Porphyrin-Based Nanostructures for Photocatalytic Applications

Abstract

Well-defined organic nanostructures with controllable size and morphology are increasingly exploited in optoelectronic devices. As promising building blocks, porphyrins have demonstrated great potentials in visible-light photocatalytic applications, because of their electrical, optical and catalytic properties. From this perspective, we have summarized the recent significant advances on the design and photocatalytic applications of porphyrin-based nanostructures. The rational strategies, such as texture or crystal modification and interfacial heterostructuring, are described. The applications of the porphyrin-based nanostructures in photocatalytic pollutant degradation and hydrogen evolution are presented. Finally, the ongoing challenges and opportunities for the future development of porphyrin nanostructures in high-quality nanodevices are also proposed.

Keywords: nano-heterojunction; nanocrystal; photocatalysis; porphyrin; self-assembly; solar energy conversion efficiency.

Figure 1

(A) Molecular structure of zinc-tetra (4-pyridyl) porphyrin (ZnTPyP); (B) photocatalytic activities of ZnTPyP-based nanospheres (●), nanospheres/nanofibers (▲), nanofibers (▼) and no catalyst (■) for rhodamine B (RhB) photodegradation under visible-light irradiation; (C) a schematic illustration on the structure of ZnTPyP nanospheres and nanofibers and their morphology-dependent photocatalytic performance. ET = electron transfer. Reproduced with permission from [51]. Copyright 2012, Royal Society of Chemistry.

Figure 2

(A) Molecular structure of meso-tetra (4-carboxyphenyl) porphyrin (TCPP); (B) possible mechanism of the formation of different morphologies of TCPP aggregates; (C) photocatalytic activity of different TCPP aggregates; (D) photoluminescence decay curves: (a) sphere, (b) rod, (c) flower and (d) monomer. Reprinted with permission from [55]. Copyright 2014, American Chemical Society.

Figure 3

(A) The high resolution transmission electron microscope (HR-TEM) image of ZnTPyP tetragonal rods. The inset shows the fast Fourier transformation (FFT) of the transmission electron microscope (TEM) image. (B) Corresponding reverse fast Fourier transformation (RFFT) image built upon the FFT image. (C) Photocatalytic activities of ZnTPyP nanocrystals: no ZnTPyP nanocrystals (a), commercially available P25 TiO₂ nanoparticles (b), tetragonal nanorods with a 200-nm length (c), same concentration of ZnTPyP in DMF (d), same concentration of ZnTPyP in 0.01 M HCl (e), nanoparticles with an 80-nm diameter (f), hexagonal nanowires with a 2-μm length (g), hexagonal rods with a 400-nm length (h) and hexagonal porous nanodiscs (i) for methyl orange (MO) photodegradation under visible-light irradiation. (D) Cycling tests of photocatalytic activity of ZnTPyP nanodiscs under visible-light irradiation. Reprinted with permission from [58]. Copyright 2014, American Chemical Society.

Figure 4

(A) The scanning electron microscope (SEM) image of tetraphenylporphyrin (H₂TPP)/ N,N-(dicyclohexyl) perylene-3,4,9,10-tetracarboxylic diimide (CH-PTCDI) nano-heterojunctions; (B) TEM image of a single p/n nanostructure; the insets are the corresponding electron diffractions; (C) The UV-visible and (D) the fluorescence spectra of the obtained samples; (E) Photocatalytic degradation of MB with different samples under visible-light irradiation (λ > 400 nm); (F) operating principle of H₂TPP/CH-PTCDI nanostructures. Reproduced with permission from [65]. Copyright 2013, Royal Society of Chemistry. MB, methyl blue.

Figure 5

(A) SEM images of the structures prepared at room temperature for all four combinations of Zn(II) and Sn(IV) in the two porphyrins (left), the corresponding unwashed platinized clovers (middle) and the washed clovers after two weeks of continuous hydrogen generation (right): Zn/Sn (a), Sn/Zn (b), Zn/Zn (c) and Sn/Sn (d) by ionic self-assembly of Zn(II) tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS) and Sn(IV) tetrakis(N-2-hydroxyethyl-4-pyridinium)porphyrin (SnT(N-EtOH-4-Py)P); (B) Total H₂ generated by the platinized porphyrin clovers (Zn/Sn, Zn/Zn, Sn/Sn, Sn/Zn) grown at room temperature (solid lines) and at 70 °C for the Zn/Sn clovers (dotted lines) versus irradiation time with visible light from a tungsten lamp. Zn/Sn clovers with (dark red symbols) and without (yellow) methylviologen. The latter are expanded by a factor of 100; (C) Hydrogen generated by free porphyrins at the same concentrations as in the clovers as a function of irradiation time by white light at 0.15 W·cm⁻². Reproduced with permission from [66]. Copyright 2011, Royal Society of Chemistry.

Figure 6

(A) SEM image of Pt/TiO₂-ZnP(Py)₄ nanorods; (B) Time dependence of hydrogen evolution: (●) Pt/TiO₂-ZnP(Py)₄ rods, (■) non-encapsulated Pt/TiO₂ + ZnP(Py)₄ composites. (C) A schematic illustration for photocatalytic hydrogen evolution. Reprinted with permission from [75]. Copyright 2013, American Chemical Society.

Figure 7

(A) Schematic illustration for the assembly of ZnTPyP 1D nanostructures via graphene oxide (GO)-based surfactant-assisted self-assembly (SAS); (B) TEM image of ZnTPyP/GO complexes; (C) photocatalytic activity of the original GO nanosheets (black ■), 1D ZnTPyP nano-assemblies formulated via the CTAB-assisted (red ●) and GO-assisted (blue ▲) SAS, for the photodegradation of RhB under visible-light irradiation. Reprinted with permission from [53]. Copyright 2013, American Chemical Society.

Figure 8

(A) The optical and (B) TEM images of free-standing meso-tetra (p-hydroxyphenyl) porphyrin (p-THPP)/rGO films; (C) photocatalytic degradation of MB with different samples under visible-light irradiation (λ > 400 nm); (D) Nyquist plots collected by EIS of free-standing rGO and p-THPP/rGO films; (E) the fluorescence spectra of the synthesized films; (F) the fluorescence decay profiles of p-THPP and p-THPP/rGO nanohybrid in H₂O (λ_exc = 405 nm); (G) proposed mechanism for the photocatalysis of the p-THPP/rGO film; (H) recycling experiment using the p-THPP/rGO for MB degradation under visible-light irradiation (λ > 400 nm). Reproduced with permission from [92]. Copyright 2014, Royal Society of Chemistry.

Figure 9

(A) SEM image of the graphitic C₃N₄ (g-C₃N₄)/m-oxo dimeric iron (III) porphyrin ((FeTPP)₂O) heterostructure including 5 wt% (FeTPP)₂O; (B) The band-structure diagram of the g-C₃N₄/(FeTPP)₂O heterostructure; (C) photocatalytic H₂ production rates over pure (FeTPP)₂O, the g-C₃N₄ + (FeTPP)₂O (5 wt%) mixture and g-C₃N₄/(FeTPP)₂O (5 wt%). Reproduced with permission from [97]. Copyright 2016, Royal Society of Chemistry.