Rational design of a 2D TiO2-MoO3 step-scheme heterostructure for boosted photocatalytic overall water splitting

The design of step-scheme (S-scheme) heterostructure photocatalysts is a promising strategy for the high utilization of photogenerated charge carriers. Herein, a novel S-scheme two-dimensional (2D) TiO2-MoO3 heterojunction photocatalyst is fabricated by a facile electrochemical method for high water splitting photocatalytic efficiency. According to X-ray photoelectron spectroscopy (XPS) assessment, electrons are transported from TiO2 to MoO3 upon close contact, creating an internal electric field (IEF) directed from TiO2 to MoO3. Hence, upon light irradiation, the photogenerated electrons in MoO3 move toward TiO2 under the IEF effect, as revealed by EPR analysis, implying that the S-scheme heterojunction was established in the TiO2-MoO3 heterostructure and significantly promoted the separation of electron-hole pairs to enhance efficient photocatalytic water splitting. Thanks to the 2D morphology of the TiO2-MoO3 heterojunction and the significantly improved redox capability of the charge carriers in the S-scheme system, the photocatalytic water splitting efficiency of the optimized TiO2-MoO3 is higher than those of both pure MoO3 and TiO2 and commercial TiO2-P25. This study, for the first time, presents the charge transfer pathways in the TiO2-MoO3 heterostructure photocatalyst via an S-scheme system. It will shed new light on the design and fabrication of novel step-scheme heterojunction photocatalysts for overall water splitting

One-Step Hydrothermal Synthesis of Anatase TiO2 Nanotubes for Efficient Photocatalytic CO2 Reduction

The hydrothermal dissolution-recrystallization process is a key step in the crystal structure of titania-based nanotubes and their composition. This work systematically studies the hydrothermal conditions for directly synthesizing anatase TiO2 nanotubes (ATNTs), which have not been deeply discussed elsewhere. It has been well-known that ATNTs can be synthesized by the calcination of titanate nanotubes. Herein, we found the ATNTs can be directly synthesized by optimizing the reaction temperature and time rather than calcination of titanate nanotubes, where at each temperature, there is a range of reaction times in which ATNTs can be prepared. The effect of NaOH/TiO2 ratio and starting materials was explored, and it was found that ATNTs can be prepared only if the precursor is anatase TiO2, using rutile TiO2 leads to forming titanate nanotubes. As a result, ATNTs produced directly without calcination have excellent photocatalytic CO2 reduction than titanate nanotubes and ATNTs prepared by titanate calcination

Construction of Bi2S3/TiO2/MoS2 S-Scheme Heterostructure with a Switchable Charge Migration Pathway for Selective CO2 Reduction

Switching between the redox potential of an appropriate semiconductor heterostructure could show critical applications in selective CO2 reduction. Designing a semiconductor photocatalyst with a wavelength-dependent response is an effective strategy for regulating the direction of electron flow and tuning the redox potential. Herein, the switching mechanism between two charge migration pathways and redox potentials in a Bi2S3/TiO2/MoS2 heterostructure by regulating the light wavelength is achieved. In situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), electron spin resonance (ESR), photoluminescence (PL), and experimental scavenger analyses prove that the charge transport follows the S-scheme approach under UV–vis–NIR irradiation and the heterojunction approach under vis–NIR irradiation, confirming the switchable feature of the Bi2S3/TiO2/MoS2 heterostructure. This switchable feature leads to the reduction of CO2 molecules to CH3OH and C2H5OH under UV–vis–NIR irradiation, while CH4 and CO are produced under Vis–NIR irradiation. Interestingly, the apparent quantum efficiency of the optimal composite at λ = 600 nm is 4.23%. This research work presents an opportunity to develop photocatalysts with switchable charge transport and selective CO2 reduction.The authors are thankful to the DST National Single Crystal Diffractometer Facility Laboratory, DoS in Physics, UPE, IOE, and DST-PURSE, Vijnana Bhavana, University of Mysore, Mysuru, for providing the required facilities. The authors extend their appreciation to the Researchers Supporting Project number (RSP-2021/381), King Saud University, Riyadh, Saudi Arabia.Scopu

Surface defect-engineered CeO2−x by ultrasound treatment for superior photocatalytic H2 production and water treatment

Semiconductor photocatalysts with surface defects display incredible light absorption bandwidth and these defects function as highly active sites for oxidation processes by interacting with the surface band structure. Accordingly, engineering the photocatalyst with surface oxygen vacancies will enhance the semiconductor nanostructure's photocatalytic efficiency. Herein, a CeO2−x nanostructure is designed under the influence of low-frequency ultrasonic waves to create surface oxygen vacancies. This approach enhances the photocatalytic efficiency compared to many heterostructures while keeping the intrinsic crystal structure intact. Ultrasonic waves induce the acoustic cavitation effect leading to the dissemination of active elements on the surface, which results in vacancy formation in conjunction with larger surface area and smaller particle size. The structural analysis of CeO2−x revealed higher crystallinity, as well as morphological optimization and the presence of oxygen vacancies is verified through Raman, X-ray photoelectron spectroscopy, temperature-programmed reduction, photoluminescence, and electron spin resonance analyses. Oxygen vacancies accelerate the redox cycle between Ce4+ and Ce3+ by prolonging photogenerated charge recombination. The ultrasound-treated pristine CeO2 sample achieved excellent hydrogen production showing a quantum efficiency of 1.125% and efficient organic degradation. Our promising findings demonstrated that ultrasonic treatment causes the formation of surface oxygen vacancies and improves photocatalytic hydrogen evolution and pollution degradation

Rational construction of plasmonic Z-scheme Ag-ZnO-CeO2 heterostructures for highly enhanced solar photocatalytic H-2 evolution

Rational design of photocatalyst with wide solar-spectrum absorption, negligible electron-hole recombination, and maximized redox potential is an essential prerequisite for achieving commercial-scale photocatalytic H-2 production. This contribution combines surface plasmon resonance and Z-scheme charge transport in a single photocatalyst (Ag ZnO CeO2 hetemstructure) aiming to improve its performance for photocatalytic H-2 production. The Ag-ZnO-CeO2 heterostructure is fabricated via sunlight-driven combustion and deposition approaches. The successful construction is confirmed by several characterization techniques. The Z-scheme configuration is verified by in situ irradiated XPS and ESR analyses. Ag plays dual rules as an electron mediator to facilitate the Z-scheme charge transport and plasmonic material to maximize the light absorption in the visible region. The designed photocatalyst exhibits significantly enhanced photocatalytic activity for H-2 production (18345 mu mol h(-1) g(-1)) under simulated sunlight irradiation. This work offers the opportunity of constructing efficient Z-scheme photocatalyst from wide bandgap semiconductors with full-visible light response, suppressed electronhole recombination, and optimized redox potential