Mikrostruktura elektroispredenih nanovlakana oksida željeza

master's thesis

• Title (english): The microstructure of iron oxide nanofibers prepared by electrospinning
• Author: Gabrijela Radić
• Mentor: Marijana Kraljić Roković (mentor)
• Mentor: Željka Petrović (komentor)
• Committee member: Marijana Kraljić Roković (predsjednik povjerenstva)
• Committee member: Jozefina Katić (član povjerenstva)
• Committee member: Željka Petrović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2019-09-27, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering

Abstract

U ovom radu istražena su morfološka, mikrostrukturna, poluvodička i električna svojstva vlakana hematita (α-Fe2O3) dobivenih procesom elektroispredanja pri tri različita protoka prekursorske otopine; 1,5 ml h^-1, 1,0 ml h^-1, 0,5 ml h^-1 i termičkom obradom na 700 °C, 1 h. Rezultati dobiveni EDS, ATR-FTIR, XRD i UV metodama potvrdili su da su dobivena čista α-Fe2O3 vlakna. SEM snimke hematitnih vlakana pokazale su kako njihova veličina (promjer) ovisi o protoku, tj. smanjuje se smanjenjem protoka. Električna svojstva α-Fe2O3 vlakana ispitana su metodom četiri točke, a korištenjem Taucova postupka utvrđeno je kako materijal posjeduje poluvodička svojstva. Loša električna provodnost usmjerila je istraživanje prema stvaranju kompozitnog materijala koji bi imao poboljšana elektrokemijska svojstva. U tu je svrhu hidrotermalnom metodom sintetiziran kompozitni materijal α-Fe2O3/reducirani grafenov oksid (rGO) iz otopina grafenova oksida (GO) i ekstrakta lista masline (ELM) u koje su dispergirana hematitna vlakna. Za ovu namjenu korištena su hematitna vlakna dobivena pri protoku 1,0 ml h^-1. Navedeni postupak provodio se pri pH 4 i pH 10, a dobiveni su kompozitni hidrogelovi. Za svaki uzorak kompozita sintetiziran je i pripadajući referentni rGO hidrogel koji nije sadržavao hematitna vlakna. Za uzorke kompozita α-Fe2O3/rGO i referentne uzorke rGO provedena je strukturna, morfološka i elektrokemijska karakterizacija. Ugradnja α-Fe2O3 vlakana u kompozit potvrđena je SEM i XRD rezultatima, a utvrđeno je i da su vlakna smanjila aglomeraciju listova rGO. Kako bi se provela elektrokemijska mjerenja sastavljeno je 6 simetričnih superkondenzatora koji su ispitani cikličkom voltametrijom (CV), elektrokemijskom impedancijskom spektroskopijom (EIS) i kronopotenciometrijom. Dobiveni rezultati pokazali su pozitivan utjecaj α-Fe2O3 vlakana na kapacitivna svojstva kompozitnog materijala.

Abstract (english)

Microstructure of the hematite fibres (α-Fe2O3) obtained by the electrospinning process at three different flow rates of the precursor solution; 1,5 ml h^-1, 1,0 ml h^-1, 0,5 ml h^-1 and thermal processing at 700 °C, 1 h has been investigated. Using EDS, ATR-FTIR, XRD and UV methods it has been confirmed that the obtained fibres consisted only of α-Fe2O3. SEM images of the hematite fibres pointed out the fibre diameter / flow rate correlation, i.e. the slowest flow rate produced fibres with the smallest diameters. Electrical properties of α-Fe2O3 fibres have been examined using the four point probe method and the semiconducting properties have been confirmed using the Tauc model. Due to the low electrical conductivity of hematite the research was directed towards the formation of a composite material with enhanced electrochemical properties. A composite material α-Fe2O3/rGO has been obtained via a hydrothermal method using graphene oxide (GO) and olive leaf extract (ELM) solution with addition of hematite fibres (1,0 ml h^-1). This procedure was carried out at two different pH values; 4 and 10, and as a result composite hydrogels were obtained. In addition to this, for each composite sample a reference hydrogel without hematite fibres was synthesised, rGO. Morphological, structural and electrochemical characterizations have been conducted for the composite (α-Fe2O3/rGO) and reference (rGO) samples. SEM and XRD results confirmed the incorporation of the hematite fibres into the composite material as well as a partial prevention of the rGO sheet agglomeration. In order to carry out electrochemical measurements 6 symmetrical supercapacitors have been assembled and tested by means of cyclic voltametry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry. The obtained results showed a positive effect of the α-Fe2O3 fibres on capacitive properties of the composite material.

• Keywords: elektroispredanje; hematit; hidrotermalna sinteza; rGO; superkondenzator
• Keywords (english): electrospinning; hematite; hydrothermal synthesis; rGO; supercapacitor
• Language: croatian
• URN:NBN: urn:nbn:hr:149:113431
• Project: Number: IP-2013-11-8825; Title: Elektrokemijski superkondenzator visoke snage i velikog sadržaja energije za primjenu u električnim vozilima; Title: High power-high energy electrochemical supercapacitor for hybrid electric vehicles; Acronym: ESUP-CAP; Leader: Zoran Mandić; Jurisdiction: Croatia; Funder: HRZZ; Funding stream: IP
• Project: Number: IP-2016-06-8254; Title: Nastajanje i svojstva 1D a-Fe2O3 nanostruktura dopiranih odabranim metalnim ionima; Acronym: 1D-DopedFeOX; Leader: Mira Ristić; Jurisdiction: Croatia; Funder: HRZZ; Funding stream: IP
• Study programme: Title: Applied Chemistry - Graduate study; specializations in: Environmental chemistry and green technologies, Advanced materials and technologies, Applied organic chemistry; Course: Advanced materials and technologies; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra primijenjene kemije (magistar/magistra primijenjene kemije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2022-02-27 13:27:30