Reduction In Specific Surface Area Research Articles

Hydrothermally Synthesized ZnCr- and NiCr-Layered Double Hydroxides as Hydrogen Evolution Photocatalysts.

The layered double hydroxides (LDHs) of transition metals are of great interest as building blocks for the creation of composite photocatalytic materials for hydrogen production, environmental remediation and other applications. However, the synthesis of most LDHs is reported only by the conventional coprecipitation method, which makes it difficult to control the catalyst's crystallinity. In the present study, ZnCr- and NiCr-LDHs have been successfully prepared using a facile hydrothermal approach. Varying the hydrothermal synthesis conditions allowed us to obtain target products with a controllable crystallite size in the range of 2-26 nm and a specific surface area of 45-83 m2∙g-1. The LDHs synthesized were investigated as photocatalysts of hydrogen generation from aqueous methanol. It was revealed that the photocatalytic activity of ZnCr-LDH samples grows monotonically with the increase in their average crystallite size, while that of NiCr-LDH ones reaches a maximum with intermediate-sized crystallites and then decreases due to the specific surface area reduction. The concentration dependence of the hydrogen evolution activity is generally consistent with the standard Langmuir-Hinshelwood model for heterogeneous catalysis. At a methanol content of 50 mol. %, the rate of hydrogen generation over ZnCr- and NiCr-LDHs reaches 88 and 41 μmol∙h-1∙g-1, respectively. The hydrothermally synthesized LDHs with enhanced crystallinity may be of interest for further fabrication of their nanosheets being promising components of new composite photocatalysts.

Exploring the Remarkably High Photocatalytic Efficiency of Ultra-Thin Porous Graphitic Carbon Nitride Nanosheets.

Graphitic carbon nitride (g-C3N4) is a metal-free photocatalyst used for visible-driven hydrogen production, CO2 reduction, and organic pollutant degradation. In addition to the most attractive feature of visible photoactivity, its other benefits include thermal and photochemical stability, cost-effectiveness, and simple and easy-scale-up synthesis. However, its performance is still limited due to its low absorption at longer wavelengths in the visible range, and high charge recombination. In addition, the exfoliated nanosheets easily aggregate, causing the reduction in specific surface area, and thus its photoactivity. Herein, we propose the use of ultra-thin porous g-C3N4 nanosheets to overcome these limitations and improve its photocatalytic performance. Through the optimization of a novel multi-step synthetic protocol, based on an initial thermal treatment, the use of nitric acid (HNO3), and an ultrasonication step, we were able to obtain very thin and well-tuned material that yielded exceptional photodegradation performance of methyl orange (MO) under visible light irradiation, without the need for any co-catalyst. About 96% of MO was degraded in as short as 30 min, achieving a normalized apparent reaction rate constant (k) of 1.1 × 10-2 min-1mg-1. This represents the highest k value ever reported using C3N4-based photocatalysts for MO degradation, based on our thorough literature search. Ultrasonication in acid not only prevents agglomeration of g-C3N4 nanosheets but also tunes pore size distribution and plays a key role in this achievement. We also studied their performance in a photocatalytic hydrogen evolution reaction (HER), achieving a production of 1842 µmol h-1 g-1. Through a profound analysis of all the samples' structure, morphology, and optical properties, we provide physical insight into the improved performance of our optimized porous g-C3N4 sample for both photocatalytic reactions. This research may serve as a guide for improving the photocatalytic activity of porous two-dimensional (2D) semiconductors under visible light irradiation.

Synergistic effect of Fe3C quantum dots, N-doped carbon and selenium on high conductive stable host for lithium sulfur batteries

