Low fouling super hydrophilic hybrid membranes for wastewater treatment

Abstract

The present disclosure provides a low-fouling super hydrophilic hybrid membrane prepared from renewable lignocellulosic sources for ultrafiltration. The hybrid membrane may be used for wastewater treatment. The hybrid membrane for ultrafiltration comprising: a fibrous cellulose substrate; and nanoparticles present in an amount from about 0.1% by weight to about 2% by weight of the hybrid membrane, wherein the hybrid membrane is porous and has pores possessing an average diameter from about 2 nm to about 100 nm, a charge density from about 0.2 mmol / g to about 1.0 mmol / g, and a contact angle from about 0° to about 3°.

Description

LOW FOULING SUPER HYDROPHILIC HYBRID MEMBRANES FOR WASTEWATER TREATMENTGOVERNMENT SUPPORT STATEMENT

[0001] This invention was made with government support under DMR-1808690, awarded by the National Science Foundation. The government has certain rights in the invention.CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of, and priority to, U.S. Provisional Patent Application Serial No. 63 / 627,830 filed on February 1, 2024. The entire contents of the foregoing application are incorporated by reference herein.BACKGROUND

[0003] Separation processes are important in many industries. Membrane separation technology has been widely adapted in many separation processes due to its broad range of advantages, including lower energy and chemical consumption, and easier operation and maintenance. These processes include water purification, desalination, air filtration / separation, etc.

[0004] Membranes used for filtration should have certain desirable properties. For example, a greater volume of material to be filtered, sometimes referred to as throughput, is one desirable property. The ability to remove contaminants, sometimes referred to as selectivity, is another desirable property. Reducing the clogging of the membranes, so that the fouling of the membranes is low and requires less frequent cleaning and / or the use of harsh chemicals or processes for cleaning is yet another desirable property.

[0005] Ultrafiltration (UF) is a low-pressure membrane-based separation technique which finds applications in medical use, dairy industry, chemical recovery and water treatment.Ultrafiltration is an efficient technique for wastewater treatment. UF employs a semi-permeable membrane which under a trans-membrane pressure can remove a variety of contaminants like bacteria, virus, suspended solids etc. Commercial UF membranes are derived from synthetic polymers such as polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polysulfone (PS) and polyethersulfone (PES). These polymeric membranes are not biodegradable and are susceptible to membrane fouling in ultrafiltration. There is a growing need and demand to find environmentally benign and cost-effective materials which exhibit efficient performance and resist fouling.

[0006] Improved membranes and methods for forming membranes, as well as uses thereof, remain desirable.SUMMARY

[0007] The present technology discloses the development of a low-fouling super hydrophilic hybrid membrane for ultrafiltration. The membrane includes cellulose obtained from renewable lignocellulosic sources and may be used for wastewater treatment in which the filtration results show comparable performance to commercial fossil-based membranes, such as those formed of PVDF and / or PES, in terms of permeate flux and separation efficiency.

[0008] According to one embodiment of the present disclosure, a hybrid membrane for ultrafiltration is disclosed. The hybrid membrane includes a fibrous cellulose substrate and nanoparticles that are present in an amount from about 0.1% by weight to about 2% by weight of the hybrid membrane. The membrane is porous and has pores possessing an average diameter from about 2 nm to about 100 nm, a charge density from about 0.2 mmol / g to about 0 mmol / g, and a contact angle from about 0° to about 30.

[0009] Implementations of the above embodiment may include one or more of the following features. According to one aspect of the above embodiment, the fibrous cellulose substrate may be formed of lignocellulose fibers obtained from a biomass source. The nanoparticles may include at least one of non-spherical silica particles, spherical silica particles, TiCh particles, ZnO particles, MgO particles, AI2O3 particles, Fe2O3 particles, or Fe3O4 particles. The nanoparticles may further include non-spherical silica particles. The fibrous cellulose substrate may include negatively charged carboxylate groups. The hybrid membrane may further include a positively charged wet-strength resin configured to crosslink with the carboxylate groups on the fibrous cellulose substrate to enhance the wet-strength of the hybrid membrane. The positively charged wet-strength resin may be polyamide amine epichlorohydrin. The nanoparticles may be negatively charged and the positively charged wet-strength resin may be configured to retain the nanoparticles in the hybrid membrane by electrostatic interactions between negatively charged nanoparticles and positively charged wet-strength resin molecules. The nanoparticles may act as physical cross-links between polymer layers or fibers of the fibrous cellulose substrate.

[0010] According to another embodiment of the present disclosure, a method of fabricating a hybrid ultrafiltration membrane is disclosed. The method includes treating cellulose fibers to introduce negatively charged carboxylate groups on the cellulose fibers and defibrillating the cellulose fibers to form a dispersion of nanostructured cellulose fibers. The method also includes adding nanoparticles and a positively charged wet-strength resin to the dispersion and performing vacuum filtration to cast the dispersion onto a substrate to form the hybrid ultrafiltration membrane.

