PVDF Membrane Surface Research Articles

Polyphenol-assisted construction of hierarchical microstructure on membrane surface with self-cleaning properties for highly efficient oil/water separation

Rational design of hydrophilic hierarchical structures on the membrane surface is a promising method to improve oil/water separation efficiency. However, oil droplets with intrinsic adhesion tend to accumulate on the membrane surface, which deteriorates membrane performance. In this study, tannic acid-Zn(II) complex was homogeneously anchored on the PVDF membrane surface and further in situ converted to ZIF-8 in the presence of 2-methylimidazole. Subsequently, Cu ion exchange was employed to transfer ZIF-8 layer to gerhardtite (Cu2(OH)3NO3) with a hierarchical structure. Accordingly, the as-prepared PVDF/TA-gerhardtite membrane possessed attractive hydrophilicity and underwater superoleophobicity with oil contact angles above 150°, therefore achieving over 98 % oil rejection towards various surfactant stabilized oil-in-water emulsions. Moreover, self-cleaning properties can be realized by activating peroxymonosulfate, and 97 % of tetracycline hydrochloride, the target pollutant, was degraded within 30 min owing to the generation of sulfate radicals and hydroxyl radicals. Due to the attractive hydrophilicity and catalytic oxidation capacity of the gerhardtite hierarchical structure, degradation and bubble generation induced fouling recovery was accomplished after PMS cleaning, and the irreversible fouling decreased to 2.2 % after consecutive soybean oil fouling. Therefore, this work provides new insights into the construction of hierarchical structures on membrane surfaces and demonstrates their potential applications in oil/water separation and fouling mitigation.

A novel superhydrophilic hyperbranched polysiloxane grafted membrane for oil-in-water emulsion separation

Oily wastewater, posing serious environmental and social issues, has aroused widespread concerns. Membrane separation is regarded as an excellent candidate to solve the problem of oily wastewater, although membrane pollution is inevitable in the process of separation. The construction of hydrophilic surface reported so far can effectively mitigate membrane pollution. Herein, we reported a novel hyperbranched polysiloxane grafted polyvinylidene fluoride membrane (HBPSi-g-PVDF), which was prepared through grafting amino-terminated hyperbranched polysiloxanes onto the PVDF membrane surface via an amidation reaction. The HBPSi-g-PVDF membrane possessed superhydrophilic/underwater superoleophobic properties and excellent resistance to oil droplet adhesion. Meanwhile, the resulting membrane presented favorable water permeance (16924 L∙m−2∙h−1∙bar−1) and permeance recovery ratio (99.0 %). In addition, the HBPSi-g-PVDF membrane displayed satisfactory separation efficiency (>99.1 %) for diverse oil-in-water emulsions having over 6000 L∙m−2∙h−1∙bar−1 permeance. Furthermore, HBPSi-g-PVDF membrane also showed excellent environmental durability and recyclability, maintaining stable performance in hash environments, highlighting its great future for the disposal of oily wastewater.

The preparation of electrically-enhanced and hydrophilic CNTs-PVDF composite hollow fiber membranes for fouling resistance

The anaerobic membrane bioreactor has great potentials to treat the wastewater with high organic matter due to the efficient anaerobic digestion process and high biomass retention. However, the existence of membrane fouling significantly increases the maintenance cost, and always requires frequent and complex cleaning process to recover the membrane performance. Thus, it is significant to fabricate a membrane with excellent anti-fouling performance for the application in membrane bioreactors. Herein, we prepared the CNTs-PVDF hollow fiber membrane with fouling resistance via loading the conductive CNTs coating on the surface of commercial PVDF membrane by a simple cross-linking reaction with hydrophilic polyvinyl alcohol and succinic acid. “Dual defense” was constructed by the combination of the hydrophilic surface and conductive CNTs coating, which lifted the anti-fouling performance of this membrane. In the assistance of electrical effect, the permeance of the membrane with −1.2 V bias could be recovered to 95 % of original state by simple hydraulic cleaning, while that of the membrane without bias was only 58 % after filtrating the sludge of 2000 mg/L. Furthermore, this membrane also exhibited the superior stability and fouling resistance in the operation of anaerobic electrochemical membrane bioreactor, which was promising for the advanced water treatment.

