Removal of anionic dye Congo red from aqueous environment using polyvinyl alcohol/sodium alginate/ZSM-5 zeolite membrane

In this study, a novel PVA/SA/ZSM-5 zeolite membrane with good regeneration capacity was successfully prepared by solvent casting technique. The properties of the membranes were assessed by employing different characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), optical microscopy (OP), thermogravimetric analysis (TGA), contact angle and universal testing machine (UTM). XRD, TGA and UTM results revealed that the crystallinity and thermo-mechanical performance of the membrane could be tuned with zeolite content. The successful incorporation of zeolite into the polymer matrix was confirmed by FT-IR, SEM and OP analysis. The adsorption ability of the as-prepared membrane was evaluated with a model anionic dye, Congo red. Adsorption studies show that the removal efficiency of the membrane could be tuned by varying zeolite content, initial concentration of dye, contact time, pH and temperature. Maximum dye adsorption (5.33 mg/g) was observed for 2.5 wt% zeolite loaded membrane, at an initial dye concentration of 10 ppm, pH 3 and temperature 30 °C. The antibacterial efficiency of the membrane against gram-positive (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli) was also reported. The results show that membrane inhibits the growth of both gram-positive and gram-negative bacteria. The adsorption isotherm was studied using two models: Langmuir and Freundlich isotherm. The results show that the experimental data fitted well with Freundlich isotherm with a high correlation coefficient (R2 = 0.998). Meanwhile, the kinetic studies demonstrate that pseudo-second-order (R2 = 0.999) model describe the adsorption of Congo red onto PVA/SA/ZSM-5 zeolite membrane better than pseudo-first-order (R2 = 0.972) and intra particle diffusion model (R2 = 0.91). The experimental studies thus suggest that PVA/SA/ZSM-5 zeolite could be a promising candidate for the removal of Congo red from aqueous solution.


Methods
Materials. The polymers polyvinyl alcohol (C 2 H 4 O, Mw = 130,000: hydrolysis degree: 99%) and anionic dye, Congo red ((C 32 H 22 N 6 Na 2 O 6 S 2 ); purity: 99.0%) was purchased from Ajax Finechem Pvt. Ltd. (Thailand). The crosslinking agent glutaraldehyde (C 5 H 8 O 2 ) were procured from Loba Chemie Products Limited. (Thailand). Sodium alginate ((C 6 H 7 NaO 6 ) n , average Mw = 60,000) were obtained from Nice chemical Pvt. Ltd. (India). Tetra propyl ammonium hydroxide ((CH 3 CH 2 CH 2 ) 4 NOH, TPAOH), tetraethyl orthosilicate (C 8 H 20 O 4 Si, TEOS) and aluminum isopropoxide (C 9 H 21 AlO 3 , AIP) were procured from Sigma Aldrich Co. Ltd (India). Soluble starch (C 6 H 10 O 5 ) n which was used as templating agent were of reagent grade and was procured from Merck (India). All the chemicals used in the study were of analytical grade and were used as received without further purification. The polymer solution and dye solution were prepared in distilled water. Figure 1 depicts the chemical structure of the materials used in the study.
Fabrication of hierarchical ZSM-5 zeolite. The procedure for the synthesis of hierarchical ZSM-5 zeolite is briefly described below. To the properly mixed tetra propylammonium hydroxide (TPAOH; 2.11 g) and aluminum isopropoxide (AIP; 0.03 g) solution, tetraethyl orthosilicate (TEOS; 3.46 g) solution was added dropwise with constant stirring for 5 h at room temperature. This was followed by the addition of meso templating agent, starch (0.2 g) and the mixture was magnetically stirred for 2 h to attain homogeneity. The resulting mixture was then concentrated in a rotavapor at 80 °C for 30 min until a viscous solution is obtained, which was transferred into a Teflon-lined stainless-steel autoclave, and kept at 80 °C for 24 h and crystallized at 175 °C for 6 h. The solid product was collected, washed with deionized water, dried in air, and calcined at 550 °C for 5 h in a muffle furnace to remove the starch and organic structure directing agents 55,56 . Fabrication of PVA/sodium alginate/ZSM-5 zeolite membrane. PVA/sodium alginate/ZSM-5 zeolite membrane was fabricated by solvent casting method. At first, required amount of polyvinyl alcohol and sodium alginate were dissolved separately in distilled water under constant stirring to obtain 9 and 1.5 wt% of PVA and SA solution respectively. The resultant solution was then mixed and magnetically stirred for 3 h. Afterwards, hierarchical ZSM-5 zeolite of varying concentration ranging from 0.5 to 2.5 wt% were added and Scientific RepoRtS | (2020) 10:15452 | https://doi.org/10.1038/s41598-020-72398-5 www.nature.com/scientificreports/ stirred at room temperature for 2 h to attain homogeneity. Once the solution was properly homogenized, 0.1 mL of cross-linker glutaraldehyde (GA) in acidic medium (HCl) were added in dropwise. The blended solution was casted on a petri dish and kept for air drying for a period of 5 days. The membrane was later peeled out from the petri dish and used for adsorption studies. The membranes containing 0, 0.5, 1.5 and 2.5 wt% of ZSM-5 zeolite is designated as PSZ-0, PSZ-1, PSZ-2, and PSZ-3 respectively. Chemical compositions of membranes are displayed in Table 1.