[0011] Implementations of the above embodiment may include one or more of the following features. According to one aspect of the above embodiment, treating the cellulose fibers mayinclude carb oxym ethylation. Carboxym ethylation may further include dispersing the cellulose fibers in a solution containing monochloroacetic acid and isopropanol, reacting the cellulose fibers in a solution containing sodium hydroxide and methanol under reflux conditions to form carboxymethylated fibers, and washing the carboxymethylated fibers to achieve a conductivity below 5 s / cm. The nanoparticles may include at least one of non-spherical silica particles, spherical silica particles, TiCh particles, ZnO particles, MgO particles, AI2O3 particles, Fe2<D3 particles, or FeiO4 particles. Defibrillation of the cellulose fibers may be performed using high pressure homogenization. The nanoparticles may be present in an amount from about 0.1% by weight to about 2% by weight of the hybrid ultrafiltration membrane. The hybrid ultrafiltration membrane may be porous and have pores possessing an average diameter from about 2 nm to about 100 nm, a charge density from about 0.2 mmol / g to about 1.0 mmol / g, and a contact angle from about 0° to about 3 °. The positively charged wet-strength resin may be polyamide amine epichlorohydrin configured to crosslink with the carboxylate groups on the cellulose fibers to enhance the wet-strength of the hybrid ultrafiltration membrane. The nanoparticles may be retained in the hybrid ultrafiltration membrane by electrostatic interactions between negatively charged nanoparticles and positively charged wet-strength resin molecules. The method may also include drying the hybrid ultrafiltration membrane to achieve a thickness from about 50 m to about 400 m and a porosity from about 10% to about 60%.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Various embodiments of the presently disclosed nanocomposite scaffolds and methods are described herein with reference to the drawings wherein:

[0013] FIG. 1 includes (A) SEM image of partially defibrillated carb oxy methylated fibers after homogenization; and (B) TEM image of nano-scale fibers separated by centrifugation.

[0014] FIG. 2 includes a depiction of the FTIR analysis of NFC and PAE cross-linked NFC membranes.

[0015] FIG. 3 includes TEM images of (A) Spherical silica, (B) Non-spherical silica particles, (C) Dynamic light scattering (DLS) analysis of silica particles, and (D) pH scan of the non- spherical silica particles.

[0016] FIG. 4 is a graph depicting the porosity and pore-size determination of NFC-NS and NFC-S membranes with varying silica concentrations.

[0017] FIG. 5 includes SEM images of (A) NFC-0.8S cross-section (EDS spectra in inset);(B) NFC-0.8NS cross-section (EDS spectra in inset); (C) NFC-0.8S (with magnified image in inset); and (D) NFC-0.8NS (with magnified image in inset).

[0018] FIG. 6 is a depiction of (A) the possible mechanism of silica particles bridging between nanofibers; (B) Illustration of the covalent bonding between carboxylate and azetidinium group of PAE and electrostatic interactions between silica and PAE; and (C) FTIR analysis of NFC, NFC-Si and NFC,PAE-Si membranes.

[0019] FIG. 7 includes graphs showing (A) mechanical strength test of the NFC-0.8NS membrane after prolonged immersion in water; and (B) flux recovery due to self-healing property of the NFC membrane.

[0020] FIG. 8 is a graph showing the average permeate flux values for wastewater filtration by NFC, PVDF and PES membranes at 7.5 psi pressure.

[0021] FIG. 9 includes graphs of (A) Turbidity rejection, and (B) Total dissolved solids and total suspended solids rejection efficiency of NFC membranes of the present disclosure compared with commercial membranes.

[0022] FIG. 10 includes graphs showing (A) Fouling experiments for NFC, PVDF and PES membranes; and (B) Flux recovery ratio (FRR%) values.

[0023] FIG. 11 includes graphs demonstrating (A) Reversible and Irreversible fouling ratios; and (B) Contact angle measurements of NFC membranes of the present disclosure and commercial membranes.DETAILED DESCRIPTION

[0024] The following detailed description of embodiments of the subject matter of the present disclosure will be made in reference to the accompanying drawings. In describing the disclosure, explanation about related functions or constructions known in the art are omitted for the sake of clearness in understanding the concept of the present disclosure to avoid obscuring the recited subject matter with unnecessary detail.

[0025] Ultrafiltration is an easy and economical separation process for wastewater treatment. Ultrafiltration (UF) finds applications in wide areas such as dairy production, cell harvesting, chemical recovery, medical use etc. It is a low-pressure driven separation process which employs a semi-permeable membrane which can separate suspended solids, virus, bacteria etc. under a trans-membrane pressure. The main mechanism involved in ultrafiltration is size exclusion. UF membranes should usually have pore-size in the range of 10 nm - 100 nm and good dry and wet mechanical strength.

