Mechanism And Application Of Rhodanine Derivative Materials For Targeted Recovery Of Silver Ions From Acid Wastewater

As a precious metal,silver is widely used in industry,which leads to the generation of a large amount of waste liquid containing silver ions.The discharge of waste liquid will not only damage the environment but also cause a waste of resources.Therefore,the recovery of silver ions is not only beneficial to the ecological environment,but also has economic value.In view of the fact that industrial wastewater is often acidic and metal ions in wastewater are complex,functional materials with acid resistance and silver ion selectivity should be designed and synthesized.In this paper,3-allylrhodanine（3-AR）,a functional monomer material targeted by silver ions,was firstly determined through theoretical calculation and analysis.A series of Rhodanine derivatives with stability were obtained by overpolymerization.The morphology,stability,adsorption properties,selectivity,adsorption mechanism and practical application performance of the materials were systematically studied.Firstly,the structure optimization and surface charge analysis of 3-AR in Dmol3showed that carbonyl O,thiocarbonyl S,S in the five-membered ring and tertiary amine bond N in 3-AR structure were the main adsorption sites that could bind silver ions.According to the fitting result of Sorption adsorption module on silver ions adsorbed by 3-AR,E_ad（c-s-Ag⁺）and E_ad（C=S-Ag⁺）at different sites of 3-AR and silver ions were-4.35 e V and-4.43 e V,which were higher than N and O groups.According to the result of binding energy,the main dependence was on the S group.The calculation of the complex stability constant further showed that 3-AR monomer exhibit a super high complex stability constant of 2.63×10⁷for silver ions,which was2 orders of magnitude higher than other metal ions,and it was easier to combine with silver ions in mixed ionic solution.Therefore,3-AR was feasible for the selective separation of silver ions.To achieve the stability of the material in water,polyallylrhodanine（PAR）was obtained by heat-initiated polymerization.SEM showed that PAR had a uniform particle size distribution of about 1.3μm,and showed good adsorption capacity and p H adaptability.The kinetic model fitting results showed that the adsorption of silver ions by PAR was in line with pseudo-second-order kinetics,and the equilibrium adsorption was achieved within 100 min,with an equilibrium adsorption capacity of242.3 mg g^-1.The results of adsorption isotherm was fitted with the Langmuir model,which proved that the Ag⁺adsorption sites of PAR were evenly distributed on the surface.In the wastewater solution containing various metal ions,PAR adsorbent showed high selectivity and preferential adsorption for Ag⁺,and the selectivity coefficient for Ag⁺was greater than 20 under neutral conditions.The adsorption capacity of PAR remained above 95%after 5 cycles of adsorption,indicating that the material had good stability.In order to explore the mechanism of enhanced adsorption capacity of PAR materials in acidic solution,the effects of PAR on silver ion adsorption capacity and selectivity were investigated by regulating the content of protons in solution.As the solution p H decreased from 2.8 to-0.2,the Ag⁺adsorption capacity of the PAR increased from 400.2 mg g^-1to 651.8 mg g^-1.As the amount of protons in the solution increased,the selectivity coefficientβincreased from 15 to more than 100,and the selectivity coefficient of Ag⁺/K⁺was as high as 744.Through characterization analysis and theoretical calculation,it was inferred that the adsorption of silver ions by PAR in acidic solution depend on the formation of S-H⁺bond with S group,and then taking place of protons.The fixed bed experiments showed that the material had a stable and efficient silver ion adsorption capacity.When p H was-0.2,PAR can reach 4015 BV fixed bed treatment volume,and 99.9%of silver ions can be quickly eluted in situ,achieving more than 20 times concentration enrichment effect.Compared with commercial resin CG-50-type1,the adsorption of silver ions by PAR was 50 times that of CG-50-type1,and could reach 100 times under acidic conditions.In order to achieve rapid separation of materials from solution,3-AR was introduced into polyvinylidene fluoride（PVDF）by blending method,and3-AR/PVDF microfiltration membrane was synthesized by phase conversion method.SEM showed that the membrane surface was smooth and had uniform pore distribution,and the cross section of the membrane was finger-like pore distribution.The effects of different synthesis ratios on the properties of the membranes were analyzed.The average pore diameter of the membranes decreased with the increase of3-AR content and the water flux decreased significantly.The results showed that the C=S and C-S groups in 3-AR are the main factors affecting the separation performance of silver ions.3-AR/PVDF-0.130 membrane had a good permeability(water flux 151.24 L m^-2h^-1)and selectivity（β>10）and Ag⁺interception performance（interception amount was 6.04 mg）.In the study on the influence of film thickness,the adsorption and retention of silver ions increased with the increase of film thickness,while the water flux decreased.When the film thickness was 0.16 mm,the maximum adsorption capacity of silver ion was 45.15 mg cm^-2.The linear fitting of film thickness with silver ion retention and water flux could provide suggestions on film thickness design for different treatment targets in practical application,which had important reference value for practical application process.Considering that the membrane was easy to be polluted by filtration in practical application,the composite membrane 3-AR/PVDF-DA/PEI was synthesized by grafting dopamine（DA）and polyethylenimide（PEI）on the surface of 3-AR/PVDF.The results of characterization showed that the average pore diameter of the membrane was about 36.42±0.5 nm,the surface roughness was about 606.22 nm,and the water contact Angle was about 76.2°,showing good hydrophilicity.The Zeta potential on the membrane surface is-14.8 m V,and the near neutral potential could effectively reduce the adsorption of protein pollutants.The membrane material showed good adsorption ability for silver ion,and reached the saturation adsorption capacity of 47.5 mg cm^-2at equilibrium.The composite membrane had a good acid resistance,and the adsorption capacity of Ag⁺remained stable in p H range of 1～6.The composite membrane showed excellent selectivity for silver ions in mixed ionic solution.The composite membrane displayed a highly water flux and BSA protein retention rates of 291.7 L m^-2h^-1and 95.1%,respectively.The the water flux recovery rate(F_RR)of 3-AR/PVDF-DA/PEI membrane was 94.2%,and the irreversible contamination rate(R_ir)was 22.5%,which proved that the surface graft modified membrane had an excellent anti-pollution ability.