Surface Fe3 Research Articles

Morphology and crystal–plane dependent catalytic activity of α-Fe2O3 for NH3-SCR de-NOx: Experimental and DFT study

Three kinds of α-Fe2O3 catalysts, each having a distinct morphology and crystal planes, were synthesized and applied for NH3-SCR reaction. The morphology and crystal-plane effects for the activity of α-Fe2O3 were investigated by a combined study of experiment and density functional theory. The experiment findings reveal that the α-Fe2O3-S, α-Fe2O3-R, and α-Fe2O3-C display the shuttle (predominantly exposed (110) and (012) crystal planes), rod (predominantly exposed (110), (104), and (012) crystal planes), and cube (only exposed (104) crystal plane) shapes, respectively. Furthermore, the α-Fe2O3-S yields the best catalytic performance because of its moderate surface acidity, the best redox capacity, and the highest contents of surface Fe3+ and chemisorbed oxygen, which may result from the morphology and crystal plane effects. Additionally, the activity of different crystal planes is significantly different. The NO and NH3 are more apt to be adsorbed on the (110) and (012) surfaces and O2 dissociation is more likely to happen on the (110) surface. Besides these, the (110) surface owns the lowest energy barrier to the decomposition of intermediate NH2NO. All of the mentioned above collectively enhance the efficiency of the SCR process. Finally, the (110) and (012) surfaces facilitate the rapid SCR process, while the (104) surface is the most difficult. The α-Fe2O3-S predominately exposes high activity of (110) and (012) surfaces, therefore, it can yield the highest catalytic activity.

Tyrosol removal by photo–Fenton–like process using CaAlFe mixed oxides synthesized via hydrocalumite from aluminum salt cake

Solids with potential application in tyrosol (Ty) removal by photo–Fenton processes have been synthesized using aluminum salt cake as a source. Two series of hydrocalumite layered double hydroxides (LDH) were synthesized: one containing structural Fe3+ (occupying octahedral positions in the LDH) and another containing surface impregnated Fe3+; all solids were calcined in air at 750 °C. The solids were characterized by powder X–ray diffraction, FT–infrared spectroscopy, thermal analysis, N2 adsorption–desorption isotherms at –196 °C, particle size distribution and electron microscopy. One of the main differences between the two series was that Fe3+ impregnation by the incipient wetness method and subsequent calcination at 750 °C did not lead to the formation of CaAlFe mixed oxides. The calcined solids were evaluated as photocatalysts in the photo–Fenton process for Ty removal (a typical compound found in olive oil mill wastewater), the samples containing surface Fe3+ showing better results. The solid prepared by impregnation of hydrocalumite with 20% iron and subsequently calcined at 750°C, under the optimum reaction conditions (catalyst dose = 0.5 g/L, [H2O2] = 0.468 g/L and [Ty]0 = 100 mg/L, in the presence of UV light), reached complete Ty removal with contaminant mineralization of 95% after only 60 min reaction. The cyclic study showed that this sample maintained its stability after 3 cycles of reuse without iron leaching, and a better performance than other materials reported in the literature.

Enhancing ROS-Inducing Nanozyme through Intraparticle Electron Transport.

Iron oxide nanoparticles (IONPs) have garnered significant attention as a promising platform for reactive oxygen species (ROS)-dependent disease treatment, owing to their remarkable biocompatibility and Fenton catalytic activity. However, the low catalytic activity of IONPs is a major hurdle in their clinical translation. To overcome this challenge, IONPs of different compositions are examined for their Fenton reaction under pharmacologically relevant conditions. The results show that wüstite (FeO) nanoparticles exhibit higher catalytic activity than magnetite (Fe3 O4 ) or maghemite (γ-Fe2 O3 ) of matched size and coating, despite having a similar surface oxidation state. Further analyses suggest that the high catalytic activity of wüstite nanoparticles can be attributed to the presence of internal low-valence iron (Fe0 and Fe2+ ), which accelerates the recycling of surface Fe3+ to Fe2+ through intraparticle electron transport. Additionally, ultrasmall wüstite nanoparticles are generated by tuning the thermodecomposition-based nanocrystal synthesis, resulting in a Fenton reaction rate 5.3 times higher than that of ferumoxytol, an FDA-approved IONP. Compared with ferumoxytol, wüstite nanoparticles substantially increase the level of intracellular ROS in mouse mammary carcinoma cells. This study presents a novel mechanism and pivotal improvement for the development of highly efficient ROS-inducing nanozymes, thereby expanding the horizons for their therapeutic applications.

