Modification Of Carbon Nanotubes By Chemical Oxidation And Their Application In Chemical Sensing

Carbon nanomaterials, such as carbon nanotubes and graphene, have the common properties as nanomaterials:surface effects, volume effects, quantum effects and macroquantum tunnel effects. They also have unique electrical properties, good mechanical hardness, large surface area and special optical properties. Therefore, recently they have attracted much attention. The prerequisite of many potential applications of carbon nanotubes is the good solubility or dispersion in water or other solvents, and thus the modification of carbon nanotubes for good solubility or dispersion became a first-line task for the potential applications. There are mainly two kinds of methods involving covalent and noncovalent modifications used to disperse the carbon nanotubes well in any solvent in recent years. For all, a simple and effective method to prepare well dispersed carbon nanotubes is one of first-line tasks in recent researches, and it is important for the research on the properties and applications of carbon nanomaterials. The near-infrared fluorescence of carbon nanotubes have been discovered since it can be applied to biochemical sensors and fluorescent imaging in vivo. But the visible fluorescence of carbon nanotubes is still unclear, which can learn about the fluorescent properties of carbon nanotubes in deeply and be applied to chemical sensors.In this study, carbon nanomaterials were treated by mixed concentrated acids, and the products with good dispersivity and strong visible fluorescence were obtained. For the fluorescent properties, these oxidized products can be used in pH and metal ions sensors. The dissertation discribed as follows: 1. The strong visible fluorescence properties and sensors of multi-walled carbon nanotubes (MWCNTs) which were obtained by oxidation were studied. The raw multi-walled carbon nanotubes was treated by mixed concentrated acids, and attained oxidized MWCNTs. Oxidized MWCNTs can dispersed well and stable in water, and the dispersivity was found to be responsible to pH value. The dispersion of oxidized MWCNTs shows green visible fluorescence under UV lamp. The visible fluorescence, implying the potential use as a pH sensor, and the main group and transition metal ions are distinguishable based on the change of the visible fluorescence.2. The strong visible fluorescence properties and sensors of single-walled carbon nanotubes (SWCNTs) which were obtained by oxidation were studied. A novel and simple method to modified SWCNTs was reported, which can prapared well dispersed SWCNTs with strong visible fluorescence in water. The visible fluorescence was found to be responsive to pH value and metal ions, which can be used as pH and metal ions sensors. The tunable emission ability of oxidized SWCNTs depending on the excitation wavelength and a novle self-excitation and emission process were found.3. Oxidized MWCNTs and graphene oxide nanoparticles (GONPs) with tunable fluorescent properties were prepared, and the selective detection of heavy metal ions were studied. Different sizes oxidized MWCNTs and GONPs were prepared by continuous chemical oxidation with MWCNTs. These GONPs were found to show multiclourful fluorescence, which is bathochromic-shifted as the increase of the level of oxidation, the visible fluorescence color changed from green to yellowish-green, following yellow and orange-red stepwisely. These results suggest the degree of oxidation of the products formed from each of oxidized steps can be monitored by fluorescence emission spectrascopy and can be used to prepare tuable fluorescent sensors. The visible fluorescence is responsible to pH value, which is expected to use as a pH sensor. All the GO nanoparticles show high sensitivity for detection of Cd2+among the usual heavy metal ions.