Distribution Of Active Sites Research Articles

Efficacy and Safety of Laser Photocoagulation in Persistent Idiopathic Central Serous Chorioretinopathy: A Prospective Interventional Study

Introduction: Central Serous Chorioretinopathy (CSCR) encompasses the macular area, secondary to the accumulation of subretinal fluid and increased permeability from the choriocapillaris resulting in focal or diffuse dysfunction of the retinal pigment epithelium. Diagnosis of CSCR is done by several procedures like clinical examination, Amsler grid testing, fluorescein angiography, ocular coherence tomography. There are several treatment options including photodynamic therapy, laser photocoagulation, etc., for CSCR. Aim: To study the efficacy and safety of laser photocoagulation in persistent idiopathic CSCR. Materials and Methods: The present prospective interventional study was conducted in the Department of Ophthalmology, BJ Government Medical College and Sassoon General Hospital, Pune, Maharashtra, India, from August 2019 to January 2021. A total of 30 patients (30 eyes) with idiopathic CSCR, persistent for duration of three months or more with worsening of visual symptoms, active leakage on Fundus Fluoresceine Angiography (FFA) were subjected to 532 nm subthreshold green laser photocoagulation treatment after routine investigations. Statistical analysis was done on International Business Machines (IBM) Statistical Package for the Social Sciences (SPSS) software version 20.0. Results: In the present study, there was male preponderance (86.7%) for the CSCR cases. The mean±Standard Deviation (SD) age of in the study was 37.7±0.07 years. All the eyes studied had unilateral involvement with 53.35% right eye involvement and 46.7% left eye involvement. The duration of current episode of CSCR in months showed a mean+SD of 5.86±1.40. The distribution of visual acuity in affected eye (before laser treatment) depicts the mean prelaser Best Corrected Visual Acuity (BCVA) of 30 patients at baseline was (0.68±0.20) in LogMAR. About 67% patients experienced central scotoma and 33% patients had metamorphopsia on Amsler chart. Distribution of active leakage site on FFA showed that 43% cases had active leakage in superonasal quadrant, 30% had active leakage in superotemporal, 17% had active leak in inferonasal quadrant and 10% had active leak in inferotemporal quadrant. CSCR associated with or without Retinal Pigment Epithelium (RPE) atrophy showed that 63.3% patients had RPE atrophy suggesting long-standing course of disease with NSD and subretinal fluid collection affecting RPE. Prelaser mean CMT on OCT of affected eye was 445.83±54.79 µm which was reduced to mean CMT of 303.57±48.49 µm at four weeks follow up, which further reduced to mean CMT of 224.9±20 µm at end of 12 weeks was statistically significant with p-value<0.001. The statistical analysis for the macular thickness at four weeks and 12 weeks showed significant probability with paired t-test with p-value<0.001. Conclusion: It can be concluded from the present study that early treatment with laser photocoagulation is efficient in the restoration of vision within a period of 12 weeks.

Facial synthesis of FeS2@Carbon nanotube composite as an efficient electrocatalyst for hydrogen evolution reaction

Iron disulfide (FeS2) has attracted extensive research interest due to its excellent catalytic efficiency. In this work, FeS2 was composited with carbon matrix to prepare a highly efficient electrocatalyst for hydrogen evolution. Two uniformly composites, namely, FeS2 @carbon nanotube (FeS2@CNT) and FeS2@carbon particle (FeS2@CP), were successfully prepared by pyrolysis and sulfuration processes. The structures of the synthesized composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. It was found that the catalytic performances of the composites were obviously improved compared to pure FeS2. Moreover, compared to FeS2@CP, the FeS2@CNT nanotubes achieved a much lower overpotential and a smaller Tafel slope. The enhanced HER kinetics and hydrogen generation rate of FeS2@CNT may be due to its more efficient charge transport, uniform distribution of active sites, and higher surface areas. This work provides a new clue for the preparation of FeS2-based composite for hydrogen evolution.

Microenvironment Modulation of Metal-Organic Frameworks (MOFs) for Coordination Olefin Oligomerization and (co)Polymerization.

