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 C--C, while the powerful oxidant HOO- produced by alkaline hydrogen peroxide can break C--C to generate biomassbased 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 mu M, 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.