Synergistic effects of PVDF membrane surface functionalization with polydopamine and titanium dioxide for enhanced oil/water separation and photocatalytic behavior

This study investigates the surface modification of poly(vinylidene fluoride) (PVDF) membranes using polydopamine (PDA) and titanium dioxide (TiO2) for effective separation of oily compounds and self-cleaning photocatalytic behavior. The aim was to improve the antifouling properties of the membrane, which was modified by varied PDA and TiO2 concentrations and evaluated regarding the water permeance, total organic carbon (TOC) rejection, and photocatalytic degradation activity. The results demonstrated considerable improvements in the membrane's antifouling properties, achieving a water permeance of 781 kg h−1 bar−1 m−2, TOC rejection of 87%, and methylene blue photocatalytic degradation of 97%, using dopamine (DA) and TiO2 concentration of 0.92 g L−1 and 1.4% (w/w), respectively, and a solution agitation speed of 106 rpm. Additionally, flux recovery reached 86% after the photocatalytic self-cleaning process, indicating that TiO2 improved the membrane's antifouling properties. These findings highlight the potential of PDA and TiO2 as effective surface modifiers for enhancing oil/water separation, reducing fouling, and promoting self-cleaning effect in photocatalytic PVDF membranes. This study’s outcomes provide valuable insights for developing efficient and sustainable membrane-based separation processes for oily wastewater treatment applications.

Effect of basic and basic/acid modifications on the surface of PVDF membranes for the insertion of TiO2 and its use in environmental applications.

Supporting titanium oxide (TiO2) on polymeric membrane surfaces is a strategy to increase the photocatalytic activity of this material as well as to modify membrane surface with antifouling properties or to develop hybrid processes of water treatment. The chemical characteristics of the polymeric membrane surfaces are a determining factor in the correct impregnation of TiO2 particles. In this work, the titanium oxide was immobilized on polyvinylidene fluoride (PVDF) membrane surface by direct impregnation during the synthesis of the inorganic particles by sol-gel route. The PVDF membranes were previously modified by treatments based on an alkaline attack followed by acid treatment. The final TiO2-modified membranes were characterized by infrared and Raman spectroscopy, as well as by scanning electron microscopy. In addition, the changes on the surface characteristics were determined by contact angle measurements. Finally, the membranes were tested on the photocatalytic degradation of methyl orange (MO). The results obtained indicate that the basic/acid pretreatment allows the generation of active sites in the membrane and that when carrying out the synthesis of TiO2 on the membrane, it can be anchored stably on its surface and through the pores. The microscopies indicate that the structure of the membrane is not compromised by the pretreatment. The amount of TiO2 deposited on the membrane was of 0.1580 ± 0.01773mg TiO2/cm2 membrane. With this amount of TiO2, a degradation percentage of 98.2% is achieved after 450min; when the membrane is used for a second cycle, a degradation percentage of 82.0% is obtained, which remains constant for 3 subsequent cycles. This method, which uses the PVDF membrane as a support for TiO2 particles, represents a low-cost and easy-to-prepare insertion procedure, with good degradation percentages, which means that the membrane can be used for subsequent studies in filtration systems in the treatment of effluents from the textile industry.

Deep pore grafting modification for PVDF membrane by supercritical carbon dioxide in combination with ultraviolet irradiation to improve permselectivity and oil/water separation performance

In order to enhance PVDF membrane’s permselectivity to oil and water during oil-water separation process, an efficient strategy that combining supercritical carbon dioxide technology (scCO2) and ultraviolet (UV) irradiation was proposed to change the wettability of PVDF membrane. The grafting of -COOH groups on PVDF membrane surface was demonstrated by FTIR-ATR, XPS and SEM. Deep pore grafting of acrylic acid in membrane pore interior was confirmed by establishing force models and corresponding wettability test. The results showed that permeate flux of deep pore modified membrane was 69.64Lm-2 h-1, which was 17.23% and 7.44% higher than that of unmodified membrane and surface modified membrane respectively. Interestingly, when reaction temperature not reached 40℃, some modified membranes were impermeable to water although they had good surface hydrophilicity, which was closely related to the critical point state of supercritical fluid mixture system.

