Method for modifying a reverse osmosis thin-film composite membrane

Abstract

The present invention relates to a method for modifying a reverse osmosis thin-film composite (TFC) membrane, the polyamide active layer of which is modified by incorporating polyamine groups, polyphosphonic groups and copper nanoparticles / ions via a chemical modification process. This modified composite membrane exhibits high biofouling resistance, which makes it suitable for use in seawater and brackish water desalination.

Description

[0001] METHOD FOR MODIFYING A THIN-LAYER COMPOSITE MEMBRANE FOR REVERSE OSMOSIS

[0002] DESCRIPTIVE MEMORANDUM

[0003] FIELD OF INVENTION

[0004] This patent application relates to a method for modifying a thin-film composite (TFC) membrane for reverse osmosis, where the membrane's active polyamide layer is modified by incorporating polyaminate groups, polyphosphonic acids, and copper nanoparticles / ions through a chemical modification process. The modified composite membrane achieves high biofouling resistance, validated for applications in seawater and brackish water desalination.

[0005] BACKGROUND OF THE INVENTION

[0006] Desalination technologies for seawater and brackish water have the potential to resolve the global freshwater crisis in the medium term. At the industrial level, and specifically in the case of mining in Chile, seawater desalination also represents an alternative for meeting the high water demands of its processes. It is expected that by 2033, seawater consumption will grow to 70% of the water required by the mining sector nationwide, with this water being primarily desalinated (Cochilco 2022).

[0007] It is well known that reverse osmosis (RO) technology is the dominant technology in the water desalination market with a 70% share and a compound annual growth rate of 7.9% for 2020, and it is expected that by 2027 contracted capacity will have increased to 39 Mm 3(DesalData (2022). Desalination Plants Inventory - Global market forecast, Global Water Intelligence), this is a result of technological advances that have allowed for increased energy efficiency, greater membrane performance and greater pretreatment efficiency.

[0008] The most commonly used commercial membranes for reverse osmosis (RO) water desalination are aromatic polyamide (PA) membranes, also known as thin-film composite (TFC) membranes. These membranes consist of two parts: an ultra-thin polyamide layer formed by interfacial polymerization on a microporous support (the ultrafiltration membrane, most commonly polysulfone - PS). However, these membranes are susceptible to fouling, which can be colloidal, inorganic, organic, or biological (biofouling). Biofouling is the leading cause (45-65%) of membrane failure and is caused by the deposition, proliferation, and metabolism of microorganisms (bacteria, algae, protozoa, and fungi) that form a biofilm on the membrane surface.

[0009] Over the past decade, several fouling control strategies have been developed and tested in large-scale TFC membrane installations. Colloidal, inorganic, and organic fouling have been successfully controlled through pretreatment, the dosing of chemicals such as antiscalants, periodic cleaning (physical or chemical), and adjustments to operating parameters. However, biofouling has become the greatest challenge for this technology.

[0010] Current research to combat biofouling has focused on 3 strategies: 1) Use of non-oxidizing biocides for the preliminary treatment of feed water, 2) modification of the geometry or components of the RO module or system, where the redesign or modification of the spacer element stands out, and 3) modification of the membrane surface, this last strategy being the option that has gained the most strength in recent years.

[0011] In this regard, the scientific and technological proposal to be protected in this patent application aligns with strategy 3), related to the chemical modification of the membrane's surface layer. The proposed route for modifying TFC membranes involves incorporating colloidal copper oxide nanoparticles and cupric ions through a chemical functionalization method that confers superior biocidal / inhibitory capabilities compared to commercial TFC membranes, without compromising their operational performance in the reverse osmosis process. Furthermore, the proposed modification prevents the passage of copper ions into the permeate during reverse osmosis operation, thus maintaining compliance with current water quality standards (Cu < 2 ppm).

[0012] The method for modifying a thin-film composite (TFC) membrane proposed in this application will address the technical problem of reducing bacterial adhesion and growth, and the subsequent formation of biofouling on the surface of these membranes. This will decrease the frequency of cleaning cycles and increase the lifespan of these membranes. This will have a direct impact on the operating costs of plants that use TFC-type reverse osmosis membranes (desalination plants, brackish water treatment plants, wastewater treatment plants, etc.).

[0013] Nanomaterials such as clays, transition metals and their oxides, carbon structures, and metal-organic frameworks, among others, have been used in the modification of TFC membranes. Specifically, copper has also been proposed for modifying TFC membranes due to its known biocidal effect and its lower cost compared to other materials such as silver (Ag).

[0014] Thus, the state of the art includes various solutions involving the use of copper-based materials to modify TFC-RO membranes, developed using different modification techniques, such as modification during the Interfacial Polymerization (IP) process or through techniques like coating, layer-by-layer, or grafting. In this regard, the invention of this application proposes a method for modifying TFC membranes by incorporating colloidal copper oxide nanoparticles and cupric ions using a chemical functionalization method such as grafting.

