Preparation Of Biochar Materials And Its Application In Electrochemical Sensors

A wide range of renewable waste biomass with almost no cost can be used to prepare biochar materials,to fabricate electrochemical sensors with good performance.Different biomass possesses different characteristics.It is necessary to optimize the preparation process for different biomass to obtain biochar with better structural and electrochemical properties.Four different preparation processes including direct heating without activation,stage heating without activation,direct heating with phosphoric acid activation,and stage heating with phosphoric acid activation were applied for respective spirogyra growing in wastewater and discarded lychee shell to prepare different types of biochar materials.Structural characterization,chemical composition characterization together with the measurement of the capacities of micropores adsorbing methylene blue were used to compare the structural differences amont these biochar materials prepared.The electrochemical performance differences of the different types of biochar prepared were evaluated with several electrochemical techniques to screen out the biochar with best comprehensive performance.The screened biochar was mixed with chitosan（CS）in a certain proportion to modify the surface of glassy carbon electrode（GCE）to prepare an electrochemical sensor for the detectation of environmental pollutants.It was found that the micro-surface of direct heating phosphoric acid activated spirogyra biochar material（DH-PSC）is relatively porous.Elemental analysis showed that DH-PSC is rich in C,O and P elements.It has many structural defect sites and absorbed the most methylene blue through micropores.Also,the signal to the redox peak was enhanced mostly by DH-PSC.Therefore,DH-PSC/CS was used to modify the surface of GCE to facilitate its response to nitrite（NO₂^-）and obtain the strongest response signal in PB buffer solution at p H 4.0.In this thesis,differential pulse voltammetry（DPV）was used to establish an analytic method to detect nitrite with a relatively wide linear range(0.02-6 mmol·L^-1)and a lower detection limit of 8.29μmol·L^-1.In addition,for the stage heating phosphoric acid activated lychee shell biochar（SH-PLSC）,dense pores as well as abundant structural defect sites were found in its microstructure.The carbon,oxygen and phosphorus elements were account for a large proportion of its composition.It possessed a high adsorption capacity for methylene blue,and exhibited an excellent electrochemical performance,and thus was used to modify the GCE electrode by being mixed with CS to detect hydroquinone（HQ）and catechol（CC）,respectively.The experimental results showed that there was a maximum response signal in the PB buffer solution at p H of 6.6.In this thesis,square wave voltammetry（SWV）was applied to set up a analytic method to detect HQ and CC with the linear ranges of 10-100μmol·L^-1 and 100-2000μmol·L^-1,and detection limits of 1.23 and 0.44μmol·L^-1,respectively.