Visible-Light-induced photo-Fenton degradation of rhodamine B over Fe2O3-diatomite materials

Original Article ra n Q uyen o C h Th stit Minh City, 700000, Viet Nam a r t i c l e i n f o cient method for organic-dye wastewater treatment [5e7]. In sive and relatively bio-silica, which is sedimentary rock aquatic unicellular n oxide [10,11]. In dvantages such as e surface area, and indicated that the to remove heavy metal ions and dyes [13e15]. However, diatomite is a chemically catalyst support instead of degrading them [13,16,17]. As mentioned above, the Fenton process often requires small amounts of H2O2 and iron salt. Recently, Fe2O3 is often chosen to support diatomite for AOPs based on the Fenton reaction [12,17,18]. Fe2O3 is an n-type semiconductor and it has more advantage than that of other materials such as TiO2, ZnO, SnO2, etc. because Fe2O3 has a narrow bandgap (about 2.2 eV at room temperature), leading * Corresponding author. Faculty of Materials Science and Technology, University of Science e VNU-HCM, 227 Nguyen Van Cu Street, District 5, Ho Chi Minh City, 700000, Viet Nam. ** Corresponding author. *** Corresponding author. E-mail addresses: pvviet@hcmus.edu.vn (P. Van Viet), ngocduy158@gmail.com (N.N. Duy), cmthi@hutech.edu.vn (C.M. Thi). Contents lists available at ScienceDirect Journal of Science: Advanc journal homepage: www.el Journal of Science: Advanced Materials and Devices 5 (2020) 308e315Peer review under responsibility of Vietnam National University, Hanoi.inert substance, so it only can adsorb organic dyes or be used as a1. Introduction Environmental pollution is becoming serious all over the world, especially, water pollution is affecting directly human health. In the textile industry, some organic dyes are often poisonously generated to water and effected humans, animals, and plants. There are many methods to remove organic dyes in wastewater such as adsorption, chemical precipitation, catalytic and photocatalytic reaction [1e4]. Recently, advanced oxidation processes (AOPs) based on the Fenton reaction and the photocatalytic reaction are considered as an effi- addition, Fenton process is a relatively inexpen safe method [8,9]. Diatomite is known as diatomaceous earth or a microscopic silica nanofabrication factory, and is composed principally of silica microfossils of algae with small quantities of alumina and iro addition, the structure of diatomite has more a high porosity (25e65%), small particle size, larg high adsorption ability [12]. A previous study diatomite is an important carrier for catalystsArticle history: Received 14 March 2020 Received in revised form 13 July 2020 Accepted 21 July 2020 Available online 27 July 2020 Keywords: Diatomite Fenton Photocatalysis Hydroxyl radical Fe2O3 Dye degradationhttps://doi.org/10.1016/j.jsamd.2020.07.007 2468-2179/© 2020 The Authors. Publishing services b ( b s t r a c t Diatomite is mined in Phu Yen province, Vietnam and the Fe2O3-diatomite materials are synthesized by a simple process for the photo-Fenton reaction of rhodamine B (RhB) degradation. The pure diatomite and Fe2O3-diatomite materials have large pore structures representing the high adsorption ability and effi- cient photocatalysis. Characterizations of diatomite-Fe2O3 materials were determined by X-ray diffrac- tion (XRD), FT-IR analysis, field emission scanning electron microscopy (FE-SEM) images, dynamic light scattering (DLS), and inductively coupled plasma mass spectrometry (ICP-MS) analysis. The catalytic activity of the Fe2O3-diatomite materials was evaluated by the degradation of the RhB dye under visible light irradiation in the effect of hydrogen peroxide (H2O2). The results show that the 3% Fe2O3-diatomite sample has the highest RhB photocatalytic degradation efficiency with approximately 81% for 150 mi- nutes under visible light. This value is 2 times higher than the degradation efficiency of the pure