Photocatalytic degradation of methyl orange by titanium dioxide-decatungstate nanocomposite films supported on glass slides

Reusable Fe2O3/TiO2/PVC Photocatalysts for the Removal of Methylene Blue in the Presence of Simulated Solar Radiation

Currently, environmental pollution by various organic pollutants (e.g., organic dyes) is a serious, emerging global issue. The aqueous environment is highly exposed to the harmful effects of these organic compounds. Furthermore, the commonly applied conventional purification techniques are not sufficient enough. Heterogeneous photocatalysis and the photo-Fenton process are effective, low-cost and green alternatives for the removal of organic pollutants. In this study, different iron(III) oxide/titanium(IV) oxide/polyvinyl chloride (Fe₂O₃/TiO₂/PVC) nanocomposites in tablet form were investigated in the photodegradation of methylene blue (MB) under simulated sunlight, and their possible antibacterial effects were examined. The newly synthesized nanocomposites were characterized by scanning electron microscope, X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, and Raman spectroscopy. The results showed a hematite crystal form in the case of Fe₂O₃₍₂₎ and Fe₂O₃ samples, while the Fe₂O₃₍₁₎ sample showed a combination of hematite and synthetic mineral akaganeite. The highest photocatalytic efficiency was achieved in the presence of Fe₂O₃/TiO₂/PVC, when 70.6% of MB was removed. In addition, the possible photo-cleaning and reuse of the mentioned photocatalyst was also examined. Based on the results, it can be seen that the activity did not decrease after five successive runs. Nanocomposites also exhibited mild antibacterial effects against the two tested Gram-positive bacteria (S. aureus and B. cereus).

Application of Composite Film Containing Polyoxometalate Ni25 and Reduced Graphene Oxide for Photoelectrocatalytic Water Oxidation

The preparation of clean energy is an effective way to solve the global energy crisis and reduce environmental pollution. The decomposition of water can produce hydrogen and oxygen, which is one of the effective ways to prepare clean energy. However, water oxidation is a bottleneck for water decomposition, thus, developing a water oxidation catalyst can accelerate the process of water decomposition to generate clean energy. Nickel-substituted polyoxometalate [Ni25(H2O)2(OH)18(CO3)2(PO4)6(SiW9O34)6]50− (Ni25) is proven as an excellent water oxidation photocatalyst. To develop the effective photoelectrocatalyst for water oxidation, in this work, we constructed two composite films containing Ni25 on ITO, [PDDA/Ni25]n, and PDDA/[Ni25/(PDDA–rGO)]n, by layer-by-layer self-assembly, which is the first combination of nickel-substituted polyoxometalates and reduced graphene oxide (rGO). The study on the photoelectrocatalytic performance of the two films indicates that the water oxidation current of the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode is increased by 33.7% after light irradiation, which is 1.71 times that of the film [PDDA/Ni25]n-modified electrode. Moreover, the transient photocurrent response of the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode demonstrates that there is a synergistic effect between rGO and Ni25, and rGO-accelerated electron transport and inhibited charge recombination. In addition, the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode exhibits good stability, indicating its great potential as an effective photoelectrocatalyst for water oxidation in practical application.

Adsorption of Methyl Orange from Aqueous Solution Using PVOH Composite Films Cross-Linked by Glutaraldehyde and Reinforced with Modified α-MnO2

A poly(vinyl alcohol) (PVOH) composite cross-linked with glutaraldehyde (GL) containing α-MnO₂ modified with stearic acid (ST) was fabricated as an efficient sorbent for capturing methyl orange (MO) dye from the water system. We investigated the factors affecting MO adsorption in detail. The adsorption process showed a high dependence on the pH value. The highest removal efficiency (96.5%) was obtained at pH 2. The adsorption isotherm study indicated that the linear Freundlich isotherm was a more appropriate model for the adsorption process. The adsorption kinetics study revealed that the adsorption data matched with a nonlinear pseudo-first-order model. Physical adsorption interactions, including electrostatic interactions, hydrogen bonds, and dipole-dipole forces, play dominant roles in this process. Thermodynamic investigations confirmed that MO adsorption was spontaneous and exothermic with physical interactions. The outcomes demonstrated that the cross-linked PVOH-GL/α-MnO₂-ST composite could be a hopeful sorbent for the efficient uptake of MO molecules from polluted waters.

Heterogeneous photocatalytic degradation of pesticides using decatungstate intercalated macroporous layered double hydroxides

Decatungstate W10O32(4-) was efficiently intercalated between the layers of three-dimensionally ordered macroporous Mg2Al-layered double hydroxide. The structural and textural properties of as-prepared intercalated compound were characterized using different solid-state characterization techniques such as X-ray powder diffraction, FTIR and Raman spectroscopies and electronic microscopy. The photocatalytic properties of immobilized W10O32 (4-) within Mg2Al structure were investigated using 2-(1-naphthyl) acetamide (NAD) as a model of pesticide. The influence of different parameters such as amount of catalyst, pH and oxygen concentration were investigated. An optimal NAD degradation was obtained for a photocatalyst concentration of 60 mg l(-1). Under our experimental conditions, this heterogeneous photocatalyst induces photodegradation of 60 % of NAD after 17 h of irradiation at 365 nm and at pH 6.6. Interestingly, pesticide photodegradation leads to the mineralization of substrates to H2O and CO2 and the photocatalyst can be recycled and reused without any loss of activity over four cycles.