[0026] Currently, UF membranes are usually derived from synthetic polymers like PVDF, PES, PAN and PS. Membrane fouling is common phenomenon for polymeric ultrafiltration membranes which leads to deterioration of permeation flux attributed to the accumulation of foulants on the membrane surface and / or within the pores. Membrane fouling depends on different factors - membrane properties, material characteristics and operating conditions. Presence of a hydrophilic membrane surface is considered to be crucial factor to resist fouling.

[0027] The present technology discloses the development of a low-fouling super hydrophilic hybrid membrane for ultrafiltration. The membrane includes cellulose obtained from renewable lignocellulosic sources and may be used for wastewater treatment in which the filtration results show comparable performance to commercial fossil-based membranes, such as those formed of PVDF and / or PES, in terms of permeate flux and separation efficiency.

[0028] The hybrid membrane is composed of nanocellulose and a small amount (less than 1%) of non-spherical silica. The membrane is formed with a wet-strength aid, such as polyamide amine epichlorohydrin (PAE), in order maintain the wet strength of the membrane and in order to retain and cross-link the silica in a favorable manner.

[0029] The present disclosure provides the fabrication of a cellulose-based membrane, which is an abundant, renewable and sustainable source. The methods of the present disclosure are applicable for use with any and all raw biomasses, including lignocellulosic wood or non-wood sources including, but not limited to, jute, bamboo, cotton, banana rachis, wheat straw, barley, hemp, flax straw, coconut fiber, soy hull, pea hull fiber, rice husk, sugarcane bagasse, pineapple leaf rachis, sisal fiber, tunicates, black spruce, eucalyptus, valonia, bacterial celluloses, and combinations thereof.

[0030] The cellulose fibers possess certain charged groups to facilitate easy defibrillation into nanostructured fibers (NFC) as well as to achieve wet strength required for the membrane. In embodiments, the functional groups may be negatively charged groups such as carboxylate groups, which can be achieved chemical pretreatments such as carboxymethylation, oxidation using nitric acid and sodium nitrite (nitro-oxidation), and oxidation using (2, 2, 6, 6- tetramethylpiperidin-l-yl)oxyl or (2,2,6,6-tetramethylpiperidin-l-yl)oxidanyl (TEMPO- oxidation). Exemplary nitro-oxidation methods include those disclosed in U.S. Provisional Patent Application No. 63 / 603,298, filed on November 28, 2023, the entire disclosure of which is incorporated by reference herein. Exemplary TEMPO-oxidation methods include those disclosed in International Patent Application No. PCT / US2023 / 070332, filed on July 17, 2023, the entire disclosure of which is incorporated by reference herein.

[0031] As described earlier, hydrophilicity, wet-strength and pore-size are important characteristics of a UF membrane. The cellulose fibers are inherently hydrophilic, so they present a suitable material for developing a UF membrane.

[0032] The wet-strength of the cellulose membrane can be improved by chemically crosslinking the negatively charged carboxyl groups of cellulose fibers with a positively charged wetstrength resin such as a polyamide amine epichlorohydrin (PAE). PAE is a commonly used nontoxic wet strength resin. The azetidinium group on PAE molecules forms an ester bond with carboxylate group on cellulose fibers which enhances the wet-strength properties of cellulose membrane. The PAE can be added by wet-end addition during the membrane fabrication process.

[0033] High amounts of cationic PAE can result in coagulation of the negatively charged fibers, so, in embodiments, The molar ratio of PAE to the NFC can be from about 0.1 to about1.5, in embodiments from about 0.5 to about 1 .0. As noted above, in embodiments, the NFC have a negative charge due to the presence of carboxylate groups. In some aspects, the fibers may have a charge density of at least 0.1 mmol / g, in embodiments from about 0.1 mmol / g to about 2.0 mmol / g, in other embodiments from about 0.2 mmol / g to about 1.0 mmol / g.

[0034] The pore-size of the hybrid membrane can be controlled by optimizing the fiber size and the addition of different inorganic nanoparticles to the membrane, such as SiCh, TiCh, ZnO, MgO, AI2O3, FezCh, Fe Ch, etc. In embodiments, the hybrid membranes of the present disclosure include silica nanoparticles (SiO?), which are abundant, inexpensive and biocompatible in nature.

[0035] The amount of silica nanoparticles added to the hybrid membrane of the present disclosure can be from about 0.05% by weight to about 10% by weight, in embodiments from about 0. 1% by weight to about 2.0% by weight. In aspects, greater amounts of silica should be avoided, as the use of higher amounts can potentially lead to aggregation of nanoparticles. Spherical or non-spherical silica nanoparticles may be used. The spherical silica particles are usually produced with surface area from 30-360 m2 / g. The non-spherical silica particles usually have a high surface area from 500-1100 m2 / g. The particles have uniform primary particle sizes (2-4 nm) but with polydisperse length aggregates.

