System and method for silver-nanoparticle-coated membranes

Abstract

The present invention provides among other things a silver nanoparticle-coated membrane that reduces biofouling. The membranes exhibit extended antimicrobial properties that prevents the buildup that causes biofouling, which in turn prolongs the life of the membranes. The membranes may be reverse osmosis membranes, microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, or any other membrane suitable for liquid processes.

We claim: 
     
         1 . An antimicrobial membrane, comprising:
 A. a membrane; and   B. a plurality of silver nanoparticles coupled to the membrane, wherein the plurality of silver nanoparticles have a silver sulfide core-shell structure.   
     
     
         2 . The membrane of  claim 1 , wherein:
 A. the membrane Component A is a reverse osmosis membrane or a nanofiltration membrane;   B. the membrane Component A is a microfiltration membrane or an ultrafiltration membrane;   C. the plurality of silver nanoparticles Component B have a weight percentage of sulfur between approximately 0.1% to approximately 7%; or   D. the plurality of silver nanoparticles Component B have a diameter of between approximately 3 nanometers (nm) to approximately 350 nm   
     
     
         3 . A method for coating a membrane with silver nanoparticles comprising:
 A. providing a membrane coating apparatus comprising:
 i. a feed tank; 
 ii. a pump coupled to the feed tank; 
 iii. a membrane housing comprising a feed end, concentrate end and a permeate end, wherein the feed end is coupled to the pump; 
 iv. a return tank coupled to the concentrate end of the membrane housing; and 
 v. plugged or unplugged permeate end 
   B. a dosing unit coupled to the return tank and the feed tank;   C. circulating a silver nitrate solution through the membrane coating apparatus;   D. circulating a nucleating agent solution through the membrane coating apparatus; and   E. circulating a solution of sodium nitrate and a sulfidation agent through the membrane coating apparatus.   
     
     
         4 . The method of  claim 3 , wherein:
 A. the nucleating agent (Component D) is selected from the group consisting of sodium borohydride, hydrazine, D-glucose, hyaluronic acid, and combinations thereof;   B. the nucleating agent (Component D) is sodium borohydride;   C. the sulfidation agent (Component E) is selected from the group consisting of sodium sulfide, sodium thiosulfate, thiocarbamide, thioacetamide, and combinations thereof;   D. the silver nitrate solution (Component C) has a concentration from approximately 1 millimolar (mM) to approximately 300 mM;   E. the nucleating agent solution (Component D) has a concentration from approximately 1 mM to approximately 300 mM;   F. the sodium nitrate (Component E) has a concentration from approximately 10 −5  mM to 10 −1  M;   G. the sulfidation agent (Component E) has a concentration from approximately 10 −5  mM to 10 −1  M;   H. the silver nitrate solution (Component C) is cycled for a time period of at least approximately 5 minutes;   I. the nucleating agent solution (Component D) is cycled for a time period of at least approximately 2 minutes; and   J. the solution of sodium nitrate and the sulfidation agent (Component E) is cycled for a time period of at least approximately 30 minutes.   
     
     
         5 . A method for coating a membrane with silver nanoparticles comprising:
 A. exposing a membrane to a silver nitrate solution;   B. exposing the membrane to a nucleating agent solution; and   C. exposing the membrane to a solution of sodium nitrate and a sulfidation agent.   
     
     
         6 . The method of  claim 5 , wherein:
 A. the nucleating agent (Component B) is selected from the group consisting of sodium borohydride, hydrazine, D-glucose, hyaluronic acid, and combinations thereof;   B. the sulfidation agent (Component C) is selected from the group consisting of sodium sulfide, sodium thiosulfate, thiocarbamide, thioacetamide, and combinations thereof;   C. the silver nitrate solution (Component A) has a concentration from approximately 1 millimolar (mM) to approximately 300 mM;   D. the nucleating agent solution (Component B) has a concentration from approximately 1 mM to approximately 300 mM;   E. the sodium nitrate (Component C) has a concentration from approximately 10 −5  M to 10 −1  M;   F. the sulfidation agent (Component C) has a concentration from approximately 10 −5  M to 10 −1  M;   G. the membrane is exposed to the silver nitrate solution (Component A) for a time period of at least approximately 5 minutes;   H. the membrane is exposed to the nucleating agent solution (Component B) for a time period of at least approximately 2 minutes; and   I. the membrane is exposed to the solution of sodium nitrate and the sulfidation agent (Component C) for a time period of at least approximately 30 minutes.   
     
     
         7 . A method for coating a membrane with silver nanoparticles comprising:
 A. providing a membrane coating apparatus comprising:
 i. a feed tank; 
 ii. a pump coupled to the feed tank; 
 iii. a membrane housing comprising a feed end, concentrate end; and a permeate end, wherein the feed end is coupled to the pump; 
 iv. a return tank coupled to the permeate end of the membrane housing; and 
 v. a dosing unit coupled to the return tank and the feed tank; 
   B. circulating a silver nitrate solution through the membrane coating apparatus;   C. circulating a D-glucose solution through the membrane coating apparatus; and   D. circulating a solution of sodium nitrate and sodium sulfide through the membrane coating apparatus.   
     
     
         8 . The method of  claim 7 , wherein:
 A. the silver nitrate solution (Component B) has a concentration of approximately 3 millimolar (mM);   B. the D-glucose solution (Component C) has a concentration of approximately 3 mM;   C. the sodium nitrate (Component D) has a concentration of approximately 10 mM;   D. the sodium sulfide (Component D) has a concentration of approximately 10 mM;   E. the silver nitrate solution (Component B) is cycled for a time period of at least approximately 5 minutes;   F. the D-glucose solution (Component C) is cycled for a time period of at least approximately 24 hours; and   G. the solution of sodium nitrate and sodium sulfide (Component D) is cycled for a time period of at least approximately 30 minutes.   
     
     
         9 . A method for coating a membrane with silver nanoparticles comprising:
 A. exposing a membrane to a silver nitrate solution;   B. exposing the membrane to a sodium borohydride solution; and   C. exposing the membrane to a solution of sodium nitrate and sodium sulfide.   
     
     
         10 . The method of  claim 9 , wherein:
 A. the silver nitrate solution (Component A) has a concentration of approximately 3 millimolar (mM);   B. the sodium borohydride solution (Component B) has a concentration of approximately 3 mM;   C. the sodium nitrate (Component C) has a concentration of approximately 10 mM;   D. the sulfidation agent has a concentration of approximately 10 mM;   E. the membrane is exposed to the silver nitrate solution (Component A) for a time period from approximately 5 minutes to approximately 15 minutes;   F. the membrane is exposed to the sodium borohydride solution (Component B) for a time period from approximately 2 minutes to approximately 10 minutes; and   G. the membrane is exposed to the solution of sodium nitrate (Component C) and the sulfidation agent for a time period from approximately 30 minutes to approximately 24 hours.