Supercritical hydrothermal synthesis of nano-ZnO: Effects of key parameters and reaction mechanism

In this paper, ZnO particles with the particle size as low as 23 nm were successfully prepared by supercritical hydrothermal synthesis technique. The particle size of nano-ZnO decreased with the increase of temperature and pressure. Nano-ZnO particles in ZnSO₄ system were spherical with smaller particle size. The discrepancy in nano-ZnO produced by different precursor of Zn(NO₃)₂, Zn(CH₃COO)₂ or ZnSO₄ is attributed to the anion effects and supersaturation. The particles in the KOH system (29 nm) were smaller than those in the NaOH system (44 nm). For precursor concentration, intermediate Zn(OH)₂ was generated at lower concentration, while Zn₄SO₄(OH)₆·4H₂O was produced at higher concentration. For alkali concentration, as the gradual increase of KOH concentration, Zn(OH)₂ began to decrease and gradually transformed into Zn(OH)₃^– and [Zn(OH)₄]²⁻. When the KOH concentration reached a certain value, [Zn(OH)₄]²⁻ occupied the dominance in the mixed solution.     

Supercritical hydrothermal synthesis of nano-zinc oxide: Process and mechanism

Nano-zinc oxide is a type of multifunctional inorganic material, which had been extensively used due to the excellent properties such as piezoelectricity, sterilization, and UV shielding. The methods used for preparing nano-zinc oxides include precipitation, low-temperature hydrothermal, sol-gel, spray pyrolysis, and gas-phase synthesis. All of the current methods share the same problems of long reaction time, large particle sizes, and uneven distribution of particle sizes. The supercritical hydrothermal synthesis is a promising method for nano-ZnO preparation, which has the advantages of fast reaction rates and uniform particle size distribution. In this paper, the mechanism of supercritical hydrothermal synthesis of ZnO (including reaction, crystallization, and growth mechanism) is introduced. Then the effects of key parameters (materials and process parameters) are summarized. Moreover, the effects of surface modification and doping on ZnO are analyzed. Some suggestions for improving the particle quality by supercritical hydrothermal synthesis are also presented, as well as the future research directions.     

超临界水热合成制备纳米微粒材料

简述了超临界水热合成法制备纳米微粒材料技术的微粒形成机理、过程基本工艺及目前所取得的研究成果。讨论了未来需要解决的问题。     

Supercritical hydrothermal synthesis of titanium dioxide nanostructures with controlled phase and morphology

A novel template- and organic-free synthesis of TiO₂ nanostructures with controlled phase and morphology was realized through batch supercritical hydrothermal treatment (400 °C) of titanate nanotubes (TNTs) with H₂O₂ in NaOH aqueous solution. Well-defined 3D titanate hierarchical spheres (THSs), 2D multilayered titanate nanosheets (TNSs), and 1D monodisperse anatase nanorods (ANRs) exposing (0 1 0) facets were prepared in 15 min by slightly varying the NaOH solution pH. Specifically, the obtained Na/H-THSs (without/with HCl neutralization) exhibited highly porous structures with large specific surface area (109 m² g⁻¹ and 196 m² g⁻¹, respectively). Temperature-dependent phase and morphology evolutions of products under subcritical condition (200 and 300 °C) were investigated. The formation of the TiO₂ nanostructures from TNTs was proposed mainly following a dissolution–nucleation-growth mechanism, suggesting that both supercritical temperature and NaOH solution pH were determinant factors governing the nucleation and growth process and thus the phase and morphology.     