Characterisation. The crystallinity of the PVA/SA/ZSM-5 zeolite membrane was identified by Rigaku miniflex 600 benchtop X-ray diffractometer with Cu-Kα radiation as X-ray source. The XRD spectrum was recorded from 5 to 50° (2θ) at a scan rate of 2°/min. The chemical structure of the membrane was monitored by using Jasco 4,700 FT-IR spectrometer in the range of 450-4,000 cm −1 with 4 cm −1 resolution. A thermogravimetric analyser Mettler Toledo TGA/DSC 3 + HT/1,600 instrument was employed to investigate the thermal stability of membranes. The analysis was carried out in the temperature range of 50-750 °C at a heating rate of 10 °C/ min in N 2 atmosphere. The surface morphology of the membranes was assessed by scanning electron microscope (FEI Quanta 450) and optical microscopy (Olympus BX43 series) instrument. Universal testing machine (QC-506M1-204) was employed to investigate the mechanical properties of the membranes. Static water contact angle of the membranes was probed using Digidrop goniometer. Adsorption experiments were conducted using UV-visible spectrometer Specord (UV-210) at a characteristic wavelength of 492 nm.
Adsorption studies. For adsorption experiments, 0.075 g of membrane was added to 40 mL of Congo red solution and stirred at room temperature. After regular time interval the dye solution was withdrawn, filtered and analysed using UV-visible spectrophotometer at a characteristic wavelength of 492nm. The concentration of Congo red at different time interval was determined from the calibration graph. The percentage dye removal  www.nature.com/scientificreports/ efficiency (R) and equilibrium adsorption capacity (q e ) of the membrane were calculated using the following equations: Here C 0 and C e (mg/L) represent the initial and equilibrium concentrations of Congo red respectively; V (L) is the volume of Congo red solution and W(g) is the weight of the dried membrane 30 .
Antibacterial studies. The disk diffusion agar method was employed to assess the antimicrobial property of the PVA/SA/ZSM-5 zeolite membranes. The culture medium was prepared using Muller-Hinton agar seeded with 100 µL of bacterial strain (Escherichia coli and Staphylococcus aureus). Membranes were cut in a circular shape with 1 cm diameter and placed on this agar plates, which was later incubated at 37 °C for 24 h. The diameter of the inhibition zone formed around the specimens was measured and photographed 57,58 . Reusability. For recyclability test, 0.075 g of Congo red loaded membrane is immersed in 0.1 N of HCl under constant stirring for 3 h. The membrane was then separated from acid solution, washed several times with distilled water, dried and reuse for further adsorption process 59 .

