Immobilization of TiO2 nanoparticles onto paper modification through bioconjugation

TiO2 is commonly used as a brightening agent for paper, but may also be used on paper as a photocatalyst. The TiO2 aggregates that typically form in/on paper are inefficient both for brightening or photooxidation. We describe, for the first time, the preparation of homogeneously distributed, non-aggregated TiO2 particles on cellulose fibers using explicit bioconjugation with the fusion protein of CBM2a-Strep-tag II/streptavidin/biotinylated TiO2. The maximum absorption of proteins and nanoparticles onto paper were determined to be ca. 6.22 x 10(-2) nm(-2) for CBM2a-Strep-tag II, 1.93 x 10(-2) nm(-2) for streptavidin, and 58 mm(-2) for TiO2 nanoparticles, respectively. The efficiency of photocatalysis of the TiO2-containing paper prepared by this bioconjugation method was demonstrated by the decolorization of UV sensitive dye (reactive black dye 5). Immobilized TiO2 efficiently degraded the dye within about 10 hours. Only after extensive photolysis (12 hours) did sufficient degradation of the bioconjugating linkers occur such that free TiO2 particles and cellulose fibers were found in the supernatant. These experiments demonstrate that bioconjugation of TiO2 to paper leads to an effective, supported photocatalyst system.