The present work focuses on the photocatalytic degradation of
methyl orange (MO) on erbium trioxide nanoparticles (
One of the sources of water contamination was the wastewater generated from textile plants employing various dyestuffs (Khataee and Kasiri, 2010; Barbe et al., 1997). Various chemical and physical in addition to biological changes for dyes could occur that consume dissolved oxygen in the water bodies. Moreover, dyes have high toxicity, which endangers aquatic life (Khataee et al., 2009; Ruiz et al., 2004). The various traditional techniques employed for the processing of pollutant textile dyes in water involve different chemical, biological and/or physical techniques. Photocatalytic degradation was demonstrated as a promising technique for processing pollution that occurs due to organic and/or inorganic compounds. The approach, as a means of removal of persistent water contaminants like dyes and pesticides, has recently attracted the attention of numerous investigators (Xu et al., 2014; Chen et al., 2014; Liu et al., 2014). Many of these researchers used (aqueous) suspension of semiconductors irradiated by UV light to photodegrade the pollutants (Daneshvar et al., 2007). The accomplishment of a semiconductor photocatalyst was strongly connected with the electronic structure of it (Daneshvar et al., 2007; Boppella et al., 2013; Xiao et al., 2012; Alenezi et al., 2013). It was established that the photocatalytic degradation of organic ions or organic molecules in solution are launched by photogenerated holes in the valence band with electrons in the conduction band of the semiconductor photocatalyst. The generated holes have high oxidative potential that permits a direct oxidation of organic ions or organic molecules to reactive intermediates. Moreover, radicals are reactive species that may help in organic substrate degradation. As seen in Fig. 1, methyl orange (MO) is a scale of acidity utilized in titration due to its clear and distinct color difference at various pH values. Methyl orange demonstrates a pink color in acidic solutions and a yellow color in basic solutions. Due to it variations in color at the pH of a mid-strength acid, it is ordinarily utilized in titration for acid solutions. Unlike a global indicator, methyl orange does not have a full spectrum of color variation, but it has a sharp end (Khodja et al., 2001; Sandberg et al., 1972).
The chemical structure of methyl orange.
The photocatalytic time vs. absorbance without SL.
Generally, MO utilizes monoazo dye in laboratory tests, textiles and
different commercial products and has to be eliminated from water because of
its toxicity (Mittal et al., 2007; Chen et al., 2010). Mittal et al. (2007) researched the elimination and recovery of MO from
wastewater employing waste materials. Chen and his coworkers (Chen et
al., 2010) examined the equilibrium and kinetic aspects of MO adsorption on
activated carbon derived from
All materials used in this work were supplied from Fluka Company and were used without further purification.
UV–visible spectra of
Photocatalytic degradation of methylene blue dye over
UV–visible spectra of
Erbium oxide nanoparticles (
The concentration of MO dye vs. absorbance, with and without irradiation. The blue and red colours signify absorbance with and without radiation respectively.
SEM image showing a distribution of erbium oxide particles at 10 000 times magnification.
The photocatalytic setup consists of a UV lamp (6 W) of
cylindrical shape, 22 cm body length and 16 arccm length of cylindrical
shape, which was used as a photo source. This lamp was positioned in a container of the sample (mixture of
SEM image showing an even distribution for erbium oxide particles at 25 000 times magnification.
SEM image of nano-sized
SEM image of nano-sized
The mixture of
Different concentrations of the MO were used in the range of (0.1, 0.2, 0.5,
1, 1.5, 2) wt % and 0.1 wt % from
XRD of
The morphology of the nanoparticles of erbium oxide nanoparticles was studied by scanning electron microscopy (SEM). It was recorded on the JEOL JSM-6390LV SEM fitted with a secondary electron detector.
The crystallinity of
To improve the photodegradation efficiency of methyl orange dye, erbium
trioxide nanoparticles were used as a common strategy. Erbium trioxide
nanoparticles were ready to synthesis and cheap. Various types of nano-metal
have been used in the previous studies, including anionic dopants, cationic
dopants, rare-earth dopants, and codopants (Samadi et al., 2014).
Additionally, many studies have shown that coupling with other semiconductors,
such as CdO (Liu et al., 2014),
XRD parameters of
The results of the methods with and without sunlight (SL) were discussed and are shown in Figs. 2 and 3. Figure 2 demonstrates the relation between the absorbance and time of
photocatalysis without sunlight radiation. The increase in the time of
photodegradation up to 3.0 h leads to the absorbance values rising, due to the degradation process of organic dye. This
is consistent with the findings of Lazar et al. (2012). Figure 3 shows the absorption
of the
Figure 3 shows the absorption spectrum of
Figure 4 shows the photocatalytic degradation of diazocompounds irradiated
under sunlight in the presence of
The rate of reaction increases and maximum rates were obtained after 4 h, as shown in Fig. 5. It may be explained by the fact that the operation time of UV source was increased, the number of photons per unit area incident on the sample also increased, resulting in a high rate of degradation in the mixture of erbium oxide and MO, which leads to an increase in the absorption value.
The increase in the dye concentration leads to increases in absorbance. The maximum change in absorbance was noticed when the concentration changed from 0.5 wt % to 1 wt %, as shown in Fig. 6. The degradation efficiency of MO was analyzed using a UV–visible spectrometer. Peaks were observed to be present between 450 and 600 nm, which was indicative of the degradation of MO. According to the Beer–Lambert law, MO concentration is directly proportional to its absorbance (Ramli et al., 2014).
When MO concentration increases, the value of absorbance increases after 15 min from irradiation. The maximum increase in absorbance was noticed when the concentration at the range 0.5–1.0 wt % was changed, as shown in Fig. 6. This might be explained based on the increase in dye concentrations that leads to the reaction average increase as additional molecules. When the dye is increased (3.0–5.0 wt %) the value of absorbance remains constant at 4.51 wt %, causing reaction retardation because of the increasing number of collisions between dye molecules, whereas collisions between dye and salt decrease. As a conclusion, the proportion of the reaction decreased (Karunakaran et al., 2004; Pandey et al., 2015). The main rate of degradation exists in the region near the irradiated side where the intensity of irradiation was much higher than on the other sides. Thus, using dye with a higher concentration, the degradation technique decreases at sufficiently long distances from the light source or the reaction zone because of retardation in the penetration of light.
The SEM micrographs of synthesized samples are shown in Figs. 7, 8, 9 and 10, showing the distribution and the morphology of
XRD was used to clarify the
Nanoparticles of
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
RMD did the experimental work. TSG contributed to writing the paper. MST and AAHK supervised the whole work. AA was the principal investigator and contributed to writing the paper.
The authors declare that they have no conflict of interest.
The authors gratefully acknowledge the UKM-YSD Chair on Sustainable Development for supporting this work with the grant 020–2017 “Malaysia”.
This paper was edited by Talis Juhna and reviewed by two anonymous referees.