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In-situ solid phase thermal transformation of self-assembled melamine phosphotungstates produce efficient visible light photocatalysts
摘要： Visible-light-driven stacked-layer heterogeneous photocatalyst carbonitride/tungstophosphate (TCN) was constructed via in-situ solid-state thermal transformation using melamine phosphotungstate (MPW). The structural, morphological and optical properties of the samples were investigated. Compared to the MPW hybrids and phosphotungstic acid hydrate, the TCN photocatalysts showed excellent visible light photocatalytic activity. During the thermal transformation, the melamine molecules polymerize to form the defective heptazine structure carbonitride attached to the surface of mixed-valence Keggin units. The interfacial POMs anions-p interactions, ligand-to-metal charge transfer and mix-valence organic-POMs structure makes the electrons fully delocalized over the MPW hybrids, and the TCN photocatalysts obtain the extended light absorption. The Keggin units accept and transfer electrons, so the recombination of photogenerated carriers is suppressed. 13TCN-390 obtains the optimal photocatalytic activity, its photocatalytic degradation efficiency of imidacloprid and rate constant k are 6.38 and 13.50 times than that of CN-390, respectively. The enhanced photocatalytic activity arises from the extended light absorption, suppressed photogenerated carriers’ recombination, surface structure defect and suitable band structure. h+ and (cid:1)OH are the main reactive species when the proposed photocatalytic mechanism was done. This study provides a promising construction strategy for polymer/POMs photocatalysts using different organic-POMs hybrids.
关键词： Melamine phosphotungstate,Visible-light-driven photocatalyst,Degradation,Thermal transformation
更新于2025-11-14 17:04:02
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Cu/Sb Codoping for Tuning Carrier Concentration and Thermoelectric Performance of GeTe-Based Alloys with Ultralow Lattice Thermal Conductivity
摘要： Pristine GeTe shows promising thermoelectric performance but is limited by the high carrier concentration (nH) from Ge vacancies and thermal conductivity. Herein, Cu/Sb was chosen as codopants to suppress the high nH and to decrease thermal conductivity. In this condition, a promising zT of ～1.62 under 773 K was acquired in the Ge0.85Te(CuSb)0.075 system proposed in this paper/work. Results show that as the dopant concentration increases, the power factor rises due to the reduction of the nH to ～1 × 1020 cm?3. Apart from this, the total thermal conductivity also declines from ～7.4 W m?1 K?1 to ～1.59 W m?1 K?1 originating from an ultralow lattice thermal conductivity, in which the multiscatter mechanism from grain boundaries and point defect disperses the frequency phonons di?erently. The ?ndings in this paper combine thermal and electronic strategies and lay the foundation to develop Pb-free thermoelectric materials.
关键词： multiscatter mechanism,Cu/Sb codoped GeTe,thermoelectric materials,ultralow lattice thermal conductivity,zT value,carrier concentration,Seebeck coefficient
更新于2025-11-14 17:03:37
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Improved negative thermal quenching effect via high sensitizer doping content in NaGdF4 based active-core/active-shell architecture
摘要： The strategies of introducing interior defects and reducing mean particle size have been applied to improve negative thermal quenching effect (TQE) in Yb3+ sensitized fluoride upconversion (UC) nanocrystals (NCs) recently. Herein, an active-core/active-shell structure with high total Yb3+ doping content is used to enhance the absorption intensity of Er3+ ions. Moreover, the Er3+ activators are doped into the shell to enable the energy migration process from activators to surface defects. In this scenario, with the rise of temperature, the suppression degree of this energy migration process is enlarged followed by an improved negative TQE. Specifically, with rising the temperature from 293 K to 413 K, the integral upconversion emission intensity of 40Yb: NaGdF4@60Yb/2Er: NaGdF4 NCs increases by ~ 8.24 times, while that of NaGdF4@20Yb/2Er: NaGdF4 NCs with a similar mean particle size only enhances ~ 3.44 times.
