Date of Award

December 2018

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Nidal H Abu-Zahra

Committee Members

Benjamin C Church, Anna M Benko

Keywords

Adsoprtion, Arsenate, Iron Oxide Nanoparticles, Membrane Technology, Surface Modification

Abstract

Arsenic (As) is one of the detrimental elements in nature, which has negative effect on human health as well as the environment. High levels of arsenic concentration in the drinking water can cause skin, bladder, lung liver, and prostate, as well as cardiovascular, pulmonary, immunological, neurological and endocrine diseases. Arsenic pollution in the water has been reported in many countries as a worldwide problem, including the United States.

To develop a separation method for removing Arsenic, various treatment technologies including precipitation, coagulation with ferric chloride or aluminum sulfate coagulants, ion exchange and adsorption with modified nanocomposite material have been extensively studied. All these methods have drawbacks in terms of costs and efficiencies by the generation of toxic sludge in coagulation and precipitation method and causing severe pressure drops in column adsorption process and high cost of operation in ion exchange. However, membrane technology, which has drawn considerable attention in the past few decades by offering a promising solution for water treatment and pollutant separation. Among the pressure driven membranes, especially nanofiltration (NF) and reverse osmosis (RO) are widely used for arsenic removal even though the process requires high operational pressure and costly membranes comparing with low pressure processes such as microfiltration (MF) and ultrafiltration (UF). In the case of removing small size pollutants such as arsenate, microfiltration (MF) and ultrafiltration (UF) membranes can overcome these disadvantages by the incorporation of Nano inorganic particle absorbents in the polymer matrix membranes.

In this research work, functionalized Iron Oxide nanoparticles (APTES-Fe3O4) were impregnated into a Polyethersulfone(PES) membrane in order to remove arsenic by exploiting the PES membranes inherent filtration capability and reaction between the Iron oxide compounds and arsenic species by adsorption mechanism, which provides high As(V) removal capacity. APTES(Aminopropyltriethoxysilane) was reacted with Iron Oxide NPs to modify their surface for generating strong repulsion between NPs. The modification also prevents those nano particles’ aggregations and leads to good dispersion in the PES membrane matrix.

To characterize the modification of NPs with APTES (A-Fe3O4 NPs), Infrared Spectroscopy was utilized to verify the surface modification of Fe3O4 NPs. TGA analyzed the degree of dispersity of A-Fe3O4 NPs in PES membrane matrix. Pore structure of prepared membrane was characterized by FESEM and surface roughness was measured with AFM (Atomic Force Microscopy). Porosity and mean pore radius size were calculated with gravimetric method by using the weight difference of wet and dry membranes. Mean pore size was gained by Guerout-Elford-Ferry equation with water flux volume and pressure drop. For analyzing As(V) ion removal capacity through ion concentration of the permeate, ICP-MS method was utilized.

To evaluate the As(V) removal performance difference and find the best rejection of As(V), pure PES membrane was developed by adding APTES-Fe3O4 NPs in different weight percentages (1, 2, 3wt %). Batch adsorption tests were conducted with different As(V) concentration solution (2ppm, 4ppm, 6ppm, 8ppm) to study isotherm model. Kinetic adsorption experiments for As(V) removal were conducted in 50mL membrane cell under 50psi pressure with 1ppm As(V) solution for better understanding of adsorption process mechanism.

It was confirmed that A-Fe3O4 NPs were dispersed in good quality with the residual weight percent from TGA value. Moreover, FESEM images and AFM results indicated that PES containing 1wt%, 2wt% and 3wt% of A-Fe3O4 NPs tends to have more porous structure and higher roughness on the surface that pure PES membrane.

Higher percentage of pores over 60% was shown with PES containing more A-Fe3O4 NPs. Sub-layer micro-void is inclined to be formed in a bigger size with the addition of A-Fe3O4 NPs. This increased micro-void size in the bottom layer affected critically on pure water flux value. The larger the pore structure with A-Fe3O4 NPs, the prepared membrane showed better performance for the pure water flux by having the highest value 23.9Lm-2h-1bar-1 (in the case of M4). Furthermore, hydrophilicity was characterized with water contact angle. These values indicated the range between 61 ֯ and 76 ֯. Lowest contact angle was found in the PES containing 3wt % A-Fe3O4.

From the batch adsorption test results, sorption isotherm models were applied to define the equilibrium adsorption capacities of membranes with different concentration of As(V) solutions. Freundlich and Langmuir models were well fitted into data by giving R2 as 0.9996 and 0.9955 in PES-A-Fe3O4 NPs 3wt% membrane, respectively. Mostly, Langmuir model gives higher R2 for the linear regression of the prepared membranes.

Dynamic adsorption results gained under pressure, 50psi in a 50mL membrane cell showed the highest rejection percentage, 76% from PES-A-Fe3O4 NPs 3wt% membrane. Most of nanocomposites with A-Fe3O4 NPs were equilibrated at 270mins.

The prepared PES membrane nanocomposite in this research proves its high capability to remove arsenate with its good thermal stability and resistance to extreme pH conditions. Physical separation through membrane, in addition to adsorption behavior of PES can propose this PES-A-Fe3O4 NPs membrane to be an efficient medium for removing As(V) from aqueous solution.

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