Sponge-Template-Directed Macroscopic Assembly Of Nanoscale Building Blocks: Fabrication And Applications

Despite the enormous progresses on the synthesis of individual nanostructures, nanoscience must now deliver truly revolutionary solutions for the practical applications of nanostructures. Since many of the applications are based not only on individual nano-objects but also on their assemblies in which these nano-objects organize in purposeful ways, the challenge that is facing nanoscience is to develop efficient ways of assembling nanocomponents. Amid a self-assembly procedure, one have little control over the dimensions and complexities of the final self-assemblies. On the contrary, the use of templates with defined dimensions and complexities should provide the opportunities to program the assembly of the nano-objects as one can define the dimensions and complexities of self-assemblies with the pre-determined structures of templates, creating predictable collective properties. In this dissertation, we focus our research interest on this topic. Firstly, we summarized resent progresses on the templates that used to guide the assembly of nano-objects and applications of nanocomposite assemblies. Although great progresses have been achieved on the fabrication of template-directed assemblies, macroscopic assembly of nano-objects by using existing processing techniques, tools and materials is still in its infancy. Based on this, we utilized facial dip-coating method and selected commercial sponge as the template to direct the macroscopic assembly of nano-objects. Combining the functions of nanobuilding blocks with the properties of the sponge template, we obtained a series of novel macroscopic nanocomposite assembles which had broad applications in the fields of shapeable electronics, pressure sensors, energy storage devices, oil/water separation, water purification and so on. The main achievements can be summarized as follows:1. By using commercial sponge as the 3D template, we for the first time constructed AgNWs into 3D porous monolith with novel binary nanowires networks through a facial dip-coating method. The resulting 3D AgNWs monolith exhibited high electrical conductivity and excellent electro-mechanical stability under mechanical deformations, which made it as promising candidate for stretchable conductors. The AgNWs networks on the sponge could be easily transformed into robust 3D Ag/AgCl nanowire networks through thermal welding and in situ chemical transformation processes. This 3D Ag/AgCl nanowire networks exhibited high photodegradation efficiency to methyl orange in a confined flow photoreactor under sunlight. Inspired by the binary network effect on the improved performance of AgNWs stretchable conductors, we also utilized commercial elastic thread with helical microfibers as the template to guide the assembly of AgNWs, and obtained a highly stretchable and conductive 3D helical AgNWs network electrode. Based on this AgNWs electrode, we fabricated a stretchable electronic fabric which had the ability of simultaneously mapping and quantifying the mechanical stresses induced by pressure, lateral strain, and flexion.2. Through dip-coating processes, we fabricated a 3D reduced graphene (RGO) monolith with open macropore structure by using commercial polymer sponge as the template. Because of this open pore structure, MnO2 nanosheets could be uniformly deposited onto the surface of this 3D RGO monolith. The obtained composites monolith combined the electronic double layer capacitor of active material RGO and pseudo-capacitance of MnO2 together, resulting in supercapacitor electrodes with high performance. Based on the resistance change caused by the mutual contact between RGO networks under compression, this 3D RGO monolith could also be used as pressure sensors. The pressure sensitivity of the 3D RGO monolith could be greatly improved by introducing a fractured microstructure design.3. Under the guide of the commercial polymer sponge, SiO2 nanoparticles (NPs) and polydimethylsiloxane (PDMS) was organized on the skeleton surfaces of the sponge, resulted in porous hydrophobic and oleophilic sorbent materials. The SiO2 NPs roughened of the sponge surface, meanwhile, the PDMS coating decreased the surface energy of the sponge surface. We further applied external pumping force on the SiO2 NPs-PDMS coated sponge to realize the continuous collection of oil spills in situ from water surface with high speed and efficiency. Based on this novel design, oil/water separation and oil recovery could be simultaneously achieved in the oil spill remediation process, and the oil sorption capacity was no longer limited to the volume and weight of the sorption material. This novel external pumping technique may bring hydrophobic oil sorbents a step closer to practical application in oil spill remediation.