Leachability of polycyclic aromatic hydrocarbons from coal tar and synthesis of the nanohybrid photocatalyst for their degradation
MetadataShow full item record
There exists a great number of industrial processes that produce coal tar as a by-product. The rate of coal tar production is higher than the rate at which it is converted to other products, and its application is very limited. As a result, coal tars produced as by-products end up being discharged into the environment and occupy the unused land.In addition, the disposal of coal tar in the environment poses threats because of the toxic, carcinogenic, mutagenic, teratogenic and skin irritants compounds it contains.These compounds are known as polycyclic aromatic hydrocarbons (PAHs). PAHs can leach into surface waters since they are mobile. It is therefore important that the water contaminated by these harmful compounds is properly treated to avert the health and environmental problems they cause. Different techniques for the removal of PAHs from water have been investigated and explored. Photocatalysis has emerged to be a promising method in terms of efficiency, sustainability, economic impact and reliability in the removal of persistent organic pollutants such as PAHs. Even though photocatalysis has been found to be effective in purifying wastewater, there is a search for an appropriate photocatalyst to degrade these organic pollutants in water. This research focused on assessing the coal tar PAH profile and investigated the factors influencing the leachability of PAHs from coal tar into the environment. It was discovered that coal tar contains the majority of the most popular PAHs, which generally include 16 priority PAHs. It was also found that the mobility of PAHs from coal is highly influenced by contact time between coal tar and chemical properties of the aqueous solution the tar may be exposed to. The findings suggest that PAHs can leach from coal tar and enter water bodies, while the leachability of low molecular weight PAHs is much higher than the leachability rate of high molecular weight PAHs. Even though the amount of HMW PAHs that is leached into the water is very small, if the leaching process takes place for prolonged periods, the amount of HMW PAHs in waters can be significant. Therefore, it is important that a photocatalyst that is able to degrade both LMW and HMW PAHs is found. In this study, RGO-Bi2MoO6 was investigated as potential photocatalyst to degrade PAHs in water. Thus, this photocatalyst was synthesised using hydrothermal methods because it allows the use of elevated temperatures, at which the RGO-Bi2MoO6 nanocomposite forms, and it is easy to operate. This research focused on using the synthesised photocatalyst in the photo degradation of coal tar PAHs. To test the photocatalytic performance of RGO-Bi2MoO6 in degrading PAHs, a degradation test was carried out using naphthalene as representative of PAHs. It was found that RGO-Bi2MoO6 is a highly effective material in degrading naphthalene. The material showed a photo degradation efficiency of about 95%, and the results also indicated that RGO-Bi2MoO6 can be reused for about five times and still achieve a photo degradation efficiency of over 80%. The small amount of RGO that was added in the photocatalyst played a significant role in improving the performance of the material.
- Engineering