Advanced Designing Of Photocatalytic Materials With Layered Structures For Improved Photocatalytic Degradation

Environmental pollution and energy shortage are two pressing challenges that currently threaten the sustainable development of human society.For instance,even at extremely low concentrations,organic pollutants in water can exhibit remarkably high biological toxicity.Traditional pollution remediation techniques such as centrifugation,filtration,precipitation,adsorption,and electrocatalysis face limitations in effectively removing organic compounds,while also consuming substantial amount of energy.Hence,the development of an effective"green technology" becomes imperative to convert toxic pollutants into non-toxic substances.In this regard,semiconductor photocatalysis technology emerges as a promising strategy to address both the energy crisis and environmental issues.By utilizing semiconductor materials as catalysts,this technology has shown potential in efficiently transforming harmful pollutants into harmless compounds while employing solar energy.Layered semiconductor photocatalytic materials,such as bismuth oxy-bromide(BiOBr)and graphitic carbon nitride(g-C3N4),have demonstrated their ability to degrade organic pollutants.These materials have earned significant attention due to their excellent photoelectric properties and high chemical stability.However,their widespread application is hindered by challenges such as rigorous recombination of photo-generated carriers,delayed charge dynamics,and surface reaction kinetics.In this study,various methods were employed to synthesis layered semiconductor photocata-lytic materials,and modifications were employed through structural design,charge transfer control,surface modification,and band matching strategies.These modifications aimed to enhance the photocatalytic degradation activity for organic pollutants.The foremost research findings of this thesis are summarized as follows:(1).BiOBr is a novel ternary layered semiconductor belong to the Ⅴ-Ⅵ-Ⅶ group.It exhibits a unique graphene-like layered structure comprising a single layer of[Bi2O2]2+ and a double layered of Br-,resulting in an inherent internal electric field.I this study,BiOBr layered structures were synthesized using the hydrothermal method,where the built-in electric field(IEF),oxygen vacancies,and growth along the {001} direction were induced.By controlling the exposure of BiOBr to the {001} plane orientation and manipulating the generation of oxygen vacancies through the optimization of ethylene glycol(EG)concentration,we achieved desirable outcomes.The introduction of abundant oxygen vacancies in BiOBr induced an IEF within the layers,effectively suppressing the recombination of photo-generated e--h+ pairs and enhancing the photocatalytic activity.For instance,the optimized BiOBr-2.5 catalyst exhibited a remarkable degradation rate,degrading 99.8%of rhodamine B(RhB)within three hours under visible light.Compared to the pure BiOBr,the degradation rate of BiOBr-2.5 was 9.8 times higher.Therefore,this research presents a novel approach to synthesize photocatalytic materials.By optimizing the amount of EG,which in turn affects the IEF and oxygen vacancy concentrations in the material.This optimization strategy significantly enhances the efficiency of photo-generated e--h+ pairs,leading to improved visible light photocatalytic degradation of RhB.(2).Nonmetallic elements,including sulfur(S),phosphorus(P),and boron(B),were introduced as dopants into the graphitic carbon nitride(g-C3N4)to modify its morphology and electronic structure,aiming to enhance its photocatalytic activity.The photocatalytic performance of the prepared nonmetallic-doped g-C3N4 materials was evaluated by investigating their ability to degrade methyl blue(MB)under visible light irradiation.During a 2-hour photo-degradation process under visible light,the removal rates of MB were approximately 99%,87%,60%,and 40%for S-g-C3N4,P-g-C3N4,B-g-C3N4,and pure gC3N4,respectively.Among the different dopants,sulfur-doped graphitic carbon nitride(S-gC3N4)exhibited the highest activity,with a pseudo first-order reaction constant "K" of 0.044 min-1,which is 7.3 times higher than that of pure g-C3N4.This enhanced activity of S-g-C3N4 can be attributed to its narrower band gap energy of 2.4 eV,allowing it to absorb a greater range of visible light.Compared to the original g-C3N4 and other nonmetallic-doped g-C3N4 composites,S-doped g-C3N4 demonstrated the strongest photodegradation activity.Additionally,the photodegradation pathway and mechanism of the nonmetallic elementdoped g-C3N4 material for MB were discussed.Shedding light on the underlying processes involved in the photocatalytic degradation.(3).Based on the previous sulfur(S)doping of g-C3N4,we expanded our research to develop composite materials by incorporating S-doped graphitic carbon nitride(GCN)with commercial activated carbon.These composites were employed for the photocatalytic degradation of pollutants.The incorporation of S doping resulted in a reduction of the energy band gap of activated carbon/GCN photocatalysts from 3.31-3.38 eV to 2.84-3.06 eV,thereby enhancing their absorption of visible light.The combination of S doping and activated carbon demonstrated a synergistic effect that significantly improved the photocatalytic degradation performance.For instance,the photodegradation rates of methylene blue after 80 minutes were 26%,43%,56%,73%,88%,and 99%for GCN-0,GCN-0.1,GCN-0.2,GCN-0.4,GCN-0.6,and GCN-0.8,respectively.With an increase in the sulfur doping content,the photocatalytic reaction constant "K" rose from 0.0035 min-1 to 0.041 min-1.This indicates that compared to pure graphitic carbon nitride,the K value for GCN-0.8 increased by 11.7 times.Therefore,the combination of activated carbon and a substantial amount of sulfur-doped GCN led to enhanced photocatalytic activity through altered charge transfer pathways and improved light absorption.This straightforward preparation process holds promise for the development of new environmental remediation materials for the photocatalytic degradation of methylene blue.(4).Furthermore,we employed metal elements(copper(Cu),manganese(Mn),and zinc(Zn))simultaneously for easy doping of g-C3N4 during high-temperature processes to enhance its photocatalytic performance.The synthesized M-g-C3N4 material was characterized and evaluated using techniques such as XRD,SEM,UV-vis DRS,and photocatalytic testing.Metal element doping resulted in a decrease in the bandgap of g-C3N4 compared to pure g-C3N4(with a bandgap of 2.79 eV).The bandgap energies of Cu-g-C3N4,Mn-g-C3N4,and Zn-g-C3N4 were measured as 2.70 eV,2.56 eV,and 2.49 eV,respectively.This indicates that metal doping effectively improves the electronic structure and visible light catalytic activity of the g-C3N4 photocatalyst.During the visible light-driven photodegradation process of methylene blue(MO)dye,the degradation rates of g-C3N4,Cug-C3N4,Mn-g-C3N4,and Zn-g-C3N4 were observed to be 60%,65%,75%,and 81%,respectively.These results highlight that the Zn-doped g-C3N4 photocatalyst exhibited the highest photocatalytic performance.This enhancement can be attributed to its lowest bandgap and the efficient separation ability of photogenerated electrons and holes in the Zn-doped gC3N4 photocatalyst.