关键词： Yb3+ concentration,upconversion,temperature sensing,negative thermal quenching
更新于2025-11-14 17:03:37
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Polycrystal Synthesis, Crystal Growth, Structure, and Optical Properties of AgGaGe <sub/><i> <i>n</i> </i> </sub> S <sub/> 2( <i> <i>n</i> </i> +1) </sub> ( <i>n</i> = 2, 3, 4, and 5) Single Crystals for Mid-IR Laser Applications
摘要： AgGaGenS2(n+1) crystal is a series of quaternary for mid-IR laser applications of nonlinear optical materials converting a 1.064 μm pump signal (Nd:YAG laser) to 4?11 μm laser output, but only AgGaGeS4 has attracted the most attention, remaining the other promising AgGaGenS2(n+1) crystal whose physicochemical properties can be modulated by n value. In this work, AgGaGenS2(n+1) (n = 2, 3, 4, and 5) polycrystals are synthesized by vapor transport and mechanical oscillation method with di?erent cooling processes. High-resolution X-ray di?raction analysis and re?nement have revealed that all the four compounds are crystallized in the noncentrosymmetric orthorhombic space group Fdd2, resulting in the excellent nonlinear optical property, and the distortion of tetrahedron with the variation of n value causes the discrepancy of physicochemical property. Besides, using the modi?ed Bridgman method, AgGaGenS2(n+1) single crystals with 15 mm diameter and 20?40 mm length have been grown. We have discussed the structure and composition of AgGaGenS2(n+1) by XPS spectra and analyzed the three kinds of vibration modes of tetrahedral clusters by the Raman spectra. The Hall measurement indicates that the AgGaGenS2(n+1) single crystals are p-type semiconductor, and the carrier concentration decreases with the increasing n value. All the transmittances of as-grown AgGaGenS2(n+1) samples exceeds 60% in the transparent range, especially the transmittance of AgGaGe2S6, is up to 70% at 1064 nm, and the band gap of as-grown crystal increases from 2.85 eV for AgGaGe2S6 to 2.92 eV for AgGaGe5S12. After a thermal annealing treatment, the absorptions at 2.9, 4, and 10 μm have been eliminated, and the band gap changed into the range of 2.89?2.96 eV.
关键词： Hall measurement,nonlinear optical materials,thermal annealing treatment,vapor transport,AgGaGenS2(n+1),Bridgman method,Raman spectra,mid-IR laser applications,XPS spectra,mechanical oscillation method
更新于2025-11-14 15:27:09
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Synthesis, characterization, optical and electrochemical band gaps of green poly(azomethine-ester)s containing oxalyl and succinyl units
摘要： A new series of poly(azomethine-ester)s (PAZ-E)s with different (turning ortho, meta and para) positions were synthesized by condensation polymerization. The chemical structure of polymers was veri?ed by 1H-NMR, 13C-NMR, FTIR and UV–Vis measurements. Electrochemical characteristics of the corresponding polymers were obtained with cyclic voltammetric (CV) analysis. Thermal characteristics of the obtained polymers were analysed by TG-DTA, DMA and DSC measurements. The ?rst degradation temperature values of PAZ-E compounds were found between 198 and 250?C from TGA measurements. Photophysical characteristics of the obtained polymers were explained with photoluminescence (PL) spectroscopy. Molecular weight distributions of (PAZ-E)s were obtained by gel permeation chromatographic (GPC) analysis. Two- and three-dimensional (2D and 3D) properties and images of the synthesized (PAZ-E)s were analysed by SEM and AFM surface analysis techniques, respectively. Electrochemical band gap (E g) values of (PAZ-E)s P-9, P-10, P-11, P-12, P-13 and P-14 were calculated as 2.58, 2.14, 1.90, 2.06, 1.89 and 1.69 eV, respectively. The E g values of the (PAZ-E)s were found to be quite low.
关键词： surface morphologies,Poly(azomethine-ester),electrochemical properties,photophysical behaviour,schiff base,thermal degradation
更新于2025-11-14 15:26:12
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Aggregation-induced emission (AIE)-active highly emissive novel carbazole-based dyes with various solid-state fluorescence and reversible mechanofluorochromism characteristics
摘要： Three new carbazole-based fluorescent molecules 1-3 functionalized with tetraphenylethene have been successfully synthesized, and these compounds have high thermal stability, and they exhibited different fluorescence in solid states with the superior luminescence quantum yields of 99.04% (1), 98.90% (2) and 39.83% (3). Their aggregation-induced behaviors were explored by the study of photoluminescence spectroscopy. The results showed that luminogens 1-3 exhibited remarkable aggregation-induced emission effect. Furthermore, their distinct mechanical stimulus-responsive fluorescence characteristics were also surveyed by solid-state photoluminescence spectroscopy. Interestingly, the various emitting colors of these luminogens could be changed into the same green, and the repeatabilities of their mechanochromic luminescence behaviors were outstanding, and the powder X-ray diffraction results indicated that the reversible conversion from a crystalline to an amorphous state was responsible for the obvious mechanofluorochromism phenomena of compounds 1-3. This work will be valuable for the exploitation of mechanical-force sensors with typical aggregation-induced emission feature.
