Preparation Of Porous Silicon-based Organic Hybrid Materials And Removal Of Cr⁶⁺,Cd²⁺ And Pb²⁺

Currently,with the vigorous development of the photovoltaic industry,the solar-grade silicon material production has exceeded 400,000 tons in our country.According to statistics,40%of high-purity silicon materials will enter the cutting fluid in the form of sub-micron cutting sawdust.The direct discharge of fine cutting waste will cause serious environmental damage and waste of resources.Nanoporous silicon has attracted much attention due to its large specific surface area,good mechanical stability and high surface activity.On the other hand,based on a large number of literature researches,it is put forward that nanoporous silicon（NPSi）powder is prepared by metal-assisted chemical etching（MACE）using kerf loss silicon waste derived from diamond-wire saw cutting silicon ingot process,which not only comprehensively recovers and efficiently utilizes diamond wire cutting waste,but also organically functionalizes nanoporous silicon is employed for the rapid and efficient enrichment and removal of heavy metal ions(Cr⁶⁺,Cd²⁺ and Pb²⁺)from waste-water,which achieve the purpose of waste treatment.In this work,the MACE-etched nanoporous silicon using kerf loss silicon waste derived from diamond-wire saw cutting silicon ingot process is organically modified by chemical covalent coupling method and subjected to Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,Thermogravimetric analysis（TGA）,N2 adsorption-desorption curve and other detection methods,which were used to analyze various parameters such as structure,composition and specific surface area of the sample before and after modification.The results show that the modified nanoporous silicon can realize the rapid and efficient enrichment and removal of Cr⁶⁺,Pb²⁺ and Cd²⁺ from waste-water.The main contents and conclusions of the study are as follows:1.Preparation of nanoporous siliconThe composition and morphology of diamond wire-cut silicon waste was systematicly analyzed and carried out by acid leaching and high-temperature calcination to achieve effective removal of impurities.Nanoporous silicon containing nano-scale pores was prepared by silver nanoparticle-assisted chemical etching（Ag-ACE）.The results show that nano-scale pore structure appears on the surface of silicon particles,but it still retains the original polycrystalline structure,and its specific surface area and pore volume are significantly increased to 94.921m2/g and 0.206 cm3/g,which shows the properties of mesoporous materials.In addition,the surface of nanoporous silicon is rich in Si-OH after strong oxidation treatment,which lays a foundation for the surface modification of nanoporous silicon.2.Functional Nanoporous silicon APTES-NPSi,AAPTS-NPSi and AAAPTS-NPSi for Cr⁶⁺removal from aqueous solutionsNanoporous silicon（NPSi）powder was prepared by silver nanoparticle-assisted chemical etching（Ag-ACE）using kerf loss silicon waste derived from diamond-wire saw cutting silicon ingot process.NPSi was subsequently functionalized by APTES,AAPTS and AAAPTS to obtain APTES-NPSi,AAPTS-NPSi and AAAPTS-NPSi hybrid materials,respectively.The results indicated that APTES-NPSi AAPTS-NPSi and AAAPTS-NPSi can high-effectively adsorb Cr⁶⁺ from aqueous solution.The APTES-NPSi was highly pH dependent,the adsorption equilibrium achieved after 60 min and the maximum adsorption capacity of Cr.⁶⁺ reached up to 103.75 mg/g at room temperature.As for the AAPTS-NPSi and AAAPTS-NPSi,the adsorption rate was extremely fast and the adsorption equilibrium was reached whthin 10 min,and the maximum adsorption capacity was found to be 154 mg/g mg/g and 271.25mg/g at room temperature,respectively.Furthermore,the adsorption kinetics and adsorption isotherms were investigated,which is in good agreement with Langmuir adsorption isotherm and pseudo second order model.Additionally,recycling experiments showed the adsorbents could be regenerated by acid treatment without altering their properties.what’s more,the XPS,FT-IR analysis manifested that Cr⁶⁺ removal might be ascribed to the Cr⁶⁺adsorption on the surface organic functional group（protonated anime groups）by chemical chelating reaction and the reduction of Cr⁶⁺ to Cr3+.Therefore,the work proposes a facile and efficient approach to synthesize functionalized nanoporous silicon using kerf loss silicon waste for the Cr⁶⁺ removal from wastewater.3.Multifunctional Nanoporous silicon EDA-MAH-APTES-NPSi for Cd²⁺ removal from aqueous solutionsEDA-MAH-APTES-NPSi hybrid materials containing amino,imino and amide groups was prepared successfully by chemical covalent coupling technique for Cd²⁺removal.The results indicated that EDA-MAH-APTES-NPSi can high-effectively adsorb Cd²⁺ from aqueous solution,the optimum pH was recorded to be 5.5,the adsorption equilibrium was gradually reached after 120 min,and the maximum adsorption capacity was found to be 210.01 mg/g at room temperature.Furthermore,the adsorption kinetics and adsorption isotherms were investigated,which is in good agreement with Freundlich adsorption isotherm and pseudo second order model.Additionally,EDA-MAH-APTES-NPSi still maintained high adsorption capacity after-five successive regenerated cycles,which showed that EDA-MAH-APTE-S-NPSi had good adsorption regeneration performance.What’s more,the XPS and FT-IR analysis manifested that Cd²⁺ removal might be ascribed to the Cd-+ adsorption on the surface organic functional group（anime groups）by chemical chelating reaction and the ion exchange reaction.Therefore,the EDA-MAH-APTES-NPSi exhibited great potential for effective removal of Cd²⁺ from wastewater.4.Multifunctional Nanoporous silicon EDA-CC-APTES-NPSi for Pb2’ removal from aqueous solutionsEDA-CC-APTES-NPSi hybrid materials containing amino,imino and triazine ring was prepared successfully by chemical covalent coupling technique for Pb²⁺ removal.The results indicated that EDA-CC-APTES-NPSi can high-effectively adsorb Pb²⁺ from aqueous solution,the optimum pH was recorded to be 6.0,the adsorption rate was extremely fast and the adsorption equilibrium was reached whthin 5 min,and the maximum adsorption capacity was found to be 253.28 mg/g at room temperature.Furthermore,the adsorption kinetics and adsorption isotherms were investigated,which is in good agreement with Langmuir adsorption isotherm and pseudo second order model.Additionally,EDA-CC-APTES-NPSi still maintained high adsorption capacity after five successive regenerated cycles,which showed that EDA-CC-APTES-NPSi had good adsorption regeneration performance.What’s more,the XPS analysis manifested that Pb²⁺ removal might be ascribed to the Pb²⁺ adsorption on the surface organic functional group（anime groups）by chemical chelating reaction and the ion exchange reaction and ion reaction of silanol with Pb²⁺.Therefore,the EDA-CCAPTES-NPSi exhibited great potential for effective removal of Pb²⁺ from waste-water.The final research results show that organic functionalized nanoporous silicon prepared by using diamond wire-cut silicon waste can achieve the rapid and efficient enrichment and removal of heavy metal ions(Cr⁶⁺,Cd²⁺and Pb²⁺)from waste-water,which can treat the recycling silicon waste and industrial wastewater.