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Synthesis of zeolite Y promoted by Fenton's reagent and its application in photo-Fenton-like oxidation of phenol
Solid State Sciences 91 (2019) 89–95
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Synthesis of zeolite Y promoted by Fenton's reagent and its application in photo-Fenton-like oxidation of phenol
T
Qiuyu Guo, Gang Li∗, Dan Liu, Yue Wei State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China
ARTICLE INFO
ABSTRACT
Keywords: Zeolite Y Fenton's reagent Crystallization kinetics Apparent activation energy Photo-Fenton-like oxidation of phenol
Zeolite Y was synthesized by hydrothermal method with adding Fenton's reagent. The materials were characterized by X-ray powder diffraction (XRD) and the crystallization kinetics was investigated. The results showed that hydroxyl free radical (∙OH) produced by Fenton's reagent accelerated both the nucleation process and the crystal growth process of zeolite Y. The apparent nucleation activation energy (En) and apparent growth activation energy (Eg) with Fenton's reagent were 67.98 and 42.66 kJ/mol, respectively. Compared with traditional synthesis of zeolite Y, the synthesis adding moderate Fenton's reagent presented shorter induction period, faster nucleation and growth rate, and lower apparent activation energy. In addition, iron was incorporated into the zeolite at the same time and the material showed high catalytic performance for photo-Fenton-like oxidation of phenol.
1. Introduction Zeolite Y is one of the most important molecular sieves in the industry [1], which has been widely used in petrochemical, fine chemical industry [2–10] and water treatment [11] for its high stability and activity. Traditionally, zeolite Y is synthesized by hydrothermal method under static crystallization condition. However, it has the shortcomings of insufficient mixing of materials, slow crystallization rate and long crystallization time. The dynamic crystallization method can solve the above problems [12]. It has advantages of mixing the materials fully, decreasing the crystallization time, improving the yield of target product, avoiding forming hetero crystals and achieving a smaller particle size and larger specific surface area. In addition, colloidal crystal seed is usually used in the synthesis of zeolite Y [13]. It contains some cageshaped structural units and plays the role of seed in the synthesis, contributing to obtaining product of good quality, small particle size and high yield. However, this method has tedious preparation process. Hydroxyl ions (OH−) can catalyze the polymerization and depolymerization of silica and alumina gel by forming and breaking the T–O–T bonds, where T stands for Si or Al, during the process of hydrothermal crystallization [14]. Compared with hydroxyl ions, most of free radicals, e.g. hydroxyl free radical (∙OH), have higher chemical activity. ∙OH has higher catalytic activity and lower energy barrier to break and form the SieOeSi bond [15]. Many methods, such as electron pulse radiolysis, synchrotron radiolysis of water, laser photolysis of H2O2, Fenton
∗
Corresponding author. E-mail address: [email protected] (G. Li).
https://doi.org/10.1016/j.solidstatesciences.2019.03.016 Received 23 March 2019; Accepted 23 March 2019 Available online 23 March 2019 1293-2558/ © 2019 Elsevier Masson SAS. All rights reserved.
and Fenton-like reactions, tethered metal chelates, disproportionation of peroxynitrous acid and high voltage electrical discharge, can generate ∙OH in solution [16]. Yu group has reported that ∙OH participates in the process of synthesizing zeolite. ∙OH generated by ultraviolet irradiation or Fenton's reagent can accelerate the nucleation processes of zeolites, such as Na-A, Na-X, NaZ-21 and silicalite-1, by promoting the depolymerization and condensation of silicon and aluminosilicate ions [17]. Moreover, sodium persulfate can also generate ∙OH in aqueous solution [18]. It can not only promote the synthesis of silicalite-1 zeolite in the hydrothermal crystallization system of TPAOHSiO2eH2OeEtOH, but also reduce the amount of organic template. Apparently, the free radicals mechanism brings new discoveries on the crystallization of zeolite materials. Up to now, there is no report on the function of ∙OH generated from Fenton's reagent in the crystallization process of zeolite Y. In addition, iron-containing zeolite can be prepared by adding Fenton's reagent in the synthesis. The iron-based material can be used as Fenton-like catalysts for the degradation of pollutants in wastewater [19–25]. Herein, zeolite Y is synthesized by hydrothermal method with adding Fenton's reagent. The optimum ratio of iron and hydrogen peroxide in Fenton's reagent and their roles in the crystallization process are investigated. Moreover, the crystallization kinetics is studied in detail. FeY zeolite with different iron content is prepared and used as the Fenton-like catalyst to catalyze the degradation of phenol in wastewater by the aid of ultraviolet light.
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2. Experimental
2.4. Crystallization kinetics
2.1. Reagents
The relative crystallinity (RC) of zeolite Y was calculated by the sum intensity of XRD characteristic diffraction peaks as shown in Eq. (1). Based on the methods in literature [26,27], the crystallization kinetics curves were drawn according to the calculated RC. The nucleation induction period (t0), nucleation rate (Vn) and crystal growth rate (Vg) of synthesized zeolite were calculated. The apparent nucleation activation energy (En) and the apparent growth activation energy (Eg) were calculated from the Arrhenius equation by plotting ln (Vn) or ln (Vg) with 1/T (Eq. (2) and (3)).
Silica sol (30 wt%) was purchased from Qingdao Haiyang Chemical Reagent Co., Ltd. Sodium hydroxide (NaOH, 96.0%, AR) was purchased from Tianjin DAMAO Chemical Reagent Factory. Sodium aluminate (NaAlO2, Al2O3 ≥ 41.0%, CP) was purchased from Sinopharm Chemical Reagent Co., Lt (Shanghai, China). Ferrous sulfate (FeSO4·7H2O, 99.0%–101.0%, AR) and phenol (AR) were purchased from Tianjin Kermel Chemical Reagents Co., Ltd. Hydrogen peroxide (H2O2, 30% (v/v), AR) was from Liaoning QuanRui Reagent Co., Ltd. Sulfuric acid (98%) was from Tianjin No. 3 Chemical Reagent Factory. All reagents were used without further purification.
