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Sn3O4 microballs as highly efficient photocatalyst for hydrogen generation and degradation of phenol under solar light irradiation
Accepted Manuscript Sn3O4 microballs as highly efficient photocatalyst for hydrogen generation and degradation of phenol under solar light irradiation
Sagar Balgude, Yogesh Sethi, Bharat Kale, Dinesh Amalnerkar, Parag Adhyapak PII:
S0254-0584(18)30697-7
DOI:
10.1016/j.matchemphys.2018.08.032
Reference:
MAC 20875
To appear in:
Materials Chemistry and Physics
Received Date:
13 June 2018
Accepted Date:
12 August 2018
Please cite this article as: Sagar Balgude, Yogesh Sethi, Bharat Kale, Dinesh Amalnerkar, Parag Adhyapak, Sn3O4 microballs as highly efficient photocatalyst for hydrogen generation and degradation of phenol under solar light irradiation, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.08.032
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ACCEPTED MANUSCRIPT
Sn3O4 microballs as highly efficient photocatalyst for hydrogen generation and degradation of phenol under solar light irradiation Sagar Balgudeab, Yogesh Sethia, Bharat Kalea, Dinesh Amalnerkarc and Parag Adhyapaka* aCentre
for Materials for Electronics Technology, Panchawati, Pashan Road, Pune-411008, India bD.
cInstitute
Y. Patil College of Engineering, Ambi, Pune-410507, India
of Nano Science & Technology, Hanyang University, Seoul-04763, South Korea
Abstract: Succinate driven facile hydrothermal method for fabrication of Sn3O4 microballs have been reported. The crystal structure of triclinic Sn3O4 was confirmed by XRD and Raman spectroscopy. The FESEM analysis reveals microball-like morphology made up of irregular contour-like nanostructures with thickness of about 40-80 nm. The optical band gap calculated from optical absorption spectroscopy was found to be 2.62 eV for synthesized Sn3O4. Considering morphology and narrowing of band gap, the photocatalytic activities for hydrogen generation and phenol degradation was investigated under solar light irradiation. Sn3O4 nanostructure exhibited enhanced photocatalytic activities for hydrogen generation and phenol degradation. A maximum H2 generation (88.4 µmol h-1/0.1 g) was obtained using the microballlike Sn3O4, which is higher than earlier reported data. Sn3O4 also exhibits good phenol degradation activity. The high photocatalytic activity of Sn3O4 was considered to be due to narrow band gap and hierarchal microball-like morphology. Key words: Sn3O4 nanostructure, microballs, Hydrothermal, Photocatalysts Corresponding Authors: Phone: +91-020-25899273, Fax: +91-020-25898180 Email: [email protected] (Dr. P. V. Adhyapak) 1
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1. Introduction Oxides of tin have been studied extensively from many decades due to abundant availability, non-toxicity, excellent optical and electrical properties [1-2] and these oxide of tin have applications in various fields such as sensitizedsolar cells, gas sensors, lithium ion batteries and photocatalysis [3-11]. Currently, research is more focused on synthesis of nonstoichiometric tin oxides with different coordination compounds such as Sn2O3, Sn3O4, and Sn5O6 with theoretical calculations and regulating Sn2+ and Sn4+ ratio [12-13]. Exploration of facile synthetic methods for obtaining pure and stable crystalline forms of these mixed-valent materials have considerably attracted a research attention recently. Sn3O4 is the first stable identified non-stoichiometric tin oxide composed by alternating atomic layers of tin and oxygen [14]. The Sn3O4 is an n-type semiconductor, having band gap in visible region (2.3-2.8 eV). Considering the band gap in visible region many researchers have synthesized various morphologies & studied their optical properties [15-16]. To mention few, Xu fang et al. have reported hydrothermally synthesized 3D flower-like structures used as anode material in lithium ion batteries [17]. Manikandan et al. have demonstrated water splitting using rectangular flexlike Sn3O4 nanostructures [18]. Suman et al. have studied the gas sensing studies of Sn3O4 nanobelts synthesized using carbothermal method [19]. Chen et al. have shown the superior photoreactivity of scaly nanoflex of Sn3O4 towards hydrogen generation and dye degradation [20]. Tian et al. have developed the H2O2 electrochemical senor using nanosheet like Sn3O4 nanostructures [21]. As can be 2
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seen from literature survey; there are very few reports which highlights the synthesis of Sn3O4 nanostructures with hierarchal morphology. Additionally, the reported results need further improvement. Considering this need, we understand the requirement of synthesis procedure for hierarchal Sn3O4 nanostructures. The hierarchal morphologies can result into better performance in view point of photocatalytic applications [22-23]. Previously, our research group have reported several hierarchal morphologies of ZnO using facile succinate mediated hydrothermal route in which succinate has shown better control over the morphology of the products [24]. So, here in present study we are reporting succinate induced hydrothermal route for the synthesis of microball-like Sn3O4 nanostructures. The synthesized Sn3O4 nanostructures have been characterized using X- Ray diffraction (XRD), Raman, Field emission scanning electron microscope (FESEM), Energy-dispersive X-ray spectroscopy (EDX),
UV-Visible
spectra
and
Particle
size
distribution
(PSD).
The
photocatalytic activities of microball-like Sn3O4 structures have been investigated for hydrogen production and were compared with that of previous reports. Additionally the degradation of phenol under sun light irradiation was also investigated. 2. Experimental 2.1 Materials All reagents used were of analytical grade. Stannous chloride dihydrate (SnCl2.2H2O), disodium succinate hexahydrate, sodium hydroxide and phenol
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were procured from Merck (India). Deionized water was used throughout all experiments. 2.2 Preparation of microball-like of Sn3O4 nanostructures In a typical synthesis procedure, stannous chloride dihydrate 2.90 g (0.015M) was dissolved in 20 ml of water and disodium succinate hexahydrate 6.27 g (0.023M) was dissolved in 20 ml water separately under continuous stirring and then it was admixed together. To this solution aq. NaOH solution (0.5M) was added dropwise for over a period of 30 min to attain a pH~12.5. After complete addition, the white suspension was formed. This suspension was stirred for 30 mins at ambient temperature and then transferred into Teflon-lined stainless-steel 200 mL autoclave. The autoclave was closed and placed in oven at 180°C for 20 h. subsequently cooled down naturally to room temperature. The yellow precipitate formed was centrifuged and washed 3-4 with deionized water and finally with ethanol and dried at 50°C in oven for 12 h.
