The use of mesoporous SnO2Al-MCM-41 under visible and ultraviolet light irradiation for photodegradation of methylene blue pigment

Dissertation for Master's degree

Abstract

According to reports, heterogeneous photocatalysts are suitable for photodegradation of polluting compounds. Many semiconductor metal oxides such as: TiO2, SnO2, ZnO2, etc. can be used as photocatalysts in water splitting reactions, synthesis of organic compounds and removal of waste water pollution. In this project, we have synthesized mesoporous AL-MCM-41 from different percentages of aluminum using the hydrothermal method and placed SnO2 nanoparticles on the mesoporous and investigated its photocatalytic properties. .

      To investigate the morphology and size of the obtained nanocomposites, X-ray diffraction (XRD), FTIR, scanning electron microscope, (SEM) transmission electron microscope were used. As a model of organic pollution, it was carried out under the irradiation of high pressure mercury lamp as an ultraviolet light source. The SnO2/Al-MCM-41 nanocomposite in an acidic environment under ultraviolet light irradiation has the highest speed constant of 0.049 per minute.

Introduction:

One of the growing fields in the field of nanomaterials is the development of nanoparticle production methods and finally its industrialization. In nanoparticles and in general in nanostructures, the small size of particles in the nanoscale creates unique properties, including electronic, electrical, optical, etc. properties. Although today, accurate determination of these gases is possible by analytical devices such as gas chromatography, mass spectroscopy, and infrared, but these devices are expensive and complicated. Working with them requires special skills. In terms of their simplicity, small volume and high sensitivity, these gas sensors can be a suitable alternative to the above systems. The destruction of organic pollutants due to the increase in environmental pollution in recent years has caused photocatalyst to be widely considered for scientific understanding and potential applications. Due to its excellent photochemical stability, low cost and non-toxicity, SnO2 photocatalyst is widely used in cleaning the environment through the destruction of organic pollutants and hydrogen production through water splitting. Since photocatalytic semiconductors have created many attractions in the last two decades in removing pollution in the environment. Therefore, in this research, we try to synthesize SnO2/Al-MCM-41 nanocomposite and investigate its photocatalytic properties in removing pollutants. [7,6,5,4,3,2,1].

The history of nanotechnology in the world

Throughout human history since the time of ancient Greece, people and especially scientists of that period believed that materials can be divided into small parts to reach particles that are indestructible and these particles form the basis of materials, perhaps the Greek philosopher Democritus He is known as the father of nanotechnology and science because around 400 years before Christ, he was the first to use the word atom, which means indivisible in Greek, to describe the particles that make up materials.

Through many researches and experiments, scientists have so far discovered 108 types of atoms and a large number of isotopes. They also discovered that atoms are made up of smaller particles such as quarks and leptons. However, these discoveries are not very important in the history of the emergence of this complex technology.

The starting point and initial development of nanotechnology is not precisely known. It can be said that the first nanotechnologists were the medieval glassmakers who used old molds (Medieval forges) to shape their glasses. Of course, these glassmakers did not know why adding gold to the glass would change its color. At that time, nanometer gold particles were used to make the glass of medieval churches, and with this, very attractive colored glass was obtained. Such glass is now found among very old glass.The color created in these glasses is based on the fact that materials with nano dimensions do not have the same properties as materials with micro dimensions. In fact, it is not difficult to find examples of the use of metal nanoparticles. The decorative pigments of the famous Lycurgus cup in ancient Rome (fourth century AD) are an example of them. This cup is still in the British Museum and has different colors depending on the direction of the light shining on it.  The light reflected from it is green, but if a light shines through it, it is seen as red. The analysis of this glass indicates the presence of very small amounts of 007 (nm) tiny metal crystals. It contains silver and gold with a molar ratio of approximately 14 to 1. The presence of these nanocrystals is the reason for the special color of the Lycurgus cup. Recently, in archaeological operations, it was discovered that some of the glazed ceramics of the Abbasid caliphate period have a very complex design and show several colors and rainbow reflections. Some of these tiles have been used in some mosques in Tunisia. When white light hits these ceramics, the color of the glaze changes depending on the angle of incidence (like the wings of a butterfly or the color on CDs). These effects are caused by the periodic juxtaposition of nanoparticles, each particle having unique optical properties. [9,8].

1-1-What is nano?

The term nanotechnology

was first used by Noriyo Tainguchi, a professor at Tokyo University of Science in 1974. He used this term to describe the construction of precise materials (devices) whose dimensional tolerance is on the order of nanometers. In 1986, this term was coined by K. Eric Drexler in a book entitled (Creation Engine: The Beginning of the Era of Nanotechnology). It was recreated and redefined. and their calculations) [10,9] A bacterial cell has a diameter equivalent to several hundred nanometers. The smallest objects visible to the naked eye are about 10,000 nanometers in size. Only about 10 hydrogen atoms in a line make one nanometer. To better understand this scale, a comparison between different length scales is shown in Figure 1-1.  

ABSTRACT

Tin oxide (SnO2) is an n-type semiconductor with excellent optical and electrical properties, partly due to its wide band gap (Eg = 3.6 eV, at 300 K). Therefore, it is an important semiconductor material and it has been widely used as gas sensors, solar cells, lithium battery anode materials, catalysts and so on. So far, few literatures have reported for SnO2 as a photocatalyst that was used to degrade dye contaminants [1-3]. High purity SnO2 nanoparticles were successfully prepared via a solvothermal process. Hence, in our present investigation, Al-MCM-41 was used as the solid acid catalyst. Mesoporous Al-MCM-41 molecular sieves in the Si/Al ratios 25, 75, 100 and 150 were synthesized under hydrothermal conditions, also SnO2 nanoparticles were coated on mesoporous Al-MCM-41. Figure 1 shows typical TEM image of SnO2/ Al - MCM-41 composite. The photocatalytic activity of the as-prepared SnO2 loaded on Al-MCM-41 was evaluated by degradation of the methylene blue under irradiation of UV and visible light. The results showed that SnO2 loaded on nanosize Al-MCM-41 has higher photocatalytic activity than that of SnO2 nanoparticles.