PANI-Related Composites in Water Purification

PANI is one of the earliest known synthetic polymers, which can date back to 1835 as aniline black for any products produced by the oxidation of aniline. The interest toward PANI increased significantly over the past decades due to its low cost, easy preparation, high conductivity, mechanical flexibility, environmentally stability, and unusually doping/dedoping chemistry. Besides, PANI also has three distinct oxidation states with different colors, naming leucoemeraldine, emeraldine, and pernigraniline. 

The inorganic materials involve the silica, montmorillonite, allapulgite, FCjO, ZnCl, CuCl, etc. The as-prepared composites can absorb versatile organic and inorganic pollutants from aqueous solutions. Different silica crystalline forms were utilized to fabricate various PANI/silica composites for water purification. PANI were coated on silica gel to modify its surface morphology and to improve its adsorption capacity for phenol [35] and acid green 25 [36] adsorption from aqueous solutions. 

Hexagonally ordered silica, SBA-15, were also fabricated with PANI to prepare PANI/hexagonally ordered silica nanocomposite, which was used to extract polycyclic aromatic hydrocarbons from aqueous solutions, including naphthalenes, biphenyl, acenaphthene, anthracene, pyrene, and so on [37]. The same nanocomposite exhibited selective adsorption toward 2,4-dini-trophenol in aqueous solution in the presence of phenol with the adsorption capacity of 55.0 mg/g [38]. Chemical oxidation of aniline on hexagonal mesoporous silica (HMS) was carried out to generate PANI/HMS nanocomposite for Ni(II) elimination from aqueous solutions [39]. This process was spontaneous and endothermic and can be applied to Freimdlich isotherm and a pseudo-second-order kinetic. The removal efficiency was 99.87% for 50 mg/L Ni(II) solution, and the maximum sorption capacity can reach 253.17 mg/g at 300 mg/L Ni(II) solution. 2,6-Dichlorophenol can be selective removed from aquatic environment by PANI/silica gel composite [40]. A spontaneous and endothermic process was also observed with a Langmuir isotherm. 

Magnetic PANI/Fe O nanocomposites were prepared via emulsion polymerization to remove nitrate ions, [41] which gave linear correlation to Freimdlich isotherm with a pseudo-second-order kinetic mechanism. The optimum sorption condition was found to be a 4.0 g/L sorbent solution with a contact time of 10 min at pH = 7.0. PANI-doped ZnCl and CuCl were used for sodium dodecyl benzene sulfonate (SDBS) removal in a spontaneous and exothermic process [42]. Toxic metallic cations, such 

Natural occurring sawdust, polysaccharides and carbon-related materials have been fabricated with PANI and widely apphed in wastewater purification. PANI/sawdust composites had been applied to adsorb diclofenac sodium, [46] Cd(II), [47] Cu(II), [48] and Cr(VI) [49]. The average adsorption capacity for Cu(II) can reach 58.23 mg/g, [48] while Cd(II) was removed by pseudo-second-order kinetics and a Freundlich model [47]. Acidic condition (pH 2) was required for Cr(VI) removal and the mechanism was proposed via an anion exchange process [49]. 

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