Improvement of the homogeneous fenton reaction for degradation of methylene blue and acid orange II

Article abstract of DOI:10.1248/cpb.c18-00097

In this study, the degradation of methylene blue (MB) and acid orange II (ORII) by the Fenton reaction was improved by using HCl and HNO₃. In addition, the effects of pH, temperature, concentration of Fenton’s reagent, and adjustment reagent of

Full text of DOI:10.1248/cpb.c18-00097

Vol. 66, No. 5
Chem. Pharm. Bull. 66, 585–588 (2018)
585
Note
Improvement of the Homogeneous Fenton Reaction for Degradation of
Methylene Blue and Acid Orange II
,a,b
Fumihiko Ogata,a Takehiro Nakamura,a and Naohito Kawasaki*
b
a Faculty of Pharmacy, Kindai University; 3–4–1 Kowakae, Higashi-Osaka, Osaka 577–8502, Japan: and Antiaging
Center, Kindai University; 3–4–1 Kowakae, Higashi-Osaka, Osaka 577–8502, Japan.
Received February 7, 2018; accepted March 2, 2018
In this study, the degradation of methylene blue (MB) and acid orange II (ORII) by the Fenton reaction
was improved by using HCl and HNO3. In addition, the effects of pH, temperature, concentration of Fen-
ton’s reagent, and adjustment reagent of solution pH on the decoloration were evaluated. The results showed
that the optimal pH for decoloration of MB and ORII was 2.5 and that the decoloration of MB and ORII
increased with higher temperature and concentration of Fenton’s reagent. Moreover, the decoloration in the
Fenton-reaction process with HCl and HNO3 was greater than the decoloration with H2SO4 by approximately
4.3–5.6 and 1.7–5.6 times for MB and 3.2–3.6 and 4.6–7.2 times for ORII compared to with H2SO4. These
results indicated that Fenton-reaction with HCl and HNO3 could be useful for the degradation technology of
dyes compared to generally Fenton-reactions.
Key words Fenton reaction; methylene blue; acid orange II; degradation
Water pollution due to dyes is a serious problem in devel-
oped countries. The removal of dyes from wastewater is a
Experimental
Materials MB and ORII were purchased from Wako Pure
challenge to relevant industries because the dyes used in the Chemical Industries, Ltd. (Osaka, Japan) and Tokyo Chemical
field are stable compounds that are difficult to decompose by Industry Co., Ltd. (Tokyo, Japan), respectively. Sulfuric acid,
common water treatments.1) Methylene blue (MB) is a cationic hydrochloric acid, nitric acid, sodium hydroxide, iron (II)
dye used extensively for dyeing and printing cotton, silk, and sulfate heptahydrate, and hydrogen peroxide (30%) were also
other materials. It is also used as a medicinal dye because of purchased from Wako Pure Chemical Industries, Ltd.
its antiseptic properties.2) In addition, the discharge of the
Effect of pH on Decoloration of MB and ORII Dye
anionic dye acid orange II (ORII) into the water stream is un- solutions (MB and ORII, 50mL) were prepared at a con-
desirable because of its color and also because of its toxicity, centration of 50mg/L and iron(II) sulfate heptahydrate and
non-biodegradability, and potential carcinogenic characteris- hydrogen peroxide (30%) were simultaneously added to each
tics.3,4) Therefore, the removal of MB and ORII from waste- dye solution (dye:Fe2+ :H2O2 molar ratios of 1.0:0.13:1.5,
water has attracted attention worldwide.
1.0:0.25:3.0, 1.0:0.50:6.0, and 1.0:2.0:24, respectively).
Oxidation with Fenton’s reagent, based on ferrous ion and Subsequently, the sample solutions were shaken at 100rpm
hydrogen peroxide, is a proven and effective technology for for 20h at 25°C. The pH of the sample solution was adjusted
the destruction of a large number of hazardous and organic by sulfuric acid or sodium hydroxide (pH 1.0, 2.5, 6.0, and
pollutants.5) Sulfuric acid (or sodium hydroxide) has often 8.0, respectively). The sample solutions were filtered through
been used for adjustment of solution pH in the Fenton-reaction a 0.45µm membrane filter and the filtrate was analyzed with
process. However, there are no reports of other acidic solu- a spectrophotometer (UV-1200, Shimadzu Co., Ltd., Kyoto,
tions being used for adjustment of solution pH. In recent Japan). The absorption wavelengths used for MB and ORII
years, heterogeneous Fenton reactions have been developed were 655 and 485nm, respectively. The decoloration percent-
by many researchers. However, the efficiency of wastewater age was calculated using Eq. 1:
treatment with many heterogeneous Fenton reactions is not
satisfactory because the heterogeneous Fenton reaction is
P=(C0 −Ce ) / C0 ×100
(1)
costly and requires the use of energy, such as ultraviolet light where P is the decoloration percentage (%), C0 is the concen-
or ultrasonic energy, to promote the reaction.6,7) In addition, tration before degradation (mg/L), and Ce is the concentration
hydroxyl radicals generated by the Fenton reaction are easily after degradation (mg/L).
affected by electrolytes in solution. Thus, if the general (ho-
The pH of the solution was measured using a digital pH
mogeneous) Fenton reaction could be improved with a simple meter (Seven Easy, Mettler Toledo, Kyoto, Japan). In the range
treatment, the value and applicability of the Fenton reaction of 0.1–10mg/L of MB and ORII, the absorbance at 655 and
for the purification of wastewater including dyes would in- 485nm of the dye versus the concentration plot showed ex-
crease substantially.
cellent linearity (r>0.998). We confirmed that the adsorption
The objective of the present study was to demonstrate the wavelength did not change at different pH conditions (before
feasibility of the Fenton oxidation process with changed pa- and after Fenton reaction) in preliminary experiment.
rameters for the degradation of dye and also investigate the
optimal operating conditions for MB and ORII degradation.
Effect of Temperature on Decoloration of MB and ORII
Dye solutions (MB and ORII, 50mL) were prepared at a con-
centration of 50mg/L, and iron(II) sulfate heptahydrate and
*To whom correspondence should be addressed. e-mail: kawasaki@phar.kindai.ac.jp
© 2018 The Pharmaceutical Society of Japan

