SPST scientists Professor Osamu Terasaki, Dr. Peter Oleynikov, Dr. Alvaro Mayoral and Dr. Ma Yanhang, have collaborated with Professor Kyung Byung Yoon to report a new layered vanadosilicate for removal of 90Sr from highly Na+-rich liquid nuclear waste. The paper was published in “Energy & Environmental Science” with the title of “Removal of 90Sr from highly Na+-rich liquid nuclear waste with a layered vanadosilicate.”
Transition-metal (TM) silicates show many characteristic chemical features especially on selective absorption of a certain molecule or ion-exchange together with their large capacities, and catalytic performances. The scientists solved their complicated structures such as ETS-10 (TM: Ti), AM-6 (TM: V), and SGU-20 (TM: Cu) by using electron microscopy (EM) combined with powder X-ray diffraction (PXRD).
New vanadosilicate (TM: V) SGU-7 was synthesized long time ago and its interesting ion-exchange feature was found by Professor KB Yoon and his group at Sogang University in Korea. However, the extremely complext structure of the plate shape crystal morphology prevented a structure analysis by EM & PXRD, and understanding the origin of chemical functions was impossible.
Three-dimensional electron-diffraction tomography (3D-EDT) led to a breakthrough and gave essential structure features. SGU has layered structure-like clays that are very thin along b axis and with a layer in ac plane. Using the newly installed GrandARM300F in the Centre for High-resolution Electron Microscopy (CℏEM) at SPST, scientists were able to confirm extreme unique and different structural features from clays, with a finite length of –V–O–V– linear chain with five V atoms and large pores running parallel to  in the layer and along b-axis, respectively.
Moreover, the scientists showed SGU-7 as the best candidate for removing 90Sr even in harsh conditions, and cleared ion-exchange process that Sr2+ ions replace Na+ in the layer first and then occupy the sites between layers changing space group from P121/a1 to C12/m1. The final atomic structures were refined against synchrotron powder XRD data obtained from samples placed in glass capillaries collected at ESRF in France.
SEM, HAADF images, synchrotron PXRD pattern and 3D EDT data of SGU-7
Adsorption of Sr and Na ions using SGU-7