SrTiO3/TiO2 heterostructure nanowires with enhanced electron--hole separation for efficient photocatalytic activity

Heterostructure is an effective strategy to facilitate the charge carrier separation and promote the photocatalytic performance. In this paper, uniform SrTiO₃ nanocubes were in-situ grown on TiO₂ nanowires to construct heterojunctions. The composites were prepared by a facile alkaline hydrothermal method and an in-situ deposition method. The obtained SrTiO₃/TiO₂ exhibits much better photocatalytic activity than those of pure TiO₂ nanowires and commercial TiO₂ (P25) evaluated by photocatalytic water splitting and decomposition of Rhodamine B (RB). The hydrogen generation rate of SrTiO₃/TiO₂ nanowires could reach 111.26 mmol·g⁻¹·h⁻¹ at room temperature, much better than those of pure TiO₂ nanowires (44.18 mmol·g⁻¹·h⁻¹) and P25 (35.77 mmol·g⁻¹·h⁻¹). The RB decomposition rate of SrTiO₃/TiO₂ is 7.2 times of P25 and 2.4 times of pure TiO₂ nanowires. The photocatalytic activity increases initially and then decreases with the rising content of SrTiO₃, suggesting an optimum SrTiO₃/TiO₂ ratio that can further enhance the catalytic activity. The improved photocatalytic activity of SrTiO₃/TiO₂ is principally attributed to the enhanced charge separation deriving from the SrTiO₃/TiO₂ heterojunction.     

Facile solvothermal synthesis of NiFe2O4 nanoparticles for high-performance supercapacitor applications

We report a green and facile approach for the synthesis of NiFe₂O₄ (NF) nanoparticles with good crystallinity. The prepared materials are studied by various techniques in order to know their phase structure, crystallinity, morphology and elemental state. The BET analysis revealed a high surface area of 80.0 m²·g⁻¹ for NF possessing a high pore volume of 0.54 cm³·g⁻¹, also contributing to the amelioration of the electrochemical performance. The NF sample is studied for its application in supercapacitors in an aqueous 2 mol·L⁻¹ KOH electrolyte. Electrochemical properties are studied both in the three-electrode method and in a symmetrical supercapacitor cell. Results show a high specific capacitance of 478.0 F·g⁻¹ from the CV curve at an applied scan rate of 5 mV·s⁻¹ and 368.0 F·g⁻¹ from the GCD analysis at a current density of 1 A·g⁻¹ for the NF electrode. Further, the material exhibited an 88% retention of its specific capacitance after continuous 10000 cycles at a higher applied current density of 8 A·g⁻¹. These encouraging properties of NF nanoparticles suggest the practical applicability in high-performance supercapacitors.     

Microwave hydrothermal synthesis of WO3(H2O)0.333/CdS nanocomposites for efficient visible-light photocatalytic hydrogen evolution

WO₃(H₂O)_0.333/CdS (WS) nanocomposites are obtained via a rapid microwave hydrothermal method, and they are served as visible light-driven photocatalysts for the H₂ generation. By using Pt as the cocatalyst, the WS nanocomposite with 70 wt.% CdS reaches the H₂ evolution rate of 10.32 mmol·g⁻¹·h⁻¹, much quicker than those of WO₃(H₂O)_0.333 and CdS. The cycling test reveals the good photocatalytic stability of the WS nanocomposite. The carrier transfer mechanism of WS nanocomposites can be explained by the Z-scheme mechanism. The existence of the Z-scheme heterojunction greatly helps to separate photogenerated carriers and thus improves the photocatalytic activity. The present work provides a rapid synthesis method for preparing Z-scheme heterojunction photocatalysts, and may be helpful for the green production of hydrogen.     

Preparation and thermal properties of layered porous carbon nanotube/epoxy resin composite films

A floating-catalyst spray pyrolysis method was used to synthesize carbon nanotube (CNT) thin films. With the use of ammonium chloride as a pore-former and epoxy resin (EP) as an adhesive, CNT/EP composite films with a porous structure were prepared through the post-heat treatment. These films have excellent thermal insulation (0.029--0.048 W·m⁻¹·K⁻¹) at the thickness direction as well as a good thermal conductivity (40--60 W·m⁻¹·K⁻¹) in the film plane. This study provides a new film material for thermal control systems that demand a good thermal conductivity in the plane but outstanding thermal insulation at the thickness direction.     