The majority of commercial polyolefins are produced by coordination polymerization using early or late transition metal catalysts. Molecular catalysts containing these transition metals (Ti, Zr, Cr, Ni, and Fe, etc.) are loaded on supports for controlled polymerization behavior and polymer morphology in slurry or gas phase processes. Within the last few years, metal-organic frameworks (MOFs), a class of unique porous crystalline materials constructed from metal ions/clusters and organic ligands, have been designed and utilized as excellent supports for heterogeneous polymerization catalysis whose high density and uniform distribution of active sites would benefit the modulations of molecular weight distributions of high-performance olefin oligomers and (co)polymers. Impressive efforts have been made to modulate the microenvironment surrounding the active centers at the atomic level for improved activities of MOFs-based catalysts and controlled selectivity of olefin insertion. This review aims to draw a comprehensive picture of MOFs for coordination olefin oligomerization and (co)polymerization in the past decades with respect to different transition metal active centers, various incorporation sites, and finally microenvironment modulation. In consideration of more efforts are needed to overcome challenges for further industrial and commercial application, a brief outlook is provided.

The Cup Whisperer

The Cup Whisperer

Enhanced phosphorus resistance of sodium-promoted Cu/CHA catalysts towards NH3-SCR

Cu/CHA and sodium-promoted Cu/CHA catalysts were prepared and applied to catalyze NH3-SCR reaction. Also, the effect of phosphorus poisoning on the catalytic performance of these two catalysts were explored. Compared with Cu/CHA catalyst, sodium-promoted Cu/CHA catalyst presented better catalytic performance, which was attributed to the optimized distribution of copper active sites. Moreover, it was proved that sodium ions as sacrificial sites could effectively protect copper active ions and improve the phosphorus poisoning resistance of the sodium-promoted Cu/CHA catalyst.

Optimizing the Proportion of Framework Elements and the Distribution of Active Sites in Pd–SSZ-13 for Better Passive NOx Adsorber Performance

This study focuses on exploring the effects of Si–Al ratio, Pd loading, and the presence of C3H6 on the performance of the Pd–SSZ-13 catalyst. When the Si–Al ratio is 15 and the Pd loading is 1%, the catalyst has the best adsorption performance. NO can be adsorbed in the form of NO+ with the cation exchange sites through two different paths. The catalyst with a Si–Al ratio of 15 has the highest Pd2+ content, so it can undergo oxidation–reduction reactions with NO to generate a large amount of NO+. A certain amount of Pd content can provide a large number of weak adsorption sites for NO and NO2, but when the Pd content increases, there will be too much palladium oxide material generated to cover the surface of the molecular sieve. C3H6 competes with NO and then blocks the pores of the molecular sieve, making the active sites difficult to use.

Development of stable La0.9Ce0.1NiO3 perovskite catalyst for enhanced photothermochemical dry reforming of methane

Solar-driven photothermochemical dry reforming of methane (PTC-DRM) is a promising technique to produce syngas using greenhouse gases (CO2 and CH4). In this work, Ce-substituted LaNiO3, i.e., La1−xCexNiO3 perovskite catalysts were synthesized for PTC-DRM reaction under concentrated sunlight. At 700 °C under 30 suns light irradiation, the CO and H2 production rates were at 616 and 620 mmol g−1 h−1, respectively, over the La0.9Ce0.1NiO3 catalyst, notably higher than those obtained in dark at the same reaction temperature and higher than those over LaNiO3 under the same light irradiation condition. The CO2 and CH4 conversion by the La0.9Ce0.1NiO3 catalyst are among the top-performing catalysts reported in the literature. The Ce substitution of La at a small fraction (x = 0.1) was found to benefit Ni active sites distribution and retention of the perovskite structure, which led to mitigation of both Ni sintering and carbon formation, thus promoting light absorption and PTC-DRM activities. A higher fraction of Ce substitution (x ≥ 0.5), however, did not show any beneficial effects. By conducting in situ DRIFTS at PTC-DRM reaction conditions and control experiment using 495 nm long-pass filter, light irradiation was found to induce photocatalytic activities on La0.9Ce0.1NiO3 and enhance CO2 adsorption and formation of active lanthanum oxycarbonates intermediates (La2O2CO3), possibly due to the generation of oxygen vacancies and electron-hole pairs. This work reports a new catalyst design and mechanistic studies for PTC-DRM reaction, and the findings are of importance for the application low-carbon fuel generation from sunlight.