Defect structures and (ferro)magnetism in Zn1-xFexO nanoparticles with the iron concentration level in the dilute regime (x = 0.001 – 0.01) prepared from acetate precursors

Zn1-xFexO nanoparticles with the iron concentrations level in the dilute regime (x = 0.001–––0.01) were produced by a sol–gel route from acetate precursors along with an un-doped and 3 at.% Fe-doped reference. The X-ray diffraction of the un-doped and 0.1–1 at.% Fe-doped samples reveal the reflections for only the ZnO wurtzite structure. Fe doping enhances the a-axis lattice constant, the unit cell volume and the microstrain. Iron doping reduces the average crystallite/particle size (confirmed by Scanning Electron Microscopy), improving the surface-to-volume ratio or the concentration of defective surface sites. XPS identifies the iron in both Fe3+ and Fe2+ states. XPS and 57Fe Mossbauer spectroscopy indicate a broad distribution (distortion) of Fe3+ sites on the surface of ZnO nanoparticles. The blue shift and broadening of the UV emission, and quenching of defect-related photoluminescence in the Fe-doped samples verify the presence of iron in the ZnO lattice and surface intrinsic defects. 0.1–1 at.% Fe-doped ZnO show room temperature ferromagnetism, RTFM, characteristic of dilute magnetic semiconductors, DMS. The magnetization measurements with temperature evidence an antiferromagnetic alignment and an increase of ferromagnetic contribution with Fe doping up to 1 at.%. Zn0.97Fe0.3O reference is a superparamagnetic ZnO/ZnFe2O4 nanocomposite with a blocking temperature of 20 K; HRTEM shows (ultra)fine ZnFe2O4 particles at the surface of ZnO nanoparticles. The analysis of experimental data of 0.1–1 at.% Fe-doped ZnO was done in terms of iron coupling with intrinsic defects, which can generate surface Fe3+ states with geometries similar to the Fe3+ in inverse spinel ZnFe2O4. The superexchange interaction (resembling that in the inverse spinel ZnFe2O4) between the Fe3+ sites with distorted configuration resulting in ferrimagnetism was hypothesised as a possible mechanism of RTFM. Experimental (structural, local chemical, magnetic, optical) and interpretation results can be used to optimize the processing conditions for Fe-doped ZnO to serve as an effective DMS, e.g. for spintronic applications.

Ti3+ self-doped TiO2 anchored with iron oxide quantum dots as an efficient persulfate catalyst for the enhanced removal of typical phenolic pollutants from water under visible light

In this work, a facile impregnation–calcination route was proposed for the synthesis of Ti3+ self−doped TiO2 anchored with iron oxide quantum dots (FeQDs/TiO2−x) as an efficient visible light−derived persulfate catalyst for organic degradation. After the successful co−doping of Fe3+ and Ti3+, the obtained FeQDs/TiO2−x exhibited quasi−full visible light absorption, with the maximum absorption edge broadened to 791 nm; furthermore, its charge separation and interfacial transport capacity were significantly enhanced, as evidenced by the fact that the lifetime of the photogenerated electrons was prolonged from 6.17 to 10.34 ns. In addition, the surface Fe3+ species on FeQDs/TiO2−x can be effectively reduced to Fe2+ by the separated electrons, establishing an efficient cycle between Fe3+ and Fe2+. Therefore, the obtained FeQDs/TiO2−x nanocomposite exhibited enhanced catalytic performance for the degradation of phenolic pollutants via PS activation under visible light. Specifically, 50 mg/L bisphenol A (BPA) and acetaminophen (AAP) can be completely degraded by FeQDs/TiO2−x with faster reaction rate constants and higher mineralization rates compared to its counterparts, including TiO2, TiO2−x, and FeQDs/TiO2. Based on the results of material characterization, degradation experiments, identification of reactive oxidizing species, and chemical quenching experiments, the mechanism of the enhanced photocatalytic activity of FeQDs/TiO2−x was elucidated. Our results demonstrated the high potential of FeQDs/TiO2−x for wastewater treatment.