[0036] The hybrid membranes of the present disclosure may have pores with a diameter from about 1 nm to about 500 nm, in embodiments from about 2 nm to about 100 nm. The hybrid membranes of the present disclosure may have a pore volume from about 10% to about 60%, in embodiments from about 20% to about 40%.

[0037] The basis weight of the membrane can be between 40-60 g / m2to maintain optimum thickness for high flux and separation efficiency. This disclosure further demonstrates theefficient performance of fabricated hydrophilic cellulose membrane in wastewater treatment and exhibits comparable performance to commercial PVDF and PES membranes.

[0038] The hybrid membranes of the present disclosure may have a thickness from about 50 pm to about 400 pm, in embodiments from about 100 pm to about 250 pm.

[0039] As noted above, the hybrid membranes of the present disclosure are hydrophilic. Hydrophilicity may be measured by the contact angle of the membrane. In embodiments, the hybrid membranes of the present disclosure have a contact angle from about 0° to about 15°, in embodiments from about 0° to about 3°.

[0040] The advantage of such an ultrafiltration membrane is a high porosity, low-fouling membrane due to super hydrophilic characteristics of the membrane and the non-fossil characteristics of the membrane and a low cost membrane.

[0041] In aspects, the hybrid membrane of the present disclosure includes cellulose fibers, silica, and a crosslinking agent. Suitable cellulose fibers are derived from plant based materials and are, in embodiments, nanostructured. The nanostructured cellulose fibers can be obtained from diverse biomass feedstock, including wood, plants, agricultural residues etc.

[0042] Cellulose-based materials can be functionalized to facilitate the defibrillation of fibers. Various chemical pretreatments such as carboxymethylation, nitro-oxidation, TEMPO-oxidation etc. and are employed to introduce negatively charged carboxymethyl or carboxyl groups on the cellulose surface. The charged fibers can be defibrillated into micro / nano scale fibers (referred as NFC) by the application of a low mechanical energy.

[0043] The defibrillated fibers can be used as a membrane scaffold to develop a hybrid ultrafiltration membrane composed of NFC and non-spherical silica. Such a cellulose membrane showed higher permeate flux and separation efficiency to commercially existing PVDF and PESmembranes, which are made of petroleum derived polymers. This invention presents a sustainable and cost-effective solution to synthetic polymer membranes as it is completely biobased derived from naturally abundant lignocellulose sources.

[0044] Several advantages of a hybrid membrane of the present disclosure include:• Diverse biomass sources such as wood, non-wooded plants as well as agricultural residues can be used to synthesize carboxymethylated fibers which can be defibrillated into micro and nano-scale fibers.• The carboxymethylated cellulose fibers are used as a membrane scaffold to develop a hydrophilic cellulose membrane which can provide a cost-effective alternative for wastewater treatment.• The nanostructured cellulose membrane is entirely based on functionalized cellulose fibers with small additions of a wet-strength agent polyamide amine epichlorohydrin (PAE) and silica nanoparticles (silica / NFC less than 1 weight %) to achieve a nano filter for wastewater treatment.• The cellulose membrane showed efficient wastewater treatment yielding flux of over 55 Lm'2h_|and average separation efficiency of over 99% at testing conditions of 7.5 psi in lab scale ultrafiltration tests.• The carboxymethylated cellulose fibers used to develop the ultrafiltration membrane are sustainable and biodegradable as they can be extracted from natural biomass sources. Moreover, the PAE and silica nanoparticles used as additives are biocompatible in nature.• The cellulose membrane was developed following a simple fabrication method involving wet end addition of PAE resin and silica nanoparticles followed by vacuum filtration to cast the membrane in contrast to complex fabrication procedures used to prepare polymeric UF membranes such as PVDF and PES.• This technology uses cellulose fibers extracted from natural biomass for developing the membrane and hence, has the potential for up-cycling of the low valued biomass sources like agricultural residues.EXAMPLESMaterials

[0045] The non-spherical silica used in the below Examples was obtained from Noury on, Sweden and has a surface area of 750 m2 / g and was in the form of a colloidal suspension of 15 wt%. The spherical silica particles used in the below Examples were obtained from Sigma Aldrich as 50 wt% colloidal suspensions.EXAMPLE 1

[0046] The nanostructured cellulose fibers (NFC) used to develop a hydrophilic UF membrane of the present disclosure were synthesized by carb oxym ethylation of wood pulp fibers. To briefly summarize, wood pulp fibers were first chemically pretreated before the carboxymethylation reaction as follows. Pulp fibers (30 grams) were dispersed in de-ionized water overnight at a stirring speed of 350 rpm. The dispersed fibers were then solvent exchanged with ethanol (300 mL) using the intermediate filtration approach. The fibers were then dispersed in a solution, consisting of 3 grams of monochloroacetic acid in 150 mL of isopropanol, for 1 hour.

