KnE Engineering | International Conference on Basic Sciences and Its Applications (ICBSA-2018) | pages: 128–140

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1. Introduction

Currently the development and progress of the textile industry in Indonesia has developed very rapidly. The textile industry can provide benefits for human life. But the development of the textile industry also has a negative impact on the environment. This was because in textile production waste was always produced, one of which is the dye waste [1]. Dyestuff waste is an organic compound that is difficult to decompose, resistant, and toxic [2]. If the waste is discharged into the nearest waters, it will cause environmental pollution [3]. In the textile industry, methylene blue is one of the thiazine dyes that are often used, because the price is economical and easy to obtain [4]. Methylene blue dye is a basic dye that is important in the process of coloring the skin, mori cloth, cotton cloth, and tannin. The use of methylene blue can cause several effects, such as irritation of the digestive tract if swallowed, causing cyanosis if inhaled, and irritation to the skin if touched by the skin [5]. Many methods are used to describe dyestuff waste including adsorption and activated sludge, but those method haves many weaknesses. An alternative photodegradation method has been developed using semiconductor photocatalysts and ultraviolet light. TiO2 which was dispersed in natural zeolite and its application for photodegradation of congo red, states that the photodegradation method was a relatively inexpensive and easy to implement method. This photodegradation can decompose dyes into components that were safe for the environment [6]. The photodegradation of methyl orange using ZnO and UV light, the use of photocatalyst semiconductors has several advantages including being able to carry out total mineralization of organic pollutants, the cost was cheap, the process was relatively fast, non-toxic, and has long-term use capability [7]. The photocatalyst material used in the photodegradation method is a semiconductor, such as: TiO2, ZnO, CeO2 and Al 2 O 3 . Photocatalyst activity increased by absorbing UV light, resulting in electrons and holes. Hole was a positive hole caused by electron displacement. Electrons and holes are the most important species to begin the photodegradation process. Currently the use of photocatalyst materials, such as CeO2 (Eg = 3.2 eV) was a concern for researchers to develop as photocatalysts because of their better properties than TiO2, ZnO, and Al 2 O 3 . Based on this reason, researchers used CeO2 photocatalysts that were doped with modified mesoporous silica to decompose methylene blue dye.

2. Materials and Methods

Chemicals and reagents

Tetraethyl orthosilicate (TEOS) for the silica source, Cetyltrimethylammonium bromide (CTAB) for surfactant, Cerium (III) nitrate hexahydrate (Ce(NO3)3.6H2O) used for precursor of CeO2, Aniline(C6H5NH2) for Base Bronsted, Besi (III) Chloride (FeCl3) for Acid Lewis, 2-propanol and methylene blue. All chemicals used purely from Merck. The equipment used in this study are: a set of glassware, analytic scales, pH meters, magnetic stirrers (magnetic stirrer), hot plates, radiation boxes, black plastic, UV C lamps, centrifuges, and SP-870 spectrophotometers.

Determination of the maximum wavelength of methylene blue solution

Methylene blue solution with a concentration of 2 ppm measured its absorbance at various wavelengths, ranging from 550 nm-675 nm. The results obtained are depicted on the graph with absorbance as the y axis and the wavelength of light as the x axis. The maximum wavelength was the wavelength that gives the maximum absorbance value.

Making a calibration curve for a methylene blue solution

Methylene blue standard solutions with concentrations of 1, 2, 3 and 4 ppm were measured by absorbance at the maximum wavelength of methylene blue. Next, a calibration curve was created by plotting concentration and absorbance.

Determination of the optimum time of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation process of methylene blue

Four 100 mL beker glasses which have been wrapped in black plastic each filled with 100 mL of 20 ppm methylene blue solution. 50 mg of Ceria, MS-Ce and MMS-Ce and 1 cup of glass without catalyst were added to each glass beaker. The glass beaker is inserted into the radiation box and the black plastic wrap was released. Furthermore, the beaker glass was irradiated with Visibel lamps for 30.60,90,120,150,180,210,240,270, and 300 minutes, during the irradiation process with Visible light the solution was stirred with magnetic stirrer. After the radiation process, the suspension of each beker glass was centrifuged at a speed of 4000 rpm for 10 minutes. The solution was then decanted to separate the supernatant and sediment. The supernatant obtained from each glass beaker measured its absorbance by UV-Vis spectrophotometer at the maximum wavelength of methylene blue. The absorbance value obtained was then entered into the linear regression equation of the methylene blue solution, so that the methylene blue concentration was obtained. The concentration value of methylene blue was then included in the percentage degradation formula (% D).