RC =
(1)
I: absolute intensities of characteristic peaks m: sample with the highest sum intensities of characteristic peaks
2.2. Synthesis methods
k = k 0 exp( Ea/ RT )
The synthetic process of zeolite Y with the molar recipe of 0.5Na2O: 0.167Al2O3: 1SiO2: 22.5H2O: xFeSO4: yH2O2 (x = 0–0.01, y = 0–0.15) was as follows. Firstly, NaAlO2 was dissolved in sodium hydroxide solution under stirring condition, and then silica sol was added. The mixture (Solution A) was vigorously stirred for 3 h at ambient temperature. Secondly, the prepared Fenton's reagent with the molar ratio of xFeSO4: yH2O2 (Solution B) was added dropwise into Solution A with stirring. Then the mixture was transferred into a flask and crystallized in a water bath with agitation at 353 K for 9 h. Solid product was obtained after filtering, washing with deionized water until pH = 7–8 and drying at 373 K for 12 h. The detailed initial synthetic conditions of zeolite Y were shown in Table 1.
lnk =
3. Results and discussion 3.1. The effect of Fenton's reagent As shown in Table 1, RC of zeolite Y synthesized using conventional method at 353 K for 9 h was only 10.55% (sample 1). There was no promotion effect when only Fe was added in the synthesis system (sample 2). Crystallization of sample 3 was accelerated by ∙OH derived from H2O2, RC of which was similar to that of sample 4 with minute quantity of Fenton's reagent. RC of sample 7 with more Fenton's reagent was much higher than that of sample with Fe (sample 2) and H2O2 (sample 3), respectively. In brief, Fenton's reagent can better promote the crystallization of zeolite Y. Effect of Fenton's reagent dosage on the crystallization process of zeolite Y was investigated. As shown in Fig. 1, when the ratio of H2O2/ FeSO4 was 15, RC increased with the increase of FeSO4/SiO2 ratio during the synthesis process (sample 4, 5 and 7). However, the crystallinity of product sharply decreased with the further increase of FeSO4/SiO2 ratio to 0.01 (sample 10). The possible reason was that the hydroxyl free radical from Fenton's reagent accelerated the
Table 1 Zeolite Y synthesized with different contents of iron and hydrogen peroxide. FeSO4/SiO2 (x)
H2O2/FeSO4 (y/x)
H2O2/SiO2 (y)
Crystallinity (%)
1 2 3 4 5 6 7 8 9 10 11
0 0.001 0 0.00004 0.0002 0.001 0.001 0.001 0.01 0.01 0.0002
0 0 ∞ 15 15 3 15 150 1.5 15 15
0 0 0.015 0.0006 0.003 0.003 0.015 0.15 0.015 0.15 0.003
10.55 11.15 60.34 59.63 83.23 76.34 86.69 100 13.01 9.27 8.60
(3)
The whole reaction device was placed in a closed-loop environment and it consisted of quartz reactor with jacket, low-temperature bath, high-voltage mercury lamp and electromagnetic stirrer. The quartz reactor was a cylinder with an internal volume of 300 mL. The lowtemperature bath controlled the reaction temperature. Two high-voltage mercury lamps with a power of 125 W irradiated the reactor evenly to provide ultraviolet light with a wavelength of 365 nm. The electromagnetic stirrer mixed the reaction fluid and the catalyst fully. For a typical reaction, the concentration of phenol solution was 100 ppm, reaction temperature was 298 K, catalyst's dosage was 1 g/L, initial pH value of the solution was 4.1, and initial concentration of hydrogen peroxide was 0.03 M. The experimental process was as follows: 0.1 g zeolite Y with various iron content was added into 100 mL phenol solution. After ultrasonic mixing and adjusting solution's pH by dilute sulfuric acid, the mixture was transferred to the quartz reactor and stirred about 0.5 h under dark condition. After adding hydrogen peroxide into the mixture and turning on the ultraviolet lamp, reaction started and samples were taken once an hour. Chemical oxygen demand (COD) of sample, whose catalyst was removed by centrifugation, was measured by microwave digestion method to analyze the degradation effect.
XRD patterns were recorded on a Smart Lab 9 diffractometer equipped with Cu Kα radiation operating (λ = 1.5418 Å, voltage: 45 kV, current: 200 mA) in the range of 5°–40° with a step of 0.02°. The UV–Vis diffuse reflectance spectroscopy was measured on a JASCO UV550 UV/Vis spectrophotometer with the spectrum scanned from 190 to 800 nm at room temperature in air. The form and state of iron species in FeY sample was measured by H2-temperature programmed reduction (H2-TPR). The N2 physical adsorption-desorption measurements were carried out at 77 K using a Micromeritics ASAP 3020 analyser after degassing of the sample under vacuum at 623 K. The total specific surface area and pore volume of the samples were calculated from adsorption data employing the Brunauer-Emmett-Teller (BET) method and the amount of nitrogen adsorbed at the relative pressure of 0.99, respectively. Micropore specific surface area and micropore volume were calculated using t-plot method. The chemical composition of sample was analyzed with Bruker SRS3400 X-ray fluorescence (XRF) spectrometer.
Sample
Ea + ln k 0 RT
(2)
2.5. Reaction of photo-Fenton-like oxidation of phenol
2.3. Characterization
a
I 100% Im
a Sample was synthesized by adding ethanol with a molar ratio of 20C2H5OH: 1H2O2.{{}}
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zeolite Y. The crystallization process of zeolite includes the following steps [14]: (a) Silicon- and aluminum species polymerize to form an amorphous and random initial gel. (b) This gel depolymerizes to form soluble alumina and silica species. (c) Bonds re-polymerize to form increasingly ordered equilibrated gel around the metal cation. (d) Attacked by mineralizer, such as OH− or F− [32], secondary gel selfassembles and transforms into crystalline zeolite product, which contains the surface nucleation step and crystal growth step. In this study, ∙OH promoted step (d) of Y zeolite's crystallization process. 3.2. Crystallization kinetics of zeolite Y The crystallization kinetics of zeolite Y were studied to further ascertain in which stage ∙OH work. Fig. 2 showed the XRD patterns of zeolite Y synthesized without and with Fenton's reagent at different temperatures, whose composition was equal to sample 1 and 5, respectively. The XRD patterns showed that RC increased with the increase of crystallization time and temperature. The induction period (t0), crystal nucleation rate (Vn) and crystal growth rate (Vg) were calculated according to the crystallization kinetic curves. As shown in Fig. 3 and Table 2, t0 of zeolite Y decreased and Vg increased with the rising of crystallization temperature. The introduction of Fenton's reagent shortened the induction period and accelerated the crystallization process of nucleation and growth of zeolite Y. The induction period of zeolite Y synthesized with Fenton's reagent at 333 K, 338 K, 343 K and 353 K was about 8 h, 6 h, 4 h and 1 h shorter than that of without Fenton's reagent (Table 2). It was worth noting that the promotion effect from Fenton's reagent at lower crystallization temperature was much stronger than that at higher temperature. As shown in Fig. 4, En and Eg of zeolite Y were calculated by Arrhenius equation (Eq. (2) and (3)). The corresponding values were 76.35 and 70.20 kJ/mol without Fenton's reagent and 67.98 and 42.66 kJ/mol with Fenton's reagent, respectively. These results showed that Fenton's reagent decreased the En and Eg of zeolite Y.
