Preparationand Catalytic Performance of Porous La0.6Sr0.4FexBi1-xO3（x=0,0.2） and Mox/BiVO4-δSσ（M=Co, Fe） for the Oxidative Removal of Orgainic Pollutants
|School||Beijing University of Technology|
|Keywords||Three-dimensionally ordered macroporous strontium-orbismuth-substituted lanthanum ferrite Sulfur-doped bismuth vanadate-supportedcobalt or iron oxide Toluene oxidation Visible-light-driven methylene blue orformaldehyde degradation Organic pollutant oxidative removal|
The waste gases and wastewater emitted from industrial and transportationactivities contain organic pollutants that are harmful to the atmosphere and humanhealth. Therefore, controlling and eliminating these pollutants are of practical andlong-term significance. Thermal catalytic or photocatalytic technology is one of themost effective pathways for the removal of organic pollutants, in which thedevelopment of novel and high-efficiency catalysts is the key issue for such atechnology. Perovskite-type oxides and visible-light-responsive catalytic materialscan be used to remove organic pollutants, and supported transition-metal oxides orhetero-atom doping can improve their catalytic performance. In the presentdissertation, we adopted the surfactant-assisted polymethyl methacrylate（PMMA）-hard-templating method to prepare three-dimensionally orderedmacroporous （3DOM） La0.6Sr(0.4FexBi1-xO3-δ（x=0and0.2） catalysts, and thesurfactant-assisted alcohol-hydrothermal strategy and incipient wetness impregnationmethod to fabricate porous olive-shaped yMOx/BiVO4-δSσ（M=Co, Fe; y=01.60wt%） photocatalysts. Physicochemical properties of the catalysts were characterizedby means of techniques, such as X-ray diffraction （XRD）, laser Raman spectroscopy（Raman）, Fourier transform infrared spectroscopy （FT-IR）, scanning electronmicroscopy （SEM）, transmission electron microscopy （TEM）, selected-area electrondiffraction （SAED）, N2adsorption-desorption （BET）, mercury porosimetry,temperature-programmed reduction （TPR）, X-ray photoelectron spectroscopy （XPS）,X-ray fluorescence spectroscopy （XRF）, and ultraviolet-visible diffuse reflectancespectroscopy （UV-vis DRS）. The catalytic activities of the3DOMLa0.6Sr(0.4FexBi1-xO3-δ materials for the oxidation of toluene and those of porousolive-shaped BiVO4-δSσand yMOx/BiVO4-δSσphotocatalysts for the oxidativedegradation of methylene blue （MB） or formaldehyde under visible-light illuminationwere evaluated. The main results obtained in the present investigations are as follows:1.3DOM La0.6Sr0.4FeO3（LSF-F127, LSF-PEG, LSF-PEG-EtOH, and LSF-Lysine）with mesoporous or nanovoid-like skeletons were prepared using the surfactant（Pluronic F127, poly（ethylene glycol）（PEG） or L-lysine）-assistedPMMA-templating method in aqueous or40%ethanol aqueous solution. It isshown that the as-prepared La0.6Sr0.4FeO3catalysts possessed a single-phaseorthorhombic crystal structure. The nature of surfactant and solvent could greatlyinfluence the pore structure and surface area of the final product. Treating theprecursors of the La0.6Sr0.4FeO3catalysts first in a N2flow at500℃and thenin an air flow at750℃could lead to the formation of3DOM-structuredLa0.6Sr0.4FeO3. The porous LSF catalysts performed well in toluene oxidation, with the LSF-PEG catalyst showing the best performance （the reactiontemperatures T10%, T50%, and T90%were54,225, and280℃at20,000mL/（g h）,respectively）. It is concluded that the good catalytic performance of3DOM-structured La0.6Sr0.4FeO3was associated with their larger surface areas,higher oxygen adspecies concentrations, better