Variation in the FTIR spectra of a biomass under impregnation, carbonization and oxidation conditions

The FTIR spectra of untreated date pits (DP) and their H3PO4-preimpregnated sample together with their chars as well as samples subjected to different activation schemes were determined. These activated carbons were prepared using phosphoric acid, steam one and two steps and potassium hydroxide. This series of activated carbons were oxidized with HNO3 and their surface modifications were detected by using FTIR spectra in the course of oxidation conditions. The presence of cellulose and hemicellulose, lignin and protein constituents were detected in the raw material. Significant changes were observed in the chemical structure of the date pits under carbonization where aromatic structures were developed and accompanied by losing most of aliphatic CH species in the intermediate char product. However, char-IR spectrum revealed the presence of trace amounts of uncarbonized material. Whereas, activated carbons possessed aromatic C=C bonds and oxygen groups. The chemical structure of the activated carbon were found to be influenced markedly depending on the scheme of activation followed. Increasing the activation temperature led to a complete destruction of C=O and C-O species simultaneously by promoted polyaromatic structures. The detectable FTIR for the oxidized activated carbons confirmed the presence of large amount of oxygen functionalities of acidic nature appearing as carbonyl, phenolic, hydroxylic, carboxylic and lactonic species groups on the carbon surface. Phosphoric acid was found to have a prominent effect on the botanical structure of the raw material. Its mechanism was based on initiation of the bond cleavage leading to dehydration and elimination reactions that release volatile products. This was followed by aromaticity and formation of a stronger cross-linked solid of new biopolymer involving phosphate esters. (C) 2005 Elsevier B.V. All rights reserved.