Christopher J. Karwacki

Structure–activity relationship of Au/ZrO2 catalyst on formation of hydroxyl groups and its influence on CO oxidation

The effect of changes in morphology and surface hydroxyl species upon thermal treatment of zirconia on the oxidation activity of Au/ZrO2 catalyst was studied. We observed using transmission Fourier transform infrared (FTIR) spectroscopy progressive changes in the presence of monodentate (type I), bidentate (type II) and hydrogen bridged species (type III) for each of the thermally treated (85 to 500 °C) supports consisting of bare zirconia and Au/ZrO2 catalysts. Furthermore, structural changes in zirconia were accompanied by an increase in crystal size (7 to 58 nm) and contraction of the supports porosity (SSA 532 to 7 m2 g−1) with increasing thermal treatment. Deposition of gold nanoparticles under similar preparation conditions on different thermally treated zirconia resulted in changes in the mean gold cluster size, ranging from 3.7 to 5.6 nm. Changes in the surface hydroxyl species, support structure and size of the gold centers are important parameters responsible for the observed decrease (>90%) in CO conversion activity for the Au/ZrO2 catalysts. Density functional theory calculations provide evidence of increased CO binding to Au nanoclusters in the presence of surface hydroxyls on zirconia, which increases charge transfer at the perimeter of the gold nanocluster on zirconia support. This further helps in reducing a model CO-oxidation reaction barrier in the presence of surface hydroxyls. This work demonstrates the need to understand the structure–activity relationship of both the support and active particles for the design of catalytic materials.

Bottom-Up Synthesis of Anatase Nanoparticles with Graphene Domains

Using alizarin and titanium isopropoxide, we have succeeded in preparing a hybrid form of nanostructured graphene-TiO2 following a bottom-up synthetic approach. This novel graphene-based composite offers a practical alternative to synthesizing photocatalytically active materials with maximized graphene-TiO2 interface. The molecular precursor alizarin was chosen because it efficiently binds to TiO2 through the hydroxyl groups and already possesses the graphene building block through its anthracene basis. XPS and Raman spectroscopy proved that the calcined material contained majority sp(2)-hybridized carbon that formed graphene-like clusters. XRD data showed the integrated structures maintained their anatase crystallography, therefore preserving the materials properties without going through phase transitions to rutile. The enhanced graphene and TiO2 interface was confirmed using DFT computational techniques. The photocatalytic activity of the graphene-TiO2 materials was demonstrated through degradation of methylene blue.

Ferrihydrite deposited on cotton textiles as protection media against the chemical warfare agent surrogate (2-chloroethyl ethyl sulfide)

An active phase of ferrihydrite was deposited on cotton using a simple dip-and-dry process. The iron loading was between 4 and 10%, depending on the form of cotton and the number of dip-and-dry cycles. The materials were tested for the removal of a mustard gas surrogate, 2-chloroethyl ethyl sulfide (CEES). The modified fibers showed enhanced photoreactivity and adsorption performance compared to bulk ferrihydrite. The analysis of the headspace and of the surface of the samples after exposure to CEES revealed the presence of reaction products, indicating the high chemical activity of the ferrihydrite phase. Reaction mechanisms involving sulfonium intermediates are proposed. The chemical activity is linked to the high dispersion of the inorganic phase, which increases the number of available catalytic sites and thus enhances the direct contact of these actives sites (OH terminal groups, Fe3+, defects) with CEES.

Optimizing Toxic Chemical Removal through Defect‐Induced UiO‐66‐NH2 Metal–Organic Framework

For the first time, an increasing number of defects were introduced to the metal-organic framework UiO-66-NH2 in an attempt to understand the structure-activity trade-offs associated with toxic chemical removal. It was found that an optimum exists with moderate defects for toxic chemicals that react with the linker, whereas those that require hydrolysis at the secondary building unit performed better when more defects were introduced. The insights obtained through this work highlight the ability to dial-in appropriate material formulations, even within the same parent metal-organic framework, allowing for trade-offs between reaction efficiency and mass transfer.

Photocatalytic Oxidation of Sulfur Mustard and Its Simulant on BODIPY-Incorporated Polymer Coatings and Fabrics

Sulfur mustard is one of the most toxic chemical warfare agents worldwide. We report the use of 4,4-difluoro-4-bora-3a,4a-diaza- s-indacene (BODIPY) photosensitizers as a fast and effective sulfur mustard decontaminant and their incorporation into various polymer coatings and fabrics, including army combat uniform. These BODIPY-embedded materials are capable of generating singlet oxygen under visible light irradiation and effectively detoxifying sulfur mustard by converting it into nontoxic sulfoxides as the major products. The rate of decontamination is found to be affected by the photosensitizer structure and concentration as well as the excitation wavelength. The most effective BODIPY-embedded self-decontamination material observed in this study shows a half-life of only 0.8 min. In comparison to the current methods, which use activated carbon as the adsorbent layer, these self-detoxifying coatings and fabrics provide constant destruction of and real-time protection against sulfur mustard.