Selective catalytic reduction of NO by CO over α-Fe2O3 catalysts

Selective catalytic reduction of nitrogen oxides using carbon monoxide is considered a promising technology due to a series of advantages. Three α-Fe2O3 catalysts for CO-SCR were prepared by hydrothermal, precipitation and sol–gel methods. A series of characterization studies were performed on these three catalysts. It was found that the catalytic efficiency of all three catalysts increased with increasing temperature, and the conversion rate reached 100 % after the temperature exceeded 250 °C. Under the same low-temperature reaction conditions, the Fe2O3-HT samples prepared by the hydrothermal method showed the best catalytic efficiency for NO, followed by the precipitation method, and the sol–gel method showed the worst catalytic efficiency. The best activity of Fe2O3-HT was probed by characterization due to its higher crystallinity resulting in higher surface Fe3+. Based on the TPD results, a possible mechanism for this catalytic reaction was inferred to be the E-R mechanism. Since CO-SCR technology has great potential and development prospects and the simplicity of the research method in this paper produced good results, it is a reference for the design of new CO-SCR catalysts in the future.

Experimental and theoretical analysis of elemental mercury removal from syngas over Fe-Ti spinel

A magnetic Fe-Ti spinel sorbent was synthesized by the co-precipitation method and applied to remove gaseous Hg0 from syngas. A superior Hg0 removal performance was achieved in the temperature range of 120–180 °C, and the highest an average removal efficiency of was approximately 95% at 150 °C under simulated syngas. H2S was adsorbed on the Fe-Ti spinel surface，which generated active sulfur species, and enhanced the Hg0 removal efficiency significantly. CO, H2 and H2O variably suppressed the Hg0 removal performance. H2S-pretreatment, X-ray photoelectron spectroscopy (XPS) and Hg0-temperature programmed desorption (Hg0-TPD) results demonstrated that Hg0 reacted with H2S over Fe-Ti spinel followed the Eley-Rideal mechanism, in which gas-phase Hg0 reacted with the active surface sulfur species generated from H2S oxidation and formed surface-bonded HgS. The surface Fe3+ and surface-active oxygen species were involved in the H2S and Hg0 adsorption and transformation process. Stability and regeneration cycling experiments indicated that Fe-Ti spinel exhibited excellent stability for Hg removal and great regeneration ability. Density functional theory (DFT) calculations showed that H2S underwent strong chemisorption on the Fe-Ti spinel surface with an adsorption energy of −116.988 kJ/mol, and then H2S further dissociated on the sorbent surface to generate active sulfur species, which reacted strongly with gas-phase Hg0 to form HgS.

Distinct effects of transition metal (cobalt, manganese and nickel) ion substitutions on the abiotic oxidation of pyrite: In view of hydroxyl radical production

The abiotic oxidation of pyrite (FeS2) is a geochemically crucial reaction involved in acid mine drainage, the release of toxic trace elements and the generation of hydroxyl radicals (•OH) that can oxidize environmental substances. Studies on •OH generation from the abiotic oxidation of pyrite have drawn wide interest, but the effects of the common substitution of transition metal ions on •OH generation are still largely unknown, and worthy of comprehensive comparison. We therefore synthesized and comprehensively characterized micron-sized pyrites containing low concentrations of cobalt (Co), nickel (Ni), or manganese (Mn) ions, and tested the relative ability of these transition metal ion-substituted pyrites to generate •OH under abiotic oxidation. We found that transition metal ion substitutions inhibited the growth of pyrite crystals to various extents and increased Fe–S bond distances, leading to distinct alterations in surface chemical composition, conductivity, and the exposure of active faces. These differences resulted in an increase in •OH generation by the oxidation of transition metal ion-substituted pyrites, relative to pure pyrite, with the order of increase being Mn2+-substituted < Ni2+-substituted < Co2+-substituted pyrites. These substituent-dependent differences were explored by linking the crystal properties and physical chemistry of these pyrites to various reaction pathways that were possible in such contexts. For pure pyrite, the heterogeneous Fenton reaction was the chief generator of •OH. The substitution of pyrite with Co2+, which was redox-active, increased the conductivity of pyrite and accelerated the reduction of surface Fe3+ to Fe2+, resulting in a significant increase in H2O2 and •OH production. The substitution of pyrite with Mn2+, which was also redox-active, likewise increased the conductivity; however, the high oxidizing ability of surface Mn4+ inhibited the reduction of Fe3+ and thus decreased •OH generation. By contrast, the substitution of pyrite with Ni2+ did not affect electron transfer but led to absolute exposure of the (111) face of pyrite, which increased its activity toward O2 and H2O, slightly increasing H2O2 and •OH generation. These results highlight the vital role of transition metal ion-substituted pyrite in various geochemical processes.

