Hollow microspheres MnCo2O4 and CoMn2O4 have been synthesized by a facile solvothermal route followed by pyrolysis of the carbonate counterparts and carbon microspheres, using carbon microspheres as the template. The NH3-selective catalytic reduction reaction was used to test the catalytic activity. The obtained hollow microspheres are composed of numerous primary particles with sizes of tens of nanometers, giving a porous shell. The obtained CoMn2O4 microsphere shows better low-temperature catalytic activity and N2 selectivity than MnCo2O4 microsphere in the NH3-selective catalytic reduction reaction. The X-ray photoelectron spectroscopy results demonstrate that CoMn2O4 microsphere has a relatively higher number content of Mn3+ and chemisorbed oxygen species. The temperature-programmed desorption by ammonia and in situ diffuse reflectance infrared Fourier transform spectroscopy results indicate that the CoMn2O4 microsphere possesses stronger Lewis acid strength than the MnCo2O4 microsphere. Additionally, the CoMn2O4 microsphere also presented outstanding stability, H2O resistance and SO2 tolerance.The NH3-SCR reaction mechanism is proposed that NH3(g) is adsorbed on the surface of Lewis acid sites and Brønsted acid sites in the shape of NH4+ ions and gaseous NH3. Besides, the adsorption of NO could exist in the form of gaseous or oxide ions NO2− on the surface of catalysts.The adsorbed NH3 species could react with NO2− species easily to produce NH4NO2, which subsequently to produce the innocuous N2 and H2O.Open image in new window

•GO nanosheets exhibited excellent removal capacity against ARGs in water.•Various forms or classes ARGs could be eliminated rapidly.•The adsorption of ARGs is monolayer rather than multilayers.•There are abundant oxygen containing groups, showing strong electron-transfer ability.In this study, removal efficiency and mechanism of four typical ARGs with two different molecular structures (i.e., cyclic (c)- and double-stranded (ds)-ARGs) by graphene oxide (GO) nanosheet were systematically investigated. The average removal of four ARGs was as high as 3.11 logs toward c-ARGs and 2.88 logs toward ds-ARGs at 300 μg/mL GO solution. The data of adsorption were fitted well with Freundlich isotherm and pseudo-second-order kinetic model. The apparent adsorption equilibrium can be obtained within 15 mins for both c-ARGs and ds-ARGs, indicating the effective removal by GO. The free-energy parameters demonstrated that the removal processes were exothermic and spontaneous. The structural differences of genetic molecular structures can be responsible for the removal discrepancy. Moreover, several removal factors containing initial ARGs concentration, pH and ion species were also investigated. The results of Raman spectra, Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) and electrochemical analysis indicated that the adsorption of ARGs by GO was mainly attributed to the oxygen containing groups and π-bonding system of GO nanosheet, which resulted in chemical binding with aromatic nucleic acid and strongly π-stacking interactions. Furthermore, a detailed verification test of real water samples was conducted and 80% of the ARGs can be removed from a natural water sample. As a result, it would be great potential to apply GO nanosheet as a novel adsorbent for effective treatment of ARG-contaminated waters.

•A series of novel MnFeOx nanorods were prepared by the hydrothermal method.•The nanorods exhibited higher NOx removal efficiency.•100% NOx conversion efficiency at 200 °C can be obtained.•The SCR reaction mechanism was proposed.A series of MnFeOx nanorods with different Fe/Mn molar ratios were successfully synthesized by the hydrothermal method for low temperature selective catalytic reduction (SCR) of NOx with NH3. These MnFeOx catalysts have been systematically characterized by SEM, TEM, XRD and XPS. Furthermore, the MnFe(0.1)Ox showed the highest catalytic performance with nearly 100% of NOx removal efficiency from 200 to 350 °C. On the basis of the TPR, BET and in situ DRIFT results, it can be found that the addition of Fe species induced a possible redox reaction process and increased the surface chemisorbed oxygen concentration and acid sites, which should be responsible for the enhanced SCR activity of MnFe(0.1)Ox. Meanwhile, several important process parameters affecting NOx removal efficiency in NH3-SCR were carried out, such as time, H2O and SO2.Download high-res image (168KB)Download full-size image

