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Single-atom catalysts (SACs) composing of low-cost, earth-abundant metals, with two-dimensional material supports have displayed great potential in a wide range of electrochemical reactions, including CO2 reduction reaction (CO2RR) to convert CO2 to valuable chemical and fuels. In recently years, substantial advances have been achieved in the preparation methodologies with improved catalytic performances, but the underlying structure-activity relationship from a general perspective remains elusive. Especially, it is urgent to summarize the SACs with diatom metal centers toward efficient CO2RR. Based on the recent progress, this review synopsizes the fundamental understandings of non-noble metal-based SACs for CO2RR using selected examples. We also highlight the representative molecular models from the latest progress, including M-N-C, heteroatom co-doping, vacancy/edge defect and bimetallic SACs, aiming to elucidating the nature of active sites on various 2D substrates. Moreover, we summarize the spectroscopic and computational studies to verify atomic-level regulation on geometric and electronic properties of SACs. We anticipate that this review will deepen the mechanistic understanding of the structure-performance relationship and inspire future study of SACs for CO2RR.

Electrochemically reducing CO 2 to valuable fuels or feedstocks is recognized as a promising strategy to simultaneously tackle the crises of fossil fuel shortage and carbon emission. Sn-based catalysts have been widely studied for electrochemical CO 2 reduction reaction (CO 2 RR) to make formic acid/formate, which unfortunately still suffer from low activity, selectivity and stability. In this work, halogen (F, Cl, Br or I) was introduced into Sn catalyst by a facile hydrolysis method. The presence of halogen was confirmed by a collection of ex-situ and in-situ characterizations, which rendered more positive valence state of Sn in halogen-incorporated Sn catalyst as compared to unmodified Sn under cathodic potentials in CO 2 RR and therefore tuned the adsorption strength of the key intermediate (*OCHO) toward formate formation. As a result, the halogen-incorporated Sn catalyst exhibited greatly enhanced catalytic performance in electrochemical CO 2 RR to produce formate.

Single-atom catalysts with a well-defined metal center open unique opportunities for exploring the catalytically active site and reaction mechanism of chemical reactions. However, understanding of the electronic and structural dynamics of single-atom catalytic centers under reaction condition is still limited due to the challenge of combining operando techniques that are sensitive to such sites and model single-atom systems. Herein, supported by state-of-the-art operando techniques, we provide an in-depth study of the dynamic structural and electronic evolution during electrochemical CO2 reduction reaction (CO2RR) of a model catalyst comprising iron only as a high-spin (HS) Fe(III)N4 center in its resting state. Operando 57Fe Mössbauer and X-ray absorption spectroscopies clearly evidence the change from a HS Fe(III)N4 to a HS Fe(II)N4 center with decreasing potential, CO2- or Ar-saturation of the electrolyte leading to different adsorbates and stability of the HS Fe(II)N4 center. With operando Raman spectroscopy and cyclic voltammetry, we identify that the phthalocyanine (Pc) ligand coordinating the iron cation center undergoes a redox process from Fe(II)Pc to Fe(II)Pc−. Altogether, the HS Fe(II)Pc− species is identified as the catalytic intermediate for CO2RR. Furthermore, theoretical calculations reveal that the electroreduction of the Pc ligand modifies the d-band center of the in situ generated HS Fe(II)Pc− species, resulting in an optimal binding strength to CO2 and thus boosting the catalytic performance of CO2RR. This work provides both experimental and theoretical evidence towards the electronic structural and dynamics of reactive sites in single-Fe-atom materials and shall guide the design of novel efficient catalysts for CO2RR.

The effects of different metal promoters in MFe/C catalysts on CO2 hydrogenation were investigated and specific Fe sites within Fe5C2 (sites II and III) were found positively correlated to the O/P ratio and olefin selectivity.