Determination of the optimum weight of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation process of methylene blue

Four 100 mL beker glasses which have been wrapped in black plastic each filled with 100 mL of 20 ppm methylene blue solution. In each glass the beaker was added 0.10,20,30,40 and 50 mg Ceria, MS-Ce and MMS-Ce and one glass beaker without catalyst. The glass beaker was inserted into the radiation box and the black plastic wrap was released. Then the glass beaker was irradiated with Visibel lamp for optimum time, during the irradiation process with Visible light the solution is stirred with a magnetic stirrer. After the radiation process, the suspension of each beker glass was centrifuged at a speed of 4000 rpm for 10 minutes. The solution was then decanted to separate the supernatant and sediment. The supernatant obtained from each glass beaker measured its absorbance by UV-Vis spectrophotometer at the maximum wavelength of methylene blue. The absorbance value obtained was then entered into the linear regression equation of the methylene blue solution, so that the methylene blue concentration was obtained. The concentration value of methylene blue was then included in the percentage degradation formula (% D).

Determination of the effectiveness of the methylene blue photodegradation process

Three 100 mL beker glasses which have been wrapped in black plastic each filled with 50 mL of 20 ppm methylene blue solution. Into each glass beaker included an optimum number of Ceria, MS-Ce and MMS-Ce. The glass was inserted into the radiation box and the black plastic wrap was released. Then the glass beaker was irradiated with UV light for optimum time, during the irradiation process with UV light the solution is stirred with a magnetic stirrer. After the radiation process, the suspension of each beker glass was centrifuged at a speed of 4000 rpm for 10 minutes. The solution was then decanted to separate the supernatant and sediment. The supernatant obtained from each glass beaker measured its absorbance by UV-Vis spectrophotometer at the maximum wavelength of methylene blue. The absorbance value obtained was then entered into the linear regression equation of the methylene blue solution, so that the methylene blue concentration was obtained.

3. Results and Discussion

Crystal structure analysis

The results of crystal structure analysis of MS-Ce, MMS-Ce and Cerium oxide can be seen from Fig. 1. The peak intensity of cerium oxide (CeO2) was absorbed in 2θ angle 28,7 , 33,2 , 47,5 , 56, 7 , 59.2 , 69.5 , 76.8 , 79.1 , 88.3 , and 95.5 . Its crystal lattices are 110, 200, 220, 311, 222, 400, 331, 420, 422 and 511 based on the JCPDS standard. 00-043-1002. The peak intensity of MS and MMS was absorbed in an angle of 2θ ie 23.5 and 24.5 . The results of this study are along with the research conducted by Bing et al., 2011 [8] suggesting that mesoporous silica (MCM-41) obtained a specific peak at 2θ angle between 20-25 when analyzed with Wide Angle XRD [8,9]. The Ceria XRD pattern encapsulated in mesoporous silica (MS) and modified mesoporous silica (MMS) shown similar XRD pattern compared with the peak of nanocrystalline cerium oxide, only increases at peak shift and peak intensity. Based on the results of the study it can be assumed that Ceria has been homogeneously dispersed into the mesopores silica.

fig-1.jpg
Figure 1
The Comparison Result of Wide Angle X-ray Diffraction of Materials.

Functional group analysis

Fig. 2 illustrates the FTIR results of the resulting material. The success of the encapsulation process can be seen by comparing the FTIR spectrum of the material before and after the encapsulation process. Comparison of MS and MMS peaks can be seen in Table 1.

Table 1

The Assignments of the bands in the FTIR spectra of of MS and MMS materials.


