Patent Publication Number: US-2023150844-A1

Title: Devices for removing metal ions from liquid

Description:
BACKGROUND 
     Efficient extraction of metal ions from water is of interest for various applications, such as resource extraction from seawater and water treatment. Removing metal ions from water is an important process, not only for drinking and sanitation purposes but also for industrial use. It is desirable to provide a water filter device for household and industrial use that is capable to remove metal ions from water and other liquid. 
     SUMMARY 
     Described herein are an apparatus for removing metal ions from water or other liquid for drinking and industrial uses. 
     In one embodiment, the disclosure describes an apparatus that includes a conduit including an inlet to receive a liquid and an outlet to discharge the liquid, a first porous electrode and a second porous electrode disposed in the conduit, and a power source configured to provide power to the first porous electrode and the second porous electrode. The first porous electrode and the second porous electrode are separated by a gap, where the gap is formed by fixed locations of electrodes or by inserting a nonconductive mesh or porous material therein. The first porous electrode is extended in a first direction. A flow direction of the liquid in the conduit is not in parallel with the first direction. 
     In some embodiments, the power source provides an electrical field between the first porous electrode and the second porous electrode such that metal ions are electro-deposited onto a surface of the first porous electrode/material or the second porous electrode/material. 
     In some instances, each of the first porous electrode and the second porous electrode comprises a plurality of sheet electrodes. The sheet electrodes of the first porous electrode are interlaced and in parallel with the sheet electrodes of the second porous electrode. In such a configuration, the flow direction of the liquid in the conduit is substantially in parallel with a normal direction of the sheet electrodes. 
     In some instances, the first porous electrode and the second porous electrode are sheet electrodes bent in a zig-zag shape with the gap separating the first porous electrode and the second porous electrode. In such a configuration, the flow direction of the liquid in the conduit traverses the zig-zag shaped sheet electrodes. 
     In some embodiments, the apparatus further includes a case that houses the conduit. The case includes a reservoir surrounding the conduit. The conduit may include a side wall having holes such that the liquid communicates from an inside of the conduit to the reservoir or from the reservoir to the conduit. 
     In some embodiments, the case includes a first compartment connected to the inlet, a second compartment configured to house the first porous electrode and the second porous electrode, and a separation structure disposed between the first compartment and the second compartment. The separation structure includes holes to allow the liquid to communicate from the first compartment to the second compartment. 
     In some embodiment, the first porous electrode and the second porous electrode comprise one of carbon felt or graphite felt with fibers. The fibers have a diameter of 1-100 μm inclusive. 
     In some embodiments, each of the first porous electrode and the second porous electrode has a thickness of 0.5-100 mm inclusive. 
     In some embodiments, at least one of the first porous electrode and the second porous electrode is functionalized with a material. As a non-limiting example, the material includes an amidoxime-based chemical. The material may include a porous coating disposed on a surface of at least one of the first porous electrode and the second porous electrode. 
     In some embodiments, the power source provides a direct current or an alternating current to the first porous electrode and the second porous electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain features of various embodiments of the present technology are set forth with particularity in the appended claims. A better understanding of the features and advantages of the technology will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIG.  1    is a diagram illustrating a water filter device that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. 
         FIG.  2    is a diagram illustrating another water filter device that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. 
         FIG.  3    is a diagram illustrating yet another water filter device that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. 
         FIG.  4    is a diagram illustrating yet another water filter device that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. 
         FIG.  5 A  is a diagram illustrating another water filter device, according to one example embodiment.  FIG.  5 B  is a diagram illustrating the water filter device shown in  FIG.  5 A  that is cut in half along a vertical plane to show its internal configurations. 
         FIG.  6 A  is a diagram illustrating another water filter device, according to one example embodiment.  FIG.  6 B  is a diagram illustrating the water filter device shown in  FIG.  5 A  that is cut in half along a vertical plane to show its internal configurations. 
         FIG.  7    is a diagram illustrating a coiled electrode set, according to one example embodiment. 
         FIG.  8    is a diagram illustrating another electrode set, according to one example embodiment. 
         FIG.  9    is a diagram illustrating a zig-zag-shaped electrode set, according to one example embodiment. 
         FIG.  10 A  is a scanning electron microscopy (SEM) image of an example electrode material.  FIG.  10 B  is an SEM image of the electrode material shown in  FIG.  10 A  with a higher magnification. 
         FIG.  11    is a diagram illustrating another water filter device, according to one example embodiment. 
         FIG.  12 A  is a diagram illustrating a water filter device that includes two water filter units stacked together to form a tandem configuration, according to one example embodiment. 
         FIG.  12 B  is a diagram illustrating a water filter device that includes three water filter units stacked together to form a tandem configuration, according to one example embodiment. 
         FIG.  13    is a diagram illustrating performances of the water filter device shown in  FIG.  1    in removing copper ions. 
