Dispersed Iron Species Research Articles

Efficient generation of 1O2 by activating peroxymonosulfate on graphitic carbon nanoribbons for water remediation

Few-layer graphitic carbon nanoribbons (GCN) with rich defective sites were prepared by pyrolysis at 800 oC in N2 of in situ-chelated Fe-polyaniline complexes synthesized via one-pot homogeneous Fenton-like oxidative polymerization of an acidic aniline solution. A minimal amount of iron (0.47 wt%) made a pivotal role in the nanoribbon growth and graphitization of GCN, and deposited highly dispersed iron species on GCN without post-synthesis acid leaching, which greatly simplified the synthesis procedure of GCN with improved yield. GCN exhibited high activity and stability for catalytic degradation of organic pollutants with peroxymonosulfate (PMS) mainly via non-radical pathways. The influences of various operating parameters on the catalytic performance of GCN were investigated. Scavenging tests, spin-trapping electron paramagnetic resonance spectra, electrochemical analyses, and theoretical calculations unveiled that 1O2 was the main reactive oxygen species generated from synergistic activation of PMS on GCN while GCN-mediated electron transfer made a minor contribution to organic degradation.

Effect of CO2 Co-Feeding on the Stabilization of Atomically Dispersed Iron Species over MgAl2O4 During Ethane Dehydrogenation Reactions

Effect of CO₂ Co-Feeding on the Stabilization of Atomically Dispersed Iron Species over MgAl₂O₄ During Ethane Dehydrogenation Reactions

Synergetic Adsorption–Photocatalytic Activated Fenton System via Iron-Doped g-C3N4/GO Hybrid for Complex Wastewater

A synergetic adsorption–photocatalytic-activated Fenton system using an iron-doped g-C3N4/GO (GO/Fe-GCN) hybrid with highly efficient performance was established. The highly dispersed iron species with a Fe2+/Fe3+ ratio (1.67) and mesopores (3.7 nm) with a relative higher specific area and pore volume benefited the reaction efficiency and the contact of organic pollutants with the active sites. In the dynamic adsorption–photo-coordinated Fenton system, the maximum removal rate of GO/Fe-GCN reached 96.5% and equilibrium was 83.6% for Rhodamine B. The GO component not only enhanced the adsorption but also provided a higher efficiency of photo-generated carrier separation and transport. The hybrid structure of GO/Fe-GCN and the high efficiency of circulation of Fe(III)/Fe(II) played an essential role in the synergy of the adsorption–enrichment and the photo-coordinated Fenton reaction. GO/Fe-GCN can also be used to treat complex waste-water containing metallic ions, metal complexes, and organic pollutants, which could allow potential applications in the treatment of water pollution.

Catalytic ozonation with γ-Al2O3 sphere supported highly dispersed iron species: Preparation, performance and catalytic mechanism

Maximizing the number of active sites is important to obtain an excellent catalytic activity for supported metal catalysts. Herein, citric acid-modified Al2O3 spheres in millimeter scale were employed as the porous support for loading iron species by a impregnation-calcination method using Fe(NO3)3‧9 H2O as the metal precursor. A good dispersion of the iron species inside the Al2O3 spheres was achieved, and the characterizations revealed that Fe sites were incorporated into the framework of Al2O3 in the form of -[Al-O-FeIII]- structure. The obtained FeIII/CA-Al2O3 catalyst was found to have a significantly increased amount of surface Lewis acid sites (LAS), showing a better performance than the counterpart catalyst Fe2O3/Al2O3 for p-nitrophenol (PNP) degradation. It was found that the presence of both oxidizable organic pollutants (as electron donator) and ozone was the prerequisite for observing the transformation from surface-ferric (FeIII) to surface-ferrous (FeII) iron on the surface of FeIII/CA-Al2O3 catalyst. In comparison with Fe2O3/Al2O3 catalyst, the FeIII/CA-Al2O3 catalyst also demonstrated a higher level of FeII during the catalytic reaction, suggesting that it had more iron active centers for the catalytic reaction. The cycle of the redox couple FeIII and FeII played an important role for producing the reactive oxygen species. This study confirms that the modification of γ-Al2O3 spheres with citric acid enabled a highly homogeneous dispersion of iron within the support matrix, providing a feasible route for the synthesis of high-performance and low-cost iron-bearing catalysts for industrial application.

