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Unmet MAGnetic properties in micro and nano-particles by synthesis through gas-diffusion electrocrystallisation (GDEx)

Periodic Reporting for period 1 - MAGDEx (Unmet MAGnetic properties in micro and nano-particles by synthesis through gas-diffusion electrocrystallisation (GDEx))

Reporting period: 2018-04-01 to 2020-03-31

Memory storage is a defining component of modern computing. It is a key issue because it determines system costs and power consumption. The ability to increase memory storage relies on the discovery, understanding, and improvement of new memory-storage materials. Recently, a third fundamental state for magnetism was experimentally realized in a novel class of matter: the spin-liquid state, after finding a way to synthesize herbertsmithite which is now prospected as a promising memory-storage material. Hydrothermal methods to grow herbertsmithite are available, but they have low production rates and yields and focus on the production of macroscopic crystals, while it is known that nano-scale dimensioned particles do have superior or different properties. Using heterogeneous (electro)catalytic routes, the main problems of the thermal synthesis can be solved. Gas-diffusion electrocrystallization (GDEx) is a new electrochemical process developed at the host organization. It is a rapid one-pot reaction crystallization process, electrochemically steered at the three-phase junction of a porous gas-diffusion cathode. The main objective of this project is to develop, optimize and validate the GDEx technology for the bottom-up synthesis of micro and nano-scaled Zn4-xCux(OH)6Cl2 particles. The project aims to obtain single-phase (pure) herbertsmithite and its polymorphs via GDEx, understanding the mechanism of formation. The project also aims to obtain these materials as solid particles, colloidal dispersions, and thin films, all with preciselly-controlled properties which can result in tailored magnetic functionalities that may result in revolutionized memory storage possibilities. Furthermore, it is aimed to obtain these particles in gram-quantities per day and at least 70% yield, obesides pening the way to a greener synthesis route, operating at mild conditions and reducing the need for hazardous reagents.
The project covered six research objectives:

RO.1: To elucidate the processing conditions of GDEx in which single-phase HBST and CACT are produced.
RO.2: To optimize the processing conditions of GDEx and electrochemical cell setup for the high-yield synthesis of Zn4-xCux(OH)6Cl2 at faster rates than state-of-the-art technologies.
RO.3: To optimize the processing conditions of GDEx to achieve the unmet micro and nano particles of Zn4-xCux(OH)6Cl2.
RO.4: To obtain stable colloidal dispersions of Zn4-xCux(OH)6Cl2 nanoparticles in water.
RO.5: To obtain highly promising and well-controlled magnetic properties (measured as per the magnetic susceptibility) linked to the micro and nano-dimensioned Zn4-xCux(OH)6Cl2 particles.
RO.6: To explore the formation of thin-films of HBST and CACT over conducting substrates by electrophoretic deposition.

which were addressed in the following work packages:

Work Package 1: Study of the GDEx formation of HBST, CACT and paratacamite (M1-M18)
Work Package 2: Manipulation of HBST, CACT and paratacamite nanocrystals properties (M10-M18)
Work Package 3: Dispersions vs electrophoretic deposition (M10-M18)
Work Package 4: Magnetic susceptibility control (M18-M24)

Two patents, co-authorship in 4 peer-reviewed publications, one book chapter, participation in five international conferences, two dissemination activities, three training activities, and participation in thee workshops including one annual conference.
The project MAGDEX has achieved its objectives and milestones, including the development, optimization and validation of the GDEx technology for the bottom-up synthesis of micro and nano-scaled Znx-Cu4-x(OH)6Cl2 materials. The project obtained these materials as solid particles and colloidal dispersions in gram-quantities per day. The approach studied the formation of magnetic properties of NPs and provided fundamental knowledge on how to yield stable compositions to make further mechanistic revelations. The results included a detailed analysis of how pH and charge evolve at the electrochemical interface, as well as other influencing parameters such as the effect of weak acid, electrode potential, on the concentration of electrosynthesized OH– and H2O2, and concentrations of removed metal ions from solution.
The magnetic properties, particle size and rate of the reaction can be precisely tuned (directly or indirectly) by manipulating the charge consumption, as well as the composition of the electrolyte.
The project results were in accord with recent studies of synthesis of spin transition compounds indicating that the presence of Zn allowed the perfect kagomé distribution of the Cu2+ ions and consequently lead the absence of long-range ordering to the lowest measured temperature. We finally contributed to the state of the art, demonstrating that the spin liquid behavior was sustained at the nanoscale in compounds of ZnCu3(OH)6Cl2. Our discovery not only confirmed redox reactions as the driving force to produce spin transition nanoparticles, but also proved a simple way to switch between these magnetic ground states within an electrochemical system, paving the way to further explore its reversibility and overarching implications.