Fig. 1. XRD patterns of zeolite Y synthesized with different contents of iron and hydrogen peroxide.
crystallization and excessive iron content was not conductive to it. Namely, proper quantity of Fenton's reagent promoted the crystallization of zeolite Y and the optimal ratio of FeSO4/SiO2 was 0.001. The roles of iron and hydrogen peroxide in Fenton's reagent during the crystallization process of zeolite Y were investigated. When Fenton's reagent was introduced, ferrous ion reacted with hydrogen peroxide to generate ferric ion and hydroxyl free radical (Eq. (4)), which promoted the crystallization of zeolite Y. When the content of H2O2 was constant, the crystallinity decreased with the increase of ferrous content (sample 5 and 6, sample 7 and 9, sample 8 and 10, Table 1). It indicated that the introduction of heteroatom iron was not conducive to the crystallization process. However, the crystallinity of sample 4–9 was still higher than that without Fenton's reagent (sample 1). Therefore, the promotion effect from hydroxyl radical was much stronger than the inhibition effect from iron. Nevertheless, excessive hydrogen peroxide were unfavorable to the crystallization (sample 9 and 10, Table 1). ·OH would be attacked by excessive H2O2 and transformed into HO2· with lower activity (Eq. (5)), which led to the decrease of crystallinity. In summary, proper amount of ∙OH promoted the crystallization process of zeolite Y.
Fe 2 + + H2 O2
H2 O2 + H2 O2
hv
HO·
Fe 3 + + HO· + OH
(4)
HO2·
(5)
+ H2 O
Fe 2 + + HO· H2 O2 + HO2·
When the promoter Fenton's reagent was introduced, the crystallization process of zeolite Y was accelerated and iron was incorporated. The chemical composition of the samples with different content of Fenton's reagent were measured by XRF analysis. As presented in Table 3, the content of components such as Na2O, Al2O3 and SiO2 varied little and Fe2O3 increased gradually with the increase of Fenton's reagent. Moreover, the ratio of H2O2/FeSO4 also had little effect on the composition of Y zeolite (sample 6, 7 and 8). The specific surface area and pore volume of Y zeolites were shown in Table 3. FeY zeolites (sample 5 and 7) exhibited higher value of micropore surface area and micropore volume compared with Y zeolite synthesized without Fenton's reagent (sample 1). It indicated that moderate Fenton's reagent contributed to the crystallization of Y zeolite, which was consistent with the XRD results in Fig. 1. When the content of Fenton's reagent was excess (sample 10), perhaps amorphous substances formed and then led to the decrease of micropore specific surface area and micropore volume. The UV–Vis spectra were used to investigate the existence form of iron species in FeY zeolite (sample 5, 7 and 10). As shown in Fig. 5, the spectra were divided into three regions: (i) The absorption band around 224 nm was attributed to the O2p→Fe3d space orbit electron transition peak produced by the tetra-coordinated iron species in the framework of FeeOeSi bond. (ii) The absorption band at 300–400 nm corresponded to the d-d transition peaks produced by non-framework iron species in the state of dimeric oligomers or ferric oxide species highly dispersed in the pore channel of the zeolite. (iii) The absorption band between 400 and 600 nm was attributed to the non-framework ferrite particles on the surface of zeolites [33]. The content of framework iron increased with the increasing amount of iron, meanwhile a great
(6)
2HO·
Fe3 + + H2 O2
3.3. Catalyst characterization
Fe 2 + + HO2· + H+
Fe 3 + + OH O2 + HO· + H2 O
(7) (8) (9)
HO· + HO·
H2 O2
(10)
HO·
+ RH
· R + H2 O
(11)
HO·
+ ·R
… CO2 + H2 O
(12)
Hydroxyl radical scavenger was also added into the crystallization process of zeolite Y to further explore the promoting effect of ∙OH. There are many kinds of hydroxyl free radical scavengers and alcohol is the most widely used one [28–31]. We introduced a certain content of ethanol as the scavenger of ∙OH. As shown in Table 1 and Fig. 1, when ethanol was added, RC of sample 11 was much lower than that of sample 5. This proved that ∙OH indeed promoted the crystallization of 91
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(caption on next page)
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Fig. 2. XRD patterns of zeolite Y synthesized without (A, B, C and D) and with (E, F, G and H) Fenton's reagent at different crystallization temperatures (A, E) 333 K, (B, F) 338 K, (C, G) 343 K, (D, H) 353 K.
Fig. 3. Kinetic curves of zeolite Y synthesized without (A) and with (B) Fenton's reagent at different temperatures (1) 333 K, (2) 338 K, (3) 343 K, (3) 353 K.
quantity of ferrite oligomer and oxides emerged. The existence form and state of iron species in sample 10 was also analyzed by H2-TPR technique. As shown in Fig. 6, the peak around 743 K was attributed to the reduction process of Fe2O3, which was dispersed in the pore channel or the surface of FeY. The shoulder peak at about 844 K was corresponded to the reduction of FeOx to Fe0 [34]. Owing to the strong interaction between Fe3+ and zeolite framework, the reduction of irons in framework at lower temperature was very difficult. The small peak at about 1183 K was attributed to the reduction of tetra-coordinated iron in framework to Fe0 [35]. From the strength and area of H2 consumption peak in Fig. 6, it can be concluded that compared with the content of iron in framework, the relative
Table 2 Induction period, crystal nucleation rate and growth rate of zeolite Y. T/K
333 338 343 353
Without Fenton's reagent −1
t0/h
Vn/h
27.56 22.26 12.74 6.13
0.0363 0.0449 0.0785 0.1631
With Fenton's reagent Vg/h
−1
2.837 3.475 4.577 11.66
t0/h
Vn/h−1
Vg/h−1
19.54 16.45 9.02 5.21
0.0512 0.0608 0.1108 0.1918
5.549 6.338 8.013 13.01
Fig. 4. Effect of crystallization temperature on nucleation rate and crystal growth rate for NaY (A, B) and FeY (C, D) zeolites.