2.3 Sample characterization The morphology of as-prepared sample was investigated by FESEM model JEOLJSM 6700F. The structural analysis and identification of Sn3O4 product was performed using Rigaku Miniflex operated with Cu Kα irradiation at λ=1.5406 Å and Ni filter. Raman spectra were recorded on Jobin Yvon T64000 triple grating spectrometer equipped with a liquid nitrogen cooled charge coupled device. UVvisible absorption spectra of aqueous suspension were recorded on a JASCOV-570
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spectrophotometer. The particle size distribution was carried using a PSSNICOMP particle sizing system, Santa Barbara, California, USA. 2.4 Evaluation of photocatalytic activity Photocatalytic H2 generation from water The as synthesized microball-like Sn3O4 nanostructures were evaluated for photocatalytic H2 evolution from water. The experimental equipment for photocatalyical water splitting is shown in Fig. 1.
Typical experiments were
carried using a 250 ml round bottom flask containing 100 mL of double distilled water and 25 ml of methanol as sacrificial reagent. Then, 100 mg of Sn3O4 catalyst preloaded with 1 wt% platinum (as a co-catalyst) was added to former solution. The dissolved oxygen was removed from reaction mixture by purging argon gas. The photocatalytic H2 evolution was studied under solar light irradiation. The process of reaction was monitored by measuring evolved gas with the help of eudiometer connected to a round bottom flask. During experiments, the amount of gas evolved as a function of time was noted and this data was used for further calculations. The quantification of hydrogen gas evolved was carried out using gas chromatography equipped with a 5 A˚ capillary column and a thermal conductivity detector. Photocatalytic degradation of phenol Further, as synthesized Sn3O4 microballs were also evaluated for their photodegradation activity using phenol as model contaminant. 250 mL Pyrex beaker was used as photoreactor. Prior to sunlight irradiation, 100 mL, 6 ppm aqueous solution of phenol containing 100 mg of catalyst was stirred in dark to 5
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achieve adsorption equilibria. After 1 hr. suspension was exposed to sunlight. During photocatalytic degradation experiments, the reaction samples were taken at regular interval and was analysed by UV-visible spectrophotometer for residual phenol concentration.
3. Results and discussion: X-ray diffraction pattern of as-prepared Sn3O4 sample is shown in Fig. 2a. The strong and sharp peaks in Sn3O4 sample indicate good crystallinity of the material. The XRD pattern shows diffraction patterns at 2θ values 23.09, 26.82, 31.29, 33.75, 37.15, 50.08 and 51.60 which corresponded to (101), (111), (210), (122), (130), (311) and (132) lattice planes and can be attributed to triclinic phase. The calculated lattice parameters of the triclinic Sn3O4 phase are a=4.85 Å, b=5.87 Å and c=8.20 Å which agrees well with reported values [JCPDS card No. 16-0737] [25]. Beyond these peaks, no other peaks related to any impurity such as SnO, SnO2 etc. were observed in XRD pattern within the detection limits of the instrument. Further structural information and impurity detection of the microball-like Sn3O4 sample was investigated by room temperature Raman spectroscopy and the results are shown in Fig. 2b. From figure, two intense peak centred at 142 cm-1 and 170 cm-1, can be assigned to characteristic of triclinic Sn3O4 [25]. The characteristic Raman peak of SnO2 (470 cm-1 and 770 cm-1) and SnO (211 cm-1) is absent in recorded spectra [26, 27]. These results indicates good crystalline quality of as synthesized Sn3O4 sample. The appearance of peak at 249 cm-1 can be
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assigned to Sn3O4 which may be due to oxidation of the sample and is in well accordance with the previous literature reports [28]. Fig. 3 illustrates the FESEM images and corresponding EDS spectra of the Sn3O4 sample synthesized using hydrothermal treatment. The images show spherical microball-like structure Fig. 3a, 3b & 3c. A low-amplification images Fig. 3 (d-e) indicate that these ball like microstructures are made up by assembly of numerous irregular contour-like structures forming a spherical microballs. These irregular contour-like structures have thickness of about 40-80 nm. The energy dispersive x-ray results are shown in Fig. 3 (f). The chemical composition of atomic ratios of Sn and O for the Sn3O4 microballs are found to be 50.03 and 49.97. The nonexistence of peaks related to any other impurity element confirms that the synthesized material is composed of Sn and O only. On the basis of the morphology obtained, the probable growth mechanism of the microball-like Sn3O4 nanostructure can be postulated. Fig. 4 represents the overall possible mechanism of formation of nanostructured Sn3O4. In succinate assisted hydrothermal synthesis, the small nanoparticles are formed initially. These nanoparticles are self-assembled and form microball-like morphology. These microballs clearly shows the nanoparticles on the surface. After prolonged time at hydrothermal condition, the microballs growth takes place due to self-assembly of same size of Sn3O4 nanoparticles [29]. Fig. 5 depicts the UV-visible absorption spectra of microball-like Sn3O4 and their corresponding Tauc plots. From figure it can be observed that the microballlike Sn3O4 exhibited broad and strong absorption in UV-visible range. The optical
