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ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent
Accepted Manuscript A facile route for fabrication of hierarchical porous Nb2O5/ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent Ying-Hui Chin, Jin-Chung Sin, Sze-Mun Lam PII: DOI: Reference:
S0167-577X(17)31908-0 https://doi.org/10.1016/j.matlet.2017.12.141 MLBLUE 23639
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
3 December 2017 21 December 2017 28 December 2017
Please cite this article as: Y-H. Chin, J-C. Sin, S-M. Lam, A facile route for fabrication of hierarchical porous Nb2O5/ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet.2017.12.141
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A facile route for fabrication of hierarchical porous Nb2O5/ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent Ying-Hui Chin a, Jin-Chung Sin a,*, Sze-Mun Lam b a
Department of Petrochemical Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia b
Department of Environmental Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia *Corresponding author. Tel.: +60 54688888; Fax +60 54667449; Email: [email protected]
ABSTRACT A facile route was demonstrated for the synthesis of hierarchical porous ZnO microspheres based on a surfactant-free chemical solution method. The as-synthesized ZnO were assembled by large numbers of interleaving nanosheets and formed an open porous structure. Under UV irradiation, the as-synthesized ZnO exhibited photocatalytic property on the degradation of palm oil mill effluent (POME) solution. The Nb2O5 decorated ZnO photocatalysts (Nb2O5/ZnO) with enhanced photocatalytic performances were also synthesized via a facile and rapid route. Compared with ZnO, the Nb2O5(3 wt%)/ZnO exhibited the best POME degradation and colour removal efficiencies of 91.7% and 100%, respectively after 240 min irradiation. Phytotoxicity of the POME after Nb2O5/ZnO photocatalysis was significantly reduced via the measurement of radicle lengths of Vigna radiata. The observed results demonstrated the photocatalytic technology using hierarchical Nb2O5/ZnO composites had the potential to effectively purify wastewater. Keywords: Semiconductors, Composite materials, Microstructure, Optical materials and properties
1. Introduction Oily wastewater from palm oil food industry is a thick brownish liquid waste containing extremely high quantities of organic pollutants. Past research report indicated a discharge of 2.5-3.75 tonnes of palm oil Page 1 of 9
mill effluent (POME) per ton of crude palm oil processed [1]. Such generated effluent can inflict serious environmental problems especially to aquatic life if discharged untreated. Among the various remediation processes, the photocatalysis has been proved as an efficient technology to degrade organic pollutants into nontoxic molecules in the presence of semiconductor materials as catalysts. ZnO is an important semiconductor with band gap of ~3.3 eV which has been widely applied as photocatalyst for wastewater treatment due to its good catalytic activity, chemical stability and low cost. ZnO also demonstrated as a promising material for spintronic applications as it can display the ferromagnetic properties [2]. It has been reported that the morphologies and sizes of ZnO have considerable effect on their physical and chemical properties. Hitherto, various of ZnO structures including nanorods, nanosheets, prism-like, hierarchical and complex ZnO microarchitectures have been synthesized [3,4]. Hierarchical architectures have garnered enormous interest among them because of their peculiar morphology, which endowed the materials with high surface area and porous properties. However, facile and large-scale synthesis of well-defined ZnO hierarchical structures via a surfactant-free method still remained a great challenge. In this work, a facile route was demonstrated to synthesize hierarchical porous ZnO microspheres by a chemical solution method without any surfactant or organic solvent. The morphological, structural, and optical properties of the as-synthesized ZnO samples were characterized using different techniques. The obtained ZnO samples were used for photodegradation of POME solution under UV irradiation. In contrast, coupling of ZnO with metal oxides can effectively improve the photocatalytic performance of ZnO [5]. Therefore, hierarchical Nb2O5/ZnO composites were also synthesized via a facile and rapid route for improved photocatalytic activities. Moreover, the potential residual toxicity of the photocatalytically treated POME on Vigna radiata was evaluated using simple and inexpensive test. It is believed that the purified effluent becoming important in enabling reuse applications such as irrigation. To our knowledge, this is the first report reporting the POME degradation and its phytotoxicity reduction subjected to photocatalytic treatment with hierarchical Nb2O5/ZnO composites. 