Green hydrothermal synthesis of high aspect ratio wollastonite nanofibers: Effects of reaction medium,temperature and time

Wollastonite 1D nanostructures have attracted widespread concern for their wide applications in biomedical, constructions and many more, which however have been synthesized via high temperature solid state method or wet precipitation method which required organic template. Herein, a controllable green hydrothermal route is used to produce high aspect ratio wollastonite nanofibers. The effect of hydrothermal synthesis parameters on the aspect ratio of synthetic wollastonite nanofibers (SWN) were investigated and the hydrothermal formation mechanism was proposed. The formation of nanofiber starts from the nuclei formation in supersaturated solution then followed by the crystal growth. The synthesis reactions were conducted under different conditions with reaction medium containing different ethanol composition and temperature from 160 °C to 240 °C for 8 h to 32 h. The SWN produced was characterized using XRD, FTIR, TGA and FESEM analysis techniques. It is proven that all wollastonite produced were in nanofiber form with the average aspect ratio ranging from 10 to 20, except for those synthesized at 160 °C which mainly has irregular grain shape. The reaction medium consisting of 80% water and 20% ethanol, which was heated at 200 °C for 16 h, resulted in SWN with the highest aspect ratio of 20.15. The study demonstrated that the hydrothermal synthesis parameters can be manipulated to produce SWN with various aspect ratios to meet its demand in different applications.     

Hydrothermal synthesis and in situ surface modification of boehmite nanoparticles in supercritical water

In situ surface modification of boehmite (AlOOH) nanoparticles during hydrothermal synthesis in supercritical water was examined by adding CH₃(CH₂)₄CHO and CH₃(CH₂)₅NH₂ as modifier reagents to the reactants. Changes in surface properties of the nanoparticles by surface modification was observed by FTIR, dispersion in solvents and TEM analyses, which demonstrated that reagents chemically binded onto the surface of the AlOOH nanoparticles. The results of SEM and TEM pictures show that the surface modification affects crystal growth and reduces the particle size and changes the morphology of the particles.     

SAPO-11分子筛的水热合成及其金属负载改性的研究进展

简述了SAPO-11分子筛的结构和合成原理,介绍了传统水热合成方法。通过几种方法对其进行改进,比较了改进前后分子筛的结构和性能。同时归纳和总结了金属负载改性对SAPO-11分子筛应用于烷烃异构化性能的影响。     

超临界连续水热法制备无机纳米材料

介绍了超临界连续水热法用于制备无机纳米材料近年来所取得的研究成果。主要介绍了此方法在反应器设计、掺杂型纳米材料的制备及纳米材料的原位改性3方面的研究进展,并对未来的发展进行了展望。     

水热合成纳米羟基磷灰石粉体的研究

采用硝酸钙和磷酸铵为反应前驱物，通过水热合成颗粒尺寸在100nm以下的短棒状或针状羟基磷灰石晶体。X射线衍射(XRD)、透射电镜(TEM)和红外光谱(FTIR)分析讨论水热温度、反应时间、表面活性剂和烧结与物相组成、晶粒尺寸和晶体形貌的关系。     

聚酰亚胺的合成与改性研究

聚酰亚胺树脂是一种耐热性好、机械强度高且介电性能优异的高分子材料。该文综述了聚酰亚胺的合成与改性方面的研究,并对聚酰亚胺的发展进行了展望。     

Imaging the continuous hydrothermal flow synthesis of nanoparticulate CeO2 at different supercritical water temperatures using in situ angle-dispersive diffraction

In situ high-energy synchrotron X-ray diffraction, a non-destructive synchrotron-based technique was employed to probe inside the steel tubing of a continuous hydrothermal flow synthesis (CHFS) mixer to spatially map, for the first time, the superheated water crystallisation of nanocrystalline ceria (CeO₂) at three different (superheated-water) temperatures representing three unique chemical environments within the reactor. Rapid hydrothermal co-precipitation at the three selected temperatures led to similarly sized ceria nanoparticles ranging from 3 to 7 nm. 2D maps of CeO₂ formation were constructed from the intensity and corresponding full width at half maximum (FWHM) values of the two most intense ceria reflections (111) and (002) for all three water inlet temperatures (350, 400 and 450 °C at 24 MPa) and subsequent changes in the particle size distribution were analysed. The accompanying high-resolution transmission electron microscopy (HRTEM) and tomographic particle size maps have confirmed that the mean ceria particle size slightly increases with temperature. This X-ray tomographic imaging study amounted to a formidable technical and engineering challenge, nevertheless one that has been met; this represents a significant achievement in imaging science, given the dynamic nature and hostile environment of a working CHFS reactor.     

