Method and apparatus for removing metal cations in fluids

Abstract

Methods and apparatus for removing metal cations within a fluid are disclosed herein. The method includes filtering the fluid with a filter membrane comprising a polymeric substrate plate and a plurality of layers of 1T / 1T '-transition metal disulfide (TMD) nanosheets deposited on the polymeric substrate plate. The filter membrane can reduce the concentration of metal cations in fluid from 2 / million to 10 / billion. The invention further discloses a device capable of removing metal cations in fluid. The device comprises the filter membrane, and the concentration of metal cations in fluid can be reduced from 2 / million to 10 / billion.

Description

Technical Field

[0001] The present invention generally relates to a method and apparatus for removing metal cations using a membrane formed by stacking 1T / 1T'-transition metal dichalcogenide (TMD) nanosheets. Background Art

[0002] Heavy metal ions (HMIs) in drinking water pose a serious threat to human health due to their high toxicity, high mobility, and non-biodegradability. Among various HMIs, lead, cadmium, and mercury are known to be the most toxic and, therefore, have attracted particular attention. Although various technologies have been developed to remove metal ions, including chemical precipitation, solvent extraction, ion exchange, and membrane separation, the removal efficiencies of these methods generally fail to meet the strict World Health Organization (WHO) limits of 10 ppb, 3 ppb, and 6 ppb for lead, cadmium, and mercury in drinking water.

[0003] Adsorption has become the most effective method for removing HMI contamination from drinking water due to its excellent adsorption capacity, selectivity, speed, ease of operation, and reproducibility. Although a variety of materials can be used to remove HMI, particularly 2D materials such as hexagonal boron nitride (h-BM), graphene oxide (GO), transition metal carbides / nitrides (MXene), and transition metal dichalcogenides (TMDs), each of these materials faces challenges, including, but not limited to, weak adsorption capacity, low selectivity, slow adsorption kinetics, and high residual lead ion concentrations.

[0004] In view of this, the relevant field urgently needs to develop an improved method and device that can reduce the concentration of metal cations in the fluid to a value that meets the value specified by the WHO (<10 ppb). Summary of the Invention

[0005] Embodiments of the present invention relate to methods for removing metal cations from fluids, particularly heavy metal ions from drinking water.

[0006] A primary objective of the present invention is to provide a method for removing metal cations from a fluid. The method comprises filtering the fluid with a filter membrane, wherein the filter membrane comprises a polymer substrate and multiple layers of 1T / 1T′-transition metal dichalcogenide (TMD) nanosheets deposited on the polymer substrate. The filter membrane is capable of reducing the concentration of metal cations in the fluid from 2 parts per million (ppm) to less than 10 parts per billion (ppb).

[0007] According to embodiments of the present invention, the fluid comprises metal cations selected from the group consisting of sodium ions, potassium ions, magnesium ions, calcium ions, copper ions, nickel ions, lead ions, zinc ions, and combinations thereof. In certain embodiments, the metal cations are a combination of copper ions and lead ions. In other embodiments, the metal cations are a combination of zinc ions, copper ions, and lead ions.

[0008] According to an embodiment of the present invention, the filter membrane is manufactured by the following steps: (i) discharging the TMD bulk material in a lithium battery to produce a lithiated TMD bulk material; (ii) subjecting the lithiated TMD bulk material to ultrasonic vibration in water to exfoliate the lithiated TMD bulk material into 1T / 1T′-TMD nanosheets; (iii) collecting the product of step (ii) by centrifugation; (iv) redispersing the product of step (iii) in water to form a 1T / 1T′-TMD nanosheet dispersion; and (v) vacuum filtering the 1T / 1T′-TMD nanosheet dispersion onto the polymer substrate to prepare the filter membrane.

[0009] Examples of polymeric substrates suitable for use in the present invention include, but are not limited to, nylon, polyvinylidene fluoride (PVDF), and the like.