Via hydrothermal synthesis of Sn-Al gels, mild dealumination and ion exchange, a bimetallic Sn-Ni-Beta catalyst was prepared which can convert glucose to methyl lactate (MLA) and methyl vinyl glycolate (MVG) in methanol at yields of 71.2 % and 10.2 %, respectively. Results from solid-state magic-angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, transmission electron microscopy, spectroscopic analysis, probe-temperature-programmed desorption, and density functional theory calculations conclusively reveal that the openness of the Sn sites, such as by the formation of [(SiO)

Summary In situ/operando Mossbauer spectroscopy is one of the most powerful techniques to quantitatively monitor the coordination and electronic structure of Mossbauer isotopes (119Sn, 57Fe, etc.) contained in heterogeneous catalysts under practical reaction conditions. To promote further progress in identifying the real structure of catalytic site(s) and revealing the underlying catalytic mechanism, herein we thoroughly summarize the recent advances of in situ/operando Mossbauer technique for probing heterogeneous catalysts and electrode materials for sustainable energy applications, including electrocatalysis, thermocatalysis, Li-ion batteries, etc. The unique role of this technique in different catalytic system is discussed with emphasis placed on several typical research advances. Moreover, the recent emerging operando Mossbauer technique for the study of single-atom catalysts, which is considered as a new eye for providing electronic-level insight into catalytic mechanism, is highlighted. Finally, the outlooks and challenges are discussed toward further application and rising influence of in situ/operando Mossbauer spectroscopy in heterogeneous catalysis.

Nuclear power, as a clean energy source, has been facing a blow after the Fukushima nuclear accident. Low public acceptance has severely restricted the nuclear power industry’s development. China government attaches great importance to the public acceptance of nuclear power and takes it as an important indicator for the approval of nuclear power projects. In the research of consumer domain, corporate social responsibility (CSR) is positively correlated with consumer support for enterprises, and the public is the ultimate consumer of nuclear power products. On this basis, hypotheses are proposed in this study: the public’s perception of the social responsibility of nuclear power enterprises can improve the public acceptance of nuclear power. Taking 211 residents around a nuclear power plant as the research object, this paper explores the impact of CSR perception on public acceptance of nuclear power and its path through questionnaire survey. The data analysis results of valid questionnaires showed that: (1) The percived CSR of nuclear power companies in China is divided into two dimensions, legal responsibility, economic&other responsibility, (2) The perceived legal responsibility has a positive effect on the public acceptance of nuclear power, and this effect is realized through the partial mediating effect of knowledge, dread risk perception and benefit perception.

Summary The lack of model single-atom catalysts (SACs) and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the designed model single-Fe-atom catalysts with well-controlled microenvironments, we have explored the exact structure of catalytic centers and provided insights into a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the developed operando 57Fe Mossbauer spectroscopy. In combination with theoretical studies, the N-FeN4C10 moiety is evidenced as a more active site for ORR. Moreover, the potential-relevant dynamic cycles of both geometric structure and electronic configuration of reactive single-Fe-atom moieties are evidenced via capturing the peroxido (∗O2−) and hydroxyl (∗OH−) intermediates under in situ ORR conditions. We anticipate that the integration of operando techniques and SACs in this work shall shed some light on the electronic-level insight into the catalytic centers and underlying reaction mechanism.

The oxygen evolution reaction (OER) is crucial in electrochemical water splitting and metal-air battery, and demands a low cost, efficient and durable electrocatalyst. An ideal OER catalyst should ...

A spinel-alumina inert oxide supported gold catalyst with high Au dispersion and excellent CO oxidation activity was developed by a deposition–precipitation method. The activation atmosphere could tune the reaction pathway by adjusting the amount of surface adsorbed water species, thus transforming the reaction intermediates from HCO3− or CO32− to COOH.

Direct conversion of syngas into aromatics with tandem catalysts containing Fe-based Fischer–Tropsch synthesis (FTS) catalysts and zeolites has been attracting significant attention because of the ...

Designing effective electrocatalysts for the carbon dioxide reduction reaction (CO2 RR) is an appealing approach to tackling the challenges posed by rising CO2 levels and realizing a closed carbon cycle. However, fundamental understanding of the complicated CO2 RR mechanism in CO2 electrocatalysis is still lacking because model systems are limited. We have designed a model nickel single-atom catalyst (Ni SAC) with a uniform structure and well-defined Ni-N4 moiety on a conductive carbon support with which to explore the electrochemical CO2 RR. Operando X-ray absorption near-edge structure spectroscopy, Raman spectroscopy, and near-ambient X-ray photoelectron spectroscopy, revealed that Ni+ in the Ni SAC was highly active for CO2 activation, and functioned as an authentic catalytically active site for the CO2 RR. Furthermore, through combination with a kinetics study, the rate-determining step of the CO2 RR was determined to be *CO2 - +H+ →*COOH. This study tackles the four challenges faced by the CO2 RR; namely, activity, selectivity, stability, and dynamics.