Wavenumber (cm -1 ) MS Wavenumber (cm -1 ) MMS
3414 vOH(Si-OH) 3657 vOH(Si-OH)
1635 δOH(Si-OH) 1852 δOH(Si-OH)
1060 vas(Si-O-Si) 1059 vas(Si-O-Si)
805 νs (Si-O-Si) 801 νs (Si-O-Si)
471 δ (Si-O-Si) 577 δ (Si-O-Si)

The FTIR spectrum of MS-Ce and MMS-Ce almost the same as for the FTIR spectrum of MS and MMS but there is only a slight peak shift, decreasing peak intensity and some peak loss. The absorption of the Ce-O stretching bond also occurs at the wavelength 400 - 600 cm -1 and cannot be clearly distinguished by vibration bending (Si–O–Si). The Vibration δ (Si-O-Si), νs (Si-O-Si), vas(Si-O-Si), vOH(Si-OH) dan δOH(Si-OH) [10] in MS and MMS experience wavelength because of the electropositive cerium ion encapsulation of the electronegative oxygen atoms in the mesoporous silica nanoparticles shown in Fig. 2.

fig-2.jpg
Figure 2
FTIR spectrum of (a) Cerium Oksida (Ceria) (b) Mesoporous Silica (MS) (c) Mesoporous Silica- Cerium (MS-Ce) (d)Modified Mesoporous Silica (MMS) (e) Modified Mesoporous Silica – Cerium (MMS-Ce).

DRS-UV VIS

Determination of optical band gap energy is done by using the reflactant value from the DRS-UV Vis analysis. The% refractant value (% R) is made into the y axis by changing it to R. The value of the wavelength (λ) from the results of the reflactant analysis with the DRS-UV Vis tool is included in the Kubelka Munk equation (Eq. 1), after which the value of hv is searched with the equation (2) where h is the plank constant = 6.626 x 10-34 Js and C is the speed of light with a value of 3 x 108 m/s. The value of alpha square ((1-R) 2 / 2R x hf)2 for each wavelength (λ) was made into the y axis and then plotted into the graph with the x-axis Energy value in eV units [11]. After making a graph the relationship between alpha square ((1-R) 2 / 2R x hf)2 with the hv value drawn by a line that intersects with the turning point on the curve as shown in Fig. 3.

FR=(1R)22R
E=h.Cλ
fig-3.jpg
Figure 3
Curve Determination Energy Band Gap (a) cerium oxide (b) Mesoporous Silica-Cerium(SM-Ce) (c) Modified Mesoporous Silica-Cerium(MMS-Ce) with Kubelka-Munk theory.

In nanomaterials the size of the material was very small so that the surface area becomes large. Energy band gap width is inversely proportional to particle size. The smaller the particle size, the greater the value of the energy band gap [12]. The greater the value of the energy band gap, the slower the recombination process will occur, so that the excitation process lasts longer than the recombination process, so that more organic compounds can be degraded [13]. The smaller the particle size, the more reactivity will increase because the smaller the particle size, the greater the surface area will cause more atomic fractions on the surface while a material reacts with other materials on the surface, so that the more atomic fractions on the surface, the reactivity of the material will increase [12,14]. The bulk band gap value of cerium oxide is ranging from 2.8 to 3.2 eV.

Based on the results of the calculation of the energy band gap value in accordance with Fig. 3, the value of the energy band gap decreased to 2.43 eV. One way to improve the photocatalytic properties of semiconductors in the degradation process is done by modification to extend the excitation period and avoid recombination speed. Modification was done by doping semiconductor material. In this study cerium was doped with mesopori silica and modified mesoporous silica. The efficiency of semiconductors can be increased by doping. Through doping the value of energy band gap (band gap) can be reduced. Metal ions and doping compounds can act as electron trappers so that the excitation time becomes longer and recombination does not occur quickly. In the study the value of cerium energy band gap doped mesoporous silica fell to 1.03 eV. The value of cerium oxide energy band gap doped with mesoporous silica modification also decreased to 1.27 eV. With a smaller band gap value, effective photocatalysts are used in visible light because only 5% of UV light from the sun reaches the earth, while 45% of visible light from the sun reaches the earth [15].

Catalytic activity

The resulting photocatalyst is used to decompose the methylene blue dye with Visibel light. Visible beam sources use fluorescent lamps whose wavelengths are 351.4 nm -698.2 nm. The resulting photocatalyst was tested for the optimum conditions of the photocatalyst application to degrade the methylene blue solution. In this photocatalyst application determine the optimum weight, time and effectiveness of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation of methylen blue.

