been observed in past studies [4]. By relating those differences with the molecules' structural features through atomistic computational studies...

Role of adsorption in catalysis: applications of NMR relaxometry

Arias Vecino, Pablo
Fonte: University of Cambridge; Department of Chemical Engineering and Biotechnology Publicador: University of Cambridge; Department of Chemical Engineering and Biotechnology
Tipo: Thesis; doctoral; PhD
EN
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35.92%
The work described in this thesis focuses on the effects that adsorption processes on catalytic surfaces pose in controlling key steps that can affect and control reaction pathways. To that, the development of Nuclear Magnetic Resonance (NMR) relaxometry methods and the comparison with traditional catalytic was performed with a series of C5 and C6 unsaturated hydrocarbons on two different alumina supports, ?- and ?-Al2O3. The developed techniques were applied in the study of liquid phase selective hydrogenation of citral on 5% Pt/SiO2. Infrared (IR) spectroscopy, volumetric adsorption isotherms, dynamic isotherms via a Tapered Element Oscillating Microbalance (TEOM), temperature programmed desorption (TPD) as well as 13C T1 NMR and 1H 2D T1-T2 relaxometry methods were employed. Energies of adsorption as a function of coverage were obtained via adsorption isotherms and the particular surface adsorbate interactions were described with IR spectroscopy. For example, 1-pentyne showed the strongest interaction with the alumina (94 kJ mol-1) while 1-pentene presented a weaker interaction (46 kJ mol-1) on ?-Al2O3. Desorption energies obtained from TPD ranged 85 ? 130 kJ mol-1, irrespective of the adsorbate. Reactivity of the aluminas was captured with TPD...

Mechanism of Cationic Surfactant Adsorption at the Solid-aqueous Interface

Atkin, R; Craig, Vincent; Wanless, Erica J; Biggs, Simon
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Until recently, the rapid time scales associated with the formation of an adsorbed surfactant layer at the solid-aqueous interface has prevented accurate investigation of adsorption kinetics. This has led to the mechanism of surfactant adsorption being inferred from thermodynamic data. These explanations have been further hampered by a poor knowledge of the equilibrium adsorbed surfactant morphology, with the structure often misinterpreted as simple monolayers or bilayers, rather than the discrete surface aggregates that are present in many surfactant-substrate systems. This review aims to link accepted equilibrium data with more recent kinetic and structural information in order to describe the adsorption process for ionic surfactants. Traditional equilibrium data, such as adsorption isotherms obtained from depletion approaches, and the most popular methods by which these data are interpreted are examined. This is followed by a description of the evidence for discrete aggregation on the substrate, and the morphology of these aggregates. Information gained using techniques such as atomic force microscopy, fluorescence quenching and neutron reflectivity is then reviewed. With this knowledge, the kinetic data obtained from relatively new techniques with high temporal resolution...