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Table 3 Chemical composition and textural property of Y zeolite with different content of Fenton's reagent. Sample
Na2O (%)
Al2O3 (%)
SiO2 (%)
Fe2O3 (%)
SBET (m2g−1)
Smicro (m2g−1)
Vpore (cm3g−1)
Vmicro (cm3g−1)
1 5 6 7 8 10
15.27 14.50 14.31 14.34 14.65 14.94
25.75 25.93 25.68 25.45 24.55 24.92
58.98 59.52 59.84 60.03 60.62 58.60
0.00 0.05 0.17 0.18 0.18 1.54
88.39 341.61 _ 340.91 _ 91.08
49.43 317.50 _ 320.42 _ 44.02
0.23 0.18 _ 0.17 _ 0.26
0.02 0.13 _ 0.13 _ 0.02
Fig. 5. UV–Vis spectra of FeY zeolite synthesized with different iron content (sample 5, 7 and 10).
Fig. 7. The catalytic performance of sample 1, 5, 7 and 10 in photo-Fenton-like oxidation of phenol.
need only derived from the irradiation of ultraviolet light (Eq. (6)). We took sample 5 as an example to analyze the reaction process of phenol degradation. The reaction took place in a heterogeneous Fentonlike system. The COD removal rate of phenol solution increased by 23.25% in first hour. The rate of Fe (III) in Y zeolite became into Fe (II) under the action of hydrogen peroxide was three times lower than that of the traditional Fenton reaction, so it showed low COD removal rate [36]. With the increase of Fe (II) content, the hydrogen peroxide consumption was accelerated, and Fe (III) and hydroxyl free radical were generated at the same time. Phenol was attacked by ∙OH and the intermediate products (catechol and hydroquinone) were formed. These intermediate products rapidly reduced Fe (III) into Fe (II) [37,38], as shown in Eqs. (5)-(12). The reaction process was accelerated and the COD removal rate increased by 54.32% in second hour. The reaction rate dropped due to the exhaustion of hydrogen peroxide. The COD removal rate increased by 9.87% in third hour. In order to investigate the effect of different iron species on the oxidation of phenol, the dosage of FeY zeolite in the reaction solution was adjusted to keep equal amount of iron species added into the system. The COD removal rates of sample 5 and 10 in 3 h were 90.13% and 81.02%, respectively. As shown in Fig. 5, the ratio of framework Fe species in sample 5 was higher and sample 10 contained more nonframework Fe species such as dimeric oligomers. When the total content of iron species added into the reaction was equal, sample 5 containing more framework-iron presented the higher catalytic performance. Therefore, Fe species in the framework had higher activity in the degradation of phenol than non-framework Fe species.
Fig. 6. H2-TPR pattern of FeY zeolite (sample 10).
content of non-framework iron species, such as Fe2O3 and FeOx, was relatively higher in sample 10, which was consistent with UV–Vis result in Fig. 5. 3.4. Reaction of photo-Fenton-like oxidation of phenol
4. Conclusions
The catalytic performance of zeolite Y (sample 1, 5, 7 and 10) in photocatalytic Fenton-like degradation of phenol was studied. As shown in Fig. 7, FeY zeolite with different FeSO4/SiO2 ratio presented similar COD removal rate in 3 h. Zeolite Y without iron species (sample 1) showed the lowest COD removal rate because ∙OH that the reaction
Zeolite Y has been rapidly prepared by hydrothermal method with adding Fenton's reagent. The effect of Fenton's reagent on the crystallization process and crystallization kinetics of zeolite Y have been 94
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studied. Hydroxyl free radical produced by Fenton's reagent can promote the crystallization of zeolite Y by shortening the induction period greatly, accelerating the crystal growth process and reducing the apparent activation energy of crystal growth. The addition of Fenton's reagent provides a fast, efficient and convenient method for the onestep synthesis of iron-containing zeolite materials. As synthesized zeolite materials can be used as catalysts in Fenton-like oxidative degradation of phenol and other reactions.
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Acknowledgements The authors acknowledge the financial support from the Program for New Century Excellent Talents in University (NCET-04-0270). References [1] D. Verboekend, N. Nuttens, R. Locus, J. Van Aelst, P. Verolme, J.C. Groen, J. PérezRamírez, B.F. Sels, Synthesis, characterisation, and catalytic evaluation of hierarchical faujasite zeolites: milestones, challenges, and future directions, Chem. Soc. Rev. 45 (2016) 3331–3352 https://doi.org/10.1039/c5cs00520e. [2] V. Nikolakis, G. Xomeritakis, A. Abibi, M. Dickson, M. Tsapatsis, D.G. Vlachos, Growth of a faujasite-type zeolite membrane and its application in the separation of saturated/unsaturated hydrocarbon mixtures, J. Membr. Sci. 184 (2001) 209–219 https://doi.org/10.1016/S0376-7388(00)00623-2. [3] T. Li, H. Liu, Y. Fan, P. Yuan, G. Shi, X.T. Bi, X. Bao, Synthesis of zeolite Y from natural aluminosilicate minerals for fluid catalytic cracking application, Green Chem. 14 (2012) 3255–3259 https://doi.org/10.1039/c2gc36101a. [4] L. Hu, S. Xie, Q. Wang, S. Liu, L. Xu, Direct synthesis of NaY zeolite with small crystal size via hydrothermal method without seed gel, Chin. J. Catal. 28 (2007) 761–765 https://doi.org/10.3321/j.issn:0253-9837.2007.09.005. [5] O.S. Travkina, M.R. Agliullin, N.A. Filippova, A.N. Khazipova, I.G. Danilova, N.G. Grigor'Eva, N. Narender, M.L. Pavlov, B.I. Kutepov, Template-free synthesis of high degree crystallinity zeolite Y with micro–meso–macroporous structure, RSC Adv. 7 (2017) 32581–32590 https://doi.org/10.1039/c7ra04742h. [6] J. Jin, C. Peng, J. Wang, H. Liu, X. Gao, H. Liu, C. Xu, Facile synthesis of mesoporous zeolite Y with improved catalytic performance for heavy oil fluid catalytic cracking, Ind. Eng. Chem. Res. 53 (2014) 3406–3411 https://doi.org/10.1021/ ie403486x. [7] J. Zhao, G. Wang, L. Qin, H. Li, Y. Chen, B. Liu, Synthesis and catalytic cracking performance of mesoporous zeolite Y, Catal. Commun. 