Molecular weight-dependent adsorption heterogeneities of humic acid on microplastics in aquatic environments: Further insights from fluorescence spectra combined with two-dimensional correlation spectroscopy and site energy distribution analysis

Microplastics as emerging environmental contaminants have attracted global attention. Ubiquitous dissolved organic matter (DOM), a heterogeneous mixture with various organic components and continuous molecular weight (MW) distribution, can significantly influence the fate, bioavailability and toxicity of microplastics in aquatic environments. However, to date, understanding of the MW-dependent adsorption heterogeneities of DOM on microplastics in aquatic environments has remained unknown. In this study, the soil humic acid (HA), a representative DOM, was fractionated into > 100 kDa HA, 30–100 kDa HA, 10–30 kDa HA, 3–10 kDa HA and < 3 kDa HA, whose adsorption behaviors on polystyrene microplastics (PSMPs) under different electrolytes at pH6.0 investigated by multispectral techniques, as well as two-dimensional correlation spectroscopy and site energy distribution analysis. High molecular weight MW-fractionated HAs dominated the soil HA. Compared to the lower molecular weight MW-fractionated HAs, the higher molecular weight counterparts exhibited higher aromaticity, showing higher adsorption affinities onto PSMPs in aquatic environments. Adsorption isotherms and kinetics of the MW-fractionated HAs onto PSMPS can be reasonably explained by Langmuir models and the linear driving force (LDF) model, respectively. Enhanced aromaticity in residual solutions was observed, suggesting that the preferable adsorption of the higher aromatic moieties in the pristine and MW-fractionated HAs on PSMPs could be subsequently replaced by the lower aromatic moieties for the limited binding sites. Combined, the humic-like materials in MW-fractionated HAs could be significantly impacted the complexation of PSMPs in aquatic environments. The heterogeneous/complicated distributions of active adsorption sites in the humic-like materials of the MW-fractionated HAs, and the subsequent subtle changes of these sites to PSMPs were characterized by synchronous fluorescence spectroscopy coupled with two-dimensional correlation spectroscopy. High molecular weight MW-fractionated HAs provided more active adsorption sites than those in the low molecular weight counterparts, which also possessed stronger adsorption affinities and higher complexation capacities to PSMPs. The site energy distributions for the adsorption of the MW-fractionated HAs on PSMPs were calculated based on Langmuir model. The adsorption heterogeneities of PSMPs at the experimental conditions were close. This study provides deep insights into the MW-dependent adsorption heterogeneities of HA on PSMPs, and the results are of significance to understand the biogeochemical behaviors of DOM and MPs in aquatic environments.

Porous Fe, N co-doped carbon with high electrocatalytic oxygen reduction reaction performance in Zn-air battery

Non-Pt electrocatalysts for oxygen reduction reactions (ORR) have been developed using metal and nitrogen co-doped carbon electrocatalysts. However, challenges remain regarding the porosity of the catalyst, distribution of active sites, and the easy aggregation of the metal components. Herein, we report a bottom-up preparation strategy to obtain a porous ethynyl-linked conjugated microporous polymer (CMP) precursor containing triazine units and bipyridine, ensuring high N content and coordination with Fe 3+ . The Fe doped CMP is then carbonization into a Fe, N co-doped nanoporous carbon material (BPCMP-Fe-800), which can be taken as the electrocatalyst in ORR. BPCMP-Fe-800 catalyst exhibits electrocatalytic performance dominated by 4e − transfer mechanism with the onset potential of 0.97 V, half-wave potential of 0.85 V, and higher kinetic current density of 11.3 mA cm −2 (0.8 V). In addition, when applied as cathode electrocatalyst in zinc-air batteries, BPCMP-Fe-800 displays more competitive power density (179.5 mW cm −2 ) and specific capacity (790.5 mAh g −1 ) compared with Pt/C. Our study demonstrates a general and facile approach for porous Fe, N co-doped carbon with the potential as alternatives to Pt catalysts for efficient ORR catalytic performances and provides new insights of multi-atom catalysts for other energy conversion related catalytic reactions.