         FIG.  14    is a diagram illustrating performances of the water filter device shown in  FIG.  1    in removing lead ions. 
         FIG.  15    is a diagram illustrating performances of the water filter device shown in  FIG.  1    that has two pairs of coiled electrodes in removing lead ions. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. Moreover, while various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. 
     Unless the context requires otherwise, throughout the present specification and claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” Recitation of numeric ranges of values throughout the specification is intended to serve as a shorthand notation of referring individually to each separate value falling within the range inclusive of the values defining the range, and each separate value is incorporated in the specification as it were individually recited herein. Additionally, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may be in some instances. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Various embodiments described herein are directed to apparatuses for removing metal ions from water and other liquids for drinking and industrial uses. In the examples provided herein, these water- or liquid-treating apparatuses are called water filter devices. In one non-limiting example, a water filter device includes a conduit that has an inlet to receive a liquid and an outlet to discharge the liquid, a first porous electrode and a second porous electrode disposed in the conduit, and a power source configured to provide power to the first porous electrode and the second porous electrode. The first porous electrode and the second porous electrode are separated by a gap. A flow direction of the liquid in the conduit is designed such that it is not in parallel with a direction in which the first porous electrode and the second porous electrode are extended. Various water filter devices are provided herein. 
     Reference is made to  FIG.  1   .  FIG.  1    is a diagram illustrating a water filter device  100  that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. The water filter device  100  includes a case  102  and a conduit  104  configured to receive pre-treated liquid and discharge treated liquid. The conduit  104  includes an inlet  104   a  that receives the pre-treated liquid and an outlet  104   b  that outputs the treated liquid. The inlet  104   a  and the outlet  104   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. In the illustrated embodiment, the inlet  104   a  and the outlet  104   b  are both disposed on a top surface of the case  102 , where the inlet  104   a  is disposed close to an edge of the top surface and the outlet  104   b  is disposed at a center of the top surface. However, this configuration is provided merely as an example. Other configurations are contemplated. For example, one of the inlet and the outlet may be disposed on the top portion of the case, while the other one is disposed on the bottom portion or a side portion of the case. 
     The conduit  104  further includes an electrode fitting compartment  106  connected to the outlet  104   b . The electrode fitting compartment  106  is configured to accommodate electrodes such as that depicted in  FIG.  7   . The electrode fitting compartment  106  includes a side wall  108  disposed inside the case  102 . The side wall  108  is surrounded by a reservoir  110  of the case  102 . The reservoir  110  is connected to the inlet  104   a . The side wall  108  of the electrode fitting compartment  106  includes holes  112  to allow the reservoir  110  to be in fluid communication with the inside of the electrode fitting compartment  106 . The water filter device  100  further includes a power source (not shown) coupled to the electrodes (not shown) disposed in the electrode fitting compartment  106 . 
     In an example, the pre-treated liquid (or water) is inputted into the reservoir  110  from the inlet  104   a . The pre-treated liquid fills in the reservoir  110  and is forced to move through the holes  112  of the side wall  108  to enter the electrode fitting compartment  106 . At least a pair of sheet electrodes (e.g., electrodes  702  and  704  of  FIG.  7   ) are fitted in the electrode fitting compartment  106 . The sheet electrodes are porous (e.g., referring to  FIGS.  10 A and  10 B  showing pores of the electrodes) to allow the liquid to pass through. As the liquid moves through the sheet electrodes, the power source provides an electrical field between porous electrodes such that metal ions are electro-deposited onto a surface of the porous electrodes so as to remove metal ions from the liquid. The post-treated liquid is then discharged from the outlet  104   b  connected to the electrode fitting compartment  106 . 
       FIG.  2    is a diagram illustrating a water filter device  200  that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. The water filter device  200  includes a case  202  and a conduit  204  configured to receive pre-treated liquid and discharge treated liquid. The conduit  204  includes an inlet  204   a  that receives the pre-treated liquid and an outlet  204   b  that outputs the treated liquid. The inlet  204   a  and the outlet  204   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. In the illustrated embodiment, the inlet  204   a  and the outlet  204   b  are both disposed on a top surface of the case  202 , where the inlet  204   a  is disposed at a center of the top surface and the outlet  204   b  is disposed close to an edge of the top surface. The conduit  204  further includes an electrode fitting compartment  206  connected to the inlet  204   a . The electrode fitting compartment  206  is configured to accommodate electrodes such as that depicted in  FIG.  7   . The electrode fitting compartment  206  includes a side wall  208  disposed inside the case  202 . The side wall  208  is surrounded by a reservoir  210  of the case  202 . The reservoir  210  is connected to the outlet  204   b . The side wall  208  of the electrode fitting compartment  206  includes holes  212  to allow the reservoir  210  to be in fluid communication with the inside of the electrode fitting compartment  206 . The water filter device  200  further includes a power source (not shown) coupled to the electrodes (not shown) disposed in the electrode fitting compartment  206 . 