73 (2016) 98–102 https:// doi.org/10.1016/j.catcom.2015.10.020. [8] D.R. Godhani, H.D. Nakum, D.K. Parmar, J.P. Mehta, N.C. Desai, Zeolite Y encaged Ru(III) and Fe(III) complexes for oxidation of styrene, cyclohexene, limonene, and α-pinene: an eye-catching impact of H2SO4 on product selectivity, J. Mol. Catal. A Chem. 426 (2017) 223–237 https://doi.org/10.1016/j.molcata.2016.11.020. [9] A.M. Doyle, T.M. Albayati, A.S. Abbas, Z.T. Alismaeel, Biodiesel production by esterification of oleic acid over zeolite Y prepared from kaolin, Renew. Energy 97 (2016) 19–23 https://doi.org/10.1016/j.renene.2016.05.067. [10] N. Li, T. Li, H. Liu, Y. Yue, X. Bao, A novel approach to synthesize in-situ crystallized zeolite/kaolin composites with high zeolite content, Appl. Clay Sci. 144 (2017) 150–156 https://doi.org/10.1016/j.clay.2017.05.010. [11] H. Hassan, B.H. Hameed, Oxidative decolorization of Acid Red 1 solutions by Fe–zeolite Y type catalyst, Desalination 276 (2011) 45–52 https://doi.org/10.1016/ j.desal.2011.03.018. [12] N. Hanif, M.W. Anderson, V. Alfredsson, O. Terasaki, The effect of stirring on the synthesis of intergrowths of zeolite Y polymorphs, Phys. Chem. Chem. Phys. 2 (2000) 3349–3357 https://doi.org/10.1039/b002314k. [13] D. He, D. Yuan, Z. Song, Y. Tong, Y. Wu, S. Xu, Y. Xu, Z. Liu, Hydrothermal synthesis of high silica zeolite Y using tetraethylammonium hydroxide as a structure-directing agent, Chem. Commun. 52 (2016) 12765–12768 https://doi.org/10. 1039/c6cc06786g. [14] C.S. Cundy, P.A. Cox, The hydrothermal synthesis of zeolites: precursors, intermediates and reaction mechanism, Microporous Mesoporous Mater. 82 (2005) 1–78 https://doi.org/10.1016/j.micromeso.2005.02.016. [15] R. Konecny, Reactivity of hydroxyl radicals on hydroxylated quartz surface. 1. cluster model calculations, J. Phys. Chem. B 105 (2001) 6221–6226 https://doi. org/10.1021/jp010752v. [16] G. Xu, M.R. Chance, Hydroxyl radical-mediated modification of proteins as probes for structural proteomics, Chem. Rev. 107 (2007) 3514–3543 https://doi.org/10. 1021/cr0682047.
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Synthesis of zeolite Y promoted by Fenton's reagent and its application in photo-Fenton-like oxidation of phenol
T
Qiuyu Guo, Gang Li∗, Dan Liu, Yue Wei State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China
ARTICLE INFO
ABSTRACT
Keywords: Zeolite Y Fenton's reagent Crystallization kinetics Apparent activation energy Photo-Fenton-like oxidation of phenol
Zeolite Y was synthesized by hydrothermal method with adding Fenton's reagent. The materials were characterized by X-ray powder diffraction (XRD) and the crystallization kinetics was investigated. The results showed that hydroxyl free radical (∙OH) produced by Fenton's reagent accelerated both the nucleation process and the crystal growth process of zeolite Y. The apparent nucleation activation energy (En) and apparent growth activation energy (Eg) with Fenton's reagent were 67.98 and 42.66 kJ/mol, respectively. Compared with traditional synthesis of zeolite Y, the synthesis adding moderate Fenton's reagent presented shorter induction period, faster nucleation and growth rate, and lower apparent activation energy. In addition, iron was incorporated into the zeolite at the same time and the material showed high catalytic performance for photo-Fenton-like oxidation of phenol.
1. Introduction Zeolite Y is one of the most important molecular sieves in the industry [1], which has been widely used in petrochemical, fine chemical industry [2–10] and water treatment [11] for its high stability and activity. Traditionally, zeolite Y is synthesized by hydrothermal method under static crystallization condition. However, it has the shortcomings of insufficient mixing of materials, slow crystallization rate and long crystallization time. The dynamic crystallization method can solve the above problems [12]. It has advantages of mixing the materials fully, decreasing the crystallization time, improving the yield of target product, avoiding forming hetero crystals and achieving a smaller particle size and larger specific surface area. In addition, colloidal crystal seed is usually used in the synthesis of zeolite Y [13]. It contains some cageshaped structural units and plays the role of seed in the synthesis, contributing to obtaining product of good quality, small particle size and high yield. However, this method has tedious preparation process. Hydroxyl ions (OH−) can catalyze the polymerization and depolymerization of silica and alumina gel by forming and breaking the T–O–T bonds, where T stands for Si or Al, during the process of hydrothermal crystallization [14]. Compared with hydroxyl ions, most of free radicals, e.g. hydroxyl free radical (∙OH), have higher chemical activity. ∙OH has higher catalytic activity and lower energy barrier to break and form the SieOeSi bond [15]. Many methods, such as electron pulse radiolysis, synchrotron radiolysis of water, laser photolysis of H2O2, Fenton
∗
Corresponding author. E-mail address: [email protected] (G. Li).
https://doi.org/10.1016/j.solidstatesciences.2019.03.016 Received 23 March 2019; Accepted 23 March 2019 Available online 23 March 2019 1293-2558/ © 2019 Elsevier Masson SAS. All rights reserved.
and Fenton-like reactions, tethered metal chelates, disproportionation of peroxynitrous acid and high voltage electrical discharge, can generate ∙OH in solution [16]. Yu group has reported that ∙OH participates in the process of synthesizing zeolite. ∙OH generated by ultraviolet irradiation or Fenton's reagent can accelerate the nucleation processes of zeolites, such as Na-A, Na-X, NaZ-21 and silicalite-1, by promoting the depolymerization and condensation of silicon and aluminosilicate ions [17]. Moreover, sodium persulfate can also generate ∙OH in aqueous solution [18]. It can not only promote the synthesis of silicalite-1 zeolite in the hydrothermal crystallization system of TPAOHSiO2eH2OeEtOH, but also reduce the amount of organic template. Apparently, the free radicals mechanism brings new discoveries on the crystallization of zeolite materials. Up to now, there is no report on the function of ∙OH generated from Fenton's reagent in the crystallization process of zeolite Y. In addition, iron-containing zeolite can be prepared by adding Fenton's reagent in the synthesis. The iron-based material can be used as Fenton-like catalysts for the degradation of pollutants in wastewater [19–25]. Herein, zeolite Y is synthesized by hydrothermal method with adding Fenton's reagent. The optimum ratio of iron and hydrogen peroxide in Fenton's reagent and their roles in the crystallization process are investigated. Moreover, the crystallization kinetics is studied in detail. FeY zeolite with different iron content is prepared and used as the Fenton-like catalyst to catalyze the degradation of phenol in wastewater by the aid of ultraviolet light.
