Evaluation of the oxidative degradation of aromatic dyes by synthesized nano ferrate(VI) as a simple and effective treatment method
Introduction
A substantial amount of the global wastewater is manufactured through various industrial mechanisms that utilize chemicals extensively. Many dyes are discharged in wastewater and a noticeable proportion of these compounds are considered to be carcinogenic and have harmful effects on human health [1], [2], [3]. Hence, it is imperative to eliminate all of these dreadful compounds from wastewater, which have compromised the water quality, prior to being discharged into the environment [4], [5], [6], [7]. A large proportion of dyes remain intact under visible light. Therefore, dye degradation by conventional methods could be rather ineffective. Although developing new and effective methods for wastewater treatment has been a priority in recent years [8], [9], [10], the majority of them are not susceptible of industrial application [11], [12], [13], [14]. Fenton, photofention and photocatalytic oxidation processes are genuinely considered as the most promising procedures for water treatment applications [15], [16], [17]. The feasibility of the these procedures is restricted by various inhibitory factors, for instance, long execution time, extreme pH conditions (highly acidic or basic mediums), high levels of energy consumption due to UV light exposure, higher oxidant loadings and costly operations [18], [19], [20]. Therefore, the need to develop an effective, environmentally friendly and cost efficient process has arisen [21], [22], [23].
Ferrate is capable of oxidizing organic compounds very fast and simultaneously killing microorganisms [24]. In an aqueous media, ferrate(VI) is known to convert to ferric(III), which offers great potential for coagulation, as ferrate reacts with water molecules during oxidation or after the redox reactions have occurred [25]. As a result, ferrate(VI) has the ability to simultaneously disinfect, coagulate and decontaminate municipal and industrial wastewater. The oxidation ability of ferrate(VI) increases as the pH of the medium decreases and thus it is considered to be one of the most powerful oxidizing agents compared with other chemicals under neutral and acidic condition [26], [27]. The problem in working with ferrate is its low life time. Temperature and light enhance self-degradation of ferrate and thus its stability can be increased by keeping it in low temperature and dark bottle.
Ferrate(VI) has been frequently used on numerous occasions in order to oxidize and remove a wide range of pollutants from wastewater [28]. Fan et al. [29] reported the oxidation and coagulation removal of p-arsanilic acid from waste water. This research suggested that almost all of the reactive p-arsanilic acid could be removed by ferrate(VI); however, the water properties such as additional anion phosphate might reduce the overall p-arsanilic acid removal efficiency.
The removal of RB 203 dye was studied by Eskandari et al. [30] using a combination of Fe(VI) as oxidant and MgO nanoparticles. The results showed that total dye degradation was attained at a pH of 10. Antibiotics including trimethoprim and flumequine were also rapidly eliminated only within 15 s using FeV/FeIV, SO3−, SO4− and OH system combined with ferrate(VI) [31]. Liu et al. [32] were able to successfully remove parathion from water using ferrate(VI) as an oxidizer. Xie and Cheng [33] also investigated the removal efficiency of phenylarsenic compounds from animal waste matrices by Fe(VI). Zhou and Jiang [34] investigated the elimination of ciprofloxacin and ibuprofen using ferrate(VI). The results obtained from this study suggested that the Fe(VI) can effectively remove ciprofloxacin from water with degradation efficiency higher than 70 %. On the other hand, the degradation efficiency of ibuprofen was very low, about 25 % in different environmental conditions.
Although ferrate(VI) particles have been used on a number of occasions to eliminate water contaminants such as antibiotics and pesticides, the application of nano sized Fe (VI) particles in water treatment is yet to be explored. In addition, the selected dyes are widely used and produced in various industries and thus extremely discharged in wastewater but comparison of their degradation by ferrate have not been studied. In this study, a thorough investigation regarding the oxidation of seven different aromatic dyes using the novel Fe(VI) nanoparticles produced by the solution plasma process (SPP) was conducted for the first time. First, in order to optimize the conditions of the oxidation process, the effects of ferrate(VI) nanoparticles dosage, pH and temperature on dye degradation were studied. After that, the effect of water constituents such as anions (Cl−, NO₃−, HCO₃−), cations (Ca2+, Mg2+, Cu2+) and humic acid (HA) was investigated on the elimination rate of dyes by ferrate. Furthermore, a feasibility study was conducted into the removal of each dye from natural water matrices using this novel oxidation technique. Also, the reaction kinetic of dye oxidation with ferrate was studied. Additionally, total organic carbon removal efficiencies of ferrate in dyes oxidation were investigated. This work would discover new insights into the oxidation of all aromatic dyes in water and wastewaters.
Section snippets
Chemicals
All of the dyes used in the experiments including Bromothymol blue (BTB), Cresol Red (CR), Methylene blue (MB), Methyl orange (MO), Methyl Red (MR) and Methyl violet (MV) were purchased from Merck and used with no further purification, except Blue 203 dye which was obtained from Alvan paint company. Other reagents were at least of analytical grade and were also used as received. These dyes were selected based on the fact that they were commonly found in wastewater effluents all over the world.
Effect of temperature on dye degradation
Temperature is one of the factors capable of altering the stability of ferrate(VI). As shown in Fig. 3, when the temperature is increased from 10 °C to 25 °C, the removal percentage of dyes also increases. This could explained by considering the enhancement of the collision frequencies between ferrate(VI) and dye particles at higher temperature levels. Subsequently, allowing a further increase in temperature from 25 °C to 45 °C leads to the reduction of the ferrate(VI) stability and
Conclusion
In this work, solution plasma process was employed for producing nano ferrate which was used as oxidation of dyes. TEM image of synthesized ferrate showed that the particle size was lower than 50 nm. Nano ferrate was demonstrated as a powerful oxidant to degrade dyes from wastewater. At optimum conditions such as 25 °C temperature and pH = 7, most of dyes indicated very high efficiencies in very low reaction time. The removal efficiency was increased by enhancing ferrate. In addition, results
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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