Research On Synergistic Removal Of Diclofenac Sodium In Aqueous Solution By Novel Polydopamine Modified Coagulant And Light Radiation

Anionic block acrylamide-polydopamine-Fe₃O₄ magnetic coagulant,chitosan polydopamine-loaded potassium permanganate hollow mesoporous silica coagulant,titanium-loaded potassium permanganate hollow mesoporous silica mixed chitosan-polydopamine coagulant and Ti O₂-polydopamine-chitosan coagulant with photocatalytic properties were prepared by polydopamine modification.The first three coagulants are combined with ultraviolet light,and the latter with visible light to realize the coagulation and degradation of typical PPCPs-diclofenac sodium（DCFS）.The main research contents and conclusions are as follows:Polyacrylamide with anionic block structure was synthesized by copolymerization of 2-acrylamido-2-methylpropanesulfonic acid（AMPS）with acrylamide（AM）using polyacyloxyethyl trimethyl ammonium chloride（PDAC）as cationic template and2-acrylamido-2-methylpropanesulfonic acid（AMPS）as anionic monomer.In addition,it modified with polydopamine and grafted with superparamagnetic Fe₃O₄ nanoparticles,named TAPAM-PDA-Fe₃O₄.In the meanwhile,taking PDAC/AMPS,AMPS/AM,AM/DA,DA/Fe₃O₄ molar ratio,irradiation time t and initial p H value of solution as independent variables and intrinsic viscosity as dependent variable,the synthesis method was optimized by response surface method.The coagulation experiments of low concentration DCFS simulated wastewater show that the stacking effect of benzene ring is dominant under neutral/alkaline conditions and the charge neutralization is dominant under acidic conditions.The DCFS coagulation process was described well with the pseudo-second-order kinetic model and Freundlich isotherm model.The coagulant was rapidly separated from the water body by an external magnetic field,and the separated coagulant was immersed in a small amount of dilute sulfuric acid solution.In addition,under acidic conditions,Fe₃O₄ nanoparticles reacted with H⁺to generate Fe²⁺.In the meanwhile,adding appropriate amount of H₂O₂,and then combined with ultraviolet irradiation to form a UV-Fenton system to achieve degradation of DCFS.The degradation experiment shows that through the coagulation of DCFS by TAPAM-PDA-Fe₃O₄,the low concentration of DCFS can be effectively degraded by the combination of UV and H₂O₂,and the maximum degradation efficiency is 98.1%.The reusability experiment of TAPAM-PDA-Fe₃O₄ shows that the coagulation and degradation efficiency of DCFS are more than 90.0%in the three continuous cycle coagulation processes.Chitosan was modified by polydopamine through Michael addition reaction and Schiff base reaction to improve the coagulation efficiency of DCFS in order to further realize the integration of coagulation and degradation of DCFS and improve the reuse cycles.In addition,it was encapsulated on the surface of potassium permanganate（PM）loaded hollow mesoporous silica nanoparticles（HMSN）.Chitosan modified by dopamine not only acts as a coagulant,but also acts as a"switch"for the controlled release of PM in an acid environment and is combined with UV to achieve the integration of DCFS coagulation and degradation.Langmuir,Freundlich and BET isotherm models were used to study the coagulation efficiency of P-HMSN@PM at different temperatures.Pseudo-first-order kinetic model,pseudo-second-order kinetic model and Weber-Morris kinetic model were used to study the coagulation process at different initial DCFS concentrations.The DCFS coagulation process was described well with the pseudo-second-order kinetic model and BET isotherm model.Combined with XPS analysis,it is confirmed that the coagulation process of DCFS is the result of the synergistic effect of chemical and physical interaction,including hydrogen bonding and aromatic stacking.The coagulation efficiency remained relatively high standard in the range of p H 4.0-9.0.The kinetic mechanism of PM release was studied semi-quantitatively by using Korsmayer-Peppas model,which showed that the release of PM was the result of the synergistic effect of case-II transport and Fickian diffusion.In addition,the generated·OH radical was detected by electron paramagnetic resonance spectrometer（EPR）,and the average quantum yield was 0.54463 mol·E^-1 under the condition of p H 4.0.In addition,Mn（V）plays a key role in the formation of·OH radical and the degradation of DCFS.The degradation intermediates were determined by high performance liquid chromatography-mass spectrometry（HPLC-MS）.The degradation mechanism of DCFS was studied