•Pt/TiO2/reduced graphene oxide photocatalysts were prepared via a step-wise strategy.•The step-wise strategy is beneficial to improve the dispersibility of Pt and TiO2 on rGO.•PTG photocatalysts have excellent activity in water splitting with good stability.•DFT calculations and photoelectrochemical tests were used to investigate the role of rGO.•RGO efficiently narrowed the band gap and enhanced the transportation of charges.Recently, developing high-efficiency photocatalytic hydrogen generation photocatalysts and clarifying the inherent mechanism behind the enhancement of hydrogen generation activity have been the research focus. Here, we present a step-wise strategy to prepare Pt/TiO2/reduced graphene oxide photocatalysts and the inherent mechanism of the enhanced photocatalytic activities were systematically investigated. Experimentally, the 2 wt% rGO doped rGO/Pt-TiO2 nanocomposites showed the superior solar-driven hydrogen generation rate (1075.68 μmol h−1 g−1), which was 81 times and 5 times higher than bare TiO2 and Pt/TiO2 samples, respectively. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectra (FT-IR) demonstrated the formation of TiOC bonds in the hybrid, which drove the shifting upwards of the valence band edge from +2.2 eV to +1.83 eV. Furthermore, photoelectrochemical tests indicated the electron density of PTG-2 was about one order of magnitude higher than TiO2. Moreover, DFT calculations displayed that the bandgap had been successfully narrowed from 2.88 eV to 2.76 eV and the original blank energy region located at TiO2 bandgap was filled with C2p orbitals, which resulted in excited electrons in TiO2 efficiently transferring to graphene. Consequently, the DFT calculations are in good agreement with the experimental results and physical characterizations. This study affords us a rational design of a high efficiency photocatalytic system for solar energy conversion.Download high-res image (154KB)Download full-size image

•Highly ordered mesoporous WO3(χ)-CeO2 have been successfully synthesized.•The ordered mesoporous WO3(χ)-CeO2 shows superior low temperature catalytic activity and N2 selectivity.•The ordered mesoporous WO3(χ)-CeO2 have stronger Lewis acid sites and higher Ce3+ concentration.•The ordered mesoporous WO3(χ)-CeO2 also presented excellent H2O resistance and alkali metal resistance.To eliminate nitrogen oxides (NOx), a series of highly ordered mesoporous WO3(χ)-CeO2 nanomaterials (χ represents the mole ratio of W/Ce) were synthesized by using KIT-6 as a hard template, which was used for selective catalytic reduction (SCR) to remove NOx with NH3 at low temperatures. Moreover, the nanomaterials were characterized by TEM, XRD, Raman, XPS, BET, H2-TPR, NH3-TPD and in situ DRIFTS. It can be found that all of the prepared mesoporous WO3(χ)-CeO2 (χ = 0, 0.5, 0.75, 1 and 1.25) showed highly ordered mesoporous channels. Furthermore, mesoporous WO3(1)-CeO2 exhibited the best removal efficiency of NOx, and its NOx conversion ratio could reach 100% from 225 °C to 350 °C with a gas hourly space velocity of 30 000 h−1, which was due to higher Ce3+ concentrations, abundant active surface oxygen species and Lewis acid sites based on XPS, H2-TPR, NH3-TPD and in situ DRIFTS. In addition, several key performance parameters of mesoporous WO3(1)-CeO2, such as superior water resistance, better alkali metal resistance, higher thermal stability and N2 selectivity, were systematically studied, indicating that the synthesized mesoporous WO3(1)-CeO2 has great potential for industrial applications.Download high-res image (241KB)Download full-size image

Mn2O3-doped Fe2O3 hexagonal microsheets were prepared for the low-temperature selective catalytic reduction (SCR) of NO with NH3. These hexagonal microsheets were characterized by SEM, TEM, XRD, BET, XPS, NH3-TPD, H2-TPR, and in situ DRIFT and were shown to exhibit a considerable uniform hexagonal microsheet structure and excellent low temperature SCR efficiency. When doped with different Mn molar ratios, Mn2O3 was detected in the Fe2O3 hexagonal microsheets based on the XRD results without the presence of other MnOX species. In addition, the hexagonal microsheets with a Mn/Fe molar ratio of 0.2 showed the best SCR removal performance among the materials, where a 98% NO conversion ratio at 200 °C at a space velocity of 30 000 h–1 was obtained. Meanwhile, excellent tolerances to H2O and SO2, as well as high thermal stability, were obtained in Mn2O3-doped Fe2O3 hexagonal microsheets. Moreover, on the basis of the XPS and in situ DRIFT results, it can be suggested that coupled Mn2O3 nanocrystals played a key role at low temperatures and produced a possible redox reaction mechanism in the SCR process.Keywords: hexagonal microsheets; low temperature; mechanism; Mn2O3-doped Fe2O3; SCR