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band gap of Sn3O4 calculated using Tauc model was found to be 2.62eV. These results are in well accordance with the previous reports [30]. In Sn3O4, the narrow band gap is due to co-existance of both Sn2+ and Sn4+ cations [18]. The particle size distribution analysis of microball-like Sn3O4 is given in Fig. 6. It was observed from the graphs, the sizes of the pale yellow product of microballlike Sn3O4 are found to be 360 nm. The photocatalytic activity of hydrothermally synthesized microball-like heterovalent Sn3O4 sample for the photocatalytic hydrogen generation via. Photodecomposition of H2O and degradation of phenol was performed. The results pertaining to amounts of H2 evolution as a function of solar light irradiation time in presence of microball-like Sn3O4 are shown in Fig.7. The maximum hydrogen evolution (88.4 μmol h-1/0.1g) was obtained using the microball-like Sn3O4 nanoparticles. These results are superior to previously reported literature [18, 21]. The data for H2 evolution via H2O splitting is summarized in Table 1.These results demonstrate the potential candidature of Sn3O4 for H2 evolution via. Water splitting under sunlight irradiation. The as-synthesized microball-like Sn3O4 were also evaluated for degradation of phenol using the under solar light. The degradation of phenol was monitored by observing changes in characteristic peak at 282 nm. The absorption spectra of aqueous phenol solution (6 ppm, 100 mL) in presence of 100 mg of Sn3O4 under solar light for various time intervals is as shown in Fig. 8(a). The phenol absorption peak at 282 nm decreases by 35% within 50 min and disappears completely after irradiation for 200 min. Fig. 8(b) shows the kinetic studies of the
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degradation of phenol with solar light irradiation time for the synthesized Sn3O4 sample. In absence of catalyst under sunlight irradiation, it was observed that there was not any significant change in phenol concentration. From Fig. 8(b), it can be suggested that the photocatalytic degradation reactions of phenol on the Sn3O4 catalyst follow the pseudo-first-order kinetics (k = 0.005 min-1& R2 = 0.9841). The results clearly indicates that, on addition of microball-like Sn3O4 photocatalysts leads to the phenol degradation. Based on these experimental results, a probable mechanism involved in H2 production and phenol degradation have been proposed & is shown in Fig. 9. Generally, upon light irradiation photogenerated electrons are excited from the valence band to conduction band of photocatalyst, leaving behind a hole in valence band, which participates in different oxidation-reduction reactions [31]. The photocatalytic activity of heterovalent Sn3O4 can be ascribed to narrow band gap, which facilitates the efficient absorption of incident solar light to induce e- and h+ pair generation. The as formed e- and h+ can then transferred to Sn3O4 surface and may undergo various reactions to generate H2 by water splitting and degraded organic pollutant as shown in following equations [31, 32].
𝒉𝝑
𝐒𝐧𝟑𝐎𝟒 (𝐩𝐡𝐨𝐭𝐨𝐜𝐚𝐭𝐚𝐥𝐲𝐬𝐭) → (𝐡 𝟐𝐇𝟐𝐎 + (𝟒𝐡 𝟐𝐇
+
+ (𝟐𝐞
𝐇 𝟐 𝐎 + (𝐡
+
+
‒
)𝐕𝐁→
𝟒𝐇
+
+
)𝐕𝐁
+ (𝐞
)𝐂𝐁
(1) (2)
+ 𝐎𝟐
)𝐂𝐁→𝐇𝟐
)𝐕𝐁→𝐎𝐇•
‒
(3) + 𝐇
+
(4)
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‒
𝐎𝐇 + (𝐡 𝐎𝟐 + (𝐞
‒
+
)𝐕𝐁→𝐎𝐇•
(5)
)𝐂𝐁→𝐎•𝟐‒
(6)
•
𝐎𝐇 + 𝐏𝐡𝐞𝐧𝐨𝐥→𝐃𝐞𝐠𝐫𝐚𝐝𝐞𝐝 𝐩𝐫𝐨𝐝𝐮𝐜𝐭𝐬 •‒ 𝟐
𝐎
+ 𝐏𝐡𝐞𝐧𝐨𝐥→𝐃𝐞𝐠𝐫𝐚𝐝𝐞𝐝 𝐩𝐫𝐨𝐝𝐮𝐜𝐭𝐬
(7) (8)
The reusability and stability of the photocatalyst was also studied by repeating the experiments under similar conditions using the microball-like Sn3O4 photocatalyst after recycling (Fig. 10). More importantly, microball-like Sn3O4 showed sustained and consistent activity up to the 3rd cycle under sunlight irradiation, which proves the stability of the catalyst. As per our information, our hydrothermally synthesized microball-like Sn3O4 gives superior photocatalytic activity than those previously reported (Table-1). The increased photocatalytic activity of Sn3O4 can be attributed to the microball-like nanostructure, good crystallinity and narrowing of the band gap i.e. in visible region. In nutshell, Sn3O4 shows enhanced H2 production and phenol degradation under solar light and was observed to be stable photocatalyst. 4. Conclusions In conclusion, the Sn3O4 nanostructures were successfully synthesized by facile hydrothermal method using stannous chloride dihydrate and disodium succinate hexahydrate, which exhibited enhanced photocatalytic activity towards the phenol degradation and H2 generation via. Water splitting under solar light irradiation. The excellent photocatalytic activity of the microball-like Sn3O4 can be ascribed to
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its photo-absorption ability due to the narrowing band gap, microball-like morphology and good crystallinity.
Acknowledgements: Dr. Parag V. Adhyapak is grateful to ISRO, Bengaluru and VSSC, Thiruvananthapuram for financial support.
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[6] Cheng Y., Chen K. S., Meyer N. L., Yuan J, Hirst L. S., Chase P. B., Xiong P, Fuctionalized SnO2 nanobelt filed-effect transistor sensors for label-free detection of cardiac troponin. Biosens. Bioelectron. 2011, 26, 4538-4544. [7] Zhiyu Wang, Deyan Luan, Freddy Yin Chiang Boey, Xiong Wen Lou, Fast Formation of SnO2 Nanoboxes with Enhanced Lithium Storage Capability, J. Am. Chem. Soc., 2011, 133 (13), pp 4738–4741 [8] Yude Wang, Igor Djerdj, Bernd Smarsly and Markus Antonietti, Antimony-Doped SnO2 Nanopowders with High Crystallinity for Lithium-Ion Battery Electrode, Chem. Mater., 2009, 21 (14), pp 3202–3209. [9] Nishant Srivastava, Mausumi Mukhopadhyay, Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwiniaherbicola and Their Photocatalytic Activity for Degradation of Dyes, Ind. Eng. Chem. Res., 2014, 53 (36), pp 13971–13979. [10] Shuisheng Wu, Huaqiang Cao, Shuangfeng Yin, Xiangwen Liu and Xinrong Zhang, Amino Acid-Assisted Hydrothermal Synthesis and Photocatalysis of SnO2 Nanocrystals, J. Phys. Chem. C, 2009, 113 (41), pp 17893–17898. [11] Shi L. A., Lin H. L., Facile Fabrication and Optical Property of Hollow SnO2 Spheres and Their Application in Water Treatment. Langmuir 2010, 26, 18718-18722. [12] Atsuto Seko, Atsushi Togo, Fumiyasu Oba, Isao Tanaka, Structure and Stability of a Homologous Series of Tin Oxides, PRL, 2008, 100, 045702. [13] T. Pal, A. K. Sinha, P. K. Manna, M. Pradhan, C. Mondal and S. M. Yusuf, Tin oxide with a p–n heterojunction ensures both UV and visible light photocatalytic activity, RSC Adv., 2013, 4, 208–211. [14]F. Lawson, Tin Oxide—Sn3O4, Nature, 1967, 215, 955–956.
