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[en] Graphical abstract: A series of novel β-Bi2O3-NiO/Ni composites were synthesized via one-step solution combustion method. The coupling of β-Bi2O3 with NiO/Ni promoted the catalytic activity under visible light irradiation, which can be ascribed to the increase of separation efficiency of electrons and holes over β-Bi2O3-NiO and the existence of metallic Ni. - Highlights: • β-Bi2O3-NiO/Ni composites were prepared via one-step solution combustion method. • The materials had excellent visible light absorption ability and narrow band gaps. • Ni may show a plasmonic property and increase the visible light absorption. • The photocatalytic mechanism of the β-Bi2O3-NiO/Ni composites was proposed. • The as-obtained samples could be recycled easily by magnetic separation. - Abstract: A series of novel β-Bi2O3-NiO/Ni heterojunctions were synthesized via one-step solution combustion method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectroscopy and terephthalic acid (TA) fluorescence. The obtained NiO/Ni samples showed visible light absorbance ability and had narrow band gap of ca. 2.20 eV. The coupling of β-Bi2O3 with NiO/Ni promoted the visible light catalytic performance. The enhanced activity could be ascribed to the increase of separation efficiency of electrons and holes and the existence of metallic Ni, which might show a plasmonic effect and could increase the light absorption ability. The scavengers’ tests demonstrated that hydroxyl radical and holes species played a major role for the methyl orange degradation. Furthermore, the as-obtained samples had magnetic properties and could be recycled easily by magnetic separation from the reaction system. Finally, the mechanism of the photocatalytic reaction over β-Bi2O3-NiO/Ni composites was proposed
[en] Graphical abstract: - Highlights: • Inexpensive Al2O3/C3N4 hybrid with high visible light activity is firstly reported. • Defect sites existed in amorphous Al2O3 are excellent electron acceptors. • G-C3N4 is surface modified by NH4OH to enhance hydroxyl groups. • The role of hydroxyl in the formation process of g-C3N4-based hybrids is discussed. • The reason responsible for the surface positive charges of Al2O3 is presented. - Abstract: Novel Al2O3/g-C3N4 heterojunction photocatalysts were fabricated through ultrasonic dispersion method. Al2O3, obtained via solution combustion, contained amorphous ingredient with lots of defect sites and was used as active component for transferring photo-induced electrons of g-C3N4. G-C3N4 was grafted surface hydroxyl groups in the presence of ammonia aqueous solution to combine with Al2O3 possessing positive charges via hydrogen bond. The XRD, SEM, element map, TEM, HRTEM, FT-IR, and XPS results indicate that these synthesized materials are two-phase hybrids of Al2O3 and g-C3N4 with interaction. The photocatalytic results for the degradation of rhodamine B (RhB) indicate that the most active heterojunction proportion is 60 wt.% g-C3N4:40 wt.% Al2O3, the visible light photocatalytic activity of which is 3.8 times that of a mechanical mixture. The enhanced performance is attributed to the high separation efficiency of photo-induced electrons from the LUMO of g-C3N4 injected into the defect sites of Al2O3, which is verified by photoluminescence spectroscopy (PL) and surface photovoltage (SPV) measurements. The electron paramagnetic resonance (EPR) signals and radical scavengers trapping experiments reveal holes (h+) and superoxide anion radical (·O2−) are the main active species responsible for the degradation of RhB
[en] Graphical abstract: N-doped P25 TiO2–amorphous Al2O3 composites were facile prepared via one-step solution combustion, which showed much higher visible-light photocatalytic activity than that of P25 TiO2 due to the N-doping in the high temperature combustion process, synergetic effect between amorphous Al2O3 and TiO2, and high specific surface area. Highlights: ► N-doped P25 TiO2–amorphous Al2O3 composites were prepared via solution combustion. ► The composites showed much higher visible light activity than that of P25 TiO2. ► Amorphous Al2O3 was firstly found to be a photocatalyst under UV light illumination. ► Probable photocatalytic mechanism under visible light irradiation was proposed. - Abstract: Nitrogen-doped Degussa P25 TiO2–amorphous Al2O3 composites were prepared via facile solution combustion. The composites were characterised using X-ray diffraction, high-resolution transmission microscopy, scanning electron microscopy, nitrogen adsorption–desorption measurements, X-ray photoelectron spectroscopy, UV–vis light-diffusion reflectance spectrometry (DRS), zeta-potential measurements, and photoluminescence spectroscopy. The DRS results showed that TiO2 and amorphous Al2O3 exhibited absorption in the UV region. However, the Al2O3/TiO2 composite exhibited visible-light absorption, which was attributed to N-doping during high-temperature combustion and to alterations in the electronic structure of Ti species induced by the addition of Al. The optimal molar ratio of TiO2 to Al2O3 was 1.5:1, and this composite exhibited a large specific surface area of 152 m2/g, surface positive charges, and enhanced photocatalytic activity. These characteristics enhanced the degradation rate of anionic methylene orange, which was 43.6 times greater than that of pure P25 TiO2. The high visible-light photocatalytic activity was attributed to synthetic effects between amorphous Al2O3 and TiO2, low recombination efficiency of photo-excited electrons and holes, N-doping, and a large specific surface area. Experiments that involved radical scavengers indicated that ·OH and O2·− were the main reactive species. A potential photocatalytic mechanism was also proposed.