clay and 2-naphthol-orange

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.

Topics: Aluminum Silicates; Azo Compounds; Benzenesulfonates; Clay; Coloring Agents; Hydrogen-Ion Concentration; Iron; Nanostructures; Oxidation-Reduction; Photochemistry; Waste Disposal, Fluid

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.

Topics: Aluminum Silicates; Azo Compounds; Bentonite; Benzenesulfonates; Catalysis; Clay; Coloring Agents; Hydrogen Peroxide; Iron; Kinetics; Oxidants; Temperature; Waste Disposal, Fluid; Water Purification

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.

Topics: Aluminum Silicates; Azo Compounds; Bentonite; Benzenesulfonates; Catalysis; Clay; Coloring Agents; Ferric Compounds; Hydrogen Peroxide; Hydrogen-Ion Concentration; Iron; Kinetics; Minerals