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[15] Y. He, D. Li, J. Chen et al., Sn3O4: a novel heterovalent-tin photocatalyst with hierarchical 3D nanostructures under visible light, RSC Advances, vol. 4, no. 3, pp. 1266– 1269, 2014. [16]W. Xu, M. Li, X. B. Chen et al., Synthesis of hierarchical Sn3O4 microflowers selfassembled by nanosheets, Materials Letters, vol. 120, pp. 140–142, 2014. [17] Xuefang Chen, Ying Huang, Kaichuang Zhang, Xuansheng Feng, Chao Wei, Novel hierarchical flowers-like Sn3O4 firstly used as anode materials for lithium ion batteries, Journal of Alloys and Compounds, 2017, 690, 765-770. [18]M. Manikandan, T. Tanabe, P. Li et al., Photocatalytic water splitting under visible light by mixed-valence Sn3O4, ACS Applied Materials & Interfaces, vol. 6, no. 6, pp. 3790–3793, 2014. [19] P. H. Suman, A. A. Felix, H. L. Tuller, J. A. Varela, and M. O. Orlandi, Comparative gas sensor response of SnO2, SnO and Sn3O4 nanobelts to NO2 and potential interferents, Sensors and Actuators, B: Chemical, vol. 208, pp. 122–127, 2015. [20] Guohui Chen, ShaozhengJi, Yuanhua Sang, Sujie Chang, Yana Wang,Pin Hao, Jerome Claverie, Hong Liu, Guangwei Yu, Synthesis of scaly Sn3O4/TiO2 nanobelt heterostructures for enhanced UV-visible lightphotocatalytic activity, Nanoscale, 2015, 7, 3117. [21] Liangliang Tian, Kaidong Xia, Wanping Hu, Xiaohui Zhong, Lu Li, A wide linear range and stable H2O2 electrochemical sensor based on Ag decorated hierarchical Sn3O4, Electrochimica Acta, 2017, 231, 190-199.
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[22] Parag V. Adhyapak, Satish P. Meshram, Dinesh P. Amalnerkar, Imtiaz S. Mulla, Structurally enhanced photocatalytic activity of flower-like ZnO synthesized by PEGassisted hydrothermal route, Ceram. Int., 2014, 40, 1951-1959. [23]
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[29] Rajendra P. Panmand, Yogesh A. Sethi, Sunil R. Kadam, Mohaseen S. Tamboli, Latesh K. Nikam, Jalinder D. Ambekar, Chan-Jin Park and Bharat B. Kale, Selfassembled hierarchical nanostructures of Bi2WO6 for hydrogen production and dye degradation under solar light, Cryst. Eng. Comm, 2015, 17, 107. [30] O. M. Berengue, R. A. Simon, A.J. Chiquito, C. J. Dalmaschio, E.R. Leite, H.A. Guerreiro, F.E.G. Guimaraes, Semiconducting Sn3O4 nanobelts: growth and electronic structure, J. Appl. Phys. 107 (2010) 033717. [31] Imran Ali, Seu-Run Kim, Sung-Pil Kim, Jong-Oh Kim, Anodization of bismuth doped TiO2 nanotubes composite for photocatalytic degradation of phenol in visible light, Catal. Today (2016). [32] K. Maeda, Photocatalytic water splitting using semiconductor particles: History and recent developments, J. Photochem. Photobiol. C Photochem. Revi. 12 (2011) 237–268.
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Figure Caption: Fig. 1: Experimental equipment of water splitting. Fig. 2: a) X-ray diffraction patterns (XRD) and b) Raman spectrum of the as-prepared Sn3O4 sample. Fig. 3: (a-e) - FESEM images and (f) EDS spectra of Sn3O4 respectively. Fig. 4: Schematic illustration of formation of microball-like Sn3O4 nanostructures. Fig. 5: UV-vis absorption spectra of Sn3O4. The inset shows (αhν)2 vs photon energy (hν) spectra for the calculation of optical band gap by extrapolating on hν axis at α=0. Fig. 6: Particle size distribution histogram of Sn3O4 nanostructures. Fig. 7: Time verses amount of H2 (µmol) evolution of Sn3O4. Fig. 8: (a) Spectral changes during the degradation of phenol in the presence of Sn3O4 and (b) a plot of the change in absorbance vs. irradiation time in the presence of the Sn3O4. Fig. 9: Possible mechanism for the photocatalytic hydrogen production and phenol degradation by Sn3O4 under sunlight irradiation. Fig. 10: Repeatability study of Sn3O4 for (a) Photocatalytic H2 evolution cycle and (b) phenol degradation under sunlight.
Table 1: Summary of recent research reports to hydrogen evolution data.
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Fig. 1: Experimental equipment of water splitting.
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Fig. 2: a) X-ray diffraction patterns (XRD) and b) Raman spectrum of the as-prepared Sn3O4 sample.
Fig. 3: (a-e) - FESEM images and (f) EDS spectra of Sn3O4 respectively.
Fig. 4: Schematic illustration of formation of microball-like Sn3O4 nanostructures.
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Fig. 5: UV-visible absorption spectra of Sn3O4.The inset shows corresponding Tauc plot.
Fig. 6: Particle size distribution histogram of Sn3O4 nanostructures.
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Fig. 7: Time verses amount of H2 (µmol) evolution of Sn3O4
Fig. 8:(a) Spectral changes during the degradation of phenol in the presence of Sn3O4 and (b) a plot of the change in absorbance vs. irradiation time in the presence of the Sn3O4.
