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According to the center for disease control (CDC), an estimated 1.7 to 2.2 million persons die from waterborne diseases annually. The majority of individuals dying from diseases resulting from unsafe drinking water, such as diarrhea and gastroenteritis, are children. This has in turn created a global water crisis. Different methods have been developed to treat contaminated water in response to the global water crisis such as adsorption, filtration, ozonolysis, catalysis, etc. Of the methods available, filtration via polymeric membranes has been one of the most successfully applied. A membrane is a thin semi-permeable barrier (often made of a polymer) used to separate differing phases in a media under pressure. Membrane filtration is ideal for water treatment due to high rejection and throughput, as well as ease of integration into other water treatment systems. Unlike other methods of water treatment, membrane filtration can be easily tuned to target specified contaminant at different size and pressure levels.

According to the center for disease control (CDC), an estimated 1.7 to 2.2 million persons die from waterborne diseases annually. The majority of individuals dying from diseases resulting from unsafe drinking water, such as diarrhea and gastroenteritis, are children. This has in turn created a global water crisis. Different methods have been developed to treat contaminated water in response to the global water crisis such as adsorption, filtration, ozonolysis, catalysis, etc. Of the methods available, filtration via polymeric membranes has been one of the most successfully applied. A membrane is a thin semi-permeable barrier (often made of a polymer) used to separate differing phases in a media under pressure. Membrane filtration is ideal for water treatment due to high rejection and throughput, as well as ease of integration into other water treatment systems. Unlike other methods of water treatment, membrane filtration can be easily tuned to target specified contaminant at different size and pressure levels.

Syed Joy will be presenting his doctoral thesis, "Understanding of Processing Additives Influence in Tin Halide Perovskites: ����vlog�ٷ����, Defect, and Photovoltaic Performance."

Syed Joy will be presenting his doctoral thesis, "Understanding of Processing Additives Influence in Tin Halide Perovskites: ����vlog�ٷ����, Defect, and Photovoltaic Performance."

Perovskites have emerged as a promising candidate for low-cost production of solar cells. However, the most critical barrier for commercialization of perovskite solar cells (PSCs) is the inadequate stability of the organic metal halide perovskites (OMHPs). The degradation of OMHPs is induced by light, heat, air, and electrical bias. The known degradation pathways involve the oxidation of I^- and Sn²⁺, dissolution of perovskites by moisture, irreversible reactions with water, ion migration, and ion segregation. To improve the stability of OMHPs various methods are adopted, such as additive engineering, perovskite surface treatment, and composition engineering. Surface ligands are used on top of perovskite thin films to passivate the undercoordinated ions leading to improved charge collection efficiency and stability of PSCs. However, not all surface ligands stay at the surface of the perovskite. Some of them penetrate the perovskite layer forming reduced dimensional phases at the surface. This kind of behavior not only alters the electronic nature at the interface, but also negatively affects the stability of the OMHPs compared to surface ligands that remain only at the surface. On the other hand, additives are commonly used to reduce defects in bulk of the perovskites and thus improve their stability. They improve the stability of OMHPs by controlling the morphology of OMHP thin films, improving the thermodynamic stability of Sn²⁺ and I^-, and lowering the ion migration and ion segregation. The stability of OMHPs is also significantly improved by incorporating bulky organic cations into the perovskite composition. Although these routes for improving the stability are optimistic, it is not clear how the surface chemistry of OMHPs and chemical nature of additives or organic cations affects stability.

Surface chemistry of OMHPs can be tuned to control the extent of ligand penetration by changing the composition and processing conditions of OMHPs. To this end, it is important to find out what affects the extent of ligand penetration. We find that the perovskite compositions used in this study have little or no effect on ligand penetration. However, the perovskite film processing conditions have a greater effect on ligand penetration. Using a family of phenethylammonium iodide (PEAI) with different substituents on the benzene ring, we show that the ligand penetration can be affected by type of substituents as well. Stabilizing the perovskite precursors is also important as degraded precursors lead to defective perovskites with poor stability. Here, we show that additives influence the thermodynamic stability of Sn²⁺ and I^- by changing the acidity of the precursor solutions. Using additives with a range of pKa we find that additives with higher pKa provide a more stabilizing chemical environment for Sn²⁺ and I^-. 

