Research Progress on the Applications of Electrospun Nanofibers in Catalysis

During the last two decades, electrospinning has become a very popular technique for the fabrication of nanofibers due to its low cost and simple handling. Nanofiber materials have found utilization in many areas such as medicine, sensors, batteries, etc. In catalysis, these materials also present important advantages, since they present a low resistance to internal diffusion and a high surface area to volume ratio. These advantages are mainly due to the diameter–length proportion. A bibliographic analysis on the applications of electrospun nanofibers in catalysis shows that there are two important groups of catalysts that are being investigated, based on TiO2 and in carbon materials. The main applications found are in photo- and in electro-catalysis. The present study contributes by reviewing these catalytic applications of electrospun nanofibers and demonstrating that they are promising materials as catalysts, underlining some works to prove the advantages and possibilities that these materials have as catalysts. On one hand, the possibilities of synthesis are almost infinite, since with coaxial electrospinning quite complex nanofibers with different layers can be prepared. On the other hand, the diameter and other properties can be controlled by monitoring the applied voltage and other parameters during the synthesis, being quite reproducible procedures. The main advantages of these materials can be grouped in two: one related to their morphology, as has been commented, relative to their low resistance and internal diffusion, that is, their fluidynamic behavior in the reactor; the second group involves advantages related to the fact that the active phases can be nanoscaled and dispersed, improving the activity and selectivity in comparison with conventional catalytic materials with the same chemical composition.

Kinetic Study on the Preparation of Aluminum Fluoride Based on Fluosilicic Acid

Reasonable mathematical derivation and mechanism model in the process of producing aluminum fluoride by fluosilicic acid is the key to the industrial treatment of fluorine resources in the tail gas of phosphate ore. In this work, aluminum fluoride was generated directly by fluosilicic acid to extract fluorine from the tail gas of phosphate rock. The uncreated-core model dominated by interfacial reaction and the uncreated-core model dominated by internal diffusion-reaction were then respectively utilized to describe the reaction kinetics of the generation of aluminum fluoride. The result showed that the uncreated-core model was dominated by interface reaction and internal diffusion, the apparent reaction order n = 1, and the activation energy Ea = 30.8632 kJ . mol–1. Product characterization and kinetic analysis were employed to deduce the reaction mechanism of preparing aluminum fluoride. The theoretical basis for the low-cost recycling of fluorine resources in the tail gas of industrial phosphate ore was provided in this work.

Biological scaling in green algae: the role of cell size and geometry

The Metabolic Scaling Theory (MST), hypothesizes limitations of resource-transport networks in organisms and predicts their optimization into fractal-like structures. As a result, the relationship between population growth rate and body size should follow a cross-species universal quarter-power scaling. However, the universality of metabolic scaling has been challenged, particularly across transitions from bacteria to protists to multicellulars. The population growth rate of unicellulars should be constrained by external diffusion, ruling nutrient uptake, and internal diffusion, operating nutrient distribution. Both constraints intensify with increasing size possibly leading to shifting in the scaling exponent. We focused on unicellular algae Micrasterias. Large size and fractal-like morphology make this species a transitional group between unicellular and multicellular organisms in the evolution of allometry. We tested MST predictions using measurements of growth rate, size, and morphology-related traits. We showed that growth scaling of Micrasterias follows MST predictions, reflecting constraints by internal diffusion transport. Cell fractality and density decrease led to a proportional increase in surface area with body mass relaxing external constraints. Complex allometric optimization enables to maintain quarter-power scaling of population growth rate even with a large unicellular plan. Overall, our findings support fractality as a key factor in the evolution of biological scaling.

The mercury removal mechanism of selenium mercury material by soda roasting

In the present work, Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were employed in the investigation of roasting mechanism, roasting dynamic model, control step of soda roasting process of selenium–mercury material. The results indicated that at the beginning of the roasting process, the control step might be interface chemical reaction for the first 30 min, and the kinetic equation might be 1−(1−R)⅓ = Kt with a activation energy E1 = 40.50 kT/mol. However, as the roasting proceeded, internal diffusion gradually became the control step for 90–135 min, and the kinetic equation might be 1−⅔R−(1−R)⅔ = Dt with a activation energy E2 = 6.75 kT/mol. The SEM analysis of the roasted selenium–mercury materials indicated that the dynamic model of soda roasting attributed to the shrinkage model was reasonable. Combined with the results obtained by SEM and EDS of the roasted selenium–mercury materials, we concluded that the addition of too much Na2CO3 might lead to the formation of molten crystalline phase in the inner of the roasted selenium–mercury materials, changing the mercury removal mechanism of the roasting process. Meanwhile, Se had a tendency to segregate at where the content of Na was relatively high. In order to study the mechanism of diffusion, Na2O2 of 9% was added to one of the samples. According to the results, we concluded that the diffusion of products (such as HgxOy) from the inside of the raw material was the control step of internal diffusion.