Synthesis, characterization and sorption properties of bentonite modified by tetraalkylammonium ions

[N.P. Jović-Jovičić]

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Materijali - zaštita životne sredine / Materials - environmental protection

Ovaj rad je posvećen sintezi organobentonita (OB) dobijenih modifikacijom kvaternernim alkilamonijum katjonima (KAAK), karakterizaciji dobijenih uzoraka, ispitivanju njihovih adsorpcionih svojstava prema organskim i neorganskim zagađivačima prisutnim u otpadnim vodama tekstilne industrije, kao i utvrđivanju multifunkcionalnog adsorbensa koji bi usled posedovanja i hidrofilne i organofilne površine uspešno mogao biti upotrebljen prilikom tretmana otpadnih voda kompleksnog sastava Sintetisani OB dobijeni su od bentonitne gline sa lokaliteta Bogovina (Srbija). Polazni uzorak frakcije <74 μm je najpre Na–izmenjen (Na–B), a zatim modifikovan KAAK jonima. Modifikacijom su dobijene dve serije organobentonita. U prvoj seriji je korišćen heksadeciltrimetilamonijum (HDTMA) bromid, pri čemu količina odgovara vrednostima Kizm=0,2–3,0 (gde je Kizm broj koji pokazuje odnos KAAK jona prema vrednosti kapaicteta katjonske izmene). Druga sereija je dobijena modifikacijom bentonita KAAK različite dužine alkil niza: HDTMA bromidom, dodeciltrimetilamonijum (DDTMA) bromidom i tetrametilamonijum (TMA) bromidom, pri čemu je Kizm=2,0. Dobijeni uzorci su označeni kao 0,2 HDTMA–B, 0,5 HDTMA–B, 1,0 HDTMA–B, 2,0 HDTMA–B, 3,0 HDTMA–B, 2,0 DDTMA–B, 2,0 TMA–B. Ispitivan je uticaj modifikacije na strukturu, teksturalna i adsorpciona svojstva bentonita. Hemijski sastav polaznog bentonita i Na–B je određen standardnom silikatnom analizom, dok je procena udela organske faze kod OB izvršena žarenjem uzoraka na 800°C, čime je potvrđeno prisustvo organske faze čiji udeo raste sa porastom Kizm i sa porastom dužine alkil niza KAAK. Fazni sastav, teksturalna i morfološka svojstva Na–B i uzoraka OB određeni su korišćenjem XRD analize, IC analize, metodom fizisorpcije N2 i SEM mikroskopije. Utvrđeno je da primenjeni postupci modifikacije dovode isključivo do izmene katjona u međulamelarnom sloju smektita, dok modifikacija ne deluje na druge prateće minerale u bentonitu (kvarc, kalcit, feldspat). Kod uzoraka 0,2, 0,5 i 1,0 HDTMA–B na osnovu vrednosti d001 utvrđeno je da dolazi do formiranja monosloja, dvosloja i pseudo-tri molekulskog sloja HDTMA katjona, dok kod uzoraka sa Kizm=1,0-3,0 HDTMA–B unutar međusloja dolazi do formiranja organske faze za koju je pretpostavljeno da je delimično sastavljena od parafinskih slojeva. IC spektri uzoraka OB ukazuju na prisustvo tri nove trake koje potiču od vibracija metilenske grupe, što je još jedna potvrda ugradnje KAAK. Kod svih OB osim 2,0 TMA–B, utvrđeno je da sa povećanjem Kizm i dužine alkil niza KAAK dolazi do značajne promene teksturalnih svojstava u odnosu na polazni Na–B. Uočen je pad specifične površine materijla i prelazak mikro i mezoporoznog materijala u gotovo potpuno neporozan. Sa druge strane, 2,0 TMA–B i Na–B imaju slične teksturalne osobine, što je posledica ugradnje kratkolančanog katjona TMA u obliku „pilara“, a posledica je stvaranje mikroporoznog materijala. Analizom SEM mikrofotografija snimljenih uzoraka analizirane HDTMA serije uočava se da svi izorci zadržavaju slojevitu strukturu filosilikata...

The synthesis of organo-bentonites (OB) obtained by modification with quaternary alkylammonium cations (QAAC), their characterization and evaluation of their efficiency as adsorbents for organic and inorganic aqueous pollutants was investigated in this work. Particular attention was dedicated to the removal of pollutants from textile industry effluents, and obtainment of a multifunctional adsorbent that incorporates both hydrophilic and hydrophobic surfaces, which can be successfully applied in the purification of wastewaters with complex composition. The synthesized OBs were obtained from smectite containing clay bentonite from Bogovina basin (Serbia). The starting material, consisted of particles with diameters of up to 74μm, was submitted to Na-exchange (Na-B), and subsequent modification with QAAC ions. Two series of OBs were obtained in this manner. The first series was obtained using hexadecyltrimethylammonium (HDTMA) bromide. The amount of introduced HDTMA was expressed as Kexch=0,2–3,0, where the value of Kexch represents the ratio between QAAC ions and the cation exchange capacity of the clay. The second series was obtained by the bentonite modification using QAACs (Kexch=2,0) with different alkyl chain lengths: HDTMA bromide, dodecyltrimethylammonium (DDTMA) bromide and tetramethylammonium (TMA) bromide. The samples were denoted as 0,2 HDTMA–B, 0,5 HDTMA–B, 1,0 HDTMA–B, 2,0 HDTMA–B i 3,0 HDTMA–B, 2,0 DDTMA–B, 2,0 TMA–B. The influence of the modification on the structural, textural and adsorption properties of bentonite was investigated. The chemical compositions of the starting and Na-exchanged bentonite were determined by standard silicate analysis, and the fraction of the organic phase in the samples was estimated after calcination at 800°C. The increasing presence of the organic phase with increased Kexch or QAAC alkyl chain length was confirmed. The phase composition, textural and morphological properties of the Na-B and OB samples were determined by XRD and IR analyses, N2 physisorption and SEM microscopy. It was found that the applied modification procedures resulted in the exclusive exchange of cations from the smectite interlamellar region, with no impact on the accompanying minerals present in bentonite (quartz, calcite, feldspar). In the case of 0,2, 0,5 i 1,0 HDTMA–B samples, it was concluded from the d001 values that the consequence of the modification was the formation of mono-, bi- or pseudotrimolecular HDTMA layers. As for the 1,0–3,0 HDTMA-B samples it is presumed that the formation of organic phase occurred within the interlamellar region, which is probably partially consisted of paraffin layers. The IR spectra of the OBs exhibited the occurrence of three new bands corresponding to methyl group vibrations, which is another proof of the incorporation of QAACs. For all OB samples, except for the 2,0 TMA–B, was established that the increase in the Kexch values and alkyl chain lengths lead to significant changes in the textural properties comparing to those of the starting Na-B material. The decrease in the specific surface was observed, and the starting micro/mesoporous material was turned almost completely nonporous. On the other hand, the 2,0 TMA–B and Na-B exhibited similar textural properties, which is a consequence of the incorporation of short-alkylchained TMA cations in the form of pillars resulting in a microporous material The analysis of the SEM micrographs of the HDTMA sample series it was observed that all the samples retained characteristic phylosilicate layered structure...

adsorpcija, karakterizacija, bentonit, kvaternerni alkilamonijum joni, tekstilne boje, teški metali, kinetika, multifunkcionalni adsorbens

adsorption, characterization, bentonite, quaternary ammonia ions, textile dyes, heavy metals, kinetics, multifunctional adsorbent

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