Joanna Kujawa

Highly Efficient Hydrophobic Titania Ceramic Membranes for Water Desalination

Hydrophobic titania ceramic membranes (300 kD) were prepared by grafting of C6F13C2H4Si(OC2H5)3 and C12F25C2H4Si(OC2H5)3 molecules and thus applied in membrane distillation (MD) process of NaCl solutions. Grafting efficiency and hydrophobicity were evaluated by contact angle measurement, atomic force microscopy, scanning electron microscopy, nitrogen adsorption/desorption, and liquid entry pressure measurement of water. Desalination of NaCl solutions was performed using the modified hydrophobic membranes in air gap MD (AGMD) and direct contact MD (DCMD) processes in various operating conditions. High values of NaCl retention coefficient (>99%) were reached. The permeate fluxes were in the range 231-3692 g·h(-1)·m(-2), depending on applied experimental conditions. AGMD mode appeared to be more efficient showing higher fluxes and selectivity in desalination. Overall mass transfer coefficients (K) for membranes tested in AGMD were constant over the investigated temperature range. However, K values in DCMD increased at elevated temperature. The hydrophobic layer was also stable after 4 years of exposure to open air.

Membrane distillation properties of TiO2 ceramic membranes modified by perfluoroalkylsilanes

Abstract The tubular and planar TiO2 ceramic membranes were modified by grafting with perfluoroalkylsilanes (PFAS) molecules. Two types of PFAS were used for grafting process: 1H,1H,2H,2H-perfluorooctyltriethoxysilane (C6) and 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (C12). Studies showed that hydrophilic surface of titania ceramic membranes can be efficiently modified as a results of the proposed grafting method. Grafting efficiency of the tubular membranes was determined by measurement of liquid water entry pressure (LEPw), whereas grafting efficiency of planar membranes was verified by contact angle measurement. The contact angle values of the planar membranes are 130 and 140° for grafting with C6 and C12, respectively. The LEPw of the tubular membranes increased from 2 bar to 10 bar after modification by C12, whereas the LEPw values were constant at 2 bar when TiO2 membrane was modified by C6 molecules. It was found that water contact angle, LEPw, and water flux in the membrane distillation (MD)...

Functionalization of Ceramic Metal Oxide Powders and Ceramic Membranes by Perfluoroalkylsilanes and Alkylsilanes Possessing Different Reactive Groups: Physicochemical and Tribological Properties

The functionalization of ceramic materials, metal oxide powders (TiO2 and ZrO2), and ceramic membranes (5 kD TiO2 and 300 kD TiO2) was performed and thoroughly discussed. The objective of the functionalization was to change the natively hydrophilic character to the hydrophobic. The hydrophilic character of the ceramics generates limitations in wider application of such materials. Material functionalization was performed using perfluoroalkylsilanes and trifunctional(octyl)silanes possessing three different reactive functional groups: -Cl, -OMe, and -OEt. The characterization of functionalized metal oxide powders and ceramic membranes was assessed by a combination of various analytical methods and techniques: NMR, TGA, HR-TEM, FT-IR, SEM-EDX, AFM, and contact goniometry. The impact of molecular structure of grafting agents (type of reactive group), time of functionalization process (5-15 min), and type of membrane morphology on the material, physicochemical, and tribological properties was studied. Effectiveness of hydrophobization was confirmed by HR-TEM technique. The thickness of the attached hydrophobic nanolayer on the surface of ceramics was around 2.2 nm. It was found that the stable hydrophobic surfaces were obtained by functionalization with both fluorinated and nonfluorinated modifiers. The materials modified with perfluoroalkylsilanes (FC6OEt3) and trichloro(octyl)silanes (C6Cl3) during 15 min hydrophobization possess comparable properties: contact angle (CA) equal to 130° and 133°; roughness RMS of 10.2 and 12 nm; adhesive force of 4.1 and 5.7 nN; and Young modulus of 135 and 130 GPa, respectively. The relation between hydrophobicity level and ceramic membrane roughness was discussed applying the Kao diagram concept. (29)Si NMR results show that type of modifier has an important influence on grafting efficiency and on the mode of the grafting molecules attachment. In case of grafting with n-octyltrichlorosilane (C6OCl3) and n-octyltrimethoxysilane (C6OMe3), an increase of lateral polymerization across the octylsilane layer was observed.

