Innovative Polymeric Hybrid Nanocomposites for Application in Photocatalysis

Abstract

The immobilization of inorganic nanomaterials on polymeric substrates has been drawing a lot of attention in recent years owing to the extraordinary properties of the as-obtained materials. The hybrid materials, indeed, combine the benefits of the plastic matter such as flexibility, low-cost, mechanical stability and high durability, with them deriving from their inorganic counterparts. In particular, if the inorganic fillers are nanostructured photocatalysts, the originated hybrid systems will be able to utilize the energy delivered by light, catalysing chemical reactions in a sustainable pathway. Most importantly, since the nanofillers can be ad-hoc anchored to the macromolecular structure, their release in the environment will be prevented, thus overcoming one of the main restrictions that impedes their applications on a large scale. In this review, several typologies of hybrid photocatalytic nanomaterials, obtained by using both organic and inorganic semiconductors and realized with different synthetic protocols, were reported and discussed. In the first part of the manuscript, nanocomposites realized by simply blending the TiO₂ or ZnO nanomaterials in thermoplastic polymeric matrices are illustrated. Subsequently, the atomic layer deposition (ALD) technique is presented as an excellent method to formulate polymeric nanocomposites. Successively, some examples of polyporphyrins hybrid systems containing graphene, acting as photocatalysts under visible light irradiation, are discussed. Lastly, photocatalytic polymeric nanosponges, with extraordinary adsorption properties, are shown. All the described materials were deeply characterized and their photocatalytic abilities were evaluated by the degradation of several organic water pollutants such as dyes, phenol, pesticides, drugs, and personal care products. The antibacterial performance was also evaluated for selected systems. The relevance of the obtained results is widely overviewed, opening the route for the application of such multifunctional photocatalytic hybrid materials in wastewater remediation.

Keywords: adsorbent materials; atomic layer deposition; hybrid materials; nanomaterials; photocatalysis; polymeric nanocomposites; water treatment.

Figure 1

(a) Scanning electron microscopy (SEM) image of the back surface of poly (methyl methacrylate) (PMMA)/TiO₂ sample with 15 wt% of nanoparticles (NPs); (b) photocatalytic activity of PMMA/TiO₂ films evaluated by the discoloration of methylene blu (MB) and stability of the film with 15 wt% of NPs; (c) methyl orange (MO), rhodamine B (RhB), and phenol degradation by PMMA/TiO₂ film with 15 wt% of NPs after 4 h of irradiation; (d) antibacterial activity of PMMA/TiO₂ film with 15 wt% of NPs after 1 h of irradiation [51].

Figure 2

(a) Mass loss and derivative weight curves of composite films containing different TiO₂ contents; (b) SEM image of of poly(ethylene terephthalate) (PET) with 10 wt% TiO₂; (c) photocatalytic degradation of antibiotics in the presence of PET 10 %wt TiO₂ composite films in a wastewater effluent. Figure 2 was adapted from [55], with the permission of Elsevier.

Figure 3

(a) SEM image of TiO₂ nanotubes (NTs) obtained by electrochemical anodization of Ti foils; (b) plan-view SEM image of the back surface of the PMMA/TiO₂ sample with 5 wt% of NTs; (c) photocatalytic activity of the PMMA/TiO₂ NTs films evaluated by the discoloration of MB and stability of the film with 15 wt% of NTs; (d) antibacterial activity of the PMMA/TiO₂ films with 15 wt% of NTs after 1 h of irradiation [59].

Figure 4

(a) Plan-view SEM image of the back surface of PMMA/ZnO NPs sample; (b) MB and sodium dodecyl sulfate (SDS) degradation under UV irradiation for 4 h in the presence of PMMA/ZnO NPs sample [61].

Figure 5

(a) Photo of ZnO/PMMA sample in a Petri dish; (b) X-ray diffraction (XRD) patterns of PMMA film and of ZnO/PMMA composite film; (c) MB photodegradation under UV light in the presence of PMMA film, ZnO/Si film, ZnO/PMMA film, the discoloration of pure MB and the photocatalytic activity of the ZnO/PMMA film after seven cycles are reported too; (d) phenol photodegradation under UV light in the presence of ZnO/PMMA film [64].

Figure 6

(a) Scanning transmission electron microscopy (STEM) image of Ag NPs on the ZnO surface and energy-dispersive X-ray spectroscopy (EDS) signals from silver, zinc, and oxygen; (b) degradation of MB, paracetamol, and SDS after 4 h under UV irradiation for blank solutions, in the presence of ZnO/PMMA, and in the presence of Ag/ZnO/PMMA; (c) bacterial survival percentage in the dark and when exposed to UV irradiation for 1 h in contact with PMMA, ZnO/PMMA, and Ag/ZnO/PMMA samples [65].

Figure 7

(a) Atomic force microscopy (AFM) image of untreated poly(2,2′-bis(3,4-dicarboxyphenoxy)phenylpropane)-2-phenylendiimide ULTEM^® 1000 (ULTEM^®) film covered with ZnO; (b) AFM image of 8 h photo-exposed ULTEM^® film covered with ZnO; (c) photocatalytic efficiency of the two samples after 4 h of UV irradiation [69].

Figure 8

(a) SEM image of graphene (GF) homo-polyporphyrin (homo-PPr); (b) photocatalytic activity GF co-polyporphyrin (co-PPr) and GF homo-PPr compared to the discoloration of pure MB under visible light irradiation [77].

Figure 9

(a) Photograph of Ni-Free/G-Porph sample; (b) SEM image of Ni-Free/G-Porph sample; (c) photocatalytic activity of Ni-Foam/G, Ni-Foam/G-Porph, Ni-Free/G-Porph toward the degradation of MB; (d) Total organic carbon (TOC) measurements of pristine PEG after 6 h of irradiation, and in the presence of Ni-Free/G-Porph after 3 and 6 h of irradiation, respectively [78].

Figure 10

(a) SEM image of poly(2-hydroxyethylmethacrylate) (pHEMA) sample; (b) SME image of ZnO/pHEMA sample; (c) MB adsorption capacity versus time for pHEMA and ZnO/pHEMA samples; (d) Fourier transform infrared spectroscopy (FTIR) spectra measured on Zn/pHEMA samples: as-prepared, after MB adsorption, and after UV light irradiation; the spectrum of pure MB is also reported as reference [81].