[0047] Separately, a solution containing 4.5 g of NaOH, 145 mL of methanol and 550 mL of isopropanol was prepared at 60 °C in a 3 L round bottom flask. The pulp fibers dispersion was added to the heated reaction solution in the round bottom flask to complete the carboxymethylation reaction for 1 hour under reflux conditions. After the carboxymethylation reaction, resulting fibers were washed in three steps: first with de-ionized water; second with 600 mL of 0.1 M acetic acid; and finally with de-ionized water again until the conductivity was below 5 pS / cm.

[0048] Carboxymethylated fibers were subsequently dispersed in 600 mL of 4 wt% sodium bicarbonate solution at room temperature for 1 hour to convert the carboxyl groups into their sodium ionic form. The resulting fibers were then washed with de-ionized water again until the conductivity became lower than 5 pS / cm. These carboxymethylated fibers were homogenized with a high-pressure homogenizer (Panda Plus, 2000) to partially defibrillate the fibers. For example, fiber dispersions with concentrations between 0.5 - 0.9 wt.% were homogenized at different pressure conditions (100 - 350 bar) to obtain microfibrillated celluloses (MFC) with different degree of delamination (fibrillation).

[0049] The carboxylate content calculated by conductometric titrations of the NFC used in the present example was 0.410 mmol / g.

[0050] High pressure homogenization was employed to partially defibrillate the carboxy methylated fibers into nanostructured cellulose fibers at different fiber concentrations (0.5 - 0.9 wt.%) and pressures ranging from 100-350 bar to achieve dispersions of wide size distribution of fibers. The apparent degree of delamination was estimated by a gravimetric method (Naderi, Lindstrom et al. 2014). The samples were diluted to 0.03% (w / w) and stirred overnight using a magnetic stirrer at 1000 rpm. The diluted samples were centrifuged at the 1000*g for 15 minutes, to separate larger fiber fragments. The concentrations before (cbc) and after (cac) the centrifugation were used to estimate the fraction of the ‘nano-sized’ cellulosic materials or degree of delamination (cvs (w / w)%) in the dry content of the dispersion using the following equation (1)

[0051] The following equation (2) was used to calculate estimated energy consumption during the homogenization process.EC (kWh / tonne) = (2221 *2*p*n) / 1600*c (2) where p is applied pressure in homogenizer, n is number of passes and c is concentration of fiber dispersion.

[0052] The comparison of homogenization conditions, apparent degree of delamination and estimated energy consumption is given below in Table 1.Table 1. Comparison for different fibers systems by high pressure homogenization

[0053] The NFC dispersion obtained by homogenization of 0.9% (w / w) for 1 pass at 100 bar was selected for developing a UF membrane of the present disclosure, as it presented an optimum fiber size. The dispersion was a mix of large microfibers with widths in the range of 20-25 pm, with lengths of several hundred microns, as well as nano-scale fibers with widths in the range of 10-20 nm and lengths of several hundred microns. The SEM and TEM images of the micro and nanoscale fibers are shown in FIG. 1.EXAMPLE 2

[0054] Membranes of the present disclosure were generally prepared as follows.

[0055] The NFC dispersion described above in Example 1, obtained by homogenization of 0.9%(w / w) for 1 pass at 100 bar, was combined with a weight ratio from 0.5 to 0.8 wt% of silica nanoparticles and a weight ratio from 0.5 to 0.8 wt% of polyamide amine epichlorohydrin (PAE)to form a dispersion. The membrane was formed by casting the materials onto a supporting substrate, such as a 0.65 pm DVPP filter (Millipore), by vacuum filtration to obtain a uniform basis weight (e.g., 50 g / m2) and the PAE was allowed to crosslink the carboxylate group on the cellulose fibers, thereby enhancing the wet-strength properties of cellulose membrane. As described in greater detail in the Examples below, the ratio of PAE to NFC was varied (from about 0.5 to 1.0), and the amount of silica, as well as whether spherical silica or non-spherical silica was used, also varied.EXAMPLE 3

[0056] Fourier transform infrared spectroscopy (FTIR) was carried out on the membrane formed in Example 2 in order to investigate the cross-linking of the negatively charged carboxylated fibers with the positively charged PAE resin. The ratio of PAE / NFC was varied from 0.5 to 1.0. The FTIR spectra of pure NFC membrane and PAE cross-linked membrane is shown in FIG. 2. The peak around 1725 cm’1corresponding to C=O bond of ester linkages formed between carboxylate and azetidinium group confirms the cross-linking between cellulose and PAE. The spectra also showed peaks around 1640 cm’1(Amide I C=O) and 1550 cm’1(Amide II N-H), further confirming the presence of PAE in the membranes. There was also a slight increase in the intensities of these new peaks due to cross-linking with an increase in PAE concentration.EXAMPLE 4

