Removal of textile dyes from water by photocatalytic degradation in the presence of titanium dioxide nanoparticles immobilized onto chitosan and alginate based hydrogels.

Abstract

The aim of this Ph.D. thesis was to investigate the possibility of immobilization of titanium dioxide (TiO2) nanoparticles onto/into hydrogels as carriers, as well as the photodegradation of textile dyes from aqueous solutions by titanium dioxide/hydrogel nanocomposites that could be exploited for treatment of textile effluents. Two types of TiO2 nanoparticles were used: (a) freshly synthetized colloidal TiO2 nanoparticles, prepared by acid hydrolysis of titanium tetrachloride; (b) commercially available TiO2 nanoparticles (Degussa P25), which were used for comparison of photocatalytic activity. The following hydrogels have been synthetized as a carriers for TiO2 nanoparticles: (a) chitosan, itaconic acid and methacrylic acid hydrogels synthesized by free radical polymerization; (b) chitosan and poly(methacrylic acid) microparticles (Ch/PMA), which were synthesized for the first time by inverse suspension polymerization; (c) sodium alginate and partially neutralized poly(methacrylic acid) interpenetrating polymer networks (IPN) obtained by free radical polymerization followed by additional cross-linking of sodium alginate with calcium ions. TiO2/hydrogel nanocomposites were obtained by immobilization of TiO2 nanoparticles onto/into hydrogels, which were afterwards characterized and their photocatalytic activity was tested. The presence of TiO2 nanoparticles onto/into hydrogels was confirmed by energy dispersive spectroscopy (EDX). The porous structure of the chitosan-based hydrogels and sodium alginate-based interpenetrating networks was observed by SEM analysis. Swelling experiments and rheological studies showed that the pore size, swelling kinetics and mechanical strength depend on the hydrogel composition, degree of crosslinking, presence of TiO2 nanoparticles and the type of immobilized TiO2 nanoparticles. SEM analysis and optical microscopy revealed that chitosan microparticles have a spherical structure. Infrared spectroscopy with Fourier transformation (FTIR) showed that all components present during hydrogel synthesis were incorporated into the polymer network. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated that the prepared samples had good thermal stability...

Cilj ove doktorske disertacije je da se ispitaju mogućnosti imobilizacije nanočestica titan-dioksida (TiO2) na hidrogelove kao nosače i fotodegradacija boja za tekstil iz vodenih rastvora pomoću titan-dioksid/hidrogel nanokompozita za potrebe prečišćavanja otpadnih voda iz tekstilne industrije. U radu su korišćene dve vrste TiO2 nanočestica: (a) sintetisane koloidne nanočestice TiO2, dobijene kiselom hidrolizom titan-tetrahlorida; (b) komercijalno dostupne nanočestice TiO2 (Degussa P25), radi poređenja fotokatalitičke aktivnosti. Kao nosači nanočestica TiO2 pripremljeni su sledeći hidrogelovi: (a) hidrogelovi hitozana, itakonske kiseline i metakrilne kiseline sintetisani radikalnom polimerizacijom; (b) mikročestice hitozana i poli(metakrilne kiseline), po prvi put sintetisane inverznom suspenzionom polimerizacijom; (c) interpenetrirajuće mreže (IPM) natrijum-alginata i delimično neutralisane poli(metakrilne kiseline) dobijene radikalnom polimerizacijom i naknadnim umrežavanjem jonima kalcijuma. Imobilizacijom nanočestica titan-dioksida na hidrogelove dobijeni su TiO2/hidrogel nanokompoziti, koji su okarakterisani i ispitana je njihova fotokatalitička aktivnost. Prisustvo nanočestica TiO2 na/u hidrogelovima je potvrđeno energetskom disperzionom spektroskopijom (EDX). Skenirajuća elektronska mikroskopija (SEM) je pokazala da hidrogelovi hitozana i interpenetrirajuće mreže natrijum-alginata imaju poroznu strukturu. Eksperimentima bubrenja i reološkim ispitivanjima je potvrđeno da veličina pora, kinetika bubrenja i mehanička jačina zavise od sastava hidrogelova, stepena umreženja, prisustva i vrste imobilisanih nanočestica TiO2. SEM analiza i optička mikroskopija su pokazale da mikročestice hitozana imaju sferičnu strukturu. Infracrvenom spektroskopijom sa Fourier-ovim transformacijama (FTIR) je utvrđeno da su u polimernu mrežu nosača ugrađene sve komponente prisutne tokom sinteze. Termogravimetrijskom analizom (TGA) i skenirajućom kalorimetrijom (DSC) je zaključeno da pripremljeni uzorci imaju dobru termičku stabilnost. Lampa koja simulira sunčevu svetlost je korišćena za fotoaktivaciju TiO2/hidrogel nanokompozita u procesu fotodegradacije sledećih boja za tekstil: kisele boje C.I. Acid Orange 7, C.I. Acid Red 18 i C.I. Acid Blue 113, reaktivne boje C.I. Reactive Yellow 17 i C.I. Reactive Black 5, direktna boja C.I. Direct Blue 78 i najčešće ispitivana test boja, bazna (katjonska) boja metilensko plavo. Uklanjanje boja iz vodenih rastvora praćeno je UV/Vis spektrofotometrom...