Chemical Oxidation Synthesis Of Poly(M-phenylenediamine) And Its Chromium(?)Removal Ability

Abstract:Along with the rapid growth of intrustry, more heavy metal wastewater is diacharged to rivers, then the environment is polluted. The governance of chromium(?) wastewater is one of the important and difficult problem, because of its toxicity, high concentration and complex state. Adsorption method is an effective way to remove pollutant, then the exploitation of new-type adsorbents became the research hotspot. The removal of chromium(?) with poly(m-phenylenediamine) adsorbent was proposed as a new thought in this paper. The potential regulation polymerization mechanism of poly(m-phenylenediamine) was illuminate, and the chromium(?) removal ability and mechanism by poly(m-pheylenediamine) was investigated. The main research contents and creative achievements are as follows:The innovative chemical oxidation synthesis flow of poly(m-phenylenediamne) was designed. The yield and performance of poly(m-phenylenediamine) was increased. The optimal polymerization conditions were decided:CO32-concentration2mol L1, polymerization time5h, polymerization temperature25?, polymerization initial pH8. The poly(m-phenylenediamine) achieved in the optimal condition had higher amorphism degree and thermostability, the yield enhanced15%compared with traditional method. The effect on the total organic carbon (TOC) during water treatment with poly(m-phenylenediamne) was investigated. The TOC datum in different pH value were all lower than6.64mg g-1, which are less than20mg g-1in integrated wastewater discharge standard. The data illustrate that there is no secondary pollution when poly(m-phenylenediamine) was used as adsorbent.The potential regulation polymerization of poly(m-phenylenediamine) was revealed. Alkali (OH-?CO32-) could observably decrease the polymerization potential of m-phenylenediamine. Base on the nernst equation, the potential of oxidant in solution decreased, oxidation capacity decreased, the oxidation of poly(m-phenylenediamine) decreased. Alkali could control the H+concentration in solution, the reaction was prompted to proceed, the yield of polymer was increased. The polymerization initial pH is in the pH butter range of carbonate system. The study found that adding CO32-could control the sharp fluctuation of polymerization pH and stabilize the oxidizing ability of oxidant.The chromium(?) adsorption behavior with poly(m-pheny-lenediamine) was investigated. The reasonable chromium(?) adsorption condition were pH2and reaction time5h. The chromium(?) maximum adsorbance was510.9mg g-1in15?,598.5mg g-1in30?,666.8mg g-1in45?. The effect of coexisting ions on adsorptivity was proved. SO42-could grab35%adsorption site, however, when Cl-and NO3-exsited, the chromium(?) adsorptivity still remained above90%. The chromium(?) adsorption process can be better described by pseudo-second-model, which illustrates that the adsorption is chemisorption. The value of enthalpy is positive, which indicates the adsorption is endothermic process. The values of free energy are negative, which indicates the adsorption reactions are spontaneous at experiment temperature.0.1mol L-1NaOH was selected as the desorption reagent. The five times accumulated adsorbance was1545mg L-1.The removal mechanism of chromium(?) with poly(m-phenylenediamine) was illuminated. X-ray photoelectron spectroscopy analysis indicates that quinoid imine and benzenoid amine are the main functional groups for electrostatic adsorption and chromium(?) reduction, respectively; chromium(?) was adsorbed to poly(m-phenylenediamine) surface as CrCl3. The redox reaction equation between chromium(?) and poly(m-phenylenediamine) was builded. The structure-function relationship between poly(m-phenylenediamine) and chromium(?) adsorption was builded. Poly(m-phenylenediamine) with lower oxidation state has lower energy state which was calculated by Minimize Energy in ChemBioOffice. It could be protonized easier, and has strongher chromium(?) adsorption ability. The quality of chromium(?) and chromium(?) in the surface of poly(m-phenylenediamine) was calculated according to the molar cariation of benzenoid amine and chromium ions before and after adsorption. Poly(m-phenylenediamine) with lower oxidation state has stronger chromium(?) reduction ability was confirmed.