Autor(es):
Valente Nabais, Joao 
; Laginhas, Carlos ; Carrott, Peter ; Ribeiro Carrott, Manuela ; Titirici, Magdalena ; Roman, Silvia
Data: 2012
Identificador Persistente: http://hdl.handle.net/10174/7003
Origem: Repositório Científico da Universidade de Évora
Assunto(s): adsorption; activated carbon
Descrição
Activated Carbons (AC) are traditionally produced by
chemical or physical activation processes, frequently using
biomass materials as precursors [1]. These procedures can be
modified in order to create particular surface characteristics
(both textural and chemical), so that the adsorption of a given
organic or inorganic compound is optimized. Recently, the use
of hydrothermal carbonization processes (HTC) to produce
carbon nanomaterials was reported [2]. This process consists
in the treatment of a material in water under soft temperature
conditions (in the range 150-350ºC) and in some cases under
pressure conditions. The HTC processes are very attractive
due to its simplicity, cheapness and efficiency; they can also
be classified as “green” since it does not involves organic
solvents, catalysts or surfactants.
By HTC, the biomass organic components are broken up and
dissolved in the water, and a carbon rich solid product is
obtained (the hydrochar) as well as a liquid phase containing
sugars and/or oligomers that can be used for a variety of
practical purposes. Previous works have reported that during
HTC oxygen accumulates at the periphery of the particles
originating a final carbonaceous material with a core–shell
structure composed of a hydrophobic core and a hydrophilic
shell containing a large number of reactive oxygen functional
groups [3]. We have published in a recent work the production
of hydrochars with acidic properties [4], which implies an
interesting novelty regarding the surface chemistry when
compared with chars obtained by pyrolysis that have basic
characteristics. Taking into account these results we have
explored the possibility of using the hydrochars to produce
ACs with controlled surface chemistry and porosity by
physical activation with air and carbon dioxide. As precursors
we used three biomass resources, which are very abundant in
the Southern part of Iberian Peninsula: walnut shell, sunflower
stem and olive stone.