[0015] In the case of modifications during the Interfacial Polymerization (IP) process, the copper base material is incorporated during this polymer manufacturing process. In this case, several proposals consider incorporating it in the form of solid nanoparticles or cupric ions (WEN, Yue et al. 2019, QUEZADA, Rodrigo et al. 2020). The IP technique has some problems associated with the synthesis parameters, which can cause defects in the membrane and agglomeration of the copper nanoparticles, negatively impacting its performance. Unlike what has been disclosed, the invention of this application proposes a different method for modifying TFC membranes, through chemical functionalization by grafting, specifically incorporating colloidal copper oxide nanoparticles and cupric ions.It should be mentioned that the term colloidal nanoparticles is key, since the proposed technique is designed to modify membranes with colloidal solutions of stable nanoparticles and is not compatible with solid nanoparticles, as in the case mentioned in the references consulted.

[0016] Other methods for modifying TFC-RO membranes include coating, where copper material is applied to the membrane surface (KARKHANECHI, ​​Hamed et al. 2013; BEN-SASSON, Moshe et al. 2014, 2016; LIU, Caihong et al. 2022; ANH NGO, Thu Hong et al. 2023). However, the coating technique has certain limitations, such as the low stability of the modification on the membrane. This limits its application over long periods of operation due to the loss of effectiveness caused by the premature loss of the incorporated copper, which affects the permeate water obtained from the RO process. The invention in this application ensures the stability of the copper modification on the membrane by using an alternative method: grafting.

[0017] Another technique found in scientific publications is layer-by-layer (W. Ma, A. Soroush, 2016). For example, one reported case highlights a novel layer consisting of polyethyleneamine with copper nanoparticles (PEI-CuNPs) deposited on the membrane, giving it biocidal and bio-anti-adherent capabilities. However, it is recognized that the lack of suitable methods for loading CuNPs onto polymeric membranes is one of the main reasons for the limited research on their application in the membrane industry.

[0018] Similar to the present proposal, there are contributions to the modification of TFC-RO membranes using the grafting technique. A publication by M. Khajouei (2018) discloses the grafting of a coupled polyaniline / copper nanoparticle as an effective biocide onto a Filmtec TFC membrane. Another document is the scientific publication by Zhang et al. (2016), where copper nanoparticles supported on a carboxylated chitosan layer (CCTS) were incorporated, achieving a biocidal capacity with high durability over time. However, both contributions differ from the present patent application because in this proposal, the modification of TFC membranes is carried out by incorporating specific colloidal copper oxide nanoparticles and cupric ions, and not copper-based composites as reported in these studies.

[0019] On the other hand, document US20140319044 A1 discloses nanoparticle-functionalized membranes, where the surface of said membranes is functionalized with said nanoparticles. The nanoparticles closest to the membrane surface are covalently bonded to the membrane surface. However, this document does not disclose that the modification of TFC membranes is carried out by incorporating colloidal copper oxide nanoparticles and cupric ions using a chemical functionalization method.

[0020] Finally, US patent 8177978 B2 discloses an interfacial polymerization (IFP) process for preparing a highly permeable thin-film reverse osmosis (TFC) RO membrane by contacting a porous IFP support membrane, a polyfunctional acyl halide monomer, and a polyamine monomer, and recovering a highly permeable thin-film reverse osmosis (TFC) membrane. The method disclosed in this document for modifying the membranes differs significantly from that proposed in the present patent application, as it does not involve modifying TFC membranes by incorporating colloidal copper oxide nanoparticles and cupric ions using a chemical functionalization method such as the one proposed here.

[0021] In general, it can be observed that the modifications reported in the state of the art for commercial membranes show very good results in terms of bactericidal and anti-adhesion effects (72-99%), but most report a decrease in permeate flux related to the modification. Furthermore, in commercially modified copper membranes, copper release occurs primarily through rapid leaching of active ions, which can affect the long-term stability of the modification and limit its lifespan.

[0022] In contrast, the modification proposed in this patent application ensures the long-term stability of the modification through the prior insertion of chelating groups that act as stabilizers and retainers of the copper species present on the surface, maintaining a controlled rate of copper release into the medium. Furthermore, the proposed modification does not adversely affect the misalignment operating parameters of the original membrane, maintaining permeate flow and salt rejection at standard values. Finally, the membrane's morphological characteristics are not drastically affected, its chemical and / or mechanical stability is not compromised, and an anti-biofouling property is added to a conventional membrane without requiring any intervention in the manufacturing process of the base TFC membrane.

[0023] SUMMARY DESCRIPTION OF THE INVENTION

[0024] The present invention relates to a method for modifying thin-film composite (TFC) membranes, aimed at providing a technique for modifying the surface chemistry of conventional reverse osmosis membranes to improve their surface antibacterial properties, by grafting functional active groups and copper (Cu) active species onto the active polyamide layer. 2+ ) in ionic and colloidal nanoparticle form. This modification directly increases resistance to biofouling (growth inhibitory effect close to 100% and bactericidal effect close to 99%), without affecting the operating performance of the modified membranes compared to their commercial counterparts.

