Aggregation Effect on Phthalocyanine Photocatalytic Degradation Efficiency Using Orange G and Methyl Orange as Test-pollutant Compounds in Aqueous Medium

摘要

The effect of aggregation on the photocatalytic behavior of two different water-soluble phthalocyanines (Pcs) bearing four carboxylic-acid-functionalized thiophenyl groups, tetrathiophe-nycarboxyphthalocyanine (H2TCPc) and tetrathiophenycarbox-yphthalocyaninato Zn(II) complex (ZnTCPc) have been investigated. The two compounds, H2TCPc and ZnTCPc, showed considerable solubility in water at pH ≈ 7.4, but were found to aggregate even at a concentration as low as 2.5 ×10~(-5) M. Two organic dyes, orange G (OG) and methyl orange (MO), were employed as test-pollutants which were photodegraded in the presence of the Pcs, with and without Triton X-100 (TX) surfactant. H2TCPc in the absence and presence of TX showed degradation efficiency (DE) of 5.80 and 8.70% respectively, for OG degradation. For the same OG degradation, ZnTCPc as photocatalyst gave DE of 6.41 and 28.0% in the absence and presence of TX, respectively. Whereas for the degradation of MO, H2TCPc DE values were respectively found to be 11.0 and 39.0% in the absence and presence of TX, while ZnTCPc gave 13.3 and 66.0%, respectively. The ZnTCPc showed considerable low aggregation compared to H2TCPc in the presence of TX, thus resulting in higher DE compared to that of the latter by a factor of 3.2 and 1.7 for OG and MO degradation, respectively. The singlet oxygen quantum yields (Φ△) obtained for the two Pcs support the observed DE values, and were measured to be 0.50 (50%) and 0.12 (12%) for the ZnTCPc and H2TCPc, respectively. The DFT/TDDFT calculated triplet yields for ZnTCPc (0.79) and H2TCPc (0.020), showed linear correlation with their experimental Φ△ yields.