Preparation Of Al-doped UiO-66-NH₂ For Adsorption Removal Of Tetracycline And Cu（Ⅱ） From Aqueous Solution

China has produced a large amount of TC-containing wastewater as a major producer and user of tetracycline（TC）,which increased the exposure risk of TC to natural water bodies.At present,the treatment of TC-containing wastewater has attracted extensive attention.In addition,once Cu（Ⅱ）appeared in the TC-containing wastewater,TC and Cu（Ⅱ）could form combined pollution and produce stronger ecotoxicity.In this study,an Al（Ⅲ）doped UiO-66-NH₂ nanomaterial（Al-UiO-66-NH₂）was developed and its adsorption removal performance for TC and Cu（Ⅱ）was evaluated.Firstly,the preparation parameters of Al-UiO-66-NH₂ were screened and the physicochemical characteristics of Al-UiO-66-NH₂were analyzed.Furthermore,the Al（Ⅲ）doping modification mechanism was explored.Secondly,the effect of different adsorption parameters on TC and Cu（Ⅱ）adsorption by Al-UiO-66-NH₂ was explored in the sole solute.Meanwhile,adsorption kinetic,isotherm and thermodynamic models were used to fit the adsorption data,and then the adsorption behaviors were investigated.The TC and Cu（Ⅱ）adsorption mechanisms were examined by comparing the physicochemical characteristics of Al-UIO-66-NH₂ before and after adsorption.Moreover,the anti-interference adsorption ability and reusability of Al-UiO-66-NH₂ were determined,and the application potential of Al-UiO-66-NH₂ was explored through the adsorption characteristics experiments（adsorption interference experiment,adsorption-desorption experiment and the simulated TC/Cu（Ⅱ）-containing wastewater adsorption experiment）.Thirdly,in the binary TC/Cu（Ⅱ）system,the adsorption experiments at different adsorption time and initial TC/Cu（Ⅱ）concentration were processed,and adsorption kinetic and isotherm models were used to fit these experimental data.In view of this,the TC/Cu（Ⅱ）adsorption performance of Al-UiO-66-NH₂ in the binary TC/Cu（Ⅱ）system were investigated.This study provides a novel,effective,and stable metal-organic-frameworks（Al-UiO-66-NH₂）for the treatment of TC-containing wastewater.The main conclusions of the study are as follows:（1）The synthesis time,Al（Ⅲ）doping ratio,synthesis temperature and DMF dosage could affect the adsorption capacity of prepared Al-UiO-66-NH₂ and its yield.Among these synthesis parameters,Al（Ⅲ）doping ratio has the most significant effect on TC adsorption capacity.Based on the single-factor experiment design,the optimum preparation parameters of Al-UiO-66-NH₂ were obtained:synthesis temperature of 130℃,synthesis time of 24 h,DMF dosage of 15 m L,Zr（IV）:Al（Ⅲ）ratio of 1:1.The results of characterization analysis suggested that part of Zr（IV）in the framework was replaced by the doped Al（Ⅲ）,and Al（Ⅲ）has successfully doped in the crystal lattice,thus Al-UiO-66-NH₂ was successfully synthesized.Although Al-UiO-66-NH₂ and UiO-66-NH₂ belonged to isomorphic structure,Al-UiO-66-NH₂ had smaller particle size,larger specific surface area and pore size,which could provide more adsorption sites and enhance the adsorption performance.（2）In the sole solute system,the TC adsorption equilibrium time was 4 h.Al-UiO-66-NH₂ had good TC adsorption capacity in the range of p H 2–10（q_e>80 mg/g）,indicating that Al-UiO-66-NH₂ had great acid–base adaptiveness for TC adsorption.The increase of Al-UiO-66-NH₂ dosage could reduce the TC adsorption capacity of Al-UiO-66-NH₂.In addition,the high initial TC concentration and adsorption temperature were beneficial to the TC adsorption by Al-UiO-66-NH₂.In general,the optimum adsorption conditions for TC adsorption by Al-UiO-66-NH₂ were p H of 7,adsorbent dosage of 0.2 g/L,and adsorption time of 4 h.Pseudo-second-order kinetic and Langmuir isotherm models fitted the TC adsorption process well.This indicated that TC adsorption behavior by Al-UiO-66-NH₂ was predominantly monolayer adsorption,and physisorption and chemisorption occurred simultaneously.According to the Langmuir isotherm model,the maximum TC adsorption capacity was 520 mg/g,which was much higher than that of most MOF-based adsorbents.Moreover,Al-UiO-66-NH₂ exhibited good reusability and a certain anti-interference performance for TC adsorption,and had a desired application potential in the treatment of TC-containing wastewater.The main adsorption mechanisms involved in the adsorption included pore filling,electronic interaction,H-bonding interaction,complexation,π-πinteraction,and Lewis acid–base interaction.（3）In the sole solute system,the Cu（Ⅱ）adsorption equilibrium time was 4 h.TC adsorption capacity increased with the rise of solution p H within 2–5.When solution p H higher than 5,Cu（Ⅱ）will suffer from hydrolysis and precipitation.The increase of Al-UiO-66-NH₂ dosage could reduce its Cu（Ⅱ）adsorption capacity.In addition,the high initial Cu（Ⅱ）concentration and adsorption temperature were beneficial to Cu（Ⅱ）adsorption by Al-UiO-66-NH₂.In general,the optimum adsorption conditions for Cu（Ⅱ）adsorption by Al-UiO-66-NH₂ were p H of 5,adsorbent dosage of 0.2 g/L,and adsorption time of 4 h.Pseudo-second-order and Elovich kinetic and Langmuir isotherm models fitted the Cu（Ⅱ）adsorption process well.This indicated that Cu（Ⅱ）adsorption behavior by Al-UiO-66-NH₂was predominantly heterogeneous monolayer adsorption,and chemisorption occurred in the adsorption process.According to Langmuir isotherm model,the maximum Cu（Ⅱ）adsorption capacity was 114.25 mg/g,which was considerable compared with that of other MOF-based adsorbents.Moreover,the adsorption characteristics experiment indicated that Al-UiO-66-NH₂ exhibited good reusability and a certain anti-interference performance for Cu（Ⅱ）adsorption,and Al-UiO-66-NH₂ had a desired application potential in the treatment of Cu（Ⅱ）-containing wastewater.The main adsorption mechanisms involved in the adsorption may include pore filling,electronic interaction,complexation,chemical bonding interaction,Lewis acid-base interaction andπ-electron coordination.（4）In the binary TC and Cu（Ⅱ）system,the TC and Cu（Ⅱ）adsorption process could be fitted by pseudo-second-order kinetic and Langmuir isotherm models,which manifested that TC and Cu（Ⅱ）adsorption by Al-UiO-66-NH₂ may be monolayer adsorption and the adsorption process involved chemisorption.The adsorption capacity of Al-UiO-66-NH₂ for TC and Cu（Ⅱ）in the binary system was lower than that in the sole solute system,and an adsorption antagonistic effect existed between TC and Cu（Ⅱ）.All the same,Al-UiO-66-NH₂still maintained a high adsorption capacity for TC and Cu（Ⅱ）,suggesting that Al-UiO-66-NH₂is a MOF-based adsorbent that can effectively adsorption removal of TC and Cu（Ⅱ）from wastewater.