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Synthesis and Characterization of Some Nanostructured Materials for Visible Light-driven Photo Processes
Linköping University, Department of Science and Technology, Physics, Electronics and Mathematics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-8150-729x
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanostructured materials for visible light driven photo-processes such as photodegradation of organic pollutants and photoelectrochemical (PEC) water oxidation for hydrogen production are very attractive because of the positive impact on the environment. Metal oxides-based nanostructures are widely used in these photoprocesses due to their unique properties. But single nanostructured metal oxide material might suffer from low efficiency and instability in aqueous solutions under visible light. These facts make it important to have an efficient and reliable nanocomposite for the photo-processes. The combination of different nanomaterials to form a composite configuration can produce a material with new properties. The new properties which are due to the synergetic effect, are a combination of the properties of all the counterparts of the nanocomposite. Zinc oxides (ZnO) have unique optical and electrical properties which grant it to be used in optoelectronics, sensors, solar cells, nanogenerators, and photocatalysis activities. Although ZnO absorbs visible light from the sun due to the deep level band, it mainly absorbs ultraviolet wavelengths which constitute a small portion of the whole solar spectrum range. Also, ZnO has a problem with the high recombination rate of the photogenerated electrons. These problems might reduce its applicability to the photo-process. Therefore, our aim is to develop and investigate different nanocomposites materials based on the ZnO nanostructures for the enhancement of photocatalysis processes using the visible solar light as a green source of energy. Two photo-processes were applied to examine the developed nanocomposites through photocatalysis: (1) the photodegradation of organic dyes, (2) PEC water splitting. In the first photo-process, we used the ZnO nanoparticles (NPs), Magnesium (Mg)-doped ZnO NPs, and plasmonic ZnO/graphene-based nanocomposite for the decomposition of some organic dyes that have been used in industries. For the second photo-process, ZnO photoelectrode composite with different silver-based semiconductors to enhance the performance of the ZnO photoelectrode was used for PEC reaction analysis to perform water splitting. The characterization and photocatalysis experiment results showed remarkable enhancement in the photocatalysis efficiency of the synthesized nanocomposites. The observed improved properties of the ZnO are due to the synergetic effects are caused by the addition of the other nanomaterials. Hence, the present thesis attends to the synthesis and characterization of some nanostructured materials composite with ZnO that are promising candidates for visible light-driven photo-processes.  

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2020. , p. 89
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2059
Keywords [en]
ZnO, Nanoparticles, Nanocomposites, Heterostructures, Photocatalysis
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-164334DOI: 10.3384/diss.diva-164334ISBN: 9789179298784 (print)OAI: oai:DiVA.org:liu-164334DiVA, id: diva2:1415330
Public defence
2020-04-17, K3 Önnesjösalen, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2020-03-18 Created: 2020-03-18 Last updated: 2020-03-24Bibliographically approved
List of papers
1. Synthesis of ZnO nanoparticles by co-precipitation method for solar driven photodegradation of Congo red dye at different pH
Open this publication in new window or tab >>Synthesis of ZnO nanoparticles by co-precipitation method for solar driven photodegradation of Congo red dye at different pH
2018 (English)In: PHOTONICS AND NANOSTRUCTURES-FUNDAMENTALS AND APPLICATIONS, ISSN 1569-4410, Vol. 32, p. 11-18Article in journal (Refereed) Published
Abstract [en]

Solar driven photocatalytic processes to remove organic pollutants from wastewater and other aqueous solutions is very important and useful due to its environmental benefits regarding sustainability aspect. In this article, we report a study on the use of bare zinc oxide (ZnO) nanoparticles (NPs) prepared by the chemical low temperature co-precipitation method and used as a catalyst to degrade the Congo red dye from aqueous solution using solar radiation. We performed the photocatalytic experiments for degradation of Congo red dye under solar radiation at different pH values. The results showed that the ZnO NPs are effective under solar radiation for degradation of Congo red dye. Even when the pH was varied down to 4 or raised to 10, the degradation was observed to be slightly improved. This result is due to the excess of radicals species, which enhance the photocatalytic process. In general, the observed degradation efficiency of the ZnO NPs is due to the deep level defects within the band gap that were introduced during the growth process of the ZnO NPs, which enhance the absorption wavelength band towards the visible light region. Recycling of the ZnO NPs for 3 successive runs have indicated the feasibility of reusing the NPs for several times. This implies that by using bare ZnO NPs an efficient approach for degradation of toxic waste can be achieved. Radical scavengers were used to evaluate the role of the radicals in the reaction mechanism.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
ZnO nanoparticles; Point defects; Photocatalytic
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-153525 (URN)10.1016/j.photonics.2018.08.005 (DOI)000451653700003 ()
Note

