Traditional Co-precipitation Method Research Articles

One-Pot Synthesis of (CrMnFeCoNi)Ox High-Entropy Oxides for Efficient Catalytic Oxidation of Propane: A Promising Substitute for Noble Metal Catalysts.

The efficient catalytic oxidation of propane, as a short-chain alkane, remains challenging in environmental catalysis. High-entropy oxides (HEOs) exhibit advantages in abundant and well-dispersed elemental composition, exceptional thermal stability, and enriched lattice defects. Herein, (CrMnFeCoNi)Ox HEO catalysts are successfully synthesized by using a continuous hydrothermal flow synthesis (CHFS) route, without any subsequent calcination processes. This route yields HEOs with fine particle sizes, high specific surface areas, and abundant near-surface lattice oxygen compared to the traditional coprecipitation method. Notably, the propane conversion over the CHFS-made (CrMnFeCoNi)Ox HEO reaches 90% at 255 °C, with an apparent activation energy of 53.2 kJ/mol, mainly attributed to its enriched lattice oxygen and enhanced oxygen mobility that prevent the accumulation of acetates and the consequent occupation of active sites. In comparison to commercial Pt/Al2O3 and Pd/Al2O3, (CrMnFeCoNi)Ox HEO demonstrates exceptional activity and can maintain long-term stability under high-temperature (upon 650 °C) and moisture-rich conditions (at 2-10 vol %). These attributes highlight its potential as a promising substitute for noble metal catalysts in industrial applications.

Ultrastable Fe-based Prussian Blue Analogs Cathode for Sodium-Ion Battery

Low-cost Iron-based Prussian blue analogs (PBAs) with ultra-high cycling performance is a promising cathode material for sodium-ion batteries. However, the presence of vacancies occupied by crystal water in the structure of PBA prepared by the traditional co-precipitation method leads to rapid capacity decay of the battery, which significantly limits its practical application. In the present work, we use a modified co-precipitation method to synthesize Fe-based PBAs, which has a cubic structure and offers a large Na+ insertion/extraction channel. The results show that 99.9% of the capacity (108.9 mAh g−1) retained after 100 cycles of tests for the sample with the most outstanding cycling stability (PB-15). In addition, the samples are heat-treated to remove the crystal water from the acquired PBAs. The freshly prepared PB-15 sample is further treated at 180 °C. Phase transformation from the cubic structure to the monoclinic phase of the samples is probed after heat treatment. The initial specific capacity of HT-PB-15 is higher than that of PB-15 by 10.2 mAh g−1 and the capacity remained at 117.6 mAh g−1 after 100 cycles, which is the most outstanding cycling performance in the reported results.

Application of precursor with ultra-small particle size and uniform particle distribution for ultra-high nickel single-crystal cathode materials by coprecipitation method

Ultra-high nickel single-crystal cathode materials have become the most promising for lithium-ion batteries. However, the preparation of ultra-high nickel single-crystal precursors by a continuous coprecipitation method has the disadvantages of large particle size, wide distribution, poor morphology. The extent of the inhomogeneous reactions can be more severe in single-crystal cathodes with larger particle size. Herein, the coprecipitation method with a solid concentrator was adopted, and citrate sodium was used as a complexing agent to improve the physical properties of precursors and electrochemical performance of single-crystal cathode materials. By analyzing the morphology and agglomeration mechanism of the precursor nucleuses under different pH values, it was found that hexagonal nanosheets grew along the 101 direction, and the primary particles showed thicker at pH of 11.4. The hexagonal nanosheets grew along the 001 direction, and the primary particles showed finer at pH of 12.2. The morphology and particle size uniformity of the secondary particles formed by agglomeration at these two pH values showed poor. However, hexagonal nanosheets grew synergistically along the 001 and 101 directions at pH of 11.8, so the primary particles with uniform particle size gradually agglomerated, and then the secondary particles with ultra-small particle size and uniform distribution obtained. Compared to materials prepared by the traditional continuous coprecipitation method, the precursor displays a smaller particle size(D50 = 1.8 µm), higher sphericity, uniformity and denser internal structure. In order to evaluate the performance of Ni0.94Co0.04Mn0.02(OH)2 with ultra-small particle size, the sintering conditions of LiNi0.94Co0.04Mn0.02O2 need to be explored. It was found that the LiNi0.94Co0.04Mn0.02O2 cathode material prepared at 790 °C exhibited higher discharge capacity, cycle and rate performance, compared to materials prepared at 760 °C and 820 °C. We further utilized TEM, EPMA, and XPS to test the internal structure and valence state of LiNi0.94Co0.04Mn0.02O2 cathode material. The results show that the LiNi0.94Co0.04Mn0.02O2 calcined at 790 °C has a good single crystal structure. The LiNi0.94Co0.04Mn0.02O2 cathode materials inherited the structure and particle size of Ni0.94Co0.04Mn0.02(OH)2 precursors, and displayed discharge capacity of 194.7 mAh/g and capacity retention rate of 89.8 % after 100 cycles at 1 C. The microstructure and phase transition of the as-prepared cathode material are well-maintained after long-term cycling, without obvious inter-crystalline micro-crack. The results indicate that its electrochemical performance is better than that of cathode materials with precursors prepared by a continuous coprecipitation method. This work provides new insights for the preparation of small-particle-size precursor and single-crystal cathode materials.