An iron–based biochar for persulfate activation with highly efficient and durable removal of refractory dyes

The magnetic biochar catalyst (Fe@BC) was synthesized by pyrolyzing Fe–tanned collagen fiber based on the tanning process and used as a high–efficiency and recyclable persulfate (PS) activator to degrade refractory dyes. In this study, methylene blue (MB) was chosen as a model pollutant to evaluate the performance of the Fe@BC/PS system. Results illustrated that MB was completely removed within 20 min with a rate constant (kobs) of 0.2246 min–1, which was much higher than that of pure biochar (0.0497 min–1), and high mineralization efficiency (92%) for MB degradation was obtained. Notably, the MB removal rate still reached 72% after 20 cycles. The high catalytic activity and excellent recycling performance could be attributed to the uniformly dispersed iron species, abundant oxygen functional groups, and defective carbon matrix. Radical quenching experiments and electron paramagnetic resonance studies illustrated that SO4•– was the predominant free radical for MB degradation. Moreover, other refractory dyes could also be rapidly and efficiently removed from the Fe@BC/PS system. This work is expected to propose a promising catalyst for the degradation of refractory dyes and open a new possibility for the durable removal of refractory organic dyes.

Economical preparation of Fe3O4/C/CG and Fe/C/CG composites as microwave absorbents by recycling of coal gangue

Pollution is a pressing problem in the context of sustainable development, a solution to which is to reutilize waste resources. Herein, coal gangue was recycled to prepare Fe3O4/C/CG and Fe/C/CG composites for microwave absorption via a facile method. The synthesis process involves loading a precursor solution of starch and ferric nitrate onto coal gangue matrix and then conducting the in-situ carbothermal reduction. The initial starch mass and carbothermal temperature significantly affect the dielectric and magnetic properties, further affect microwave absorption performance of the composites. For the Fe3O4/C/CG and Fe/C/CG composite, the minimum reflection loss could reach −45.1 dB and −27.8 dB, respectively. And the maximum effective absorption bandwidth of Fe/C/CG was 4.7 GHz. The strong microwave attenuation and impedance matching, which stemmed from the conductive graphitized carbon, the abundant interfaces of the highly dispersed carbon and iron species on the matrix, must account for the excellent performance.

Engineering Single-Atomic Iron-Catalyst-Integrated 3D-Printed Bioscaffolds for Osteosarcoma Destruction with Antibacterial and Bone Defect Regeneration Bioactivity.

Effective antitumor therapeutics with distinctive bactericidal and osteogenic properties are in high demand for comprehensive osteosarcoma treatment. Here, a "scaffold engineering" strategy that integrates highly active single-atomic iron catalysts (FeSAC) into a 3D printed bioactive glass (BG) scaffold is reported. Based on the atomically dispersed iron species within the catalysts, the engineered FeSAC displays prominent Fenton catalytic activity to generate toxic hydroxyl radicals (•OH) in response to the microenvironment specific to osteosarcoma. In addition, the constructed FeSAC-BG scaffold can serve as a sophisticated biomaterial platform for efficient osteosarcoma ablation, with concomitant bacterial sterilization via localized hyperthermia-reinforced nanocatalytic therapeutics. The destruction of the osteosarcoma, as well as the bacterial foci, can be achieved, further preventing susceptible chronic osteomyelitis during osteogenesis. In particular, the engineered FeSAC-BG scaffold is identified with advances in accelerated osteoconduction and osteoinduction, ultimately contributing to the sophisticated therapeutics and management of osteosarcoma. This work broadens the biomedical potential of single-atom catalysts and offers a comprehensive clinically feasible strategy for overall osteosarcoma therapeutics, bacterial inhibition, and tissue regeneration.

