Wan-Zhong Lang

The effects of hydroxyapatite nano whiskers and its synergism with polyvinylpyrrolidone on poly(vinylidene fluoride) hollow fiber ultrafiltration membranes

By introducing hydroxyapatite (HAP) nano whiskers as well as polyvinylpyrrolidone (PVP), poly(vinylidene fluoride) (PVDF)/PVP/HAP hollow fiber membranes were fabricated with the wet spinning method. The aqueous solution containing 90 wt% N-methyl-2-pyrrolidone (NMP) is used as bore liquid. The effects of two additives and the synergism on the morphologies, surface properties, permeation performances, antifouling ability and mechanical properties of the PVDF/PVP/HAP membranes were characterized by numerous state-of-the-art analytical techniques, and reasonably elucidated accompanying with precipitation kinetics and shear viscosity of dopes. The results show that with the addition of HAP, the finger-like structure of PVDF/PVP/HAP membranes is gradually suppressed and replaced by sponge-like structure, and the hydrophilicity is evidently improved. The hydraulic permeability Jw firstly increases from 224.2 of M-1 to 549.1 L M−2 H−1 bar−1 by adding 1.0 wt% HAP nano whiskers of M-2, and then decreases to 425.9 and 316.3 L M−2 H−1 bar−1 for M-3 and M-4. The rejections of three proteins and humic acid range from 31.4% to 98.4%, and slightly decrease as HAP content increases in the membranes. The mechanical properties of the membranes are markedly improved with the addition of HAP nano whiskers. The membranes containing dual additives have higher permeability and mechanical strength than those of the fibers containing either single additive, implying the synergism of them in improving membrane properties.

Novel PVDF hollow fiber ultrafiltration membranes with antibacterial and antifouling properties by embedding N-halamine functionalized multi-walled carbon nanotubes (MWNTs)

Multi-walled carbon nanotubes grafted with (3-chloro-2-hydroxypropyl)-(5,5-dimethylhydantoinyl-1-ylmethyl)-dimethylammonium chloride (MWNTs-g-CDDAC) are doped in a PVDF spinning solution to prepare a kind of novel PVDF/MWNTs-g-CDDAC hollow fiber ultrafiltration membrane with antibacterial and antifouling properties. The MWNTs-g-CDDAC are firstly synthesized and characterized by FTIR, XPS and TGA. With the addition of MWNTs-g-CDDAC in the dopes, the sponge-like structure is suppressed and the finger-like macrovoids grow wider for the PVDF/MWNTs-g-CDDAC hollow fiber membranes. The surface hydrophilicity and antifouling ability of the membranes are evidently improved by introducing MWNTs-g-CDDAC onto the membranes. The pure water permeability gradually increases with the loading of MWNTs-g-CDDAC in the hybrid membranes, and the highest value of 94.7 L m−2 bar−1 h−1 is obtained with 0.5 wt% MWNTs-g-CDDAC addition in the dope. The permeation flux recovery ratio (Rf) increases with the addition of MWNTs-g-CDDAC, and M-75 (0.75 wt% MWNTs-g-CDDAC loading in dope) exhibits the highest Rf value of 90.6% after two ultrafiltration-cleaning cycles for a BSA aqueous solution. The fabricated PVDF/MWNTs-g-CDDAC membranes have favorable antibacterial efficacy, and M-75 shows the utmost sterilization ratios of 92.7% and 95.2% against E. coli and S. aureus, respectively.

Hydrophilic modification of polyvinyl chloride hollow fiber membranes by silica with a weak in situ sol–gel method

A weak in situ sol–gel method is proposed for the hydrophilic modification of polyvinyl chloride (PVC) hollow fiber membranes by silica, which is generated by the soft hydrolysis of tetraethoxysilane (TEOS) in a deionized water bath. The silica is uniformly distributed on the membrane surface. The sponge-like structure of the modified PVC membranes becomes thicker with the addition of TEOS. The surface hydrophilicity of the membranes gradually increases due to the introduction of silica. The hydraulic permeability increases from 34.8 L M−2 H−1 bar−1 to 89.1 L M−2 H−1 bar−1, and then decreases to 45.3 L M−2 H−1 bar−1 for the membranes of M0(1,3,5)E50 with the addition of TEOS from 0 to 5 wt% in dope content when 50 wt% ethanol aqueous solution is used as the bore liquid. A similar tendency is found for the membranes M0(1,3,5)D95 with 95 wt% DMAc aqueous solution as the bore liquid. The anti-fouling experiments illustrate that the membranes with the addition of TEOS show higher anti-fouling ability. Moreover, the mechanical properties of PVC membranes are also enhanced with the introduction of silica. This work demonstrates that PVC inorganic–organic composite hollow fiber membranes are prepared by a weak in situ sol–gel method, which avoids the use of corrosive substances during membrane preparation.

