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IMIDAZOLE-2yl-PHOSPHONIC ACID DERIVATIVE GRAFTED ONTO MESOPOROUS SILICA SURFACE AS A NOVEL HIGHLY EFFECTIVE SORBENT FOR URANIUM(VI) IONS EXTRACTION Tetyana M Budnyak, Agnieszka G#adysz-P#aska, Alexander V. Strizhak, Dariusz Sternik, Igor V. Komarov, Marek Majdan, and Valentin A. Tertykh ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17594 • Publication Date (Web): 25 Jan 2018 Downloaded from http://pubs.acs.org on January 27, 2018
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ACS Applied Materials & Interfaces
IMIDAZOLE-2yl-PHOSPHONIC ACID DERIVATIVE GRAFTED ONTO MESOPOROUS SILICA SURFACE AS A NOVEL HIGHLY EFFECTIVE SORBENT FOR URANIUM(VI) IONS EXTRACTION Tetyana M. Budnyak1,2, Agnieszka Gładysz-Płaska3, Alexander V. Strizhak4, Dariusz Sternik3, Igor V. Komarov4, Marek Majdan3, Valentin А. Tertykh1 1
Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, 17 General Naumov Str., 03164 Kyiv, Ukraine 2 KTH Royal Institute of Technology, Teknikringen 56-58, SE-100 44 Stockholm, Sweden 3 Maria Curie Skłodowska University, 2 M. Curie Skłodowska Sq., 20-031 Lublin, Poland 4 Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska Str., 01601 Kyiv, Ukraine Corresponding author: T.M. Budnyak,
[email protected] Abstract A new imidazol-2yl-phosphonic acid/mesoporous silica sorbent (ImP(O)(OH)2/SiO2) was developed and applied for the uranium(VI) ions removal from aqueous solutions. The synthesized material was characterized by fast kinetics and extra high adsorption capacity with respect to uranium. The highest adsorption efficiency of U(VI) ions was obtained for the reaction system at pH 4, and exceeded 618 mg/g. As follows the uranium(VI) sorption proceed fast in the first step within 60 min of the adsorbent sites and ions interactions. Moreover, the equilibrium time was determined to be 120 min. The equilibrium and kinetic characteristics of the uranium(VI) ions uptake by synthesized sorbent was found to follow the Langmuir-Freundlich isotherm model and pseudo-second order kinetics, rather than the Langmuir, Dubinin-Radushkevich, Temkin models, pseudo-first order or intraparticle diffusion sorption kinetics. The adsorption mechanism for uranium on the sorbent was clarified basing on the XPS analysis. The model of UO22+ binding to surface of the sorbent was proposed according to the results of XPS, i.e 1:1 U/P ratio in the sorbed complex was established. The regeneration study confirms the ImP(O)(OH)2/SiO2 sorbent can be reused. 45 % of uranium ions was determined as originating from the sorbent leaching in the acidic solutions whereas using the basic solutions, the removal efficiency was 12 %. Keywords: uranium, adsorption, phosphonic acid, silica, sorption
1. INTRODUCTION Uranium occurs naturally in the environment in the rock samples and sea water. However, it can be found in nature also due to human activity. Being a source of the nuclear fuel cycle and the reason for waste component it is one of the crucial elements. Among other anthropological sources of U(VI) pollution one can name the following: uranium from the production of weapons, from nuclear actions and from scientific and other applications.1 Its presence in the environment induces some fears as well as serious hazards. The significant importance is removal of uranium(VI) ions as environmental pollutants which are radioactive and toxic. Various methods have been developed in recent years, such as solvent extraction,2-5 ion exchange68 and adsorption9-16 in the decontamination of uranium effluents. At present, the most popular way is the adsorption method with the application of various adsorbents such as metal oxides,14 activated carbon,16 aluminosilicates15 for the purpose of eliminating of uranium from the aqueous media. Natural materials such as biopolymers,17-19 zeolites,20 nanooxides11, 21 magnetite,19, 22-23 wood 1 ACS Paragon Plus Environment
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powder24-28 and some bacterial biomass are classified as promising adsorbents due to their low price and local accessibility.29-31 Nowadays mesoporous materials are in focus due to their characteristics, makes them prosperous object for surface functionalization for providing a new target physical and chemical properties10, 32-35 Recently, mesoporous silica-based materials have proved to be excellent candidate for water purification processes.9, 36-40 Among them, many studies have been carried out to obtain highly efficient sorbents for uranium ions, with particular relation to the sorption in acidic environments. This is a very important parameter for the treatment of acidic radioactive wastes. Most sorbents listed in the literature are characterized by high sorption capacity, however, operational only in neutral or near neutral media (pH 5-7).13, 29, 41-47 In the work40 several materials based on mesoporous silica with grafted amidoxime-, imide dioxime-, phosphonate-, and carboxylate functional groups for uranium extraction from seawater were proposed. It was found that the phosphonic acid-modified mesoporous silica material extract uranium from water with maximum capacity up to 185.2 lg U for 1 mg of sorbent and in artificial seawater – 66.7 lg U for 1 mg of sorbent.40 In our previous study48 we have obtained benzoimidazol-2yl-phenylphosphinic acid-derived ligand immobilized on the silica surfaces with comparable adsorption capacity towards uranium(VI) ions in neutral media comparing with other literature examples of phosphinic or phosphonic acid derevatives.12, 43, 45, 49-53 This paper aimed at preparing a novel sorbent based on silica with grafted phosphonic acid derivative, effective in removal of uranium ions from acidic environment (pH
