Kapacitivna svojstva grafena dobivenog upotrebom ekološki prihvatljivih reducensa

master's thesis

• Title (english): Capacitive properties of graphene obtained by green method of reduction
• Author: Matea Vrdoljak
• Mentor: Marijana Kraljić Roković (mentor)
• Committee member: Marijana Kraljić Roković (predsjednik povjerenstva)
• Committee member: Suzana Sopčić (član povjerenstva)
• Committee member: Nataša Perin (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2016-07-04, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering; Chemical Engineering in Material Development

Abstract

Svrha ovog rada bila je pripraviti grafen (rGO) iz grafenova oksida (GO) uporabom ekološki prihvatljivog reducensa te ispitati kapacitivna svojstva dobivenog produkta. Tijekom provedbe redukcije cilj je postići što veći stupanj redukcije te pronaći uvjete u kojima neće biti izražena aglomeracija produkta. Određivanje kapacitivnih svojstava dobivenog produkta može dati uvid u uspješnost provedbe samog procesa. Redukcija GO proveden je kemijskim putem kod pH=7 i pH= 10 pri 80˚C uporabom ekstrakta lista masline (ELM) i pročišćene otpadne vegetacijske vode masline (OMW). Strukturna svojstva dobivenog rGO karakterizirana su FT-IR spektroskopijom i termogravimetrijom analizom (TGA). Utvrđeno je da u procesu redukcije GO s ELM-om i OMW-om dolazi do smanjenja broja kisikovih funkcionalnih skupina te regeneracije sp2 hibridizacije. TGA analiza pokazala je da je najmanje kisika uklonjeno kod rGO (ELM, pH=7), a najviše kod rGO (ELM, pH=10). Dobiveni rezultati su u suglasnosti s vrijednostima električne provodnosti za razne uzorke rGO. Najveća vrijednost je zabilježena za rGO (OMW, pH=10), 15,4 S cm^-1, dok je najmanja vrijednost zabilježena kod rGO ( ELM, pH=7), 1,2 S cm^-1. Kapacitivna svojstva rGO određena su metodom cikličke voltametrije i elektrokemijske impedancijske spektroskopije (EIS). Iz oblika cikličkog voltamograma može se zaključiti da je kod svih uzoraka rGO koji su reducirani s ELM-om dobivena konstantna struja s promjenom potencijala bez karakterističnih strujnih vrhova što ukazuje na dobro kapacitivno ponašanje. Kod rGO uzorka reduciranog s OMW-om u cikličkom voltamogramu zabilježen je dodatan strujni vrh koji se odnosi na redoks reakciju fenolnih spojeva zaostalih u strukturi rGO. Najveće vrijednosti specifičnih kapaciteta dobivene su za najtanji uzorak rGO ( ELM, pH=10), 33,96 F g^-1 i uzorak rGO (OMW, pH=10), 32,26 F g^-1. Deblji slojevi pokazuju manje vrijednosti specifičnih kapaciteta s time da je najbolje ponašanje dobiveno za rGO (OMW, pH=10). Iz dobivenih rezultata se može zaključiti da je najveći stupanj redukcije GO i najbolja kapacitivna svojstva rGO zabilježeni kad je redukcija provedena kod pH=10 dok vrsta reducensa nije značajno utjecala na svojstva rGO.

Abstract (english)

The purpose of this study was to prepare graphene ( rGO ) from graphene oxide ( GO ) using environmentally friendly reducing agents and examine the capacitive properties of the obtained rGO. The objective of this process is to achieve a high degree of reduction and to provide conditions where agglomeration of rGO will be prevented. Determination of capacitive properties may provide insight into the progress of process. Reduction of GO has been succesfully carried out using olive leaf extract (ELM) and olive mill wastewater (OMW) as environmentally friendly reducing agent. Reduction with olive leaf extract was carried out at pH 7 and 10, and with olive mill wastewater at pH 10 and temperature 80˚C. The structural properties of the rGO samples were characterized by FT-IR spectroscopy and thermogravimetric analysis ( TGA ). It was found that reduction of GO with ELM and OMW resulted in a significant decrease of oxygen functional groups and regeneration of sp2 hybridization. By using the thermogravimetric analysis it has been determined that the sample of rGO ( ELM, pH=7) shows the highest oxygene content while the lowest oxygene content was obtained for rGO (ELM, pH=10). The results are in agreement with the values of electrical conductivity for various rGO samples. The highest conductivity is recorded for rGO ( OMW , pH = 10 ) 15.4 S cm^-1, while the lowest conductivity was observed for rGO (ELM, pH=7 ) , 1.2 S cm^-1. Capacitive properties are determined by using cyclic voltammetry and electrochemical impedance spectroscopy ( EIS ) techniques. From the cyclic voltammetry results it can be concluded that for all rGO samples reduced by ELM, constant current is obtained within the potential range of examination which indicates a good capacitive behavior . For rGO ( OMW, pH=10) sample cyclic voltammograms recorded additional current peak related to the redox reaction of the phenolic compounds present within the structure of rGO. The highest specific capacitance values is obtained for the thinnest sample of rGO (ELM, pH=10), 33,96 F g^-1 and for the rGO (OMW, pH=10), 32,26 F g^-1. Thicker layers show smaller specific capacitance values and the best capacitive properties were obtained for rGO (OMW , pH = 10 ) . From the obtained results it can be concluded that the greatest degree of GO reduction and the best capacitive properties of rGO were obtained for the reduction process carried out at pH = 10 while reducing agents used during the synthesis did not significantly affect the properties of the rGO.

• Keywords: grafen; grafenov oksid; ekstrakt lista masline; vegetacijska voda maslina; kapacitivna svojstva
• Keywords (english): graphene; graphene oxide; olive leaf extract; olive mill wastewater; capacitive properties
• Language: croatian
• URN:NBN: urn:nbn:hr:149:328128
• Study programme: Title: Applied Chemistry - Graduate study; specializations in: Environmental chemistry and green technologies, Advanced materials and technologies, Applied organic chemistry; Course: Applied organic chemistry; 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
• Public note: Službeni naslov rada je Kapacitivna svojstva grafena dobivenog upotrebom ekološki prihvatljivih reducensa, dok je u izvornom diplomskom radu u tekstualnom obliku i u dokumentu u PDF formatu naslov pogrešno napisan kao Kapacitivna svojstva grafena dobivenog upotrebom ekološki prihvatljivog reducensa.
• Repository: Repository of Faculty of Chemical Engineering and Technology University of Zagreb
• Created on: 2017-04-18 11:45:48