Polymeric membrane with nanohybrids of Cu nanocomposites and metalloporphyrin-based nanosheets for enzyme-like catalytic degradation of Congo Red

Metalloporphyrin-based nanozymes are effective peroxidase-like catalysts for dye degradation; however, their reusability is a challenge due to the nanoscale dimensions. Membrane technology has the advantages of high efficiency, low energy consumption, and easy operation. Here, we integrate poly (vinylidene fluoride) (PVDF) membrane with nanozyme for effective decolorization of Congo Red (CR). A nanozyme (Cu@Cu-FeTCPP) is prepared by growth of copper hydroxide-copper oxide (Cu(OH)2-CuO) nanocomposites onto the metal organic framework (MOF) nanosheet consisting of tetrakis-(4-carboxyphenyl)-porphyrin iron ligands and cupric ion nodes. The functional membrane is achieved by loading Cu@Cu-FeTCPP nanozyme on the PVDF membrane surface (Cu@Cu-FeTCPP/PVDF). The as-prepared membrane shows catalytic activity for the degradation of CR. Under flow through conditions, the catalytic degradation in tangential flow plays a major role in overall decolorization of CR, far exceeding the contribution of adsorption. The membrane can rapidly catalyze the dye degradation even at different operating pressures (0.1–0.7 kPa) and feed solutions with higher CR concentrations (eg. 60 mg·L-1). Compared with the static batch catalysis and the free nanozyme catalysis, the membrane exhibits higher decolorization efficiency and outstanding reusability in the continuous flow process owing to the promoted mass transfer. After 40 min of continuous flow reaction in a feed solution containing CR (40 mg·L-1) and H2O2 (50 mM), the decolorization efficiency approaches 90% and remains above 85% after five catalytic cycles. The membrane with enzyme-mimicking ability has application prospect in wastewater treatment.

Antifouling polyamide-amine/PVDF gel membrane via click chemistry method for high-efficiency oil/water emulsion separation

Membrane fouling is an inevitable problem during the process of oil/water separation by membrane separation technology. In this work, we fabricated a polyamide-amine/PVDF gel membrane with hydrophilic surfaces via a thiol-alkene click chemical method. The polyamide-amine (PAMAM) dendrimer gel was grafted on the surface of PVDF membranes to improve hydrophilicity of membranes. The results showed that the obtained membrane possesses superhydrophilicity and underwater superoleophobicity repellent properties, along with excellent oil adhesion resistance. The water permeance can reach 12,300 L∙m‐2∙h‐1∙bar‐1 with a high recovery rate of 98%, with a prominent separation efficiency surpassing 98.5%. Furthermore, the gel membrane also displays remarkable environmental durability and recyclability, ensuring durable and effective separation of oily wastewater even in harsh chemical environments.

The structure and hydrophilicity of MWCNT-COOH /TiO2 modified PVDF membrane

MWCNT-COOH/TiO2 modified PVDF ultrafiltration membrane was created using a blended modification process with carboxyl carbon nanotubes (MWCNT-COOH) and TiO2 nanoparticles as modification additives in order to further enhance the hydrophilicity of the PVDF membrane surface. Using the techniques of scanning electron microscopy, Fourier transform infrared spectrum, and a water angle of engagement analyzer, the membrane’s structure and hydrophilicity were identified. Investigations were conducted into the effects of various MWCNT-COOH dosages on membrane structure and hydrophilicity. The results of the investigation indicated that 0.03 g of MWCNT-COOH in the casting solution was the ideal dose. The manufactured MWCNT-COOH/TiO2 modified PVDF ultrafiltration membrane had the best hydrophilicity.

Surface modification of a PVDF membrane by co‐grafting hydroxyl and zwitterionic polymers to enhance wettability and antifouling property

AbstractPolyvinylidene fluoride (PVDF) membranes have been widely applied in the separation of various organic matters owing to their excellent properties. However, they possess low wettability and undergo fouling because of the hydrophobic nature of PVDF. In this study, poly (2‐hydroxyethyl methacrylate) (PHEMA) and poly (sulfobetaine methacrylate) (PSBMA) were co‐introduced to modify the highly hydrophobic PVDF membrane surface via UV photo‐irradiation. Facile UV photo‐grafting was performed by irradiating the pristine PVDF membrane immersed in a PHEMA/PSBMA mixture solution with UV light for 5 min. The performance of the as‐prepared PHEMA/PSBMA‐grafted membrane was compared with that of membranes modified with solely PHEMA or PSBMA. The hydroxyl and zwitterionic groups of the grafted membranes enhanced wettability and increased flux. A tightly bound water layer was formed because of the enhanced wettability, significantly suppressing protein adsorption. The initial flux of bovine serum albumin (BSA) solution through the PHEMA/PSBMA‐grafted membrane was 2861 LMH, which was 3.1 times higher than that obtained by the pristine PVDF membrane. Furthermore, the flux decline of the modified membrane caused by BSA fouling was 49% lower than that of the pristine PVDF membrane. Finally, the PHEMA/PSBMA‐grafted PVDF membrane showed antifouling properties after three BSA filtration cycles.