Lithium-sulfur batteries are considered as one of the most promising energy storage devices. However, their development is still hindered by significant obstacles, particularly the well-known "shuttle effect". To overcome the issues, a three-dimensional porous biochar composite GC(Fe3C)x with Fe3C quantum dots/ C heterostructure is prepared by a simple one-stage chemical activation method as a sulfur host. A small amount of selenium is also added to form GC/Fe3C@SSe and improved electrochemical performances are obtained. The influence of Fe3C content on the structure and properties of the composites is investigated. It has been observed that an increase in Fe3C content leads to a reduction in specific surface area, thereby enhancing chemical adsorption while simultaneously weakening physical adsorption. When the Fe3C content reached 2.7%, the composite achieved a specific surface area of 1150.0 m² g−1. The synergistic effect of Fe3C quantum dots, N-doped carbon, and selenium resulted in outstanding electrochemical properties exhibited by the composite. At 1 C, GC/(Fe3C)2.7@SSe provides an initial specific discharge capacity of 803.7 mAh g−1. After 1000 long cycles, the specific discharge capacity is maintained at 363.1 mAh g−1, and the per-cycle capacity loss rate is 0.055%. Even at the current density of 5 C, the initial discharge capacity is 424.5 mAh g−1, and the capacity after 500 cycles is 322.9 mAh g−1, with a single cycle capacity decay rate of 0.048%. This work provides guidance for the design of lithium-sulfur battery cathode materials with synergetic physisorption and chemisorption for inhibiting shuttle effect.

Evolution of nano-pores in illite-dominant clay during consolidation

AbstractIn this paper, the evolution of nanoscale pores, covering inter-particle pores and inter-layer pores, in illite-dominant clay during consolidation is monitored using small angle X-ray scattering (SAXS) and nitrogen gas adsorption (N2GA) techniques. No obvious change observed in the characteristic peaks of SAXS intensity curves during consolidation suggests that the intra-particle structure of the clay, including interlayer spacings, is not affected by mechanical loading, at least up to 4 MPa. The N2GA test results show that the volume of inter-particle pores inside the aggregates does decrease gradually as the compression proceeds, which is accompanied by a gradual reduction in specific surface area, probably due to the rearrangement of the particles composing the aggregates. The inter-particle pores are compressed as a whole during consolidation instead of the progressive collapse in an ordered manner, from the larger to the smaller. By comparing the pore-size distributions of illite-dominant clay obtained by MIP (mercury intrusion porosimetry) and N2GA techniques, it is found that the shapes of the two distributions in the common measurement range are obviously not matched, essentially due to the sequential nature of the drying and wetting processes. While filling the research gap in the evolution of intra-aggregate pores during consolidation, this study also shows that the N2GA technique and SAXS measurement used in conjunction with each other appear as a powerful approach for clay nano-pores identification.

Hydrolysis stability and its mechanism of porous boron nitride fibers in a watery environment

BackgroundPorous boron nitride fibers (PBNFs) show potentially important applications in solving environmental and energy problems, especially in wastewater treatment, air purification, and drug transport, due to their high specific surface area, large pore capacity, and high density of adsorption active sites. In all these applications, these materials are required to be highly stable in a range of chemical environments, especially in water. MethodsIn this paper, the stability of PBNFs in an aqueous environment is studied systematically for the first time, its hydrolysis mechanism is explored, and the factors affecting the stability of the material are summarized. Meanwhile, improvement measures and optimization schemes are given to prepare porous boron nitride-based materials with excellent performance. Significant findingsIt was found that the oxygen-containing reactive groups and the low crystallinity part of PBNFs can chemically react with water molecules and hydrolyze to form ammonium borate hydrate, resulting in the destruction of the microstructure of PBNFs, the reduction of specific surface area, and the change of chemical composition. Therefore, a method to improve the purity of PBNFs by functionalizing the unstable groups of PBNFs with the help of highly reactive NH3 was proposed, and SN-PBNFs with water stability and active adsorption capacity were synthesized.