[0010] Examples of suitable 1T / 1T′-TMD nanosheets for use in the present invention include, but are not limited to, 1T′-MoS2 nanosheets, 1T′-WS2 nanosheets, 1T-TaS2 nanosheets, or 1T-TiS2 nanosheets. Preferably, the 1T / 1T′-TMD nanosheets are 1T′-MoS2 nanosheets.

[0011] According to an embodiment of the present invention, the 1T / 1T′-TMD nanosheets have an adsorption capacity for lead ions of approximately 175-530 mg / g. In one embodiment, the 1T′-MoS2 nanosheets have an adsorption capacity for lead ions of approximately 530 mg / g. In other embodiments, the 1T′-WS2 nanosheets have an adsorption capacity for lead ions of approximately 330 mg / g. In further embodiments, the 1T-TaS2 nanosheets have an adsorption capacity for lead ions of approximately 175 mg / g. In an even further embodiment, the 1T-TiS2 nanosheets have an adsorption capacity for lead ions of approximately 390 mg / g.

[0012] Therefore, a second object of the present invention is to provide a device for removing metal ions from a fluid. The device is characterized by having a filter membrane capable of reducing the concentration of metal cations in the fluid from 2 parts per million to less than 10 parts per billion, wherein the filter membrane comprises a polymer substrate and multiple layers of 1T / 1T′-TMD nanosheets deposited on the polymer substrate.

[0013] According to an embodiment of the present invention, the metal cation is sodium ion, potassium ion, magnesium ion, calcium ion, copper ion, nickel ion, lead ion, zinc ion or a combination thereof. In certain embodiments, the metal cation is a combination of copper ion and lead ion.

[0014] According to an embodiment of the present invention, the filter membrane is manufactured by the following steps: (i) discharging the TMD bulk material in a lithium battery to produce a lithiated TMD bulk material; (ii) ultrasonically vibrating the lithiated TMD bulk in water to exfoliate the lithiated TMD bulk into 1T / 1T′-TMD nanosheets; (iii) collecting the product of step (ii) by centrifugation; (iv) redispersing the product of step (iii) in water to form a 1T / 1T′-TMD nanosheet dispersion; and (v) vacuum filtering the 1T / 1T′-TMD nanosheet dispersion onto the polymer substrate to prepare the filter membrane.

[0015] Examples of polymeric substrates suitable for use in the present invention include, but are not limited to, nylon, polyvinylidene fluoride (PVDF), and the like.

[0016] Examples of 1T / 1T′-TMD nanosheets suitable for use in the present invention include, but are not limited to, 1T′-MoS2 nanosheets, 1T′-WS2 nanosheets, 1T-TaS2 nanosheets, or 1T-TiS2 nanosheets. Preferably, the 1T / 1T′-TMD nanosheets are 1T′-MoS2 nanosheets.

[0017] According to an embodiment of the present invention, the 1T / 1T′-TMD nanosheets have an adsorption capacity for lead ions of approximately 175-530 mg / g. In one embodiment, the 1T′-MoS2 nanolayer has an adsorption capacity for lead ions of approximately 530 mg / g. In other embodiments, the 1T′-WS2 nanosheets have an adsorption capacity for lead ions of approximately 330 mg / g. In further embodiments, the 1T-TaS2 nanosheets have an adsorption capacity for lead ions of approximately 175 mg / g. In an even further embodiment, the 1T-TiS2 nanosheets have an adsorption capacity for lead ions of approximately 390 mg / g.

[0018] Details of one or more embodiments of the present invention can be found in the following detailed description of the invention. Other features and advantages of the present invention can also be found in the detailed description of the invention and the scope of claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The details of the present invention can be better understood through the following drawings and their descriptions, wherein

[0020] Figure 1 FIG1 is a flow chart of a method 10 for manufacturing a filter membrane according to an embodiment of the present invention;

[0021] Figures 2a-2f Figure 1 is a graph showing the removal of various ions by the TMD nanosheets of Example 1, wherein panels a, b, c, and d are the percentages of various ion solutions (concentration 2 mg / L) removed by the sheet-like TMD (i.e., MoS2, WS2, TaS2, or TiS2) nanosheets, panel e is the isotherm of lead ion adsorption by the TMD nanosheets, and panel f is the kinetic curve of lead ion adsorption by the TMD nanosheets;

