Synthesis Of UiO-66-NH₂ Composite Material And Its Adsorption Properties For Boron In Desalinated Seawater

With the increasing shortage of freshwater resources,desalination of seawater for industrial and agricultural production and human daily drinking has become an inevitable trend.However,in desalinated seawater,there is usually a problem of too high boron concentration,which can be toxic to humans and plants.Therefore,much attention has been paid to the removal of boron in desalinated seawater.Because the adsorption method has the advantages of low cost of adsorbent,easy regeneration,and good adsorption effect,it has become one of the most boron removal technologies with development potential and application prospects.In this paper,the solvothermal method was used to prepare the water-stable metal organic framework UiO-66-NH₂ and two composite adsorbents based on UiO-66-NH₂.They are UiO-66-NH2/GO composed of graphene oxide?GO?and UiO-66-NH2,and UiO-66-NH2/GO/Fe3O4composed of GO,UiO-66-NH2 and magnetic nanoparticles?Fe3O4?.The boron adsorption properties of the two were studied.By nitrogen adsorption/desorption isotherm,scanning electron microscope?SEM?,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,thermogravimetric analysis?TGA?,X-ray photoelectron spectroscopy?XPS?And hysteresis loop?VSM?were used to characterize UiO-66-NH2 and its composite materials.Through single-factor static experiments,the effects of adsorbent dosage,pH,adsorption time and Initial concentration of boron on the adsorption of boron on two UiO-66-NH₂ composite materials were studied,and the kinetics,isotherms and thermodynamics during the boron adsorption process were analyzed feature.The process of absorbing boron by UiO-66-NH₂/GO and UiO-66-NH₂/GO/Fe₃O₄ was optimized by response surface method,and the best adsorption conditions and corresponding response values were fitted.Ui O-66-NH₂/GO is similar to UiO-66-NH₂ in morphology and crystal structure.Its terephthalic acid organic ligand structure is intact.The introduction of GO will not interfere with the crystallization of UiO-66-NH₂.Compared with Ui O-66-NH₂,the thermal stability of UiO-66-NH2/GO has decreased,but the specific surface area,total pore volume and micropore volume have been improved,respectively 1048 m²/g,0.337 m³/g and 0.273 m³/g.UiO-66-NH₂/GO adsorbs boron in water better than UiO-66-NH₂,and has better regeneration ability.After 3 cycles,the adsorption of boron is only reduced by 6%,which can be desalinated It is recycled in applications for removing boron from seawater.Its adsorption performance is greatly affected by factors such as dosage,pH value,adsorption time,initial concentration of boron,etc.Acidic conditions and higher temperature are more conducive to UiO-66-NH₂/GO adsorption of boron.The adsorption kinetic model of boron on UiO-66-NH2/GO conforms to the pseudo-second-order kinetic model and intra-particle diffusion model,indicating that the adsorption rate is mainly controlled by chemical adsorption,and the adsorption rate in the pores is higher than that of boron in the particles.Rate,diffusion within particles is not the only rate control step.The fitting result of the adsorption isotherm is more in line with the Langmuir model,indicating that the adsorption of boron on UiO-66-NH₂/GO is a single layer with a maximum adsorption capacity of 204.08 mg/g.Adsorption thermodynamics show that the adsorption of boron on UiO-66-NH₂/GO is spontaneous,and the higher the temperature,the better the adsorption performance of boron.UiO-66-NH2/GO's adsorption of boron is an endothermic process and has a good affinity for boron.The response surface optimization study shows that the response surface optimization model of UiO-66-NH₂/GO adsorbed boron is highly compatible and can be used to design and optimize experimental conditions.The dosage of 75.49mg/L,pH value of 5.3,and temperature of 322.11k is the best condition for model fitting.The predicted maximum boron adsorption capacity is 27.04 mg/g,which is only 2.2%deviation from the actual experimental value.The crystal structure of UiO-66-NH₂/GO/Fe₃O₄ is good,and the diffraction peaks of UiO-66-NH2/GO and Fe3O4 exist simultaneously in the XRD spectrum.The FT-IR spectrum shows a strong Fe-O-Fe typical absorption peak near 580 cm^-1,and the characteristic peak of Fe³⁺can be observed in the XPS spectrum,which indicates the presence of Fe3O4 in the composite.Compared with UiO-66-NH2,the thermal stability and specific surface area of UiO-66-NH2/GO/Fe3O4 have decreased,but the micropore volume and total pore volume are still higher than UiO-66-NH₂.The saturation magnetization of UiO-66-NH2/GO/Fe3O4 is 50.89 emu/g,which has enough magnetism to be separated from the solution by the magnetic field.UiO-66-NH2/GO/Fe3O4 adsorbs boron in water slightly lower than UiO-66-NH2/GO,but still higher than UiO-66-NH2 and many other boron adsorbents,which also maintains good regeneration Performance,after 3 cycles,the amount of boron adsorption decreased by 4.2%.The pseudo-second-order kinetic model and the intra-particle diffusion model can also fit the adsorption data of boron well,indicating that the adsorption rate is mainly controlled by chemical adsorption,and the adsorption rate in the pore is higher than the diffusion rate of boron in the particle.Not the only rate control step.The fitting result of the adsorption isotherm is also more in line with the Langmuir model,indicating that the adsorption of boron on UiO-66-NH2/GO/Fe3O4 is a single layer with a maximum adsorption capacity of 192.31 mg/g.Adsorption thermodynamics show that the adsorption of boron on UiO-66-NH₂/GO/Fe₃O₄ is also spontaneously feasible.The adsorption of boron is an endothermic process and has a good affinity.Within the specified test range,the response surface optimization model also showed a high degree of compatibility.The dosage of 94.712 mg/L,pH value of 4.101,and temperature of 318k are the best conditions for model fitting.The maximum boron expected The adsorption capacity is 25.36 mg/g,which is only 1.3%deviation from the actual experimental value.Both adsorbent materials show good adsorption properties for boron,proving that both are highly practical adsorbents that can be used to remove boron from desalinated seawater.The study uses metal-organic framework composite materials as adsorbents,which provides a new direction and ideas for the theoretical research and engineering application of boron removal in desalinated seawater.