A series of uniform microspheres of spinel-type Mn-doped ferrites (MnxFe3-xO4) with different Fe/Mn ratios were employed for the Fischer-Tropsch-to-olefins reaction (FTO). The highest selectivity of 54.4% and the space-time-yield (STY) of 73.0g·kgcat−1·h−1 to lower olefins (C2-4=) were achieved over an Fe-Mn catalyst with 13 wt% Mn. A panoramic view of structure evolution of MnxFe3-xO4 was revealed using multiple in/ex situ techniques. We demonstrated that the expansion of lattice spacing induced by Mn exerted remarkable effects on the stabilization of MnxFe1-xO and e-Fe2C during activation and reaction. Moreover, Mn endows Fe catalysts with strong surface basicity and consequently enhances the adsorption and dissociation of CO; while weakening the H availability and readsorption of olefinic intermediates. In addition, the impeded carburization of MnxFe1-xO and the reduction in particle size of catalysts jointly contribute to the volcano curve in the catalytic activity. The insights presented could guide the rational design of high performance catalysts via heteroatom doping.

The maximization of the numbers of exposed active sites in supported metal catalysts is important to achieve high reaction activity. In this work, a simple strategy for anchoring single atom Fe on SBA-15 to expose utmost Fe active sites was proposed. Iron salts were introduced into the as-made SBA-15 containing the template and calcined for simultaneous decomposition of the iron precursor and the template, resulting in single atom Fe sites in the nanopores of SBA-15 catalysts (SAFe-SBA). X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and extended X-ray absorption fine structure (EXAFS) imply the presence of single atom Fe sites. Furthermore, EXAFS analysis suggests the structure of one Fe center with four O atoms, and density functional theory calculations (DFT) simulate this structure. The catalytic performances of SAFe-SBA were evaluated in Fenton-like catalytic oxidation of p-hydroxybenzoic acid (HBA) and phenol. It was found that the single atom SAFe-SBA catalysts displayed superior catalytic activity to aggregated iron sites (AGFe-SBA) in both HBA and phenol degradation, demonstrating the advantage of SAFe-SBA in catalysis.

As a type of important non-precious catalyst for the oxygen reduction reaction (ORR), the regulating role of a metal centre in metal-macrocycles and other complexes for activity has been extensively studied. However, a common guideline to explain the effect of peripheral coordinated-ligands has not been reached. Herein, a series of organic iron complexes (denoted as FeL, L = TAA, Pc, TPP, Corrole, Tim and Salen) were synthesized as ORR catalysts and an explicit relationship of structure-activity was constructed. The kinetic current density for these compounds was identified to follow the order of FeTAA > FePc > FeTPP > FeCorrole > FeTim > FeSalen. An electron-transfer number close to 4 was derived for all these complexes except for FeTim and FeSalen, implying a near complete reduction of oxygen to water. X-ray absorption near edge structure spectroscopy (XANES) and Mössbauer spectroscopy were used to probe the nature of the distinct activities by investigating the iron-centre electron structures. Density function theory (DFT) calculations were carried out to study the charge redistribution across the iron complexes. Novel activity descriptors including the charge and spin densities on the Fe site were proposed and validated by available experimental data, presenting a strategy to design highly-active nonprecious metal complex catalysts with specific supporting ligands. Published version Q.H. acknowledges the financial support from the National Natural Science Foundation of China (grant nos. 21978260, 21676241, and U1732111).

In situ/operando characterization techniques are powerful to provide fundamental information about molecular structure–activity/selectivity relationships for various catalytic systems under controlled condition. However, the lack of model catalyst, as the major obstacle for deeper understanding on the nature of active sites and reaction mechanisms, hinders the further advancements in catalysis. Fortunately, the rapid development of single-atom catalysts (SACs) offers us new opportunities for capturing the reaction intermediates, identifying the active sites, and even monitoring the dynamic behaviors of both the geometric structure and electronic environment of the catalytic sites at atomic scale. In this Perspective, the recent advances on the in situ/operando characterization techniques including X-ray absorption spectroscopy, scanning tunneling microscopy, Fourier-transform infrared spectroscopy, among other methods, for the characterization of SACs are thoroughly summarized. The results from these in situ/operando measurements reveal the crucial role of SACs as model systems for sharpening our understanding on the nature of catalytic sites. Furthermore, the challenges and outlooks in developing in situ/operando techniques for single-atom catalysis are discussed. Ministry of Education (MOE) Accepted version This work was supported by the National Key R&D Program of China (2016YFA0202804), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17000000), Dalian National Laboratory for Clean Energy (DNL180401), the Youth Innovation Promotion Association CAS, Nanyang Technological University (M4080977.120), and Ministry of Education of Singapore (AcRF Tier 1 M4011021.120 and Tier 2 2015-T1-002-108).