Effect of the Rare Earth Metals (Tb, Nd, Dy) addition for the modification of nickel catalysts supported on alumina in CO2 Methanation

In the current research, a group of rare-earth metals functionalized mesoporous Ni-M/Al2O3 (M = Tb, Dy, Nd) composite oxides were prepared by the one-pot sonochemical pathway and applied in the CO2 methanation procedure. Promoters can partially influence the textural and catalytic characteristics of Ni–Al2O3 catalysts. Physicochemical characteristics of the as-fabricated catalysts were identified utilizing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), Temperature Programmed Reduction (H2-TPR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analyses. Among the specimens, the catalyst modified by Terbium (Tb) manifested better catalytic performance and CH4 selectivity, particularly at low temperatures (350–400 °C). The influence of reaction temperature (200–500 °C) was scrutinized below space velocity (GHSV) of 25,000 ml/gcath, atmospheric pressure, and stoichiometric ratio of CO2 to H2 (1: 4). The impact of the desired content of nickel and terbium was examined. The 25Ni–5Tb–Al2O3 operates the best function for CO2 methanation, which can attain the highest CO2 conversion of 66.93% at 400 °C at atmospheric pressure. The superior catalytic performance of 25Ni–5Tb–Al2O3 could be assigned to the appropriate fabrication method and the promotion effect of Terbium. The synthesis effect could be assigned to its large surface area, obtaining by the hot spot mechanism. The addition of Terbium promotes the Ni distribution on the supports as well as accelerates the positive reaction due to the oxygen vacancies of Terbium. Besides, these outcomes could be defined with the maximum distribution of active nickel sites on the catalyst and improvement in the catalyst reduction ability at low temperatures.

Rotation induced by non-uniform gas–solid phase reactions of a non-spherical particle

• The particle rotation induced by gas–solid phase reactions is revealed; • The non-uniform gas–solid phase reaction directly results to the rotation of non-spherical particle; • The rotation characteristics of coal particle during combustion are discussed. Particle rotation plays an important role in gas–solid flow. The particle rotation induced by gas–solid phase reaction is investigated in this work. The non-uniform gas–solid phase reaction direct results to the rotation of a non-spherical particle. Based on the random distribution of active sites, the combustion of non-spherical particles is numerical investigated. According to the numerical results of chemical reaction rate on the particle surface, the net force and the rotation frequency of non-spherical particle were obtained by post-processing. The bearing force and rotation of cubic particles caused by gas–solid chemical reactions are systematically numerically studied. The rotational frequency is basically consistent with the experimental results in the reference. For coal char particles with an active area ratio of 0.8, the rotational frequency can reach 1000 Hz at side length of 60 μm. The effects of active area ratio, ambient gas temperature and particle size on the induced thrust and the rotational frequency of coal char particles are analyzed. The unbalanced force on the particle surface increase with the reaction rates. The rotation velocity increases with the decrease of particle size. And it increases with the increase of ambient temperature..

Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Recently, the Cu-based catalyst has attracted wide attention for the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) due to its high catalytic activity and it is low cost. However, its poor stability, ease of agglomeration, and the short life of the catalyst restrict its further development in industrial applications. Here, we constructed a novel MOF-derived Cu/SiO2 catalyst (MOF-CmS for short) with a controllable distribution of Cu active sites for the hydrogenation of the DMO to EG reaction. The catalyst was prepared by a hydrothermal method with the HKUST-1 uniformly coated on the surface of the silica microspheres. After the calcination, the highly dispersed and uniform Cu species were loaded on the surface of the silica. The resulted MOF-CmS catalyst showed a 100% conversion of DMO and over 98% selectivity of EG at 200 °C and 2 MPa while a traditional Cu/SiO2 catalyst exhibited serious agglomeration of Cu active sites and low catalytic activity (DMO conversion of 86.9% and EG selectivity of 46.6%). It is believed that the highly dispersed active metal center and the interaction between the active metal and carrier were the main reasons for higher catalytic activity of the MOF-CmS catalyst. Therefore, the developed method opened another avenue to synthesize highly dispersed and stable Cu-based catalysts.