Catalytic performance of gallium oxide based-catalysts for the propane dehydrogenation reaction: effects of support and loading amount

The different materials (ZSM-5, SBA-15, γ-Al2O3 and SiO2) were used as supports for Ga2O3-based catalysts for the propane dehydrogenation reaction, and the effect of Ga2O3 content (1–9 wt%) for xGa2O3/SBA-15 catalysts on the catalytic activity was discussed. It is found that the supports determine the porous features, the state and dispersion of Ga species, and the acid–base properties of the corresponding catalysts. The existence of strong acid sites in catalyst can lead to more well-dispersed Ga species. The satisfied catalytic performances are obtained over 5Ga2O3/ZSM-5 and 5Ga2O3/SBA-15 catalysts. Among the Ga2O3-based catalysts with different supports, the 5Ga2O3/ZSM-5 sample exhibits the highest catalytic activity, which possesses the maximum well-dispersed gallium species and high dehydrogenation efficiency gallium ions (Gaδ+ cations, δ < 2), and the 5Ga2O3/SBA-15 catalyst exhibits the highest catalytic stability. Furthermore, as for the xGa2O3/SBA-15 samples, the 5Ga2O3/SBA-15 sample exhibits the best catalytic performance. The initial propane conversion and propylene selectivity are above 32.0% and 90.0% respectively, and a final propane conversion of 17.0% is obtained after 30 h reaction. With the increase of Ga loading, the Ga species are easily agglomerated and destroy the structural integrity of the SBA-15 support, which is unfavorable to the propane dehydrogenation reaction.

Analysis of the catalytic activity induction and deactivation of PtIn/Mg(Al)O catalysts for propane dehydrogenation reaction

The catalytic activity induction and deactivation of PtIn/Mg(Al)O catalysts for propane dehydrogenation reaction are experimentally verified. Numerous physical–chemical characterizations are employed to probe the basis and structure–activity relationships, and a mechanism for the activity induction and deactivation is proposed with the help of a schematic diagram. XPS results prove that the valence state of In exhibits almost no change during the entire dehydrogenation reaction. In the activity induction period, the average metal particle size of the PtIn/Mg(Al)O catalyst presents a decreasing trend, and the specific surface area increases. Moreover, the crystal phase changes from primarily periclase (MgO) to dominantly meixnerite (Mg6Al2(OH)18·4H2O). Coke is mainly deposited on the carrier. Nevertheless, in the deactivation period, the metal particles tend to agglomerate and grow. The specific surface area decreases and crystal phase returns to the unique periclase crystal phase. A large amount of coke is formed over the catalyst and partially covers the active sites, which leads to the evident decrease of catalytic activity.

Preparation and synergetic catalytic effects of amino-functionalized MCM-41 catalysts

Four amine functionalized mesoporous catalysts were synthesized by grafting primary, dualistic and two secondary amines onto the channel walls of mesoporous silica, MCM-41. We examined the effects of organoamine loading amount on the acid-base synergism of the catalysts in the self-condensation reaction of n-butanal, a Knoevenagel condensation and a Henry reaction. We observed the balance of the amine and residual silanol amounts is crucial to the catalytic performances of the functionalized mesoporous catalysts. An optimum organoamine loading amount exists, which is dependent on the organoamine type. There is little difference in the optimum organoamine loading amount between different reactions. The secondary organoamine functionalized MCM-41 exhibits the best catalytic performance in the experimental range.