Porous LaFeO3 perovskite catalysts synthesized by different methods and their high activities for CO oxidation.

In this study, spherical α-Fe2O3 prepared by the hydrothermal method was used as a template for the first time; LaFeO3 perovskite catalysts were successfully synthesized by the molten salt method (M-LF-T), sol-gel method (S-LF-T), and co-precipitation method (C-LF-T), respectively. To determine the optimal synthesis method, X-ray diffraction patterns were obtained and showed that single phase LaFeO3 with good crystallinity was prepared by the molten salt method after calcination at 600 °C for 4 h. SEM and TEM images showed that the M-LF-600 catalyst preserved the spherical structure of α-Fe2O3 template. Compared with the catalysts synthesized by the sol-gel method and co-precipitation method, the M-LF-600 catalyst had the highest BET surface area of 16.73 m2 g-1. X-ray photoelectron spectroscopy analysis showed that the M-LF-600 catalyst had the highest surface Fe3+/Fe2+ molar ratio and the best surface oxygen adsorption capacity. The CO oxidation of the LaFeO3 catalyst demonstrated that the M-LF-600 catalyst had the best catalytic performance.

Removal of gaseous elemental mercury from simulated syngas over Fe2O3/TiO2 sorbents

Fe2O3/TiO2 sorbents synthesized by the sol-gel method were employed to capture elemental mercury in simulated syngas. It was found that Fe2O3/TiO2 sorbents exhibited an outstanding Hg0-removal efficiency of over 95% in the temperature range 50–150 °C; however, the Hg0-adsorption capacity was limited by high temperatures (above 150 °C). H2S significantly promoted Hg0 capture, whereas CO, H2, and H2O suppressed Hg0 removal. After a 10-hour adsorption test, and five adsorption–regeneration cycles at 150 °C, the Hg0-removal efficiency was maintained at approximately 95% and 90%, respectively, confirming that the sorbent showed stability and reusability. Hg0 adsorption with H2S over the Fe2O3/TiO2 sorbents occurred via the Eley–Rideal mechanism, in which active sulfur sites originating from the oxidation of H2S reacted with gaseous Hg0 to form HgS. A possible reaction pathway for Hg0 removal has also been proposed. The fresh and spent sorbents were explored by X-ray photoelectron spectroscopy and Hg0-temperature-programmed desorption, indicating that the surface Fe3+ species and stored oxygen both contributed to H2S oxidation and Hg0 capture. It can be concluded that Fe2O3/TiO2 sorbents appeared to be promising and efficient sorbent for mercury removal from syngas in industrial application.

Ce/Cr and Ce/Co modified ferrite catalysts for high temperature water-gas shift reaction at elevated pressures