TiO2–Bi2WO6 binanosheet (TBWO), synthesized by a facile two-step hydrothermal method, was used as an effective visible-light-driven photocatalyst for the inactivation of E. coli and was characterized by TEM, SEM, XRD, FTIR, XPS, and BET. A series of TBWOs with different doping ratios of TiO2 loading from 10 to 55 wt % were synthesized. Among all of the TBWOs, 40% TBWO exhibited the best bacteria disinfection efficiency, and the quantity of viable bacteria could reach 10° with 40% TBWO (100 μg/mL) after being illuminated for 4 h. Furthermore, the confocal fluorescent-based cell live/dead test and the SEM technology were applied to verify the photocatalytically lethal effect toward E. coli and the rupture of bacterial membranes. The leak of bacterial contents, including the bacterial genome represented by relevant 16srDNA, and total protein were detected by PCR and bicinchoninic acid assay. In this work, the antibacterial mechanism was studied by employing photoelectrochemical techniques, electron spin resonance (ESR), and scavengers of different reactive species, revealing the pivotal roles of electron hole (h+) and electron (e–) in the photocatalytic process. In addition, the •O2– and •OH radicals were also detected in the TBWOs system by ESR. It was found that the adsorption of visible light and separation of photogenerated carriers within TiO2 have been largely promoted after being coupled with Bi2WO6, which should be responsible for the improved bactericidal effect.Keywords: Bi2WO6; binanosheet; leakage of cell contents; photocatalytic disinfection; TiO2

To investigate the corresponding relationship between catalytic efficiency and structure, MnO2 nanomaterials (nanospheres, nanosheets, nanorods) have been prepared successfully, and were thoroughly characterized by SEM and TEM. Furthermore, the selective catalytic reduction (SCR) performance of NOX under ammonia was used as an indicative reaction. Among the MnO2 nanomaterials with different morphologies, it was found that their SCR activities showed an interesting variation tendency: nanospheres > nanosheets > nanorods of MnO2. The NO conversion ratio of the MnO2 nanospheres could reach 100% from 200 to 350 °C. Moreover, in order to study the probable mechanism for the best removal efficiency of the nanospheres, XRD, H2-TPR, NH3-TPD, BET, XPS and in situ DRIFTS were performed in detail. It is found that surface chemisorbed oxygen, specific surface area, reducibility and acid sites have great influence on the NO removal efficiency in the SCR reaction. In addition, how several process parameters affect the NOX removal efficiency was carried out, such as time, H2O and SO2.

Ag-CoFe2O4-graphene oxide (Ag-CoFe2O4-GO) nanocomposite was synthesized by doping silver and CoFe2O4 nanoparticles on the surface of GO, which was used to purify both bacteria and Pb(II) contaminated water. The Ag-CoFe2O4-GO nanomaterial was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), cyclic voltammetry (CV), and magnetic property tests. It can be found that Ag-CoFe2O4-GO nanocomposite exhibited excellent antibacterial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus compared with CoFe2O4, Ag-CoFe2O4, and CoFe2O4-GO composite. This superior disinfecting effect was possibly attributed to the combination of GO nanosheets and Ag nanoparticles. Several antibacterial factors including temperature, time, and pH were also investigated. It was obvious that E. coli was more susceptible than S. aureus toward all the four types of nanomaterials. The structural difference of bacterial membranes should be responsible for the resistant discrepancy. We also found that Ag-CoFe2O4-GO inactivated both bacteria in an irreversibly stronger manner than Ag-CoFe2O4 and CoFe2O4-GO. The Pb(II) removal efficiency with all the nanomaterials showed significant dependence on the surface area and zeta potential of the materials. In this work, not only did we demonstrate the simultaneous superior removal efficiency of bacteria and Pb(II) by Ag-CoFe2O4-GO but also the antibacterial mechanism was discussed to have a better understanding of the interaction between Ag-CoFe2O4-GO and bacteria. In a word, taking into consideration the easy magnetic separation, bulk availability, and irreversibly high antibacterial activity of Ag-CoFe2O4-GO, it is the very promising candidate material for advanced antimicrobial or Pb(II) contaminated water treatment.Keywords: disinfection; graphene; magnetic separation; nano-Ag; Pb(II);

