Nanocomposites and nanomaterials

Catalytic activity of the nanostructured composite CuO/SiO2/CoFe2O4 in the Fenton system
Makido O.Yu.1, Khovanets’ G.I.1, Kurilets’ O.G.2, Kovalchuk Kh.I.2
1 Department of PhChFF InPOCC NAS of Ukraine.
Naukova Str., 3а, Lviv-79060, Ukraine.
E-mail: khovanetsgalyna@gmail.com
2 Lviv Polytechnic National University.
S. Bandery str., 12, Lvіv-79013, Ukraine.

With the development of industry, the issue of wastewater treatment from dyes, which are characterized by persistence and high toxicity even at minimal concentrations, is becoming increasingly relevant [1]. One of the promising directions to solve this problem is the use of Advanced Oxidation Processes (AOPs). The essence of AOPs lies in the liquid-phase oxidation of compounds by highly reactive radicals until they are fully mineralized [2]. The Fenton reaction, as a typical AOP, is effective for producing highly effective hydroxyl radicals. But its active use is limited to a narrow range of pH = 3-4, the formation of a large amount of finely dispersed iron precipitate and the high cost of catalyst utilization. In recent years, Cu-based systems have been considered as an alternative, since Cu+ reacts with H2O2 similarly to Fe2+, but at a higher rate [3].
The catalytic activity of pre-synthesized multilayer composites of the type "core-shell" based on CuO was carried out. The core of the composite is cobalt ferrite, which has magnetic properties. This allows you to remove the catalyst from the reaction medium using a magnet, which greatly simplifies its regeneration and reuse in the process. For stabilization, the core is covered by a layer of porous SiO2, on which copper oxide clusters are deposited, that serve as catalytic centers. The investigations were carried out by spectrophotometric method at a wavelength of 620 nm on a model solution of methylene blue (MB) in a static reactor at room temperature without forced stirring.
	
Fig. 1. Dependence of the degree of MB destruction on the reuse cycles of the catalyst CoFe2O4/SiO2/CuO.	
The results showed that this catalyst is characterized by high activity in the Fenton process. Under optimal conditions, the MB destruction reached 80% after 30 min. of the process, 90% − after 60 min (Table 1.). It was determined that the degree of dye degradation depends on the ratio of the catalyst and dye concentrations and the presence of a preliminary dye adsorption stage. The cyclic use of the catalyst showed that although the reuse of the catalyst without heat treatment decreases its activity by 20%, but after the third cycle the MB destruction reaches 80% (Fig. 1.). It is likely that the activity decrease is primarily due to the residual amount of degradation products adsorbed on the catalyst surface. This leads to a slowing down of the reaction rate due to its limitation by the stage of dye diffusion to the active centers.

Table 1. The degree of catalytic destruction (Р) of methylene blue on the catalyst CoFe2O4/SiO2/CuO, %
The amount catalyst in terms of CuO, mol	3·10-5	6·10-5	9·10-5	1,2·10-4	1,5·10-4	
The duration of the process, min.	30	42	64	82	79	80	
	60	61	82	92	88	89	
	76	66	83	93	91	91	
	106	75	89	94	91	92	

1.	Grace Pavithra K., Senthil Kumar P., Jaikumar V., Sundar Rajan P. Removal of Colorants from Wastewater: A Review on Sources and Treatment Strategies // J Ind Eng Chem.-2019.-75.-P. 1-19. 
2.	Sekhar Mishra N., Reddy R., Kuila A., Rani A., Mukherjee P., Nawaz A., Pichiah S. A Review on Advanced Oxidation Processes for Effective Water Treatment // Cur World Envir.-2017.-12, N. 3.-P. 470-490. 
3.	Bonfim D. P. F., Santana C. S., Batista M. S., Fabiano D. P. Catalytic evaluation of CuO/[Si]MCM‐41 in Fenton‐like reaction // Chem Eng Technol.-2019.-42, N. 4.-P. 882-888.