Preparation Process Research Articles

Research on aliphatic resin-reinforced bamboo spun fiber bundles based on optimal twisting process

Bamboo, recognized as a sustainable material with remarkable properties, has found extensive application in the textile industry. This paper presents the findings of an investigation into the mechanical properties of twisted bamboo spun fiber bundles. The bundles were produced through the delignification and thinning of moso bamboo, followed by twisting in both the Z-direction and the S-direction, with varying twisting angles as experimental variables. The results indicated that the mechanical properties of the bamboo spun fiber bundle, produced under a single-strand Z-twist direction with a 20° twist angle, were optimal. These properties included the highest tensile strength of 154.25 MPa, a low modulus of elasticity, and a high elongation at break of 6.9 %, which represented superior preparation parameters. To enhance the bamboo spun fiber bundles during the preparation process—particularly because they tend to absorb moisture easily and disintegrate due to the removal of some lignin—a mixture of aliphatic epoxy resin and amine curing agents is employed. Following resin impregnation, both the expansion rate and orientation of the bamboo spun fiber bundles demonstrated a reduction compared to the unimpregnated one. The epoxy resin conferred dimensional stability and flexibility to the fiber bundles. Additionally, compared with those without impregnation, resin-impregnated bamboo spun fiber bundles resulted in a strength increase of 6.81 %, an enhancement in elongation at break of 9.79 %, a reduction in modulus of 2.67 %, a small plastic deformation of 13.96 % under cyclic loading, and a decrease in performance of only 3.5 % after high-temperature light ageing. This material demonstrated improved strength, toughness, and durability, aligning more closely with the requirements for textile fiber raw materials. The findings of this study refine processing parameters and broaden the application of bamboo spun fiber bundles in home furnishings and decorative contexts.

Facile synthesis of hierarchically porous carbon monolith without templating agent for various applications in energy and catalysis

Monolithic carbon with hierarchically porous structure has a promising prospect for a wide range of applications in the fields of energy, environment, catalysis, etc. Due to the reliance on the utilization of templating agents, conventional preparation approaches often suffer from time-consuming preparation, complex post-processing, and uneconomical cost. Herein, we develop a novel strategy to match the sol-gel transition with the phase separation process for the direct preparation of hierarchically porous carbon monolith (HPCM) without templating agent. Resorcinol and resol are employed as carbon sources to adjust the polymerization for the formation of bi-continuous microstructure. Well-defined hierarchical pores and large specific surface area for fast mass diffusion enable the HPCM to be a prospective kind of electrode material in supercapacitor with an outstanding specific capacitance over 350 F g−1 (1.0 A g−1). After facile sulfonation, the modified HPCM can act as solid acid catalyst to realize a high-performance production of 5-hydroxymethylfurfural (5-HMF) in a 90 % yield with turnover frequency (TOF) value up to 155.9 h−1. Additionally, HPCM also exhibits an excellent Joule heating effect, which can be applied to the thermal management after compounding with phase change materials. The desirable integrated performance enables HPCM to be a valuable material suitable for various applications.

Spatial Memory of Notable Hurricane Tracks and Their Geophysical Hazards

Previous research has shown that people use a benchmark hurricane as part of their preparation and evacuation decision-making process. While hurricanes are a common occurrence along the Gulf Coast, research on personal memories of past storms is lacking. Particularly, how well do people remember the track and geophysical hazards (wind speed, storm surge, and total rainfall) of past storms? The accurate or inaccurate recollection and perception of previous storm details can influence personal responses to future storms, such as the decision to evacuate or take other life-saving actions. Survey responses of residents in Alabama and Mississippi were studied to determine if people were accurately able to recall a notable storm’s name when seeing an image of the storm’s track. Those who were able to identify the storm by its track were also asked if they could remember the storm’s maximum reported rainfall, maximum sustained winds, and storm surge at landfall. Results showed that there were statistically significant differences between the levels of accurate recall for different storms, with Hurricanes Katrina and Michael having the most correct responses. Regardless of the storm, most people struggled to remember geophysical hazards. The results of this study are important as they can inform broadcast meteorologists and emergency managers on forecast elements of the storm to better emphasize in future communication in comparison to the actual values from historical benchmark storms.

