Yttrium-modified Graphene Oxide Based Adsorbents For The Removal Of Tetracycline And Phosphorus In Wastewater

The rapid development of livestock and poultry farming brings huge benefits to the economy,but also brings various hazards to the environment.The combined pollution of tetracycline（TC）and phosphorus（P）was taken as a typical example.P mainly exists in the form of phosphate in wastewater,and excessive P can cause eutrophication.However,TC can induce drug resistance in bacteria,and their coexistence can produce higher toxic effects.Moreover,the transformation mode and removal mechanism of these two pollutants are different,resulting in the difficulty of removal.Graphene oxide（GO）-based materials are rich in oxygen-containing functional groups,which can efficiently remove TC.However,their affinity for P is not high,and they are easily dispersed in water,which is easy to cause secondary pollution.In addition,the rare earth element yttrium（Y）exhibits an excellent affinity for P.In order to solve the problem of difficult removal of TC-P complex pollution in wastewater,from the point of view of adsorbent design,this study intends to develop two yttrium-modified GO-based materials,yttrium-modified magnetic graphene oxide（YMGO）and yttrium-modified reduced graphene oxide hydrogel（Yr GO）,with efficient TC-P coexistence system adsorption performance and easy separation.The removal efficiency of TC and P of two adsorbent materials in single and composite systems was systematically investigated,and the adsorption mechanism was preliminarily derived,which could provide new materials for the treatment of TC-P composite pollution.Key findings were as follows:（1）Yttrium-modified magnetic graphene oxide was successfully prepared by co-precipitation method.Scanning electron microscopy-energy dispersive X-ray spectroscopy（SEM-EDS）showed that small irregular particles were gathered on the wrinkled surface of GO.Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）further confirmed the successful and uniform in situ generation of Y-Fe based particles on the GO matrix.The prepared YMGO has a large specific surface area and good magnetic properties,and can be effectively separated and recovered under an applied magnetic field.Among the four YMGO adsorbents with different Y-Fe ratios,YMGO-2showed the highest adsorption capacity for TC and P（171.84 mg/g and 38.36 mg/g,respectively）.In the TC/P unary system,the adsorption capacity of TC increased first and then decreased with increasing p H,while the adsorption capacity of P decreased significantly with increasing p H.Compared with the TC/P single system,the presence of TC or P significantly inhibited the adsorption of P or TC in the composite system,and the presence of high concentrations of Na NO₃ and humic acid（HA）inhibited the adsorption of TC and P.YMGO-2 has good regeneration performance,and the adsorption amount of TC and P can still maintain a high level after 5 cycles.Based on the results of two-dimensional correlation Fourier transform infrared spectroscopy（2D-FTIR-COS）and XPS analysis,it is inferred that TC mainly participates in the adsorption process through electrostatic attraction,π-πelectron donor-acceptor,n-πelectron donor-acceptor,hydrogen bonding and cation bridge interaction in the mono-and binary TC/P systems.P is mainly adsorbed on YMGO-2 by electrostatic attraction and ligand exchange in the form of phosphate.However,when TC and P coexist,they compete for the same adsorption site,resulting in reduced adsorption.In addition,even in pig wastewater with complex composition,YMGO-2 still had a certain treatment effect on TOC and P,which initially confirmed the feasibility of YMGO-2 in practical application.（2）Yttrium-modified r GO hydrogel was prepared by the self-assembly of GO sheets and the coordination reaction between yttrium and yttrium.SEM-EDS showed that Yr GO was a spherical hydrogel with a diameter of about 2 mm and a surface with many folding;FTIR and XPS analysis showed that Yr GO had a variety of oxygen-containing functional groups,and Y was successfully loaded on GO.In the TC/P unary system,the adsorption capacity of TC increased first and then decreased with the increase of p H,while the adsorption capacity of P decreased significantly with the increase of p H.The adsorption kinetics of TC and P by Yr GO conformed to the quasi-second-order kinetic model.The maximum adsorption capacity of Yr GO for TC and P was 337.10 mg/g and 33.41 mg/g,respectively.In the TC-P composite system,TC and P mutually inhibit the adsorption process,and the thermodynamic results show that the adsorption of TC and P on Yr GO is a spontaneous and endothermic process.In addition,SO₄^2-and CO₃^2-in water,as well as high concentrations of HA,can inhibit the adsorption process of Yr GO to P.Yr GO hydrogel as a filler in the dynamic filtration adsorption can treat about 200 m L of TC-P contaminated wastewater at a flow rate of 0.1 m L/min.The Thomas model fitting results showed that the maximum adsorption capacity of Yr GO for TC and P could reach 8.74 mg/g and 9.50 mg/g.After 5 cycles,the adsorption of TC and P by Yr GO could still maintain 90.21%and 84.31%of the first cycle.Based on the results of 2D-FTIR-COS and XPS analysis,it is speculated that TC mainly participates in the adsorption process through electrostatic attraction,π-πelectron donor-acceptor,n-πelectron donor-acceptor,hydrogen bonding and cation bond-bridge interaction in the mono-and binary TC/P systems.P was adsorbed on Yr GO mainly in the form of phosphate by electrostatic attraction and ligand exchange.However,when TC and P coexist,they compete for the same adsorption sites,resulting in reduced adsorption.In addition,Yr GO also had a certain treatment effect on TOC and P in actual pig wastewater,which also confirmed the feasibility of Yr GO in practical application.This study provides two new graphene oxide based materials for the removal of TC-P complex pollution in water by adsorption,analyzes the physical and chemical behaviors during the adsorption process,evaluates the removal effect of TC-P complex pollution in actual water,and provides a new idea for the prevention and treatment of TC-P complex pollution in water.