How To Functionalize Ceramics by Perfluoroalkylsilanes for Membrane Separation Process? Properties and Application of Hydrophobized Ceramic Membranes

The combination of microscopic (atomic force microscopy and scanning electron microscopy) and goniometric (static and dynamic measurements) techniques, and surface characterization (surface free energy determination, critical surface tension, liquid entry pressure, hydraulic permeability) was implemented to discuss the influence of perfluoroalkylsilanes structure and grafting time on the physicochemistry of the created hydrophobic surfaces on the titania ceramic membranes of 5 kD and 300 kD. The impact of molecular structure of perfluoroalkylsilanes modifiers (possessing from 6 to 12 carbon atoms in the fluorinated part of the alkyl chain) and the time of the functionalization process in the range of 5 to 35 h was studied. Based on the scanning electron microscopy with energy-dispersive X-ray spectroscopy, it was found that the localization of grafting molecules depends on the membrane pore size (5 kD or 300 kD). In the case of 5 kD titania membranes, modifiers are attached mainly on the surface and only partially inside the membrane pores, whereas, for 300 kD membranes, the perfluoroalkylsilanes molecules are present within the whole porous structure of the membranes. The application of 4 various types of PFAS molecules enabled for interesting observations and remarks. It was explained how to obtain ceramic membrane surfaces with controlled material (contact angle, roughness, contact angle hysteresis) and separation properties. Highly hydrophobic surfaces with low values of contact angle hysteresis and low roughness were obtained. These surfaces possessed also low values of critical surface tension, which means that surfaces are highly resistant to wetting. This finding is crucial in membrane applicability in separation processes. The obtained and characterized hydrophobic membranes were subsequently applied in air-gap membrane distillation processes. All membranes were very efficient in MD processes, showing good transport and selective properties (∼99% of NaCl salt rejection). Depending on the membrane pore size and used modifiers, the permeate flux was in the range of 0.5-4.5 kg·m(-2)·h(-1) and 0.3-4.2 kg·m(-2)·h(-1) for 5 kD and 300 kD membranes, respectively.

Molecular Grafting of Fluorinated and Nonfluorinated Alkylsiloxanes on Various Ceramic Membrane Surfaces for the Removal of Volatile Organic Compounds Applying Vacuum Membrane Distillation

Four main tasks were presented: (i) ceramic membrane functionalization (TiO2 5 kDa and 300 kDa), (ii) extended material characterization (physicochemistry and tribology) of pristine and modified ceramic samples, (iii) evaluation of chemical and mechanical stability, and finally (iv) assessment of membrane efficiency in vacuum membrane distillation applied for volatile organic compounds (VOCs) removal from water. Highly efficient molecular grafting with four types of perfluoroalkylsilanes and one nonfluorinated agent was developed. Materials with controllable tribological and physicochemical properties were achieved. The most meaningful finding is associated with the applicability of fluorinated and nonfluorinated grafting agents. The results of contact angle, hysteresis of contact angle, sliding angle, and critical surface tension as well as Youngs modulus, nanohardness, and adhesion force for grafting by these two modifiers are comparable. This provides insight into the potential applicability of environmental friendly hydrophobic and superhydrophobic surfaces. The achieved hydrophobic membranes were very effective in the removal of VOCs (butanol, methyl-tert-butyl ether, and ethyl acetate) from binary aqueous solutions in vacuum membrane distillation. The correlation between membrane effectiveness and separated solvent polarity was compared in terms of material properties and resistance to the wetting (kinetics of wetting and in-depth liquid penetration). Material properties were interpreted considering Zisman theory and using Kao diagram. The significant influence of surface chemistry on the membrane performance was noticed (5 kDa, influence of hydrophobic nanolayer and separation controlled by solution-diffusion model; 300 kDa, no impact of surface chemistry and separation controlled by liquid-vapor equilibrium).

Enhanced starch hydrolysis using α-amylase immobilized on cellulose ultrafiltration affinity membrane.

In order to prepare ultrafiltration membranes possessing biocatalytic properties, α-amylase has been immobilized on cellulose membranes. Enzyme immobilization was based on a covalent bonding between chitosan and a surface of cellulose membrane, followed by an attachment of Cibacron Blue F3G-A dye as affinity ligand. Various factors affecting the immobilization process, such as enzyme concentration, pH of modifying solution, zeta-potential of membrane surface, and stability of immobilized enzyme were studied. The applicability of immobilized α-amylase has been investigated in ultrafiltration processes. The immobilization of α-amylase on membrane surface allows to increase the value of mass transfer coefficient and to decrease the concentration polarization effect during ultrafiltration of starch solutions. The enzyme layer on the membrane surface prevents a rapid increase of starch concentration due to the amylase hydrolysis of starch in the boundary layer. The presented affinity immobilization technique allows also for the regeneration of membranes from inactivated enzyme.

Driving force and activation energy in air-gap membrane distillation process

The present study investigated the impact of the driving force (Δp) on the transport properties. All the experiments and calculations were performed for air-gap membrane distillation (AGMD). In the course of the experiments, it was found that an identical value of Δp could be attained by applying different values of feed and permeate temperatures. It was highlighted that constant values of water fluxes could be achieved using the constant driving force created by different temperatures. Moreover, the relation between

Ab initio study of cationic polymeric membranes in water and methanol

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The Effect of Reactive Ionic Liquid or Plasticizer Incorporation on the Physicochemical and Transport Properties of Cellulose Acetate Propionate-Based Membranes

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Advanced Material-Ordered Nanotubular Ceramic Membranes Covalently Capped with Single-Wall Carbon Nanotubes

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