11 results
Now showing1 - 10 of 11
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Characterizing macroporous ion exchange membrane adsorbers for natural organic matter (NOM) removal-adsorption and regeneration behavior(Multidisciplinary Digital Publishing Institute (MDPI), 2024-06); ; ; Addressing the characterization of Natural Organic Matter (NOM) removal by functionalized membranes in water treatment, this study evaluates the effectiveness of two commercial ion-exchange membrane adsorbers: Sartobind® Q (with quaternary amines) and D (with tertiary amines). Using Suwannee River NOM (SRNOM) as a surrogate, Langmuir adsorption isotherms revealed maximum capacities (Qmax) of 2966 ± 153 mg C/m2 and 2888 ± 112 mg C/m2, respectively. Variations in flux from 50 to 500 LMH had a minimal impact on breakthrough times, proving low diffusion limitations. The macroporous (3-5 µm) functionalized cellulose-based membranes exhibited high permeabilities of 10,800 L/(h m2 bar). Q maintained positive zeta potential vs. pH, while D's zeta potential decreased above pH 7 due to amine deprotonation and turning negative above an isoelectric point of 9.1. Regeneration with 0.01 M NaOH achieved over 95% DOC regeneration for Sartobind® D, characterizing reversibility through a pH-swing. Cyclic adsorption showed that Q maintained its capacity with over 99% DOC regeneration, while D required acidic conditioning after the first regeneration cycle to mitigate capacity reduction and re-deprotonate the adsorber. These results have demonstrated the potential suitability of adsorber membranes, designed originally for biotechnological purposes, for the possible removal of disinfection byproduct precursors in drinking water treatment.Publicationtype: Journal Article36 31 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electro-sorption and -desorption characteristics of electrically conductive polyacrylonitrile membranes to remove aqueous natural organic matter in dead-end ultrafiltration system(Elsevier, 2024-02); ; ; ; Electrically conductive (EC) membranes have emerged as an innovative approach in removing natural organic matter (NOM) by electro-sorption (e-sorption) when external anodic potential (AP) is applied. In this study, the EC membranes were established by a forming a porous nanolayer of Pt nanoparticles via magnetron sputtering on both sides of virgin and chemically modified PAN ultrafiltration (UF) membranes. The modified PAN membranes were functionalized with ethylenediamine (PAN-EDA) and sodium hydroxide (PAN-NaOH). The virgin PAN membrane material contains nitrile group and demonstrated a negative zeta potential in the analyzed pH range. The PAN-EDA membrane owned amidine and amine groups, whereas PAN-NaOH membrane possessed carboxyl and amide groups in the membrane matrix. The PAN-NaOH and PAN-EDA membranes exhibited isoelectric points at 3.7 and 7.8, respectively. Electrical field-assisted UF experiments were conducted with Suwannee River NOM in dead-end mode and NOM removal was monitored using different methods of NOM characterization (e.g., SEC, DOC and UV254 absorbance). The results revealed that the non-electrically conductive (NEC) and EC virgin PAN membranes exhibited almost no intrinsic adsorption (at 0 V external potential) and e-sorption of NOM at 2.5 V AP respectively. However, NEC PAN-NaOH and PAN-EDA membranes showed DOC intrinsic sorption loadings of 17 mg·m−2 and 258 mg·m−2 at permeate flux 100 L·m−2·h−1 and pH 7 respectively. In comparison, the DOC e-sorption loadings of the EC PAN-NaOH and EC PAN-EDA membranes at 2.5 V AP were 197 mg·m−2 and 525 mg·m−2 under same test conditions respectively. The NOM e-desorption characteristics of the EC modified PAN membranes were also investigated to regenerate membranes for a sustainable filtration process. The results indicated that the EC PAN-NaOH and PAN-EDA membranes can be regenerated by reversing the electrical polarity almost completely. In conclusions, the outcomes of this work confirm that the presence of the derivatives of amines (e.g., amines, amidine and amide groups) and carboxyl group are necessary in the membrane matrix to induce e-sorption and -desorption characteristics.Publicationtype: Journal ArticleScopus© Citations 1 28 112 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Surface grafted N-Oxides have low-fouling and antibacterial properties(Wiley, 2023-12-13)Scopus© Citations 4 21 66 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Adsorptive dead-end filtration for removal of Cr(vi) using novel amine modified polyacrylonitrile ultrafiltration membranes(Royal Society of Chemistry (RSC), 2022-10-18); ; ; ; The present study investigates the concept of combining the processes of ultrafiltration (UF) and ion exchange into one single filtration step. By this, particulate matter and dissolved toxic hexavalent chromium (Cr(vi)) ions are removed by adsorptive dead-end filtration. For this purpose, we modified a conventional polyacrylonitrile (PAN) UF membrane with two methods to generate weak-base and strong-base anion exchanger functional groups on the membrane surface and in its pore structure. The pristine PAN membranes were chemically modified to generate primary (PAN-NH) and quaternary (PAN-Q) amine groups. Pristine PAN, PAN-NH and PAN-Q membranes were characterized and compared regarding their chemical and mechanical properties. The modified PAN membranes were tested in chromium filtration experiments at pH 5.5, pH 7 and pH 8.5. The fully loaded membranes were regenerated by caustic solution for desorption of the chromium. The effect of the membrane modifications on the pure water permeability, contact angle and BET surface was negligible. However, the charge of the membrane was affected significantly seen by the reversal of zeta potential from negative to positive values after modification. The filtration experiments