2. Experimental Details about the hierarchical porous ZnO microspheres and Nb2O5/ZnO composites preparation, catalyst characterizations, photocatalytic measurements and phytotoxicity evaluation can be found in Page 2 of 9
Supplementary material. The formation of hierarchical porous ZnO microspheres can be explained by the chemical reactions as follows: Zn(NO3)2•6H2O + 2 NaOH → Zn(OH)2 + 2 NaNO3 + 6 H2O
(1)
Zn(OH)2 + 2 OH- → ZnO + H2O + 2 OH-
(2)
3. Results and discussion FESEM images of the as-synthesized ZnO samples are shown in Figs. 1(a) and (b). It was clear that the samples were entirely composed of spheroidal structures with diameters of 2.2-4.0 µm (Fig. 1(a)). The high magnification FESEM image showed that the samples were composed of layered nanosheets with jagged edges assembling into irregularly hierarchical porous microspheres through oriented aggregation (Fig. 1(b)). Further observation from TEM image indicated that the ZnO consisted of a large number of nanosheets arranged in an ordered manner to form spherical-shaped morphology (Fig. 1(c)), which agreed well with the FESEM observation. The HRTEM analysis revealed that the synthesized microspheres had very clear lattice fringes with interplanar spacing of 0.26 nm corresponded to the ZnO (002) plane, which also indicated their high degree of crystallinity (Fig. 1(d)). The micrographs (Fig. 1) also witnessed that the obtained samples were submicro/nanograined and contained the very developed grain boundaries and free surfaces. The physical properties of pure and doped nanograined ZnO have recently been reported to be strongly dependent on the presence of defects like grain boundaries and interphase boundaries [2]. It was also stated that their physical properties also depended on the presence of doping atoms in the (invisible for XRD) amorphous surficial, interfacial and intergranular layers [6]. The XRD pattern of the hierarchical porous ZnO microspheres is shown in Fig. 2(a). All diffraction peaks can be indexed to the hexagonal wurtzite ZnO (JCPDS card no. 36-1451). The sharp and strong peaks further suggested that the samples were highly crystalline. No other diffraction peaks for impurities were found, indicating high purity of the samples. The UV-vis DRS spectrum in Fig. 2(b) showed that the assynthesized ZnO had significant absorption in the UV region due to the charge transfer from the valence band to the conduction band (O2p → Zn3d) [7]. The equation Eg (eV) = 1240/λ was used to determine the band gap energy of as-synthesized samples, where λ is the absorption edge and Eg is the band gap energy. The Eg was Page 3 of 9
measured to be 3.22 eV (inset of Fig. 2(b)), which was corresponded with the values reported in literatures [5,7]. The photocatalytic activities of as-synthesized samples were evaluated by POME degradation under UV irradiation (Fig. 3(a)). Noticeably, the POME removal solely due to the photolysis and dark adsorption onto ZnO were negligible (7.1% and 5.7% of COD removal, respectively). However, the POME was degraded to different extents at much higher efficiencies under photocatalysis experiments. The photodegradation using ZnO showed a COD removal of 25.0% after 240 min irradiation. More importantly, the photocatalytic activities enhanced significantly by decorating Nb2O5 nanoparticles on the ZnO surface. Under identical conditions, the COD removal reached 61.1% and 91.7% over Nb2O5(1 wt%)/ZnO and Nb2O5(3 wt%)/ZnO, respectively. Furthermore, the bar charts showed that complete colour removal of the POME solution can be obtained after 30 min irradiation over Nb2O5(3 wt%)/ZnO, whereas with ZnO, only 97.9% colour removal after 240 min irradiation (Fig. 3(b)). The superior photocatalytic performance of Nb2O5/ZnO can be explained by the successful hindering of charge carriers recombination via the hybridization process [8] as evidenced by the PL analysis (Supplementary material, Fig. S1). The phytotoxicity