Carbon nanotubes

Carbon nanotubes and sodium dodecyl sulfate were obtained from Sigma–Aldrich (Saint Louis, MO, USA). The source of cellulose is a type of bacterial cellulose (BC) hydrogel. BC will degrade naturally in pH 5 and must be filtered and washed with deionized water before being used. The weight-average degree of polymerization (DPw) of bacterial cellulose remained in the range of 14,000 of 16,000 during cultivation at pH 4, but at pH 5, the DPw decreased from 16,800 to 11,000. Figure 1 shows the fresh BC and degraded BC. Sodium bromide was purchased from SYSTERM.

A mixture of sulfur powder (Sigma-Aldrich), Li₁₀GeP₂S₁₂ (MSE supplies), and carbon nanotubes (Sigma-Aldrich) with a weight ratio of 36:40:24 was transferred into a 50 mL agate ball-milling jar filled with 40 g of 5 mm zirconia balls under an Ar atmosphere (H₂O < 0.1 ppm, O₂ < 0.1 ppm). The mixture was ball-milled using a high-speed ball-milling machine at 200 rpm for 4 h. The same procedure was used to prepare the LiI-incorporated S composite electrodes.

Carbon nanotubes (Sigma-Aldrich) were shortened and carboxylated by heating in acid to yield highly functionalized nanotubes. Oxidized CNTs were reacted with fluorescein-5-thiosemicarbazide (FC) (1 mg/ml) and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) for 2 h at room temperature (RT). The mixture was filtered with a molecular weight cut-off of 100,000. The residue was washed with PBS several times and then collected and dispersed in PBS by sonication to make a suspension of CNT–FC of 0.25 mg/ml.

All of the carbon materials
were used as purchased without further purification. Activated carbon,
carbon nanofibers, and carbon nanotubes (multi-walled) were purchased
from Sigma-Aldrich, and carbon black was purchased from Alfa Aesar.
The iron catalyst supported by silicon carbide was prepared by
an incipient wetness impregnation method. The iron nitrate Fe(NO₃)₃·9H₂O (iron(III) nitrate nonahydrate,
Sigma-Aldrich) was used as the metal precursor, and SiC (silicon carbide,
Fisher Scientific) was used as the supporting material. A certain
amount of iron nitrate was dissolved in distilled water to prepare
an aqueous solution, the concentration of which was calculated to
produce a desired Fe loading (in this study, a 5 wt % Fe loading was
applied). SiC powder was then added to the solution and mixture stirred
at 150 °C for 3 h. The formed slurry was then moved into the
drying oven and left overnight. A mortar was used to grind the dried
bulk into a powder, which was calcined in a furnace at 350 °C
for 3 h. Finally, the active Fe/SiC catalyst was obtained by reducing
in 10% H₂/Ar gases at 800 °C for 6 h.^{27 (link),39 (link)}

Saccharomyces cerevisiae 21PMR (MAT leu2 ura3-52) was used throughout the conducted experiments. D-glucose powder, yeast extract, peptone powder, and carbon nanotubes were obtained from Sigma-Aldrich (Steinheim, Germany). Double distilled water has been used throughout the experimental work. All other essential reagents and chemicals used in the study were of analytical grade.
For biofuel cell, dried yeast was purchased from a food supplier “Dr. Oetker Lietuva” (Vilnius, Lithuania). 1 g of YPD-broth was mixed with 20 mL distilled water to get medium with YPD-broth 50 g/L concentration. 500 mg of dried yeast was introduced to prepared suspension. A further culture was grown in shaking incubator at 200 rpm till yeast reaches Logarithmic Phase (20–24 h).