Abstract
Activated carbon (AC) with a very high surface area of over 2000 m2/g was produced from low sulfur acid hydrotropic lignin (AHL) from poplar wood using H3PO4 at a moderate temperature of 450 °C (AHL-AC6). ACs with similar surface areas were also obtained under the same activation condition from commercial hardwood alkali lignin and lignosulfonate. Initial evaluation of AC performance was carried out using nitrogen adsorption-desorption and dye adsorption. AHL-AC6 exhibited the best specific surface area and dye adsorption performance. Furthermore, the adsorption results of congo red (CR) and methylene blue (MB) showed AHL-AC6 had greater adsorption capacity than those reported in literature. The dye adsorption data fit to the Langmuir model well. The fitting parameter suggests the adsorption is nearly strong and near irreversible, especially for MB. The present study for the first time provided a procedure for producing AC from lignin with Brunauer–Emmett–Teller (BET) surface area >2000 m2/g using low cost and low environmental impact H3PO4 at moderate temperatures.
Highlights
Lignin is the second most abundant terrestrial biopolymer on earth, just after cellulose [1]
The surface area was calculated by the BET model from relative pressures (P/Po) in the range of 0.01–0.35; the total pore volume was obtained by single-point adsorption of N2 at a high relative pressure (0.99); micropore area and micropore volume were determined by the t-plot method; mesoporous area and mesoporous volume were calculated using the Barrett–Joiner–Halenda (BJH) model; pore size distribution was auto-generated by applying density functional theory (DFT) to the N2 adsorption isotherms using the software supplied by the TriStar II
A BET surface area of over 2000 m2 /g, substantially higher than
Summary
Lignin is the second most abundant terrestrial biopolymer on earth, just after cellulose [1]. Speaking, activated carbons with BET surface area below 2000 m2 /g are widely used for applications associated with low-cost absorption such as heavy metals removal, dyes adsorption, and air pollution control. ACs with specific BET surface area greater than 2000 m2 /g are considered as super activated carbon [21] with higher added value for applications such as catalyst carrier, gas (CH4 , H2 , and CO2 ) storage materials, electrode for supercapacitors, and adsorbents requiring high adsorption capacity [22]. The novelty of the present study are two-fold: (1) focusing on producing AC with specific BET surface area of greater than 2000 m2 /g for high value applications using low cost H3 PO4 activation; and (2) examining lignin from low temperature acid hydrotropic fractionation (AHF) [23] that is metal-free and theoretically sulfur-free for producing super AC. Evaluation of sulfur-free acid hydrotropic lignin (AHL) has environmental significance
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