diat- omite. In addition, the Fe2O3-diatomite photocatalysts are indicated as potential materials for photo- Fenton degradation of organic contaminants due to their highly stable abilities. © 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license ( photo-Fenton deg Fe2O3-diatomite materials Pham Van Viet a, b, *, Duong Van Chuyen a, c, Nguye Cao Minh Thi c, *** a Faculty of Materials Science and Technology, University of Science e VNU-HCM, 227 Ng b Vietnam National University - Ho Chi Minh City, Linh Trung Ward, Thu Duc District, H c Ho Chi Minh City University of Technology (HUTECH), 475A Dien Bien Phu Street, Bin d Research and Development Center for Radiation Technology, Vietnam Atomic Energy Iny Elsevier B.V. on behalf of Vietnamdation of rhodamine B over uoc Hien d, Nguyen Ngoc Duy d, **, Van Cu Street, District 5, Ho Chi Minh City, 700000, Viet Nam hi Minh City, 700000, Viet Nam anh District, Ho Chi Minh City, 700000, Viet Nam ute, 202A Street 11, Linh Xuan Ward, Thu Duc District, Ho Chi ed Materials and Devices sevier .com/locate/ jsamdNational University, Hanoi. This is an open access article under the CC BY license To evaluate the photocatalytic activity of Fe2O3-diatomite, a sun- tence of the high Fe O content into the sample that is expected ncedto advantage for in the visible-light-driven photocatalysis [19e22]. Therefore, the combination of the Fe3þ and diatomite can improve the photocatalytic activity of the raw diatomite materials [23]. In addition, Fe2O3 has a good chemical stability in an aqueous me- dium, which is also relatively inexpensive and non-toxic and therefore promising for photocatalytic water treatment [24]. In this study, Fe2O3-diatomite composites have been prepared by a simple process with the acid treatment and the thermal annealing process. Characterizations of the photocatalysts were determined by X-ray diffraction (XRD), FT-IR analysis, field emission scanning electronmicroscopy (FE-SEM) image, dynamic light scattering (DLS), and inductively coupled plasma mass spectrometry (ICP-MS) anal- ysis. The visible-light-induced photo-Fenton activity of these mate- rials has been investigated systematically to determine the optimal synthesized parameters, the adsorption ability, the effect of H2O2, and the photocatalytic stability. The photo-Fenton reaction mecha- nism has also been proposed in this study. 2. Experimental 2.1. Materials an chemicals The diatomite material was obtained from Tri An, Phu Yen province, Vietnam and was milled to form the powder with small and fairly uniform particle size. Ferric nitrate (Fe(NO3)3$9H2O), sodium carbonate (Na2CO3), hydrogen peroxide (H2O2, 30% wt.), rhodamine B (RhB), and deionized water (DI water) was used in all experiments. 2.2. Synthesis of Fe2O3-diatomite materials First, 100 mL Fe(NO3)3 solution was prepared at different con- centrations to achieve the weight percent (wt.) of Fe2O3 precursor in the sample with 0.75%, 3%, 6%, and 12%. Second, 100 mL Na2CO3 solution was added slowly into Fe(NO3)3 solution with ratio [Naþ]:[Fe3þ] ¼ 1.5:1. Next step, this mixture was magnetically stirred at 60 C for 2 h. Third, 8 g diatomite was added the above solution and was continuously stirred at 60 C for 2 h. Fourth, the suspensionwas filtered, washed many times by DI water, and dried before calcinating at 350 C for 2 h in the atmosphere to form Fe2O3-diatomite materials. The synthesis processes of diatomite- Fe2O3 materials are illustrated in Fig. 1. 2.3. Characterizations of materials The crystal structure of Fe2O3-diatomite was investigated by X- ray diffraction (XRD) on Bruker D8eAdvance 5005 device (Cu-Ka radiation, l ¼ 0.154064 nm) with 2q ¼ 20 - 80. The vibration modes of molecules in materials were determined by FTIR spec- trophotometer, JASCO-4700 in the range from 4000 cm1 to 400 cm1. To observe the morphology of materials, field emission scanning electron microscopy (FE-SEM S4800 HITACHI, Japan) was used to analyze. The average particle size and its distribution were characterized by dynamic light scattering method (DLS) on a par- ticle size analyzer (Horiba/LB550-Japan). 