Influence of Metal Cation and Temperature on Localized Corrosion Behavior of Steels in Aqueous Environments

Steels are abundantly used in many areas because of their good formability and low price. Steels suffer from corrosion in aqueous environments with chloride ions. Corrosion of steels is also a serious problem for long-term usage of steel structures such as bridges and buildings. There are many studies focused on chloride ions. There are reports that metal cations have a tendency to inhibit the corrosion of steels in a chloride aqueous environment by forming a layer on the steel.The other important factor for corrosion of steels in an aqueous environment is temperature. The corrosion rate of metal in cold regions is expected to slow because of low temperature. A recent study on atmospheric exposure tests carried out in different places in Hokkaido, it has elucidated that the corrosion rate in the cold region is the same as in the warm region.However, it is not fully elucidated that temperature, especially below freezing point, and metal cations on corrosion behavior and distribution of active dissolution site. The purpose of this study is to investigate the influence of temperature and metal cations on thecorrosion behavior of steels.Steel sheets of 15 x 20 mm and 20 x 20 mm were used as specimens. Three solutions of 0.1 mM ZnCl2, 0.5 mM ZnCl2 and 1.0 mM ZnCl2 were used for examination of the effect of metal cations, and 20 mass % NaCl solution was used for examination of effect of temperature. After the tests, the morphology of specimens was examined by optical microscope and scanning electron microscope.After the wet/dry corrosion tests used 10 mL solutions droplets, corrosion products were formed on the specimens. The corrosion processes under NaCl and MgCl2 were similar. Yellow corrosion products were firstly observed in the solution during the wet period. In the case of under ZnCl2, after the formation of oxide layer on the specimens the corrosion proceeded in localized areas. The color of almost half area of the exposed surface was light, which might indicate less corrosion occurred in the area. The initial corrosion stage of steel preferred to form a brown area in the center of the droplet. There are no similar corrosion products thatcan be observed in comparison to the samples under MgCl2 and NaCl solutions.A lot of corrosion products and localized corroded areas were formed on specimens after being immersed at 273 K, while less corrosion products and homogenously corroded surface were observed on specimens after being immersed at 293K.The results indicated that corrosion morphology and preferentially corroded area were changed with the kind of metal cation and temperature.

Differentiating supported platinum single atoms, clusters and nanoparticles by styrene hydrogenation

Supported metal catalysts often consist of metal sites ranging from nanoparticles to subnanometer clusters and single atoms. It remains a necessity to differentiate these sites to guide design of optimal catalysts. Here we report a simple method to assess the distribution of metal active sites in catalyst samples. The method takes the advantage of the structure sensitivity of styrene hydrogenation over titania supported platinum (Pt) catalysts with Pt aggregates varied from single atom to ∼1.40 nm nanoparticles. The physicochemical properties were characterized by STEM, XPS, XANES, H2-TPR and CO-chemisorption measurements. The reactivity of Pt sites was quantified by styrene hydrogenation at ambient conditions. The nanometer-sized Pt clusters have significantly higher activity than Pt nanoparticles, sub-nanometer clusters or isolated single atoms. The relationship between activity and structural/electronic properties of Pt sites influenced by particle sizes was discussed. Similar relationship was found in the carbon supported Pt catalysts.

Low supported nickel-cobalt catalyst for hydrogenation of maleic anhydride

In order to prepare supported catalysts with low-metal loading, a series of NiCo/Clay catalysts were prepared and used in the hydrogenation of maleic anhydride. The hydrogenation reaction was carried out in a fixed-bed for 8 h with reaction pressure = 1 MPa, reaction temperature = 180 °C, molar ratio of H2: maleic anhydride = 50, WHSV = 2 h−1. Ni4Co1/Clay (loaded 3 wt%Ni and 0.75 wt%Co) can maintain no obvious catalyst deactivation within 8 h. The overall conversion of maleic anhydride is not less than 95 %, and the selectivity of succinic anhydride is up to 100 %. N2 adsorption–desorption characterization, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption, X-ray photoelectron spectroscopy and transmission electron microscopy were performed to verify the changes in catalyst morphology, active species, reduction performance and hydrogenation activity after adding Co as a promoter. With the addition of Co additive, the distribution of active sites on the carrier is more uniform, the grain size of active metal becomes smaller and the reduction temperature decreases. The addition of Co not only increased the active center of the catalyst but also effectively avoided the catalyst's deactivation.