Herein, we, for the first time, report a high spin Co-Fe Prussian blue analogue (Co-Fe PBA) as a highly efficient Fenton-like catalyst for sulfate radical (SO4˙-) production. Our experiments and density functional theory (DFT) calculations show that the largely elongated SO4-OH bond length, strengthened adsorption and facilitated electron transfer for peroxymonosulfate (PMS) activation catalyzed by high-spin (HS) CoII are the main factors contributing to its excellent activity.

Their wide availability in nature, low cost, high reactivity, and low toxicity make Fe-based catalysts versatile in various catalysis fields, including photocatalysis, Fenton-like reaction, electrocatalysis, Li-ion batteries (LIBs), Fischer–Tropsch synthesis (FTS), biomass conversion, N2O decomposition and etc. Mossbauer spectroscopy, a powerful technique that is able to give account of structural features for all iron species taking part in the catalysis process, is considered to be a crucial technique for determining catalyst phase, identifying active site, and investigating correlations between catalytic behavior and the coordination structure of catalysts, which are highly desirable for clarifying the catalytic mechanisms. Each kind of Fe-based materials could be functionalized in the most suitable catalysis field, wherever Mossbauer technique may play a unique role. For instance, Fe-N-C based materials are extensively investigated as electrocatalysts for oxygen reduction reaction and Mossbauer spectroscopy application in this field has been utilized to identify the chemical nature of the active site on the Fe-N-C catalyst. Iron carbides are considered as the most active phase for FTS and Mossbauer technique is widely applied in determining the chemical phase of catalysts. Fe-based silicates, phosphates or polyanionic compounds are recognized as promising cathode materials for LIBs, for which Mossbauer technique has been mainly applied for tracking of the oxidation state and coordination environment change of Fe between charged and discharged states of the batteries. Similar phenomena can also be found in other catalysis fields. To give a clear understanding of which field is most suitable for a certain Fe-based catalyst and the best role of the Mossbauer technique in a certain catalysis field associated with the investigation of the mechanism, in this review, the recent advances of applying Mossbauer technique in catalysis are thoroughly summarized, including results from environmental catalysis and energy catalysis. Remarkable cases of study are highlighted and brief insight into applying Mossbauer technique for various Fe-based materials in their special catalysis field is presented. Finally, the trends for future potential applications of Mossbauer technique are discussed.

Xuning Li is a research fellow at Nanyang Technological University (NTU). He earned his PhD at Dalian Institute of Chemical Physics (DICP) in 2017. His current research interest focuses on in situ/operando characterization techniques in single-atom catalysis. Yanqiang Huang received his PhD from DICP in 2008. Afterward, he joined DICP as a staff scientist and was promoted to full professor in 2016. His research interests include propellant catalytic decomposition, CO2 capture and utilization, and C1 chemistry. Bin Liu received his PhD from the University of Minnesota (2011) and then moved to the University of California, Berkeley, as a postdoctoral researcher (2012). He is now an associate professor at NTU. His main research interests are electrocatalysis, photovoltaics, and photo-electrochemistry.

Fischer–Tropsch synthesis of light olefins plays a vital role in the production of major chemical building blocks from non-petroleum resources, having great academic and commercial importance. Herein, Na and S modulated FeMnOx catalysts were employed to systematically investigate the influence of additives, which not only enhanced the CO conversion but also facilitated the olefin formation and suppressed the undesired methane formation. Multiple characterizations confirmed that the existence of promoters would enhance the formation of active species of Fe5C2 at FTO conditions because of the promoted carbon insertion into the iron species from the intermediates dissociation. Combined the steady-state isotopic transient kinetic analysis with dynamic calculation, it confirmed that the promoters indeed had the ability to lower CO activation energy, as well as increase the carbon chain growth activity and the energy barrier to hydrogenation. This study provides a practical strategy for exploring the highly active and stable FTO catalysts.

