Nanoarchitectured biomass-waste derived activated charcoal nanozymes and its application in visual analysis of nitrite in pickled food

The emerging field of nanozymes has introduced unprecedented opportunities and challenges for activated charcoal materials derived from biomass waste. By incorporating specific nanostructures or elements, it is possible to overcome the limitations of traditional activated charcoal, such as insufficient catalytic active sites and poor electron transfer efficiency, thereby unlocking its full potential for various applications. In this study, we successfully synthesized trace Fe-doped activated charcoal (Fe-AC) with a graphene-like structure from biomass waste. The Fe atoms were uniformly dispersed on the activated charcoal support, which possessed a high surface area. This not only significantly increased the number of catalytic active sites but also enhanced electron transfer efficiency, substrate mobility, and collision probability. Compared to pristine activated charcoal, the synthesized Fe-AC exhibited multiple enzyme-mimetic activities, including oxidase-like, peroxidase-like, and catalase-like activities. By leveraging its peroxidase-like activity in conjunction with nitrite-specific diazotization reactions, we developed a portable, smartphone-assisted, on-site ratiometric colorimetric hydrogel sensor for nitrite detection. Utilizing smartphone-based digital imaging, this sensor enabled the quantitative analysis of nitrite at concentrations ranging from 1 to 200 μmol/L, with a detection limit as low as 1 μmol/L. The approximate range of hazardous nitrite concentrations could be easily identified with the naked eye, and the proposed strategy was successfully applied to real sample analysis. This sensor not only maximizes the utilization of waste resources, thereby reducing production costs, but also offers greater economic feasibility and environmental sustainability. Given these advantages, it holds promise for broader applications in various fields.