[0022] Figure 3a is the concentration of residual lead ions after the TMD nanosheets adsorbed lead ion solution was left to stand for 24 hours according to Embodiment 2 of the present invention; and

[0023] Figure 3b The figure shows the lead ion removal effect of the TMD nanosheets according to the first embodiment of the present invention after adsorbing lead ions and standing for 24 hours. DETAILED DESCRIPTION

[0024] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings. However, it should be noted that the disclosed descriptions and drawings are only for illustrative purposes and the scope of the present invention is not limited thereto.

[0025] The primary purpose of the present invention is to provide a method for removing metal ions in a fluid, particularly a method for removing heavy metal cations (eg, copper and lead ions) from a fluid through a filtration membrane.

[0026] According to an embodiment of the present disclosure, the filter membrane structurally comprises: a polymer substrate and multiple layers of 1T / 1T′-TMD nanosheets deposited on the polymer substrate, and the filter membrane can reduce the concentration of metal cations in the fluid from 2 parts per million (ppm) to less than 10 parts per billion (10 ppb).

[0027] As used herein, the term "1T / 1T'-TMD nanosheet" refers to a TMD nanosheet in a 1T-phase or a 1T'-phase. Therefore, a 1T / 1T'-TMD nanosheet can be either a 1T-phase TMD nanosheet or a 1T'-phase TMD nanosheet.

[0028] In order to obtain the filter membrane of the present invention, 1T / 1T′-TMD nanosheets were prepared by electrochemical lithium ion embedding and water exfoliation technology. The detailed steps are disclosed in Figure 1 Based on this, first construct a suitable execution flow chart. Figure 1 The lithium battery of method 10 described in the process. In detail, TMD bulk powder, carbon black, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) are mixed into a slurry mixture, which is then made into a cathode. The prepared cathode is assembled with an anode (i.e., lithium foil) and an electrolyte to form a lithium battery, and a potential is applied to embed lithium ions into the cathode. According to an embodiment of the present invention, the lithium battery is discharged at a constant current of 0.025-0.1 mA and a voltage of 0.7-0.9 V to obtain a lithiated TMD bulk material ( Figure 1 , step 101). Then, the lithiated TMD bulk material is subjected to ultrasonic vibration in water to exfoliate the lithiated TMD bulk material into 1T / 1T′-TMD nanosheets ( Figure 1 , step 102). According to the embodiment of the present invention, the 1T / 1T′-TMD nanosheets peeled off are single-layer or double-layer structures, have metallic properties (1T / 1T′ phase) and carry negative charges. Next, the 1T / 1T′-TMD nanosheets obtained in step 102 are collected by centrifugation ( Figure 1 , step 103). In order to obtain the filter membrane of the present invention, the 1T / 1T′-TMD nanosheets obtained in step 103 are redispersed in water to form a 1T / 1T′-TMD nanosheet dispersion ( Figure 1 , step 104).

[0029] According to embodiments of the present invention, examples of suitable 1T / 1T′-TMD nanosheets include, but are not limited to, 1T′-MoS2 nanosheets, 1T′-WS2 nanosheets, 1T-TaS2 nanosheets, or 1T-TiS2 nanosheets. Preferably, the 1T / 1T′-TMD nanosheets are 1T′-MoS2 nanosheets.

[0030] According to embodiments of the present invention, the 1T / 1T′-TMD nanosheets can adsorb metal ions thereon, making them suitable for removing metal cations from fluids contaminated with metal ions. According to embodiments of the present invention, the fluid may contain metal cations selected from the group consisting of sodium ions, potassium ions, magnesium ions, calcium ions, copper ions, nickel ions, lead ions, zinc ions, and combinations thereof. In certain embodiments, the metal cations are a combination of copper ions and lead ions. In other embodiments, the metal cations are a combination of zinc ions, copper ions, and lead ions.

