Surface Functionalized Carbon Materials For Electrochemical Detection Of Nitroaromatic Compounds

Nitroaromatic compounds (NACs) are widely used in the manufacture of dye, pesticides, medicines, and chemical fibers. NACs are toxic and persistent so that may contaminate the soil and rivers seriously in the vicinity of places where they are manufactured, used, stored and transported. NACs are the main constituent of explosives that are always utilized by terrorists to make weapons, which is a serious threat to social security. We need to improve detecting methods to realize real-time detection and field detection, which should be sensitive, reliable, portable and easy to operate. Based on the electrochemical technologies for detecting NACs reported before, we synthesized metal nanoparticles modified BP carbon and nonmetallic functional groups modified carbon structures as sensing materials. The mechanism of electrochemical reduction of NACs on each material was observed and the detecting condition was selected to optimize the sensing performance for ultra-trace NACs with high sensitivity, low limit of detection and high efficiency.First, Cu and CuNi nanoparticles were loaded on oxidized BP carbon (o-BPC) aiming to enhance the sensitivity of detecting nitrobenzene on o-BPC. However, the sensitivity was not enhanced by loading of Cu of CuNi and was not decreased by elimination of metal nanoparticles by HCl, which indicating that O-containing groups on the surface of oxidized BP carbon mainly contribute to the enhancement of sensitivity of nitrobenzene.Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron emission microscopy (XPS) was employed to characterize BP carbon before and after oxidation, which proved that the atomic O/C ratio increased from 3.77% to 8.53% and hydroxyl groups (-OH) were largely introduced to the surface of BP carbon. Sensitivity was enhanced by 2 times and onset potential by 121 mV, peak potential by 143 mV, which mainly due to the interaction between the electron-donating -OH and the electron-accepting nitroaromatic molecules. Meanwhile, the background current has also increased by 3 to 4 times. The sensitivity of 0-1000 ppb nitrobenzene on oxidized BP carbon modified glassy carbon electrode was-3.67 nA·ppb-1, while the linear correlation coefficient was 0.9685 and the limit of detecion was 10.9 ppb.Then, N-doped nanoporous carbon (NPC) was synthesized from tripolycyanamide and EDTA in a catalytic pyrolysis way, which was catalyzed by Cu(NO3)2. NPC was characterized by XPS and Transmission electron microscopy (TEM) and was proved to contain more N and O and be full of nano pore path. Sensitivity of nitrobenzene on NPC was 3 times while background current was more than 7 times as much as on oxidized BP carbon, which made it hard to detect ultra-trace NACs. The ensitivity for the detection of nitrobenzene in the range from 0 to 1000 ppb on NPC was -21.1 nA·ppb-1 while the linear correlation coefficient was 0.9820 and the limit of detecion was 85.3 ppb.Finally, hydroxyl-rich carbon spheres (HCSs) were synthesized from glucose in hydrothermal way to achieve microspherical carbon in diameter of 250-600 nm. HCSs were characterized by XPS and FT-1R and were illustrated to have large amount of C-OH on the surface, which was of 80% in all surface C atoms that substituted by functional groups. The sensitivity of nitrobenzene on HCSs was enhanced by the rich -OHs as electron-donating groups interacting with nitroaromatic molecules as electron-accepting groups to strengthen the deposition process. Nitrobenzene, dinitrobenzene and trinitrobenzene of 0-100μM and 0-1000 ppb were detected on HCSs by square wave voltammetry. The sensitivities were -6.71 nA·ppb-1,-6.80 nA·ppb-1,-6.65 nA·ppb-1, the linear correlation coefficient were 0.9978, 0.9995,0.9994, respectively and the limit of detection was 1.2 ppb for each compound. In addition, according to the linear sweep voltammetry and cyclic voltammetry under different scan rates, it is infered that the reduction of nitrobenzene on HCSs was a product diffusion controlled reaction. All the work listed above presents a effective solution for detecting NACs with high sensitivity, stability, reliability and low background current and low limit of detection.