Kostenko L. Silica-containing oxide materials functionalized by alkylaminophosphonic groups: synthesis, structure of the grafted layer and properties

The dissertation is devoted to the synthesis of materials based on silica (SіO2), bentonite (Bnt), and magnetite (Fe3O4/ SіO2), functionalized with complexing groups of alkylaminophosphonic acids (APA) and to determine the effect of the surface layer composition of materials on their chemical and sorption properties. Conditions for obtaining silicas with fixed alkylaminophosphonic groups using the method of "assembly on the surface" via Kabachnik-Fields reaction have been optimized. It was found that the degree of conversion of amino groups to aminophosphonic groups depended on the basicity of the immobilized amino groups and increased with their surface concentration due to the weaker binding to silanol groups. The highest yields of aminomethylenephosphonic acids are achieved by phosphonomethylation in the presence of formaldehyde and phosphorous acid in n a polar medium of diglyme. The XPS method established the zwitterionic form of grafted aminophosphonic groups and the presence of residual amino groups in the immobilized layer of SіO2-APA. According to solid-state 31P NMR spectroscopy, only samples with high concentrations of fixed aminophosphonic groups (C > 1 μmol m-2) have a locally homogeneous environment due to weakening of the interaction between groups of the surface layer. Immobilized alkylaminophosphonic acids are thermally stable at 300 ° C, and the destruction of SіO2-APA is limited by substituents in the NCP(O) fragment of the ligand. The protolytic properties of SіO2-APA were characterized using the continuous distribution of equilibrium constants model and chemical reactions model. It was shown that hydrophobization of the SiО2-MAPA surface significantly reduces the heterogeneity of the methylaminophosphonic acid nearest environment. The decrease in immobilized aminodiphosphonic acids acidity after the second stage is a result of their interaction with residual amino groups in the absence of surface silanol groups. Neutralization of SіO2-ADPA in the presence of metal ions (pH 3-9) accounts for more than two equivalents of alkali, which leads to the formation of protonated complexes of equimolar composition on the surface according to: , where x = 1, 2. As expected, the most stable complexes formed highly charged lanthanide ions. Obtained stability series of the surface metal complexes correspond to the order of decreasing stability constants of complexes in solution. For the first time, the functionalization of magnetite and bentonite nanoparticles with ADPA groups was carried out. It has been shown that Fe3O4 nanoparticles coated with a dense silica shell have a higher chemical resistance compared to Fe3O4 coated with a dopamine monolayer. The developed surface of Fe3O4/SiO2-ADPA in combination with magnetic properties and hydrolytic stability is a prerequisite for using it as a sorbent with magnetic separation from the solution. In the process of the two-stage production of Bnt-APA, the structure of the mineral framework of bentonite does not change. According to X-ray phase studies, the interlayer distance of silanized bentonites depends on the nature of the intercalated aminosilane. Compared to the initial Bnt, the largest increase (by 42%) in the interlayer spacing was observed for Bnt-NH2. A high concentration of fixed amino groups was a proof of silanes oligomerization after hydrolysis. Washing a part of the condensed aminosilane layer out in acidic conditions during phosphorylation caused low concentrations of fixed aminophosphonic groups. Nevertheless, the obtained phosphorus-containing bentonites had high hydrolytic stability. Obtained sorbents have a high affinity for ions of heavy metals and REE, are characterized by the rapid establishment of sorption equilibrium, and are capable of regeneration without loss of sorption capacity. Ions are better removed on silicas with aminodiphosphonic groups, and interaction with monophosphonic groups occurs in less acidic solutions. SiO2-ADPA removes REE at pH <3, and its sorption capacity remains constant for at least five regeneration cycles. The introduction of SiO2-ADPA into hydrophobic polyvinylidenefluoride membranes gives them hydrophilic properties, and an increase in the water throughput of such a proton-conducting membrane is due to the high volume migration of protons of aminodiphosphonic groups. Fe3O4/SiO2-ADPA is shown to be promising for multiple uptaking of Eu(III) ions and concentration from dilute solutions, which, in combination with magnetic properties, can be utilized for fast magnetic separation of the sorbent. It is shown that an increase in the interlayer spacing in Bnt-APA compared to unmodified bentonite significantly improves its filtration characteristics. This makes it possible to use Bnt-APA for the purification of river water under dynamic conditions and achieves complete removal (>97%) of Pb(II) and significant decrease (59-65%) of Cu(II) and Zn(II) ions was achieved upon simple filtration.