Funkcionalizirani mezoporozni SiO2 delci z vgrajenim barvilom za indikacijo relativne vlažnosti

Ajdovec, Anja (author), Sever Škapin, Andrijana (mentor), Cerc Korošec, Romana (co-mentor)

Mezoporozno strukturirani delci SiO2 so silikatni materiali z dobro definiranimi kanali por s premerom med 2 nm in 50 nm, ozko porazdelitvijo velikosti por in visoko specifično površino (nad 1000 m2 g-1). Površina v porah delcev predstavlja t. i. notranjo površino, površina na zunanji strani delcev pa t. i. zunanjo površino. Mezoporozni materiali so lahko selektivno modificirani z različnimi 'in situ' ter posinteznimi metodami, s katerimi uvedemo številne nove funkcionalnosti, ki so uporabne v katalizi, separaciji, sistemih za dostavo zdravilnih učinkovin in senzoriki. V okviru magistrske naloge sem sintetizirala in analizirala mezoporozne SiO2 delce za potencialno uporabo v senzoriki, in sicer kot indikatorje relativne vlažnosti. Raziskovala sem vpliv metiliranja zunanje površine treh tipov SiO2 mezoporoznih delcev, ki imajo različen premer por in vgrajeno barvilo, na adsorpcijo vode in raztapljanje barvila, kar povzroča nadaljnjo spremembo barve. Ko so mezoporozni materiali izpostavljeni določeni relativni vlažnosti, se molekule vode adsorbirajo na površino delcev SiO2 najprej v eni plasti, nato pa se nalagajo v več plasteh. Pri določeni relativni vlažnosti in ustreznem premeru por pa poteče kapilarna kondenzacija, pri čemer se delež vezane vode znatno poveča. Za določanje adsorpcijskih izoterm vode iz plinaste faze pri sobnih pogojih ter merjenje spremembe barve sem uporabila gravimetrično in kolorimetrično metodo ter termogravimetrično analizo. Morfološke lastnosti por smo ugotovili s presevno elektronsko mikroskopijo, porazdelitev velikosti por in specifično površino sem določila z dušikovo sorpcijo, funkcionalne skupine pa sem potrjevala s FT-IR spektroskopijo. Ugotovila sem, da se relativna vlažnost, pri kateri poteče kapilarna kondenzacija, povečuje skladno z naraščanjem premera por v materialu. Odziv spremembe barve pri nefunkcionaliziranih vzorcih mezoporoznega SiO2 ne sledi poteku adsorbirane vode v odvisnosti od relativne vlažnosti. Razlog za to je verjetno vpliv vode, ki se je adsorbirala na zunanji površini materiala in s tem vplivala na raztapljanje barvila. Po selektivni funkcionalizaciji mezoporoznega SiO2 z različnim premerom por pa kapilarno kondenzirana voda v notranjosti por povzroči raztapljanje barvila in s tem največjo spremembo barve samo nad določeno vrednostjo relativne vlažnosti. Pri delcih z najmanjšim premerom por je to nad 85 % relativne vlažnosti, pri največjih pa nad 92 % relativne vlažnosti.

• Language: Slovenian
• Keywords: silicijev dioksid, mezoporozni materiali, kapilarna kondenzacija, relativna vlažnost
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2020
• PID: 20.500.12556/RUL-115008
• COBISS.SI-ID: 1538566851
• Publication date in RUL: 08.04.2020

Secondary language

• Language: English
• Title: Functionalized mesoporous SiO2 particles with integrated dye for indication of relative humidity

Abstract

Mesoporous structured silica particles are silicates with well-defined pore systems which exhibit uniform pore diameters between 2 nm and 50 nm, narrow pore size distributions and high specific surface areas that may exceed 1000 m2 g-1. The internal surface is defined as the surface of pore walls, while the external surface represents the surface outside the pores. Mesoporous materials can be selectively modified via various in-situ and post-synthetic methods. The incorporation of different functionalities offers great potential for numerous applications, including catalysis, separation, drug delivery and as sensors. For the purpose of this master’s thesis, mesoporous SiO2 particles were synthesized and analysed in order to assess their potential application for indicating relative humidity. The effect of external surface methylation on the adsorption of water and dissolution of dye (thus causing a change in color) was studied in three different types of mesoporous silica particles with varying pore diameters and integrated with dye. When mesoporous materials are exposed to a certain relative humidity, water molecules adsorb on the surface of the silica particles, initially forming a monolayer-multilayer film. At a specific relative humidity and appropriate pore diameter, capillary condensation occurs, causing a significant increase in the amount of adsorbed water. Water vapour isotherms of samples were determined by gravimetric method. The colour change was evaluated by means of colorimetry. The morphological properties of prepared samples were determined by transmission electron microscopy, pore size distribution and specific surface area by means of nitrogen sorption and functional groups using FT-IR spectroscopy. It was observed that capillary condensation occurs at a higher relative humidity when the pore diameter is larger, yet the total change in colour of unfunctionalized silica samples was not related to the adsorption isotherms of water. The main reason for this is most likely the influence of water, which is adsorbed on the external surface of the material and thus affects the dissolution of dye. However, after selective functionalization of mesoporous SiO2 with varying pore diameters, the capillary-condensed water inside the pores caused the dye to dissolve and consequently the greatest colour change only occurred above a certain level of relative humidity. This occurred at 85 % relative humidity for particles with the smallest pore diameters, compared to 92 % for the largest.

• Keywords: silicon dioxide, mesoporous materials, capillary condensation, relative humidity