Hydrophilic imprinted MnO2 nanowires “coating” membrane with ultrahigh adsorption capacity for highly selective separation of Artemisinin/Artemether

The selective separation and purification of ART and ARE using molecularly imprinted membrane (MIM) has attracted considerable attention, but most of conventional blending MIM face low adsorption capacity and poor selectivity due to the blockage of imprinting sites. Herein, an alternative ART imprinted MnO2 nanowires “coating” membrane (MINM) withhydrophilicity was fabricated by vacuum filtration of imprinted MnO2 nanowires and graphene oxide nanosheets on PVDF membrane surface for selective ART separation. For the MINM, the imprinted MnO2 nanowires coating offers more available exposed imprinting sites on the MINM surface compared to that of the blending MIM, while the introduction of graphene oxide improves the hydrophilicity of MINM, significantly reducing the non-specific absorption. Consequently, the MINM exhibits ultrahigh ART adsorption capacity and selectivity, with the ART adsorption amount of 335 mg g−1 at 5 min using dynamic cross-flow separation system, about 12.18 times higher than that of ARE (27.5 mg g−1), and the separation factor (a) value of 12.39. Moreover, the ATR FT-IR dynamic spectrum discloses the in-situ formation of H-bond between ART and MINM, playing a key role in the selective adsorption process. This work provides an alternative strategy to prepare “coating” MIM for high-efficient and selective separation of complex analogue systems.

High-throughput imprinted non-metal S-scheme heterojunction self-cleaning membrane with tight adhesion via dopamine for selective photodegradation of TC

The traditional photocatalysts have no selective photocatalysis ability and are difficult to separate and recycle. Herein, the imprinted modified non-metal S-scheme heterojunction photocatalytic membrane (IM-NSH-PM) was prepared via imprinting modification technology and dopamine (DA) tight adhesion method, which possessed high throughput (2548.6 L m−2 h−1 bar−1), good self-cleaning performance, excellent stability and recovery performance. The cross-linking and polymerization of DA on PVDF membrane surface can form a strong interaction between basement membrane and imprinted modified non-metal S-scheme heterojunction (IM-NSH), which made IM-NSH-PM adhered closely together. Besides, the formed S-scheme heterojunction between PDI and g-C3N4, which weakened the recombination rate of electrons and holes and further improved the photodegradation ability. The photodegradation rate of TC by IM-NSH-PM reached 71.88%. More importantly, under the action of imprinting modification, IM-NSH was endowed with many imprinted cavities consistent with the three-dimensional structure of tetracycline (TC), thereby TC can be preferentially selective adsorbed and degraded, and the selectivity coefficient of IM-NSH-PM to non-imprinted modified non-metal S-scheme heterojunction photocatalytic membrane (NIM-NSH-PM) was 1.88. This work shows a meaningful idea for exploring self-cleaning membranes with good selective photodegradation ability for the target pollutant.

Preparation of Modified Membrane Based on Covalent Grafting of Poly(N-isopropyl acrylamide) on PVDF Membrane Surface by Gamma-Ray Irradiation

Preparation of Modified Membrane Based on Covalent Grafting of Poly(N-isopropyl acrylamide) on PVDF Membrane Surface by Gamma-Ray Irradiation

Preparation of sodium alginate-polyvinyl alcohol@PVDF hybrid membrane for efficient oil-water separation

Oily sewage is widespread in petrochemical and machinery manufacturing industries. Direct discharge not only wastes water and oil resources, pollutes the ecological environment, but also affects the survival and health of humans and other organisms. The traditional oil-water separation method has strong limitations, poor economy and low separation efficiency. Sodium alginate (SA) and polyvinyl alcohol (PVA) were uniformly coated on the surface of PVDF membrane, and superhydrophilic SA-PVA@PVDF hybrid membrane was prepared by multiple cyclic self-assembly. The oil-water separation experiment was carried out by using the membrane. The initial separation efficiency was 99.8%, and the overall separation efficiency remained above 98.3% after 10 cycles of regeneration experiments. This study provides a new idea for the low-cost, green and simple preparation of superhydrophilic-underwater superoleophobic separation materials.

