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Contact-active cationic particles made by tethering cationic polymers or peptides onto particle surfaces are a new type of antimicrobial agents.We have previously discovered that cationic polysaccharides have generally lower toxicity and similar effectiveness compared to non-saccharide-based antimicrobial peptides and polymers.Herein,we synthesized graphene oxide-graft-quaternized chitosan（GO-QC） nanohybrid particles by covalently grafting cationic QC,specifically dimethyldecyl-ammonium chitosan（DMDC）,onto GO（Figure la）.The GO-QC in water shows improved broad spectrum antimicrobial activity against Gram+/- bacteria and fungi,better than the QC polymer or GO alone（Figure lb）.Water disinfection materials should ideally be broad spectrum active,non-leachable and non-contaminating to the liquid needing sterilization.We demonstrate a high performance capacitive deionization disinfection（CDID） electrode made by coating an activated carbon（AC）electrode with cationic GO-QC（Figure 2）.Our GO-QC/AC CDID electrode can achieve at least99.9999%killing（i.e.6-log reduction） of E.coli in water flowing continuously through the CDID cell.Without the GO-QC coating,the AC electrode alone cannot kill the bacteria and adsorbs a much smaller fraction（< 82.8 ± 1.8%） of E.coli from the same bio-contaminated water.This CDID process consists of alternating cycles of water disinfection followed by electrode regeneration,and it only needs a small electrode voltage（2V）.With a typical brackish water bio-contamination(with 104 CFU mL-1 bacteria),the GO-QC/AC electrodes can kill 99.99%of the E.coli in water longer than 5 hours.The disinfecting GO-QC is securely attached on the AC electrode surface so that it is non-contaminating to water,unlike many other chemicals used today.This CDID process offers an economical method towards ultrafast,contaminant-free and continuous killing of bacteria in bio-contaminated water.