17O Labeling Reveals Paired Active Sites in Zeolite Catalysts

Current needs for extending zeolite catalysts beyond traditional gas-phase hydrocarbon chemistry demand detailed characterization of active site structures, distributions, and hydrothermal impacts. A broad suite of homonuclear and heteronuclear NMR correlation experiments on dehydrated H-ZSM-5 catalysts with isotopically enriched 17O frameworks reveals that at least two types of paired active sites exist, the amount of which depends on the population of fully framework-coordinated tetrahedral Al (Al(IV)-1) and partially framework-coordinated tetrahedral Al (Al(IV)-2) sites, both of which can be denoted as (SiO)4-n-Al(OH)n. The relative amounts of Al(IV)-1 and Al(IV)-2 sites, and subsequent pairing, cannot be inferred from the catalyst Si/Al ratio, but depend on synthetic and postsynthetic modifications. Correlation experiments demonstrate that, on average, acidic hydroxyl groups from Al(IV)-1/Al(IV)-2 pairs are closer to one another than those from Al(IV)-1/Al(IV)-1 pairs, as supported by computational DFT calculations. Through-bond and through-space polarization transfer experiments exploiting 17O nuclei reveal a number of different acidic hydroxyl groups in varying Si/Al catalysts, the relative amounts of which change following postsynthetic modifications. Using room-temperature isotopic exchange methods, it was determined that 17O was homogeneously incorporated into the zeolite framework, while 17O → 27Al polarization transfer experiments demonstrated that 17O incorporation does not occur for extra-framework AlnOm species. Data from samples exposed to controlled hydrolysis indicates that nearest neighbor Al pairs in the framework are more susceptible to hydrolytic attack. The data reported here suggest that Al(IV)-1/Al(IV)-2 paired sites are synergistic sites leading to increased reactivity in both low- and high-temperature reactions. No evidence was found for paired framework/nonframework sites.

Advances in cutting‐edge electrode engineering toward CO2 electrolysis at high current density and selectivity: A mini‐review

AbstractElectrochemical CO2 conversion has been raised as a promising solution for building a carbon‐neutral economy under today's circumstances of increasing energy shortages and air pollution from human activities. Research on electrochemical CO2 reduction reaction (CO2RR) is gradually entering a pilot‐scale stage. The use of device‐level CO2 electrolysis in the production of value‐added chemicals and fuels at a high production rate and selectivity is highly required to make the technology economical and sustainable. With more exploration toward device‐level performance optimization, it gradually becomes clear that electrode engineering on structures, surface properties, active site distribution, and density, as well as the electrode–electrolyte interface, is more critical than the intrinsic activity of catalytic sites. Taking this into account, this review focuses on interpreting the design principles in aspects with the aim of enhancing the CO2RR toward a specific product yield and production rate. This mini‐review summarizes the advances in this dynamic field in the most recent 5 years, including the fabrication of porous gas diffusion electrodes, and self‐supporting electrodes, establishment of tandem or cascade electrode function, as well as tuning of interfacial cation buffering and wettability, and analyze the trends in the future scientific and technological development of device‐level CO2 electrolysis. Hopefully, this mini‐review could provide some insights into the opportunities in the next‐generation electrode design for the industrial carbon cycle.

Enhanced photocatalytic organic pollutant degradation and H2 evolution reaction over carbon nitride nanosheets: N defects abundant materials

Post thermal treatment of bulk graphitic carbon nitride (g-C3N4) by ammonia gas acts as a significant structure regulation approach, while pure ammonia-assisted g-C3N4 synthesis from precursors like melamine is rarely investigated. Here we prove the synthesis of N-defects abundant carbon nitride nanosheets (ACN) through a one-pot thermal polymerization of melamine in pure ammonia gas, for photocatalytic organic pollutant removal in water and H2 evolution applications. Compared to bulk g-C3N4 (BCN), ACN-550 (ACN prepared at 550 °C) exhibited thin-layered porous morphology with higher surface area and abundant N defects, resulting in wider distribution of active sites. Moreover, the abundant N defects in the heptazine heterocycle structure could change the electronic structure of g-C3N4, leading to more efficient transport of photogenerated charge carriers and enhanced photoreduction potential, which gives rise to notable improvement activities in photocatalytic reaction. With superoxide ion radical and photoinduced holes as the predominant reactive species, ACN-550 realized efficient photocatalytic bisphenol A (BPA) degradation, which is 1.6- and 4.7-fold high over commercial TiO2 (P25) and BCN, respectively. ACN-550 exhibited excellent reusability and stability in five consecutive photocatalytic BPA degradation tests. In photo-reductive H2 production system by ACN-550, 761.8 ± 4.3 μmol/h/g H2 was produced, which was 11.6-fold as high as that by BCN.

