Influence of citric acid content on magnetic properties of BaFe12O19 powder prepared by sol-gel auto-combustion method

BaFe12O19 powders with nanocrystaUine sizes were produced by sol-gel auto-combustion method. The precursors were prepared under the molar ratios of citric acid to the metal nitrate of 0.5, 1.0 and 1.5. Appropriate ethylene diamine （C2H8N2） was added in order to adjust pH of 7. The ions distribution of citric acid at different pH explains the effect of citric acid in the starting solution. The XRD patterns of the as-burnt powders and annealing powders show different phases for different citric acid content. In addition, the lattice constants （a, c） derived from X-ray diffraction pattern were changed from 0.58881 nm to 0.58997 nm and 2.32057 nm to 2.32296 nm respectively. The data from VSM indicated that the powder with high citric acid content took on good magnetic properties. Pure single BaFe12O19 of the specific maximum magnetization M（1 T）≈ 49.73 Am^2/kg, the specific remanent magnetization Mr ≈ 30.77 Am^2/kg and the coercive force He≈ 467 kA/m was produced when the molar ratios of citric acid to the metal nitrate was 1.5.

Synthesis of CaCu_3Ti_4O_(12)powders and ceramics by sol-gel method using decanedioic acid and its dielectric properties

The CaCu3Ti4O12 xerogels, powders and ceramics were prepared through the sol-gel method using two kinds of organic acid （decanoic acid and decanedioic acid）. The xerogels, powders and ceramics were characterized by the methods of TG-DTG, FT-IR, XRD, SEM and TEM. The dielectric properties of the ceramics were also measured. The results indicated that the powders calcined at 850 ℃ for 2 h are both nanometer scale particles. After sintering, the ceramics mainly consist of the CaCu3Ti4O12 phase. Compared with the powders prepared using monoacid, the particle size of the powders prepared using diacid obviously increases, and the grain size, the relative density and the whole permittivity of the ceramics increase as well. Specially, the ceramic prepared using decanedioic acid has higher relative density （97.3%）, dielectric constant （316 808） and lower dielectric loss （0.242 5） at 30 ℃ （10 kIaz）

The Mechanism of Sol-Gel Synthesis of Normal Spinel LiMn_2O_4 with Chelation of Citric Acid

The sol-gel process of citric acid chelating with metal cations for the synthesis of normal spinel LiMn 2O 4 and the reaction mechanism were investigated by means of XRD,IR,TG-DTA, and SEM.The results show that at the beginning lithium citrate and chelate compound of citric acid with manganese ions formed,and then with heating the esterification and condensation reactions occured between them and glycol.The products obtained are polymers in which metal cations are distributed homogeneously on atomic scale that ensure high reactivity to cations of Li + and Mn 2+.Firing the gel prepared by this process,the lattice diffusions of solid reactant ions caused by non-homogeneity of reactants are eliminated and avoided.At 400℃ phase-pure LiMn 2O 4 with nanometer scale crystallization having precise stoichiometry and perfect crystallization can be obtained.The model of chelate coordinate of double-molecule between citric acid and Mn 2+ in the gel network is proposed.It is important for explaining the dispersion state of Mn 2+ and the formation process of gel by this model.

Research on the High-Strength Coating Preparation Methodology based on Acid Catalytic and Sol-Gel Method

In this paper, we conduct research on the high-strength coating preparation methodology based on acid catalytic and Sol-Gel method. This method has been widely used in the preparation of various functional thin film, film and protective film structure, etc. As a result of sol gel process continuously broaden the application field, this method has been more and more get the favor of people. Compared with other traditional preparation methods of inorganic material, sol-gel process has many characteristics. To adjust the solution acidity and add a small amount of acid or alkali can have the effect of＂ catalyst, its reaction process on sol to get and gel structure may also be affected. Our research analyze the topic theoretically and numerically which is meaningful.

