Biochar-based Composites Synergistic Adsorption-Photocatalytic Efficient Degradation Of Organic Dyes

The pollution of natural waters by various organic dyes has become one of the prominent environmental problems which need to be solved urgently.Any single treatment method of dye wastewater has some limitations.The integrated adsorption-photocatalysis technology has the advantages of high removal efficiency,environmental friendliness and low energy consumption,which is considered to have a broad application prospect in the efficient removal of dye pollutants from aqueous solutions.Thus,it is crucial to develop the outstanding composite material with high adsorption efficiency and photocatalytic performance.Among many functional carbon materials,biochar has become a potential support of adsorption-photocatalytic composites due to its advantages such as low price,large specific surface area,abundant surface functional groups and strong adsorption capacity,which has gained extensive attention.In this thesis,based on biochar,two methods of functionalizing the pristine biochar were developed,and a porous biochar-based composite photocatalyst was obtained.Combining the advantages of functional biochar and inorganic semiconductor materials,the adsorption-photocatalysis synergy is maximized to efficiently remove organic pollutants.Meanwhile,the structure-activity relationship between enhanced adsorption and photocatalytic performance and texture properties,energy band structure,electronic transport between interfaces,and photoelectric properties was systematically discussed,and possible mechanisms and pathways for the removal of methylene blue model pollutants were revealed.The specific content of this work are as follows:1.Novel synthesis of porous biochar supported Ag3PO4 photocatalyst for synergistic removal of aqueous methylene blue under visible light irradiationTo take advantage of the synergy between adsorption and photocatalysis,we synthesized a novel porous bamboo biochar supported Ag₃PO₄ photocatalyst（AP/PBB）through a facile ball mill-pyrolysis-precipitation method.The AP/PBB composite exhibited extremely high methylene blue（MB）degradation rate（95.6%）after 1h of visible light irradiation.This can be attributed to the synergistic interaction between PBB’s rapid adsorption ability and AP’s high photo-oxidative capability.Characterization results manifested that the irregular Ag⁰ and AP particles were dispersed uniformly on the surface of PBB owing to its large specific surface area and porosity to provide more active sites compared with common biochar,which is beneficial for the improvement of adsorption and photocatalytic performance.Besides,Ag⁰ presented in the AP/PBB acted as a bridge for charge transmission enhancing visible light harvesting as well as the separation and transfer efficiency of charge carriers and thus significantly improved the photocatalytic performance of the composite.This work affords a novel strategy for preparing related efficient porous biochar supported photocatalysts for effective removal of organic contaminants form wastewater.2.Preparation of MgO/CeOCl/porous biochar composite for photocatalytic degradation of methylene blueThe preparation method of the previous research work is relatively cumbersome,and also wastes MgO template agent.To solve this problem,a simple one-step method was developed for the successful synthesis of MgO/CeOCl/porous biochar nanocomposites（MgO/CeOCl/PBC）.FT-IR results show that there are more-OH and NH groups on the surface of the composite,which is conducive to the adsorption and activation of reactant molecules.Meanwhile,under light irradiation,it is easy to be photosensitized to produce more reactive oxygen free radicals with strong oxidation.In addition,the results of texture properties and photoelectric properties show that the composite has a high specific surface area,uniform pore size distribution and rapid photogenerated charge separation efficiency,which are conducive to the adsorption of the reactant molecule MB and play a role in promoting the photocatalytic degradation of MB.3.Study on the mechanism of CeO2/g-C3N4 Z-Scheme heterojunction photocatalyst prepared by ball milling in the synergistic removal of methylene blue by adsorption-photodegradationIn this work,a novel CeO₂/g-C₃N₄ Z-Scheme heterojunction photocatalyst was obtained by direct high-energy ball milling CeO₂ and g-C₃N₄.In comparison to individual CeO₂ and g-C₃N₄,the 70%CeO₂/g-C₃N₄ nanocomposites showed stronger UV light response,higher charge carrier separation efficiency,greater photodegradation potential,higher photocurrent intensity,and faster electron transfer,indicating much better photocatalytic activity.The kinetic model simulation results show that there is a synergistic interact between adsorption and photodegradation of the CeO₂/g-C₃N₄ nanocomposites,and a strong positive correlation（r=0.834 and r_s=0.777）between adsorption and photocatalysis was identified.Thus,adsorption can promote photodegradation by accelerating the kinetics,while photodegradation can regenerate adsorption sites.This work provides not only a strategy for the facile synthesis of Z-scheme heterojunction photocatalysts but also a novel perspective for better understanding the synergy between adsorption and photocatalysis.