Cellulose nanocrystals (CNC), MnO 2 , CNC-doped MnO 2 , and Zr/CNC-doped MnO 2 were prepared with a hydrothermal method to assess their photocatalytic and antibacterial properties. Various characterizations were undertaken to determine the phase composition, the existence of functional units, optical characteristics, elemental analysis, surface topography, and microstructure of the prepared materials. Sample crystallinity was improved, whereas a decrease in crystallite size was observed with increasing amounts of dopants. Incorporation of dopants (CNC and Zr) into MnO 2 instigated a transformation in morphology from nanoclusters to nanorods with different diameters. Furthermore, photocatalytic activity experiments indicated a more effective degradation of methylene blue (MB) dye with CNC-doped MnO 2 and Zr/CNC-codoped MnO 2 while enhancing the bacterial efficacy for both G +ve and G −ve. Density functional theory was utilized to model the structures and elucidate their bonding and charge transfer mechanisms. The Zr/CNC-MnO 2 system showed charge depletion around Mn atoms, while charges were observed to accumulate around oxygen atoms.