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Photocatalysis has received much attention as it is considered one of the potential solutions for solar energy conversion and counteracting environmental degradation. In order to promote the research work of the field and meet the requirements of practical applications, it is necessary to develop high efficiency visible-light-driven photocatalysts, especially the red semiconductor photocatalysts. This review aims to sum up the progress recently made in this field, concentrating on the scientific and technological possibilities offered by three kinds of red semiconductor photocatalysts for water splitting, organic contaminant decomposition, and CO2 photoreduction. The important progress is discussed and explained in detail, including the synthesis, characterization, and specific applications of red semiconductor photocatalysts. Finally, the review concludes by summarizing both findings and perspectives.

Abstract: A facile method was used to prepare hollow mesoporous TiO2 and Au@TiO2 spheres using polystyrene (PS) templates. Au nanoparticles (NPs) were simultaneously synthesized and attached on the surface of PS spheres by reducing AuCl4− ions using sodium citrate which resulted in the uniform deposition of Au NPs. The outer coating of titania via sol‐gel produced PS@Au@TiO2 core–shell spheres. Removing the templates from these core–shell spheres through calcination produced hollow mesoporous and crystalline Au@TiO2 spheres with Au NPs inside the TiO2 shell in a single step. Anatase spheres with double Au NPs layers, one inside and another outside of TiO2 shell, were also prepared. Different characterization techniques indicated the hollow mesoporous and crystalline morphology of the prepared spheres with Au NPs. Hollow anatase spheres with Au NPs indicated enhanced harvesting of visible light and therefore demonstrated efficient catalytic activity toward the degradation of organic dyes under the irradiation of visible light as compared to bare TiO2 spheres. [ABSTRACT FROM AUTHOR]

Hematite (α-Fe2O3) is a red material with a band gap of about 2.0 eV, which indicates that it can absorb more solar light. It is a promising photocatalyst applied in many fields. In this paper, α-Fe2O3 single crystal hollow hexagonal bipyramids were synthesized by a simple one-pot hydrothermal method. The morphology and structure of the prepared α-Fe2O3 hollow hexagonal bipyramids were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The hollow single crystals show a good light absorption and performance in photodegradation of methylene blue (MB). Due to the strategy of depositing ultra-thin layers of Al2O3 by atomic layer deposition (ALD), the photoelectrochemical (PEC) performance of α-Fe2O3 under the simulated solar light irradiation is also improved. [ABSTRACT FROM AUTHOR]

A simple method allows the preparation of core/shell photocatalysts with spatially separated co‐catalysts for efficient water splitting. The high activity was attributed to the core/shell structure and separated co‐catalysts that assisted separation and collection of the electrons and holes at the respective co‐catalysts, owing to active rectification of electron and hole transport (see picture; Eg=2.1 eV). [ABSTRACT FROM AUTHOR]

Abstract: Well-aligned TiO2 nanotube (NT) arrays with multilayer architecture were fabricated using periodic anodization method. Periodic pulses, consisting of high and low voltages, were applied to fabricate TiO2 NTs with periodically changing morphology. The approach was simple and allowed for better control in the continuous fabrication of various multilayer TiO2 NT arrays. These TiO2 NT arrays with multilayer morphologies showed a better photocatalytic property than smooth TiO2 NTs, and it is expected to have extensive applications in the fields of selective filters, targeted delivery, solar cells, and photocatalysis. [Copyright &y& Elsevier]

Hollow mesoporous TiO 2 photocatalysts with dual co-catalysts, located at specific positions, were prepared using Polystyrene (PS) as sacrificial templates. Au nanoparticles (NPs) were in situ loaded on the surface of PS spheres and the resulting nanocomposites were coated with TiO 2 shell using sol-gel reaction. The outer surface of core-shell spheres was impregnated with Ru and the subsequent calcination produced hollow anatase spheres with Au and RuO 2 dual co-catalysts. The hollow mesoporous spheres of Au@TiO 2 @RuO 2 were proved by various techniques such as TEM, EDX, and SEM images. Photocatalysts were applied for hydrogen generation from water splitting and that with dual co-catalysts showed efficient catalytic activity under simulated solar light. The catalytic activity of photocatalysts with both oxidation and reduction co-catalysts (Au@TiO 2 @RuO 2) showed hydrogen evolution (3165 μmol g−1) almost two times more than that Au@TiO 2 and TiO 2 @RuO 2 with single co-catalysts. And the hydrogen evolved is more than three times as compared to TiO 2 (935 μmol g−1) without any co-catalyst. Hollow mesoporous morphology with different co-catalysts on inner and outer surfaces is believed to enhance photocatalytic activity which is due to better separation of photo-generated charges. Image 1 • Polystyrene template used in synthesis of hollow and mesoporous TiO 2 , Au@TiO 2 , Au@TiO 2 @RuO 2. • Core-shell spheres were produced through sol-gel technique. • The spheres in single step of calcination produced hollow, mesoporous and crystalline catalysts. • Photocatalysts with dual co-catalysts showed better hydrogen evolution under solar light. • Photocatalysts with dual co-catalysis showed better charge separation. [ABSTRACT FROM AUTHOR]

Graphical abstract The controllable phase heterojunction structure is afforded with augmented light absorption, high separation of photogenerated electron and hole pairs and unique band structure derived from the synergistic effect of the disordered layer, oxygen vacancy, branched and ordered structure, and phase heterojunction. Particularly, a high photocurrent density of 3.88 mA cm−2 is achieved by this photoelectrode. Highlights • The controllable fabrication of phase heterostructures is implemented by ALD. • The unique band structures suppress the recombination of photogenerated carriers. • The synergistic effect enhances the photocatalytic activity for water splitting. • The hydrogenated photoanode shows high photocurrent density of 3.88 mA cm−2. Abstract In this study, hydrogenated TiO 2 anatase/rutile phase heterojunction is fabricated and used for photoelectrochemical water splitting to generate clean H 2 energy under solar light. This TiO 2 phase heterojunction photocatalyst material with core-shell structures is accurately prepared by a hydrothermal method to grow the core of rutile TiO 2 nanorod arrays and an ALD technology to form the shell of the anatase TiO 2 layer with a controllable thickness, followed with a hydrogenated treatment to introduce some disordered structures and oxygen vacancies to the TiO 2 phase heterojunction. This new structured TiO 2 photocatalyst material yields a high photocurrent density of 3.88 mA cm−2 at 1.23 V vs.RHE under simulated solar light (100 mW cm−2) with a maximum IPCE of 59.7% at the wavelength of 380 nm. These values are almost 3.8 and 7.4 times higher than that of the bare rutile TiO 2 , respectively. The enhanced photoelectrochemical performances are mainly attributed to the synergistic effect of the core-shell phase heterojunction, highly ordered structure and post-hydrogenated treatment to accelarate the separation and transmission of the photogenerated electrons and holes. This hydrogenated TiO 2 core-shell phase heterojunction indicates promising potential applications in the fields of photoelectrocatalysis and photovoltaic devices under solar light. [ABSTRACT FROM AUTHOR]