Boosting adsorption of ciprofloxacin on Fe3O4 nanoparticles modified sepiolite composite synthesized via a vacuum-filtration assisted coprecipitation strategy

Treatment of antibiotics-containing wastewater is imperative for ensuring environmental and public health. However, effectively removing antibiotics in environment is still a great challenge. Fabrication of sepiolite-supported iron oxide nanomaterials with large specific surface area and high reactivity is a promising solution for efficient antibiotics removal. In this work, a highly dispersed Fe3O4 nanoparticle modified sepiolite composite (Fe3O4-sep-vacuum) was synthesized in-situ by employing a novel vacuum-filtration assisted coprecipitation strategy for the first time. Fe3O4-sep-vacuum exhibited the highest adsorption capacity to ciprofloxacin compared with those of pure Fe3O4 nanoparticles, sepiolite, and those composites obtained by traditional coprecipitation methods. Approximately 93 % of CIP (20 mg/L) could be removed by Fe3O4-sep-vacuum within 20 min at initial pH 6.0. The kinetic and adsorption isotherms followed pseudo-second-order and Temkin models, respectively. The maximum adsorption capacity (qm) of Fe3O4-sep-vacuum for CIP was 18.4 mg/g at initial pH 6.0. The solution pH, temperature, coexisting divalent cations, and HA concentration were demonstrated to play substantial roles in the adsorption processes of ciprofloxacin on Fe3O4-sep-vacuum surface. The Fe3O4-sep-vacuum maintained excellent stability and reusability during CIP adsorption process. Electrostatic interactions play a decisive role in the adsorption process of ciprofloxacin by Fe3O4-sep-vacuum. Hydrogen bonds and hydroxyl groups on the Fe3O4-sep-vacuum surface also play important roles in the adsorption process of ciprofloxacin. Fe3O4-sep-vacuum also exhibited excellent adsorption capacity to ofloxacin. These results indicate that the vacuum-filtration assisted coprecipitation strategy could be used to fabricate monodispersed nanoparticles modified sepiolite composites, which could be acted as promising materials for highly efficient remediating antibiotics contaminated wastewater.

A novel pretreatment method for analysis the oxygen isotopic compositions of inorganic phosphorus pools in freshwater sediment

