Preparation Of Carbon Nitride Composite And Its Application In Pretreatment Of Samples

A new non-metallic material,graphitic carbon nitride（g-C₃N₄） can be used as sample pretreatment adsorbent due to its unusual numberous intrinsic properties,such as simple preparation method,excellent thermal and chemical stability,as well as good biocompatibility and non-toxicity.In this study,g-C₃N₄ was synthesized from melamine by using high temperature calcination.And nanoscale g-C₃N₄ （nano-g-C₃N₄） was prepared by alkali solution treatment,then,nanoscale g-C₃N₄ hybridized with CuO（nano-g-C₃N₄/CuO） which was prepared by a facile chemical precipitation method in water bath with heating.Meanwhile,nano-g-C₃N₄/UiO-66-NH₂ composites were synthesized by solvent thermal method.The g-C₃N₄ and nano-g-C₃N₄/CuO were utiliaed as the solid phase microextraction（SPME） coatings,respectively.The volatile and non-volatile components in food and environment were studied by gas chromatography.And the nano-g-C₃N₄/UiO-66-NH₂ composites were used as an adsorbent to extract food colourings in foodstuffs.The thesis is mainly divided into four chapters.In chapter 1,the general introduction,which included the structure,properties,preparation and application of g-C₃N₄ as well as its compounds are introduced.Then the concept and principle of solid phase extraction（SPE） were described.Dispersive solid-phase extraction（dSPE） was introduced on the basis of SPE.Meanwhile,the preparation,extraction method and extraction mechanism of SPME were introduced in detail.Finally,the research content and significance of this thesis were briefly expounded.In chapter 2,the as-prepared g-C₃N₄ was utilized as the SPME coating by means of layer-by-layer assembly with sol-SiO₂ as the binder.A HS-SPME based on g-C₃N₄ fiber coating coupled with GC and the flame ionization detection（FID） method was developed for the determination of food additives including methyl cinnamate,ethyl cinnamate,benzyl cinnamate,isobutyl cinnamate,and butylated hydroxytoluene（BHT）.The experiment improved the detection sensitivity by optimizing method of parameters such as extraction time,extraction temperature,desorption time,desorption temperature,stirring speed and ion strength.And also measure the linear range,precision and recovery.A new method for the rapid,sensitive and efficient detection of the flavors and preservatives in foods has been established.In chapter 3,nano-g-C₃N₄/CuO composite was prepared and used as the SPME coating for simultaneous determination of six PAHs from water and soil samples prior to gas chromatography（GC） analysis.Compared with nano-g-C₃N₄,CuO and bulk-g-C₃N₄/CuO,the results demonstrated that nano-g-C₃N₄/CuO provided higher adsorption affinity for PAHs than others.The composites were characterized by transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,thermogravimetric analysis（TGA）,X-ray diffraction（XRD） and Fourier transform infrared（FT-IR） spectroscopy.The optimum conditions for the target analyte were obtained by optimizing method of parameters such as extraction time,extraction temperature,desorption time,desorption temperature,stirring rate and NaCl concentration.The developed method was successfully applied to the analysis of various pollutants in environmental samples,and it is expected to provide a more effective method for the pretreatment analysis of trace compounds in complex samples.In chapter 4,nano-g-C₃N₄/UiO-66-NH₂ composite materials were prepared by solvent thermal synthesis.The as-prepared nano-g-C₃N₄/UiO-66-NH₂ composite was used as sorbent of dSPE to adsorption of six food colourings including tartrazine,amaranth,carmine,sunset yellow,allura red and brilliant blue from foodstuffs before High Performance Liquid Chromatography（HPLC） analysis.Compared with the traditional SPE,this developed method has the advantages of less solvent consumption,simple operation,short time and high recovery.The experiment improved the detection sensitivity by optimizing a series of parameters.A new method for simultaneous determination and quantification of a variety of food colourings in foodstuffs was established,and good experimental results were obtained.