Minimising non-selective defects in ultrathin reduced graphene oxide membranes with graphene quantum dots for enhanced water and NaCl separation

Reduced graphene oxide (rGO) membranes have been intensively evaluated for desalination and ionic sieving applications,benefiting from their stable and well-confined interlayer channels.However,rGO membranes generally suffer from low permeability due to the high transport resistance resulting from the narrowed two-dimensional (2D) channels.Although high permeability can be realized by reducing membrane thickness,membrane selectivity normally declines because of the formation of non-selective defects,in particular pinholes.In this study,we demonstrate that the non-selective defects in ultrathin rGO membranes can be effectively minimised by a facile posttreatment via surface-deposition of graphene quantum dots (GQDs).The resultant GQDs/rGO membranes obtained a good trade-off between water permeance (14 L·m-2·h-1·MPa-1) and NaCl rejection (91％).This work provides new insights into the design of high quality ultrathin 2D laminar membranes for desalination,molecular/ionic sieving and other separation applications.     

Antifouling performance of poly(acrylonitrile)-based membranes: From green synthesis to application

In order to develop clean ultrafiltration membranes able to prevent the fouling of biological compounds in filtration processes, poly(ethylene glycol) methyl ether acrylate (PEGA) was grafted to poly(acrylonitrile) (PAN) by free-radical polymerization in supercritical carbon dioxide (scCO₂) and the grafted copolymer was blended with PAN to fabricate porous membranes using scCO₂-induced phase inversion method. Fourier transform infrared (FT-IR) analysis, ¹H nuclear magnetic resonance (¹H NMR) and differential scanning calorimetry (DSC) confirmed that the poly(acrylonitrile)-graft-poly(ethylene oxide) (PAN-g-PEO) was successfully synthesized, for the first time, in scCO₂. The effect of increasing PEGA content on the initial monomer feed mixture on graft polymer morphology and average molecular weight was studied. Blended membranes with different PEGA contents were investigated by scanning electron microscopy (SEM), mercury porosimetry and dynamical mechanical analysis (DMA) to characterize their morphological, physico-chemical and mechanical properties. Moreover, water contact angle measurements, pure water permeability and filtration experiments were performed to evaluate membrane hydrophilicity and fouling resistance properties. Permeation experiments of model foulants, bovine serum albumin (BSA) and starch solutions were used to investigate antifouling character of blend membranes at different pHs. PAN:PAN-g-PEO (70:30) showed to be the ultrafiltration membrane with best performance. Furthermore, comparing with conventional technologies blended membranes of PAN:PAN-g-PEO prepared by a scCO₂-assisted process showed enhanced hydrophilicity, larger protein and starch solution permeabilities and good resistance to irreversible fouling, indicating that the technology is an efficient process to prepare fouling resistant membranes for biomacromolecule separations.     

Modification of polypropylene filter with metal oxide and reduced graphene oxide for water treatment

A hydrothermal method for the synthesis of reduced graphene oxide/titanium dioxide filter (RGO/TiO₂) and reduced graphene oxide/zinc oxide filter (RGO/ZnO) by using polypropylene (PP) porous filter is reported. Field emission scanning electron microscopy illustrated that the nanoparticles were uniformly distributed on the reduced graphene oxide nanosheets. Flexural tests showed that the physical properties of the modified filters have greater strength than the original filter. Thermogravimetric analysis revealed that the thermal property of the modified filters is the same as that of the original filter. Under a halogen lamp, the modified filter exhibited excellent photocatalytic degradation of methylene blue. The RGO/TiO₂ filter maintained its ability to degrade MB efficiently, even after five cycles of photocatalysis.     

Effect of nickel doping on structure and suppressing boron volatility of borosilicate glass sealants in solid oxide fuel cells

The high volatility of boron from borosilicate glass sealants often leads to boron deposition and poisoning of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathode, presenting a challenge for the development of reliable solid oxide fuel cells (SOFCs). In this paper, we report that boron volatilization from borosilicate glass at 700 °C can be significantly suppressed by appropriate NiO dopant, mainly due to the increase of Si-O-B linkages in the combining B-O^? and Si-O^? network. Also, the formation of boron-containing phase in NiO-doping glass-ceramics has been studied, which suppresses the reaction between glass and LSCF cathode after heat treatment at 700 °C for 1000 h. Moreover, the change of crystalline phases leads to an improvement in thermal and electrical properties. We believe that our findings will open a new way for the design and development of the reliable sealing glass for SOFCs applications.     

