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For practical applications, catalyst reusability is a pivotal factor which must be considered. In order to evaluate the reusability of TiO2 for HA degradation, recycling experiments were conducted under identical conditions. After being used three times, the HA degradation efficiencies decrease by about 20%. At the sixth cycle, the percentages of the HA degradation obtained are 74% for UVA and 57% for UVC (Figure 9). These decreases of HA degradation over time may be due to deposition of HA degradation by-products which hinder the absorption of light and adsorption of HA. Although the amount of HA degradation by-products attached on the catalyst surface is insignificant according to the results of the TOC solid phase (Table 4), such small organic compounds could contribute to the reduced degradation efficiency. It should be possible to improve the catalyst reusability by selecting appropriate pretreatment techniques before reuse so as to remove the attached molecules on the surface and hence increase the adsorption ability of the surface. Another reason for the reduced catalyst performance is agglomeration of the catalyst particles which results in decreased total surface area. In fact, agglomeration of the catalyst particles was observed after reuse. Proper pretreatment before reuse is therefore necessary to maintain catalyst performance.
Table 4

TOC removal under UVA and UVC light

 TOC
Mineralization (%)
Liquid phase (mg/L)Solid phase
%(mg C/g)
Initial 6.425 – – – 
TiO2 (UVA) 2.063 0.1037 0.0098 68% 
TiO2 (UVC) 3.116 0.5321 0.0787 49% 
 TOC
Mineralization (%)
Liquid phase (mg/L)Solid phase
%(mg C/g)
Initial 6.425 – – – 
TiO2 (UVA) 2.063 0.1037 0.0098 68% 
TiO2 (UVC) 3.116 0.5321 0.0787 49% 

Conditions: HA concentration = 14 mg/L, catalyst dose = 0.3 g/L, contact time = 180 min, UVA light intensity = 0.236 mW/cm2, UVC light intensity = 0.284 mW/cm2.

Figure 9

Catalyst reusability under UVA and UVC light (contact time = 180 min, HA concentration = 14 mg/L, catalyst dose = 0.3 g/L, UVA light intensity = 0.236 mW/cm2, UVC light intensity = 0.284 mW/cm2).

Figure 9

Catalyst reusability under UVA and UVC light (contact time = 180 min, HA concentration = 14 mg/L, catalyst dose = 0.3 g/L, UVA light intensity = 0.236 mW/cm2, UVC light intensity = 0.284 mW/cm2).

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