Efficiency of Poly(m-Aminophenol) as a Novel Adsorbent for Individual/Simultaneous Removal of Organic Dyes and Hexavalent Chromium from Water Sources

Excessive levels of dyes and heavy metals in water sources continue to pose a serious threat to the ecosphere and public health, and their removal by adsorption is a proven viable process among others. In this work, a conducting polymer, poly(m-aminophenol) (PmAP), was synthesised via a facile oxidative polymerisation, characterised, and employed for adsorptive removal of cationic (methylene blue)/anionic (Congo red) dyes as well as Cr(VI) in aqueous medium. Lower pH (<= 5.0) favoured the adsorption of Congo red and Cr(VI), while methylene blue adsorption followed a reverse trend. The experimental data were best represented by the Langmuir isotherm model rather than Freundlich and Temkin model and yielded monolayer adsorption capacities of 64.1, 34.5, and 42.6 mg/g for Congo red, methylene blue, and Cr(VI), respectively. The kinetic data were best fitted by the second-order equation as the per closeness of the calculated equilibrium adsorption capacities to the experimental values. The adsorbed dyes/Cr(VI) on PmAP can be desorbed on treatment with 0.1 M NaOH/0.1 M HCl to regenerate the adsorbent for further use without a significant decrease in adsorption efficiency (< 10%) up to the fourth cycle. Based on the characterisation of absorbed PmAP, pH dependence, and regeneration study, the mechanisms for adsorption of dyes/Cr(VI) were proposed. Overall, the present study demonstrated that PmAP can be used as an efficient and recyclable adsorbent to remove the aqueous dyes/Cr(VI) and in the treatment of wastewater.