This study presents a novel nitrogen-doped carbon-wrapped Co3O4 prepared by a facile impregnation–carbonization process using low-cost raw materials. The optimized catalyst exhibits the highest ...activity reported to date for Co-based catalysts used in the reduction of p-nitrophenol to p-aminophenol with NaBH4 and remains highly stable over seven continuous runs.
Fe3O4 magnetic nanoparticles (MNPs) were employed for electro-Fenton (Fe3O4–electro-Fenton) degradation of C.I. Reactive Blue 19 (RB19) in an undivided electrochemical reactor with an activated ...carbon fiber felt cathode and a platinum anode. On the basis of physicochemical characterization of the Fe3O4 MNPs as well as quantitative measurements of iron leaching and H2O2 generation, it is concluded that the Fe3O4 MNPs facilitated the decomposition of H2O2 to generate hydroxyl radicals (•OH). Moreover, the cathodic electro-Fenton facilitated electro-regeneration of ferrous ion and maintained continuous supply of H2O2. The effect of several operational parameters such as pH, current density, amount of added Fe3O4 MNPs, initial RB19 concentration, and temperature on the removal of total organic carbon was investigated. It was found that the Fe3O4–electro-Fenton degradation of RB19 followed two-stage first-order kinetics with an induction period and a rapid degradation stage. Mineralization of RB19 proceeded rapidly only at pH 3.0. Increasing the current density and the dosage of Fe3O4 MNPs enhanced the rate of RB19 degradation. However, higher current densities and Fe3O4 dosages inhibited the reaction. The rate of RB19 degradation decreased with the increase in initial RB19 concentration and increased with the increase in temperature. The removal efficiency of total organic carbon reached 87.0% after 120 min of electrolysis at an initial pH of 3.0, current density of 3.0 mA/cm2, 1.0 g/L concentration of added Fe3O4 MNPs, 100 mg/L initial dye concentration, and 35 °C temperature. On the basis of the analytical results for the intermediate products and the assumption that •OH radicals are the major reactive species, we propose a possible pathway of RB19 degradation during the cathodic electro-Fenton process using Fe3O4 MNPs as iron source.
Photocatalytic reduction of carbon dioxide can activate chemically inert carbon dioxide by the use of renewable energy. In the present work, the main products of photocatalytic reduction of CO2 in ...aqueous TiO2 suspensions were found to be methane, methanol, formaldehyde, carbon monoxide, and H2. Anatase TiO2 catalysts with various morphologies, such as nanoparticle, nanotube, and nanosheet, were synthesized through a hydrothermal method. The TiO2 nanosheets were more active than the nanotubes or nanoparticles in the reduction of CO2 in aqueous solution. This is because the photogenerated carriers prefer to flow to the specific facets. The TiO2 sheet with high-energy exposed {001} facets facilitates the oxidative dissolution of H2O with photogenerated holes, leaving more photogenerated electrons available for the reduction of CO2 on {101} facets. Moreover, surface fluorination promotes the formation of Ti3+ species, which is helpful in the reduction of CO2 to CO2 – and in extending the lifetime of photogenerated electron–hole pairs. The optimum ratio of exposed {001} to {101} facets for surface-fluorinated TiO2 nanosheets was found to be ∼72:28, which corresponds to an initial F/Ti ratio of 1. From our analysis of the effect of adding of known intermediates on the photocatalytic reduction of CO2, we propose that the photocatalytic reduction of CO2 with H2O on surface-fluorinated TiO2 nanosheets proceeds via a mechanism involving generation of hydrogen radicals and carbon radicals.
TiO2 nanomaterial is widely used for catalytic ozonation. In the present work, TiO2 nanostructures with various morphology and crystallite phases were synthesized by a hydrothermal method, followed ...by calcination using Degussa P25 as precursor. The nanotube, nanorod, and nanowire forms were obtained by varying the hydrothermal temperature, and the anatase/rutile ratios were adjusted by controlling the annealing temperature. The catalytic activity of the samples was evaluated by degradation of phenol in aqueous solution in the presence of ozone. We found that the initial degradation rates (IDR) of phenol were dominated primarily by the surface OH groups. Thus, with the help of transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer−Emmett−Teller (BET) analyses, the number of surface OH groups per unit area of TiO2 was correlated with the morphology and crystallite phases. Finally, we conclude that the vast surface area and higher rutile phase ratios are favorable for the catalytic ozonation of phenol and the morphology of TiO2 had negligible effect in our experiments.
A series of TiO2 with different crystal phases and morphologies was synthesized via a facile hydrothermal process using titanium nbutoxide and concentrated hydrochloric acid as raw materials. The ...photocatalytic activity of the samples was evaluated by degradation of Methyl Orange in aqueous solution under UV-Visible light irradiation. On the basis of detailed analysis of the characterizing results of high-resolution transmission electron microscopy, X-ray powder diffraction measurements, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller measurement, it was concluded that the photo-activity of the catalyst is related directly to the 3D morphology and the crystal phase composition. An excellent catalyst should have both a futile 3D flower-like structure and anatase granulous particles. The 3D flower-like structure could enhance light harvesting, as well as the transfer of reactant molecules from bulk solution to the reactive sites on TiO2. In addition, the optimum anatase/rutile phase ratio was found to be 80：20, which is beneficial to the effective separation of the photogenerated electron-hole pairs.
