Bin Zhang,Jingmiao Zhang,Ao Xia,Xinru Tang,Xianqing Zhu,Yun Huang,Xun Zhu,Qiang Liao
Hydrothermal carbonization facilitates microalgae utilization but suffers from low product quality, with no effective solutions. This study investigated the product characteristics and quality enhancement methods of hydrochar, bio-oil, and carbon dots prepared through hydrothermal carbonization of microalgae assisted by non-polar organic solvents (petroleum ether and n -hexane) and polar organic solvents (ethyl acetate, isopropanol, and ethanol). The results showed that non-polar organic solvents were more effective than polar organic solvents in extracting fatty acids hydrolyzed from lipids into the organic phase, reducing amidation with amino acids and lowering bio-oil nitrogen content by 47.0%, with n -hexane exhibiting the best effect. They also promoted Maillard reactions, increasing hydrochar and carbon dots yields by 41.2% and 63.3% while boosting nitrogen content by 48.9% and 15.7%, respectively. This study explored the co-production and upgrading of multiple products in microalgae hydrothermal carbonization with organic solvent assistance, offering insights into process optimization for efficient utilization of microalgae.
Single-step environmentally friendly synthesis of biochar dots (BCDs) was developed using hydrothermal treatment of waste biomass. Using soy residue as the carbon precursor, the resultant BCDs had strong and stable photoluminescence. Characterization by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy indicates that the BCDs prepared were water soluble, spherical, oxygenous and nitrogen-doped carbon nanoparticles with 10–20 nm in diameter. The fluorescence quantum yield of the BCDs was 3.7%. The use of the BCDs as a very effective fluorescent probe for label-free, rapid, and selective detection of Hg2+ and Fe3+ ions was further demonstrated with good linear relationships at 0–50 μM and 10–50 μM, respectively. The minimum detection limits of Hg2+ and Fe3+ were 100 nM and 30 nM. Furthermore, the feasibility of using the BCDs for monitoring of Hg2+ and Fe3+ in open waters was also established.
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