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Chem. Pharm. Bull.
Vol. 66, No. 5 (2018)
hydrogen peroxide (30%) were simultaneously added to each for decoloration of MB and ORII was 2.5 (decomposition per-
dye solution (dye:Fe2+ :H2O2 molar ratios of 1.0:0.13:1.5, centage of 100%). Other pH conditions were not suitable for
1.0:0.25:3.0, and 1.0:0.50:6.0, respectively). Subsequently, decoloration. The decoloration of MB and ORII was greater
the sample solutions were shaken at 100rpm for 20h at 1, 25, at higher concentration of Fenton’s reagent. The traditionally
and 50°C. The pH of each sample solution was adjusted by accepted Fenton mechanism has been represented by many
sulfuric acid (pH 2.5). The decoloration percentage was calcu- researchers. Equation 2 depicts the Fenton reaction, which
lated using Eq. 1. In addition, total organic carbon (TC) was implies oxidation of ferrous iron to ferric iron to decompose
measured using a TOC-500 analyzer (Shimadzu Co., Ltd.).
H2O2 into hydroxyl radicals.8) Subsequently, the ferric ions
Effects of Sulfuric Acid, Hydrochloric Acid, and Ni- generated can be reduced by reaction with hydrogen peroxide,
tric Acid on Adjustment of Solution pH Dye solutions as shown in Eq. 3. This reaction is called the Fenton like reac-
(MB and ORII, 50mL) were prepared at a concentration of tion in an effective cyclic mechanism.
50mg/L, and iron(II) sulfate heptahydrate and hydrogen per-
Fe2++H2O2 → Fe3++OH− + ⋅ OH
Fe3++H2O2 → Fe2++HO2⋅ +H+
(2)
oxide (30%) were simultaneously added to each dye solution
(dye:Fe2+ :H2O2 molar ratios and other conditions were the
(3)
same as in section 2.3). The sample solution was adjusted by
sulfuric acid, hydrochloric acid, or nitric acid (pH 1.0). The
decoloration percentage was calculated using Eq. 1.
·
It is clear that OH radicals are the active species in the MB
and ORII degradation processes. The degradation pathways
of MB and ORII by the Fenton reaction have been reported
by previous studies. MB is degraded to azure B, azure A,
Results and Discussion
Effect of pH on Decoloration of MB and ORII The azure C, thionin, and finally phenothiazine.9) Moreover, the
decoloration percentages are shown in Fig. 1. The optimal pH degradation process of ORII is initiated by the cleaving of the
C–N bond due to the oxidative attack of hydroxyl radicals,
which leads to the formation of 2-naphtol and 4-hydrazino-
benzenesulfonic acid. The intermediate compounds then can
be oxidized further, causing their rings to open, and finally
mineralized into CO2 and H2O.3,10,11) We were able to confirm
the decoloration of MB and ORII in the Fenton-reaction pro-
cess (Fig. 2). The decomposition of MB and ORII in the more
acidic condition (at pH 1.0) was lower than that at pH 2.5
(decomposition percentage of MB and ORII of 4.0–59.5 and
2.2–68.8%, respectively), indicating that the higher concentra-
tion of H+ results in the prevention of regeneration of the fer-
rous ion. In addition, iron complex species [Fe(H2O)6]2+ exist
at very low pH values, and these species react more slowly
with hydrogen peroxide than other species.12) The decomposi-
Fig. 1. Effect of pH on the Decoloration of Dyes
Initial concentration: 50mg/L, solution volume: 50mL, temperature: 25°C,
tion of MB and ORII at pH 6.0 and 8.0 was also lower than
agitation speed: 100rpm, contact time: 20h, pH: 1–8. Dye:Fe2+ :H2O2 molar ratio
the decomposition at pH 2.5. Firstly, the reactivity of Fe2+ was
of 1.0:0.13:1.5 (●), 1.0:0.25:3.0 (■), 1.0:0.50:6.0 (◆), and 1.0:2.0:24 (▲), re-
spectively.
lower at the higher pH values. Secondly, autolysis of hydrogen
Fig. 2. Changes in Dyes before and after Fenton Reaction

