Studies have shown that there are multiple co-existence pollutants in environmental water over recent years. In this study, we report the design and synthesis of magnetic adsorbents incorporating chitosan-silanol groups (Fe3O4@Si-OH@CS) with improved physicochemical properties for the removal of various heavy metals and bacteria from polluted water. Fe3O4@Si-OH@CS was synthesised using the co-precipitation method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET), Vibrating sample magnetometer (VSM), and Zeta techniques were used to characterise. The effects of factors such as pH, adsorption time, and adsorbent dosage were optimised. The results indicated that Fe3O4@Si-OH@CS had high adsorption efficiency and adsorption capacity for Cr (VI), As, Hg and Se. Moreover, Cr (VI) and As have a preferential adsorption effect when multiple metal ions coexist. The adsorption performance of Fe3O4@Si-OH@CS to bacteria was verified using E. coli (gram-negative) and S. aureus (gram-positive). The developed adsorbent also showed good adsorption efficiency for both gram-negative and gram-positive bacteria. Overall, the synthesised Fe3O4@Si-OH@CS adsorbent showed high removal efficiency and adsorption capacity with a stable structure and easy separation. It has promising applications for the removal of heavy metals and bacteria from water.