Pengyi Zhang

Efficient Removal of Formaldehyde by Nanosized Gold on Well-Defined CeO2 Nanorods at Room Temperature

Gold (Au) nanoparticles (NPs) supported on well-defined ceria (CeO2) nanorods with exposed {110} and {100} facets were prepared by a deposition-precipitation method and characterized by powder X-ray diffraction, micro-Raman spectroscopy, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption, transmission electron microscopy, high-resolution transmission electron microscopy, and high-angle annular dark-field scanning transmission electron microscopy. Both nanometer and subnanometer gold particles were found to coexist on ceria supports with various Au contents (0.01-5.4 wt %). The catalytic performance of Au/CeO2 catalysts was examined for formaldehyde (HCHO) oxidation into CO2 and H2O at room temperature and shown to be Au content dependent, with 1.8 wt % Au/CeO2 displaying the best performance. On the basis of the results from hydrogen temperature-programmed reduction and in situ Fourier transform infrared spectroscopy observations, the high reactivity and stability of Au/CeO2 catalysts is mainly attributed to the well-defined ceria nanorods with {110} and {100} facets which present a relatively low energy for oxygen vacancy formation. Furthermore, gold NPs could induce the weakened Ce-O bond which in turn promotes HCHO oxidation.

Enhanced catalytic activity of hierarchically macro-/mesoporous Pt/TiO2 toward room-temperature decomposition of formaldehyde

Hierarchically macro-/mesoporous Pt/TiO2 is prepared by hydrothermally treating the tetrabutyl titanate (Ti(OC4H9)4) precipitates in pure water, followed by a combined NaOH-assisted NaBH4-reduction deposition of Pt nanoparticles (NPs) on the TiO2 surface. The catalytic activity toward the catalytic decomposition of formaldehyde (HCHO) vapor in air at ambient temperature is evaluated. The prepared Pt/TiO2 catalyst exhibits excellent catalytic activity and recyclability, and 90.6% HCHO with an initial concentration of ca. 265 ppm can be completely decomposed within 60 min, which is significantly higher than that using commercial-grade Degussa P25 TiO2 with an equal Pt-loading amount (56.2% HCHO decomposition). The high catalytic activity can be mainly attributed to the hierarchically macro-/mesoporous structures of the TiO2 support with large specific surface area and optimal pore size. These characteristics not only enhance the adsorption of HCHO molecules, as well as facilitate the diffusion and transport of reactants and products, but also promote the dispersion of Pt NPs with small particle size inside and outside the pores. This study demonstrates that hierarchically macro-/mesoporous Pt/TiO2 can serve as an efficient catalyst for indoor HCHO decomposition and will provide new insights into the environmentally benign design and preparation of low-cost and high-performance catalysts for indoor air purification.

Layered manganese oxides for formaldehyde-oxidation at room temperature: the effect of interlayer cations

A series of K-, Mg-, Ca-, and Fe-containing birnessites were prepared by a facile comproportionation reaction of Mn2+ and MnO4− in the presence of different metal cations. The as-synthesized birnessite samples were characterized by FESEM, XRD, TG, and XPS. The catalytic activity toward decomposition of HCHO was evaluated under ambient temperature. Fe-birnessite showed the highest HCHO oxidation activity due to its highest content of surface hydroxyl groups. However, the CO2 generation by Fe-birnessite was relatively low due to the accumulation of formate species without further oxidation. The influence of different interlayer cations on the activity of birnessite was studied by H2-TPR, O2-TPD, and HCHO in situ DRIFTS. The result indicates that K+ leads to a considerable enhancement of surface oxygen activity which then facilitates the regeneration of surface hydroxyls by activating H2O, therefore K-birnessite showed the highest CO2 generation performance during HCHO removal at ambient temperature. HCHO of 0.5 mg m−3 and the gas hourly space velocity (GHSV) of 1 200 000 h−1 (the corresponding contact time is 0.003 s) were selected to check the stability of the samples. K-Bir still showed stable activity with the removal efficiency reaching 40% under these critical test conditions. Considering the effect of introducing different metal cations, this work provides new insight into designing high performance catalysts for indoor air purification.

The effect of morphology of α-MnO2 on catalytic decomposition of gaseous ozone

To learn the effect of morphology of α-MnO2 on its catalytic activity for ozone decomposition, three α-MnO2 nanostructures with different morphologies including nanofibres, nanorods and nanotubes were prepared via a hydrothermal process and characterized by XRD, BET, TEM, H2-TPR, O2-TPD, TGA and XPS. The three α-MnO2 show differences in surface area, average oxidation state of Mn and adsorbed surface oxygen species, as well as exposed crystal facets, i.e. (211), (110) and (200) corresponding to nanofibres, nanorods and nanotubes, respectively. It is found that the catalytic activity of α-MnO2 is dependent on the amount of oxygen vacancies. The α-MnO2 nanofibers with the most abundant oxygen vacancies exhibit the best activity, which is ascribed to their largest specific surface area and exposed (211) facet. In situ Raman analysis indicated that intermediate peroxide species formed on the α-MnO2 surface during ozone decomposition, and peroxide species over the α-MnO2 nanofibres are produced at lower Raman band due to their uniform dispersion, which is favorable to ozone decomposition. Finally, the ozone decomposition steps involving oxygen vacancy is proposed.

Room temperature synthesis of manganese oxide quantum dots and their application as a fluorescent probe for the detection of metal ions in aqueous media

A rapid and facile route to access manganese oxide quantum dots (MOQDs) has been developed for the first time at room temperature by separating them from a manganese oxide nanosheet colloidal suspension using ultrafiltration. The size and thickness of the as-prepared MOQDs was 3.0–9.0 nm and 1.0–2.5 nm, respectively, which can be controlled by changing the molecular weight cut-off of the membrane. The photoluminescence behavior of the MOQDs is found to be strongly dependent on the excitation wavelength as well as particle size, but insignificant dependence on pH. Moreover, the MOQDs showed excellent long term resistance to photobleaching. The features of excellent photostability, mild pH variation and air resistance, make MOQDs a good candidate as a fluorescent probe for the detection of metal ions in aqueous media. The experiments of selectivity and competition towards various metal ions indicate that the MOQDs exhibit high selectivity for Mn2+ and Fe3+, and the other metal ions have an insignificant effect on the sensing system.

Environmental Photocatalysis 2013

1 State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Luoshi Road No. 122, Wuhan 430070, China 2 Institute of Materials Science, National Centre for Scientific Research “Demokritos,” Ag. Paraskevi, Attikis, Greece 3 State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China 4Department of Chemistry, Key Laboratory of Resource Chemistry of Ministry of Education, Shanghai Normal University, Shanghai 200234, China 5 Department of Chemistry, School of Science, Wuhan University of Technology, Wuhan 430070, China