Matching Items (4)
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- All Subjects: Graphene
- All Subjects: Leaching
- Creators: Perreault, Francois
Description
With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane.
This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.
The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.
This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.
The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.
ContributorsHan, Bingru (Author) / Westerhoff, Paul (Thesis advisor) / Perreault, Francois (Committee member) / Sinha, Shahnawaz (Committee member) / Arizona State University (Publisher)
Created2017
Description
The volume of end-of-life photovoltaic (PV) modules is increasing as the global PV market increases, and the global PV waste streams are expected to reach 250,000 metric tons by the end of 2020. If the recycling processes are not in place, there would be 60 million tons of end-of-life PV modules lying in the landfills by 2050, that may not become a not-so-sustainable way of sourcing energy since all PV modules could contain certain amount of toxic substances. Currently in the United States, PV modules are categorized as general waste and can be disposed in landfills. However, potential leaching of toxic chemicals and materials, if any, from broken end-of-life modules may pose health or environmental risks. There is no standard procedure to remove samples from PV modules for chemical toxicity testing in the Toxicity Characteristic Leaching Procedure (TCLP) laboratories as per EPA 1311 standard. The main objective of this thesis is to develop an unbiased sampling approach for the TCLP testing of PV modules. The TCLP testing was concentrated only for the laminate part of the modules, as they are already existing recycling technologies for the frame and junction box components of PV modules. Four different sample removal methods have been applied to the laminates of five different module manufacturers: coring approach, cell-cut approach, strip-cut approach, and hybrid approach. These removed samples were sent to two different TCLP laboratories, and TCLP results were tested for repeatability within a lab and reproducibility between the labs. The pros and cons of each sample removal method have been explored and the influence of sample removal methods on the variability of TCLP results has been discussed. To reduce the variability of TCLP results to an acceptable level, additional improvements in the coring approach, the best of the four tested options, are still needed.
ContributorsLeslie, Joswin (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Srinivasan, Devarajan (Committee member) / Kuitche, Joseph (Committee member) / Arizona State University (Publisher)
Created2018
Description
The purpose of this research was to produce reduced graphene oxides for the fabrication of desalination membranes. Graphene has typically been considered a way to create more energy efficient desalination membranes. However, graphene is expensive and unstable, while graphene oxide has similar properties, but is less expensive and more stable. Graphene oxide membranes have the potential to perform above the permeability-selectivity tradeoff that is typical in membranes through size-based exclusion. Reduction through heat or Vitamin C reduces the size of graphene oxide nanochannels so salt and organic materials can be rejected in higher numbers. Both reduced and unreduced graphene oxide membranes were created and evaluated by their ability to filter dye and salt in a pressurized membrane cell. The permeability and rejection of the graphene oxide membrane is found to be dependent on the oxidation level of the graphene oxide material and the concentration on the graphene oxide on the membrane. Unreduced graphene oxide membranes were created in three concentrations: 7.37, 14.74, and 29.47 μg/cm2. As graphene oxide concentration increased, dye rejection and salt rejection increased, while water flux decreased. Graphene oxide was reduced in solution using Vitamin C and was used to create a 14.74 μg/cm2 membrane. The reduction resulted in an increase in salt rejection from 12.59% to 100%, an increase in dye rejection from 30.44% to 100%, and a decrease in water flux from 9.502 to 0.198 L/(hr*m2*bar). Future research should focus on creating membranes using different methods of synthesizing graphene oxide from graphene and creating a reduced graphene oxide membrane with a higher water flux.
ContributorsAlbrecht, Alissa Marie (Author) / Perreault, Francois (Thesis director) / Laurin, Eric (Committee member) / Civil, Environmental and Sustainable Engineering Program (Contributor) / School of Geographical Sciences and Urban Planning (Contributor) / Barrett, The Honors College (Contributor)
Created2017-12
Description
Reverse osmosis (RO) membranes are considered the most effective treatment to remove salt from water. Specifically, thin film composite (TFC) membranes are considered the gold standard for RO. Despite TFC membranes good performance, there are drawbacks to consider including: permeability-selectivity tradeoff, chlorine damage, and biofouling potential. In order to counter these drawbacks, polyamide matrixes were embedded with various nanomaterials called mixed matrix membranes (MMMs) or thin film nanocomposites (TFNs). This research investigates the use of graphene oxide (GO) and reduced graphene oxide (RGO) into the polyamide matrix of a TFC membrane. GO and RGO have the potential to alter the permeability-selectivity trade off by offering nanochannels for water molecules to sieve through, protect polyamide from trace amounts of chlorine, as well as increase the hydrophilicity of the membrane thereby reducing biofouling potential. This project focuses on the impacts of GO on the permeability selectivity tradeoff. The hypothesis of this work is that the permeability and selectivity of GO can be tuned by controlling the oxidation level of the material. To test this hypothesis, a range of GO materials were produced in the lab using different graphite oxidation methods. The synthesized GOs were characterized by X-ray diffraction and X-ray photoelectron microscopy to show that the spacing is a function of the GO oxygen content. From these materials, two were selected due to their optimal sheet spacing between 3.4 and 7 angstroms and embedded into desalination MMM. This work reveals that the water permeability coefficient of MMM embedded with GO and RGO increased significantly; however, that the salt permeability coefficient of the membrane also increased. Future research directions are proposed to overcome this limitation.
ContributorsInurria, Adam A (Author) / Perreault, Francois (Thesis advisor) / Fox, Peter (Thesis advisor) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2017