Analysis of structural properties of activated carbons by HRTEM

1. Context and Objectives Activated Carbons - chemical composition, textural and nanostructural characteristics H. Marsh Carbon Conference 2006 Experimental studies & Results Computerized HRTEM image analysis - Nanostructural data -L length of the layers -d interlayer spacing -% NSL non stacked layers -La and Lc :diameter and height of the coherent domain (BSU) PIO SIT J.N.Rouzaud and C.Clinard Fuel Processing Technology, 2002, 77-78, 229-235 Conclusion Analysis of structural properties of activated carbons by HRTEM and their influence on the oxidation and ignition characteristics T.JAYABALAN, P. PRE, V. HEQUET, J.N. ROUZAUD and P. LE CLOIREC Ecole des Mines de Nantes, GEPEA UMR CNRS 6144, 4 rue Alfred Kastler, BP 20722, 44307 Nantes cedex 3, France. thangavelu.jayabalan @emn.fr Laboratoire de géologie de l’Ecole Normale Supérieure de Paris, UMR CNRS-ENS 8538, 24 rue Lhomond 75231-Paris Cedex 5, France. rouzaud@geologie.ens.fr Activated carbons are widely used as adsorbents in air treatments. They are prone to early oxidation and self heating due to various interacting factors like exothermic chemical and adsorption reactions, heat exchange with the surroundings and intrinsic properties of the materials. The aim of this work is to determine the relationships between the nanostructural characteristics of activated carbons by analysis of High Resolution Transmission Electron Microscope (HRTEM) imagesand their influence on the reactivity of the carbon material. Structural analysis Activated Carbon samples differ structurally Physically activated carbons have low O/C ratio: nanometer-sized graphene layer Chemically activated carbons (like Picabiol) have high O/C ratio:short, non-stacked and distorted graphene layers 5 nm 5 nm Thermal analysis NC-100 Picabiol PIO: Point of Initial Oxidation SIT: Spontaneous Ignition Temperature Reactivity data (PIO and SIT) are obtained from TG-DSC Chemically activated carbons have lower PIO and SIT compared to physically activated carbons Multiple Linear Regression PIO = 83.3 – 1.38 O/C (%) + 27.5 L>1ring (Å) S = 15 °C R2 = 94% Results are coupled with structural parameters using Multiple Linear Regression PIO = 271 – 2,7 O/C (%) R2 = 87% SIT = 537 - 4,7 O/C (%) R2 = 96% The results show that oxygen to carbon ratio in the form of surface oxygenated groups and the characteristics of the graphene layer length (from HRTEM image analysis) influenced the reactivity of activated carbons. The organization of the graphitic structure and the properties of the activated carbon samples were dependant on the mode of activation and the nature of the material precursor. The structure of highly stable carbons was found to contain less oxygen to carbon ratio with larger and better stacked polyaromatic layers. Physically activated carbons appear much stable than chemically activated carbons.