Nanowire-Based Energy Conversion Devices and Technologies for Waste Heat Scavenging and Water Disinfection
Authors: Vaddiraju Sreeram 
Published: February 2020

Over the last two decades, nanowires have been demonstrated to be useful in a host of energy conversion devices and applications, including solar cells, thermoelectrics, and photocatalysis. Enhanced charge transfer resulting from the single-crystalline nature of nanowires, coupled with the ability to control their electrical, thermal and electronic properties through diameter variations, has allowed for accomplishing this task. In a series of papers, our group has also demonstrated the following: (a) Ultrathin nanowires of compound semiconductors could be obtained using thermal decomposition (1), and this process could subsequently be employed for engineering the bandgaps of compound semiconductors; and (b) large-scale assembly of nanowires could be made to exhibit thermal and electrical transport properties different from their bulk crystal counterparts, similar to those reportedly observed in individual nanowires (2-4). In accomplishing these tasks, we have developed strategies for the mass production of nanowires, their surface functionalization/decoration using organic/inorganic molecules, and their assembly in an interface-engineered manner into bulk devices (1-7). These all-dry routes for mass producing and assembling nanowires have been employed to precisely control the chemical compositions and ultimately the thermal, electrical and chemical properties of large-scale nanowire assemblies (2-7). Encouraged by these successes, our group has recently started studying the use of nanowires and their assemblies as photocatalysts for disinfecting water off harmful bacteria, such as E.coli.

In this talk, strategies developed for the mass production of nanowires that involve the direct reaction of component elements in a chemical vapor deposition (CVD) chamber will be discussed (5). Extension of these strategies for mass producing nanowires in a byproduct-free manner (i.e., without the associated production of nanoparticles or other bulk crystal byproducts) will be presented and discussed (8). The latter strategy aids in fabricating energy conversion devices with precisely controlled performances, by eliminating the need to purify nanowires before they are incorporated into devices. Vapor phase in-situ methods useful in the decoration of nanowire surfaces with inorganic/organic molecules immediately after their synthesis for imparting them resistance against moisture- and acid-assisted degradation will also be discussed (5-6). Use of all-dry hot uniaxial pressing for assembling the mass produced nanowires into bulk devices will also be discussed, with a specific emphasis on interface-engineered assembly of nanowires (2-4, 7). Finally, the performances of these bulk nanowire assemblies as thermoelectric devices (2-4) and as photocatalysts for disinfecting water will be discussed in detail. In the latter case, specific discussion on visible light-assisted photocatalysis for the removal of harmful bacteria from water will be discussed. The kinetics of the disinfection process, the possible disinfection mechanisms along with the photocatalyst lifetimes will be discussed in this talk. The efficacy of this disinfection process relative to those accomplished using current state-of-the-art approaches, such as UV-assisted water disinfection, will be discussed. Finally, the possibility of deploying photocatalysis-based disinfection technologies on a large-scale will be explored and discussed.