Study On Modification Of Mg-Al-LDH And Its Application In Water Treatment

Water,the source of life.However,water pollution problems exist continuously and the water environment is causing a future trouble.With the industry developing,the contaminants are emerging with a great variety,wide range sources and great harm.Therefore,it is of great practical significance to remove pollutants from wastewater.In numberous water treatment methods,adsorption method is more and more popular due to its low cost,simple operation and practical application properties.However,the drawback still exist that need to be promoted,such as long reaction time,low adsorption capacity and hard to recycle.The LDH(Layered Double Hydroxide),magnetic LDH/MCNOs composite,CLDH(Calcined LDH)and CLDH/MCNOs(Calcined LDH/MCNOs)were prepared and characterized,and its adsorption property on CR(Congo Red)and F-(Fluorine)were investigated.The experimental results were shown as follows:(1)Mg-Al-CO3 LDH was prepared via the hydrothermal method,and characterized by SEM(Scanning Electron Microscope),XRD(X-Ray Diffraction),BET,FTIR(Fourier-transform infrared spectroscopy)and TG-DSC.The influence of adsorption processes,ultrasonic power,and CR initial concentration on the adsorption of CR onto the LDH were studied by static adsorption method.The ultrasound-assisted adsorption mechanism was explored by characterization methods of SEM,BET,FTIR,Zeta potential,and LDH was regenerated by thermal regeneration.The results showed that the LDH was well dispersed with a lamellar structure and had a surface area of 98.63 m2/g.Ultrasound-assisted adsorption resulted in a significantly shorter adsorption equilibrium time of 2 h under initial 200 mg/L CR,and the optimal ultrasonic power was 180 W at which the adsorption efficiency and a maximum adsorption capacity of 90.79% and 934.43 mg/g were achieved,respectively.The adsorption kinetics and adsorption isotherms fitted the pseudo-second order kinetic model and Langmuir isotherm model well,respectively.The adsorption of LDH on CR is an ordered spontaneous exothermic process and its adsorption equilibrium time was reduced by the assist of ultrasound.The ultrasound-assisted adsorption mechanism was mainly attributed to electrostatic force and ion exchange.The adsorption efficiency remained above 60% after three cycles.(2)The magnetic LDH/MCNOs composite was synthesized by hydrothermal method and its structure was characterized by SEM,XRD,BET,FTIR,TG-DSC and VSM.The effect of initial CR concentration on the adsorption of CR onto LDH/MCNOs,together with adsorption mechanism and regeneration capability of LDH/MCNOs were studied.The results showed that LDH/MCNOs was the magnetic composite combined with LDH and MCNOs in a physical way,which had a specific surface area of 77.22 m2/g and a saturation magnetization of 70.52 emu/g.The saturation concentration for CR onto LDH/MCNOs was 100 mg/L,correspondingly its adsorption efficiency was 90.44%.But its maximum adsorption capacity was 591.15 mg/g,and the adsorption followed the pseudo-second order kinetic model well.After adsorption,the LDH/MCNOs could be recycled from the aqueous solution by magnetic separation to reuse.Its cycles of adsorption-regeneration could be up to six times,and the adsorption efficiency remained at 99% in the first five cycles.(3)The optimal calcination temperature,calcination time and Finitial concentration for the CLDH/MCNOs were investigated by orthogonal experiment.The adsorbents of CLDH and CLDH/MCNOs were characterized by SEM,XRD,BET,FTIR,VSM,and used to remove F-from the aqueous solution.Its adsorption mechanism and regeneration capability were elucidated.The results showed that the optimal calcination temperature,calcination time and F-initial concentration were 550°C,2 h and 10 mg/L,respectively.Correspondingly,its adsorption efficiency of 53.82% and adsorption capacity of 28.24 mg/g.The CLDH and CLDH/MCNOs had an amorphous flocculent structure,and were both mesoporous materials with the specific surface area of 208.31 m2/g and 104.95 m2/g,respectively.And the saturation magnetization of CLDH/MCNOs was 1.10 emu/g.The adsorption mechanism was the memory effect of LDH.And the adsorption efficiency of F-onto CLDH and CLDH/MCNOs reduced to 24.80% and 18.97% after three cycles respectively.Thus it can be seen that,the as-prepared adsorbent materials can remove the CR and F-from wastewater effectively,and ultrasound-assisted adsorption is a high-efficient technique for waste treatment,providing a theoretical basis on the practical application.