Room temperature synthesis of a novel gamma-MnO2 hollow structure for aerobic oxidation of benzyl alcohol.

A novel gamma-MnO(2) hollow structure has been synthesized at room temperature using a simple chemical reaction between MnSO(4) and KMnO(4) in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. The synthesized gamma-MnO(2) hollow structure was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET analysis. It was found that the hollow structure consisting of short gamma-MnO(2) nanorods with diameters of 5-10 nm and lengths of 50-100 nm could form when the MnSO(4)/KMnO(4) mole ratio was equal to or larger than 2.3. The excess amount of Mn(2+) in solution was observed to promote the crystallization of gamma-MnO(2) nanorods and the formation of the gamma-MnO(2) hollow structure. In addition, the evolution of microstructure and morphology of the products obtained with a MnSO(4)/KMnO(4) mole ratio of 2.3 at different reaction times revealed that the hollow structure was formed via an Ostward ripening process. Furthermore, the obtained gamma-MnO(2) hollow structure was found to exhibit a better catalytic performance than conventional gamma-MnO(2) in the aerobic oxidation of benzyl alcohol to benzaldehyde, demonstrating its possible application in alcohol oxidation.

The formation of hollow poly(methyl methacrylate)/multiwalled carbon nanotube nanocomposite cylinders by microwave irradiation.

Poly(methyl methacrylate) (PMMA)/multiwalled carbon nanotube (MWCNT) nanocomposite particles with 1, 2 and 4 wt% of MWCNTs were prepared by mechanical grinding of PMMA and MWCNT powders in a mortar at room temperature. Both scanning electron microscopy and Raman scattering characterizations revealed that these nanocomposite particles consist of a PMMA core and a MWCNT shell. The PMMA/MWCNT nanocomposite particles were used to fabricate the corresponding nanocomposites in the form of a hollow cylinder with various diameters and heights under 700 W microwave irradiation within 1 min. A mechanism for the fast microwave assisted forming process is proposed. These experimental results may lead to a new technology for forming hollow polymeric articles that is different from the conventional injection and blowing process.

Effect of initial solution pH on the degradation of Orange II using clay-based Fe nanocomposites as heterogeneous photo-Fenton catalyst.

Effect of initial solution pH on the discoloration and mineralization of 0.2 mM Orange II by using two clay-based Fe nanocomposites (Fe-B (Fe supported on bentonite clay) and Fe-Lap-RD (Fe supported on laponite clay)) as catalysts was studied in detail. It was found that the initial solution pH not only influences the photo-catalytic activity of Fe-B and Fe-Lap-RD but also the Fe leaching from the two catalysts. Both catalysts show the best photo-catalytic activity at an initial solution pH of 3.0, and the activity of the catalysts decreases as the initial solution pH increases. At optimal conditions, 100% discoloration and mineralization of 0.2 mM Orange II are achieved in 60 and 120 min reaction in the presence of 10 mM H2O2, 1.0 g/L Fe-B, and 1 x 8 W UVC at initial solution pH of 3.0. 100% discoloration and 90% mineralization of 0.2 mM Orange II are achieved when Fe-Lap-RD is used as catalyst under the same conditions. Both catalysts also display a reasonable good photo-catalytic activity and negligible Fe leaching at an initial solution pH of 6.6 that is very close to neutral pH. This characteristic makes it possible for the Fe-B and Fe-Lap-RD to have a long-term stability. It also becomes feasible for the photo-Fenton process to treat the original wastewater without the need to pre-adjust the solution pH.

Discoloration and mineralization of Orange II by using a bentonite clay-based Fe nanocomposite film as a heterogeneous photo-Fenton catalyst.

Discoloration and mineralization of an azo dye Orange II was conducted by using a bentonite clay-based Fe nanocomposite (Fe-B) film as a heterogeneous photo-Fenton catalyst in the presence of UVC light and H(2)O(2). Under optimal conditions (pH=3.0, 10 mM H(2)O(2), and 1 x 8W UVC), 100% discoloration and 50-60% TOC removal of 0.2 mM Orange II can be achieved in 90 and 120 min, respectively. The mineralization kinetics of 0.2 mM Orange II is much slower than the corresponding discoloration kinetics. Under the same conditions, the Fe leaching from the Fe-B-coated catalyst film is very low. The Fe-B-coated catalyst film could be used in the pre-treatment of wastewater for an integrated system consisting of a photochemical reactor and a biological reactor. Multi-run experimental results reveal that the Fe-B-coated catalyst film could have a long-term stability for the discoloration and mineralization of Orange II. A comparison between the performance of the Fe-B-coated catalyst film and a suspended Fe-B catalyst in the discoloration and mineralization of Orange II was also discussed.

Discoloration and mineralization of Reactive Red HE-3B by heterogeneous photo-Fenton reaction.

