SYNTHESIS OF ZINC OXIDE (ZnO) CATALYST AND DEGRADATION OF DYES

CHEMISTRY Chapter 1

Rabia Irshad

ZINC OXIDE
SYNTHESIS OF ZINC OXIDE (ZnO) CATALYST  AND DEGRADATION OF DYES

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Medicascientists.com

 

 

INTRODUCTION

It is still unknown what kinds of zinc compounds early people used as paint or medical ointments. The use of pushpanjan, perhaps zinc oxide, for eyes and wounds is mentioned in the 500 BC Indian medical classic Charaka Samhita (Craddock et al., 2000). Both Galen and the Greek physician Dioscorides from the first century AD advocated zinc oxide for the medical treatment of ulcerating tumours. Zinc oxide is still included in baby powder, diaper rash treatments, calamine lotion, shampoos for dandruff prevention as well as antiseptic ointments even though it is no longer used to treat skin cancer (Harding, 2006).

The Romans developed a cementation method to transform copper into brass somewhere about 200 BC by treating it with zinc oxide (Curley, 2009). In the first century AD, Dioscorides wrote about this strategy (Craddock, 2009). Beginning in India in the seventeenth century, the production of zinc and zinc oxide quickly spread to China. In Bristol, United Kingdom, in 1743, the first zinc smelter in Europe was founded (Irwin et al., 2012). According to Battez et al. (2008), ZnO is presently utilised in a wide range of goods and materials, including paints, rubber, plastics, ceramics, and more.

Zinc oxide (ZnO) is an inorganic material that is used as a component in a wide range of goods, including paint, rubber, plastics, ceramics, and many others (Völz et al., 2000). It is a semiconductor with native doping and a huge bandgap that shows n-type characteristics (zgür et al., 2005). Because of its transparency and high electron mobility, ZnO is beneficial in creative applications such as transparent electrodes in LCDs, energy-efficient windows, and thin-film transistors (zgür et al., 2005).

 

Figure1; A FE-SEM micrograph of synthesised zinc oxide is displayed at various magnifications.

Nanotechnology

Nanotechnology is a relatively new discipline that has the potential to dramatically transform various fields of study (Whitesides, 2005). Applications for this technology include optics, electronics, healthcare, and materials research. Nanotechnology research has accelerated dramatically in recent years, yielding ground-breaking results in a wide range of scientific fields. The use of nanotechnology includes the examination of small particles, that are atoms and molecular structures having sizes smaller than 100nm. These nanoparticles are fundamentally changed versions of fundamental components by modifying their atomic and molecular properties (Daniel and Astruc, 2004, Kato, 2011). Because of their numerous applications, nanoparticles have garnered more attention than their bulk counterparts.

Nano-sized zinc oxide particles

Water cannot be used to dissolve white inorganic zinc oxide, often known as ZnO. ZnO powder has several uses, including as a zinc supply in food, batteries, ferrites, ceramics, glass, cement, rubber (such that used in car tires), lubricants, and paint, creams and lotions glues, adhesives plastic, sealers, and pigment. ZnO, a manufactured version of zinc oxide, is the most prevalent form of zincite, while it may also be found naturally in the earth's outermost layer.

The most common configuration for Zn(II) when ZnO is grown on substrates with a cubic lattice structure is tetrahedral geometry, which makes the zincblende structure more stable than the more stable and frequently observed wurtzite structure under normal circumstances.

Wurtzite (B4), which has a hexagonal unit cell and the lattice constants a and c, makes up the crystal structure of zinc oxide. Tetrahedral coordination and sp3 covalent bonding are present among the four cations that each anion is surrounded by in this hexagonal arrangement. The tetrahedral structure of ZnO led to a noncentrosymmetric form, according to Nomura et al. (2003) and Pearton et al. (2005).

 

 

 

Figure 2; Wurtzite architecture

 

Unlike pigments, which are coloured chemicals that physically adhere to the surface they are applied on, dyes chemically bind to it. Since dyes are frequently used in aqueous solutions, it may be necessary to add a mordant to extend the life of the dye on a fibre (Daniel and Astruc, 2004).

Dye and pigment both have colour because of their capacity to absorb specific visible light wavelengths. Pigments, unlike dyes, are frequently soluble in water. Some dyes can be rendered insoluble by adding salt, resulting in lake pigments.

During the process of dye degradation, large dye molecules are chemically broken down into smaller dye molecules. As a consequence, water, carbon dioxide, and mineral byproducts are produced, all of which brighten the original dye's colour. Due to the fact that not all dye molecules are used throughout the dyeing process, some dye molecules end up in industrial waste water.

Colors made from synthetic organic compounds are used in a variety of industries, including textiles, paper, printing, leather, food, and cosmetics. As a result, colored rubbish is dumped into waterways such as rivers and lakes. It is critical to remove these colors from industrial waste before dumping it into bodies of water (Hossain et al., 2016). Wastewater dyes, among other things, have a detrimental influence on the biological activity of aquatic plants and animals, as well as photosynthesis. Dye and metal ions can also combine to generate chelates, which are poisonous to fish and other animals. Some colours even display harmful and cancer-causing characteristics, putting people in danger (Baeissa, 2016).

Although the industry already employs a number of dye removal techniques, they fall short when it comes to totally eliminating colours from the environment (Mathur et al., 2012). In order to protect human health, innovative techniques for eliminating hazardous dyes from the environment are required.

A new promising research field is the development of different semiconductor nanoparticles for the removal of textile pollutants from wastewater (Isai and Shrivastava, 2015). Advanced oxidation processes (AOPs) use a powerful oxidising agent, such as the OH radical, to efficiently remove pollutants from wastewater. Traditional AOPs, on the other hand, may not be as successful in lowering the amount of dyes. Semiconducting nanomaterial photocatalysis has sparked attention as a solution to the demand for more affordable, more efficient AOPs.

When semiconductor nanomaterials absorb energy that is greater than their bandgap energy, electrons and holes develop and move conducting bands to the band of valence transition.  Unlike superoxide radicals, which are created when electrons come into contact with oxygen molecules, hydroxyl radicals are formed when valence band holes come into contact with water molecules and hydroxide ions. According to ASSI et al. (2014), these free radicals are necessary for the oxidation of organic pigments, which leads in the generation of carbon dioxide (CO2) and water (H2O).