Kychkyruk, O.

Savchenko, I.

Sternik, D.

Vretik, L.

Yanovska, E.

Zhytomyr State University Library

Syntheses, characterization, and adsorption properties formetal ions of silica-gel functionalized by poly[8-methacroyloxy-quinoline]I. Savchenkoa, E. Yanovskaa, L. Vretika, D. Sternikb, and O. KychkyrukcaNational Taras Shevchenko University of Kyiv, Kyiv, Ukraine; bMaria Curie-Skłodowska University, MariaCurie-Sklodowska Sq, Lublin, Poland; cIvan Franko Zhytomyr State University, Zhytomyr, UkraineABSTRACTBy mean of heterophase polymerization on the silica gel surface hasbeen made in situ immobilization of poly [8-methacroyloxy-quin-oline], has been received new organic-mineral composite material.Infrared and mass spectroscopy as well as termogravimetry (TG) ana-lysis have been used to elucidate the structure of immobilized poly-mer. An adsorption capacity of the synthesized composite towardCu(II), Pb(II), Mn(II), Fe(III), Cd(II) ions has been estimated. Adsorptionactivity to microquantities of Cu(II), Mn(II), Fe(III), Cd(II) in a neutralaqueous medium has been observed.KEYWORDSAdsorption; in situimmobilization; metalcomplexes; modified silica;poly [8-methacroyloxy-quinoline1. IntroductionAdsorbent materials are of great scientific and technological interest owing to their abil-ity to interact with specific substances and efficiently separate them from amixture. Owing to their superior physical and chemical features, including a large spe-cific surface area, unique pore structure and tunable pore surface property, adsorbentmaterials have found utility in multiple applications, such as adsorption [1], separation/purification [2], biosensors [3], drug delivery systems [4] and so on.Silica based porous materials are considered as promising adsorbents for waterremediation due to their high surface area, well-defined tunable pore size and highadsorption capacity. Owing to their economic feasibility, high thermal and mechanicalstabilities, they can be utilized as inorganic solid matrixes in the inorganic–organichybrid materials. Several researchers have contributed in the development of functional-ized silica based adsorbents for the removal of heavy metals [5–7].A large number of sorption methods have been proposed and used for the pre-con-centration and removal of trace elements in the food and pharmaceutical industry,water purification, etc. With the purpose of concentrating and removing traces of metalspecies occurring in aqueous solutions several adsorbents have been studied, there areincluded activated carbon, polymers, ion exchangers, chelating resins and manyothers [8–10].CONTACT I. Savchenko irassavchenko@gmail.com National Taras Shevchenko University of Kyiv, 60,Volodymyrska Str, Kyiv 01601, Ukraine. 2020 Taylor & Francis Group, LLCMOLECULAR CRYSTALS AND LIQUID CRYSTALS2021, VOL. 719, NO. 1, 103–115https://doi.org/10.1080/15421406.2020.1862466The modification of the surface of porous inorganic materials by nitrogen-containingpolymers allows to obtain sorbents for removing toxic metals from the waste water dueto their complexation with nitrogen atoms of immobilized polymer [11–13]. One of thepromising ways of creating organo-mineral composite materials with valuable sorptionproperties is polymerization or in situ immobilization, which consists in the direct for-mation of an immobilized polymeric layer in the presence of particles of inorganicmatrix [13–15].This work is dedicated in situ immobilization of poly [8-methacroyloxy-quinoline] onthe surface of silica gel, the study of surface morphology of modified silica gel andadsorption properties of the synthesized composite material on ions Cu(II), Pb(II),Mn(II), Fe(III), Cd(II).2. Experimental2.1. SynthesisThe synthesis of 8-methacroyloxy-quinoline is given below: 8-hydroxyquinoline (18.15 g,.0125mol) was dissolved in 100ml anhydrous THF, and freshly distilled triethylamine(34.78ml, 0.25mol) was added to the solution. The reaction mixture was then cooled to0–5 C. Methacryloyl chloride (24.41ml, 0.25mol) in THF (50ml) was injected graduallyto the above solution via a glass syringe while the solution temperature was kept below5 C. The reaction mixture was stirred overnight at room temperature. The resultingprecipitate was filtered off. Purification was followed by recrystallization from methanol.Yield: 86%.2.1.1. 