Catalytic Activation Of Peroxymonosulfate By Co/Carbon-based Materials For The Degradation Of Dinitrophenol

Nitrophenols are widely used in petrochemical,agriculture,printing,dyeing,medicine and other industries,but they pollute the environment and ecosystem in the process of production and application.Nitrophenol organic pollutants are carcinogenic,teratogenic,mutagenic,bioaccumulative,and resistant to chemical/biological degradation,and they pose potential hazards to human body and ecological environment.Therefore,it is of great scientific significance and application value to explore a feasible and efficient treatment method for nitrophenol pollutants.Presently among the various treatment methods for nitrophenols,the sulfate radical based advanced oxidation processes are popular,because they have some advantages,such as rapid and thorough oxidation,broader pH applicability and high efficiency.Peroxymonosulfate is widely used in SR-AOPs due to its asymmetrical structure and easy activation property.Thermal activation,alkali activation and ultrasonic activation are common activation methods of PMS.Compared with them,the homogeneous catalytic activation of PMS by transition metal ions and the heterogeneous catalytic activation of PMS by carbon materials have advantages of mild reaction conditions,easy operation and high efficiency.Co2+and graphene show the best catalytic activity for PMS in the homogeneous transition metal catalyst system and heterogeneous carbon material catalyst system.However,Co2+homogeneous catalytic system has some problems,such as secondary pollution caused by residual ions and difficulty to separate and recycle.For the heterogeneous catalytic activation of PMS by graphene,the chemical inertness caused by the electronic layout of sp2-hybrid C limits the reaction efficiency and stability of the catalytic activation of PMS by graphene.In addition,the adsorption performance of organic pollutants by graphene needs to be further improved.These problems with SR-AOPs technology have become important constraints for its further development and application.Therefore,it is of great significance to develop cobalt/carbon based heterogeneous catalytic materials with good structural stability,low metal ion leaching rate,high catalytic activation efficiency,strong adsorption performance and easy separation and recovery.In view of the problems,a series of heterogeneous cobalt/carbon-based materials,such as meso-Co3O4,nitrogen doped graphene aerogels,cobalt/nitrogen co-doped graphene aerogels and carbon nitride/nitrogen doped graphene aerogels,were designed and prepared.The structure activity relationship between catalyst structure,composition,morphology and catalytic performance was studied systematically.On this basis,catalytic activation of PMS by the above catalytic materials for the degradation of DNBP was investigated,and the study provided theoretical and experimental basis for the creation and application of stable,efficient,easy to recover and reuse heterogeneous PMS activated catalytic materials.The main research contents and results of this paper are as follows:(1)Mesoporous Co3O4(meso-Co3O4)heterogeneous catalysts were constructed based on lattice constraint and structure modification,which solved the problems of catalyst loss and secondary pollution in the process of homogeneous catalytic activation of PMS.The Co2O3 lattice inhibited cobalt ions from leaching,so the uniform dispersion of active centers was achieved.Mesoporous structure increased the contact and transport channels between Co and PMS,so it provided more adsorption sites for organic pollutants and improved the catalytic activation efficiency.The feasibility of a simple and novel approach for preparing mesoporous Co3O4 catalysts by precipitating of Co(OH)2/EW in EW/water colloidal solution and postcalcination treatment was studied.The synthesized mesoporous Co3O4 materials were of high crystallinity and large specific surface area.The organic groups in egg white could help to inhibit the excessive growth of Co3O4 grains and form mesoporous structure of Co3O4.The synthesized mesoporous Co3O4 materials were applied to activating PMS for the catalytic degradation of DNBP in aqueous solution.The result showed the mesoporous Co3O4 materials exhibited excellent reproducibility and catalytic performance.(2)Based on the idea of electronic properties and structural morphology modulation,Ndoped graphene aerogels(NGAs)heterogeneous catalysts were developed to solve the problems of low catalytic and adsorption capacity in the activation of PMS by non-metallic carbon based graphene.The spin distribution and charge distribution of graphene sp2-hybrid C were changed by N doping,and the interaction and electron transfer between C atoms and PMS were enhanced.The multi-scale pore structure of aerogel promoted the efficient adsorption and oxidation degradation of organic pollutants.To achieve these goals,NGAs materials with interconnected hierarchical porous structures were facilely prepared via hydrothermal process in the mixed aqueous solution of EDA and urea and post-freeze-drying treatment.The prepared NGAs were employed as metal-free carbocatalysts in the adsorption of DNBP and the activation of PMS for DNBP degradation in aqueous solution.(3)Co/N co-doped graphene aerogel(Co/NGAs)composite catalysts were constructed based on the research idea of excellent catalytic properties and synergistic coupling of cobalt based and carbon based materials.N doped graphene aerogels had advantages of large specific surface area,strong adsorption properties and active groups,so organic pollutants stable anchored,uniform dispersed and accumulated in the graphene carbon carriers.The catalytic transport cycle was promoted by the special electron transfer effect between cobalt and the carrier,so PMS was efficiently and rapidly activated.To achieve these goals,a facile "one-pot"and post-freeze-drying treatment approach for Co/NGAs composite.The prepared Co/NGAs were employed as metal-carbocatalysts in the activation of PMS for DNBP degradation in aqueous solution.The result showed Co doping improved the electron transfer ability of NGA,which maked the O-O bond in PMS easy to be dissociated to form active radicals,so the degradation rate of DNBP is improved.(4)g-C3N4/N doped graphene aerogel(g-C3N4/NGAs)composite catalysts were developed based on the study idea of semiconductor photocatalysis and the synergistic catalytic activation of graphene carbon based catalysts.The conductivity of graphene was used to improve the efficiency of carrier separation.g-C3N4 with similar structure to graphene could promote the electron transfer between carbon and PMS to form a visible light/heterogeneous catalyst composite activation system,which could realize the efficient and rapid activation of PMS and enhance the degradation effect of organic pollutants.To achieve these goals,the g-C3N4/NGAs composites were prepared with a method by g-C3N4 as a nonmetallic semiconductor material composited with GO and post-freeze-drying.The prepared g-C3N4/NGAs were employed as nonmetal-carbocatalysts in the photocatalysis of PMS for DNBP degradation in aqueous solution.The result showed photoactivation was an important activation method,which greatly improved the efficiency of activated PMS.