Immobilized high-performance heparin lyase III for efficient preparation of low molecular weight heparin

Heparin lyase III has garnered widespread attention due to its high specificity and minimal loss of anticoagulant activity during the preparation of low molecular weight heparin (LMWH), a crucial anticoagulant drug in clinical practice. However, low expression levels and complex preparation processes limit its practical application. To address these challenges, high-performance Bacteroides thetaiotaomicron heparin lyase III (Bhep III) variants were engineered and immobilized for LMWH preparation. First, we enhanced enzyme expression by adding a solubility-enhancing tag and optimizing the N-terminal coding sequence, which resulted in a Bhep III activity level of 2.9 × 103 U/L with 8-fold increase. After evolution guided the design of rational mutations, the variant Bhep III K85A/Q95F/S471T generated higher activity (5.4 × 104 U/L in 5-L fermenter), which is, to our knowledge, the highest reported to date in the literature, being 1.7-fold that of the wild type and demonstrating 2-fold increase of the thermal stability. By screening and optimizing the C-terminal self-assembling tag, we successfully immobilized Bhep III, further increasing its thermal stability by 12-fold, and allowing for the multi-batch preparation of LMWH with simple centrifugation. The immobilized heparin lyase III demonstrated sufficient reusability in enzymatic reactions, facilitating efficient industrial-scale production of LMWH.

The Effect of the Number of Precursor Spin-Coating on the Properties of Sb<sub>2</sub>(S,Se)<sub>3</sub> Thin Film

Preparing of Sb2S3 precursor by sol gel method and the post selenization is a simple and low-cost method for preparing Sb2(S, Se)3. In the preparation process of this method, the number of spin-coating of Sb2S3 precursor determines the film thickness, structure, and S/Se ratio. In this work, the effects of different spin-coating times (1 to 5) on the structure, optical and electrical properties of the film were studied. The results showed that when the number of spin-coating increased from 1 to 5, the thickness of the film increased from 0.24 μm to 1.17 μm. When spin-coating twice, the strongest diffraction peak of the film changed from (120) to (230); as the spin-coating frequency continued to increase, the film gradually exhibited Sb2S3 characteristics, accompanied by a small amount of Sb2O3 impurities. In addition, excessive spin-coating cycles can cause large voids to appear on the surface of the film. From the UV-visible spectrum, it can be seen that as the thickness of the film increases, the light absorption also gradually improve, and the band gap increases from 1.34 eV to 1.66 eV. The Mott-Schottky test showed that the prepared thin films were all P-type semiconductor. When spin-coated twice, the carrier concentration of the thin film reached 5.8×1015cm-3.

Optimization of pore structure and surface chemical properties of activated carbon fiber via liquid-phase stabilization for enhanced supercapacitor performance

Stabilization is a crucial factor influencing both the structure and properties of pitch-based activated carbon fiber (PACF). The traditional air stabilization not only requires a high softening point of precursor but also consumes a considerable amount of time and energy. In this study, liquid-phase stabilization was employed to streamline the preparation process, and its influence on resultant PACF was investigated. The oxidation stabilization process is fully conducted in just 1 h through liquid-phase stabilization. The obtained N-doped pitch-based activated carbon fiber (NPACF) possessed higher specific surface area and higher nitrogen content (3.77 wt%) compared to PACF obtained by air oxidization. The specific capacitance of NPACF electrode attained 325 F/g at 0.5 A/g. The device based on two equal NPACF electrodes exhibited a specific capacitance of 222 F/g at 0.5 A/g, an energy density of 7.6 Wh/kg at 248 W/kg, and excellent cycle stability of 92.0 % after 10,000 cycles.

