Freestanding photocatalytic materials based on 3D graphene and polyporphyrins

Abstract

A new concept in the formulation of hybrid nanostructured materials combining high quality graphene 3D supported by Nickel foam and polyporphyrins for visible light photocatalytic application is here reported. Our innovative approach involves the development of a freestanding device able to: i) offer a high surface area to bind the photosensitizers by π-π interactions, and ii) enhance stability and photocatalytic efficiency by using cyclic porphyrin polymers. For these purposes, homo- and co-polymerization reactions by using different porphyrin (free or zinc complexed) monomers were performed. The microscopic structures and morphology of graphene polymer nanocomposites were investigated by using Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM). Finally, photocatalytic activity under visible light irradiation of the obtained nanocomposites was tested, by using methylene blue (MB) as organic pollutant. The obtained data suggested that hindered cyclic polymeric structures stacked on graphene surface by non-covalent interactions, restrict the formation of non photoactive aggregates and, as a consequence, induce an enhancement of photocatalytic activity. Remarkably, our systems show a degradation efficiency in the visible-light range much higher than other similar devices containing nanoporphyrin units reported in literature.

Hybrid nickel-free graphene/porphyrin rings for photodegradation of emerging pollutants in water

“…The graphene platform used to prepare the device was obtained by CVD deposition on a Nickel foam template (see experimental section). To cover the nickel-graphene foam (Ni-G), a water insoluble polymeric materials based on porphyrin rings having a M w of 10 600 Da were properly selected 19,38 as photoactive coating lm. The hybrid material preparation is reported and discussed in the following sections.…”

“…2b revealing that the graphene adheres to the surface of the nickel foam, reproducing its morphology. 19,38 As described in the experimental part, the G was drop-coated with the cyclic polymer obtaining a homogeneous coverage, as shown in Fig. 2c.…”

“…The signal consists of two components centered at 400.2 eV and at 398.2 eV, indicating the presence of the pyrrolic (-NH-) and to the iminic (-N]) species of the porphyrin rings respectively. 19,41,42 Furthermore, the C 1s region [ Fig. 3b] reveals two components positioned at 285.0 eV (FWHM of 1.5 eV) and at 286.5 eV (FWHM of 1.7 eV), due respectively to the C-C, C]C, C-H of the graphene and to the C-O, C]N, C-N species of the 3DG copolymer-porphyrin structure.…”

“…[9][10][11][12][13][14][15][16] Nevertheless, the ISC for such kind of materials is strongly limited by rapid electron-hole recombination between the singlet excited state and the ground state, mainly due to aggregation phenomena. 13,16 To turn this limitation, the combination of porphyrins with carbon-based nanostructures, such as carbon nanotubes and graphene [17][18][19][20][21][22][23] was exploited. Indeed, these materials are considered ideal candidates as co-catalyst carriers, having specic features such as high-surface area and conjugated networks.…”

“…20,21 It was demonstrated as the non-covalent assembly of porphyrin based polymers (Porph rings) with a graphene platform supported by nickel, represents an efficient method to avoid the electron-hole recombination mechanism as well as other critical issues deriving from the use of G derivatives. 19,[24][25][26] The present paper describes the formulation of a novel nickel free photoactive material, its characterization as well as the related photocatalytic attitudes on different classes of contaminants. Undeniably, Ni removal is strictly required for applications in water and medical elds, being an allergen and a water contaminant ($0.010 ppm) harmful for aquatic and human life.…”