In this work, Ce and Cr/Co co-doped iron oxide (FeCeMOx, where M = Cr or Co) ferrites were investigated for high-temperature water-gas shift (HT-WGS) under industrially relevant pressures (20 bars). The Ce and Cr/Co bi-doping has greatly promoted the catalytic performance in comparison to the single Ce-doping. Especially, the FeCeCoOx ferrite demonstrated the best HT-WGS activity without any deactivation at a steam to CO ratio of 3.5. The ternary FeCeCrOx and FeCeCoOx catalysts also exhibited reasonably stable performance with a slight methanation activity (<2.5%) even under low steam to CO ratio of 1.5. The hematite phase (Fe2-xCex/2Mx/2O3, where M = Cr or Co and × = 0.33) of the fresh (calcined) catalysts became [A(1-δ)Bδ]T[AδB(2-δ)]OO4 type magnetite spinel structure (Fe3-xCex/2Mx/2O4, where M = Cr or Co and × = 0.5) during the activation process, which is regarded as the active phase for the WGS reaction. The co-doping of Cr or Co increased the stability of the active magnetite phase against sintering and suppressed the coke formation during the WGS reaction, which should be responsible for the stable activity. The addition of Cr or Co to iron oxide also delays the formation and over-reduction of active magnetite phase. Mössbauer spectra confirmed that the Cr or Co ions were incorporated into the octahedral sites of [A(1-δ)Bδ]T[AδB(2-δ)]OO4 spinel framework during the activation and modifies the local structure. The superparamagnetic behavior of the spinel ferrites has significantly enhanced upon the co-doping of Ce and Cr/Co into the iron oxide lattice, indicating a high fraction of nanoparticles in the ternary spinel ferrites. The Cr or Co addition resulted in the decreased surface Fe3+/Fe2+ ratio which could be due to the replacement of Fe3+ ions by Cr or Co ions. Most importantly, no evident change was observed in the surface structure of ternary spinel ferrites even after the reaction, which could be responsible the stable performance of the catalysts.

High surface area magnetic double perovskite La2AlFeO6 as an efficient and stable photo-Fenton catalyst under a wide pH range

Photo-Fenton process is an efficient way to treat the organic pollutants in wastewater. However, the efficiency is limited by serious leaching of iron ions, separation of spent catalyst from reaction system for facile recycling, acidic reaction environment (pH＜4). Herein, a novel double perovskite photocatalyst La2AlFeO6 with high surface area was developed to counter these issues. By altering complexing agents, iron ion content discrepancy and B’-O-B” varies in La2AlFeO6 led to a high surface Fe3+ ratio and an excellent magnetic property. >98.4% of phenol could be degraded in a wide pH range over La2AlFeO6 because of the high surface Fe3+ ratio and promotion of generated ·OH, ·O2– and 1O2. The excellent magnetic property would contribute to separate catalyst from water, and led the used La2AlFeO6 to be reused after simple deionized water rinsing and air drying without any further treatment or calcination.

Synthesis of magnetic CuFe2O4/Fe2O3 core-shell materials and their application in photo-Fenton-like process with oxalic acid as a radical-producing source

ABSTRACT In this work, we proposed to synthesize CuFe2O4/Fe2O3 core-shell materials with different Fe2O3 contents in order to create new and efficient photo-Fenton-like catalysts for the degradation of methylene blue with oxalic acid as a radical-producing source. The catalysts were prepared through two stages: first, CuFe2O4 was prepared by a hydroxide coprecipitation – annealing method and then, Fe2O3 was immobilized on CuFe2O4 surface by a simple impregnation – annealing procedure. According to the experimental results, our CuFe2O4/Fe2O3 core-shell materials exhibit high photo-Fenton-like catalytic activity for the degradation of methylene blue under both UVA light and visible light, as well as good ferromagnetic properties, which allows them to be easily separated from the solution by a magnet. Among them, the catalyst prepared with the molar CuFe2O4/Fe2O3 ratio of 1:2 showed the best catalytic performance with the rate constant of 2.103 h–1 under UVA light and 0.542 h–1 under visible light, which were 2 times higher than CuFe2O4 sample. The enhanced catalytic activities of our core-shell materials can be attributed to the high content of surface Fe3+ species, high specific surface area and the presence of rod-like Fe2O3 particles on their surface.

Impact of the charge transfer process on the Fe2+/Fe3+distribution at Fe3O4 magnetic surface induced by deposited Pd clusters

Magnetic iron oxide particles decorated with transition-metal nanoparticles have become increasingly attractive in catalysis regarding the environment modifications, such as an additive ligand or carrier, which could significantly influence their performances. In this work, we used the Density Functional Theory (DFT) in the gradient approximation to study the interaction between the metal and its support for palladium and palladium oxide clusters on the surface of Fe3O4(001)magnetite. We report a dynamic process promoted by the palladium deposition with charge transfer from the metal host. An increase in the Fe2+/Fe3+ ratio at the topmost surface of the support was determined. The reduction of surface Fe3+ ions with electrons located at the interface has been proposed. Surprisingly, this slight increase in the surface density in Fe2+ ions was not observed in palladium oxide when the charge transfer from the support was significantly enhanced. Finally, the impact of the charge transfer process between the surface and the adsorbed species on palladium in terms of structure stability was discussed.