     In an example, the pre-treated liquid (or water) is inputted into the electrode fitting compartment  206  from the inlet  204   a . The pre-treated liquid is forced through at least a pair of sheet electrodes (e.g., electrodes  702  and  704  of  FIG.  7   ) disposed in the electrode fitting compartment  206 . The sheet electrodes are porous (e.g., referring to  FIGS.  10 A and  10 B  showing pores of the electrodes) to allow the liquid to pass through. As the liquid moves through the sheet electrodes, the power source provides an electrical field between porous electrodes such that metal ions are electro-deposited onto a surface of the porous electrodes so as to remove metal ions from the liquid. The post-treated liquid is then moved to the reservoir  210  through the holes  212  on the side wall  208  of the electrode fitting compartment  206 , and is discharged from the outlet  204   b.    
     Reference is made to  FIG.  3   .  FIG.  3    is a diagram illustrating a water filter device  300  that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. The water filter device  300  includes a case  302  and a conduit  304  configured to receive pre-treated liquid and discharge post-treated liquid. The conduit  304  includes an inlet  304   a  that receives the pre-treated liquid and an outlet  304   b  that outputs the treated liquid. The inlet  304   a  and the outlet  304   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. In the illustrated embodiment, the inlet  304   a  is disposed close to an edge of the bottom surface of the case  302 . The outlet  304   b  is disposed at a center of the top surface of the case  302 . However, this configuration is provided merely as an example. Other configurations are contemplated. 
     The conduit  304  further includes an electrode fitting compartment  306  connected to the outlet  304   b . The electrode fitting compartment  306  is configured to accommodate electrodes such as that depicted in  FIG.  7   . The electrode fitting compartment  306  includes a side wall  308  disposed inside the case  302 . The side wall  308  is surrounded by a reservoir  310  of the case  302 . The reservoir  310  is connected to the inlet  304   a . The side wall  308  of the electrode fitting compartment  306  includes holes  312  to allow the reservoir  310  to be in fluid communication with the inside of the electrode fitting compartment  306 . The water filter device  300  further includes a power source (not shown) coupled to the electrodes (not shown) disposed in the electrode fitting compartment  306 . 
     In an example, the pre-treated liquid (or water) is inputted into the reservoir  310  from the inlet  304   a . The pre-treated liquid fills in the reservoir  310  and is forced to move through the holes  312  of the side wall  308  to enter the electrode fitting compartment  306 . At least a pair of sheet electrodes (e.g., electrodes  702  and  704  of  FIG.  7   ) are fitted in the electrode fitting compartment  306 . The sheet electrodes are porous (e.g., referring to  FIGS.  10 A and  10 B  showing pores of the electrodes) to allow the liquid to pass therethrough. As the liquid moves through the sheet electrodes, the power source provides an electrical field between porous electrodes such that metal ions are electro-deposited onto a surface of the porous electrodes so as to remove metal ions from the liquid. The post-treated liquid is then discharged from the outlet  304   b  connected to the electrode fitting compartment  306 . 
       FIG.  4    is a diagram illustrating a water filter device  400  that is cut in half along a vertical plane to show its internal configurations, according to one example embodiment. The water filter device  400  includes a case  402  and a conduit  404  configured to receive pre-treated liquid and discharge treated liquid. The conduit  404  includes an inlet  404   a  that receives the pre-treated liquid and an outlet  404   b  that outputs the post-treated liquid. The inlet  404   a  and the outlet  404   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. In the illustrated embodiment, the inlet  404   a  is disposed at a center of the bottom surface of the case  402 . The outlet  404   b  is disposed close to an edge of the top surface of the case  402 . However, this configuration is provided merely as an example. Other configurations are contemplated. 
     The conduit  404  further includes an electrode fitting compartment  406  connected to the inlet  404   a . The electrode fitting compartment  406  is configured to accommodate electrodes such as that depicted in  FIG.  7   . The electrode fitting compartment  406  includes a side wall  408  disposed inside the case  402 . The side wall  408  is surrounded by a reservoir  410  of the case  402 . The reservoir  410  is connected to the outlet  404   b . The side wall  408  of the electrode fitting compartment  406  includes holes  412  to allow the reservoir  410  to be in fluid communication with the inside of the electrode fitting compartment  406 . The water filter device  400  further includes a power source (not shown) coupled to the electrodes (not shown) disposed in the electrode fitting compartment  406 . 
     In an example, the pre-treated liquid (or water) is inputted into the electrode fitting compartment  406  from the inlet  404   a . The pre-treated liquid is forced through at least a pair of sheet electrodes (e.g., electrodes  702  and  704  of  FIG.  7   ) disposed in the electrode fitting compartment  406 . The sheet electrodes are porous (e.g., referring to  FIGS.  10 A and  10 B  showing pores of the electrodes) to allow the liquid to pass therethrough. As the liquid moves through the sheet electrodes, the power source provides an electrical field between porous electrodes such that metal ions are electro-deposited onto a surface of the porous electrodes so as to remove metal ions from the liquid. The post-treated liquid is then moved to the reservoir  410  through the holes  412  on the side wall  408  of the electrode fitting compartment  406 , and is discharged from the outlet  404   b.    