2.4. Adsorption and photocatalytic activity evaluation To determine the adsorption equilibrium, the kinetic models are represented the mathematical relation of the amount of adsorbed target per gram of adsorbent to the equilibrium solution concen- tration at a fixed temperature. The Langmuir isotherm is based on the assumption of mono- layer adsorption without interactions between the adsorbed mol- P. Van Viet et al. / Journal of Science: Advaecules with Langmuir equation (eq. (1))light simulator lamp (Osram UltraeVitalux 300 W, 230 V) with UV cuteoff filter (l > 420 nm) was used as a visible-light source in all photocatalytic experiments. The photocatalytic activity of Fe2O3-diat- omite was surveyed in two cases: without and having H2O2 presence under visible light irradiation. In a typical experimentprocess,wehave used 0.02 g of the catalyst thatwas dispersed in 60mL of RhB aqueous (100mg/L)and1mLFenton(30%wt.). Then, thesuspensionwasstirred for 90 min in the dark to achieve the adsorptionedesorption equilib- rium. After that, a 3 mL sample was collected after every 30 min light irradiationandcentrifuged formeasuring the concentrationof theRhB aqueous through UV-Vis spectrumby a Hitachi UH2910 spectrometer. The RhB photocatalytic efficiency of Fe2O3-diatomite is determined according to eq. (3). hð%Þ¼C0  Ct C0  100 (3) where h (%) is the RhB photocatalytic degradation efficiency, C0 is the absorption intensity of the RhB solution after the adsorption/ desorption reached equilibrium, Ct is the absorption intensity of the RhB solution at a certain reaction time t. 3. Results and discussion 3.1. XRD analysis Crystal structures of the as-prepared samples were identified by XRD and the results showed in Fig. 2. There are typical diffraction peaks of diatomite at 2q¼ 21.07, 26.5, and 50.1, corresponding to (100), (011), and (112) plan of SiO2, respectively (JCPDS Card no. 13- 0026). Besides, the appearance of the typical peaks at 25.17, 35.09, 60.2, and 61.77 assigning to (012), (110), (108), and (214) plan of Fe2O3, respectively (JSPDS Card no. 24-0072). These diffraction patterns were well matched with the literature [12,26]. These re- sults indicated that the diatomite of Phu Yen province, Vietnam exists the Fe2O3 crystal in SiO2 main compound. In addition, the diffraction peaks of (012) and (110) characterize Fe2O3 that have changed significantly compare to the pure diatomite. In particular, the intensity and full-width at half-maximum of these typical diffraction peaks were increased and slightly shifted when the content of the Fe2O3 precursor increased. This indicated the exis-Ce qe ¼ 1 KL:qm þ 1 qm :Ce (1) where, qe (mg$g1) is the amounts of RhB adsorbed at equilibrium; Ce (mg$L1) is the liquid-phase concentration of dye at the equi- librium; qm (mg$g1) and KL (L$mg1) are the Langmuir adsorption constants related to adsorption capacity and adsorption rate, respectively. The Freundlich isotherm can be used to describe heterogeneous surfaces and multilayer adsorption systems with Freundlich equa- tion (eq. (2)) qe ¼ KF :C1=ne (2) where qe (mg$g1) is the amounts of RhB adsorbed at equilibrium; Ce (mg$L1) is the liquid-phase concentrations of dye at the equi- librium; KF (L$mg1) and 1/n are the Freundlich adsorption con- stant, which represent adsorption capacity and adsorption intensity, respectively [25]. Materials and Devices 5 (2020) 308e315 3092 3 improving the photocatalytic degradation ability of raw materials. P. Van Viet et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 308e3153103.2. FT-IR analysis The vibration of molecules in the samples was investigated by FT-IR spectra. Fig. 3 shows the vibration peakwith thewavenumber at 3436 