CHAPTER ONE
Introduction
There is a wide attention to the activated carbons with highly developed surface area to use in the various industrial applications such as separation/purification of liquids and gases, water treatment, as supporting substrate of catalytic materials, super-capacitors, electrodes, gas storage devices and etc. In recent decades, alternative technologies have been developed for reducing pollution in gaseous and liquid phases. Solutions such as the use of granular activated carbon (GAC), powder activated carbon (PAC), fibers carbon (FAC) and activated carbon monoliths (ACM), among others, have been widely implemented due to the increasing demand and great versatility of these materials. The characteristics of ACM have resulted in it being termed a “new material” and it has been used in a wide range of areas such as the operation of air conditioning systems, in supporting the catalytic and the chemical industry in the removal of compounds such as benzene, acetone, dichloromethane, hexane and acrylonitrile, among others (Vargas-Delgadillo, et al. 2010). The porous structure of the ACM is made up mostly by micropores, whereas other activated carbons have a complex structure consisting of micropores, mesopores and macropores. The word “monolith” means “one stone” and refers to compact structures such as monoliths of the disc and honeycomb types. The latter are unit structures crossed lengthwise by parallel canals and constitute a new concept in the design of catalysts and adsorbents. This has allowed major innovations to emerge in recent decades. These new structures offer low values drop to the passage of gases, facilitating the uniform flow of the same, excellent mechanical properties, a large surface area per unit weight or volume and they also behave like most adiabatic systems and reduce the constraints generated by the phenomenon of internal diffusion (Vargas-Delgadillo, et al. 2010). When comparing the properties of monolithic catalysts with those of catalysts with more conventional forms (cylinders, spheres, rings, etc.), it was found that the compact structure not only facilitates management but allows freedom of orientation in the reactor and significantly reduces the problems of the restriction granular catalysts.
Activated carbon (AC) is a carbonaceous material that can be prepared by the pyrolysis of many inexpensive materials that have a high carbon content and low inorganic content (Alothman, et al., 2011). On a commercial scale, activated carbon is produced by the pyrolysis and activation of high-cost starting materials, such as wood, petroleum and coal, making it expensive and unjustified as a method of pollution control (Bouchelta and Pierre, 2008). Activated carbons having high specific porosity, high surface areas are extremely versatile adsorbents of major industrial significance. These are used in wide range of applications concerned principally with the removal of species by adsorption from the liquid or gas phase. Activated carbons can be produced from a number of precursor materials including wood, agricultural wastes, coal and synthetic resins (Sivakumar, et al., 2012). These precursors are normally exposed to a number of different activation method such as physical or chemical in an effort to achieve- carbon with the high adsorption capacity for a particular application. Activated carbon, is widely used adsorbent in industrial processes, is composed of a microporous, homogenous structure with high surface area and shows radiation stability. The process for producing high-efficiency activated carbon is not completely investigated in developing countries. Furthermore, there are many problems with the regeneration of used activated carbon. Nowadays, there is a great interest in finding inexpensive and effective alternatives to the existing commercial activated carbon. Exploring effective and low-cost activated carbon may contribute to environmental sustainability and offer benefits for future commercial applications. The cost of activated carbon prepared from biomaterials is very low compared to the cost of commercial activated carbon (Sivakumar, et al., 2012).
For the past few decades, attention has been shifted towards adsorption technique, which emerged as one of the widely accepted methods for the removal contaminants from wastewater. Activated carbon adsorption has been cited by the US Environmental Protection Agency (USEPA) as one of the best available environmental pollution control technologies. One of the major challenges associated with adsorption using activated carbon is its cost-effectiveness. Researchers in the recent past have mainly focused on the preparation of the activated from agricultural waste materials as an alternative for the commercial activated carbon. Consequently, numerous low cost alternatives have been proposed including sago waste, waste coir pith, pine sawdust, sugarcane dust, rubber wood sawdust, bottom ash and de-oiled soya. In recent years, a number of adsorptive material, such as moss peat, melon seed husk, tea factory waste, sheep manure waste, etc., which have been fruitfully used for the preparation of activated carbon (Sivakumar, et al., 2012).
1.1 History of Activated Carbon
The useful properties of activated carbon have been known since ancient times. This traces back to 1500 BC when Egyptians used charcoal as an adsorbent for medicinal purposes and a purifying agent. Around 420 BC it was observed that Hippocrates dusted wounds with powdered charcoal to remove their odor. Ancient Hindu societies purified their water by filtration through charcoal (Bansal and Goya, 2005). In 1773, the Swedish chemist Karl Wilhelm Scheele was the first to observe adsorption of gases on charcoal. A few years later activated carbons began being used in the sugar industry as a decolorizing agent for syrup.
In the early 20th century the first plant to produce activated carbon industrially was built for use in sugar refining industry in Germany. Many other plants emerged in the early 1900’s to make activated carbons primarily for decolorization. During World War I activated carbon was used in gas masks for protection against hazardous gases and vapors. Today, activated carbons are used to remove color from pharmaceutical and food products, as air pollution control devices for industrial and automobile exhaust, for chemical purification, and as electrodes in batteries. 500,000 tons per year of activated carbon are produced globally (Jankowska, et al., 1991). 80% of this is used for liquid phase applications, and 20% is used for solid phase applications.
1.2 AIMS AND OBJECTIVES OF STUDY
The objectives of this study are for the following reasons:
- To prepare acid activated carbon from dog teeth sample.
- To identify the unknown crystalline materials present in the sample using the X−ray powder diffraction instrument (XRD).
- To reveal information about the sample including external morphology (texture), chemical composition, porosity, homogeneity and crystalline structure and orientation of materials making up the acid activated bone (dog teeth) sample.
1.3 SCOPE OF STUDY
This research is limited to the collection of bone sample (dog teeth), subjecting it to carbonization, grinding it to a powdered form, and acid activation using citric acid (C6H8O7) then, carrying out XRD (X−ray powder diffraction) and SEM (Scanning Electron Microscopy) analysis on the sample.
1.4 SIGNIFICANCE OF STUDY
Activated carbon (which includes that from animal bone and plants) is well known for its application in water filtration, in medicine as anti-poison, sugar refining, as a black pigment for artists paint, printmaking, calligraphic and drawing inks, as well as in crude oil production of petroleum jelly.
Recently, it has also been reported to have very excellent wound healing properties, even more than the well-known Cicatrin powder (Ezema, 2015).
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