Date of Award

12-28-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Wei Zhao

Abstract

High demand of energy consumption and a decline in available water sources are two critical issues our growing world is facing today. There are urgent needs to develop efficient ways to convert and store renewable energy and to remove contaminants from wastewater to obtain clean water. To solve the energy issue, hydrogen production from water splitting using renewable energy is one of the solutions, which calls for highly efficient water-splitting electrocatalysts. To solve the clean water issue, filtration membranes using graphene-based nanostructures have received increased attention. In the first project of this work, we use two approaches to synthesize the promising oxygen evolution reaction (OER) nanocatalysts, nanostructural NiFe oxides (NiFeOx) grown on three-dimensional carbon nanostructures for water splitting. The first approach is directly using biomass algal cells as a biotemplate for growing NiFeOx nanoparticles under relatively mild and facile conditions. In the second approach, algal cells are first converted to carbon nanostructures by thermal annealing. The resulting carbon nanostructures then react with metal ions via hydrothermal reactions. The as-prepared samples have been characterized by various methods including X-ray diffraction and transmission electron microscopy. Their OER electrocatalytic properties have been studied by cyclic voltammetry and linear sweep voltammetry, which show promising OER activities superior to those of benchmark OER catalyst Ir/C. In the second project, we synthesize reduced graphene oxide (RGO) membranes for wastewater purification using forward osmosis. The RGO membranes have been characterized to determine the optimal structures. The filtration efficiency of the membranes has been evaluated based on the types of polymer filter membranes, the pore sizes of the polymer filter membranes, RGO mass loadings, heating annealing temperatures, heating times, reaction atmosphere, and RGO interlayer spacings. The performance of RGO membranes is superior to a commercial membrane, with excellent reverse flux selectivity, 7 times better than that of the commercial one. The potential of our membranes for wastewater purification, crucial for large scale applications has also been examined, which shows over 99% rejection of wastewater components. Our research might lead to low-cost, highly efficient water-splitting catalysts for hydrogen production and RGO membranes for seawater desalination and wastewater purification.

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