Sulphur vacancy derived anaerobic hydroxyl radical generation at the pyrite-water interface: Pollutants removal and pyrite self-oxidation behavior

We demonstrate that FeS2 possessing sulfur vacancies (SVs), under anaerobic water environment, can stabilize the H2O adsorption with a strong exothermic effect to compensate the apparent energy barrier of H2O oxidation on pyrite surface. Adsorbed H2O dissociates at SV site via π-back donation of localized electron, and thus breaks through thermodynamic restriction of H2O oxidation to generate bound hydroxyl radical through a one-electron transfer process of localized holes (Vs+). Meanwhile, the synergistic effect of surface Fe3+ and circumjacent H2O molecule can also promote the oxidation of H2O adsorbed at Fe3+ site to produce free hydroxyl radical via oxidation reaction. The generated hydroxyl radical on pyrite surface can induce the oxidation of different pollutants, and also contribute to the pyrite self-oxidation process. These findings clarify the in-depth mechanism of anaerobic hydroxyl radical generation at pyrite-water interface, and shed light on anaerobic environmental effect of pyrite and other natural iron sulfide minerals.

Facet-Dependent Photodegradation of Methylene Blue by Hematite Nanoplates in Visible Light.

The expression of specific crystal facets in different nanostructures is known to play a vital role in determining the sensitivity toward the photodegradation of organics, which can generally be ascribed to differences in surface structure and energy. Herein, we report the synthesis of hematite nanoplates with controlled relative exposure of basal (001) and edge (012) facets, enabling us to establish direct correlation between the surface structure and the photocatalytic degradation efficiency of methylene blue (MB) in the presence of hydrogen peroxide. MB adsorption experiments showed that the capacity on (001) is about three times larger than on (012). Density functional theory calculations suggest the adsorption energy on the (001) surface is 6.28 kcal/mol lower than that on the (012) surface. However, the MB photodegradation rate on the (001) surface is around 14.5 times faster than on the (012) surface. We attribute this to a higher availability of the photoelectron accepting surface Fe3+ sites on the (001) facet. This facilitates more efficient iron valence cycling and the heterogeneous photo-Fenton reaction yielding MB-oxidizing hydroxyl radicals at the surface. Our findings help establish a rational basis for the design and optimization of hematite nanostructures as photocatalysts for environmental remediation.

Surface defect engineering of Fe-doped Bi7O9I3 microflowers for ameliorating charge-carrier separation and molecular oxygen activation

Effective charge-carrier separation and molecular oxygen activation are crucial factors for photocatalytic environmental purification. Herein, an efficient Fe-doped Bi7O9I3 microflowers photocatalyst was synthesized. It was discovered that Fe doping could not only tune the concentration of oxygen vacancies of Bi7O9I3 to optimize the dissociation of excitons, but also promote the separation of charge-carriers and the activation of oxygen molecules. Meanwhile, the inducing of surface oxygen vacancies and Fe3+/Fe2+ by Fe optimal doping can act as the activation center for catalytic reactions, which also significantly enhances the photocatalytic activity. Benefiting from the optimized properties, the photocatalytic activity of Fe-doped Bi7O9I3 photocatalyst has been significantly improved by more than 4 times. Finally, we proposed that a highly efficient catalytic oxidation reaction mechanism can be achieved via modulating Fe doping to induce oxygen vacancies to promote charge separation and molecular oxygen activation. This work provides a novel approach for designing efficient photocatalysts.

