3D PRINTING AND DIFFUSION MODELING OF COLORIMETRIC CHEMO-RESPONSIVE ANION-EXCHANGE MEMBRANES: AN INNOVATIVE SMART MATERIAL FOR THE DETECTION AND FILTRATION OF HARMFUL CONTAMINANTS IN DRINKING WATER

Open Access
Author:
Pohlmann, Hannah Katherine
Area of Honors:
Interdisciplinary in Mathematics and Materials Sciences and Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Dr. Michael Hickner, Thesis Supervisor
  • Dr. Robert Allen Kimel, Honors Advisor
  • Dr. Diane Henderson, Honors Advisor
  • Dr. Long-Qing Chen, Thesis Supervisor
  • Timothy Charles Reluga, Thesis Supervisor
Keywords:
  • 3D printing
  • membranes
  • mercury
  • lead
  • pH
  • zinc
  • materials sceince
  • colorimetric response
Abstract:
3D printed water purification membranes are of great importance as the need for clean water rises with the demands of a growing population. In this study, both neutral and charged anion-exchange membranes were 3D printed using digital light sterolightography. These functional membranes contained color responsive dyes capable of detecting contaminants in water. In the first part of the study, thymol blue was used as a pH sensitive dye. The neutral membranes exhibited color changes between blue, green, yellow, orange, and red over a range of pHs with the anion-exchange membranes giving a blue/yellow color change between high and low pH. Switching from yellow at pH 7 to blue at pH 12 took 5 minutes for the neutral membranes and 30 seconds for the anion-exchange membranes. Data for the mechanical properties showed tensile strengths of 0.4 MPa and 0.1 MPa for the neutral and anion-exchange membranes, respectively. The anion-exchange membranes were of particular interest as they may ultimately be used to not only detect but also filter out the contaminants. As an extension of these results, another dye, dithizone, was used for detection of mercury ions (Hg2+) in water. This dye, when introduced into the neutral membrane, gave a distinct color change from yellow/green to red in the presence of as little as 10 ppm mercury in 15-30 min depending on the concentration of the dye in the membrane and the Hg2+ in solution. The dye was also reactive with zinc leading to a deep red color change in under a minute. Finally, a mathematical modeling using Fick’s second law was used with numerical analysis to estimate the diffusion coefficients of the membranes. For the anion-exchange membranes, the diffusion coefficient was estimated to be 8.45 x 10-10 m2/s, while the diffusion coefficient for the mercury-sensing membranes was estimated to 8.12 x 10-10 m2/s. As the development of new functional membranes continues, safer drinking water and better sensing of contaminants in membrane systems will improve water purification processes and systems across the globe.