As the world continues to develop with almost every habitat of man gearing towards urbanization, there is every tendency that the need for activated carbon would also increase, hence, the need for individuals, companies, and countries to be prepared to meet this demand. The production of activated carbon from agricultural byproducts has both economic and environmental effects, as it converts unwanted, low-value agricultural waste to useful high-value adsorbent [ 7 ].
Plantain Musa paradisiaca is a plant of banana family Musaceae closely related to common banana Musa sapientum. Its fruits are edible and are generally used for cooking. This is different from the soft and sweet banana. Despite the downward trend of plantain production in Nigeria between and , it was still ranked fifth in the world [ 9 , 10 ] with eight African countries named among the top ten plantain producers in the world [ 11 ]. Despite its prominence, Nigeria does not feature among plantain exporting nations; it produces more for local consumption than export [ 12 ].
The production of activated carbon from agricultural byproducts has potential economic and environmental impacts. Firstly, it converts unwanted low-value agricultural waste to high-value adsorbents. Secondly, activated carbons are increasingly used in water to remove organic chemicals and metals of environment and economic concern. Finally, it will reduce the importation of activated carbon wherefore increasing our economic base as a country [ 2 ].
Thus the purpose of this purpose of this study is to prepare and characterize the carbons obtained from plantain fruit stem, activated with orthophosphoric acid zinc chloride and the untreated carbon. The charcoal product was allowed to cool down and then divided into two parts, A and B, using H 3 PO 4 and ZnCl 2 as activating agents [ 2 , 3 , 7 , 13 , 14 ].
The activated carbons were produced with a slight modification using standard methods of Ekpete [ 2 ] and Sugumaran [ 3 ]. Two beakers were used in the activation process. The paste was then transferred into a crucible. The pH was determined by using the method of Abdullah [ 15 ] with a slight modification.
Determination of bulk density was used done using the methods of Sugumaran [ 3 ] with a slight modification. Thermal drying method was used in the determination of moisture content of the samples. The difference between the initial and final mass of the carbon represents the moisture content. The ash content was calculated using the equation For volatile matter determination , 1.
The volatile matter was calculated using the equation where volatile weight is the difference in weight before and after heating of the samples. For iodine number test, each sample of carbon 0. The mixture was filtered using a filter paper. The percent iodine adsorbed by each carbon was calculated by applying the formula below. The Boehm titration method as used by Ekpete and Horsfall [ 7 ] was used for this analysis with a slight modification.
Subsequently the aqueous solutions were back-titrated with HCl 0. The number and type of acidic sites were calculated by considering that NaOH neutralizes carboxylic, lactonic, and phonetic groups. Carboxylic groups were therefore quantified by direct titration with NaHCO 3 -; the difference between the groups titrated with Na 2 CO 3 and those titrated with NaHCO 3 was assumed to be lactones and the difference between the groups titrated with NaOH and those titrated with Na 2 CO 3 was assumed to be phenols.
Basic site was determined by titration with HCl. Neutralization points were known using pH indicators of phenolphthalein solution for titration of strong base and strong acid, while methyl red solution was used for the titration of weak base and strong acid. For sample analysis, 0. The mixture thus obtained was crushed in a mortar to obtain a homogeneous powder which was then introduced into a mould to obtain very fine plates.
The plates were then introduced into the spectrophotometer for analysis. The temperature for carbonization is a factor that is usually taken into consideration because of how dependent all other properties of the carbon are on it.
Precautionary measures are usually taken when choosing a temperature due to the fact that above certain temperatures the sample will completely change to ash. Despite its environmental unfriendliness, chemical activation method has been thriving over physical activation method due to its low energy cost, high carbon yield, and easy recovery process of activating agents which have been reported to act as dehydrating agents, tar formation inhibitor, carbon yield enhancer, and bond cleavage promoter [ 3 , 17 ].
Low amount of moisture, ash, and volatile matter indicates that the particle density is relatively small and that the biomaterial should be an excellent raw material for adsorbents to be used in column or fixed-bed reactors [ 7 ]. As presented in Figure 1 and Table 1 , it can be observed that they all had low amount of moisture, with the CPZAC having the lowest moisture content value of ; the moisture value of all samples was also lower than the observed by Ekpete and Horsfall [ 7 ].
The ash value and volatile matter values made CPPAC more preferable for adsorption; ash content influences ignition point of the carbon, which is a major consideration where adsorption of certain solvents is applied; it reduces the overall activity of activated carbon and the efficiency of reactivation; the lower the ash value, the better the activated carbon for use as adsorbent. Abdullah et al. This difference can be attributed to carbonization and activation processes which have to a large extent dried and volatilized all noncarbon materials [ 7 ].
Iodine number is usually used to roughly estimate the surface area of activated carbon at room temperature condition. It is used as an indicator for the porosity and adsorbent capacity of the activated carbon.
The micropore structure, adsorption properties, and surface morphology of activated carbons obtained under atmosphere and vacuum were investigated. It was found that the structure of the starting material is kept after activation. The activated carbon prepared under vacuum exhibited higher values of the BET surface area up to m2 g -1 and total pore volume up to 0. Chem Eng Res Des — Ecotoxicology — Fuel Process Technol — Deng H, Yang L, Tao G, Dai J Preparation and characterization of activated carbon from cotton stalk by microwave assisted chemical activation—application in methylene blue adsorption from aqueous solution.
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