Synthesis Of Adsorbent Materials For Citrus Peels Of The Genus Citrus

Citrus peel is a common agricultural waste,which is rich in resources,low in price and biodegradable.Its interior is loose and porous with a three-dimensional network structure.The chemical composition of plants contains active groups such as carboxyl,hydroxyl and phenolic hydroxyl groups,which is a very ideal ion exchange material or ion exchange material skeleton.In order to improve the performance of citrus peel and expand its application field,natural plant polyphenols were used to modify citrus peel,aiming to effectively utilize citrus peel and endow it with new properties.The biosorption material based on citrus peel not only solves the problem of agricultural waste disposal,but also overcomes the shortcomings of traditional heavy metal removal methods,such as high cost,complex operation,low efficiency and secondary pollution.It turns waste into treasure and saves a lot of resources and costs.In this project,citrus peel is used as the skeleton,and dopamine,gallic acid,tannin and baicalein are used as modifiers.Modification of citrus peels by three methods:"dopamine modification","polyphenol modification"or"polyphenol modification supplemented with cross-linking agent".to obtain high adsorption selectivity,high adsorption performance,low cost,reusable,green and environmentally friendly new adsorption materials.The modified adsorption materials were applied to the purification of excessive heavy metal wastewater and the removal of excessive heavy metals from Chinese patent medicines.The research contents are as follows:1)Pre-treatment of citrus peels with physical crushing,soxhlet extraction（water extraction,alcohol extraction,water extraction before alcohol extraction）,alkaline activation（6h,12h,24h）and acid activation（0.5M,1M,1.5M）to purify the cellulose skeleton in citrus peels,release the active groups and increase the porosity for the next step of chemical modification and adsorption application.2)Modification of citrus peels with dopamine,gallic acid,tannin and baicalin etc（BM）.The structure of the modified citrus peel was characterized by naked eye observation,SEM,UV,FT-IR and XRD.3)Using gallic acid,tannin,baicalein and cross-linking to modify the acid/alkali activated citrus peel cellulose skeleton（MC）,to obtain polyphenols and cross-linking agent modified alkali treated citrus peel(MC-N_WE)and polyphenols and cross-linking agent modified acid treated citrus peel(MC-H_WE).The modified citrus peel was characterized by naked eye observation,SEM,UV,FT-IR and XRD.4)Static adsorption was used to optimize the adsorption conditions,and the test items mainly include adsorption temperature,contact time,solid/liquid ratio,initial concentration of heavy metals,p H of adsorption solution,etc.The optimum adsorption conditions were obtained as follows:25°C,6h,0.1g/20m L,60μg/m L,p H6.The results showed that the adsorption effect of MC method modified citrus peel was stronger than that of BM method,and the adsorption effect of MC-N_WEwas stronger than that of MC-H_WE.Six kinds of modified citrus peel adsorption materials were optimized:polyphenol-modified water followed by alcohol citrus peel（BA-WE,TA-WE,GA-WE）and polyphenol and epichlorohydrin modified alkali treated citrus peel(BA-EPI-N_WE,TA-EPI-N_WE,GA-EPI-N_WE).which showed the best adsorption performance for Pb²⁺,Cu²⁺,Cr³⁺and Cr⁶⁺heavy metal ions.At the same time,different concentrations of nitric acid were used to elute the adsorbed BA-WE,TA-EPI-N_WE and GA-EPI-N_WE at different time conditions.The results showed that under the condition of 6h,2M HNO₃ had the best elution effect on BA-WE,1.5M HNO₃ had the best elution effect on TA-EPI-N_WE and GA-EPI-N_WE.5)The experiments of HM repulsion in the Chinese patent medicines Sanhuang Tablet,Compound Danshin Tablet,Rhinitis Kang Tablet and Brain Heart Clear Tablet.The four heavy metal ions of Pb²⁺,Cu²⁺,Cr³⁺and Cr⁶⁺that do not exceed the standard in Chinese patent medicine were artificially added and then subjected to simulated repulsion tests.The above six best modified citrus peels(BA-WE,TA-WE,GA-WE,BA-EPI-N_WE,TA-EPI-N_WE,GA-EPI-N_WE)were used to remove the excessive HM in the above four Chinese patent medicines.The results showed that the removal rates of Pb²⁺in four Chinese patent medicines by six modified materials were higher than 80%.The recovery rates of berberine hydrochloride,salvianolic acid B and baicalin by BA-WE,TA-WE and GA-WE were more than 90%.The removal rates of Cu²⁺in four Chinese patent medicines by GA-EPI-NWE,TA-EPI-NWE and BA-EPI-N_WE were not less than 70%.The removal rates of Cu²⁺in Sanhuang Tablets by TA-EPI-N_WE and BA-EPI-N_WE were more than 95%.and TA-EPI-NWE has the best recovery rate of quercetin,which is close to 100%.6)Purification of excess heavy metal wastewater.Three kinds of simulated HM wastewater were purified by BA-WE,TA-EPI-N_WE and GA-EPI-N_WE.（1）Removal of excessive heavy metals in HM wastewater.（2）The effect of external interfering metal cations(Mg²⁺,Na⁺,Ca²⁺,K⁺)on the adsorption performance of modified orange peel.（3）The effect of external interfering acid anions(Cl^-,SO₄^2-)on the adsorption performance of modified orange peel.The adsorption results show that the three modified materials have high adsorption capacity and adsorption selectivity for Pb²⁺and Cu²⁺in wastewater without interfering ions.With the increase of the concentration of metal cations and acid anions,TA-EPI-N_WE and GA-EPI-N_WE had almost no effect on the adsorption performance of Pb²⁺,and the removal effect of Cu²⁺,Cr³⁺and Cr⁶⁺was negatively affected.The adsorption efficiency of BA-WE for Pb²⁺,Cu²⁺,Cr³⁺and Cr⁶⁺was negatively affected to some extent.From the above,DA,GA,TA and BA can be used as modifiers to modify the pretreated citrus peel.The modification of citrus peels by natural plant polyphenols can realize the recycling of agricultural waste,and also provided a new idea for the design and preparation of efficient,economical and environmentally friendly biosorption materials,which expanded the application field of biosorption materials.