Mo--V--Nb--O-based catalysts for low-temperature selective oxidation of Cα--OH lignin model compounds

Mo–V–Nb tri-component oxide catalysts were prepared and firstly used for the selective oxidation of C_α−OH lignin compounds. The catalytic performance of the composite oxides was obviously enhanced due to the synergistic effects of Mo and V elements. Mo_5−xV_xO₁₄ phase with a variable Mo/V ratio provided suitable active sites for the oxidative dehydrogenation (ODH) of C_α−OH lignin model compound. The optimized Mo–V–Nb molar composition was confirmed as Mo_0.61V_0.31Nb_0.08O_x/TiO₂, which exhibited the prominent catalytic activity with the turnover frequency of 1.04×10⁻³ mmol· g(cat)⁻¹·s⁻¹. Even at room temperature, the catalysts showed highly-efficient ODH reaction activities. The active phase for selective oxidation reaction and the inhibiting effect of α-MoO₃ phase were also discussed in the study.     

Controlled synthesis of Pt-loaded yolk–shell TiO2@SiO2 nanoreactors as effective photocatalysts for hydrogen generation

Yolk–shell and hollow structures are powerful platforms for controlled release, confined nanocatalysis, and optical and electronic applications. This contribution describes a fabrication strategy for a yolk–shell nanoreactor (NR) using a post decoration approach. The widely studied yolk–shell structure of silica-coated TiO₂ (TiO₂@SiO₂) was used as a model. At first, anatase TiO₂ spheres were prepared, and subsequently were given a continuous coating of carbonaceous and silica layers. Finally, the carbonaceous layer was removed to produce a yolk–shell structure TiO₂@SiO₂. By using an in-situ photodeposition method, Pt-encased spheres (Pt-TiO₂@SiO₂) were synthesized with Pt nanoparticles grown on the surface of the TiO₂ core, which contained void spaces suitable for use as NRs. The NR showed enhanced hydrogen production with a rate of 24.56 mmol·g⁻¹·h⁻¹ in the presence of a sacrificial agent under simulated sunlight. This strategy holds the potential to be extended for the synthesis of other yolk–shell photocatalytic NRs with different metal oxides.     

Crystalline and amorphous MnO2 cathodes with open framework enable high-performance aqueous zinc-ion batteries

Currently, δ-MnO₂ is one of the popularly studied cathode materials for aqueous zinc-ion batteries (ZIBs) but impeded by the sluggish kinetics of Zn²⁺ and the Mn cathode dissolution. Here, we report our discovery in the study of crystalline/amorphous MnO₂ (disordered MnO₂), prepared by a simple redox reaction in the order/disorder engineering. This disordered MnO₂ cathode material, having open framework with more active sites and more stable structure, shows improved electrochemical performance in 2 mol·L⁻¹ ZnSO₄/0.1 mol·L⁻¹ MnSO₄ aqueous electrolyte. It delivers an ultrahigh discharge specific capacity of 636 mA·h·g⁻¹ at 0.1 A·g⁻¹ and remains a large discharge capacity of 216 mA·h·g⁻¹ even at a high current density of 1 A·g⁻¹ after 400 cycles. Hence disordered MnO₂ could be a promising cathode material for aqueous ZIBs. The storage mechanism of the disordered MnO₂ electrode is also systematically investigated by structural and morphological examinations of ex situ, ultimately proving that the mechanism is the same as that of the δ-MnO₂ electrode. This work may pave the way for the possibility of using the order/disorder engineering to introduce novel properties in electrode materials for high-performance aqueous ZIBs.     

Two-step preparation of carbon nanotubes/RuO2/polyindole ternary nanocomposites and their application as high-performance supercapacitors

A ternary single-walled carbon nanotubes/RuO₂/polyindole (SWCNT/RuO₂/PIn) nanocomposite was fabricated by the oxidation polymerization of indole on the prefabricated SWCNT/RuO₂ binary nanocomposites. The nanocomposite was measured by FTIR, XRD, SEM, TEM, EDS and XPS, together with the electrochemical technique. The electrochemical results demonstrated that the symmetric supercapacitor used SWCNT/RuO₂/PIn as electrodes presented 95% retention rate after 10000 cycles, superior capacitive performance of 1203 F·g⁻¹ at 1 A·g⁻¹, and high energy density of 33 W·h·kg⁻¹ at 5000 W·kg⁻¹. The high capacitance performance of SWCNT/RuO₂/PIn nanocomposite was mainly ascribed to the beneficial cooperation effect among components. This indicated that the SWCNT/RuO₂/PIn nanocomposite would be a good candidate for high-performance supercapacitors.     