8-Methacroyloxy-quinoline1H NMR (400MHz, DMSO, d, ppm): d 7.48–7.59 (t, 3H), 8.85 7.85 (s, 2H), 6.40 (s,1H C¼CH2, cis), 5.85 (s, 1H C¼CH2, trans), 2.11 (s, 3H, ¼C-CH3).The polymerization of 8-methacroyloxy-quinoline in the presence of silica gel (frac-tion of particles with a diameter of 0.1–0.2mm, specific surface 428.61m2/g, Merck) hasbeen carried out under the argon atmosphere. A solution of 6.5 g 8-methacroyloxy-quinoline and 0.065 g of 2,20-azobisisobutyronitrile (AIBN) in 150ml tetrahydrofuran(THF) were poured into a flask containing 19.5 g of silica gel. When argon blowing wasfinished after 15min, the reaction mixture was heated to 78 C; polymerization contin-ued for 5 h with stirring. The reaction was stopped by cooling the reaction mixture. Theresulting suspension was poured into a porcelain cup and left overnight to evaporatethe solvent; the synthesized composite was washed three times with isopropyl alcohol,filtered and air-dried for 24 h at room temperature.2.2. Characterization methodsIR spectra of the original and modified silica gel were recorded using an infrared spec-trophotometer “Spectrum BX” (Perkin Elmer, Germany) in the range 500–4000 cm1 intablets KBr.104 I. SAVCHENKO ET AL.The amount of immobilized polymer on the silica gel surface was evaluated by ther-mogravimetric analysis results obtained with simultaneous TG/DTA analyzer ShimadzuDTG-60H (Japan) with computer registration of data in the 15–1000 C temperaturerange. The heating rate of samples is 10 C/min.Thermal analysis was carried out on a STA 449 Jupiter F1, Netzsch (Germany) withmass spectroscopy console QMS 403C Ae€olos (Germany)The values of the surface area, average volume and average pore diameter were calcu-lated from the data of low temperature nitrogen adsorption/desorption isotherms usingthe "ASAP 2420 V1.01" (Micromeritics, USA) sorbetometric software. Before measure-ments, samples were degassed at 60 C for 24 h.The morphology of the surface of silica gel before and after modification by polymerwas investigated by scanning electron microscopy using the electron microscope "SEMLEO 1430 VP" (Carl Zeiss, Germany).Sorption characteristics of the synthesized material with respect to Cu (II), Cd (II),Pb (II) and Fe (III) ions were studied in static mode. At the same time, 0.1 g of thecomposite was contacted with 25-100ml of working solutions of nitrates of the corre-sponding metals. The interaction took place for 10, 30, 60, 90min and day with mech-anical shaking. The equilibrium concentration of metal ions was fixed by the atomicabsorption method.The working solutions of the nitrates of the selected metals for the study of the sorp-tion properties of the modified silica gel were prepared from the sets of "standard sam-ples of solutions" of these salts (produced by AV Bogatsky, Odessa) on the backgroundof 1 MNO3 at concentrations of 1 and 10mg/ml.To create a medium with pH 4, a phthalate buffer solution was used from a set of"Standard buffer solutions" (DSTU 8.135: 2009, manufacturer of OJSC "Kiev plant ofRIAP"). pH 2.8 was made by adding 0.1M acetic acid, which was prepared from fixanal.The exact pH of the working solutions was determined using the pH meter "HANNATESTER WP" (Hanna instrument, China).The adsorption capacity (A) was calculated using the formula:A ¼ ðcj– M½ Þ V = mwhere co – initial molar metal concentration, [M] – balanced molar metal concentration,V – is the volume of the working solution, m – is mass of the adsorbent (g).The adsorption rate (R) was calculated according to the equation:R ¼ mads=moð Þ  100% ¼ mo  ½mð Þ=mo  100where mo – is mass of metal in the starting solution (mkg), mads – is mass of the metaladsorbed, [m] – is mass of the metal at