Study On The Preparation And Performance Of Building And Environmental Catalytic Materials Based On The Enrichment Of Heavy Metal Cadmium Kenaf Straw

For a long time,frequent human activities have caused serious soil heavy metal pollution and threatened ecological security.The heavy metals are absorbed by agricultural products and enter the human body through the food chain,endangering human health.Compared with chemical and physical soil pollution prevention and control measures,phytoremediation technology has the advantages of environmental friendliness,safety,and low cost,and has been widely used in the treatment of heavy metal pollution and site pollution in mining areas.However,during the implementation of phytoremediation technology,a large number of heavy metal-rich plant bodies are produced,and its safe and reasonable treatment is a major problem in the prior art.Plants that accumulate heavy metals are often treated as waste at this stage,which not only wastes plant resources,violates the concept of recyclable development,and may cause secondary pollution at the same time.Therefore,seeking common technologies that are harmless,resource-based,and environmentally friendly to heavy metal-rich plants has become the key to whether phytoremediation technology can be promoted and applied in the remediation of heavy metal-contaminated soils.Kenaf straw core enriched with heavy metal cadmium is the research object in this article.Kenaf straw core and fly ash-based polymer,hydrophobic kenaf straw core-based cement mortar,geopolymer catalyst,Cd S@C photocatalyst were prepared separately to realize the multi-field application of enriching heavy metal cadmium kenaf straw core.There are mainly the following four parts:（1）Using sodium silicate and sodium hydroxide as alkali activator,fly ash was mixed with cadmium kenaf stalk which had been treated properly in a certain proportion to prepare fly ash base polymer of kenaf stalk core.After standard curing to a certain age,the mechanical properties,microstructure and physical and chemical properties of the geomer were tested by electronic universal testing machine,SEM,IR,TGA,etc.,and the fixation effect of heavy metal Cd²⁺was evaluated by horizontal shock method.The experimental results showed that the dry density of geopolymer was between 0.7 and 1.6 g/cm³,which made the material lighter.When the straw core content was 3 wt%,the compressive strength and flexural strength of the geopolymer after curing for 28 d were 12.61 MPa and 2.14 MPa,which reached the standard of building mortar material.The geopolymer had a good fixation effect on Cd²⁺,and the fixation rate reached 99.9%.This scheme can not only prepare a new lightweight geopolymer building material,but also realize the large-scale and safe utilization of enriched heavy metal kenaf straw,and avoid the problem of cadmium secondary pollution in kenaf straw core.（2）The hydrophobic kenaf straw core（HKC）was prepared by simple sol-gel method and used to produce biomatery-based cement mortar（CM）with excellent mechanical properties.The characterization of HKC was analyzed by SEM,XPS and IR,etc.The results showed that the coating based on silane successfully blocked the hydroxyl group on the surface of natural kenaf straw core（NKC）,and gave the stable hydrophobicity of HKC.Surface hydrophobic treatment reduced the water consumption in the preparation process of cement mortar,and inhibited the negative effect of straw absorbency on cement hydration reaction,which provided a larger space for the growth of hydrated calcium silicate gel（C-S-H）,which was conducive to the development of mechanical properties of CM.In the strength test,when the amount of HKC was 6 wt%,the flexural strength and compressive strength of hydrophobic kenaf straw core cement mortar（HKC-CM）for 28 d reached 5.7 MPa and 16.43 MPa respectively,which was significantly improved compared with natural kenaf straw core cement mortar（NKC-CM）.Even after the addition of HKC was doubled,the mechanical properties of HKC-CM did not significantly decrease.These results prove that the hydrophobic treatment can realize the large-scale use of straw biomass in the construction field,and ensure that the corresponding building materials have excellent mechanical energy,which provides an idea for the industrial utilization of agricultural waste and the design of green materials in the construction field.（3）In this study,grid nano-Fe₃O₄ geopolymer catalyst was synthesized in situ from kenaf straw core of agricultural waste and fly ash of industrial waste,and was used to activate persulfate to degrade organic pollutants.The results of SEM,XRD and XPS confirmed that after calcined at 700℃in nitrogen atmosphere,kenac straw core was transformed into biochar and Fe₂O₃ in fly ash was further reduced,thus Fe₃O₄ nanoparticles were generated in situ.Fe₃O₄nanoparticles were meshlike in the geopolymer material,which was conducive to contact with the reactants and promote catalysis.The geopolymer catalyst had a good catalytic effect on persulfate.When the catalyst concentration was 0.6 g/L,100 m L and 50 mg/L methylene blue was catalytically degraded by PMS within 90 min.ESR experiments showed that the prepared catalyst activated PMS during the reaction process to generated active species（O₂·^-,SO₄·^-,and·OH）,thus achieving the degradation of methylene blue.It provides a new idea for the recycling of solid waste and catalytic degradation of organic wastewater.（4）In this experiment,a carbon-supported Cd S photocatalyst（Cd S@C）was prepared by using a combination of pyrolysis carbonization and hydrothermal reaction,using cadmium-enriched kenaf straw core.XRD and XPS proved the in-situ generation of Cd S.Other characterization methods proved that the Cd S@C composite had a wide light absorption range,a lower band gap energy（2.48 e V）,and an instantaneous photocurrent response（25 n A）.The carbon material base also made the resistance of the catalyst lower than that of pure Cd S material,indicating that it had good light-harvesting capacity and photocatalytic efficiency.The Cd S@C composite material showed good catalytic degradation effect under visible light.The composite material prepared under the optimal conditions could photocatalytic degradation of100%of 100 m L 100 mg/L tetracycline hydrochloride solution in 50 min,and proved that the photocatalytic degradation performance of Cd S@C composite material is due to the successful formation of active species O₂·^-and·OH in the photocatalytic process.This provides new ideas for the application of cadmium-rich plants.