Study On The Controllable Preparation Of Zirconium-Based Metal-Organic Frameworks And Mechanism Of Selective Capture Of Ag(?) From Wastewater

The extensive application of silver and its compounds in many fields such as electronic plating,medicine,catalysis,photography,and jewelry makes toxic silver inevitably exposed to the water environment,which not only harms the ecological environment and human health,but also causes a large amount of resources waste.Selective capture and maximum recovery of Ag(?)from wastewater are of great significance for a sustainable future.How to improve the concentration distribution coefficient,diffusion rate,selectivity coefficient,and adsorption stability of the adsorbent for Ag(?)in the solid-liquid medium are the key issues that need to be resolved to maximize the recovery of silver and increase the cost-effectiveness of recovery.Focusing on these technical difficulties,this paper examines the coordination and recognition capabilities of Ag(?)by functional groups containing different atoms such as N,O,and S,and their spatial structure,and the effects of different preparation methods on the concentration distribution coefficient,diffusion rate,selectivity coefficient,and adsorption stability of functionalized UiO-66 for Ag(?)are explored.This work provides new thoughts and insights for the functional design of MOFs and heavy metal pollution control and reutilization.The main contents are as follows:1.In-situ preparation of UiO-66-X(X=(OH)₂,(COOH)₂,NO₂,NH₂,SO₃H,(SH)₂)and study on their adsorption performance and mechanism of Ag(?)To explore the coordination and recognition capabilities of Ag(?)for common functional groups containing atoms such as N,O or S,a series of functionalized UiO-66(i.e.,UiO-66-(OH)₂,UiO-66-(COOH)₂,UiO-66-NO₂,UiO-66-NH₂,UiO-66-SO₃H and UiO-66-(SH)₂)are prepared in situ by introducing common functional groups(e.g.,hydroxyl,carboxyl,nitro,amino,sulfonic and thiol)on terephthalic acid organic ligands.Isothermal adsorption indicates that-NH₂,-OH,-COOH,and-SH groups can effectively increase the concentration distribution coefficient of UiO-66 for Ag(?)in the solid-liquid medium.UiO-66-(SH)₂ has the largest concentration distribution coefficient,which are 45.1,31.6,20.7,10.8,5.0 and 4.5 times that of UiO-66,UiO-66-NO₂,UiO-66-SO₃H,UiO-66-NH₂,UiO-66-(OH)₂ and UiO-66-(COOH)₂,respectively.Meanwhile,UiO-66-(SH)₂ has the fastest adsorption rate,the initial adsorption rates(h₀)is UiO-66-(SH)₂>UiO-66-(COOH)₂>UiO-66-NH₂>UiO-66-(OH)₂.In addition,UiO-66-(SH)₂ has exhibited a remarkable selectivity for Ag(?)capture,with a minimum selectivity coefficient of 111.10.The results of adsorption mechanism research and normalized quantitative analysis indicate that the adsorption process mainly depends on the chemical coordination between N,O or S atoms in the surface functional group and Ag(?),and the coordination capabilities of Ag(?)of Ag(?)is-SH>-COOH>-OH>-NH₂>-SO₃H>-NO₂.2.In-situ solvothermal preparation of rhodanine-functionalized UiO-66 and study on its adsorption performance and mechanism of Ag(?)To investigate the effect of the spatial structure of functional groups on the selectivity coefficient of Ag(?),rhodanine-3-acetic acid containing a ring-like space structure composed of multiple N,O,and S atoms is rationally selected as functional moiety for surface grafting of UiO-66,and the rhodanine functionalized UiO-66(UiO-66/8Rd)with the best adsorption performance is prepared in situ by solvothermal method.XRD,FT-IR,SEM,and BET characterization techniques confirm that rhodanine is successfully introduced into the UiO-66 framework,and the content of rhodanine was 0.46 mmol/g.The maximum adsorption capacity(109.2 mg/g)of UiO-66/8Rd is 4.2 times that of UiO-66.One mole of rhodanine introduced into UiO-66 can adsorb 1.8 mol of Ag(?),which is 3.5,11.3,12.9,and 13.8-fold larger than those of-SH,-COOH,-OH,and-NH₂-functionalized UiO-66,respectively,indicating the rhodanine group with ring-like space structure and multiple coordination sites has superb coordination ability to Ag(?).The adsorption equilibrium time of UiO-66/8Rd is approximately 60 min,and internal diffusion is the main rate-controlling factor.In addition,UiO-66/8Rd has excellent recognition ability and selectivity for Ag(?),with a minimum selectivity coefficient as high as 268.0,which is 2.4times that of UiO-66-(SH)₂.These demonstrate that rhodanine with a ring-like space structure composed of multiple coordination sites can effectively improve the selectivity of UiO-66 for Ag(?).3.Solvent-assisted ligand replacement for the preparation of rhodanine-functionalized UiO-66 and study on its adsorption performance of Ag(?)To