Photocatalytic Activity Of Heterostructure Research Articles

Enhanced Photocatalytic Activity in 2D‐1D WS2/TiO2 and 2D‐2D MoS2/WS2 Heterosystems

AbstractTwo‐dimensional (2D) tungsten disulphide (WS2) based heterostructures with modified interfaces have huge potential for photocatalytic applications. Integrating WS2 with one‐dimensional (1D) titanium dioxide (TiO2) and 2D molybdenum disulphide (MoS2) structures to form heterostructures, enhances its photocatalytic activity. The enrichment in photocatalytic activity of heterostructures may get affected by the electronic interaction at the interface as well as morphology and dimensionality also affect the catalytic activity. In this context, the present work focuses on the enrichment of photocatalytic activity by different tungsten disulphide (WS2) based heterostructures, which may get influenced by the interfacial interaction. In the present work, two different heterostructures 2D‐1D WS2/TiO2 and 2D‐2D MoS2/WS2 are formed using the hydrothermal method. Scanning electron microscopy (SEM) confirmed the morphology of prepared heterostructures. X‐ray photoelectron spectroscopy (XPS) analysis further revealed that the integration of 1D and 2D nanostructures with WS2 has been found effective to alter the interface by the development of the Ohmic and Schottky barrier. Moreover, Fourier transformation infra‐red (FTIR) spectroscopy confirms the presence of W−S, S−S, Mo−S, and Ti−O bonds in the prepared heterostructures. Furthermore, current‐voltage (I–V) data graphically illustrated the conductivity of catalysts. I–V curves confirm the presence of Schottky and ohmic barriers and the higher electrical conductivity of 2D‐2D MoS2/WS2 heterostructures, which facilitates the charge carrier's transportation. 2D‐1D WS2/TiO2 and 2D‐2D MoS2/WS2 heterostructures are further explored for photocatalytic activity by the methylene blue dye degradation. The overall catalytic activity of 2D‐2D MoS2/WS2 is better than 2D‐1D WS2/TiO2 and WS2, respectively. This result was accounted as 2D‐2D MoS2/WS2 had the highest conductivity and better charge separation at the interface in comparison to the other two synthesised catalysts.

The synthesis and enhanced photocatalytic activity of heterostructure BiOCl/TiO2 nanofibers composite for tetracycline degradation in visible light

Heterojunction of TiO2 nanoparticles and BiOCl nanosheets grown on the carbon nanofibers (CNFs) were prepared by simply process that combine of electrospinning, solvothermal, and calcine. The photocatalytic activity of the as-obtained samples was evaluated by photodegradation of tetracycline (TC) in visible light irradiation (λ ≥ 420 nm). Compared with CNFs and TiO2/CNFs, BiOCl/TiO2/CNFs composites performed the best photocatalytic degradation performance (82%) and good stability. Moreover, the degradation rates of Norfloxacin, Ciprofloxacin, and Oxytetracycline are all more than 90%. Finally, trapping experiments were carried out, and a possible photocatalytic degradation mechanism was proposed.

Enhanced visible-light-driven photocatalytic activity of heterostructure Ag/Bi2MoO6 nanocomposites synthesized by photoreduction method

Heterojunction Ag/Bi2MoO6 nanocomposites with different contents of the loaded Ag nanoparticles were successfully synthesized by photoreduction method. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The analyses certified that the unloaded nanosample was composed of pure orthorhombic Bi2MoO6 nanoplates and that the loaded nanosamples were composed of FCC metallic silver nanoparticles as minor phase on top of orthorhombic Bi2MoO6 nanoplates as major phase. The photocatalytic activities of pure Bi2MoO6 nanoplates and Ag/Bi2MoO6 nanocomposites were investigated through photodegradation of rhodamine B (RhB) and phenol under visible light irradiation. They were found that the Ag/Bi2MoO6 nanocomposites exhibited significant photocatalysis better than pure Bi2MoO6 nanoplates. The enhanced photocatalytic performance of Ag/Bi2MoO6 nanocomposites was ascribed to the formation of Schottky barrier at metal-semiconductor interface.