Highly dispersed iron-doped biochar derived from sawdust for Fenton-like degradation of toxic dyes

Wastewater pollution is a global challenge in the field of environmental remediation. Functional biochar as Fenton-like catalyst receives growing attention for degradation of refractory organic contaminants in wastewater. This work provides a step-forward to develop effective functional biochar via revealing the mechanism of surface catalysis. The synthesis of iron-doped biochar (Fe@BC) was conducted through iron impregnation and carbonization of waste sawdust. Highly dispersed iron species on graphitic biochar is verified by multi-techniques including electron probe microanalyzer, transmission electron microscope, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrum and Raman spectrum. Rhodamine B (RhB) degradation above 92.7% is obtained within 140 min. Surface catalysis for generating hydroxyl radical is proved by iron determination, radical identification, and catalyst characterizations. Effective degradation of binary dyes is achieved. Fe@BC is an excellent catalyst with broad operation pH and highly stability. Promising application of the functional biochar provides a sustainable and ecofriendly strategy for wastewater treatment.

Novel synthesis and characterization of Fe-ZSM-5 nanocrystals in hot compressed water for selective catalytic reduction of NO with NH3

Abstract This paper describes a new synthetic method to prepare a composite of metal oxide nanoparticles and zeolite (Fe-ZSM-5) in hot compressed water. Two approaches, one-pot immobilization of iron oxide on ZSM-5 and post-ZSM-5-synthesis iron oxide impregnation are studied. The products show various morphologies, which lead to different activities during the selective catalytic reduction of NO with NH3. In the first approach, Fe-ZSM-5 is synthesized in hot compressed water from precursors with various concentrations of Fe(NO3)3, while in the second route, firstly, ZSM-5 powder is prepared and then impregnated with iron oxide. The state of Fe in Fe-ZSM-5 was studied through TEM, XPS, XRD, NH3-TPD, and H2-TPR. Both methods result in the production of highly dispersed iron species, however, Fe-ZSM-5 prepared from the one-pot synthesis method contains more acidic sites and more reducible iron species because of the presence of FeOx nanoparticles mainly in the intra-framework of the zeolite. Furthermore, it is observed that the increase in iron concentration in the precursor has an adverse effect on the surface area and acidity of the final Fe-ZSM-5 product. On the other hand, Fe-ZSM-5 obtained from the impregnation process contains higher quantities of iron in the extra-framework position in the form of bulky aggregates with lower activity. Consequently, Fe-ZSM-5 synthesized through the one-pot route showed higher activity because of the well dispersive iron oxide in the zeolite support. The highly dispersive state is attributed to the predominant presence of iron bound to the framework of aluminum in the zeolite. The results also show that the protonation of the catalyst has no crucial effect on the activity of the catalyst, while the oxidation state of iron oxide is greatly responsible for the SCR activity of the catalyst.

Selective oxidation of H2S over Fe supported on Zr-intercalated Laponite clay mesoporous composite catalysts at low temperature

A series of iron supported on Zr-intercalated clay composite catalysts with mesoporous structure, a high specific surface area, and high thermal stability were successfully synthesized (named Fe/Zr-Lap catalysts) and tested for H2S selective oxidation. The structural characteristics and physicochemical properties of the catalysts were investigated using various methods. The iron species existed mainly as isolated Fe3+ and polymeric (FeO)n species in an octahedral coordination. All of the Fe/Zr-Lap catalysts exhibited excellent catalytic activity at relatively low temperatures (120–200 °C). The 8% Fe/Zr-Lap catalyst presented the best catalytic performance at 180 °C. It is likely that highly dispersed iron species, abundant chemically adsorbed oxygen vacancies, synergistic effect of iron and zirconium species, and improved reducibility played important roles in the reaction. Besides, the reaction and deactivation mechanisms were also proposed.