Investigation of the regulatory mechanism of monolayer colloidal crystals prepared by gas-liquid-solid three-phase interfacial self-assembly method

In recent years, the gas-liquid interface self-assembly method has emerged as a recognized and efficient technique for preparing two-dimensional monolayer colloidal crystals. However, challenges such as limited preparation area, dependence on complex equipment, and high costs persist in the conventional preparation process. This paper proposes a straightforward, rapid, and cost-effective method to implement a gas-liquid-solid three-phase interfacial self-assembly strategy. This approach enhances the gas-liquid interfacial self-assembly method, allowing for the preparation of large-area, high-quality single-layer colloidal crystals (>10 cm2) without using any surfactant. The gas-liquid-solid three-phase interfacial self-assembly process was analyzed in detail, and it was found that the main factors affecting the quality of the monolayer colloidal crystals were the volume ratio of PS colloidal solution to ethanol and the self-assembly temperature. It was shown that the optimal self-assembly conditions were achieved after dispersion by ultrasonic dispersion in a water bath at 32 °C–30 °C at a volume ratio of 1:2.5 of PS colloidal solution to ethanol. In addition, particles of various sizes can be prepared by this method to produce tightly arranged monolayer films that can be transferred to a variety of different substrates with great versatility. The demonstrated efficiency of this self-assembly method underscores its significant potential for application in large-scale manufacturing and practical industrialization.

Repeated lyophilization: A neo-method for urine-based reference materials preparation

In urine drug testing, a cut-off value is often imposed to determine whether the sample is negative or positive. A matrix containing a reference substance helps counteract the adverse effects of the urine matrix across different laboratories to improve the consistency of final results. However, as a biological matrix, urine is prone to corruption and other problems that make it difficult to use as a reference sample. In this study, morphine, nitrazepam, lorazepam, buprenorphine, zolpidem, midazolam, diazepam, and clozapine commonly used in clinical practice were selected as target analytes, and the preparation process was further optimized to repeated lyophilization, in order to obtain more effective, stable, and accurate urine matrix reference materials (mRMs). The appropriate urine density (1.010–1.017 kg/m3) for preparing lyophilized samples was investigated through density determination. Conducting repeated lyophilizations resulted in a denser powder with reduced susceptibility to collapse and improved the quality of lyophilized urine samples. Lyophilized urine mRMs could be stored at room temperature for one month or under refrigeration conditions (4 ℃) for six months.

A novel diglycosidase for the transformation of naringin to naringenin and neohesperidose

A novel fungal diglycosidase that transforms naringin into naringenin and neohesperidose, a rare biotransformation, has been purified to homogeneity using a simple procedure involving precipitation of the enzyme from the culture filtrate of the fungal strain using 80 % saturation of ammonium sulphate, dissolving the precipitate in minimum volume of the buffer and dialysing that against the buffer. The purified enzyme gives single protein bands of molecular mass 64.6 kDa in SDS-PAGE analysis. The purity of the enzyme has been further confirmed by the appearance of single protein band in native page analysis. Using naringin as the substrate, the diglycosidase has Km and kcat values of 0.20 m mol L−1 and 0.66 s−1, respectively, at pH 4.0 and 313 K. The specific activity of the purified enzyme using naringin as the natural substrate is 1.018 katal/kg. The diglycosidase also transforms rutin into quercetin and rutinose but has no effect on hesperidin. The feasibilities of preparing neohesperidose from naringin and rutinose from rutin on milligram scales using the pure enzyme have been demonstrated. These results open the way for developing an enzymatic process for preparation of neohesperidose from naringin. The reported diglycosidase has immense future applications in food and pharmaceutical industries.

