Electrospun Zn-doped Ga2O3 nanofibers and their application in photodegrading rhodamine B dye

Ultrawide band gap semiconductor materials have attracted considerable attention in recent years owing to their great potential in the photocatalytic field. In this study, Zn-doped Ga₂O₃ nanofibers with various concentrations were synthesized via electrospinning; they exhibited a superior photocatalytic degradation performance of rhodamine B dye compared to that of undoped Ga₂O₃ nanofibers. The Zn dopant replaced Ga sites via replacement doping, which could increase the concentration of oxygen vacancies and lead to enhanced photocatalytic properties. When the Zn concentration increased, a Ga₂O₃/ZnGa₂O₄ hybrid structure formed, which could further enhance the photocatalytic performance. The separation of photogenerated carriers due to Zn doping and heterojunctions were the primary causes of the enhanced photocatalytic performance. This study provides experimental data for the fabrication of high-performance photocatalysts based on Ga₂O₃ nanomaterials.     

以线性酚醛树脂为炭前驱体制备有序介孔炭及其表征

以三嵌段共聚物F127和P123为模板剂,线性酚醛树脂(PF)为炭前驱体,利用有机-有机自组装制备了具有二维六方结构和蠕虫结构的介孔炭.采用XRD、TEM、N2吸附/脱附等方法对介孔炭的结构进行了表征,研究了模板剂用量和模板剂类型对上述介孔炭结构的影响.结果表明:当模板剂F127与PF的质量比由1:2变为1:1时,所得介孔炭的孔壁厚度有所下降,但比表面积、孔容和孔径分别从576 m2·g-1、0.29 cm3·g-1和2.7 nm提高到670m2·g-1、0.40 cm3· g-1和3.2 nm;分别以F127和P123为模板剂制备的介孔炭F-1-500和P-1-500的孔径大小基本相同,但P-1-500的孔壁厚度相对于F-1-500降低了37.4％,且有序性下降,仅能得到蠕虫状结构.     

Pore structure control of mesoporous carbon monoliths derived from mixtures of phenolic resin and ethylene glycol

Mesoporous carbon monoliths derived from phenolic resin mixtures have been prepared in the process based on polymerization-induced phase separation. The effect of the composition of resin mixtures and the resin curing temperature on the pore structure of carbon monoliths has been systematically investigated, with emphasis on controlling the apparent porosity and pore size distribution. Fractal dimensions have been introduced to evaluate the morphologies of the carbon monoliths. The results showed that mesoporous carbon monoliths with narrow pore size distribution were obtained. The pore structure of carbon monoliths could be controlled by changing the resin curing temperature and the content of ethylene glycol, curing catalyst and water in the resin mixtures. The apparent porosity of carbon monoliths varied from 54.27% to 26.83%. Carbon monoliths had narrower pore size distribution when more ethylene glycol and higher resin curing temperature were employed. The pore structure of carbon monoliths would be changed radically when the initial resin samples were prepared with excess water (9.8 wt%), i.e. porous carbon foams with sponge structure were obtained. Carbon monoliths inherit their porosity from precursing cured resins where it was formed as a result of phase separation of resin-rich and glycol-rich phases. Volume contraction had certain effect on the pore structure of carbon monoliths.     

Oxidation of carbon derived from phenolic resin

The oxidation of carbon derived from phenolic resin and heat-treated at temperatures ranging from 1000 to 2400°C for 1 hr was studied in a flowing oxygen atmosphere at temperatures between 424 and 692°C. The heat-treatment alters the crystallite size, L_c, from 10.7 to 21.4 Å; the interlayer spacing, d₀₀₂, from 3.74 to 3.52 Å and the surface area from 0.22 to 1.34 m²/g. $\text{L}{}_{\mathrm{a}}\text{L}{}_{\mathrm{c}}$ ratio ranges from 1.62 to 2.22 and appears to be independent of heat treatment temperature and oxidation level. The surface area of the carbon and its change with oxidation were found to be sensitive to the heat treatment process. Heat treatments at 1000 and 1400°C produce carbon with surface area which increases by nearly two orders of magnitude after 10% oxidation. The oxidation rate decreases with increasing heat treatment temperature with the largest change between 1000 and 1400°C. Samples heat-treated at different temperatures give slightly different activation energies with an average value of 41.5 kcal/mole.     

Study of phenolic resin and their tendency for carbon graphitization

Phenolic resins are important materials in various application sectors due to their outstanding mechanical and thermal properties. However, phenolic resins are known as typical non-graphitized carbon precursor. In this work, important parameters related to the synthesis of PRs were studied: the concentration of the catalyst and the molar ratio between phenol and formaldehyde. The structural information was performed by Fourier Transformation Infrared Spectroscopy and solid state nuclear magnetic resonance of carbon analysis to define mainly between novolac or resol resin. The thermal characteristics of the resins were studied for TGA and their tendencies for graphitization were verified by powder x-ray diffraction and Raman spectroscopy and SEM/HRTEM analysis. As a conclusion, it was verified that the phenolic resins prepared with excess of formaldehyde in acidic medium can present different properties according to their composition, which allows for qualifying them as potential materials for different applications in the technological area that involves graphitized carbon.     

