Preparation Of Pectin/poly（m-phenylenediamine） Microsphere And Its Application For Pb²⁺ Removal

With the rapid development of industry,heavy metal ions(such as Pb²⁺)are directly or indirectly discharged into the water environment,are enriched in organisms through environmental media,and then enter the human body through the food chain,bringing great health hazard to human body.In recent years,there have been frequent occurrences of heavy metal contamination in food,and research on the removal of heavy metals has also received widespread attention.At present,the adsorption method has always been favored by people because of its cheap and easy-to-obtain materials,low cost,good removal effect,and easy recycling,most of the practical applications are the method of adsorption.A large number of studies have showed that pectin has the ability to adsorb heavy metals,but the direct use of pectin as an adsorbent will have many problems:such as the adsorption capacity is little;it is difficult to separate from the water after adsorption,and it cannot be desorbed and reused.In order to solve the above problems,this study prepared pectin microspheres by the classical pectin-Ca²⁺cross-linking technology,and then assembled poly（m-phenylenediamine）on the pectin microspheres to prepare a new type of pectin/poly（m-phenylenediamine）microspheres to study the removal effect and adsorption mechanism of lead ions.The main research results of this paper are as follows:1.Novel composite biosorbent-P/Pm PDA microspheres with different content of poly（m-phenylenediamine）were prepared by assembling poly（m-phenylenediamine）on the surface of pectin microspheres(the content of poly（m-phenylenediamine）were64.8%,60.8%,55.5%and 41.2%,respectively named P/Pm PDA_160-1,P/Pm PDA_80-1,P/Pm PDA_40-1 and P/Pm PDA_20-1)to remove Pb²⁺.Its structure was characterized by Fourier infrared spectroscopy,elemental analysis,X-diffraction,thermogravimetric analysis,scanning electron microscopy,specific surface area and porosity,etc.,which confirmed the successful assembly of poly（m-phenylenediamine）on the surface of pectin microspheres.,and the amount of poly（m-phenylenediamine）can be achieved by adjusting the mass ratio of m-phenylenediamine to pectin microspheres.The results showed that compared with pectin microspheres,the specific surface area and porosity of P/Pm PDA microspheres are larger,and the thermal stability is also improved.The adsorption process of Pb²⁺on P/Pm PDA microspheres depends on the initial p H of Pb²⁺solution,adsorption time,the dosage of P/Pm PDA microspheres and the initial Pb²⁺concentration.In terms of p H,P/Pm PDA microspheres had the best adsorption performance when p H=5.0.In different P/Pm PDA microspheres,P/Pm PDA_20-1 only needs 4 h to reach the adsorption equilibrium,and it still has good adsorption performance for high concentration Pb²⁺solution.In addition,research showed the adsorption process of Pb²⁺on P/Pm PDA microspheres conforms to the Langmuir adsorption isotherm model and the quasi-second-order kinetic model,inferring that the adsorption process is a monolayer and is dominated by chemical adsorption.The Langmuir model predicts that the maximum adsorption capacity of P/Pm PDA microspheres for Pb²⁺is 390.09 mg/g.P/Pm PDA microspheres have good recyclable properties after 5 consecutive adsorption/desorption regeneration cycles.Finally,in terms of mechanism exploration,it is speculated that the adsorption mechanism of P/Pm PDA microspheres on Pb2+mainly includes a combination of multiple effects such as:porous effect,electrostatic interaction,ion exchange between Pb²⁺and Ca²⁺,H⁺,and the chelation of Pb²⁺with oxygen-containing and nitrogen-containing functional groups.2.In a multi-cation system,the adsorption performance of P/Pm PDA microspheres for Pb²⁺is reduced with a certain extent.The coexistence of Na⁺and Ca²⁺systems can inhibit the adsorption of Pb²⁺by P/Pm PDA microspheres.As the Na⁺concentration increases,the inhibitory effect becomes more obvious.But with the increase of Ca²⁺concentration,for P/Pm PDA microspheres,the adsorption capacity of Pb²⁺showed a trend of first decreasing and then increasing.The coexistence of heavy metal ions(Pb²⁺,Fe²⁺and Cu²⁺)has little effect on the adsorption of Pb²⁺,indicating that P/Pm PDA microspheres have multi-surface adsorption in this system.The affinity of P/Pm PDA microspheres to three heavy metal ions was further compared,and the relationship between the magnitudes of P/Pm PDA microspheres was Pb²⁺>Fe²⁺>Cu²⁺.The coexisting chelating agent has a significant inhibitory effect on the adsorption of Pb²⁺.As the concentration of the chelating agent increases,the adsorption performance of P/Pm PDA microspheres on Pb²⁺remains at a low level.In addition,P/Pm PDA microspheres have excellent inhibitory properties against mold,and the diameter of the inhibition zone measured by the Oxford cup method is 27-35 mm.3.P/Pm PDA microspheres also have a certain adsorption performance for Pb²⁺under the dynamic packed column system.The adsorption process is mainly affected by the water flow rate,the filling height of the adsorbent and the initial Pb²⁺concentration.The decrease of the flow rate,the increase of the column height and initial Pb²⁺concentration will prolong the breakthrough time of the adsorption column.After three consecutive cycles of adsorption,desorption and regeneration of P/Pm PDA microspheres,the total amount of Pb²⁺adsorbed decreased to a certain extent,but Pb²⁺could still be removed.The P/Pm PDA microspheres prepared in this study have excellent adsorption performance for Pb²⁺,can be recycled and are resistant to storage,and are a biosorbent with good comprehensive performance.