[0025] DESCRIPTION OF THE FIGURES

[0026] Figure 1 shows a scheme of surface chemical modification of the active layer of a commercial TFC-RO membrane using the method proposed in this patent application.

[0027] Figure 2 shows the methodology of step I, surface activation of the membrane by surface formation of NHS (N-hydroxysucinimide) esters.

[0028] Figure 3 shows an FTIR spectrum for TFC membranes activated by step I with NHS aster formation.

[0029] Figure 4 shows the methodology of step II, surface amination with PEI of the TFC membrane previously activated with NHS esters. Figure 5 shows an FTIR spectrum demonstrating the increase in NH2 surface groups on the TFC-PEI membrane.

[0030] Figure 6 shows the methodology of stage III, surface phosphorylation by forming covalent / ionic bonds with diethylenetriaminepentakinase-(methylphosphonic acid) (DTPMP) on the TFC-PEI membrane.

[0031] Figure 7 shows an FTIR spectrum of the modified TFC-PEI-DTPMP membranes (stage III) showing the presence of characteristic DTPMP bonds.

[0032] Figure 8 shows the methodology of stage IV to obtain a TFC-Cu membrane modified with copper-rich colloidal nanoparticles and cupric ions.

[0033] Figure 9 shows an XPS spectrum of the modified TFC-Cu membranes at different exposure times (stage IV) where the presence of copper (Cu2p) and phosphorus (P2s) is confirmed, which are absent in the unmodified commercial membrane.

[0034] Figure 10 shows AFM micrographs of different modified TFC-Cu membranes where the modification increases surface roughness compared to commercial TFC membranes.

[0035] Figure 11 shows the effective change in roughness attributed to the modification of TFC membranes by the applied methodology.

[0036] Figure 12 shows the operational performance of copper-modified TFC membranes versus commercial brackish water BW30 type TFC membranes.

[0037] Figure 13 shows the operational performance of copper-modified TFC membranes versus commercial SW30 seawater TFC membranes.

[0038] Figure 14 shows bacterial growth (E. coli) expressed in CFU / mL on copper-modified membrane samples versus a commercial membrane. Bacterial death rates range from 80-88%.

[0039] Figure 15 shows the inhibitory halo formed by the biocidal / inhibitory effect of the modified TFC-Cu membranes where normal bacterial growth on the commercial membrane is observed.

[0040] Figure 16 shows the release rate of Cu ions 2+ to the aqueous medium from modified commercial RO membranes of the TFC-Cu type determined by ICP-OES.

[0041] DETAILED DESCRIPTION OF THE INVENTION

[0042] This patent application seeks to protect a method for modifying a thin-film composite (TFC) membrane, membranes generally used for reverse osmosis of seawater and brackish water. Figure 1 is a simplified representative scheme of the surface chemical modification of the active layer of a commercial TFC-RO membrane, carried out using the surface modification method proposed herein on a thin-film composite (TFC) membrane following a four-step route: I. Surface activation by the formation of NHS-type reactive esters (N-hydroxysucinimide already reacted by activation).

[0043] II. Surface insertion of polyethyleneimine (PEI) molecules.

[0044] III. Surface functionalization by reaction with Diethylenetriaminepentakis-(methylphosphonic acid).

[0045] IV. Incorporation of colloidal copper oxide nanoparticles and cupric ions.

[0046] The steps involved in the modification method, which is designed to functionalize active areas of a 4 cm membrane, are described in detail below. 2 However, the above is not a limitation for the proposed invention since it can be scaled proportionally up to a maximum surface area of ​​50 cm² 2 without considering changes in concentrations and only increasing the amounts involved linearly.

[0047] 1. Surface activation by the formation of NHS-ester reactive asters

[0048] This step is aimed at the surface activation of conventional polyamide TFC-RO membranes. As previously reported, the density of carboxyl functional groups on the surface of these membranes is close to 7.2 COOH groups / nm. 2In the proposed modification technique, these groups are utilized by in situ formation of an NHS-type reactive ester on each free carboxyl functional group.

[0049] Figure 2 shows the methodology used to complete this synthesis step. To activate an area of ​​4 cm 2The sample is first immersed for 15 minutes in 20 mL of 0.1 M (2-(N-morpholino)ethanesulfonic acid) (MES) buffer, obtained by dilution from a MES stock buffer solution with a concentration ranging from 0.4 to 0.6 M in 0.5 M sodium chloride (NaCl) with pH adjusted between 5.8 and 6.2 using 10 M NaOH. Then, sufficient amounts are added to reach a concentration of 4 mM of EDC (N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide) and 10 mM of NHS (N-Hydroxysuccinimide), and the mixture is subjected to constant ultrasonic stirring for 60 minutes (40-70 Hz, 25°C). This generates catalytic activation of the surface in two steps: (i) the formation of unstable O-Acylisourea intermediates at the carboxyl sites (EDC + -COOH) and (i) stabilization by formation of reactive NHS esters (-CO-NHS).

