The crystal structure, physical and chemical properties, preparation methods and applications of titanium suboxides (TinO2n−1,n= integer greater than one) have recently attracted tremendous attention.
When alumina is produced by the Bayer process with high-sulfur bauxite, the sulfur would strongly corrode the 12Cr1MoV steel made heat exchanger. This study investigated the initial corrosion behavior of the 12Cr1MoV steel exposed to a thiosulfate-containing sodium aluminate (TCSA) solution under the evaporation conditions of alumina production. The obtained corrosion rate equation is V = 6.306·t·exp(−0.71). As corrosion progressed, with the corrosion product film growing, the corrosion current density declines slowly, and the corrosion resistance of the steel is increased. At 1–3 days, the corrosion product film consisted of FeO, Fe2O3, and FeOOH. S2O32− lead to corrosion in local areas of the steel and pits appeared. AlO2− is transformed into Al(OH)3 and filled in the corrosion pits. At 4 and 5 days, Fe3O4 is generated in the outermost layer, and Al(OH)3 is shed from the corrosion pits. The corrosion mechanism of 12Cr1MoV steel in a TCSA solution is proposed based on the experimental results.
Morphological tuning or additional cation doping is one of the potential and simple methods to enhance the photocatalytic properties of ceria, in which rare-earth element doped ceria nanorods (CeO2-RE NRs) are expected to be a promising photocatalyst with high activity. But the optimal doping conditions, including the variety and concentration of RE elements are ambiguous, and the contribution of doped RE ions to the enhancement of photocatalytic activity needs to be further studied. In this work, we doped La, Y and Sm with a wide range of 0%-30% into CeO2 NRs, and investigated the phase, morphology, band gap, oxygen vacancy concentration, PL spectra and photocatalytic activity variation under different doping conditions. All synthesized CeO2-RE NRs possessed a good nanorod morphology except the 15 and 30% Y-doped samples. The energy band gaps of the synthesized samples changed slightly; the 10% CeO2-RE NRs with the narrowest band gaps possessed the higher photocatalytic performance. The most outstanding photocatalyst was found to be the 10% Y-doped CeO2 NRs with a methylene blue photodegradation ratio of 85.59% and rate constant of 0.0134 min-1, which is particularly associated with a significant higher oxygen vacancy concentration and obviously lower recombination rate of photogenerated e-/h+ pairs. The doped RE ions and the promotion of oxygen vacancy generation impede the recombination of photogenerated carriers, which is proposed as the main reason to enhance the photocatalytic property of CeO2.
Oxygen vacancies (OVs) have critical effects on the photoelectric characterizations and photocatalytic activity of nanoceria, but the contributions of surface OVs on the promoted photocatalytic properties are not clear yet. In this work, we synthesized ceria nanopolyhedron (P-CeO2), ceria nanocube (C-CeO2) and ceria nanorod (R-CeO2), respectively, and annealed them at 600 °C in air, 30%, 60% or pure H2. After annealing, the surface OVs concentration of ceria elevates with the rising of H2 concentration. Photocatalytic activity of annealed ceria is promoted with the increasing of surface OVs, the methylene blue photodegradation ratio with pure hydrogen annealed of P-CeO2, C-CeO2 or R-CeO2 is 93.82%, 85.15% and 90.09%, respectively. Band gap of annealed ceria expands first and then tends to narrow slightly with the rising of surface OVs, while the valence band (VB) and conductive band (CB) of annealed ceria changed slightly. Both of photoluminescence spectra and photocurrent results indicate that the separation efficiency of photoinduced electron-hole pairs is significantly enhanced with the increasing of the surface OVs concentration. The notable weakened recombination of photogenerated carrier is suggested to attribute a momentous contribution on the enhanced photocatalytic activity of ceria which contains surface OVs.
It is of great scientific and industrial value to develop cheap and efficient supported non-noble metal-based catalysts for the selective hydrogenation of halogenated nitrobenzenes. In this work, hollow structure Ni-based nano-catalyst coated with ultrathin nitrogen-doped carbon layers (H-Ni@NC) have been prepared. The etching of SiO2 template before calcination and decomposition of residual Ni3Si2O5(OH)4 shell into SiO2 leads the catalysts could maintain good mechanical property and stability. The H-Ni@NC catalyst prepared at 600 oC exhibits the optimal catalytic performance for the catalytic selective hydrogenation of halogenated nitrobenzenes under mild conditions (60 oC) when using hydrazine hydrate (N2H4·H2O) as the reducing agent, and could maintain its catalytic properties even after 5 consecutive runs. The contrast experiments confirm that the combination of hollow structure and N-doped carbon protective layer make the catalyst show the best catalytic effect, and the synergistic effects are further discussed in detail combine with characterization analysis. In addition, this work further reveals the mechanism of Ni-based catalyst for the transfer hydrogenation of halogenated nitrobenzenes, which may provide a reference idea for the preparation of other Ni-based catalysts.
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