Copper(II) Oxide-Based Nanomaterials as Hydrogen Sulfide Adsorbents and Glucose Sensors

Abstract

Copper(II) oxide (CuO) is a low-priced material and a p-type semiconductor with a band gap of 1.2 eV. It has been investigated in a variety of fields as a material for batteries, sensors, catalysts, supercapacitors, and adsorbents. This dissertation focuses on copper(II) oxide-based materials used as hydrogen sulfide adsorbents and non-enzymatic glucose sensors.This dissertation starts with an introduction to CuO structures, properties and applications followed by an explanation of the H2S adsorption needs and glucose sensing requisites. Then, a series of detailed studies is presented on how CuO behaves in the two applications. In the hydrogen sulfide adsorption application, pure CuO particles are susceptible to the high operating temperatures during sorbent regeneration processes and suffer from structural instability. Therefore, hierarchically structured nanocomposites were designed in which different types of shells stabilize the CuO nanoparticles. The synthetic layered clay Laponite was first selected because it can be delaminated into single platelets capable of wrapping around CuO nanoparticles. A charge-assisted approach was established to achieve a CuO/clay composite with the targeted morphology. After estimation of the H2S adsorption capacity of the material, we found the structure is too flexible to prevent the morphology change of CuO. Then, we moved forward to another protective support, mesoporous silica, and designed a core-shell CuO@mSiO2 material. We discovered a surprising morphological transformation during the sulfidation and regeneration (oxidation) of the CuO@mSiO2. The sulfidated product (CuS) was still encapsulated within the silica shells after sulfidation, but hollow silica shells formed during the regeneration step as CuO leached out of the shell and aggregated into larger particle. After investigating how morphology changes in each stage of the H2S adsorption process, we are able to address where hollow silica started to occur. In addition, we propose a possible mechanism for the hollow silica formation, which involves outward diffusion of copper ions through the mesoporous silica, leading to the migration of core particles. This work provides insights into the stability of core-shell structured materials with mesoporous silica serving as the coating material under the influence of diffusion-driven structural transformations. In the glucose sensing application, our goal was to study how the particle morphology affects glucose sensing performance, so we synthesized CuO nanoparticles with different morphologies (spheres, platelets and needles) by optimizing synthesis parameters. Then with a systematic investigation of the role of CuO particle morphologies, we provide an understanding on which specific morphological factor(s) contribute predominantly to the electrocatalytic performance. Our results show that the primary driving factor for glucose sensing with CuO materials is the grain size of copper oxide, whereas specific crystal faces or pore volume have little influence on the sensitivity. This work provides insight into the potential use of CuO-based materials in commercialized biosensors and into the major contributing factors of metal oxide-based nanoparticles on sensing applications. At the end, this dissertation provides a critical evaluation and overlook of CuO-based materials on H2S adsorption and glucose sensing applications.