Preparation and characterization of tungsten-loaded titanium dioxide photocatalyst for enhanced dye degradation
Introduction
The presence of colour and its causative compound is undesirable for domestic or industrial uses as colour is visible and can be an indication of pollution [1]. WHO guidelines for drinking water quality, has set the maximum value for permissible colour at 15–20 units [2]. Several new technologies in wastewater decolourization have emerged with improved performance and more environmentally friendly. These include Advanced Oxidation Processes (AOPs) such as heterogeneous photocatalysis, Fenton and Photo-Fenton, and ozonation which have received considerable attention due to their compliance with Green Chemistry concept in promoting innovative technologies that reduce or eliminate the use or generation of hazardous substances in the design, manufacturing and use of chemical products [3]. Heterogeneous photocatalysis especially has several advantages, as it uses no reagent. The only chemical used, metal oxide photocatalyst such as titanium dioxide (TiO2) is abundant and harmless. However, TiO2 photocatalysis lacks efficiency due to the high rate of recombination of electrons and holes [4]. In addition, due to its large bandgap energy, Eg of 3.0−3.2 eV, it can only be activated by UV light, which accounts only 3–4% of sunlight spectrum [5]. Efforts have been made using chemical or physical methods, to enhance the photocatalytic activity of TiO2 through modification with different group of metals such as alkaline metals [6], earth alkaline metals [7], transition metals [8], rare earth metals [9], and noble metals [10], but with varying degree of results.
TiO2 has three natural phases—anatase, rutile, and brookite. Modification with certain metals such as Ni [11], Fe [11], [12], Th [12], Cu [12], V and Mo [13], Co [14], Sn [15], and Ag [16], may alter the phase transformation of TiO2 from active anatase to inactive rutile by lowering the activation energy. The activation energy is further affected by metal dosage and method of preparation. On the other hand, metals such as Mg and Ba [17], Mn [18], Tb, Eu and Sm [19], La [20], and Sc and Nb [21] have been reported to inhibit phase transformation.
Degradation of pollutant can be influenced by both intrinsic and extrinsic factors. Intrinsic factors include the nature of the photocatalyst itself such as crystallinity, surface area, morphology, and optical absorption. Extrinsic factors are the process parameters that affect the photodegradation rate such as dye concentration, catalyst loading, pH, light wavelength and intensity, temperature, and oxygen pressure [22], [23], [24]. In addition, the presence of oxidants and dissolved metal ions and organic materials also affect the degradation rates [24]. From both application and economic point of view for operational effectiveness of a photocatalyst, the effects of extrinsic factors are important to be determined particularly the optimum decolourization conditions and limitations.
The objective of this study was to evaluate the effect of TiO2 modification with tungsten trioxide, WO3, using impregnation method, on the photocatalytic activity. Characterization of the photocatalyst was carried out using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), diffuse reflectance ultraviolet visible spectroscopy (DRUV-Vis) and point of zero charge (PZC) methods to understand the physico-chemical properties of the photocatalyst. The photocatalytic activity was tested against the decolourization of methylene blue (MB), methyl violet (MV), and methyl orange (MO) as model dyes in wastewater streams. The effects of process parameters such as initial dye concentration, catalyst loading, and initial pH were investigated.
Section snippets
Chemicals
TiO2 P25 was purchased from Evonik Degussa (Germany) while ammonium metatungstate (AMT) was from Fluka (Germany). Dyes used in the experiment such as methylene blue and methyl orange were from Merck (Germany), while methyl violet was from Acros Organics (USA).
Preparation
The photocatalyst TiO2 P25 was weighed and dispersed in distilled water and an appropriate amount of aqueous solution of AMT solution was added to provide the required tungsten trioxide (WO3) loading. The suspension was stirred overnight
TEM and spectral analyses
The photocatalyst TiO2 is normally white in colour, while the typical colour of WO3 is yellow. Upon calcinations, the tungsten-loaded TiO2 photocatalyst turned pale yellow with a tinge of bluish colour. The bluish colour became more intense when tungsten loading was increased. As shown by the TEM micrograph (Fig. 1), the particles tend to stick-to-each other forming bigger particles with increasing WO3 loading and also with increasing calcinations temperatures. Based on XRD, tungsten trioxide
Conclusions
The tungsten-loaded TiO2 photocatalyst has been successfully synthesized and characterized. Tungsten–TiO2 interaction stabilized the active anatase phase from transforming into inactive rutile phase and γ-WO3 into β-WO3. The higher the tungsten loading, the more stable the photocatalyst became, as compared to the unmodified TiO2. However, the impregnation method used in the synthesis did not shift the optical absorption to the visible region. Optimum degradation of MB was achieved at dilute dye
Acknowledgements
The authors would like to thank Universiti Teknologi Petronas for the scholarship to Saepurahman and for the research facilities. The STIRF Grant no. 10/06.07 that funded this project is highly acknowledged.