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Fig. 9: Possible mechanism for the photocatalytic hydrogen production and phenol degradation by Sn3O4 under sunlight irradiation.
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b)
100
40
60 40 20
Third cycle
60
80
First cycle
80
Second cycle
a) % Phenol Degradation
Amount of H2 (mole/0.1g/h)
100
20 0
0
cycle 1
cycle 2
cycle 3
0
100 200 300 400 500 Sunlight irradiation time (min)
Fig. 10: Repeatability study of Sn3O4 for (a) Photocatalytic H2 evolution cycle and (b) phenol degradation under sunlight.
Table. 1: Sr. No
Photocatalyst material
Catalyst quantity
Light source used
Remarks
40 μmol h-1 01
Sn3O4
0.3 g
300 W Xe arc lamp
References
Manikandan et al;[18]
g-1 83.5 μmol h-1
02
Sn3O4/TiO2
0.2 g
300 W Xe arc lamp
Chen et al; [20] g-1 88.4 μmol h-1
03
Sn3O4
0.1 g
Solar light
Current work g-1
22
600
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Highlights
Highly efficient microball-like Sn3O4 prepared. Succinate assisted simple hydrothermal approach was used for synthesis. Sn3O4 exhibit superior photocatalytic activity. The improved photocatalytic activity due to narrow band gap, morphology and good crystallinity.
Sagar Balgude, Yogesh Sethi, Bharat Kale, Dinesh Amalnerkar, Parag Adhyapak PII:
S0254-0584(18)30697-7
DOI:
10.1016/j.matchemphys.2018.08.032
Reference:
MAC 20875
To appear in:
Materials Chemistry and Physics
Received Date:
13 June 2018
Accepted Date:
12 August 2018
Please cite this article as: Sagar Balgude, Yogesh Sethi, Bharat Kale, Dinesh Amalnerkar, Parag Adhyapak, Sn3O4 microballs as highly efficient photocatalyst for hydrogen generation and degradation of phenol under solar light irradiation, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.08.032
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Sn3O4 microballs as highly efficient photocatalyst for hydrogen generation and degradation of phenol under solar light irradiation Sagar Balgudeab, Yogesh Sethia, Bharat Kalea, Dinesh Amalnerkarc and Parag Adhyapaka* aCentre
for Materials for Electronics Technology, Panchawati, Pashan Road, Pune-411008, India bD.
cInstitute
Y. Patil College of Engineering, Ambi, Pune-410507, India
of Nano Science & Technology, Hanyang University, Seoul-04763, South Korea
Abstract: Succinate driven facile hydrothermal method for fabrication of Sn3O4 microballs have been reported. The crystal structure of triclinic Sn3O4 was confirmed by XRD and Raman spectroscopy. The FESEM analysis reveals microball-like morphology made up of irregular contour-like nanostructures with thickness of about 40-80 nm. The optical band gap calculated from optical absorption spectroscopy was found to be 2.62 eV for synthesized Sn3O4. Considering morphology and narrowing of band gap, the photocatalytic activities for hydrogen generation and phenol degradation was investigated under solar light irradiation. Sn3O4 nanostructure exhibited enhanced photocatalytic activities for hydrogen generation and phenol degradation. A maximum H2 generation (88.4 µmol h-1/0.1 g) was obtained using the microballlike Sn3O4, which is higher than earlier reported data. Sn3O4 also exhibits good phenol degradation activity. The high photocatalytic activity of Sn3O4 was considered to be due to narrow band gap and hierarchal microball-like morphology. Key words: Sn3O4 nanostructure, microballs, Hydrothermal, Photocatalysts Corresponding Authors: Phone: +91-020-25899273, Fax: +91-020-25898180 Email: [email protected] (Dr. P. V. Adhyapak) 1
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1. Introduction Oxides of tin have been studied extensively from many decades due to abundant availability, non-toxicity, excellent optical and electrical properties [1-2] and these oxide of tin have applications in various fields such as sensitizedsolar cells, gas sensors, lithium ion batteries and photocatalysis [3-11]. Currently, research is more focused on synthesis of nonstoichiometric tin oxides with different coordination compounds such as Sn2O3, Sn3O4, and Sn5O6 with theoretical calculations and regulating Sn2+ and Sn4+ ratio [12-13]. Exploration of facile synthetic methods for obtaining pure and stable crystalline forms of these mixed-valent materials have considerably attracted a research attention recently. Sn3O4 is the first stable identified non-stoichiometric tin oxide composed by alternating atomic layers of tin and oxygen [14]. The Sn3O4 is an n-type semiconductor, having band gap in visible region (2.3-2.8 eV). Considering the band gap in visible region many researchers have synthesized various morphologies & studied their optical properties [15-16]. To mention few, Xu fang et al. have reported hydrothermally synthesized 3D flower-like structures used as anode material in lithium ion batteries [17]. Manikandan et al. have demonstrated water splitting using rectangular flexlike Sn3O4 nanostructures [18]. Suman et al. have studied the gas sensing studies of Sn3O4 nanobelts synthesized using carbothermal method [19]. Chen et al. have shown the superior photoreactivity of scaly nanoflex of Sn3O4 towards hydrogen generation and dye degradation [20]. Tian et al. have developed the H2O2 electrochemical senor using nanosheet like Sn3O4 nanostructures [21]. As can be 2
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seen from literature survey; there are very few reports which highlights the synthesis of Sn3O4 nanostructures with hierarchal morphology. Additionally, the reported results need further improvement. Considering this need, we understand the requirement of synthesis procedure for hierarchal Sn3O4 nanostructures. The hierarchal morphologies can result into better performance in view point of photocatalytic applications [22-23]. Previously, our research group have reported several hierarchal morphologies of ZnO using facile succinate mediated hydrothermal route in which succinate has shown better control over the morphology of the products [24]. So, here in present study we are reporting succinate induced hydrothermal route for the synthesis of microball-like Sn3O4 nanostructures. The synthesized Sn3O4 nanostructures have been characterized using X- Ray diffraction (XRD), Raman, Field emission scanning electron microscope (FESEM), Energy-dispersive X-ray spectroscopy (EDX),
UV-Visible
spectra
and
Particle
size
distribution
(PSD).
