Preparation And Properties Of Hydrotalcite Based Persulfate Catalyst

Compared with traditional advanced oxidation techniques（AOPs）that mainly rely on hydroxyl radicals（·OH）,AOPs based on sulfate radicals（·SO₄^-）have higher redox potentials,longer lifetimes,and better resistance to electron-rich compounds.high selectivity.How to activate peroxodisulfate（PDS）more quickly and efficiently is the top priority of this technology.The activation of PDS includes light,heat,alkali,transition metal activation and other methods.Among them,the transition metal multiphase activated PDS technology has the advantages of high efficiency,energy saving,and environmental protection,and can effectively degrade organic pollutants（OCs）.The study of heterogeneous catalysts based on this reaction has become the focus of researchers.The transition metals represented by copper and nickel have the advantages of low cost and high activity,but the leaching of metal ions is often serious,which will cause secondary pollution and increase the processing cost.Therefore,it is urgent to improve their stability.Hydrotalcite（LDH）has high alkalinity and buffering capacity,which can effectively avoid the leaching of metal ions,promote the synergy between each other and accelerate the interfacial electron transfer,thereby promoting the generation of active species.Therefore,this thesis is mainly based on the preparation of hydrotalcite-based persulfate catalyst and its performance in activating PDS.The main contents of the research can be summarized as follows:（1）LDH-supported CuO and CuO-LDH composite catalysts were synthesized by two-step precipitation method and co-precipitation method,respectively.A series of characterization analyses were then performed,and it was found that LDH-loaded CuO had larger specific surface area,higher basicity,and more exposed CuO active sites.Through performance tests,the activities of the two catalysts for activating PDS to degrade ciprofloxacin（CIP）were compared.LDH-loaded CuO has higher catalytic activity,which may be due to the exposed more active sites of LDH-loaded CuO.Next,the optimal ratio of LDH-loaded CuO was explored,and it was found that the optimal activity was exhibited when the Cu:Mg ratio was 1:1（Cu4/LDH）.And no leaching of copper ions was detected under different conditions,which may be due to the alkalinity and buffering capacity of LDH.Then,the effects of reaction conditions and common substances in water on the catalytic performance of LDH-supported CuO were investigated.Finally,through radical trapping experiments and electron paramagnetic resonance spectroscopy（EPR）studies,it was found that in the LDH-supported CuO/PDS system,activated PDS and·SO₄^-were the main active species for degrading CIP.According to the analysis results of liquid chromatography mass spectrometry（LC-MS）,a possible pathway to degrade CIP was proposed.（2）LDH-supported Ni O（Ni-LDH-TP）and Ni-doped LDH catalysts（Ni-LDH-CP and Ni-LDH-SP）were prepared by two-step precipitation method and co-precipitation method,respectively.The structure,morphology,specific surface area,pore size and surface chemical properties of the catalyst were characterized.The results show that Ni-LDH-TP possesses the largest specific surface area and the most exposed active sites.Using CIP as the target pollutant,their PDS activation performance was compared.The experimental results showed that Ni-LDH-TP had the best activity for activating PDS to degrade CIP.This may be related to its large specific surface area and more exposed active sites.Then,the effects of PDS dosage,catalyst dosage and different ions in water on PDS activation were studied for Ni-LDH-TP catalyst.The Ni-LDH catalyst also maintains high activity in a wide p H range.At p H 6-10,no leached nickel ions were detected,and excellent reusability and stability were exhibited.Finally,the active species of this system were determined to be activated PDS and·SO₄^-by PDS decomposition experiment,free radical trapping experiment and EPR experiment.（3）NiAl-LDHs and NiAl-LDHs-U were synthesized by water-bath co-precipitation method and hydrothermal urea method,respectively,and their degradation performances as PDS multiphase activators for CIP were investigated.The results show that NiAl-LDHs have higher catalytic activity.Through the relevant characterization tests and activity experiments,the optimal synthesis conditions of the co-precipitation method were further determined.Subsequently,the effect of reaction parameters on the degradation of CIP by NiAl-LDHs activated PDS was investigated,and the optimal reaction parameters were determined.Next,the interference of common ions in water on the degradation process was investigated.Finally,it was determined by free radical capture experiment,PDS decomposition experiment and EPR experiment that the main active species for degrading CIP was the activated PDS produced by non-radical pathway.In addition,·SO₄^-generated through the free radical pathway also played a role.