Fabrication of electronspun porous CeO2 nanofibers with large surface area for pollutants removal

The porous CeO₂ nanofibers with diameter of 100–140 nm were successfully synthesized by single-capillary electrospinning of a Ce(NO₃)₃·6H₂O/PVP precursor solution, followed by calcination. The preparation parameters, including solution parameters and process parameters, affecting the spinnability and the morphology of nanofibers were investigated and discussed systematically. And the effects of different calcination temperatures on the microstructure CeO₂ nanofibers were also studied. A plausible mechanism was proposed to explain the formation process of the CeO₂ nanofibers. The N₂ adsorption-desorption isotherm analysis showed that the specific surface area and average pore size of the nanofibers were 195.75 g/m² and 2.4 nm, respectively. Moreover, as absorbent, the porous CeO₂ nanofibers adsorbed the MO effectively. The adsorption experiment indicated that the adsorption process can be divided into two stages, including quick adsorption and gradual adsorption. And the adsorption capacities were not only determined by the specific surface area, but closely related to the pore size. Finally, the adsorption data were modeled by the pseudo-first-order and pseudo-second-order kinetics equations. The results showed that the pseudo-second order kinetics could best describe the adsorption of MO onto the porous CeO₂ nanofibers.     

Morphologically controlled synthesis of mesoporous alumina

The morphologically controlled synthesis of mesoporous alumina using Al(NO₃)₃/NH₃/urea/surfactant reaction system is demonstrated. Both the mesostructures and morphologies of the resulting alumina can be effectively controlled via adjusting the synthesis parameters, including reactant compositions, surfactant kinds and hydrothermal conditions. With the aid of surfactants, mesoporous alumina with spheres, rods, fibers and three-dimensional dumbbell, flower-like hierarchical superstructures on the microscopic scale has been obtained. Through characterization by N₂ physisorption, X-ray diffraction, electron microscopy and thermogravimetry analysis, the effects of synthesis conditions on structures and shapes of products are explained and the possible formation mechanism of the controlled morphologies is also proposed.     

The defluoridation of water by acidic alumina

Fluoride is considered as a major inorganic pollutant present in drinking water. To remove this excess fluoride, defluoridation was done by alumina. In the present study, alumina used was acidic in nature and hence considered as a good fluoride removing adsorbent. Characterization of the adsorbent was done by XRD, SEM, BET and FTIR with BET surface area of 144.27 m²/g. Systematic adsorption experiments were carried out with different process parameters such as contact time, adsorbent mass, pH, temperature and stirring speed. Fluoride adsorption by alumina was highly pH dependent. Maximum fluoride was removed from water at pH 4.4. At very low and very high pH, fluoride removal efficiency was affected. The study of thermodynamic parameters inferred that physical adsorption was dominant with activation energy of 95.13 kJ/mol and endothermic behavior of the process. The kinetics study concluded that pseudo second order kinetics was followed by the adsorption process. Adsorption equilibrium was studied with Langmuir and Freundlich isotherm models. The adsorption process followed Langmuir isotherm with an adsorption capacity of 8.4 mg/g. A regeneration study was proposed in order to reuse the adsorbent for better economy of the process. Finally, a process design calculation was reported to know the amount of adsorbent required for efficient removal of fluoride from aqueous medium.     

Capacitance limits of high surface area activated carbons for double layer capacitors

A large specific surface area (SSA) of carbon materials used for electrochemical double layer capacitors (EDLC) is the most important parameter leading to a large gravimetric capacitance (C_g). However, for a SSA determined with the differential functional theory (DFT) model above a value of 1200 m²/g the plot of C_g versus S_DFT exhibits a plateau. We suggest that this limitation of C_g can be ascribed to a space constriction for charge accommodation inside the pore walls. As a consequence, the use of extremely high surface area carbons for EDLCs may be unprofitable.     

