Design And Synthesis Of Hydrothermal Carbon And Modified Carbon-Based Materials With Their Adsorption And Catalytic Performances And Mechanisms Toward Typical Endocrine Disrupting Chemicals

Recently,hydrothermal carbon,as a novel type of carbon material,has shown great application prospects in the fields of adsorption,porous carbon preparation,catalyst supports,and clean energy.Compared with traditional carbon materials,it has the advantages of abundant sources of biomass components,environmentally-friendly preparation methods,rich oxygen content,and adjustable surface physical and chemical properties.In this thesis,a series of hydrothermal carbons and their modified carbon-based materials have been designed and synthesized based on critical water environmental issues by endocrine disrupting chemicals（EDCs）,combined with the potential of carbon-based materials used in adsorption and catalysis reactions.Various advanced characterization techniques were applied to qualitatively and quantitatively analyze the structures,compositions and morphologies of the as-prepared materials;the adsorption and catalytic performances toward several typical EDCs in water were systematically investigated activated by peroxides such as hydrogen peroxide（H₂O₂）or peroxymonosulfate（HSO₅^-,PMS）;the influencing factors and corresponding mechanisms were explored;the intrinsic relationships between the microstructure properties of the materials and activities were proposed based on the reaction systems.Besides,the stability of the materials and possible applications for practical water treatment are evaluated through cyclic testing and standard addition experiments in actual water samples.The study content is composed of five chapters,details are as follows:Hydrochars（HCs）have been synthesized from pinewood biomass by high-temperature pyrolysis and applied as environmental-friendly adsorbents and catalysts in the removal of bisphenols from water.It is found that the prepared HCs have enlarged specific surface area and structural oxygen defects.The hydrochar pyrolyzed at 800℃（HC-800）showed the superior adsorption and catalytic performances toward BPS and BPF removal in a wide pH range,and the removal efficiencies were hardly inhibited by the coexistent inorganic anions and humic acid.Particularly,the nonradical reaction is the dominated catalytic oxidation process in H₂O₂/HC-800 system,different from the traditional radical-based process with persistent free radicals on hydrochars derived from low-temperature pyrolysis.The H₂O₂/HC system can achieve satisfiedremovalefficienciestoward the bisphenols mixed in the actual water samples,which provide a novel route for actual application of EDCs removal via the synergistic adsorption and nonradical catalysis.A series of N-doped hydrochars（NHCs）have been prepared from pinewood biomass and used in carbocatalysis toward PMS activation to degrade several typical EDCs.Herein,nitrogen heteroatoms mediation onto biomass-based hydrochar is achieved by a facile doping then heat-treatment method.The doped nitrogen located at the defects of graphitic structure could activate the adjacent sp²-hybridized C in the carbon-based framework,and further regulate the concentrations and types of PFRs on hydrochar.The NHCs presented enhanced catalytic degradation of BPA,BPF,E1,and E2 via PMS activation,and fitted with pseudo-first-order reaction,which showed a significant improvement over the activity of pristine hydrochar.Mechanistic studies revealed that graphitic N not only shows a strong electron transfer to facilitate PMS activation in a nonradical pathway,but also induces the formation of oxygen-centered PFRs from the structure defects for a radical oxidation pathway.In addition,the PMS/NHC system demonstrates efficient degradation and satisfactory stability for real water treatment,demonstrating a great promising route to degrade the organic pollutants efficiently for green remediation.To further improve the stability toward the two-dimensional（2D）structure of nitrogen-doped carbon-based materials,a three-dimensional（3D）interconnected porous N-doped carbon（CN-3）was synthesized by stepwise pyrolysis of dicyandiamide and nanocellulose.A solid-state-growth and rolling-up mechanism was proposed for the stepwise transformation from stacking layered structures（melem and g-C₃N₄）into CN-3 with 3D interconnected network nano-architectures,based on structural characterization and comparative analysis.It was found that CN-3 presented～100%estrone（E1）removal in 10 min,much higher than the layered carbons.The prepared CN-3 presented a superior catalytic performance of PMS activation for E1 removal,which was 52-fold of that on the layered carbons.Interestingly,free radicals（HO·and SO·₄^-）were less generated from the high-degree carbonized carbon,showing the temperature-dependent mechanisms from radical-dominated reaction to nonradical oxidation via enhanced singlet oxygenation.The stabilized 3D functional carbons transformed from nanocellulose offer attractive insights to the relationship between the carbon structural transformation and catalytic PMS activation to induce different oxidative pathways,and are expected to extend the practical application of the metal-free catalytic systems.A kind of iron（hydr）oxides immobilized hydrochar（Fe/HC）by pyrolysis of Fe²⁺treated hydrothermal carbonization（HTC）of pinewood was synthesized,characterized,and applied to remove estrogens in water.Batch experiments results showed that estrogens could be efficiently removed over Fe/HC material under a wide pH range of 4-9.It was found that the desirable removal of estrogens is ascribed to the synergistic effect between catalysis and adsorption,which is different from traditional homogeneous Fenton oxidation reaction.The interactive effects of iron and H₂O₂ with persistent free radicals（PFRs）from hydrochar in the removal of several estrogens are systematically investigated to understand the removal performance and related mechanism,for a better understanding of the role of multi-component in reaction systems.In order to get rid of the problems from low atomic utilization,poor catalysts durability and difficult after-treatment,an Fe–and nitrogen-codoped carbon（Fe–N–C）originated from nanocellulose-based hydrochar,nitrogen source,and iron salt precursor was developed for improved PMS activation and identification of exclusive role of each species.The characterization results demonstrated the Fe–N–C possessed the coexistence of atomic Fe cluster and Fe–N configuration sites,and the particle size effects happened in the structural transformation,which generated the interconnected bamboo-shaped 3D tubular structures.Besides,Fe–N–C catalyst exhibited excellent efficiencies in oxidative degradation of various aromatic compounds,including PE,BPA,BPF,BPS,E1,E2 and SMZ.For example,BPA could achieve nearly 100%removal within 10 min,fitted well with the pseudo-first-order kinetic equation,and the rate constant is 0.45 min^-1.Further mechanistic insights highlighted that enhanced PMS activation with Fe–N–C for catalytic oxidation were benefitted from both radical and singletoxygen（¹O₂）generated nonradical pathways.This Fe–N–C/PMS-coupled process provides a designed strategy to construct the highly active and stable metal-nitrogen-codoped hydrothermal carbons,and deepens insights on structure-activity-stability relationship for persulfate-based environmental remediation.The results of this study are beneficial to enrich the theoretical supports and technical applications of the functionalized hydrothermal carbon and its modified carbon-based materials for the adsorption and catalytic oxidation reactions toward endocrine disrupting chemicals in water environment.Such fascinating hydrothermal carbon-based materials not only provide potential functional strategies for the optimal design and controllable synthesis,but also afford tremendous opportunities to extend their applications in new catalytic chemical reactions and to address the bottlenecks in cross fields toward sustainable production.Considering the wide types of biomass source,insufficient structural engineering methods,and complex reaction systems,future research still needs to develop the specific structural properties and potential applications for hydrothermal carbon-based materials,and advanced water treatment technologies,and their corresponding relationships.