*2.3. Preparation of Fe3O4@ZnS@MPS*

A quantity of 5 mL of Fe3O4@ZnS ethanol solution was placed in a round-bottom flask. Then, 5 mL 3-sulfhydryl-1-propane sodium (MPS) (89.105 mg, 0.1 mmol/L) ethanol solution was added. The mixture was then stirred in a water bath at 40 ◦C for 4 h in the dark. After the item was attracted by a magnetic force, it underwent a thorough cleansing process with ultrapure water and ethanol. Water was added to the prepared Fe3O4@ZnS@MPS microspheres to make a dispersion solution.

#### *2.4. Instrumentation*

The surface topography of the microspheres was observed via a scanning electron microscope (SEM) (Quanta 200, FEI, Hillsboro, OR, USA) (EHT = 5.00 kV) and a transmission electron microscope (TEM) (JEM 2100, JEOL, Tokyo, Japan) (Accelerating Voltage = 200 kV). Fourier transform-infrared (FTIR) spectra were obtained from a spectrometer (Thermo Scientific Nicolet IS50, Thermofisher, Waltham, MA, USA). X-ray diffraction (XRD) images were obtained using an X-ray diffractometer (D8FOCUS, Bruker, Berlin, German). The measurement was conducted using CuKα radiation (λ = 1.5406 Å) in the range of 2θ = 20◦–80◦ at a scan speed of 2◦/min. XPS spectra data were obtained on an X-ray photoelectron spectrometer (Krayos AXIS Ultra DLDX, Shimadzu, Tokyo, Japan) (Analyzer Mode: Constant Analyzer Energy: Pass Energy 30.0 eV; Energy Step Size: 0.100 eV). The magnetism (VSM) was measured using a vibrating sample magnetometer (7404 vibrating sample magnetometer, LakeShore, Carson, CA, USA). The thermogravimetric (TG) curves were obtained using a thermalgravimetric analyzer (Discovery SDT650 synchronous TGA-DTA Instrument, TA, Los Angeles, CA, USA). Fluorescence spectra were measured on a fluorescence spectrophotometer (FluoroMax-plus instrument, Horiba, Austin, TX, USA) with an excitation of (370) nm. The concentration of Ag<sup>+</sup> in solution was determined by atomic absorption spectrometry (AAS) (ICP-OES:Thermo Fisher iCAP 7400, Thermofisher, USA).

#### *2.5. Materials*

Other chemicals used in this study, such as FeCl3·6H2O, CH3COONa·3H2O, Zn(ac)2, Na2S, polyethylene glycol 2000, 3-sulfhydryl-1-propane sodium, Co2+, Pb2+, Ni2+, Hg2+ , Al3+, Cu2+, Zn2+, Cd2+, Fe3+, Fe2+, K<sup>+</sup> , Ca2+, and NaCl, were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd. (Shanghai, China).