Forming performance and environmental impact of bamboo fiber reinforced polypropylene composites based on injection molding process for automobiles

AbstractTo explore the potential application of plant fiber reinforced composites for automotive component applications, this study prepared bamboo fiber (BF)/nano‐talc/polypropylene (PP) composites based on the injection molding process, comprehensively evaluated the effect of reinforcement materials on the forming properties of composites, including thermal performance, mechanical properties, water absorption, etc. Furthermore, taking a certain automotive injection molded interior part as the object, a life‐cycle assessment from production to the gate was conducted based on the real energy and material consumption during the composite preparation process. The results indicate that adding BF and talc powder increased the thermal stability, density, hardness, viscosity, and crystallinity of the composites while reducing the water contact angle on the surface. Surface‐modified BF and PP showed good compatibility. Talc powder exhibited good dispersibility in PP, and the synergistic effect of BF and talc powder effectively enhanced the composite performance. The tensile, flexural, and impact strength of the composites were improved by 40.64%, 51.48%, and 66.51%, respectively, compared with pure PP. The modulus of the composite increased nearly 2 times compared with pure PP. Additionally, the composite demonstrated good friction and wear properties. The environmental impact of the BF composite manufacturing process was significantly higher than that of pure PP. The substantial consumption of electricity, chemicals, and water resources in the extraction and modification processes of BF were the main factors. The findings of this study contribute to achieving green, high‐performance BF composite manufacturing and the expansion of its applications.Highlights Composites have a higher environmental impact compared to PP. BF and talc can synergistically enhance the performance of composites. BF shows good compatibility with PP. Composites exhibit good friction and wear characteristics.

Preparation, Evaluation, and Bioinformatics Study of Hyaluronic Acid-Modified Ginsenoside Rb1 Self-Assembled Nanoparticles for Treating Cardiovascular Diseases.

(1) Objective: To optimize the preparation process of hyaluronic acid-modified ginsenoside Rb1 self-assembled nanoparticles (HA@GRb1@CS NPs), characterize and evaluate them in vitro, and investigate the mechanism of action of HA@GRb1@CS NPs in treating cardiovascular diseases (CVDs) associated with inflammation and oxidative stress. (2) Methods: The optimal preparation process was screened through Plackett-Burman and Box-Behnken designs. Physical characterization of HA@GRb1@CS NPs was conducted using transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. Stability experiments, in vitro drug release studies, and lyophilisate selection were performed to evaluate the in vitro performance of HA@GRb1@CS NPs. The anti-inflammatory and antioxidant capabilities of HA@GRb1@CS NPs were assessed using H9c2 and RAW264.7 cells. Additionally, bioinformatics tools were employed to explore the mechanism of action of HA@GRb1@CS NPs in the treatment of CVDs associated with inflammation and oxidative stress. (3) Results: The optimal preparation process for HA@GRb1@CS NPs was achieved with a CS concentration of 2 mg/mL, a TPP concentration of 2.3 mg/mL, and a CS to TPP mass concentration ratio of 1.5:1, resulting in a particle size of 126.4 nm, a zeta potential of 36.8 mV, and a PDI of 0.243. Characterization studies confirmed successful encapsulation of the drug within the carrier, indicating successful preparation of HA@GRb1@CS NPs. In vitro evaluations demonstrated that HA@GRb1@CS NPs exhibited sustained-release effects, leading to reduced MDA (Malondialdehyde) content and increased SOD (Superoxide Dismutase) content in oxidatively damaged H9c2 cells. Furthermore, it showed enhanced DPPH (2,2-Diphenyl-1-picrylhydrazyl) and ABTS+ [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] free radical scavenging rates and inhibited the release of inflammatory factors NO (Nitric Oxide) and IL-6 (Interleukin-6) from RAW264.7 cells. (4) Conclusions: The HA@GRb1@CS NPs prepared in this study exhibit favorable properties with stable quality and significant anti-inflammatory and antioxidant capabilities. The mechanisms underlying their therapeutic effects on CVDs may involve targeting STAT3, JUN, EGFR, CASP3, and other pathways regulating cell apoptosis, autophagy, anti-lipid, and arterial sclerosis signaling pathways.