Identifying the sources and cycling of phosphorus (P) is particularly important for formulating effective P management strategies in inland water. The oxygen isotopic compositions of phosphate (δ18OP) are recognized as a promising tool to solve this problem. However, the application of δ18OP in freshwater sediment is currently constrained by multiple difficulties. In this study, we presented a novel pretreatment method for δ18OP analysis of sediment inorganic P pools. Our results showed that the new method has advantages of simple operation, less time-consuming, and high P recovery rates. Specifically, we replaced the traditional Mg-induced co-precipitation (MAGIC) method by introducing Zr-Oxides gels with high selective adsorption function for phosphate. This made subsequent processing simpler and reduced the time consumption to ∼10 days, and the range of P recovery rates were from 88 % to 104 %. Furthermore, we emphasized the necessity of vacuum roasting following lyophilized Ag3PO4 to eliminate residual oxygen-containing impurities (e.g., NO3−, Ag2O, and organic matter). Additionally, evidences from microscopy and spectroscopy confirmed that this method ultimately yielded high-purity Ag3PO4 with the Ag:P molar ratios of 3.35:1. Importantly, combining direct synthesis Ag3PO4 between KH2PO4 and AgNO3 with the Ag3PO4 obtained by the method revealed no stark oxygen isotopic fractionation of phosphate during the pretreatment processes. The newly established δ18OP pretreatment methods here can also be extended to broader studies of the biogeochemical cycling of P in aquatic ecosystems, potentially advancing the understanding of the global P cycle.

Preparation of CeO2 particles via ionothermal synthesis and its application to chemical mechanical polishing

CeO2 is a widely used abrasive for the chemical mechanical polishing of silicon during chip manufacturing. CeO2 can be synthesized via traditional coprecipitation, hydrothermal, and solvothermal methods; however, these methods have some issues, including high vapor pressure, flammability, toxicity, volatile solvents, and narrow heating temperature range. To overcome these issues, we developed a new ionothermal synthesis approach for high-quality CeO2 particles using 1-ethyl-3-methylimidazolium tetrafluoroborate as an imidazole ionic liquid without a template. Based on the scanning electron microscopy and particle size distribution, CeO2 particles synthesized at a reaction temperature of 210 °C for 16 h displayed sizes ranging between 0.1 and 0.3 μm. Additionally, the spherical shapes exhibited good crystallinity, regular morphology, and uniform dispersion. The results of CMP experiments indicated that the abrasives could reduce the surface roughness from 1.63 to 0.29 nm (scanning area is 5 μm × 5 μm). The obtained synthesized CeO2 particles demonstrated promising performance in Si polishing, achieving removal rates of up to 255.5 nm/min. It found that the removal rate of the abrasive prepared by ionic thermal synthesis in Si polishing was twice as much as other abrasives. Further, a possible mechanism was put forward to explain the formation of CeO2 structures with various morphologies. The proposed method presents a new approach for synthesizing CeO2 particles with uniform morphology and excellent polishing properties.

Ultrafast spray pyrolysis for synthesizing uniform Mg-doped LiNi0.9Co0.05Mn0.05O2

Nickel-rich cathode materials have received widespread attention due to their high energy density. However, the poor rate capability and inferior cycle stability seriously hinder their large-scale application. The traditional co-precipitation method for preparing them has a long process and easily arises agglomeration leading to inhomogeneous element distribution. Here, a novel precursor containing Li element was prepared by ultrafast spray pyrolysis (SP) in 3-5 s. Then the precursor was used to synthesize pristine LiNi0.9Co0.05Mn0.05O2 (NCM90) and 1% Mg modified LiNi0.9Co0.05Mn0.05O2 (NCM90-Mg1). This method gets rid of mixing Li/Mg source and the precursor prepared by common co-precipitation, thus could achieve homogeneous lithiation and Mg2+ doping. The cell parameter c is expanded, and the cation disorder is reduced after Mg2+ doping. Furthermore, the harmful H2-H3 phase transition in NCM90-Mg1 is also well suppressed. As a result, the obtained NCM90-Mg1 shows better electrochemical performance than NCM90. Within 2.8-4.3 V (25 °C), the specific discharge capacity of NCM90-Mg1 at 5 C is as high as 169.1 mAh/g, and an outstanding capacity retention of 70.0% (10.0% higher than NCM90) can be obtained after 400 cycles at 0.5 C. At 45 °C, a capacity retention of 81.9% after 100 cycles at 1 C is recorded for NCM90-Mg1. Moreover, the NCM90-Mg1 also exhibits superior cycle stability when cycled at high cut-off voltage (4.5 V, 25 °C), possessing the capacity retention of 79.2% after 200 cycles at 1 C. Therefore, SP can be proposed as a powerful method for the preparation of multi-element materials for next-generation high energy density LIBs.

Polymer-confined synthesis of gram-scale high-entropy perovskite fluoride nanocubes for improved electrocatalytic reduction of nitrate to ammonia.

