Photocatalytic activity of TiO2/Nb2O5/PANI and TiO2/Nb2O5/RGO as new nanocomposites for degradation of organic pollutants

doi:10.1016/j.jhazmat.2018.02.052

Journal of Hazardous Materials

Volume 351, 5 June 2018, Pages 147-159

https://doi.org/10.1016/j.jhazmat.2018.02.052 Get rights and content

Highlights

•
The TiO₂/Nb₂O₅/PANI and TiO₂/Nb₂O₅/RGO nanocomposites were first synthesized via hydrothermal method.
•
Photocatalytic degradation of organic dyes were evaluated under visible light irradiation.
•
TiO₂/Nb₂O₅/RGO exhibits outstanding photocatalytic efficiency under visible light.
•
TiO₂/Nb₂O₅/RGO nanocomposite is stable and shows excellent reusability.

Abstract

In this study, highly active titanium dioxide modified by niobium oxide (Nb₂O₅), polymer (PANI) and reduced graphene oxide (RGO) were successfully prepared. The morphology, structure, surface area and light absorption properties of the present nanocomposites for removal of methylene blue (MB) and methyl orange (MO) were investigated and compared with those of TiO₂/Nb₂O₅ and TiO₂ nanoparticles. The characterization techniques such as XRD, FT-IR, UV–vis, SEM, EDX, BET and TEM were employed in order to identify the nanocomposites. Also, photocatalytic properties of TiO₂/Nb₂O₅/PANI and TiO₂/Nb₂O₅/RGO nanocomposites under visible light irradiation were studied. In this way, the obtained results were compared to each other and also compared to TiO₂/Nb₂O₅ and TiO₂ nanoparticles. In this context, the chemical oxygen demand (COD) removal follows the photodegradation in observed performance. The results indicate that reduced TiO₂/Nb₂O₅ nanocomposite is effectively modified by graphene oxide to give TiO₂/Nb₂O₅/RGO composite. The TiO₂/Nb₂O₅/RGO exhibits significantly higher photocatalytic activity in degradation of organic dyes under visible light rather than that of TiO₂/Nb₂O₅/PANI, TiO₂/Nb₂O₅ and pure TiO₂.

Graphical abstract

Excellent photocatalytic activity of the TiO2/Nb2O5/RGO nanocomposite for MB and MO degradation under visible light irradiation.

Introduction

Along with the increase of consciousness in environmental protection and the development of global environmental standards, the control of environmental pollutions has received too much attention. In recent decades, many researchers have tried to find an environmentally friendly, convenient and simple method which is able to remove organic compounds from industrial and municipal wastes [1]. Several catalytic techniques have been applied in the field of environmental protection [2]. Among them, the photocatalytic activity of the titanium dioxide (TiO₂) has attracted too much attention for environmental applications including pollutant elimination from water. It is due to its appropriate optical absorption, chemical stability, environmentally friendly, non-toxic, facile synthesis, low cost and high reactivity [[3], [4], [5], [6], [7], [8], [9], [10], [11]]. However, the recombination rate for the photo-generated hole–electron pairs on TiO₂ is too large. This problem significantly decreases the photocatalytic efficiency of TiO₂ and restricted its industrial application [12,13]. In order to avoid this problem, various strategies have been suggested in the field of TiO₂ photocatalysis, such as loading different amounts of metals or metal oxides on the surface of TiO₂ [14,15], use of non-metals [16,17], combining the TiO₂ with adsorbents [[18], [19], [20]] or semiconductors to form heterojunctions [[21], [22], [23]] and finally carbonaceous materials [24]. Several investigations demonstrated that the recombination is reduced by semiconductor-metal composites or using two different semiconductors [[25], [26], [27], [28], [29]]. Different types of heterojunctions, such as WO₃/BiVO₄ [30], CdS/TiO₂ [31], Ag₃PO₄/BiVO₄ [32], TiO₂/SnO₂ [33] and organic semiconductor hetero-structures [34], have been prepared and successfully applied in photocatalysis processes for the degradation of organic pollutants. Qu et al. [35] prepared TiO₂/WO₃ composite nanotubes and employed them in the photocatalytic degradation of “methyl orange” under UV light irradiation. This nanocomposite showed a high photocatalytic activity, being probably attributed to the presence of WO₃ semiconductor which enhances the charge separation efficiency.

