Quasi-crystalline alloys (QCA) Al–Cu–Fe, which have unique physical and chemical properties, attract attention as promising catalytic materials. Formation of a porous structure on their surface allows to significantly increase the area of the active surface, which directly affects the catalytic activity.
Studying the evolution of the porous structure is key to optimizing the catalytic properties of KKS. Etching, dealloying, and electrochemical processing methods allow controlled creation of pores of various sizes and shapes. An important aspect is the selective removal of one or more alloy components, which leads to the formation of a developed pore network.
In this work, the process of selective etching of aluminum from quasicrystalline regions of the alloy was studied in order to create nanoparticles of metals and their oxides in a microporous structure. For selective removal of aluminum from cast and annealed quasicrystalline AlCu25Fe12 alloy, treatment with 10M NaOH solution with different duration of action was used. It was found that a more developed porous structure is formed in the cast sample than in the annealed alloy. After removing aluminum for 4 and 8 hours, nanoparticles of various sizes were found on the quasicrystalline surface (of both alloys), while smaller particles are formed during the 8-hour treatment. An increase in the dealumination time led to an increase in the density and a decrease in the size of the nanoparticles.
X-ray diffraction analysis was used to analyze the structure of the obtained samples. The surface microstructure, internal morphology, and elemental composition were studied using scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis. Copper and iron nanoparticles and their oxides were identified on the quasi-crystalline surface as a result of chemical etching. In addition, the catalytic activity of the obtained materials in the decomposition reaction of non-biodegradable and toxic methylene blue (an organic dye) was studied.
Studies show that the pore size and distribution have a significant impact on the catalytic activity of KKS in various reactions such as CO oxidation, olefin hydrogenation and N2O decomposition. Increasing the surface area due to the porous structure helps to increase the adsorption of reagents and, therefore, increase the reaction rate.
However, in addition to the morphological characteristics, the composition of the KKS surface is also important. Enrichment of the surface with one of the components, for example, copper, can lead to the formation of active centers that facilitate the catalytic reaction.
Thus, control over the evolution of the porous structure on the surface of Al–Cu–Fe CCSs allows us to purposefully improve their catalytic properties and create effective catalysts for various industrial processes.
Author: SS Mishra, TP Yadav, SP Singh, AK Singh, MA Shaz, NK Mukhopadhyay, ON Srivastava
Institute: Center for Hydrogen Energy, Department of Physics, Institute of Sciences, Banaras University, Varanasi, 221005, India, Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, 208016, India, Department of Biotechnology, Mahatma Gandhi Central University, Motihari, 845401, Bihar, India, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi, 221005, India