Application Of Some Nanomaterials In Environmental Detection

According to United Nations, the population of the world would continue to grow until at least2050and could reach as high as8.9billion. That will hugely increase enormous needs of resources in particular foods, energy and convenience living. As the natural resources of the world e.g. fossil fuels, arable land and fresh water are finite;it is evident that the introduction of different anthropogenic sources is and will be a necessity. With such substances, the stocks of world natural resources that support livelihood of human such as fresh water, quality soil, and biodiversity will be highly polluted, degraded or otherwise depleted. Owing to these unavoidable impact environmental pollution on livelihood of human, numerous research efforts have been devoted on developing ways of monitoring and preventing the environment in which electrochemistry and Surface Enhanced Raman Scattering (SERS) sensors were found to be the most promising method. An arousing demand for environmental protection, chemical industry, pharmaceutical and agricultural or in emergency detection has made these kinds of sensor as indispensible technique.Two different techniques of sensor, namely, SERS and electrochemical technique have accordingly been employed via simple and cost effective methods to detect some chemical compounds. Both SERS and electrochemical technique are based on surface modification with nanomaterials:In the electrochemical technique, multi-walled carbon nanotubes (MWCNT) were used to modify the working electrode of screen-printed electrode (SPE) in order to enhance the properties of the electrode. The assembly obtained was used as sensor for the detection of nitrophenol isomers which electrochemical peaks are very close due to their similar electrochemical properties. The response obtained from this sensor has shown three well-defined redox peaks of current and independent of each other. It is thought that the MWCNTs could improve the sensitivity of bare SPE electrode displaying well redox peaks and interestingly capacitance. The presence of MWCNTs may lead to great electrocatalytic properties by increasing the surface area and conductivity of SPE. MWCNTs are therefore believed to promote a redox reaction by enhancing the direct electron transfer through their electrically conductive surfaces surrounded.On the other side, two SERS substrates namely copper foil coated by Ag/β-AgVO3(Cu@Ag/β-AgVO3) and silicon wafer coated by Ag2MoO4(Si@Ag/Ag2MoO4), were fabricated and used for the detection of organic compounds. In fact, vanadate and molybdate species are known to be excellent materials with wide application. Their combinations with certain metals are intensively explored in order to increase their properties as well as to extend their applicability in other areas such as sensors.Cu@Ag/β-AgVO3was typically employed for the detection of carbamate pesticides. In contrary to Ag colloid nanoparticles which have been found to have poor activities for carbofuran, isoprocarb and propoxur, this SERS sensor has exhibited an excellent sensitivity for all carbamate pesticides (carbaryl, carbofuran, isoprocarb and propoxur) examined. This behavior is supposed to result from the high surface area and hot spots or active sites generated by the combination of Ag nanoparticles and β-AgVO3nanobelts.In the3rd part of our work, hydrothermal method was successfully employed to synthesized wide phases of silver molybdate (Ag/a-MoO3, Ag/h-MoO3, Ag/β-MoO3, Ag2Mo2O7, and Ag2MoO4) by acting on the pH of the media and using glucose as catalyst. Besides, the investigation with cysteamine as catalyst revealed that Ag/α-MoO3can be synthesized at room temperature. The synthesis method employed involves ammonium heptamolybdate tetrahydrate and silver nitrate as reagents with additional organic catalyst (glucose or cysteamine) or a simple conversion of AgxMoxO4x-1(with x=1,2) using cysteamine as catalyst. Compared to the previous methods, these methods required low synthesis temperature and short reaction time which could be attributed to the contribution of organic additive agent. The use of additive agents can lead to decrease significantly the temperature, to reduce the reaction time and also to achieve certain morphology or phase.In Ag/Ag2MoO4case, AgxMoO4x-1(x=1,2) and Ag nanoparticles are the starting reagents without any additive agent, In this mixture, the reaction between AgxMoxO4x-1and Ag leads easily to Ag/Ag2MoO4and can be realized at room temperature. The nature and physical structures of the products were evaluated by XRD, Raman, TEM. Finally, Si wafer coated by Ag/Ag2MoO4(Si@Ag/Ag2MoO4) is fabricated and applied for the detection of ascorbic acid, aniline, dopamine chloride and para-phenylenediamine performed in their mixtures. The results reveal that Si@Ag/Ag2MoO4has an excellent sensitivity and stability.These sensors could be highly advantageous for applications where facile and sensitive analysis is of paramount importance; e.g. those in areas such as environment protection, and chemical, industry, as well as pharmaceutical, agricultural or general emergency detection.