Impact of Silicon Content and Particle Size in Lithium-Ion Battery Anodes on Particulate Properties and Electrochemical Performance

Silicon (Si) is considered a promising anode active material to enhance energy density of lithium-ion batteries. Many studies have focused on new structures and the electrochemical performance, but only a few investigated the particulate properties in detail. Therefore, a comprehensive study on the impact of Si content (5, 10, 15 wt.%) and particle size (120, 160, 250 nm) of core–shell structured Si@Gr composites on particulate and electrode properties was conducted. It was shown that both parameters had significant impact on the specific surface area (SSA) of particles, which was later correlated to the initial capacities and coulombic efficiencies (ICEs). Furthermore, changes in pore size distribution and electrical conductivity were found. The built full cells showed high initial capacities (>150 mAh g−1), good rate capability (75% at 1 C, 50% at 2 C) and ICEs (>80%). The energy density was found to increase by 32% at 15 wt.% Si compared to graphite (Gr), indicating the future potential of Si. In addition, the impact of a carbon coating was investigated (Si@Gr/C), which led to a reduction in SSA, improved particle stability and higher capacity retention. Consequently, this study emphasizes the importance of also investigating the particulate properties of Si anodes.

Optimizing adsorption performance of sludge-derived biochar via inherent moisture-regulated physicochemical properties

Understanding the impact of abundant inherent moisture in sewage sludge on the physicochemical properties and adsorption applications of sludge-derived biochar (SDB) contributed significantly to promoting economical sludge reuse. The moisture (0–80%) contributed to the development of micropore and mesopore in SDB at 400 °C, resulting in a maximum increase in specific surface area (SSA) and total pore volume (TPV) of SDB by 38.47% (84.811–117.437 m2/g) and 92.60% (0.0905–0.1743 m3/g), respectively. At 600/800 °C, moisture only facilitated mesopore formation, while was exacerbated with increasing moisture content. Despite reduction in SSA during this stage, TPV increased by a maximum of 20.47% (0.1700–0.2048 m3/g). The presence of moisture during pyrolysis led to an increase in the formation of 3–5 thickened benzene rings and defective structures in SDB, along with more C=O, O–C=O/–OH, pyrrole N, pyridine N, and thiophene. As a result, moisture (40%/80%) increased the maximum adsorption capacity (76.2694–88.0448/90.1190 mg/g) of SDB (600 °C) for tetracycline, mainly due to enhanced pore filling effect and hydrogen bonding induced by improved physicochemical properties. This study offered a novel approach for optimizing the performance of SDB adsorption applications by manipulating the sludge moisture, which is critical for practical sludge management.

Deactivation induced by metal sulfate over MnCeOx catalyst in NH3-SCR reaction at low temperature

Sulfate adsorption is one of the factors that cause the poisoning of catalyst in the low-temperature NH3 selective catalytic reduction reaction (NH3-SCR). In this paper, by controlling the co-adsorption time of SO2 and O2 at 150 °C, a range of sulfated MnCeOx catalysts with different contents of metal sulfate species were prepared to reveal the influence of metal sulfate species content on the catalytic performances and reaction mechanisms at low temperature. The catalytic activity below 250 °C rapidly decreases with increasing metal sulfate species content. The results of characterizations shed light on the reduction of specific surface area, Mn4+ and Ce3+ content, and redox ability of MnCeOx owing to the formation of metal sulfate species. Further experiments reveal that metal sulfate species preferentially absorb on MnOx domains rather than on CeO2 domains, and the adsorbed metal sulfate species can suppress the Eley-Rideal and the Langmuir–Hinshelwood reaction mechanisms over the sulfated MnCeOx. All the above results are detrimental to the activity of sulfated MnCeOx in the low-temperature NH3-SCR reaction.

Failure analysis of three-way catalysts through comprehensive characterization and understanding the role of pretreatment

Currently, most of the studies on waste three-way catalysts (TWCs) have focused on the extraction of platinum group metals (PGMs), with less characterization and analysis of their properties. This can lead to an incomplete understanding of the physicochemical properties and causes of failure of waste TWCs, which in turn affects the recovery of PGMs. This paper conducted various characterization analyses on waste TWCs, including their chemical composition, particle size, surface elements, microscopic morphology, specific surface area, and thermal stability. The PGMs content in the waste TWCs is 1468 g/t, and the total content of rare earth elements is about 1.58%, which has high recovery value. The analysis identified several reasons for TWC failure: the presence of S and P elements caused sulfidation and phosphorylation poisoning of PGMs; PGMs were also partially oxidized to PtO2, PdO2 and Rh2O3; in addition, sintering and agglomeration of waste TWC powder, encapsulation of PGMs in the substrate, reduction of specific surface area and total pore volume, and adsorption of accumulated carbon were also considered as causes of failure. The physicochemical properties of waste TWCs are extremely important for the selection of the PGM extraction process among them. Therefore, the effects of several pretreatment methods on the leaching efficiency of PGM were investigated. The results showed that grinding reduced the leaching rate of PGMs, and HCOOH reduction and NaHSO4 calcination pretreatment could improve the leaching rate of Pt and Rh, respectively; while the Li2CO3 calcination pretreatment could result in 70.87% leaching of Pt directly in HCl. The feasibility of extracting PGMs from waste TWCs using a Li2CO3 calcination pretreatment followed by direct HCl leaching was validated.

