Synthesis of nanocellulose aerogels and Cu-BTC/nanocellulose aerogel composites for adsorption of organic dyes and heavy metal ions (original) (raw)

MOFs compounds with open metal sites, particularly Cu-BTC, have great potential for adsorption and catalysis applications. However, the powdery morphology limits their applications. One of the almost new ways to overcome this problem is to trap them in a standing and flexible aerogel matrix to form a hierarchical porous composite. In this work, Cu-BTC/CNC (crystalline nanocellulose) and Cu-BTC/NFC (nanofibrillated cellulose) aerogel composites were synthesized using a direct mixing method by the addition of Cu-BTC powder to the liquid precursor solution followed by gelation and freeze-drying. Also, pure nanocellulose aerogels (CNC and NFC aerogels) have been synthesized from cellulose isolated from peanut shells. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra, and X-ray diffraction (XRD) were utilized to evaluate the structure and morphology of the prepared materials. The adsorption ability of pure CNC aerogel and Cu-BTC/NFC aerogel composite for organic dye (Congo Red) and heavy metal ion (Mn 7+) was studied and determined by the UV-Vis spectrophotometry and inductively-coupled plasma optical emission spectrometry (ICP-OES), respectively. It was concluded that Cu-BTC/NFC aerogel composite shows excellent adsorption capacity for Congo Red. The adsorption process of this composite is better described by the pseudosecond-order kinetic model and Langmuir isotherm, with a maximum monolayer adsorption capacity of 39 mg/g for Congo Red. Nevertheless, CNC aerogel shows no adsorption for Congo Red. Both CNC aerogel and Cu-BTC/NFC aerogel composite act as a monolith standing solid reducer, which means they could remove permanganate ions from water by reducing it into manganese dioxide without releasing any secondary product in the solution. Metal-organic frameworks (MOFs) are porous crystalline polymer networks of metal nodes (metal ions or clusters) connected to multidentate organic linkers, which are themselves linked by strong covalent bonds forming one-, two-, or three-dimensional networks 1-3. MOFs are also known as porous coordination polymers (PCPs) or porous coordination networks (PCNs) 4-6. In addition to combining the beneficial properties of organic and inorganic ingredients, they show unique properties that exceed expectations of a simple mixture of these parts 5,7. Due to their specific characteristics including their record-breaking surface areas (more than 7000 m 2 /g) 8 , ultrahigh porosities 9 , low density 10 , high thermal stability 11 , and tunable pore structure 12 , MOFs have received specific attention for many applications such as gas separation and storage 13 , catalysis 14 , adsorption 15,16 , energy storage 17 , drug delivery 18-20 , chemical sensing 21,22 and so on 23. Among the various types of MOFs, copper benzene tricarboxylate Cu-BTC or Cu 2 (BTC) 3 (also called HKUST-1 or MOF-199) 24,25 is one of the distinguished structure together with the IRMOF series. Cu-BTC was first reported in 1999 by Chui et al. 26 and has attracted considerable attention both theoretically and experimentally 27. Due to its open metal sites and large pore windows 28 , Cu-BTC has particular potential for