Konstrukcija polšaržnega hidrotermalnega reaktorja z dodajanjem substrata za sintezo kristalnih dvojčkov rutila

Vrečer, Barbara (author), Podgornik, Aleš (mentor)

Na številnih področjih znanosti in tehnike, kot so npr. kataliza, separacijski procesi, akumulatorski in kondenzatorski elementi, sončne celice, gorivne celice ipd., želimo imeti materiale z veliko specifično površino, poroznostjo in ustrezno strukturo lahko dostopnih por. Material, ki ga lahko sintetiziramo v kompleksnih 3-D razvejanih morfologijah, je najstabilnejša polimorfna modifikacija TiO2 - rutil. Tekom eksperimentalnega dela magistrske naloge smo skonstruirali in okarakterizirali polšaržni sistem, ki vključuje hidrotermalni reaktor z možnostjo dodajanja substrata v sistem tekom hidrotermalne sinteze. S postavljenim sistemom smo želeli izvesti hidrotermalno sintezo rutila in podrobno raziskati mehanizem rasti kristalov TiO2 pod hidrotermalnimi pogoji. Med opravljanjem eksperimentov smo ugotovili, da na hidrotermalno sintezo kristalov rutila bistveno vpliva hitrost segrevanja reaktorja. Reaktor smo segreli na 200 °C pri različnih časih, in sicer med 15 min in 6 ur. Tem počasnejše kot je segrevanje reaktorja, več kristalov rutila dobimo v produktu ter vse manj anatasne oblike. S hitrostjo segrevanja ne vplivamo na velikost kristalov rutila, vplivamo pa na obliko kristalov. Počasnejše kot je segrevanje, več 1. generacije dvojčkov rutila dobimo, ter vse manj paličastega rutila. Do sedaj to še ni bilo poznano. Prav tako smo želeli s postavljenim polšaržnim sistemom ustvariti večgeneracijske dvojčke kristalov rutila, ki bi pripomogli k še večji specifični površini kristala. Večgeneracijskih dvojčkov nismo uspeli pripraviti, ker na njihov nastanek vpliva veliko parametrov, ki so med seboj variabilni ter le ob določenih kombinacijah lahko povzročijo njihovo tvorbo. Parametri so: reakcijska temperatura in čas, koncentracija ter pH morebitnega substrata, kdaj in pri kateri temperaturi dodajamo substrat v sistem, nečistoče prisotne v substratu ali osnovni raztopini ipd. V nadaljevanju raziskovanja te tematike, bi bilo potrebno omenjene parametre identificirati ter definirati razmerja med njimi, kar bi nam dalo možnost pridobivanja dvojčkov višjih generacij. Morfologijo dobljenih prašnatih produktov smo okarakterizirali s SEM in RTG analitskima metodama.

• Language: Slovenian
• Keywords: TiO2, rutil, polšaržni reaktor, hidrotermalna sinteza, dvojčičenje
• 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-113527
• COBISS.SI-ID: 1538512835
• Publication date in RUL: 16.01.2020

Secondary language

• Language: English
• Title: Construction of a semi-batch hydrothermal reactor by adding a substrate for the synthesis of a rutile crystal twins

Abstract

In many fields of science and technology, such as catalysis, separation processes, elements of batteries and capacitors, solar cells, fuel cells etc., our goal is to produce materials with large specific surface area, porosity and appropriate structure of easily accessible pores. Material that can be synthesized in complex 3-D branching morphologies is the most stable polymorphic modification of TiO2 – rutile. During the experimental part of the master’s thesis, we designed and characterized a semi-batch system that included a hydrothermal reactor with the possibility of adding a substrate to the system during the hydrothermal synthesis. With the system in place, we wanted to understand in detail the mechanism of growth of TiO2 crystals under the hydrothermal condition. During the experiments, we found out that the hydrothermal synthesis of rutile crystals is significantly influenced by the reactor-heating rate. The reactor was heated up to 200 °C in range between 15 min and 6 hours. When the heating rate was slower, more crystals of rutile-type TiO2 were formed and less anatase form was produced. The heating rate did not affect the size of the rutile crystals, but did affect the shape of the crystals. The slower the heating rate was, the more 1st generation of twins we got, and less of rod like rutile form was made. Until now, this was unknown. We also wanted to create multigenerational twins of rutile crystals that would contribute to an even larger specific surface of the crystals. We found out that their formation is influenced by many parameters that are variable and can cause formation of twins only in certain combinations. These parameters are reaction time and temperature, concentration and pH of a possible substrate, when and at what temperature a possible substrate is added to the system, impurities present in the substrate or basic solution etc. In the continuation of the research, these parameters and the relationships between them should be identified, and that would give us the opportunity to generate multiple twins. Precipitates were analysed by XRD and SEM.

• Keywords: TiO2, rutile, semi-batch reactor, hydrothermal synthesis, twinning