Effect of Anealing Process

by Elaine Wong
(Malaysia)

Original Text:


Annealing process can increase the presence of anatase phase and also decrease the pore volume and specific surface area in titanate nanotubes. The presence of the crystallinity of anatase phase encourages the photocatalytic degradation rate. Pore volume is related to the diffusion of pollutants and samples during the photocatalytic reaction. The higher the pore volume of the samples, the diffusion between pollutants and samples becomes rapid and fast. The bigger of the surface area of the sample will increase the adsorption of pollutants on the surface of catalyst, which lead to the increase in the photocatalytic degradation of pollutants. This is in contrast to the result of Lee et al. 13. They stated that an increment of heat treatment temperature will influence the photocatalytic activity of titanate nanotubes in the reduction of basic dye BV10, relating to the two obvious factors: (1) decrease in pore volume and specific surface area; and (2) increment of crystallinity of anatase phase.
Hence, the photocatalytic activity of pollutant strongly depends on the operating temperature of annealing process. Based on major researches, the photocatalytic degradation rate increased with the increasing of the heat temperature up to certain level due to the increment of anatase phase and reduction of pore volume and surface area. On the other hand, the photocatalytic activity of the nanotubes decreases when the calcination temperature is further increased.
Lee et al. 59 observed that the photodegradation rate slightly increased with increasing heat temperature from 150 to 300 oC. Furthermore, the photocatalytic activity was reduced rapidly at 400-700 oC due to the diminishment of the pore volume and specific surface area, even though the anatase phase was improved.
Otherwise, Vuong and co-workers 19 also agreed to the work of Lee et al.. They stated that increasing the annealing temperature up to 600 oC will increase the photodegradation activity of TiO2 nanotubes in removal of methylene blue. The removal rate decreased with further increasing annealing temperature due to the collapse of tube-like structures.
Srimala and Lai 46 investigated the photocatalytic degradation of methyl orange (MO) solution with different crystallinity and surface area of TiO2 (nanoparticles or nanotubes). TiO2 synthesized at 150 oC had better catalytic behaviour in the photodegradation of MO due to the high percentage of anatase phase and high surface area of tube-shaped structures.
On the contrast, Qamar and his workers 63 stated that the photocatalytic activity increased with increasing annealing temperature presumptively because of the crystallinity of anatase phase. The smaller of the surface area and the disappearance of the anatase phase will induce a decrease of the photocatalytic performance of titanate nanotubes at high temperatures.

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Revised Text:

The annealing process can increase the presence of anatase phase and also decrease the pore volume and specific surface area in titanate nanotubes.

The presence of the crystallinity of anatase phase encourages the photo-catalytic degradation rate. Pore volume is related to the diffusion of pollutants and samples during the photocatalytic reaction. The higher the pore volume of the samples, the diffusion between pollutants and samples becomes more rapid. A larger surface area of the sample will increase the adsorption of pollutants on the surface of the catalyst, which leads to the increase in the photo-catalytic degradation of pollutants.

This is in contrast to the result of Lee et al. (13). They stated that an increment of heat treatment temperature will influence the photo-catalytic activity of titanate nanotubes in the reduction of basic dye BV10, relating to the two obvious factors: (1) decrease in pore volume and specific surface area; and (2) increment of crystallinity of anatase phase.

Hence, the photo-catalytic activity of pollutants strongly depends on the operating temperature of the annealing process. Based on major researches, the photo-catalytic degradation rate increased with the increasing of the temperature up to a certain level due to the increment of anatase phase and the reduction of pore volume and surface area.

On the other hand, the photo-catalytic activity of the nanotubes decreases when the calcination temperature is further increased.

Lee et al. (59) observed that the photo-degradation rate slightly increased with increasing temperature from 150 to 300 o C. Furthermore, the photo-catalytic activity was reduced rapidly at 400-700 o C due to the diminishing of the pore volume and specific surface area, even though the anatase phase was improved.

Otherwise, Vuong and co-workers (19) also agreed with the work of Lee et al.. They stated that increasing the annealing temperature up to 600 o C will increase the photo-degradation activity of TiO2 nanotubes in removal of methylene blue. The removal rate decreased with further increasing the annealing temperature due to the collapse of tube-like structures.

Srimala and Lai (46) investigated the photo-catalytic degradation of methyl orange (MO) solution with different crystallinity and surface area of TiO2 (nanoparticles or nanotubes). TiO2 synthesized at 150 o C had better catalytic behavior in the photo-degradation of MO due to the high percentage of anatase phase and high surface area of tube-shaped structures.

In contrast, Qamar and his workers (63) stated that the photo-catalytic activity increased with increasing annealing temperature presumably because of the crystallinity of anatase phase.

The smaller the surface area and the disappearance of the anatase phase will induce a decrease of the photo-catalytic performance of titanate nanotubes at high temperatures.

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