Fabrication and Characterization of PSf/GO-SiO2 Membranes as Filtration of Detergent Contaminated Water

The increasing use of detergents in daily life can cause environmental pollution. So, to solve the problem, membrane technology is suitable to reduce various pollution from water. Graphene Oxide (GO) and SiO2 are very much of concern and have been studied in recent years because they can change many characteristics of materials and can expand the range of applications in membrane manufacturing. So, this study aims to analyze the results of PSf/GO-SiO2 membrane fabrication by phase inversion method and analyze the results of PSf/GO-SiO2 membrane performance as detergent polluted water filtration. In GO synthesis using Hummer’s method, GO-SiO2 composite synthesis using Tetraethylorthosilicate (TEOS) in-situ hydrolysis method, and PSf/GO-SiO2 membrane fabrication using the phase inversion method. So, it is concluded that the PSf/GO-SiO2 membrane fabrication has been successfully carried out, as indicated by the SEM results; with the increasing presence of SiO2, the membrane pore size is getting bigger. For the performance of the PSf/GO-SiO2 membrane with UV-Vis test, the results showed that the flux value of the PSf; PSf/GO and PSf/GO-SiO2 (0.6) membranes was 119.58 L/m2.h; 140.35 L/m2.h and 157.79 L/m2.h respectively. In line with the results of the membrane rejection values are 95.22%, 97.68%, and 98.55%, respectively. The membrane with the best performance in the filtration of detergent-polluted water is the PSf/GO-SiO2 (0.6) membrane. The presence of SiO2 in the membrane causes a higher flux value because the larger membrane pore size influences it, so the PSf/GO-SiO2 membrane can be used to filtrate detergent-contaminated water.


Introduction
In this life, water is an essential environmental component for all creatures in the world.Without water, this life cannot take place.According to data from the Central Statistics Agency (BPS), in 2021, Indonesia experienced around 10,683 cases of water pollution spread across all villages.This water pollution contains various substances or microorganisms that exceed the permissible limits so that the water quality will deteriorate.Poor water quality will result in water that cannot be adequately used for daily purposes such as drinking or other purposes.Washing (laundry) waste containing detergent is then channeled into rivers, which can pollute the water in the river [1].The manufacture of detergents usually uses ingredients such as synthetic chemicals (surfactants), fillers, forming agents, and additives [2].
With the increasing use of detergents, it can cause problems, especially causing environmental pollution.Some water treatment techniques to overcome the problem can use techniques such as filtration, adsorption, membrane technology, and advanced oxidation methods (photocatalysis, ozonation, and biodegradation) [3].Among these water treatment techniques, one strategy that attracts attention and easy strategies is the membrane technology-based technique.Membrane technology-based techniques have advantages such as high efficiency in removing contaminants from water, simple operation, and environmental friendliness [4].In recent years, Graphene Oxide (GO) and SiO 2 have been of great interest and widely studied because they can change many characteristics of materials and can expand the range of applications in membrane manufacturing.Silica nanoparticles become the supporting layer of the membrane to achieve high permeability [5].The GO layer can be an insulating layer to prevent deposits of various contaminants so that the GO-SiO2 composite has the advantage of high separation capacity and can improve anti-fouling performance.
After the GO-SiO2 composite was made, it was continued with the membrane fabrication process using the phase inversion method.The method refers to research conducted by Angesti and Munasir [6].In making the membrane for the GO-SiO2 composite, it is added with Polysulfone (PSf) polymer solution.In this case, Polysulfone (PSf) is a good candidate because it has excellent chemical properties and thermal stability [7].In making the membrane, a solvent is also needed.The solvent used in this experiment is Dimethylacetamide (DMAc) solvent.DMAc solvent is a solvent that is often used to dissolve PSf.This solvent has a boiling point above 164.5-166o C to dissolve PSf well [8].In its development, membrane is a material science that is very influential for technological progress [9].So, there is a feed flow in membrane filtration, namely unidirectional flow filtration (dead-end filtration), a filtration module usually used for laboratory research.When the water flow is perpendicular to the membrane surface, it can reduce the polarization concentration [10].This flow has the advantage of low energy consumption, operating pressure, and operating costs [11].
So, in the current era, according to Lu and Astruc [12], organic pollutants are a critical environmental problem because organic pollutants include heavy metals in water that negatively impact the environment.Detergent is an example of an organic pollutant.So, this experiment was carried out using the membrane technology method to reduce surfactant levels in detergents.An illustration of the detergent solution filtration membrane is shown in Figure 1.From this illustration, it is expected that when performing membrane filtration, the resulting permeate is water-free from detergents.Previous research conducted by Khery et al. [13] for gravity-based polyacrylonitrile ultrafiltration membranes with low pressure explained that filtration in detergent solutions has a deficiency in the membrane's permeability (water flux).This happens because the higher pressure carried out during filtration can result in foulants, so there is a decrease in permeability.The membrane also has poor rejection due to the size of the detergent molecules, which are relatively more accessible and large compared to the membrane's pore size.
A previous study used PS-35 Polysulfone UF membrane (Nanostone Water, CA) and NF-8 polyamide NF membrane (Nanostone Water, CA) for 100 ppm surfactant filtration.From the experiment, it was found that the flux and rejection values could have been more optimal [14].Therefore, this research was conducted to optimize the PSf/GO-SiO 2 membrane using DMAc solvent, which is used as a detergent in polluted water filtration.This study aims to analyze the results of PSf/GO-SiO2 membrane fabrication results by phase inversion method and the results of PSf/GO-SiO2 membrane performance as detergent polluted water filtration.