     Reference is made to  FIGS.  5 A and  5 B .  FIG.  5 A  is a diagram illustrating a water filter device  500 , according to one example embodiment.  FIG.  5 B  is a diagram illustrating the water filter device  500  cut in half along a vertical plane to show its internal configurations. The water filter device  500  includes a case  502  and a conduit  503  configured to receive pre-treated liquid and discharge treated liquid. The conduit  503  includes an inlet  503   a  that receives the pre-treated liquid and an outlet  503   b  that outputs the post-treated liquid. The inlet  503   a  and the outlet  503   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. In the illustrated embodiment, the inlet  503   a  is disposed on a top surface of the case  502 , while the outlet  503   b  is disposed on a bottom surface of the case  502 . However, this configuration is provided merely as an example. Other configurations of the inlet  503   a  and the outlet  503   b  are contemplated. 
     Referring to  FIG.  5 B , the case  502  includes a first compartment  504 , a second compartment  506 , and a third compartment  508 . The first compartment  504  is connected to the inlet  503   a , while the third compartment  508  is connected to the outlet  503   b . The second compartment  506  is configured to house electrodes (not shown) therein. In some embodiments, the case  502  further includes a first separation structure  510  disposed between the first compartment  504  and the second compartment  506  and a second separation structure  512  disposed between the second compartment  506  and the third compartment  508 . These separation structures may be provided to reinforce the structure of the case  502  and optional for the water filter device  500 . The first separation structure  510  and the second separation structure  512  are provided with holes so that the compartments can be in fluid communication with each other. 
     The second compartment  506  includes electrode fitting structures  514  to house the liquid-filtering electrodes (e.g., electrodes shown in  FIGS.  8  and  9   ). For example, the electrode fitting structures  514  may be one or more slits, notches, latches, ribs, bumps, etc. formed on the side walls of the case  502  to secure electrodes in the second compartment  506 . In the illustrated embodiment shown in  FIGS.  5 A and  5 B , a plurality of slits are provided in the side walls of the case  502  as electrode fitting structures  514 . Each of these slits may be fitted with an end portion of a sheet electrode. To protect the sheet electrodes from liquid/water pressure during the filtering process, the first separation structure  510  and the second separation structure  512  may be disposed on top and bottom of the second compartment to provide additional support for the sheet electrodes. 
     In one example, the pre-treated liquid (or water) is inputted into the first compartment  504  from the inlet  503   a . The pre-treated liquid is then moved to the second compartment  506  through the holes in the first separation structure  510 . In the second compartment  506 , the pre-treated liquid is forced through at least a pair of sheet electrodes (e.g., sheet electrodes shown in  FIGS.  8  and  9   ) disposed in the second compartment  506 . The sheet electrodes are porous (e.g., referring to  FIGS.  10 A and  10 B  showing pores of the electrodes) to allow the liquid to pass therethrough. As the liquid moves through the sheet electrodes, a power source (not shown) provides an electrical field between porous electrodes such that metal ions are electro-deposited onto a surface of the porous electrodes so as to remove metal ions from the liquid. The post-treated liquid is then moved to the third compartment  508  through the holes of the second separation structure  512 , and is discharged from the outlet  503   b.    
       FIG.  6 A  is a diagram illustrating a water filter device  600 , according to one example embodiment.  FIG.  6 B  is a diagram illustrating the water filter device  600  cut in half along a vertical plane to show its internal configurations. The water filter device  600  includes a case  602  and a conduit  603  configured to receive pre-treated liquid and discharge treated liquid. The conduit  603  includes an inlet  603   a  that receives the pre-treated liquid and an outlet  603   b  that outputs the post-treated liquid. The inlet  603   a  and the outlet  603   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. In the illustrated embodiment, the inlet  603   a  is disposed on a top surface of the case  602 , while the outlet  603   b  is disposed on a bottom surface of the case  602 . However, this configuration is provided merely as an example. Other configurations of the inlet  603   a  and the outlet  603   b  are contemplated. 
     Referring to  FIG.  6 B , the case  602  includes a first compartment  604 , a second compartment  606 , and a separation structure  608  disposed between the first compartment  604  and the second compartment  606 . The first compartment  604  is connected to the inlet  603   a , while the second compartment  608  is connected to the outlet  603   b . The second compartment  606  is configured to house electrodes (not shown) therein. In some embodiments, the case  602  further includes a second separation structure  610  disposed between the second compartment  606  and the outlet  603   b . These separation structures  608  and  610  may be provided to reinforce the structure of the case  602  and optional for the water filter device  600 . The first separation structure  610  and the second separation structure  612  are provided with holes so that the compartments can be in fluid communication with each other. 
     In some embodiments, the second compartment  606  is configured to house Zig-Zag-shaped sheet electrodes (e.g., electrodes shown in  FIG.  9   ). In some instances, the Zig-Zag-shaped sheet electrodes may be disposed vertically (as shown in  FIG.  9   ) in the second compartment  606 . In other instances, the Zig-Zag-shaped sheet electrodes may be disposed horizontally (when the electrodes shown in  FIG.  9    is rotated 90 degrees) in the second compartment  606 . In some embodiments, a portion of the sheet electrodes is disposed to abut against the side walls of the case  602  to ensure that the liquid/water is force to move through the electrodes. 
     In some embodiments, the second compartment  606  may include electrode fitting structures (not shown in  FIGS.  6 A and  6 B ) for housing the liquid-filtering electrodes (e.g., electrodes shown in  FIGS.  8  and  9   ). For example, the electrode fitting structures may be one or more slits, notches, latches, ribs, bumps, etc. formed on the side walls of the case  602  to secure electrodes in the second compartment  606 . To protect the sheet electrodes from liquid/water pressure during the filtering process, the first separation structure  608  and the second separation structure  610  may be disposed on top and bottom of the second compartment to provide additional support for the sheet electrodes. 