A Python toolkit for integrating geographic information system into regulatory dispersion models for refined pollution modeling

AERMOD is designated as U.S. Environmental Protection Agency (EPA)'s preferred air dispersion model for refined transportation project hot-spot analyses beginning in 2020. One of the key challenges in its modeling process is spatially encoding roadway geometry, especially when simulating highways with complex geometric designs. This research proposed an open-source Python package, GTA, which enables conversion of publicly available roadway Geographic Information System (GIS) layers into defined sources, and source-based emission rates from MOtor Vehicle Emissions Simulator (MOVES) output for AERMOD modeling. The research selected a suburban area in Atlanta, and conducted a comprehensive analysis in terms of annual PM2.5 concentration results and the speed of preparing AERMOD input files for highway network modeling both manually and using software developed based on the proposed methodology. The results prove that the proposed methodology significantly expedites the AERMOD input preparation process, and facilitates convenient testing of multiple modeling configurations for multi-scenario or sensitivity analysis.

Targeted construction of porous biochar with well-developed pore structure for high-performance CO2 adsorption

Targeted construction of porous biochar is vital for the development of carbon capture. In this paper, we use the KOH chemical activation with walnut shell as raw material, to investigate the effects of the preparation process on the targeted construction of CO2 adsorbents. We have revealed the vital factors influencing CO2 adsorption and developed the design strategy for porous biochar under different application conditions. The specific surface area can up to 2115 m2 g−1, and the microporosity can up to 95.5 %. The CO2 adsorption capacities are 6.75 mmol g−1 and 17.59 mmol g−1 at 0°C, 1 bar and 10 bar. Meanwhile, the heat of adsorption ranges from 18 to 30 kJ mol−1. In addition, the sample exhibits outstanding adsorption kinetics, good adsorption selectivity, and its CO2 adsorption capacity fluctuates within 5 % after 10 adsorption-desorption cycles. Therefore, the strategy developed in this paper can be applied to the high-performance adsorption of CO2 under different conditions.

Development of a multifunctional bio-based insulation material with corncob and silica aerogel

Bio-based insulation materials with superior comprehensive properties are crucial to building energy conservation. This study aims to develop a multifunctional bio-based insulation material that integrates good insulation, mechanical strength, and waterproofing. In this work, using corncob as the raw material, foamed geopolymer as the binder, silica aerogel and silicone oil as additives, a novel bio-based insulation material was prepared. Moreover, the effect of corncob size, silica aerogel content and silicone oil content on the microstructure, density, thermal conductivity, compressive strength, water absorption, moisture absorption and water contact angle properties were discussed. The results showed that, a desirable bio-based insulation material with a corncob size of 20 mesh, silica aerogel/geopolymer mass ratio (A/G) being 1.71 %, silica aerogel/ silicone oil mass ratio (A/O) being 0.2, is recommended, of which the thermal conductivity is 0.111 W/(m.K) with the compressive strength being 2.2 MPa, the density being 350 kg/m3, the water absorption being 7.1 %, the moisture absorption being 9.4 % and the water contact angle being 133°. With a simple preparation process, low cost and low energy consumption, this bio-based insulation material has good application prospects in buildings. Meanwhile, the preparation method of bio-based insulation materials proposed in this study provides new ideas for the development of multifunctional insulation materials in the future.

Exploring the Influence of Food Culture Attributes on Visitor Satisfaction and Motivations at Food Festivals

