Korelacija funkcionalnih i fizičko-hemijskih svojstava prahova ZnO dobijenih različitim metodama sinteze

The Correlation between Functional and Physico-Chemical Properties of ZnO Powders Obtained by Various Methods of Synthesis

Poznato je da funkcionalna svojstva cink oksidnih prahova zavise od fizičko-hemijskih karakteristika kao što su optičke karakteristike i specifična površina, a koje su određene strukturnim svojstvima praha u kao što su: fazni sastav, veličina kristalita, stepen kristaliničnosti, uređenje kristalne strukture tj. prisustvo defekata kao i morfologija čestica. Navedene karakteristike mogu se podešavati optimizacijom reakcionih uslova tokom procesa sinteze. Cilj ovog istraživanja bio je, kao prvo, sinteza prahova ZnO različitih fizičko-hemijskih karakteristika putem optimizacije reakcionih uslova različitih metoda procesiranja. Nakon toga, ideja je bila da se ispitaju neka od funkcionalnih svojstava sintetisanih prahova ZnO, konkretno, katalitička i antibakterijska svojstva. Konačno, uspostavljena je korelacija između ispitivanih funkcionalnih svojstava i fizičko-hemijskih karakteristika sintetisanih prahova ZnO.
U ovom radu primenjena su tri postupka sinteze: hidrotermalno, ultrazvučno i mikrotalasno procesiranje. U slučaju hidrotermalnog procesiranja, promenom pH vrednosti reakcionog sistema, od slabo bazne (pH 8) do jako bazne (pH 12) sredine, uz prisustvo određene količine površinski aktivne komponente, bilo je moguće značajno modifikovati morfologiju i srednju veličinu čestica sintetisanih prahova ZnO. Sintetisane su čestice od štapićastih mikrometarskih formi, pri pH vrednosti reakcionog sistema 8-10, preko elipsoidnih submikrometarskih oblika pri pH 11, do sferičnih nanometarskih čestica pri pH 12-13. Ispitan je i uticaj energije, koja se tokom ultrazvučnog i mikrotalasnog procesiranja unosi u reakcioni sistem, na morfologiju čestica ZnO; zadržani su identični reakcioni uslovi kao i u slučaju hidrotermalnog procesiranja. Utvrđeno je da energija primenjenog spoljašnjeg polja (ultazvučnog ili mikrotalasnog) u značajnoj meri utiče na morfologiju čestica, uređenost strukure i defekte rešetke u molekulu ZnO, što doprinosi poboljšanju ispitivanih funkcionalnih svojstava materijala.
Ispitana su optička svojstva sintetisanih prahova ZnO, tačnije, uspostavljena je korelacija između oblika i srednje veličine čestica sa jedne strane i procenta refleksije i energije procepa sa druge strane. Utvrđeno je da se modifikacijom oblika i dimenzija čestica značajno mogu poboljšati optička svojstva ZnO u vidljivom delu spektra.
Primenom postupaka heterogene fotokatalize i sonokatalize za razgradnju organske boje metilensko plavo (MB), ispitana su katalitička svojstva prahova ZnO. S obzirom da su sintetisani prahovi čija je energija procepa u vidljivom delu spektra (Ebg=3,25 eV) bilo je moguće povećati efikasnost razgradnje toksične boje (MB) u prisustvu ZnO prahova dodatnim delovanjem svetlosti (fotokataliza) tokom eksperimenata. Delovanjem ultrazvučnog polja (sonokataliza) tokom procesa razgradnje boje MB u prisustvu praha ZnO uočeno je značajno povećanje efikasnosti. U oba slučaja, foto- i sono-katalize, postignuta je dodatna aktivacija čestica ZnO tj. ubrzano je oslobađanje peroksidnih radikala što je za rezultat imalo i visok procenat efikasnosti razgradnje organske boje u ispitivanim disperzijama.
Antibakterijska svojstva sintetisanih prahova cink oksida ispitivana su na dve bakterijske ćelijske vrste, gram pozitivne Staphylococcus aureus i gram negativne Escherichia coli. Utvrđeno je da prah ZnO izgrađen od nanosfernih čestica, relativno velike specifične površine, pokazuje najveći procenat redukcije broja živih ćelija tj. najbolju antibakterijsku aktivnost u slučaju ćelija Escherichia coli, dok je najbolju antibakterijsku aktivnost u slučaju ćelija Staphylococcus aureus pokazao prah ZnO izgrađen od heksagonalnih mikronskih štapićastih formi. Ovi rezultati potvrdili su da osim veličine i morfologije čestica na antibakterijsku aktivnost ispitivanog uzorka utiče niz faktora od kojih se posebno ističe vrsta i svojstva bakterijske linije koja se proučava.
It is known that the functional properties of zinc oxide powders depend on their physico-chemical properties, such as optical properties and specific surface area wich are defined with structural characteristics for example: the particle size and morphology, phase composition, crystallite size, crystallinity degree, as well as the crystal structure ordering, i.e. the presence of defects. All of these characteristics can be designed by optimizing the reaction conditions during the synthesis. The primary purpose of this study is to synthesize zinc oxide powders with various physico-chemical properties by optimizing the reaction conditions in different processing methods. Furthermore, the aim was to test some of the functional properties of the synthesized ZnO powders – namely, their catalytic and antibacterial properties. Finally, a correlation between the tested functional properties and physico-chemical characteristics of the synthesized ZnO powders has been established.
