Transient Laser Photothermal Generation of 3D Graphene for Sensing and Energy Applications

Nanomaterials have shown potential for high-performance functional materials especially in sensing and energy applications. Structuring of nanomaterials, including atomically-thin two-dimensional (2D) materials (e.g. graphene) and combining 2D materials with conventional materials such as metals and polymers can enable new functionalities and high performance by engineering exceptional and outstanding mechanical, electrical, and optical properties. We present a facile and rapid laser photothermochemical processing method to produce 3D porous graphene as well as a nanoassembly of 3D porous graphene and PdNPs from polymer films. Multi-dimensional hybrid nanomaterials combining 3D graphene and 1D metallic nanoparticles are produced in large scale with low production cost by transient laser photothermal processing. The films are photothermally processed using a laser to generate a nanohybrid via photo-induced thermal and chemical processes. The nanohybrid exhibits four-times-enhanced electrical conductivity compared to plain porous graphene, high crystallinity, and coherent covalent metal bonds with a homogeneous size and distribution of PdNPs in the hierarchical micro/meso/macro porous graphene structures, allowing high-performance hydrogen sensing (1 ppm) with outstanding mechanical reliability, flexibility, and durability upon bending and twisting. The nanoassembly is integrated with a wireless sensing platform and hydrogen leakage (1 ppm) is detected by a smartphone. This laser-based nanomanufacturing of the nanoassembly can potentially be applied to wearable detector production platforms in the military and industry. A facile, fast, and scalable laser-induced photothermal method was also used to achieve flexible monolithic bilayer sheets (MBS) of hierarchically porous graphitic carbon (HPGC) and polymeric foam for use in salt-resistant and flexible solar steam generators. The MBS-based self-floating solar steam generator shows outstanding solar desalination performance with a solar thermal efficiency of 83.2% under 1-sun illumination and a high salt-rejection ratio (99.9%). The all-in-one multi-functionalities of the MBS, including broad-spectrum solar light absorption, heat localization, and capillary action enabled efficient solar thermal energy transformation. Our laser-based photothermal method holds promise to achieve high-performance solar thermal systems with substantial cost reduction by scalable production of multiscale hierarchically structured materials from micro-structured polymers.