The need for clean water has led to the development of several different water treatment methods as well as to a large number of organic, inorganic, hybrid and/or composite materials that are used in these methods. Cellulose, being a highly abundant biopolymer with meritorious properties, such as high mechanical strength, tunable surface chemistry, high aspect ratio and surface area, to mention a few, is exploited in the current thesis for water treatment applications. Cellulose and its nanoscaled derivatives (i.e. cellulose nanocrystals and cellulose nanofibers) are modified or hybridized to achieve multiple functionalities.

Cellulose and lignocellulose nanocrystals were successfully prepared by mechanical treatment from the residue of bioethanol production and were decorated with zwitterionic polymer grafts through controlled radical polymerization reactions. The presence of residual lignin and polymer grafts was investigated which showed that especially the polymer grafting can significantly improve the antibacterial and antifouling performance of nanocellulose.

Functional cellulose-based membranes were prepared in a one-step water-based process. The membranes were evaluated as adsorbents for the removal of dyes and metal ions as well as metal-free catalysts for the decolorization of dyes Methylene Blue (MB) and Rhodamine B (RhB). The membranes exhibited maximum adsorption capacity of 78.6 mg/g for Co2+, up to 100 % of MB removal efficiency and up to 3-fold increase in the decolorization of MB.

Both in-situ and ex-situ growth of ZIF-8 crystals was performed on the surface of cellulose and nanocellulose and cellulose/ZIF hybrid membranes were manufactured. The adsorption capacity of the membranes was tested with Cd2+, Cu2+, Fe3+, and Pb2+, exhibiting a maximum adsorption capacity of 354 mg/g for Cu2+. Furthermore, the membranes showed potential for use as self-standing electrode for the detection of Pb2+.

Processing of cellulose/alginate composite hydrogels in the form of highly porous beads was successful. The surface of the beads was modified via in-situ TEMPO oxidation for the introduction of carboxyl groups. Adsorption of cationic contaminants as dyes and metal ions (MB and Cd2+ were used as models, respectively) was enhanced with in-situ modification. Removal of metal ions from the mining industry wastewater using modified cellulose/alginate hydrogel beads confirmed the potential of the adsorbent in complex water sources.

All-cellulose flat sheets (100 × 20 cm) were produced via a water-based process using a Formette dynamic sheet former. The sheets exhibited excellent mechanical properties attributed to the alignment of the micro and nanofibers that this process offers. The adsorption performance of the sheets was evaluated both with Irgalite Blue RL and Irgalite Violet H dyes, which are highly used in paper and pulp industries as dyes models, and Fe3+, Mg2+, Cd2+, Co2+, Cr3+, and Mn2+ as metal ion models. A maximum removal efficiency of 83% for IB RL and maximum adsorption capacity of 737 mg/g for Mg2+.

The work shows the potential of cellulose as a sustainable and scalable platform for the tailoring of multifunctional materials for water treatment with cationic pollutants removal, antifouling, antibacterial and sensing capabilities.