[0050] Once this step is completed, the samples are considered to have been surface-activated with labile NHS asters and will have an approximate stability of 1–6 hours, during which they will be suitable for the subsequent step. Figure 3 shows the surface activation of the membrane through the appearance of characteristic bands in the Fourier Transform Infrared (FTIR) spectrum of the NHS aster, specifically for the -CO-NHS groups around 1700–1730 cm⁻¹. 1 in the TFC membrane samples subjected to step I. The effective decrease of available carboxyl groups (-COOH) is also observed in the activated sample (band 1.690 - 1.660 cm -1 ) with respect to the original commercial sample.

[0051] 2. Surface Insertion of Polyethyleneimine (PEI) Molecules: Grafting Amination. In this step, a surface amination reaction is directly performed on TFC-RO membranes activated with hydroxysuccinimide esters (TFC-NHS) through a direct covalent bond formation reaction with a polymer molecule containing primary amine-type active groups: polyethyleneimine (PEI). This direct reaction takes place at the reactive sites resulting from step I (-CO-NHS) and is spontaneously favorable with any molecule containing a primary amine (-NH2), forming amide-type covalent bonds in a single step and releasing the NHS intermediate. In this case, the reaction occurs between the -NHS esters present on the activated TFC-NHS surface and the primary amine groups of the introduced crosslinked polyethyleneimine molecule (PEI).

[0052] Figure 4 shows the methodology for obtaining an aminated membrane surface (TFC-PEI) using step II. A 4 cm membrane sample 2 The area previously activated in step I (TFC-NHS) is immersed in 10 mL of a piperazine-N,N'bis(2-ethanesulfonic acid) buffer solution (PIPES) at a concentration between 0.05 and 0.15 M, adjusted with 10 M NaOH in the pH range of 7-7.2. As an alternative buffer solution with interchangeable action, a conventionally prepared phosphate-buffered saline solution at pH 7 (PBS, pH 7) can be used. Subsequently, 20 mL of a previously prepared solution of low molecular weight crosslinked PEI (PEI, Mw -800 - Mn -600 max.) at 3% by weight are added, maintaining ultrasonic stirring for 60 minutes (40-70 Hz, 25°C).

[0053] At the end of this stage, a TFC-PEI membrane sample with an aminated surface is obtained through the covalent grafting of PEI molecules and the release of the NHS intermediate. The mechanism begins with the reduction of NHS ester groups on the surface and their replacement with PEI molecules containing multiple primary amino groups. This reaction generates amide-type covalent bonds (-CO-NH-), permanently attaching the PEI molecules to the surface. This change can be monitored using FTIR spectroscopy, as shown in Figure 5, where the attenuation of the free hydroxyl band around 3,250–3,300 cm⁻¹ relative to the TFC-NHS membrane is observed. -1 (-OH) and the appearance of two bands corresponding to the primary amino groups (-NH2) now present on the TFC-PEI surface at 3,500 - 3,520 cm -1 and 3,600 - 3,620 cm -1These TFC-PEI membranes are stable and can be used for up to 12 hours without diminishing their functionality.

[0054] 3. Surface functionalization by reaction with diethylenetriaminepentakis-(methylphosphonic acid): phosphorylation with a polyphosphonic acid

[0055] This step involves the surface functionalization of the membrane sample previously subjected to steps I and II (TFC-PEI) with molecules of a polyphosphonic organic acid, taking advantage of the related functional groups obtained (-NH2). Similar to step II, the reaction in this step occurs directly between the exposed primary amino groups and the multiple -(PO2)OH groups present in the undissociated diethylenetriaminepentakinase-(methylphosphonic acid) or DTPMP molecules, through the formation of phosphoryl-amide covalent bonds and salt-bridge ionic interactions.

[0056] Figure 6 shows a schematic of step III, where a phosphorylated TFC-PEI-DTPMP membrane is obtained. This step begins with a 4 cm² membrane sample. 2 of area subjected to consecutive steps I and II (TFC-PEI), which is directly immersed in 25 mL of a previously prepared DTPMP solution at a concentration ranging from 0.5% to 1.5% adjusted with 10 M NaOH to a pH range of 4 - 4.5. The reaction takes place under ultrasonic stirring for a period of 60 min (40-70 Hz, 25°C).

[0057] Once this step is completed, a TFC membrane is obtained that is functionalized with both free amino groups from PEI and free phosphonic groups from DTPMP attached to the surface by grafting and ionic interactions. This membrane exhibits high stability and can be used within a window of no more than 12 hours for the next stage, being stored in a wetting medium (deionized water / isopropanol 1:1). To confirm the effectiveness of the modification, Figure 7 shows the presence of characteristic DTPMP molecule bonds with signals corresponding to P-0 bonds around 960–975 cm⁻¹ 1 and the appearance of a band corresponding to the COP bond characteristic of polyphosphonic acid at 920 cm' 1 .