Versatile polyvinylidene fluoride hybrid ultrafiltration membranes with superior antifouling, antibacterial and self-cleaning properties for water treatment

Novel ultrafiltration membranes with both superior antibacterial and self-cleaning properties were fabricated. By using a non-solvent induced phase separation method (NIPS), N-halamine epoxide and siloxane were grafted onto the multi-walled carbon nanotubes (N-Si-MWNTs) to fabricate polyvinylidene fluoride (PVDF) hybrid membranes. The membrane morphology was observed under a field emission scanning electron microscopy. The results demonstrated that the PVDF hybrid membranes had an asymmetrical structure, and their hydraulic permeability was evidently enhanced with the addition of modified MWNTs. When compared with the primitive PVDF membrane, the hybrid membranes presented improved surface hydrophilicity. After three ultrafiltration-regeneration cycles with bovine serum albumin as model biofoulant and pure water as detergent, the PVDF hybrid membranes exhibited a high flux recovery ratio (FRR). Furthermore, when compared with other membranes, the membrane containing N-Si-MWNTs displayed the highest FRR value of above 96.5% after the entire fouling and cleaning experiment. The fabricated PVDF/N-Si-MWNTs hybrid membranes had excellent antibacterial efficacy, presenting maximum antibacterial efficacy of 98.0% and 95.6% against Staphylococcus aureus and Escherichia coli, respectively. Thus, the PVDF/N-Si-MWNTs membranes fabricated in this study are environment-friendly with both benign antibacterial and self-cleaning properties.

Hydrothermally prepared chromia-alumina (xCr/Al2O3) catalysts with hierarchical structure for propane dehydrogenation

Propane dehydrogenation was investigated over a series of chromia-alumina (xCr/Al2O3) catalysts containing 2.5–10 wt% chromium (Cr), synthesized via a hydrothermal synthesis method. The synthesized xCr/Al2O3 catalysts with hierarchical spindle-like morphology have high specific area and highly dispersed chromia on the surface of γ-Al2O3. Besides, the higher Cr6+/Cr3+ ratio is advantageous to obtain higher propane conversion and lower propylene selectivity. The synthesized 7.5Cr/Al2O3 catalyst exhibits the highest propane conversion of 62% accompanied by 89% propylene selectivity at 873 K. After regenerated by re-calcinating in air, the original activity of the spent catalyst is well recovered.

Synthesis of Tubular Faujasite X-Type Membranes with Mullite Supports and their Gas Permeances for N2/CO2 Mixtures

The present work reports the synthesis of tubular faujasite (FAU) X-type membranes with mullite supports for the permeation separation of N2/CO2. The external surfaces of mullite supports were modified and seeded with X-type zeolite crystals prior to film growth in synthesis solutions. We investigated the effects of synthesis conditions including the composition of synthesis solution and the process of hydrothermal treatment on the formation of FAU X-type membranes. We also characterized the membrane morphology and phases using scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, we evaluated the permeation separation of N2/CO2 with the as-synthesized membranes. The results indicated that increasing aging time accelerated the crystal growth rate, but overlong aging time could cause the generation of P-type zeolite and thicker membrane layer. Prolonging crystallization time and raising temperature would increase the rate of crystal nucleation, but readily made trans-crystallization phenomena occur. The Na/Si ratio did not play a significant role in synthesizing FAU X-type membranes in the tested range. The as-synthesized zeolite membranes with higher ratio of Si/Al accompanied with the formation of P-type crystal and the particle size on the membrane surface obviously increased. The membrane with a smoother zeolite surface and a thinner top layer was obtained with increasing H2O content. For single-gas permeation, CO2 had a lower permeance than N2. For the gas mixtures of N2/CO2, the separation factor α of 7.89 was gained.

Pervaporation separation of dimethyl carbonate/methanol binary mixtures with poly(vinyl alcohol)-perfluorslulfonic acid/poly(acrylonitrile) hollow fiber composite membranes

Using poly(vinyl alcohol) (PVA) and perfluorslulfonic acid (PFSA) as coating materials, poly(acrylonitrile) (PAN) hollow fiber ultrafiltration membrane as substrate, PVA-PFSA/PAN composite membranes were fabricated by dip-coating method. The fabricated composite membranes were used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) binary mixtures by pervaporation process. SEM images verify that the coated layer is well combined with substrate and the thickness nearly linearly increases with the coating solution concentration. The separation factor increases but at cost of the decline of permeation flux when the concentration of the coating solution or its PVA mass fraction increase. The permeation flux increases and separation factor slightly increases with the feed temperature increasing at 30–60 °C. The increase of feed MeOH concentration leads to an improvement of permeation flux and a decline of separation factor.