of samples before and after the photodegradation of POME were investigated using Vigna radiata (Fig. 3(c)). Clearly, the untreated POME solution showed a noteworthy degree of initial phytotoxicity of 84.7% compared to the control (0%). After photodegradation, a decrease of phytotoxicity in POME was observed and reached 58.6%. The decrease of phytotoxicity was reflected by the radicle length of Vigna radiata. The average radicle lengths of Vigna radiata for the samples before and after photodegradation were 2.1 and 5.6 cm, respectively. These findings demonstrated the efficiency of photocatalysis using Nb2O5(3 wt%)/ZnO in the reduction of phytotoxicity of wastewater. The formation of hierarchical Nb2O5/ZnO composites was tested by XRD, FESEM and EDX techniques. The XRD results in Fig. 4(a) showed the formation of a mixture of hexagonal phase ZnO (JCPDS card no.36-1451) and monoclinic phase Nb2O5 (JCPDS card no.37-1468). No other peaks for impurities were detected. The TEM image indicated that the morphology of Nb2O5/ZnO had negligible differences with that of ZnO. The Nb2O5 nanoparticles with diameters 26-79 nm were deposited on the ZnO surface (Fig. 4(b)). Moreover, the EDX analysis revealed the existence of Zn, O and Nb elements in the samples (Fig. 4(c)). The EDX mapping of Nb2O5(3 wt%)/ZnO is shown in Figs. 4(d)-(f). The different colour images revealed that the Page 4 of 9
Zn, O and Nb elements distributed throughout sample coverage area, verifying the formation of hierarchical Nb2O5/ZnO composites
4. Conclusions In summary, a facile surfactant-free chemical solution method was demonstrated to synthesize hierarchical porous ZnO microspheres, which were built up by lots of layered nanosheets through oriented aggregation. Moreover, hierarchical Nb2O5/ZnO composites with enhanced photocatalytic performance have been successfully synthesized via a facile and rapid route. Compared with ZnO, the Nb2O5(3 wt%)/ZnO exhibited the best POME degradation and colour removal efficiencies of 91.7% and 100%, respectively after 240 min irradiation. Phytotoxicity of the POME after Nb2O5/ZnO photocatalysis was significantly reduced via the measurement of radicle lengths of Vigna radiata. The observed results revealed the potential applications of photocatalysis on wastewater purification over the hierarchical Nb2O5/ZnO composites.
Acknowledgments This work was supported by Universiti Tunku Abdul Rahman (UTARRF/2016-C2/S03 and UTARRF/2017C1/L02) and Ministry of Higher Education of Malaysia (FRGS/1/2015/TK02/UTAR/02/2 and FRGS/1/2016/TK02/UTAR/02/1). References [1] A.L. Ahmad, S. Ismail, S. Bhatia, Desalination 157 (2003) 87-95. [2] B.B. Straumal, S.G. Protasova, A.A. Mazilkin, E. Goering, G. Schütz, P.B. Straumal, B. Baretzky, Beilstein J. Nanotechnol. 7 (2016) 1936-1947. [3] S.W. Duo, Y.Y. Li, Z. Liu, R.F. Zhong, T.Z. Liu, H.M. Xu, J. Alloys Compd. 695 (2017) 2563-2579. [4] Q.L. Huang, J. Li, Mater. Lett. 204 (2017) 85-88. [5] S.M. Lam, J.C. Sin, A.Z. Abdullah, A.R. Mohamed, Sep. Purif. Technol. 132 (2014) 378-387.
Page 5 of 9
[6] B.B. Straumal, A.A. Mazilkin, S.G. Protasova, S.V. Stakhanova, P.B. Straumal, M.F. Bulatov, G. Schütz, Th. Tietze, E. Goering, B. Baretzky, Rev. Adv. Mater. Sci. 41 (2015) 61-71. [7] A.K. Zak, M.E. Abrishami, W.H. Abd. Majid, R. Yousefi, S.M. Hosseini, Ceram. Int. 37 (2011) 393-398. [8] S.M. Lam, J.C. Sin, I. Satoshi, A.Z. Abdullah, A.R. Mohamed, Appl. Catal. A: Gen. 471 (2014) 126-135. Figure captions: Fig. 1. Low (a) and high-magnification (b) FESEM images, (c) TEM image and (d) HRTEM image of ZnO. Fig. 2. (a) XRD pattern and (b) UV-vis DRS spectrum of ZnO. Inset of (b): plot of R% versus photon energy. Fig. 3. (a) COD/CODo and (b) Decolourization percentage of POME over different photocatalysts. (c) Phytotoxicity of POME before and after the photodegradation using Nb2O5(3 wt%)/ZnO. Fig. 4. (a) XRD pattern of Nb2O5/ZnO composites (■ is hexagonal ZnO and # is monoclinic Nb2O5). (b) TEM image, (c) EDX spectrum and (d) EDX mapping images of Nb2O5(3 wt%)/ZnO.
Fig. 1. Page 6 of 9
Fig. 2.
Fig. 3.
Page 7 of 9
Fig. 4.
Page 8 of 9
Highlights • • • •
A facile and surfactant-free route prepared hierarchical porous ZnO microspheres. Morphological, structural and optical characterization of synthesized ZnO. Effectively photodegradation of palm oil mill effluent over Nb2O5/ZnO composites. Significant decrease of phytotoxicity on the photodegraded palm oil mill effluent.