[0031] According to the embodiment of the present invention, the 1T / 1T′-TMD nanosheets exhibit excellent affinity for lead ions, and the distribution coefficients (K d ) values ​​are approximately 5.57×10 7 , 3.59×10 7 , 3.9×10 7 and 1.8×10 7 mg / L. According to an embodiment of the present invention, the adsorption capacity of the 1T / 1T′-TMD nanosheets for lead ions is about 175-530 mg / g. In one embodiment, the adsorption capacity of the 1T′-MoS2 nanosheets for lead ions is about 530 mg / g. In other embodiments, the adsorption capacity of the 1T′-WS2 nanosheets for lead ions is about 330 mg / g. In a further embodiment, the adsorption capacity of the 1T-TaS2 nanosheets for lead ions is about 175 mg / g. In a further embodiment, the adsorption capacity of the 1T-TiS2 nanosheets for lead ions is about 390 mg / g.

[0032] Next, the 1T / 1T′-TMD nanosheet dispersion collected in step 104 is vacuum filtered onto a polymer substrate to prepare the filter membrane ( Figure 1 , step 105). Examples of suitable polymer substrates for the present invention include, but are not limited to, nylon, polyvinylidene fluoride (PVDF), and the like. According to a preferred embodiment of the present invention, the 1T / 1T′-TMD nanosheet dispersion collected in step 104 is vacuum filtered onto PVDF to form the filter membrane. The resulting filter membrane can be used to construct a point-of-use (POU) device capable of removing metal cations from fluids.

[0033] Therefore, a second object of the present invention is to provide a device for removing metal ions from a fluid. The device comprises the aforementioned filter membrane, comprising a polymer substrate and multiple layers of 1T / 1T′-TMD nanosheets deposited on the polymer substrate, and is capable of reducing the concentration of metal cations in a fluid from 2 parts per million to less than 10 parts per billion.

[0034] Examples of suitable 1T / 1T′-TMD nanosheets for use in the present invention include, but are not limited to, 1T′-MoS2 nanosheets, 1T′-WS2 nanosheets, 1T-TaS2 nanosheets, or 1T-TiS2 nanosheets. Preferably, the 1T / 1T′-TMD nanosheets are 1T′-MoS2 nanosheets. According to a preferred embodiment of the present invention, the filter membrane comprises 1T′-MoS2 nanosheets having a thickness of approximately 500 nm on a PVDF substrate.

[0035] According to embodiments of the present invention, the fluid may contain metal cations selected from the group consisting of sodium ions, potassium ions, magnesium ions, calcium ions, copper ions, nickel ions, lead ions, zinc ions, and combinations thereof. In certain embodiments, the metal cations are a combination of copper ions and lead ions. In other embodiments, the metal cations are a combination of zinc ions, copper ions, and lead ions.

[0036] According to an embodiment of the present invention, the filter membrane can remove approximately 100% of lead ions, approximately 90% of copper ions, and approximately 10-50% of other ions, including but not limited to sodium ions, potassium ions, magnesium ions, calcium ions, nickel ions, zinc ions, or combinations thereof, from a solution with an initial concentration of approximately 2 mg / L.

[0037] According to embodiments of the present invention, after the filter membrane has been adsorbed or saturated with metal cations, it can be regenerated by repeated washing with a solution containing a chelating agent (e.g., ethylenediaminetetraacetic acid (EDTA)). According to specific embodiments, the regenerated filter membrane is still capable of removing metal ions (e.g., lead ions) from a solution initially containing approximately 1 mg / L to a concentration below 10 μg / L.

[0038] According to a further embodiment of the present invention, the filter membrane of the present invention can remain stable in a solution with a pH value between 0 and 14. After soaking for three days, the XRD spectrum of the TMD membrane does not change significantly compared to before soaking.

[0039] The present invention will be described below based on embodiments. The embodiments provided are merely examples, and the scope of the present invention is not limited to the disclosed embodiments.