equilibrium after the adsorption, which wasfound [m]¼V, where  – is concentration of the metal at equilibrium (mrg/ml) andV – is the volume of the solution at equilibrium (ml).The balanced metal ions concentration was defined by atom-absorption method.Atom-absorption measuring was made with the help flame atom-absorption spectropho-tometer "Saturn" (Ukraine) in flame solution "air - propane - butane". The wavelengthswere: for cuprum  324.7 nm, cadmium  228.8 nm, plumbum  283.3 nm, ferum 248.3 nm, and the width of the crack of 0.58 cm. The balanced concentrations calcula-tions in solution were made by comparing method of their lines intensity in theMOLECULAR CRYSTALS AND LIQUID CRYSTALS 105standard solutions intensity spector. Standard solutions were prepared with metal con-centrations of 0.1–1.5 lg/ml.3. Results and discussionThe generalized scheme in situ immobilization of 8-methacroyloxy-quinoline on the sil-ica gel surface is shown in Fig. 1.The surface functionalization of silica gel with polymer was affirmed by FTIR spec-troscopic analysis (Fig. 2). The bands at 1054 and 791 cm1 are characteristic of asym-metric and symmetric vibrations of Si–O–Si. The surface modification of polymer wasconfirmed by the appearance of stretching vibrations t (C-N) observed at 1580 cm1. Anumber of bands at 1507, 1474, 1375 cm1 can be attributed to the valence vibrationsof the C-C aromatic system [16]. The C¼O stretching vibration at 1680 cm1 and fur-ther supported the immobilization of polymer on the surface of silica gel.Thus, the results of IR spectroscopy confirm the presence of a polymer on the surfaceof silica gel.In order to determine the concentration of immobilized polymer, a thermogravimet-ric analysis of the synthesized composite and the original silica gel was performed.Figures 3 and 4 show the thermograms of the original silica gel and the synthe-sized composite.The comparative analysis of the thermograms (Figs. 3 and 4) shows that the mainloss of the composite mass due to the thermal decomposition of the immobilized poly-mer the loss of structured water in the composition of silica gel occurs in the rangefrom 88 to 570 C. In this case, about 9.3% of the composite weight is lost. And thegreatest mass losses are observed at temperatures from 388 to 515 C. According to Fig.4 the weight of water in the source silica gel is 5.4%. Therefore, the mass of the immo-bilized polymer is 3.9%.In order to detail the process of thermodestruction of the composite, its thermogram,combined with mass spectrum, was obtained in 3D format (Fig. 5a), mass spectrum 2Dformat (Fig. 5b) and thermogram combined with infrared spectrum, in 3D format(Fig. 5c).Mass spectral studies show that, as a result of thermal degradation of a polymer attemperatures above 400 C, particles with a mass of 1,82,628 and 44Da are most likelyformed, which most likely correspond to the formation of water, CN-groups, ethine andCO2. In the temperature range of 200–400 C, the formation of a small number ofFigure 1. The scheme of in situ polymerization of 8-methacroyloxy-quinoline.106 I. SAVCHENKO ET AL.Figure 2. The FTIR-spectra of the original silica gel (1) and synthesized composite (2).Figure 3. TG-, DTG-, DSC-curves of the silica gel.MOLECULAR CRYSTALS AND LIQUID CRYSTALS 107particles with molecular masses 54 and 70, which most likely correspond to fragmentsof the carbon chain of a polymer.To investigate the parameters of the surface of synthesized composites, the method ofBET (low-temperature adsorption–desorption of nitrogen) was used. The resultingadsorption-desorption nitrogen isotherms for the original silica gel and the synthesizedcomposite are similar and belong to the type IV isotherm according to the classificationof IUPAC [17]. This suggests that the structure of the surface of silica gel as a result offixing the polymer is unchanged practically.The surface area, average volume, and pore size of the surface of the synthesizedcomposite, calculated by computerized isotherm processing, are shown in Table 