Discoloration and mineralization of Reactive Red HE-3B were studied by using a laponite clay-based Fe nanocomposite (Fe-Lap-RD) as a heterogeneous catalyst in the presence of H2O2 and UV light. Our experimental results clearly indicate that Fe-Lap-RD mainly consists of Fe2O3 (meghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide) which have tetragonal and monoclinic structures, respectively, and has a high specific surface area (472 m2/g) as well as a high total pore volume (0.547 cm3/g). It was observed that discoloration of HE-3B undergoes a much faster kinetics than mineralization of HE-3B. It was also found that initial HE-3B concentration, H2O2 concentration, UV light wavelength and power, and Fe-Lap-RD catalyst loading are the four main factors that can significantly influence the mineralization of HE-3B. At optimal conditions, complete discoloration of 100 mg/L HE-3B can be achieved in 30 min and the total organic carbon removal ratio can attain 76% in 120 min, illustrating that Fe-Lap-RD has a high photo-catalytic activity in the photo-assisted discoloration and mineralization of HE-3B in the presence of UV light (254 nm) and H2O2.

Novel bentonite clay-based Fe-nanocomposite as a heterogeneous catalyst for photo-Fenton discoloration and mineralization of Orange II.

A novel bentonite clay-based Fe-nanocomposite (Fe-B) was successfully developed as a heterogeneous catalyst for photo-Fenton discoloration and mineralization of an azo-dye Orange II. X-ray diffraction (XRD) analysis clearly reveals that the Fe-B nanocomposite catalyst mainly consists of Fe2O3 (hematite) and SiO2 (quartz) crystallites, and the Fe concentration of the Fe-B catalyst determined by X-reflective fluorescence (XRF) is 31.8 wt %. The catalytic activity of the Fe-B was evaluated in the discoloration and mineralization of Orange II in the presence of H2O2 and UVC light (254 nm). It was found that the optimal Fe-B catalyst dosage is around 1.0 g/L, and the efficiency of discoloration and mineralization of Orange II increases as initial Orange II concentration decreases or reaction temperature increases. In addition, at optimal conditions (10 mM H2O2, 1.0 g of Fe-B/L, 1 x 8W UVC, and pH = 3.0), complete discoloration and mineralization of 0.2 mM Orange II can be achieved in less than 60 and 120 min, respectively. The result strongly indicates that the Fe-B nanocomposite catalyst exhibits a high catalytic activity not only in the photo-Fenton discoloration of Orange II but also in the mineralization of Orange II. The reaction kinetics analysis illustrates that the photo-Fenton discoloration of Orange II in the first 15 min obeys the pseudo-first-order kinetics. The reaction activation energy calculated was 9.94 kJ/mol, indicating that the photo-Fenton discoloration of Orange II is not very sensitive to reaction temperature.

Discoloration and mineralization of Orange II using different heterogeneous catalysts containing Fe: a comparative study.

Four heterogeneous catalysts containing Fe including a bentonite-clay-based Fe nanocomposite (Fe-B), hematite (alpha-Fe2O3), amorphous FeOOH, and calcined FeOOH (denoted as FeOOH-M) were employed for the photo-Fenton discoloration and mineralization of 0.2 mM Orange II in the presence of 10 mM H2O2 and 8 W UVC at two different initial solution pH values (3.0 and 6.6). It was found that, at an initial solution pH of 3.0, their photocatalytic activities follow the order Fe-B > FeOOH, FeOOH-M > alpha-Fe2O3. When the Fe-B nanocomposite, FeOOH, and FeOOH-M were used as heterogeneous catalysts, both heterogeneous and homogeneous photo-Fenton reactions were responsible for the discoloration and mineralization of 0.2 mM Orange II because homogeneous photo-Fenton reaction occurred due to the presence of Fe ions leached from the catalysts. At an initial solution pH of 6.6, their photocatalytic activities still follow the order Fe-B > FeOOH, FeOOH-M >> alpha-Fe2O3. However, only heterogeneous photo-Fenton reaction accounted for the discoloration and mineralization of 0.2 mM Orange II because Fe leaching from the catalysts was significantly depressed. In the case of alpha-Fe2O3 as a catalyst, whether at an initial solution pH of 3.0 or 6.6, only heterogeneous photo-Fenton reaction happened for the discoloration and mineralization of 0.2 mM Orange II because Fe leaching from the catalyst is negligible. The apparent discoloration kinetics of Orange II with the four catalysts at two different initial solution pH values was also investigated.

Discoloration and mineralization of non-biodegradable azo dye Orange II by copper-doped TiO2 nanocatalysts.

Copper-doped TiO2 nanocatalysts were synthesized by photo-deposition and sol-gel methods. The nanocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and the BET method. The catalysts' activities in the discoloration and mineralization of 0.2 mM Orange II were evaluated. The results indicated that the Cu-doped TiO2 nanocatalysts with a low copper concentration prepared by the photo-deposition method showed enhanced photocatalytic activity; while catalysts synthesized by the sol-gel method did not. In particular, the TiO2 nanocatalyst doped with 1% Cu showed the best performance. Complete color removal and 99% of total organic carbon (TOC) removal were achieved after 150-min of reaction. TiO2 nanocatalysts doped with more than 1% Cu by the photo-deposition method showed decreased photocatalytic activities.