Woo-Jae Kim

The global accumulation of plastic waste has spurred extensive research into chemical recycling methods to mitigate environmental issues and convert waste into valuable resources. A major challenge in plastic recycling is the requirement for presorting, which complicates processing and increases costs. Here, we demonstrate alkaline thermal treatment (ATT) as a highly efficient strategy for directly converting mixed plastic waste, including polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP), into clean hydrogen energy at low temperatures and atmospheric pressure. Unlike conventional gasification, NaOH-assisted ATT enables plastic decomposition at significantly lower temperatures while producing high-purity hydrogen and minimizing carbon emissions. A key advancement in this work is the oxidation pretreatment of PP and PE, which enhances their reactivity in ATT and allows efficient hydrogen generation even from typically resistant polyolefins. Through systematic optimization of the NaOH-to-plastic ratio and thermal oxidation conditions, hydrogen yields of 43.7, 51.9, and 30.2 mmol/g _plastic were achieved for PET, PE, and PP, respectively. Furthermore, ATT efficiently converts both individual and mixed plastic waste without requiring extensive separation, demonstrating its commercial potential and scalability with real-world waste compositions. Overall, this study establishes ATT as a promising and sustainable solution for plastic waste management and clean energy production, providing an economically viable low-carbon pathway for hydrogen generation.

This study presents a novel single‐step method for producing sodium silicate and high‐purity hydrogen from rice husk biomass with reduced CO ₂ emission using alkaline thermal treatment (ATT). Conventional methods extract amorphous silica from rice husk through an energy‐intensive, CO ₂ ‐emitting process, followed by a separate reaction with sodium carbonate to synthesize sodium silicate. In contrast, the proposed method eliminates this additional step by directly generating sodium silicate while simultaneously producing hydrogen, ensuring a reduced carbon‐emission process. ATT enables interconnected reactions, including in‐situ CO ₂ capture, enabling decarbonized hydrogen production as an energy carrier and sodium silicate for high‐value applications. The use of NaOH promotes hydrogen generation at lower temperatures while capturing CO ₂ as solid carbonates, distinguishing this process from conventional gasification. Additionally, sodium carbonates formed in situ react with SiO ₂ in rice husk ash, enabling direct sodium silicate synthesis. Experimental results demonstrate that ATT at 950°C, with a rice husk‐to‐NaOH ratio of 1:3 and 1.9 g of SiO ₂ , yields up to 5.1 g of sodium silicate and 51 mmol of hydrogen per gram of rice husk, with reduced CO ₂ emission. Optimizing reaction conditions through elemental analysis enhances hydrogen yield and improves sodium silicate synthesis, highlighting the sustainability of this approach.

Carbon nanotubes (CNTs), having either metallic or semiconducting properties depending on their chirality, are advanced materials that can be used for different devices and materials (e.g., fuel cells, transistors, solar cells, reinforced materials, and medical materials) due to their excellent electrical conductivity, mechanical strength, and thermal conductivity. Single-walled CNTs (SWNTs) have received special attention due to their outstanding electrical and optical properties; however, the inability to selectively synthesize specific types of CNTs has been a major obstacle for their commercialization. Therefore, researchers have studied different methods for the separation of SWNTs based on their electrical and optical properties. Gel chromatography methods enable the large-scale separation of metallic/semiconducting (m/s) SWNTs and single-chirality SWNTs with specific bandgaps. The core principle of gel chromatography-based SWNT separation is the interaction between the SWNTs and gels, which depends on the unique electrical properties of the former. Controlled pore glass, silica gel, agarose-based gel, and allyl dextran-based gel have been exploited as mediums for gel chromatography. In this paper, the interaction between SWNTs and gels and the different gel chromatography-based SWNT separation technologies are introduced. This paper can serve as a reference for researchers who plan to separate SWNTs with gel chromatography.

Current thermochemical methods to generate H₂ include gasification and steam reforming of coal and natural gas, in which anthropogenic CO₂ emission is inevitable. If biomass is used as a source of H₂, the process can be considered carbon-neutral. Seaweeds are among the less studied types of biomass with great potential because they do not require freshwater. Unfortunately, reaction pathways to thermochemically convert salty and wet biomass into H₂ are limited. In this study, a catalytic alkaline thermal treatment of brown seaweed is investigated to produce high purity H₂ with substantially suppressed CO₂ formation making the overall biomass conversion not only carbon-neutral but also potentially carbon-negative. High-purity 69.69 mmol-H₂/(dry-ash-free)g-brown seaweed is produced with a conversion as high as 71%. The hydroxide is involved in both H₂ production and in situ CO₂ capture, while the Ni/ZrO₂ catalyst enhanced the secondary H₂ formation via steam methane reforming and water-gas shift reactions.