Stabilizing Oxidative Dehydrogenation Active Sites at High Temperature with Steam: ZnFe2O4-Catalyzed Oxidative Dehydrogenation of 1-Butene to 1,3-Butadiene

Author(s): Zeng, T; Sun, G; Miao, C; Yan, G; Ye, Y; Yang, W; Sautet, P | Abstract: Dehydrogenation reactions are central for the production of functional molecules. Steam plays a pivotal role in ZnFe2O4-catalyzed 1-butene oxidative dehydrogenation (ODH). However, the essential effect of steam on this reaction is still unclear. Herein, we describe the structure-performance relationships of ZnFe2O4 in the presence/absence of steam by combined density functional theory and experimental studies. The catalytic performances of ZnFe2O4 under different reaction conditions were investigated. The ZnFe2O4(110) surface properties under reaction conditions and molecular reaction pathways were modeled. Free-energy profiles were calculated. We found that an oxygen-excess ZnFe2O4(110)-O termination, with an extra O atom bridging two Fe cations, is preferred under oxygen-rich conditions. However, both experimental and theoretical approaches indicate that this surface bicoordinated O is not stable at relatively high temperatures in the absence of steam, resulting in the reduction of surface Fe3+ cations to Fe2+ which are inactive in the 1-butene ODH reaction. It was found that steam interacts strongly with the ZnFe2O4(110)-O surface. Steam stabilizes the catalyst surface Fe3+ ions by converting bicoordinated O to more thermally stable hydroxyl groups. Surface hydroxyls are active sites for C-H bond cleavage in the 1-butene ODH reaction in the presence of steam. We propose that the role of steam elucidated here represents a general mode of steam influence in ODH reactions over oxide surfaces.

Adsorption and Reaction of Trimethyl and Triethyl Phosphite on Fe3O4 by Density Functional Theory

First-principle density functional theory (DFT) calculations are used to calculate the most stable structures and heats of adsorption of trimethyl and triethyl phosphites on an Fe3O4 surface in order to understand their behavior as lubricant additives. Previous surface science studies of phosphate and phosphite esters on iron oxide surface have shown that they react by sequentially desorbing the corresponding alcohol and aldehyde in equimolar amounts. This implies that the reactions are limited by the rate of alkoxide removal, followed by a rapid reaction to form the alcohol and aldehyde. It is found that the trialkyl phosphites, dialkyl phosphite, and monoalkyl phosphite all adsorb with the phosphorus atoms bound to surface Fe3+ ions, with the alkoxy groups close to parallel to the surface. The heat of adsorption increases as the alkoxide groups are removed. The postulate that the rate-limiting step in the decomposition of the phosphate esters is the sequential removal of the alkoxide group is tested by plotting the experimental activation energy obtained from temperature-programed desorption experiments versus the corresponding heats of adsorption calculated by DFT. A linear dependence shows that the reaction obeys the so-called Evans–Polanyi relation, thereby confirming the above postulate. The slope of the plot is close to unity and thus implies that the structure of the transition state of the reaction resembles the product.

Synergistic effect and mechanism of catalytic degradation toward antibiotic contaminants by amorphous goethite nanoparticles decorated graphitic carbon nitride

Cost-effective ultrafine amorphous goethite nanoparticles with size of around 5 nm decorated graphitic carbon nitride (g-C3N4/FeOOH) heterojunction was fabricated by a simple chemical reaction which exhibited efficient photo-Fenton-like activity for antibiotic tetracycline (TC) degradation in the presence of H2O2 and visible light irradiation. Within the reaction time of 60 min, approximately 88% of TC molecules can be degraded and this value was obviously higher than those in the corresponding Fenton-like and photocatalytic processes. Compared with those common iron-based oxide counterparts, the photo-Fenton-like performance of g-C3N4/FeOOH was also significantly higher. In addition, the efficient degradation of TC in actual water bodies was observed for g-C3N4/FeOOH through using natural sunlight to drive the photo-Fenton-like reaction. Meanwhile, g-C3N4/FeOOH can maintain stable performance in the repeated experiment and the effects of different conditions (TC concentration, H2O2 concentration, catalyst dosage, initial pH, reaction temperature, and anion coexistence) were revealed. The improved separation and transfer of photogenerated charge carriers and accelerated conversion from surface Fe3+ to Fe2+ brought about enhanced catalytic activity of g-C3N4/FeOOH. The holes, O2− and OH radicals were major oxide species and possible TC degradation mechanism was revealed. This study might give some important inspiration for development of efficient heterogeneous Fenton-like catalysts in the treatment of antibiotic wastewaters.