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2. Experimental
2.4. Crystallization kinetics
2.1. Reagents
The relative crystallinity (RC) of zeolite Y was calculated by the sum intensity of XRD characteristic diffraction peaks as shown in Eq. (1). Based on the methods in literature [26,27], the crystallization kinetics curves were drawn according to the calculated RC. The nucleation induction period (t0), nucleation rate (Vn) and crystal growth rate (Vg) of synthesized zeolite were calculated. The apparent nucleation activation energy (En) and the apparent growth activation energy (Eg) were calculated from the Arrhenius equation by plotting ln (Vn) or ln (Vg) with 1/T (Eq. (2) and (3)).
Silica sol (30 wt%) was purchased from Qingdao Haiyang Chemical Reagent Co., Ltd. Sodium hydroxide (NaOH, 96.0%, AR) was purchased from Tianjin DAMAO Chemical Reagent Factory. Sodium aluminate (NaAlO2, Al2O3 ≥ 41.0%, CP) was purchased from Sinopharm Chemical Reagent Co., Lt (Shanghai, China). Ferrous sulfate (FeSO4·7H2O, 99.0%–101.0%, AR) and phenol (AR) were purchased from Tianjin Kermel Chemical Reagents Co., Ltd. Hydrogen peroxide (H2O2, 30% (v/v), AR) was from Liaoning QuanRui Reagent Co., Ltd. Sulfuric acid (98%) was from Tianjin No. 3 Chemical Reagent Factory. All reagents were used without further purification.
RC =
(1)
I: absolute intensities of characteristic peaks m: sample with the highest sum intensities of characteristic peaks
2.2. Synthesis methods
k = k 0 exp( Ea/ RT )
The synthetic process of zeolite Y with the molar recipe of 0.5Na2O: 0.167Al2O3: 1SiO2: 22.5H2O: xFeSO4: yH2O2 (x = 0–0.01, y = 0–0.15) was as follows. Firstly, NaAlO2 was dissolved in sodium hydroxide solution under stirring condition, and then silica sol was added. The mixture (Solution A) was vigorously stirred for 3 h at ambient temperature. Secondly, the prepared Fenton's reagent with the molar ratio of xFeSO4: yH2O2 (Solution B) was added dropwise into Solution A with stirring. Then the mixture was transferred into a flask and crystallized in a water bath with agitation at 353 K for 9 h. Solid product was obtained after filtering, washing with deionized water until pH = 7–8 and drying at 373 K for 12 h. The detailed initial synthetic conditions of zeolite Y were shown in Table 1.
lnk =
3. Results and discussion 3.1. The effect of Fenton's reagent As shown in Table 1, RC of zeolite Y synthesized using conventional method at 353 K for 9 h was only 10.55% (sample 1). There was no promotion effect when only Fe was added in the synthesis system (sample 2). Crystallization of sample 3 was accelerated by ∙OH derived from H2O2, RC of which was similar to that of sample 4 with minute quantity of Fenton's reagent. RC of sample 7 with more Fenton's reagent was much higher than that of sample with Fe (sample 2) and H2O2 (sample 3), respectively. In brief, Fenton's reagent can better promote the crystallization of zeolite Y. Effect of Fenton's reagent dosage on the crystallization process of zeolite Y was investigated. As shown in Fig. 1, when the ratio of H2O2/ FeSO4 was 15, RC increased with the increase of FeSO4/SiO2 ratio during the synthesis process (sample 4, 5 and 7). However, the crystallinity of product sharply decreased with the further increase of FeSO4/SiO2 ratio to 0.01 (sample 10). The possible reason was that the hydroxyl free radical from Fenton's reagent accelerated the
Table 1 Zeolite Y synthesized with different contents of iron and hydrogen peroxide. FeSO4/SiO2 (x)
H2O2/FeSO4 (y/x)
H2O2/SiO2 (y)
Crystallinity (%)
1 2 3 4 5 6 7 8 9 10 11
0 0.001 0 0.00004 0.0002 0.001 0.001 0.001 0.01 0.01 0.0002
0 0 ∞ 15 15 3 15 150 1.5 15 15
0 0 0.015 0.0006 0.003 0.003 0.015 0.15 0.015 0.15 0.003
10.55 11.15 60.34 59.63 83.23 76.34 86.69 100 13.01 9.27 8.60
(3)
The whole reaction device was placed in a closed-loop environment and it consisted of quartz reactor with jacket, low-temperature bath, high-voltage mercury lamp and electromagnetic stirrer. The quartz reactor was a cylinder with an internal volume of 300 mL. The lowtemperature bath controlled the reaction temperature. Two high-voltage mercury lamps with a power of 125 W irradiated the reactor evenly to provide ultraviolet light with a wavelength of 365 nm. The electromagnetic stirrer mixed the reaction fluid and the catalyst fully. For a typical reaction, the concentration of phenol solution was 100 ppm, reaction temperature was 298 K, catalyst's dosage was 1 g/L, initial pH value of the solution was 4.1, and initial concentration of hydrogen peroxide was 0.03 M. The experimental process was as follows: 0.1 g zeolite Y with various iron content was added into 100 mL phenol solution. After ultrasonic mixing and adjusting solution's pH by dilute sulfuric acid, the mixture was transferred to the quartz reactor and stirred about 0.5 h under dark condition. After adding hydrogen peroxide into the mixture and turning on the ultraviolet lamp, reaction started and samples were taken once an hour. Chemical oxygen demand (COD) of sample, whose catalyst was removed by centrifugation, was measured by microwave digestion method to analyze the degradation effect.