The
photocatalytic activities of microball-like Sn3O4 structures have been investigated for hydrogen production and were compared with that of previous reports. Additionally the degradation of phenol under sun light irradiation was also investigated. 2. Experimental 2.1 Materials All reagents used were of analytical grade. Stannous chloride dihydrate (SnCl2.2H2O), disodium succinate hexahydrate, sodium hydroxide and phenol
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were procured from Merck (India). Deionized water was used throughout all experiments. 2.2 Preparation of microball-like of Sn3O4 nanostructures In a typical synthesis procedure, stannous chloride dihydrate 2.90 g (0.015M) was dissolved in 20 ml of water and disodium succinate hexahydrate 6.27 g (0.023M) was dissolved in 20 ml water separately under continuous stirring and then it was admixed together. To this solution aq. NaOH solution (0.5M) was added dropwise for over a period of 30 min to attain a pH~12.5. After complete addition, the white suspension was formed. This suspension was stirred for 30 mins at ambient temperature and then transferred into Teflon-lined stainless-steel 200 mL autoclave. The autoclave was closed and placed in oven at 180°C for 20 h. subsequently cooled down naturally to room temperature. The yellow precipitate formed was centrifuged and washed 3-4 with deionized water and finally with ethanol and dried at 50°C in oven for 12 h.
2.3 Sample characterization The morphology of as-prepared sample was investigated by FESEM model JEOLJSM 6700F. The structural analysis and identification of Sn3O4 product was performed using Rigaku Miniflex operated with Cu Kα irradiation at λ=1.5406 Å and Ni filter. Raman spectra were recorded on Jobin Yvon T64000 triple grating spectrometer equipped with a liquid nitrogen cooled charge coupled device. UVvisible absorption spectra of aqueous suspension were recorded on a JASCOV-570
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spectrophotometer. The particle size distribution was carried using a PSSNICOMP particle sizing system, Santa Barbara, California, USA. 2.4 Evaluation of photocatalytic activity Photocatalytic H2 generation from water The as synthesized microball-like Sn3O4 nanostructures were evaluated for photocatalytic H2 evolution from water. The experimental equipment for photocatalyical water splitting is shown in Fig. 1.
Typical experiments were
carried using a 250 ml round bottom flask containing 100 mL of double distilled water and 25 ml of methanol as sacrificial reagent. Then, 100 mg of Sn3O4 catalyst preloaded with 1 wt% platinum (as a co-catalyst) was added to former solution. The dissolved oxygen was removed from reaction mixture by purging argon gas. The photocatalytic H2 evolution was studied under solar light irradiation. The process of reaction was monitored by measuring evolved gas with the help of eudiometer connected to a round bottom flask. During experiments, the amount of gas evolved as a function of time was noted and this data was used for further calculations. The quantification of hydrogen gas evolved was carried out using gas chromatography equipped with a 5 A˚ capillary column and a thermal conductivity detector. Photocatalytic degradation of phenol Further, as synthesized Sn3O4 microballs were also evaluated for their photodegradation activity using phenol as model contaminant. 250 mL Pyrex beaker was used as photoreactor. Prior to sunlight irradiation, 100 mL, 6 ppm aqueous solution of phenol containing 100 mg of catalyst was stirred in dark to 5
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achieve adsorption equilibria. After 1 hr. suspension was exposed to sunlight. During photocatalytic degradation experiments, the reaction samples were taken at regular interval and was analysed by UV-visible spectrophotometer for residual phenol concentration.
3. Results and discussion: X-ray diffraction pattern of as-prepared Sn3O4 sample is shown in Fig. 2a. The strong and sharp peaks in Sn3O4 sample indicate good crystallinity of the material. The XRD pattern shows diffraction patterns at 2θ values 23.09, 26.82, 31.29, 33.75, 37.15, 50.08 and 51.60 which corresponded to (101), (111), (210), (122), (130), (311) and (132) lattice planes and can be attributed to triclinic phase. The calculated lattice parameters of the triclinic Sn3O4 phase are a=4.85 Å, b=5.87 Å and c=8.20 Å which agrees well with reported values [JCPDS card No. 16-0737] [25]. Beyond these peaks, no other peaks related to any impurity such as SnO, SnO2 etc. were observed in XRD pattern within the detection limits of the instrument. Further structural information and impurity detection of the microball-like Sn3O4 sample was investigated by room temperature Raman spectroscopy and the results are shown in Fig. 2b. From figure, two intense peak centred at 142 cm-1 and 170 cm-1, can be assigned to characteristic of triclinic Sn3O4 [25]. The characteristic Raman peak of SnO2 (470 cm-1 and 770 cm-1) and SnO (211 cm-1) is absent in recorded spectra [26, 27]. These results indicates good crystalline quality of as synthesized Sn3O4 sample. The appearance of peak at 249 cm-1 can be
