Synthesis Of Tannin-based Adsorbent From Seeds Of Paeonia Ostii And Its Adsorption Performance On Heavy Metals

"The peony stands as the epitome of national beauty,with its breathtaking blooms captivating the whole city".The peony,a cherished traditional flower in China,boasts remarkable ornamental value and holds significant importance in oil and medicinal applications.However,during the extraction of peony seed oil,the resulting seed residue is often disregarded as waste,leading to resource wastage and environmental pollution.Tannins,a class of polyphenolic compounds,possess not only antioxidative,anti-inflammatory,and antimicrobial properties but also the ability to adsorb heavy metal ions.Through the utilization of seed residue from Paeonia ostii after oil extraction,this study aimed to tackle waste disposal concerns and transform it into a valuable resource for remedying heavy metal pollution,thereby achieving the effect of"turning waste into treasure".The study primarily focuses on the seed residue of P.ostii following the oil extraction process.Initially,single-factor experiments were conducted to investigate the extraction and purification processes of tannins from the seed residue.Subsequently,NaOH modification was employed to examine the adsorption efficacy of the modified adsorbent on lead ions.Finally,the adsorption kinetics and mechanisms of the NaOH-modified tannin adsorbent were analyzed using adsorption models and characterization techniques.The key findings of this research are as follows:(1)The optimal conditions for extracting tannins from the seed residue of P.ostii were determined as follows:utilizing an ultrasound-assisted extraction method with an ultrasound power of 300 W,an ethanol concentration of 60%,a liquid-to-material ratio of 20:1,an extraction temperature of 60℃,and an extraction time of 80 minutes.(2)The optimal purification conditions for the extracted tannins from the seed residue were achieved using AB-8 macroporous resin.The sample solution,with a pH value of 4 and a concentration of 1.2 g/L,underwent loading at a flow rate of 3 mL/min with a sample volume of 120 mL.Elution was performed using 40 mL of 60%ethanol at a flow rate of 2 mL/min.This purification method resulted in a tannin content of 6.170.12%in the purified sample.(3)The optimal conditions for preparing NaOH-modified tannin adsorbents from the seed residue were determined as follows:employing a NaOH concentration of 0.2 mol/L,a liquid-to-material ratio of 0.2,a mixing time of 3 hours,and a drying temperature of 65℃.The modified tannin adsorbent exhibited an adsorption capacity for heavy metals 1.79 times higher than that of unmodified tannins.Comparative analysis with commercial adsorbents revealed that the modified adsorbent achieved a similar level of adsorption for Pb(Ⅱ)ions.(4)The adsorption process was modeled using adsorption kinetics models and the Langmuir isotherm model.The pseudo-second-order rate model demonstrated a high correlation coefficient of 0.99,indicating its effectiveness in predicting the adsorption performance of the adsorbent under specific conditions.Scanning electron microscopy revealed that the modified tannin adsorbent derived from the seed residue of P.ostii exhibited an increased number of crevices and protrusions,resulting in a larger contact area and more active sites for adsorption,thus enhancing the adsorption of heavy metal ions.