Low-temperature selective catalytic reduction of NO with NH3 over an FeO x /ß-MnO2 composite.

A series of Fe-modified ß-MnO2 (FeO x /ß-MnO2) composite catalysts were prepared by an impregnation method with ß-MnO2 and ferro nitrate as raw materials. The structures and properties of the composites were systematically characterized and analyzed by X-ray diffraction, N2 adsorption-desorption, high-resolution electron microscopy, temperature-programmed reduction of H2, temperature-programmed desorption of NH3, and FTIR infrared spectroscopy. The deNO x activity, water resistance, and sulfur resistance of the composite catalysts were evaluated in a thermally fixed catalytic reaction system. The results indicated that the FeO x /ß-MnO2 composite (Fe/Mn molar ratio of 0.3 and calcination temperature of 450 °C) had higher catalytic activity and a wider reaction temperature window compared with ß-MnO2. The water resistance and sulfur resistance of the catalyst were enhanced. It reached 100% NO conversion efficiency with an initial NO concentration of 500 ppm, a gas hourly space velocity of 45 000 h-1, and a reaction temperature of 175-325 °C. The appropriate Fe/Mn molar ratio sample had a synergistic effect, affecting the morphology, redox properties, and acidic sites, and helped to improve the low-temperature NH3-SCR activity of the composite catalyst.

Tungsten modified natural limonite catalyst for efficient low-temperature selective catalytic reduction of NO removal with NH3: preparation and characterization.

With natural limonite as the precursor and an ammonium tungstate hydrate as modification, the W/limonite composite catalysts were synthesized by the impregnation method. Their structures and properties were systematically characterized and analyzed; the denitrification activity and resistance to water and sulfur on catalysts were investigated. The results indicated that the W/limonite composite with W/Fe mass ratio of 9% and calcination temperature of 300 °C had highly catalytic activity, enhanced resistance to sulfur and water. The NO conversion efficiency was maintained over 85% with NO initial concentration of 500 ppm, the gas hourly space velocity (GHSV) of 36,000 h-1, and reaction temperature of 100 °C, while it was greater than 98% with addition of 200 ppm SO2 and 3 vol. % H2O at the reaction temperature of 250 °C. The superior performance was mainly ascribed to the formation of W-OH species and W = O species with wide dispersion on the surface of goethite or in Fe2O3 lattice defects, to generate more acidic hydroxyl groups and more oxygen defects and strong acidity Brønsted for the SCR reaction.

Ce(SO4)2/α-Fe2O3 selective catalytic reduction of NOx with NH3: preparation, characterization, and performance.

To achieve a low-cost, high-activity denitrification catalyst with excellent water and sulfur resistance, goethite and Ce(SO4)2·4H2O were used to prepare Ce(SO4)2/α-Fe2O3 composite catalyst by the impregnation way and investigated the effect of Ce(SO4)2 on the properties of goethite. Ce(SO4)2/α-Fe2O3 with various preparation conditions for denitration was systematically discussed, and its structure and properties were characterized by XRD, BET, TEM, XPS, H2-TPR, and NH3-TPD methods. The results showed that Ce(SO4)2/α-Fe2O3 over the Ce/Fe molar ratio of 0.02 and calcination temperature of 350 ℃ had excellent catalytic activity, resistance to sulfur, and water properties and stability. When NOx initial concentration was 500 ppm, gas hourly space velocity was 36,000 h-1 and its reaction temperature was 300 ℃; the NOx conversion efficiency was maintained at over 95% along with 300 ppm SO2 and nearly 100% couple with 10% H2O. Its superior performance was mainly attributed to the enhancement of the surface adsorbed oxygen and acidity of α-Fe2O3 by cerium sulfate. The multiple advantages of Ce0.02/α-Fe2O3(350) made it feasible for practical engineering application.

Development of bacterial resistance induced by low concentration of two-dimensional black phosphorus via mutagenesis.

