Preparation And Adsorption Properties Of Paeonia Ostii Seed Coats-Based Adsorbent

With the acceleration of industrialization and urbanization,the global shortage of resources,environmental pollution and other issues have become increasingly prominent.Paeonia ostii seeds coats（PSC）are the byproducts of seed oil processing.In Luoyang,which enjoys the reputation of"Millennium Emperor Capital,Peony Flower City",a large number of peony shells are discarded as wastes every year,resulting in the waste of resources and environmental pollution.The use of PSC-based adsorbent in the process of wastewater treatment has great scientific value and practical meanings.Three novel biosorbents,PSC modified with iminodiacetic acid（IDA-PSC）,PSC modified with sodium hydroxide（AP-PSC）and PSC activated carbon modified with nitric acid（NA-PSCAC）were prepared from the PSC waste and were successfully applied to the removal of copper ions and methylene blue from water.The influential factors and mechanisms of adsorption process were detailedly discussed,as well as the reusability of adsorbents.The effects of process conditions on the removal efficiency of the IDA-PSC adsorbent for copper ions were investigated.The suitable conditions for the preparation of IDA-PSC were determined as follows:the concentration of NaOH 3.0mol L^-1,the dosage of epichlorohydrin 30 mL,the dosage of iminodiacetic acid 2.0 g and the modified time 16 h.The results of Scanning electron microscopy（SEM）,nitrogen adsorption and Fourier transform infrared spectroscopy（FT-IR）showed that the surface pores of IDA-PSC were fully opened,and the wrinkles on the inner wall were clearly visible.The specific surface area and total pore volume increased significantly.The introduction of-N（CH₂COOH）₂ confirmed that the iminodiacetic acid was successfully grafted onto the surface of PSC.With the increase of pH value,the adsorption capacity of IDA-PSC remarkably increased initially and then tended to equilibrium and the optimum pH value was found to be 5.0.Meanwhile,the adsorption amount of copper ions rapidly decreased with the ionic strength initially and then tended to equilibrium.The IDA-PSC adsorbent presented high adsorption capacity for Cu（Ⅱ）even at pH values as low as 2.0(q_e=21.25 mg g^-1),or the CaCl₂concentration of 0.12 mol L^-1(q_e=20.3 mg g^-1).The experimental data fitted well with the Langmuir isotherm,yielding maximum adsorption capacity of 36.6 mg g^-11 at 298K.The kinetic data verified that Cu（Ⅱ）adsorption could be represented by the Pseudo-second-order model,and the equilibrium could be reached within 2 h.Thermodynamic parameters indicated that the adsorption process was spontaneous,endothermic and entropy increment.The desorption study demonstrated that the IDA-PSC could be readily regenerated using 0.5 mol L^-1HCl solution and the desorption ratio was of 98.5%.The desorbed IDA-PSC could be reused at least six times without significant adsorption efficiency reduction.According to the results of batch experiments and adsorbent characterizations,the adsorption process of copper ions on IDA-PSC could be controlled jointly by several mechanisms,including intraparticle diffusion,electrostatic attraction,as well as ion-exchange and surface complexation that occur concomitantly.The orthogonal array design was applied to optimize the modification conditions of PSC with sodium hydroxide solution.The results revealed that the optimal conditions were at 0.8%（w/w）NaOH with liquid-solid ratio of 0.35 L g^-1treating for50 min.SEM and nitrogen adsorption analyses indicated that the holes on the surface of PSC were opened and the three-dimensional layered structure was clearly visible.Both the specific surface area and total pore volume increased.The MB adsorption process was evaluated using Response Surface Methodology involving Central Composite Design.Optimum adsorption was achieved at pH 5.1,0.5 g L^-11 adsorbent,and dye concentrations 328 mg L^-1at 249 min.The adsorption isotherms were best fitted by the Langmuir equation while the adsorption kinetics were well described by Pseudo-second-order equation.The adsorption equilibrium time for AP-PSC was near4 h,which was controlled jointly by intraparticle and film diffusion mechanisms.The maximum monolayer adsorption capacity of AP-PSC for MB was of 368.2 mg g^-11 at298 K.Thermodynamic parameters suggested that the adsorption process was spontaneous,endothermic and entropy increment.According to the results of batch experiments and adsorbent characterizations,the adsorption process of MB on AP-PSC could be controlled jointly by several mechanisms,including hydrogen bonds,π-πelectron donor-accepter interaction,as well as ion-exchange that occur concomitantly.The effects of process conditions on the iodine and methylene blue adsorption of paeonia ostii seed coats activated carbon（PSCAC）were investigated.The results suggested that the optimum conditions for the preparation of PSCAC were:impregnation with a mass ratio of 2.5:1 and activation temperature at 873 K for 40min.The NA-PSCAC was prepared by means of oxidation of PSCAC with nitric acid.Nitrogen adsorption indicated that specific area and total pore volume of NA-PSCAC decreased by 73%and 76%,respectively.Boehm titration analyses revealed that the amounts of superficial oxygenated acidic groups increased from 0.85 to 4.07 mmol g^-1.The Cu（Ⅱ）adsorption by NA-PSCAC was strongly affected by contact time,initial concentration,solution pH and ionic strength.Pseudo-second-order equation and Langmuir isotherm could satisfactorily describe the experimental data.Maximum adsorption capability was found to be 39.4 mg g^-1for Cu（Ⅱ）at 298 K.The adsorption equilibrium was reached within 60 min.The adsorption thermodynamic experiment revealed that the adsorption of NA-PSCAC towards Cu（Ⅱ）was endothermic,spontaneous and entropy increment.Desorption study demonstrated that NA-PSCAC could be readily regenerated using 0.2 mol L^-11 HCl solution and the desorption ratio was of 90.3%.The desorbed IDA-PSC could be reused at least six times without significant adsorption efficiency reduction.Compared with IDA-PSC,the NA-PSCAC adsorbent has the characteristics of simpler process,less environmental pollution and good adsorption capacity.Based on the well correlated adsorption isotherm of Cu（Ⅱ）on NA-PSCAC,a two-stage batch adsorption process design was presented and the analysis results indicated that the two-stage batch could save more NA-PSCAC than single-stage batch.It is particularly suitable for optimizing the use of NA-PSCAC adsorbent to minimize capital investment costs and especially when the requirement for copper ions removal efficiency is very high.