cm1 and 1632 cm1, representing HeOH stretching and bending vibrations of the hydroxyl group and/or water molecules, respectively [27]. The peaks at 467 cm1 and 1100 cm1 might be the asymmetric stretching of SieOeSi bonds that can be also created addition the bending vibration at 796 cm1 [12,28,29]. The peaks at 535 cm1 and 467 cm1 could be attributed FeeO vibra- tional in Fe2O3 [28,30e32]. Moreover, to determine the Fe content Fig. 1. Schematic of synthesis procedu Fig. 2. XRD patterns of diatomite (a) and diatomite with different Fe3þ contents: 0.75% (b), 3% (c), 6% (d), and 12% (e).in the synthesized samples, the inductively coupled plasma mass spectrometry (ICP-MS) analysis was conducted. The results showed that the contents of Fe3þ in the pure diatomite and 3%Fe2O3-diat- omite are 0.89% and 2.38%, respectively. These results demon- strated the existence of Fe2O3 in the samples for both the pure diatomite and the synthesized sample. However, the content of Fe3þ in the synthesized sample is smaller than that of the content of the theoretically initial Fe2O3 precursor demonstrating the small mass loss in the synthesis process. res of Fe2O3-diatomite materials. Fig. 3. FT-IR spectra of diatomite (a) and diatomite with different Fe3þ contents: 0.75% (b), 3% (c), 6% (d), and 12% (e). 3.3. FE-SEM image observation Fig. 4 presents the morphology of the pure diatomite and 3% Fe2O3-diatomite composite. It was worth noting that the FE-SEM result of diatomite powder shows that the diatomite has high porosity and lots of pores (Fig. 4a). The structure of these pores is shown clearly in Fig. 4b, therein, the diameter of the pores was about 700 nme1300 nm. Fig. 4c shows that 3% Fe2O3-diatomite composite has the similar structure of the high pore representing to the diatomite and some shapes with different sizes, corresponding to the existence of the Fe2O3. Fig. 4d shows the porous structure of these shapes of Fe2O3 with the size about 500 nm. 3.4. Particle size distribution analysis The distribution of the particle size of the diatomite and 3%Fe2O3- diatomitecompositewasmeasuredbyDLSmethodthat ispresented in Fig. 5. Result indicate a different observation of particle size for the materialsbeforeandaftercombiningtheFe2O3.Detail,Fig.5ashowsthe particle size in the diatomite sample with a diameter of 668.7nme6000nm.Therein, themainparticlesize inthis samplehasa diameterofabout1509.9nme2976.3nm(67%intotaltheparticleswere analyzed). Fig. 5b shows that the3%Fe2O3-diatomite compositehas the averageparticle sizeofabout1004.8nme5122.3nmandabout85%the particle having a particle size of about 1980.8 nme3904.5 nm. This result also demonstrated that the combination of Fe2O3 particles and the rawmaterial increased significantly the particle size in the sample. 3.5. Visible-light-induced photo-Fenton activity of Fe2O3-diatomite have been investigated and indicated in Figure S1 (Supplementary Document). After that, the effect of hydrogen peroxide (H2O2) to photocatalytic activity of materials has also been evaluated in two cases: First, 0.02 g catalyst and 60 mL RhB 100 ppm solution without H2O2 under visible light irradiation (Fig. 6a), and with the same experimental condition with the existence of 1.0 mL H2O2 (Fig. 6b). Results in Fig. 6a show that the photocatalytic activity of all samples is not good with the highest RhB photocatalytic degradation efficiency about 12% after 150 min under visible light. On the contrary, the presence of H2O2 has improved significantly the RhB degradation. In detail, Fig. 6b shows that the presence of H2O2 did not significantly increase the catalytic ability of pure diatomite compared to the Fe2O3-diatomite materials. The RhB degradation efficiency of the pure diatomite, 0.75% Fe2O3-diato- mite, 3%Fe2O3-diatomite, 6%Fe2O3-diatomite, and 12%Fe2O3-diato- mite for 150 min under visible light were 37.5%, 46.1%, 80.6%,73.2%, and 74.3%, respectively. This