revealed that the total adsorption capacities of PAN-NH and PAN-Q membranes are 151 mg and 145 mg Cr(vi) per m2 membrane surface after complete membrane saturation (cfeed = cpermeate), respectively. When compared with pristine PAN and PAN-Q membrane, the PAN-NH membrane has demonstrated high removal rates (>90%) for Cr(vi) in the first ten hours of filtration and thus more relevant for application-orientated membrane water treatment systems. Desorption of previously adsorbed Cr(vi) was achieved by filtering a regeneration solution (1 M NaCl and 0.01 M NaOH) through the loaded membranes. After regeneration, the adsorption capacity was almost completely recovered. The findings of this study verify that low-pressure amine-modified PAN membranes provide an effective and energy-efficient way to process Cr(vi) contaminated water for possible drinking water purposes.Publicationtype: Journal Article48 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Modification of polyacrylonitrile ultrafiltration membranes to enhance the adsorption of cations and anions(Multidisciplinary Digital Publishing Institute (MDPI), 2022-05-31); ; ; ; Ion adsorbing ultrafiltration membranes provide an interesting possibility to remove toxic ions from water. Furthermore, it is also possible to recover valuable elements. In this work, we demonstrate two easy strategies to modify polyacrylonitrile membranes with anion and cation adsorbing groups. The membranes were modified to have positively charged amine groups or negatively charged carboxyl groups. The success of the reactions was confirmed using IR spectroscopy and zeta-potential measurements. The membranes carrying negatively charged groups provided a negative zeta-potential and had an isoelectric point at pH 3.6, while the membranes carrying positively charged groups had a positive zeta-potential in the analyzed pH range. Since only the surface of the polymer was modified, the pore size and permeance of the membranes were not drastically affected. The membranes prepared by both modification strategies had a pure water permeance higher than 1000 L/(m2 h bar) and a water contact angle of 44.3 and 57.2°, respectively. Therefore, the membranes can be operated at low pressures with reasonable flux. Additionally, SEM images showed that the membranes were still open-pored. Adsorption tests using a positively and a negatively charged dye as well as a toxic cation and an anion were performed to analyze the adsorption behavior. Both membranes were able to adsorb the oppositely charged dyes as well as the copper and chromate ions. Therefore, these membranes are good candidates to purify water streams containing hazardous ions.Publicationtype: Journal ArticleScopus© Citations 14 89 200 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Elektrisch angesteuerte Gold-Polymer-Gold-Ultrafiltrationsmembranen zur Aufbereitung NOM-haltiger Wässer(2022-04-08); Humanity is facing a water crisis due growing water demand of an increasing population, economic development, water pollution, and climate change. Ultrafiltration (UF) is a promising technology for countering the global water crisis due to its high removal potential for pathogens and turbidity at high recovery and low demand of chemicals. However, it suffers from membrane fouling and low removal performance for organic water constitutes such as natural organic matter (NOM). The selectivity for NOM increases when the pore size of the UF membrane is decreased but this also leads to reduction of permeability and energy efficiency. This problem is called the selectivity-permeability trade-off. Electrically conductive UF membranes are a new approach which might offer a solution to these problems. Most NOM are negatively charged. By application of a negative or positive electrical potential to the membrane surface, a repulsive or attractive force is induced on the charged substances in the feed water, respectively, which influences the rejection and fouling behavior of these membranes. In this work, an ultra-thin gold coating was applied on the active and support layer of flat-sheet polymer membranes to achieve electrical conductivity. Due to the coating of both sides of the membrane, no additional counter electrode was necessary to apply an external potential. An intrinsically negatively charged polyethersulfone (PES, UP150) and an intrinsically positively charged polyamide (M5) membrane were used for electro-repulsive and electro-sorptive filtration experiments, respectively. In the first part of this thesis, the membranes were characterized before and after the gold-coating regarding its filtration and electrochemical properties. Sputter coating only slightly changed the filtration properties of the membranes. The molecular weight cut-off was almost not affected by the gold coating. However, the pure-water permeability was reduced by 15 % and 40 % for the M5 and UP150 membrane, respectively. In the second part of this thesis, electro-repulsive filtration was conducted with model NOM solutions and natural lake water with the UP150 membrane. At filtration of Hohloh lake water the permeability decreased by 49 % (± 2 %) when no external potential was applied (0 V). However, when negative potential was applied the permeability only decreased by 17 % (± 3 %) (at -2.5 V). The application of negative potential to the membrane active layer led to less fouling and an increased NOM rejection at cross-flow mode. The molecular weight cut-off was shifted from 150 kDa at no applied potential to 5 kDa at -2.5 V (cell potential). Therefore, it could be seen that the duplex-coated membrane configuration was almost as effective as conventional counter electrode configuration in fouling mitigating and rejection enhancement. In the third part, electro-sorptive dead-end filtration experiments showed that the application of a positive potential led to adsorption of NOM and negatively charged organic dye molecules. When the potential was reversed to negative potential, the previously adsorbed substances could be desorbed. The process of electrosorptive UF worked with the intrinsically positively charged M5 membrane but not with the intrinsically negatively charged UP150. The molecular weight cut-off of the M5 membrane was shifted from approx. 