COSTE NETO:
15. Deuda financiera
·O2H O2
·OH
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Page 27/27 3.7. Reuse of spent WO3/TiO2/SiO2 photocatalyst
Regeneration of a photocatalyst that enables it to maintain its photocatalytic activity for subsequent use without changing its original chemical structure is important for water technology. Fig. 13 presents the regeneration efficiency of the spent 3WTS (3% (w/w)).
The spent 3WTS still remained stable after being regenerated for four consecutive times without significant changes with respect to its removal capacities. As indicated in Fig. 11, the photodegradation rate of Ace by the spent 3WTS was still 82% under the same concentration of 5 mg/L. This indicates that the 3% (w/w) of WTS photocatalyst was promising for practical applications.
cycle1 cycle2 cycle3 cycle4
0 20 40 60 80 100
Ace removal (%)
Fig. 13. Reusability of spent 3% (w/w) of WO3/TiO2/SiO2 composite on Ace removal (5 mg/L of Ace; 1.5 g/L of 3% (w/w) WO3/TiO2/SiO2; pH 9.0; 25°C; 4 h).
3.8. Comparison of photodegradation performance among various photocatalysts
In order to evaluate the photocatalytic performance of the WTS composite in this study, a comparative study is presented in terms of photocatalyst dosage (g/L), concentration (mg/L), light sources, pH and removal efficiency. Table 4 summarizes the photocatalytic
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Page 28/27 degradation of organic pollutants in previous studies. Although this comparison has a relative meaning due to varying operating conditions (dose (g/L), light sources, energy (W), reaction time (min) and pH), this comparison is still useful to evaluate the overall performance of those photocatalysts for water treatment applications.
Table 4 shows that semiconductor materials such as TiO2, SiO2, WO3 and ZnO present outstanding performances among the various photocatalysts. As for contaminants like endocrine-disrupting compounds (EDC) or PPCPs, Hunge et al. [44] found that only 65%
removal of 4-chlorpphenol was achieved after 3 h with an initial concentration of 25 mg/L [44], while Yan et al. [45] achieved 95% of Ace removal using In2S3/Zn2GeO4 with its initial concentration of 5 mg/L. Although various photocatalysts can be applied, key factors in the selection of wastewater treatment containing PPCPs are its photocatalytic activity and the pollutants’ removal rate. The reaction time, pH and the required intensity of UV-VIS light irradiation that affect the removal efficiency depend on the concentration of target pollutants and the type of semiconductor materials.
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Page 29/27 Table 4
Summary of photocatalytic performance of various photocatalysts.
Target
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Page 30/27 d MO: methyl orange
e 4-CP: 4-chlorpphenol f MA: mefenamic acid
g NCP: clinoptilolite nanoparticles
h GR-TNT: Graphene-Titanium dioxide nanotube i C-dropped: carbon self-dropped
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Page 31/27 4. Conclusions
This study has demonstrated that the incorporation of the WO3 into the TiO2/SiO2 composite has significantly enhanced the photocatalytic degradation of Ace from synthetic wastewater under the UV-VIS irradiation. Under optimized conditions (1.5 g/L of 3% (w/w) of WO3/TiO2/SiO2 composite, pH 9 and 4 h of reaction time), 95% of Ace removal could be achieved at the same 5 mg/L of initial Ace concentration. Under those same conditions, the result of Ace photodegradation by the 3% (w/w) of the WO3/TiO2/SiO2 composite was significantly higher (95%) than that by the individual TiO2/SiO2 (42%) and/or the TiO2 alone (33%). It is important to note that the treated effluents still could not meet the maximum limit of less than 0.2 mg/L set by China’s and US legislation. This indicates that further subsequent treatment like biological processes is still necessary for completing the removal of target pollutant from wastewater samples.
Acknowledgements
The authors express their profound gratitude to the Xiamen University’s Foundation of Technology for the research grant No. 20720150070.
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Page 38/27 Graphical abstract
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Highlights
1. The WO3/SiO2/TiO2 is a promising composite for acetaminophen photodegradation;
2. The WTS composite has stable characteristics;
3. The spent composite could be regenerated with stable removal efficiency of Ace.