Detailed interface composition of graphitized soot and carbon T900: Reference material for atmospheric studies investigated by a flowing gas experiment

Two graphitized thermal soot samples (GTS6, GTS80) and graphitized soot with a deposited overlayer of organic carboxylic acid (GTS80 impregnated with 1,2,4-benzenetricarboxylic acid (4.88 % (w/w) 1,2,4 BTCA)) have been investigated in a flowing gas experiment under molecular flow conditions using a Knudsen flow reactor. As a comparison, a typical commercial amorphous carbon T900 has a significantly larger coverage of surface functional groups (SFG’s) than both processed carbons GTS6 and GTS80 probed by NO 2 , O 3 , NH 2 OH, CF 3 COOH, HCl and N(CH 3 ) 3 . Despite the high temperature processing, the interface of GTS6 and GTS80 still retains a significant coverage of reduced sites using O 3 as a probe gas, namely approximately 10 and 1 % of a monolayer (ML), respectively, compared to 46 % for T900. Using N(CH 3 ) 3 as a probe gas we established that the tailor-made BTCA-covered GTS80 sample is highly acidic as expected having a -COOH group coverage of 51.7 ± 10.5 % of a molecular layer (ML). The corresponding initial uptake probability of most probe gases on T900 are significantly larger than for both GTS carbons, in line with the trends in coverage after saturating adsorption of probe gases. • 3000 K processing significantly reduces the number of interfacial adsorption sites • Thermal treatment destroys weakly reducing sites compared to strongly ones • No strongly basic sites have been found on the three amorphous carbons • Weakly basic sites reveal the presence of aromatic pyrones • The BTX-coated sample (52% of a ML) has a significant fraction of surface –OH