1000 kDa at no applied potential to approx. 0.7 kDa at +2.5 V (cell potential). Therefore, the electrosorptive UF achieved a NOM rejection performance in the range of commercially available nanofiltration membranes. At the same time, the positively charged M5 membrane showed permeability in the range of loose UF membranes and fouling was not observed to be problematic. The additional energy consumption for the application of the external potential was low with 0.03 kWh/m³ of permeate. Overall, electro-repulsive and electro-sorptive UF membranes, both, broke the selectivity-permeability trade-off of the UF process. Whereas, the electrosorptive enhancement of NOM removal was more pronounced than the electro-repulsive.Publicationtype: Doctoral Thesis261 989 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Amine‐terminated PAN membranes as anion‐adsorber materialsAnion-adsorbing membranes provide an interesting possibility to remove toxic arsenate and chromate from drinking water. A promising way to prepare anion-exchange materials is to introduce positively charged amine groups on polymers. In this study, polyacrylonitrile (PAN) ultrafiltration membranes were modified with amine functionalities on the mem-branes. The success of the modifications was demonstrated using infrared spectroscopy and zeta potential measurements. Additionally, the arsenate adsorption was analyzed. The modified membrane showed arsenate adsorption 5 times higher than the pristine PAN membrane.Publicationtype: Journal ArticleScopus© Citations 20 290 351 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electrosorptive removal of organic water constituents by positively charged electrically conductive UF membranesNegatively charged electrically conductive ultrafiltration (UF) membranes have been intensively investigated for fouling mitigation and rejection enhancement in recent years. This study reports the novel approach of applying positive charge (+2.5 V cell potential) to a conductive membrane to induce electrosorption of negatively charged substances onto the membrane. Subsequently, desorption of negatively charged substances is achieved by changing the potential periodically (e.g., after 30 min) to negative charge (-2.5 V cell potential). For this purpose, sputter deposition of ultra-thin gold layers (40 nm) is used to generate electrically conductive gold-polymer-gold flat sheet membranes by coating the active and the support layer of two commercial polymer UF membranes (polyethersulfone UP150, polyamide M5). When M5 membrane was charged positively during filtration (+2.5 V), Suwannee River NOM, Hohloh lake NOM, humic acid and Brilliant Blue ionic dye showed removal rates of 70 %, 75% and 93% and 99%, respectively. Whereas, when no potential was applied (0 V) removal rates were only 1 – 5 %. When a positive potential was applied to the active membrane layer and a negative potential was applied to the support layer (cell potential 2.5 V), a significant increase of flux with 25 L/(m² h) was observed due to the induction of electro-osmosis. Electrosorption was only observed for M5 membrane (ζ: +13 mV, pH 7) and not with UP150 membrane (ζ: -29 mV, pH 7). Due to a low current density of 1.1 A/m² at a flux of 100 L/(m² h), the additional energy consumption of electrosorption and desorption process was low with 0.03 kWh per m³ of permeate. This study delivered the proof of concept for the novel process of electrosorptive UF with energy consumption between microfiltration and ultrafiltration but NOM removal rates of nanofiltration membranes.Publicationtype: Journal Article70 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electrically conducting duplex-coated gold-PES-UF membrane for capacitive organic fouling mitigation and rejection enhancement(2021-02-15); ; Recent studies showed that the application of an electrical potential onto an ultrafiltration membrane surface exhibit several advantages with respect to the fouling and rejection behaviour. Sputter deposition of ultra-thin metal layers onto commercial flat sheet membranes proved to be a simple way of producing conductive metal-polymer-composite membranes. Adopting the novel approach of duplex-coating the active and support layer of a flat sheet membrane eliminates the need for an additional counter electrode and significantly simplifies module design for conductive flat sheet systems. Cross-flow filtration experiments were conducted with organic model foulants such as sodium alginate, bovine serum albumin (BSA), humic acids as well as with natural organic matter (NOM) from Hohloh lake water. The duplex-coating induced an additional electric field through the membrane itself, resulting in enhanced performance not only for cathodic but also for anodic charging of the active membrane layer. Hohloh lake water fouling experiments showed decreased permeability of 47% for the uncharged membrane to 16% and 38% for the cathodic and anodic charging, respectively. Moreover, a significant increase in NOM-rejection was observed with 27% for the uncharged membrane and 72% and 49% for the cathodic and anodic potentials, respectively. Finally, the effectiveness of externally charged duplex-coated membranes was demonstrated by comparing rejection and fouling rates with conventional membrane-electrode vs. counter electrode configuration, showing an almost similar enhancement in performance.Publicationtype: Journal Article107 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 218 1