Nanomateriais Plasmônicos: Parte III: Mecanismos de formação e métodos de síntese

In addition to the series of articles related to metallic nanoparticles applied to plasmonics, the aim of this review is to discuss the main factors that influence the process of obtaining this type of material. Thus, the article is divided into two main parts: 1) Mechanism, in which a general idea is given regarding the evolution of the concepts involved in the steps of nucleation and growth of metallic nanoparticles, as well as a discussion on the parameters that favor the control of the reaction by kinetics or thermodynamics. Additionally, the main strategies used for composition and shape control, also a brief explanation about the surface of the obtained products are presented. 2) Synthesis, in this section, the main methodologies for obtaining metallic nanoparticles on a laboratory scale are demonstrated, namely those in batch and by electrochemical routes, in addition to the discussion on flow methods, which is believed to be the most effective and viable strategy for obtaining nanoparticles on a large scale.Em complemento à série de artigos relacionada a nanopartículas metálicas aplicadas em plasmônica, o objetivo desta revisão é transcorrer sobre os principais fatores que influenciam no processo de obtenção desse tipo de material. Dessa forma, o artigo se divide em duas partes principais: 1) Mecanismo, em que é dado uma ideia geral a respeito da evolução dos conceitos envolvidos nas etapas de nucleação e crescimento de nanopartículas metálicas, assim como, uma discussão sobre os parâmetros que favorecem o controle da reação por via cinética ou termodinâmica. Adicionalmente, as principais estratégias utilizadas para controle de composição e forma, além de uma breve explanação sobre a química da superfície dos produtos obtidos também são apresentadas. 2) Síntese, nesta seção são demonstradas as principais metodologias para a obtenção de nanopartículas metálicas em escala laboratorial, sendo elas, as em batelada e por via eletroquímica, além da discussão sobre os métodos em fluxo, que, acredita-se ser a estratégia mais eficiente e viável para a obtenção de nanopartículas em larga escala

A fundamental approach about gold nanoparticles

O estudo sistemático de nanopartículas de ouro utilizando conceitos fundamentais de química de coordenação e físico-química é o foco principal desta tese, que trata principalmente da natureza das interações moleculares na superfície de nanopartículas. Para tal finalidade, estudou-se como as variações dos parâmetros experimentais influenciam no mecanismo de formação das partículas pelo \"método de Turkevich\". Observou-se que, não somente, a morfologia e as propriedades ópticas estão atreladas aos processos de nucleação e crescimento, mas também a composição e as propriedades químicas da camada molecular ao redor das partículas. Dessa forma, foi possível comprovar, teórica e experimentalmente, que um intermediário instável da reação de oxidação do citrato de sódio, a acetonadicarboxilato, se torna estável devido a coordenação aos átomos superficiais de ouro. Isto leva a propriedades químicas e espectroscópicas distintas, principalmente, frente a reações de troca de ligantes na superfície das partículas. Foi feito um estudo, teórico e experimental, sistemático das propriedades das moléculas de etanobis(tioamida) na superfície de diferentes nanopartículas de ouro, comprovando que a presença de acetonadicarboxilato, ao final da síntese das partículas, influencia drasticamente nas propriedades do sistema.The systematic study of gold nanoparticles using fundamental concepts of coordination and physical chemistry is the focus of this thesis, devoting an especial attention for molecular interactions nature at the particles surface. For this goal, the effects of many experimental parameters on the gold nanoparticles formation by the Turkevich method have been studied. It has been shown that not only the morphology and optical properties are controlled by the nucleation and growth processes, but also the chemical properties of the molecular layer at the particles surface. In this way, it has been proved, theoretical and experimentally, that an instable oxidation product of the sodium citrate reaction with the gold salt, a ketonedicarboxilate species, is stabilized by coordination with the superficial gold atoms. This fact leads to distinct chemistry and spectroscopic properties, mainly, related to the reactions at the gold surface. IN addition, a carefully theoretical and experimentally study has been carried out exploring the characteristics of the ethanebis(thioamide) molecules on the surface of different particles. It has been demonstrated that the ketonedicarboxilate presence, from the synthesis process, drastic influences the system properties

Exploring the metallochromic behavior of pentacyanidoferrates in visual, electronic and Raman spot tests

Abstract: Pentacyanidoferrate(II) complexes of aromatic N-heterocycles, such as 4-cyanopyridine, exhibit characteristic colors and strong metallochromism associated with the donor-acceptor interactions of the metal ions with the cyanide ligands. In the presence of transition metal ions insoluble polymeric complexes are formed, displaying bright yellow, red, brown and green colors with zinc(II), nickel(II), copper(II) and iron(III) ions, respectively. Such metallochromic response is better observed on filter paper, allowing applications in analytical spot tests. The effects can be explored visually and probed by means of modern instrumental facilities, including spectrophotometric and resonance Raman techniques. In this way, by using the cyanopyridinepentacyanidoferrates, the Prussian Blue test for ferric ions can be extended to the entire row of transition metal elements, providing a new and modern insight of such classical Feigl’s spot tests

Surfactant delivery systems for enhanced oil recovery

Global consumption of petroleum is increasing, and there is a significant prospect of a further surge in oil demand in the upcoming years. An alternative to meet this energy need is the increase of oil recovery in new or mature oils reservoirs. Research in the advanced oil recovery sector, specifically focusing on surfactant injection, has shown promising results and the potential to contribute to global oil production. However, the high costs associated with surfactant injection, attributed to losses through adsorption on the rock, is a major concern. Surfactants play a crucial role in reducing interfacial tension and modifying wettability, crucial parameters to increase the oil recovery factor. To mitigate the issues of surfactant injection, the utilization of surfactant carriers has proven effective. This comprehensive article reviews four major classes of surfactant-carrying materials, namely inorganic nanoparticles, carbon materials, polymers, and supramolecular systems, with the objective of minimizing surfactant loss in enhanced oil recovery. The review identifies challenges, proposes alternative approaches, and explores opportunities for applying different surfactant nanocarrires systems for EOR. Furthermore, it discusses the classification, mechanisms of action, and synergistic effects between carrier-surfactant systems, addressing the importance of systematically grouping these systems for the advancement of science and technology. The review also highlights the permeation capabilities of these carrier materials through porous media, their size-based rock adsorption, and the potential synergistic effects on interfacial properties in the reservoir. By examining these aspects, innovative techniques for EOR can be developed and a deeper understanding of the subject can be achieved

Photocatalytic Activity of Reduced Graphene Oxide–Gold Nanoparticle Nanomaterials: Interaction with Asphaltene and Conversion of a Model Compound

Asphaltenes are residual materials from the oil industry and are usually converted, after exhaustive distillation, into coke and asphalt. However, conversion of asphaltenes into more valuable raw materials, for instance, by photocatalytic cracking using suitable catalysts, would be a better, more economic option. To explore this idea, we combined the electronic and chemical properties of asphaltene and graphene derivatives with the plasmonic nature of gold nanoparticles. For this purpose, a hybrid material was generated <i>in situ</i>, containing reduced graphene oxide and gold nanoparticles (RGO@AuNP). Evaluation of the interaction between the hybrid material and asphaltenes by hyperspectral dark-field optical microscopy indicated the occurrence of charge transfer between the two species. Using 9-anthraldehyde (9-ATA) as a model compound for asphaltene, photocatalytic experiments performed with RGO@AuNP at room temperature, under visible light irradiation, revealed the formation of cyclic endoperoxides, which undergo further reactions, resulting in their cleavage, with 90% yield for the 9-ATA degradation