Page 9 of 9
S0167-577X(17)31908-0 https://doi.org/10.1016/j.matlet.2017.12.141 MLBLUE 23639
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
3 December 2017 21 December 2017 28 December 2017
Please cite this article as: Y-H. Chin, J-C. Sin, S-M. Lam, A facile route for fabrication of hierarchical porous Nb2O5/ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet.2017.12.141
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A facile route for fabrication of hierarchical porous Nb2O5/ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent Ying-Hui Chin a, Jin-Chung Sin a,*, Sze-Mun Lam b a
Department of Petrochemical Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia b
Department of Environmental Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia *Corresponding author. Tel.: +60 54688888; Fax +60 54667449; Email: [email protected]
ABSTRACT A facile route was demonstrated for the synthesis of hierarchical porous ZnO microspheres based on a surfactant-free chemical solution method. The as-synthesized ZnO were assembled by large numbers of interleaving nanosheets and formed an open porous structure. Under UV irradiation, the as-synthesized ZnO exhibited photocatalytic property on the degradation of palm oil mill effluent (POME) solution. The Nb2O5 decorated ZnO photocatalysts (Nb2O5/ZnO) with enhanced photocatalytic performances were also synthesized via a facile and rapid route. Compared with ZnO, the Nb2O5(3 wt%)/ZnO exhibited the best POME degradation and colour removal efficiencies of 91.7% and 100%, respectively after 240 min irradiation. Phytotoxicity of the POME after Nb2O5/ZnO photocatalysis was significantly reduced via the measurement of radicle lengths of Vigna radiata. The observed results demonstrated the photocatalytic technology using hierarchical Nb2O5/ZnO composites had the potential to effectively purify wastewater. Keywords: Semiconductors, Composite materials, Microstructure, Optical materials and properties
1. Introduction Oily wastewater from palm oil food industry is a thick brownish liquid waste containing extremely high quantities of organic pollutants. Past research report indicated a discharge of 2.5-3.75 tonnes of palm oil Page 1 of 9
mill effluent (POME) per ton of crude palm oil processed [1]. Such generated effluent can inflict serious environmental problems especially to aquatic life if discharged untreated. Among the various remediation processes, the photocatalysis has been proved as an efficient technology to degrade organic pollutants into nontoxic molecules in the presence of semiconductor materials as catalysts. ZnO is an important semiconductor with band gap of ~3.3 eV which has been widely applied as photocatalyst for wastewater treatment due to its good catalytic activity, chemical stability and low cost. ZnO also demonstrated as a promising material for spintronic applications as it can display the ferromagnetic properties [2]. It has been reported that the morphologies and sizes of ZnO have considerable effect on their physical and chemical properties. Hitherto, various of ZnO structures including nanorods, nanosheets, prism-like, hierarchical and complex ZnO microarchitectures have been synthesized [3,4]. Hierarchical architectures have garnered enormous interest among them because of their peculiar morphology, which endowed the materials with high surface area and porous properties. However, facile and large-scale synthesis of well-defined ZnO hierarchical structures via a surfactant-free method still remained a great challenge. In this work, a facile route was demonstrated to synthesize hierarchical porous ZnO microspheres by a chemical solution method without any surfactant or organic solvent. The morphological, structural, and optical properties of the as-synthesized ZnO samples were characterized using different techniques. The obtained ZnO samples were used for photodegradation of POME solution under UV irradiation. In contrast, coupling of ZnO with metal oxides can effectively improve the photocatalytic performance of ZnO [5]. Therefore, hierarchical Nb2O5/ZnO composites were also synthesized via a facile and rapid route for improved photocatalytic activities. Moreover, the potential residual toxicity of the photocatalytically treated POME on Vigna radiata was evaluated using simple and inexpensive test. It is believed that the purified effluent becoming important in enabling reuse applications such as irrigation. To our knowledge, this is the first report reporting the POME degradation and its phytotoxicity reduction subjected to photocatalytic treatment with hierarchical Nb2O5/ZnO composites. 2. Experimental Details about the hierarchical porous ZnO microspheres and Nb2O5/ZnO composites preparation, catalyst characterizations, photocatalytic measurements and phytotoxicity evaluation can be found in Page 2 of 9