► Iodine-doped TiO2 using silica-coated Fe3O4 as the magnetic core. ► Photocatalysts for phenol degradation. ► Increasing the molar ratio of Ti/Fe will increase the catalytic activity. ► Increasing ...the molar ratio of Ti/Fe will decrease the saturation magnetization. ► An optimum molar ratio of I/TiO2 is 1:10.
A series of iodine-doped titanium dioxide (I-TiO2) photocatalysts was synthesized by using silica-coated Fe3O4 (SF) as the magnetic core (abbreviated here as ITSF), in order to facilitate the efficient recovery of these photocatalysts. Transmission electron microscopy and X-ray diffraction results indicated that the ITSF nanoparticles had a ternary structure with a core of Fe3O4, a SiO2 mesosphere and an I-TiO2 crust with a mixture of anatase and rutile phases. Magnetic measurements with a vibrating sample magnetometer showed that the ITSF core–shell structures exhibited favorable superparamagnetic behaviors and the magnetic saturation value decreased after coating with the non-magnetic I-TiO2 layer. The photocatalytic activity of the particles was tested by degrading an aqueous phenol solution under visible-light illumination. The photocatalytic activity of the multi-functional hybrid magnetite nanoparticles was enhanced with increasing content of TiO2, while the magnetism of the composite particles decreased. Moreover, an optimum molar ratio of 1:10 I/TiO2 was determined for the efficient degradation of phenol. The study showed that the presence of SF magnetic core would be helpful in the separation and recovery of I-TiO2 photocatalysts.
The photocatalytic degradation of C.I. Direct Red 23 (4BS) in aqueous solutions under UV irradiation was investigated with SrTiO3/CeO2 composite as the catalyst. The SrTiO3/CeO2 powders had more ...photocatalytic activity for decolorization of 4BS than that of pure SrTiO3 powder under UV irradiation. The effects of catalytic dose, pH value, initial concentration of dye, irradiation intensity as well as scavenger KI were ascertained, and the optimum conditions for maximum degradation were determined. Under the irradiation of a 250 W mercury lamp, the best catalytic dose was 1.5 g/L and the best pH was 12.0. Light intensity exhibited a significant positive effect on the efficiency of decolorization, whereas the initial dye concentration showed a significant negative effect. Under the conditions of a catalytic dose of 1.5 g/L, pH of 12.0, initial dye concentration of 100mg/L, light intensity of 250 W, and air flow rate of 0.15 m3/h, complete decolorization, as determined by UV-visible analysis, was achieved in 60 min, corresponding to a reduction in chemical oxygen demand (COD) of 69% after a 240 min reaction. A tentative degradation pathway based on the sensitization mechanism of photocatalysis is proposed.
Electrochemical oxidation of 4-chloro-3-methyl phenol (CMP) was examined using Ti/SnO(2)-Sb/PbO(2) anodes. The physicochemical properties of the electrodes were characterized by X-ray diffraction ...(XRD), scanning electron microscopy (SEM) and electrochemical measurements. The degradation was studied by monitoring the total organic carbon (TOC) removal of CMP, and variation of the concentration of intermediates by high-performance liquid chromatography (HPLC), ion chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). The mineralization of CMP is confirmed to be controlled by mass transfer or by both chemical reaction and mass transfer. Hydroxyl radicals (OH) and active chlorine on the electrode surface had a dominant role in the electro-oxidation process. The chloride element in CMP was immediately driven away from parent substance by OH attack, and then accelerated the ring cleavage of methyl-p-benzoquinone, which was formed during the anodic oxidation of CMP. Ultimately, the chlorine of CMP was mainly transformed to hypochlorite and chloride ion in aqueous solution. Additionally, formic acid and acetic acid were relatively stable products that were not electro-oxidized efficiently in our experiments. The degradation pathway of CMP is proposed on the basis of these results.
Iodine-doped TiO
2 nanotubes (I-TNTs) were synthesized, characterized and evaluated in the photocatalytic degradation of phenol. The photocatalytic activity of these new I-TNTs is much greater than ...that of I-doped TiO
2 nanoparticles, pure TNTs and P25 under visible light irradiation, and the I-TNTs hydrothermally synthesized at 150
°C are superior to those synthesized at 200
°C.
A novel class of iodine-doped TiO
2 nanotubes (I-TNTs) has been synthesized via a hydrothermal route using Degussa P25 as a precursor and subsequent calcination. The photocatalytic ability of the products was evaluated in terms of phenol degradation in an aqueous solution under visible light irradiation. The structural properties of the catalysts were characterized by X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra. According to the XRD data, I-TNTs are pure anatase, revealing a shift of crystallite phase for P25 from rutile to anatase. The surface area of I-TNTs is significantly larger than that of I-doped TiO
2 (I-TiO
2) nanoparticles, which is an important advantage of the photocatalysts formed with a hydrothermal procedure. XPS and UV–vis spectroscopy show that iodine was incorporated into the TiO
2 lattice, and such incorporation extends the photoresponse of TiO
2 from UV to the visible light region. As far as phenol degradation is concerned, the I-TNTs are clearly superior to I-TiO
2 nanoparticles, pure TNTs and P25. The photocatalytic activity of I-TNTs hydrothermally synthesized at 150
°C had a significantly higher level than that synthesized at 200
°C. This is attributed to the increase of reactive sites and the enhancement of mass transfer that result from the large surface areas associated with the tubular morphology. Additionally, the increase of Ti
3+ content also contributes to the improvement of photocatalytic activity of I-TNTs.
