Synthesis of visible light active doped TiO2 for the degradation of organic pollutants—methylene blue and glyphosate
© The Author(s). 2016
Received: 8 August 2016
Accepted: 30 November 2016
Published: 9 December 2016
A simple hydrothermal process was applied to synthesize the doped TiO2 particles with different concentrations as well as different metal ions (Mn, Ce and La).
The synthesis of Mn-doped-TiO2 nanoparticles was done by using a hydrothermal method from hydrolysis of titanium tetrachloride in aqueous solution. The photocatalytic activities were checked by studying the degradation of two model organic pollutants.
The material was characterized by X-ray diffraction, scanning electron microscopy, and UV–Visible spectroscopy. The X-ray diffraction pattern studied for doped TiO2 particles suggests the anatase phase with a crystalline nature. Doped TiO2 particles showed a porous and complex nature with a highly rough surface. The photocatalytic activity of Mn- Ce- and La-doped TiO2 with different metal-ion concentrations of 0.15-0.60% show that the degradation rate of all of the pollutants increases with an increase in the dopant concentration from 0.15 to 0.45%, and a further increase in the dopant concentration decreased the degradation rate.
The results indicate that TiO2 with a concentration of 0.45% for all metal ions (Mn, Ce and La) shows the highest activity. Among studied dopent TiO2 with Mn (0.45%) showed the best degradation activity.
During the past three decades, photocatalytic processes that involve semiconductor particles irradiated by UV light have been shown to be potentially beneficial in the degradation of various types of pollutants in aqueous suspensions (Blake 2001; Neppolian et al. 2002; Chaleshtori et al. 2013; Geng et al. 2009; Kim et al. 2016; Zhang et al. 2015; Han et al. 2016; Liu et al. 2016; Yang and Xu 2016; Umar et al. 2013a; Akpan and Hameed 2009; Lv et al. 2009; Arslan et al. 2002; Umar et al. 2015). Several metal chalcogenides (ZnS, CdS, CdSe) and metal oxides (ZrO2, TiO2, ZnO, SnO2) have been extensively used for the degradation of a variety of pollutants. Among these semiconductors, TiO2 is the most widely used oxide because it is chemically and biologically inert, photo catalytically stable, resistant to strong acids and bases, and stable under illumination (Fox and Dulay 1993). According to the estimated valence band (VB) and conduction band (CB) energies of TiO2, the band gap energy is found to be 3.2 eV. Therefore, it can only be performed its activity by UV light due to its large band gap energy. Recently, doping of TiO2 with metals and non-metals has received great attention because it can shift the photocatalytic response of catalysts from the UV region to the visible-light region and ultimately can harvest solar energy (Umar et al. 2013b; Colon et al. 2006; Fan et al. 2010; Zhang and Zhu 2012; Liu et al. 2009; Binas et al. 2012; Uhm et al. 2006). Up to date, there are some studies reported in the literature on the doping of TiO2 by various routes and their photocatalytic performance for the degradation of various types of pollutants (Stengl and Bakardjieva 2010; Devi and Murthy 2008; Devi et al. 2009a; Papadimitriou et al. 2011; Jin et al. 2008; Peng et al. 2005; Stengl et al. 2009; Liqiang et al. 2004; Chen et al. 2011). In brief, Rashad et al. (2013) prepared TiO2 nanoparticles doped with (Co and Mn) by hydrothermal technique and checked their performance on degradation of methylene blue (MB) under UV light. The decomposition of phenol in the presence of Mn-doped TiO2 have been reported by Paul et al. (2014). Recently, Rangel-Vázqueza et al. (2015) prepared the Sn-doped TiO2 using sol gel method and tested its activity for the degradation of 2,4-dichlorophenoxyacetic acid. On the other hand, Kuyumcu et al. (2015) synthesizes the doped TiO2 using different metal ions and degradation of two dyes under visible light has also been reported.
Dyes and pesticides have been used by mankind for many decades for different useful purposes. However, their existence in water bodies at this time has become a challenge for researchers and environmental authorities because these pollutants create some serious problems to the surrounding ecosystems and causes human health disorders. The worldwide annual production of dyes increases day by day, a prominent portion of which is vanished during the dyeing process in various types of industries, which finally pollutes our aquatic environment (Ajit et al. 2006; Kolpin et al. 2002; Umar et al. 2012). Furthermore, many pesticides have been detected in both surface and ground water in different localities worldwide (Knee et al. 2010; STORET water quality file 1988; Rovedatti et al. 2001). This polluted water is not useful for irrigation or domestic purposes. Therefore, these pollutants must be eliminated from water bodies before they can be used.
The objective of this study was to fabricate visible-light-responsive photo catalyst using different concentrations of dopent using a simple hydrothermal process. The paper also addresses the enhanced photocatalytic activities of metal-doped TiO2 for the degradation of organic compounds, such as methylene blue (dye) and glyphosate (pesticide).