[0057] Negatively charged silica particles were used as wet-end fillers to control the pore-size of the NFC membranes. Two types of silica, spherical (S) and non-spherical (NS), were used.The TEM images of these two types of silica are shown in FIG. 3. Dynamic light scattering(DLS) analysis of spherical silica showed a single peak at around 23 nm, whereas there were two peaks for non-spherical silica, around 10 nm and 50 nm, showing a wide size distribution of these particles. Zeta potential scan at a pH range of 4-10 was done for non-spherical silica, which shows the negative surface charge of these particles for the entire pH range. The DLS and zeta scans are shown in FIG.s 3C and 3D, respectively.

[0058] The addition of silica particles, both spherical and non-spherical, helped reduce the average pore-size of the membranes from 0.5 pm for pure NFC membrane to below 0.1 pm for NFC-0.8S (NFC membrane having 0.8% by weight spherical silica) and NFC- 0.8NS (NFC membrane having 0.8% by weight non-spherical silica) membranes as shown in FIG. 4. The porosity of the NFC-NS remained similar to the pure NFC membrane, with a slight decrease for NS / NFC ratio 0.8, whereas the porosity of NFC-S membranes decreased slightly as the concentration of spherical silica with respect to NFC increased from 0.5 to 0.8%. The pore-size determination was done by solute rejection measurement and porosity was determined by gravimetric method.EXAMPLE 5

[0059] Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) analysis was done to study the morphology as well as investigate the retention of silica nanoparticles in the fiber matrix. FIG. 5 shows the top view and cross-section view of NFC- 0.8NS and NFC-0.8S membranes. The cross-section image of NFC-0.8S shows the aggregation of spherical silica particles in the fibers. However, no aggregation of non-spherical silica particles was seen in the cross-section images of NFC-0.8NS.EXAMPLE 6

[0060] The negatively charged silica particles are retained by positively charged PAE molecules by electrostatic attractions. The nanoparticles can act as physical cross-links between polymer layers or fibers. FTIR analysis was done for NFC-PAE-0.8NS showed peak at 1035 cm- 1 for O-Si-O bending and 775 cm-1 for O-Si-O stretching peaks. The IR spectra of NFC-0.8NS and pure NFC do not show these peaks, which confirms the retention of silica particles by cationic PAE molecules. The possible mechanism and FTIR analysis are shown in FIG. 6.EXAMPLE 7

[0061] The durability of the membrane NFC-NS membrane was investigated by immersing the membrane in water for 14 days and the mechanical strength was measured at different intervals after redrying the membrane. The tensile strength of the membrane remained stable and then decreased slightly after 7 days but still showed high mechanical stability. The self-healing property of the membrane was analyzed by making a small scratch on the membrane surfaces after initial compaction with DI water and measuring initial water flux. The scratched membrane was then inserted in the dead-end cell and water fdtration was carried out. The flux was higher than the initial water flux, but NFC restored its flux in around 20 minutes while PVDF membranes failed to recover the flux. This self-healing behavior of the NFC membrane was due to its water absorption and swelling nature. The mechanical strength analysis and scratch tests are shown in FIG. 7.EXAMPLE 8

[0062] The performance of the cellulose membrane was evaluated for municipal wastewater employing a dead-end fdtration system (Model HP4750X, Sterlitech Corporation, USA). Thewastewater samples were obtained from the local wastewater treatment plant at Stony Brook. The membranes with an effective surface area of 14.6 cm2was compressed with deionized (DI) water for 60 minutes at a pressure of 7.5 psi before filtration experiments. The permeate water flux was measured by monitoring the mass gain in the permeate reservoir using a digital balance connected to a computer at intervals of 2 minutes. The separation efficiency was measured in terms of turbidity, total suspended solids (TSS) and total dissolved solids (TDS). Turbidity was measured using a turbidity meter (Thermo Scientific Orion AQ3010). The filtration results of cellulose membrane were compared with commercial PVDF and PES membranes - PVDF A6 (MWCO 500 kDa), PVDF V6 (MWCO 500 kDa) and PES-LX (MWCO 300 kDa) purchased from the Sterlitech Corporation.

