Augmented photocatalysis induced by 1T-MoS2 bridged 2D/2D MgIn2S4@1T/2H-MoS2 Z-scheme heterojunction: mechanistic insights into H2O2 and H2 evolution

In the realm of composite photocatalysts, the fusion of the co-catalyst effect with interfacial engineering is recognized as a potent strategy for facilitating the segregation and migration of photo-induced charge carriers. Herein, an innovative mediator-based Z-scheme hybrid, i.e. MIS@1T/2H-MoS2, has been well designed by pairing MIS with 1T/2H-MoS2via a facile hydrothermal strategy as a competent photocatalyst for H2O2 and H2 generation. The co-catalyst, i.e. metallic 1T-phase bridging between semiconducting 2H-MoS2 and MIS, serves as a solid state electron mediator in the heterostructure. Morphological findings revealed the growth of 1T/2H-MoS2 nanoflowers over MIS microflowers, verifying the close interaction between MIS and 1T/2H-MoS2. By virtue of accelerated e−/h+ pair separation and migration efficiency along with a proliferated density of active sites, the MMoS2-30 photocatalyst yields an optimum H2O2 of 35 μmol h−1 and H2 of 370 μmol h−1 (ACE of 5.9%), which is 3 and 2.7 fold higher than pristine MIS. This obvious enhancement can be attributed to photoluminescence and electrochemical aspects that substantiate the diminished charge transfer resistance along with improved charge carrier separation, representing a good example of a noble metal-free photocatalyst. The proposed Z-scheme charge transfer mechanism is aided by time-resolved photoluminescence (TRPL), XPS, radical trapping experiments, and EPR analysis. Overall, this endeavour provides advanced insights into the architecture of noble metal-free Z-scheme heterostructures, offering promising prospects in photocatalytic applications.


Characterization techniques:
Diffraction (XRD) analysis was carried out using a Rigaku Miniflex X-ray diffractometer equipped with a monochromator and Cu Kα radiation ( = 0.154 nm, 30 KV/50 mA).For identifying the chemical states of the samples, X-ray photoelectron spectroscopy (XPS) was conducted with a VG Microtech Multilab ESCA-3000 spectrometer, employing Mg-Kα as the X-ray source.The morphological verification, including Field Emission Scanning Electron Microscopy (FESEM) was performed using a FEIN Quanta-400 FEG-SEM.The internal structure of the synthesized materials was analysed through High Resolution Transmission Electron Microscopy (HRTEM) using a JEOL-JEM-2100 transmission electron microscope.
For determining the bandgap and absorbance characteristics, UV-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS) was conducted with a JASCO-V-750 UV-Vis spectrometer with BaSO 4 as the reference, covering a range of 200-800 nm.Photoluminiscence (PL) spectra including excitation and emission spectra were examined using a JASCO FP-8300 fluorescence spectrometer, employing an excitation wavelength of 325 nm and a xenon (Xe) lamp as the light source.The average life span of exciton pairs was examined through TRPL analysis using life spec II EDINBURGH PHOTONICS instrument.

Photoelectrochemical measurements:
A multi-channel Ivium potentiostat-galvanostat electrochemical workstation (IVIUM-N-STAT) was employed for photoelectrochemical measurements utilizing a three-electrode configuration consisting of a counter electrode (Pt foil), a reference electrode (Ag/AgCl) and a working electrode (fluorine-doped Tin oxide-FTO).0.5 M H 2 SO 4 and 0.5 M Na 2 SO 4 aqueous solution was utilized as electrolytes for 1T/2H-MoS 2 and MIS.To prepare the working electrode, a mixture containing 10 mg of sample, 0.7 ml of ethanol and 1% nafion (20 µl) was coated onto the conducting surface of the FTO by drop-casting method.The FTO-coated electrode was then dried in an oven at 90 °C for 12 hours.The light source was provided by 300 W Xenon lamp equipped with a 400 nm cut-off filter.

Photocatalytic H 2 O 2 production experiment:
The photocatalytic generation of H 2 O 2 from pristine 1T/2H-MoS 2 , MIS and MMoS 2 -x photocatalysts was conducted under visible light exposure in an oxygen-saturated environment.
Initially, 0.02 grams of the photocatalysts were dispersed in a mixed solution of 19 mL DI water and 1 mL ethanol through 10 min of ultrasonication to ensure complete dispersion.Subsequently, the sample was exposed to O 2 gas for 30 min before being irradiated to 250 W visible light to create an oxygen equilibrated environment.After 2 hours of light exposure, the photocatalysts were collected from the solution by centrifugation and filtration.Then 1 mL of the resulting solution was mixed with 2 mL of KI (0.1 M) solution, followed by the addition of 0.05 mL of ammonium molybdate (0.01 M) solution to yield a light yellow colour.Then finally, the concentration of of H 2 O 2 was determined by measuring the absorbance at a wavelength of 350 nm using an UV-Vis spectrophotometer.

Photocatalytic H 2 evolution experiment:
The photocatalytic water splitting reaction was performed inside a pyrex quartz glass photoreactor connected to a 150 W Xenon lamp emitting light with a wavelength greater than 420 nm.For the experiment, 20 mg of photocatalysts (1T/2H-MoS 2 , MIS, MMoS 2 -x composites) were dispersed in 20 mL of a 10% methanol solution (used as a sacrificial agent).
The suspension was continuously stirred to prevent the catalysts from settling at the bottom of the reactor.Prior to exposing the system to light, the reactor's atmosphere was rendered inert by purging it with N 2 gas multiple times.After 1 hour of light exposure, the hydrogen gas produced was collected through water displacement method.The quantity of H 2 evolution was quantified using a GC-7890B (Agilent technology) equipped with a thermal conductivity detector (TCD) and a 5 Å molecular sieve packed column.

Figure
Figure S2.(a) EDX spectra of MMoS 2 -30 composite and (b) Elemental mapping of Mg, In, Mo and S elements for MMoS 2 -30.

Table S1 .
Comparative study of photocatalytic H 2 evolution

Table S2 .
Comparative study of photocatalytic H 2 O 2 production