Facile synthesis of carbon nanotubes covalently modified with ZnO nanorods for enhanced photodecomposition of dyes

Utilizing a one-pot solvothermal procedure novel one-dimensional zinc oxide–carbon nanotube nanohybrids (ZnCT) were synthesized in alcohol-alkali solution, free of catalytic assistance. The ZnCT hybrids were prepared through covalent modification of zinc oxide nanorods (ZnO NRs) with functionalized carbon nanotubes (f-CNTs). The morphology and microstructure of as-prepared ZnCT hybrids were characterized by scanning electron microscopy (SEM), powder X-ray diffraction, Raman, X-ray photoelectron and UV–vis absorption spectroscopies. SEM images of the ZnCT hybrids indicated that the ZnO_ethanol NRs grew longer along the vertical radial (0 0 0 1) surface and aggregated to a lesser extent than the analogous ZnO_methanol NRs. Photodegradation analysis showed that the off-white ZnCT_ethanol hybrid with ascendant UV–visible light absorption had displayed superior photocatalytic activity towards Rhodamine B (RhB) dyes than either pure ZnO_ethanol, ZnO_methanol NRs or ZnCT_methanol hybrid, among which the photocatalytic activity of ZnO_ethanol NRs was better than that of ZnO_methanol NRs. Raman and X-ray photoelectron spectroscopy analyses confirmed a strong interaction between f-CNTs and ZnO_ethanol NRs in ZnCT_ethanol hybrid, in which Zn ions were chemically bonded to negatively charged oxygen-containing groups at the graphene-like surface of f-CNTs. The enhanced separation lifetime of the photogenerated electron-hole observed by surface photovoltage and photocurrent measurements of the ZnCT_ethanol hybrid was attributed to the efficient covalent linking of Zn–O–C and close contact configuration between the f-CNTs and ZnO_ethanol NRs. Further controlled photodegradation and electron spin resonance (ESR) analyses revealed that the photodegradation of RhB dyes resulted from photogenerated holes, and radical species, such as ^[rad]O²⁻, ^[rad]OH⁻, which were formed in-situ. Details of the photocatalytic mechanism were also explored herein.