Poly M-phenylenediamine Synthesis And Adsorption Characteristics Of Sulfate Ion

Sulfate-containing wastewater is mainly resulted from melting and chemical industries. Its emission load is large while its concentration is always very high, which is not only harmful to environment and biological system, but also negative to the industries production. Developing effective disposal technique is very urgent. In this paper, a new type ofπ-conjugated poly(m-phenylenediamine) was synthesized by chemically oxidative polymerization with m-phenylenediamine as monomer and ammonium persulfate as oxidant, and was used as sulfate absorbent. The effect of various factors on the synthesis was investigated while the product as-prepared was taken to test its absorbability for sulfate ions. The adsorption and desorption mechanism was discussed with the aid of FTIR, XPS and calculation of minimized energy of molecules. Moreover, based on the polymerization mechanism, oxidative polymerization-acid/base manipulation mehtod (OPab) was proposed to modify the polymerization technique. Results are shown as follows:(1)The synthesis of poly(m-phenylenediamine) shown that yield, oxidation state and solubility in water of poly(m-phenylenediamine) are affected heavily by the type of oxidant, oxidant/monomer molar ratio and initial polymerization pH. Poly(m-phenylenediamine) with high yield and low solubility in water can be synthesized using ammonium persulfate as oxidant; decreasing the oxidant/monomer molar ratio would bring down the yield and oxidation state of the product; increasing the initial polymerization pH would promote the yield but decrease the oxidation state.(2)The systematically adsorption experiments indicates that nearly 99.8% of sulfate ions can be removed with poly(m-phenylenediamine) while the absorbance can reach 107.9 mg·g-1. The adsorption ability of poly(m-phenylenediamine) was improved with declining the oxidation state of it. The adsorption performance of poly(m-phenylenediamine) increases with lowering the intial solution pH. In the five times of adsorption-desorption experiment the performance of poly(m-phenylenediamine) did not attenuate and the accumulative absorbance went up to 487.95 mg·g-1.(3)As suggested by the adsorption mechanism, physical adsorption is the major interaction, when initial solution pH is more than 3. But as initial solution pH is less than 3, absorbing sulfate ions is mainly relied on the protonation (doping) of imino groups. Part of the quinoid imine units were transformed into the protonated benzenoind amine units to absorb sulfate ions. The desorption is accomplished effectively by adding base solution to neutralize the protonic acid.(4)Oxidative polymerization modified with acid/base manipulation (OPab method) was proposed based on the response of reactivity of monomer and oxidant to pH. High yield and low oxidation state of poly(m-phenylenediamine) were gained by the OPab method through concurrently adding oxidant and NaOH solutions with specific concenration. The yield and the increment of adsorption performance is high when poly(m-phenylenediamine) was synthesized by using 2 mol·L-1 of NaOH solution [named PmPD(NaOH2)]. The highest sulfate absorbance of PmPD(NaOH2) is 125 mg·g-1 while the highest silver ions absorbance is 1886 mg·g-1.(5)The performance-oxidation state relationship was stuied on the basis of molecular energy minimization and molecular stability.