Fluorescent silver nanoclusters (Ag NCs) are an important kind of luminescent nanomaterial with many practical applications. In this report, a facile route was designed for the preparation of fluorescent Ag NCs–chitosan hybrid nanocomposites based on the reduction of Ag+ with NaBH4. The hybrid nanocomposites had a spherical morphology with a size of 80 ± 10 nm. Moreover, the as-prepared nanospheres displayed high fluorescence with the emission peak center at 562 nm due to the formation of Ag NCs. In addition, chitosan, a natural polymer, worked as a stabilizing agent, and made the nanocomposites biocompatible, biodegradable and have low-toxicity. These properties mean that the nanospheres are promising materials for bio-applications. The methyl thiazolyl tetrazolium assay confirmed that the fluorescent chitosan–Ag NCs hybrid nanospheres had almost negligible toxicity to normal cells of MC3T3-E1. The outstanding low virulence of the as-prepared fluorescent chitosan–Ag NCs hybrid nanospheres was tested and verified by MC3T3-E1 cells and CAL-27 cells for bio-imaging as well.

The development of compact hydrogen separator based on membrane technology is of key importance for hydrogen energy utilization, and the Pd-modified carbon membranes with enhanced hydrogen permeability were investigated in this work. The C/Al2O3 membranes were prepared by coating and carbonization of polyfurfuryl alcohol, then the palladium was introduced through impregnation–precipitation and colloid impregnation methods with a PdCl2/HCl solution and a Pd(OH)2 colloid as the palladium resources, and the reduction was carried out with a N2H4 solution. The resulting Pd/C/Al2O3 membranes were characterized by means of SEM, EDX, XRD, XPS and TEM, and their permeation performances were tested with H2, CO2, N2 and CH4 at 25 °C. Compared with the colloid impregnation method, the impregnation–precipitation is more effective in deposition of palladium clusters inside of the carbon layer, and this kind of Pd/C/Al2O3 membranes exhibits excellent hydrogen permeability and permselectivity. Best hydrogen permeance, 1.9 × 10−7 mol/m2 s Pa, is observed at Pd/C = 0.1 wt/wt, and the corresponding H2/N2, H2/CO2 and H2/CH4 permselectivities are 275, 15 and 317, respectively.Highlights► Composite C/Al2O3 membranes were modified by palladium. ► Pd clusters were dispersed into the carbon pores via impregnation–precipitation. ► Hydrogen permeability and permselectivity were significantly improved.

•The surface of porous stainless steel substrate was improved by silver coating.•H2-permeable Pd/Ag/PSS membranes were successfully prepared.•Permeation performance and stability were investigated at 350−500 °C.The H2-permeable palladium membranes based on porous stainless steel (PSS) substrate are important for development of various hydrogen energy systems. To improve the surface of the PSS, a microporous silver layer was deposited successively by a coating with a suspension of silver powder in polyvinyl alcohol (PVA) solution, a heating under nitrogen at 500 °C for carbonization of PVA, an air treatment and a hydrogen reduction. The formation of carbon from PVA helps to maintain the porosity and integrity of the silver layer. After an activation of the resulting Ag/PSS surface through galvanic-cell reaction, palladium membranes with a thickness around 4 μm were successfully prepared by a suction-assisted electroless plating. SEM, EDS, metallography and porometry analyzes were conducted for material characterizations. The prepared Pd/Ag/PSS membrane is permeable and selective as compared with similar those reported in literature. The permeation tests were carried out at 350, 400, 450 and 500 °C for 48, 48, 48 and 60 h, respectively, and the membrane was found to be unstable at 500 °C due to the presence of pinholes. No significant intermetallic diffusion between the silver and palladium layers was observed.

The development of hydrogen energy systems has placed a high demand on hydrogen-permeable membranes as compact hydrogen separators and purifiers. Although Pd/Ceramic composite membranes are particularly effective in this role, the high cost of these membranes has greatly limited their applications; this high cost stems largely from the use of expensive substrate material. This problem may be solved by substrate recycling and the use of lower cost substrates. As a case study, we employed expensive asymmetric microporous Al2O3 and low-cost macroporous symmetric Al2O3 as membrane substrates (average pore sizes are 0.2 and 3.3 μm, respectively). The palladium membranes were fabricated by electroless plating, and substrate recycling was carried out by palladium dissolution with a hot HNO3 solution. The functional surface layer of the microporous Al2O3 was damaged during substrate recycling, and the reuse of the substrate led to poor membrane selectivity. With the assistance of pencil coating as a facile and environmentally benign surface treatment, the macroporous Al2O3 can be successfully utilized. Furthermore, the macroporous Al2O3 can be also recycled and reused as membrane substrate, yielding highly permeable, selective and stable palladium membranes. Consequently, the substrate cost can be further decreased, and the applications of this kind of membranes would expand.Highlights► Conventional membrane substrate materials are expensive and non-reusable. ► We used a low-cost macroporous Al2O3 as membrane substrate via pencil coating. ► We also prepared perfect Pd membranes using recycled macroporous Al2O3 substrate. ► The cost of hydrogen separation with Pd/ceramic membranes will be greatly decreased.