It is known that bulky organic cations improve the stability of OMHPs by shielding the metal-halide octahedra from air. However, how the structure of the organic cations affect the air, oxygen, and moisture stability of the OMHPs is not well understood. Using twelve different organic cations we show that the stronger the attractive interactions between the organic cations in two dimensional (2D) OMHPs the higher is the stability. The stability of 2D-OMHP thin films decreases as the orientation of the 2D sheets deviates from planarity with respect to the substrate plane.

Perovskites have emerged as a promising candidate for low-cost production of solar cells. However, the most critical barrier for commercialization of perovskite solar cells (PSCs) is the inadequate stability of the organic metal halide perovskites (OMHPs). The degradation of OMHPs is induced by light, heat, air, and electrical bias. The known degradation pathways involve the oxidation of I^- and Sn²⁺, dissolution of perovskites by moisture, irreversible reactions with water, ion migration, and ion segregation. To improve the stability of OMHPs various methods are adopted, such as additive engineering, perovskite surface treatment, and composition engineering. Surface ligands are used on top of perovskite thin films to passivate the undercoordinated ions leading to improved charge collection efficiency and stability of PSCs. However, not all surface ligands stay at the surface of the perovskite. Some of them penetrate the perovskite layer forming reduced dimensional phases at the surface. This kind of behavior not only alters the electronic nature at the interface, but also negatively affects the stability of the OMHPs compared to surface ligands that remain only at the surface. On the other hand, additives are commonly used to reduce defects in bulk of the perovskites and thus improve their stability. They improve the stability of OMHPs by controlling the morphology of OMHP thin films, improving the thermodynamic stability of Sn²⁺ and I^-, and lowering the ion migration and ion segregation. The stability of OMHPs is also significantly improved by incorporating bulky organic cations into the perovskite composition. Although these routes for improving the stability are optimistic, it is not clear how the surface chemistry of OMHPs and chemical nature of additives or organic cations affects stability.

Surface chemistry of OMHPs can be tuned to control the extent of ligand penetration by changing the composition and processing conditions of OMHPs. To this end, it is important to find out what affects the extent of ligand penetration. We find that the perovskite compositions used in this study have little or no effect on ligand penetration. However, the perovskite film processing conditions have a greater effect on ligand penetration. Using a family of phenethylammonium iodide (PEAI) with different substituents on the benzene ring, we show that the ligand penetration can be affected by type of substituents as well. Stabilizing the perovskite precursors is also important as degraded precursors lead to defective perovskites with poor stability. Here, we show that additives influence the thermodynamic stability of Sn²⁺ and I^- by changing the acidity of the precursor solutions. Using additives with a range of pKa we find that additives with higher pKa provide a more stabilizing chemical environment for Sn²⁺ and I^-. 

It is known that bulky organic cations improve the stability of OMHPs by shielding the metal-halide octahedra from air. However, how the structure of the organic cations affect the air, oxygen, and moisture stability of the OMHPs is not well understood. Using twelve different organic cations we show that the stronger the attractive interactions between the organic cations in two dimensional (2D) OMHPs the higher is the stability. The stability of 2D-OMHP thin films decreases as the orientation of the 2D sheets deviates from planarity with respect to the substrate plane.

Abstract: Over the years, nanomaterials research has advanced towards discovering versatile and readily accessible materials tailored for a diverse range of applications. A comprehensive understanding of materials’ phases and their transformations are integral to this effect to enable better synthetic control as well as the functionalization of nanomaterial properties. Among advanced characterization techniques, the transmission electron microscope (TEM) is a powerful tool that provides direct access to the nanoscale and, therefore, an indispensable tool in studying fundamental materials problems. This dissertation discusses several nanomaterial systems where TEM tools and techniques are utilized to gain a deep understanding of their chemistry. 

This dissertation focuses on structural and phase transformations of nanomaterials using in situ heating in the TEM, which allows direct observation of these dynamic processes. Reported here are studies of the phase transformation and stabilization of the mackinawite phase of iron(II) sulfide nanoplatelets, the structural transformation of gold-catalyzed tin(IV) oxide nanowires into gold core/tin(IV) oxide shell nanowire heterostructures, and finally the interaction between aluminum oxide and lead (at. 17%) lithium alloy proposed for use as a coolant in nuclear fusion reactors. These studies showcase the significance of knowledge of the mechanistic details of phase transformations, with the eventual goal of being able to determine and control structure-property relationships. 