聚乙二醇聚合度对介孔η-Al2O3纤维形貌及吸附能力的影响

分别以2种不同聚合度的聚乙二醇（PEG）PEG600和PEG2000为模板导向剂,采用水热法合成η-Al₂O₃（PEG600）和η-Al₂O₃（PEG2000）介孔纤维,借助XRD、TEM和N₂吸附测试对材料进行表征,研究了PEG聚合度对介孔η-Al₂O₃纤维性质的影响。通过静态吸附平衡实验考察了介孔η-Al₂O₃纤维对亚甲基蓝的吸附特性。结果表明：2种模板导向剂均可用于合成介孔η-Al₂O₃纤维。PEG聚合度对介孔结构、比表面积、孔体积和孔径有较大影响。η-Al₂O₃（PEG600）的比表面积和孔体积分别为189.899 m²·g^-1和0.329 cm³·g^-1,分别是η-Al₂O₃（PEG2000）的1.4倍和1.2倍,平均孔径也比η-Al₂O₃（PEG2000）的大。2种介孔η-Al₂O₃纤维对亚甲基蓝的吸附机制均为多分子层吸附。根据BET多层分子吸附方程计算得η-Al₂O₃（PEG600）和η-Al₂O₃（PEG2000）对亚甲基蓝的平衡吸附量分别为256.391 3 mg·g^-1和204.045 9 mg·g^-1。     

A novel and simple nitrogen-doped carbon/polyaniline electrode material for supercapacitors

We demonstrated a simple and environment-friendly method in thepreparation of N-doped carbon/PANI(NCP)composite without binder.The structureand the property of NCP have been characterized by XPS,IR,XRD,SEM,CV,GCD and EIS.The results reveal that NCP has high capacitance performance of up to 615 F·g^-1at 0.6A·g^-1.Additionally,the asymmetric NCP₃₀₀/lcarbon supercapacitor delivers a highcapacitance(111 F·g^-1at 1A·g^-1)and a capacity retention rate of 82%after 1200 cyclesat 2A·g^-1.The ASC cell could deliver a high energy density of 39.1 W·h·kg^-1at a powerdensity of 792.6 W·kg^-1.     

FeS2@C nanorods embedded in three-dimensional graphene as high-performance anode for sodium-ion batteries

FeS₂ has drawn tremendous attention as electrode material for sodium-ion batteries (SIBs) due to its high theoretical capacity and abundant resources. However, it suffers from severe volume expansion and dull reaction kinetics during the cycling process, leading to poor rate capacity and short cyclability. Herein, a well-designed FeS₂@C/G composite constructed by FeS₂ nanoparticles embedded in porous carbon nanorods (FeS₂@C) and covered by three-dimensional (3D) graphene is reported. FeS₂ nanoparticles can shorten the Na⁺ diffusion distance during the sodiation–desodiation process. Porous carbon nanorods and 3D graphene not only improve conductivity but also provide double protection to alleviate the volume variation of FeS₂ during cycling. Consequently, FeS₂@C/G exhibits excellent cyclability (83.3% capacity retention after 300 cycles at 0.5 A·g⁻¹ with a capacity of 615.1 mA·h·g⁻¹) and high rate capacity (475.1 mA·h·g⁻¹ at 5 A·g⁻¹ after 2000 cycles). The pseudocapacitive process is evaluated and confirmed to significantly contribute to the high rate capacity of FeS₂@C/G.     

Stabilizing Co3O4 nanorods/N-doped graphene as advanced anode for lithium-ion batteries

Tricobalt tetroxide (Co₃O₄) is one of the promising anodes for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, the poor electrical conductivity and the rapid capacity decay hamper its practical application. In this work, we design and fabricate a hierarchical Co₃O₄ nanorods/N-doped graphene (Co₃O₄/NG) material by a facile hydrothermal method. The nitrogen-doped graphene layers could buffer the volume change of Co₃O₄ nanorods during the delithium/lithium process, increase the electrical conductivity, and profit the diffusion of ions. As an anode, the Co₃O₄/NG material reveals high specific capacities of 1873.8 mA·h·g⁻¹ after 120 cycles at 0.1 A·g⁻¹ as well as 1299.5 mA·h·g⁻¹ after 400 cycles at 0.5 A·g⁻¹. Such superior electrochemical performances indicate that this work may provide an effective method for the design and synthesis of other metal oxide/N-doped graphene electrode materials.     