The wide use of nano-antibacterial materials has triggered concerns over the development of nanomaterials-associated bacterial resistance. Two-dimensional (2D) black phosphorus (BP) as a new class of emerging 2D nanomaterial has displayed excellent antibacterial performance. However, whether bacteria repeatedly exposed to 2D BP can develop resistance is not clear. We found that wild type E. coli K-12 MG 1655 strains can increase resistance to 2D-BP nanosheets after repeated exposure with subinhibitory concentration of 2D-BP nanosheets. Adaptive morphogenesis including the reinforced barrier function of cell membrane were observed in the resistant bacteria, which enhanced the resistance of bacteria to 2D-BP nanosheets. The whole-genome sequencing analysis showed that the three mutation genes including dmdA, mntP, and gyrA genes were observed in the 2D-BP resistant strains, which controlled catabolism, membrane structure, and DNA replication, respectively. Furthermore, transcriptional sequencing confirmed that these genes related to metabolization, membrane structure, and cell motility were upregulated in the 2D-BP resistant bacteria. The development of resistance to 2D-BP in bacteria mainly attributed to the changes in energy metabolism and membrane structure of bacteria caused by gene mutations. In addition, the up-regulated function of cell motility also helped the bacteria to develop resistance by escaping external stimuli. The results provided new evidence for understanding an important effect of nano-antibacterial materials on the development of bacterial resistance.

Study of the denitration performance of a ceramic filter using a manganese-based catalyst.

A MnO x /γ-Al2O3 catalyst was prepared by impregnation of manganese acetate and alumina. After optimizing the composition, it was loaded into a ceramic filter (CF) by a one-step coating method. The results show that MnO x /γ-Al2O3 had the best denitration activity when the Mn loading was 4 wt% with a calcination temperature of 400 °C. The MnO x /γ-Al2O3 catalyst ceramic filter (MA-CCF) was made by loading the CF twice with MnO x /γ-Al2O3. When face velocity (FV) was 1 m min-1, MA-CCF displayed more than 80% NO conversion at 125-375 °C and possessed a good resistance of H2O and SO2. The abundant surface adsorbed oxygen, dense membrane and high-density fiber structure on the outer layer of CF effectively protected the catalyst and could improve MA-CCF denitration activity. The multiple advantages of MA-CCF made it possible for good application prospects.

Decomposition of gaseous chlorobenzene using a DBD combined CuO/α-Fe2O3 catalysis system.

Copper oxide and hematite (CuO/α-Fe2O3) composite catalysts were prepared by using goethite as precursor adopted impregnation way and applied to the dielectric barrier discharge (DBD) catalytic decomposition of gaseous chlorobenzene. The CuO/α-Fe2O3 composite was characterised by X-ray diffraction, Brunauer-Emmett-Teller method, scanning electron microscopy and X-ray photoelectron spectrometer technique. The decomposition efficiency and energy yield of gaseous chlorobenzene in DBD catalysis system were studied by a function of gas flow rate, initial concentration and input voltage. The results showed that the CuO/α-Fe2O3 composite catalyst exhibited remarkable performance on chlorobenzene decomposition when the molar ratio was 0.4 and calcination temperature was 450°C. When the chlorobenzene initial concentration was 230 mg m-3, the chlorobenzene decomposition efficiency and mineralisation rate on the DBD catalysis system reached 73.33% and 63.37%, respectively, its decomposition and mineralisation efficiency were enhanced about 20.5% and 16.61%, respectively, compared with the bare DBD system, and it also benefited to significantly reduce the ozone and NO2 by-products. The possible pathway of chlorobenzene decomposition in the DBD catalytic hybrid system was proposed based on the products analysis.

Photochemical reactions between superoxide ions and 2,4,6-trichlorophenol in atmospheric aqueous environments.