References (54)
- et al.
Effect of alkaline-doped TiO2 on photocatalytic efficiency
J. Photochem. Photobiolol. A
(2004) - et al.
Sol–gel preparation and characterization of alkaline earth metal doped nano-TiO2: efficient photocatalytic degradation of 4-chlorophenol
J. Mol. Catal. A: Chem.
(2007) - et al.
The preparation, characterization, and their photocatalytic activities of rare-earth-doped TiO2 nanoparticles
J. Catal.
(2002) - et al.
Synthesis, characterization and photocatalytic activity of different metal-doped titania systems
Appl. Catal. A
(2006) - et al.
Phase transformation study of titania in V2O5/TiO2 and MoO3/TiO2 catalysts by X-ray diffraction analysis
Mater. Chem. Phys.
(1994) - et al.
Effect of Sn doping on the structural and optical properties of sol–gel TiO2 thin films
J. Cryst. Growth
(2004) - et al.
Investigation on sol–gel synthesized Ag-doped TiO2 cermet thin films
Thin Solid Films
(2005) - et al.
Alkaline earth metal doped nanoporous TiO2 for enhanced photocatalytic mineralisation of bisphenol-A
Catal. Commun.
(2007) - et al.
Influence of manganese ions on the anatase-rutile phase transition of TiO2 prepared by the sol–gel process
Mater. Lett.
(2002) - et al.
Titanium dioxide nanomaterial doped with trivalent lanthanide ions of Tb, Eu and Sm: preparation, characterization and potential applications
Inorg. Chim. Acta
(2007)
Heterogeneous photocatalysis: fundamentals and applications to the removal of various types of aqueous pollutants
Catal. Today
TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations: a review
Appl. Catal. B
Influence of thermal treatment on the structure and photocatalytic activity of TiO2 P25
Catal. Today
Surface characterisation of metal ions loaded TiO2 photocatalysts: structure–activity relationship
Appl. Catal. B
Flame-made WO3/TiO2 nanoparticles: relation between surface acidity, structure and photocatalytic activity
Appl. Catal. B
A study on the dispersion of NiO and/or WO3 on anatase
J. Catal.
Surface structures of supported tungsten oxide catalysts under dehydrated conditions
J. Mol. Catal. A: Chem.
Interfacial structure dependence of layered TiO2/WO3 thin films on the photoinduced hydrophilic property
Vacuum
Photocatalytic behavior of WO3-loaded TiO2 in an oxidation reaction
J. Catal.
The preparation of coupled WO3/TiO2 photocatalyst by ball milling
Powder Technol.
Photocatalytic activity of WOx–TiO2 under visible light irradiation
J. Photochem. Photobiol. A
Efficient degradation of organic pollutant with WOx modified nano-TiO2 under visible irradiation
J. Photochem. Photobiol. A
Photocatalytic degradation of organic compounds in aqueous systems by transition metal doped polycrystalline TiO2
Catal. Today
The design and development of highly reactive titanium oxide photocatalysts operating under visible light irradiation
J. Catal.
Preparation and photocatalytic activity of WO3/TiO2 nanocomposite particles
Mater. Lett.
Thermal behaviour of WO3 and WO3/TiO2 materials
Thin Solid Films
Kinetics of photocatalytic degradation of reactive dyes in a TiO2 slurry reactor
J. Photochem. Photobiol.
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2021, Environmental Technology and InnovationCitation Excerpt :WO3 is another photocatalyst which has attracted great prospects in wastewater restoration. Nevertheless, WO3 is prone to photo-corrosion under light radiation for extended time, the optical absorption edge is very narrow and unable to absorb visible light (Abdullah and Chong, 2010). More importantly, WO3 performs poorly for the remediation of TPOME as indicated by its lower COD removal efficiency (51.15%) under visible light irradiation (Cheng et al., 2017).