Magnetic Fe3O4/graphene composite (abbreviated as G-Fe3O4) was synthesized successfully by solvothermal method to effectively remove both bacteriophage and bacteria in water, which was tested by HRTEM, XRD, BET, XPS, FTIR, CV, magnetic property and zeta-potential measurements. Based on the result of HRTEM, the single-sheet structure of graphene oxide and the monodisperse Fe3O4 nanoparticles on the surface of graphene can be observed obviously. The G-Fe3O4 composite were attractive for removing a wide range of pathogens including not only bacteriophage ms2, but also various bacteria such as S. aureus, E. coli, Salmonella, E. Faecium, E. faecalis, and Shigella. The removal efficiency of E. coli for G-Fe3O4 composite can achieve 93.09%, whereas it is only 54.97% with pure Fe3O4 nanoparticles. Moreover, a detailed verification test of real water samples was conducted and the removal efficiency of bacteria in real water samples with G-Fe3O4 composite can also reach 94.8%.Keywords: graphene; magnetic nanoparticles; pathogenic bacteria

Fe3O4-TiO2 nanosheets (Fe3O4-TNS) were synthesized by means of lamellar reverse micelles and solvothermal method, which were characterized by TEM, XRD, XPS, BET, and magnetic property analysis. It can be found that Fe3O4-TNS nanosheets exhibited better photocatalytic antibacterial activity toward Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus than pure Fe3O4 and TNS, and the antibacterial efficiency could reach 87.2% and 93.7% toward E. coli and S. aureus with 100 μg/mL Fe3O4-TNS after 2 h of simulated solar light illumination, respectively. The photocatalytic destruction of bacteria was further confirmed by fluorescent-based cell live/dead test and SEM images. It was uncovered that Fe3O4-TNS inactivated G- E. coli and G+ S. aureus by different mechanisms: the destruction of outer membranes and ruptured cell bodies were responsible for the bactericidal effect against E. coli, while the antibacterial effect toward S. aureus were due to the fact that the cells were adsorbed in form of clusters by massive Fe3O4-TNS, which could restrict their activities and cause malfunction of the selective permeable barriers. Furthermore, the antibacterial mechanism was studied by employing scavengers to understand exact roles of different reactive species, indicating the key roles of h+ and H2O2. The recovery and reusability experiments indicated that Fe3O4-TNS still retained more than 90% bacteria removal efficiency even after five cycles. Considering the easy magnetic separation, bulk availability, and high antibacterial activity of Fe3O4-TNS, it is a promising candidate for cleaning the microbial contaminated water environment.Keywords: antibacterial; E. coli; magnetic; photocatalysis; TiO2 nanosheets

Magnetic mesoporous γ-Fe2O3@Ti0.9Si0.1O2 (abbreviated as Fe@TiSi) core–shell nanofibers were prepared using sol–gel chemistry combined with coaxial-electrospinning technology by adjusting the inner and outer feed ratios. The properties of these novel core–shell nanofibers were characterized by SEM, HRTEM, XRD, FTIR, BET, XPS, and UV–vis spectra. To evaluate the chemical properties of the nanofibers for cleaning typical organic wastewater, methylene blue (MB) was used as a target organic pollutant and was cleaned under irradiation with sunlight and visible light. The Fe@TiSi hierarchical nanofibers composed of a 1:10 feed ratio displayed a mesoporous structure and showed the highest photocatalytic activity for the degradation of MB in water. Furthermore, 86.8% and 71.1% of the MB, which was added at an original concentration of 1 mg/L, was removed after 60 min of irradiation with sunlight and visible light in the presence of Fe@TiSi at a concentration of 0.2 g/L, and 100% of the MB was removed after 75 min. It is very important that the magnetic nanofibers could be recycled rapidly with an outside magnet, and the actual water treatment process was easy to achieve. Moreover, the mechanism of MB degradation by Fe@TiSi core–shell nanofibers was proposed.Keywords: core−shell; magnetic; MB; mesoporous nanofibers; photodegradation

Mesoporous Fe2O3-doped TiO2 nanostructured fibers were fabricated through electrospinning the relevant gel precursor. The prepared fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and surface analysis, respectively. The photocatalytic activity of these mesoporous composite fibers was evaluated by photocatalytic degradation of methylene blue (MB) in water under UV irradiation. Compared with different types of photocatalysts, the 1% Fe2O3-doped TiO2 fibers exhibited super photocatalytic activity.Graphical abstractMesoporous Fe2O3-doped TiO2 nanostructured fibers were fabricated through electrospinning relevant gel precursors. Compared with different types of photocatalysts, the 1% Fe2O3-doped TiO2 fibers exhibited higher photocatalytic activity.Research highlights► Long mesoporous Fe2O3-doped TiO2 fibers with high surface areas were prepared by the sol–gel and electrospinning techniques. ► The mesoporous fibers were as long as 20 cm with diameters of 0.5–2 μm. ► N2 adsorption–desorption isotherms gave a BET surface area of 200–228 m2/g and average pore size of 6.5 nm. ► These mesoporous 1% Fe2O3-doped TiO2 fibers showed higher photocatalytic activity toward decomposition of MB than many other catalysts. ► In addition, the long composite fibers can be conveniently fixed and reclaimed so that they are good candidates for photocatalytic applications.

