Study On Electrochemical Detection And Removal Of Arsenic In Water

The pollution of arsenic is one of the most serious pollutions due to its harm, persistence and universality. How to detect the heavy metal ions accurately, quickly and conveniently has become a common project for researchers all over the world. Compared with traditional spectrometric technologies, electrochemical method has a lot of advantages such as fast detection speed, simple operation, low cost, portable and ease of real-time online monitoring. In addition, the toxicity of As(III) is far higher than As(V). Therefore, it is significant to investigate the electrochemical sensors for As(III) detection. On the other hand, how to remove arsenic promptly and efficiently out of polluted water is another issue that needs to be addressed urgently. Chitosan is a kind of green, non-toxic and rich source of adsorbent. Whereas, adsorbents based on chitosan need harsh conditions(acid medium), which limits its wide application. Therefore, study of preparation of new and efficient absorbent based on chitosan for removal of As(III) from water is important to environmental protection and human health.The Cu2 O and ionic liquid(IL) modified carbon paste electrode, nanoporous gold electrode were prapared. Electrochemical properties and microstructures of the two electrodes were studied, and the responses of As(III) were discussed by cyclic voltammetry and square wave anodic stripping voltammetry. Besides, The sulfhydryl chitosan/active carbon composite functional membrane(CS-SH/CL), a green arsenic adsorption material, was synthesized and its arsenic-adsorbing capacity was studied. The details are listed below:1. Preparation of Cu2 O and IL modified carbon paste electrode and its application in detection of As(III)The feasibility of determination of trace As(III) in water samples with Cu2O/IL/CPE, carbon paste electrode modified simultaneously with Cu2 O and ionic liquid(1-butyl-3-methylimidazolium hexafluorophosphate), was studied. The Cu2O/IL/CPE electrode was characterized by electrochemical methods and the parameters for detection of As(III) were optimized. The experimental results show that reduction current of As(III) on Cu2O/IL/CPE electrode at-0.4V is well linear with logarithm of As(III) concentration under the condition of the best ratio of 25 wt% of Cu2 O,55 wt% of graphite powder and 20 wt% of adhesive(ionic liquid:paraffin oil=1:1), 0.1 mol L-1 of phosphate buffer(p H 6.0) as the optimal support electrolyte and 100 m V s-1 of scan rate. Determination of As(III) on Cu2O/IL/CPE electrode has a wide linear range from 0.1 nmol L-1- 100 μmol L-1, the corresponding linear equation is I = 26.26 log C + 437.9(R2 = 0.9961) with a low detection limit of 0.049 nmol L-1(S/N=3). The Cu2O/IL/CPE electrode has many advantages such as simple preparation procedure, excellent catalytic activity, good reproducibility, satisfactory selectivity and long-term stability of signal response to reduction of As(III). The proposed modified electrode was successfully applied to detect the amounts of As(III) in water samples.2. Preparation of nanoporous gold electrode via a roughing method and its application indetection of As(III)A highly sensitive and selective sensor for As(III) detection by square anodic stripping voltammetry(SWASV) on nanoporous gold electrode(NPGE) was successfully developed via open circuit potential oxidation method following reduction by chemical reagant. The morphology and electrochemical properties of the NPGE were respectively characterized by scanning electron microscopy(SEM), cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). Effects of three different anodic stripping voltammetries(square, linear sweep, differential pulse), deposition time and electrolyte solution on the electrochemical reponses of As(III) on NPGE were studied. The results show that the optimal electrochemical oxidation time is 140 s for prepartion of NPGE, the best detection method is SWASV, the optimal depostion time is 60 s and the best support electrolyte solution is 0.1 mol L-1 of HCl. Under the optimal conditions, the stripping peak current of As(III) after predeposition show good linear relationship with the logarithm of concentration of As(III). The linear range is 0.069 nmol L-1- 475.6 μmol L-1, with a limit of detection 0.0533 nmol L-1(S/N=3). The NPGE have many advantages such as simple preparation procedure, excellent catalytic activity, good reproducibility and long-term stability of signal response to As(III). Finally, the proposed NPGE was successfully applied to detect the amount of As(III) in tap water sample.3. Study on arsenic-adsorbing capacity and the preparation of the sulfhyryl chitosan/active carbon function membraneThe part of the paper is engaged in a study of the arsenic-adsorbing capacity of sulfhydryl chitosan/active carbon functional membrane. As is known, the said functional membrane is a green arsenic-adsorbing chemical compound, which can be synthesized by blending sulfhydryl chitosan and active carbon to form a membrane as the result of a cross-linking reaction and a sulfidation reaction to chitosan in it. The successful sulfhydryl functionalization of chitosan to form a sulfhydryl chitosan/active carbon composite can be confirmed through the analysis of the infrared spectroscopy, the organic element analysis and X-ray powder diffraction. The result of scanning with an electronic microscope helps to reveal the porous surface structure with a large surface area of the functional membrane. And, next, we have successfully tested the removing capacity of the membrane of As(III)and As(V). The results of our study with the functional membrane of sulfhydryl chitosan/active carbon composite verify that the functional membrane enjoys a very high capacity to adsorb As(III)and As(V). To be accurate, the maximum adsorption capacities of the membrane are 470 mg g-1 and 398 mg g-1 respectively, moreover, its capacities can hardly be affected by the p H value. In the range of p H 2.0- 9.0, the removal efficiency of As(III) and As(V) by the functional membrane can be made as high as over 90% with the optimal p H range of 6.0- 8.0, for As(III) and As(V) removal in the water with the membrane as a functional adsorbent. The membrane proves to be especially suitable for removing As(III) and As(V) in the drinking water. What is more, no effects can be found on the removal efficiency in the presence of HCO3- not beyond 60 times of arsenic, 10 times of Cl- and PO43- of arsenic. Besides, the functional membrane can also be used to adsorb As(III) and As(V), while its function can bewell kept with no remarkable decline even after it was reused for 5 times. What is more precious, The function of the membrane saturated by adsorption of arsenic can be regenerated by being immersed into saturated sodium sulfide solution and mild-agitated for two hours and then washed out in the deionized water. The procedure of the membrane regeneration is simple and easy in operation.