TiO2-MoS2-PMMA Nanocomposites for an Efficient Water Remediation

Abstract

An improvement of water supply and sanitation and better management of water resources, especially in terms of water reuse, is one of the priorities of the European Green Deal. In this context, it is crucial to find new strategies to recycle wastewater efficiently in a low-cost and eco-friendly manner. The immobilization of inorganic nanomaterials on polymeric matrices has been drawing a lot of attention in recent years due to the extraordinary properties characterizing the as-obtained nanocomposites. The hybrid materials, indeed, combine the properties of the polymers, such as flexibility, low cost, mechanical stability, high durability, and ease of availability, with the properties of the inorganic counterpart. In particular, if the inorganic fillers are nanostructured photocatalysts, the materials will be able to utilize the energy delivered by light to catalyze chemical reactions for efficient wastewater treatment. Additionally, with the anchoring of the nanomaterials to the polymers, the dispersion of the nanomaterials in the environment is prevented, thus overcoming one of the main limits that impede the application of nanostructured photocatalysts on a large scale. In this work, we will present nanocomposites made of polymers, i.e., polymethyl methacrylate (PMMA), and photocatalytic semiconductors, i.e., TiO₂ nanoparticles (Evonik). MoS₂ nanoflakes were also added as co-catalysts to improve the photocatalytic performance of the TiO₂. The hybrid materials were prepared using the sonication and solution casting method. The nanocomposites were deeply characterized, and their remarkable photocatalytic abilities were evaluated by the degradation of two common water pollutants: methyl orange and diclofenac. The relevance of the obtained results will be discussed, opening the route for the application of these materials in photocatalysis and especially for novel wastewater remediation.

Keywords: molybdenum disulfide; nanomaterials; photocatalysis; polymer; titanium dioxide; water treatment.

Figure 1

Pictures of the prepared composites: PMMA, TiO₂—PMMA, TiO₂—10% MoS₂—PMMA, TiO₂—20% MoS₂—PMMA, TiO₂—30% MoS₂—PMMA.

Figure 2

HAADF S-TEM picture of the TiO₂—10% MoS₂—PMMA sample (a); Ti (yellow), O (green), Mo (cyan), and S (blue) elemental distribution extracted by the fitting of EELS spectra collected in SI mode (b); diffraction patterns of the TiO₂—10% MoS₂—PMMA sample showing diffraction spots from anatase-TiO₂ (a-TiO₂), rutile TiO₂ (r-TiO₂), and MoS₂ (c).

Figure 3

X-ray diffractograms of TiO₂—PMMA (red curve) and TiO₂—10% MoS₂—PMMA (blue curve). The peaks corresponding to TiO₂ and MoS₂, respectively, are specified.

Figure 4

XPS spectra recorded for (a) Ti2p, (b) O1s, (c) Mo3d, and (d) S2p for the different samples.

Figure 5

(100-Reflectance)% spectra of MoS₂ (a), TiO₂—PMMA (b), and TiO₂—30% MoS₂—PMMA (c) sample. The insets of the figures show the Tauc-plots (continuous line) and the relative fit (dashed line) for all the samples.

Figure 6

(a) Thermogravimetry (TGA) and (b) derivative thermogravimetry (DTG) thermograms of the studied samples. The number 1, 2 and 3 represent typical three-step decomposition of PMMA.

Figure 7

MO photo-degradation under UV light irradiation for six aqueous solutions with MO (diamonds), MO with PMMA (pentagons), MO with TiO₂—PMMA composite (squares), MO with TiO₂—10% MoS₂—PMMA composite (circles), MO with TiO₂—20% MoS₂—PMMA composite (up-triangles), MO with TiO₂—30% MoS₂—PMMA composite (down-triangles). The grey region indicates the preliminary adsorption test in the dark.

Figure 8

Diclofenac photo-degradation under UV light irradiation for six aqueous solutions with diclofenac (diamonds), diclofenac with PMMA (pentagons), diclofenac with TiO₂—PMMA composite (squares), diclofenac with TiO₂—10% MoS₂—PMMA composite (circles), diclofenac with TiO₂—20% MoS₂—PMMA composite (up-triangles), diclofenac with TiO₂—30% MoS₂—PMMA composite (down-triangles). The grey region indicates the preliminary adsorption test in the dark.

Figure 9

XRD patterns of TiO₂—10% MoS₂—PMMA samples after the photocatalytic degradation test of MO (yellow curve) and after the photocatalytic degradation test of diclofenac (green curve).

Figure 10

Schematic illustration of the photocatalytic process in the presence of MoS₂ as co-catalyst.