Plasmonic Water Purification for Developing Countries

Authors: Justin Hayes¹, Daniel Willis², Dr. Kevin M. Mcpeak²

¹University of Rhode Island, Kingston, RI

²Louisiana State University, Baton Rouge, LA

Affiliation: Cain Department of Chemical Engineering at Louisiana State University

Contacts: justin_hayes@my.uri.edu (Presenting Author), dwillis25@gmail.com, kmcpeak@lsu.edu

Topical Area: General

Abstract: In the world, there are approximately 1 billion people without access to clean water [1], and every 20 seconds 1 child will die from a pathogenic water related illness [2]. Poor citizens in developing countries can spend up to 45% of their annual income on clean water [3]. In poor rural areas, SODIS, a solar water disinfection process, takes 6-48 hours to clean 1L of water [4]. Reactive oxygen species are capable of pathogen disinfection [5]. The study focused on developing a plasmonic device which disinfects water with visible light at a low monetary cost. The plasmonic device is a flexible layered substrate which utilizes gold plasmon resonances to harness solar energy and disinfect water. Stimulated gold nanoparticle plasmons can produce hot electrons and when injected into water, can react with H⁺ ions and dissolved O₂ to form hydrogen peroxide. The device was layered in the following order: 1mm thick Kapton, 100nm of aluminum via thermal evaporation, 50nm of zinc oxide spin coated and annealed, and 20nm gold nanoparticles reduced on top. To adhere the gold nanoparticles on top, the substrate was placed in a gold salt solution (AuCl₂^- in solvent) and exposed to UV light. Utilizing the band gap of zinc oxide (~3.3eV), electrons were produced which reduced the AuCl₂^- salt, to Au⁰ and Cl^- ions. By means of Van der Waals interactions, the Au particles stay atop the zinc oxide layer. The conditions of the gold photo deposition were investigated to produce optimal sized nanoparticles and reasonable stability. Solvent used in photo deposition, UV irradiation time, and diffusion of salt solution were the variables. The substrates produced showed different stabilities when exposed to the solvents ethanol and acetonitrile, with acetonitrile yielding less stable substrates. Constant or pulsed UV irradiation times were used to deposit gold nanoparticles. Longer UV irradiation time negatively affected stability of substrates by means of zinc oxide degradation. The transport of AuCl₂^- ions to the substrate surface was increased by mixing the gold salt solution during photo deposition. This increased gold deposition rate while reducing UV irradiation time. To investigate hydrogen peroxide production, the finished substrate was placed in DI water and exposed to artificial sunlight. Hydrogen peroxide production was tested using Amplex Red. In a flow reactor, a 2x2 inch substrate produced 16.2 uM/(min*mL) of hydrogen peroxide when exposed to 400-900nm light. Other reactive oxygen species present in the system are being investigated. Materials cost of the substrate is about $0.12, which is only 0.052% of the average minimum annual income of citizens in Southeast Asia [6]. Future research will substitute pathogen infected water for the DI water, to test the system efficacy. Substrate longevity will also be investigated.

References:

• UNICEF, Progress on Drinking water and sanitation. WHO. 2012.
• Shannon et al. Nature 2008, 452, 301-310.
• "World's Poorest Spend the Most." WaterAid America. N.p., 10 Aug. 2016. Web.
• “How Does It Work?” SODIS, sodis.ch/methode/anwendung/index_EN.
• Liu et al. Rapid water disinfection using vertically aligned MoS₂ nanofilms and visible light. Nature Nanotechnology 15 August 2016,
• "Minimum Salaries in Southeast Asia 2016." Check in Price. N.p., 31 Dec. 2016. Web..