title: pH manipulation: a facile method for lowering oxidation state and keeping good yield of poly(m-phenylenediamine) and its powerful Ag+ adsorption ability.
abstract: A method of pH manipulation has been used to improve chemically oxidative polymerization of m-phenylenediamine (mPD) through concurrent addition of NaOH when adding oxidant (NH(4))(2)S(2)O(8). pH detection and open-circuit potential technique were adopted to monitor the polymerization process of mPD and to explain the oxidation state-pH and yield-pH relationships. Results from Fourier transformed infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies indicate that a low oxidation state is under control by regulating NaOH concentration. At 2.5 M NaOH, the oxidation state of poly(m-phenylenediamine) (PmPD) is 64.7 mol % (measured by molar content of quinoid imine from XPS), while the yield is 84%. The synthesized PmPD possesses better Ag(+) adsorption performance when lowering its oxidation state. Moreover, the Ag(+) adsorbance of PmPD can reach 1693 mg g(-1). Meanwhile, Ag(+) adsorption mechanism was studied by pH tracking, X-ray diffraction (XRD) patterns, and X-ray photoelectron spectroscopy. The adsorption process includes redox reaction, chelation, and physical adsorption.
authors.affiliation: Department of Environmental Engineering, School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China.
authors.forename: Liyuan
authors.initials: L
authors.lastname: Zhang
authors.forename: Liyuan
authors.initials: L
authors.lastname: Chai
authors.forename: Jin
authors.initials: J
authors.lastname: Liu
authors.forename: Haiying
authors.initials: H
authors.lastname: Wang
authors.forename: Wanting
authors.initials: W
authors.lastname: Yu
authors.forename: Peilun
authors.initials: P
authors.lastname: Sang