Immobilization of tannery industrial sludge in ceramic membrane preparation and hydrophobic surface modification for application in atrazine remediation from water

Chromium laden waste produced from tannery industry was immobilized in ceramic matrix for fabrication of the tubular single channel microfiltration membranes by extrusion. The presence of chromia resulted in substitutional solid solution formation with alumina and catalyzed mullite phase growth, hence increasing the mechanical and chemical stability of the membranes. The structural, morphological and water permeation characteristics of the membranes were studied to analyze their formation mechanism and effect of different parameters, viz. the sintering temperature, amount of waste added, presence of organics and extent of chromium immobilization. The surface of the macroporous membrane was hydrophobically modified, by polydimethylsiloxane (PDMS), producing contact angle of 141°. The process efficiency of the hydrophobic membrane was assessed in terms of the removal of atrazine, a contaminant of emerging concern, following the principle of hydrophobic interaction. Effect of different operating parameters affecting atrazine removal, viz. transmembrane pressure, cross flow velocity and filtration time was studied in cross flow filtration mode. High atrazine removal of >95% was obtained along with the maintenance of high flux during the filtration operation. The prepared cost-effective microfiltration membranes can thus be further modified for efficient water treatment applications.     

Waste water treatment using reverse osmosis: real osmotic pressure and chemical functionality as influencing parameters on the retention of carboxylic acids in multi-component systems

The influence of chemical functionality in carboxylic acids and osmotic pressure of multi-component solutions on the retention in the reverse osmosis process are discussed. Therefore formic-, acetic-, propionic-, glycolic-, acrylic- and methoxyacetic acid (target substances) were combined with one or two other carboxylic acids (active substances), chosen out of a pool of 16. All investigations were carried out with an aromatic polyamide membrane and the operating conditions were kept constant. Although the combination of all effects is extremely complex, the experiments showed that the influence on the retention of a substance equate as an outcome of molecular mass, acidity, functionality and spatial requirement. The influence of functionality in the active substances could be further divided into an additional carboxylic group, double bond and aromaticity. The calculation of the osmotic pressure demonstrated that there was no observable difference between the real and ideal one when the solution contained the same number of components. Therefore it can be concluded that in this study the osmotic pressure has no influence on the retention of the target substance.     

Experimental and theoretical evaluation of the membrane affinity to water: role of modifiers in the control of the matrix performance

This work was aimed at evaluating adsorption of water molecules onto membrane surfaces modified by sulphonamide derivates. Controlling interfacial forces at the membrane-feed interface were assessed by combining experimental and theoretical studies. The phenomena experimentally observed were also interpreted by using quantum-chemical and dynamic approaches in order to correlate the membrane affinity to water with the availability and accessibility of polar moieties, enabling to form intermolecular interactions such as hydrogen bonds.     

Distribution of Tm3+ and Ni2+ in chalcogenide glass ceramics containing Ga2S3 nanocrystals: Influence on photoluminescence properties

The distribution of Tm³⁺ and Ni²⁺ ions is unambiguously exhibited in 80GeS₂-20Ga₂S₃ chalcogenide glass ceramics (GCs) containing Ga₂S₃ nanocrystals (NCs) by using advanced analytical transmission electron microscopy. Distinctively different distribution patterns of Tm³⁺ and Ni²⁺ ions are observed in the GCs obtained by controlled crystallization. The distribution of the dopants imposes strong influence on their optical properties which are revealed by absorption and photoluminescence (PL) spectra. Detailed discussions are given of the mechanisms of the crystallization-induced PL enhancement and quenching of the Tm³⁺ mid-infrared and Ni²⁺ near-infrared emissions, respectively.     

Study on the control of pore sizes of membranes using chemical methods: Part III. The performance of carbonates and bicarbonates in the membrane-making process by the chemical reaction

In this paper, polyvinylidene fluoride (PVDF)/polymethyl acrilate (PMMA)/cellulose acetate (CA) blend UF membranes were prepared by chemical reaction introduced phase-inversion method. The results of the experiment show that: (1) The membrane pore size distribution is more uniform due to the presence of carbonates or bicarbonates in the coagulation bath; (2) No more than the stoichiometric ratio amount of carbonates or bicarbonates in the coagulation bath can effectively improve the membrane pore size distribution and make the pore size of membrane more uniform; (3) The membrane prepared by carbonates solution as a working solution in coagulation bath possess superior performance than that by bicarbonates.