In recent years, many applications of Nb₂O₅ as a promising photocatalyst or an appropriate semiconductor have been reported [36,37]. Yan et al. [38] synthesized TiO₂/Nb₂O₅ through a simple direct hydrolysis route under strong acidic conditions. They also applied the composite in the photocatalytic degradation of “α-phenethyl” alcohol under UV light exposure. This nanocomposite exhibited a high photocatalytic activity which is due to that the photo-generated electrons in the conduction band of Nb₂O₅ will transfer to TiO₂, and the photo-generated holes are reversely transferred. In such conditions, the difference in Fermi energy between two semiconductors plays the role of driving force. For this reason, the coupling of two semiconductors can effectively prevent the recombination of the electron-hole pairs.

Recently, the applications of conductive organic polymers, showing conductivity like metals, e.g. polypyrrole (PPY), polyaniline (PANI) and polythiophene (PTP), have attracted a great attention [[39], [40], [41], [42]]. Moreover, polyaniline have been investigated by several research groups due to its unique electrical, optical and electro-optical properties and also its potential applications. Furthermore, it has widely been studied as a conductive and conventional polymer in order to improve the photocatalytic efficiency of the titanium dioxide [[43], [44], [45], [46]]. However, application of this new kind of absorbents in wastewaters refinement, particularly in elimination of dyes, is still rare in the literature. Chen et al. [47] provided TiO₂/PANI nanobelts via in-situ chemical oxidative polymerization method and applied the nanobelts in the photocatalytic degradation of “rhodamine b” under visible light exposure where the presence of PANI resulted in the high absorption of organic pollutants. Moreover, the photocatalytic activity and the enhanced absorption are due to the decreased recombination of the electron-hole pairs, efficient charge transportation and enhanced charge separation efficiency. Polyaniline (PANI) and its derivatives show many advantages in combination with TiO₂. The large internal interface area in the nanocomposite makes an efficient charge separation which is very important for the photocatalytic application [48,49]. In addition, the delocalized π-conjugated system in PANI can be beneficial to accelerate charge separation, therefore, the separation efficiency of photogenerated electron (e⁻)–hole (h+) pairs can be significantly developed [50].

Graphene has attracted a remarkable interest due to its unique properties, e.g. exceptional electrical conductivity, outstanding mechanical strength, large specific surface area and adsorption capacity [51,52]. The mixture of graphene and reduced graphene oxide (RGO) with TiO₂ improves the charge separation by transferring the excited electrons to graphene or RGO. Besides, such mixture increases the specific surface area of the nanocomposite in order to receive more absorbance. Therefore, TiO₂/RGO nanocomposites are able to improve the photodegradation efficiency of TiO₂. Luo et al. [53] synthesized TiO₂-reduced graphene oxide (RGO) nanocomposites via hydrothermal synthesis for the photocatalytic degradation of “bisphenol A” under UV light irradiation. The results showed that the reduced graphene oxide (TiO₂/RGO) not only improve the adsorption ability, but also significantly improve the photocatalytic activity of TiO₂ for degradation of bisphenol A.

In the present study, TiO₂ nanoparticles modified by niobium oxide, polyaniline (PANI) and reduced graphene oxide (RGO) have been synthesized using the hydrothermal method with in-situ chemical oxidative polymerization. The morphology, structure and phase composition of the obtained nanocomposites were studied in detail. The photodegradation capability of the synthesized materials has also been investigated toward methylene blue (MB) and methyl orange (MO) as organic dyes in the presence of small amount of nanocomposite. Then, the results for the nanocomposites were compared to each other and also with TiO₂/Nb₂O₅ nanocomposite and TiO₂ nanoparticles. The obtained results indicated that addition of both niobium oxide and reduced graphene oxide to the titanium dioxide enhances the photocatalytic efficiency of the TiO₂/Nb₂O₅/RGO in comparison to TiO₂/Nb₂O₅/PANI, TiO₂/Nb₂O₅ and pure TiO₂ under visible light irradiation, respectively. The present recoverable TiO₂/Nb₂O₅/RGO nanocomposite photocatalysts can be regarded as one of the ideal photocatalysts for the various photocatalytic applications.

Section snippets

Experimental section

The TiO₂ nanoparticles together with the TiO₂/Nb₂O₅ and TiO₂/Nb₂O₅/RGO nanocomposites have been prepared using the hydrothermal method. Similarly, the TiO₂/Nb₂O₅/PANI nanocomposite has been prepared by hydrothermal method nanocomposite accompanied by the in situ chemical oxidative polymerization method. Details of the syntheses are provided in supplementary materials [54,55]. Furthermore, materials, characterization of synthesized nanocomposites and details of photocatalytic experiments are