[0040] Example

[0041] Materials and Methods

[0042] Preparation of TMD nanosheet monolayer or bilayer

[0043] TMD nanosheets (e.g., MoS2, WS2, TaS2, or TiS2) are prepared using electrochemical lithium ion intercalation stripping technology. Briefly, a mixture of TMD bulk powder, carbon black, and polyvinylidene fluoride (PVDF) (mass ratio 8:1:1) and N-methyl-2-pyrrolidone (NMP) is coated on a copper foil to form an electrode plate. This electrode plate is used as the cathode, and then assembled into a button cell and discharged to trigger lithium insertion. After the discharge is completed, the cathode with lithium insertion (Li xAfter removing the MoS2, the TMD nanosheets are exfoliated by ultrasonication in deionized water. Hydrogen gas is generated during this process, further accelerating the exfoliation process. The exfoliated TMD nanosheets are collected by centrifugation and redispersed in deionized water. This step is repeated three times to obtain clean single-layer or double-layer TMD nanosheets.

[0044] Preparation of TMD filter membrane

[0045] The TMD nanosheets prepared above are redispersed in water. The dispersion is then vacuum filtered onto a porous substrate (PVDF) to form the filter membrane of the present invention. The thickness of the filter membrane can be controlled by adjusting the mass of the TMD nanosheets being filtered.

[0046] Adsorption of metal cations using TMD nanosheets

[0047] Batch tests were conducted on the prepared TMD nanosheets to verify their ability to adsorb various metal cations. In this experiment, a total of 9 cations (including Pb 2+ ,Cu 2+ ,Cd 2+ ,K + ,Ni 2+ ,Na + ,Zn 2+ ,Ca 2+ , and Mg 2+ ) nitrate solution to eliminate the interference of anions in this experiment. The peeled and washed TMD nanosheet solution was mixed with each metal cation solution (concentration of 2 mg / L) and stirred for 12 hours. Then, the TMD nanosheet solution adsorbed with metal cations was separated by 0.22 μm pore size PVDF filtration, and the metal cation concentration in the remaining solution was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS). The formula R = [(C0-C f ) / C f ]×100% to calculate the removal rate (R), where C0 and C f Represent the initial and final concentrations of cations (mg / L). d =[(C0-C f ) / C f ]V / mCalculate the distribution coefficient (K d), where V represents the volume of the solution (ml) and m represents the weight of the adsorbent (g). The TMD nanosheets were digested in a solution consisting of nitric acid and hydrogen peroxide, and the concentration of soluble Mo / W / Ta / Ti species was then determined by ICP-OES to determine the concentration of TMD. These batch experiments were carried out at room temperature to evaluate the adsorption capacity, selectivity, and adsorption kinetics of the TMD nanosheets. To evaluate the adsorption capacity, different concentrations (2-80 mg / L) of lead ions were added to the TMD nanosheet solution. After continuous stirring for 12 hours, the residual lead ion concentration was quantified by ICP-MS. In order to explore the kinetics of the lead ion adsorption process, the mixture of the TMD nanosheet solution and the lead ion solution (2 mg / L) was stirred for approximately 1, 2, 4, 8, 16, 30 and 60 minutes, respectively, and the residual lead ion concentration in the solution after adsorption was quantified by ICP-MS.

[0048] Removal of lead ions by MoS2 membrane filtration

[0049] The lead ion removal capacity of a MoS2 membrane was measured at room temperature using a pressure-assisted filtration chamber (300 ml volume). Before the test began, a MoS2 membrane (1 cm diameter) was loaded into the chamber, followed by the introduction of different lead ion concentrations (1 mg / L and 0.25 mg / L). The filtration reaction was initiated with compressed nitrogen at 1 bar. Subsequently, 10 ml of the filtrate was removed at regular intervals and analyzed for lead ion concentration by ICP-MS. After the lead ion was removed, the membrane was regenerated by washing with a solution containing EDTA. The regenerated membrane was reused for the next batch of filtration tests.