[0063] The pure NFC membrane showed higher flux than NFC-0.8NS and NFC-0.8S membranes which could be attributed to the higher porosity and larger pore-size of the pure NFC membrane. The NFC-0.8NS (-55.3 Lm'2h-1) and NFC-0.8S membranes (-53.5 Lm'2h_1) exhibited comparable permeate flux to PVDF V6 (-51.5 Lm‘2h_1) but higher than PVDF A6 (-41 Lm^h'1) and PES (-16 Lm'2h-1) membranes. The average permeate flux values were plotted over time and are shown in FIG. 8.EXAMPLE 9

[0064] The separation efficiency was calculated by measuring turbidity, TDS and TSS values. The pure NFC-0.8 NS and NFC-0.8S membranes showed comparable separation efficiency (-99.9%) for TSS and turbidity to PVDF-V6, PVDF-A6 and PES membranes. The rejection results are shown in FIG. 9.EXAMPLE 10

[0065] The antifouling performances of NFC-silica membranes were evaluated and compared with PVDF and PES membranes against wastewater by sequential filtration of pure water, wastewater and pure water post cleaning of the membranes with water. The flux recovery ratios (FRR) were also calculated for all the membranes. The NFC-0.8NS showed the highest water flux recovery post hydraulic cleaning of the membrane. The flux recovery ratio of NFC-NS membrane was approximately 90% while the NFC-S showed a slightly lower flux recovery ratio at approximately 77% which was similar to PVDF-V6 at 78% and higher than that of PVDF-A6 and PES membranes. The results of fouling experiments and FRR values are shown in FIG. 10.

[0066] The total fouling of the membranes was determined in terms of reversible fouling ratio (Rr) and irreversible fouling ratio (Rir). The NFC-NS membrane showed high reversible fouling ratio (~ 83%) and lower irreversible fouling (-15%). The PVDF-A6 and PES membranes had higher Rir values ( -65%) and lower Rr values (< 30%) which implies that the fouling mechanism in the PVDF-A6 and PES membranes was mostly irreversible and could not be recovered with membrane cleaning. The contact angle evaluation of pristine, fouled and cleaned membranes was carried out to evaluate hydrophilicity of membranes. The contact angles for pristine NFC-NS and NFC-S were almost zero in a matter of -20 s which shows the membranes are highly hydrophilic whereas the PVDF-V6, PVDF-A6 and PES membranes were quite high at 66.6°, 62.7° and 53.3°, respectively showing lower hydrophilicity of the commercial membranes. The contact angle of the NFC membranes could be restored almost to initial values after hydraulic cleaning of the membranes whereas the contact angle of commercial membranes could not be recovered fully even after cleaning. The results of reversible fouling, irreversible fouling and contact angle measurements are shown in FIG. 11.

[0067] The comparison of various characteristics of both commercially available membranes and membranes produced herein, including porosity, thickness and contact angle, is set forth below in Table 2.Table 2. Comparison of membrane characteristics of cellulose membranes and commercial PVDF and PES membranes.

[0068] Alternate embodiments may be devised without departing from the spirit or the scope of the present technology. Additionally, well-known elements of embodiments of the systems, apparatuses, and methods have not been described in detail or have been omitted so as not to obscure the relevant details of the systems, apparatuses, and methods.

[0069] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms “comprises,” “comprising,” or any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises ... a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. The terms “including” and / or “having,” as used herein, are defined as comprising (i.e., open language). The terms “a” or “an”, as used herein, aredefined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The description may use the terms “embodiment” or “embodiments,” which may each refer to one or more of the same or different embodiments.

[0070] When the terms “coupled” and “connected,” along with their derivatives, are used, these terms are not intended as synonyms for each other. For example, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” may mean that two or more elements are in direct physical or electrical contact (e.g., directly coupled) or that two or more elements are not in direct contact with each other but yet still cooperate or interact with each other (e.g., indirectly coupled).

[0071] For the purposes of the description, a phrase in the form “A / B” or in the form “A and / or B” or in the form “at least one of A and B” means (A), (B), or (A and B), where A and B are variables indicating a particular object or attribute. When used, this phrase is intended to and is hereby defined as a choice of A or B or both A and B, which is similar to the phrase “and / or”. Where more than two variables are present in such a phrase, this phrase is hereby defined as including only one of the variables, any one of the variables, any combination of any of the variables, and all of the variables, for example, a phrase in the form “at least one of A, B, and C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0072] Relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The description may use perspective-based descriptions such as up / down, back / front, top / bottom, and proximal / distal. Such descriptions are merely used to facilitate the discussion and are notintended to restrict the application of disclosed embodiments. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding embodiments; however, the order of description should not be construed to imply that these operations are order dependent.

[0073] As used herein, the term “about” or “approximately” applies to all numeric values, whether or not explicitly indicated. These terms generally refer to a range of numbers that one of skill in the art would consider equivalent to the recited values (i.e., having the same function or result). In many instances these terms may include numbers that are rounded to the nearest significant figure. As used herein, the terms “substantial” and “substantially” means, when comparing various parts to one another, that the parts being compared are equal to or are so close enough in dimension that one skill in the art would consider the same. Substantial and substantially, as used herein, are not limited to a single dimension and specifically include a range of values for those parts being compared. The range of values, both above and below (e.g., or greater / lesser or larger / smaller), includes a variance that one skilled in the art would know to be a reasonable tolerance for the parts mentioned.

