Reversible CO2 capture by ZnO slurry leading to formation of fine ZnO particles

ZnO powders were synthesized by heating precursors, prepared by the addition of ethylene diamine tetraacetate to an aqueous solution of zinc acetate, at 500?°C in air. A ZnO slurry was prepared by adding distilled water to the synthesized ZnO powder. X-ray diffraction studies confirmed that the ZnO slurry adsorbed CO₂ at 25?°C under a CO₂ gas flow to produce Zn₅(CO₃)₂(OH)₆. The CO₂ adsorption ratio of the ZnO slurry was influenced by the amount of added water. When the weight ratio of water/ZnO was 1, the ZnO slurry had the largest CO₂ adsorption ratio. Scanning electron microscopy and thermal gravimetry showed that the plate-like Zn₅(CO₃)₂(OH)₆ particles thermally decomposed at 300?°C in air leading to a single-phase ZnO powder consisting of nanoparticles with approximately 20?nm in diameter. The specific surface area of the reformed ZnO powder increased to approximately 82?m²/g through the thermal decomposition of Zn₅(CO₃)₂(OH)₆. The ZnO slurry was capable of adsorbing CO₂ under a CO₂ flow at 25?°C and desorbing CO₂ under an air flow at 300?°C. The CO₂ adsorption ratio of the ZnO slurry reached 80%–90% at 25?°C even after the fifth CO₂ adsorption and desorption cycle.     

Preparation of stabilized lidocaine particles by a combination of supercritical CO2 technique and particle surface control

Lidocaine particles were prepared by the rapid expansion of the supercritical fluids into aqueous solution (RESAS). About 150–300 nm lidocaine particles could be temporarily observed when collected in water at concentration of 10 mg/cc, but the particles developed into 50 μm needle crystals just 30 min later. To prevent the fast aggregation of the particles as well as further crystal growth, modifications on particle surfaces by adding surfactants and introduction of electrostatic repulsion between particles were conducted. When a surfactant (sucrose stearic acid ester S-1570) was added to the collecting aqueous solution, the particle growth was alleviated and no large needle crystals were formed. However, the long-term stability needs to be improved because the lidocaine particles tend to grow from submicron to a few microns in a few days even stored in the 1% S-1570 solution. Electrostatic repulsion between particles is found effective to stabilize the submicron particles during the storage. When the pH value of the aqueous solution with 1% S-1570 was adjusted to 8.5 by adding KOH, the lidocaine particles suspending in this solution showed good stability that the particle size was able to be controlled in submicron level in 3 months.     

超临界CO2辅助制备PHAs载药微球研究概况

聚羟基烷酸酯(PHAs)是一种具有良好生物相容性的可降解生物材料。主要介绍了超临界二氧化碳抗溶剂法(SAS)辅助制备PHAs空白微球及载药微球的研究现状,探讨了该方法制备载药微球的原理及优势。最后对其研究发展方向进行了展望。     

超临界CO2流体干燥合成ZrO2气凝胶及其表征

以无机盐为原料,采用沉淀法结合超临界CO2流体干燥技术成功地制备了ZrO2气凝胶.借助TG/DSC、XRD、TEM、DLS以及N2物理吸附等手段对其性能进行表征.结果显示,超临界CO2流体干燥可以有效地防止干燥过程中胶体粒子之间的硬团聚作用,在基本保持湿凝胶网络结构的情况下实现液相的脱除,从而使合成的ZrO2具有高比表面积和大孔体积等特点.此外,样品的TEM和DLS分析显示,纳米ZrO2颗粒首先形成具有空间网络结构的簇团,尺寸为数百个纳米的簇团堆积形成ZrO2气凝胶;气凝胶的空间网络结构特征在中等温度的热处理过程中不会遭到完全破坏.     

超临界CO2抗溶剂法制备紫杉醇缓释微球

采用超临界流体强制分散溶液技术,以D,L-聚乳酸和D,L-聚乳酸-聚乙二醇共聚物为载体材料,分别制备了紫杉醇缓释微球.通过扫描电镜、激光粒度仪检测微球外形及粒径分布;紫外吸光度法测量其载药量和包封率,恒温振荡透析法检测药物的体外释放性能;MTT法检测载药微球对Hela细胞的抑制作用.实验表明,两种载体的缓释微球球形度均较好,表面光滑,平均粒径较小,且粒径分布较窄.以聚乳酸和共聚物为载体的缓释微球载药量分别为5.4%±0.3%和5.3%±0.4%,包封率分别为51%±3%和45%±3%;药物释放呈缓释模式,共聚物载药微球药物释放速率较快.MTT法检测结果表明,载药微球对Hela细胞的增殖有明显抑制,共聚物载药微球对细胞增殖抑制更为明显.     