The superoxide anion radical (O2•-) is an important reactive oxygen species (ROS), and participates in several chemical reactions and biological processes. In this report, O2•- was produced by irradiating riboflavin in an O2-saturated solution by ultraviolet light with a maximum emission at 365 nm. And the contribution of O2•- to 2, 4, 6-trichlorophenol (2, 4, 6-TCP) was investigated by a combination of laser flash photolysis (LFP) and UV light steady irradiation technique. The results of steady-state experiments showed that the photochemical decomposition efficiency of 2, 4, 6-TCP decreased with the increase of the initial concentration of TCP, while the increase of pH and riboflavin concentration promoted the photochemical reaction. The second-order rate constant of the reaction of the superoxide anion radical with 2, 4, 6-TCP phenoxyl radical (TCP•) was (9.9 ± 0.9) × 109 L mol-1 s-1 determined by laser flash photolysis techniques. The dechlorination efficiency was 61.5% after illuminating the mixed solution with UV light for 2 h. The conversion of 2, 4, 6-trichlorophenol was accompanied by the reductive dechlorination process induced by superoxide ions. The main steady products of the photochemical reaction of 2, 4, 6-TCP with O2•- were 2, 6-dichlorophenol (DCP), 2, 6-dichloro-1, 4-benzoquinone (DCQ) and 2, 6-dichlorohydroquinone (DCHQ). The addition process was the preferred process in the total reaction of superoxide ions with 2, 4, 6-TCP phenoxyl radical. These results indicated that the reaction of 2, 4, 6-TCP with O2•- was a potential conversion pathway and contribute to atmospheric aqueous phase chemistry.

Photochemical reactions between 1,4-benzoquinone and O2•.

The superoxide anion radical (O2•-) is one of the most predominant reactive oxygen species (ROS), which is also involved in diverse chemical and biological processes. In this study, O2•- was generated by irradiating riboflavin in an O2-saturated solution using an ultraviolet lamp (λem = 365 nm) as the light source. The photochemical reduction of 1,4-benzoquinone (p-BQ) by O2•- was explored by 355-nm laser flash photolysis (LFP) and 365-nm UV light steady irradiation. The results showed that the photodecomposition efficiency of p-BQ was influenced by the riboflavin concentration, p-BQ initial concentration, and pH values. The superoxide anion radical originating from riboflavin photolysis served as a reductant to react with p-BQ, forming reduced BQ radicals (BQ•-) with a second-order rate constant of 1.1 × 109 L mol-1 s-1. The main product of the photochemical reaction between p-BQ and O2•- was hydroquinone (H2Q). The present work suggests that the reaction with O2•- is a potential transformation pathway of 1, 4-benzoquinone in atmospheric aqueous environments.

Biomaterials cross-linked graphene oxide composite aerogel with a macro-nanoporous network structure for efficient Cr (VI) removal.

Chitosan (CS) is an attractive bio-adsorbent in pollutant removal due to its environment-friendly properties and abundant adsorption sites. However, the weak mechanical properties and strong dissolubility in acidic conditions of CS hinder its wide application. Herein, a facile method was proposed to fabricate polydopamine (PDA) and CS cross-linked graphene oxide (GO) (GO/CS/PDA) composite aerogel for Cr (VI) removal. GO was cross-linked with CS, forming a reinforced and three-dimensional macroporous structure; the introduced PDA was simultaneously cross-linked with CS and GO, providing more abundant nanopores and active sites for Cr(VI) removal. Based on the batch experiment results, GO/CS/PDA exhibited an optimized mass ratio (1:20:2) of GO, CS, and PDA for the most effective Cr(VI) adsorption; the adsorption removal rate of Cr(VI) was pH dependent, with the highest removal rate at pH = 3.0. The pseudo-second-order kinetic and Freundlich models were more suitable for fitting the adsorption kinetics and adsorption isotherms, respectively, and the maximum adsorption capacity for GO/CS/PDA was 312.05 mg/g at 298 K. Thermodynamics parameters indicated that the adsorption was a spontaneous and exothermic process. The excellent mechanical integrity and reusable adsorption performance of GO/CS/PDA promise the adsorbent with satisfactory reusability.

Photochemical reaction kinetics and mechanistic investigations of nitrous acid with sulfamethazine in tropospheric water.