The α-Fe2O3 fibers have been prepared by electrospinning the corresponding sol–gel precursor, then these fibers were characterized by TGA, SEM, XRD, BET and FT-IR respectively, indicating that the hierarchical α-Fe2O3 nanostructured fibers came into being. Photocatalytic degradation of methylene blue (MB) in water was carried out under ultraviolet (UV) light, showing that the fibers had better efficiency for removing MB than other catalysts. And several process parameters have also been studied, which showed that the removal effect of MB was influenced by the process parameters, such as the initial dye concentration, catalyst amounts, inorganic anions, and so on.

In this study, one-dimensional (1D) cerium niobate nano-crystalline fibers were first prepared by a facile sol–gel and electrospinning process, followed by heat treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were used to characterize the samples. It can be seen from SEM images that the as-prepared xerogel samples and those annealed at 900 °C presented uniform fibrous morphology, with the diameter of 100–300 nm and length of several centimeters. The XRD and FT-IR results showed that cerium niobate samples had well-crystallized phase of CeNbO4.25 with the crystallite size of about 28.6 nm at a heat treatment temperature of 900 °C, which can also be validated with the TEM image. The AC impedance of annealed disks made from the CeNbO4.25 nano-crystalline fibers has been probed.

A typical salt-free zero-charged catanionic system was constructed by mixing C14H29N+(CH3)3OH-C14H29N+(CH3)3OH- (TTAOH) and lauric acid (LA). The electrochemical behaviors of K4[Fe(CN)6] in salt-free TTAOH/LA micelle phase and vesicle phase solutions at glassy carbon (GC) electrode at different scan rate were obtained. A pair of well-defined redox peaks of [Fe(CN)6]3-/4-[Fe(CN)6]3-/4- is observed in TTAOH/LA vesicular solution with ΔEp = 61 mV at the scan rate of 0.001 V/s. Compared to the electrochemistry of K4[Fe(CN)6] in aqueous solution and TTAOH/LA micellar aqueous solution, the reversibility of [Fe(CN)6]3-/4-[Fe(CN)6]3-/4- is significantly improved in TTAOH/LA vesicular aqueous solution.

SiO2 hollow nanostructured fibers with hierarchical walls have been fabricated by the sol–gel combined two-capillary spinneret co-electrospinning technique using triblock copolymer as the porous directing agent. The as-prepared SiO2 hollow nanostructured fibers were as long as 10 cm with the outer diameter of 400–600 nm and shell thickness of 50–200 nm, and their walls contained the random mesopores with the size of 6.6 nm and the micropores with size of 0.6 nm based on the N2 absorption–desorption isotherm.SiO2 hollow nanostructured fibers with hierarchical meso/microporous walls have been fabricated by the sol–gel combined two-capillary spinneret co-electrospinning technique.

•Ag/g-C3N4 composite photocatalyst was synthesized successfully.•The composite nanosheet exhibited excellent photocatalytic disinfection efficiency.•The mechanism of enhanced disinfection activity was systematically investigated.Ag/g-C3N4 composite photocatalyst, which was synthesized by thermal polymerization of melamine precursor combined with the photo-assisted reduction method, was applied as an efficient visible-light-driven photocatalyst for inactivating Escherichia coli (E. coli). The composite photocatalysts exhibited significantly enhanced photocatalytic disinfection efficiency than pure g-C3N4 powders. The mechanism of enhanced disinfection activity was systematically investigated by UV–visible diffuse reflectance spectra, photoluminescence spectra, and photo-electrochemical methods including photogenerated current densities, electrochemical impedance spectroscopy (EIS) spectra and Mott–Schottky plots. The enhanced photocatalytic bactericidal effect was attributed to the hybrid effect from Ag and g-C3N4, which resulted in enhanced adsorption of visible light, reduced recombination of free charges, rapid separation and transportation of photogenerated electrons–holes. The disinfection mechanism was studied by employing chemical scavengers and ESR technology, indicating the important role of h+ and e−. Considering the bulk availability and excellent disinfection activity of Ag/g-C3N4, it is a promising solar-driven photocatalyst for cleaning microbial contaminated water in practice.Download full-size image