Vol. 66, No. 5 (2018)
Chem. Pharm. Bull.
587
Fig. 3. Effect of Temperature on the Decoloration of Dyes
Initial concentration: 50mg/L, solution volume: 50mL, temperature: 25°C, agitation speed: 100rpm,contact time: 20h, pH: 2.5. Dye:Fe2+ :H2O2 molar ratio of
1.0:0.13:1.5 (A), 1.0:0.25:3.0 (B), and 1.0:0.50:6.0 (C). ■ Dye, □ TC.
Fig. 4. Effect of Acidic Solution on the Decoloration of Dyes
Initial concentration: 50mg/L, solution volume: 50mL, temperature: 25°C, agitation speed: 100rpm, contact time: 20h, pH: 1.0. Dye:Fe2+ :H2O2 molar ratio of
1.0:0.13:1.5 (A), 1.0:0.25:3.0 (B), and 1.0: 0.50: 6.0 (C).
peroxide occurred. Previous study has shown that hydrogen
Effect of Temperature on Decoloration of MB and ORII
peroxide is decomposed easily in the presence of heavy metals Figure 3 shows the effect of temperature on the decoloration
(Cu, Fe, Cr, Mn, etc.) in the basic condition (Eqs. 4 and 5).13)
of MB and ORII. Decomposition of the dyes increased with
increasing temperature (decoloration percentage was 100% at
25 and 50°C). A previous study reported that a substantial in-
crease in the extent of degradation of MB was observed when
the reaction temperature was raised from 8 to 26°C.5) Similar
H2O2+OH− → H2O+HO−2
2HO−2 → 2HO− +O2
(4)
(5)
In addition, Fe3+ was not reduced in the basic condition and trends were observed in this experimental condition. However,
Fe2O3 precipitated (Eq. 6), suggesting that the Fenton reaction in the previous study, further increase in the reaction tempera-
and the Fenton like reaction did not occur smoothly.
ture from 26 to 40°C resulted in a decrease in the extent of
degradation of MB.5) On the other hand, we could not confirm
a decrease in the extent of degradation of MB and ORII in
2Fe3++6OH− +(n −3)H2O → Fe2O3 ⋅nH2O
(6)
However, the decomposition of MB and ORII with excess this experimental condition. The experimental condition of the
concentration of Fenton’s reagent was faster than the above- previous study (dye:Fe2+ :H2O2 molar ratio of 1.0:1.14:14.1)
mentioned reactions (Eqs. 4–6). Differences in the decomposi- was harsher than the experimental condition of this study. The
tion of MB and ORII were attributed to differences in their differences in the results were not elucidated, but increasing
molecular structures.
the temperature did not affect the decomposition of hydrogen
peroxide; it did increase the thermal energy and subsequently

