Fenolik Bileşiklerin Katalitik Olarak İndirgenmesinde Kullanilmak Üzere Kitosan ve Titanyum Dioksit Destekli Plazmonik Katalizör Sentezi

Abstract

The purpose of this thes is is the fabrication and performance evaluation of new catalysts which enable the elimination of toxic pollutants such as 4 - Nitrophenol (4 - NP) by means of heterogeneous catalytic reduction in an aq ueous environment. Production of two different catalysts was achieved by the immobilization of the plasmonic gold nanoparticles (AuNP) into the chitosan and titanium dioxide support materials, respectively. The plasmonic catalytic activities of fabricated catalysts were evaluated within the reduction of 4 - Nitrophen ol in the presence of sodium borohydride (NaBH 4 ) as a reducin g agent. The effects of type of support material and size of nanoparticle as performance enhancing parameter, loading amount of nanoparticle, catalyst amount and initial 4 - Nitrophenol concentrati on as operational parameters are evaluated in batch fashion. In line with this purpose, firstly the support materials were synthesized. Chitosan microgel beads were obtained by the chemical modification of chitosan solution. The monodisperse chitosan micr ogel beads, 3 mm in size with the specific surface area of 1.3 m 2 /g, were synthesized by crosslinking reaction in which glutaraldehyde served as a cross - linker. Titanium dioxide (TiO 2 ) spheres as second support material, were obtained by one - step sol - gel m ethod. TiO 2 spheres in the size range of 0.7 - 1.2  m with the specific surface area 277.4 m 2 /g were synthesized along with the hydrolysis of titania precursor, titanium ii isopropoxide in a continuous medium including methanol and acetonitrile. TiO 2 spheres were derivatized with Aminopropyltriethoxysilane (APTES), that enables TiO 2 to adsorb gold atoms through the amine groups on its surface. In the next stage, the support materials were added into the solutions of gold nanoparticles that have been s ynthesized with Turkevich (12 nm) and Martin (3 nm) Methods, respectively. The bare, Turkevich AuNP decorated and Martin AuNP decorated support materials were characterized by energy - dispersive x - ray spectroscopy, scanning electron microscopy, transmission electron microscopy, x - ray diffaraction spectrophotometry and surface area analysis via nitrogen adsorption - desorption method. The gold nanoparticle decorated chitosan microgel beads and TiO 2 spheres were used in the reduction of 4 - Nitrophenol, individually. The decoration with Martin AuNPs with lower size resulted in a significant enhancement in the plasmonic catalytic reduction rate owing to the electron transfer characteristics of AuNPs wit h lower size. The complete reduction of 4 - Nitrophenol having initial concentration of 7.5 ppm was achieved within 12 minutes in the presence of 10 mg Martin AuNP decorated chitosan microgel beads as catalyst (%2.5 (%w/w) AuNP loading). On the other hand, t he complete reduction of 4 - Nitrophenol having initial concentration of 7.5 ppm was achieved within 60 seconds in the presence of 12.5 mg Martin AuNP decorated TiO 2 spheres as catalyst (%2 (%w/w) AuNP loading). The recovery and reusability studies, conducte d under the same experimental conditions, indicated that the catalysts are reusable for reduction of 4 - Nitrophenol. In the plasmonic catalytic reduction of 4 - Nitrophenol via Au/chitosan and Au/TiO 2 catalysts, higher catalytic activities were obtained when compared to the other treatment methods, introduced in literature, involving catalysts supported with similar forms of different materials or different forms of similar materials. In this thesis, for the first time, Au/chitosan catalyst in the microgel bea d form and Au/TiO 2 catalyst in sphere form having novel structures and sizes were synthesized via simple, cost - effective, energy and time saving and environmentally friendly methods. Moreover, this study introduces biodegradable, porous, low - cost, mechanic ally stable catalysts that are able to form strong interaction with metal nanoparticles to the catalytic applications in favor of high catalytic activities