In this thesis, three methods of synthesis have been applied: hydrothermal, ultrasound and microwave processing. In the case of hydrothermal processing it is possible to significantly alter the morphology and the average particle size of the synthesized ZnO particles by changing the pH value of the reaction system, from a weak base (pH 8) to a very strong base (pH 12), in the presence of an amount of surface-active agents. The synthesized particles ranged from rod-shaped micrometer-sized forms at the pH 8–10 reaction system, over submicron ellipsoidal shapes at pH 11, down to the spherical nano-scaled particles obtained at a pH 12–13. The impact of energy introduced into the reaction system during sonochemical and microwave processing on the morphology of ZnO particles has also been examined under the identical reaction conditions as in hydrothermal processing. It has been found that the energy of the applied external field (ultrasound or microwave) considerably affects the particle morphology, the order of the structure and the lattice defects in the ZnO molecule, which contributes improuvement of the tested functional properties of the material.
The optical properties of the synthesized powders have been examined; more precisely, the correlation between the shape and the average particle size as well as the reflection percentage and band gap energy has been established. It has been demonstrated that the modification of the particle shape and dimensions can significantly improve the optical properties of ZnO in the visible spectrum.
The catalytic properties of ZnO powders have been investigated by heterogeneous photocatalytic and sonocatalytic degradation of an organic dye, methylene blue (MB). Having in mind that the synthesized powders whose energy gaps are in the visible spectrum (Ebg = 3.25 eV), it is possible to increase the efficiency of the degradation of the toxic dye (MB) in the presence of ZnO powders by an additional exsposure to the light (photocatalysis) during the experiments. When an ultrasonic field (sonocatalysis) is applied during the decomposition process of MB in the presence of a ZnO powder, a significant increase in efficiency is observed. In both cases, photo- and sonocatalysis, an additional activation of ZnO particles, i.e. an accelerated release of peroxide radicals is observed, which results in a high efficiency of the degradation of the organic dye in the tested dispersions.
The antibacterial properties of the synthesized ZnO powders were tested on two types of bacterial cells, gram positive – Staphylococcus aureus and gram – negative Escherichia coli. It has been found that the ZnO powder consisting of nanospherical particles with a relatively large specific surface area, shows the greatest percentage of the reduction in the number of viable cells, i.e. the best antibacterial activity in the case of Escherichia coli cells, while the best antibacterial activity in the case of Staphylococcus aureus cells was exhibited by the ZnO powder consisting of hexagonal ZnO micron-sized rod-like forms. These results have confirmed that in addition to particle size and morphology, the antibacterial activity of the examined sample is influenced by a number of factors; particularly important among them are the type and properties of the investigated bacterial lines.

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Metadaten
Author:Ana Stanković
Publisher:University of Belgrade, Faculty of Physical Chemistry
Place of publication:Belgrade
Referee:Dragan Uskoković, Nikola Cvjetićanin, Ljiljana Damnjanović, Smilja Marković
Advisor:Dragica Minić
Document Type:Doctoral Thesis
Language:srp
Date of Publication (online):18.10.2014
Year of first Publication:2014
Publishing Institution:University of Belgrade, Faculty of Physical Chemistry
Granting Institution:Institute of Technical Sciences of the Serbian Academy of Sciences and Arts
Date of final exam:03.10.2014
Tag:antibacterical properties; catalytic activity; materials synthesis; optical properties; zinc oxide
Pagenumber:185
Institutes:Institute of Technical Sciences of the Serbian Academy of Sciences and Arts
Open access:
Collections:PhD Theses
Licence (English):License LogoCreative Commons - Attribution-Noncommercial-No Derivative Works 3.0 Serbia