*2.1. Synthesis of SiO2 Microspheres*

The chemical reagents used in this experiment were obtained from Sinopharm Group Co., Ltd. (Shanghai, China). SiO2 microspheres were prepared using the well−established Stöber method [18]. First, 200 mL ethanol–water mixture (VE:VW = 4:1) was prepared, and ultrasonic treatment was performed for 3 h to form a uniformly dispersed solution. Then, 5 mL ammonia and 3 mL tetraethylorthosilicate (TEOS) were added separately into the above solution and reacted for 24 h. SiO2 microspheres were collected by centrifugation, washed with ethanol–water, and vacuum dried for 12 h.