XRD patterns were recorded on a Smart Lab 9 diffractometer equipped with Cu Kα radiation operating (λ = 1.5418 Å, voltage: 45 kV, current: 200 mA) in the range of 5°–40° with a step of 0.02°. The UV–Vis diffuse reflectance spectroscopy was measured on a JASCO UV550 UV/Vis spectrophotometer with the spectrum scanned from 190 to 800 nm at room temperature in air. The form and state of iron species in FeY sample was measured by H2-temperature programmed reduction (H2-TPR). The N2 physical adsorption-desorption measurements were carried out at 77 K using a Micromeritics ASAP 3020 analyser after degassing of the sample under vacuum at 623 K. The total specific surface area and pore volume of the samples were calculated from adsorption data employing the Brunauer-Emmett-Teller (BET) method and the amount of nitrogen adsorbed at the relative pressure of 0.99, respectively. Micropore specific surface area and micropore volume were calculated using t-plot method. The chemical composition of sample was analyzed with Bruker SRS3400 X-ray fluorescence (XRF) spectrometer.
Sample
Ea + ln k 0 RT
(2)
2.5. Reaction of photo-Fenton-like oxidation of phenol
2.3. Characterization
a
I 100% Im
a Sample was synthesized by adding ethanol with a molar ratio of 20C2H5OH: 1H2O2.{{}}
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zeolite Y. The crystallization process of zeolite includes the following steps [14]: (a) Silicon- and aluminum species polymerize to form an amorphous and random initial gel. (b) This gel depolymerizes to form soluble alumina and silica species. (c) Bonds re-polymerize to form increasingly ordered equilibrated gel around the metal cation. (d) Attacked by mineralizer, such as OH− or F− [32], secondary gel selfassembles and transforms into crystalline zeolite product, which contains the surface nucleation step and crystal growth step. In this study, ∙OH promoted step (d) of Y zeolite's crystallization process. 3.2. Crystallization kinetics of zeolite Y The crystallization kinetics of zeolite Y were studied to further ascertain in which stage ∙OH work. Fig. 2 showed the XRD patterns of zeolite Y synthesized without and with Fenton's reagent at different temperatures, whose composition was equal to sample 1 and 5, respectively. The XRD patterns showed that RC increased with the increase of crystallization time and temperature. The induction period (t0), crystal nucleation rate (Vn) and crystal growth rate (Vg) were calculated according to the crystallization kinetic curves. As shown in Fig. 3 and Table 2, t0 of zeolite Y decreased and Vg increased with the rising of crystallization temperature. The introduction of Fenton's reagent shortened the induction period and accelerated the crystallization process of nucleation and growth of zeolite Y. The induction period of zeolite Y synthesized with Fenton's reagent at 333 K, 338 K, 343 K and 353 K was about 8 h, 6 h, 4 h and 1 h shorter than that of without Fenton's reagent (Table 2). It was worth noting that the promotion effect from Fenton's reagent at lower crystallization temperature was much stronger than that at higher temperature. As shown in Fig. 4, En and Eg of zeolite Y were calculated by Arrhenius equation (Eq. (2) and (3)). The corresponding values were 76.35 and 70.20 kJ/mol without Fenton's reagent and 67.98 and 42.66 kJ/mol with Fenton's reagent, respectively. These results showed that Fenton's reagent decreased the En and Eg of zeolite Y.
Fig. 1. XRD patterns of zeolite Y synthesized with different contents of iron and hydrogen peroxide.
crystallization and excessive iron content was not conductive to it. Namely, proper quantity of Fenton's reagent promoted the crystallization of zeolite Y and the optimal ratio of FeSO4/SiO2 was 0.001. The roles of iron and hydrogen peroxide in Fenton's reagent during the crystallization process of zeolite Y were investigated. When Fenton's reagent was introduced, ferrous ion reacted with hydrogen peroxide to generate ferric ion and hydroxyl free radical (Eq. (4)), which promoted the crystallization of zeolite Y. When the content of H2O2 was constant, the crystallinity decreased with the increase of ferrous content (sample 5 and 6, sample 7 and 9, sample 8 and 10, Table 1). It indicated that the introduction of heteroatom iron was not conducive to the crystallization process. However, the crystallinity of sample 4–9 was still higher than that without Fenton's reagent (sample 1). Therefore, the promotion effect from hydroxyl radical was much stronger than the inhibition effect from iron. Nevertheless, excessive hydrogen peroxide were unfavorable to the crystallization (sample 9 and 10, Table 1). ·OH would be attacked by excessive H2O2 and transformed into HO2· with lower activity (Eq. (5)), which led to the decrease of crystallinity. In summary, proper amount of ∙OH promoted the crystallization process of zeolite Y.
Fe 2 + + H2 O2
H2 O2 + H2 O2
hv
HO·
Fe 3 + + HO· + OH
(4)
HO2·
(5)
+ H2 O
Fe 2 + + HO· H2 O2 + HO2·
When the promoter Fenton's reagent was introduced, the crystallization process of zeolite Y was accelerated and iron was incorporated. The chemical composition of the samples with different content of Fenton's reagent were measured by XRF analysis. As presented in Table 3, the content of components such as Na2O, Al2O3 and SiO2 varied little and Fe2O3 increased gradually with the increase of Fenton's reagent. Moreover, the ratio of H2O2/FeSO4 also had little effect on the composition of Y zeolite (sample 6, 7 and 8). The specific surface area and pore volume of Y zeolites were shown in Table 3. FeY zeolites (sample 5 and 7) exhibited higher value of micropore surface area and micropore volume compared with Y zeolite synthesized without Fenton's reagent (sample 1). It indicated that moderate Fenton's reagent contributed to the crystallization of Y zeolite, which was consistent with the XRD results in Fig. 1. When the content of Fenton's reagent was excess (sample 10), perhaps amorphous substances formed and then led to the decrease of micropore specific surface area and micropore volume. The UV–Vis spectra were used to investigate the existence form of iron species in FeY zeolite (sample 5, 7 and 10). As shown in Fig. 5, the spectra were divided into three regions: (i) The absorption band around 224 nm was attributed to the O2p→Fe3d space orbit electron transition peak produced by the tetra-coordinated iron species in the framework of FeeOeSi bond. (ii) The absorption band at 300–400 nm corresponded to the d-d transition peaks produced by non-framework iron species in the state of dimeric oligomers or ferric oxide species highly dispersed in the pore channel of the zeolite. (iii) The absorption band between 400 and 600 nm was attributed to the non-framework ferrite particles on the surface of zeolites [33]. The content of framework iron increased with the increasing amount of iron, meanwhile a great
(6)
2HO·
Fe3 + + H2 O2
3.3. Catalyst characterization
Fe 2 + + HO2· + H+
Fe 3 + + OH O2 + HO· + H2 O
(7) (8) (9)
HO· + HO·
H2 O2
(10)
HO·
+ RH
· R + H2 O
(11)
HO·
+ ·R
… CO2 + H2 O
(12)
Hydroxyl radical scavenger was also added into the crystallization process of zeolite Y to further explore the promoting effect of ∙OH. There are many kinds of hydroxyl free radical scavengers and alcohol is the most widely used one [28–31]. We introduced a certain content of ethanol as the scavenger of ∙OH. As shown in Table 1 and Fig. 1, when ethanol was added, RC of sample 11 was much lower than that of sample 5. This proved that ∙OH indeed promoted the crystallization of 91
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Fig. 2. XRD patterns of zeolite Y synthesized without (A, B, C and D) and with (E, F, G and H) Fenton's reagent at different crystallization temperatures (A, E) 333 K, (B, F) 338 K, (C, G) 343 K, (D, H) 353 K.