Preparation and characterization
The synthesis of Mn-doped-TiO2 nanoparticles was done by using a hydrothermal method from hydrolysis of titanium tetrachloride in aqueous solution. In a typical synthesis, 1.6 mL of titanium tetrachloride was added dropwise into 30 mL of deionized water under stirring at room temperature to obtain solution 1. The calculated amount of manganese (II) sulfate monohydrate (0.15–0.60%) were dissolved to 15 mL of deionized water at room temperature to form solution 2. The above solutions 1 and 2 were mixed and stirred for 15 min. The resulting mixture was transferred into a 50-mL stainless steel autoclave and heated at 140 °C for 5 h. The obtained precipitate was washed with distilled water and then dried at 110 °C for 10 h in an oven. For Ce- and La-doped and undoped TiO2, the procedure was the same except the difference in dopants.
The samples of undoped and doped TiO2 particles were analyzed by XRD using Bruker AXS D8 Advance over the range of 20 to 80 kV with Cu Kα radiations (λ = 1.5418 Å), which was operated at 4°/min scanning rate with a voltage of 30 kV and a current of 15 mA. The Shimadzu UV–vis spectrophotometer (Model 1601) was used to record the UV–vis spectra in the range of 300–800 nm. Using SEM (LEO, 435 VF) at different magnifications, WD 15 mm, the prepared material was examined for structural morphology.
Stock solution of organic pollutants, methylene blue (dye), and glyphosate (pesticide) containing desired concentrations were prepared in double-distilled water. An immersion well photochemical reactor made of Pyrex glass equipped with a magnetic stirring bar, water circulating jacket, and an opening for supply of atmospheric oxygen was used. An aqueous solution (250 mL) of the organic pollutants was poured into the photoreactor. Then, required amount of photocatalyst was added to conduct irradiation process. The solution was stirred and bubbled with atmospheric oxygen for at least 10 min, prior to illumination in order to allow equilibration of the system. The visible-light halogen linear lamp (500 W, 9500 Lumens) was used to conduct irradiation experiments. The samples (8 mL) were collected before and at regular intervals during the irradiation, and the analysis were done after removal of photocatalyst using centrifugation.
Results and discussion
Crystallite size of undoped and doped-TiO2 with different concentration of Mn, Ce and La
Dopant concentration (%)
Dopant/crystallite size (nm)
Dopant/crystallite size (nm)
Dopant/crystallite size (nm)
Ce / 9.2
Ce / 8.0
Band gap energy of undoped and doped-TiO2 with different concentration of Mn, Ce and La
Dopant concentration (%)
Dopant/ Band gap (eV)
Dopant/Band gap (eV)
Dopant/Band ap (eV)
The photodegradation of organic pollutants methylene blue (dye) and glyphosate (pesticide) was monitored by measuring the absorbance at their λmax as a function of the irradiation time using the UV spectroscopic analysis technique (Shimadzu UV–vis 1601). The concentrations of organic pollutants were calculated based on the standard calibration curve, which was obtained from the individual absorbance of these compounds at different known concentrations.
Photocatalysis of methylene blue in presence of Mn-doped TiO2
Photocatalysis of glyphosate in presence of Mn-doped TiO2
The degradation rate was calculated in terms of moles per liter per minute.
Photocatalytic activity of Mn-, Ce-, and La-doped TiO2 for the degradation of organic pollutants
Photodegradation of methylene blue and glyphosate in presence of different photocatalysts
TiO2 particles were doped with different concentrations of Mn and La (0.15–0.60%), and their photocatalytic activity was tested by studying the degradation of methylene blue and glyphosate as organic pollutants. The anatase phase with crystalline nature is shown in the XRD analysis. The SEM image of undoped TiO2 exhibits a sponge-like network of high roughness, whereas the doped TiO2 particles show a porous and complex nature with a highly rough surface. The photocatalytic results show that TiO2 with a dopant concentration of 0.45% for both the metal ions has the highest photocatalytic performance using visible light. Among the photocatalysts, the Mn-doped TiO2 (0.45%) photocatalyst shows a better degradation rate than the other photocatalysts.
The authors gratefully acknowledged the post doctoral financial support by the Research University Grant (PY/2014/03059), Universiti Teknologi Malaysia and the Ministry of Education Malaysia for providing LRGS Grant on Water Security entitled Protection of Drinking Water: Source Abstraction and Treatment (203/PKT/6720006). One of the authors, Dr. Hilal Ahmad has acknowledged the Science and Engineering Research Board (SERB), India within the “National Postdoctoral Fellowship” program in the year 2016, Project No. NPDF-0000995.
AA and KU designed the experiments. KU and HA carried out the synthesis and characterization. JJ and ZAM edited the manuscript. The rest of the authors performed the experiments and wrote their experimental section. Moreover, KU and HA revised the whole manuscript and resubmitted after due revision. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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