Increasing hydrogen energy utilization has greatly stimulated the development of the hydrogen-permeable palladium membrane, which is comprised of a thin layer of palladium or palladium alloy on a porous substrate. This work chose the low-cost macroporous Al2O3 as the substrate material, and the surface modification was carried out with a conventional 2B pencil, the lead of which is composed of graphite and clay. Based on the modified substrate, a highly permeable and selective Pd/pencil/Al2O3 composite membrane was successfully fabricated via electroless plating. The membrane was characterized by SEM (scanning electron microscopy), field-emission SEM and metallographic microscopy. The hydrogen flux and H2/N2 selectivity of the membrane (with a palladium thickness of 5 μm) under 1 bar at 723 K were 25 m3/(m2 h) and 3700, respectively; the membrane was found to be stable during a time-on-stream of 330 h at 723 K.

Composite palladium membranes are particularly useful in hydrogen separation because of their perfect permeability and permselectivity toward hydrogen, and porous ceramics are their most common substrate materials. High working temperatures favor membrane output, but create difficulties with membrane sealing and assembling. This work suggests a kind of facile and effective connector with graphite as the sealing material. The connector is resistant to temperature cycling, and the leakage kinetics was discussed. The possible graphite hydrogenation and the consequent membrane contamination at high temperature were also investigated.

The one-step hydroxylation of benzene to phenol with oxygen and hydrogen is a promising process, but there are severe challenges associated with the low phenol production. It was reported that the reaction can be greatly promoted by the simultaneous use of a dense palladium membrane as a catalyst and as a hydrogen distributor. We also carried out this reaction concept with palladium membranes under different reaction conditions, but found that the palladium membranes were almost inert for both the target reaction and the benzene combustion. This work summarized and compared among the literature results as well as ours, investigating the effects of the membrane preparation method and the combustion of hydrogen and benzene. The arguments on the mechanism and feasibility of the membrane concept were given in detail.

The design and control of the surface is extremely important for the development of heterogeneous catalysts because surface properties always play a key role in catalytic performance. Therefore, it is of great interest to investigate the evolution of the surface state during the preparation of a catalyst. Mixed oxides are a particularly important group of catalytic materials. This work studied Fe2O3–MoO3 as a model system, investigating the surface states jointly influenced by the thermal spreading of MoO3 and the solid-state reaction that produces Fe2(MoO4)3 during heat treatment. X-ray photo-electron spectroscopy, scanning electron microscopy and 57Fe Mössbauer analysis were used to characterize the evolution of the surface and the bulk of solids, and the oxidation of methanol to formaldehyde was also used as a probe reaction. It was found that the evolution of the surface layer takes place mainly as follows: (i) a small amount of MoO3 can be dispersed onto the surface of Fe2O3 via grinding; (ii) the thermal spreading of MoO3 and the solid-state reaction start almost simultaneously at around 400 °C, leading to the coexistence of MoO3 and Fe2(MoO4)3 species on the surface of Fe2O3 grains; (iii) further thermal spreading and the solid-state reaction yield a shell of Fe2(MoO4)3 encapsulating the remaining Fe2O3 grains, but a small amount of MoO3 remains on the external surface of the resulting Fe2(MoO4)3 shell; (iv) when the MoO3 grains run out, the surface MoO3 species also disappears.Mixed oxides are a particularly important group of catalytic materials, and it is of great interest to investigate the evolution of the surface state during the preparation of a catalyst. This work studied Fe2O3–MoO3 as a model system, investigating the surface states jointly influenced by the thermal spreading of MoO3 and the solid-state reaction that produces Fe2(MoO4)3 during heat treatment.

Composite palladium membranes can be used as a hydrogen separator because of their excellent permeability and permselectivity. The total membrane area in a hydrogen separator must be reasonably large for industrial use, and it is important that each membrane provides a large enough area. Such a demand can be well met by introducing multichannel composite membranes. In this work, a commercially available microporous ceramic filter with 19 channels was used as a membrane substrate, and the diameter of each channel was 4 mm. A uniform thin palladium layer was fabricated inside the narrow channels by using an electroless plating method, and the resulting membranes were highly permeable and selective. This membrane concept provides a high surface-to-volume ratio without causing significant pressure loss, making the hydrogen separator compact and capable. However, special attention should be paid to cleaning the membrane after electroless plating.

The integrity of thin composite palladium membranes is influenced by the surface roughness of the porous support. Supports with smooth surface and small pore size are expensive as they are composed of several layers with decreasing pore size which require multiple successive energy and time consuming sintering steps. In addition, smooth surfaces may cause poor membrane adhesion. It is therefore of interest to develop methods for preparation of thin defect-free palladium membranes over supports with rough surfaces. Porous stainless steel tubes coated by atmospheric plasma spraying with a porous layer of yttria-stabilized zirconia (YSZ) were used in this work as a support for palladium composite membranes. The YSZ layer served as a barrier against intermetallic diffusion between the palladium membrane and the metallic support. Three different techniques to create the membranes were compared: magnetron sputtering did not result in sufficiently dense films. Atmospheric plasma spraying produced relatively thick continuous films, but with some residual open porosity. Electroless plating gave the densest layers. Yet rather thick layers were required to limit the number of defects, which is associated with high cost and low hydrogen flux. Activation of the support surface by metal organic chemical vapor deposition of palladium instead of the conventional sensitization and activation pretreatment based on successive immersion in SnCl2 and PdCl2 solutions allowed to reduce the membrane thickness without compromising its integrity. The resulting membrane showed significantly higher permselectivity but at the same time decreased hydrogen permeability.