demonstrated that the combination of Fe2O3 and diatomite has improved significantly the visible-light photo-Fenton degradation reaction of pure diatomite. For instance, the visible-light photo-Fenton degradation efficiency of is 3%Fe2O3-diatomite composite is 2 times higher than the pure diatomite. Fig. 6c expresses the change of the absorption spectra of RhB solution under visible light irradiation versus irradiation time. The typical absorption peak position at 553.5 nm of wavelength of RhB was slightly shifted toward longer wavelength while the peak at 515 nm has a tendency to decrease the intensity. In general, the decrease of this peak intensity along as well as a slight shift in the position of the typical peaks showed the decomposition of RhB into intermediate products before being completely decomposed by P. Van Viet et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 308e315 3113.5.1. Effect of hydrogen peroxide to photocatalytic activity of Fe2O3-diatomite Before measuring the photocatalytic activity of Fe2O3-diatomite under visible light, the adsorption characterizations of materialsFig. 4. FE-SEM images of diatomite (aephoto-Fenton. In addition, the reaction rate of the photo-Fenton of Fe2O3-diatomite has been determined by the fix of the linear plots of ln (C/C0) versus irradiation time that are presented in Fig. 6d. The result shows that the initial rate constant on 3%Fe2O3-diatomite composite is highest, approximately 0.112 min1 while the rateb) and 3%Fe2O3/diatomite (ced). ncedP. Van Viet et al. / Journal of Science: Adva312constant of the others samples with pure diatomite, 0.75%, 6%, and 12% Fe2O3-diatomite is 0.0033 min1, 0.0048 min1, 0.0084 min1, and 0.0082 min1, respectively. It can conclude that the 3%Fe2O3- diatomite composite has the fastest photo-Fenton reaction rate. From these results, it can infer that the presence of H2O2 played a very important role in the photocatalytic process of diatomite due to the formation of OH radicals which are the main factor in the degradation of RhB under visible light [33]. Further insights into the effect of H2O2 on the photocatalytic activity of diatomite, the volume of H2O2 is changed from 0.25 mL to 10 mL and kept constant other parameters. Results of the RhB photocatalytic degradation of the 3%Fe2O3-diatomite composite with different H2O2 volumes are shown in Fig. 7. It can be seen that Fig. 5. Particle size distribution by DLS of d Fig. 6. Plot C/C0 of Fe2O3-diatomite composites versus visible light irradiation time in witho Fenton, and the linear plots of ln (C/C0) versus irradiation time.Materials and Devices 5 (2020) 308e315when the volume of H2O2 increased, the RhB photocatalytic degradation efficiency also increased. Therein, the degradation of RhB increased strongly when the volume of H2O2 increased from 0.5 mL to 1 mL (from 35.6% to 80.5%). After that, the photocatalytic efficiency was kept raising steadily. At 10 mL H2O2, the degrada- tion of RhB reached to 98.85% after 150 min under visible light irradiation. This can be explained that the H2O2 volume increases leading to increasing the OH radicals enhancing the photo- catalytic efficiency [34,35]. However, because H2O2 is a strong oxidizer, strong corrosive, and can cause burn skin, eyes, etc. Therefore, the large volume of H2O2 was not to be considered in this study and the next investigation will use a low volume of H2O2. iatomite (a) and 3%Fe2O3-diatomite (b). ut H2O2 (a), 1.0 mL H2O2 (b), typical absorption peak of RhB under visible-light photo- (eqs. (7) and (8)). In addition, the formation of OH radicals has been also formed by the reaction of Fenton agentwith the photogenerated electrons, Fe2þ ions, and Fe3þ ion in eqs. 9e12. The OH radicals will oxidize dyes organic become CO2 and H2O (eq. (13)). Fe2O3þhv/Fe2O3ðe þhþÞ (4) Fe3þ þ e/Fe2þ (5) e þO2/O2 (6) O2 þH2O/·HO2 þ OH (7) H2Oþhþ/O H (8)  P. Van Viet et