WS2-intercalated Ti3C2Tx MXene/TiO2-stacked hybrid structure as an excellent sonophotocatalyst for tetracycline degradation and nitrogen fixation

Abstract

Designing a heterostructure nanoscale catalytic site to facilitate N₂ adsorption and photogenerated electron transfer would maximize the potential for photocatalytic activity and N₂ reduction reactions. Herein, we have explored the interfacial TiO₂ nanograins between the Ti₃C₂T_xMXene-WS₂ heterostructure and addressed the beneficial active sites to expand the effective charge transfer rate and promote sonophotocatalytic N₂ fixation. Benefiting from the interfacial contact and dual heterostructure interface maximizes the photogenerated carrier separation between WS₂ and MXene/TiO₂. The sonophotocatalytic activity of the MXene@TiO₂/WS₂ hybrid, which was assessed by examining the photoreduction of N₂ with ultrasonic irradiation, was much higher than that of either sonocatalytic and photocatalytic activity because of the synergistic sonocatalytic effect under photoirradiation. The Schottky junction between the MXene and TiO₂ on the hybrid MXene/TiO₂-WS₂ heterostructure resulted in the sonophotocatalytic performance through effective charge transfer, which is 1.47 and 1.24 times greater than MXene-WS₂ for nitrogen fixation and pollutant degradation, respectively. Under the sonophotocatalytic process, the MXene/TiO₂-WS₂ heterostructure exhibits a decomposition efficiency of 98.9 % over tetracycline in 90 min, which is 5.46, 1.73, and 1.10 times greater than those of sonolysis, sonocatalysis, and photocatalysis, respectively. The production rate of NH₃ on MXene/TiO₂-WS₂ reached 526 μmol g^-1h^-1, which is 3.17, 3.61, and 1.47 times higher than that of MXene, WS₂, and MXene-WS₂, respectively. The hybridized structure of MXene-WS₂ with interfacial surface oxidized TiO₂ nanograins minimizes the band potential and improves photocarrier use efficiency, contributing directly to the remarkable catalytic performance towards N₂ photo fixation under visible irradiation under ultrasonic irradiation. This report provides the strategic outcome for the mass carrier transfer rate and reveals a high conversion efficiency in the hybridized heterostructure.

Keywords: Interfacial contact; MXene; N(2) fixation; Sonophotocatalysis; Transition metal dichalcogenide.

Fig. 1

(a) Schematic synthesis route for fabricating the MXene/TiO₂-WS₂ hybrid heterostructure. (b) X-ray diffraction pattern and (c) FTIR spectra of MXene, MXene/TiO₂, WS₂, MXene-WS₂, and MXene/TiO₂-WS₂ nanostructures.

Fig. 2

FESEM images of (a-c) MXene, (d-f) MXene/TiO₂, (g-i) WS₂, and (j-l) MXene/TiO₂-WS₂ nanostructures in different magnifications.

Fig. 3

Typical TEM and HRTEM images of (a-c) MXene; (d-f) MXene/TiO₂; (g–i) WS₂ and (j-l) MXene/TiO₂-WS₂ heterostructure. (m) EDAX mapping images of the MXene/TiO₂-WS₂ heterostructure. The inset shows the SAED pattern of the respective images.

Fig. 4

High-resolution XPS profile: (a) C 1s and (b) Ti 2p of MXene; (c) W 4f and (d) S 2p of WS₂; (e) C 1s, (f) Ti 2p, (g) W 4f, and (h) S 2p of MXene-WS₂ heterostructure; (i) C 1s, (j) Ti 2p, (k) W 4f, and (l) S 2p of MXene/TiO₂-WS₂ heterostructure.

Fig. 5

UV–Vis spectra of TC with a catalyst under different reaction conditions in 90 min. (b) the degradation efficiency of TC with MXene/TiO₂-WS₂ catalyst by absorption, sonolysis, sonocatalysis, photocatalysis, and sonophotocatalysis. (c) Effects of different MXene compositions on the sonophotocatalytic degradations of TC. (d) Synergy factors for the sonophotocatalytic degradations of TC by MXene/TiO₂-WS₂. Sonophotocatalytic efficiency over (e) different WS₂ loading densities and (f) different oxidization temperatures of MXene/TiO₂ (100–400 °C). Operational conditions: [MXene/TiO₂-WS₂] = 1 g L⁻¹, TC = 10 mg L⁻¹, and neutral pH.

Fig. 6

(a)Yield of NH₃ concentration over different catalysts during the sonophotocatalytic process respective to time. (b) NH₃ concentration and (c) NH₃ production rate under different conditions with the MXene/TiO₂-WS₂ catalyst. (d) sonication power on the formation of NH₃, (e) cycling experiment on MXene/TiO₂-WS₂ catalyst. (f) XRD and SEM image of the MXene/TiO₂-WS₂ catalyst after four reusable catalytic cycles.

Fig. 7

(a) Photoluminescence spectra of the as-prepared MXene-based heterostructures. (b) XPS valance band spectra of WS₂, MXene-WS₂, and MXene-TiO₂-WS₂. (c) Mott Schottky plot of the WS₂, MXene/TiO₂, MXene-WS₂, and MXene/TiO₂-WS₂. (d) Transition photocurrent response of WS₂, MXene-WS₂, and MXene/TiO₂-WS₂ under visible irradiation using three-electrode measurements. (e) Electrochemical impedance spectrometry (EIS) spectra of the MXene-based heterostructure. (f) Sonophotocatalytic nitrogen fixation of MXene/TiO₂-WS₂ in the presence of alcohol hole scavengers (methanol, ethanol, and tert-butanol) and electron scavengers (AgNO₃).

Fig. 8

Sonophotocatalytic nitrogen fixation mechanism of the MXene/TiO₂-WS₂ heterostructure.