Photocatalysts market is estimated to cross the $6 bn mark by 2029

It is important to understand low-temperature oxidation to inhibit the spontaneous combustion of lignite for its safe transportation and efficient utilization. The study investigates the effect of temperature on microstructure and mass change during low-temperature oxidation of Shengli lignite (SL) and further explores the promoting effect of iron species. In this work, inherent minerals of Shengli lignite were first demineralized by HCl leaching (SL+), Fe3+ were then loaded by impregnation method (SL+-Fe), and low-temperature (200–300 °C) oxidation was carried out in laboratory-scale fixed bed reactor. The structures of low-temperature oxidation treated coal samples were characterized by SEM-EDS, FT-IR, XPS, XRD and Raman spectroscopy. The low-temperature oxidation experiment results showed that coal displayed noticeable jump in mass change at particular oxidation temperatures (called jump temperature). The jump temperature of SL+-Fe was approximately 20 °C lower than that of SL+. The FT-IR analysis indicated presence of analogous quinone structure that was originating from SL+-Fe after low-temperature oxidation at 200–210 °C, which was approximately 20–30 °C lower than that of SL+. XRD and XPS results revealed that iron species changed from highly dispersed or unknown chemical state to α-Fe2O3 before and after jump temperature. It is deduced that the jump phenomenon of coal samples maybe attributed to the oxidation decomposition of analogous quinone structure, and highly dispersed iron species caused shifts in jump temperature of SL+-Fe to lower values.

Microstructural characteristics of Shengli lignite during low-temperature oxidation and promotion effect of iron species

It is important to understand low-temperature oxidation to inhibit the spontaneous combustion of lignite for its safe transportation and efficient utilization. The study investigates the effect of temperature on microstructure and mass change during low-temperature oxidation of Shengli lignite (SL) and further explores the promoting effect of iron species. In this work, inherent minerals of Shengli lignite were first demineralized by HCl leaching (SL+), Fe3+ were then loaded by impregnation method (SL+-Fe), and low-temperature (200–300 °C) oxidation was carried out in laboratory-scale fixed bed reactor. The structures of low-temperature oxidation treated coal samples were characterized by SEM-EDS, FT-IR, XPS, XRD and Raman spectroscopy. The low-temperature oxidation experiment results showed that coal displayed noticeable jump in mass change at particular oxidation temperatures (called jump temperature). The jump temperature of SL+-Fe was approximately 20 °C lower than that of SL+. The FT-IR analysis indicated presence of analogous quinone structure that was originating from SL+-Fe after low-temperature oxidation at 200–210 °C, which was approximately 20–30 °C lower than that of SL+. XRD and XPS results revealed that iron species changed from highly dispersed or unknown chemical state to α-Fe2O3 before and after jump temperature. It is deduced that the jump phenomenon of coal samples maybe attributed to the oxidation decomposition of analogous quinone structure, and highly dispersed iron species caused shifts in jump temperature of SL+-Fe to lower values.

Preparation of highly dispersed iron species over ZSM-5 with enhanced metal-support interaction through freeze-drying impregnation

Supported metal catalysts play a vital role in the chemical industry, and the metal-support interaction is an important property of the catalyst. However, in the traditional impregnation method, it is difficult to obtain sufficient metal-support interactions owing to the mobility of the metal precursor during evaporation drying. Here, freeze drying is applied during impregnation instead of evaporation drying for enhancing the metal-support interactions. 57FeZSM-5 was chosen as a representative catalyst. A quantitative analysis was conducted based on Mössbauer spectroscopy. Compared with traditional evaporation-drying catalyst, freeze-drying catalyst has stronger metal-support interactions. In addition, more iron species are confined in the channel and smaller metal sizes and less diversity are obtained. The compositional change is also proved because of the superior performance of the freeze-drying catalyst during N2O decomposition. This method can be extended to other supported metal catalysts prepared through an impregnation method, which can be used to tune the metal-support interactions and metal sizes.

