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- All Subjects: Water--Purification--Particle removal.
- Creators: Herckes, Pierre
Description
Nanotechnology is becoming increasingly present in our environment. Engineered nanoparticles (ENPs), defined as objects that measure less than 100 nanometers in at least one dimension, are being integrated into commercial products because of their small size, increased surface area, and quantum effects. These special properties have made ENPs antimicrobial agents in clothing and plastics, among other applications in industries such as pharmaceuticals, renewable energy, and prosthetics. This thesis incorporates investigations into both application of nanoparticles into polymers as well as implications of nanoparticle release into the environment. First, the integration of ENPs into polymer fibers via electrospinning was explored. Electrospinning uses an external electric field applied to a polymer solution to produce continuous fibers with large surface area and small volume, a quality which makes the fibers ideal for water and air purification purposes. Indium oxide and titanium dioxide nanoparticles were embedded in polyvinylpyrrolidone and polystyrene. Viscosity, critical voltage, and diameter of electrospun fibers were analyzed in order to determine the effects of nanoparticle integration into the polymers. Critical voltage and viscosity of solution increased at 5 wt% ENP concentration. Fiber morphology was not found to change significantly as a direct effect of ENP addition, but as an effect of increased viscosity and surface tension. These results indicate the possibility for seamless integration of ENPs into electrospun polymers. Implications of ENP release were investigated using phase distribution functional assays of nanoscale silver and silver sulfide, as well as photolysis experiments of nanoscale titanium dioxide to quantify hydroxyl radical production. Functional assays are a means of screening the relevant importance of multiple processes in the environmental fate and transport of ENPs. Four functional assays – water-soil, water-octanol, water-wastewater sludge and water-surfactant – were used to compare concentrations of silver sulfide ENPs (Ag2S-NP) and silver ENPs (AgNP) capped by four different coatings. The functional assays resulted in reproducible experiments which clearly showed variations between nanoparticle phase distributions; the findings may be a product of the effects of the different coatings of the ENPs used. In addition to phase distribution experiments, the production of hydroxyl radical (HO•) by nanoscale titanium dioxide (TiO2) under simulated solar irradiation was investigated. Hydroxyl radical are a short-lived, highly reactive species produced by solar radiation in aquatic environments that affect ecosystem function and degrades pollutants. HO• is produced by photolysis of TiO2 and nitrate (NO3-); these two species were used in photolysis experiments to compare the relative loads of hydroxyl radical which nanoscale TiO2 may add upon release to natural waters. Para-chlorobenzoic acid (pCBA) was used as a probe. Measured rates of pCBA oxidation in the presence of various concentrations of TiO2 nanoparticles and NO3- were utilized to calculate pseudo first order rate constants. Results indicate that, on a mass concentration basis in water, TiO2 produces hydroxyl radical steady state concentrations at 1.3 times more than the equivalent amount of NO3-; however, TiO2 concentrations are generally less than one order of magnitude lower than concentrations of NO3-. This has implications for natural waterways as the amount of nanoscale TiO2 released from consumer products into natural waterways increases in proportion to its use.
ContributorsHoogesteijn von Reitzenstein, Natalia (Author) / Westerhoff, Paul (Thesis advisor) / Herckes, Pierre (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2015
Description
The production and applications of engineered nanomaterials (ENM) has increased rapidly in the last decade, with release of ENM to the environment through the sewer system and municipal wastewater treatment plants (WWTPs) being of concern. Currently, the literature on ENM release from WWTPs and removal of ENM by WWTPs is insufficient and disorganized. There is little quantitative data on the removal of multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), or few-layer graphene (FLG), from wastewater onto biomass. The removal of pristine and oxidized MWCNTs (O-MWCNTs), graphene oxide (GO), few-layer graphene (FLG) and Tween™ 20-coated Ag ENM by the interaction with biomass were determined by programmable thermal analysis (PTA) and UV-Vis spectrophotometry. The removal of pristine and O-MWCNTs was 96% from the water phase via aggregation and 30-min settling in presence or absence of biomass with an initial MWCNT concentration of 25 mg/L. The removal of 25 mg/L GO was 65% with biomass concentration at or above 1,000 mg TSS/L. The removal of 1 mg/L FLG was 16% with 50 mg TSS/L. The removal of Tween™ 20 Ag ENM with concentration from 0.97 mg/L to 2.6 mg/L was from 11% to 92% with biomass concentration of 500 mg TSS/L to 3,000 mg TSS/L, respectively.
A database of ENM removal by biomass was established by analyzing data from published papers, and non-linear solid-liquid distribution functions were built into the database. A conventional activated sludge (CAS) model was built based on a membrane bioreactor (MBR) model from a previous paper. An iterative numeric approach was adapted to the CAS model to calculate the result of non-linear adsorption of ENM by biomass in the CAS process. Kinetic studies of the CAS model showed the model performance changed mostly in the first 10 days after changing influent chemical oxygen demand (COD) concentration, and reached a steady state after 11 days. Over 60% of ENMs which have distribution coefficients in the database reached higher than 50% removal by the CAS model under general operational conditions. This result suggests that traditional WWTP which include the CAS process can remove many known types of ENMs in certain degree.
A database of ENM removal by biomass was established by analyzing data from published papers, and non-linear solid-liquid distribution functions were built into the database. A conventional activated sludge (CAS) model was built based on a membrane bioreactor (MBR) model from a previous paper. An iterative numeric approach was adapted to the CAS model to calculate the result of non-linear adsorption of ENM by biomass in the CAS process. Kinetic studies of the CAS model showed the model performance changed mostly in the first 10 days after changing influent chemical oxygen demand (COD) concentration, and reached a steady state after 11 days. Over 60% of ENMs which have distribution coefficients in the database reached higher than 50% removal by the CAS model under general operational conditions. This result suggests that traditional WWTP which include the CAS process can remove many known types of ENMs in certain degree.
ContributorsYu, Zhicheng (Author) / Westerhoff, Paul (Thesis advisor) / Rittmann, Bruce (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2015
Description
New sol-gel routes were developed to fabricate transparent conducting oxide coatings for energy applications. Sol-gel synthesis was chosen because the metal oxide products have high surface area and porosity. Titanium sol-gel chemistry was the main focus of the studies, and the synthesis of macroporous antimony-doped tin oxide was also explored. The surface chemistry and band characteristics of anatase TiO2 show promise for solar energy purposes as photoelectrodes in DSSCs and as photocatalysts to degrade organic dyes and to split water. Modifying the band structure by increasing the conduction band edge energy is specifically of interest for reducing protons in water. To this end, a new sol-gel method was developed for incorporating Zr-dopant in nanoporous anatase TiO2. The products follow Vegard’s law up to 20 atom%, exhibiting surface area of 79 m2/g and pore volume of 0.20 cm3/g with average pore diameter of 10.3 nm; the conduction band edge energy increased by 0.22 eV and the band gap increased by 0.1 eV.
In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.
Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.
Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
ContributorsMieritz, Daniel (Author) / Seo, Dong-Kyun (Thesis advisor) / Petuskey, William (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2016