Template-free hierarchical TiO2 synthesis: Investigations of structural, optical, and photocatalytic property relationships

Researchers have recently been able to pinpoint a number of factors that affect the photocatalytic activity of semiconductors, but to date no clear correlation between them has been revealed. In this work, the photocatalytic activity of hierarchical titanium dioxide (TiO2) nanoparticles was studied in terms of phase concentration, morphology, surface area, and band gap energy (Eg). Particles were produced in acetone (AH), acetone–water (AHW), chloroform (CU), and chloroform-water (CUW). Anatase (A)-, rutile (R)-, and bronze (B)-containing TiO2 particles were ultimately formed. AH produced hollow and solid (A-R) urchins. AHW produced (A-R-B) spheres. CU formed (B) spheres. CUW provided (R) fibers. CU and CUW did not have many Ti3+ defects, in contrast to AH and AHW, which did. With the addition of water to acetone and chloroform, a significant reduction in specific surface area of TiO2 particles was observed, from 66.41 to 57.50 m2/g in AH and AHW and from 82.23 to 11.01 m2/g in CU and CUW, respectively. The Eg values of the associated particles were relatively comparable to one another (2.9–3.1 eV); however, their photocatalytic degradation performances were entirely distinct. In spite of having the lowest surface area, (R) fibers of CUW displayed the fastest photodegradation rate (0.20 h−1), which was followed by the hollow and solid (A-R) urchins of AH (0.04 h−1). The degradation rates of AHW and CU were similar. Surface area alone could not be correlated to the photocatalytic degradation capability, but this study originally showed that TiO2′s photocatalytic capability was mainly governed by its phase composition, not its hierarchical-morphology-driven surface area, despite having similar values of Eg. For the first time in the literature, (B) spheres were straightforwardly produced without the need for templates or high temperatures.

Synthesis of carbon spheres from glucose using the hydrothermal carbonization method for the fabrication of EDLCs

Carbon spheres (CSs) from glucose were synthesized by the hydrothermal carbonization method. We explored the effect of glucose concentration used in the synthesis on the yield as well as on the morphology of the CSs, and how this affects their electrochemical capacitance. For the possible application of CSs in commercial electrical double-layer capacitors (EDLCs), it is necessary to synthesize them in large quantities. For this reason, one of the main goals of this work was to increase the amount of CSs synthesized by increasing the concentration of glucose used in the synthesis process, affecting their electrochemical properties as little as possible for its use in EDLCs. Two post-synthesis procedures were performed on the CSs: 1) heat treatment at 800 °C in an argon atmosphere and 2) sulfonation process with subsequent heat treatment. The morphology of the six synthesized samples was analyzed. All the synthesized samples have the characteristic of generating large agglomerates of CSs; some are interconnected and fused forming a three-dimensional network of microspheres and other irregular shapes. This agglomeration of CSs may appear to be a negative effect on the performance of the electrodes, due to the apparent reduction in specific surface area. However good electrochemical capacitance results are obtained, because this morphology favors the creation of mesopores and, therefore, a greater facility for the insertion of ions in charging and discharging processes. The electrodes of CSs with better performance showed a capacitance of 85 F g−1 at 50 mV s−1.