Synthesis of benzxazine-based nitrogen-doped mesoporous carbon spheres for methyl orange dye adsorption

In this work, nitrogen-doped mesoporous carbon spheres (NMCS) were synthesized through a hard template method by using benzoxazine resin as precursor and ordered mesoporous silica spheres as template. The obtained N-doped mesoporous carbons were amorphous spherical nanoparticles with worm-like mesoporous channels and possessed high surface area of 789 m²/g, large pore volume of 0.49 cm³/g and high nitrogen content of 3.50 wt.%. The adsorption capacity of methyl orange (MO) by NMCS could attain 352.1 mg/g at an optimal condition, while the adsorption capacity of MO by non-doped mesoporous carbon spheres (MCS) was 251.9 mg/g at the same condition. The adsorption process fitted the pseudo-second-order kinetic model and the Langmuir isotherm well. Thermodynamic analysis indicated that the removal of MO by NMCS was spontaneous, endothermic and feasible process. In addition, the adsorption capacity of regenerated adsorbent was 89.04% of the initial level after four regeneration cycles.     

Synthesis of an ordered mesoporous carbon with graphitic characteristics and its application for dye adsorption

An ordered mesoporous carbon (OMC) was prepared by a chemical vapor deposition technique using liquid petroleum gas (LPG) as the carbon source. During synthesis, LPG was effectively adsorbed in the ordered mesopores of SBA-15 silica and converted to a graphitic carbon at 800 °C. X-ray diffraction and nitrogen adsorption/desorption data and high-resolution transmission electron microscopy (HRTEM) of the OMC confirmed its ordered mesoporous structure. The OMC was utilized as an adsorbent in the removal of dyes from aqueous solution. A commercial powder activated carbon (AC) was also investigated to obtain comparative data. The efficiency of the OMC for dye adsorption was tested using acidic dye acid orange 8 (AO8) and basic dyes methylene blue (MB) and rhodamine B (RB). The results show that adsorption was affected by the molecular size of the dye, the textural properties of carbon adsorbent and surface-dye interactions. The adsorption capacities of the OMC for acid orange 8 (AO8), methylene blue (MB) and rhodamine B (RB) were determined to be 222, 833, and 233 mg/g, respectively. The adsorption capacities of the AC for AO8, MB, and RB were determined to be 141, 313, and 185 mg/g, respectively. The OMC demonstrated to be an excellent adsorbent for the removal of MB from wastewater.     

The characterization and application of p-type semiconducting mesoporous carbon nanofibers

The microstructures of mesoporous carbon nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, nano-Raman, nitrogen adsorption-desorption and optical transmission. They possessed a high specific surface area 840 m² g⁻¹ and a 1.07 eV band gap. All mesoporous carbon nanofiber network can act as the channel material in p-type field-effect transistor devices with field-effect mobilities over 10 cm²/V s. Furthermore, mesoporous carbon nanofiber network exhibits better sensitivity and faster response to NO₂ gas than that of carbon nanotubes, which makes it a promising candidate as poisonous gas sensing nanodevices.     

中孔炭对葡萄叶中白藜芦醇静态吸附性能的研究

本研究以中孔炭为吸附材料,吸附葡萄叶中的白藜芦醇。通过静态吸附实验,研究其吸附机理。结果表明,Langmuir和Freundlich方程均可以较好地表述中孔炭对白藜芦醇的吸附;中孔炭对白藜芦醇的吸附符合二级动力学模型(R~2>0.99),外扩散和粒子内扩散共同控制吸附过程;中孔炭对白藜芦醇的吸附是自发进行的吸热反应(ΔH<0,ΔG<0),且混乱度增加(ΔS>0)。研究为中孔炭在白藜芦醇的纯化应用方面提供了理论依据,以期为吸附法纯化白藜芦醇提供新的吸附剂。     

Adsorption properties and microporous structure of adsorbents produced from phenolic resin and biomass

Mixtures of novolac resin and olive stone biomass in proportions 20 : 80 (w : w) are cured, pyrolyzed up to 1000°C (material C20a), and activated with steam (material C20a). The adsorption properties of these materials and a commercial activated carbon (CC) are investigated based on the adsorption of nitrogen and pentane. The adsorption capacity, the surface area determined by the BET and DRK equation, and the pore volume determined as micropore volume by the DR equation, and as cumpulative pore volume related to the Kelvin equation, for the materials follow the order C20a > CC > C20. The DR equation can be applied for the adsorption of nitrogen on the materials examined in the region of P/P_o = 0.005 up to 0.3 that exceeds in both sides the common range for the applicability of the DR equation. The activated materials C20a and CC are mainly microporous and reveal the type I isotherms of the Brunauer classification for nitrogen adsorption. The only pyrolyzed material, C20, contains both micropores and mesopores and reveals characteristics of both types I and II. The number of layers for C20a and CC is lower than 2 and for C20 is more than 2. © 1995 John Wiley & Sons, Inc.     