GO Synthesis
The first step is to weigh 5 g of graphite powder and 2.5 g of sodium nitrate powder (NaNO 3) dissolved with 120 mL of 97% sulfuric acid (H2SO4) in ice bath conditions.Second, stir at 8 rpm for 30 minutes using a hot plate magnet stirrer.Third, 15 g of potassium permanganate (KMnO4) was slowly added to the solution and stirred at 8 rpm at 20°C for 30 minutes until the solution turned purple.Fourth, continue with an 8 rpm stirrer for 3 hours at room temperature.Fifth, the solution turned brown at this stage, then 150 mL of distilled water was added and the temperature was set to 95-100°C for 3 hours.After the solution is greenish yellow, 50 mL of 30% hydrogen peroxide (H 2O2) is added slowly to remove manganate compounds.Sixth, conduct with 1 M HCl and distilled water until the pH was neutral and continue the drying process at 60°C for 6 hours.

Synthesis of GO-SiO 2
First, 0.125 g of GO was dispersed in 150 mL of ethanol: H 2O in a ratio of 1:5 and sonified for 30 minutes.Second, add ammonia to the reaction mixture until the pH approaches 9. Third, add 0.6 mL of TEOS to the solution and re-sonicate for 30 minutes.Fourth, the solution was stirred at room temperature at 8 rpm for 24 hours.Fifth, the solution was centrifuged to obtain the residue and washed using distilled water and ethanol.Sixth, drying at 60°C for 12 hours.

Fabrication of GO-SiO 2/PSf Membrane
The first step was to weigh 1 g of polysulfone (PSf) mixed into 5,469 mL of dimethylacetamide (DMAc) and stir at 8 rpm for 3 hours until the solution was homogeneous.Secondly, 0.0333 g of GO-SiO2 composite was added into the solution to produce 0.5 wt% solution.Third, the solution was sonicated for 30 minutes to accelerate the dissolution without air bubbles.Fourth, the formed solution was molded on a glass plate and pressed using an iron cylinder.Sixth, soaking using distilled water for 24 hours.Seventh, followed by the drying process at room temperature for 24 hours.The membrane fabrication process is shown in Figure 2.