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Chem. Pharm. Bull.
Vol. 66, No. 5 (2018)
prompt the Fenton reaction. We are currently planning to
investigate the degradation mechanisms of MB and ORII in
Conclusion
We evaluated the degradation of MB and ORII by the ho-
detail. Moreover, the removal percentage of TC in MB and mogeneous Fenton reaction. The optimal pH for degradation
ORII was greater at higher temperature. These results sug- of MB and ORII is 2.5. The decoloration and removal of TC
gest that the Fenton reaction could cause the decomposition increased with increasing concentration of Fenton’s reagents
of MB and ORII at a wide temperature range. However, this and temperature, which indicates that the thermal energy was
treatment could not perfectly remove the total organic carbon increased and subsequently prompted the Fenton reaction.
produced from MB and ORII decomposition. Similar trends Finally, we found that the decoloration of MB and ORII was
were observed in the previous study.1)
greater in the Fenton reaction with HCl and HNO3 than in
Effects of Sulfuric Acid, Hydrochloric Acid, and Nitric the reaction with H2SO4. These results indicate that the sta-
Acid on Adjustment of Solution pH Previous studies have bility of complex formation with Fe3+ increases in the order
reported that sulfuric acid and sodium hydroxide are used NO−3 <Cl−<SO24−. Therefore, the Fe3+ generated in the Fenton
only for the adjustment of solution pH in the Fenton reac- reaction reacted with each anion and subsequently complex
tion.5,6,10,14,15) The main chemical cost of Fenton’s reagent is the formation occurred and the Fenton like reaction was inhibited.
cost of the H2O2 and other compounds (the price of H2O2 is This study elucidated an efficient technology for degradation
1150-Japanese yen/500mL, HCl is 850-Japanese yen/500mL, of MB and ORII by Fenton reaction with HCl and HNO3.
HNO3 is 1300-Japanese yen/500mL, and H2SO4 is 800-Japa-
nese yen/500mL), so it is important to optimize the amount
Acknowledgments Ministry of Education, Culture,
of Fenton’s reagents in the Fenton’s oxidation technology. That Sports, Science and Technology (MEXT)-supported Program
is, there is need to develop low cost oxidation technology. In for the Strategic Research Foundation at Private Universities,
this study, we focused on the adjustment reagent of solution 2014–2018 (S1411037).
pH. Dutta et al. reported the effect of electrolytes on degrada-
tion of MB.5) The presence of halide salts at the same con-
Conflict of Interest The authors declare no conflict of
centration level substantially decreased the rate and extent of interest.
degradation, whereas the lowering in the extent of degradation
was much less pronounced for sulfate salts, suggesting that it
is important to select the most useful reagent for efficient deg-
radation of MB and ORII by the Fenton reaction. We selected
several acidic solutions in this study. Figure 4 shows the
effects of the acidic solutions on the decoloration of the dyes.
The decoloration percentage of both MB and ORII was in the
order H2SO4<HCl<HNO3. The decoloration was not posi-
tively correlated with pKa (HCl (−8.0)<H2SO4 (−3.0)<HNO3
(−1.4)) neither was there a correlation to the oxidative effect
(HCl<H2SO4<HNO3) of the reagents. The Fenton reaction
followed Eqs. 2 and 3. The stability of complex formation
with Fe3+ was in the order NO−3 <Cl−<SO42−,16) which suggests
that the Fe3+ generated in the Fenton reaction reacted with
each anion and that subsequently complex formation occurred
and the Fenton like reaction was inhibited (the reactivity of
Fe3+ was lower). These results indicate that the decoloration
percentage using HCl and HNO3 was greater than that using
H2SO4, which is often used in the Fenton reaction. The dif-
ference was approximately 4.3–5.6 and 1.7–5.6 times for HCl
and HNO3 in MB decoloration and approximately 3.2–3.6 and
4.6–7.2 times for HCl and HNO3 in ORII decoloration, respec-
tively. As mentioned previously, the cost of HCl and HNO3
used in this study is 1.06 and 1.63 times higher compared to
that of H2SO4. However, the decoloration capacity of MB and
ORII using HCl and HNO3 is over 1.06 and 1.63 times higher
when compared to H2SO4 (Fig. 4(C)). This finding has not
been reported previously and is a novel result pertaining to
the homogeneous Fenton reaction process. However, we still
need to evaluate the degradation mechanism of MB and ORII
when using HCl and HNO3 in the Fenton reaction in detail.
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