Preparation Of Nanomaterials With Different Dimensions And Their Application In Detection And Electrocatalytic Nitrate Reduction

The development of nanomaterials has made an important contribution to promoting basic scientific research.The unique microstructure and unique properties of nanomaterials lay the foundation for their applications in a variety of fields including photocatalysis,detection and environment,new energy,energy storage for transport and nanomedicine.Nanomaterials of different dimensions have their advantages,such as volume effect,macroscopic quantum tunneling effect,surface effect,dielectric domain effect and quantum size effect,etc.Combining the different properties of different materials with the target effect has become the main strategy to expand the types and applications of nanomaterials.With the rapid development of industry,environmental problems are becoming increasingly serious.The pollution of soil,water and air is a great threat to the ecological environment and life health of living organisms.In recent years,with the rise and development of nanotechnology,various nanomaterials have been widely used in the treatment of environmental pollutants.The development of nanotechnology brings new opportunities for the treatment of environmental pollutants.In this paper,the main starting point is to solve environmental problems.Through reasonable design with goals,nanomaterials capable of detecting manganese ions in the environment and electrocatalytic reduction of nitrate have been successfully prepared.The specific research work is as follows:(1)Using the unique natural porous structure of three-dimensional wood,zero-dimensional material carbon dots were grown in situ in the wood channel by the hydrothermal method.A new type of composite material CDs@wood was successfully prepared.The large surface of the fiber microchannel of wood and its cell fiber wall can not only enhance the light absorption based on light trapping and multiple scattering effects but also provide enough positions to anchor the carbon dots to avoid the aggregation and self-quenching of excited states,to promote the inter-system channeling(ISC)process.The singlet oxygen efficiency generation of CDs@wood is improved,the ability of Mn(III)to oxidize TMB is significantly enhanced,and the photothermal signal generated is also improved.The portable thermometer can easily capture the change of the photothermal signal,but other divalent metal ions except for Mn(II)have no such effect.Therefore,the portable thermometer can achieve high sensitivity and selectivity to Mn(II)detection.(2)Bimetallic coordination polymers were synthesized by hydrothermal method with host macrocyclic pillar[5]ene as precursor and cobalt and nickel as metals.Co-Ni O CFs obtained by high temperature annealing is a transition metal-based catalyst for nitrate reduction.Ligand pillar[5]ene with electron-rich cavity can expose more active sites.The experimental results show that the material we designed is conducive to the electrocatalytic reduction of nitrate to ammonia.In the 52 h,the conversion rate of NO₃^--N can reach 90.1%,and the selectivity of NH₄⁺-N is 78.8%through the analysis of related experiment results.Non-noble metals-based electrocatalyst demonstrated in this work not only reduces the cost,while maintaining good catalytic activity and selectivity but also provides ideas for the design of subsequent transition metal advanced functional catalysts.(3)Under the modulation of pyridine,a two-dimensional nickel-based MOF hexagonal nanosheet(HXP)was synthesized from Ni(NO₃)₂·H₂O,terephthalic acid(BDC)and 1,4-diazabicyclo[2.2.2]octane(DABCO).Ni²⁺coordinates with 8 oxygen atoms in 4 BDC anions to form a secondary structural unit(SBU),which is then connected to the DABCO molecule through the terminal nitrogen atom to form a regular hexagonal geometry.Subsequent pyrolysis,phosphating converts HXP into N-doped HXP-P@NC nanocomposite,which can be used as a very efficient catalyst for electrocatalytic conversion of nitrate to ammonia.(4)A large number of monodisperse Cu NPs were prepared with Cu Cl₂·2H₂O as raw material and sodium borohydride as reducing agent.Using the Cu NPs as a catalyst,the electrocatalytic reduction activity of the Cu NPs to nitrate was investigated.The results showed that the Cu NPs had good catalytic activity and high selectivity to nitrate of 50-500 mg/L in a mild neutral system.It is calculated that a conversion rate of NO₃^--N in 500 mg/L high concentration of nitrate can reach 99.6%,the selectivity of NH₄⁺-N is up to 91.1%,and the Faraday efficiency is up to 94.9%.After 10 cycles,the catalyst can still maintain a conversion rate of more than 87%.The reduction results showed that Cu NPs prepared in large quantities had a positive effect on the realization of high nitrate concentration under the synergistic effect of size effect and monodisperse exposure of more active sites,which also provided ideas for the design of low-cost non-noble metal functional catalysts.