Result and discussion
Polymer with good crystallinity tends to improve the thermal and mechanical stability of the membrane. This prompted us to evaluate the effect of zeolite on the crystalline nature of PVA/SA membrane. The XRD pattern of PVA/SA/ZSM-5 zeolite membrane is shown in Fig. 2a. The crystalline peak centered at 2θ = 20°, is attributed to the reflection from (100) and (200) plane of PVA and SA 60,61 . Comparison of XRD pattern of pristine PVA/SA membrane with PVA/SA/ZSM-5 zeolite membranes shows that both the membrane possesses similar diffraction pattern. However, with increases in zeolite concentration the intensity of peak at 2θ = 22-25° increases; attributed to the characteristic MFI peak of zeolite 62 . The XRD result thus shows that zeolite retains the overall crystallinity of the membrane. FTIR is one of the powerful tools to identify the functional groups and to understand the chemical interaction between molecules. FTIR spectrum of PVA/SA/ZSM-5 zeolite membranes are illustrated in Fig. 2b. The peak observed at 3,233 cm −1 is assigned to the hydroxyl stretching band of PVA, sodium alginate and zeolite 63 . The alkyl stretching present in PVA, sodium alginate and zeolite can be seen at 2,915 cm −1 and the sharp peak centered at 1,630 cm −1 is assigned to the characteristic C=O stretching of carboxyl group of sodium alginate 64 . A prominent band at 1,075 cm −1 can be seen in the FTIR spectra and is attributed to the acetal bridge (C-O-C) present in the crosslinked structure of PVA and GA. In the case of zeolite loaded membrane, we can observe a new peak at 550 cm −1 , assigned as the characteristic structure of zeolite 30 . The intensity of this characteristics peak is found to increase with zeolite content, thus confirming successful incorporation of zeolite in PVA/ SA membrane. A prominent blue shift observed in the characteristic peak of zeolite indicates the formation of hydrogen bond between PVA and zeolite (Fig (S1)). Contact angle measurement is an important analysis which is used to elucidate the hydrophilicity or wettability of the membrane. Perhaps, contact angle and hydrophilicity is inversely related to each other. Membrane with low contact angle is said to possess high hydrophilic character. On the other hand, a high value of contact angle implies greater hydrophobicity. The contact angle measurement of PVA/SA/ZSM-5 zeolite membrane is presented in Fig. 2c. It can be seen from Fig. 2c that the PVA/ SA membrane possess low contact angle (23.5°). This could be due to the presence of hydrophilic functional groups such as -OH and -COOH. However, the contact angle of PVA/SA/ZSM-5 zeolite membrane is relatively higher than pristine membrane and its value is found to escalates from 23.5° to 81.93° with zeolite loading. This implies that PVA/SA/ZSM-5 zeolite membrane is less hydrophilic than pristine membrane. Therefore, the water drop placed on the surface of zeolite loaded membrane becomes more spherical ( Fig. 2c) with increasing zeolite content. This is agreement with the previous report 65, 66 . The thermal behavior of the membrane was examined using TGA analysis and the result is presented in Fig. 2d. It can be noticed that the membranes exhibit weight loss in three stages. The initial weight loss occurred in the temperature range 50-150 °C corresponds to the removal of loosely bound moisture in the membrane. The second stage of degradation around 170 to 310 °C is due to decomposition of PVA and sodium alginate. Final stage observed around 330-520 °C corresponds to degradation of zeolite crystals 2,67 . Wang et al. 68 noted a similar degradation temperature (100, 200 and > 350 °C) for PVA/SA/ZSM-5 zeolite membrane and is ascribed to the removal of water, PVA, SA and zeolite from the membrane framework. It is evident from Fig. 2d that weight loss and the slope of degradation gets gradually reduced from membrane PSZ-0 to PSZ-3 (84.82% to 58.37%). This is expected owing to the high zeolite content which increases the thermal stability of the membrane. Mechanical strength and mechanical stability are important factor for membrane studies. Earlier report shows that addition of nanoparticles such as zeolites, clay, laponite will improve the polymer stability 69,70 . The mechanical properties of different membrane were shown in Fig. 2e. An improvement in the tensile strength of the membrane with zeolite percentage was noted. This is attributed to the enhancement of chemical interaction between the zeolite and polymer matrix. However, the elongation at break decrease with zeolite content. Prasad et al. also observed a similar type of behavior for PVA/ SA/ZSM-5 zeolite system 71 .
The effect of zeolite on the surface morphology of the pristine PVA/SA membrane was evaluated using SEM and optical microscopic technique. The surface morphology of pristine PVA/SA and PVA/SA membrane loaded With increase in zeolite percentage, the distribution of these particles is found to increase and at high concentration, a slight agglomeration can be noted. The SEM analysis thus proved that zeolite particle is successfully incorporated in PVA/SA membrane. Optical microscopic images were in complimentary to SEM analysis and supports the distribution of zeolite in the polymer matrix ( Fig. 3(II)).
