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postgraduate thesis: Modified nanoscale zero-valent iron with core-shell structures for environmental remediation
Title | Modified nanoscale zero-valent iron with core-shell structures for environmental remediation |
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Authors | |
Advisors | |
Issue Date | 2018 |
Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
Citation | Hu, Y. [胡奕博]. (2018). Modified nanoscale zero-valent iron with core-shell structures for environmental remediation. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. |
Abstract | Nanoscale zero-valent iron (NZVI) is a versatile material that can be applied to remove or detoxify contaminants in water and subsurface environment. However, NZVI often suffers from problems such as magnetic agglomeration, poor mobility, aqueous corrosion and surface passivation in field applications. In the present study, a novel surface modification technique is developed for NZVI to improve the stability, mobility, corrosion resistance and chemical reactivity of NZVI particles for in-situ environmental remediation.
Aluminum hydroxide–coated NZVI (NZVI@Al(OH)3) was synthesized as core-shell structured NZVI, using a rate-control precipitation technique. The surface of NZVI@Al(OH)3 was covered with a thin shell of amorphous Al(OH)3. NZVI@Al(OH)3 exhibited a remarkably higher suspension stability in the aqueous phase than bare NZVI, owing mainly to the increased electrostatic repulsion force. The pH buffering capacity of the Al(OH)3 shell and the enlarged surface area benefitted the reductive reactivity of NZVI@Al(OH)3 for the degradation of environmental contaminants. Additionally, the adsorption capability of the Al(OH)3 shell facilitated the reduction of contaminants on the NZVI surface.
A hybrid polyacrylic acid/aluminum hydroxide (PAA/Al(OH)3) shell was coated more homogeneously on the surface of NZVI. PAA was selected as a cross-linker to functionalize the NZVI particle surface for further improved property and performance. A higher suspension stability was obtained with the PAA/Al(OH)3 shell. Compared to bare NZVI, the Cr(VI) reduction capacity of NZVI@PAA/Al(OH)3 increased from 49.4 to 92.6 mg/g with a coating dose of 50 wt% PAA and 2 wt% Al. The surface carboxylic groups of PAA provided more effective sites of binding with Fe(II) for Cr(VI) reduction. The coating surface also bound the Cr(III) and Fe(III) products, which helped decrease the hydroxide formation. The reduced formation of the passivated hydroxides layer extended the longevity of NZVI for Cr(VI) reduction.
A new surface modification approach was developed by coating the NZVI with a soluble Mg(OH)2 shell to form Mg(OH)2-coated NZVI (NZVI@Mg(OH)2) nanoparticles. The Mg(OH)2 shell significantly reduced the magnetic attraction between NZVI particles. Consequently, NZVI@Mg(OH)2 had an increased stability in suspension and considerably improved mobility in saturated porous media. The Mg(OH)2 shell effectively decreased the attachment, blocking, and straining effects during the transport of NZVI particles through a sand column. With the Mg(OH)2 shell, the reactivity of NZVI can be well preserved during the NZVI storage and transport. When NZVI@Mg(OH)2 is used in field applications, the NZVI reactivity would be progressively and fully recovered with the dissolution of the Mg(OH)2 shell in the background water.