In-Situ observation and quantitative analysis on sintering process of Li4SiO4 sorbents

High-temperature CO2 adsorption has an attractive prospect in reducing CO2 emissions efficiently. As the core of CO2 adsorption technology, sorbents suffer from a well-known problem of capacity degradation as a result of sintering during cyclic CO2 adsorption and desorption at high temperatures. This work aims to understand the microstructural evolution of Li4SiO4, one of the most typical and promising sorbents, during CO2 capture. In-situ Transmission Electron Microscopy was used to directly capture the morphological variation of Li4SiO4 sorbents. Comprehensive characterization techniques were adopted to quantify microstructural parameters of Li4SiO4 under different conditions. The real-time shrinkage of Li4SiO4 particles was demonstrated and equations on grain growth, specific surface area reduction, and pore volume evolution were established. The work can not only reveal the reason for the reduction of CO2 capacity, but provide a theoretical guidance for the development of sintering-resistant CO2 sorbents.

Microstructural evolution of saturated normally consolidated kaolinite clay under thermal cycles

This study aims to quantify the microstructural evolution of saturated clay during one thermal cycle. For this purpose, five saturated normally consolidated kaolinite clay triaxial specimens were consolidated under the same conditions. One specimen was subjected to a mechanical consolidation only; while the other four specimens were subjected to different thermal paths: freezing (F), freezing-thawing (FT), freezing-thawing-heating (FTH), and freezing-thawing-heating-cooling (FTHC). After completing the mechanical and thermal stages, thin disks were cut from the bottom of each specimen. The microstructures of these disks were preserved using flash freezing and freeze-drying. The evolutions of the microstructure of the specimens during the thermal cycle was assessed using mercury intrusion porosimetry, gas adsorption methods, and processing of scanning electron microscopy (SEM) images. The results show that (1) freezing increased the modal throat size and the specific surface area (SSA); (2) freezing-thawing decreased both modal throat and pore sizes, while the SSA recovered to its initial value; (3) freezing-thawing-heating reduced the pore and throat sizes and SSA even further; and (4) freezing-thawing-heating-cooling caused permanent reduction in SSA and throat and pore size distributions. Finally, the shape of the pores became more circular after temperature changes, while the number of pores increased during the thermal cycle with the highest number corresponding to the end of heating (i.e., the third stage in the thermal cycle).

Simultaneous stabilization of Pb, Cd, and As in soil by rhamnolipid coated sulfidated nano zero-valent iron: Effects and mechanisms.

Sulfidation effectively improves the electron transfer efficiency of nanoscale zero-valent iron (nZVI), but decreases the specific surface area of nZVI. In this study, sulfidated nZVI (S-nZVI) coated with rhamnolipid (RL-S-nZVI) was synthesized and used to stabilize Pb, Cd, and As in combined polluted soil. The stabilization efficiency of 0.3% (wt) RL-S-nZVI to water soluble Pb, Cd, and As in soil reached 88.76%, 72%, and 63%, respectively. Rhamnolipid coating inhibited the reduction of specific surface area and successfully encapsulated nZVI, thus reducing the oxidation of Fe0. The types of iron oxides in RL-S-nZVI were reduced compared to S-nZVI, but the content and strength of Fe0 iron were obviously enhanced. Furthermore, rhamnolipid functional groups (-COOH and -COO-) were also involved in the stabilization process. In addition, the stabilization efficiency of RL-S-nZVI to the bioavailable Pb, Cd, and As in soil increased by 41%, 41%, and 50%, respectively, compared with nZVI. The presence of organic acids, especially citric acid, improved the stabilization efficiency of RL-S-nZVI to the three metals. The result of BCR sequential extraction indicated that RL-S-nZVI increased the residual state of Pb, Cd, and As and reduced the acid-soluble and reducible state after 28 days of soil incubation. XRD and XPS analyses showed that the stabilization mechanisms of RL-S-nZVI on heavy metals involved in ion exchange, surface complexation, adsorption, co-precipitation, chemisorption, and redox.

