Facile Green One-Pot Synthesis of Pyrimidine Based Hydroxy Azo-Polymer for Selective Adsorption of Cationic Dyes

Porous organic polymers (POPs) decorated with specific functional groups possessing high surface area have been extensively utilized for removal of organic dyes from water. However, synthesis of these polymers demands stringent experimental conditions such as high polymerization temperatures, inert atmosphere and the use of transition metal catalysts. Here, a pyrimidine based hydroxyl azo polymer PBHAP has been fabricated via one-pot azo coupling green synthesis in water under ambient conditions in absence of any catalyst. Strategic functionalization of polymer with azo (-N = N-) and free phenolic (-OH) groups has been carried out to impart adsorption properties via hydrogen bonding and electrostatic interactions of peripheral groups between polymer and nitrogen-containing aromatic ring of organic dyes. The adsorbent's efficacy in removing the hazardous dyes, Methylene Blue (MB), Crystal Violet (CV) and Rhodamine B (RHB) has been investigated. Various characterization methods have been employed to investigate the physicochemical characteristics of polymer and monitor the adsorption kinetics of dye's eradication from aqueous solution. The adsorption studies have been performed in ambient conditions at room temperature, resulting in maximum removal efficiencies of 98%, 96.2%and 95.7% for cationic dyes CV, RHB and MB respectively. Langmuir isotherm and pseudo-second-order kinetic models have been employed to probe the interactions between adsorbate and adsorbent during the dye removal process. The maximum theoretical adsorptive capacities of 151, 97 and 75 mg/g have been achieved for CV, RHB and MB respectively. Long-term cycle stability experiments have elucidated the regenerative behavior of PBHAP polymer without significant loss in the adsorption efficiency. The polymer displays high adsorptive capacity and preferential selectivity for cationic dyes from a binary mixture of cationic and anionic dyes, monitored using kinetic and Zeta Potential studies (-24 mV) for the polymer. The synthesized polymer has displayed exceptional porosity with a high surface area of 181 m2 /g as confirmed by BET studies and excellent surface wettability validated by water contact angle studies. Owing to these findings, the synthesized polymer has an excellent tendency to remove organic pollutants and holds enormous potential as a versatile adsorbent for wastewater remediation and environmental protection.