Modern applications of scanning electrochemical microscopy in the analysis of electrocatalytic surface reactions

Development of reaction-tailored electrocatalysts is becoming increasingly important as energy and environment are among key issues governing our sustainable future.Electrocatalysts are inherently optimized for application towards reactions of interest in renewable energy,such as those involved in water splitting and artificial photosynthesis,owing to its energy efficiency,simple fabrication,and ease of operation.In this view,it is important to secure logical design principles for the synthesis of electrocatalysts for various reactions of interest,and also understand their catalytic mechanisms in the respective reactions for improvements in further iterations.In this review,we introduce several key methods of scanning electrochemical microscopy(SECM)in its applications towards electrocatalysis.A brief history and a handful of seminal works in the SECM field is introduced in advancing the synthetic designs of electrocatalysts and elucidation of the operating mechanism.New developments in nano-sizing of the electrodes in attempts for improved spatial resolution of SECM is also introduced,and the application of nanoelectrodes towards the investigation of formerly inaccessible single catalytic entities is shared.

Electro Analytical Determination of Di Hydroxybenzene Isomers Using Glassy Carbon Electrode

In this study, the electrochemical oxidation of CT （catechol）, HQ （hydroquinone） and RS （resorcinol） was investigated using cyclic and linear sweep voltammetries at GCE （glassy carbon electrode）. The GCE showed an excellent electro activity and reversibility towards the oxidation of these isomers at different conditions. HQ and CT showed one defined oxidation peak and one defined reduction peak while RS showed one defined oxidation peak. These isomers were determined also in their binary and tertiary mixtures. The calibration curves for CT, HQ and RS were obtained in the ranges of 5 × 10-6 to 1 × 10-3 mol.dm-3, 5 × 10-6 to 5 × 10-4mol.dm-3 and 1 × 10-5 to 1× 10-3 mol.dm-3, respectively. The detection limits were 9 ×10-7, 3 × 10-7, 6 × 10-6 mol.dm3 for CT, HQ and RS, respectively. At the optimal experimental conditions, these isomers were determined in different water samples. Also, the removal of catechol from aqueous solution by adsorption on activated charcoal and alumina was studied. After 24 h, 88.7% and 65.9% of catechol was removed using charcoal and alumina, respectively.

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.