Nitrous acid (HONO) is an important atmospheric pollutant that can strongly absorb ultraviolet irradiation in the region of 300-400 nm, as previously reported. Since the solar irradiance that reaches the surface of the earth has wavelengths greater than 290 nm, the photodissociation of HONO is considered the major method of hydroxyl radical formation in the troposphere. Thus, the photoinduced chemical reactivity of HONO is important. The present work investigated the reaction mechanism and kinetic parameters of HONO and sulfamethazine by using a laser flash photolysis technique and liquid chromatography-mass spectrometry. The results indicated that the sulfamethazine degradation rate was influenced by the HONO concentration and the initial concentration of sulfamethazine. Hydroxyl radicals derived from the photolysis of HONO attacked the aromatic ring of sulfamethazine to form sulfamethazine-OH adducts with a second-order rate constant of (3.8 ± 0.3) × 109 L mol-1 s-1. This intermediate would then react with HO· and oxygen molecules. The reaction rate constants of sulfamethazine-OH adducts with oxygen are (1.3 ± 0.1) × 107 L mol-1 s-1. The generation of sulfanilic acid and pyrimidine implies that the breaking down of S-N bonds of sulfamethazine and its HO adducts probably occur at the same time.

Photochemical oxidation of di-n-butyl phthalate in atmospheric hydrometeors by hydroxyl radicals from nitrous acid.

The photochemical oxidation of di-n-butyl phthalate (DBP) by •OH radicals from nitrous acid (HONO) in atmospheric hydrometeors was explored by two techniques, steady-state irradiation, and laser flash photolysis (LFP). The effects of atmospheric liquid parameters on DBP transformation were systematically evaluated, showing that DBP does not react with HONO directly and •OH-initiated reactions are crucial steps for consumption and transformation of DBP. Two reaction channels are operative: •OH addition and hydrogen atom abstraction. The overall rate constant for the reaction of DBP with •OH is 5.7 × 109 M-1 s-1, and its specific rate constant for addition is 3.7 × 109 M-1 s-1 determined by using laser flash photolysis technique. Comparing the individual reaction rate constant for aromatic ring addition with the total rate constant, the majority of the •OH radicals (about 65%) attack the aromatic ring. The major transformation products were identified by GC-MS, and the trends of their yields derived from both ring addition and H-abstraction with time are discussed. These results provide important insights into the photochemical transformation of DBP in atmospheric hydrometeors and contribute to atmospheric aerosol chemistry.

Photochemical transformation of dimethyl phthalate (DMP) with N(iii)(H2ONO+/HONO/NO2-) in the atmospheric aqueous environment.

The photochemical transformation of dimethyl phthalate (DMP) with N(iii)(NO2-/HONO/H2ONO+) was investigated using 365 nm steady-state irradiation and 355 nm laser flash photolysis (LFP) techniques. The results showed that N(iii) concentration, DMP initial concentration and pH values all strongly affected the oxidation efficiency of DMP. The primary step of the reaction was the attack of ˙OH radicals on the aromatic ring to form a DMP-OH adduct, and the bimolecular rate constant was determined to be (5.5 ± 0.4) × 109 M-1 s-1. The DMP-OH adduct not only underwent monomolecular self-decay with a rate constant of (1.6 ± 0.3) × 104 s-1 but also interacted with HONO, H2ONO+ and O2 with rate constants of (6.4 ± 0.4) × 106 M-1 s-1, (8.8 ± 0.5) × 106 M-1 s-1 and (1.6 ± 0.1) × 108 M-1 s-1, respectively. Major transformation products including methyl salicylate, monomethyl phthalate, dimethyl 4-hydroxyphthalate and dimethyl 4-nitrophthalate were identified by GC-MS and characteristics of these secondary contaminants required extra attention.

Performance of selective catalytic reduction of NO with NH3 over natural manganese ore catalysts at low temperature.

Natural manganese ore catalysts for selective catalytic reduction (SCR) of NO with NH3 at low temperature in the presence and absence of SO2 and H2O were systematically investigated. The physical and chemical properties of catalysts were characterized by X-ray diffraction, Brunauer-Emmett-Teller (BET) specific surface area, NH3 temperature-programmed desorption (NH3-TPD) and NO-TPD methods. The results showed that natural manganese ore from Qingyang of Anhui Province had a good low-temperature activity and N2 selectivity, and it could be a novel catalyst in terms of stability, good efficiency, good reusability and lower cost. The NO conversion exceeded 85% between 150°C and 300°C when the initial NO concentration was 1000 ppm. The activity was suppressed by adding H2O (10%) or SO2 (100 or 200 ppm), respectively, and its activity could recover while the SO2 supply is cut off. The simultaneous addition of H2O and SO2 led to the increase of about 100% in SCR activity than bare addition of SO2. The formation of the amorphous MnOx, high concentration of lattice oxygen and surface-adsorbed oxygen groups and a lot of reducible species as well as adsorption of the reactants brought about excellent SCR performance and exhibited good SO2 and H2O resistance.

