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Novel β-feooh/polymeric composites for remediation of wastewaters
Akharame, Michael Ovbare
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Water reclamation and sustainability through nano-based treatment processes has a promising prospect. The safe application of the numerous nanomaterials being applied for water treatment purposes is of utmost importance in this new phase of nanotechnology deployment. This is pertinent due to their potential adverse environmental and health concerns. This study was designed to investigate the suitability of polyamide matrix as immobilization support for the established catalyst- β-FeOOH nanoparticles. The synthesized polymeric nanocomposites (PNCs) were utilized for the remediation of 4-chlorophenol (4CP) and 4-nitrophenol (4NP). The analytes were selected to investigate the role of the attached groups (chloro- and nitro-) in the degradation intermediates, pathways and kinetics using the liquid chromatography/mass spectrometry time-of-flight (LCMS-TOF) instrumentation. The hydrothermally synthesized β-FeOOH nanoparticles and the PNCs fabricated via the in situ route were characterized using attenuated total reflectance-Fourier transform infrared (ATR-FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption-desorption (Brunauer-Emmet-Teller and Barrett-Joyner-Halenda), which confirmed the clear-phase β-FeOOH nanoparticles and its successful incorporation into the polyamide matrix. Daphnia magna acute toxicity test was done to establish the safe application of the polymeric nanocomposites and the optimum treatment duration for the wastewater. The ozonation of the analytes solution (100 mL of 2 x 10-3 M) was done in a sintered glass reactor, with samples collected at different intervals over 60 min. The comparative oxidation results revealed that the 4-chloro- and 4-nitrocatechol pathways via hydroxylation were the major degradation route for 4CP and 4NP. Catechol intermediate was present as a primary breakdown product for the two analytes. Hydroquinone was observed as the transient degradation intermediate for 4CP but was absent for 4NP. Rather, an ozonation intermediate 2, 4-dinitrophenol was identified which was further oxidized to 3,6-dinitrocatechol. Several dimer products (C12H8Cl2O2, C12H8Cl2O3, C12H8Cl2O4, C12H8N2O6, C12H8N2O7, etc.) were identified in the oxidation processes, favoured by alkaline conditions with more versatility shown by 4CP. Catalytic properties of the β-FeOOH/polyamide nanocomposites were evaluated during the degradation of 4CP and 4NP aqueous solutions through catalytic ozonation processes. The catalysed ozonation results showed 98.52% and 89.66% degradation of 4CP and 4NP using the optimum performing catalyst (1.25 wt% β-FeOOH loading) within 40 min relative to 62.94% and 55.21% degradation for the simple ozonation, respectively. The effect of pH on the degradation efficiency revealed that the catalysed ozonation is more favourable at higher pH values (pH 10 > 7 > 3). The COD and TOC values for real wastewater was effectively reduced by 54.62% and 89.22% by the polymeric nanocomposites compared to 33.92% and 47.06% removal obtained in the uncatalysed ozonation. The involvement of hydroxyl radicals in the breakdown of the phenols was confirmed by using methanol as a scavenger, which reduced the degradation efficiency of 4CP from 98.52% to 25.64% when it was added to the analyte solution. The composite exhibited excellent reuse potential with minimal decrease in its degradation ability over six cycles, and no leaching of iron was observed when applied in acidic, neutral and alkaline conditions. The complete degradation of 4CP after the treatment of the contaminated water for 1 h was established using the LCMS-TOF. However, the toxicity results showed that the treated water obtained at 1.5 h had better quality. Toxic intermediates persist in solution even though the parent analyte was completely degraded. Hence, toxicity assays should be encouraged on a complementary basis to the standard chemical methods. The study provided a great insight into the ozone degradation intermediates and pathways of 4CP and 4NP. The novel polymeric nanocomposites gave promising remediation ability for the removal of 4CP and 4NP from aqueous solutions and provided a safe deployment of the catalyst utilized.