Adsorption studies. The adsorption ability of the prepared membranes was tested using a model anion dye, Congo red. The effect of operation parameters such as zeolite loading, initial dye concentration, contact time, pH and temperature on the adsorption behavior of the membranes was investigated in detail. Zeolite is one of the versatile materials with high surface area and has been widely used for the adsorption of dyes, toxic metal and gases 43 . Our previous reports show that it is an excellent adsorbent for the removal of methylene blue (MB) and methyl orange (MO) from aqueous solution 54,72 . In order to optimize the adsorbent dosage, we have varied the zeolite dosage from 0.5 to 2.5 wt% and investigated its effect on the adsorption capacity of the membrane. It can be deduced from Fig. 4a that with increase in zeolite dosage, the adsorption capacity increases and the membrane loaded with 2.5 wt% of zeolite exhibits maximum adsorption capacity (5.33 mg/g). The linear increase in the adsorption capacity with adsorbent dosage is in agreement with the previous reported work and could be explained on the basis of availability of vacant active site on the membrane 73 . With increase in zeolite content, the number of active site and surface area of the membrane increases. Thus, zeolite provides a favorable environment for the adsorption of Congo red onto the membrane. Our observation agrees well with the work of Briao et al. 74 The authors noticed a significant enhancement in the adsorption capacity of chitin/zeolite membrane for crystal violet with zeolite dosage. Initial dye concentration plays a significant role in dye adsorption process. The effect of initial dye concentration on the adsorption capacity and percentage dye removal was investigated by varying initial dye concentration from 10 to 50 ppm and the results are presented in Fig. 4b. It is evident from Fig. 4b that with increase in C o , the q e increases from 5.33 to 24.45 mg/g, while the removal efficiency decreases from 99.9 to 90%. Our result is in consistent with the previous reports which stated that initial dye concentration renders necessary driving force to reduce the resistance of mass transfer from liquid to solid phase 75 . Consequently, the www.nature.com/scientificreports/ collision between dye and the adsorbent increases and the adsorption process become more favorable. Baheri et al. 76 reported that that adsorption capacity of PVA/4A zeolite membrane for methylene blue (MB) dye rises from 4.90 to 41.08 mg/g on increasing the initial dye concentration from 5 to 100 mg/g. The decreases in dye removal percentage with initial concentration of Congo red dye is attributed to the saturation of active site under high concentration condition of Congo red 77 . Contact time is an important parameter in dye adsorption studies. The effect of contact time on the Congo red removal is depicted in Fig. 4c. It can be noted that during the initial period the adsorption capacity shoots up sharply and after 2.5 h it almost attain equilibrium. This is probably due to the availability of large number of active sites in the initial phase of the adsorption process which facilitates the binding of Congo red onto the membrane. However, with passage of time as more and more dye molecules get adsorbed on the surface of the membrane the adsorption process become less favoured. Eventually, all active sites get occupied by dye molecules and the adsorption capacity remains almost constant 78 . Chen et al. 79 reported that on increasing the contact time from 20 to 180 min, Congo red adsorption capacity of PDA@ DCA-COOH membrane enhances from 30 mg/g to 79.33 mg/g. After 180 min, no further improvement in the adsorption capacity was noted and thus the authors selected 180 min for performing the adsorption studies. Solution temperature is reported to influence the adsorption behavior of the membrane. The variation of temperature on the dye uptake ability of PVA/SA/ZSM-5 zeolite membrane is shown in Fig. 4d. It can be noted that the adsorption capacity drops from 5.33 to 4.62 mg/g on increasing the solution temperature from 30 to 60 °C. The negative effect of temperature on the adsorption capacity could be correlated with previous reported work and implies that Congo red adsorption onto the membrane is exothermic in nature 80 . Another plausible reason could be the weakening of electrostatic interaction between dye and the membrane with temperature. Thus, we can conclude that high temperature is unfavorable for the adsorption of Congo red by PVA/SA/ZSM-5 zeolite membrane. Solution pH play a crucial role in dye adsorption studies, especially if the mechanism of adsorption is electrostatic in nature. A change in solution pH will alter the properties of both dye as well as the adsorbent. Therefore, optimizing solution pH is a necessary requirement for adsorption process. The role of pH on the Congo red adsorption by PVA/SA/ZSM-5 zeolite membrane was studied by varying the pH from 3 to 11. It can be seen from Fig. 4e that with increase in pH, the adsorption capacity of the membrane decreases from 5.33 to 2.92 mg/g. This could be due to difference in the surface charge of the membrane with pH. At low pH, the surface of membrane gets protonated and thus attracts anionic Congo red 81 . However, in basic pH the membrane surface tends to become negative and repel the anionic Congo red. In addition to this, high pH increases the competition between Congo red dye and hydroxide (OHˉ) for the same adsorption site.
