Rice Husk-Derived High Surface Area Nanoporous Carbon Materials with Excellent Iodine and Methylene Blue Adsorption Properties

Lok Shrestha,Raja Pradhananga,Mamata Thapa,Rekha Shrestha,Katsuhiko Ariga,Subrata Maji

doi:10.3390/c5010010

Abstract

Iodine and methylene blue adsorption properties of the high surface area nanoporous carbon materials derived from agro-waste and rice husk is reported. Rice husk was pre-carbonized at 300 °C in air followed by leaching out the silica nanoparticles by extraction with sodium hydroxide solution. The silica-free rice husk char was mixed with chemical activating agents sodium hydroxide (NaOH), zinc chloride (ZnCl2), and potassium hydroxide (KOH) separately at a mixing ratio of 1:1 (wt%) and carbonized at 900 °C under a constant flow of nitrogen. The prepared carbon materials were characterized by scanning electron microscopy (SEM), Fourier transformed-infrared spectroscopy (FT-IR), powder X-ray diffraction (pXRD), and Raman scattering. Due to the presence of bimodal micro- and mesopore structures, KOH activated samples showed high specific surface area ca. 2342 m2/g and large pore volume ca. 2.94 cm3/g. Oxygenated surface functional groups (hydroxyl, carbonyl, and carboxyl) were commonly observed in all of the samples and were essentially non-crystalline porous particle size of different sizes (<200 μm). Adsorption study revealed that KOH activated samples could be excellent material for the iodine and methylene blue adsorption from aqueous phase. Iodine and methylene blue number were ca. 1726 mg/g and 608 mg/g, respectively. The observed excellent iodine and methylene blue adsorption properties can be attributed to the well-developed micro- and mesopore structure in the carbon material. This study demonstrates that the agricultural waste, rice husk, and derived nanoporous carbon materials would be excellent adsorbent materials in water purifications.

Highlights

Activated nanoporous carbons materials (NCMs) represent porous carbonaceous materials that have been processed to increase porosity and specific surface area so that they can be widely used as adsorbents to adsorb metal ions and organic molecules, catalysts, and catalyst supports for the removal of pollutant species from gases or liquids and as electrode materials for batteries and supercapacitors [1,2,3,4,5,6]
Most of the functional groups disappeared in NCMs due to high temperature carbonization (Figure 1b)
NCMs derived derived from rice husk husk using different activating not exhibit exhibit significant significant differences

Summary

Introduction

Activated nanoporous carbons materials (NCMs) represent porous carbonaceous materials that have been processed to increase porosity and specific surface area so that they can be widely used as adsorbents to adsorb metal ions and organic molecules, catalysts, and catalyst supports for the removal of pollutant species from gases or liquids and as electrode materials for batteries and supercapacitors [1,2,3,4,5,6]. Surface area and pore volume of porous carbon materials range from 250–2410 m2 /g and 0.022–91.4. Direct carbonization and activation of the carbonaceous precursors are the general methods for the fabrication of NCMs. Direct carbonization is performed by mild- or high temperature heat-treatment in which pyrolytic decomposition of the precursor occurs with the elimination of many non-carbon elemental species (H, N, O and S), resulting in the formation of fixed carbonaceous char with porous structure. Physical activation includes two-step processes involving carbonization of the precursor material, followed by gasification of the char at elevated temperatures between

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Conclusion