Development of core-shell microcapsules by a novel supercritical CO2 process

5-fluorouracil-SiO₂-poly(L-lactide) (5-Fu-SiO₂-PLLA) microcapsules were prepared in a novel process of solution-enhanced dispersion by supercritical CO₂ (SEDS). The SiO₂ nanoparticles were loaded with 5-Fu by adsorption at the first place, then the 5-Fu-SiO₂ nanoparticles were coated with PLLA by a modified SEDS process. The resulted microcapsules were characterized by scanning electron microscope (SEM), laser diffraction particle size analyzer, Fourier transform infrared spectrometer (FTIR) and thermogravimeter-differential scanning calorimeter (TG-DSC). The drug load, encapsulation efficiency and drug release profiles were also determined. The resulted microcapsules exhibited a rather spherical shape, smooth surface, and a narrow particle size distribution with a mean particle size of 536 nm. The drug load and encapsulation efficiency of the samples were 0.18% and 80.53%, respectively, 25.05% of 5-Fu was released in the first half hour, then drug released in a sustained process, which was much slower than that of without coated by PLLA. The results indicated that the modified SEDS process could be used to produce drug-polymer microcapsules with a core-shell structure, high encapsulation efficiency and sustained drug release effect.     

用超临界CO2法制备聚乳酸三维多孔支架材料

在超临界CO2(SC—CO2)条件下制备了生物相容性良好的聚乳酸(PLA)多孔材料，研究了PLA的分子量、SC—CO2的压力、温度和处理时间对多孔材料的结构形态、孔隙率和玻璃化温度的影响。结果表明：支架材料的孔洞分布、结构形态和孔隙率不仅与聚乳酸的分子量有关，而且与处理样品的压力、温度和时间关系密切；经超临界CO2处理后材料的玻璃化温度(Tg)有所升高，与传统的方法所制得的材料相比较，多孔材料不仅杂质少，孔径孔率分布均匀，孔洞表面粗糙，而且在大孔之间几乎布满了直径为10—20μm的微孔，该结构提供了营养物质和新陈代谢的通道，且细胞和生长因子也能通过。     

小球藻光生物反应器脱除空气中二氧化碳的研究

采用自制的光生物反应器,研究了不同条件对小球藻脱除空气中CO2效果的影响.光生物反应器为圆柱形有机玻璃容器,底面积0.0154m2,高0.2m,容积为3L,反应器内小球藻藻体干重约为7.2g.实验结果表明,用小球藻来固定CO2不仅能脱除通入气体中的CO2,而且可以促进小球藻生长.通入气体的流量和CO2浓度对CO2的脱除率有很大影响.在适宜的实验条件下(通入气体流速为0.6L/min、CO2浓度约1%、温度25~30℃、光强3500lux、pH9.5~8.5),入口气体中CO2约有50%被脱除,该光生物反应器脱除CO2的能力约为0.118g/(L.h).可见利用小球藻光生物反应器固定CO2具有较好的脱除效果,值得进一步研究.     

Histological evaluation of xenogeneic bone treated by supercritical CO2 implanted into sheep

Untreated xenogeneic bone is known to be rejected when implanted into human or animal bone. It contains bone marrow tissue which is highly antigenic. To be used as an alternative to auto and allografts, this antigenic material must be entirely removed. Removal of this soft tissue contained in the bone structure was performed using a delipidation process with supercritical CO₂ followed by a deproteination with hydrogen peroxide or protease extraction. Such prepared materials were implanted into sheep bone for periods of 3 weeks, 2 months and 4 months. Bone whose organic matrix was destroyed by sintering, and untreated xenogeneic bone were used as controls. Qualitative histology and histomorphometry, measuring the percentage of the material in contact with newly formed, bone were performed on implant sections. This showed that the osseointegration of the supercritical CO₂-treated bone samples was equivalent to that of bone made anorganic by sintering while the untreated bone was embedded into an inflammatory tissue made up of macrophages, giant cells and plasmocytes.     

Production of graphene nanosheets by supercritical CO2 process coupled with micro-jet exfoliation

A facile and cost-effective method which combines supercritical CO₂ and micro-jet exfoliation has been developed for producing graphene nanosheets with high-quality. CO₂ molecules can intercalate into the interlayer of graphite because of their high diffusivity and small molecule size in supercritical operation. The tensile stress induced by graphite interfacial reflection of compressive waves exert on the graphite flakes, which lead to further exfoliation of graphite. Scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM), Raman spectrum and X-ray diffraction (XRD) are used to identify morphology and quality of the exfoliated graphene nanosheets, which reveal that the graphite was successfully exfoliated into graphene and more than 88% of graphene nanosheets are less than three layers. The yield of graphene nanosheets is about 28 wt% under optimum conditions, which can be greatly improved by repeated exfoliation of the graphene sediment. The pure graphene film has a high conductivity of 2.1 × 10⁵ S/m.     

