Zinc tetraamino-phthalocyanine (ZnTAPc) supported by multi-walled carbon nanotubes (MWCNTs) hybrid materials were successfully fabricated by the method of chemical grafting and their photocatalysis behavior was reported. The as-prepared products were thoroughly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV-vis spectra, thermogravimetric analysis (TGA) and FT-IR spectra. The results showed that the ZnTAPc nanostructures were not only grown on the multi-walled carbon nanotubes but also uniformly distributed without aggregation. The photocatalytic studies revealed that the ZnTAPc–MWCNTs hybrid materials exhibited high absorption capacity and simultaneously excellent visible-light-driven photocatalytic performance for rhodamine B (RB) under visible-light irradiation. A possible mechanism for the photodegradation of rhodamine B (RB) was suggested. The hybrid materials provide great potential as active photocatalysts for degrading organic pollutions.

TiO2 nanoparticles obtained by an improved polymerization-induced colloid aggregation (Im-PICA) method were sensitized by three squaraine dyes to construct dye/TiO2 nanocomposite photocatalysts (1:3 mass ratios) with visible-light responses by a facile hydrothermal method. Scanning electron microscopy (SEM) and transmission electron miscroscopy (TEM) were employed to visually observe the surface morphologies of the samples. We studied the visible-light response using UV–vis diffuse reflectance spectroscopy and optical band gap calculations using the Tauc plot equation. The dyes exhibit excellent thermal stability, which is ascribed to the decomposition temperature reaching 300 °C based on thermogravimetric–differential thermogravimetric (TG–DTG) analysis. The photocatalytic activities of the as-prepared SQ/TiO2 composites were assessed in terms of the degradation rate of methylene blue (MB) under visible-light irradiation. The ISQ/TiO2 composites achieved best enhancement of photocatalytic activity under 150 min of visible-light irradiation. When ISQ/TiO2 nanocomposites were applied for different photocatalytic degradation cycling times, the degradation rate still reached 68%, which reflects the fact that SQ/TiO2 composites have a high photostability in the photocatalytic process. When taking the degradation rate and photoresponse into consideration, the combination mode between the ISQ dye and TiO2 that obtained the optimal degradation rate tended to be a hydrogen bond, which exhibited a stronger binding force than the simple physical absorption of m-ISQ/TiO2 and c-BSQ/TiO2 based on the FT-IR analysis. Using total organic carbon (TOC) test and liquid chromatography (LC) results, we verified the degree of mineralization of the MB molecule. Based on the fluorescence spectra, the highest fluorescence quantum yield of ISQ dye (0.124) was far greater than those of c-BSQ (0.036) and m-ISQ (0.02). The molecular structures of the squaraine dyes and the electron distributions of their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states were given by geometrical optimization with Gaussian 98 at the B3LYP/6-311+G(d,p) level. Compared with the optical band gap calculated using the Tauc plot equation, we suggest that its energy was slightly less than the band gap due to the absorbed photon. This might be related to the localized central electronic, phonon, and local energy levels between the conduction band (CB) and the valence band (VB). The value of the optical band gap calculated from UV diffuse reflection spectroscopy (DRS) becomes less than the theoretical calculated energy band gap.

A novel 1,3-bis(N-3H-3,3-dimethyl-2-methylene indolenine) squaraine dye (ISQ) sensitized TiO2 nanocomposites (ISQ/TiO2) were facilely prepared by mixing the solution of ISQ and TiO2 nanoparticle suspension in ethanol. The crystal structure, morphology and UV–vis diffuse reflectance spectroscopy of ISQ/TiO2 nanocomposites were analyzed. The XRD results showed that the synthesized ISQ/TiO2 nanocomposites were mixture of anatase and rutile crystals. The photocatalytic activity of ISQ/TiO2 nanocomposites was investigated by degrading methylene blue (MB) under visible-light irradiation (λ>400 nm). The photo-response of the ISQ/TiO2 nanocomposites was remarkably extended to visible-light region, and the photocatalytic activity of the ISQ/TiO2 nanocomposites was significantly enhanced. The photodegradation rate of MB for the ISQ/TiO2 nanocomposites reached approximately 98% after 2 h of visible-light irradiation. Furthermore, ISQ/TiO2 nanocomposites showed excellent photocatalytic stability after 5 successive cycles under visible-light.Highlights► ISQ/TiO2 nanocomposites exhibited significantly enhanced visible-light activity. ► ISQ/TiO2 nanocomposites showed remarkable visible-light photocatalytic activity. ► ISQ/TiO2 nanocomposites exhibited excellent photocatalytic stability.