Heterostructures based on nanodispersed TiO2 and binary systems TiO2-CdTe, TiO2-Cu(In,Ga)Se2 sensitized by polymethyn dye, as photocatalysts of redox processes

New light-sensitive heterostructures of semiconductors (TiO2, TiO2-CdTe, TiO2-Cu(In,Ga)Se2) sensitized with an anionic polymethine dye with three conjugated chromophores have been developed. Based on the analysis of the results of spectral, electrochemical and energy characteristics of the studied dye, the possibility of its use as an effective sensitizer of these semiconductor materials is shown. It was found that the deposition of the dye on TiO2 leads to both batochromic and hypsochromic shifts of long wavelength absorption bands, the values ​​of which depend on the dye content in the heterostructure. This leads to a redistribution of the intensities of the absorption bands, they expand and cover almost the entire part of the visible and near-IR regions of the spectrum. This feature of the created heterostructure allows to increase the efficiency of their photocatalytic action through the use of light quanta of a wide energy range. The results of the analysis of the absorption spectra of heterostructures testify to the significant influence of semiconductors on the electronic system of dye molecules. As a result, the angle between the directions of the chromophores changes. The antibate dependence of the degree of conformational changes on the amount of dye in the heterostructure is revealed. This indicates a decrease in the interaction with the semiconductor with increasing concentration and explains the decrease in the photocatalytic activity of heterostructures at a significant content of sensitizer. Using the method of cyclic voltammetry, for the first time the oxidation and reduction potentials of the investigated polymethine dye were determined. The values ​​of HOMO and LUMO energy levels are calculated, a forecast is made regarding the possibility of their use as sensitizers of the studied semiconductors and the creation of highly efficient redox systems. The photocatalytic activity of heterostructures in the reactions of reduction of methylene blue and oxidation of iodide ions under irradiation with light absorbed by a semiconductor and a sensitizer has been revealed. Based on the analysis of energy parameters of electronic processes, the scheme of this photocatalytic transformation is proposed and substantiated.

Photocatalytic reduction of methylene blue by the heterostructure of Titanium (IV) oxide and symmetric cationic polymethine dye

The results of the spectral, electrochemical and energy characteristics of symmetric cationic polymethine dye 2 - [(1E) -1,3,5-hexatrienyl -] - 1- (phenylmethyl)-benzindolium boron fluoride (D) indicate the possibility of its use as an effective titanium(IV) sensitizer oxide. Comparison of the absorption spectra of the dye solution and the reflectance spectra of the D/TiO2 heterostructures showed that the deposition of the dye on the TiO2 surface leads to bathochrome and hypochromic shifts of the absorption bands, the value of which depends on the content of this component in the heterostructure (HS). The obtained changes in the spectra of heterostructures indicate the possibility of formation of both J- and H-aggregates. Cyclic voltammetry determines the oxidation and reduction potentials of the investigated polymethine dye and calculates their redox potentials in the excited state. They have been found to be sufficient for sensitization by electron transfer to the TiO2 conduction band. The photocatalytic activity of HS D/TiO2 in the model reaction of methylene blue reduction depending on irradiation conditions and dye concentration has been determined. It is shown that, when irradiated with D/TiO2 heterostructures with light with λ <400 nm, their photocatalytic activity decreases with increasing dye content in the whole concentration range of the studied concentrations. When irradiated with heterostructures by light absorbed by the dye (λ = 872 nm), the photocatalytic activity increases to a maximum value at a concentration of the dye equal to 0,20 mg/g, and then decreases with increasing concentration. The energy of possible electronic processes caused by the action of light absorbed by a semiconductor and a dye-sensitizer is considered. The possibility of using created heterostructures as functional materials with a given level of photocatalytic activity and extended range of light sensitivity is shown.

Microwave-assisted synthesis, photocatalysis and antibacterial activity of Ag nanoparticles supported on ZnO flowers

ZnO flowers with different Ag contents were successfully synthesized by a simple microwave method. Phase and morphologies of heterostructure Ag/ZnO composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that heterostructure Ag/ZnO composites were composed of face centered cubic Ag supported on hexagonal ZnO flowers of hexagonal prism nanorods with 100 nm wide and about 2–3 μm long, including the detection of Ag 3d5/2 and Ag 3d3/2 for metallic Ag of 10 wt% Ag/ZnO composites. The photocatalytic activity of heterostructure Ag/ZnO composites was evaluated through photodegradation of methylene blue under UV light. Escherichia coli DH5α (gram-negative bacteria) and Stapphylococcus aureus ATCC 25923 (gram-positive bacteria) were used to test for antibacterial activity. The 10 wt% Ag/ZnO composites showed the best performance for photocatalysis and had the antibacterial activity.