Preparation Of Functional Layered Double Oxide For Removal Of Polystyrene Microplastics

Microplastics have attracted much attention as emerging pollutants in water bodies due to their characteristics of small particle size（<5 mm）,uneven distribution,and difficult biodegradation.Microplastics can enter the human body through the food chain and cause diseases such as digestive system,cardiovascular obstruction and endocrine system disorders,becoming the"invisible killer"of human health.Therefore,the removal of microplastics from water environment has become an urgent environmental problem.At present,there are adsorption method,catalytic method,biological method,etc.,among which adsorption method has attracted wide attention because of its advantages of low economic cost,simple operation and high removal efficiency.Layered bimetallic oxides（LDO）can efficiently and stably adsorb a variety of organic pollutants in water environment,and are widely used in organic wastewater treatment.The functional modification of the material is beneficial to improve its adsorption stability and increase the adsorption site.Therefore,the preparation of suitable functional LDO is worthy of expectation in the water treatment application for microplastics.In this paper,three-dimensional organic layered bimetallic hydroxide（3D-LDH）was used as a precursor to synthesize three-dimensional layered bimetallic oxide（3D-LDO）carrying sulfur by high temperature aerobic calcination.By studying the factors that influence the synthesis of materials,Combined with scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）,Zeta potential analysis,specific surface area analyzer（BET）and X-ray photoelectron spectroscopy（XPS）,the structure,morphology and physicochemical properties were analyzed to determine the optimal synthesis process of 3D-LDO.Based on this,polystyrene（PS）,which is common in water environment,is selected as the representative of microplastics.Through static batch adsorption experiments,the effects of adsorbent dosage,initial solution concentration,reaction time,reaction temperature and pH of the system on the adsorption effect of PS are explored.With the help of adsorption kinetics,adsorption isothermal model,thermodynamic calculation and solid phase characterization analysis before and after the reaction.The removal mechanism of PS by materials was elucidated.Finally,through the comprehensive evaluation of recycling performance experiment,coexistence ion effect and actual wastewater experiment,3D-LDO is proved to be a stable and efficient deplastizer.Specific research results are as follows:（1）By analyzing the microcosmic characterization of materials and the adsorption effect of PS at different ratios of Zn:Al and calcination temperatures,it is shown that the optimal 3D-LDO can be prepared when the molar ratio of Zn:Al is 2:1and the calcination temperature is 700℃.It is found that 3D-LDO is composed of ZnAl2O4 and ZnO,and its surface is supported by SO₄^2-group.It presents the three-dimensional flower morphology of staggered nanosheets,with the specific surface area and pore volume of 51.6 m²/g and 0.19 cm³/g,respectively.（2）The removal behavior of PS by 3D-LDO was systematically investigated by changing different influencing factors.The results showed that when the reaction temperature was 298 K,the reaction time was 8 h,and the dosage of adsorbent was 1g/L,the maximum adsorption capacity of 3D-LDO for PS with the initial concentration of 50 mg/L could reach 54.3 mg/g.The adsorption of PS by 3D-LDO increased by the elevated temperature.Solution pH exhibited little influence on the PS removal.Kinetic study revealed that the adsorption of PS by 3D-LDO was affected by the initial concentration of microplastics:at low concentration（25 mg/L）,PS removal was in consistence with the quasi-first-order kinetic model while quasi-second-order kinetic model matted better at medium and high concentrations（50 and 200 mg/L）.Thermodynamic analysis showed that the adsorption of PS by 3D-LDO was a spontaneous reaction,accompanied by endothermic phenomenon.Combined with the characterization of the materials before and after adsorption of PS,the results showed that the adsorption of PS by 3D-LDO was mainly due to the pore filling and electrostatic effect,and the pore filling effect increased with the increase of PS concentration.It is worth noting that when PS is at a medium high concentration,PS will also be complexed with the metal-oxygen bond in LDO.（3）3D-LDO has excellent stability and anti-interference ability.3D-LDO maintained good adsorption capacity for PS after 5 times of adsorption-desorption cycle experiments,which confirmed that 3D-LDO material has excellent recycling performance and is an excellent adsorbent for microplastics.