Polymeric carbon nitride photocatalyst has attracted much attention due to its visible light response and high chemical stability. However, bulk carbon nitride has a wide band gap and low polymerization, limiting its photocatalytic performance for water splitting. Synthesizing highly polymerized carbon nitride with a narrow band gap still remains challenging. Herein, we propose an ionothermal protocol using supramolecular precursors to fabricate highly polymerized wine-red carbon nitride (WRCN) nanosheets. Both theoretical and experimental investigations revealed that the supramolecular precursor with a high C:N ratio leads to an upward shift of the valence band edge, while the ionothermal synthesis promotes a high polymerization degree, leading to a narrow band gap of 1.82 eV for WRCN. Benefiting from enhanced light absorption and charge separation efficiency, WRCN-loaded hematite photoanode exhibits a much higher photocurrent density than both pristine hematite and bulk carbon nitride decorated hematite. This work may provide a novel strategy to manipulate the electronic structures of carbon nitrides for enhanced photoelectrochemical performances.

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Hematite is a promising photoanode for solar water splitting because of its favorable bandgap, excellent chemical stability and low cost. However, it suffers from both severe bulk and surface-charge recombinations, resulting in photoactivities much lower than the theoretical value. In this work, a facile new strategy is proposed by annealing hematite in the presence of potassium chloride (KCl) flux at 800°C. The photocurrent density of the annealed hematite, denoted ‘KCl-hematite’, increases from 0·34 mA/cm2 for pristine hematite to 0·54 mA/cm2 at 1·23 VRHE and further to 0·90 mA/cm2 after cobalt–phosphate (Co-Pi) deposition. Moreover, the photocurrent onset potential of KCl-hematite shows a cathodic shift of 120 mV compared with that of pristine hematite. It is demonstrated that potassium chloride flux can enhance the crystallinity and orderliness of hematite on the surface, reducing surface recombinations. This facile strategy by a flux offers a new insight to passivate surface recombinations of photoelectrodes and can be easily extended to other materials to enhance their photoactivities.

Nd 3x Y 3¹3x Al 5 O 12 (Nd:YAG) powders with high uniformity were synthesized by reverse-titration co-precipitation method. The precipitation formation process and dispersion mechanism of Nd:YAG precursor in coprecipitation process were analyzed, and the influence of the preparation technology on the dispersion of powders was explored by adjusting the concentration of precipitator, alcohol-water solvent and ratio of composite dispersant. In addition, through the analysis of the precursor calcination process, combined with SEM and particle size analysis, it is shown that, under optimum processing conditions, the powders have excellent particle uniformity, narrow particle size distribution and appropriate crystal size when calcined at 1150°C for 2 h.