Adsorption isotherm. Knowledge of adsorption isotherm is essential to design the adsorption system, as it shed light on adsorbate-adsorbent interaction and adsorption capacity of the adsorbent. Freundlich, Langmuir, Temkin and Dubinin-Radushkevich isotherm models are commonly used to understand the adsorption process 79,81 . In the present work, the adsorption behavior of the prepared membrane was evaluated using Freundlich and Langmuir isotherm models.
Langmuir model. According to Langmuir model, the surface of adsorbent is homogenous and possesses finite number of energetically equivalent adsorption sites. This model thus suggests a uniform adsorption of adsorbate on the surface of adsorbent and neglects any interaction between the adsorbed molecules 78 . Langmuir model is given by the following expression.
Here, q e corresponds to the equilibrium amount of adsorbate or adsorption capacity (mg/g), while C e represents equilibrium concentration of adsorbate (mg/L). K L and q m represent Langmuir constant and is related to adsorption energy and adsorption capacity respectively. The linear form of Langmuir isotherm model is expressed as follows The plot of C e /q e vs C e results in a straight line with q m as slope and K L as intercept. Another important parameter obtained from Langmuir model is Langmuir separation factor, R L . This dimensionless constant can be used to predict the feasibility and favorability of the adsorption process. The adsorption is said to be favorable if R L is between 0 and 1, irreversible if R L = 0, linear if R L = 1 and unfavorable if R L > 1. R L is related to K L and C o by the following expression.
Freundlich model. This model assumes non-uniform distribution of adsorbate on the surface of adsorbent and describes a multilayer adsorption. The non-linear form of Freundlich isotherm is given below; (3) q e = q m K L C e 1 + K L C e (4) C e q e = C e q m + 1 K L * q m   Figure 6. Plots of the pseudo-first, pseudo-second and intra-particle diffusion model for Congo red adsorption onto PVA/SA/ZSM-5 zeolite membrane (adsorbent dosage = 2.5 wt%, initial CR concentration = 10 ppm, contact time = 130 min, pH = 3 and temperature = 30 °C). Table 3. Kinetic parameter values for the Congo red adsorption on zeolite loaded PVA/SA membrane.

Exp
Pseudo-first-order Pseudo-second-order Intra-particle diffusion q e , exp (mg g −1 ) K 1 (min −1 ) q e (mg g −1 ) R 2 K 2 (g mg -1 min −1 ) q e (mg g −1 ) R 2 K id (g mg -1 min −1/2 ) C (mg g −1 ) R 2 5 www.nature.com/scientificreports/ where q e is the amount of Congo red adsorbed onto the membrane at equilibrium (mg/g) and C e is the equilibrium concentration of Congo red in solution (mg/L). K F and 1/n are adsorption capacity and adsorption intensity (surface homogeneity) which is obtained from the slope and intercept of the plot between ln q e and ln C e respectively. The value of 1/n is indicative of favorability of the adsorption. For instance, 1/n value between 0 and 1 implies favorable adsorption while 1/n > 0 and equal to zero is considered as irreversible and unfavorable adsorption respectively 82 . The linear form of Freundlich isotherm is represented as follows; The applicability of these two models to explain the Congo red adsorption onto PVA/SA/ZSM-5 zeolite membrane was verified by fitting the experimental adsorption data into the models (Fig. 5a,b) and the characteristic isotherm parameters derived from the isotherm models are presented in Table 2. It is evident from Fig. 5 that the experimental adsorption data fitted well with Freundlich model with high correlation ratio, (R 2 : 0.9985). Also, there is good agreement between calculated (4.8 mg/g) and experimental q e value (5.33 mg/g) thus suggesting that the Freundlich isotherm model is more suitable to describe the adsorption of Congo red onto PVA/SA/ ZSM-5 zeolite membrane and involves a multilayer adsorption process. The value of Freundlich constant, n was found to be 4.4 (Table 2), implying the favourable nature of adsorption process 83 . Adsorption kinetics. Adsorption kinetics gives an idea about the controlling mechanism of adsorption process (chemical reaction, diffusion and mass transfer process) and provides information regarding adsorption rate and adsorbate residue time. To investigate the kinetics of Congo red adsorption on the PVA/SA/ZSM-5 zeo-  www.nature.com/scientificreports/ lite membrane pseudo-first-order (PFO), pseudo-second-order (PSO) and intra-particle diffusion model were employed. The linear form of PFO and PSO is given below. PFO model PSO model where K 1 (min −1 ) is the pseudo-first-order rate constant, K 2 (g/mg min −1 ) is the pseudo-second-order rate constant, q t (mg/g) is the adsorption capacity at time t (min) and q e (mg/g) is the adsorption capacity at equilibrium respectively, which is determined from the slope of log (q e − q t ) versus time and t/qt versus time of linear plot. According to intra-particle diffusion model, the kinetics of adsorption involves diffusion of adsorbent into the pores of adsorbent and is represented as where K id and C are intraparticle constants and is estimated from the slope and intercept of the plot between q t vs t 1/2 .