Funding Agencies|department of Science and Technology, Linkoping University, Sweden

Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2020-03-18
2. Synthesis of Mg-doped ZnO NPs via a chemical low-temperature method and investigation of the efficient photocatalytic activity for the degradation of dyes under solar light
Open this publication in new window or tab >>Synthesis of Mg-doped ZnO NPs via a chemical low-temperature method and investigation of the efficient photocatalytic activity for the degradation of dyes under solar light
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2020 (English)In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 99, article id 106053Article in journal (Refereed) Published
Abstract [en]

Doped semiconductors nanostructures (NSs) have shown great interest as a potential for green and efficient photocatalysis activities. Magnesium (Mg)-doped zinc oxide (ZnO) nanoparticles (NPs) has been synthesized by a one-step chemical low temperature (60 °C) co-precipitation method without further calcination and their photocatalytic performance for photodegradation of Methylene blue (MB) dye under the illumination of solar light is investigated. The crystal structure of the synthesized NPs is examined by X-ray diffraction (XRD). XRD data indicates a slight shift towards higher 2θ angle in Mg-doped samples as compared to the pure ZnO NPs which suggest the incorporation of Mg2+ into ZnO crystal lattice. X-ray photoelectron spectroscopy (XPS), UV–Vis spectrophotometer and cathodoluminescence (CL) spectroscopy, were used to study electronics, and optical properties, respectively. The XPS analysis confirms the substitution of the Zn2+ by the Mg2+ into the ZnO crystal lattice in agreement with the XRD data. The photocatalytic activities showed a significant enhancement of the Mg-doped ZnO NPs in comparison with pure ZnO NPs. Hole/radical scavengers were used to reveal the mechanism of the photodegradation. It was found that the addition of the Mg to the ZnO lattices increases the absorption of the hydroxyl ions at the surface of the NPs and hence acts as a trap site leading to decrease the electron-hole pair and consequently enhancing the photodegradation.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
ZnO nanoparticles, Mg-doped ZnO NPs, Photocatalytic, Photodegradation, Methylene blue, Congo red
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-164333 (URN)10.1016/j.solidstatesciences.2019.106053 (DOI)000516720100024 ()2-s2.0-85074706430 (Scopus ID)
Available from: 2020-03-18 Created: 2020-03-18 Last updated: 2020-03-24Bibliographically approved
3. Graphene-based plasmonic nanocomposites for highly enhanced solar-driven photocatalytic activities
Open this publication in new window or tab >>Graphene-based plasmonic nanocomposites for highly enhanced solar-driven photocatalytic activities
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 52, p. 30585-30598Article in journal (Refereed) Published
Abstract [en]

High-efficiency photocatalysts are crucial for the removal of organic pollutants and environmental sustainability. In the present work, we report on a new low-temperature hydrothermal chemical method, assisted by ultrasonication, to synthesize disruptive plasmonic ZnO/graphene/Ag/AgI nanocomposites for solar-driven photocatalysis. The plasmonic nanocomposites were investigated by a wide range of characterization techniques, confirming successful formation of photocatalysts with excellent degradation efficiency. Using Congo red as a model dye molecule, our experimental results demonstrated a photocatalytic reactivity exceeding 90% efficiency after one hour simulated solar irradiation. The significantly enhanced degradation efficiency is attributed to improved electronic properties of the nanocomposites by hybridization of the graphene and to the addition of Ag/AgI which generates a strong surface plasmon resonance effect in the metallic silver further improving the photocatalytic activity and stability under solar irradiation. Scavenger experiments suggest that superoxide and hydroxyl radicals are responsible for the photodegradation of Congo red. Our findings are important for the fundamental understanding of the photocatalytic mechanism of ZnO/graphene/Ag/AgI nanocomposites and can lead to further development of novel efficient photocatalyst materials.