[0058] Finally, step IV has the main objective of providing biocidal and anti-adherent properties to conventional TFC membranes by incorporating previously synthesized stable colloidal copper oxide (CuO) nanoparticles and cupric ions (Cu 2+ ) , both chelated. In view of this, the surface functionalization obtained in the previous steps is directly utilized, with the amino (NH2) sites generated by PEI and the active sites of aminophosphonic acid (-(PO2)OH) serving as receptor groups for the copper-based antibacterial species. Functionalization with chelating groups is essential for membrane modification. These groups, R-NH2, generated in step II, and R-PO(OH)2, generated in step III, are responsible for fixing the free copper(II) ions and the colloidal nanoparticles, respectively, to the surface of the modified membrane through direct chemical interactions.

[0059] 4. Incorporation of colloidal copper oxide nanoparticles and cupric ions: biocidal functionalization

[0060] In step IV of the modification method, the main objective is to provide biocidal and anti-adherent properties to the conventional TFC membranes in question, by incorporating stable colloidal nanoparticles of copper oxide CuO and cupric ions (Cu 2+ chelated. Thus, the surface functionalization obtained in the previous stages is directly utilized, using the amino (NH2) sites generated by PEI and the active sites of aminophosphonic acid (-(PO2)OH) as receptor groups for the copper-based antibacterial species.

[0061] To carry out step IV, 100 mL of a CuO-CTAB Nps colloidal nanoparticle solution was previously obtained at a concentration ranging from 0.03 to 0.04% w / w by the following steps: (i) 49.5 mL of a 16 mM hexadecyltrimethylammonium bromide (CTAB) solution were mixed with 49.5 mL of 4.4 mM NaOH by stirring in ultrasound (70Hz, 25°C) for 1 minute; (ii) 0.33 mL of a 4 M copper sulfate (CuSC) solution was added to this stirred and stable solution and stirred in ultrasound under the same conditions for 5 minutes; (iii) At this point, 0.66 mL of a freshly prepared reducing solution in ice water (1-4°C) of 2 M sodium borohydride (NABH4) is added and sonicated for 15 minutes under the same conditions mentioned above; and finally, (iv) the resulting solution is kept between 25-35°C for direct use in the proposed modification within 24 hours.It should be noted that the proposed modification technique is not compatible with solid nanoparticles, since these could not guarantee the formation of strong ionic interactions (electrostatic, ionic bond and salt bridge) such as those that occur between the exposed quaternary ammonium groups of the CTAB molecules (Hexadecyltrimethylammonium bromide or Cetyltrimethylammonium bromide) surrounding the stabilized colloidal CuO nanoparticles and the terminal groups (-(PO2)OH) or (NH2) of the functionalized membrane according to the steps described above.

[0062] Figure 8 shows the methodology used in the final step IV of the synthesis, leading to the production of a modified biocidal membrane called TFC-Cu. The copper species were incorporated into a membrane with an area of ​​2 cm². 2The moistened membrane sample, previously subjected to steps I-III (TFC-PEI-DTPMP), is directly immersed in 8.33 mL of a 0.033% colloidal nanoparticle solution (CuO-CTAB Np). Subsequently, 10 mL of a 3-5 M (CuSC) solution is added as a source of cupric ions, while maintaining ultrasonic stirring of the entire mixture for 30 minutes. Finally, the process is completed with a static exposure selected from 30 minutes, 60 minutes, or 24 hours, using sonication at 40-70 Hz for 30 minutes at 25°C, followed by a static exposure of at least 30 minutes (or up to 60 minutes or 24 hours) in a sealed container.

[0063] Once this stage is completed, a simple wash is performed by immersion with 20 mL of deionized water (5-50 µS / cm), and the sample is kept in a wetting preservation solution (deionized water / isopropanol 1:1). This sample can be used directly in the necessary operational tests without any further treatment.

[0064] Figure 9 shows the X-ray photoelectron emission spectrum, which can be used to verify the presence of copper species on the surface of the membrane modified by the method proposed in this application. Clear signals from the Cu2p family are detected. 3 / 2 in the vicinity of 930 eV with adjacent satellite bands in the 930-960 eV range that correspond to characteristic satellite signals of CuO (S1 and S2 for 2p 3 / 2and S1 and S2 for 2p2. Similarly, the XPS spectrum confirms the presence of representative P2s phosphor bands in the vicinity of 200 eV, confirming the stability of the functionalization in the previous step. These bands are present to a similar extent for all the modification times evaluated (30 min, 60 min, 24 hours), with no significant differences in the position of the signals and / or shifts detected.

[0065] This confirms the interaction of colloidal nanoparticles and cupric ions with the surface functionalized with free amino and phosphonic groups through the formation of strong ionic interactions (electrostatic, ionic bonding, and salt bridge) between the exposed quaternary ammonium groups of CTAB molecules (hexadecylmethylammonium bromide or cetyltrimethylammonium bromide) surrounding the stabilized CuO nanoparticles and the terminal (-(PO2)OH) or (NH2) groups. These groups, in turn, act as receptors for free cupric ions, forming stable coordination interactions on the surface.

