Nanocomposites and nanomaterials

Influence of surfactants on adsorption and catalytic properties of Fenton-like catalysts
Makido O.Yu.1, Khovanets’ G.I.1, Kurilets’ O.G.2, Diadenchuk A.V.2
1 Department of PhChFF InPOCC NAS of Ukraine.
Naukova Str., 3а, Lviv-79060, Ukraine.
E-mail: khovanets_galyna@ukr.net
2 Lviv Polytechnic National University.
S. Bandery str., 12, Lvіv-79013, Ukraine.

Obtaining composite materials of a given composition, structure and physico-mechanical properties is one of the most important tasks of modern materials science. Advanced technological solutions in recent years, related to the creation of composites with catalytic and adsorption properties to solve the problem of wastewater treatment from organic pollutants, are based on the study of the relationship "composition - structure - properties". The use of surfactants in the synthesis of nanostructured magnetically sensitive Fenton-like catalysts improves their porosity. This requires additional study of the influence of the nature of surfactants (natural and synthetic origin) on the properties of the synthesized catalysts, which work simultaneously by two mechanisms: adsorption and destruction.
For this purpose, investigations of the catalytic and adsorption activity of pre-synthesized multilayer composites of the "core - shell" type based on CuO were carried out. The core of the composite is cobalt ferrite precipitated on amorphous SiO2, which has magnetic properties. The presence of a magnetic core in the catalyst greatly simplifies its separation from the reaction volume by magnetic separation and allows reuse. To stabilize, the core is covered with a layer of porous SiO2 with the addition of surfactants of various natures, on which clusters of copper oxide, which serve as catalytic centers, are precipitated. Investigations of the adsorption process were carried out by spectrophotometric method at a wavelength of 620 nm on a model solution of methylene blue (MB) with a volume of 5 ml and a concentration of 5·10-5 mol/L in a static reactor at room temperature with stirring. Catalyst weight − 10 mg, surfactant − 500 mg.
To investigation the influence of surfactants of different nature, we compared the SiO2/CoFe2O4/SiO2/CuO composite with the addition of sodium dodecyl sulfate (NaDS) (C12H25SO4Na) (sample 1) and rhamnolipid (RL) (Pseudomonas sp.) (sample 2). The influence of the nature of surfactants on the kinetic regularities of MB adsorption by the composite structure CoFe2O4/SiO2+NaDS/CuO (sample 3) and CoFe2O4/SiO2+RL/CuO (sample 4) was also investigated.
	
Fig. 1. The dependence of the degree of MB adsorption on the structure of the synthesized catalysts in the dynamics of time: (II) − reuse of catalysts	
As shown by the results presented in Fig. 1, catalyst - sample 1 is characterized by high activity in the process of MB adsorption. Under optimal conditions, the MB adsorption for sample 1 reached 80.4% already after 15 min process, 91.8% − after 30 min, 96.4% − after 60 min. For sample 2 − 63.3%, 79.7% and 82.1%, respectively. For both samples, there is a sharp increase in the rate of MB adsorption from the beginning of the process for 20 min: P1=89.1%, P2=73.3%. Reuse of these catalysts after drying at 1000C showed their high efficiency. A significant difference is observed for the kinetic curves of MB adsorption for samples 3 and 4. Thus, the MB adsorption for sample 3 reached 63% already after 15 min process, 71.4% − after 30 min, 76.2% − after 60 min, and for sample 4 − 21.6%, 36.4% and 54.2%, respectively.
It has been determined that the nature of surfactants has a positive effect both on the structure of the synthesized catalysts and on their properties. As can be seen from the results of samples 1 and 3, despite the different synthesis technology, the addition of surfactants of synthetic origin (sodium dodecyl sulfate) has a greater influence on the porosity of the structure than surfactants of natural origin (rhamnolipid) and, accordingly, improves the adsorption properties of catalysts.
The effectiveness of practical use of the synthesized heterogeneous nanostructured magnetically separable catalyst SiO2/SiO2/CoFe2O4/SiO2+NaDS/CuO in the Fenton system for fine post-treatment of dairy production wastewater has been established. This process does not require the addition of H2O2 to the system, because the supply of atmospheric oxygen to the reaction medium on the catalyst is the formation of peroxide compounds, which are involved in the oxidation of organic pollutants. This fact, together with the possibility of easy removal of the catalyst from the reaction medium by magnetic field and its reuse without loss of efficiency, makes this system economically viable and environmentally friendly.