改性活性氧化铝除氟性能研究

通过静态实验,研究了改性活性氧化铝(MAA)对F-的吸附性能,考察了吸附时间、改性活性氧化铝的用量对除氟性能的影响,并与新型除氟树脂的除氟性能进行了比较.研究结果表明:活性氧化铝的用量为4 g时,除氟效率最高,为94.57%;活性氧化铝与含氟水的最佳接触时间为3 h;MAA在较低用量(＜4 g)时,除氟效率不如除氟树脂高,但是在较高用量(≥4 g)下,MAA则高于树脂的除氟效率.     

改性石英砂及沸石滤料除氟性能比较

研究了以石英砂和沸石为骨架的吸附材料经铝盐改性处理后,对饮用水中过量氟的处理行为,比较两种改性滤料处理能力的不同并对差异进行分析。实验表明,物理空间结构性强的沸石作为改性滤料的应用有着独到的优越性,除氟效率达98%以上,是一种无毒无害的除氟处理方法。     

Dendritic porous alumina with high porosity by directional freeze casting using a binary solution for bacterial removal

High-porosity dendritic porous alumina was fabricated by using tertiary butanol (TBA) hydrate crystals combined with directional freeze casting. The porosity of this porous alumina approximated 80 %, and its high porosity resulted in high water flux. Dendritic pores improved the physical interception capability of porous ceramics due to the intrinsic moving paths and intercepts from the pore structure. Changes in the TBA content (from 70 vol.% to 85 vol.%) caused a change in pore size from 36.58 μm to 11.54 μm and pore structure (change order: snowflake, dendritic, rod-like, and needle-like), which are important factors affecting water flux and interception capability. The interception and removal of Escherichia coli by 7 mm-height porous ceramics with dendritic structure and an average pore size of 27.90 μm reached 100 % at pH 7.2. This study provides a simple and low-cost method for the effective removal of bacteria.     

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.     

聚硅酸改性对活性氧化铝除氟性能的影响

采用聚硅酸对活性氧化铝进行改性,研究了SiO2百分含量、聚硅酸浸泡时间、焙烧温度及焙烧时间对改性活性氧化铝除氟性能的影响。结果表明,改性活性氧化铝能将水中的氟离子浓度从9.5 mg/L降低到0.89 mg/L,吸附容量提高了30%。因此,聚硅酸改性能有效提高活性氧化铝的除氟性能。     

Organic/inorganic double-precursor cross-linked alumina aerogel with high specific surface area and high-temperature resistance

Alumina aerogel has drawn a great research interest in the aerogel community owing to its great high-temperature heat resistance. The typical preparation can be divided into two approaches depending on the type of precursors. However, the alumina aerogel derived from organic aluminum alkoxides suffers from poor monolithic integrity, whereas the one from inorganic aluminum salts presents unsatisfied thermal stability. In this work, we develop a novel organic/inorganic double-precursor cross-linking method to prepare alumina aerogels. Aluminum chloride hexahydrate is used to provide an acid condition for the hydrolysis and condensation reaction of aluminum sec-butoxide (ASB), and serves as a reactant to co-condensate with the hydrolyzed ASB to form an interpenetrating chain structure. The resulting alumina aerogel exhibits a high specific surface area (SSA) of 667 m²/g and good high-temperature thermal insulation performance. Moreover, it can still retain SSA of 224 and 105 m²/g after heating at 1000 and 1300°C, respectively.     

Removal of fluoride from drinking water by adsorption onto alum-impregnated activated alumina

The ability of the alum-impregnated activated alumina (AIAA) for removal of fluoride from water through adsorption has been investigated in the present study. All the experiments are carried out by batch mode. The effect of various parameters viz. contact time, pH effect (pH 2–8), adsorbent dose (0.5–16 g/l), initial fluoride concentration (1–35 mg/l) has been investigated to determine the adsorption capacity of AIAA. The adsorbent dose and isotherm data are correlated to the Bradley equation. The efficacy of AIAA to remove fluoride from water is found to be 99% at pH 6.5, contact time for 3 h, dose of 8 g/l, when 20 mg/l of fluoride is present in 50 ml of water. Energy-dispersive analysis of X-ray shows that the uptake of fluoride at the AIAA/water interface is due to only surface precipitation. The desorption study reveals that this adsorbent can be regenerated following a simple base–acid rinsing procedure, however, again impregnation of the regenerated adsorbent (rinsed residue) is needed for further defluoridation process.     

