Removing Perfluorooctanoic Acid And Perchlorate From Aqueous Media Using Newly Synthesized LDH-system

Perfluorooctanoic acid?PFOA?is a group of organic compounds that are persistent and very toxic to living organisms and the environment.In this study,two types of Mg-Al double hydroxide layers?i.e.,LDH-1?Mg-Al-Cl?,synthesized hydrothermally and LDH-2?Mg-Al-NO₃?,synthesized by dry grinding process?were synthesized using dry grinding and hydrothermal methods to remove PFOA from the aqueous solution.The kinetic study was carried out to identifying sorption kinetics and highlighting the physicochemical interaction between PFOAs and LDHs.The synthesized LDHs achieved a minimum equilibrium time without thermal treatment and activation.The isotherm model“Freundlich”was best suited for studying sorption isotherms.According to the Langmuir isotherm model,the maximum adsorption capacity of LDH-1 was(667 mg g^-1)and LDH-2(244 mg g^-1).Likewise,the mechano-chemically prepared LDH-2 possessed high adsorption capacity compared to that of LDH-1.The rates of PFOA adsorption with LDH-1 and LDH-2 were 90%and 98.9%,respectively,by using 0.05g adsorbent at the lowest time compared to a similar previous study using different adsorbents.The possible mechanism behind the adsorption could be electrostatic attractive,i.e.,hydrogen bonding and anion exchange.The concatenations of LDH-1 and LDH-2 were very influential on the overall rate of adsorption.In contrast,an increased rate of adsorption was observed using amounts,i.e.,10 mg L^-1 to 100 mg L^-1,owing to the higher availability of PFOA in the solution.The anion-exchange and the electrostatic attraction could have played significant roles in the sorption process.The PFOA–sorption was cost and time effective,pH-dependent,and influenced by elevated background concentration of electrolytes.The prepared LDHs bear prospects for PFOA removal from the aqueous medium,with the potential of using synthesized LDHs in a fixed bed filter for environmental remediation of PFOA-contaminated wastewater bodies.The pine leaves powder?PiP?and dandelion flower powder?DFP?were also reused in this study for the synthesis of LDH-based sorbents to enhance the capacity of adsorption for repeating perchlorate in water media.The impact of adsorbent-dose,pH,thermodynamics,and co-existing ions was evaluated during the batch experiment.The results showed that 0.1 g of adsorbent?PiP and DFP-LDH?removed 97%and 93%of the perchlorate impurities in 20and 40minutes respectively as compared to the N-LDH's 2hrs equilibrium time.In this study,the second-order's R² of all LDHs was greater.The calculated and experimental equilibrium adsorption values corresponded to the pseudo-2^nd order model.The LDH produced were mesoporous;the surface of PiP-LDH had higher adsorption sites than the other two LDH,which made it suitable for perchlorate adsorption.Therefore,the model suggested possible physicochemical interactions behind perchlorate uptake by LDH.The inhibitory effect of the anions was PO₄^3->SO₄²->NO^3-.Multivalent anions are more readily adsorbed as monovalent anions due to the increased radius values.The highest proportion of adsorption as suggested by the Langmuir model was 909 mg g^-11 for PiP,771 mg g^-11 for DFP,and 246 mg g^-1 for N-LDH,indicating PiP-LDH's highest adsorption capacity among three LDHs.In general,the ion exchange and surface adsorption facilitated the perchlorate adsorption by DFP-LDH,while that by N-LDH was apparently facilitated by electrostatic interaction.While Pip-LDH processes“Re-built”and anion-exchange mechanism.These interactions were confirmed by the results of the FTIR,XPS,and XRD analyses.The shortest equilibrium time observed was 20m and 40m with PiP-LDH,followed by DFP-LDH,respectively.The information entailed by the model suggested the Physiochemical interactions behind the sorption of perchlorate on all the studied LDHs.The ion exchange and surface adsorption were possible mechanisms behind the adsorption of perchlorate by DFP-LDH and N-LDH,through hydrogen bonding.In contrast,the ion exchange and“re-built”mechanisms facilitated perchlorate adsorption by PiP-LDH.These improved LDHs could be very helpful in the environmental remediation of wastewater bodies.