More adsorption sites were exposed in the adsorption tubes than in aggregated CNTs due to the aligned structure of the CNTs, which were separated individually and linearly stretched. To increase the adsorption capacity of the CNT adsorption tubes, an appropriate fabrication method or functionalization of CNTs is required. However, it is a challenge to estimate the remaining life of the adsorbents or to determine when the adsorbents must be replaced.
Hazardous chemicals
Several types of well-known CWAs such as nerve agents, blister and blood agents, etc. After the development of G-agents, V-agents such as VX gas, which can work in contact with the skin and are stable for a long time without degradation, were developed. They cause severe blistering of the skin and damage to the eyes, and they also attack the respiratory system, such as the respiratory tract and lungs.
Removal of hazardous chemicals
It uses adsorbents with a high specific surface such as activated carbon, zeolite, charcoal and silica and can remove organic pollutants efficiently. Mechanical filtration: This cleaning method uses a size exclusion method using filters such as the HEPA filter. However, the oxidation process can produce dangerous by-products such as formaldehyde and acetone, and maintaining the catalysts is complicated.16 Various methods are also used to increase the efficiency of air cleaning.
Carbon nanotubes
- Structure of CNT
- Synthesis of CNTs
- Adsorption properties of CNTs
- Application of adsorption properties of CNTs
In addition, CNTs can also be classified according to the number of CNT walls: SWNTs and MWNTs. Thus, relatively narrow diameter and uniform CNTs can be synthesized (Fig. 5a, b left and right). The π-π coupling between them can cause the adsorption of chemicals on the CNT surface.
Development of the CNT adsorption tube
Fabrication of CNT based adsorption tubes
- Synthesis of vertically aligned carbon nanotubes
- Fabrication of CNT-adsorption tube using heat shrink tubing
- Characterization of CNT-adsorption tube
In this study, two types of CNT-adsorbing tubes were prepared; pristine CNT adsorption tubes and acid-treated CNT adsorption tubes. A VA-CNT array which has an array diameter of 1.7 mm was delicately detached from the silicon substrate without any collapse of the CNT array structure. To prepare acid-treated CNT adsorption tubes, pristine CNT adsorption tubes were elongated using a Pharmed BPT tube, and then 20% (w/w) nitric acid heated to 80°C was poured into the tubes of CNT adsorption through a peristaltic pump for 1. h. Properties of pristine VA-CNTs.
The morphological changes of the produced CNT-adsorption tube were observed by optical microscopy and SEM (Figure 16). Although the diameter of the PTFE heat-shrink tube can be reduced by about 50% according to the data sheet, the diameter of the CNT-adsorption tube radially decreased by about 35% from 1.7 mm to 1.1 mm due to insufficient contractile force to fully densify the CNT- is in. (Figure 16a). Most of the VA-CNTs were curled and partially collected before heat treatment (Figure 16b left).
On the other hand, VA-CNTs were straightened and the gaps between each VA-CNT were reduced by compaction caused by Van der Waals interaction between CNTs after heat treatment (Figure 16b, right).91 As a result of the heat treatment, the smaller pores for adsorption in the VA-CNT adsorption tube were made. In the CNT adsorption tubes, we expected that the two types of pores between CNTs were mainly formed: interstitial pores and external surface pores (Figure 17a). Images of CNT-embedded heat shrink tubing. a) Optical images of adsorption tubes before and after heat treatment.
The acid-treated CNT adsorption tube was also fabricated for further improving the adsorption capacity.
Adsorption properties of CNT based adsorption tubes
- Adsorption experiment procedures
- Flow rate dependent adsorption
- pH dependent adsorption
- Concentration dependent adsorption
- Comparison of adsorption capacity
- Stability of CNT-adsorption tubes
In both CNT adsorption tubes, the maximum adsorption capacities were obtained at a flow rate of 10 µl/h. The maximum adsorption capacity of the pristine and acid-treated CNT adsorption tubes was 43.3 mg/g and 109 mg/g at 10 µl/h, respectively. When these results were compared, the pH-dependent adsorption capacity of the solution was predominantly affected in the acid-treated CNT adsorption tubes (Figure 20, right).
In both pure and acid-treated CNTs, the adsorption capacity increased continuously as the concentration of analytes increased. The adsorption capacities of the pristine CNT adsorption tube for the three phenolic compounds prepared as variable concentrations were shown in Figure 23 (left). The amorphous carbon atoms were almost removed by acid treatment (Figure 24b), which increased the number of exposed adsorption sites of the CNTs.
As a result of cleaning, the adsorption capacities of acid-treated CNTs increased significantly for each phenolic compound. Therefore, most of the adsorptions of phenolic compounds appeared to occur on the outer single walls of CNTs based on these results. The adsorption capacities of the CNT-adsorbing tubes were compared with those from previous studies to confirm the improved performance (Table The CNT adsorption tube in this study showed outstanding adsorption capacities for phenolic compounds.
This dramatic improvement in adsorption capacity is attributed to the heat-assisted densification of the CNTs, which made them highly aligned.
Further application in toxic gas adsorption
- Preparation of CNT-adsorption tubes for gas
- Adsorption performance of CNT adsorption tubes
- Assessment of service life of CNT adsorption tubes
- Regeneration and stability of the CNT-adsorption tubes
Design of the active end of service life indicator based on the CNT gas sensors. The sensor module consisted of the metal support, Teflon coatings, a branched flexible printed circuit board (FPCB), and CNT-based gas sensors (Figure 39a). Openings of the sensor module and the lower screen. a) Opening the sensor module (red arrow).