High-entropy perovskite fluoride (HEPF) has gradually attracted attention in the field of electrocatalysis due to its unique properties. Although traditional co-precipitation methods can efficiently produce HEPF, the resulting catalysts often lack regular morphology and tend to aggregate extensively. Here, nanocubic K(CuMgCoZnNi)F3 HEPF (HEPF-2) was successfully prepared on a gram-scale by a polyvinylpyrrolidone (PVP)-confined nucleation strategy. Benefiting from its large electrochemically active surface area and well-exposed active sites, the HEPF-2 demonstrates dramatically enhanced electrocatalytic activity in electrocatalytic nitrate reduction to ammonia, leading to an improved ammonia yield rate (7.031 mg h-1 mgcat.-1), a high faradaic efficiency (92.8%), and excellent long-term stability, outperforming the irregular HEPF nanoparticles (HEPF-0) prepared without the assistance of PVP. Our work presents an efficient and facile method to synthesize perovskite fluorides with a well-defined structure, showing great promise in the field of high-performance electrocatalysis.

Low-temperature CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation for selective catalytic reduction of NO using NH3: A structure–activity relationship study

CeCoMnOx spinel-type catalysts for the selective catalytic reduction of NO using NH3 (NH3-SCR) are usually prepared by alkaline co-precipitation. In this paper, a series of CeCoMnOx spinel-type catalysts with different calcination temperatures were prepared by acidic oxalate co-precipitation. The physicochemical structures and NH3-SCR activities of the CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation and conventional ammonia co-precipitation were systematically compared. The results show that the CeCoMnOx spinel-type catalysts prepared by the oxalate precipitation method (CeCoMnOx-C) have larger specific surface area, more mesopores and surface active sites, stronger redox properties and adsorption activation properties than those prepared by the traditional ammonia co-precipitation method at 400 °C (CeCoMnOx-N-400), and thus CeCoMnOx-C have better low-temperature NH3-SCR performance. At the same calcination temperature of 400 °C, the NO conversion of CeCoMnOx-C-400 exceeds 89 % and approaches 100 % within the reaction temperature of 100–125 °C, which is 14.8 %-2.5 % higher than that of CeCoMnOx-N-400 at 100–125 °C. In addition, the enhanced redox and acid cycle matching mechanisms on the CeCoMnOx-C surface, as well as the enhanced monoadsorption Eley-Rideal (E-R) and double adsorption Langmuir-Hinshelwood (L-H) reaction mechanisms, are also derived from XPS and in situ DRIFTS characterization.

Sono-enhanced heterogeneous Fenton catalysis: magnetic halloysite nanotube synthesis and accelerated free radical generation.

Although heterogeneous Fenton catalysis has captured increasing attention compared to its homogeneous counterpart, it still confronts some inherent drawbacks in use, such as the dilemma in solid-liquid separation and greater mass transfer resistance. Driven by the acoustic cavitation effect, herein, a sono-enhanced heterogeneous Fenton catalysis process was built to overcome the above two shortcomings, by rapidly synthesizing magnetic Fenton-like catalysts and accelerating electron transfer during the catalytic reaction. The results show that, compared to the traditional chemical coprecipitation method, Fe3O4 with smaller particle size and better crystallinity grew on the surface of halloysite nanotubes (HNTs) by using the sonochemical strategy, leading to displaying the higher catalytic activity toward the degradation of methylene blue (MB, improved by ~2.5 times). In parallel, more •OH and •O2- were produced after the ultrasound was further introduced to the routine Fenton-like catalysis system, thus highly accelerating the removal of MB (improved by ~50%). Besides, benefiting from the robust chemical integration of Fe3O4 and HNTs, Fe3O4@HNTs-S had a lower iron ion leaching in use, showing superior catalytic stability. The speed, simplicity, and generality, together with the enhanced mass transfer rate, make the use of ultrasound an enabling methodology to improve the heterogeneous Fenton catalysis.

