عنوان

Synthesis and Design Cationic Metal-Organic Frameworks for Perchlorate Remediation and Bactericidal Applications

شماره

TL4862f6c6

زبان متن نوشتاري يا گفتاري و مانند آن

انگلیسی

عنوان اصلي

Synthesis and Design Cationic Metal-Organic Frameworks for Perchlorate Remediation and Bactericidal Applications

نام عام مواد

[Thesis]

نام نخستين پديدآور

Colinas, Ian Rodrigo

نام ساير پديدآوران

Oliver, Scott RJ

تاریخ نشرو بخش و غیره

2018

کسي که مدرک را اعطا کرده

Oliver, Scott RJ

امتياز متن

2018

متن يادداشت

The issue of perchlorate (ClO4-) as an emerging pollutant has gained significant attention globally as it has been detected in groundwater, surface water, soils, and crops of many countries including the United States, Japan, China, India, Korea, and Germany. The toxic effects of this anionic pollutant result from the disruption of the thyroid gland, which is blocked and inhibited from iodide uptake due to the slightly larger ionic radii of perchlorate. Such impairment of the thyroid gland can occur upon exposure to parts per billion (ppb) perchlorate levels, and it has been associated with detrimental development effects in fetuses and children. Most perchlorate is manufactured for its use as a primary ingredient in solid rocket propellants in both military and aerospace technology, and its widespread occurrence in the environment has resulted from its improper disposal and high mobility in aqueous environments. Currently, anion exchange resins are the standard material used for perchlorate remediation. These consist of inexpensive polymeric matrices with limited chemical and thermal stability due to their organic nature. In addition, their performance is severely affected by their poor selectivity towards perchlorate and lack of recyclability. Therefore, high performance anion exchangers that can efficiently capture perchlorate are sought. Extended inorganic crystalline materials are promising candidates for the replacement of organic resins due to their higher stability but these materials are often neutral or anionic, thus extended cationic structures are of special interest in the field of anion separation. Layered double hydroxides (LDHs) are cationic isostructural clay-like materials that have been widely studied for their anion exchanging properties. However, LDHs are known to have a high affinity towards ubiquitous carbonate ions, as well as tendency to re-intercalate water molecules immediately after calcination. This drastically decreases their overall uptake capacity and selectivity for the capture of anionic pollutants from wastewater. Metal-organic frameworks are promising materials in the field of separation due to the tunability in their structure and function. Cationic metal-organic frameworks are a subclass of these crystalline extended materials, which can be easily prepared by introducing neutral organic ligands for cationic metals and weakly coordinating anions that balance the overall cationic charge of the framework. These cationic materials offer a viable alternative to conventional anion exchangers due to their robust tunable frameworks that can exchange anions reversibly at high adsorption capacities. A detailed methodology for the efficient separation of perchlorate from water was demonstrated by utilizing a cationic MOF consisting of three-dimensional [Ag-bipy]+ chains arranged in a T-shaped pattern with nitrate anions counter-balancing the framework. Ambient conditions were used for both the synthesis of this cationic material, silver 4,4'-bipyridine nitrate (SBN), as well as the exchange resulting in the formation silver 4,4'-bipyridine perchlorate (SBP). The exchange was complete within 90 minutes and the capacity was 354 mg of ClO4-/g of SBN, representing 99% ClO4- removal. SBN exhibited superior performance compared to that of current anion exchangers such as the resins Amberlite IRA-400 (249 mg/g) and Purolite A530E (104 mg/g), as well as layered double hydroxides (28 mg/g). Unlike resins and layered double hydroxides, SBN could be successfully regenerated in nitrate solution at 70 °C with new crystal formation, allowing indefinite cycling for perchlorate capture. An in-depth investigation of the host-guest interaction of cationic [Ag-bipy]+ MOFs with perchlorate was carefully performed. The structural transformation and flexibility of SBN upon formation of SBP was evaluated by monitoring the anion exchange dynamics using a combination of powder X-ray diffraction (PXRD) with multinuclear 13C, 15N and 109Ag solid-state nuclear magnetic resonance (NMR) spectra at different time intervals of the anion exchange. The structural transformation from SBN to SBP is complete within 70 minutes and was determined to take place by a solvent-mediated process. This pathway is confirmed by the morphological changes of the two crystalline materials observed by scanning electron microscopy (SEM). The understanding of such structural dynamics highlighted in this study provides crucial insights for the rational design of related MOFs toward the selective capture of environmental pollutant oxo-anions Increasing antibiotic resistance of pathogens has become a serious threat to public health. An effective approach to control the spread of antibiotic resistant bacteria is to consider a material that exhibits this broad-spectrum biocidal activity both in liquid environments, and on solid surfaces. Recently, the field of nanotechnology has incorporated these metals into nanostructured systems for improved dosage forms and therapeutic effects. Unlike conventional antibiotics, the antibacterial activity of nanomaterials is broad-spectrum, and includes physical damage to bacterial cells. Recently, MOFs and coordination polymers (CPs) have gained significant attention for their potential use as bactericidal materials. Their antibacterial properties typically originate from the metals in their cationic form, with the structures acting as metal ion reservoirs. We successfully performed a study highlighting the synthesis, antibacterial properties and mechanism of two Zn-based coordination polymers. The first, [Zn(bipy)(OH2)42+]1.5[ClO4-]3•(bipy)3(H2O), consists of a one-dimensional (1D) structure with two crystallographically independent octahedral zinc centers trans-coordinated by two 4,4'-bipy units and water groups. The second, [Zn1.5(CH3CO2)2(bipy)2+][ClO4-]•H2O, is a two-dimensional (2D) layered structure with the same polymers but bridged together into a layer by acetate and 4,4'-bipy. Both compounds exhibit sustained release of Zn2+ ions upon their gradual degradation in aqueous solution, which results in highly effective antibacterial activity towards Escherichia coli and particularly towards Staphylococcus epidermidis cells. This activity was evaluated in solution by broth dilution assays to determine minimal inhibition concentrations (MICs) as well as in the solid phase by agar diffusion tests to quantify the zones of inhibition (ZOI), and were in close agreement. Further, the biocidal mechanisms of the coordination polymers were investigated in vivo by fluorescence microscopy utilizing CellRox Green and propidium iodide as reactive oxygen species (ROS) and membrane disruption indicators, respectively. Both CPs show superior antibacterial activity compared to two standards, zinc acetate and zinc oxide. This superior activity is attributed to the gradual and localized release of Zn2+ ions, as well as the electrostatic attraction to the bacterial cell surface afforded by their unique structures.

مستند نام اشخاص تاييد نشده

Keebaugh, Andrew James

مستند نام اشخاص تاييد نشده

Colinas, Ian Rodrigo

مستند نام تنالگان تاييد نشده

UC Santa Cruz

نام الکترونيکي

فرمت انتشار

p

نوع ماده

[Thesis]

کد کاربرگه

276903

سطح دسترسي

a

تكميل شده

Y