Graphitic mesoporous carbon-silica composites from low-value sugarcane by-products for the removal of toxic dyes from wastewaters

Abstract

Highly porous carbon-silica composites (CSC) were prepared for the first time through a simple wet impregnation process and subsequent pyrolysis of low-value sugarcane by-products, namely molasses. These CSC materials demonstrate a distinct range of functionalities, which significantly differ from similar materials published in the literature. Importantly, the carbon-silica composites prepared at 800°C exhibited exceptional adsorption capacities for the azo-dye congo red (445 mg g −1 ), due to the graphitic carbon coating and unique functionality including C-O-C within the porous structure. Congo red adsorption capacity of the highly mesoporous graphitic carbon-silica composites significantly exceeds that of commercial activated carbon and silica, these carbon-silica composites therefore represent an effective step towards the development of porous bio-derived adsorbent for remediation of dye wastewaters. Both the porous properties (surface area and pore size distribution) and the functionality of the carbon coating were dependent on the temperature of preparation. The sustainable synthetic methods employed led to a versatile material that inherited the mesoporosity characteristics from the parent silica, demonstrating mesoporous volumes greater than 90% (as calculated from the total pore volume). Adsorption on the 800°C prepared carbon-silica composites demonstrated an excellent fit with the Langmuir isotherm and the pseudo-first-order kinetic model.

Microstructure of Fine Clay Soils Stabilized with Sugarcane Molasses

“…Indeed, the size of a micropore being very small (<2 nm), a single gas molecule occupies the pore and leads to the reduction of the size and the filling of the pore. In micropores, there is no layer formation [11] [12].…”

Adsorption Isotherm of BET Nitrogen of Concretes with Consolidated Soil by Sugar Cane Molasses

“…Phuong T. (2013). [9], Mathlouthi Mohamed(1998) [10] and Janekarn et al [11] have done the same report.…”

“…The pattern of BET (Brunauer, Emmett and Teller), known under the initials BET, and dated from 1938, is based on physical adsorption of nitrogen gas (N2) at the low temperature (77 K) [9][10][11]. The analytic treatment from the experience of the determinate adsorption isotherm allows defining the quantity of absorbed gas in a full monolayer, and then calculating the area of that layer which is the specific area of the solid.…”

“…The sugarcane molasses serves as a binder in the latter case. Janekarn et al (2020) reported that the nitrogen adsorption-desorption isotherms of CSC400 and CSC800 exhibited type IV isotherms. The molasses-stabilized clayey fine soil (kaolinite) has the same characteristics as the cane molasses-doped silicate composites, therefore these materials exhibit the same nitrogen adsorption behavior, i.e., the same type of isotherm (IV) [11].…”

“…Janekarn et al (2020) reported that the nitrogen adsorption-desorption isotherms of CSC400 and CSC800 exhibited type IV isotherms. The molasses-stabilized clayey fine soil (kaolinite) has the same characteristics as the cane molasses-doped silicate composites, therefore these materials exhibit the same nitrogen adsorption behavior, i.e., the same type of isotherm (IV) [11]. However, for Sing and Williams (2004), H3 hysteresis loops are typical for N2 adsorption by montmorillonite and lamellar particle aggregates, while H4 loops are observed for carbon isotherms [25].…”