(Invited) Rapid and Green Synthesis of Metal Oxide Quantum Dots By Plasma Induced Non-Equilibrium Electrochemistry (PiNE)

Abstract

Metal oxides (MOs) are a class of materials that has significant role in material science and engineering. Particularly, MO semiconductors have shown to play a key role in a range of applications therefore contributing to a sustainable future.1 , 2 , 3 MO nanoparticles in particular have been studied widely for application in energy harvesting and solar conversion. However, ultrasmall MO nanoparticles or MO quantum dots (MOQDs) still present synthesis challenges and while these may offer exciting opportunities, the understanding of their properties is still limited.Here we first demonstrate the synthesis of cupric oxide quantum dots (CuO QDs) by plasma induced non-equilibrium electrochemistry (PiNE). In this technique, we produced size-controlled QDs with diameter below 5 nm simply using a copper foil and ethanol as precursors for Cu and O, respectively. PiNE is a plasma-induced chemical process4 , 5 initiated at a plasma-liquid interface, which allows for rapid and simple production of highly stable, surfactant-free colloidal suspension of QDs.6 With this technique, we have shown production of range of MO QDs that include Cu, Ni, Co, Mo and Zn oxides.7 , 8 , 9 , 10 In addition to the QDs material characterisation, at the different stages of the synthesis, we have studied the colloidal solution by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, nuclear magnetic resonance, mass-spectroscopy etc. to provide an understanding of the mechanisms leading to nucleation and QD growth. Overall, this work discloses important aspects of a new generalized method for the synthesis of MO QDs. The study of the properties of our MO QDs reveals quantum confinement effects that can become particularly useful in many applications. We therefore present examples of MO QDs integration in solar cell devices, for solar-thermal conversion and other applications. Reference: 1 X. Yu, T. J. Marks and A. Facchetti, Nat. Mater., 2016, 15, 383–396.2 N. K. Elumalai, C. Vijila, R. Jose, A. Uddin and S. Ramakrishna, Mater. Renew. Sustain. Energy, 2015, 4, 11.3 H. Hosono, K. Hayashi, T. Kamiya, T. Atou and T. Susaki, Sci. Technol. Adv. Mater., 2011, 12, 034303.4 C. Richmonds and R. M. Sankaran, Appl. Phys. Lett., 2008, 93, 131501.5 D. Mariotti, J. Patel, V. Švrček and P. Maguire, Plasma Process. Polym., 2012, 9, 1074–1085.6 T. Velusamy, A. Liguori, M. Macias-Montero, D. B. Padmanaban, D. Carolan, M. Gherardi, V. Colombo, P. Maguire, V. Svrcek and D. Mariotti, Plasma Process. Polym., 2017, 14, 1600224.7 T. Velusamy, A. Liguori, M. Macias-Montero, D. B. Padmanaban, D. Carolan, M. Gherardi, V. Colombo, P. Maguire, V. Svrcek and D. Mariotti, Plasma Process. Polym., 2017, 14, 1600224.8 C. Ni, D. Carolan, C. Rocks, J. Hui, Z. Fang, D. B. Padmanaban, J. Ni, D. Xie, P. Maguire, J. T. S. Irvine and D. Mariotti, Green Chem., 2018, 20, 2101–2109.9 C. Ni, D. Carolan, J. Hui, C. Rocks, D. Padmanaban, J. Ni, D. Xie, Z. Fang, J. Irvine, P. Maguire and D. Mariotti, Cryst. Growth Des., 2019, 19, 5249–5257.10 S. Chakrabarti, D. Carolan, B. Alessi, P. Maguire, V. Svrcek and D. Mariotti, Nanoscale Adv., , DOI:10.1039/C9NA00299E.