Preparation and optical characteristics of ZnO films by chelating sol-gel method

The effect of different annealing temperatures on the structure, morphology,and optical properties of ZnO thin films prepared by the chelating sol-gel method was investigated.Zinc-oxide thin films were coated on quartz glass substrates by dip coating. Zinc nitrate, absoluteethanol, and citric acid were used as precursor, solvent, and chelating agent, respectively. Theresults show that ZnO films derived from zinc-citrate have lower crystallization temperature (below400℃), and that the crystal structure is wurtzite. The films, treated over 500℃, consist ofnano-particles and show to be porous at 600℃. The particle size of the film increases with theincrease of the annealing temperature. The largest particle size is 60 nm at 600℃. The opticaltransmittances related to the annealing temperatures become 90% higher in the visible range. Thefilm shows a starting absorption at 380 nm, and the optical band-gap of the thin film (fired at500℃) is 3.25 eV and close to the intrinsic band-gap of ZnO (3.2 eV).

Improved activity of Ni-Mo/SiO_(2) bimetallic catalyst synthesized via sol-gel method for methylcyclohexane cracking

To improve the cracking behavior of hydrocarbon,Ni-Mo/SiO_(2) bimetallic catalysts were synthesized by different preparation methods(sol-gel,co-impregnation and single-impregnation) and added the additives(citric acid,polyethylene glycol and cetyltrimethylammonium bromide) based on the most suitable method above.The cracking reaction of methylcyclohexane under supercritical conditions was performed as the probe reaction to estimate the catalytic performance,and the properties of Ni-Mo/SiO_(2) catalyst were characterized by N_(2) absorption-desorption,XRD,XPS,H_(2)-TPR,NH_(3)-TPD,in-situ IR of NH_(3) desorption,HRTEM and STEM-mapping so as to study the structure-activity relationship.The catalyst synthesized via sol-gel method showed the best conversion and heat sink,being 81.8% and 3.81 MJ/kg,which was closely related to strong mutual effect between active components and SiO_(2) as well as strong acid sites.Besides,the introduction of additives by sol-gel method has an affirmative influence on properties of Ni-Mo/SiO_(2) catalysts,being that the acidity(more L and B acid sites) was modulated and organic groups interact with metal to suppress the aggregation of metal species(Ni and Mo),thereby enhancing the catalytic activity.At 750℃,the conversion(89.3%) as well as heat sink(3.99 MJ/kg) of MCH cracking obtained an optimum over Ni-Mo/SiO_(2) catalyst with addition of citric acid.

Preparation and electrochemical performance of Li_2Mn_(0.5)Fe_(0.5)SiO_4 cathode material with sol-gel method for lithium ion batteries

Li2Fe0.5Mn0.5SiO4 material was synthesized by a citric acid-assisted sol-gel method. The influence of the stoichiometric ratio value of n(citric acid) to n(Fe2+-Mn2+) on the electrochemical properties of Li2Fe0.5Mn0.5SiO4 was studied. The final sample was identified as Li2Fe0.5Mn0.5SiO4 with a Pmn21 monoclinic structure by X-ray diffraction analysis. The crystal phases components and crystal phase structure of the Li2Fe0.5Mn0.4SiO4 material were improved as the increase of the stoichiometric ratio value of n(citric acid) to n(Fe2+-Mn2+). Field-emission scanning electron microscopy verified that the Li2Fe0.5Mn0.5SiO4 particles are agglomerates of Li2Fe0.5Mn0.5SiO4 primary particles with a geometric mean diameter of 220 nm. The Li2Fe0.5Mn0.5SiO4 sample was used as an electrode material for rechargeable lithium ion batteries, and the electrochemical measurements were carried out at room temperature. The Li2Fe0.5Mn0.5SiO4 electrode delivered a first discharge capacity of 230.1 mAh/g at the current density of 10 mA/g in first cycle and about 162 mAh/g after 20 cycles at the current density of 20 mA/g.