and the most probable degradation pathway was proposed.Considering the potential economic benefits of P-HMSN@PM,the reuse times and coagulation efficiency of the coagulant were studied.The experimental results show that the coagulant can be reloaded with PM for 10 cycles.In addition,the coagulant loaded each time can coagulate and degrade DCFS 6 cycles efficiently and continuously,and the degradation efficiency can be kept above 90.0%.HMSN loaded with PM-doped polydopamine-modified chitosan coagulant was coated on the surface of titanium tablet combined with UV irradiation in order to realize the integration of DCFS in-situ coagulation-degradation and further improve the separation efficiency between coagulant and water,which was named CS-PDA/HMSN@PM/Ti.The conversion and polymerization rate of polydopamine and chitosan were studied by colloid titration.As a result,it showed that the conversion and polymerization rate reached the maximum when the initial concentration of initiator was 0.536 m M and the molar ratio of chitosan to dopamine was 1.50.The coagulation efficiency of CS-PDA/HMSN@PM/Ti at different temperatures was studied by using Langmuir,Freundlich and T（?）мкинisotherm models.The coagulation process of DCFS was well described by Langmuir model and T（?）мкинisotherm model at 303.15 K,which confirmed the monolayer unsaturated coagulation state of DCFS.The pseudo-first-order,pseudo-second-order and Weber-Morris kinetic models were used to study the coagulation process under different initial concentrations of DCFS.Compared with the Weber-Morris model,the pseudo-first-order and pseudo-second-order kinetic models better simulated the process.It confirmed that the coagulation process of DCFS was the result of the synergistic effect of chemical and physical interactions,including hydrogen bonding and aromatic stacking.In addition,the·OH radicals was detected by EPR,and the average quantum yield was 0.0421 mol·E^-1 under the condition of p H 4.0.In addition,Mn（V）plays a key role in the formation of·OH radicals and the degradation of DCFS.In the meanwhile,the degradation intermediates were determined by HPLC-MS,the degradation mechanism of DCFS was studied and the most probable degradation pathway was proposed.Finally,the reuse times and efficiency of CS-PDA/HMSN@PM/Ti were studied.DCFS can be coagulated and degraded by the coagulant for 10 cycles simultaneously without cleaning process,and its degradation efficiency can be kept above 90.0%.Aminopropyl triethoxysilane（APS）was used to modify Ti O₂ nanoparticles in order to further make the integrated coagulation-degradation process of DCFS safer,more energy-saving and more environmentally friendly.In addition,polydopamine modified chitosan was grafted on its surface to synthesize a new coagulant with visible light catalytic properties,named Ti O₂-APS-PDA-CS.At the same time,the change of hydrophilicity with temperature was studied.When the temperature decreased from313.15 K to 293.15 K,the polydopamine modified chitosan swelled and stretched,and the photocatalytic activity of Ti O₂ nanoparticles was activated.As a consequence,polydopamine modified chitosan can be used as a coagulant at the same time as a"switch".The shielding and de-shielding effect of Ti O₂ nanoparticles can be realized by regulating the temperature to change its hydrophilicity.In addition,the photocatalytic rate can be controlled to realize the coagulation and degradation of DCFS under visible light at the same time.The coagulation efficiency of Ti O₂-APS-PDA-CS at different temperatures was studied by Langmuir,BET and T（?）мкинisotherm models.The experimental results show that it is consistent with the BET model.It indicates that DCFS forms a multi-layer structure through the stacking effect of benzene rings.The pseudo-first-order kinetic model,pseudo-second-order kinetic model and Elovich kinetic model were used to study the coagulation under different initial DCFS concentrations.The results showed that it was simultaneously consistent with the pseudo-first-order and pseudo-second-order kinetic model.It confirmed that physical and chemical interaction both played an important role in the coagulation process.In addition,the active free radical detected by EPR was·OH under the condition of visible light and acid.The degradation intermediates were determined by HPLC-MS and the most probable degradation pathway was proposed.The reuse efficiency of Ti O₂-APS-PDA-CS shows that the coagulation-degradation efficiency of DCFS is more than 90.0%in 20 cycles under the condition of p H 5.0.