A new approach to obtain calcium cobalt oxide by microwave-assisted hydrothermal synthesis

This study describes the effect of microwave-assisted hydrothermal synthesis on the crystalline phase-formation, microstructural characteristics, and thermoelectric performance of Ca₃Co₄O₉. Synthesis parameters, such as time, temperature, KOH concentration, and oxidation states of Co ions, to produce this compound, were studied. X-ray diffraction and X-ray photoelectron spectroscopy showed that the most critical parameters for the phase formation are the oxidation states of Co ions. Ca₃Co₄O₉ can be obtained by microwave-assisted hydrothermal synthesis at 503 K for 30 min and thermal treatment at 1173 K for 120 min. Scanning electron microscopy images showed that the sample exhibits randomly oriented particles with plate-like morphology and range size between 0.4 and 1.2 μm. From measurements of electrical resistivity, thermal conductivity, and Seebeck coefficient, we obtained a figure of merit of ~0.008 at 300 K.     

活性氢氧化镁水热改性制备分散性氢氧化镁

探索了活性氢氧化镁经水热改性制备形貌规则、分散良好的片状氢氧化镁的方法。研究了焙烧-水化对活性氢氧化镁性质的影响及活性氢氧化镁水热改性制备分散性氢氧化镁的工艺规律,并用扫描电子显微镜（SEM）、X射线衍射仪（XRD）、物理吸附仪和激光粒度仪等对水热产物进行了表征。研究结果表明：通过低温焙烧及水化可将团聚态的工业氢氧化镁先转化为活性较高的氢氧化镁,再经温和水热改性即可制得形貌规则、分散性良好的片状氢氧化镁。     

水热法合成羟基氧化镓与优化探索

羟基氧化镓（GaOOH）是合成氮化镓的重要原料,其微观形态特征对所制备氮化镓的物理性能有着重要影响。以氧化镓、浓盐酸、氨水为原料,用水热法合成出羟基氧化镓,并探讨了浓盐酸用量对羟基氧化镓纯度的影响。对合成产物进行XRD表征,结果表明合成产物为羟基氧化镓,且随着浓盐酸用量的增加,羟基氧化镓产品的纯度提高。     

Zirconia nano-colloids transfer from continuous hydrothermal synthesis to inkjet printing

Water dispersions of nanometric yttria stabilized zirconia (YSZ) particles synthesized by Continuous Hydrothermal Synthesis are transferred into nano-inks for thin film deposition. YSZ nanoparticles are synthesized in supercritical conditions resulting in highly dispersed crystals of 10 nm in size. The rheology of the colloid is tailored to achieve inkjet printability (Z) by using additives for regulating viscosity and surface tension. Inks with a wide range of properties are produced. A remarkable effect of nanoparticles on the ink printability is registered even at solid load < 1%vol. In particular, nanoparticles hinder the droplet formation at low values of the printability while suitable jetting is observed at high Z values, i.e. Z ≈ 20. For the optimized inks, we achieve high quality printing with lateral and thickness resolutions of 70 μm and ca. 250 nm respectively, as well as self-levelling effect with a reduction of the substrate roughness. Densification is achieved at sintering temperatures below 1200 °C.     

