Highly Efficient Defluoridation of Water through Reusable poly(aniline-co-o-aminophenol) Copolymer Modified Electrode Using Electrochemical Quartz Crystal Microbalance

Abstract

Although the World Health Organization (WHO) recommends a limit of 1.5 mg l−1 fluoride ions in drinking water, this is not satisfied in many parts of the world. When this limit is exceeded, the electrochemically switched ion-exchange (ESIX) technique (mainly based on conductive polymers) has been identified as a promising method for removing the excess fluoride ions. The present study aimed to develop an efficient method based on the ESIX technique by using poly(aniline-co-o-aminophenol) copolymer to extract fluoride ions. Electrochemical quartz crystal microbalance (EQCM) and acoustic admittance data were utilized to assay the synthetic efficiency of copolymer deposition, and to evaluate the dependence of the defluoridation process on the proportions of the monomers in the copolymer matrix and on film thickness. The resulting films were characterised by Fourier transform infrared spectroscopy (FTIR) and scanning electrochemical microscopy (SEM) techniques. For optimized co-monomer ratio in the feedstock, poly(aniline-co-o-aminophenol) at an applied potential of 0.30 V showed excellent performance for fluoride removal from water at pH 6.6, to the extent of 20 (mg F−) (g polymer)−1. Comparison of the performance of ESIX using poly(aniline-co-o-aminophenol) with that of other techniques and materials reveal that it has significant potential for water defluoridation.

Electrogravimetric analysis of poly(aniline-co-o-toluidine) copolymer films in the presence of fluoride ions

“…Following the completion of deposition, a green acoustically thin film was observed on the quartz crystal surface [36]. Similarly, the POT film was produced in a solution consisting of 0.1 M o-toluidine and 1 M H2SO4 by cycling between -0.2 V and 0.95 V at 10 mV s -1 scan rate over 20 cycles.…”

“…2A, electrochemical deposition of the POT film revealed three anodic peaks at 0.38 V / 0.54 V / 0.76 V, respectively. In the reverse cycle, three cathodic peaks appeared in the POT curve at 0.22 V / 0.50 V / 0.65 V. On the other hand, several reports shows that growth of a polyaniline film reveals two anodic peaks at 0.33 V / 0.61 V and two cathodic peaks at 0.23 V / 0.49 V [36,49]. Increase in redox peak current density of POT with cycling while lowering the irreversible peak current density is quite diverse behaviour than Pani [36,49].…”

“…In the reverse cycle, three cathodic peaks appeared in the POT curve at 0.22 V / 0.50 V / 0.65 V. On the other hand, several reports shows that growth of a polyaniline film reveals two anodic peaks at 0.33 V / 0.61 V and two cathodic peaks at 0.23 V / 0.49 V [36,49]. Increase in redox peak current density of POT with cycling while lowering the irreversible peak current density is quite diverse behaviour than Pani [36,49]. Additionally, the current density of the redox peaks of POT increases is in a gradual trend of only over 10 cycles.…”

“…The proposed concentration of fluoride in drinking water is 1.5 mg L -1 by World Health Organisation [27][28][29][30]. Therefore, numerous techniques have emerged for defluoridation processes, such as precipitation [31,32], adsorption onto activated alumina [33], nanofiltration [34], and electrochemically switched ion-exchange (ESIX) techniques based on conducting polymers [35,36], and the last one is the one of the most promising methods due to its simplicity and inexpensiveness [37]. Studies published in the literature also confirm that the ESIX technique is a highly convenient to extract silver [38], chromium (VI) [39] and perchlorate ions [40] from water and wastewater.…”

Artificial Biomimetic Electrochemical Assemblies

“…In this way, the counterions can be either inserted or ejected to maintain electroneutrality. The movement of the counterions can also cause the transfer of neutral species, such as solvent molecules, into or out of the film [ 114 , 156 ]. Another unique feature of the poly( o -aminophenol) film is the electron-donating hydroxyl group, which has two functions: (1) positioned next to the imine nitrogen, it increases the electron density at the imine sites; (2) it is itself a potential coordination site [ 114 ].…”