[0066] Finally, the relative stability of these interactions confers upon the modified membranes the capacity for surface retention of copper biocidal species without affecting their morphological conditions and overall structure, which is necessary for the reverse osmosis process for which they were originally designed. In summary, the technique proposed in this patent application is designed to modify membranes with colloidal solutions of stable nanoparticles, since these allow them to remain in suspension and to be effectively incorporated into the previously functionalized membrane (according to the detailed methodology of the invention and Figure 1).Figure 1 shows a schematic representation of the structures of commercial membranes modified using the method proposed in this application (left side of the figure). It clearly shows that the commercial TFC_RO membrane is composed of two layers: one of polysulfone (PS) and another of polyamide (PA). The modification route is applied to the latter, highlighting the functional groups of the chemical structure that are utilized by the proposed modification technique. The right side of the figure shows the modified membrane after the application of the modification method disclosed herein (steps I to IV), with a schematic representation of the chemical structure of the modified membrane and the incorporation of the colloidal nanoparticles.

[0067] APPLICATION EXAMPLES

[0068] EXAMPLES OF PREFERRED REALIZATIONS

[0069] The following are examples of applications of this patent application. These examples are provided for illustrative purposes only to provide a better understanding of the invention, but in no way should they be considered as limiting the scope of the protection sought. Specifications of different technical features described in the examples may be combined with each other, or with other technical features previously described, without limiting the scope of the protection sought.

[0070] EXAMPLE 1.

[0071] MORPHOLOGICAL CHARACTERISTICS, OPERATIONAL PERFORMANCE AND BIOCIDAL PROPERTIES OF MEMBRANES MODIFIED WITH COPPER SPECIES

[0072] The surface characteristics of reverse osmosis membranes are a key factor in their filtration and salt rejection performance, since the active polyamide layer (200–300 µm thick, non-porous) is the only barrier against dissolved ions. The subsequent internal layers of polysulfone (40–60 µm, microporous) and polyester (120–130 µm, non-woven fabric) provide permeability and mechanical support. Thus, although the barrier layer is relatively resistant, any chemical or physical damage can cause widespread impairment in the reverse osmosis process.In order to verify the surface characteristics, operational performance and new biocidal properties of the modified membranes with respect to their commercial counterparts, various characterizations were carried out, including morphological analyses with tools such as atomic force microscopy (AFM), determinations of operational performance parameters (permeate flow and salt rejection in BWRO (brackish water reverse osmosis) and SWRO (seawater reverse osmosis)) and determination of the biocidal / inhibitory properties of the new modified membranes including the ability to release the active agent (Cu) to the aqueous medium.

[0073] AFM

[0074] The preparation of the sample for atomic force microscopy (AFM) consists of cutting a piece of membrane treated with liquid nitrogen, to obtain a clean cut that can be taken to the microscope.

[0075] Figure 10 shows the surface morphological patterns determined by AFM, formed post-modification on the membranes. The surface roughness of the membranes increases after chemical modification steps (I-IV), rising from a roughness level of 74.7 ± 16.8 nm in the commercial membrane to a maximum of 97.0 ± 17.7 nm for TFC-Cu (24 h). The percentage increase in roughness generated by the proposed modification, when compared to the commercial membrane, corresponds to approximately 20.4% for TFC-Cu (30 min), 21.81% for TFC-Cu (30 min), and 29.9% for TFC-Cu (24 h).

[0076] These gradual increases in membrane roughness values ​​can be observed in Figure 11. The results confirm the surface modification and the change in topographic parameters directly related to molecular grafting and nanoparticle addition. The exposure time in step IV increases the final surface roughness of the modified membrane. Although the variations are substantial in percentage terms, these surface changes do not reveal damage (abrupt variations) or significant changes in the normal topography of the TFC membranes compared to normal values.

[0077] Flux and rejection experiment

[0078] Reverse osmosis operating tests of the modified membranes to evaluate their flux and rejection were performed using a pilot plant with a cross-flow system with a membrane module of effective area of ​​25 cm² 2It was tested in both brackish water (BWRO, 2000 ppm NaCl, 600 psi) and seawater (SWRO, 32000 ppm NaCl, 800 psi), compared to commercial membranes of the FT30 series (BW30 and SW30). The experiments were carried out for 6 hours and the permeate flux was obtained using the following equation:

[0079] Where J (Lm -2 h -1 ) is the membrane flux, V(L) is the volume of permeated water, A(m 2 ) is the membrane area and Aí(h) is the permeation time. The experiments were carried out at room temperature. Salt rejection was calculated from the concentrations of the feed and permeate solutions using the following equation: 100

[0080] Where and are the concentrations of the feed solution and permeate, respectively. These are obtained from measuring the conductivity of the solution and a previously prepared calibration curve.