To investigate the role of Fe ions for oxygen evolution reaction, a series of BaZrxFe1-xO3-δ (0 ≤ x ≤ 0.2) perovskite oxides were synthesized and systematically evaluated as electrocatalysts. The OER activity of cubic BaZrxFe1-xO3-δ (0.05 ≤ x ≤ 0.2) is higher than that of the parent BaFeO3-δ with a monoclinic structure and close to that of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), indicating cubic perovskite structure is favorable to the OER, and Fe ions are active for the reaction. Moreover, for cubic BaZr0.15Fe0.85O3-δ samples, the OER performance is closely related to the ratio of Fe4+ to Fe3+, which was tuned by treating BaZr0.15Fe0.85O3-δ powders at 500 °C for 5 h at different atmospheres, such as O2, air, Ar and 5% H2/Ar mixture.

LiNi1–xFexO2 (0 ≤ x ≤ 0.3) and LiyNi0.8Fe0.2O2 (0.8 ≤ y ≤ 1.2) catalysts for the oxygen evolution reaction (OER) were systematically investigated to discover the influence of the composition and layered structure on electrochemical activity. LiNi0.8Fe0.2O2 exhibits OER activity that is better than that of LiNiO2 and other Fe-substituted LiNiO2 catalysts, while Li1.2Ni0.8Fe0.2O2 shows OER activity that is much higher than that of LiNi0.8Fe0.2O2 and Li0.8Ni0.8Fe0.2O2. The best OER activity is achieved on Li1.2Ni0.8Fe0.2O2 with a Tafel slope of 59 mV dec–1 and a current density of 10 mA cm–2 at an overpotential of 302 mV, better than that for the benchmark IrO2 catalyst. Combined with the density functional theory calculations, the enhanced OER activity is mainly attributed to the unique electronic structure derived from the interaction of Li, Ni, and Fe in the materials and the layered structure which plays an important role in stabilizing the high valence states of Ni and Fe during the OER.

Microenvironment engineering of single-atom catalysts paves the way toward efficient electrochemical energy conversion., Single-atom catalysts (SACs) have become the most attractive frontier research field in heterogeneous catalysis. Since the atomically dispersed metal atoms are commonly stabilized by ionic/covalent interactions with neighboring atoms, the geometric and electronic structures of SACs depend greatly on their microenvironment, which, in turn, determine the performances in catalytic processes. In this review, we will focus on the recently developed strategies of SAC synthesis, with attention on the microenvironment modulation of single-atom active sites of SACs. Furthermore, experimental and computational advances in understanding such microenvironment in association to the catalytic activity and mechanisms are summarized and exemplified in the electrochemical applications, including the water electrolysis and O2/CO2/N2 reduction reactions. Last, by highlighting the prospects and challenges for microenvironment engineering of SACs, we wish to shed some light on the further development of SACs for electrochemical energy conversion.

Designing effective electrocatalysts for the carbon dioxide reduction reaction (CO

The Ministry of transport and provincial transportation departments recommend outstanding transportation scientific and technological achievements every year, and carried out a large number of highway construction demonstration projects. However, the selection of “four new technologies” has become a difficult problem for managers and builders. This paper analyzes the current situation of suitability evaluation and “Four-New Technology” in Zhejiang Province. After a large number of research on green road policy, demonstration project, standard and technological promotion results, the suitability evaluation standard of “four new technologies” of green road is established.

The development of highly efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) has been considered as a great challenge to the practical applications for water splitting and in rechargeable metal–air batteries. Herein, we report active and robust OER catalysts of Fe3+-doped β-Ni(OH)2 prepared via an atomic-scale topochemical transformation route. Based on the premise that all Fe3+ is incorporated into the β-Ni(OH)2 lattice, the OER activity increases directly with the content of Fe3+. The Fe(0.5)-doped β-Ni(OH)2 catalyst affords a current density of 10 mA cm−2 at an overpotential as low as 0.26 V and a small Tafel slope of 32 mv dec−1. Comparing the state-of-the-art IrO2 catalyst, the Fe(0.5)-doped β-Ni(OH)2 catalyst exhibits higher activity and stability from galvanostatic tests at 10 mA cm−2. Additionally, we experimentally demonstrate that Fe(0.5)-doped β-Ni(OH)2 exerts higher OER activity than Fe(0.5)-doped α-Ni(OH)2. All evidence indicates that Fe and the β-Ni(OH)2 matrix play an important role in NiFe-based catalysts.

