V-Porphyrins Encapsulated or Supported on Siliceous Materials: Synthesis, Characterization, and Photoelectrochemical Properties

Abstract

Metalloporphyrin-containing mesoporous materials, named VTPP@SBA, were prepared via a simple anchoring of vanadyl porphyrin (5,10,15,20-Tetraphenyl-21H,23H-porphine vanadium(IV) oxide) through a SBA-15-type mesoporous material. For comparison, vanadyl porphyrin was also impregnated on SiO2 (VTPP/SiO2). The characterization results of catalysts by XRD, FTIR, DR-UV-vis, and EPR confirm the incorporation of vanadyl porphyrin within the mesoporous SBA-15. These catalysts have also been studied using electrochemical and photoelectrochemical methods. Impedance measurements confirmed that supporting the porphyrin in silica improved the electrical conductivity of samples. In fact, when using mesoporous silica, current densities associated with oxidation/reduction processes appreciably increased, implying an enhancement in charge transfer processes and, therefore, in electrochemical performance. All samples presented n-type semiconductivity and provided an interesting photoelectrocatalytic response upon illumination, especially silica-supported porphyrins. This is the first time that V-porphyrin-derived materials have been tested for photoelectrochemical applications, showing good potential for this use.

Influence of the Polymeric Matrix on the Optical and Electrical Properties of Copper Porphine-Based Semiconductor Hybrid Films

“…The second energy (2.16 and 2.86 eV for PMMA:CuP and PS:CuP, respectively) is the optical band gap, E g opt , and corresponds to the energy gap between the valence band and the conduction band [ 11 , 43 ]. These results are important not only because they are in the same order of magnitude as those obtained for other porphine and their derivatives [ 36 , 37 , 38 , 39 , 40 , 41 , 42 ], but also because the PMMA or PS polymeric matrix does not increase the porphine band gap in hybrid films. One of the drawbacks in hybrid films, due to the presence of the polymeric matrix, is that it can reduce charge transport due to the interfaces that occur between the polymer and the porphine.…”

“…For PMMA:CuP the spectra show the three bands at 398 (Soret-band), 539 (β-band), and 586 nm (∝-band). The peaks of Soret and Q-bands are interpreted as the excitation between bonding and antibonding molecular orbital in the porphine, in terms of π-π* [14] and the results obtained for the PMMA:CuP and PS:CuP films coincide with those obtained for other structures with porphines [8,37]. The absorption capacity of the CuP makes hybrid films susceptible to participate in photoinduced charge transfer processes in optoelectronic and photovoltaic devices.…”

“…The PS:CuP film ( Figure 5 a), in addition to the broad diffused peak at approximately 14°–35°, presents sharp Bragg peaks at approximately 2θ = 7.11°, 7.89°, and 19° indicating some degree of π–π stacking of the CuP molecules in certain regions of the hybrid film, which suggest that the PS:CuP film has a crystalline structure [ 35 ]. Apparently, there is a small nucleation and crystallization of the CuP with a preferential direction of growth [ 35 , 36 , 37 ]. The greater crystallinity in the PS:CuP hybrid film could be reflected in better optical and electrical properties; however, it is important to consider that the porphine is embedded in an amorphous polymeric matrix; therefore, the predominant structure of the hybrid film is amorphous.…”

Influence of the Polymeric Matrix on the Optical and Electrical Properties of Copper Porphine-Based Semiconductor Hybrid films

“…The PS:CuP film (Figure 5a), in addition to the broad diffused peak at approximately 14 • -35 • , presents sharp Bragg peaks at approximately 2θ = 7.11 • , 7.89 • , and 19 • indicating some degree of π-π stacking of the CuP molecules in certain regions of the hybrid film, which suggest that the PS:CuP film has a crystalline structure [35]. Apparently, there is a small nucleation and crystallization of the CuP with a preferential direction of growth [35][36][37]. The greater crystallinity in the PS:CuP hybrid film could be reflected in better optical and electrical properties; however, it is important to consider that the porphine is embedded in an amorphous polymeric matrix; therefore, the predominant structure of the hybrid film is amorphous.…”