One-pot manufacture of nanoparticle-based films in aqueous media via an electric field-driven assembly process†
Assembly of nanoparticles on multiple length scales and large areas is crucial for the manufacture of nanostructured devices. Nowadays, major problems in nanoparticle synthesis and their processing are the handling of waste (such as solvents, sub-products and unreacted precursors) and the search for environmental tolerable procedures. Environmental and economical pressures are now forcing the chemical community to search for more efficient ways of performing particle synthesis and processing. Thus, it would be much more efficient if both processes synthesis and processing could be realized in one sequence without isolating the intermediates. Here, we detail the results of a sustainable approach in which synthesis and the as-synthesized nanoparticles assembly are realized in one sequence without any intermediate step such as drying, sieving or centrifuging. The one pot process proposed emphasized the synergy between the mild hydrothermal synthesis of yttrium stabilized zirconia (YSZ) nanoparticles and their processing based on an electric field-driven mechanism that provides the assembly of the as-synthesized nanoparticles suspended in the synthesis mother water with low solid loading (<1 g L−1). The layer-by-layer or Frank–van-der-Merwe growth of an extremely densely packed nanoparticle-based film consolidated by green technologies was highlighted. Results suggest a fast (<1 h) and reliable shaping process that could approach a full yield. The approach is described for YSZ nanospheres, but it could be applicable to any nanoparticle and/or synthesis process offering a controlled, robust, inexpensive route for the large-scale manufacture of densely packed nanoparticle-based films. The key step of the process is the stabilization of the as-synthesized nanoparticle in the post-reaction medium using the synthesis catalyst itself, urea, and an additional dispersant, polyethyleneimine (PEI). The presence of organic modifiers in a low concentration (<2 wt% on the base of solids in the suspension) is critical and determines movement and re-arrangement of nanoparticles under the influence of an electric field during film growth.