Study On Adsorption Of Water Pollutants By Ag-Triazole Metal-Organic Frameworks

In this master thesis research work,we used 3,5-diphenyl-1,2,4-triazole?Ph₂tz H?and 3,5-di-tert-butyl-1,2,4-triazole?^tBu₂tz H?as ligands to react with Ag NO₃ and Ag BF₄ respectively,which obtain two cationic MOFs with the same structure:Ag Tz-1:Ag₈?3,5-Ph₂-tz?₆]?NO₃?₂·6H₂O and doped MOF Ag Tz-1/2:Ag₈[?3,5-Ph₂-tz?_5.6?3,5-^tBu₂-tz?_0.4]?BF₄?₂·6H₂O.The thesis is composed of three parts:First,we study on the adsorption of p-Nitrophenol?PNP?by Ag Tz-1.Then the adsorption of new pollutant Diclofenac sodium?DCF?by Ag Tz-1/2 is analyzed.Finally,the adsorption of Methyl orange?MO?and Methyl blue?MB?by Ag Tz-1/2 is studied.1.Study on the adsorption performance of Ag Tz-1 on PNP?1?We systematically studied the adsorption behavior of Ag Tz-1 on PNP under different p H conditions.The experimental results show that the adsorption effect is best at p H=7.?2?We measured the adsorption kinetics curves of Ag Tz-1 on PNP at 288 K,298K and 308 K.Experimental data show that the adsorption behavior of Ag Tz-1 on PNP complies with the pseudo-second-order kinetic equation.At 288 K,298 K and308 K,the adsorption rate constants of Ag Tz-1 on PNP are 9.25×10^-4 g·mg^-1·min^-1,?3?We studied the effect of temperature on the maximum adsorption amount of Ag Tz-1.The maximum adsorption amount(110.8 mg·g^-1)is obtained at 288 K at the low concentration range.However,as the temperature and the PNP concentration increase,the isothermal adsorption curves at 298 K and 308 K show different degrees of jumping,which are higher than the maximum adsorption capacity at 288K and theoretical adsorption capacity based on"one in,one out"anion exchange(114.5 mg·g^-1).The maximum adsorption capacity at 298 K and 308 K are 143.5mg·g^-1 and 184.8mg·g^-1 respectively.?4?XRD data depict that the structure of Ag Tz-1 expands at high adsorption levels at 298 K and 308 K.The detection of NO₃^-concentration shows that the amount of NO₃^-released during the adsorption process is always less than the adsorption at lower p H?p H<7?.Only at high p H?p H>8?,the amount of NO₃^-released is close to the amount of adsorbed PNP.According to these data,we speculate that the adsorption of PNP by Ag Tz-1 is based on the anion exchange mechanism.At lower p H value,some neutral PNP molecules form hydrogen bond associated with PNP negative ions and enter the pores of MOF,thereby improving the adsorption amount of Ag Tz-1.?5?Based on the study on the adsorption-desorption cycle of PNP by Ag Tz-1,it can be found that after 5 cycles,Ag Tz-1 still has a good adsorption effect on PNP.The original structure remains unchanged.It shows that Ag Tz-1 is a recyclable PNP-absorbing material.2.Study on the Adsorption of DCF and Dyes by Doped MOF Ag Tz-1/2?1?Combined with the synthesis method of Ag Tz-1,we mixed3,5-di-tert-butyl-1,2,4-triazole and 3,5-diphenyl-1,2,4-triazole and obtained a MOF with the same structure as Ag Tz-1,which is Ag Tz-1/2.After a series of characterizations,the results demonstrate that we successfully doped ^tBu₂tz H into MOF.?2?We used two dyes?MO,MB?and DCF to test the adsorption performance of doped MOF Ag Tz-1/2.The experimental results show that the adsorption behaviors of MO,MB and DCF are consistent with quasi-second-order kinetic equations.Compared with Ag Tz-1,the reaction rate constants of the doped MOF to the three pollutants are 1.35,1.13 and 5.72 times that of the parent MOF Ag Tz-1.?3?Isothermal adsorption of Ag Tz-1/2 on MO,MB and DCF are analyzed.We conclude that their adsorption processes are in accordance with the Langmuir isotherm adsorption model.The maximum adsorption of three pollutants by doped MOF has increased by 20.6%,26.8%,19.8%compared with Ag Tz-1.The mechanism analysis shows that the adsorption of DCF by doped MOF is an anion exchange process.?4?Cyclic experiments show that Ag Tz-1/2 can still maintain a good adsorption effect after 5 cycles of adsorption of MO,MB and DCF.In addition,the sample after each cycle is characterized by PXRD,we found that it maintains good stability during adsorption.It is concluded that the proposed method by doping ligands to modify MOF is feasible.?5?To be brief,compared with Ag Tz-1,the Ag Tz-1/2 synthesized by introducing the second ligand has improved the adsorption rate and maximum adsorption capacity of the three pollutants.The stability has also been enhanced.It may be useful for us to synthesize new materials and improve their properties.