[0050] Example 1: Fabrication and Analysis of TMD Nanosheets

[0051] In this embodiment, the TMD nanosheets of the present invention were manufactured using the electrochemical lithium ion intercalation and exfoliation technique according to the steps in “Materials and Methods”.

[0052] Atomic force microscopy (AFM) results confirmed that these nanosheets, including MoS2, WS2, TaS2, and TiS2 nanosheets, were extremely thin (monolayer or bilayer, with yields >92%), metallic in nature (1T / 1T' phase), and negatively charged. Specifically, approximately 93% of the MoS2 and 92% of the TaS2 nanosheets were monolayer, while approximately 92% of the WS2 and 93% of the TiS2 nanosheets were bilayer.

[0053] Example 2: TMD nanosheets of Example 1 selectively adsorb metal ions

[0054] In this example, the TMD nanosheets of Example 1 were tested for their ability to remove highly toxic transition metal cations (e.g., Pb2+ ,Cu 2+ ,Ni 2+ , and Zn 2+ ) and background cations (e.g., K + ,Na + ,Ca 2+ and Mg 2+ ) ability, and the results are shown in Figure 2 and Tables 1-4.

[0055] The results showed that all the TMD nanosheets of Example 1 could remove nearly 100% of the lead ions in the solution with an initial concentration of 2 mg / L (see Figure 2a , 2b, 2c and 2d), about 87-90% copper ions, about 10-50% other ions (including K + ,Na + ,Ni 2+ ,Zn 2+ ,Ca 2+ and Mg 2+ ) (See Table 1-4). In addition, the MoS2, WS2, TaS2 and TiS2 nanosheets of Example 1 exhibited excellent adsorption selectivity for lead ions, and their distribution coefficients (K d ) values ​​are approximately 5.57×10 7 , 3.59×10 7 , 3.9×10 7 and 1.8×10 7 mg / L, compared to other metal cations (i.e., Cu 2+ ,Zn 2+ ,K + ,Na + ,Mg 2+ and Ca 2+ ) is 2-4 orders of magnitude higher, indicating its specific adsorption to lead ions.

[0056] Table 1. Ability of MoS2 nanosheets to adsorb metal cations C(MoS2)=34.65mg / L, contact time: 12 hours

[0057] Table 2. Ability of WS2 nanosheets to adsorb metal cations C(WS2)=53.67mg / L, contact time: 12 hours

[0058] Table 3. Ability of TaS2 nanosheets to adsorb metal cations C(TaS2)=81.60mg / L, contact time: 12 hours

[0059] Table 4. Ability of TiS2 nanosheets to adsorb metal cations C(TiS2)=32.99mg / L, contact time: 12 hours

[0060] Furthermore, because drinking water contains high levels of calcium and sodium ions, the effects of these high concentrations on TMD lead adsorption were also investigated. The results showed that 20 mM NaNO₃, 20 mM Ca(NO₃)₂, and tap water did not affect TMD's lead removal ability (results not shown).

[0061] In addition, the thermodynamic and kinetic behaviors behind this adsorption experiment were also explored. The adsorption isotherm refers to the relationship curve between the concentrations of solute molecules in the two phases when the adsorption process at the interface of the two phases reaches equilibrium at a certain temperature. Here, it refers to the dynamic equilibrium relationship between the concentration of residual metal ions in the solution and the concentration of metal ions adsorbed on the adsorbent (i.e., TMD nanosheets). Figure 2e As shown in Figure 2, the adsorption isotherms of lead ions on MoS2, WS2, TaS2 and TiS2 nanosheets can be fitted with the Langmuir adsorption model, indicating that the lead ions adsorbed on TMD nanosheets are monolayer adsorption. According to this model, the maximum capacity of MoS2 nanosheets for adsorbing lead ions is 529 mg / g, while the maximum capacity of WS2, TaS2 and TiS2 nanosheets for adsorbing lead ions are 332 mg / g, 175 mg / g and 388 mg / g, respectively. The kinetics of lead ion adsorption on MoS2, WS2, TaS2 and TiS2 nanosheets are shown in Figure 2. Figure 2f All tested TMD nanosheets exhibited rapid lead ion adsorption kinetics, reducing lead ion concentrations from an initial 2 mg / L to less than 10 μg / L within 1, 1, 4, and 4 minutes, respectively. This result precisely complies with the WHO's standard for lead ion concentrations in drinking water to no greater than 10 μg / L.

