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Synthesis of Zinc Oxide Nanorods via the Formation of Sea Urchin Structures and Their Photoluminescence after Heat Treatment
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.ORCID iD: 0000-0002-4782-4969
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2018 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 17, p. 5079-5087Article in journal (Refereed) Published
Abstract [en]

A protocol for the aqueous synthesis of ca. 1-mu m-long zinc oxide (ZnO) nanorods and their growth at intermediate reaction progression is presented, together with photoluminescence (PL) characteristics after heat treatment at temperatures of up to 1000 degrees C. The existence of solitary rods after the complete reaction (60 min) was traced back to the development of sea urchin structures during the first 5 s of the precipitation. The rods primarily formed in later stages during the reaction due to fracture, which was supported by the frequently observed broken rod ends with sharp edges in the final material, in addition to tapered uniform rod ends consistent with their natural growth direction. The more dominant rod growth in the c direction (extending the length of the rods), together with the appearance of faceted surfaces on the sides of the rods, occurred at longer reaction times (>5 min) and generated zinc-terminated particles that were more resistant to alkaline dissolution. A heat treatment for 1 h at 600 or 800 degrees C resulted in a smoothing of the rod surfaces, and PL measurements displayed a decreased defect emission at ca. 600 nm, which was related to the disappearance of lattice imperfections formed during the synthesis. A heat treatment at 1000 degrees C resulted in significant crystal growth reflected as an increase in luminescence at shorter wavelengths (ca. 510 nm). Electron microscopy revealed that the faceted rod structure was lost for ZnO rods exposed to temperatures above 600 degrees C, whereas even higher temperatures resulted in particle sintering and/or mass redistribution along the initially long and slender ZnO rods. The synthesized ZnO rods were a more stable Wurtzite crystal structure than previously reported ball-shaped ZnO consisting of merging sheets, which was supported by the shifts in PL spectra occurring at ca. 200 degrees C higher annealing temperature, in combination with a smaller thermogravimetric mass loss occurring upon heating the rods to 800 degrees C.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2018. Vol. 34, no 17, p. 5079-5087
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-228274DOI: 10.1021/acs.langmuir.8b01101ISI: 000431463500016PubMedID: 29630844Scopus ID: 2-s2.0-85046301419OAI: oai:DiVA.org:kth-228274DiVA, id: diva2:1209028
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2024-03-15Bibliographically approved
In thesis
1. Fundamentals of Polyethylene Composites for HVDC Cable Insulation – Interfaces and Charge Carriers
Open this publication in new window or tab >>Fundamentals of Polyethylene Composites for HVDC Cable Insulation – Interfaces and Charge Carriers
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Power transmission over long distances by using high voltage direct current (HVDC) cables is important for the transition from fossil energy to using renewable energy sources, e.g. wind, solar and water. Higher operating voltages enable longer transmission lines but better insulation materials with a much lower conductivity than today´s crosslinked polyethylene (PE) are required to reach the goal of 1 MV by 2030. Nanocomposites consisting of small fractions of metal oxide nanoparticles in PE are promising insulation materials, showing ca. 100 times lower conductivity. The reasons for the better insulating properties are however not fully understood.

The properties of PE and inorganic nanoparticles were studied in this project to evaluate the influence of different material parameters on the conductivity of the cable insulation material. For pristine PE, the polymer morphology and oxidation were found to have a significant impact on the conductivity. For PE nanocomposites, the particle/polymer interface was shown to adsorb polar molecules, which are present in PE cable insulation. A suggested hypothesis is that the adsorption on particle surfaces results in cleaning of the bulk polymer from impurities, which in turn contributes to decreased nanocomposite conductivity. Since the particle interface is believed to be decisive for the nanocomposite properties, the role of particle terminations was investigated in detail. Oxygen dominated particle terminations resulted in 2 times higher composite conductivity than with zinc dominated surfaces, while fully oxygen covered surfaces showed 10 times higher conductivity. Composite systems with micro-sized particles allowed for evaluating parameters independently, which is not possible for nanocomposites. Terminations of ‘PE-like’ hydrocarbon chains lowered the conductivity and these trends could also be transferred to similar zinc oxide nanocomposite systems.

Abstract [sv]

Distribution av elektrisk energi över långa avstånd genom att använda högspänd likström (HVDC) blir allt viktigare för att ställa om till en förnyelsebar energiproduktion (t.ex. solkraft, vindkraft och vattenkraft). Med ökad driftspänning kan längre kabelsystem användas på grund av minskade förluster, men detta ställer högre krav på isoleringsmaterialet. Nya koncept med bättre isolerande egenskaper (t.ex. lägre konduktivitet) än dagens tvärbundna polyeten (PE) måste utvecklas för att kunna uppnå målet med en driftspänning på 1 MV till 2030. Kompositer bestående av nanopartiklar i PE är ett lovande alternativ som är ca. 100 gånger mer isolerande än PE men kunskapen om varför kompositer uppvisar bättre isolerande egenskaper är inte komplett.

Egenskaper hos PE och inorganiska nanopartiklar studeras i detta projekt för att utvärdera vilken betydelse olika parametrar har för DC konduktiviteten. För ren PE så påverkade polymerens morfologi och oxidation konduktiviteten signifikant. För nanokompositer är gränsytan mellan partikel och polymer viktig för kompositens egenskaper och det visades att polära molekyler som finns i kabelisolering av PE adsorberades på partikelytorna. Det föreslogs att adsorptionen bidrar till en renare polymer i kompositerna, vilket i sin tur minskar konduktiviteten. Termineringar på zinkoxidpartiklar undersöktes i detalj och partiklar med en majoritet av syre på ytan ökade kompositens konduktivitet 2 gånger jämfört med dominerande termineringar av zink. Ytor helt täckta av syre ökade konduktiviteten 10 gånger. Påverkan av funktionaliteten på partikelytan kunde studeras oberoende av andra parametrar genom att använda större mikropartiklar, vilket inte är möjligt för nanopartiklar. Slutsatsen att partikelytor med kolväten som liknar PE sänkte konduktiviteten jämfört med syredominerande ytor kunde även bekräftas för kompositer med nanopartiklar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 98
Series
TRITA-CBH-FOU ; 2020:27
Keywords
polyethylene, nanocomposites, HVDC, conductivity, metal oxide, nanoparticles, surface functionality, polyeten, nanokompositer, HVDC, konduktivitet, metalloxider, nanopartiklar, ytfunktionalitet
National Category
Composite Science and Engineering Textile, Rubber and Polymeric Materials Nano Technology
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-273541 (URN)978-91-7873-547-1 (ISBN)
Public defence
2020-08-26, https://kth-se.zoom.us/webinar/register/WN_wQLokbhFTZOvJq6GIKSMmQ, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, ML8
Note

QC 2020-05-25

Available from: 2020-05-25 Created: 2020-05-21 Last updated: 2022-09-08Bibliographically approved

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