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assigned to Sn3O4 which may be due to oxidation of the sample and is in well accordance with the previous literature reports [28]. Fig. 3 illustrates the FESEM images and corresponding EDS spectra of the Sn3O4 sample synthesized using hydrothermal treatment. The images show spherical microball-like structure Fig. 3a, 3b & 3c. A low-amplification images Fig. 3 (d-e) indicate that these ball like microstructures are made up by assembly of numerous irregular contour-like structures forming a spherical microballs. These irregular contour-like structures have thickness of about 40-80 nm. The energy dispersive x-ray results are shown in Fig. 3 (f). The chemical composition of atomic ratios of Sn and O for the Sn3O4 microballs are found to be 50.03 and 49.97. The nonexistence of peaks related to any other impurity element confirms that the synthesized material is composed of Sn and O only. On the basis of the morphology obtained, the probable growth mechanism of the microball-like Sn3O4 nanostructure can be postulated. Fig. 4 represents the overall possible mechanism of formation of nanostructured Sn3O4. In succinate assisted hydrothermal synthesis, the small nanoparticles are formed initially. These nanoparticles are self-assembled and form microball-like morphology. These microballs clearly shows the nanoparticles on the surface. After prolonged time at hydrothermal condition, the microballs growth takes place due to self-assembly of same size of Sn3O4 nanoparticles [29]. Fig. 5 depicts the UV-visible absorption spectra of microball-like Sn3O4 and their corresponding Tauc plots. From figure it can be observed that the microballlike Sn3O4 exhibited broad and strong absorption in UV-visible range. The optical
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band gap of Sn3O4 calculated using Tauc model was found to be 2.62eV. These results are in well accordance with the previous reports [30]. In Sn3O4, the narrow band gap is due to co-existance of both Sn2+ and Sn4+ cations [18]. The particle size distribution analysis of microball-like Sn3O4 is given in Fig. 6. It was observed from the graphs, the sizes of the pale yellow product of microballlike Sn3O4 are found to be 360 nm. The photocatalytic activity of hydrothermally synthesized microball-like heterovalent Sn3O4 sample for the photocatalytic hydrogen generation via. Photodecomposition of H2O and degradation of phenol was performed. The results pertaining to amounts of H2 evolution as a function of solar light irradiation time in presence of microball-like Sn3O4 are shown in Fig.7. The maximum hydrogen evolution (88.4 μmol h-1/0.1g) was obtained using the microball-like Sn3O4 nanoparticles. These results are superior to previously reported literature [18, 21]. The data for H2 evolution via H2O splitting is summarized in Table 1.These results demonstrate the potential candidature of Sn3O4 for H2 evolution via. Water splitting under sunlight irradiation. The as-synthesized microball-like Sn3O4 were also evaluated for degradation of phenol using the under solar light. The degradation of phenol was monitored by observing changes in characteristic peak at 282 nm. The absorption spectra of aqueous phenol solution (6 ppm, 100 mL) in presence of 100 mg of Sn3O4 under solar light for various time intervals is as shown in Fig. 8(a). The phenol absorption peak at 282 nm decreases by 35% within 50 min and disappears completely after irradiation for 200 min. Fig. 8(b) shows the kinetic studies of the
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degradation of phenol with solar light irradiation time for the synthesized Sn3O4 sample. In absence of catalyst under sunlight irradiation, it was observed that there was not any significant change in phenol concentration. From Fig. 8(b), it can be suggested that the photocatalytic degradation reactions of phenol on the Sn3O4 catalyst follow the pseudo-first-order kinetics (k = 0.005 min-1& R2 = 0.9841). The results clearly indicates that, on addition of microball-like Sn3O4 photocatalysts leads to the phenol degradation. Based on these experimental results, a probable mechanism involved in H2 production and phenol degradation have been proposed & is shown in Fig. 9. Generally, upon light irradiation photogenerated electrons are excited from the valence band to conduction band of photocatalyst, leaving behind a hole in valence band, which participates in different oxidation-reduction reactions [31]. The photocatalytic activity of heterovalent Sn3O4 can be ascribed to narrow band gap, which facilitates the efficient absorption of incident solar light to induce e- and h+ pair generation. The as formed e- and h+ can then transferred to Sn3O4 surface and may undergo various reactions to generate H2 by water splitting and degraded organic pollutant as shown in following equations [31, 32].
𝒉𝝑
𝐒𝐧𝟑𝐎𝟒 (𝐩𝐡𝐨𝐭𝐨𝐜𝐚𝐭𝐚𝐥𝐲𝐬𝐭) → (𝐡 𝟐𝐇𝟐𝐎 + (𝟒𝐡 𝟐𝐇
+
+ (𝟐𝐞
𝐇 𝟐 𝐎 + (𝐡
+
+
‒
)𝐕𝐁→
𝟒𝐇
+
+
)𝐕𝐁
+ (𝐞
)𝐂𝐁
(1) (2)
+ 𝐎𝟐
)𝐂𝐁→𝐇𝟐
)𝐕𝐁→𝐎𝐇•
‒
(3) + 𝐇
+
(4)
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‒
𝐎𝐇 + (𝐡 𝐎𝟐 + (𝐞
‒
+
)𝐕𝐁→𝐎𝐇•
(5)
)𝐂𝐁→𝐎•𝟐‒
(6)
•
𝐎𝐇 + 𝐏𝐡𝐞𝐧𝐨𝐥→𝐃𝐞𝐠𝐫𝐚𝐝𝐞𝐝 𝐩𝐫𝐨𝐝𝐮𝐜𝐭𝐬 •‒ 𝟐
𝐎
+ 𝐏𝐡𝐞𝐧𝐨𝐥→𝐃𝐞𝐠𝐫𝐚𝐝𝐞𝐝 𝐩𝐫𝐨𝐝𝐮𝐜𝐭𝐬
(7) (8)
The reusability and stability of the photocatalyst was also studied by repeating the experiments under similar conditions using the microball-like Sn3O4 photocatalyst after recycling (Fig. 10). More importantly, microball-like Sn3O4 showed sustained and consistent activity up to the 3rd cycle under sunlight irradiation, which proves the stability of the catalyst. As per our information, our hydrothermally synthesized microball-like Sn3O4 gives superior photocatalytic activity than those previously reported (Table-1). The increased photocatalytic activity of Sn3O4 can be attributed to the microball-like nanostructure, good crystallinity and narrowing of the band gap i.e. in visible region. In nutshell, Sn3O4 shows enhanced H2 production and phenol degradation under solar light and was observed to be stable photocatalyst. 4. Conclusions In conclusion, the Sn3O4 nanostructures were successfully synthesized by facile hydrothermal method using stannous chloride dihydrate and disodium succinate hexahydrate, which exhibited enhanced photocatalytic activity towards the phenol degradation and H2 generation via. Water splitting under solar light irradiation. The excellent photocatalytic activity of the microball-like Sn3O4 can be ascribed to
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its photo-absorption ability due to the narrowing band gap, microball-like morphology and good crystallinity.
Acknowledgements: Dr. Parag V. Adhyapak is grateful to ISRO, Bengaluru and VSSC, Thiruvananthapuram for financial support.
