The application of thermally activated persulfate for degradation of Acid Blue 92 in aqueous solution

International Journal of Industrial Chemistry https://doi.org/10.1007/s40090-019-0188-1 RESEARCH The application of thermally activated persulfate for degradation of Acid Blue 92 in aqueous solution Shahin Ahmadi1 · Chinenye Adaobi Igwegbe2 · Somayeh Rahdar1 Received: 28 October 2018 / Accepted: 4 June 2019 © The Author(s) 2019 Abstract Thermally activated persulfate (TAP) was applied for the degradation of Acid Blue 92 (AB92) dye in its aqueous solution. The effects of pH (3–11), temperature (298–333 K), contact time (15–75 min), sodium persulfate (SPS) concentration (0.05–0.5 mM) and initial AB92 concentration (50–400 mg/L) on the degradation of AB92 using TAP were examined. The initial and residual AB92 concentrations were determined spectrophotometrically at the wavelength of 260 nm and the dye mineralization was examined via the total organic carbon analysis. In addition, the chemical oxygen demand was also measured. The activation energy (Ea) of AB92 degradation was calculated as 17.38 kJ mol−1 based on the Arrhenius equation. Maximum degradation efficiency of 86.47% was reached after 75 min of treatment at a pH of 5, AB92 concentration of 200 mg/L, SPS concentration of 0.5 mM and temperature of 333 K. The degradation efficiency declined with the addition of different sodium chloride concentrations and organic radical scavengers. AB92 degradation was reduced from 86.5 to 74%, 65, and 59.1% using ethylenediaminetetraacetic acid, tert-butanol, and ethanol, respectively. A kinetic model was also developed to estimate the pseudo-first-order constants as a function of the main operational parameters (initial dye concentration and TAP concentration). Decolorization rate constants (k) of 0.0009, 0.001, 0.0012, 0.0014, and 0.0018 min−1 were obtained at 303, 308, 313, 328, and 333 K, respectively, using the Langmuir–Hinshelwood kinetic model. The results obtained indicate that the TAP degradation process has great potential for the reduction of azo dyes in aqueous environments. Keywords Acid Blue 92 · Thermally activated persulfate · Degradation efficiency · Total organic carbon · Chemical oxygen demand Introduction The textile industry is considered as a prominent dye production sector [1]. The utilization of various types of colors in addition to chemical substances in dyeing processes generates wastewater with unique characteristics such as pH, color, and composition [2]. The disposal of colored wastewater into the aquatic ecosystem significantly hinders the penetration of light into the deep waters [3, 4]. It may also disturb the process of photosynthesis; this can also lead to the obliteration of aquatic plants [4]. In addition, colored dye effluents are significantly hazardous to the environment even at lower concentrations [5]. Moreover, the majority of * Shahin Ahmadi 1 Department of Environmental Health, Zabol University of Medical Sciences, Zabol, Iran 2 Department of Chemical Engineering, Nnamdi Azikiwe University, Awka, Nigeria dyes employed by textile industries are of organic origin; they are produced from phthalocyanine, diazo and anthraquinone salts which contain benzene rings that are highly carcinogenic and toxic in nature [6, 7]. An example of such dye is the C.I. Acid Blue 92(AB92), which is utilized on a regular basis by textile industries. Many researchers have proven that dyes are not completely removed during biological treatment, and they enter into water resources via wastewater effluents originating from treatment plants [8]. These compounds are not eliminated effectively through traditional wastewater removal procedures since they are non-biodegradable. Several techniques have been employed for the elimination of dyes from polluted waters including coagulation–flocculation [9, 10], chemical treatment [11], oxidation [12, 13], adsorption [14–22] and photocatalytic degradation [23–35]. Adsorption is the most widely used because of its simplicity, low cost and adsorption recovery properties in removing contaminants [36]. Adsorption is usually done 13 Vol.:(0123456789) International Journal of Industrial Chemistry with an adsorbent such as activated carbon to eliminate dyes, but this process only transfers pollutants from one phase to another [37]. Several advanced techniques in recent studies have been reported for wastewater treatment containing azo dyes [38–40]. Among various implemented methods for dye removal, the advanced oxidation process (AOP) is applied favorably to destroy resistant contaminants. This process fundamentally creates hydroxyl radicals (·OH) and sulfate radicals (SO·− 4 ) [41]. The sulfate radical contains significant oxidation potential (E0 = 2.6 V) in addition to being selective in reactions with organic compounds via electron transfer [42], whereas ·OH is non-selective and reacts with various compounds [43–45]. Activated persulfate is applied extensively for environmental remediation because the produced radicals react easily with the organic compounds by complete or partial mineralization [46]. The radical is typically created from potassium peroxymonosulfate (KHSO5, PMS) or sodium persulfate ( Na2S2O8, SPS) using thermal, transition metal and UV activation methods [47–49]. In addition, they can be applied alone to eliminate pollutants of high concentrations, since they usually possess a strong adsorption capacity [43, 50]. Even though S2O82− is a formidable oxidant, it reacts efficiently with pollutants at slow rates that are deemed impractical. This is due to the fact that S2O82− may be activated into hydroxyl (·OH) and sulfate (SO·− 4) radicals which are extremely powerful oxidants that react with pollutants within close diffusion-limited rates [51, 52]. The production of a highly reactive sulfate radical is depicted in Eqs. 1–6 [53, 54]: SO·− 4 has been proven to possess great potential for methylparaben degradation via UV-activated persulfate compared to other activators [57]. Cai et al. [58] proved that the bimetallic Fe–Co/GAC catalyst may be utilized to heterogeneously activate SPS oxidation for Acid Orange 7 degradation, which has also been proven in other studies. Also, very toxic persistent organic pollutants (POPs) can be decontaminated with persulfates [59]. The thermally activated persulfate (TAP) process is widely applied in ISCO procedures to treat hazardous and organic contaminants in water. Thermal activation may basically reduce the reaction time and cause higher drops in SPS usage in comparison to other methods [60]. When temperature increases, S2O82− is disintegrated into sulfate ions (SO42−) as seen in the reaction below [61]: S2 O2− + heat → 2SO⋅− 8 4 303 K < T < 363 K. (7) ( ⋅− ) + S2 O2− + activator → 2SO⋅− SO4 or SO2− 8 4 , 4 (1) It is clear that SPS reaction with heat (Eq. 7) causes the generation of SO·− 4 [62]. Thus, in this research, the impact of heat activation on SPS for the elimination of AB92 from its aqueous solution was examined. The impact of different operating (...truncated)