Hydrothermally-Derived Silver-Decorated Nanocrystalline Anatase Photocatalyst for Reactive Violet 2 Photodegradation

A photocatalyst comprised of Ag nanoparticles dispersed on an anatase matrix has been prepared using a simple hydrothermal method without additional thermal treatment. The prepared material was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy, and N2 adsorption–desorption isotherms. The prepared catalyst activity was evaluated by photocatalytic degradation of C.I. Reactive Violet 2 (RV2) aqueous solution under UVA and visible light illumination. SEM revealed the non-uniform dispersion of silver particles throughout the matrix composed of fine particles. According to XRD analysis, the matrix was composed of pure anatase with a crystallite size of 8 nm calculated through the Scherrer equation. HRTEM micrograph analysis showed that anatase nanoparticles possess a spherical morphology and a narrow size distribution with an average particle size of 8 nm with more active anatase {100} crystal surface exposed, while silver nanoparticles were between 60 and 90 nm. A bandgap of 3.26 eV has been calculated on the basis of the DRS UV-Vis spectrum, while a specific surface area of 209 m2g−1 has been established from adsorption isotherms. Thus, through a simple synthesis approach without subsequent thermal treatment, the agglomeration of nanoparticles and the reduction of specific surface area have been avoided. Prepared nano Ag/anatase photocatalyst exhibits excellent efficiency for the photodegradation of RV2 under UVA and visible irradiation.

Impact of Sterilization on the Colloidal Stability of Ligand-Free Gold Nanoparticles for Biomedical Applications.

Sterilization is a major prerequisite for the utilization of nanoparticle colloids in biomedicine, a process well examined for particles derived from chemical synthesis although highly underexplored for electrostatically stabilized ligand-free gold nanoparticles (AuNPs). Hence, in this work, we comprehensively examined and compared the physicochemical characteristics of laser-generated ligand-free colloidal AuNPs exposed to steam sterilization and sterile filtration as a function of particle size and mass concentration and obtained physicochemical insight into particle growth processes. These particles exhibit long-term colloidal stability (up to 3 months) derived from electrostatic stabilization without using any ligands or surfactants. We show that particle growth attributed to cluster-based ripening occurs in smaller AuNPs (∼5 nm) following autoclaving, while larger particles (∼10 and ∼30 nm) remain stable. Sterile filtration, as an alternative effective sterilizing approach, has no substantial impact on the colloidal stability of AuNPs, regardless of particle size, although a mass loss of 5-10% is observed. Finally, we evaluated the impact of the sterilization procedures on potential particle functionality in proton therapy, using the formation of reactive oxygen species (ROS) as a readout. In particular, 5 nm AuNPs exhibit a significant loss in activity upon autoclaving, probably dedicated to specific surface area reduction and surface restructuring during particle growth. The filtered analog enhanced the ROS release by up to a factor of ∼2.0, at 30 ppm gold concentration. Our findings highlight the need for carefully adapting the sterilization procedure of ligand-free NPs to the desired biomedical application with special emphasis on particle size and concentration.

Immobilization of HPW on UiO-66-NH2 MOF as efficient catalyst for synthesis of furfuryl ether and alkyl levulinate as biofuel

Phosphotungustic Acid (HPW) is an inorganic super acid, that is highly soluble in polar solvents limiting its applicability as acid catalysis. To overcome these limitations immobilization of HPW was carried out at room temperature by protonation of -NH2 group of UiO-66-NH2 MOF to UiO-66-NH2HPW. ATR-FTIR spectroscopy and XPS results confirmed the protonation and chemical interaction between HPW and UiO-66-NH2. STEM-EDS mapping showed homogeneous distribution of HPW on UiO-66-NH2. BET and NH3-TPD confirmed the reduction in specific surface area, total pore volume, and increase in total acidity for UiO-66-NH2HPW. Further, powder XRD, SEM, and HR-TEM prevailed that there is no change in phase and morphology after post-synthetic modification of UiO-66-NH2. The prepared catalyst is found to be effective for etherification and alcoholysis of furfuryl alcohol (FALc) to Furfuryl ether (FE) and Alkyl levulinate (AL). UiO-66-NH2HPW has shown 97 mol% FALc conversions in ethanolic media and 31 mol% Ethyl furfuryl ether (EFE) yield and 29 mol% Ethyl levulinate (EL) yield. UiO-66-NH2HPW is also found to be efficient for the multistep conversion of Furfural (FFR) to FALc, FE, and AL.

