Yingchao Dong

Recycling of fly ash for preparing porous mullite membrane supports with titania addition

In order to effectively utilize industrial waste fly ash, porous mullite ceramic membrane supports were prepared from fly ash and calcined bauxite with chemically pure titania as sintering additive. The effects of TiO(2) on the sintering behaviors and main properties of porous mullite were studied in detail. Due to the addition of titania, the sintering of the flyash-based mullite was inhibited at low temperatures, but effectively improved at high temperatures, the latter is suitable for preparing porous mullite membrane supports by incomplete sintering. Titania entered into liquid glassy phase with low high-temperature viscosity during sintering, resulting in the improvement of sintering activity, as well as the lowering of secondary mullitization temperature (where 2.0% titania). Between 1300 and 1500 degrees C, with increasing titania content, the samples exhibit increased trends in both linear shrinkage percent and bulk density, but a slightly decreased trend in open porosity, at all sintering temperatures. At 1300-1500 degrees C, the samples sintered at 1450 degrees C for 2h exhibit the lowest shrinkage and bulk density, as well as the highest open porosities in the investigated titania content range of 0-6.0 wt.%. Also, with increasing titania content, the pore size decreases slightly but the three-point flexural strength increases gradually at 1450 degrees C.

Reaction-sintered porous mineral-based mullite ceramic membrane supports made from recycled materials

Bulk porous mullite supports for ceramic membranes were prepared directly using a mixture of industrial waste fly ash and bauxite by dry-pressing, followed by sintering between 1200 and 1550 degrees C. The effects of sintering temperature on the phase composition and shrinkage percent of porous mullite were studied. The XRD results indicate that secondary mullitization reaction took place above 1200 degrees C, and completed at 1450 degrees C. During sintering, the mixture samples first shrunk, then expanded abnormally between 1326 and 1477 degrees C, and finally shrunk again above 1477 degrees C. This unique volume self-expansion is ascribed to the secondary mullitization reaction between bauxite and fly ash. More especially, the micro-structural variations induced by this self-expansion sintering were verified by SEM, porosity, pore size distribution and nitrogen gas permeation flux. During self-expansion sintering, with increasing temperature, an abnormal increase in both open porosity and pore size is observed, which also results in the increase of nitrogen gas flux. The mineral-based mullite supports with increased open porosity were obtained. Furthermore, the sintered porous mullite membrane supports were characterized in terms of thermal expansion co-efficient and mechanical strength.

Environment-oriented low-cost porous mullite ceramic membrane supports fabricated from coal gangue and bauxite.

Porous mullite ceramic supports for filtration membrane were successfully fabricated via recycling of coal gangue and bauxite at sintering temperatures from 1100 to 1500°C with corn starch as pore-forming agent. The dynamic sintering behaviors, phase evolution, shrinkage, porosity and pore size, gas permeation flux, microstructure and mechanical property were systematically studied. A unique volume-expansion stage was observed at increased temperatures from 1276 to 1481°C caused by a mullitization-crystal-growth process. During this stage, open porosity increases and pore size distributions broaden, which result in a maximum of nitrogen gas flux at 1400°C. The X-ray diffraction results reveal that secondary mullitization took place from 1100°C and the major phase is mullite with a content of ∼84.7wt.% at 1400°C. SEM images show that the as-fabricated mullite supports have a porous microstructure composed of sintered glassy particles embedded with inter-locked mullite crystals, which grew gradually with increasing temperature from rod-like into blocky-like morphologies. To obtain mullite membrane supports with sufficient porosity and acceptable mechanical strength, the relationship between porosity and mechanical strength was investigated, which was fitted using a parabolic equation.

Enhancing the photocatalytic H2 evolution activity of red phosphorous by using noble-metal-free Ni(OH)2 under photoexcitation up to 700 nm

Ni(OH)2 nanoparticles are demonstrated to be cost-efficient alternatives to Pt co-catalysts for enhancing the visible-light photocatalytic H2 evolution activity of red phosphorous (P) when deposited onto its surface. Ni(OH)2-modified red P exhibits 1.12 times higher photocatalytic activity for H2 evolution than that of Pt-deposited red P under a wide range of visible light.

Fabrication and Water Treatment Application of Carbon Nanotubes (CNTs)-Based Composite Membranes: A Review

Membrane separation technology is widely explored for various applications, such as water desalination and wastewater treatment, which can alleviate the global issue of fresh water scarcity. Specifically, carbon nanotubes (CNTs)-based composite membranes are increasingly of interest due to the combined merits of CNTs and membrane separation, offering enhanced membrane properties. This article first briefly discusses fabrication and growth mechanisms, characterization and functionalization techniques of CNTs, and then reviews the fabrication methods for CNTs-based composite membranes in detail. The applications of CNTs-based composite membranes in water treatment are comprehensively reviewed, including seawater or brine desalination, oil-water separation, removal of heavy metal ions and emerging pollutants as well as membrane separation coupled with assistant techniques. Furthermore, the future direction and perspective for CNTs-based composite membranes are also briefly outlined.