Study on the hydrophobic modification of PVDF membrane by low-temperature plasma etching in combination with grafting in supercritical carbon dioxide

Poly (vinylidene fluoride) (PVDF) membrane has good resistance to acid and alkali, chemical stability, high mechanical strength, piezoelectric performance features, especially has good hydrophobic, can be used as blood purification, aerospace flexible sensor pieces, architectural membrane material, water desalination, etc., but for a particular application scenario, the hydrophobic properties still need further improvement. In this study, based on the principle of bionics, low-temperature plasma was used to construct a rough structure and generate active groups on the PVDF membrane surface. Fluorinated monomers were grafted onto the PVDF membrane in supercritical carbon dioxide (scCO2) fluid. The bionic effect of the lotus leaf was constructed on the membrane surface, and the hydrophobicity of the PVDF membrane was significantly improved. The results showed that the rough structure of the PVDF membrane surface was better when the plasma etching conditions were 600W and 300s. When PVDF membrane was swelled for 3h at 35 °C and 13.56 MPa, and grafted for 6h at 100.7°Cand 26.08MPa in scCO2, the PVDF membrane contact angle could reach 140.6°, which was close to superhydrophobic. The hydrophobic reagent was covalently grafted onto the surface of the PVDF membrane by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. The atomic force microscopy (AFM) test showed that the membrane surface modified by this method had a combination of micro and nanostructure. Further, it confirmed the contribution of a rough surface with low surface energy to water resistance. The processing method meets the requirements of peak carbon emission and net zero carbon dioxide emission, which has important guiding significance for developing hydrophobic surfaces.

Effect of spraying polyvinyl alcohol solution on the surface of liquid film on the structure and antifouling properties of polyvinylidene membrane

Abstract Polyvinylidene fluoride (PVDF) membrane was prepared by a two-step method of surface gelation-immersion precipitation. The surface of the scraping solution film was sprayed with polyvinyl alcohol (PVA) aqueous solution to gel the film surface first, and then the liquid film was immersed in a coagulation bath for phase transformation to obtain the surface modified PVDF membrane. The effects of PVA solution with different mass fraction on the structure and properties of PVDF membrane were studied. The results showed that with the increase of spraying PVA mass fraction, the contact angle of the upper surface of PVDF membranes gradually decreased, the porosity and mean pore size of PVDF membranes gradually increased, and the crystallinity of PVDF membranes gradually decreased. The pores on upper surface of the membranes first increased and then decreased, and the finger-like macropore structure appeared inside the membranes, the water flux first increased and then decreased, and the rejection rate increased. Dynamic cycle filtration experiment of bovine serum protein (BSA) solution showed an increase in membrane flux recovery from 68.31 to 95.08% and a decrease in the irreversible fouling rate from 31.69 to 4.92%, indicating an improvement in the hydrophilicity and antifouling properties of the modified PVDF membrane.

A Facile Strategy toward the Preparation of a High-Performance Polyamide TFC Membrane with a CA/PVDF Support Layer.

In this study, polyamide (PA) thin-film composite (TFC) nanofiltration membranes were fabricated via interfacial polymerization on cellulose acetate (CA)/poly(vinylidene fluoride) (PVDF) support layers. Several types of CA/PVDF supports were prepared via the phase inversion method. With increasing CA, the PVDF membrane surface pore size decreased and hydrophilicity increased. The effect of the support properties on the performance and formation mechanism of PA films was systematically investigated via an interfacial polymerization (IP) process. The permselectivity of the resulting TFC membranes was evaluated using a MgSO4 solution. The results show that the desired polyamide TFC membrane exhibited excellent water flux (6.56 L/(m2·h·bar)) and bivalent salt ion rejection (>97%). One aim of this study is to explore how the support of CA/PVDF influences the IP process and the performance of PA film.

