| Oxalic acid (OA) widely exists in plants, animals and microbes in the nature, and it can beabsorbed into the human body by food. Stone disease may be triggered if high content of oxalicacid maintain long-term in our body. Stone disease can be prevented by food or urinary oxalatedetection. So it is necessary to develop a simple, low cost, rapid and sensitive analytical methodfor the detection of oxalic acid. Biomolecule ascorbic acid (AA) and dehydroascorbic acid areknown as a vitamin C, which is widely found in fresh fruits and vegetables. It is also a necessarytrace regulator of human body physiology. Ascorbic acid is used for auxiliary treatment ofvarious diseases in clinical medicine, and it is a specific drug for prevention and treatment ofscurvy. Therefore it has important significance for detection of ascorbic acid, and a large numberof researchers enthusiasm are attracted.In recent years the photoelectrochemical detection has obtained the rapid developmentbecause of its unique characteristics. This detection method has many advantages, such as simpledetection device, low cost, small size, convenient portability, simple operation and so on. Thecurrent-time detection by two electrode system has been improved successfully by ourexperimental group and this further strengthen the above advantages. The detection method canmeet the normal detection requirements because of its high sensitivity, good selectivity, widedetection range and short response time.The main work of this paper is that we respectively realize quantitative detection of oxalicacid and ascorbic acid by development of photoelectrochemical sensor. Photoelectrochemicaletching technique was used in the preparation of photoelectrochemical sensor core that iselectrode with nano-structure. The detected target selection and sensitive detection was realizedby changing the photoelectrochemical etching conditions and replacing catalytic metal on thesurface of the electrode.In this paper, the content of this study mainly includes the following two parts:1. Photoelectrochemical detection of oxalic acid by etched Pt/n-n+-Si electrodeIn this experiment, n-n+-Si was used as the electrode substrate. The platinum metal layer of40nm thickness is modified to the substrate polishing surface, and then it is annealed at a hightemperature to form Si and Pt alloy layer. Photoelectrochemical sensor with nanostructuredplatinum layer was eventually prepared by exploring the photoelectrochemical etchingconditions. Scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS) were used to characterize the morphology and composition of the surface of modified electrodes.Keeping light and micro stirring, using two electrode system and the current time detectionmethod, oxalic acid can be detected by using etched electrodes at zero bias byphotoelectrochemical detection method. The results show that the linear range of the detection ofoxalic acid is20-600μM and the linear correlation coefficient is0.9956. As the aging timelonger, the detection limit of oxalic acid can be reduced to4μM, but the linear relation couldimmolate in a way. This sensor has good selectivity, and it can be applied in the detection ofoxalic acid in urine.2. Photoelectrochemical detection of ascorbic acid by etched Pd/n-n+-Si electrodeIn this experimental part, n-n+-Si is also used as the photoelectrochemical sensor electrodesubstrate. However, platinum metal layer is replaced with a palladium metal layer. The electrodethat was treated in the same etching conditions used in the detection of oxalic acid, butexperimental results are not satisfactory. After exploring various etching conditions, an electrodewas modified with a nanostructure palladium metal layer by using mixed acid etching. The samecharacterization methods were used on this etched Pd/n-n+-Si electrode. Etched electrodes hasgood photoelectric response on the ascorbic acid. There are two linear ranges:2-42μM and82-642μM, and linear correlation coefficients were0.992and0.993, respectively. Its selective canmeet the actual demand for detection of ascorbic acid. Other etching conditions were alsoexplored in this article. |
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