[0081] Figure 12 shows the performance of a modified BW30 membrane compared to its commercial version in BWRO operation. The permeate flux (J) shows similar behavior throughout the test period, with stabilization values ​​in the 15–16 LMH range for both membranes. Salt rejection shows stable values ​​in both cases, in the 95–96% range. No significant differences attributable to the modification were observed in the BWRO operating performance of the membrane samples.

[0082] In the case of desalination membranes, Figure 13 shows the operational performance of modified and unmodified SW30 membrane samples. The permeate flux (J) behavior is similar for both membrane types, with values ​​stabilized in the 39–40 LMH range. Salt rejection shows high and stable values ​​in both cases, close to 98–99%. Again, no significant differences in operational performance are observed between the modified TFC version and the commercial SWRO version. These results confirm that the modification does not adversely affect the integrity or operational performance of the TFC membranes subjected to the process, nor is there a detectable improvement in the operating parameters. Biocidal and inhibition halo tests

[0083] In general, membrane modification is primarily aimed at providing biocidal / inhibitory properties to the modified membranes without negatively impacting their performance and structural characteristics. Figure 14 shows the effective biocidal capacity of the modified membrane samples against a standard microorganism (E. coli). Bacterial kill rates range from 80–88%, depending on the type of modified sample, compared to the growth observed on the commercial membrane. The modified TFC-Cu membrane (60 min) exhibits the highest biocidal effectiveness (88 ± 4%). These values ​​can be considered high, as this antibacterial property is achieved without critically affecting the operational performance and morphological characteristics of the commercial membranes.

[0084] Tests were performed to observe the inhibitory effect on the localized growth of microorganisms. In this case, samples of commercial and copper-modified membranes were subjected to surface bacterial growth in a favorable medium. The results show a clear biocidal / inhibitory effect on the modified membranes, with the formation of a clear inhibitory halo in the vicinity of the TFC-Cu samples. The commercial membrane showed normal surface growth without any ability to prevent the development of local microorganisms (Figure 15).

[0085] Antibacterial testing of the membranes was performed using Escherichia coli (E. coli) as a model bacterium. For this purpose, 2x2 cm pieces of the modified membrane were immersed in 5 mL of LB culture medium (10 g / L tryptone, 5 g / L yeast extract, and 5 g / L salt) inoculated with E. coli and incubated at 37°C in a rotary shaker (200 rpm). The initial bacterial concentration was 10 9 CFU / mL was determined by measuring the optical density (OD) at 600nm. The variation in bacterial concentration over time was measured by the colony-forming units (CFU) method on solid plates, and the biocidal effect was compared with an unmodified commercial membrane.

[0086] On the other hand, the inhibition halo tests consisted of making plate cultures of £ coli with a known initial concentration of 10 9CFU / mL. And distributed homogeneously on the plate. The plate was incubated for 12 hours. Then, 1x1 cm pieces of the modified membrane were deposited on the plate, using an unmodified commercial membrane as a negative control. The plate was incubated for 24 hours, and the size of the inhibition zone was measured to obtain an inhibition rate. These novel biocidal capabilities observed in the modified TFC-Cu membranes are not only related to contact killing mechanisms but also to the potential release of copper ions into the medium, which act as antibacterial agents through intracellular mechanisms.Although these combined effects may increase the bacterial inhibition capacity in the membranes, ion release must be controlled, as an excessive rate of copper leaching into the medium may result in a detrimental effect or contamination of the treated medium due to heavy metal concentrations above recommended standards.

[0087] ICP-OES

[0088] To verify the effective release of copper into the medium, the concentration of Cu (II) ions was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) in aqueous samples resulting from the immersion of modified membranes (TFC-Cu) with determined areas subjected to different leaching times.

[0089] The modified membrane is pre-digested to generate a liquid solution that can be delivered to the ICP-OES instrument. The liquid sample is transformed into an aerosol using a nebulizer and excited with an argon plasma. The emissions from the excited atoms are collected by an optical system based on a polychromator combined with CCD detectors, obtaining emission spectra for the selected lines in each element.

[0090] The results presented in Figure 16 show a relatively high release of copper ions into the medium during the first few hours of immersion, with a tendency to stabilize over longer periods for membranes with longer functionalization times in process stage IV (TFC-Cu (60 min) and TFC-Cu (24 h)). Membranes with shorter functionalization times (TFC-Cu (30 min)) show a steadily increasing ion release rate without gradual change.

[0091] The amounts released into the environment range between 0.013 - 0.023 ppm / cm 2 After 144 hours of leaching, higher release rates were observed for membranes with a longer effective functionalization time (step IV). These results suggest that the membranes will tend to deplete the active biocidal agent after a certain processing time, although it is possible to regenerate their properties using the same methodology. Thus, it can be stated that in the modified membranes, the bactericidal effect is linked both to bacterial death by contact (Cu retained on the surface) and to the effective release of copper ions into the medium (Cu 2+It should be noted that no measurable copper concentrations were detected in the resulting permeate in any of the operational tests performed in BWRO / SWRO (ICP-OES, result: N / A). In any case, the release of biocidal metal ions will always occur on the feed side (brackish water or seawater), where the functional membrane face is exposed; therefore, the copper in solution must pass through the PA barrier to reach the permeate.