[0062] In addition, the stability of lead ions adsorbed on TMD nanosheets was also investigated. The results showed that the lead ion concentration in the adsorption solution of each of the four TMD nanosheets (i.e., MoS2, WS2, TaS2, and TiS2 nanosheets) was below 10 μg / L, indicating that the adsorbed lead ions did not desorb from the TMD nanosheets (Figure 3).

[0063] TMD nanosheets that have adsorbed lead ions can be regenerated using a chelating agent. In this example, ethylenediaminetetraacetic acid (EDTA) was used to treat TMD nanosheets (e.g., MoS2-Pb) that had adsorbed lead ions. X-ray photoelectron (XPS) spectra showed that after EDTA treatment, the lead ion signal on MoS2-Pb decreased significantly, indicating that most of the lead ions had been chelated by EDTA and desorbed from the MoS2-Pb. Further results showed that even after five regeneration cycles, the MoS2 nanosheets could still remove up to 94% of the lead ions in the fluid.

[0064] Example 3: Portable Point-of-Use (POU) Filter Device for Removing Lead Ions from Drinking Water

[0065] In this embodiment, a portable point-of-use (POU) filter device was constructed for removing lead ions from drinking water. MoS nanosheets were chosen to construct the POU filter membrane due to their superior adsorption capacity and strong affinity for lead ions compared to other TMD nanosheets. The membrane was prepared using vacuum filtration according to the procedures described in the "Materials and Methods" section.

[0066] The layered structure of the MoS2 membrane is clearly visible in the SEM image, with the MoS2 nanolayer thickness approximately 500 nm. Pressure filtration was then performed on the MoS2 membrane using a feed solution containing lead ions ranging from 0.25 mg / L to 1 mg / L. The results showed that, with a feed solution containing 1 mg / L of lead ions, the volume of wastewater that could be treated was 200 ml before the lead ion concentration exceeded the WHO standard of 10 μg / L. When the lead ion concentration in the feed solution dropped to 0.25 mg / L, the volume of wastewater that could be treated increased to 670 ml.

[0067] Furthermore, when the MoS2 membrane becomes saturated with lead ion adsorption, it can be regenerated using an EDTA solution. The regenerated MoS2 membrane is reused for filtration (a second cycle), again reducing the lead ion concentration in the feed solution from 1 mg / L to below 10 μg / L. The volume of wastewater that can be treated is 184 ml, approximately 92% of the volume of wastewater that can be treated in the first round (200 ml). Furthermore, when the lead ion concentration is reduced from 0.25 mg / L to below 10 μg / L, the regeneration efficiency is approximately 97% (650 ml vs. 670 ml). This high regeneration efficiency also indicates that the MoS2 membrane of the present invention can be reused to remove lead ions with excellent results.

[0068] The MoS2 membrane also exhibited excellent stability in aqueous solutions. Even after being immersed in water for a month, the membrane showed no signs of separation or detachment from the polymer substrate. Other membranes made from WS2, TaS2, or TiS2 nanosheets also exhibited similar stability.

[0069] Furthermore, the aforementioned TMD membranes were immersed in solutions with pH values ​​ranging from 0 to 14 for three days, and it was found that there was no significant difference in the XRD patterns between them and the original TMD membranes (MoS2, WS2, TaS2, and TiS2 membranes), indicating that the structure of the TMD nanosheets in the TMD membranes is stable and does not change due to changes in pH.

[0070] Although the above embodiments disclose specific embodiments of the present invention, they are not intended to limit the present invention. Those skilled in the art may make various changes and modifications without departing from the principles and spirit of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the accompanying patent applications.