Coal fly ash industrial waste recycling for fabrication of mullite-whisker-structured porous ceramic membrane supports

With recyclable industrial waste coal fly ash and bauxite as starting materials, porous mullite-whisker-structured ceramic membrane supports were fabricated at sintering temperatures ranging from 1100 to 1400 °C with addition of AlF3 and MoO3 as crystallization catalyst and mineralizer, respectively. Dynamic sintering of mullite membrane supports was first studied. Then the characterizations were focused on open porosity, pore size distribution, gas flux and mechanical properties, microstructure and phase evolution. It shows that the introduction of MoO3 effectively promoted the growth of elongated mullite crystals in the membrane support by reducing the high temperature viscosity of the liquid melt. Addition of 5 wt% MoO3 lowered the secondary mullitization temperature, resulting in more mullite formation at temperatures as low as 1200 °C, while a porosity of 45.4 ± 0.9% was obtained. After sintering at 1200 °C, the open porosity was 47.3 ± 0.6% for the sample containing 4 wt% AlF3. The co-introduction of MoO3 and AlF3 promoted formation of a whisker-interlocked porous structure, which effectively improved open porosity and permeation flux without significant mechanical strength degradation.

A high-strength Sm-doped CeO2 oxide-ion conducting electrolyte membrane for solid oxide fuel cell application

Nano-sized Ce0.79Sm0.2Cu0.01O2−δ (CSCO) and Ce0.80Sm0.2O2−δ (CSO) electrolyte powders were synthesized by the PVA-assisted combustion method, sintered at various temperatures and electrochemical properties, mechanical properties and microstructures were characterized in detail. The results demonstrate that besides a considerable lowering of sintering temperature to achieve high levels of densification, the addition of very minor amounts of CuO as a co-dopant to CSO significantly enhanced mechanical properties (strength and hardness) without great degradation in electrochemical performance. The CSCO sintered at 1100 °C exhibits a biaxial flexural strength of 319 ± 41 MPa which compared with 194 ± 57 MPa for CSO with a slightly lower relative density sintered at 1400 °C. The enhancement of biaxial flexural strength is due to the formation of stronger CuO-rich grain boundaries during sintering as a consequence of the slight modification in grain boundary chemistry which leads to changes in fracture mode from intergranular to transgranular.

Application of surface complexation modeling on modification of hematite surface with cobalt cocatalysts: a potential tool for preparing homogeneously distributed catalysts

The knowledge required to synthesize homogeneously distributed catalysts on the support surfaces is strongly reliant on understanding the interaction between the catalyst and surface of support, which is identical to the descriptions of interactions between environmental pollutants and adsorbents in the field of environmental chemistry. The connection between catalyst synthesis and environmental chemistry is demonstrated herein by using surface complexation modeling (SCM), whose physical foundation is built on the stoichiometric reaction between one solute and one adsorption site on the surface of adsorbents. As suggested by our simulation and supported by TEM images, the manipulation of either homogeneous distribution or coarse clusters of cobalt cocatalysts over hematite surfaces can be achieved by adjusting the pH and initial Co2+ concentration. This is attributed to the conversion of adsorbed Co2+ or Co(OH)2 precipitates on hematite surfaces. Different surface distributions of cobalt cocatalysts further influence the reactivity of photodegradation of organic dyes and photoelectrochemical reactions, which is strongly dependent on the occurrence of the Fenton reactions or charge transport. Our results not only demonstrate the potential of SCM on guiding the preparation of homogeneously distributed catalysts but also indicate that the abundant amount of knowledge in environmental science could be adopted to design an appropriate protocol for catalyst synthesis.

Incorporation of zinc for fabrication of low-cost spinel-based composite ceramic membrane support to achieve its stabilization.

In order to reduce environment risk of zinc, a spinel-based porous membrane support was prepared by the high-temperature reaction of zinc and bauxite mineral. The phase evolution process, shrinkage, porosity, mechanical property, pore size distribution, gas permeation flux and microstructure were systematically studied. The XRD results, based on a Zn/Al stoichiometric composition of 1/2, show a formation of ZnAl2O4 structure starting from 1000°C and then accomplished at 1300°C. For spinel-based composite membrane, shrinkage and porosity are mainly influenced by a combination of an expansion induced by ZnAl2O4 formation and a general densification due to amorphous liquid SiO2. The highest porosity, as high as 44%, is observed in ZnAl4 membrane support among all the investigated compositions. Compared with pure bauxite (Al), ZnAl4 composite membrane support is reinforced by ZnAl2O4 phase and inter-locked mullite crystals, which is proved by the empirical strength-porosity relationships. Also, an increase in average pore diameter and gas flux can be observed in ZnAl4. A prolonged leaching experiment reveals the zinc can be successfully incorporated into ceramic membrane support via formation of ZnAl2O4, which has substantially better resistance toward acidic attack.

Water Permeates in Ceramic Membrane Modified with Nano Inorganic Coating

Membrane surface modification is the important method to decrease membrane fouling. The hydrophilic modification of ceramic membrane with nano-sized inorganic coating is prepared by the wet chemical methods. The thin nano coating is not a separating top layer but distributes uniformly on the surface of the membrane pore wall. The coating does not change the structure of the membrane pores. Therefore, water flows on not the pore wall but the nano coating surface. The results show that the water flux of the modified membrane is higher than that of the unmodified membrane despite that the mean pore size of the modified membrane decreases. The “boundary slip” is used to explain this special phenomenon. What generates the slippage The slippage is relative with the molecular layer adhered tightly on the hydrophilic pore wall, the roughness and the surface charge of the nano coating, the interaction between the ions in water and the nano coating, et al.