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[15] Y. He, D. Li, J. Chen et al., Sn3O4: a novel heterovalent-tin photocatalyst with hierarchical 3D nanostructures under visible light, RSC Advances, vol. 4, no. 3, pp. 1266– 1269, 2014. [16]W. Xu, M. Li, X. B. Chen et al., Synthesis of hierarchical Sn3O4 microflowers selfassembled by nanosheets, Materials Letters, vol. 120, pp. 140–142, 2014. [17] Xuefang Chen, Ying Huang, Kaichuang Zhang, Xuansheng Feng, Chao Wei, Novel hierarchical flowers-like Sn3O4 firstly used as anode materials for lithium ion batteries, Journal of Alloys and Compounds, 2017, 690, 765-770. [18]M. Manikandan, T. Tanabe, P. Li et al., Photocatalytic water splitting under visible light by mixed-valence Sn3O4, ACS Applied Materials & Interfaces, vol. 6, no. 6, pp. 3790–3793, 2014. [19] P. H. Suman, A. A. Felix, H. L. Tuller, J. A. Varela, and M. O. Orlandi, Comparative gas sensor response of SnO2, SnO and Sn3O4 nanobelts to NO2 and potential interferents, Sensors and Actuators, B: Chemical, vol. 208, pp. 122–127, 2015. [20] Guohui Chen, ShaozhengJi, Yuanhua Sang, Sujie Chang, Yana Wang,Pin Hao, Jerome Claverie, Hong Liu, Guangwei Yu, Synthesis of scaly Sn3O4/TiO2 nanobelt heterostructures for enhanced UV-visible lightphotocatalytic activity, Nanoscale, 2015, 7, 3117. [21] Liangliang Tian, Kaidong Xia, Wanping Hu, Xiaohui Zhong, Lu Li, A wide linear range and stable H2O2 electrochemical sensor based on Ag decorated hierarchical Sn3O4, Electrochimica Acta, 2017, 231, 190-199.
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[29] Rajendra P. Panmand, Yogesh A. Sethi, Sunil R. Kadam, Mohaseen S. Tamboli, Latesh K. Nikam, Jalinder D. Ambekar, Chan-Jin Park and Bharat B. Kale, Selfassembled hierarchical nanostructures of Bi2WO6 for hydrogen production and dye degradation under solar light, Cryst. Eng. Comm, 2015, 17, 107. [30] O. M. Berengue, R. A. Simon, A.J. Chiquito, C. J. Dalmaschio, E.R. Leite, H.A. Guerreiro, F.E.G. Guimaraes, Semiconducting Sn3O4 nanobelts: growth and electronic structure, J. Appl. Phys. 107 (2010) 033717. [31] Imran Ali, Seu-Run Kim, Sung-Pil Kim, Jong-Oh Kim, Anodization of bismuth doped TiO2 nanotubes composite for photocatalytic degradation of phenol in visible light, Catal. Today (2016). [32] K. Maeda, Photocatalytic water splitting using semiconductor particles: History and recent developments, J. Photochem. Photobiol. C Photochem. Revi. 12 (2011) 237–268.
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Figure Caption: Fig. 1: Experimental equipment of water splitting. Fig. 2: a) X-ray diffraction patterns (XRD) and b) Raman spectrum of the as-prepared Sn3O4 sample. Fig. 3: (a-e) - FESEM images and (f) EDS spectra of Sn3O4 respectively. Fig. 4: Schematic illustration of formation of microball-like Sn3O4 nanostructures. Fig. 5: UV-vis absorption spectra of Sn3O4. The inset shows (αhν)2 vs photon energy (hν) spectra for the calculation of optical band gap by extrapolating on hν axis at α=0. Fig. 6: Particle size distribution histogram of Sn3O4 nanostructures. Fig. 7: Time verses amount of H2 (µmol) evolution of Sn3O4. Fig. 8: (a) Spectral changes during the degradation of phenol in the presence of Sn3O4 and (b) a plot of the change in absorbance vs. irradiation time in the presence of the Sn3O4. Fig. 9: Possible mechanism for the photocatalytic hydrogen production and phenol degradation by Sn3O4 under sunlight irradiation. Fig. 10: Repeatability study of Sn3O4 for (a) Photocatalytic H2 evolution cycle and (b) phenol degradation under sunlight.
Table 1: Summary of recent research reports to hydrogen evolution data.
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Fig. 1: Experimental equipment of water splitting.
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Fig. 2: a) X-ray diffraction patterns (XRD) and b) Raman spectrum of the as-prepared Sn3O4 sample.
Fig. 3: (a-e) - FESEM images and (f) EDS spectra of Sn3O4 respectively.
Fig. 4: Schematic illustration of formation of microball-like Sn3O4 nanostructures.
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Fig. 5: UV-visible absorption spectra of Sn3O4.The inset shows corresponding Tauc plot.
Fig. 6: Particle size distribution histogram of Sn3O4 nanostructures.
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Fig. 7: Time verses amount of H2 (µmol) evolution of Sn3O4
Fig. 8:(a) Spectral changes during the degradation of phenol in the presence of Sn3O4 and (b) a plot of the change in absorbance vs. irradiation time in the presence of the Sn3O4.
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Fig. 9: Possible mechanism for the photocatalytic hydrogen production and phenol degradation by Sn3O4 under sunlight irradiation.
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b)
100
40
60 40 20
Third cycle
60
80
First cycle
80
Second cycle
a) % Phenol Degradation
Amount of H2 (mole/0.1g/h)
100
20 0
0
cycle 1
cycle 2
cycle 3
0
100 200 300 400 500 Sunlight irradiation time (min)
Fig. 10: Repeatability study of Sn3O4 for (a) Photocatalytic H2 evolution cycle and (b) phenol degradation under sunlight.
Table. 1: Sr. No
Photocatalyst material
Catalyst quantity
Light source used
Remarks
40 μmol h-1 01
Sn3O4
0.3 g
300 W Xe arc lamp
References
Manikandan et al;[18]
g-1 83.5 μmol h-1
02
Sn3O4/TiO2
0.2 g
300 W Xe arc lamp
Chen et al; [20] g-1 88.4 μmol h-1
03
Sn3O4
0.1 g
Solar light
Current work g-1
22
600
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Highlights
Highly efficient microball-like Sn3O4 prepared. Succinate assisted simple hydrothermal approach was used for synthesis. Sn3O4 exhibit superior photocatalytic activity. The improved photocatalytic activity due to narrow band gap, morphology and good crystallinity.