     In one example, the pre-treated liquid (or water) is inputted into the first compartment  604  from the inlet  603   a . The pre-treated liquid is then moved to the second compartment  606  through the holes in the first separation structure  608 . In the second compartment  606 , the pre-treated liquid is forced through at least a pair of sheet electrodes (e.g., sheet electrodes shown in  FIGS.  8  and  9   ) disposed in the second compartment  606 . The sheet electrodes are porous (e.g., referring to  FIGS.  10 A and  10 B  showing pores of the electrodes) to allow the liquid to pass therethrough. As the liquid moves through the sheet electrodes, a power source (not shown) provides an electrical field between porous electrodes such that metal ions are electro-deposited onto a surface of the porous electrodes so as to remove metal ions from the liquid. The post-treated liquid is then moved through the holes of the second separation structure  610  and is discharged from the outlet  603   b.    
       FIG.  7    is a diagram illustrating a coiled electrode set  700 , according to one example embodiment. The coiled electrode set  700  includes a first porous electrode  702  and a second porous electrode  704  separated by a gap  706 . In some embodiments, the gap  706  may be at least partially filled with an insulating mesh or porous separator. The first porous electrode  702  and the second porous electrode  704  are coupled to a power resource  708 . The power source  708  is configured to provide power to the porous electrodes  702  and  704 . In one embodiment, the power source  708  supplies a first type of voltage to the first porous electrode  702 , and supplies a second type of voltage to the second porous electrode  704 . The second type is opposite to the first type. For example, the first type and the second type could be positive and negative, respectively, or vice versa. In some embodiments, a voltage difference between the first type of voltage and the second type of voltage is about 0 and to about 40 Volts or about 5 Volts and to about 40 Volts. In some embodiments, a voltage across the porous electrodes alternates between a negative value and zero. For example, a square wave with voltages of −5 V to 0 V and frequency of 400 Hz was chosen based on fast kinetics and minimum water splitting. 
     In some embodiments, the power source  708  provides a direct current or an alternating current to the porous electrodes  702  and  704 . In some embodiments, the alternating current includes sine waves or square waves. 
     In some embodiments, the pre-treated liquid may be introduced to the center of the coiled porous electrodes  702  and  704  as indicated by an arrow  710 . The liquid then traverses the porous electrodes  702  and  704  as indicated by an arrow  720  that is substantially perpendicular to a tangential direction of the coiled electrodes  702  and  704 . In other embodiments, the pre-treated liquid may be forced to traverse the porous electrodes  702  and  704  as indicated by an arrow  730  that is substantially perpendicular to a tangential direction of the coiled electrodes  702  and  704 , to arrive at the center of the coiled electrodes  702  and  704 . The post-treated liquid is then discharged at a vertical path to the top or bottom of the electrode set  700  indicated by an arrow  740 . As the liquid moves through the electrodes  702  and  704 , the power source  708  provides an electrical field between porous electrodes  702  and  704  such that metal ions are electro-deposited onto a surface of the porous electrodes  702  and  704  to remove metal ions from the liquid. 
       FIG.  8    is a diagram illustrating another electrode set  800 , according to one example embodiment. The electrode set  800  includes sheet electrodes  802 - 816 , each separated by a gap  820 . The sheet electrodes  802 - 816  are porous to allow liquid/water to pass through. The sheet electrodes  802 - 816  are coupled to a power resource (not shown). Adjacent electrodes in the electrode set  800  are configured to receive different voltages so as to produce an electrical field therebetween. As a non-limiting example, a positive voltage is provided to the electrodes  802 ,  806 ,  810 , and  814 , and a negative voltage is provided to the electrodes  804 ,  808 ,  812 , and  816 , or vice versa. The pre-treated liquid is supplied from the top or the bottom of the electrode set  800  and traverses the electrodes  802 - 816 . As the liquid moves through the electrodes  802 - 816 , the power source provides an electrical field between porous electrodes  802 - 816  such that metal ions are electro-deposited onto a surface of the porous electrodes  802 - 816  to remove metal ions from the liquid. In some embodiments, each of the gaps  820  may be at least partially filled with an insulating mesh or porous separator. 
       FIG.  9    is a diagram illustrating a zig-zag-shaped electrode set  900 , according to one example embodiment. The zig-zag-shaped electrode set  900  includes a first porous electrode  902  and a second porous electrode  904  separated by a gap  906 . In some embodiments, the gap  906  may be at least partially filled with an insulating mesh or porous separator. The first porous electrode  902  and the second porous electrode  904  are coupled to a power resource (not shown). The power source is configured to provide power to the porous electrodes  902  and  904 . In one embodiment, the power source supplies a first type of voltage to the first porous electrode  902 , and supplies a second type of voltage to the second porous electrode  904 . The second type is opposite to the first type. For example, the first type and the second type could be positive and negative, respectively, or vice versa. In some embodiments, a voltage difference between the first type of voltage and the second type of voltage is about 0 and to about 40 Volts or about 5 Volts and to about 40 Volts. In some embodiments, a voltage across the porous electrodes  902  and  904  alternates between a negative value and zero. 