微波辅助高效水热合成SAPO-11分子筛

采用微波辅助的方法,以拟薄水铝石、硅溶胶等为原料,合成出纯相SAPO-11分子筛,大大减少了晶化时间,节约了合成成本。通过X射线衍射（XRD）,扫描电子显微镜（SEM）对合成的样品进行表征,详细考察了硅源、模板剂、硅铝比及晶化条件（晶化时间、晶化温度、pH）对合成的影响。结果表明,pH及晶化时间的影响较为显著,以硅溶胶为硅源,以二正丙胺为模板剂,在n(SiO2)∶n(Al2O3)=0.6、pH=5.7、晶化温度为185 ℃、晶化时间为10 h的条件下,采用微波辅助可以高效地合成纯相的SAPO-11分子筛。     

合成条件及添加三乙醇胺对水热法合成TS-1分子筛及其性能的影响

以正硅酸乙酯(TEOS)、钛酸丁酯(TBOT)、四丙基氢氧化铵(TPAOH)分别作硅源、钛源及模板剂水热合成了TS-1分子筛.考察了TEOS水解时的水硅比、TEOS水解温度、TPAOH用量及添加三乙醇胺(TEA)对TS-1分子筛合成及其性能的影响.采用XRD、SEM、N2吸附等手段对试样进行表征,同时以环己酮氨肟化反应考察试样的催化活性.结果表明,TEOS水解过程中,n(H2O)/n(S iO2)在20~40的范围内对TS-1的合成及性能影响不大.水解温度较高(60℃)时,加入少量TPAOH(n(TPAOH)/n(S iO2)=0.125)即可得到性能较好的TS-1,而在水解过程中添加适量TEA则能进一步改善TS-1分子筛的性能.在水解温度为60℃、n(S iO2)∶n(TPAOH)∶n(TEA)∶n(H2O)为1∶0.125∶0.065∶20时合成出的TS-1用于环己酮氨肟化反应,环己酮转化率达到90.7%,环己酮肟选择性达到92.4%,催化活性与高TPAOH用量合成的TS-1接近,而TPAOH的用量大大降低.     

酮醛树脂的合成与改性研究进展

酮醛树脂具有良好的溶剂相溶性和树脂相容性,是重要的涂料多功能助剂。对国内外酮醛树脂合成和改性研究进行了综述,较详细地介绍了酮醛原位改性、接枝和缩合改性研究进展,指出功能化将是酮醛树脂的发展方向,并对我国酮醛树脂的发展提出了建议。     

氢氧化镁晶须制备表征及改性研究

以碱式硫酸镁晶须(MHSH)和氢氧化钠为原料通过水热合成法制备出氢氧化镁晶须。实验确定了制备氢氧化镁晶须的适宜条件:n(碱式硫酸镁晶须)∶n(氢氧化钠)=1∶2,反应温度为200℃,反应时间为3 h,碱式硫酸镁晶须料浆质量分数为4%,氢氧化钠浓度为0.3 mol/L。对氢氧化镁晶须进行扫描电镜、X射线衍射及热分析得出,制备的氢氧化镁晶须为扇状,直径为1～2μm,长度为100～200μm,长径比为100～200。利用硅烷KH-550、硬脂酸、十二烷基苯磺酸钠、硬脂酸钠、油酸钾等表面改性剂对氢氧化镁晶须进行表面改性。结果表明:用油酸钾作表面改性剂,在氢氧化镁晶须料浆质量分数为5%、改性时间为30 min、改性温度为90℃、油酸钾用量为5%(质量分数)条件下可获得较好的改性效果,改性后晶须的活化指数达到99.48%。     

双马来酰亚胺树脂合成与改性研究进展

双马来酰亚胺(BMI)树脂具有良好的耐热性、电绝缘性、耐候性、力学性能和尺寸稳定性,但其脆性较大,不能满足使用要求。介绍了目前国内外BMI树脂的合成工艺(包括乙酸酐脱水法、热脱水闭环法和共沸蒸馏脱水法),简述了BMI的增韧改性方法(包括内扩链法改性、烯丙基化合物改性、胺类化合物改性、热塑性树脂改性、热固性树脂改性和橡胶增韧改性等),并提出了未来BMI树脂合成与改性的发展方向。