Supplementary material. The formation of hierarchical porous ZnO microspheres can be explained by the chemical reactions as follows: Zn(NO3)2•6H2O + 2 NaOH → Zn(OH)2 + 2 NaNO3 + 6 H2O
(1)
Zn(OH)2 + 2 OH- → ZnO + H2O + 2 OH-
(2)
3. Results and discussion FESEM images of the as-synthesized ZnO samples are shown in Figs. 1(a) and (b). It was clear that the samples were entirely composed of spheroidal structures with diameters of 2.2-4.0 µm (Fig. 1(a)). The high magnification FESEM image showed that the samples were composed of layered nanosheets with jagged edges assembling into irregularly hierarchical porous microspheres through oriented aggregation (Fig. 1(b)). Further observation from TEM image indicated that the ZnO consisted of a large number of nanosheets arranged in an ordered manner to form spherical-shaped morphology (Fig. 1(c)), which agreed well with the FESEM observation. The HRTEM analysis revealed that the synthesized microspheres had very clear lattice fringes with interplanar spacing of 0.26 nm corresponded to the ZnO (002) plane, which also indicated their high degree of crystallinity (Fig. 1(d)). The micrographs (Fig. 1) also witnessed that the obtained samples were submicro/nanograined and contained the very developed grain boundaries and free surfaces. The physical properties of pure and doped nanograined ZnO have recently been reported to be strongly dependent on the presence of defects like grain boundaries and interphase boundaries [2]. It was also stated that their physical properties also depended on the presence of doping atoms in the (invisible for XRD) amorphous surficial, interfacial and intergranular layers [6]. The XRD pattern of the hierarchical porous ZnO microspheres is shown in Fig. 2(a). All diffraction peaks can be indexed to the hexagonal wurtzite ZnO (JCPDS card no. 36-1451). The sharp and strong peaks further suggested that the samples were highly crystalline. No other diffraction peaks for impurities were found, indicating high purity of the samples. The UV-vis DRS spectrum in Fig. 2(b) showed that the assynthesized ZnO had significant absorption in the UV region due to the charge transfer from the valence band to the conduction band (O2p → Zn3d) [7]. The equation Eg (eV) = 1240/λ was used to determine the band gap energy of as-synthesized samples, where λ is the absorption edge and Eg is the band gap energy. The Eg was Page 3 of 9
measured to be 3.22 eV (inset of Fig. 2(b)), which was corresponded with the values reported in literatures [5,7]. The photocatalytic activities of as-synthesized samples were evaluated by POME degradation under UV irradiation (Fig. 3(a)). Noticeably, the POME removal solely due to the photolysis and dark adsorption onto ZnO were negligible (7.1% and 5.7% of COD removal, respectively). However, the POME was degraded to different extents at much higher efficiencies under photocatalysis experiments. The photodegradation using ZnO showed a COD removal of 25.0% after 240 min irradiation. More importantly, the photocatalytic activities enhanced significantly by decorating Nb2O5 nanoparticles on the ZnO surface. Under identical conditions, the COD removal reached 61.1% and 91.7% over Nb2O5(1 wt%)/ZnO and Nb2O5(3 wt%)/ZnO, respectively. Furthermore, the bar charts showed that complete colour removal of the POME solution can be obtained after 30 min irradiation over Nb2O5(3 wt%)/ZnO, whereas with ZnO, only 97.9% colour removal after 240 min irradiation (Fig. 3(b)). The superior photocatalytic performance of Nb2O5/ZnO can be explained by the successful hindering of charge carriers recombination via the hybridization process [8] as evidenced by the PL analysis (Supplementary material, Fig. S1). The phytotoxicity of samples before and after the photodegradation of POME were investigated using Vigna radiata (Fig. 