Construction of controllable size silver nanoparticles immobilized on nanofibers of chitin microspheres via green pathway

In the present work, nanofibrous chitin microsphere (NCM) was prepared via sol-gel transition from a chitin solution dissolved in a NaOH/urea aqueous system at low temperatures. Ag nanoparticles (AgNPs) were synthesized via an in situ reduction of silver nitrate using trisodium citrate dehydrate and were immobilized on chitin nanofibers to obtain composite microspheres that consist of nanofibers and AgNPs (NCM-Ag). The size of AgNPs could be controlled in the range of 10 to 70 nm, depending on the concentration of AgNO3. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) analyses showed that the chitin nanofibers have a strong affinity toward AgNPs, resulting from the interaction between the acetamino group of chitin and the AgNPs. The NCM-Ag exhibited a perfect nanoporous structure and high surface area, as well as high stability in organic solvents. Moreover, in the catalytic epoxidation of olefin (particularly, the conversion of styrene to styrene epoxide), NCM-Ag exhibited an excellent selectivity of up to 90%. Converting chitin powder into chitin microspheres using an environmentally friendly technique is a green process, which is beneficial for the large-scale synthesis of industrial products. More importantly, this work provides a green synthetic pathway for the construction of size-controlled noble metal nanoparticles immobilized on nanofiber support, which have a wide range of potential applications.