explore the effects of functionalized UiO-66 on the diffusion rate of Ag(?)by post-modification and in-situ preparation methods,the solvent-assisted ligand replacement method is used to modify the rhodanine group on the surface of UiO-66 to obtain the best-adapted rhodanine-functionalized UiO-66(UiO-66-Rd).XRD,FT-IR,SEM,BET,and XPS characterization analysis confirm that rhodanine is modified on the surface of UiO-66 and the crystal structure remains unchanged,with a grafting amount of up to 0.51 mmol/g.The maximum adsorption capacity of UiO-66-Rd is 112.3 mg/g,and the concentration distribution coefficient is 1.2 times that of UiO-66/8Rd.UiO-66-Rd can reach adsorption equilibrium within 15 minutes,and the initial adsorption rate(h₀)is 3.3 times higher than UiO-66/8Rd.Meanwhile,UiO-66-Rd has remarkable selectivity for Ag(?)capture.The maximum selectivity coefficient(1.7×10⁴)is about 15 folds higher than that of UiO-66/8Rd.These prove that compared to the solvothermal in situ preparation method,the post-modification method of solvent-assisted ligand replacement can modify the rhodanine mainly on the surface of UiO-66,which results in higher diffusion rate and selectivity coefficient.In addition,D-A isotherm model site energy distributions confirm that UiO-66-Rd prepared by solvent-assisted ligand replacement has more effective Ag(?)adsorption sites.4.Preparation of rhodanine-functionalized UiO-66-NH₂ via amidation and study on its adsorption performance and mechanism of Ag(?)To investigate the influence of post-modification method by chemical and coordination bonds on the adsorption stability of functionalized UiO-66 to Ag(?),NH₂-functionalized UiO-66 in replacement of original UiO-66 has been employed as new substrate to anchor the rhodanine through the amidation reaction.FT-IR,XPS,NMR characterization techniques certify that the formation of amide bonds and the successful modification of rhodanine onto the surface of UiO-66-NH₂.The grafting amount(0.73 mmol/g)is about 1.5times that of UiO-66-Rd.Meanwhile,the maximum adsorption capacity(163.1 mg/g)and concentration distribution coefficient of UiO-66-NH₂-Rd are approximately 1.5 and 1.4times that of UiO-66-Rd,respectively,indicating that the amount of rhodanine on the surface is positively correlated with the adsorption capacity.The initial adsorption rate(h₀)and maximum selectivity coefficient(4.1×10⁴)of UiO-66-NH₂-Rd is 1.2 and 1.5 times higher than that of UiO-66-Rd,indicating that the amount of rhodanine grafted by amidation leads to higher diffusion rate and selectivity coefficient.In addition,compared with UiO-66-Rd,UiO-66-NH₂-Rd has excellent recyclability and long-term durability,demonstrating the bonding strength between rhodanine and UiO-66 can be enhanced by chemical bond modification to obtain better long-term durability.FT-IR,XPS and DFT theoretical calculation validate that the S atoms of C–S and C=S bonds participate in the coordination of Ag(?),and Ag(?)can be mono-coordinated with S on the UiO-66-NH₂-Rd.5.Preparation of rhodanine-functionalized UiO-66 derivatives via acyl chloride and study on their adsorption performance and application of Ag(?)To explore the effects of functionalized UiO-66 prepared by acyl chloride and acid of rhodanine on the concentration distribution coefficient of Ag(?),the rhodanine acid is converted into more active rhodanine acyl chloride,then the acyl chloride undergoes esterification or amidation with UiO-66 and UiO-66-NH₂ to prepare rhodanine-functionalized UiO-66 derivatives(UiO-66@20Rd and UiO-66-NH₂@20Rd).The maximum grafting amount of rhodanine(3.78 mmol/g)was 4.2 times higher than that of UiO-66-NH₂-Rd.The adsorption capacities of UiO-66@20Rd and UiO-66-NH₂@20Rd(819.6 and 923.9 mg/g)are 5.0 and 5.7-fold higher than UiO-66-NH₂-Rd,respectively,and the concentration distribution coefficients are 8.2 and 11.2 times larger than that of UiO-66-NH₂-Rd.The diffusion rate of UiO-66-NH₂@20Rd is very fast,the removal efficiency is as high as 90%within 1 min.Meanwhile,UiO-66-NH₂@20Rd has outstanding selectivity and excellent recyclability and durability.The removal efficiencies are still as high as 93.7%and98.9%even after six cycles of repeated use.Moreover,fixed-bed column adsorption experiment demonstrates that the effective treatment volume for Ag(?)is up to 21780 BV,indicating the UiO-66-NH₂@20Rd has a great potential for selective capture of Ag(?)from wastewater.These certify that increasing the functionalization efficiency of UiO-66 by acyl chloride is the most effective way to improve the concentration distribution coefficient,adsorption rate,selectivity coefficient,and adsorption stability of Ag(?) from wastewater.