Development and Characterization of Optical Sol-Gel Sensor for pH Determination

Cilj ovoga diplomskog rada je pripraviti optički sol-gel senzor za mjerenje pH. Sol-gel struktura sintetizirana je kombiniranjem dviju prekursorskih molekula, tetraetoksisilana (TEOS), propiltrimetoksisilana (pTriMOS) u etanolu kao otapalu, a uz HCl kao katalizator. Unutar gel strukture su ugrađene molekule pH indikatora bromokrezol ljubičasto i bromokrezol zeleno i njihova kombinacija. Pripravljeni senzorski slojevi pokazuju gotovo identična svojstva kao i same otopine indikatora. Količina indikatorske boje utječe na apsorbanciju slojeva, što je više indikatora veća je apsorbancija i između količine indikatora i apsorbancije postoji linearna ovisnost. Kod slojeva je uočen efekt ispiranja boje iz gel strukture. Staklo je pokazano kao bolji nosač sol-gela u odnosu na PVC foliju. Pripremljeni senzosrki slojevi mogu biti korišteni kao indikatori završne točke kod titriranja. U metodičkom djelu rada opisana je obrada teme kiselo-bazne reakcije za učenike drugog razreda srednje škole. Učenici bi prvo upoznali pojmove vezane za kiselobazne reakcije (neutralizacija, indikatori i titracije), a zatim bi samostalno izveli pokus i rješavali postavljene zadatke.The aim of thesis is to prepare optical sol-gel sensor for pH determination. Sol-gels are prepared from two precursors molecules, tetraetoxysilane (TEOS) and propyltrimethoxysilane (pTriMOS) in ethanol as solvent and HCl solution as catalyst. Molecules of pH indicator dyes bromocresol purple and bromocresol green and their combination are immobilised inside gel structure. Sensor layers with pH dyes shows almost the same properties as pH dyes in solution. Amount of pH indicator dyes have influence on UV-Vis apsorbance, more dye in sensor layer gives higher apsorbance. This dependence is linear. Leaching effect was observed on sensor layers, some dye molecules came out of gel in water. Glass showed better properties for sol-gel sensor carrier than PVC foil. This sol-gel sensors can be used for determination of end point in titrations. In teaching part of this thesis there is an interpretation of two high school chemistry lessons where students would learn about acidbase reactions. Students are taught the acid-base reactions, titrations and pH indicators in the first lesson. The second one would be dedicated to student's practical work and solving chemistry problems