1. Theobtained data indicate that after the immobilization of the polymer, the surface area ofthe silica gel decreases slightly (from 447 to 389.7 m2/g).The mean pore volume decreases from 0.67 to 0.62 cm3/g, and the average porediameter increases from 5.92 to 6.08 nm.Changes in the surface morphology of silica gel after modification by polymer werefollowed by scanning electron microscopy (CEM). The CEM-photos of modified silicagel are shown in Figs. 6–8.As can be seen from the above photos, the polymer is on the surface of silica gel inthe form of balls and convex agglomerates due to its hydrophobicity, which do notaffect the structure of silica gel.Since the immobilized polymer is composed of 8-oxyquinoline groups, it must exhibitcomplex-forming activity with respect to transition metal ions due to nitrogen oxide.To confirm these considerations, we investigated the sorption of transition metal ionswith a high affinity for nitrogen-containing ligands.Investigation of the sorption capacity of the synthesized composite for these metalions included: study of the rate of sorption of selected ions on the surface of the synthesizedcomposite in static mode from aqueous nitrate solutions;Figure 4. TG-, DTG-, DSC-curves of the synthesized composite.108 I. SAVCHENKO ET AL.Figure 5. Mass spectrum DSC-QMS-3D (ff), mass spectrum QMS-2D (B) and thermogram combinedwith infrared spectrum, in 3D format (C) of the synthesized composite.MOLECULAR CRYSTALS AND LIQUID CRYSTALS 109 construction of isotherms of sorption of each of the investigated metal ions onthe surface of the synthesized composite; determination of sorption capacity for each of the investigated metal ions andcomparison with the original silica gel.The kinetics of sorption of selected metal ions by the composite surface is presentedin Fig. 9.The obtained data indicate that Cu(II) and Pb(II) ions are quantitatively adsorbedwithin the first ten minutes of contact with the composite surface. The Fe(III) andCd(II) ions are maximally sorbed during the first minutes of contact. The degree ofsorption of Zn(II) ions gradually increases over the course of an hour of contact, andthen they are partially washed back into solution. Mn(II) ions are gradually sorbed dur-ing the first hour of contact, and completely washed back into solution within an hour.Based on the obtained data, the contact time of all metal ions with the surface of thecomposite during the experiments for the construction of sorption isotherms wasone hour.All the obtained isotherms (Figs. 10–14) belong to the 2L species, which indicatesthe uniform location of the sorbed metal ions on the surface of the composite. ThisTable 1. Characteristics of the surface of silica gel and synthesized composite.SampleSurface area (m2/g)Average pore volume (cm3/g) Average pore size (nm)P/P0 BET LangmuirSilica gel 447.00 463.53 686.91 0.686 5.92Composite 389.70 407.31 609.77 0.619 6.08Figure 6. ð photo of the surface of the composite at an increase of 25,000 times.110 I. SAVCHENKO ET AL.type of isotherms is typical of silica matrices modified by complexing substances.The obtained isotherms allow to calculate the sorption capacity of the synthe-sized composite.Figure 7. ð photo of the surface of the composite at an increase of 50,000 times.Figure 8. ð photo of the surface of the composite at an increase of 1,00,000 times.MOLECULAR CRYSTALS AND LIQUID CRYSTALS 111Figure 9. Kinetics of sorption of u2þ, Pb2þ, Zn2þ, Fe3þ, Mn2þ, Cd2þ ions on the surface of silicagel, in situ modified poly [8-methacroyloxy-quinoline], in static sorption mode.Figure 10. Adsorption isotherm of ions Pb(II) on silica gel with immobilized poly [8-methacroy-loxy-quinoline].Figure 11. Adsorption isotherm of ions Fe(II) on silica gel with immobilized poly [8-methacroy-loxy-quinoline].112 I. SAVCHENKO ET AL.Comparison of the values of the sorption capacity of the synthesized composite withrespect to u2þ, Pb2þ, Zn2þ, Fe3þ, Mn2þ, Cd2þ ions found as a result of the processingof sorption isotherm data and