KEYWORDS: phase transformations, nanomaterials, transmission electron microscopy (TEM), in situ TEM

Abstract: Over the years, nanomaterials research has advanced towards discovering versatile and readily accessible materials tailored for a diverse range of applications. A comprehensive understanding of materials’ phases and their transformations are integral to this effect to enable better synthetic control as well as the functionalization of nanomaterial properties. Among advanced characterization techniques, the transmission electron microscope (TEM) is a powerful tool that provides direct access to the nanoscale and, therefore, an indispensable tool in studying fundamental materials problems. This dissertation discusses several nanomaterial systems where TEM tools and techniques are utilized to gain a deep understanding of their chemistry. 

This dissertation focuses on structural and phase transformations of nanomaterials using in situ heating in the TEM, which allows direct observation of these dynamic processes. Reported here are studies of the phase transformation and stabilization of the mackinawite phase of iron(II) sulfide nanoplatelets, the structural transformation of gold-catalyzed tin(IV) oxide nanowires into gold core/tin(IV) oxide shell nanowire heterostructures, and finally the interaction between aluminum oxide and lead (at. 17%) lithium alloy proposed for use as a coolant in nuclear fusion reactors. These studies showcase the significance of knowledge of the mechanistic details of phase transformations, with the eventual goal of being able to determine and control structure-property relationships. 

KEYWORDS: phase transformations, nanomaterials, transmission electron microscopy (TEM), in situ TEM

Abstract: Compared to ubiquitous functional groups such as alcohols, carboxylic acids, amines, and amides, which serve as central “actors” in most organic reactions, sulfamates, phosphoramidates, and di-tert-butyl silanols have historically been viewed as “extras”. Largely considered functional group curiosities rather than launchpoints of vital reactivity, the chemistry of these moieties is underdeveloped. Our research program has uncovered new facets of reactivity of each of these functional groups, and we are optimistic that the chemistry of these fascinating molecules can be developed into truly general transformations, useful for chemists across multiple disciplines. In the ensuing sections, I will describe our efforts to develop new reactions with these “unusual” functional groups, namely sulfamates, phosphoramidates, and di-tert-butyl silanols.

Abstract: Low-dimensional (LD) organic-inorganic hybrids have recently emerged as exciting electrocatalytic nanomaterials in which the 0D-1D, 1D-2D or 2D-2D electrochemical interfaces can be finely tuned to generate unprecedented features that are not perceived in the individual counterparts (Scheme 1). 

Low-dimensional interfaces have shown incredible advantages in regulating electron transfer, charge polarization, bonding energy and the adsorption energy of intermediates, thus markedly boosting crucial electrocatalytic parameters such as current density, onset overpotential and faradaic efficiency in many relevant energy conversion reactions including oxygen reduction (ORR), oxygen evolution (OER), and CO₂ electroreduction (CO₂RR). In this seminar, key learning points about the chemical aspects that govern the interfacial effects of low-dimensional hybrids in crucial electrocatalytic reactions will be provided based on both experimental and theoretical findings. The discussion will also cover an in-depth understanding of the heterointerface-electrocatalytic performance relationships as well as their impact for the fabrication of future energy-related devices.

Bio: Alain R. Puente Santiago received his Ph.D. degree in Physical-����vlog�ٷ���� with distinction (July 2017) from the University of Cordoba, Spain. He has worked as a Research Fellow in Prof. Goodenough’s group (Nobel Prize in ����vlog�ٷ���� 2019) at the University of Texas at Austin in the development of nanocluster-based electrocatalytic materials. Currently, he is working as a Postdoctoral Associate in the Department of ����vlog�ٷ���� at the Florida International University. He has published 67 articles in very prestigious journals such as Journal of the American Chemical Society (7), ACS Sustainable ����vlog�ٷ���� and Engineering (5), Journal of Materials ����vlog�ٷ���� A (5), Angewandte Chemie (3), Nanoscale (3), ACS Applied Materials and Interfaces (2), Green ����vlog�ٷ���� (2), Chemical Society Reviews (2), Advanced Energy Materials (1) and Journal of Catalysis (1).Dr. Santiago’s articles have reached more than 2500 citations and an H index of 27 in the last 5 years. His research interests tackle the development of low-dimensional heterostructures for electrocatalytic, sensing, and energy storage applications.