Fig. 3. Kinetic curves of zeolite Y synthesized without (A) and with (B) Fenton's reagent at different temperatures (1) 333 K, (2) 338 K, (3) 343 K, (3) 353 K.
quantity of ferrite oligomer and oxides emerged. The existence form and state of iron species in sample 10 was also analyzed by H2-TPR technique. As shown in Fig. 6, the peak around 743 K was attributed to the reduction process of Fe2O3, which was dispersed in the pore channel or the surface of FeY. The shoulder peak at about 844 K was corresponded to the reduction of FeOx to Fe0 [34]. Owing to the strong interaction between Fe3+ and zeolite framework, the reduction of irons in framework at lower temperature was very difficult. The small peak at about 1183 K was attributed to the reduction of tetra-coordinated iron in framework to Fe0 [35]. From the strength and area of H2 consumption peak in Fig. 6, it can be concluded that compared with the content of iron in framework, the relative
Table 2 Induction period, crystal nucleation rate and growth rate of zeolite Y. T/K
333 338 343 353
Without Fenton's reagent −1
t0/h
Vn/h
27.56 22.26 12.74 6.13
0.0363 0.0449 0.0785 0.1631
With Fenton's reagent Vg/h
−1
2.837 3.475 4.577 11.66
t0/h
Vn/h−1
Vg/h−1
19.54 16.45 9.02 5.21
0.0512 0.0608 0.1108 0.1918
5.549 6.338 8.013 13.01
Fig. 4. Effect of crystallization temperature on nucleation rate and crystal growth rate for NaY (A, B) and FeY (C, D) zeolites.
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Table 3 Chemical composition and textural property of Y zeolite with different content of Fenton's reagent. Sample
Na2O (%)
Al2O3 (%)
SiO2 (%)
Fe2O3 (%)
SBET (m2g−1)
Smicro (m2g−1)
Vpore (cm3g−1)
Vmicro (cm3g−1)
1 5 6 7 8 10
15.27 14.50 14.31 14.34 14.65 14.94
25.75 25.93 25.68 25.45 24.55 24.92
58.98 59.52 59.84 60.03 60.62 58.60
0.00 0.05 0.17 0.18 0.18 1.54
88.39 341.61 _ 340.91 _ 91.08
49.43 317.50 _ 320.42 _ 44.02
0.23 0.18 _ 0.17 _ 0.26
0.02 0.13 _ 0.13 _ 0.02
Fig. 5. UV–Vis spectra of FeY zeolite synthesized with different iron content (sample 5, 7 and 10).
Fig. 7. The catalytic performance of sample 1, 5, 7 and 10 in photo-Fenton-like oxidation of phenol.
need only derived from the irradiation of ultraviolet light (Eq. (6)). We took sample 5 as an example to analyze the reaction process of phenol degradation. The reaction took place in a heterogeneous Fentonlike system. The COD removal rate of phenol solution increased by 23.25% in first hour. The rate of Fe (III) in Y zeolite became into Fe (II) under the action of hydrogen peroxide was three times lower than that of the traditional Fenton reaction, so it showed low COD removal rate [36]. With the increase of Fe (II) content, the hydrogen peroxide consumption was accelerated, and Fe (III) and hydroxyl free radical were generated at the same time. Phenol was attacked by ∙OH and the intermediate products (catechol and hydroquinone) were formed. These intermediate products rapidly reduced Fe (III) into Fe (II) [37,38], as shown in Eqs. (5)-(12). The reaction process was accelerated and the COD removal rate increased by 54.32% in second hour. The reaction rate dropped due to the exhaustion of hydrogen peroxide. The COD removal rate increased by 9.87% in third hour. In order to investigate the effect of different iron species on the oxidation of phenol, the dosage of FeY zeolite in the reaction solution was adjusted to keep equal amount of iron species added into the system. The COD removal rates of sample 5 and 10 in 3 h were 90.13% and 81.02%, respectively. As shown in Fig. 5, the ratio of framework Fe species in sample 5 was higher and sample 10 contained more nonframework Fe species such as dimeric oligomers. When the total content of iron species added into the reaction was equal, sample 5 containing more framework-iron presented the higher catalytic performance. Therefore, Fe species in the framework had higher activity in the degradation of phenol than non-framework Fe species.
Fig. 6. H2-TPR pattern of FeY zeolite (sample 10).
content of non-framework iron species, such as Fe2O3 and FeOx, was relatively higher in sample 10, which was consistent with UV–Vis result in Fig. 5. 3.4. Reaction of photo-Fenton-like oxidation of phenol
4. Conclusions
The catalytic performance of zeolite Y (sample 1, 5, 7 and 10) in photocatalytic Fenton-like degradation of phenol was studied. As shown in Fig. 7, FeY zeolite with different FeSO4/SiO2 ratio presented similar COD removal rate in 3 h. Zeolite Y without iron species (sample 1) showed the lowest COD removal rate because ∙OH that the reaction
Zeolite Y has been rapidly prepared by hydrothermal method with adding Fenton's reagent. The effect of Fenton's reagent on the crystallization process and crystallization kinetics of zeolite Y have been 94
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studied. Hydroxyl free radical produced by Fenton's reagent can promote the crystallization of zeolite Y by shortening the induction period greatly, accelerating the crystal growth process and reducing the apparent activation energy of crystal growth. The addition of Fenton's reagent provides a fast, efficient and convenient method for the onestep synthesis of iron-containing zeolite materials. As synthesized zeolite materials can be used as catalysts in Fenton-like oxidative degradation of phenol and other reactions.
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