The principle of action and influencing factors of activated carbon nanotubes
This is an activation method commonly used in high specific surface area activated carbon, called chemical activation. The activation process is as follows: the activated carbon nanotubes (or graphite nanotubes) are immersed in a solution of a certain amount of KOH to prepare a mixed slurry, which is then sonicated; then the mixed slurry is allowed to stand for 12 hours and then dried at 110 ° C. The resulting mixture is placed in an activation furnace, heated to a activation temperature (600 to 1000 ° C) at a certain rate of temperature under nitrogen protection, and then kept at this temperature for a certain period of time (30 min to several hours), followed by nitrogen protection. Naturally cool to room temperature; remove the activation mixture, soak for 1-3h with hydrochloric acid and the solution is acidic, then rinse repeatedly with deionized water until the filtrate is neutral, and after the human solution is dropped, no white precipitate is formed in the filtrate, it will be cleaned. The activated carbon nanotubes (or active graphite nanotubes) were weighed at 110 ° C for 12 h.
Effect of nitric acid treatment on activated carbon nanotubes
Effect of nitric acid treatment on activated carbon nanotubes and graphite nanotubes: Under the condition of nitric acid oxidation treatment time of 24h, the effect of oxidation treatment of nitric acid on activated carbon nanotubes and graphite nanotubes was investigated. It was found through experiments that the same oxidation Under the conditions, the yields of activated carbon nanotubes and active graphite nanotubes are different, the yield of MWCNTs without high temperature treatment is only 15%, and the yield of high temperature treated MWGNT is 100%. The regular structure of graphite nanotubes is responsible for their superior oxidation resistance to activated carbon nanotubes.
The effect of nitric acid treatment time on the yield of activated carbon nanotubes: the yield of activated carbon nanotubes from 1h to 24h when the activated carbon nanotubes were treated by pure concentrated nitric acid (2.6mol/L). The same concentration was found, and the activated carbon nanotubes were treated with nitric acid for a short time, and the yield was 100%. With the increase of the treatment time, the yield gradually decreased, and the yield was only 15% when the time was extended to 24 hours.
Effect of mixed acid system on the yield of activated carbon nanotubes
Effect of mixed acid system on the yield of activated carbon nanotubes: The oxidation of the mixed acid is very strong, and the non-graphitized multi-wall activated carbon nanotubes can be oxidized to a level that is difficult to recover, mainly because of the ungraphitized activated carbon. Nanotubes have poor structural regularity and are easily oxidized. The oxidation effect of the mixed acid system on the graphite nanotubes with good structural regularity can determine the correlation between the strong oxidizing property of the mixed acid and the structural regularity of the activated carbon tube.
In the mixed acid, the yield of the active graphite nanotubes decreases as the treatment time increases. When the treatment time is 60 min, the yield has been reduced to 13.6; when the treatment time is extended to 120 min, the graphite nanotubes can also be oxidized to the extent that it is difficult to recover. Even so, graphite nanotubes still show better oxidation resistance than activated carbon nanotubes in mixed acid. This indicates that the graphite nanotubes have better structural regularity than the activated carbon nanotubes and are more difficult to be oxidized and etched.
Test method for activated carbon packing density
The test method of activated carbon packing density is relatively simple. The dried activated carbon sample is freely dropped into a suitable size measuring cylinder at a speed of 0.75~1.0mL/s through a vibrating feeder, and the filled volume is weighed and weighed. The quality of activated carbon is known.
There are two special points to be aware of when measuring the packing density: one is that the filling method used is different; different packing densities will be produced. The GB standard stipulates that the measuring cylinder should also vibrate together with the feeder, while the latest ASTM standard stipulates that only the feeder vibrates. The measuring cylinder does not vibrate; the second is that the size of the measuring cylinder used is different, and different packing density is also generated. The size of the measuring cylinder used in the GB standard is 100 mL. Regardless of the particle size of the activated carbon sample tested, the ASTM standard requires The size of the measuring cylinder is to be measured to select the size of the measuring cylinder. The basis of selection is that the inner diameter of the measuring cylinder should be at least 10 times the average particle diameter measured by the particle size distribution method. In addition, the two standards are different for the packing density. The GB standard is expressed in g/L, and the ASTM standard is expressed in g/mL.
The size of the packing density is closely related to the adsorption performance and strength of the activated carbon. Generally, for the activated carbon products produced by the same raw materials and processes, the higher the packing density, the better the strength, the worse the adsorption performance, and the packing density. The detection index is often used in activated carbon production, trade and scientific research because it is simple to detect and can basically determine the activation degree of living carbon. It is one of the most commonly used indicators for evaluating activated carbon.
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