ChE PhD Dissertation Defense: Changyu Wang

Name: Changyu Wang

Title: Surface Engineered Porous Geopolymer to Remove Anionic Contaminants in Water

Date: 12/02/2024

Time: 11:15:00 AM

Committee Members:
Prof. Ming Su (Advisor)
Prof. Sara Hashmi
Prof. Kai-Tak Wan
Prof. Qing Zhao

Location:
EXP 610 and Teams

Abstract:
Geopolymers are inorganic polymers synthesized from aluminosilicate sources and alkali. They have good nanoporosity and are suitable for adsorption processes in water treatment. This research project aimed to create a hierarchical porous structure within the geopolymer monolith to facilitate the use of inner nanoporosity and modify the porous geopolymer to remove anionic contaminants from water.

The porous structure is adjusted by controlling the geopolymerization and foaming process using a pourable geopolymer slurry. Geopolymerization is controlled by temperature and active ingredients in the formulation to have optimal pot life. Sufficient pot life of the slurry is critical to form pores of the desired amount and size. With the aid of appropriate surfactants and foaming agents, a uniform, interconnected macroporous structure forms within the geopolymer. This process creates porous monoliths with any desired shape.

A post-modification process is accomplished by using iron salt solutions with sufficient concentration and appropriate pH. Unmodified and modified geopolymers were characterized by gas adsorption analyzer, SEM/EDS, XRD, and FTIR, indicating that nano iron oxyhydroxide is incorporated within and changes the porous geopolymer structure. The BET surface area increases from 31 m2/g to 224 m2/g; Micropores and mesopores become dominant nanopores instead of macropores. SEM, gas adsorption isotherm, and capillary flow porometry verify that the modified geopolymers have a hierarchical, interconnected porous structure ranging from half a millimeter to less than two nanometers. The high specific surface area and positively charged iron oxyhydroxide on the porous geopolymer make it an excellent adsorbent to attract anionic contaminants through adsorption. During water treatment, the macropores act as conduits for the adsorbate in water to contact the interior surface, and adsorption of contaminants takes place in micropores and smaller mesopores. The modified porous geopolymer was shown to be effective in removing phosphate and rose bengal (an anionic dye with similar adsorption properties to PFAS). After saturation, the media can be regenerated using sodium hydroxide solution and reused multiple times.