Synthesis, characterization of a sustainable Fe/Ce Doped Poly-(para-phenylenediamine) adsorbent and its potential for simultaneous removal of fluoride, arsenite and pathogens in aqueous

Abstract

Water pollution due to natural and anthropogenic sources remains one of the global problems which require attention due to its long-term effect on human and the environment. Prolonged exposure to chemical and microbial contaminated water may cause both acute and chronic health hazards. The occurrence of arsenic, fluoride, and pathogen in drinking water has raised severe health issues to human beings. The health impact of consuming arsenite, fluoride, and pathogens has resulted in adverse health effects such as skin cancer, dental and skeletal fluorosis, and water-borne diseases. Thus, the present research has been conducted for their simultaneous removal from water bodies. Generally, various methods have been developed to remediate water pollution which includes membrane filtration, ion-exchange, and adsorption. Within, these developed methods adsorption methods have gained attention due to the use of various materials including natural adsorbents such as clays, agro-waste, etc, and novel conjugated polymeric composites because they are easy to operate, less expensive, and eco-friendly. The use of hydrous oxides (Fe, Ce, and Mn) of rare earth elements have been studied and have shown high affinity for fluoride, arsenite, and other toxic elements. This study focused on the systemic synthesis of novel conjugated polymeric adsorbents by the incorporation of Fe/Ce oxides onto a phenylenediamine (pPD) polymer matrix through chemical co-polymerization route and its fluoride, arsenic and pathogen removal potentials at optimal conditions in an aqueous solution evaluation. The morphology and structural analysis of the synthesized Fe; Ce and Fe/Ce doped pPD were comparatively evaluated using the Fourier Transform Infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive-X-ray spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Modified Fe/Ce was successfully incorporated onto the pPD matrix as confirmed by the different morphological characterizations. The functional groups of pPD were not altered by the incorporation of the metal oxides as shown by the FTIR results. The synthesized material has an irregular shape within an average particle size between 20 -100 nm, with a low crystalline phase pattern when compared to the amorphous plain pPD. Relatively, the optimized composite samples of 2.5 % Fe-pPD, 5 % Ce-pPD and 1:1 Fe/Ce-pPD (2.5%) showed efficient and higher fluoride and arsenic sorption as well as disinfection ability against water borne pathogens. ii Moreover, the effect of contact time, adsorbent dosage, pH, initial concentration, temperature, and co-ions was assessed to determine their significance in Fˉ and As3+ removal in aqueous solution. The obtained results revealed that all the reported experimental conditions have significant effect on pollutants uptake. The kinetic data for 2.5 % Fe-pPD, 5 % Ce-pPD and 1:1 Fe/Ce-pPD composite fitted well to pseudo-second-order kinetic model for both Fˉ and As3+. Thus, chemo-sorption is the limiting step for fluoride and arsenite uptake. However, the intra-particle diffusion plot has shown three distinctive phases for the synthesized adsorbents, thus, the adsorption process occurs with more than one sorption mechanism step. Equally, the Freundlich isotherm model better described the sorption process of the synthesized materials, hence, adsorption process was occurring on a heterogeneous surface. The fitness of the kinetics and isotherm data was validated by lower values of goodness of fit (error factors). Thermodynamically, the removal process for both pollutants when using the 2.5 % Fe-pPD and 1:1 Fe/Ce-pPD adsorbents was endothermic, whereas for 5 % Ce-pPD was exothermic and endothermic (As3+ (1.86, 2.11, 4.71 mg/g) and Fˉ(6.79, 13.29, 14.75 mg/g)). The synthesized adsorbents can be regenerated up to four cycles when using H2O, NaOH and HCL, with H2O being the best regenerant for both adsorbents. Further, antibacterial results showed that 2.5 % Fe-pPD, 5 % Ce-pPD and 1:1 Fe/Ce-pPD (25 % :2.5%) composite inhibited the growth of common water-borne bacterial strains. Thus, the modified composites have not only portrayed the potential ability for metal ions removal but also showed strong antimicrobial activity against water-borne pathogens.