The widespread heterojunction or p–n junction strategies fabricated between different semiconductors are generally used to promote the spatial charge separation in photocatalysis and solar cells, which originated from the principle that the junction composites possess totally different crystalline and energy structures. A vagarious and supreme challenge remained as to whether a junction could be formed between the identical composites with the same semiconductors and the crystalline phases. Herein, taking model semiconductor TiO2 as a prototype and proof-of-concept, a homophase junction was fabricated between the same crystalline phases of TiO2 with large and small nanoparticles. Photocatalytic H2 evolution and water splitting performances on three common TiO2 phases, brookite, anatase, and rutile, can be remarkably enhanced using such homophase junction strategy. The high photocatalytic activities are proposed to be attributed to the different surface band bending inducing the formation of a built-in electric field at the interface of large and small particles, which facilitates the spatial charge separation and inhibits the charge recombination. Our work provides a strategy for spatial charge separation in constructing highly efficient solar energy conversion systems, which is differentiated from the traditional junction strategies.

To make full use of natural waste, a novel Mg-Al mixed oxide adsorbent was synthesized by the dip-calcination method using the fluff of the chinar tree (FCT) and an Mg(II) and Al(III) chloride solution as raw materials. The adsorbents were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The effects of the Mg/Al molar ratio and calcination temperature on the performance of the novel Mg-Al mixed oxide adsorbent were investigated. The optimized Mg-Al mixed oxide adsorbent had a Langmuir adsorption capacity of 53 mg/g. This adsorption capacity was higher than that of the separate Mg oxide and Al oxide. The synergy between Mg and Al is beneficial to the adsorption performance of the material. The fluoride adsorption capacity of the optimized Mg-Al mixed oxide adsorbent is only slightly affected by ions such as Cl−, NO3−, SO42−, Na+, and K+ and is excellent for use in recycling and real water. The hydroxyl groups on the surface of the Mg-Al mixed oxide adsorbent play a key role in the adsorption of fluorine. The as-obtained novel Mg-Al mixed oxide adsorbent is an efficient and environmentally friendly agent for fluoride removal from drinking water.

Exquisite control over the interface structure is highly desired for the successful fabrication of a semiconductor heterojunction, which has been confirmed to effectively promote charge separation and transfer. However, the influences of the interface microstructure in the heterojunction on the charge separation and transfer efficiency are still unclear. Herein, taking the TiO 2 heterophase junction (A/R) between anatase and rutile phases and the TiO 2 homophase junction (R s /R) between large rutile rodlike particles and small rutile nanoparticles (∼20 nm) as a prototypical model, it is found that the lattice match at the interface is a key factor determining the charge separation and transfer efficiency and the photocatalytic activity. As compared with A/R, the atomically smooth interface with a highly matched lattice in R s /R leads to a less-defective and abrupt interface and provides a smooth interfacial charge separation and transfer path, leading to improved charge separation and transfer efficiency and a great enhancement in photocatalytic activity. This study provides a novel insight into optimizing the heterojunction structure by designing a highly matched lattice interface between two components.

A triple sequential junction providing a continuous charge separation and transfer channel was successfully fabricated by rational combining the anatase/rutile TiO2 heterophase and rutile/rutile TiO2 homophase junctions.