The bend points of the gas sensors were min and the last bend point was observed before the container breakthrough (Fig. 44b, middle). Determining the location of the sensor module in the vessel is also important for the accuracy of the ESLI system. The structure of the sensor module and container was fabricated as shown in Figure 51b.
The sensor module was placed at three points along with distances far from the center of the vessel. E(t)∆t (6) The residence time of the tracer in the container can be predicted from this calculation. CFD simulations along with the location of the sensor module. a) Location of the sensor module in the containers.
The curved and branched structure of the sensor module is designed to separate each sensor individually.
Design of the active end of service life indicator based on the CNT
Development of a custom-designed sensor module
- Fabrication of CNT-based gas sensor
- Assembly of the gas canister with custom designed sensor module
- Breakthrough experimental procedures
- Optimization of the sensor module
- Comparison of filter performances between the canisters with embedded gas sensors and
The assembled sensor module was located on an opening on a lower screen of the gas containers (Figure 39c). Due to the manual assembly in each procedure, the resistance of the sensors was changed (Figure 41). Although the resistance changes were found during the assembly of the sensor module, the performance of the gas sensors was not significantly affected.
Breakthrough experiment of DMMP using planar sensor module. a) Optical images of a printed circuit board with four CNT chemiristors labeled #1 to #4 (left) with a series connection and a linear printed circuit board housing with an opening to allow gas flow (right). The resolution in predicting the remaining life of the vessel can increase as the number of gas sensors increases. The resistance of the sensors increased almost 2.2 times (Figure 44b, top), and the inflection points of the sensor signals were used to estimate the remaining life of the vessel.
Instead of a flat sensor module, the ESLI system adopted a sensor module that has a branching structure for separate separation of sensors. For these reasons, the sensors were arranged horizontally along the gas flow direction. I expected that this folded structure can help separate each sensor separately in the vertical axis of the sensor module and dissect the flat structure.
The pressure drop for the vessel without the sensor module was typically 45-50 mmH2O, and the pressure drop in the vessel with the sensor module was 45 mmH2O (Figure 50b).
Optimization of sensor module installment
- Details of CFD simulation
- Results of CFD simulation
- Breakthrough experiments depends on location of the sensor module
The amount of tracer at the outlet of the box is measured as a function of time. This pillar structure can act as a barrier to the airflow, so the interference of the airflow reaching the sensor module installed in location A can be observed. Likewise, installing the sensor module in location C can provide a more inaccurate and delayed service life prediction than that at location B.
Based on these simulation results, location B appears to be suitable to install the sensor module for accurate cylinder service life prediction. Although the above results are different from the simulation results that revealed reverse-ordered sensor responses. This assumption was supported by previous simulation results which reported that the airflow was unsteady near the blocked center of the box.
In contrast, there was no significant airflow interference when the sensor module was installed at location B even though location B is still close to the center axis of the canister. The velocity of the air flow passing through them was relatively slower than that in the center of the box based on the simulation results (Figure 52) and previous studies. New experiments along with sensor module location. undesirable delay of sensor responses based on any simulation and experimental results.
Summarizing the experimental and simulation results, the placement of the sensor module at location B is optimal for the container used in this study.
Performances of the gas canister with embedded a sensor module
- Breakthrough experiment using DMMP
- Breakthrough experiment using ammonia
- Breakthrough experiment using cyclohexane
- Reproducibility and reliability test using DMMP
- Stability and reusability of the ESLI system
- Versatility of the ESLI system
The container breakthrough was observed at 391 min in the breakthrough graph, and it appeared after the inflection point of sensor #4 (Figure 56, bottom). The resistance of the embedded sensors increased as the breakthrough of the container continued, and appeared to respond sequentially (Figure 58, top). However, the lifetime of the container was not accurately estimated because the inflection points of the sensors were not clearly observed.
When the responses of the gas sensors were compared during breakthrough experiments, the sensor response was maximized to DMMP (DMMP > ammonia > cyclohexane) (Table 9). This comparison showed that the performances of the gas sensors are required to be improved for the accurate estimation of the lifetime of the containers against various gas models. The black dots coated on the surface of the CNT gas sensors were observed in the optical image after Ppy coating (Figure 59a) and the CNTs faded through Ppy polymer when observed with SEM (Figure 59b) .
In this study, the mechanical stability of the bus was tested using a wheel-like rotation. The infection points of the sensor resistors can roughly indicate the remaining life of the bus in 5 steps. Chen, J.; Xu, X.; Zhang, L.; Huang, S., Controlling the diameter of single-walled carbon nanotubes by improving the dispersion of the uniform catalyst nanoparticles on substrate.
H.; Goodarzi, M.; Garshasbi, A., Study on the removal of heavy metal ions from industrial wastes by carbon nanotubes: Effect of the surface modification: a review. Windey, B.; Van Riet, R.; Boutillara, Y.; Lodewyckx, P., The influence of the flow pattern of the contaminated air on the adsorption behavior of an activated carbon filter. Sedlák, P.; Kuberský, P., The effect of the orientation on analyte flow on electrochemical sensor performance and current fluctuations.
