Electrochemical reduction of Cr(Ⅵ)in the presence of sodium alginate and its application in water purification

Chromium(Cr)is used in many manufacturing processes,and its release into natural waters is a major environmental problem today.Low concentrations of Cr(Ⅵ)are toxic to human health and living organisms due to the carcinogenic and mutagenic nature of this mineral.This work examined the conversion of Cr(Ⅵ)to Cr(Ⅲ)via electrochemical reduction using gold electrode in an acidic sodium alginate(SA)solution and subsequent removal of the produced Cr(Ⅲ)-SA by the polymer-enhanced ultrafiltration(PEUF)technique.A solution of SA in nitric acid was used both as an electrolytic medium during the voltammetric measurements and bulk electrolysis and as an extracting agent during the PEUF technique.The electroanalysis of Cr(Ⅵ)was performed by linear sweep voltammetry in the presence of acidic SA solution to study its voltammetric behavior as a function of the Cr(Ⅵ)concentration,pH,presence of Cr(Ⅲ),SA concentration and scan rate.In addition,the quantitative reduction of Cr(Ⅵ)to Cr(Ⅲ)was studied through the bulk electrolysis technique.The results showed efficient reduction with well-defined peaks at approximately 0.3 V vs.Ag/AgCl,using a gold working electrode.As the pH increased,the reduction signal strongly decreased until its disappearance.The optimum SA concentration was 10 mmol/L,and it was observed that the presence of Cr(Ⅲ)did not interfere in the Cr(Ⅵ)electroanalysis.Through the quantitative reduction by bulk electrolysis in the presence of acidic SA solution,it was possible to reduce all Cr(Ⅵ)to Cr(Ⅲ)followed by its removal via PEUF.

Enzyme-catalyzed deposition of polydopamine for amplifying the signal inhibition to a novel Prussian blue-nanocomposite and ultrasensitive electrochemical immunosensing

The uncontrollable synthesis of Prussian blue (PB) and its weak stability toward OH -are great challenges affecting its electrochemical biosensing application. Herein we utilize the unique properties of chitosan (CS) to realize the facile and controllable synthesis of a CS-PB nanocomposite and combine it with the urease-catalyzed deposition of polydopamine (PDA) for amplifying the electrochemical signal inhibition of PB to develop a novel immunosensing method for protein detection. The immunosensor was constructed on a CS-PB modified electrode, and a urease-functionalized silica nanoprobe was prepared for tracing its sandwich immunoassay toward the model analyte of carcinoembryonic antigen. Besides the electrochem- ical impedance effect of the quantitatively captured nanoprobes, their enzymatic reaction can release numerous OH -to destroy the PB crystals and also induce the PDA deposition onto the immunosensor. These caused drastic electrochemical signal inhibition to PB. Based on the above multi-signal amplification mechanism, the method exhibits a very low detection limit of 0.042 pg mL^(-1) along with a very wide linear range of six-order of magnitude. In addition, the CS-PB based immunosensor has excellent specificity, repeatability, stability and reliability. Thus this PB nanocomposite and the proposed electrochemical immunosensing method reveal a promising potential for future applications.