Remediation Of Porous Nano-modified Materials On Cd And Pb In Soil

In recent years,the pollution of heavy metals in water bodies and soils has become a problem that impedes agricultural development.Although there are many technologies and materials for the remediation of heavy metal pollution all over the world,few of these involve in fields of porous nanomaterials.Porous nanomaterials have superior adsorption capacity due to their complex mesoporous features and extremely high specific surface area,and have increasingly become hot spots in the preparation and research of heavy metal pollution remediation at home and abroad.In this paper,the porous nano-modified materials?PNM?were studied to explore their physical and chemical properties and characterization through elemental analysis,Zeta potential,XRD analysis,SEM,Boehm titration and other methods;The adsorption characteristics of porous nano-modified materials for Cd²⁺and Pb²⁺were studied through kinetic adsorption tests for Cd²⁺and Pb²⁺in water,adsorption experiments at different initial concentrations,adsorption experiments at different pH and solid-liquid ratios.Pot experiments were conducted to study the effect of porous nano-modified materials on Cd,Pb activity and bioavailability in soil.The main results were shown as follows:?1?PNM is a kind of porous nano-ceramic modified materials with a specific surface area of 184.34¹89.59 m²/g,a mesopore range of 4.35⁵.82 nm,and in a columnar pore structure;The functional group of PNM is primarily Si-O with rich basic groups and large polarity;It is negatively charged in the pH range of 2-11;This PNM exhibits natural adsorption properties for positively-charged heavy metal ions in its own structure and nature.?2?PNM reached adsorption equilibrium within 720 min?12 h?for Cd²⁺?60 mg/L?,and 480 min?8 h?for Pb²⁺?150 mg/L?,while within 5 minutes for Cr₂O₇^2-?50 mg/L?;PNM had relatively strong adsorption of positively charged ions,and weak adsorption of negative ions,presenting a typical adsorption process of Cd²⁺"first quick back slow trend";The higher the pH value,the smaller the solid-liquid ratio and higher unit adsorption amount;And the higher the initial concentration of heavy metals,the faster the adsorption rate.?3?PNM had a significant inhibitory effect on Cd and Pb uptake by plants.When the concentration of Cd was no more than 1 mg/kg,the decreasing trend of Cd content in the shoot began to alleviate with more than 3 t/ha PNM application;When Cd reached highly contaminated concentration?3 mg/kg?,the addition of 12 t/ha PNM was needed.From low to high Pb concentration,0.75 t/ha PNM can effectively reduce the Pb content in shoots and the aboveground Pb content,which particularly decreased at high pollution?500 mg/kg?,however,there was still a falling space of Pb content at 12 t/ha PNM application.The Cd and Pb content of roots in low and medium Cd and Pb pollution conditions showed a relatively smaller reduction and a greater one in high pollution conditions.With the increase of PNM application,there was an evident decreasing trend for the accumulation of Cd and Pb both in shoots and roots.?4?There was no significant change for the contents of Cd and Pb in soil.With the increase of PNM application,the contents of available Cd and Pb in soil showed a decreasing trend,while a rising trend for pH,indicating that PNM had passivation of Cd and Pb activity in soil and increased the soil pH,which indirectly reduce the biological effectiveness of Cd and Pb.In summary,it is feasible to use PNM for remediation of heavy metal contamination in water and soil.When the solid-liquid ratio was 2 g/L and pH=5,the unit adsorption capacity of PNM on Cd and Pb was around 25 mg/g and 47 mg/g,respectively,while the unit adsorption amount of Cr₂O₇^2-is close to 2.5mg/g.PNM can effectively inhibit the uptake of Cd and Pb in shoots and roots of pakchoi,and meanwhile cause the increase of soil pH,significantly Significantly reduce the content of available heavy metals in soil with a superior effect for Cd than Pb.