Synthesis of magnetic composite materials using a low-cost method.

What is it about?

Self-propagating synthesis (combustion method or SOLUTION COMBUSTION METHOD) is currently considered one of the cheapest methods for the preparation of Ni/NiO nanocomposites. This method employs an exothermic combustion reaction (Figure 6) between a given fuel (glycine, urea, citric acid or starch). Recent studies by our group have shown that, depending on the amount of fuel (starch) used in the solution combustion reaction, Ni/NiO composites with 2D or 3D porosity can be obtained, which significantly affect the electrochemical performance of these materials, with the 3D macro porous structure showing the best performance and an oxidant (metallic nitrates, for example). Combustion can be carried out in a conventional or microwave oven, or on hotplates, at temperatures below 300-400 °C. However, during the combustion process, the system reaches temperatures above 1200 °C. In this method, there is no need for an external high-temperature source, making it a simple and fast procedure and, therefore, attractive from a scientific point of view. In general, the combustion method is carried out under an open atmosphere, although a reducing or inert atmosphere can also be employed to maintain the fuel/oxidation ratio during the process. The use of starch as a fuel has several advantages, including abundance, low cost, non-toxicity, and being renewable, which makes its application very interesting from the point of view of Green Chemistry. Starch is also a very versatile compound, as it can play a role as a coating, functionalization, stabilization, complexing agent, and pore generator. Recent studies by our group have shown that, depending on the amount of fuel (starch) used in the combustion reaction in solution, Ni/NiO composites with 2D or 3D porosity can be obtained, which significantly affect the electrochemical performance of these materials, with the 3D macro porous structure showing the best performance.

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Photo by Bruno on Unsplash

Photo by Bruno on Unsplash

Why is it important?

This research demonstrated the versatility of the solution combustion method, in which different routes yielded materials with diverse applications, including metallic nickel, cobalt/nickel alloy, nickel oxide and Ni/NiO composites. The most interesting thing was to realize that we were able to control the reaction, that is, depending on the product we wish to obtain, we can increase or decrease the starch:nitrate ratio, change the proportion of ammonium hydroxide added to the reaction medium or the cobalt content. In all cases, a synthesis was carried out under mild conditions (temperature of 65°C and subsequent heating to 200°C and atmospheric pressure), which is an interesting aspect from the point of view of the application of this methodology in industrial terms, as it becomes a less costly process. The Rietveld method, as expected, proved to be essential for a deeper understanding of the microstructure of materials, especially Ni/NiO composites. Correlating the 3D profile of microdeformation with the Williamson-Hall method could be a good direction for the new materials developed by the group. In terms of production costs, the fact that we used starch in all reactions was extremely important, as it is a low-cost and easily accessible reagent. We obtained unprecedented and high-quality data correlating the structural (and microstructural) behavior with the photoluminescence phenomenon, opening up a range of applications for sensors, photoluminescent materials, among others.