Effect of the Composition and Synthesis Procedure of the Catalysts Based on the CoAl-Hydroxides on their Properties in Furfural Hydrogenation

CoAl-hydroxides with Co/Al = 2 and 4 were synthesized by traditional coprecipitation method and mechanochemical route. Structure properties of the samples on the all preparation stages of the catalysts, the transformations occurred during cobalt reduction from corresponding oxides, textural characteristics of calcined and reduced samples, as well as size, morphology and composition of the particles that formed after high temperature treatments were studied in detailed. It was established, that synthesis procedure of CoAl-hydroxides has a significant impact on phase composition and properties of obtained systems. The phase of layered double hydroxide formed only when using coprecipitation method. The mechanochemical approach allowed to obtained the materials with higher specific surface area. According to TEM data, the samples prepared by coprecipitation (after oxidative and reductive treatments) had a “core-shell” structure where metallic atoms of Co were in core and shell consisted of CoAl-spinel. The samples synthesized by mechanochemical route had Co nanoparticles with high dispersion on the surface. The catalysts based on CoAl-systems prepared by mechanochemical method were more active in the furfural hydrogenation. Conversion of furfural achieved 97% for the sample with Co/Al = 4. Herewith, selectivity of furfural formation for all studied catalysts was almost 100% irrespective of synthesis procedure and Co/Al ratio.

Electrochemically Engineering a Single-Crystal Nickel-Rich Layered Cathode.

Nickel-rich layered electrode material has been attracting significant attention owing to its high specific capacity as a cathode for lithium-ion batteries. Generally, the high-nickel ternary precursors obtained by traditional coprecipitation methods are micron-scale. In this work, the submicrometer single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM) cathode is efficiently prepared by electrochemically anodic oxidation followed by a molten-salt-assisted reaction without the need of extreme alkaline environments and complex processes. More importantly, when prepared under optimal voltage (10 V), single-crystal NCM exhibits a moderate particle size (∼250 nm) and strong metal-oxygen bonds due to reasonable and balanced crystal nucleation/growth rate, which are conducive to greatly enhancing the Li+ diffusion kinetics and structure stability. Given that a good discharge capacity of 205.7 mAh g-1 at 0.1 C (1 C = 200 mAh g-1) and a superior capacity retention of 87.7% after 180 cycles at 1 C are obtained based on the NCM electrode, this strategy is effective and flexible for developing a submicrometer single-crystal nickel-rich layered cathode. Besides, it can be adopted to elevate the performance and utilization of nickel-rich cathode materials.

An improved method of MgFe-layered double hydroxide/ biochar composite synthesis

Layered double hydroxides (LDHs) and their composites are a promising platform for a wide range of applications, especially in the environmental field. However, the facile and efficient synthesis of high-quality LDHs and their composites remains a challenge. Here, an improved co-pyrolysis method has been developed to synthesize LDH/biochar composites. A composite material was prepared by directly anchoring MgFe-LDH on corn stover by co-precipitation with FeCl3 and Mg(OH)2, and then through pyrolysis. The main features of this improved method are the use of the solubility product Mg(OH)2 to maintain the pH of the mixture at ∼10 (the optimum for LDH precipitation), eliminating the cumbersome pH control steps of the traditional co-precipitation method, and the low rate of solid-liquid reaction to obtain high LDH crystallinity and purity. This produces improved properties of the MgFe-LDH/biochar composite after pyrolysis: higher loading of MgFe-LDH, larger specific surface area of the composite, a more stable layered structure, and a more customizable LDH. The theoretical maximum adsorption capacity of phosphorus for the composite was 379.4 mg L−1 according to an adsorption isotherm study, and the dominant adsorption mechanism is chemical adsorption accompanied by physical adsorption. In actual wastewater applications, >80% of total phosphorus in biogas slurry was removed via adsorption, indicating that the composite is highly efficient in phosphorus selectivity in wastewaters with complex components. Here, a more sustainable synthesis method of LDH/biochar composite has been developed with high application potential.

