Exclusion of Salt Solutions from Activated Carbon Pores and the Relationship to Contact Angle on Graphite

Abstract

The exclusion of salts from the pores of activated carbon granules is demonstrated for the first time for the salts K 2 CO 3 , K 2 HPO 4 and K 3 PO 4 . In soaking experiments, the concentrations of solutions of K 2 CO 3 , K 2 -HPO 4 , and K 3 PO 4 inside the pores are less than in the bulk solutions. This phenomenon is observed by measuring the bulk concentration, which increases upon addition of carbon. This suggests that these salts are repelled by the carbon surface. In incipient wetness experiments, the three aforementioned salts do not enter the carbon at concentrations greater than ∼1 M. The contact angles of these three salt solutions on highly oriented pyrolitic graphite and polished resin-impregnated graphite surfaces rise with concentration and approach 90°, which suggests that these solutions would not enter activated carbon pores. By contrast, soaking, incipient wetness, and contact angle measurements for salts like ZnCl 2 and Zn(CH 3 COO) 2 show preferential adsorption by soaking (the salt is depleted from the solution), high imbibing limits (maximum incipient wetness volumes) at high solution concentrations, and a reduction of contact angle with increase in concentration. It is found that the behavior of these solutions on graphite surfaces approximates the solution behavior on an activated carbon that is relatively low in acidic surface functional groups.

Ammonia, cyclohexane, nitrogen and water adsorption capacities of an activated carbon impregnated with increasing amounts of ZnCl2, and designed to chemisorb gaseous NH3 from an air stream

“…6 and 13), the sample with 4.11 mmol/g AC was also produced via the double imbibing technique for reasons to be explained later. As shown in the manuscript by Westreich et al [38] and the thesis by Fortier [39], ZnCl 2 solutions are good imbibers at all solution concentrations. The imbibing limits are 0.70 and 0.49 mL/g AC in GC for water and 10 M ZnCl 2 respectively.…”

“…The number of acidic sites determined using KHCO 3 , K 2 CO 3 and KOH were 0.00, 0.07 and 0.09 mmol/g AC, respectively. ZnCl 2 (Aldrich, ACS reagent grade) was impregnated on GC via the incipient wetness method [37][38][39]. The concentrations of the ZnCl 2 imbibing solutions were selected to produce the desired loadings of impregnant, 0.137 to 4.45 mmol ZnCl 2 /g AC, when the imbibing limits were reached.…”

“…This is in contrast with concentrated solutions of K 2 CO 3 which do not penetrate the pore system of activated carbons. The imbibing limit is 0.70 mL/g AC in GC for water and 0.07 mL/g AC for 2.0 M K 2 CO 3 , respectively [37][38][39]. The ZnCl 2 loadings were assessed gravimetrically.…”

“…In the latter state, ZnCl 2 interacts favorably with activated carbon. The preferential adsorption of ZnCl 2 on GC and the increasing energy of adhesion of ZnCl 2 solutions on graphite with increasing solution concentration have been measured and discussed by Westreich et al [36,38]. Since the impregnant interacts favorably with the activated carbon, the ZnCl 2 impregnated on activated carbon interacts less favorably with NH 3 than bulk ZnCl 2 .…”

Understanding the intrinsic water wettability of graphite

“…Graphite, graphene, TMDCs, and rare earth oxides (REOs) are well established as low energy materials that suffer little consequence from hydrocarbon contamination, i.e., the low energy surface has little tendency to adsorb hydrocarbon contaminants. Decades of research on graphite since the 1940s [19][20][21][22][23][24][25][26][27][28][29][30][31] has substantiated this belief and only a few researchers [32][33][34] -until recently -have provided contradictory evidence. Consequentially, research on 2D and bulk lamellar materials predominately excludes considerations based on hydrocarbon contamination although spontaneous hydrocarbon adsorption is well known to occur on high surface energy metals.…”