Áine Coogan1,Lucia Hughes1,Finn Purcell-Milton1,2,3,Seán Cardiff1,Valeria Nicolosi1,Yurii Gun'ko1,3
Trinity College Dublin, The University of Dublin1,Technological University Dublin2,University College Dublin3
Áine Coogan1,Lucia Hughes1,Finn Purcell-Milton1,2,3,Seán Cardiff1,Valeria Nicolosi1,Yurii Gun'ko1,3
Trinity College Dublin, The University of Dublin1,Technological University Dublin2,University College Dublin3
In recent years, significant research efforts have been directed towards the developmemt of chiral and chiroptically active inorganic nanomaterials, resulting in many new nanomaterials of various forms and morphologies, including quantum dots, nanowires, and tetrapods, among others.<sup>1-3</sup> Layered double hydroxides (LDHs) have emerged as a distinct class of ionic two-dimensional (2D) nanomaterials, renowned for their exceptional anion exchange properties, allowing for the incorporation of diverse species within their interlayer spaces, including chiral molecules. Surprisingly, despite this unique characteristic, there is a notable absence of reported studies exploring the utilisation of LDHs treated with chiral ligands to induce chiroptical activity.<br/>While chiral copper (II) oxide (CuO) nanostructures have previously been documented in literature, their synthesis often requires harsh, high-temperature synthetic conditions and the inclusion of expensive surfactants and symmetry-breaking agents to induce circular dichroism (CD) responses in the visible range.<sup>4-5</sup> Prior to this work, the room temperature synthesis of chiral CuO has remained un-explored to the best of our knowledge. Additionally, the potential for chirality transfer from chiral ligands to LDH-based nanostructures has not been reported.<br/>Herein, we present the unique facile approach to the synthesis of chiral CuO nanostructures through an alkaline room-temperature, aqueous treatment of carbonate-intercalated copper-aluminium LDHs (CuAl-CO<sub>3</sub> LDHs) with L- and D-Phenylalanine (L- and D-Phe). The resulting 2D CuO nanosheet bundles display remarkable chiroptical activity, with <i>g</i>-factors up to 0.0035. Time-dependent circular dichroism (CD), powder X-ray diffraction (pXRD) and Fourier transform infrared spectroscopy (FT-IR) studies reveal that the initial chirality transfer arises from Phe coordination to the Cu<sup>2+</sup> sites, leading to decomposition of the CuAl-CO<sub>3</sub> LDH to CuO. Self-assembly of the Phe-functionalised CuO nanosheets results in enhancement of the chiroptical activity. This work represents a novel, facile route of accessing chiral metal oxides through decomposition of LDH precursors. The ease of synthesis and induction of strong chiroptical activity in the visible range (400-800 nm) highlights the significance of this work. The resultant new chiral metal oxides hold promise for potential applications in enantiomeric separation and asymmetric catalysis, paving the way for advancements in chiral nanomaterial research.<sup>6</sup><br/><br/><u>References:</u><br/>1 - F. Purcell-Milton, R. McKenna, L. J. Brennan, C. P. Cullen, L. Guillemeney, N. V. Tepliakov, A. S. Baimuratov, I. D. Rukhlenko, T. S. Perova, G. S. Duesberg, A. V. Baranov, A. V. Fedorov and Y. K. Gun’ko, <i>ACS Nano</i>, 2018, <b>12</b>, 954–964.<br/><br/>2 - D. Kehoe, E. Mates-Torres, P. Samokhvalov, M. García-Melchor and Y. K. Gun’ko<i>, J. Phys. Chem. C,</i> 2022, <b>126</b>, 434–443.<br/><br/>3 - J. E. Govan, E. Jan, A. Querejeta, N. A. Kotov and Y. K. Gun’ko, <i>Chem. Commun</i>., 2010, <b>46</b>, 6072– 6074.<br/><br/>4 - Y. Duan, X. Liu, L. Han, S. Asahina, D. Xu, Y. Cao, Y. Yao and S. Che, <i>J. Am. Chem. Soc</i>., 2014, <b>136</b>, 7193–7196.<br/><br/>5 - C. Hao, A. Qu, L. Xu, M. Sun, H. Zhang, C. Xu and H. Kuang, <i>J. Am. Chem. Soc</i>., 2019, <b>141</b>, 1091–1099.<br/><br/>6 - Á. Coogan, L. Hughes, F. Purcell-Milton, S. Cardiff, V. Nicolosi and Y. K. Gun’ko,<i> J. Phys. Chem. C,</i> 2022, <b>126</b>, 18980–18987.