Detergent Contaminated Water Filtration Process
The first step for filtration tests on membranes was made by making a solution of organic pollutants using the main ingredient, powder detergent, for washing clothes.The detergent solution was made with a concentration of 100 ppm (0.01 g detergent powder dissolved in 100 ml of distilled water) with 7 rpm stirring for 5 minutes.Then, the membrane filtration experiment was continued using a detergent solution with a set of vacuum pumps (Rocker 300) [15].The detergent solution was then poured into the membrane with a predetermined area and controlled volume to determine the membrane flux was calculated using equation (1) [16]: Information: Furthermore, the detergent solution was calculated using equation ( 2) [16]: Information: R = Rejection (%) ‫ܥ‬ = Permeate Solution (mg/L) ‫ܥ‬ = Feed Solution (mg/L)

SEM test and analysis of membrane pore size
Scanning Electron Microscope (SEM) was used to determine the membrane pore size using FEI Brand test equipment, Type: Inspect-S50.In Figure 4 SEM test results on PSf, PSf/GO, and PSf/GO-SiO2 (0.6) membranes have membrane pore sizes of 0.31 μm, 0.35 μm, and 0.42 μm, which are getting bigger.The presence of SiO2 can form a larger membrane pore size to benefit the membrane flux results.
The results of the SEM test of the PSf membrane can be seen in the 20.000 times magnification image.The pore size of the membrane can make the membrane able to pass water even though it has high hydrophilic properties.Around the membrane pore are clumps like PSf that have not dissolved completely.Meanwhile, the PSf/GO membrane can be seen in the 20.000 times magnification image, which looks like sheets, indicating the presence of GO which usually looks like sheets.In the PSf/GO-SiO2 (0.6) membrane, it can be seen in the 20.000 times magnification image that there has been a homogeneous mixture due to the GO-SiO 2 composite in contrast to the PSf/GO membrane, which looks like a sheet indicating the presence of GO.With the addition of SiO2, it can be seen that the pore membrane is getting bigger and does not look like sheets.
So, the greater the SiO2, the larger the membrane surface pores will be.As in research [17] with, increasing amounts of SiO2 can form larger membrane pores so that it can benefit the results of membrane flux.The SEM test results on the membrane surface are shown in Figure 4.