Preparation and characterization of carbon foams derived from aluminosilicate and phenolic resin

Aluminosilicate-reinforced carbon foams have been prepared by chemical foaming with phenolic resin as matrix precursor and aluminosilicate as the additive. The effects of the amount of aluminosilicate used on the microstructure, mechanical properties and oxidation resistance of the carbon foams have been investigated by scanning electronic microscopy, mechanical testing, and oxidation weight loss, respectively. The results show that the amount of aluminosilicate added has a significant influence on the surface roughness and the structure uniformity of carbon foams. The compressive strengths are usually higher than that of the pure carbon foam sample by as much as 60%. The percentage of weight loss of the carbon foams drops with increasing aluminosilicate content up to 11 wt%, but then increases.     

钴氮碳/碳纳米管的制备及染料吸附性能

为了解决沸石咪唑酯骨架(ZIF-67)基碳材料比表面积和孔体积较小、氮含量较低、孔径分布不集中的问题,以微米级ZIF-67为模板,引入聚多巴胺(PDA)和三聚氰胺(MA)为共同碳氮前驱体以提升氮掺杂量和调节孔结构,在氢气和氩气的氛围中,利用ZIF-67中钴的自催化作用,经800℃高温一步碳化制备得到钴氮掺杂的中空立方形...     

介孔炭的改性及其吸附脱硫选择性研究

用4种方法(浓硝酸、磷酸、双氧水、350℃焙烧)对介孔炭进行改性,并考察改性后的介孔炭在4种不同成分的模拟油中的吸附脱硫性能。对于仅含有芳烃或烯烃以及芳烃和烯烃均含有的模拟油,改性介孔炭的脱硫能力与未改性的介孔炭相比均有不同程度的下降。浓硝酸改性的介孔炭在仅含饱和烃的模拟油中的吸附脱硫性能优于其它方法;350℃焙烧处理的介孔炭与未改性的介孔炭在芳烃和烯烃均含有的模拟油中的吸附脱硫性能优于其它方法。考察了在350℃焙烧及浓硝酸处理后的介孔炭在不同温度下的脱附性能。结果表明,350℃焙烧处理的介孔炭在90℃下脱附率能达到66.91%。     

介孔炭的改性及其吸附脱硫选择性研究

用4种方法(浓硝酸、磷酸、双氧水、350℃焙烧)对介孔炭进行改性,并考察改性后的介孔炭在4种不同成分的模拟油中的吸附脱硫性能。对于仅含有芳烃或烯烃以及芳烃和烯烃均含有的模拟油,改性介孔炭的脱硫能力与未改性的介孔炭相比均有不同程度的下降。浓硝酸改性的介孔炭在仅含饱和烃的模拟油中的吸附脱硫性能优于其它方法;350℃焙烧处理的介孔炭与未改性的介孔炭在芳烃和烯烃均含有的模拟油中的吸附脱硫性能优于其它方法。考察了在350℃焙烧及浓硝酸处理后的介孔炭在不同温度下的脱附性能。结果表明,350℃焙烧处理的介孔炭在90℃下脱附率能达到66.91%。     

Template-free synthesis of MgO mesoporous nanofibers with superior adsorption for fluoride and Congo red

MgO mesoporous nanofibers were obtained by a template-free electrospinning method. The unique bumpy-structure was obtained on the surface of nanofibers that could enhance the surface area and provide more active sites for adsorption. The formation mechanism of the bumpy-structure has been investigated. The as-prepared MgO nanofibers with a high surface area of 194.17?m² g^?1 exhibited excellent adsorption capacities for fluoride of 237.49?mg?g^?1. Furthermore, the MgO nanofibers showed selective adsorption for different organic dyes and have superior adsorption capacity for Congo red (4802.27?mg?g^?1). The adsorption processes for both fluoride and Congo red were systematically investigated, which were found to follow the pseudo-second-order kinetic model. By comparison with the reported fabrication routes and adsorption capacities of mesoporous MgO, the synthesis process is simple, controllable and template-free, and the superior adsorption performance provided a potential adsorbent for the removal of fluoride and Congo red in wastewater treatment. The high surface area of the MgO mesoporous nanofibers might also promote its application in basic catalysis and other fields.     

Dual formation of carpets of large carbon nanofibers and thin crystalline carbon nanotubes from the same catalyst-underlayer system

A dense, micron-tall layer of carbon nanofibers (CNFs) was grown above a layer of carbon nanotubes (CNTs) during the same synthesis using a thick cobalt catalyst (15 nm). The CNFs had large diameters (100 nm) and were amorphous while the CNTs had small diameter (10–20 nm) and were crystalline. Base growth mechanism was at play for both the nanofibers and the nanotubes. High-resolution transmission electron microscopy characterization suggested that the main mechanisms leading to the growth of the two structures were based on the dewetting of the catalyst layer and its subsequent alloying with the Ta underlayer. We can extend these principles to grow diverse carbon nanostructures during the same synthesis using appropriate multilayer thin films for different applications, especially for electrochemical cells and supercapacitors.