Mn-doped perovskite-type oxide LaFeO3 as highly active and durable bifunctional electrocatalysts for oxygen electrode reactions

Perovskite oxides based on the alkaline earth metal lanthanum for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolytes are promising catalysts, but their catalytic activity and stability remain unsatisfactory. Here, we synthesized a series of LaFe_1−xMn_xO₃ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) perovskite oxides by doping Mn into LaFeO₃ (LF). The results show that the doping amount of Mn has a significant effect on the catalytic performance. When x = 0.5, the catalyst LaFe_0.5Mn_0.5O₃ (LFM) exhibits the best performance. The limiting current density in 0.1 mol·L⁻¹ KOH solution is 7 mA·cm⁻², much larger than that of the commercial Pt/C catalyst (5.5 mA·cm⁻²). Meanwhile, the performance of the doped catalyst is also superior to that of commercial Pt/C in terms of the long-term durability. The excellent catalytic performance of LFM may be ascribed to its abundant O²⁻/O⁻ species and low charge transfer resistance after doping the Mn element.     

Double core---shell nanostructured Sn---Cu alloy as enhanced anode materials for lithium and sodium storage

Sn-based alloy materials are considered as a promising anode candidate for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), whereas they suffer from severe volume change during the discharge/charge process. To address the issue, double core–shell structured Sn–Cu@SnO₂@C nanocomposites have been prepared by a simple co-precipitation method combined with carbon coating approach. The double core–shell structure consists of Sn–Cu multiphase alloy nanoparticles as the inner core, intermediate SnO₂ layer anchored on the surface of Sn–Cu nanoparticle and outer carbon layer. The Sn–Cu@SnO₂@C electrode exhibits outstanding electrochemical performances, delivering a reversible capacity of 396 mA·h·g⁻¹ at 100 mA·g⁻¹ after 100 cycles for LIBs and a high initial reversible capacity of 463 mA·h·g⁻¹ at 50 mA·g⁻¹ and a capacity retention of 86% after 100 cycles, along with a remarkable rate capability (193 mA·h·g⁻¹ at 5000 mA·g⁻¹) for SIBs. This work provides a viable strategy to fabricate double core–shell structured Sn-based alloy anodes for high energy density LIBs and SIBs.     

压电-磁致伸缩双层磁电复合材料的机电谐振

基于压电相和磁致伸缩相的本构方程以及弹性体的运动方程,简要推导了一维机电谐振模式下压电-磁致伸缩双层磁电复合材料横向磁电电压系数的表达式。采用相应的材料参数计算分析了Tb_1-x Dy_x Fe_2-y (TDF)-Pb(Zr,Ti)O₃(PZT)双层磁电复合材料的横向磁电电压系数与交流磁场频率的关系,以及复合材料的长度和压电相体积分数对机电谐振频率的影响。计算与分析结果表明,双层磁电复合材料在机电谐振频率处具有明显的磁电 响应特性。当有效机械品质因数为50,在谐振频率55.2 kHz处横向磁电电压系数达到峰值11.2 V·cm^-1·Oe^-1,是低频下峰值(281.9 mV·cm^-1·Oe^-1)的40倍。机电谐振频率随复合材料长度的减小和压电相体积分数的增加而上升。实验结果说明TDF-PZT双层磁电复合材料在机电谐振频率处具有显著增强的磁电效应,实际有效机械品质因数约为48。     

Microwave hydrothermal synthesis of lanthanum oxyfluoride nanorods for photocatalytic nitrogen fixation: Effect of Pr doping

Photocatalytic fixation of nitrogen has been recognized as a green and promising strategy for ammonia synthesis under ambient conditions. However, the efficient reduction of nitrogen remains a challenge due to high activation energy of nitrogen and low utilization of solar energy. Herein, lanthanum oxyfluoride with different doping content of Pr³⁺ (LaOF:xPr³⁺) upconversion nanorods were synthesized by microwave hydrothermal method. Results indicated that the doping of Pr³⁺ generated considerable defects on the surface of LaOF which acted as the adsorption and activation center for nitrogen. Meanwhile, the Pr³⁺ ion narrowed the band gap and broadened the light response range of LaOF because LaOF:Pr³⁺ can upconvert visible light into ultraviolet light, which excite LaOF nanorods and improve the utilization of solar light. The doping amount of Pr³⁺ had critical effect on the photocatalytic nitrogen fixation performance which reached as high as 180 μmol·L⁻¹·h⁻¹ when the molar ratio of Pr³⁺ to LaOF was optimized to be 2%.     