X-ray diffraction patterns

XRD patterns of pure TiO₂ nanoparticles together with TiO₂/Nb₂O₅, TiO₂/Nb₂O₅/PANI and TiO₂/Nb₂O₅/RGO nanocomposites are shown in Fig. 1. For each sample, the crystallite size of TiO₂ nanoparticles was calculated by FWHM value, using Scherrer formula (D = 0.89λ/β cosθ) where D, λ, β and θ are respectively average of crystallite size (A°), X-ray wavelength (CuKα), full width half maximum (FWHM) and diffraction angle (degree °) [62]. Using this formula, the particle sizes of TiO₂, TiO₂/Nb₂O₅, TiO₂

Conclusion

The TiO₂/Nb₂O₅/PANI and TiO₂/Nb₂O₅/RGO nanocomposites were successfully prepared using hydrothermal method, accompanied by the in situ chemical oxidative polymerization. The prepared nanocomposites were employed as photocatalyst for removal of MB and MO dyes from aqueous solution. Using characterization techniques such as XRD, FT-IR, SEM, EDX, BET and TEM, it has been proved that the TiO₂/Nb₂O₅ nanocomposite was successfully deposited on conductive polymer to give the TiO₂/Nb₂O₅/PANI

Acknowledgment

The authors are grateful to K.N. Toosi University of Technology for the help to undertake this work.

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Photocatalytic activity of TiO2/Nb2O5/PANI and TiO2/Nb2O5/RGO as new nanocomposites for degradation of organic pollutants

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental section

X-ray diffraction patterns

Conclusion

Acknowledgment

Electrochem. Commun.

Appl. Catal. B: Environ.

Ceram. Int.

Appl. Surf. Sci.

Mater. Res. Bull.

J. Mol. Catal. A Chem.

Carbon

Ceram. Int.

J. Photochem. Photobiol. A

J. Hazard. Mater.

Appl. Surf. Sci.

Compos. Sci. Technol.

Sens. Actuators B Chem.

Appl. Surf. Sci.

Mater. Lett.

Chin. J. Catal.

J. Hazard. Mater.

Mater. Lett.

Electrochem. Commun.

Catal. Today

Catal. Today

J. Non-Cryst. Solids

J. Electroanal. Chem.

J. Mol. Catal. A: Chem.

Chem. Eng. J.

J. Non-Cryst. Solids

Appl. Catal. B

J. Power Sour.

Dyes Pigments

Surf. Coat. Technol.

Physica E

J. Colloid Interface Sci.

J Colloid Interface Sci.

Mater. Res. Bull.

Biogas harvesting from organic fraction of municipal solid waste as a renewable energy Resource in Malaysia: a review

Pol. J. Environ. Stud.

The effects of Fe, Co and Ni dopantson TiO2 structure of sol–gel nanopowders used as photocatalysts for environmental protection: a comparative study

Ceram. Int.

Shape-controlled synthesis of highly crystalline titania nanocrystals

ACS Nano

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Phys. Chem. Chem. Phys.

Self-assembled TiO2–graphene hybrid nanostructures for enhanced Li-ion insertion

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Significant enhancement in visible light absorption of TiO2 nanotube arrays by surface band gap tuning

J. Phys. Chem. C

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Understanding the effect of surface/bulk defects on the photocatalytic activity of TiO2: anatase versus rutile

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TiO2 nanosheets with exposed {001} facets for photocatalytic applications

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Fabrication of CaFe2O4/TaON heterojunction photoanode for photoelectrochemical water oxidation

J. Am. Chem. Soc.

Photocatalytic activity of TiO₂/Nb₂O₅/PANI and TiO₂/Nb₂O₅/RGO as new nanocomposites for degradation of organic pollutants

The effects of Fe, Co and Ni dopantson TiO₂ structure of sol–gel nanopowders used as photocatalysts for environmental protection: a comparative study

Effective increasing of optical absorption and energy conversion efficiency of anatase TiO₂ nanocrystals by hydrogenation

Self-assembled TiO₂–graphene hybrid nanostructures for enhanced Li-ion insertion

Significant enhancement in visible light absorption of TiO₂ nanotube arrays by surface band gap tuning

In-situ-reduced synthesis of Ti³⁺ self-doped TiO₂/g-C₃N₄ heterojunctions with high photocatalytic performance under LED light irradiation

TiO₂ nanosheets with exposed {001} facets for photocatalytic applications

Boosting photovoltaic performance of dye-sensitized solar cells using silver nanoparticle-decorated N,S-co-doped-TiO₂ photoanode

Visible light activity of sulfur-doped TiO₂ nanostructure photoelectrodes prepared by single-step electrochemical anodizing process

Role of bentonite adsorbent sub-layer in the photocatalytic-adsorptive removal of methylene blue by the immobilized TiO₂/bentonite system

Fabrication of CaFe₂O₄/TaON heterojunction photoanode for photoelectrochemical water oxidation