     Liquid for treatment may be supplied to traverse the porous electrodes  902  and  904  horizontally (as indicated by an arrow  910 ) or vertically (as indicated by an arrow  920 ). As the liquid moves through the electrodes  902  and  904 , the power source provides an electrical field between porous electrodes  902  and  904  such that metal ions are electro-deposited onto a surface of the porous electrodes  902  and  904  to remove metal ions from the liquid. 
     In some embodiments, the electrodes (e.g., electrodes  702 ,  704 ,  802 - 816 ,  902 ,  904 ) disclosed herein may include one of carbon felt or graphite felt with fibers.  FIG.  10 A  is a scanning electron microscopy (SEM) image of an example electrode material.  FIG.  10 B  is an SEM image of the electrode material shown in  FIG.  10 A  with a higher magnification. As shown in  FIGS.  10 A and  10 B , the electrodes are porous and contains micro pores between the fibers. In some embodiments, the fibers have a diameter of 1-100 μm inclusive. For example, the fibers may have a diameter of 1-10 μm, 1-20 μm, 1-30 μm, 1-40 μm, 1-50 μm, 1-60 μm, 1-70 μm, 1-80 μm, 1-90 μm, 5-10 μm, 5-20 μm, 5-30 μm, 5-40 μm, 5-50 μm, 5-60 μm, 5-70 μm, 5-80 μm, 5-90 μm, 10-20 μm, 10-30 μm, 10-40 μm, 10-50 μm, 10-60 μm, 10-70 μm, 10-80 μm, 10-90 μm, 20-30 μm, 20-40 μm, 20-50 μm, 20-60 μm, 20-70 μm, 20-80 μm, 20-90 μm, 30-40 μm, 30-50 μm, 30-60 μm, 30-70 μm, 30-80 μm, 30-90 μm, 40-50 μm, 40-60 μm, 40-70 μm, 40-80 μm, 40-90 μm, 50-60 μm, 50-70 μm, 50-80 μm, 50-90 μm, 60-70 μm, 60-80 μm, 60-90 μm, 70-80 μm, 70-90 μm, or 80-90 μm, inclusive. 
     In some embodiments, each of the electrodes disclosed herein has a thickness of 0.5-100 mm inclusive or 0.5-20 mm inclusive. In some embodiments, the electrodes may be functionalized with a material. For example, the material may be an amidoxime-based chemical. In some embodiments, the material may be in a form as a porous coating disposed on a surface of fibers of an electrode. 
       FIG.  11    is a diagram illustrating another water filter device  1100 , according to one example embodiment. The water filter device  1100  includes a case  1102  and a conduit  1104  configured to receive pre-treated liquid and discharge post-treated liquid. The conduit  1104  includes an inlet  1104   a  disposed on a top portion of the case  1102  and configured to receive the pre-treated liquid. The conduit  1104  further includes an outlet  1104   b  disposed on a side portion of the case  1102  and configured to output the treated liquid. It should be understood that the location of the inlet  1104   a  and the outlet  1104   b  may be interchangeable depending on the design. The inlet  1104   a  and the outlet  1104   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. 
     In some embodiments, two or more water filter units may form a tandem configuration to improve filtering performance (e.g., capacity and effectiveness). Examples are shown in  FIGS.  12 A and  12 B .  FIG.  12 A  is a diagram illustrating a water filter device  1200  that includes two water filter units stacked together to form a tandem configuration, according to one example embodiment. The water filter device  1200  includes two water filter units  1202   a  and  1202   b , and a conduit  1204  configured to receive pre-treated liquid and discharge post-treated liquid. The water filter units  1202   a  and  1202   b  are stacked vertically to each other to reduce its footprint size. However, it should be noted that this disclosure is not limited to this particular configuration. Other tandem configurations are contemplated. For example, the two water filter units may be placed in juxtaposition to each other. The conduit  1204  includes an inlet  1204   a  disposed on a top portion of the water filter unit  1202   a  and configured to receive the pre-treated liquid. The conduit  1204  further includes an outlet  1204   b  disposed on a side portion of the water filter unit  1202   b  and configured to output the treated liquid. It should be understood that the location of the inlet  1204   a  and the outlet  1204   b  may be interchangeable depending on the design. The inlet  1204   a  and the outlet  1204   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. 
       FIG.  12 B  is a diagram illustrating a water filter device  1210  that includes three water filter units stacked together to form a tandem configuration, according to one example embodiment. The water filter device  1210  includes three water filter units  1212   a ,  1212   b , and  1212   c , and a conduit  1214  configured to receive pre-treated liquid and discharge post-treated liquid. The water filter units  1212   a - 1212   c  are stacked vertically to each other. However, it should be noted that this disclosure is not limited to this particular configuration. Other tandem configurations are contemplated. For example, the three water filter units may be placed in juxtaposition to each other. In one embodiment, two of the water filter units may be stacked vertically while the third water filter is juxtaposed with one of the two vertically-stacked units. 
     The conduit  1214  includes an inlet  1214   a  disposed on a top portion of the water filter unit  1212   a  and configured to receive the pre-treated liquid. The conduit  1214  further includes an outlet  1214   b  disposed on a side portion of the water filter unit  1212   c  and configured to output the treated liquid. It should be understood that the location of the inlet  1214   a  and the outlet  1214   b  may be interchangeable depending on the design. The inlet  1214   a  and the outlet  1214   b  may include fitting mechanisms (not shown) to connect with an upstream pipe or container and a downstream pipe or container, respectively. 
     Example I 
     Table 1 shows test result of metal-ion removal effectiveness for the water filter device  100  of  FIG.  1   . The electrodes of the water filter device  100  are made of carbon felt. The electrodes are 25 cm in length, 2.5 cm in height, and 3 mm in thickness. The to-be-filtered water has total dissolved solids (TDS) of 200 ppm and a pH of about 8.5. The water flows through the water filter device  100  in a flow rate of 0.5 or 1.5 L/min. The power source provides various DC voltages of 2.5-10 V and an AC voltage between 0-10 V in 10 or 100 Hz. The removal rate of copper metal ions are effective at about 65% to about 90%. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Removal rate  
               
