**4. Conclusions**

The combination of the zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) and the hydrophilic bacterial nanocellulose yielded nanocomposite membranes that are proficient in adsorbing anionic and cationic organic dyes. The optically transparent nanocomposites display high water-uptake capacity in different pH media, thermal stability up to 250 ◦C, and good mechanical properties (Young's modulus ≥ 430 MPa). Moreover, these zwitterionic membranes inhibited the growth of both Gram-positive (*S. aureus*) and Gram-negative (*E. coli*) pathogenic bacteria with maxima of 4.3– and 1.8–log CFU reduction, respectively, for the nanocomposite composed of 79 wt.% of cross-linked PMPC. Furthermore, their dye removal capacity was demonstrated by a dye adsorption amount of 4.44 ± 0.32 mg g<sup>−</sup><sup>1</sup> of MB and 4.56 ± 0.43 mg g<sup>−</sup><sup>1</sup> of MO for the membrane with the higher content of zwitterionic polymer (*i.e*. 79 wt.% of PMPC). The successful fabrication of these zwitterionic PMPC/BNC nanocomposite membranes with antibacterial activity opens novel avenues for the generation of bio-based adsorbents to address the complex issue of water remediation of anionic and cationic dyes.

**Author Contributions:** C.V. designed and performed the experiments, analyzed the data and wrote the paper; C.M. and A.A. carried out the antibacterial assays and analyzed the corresponding data; A.J.D.S. and C.S.R.F. contributed to the structural, morphological, thermal and mechanical data interpretation; all authors participated in the critical revision of the paper.

**Funding:** This work was developed within the scope of the projects CICECO – Aveiro Institute of Materials (UID/CTM/50011/2019) and CESAM (UID/AMB/50017/2019), financed by national funds through the FCT/MEC. The research contract of C. Vilela is funded by national funds (OE), through FCT – Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. FCT is also acknowledge for the research contract under Stimulus of Scientific Employment 2017 to C.S.R. Freire (CEECIND/00464/2017).

**Conflicts of Interest:** The authors declare no conflict of interest.
