Seshat’s HD-1D-DNTs: A Green Chemistry Route to Ultra-High-Strength Diamond Nanothreads from Renewable Hemp Biomass

Seshat's HD-1D-DNTs: A Green Chemistry Route to Ultra-High-Strength Diamond Nanothreads from Renewable Hemp Biomass

Abstract

The synthesis of one-dimensional diamond nanothreads (DNTs), materials possessing extraordinary theoretical specific strength, has traditionally relied on high-pressure polymerization of petrochemical aromatic precursors. We report a novel, highly sustainable synthesis route for Hemp-Derived 1D Diamond Nanothreads (HD-1D-DNTs), which we term Seshat's HD-1D-DNTs. This approach adheres strictly to green chemistry principles by sourcing carbon from hemp biomass via a two-stage process: (1) Hydrothermal Liquefaction (HTL) and Catalytic Hydrodeoxygenation (HDO) transform hemp lignin into purified aromatic precursors. (2) These precursors undergo Pressure-Induced Polymerization (PIP) under controlled isothermal compression (~20 GPa) within a Diamond Anvil Cell (DAC). Successful transformation from sp² to the diamond-like sp³ structure is confirmed by the characteristic ~1332 cm⁻¹ band in Raman spectroscopy. This methodology offers a carbon-negative pathway to produce high-performance nano-reinforcement. We propose the integration of functionalized Seshat's HD-1D-DNTs into bio-based Hempoxies, projecting a revolutionary increase in composite tensile strength and fracture toughness, thereby enabling the next generation of lightweight, sustainable materials for aerospace, automotive, and high-performance structural applications.

1. Materials and Methods: Synthesis Protocol

This protocol outlines the lab-scale synthesis of HD-1D-DNTs, emphasizing green chemistry throughout the process.

1.1. Hemp Valorization and Aromatic Precursor Isolation

1. Feedstock Preparation: Dried industrial hemp hurds (lignocellulosic biomass) are milled into a fine powder (< 100 µm) to maximize surface area for subsequent processing.
2. Hydrothermal Liquefaction (HTL): The hemp powder (100 g) is mixed with deionized water in a high-pressure batch reactor. The mixture is heated to 300–350 °C and held at 10–20 MPa for 30 minutes. This process efficiently separates the biomass into a high-quality bio-oil (rich in aromatic oxygenates from lignin), residual char, and an aqueous phase.
3. Catalytic Hydrodeoxygenation (HDO): The bio-oil is combined with supercritical CO₂ (scCO₂)—used as a green, tunable solvent—and passed through a fixed-bed reactor containing a heterogeneous catalyst (e.g., Ni/SiO₂-Al₂O₃). The reaction occurs at 350 °C and 15 MPa under a continuous flow of H₂. This step removes oxygen atoms, yielding highly pure, crystalline aromatic precursors (e.g., furan or benzene derivatives).
4. Purification: The precursor is fractionally condensed, and its purity is verified via Gas Chromatography-Mass Spectrometry (GC-MS).

1.2. Pressure-Induced Polymerization (PIP)

1. High-Pressure Setup: A highly pure, microscopic crystal of the hemp-derived aromatic precursor is loaded into the 100–300 µm bore of a Rhenium gasket within a Diamond Anvil Cell (DAC). A small ruby chip is co-loaded for in situ pressure measurement via fluorescence.
2. Compression and Reaction: Pressure is increased slowly and isothermally (ambient temperature) at a controlled rate of approximately 1.0 GPa/h until the target polymerization pressure of 18–22 GPa is achieved. The pressure is held constant for 12 hours to facilitate the solid-state [4+2] cycloaddition and C-C bond reorganization, forming the sp³ backbone of the HD-1D-DNTs.
3. Decompression: The pressure is released slowly (maintaining the rate of 1.0 GPa/h) to ambient conditions. This critical step preserves the metastable nanothread structure.

2. Characterization and Structure Confirmation

Rigorous analytical techniques are essential to confirm the successful synthesis and diamond-like structure.

• Raman Spectroscopy (Structure Confirmation): This is the primary diagnostic tool. The successful formation of the sp³ diamond structure is confirmed by the complete disappearance of the sp² aromatic vibrational modes (~1600 cm⁻¹) and the appearance of a characteristic broad band near 1332–1350 cm⁻¹, consistent with the diamond nanothread lattice.
• Transmission Electron Microscopy (TEM): High-Resolution TEM (HRTEM) is used to visually confirm the one-dimensional structure and measure the thread diameter (~0.2–0.6 nm). Selected Area Electron Diffraction (SAED) patterns verify the unique crystalline packing.
• X-ray Diffraction (XRD): Powder XRD provides data to confirm the formation of a novel, highly dense, crystalline phase, verifying the transformation from the precursor lattice to the DNT structure.

3. Discussion: Applications and Sustainability Impact

3.1. Competitive Advantages

The use of hemp as a feedstock for HD-1D-DNTs confers both performance and sustainability benefits:

• Renewable Sourcing: Sourcing carbon from hemp biomass, a rapidly renewable and CO₂-sequestering crop, provides a strong Green Chemistry advantage over petrochemical-derived DNTs.
• Superior Specific Strength: DNTs possess a theoretical ultimate tensile strength of ~134 GPa, potentially doubling that of the highest-performing carbon nanotubes (CNTs). This results in the highest specific tenacity known for any fiber material.
• Interface Optimization: The sp³ backbone results in a highly functionalizable surface (e.g., hydrogen-capped), enabling direct covalent coupling with the bio-epoxy matrix of Hempoxies. This maximizes interfacial load transfer, addressing the common weakness in conventional nanocomposites.

3.2. Integration into Hempoxies and Industrial Applications

The primary application is the reinforcement of Hempoxies—bio-based thermoset composites.

• Hempoxies Enhancement: Integration of Seshat's HD-1D-DNTs is expected to dramatically increase the composite's Young's Modulus, tensile strength, and fracture toughness, positioning these bio-composites as high-performance, lightweight structural materials suitable for demanding applications.
• Industrial Scale-Up: Industrial production will necessitate replacing the batch-mode DAC with continuous high-pressure systems, such as modified Belt-Type Presses, alongside large-scale, continuous-flow biorefining for precursor generation.
• Other Markets: Beyond Hempoxies, Seshat's HD-1D-DNTs are targeted for use in aerospace structural components (where weight savings are critical), ballistic materials, and advanced nano-energy storage devices due to their unparalleled strength-to-weight ratio.