Modification And Application Of Copper Based Hydrotalcite For Adsorption Of Tetracycline Hydrochloride

With the abuse of antibiotics by human,the ecology of water has been seriously harmed and polluted,and it is time to seek an effective way to control antibiotic pollution in water bodies.Compared with traditional oxidation,photodegradation and biodegradation,adsorption has been widely used in water pollution treatment due to its advantages of simplicity,efficiency,environmental protection and low cost.In this paper,three different types of hydrotalcite adsorbents were designed and prepared based on the copper hydrotalcite with unique two-dimensional layered structure,excellent ion exchange property,modifiability,and affordability,by combining hydrothermal and high temperature calcination.The morphological structure and compositional properties of the adsorbents were analyzed by FT-IR,XRD,SEM and XPS characterization.The adsorption performance of three adsorbents was investigated using tetracycline hydrochloride（TC）as the adsorption target.The adsorption mechanism was investigated by a series of static adsorption experiments analyzing kinetics,thermodynamics and isotherms.The research work in this paper provides ideas for the modification of hydrotalcite-based materials and expands the application of modified classes of hydrotalcite materials as adsorbents in the field of water pollution treatment.The details are as follows:1.A series of copper-based ternary hydrotalcite materials（Mg Cu）_xFe-LDH were prepared by a one-step hydrothermal synthesis using nitrate as raw material with different（Mg Cu）/Fe ratios.Characterization analysis such as SEM and XRD revealed that the materials exhibited the most obvious layered nanosheet structure and crystalline features at（Mg Cu）/Fe of 3:1.In the static adsorption experiments on TC solution(c₀=300 mg·L^-1),（Mg Cu）₃Fe-LDH showed the best adsorption performance and the maximum adsorption capacity was 851 mg·g^-1.The adsorption process fited the pseudo-secondary kinetic and Langmuir isotherm models most closely,indicating that the adsorption process was chemisorption of a single molecular layer.Thermodynamically relevant parameters proved that it was a spontaneous heat absorption process.Experiments with different p H and interfering ions could infer that the adsorption process was a synergistic adsorption with electrostatic interactions,hydrophobic interactions and a small amount of metal complexation.In addition,（Mg Cu）₃Fe-LDH was able to maintain more than 90%removal of TC after five cycles of"adsorption-desorption".2.Two-dimensional layered Cu Al oxide material（Mo-Cu Al-LDO）with Mo impurity was prepared by introducing metal Mo into Cu-based hydrotalcite monomer by in situ synthesis followed by high temperature calcination.The Mo doping exposed more active sites on the adsorbent surface,changed the electronic layout on the material surface,and enhanced the electrostatic interaction between Mo-Cu Al-LDO and TC.Compared with the Cu Al-LDH and Cu Al-LDO without Mo doping,the adsorption capacity of Mo-Cu Al-LDO to TC was enhanced by 105.6%and 79.2%,the maximum adsorption capacity was achieved to 2317 mg·g^-1 at an initial concentration of 500mg·L^-1 in TC solution.The adsorption process was consistent with pseudo-secondary kinetics and the langmuir isotherm model,and it was a spontaneous endothermic reaction.Based on static adsorption experiments with different p H and interfering ions,it could be inferred that the adsorption mechanism is mainly electrostatic interaction and ion exchange.3.C₃N₄-loaded Cu Zn-LDH nanocomposites（Cu Zn/CN-x）were synthesized with introducing non-metallic two-dimensional nanomaterial carbon nitride（C₃N₄）by combining hydrothermal and high-temperature calcination.The best performing Cu Zn/CN-x composites were screened by modulating different C₃N₄ loadings.The characterization results based on SEM,FT-IR,XRD and XPS showed that Cu Zn-LDH successfully loaded on C₃N₄ nanosheets,and all elements were uniformly distributed on the surface of the nanosheets.The best lamellar characteristics and adsorption capacity were exhibited when the loading of C₃N₄ was 150 mg,which enhanced by 630%and 27%over single C₃N₄ or Cu Zn-LDH,respectively.The maximum adsorption capacity was achieved to 3841 mg·g^-1 at an initial concentration of 800 mg·L^-1 in TC solution.The pseudo-secondary kinetics and Langmuir isotherm model could best describe the adsorption process.The cycle stability of Cu Zn/CN-150 was excellent,and the TC removal rate remained 90%after 10 cycles of reuse.It was speculated that the adsorption mechanism mainly involved synergistic electrostatic interactions,intermolecular interactions,and hydrophobic interactions.