Photocatalytic application of nanosized CdS immobilized onto functionalized MWCNTs

Nanosized semiconductor CdS immobilized onto modified multi-walled carbon nanotubes (MWCNTs) carrying poly(amidoamine) dendron units were visualized by HR-TEM. Evidently, spherical CdS nanoparticles 3-5 nm in diameter were identified. Moreover, EDX spectroscopy gave additional spectroscopic proof of the presence of CdS in the CdS-MWCNTs hybrid material. The photocatalytic activity of CdS-MWCNTs toward the decomposition of rhodamine B (RhB) was examined by monitoring spectral changes in the characteristic absorption band of RhB centred at 554 nm. The latter absorption band of RhB was found to continuously depress during visible light irradiation in the presence of CdS-MWCNTs, with faster kinetic rates as compared with the case when only reference CdS was present. The current result was rationalized in terms of efficient photoinduced electron-transfer from CdS to MWCNTs within the intrahybrid CdS-MWCNTs. In this frame, the suggested mechanism for the high and fast photocatalytic decomposition of RhB supports the accumulation of electrons in MWCNTs, which then react with molecular oxygen, thus reducing it to superoxide radical anion O2˙(-) responsible for the generation of the highly reactive species of HO˙ and HOO˙. The latter together with the holes generated in photoexcited CdS were responsible for the decomposition of RhB. Finally, the photocatalyst CdS-MWCNTs was recovered and efficiently reused for four consecutive catalytic cycles, thus highlighting its wider applicability in removing organic pollutants from water.