Effects of Flue Gas Impurities on the Performance of Rare Earth Denitration Catalysts

Selective catalytic reduction (SCR) is still the most widely used process for controlling NOx gas pollution. Specifically, commercial vanadium-based catalysts have problems such as narrow operating temperature range and environmental pollution. Researchers have developed a series of cerium-based catalysts with good oxygen storage performance and excellent redox performance of CeO2. However, the anti-poisoning performance of the catalyst is the key to its application. There are many kinds of impurities in the flue gas, which has a huge impact on the catalyst. The deposition of substances, the reduction of active sites, the reduction of specific surface area, and the reduction of chemically adsorbed oxygen will affect the denitration activity of the catalyst to varying degrees, and the poisoning mechanism of different impurities on the catalyst is also different. Therefore, this review divides the impurities contained in flue gas into different types such as alkali metals, alkaline earth metals, heavy metals, and non-metals, and summarizes the effects and deactivation mechanisms of various types of impurities on the activity of rare earth catalysts. Finally, we hope that this work can provide a valuable reference for the development and application of NH3-SCR catalysts for rare earth denitration in the field of NOx control.

Morphological and chemical evolution of transient interfaces during zinc oxide cold sintering process

Although zinc oxide has a high melting point of 1975 °C, the recent development of the cold sintering process has shown that highly dense polycrystalline ceramics can be obtained at 150 °C or below. As such unusual densification does not yet have fully elucidated underlying mechanisms, this study aims to provide a comprehensive investigation of transient morphological and chemical interfaces during isothermal dwell. The chemical “transient” interface involves the formation of a zinc carboxylate complex by reacting the host zinc oxide powder and acetic acid solution, which is later consumed for the recrystallization on the lattice of an adjacent grain with a decomposition of the complex. Hence, the final outcome can be a residual-free zinc oxide phase. Regarding the morphological evolution, gas physisorption studies were conducted to quantify the area of solid–vapor interfaces and the Schlaffer model was used to analyze the activation energy for specific surface area reduction. Moreover, transmission electron micrographs revealed that the recrystallization occurs at the interface between crystalline grain and carbon-rich amorphous phase. After 30 minutes of isothermal dwell, the area of the amorphous phase was significantly decreased while grain size was increased, potentially indicating the recrystallization-induced grain growth and pore closure. The chemical transition at the zinc oxide surface was further investigated using ReaxFF molecular dynamics simulation, observing that acetate molecule acts as a bridging complex to connect zinc ions to the surface. Overall, understanding the evolution of the transient interface is a crucial subject to obtaining a residual-free cold-sintered sample with desired grain size and properties for application developments.

An integrated optimization of composition and pore structure boosting electrocatalytic oxygen evolution of Prussian blue analogue derivatives

Exploring efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) is of great importance for renewable energy-related systems. Prussian blue analogues (PBAs) are considered as promising precursors to derive advanced heteroatom-doped carbonaceous materials. However, the pyrolysis treatment usually results in an inevitable aggregation of active sites as well as the reduction of specific surface area, apart from the uncontrollable composition and morphology. Herein, we develop a straightforward synthetic protocol for fabricating highly-active OER electrocatalysts of Co7Fe3, Co, N-codoped carbon (Co7Fe3/Co@NC) by annealing trimetallic CoZnFe-PBA precursors. The surface modification of cobalt species over ZnFe-PBA effectively tailors the active composition for as-derived products, whereas Zn volatilization at a high temperature not only promotes the dispersion of active sites but also fabricates the formation of an intriguing hierarchical structure with multimodal porosity and high specific surface area. The integrated advantages of multinary composition and fabulous pore structure endow the elegantly-designed Co7Fe3/Co@NC with a remarkable catalytic performance towards OER in alkaline electrolyte, as evidenced by an overpotential of 290 mV without iR-correction at a current density of 10 mA cm−2 and impressive long-term durability. The present synthetic strategy offers valuable insights for developing highly-efficient PBAs-derived electrocatalysts with compositional multiplicity and interesting pore texture.