Hierarchically Porous Silicon–Carbon–Nitrogen Hybrid Materials Towards Highly Efficient And Selective Adsorption Of Organic Dyes

Polymer-derived Si-C-N ceramics possess excellent properties, such as high temperature resistance and chemical inertness, which have been used in high temperature materials, electrode materials and electrical engineering fields. Thus, the latest research has been dedicated to developing new functional properties of Si-C-N material. In this thesis, the nickel-containing hierarchically macro/micro-porous Si-C-N hybrid material was presented with novel functionalities of selective and efficient adsorption for organic dyes. The hybrid material was conveniently generated by pyrolysis of commercial polysilazane(PSZ) at lower temperature(600 oC) coupled with the addition of polydivinylbenzene microspheres(PDVB) as sacrificial fillers.First, the PSZ, PDVB and Ni Cp2 were used as starting materials to prepare the precursor mixture, followed by pyrolysis in a vacuum furnace to obtain the Si-C-N porous material. Meanwhile, the pyrolysis behaviors of different components derived from the precursor mixture were tracked by TGA/DSC-MS. Second, PXRD, Raman,and XPS tests were carried out for determination of crystal structure, composition of free carbon as well as elemental composition of different pyrolysis products. Besides,SEM and nitrogen adsorption-desorption tests were couduced to characterize the macro/micro-porous structure of Si-C-N hybrid material. Third, the macro/micro porous Si-C-N hybrid material with large specific surface area and interconnected pore structure was used as the targeted absorbent to systematically evaluate the adsorption kinetics and adsorption isotherm towards methyl blue and acid fuchsin.The adsorption experiments were also carried out on several dyes with different structures.Owing to the Van der Waals force between sp2-hybridized carbon domains of Si-C-N matrix and triphenyl structure of dyes as well as electrostatic interaction between dyes and Si-C-N material, the macro/micro porous Si-C-N hybrid material exhibits high adsorption capacity and good regeneration and recycling ability for the dyes with triphenyl structure, such as methyl blue(MB), acid fuchsin(AF), basic fuchsin(BF) and malachite green(MG). The adsorption process is determined by both surface adsorption and intraparticle diffusion. The well-known mass transfer resistance caused by micropores during the diffusion process can be greatly reduced by the presence of interconnected macropores. According to the Langmuir model, the adsorption capacity is 1327.7 mg/g and 1084.5 mg/g for MB and AF, respectively,which is much higher than that of many other adsorbents. On the contrary, the porous Si-C-N hybrid materials do not adsorb several dyes with azo benzene structures, such as methyl orange and congo red.Thus, the hierarchically macro/micro-porous Si-C-N hybrid material from a facile and low cost polymer-derived strategy provides a new perspective and possesses a significant potential in the treatment of dye wastewater with complex organic pollutants.