Kinetics analysis of interfacial electron-transfer processes in goethite suspensions systems.

The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (ecb-) and hole (h+). The conduction band electron (ecb-) reacted with an electron acceptor, methylviologen dichloride hydrate (MV2+), forming reduced methylviologen (MV+) with a second-order rate constant of (2.6 ± 0.3) × 109 L mol-1 s-1. The concentration of MV+ was strongly influenced by MV2+ initial concentration and pH values. The flat band potential of goethite was calculated to be Efb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite.

Photochemical reaction between biphenyl and N(III) in the atmospheric aqueous phase.

The photochemical reaction between biphenyl (Bp) and N(III) under irradiation at 365 nm UV light was investigated. The results showed that Bp conversion efficiency was strongly influenced by N (III) concentration, Bp initial concentration and pH. Species-specific rate constants determined by reaction of Bp with H2ONO+ (k1), HONO (k2) and NO2- (k3) were k1 = (0.058 ± 0.005 L mol-1 s-1), k2 = (0.12 ± 0.06 L mol-1 s-1) and k3 = (0.0019 ± 0.0003 L mol-1 s-1), respectively. Laser flash photolysis studies confirmed that OH radical deriving from the photolysis of N(III) attacked aromatic ring to form Bp-OH adduct with a rate constant of 9.4 × 109 L mol-1 s-1. The products analysis suggested that Bp-OH adduct could be nitrated by N (III) and NO2 to generate nitro-compounds.

[Preparation of γ-Fe2O3 Catalyst by Heat Treatment of Natural Limonite for Selective Catalytic Reduction of NO by NH3].

Natural limonite was used as a precursor to prepare γ-Fe2O3 via thermal treatment. The influences of reaction temperature, manganese oxides existing in limonite and coexisting SO2 and H2O on the catalytic reduction activity of the preparedγ-Fe2O3 were evaluated, and the activity of SCR was compared with that of α-Fe2O3, by means of XRD, XRF, XPS, NH3-TPD, FT-IR and so on. The results showed that because the surface acidity of γ-Fe2O3 is stronger, the SCR temperature window of γ-Fe2O3 was 200-350℃ being broader than that of α-Fe2O3 (200-300℃), and in the active temperature window, the NO removal reached over 99%. The existence of MnO2 in the newly formed γ-Fe2O3 slightly decreased the SCR reactivity at lower temperature (100-200℃), while it decreased the SCR reactivity at higher temperature (400-450℃). The existence of SO2 led to the shifting of temperature window by 100℃ from 200-350℃ to 300-450℃, and the volume fraction of 5%H2O only had a tiny negative effect on the SCR reactivity of γ-Fe2O3. However, the coexisting SO2 and H2O, especially when the volume fraction of SO2 reached 0.12%, significantly decreased the SCR reactivity due to the generation of ammonium sulfate. Besides, although the magnetic susceptibility of reacted γ-Fe2O3 experienced a slight decrease compared with the newly prepared γ-Fe2O3, the catalysts could still be used repeatedly by magnetic recycling.

[Photolysis of Gaseous HNO3 on the α-Fe2O3 Films Under 308 nm UV Light].

Under 308 nm UV light, photolysis of HNO3 in the gas phase and on the α-Fe2O3 films was studied by using ultraviolet-visible spectrophotometer (UV-Vis), Fourier transform infrared spectrometer (FTIR) combined with ion chromatography (IC) technique. The effects of HNO3 initial concentration, relative humidity (RH) and illumination time were systematically investigated. Results showed photolysis of HNO3 could produce NO2 and NO in the gas phase and on the α-Fe2O3 films. With the increase of reaction time and HNO3 initial concentration, the concentration of NO2 and NO were all increased exponentially. NO2 and NO concentrations produced from photolysis of HNO3 on α-Fe2O3 films were about 3.27 and 3.87 times higher than those in gas phase, respectively. And NO2 concentration was about 2 times higher than that of NO whatever photolysis of HNO3 in gas phase or on α-Fe2O3 films. HONO concentration increased in exponent regularity along with the increase of RH. The yield of HONO increased from 0.023 to 0.087 when RH from 20% increased to 90%. Surfaces effect played a leading role in photochemical reaction of gaseous HNO3 on the α-Fe2O3 films.

