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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).

Metalo-organske mreže (MOF) tip su poroznih materijala izgrađenih od metalnih kationa međusobno povezanih organskim komponentama, odnosno poveznicama. Velika poroznost MOF rezultira velikom specifičnom površinom spojeva zbog čega se koriste u katalitičke svrhe [1] i za skladištenje plinova [2]. U ovom istraživanju su solvotermalnom metodom sintetizirani MOF-ovi na osnovi lantana, cerija i praseodimija, te jantarne kiseline (SA). Kao otapalo je korištena kombinacija N, N-dimetilformamida (DMF) i vode. Sintetiziranim spojevima struktura je okarakterizirana pomoću infracrvene spektroskopije s Fourierovom transformacijom (FTIR) i rentgenske difrakcije na prahu (PXRD). Termička svojstva spojeva su okarakterizirana termogravimetrijskom analizom (TGA) i diferencijalnom pretražnom kalorimetrijom (DSC). Piroliza sintetiziranih spojeva provedena je u inertnoj i oksidativnoj atmosferi. Nadalje, pretražna elektronska mikroskopija (SEM) sintetiziranih spojeva ukazala je na morfologiju nanoštapića. Fizisorpcijskim mjerenjima je određena specifična površina i poroznost spojeva. Podaci dobiveni UV/Vis spektroskopijom su analizirani Taucovom metodom kako bi se odredile vrijednosti optičkih energijskih procijepa. Fotokatalitička razgradnja organskih bojila metilen plavo (MB) i rodamin B (RDB) uz dodatak sintetiziranih spojeva i/ili vodikovog peroksida kao kokatalizatora praćena je pomoću UV-VIS spektroskopije.

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.

Five different rare-earth-based high entropy oxides (HEOs) nanoparticles with fluorite type of structure and average crystallite sizes between 6 and 9 nm are prepared and their photocatalytic behaviour towards AZO dye degradation and photoelectrochemical water splitting for hydrogen generation is 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 mostly attributed to the accessibility of more photocatalytic active sites which provided radicals responsible for the AZO dye degradation. The material successfully produces 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 engender hydrogen in 9.2 µmolmg–1 per hour that is much higher content than for pristine CeO2 material which amounts to 0.8 µmolmg–1 per hour.

Metal-organic frameworks (MOFs) are a type of porous materials built from metal cations coordinated by organic ligands, the so-called linkers, in the form of one-, two- or three- dimensional structures. Due to the large specific surface area of MOFs and the ability to easily release and accept electrons from lanthanide metals, they have potential applications in electrocatalysis, photocatalysis [1], and gas storage [2]. In this research, nanocrystalline succinate MOFs based on lanthanides La, Ce, and Pr were synthesized. The synthesis was carried out via the solvothermal method, in which a mixture of DMF and water was used. The structure of the obtained crystals was characterized using Fourier transform infrared spectroscopy (FTIR), powder X- ray diffraction (PXRD), and thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC). Morphology was determined using scanning electron microscopy (SEM). Pyrolysis of the obtained MOFs in the oxidative and inert atmosphere was monitored in situ by TGA/DSC, and residues were characterized by PXRD. Performed analyses revealed nanocrystalline rod-like nanostructures which could be used directly in catalysis or as storage materials. Synthesized MOFs are also suitable for application as precursors for the synthesis of shape-controlled lanthanide oxides and lanthanide-doped carbon nanostructures.

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. 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 mostly 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 that 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 disclose that a strong interaction between AZO dye methylene blue (MB) and CZLPY(111) is responsible for 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).