The magnetic biochar derived from banana peels as a persulfate activator for organic contaminants degradation

The magnetic biochar (γ-Fe2O3@BC) derived from banana peels was synthesized by a facile one-pot thermal process and used as the cost-effective and recyclable persulfate (PS) activator for organic contaminants degradation. The results showed that the encapsulated iron oxide nanoparticles not only introduced the magnetism into biochar for easy separation, but also influenced the catalytic ability for PS activation. The γ-Fe2O3@BC was found to be highly effective for bisphenol A (BPA) degradation without pH adjustment. A complete removal of BPA was obtained within 20 min with an observed rate constant (kobs) of 0.1849 min−1, which was almost two times as large as that (0.0956 min−1) of pure biochar. Further, it exhibited high mineralization efficiency for the degradation of various organic contaminants. The high catalytic activity could be attributed to large BET surface area, dispersed iron species, abundant oxygen functional groups and rich doped nitrogen. Radical quenching experiments and electron spin resonance (ESR) studies confirmed that OH, SO4− and O2− were all involved in the radical oxidation process which was responsible for BPA degradation. A mechanism of PS activation by the γ-Fe2O3@BC catalyst was proposed based on the synergistic effect of biochar and iron.

Finely Iron-Dispersed Particles on β Zeolite from Solvated Iron Atoms: Promising Catalysts for NH3-SCO

β zeolite has been functionalized with 2 wt % Fe to obtain catalysts for the ammonia selective catalytic oxidation (NH3-SCO) reaction. Iron deposition was performed on the zeolite surface by solvated metal atom dispersion (SMAD) and ion-exchange (IE) procedures. ZSM-5 was selected as the reference structure known to assure high dispersion of isolated centers when functionalized with iron by IE. Transmission electron microscopy techniques combined with element maps enlightened on the iron-species distribution and dimension on the two zeolites. As expected, highly homogeneous dispersed iron species were present on the ZSM-5 sample prepared by IE, while with β zeolite, the same deposition method led to the formation of FeOx aggregates (2.5–10 nm) together with isolated iron species. On the other hand, by the SMAD approach, well-formed FeOx nanoparticles ranging from 1.0 to 4.5 nm were revealed on β zeolite. NH3-SCO on iron-containing zeolites started at approximately 300 °C, without any clear effect of the s...

Ce-doped mesoporous alumina supported Fe-based catalyst with high activity for oxidative dehydrogenation of 1-butene using CO2 as soft oxidant

Ce-doped mesoporous alumina supported Fe-based catalyst (Fe2O3/Meso-CeAl) was prepared and employed for 1,3-butadiene (BD) synthesis by oxidative dehydrogenation of 1-butene, using CO2 as soft oxidant. The worm-like porous structure of Fe2O3/Meso-CeAl catalyst with highly dispersed Ce in alumina matrix and high dispersion of iron species on Meso-CeAl surface was confirmed by N2 adsorption, transmission electron microscopy and X-ray diffraction results. Compared with Fe2O3/γ-Al2O3 and Fe2O3/Meso-Al2O3 catalysts, X-ray photoelectron spectroscopy and CO2-TPD results respectively demonstrated the increasing in oxygen storage capacity and improvement in CO2 adsorption and activation ability for Fe2O3/Meso-CeAl-100 catalyst. Consequently, the Fe2O3/Meso-CeAl-100 catalyst showed excellent catalytic activity (1879 gBD/kgcat/h), high CO2 conversion (14%) and high BD selectivity (51%). Not only the structural properties and highly dispersed iron species, but also the good oxygen storage capacity and thus good CO2 adsorption and activation ability contributed positively to the good performance of Fe2O3/Meso-CeAl-100 catalyst.

Highly selective oxidation of methane to methanol at ambient conditions by titanium dioxide-supported iron species