Claims

1. A method for removing metal cations from a fluid, comprising filtering the fluid with a filter membrane, wherein the filter membrane comprises a polymer substrate and multiple layers of 1T / 1T′-transition metal dichalcogenide (TMD) nanosheets deposited on the polymer substrate, and the filter membrane is capable of reducing the concentration of metal cations in the fluid from 2 parts per million to less than 10 parts per billion.

2. The method of claim 1, wherein the metal cation is sodium ion, potassium ion, magnesium ion, calcium ion, copper ion, nickel ion, lead ion, zinc ion, or a combination thereof.

3. The method according to claim 2, wherein the filter membrane is prepared by the following steps: (i) discharging the TMD bulk material in a lithium battery to produce a lithiated TMD bulk material; (ii) ultrasonically vibrating the lithiated TMD bulk material in water to exfoliate the lithiated TMD bulk material into 1T / 1T′-TMD nanosheets; (iii) collecting the product of step (ii) by centrifugation; (iv) redispersing the product of step (iii) in water to form a 1T / 1T′-TMD nanosheet dispersion; and (v) vacuum filtering the 1T / 1T′-TMD nanosheet dispersion onto the polymer substrate to prepare the filter membrane.

4. The method according to claim 3, wherein The 1T / 1T′-TMD nanosheets are 1T′-MoS2 nanosheets, 1T′-WS2 nanosheets, 1T-TaS2 nanosheets, or 1T-TiS2 nanosheets; and The polymer substrate is made of nylon or polyvinylidene fluoride (PVDF).

5. The method according to claim 4, wherein the adsorption capacity of the 1T / 1T′-TMD nanosheets for lead ions is about 175-530 mg / g.

6. The method of claim 5, wherein the adsorption capacity of the 1T′-MoS2 nanosheets is approximately 530 mg / g, the adsorption capacity of the 1T′-WS2 nanosheets is approximately 330 mg / g, the adsorption capacity of the 1T-TaS2 nanosheets is approximately 175 mg / g, and the adsorption capacity of the 1T-TiS2 nanosheets is approximately 390 mg / g.

7. A device for removing metal ions from a fluid, comprising a filter membrane comprising a polymer substrate and multiple layers of 1T / 1T′-transition metal dichalcogenide (TMD) nanosheets deposited on the polymer substrate, wherein the filter membrane is capable of reducing the concentration of metal cations in the fluid from 2 parts per million to less than 10 parts per billion.

8. The device of claim 7, wherein the metal cation is sodium ion, potassium ion, magnesium ion, calcium ion, copper ion, nickel ion, lead ion, zinc ion, or a combination thereof.

9. The device according to claim 8, wherein the filter membrane is made by the following steps: (i) discharging the TMD bulk material in a lithium battery to produce a lithiated TMD bulk material; (ii) subjecting the lithiated TMD bulk material to ultrasonic vibration in water to exfoliate the lithiated TMD bulk material into 1T / 1T′-TMD nanosheets; (iii) collecting the product of step (ii) by centrifugation; (iv) redispersing the product of step (iii) in water to form the 1T / 1T′-TMD nanosheet dispersion; and (v) vacuum filtering the 1T / 1T′-TMD nanosheet dispersion onto the polymer substrate to prepare the filter membrane.

10. The device according to claim 9, wherein The 1T / 1T′-TMD nanosheets are 1T′-MoS2 nanosheets, 1T′-WS2 nanosheets, 1T-TaS2 nanosheets, or 1T-TiS2 nanosheets; and The polymer substrate is made of nylon or polyvinylidene fluoride (PVDF).

11. The device according to claim 10, wherein the adsorption capacity of the 1T / 1T′-TMD nanosheets for lead ions is about 175-530 mg / g.

12. The device of claim 11 , wherein the adsorption capacity of the 1T′-MoS2 nanosheets is approximately 530 mg / g, the adsorption capacity of the 1T′-WS2 nanosheets is approximately 330 mg / g, the adsorption capacity of the 1T-TaS2 nanosheets is approximately 175 mg / g, and the adsorption capacity of the 1T-TiS2 nanosheets is approximately 390 mg / g.

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