The preparation of 3.0F-Co3O4 catalyst with “Yardang Landform” structure and its performance for catalyzing N2O decomposition

In this work, the 3.0F-Co3O4 catalyst was synthesized by sol-gel method with the assistance of F127 and used for eliminating the N2O pollution from nitric acid plants. Research indicated that the presence of F127 in the preparation process endowed the 3.0F-Co3O4 catalyst with unique “Yardang Landform” microstructure, which possessed a rich number of “edges and corners”. The unique microstructure enables the 3.0F-Co3O4 catalyst to mainly expose highly active (400) and (511) crystal planes. Based on this unique microstructure, the surface active site density for 3.0F-Co3O4 catalyst was 7.62 µmol g−1 m2, which was about 9 times that of Co3O4(CP) catalyst prepared by traditional co-precipitation method. In addition, the 3.0F-Co3O4 catalyst demonstrated high catalytic activity and stability for the reaction in presence of impurity gases. For example, the catalyst can maintain a conversion of more than 60% for N2O at least 10 h in the feed stream of 2000 ppmv N2O/Ar with 5 vol% O2, 100 ppmv NO and 2 vol% H2O at 400 °C and GHSV = 20,000 h−1.

Biosurfactant assisted in situ green and clean preparation route for layered double hydroxides and their green metrics-based sustainability assessment

Hybrid advanced multifunctional materials based on layered double hydroxides (LDH) and intercalated guest biomolecule(s) are of high industrial and academic importance and have found promising applications in diverse fields such as biomedical, energy, environment, agriculture, etc. This report strategically develops a new innovative green sonochemical route to incorporate rhamnolipid (RL) and surfactin (SR) into 3D hierarchical flower-like Mg-Al-LDH micro-nano-structures. When compared to traditional mechanochemical co-precipitation and ion-exchange methods, the designed one-pot and scalable method was sustainable and green chemistry compliant, with improved time, energy, and solvent efficiency. RL/SR anions act as an interlayer anion and a template for the fabrication of LDH sheets leads to the increase in the basal spacing and impair LDH sheet interaction. Consequently the vesicle-type phase can be fabricated using biosurfactant in aqueous media under the influence of metal cations induced the curved growth of RL/SR-intercalated LDH nuclei and the flower-like assemblage of LDH particles. The structure, morphology, surface properties, and thermal stability were evaluated. The release profile and kinetics of RL/SR of the intercalated LDHs was studied. Slow and controlled release of SR from the Mg/Al-LDH micro-nano-structures was observed for a prolonged time up to 10 h and followed zeroth-order kinetics, whereas RL release was well described in Higuchi model, indicating the release of the biomolecule via a diffusion mechanism. Cytotoxicity (in L929 and 3T3 fibroblast cells) and haemolytic tests suggested that cytotoxic effect in the range of 25–400 mg/ml and the haemolytic ratio was <4 % at 25–600 mg/ml, showing good biocompatibility of the biosurfactant-intercalated LDHs. Taken together, these micro-nano-structures can be used as potential sustained- or extended-release candidate for agricultural, biomedical or water treatment applications.

Prussian Blue Analogue-Derived Cobalt Sulfide Nanoparticles Embedded in N/S-Codoped Carbon Frameworks as a High-Performance Anode Material for Sodium-Ion Batteries

Metal sulfides display considerable theoretical capacities as anode materials in sodium-ion batteries (SIBs), but their application is limited by their large volume expansion, sluggish charge-transfer kinetics, and poor cycling performances. In this study, unlike the traditional coprecipitation method to prepare the Prussian blue analogue (PBA), PBA with a tremella-like microflower structure is first synthesized by the hydrothermal method under the synergistic effect of trisodium citrate dihydrate (TSC, Na3C6H5O7·2H2O) and K3[Co(CN)6], and two kinds of cobalt sulfide nanoparticles embedded in N/S-codoped carbon frameworks (namely, Co3S4@C–N/S and Co9S8@C–N/S) are successfully synthesized by a subsequent solid sulfidation process. Herein, N/S-codoped carbon frameworks improve the electronic conductivity and provide more active sites for sodium storage. As the anode material in SIBs, the Co3S4@C–N/S 1.8-based anode exhibits an excellent initial charge/discharge specific capacity of 685.3/745.2 mAh g–1 with a high initial Coulombic efficiency of 91.97% at 0.1 A g–1 and a superior cycling performance (599.1 mAh g–1 in the 600th cycle at 1 A g–1 with a capacity retention of 89.4%). However, the Co9S8@C–N/S 1.8-based anode also delivers considerable initial Coulombic efficiency (86.1% at 0.1 A g–1) with high cycling stability (391.9 mAh g–1 even in the 1200th cycle at 2 A g–1 with a capacity retention of 78.1%). This study provides a material synthesis route for high-performance anode materials used in SIBs and other alkali metal-ion batteries.

