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• TiO 2 /RGO nanocomposite was fabricated via a hydrothermal method for photocatalysis. • Existence of graphene greatly improved the photocatalytic activity of the TiO 2 NPs. • TiO 2 /RGO photoanode showed 3.3-fold higher photocurrent compared to pure TiO 2. • Mott-Schottky plot showed 7.4-fold increase in N D and 64% decrease in W SCL. • RGO enhanced the PEC performance of TiO 2 with increasing N D and decreasing W SCL. In this study, TiO 2 nanoparticles (NPs) /reduced graphene oxide (RGO) composites were prepared by hydrothermal process and physiochemical, optical, photocatalytic and photoelectrochemical properties of prepared materials was investigated. Photocatalytic activity measurement showed that methylene blue (MB) photodegraded faster by TiO 2 -RGO composites compared to bare TiO 2. Furthermore, photoelectrochemical (PEC) properties of TiO 2 and TiO 2 -RGO electrodes were investigated under the illumination of a 150 W Xe lamp in 1M aqueous solution of KOH as the electrolyte. Moreover, TiO 2 -RGO electrodes showed greatly improved photocurrent density which is 3.3-fold higher than pure TiO 2. Combined analyses of Mott-Schottky plots and electrochemical impedance spectroscopy (EIS) confirmed that RGO in the TiO 2 -RGO nanocomposite increased the donor concentration (N D), decreased recombination process of charge carriers (τ D), thinner the space charge layer (W SCL) and reduced flat band potential (V Fb) of the TiO 2 , thereby greatly enhancing the PEC performances of the TiO 2 photoanodes. The improved PEC performance of the TiO 2 -RGO nanocomposite compared to TiO 2 NPs attributed to great enhancement of electron transport through the RGO in the TiO 2 - RGO film and consequently charge separation. [ABSTRACT FROM AUTHOR]

This study reports the effect of the Ti source (Ti foil or TiO 2 thin layer) and NaOH concentration on the growth of sodium titanate nanostructures via hydrothermal treatment to improve the photoelectrochemical (PEC) water splitting performance. An optimal condition to grow sodium titanate nanoflower composed of ultrathin nanosheets on the surface of the thin TiO 2 film led to the formation of a novel nanocomposite TiO 2 /Na 2 Ti 3 O 7 photoelectrode with great adhesion of the two phases. The Ti/TiO 2 /Na 2 Ti 3 O 7 photoanode demonstrated a significant enhancement in photocurrent density and shifted the onset potential to a more negative value compared to the pure Ti/TiO 2 and Ti/Na 2 Ti 3 O 7 samples. This noticeable improvement is attributed to the suitable band alignment between the TiO 2 and Na 2 Ti 3 O 7 phases and their direct contact with the Ti foil, as well as the large surface area of nanoflower sodium titanate, which significantly facilitate the generation, separation, and transfer of photogenerated electrons from the active phases to the substrate. More interestingly, the prepared photoanode retained its initial photocurrent density even after 16 h. An ion-exchange method and calcination treatment were used at different temperatures to convert the Na 2 Ti 3 O 7 phase in the Ti/TiO 2 /Na 2 Ti 3 O 7 photoanode to TiO 2 to investigate the role of type II heterojunction for efficient photogenerated charge carrier separation in this photoanode. It was concluded that converting Na 2 Ti 3 O 7 into TiO 2 in the Ti/TiO 2 /Na 2 Ti 3 O 7 system would reduce its PEC performance due to the formation of a pure phase of TiO 2 in the Ti/TiO 2 /TiO 2 photoanode. [Display omitted] • The Ti/TiO 2 /Na 2 Ti 3 O 7 photoanode demonstrated a significant enhancement in photocurrent density. • The Ti/TiO 2 /Na 2 Ti 3 O 7 photoanode retained its initial photocurrent density even after 16 h. • Ti/TiO 2 /Na 2 Ti 3 O 7 showed a photocurrent density of around 0.46 mA/cm2 at 0.3 V vs. Ag/AgCl. • Any morphological and phase changes in Ti/TiO 2 /Na 2 Ti 3 O 7 reduce its photocatalytic activity. [ABSTRACT FROM AUTHOR]

• α-Fe 2 O 3 /BiVO 4 /MoS 2 photoanode was prepared through low-cost methods. • α-Fe 2 O 3 heterojunction with BiVO 4 and MoS 2 greatly improved the PEC performance. • The multi heterojunction increase the efficiently of the charge separation and injection. • α-Fe 2 O 3 /BVO/MoS 2 generated 46.5 μmol cm−2 of H 2 and 22.3 μmol cm−2 of O 2 after 2 h. [Display omitted] Metal oxide semiconductors are among the most promising photoelectrode materials for solar water splitting, mainly due to their robustness in aqueous solutions. In this work, a multi heterojunction with metal oxides is fabricated to enhance the photoelectrochemical (PEC) water splitting through unified surface modification. The two-dimensional MoS 2 nanosheets are synthesized through the liquid-phase exfoliation (LPE) process. The characteristics of the MoS 2 nanosheets for improving light harvest and charge separation, including thickness, number of layers, and concentration, are all estimated using the proper techniques. The best photocurrent density of the α-Fe 2 O 3 /BiVO 4 /MoS 2 at 1.23 V vs. RHE under 100 mW/cm2 (AM 1.5) illumination that was identified around 15 times greater than that of the α-Fe 2 O 3 photoanode. The α-Fe 2 O 3 /BiVO 4 /MoS 2 electrode shows the highest donor concentration value (4.36E+26 m3) with the lowest flat band potential (0.15 V) among all the prepared electrodes. Furthermore, the obtained hydrogen and oxygen production in 2 h irradiation for α-Fe 2 O 3 /BiVO 4 /MoS 2 is 46.5 and 22.3 μmol cm−2, respectively. [ABSTRACT FROM AUTHOR]