Electrochemical performances of NiO/Ni2N nanocomposite thin film as anode material for lithium ion batteries

Despite the high specific capacities, the practical application of transition metal oxides as the lithium ion battery (LIB) anode is hindered by their low cycling stability, severe polarization, low initial coulombic efficiency, etc. Here, we report the synthesis of the NiO/Ni₂N nanocomposite thin film by reactive magnetron sputtering with a Ni metal target in an atmosphere of 1 vol.% O₂ and 99 vol.% N₂. The existence of homogeneously dispersed nano Ni₂N phase not only improves charge transfer kinetics, but also contributes to the one-off formation of a stable solid electrolyte interphase (SEI). In comparison with the NiO electrode, the NiO/Ni₂N electrode exhibits significantly enhanced cycling stability with retention rate of 98.8% (85.6% for the NiO electrode) after 50 cycles, initial coulombic efficiency of 76.6% (65.0% for the NiO electrode) and rate capability with 515.3 mA·h·g⁻¹ (340.1 mA·h·g⁻¹ for the NiO electrode) at 1.6 A·g⁻¹.     

Catalytic CVD growth and properties of a-C:H and a-C:N

Hydrogenated amorphous carbon (a-C:H) and nitrided amorphous carbon (a-C:N) films have been synthesized on quartz substrates at a substrate temperature of 700 °C using a catalytic chemical vapor deposition (Cat-CVD) method. Raman spectra of a-C:H films showed two principal bands, the G-band at 1600 cm⁻¹ and the D-band at 1350 cm⁻¹. Those of a-C:N films showed similar spectra, with a G′ band at 1640 cm⁻¹, the peak energy of which is higher than that of the G-band in a-C:H. The intensity ratio /I_D, which is a measure of the degree of order in a-C:H, decreased for a-C:H with increasing CH₄/H₂ gas-flow ratio. On the contrary, the /I_D ratio increased with increasing CH₄/H₂ gas-flow ratio.     

介孔电气石/TiO2复合材料的制备及其模拟太阳光光催化性能

采用一步溶胶-凝胶共缩合结合溶剂热合成技术制备出一系列介孔电气石/TiO₂复合材料,表征了复合材料的相结构、形貌、孔隙率、光吸收性质以及组成结构.结果表明:制备的电气石/TiO₂复合材料具有纯锐钛矿晶相、均匀的介孔结构、较大的比表面积(205~242 m²·g^-1)、均匀的孔径分布(3.4~3.8 nm)以及较低的带隙能(3.0 eV).在模拟太阳光照射下,电气石/TiO₂复合材料可以被成功地应用于水中有机污染物罗丹明B和诺氟沙星的降解.降解动力学研究表明:电气石的掺杂提高了TiO₂的光催化量子效率,降低了TiO₂的带隙能.对罗丹明B的降解,电气石掺杂量为1wt%~5wt%的电气石/TiO₂复合材料表现出比纯TiO₂更高的降解速率,对诺氟沙星的降解,电气石/TiO₂复合材料的降解速率高于纯TiO₂的.     

Conductive polypyrrole incorporated nanocellulose/MoS2 film for preparing flexible supercapacitor electrodes

Conductive films have emerged as appealing electrode materials in flexible supercapacitors owing to their conductivity and mechanical flexibility. However, the unsatisfactory electrode structure induced poor output performance and undesirable cycling stability limited their application. Herein, a well-designed film was manufactured by the vacuum filtration and in-situ polymerization method from cellulose nanofibrils (CNFs), molybdenum disulfide (MoS₂), and polypyrrole. The electrode presented an outstanding mechanical strength (21.3 MPa) and electrical conductivity (9.70 S·cm⁻¹). Meanwhile, the introduce of hydrophilic CNFs induced a desirable increase in diffusion path of electrons and ions, along with the synergistic effect among the three components, further endowed the electrode with excellent specific capacitance (0.734 F·cm⁻²) and good cycling stability (84.50% after 2000 charge/discharge cycles). More importantly, the flexible all-solid-state symmetric supercapacitor delivered a high specific capacitance (1.39 F·cm⁻² at 1 mA·cm⁻²) and a volumetric energy density (6.36 mW·h·cm⁻³ at the power density of 16.35 mW·cm⁻³). This work provided a method for preparing composite films with desired mechanical and electrochemical performance, which can broaden the high-value applications of nanocellulose.