Methane activation under moderate conditions and with good selectivity for value-added chemicals still remains a huge challenge. Here, we present a highly selective catalyst for the transformation of methane to methanol composed of highly dispersed iron species on titanium dioxide. The catalyst operates under moderate light irradiation (close to one Sun) and at ambient conditions. The optimized sample shows a 15% conversion rate for methane with an alcohol selectivity of over 97% (methanol selectivity over 90%) and a yield of 18 moles of alcohol per mole of iron active site in just 3 hours. X-ray photoelectron spectroscopy measurements with and without xenon lamp irradiation, light-intensity-modulated spectroscopies, photoelectrochemical measurements, X-ray absorption near-edge structure and extended X-ray absorption fine structure spectra, as well as isotopic analysis confirm the function of the major iron-containing species—namely, FeOOH and Fe2O3, which enhance charge transfer and separation, decrease the overpotential of the reduction reaction and improve selectivity towards methanol over carbon dioxide production. Methanol synthesis from methane is a promising route to valorize this abundant natural gas, but existing thermal processes require harsh reaction conditions. Now, a photocatalytic approach based on TiO2-supported iron oxide species is described, which affords methanol in high yield and selectivity at ambient conditions.

Comparison of preparation methods of iron-based catalysts for enhancing Fischer-Tropsch synthesis performance

Carbon supported iron catalysts for Fischer-Tropsch synthesis, with the same iron loading of ca. 35 wt.%, were prepared by pyrolysis process and incipient wetness impregnation methods. The effect of the preparation methods on the catalyst structure, catalytic properties, and the direct conversion of syngas via Fischer-Tropsch synthesis was investigated. The iron species, iron particle size and iron reducibility depended on the preparation method. The pyrolysis of homogeneous fusion yielded a unique core-shell structure with dispersed iron species embedded in a matrix of porous carbon. The FeOx/AC catalyst obtained by incipient wetness impregnation contained Fe2O3 species after calcination, while the core-shell structured catalyst obtained by pyrolysis process contained Fe3C species after calcination. The results show that the core-shell structure iron-based catalyst had higher extent of carburization and dispersion, which led to higher activity for Fischer-Tropsch reaction than that of other two catalysts obtained by different synthesis methods. Furthermore, the Fe3C@C catalyst promoted by alkali metals (Na, Mg, K, Ca) resulted in the increase of O/P ratio and low carbon olefin selectivity, and the decrease of methane selectivity.

Platinum group metal-free electrocatalysts: Effects of synthesis on structure and performance in proton-exchange membrane fuel cell cathodes

Abstract Development of platinum group metal free catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) requires understanding of the interactions between surface chemistry and performance, both of which are strongly dependent on synthesis conditions. To elucidate these complex relationships, a set of Fe-N-C catalysts derived from the same set of precursor materials is fabricated by varying several key synthetic parameters under controlled conditions. The results of physicochemical characterization are presented and compared with the results of rotating disk electrode (RDE) analysis and fuel cell testing. We find that electrochemical performance is strongly correlated with three key properties related to catalyst composition: concentrations of 1) atomically dispersed Fe species, 2) species in which N is bound to Fe, and 3) surface oxides. Not only are these factors related to performance, these types of chemical species are shown to correlate with each other. This study provides evidence supporting the role of iron coordinated with nitrogen as an active species for the ORR, and offers synthetic pathways to increase the density of atomically dispersed iron species and surface oxides for optimum performance.

Synthesis of highly dispersed iron species within mesoporous (Al-)SBA-15 silica as efficient heterogeneous Fenton-type catalysts

Iron and iron-aluminium containing ordered SBA-15 silica catalysts were synthesized for the first time at relatively high iron content (Si/Fe molar ratio down to ∼21) using an adapted two-step pH-adjustment approach needed for the incorporation of heteroatom species in the mesostructure. The pH applied for the second step of synthesis significantly affected (i) the content of inserted iron and (ii) the state of iron species. Thus, under acidic conditions, the iron heteroatoms were partly incorporated within the mesoporous SBA-15 structure. The solids displayed a moderate activity in the Fenton-type peroxidation of Reactive Red 120 azo dye owing to the low density of active sites for H2O2 activation. Nearly complete iron incorporation was achieved at slightly basic pH with iron mostly presented as isolated and/or highly dispersed species. Furthermore, it was observed that the co-addition of aluminium to iron significantly promoted stabilization of iron species in isolated and/or highly dispersed state, which exhibited improved catalytic properties for the dye degradation with fast cleavage of azo-chromophore into intermediates and high mineralization level.