Many sustainable technologies, such as chemical recycling of waste plastics or the low-carbon intensity production of clean-burning hydrogen gas, have existed for decades. However, despite current political and societal initiatives to minimize plastic waste or transition to hydrogen energy sources, little global progress has been made in their widescale adoption. Over-complexity or critical shortcomings in the economic viability and scalability of these processes often limit their industrial implementation and overall impact. Similarly, although hailed a 21st century ‘wonder-material’, graphene has followed a related trajectory because of the same limiting factors. Flash Joule heating represents a new strategy that can be adapted to address many applications including plastic recycling or upcycling, low-carbon intensity hydrogen production, and graphene synthesis. Flash Joule heating is scalable, low in process complexity, and affords low-cost, efficient, and environmentally friendly production of high-value nanomaterials. This thesis begins by introducing current industrial graphene production methods and applications in chapter 1. Chapters 2-4 highlight the synthesis, characterization, and application of turbostratic graphene from amorphous carbonaceous feedstocks. In chapter 2, simple flash Joule heating synthesizes graphene from waste materials such as ash resulting from the chemical recycling of plastics. The graphene quality is optimized and characterized, and the value of the produced graphene is demonstrated as a reinforcing additive in various composite applications. In chapter 3, graphene with varying 13C/12C isotopic content is prepared, up to 99% 13C content, which results in unexpected spectroscopic findings. In chapter 4, graphene is formed from mixed waste plastics, with quantified efficiency and tabulated environmental burdens, and compared to current industrial methods, using a perspective life-cycle assessment. Taking inspiration from chemical vapor deposition and different bottom-up reaction strategies, other exciting classes of graphitic carbon nanomaterials can be synthesized using flash Joule heating. Holey and wrinkled graphene with significantly increased surface area is synthesized from mixed waste plastics in chapter 5, and applied in electrocatalytic and energy-storage applications. A similar material can be synthesized in a scalable manner using simple alkaline salt templating, and used for water purification applications, as demonstrated in chapter 6. Carbon nanotubes, nanofibers, and hybrid 1-dimensional and 2-dimensional materials can also synthesized through the in situ formation of catalytic growth nanoparticles, upcycling mixed waste plastic to outperform carbon nanotubes and graphene in composite applications, with significant improvements in environmental impact as compared to current carbon nanotube production methods. Lastly, in chapter 8, production of clean hydrogen gas from waste plastic at zero net-cost is demonstrated, due to the co-production of high-value graphene. Through process optimization, flash Joule heating of plastics, with no added catalyst, the highest yet-published yields of hydrogen gas from plastics is achieved and demonstrated for all common consumer waste plastics. Life-cycle assessment and techno-economic analysis demonstrate that the flash Joule heating hydrogen production strategy releases less CO2 than all current methods excluding electrolysis, while affording extreme cost-competitiveness for hydrogen production. Further, through study of the reaction intermediates and other volatiles coupled with thermodynamic and molecular dynamics simulations, the seed-growth, bottom-up hypothesis of graphene formation during flash Joule heating can be further substantiated.