Prussian blue analogues (PBAs) with tunable compositions and morphologies have demonstrated great potential in many applications. We successfully synthesized a series of KFexZn1−x[Co(CN)6] (FexZn1−x–Co) PBAs with well-controlled compositions and morphologies and used them as adsorbents for the removal of Cs+ ions. The increase of Zn : Fe ratio had a significant influence on the final morphology and improved the sorption capacity for Cs. X-ray diffraction and X-ray absorption fine structure spectra were used to confirm that the Cs+ ions were inserted into the crystal channels rather than simply adsorbed on the surface of the PBAs. Based on the quantitative correlation between the concentration of ions released from the PBAs and the Cs+ ions adsorbed, the mechanism of Cs+ sorption in the FexZn1−x–Co PBAs was studied and a Zn2+-modulated Cs+ sorption model, which illustrated the difference in sorption behavior between the FexZn1−x–Co PBAs, was proposed and confirmed by FTIR spectra, extended X-ray absorption fine structure spectra and 57Fe Mossbauer spectra. The results indicated that the FexZn1−x–Co PBAs are excellent candidates for the removal of radioactive 137Cs from nuclear waste.

Herein, for the first time it has been demonstrated that hydrazine (Hz) could significantly promote the bisphenol A (BPA) degradation in the Fenton reaction catalysed by Fe[Co(CN)6] 2H2O Prussian blue analogue (FeIII–Co PBA). Results indicate that the dramatic enhancement of BPA degradation could be partly attributed to the induced homogeneous Fenton reaction by the enhanced dissolution of FeIII–Co PBA. Meanwhile, the Hz coordinated iron site (H2NH2N–Fe), which is evolved from the original water coordinated iron site (H2O–Fe), was identified as the main active site. A possible reaction pathway involving the proposed active iron species was proposed.

Here we report a facile strategy to synthesize porous FexCo3−xO4 nanocages by heating Prussian blue analogues FeyCo1−y[Co(CN)6]0.67 nH2O nanospheres with tunable size and morphology. The iron doping amount had significant influence on the final morphology and the most uniform nanocages were obtained from x = 0.8. The catalytic performance of the nanocages was thoroughly evaluated by activation of peroxymonosulfate (PMS) for removal of bisphenol A (BPA) in water. The influence of different process parameter on the BPA degradation efficiency was examined and the catalytic stability was tested. The BPA degradation pathway was proposed based on GC–MS and LC–MS results. The involved radicals were identified through radical scavenging experiments and electron paramagnetic resonance spectroscopy. Mossbauer and XPS techniques were applied to illustrate the catalytic mechanism and B-site CoII on the surface of FexCo3−xO4 nanocages was determined as the main factor for PMS activation. Results indicate that porous FexCo3−xO4 nanocages are available to serve as alternative environmentally friendly catalysts for pollutants removal by activation of PMS.

A series of nitrogen-doped graphene encapsulated FexCoy bimetallic (FexCoy@C) nanocages were newly fabricated via a one-step thermal decomposition of Prussian blue analogue FeyCo1−y[Co(CN)6]0.67·nH2O nanospheres at different temperatures. The as-synthesized FexCoy@C nanocages were systematically characterized and applied as effective catalysts to activate peroxymonosulfate (PMS) for the removal of bisphenol A (BPA). The catalytic activity of Fe3Co7@C-650 obtained at 650 °C was found to be the highest and also much higher than that of metallic cobalt, cobalt oxide and cobalt–iron spinels. The nitrogen-doped graphene shells were demonstrated to be effective in preventing the release of metal ions, thus resulting in a better stability. Furthermore, the BPA degradation pathway was proposed based on GC-MS and LC-MS results. The involved radicals were identified through electron paramagnetic resonance and radical scavenger experiments. Based on the systematic characterization of the catalyst before and after the catalytic oxidation reaction, the overall mechanism of PMS activation over FexCoy@C nanocages was proposed. Results indicate that FexCoy@C nanocages are available to serve as promising materials for environmental remediation by activation of PMS.

NiFe/NiFeOx core/shell electrocatalysts show excellent OER activity by taking advantage of the synergetic effect between the metal core and the oxide/hydroxide shell, i.e. the metal core provides good bulk electron conduction and thus extends the OER active sites to the whole oxide/hydroxide shell, and the shell catalyzes the OER and protects the metal core from oxidation.

