Invasive wood derived nanoporous carbons for mitigation of water and air pollution

Abstract

Activated carbons (ACs) are well-known adsorbents widely used in a variety of applications due to large specific surface areas arising from their highly developed porous structures. Continuous growth of activated carbons consumption is especially linked to their use in mitigation of environmental pollution. Novel precursors as well as sustainable, efficient activation processes are being steadily investigated to fulfill the forecasted increasing demand. In particular, invasive wood species as non-conventional precursors for activated carbons development may represent an interesting alternative, that has been scarcely explored. The present chapter reports chemical activation of invasive Parkinsonia aculeata wood into activated carbons using solutions of potassium carbonate and potassium hydroxide as main activating reagents at pre-established experimental conditions. Potentialities of the resulting ACs for mitigation of water and air pollution were evaluated. A commercial activated carbon was also used for the sake of comparison. Physicochemical characteristics indicate that the activated carbons obtained with both reagents show similar BET surface areas of ~770?780 m2/g and predominance of pores smaller than 2 nm, even though contribution of these pores to the total pore volume was greater for those obtained with KOH. Effectiveness of the carbons in adsorption of phenol, as representative model of priority water contaminants, was investigated. The effects of the adsorbent?s dose and solution pH were first examined to establish optimal conditions. Kinetics of phenol adsorption onto the derived activated carbons was determined and properly described by a pseudo-second order model. Adsorption isotherms were also obtained and well represented by conventional models. High adsorption capacities point to possible use of the ACs for the removal of phenolic compounds usually found in industrial wastewater. Their performance exceeds that of the commercial sample possessing a higher BET surface area but a lower volume of pores smaller than 2 nm. On the other hand, the capacity of the samples developed with K2CO3 solution in adsorption of CO2, the largest anthropogenic greenhouse gas on the planet contributing to the global warming, was investigated. CO2 adsorption capacity from gaseous streams approaching post-combustion conditions was evaluated by gravimetric adsorption tests and breakthrough curves determined in a fixed-bed column at 30°C and 50°C and atmospheric pressure. The amounts of CO2 adsorbed as determined by both methodologies were around the order of those reported in the literature for similar conditions, and would be associated to the nanoporous structure of the ACs. Accordingly, the nanoporous carbons derived from invasive P. aculeata wood demonstrate ability for their potential use in the removal of contaminants from water and air.