Revisão sobre a síntese de grafeno por esfoliação em fase líquida: Mecanismos, fatores e técnicas

El objetivo del presente trabajo es crear un consenso acerca del método de exfoliación en fase líquida (LPE) para la producción de grafeno y, a su vez, conocer las causas y los diversos factores que afectan el rendimiento y la calidad del grafeno obtenido. Para lograr este objetivo, se realiza una revisión bibliográfica sistemática usando el buscador de Google Académico por la extensión de su acervo. En el presente escrito los resultados obtenidos de esta revisión bibliográfica exhaustiva de la LPE de grafeno se ordenan de acuerdo con su relevancia, dando prioridad en conocer las causas y los fenómenos físicos claves relacionados con la LPE. Los artículos centrados en entender los fenómenos físicos y químicos que gobiernan la LPE fueron clasificados en la sección mecanismo, con el fin de tener una mejor comprensión del fenómeno a nivel molecular. Con esta información, se propone una clasificación de acuerdo con las técnicas más comúnmente usadas (sonicación, microfluídica, etc) para lograr un consenso sobre las técnicas que se clasifican dentro del método de LPE de grafeno con base en el mecanismo, lo que da pauta al desarrollo de nuevas técnicas que mejoren significativamente el desempeño de este método. De la revisión sistemática se concluye que el método de exfoliación en fase líquida es un método robusto, atractivo para la industria, de fácil escalabilidad y de alto rendimiento en general dependiendo de las técnicas de preparación. The objective of this article is to create a consensus about the graphene production by the liquid-phase exfoliation (LPE) method, as well as to understand the key causes and factors affecting the yield and quality of the graphene obtained. An exhaustive bibliographic search was conducted in Google Scholar given the extent of its collection. The results of the search are ordered by relevance, giving priority to key causes and physical phenomena related to LPE. The articles focused on understanding physical and chemical phenomena were classified in the mechanism section, in order to have a better understanding of the method at the molecular level. With this information, a classification of the most common LPE techniques (sonication, microfluidics, etc.) is proposed in order to reach a consensus on which techniques belong to the LPE method in function of their mechanism. The proposed classification aims at developing new techniques to significantly improve the performance of this method. From this systematic review, it is concluded that the liquid-phase exfoliation method is robust and very attractive to the industry and has easy scalability with high performance in relation to the techniques analyzed.O objetivo do presente trabalho é criar um consenso no que diz respeito ao método de esfoliação em fase líquida (LPE) para a produção de grafeno e, por sua vez, conhecer as causas e os diversos fatores que afetam o desempenho e a qualidade do grafeno obtido. Para alcançar este objetivo, realiza-se uma revisão bibliográfica sistemática usando o buscador do Google Acadêmico na extensão de seu acervo. No presente escrito, os resultados obtidos desta revisão bibliográfica exaustiva da LPE de grafeno são ordenados segundo sua relevância, dando prioridade em conhecer as causas e os fenômenos físicos fundamentais relacionados com a LPE. Os artigos centralizados em entender os fenômenos físicos e químicos que governam a LPE foram classificados na seção mecanismo, objetivando ter uma melhor compreensão do fenômeno no âmbito molecular. Com essa informação, propõe-se uma classificação de acordo com as técnicas usadas com mais frequência (sonicação, microfluídica, etc.) para obter um consenso sobre as técnicas que são classificadas dentro do método de LPE de grafeno com base no mecanismo, o que dá pauta para o desenvolvimento de novas técnicas que melhorem significativamente o desempenho deste método. Da revisão sistemática, conclui-se que o método de esfoliação em fase líquida é um método robusto e atraente para a indústria, de fácil escalabilidade e de alto desempenho em geral, dependendo das técnicas de preparação

Evolution of the Spin Magnetic Moments and Atomic Valence of Vanadium in VCux+, VAgx+, and VAux+ Clusters (x = 3–14)

The atomic structures, bonding characteristics, spin magnetic moments, and stability of VCUx+, VAgx+, and VAux+ (x = 3-14) clusters were examined using density functional theory. Our studies indicate that the effective valence of vanadium is size-dependent and that at small sizes some of the valence electrons of vanadium are localized on vanadium, while at larger sizes the 3d orbitals of the vanadium participate in metallic bonding eventually quenching the spin magnetic moment. The electronic stability of the clusters may be understood through a split-shell model that partitions the valence electrons in either a delocalized shell or localized on the vanadium atom. A molecular orbital analysis reveals that in planar clusters the delocalizatibn of the 3d orbital of vanadium is enhanced when surrounded by gold due to enhanced 6s-5d hybridization. Once the clusters become three-dimensional, this hybridization is reduced, and copper most readily delocalizes the vanadium\u27s valence electrons. By understanding these unique features, greater insight is offered into the role of a host material\u27s electronic structure in determining the bonding characteristics and stability of localized spin magnetic moments in quantum confined systems

DFT exchange: sharing perspectives on the workhorse of quantum chemistry and materials science

In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method developers and practitioners. The format of the paper is that of a roundtable discussion, in which the participants express and exchange views on DFT in the form of 302 individual contributions, formulated as responses to a preset list of 26 questions. Supported by a bibliography of 777 entries, the paper represents a broad snapshot of DFT, anno 2022

Density functional static dipole polarizability and first-hyperpolarizability calculations of Na<SUB>n</SUB> (n = 2, 4, 6, 8) clusters using an approximate CPKS method and its comparison with MP2 calculations

We report the static dipole polarizability and first-hyperpolarizability of the sodium atom clusters, Nan, n = 2, 4, 6 and 8, using our recent implementation of a numerical-analytical approach to the coupled-perturbed Kohn-Sham (CPKS) equations in deMon2k. The calculations are reported for VWN and BP86 exchange-correlation functionals using Sadlej and TZVP-FIP1 basis sets which have been previously optimized for polarizability calculations. All-electron calculations were performed for the optimizations at the VWN/DZVP/A2 and PW86/DZVP/A2 levels. Comparisons are made with Hartree-Fock (HF) and MP2 benchmark calculations

Theoretical study of the structure and properties of Na-MOR and H-MOR zeolite models

International audienc

Theoretical Study of Host-Guest Interactions in the Large and Small Cavities of MOR Zeolite Models

International audienceSmall probe molecules like CO and CH3CN are used to estimate the acid strength of Brønsted sites in mordenite (H-MOR) models, depending on their framework location, main channel (MC) or side pocket (SP). Adsorption strength on Brønsted sites has often been correlated with the concept of confinement, smaller cavities being considered as catalytically more active. In this work, we show that, at zero coverage (1 molecule per site, per cavity), the host guest energetic interactions do not depend on the cavity volumes, leading to similar adsorption energies for MC and SP sites. This unexpected result is in agreement with recent experimental studies which show that confinement is more related with higher concentration of host molecules in small rather than large cavities at high pressure