Selective collection of fine particles by water drops

This study was concerned with the interaction between a gaseous dispersion of fine particles travelling in the horizontal direction and discrete drops of water falling vertically through the dispersion. A simple analytical model of the particle–drop collision was developed to describe the particle recovery by the drops as a function of the water flux, covering two extremes of relative velocity between the particles and drops. The Discrete Element Method was used to validate the analytical model. Further validation of the model and insights were obtained through experimental studies. The physical process of wetting was observed to be important in influencing the tendency of particles to become engulfed by the drops of water, or to either adhere to the drops or by-pass the drops altogether. Hydrophilic particles were readily engulfed while hydrophobic particles, at best, adhered to the surface of the drop, or failed to attach. Moreover, the recovery of the hydrophilic silica particles was significantly higher than the recovery of hydrophobic coal particles, with the selectivity ratio approximately 1.5. Spherical ballotini particles were the most sensitive, with a notable increase in recovery when cleaned, and evidence of increased recovery with increasing particle size. The recovery of irregular shaped silica flour particles, however, was largely independent of the particle size. A similar result was observed for irregular coal particles, though the recoveries were all lower than relatively more hydrophilic ballotini or silica flour.     

Tuning a grating-controlled CO2 laser by means of a scanning slit

The use of diffraction gratings as tuning devices in laser resonators is well known and has been demonstrated abundantly for CO2 lasers. As the grating rotates, the lines of the infrared spectrum of the CO2 molecule reach threshold and oscillate one by one. Here it is shown that it is possible to obtain the same spectrum by moving an aperture inside the cavity perpendicularly to the laser axis while keeping the grating stationary. The conditions for obtaining a well-resolved spectrum are formulated for both the rotating grating and the moving aperture case.     

Ultra-fine particles of amorphous TiO2 studied by means of positron annihilation spectroscopy

Microscopic structures and mechanical properties of amorphous TiO2 ultra-fine particles have been studied by positron annihilation spectroscopy. A positron lifetime of about 1.5 ns was found as the longest lifetime component 3 which is attributed to the ortho-positronium annihilation in open space. The lifetime 3 and the corresponding intensity I3 was independent of atmosphere: vacuum and various gasses. Accordingly, a micro-void is contained inside the particle as the open space. An intermediate lifetime 2 was approximately 0.4 ns. The intensity I2 was strongly affected by the atmosphere. No effect was found for the particles, the surface of which was coated by silicon dioxide film. This component is arisen from the positron annihilation on the particle surface and the particles contain the surface cracks. When the volume of particles packed in an ampoule was decreased by 1/4 times by compression, the longest component as well as the intermediate one disappeared and only the shortest-lifetime component 1 of about 0.24 ns remained. To conclude, the particles are so soft that the micro-voids and the surface cracks are collapsed by compression.     

Control of morphological properties of porous biodegradable scaffolds processed by supercritical CO2 foaming

A low cost supercritical CO₂ foaming rig with a novel design has been used to prepare fully interconnected and highly porous biodegradable scaffolds with controllable pore size and structure that can promote cancellous bone regeneration. Porous polymer scaffolds have been produced by plasticising the polymer with high pressure CO₂ and by the formation of a porous structure following the escape of CO₂ from the polymer. Although, control over pore size and structure has been previously reported as difficult with this process, the current study shows that control is possible. The effects of processing parameters such as CO₂ saturation pressure, time and temperature and depressurisation rate on the morphological properties, namely porosity, pore interconnectivity, pore size and wall thickness- of the scaffolds have been investigated. Poly(d,l)lactic acid was used as the biodegradable polymer. The surfaces and internal morphologies of the poly(d,l)lactic acid scaffolds were examined using optical microscope and micro computed tomography. Preosteoblast human bone cells were seeded on the porous scaffolds in vitro to assess cell attachment and viability. The scaffolds showed a good support for cell attachment, and maintained cell viability throughout 7 days in culture. This study demonstrated that the morphology of the porous structure can be controlled by varying the foaming conditions, allowing the porous scaffolds to be used in various tissue engineering applications.     

Determination of solubilities of uranium complexes in supercritical CO2 by on-line laser-induced fluorescence

A new approach to the measurement of solubilities in supercritical CO2 is reported, utilizing laser-induced fluorescence. This selective technique was found to be capable of rapid multipoint solubility measurements with high sensitivity (10(-9) M). The sensitivity enables measurements to be performed with small amounts of analytes and at low pressure, 80-130 atm, typically below the range of other methods. Four uranyl complexes were investigated using this method, UO2(TTA)2.H20, UO2(TTA)2.TBP, UO2(TTA)2.TOPO, and UO2(NO3)2.2TBP (where TTA = thenoyltrifluoroacetone, TBP = tributyl phosphate, and TOPO = trioctyl phosphine oxide). Comparison with solubility data previously obtained with UV-visible spectroscopy shows good agreement between the techniques. We have shown that the Chrastil solubility equation is equally valid at lower ScF densities, and consequently, solubility values determined at high pressures can be extrapolated to the low-pressure regions and vice versa for solid materials.