low-temperature reducibility, andhigh-quality3DOM structures.2.3DOM-structured La0.6Sr0.4Fe0.8Bi0.2O3-δ catalysts were prepared using thesurfactant （Pluronic F127, PEG, L-lysine or xylitol）-assisted PMMA-templatingstrategy. It is shown that the La0.6Sr0.4Fe0.8Bi0.2O3-δ catalysts were ofsingle-phase orthorhombic crystal structure. The nature of surfactant and solventhad an important influence on the pore structure and surface area ofLa0.6Sr0.4Fe0.8Bi0.2O3-δ. The surface Fe4+/Fe3+or Oads/Olattmolar ratio andlow-temperature reducibility were important factors influencing the catalyticperformance of La0.6Sr0.4Fe0.8Bi0.2O3-δ. The porous La0.6Sr0.4Fe0.8Bi0.2O3-δ catalysts much outperformed the bulk counterpart, with theLa0.6Sr0.4Fe0.8Bi0.2O3-δ catalyst derived with xylitol showing the highest activity（T50%=220℃and T50%=242℃at20,000mL/（g h））. Apparent activationenergies of the porous La0.6Sr0.4Fe0.8Bi0.2O3-δ catalysts were in the range of4674kJ/mol. It is concluded that the high oxygen adspecies concentration andgood low-temperature reducibility were responsible for the excellent activity ofthe porous La0.6Sr0.4Fe0.8Bi0.2O3-δ catalyst derived with xylitol.3. Porous monoclinic BiVO4and S-doped bismuth vanadate (BiVO4S0.05,BiVO4S0.08, and BiVO4S0.12) photocatalysts were fabricated using thedodecylamine-assisted alcohol-hydrothermal method in the absence and presenceof Na2S and thiourea. The as-prepared photocatalysts exhibited a surface area of8.4–12.5m2/g and a bandgap energy of2.40–2.48eV. There was the presence ofsurface Bi5+, Bi4+, V5+, and V4+species on the surface of BiVO4S0.05,BiVO4S0.08, and BiVO4S0.12. The BiVO4S0.08photocatalyst possessed thehighest surface adsorbed oxygen species concentration. S-doping had animportant impact on the photocatalytic activity of the BiVO4photocatalyst. Forthe oxidative degradation of MB and formaldehyde under the visible-lightillumination, the highest photocatalytic activity of the BiVO4S0.08photocatalystwas related to its higher surface adsorbed oxygen species concentration andlower bandgap energy.4. Porous monoclinic scheetlite yCoOx/BiVO4S0.08（y=0.1,0.8, and1.6wt%）photocatalysts with an olive-like morphology were fabricated using thedodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnationmethods. The yCoOx/BiVO4S0.08photocatalysts possessed a surface area of 8.99.2m2/g and a bandgap energy of2.382.41eV. There was the co-presenceof surface Bi5+, Bi3+, V5+, V4+, Co3+, and Co2+species on the surface of yCoOx/BiVO4S0.08. The0.8wt%CoOx/BiVO4S0.08photocatalyst performed the bestfor MB degradation under visible-light irradiation. It is concluded that the sulfur-and CoOx-doping, higher surface oxygen species concentration, and lowerbandgap energy were responsible for the good visible-light-driven photocatalyticactivity of0.8wt%CoOx/BiVO4S0.08.5. Porous monoclinic scheetlite yFeOx/BiVO4S0.08（y=0.06,0.76, and1.40wt%）photocatalysts with an olive-like morphology were obtained using thedodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnationmethods. The yFeOx/BiVO4S0.08photocatalysts exhibited a surface area of4.97.3m2/g and a bandgap energy of2.392.42eV. There was the co-presenceof surface Bi5+, Bi3+, V5+, V4+, Fe3+, and Fe2+species on the surface ofyFeOx/BiVO4S0.08. The1.40wt%FeOx/BiVO4S0.08photocatalyst performedthe best for MB degradation under visible-light illumination. We believe that thesulfur and FeOxco-doping, higher oxygen adspecies concentration, and lowerbandgap energy accounted for the good visible-light-driven photocatalyticperformance of1.40wt%FeOx/BiVO4S0.08.