3(c)). Clearly, the untreated POME solution showed a noteworthy degree of initial phytotoxicity of 84.7% compared to the control (0%). After photodegradation, a decrease of phytotoxicity in POME was observed and reached 58.6%. The decrease of phytotoxicity was reflected by the radicle length of Vigna radiata. The average radicle lengths of Vigna radiata for the samples before and after photodegradation were 2.1 and 5.6 cm, respectively. These findings demonstrated the efficiency of photocatalysis using Nb2O5(3 wt%)/ZnO in the reduction of phytotoxicity of wastewater. The formation of hierarchical Nb2O5/ZnO composites was tested by XRD, FESEM and EDX techniques. The XRD results in Fig. 4(a) showed the formation of a mixture of hexagonal phase ZnO (JCPDS card no.36-1451) and monoclinic phase Nb2O5 (JCPDS card no.37-1468). No other peaks for impurities were detected. The TEM image indicated that the morphology of Nb2O5/ZnO had negligible differences with that of ZnO. The Nb2O5 nanoparticles with diameters 26-79 nm were deposited on the ZnO surface (Fig. 4(b)). Moreover, the EDX analysis revealed the existence of Zn, O and Nb elements in the samples (Fig. 4(c)). The EDX mapping of Nb2O5(3 wt%)/ZnO is shown in Figs. 4(d)-(f). The different colour images revealed that the Page 4 of 9
Zn, O and Nb elements distributed throughout sample coverage area, verifying the formation of hierarchical Nb2O5/ZnO composites
4. Conclusions In summary, a facile surfactant-free chemical solution method was demonstrated to synthesize hierarchical porous ZnO microspheres, which were built up by lots of layered nanosheets through oriented aggregation. Moreover, hierarchical Nb2O5/ZnO composites with enhanced photocatalytic performance have been successfully synthesized via a facile and rapid route. Compared with ZnO, the Nb2O5(3 wt%)/ZnO exhibited the best POME degradation and colour removal efficiencies of 91.7% and 100%, respectively after 240 min irradiation. Phytotoxicity of the POME after Nb2O5/ZnO photocatalysis was significantly reduced via the measurement of radicle lengths of Vigna radiata. The observed results revealed the potential applications of photocatalysis on wastewater purification over the hierarchical Nb2O5/ZnO composites.
Acknowledgments This work was supported by Universiti Tunku Abdul Rahman (UTARRF/2016-C2/S03 and UTARRF/2017C1/L02) and Ministry of Higher Education of Malaysia (FRGS/1/2015/TK02/UTAR/02/2 and FRGS/1/2016/TK02/UTAR/02/1). References [1] A.L. Ahmad, S. Ismail, S. Bhatia, Desalination 157 (2003) 87-95. [2] B.B. Straumal, S.G. Protasova, A.A. Mazilkin, E. Goering, G. Schütz, P.B. Straumal, B. Baretzky, Beilstein J. Nanotechnol. 7 (2016) 1936-1947. [3] S.W. Duo, Y.Y. Li, Z. Liu, R.F. Zhong, T.Z. Liu, H.M. Xu, J. Alloys Compd. 695 (2017) 2563-2579. [4] Q.L. Huang, J. Li, Mater. Lett. 204 (2017) 85-88. [5] S.M. Lam, J.C. Sin, A.Z. Abdullah, A.R. Mohamed, Sep. Purif. Technol. 132 (2014) 378-387.
Page 5 of 9
[6] B.B. Straumal, A.A. Mazilkin, S.G. Protasova, S.V. Stakhanova, P.B. Straumal, M.F. Bulatov, G. Schütz, Th. Tietze, E. Goering, B. Baretzky, Rev. Adv. Mater. Sci. 41 (2015) 61-71. [7] A.K. Zak, M.E. Abrishami, W.H. Abd. Majid, R. Yousefi, S.M. Hosseini, Ceram. Int. 37 (2011) 393-398. [8] S.M. Lam, J.C. Sin, I. Satoshi, A.Z. Abdullah, A.R. Mohamed, Appl. Catal. A: Gen. 471 (2014) 126-135. Figure captions: Fig. 1. Low (a) and high-magnification (b) FESEM images, (c) TEM image and (d) HRTEM image of ZnO. Fig. 2. (a) XRD pattern and (b) UV-vis DRS spectrum of ZnO. Inset of (b): plot of R% versus photon energy. Fig. 3. (a) COD/CODo and (b) Decolourization percentage of POME over different photocatalysts. (c) Phytotoxicity of POME before and after the photodegradation using Nb2O5(3 wt%)/ZnO. Fig. 4. (a) XRD pattern of Nb2O5/ZnO composites (■ is hexagonal ZnO and # is monoclinic Nb2O5). (b) TEM image, (c) EDX spectrum and (d) EDX mapping images of Nb2O5(3 wt%)/ZnO.
Fig. 1. Page 6 of 9
Fig. 2.
Fig. 3.
Page 7 of 9
Fig. 4.
Page 8 of 9
Highlights • • • •
A facile and surfactant-free route prepared hierarchical porous ZnO microspheres. Morphological, structural and optical characterization of synthesized ZnO. Effectively photodegradation of palm oil mill effluent over Nb2O5/ZnO composites. Significant decrease of phytotoxicity on the photodegraded palm oil mill effluent.
Page 9 of 9