Carbon nanocomposites and their potential application in different fields of industry

Mateo Ramos Velasco, Master's student in Engineering with Emphasis in Chemical Engineering. Credit: Communications Office, Faculty of Engineering.

Carbon can form complex and ordered structures at nanometer scales, whose properties are of high interest to the electronics industry for their possible application in the manufacture of electrodes, supercapacitors, detectors, among others. However, the synthesis methods of different carbon nanocomposites require high-cost processes and raw materials. An alternative for the synthesis of these nanomaterials is colombian anthracite carbon. A research is proposed to analyze the different minerals and substances that make up the coal for further applications in this area. 

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A commitment to the full utilization of domestic raw materials: the case of coal 

The exploitation of hydrocarbons in coal mines in Colombia has traditionally focused on supplying demand in international markets, in countries such as Canada, China and Japan, making it one of the main exporters of this type of raw material in the region. This scenario implies a lag in the use of these resources in the face of the needs that exist in the national industry.  

Seeking to offer alternative uses related to carbon, Mateo Ramos Velasco, a student of the Master's Degree in Engineering with Emphasis in Chemical Engineering, developed a research which seeks to evaluate the effect of mineral and volatile matter inside the coal in order to obtain nanocomposites that are useful for the generation of value-added products.  

This research is led by Professor Juan Sebastián Gutiérrez, researcher of the Coal Science and Technology Research Group and PhD, with the participation of Billy Rodríguez, from the Colombian Geological Service. Its objective is to expand the margins of use currently given to coal (as term coal and coal for metallurgy), so that in the future there may be new markets and utilities both nationally and internationally. 

Carbon nanocomposites: a window of opportunity not yet explored 

Given its origin, which dates back millions of years, coal has a conformation of multiple materials in its interior, whose effects increase or decrease depending on the type of exploitation to which it is subjected, which brings with it effects when it is used for new purposes. One of these materials obtained after different extraction processes are carbon nano-onions (CNOs), concentric layers of carbon whose structure resembles onions and which have a size on a nanometer scale.  

These compounds have striking properties, since due to their characteristics they have applications related to electrodes and detectors, in addition to allowing the addition of chemical groups of different classes with the objective of being used in medical and electronic applications. The obtaining of this type of nanocomposites is currently produced by means of nano-diamonds, which implies a high operation cost due to the market value of this type of materials. Faced with this, the Coal Science and Technology Research Group has proposed to obtain such nanocomposite from the synthesis of carbon, for which they used different types (bituminous, anthracite, among others), having as a result that high rank coals, such as anthracite, allow this synthesis, through a technique called thermal annealing (a process that heats the coal sample to a temperature above 1,600°C, in a nitrogen atmosphere that prevents its combustion).  

Then, they set themselves the task of determining the optimal conditions for such synthesis. For this purpose, areas such as resistance time and thermal annealing temperature were taken as a reference to evaluate which presented the best results in order to obtain these carbon nano-onions.  

The work of researcher Mateo Ramos Velasco, who is in charge of evaluating the effect of the volatile and mineral matter present in the carbon during the aforementioned processes, is framed within this point of the research process. 

"It turns out that coal, given its biological process, has many volatile compounds. They are characterized by having a relatively low boiling point. What happens is that they volatilize and leave empty space inside the coal. What we want to study is whether the volatile and mineral matter have an impact on the whole thermal annealing process", says the researcher Ramos, and explains that, in the case of the mineral matter, when mining is done, the geological layers contain a great variety of minerals (such as silicon oxide and aluminum), which remains in the matrix of the coal that is then subjected to the annealing process.  

According to the researcher, his objective was to determine the influence of these materials inside the carbon, in order to know to what extent they inhibit or promote the formation of nano-onions. This in order to evaluate the need to remove these particles, which usually represents additional costs and delays in the processes for the industries. 

The research 

For his analysis, researcher Mateo Ramos Velasco used coal samples from Jamundí, Valle del Cauca, provided by the Colombian Geological Service. The decision to work with coal from this area of the country was due to the fact that it was necessary to have high rank coal for the study. Although there were other options, such as Santander, Boyacá and Cundinamarca, the researcher chose Jamundí because of its proximity and the facilities that this implied. This coal source had the following characteristics: 1.34% residual moisture, 11.98% volatile matter, 12.83% ash and 68.45% fixed carbon.  

Given the difficulty of subjecting the samples to an analysis process that would accurately determine the presence of nano-onions in the coal, since the country does not currently have the technology for this, researcher Ramos opted to indirectly measure other parameters of interest by means of Raman spectroscopy, a technique widely used in coals, which subjects the samples to a visible light laser that detects the phenomena inside the coal.  

The result of this process is the production of characteristic bands: D (which refers to the disorder evidenced in the structure of the sample) and G (which refers to the graphitization process or order in its structure). This process was carried out with samples, according to the following treatments to which they were subjected: untreated, annealed, floated-annealed, devolatilized-reannealed and floated-devolatilized-reannealed, which refer to the different test scenarios that included volatile and mineral matter in the coals.  

"Basically what is done is that Raman spectroscopy is performed on the original sample without any treatment and it is compared with samples that have undergone other treatments," explains researcher Ramos.  

Other methods used in the research were thermogravimetric analysis (TGA) -which allows representing the combustion peaks produced in the coal. It is expected that, as the thermal annealing is performed, this combustion peak will occur at higher temperatures, given the rearrangement in the coal structure, and Fourier transform infrared spectroscopy (FTIR) -which allows observing the functional groups of the sample before and after being subjected to thermal annealing-. 

Results and innovative nature of the research 

Currently, researcher Mateo Ramos Velasco is awaiting the results of the analyses performed by thermogravimetric analysis (TGA) and the processing of the data obtained through Fourier transform infrared spectroscopy (FTIR). However, the results of Raman spectroscopy allow him to foresee a high degree of success in his research. 

 "So far we have obtained a behavior similar to what has been seen in other research, which tells us that it is possible to have nano-onions within the sample. As for the action of mineral and volatile matter, there are evident changes," says the researcher. According to him, the changes in the charcoal are noticeable when the ash and volatile matter are removed.  

Given the trend and the need to promote more sustainable alternatives in energy, derived from climate change in the world, the research carried out by the researcher Ramos Velasco becomes a regional and national reference for new uses of coal in the industry.  

For the researcher, the results could contribute in this sense: "First, it would define the pretreatments that must be done to the carbon to be applied in the production of nano-onions. And that, in the long run, is important, since it defines production costs. The production of nano-onions is quite expensive. Firstly because of the process itself, which is not entirely cheap, and secondly because the raw material is synthesized from nano-diamonds, which are very expensive", he concludes. 

If interested in being in touch with the student or any further information about the investigation, please write the Faculty of Engineering Communications Office: comunicaingenieria@correounivalle.edu.co.