Processing of large and complex-shaped fine-grained alumina bodies with high transparency

The paper presents the development of unique processing methods for large alumina windows, domes, and thin sheets with a fine-grained structure and high optical transmission. Gelcasting combined with post-hot isostatic pressing proved to be a suitable processing method for windows and domes. This method provided alumina ceramics with a real in-line transmission of up to 72 % at a wavelength of 633 nm and with a theoretical in-line transmission in the infrared region between 1500 and 4000 nm for 0.8 mm thick bodies. Complex-shaped bodies, domes, were prepared with minimum warping during sintering. Thin transparent alumina sheets were prepared by gel-tape casting. This novel tape casting method utilized the advantages of the gelcasting method. The real in-line transmission of the tapes was lower compared with the windows. Nevertheless, the thin tapes with a thickness below 350 μm exhibited reasonable transparency even after pressureless sintering and without a polishing of sintered samples.     

Development of a novel nano-biosorbent for the removal of fluoride from water

The study was designed to investigate the use of two sorbents namely (i) Fe₃O₄ nanoparticles immobilized in sodiumalginate matrix (FNPSA) and (ii) Fe₃O₄ nanoparticles and saponified orange peel residue immobilized in sodium alginate matrix (FNPSOPR) as sorbents for fluoride removal from contaminated water. The synthesized nanoparticles were analyzed and characterized by dynamic light scattering, X-ray diffraction, vibrating sample magnetometry, and scanning electron microscopy with energy dispersive X-ray spectroscopy and Fourier transform-infrared spectrometry. The sorbentmatriceswere prepared in the formof beads and surface functionalized to enable enhanced sorption of fluoride ions. Batch sorption studieswere carried out and the sorption isotherm and reaction kinetics were analyzed. Both the sorbents followed Langmuir model of isotherm and fitted well with Pseudo first order reaction. The maximum sorption capacity exhibited by FNPSA and FNPSOPR was 58.24 mg·g^-1 and 80.33 mg·g^-1 respectively. Five sorption–desorption cycles exhibited 100%, 97.56%, 94.53%, 83.21%, and 76.53% of regeneration of FNPSOPR. Accordingly, it is demonstrated that FNSOPR could be used as a promising sorbent for easy and efficient removal of fluoride from contaminated water with good reusability. The current work suggests a simple and effective method to remove fluoride from contaminated water.     

Preparation of ordered mesoporous SiCN ceramics with large surface area and high thermal stability

For the first time, highly ordered two-dimensional (2-D) and three-dimensional (3-D) mesoporous SiCN ceramics with high surface area and high thermal stability were prepared by nanocasting a preceramic polymer solution into mesoporous carbon templates, CMK-3 and CMK-8, respectively. As a negative replica of CMK-3 carbon, the obtained mesoporous SiCN ceramic possessed an ordered 2-D hexagonal mesostructure, which is similar to the structure of SBA-15 silica except for the reduced dimensions. An ordered 3-D cubic mesoporous SiCN ceramic was also fabricated using CMK-8 as a template. The wall of the mesoporous SiCN replicas consisted of an amorphous SiCN ceramic phase, which possessed high thermal stability at high temperature up to 1000 °C. N₂-sorption isotherms revealed that these ordered mesoporous SiCN ceramics have high BET surface areas (up to 472 m² g⁻¹) and narrow pore-size distributions, which was preserved even after a re-treatment at 1000 °C in air. The use of carbon template played an important role in the preparation of mesoporous SiCN replicas and enhanced the thermal stability of the SiCN products. It is expected that many other types of ordered mesoporous ceramics can be prepared from nanoporous carbon by nanocasting method.     

