Hydrothermal carbonization of Azolla biomass for derived carbon as potential sustainable materials for efficient photosynthesis in agricultural plants and as electrochemical electrode materials

Using biomass to synthesize carbon-based materials has garnered significant interest due to its broad range of applications. Additionally, biomass is a sustainable source with the potential to produce various carbon products. However, the development of practical and efficient processes to enable the high-efficiency utilization of biomass is increasingly attracting attention. To maximize this potential, biomass-derived carbon dots (BioCDots) and hydrochar carbons (HCs) were obtained through a single-step hydrothermal carbonization (HTC) process (140–200 °C for 3 h) from Azolla biomass, without any activation. The physicochemical properties, plant photosynthesis, and electrochemical behavior of the synthesized carbon were evaluated. The BioCDots exhibited a small size and emitted a strong blue fluorescent under UV light. A quantum yield of 20.97% was attained at 200 °C for 3 h. Meanwhile, the obtained residual solids (HCs) exhibited micro/mesopore structure with surface area, pore volume, and average pore diameter of 81.20 m²/g, 0.3963 cm³/g, and 17.18 nm, respectively. For agricultural applications, BioCDots demonstrated a dose-dependent effect on seed germination and could enhance photosynthesis activity in tomato plants, increasing chlorophyll and carotenoid content by approximately 14–35% and 17–31%, respectively, under foliar application at concentrations of 50–300 µg/mL. The HCs revealed a noticeable nitrogen-self-doped hydrochar carbon (NHCs) and delivered a specific capacitance of 83.91 Fg⁻¹ at 0.1 Ag⁻¹ and retains 72% at a current density of 5 Ag⁻¹ in 1 M H₂SO₄ aqueous solution. Promising preliminary results exhibit great potential of BioCDots and HCs from Azolla biomass as foliar agents for stimulating agricultural plant growth and provided a novel proper carbon electrode materials selection for energy storage applications.

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