Zhentao Wu

Highly Water-Stable Zirconium Metal–Organic Framework UiO-66 Membranes Supported on Alumina Hollow Fibers for Desalination

In this study, continuous zirconium(IV)-based metal-organic framework (Zr-MOF) membranes were prepared. The pure-phase Zr-MOF (i.e., UiO-66) polycrystalline membranes were fabricated on alumina hollow fibers using an in situ solvothermal synthesis method. Single-gas permeation and ion rejection tests were carried out to confirm membrane integrity and functionality. The membrane exhibited excellent multivalent ion rejection (e.g., 86.3% for Ca(2+), 98.0% for Mg(2+), and 99.3% for Al(3+)) on the basis of size exclusion with moderate permeance (0.14 L m(-2) h(-1) bar(-1)) and good permeability (0.28 L m(-2) h(-1) bar(-1) μm). Benefiting from the exceptional chemical stability of the UiO-66 material, no degradation of membrane performance was observed for various tests up to 170 h toward a wide range of saline solutions. The high separation performance combined with its outstanding water stability suggests the developed UiO-66 membrane as a promising candidate for water desalination.

High‐Performance, Anode‐Supported, Microtubular SOFC Prepared from Single‐Step‐Fabricated, Dual‐Layer Hollow Fibers

Microtubular solid oxide fuel cells (SOFCs) have been developed in recent years mainly due to their high specifi c surface area and fast thermal cycling. Previously, the fabrication of microtubular SOFCs was achieved through multiple-step processes. [ 1–3 ] A support layer, for example an anode support, is fi rst prepared and presintered to provide mechanical strength to the fuel cell. The electrolyte layer is then deposited and sintered prior to the fi nal coating of the cathode layer. Each step involves at least one high-temperature heat treatment, making the cell fabrication time-consuming and costly, with unstable control over cell quality. For a more economical fabrication of microtubular SOFCs with reliability and fl exibility in quality control, an advanced dry-jet wet-extrusion technique, i.e., a phase inversion-based coextrusion process, was developed. Using this technique, an electrolyte/electrode (either anode or cathode) dual-layer hollow fi ber (HF) can be formed in a single step. Generally, the electrolyte and electrode materials are separately mixed with solvent, polymer binder, and additives to form the outer and inner layer spinning suspensions, respectively, before being simultaneously coextruded through a triple-orifi ce spinneret, passing through an air gap and fi nally into a non-solvent external coagulation bath. In the mean time, a stream of nonsolvent internal coagulant is supplied through the central bore of the spinneret. The thickness of the two layers is largely determined by the design of the spinneret and can be adjusted by the corresponding extrusion rate, while the macrostructure or morphology of the prepared HF precursor can be controlled by adjusting coextrusion parameters such as suspension viscosity, air gap, and fl ow rate of internal coagulant. The dual-layer HF precursor obtained is then co-sintered once at high temperature to remove the polymer binder and form a bounding between the ceramic materials. In previous work, [ 4–6 ] a dual-layer HF support for microtubular SOFCs, which consisted of an electrolyte outer layer of approximately 80 μ m supported by an asymmetric anode inner layer with 35% fi ngerlike voids length, was successfully fabricated using the coextrusion and cosintering process. A single cell that was obtained after deposition

Advances in ceramic membranes for water treatment

Abstract Porous ceramic membranes can offer a more robust and long-term alternative to polymeric membranes in aqueous microfiltration and ultrafiltration processes. Their superior chemical, thermal and mechanical properties mean that not only can they be operated under harsh conditions, they can also be backwashed and cleaned with strong cleaning agents as well as sterilized at high temperatures, offering reliable performance over long periods of time. These ceramic membranes are conventionally fabricated via multiple layer deposition steps on top of a membrane substrate followed by several heat treatment sessions to achieve the desired final selectivity for micro- or ultrafiltration. Because of the large number of steps required, conventional methods are time- and energy-consuming, contributing to the high capital costs of ceramic membranes. The combined phase-inversion and sintering technique is an emerging method for the fabrication of ceramic membranes and considerably reduces the number of steps required by eliminating the need to deposit layers on a substrate; thus, only one heat treatment step is required. Furthermore, it can produce membranes with a wide range of unique microstructures, which can be tailored for the application. The ability to produce much thinner hollow-fibre membranes can improve packing density considerably compared with the commonly used flat-sheet and tubular modules. This simpler fabrication cycle can potentially reduce the costs of ceramic membranes, but currently further research and development is required before commercialization of this method can commence. Potential applications of ceramic membranes for water treatment include the production of drinking water, treatment of municipal and industrial wastewater, treatment of produced water and use in the food and beverage industries. Successful implementation of ceramic membranes in these industries has been achieved with stable and long-term operation but the high capital cost of ceramic membranes remains the main deterrent to large-scale water treatment. However, anticipated cheaper ceramic membranes with higher packing densities of hollow-fibre configuration will increase applications in municipalities.

Use of a Ceramic Membrane to Improve the Performance of Two-Separate-Phase Biocatalytic Membrane Reactor

Biocatalytic membrane reactors (BMR) combining reaction and separation within the same unit have many advantages over conventional reactor designs. Ceramic membranes are an attractive alternative to polymeric membranes in membrane biotechnology due to their high chemical, thermal and mechanical resistance. Another important use is their potential application in a biphasic membrane system, where support solvent resistance is highly needed. In this work, the preparation of asymmetric ceramic hollow fibre membranes and their use in a two-separate-phase biocatalytic membrane reactor will be described. The asymmetric ceramic hollow fibre membranes were prepared using a combined phase inversion and sintering technique. The prepared fibres were then used as support for lipase covalent immobilization in order to develop a two-separate-phase biocatalytic membrane reactor. A functionalization method was proposed in order to increase the density of the reactive hydroxyl groups on the surface of ceramic membranes, which were then amino-activated and treated with a crosslinker. The performance and the stability of the immobilized lipase were investigated as a function of the amount of the immobilized biocatalytst. Results showed that it is possible to immobilize lipase on a ceramic membrane without altering its catalytic performance (initial residual specific activity 93%), which remains constant after 6 reaction cycles.

Functional ceramic hollow fibre membranes for catalytic membrane reactors and solid oxide fuel cells

Abstract: This chapter introduces major developments and use of functional ceramic hollow fibre membranes, that is a membrane design consisting of a dense outer layer for separation supported on a highly porous inner catalytic substrate layer, for energy utilization in methane conversion and micro-tubular solid oxide fuel cells (SOFCs). The advantages of the dual-layer hollow fibre membrane design and the single-step co-extrusion and co-sintering process employed to achieve this membrane design are addressed. The key factors that affect the fabrication and performance of the developed membranes are discussed and future technology challenges are also outlined.