Jingtao Hou

Tuning the K+ concentration in the tunnel of OMS-2 nanorods leads to a significant enhancement of the catalytic activity for benzene oxidation.

OMS-2 nanorods with tunable K(+) concentration were prepared by a facile hydrothermal redox reaction of MnSO4, (NH4)2S2O8, and (NH4)2SO4 at 120 °C by adding KNO3 at different KNO3/MnSO4 molar ratios. The OMS-2 nanorod catalysts are characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption and desorption, inductively coupled plasma, and X-ray photoelectron spectrometry. The effect of K(+) concentration on the lattice oxygen activity of OMS-2 is theoretically and experimentally studied by density functional theory calculations and CO temperature-programmed reduction. The results show that increasing the K(+) concentration leads to a considerable enhancement of the lattice oxygen activity in OMS-2 nanorods. An enormous decrease (ΔT50 = 89 °C; ΔT90 > 160 °C) in reaction temperatures T50 and T90 (corresponding to 50 and 90% benzene conversion, respectively) for benzene oxidation has been achieved by increasing the K(+) concentration in the K(+)-doped OMS-2 nanorods due to the considerable enhancement of the lattice oxygen activity.

Preparation and Enhanced Photocatalytic Activity of TiO2 Nanocrystals with Internal Pores

Anatase TiO2 nanocrystals with internal pores are prepared by a novel facile microwave-assisted hydrolysis of a mixture of TiOCl2 and HF aqueous solutions, followed by calcination at 400 °C. The TiO2 nanocrystals with internal pores are characterized by XRD, TEM, SEM, BET, EDS, and XPS. The formation mechanism of the TiO2 nanocrystals with internal pores is discussed by investigating the role of fluorine and the calcination. The photocatalytic measurement shows that the TiO2 nanocrystals with internal pores exhibit much higher photocatalytic activity for the photodegradation of crystal violet, methyl orange, and 4-chlorophenol than the TiO2 solid nanocrystals. The photocatalytic enhancement is due to the fluorination of TiO2 nanocrystals as well as its unique hollow nanostructure, which results in the higher separation efficiency of photogenerated electrons and holes in the TiO2 nanocrystals with internal pores than in its solid counterpart.

Effect of giant oxygen vacancy defects on the catalytic oxidation of OMS-2 nanorods

We have developed a novel and facile approach of hydrothermal redox reaction to prepare cryptomelane-type octahedral molecular sieve (OMS-2) nanorods with tunable concentration of oxygen vacancy defects (OVDs). We demonstrate a giant OVD effect on the catalytic performance of OMS-2. Increasing the OVD concentration considerably enhances the lattice oxygen reactivity, thus tremendously promoting the catalytic activity for the oxidation of benzene.

Tremendous Effect of the Morphology of Birnessite-Type Manganese Oxide Nanostructures on Catalytic Activity

The octahedral layered birnessite-type manganese oxide (OL-1) with the morphologies of nanoflowers, nanowires, and nanosheets were prepared and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric/differential scanning calorimetry (TG/DSC), Brunnauer-Emmett-Teller (BET), inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS). The OL-1 nanoflowers possess the highest concentration of oxygen vacancies or Mn(3+), followed by the OL-1 nanowires and nanosheets. The result of catalytic tests shows that the OL-1 nanoflowers exhibit a tremendous enhancement in the catalytic activity for benzene oxidation as compared to the OL-1 nanowires and nanosheets. Compared to the OL-1 nanosheets, the OL-1 nanoflowers demonstrate an enormous decrease (ΔT(50) = 274 °C; ΔT(90) > 248 °C) in reaction temperatures T50 and T90 (corresponding to 50 and 90% benzene conversion, respectively) for benzene oxidation. The origin of the tremendous effect of morphology on the catalytic activity for the nanostructured OL-1 catalysts is experimentally and theoretically studied via CO temperature-programmed reduction (CO-TPR) and density functional theory (DFT) calculation. The tremendous catalytic enhancement of the OL-1 nanoflowers compared to the OL-1 nanowires and nanosheets is attributed to their highest surface area as well as their highest lattice oxygen reactivity due to their higher concentration of oxygen vacancies or Mn(3+), thus tremendously improving the catalytic activity for the benzene oxidation.

Synergetic effect between photocatalysis on TiO2 and solar light-driven thermocatalysis on MnOx for benzene purification on MnOx/TiO2 nanocomposites

MnOx/TiO2 nanocomposites are prepared by the hydrothermal redox reaction of Mn(NO3)2 and KMnO4 with KMnO4/Mn(NO3)2 molar ratio of 2 : 1 in the presence of TiO2(P25). The MnOx/TiO2 nanocomposites are characterized by XRD, TEM, EDX, XPS, and BET. Manganese oxide supported on TiO2 nanoparticles is amorphous. The MnOx/TiO2 nanocomposites can efficiently transform absorbed solar energy into thermal energy, resulting in a considerable increase of temperature. The MnOx/TiO2 nanocomposites exhibit excellent catalytic activity and durability for the gas-phase oxidation of carcinogenic and recalcitrant benzene under the irradiation of full solar spectrum light and visible-infrared light. For the first time, we find a synergetic effect between photocatalysis on TiO2 and solar light-driven thermocatalysis on supported manganese oxide, which significantly improves the catalytic activity of the MnOx/TiO2 nanocomposites.

Densely populated mesopores in microcuboid CeO2 crystal leading to a significant enhancement of catalytic activity

Unique mesoporous microcuboid CeO2 crystals were prepared by a facile method, involving the hydrothermal hydrolysis of a Ce(NO3)3 aqueous solution in the presence of urea at 180 °C followed by calcination at 400 °C, and characterized with XRD, SEM, TEM, BET, Raman, XPS, positron annihilation spectroscopy and TPR. It was found for the first time that the presence of densely populated mesopores in the microcuboid CeO2 crystals results in highly reactive surface lattice oxygen due to the exposure of the mesopore wall surface with high interfacial curvature, thus leading to a significant enhancement in catalytic activity as compared to single crystal CeO2 nanocubes without mesopores.

Efficient UV-vis-IR light-driven thermocatalytic purification of benzene on a Pt/CeO2 nanocomposite significantly promoted by hot electron-induced photoactivation

Complete oxidation of volatile organic compounds (VOCs) as major air pollutants on supported noble metal catalysts is a very important industrial reaction for environmental purification. It is highly desirable but greatly challenging to find a green process with low energy consumption and high catalytic efficiency for VOC abatement by using renewable solar energy. Here, we achieve highly efficient catalytic oxidation of benzene (one of the typical VOCs) on a nanocomposite of Pt nanoparticles partially confined in the mesopores of microsized mesoporous CeO2 (Pt/CeO2-MM) with the irradiation of full solar spectrum or visible-infrared light, even with infrared light irradiation. The highly efficient catalytic activity arises from the solar light-driven thermocatalysis on Pt/CeO2-MM due to the excellent thermocatalytic activity and the local heating effect induced by strong surface plasmonic absorption of the Pt nanoparticles in the entire solar spectrum region from 200 to 2500 nm. Remarkably, it is found that a novel hot electron-induced photoactivation process significantly enhances the solar light-driven thermocatalytic activity. In situ FTIR in the dark and with solar light irradiation reveals that the hot electron-induced photoactivation of benzene adsorbed on the Pt nanoparticles in Pt/CeO2-MM plays a decisive role in the catalytic enhancement.