This study examines the impact of food culture aspects such as taste, display, and preparation process on visitor satisfaction and motivation during food festivals. Data from 150 participants were analyzed utilizing SPSS 25 for data analysis. The study uses Spearman's Rank Correlation, Confirmatory Factor Analysis (CFA), and Chi-Square testing to investigate how these characteristics influence festival experiences. Significant positive correlations were found using Spearman's Rank Correlation, taste had a strong correlation with visitor satisfaction (ρ = 0.65,p = 0.01) and motivation (ρ = 0.60,p = 0.02), while display also had a moderately positive correlation with both (ρ = 0.55,p = 0.05) satisfaction and motivation (ρ = 0.50,p = 0.04). The association for the preparation process, however, was not statistically significant and was much weaker. It was established that CFA had high dependability with estimates of 0.78 for taste, 0.85 for display, and 0.80 for the preparation procedure, all of which met high CR and AVE values. The relationships between aspects of food culture and visitor outcomes were evaluated using the Chi-Square Test. Taste was found to have significant correlations with motivation (χ² = 10.45, p = 0.05) and satisfaction. While the display was only significantly connected with satisfaction (χ² = 7.89, p = 0.10), the preparation process was strongly associated with satisfaction (χ² = 12.34, p = 0.03). These results emphasize how important taste is to improving visitor experiences and show how particular characteristics of food cultures can affect festivalgoers' motivation and level of satisfaction. The study found that taste has a substantial impact on both satisfaction and motivation, emphasizing its importance for good event planning and increased attendee involvement.

Study on the surface performance strengthening of AlCrN coated cemented carbide by micro-texture laser preparation process

The combined application of coating and surface texture technology on the material surface can enhance its performance. However, the two procedure and their joint mechanism have not been fully revealed. Therefore, this paper takes the micro-textured coated cemented carbide as the research object, and focuses on the influence of preparation procedure and process parameters on surface characteristics and friction behavior. The results show that compared with the coating textured (XT) sample, the textured coating (XW) sample has more advantages in micro-hardness, microstructure and wear degree. The Rockwell hardness of the XT sample is better. Compared with the single coating sample, the coating micro-hardness of the XW sample is increased by 10 %, the Rockwell hardness is reduced by 2 %, the average grain size is reduced by 7.9 %, and the friction force is reduced by 6.2 %. Additionally, within a certain range, the increase of Al content will increase the sample hardness, reduce friction, and inhibit the Cr content and the growth of CrN phase grains. Complete process parameter optimization based on the ideal solution.

Synergic process of molybdenum recovery and ceramic preparation for clean and efficient utilization of industrial leaching residues

Ammonia-leaching residues of roasted molybdenite concentrates are intractable wastes and are mostly stockpiled in factories. Common treatments suffer from low Mo recovery and secondary pollution. This study has developed a synergistic process involving a single-step roasting with the addition of Al2O3 and MoO3 to recover Mo and simultaneously prepare porous refractories from the residues containing 5.6% Mo. The Mo separation efficiency, ceramic properties, and thermal behaviors—including chemical reactions, melting transformations, ceramic structure evolutions, and Mo species migrations—were comprehensively investigated. It was found that the addition of Al2O3 facilitated CaMoO4 decomposition to release volatile MoO3, thus promoting Mo recovery. The mullite started to form at about 900 °C, grew into whiskers, and further into interconnected clusters, under the catalytic effect of liquid MoO3 and the sintering effect of glassy melt. Liquid MoO3 was scattered on the outer surface of whisker clusters, achieving a high separation efficiency of over 98% after roasting at 1300 °C for 150 min. Meanwhile, a ceramic with a high porosity of 64.2% and a high compressive strength of 21.2 MPa was obtained, exhibiting promise for serving as a high-temperature insulation refractory. Overall, this study presents a novel approach for both the profound recovery of Mo and the value-added utilization of gangue minerals derived from CaMoO4-bearing wastes.

