Correlation of the photoinduced total transmission with the degree of surface functionalization of carbon materials obtained from natural renewable sources

Abstract

For the first time, a contactless express method, which is based on the self-action of picosecond range laser pulses at 1064 nm, is used for the characterization of an optically dense porous layer of carbon material (CM) bulk particles obtained from a lignocellulosic source. It is found that the oxidation treatment reduces the Brunauer-Emmett-Teller (SBET) surface area from 9.52 × 105 m2/kg to 2.73 × 105 m2/kg. This reduction occurs due to the destruction of the carbon matrix fraction and to the formation of novel O-containing surface groups. The concentrated 30-mass% HNO3 is found to be the most efficient oxidant giving the highest yield of carboxylic (Cb), anhydridic, lactonic, and phenolic surface functionalities. The concentration of the surface functional groups is determined in a dynamic argon atmosphere by thermogravimetric (TG) analysis and thermoprogrammed desorption coupled with IR (TPD-IR) spectroscopy. The surface acidity defined from data of the Boehm titration shows the acceptable agreement with the data of TG-TPD-IR examination. An enhancement of the surface hydrophilicity allows the use of carbon matrix for the covalent binding of bioligands, amino acids, their residues, and proteins to the oxygen-containing functionalities, such as Cb groups. The observed photoinduced absorption efficiency of the bulk carbon particles Im(χC(3)) ∼ 10−16 m2/W is in the range of that of nanosized carbons. A slight variation of the ratio Im(χC(3))/SBET within the limits of experimental errors indicates a certain correlation between the absorptive NLO response and the CM specific surface. We suggest to utilize Im(χC(3)) as a quality parameter for carbon materials subjected to the oxidation, which is a typical initial step of the most commonly used functionalization routes for the preparation of biomedical materials.