Investigation of Thermal Behavior of Layered Double Hydroxides Intercalated with Carboxymethylcellulose Aiming Bio-Carbon Based Nanocomposites

Vagner R Magri,Alfredo Duarte,Gustavo F Perotti,Vera R.L Constantino

doi:10.3390/chemengineering3020055

Vagner R Magri, Alfredo Duarte + Show 2 more

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https://doi.org/10.3390/chemengineering3020055

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Abstract

Carboxymethylcellulose (CMC), a polymer derived from biomass, was intercalated into layered double hydroxides (LDH) composed by M2+/Al3+ (M2Al-CMC, M = Mg or Zn) and evaluated as precursors for the preparation of biocarbon-based nanocomposites by pyrolysis. M2Al-CMC hybrids were obtained by coprecipitation and characterized by X ray diffraction (XRD), vibrational spectroscopies, chemical analysis, and thermal analysis coupled to mass spectrometry. Following, pyrolyzed materials obtained between 500–1000 °C were characterized by XRD, Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Above 600 °C, Raman spectra of all samples showed the presence of graphitic carbon, which plays a role in the degree of crystallinity of produced inorganic phases (for comparison purposes, M2Al-CO3 materials were investigated after calcination in the same experimental conditions). XRD patterns of Mg2Al-CMC pyrolyzed between 600–1000 °C showed poorly crystallized MgO and absence of spinel reflections, whereas for Zn2Al-CMC, it was observed well crystallized nanometric ZnO at 800 °C, and ZnAl2O4 and γ-Al2O3 phases at 1000 °C. Above 800 °C, the carbothermic reaction was noticed, transforming ZnO to zinc vapour. This study opens perspectives for nanocomposites preparation based on carbon and inorganic (mixed) oxides through precursors having organic-inorganic interactions at the nanoscale domain.

Highlights

More than forty minerals have been identified as layered double hydroxide (LDH) phases which structures are analogous to brucite mineral, Mg(OH)2 [1]
LDH materials intercalated with CMC polymer, a carbon source derived from biomass, were evaluated as a precursor for the preparation of MMO/C nanocomposites
Pyrolysis step conducted above 600 ◦C produced materials comprising graphitic carbon, which structural organization is increased at higher temperature values

Summary

Introduction

More than forty minerals have been identified as layered double hydroxide (LDH) phases which structures are analogous to brucite mineral, Mg(OH)2 [1]. Divalent cations like Zn2+, Ni2+, Fe2+ or Mn2+ are present instead of magnesium. These materials are called as hydrotalcite-type compounds given that the first identified LDH phase was nominated hydrotalcite (due to its textural resemblance with talc) [2]. The chemical composition of LDH materials is usually represented by the general formula [(M2+(1−x)M3+x)(OH)2]x+[Am−x/m·nH2O]x− and denoted as M2+RM3+-A, where M is the metal ion, R is the M2+/M3+ molar ratio and Am− is a hydrated anion [2,3]. The M2+/M3+ molar ratio in the minerals is usually 3 or 2 as for example in hydrotalcite ([Mg6Al2(OH)16]CO3·4H2O) and quintinite

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