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The influence of the cation of imidazolium‐derived ionic liquids (ILs) on a low‐temperature solution‐based synthesis of hexagonal tungsten bronze (HTB) type Ti(OH)OF ⋅ 0.66 H2O and bronze‐type TiO2(B) is investigated. The IL (Cxmim BF4) acts as solvent and also as reaction partner with respect to the decomposition of [BF4]−, releasing F−. In the present study, the chain length of the alkyl chain side groups attached to the imidazolium ring was varied (C2mim BF4 to C10mim BF4), and the obtained solids were analyzed by Powder X‐Ray diffraction (PXRD) followed by Rietveld refinement. As a main finding these analyses indicate a transformation of Ti(OH)OF ⋅ 0.66 H2O into TiO2(B), and upon prolonged reaction time finally also into anatase TiO2. Rietveld analysis suggests that when using ILs with longer alkyl chains, the conversion of Ti(OH)OF ⋅ 0.66 H2O is slower compared to syntheses performed with smaller alkyl chains. Hence, Ti(OH)OF ⋅ 0.66 H2O appears to be metastable and is stabilized by long‐chain ILs serving as surfactant attached to the crystallites’ surface. In this view, the ILs shield the nanoparticles and thus slow down the conversion into the more stable compounds. This confirms previous findings that ILs act as both, solvent and reaction medium in this reaction, thus enabling the synthesis of peculiar Ti‐oxides., Under the influence: In this study the influence of the alkyl chain lengths of imidazolium‐based ionic liquids (ILs) on the a low‐temperature synthesis of Ti(OH)OF ⋅ 0.66 H2O and TiO2(B) nanoparticles is investigated.

Five different rare-earth-based nanocrystalline high entropy oxides (HEOs) with fluorite structures and average crystallite sizes between 6 and 8 nm were prepared and their photocatalytic behavior towards AZO dye degradation and photoelectrochemical water splitting for hydrogen generation was examined. The cationic site in the fluorite lattice consists of five equimolar elements selected from the group of rare-earth elements including La, Ce, Pr, Eu, and Gd, and second-row transition metals, Y and Zr. Studied HEOs exhibit bandgaps in the range from 1.91 eV to 3.0 eV and appropriate valence and conduction bands for water splitting. They reveal high photocatalytic activity that is mainly attributed to the accessibility of more photocatalytic active sites which provided radicals responsible for the AZO dye degradation. The materials successfully produce hydrogen by photocatalytic water splitting, suggesting the potential of HEOs as new photocatalysts. The photocatalytic performances of all studied HEOs outperform the single fluorite oxides or equivalent mixed oxides. The Ce0.2Zr0.2La0.2Pr0.2Y0.2O2 (CZLPY) engender hydrogen in 9.2 µmolmg–1 per hour is much higher content than for pristine CeO2 material which amounts to 0.8 µmolmg–1 per hour. The explanation of the obtained experimental results is supported by density functional theory (DFT) calculations. The density of states (DOS) and the projected DOS after high-entropy equimolar doping (CZLPY) of starting pristine CeO2 indicated that the bandgap is significantly reduced from 3.48 to 2.71 eV due to Pr 4f and O 2p orbital mixing. DFT calculation also discloses that a strong interaction between AZO dye methylene blue (MB) and CZLPY(111) is responsible for the observed higher photodegradation of MB by CZLPY compared to pristine CeO2. This occurs due to the existence of three solid bondings of MB with the surface of CZLPY(111) compared to only one solid bonding with the surface of CeO2 (111).

Five different rare-earth-based nanocrystalline high-entropy oxides (HEOs) with fluorite type of structure and average crystallite sizes between 6 and 8 nm were prepared and their photocatalytic behaviour towards AZO dye degradation and photoelectrochemical water splitting for hydrogen generation was examined. The cationic site in the fluorite lattice consists of five equimolar elements selected from the group of rare-earth elements, including La, Ce, Pr, Eu, and Gd and second-row transition metals, Y and Zr. They reveal high photocatalytic activity which is mostly attributed to the accessibility of more photocatalytically active sites [1] which provided radicals responsible for the AZO dye degradation [1-3]. The materials successfully produce hydrogen by photocatalytic water splitting, suggesting the potential of HEOs as new photocatalysts. The photocatalytic performances of all studied HEOs outperform the single fluorite oxides or equivalent mixed oxides. The Ce0.2Zr0.2La0.2Pr0.2Y0.2O2 (CZLPY) engender hydrogen in the quantity of 9.2 µmol mg–1 per hour, which is much higher content than for pristine CeO2 material which amounts to 0.8 µmol mg–1 per hour.