From Biomass Wastes to Highly Efficient CO₂ Adsorbents: Graphitisation of Chitosan and Alginate Biopolymers

Abstract

Carbon spheres from natural biopolymers (alginate and chitosan) are easily synthesised by thermal treatment between 400 and 800 °C under an inert atmosphere. All the samples, including the untreated natural biopolymers, as well as the resulting carbon materials, exhibit a remarkable CO₂-adsorption capacity. The sample that exhibits the highest adsorption capacity was that obtained by carbonisation of alginate at 800 °C and subsequent treatment with KOH at 800 °C. This material exhibits a specific surface area of 765 m² g⁻¹, specific micropore volume of 0.367 cm³ g⁻¹, ultra-micropore volume of 0.185 cm³ g⁻¹, average ultra-micropore size of 0.7 nm and CO₂-adsorption capacity of 5 mmol g⁻¹ measured at 0 °C and atmospheric pressure. This value is close to the absolute record for CO₂ adsorption and, by far, the highest if we compare unit areas or consider the density of the material. The combination of the high N content already included in the chitosan structure and the elevated microporosity in the case of alginate are crucial factors to obtain these satisfactory values with an easy and green preparation procedure. Also, owing to the high conductivity of the alginate-derived carbon (better than graphite), it has been possible to develop a process of reversible adsorption-desorption by applying a voltage, which is a low-energy desorption method compared with the conventional method of vacuum and high temperatures. All these properties, together with the spherical shape of the material of 0.1 mm, which is the most suitable form to favour mass transfer in fluidised-bed reactors, make this material a highly promising adsorbent for industrial applications.

Biomass‐Derived Porous Carbon Materials: Synthesis and Catalytic Applications

“…on the design of aerogel materials from different marine polysaccharides 47. More recently, a graphitization technique has been reported to prepare N ‐doped high surface area carbonaceous materials from chitosan 48. Chitin, the parent polysaccharide of chitosan, can also be employed in the synthesis of aerogels with high microporosity 49…”

Innovative preparation of MoS2–graphene heterostructures based on alginate containing (NH4)2MoS4 and their photocatalytic activity for H2 generation

“…During pyrolysis, alginic acid will form G, as it has been reported, (30,31) (all values in %wt) Fig. 4 shows the Raman spectra for MoS 2 -G10 material.…”

Shell Biorefinery: Dream or Reality?

“…and thus reduces energy consumption. García and co‐workers described the synthesis of highly porous N‐doped carbon sheets from chitosan by direct carbonization under an inert atmosphere . Chitosan aerogel beads, obtained by scCO 2 drying, were added into saturated (NH 4 )SO 4 solution and stirred for 1 h. The wet beads were annealed at 200 °C and calcined at 400–800 °C under Ar.…”

“…Garcíaa nd co-workers described the synthesis of highly porous N-doped carbons heets from chitosanb yd irectc arbonization under an inert atmosphere. [112] Chitosan aerogel beads, obtained by scCO 2 drying, were added into saturated (NH 4 )SO 4 solutiona nd stirred for 1h.T he wet beads were annealed at 200 8Ca nd calcined at 400-800 8C under Ar.T he sample calcined at 800 8Cw ith KOH activation had the highest surface area of 970 m 2 g À1 and at otal volume of 0.618 cm 3 g À1 .S pecifically,t he synthesized carbon materials contained ah igh nitrogen content of 11.5 %, and possessed as heet-like structure with graphitic layers stackeda long the Z axis. Due to the high nitrogen contenta nd porosity,t he carbon materials exhibitede xcellent CO 2 adsorption capacity (> 3mmol g À1 ).…”