Preparation of high-yield carbon quantum dots and paper-based sensors from biomass wastes by mechano-chemical method

The synthesis of carbon quantum dots (CQDs) from biomass through a "bottom-up" method has attracted a great deal of interest because of its outstanding environmental and economic advantages. However, the yield of biomass-based CQDs is still low due to the high polymerization of biochar. In this study, we propose a new approach for harvesting high-yield biomass-based CQDs by integrating mechanochemistry and strong chemical oxidation. Ball milling can reduce the particle size and resistance of biochar and increase the contents of CC, while the powerful oxidant HOO- produced by alkaline hydrogen peroxide can break CC to generate biomass-based CQDs. Using this two-step process, the yields of biomass-based CQDs reached 57.75% for blue-green algae, 65.8% for straw, 47.9% for corn protein meal, and 45.35% for Typha angustifolia. Based on the excellent sensitivity and selectivity for Fe3+ of biomass-based CQDs, CQDs paper-based sensors were prepared for expedient and precise detection of Fe3+ in surface water, wastewater treatment plant effluent, and tap water. When the Fe3+ content is between 0 and 60 μM, the R2 of Fe3+ detection by blue-green algae CQDs can reach 0.9956. This work provides a new and reliable method for the large-scale preparation of biomass-based CQDs and expands their environmental applications.