Laboratory experiments were conducted on the NZVI injected through the sand column for in-situ groundwater remediation. The results showed that the aqueous corrosion decreased the remediation capacity of bare NZVI along the flow. However, the Mg(OH)2 coating layer could effectively inhibit the aqueous corrosion of NZVI in the downstream region. As a result, the Mg(OH)2 shell increased the remediation longevity and capacity of NZVI for in-situ Cr(VI) immobilization in a wide pH range. Thus, the technique of NZVI surface modification with an environmentally benign coating layer can greatly improve the feasibility of NZVI for applications in in-situ environmental remediation. |
Degree | Doctor of Philosophy |
Subject | Bioremediation Iron - Oxidation |
Dept/Program | Civil Engineering |
Persistent Identifier | http://hdl.handle.net/10722/301495 |
DC Field | Value | Language |
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dc.contributor.advisor | Li, XY | - |
dc.contributor.advisor | Shih, K | - |
dc.contributor.author | Hu, Yibo | - |
dc.contributor.author | 胡奕博 | - |
dc.date.accessioned | 2021-08-04T07:12:06Z | - |
dc.date.available | 2021-08-04T07:12:06Z | - |
dc.date.issued | 2018 | - |
dc.identifier.citation | Hu, Y. [胡奕博]. (2018). Modified nanoscale zero-valent iron with core-shell structures for environmental remediation. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. | - |
dc.identifier.uri | http://hdl.handle.net/10722/301495 | - |
dc.description.abstract | Nanoscale zero-valent iron (NZVI) is a versatile material that can be applied to remove or detoxify contaminants in water and subsurface environment. However, NZVI often suffers from problems such as magnetic agglomeration, poor mobility, aqueous corrosion and surface passivation in field applications. In the present study, a novel surface modification technique is developed for NZVI to improve the stability, mobility, corrosion resistance and chemical reactivity of NZVI particles for in-situ environmental remediation. Aluminum hydroxide–coated NZVI (NZVI@Al(OH)3) was synthesized as core-shell structured NZVI, using a rate-control precipitation technique. The surface of NZVI@Al(OH)3 was covered with a thin shell of amorphous Al(OH)3. NZVI@Al(OH)3 exhibited a remarkably higher suspension stability in the aqueous phase than bare NZVI, owing mainly to the increased electrostatic repulsion force. The pH buffering capacity of the Al(OH)3 shell and the enlarged surface area benefitted the reductive reactivity of NZVI@Al(OH)3 for the degradation of environmental contaminants. Additionally, the adsorption capability of the Al(OH)3 shell facilitated the reduction of contaminants on the NZVI surface. A hybrid polyacrylic acid/aluminum hydroxide (PAA/Al(OH)3) shell was coated more homogeneously on the surface of NZVI. PAA was selected as a cross-linker to functionalize the NZVI particle surface for further improved property and performance. A higher suspension stability was obtained with the PAA/Al(OH)3 shell. Compared to bare NZVI, the Cr(VI) reduction capacity of NZVI@PAA/Al(OH)3 increased from 49.4 to 92.6 mg/g with a coating dose of 50 wt% PAA and 2 wt% Al. The surface carboxylic groups of PAA provided more effective sites of binding with Fe(II) for Cr(VI) reduction. The coating surface also bound the Cr(III) and Fe(III) products, which helped decrease the hydroxide formation. The reduced formation of the passivated hydroxides layer extended the longevity of NZVI for Cr(VI) reduction. A new surface modification approach was developed by coating the NZVI with a soluble Mg(OH)2 shell to form Mg(OH)2-coated NZVI (NZVI@Mg(OH)2) nanoparticles. The Mg(OH)2 shell significantly reduced the magnetic attraction between NZVI particles. Consequently, NZVI@Mg(OH)2 had an increased stability in suspension and considerably improved mobility in saturated porous media. The Mg(OH)2 shell effectively decreased the attachment, blocking, and straining effects during the transport of NZVI particles through a sand column. With the Mg(OH)2 shell, the reactivity of NZVI can be well preserved during the NZVI storage and transport. When NZVI@Mg(OH)2 is used in field applications, the NZVI reactivity would be progressively and fully recovered with the dissolution of the Mg(OH)2 shell in the background water. Laboratory experiments were conducted on the NZVI injected through the sand column for in-situ groundwater remediation. The results showed that the aqueous corrosion decreased the remediation capacity of bare NZVI along the flow. However, the Mg(OH)2 coating layer could effectively inhibit the aqueous corrosion of NZVI in the downstream region. As a result, the Mg(OH)2 shell increased the remediation longevity and capacity of NZVI for in-situ Cr(VI) immobilization in a wide pH range. Thus, the technique of NZVI surface modification with an environmentally benign coating layer can greatly improve the feasibility of NZVI for applications in in-situ environmental remediation. | - |
dc.language | eng | - |
dc.publisher | The University of Hong Kong (Pokfulam, Hong Kong) | - |
dc.relation.ispartof | HKU Theses Online (HKUTO) | - |
dc.rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works. | - |
dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
dc.subject.lcsh | Bioremediation | - |
dc.subject.lcsh | Iron - Oxidation | - |
dc.title | Modified nanoscale zero-valent iron with core-shell structures for environmental remediation | - |
dc.type | PG_Thesis | - |
dc.description.thesisname | Doctor of Philosophy | - |
dc.description.thesislevel | Doctoral | - |
dc.description.thesisdiscipline | Civil Engineering | - |
dc.description.nature | published_or_final_version | - |
dc.date.hkucongregation | 2018 | - |
dc.identifier.mmsid | 991044393779803414 | - |