**2. Method**

*Nanofibers - Synthesis, Properties and Applications*

Each of these individual chains clusters into larger units, called fibrils or microfibrils, which in turn clump together and form cellulose fibers. This organization may present amorphous regions, in which fibers exhibit an undefined arrangement, or highly organized segments with fibers arranged parallel to each other. Notwithstanding other arrangements, crystalline and amorphous stretches constitute the most common fiber configurations in the polymeric structure of

The degree of polymerization (DP) of this semi-crystalline biopolymer varies according to the raw material used to obtain it and the method used for its extraction. For instance, wood pulp has a DP between 10,000 and 15,000 glycosidic units,

At nanoscale, cellulose can be obtained by chemical or physical methods or both.

while values for cellulose of bacterial origin range from 2,000 to 6,000 [4].

Cellulose nanofibrils are usually obtained by physical methods, e.g., high shear rate mechanical treatment, whereas cellulose nanocrystals are usually obtained by chemical methods, e.g., acid hydrolysis. The difference between mechanically-produced nanocellulose and chemically-produced cellulose is that the former can reach a length of up to 2 μm, while the latter, in addition to being crystalline, exhibits a

Besides its physical–chemical properties, such as low cost, biodegradability, renewability, low toxicity, and stability in organic solvents, nanocellulose exhibits a high aspect ratio and a high specific surface area. These properties combined promote its use in nanocomposites [7–9], hydrogels and aerogels [10, 11], biomedical products [12, 13], pharmaceuticals [14], environmental applications [15], and electrochemistry. In the latter case, it is used mainly in sensors [16], transistors, and

The introduction of strong electron withdrawing groups such as malononitrile groups in dyes and polymers has been reported in the literature [19, 20], and the presence of these groups leads to Intramolecular Charge Transfer (ICT), increasing

Electrochemical CO2 reduction is not only an effective way of lowering CO2 concentrations in the atmosphere, but it is also advantageous. CO2 can be effectively reduced to renewable fuels, such as ethanol, methane, and methanol, which can contribute to meeting today's growing demand for renewable energy sources [21, 22]. So, some studies on CO2 reduction catalysis have used conducting polymers as polyethylenimine (PEI) [23], and polyaniline (Pan) [24] that causes an effect of reducing catalytic overpotential and increasing current density and efficiency, besides increased

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cellulose [1].

**Figure 1.**

*Molecular structure of cellulose.*

solar cells [17, 18].

length of the order of 150 nm [5, 6].

the electron density in dicyano groups.

#### **2.1 Nanocellulose functionalization**

In a flask, 0.5 g (3.1 mmol) by mass of an aqueous dispersion of 3% w/v CNFs (SuzanoPapel & Celulose) was placed under agitation. At that point, sodium hydroxide (NaOH) solution (0.1 M; Vetec; 97%) was added by means of a pipette (dropwise) until pH 10 was reached. The mixture was left under agitation for 30 minutes. Afterwards, EMMN (1.14 g; 9.3 mmol; Sigma Aldrich; 98%) was added to the mixture and left to react at room temperature (**Figure 2**), varying the reaction time and keeping the stoichiometry at 1:3 molar ratio (nanocellulose:malononitrile). The effect of stoichiometry and temperature on the reaction efficiency was evaluated for the best experimental condition.

After the programmed reaction time, the reaction medium was placed in a sintered glass funnel (no. 4) and rinsed with acetone (Vetec; 99.5%), ethanol (Vetec; 99.5%), methanol (Vetec; 99.8%), and distilled water until neutral pH was reached. The sample was then placed in an amber glass bottle and stored in a refrigerator.

#### **2.2 Atomic force microscopy**

AFM was conducted on a Dimension ICON microscope (Bruker). The sample was prepared by dripping 5 microliters of a solution containing the CNFs on a mica surface. The mica was cleaved twice right before applying the solution dropwise onto the surface and left to dry for 1 hour at room temperature. To prevent CNFs from dragging, intermittent contact mode with a rectangular silicon probe was used (cantilever spring constant = 40 N/m; oscillation frequency = 330 kHz).

**Figure 2.** *CNF functionalization with EMMN.*
