Xiaozhen Zhang

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.

Preparation and application of positively charged quaternized chitosan/PEI composite nanofiltration membranes

AbstractMembrane processes are gaining importance in water applications as a result of the advances in membrane technology and the increasing requirements on water quality. In this work, 2-hydroxypropyltrimethyl ammonium chloride chitosan with positively charged character and good membrane-forming ability was utilized to fabricate the functional layer of the composite nanofiltration (NF) membrane. Reinforced polyetherimide ultrafiltration membrane was used as the support layer for its excellent thermal and solvent resistance. Effects of polymer concentration, reaction time, cross-linking agent concentration, and cross-linking temperature on membrane performance were studied in detail. When the composite membrane was prepared under optimized conditions and tested at 0.3 MPa and 20°C, the flux of the composite NF membrane was about 10.9 L/m2h and the MgCl2 rejection of it was about 83.1%. The surface morphologies of the composite membrane and substrate membrane were observed by scanning electron microscopy....

Evidence of ZrO2 sol–gel transition by gelation time and viscosity

Sol–gel transition is a stage of the sol that evolves towards the formation of a gel-like network and that exhibits gradually a mobility loss. Hence, the measurement of both viscosity and gelation time is expected to evidence the sol–gel transition occurrence. ZrO2 sols were prepared using zirconium oxychloride octahydrated as precursor material. The structures of the sols before and after gelation were characterized by TEM. Gelation time depends on the concentrations of the reactants and the aging temperature. Viscosity increases linearly with the gelation time firstly, and then increases exponentially nearby the sol–gel transition point. TEM results show the gel is granular before the sol–gel transition point, and appears as brain-like structure after this point. The determination of the sol–gel transition point is to enable the optimum aging time of a sol and to perform the next operations which determine the desired shape of gel (bulk, film, powder, etc.).

Effect of hydrophilic modification with nano-titania and operation modes on the oil–water separation performance of microfiltration membrane

AbstractThe tubular Al2O3 microfiltration membranes modified with nano-TiO2 coating were applied in the separation of waste oil-in-water emulsion. The separation performances of the MF membranes with and without nano-TiO2 modification were studied under two different operation modes, i.e. the circulation mode and the concentration mode, respectively. The circulation mode in which the oil concentration in feed keeps constant simulates the condition of the great amount of feed to be treated, while the concentration mode in which the oil concentration in feed increases with the extraction of the filtrate simulates the condition of a small amount of feed to be treated. The results show that the operation mode has a less effect on the flux of the MF membranes, but has an important effect on the oil concentration of filtrate for the unmodified membrane. The oil concentration in filtrate under concentration mode is higher than that of circulation mode. For the modified membrane, the operation mode has a less eff...

Efficient reduction of graphene oxide film by low temperature heat treatment and its effect on electrical conductivity

Abstract Graphene-based conductive films have already attracted great attention due to their unique and outstanding physical properties. In this work, in order to develop a novel, effective method to produce these films with good electrical conductivity, a simple and green method is reported to rapidly and effectively reduce graphene oxide film using a low temperature heat treatment. The reduction of graphene oxide film is verified by XRD, FT-IR and Raman spectroscopy. Compared with graphene oxide film, the obtained reduced graphene oxide film has better electrical conductivity and its sheet resistance decreases from 25.3 kΩ × sq−1 to 3.3 kΩ × sq−1 after the heat treatment from 160 to 230 °C. The mechanism of thermal reduction of the graphene oxide film mainly results from the removal of the oxygen-containing functional groups and the structural changes. All these results indicate that the low temperature heat treatment is a suitable and effective method for the reduction of graphene oxide film.

Microstructure evolution and properties of YSZ hollow fiber microfiltration membranes prepared at different suspension solid content for water treatment

AbstractYttria-stabilized zirconia (YSZ) hollow fiber ceramic membranes for microfiltration applications were prepared by the phase inversion and sintering technique. The influence of suspension solid content on the rheological behavior of suspension, and the microstructure and properties of the hollow fiber membranes were investigated. With the addition of YSZ powder, the viscosity of the spinning suspension increased obviously, and the rheological behavior of the suspension changed from Newtonian fluid into thinning behavior fluid. The increment of suspension viscosity upon the YSZ content led to a more porous inner surface, larger inner finger-like pores extending outward, and reduced outer finger-like layer for the prepared hollow fiber membrane. When the YSZ content was increased to 65%, a double-layer structure mostly consisting of outer sponge-like layer and inner finger-like structure layer was formed. The pure water flux of the hollow fiber membrane decreased with the increment of YSZ content, wh...

A Comparative Study on the Addition Methods of TiO2 Sintering Aid to the Properties of Porous Alumina Membrane Support

TiO2 is usually used as a sintering aid to lower the sintering temperature of porous alumina membrane support. Two ways of the addition of TiO2 are chosen: in-situ precipitation and in-situ hydrolysis. The results show that the distribution status of TiO2 has an important effect on the property of porous alumina membrane support. In in-situ hydrolysis method, the nano-meter scale TiO2 distributes evenly on the alumina particles’ surface. The bending strength of the support increases sharply and the pore size distribution changes more sharply along with the content of TiO2 which slightly increases from 0.3 wt.% to 0.4 wt.%. The distribution of the nano-meter scale TiO2 is not so even added by in-situ precipitation method. Neither the bending strength nor the pore size distribution of the support is worse than that of the support added by in-situ hydrolysis even if the content of TiO2 is high to 2 wt.%. The permeating flux has a similar tendency. Consequently, the porous alumina membrane support has the porosity of 30.01% and the bending strength of 77.33 MPa after sintering at 1650 °C for 2 h with the optimized TiO2 content of 0.4 wt.% added by the in-situ hydrolysis method.

Preparation and Modification of Ceramic Membrane and Its Application in Oil/Water Wastewater Treatment

Using the alumina powders with different average particle sizes as main raw materials, the tubular ceramic membrane support was prepared by extrusion method, and the membrane interlayer (thickness ~20 μm) and top layer (thickness ~5 μm) were deposited on the membrane support surface by dip coating process. In order to improve the separation performance of the membrane, it was modified with FAS, nano metal oxide or graphene oxide, respectively. During the oil/water treatment, the water flux of the modified membrane is higher about 27.8–43% than that of the original membrane. The modified membrane has higher oil rejection (99%) than that of the original membrane. The results show the modification has an important role on the oil/water separation performance of the membrane.

Application of integrated membrane technology in purification of chlorogenic acid

AbstractIntegrated membrane technology is a membrane separation system, which can overcome the disadvantage of single membrane, save the cost, and improve the product quality. Chlorogenic acid, which is an effective component of Chinese medicine and a heat-sensitive substance, is not stable at high operation temperature. Chlorogenic acid with molecular weight of 354 Da and good solubility in water can be treated by nanofiltration (NF) membrane. In this work, polyetherimide (PEI) ultrafiltration (UF) membrane with good chemical and thermal stability is used in the purification of chlorogenic acid solution. Positively charged HACC/PEI NF membrane with good antibacterial performance and hydrophilicity is used to concentrate chlorogenic acid solution. It is found that, the PEI UF membrane can separate chlorogenic acid with other components and improve the purity of chlorogenic acid. At the same time, the rejection to chlorogenic acid of the positively charged NF membrane is about 92% which is suitable for the...