A temperature-sensitive and fluorescent Tr-CD/AuNP-based catalyst for efficient, monitorable, and recyclable catalytic reactions

Gold nanoparticles (AuNPs) have been widely used as efficient and environmentally friendly catalysts due to their high specific surface area and abundant active sites. However, AuNP-based catalytic systems face several challenges, including the instability of AuNPs during the reaction, the difficulty in monitoring the process, which can easily result in insufficient reaction due to short reaction time or waste of resources due to long reaction time, as well as issues of catalyst recovery. This study proposes a novel catalyst integrating various functions, such as high stability, the capacity for real-time monitoring of the catalytic process, and rapid recycling. Temperature-sensitive polymers (HPEI-IBAm) terminated with isobutyramide (IBAm) groups were prepared by reacting isobutyric anhydride with hyperbranched polyethyleneimine (HPEI). Subsequently, temperature-sensitive and reducing fluorescent carbon dots (Tr-CDs) were synthesized using HPEI-IBAm as a carbon source. Tr-CDs can reduce the HAuCl₄ precursor in situ, yielding high-performance catalysts, Tr-CDs/AuNPs, with both temperature-sensitive and fluorescence properties. With the help of changes in fluorescence intensity and the real-time synchronous change in the reaction conversion rate, monitoring of the catalytic reaction process is achieved. Moreover, their temperature sensitivity enables the rapid recovery of the catalysts. Using the reduction of p-nitrophenol as a model, we thoroughly investigated the catalytic performance of Tr-CDs/AuNPs. Importantly, the catalytic process exhibited a good linear relationship between the change in fluorescence intensity and the reaction time (R² = 0.9993) and maintained a synchronous change with the conversion rate, enabling the monitoring of the reaction process. Meanwhile, the catalytic efficiency of this catalyst remained above 90% after five recycling and reuse cycles, indicating no obvious decline in catalytic activity. This catalyst demonstrates good performance, reusability, and real-time reaction monitoring, promising bright application prospects.