[0092] The foregoing confirms the effectiveness of modifying commercial membranes using the four-step (I-IV) route proposed in this application. The resulting TFC membranes (TFC-Cu) possess operational performance characteristics similar to conventional commercial membranes, exhibit minimal changes in surface morphology, and have proven biocidal / inhibitory activity, including the release of ions into the medium.

Claims

CLAIMS 1. Method for modifying a thin-film composite (TFC) membrane, CHARACTERIZED in that it comprises the following steps: I. Activate the membrane surface by forming NHS-type reactive asters; II. insert polyethyleneimine (PEI) molecules into the surface; III. functionalize the surface by means of a reaction with diethylenetriaminepentakis-(methylphosphonic acid); and IV. Incorporate colloidal nanoparticles of copper oxide and cupric ions.

2. The method according to claim 1 CHARACTERIZED in that step I comprises wetting the membrane, immersing the membrane in a buffer of (2-(N-morpholino)ethanesulfonic acid) (MES) and then adding EDC (N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide) and NHS (N-Hydroxysuccinimide) to constant ultrasonic stirring.

3. The method according to claim 2 CHARACTERIZED in that the concentration of (2-(N-morpholino)ethanesulfonic acid) (MES) varies between 0.4 and 0.6 M.

4. The method according to claim 2 CHARACTERIZED in that the ultrasonic stirring is performed at room temperature for at least 60 minutes.

5. The method according to claim 1 CHARACTERIZED in that step II comprises immersing the membrane in a piperazine-N,N'bis(2-ethanesulfonic acid) buffer solution (PIPES) adjusted with 10M NaOH in a pH range of 7-7.

2.

6. The method according to claim 5 CHARACTERIZED in that it further comprises adding a previously prepared solution of low molecular weight crosslinked PEI while maintaining constant ultrasonic stirring.

7. The method according to claim 5 CHARACTERIZED in that it comprises adding at least 10 ml of PIPES of a concentration ranging from 0.05 to 0.15 M.

8. The method according to claim 6 CHARACTERIZED in that the ultrasonic stirring is performed at room temperature for at least 60 minutes.

9. The method according to claim 1 CHARACTERIZED in that step III comprises immersing in a previously prepared solution of DTPMP adjusted with 10M NaOH to a pH range of 4-4.5 with constant ultrasonic stirring.

10. The method according to claim 9 CHARACTERIZED in that it comprises adding at least 25 ml of DTPMP of a concentration ranging from 0.5% to 1.5% w / w.

11. The method according to claim 9 CHARACTERIZED in that the ultrasonic stirring is performed at a frequency of between 40 and 70 Hz and is performed at room temperature for at least 60 minutes.

12. The method according to claim 1 CHARACTERIZED in that step IV comprises immersing the moistened membrane in a colloidal nanoparticle solution, CuO-CTAB Np, and subsequently adding a CuSO4 solution as a source of cupric ions while maintaining constant ultrasonic stirring.

13. The method according to claim 12 CHARACTERIZED in that it comprises adding at least 10 ml of CuSO4 of a concentration ranging from 3 to 5 M.

14. The method according to claim 12 CHARACTERIZED in that it comprises adding at least 8 ml of CuO-CTAB Np of a concentration ranging from 0.03 to 0.04% w / w.

15. The method according to claim 12 CHARACTERIZED in that it further comprises subjecting a frequency of 40 and 70 Hz to a static exposure time for at least 30 minutes ca, with sonication at room temperature.

16. The method according to claim 12 CHARACTERIZED in that, prior to carrying out step IV, it comprises synthesizing the colloidal copper nanoparticles.

17. A modified reverse osmosis membrane, according to any of the preceding claims, CHARACTERIZED in that in its operation it produces a flow of permeate and rejection of salts.

18. The membrane according to claim 17, CHARACTERIZED in that the rejection of salts is carried out using BWRO and SWRO.

19. The membrane according to claims 17 and 18, CHARACTERIZED in that the permeate flux (J) in the BWRO operation shows stabilized values ​​in the range of 15-16 LMH.

20. The membrane according to claims 17 and 18, CHARACTERIZED in that the salt rejection in the BWRO operation remains stable in the range of 95-96%.

21. The membrane according to claims 17 and 18, CHARACTERIZED in that in the SWRO operation the permeate flux (J) shows stabilized values ​​in the range of 39-40 LMH.

22. The membrane according to claims 17 and 21, CHARACTERIZED in that the rejection of salts in the SWRO operation reaches values ​​between 98-99%.

23. The membrane according to claim 17, CHARACTERIZED in that it has biocidal properties.

24. The membrane according to claims 17 and 24, CHARACTERIZED in that, due to its biocidal properties, it exhibits bacterial death rates between 80-88%.

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