               
                   
                   
                   
                 (pH ~8.5,  
               
               
                   
                 Flow rate 
                 Applied voltage 
                 TDS ~200 ppm) 
               
               
                   
                   
               
             
            
               
                   
                 0.5 L/min 
                 2.5 V DC 
                 72.5% 
               
               
                   
                   
                 5 V DC 
                 91.0% 
               
               
                   
                   
                 10 VDC 
                 92.2% 
               
               
                   
                   
                 (0, 10 V) AC, 10 Hz 
                 75.6% 
               
               
                   
                   
                 (0, 10 V) AC, 100 Hz 
                 78.3% 
               
               
                   
                 1.5 L/min 
                 2.5 V 
                 64.9% 
               
               
                   
                   
                 5 V 
                 76.3% 
               
               
                   
                   
                 10 V 
                 86.0% 
               
               
                   
                   
               
            
           
         
       
     
     Example II 
     Table 2 shows test results of metal-ion removal effectiveness for the electrode set  800  of  FIG.  8   . The electrodes are made of carbon felt. The to-be-filtered water has TDS of 200 ppm and a pH of about 8.5. The water flow rate for the tests is 0.5 or 1.5 L/min. The power source provides various DC voltages of 5, 10, and 15 V. The removal rate of copper metal ions are effective at more than 50% to about 75%. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Flow rate (L/min) 
                 Voltage (V) 
                 Removal rate 
               
               
                   
                   
               
             
            
               
                   