Application of PSf/GO-SiO2 Membrane as Detergent Contaminated Water Filtration
The detergent-contaminated water filtration experiment was carried out by making a detergent solution with a concentration of 100 ppm in the filtration process using dead-end filtration flow with a set of vacuum pumps (Rocker 300) at a controlled pressure of 675 mmHg.The 100 ppm detergent solution was then poured on the PSf/GO-SiO 2 membrane with a membrane area of 0.0009 m 2 , and the volume of detergent solution used was 20 mL.The calculation process of this membrane flux uses Equation 1, and the following results are shown in Table 1.The results of the calculation of membrane flux using Equation 1 obtained flux values in PSf; PSf/GO and PSf/GO-SiO2 (0.6) membranes of 119.58 L/m 2 .h;140.35 L/m 2 .hand 157.79 L/m 2 .h.These data show that the membrane with SiO2 has a higher flux value because the larger membrane pore size influences it.The faster Time when filtration is carried out produces a large flux value due to the larger membrane pore size, making the detergent solution easier to penetrate the membrane.The presence of SiO 2 is also able to increase membrane flux [18].So, in the research conducted by Feng [5], silica nanoparticles become a supporting layer to achieve high flux.At the same time, the GO layer can be an insulating layer to prevent precipitation from various contaminants so that the merger or GO-SiO2 composite has the advantage of high separation capacity and can improve anti-fouling performance.
Furthermore, the calculation of membrane rejection is carried out with dead-end filtration flow.The first step is making a calibration curve with a UV-Vis test.The first step is making a calibration curve by doing a UV-Vis test.The equation y = 0.0069x + 3.354 was obtained from the calibration curve.After that, we continued the filtration process on the detergent solution with several membrane variations and continued with UV-Vis test to get the absorbance value.From the UV-Vis test data of the detergent solution after filtration, the absorbance value (y) was obtained on the PSf; PSf/GO and PSf/GO-SiO2 (0.6) membranes of 3.387, 3.370, and 3.364.Then, the data into the equation y = 0.0069x + 3.354.The data produces a concentration value (x), which can be used as a Cp value.The x value obtained on the PSf; PSf/GO and PSf/GO-SiO2 (0.6) membranes was 4.783 mg/L, 2.319 mg/L and 1.449 mg/L respectively.Then, proceed with the calculation of rejection using Equation 2. The results of the membrane rejection value are obtained from this equation, as shown in Table 2.The results of the calculation membrane rejection PSf; PSf/GO and PSf/GO-SiO2 (0.6) amounted to 95.22%, 97.68%, and 98.55%, respectively.According to Wu et al. [19], silica particles are smaller and useful for improving membrane performance.Meanwhile, according to Fathanah and Meilina [20], combining polymers with inorganic compounds such as SiO2 can produce selectivity (rejection) and excellent and profitable permeability.So, the merger or GO-SiO 2 composite has the advantage of high separation capacity.
PSf membrane produces a good rejection value, which can be caused by membrane fouling so that water polluted with detergents does not easily escape with a long filtration time.So that it can make the detergent molecules settle on the surface of the membrane and produce a good rejection value.The membrane pore size can also influence this membrane rejection.Good rejection can indicate that all solutes are perfectly retained by the membrane or unable to pass through the membrane [21].Apart from the membrane pore size, the repulsive and attractive forces on the membrane surface are essential in membrane rejection.According to Alkindy et al. [22], the PES membrane has a negative charge.In his research, oily wastewater has a positive charge so that charge rejection can occur, which is associated with membrane rejection.PSf membrane has a negative charge [23].Meanwhile, according to Hidayat [24], surfactants for detergents have a positive charge in solution.So that there is a repulsion between the negative charge of the PSf membrane surface and the positively charged detergent solution.This can create rejection on the membrane surface and produce a good membrane rejection value.An illustration of PSf/GO-SiO 2 membrane as detergent-contaminated water filtration is shown in Figure 5.
Figure 5 shows a rejection of detergent molecules to produce a good rejection value.From the illustration of the figure, it is expected that water polluted with detergents after filtration using PSf/GO-SiO2 membrane can produce water free from detergent solution contamination.From the overall data above, the flux value and membrane rejection value are shown in Figure 6. Figure 6 shows the outcome of flux and membrane rejection as an application of detergent-polluted water filtration employing the dead-end filtering method.The results of the membrane flux value obtained on the PSf; PSf/GO and PSf/GO-SiO 2 (0.6) membranes were 119.58 L/m 2 .h,140.35 L/m 2 .hand 157.79 L/m 2 .hrespectively.While the results of membrane rejection values obtained on PSf, PSf/GO, and PSf/GO-SiO 2 (0.6) membranes amounted to 95.22%, 97.68%, and 98.55%, respectively.So, from these data, the flux and membrane rejection values increase with the GO-SiO2 composition.The best membrane is obtained in the PSf/GO-SiO 2 (0.6) membrane, which has the highest membrane rejection value for detergent-polluted water filtration.

Conclusion
Based on the results and discussion above, the following conclusions can be drawn: the fabrication of PSf/GO-SiO 2 membranes with the phase inversion method has been successfully carried out.SEM results show that the membrane pores are getting bigger.For the performance of the PSf/GO-SiO2 membrane as a detergent, polluted water filtration in the presence of SiO2 makes the membrane pores larger so that the flux and membrane rejection values increase.

Figure 1 .
Figure 1.Illustration of membrane filtration of detergent-contaminated water.
X-Ray Diffraction (XRD) is used to determine the diffraction peaks using X-ray diffraction (on an XPert MPD Diffractometer with Radiation of CuKα (λ=1.5406Å).It can be seen that there is a GO peak located around 2θ = 10.2 o (002) indicating the oxidation of graphite with a hexagonal crystal structure and 2θ = 42.37 o which can be caused by irregular turbostatic bands on carbon materials.Meanwhile, GO-SiO2 is located at peaks around 2θ = 11.97 o , 23 o and 42.66 o which have amorphous properties.The presence of a new peak at 2θ = 23 o can indicate a successful presence of silica nanoparticles on the GO surface due to the destruction of GO piles.Based on the XRD test results of the synthesis with previous research references have similarities.So that it can prove that the synthesis of GO and GO-SiO2 has been successfully synthesized.

Figure 3 .
Figure 3. XRD test results of GO and GO-SiO2.

Figure 4 .
Figure 4. SEM test results of the membrane with 20.000 times magnification.

Figure 5 .
Figure 5. Illustration of PSf/GO-SiO 2 membrane as filtration of detergent contaminated water.