Studies Of Environmental Pollutants:Heavy Mental Ag~+and Dihydroxybenzene Isomers Based On Carbon Nanomaterials Fabricated Sensor

With the increase of mining, industrial sewerage disposal, exhaust emission, processing and commercial manufacturing activities, causing serious pollution of heavy mental ions and small organic molecules to environment. The metal ions can’t be biodegradable. On the opposite, they get across food chains into biogeocenose and enrich in the body or biogencenose. Thus, they will result in strong toxicity to the organism. Small organic molecules such as phenols with high toxicity and low degradability are considered to be significant environmental pollutants. Inorganic pollutant such as the most typical NO2is widely used as additive and corrosion inhibitor in food and environmental systems. What’s more, NO2can react with various amines to form the highly carcinogenic N-nitrosamines. Human-health impacts from seriously environmental pollution have generated increasing interest in the development of new method to detect the concentration of these pollutants. Currently, the available methods are used to determine pollutants in the environment such as spectrophotometry, atomic absorption spectrometry, fluorescence, chromatography, etc. However, the above methods are labor, time consuming and involve multiple sample pretreatment and require expensive instruments. So, it is necessary to develop a sensitive, convenient and economical method to determine the concentration of environmental pollutants.Electrochemical sensor turns out to be an effective way and attracts more attentions due to its advantages of high sensitivity, excellent selectivity, fast response, cheap instrument, simple operation and time-saving. Modifiers are very crucial factor for the chemical modified electrodes. They will affect electrodes’performance. Nowadays, carbon nanomaterials, especially carbon nanotubes and graphene, are hot researched, because of their high surface area, excellent electric conductivity and high electrocatalytic activity. In this work, combining superior performance of multi-walled carbon nanotubes and graphene with the superiority of electrochemical sensor to test environmental pollutants, we constructed sensors modified with carbon nanomaterials and their composites. The developed silver ion sensors show good selectivity, high sensitivity and fast response time. Importantly, the new method of constructing silver ion sensors successfully solved the universal problem of the electrode components loss from ion-selective electrode. The proposed sensor modified with composite material of carbon nanotubes and graphene realized simultaneous determinations of two phenol islmer and inorganic pollutant niteite.This paper studies the content of the following:1. Studies on the hybrid materials of multi-walled carbon canotubes covalently linking ligands modified Ag+carbon paste electrodeThree ligands with similar construction have been synthesized by reacting between thiophene-2-carbaldehyde, pyridine-2-carbaldehyde, furan-2-carbaldehyde and0-phenylenediamine, respectively. The ligands N-(2-vinylsulfanyl-ethylidene)-benzene-1,2-dimine (SBD), N-pyridin-2-ylmethylene-benzene-1,2-dimine (NBD) and N-furan-2-ylmethylene-benzene-1,2-dimine (OBD) covalently linked to functionalized multi-walled carbon canotubes (MWCNT-COOH), respectively, obtaining three novel multi-walled carbon canotubes hybrid materials:SBD-g-MWCNTs, NBD-g-MWCNTs and OBD-g-MWCNTs. The hybrid materials were used as both ionophores and ion-to-electron transducers to construct Ag+carbon paste electrodes, respectively. The performances of three MWCNT hybrid electrodes tend to improve in this order of modifier:OBD-g-MWCNTs, NBD-g-MWCNTs and SBD-g-MWCNTs. The SBD-g-MWCNTs modified electrode shows the widest linear concentration range8.8×10-8to1.0×10-1mol/L, the lowest detection limit6.3×10-8mol/L and the fastest response time5s. The result is reasonable according to HSAB theory. It is well known that the reaction of a soft acid with a soft base is the easiest among acid-base reactions, and the reaction of a soft acid with a borderline base is easier than that of a soft acid with a hard base. The heavier transition metal Ag+is a soft acid. The OBD-g-MWCNTs is a hard base and the SBD-g-MWCNTs is a relatively soft base. The basicity of NBD-g-MWCNTs, called a borderline base, is between OBD-g-MWCNTs and SBD-g-MWCNTs.2. Conjugates of graphene oxide covalently linked ligands and gold nanoparticles to construct Ag+graphene paste electrodeIn this work, we reported on the synthesis and application of ionophore-gold nanoparticle conjugates (NGO-AuNP-TPC) in Ag+graphene paste electrode. Ionophore was a novel graphene hybrid material (NGO-TPC) by covalently grafting NGO and2-thiophenecarboxylic (TPC). In order to make more ligands TPC graft to the surface of NGO,-OH and alkoxyl groups on the NGO sheets were converted to-COOH groups. This results in ligand molecules are close to each other. And the configuration is benefit for the formation of sandwich complexes between two ligand molecules and the silver ion. NGO-TPC was decorated with gold nanoparticles (Au NPs), obtaining target electrode modifier NGO-AuNP-TPC. Au NPs further improve NGO-AuNP-TPC modified electrode response for Ag+. The electrode exhibited an excellent nernstian slope59.30mV/dec, wide linear range8.4×10-7-1.0×10-1mol/L and low detection limit6.3×10-7mol/L. Moreover, the response time of the developed electrode is very fast, and the used lifetime is very long. Importantly, the universal problem of the electrode components loss from ion-selective electrode has been successfully solved by the new method of immobilizing ligands on NGO nanosheets to construct electrode.3. Based on graphene nanohybrid bridged functional multiwall carbon nanotubes modified sensor for the simultaneous determination of dihydroxybenzene isomers and nitriteIn this work, we respectively synthesized two dimensional (2D) gold nanoparticles-graphene nanohybrid (Au-GR) and1D3-amino-5-mercapto-1,2,4-triazole-functionalized multiwall carbon nanotubes (MWCNT-SH). Because of the interaction between gold nanoparticles of Au-GR and SH groups of MWCNT-SH, a novel hybird material MWCNT-SH@Au-GR was obtained The MWCNT-SH@Au-GR as a modifier was used to fabricate sensor for simultaneously determining hydroquinone (HQ), catechol (CC), resorcinol (RC) and nitrite (NO2), because of the synergistic effects between MWCNT-SH and Au-GR and excellent film forming ability of MWCNT-SH@Au-GR. The morphology of MWCNT-SH@Au-GR was characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques was used to investigate the electrochemical behavior of the sensor. Results showed that linear response ranges of the sensor for HQ, CC, RC and NO2were54.50-1250.50μmol/L,11.00-126.00μmol/L,43.50-778.50μmol/L and86.00-7500.00μmol/L,and the detection limits (S/N=3) were4.17μmol/L,1.00μmol/L,7.80μmol/Land23.50μmol/L, respectively.