关键词： Carbazole,Mechanofluorochromism,Tetraphenylethene,Aggregation-induced emission,Different fluorescence,High thermal stability
更新于2025-11-14 15:23:50
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Synthesis of luminescent polymers in the UV light region from dimethacrylate monomer using novel quinoline dyes
摘要： This study aims at thermal and morphological features, as well as the degree of conversion these luminescent polymers obtained using a dimethacrylate monomer, and quinoline dyes as photoinitiator. The photoinitiators provide a ?uorescent propriety to the ?nal polymer. Thermal properties such as thermal stability, steps of mass loss, and glass transition are obtained by thermogravimetry-differential thermal analysis and derivative thermogravimetric and differential scanning calorimetry. Using the mid-infrared spectroscopy, it is possible to calculate the degree of conversion/rate of polymerization; the data indicate that the quinoline derivatives could be used as photoinitiators in lower concentration (0.1%) resulting in solid rigid polymers with higher conversion (74.24, 71.81, 66.36, and 61.09%). The morphological characteristics of polymers are analyzed by scanning electronic microscopy. Finally, solid ultraviolet–visible (UV–vis) analysis shows a bathochromic shift, due to the stabilization of the molecules in the solid state, compared to liquid UV–vis analysis. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47461.
关键词： thermal analysis,quinoline dyes,photopolymerization,luminescent polymers,high conversion
更新于2025-11-14 15:18:02
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Performance optimization of bi-layer solar steam generation system through tuning porosity of bottom layer
摘要： In recent years, solar steam generation has attracted many attentions due to its potential applications in desalination, etc. In the present work, a bi-layer solar steam generation system is prepared by daubing carbon particles on the sintered sawdust film, which possesses an advantage of adjustable porosities compared to widely used wood. Then, the influence of the porosity on the evaporation performance is explored. The experimental result indicates that: the porosity could significantly affect the water transportation in the film, and the water diffusivity increases almost linearly with the increase of the porosity. The evaporation efficiency increases with the increasing porosity, until the porosity reaches about 0.52 then decrease slowly. The positive effect of the increased water diffusivity and the negative effect of the increased thermal conductivity of the bottom film layer determine that the porosity of 0.52 is optimal for improving the evaporation efficiency. Under a solar light power of 1 kW·m?2, the optimal porosity gives an evaporation efficiency of 77.64%, which is comparable to the best performance of bi-layer systems reported in previous works. The conduction of heat through the bottom layer to the bulk water and the convection heat loss on the top surface contribute 83% to the total heat losses in the system, suggesting that the energy losses of these two modes should be further reduced in the future applications. Considering the accessible materials, easy preparation, low cost and high efficiency, we conclude that the 0.52-porosity system is suitable for being used as an efficient solar steam generation device.
关键词： Solar steam generation,Thermal conductivity,Solar energy,Porous material
更新于2025-11-14 15:14:40
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A novel orange–red emitting phosphor Sr2LuTaO6:Sm3+ for WLEDs
摘要： A novel double perovskite tantalite orange–red light emitting Sr2LuTaO6:Sm3+ phosphor was synthesized by the solid state reaction. The phase, crystal structure, photoluminescence properties, thermal stability and decay curves were studied. The X-ray diffraction patterns indicated that the phosphor has a pure phase of cubic phase structure. Excited by near-ultraviolet light at 407 nm, the sample exhibited three sharp emission peaks at 564 nm, 600 nm, 645 nm corresponding to the 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, respectively. The optimum doping concentration of Sm3+ ions was determined to be 5 mol% and the concentration quenching process comes from the energy transfer among nearest-neighbor ions. The as-prepared phosphors showed excellent thermal stability, the integral intensity at 423 K is about 91.10% of the initial intensity. The CIE chromaticity coordinates of Sr2LuTaO6:Sm3+ phosphors located in orange–red region. The results suggest that Sr2LuTaO6:Sm3+ phosphors have great potential application in white light-emitting diodes.
关键词： luminescence,thermal stability,white light-emitting diodes,Sr2LuTaO6:Sm3+,phosphor
更新于2025-11-14 15:13:28
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Revealing the correlation between molecular structure and dielectric properties of carbonyl‐containing polyimide dielectrics
摘要： Polymer dielectrics with outstanding heat resistance and advanced dielectric properties are of great importance for high-temperature capacitors in the applications of hostile circumstances. In this work, a series of aromatic carbonyl-containing polyimides (CPI) are prepared from the carbonyl dianhydride and different diamines. The correlation between molecular structure (i.e., different linked structure ( O , CH2 , SO2 ) in diamines, the length of repeating unit and the linked position (para-para or meta-meta), and properties is revealed in detail to obtain CPI dielectrics with excellent thermal resistance (glass transition temperature, Tg: 241~352°C), reasonably high dielectric constant (3.99~5.23), low dissipation factor (0.00307~0.00395), and admirable breakdown strength (425~552 MV/m) simultaneously. Particularly, CPI-5 with carbonyl structure in dianhydride and sulfonyl group in diamine proves to exhibit discharged energy density and charge–discharge efficiency of 6.34 J/cm3 and 92.3% at 500 MV/m, respectively. In addition, CPI-5 also displays stable dielectric properties in temperature range of ?50?200°C. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47883.
关键词： dielectric properties,films,thermal properties,polyimides
更新于2025-11-14 14:48:53