Preparation of Spherical Tungsten Particles Assisted by Hydrothermal Method

We presented a strategy to prepare spherical tungsten powder by the combination of hydrothermal method and H2reduction process.In hydrothermal process,the micelle of tetraethylammonium bromide(TEAB)act as spherical templates for the deposition of tungsten oxide,whereas the excessive TEAB inhibit the formation of spherical tungsten oxide due to the dense molecular layer of TEAB on the tungsten oxide particles.Citric acid(CA)can control the formation rate and structure of the tungsten oxide when its concentration is more than 0.2 mol/L,because of its ability to coordinate with tungsten atoms.The synergistic effect of TEAB and CA facilitates the formation of spherical tungsten oxide with nanorod crown.After being treated by H_(2)at 600 and 650℃,the tungsten oxide particles are reduced to tungsten particles,which maintain the spherical structure of tungsten oxide and have porous structure.

不同提取工艺对刺梨中维生素C提取量的影响研究

本文以柠檬酸为提取剂,分别采用浸提法、超声辅助法、微波辅助法提取刺梨果肉中维生素C,并利用紫外分光光度计测定维生素C提取量。结果表明,超声辅助提取法的提取率最高,在超声功率为80 W、超声时间为8 min条件下,维生素C的提取量为35.9 mg·g^(-1)。

A novel and facile wet-chemical method for synthesis of silver microwires

A novel and facile wet-chemical method for synthesis of silver microwires was developed.The well-defined particles were prepared by adding an iron（Ⅱ） sulfate heptahydrate solution into a silver nitrate solution containing citric acid drop by drop at 50 °C.The resulting products were characterized by scanning electron microscopy and X-ray diffraction.It was found that the particles consisted of numerous silver microwires.The reaction temperature greatly affected the morphologies of the as-prepared particles.Both of the mean length and width of the silver microwires increased with the decrease of the concentration of silver nitrate.And the lower concentration was unfavorable for the formation of more silver microwires.Similar findings were also observed when the concentration of iron（Ⅱ） sulfate was decreased.The amount of citric acid also greatly affected the shape of the as-prepared particles.It was concluded that citric acid was the key role in the formation of silver microwires via the Oswald ripening mechanism.

酸热法提取黑水虻鲜幼虫油脂工艺研究

【目的】构建黑水虻油脂的快速、高效的新型提取工艺,解决传统提取工艺中因乳化作用和细胞破碎不足导致油脂提取率较低的问题,为黑水虻油脂的提取及黑水虻油脂的规模化发展提供新思路。【方法】使用酸热法提取黑水虻鲜幼虫油脂,通过控制变量法选取黑水虻鲜幼虫油脂的预处理方法和提取溶剂,经单因素试验和正交试验对提取工艺进行优化,分析黑水虻鲜幼虫油脂的理化指标,并通过高效气相色谱仪分析其脂肪酸组成。【结果】酸热法提取黑水虻鲜幼虫油脂的最佳预处理方法为添加质量分数5.0%的柠檬酸溶液匀浆破碎(m(鲜幼虫/g)∶V(溶液/mL)=1∶1),最佳提取溶剂为石油醚,提取工艺条件为柠檬酸溶液质量分数5.0%、料液比m(鲜幼虫/g)∶V(石油醚/mL)=1∶5、提取时间60 min和提取温度50℃。在此条件下,油脂提取率达到94.67%,且耗时4 h便可得到黑水虻鲜幼虫油脂。黑水虻鲜幼虫油脂的酸值为9.30 mg·g-1,过氧化值为1.74 mmol·kg^(-1),皂化值为227.23 mg·g-1。鲜幼虫油脂共检测出20种脂肪酸,其中,亚油酸与月桂酸的含量最高,分别为32.72%和30.75%。【结论】酸热法能快速、高效地提取黑水虻鲜幼虫油脂,既节省了干燥成本,又保证了油脂的品质和脂肪酸组成。

A novel wet-chemical method for preparation of silver flakes

A novel wet-chemical method for the preparation of silver flakes was studied. The well-defined particles were prepared by directly adding FeSO4 solution into AgNO3 solution containing citric acid at an agitation speed of 150 r/min at room temperature. The products were characterized by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that particles are irregular thin silver flakes. And the sizes of them range from 2 to 10 μm. It is found that citric acid plays an important role in the formation of sliver flakes. There is an optimum amount of citric acid for the preparation of silver flakes by this method. It is also found that high reduction rate is favorable for the formation of silver flakes.