Computational Prediction of Graphdiyne-Supported Three-Atom Single-Cluster Catalysts

Computational Prediction of Graphdiyne-Supported Three-Atom Single-Cluster Catalysts

Precise determination of optical band gap in Cr-doped semiconductor nanowires

Pristine and chromium-doped ZnO nanowires were prepared following the traditional co-precipitation method. X-ray diffraction data identified a pure wurtzite hexagonal crystal structure characteristic for ZnO, irrespective of the doping level. The particle size, as deduced form Williamson–Hall plots, was found to be 45–55 nm for all samples. Scanning electron microscopy revealed a clear nanowires morphology for the pure and doped samples, while elemental analysis ensured the successful Cr-doping. Distinct spectroscopic signatures of Cr-doping were revealed from a detailed deconvolution process applied to optical spectra of doped samples, where Cr3+ optical transitions were unambiguously identified at ~ 420 and ~ 665 nm. Particularly relevant, is the spectral decomposition here performed for the superimposed absorption edge (~ 385 nm) and Cr3+ optical resonance at ~ 420 nm, allowing to claim practically doping-independent optical band gap behavior in the present doping regime. This is further supported by identifying the characteristic ZnO near edge photoluminescence peak (~ 392 nm) which maintains fixed wavelength after Cr-doping. These findings contrast earlier studies on Cr-doped semiconductor nanoparticles and glass systems where the optical band gap has been largely underestimated. We attribute the inconsistence band gap values reported in literature for Cr-doped semiconductors to the proximity of Cr optical transitions to the semiconductor absorption edge.

Post-doping induced morphology evolution boosts Mn2+ luminescence in the Cs2NaBiCl6:Mn2+ phosphor.

As we know, defects caused in the synthetic process of metal halide perovskite are the most difficult to overcome, and greatly limit their photoelectric performances. Herein, a post-doped strategy was utilized to achieve an interesting morphology evolution from a standard octahedron to a snowflake-like sheet during the Mn2+-doped Cs2NaBiCl6 process, which realizes the obvious photoluminescence quantum efficiency (PLQY) enhancement of the Cs2NaBiCl6:Mn2+ phosphor. This surprising evolution is ascribed to the morphology collapse and reconstruction induced by Mn2+ exchange. The obtained phosphor exhibits enhanced 31.56% PLQY, which is two-fold higher than that synthesized by the traditional co-precipitation method, with broad emission spectrum and good PL color stability at 150 °C. Combined with the Cs2SnCl6 : 1mol%Bi3+ phosphor to fabricate the phosphor-converted light-emitting diode, bright white light emission with Ra = 88, CCT = 4320 K, CIE (0.36, 0.33) and a good application potential in high-resolution PL imaging agents was obtained. This work provides a possible effective strategy to improve the PL performance for impurity-doped lead-free metal halide perovskite.

In situ polyaniline coating of Prussian blue as cathode material for sodium-ion battery.

Prussian blue (PB) has great potential for use as a sodium cathode material owing to its high working potential and cube frame structure. Herein, this work reports a two-step method to synthesize PB with ascorbic acid as the ball-milling additive, which improves the electrochemical rate performance of PB during the traditional co-precipitation method. The obtained PB sample exhibited a superior specific capability (113.3 mAh g−1 even at 20 C, 1 C = 170 mA g−1) and a specific capacity retention of 84.8% after 100 cycles at 1 C rate. In order to enhance the cycling performance of the PB, an in situ polyaniline coating strategy was employed in which aniline was added into the electrolyte and polymerized under electrochemical conditions. The coated anode exhibited a high specific capacity retention of 62.7% after 500 cycles, which is significantly higher than that of the non-coated sample, which only remains 40.1% after 500 cycles. This development has shown a great potential as a low-cost, high-performance and environment-friendly technology for large-scale industrial application of PB.