Fabrication And Properties Of Chemosensors Based On Nano-Precise Coating Of Nature Cellulosic Materials

The optical sensors that allow on-site, real time qualitative or semiquantitative detection without the use of any complicated spectroscopic instrumentation have received a great deal of attention. Colorimetric sensors, in particular, are extremely attractive because they can be observed easily by the naked eyes and own the advantage of simple-to-use. As we known, cellulosic substances are the world's most abundant organic raw materials. In natural cellulosic materials, such as paper, cotton, wood, cloth, cellulose is organized in a will-defined cellular hierarchical structure with large surface area through multiple hydrogen bonding. Therefore, it's an ideal choice to employ natural cellulosic substances as scaffold to design chemosensors.Herein, with natural cellulose substance employed as the starting material, heavy metal ion-trapping materials and colormetric chemosensors were prepared through combination of the surface sol-gel process and subsequent further modification. These materials were used for the detection and adsorption of heavy metal ions, and colormetric sensing of Hg2+ or anions (such as F-, NO2-) in aqueous media. The details are as follows:1. The fabrication and properties of heavy metal ion-trapping materials. With commercial filter paper employed as the starting material, the heavy metal ion-trapping materials were developed. The approach is based on the surface sol-gel process as applied to covering of cellulose nanofibers with SiO2 gel layers by using tetramethyl orthosilane (TMOS) as precursor, and followed by further modified with N-[3-(trimethoxy- silyl)- propyl] ethylendiamine or (3-Mercaptopropyl) trimethoxy silane. The resulting functional materials can be employed to adsorb trace level of heavy metal ions (Cu2+, Hg2+) from aqueous solutions. Beyond the immediate applications in environmental cleanup, the method provides a unique technology to design and fabricate hybrid metal oxide nanotubular materials by calcining the functional substances which have adsorb heavy metal ions already. 2. The fabrication of colorimetric sensing material based on natural cellulose substance, and used for the detection of Hg2+ in aqueous media. Employing a repetitive surface sol-gel technique, ultrathin metal oxide gel layers can be deposited onto the individual nanofibres of cellulosic materials. Such a nanocoating process made it possible to convert the cellulose substances into advanced functional materials, i.e., metal ion chemosensors. Herein, a novel, reversible cellulose based colorimetric sensing material was prepared by immobilization of ruthenium dye (N719) monolayer onto titania ultrathin gel film pre-coated cellulose nanofibres. With commercial filter paper employed as the starting material, the resultant sensor exhibits an extraordinary selectivity and sensitivity, as well as an obvious color change from dark purple to orange in the presence of mercury salt in aqueous solution with the detection limit for Hg2+ estimated to be～10 ppb by naked eyes. Furthermore, the coloration response in the presence of Hg2+ is not influenced by addition of other metal ions (100 times of the concentration of Hg2+). The colorimetric sensing material also processes preferable detection reversibility of Hg2+ by treatment with KI aqueous solution. In addition, the ultrathin titania coating of cellulose nanofibres provides the essential platform for N719 molecularsto be deposited, but the thickness of the titania ultrathin film has no obvious influence for the colorimetric sensing of Hg2+3. The fabrication of colorimetric sensing material based on natural cellulose substance, and used for the detection of F- in aqueous media. Herein, a filter paper based colorimetric sensing material was prepared by immobilization of alizarin complexone (AC) monolayer onto titania ultrathin gel film pre-coated cellulose nanofibres. The resultant sensor exhibits an extraordinary selectivity and sensitivity, as well as an immediate and obvious color change from yellow to orange in the presence of F- in aqueous solution, and the detection limit is estimated to be～500 nM by naked eyes. The selectivity of F- over other anions is remarkably high. And the coloration response can be observed only in the presence of F-4. The fabrication of colorimetric sensing material based on natural cellulose substance, and used for the detection of NO2- in aqueous media. Herein, a colorimetric sensing material was prepared by immobilization of naphthylamine monolayer onto titania ultrathin gel film pre-coated cellulose nanofibres. Then the functional modified paper was immersed into the mixed aqueous solutions of Aminobenzene sulponic acid and anions for the detection of NO2-. The sensing material exhibits an extraordinary selectivity and sensitivity, as well as an obvious color change in the presence of NO2- in aqueous solution with the detection limit for NO2- estimated to be 2μM by naked eyes. Furthermore, the coloration response in the presence of NO2- is not influenced by addition of other anions.