The kinetics of Congo red adsorption onto PVA/SA/ZSM-5 zeolite membrane was assessed by fitting the experimental kinetic data into the linearized form of PFO, PSO and intraparticle diffusion models (Fig. 6). The kinetic parameters obtained from the result are displayed in Table 3. It is evident from figure that our data fitted well in PSO model (R 2 -0.999) and the experimental value was very much close to the q e value predicted using PSO model. This implies the suitability of the PSO model for describing the kinetic mechanism of Congo red adsorption on PVA/SA/ZSM-5 zeolite membrane.
An adsorbent with good antibacterial property is beneficial for water treatment application. This prompted us to investigate the antibacterial property of the prepared membrane. The antimicrobial activity of pure PVA, PVA/SA and zeolite loaded PVA/SA was tested against gram-negative (E. coli) and gram-positive (S. aureus) by inhibition zone method (Fig. 7). Absence of inhibition zones surrounding the PVA/SA membrane, suggest that pristine PVA/SA membrane have no antibacterial property. One can observe that zeolite loaded membrane displayed significant inhibition action against gram-positive (S. aureus) and gram negative bacteria (E. coli). The diameter of inhibition zone is found to increase with zeolite content thus indicating that the antibacterial property of the PVA/SA membrane could be improved by incorporating ZSM-5 zeolite. The mechanism of action of zeolite on gram-positive bacteria remains uncertain. But, we presume that negatively charged zeolite could easily bind with the surface of gram-positive bacteria and causes the disruption of cell wall. This perhaps leads to the leakage of cellular material and leads to bacterial death. The weak inhibition action of zeolite against gram-negative bacteria could be due to the repulsion between zeolite and negatively charged surface of gram-negative bacteria.
Reusability test is generally employed to access the practicability of the membrane. So, in the present study we subjected the membrane to five desorption-adsorption cycle and the results is presented in Fig. 8. It is evident from the Fig. 8 that the membrane possesses good regeneration capacity even after 5 cycle. The small decrease in the removal efficiency while going from first (99.3%) to firth cycle (95.1%) could be due to the incomplete desorption of Congo red from the membrane 84 . conclusion In this work, we have successfully developed an ecofriendly adsorbent for the removal of toxic anionic dye, Congo red from aqueous medium. Based on different characterization technique's such as XRD, FTIR, TGA and contact angle we found that the membrane is stable and the properties of the membrane such as crystallinity, thermal stability and hydrophilicity could be tuned by varying zeolite content. SEM and optical analysis revealed that the zeolite particle is successfully incorporated in the polymer matrix. The membrane was tested for Congo red removal from water. The optimized condition for the removal of Congo red from membrane is found to be as follows: zeolite content = 2.5 wt%; initial CR concentration = 10 ppm, contact time = 130 min, temperature = 30 °C and pH = 3. The adsorption isotherm and kinetics analysis revealed that the adsorption can be best described by Freundlich and PSO model respectively. The prepared membrane also possesses prominent antibacterial property and recyclability. Thus, from the current work, we can conclude that PVA/SA/ZSM-5 zeolite membrane could be a promising candidate for the removal of Congo red from polluted water. www.nature.com/scientificreports/