[0074] Various embodiments of the systems, apparatuses, and methods have been described, and in many of the different embodiments many features are similar. To avoid redundancy, repetitive description of these similar features may not be made in some circumstances. It shall be understood, however, that description of a first-appearing feature applies to the later described similar feature and each respective description, therefore, is to be incorporated therein without such repetition.

Claims

WHAT IS CLAIMED IS:

1. A hybrid membrane for ultrafiltration comprising: a fibrous cellulose substrate; and nanoparticles present in an amount from about 0.1% by weight to about 2% by weight of the hybrid membrane, wherein the hybrid membrane is porous and has pores possessing an average diameter from about 2 nm to about 100 nm, a charge density from about 0.2 mmol / g to about 1.0 mmol / g, and a contact angle from about 0° to about 3°.

2. The hybrid membrane according to claim 1, wherein the fibrous cellulose substrate is formed of lignocellulose fibers obtained from a biomass source.

3. The hybrid membrane according to claim 1, wherein the nanoparticles include at least one of non-spherical silica particles, spherical silica particles, TiCh particles, ZnO particles, MgO particles, AI2O3 particles, Fe2O3 particles, or Fe CU particles.

4. The hybrid membrane according to claim 1, wherein the nanoparticles include non- spherical silica particles.

5. The hybrid membrane according to claim 1, wherein the fibrous cellulose substrate includes negatively charged carboxylate groups.

6. The hybrid membrane according to claim 5, further comprising: a positively charged wet-strength resin configured to crosslink with the carboxylate groups on the fibrous cellulose substrate to enhance the wet-strength of the hybrid membrane.

7. The hybrid membrane according to claim 6, wherein the positively charged wet-strength resin is polyamide amine epichlorohydrin.

8. The hybrid membrane according to claim 6, wherein the nanoparticles are negatively charged and the positively charged wet-strength resin is configured to retain the nanoparticles in the hybrid membrane by electrostatic interactions between negatively charged nanoparticles and positively charged wet-strength resin molecules.

9. The hybrid membrane according to claim 8, wherein the nanoparticles act as physical cross-links between polymer layers or fibers of the fibrous cellulose substrate.

10. A method of fabricating a hybrid ultrafiltration membrane, comprising: treating cellulose fibers to introduce negatively charged carboxylate groups on the cellulose fibers; defibrillating the cellulose fibers to form a dispersion of nanostructured cellulose fibers; adding nanoparticles and a positively charged wet-strength resin to the dispersion; and performing vacuum filtration to cast the dispersion onto a substrate to form the hybrid ultrafiltration membrane.

11. The method according to claim 10, wherein treating the cellulose fibers includes carboxymethylation.

12. The method according to claim 11, wherein carboxymethylation further includes: dispersing the cellulose fibers in a solution containing monochloroacetic acid and isopropanol; reacting the cellulose fibers in a solution containing sodium hydroxide and methanol under reflux conditions to form carboxymethylated fibers; and washing the carboxymethylated fibers to achieve a conductivity below 5 pS / cm.

13. The method according to claim 10, wherein treating the cellulose fibers includes at least one of nitro o-oxidation or TEMPO-oxidation.

14. The method according to claim 10, wherein the nanoparticles include at least one of non- spherical silica particles, spherical silica particles, TiCh particles, ZnO particles, MgO particles, AI2O3 particles, Fe2O3 particles, or FesCU particles.

15. The method according to claim 10, wherein defibrillation of the cellulose fibers is performed using high pressure homogenization.

16. The method according to claim 10, wherein the nanoparticles are present in an amount from about 0.1% by weight to about 2% by weight of the hybrid ultrafiltration membrane.

17. The method according to claim 10, wherein the hybrid ultrafiltration membrane is porous and has pores possessing an average diameter from about 2 nm to about 100 nm, a charge density from about 0.2 mmol / g to about 1.0 mmol / g, and a contact angle from about 0° to about 3°.

18. The method according to claim 10, wherein the positively charged wet-strength resin is polyamide amine epichlorohydrin configured to crosslink with the carboxylate groups on the cellulose fibers to enhance the wet-strength of the hybrid ultrafiltration membrane.

19. The method according to claim 10, wherein the nanoparticles are retained in the hybrid ultrafiltration membrane by electrostatic interactions between negatively charged nanoparticles and positively charged wet-strength resin molecules.

20. The method according to claim 10, further comprising: drying the hybrid ultrafiltration membrane to achieve a thickness from about 50 pm to about 400 pm and a porosity from about 10% to about 60%.

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