Engineering a superwetting membrane with spider-web structured carboxymethyl cellulose gel layer for efficient oil-water separation based on biomimetic concept

Superhydrophilic and underwater superoleophobic membranes have recently attracted significant interest as materials for effective oil-water emulsion separation.In this work, a superwetting membrane with a spider web structured gel layer was designed for efficient oil-water separation. Biomaterial, carboxymethyl cellulose (CMC), was used as the raw material, a spider web structured gel layer was constructed on the PVDF membrane surface by heat-treatment and chemical cross-linking. The hydrophilic gel layer imparted excellent superhydrophilic and underwater superoleophobic properties to the membrane, while the special spider web structure improved the membrane mechanical stability. The fabricated membrane exhibited superhydrophilicity and underwater superoleophobicity. Among different CMC concentration-modified membranes, the M-0.5 membrane containing 0.5 wt% CMC exhibited a flux of 612 L·m−2 h−1 during dichloromethane oil-water emulsion separation, which was 4.2-fold higher than that of the pristine PVDF membrane, while the membrane showed efficient oil-water separation capacity. Additionally, the water flux recovery reached as high as 93.3 %, and oil rejection attained 99.1 %. Meanwhile, the spiderweb-structured gel layer on the membrane surface displayed good mechanical stability. In summary, this novel membrane-modification method, inspired by the spider web structure, was simple, cost effective and environmentally friendly, thereby making it promising for future preparation of highly efficient oil-water emulsion separation membranes.

Preparation of loose nanofiltration PVDF membrane coated with dopamine and EPPTMS layers based on mussel inspired technique and ring-opening reaction via a facile VIPS-NIGPS method for dye separation applications

In this work, vapor-induced phase separation (VIPS) coupled with non-solvent induced gelation phase separation (NIGPS), in which water was used as an additive to tailor loose nanofiltration (NF) membrane, was utilized to obtain an optimized and smoother primer PVDF membrane for efficient dye separation. Next, a polydopamine (PDA) layer was formed through the Mussel-inspired technique on the surface of the as-prepared PVDF membrane. Subsequently, an epoxy-propoxypropyl-trimethoxysilane (EPPTMS) layer was also fabricated on the PDA layer in order to enhance hydrophilicity and rejection performance of the prepared membrane. It was demonstrated that through the addition of external H2O (4%), viscosity was escalated due to the pre-gelation. Moreover, the NIGPS-VIPS process resulted in better consolidation of PVDF chains during de-mixing process, and therefore, led to the improved porosity and surface pore size. After the formation of PDA and EPPTMS layers, extraordinary separation and flux performance were obtained. The permeation rate across the membrane was as high as 15.5 L.m−2.h−1.bar−1, and the rejections of Crystal violet (CV), Methylene blue (MB), Methyl green (MG), Reactive red 120 (RR), and Direct yellow (DY) dye solutions (0.2 g/L) by the prepared PVDF/PDA/EPPTMS membrane were 99.1%, 98.1%, 98.6%, 90.3%, and 97.3%, respectively. Moreover, flux recovery rate was also enhanced from 59.0% to 94.2%, which was about 60% enhancement. The optimum membrane also exhibited an outstanding long-term rejection and long-term flux. All the separation tests demonstrated the extraordinary performance of the optimum membrane for dye rejection applications.

Fabrication and characterization of nanocomposite membranes for the rejection of textile dye

In current study nanodiamonds (NDs) and LiCl were added into poly (vinylidene fluoride) (PVDF) matrix to prepare PVDF/ND/LiCl nancomposite membranes by using phase inversion method. Fabrication of nanocomposite membranes was then confirmed by XRD, SEM, FTIR and TGA. The results showed that the nanodiamonds were incorporated into the pores and onto the surface of PVDF membranes. The effect of NDs loading (0.1 to 0.7 wt%) on nanocomposite membranes properties was studied. The presence of NDs in PVDF substrate provided it a hydrophilic character thus improved permeability, antifouling performance and decreased shrinkage ratio. PNL-0.5 (adding 0.5% NDs with PVDF membrane) exhibited the best results with fouling recovery ratio of 95%, malachite green dye rejection of 95%, decolorization rate of 89% and and mechanical stability up to 15 cycles. These results showed that the characteristics of PNL-0.5 were best and can be used for the removal of dyes from industrial effluent.