净制对乌梅质量的影响及乌梅肉质量标准的研究

目的:研究净制对乌梅质量的影响,完善乌梅肉质量标准。方法:首先采用蒸与润2种方法分别净制3批乌梅肉样品,比较其产率、浸出物以及枸橼酸含量差异,确定净制方法;根据确定的净制方法,对12批乌梅药材进行净制,比较乌梅肉和核中浸出物及枸橼酸含量差异,探讨净制对乌梅质量的影响。对21批乌梅肉饮片的外观性状、显微、薄层鉴别、水分、水溶性浸出物和枸橼酸含量分别按照药典要求进行测定,拟定乌梅肉质量标准限度。结果:蒸法与润法净制乌梅质量(产率、水分、枸橼酸及浸出物)无显著性差异,但蒸法所用时间为30 min,远短于润法润制过夜。乌梅肉的浸出物及枸橼酸的含量72.5%、33.1%远高于乌梅核17.9%、8.0%,二者存在极显著差异。乌梅肉的平均水分为(11.0±1.4)%;浸出物为(72.0±3.4)%;枸橼酸含量为(33.8±4.5)%。结论:乌梅净制可以去除非药用部位,提高枸橼酸及浸出物含量,具有科学道理,蒸法和润法2种净制方法均可行,蒸法更易操作。

亲水性CIT-NaYF_(4)∶Yb^(3+),Ho^(3+)纳米粒子的制备及其发光性能研究

采用溶剂热法制备了油溶性稀土掺杂上转换纳米粒子NaYF_(4)∶Yb^(3+),Ho^(3+),并利用TEM、XRD、IR、荧光光谱法等考察了反应温度、反应时间、掺杂比等反应条件对纳米粒子形貌、结构、发光性能的影响。结果表明,在反应温度为300℃、反应时间为50 min、稀土离子掺杂比为NaYF_(4)∶20%Yb^(3+),2%Ho^(3+)条件下,制备出的油溶性NaYF_(4)∶Yb^(3+),Ho^(3+)纳米粒子呈标准六方晶型,尺寸均一、单分散性好,平均粒径为31.55 nm。通过表面配体交换法成功将柠檬酸修饰在其表面,转为亲水性CIT-NaYF_(4)∶Yb^(3+),Ho^(3+)纳米粒子。

sol-gel法制备Ba_(3.99)Sm_(9.34)Ti_(18)O_(54)微波介质陶瓷

以柠檬酸为络合剂,通过sol-gel法制备了Ba3.99Sm9.34Ti18O54陶瓷前驱体;经1100℃预烧2h压片成型后,再在1300℃保温3h,即得到了烧结致密的陶瓷样品。与传统固相法相比,其烧结温度降低了50℃,且陶瓷晶粒细小,晶粒分布均匀,具有更加优良的微波介电性能:εr=79.56,Q·f=9636GHz(4.71GHz),τf=–1.23×10–6/℃。

溶胶-凝胶法合成钛酸锌锂负极材料

以溶胶-凝胶法制备锂离子电池Li_(2)ZnTi_(3)O_(8)(LZTO)负极材料,考察退火温度和退火时间对LZTO电化学性能的影响,得到了最佳工艺条件:退火温度为700℃,退火时间为3 h。在最佳工艺条件下制备的LZTO中添加络合剂柠檬酸进行了改性。结果表明,当金属离子与柠檬酸的物质的量比为2.00∶1.50时,制备的样品LZTO-2/1.50颗粒小、分散均匀,表现出良好的电化学性能;当电流密度为0.5 A/g时,恒流充放电300次后放电比容量为203.6 mA·h/g。

