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Item Colloidal Synthesis of Single-Layer Quasi-Ruddlesden–Popper Phase Bismuth-Based Two-Dimensional Perovskite Nanosheets with Controllable Optoelectronic Properties(ACS, 2021-07) Lee, Jacob T.; Seifert, Soenke; Sardar, Rajesh; Chemistry, School of ScienceSingle- and few-layered two-dimensional (2D) nanomaterials have attracted intense research interest in the last two decades due to their unique electronic and optoelectronic properties leading to various potential applications. Herein, we report the colloidal synthesis of Bi-based 2D perovskite nanosheets (PEG6-NH3+)nCs3–nBi2X9, where X = Cl, Br, and I, through careful design of reaction conditions and selection of poly(ethylene glycol) (PEG6) surface passivating ligands. The 2D nanosheets are ∼5 nm in thickness with micron-sized lateral dimensions and display composition-dependent band gap and work function modulation. Small-angle X-ray scattering analysis substantiates that the individual inorganic crystal layer, Cs3–nBi2X9, is separated by the spacer, PEG6 ligand. Additionally, we determined that PEG6-NH2 is an essential passivating ligand and spacer for the formation of Bi-based 2D nanosheets. Most importantly, controlled crystallization of the colloidal dispersion of nanosheets results in the formation of superlattice microstructures of the quasi-Ruddlesden–Popper phase. These microstructures can be exfoliated to ultrathin nanosheets by overcoming the van der Waals interaction between the organic passivating layers. The controlled synthesis of lead-free 2D perovskite nanosheets presented here can expand their utility to photocatalytic and optoelectronic applications with reduced toxicity.Item Covalent Surface Modification of Ti3C2Tx MXene with Chemically Active Polymeric Ligands Producing Highly Conductive and Ordered Microstructure Films(American Chemical Society (ACS), 2021-11-17) Lee, Jacob T.; Wyatt, Brian C.; Davis, Gregory A., Jr.; Masterson, Adrianna N.; Pagan, Amber L.; Shah, Archit; Anasori, Babak; Sardar, Rajesh; Chemistry, School of ScienceAs interest continues to grow in Ti3C2Tx and other related MXenes, advancement in methods of manipulation of their surface functional groups beyond synthesis-based surface terminations (Tx: −F, −OH, and ═O) can provide mechanisms to enhance solution processability as well as produce improved solid-state device architectures and coatings. Here, we report a chemically important surface modification approach in which “solvent-like” polymers, polyethylene glycol carboxylic acid (PEG6-COOH), are covalently attached onto MXenes via esterification chemistry. Surface modification of Ti3C2Tx with PEG6-COOH with large ligand loading (up to 14% by mass) greatly enhances dispersibility in a wide range of nonpolar organic solvents (e.g., 2.88 mg/mL in chloroform) without oxidation of Ti3C2Tx two-dimensional flakes or changes in the structure ordering. Furthermore, cooperative interactions between polymer chains improve the nanoscale assembly of uniform microstructures of stacked MXene-PEG6 flakes into ordered thin films with excellent electrical conductivity (∼16,200 S·cm–1). Most importantly, our covalent surface modification approach with ω-functionalized PEG6 ligands (ω-PEG6-COOH, where ω: −NH2, −N3, −CH═CH2) allows for control over the degree of functionalization (incorporation of valency) of MXene. We believe that installing valency onto MXenes through short, ion conducting PEG ligands without compromising MXenes’ features such as solution processability, structural stability, and electrical conductivity further enhance MXenes surface chemistry tunability and performance and widens their applications.Item Fatty acid elongation by ELOVL condensing enzymes depends on a histidine nucleophile(Springer, 2021-06) Blacklock, Brenda J.; Chemistry, School of ScienceItem Photoactivities of thiophene monomer/polymer transition in gel–based photoelectrochemical assembly: A theoretical/experimental approach(Elsevier, 2023-04) Kasem, Kasem K.; Pu, Jingzhi; Cox, Logan; Chemistry, School of SciencePhotoactivities of bithiophene and/or terthiophene monomers and their mixtures were studied before and after being subjected to in situ oxidative electropolymerization in gel electrolyte (GE). Measured band gaps and density functional theory calculations supported the presence of oligomers in conjunction with the expected polymers. More oligomers formed during polymerization of the mixed monomers than with pure monomers. The generated photocurrent from the polymer/oligomer was always greater than that of the monomer. These results support the assumption that increasing π-bond conjugation leads to better e/h formation, and charge separation. The study also shows that the increase of the TerTh percentage in the monomer’s mix increased the generated photocurrent by the existing polymer/oligomer mix in a linear monotonic relationship.