Surface modification of natural cellulose substances: toward functional materials and applications

Combining various synthetic chemical processes and biological assemblies provides a promising strategy for the design and fabrication of functional materials with tailored structures and properties. The unique multilevel structures and morphologies of natural cellulose substances such as ordinary commercial laboratory filter paper make them ideal platforms for the self-assemblies of various functional guest molecules that are to be deposited on the surfaces of their fine structures, and the resulting composite matters show significant potentials for various applications. The surface sol-gel process was employed to deposit ultrathin metal-oxide (e.g., titania and zirconia) gel films to coat the cellulose nanofibers in bulk filter papers; thereafter, monolayers of specific guest substrates were immobilized onto the surfaces of the metal-oxide gel films. Highly selective, sensitive, and reversible chemosensors based on the surface modification of filter paper were obtained toward the fluorescence and colorimetric detection of various analytes such as heavy-metal ions, inorganic anions, amino acids, and gases. Cellulose-based composite materials with superhydrophobic, antibacterial, or luminescent properties were fabricated by self-assembly approaches toward practical applications.