Facile High-Yield Synthesis Of Poly(Aniline-co-m-sulfophenylenediamine) For Dye Removal

Polyaniline (PANI) and its copolymers had attracted considerable attention aspolymeric adsorbents for dyes due to their good environmental stability and excellentabsorption properties. High-yield poly(aniline-co-m-sulfophenylenediamine)(PANSP)particles were synthesized by oxidative copolymerization of aniline (AN) andm-sulfophenylenediamine (SP) in HCl solution without any additional initiators. Bysimply adjusting AN/SP molar ratios, the morphologies and chemical structures of theas-synthesized PANSP were totally different. And the as-synthesized PANSP werecharacterized by SEM, TEM, zeta potential, surface area, XRD, FTIR, UV-Vis andXPS spectra. Adsorption characteristics of the PANSP were examined using a cationicdye methylene blue (MB) as the adsorbate, and the effects of the composition ofcopolymer, adsorption temperature, contact time, pH, initial concentration of MB andionic strength were studied through batch adsorption tests.Results showed that using a new method of copolymerization, which was thatAN was first reacted with APS before SP addition to produce a “pre-polymer”, whichwas proposed as the initiator for further copolymerization of SP. By simply adjustingthe adding mode of reactants, the product yields of PANSP could be remarkablyincreased by2-20%. Morphologies, chemical structures and adsorption properties ofthe copolymers varied significantly with AN/SP molar ratios. For example, with theincrement of SP content, the copolymer particles become larger in size (50-300nm)and more uniform in size distribution. The PANSP copolymers showed no internalpores in their structures. With the increment of SP content, the zeta potential ofPANSP became more negative, and PNASP showed a much lower pHPZC(pHPZC<1.9)than PANI (pHPZC=5-6), which could be attributed to the sulfonic groups in SP unit.The BET surface area of PANSP was9.7-43.0m2/g.The adsorption experiments showed that as compared with PANI, thecopolymers exhibited much higher MB adsorption capacities and the best adsorptionwas achieved by PANSP (8:2)(AN/SP molar ratio8:2). The adsorption isotherm and kinetic could be well fitted by the Langmuir model and the persudo-second-ordermodel, respectively. The calculated Qmof PANSP (8:2) for MB was118mg/g, muchhigher than previously reported PANI adsorbents. The optimal solution pHefor MBadsorption was3.5-6.0, and ionic strength showed no significant influence on MBadsorption. The proposed adsorption mechanisms were ion exchange between MB+and H+on sulfonic groups and electrostatic interaction between MB+and negativelycharged sulfonic groups.The new method used in this study for the synthesis of copolymers is low cost,easy to implement, and high yield, which can provide a reference for the synthesis ofother copolymers. The PANSP (8:2) copolymer has a good adsorption of MB, whichextends the application of polyaniline on cationic dye adsorption area.