Design,Synthesis And Performance Study Of G-C₃N₄ And MoS₂-based Non-noble-metal Photo/piezo-catalysts

In recent years,environmental pollution and energy shortages have become global concerns.The development of green and efficient technologies for energy conversion and environmental remediation has become particularly urgent.Photocatalysis and piezo-catalysis technologies,as well as the combination of both in piezo-photocatalysis,can achieve the comprehensive utilization of various renewable energy sources existing in nature,such as solar energy,water flow,wind energy and tidal energy.These serve as environment-friendly and sustainable methods,which have attracted widespread research interest.Non-noble-metal-based photo/piezo-catalysts have received considerable attention due to their low cost,abundant sources and excellent catalytic activity.However,current photo/piezo-catalysts commonly suffer from issues such as narrow light absorption range,low piezo-response,inefficient charge carrier separation and transport as well as limited active sites.Addressing these challenges is currently the focus and difficulty of research.Therefore,the study of non-noble-metal-based photo/piezo-catalysts with efficient light response and piezoelectricity is of great significance.This thesis focuses on the design,synthesis and performance study of the novel photo/piezo-catalysts based on non-noble-metal graphitic carbon nitride（g-C₃N₄）and molybdenum disulfide（MoS₂）with good light and piezo-response.Through the modification of the compositions and structures of catalyst,the effective utilization of environmental solar and mechanical energy has been achieved,greatly enhancing the catalytic degradation of pollutants and hydrogen evolution efficiency.Based on comprehensive characterizations and theoretical calculations,the novel structures with high activity and unique reaction mechanisms for the designed catalysts have been elucidated.The research provides novel insights for designing novel non-noble-metal-based photo/piezo-catalysts,offering possibilities for the comprehensive utilization of various renewable green energies in nature.The research achievements of the thesis are as follows:1.By the ultrasonic-assisted in-situ growth method,0D/2D sulfur quantum dots（S QDs）/ultrathin nanoporous g-C₃N₄ nanosheets（LN CN）composite was prepared.Characterization studies including XRD,XPS,AFM,TEM and HRTEM indicate the uniform and tight anchoring of sulfur quantum dots with the size of 1-3.5 nm on the surface of ultrathin nanoporous g-C₃N₄,forming a compact Z-scheme heterojunction.This structure enhances the redox activity and migration efficiency of photogenerated electron（e^-）-hole（h⁺）and induces the generation of·OH（hydroxyl radicals）and·O₂^-（superoxide radicals）.The photocatalytic activity studies under visible light show that the optimized 10%S QDs/LN CN achieves nearly 100%degradation of Rh B within 90 min,which is 1.9 times higher than that of pure LN CN and demonstrates high stability.2.A novel sailboat-like vertical MoS₂ nanosheet（SVMS）with controllable phase composition and enhanced piezo-response was synthesized through a facile liquid-phase mixing and calcination method.Experiments,molecular dynamics simulation as well as density functional theory calculations demonstrate that the dense 1T/2H phase interfaces and vertical interfaces in SVMS are induced by stress during the nucleation and growth process.The enhanced in-plane/out-of-plane polarization,multi-directional high piezo-response and abundant active edge sites in SVMS eliminate layer dependence and generate higher piezo-potential.Under ultrasonic or stirring conditions,SVMS（2H）with the highest piezo-response exhibits degradation rates and hydrogen evolution rates for piezo-catalysis of 0.16 min^-1 and 1598μmol·g^-1·h^-1,respectively,which are 1.6 times and 3.1 times higher than that of 2D few-layer MoS₂ nanosheets.Under water flowing,94%of Rh B is degraded within60 min.The piezo-catalytic mechanism of SVMS primarily involves e^-,h⁺,and·O₂^-.3.High piezo-responsive（9.1 pm/V）nitrogen-defective nanoporous g-C₃N₄ nanosheets（NPCNs）were prepared by synergistic thermal etching and gas-shocking,followed by surface protonation.Further,through electrostatic self-assembly,a non-noble-metal Z-scheme PC（H）/VM heterojunction with broad spectrum absorption,strong piezo-response,and tight triple-interface was constructed that achieved efficient multi-source-driven piezo-photocatalysis.By systematically controlling the morphology,grain size,phase composition and surface conditions of the catalyst,the optimized PC（3.6H）/VM（u2）exhibits the highest piezo-photocatalytic rates of degradation of organic dyes and antibiotic under visible light and ultrasonic wave(Rh B:0.57 min^-1,MO:0.05min^-1,MB:1.56 min^-1,TC:0.06 min^-1)as well as hydrogen evolution(3528μmol·g^-1·h^-1).Benefiting from the up-conversion effect induced by nitrogen defects,it also demonstrates efficient piezo-photocatalytic activity under near-infrared light(λ_max=1000 nm)(Rh B:0.21 min^-1,H₂:2355μmol·g^-1·h^-1).4.A supramolecular precursor of melamine hydrochloride-cyanuric acid-molybdate anion（MAH-MAO/Mo）was constructed through protonation and hydrolysis processes.Further thermal condensation with sulfur yielded micron-sized vertical MoS₂/porous foam-like g-C₃N₄ heterojunction（CMx）with high piezoelectric and light response that can be controlled by changing the x value of Mo content.CM0.05,mainly composed of g-C₃N₄,exhibits piezo-photocatalytic activity,while with increasing x value,the contribution of CMx’s piezo-catalytic activity significantly increases.The CM0.77 with the best performance shows piezo-catalytic degradation rates for Rh B,MO,MB,and TC under ultrasonic wave in the dark:0.47 s^-1,0.05 s^-1,0.21 s^-1,and 0.03 s^-1,respectively;and piezo-catalytic hydrogen evolution rate of 2431μmol·g^-1·h^-1.