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Bench-Top Electrochemical Crystal Growth: In-Situ Synthesis of Extended Solids Containing Polyoxometalate Anions

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Bench-Top Electrochemical Crystal Growth: In-Situ Synthesis of Extended Solids Containing Polyoxometalate Anions Clemson University TigerPrints All Dissertations Dissertations August 2020 Bench-Top Electrochemical Crystal Growth: In-Situ Synthesis of Extended Solids Containing Polyoxometalate Anions Qiuying Zhang Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Recommended Citation Zhang, Qiuying, "Bench-Top Electrochemical Crystal Growth: In-Situ Synthesis of Extended Solids Containing Polyoxometalate Anions" (2020). All Dissertations. 2669. https://tigerprints.clemson.edu/all_dissertations/2669 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. BENCH-TOP ELECTROCHEMICAL CRYSTAL GROWTH: IN-SITU SYNTHESIS OF EXTENDED SOLIDS CONTAINING POLYOXOMETALATE ANIONS A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Chemistry by Qiuying Zhang August 2020 Accepted by: Dr. Shiou-Jyh Hwu, Committee Chair Dr. Stephen Creager Dr. Andrew Tennyson Dr. Jian He ABSTRACT A set of proof-of-concept in-situ synthesis of polyoxometalate-containing compounds is presented in this dissertation showing that room-temperature electrochemical crystal growth is a promising technique for the exploratory synthesis of new materials with functional architectures. Most polyoxometalate(POM)-based crystalline materials, if not all, have been synthesized via conventional hydrothermal/solvothermal methods. However, the high temperature and pressure required by these methods proves destructive towards thermally sensitive POM anions, resulting in greater uncertainty of the synthesis of crystalline materials based upon these plenary POM structures. We have explored a new approach for the “bench-top” synthesis of POM-containing materials at ambient conditions by employing electrochemical (e-chem) energy as a driving force for new compound formation. We have demonstrated that the e-chem approach allows for convenient synthesis of POM- containing compounds in aqueous solution without using any specialized reaction container. Compared to conventional hydrothermal/solvothermal synthesis, the new approach offers additional benefits especially towards the synthesis of POM materials that are otherwise subject to thermal decomposition. Furthermore, using e- chem methods for crystal growth facilitates a means for the selective synthesis of compounds with desired frameworks for electrical conductivity. We have had some success with e- chem crystal growth in which newly discovered compounds exhibit fascinating structures such as one-dimensional (1D), alternating POM anion and transition metal (M) cations, and two-dimensional (2D) frameworks featuring tethered POM clusters on ii metal-oxide chains. In addition to the use of X-ray diffraction methods to investigate crystal structures, we have employed TGA/DSC (Thermogravimetric Analysis/ Differential Scanning Calorimetry) methods to examine the thermal behaviors of new compounds, and XPS (X-ray Photoelectron Spectroscopy) to determine the oxidation states of the metal cations and etc. Inspired by previous work, an electrochemical synthetic system for the design of POM-based complex metal oxides has been adapted to explore organic-inorganic hybrid materials. This represents a key step in adaptation of the mild reaction system for use in the synthesis of polyoxometalate-organic- frameworks (POMOFs), a class of compounds previously dominated by synthesis via conventional hydrothermal or solvothermal methods, and more recently, ionothermal methods. Applications of such materials include use in lithium ion batteries owing to the multi- electron reduction of polyoxometalate clusters and tunability of pores allowing lithiation. Interestingly, the emerging electrochemical synthetic method enables synthesis of many micrometer scale single crystals and does not require a polymer matrix, differing from previous reports of electrodeposition used to grow thin film organic-inorganic hybrids. Most notably, conventional hydrothermal techniques prove destructive to POM anions with low thermal stability, precluding synthesis or creating reliance upon self-assembly of POM anions. This bench top, one-pot reaction system allows control of potential or current density, temperature, concentration, pH, timescale, and electrode material resulting in potential for enhanced tunability. Furthermore, the electrochemical pathway utilized allows greater selectivity for the synthesis of conductive materials. iii DEDICATION This dissertation is dedicated to my loving parents. Without their support and sacrifices I could never have walked this far. I also dedicate this work to my undergraduate research advisor Dr. Fei Teng. Without his enlightenment on chemistry this dissertation would not have been possible. iv ACKNOWLEDGMENTS I would like to thank and appreciate my research advisor Dr. Shiou-Jyh Hwu for his guidance and support through my PhD program. His patience, teachings and encouragement molded me to be a better person and a better chemist. My deepest gratitude goes out to my committee members Dr. Stephen Creager, Dr. Andrew Tennyson and Dr. Jian He for their help and judgment to my research work. I would like to thank Dr. Colin McMillen who instructed me a lot in X-ray crystallography. A special thank you goes out to the chemistry department which provided funding for my research. Also, I really appreciate my outstanding undergraduate students including Joseph Ondus, Juliana Mills, Ardeshir Bahadori and Jacob smith who dedicated a lot on my research and provided many good suggestions and ideas. I also thank the current and past student of Dr. Hwu’s group, Kirkland Sheriff, Justin Talbert, Yu Shen and Dr. Dino Sulejmanovic for teaching me everything I needed to know in the lab. In addition, I would like to thank the staff of Advanced Materials Research Center for their help on the operation of the instruments. Also, my sincere appreciation to my parents’ support. I would like to thank two best friends of mine, Xiaotian Xu and Chi Zhang. Xiaotian accompanied me to peregrinate many beautiful places of the United States in the past years. Chi always listened and encouraged me when I felt exhausted and even did not believe myself. I would not have had a colorful five-year without them. Finally, I would like to appreciate the company and encouragement from Ziyi Chen, a lovely angel dispatched by God, in this hard year. She has shown me a different v world and inspired me to keep fighting for a bright future with her. I look forward to looking back on this dissertation with Ziyi together when we are old. vi TABLE OF CONTENTS Page TITLE PAGE ................................................................................................................ i ABSTRACT................................................................................................................. ii DEDICATION ............................................................................................................ iv ACKNOWLEDGMENTS ............................................................................................ v LIST OF TABLES ...................................................................................................... ix LIST OF FIGURES ...................................................................................................... x CHAPTER I. INTRODUCTION......................................................................................... 1 Polyoxometalate chemistry .................................................................... 1 The synthesis of polyoxometalate-containing materials ....................... 11 Electrochemical synthesis.................................................................... 15 Literature cited .................................................................................... 20 II. EXPERIMENTAL METHODS ................................................................... 25 Isothermal/Hydrothermal synthesis ..................................................... 27 Reflux synthesis .................................................................................. 28 Electrochemical synthesis.................................................................... 29 Starting materials ................................................................................ 30 Characterization Techniques ............................................................... 33 Literature cited .................................................................................... 45 III. EXPLORATORY SYNTHESIS OF EXTENDED OXIDES FEATURING INTERLINKED Α-KEGGIN CLUSTERS VIA IN-SITU ELECTROCHEMICAL CRYSTAL GROWTH AT AMBIENT ................. 47 Abstract............................................................................................... 47 Introduction......................................................................................... 48 Synthetic procedures ........................................................................... 51 Characterizations ................................................................................. 54 Results and discussion ......................................................................... 57 vii Table of Contents (Continued) Page Conclusions and future work ............................................................
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