Bubble-promoted assembly of hierarchical, porous Ag₂S nanoparticle membranes

Controlled assembly of nanoparticles can lead to a variety of interesting structures and also is an important step in exploring potential applications. Here, we report a solution process for the self-assembly of macroporous, single-layer to hierarchical Ag₂S nanoparticle membranes at the air-liquid interface, in which the trapping and releasing of air bubbles leads to the formation of a three-dimensional porous structure without the need to use a template. The resulting membranes contain close-arranged arrays of polygonal holes (mostly pentagons and hexagons) of a few micrometers in size, which are unanimously open upwards and are surrounded by thin nanoparticle walls. Energy and environmental-related applications are demonstrated based on these multifunctional Ag₂S membranes, including photo-sensing, photocatalysis and photoelectrochemical solar cells. The porous nanoparticle membranes are distinct from other extensively studied structures such as densely packed crystal-like films and superlattices.