锂硫电池非均相电催化剂

<p indent="0mm">With the rapid development of electronic transportation and portable electronics, commercial lithium-ion batteries would be unsatisfactory to meet the needs of future markets owing to the relatively low energy density. Seeking a reliable substitution system is becoming imperative. Lithium-sulfur (Li-S) battery has been recognized as a cutting-edge energy storage system because of its high theoretical capacity (1672 mAh g^–1) and cost-effectiveness of sulfur resources. Nevertheless, the severe shuttle effect and sluggish reaction kinetics significantly restrict its further commercialization. In the developing history of Li-S batteries, physical confinement and chemical adsorption have often been employed to achieve the anchoring of polysulfides. However, these strategies are still difficult to fully solve the problems of slow reaction kinetics and poor cycle performance. Recent years have witnessed the introduction of heterogeneous electrocatalysts into the Li-S system, which readily meets with great success in suppressing the shuttle effect and elevating the reaction kinetics. In this review, we introduce the basic reaction of Li-S battery and point out the main challenges in its current development stage, followed by summarizing the effects of electrocatalysts. Firstly, the polar electrocatalyst is able to effectively adsorb polysulfide and inhibit its diffusion in the electrolyte. Secondly, the electrocatalyst can effectively promote the conversion of polysulfide and improve the utilization rate of sulfur species. Thirdly, the uniform distribution of active sites in the electrocatalyst also contributes to the uniform deposition of short-chain polysulfides. In addition, the concepts and comparisons of homogeneous and heterogeneous electrocatalysts are presented, manifesting the essential significance of heterogeneous electrocatalysts in Li-S system. Homogeneous electrocatalysts usually refer to small soluble organic molecules with the same phase state as soluble polysulfides in the reaction system. Homogeneous electrocatalysts have more specific catalytic sites, whilst heterogeneous electrocatalysts have more diverse morphologies and higher possibility of multi-site synergistic catalysis. Then the common regulation strategies for heterogeneous electrocatalysts are classified, including vacancy regulation, doping regulation, heterostructure modulation, size control, and phase modulation. In further contexts, the underlying mechanisms of different regulation strategies for promoting polysulfide conversion are discussed. The introduction of heterogeneous electrocatalysts can effectively promote the reaction kinetics and improve their electrochemical performance. However, there are still many obstacles waiting to be solved in the practicability of Li-S batteries. For instance, there is a lack of highly selective and stable electrocatalysts. The identification of real catalytic sites in the electrocatalysts still remains unclear. Moreover, Li-S batteries have poor performance under lean electrolyte and low lithium consumption. In view of these issues, future development strategy is put forward from four aspects, encompassing material exploration, precise synthesis, characterization methods and practical application, aiming to bridge the gap between the reality and ideal in working Li-S batteries.

Cation‐Vacancy Ordered Superstructure Enhanced Cycling Stability in Tungsten Bronze Anode

AbstractNiobium‐based tungsten bronze oxides have recently emerged as attractive fast‐charging anodes for lithium‐ion batteries (LIBs), owing to their structural openings and adjustability. However, electrodes with tungsten bronze structures usually suffer from structural variability induced by Li+ intercalation/de‐intercalation, leading to unsatisfactory cycling performance. To circumvent this limitation, a novel tetragonal tungsten bronze (TTB) structure, Ba3.4Nb10O28.4 (BNO), is developed as an anode material for LIBs with prominent cycling performance. An unprecedented cation‐vacancy ordered superstructure with a periodic distribution of active and inactive sites is revealed inside the BNO. Through multiple characterizations and theoretical studies, it is demonstrated that this superstructure can improve the lithium‐ion diffusion and disperse the structural strain induced by Li+‐intercalation to enable stable Li+‐storage. Benefiting from the superstructure‐induced local structural stability, both the BNO bulk and Ba3.4Nb10O28.4@C (BNO@C) microspheres can deliver &gt;90% capacity retention after 250 cycles at 2 C and close to 90% capacity retention after 2000 cycles at 10 C. These results are of significant importance for establishing the structure–property relationship between the cation‐vacancy ordered superstructure and Li+‐storage performance, facilitating the rational design of stable tungsten bronze anodes.