Determination of the optimum time of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation process of methylene blue

Cerium Oxide was used as a photocatalyst because of it was semiconductor properties. Photocatalyst was a catalyst process used visible or UV light. Before determining the percentage of dyestuff degradation, the maximum wavelength of the methylene blue solution was determined first. The maximum wavelength is determined by measuring the absorbance value of a 2 ppm methylene blue solution at a wavelength of 550-700 nm. From the measurement results obtained the maximum wavelength of 2 ppm blue methyl solution was 663 nm with an absorbance value of 0.41547. The maximum wavelength of this blue methylene solution will be used to measure the absorbance of the blue methylene solution in future studies. After that, a calibration curve is made by measuring the absorbance values of several concentrations of standard methylene blue solutions 0, 1, 2, 3 and 4 ppm at a maximum wavelength of 663 nm. Based on the calibration curve obtained the correlation coefficient (r) = 0.996. The r value close to 1 shows the linear relationship between concentration and absorbance. The linear regression equation obtained was y = 0.1632x -0.0065. The equation will be used to calculate the concentration of methylene blue solution by entering its absorbance value.

Determine optimum time of Ceria, MS-Ce and MMS-Ce Photocatalyst used 50 mg with photocatalysis processing time of 30, 60, 90,120, 150, 180, 210,240, 270, and 300 minutes while being sterilized and exposed to visible light shown in Fig. 4. Photocatalyst process uses visible light from fluorescent lamps and photocatalyst boxes. The results of the optical condition test when it was found that the optimum time of degradation of methylene blue using ceria photocatalyst was150 minutes, MS-Ce 300 minutes and MMS-Ce 120 minutes. Base on this data showed that MMS-Ce give the shortets time to degradation methylene blue.

fig-4.jpg
Figure 4
Curve of the optimum time of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation process of methylene blue.

Determination of the optimum weight of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation process of methylene blue

Based on the optimum time we determine the optimum weight of photocatalyst in degrading methylene blue. The weight of the photocatalyst that used were 10, 20.30, 40 and 50 mg. Ceria photocatalysts were tested for optimum weight in a radiation time of 150 minutes. MS-Ce photocatalyst was tested for optimum weight in 300 minutes of radiation time. Photocatalyst MMS-Ce was tested for optimum weight in a radiation time of 120 minutes. Fig. 5 showed that the optimum weight of Ceria, MS-Ce and MMS-Ce were 50 mg, 50 mg and 40 mg. Base on this data showed that weight of MMS-Ce give the littlest to degradation methylene blue.

fig-5.jpg
Figure 5
Curve of the optimum weight of Ceria, MS-Ce and MMS-Ce photocatalyst for photodegradation process of methylene blue.

Determination of the effectiveness of the methylene blue photodegradation process

The effectiveness of Ceria photocatalyst in degrading methylene blue dye by using as much as 50 mg of Ceria photocatalyst with a 150-minute irradiation time can degrade 68.85% of the dye. SM-Ce was able to degrade as much as 97.38% by using 50 mg of photocatalyst SM-Ce with irradiation time of 300 minutes. The MMS-Ce photocatalyst was able to degrade as much as 99.98% with a long irradiation of 120 minutes shownin Fig. 6. The number of MMS-Ce photocatalysts used is 40 mg. Of the three photocatalysts, the MMS-Ce photocatalyst is best at degrading dyes with fewer photocatalysts and shorter radiation times and more degraded dyes.

fig-6.jpg
Figure 6
Histogram of the effectiveness of the methylene blue photodegradation process.

4. Conclusions

The photocatalytic activity of cerium oxide increases after being doped with mesoporous silica. DRS UV VIS Analysis showed that Cerium oxide nanoparticles band gap value of 2.43 eV and mesoporous silica band gap value 1.27 eV. The smaller bandgap result in effective photocatalysts used in visible light. The results showed that the optimum conditions obtained were the optimum catalyst weight of Ceria, MS-Ce and MMS-Ce,were 50 mg, 50 mg and 40 mg. The optimum time for Ceria, MS-Ce and MMS-Ce photocatalyst degrades used visible light was 150 minutes, 300 minutes and 120 minutes. Effectiveness of methylene blue degradation using Ceria, MS-Ce and MMS-Ce photocatalysts was 68.85%, 97.38% and 99.98%.

Acknowledgments

The authors are thankful to Direktorat Riset Penelitian dan Pengabdian Kepada Masyarakat (DRPM) Direktorat Jenderal Pendidikan Tinggi (DIKTI) Indonesia that has funded this research, Koordinasi Perguruan Tinggi Wilayah X (Kopertis X), Sekolah Tinggi Ilmu Kesehatan SYEDZA SAINTIKA and Chemistry Department of Universitas Andalas.

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