A facile and green method was utilized for preparing an efficient dual function adsorbent as a filter for capturing crystal violet (CV) dye and an inhibitor for the growth of Escherichia coli based on interpenetrating networks (IPNs) between N,N,N-trimethyl chitosan (TMC) and xanthan gum (XG) in different weight ratios. The IPNs showed an excellent CV dye adsorption capacity (94.4%, Q_max = 555.6 mg g⁻¹) at the optimum conditions chosen in this study, where 40 mg of the adsorbent was used for 50 mL of the 450 mg L⁻¹ CV solution at pH 7, temperature of 30 °C and the equilibrium adsorption time of 6 h. The adsorption data were well fitted to the Langmuir isotherm model. The adsorption kinetics exhibited pseudo-first order and intraparticle diffusion model participating in the mechanism of CV adsorption on IPN surface. The antibacterial activity test exhibited that all TMC/XG IPNs inhibited growth of E. coli, suggesting potential application as an antibacterial adsorbent in wastewater treatment.