# Electrospinning-Based Carbon Nanofibers for Energy and Sensor Applications
## 4 Application of Carbon Nanofibers
### Sensor Applications
#### 4.2.2 Warfare Agent Chemical Sensors  
Warfare nerve agents are toxic organophosphorus compounds that were developed during World War II, including G, V, and A types. Due to the quick and clear visible response to the presence of the detecting target, optical measurements have been widely used in research and real-life applications [137]. [PERSON] et al. developed an organic-inorganic hybrid material from conjugated polymer dots, silica, and PVA (Figure 19a) [138]. The dots were attached to the amine function group on half-carbonized PVA-silica NFs. The authors suggested an interesting interaction between the components of the fibers that helps to enhance the fluorescence intensity in the measurements.  
Although the spectroscopy-detecting method has been used for a long time, it still has many limitations caused by its low selectivity and cannot be reused. The use of electrical analysis can overcome these limitations and increase its potential in the field of warfare-agent detection [139]. [PERSON] et al. studied the fabrication of cactus-like CNFs for the detection of dimethyl methylphosphonate (DMMP) (Figure 19b) [140]. The CNFs were embedded with Ni nanoparticles as a seed for the development of smaller-sized carbon fibers from cellulose acetate through the chemical vapor deposition method. It is noted that though the Ni nanoparticles themselves can enhance the signal from the interaction with DMMP, the structure of the cactus-like CNFs was able to significantly improve the surface area and the response signal. In addition, the developed material also has high selectivity  
Figure 18: (**a**) Trichoroacetic acid (TCA), KBrO\({}_{3}\), and NaNO\({}_{2}\) using Co\({}_{3}\)O\({}_{4}\) embedded CNFs [132]. (**b**) Multichannel CNFs decorated with Co\({}_{3}\)O\({}_{4}\) as a glucose sensor [133]. (**c**) CNFs modified using MoS\({}_{2}\) and embedded with SnO\({}_{2}\) for phenacetin/ indomethacin detection [134]. (**d**) Porous CNFs with Fe\({}^{3+}\) for the detection of BPA [136].  
towards DMMP. [PERSON] et al. later introduced a study based on cactus-like CNFs but with the modification of the hexafluoroisopropanol (HFIP) function group (Figure 19c) [141]. The cactus CNFs were doped with HFIP using carboxyl groups formed on the carbon surface by treatment with a strong acid. It is mentioned that HFIP can decrease the response and recovery time of material when there is a change in DMMP in the environment, even with a low concentration of 0.1 ppm.  
Using a PAN/PVP solution mixed with CuCl\({}_{2}\) and CoCl\({}_{2}\) as the precursor of electrospinning, [PERSON] et al. presented CNF composites containing CuO and Co\({}_{3}\)O\({}_{4}\) to study the effects of HFIP on the working performance of the device (Figure 19d) [142]. The fibers were treated with a silane coupling agent to attach carboxyl function groups, which were later used as a bridge to embed a modified HFIP. It was shown that with only a metal-oxide composite, even though the material can detect DMMP, the selectivity is low since the material also responds to other chemicals such as benzene, ethanol, or acetone. The presence of HFIP can enhance the response resistance and response/recovery time. Moreover, it seems that HFIP only enhances the response to DMMP, so it gives the material selectivity.