the original silica gel (according to the literature) areshown in Table 2.The data in this table suggest that the sorption capacity of silica gel after modifi-cation of poly [8-methacroyloxy-quinoline] with respect to Cu(II), Fe(III), andMn(II) ions increases by approximately 1.5 times as a result of immobilization onthe surface of the complexing polymer. But it remains unchanged with respect toPb(II) ions.Figure 12. Adsorption isotherm of ions Cu(II) on silica gel with immobilized poly [8-methacroy-loxy-quinoline].Figure 13. Adsorption isotherm of ions Mn(II) on silica gel with immobilized poly [8-methacroy-loxy-quinoline].MOLECULAR CRYSTALS AND LIQUID CRYSTALS 1134. ConclusionsIn summary, new organic composite material has been synthesized by in situ immobil-ization of poly [8-methacroyloxy-quinoline] on the surface of silica gel. Silica gel wasfunctionalized with polymer to improve the adsorption behavior toward u2þ, Pb2þ,Zn2þ, Fe3þ, Mn2þ, Cd2þ ions. The removal efficiency of polymer functionalized silicawas compared with the original silica.From the results of studies options after silica surface modified polymer by BET andaccording to scanning electron microscopy shows that immobilized polymer has noeffect on the structure of the surface layer of silica gel practically.The small increase in the sorption capacity of the synthesized compositewith respect to the selected metal ions can be explained by the agglomeratearrangement of the immobilized polymer on the silica gel surface (Fig. 8) and,consequently, the steric inaccessibility of most complex metal centers for themetal ions.The present study revealed that synthesized composite is promising materials for theremoval of Cu(II), Fe(III), and Mn(II) ions from aqueous mediaFigure 14. Adsorption isotherm of ions Cd(II) on silica gel with immobilized poly [8-methacroy-loxy-quinoline].Table 2. Adsorption capacity of the synthesized composite.ationAdsorption capacityOriginal silica gel Compositemmol/g mg/g mmol/g mg/gCu(II) 0.006 0.11 0.009 0.16Pb(II) 0.002 0.04 0.002 0.04Fe(III) 0.008 0.14 0.012 0.22Mn(II) 0.010 0.55 0.014 0.25Cd(II) 0.06 0.67 0.008 0.14114 I. SAVCHENKO ET AL.References[1] S. Nayab et al., RSC Adv. 8 (42), 23963 (2018). doi:10.1039/C8RA04209H[2] H. Hongxing, G. Qiang, and F. Changgen, RSC Adv. 7, 15102 (2017).[3] G. Fu, X. Yue, and Z. Dai, Biosens. Bioelectron. 26 (9), 3973 (2011). doi:10.1016/j.bios.2011.03.007[4] G. H. Gwak, S. M. Paek, and J. M. Oh, Eur. J. Inorg. Chem. 2012 (32), 5269 (2012). doi:10.1002/ejic.201200583[5] S. Babak, C. Chil-Hung, and W. Jiangning, Materials 7, 673 (2014).[6] L. Hanyu et al., J. Mol. Liq. 273, 305 (2019).[7] X. Zhijun et al., Separation and Purification Technology 191 (31), 61 (2018).[8] E. Yanovska et al., Nanoscale Res. Lett. 12 (1), 313 (2017). doi:10.1186/s11671-017-2066-0[9] H. Hong-Xing, G. Qiang, and F. Chang-Gen, Chin. J. Polym. Sci. 36 (4), 462 (2018).[10] R. T. Deniz et al., Eclet. Quım. 32 (2), 13 (2007). doi:10.1590/S0100-46702007000200002[11] A. D. Dadashev et al., Am. J. Anal. Chem. 07 (05), 411 (2016). doi:10.4236/ajac.2016.75038[12] I. Savchenko et al., Mol. Cryst. Liq. Cryst. 671 (1), 164 (2018). doi:10.1080/15421406.2018.1542099[13] Y. Polonska et al., Mol. Cryst. Liq. Cryst. 673 (1), 39 (2018). doi:10.1080/15421406.2019.1578492[14] V. Mittal, Materials 2 (3), 992 (2009). doi:10.3390/ma2030992[15] K. V. Ryabchenko et al., Adsorption Sci. Technol. 32, 88 (2014).[16] A. L. Smith, Applied IR Spectroscopy. Moscow: World (1982) (in Russian).[17] G. D. Parfitt, Adsorption from Solution at the Solid Liquid Interface. Moscow: Mir (1986).MOLECULAR CRYSTALS AND LIQUID CRYSTALS 115

Syntheses, characterization, and adsorption properties for metal ions of silica-gel functionalized by poly[8-methacroyloxy-quinoline]

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Syntheses, characterization, and adsorption properties for metal ions of silica-gel functionalized by poly[8-methacroyloxy-quinoline]

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