A facile hydrothermal method was firstly employed to synthesize iron oxide coupled and doped titania nanocomposites using an aqueous solution of titanium nitrate. The present nanocomposites exhibit altered compositional, optical, electrical, magnetic and photocatalytic properties with respect to varying dosage of iron in the titania matrix. The architecture of characteristic iron oxide such as Fe2O3 coupled with titania was confirmed by 57Fe Mossbauer spectroscopy and X-ray absorption fine structure spectroscopic measurements. The enhanced photocatalytic activity was demonstrated by comparing with that of pure hematite, anatase TiO2, rutile TiO2 and P25 in the degradation of methylene blue under visible light (λ > 480 nm) irradiation in an aqueous suspension. The strategy presented here gives a promising route towards the development of a metal oxide coupled and doped semiconductor material for applied photocatalysis and related applications.

Two kinds of Fe–Co Prussian blue analogues (Fe–Co PBAs) with different iron valence state, Fe3[Co(CN)6]2·12H2O and Fe[Co(CN)6]·2H2O, were developed as the photo-Fenton catalysts for in-depth investigation of the heterogeneous Fenton reaction mechanism. These two catalysts showed exceptionally high efficiencies for the degradation of Rhodamine B. The efficient redox cycling of iron species in the Fe–Co PBAs photo-Fenton process was deeply explored by Mossbauer spectroscopy. The excellent photo-Fenton activities of these Fe–Co PBAs were ascribed to the existence of highly dispersed water coordinated iron sites and abundant vacancies in the metal-organic-frameworks. Singlet oxygen was identified by radical scavenger experiments and electron paramagnetic resonance spectroscopy, which plays a key role in the photo-Fenton process. Based on these comprehensive experimental results, a novel radical reaction mechanism was proposed. This work not only opens up a new avenue for the application of Fe–Co PBAs, but also gives a deeper insight into the mechanisms of heterogeneous Fenton reactions.

We report on the crystal structure refinements in the novel electron-transfer-active Prussian Blue analogs (PBA) KMn 4 II [ Co 1 − x III Fe x III ( CN ) 6 ] 3 · n H 2 O ( n ≃ 12 ). The series of novel PBA with the end members of KMn 4 [ Co ( CN ) 6 ] 3 · 11.8 H 2 O and KMn 4 [ Fe ( CN ) 6 ] 3 · 10.5 H 2 O have been synthesized for the first time, all showing a number of extra-reflections incompatible with ordinary face-centered cell of the Fm-3m symmetry group. We have analyzed the Rietveld patterns for x = 0 , 0.53 , 1 and found that the extra-reflections could be well fitted using several primitive (P) cell symmetries. The best fitting quality was obtained using the noncentrosymmetric space group (S.G.) P 4 ¯ 3 m (Z=1) with the origin of coordinate system shifted into a zeolitic site. In this structure model, the Co–CN–Mn entities are bent owing to the charge introduced by the K+ insertion that induces also the electron transfer between Mn and Fe. Using Mossbauer spectroscopy the electron transfer activity is identified with the appearance of unsplit resonance at the isomer shift of typically −0.15 mm/s evidencing the low-spin state for Fe3+ and Fe2+ species. In the same P 4 ¯ 3 m phases doped with Fe 2 + 57 into the Mn site, a sequence of discrete values of quadrupole splitting (0 mm/s, 0.9 mm/s, 1.8 mm/s) is observed and attributed to different conformations of the polyhedra, in which the ground states are orbital triplet, doublet and singlet, respectively.

Controllable synthesis of metal-organic frameworks with well-defined morphology, composition, and size is of great importance toward understanding their structure-property relationship in various applications. Herein, we demonstrate a general strategy to modulate the relative growth rate of the secondary building units (SBUs) along different crystal facets for the synthesis of Fe-Co, Mn0.5Fe0.5-Co, and Mn-Co Prussian blue analogues (PBAs) with tunable morphologies. The same growth rate of SBUs along the {100}, {110}, and {111} surfaces at 0 °C results in the formation of spherical PBA particles, while the lowest growth rate of SBUs along the {100} surface resulting from the highest surface energy with increasing reaction temperature induces the formation of PBA cubes. Fenton reaction was used as the model reaction to probe the structure-catalytic activity relation for the as-synthesized catalysts. The cubic Fe-Co PBA was found to exhibit the best catalytic performance with reaction rate constant 6 times higher than that of the spherical counterpart. Via density functional theory calculations, the abundant enclosed {100} facets in cubic Fe-Co PBA were identified to have the highest surface energy and favor high Fenton reaction activity.