                 0.5 
                  5 
                 58.1% 
               
               
                   
                   
                 10 
                 67.9% 
               
               
                   
                   
                 15 
                 74.9% 
               
               
                   
                 1.5 
                  5 
                 52.2% 
               
               
                   
                   
                 10 
                 54.3% 
               
               
                   
                   
                 15 
                 59.7% 
               
               
                   
                   
               
            
           
         
       
     
     Example III 
     Table 3 shows test results of metal-ion removal effectiveness for the electrode set  900  of  FIG.  9   . The electrodes are made of carbon felt. The to-be-filtered water has TDS of 200 ppm and a pH of about 8.5. The water flow rate for the tests is 0.5 or 1.5 L/min. The power source provides various DC voltages of 5 and 10 V. The removal rate of copper metal ions are effective at about 50%. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Flow rate (L/min) 
                 Voltage (V) 
                 Removal rate 
               
               
                   
                   
               
             
            
               
                   
                 0.5 
                  5 
                 47.2% 
               
               
                   
                   
                 10 
                 50.3% 
               
               
                   
                 1.5 
                  5 
                 40.2% 
               
               
                   
                   
               
            
           
         
       
     
     Example IV 
     Table 4 shows test results of metal-ion removal effectiveness for the water filter device  1210  shown in  FIG.  12 B . The electrodes are made of carbon felt. To test lead (Pb) removal effectiveness, the to-be-filtered water has TDS of about 152 ppb and a pH of about 6.5 or 8.5. To test copper (Cu) removal effectiveness, the to-be-filtered water has TDS of about 3050 or 3222 ppb and a pH of about 6.5 or 8.5. The water flow rate for the tests is 2.27 L/min. The removal rates are very effective at more than 97.5% and 80% for lead and copper metal ions, respectively. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                 Influent 
                 Filter  
                   
               
               
                 Target  
                 Testing 
                 Concentration 
                 Effluent  
                 Percent 
               
               
                 Metal 
                 parameter 
                 (ppb) 
                 (PPb) 
                 Reduction 
               
               
                   
               
             
            
               
                 Pb 
                 pH 6.5 
                  152.01 
                  &lt;3.20 
                 &gt;97.89% 
               
               
                   
                 pH 8.5 
                  152.16 
                  &lt;3.42 
                 &gt;97.75% 
               
               
                 Cu 
                 pH 6.5 
                 3049.90 
                 &lt;600 
                 &gt;80.00% 
               
               
                   
                 pH 8.5 
                 3222.38 
                 &lt;620 
                 &gt;80.80% 
               
               
                   
               
            
           
         
       
     
     Example V 
       FIG.  13    is a diagram illustrating metal-ion removal rates versus water volumes for the water filter device  100  of  FIG.  1   . The electrodes of the water filter device  100  are made of carbon felt. The electrodes are 25 cm in length, 2.5 cm in height, and 3 mm in thickness. The to-be-filtered water has total dissolved solids (TDS) of 200 ppm and a pH of about 8.5. The water flows through the water filter device in a flow rate of 1.0 L/min. As shown in  FIG.  13   , the metal-ion (copper) removal rate is at more than 50% at the beginning to about 65% after treating about 180 L of the water. This indicates that the water filter device  100  is durable and effective in removing the Cu metal ions. 
     Example VI 
       FIG.  14    is a diagram illustrating metal-ion removal rates versus water volumes for the water filter device  100  of  FIG.  1   . The electrodes of the water filter device  100  are made of carbon felt. The electrodes are 25 cm in length, 2.5 cm in height, and 3 mm in thickness. The to-be-filtered water has total dissolved solids (TDS) of 200 ppm and a pH of about 8.5. The water flows through the water filter device in a flow rate of 1.0 L/min. As shown in  FIG.  12   , the metal-ion (lead) removal rate is at more than 90% at the beginning more than 80% after treating about 170 L of the water. This indicates that the water filter device  100  is durable and effective in removing the lead metal ions. 
     Example VII 
       FIG.  15    is a diagram illustrating metal-ion removal rates versus water volumes for the water filter device  100  of  FIG.  1   . The electrodes of the water filter device are made of carbon felt. The electrodes are 25 cm in length, 2.5 cm in height, and 3 mm in thickness. In this test, the water filter device  100  includes two pairs of coiled electrodes. The to-be-filtered water has a lead ion concentration of 150 ppb. The water flows through the water filter device in a flow rate of 2.0 L/min. As shown in  FIG.  15   , the metal-ion (lead) removal rate is at more than 95% at the beginning more than 96% after treating 1600 L of the water. This indicates that the water filter device  100  is durable and effective in removing the lead metal ions. 
     The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. Many modifications and variations will be apparent to the practitioner skilled in the art. The modifications and variations include any relevant combination of the disclosed features. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.