Template synthesis of large pore ordered mesoporous carbon

Nanocast carbon (NCC-1) with large pores and ordered structure was synthesized via a nanocasting process using aluminum-containing SBA-15 as template and furfuryl alcohol (FA) as carbon precursor. This carbon has several interesting features, such as two steps with distinguished hystereses in the nitrogen sorption isotherm, high surface area of 2000 m²/g and large pore volumes of 3.0 cm³/g. It was found that the key factors in the synthesis of such carbons are the aging temperature of the SBA-15 template, the concentration of furfuryl alcohol (dissolved in trimethylbenzene), and the carbonization temperature. The optimal conditions for materials with high surface area and pore volumes are SBA-15 starting materials aged at 140 °C, 25 vol% of FA solution and 850–1100 °C carbonization temperatures. Moreover, it has been demonstrated that such nanocast carbon can be synthesized in a more facile way than previously reported. Purely siliceous SBA-15 without the need of Al³⁺-incorporation can be directly used as template. In this case, the polymerization catalyst—oxalic acid and FA were simultaneously introduced into the pore space of SBA-15.     

Compound surfactant-based emulsion method for the preparation of high-porosity alumina microspheres

Porous alumina microspheres have attracted significant attention owing to their high mechanical strength and excellent chemical and thermal stability. The emulsion method is considered as a simple and controllable method for the preparation of inorganic microspheres. However, preparing alumina microspheres with the emulsion method is challenging because the emulsification of the precursor is inhibited by the rapid hydrolysis of aluminum alkoxide. Herein, we report a new emulsion method for the preparation of high-porosity alumina microspheres using a combination of ionic and non-ionic surfactants; in this method, the compound surfactants act as a template agent to guide aluminum alkoxide to form a lamellar structure through self-assembly. The decomposition of the templating agent and transformation of the alumina crystal at a high temperature result in structural collapse and formation of lamellar pores. Compound surfactants increased the spheroidization rate of the emulsion from 47% to 63% after hydrolysis, whereas the particle size was decreased by almost half. Additionally, the morphology and porosity of the alumina microspheres were changed. With increasing anionic surfactant content, the porosity increased initially and then decreased. The porosity of the alumina microspheres reached a maximum value of 76% at the 1:1 mass ratio of the non-ionic to anionic surfactants. Heat treatment was found to change the size of lamellar pores, with the pore diameter reaching maximum value at 1300 °C. The compound surfactants also increased the compressive stress and specific surface area of the porous alumina microspheres.     

Template-directed synthesis of porous alumina particles with precise wall thickness control via atomic layer deposition

Highly porous alumina particles with precise wall thickness control were synthesized by atomic layer deposition (ALD) of alumina on highly porous poly(styrene-divinylbenzene) (PS-DVB) particle templates. Alumina ALD was carried out using alternating reactions of trimethylaluminum and water at 33 °C. The growth rate of alumina was ∼0.3 nm per coating cycle. The wall thickness can be precisely controlled by adjusting the number of ALD coating cycles. Thermo-gravimetric analysis, X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and transmission electron microscopy were used to characterize the fabricated porous alumina particles. The effect of number of ALD coating cycles and calcination temperature on the mesoporous structure of the alumina particles was investigated. γ-Alumina was formed at temperature above 600 °C. Porous alumina particles with a surface area of 80-100 m²/g were obtained and thermally stable at 800 °C. The pore volume of the porous particles can be as high as 1 cm³/g after calcination at 800 °C. Such porous alumina particles may find wide application in nanotechnology and catalysis.     

One-step synthesis of few-layered-graphene/alumina powders for strong and tough composites with high electrical conductivity

The chemical vapor deposition of carbon onto a commercial α-Al₂O₃ powder bed produces a pristine film of few-layered-graphene (FLG) uniformly covering the α-Al₂O₃ grains. This obviates both the manipulation of nanocarbons, lengthy mixing steps and the risk of damaging any pre-existing graphene platelets. The powders are consolidated to 99 % by SPS, producing samples where a FLG film is located along the grain boundaries of the submicron α-Al₂O₃. Compared to the pure α-Al₂O₃, the composites are moderately stronger and similarly tough and hard due to crack-deflection and crack-bridging and they are electrically conducting with a percolation threshold below 0.74 vol.% of carbon. The high conductivity values reflect the high quality of the thin FLG film and its continuous nature over very long distances. The samples are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy.