Piezoelectric materials produce an electric potential in response to a mechanical strain. They are, therefore, capable of converting ambient waste mechanical energy into useful electrical energy which, in turn, may be harnessed and used as a supplemental source of power in a variety of applications. Engineered piezoelectric materials may be deployed to improve treatment efficiency during the production of potable water, which is both chemically and energetically intensive. Ambient mechanical energy is prevalent in municipal water treatment. Vibrations induced by water treatment plant pumps (such as High Service Pumps), turbulence resulting from cross-flow or dead-end membrane filtration, or agitation from mechanical mixing (paddle or impeller) may provide sufficient input mechanical input energy to activate a piezoelectric response.
The objective of this work was to fabricate and characterize a range of nanofiber-based piezoelectric materials and demonstrate their application as an alternative energy supply for driving environmental treatment (e.g., pollutant degradation) via simple mechanical agitation. To achieve this objective, we fabricated a variety of piezoelectric nanofiber composite mats consisting of barium titanate (BTO) nanocrystals grown via an alkaline hydrothermal method atop an electrospun carbon nanofiber (CNF) support.
We hypothesized that the greatest degree of piezoelectric activity (as measured by the voltage produced as a function of mechanical strain) would be achieved for nanofiber composites containing BTO with the largest fraction of tetragonal crystal structure, known to be piezoelectrically active. A systematic study on the impacts of hydrothermal treatment time, temperature, as well as the influence of ethylene glycol as an organic co-solvent on BTO crystal size and morphology was performed. For example, ethylene glycol was found to disrupt the dissolution-precipitation mechanism of BTO crystal growth and instead spurred the growth of BTO nanorods and nanosheets on the CNF support.
After characterization, the strength and electromechanical properties of various BTO-CNF composites was assessed. In some cases, output voltages have been measured on the order of 2.0 V/cm2 in response to surface bending strain induced by a custom cantilever-oscillometer apparatus. Optimal fractions of BTO loading in the composites were assessed through mass-loading electromechanical studies.
As a proof of concept application, BTO nanoheterostructures were shown to utilize ultrasonic vibrations to degrade sodium orange II salt (4-(2-Hydroxy-1-naphthylazo)benzenesulfonic acid sodium salt) via piezocatalysis. Ongoing and future work will continue to develop optimized piezocatalytic nanoheterostructures able to harvest the electrochemical potential generated from mechanical agitation and structural deformation for the production of oxidizing and reducing equivalents for degradation of persistent and emerging organic contaminants and disinfection in water treatment.