Supercritical CO2-promoted degradation of polystyrene to aromatic oils with NiO@C catalyst

Exploring new system for chemical recycling of plastic is an effective way to convert plastic waste into energy. Herein, the use of supercritical CO2 (ScCO2) to promote the catalytic degradation of polystyrene (PS) with high yield of aromatic oils was proposed. ScCO2 provided a homogeneous environment for the reaction, which not only facilitated the swelling of PS, but also inhibited the formation of coke, beneficial for the degradation of PS to aromatic oils. In addition, CO2 as an oxidant reacted with PS or intermediates to generate new products. NiO@C catalyst prepared by doping carbon material in NiO had a simple preparation process, an abundance of porous structure and strong acidic sites, thus improving the catalytic activity. Under the co-action of ScCO2 and NiO@C, the yield of aromatic oils produced from PS was up to 89.3 ± 0.6 wt% at 300 °C with a reaction time of 2 h and a catalyst loading amount of 10 wt%. Moreover, the NiO@C catalyst was used for three cycles without obvious change in the catalytic performance. The efficient catalytic degradation of PS to aromatic oils by ScCO2 promoted NiO@C catalysis provides a potential route for simultaneously recycling plastic and sequestering carbon.

3D‐Shape Recoverable Hydrogel with Highly Efficient Water Transport for Solar Water Desalination

AbstractPorous hydrogels have been developed to be highly efficient interfacial solar vapor generation materials for obtaining affordable freshwater supplies. However, realizing hydrogel materials with portability, adequate water supply, and durable mechanical properties remains challenging. Herein, a scalable and portable hydrogel with 3D‐shaped recovery, highly efficient water transport, and robust mechanical stability is reported, which is prepared by foaming polyvinyl alcohol (PVA) and modification of phosphotungstic acid (PTA). Due to the interconnected porous structure and highly permeable polymer network, the PVA/PTA‐PH hydrogel has good repetitive compressibility and rapid shape recovery when in contact with water. Combined with light‐absorbing nanoparticles, the PVA/PTA‐PH hydrogel presents an impressive solar evaporation rate of 3.876 kg m−2 h−1 and a photothermal conversion efficiency of ≈94% under 1‐sun irradiation. With 3D‐shape recovery and highly efficient water transport, the compressed hydrogel can be quickly unfolded without human intervention and restored to five times the original size for the working state. The good portability, excellent seawater desalination performance, and simple preparation process are anticipated to make the PVA‐/PTA‐PH hydrogel a promising material to continuously and conveniently produce pure water from seawater.

A red-emitting phosphor Na3AlF6:Mn4+: Green synthesis, optical characteristics, thermal stability and application in high-performance warm WLED

Mn4+-doped fluoride red phosphors have been widely used in warm WLEDs, but the preparation of such phosphor requires the use of a large amount of HF as a fluorine source and an acidic environment. How to reduce the excessive use of highly toxic HF in the preparation process and achieve green synthesis has become a hot research topic. Therefore, a simple green synthesis strategy is proposed in this work to synthesize a series of red-emitting phosphors Na3AlF6:Mn4+. The highly toxic HF solution is replaced by using a low toxicity reaction system (HCl/HNO3 + NH4F), which reduces the direct use of HF. X-ray powder diffraction, energy-dispersive X-ray spectrometer and scanning electron microscope are employed to determine the crystal structure, composition and morphology of all samples. Optical properties are characterized using excitation spectra, emission spectra and fluorescence lifetime curves. The calculation results indicate that the red-light has low correlated color temperature and the excellent color purity, and Na3AlF6 host can provide a strong crystal field environment for Mn4+. In addition, different aluminum sources and Mn4+ doping concentrations are used to explore the optimal preparation condition. The mechanisms of concentration quenching and thermal quenching have also been systematically explored. The stabilities of red-light emission intensity and color are investigated under the high temperature. The integral PL intensity at 423 K is 47 % of the initial value at 298 K. The activation energy, the chromaticity shift and the chromaticity coordinate variation are also systematically calculated. More importantly, a high-performance warm WLED with low correlated color temperature (CCT = 3296 K) and high color rendering index (Ra = 94.7) is achieved by using Na3AlF6:Mn4+ as a red-emitting material. Not only that, the warm WLED exhibits strong output stability under high driving current. The discovery of this work provides a comprehensive understanding for the rational design of high-performance Mn4+-activated fluoride red phosphors via a simple green synthesis strategy.