[Photocatalytic Degradation of Gaseous Toluene by a Photo-Fenton Reaction].

In this study, the performance of photo-Fenton reaction on decomposition of toluene was investigated by a flowing column using toluene as a representative of volatile organic pollutants (VOCs). The effects of initial pH, H2O2 concentration, Fe2+ concentration, initial concentration of toluene on degradation of toluene by photo-Fenton reaction were evaluated. Mass spectrometry and gas chromatograph were utilized to detect the products. The results showed that the introduction of UV greatly enhanced the Fenton reaction by improving the generation of hydroxyl radicals. When the initial concentration of toluene was 260 mg x m(-3), the toluene removal can achieve 98% under the following experimental conditions: initial pH = 3.0, H2O2 20 mmol x L(-1), Fe2+ 0.3 mmol x L(-1). Furthermore, no other intermediate except CO2 was detected in the reaction that photocatalytic degradation of toluene in waste gas by the photo-Fenton, which indicates all the degraded toluene was mineralized into CO2.

PAHs in sediment cores at main river estuaries of Chaohu Lake: implication for the change of local anthropogenic activities.

In the present study, 28 polycyclic aromatic hydrocarbons (PAHs) were investigated in four sediment cores collected from the main river estuaries of Chaohu Lake, one of the severely polluted lakes in China. The results indicate that elevated concentrations of total PAHs (Σ28PAH) were found in the samples from the estuary of Nanfei River (ENF), considering BaP-based total toxicity equivalent (TEQ-BaP) and toxic unit (TU) results; there are potential adverse environmental implications. The total organic carbon (TOC) played an important role on the accumulation of PAHs at ENF and the estuary of Tongyang River (ETY). The predominant PAHs are high molecular weight (HMW) homologous for all samples; as a result, industrial wastewater from a steel company is expectedly the key source of PAHs in ENF, while coke consumption would be the important source of PAHs at other three sampling sites. Vertical distribution of PAHs in the sediment cores could be explained by the local social and economic activities. Furthermore, a minor variation of PAH composition in the sediment core could be justified by the stable structure of energy consumption in the Anhui Province. These results justify the need for further enhancement of industrial wastewater treatment and development of renewable energies which are the key factors on the control of PAH pollution in China.

PAHs in the Chinese environment: levels, inventory mass, source and toxic potency assessment.

This paper presents a systematic but preliminary study on the levels, inventory mass, emission sources and risk of exposure to PAHs in China by examining 14 polycyclic aromatic hydrocarbons (from the 16 priority PAHs listed by the U.S. EPA, excluding naphthalene and acenaphthylene) in four main environmental media (air, water, soil and sediment). The concentration of individual PAHs in the air, soil, freshwater, seawater, freshwater sediment and marine sediment of China was compared with the global concentration range (GCR) of PAHs from a large number of studies. The PAH levels were found at the high end of the GCR in the air, at the upper middle of the GCR in the water body, and at the middle of the GCR in the soil and sediment. These indicate that PAHs still are emitted heavily in China. About 530 000 tons of Σ14PAH was estimated to be distributed into these four media in China. Soil possesses the highest proportion of the PAHs (60%), and the air has the lowest proportion (<0.5%). Therefore, the soil and sediment play an important role in the storage of PAHs. More than 10 thousand tons of PAHs are emitted from all kinds of sources. Firewood, straw, domestic and coking were considered as the main emissions of PAHs in the energy supply. A benzo[a]pyrene (BaP) based hazard quotient (HQ) was introduced to assess the potential toxic risk of exposure. The terrestrial water environment was found to have a high BaP exposure. The HQ value was more than 1 for 58% of freshwater and 39% of freshwater sediment samples. Urban and developed sites were considered to have high BaP exposure risk.