Place, publisher, year, edition, pages
Royal Meteorological Society, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160568 (URN)10.1039/C9RA06273D (DOI)000487989300064 ()
Note

Funding agencies: Department of Science and Technology (ITN) at Campus Norrkoping, Linkoping University, Sweden; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation

Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2020-03-18Bibliographically approved
4. n–n ZnO–Ag2CrO4 heterojunction photoelectrodes with enhanced visible-light photoelectrochemical properties
Open this publication in new window or tab >>n–n ZnO–Ag2CrO4 heterojunction photoelectrodes with enhanced visible-light photoelectrochemical properties
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 14, p. 7992-8001Article in journal (Refereed) Published
Abstract [en]

In this study, ZnO nanorods (NRs) were hydrothermally grown on an Au-coated glass substrate at a relatively low temperature (90 °C), followed by the deposition of Ag2CrO4 particles via a successive ionic layer adsorption and reaction (SILAR) route. The content of the Ag2CrO4 particles on ZnO NRs was controlled by changing the number of SILAR cycles. The fabricated ZnO–Ag2CrO4 heterojunction photoelectrodes were subjected to morphological, structural, compositional, and optical property analyses; their photoelectrochemical (PEC) properties were investigated under simulated solar light illumination. The photocurrent responses confirmed that the ability of the ZnO–Ag2CrO4 heterojunction photoelectrodes to separate the photo-generated electron–hole pairs is stronger than that of bare ZnO NRs. Impressively, the maximum photocurrent density of about 2.51 mA cm−2 at 1.23 V (vs. Ag/AgCl) was measured for the prepared ZnO–Ag2CrO4 photoelectrode with 8 SILAR cycles (denoted as ZnO–Ag2CrO4-8), which exhibited about 3-fold photo-enhancement in the current density as compared to bare ZnO NRs (0.87 mA cm−2) under similar conditions. The improvement in photoactivity was attributed to the ideal band gap and high absorption coefficient of the Ag2CrO4 particles, which resulted in improved solar light absorption properties. Furthermore, an appropriate annealing treatment was proven to be an efficient process to increase the crystallinity of Ag2CrO4 particles deposited on ZnO NRs, which improved the charge transport characteristics of the ZnO–Ag2CrO4-8 photoelectrode annealed at 200 °C and increased the performance of the photoelectrode. The results achieved in the present work present new insights for designing n–n heterojunction photoelectrodes for efficient and cost-effective PEC applications and solar-to-fuel energ

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-155657 (URN)10.1039/C9RA00639G (DOI)000462646000051 ()2-s2.0-85062919263 (Scopus ID)
Note

Funding agencies: University of Mohaghegh Ardabili-Iran and Linkoping University-Sweden; AForsk [17-457

Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2020-03-18Bibliographically approved
5. ZnO/Ag/Ag2WO4 photo-electrodes with plasmonic behavior for enhanced photoelectrochemical water oxidation
Open this publication in new window or tab >>ZnO/Ag/Ag2WO4 photo-electrodes with plasmonic behavior for enhanced photoelectrochemical water oxidation
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 15, p. 8271-8279Article in journal (Refereed) Published
Abstract [en]

Ag-based compounds are excellent co-catalyst that can enhance harvesting visible light and increase photo-generated charge carrier separation owing to its surface plasmon resonance (SPR) effect in photoelectrochemical (PEC) applications. However, the PEC performance of a ZnO/Ag/Ag2WO4 heterostructure with SPR behavior has not been fully studied so far. Here we report the preparation of a ZnO/Ag/Ag2WO4 photo-electrode with SPR behavior by a low temperature hydrothermal chemical growth method followed by a successive ionic layer adsorption and reaction (SILAR) method. The properties of the prepared samples were investigated by different characterization techniques, which confirm that Ag/Ag2WO4 was deposited on the ZnO NRs. The Ag2WO4/Ag/ZnO photo-electrode showed an enhancement in PEC performance compared to bare ZnO NRs. The observed enhancement is attributed to the red shift of the optical absorption spectrum of the Ag2WO4/Ag/ZnO to the visible region (>400 nm) and to the SPR effect of surface metallic silver (Ag0) particles from the Ag/Ag2WO4 that could generate electron–hole pairs under illumination of low energy visible sun light. Finally, we proposed the PEC mechanism of the Ag2WO4/Ag/ZnO photo-electrode with an energy band structure and possible electron–hole separation and transportation in the ZnO/Ag/Ag2WO4 heterostructure with SPR effect for water oxidation. ER

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-155655 (URN)10.1039/C8RA10141H (DOI)000461445300016 ()
Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2020-03-18Bibliographically approved

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Adam, Rania Elhadi

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