基于溴酸钾氧化酚藏花红的荧光猝灭法测定柠檬酸

在稀H_(2)SO_(4)介质中,用柠檬酸活化钒(V)可催化溴酸钾氧化酚藏花红,导致酚藏花红的荧光猝灭,由此建立了荧光猝灭法测定柠檬酸的新方法。探讨了硫酸、溴酸钾、偏钒酸铵、酚藏花红用量、反应温度、反应时间对体系的影响,优化了测定条件。在最佳实验条件下,方法的线性范围为0.833~3.750μg·mL^(-1),线性方程为ΔF=-2.359+67.483ρ,相关系数R^(2)为0.9929,检出限为0.42μg·mL^(-1)。该方法用于饮料中柠檬酸的测定,测定结果的回收率为95.5%~108%,RSD为3.5%~4.1%,表明本分析方法可行。

低剂量两段法局部枸橼酸抗凝对高危出血风险患者行含钙透析液血液透析的影响研究

目的探讨低剂量两段法局部枸橼酸抗凝对高危出血风险患者行含钙透析液血液透析的影响。方法选择纳入我院2020.7-2022.7收治的80例高危出血风险患者行含钙透析液血液透析患者,按照随机法将其分为对照组与研究组,每组各40例,均采用局部枸橼酸抗凝和标准含钙透析液,其中对照组注入常规剂量,设定前段4%枸橼酸钠溶液输注量为血流量的1.5倍;研究组注入低剂量,设定输注量改为1.0倍,比较两组实际抗凝效果。结果两组基线资料对比,差异无统计学意义(P>0.05)。在枸橼酸抗凝不同剂量下,研究组透析器和静脉壶的抗凝有效率均高于对照组(P<0.05),两组干预前凝血功能指标比较无明显差异(P>0.05);两组干预后凝血功能各指标均有所改善,但组间对比不存在统计学差异(P>0.05),研究组透析器前和静脉壶的枸橼酸溶液输注量以及实际血流量均高于对照组(P<0.05)。结论在两段法局部枸橼酸抗凝的基础上,选择低剂量抗凝,不仅能够达到理想的抗凝效果,同时也明显提高透析充分性,是一种安全有效可行的抗凝方案。

A new solid acid SO_4^(2-)/TiO_2 catalyst modified with tin to synthesize 1,6-hexanediol diacrylate

A new solid acid catalyst,SO4^2-/TiO2 modified with tin,was prepared using a sol-gel method and its physicochemical properties were revealed by nitrogen adsorption-desorption,X-ray powder diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,infrared spectroscopy of adsorbed pyridine,temperature-programmed desorption of ammonia and thermal gravimetric analysis.The structure,acidity and thermal stability of the SO4^2-/TiO2-SnO2 catalyst were studied.Incorporating tin enlarged the specific surface area and decreased crystallite size of the SO4^2-/TiO2 catalyst.The total acid sites of the modified catalyst increased and Bronsted acid strength remarkably increased with increasing tin content.The decomposition temperature of sulfate radical in the modified catalyst was 100 ℃ greater and its mass loss was more than twice that of the SO4^2-/TiO2 catalyst.The SO4^2-/TiO2-SnO2 catalyst was designed to synthesize 1,6-hexanediol diacrylate by esterification of 1,6-hexanediol with crylic acid.The yield of 1,6-hexanediol diacrylate exceeded 87% under the optimal reaction conditions：crylic acid to 1,6-hexanediol molar ratio = 3.5,catalyst loading = 7%,reaction temperature = 130 ℃ and reaction time = 3 h.The modified catalyst exhibited excellent reusability and after 10 cycles the conversion of 1,6-hexanediol was above 81%.

SYNTHESIS OF MESOPOROUS POLY(STYRENE-co-MALEIC ANHYDRIDE)/SILICA HYBRID MATERIALS VIA A NONSURFACTANT-TEMPLATED SOL-GEL PROCESS

Mesoporous poly(styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis was achieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymer in the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template or pore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m(2)/g) and pore volumes (e.g. 0.6 cm(3)/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, pore volumes and pore diameters of the hybrid materials increase.