Developing sorbent materials for the removal of oil spills has become an attractive research topic in recent years for its impact on environmental and ecological concerns. The sorbents should be light, low cost, oil selective, environmentally friendly, mechanically robust, easily collected, and recyclable, besides having high absorption capacities. Here, magnetic carbon nanofiber (MCF) aerogels have been developed from bacterial cellulose-based nanocomposites as efficient and recyclable oil sorbents. The MCF aerogels comprise a three-dimensional (3D) interconnected structure of carbon nanofibers, with very high porosity, decorated with uniformly dispersed magnetic nanoparticles (NPs), with an Fe/Fe 3 O 4 core− shell structure. The MCF aerogels exhibit very high magnetization (>100 emu g −1 ), compared to other previously reported magnetic aerogels, due to the Fe core/Fe 3 O 4 shell NPs, but additionally with an ultralow density of only ∼7 mg cm −3 . Furthermore, the MCF aerogel is highly compressible up to 90% strain and instantly returns to the original shape after release without any plastic deformation. It is also highly durable, up to 100 compressive stress−strain cycles. As for oil sorbents, the MCF aerogel can absorb oils directly without any postsurface treatment, due to its hydrophobic/oleophilic property. The absorption capacities are in the range of 37−87 g g −1 for various types of oils and organic solvents. These values are comparably large among magnetic carbon aerogels. Additionally, due to their large magnetization, the MCF aerogels can be easily manipulated during oil absorption and collected via external magnetic fields, which is beneficial for avoiding direct contact with possible hazardous solvents. They can then be recycled several times by dissolution with hardly any reduction in absorption capacity. This work has demonstrated that environmentally friendly biomass-derived MCF aerogels could be candidates for the absorption and recycling of oils and organic solvents from wastewater.

In this research, a flexible thermoelectric (TE) paper was fabricated from bacterial cellulose/silver selenide (BC/Ag2Se) nanocomposites. Ag2Se particles were in situ synthesized in the network of BC nanofibers. Several synthesis parameters that crucially affect the formation of Ag2Se particles in the BC structure were investigated to understand the phase formation mechanism. Under the optimized conditions, the BC/Ag2Se paper with a large proportion of Ag2Se up to 75 wt % was successfully obtained. The in situ synthesis limits the Ag2Se formation within the nanopores of the BC structure. As a result, the submicrosize Ag2Se particles with a narrow size distribution were homogeneously dispersed in the BC nanofiber network. The microstructure was further improved by hot-pressing, which increases the density of the BC/Ag2Se paper and makes the BC layered structure more compact. These contributed to a significant enhancement of the TE properties, with the electrical conductivity of 23,000 S/m and the Seebeck coefficient of −167 μV/K at 400 K. The power factor was 642 μW/mK2 at 400 K, a very high value compared to other flexible TE research. The measurement of thermal conductivity yielded the κ value of 0.36 W/mK at 400 K, which led to the maximum ZT of 0.70 at 400 K. To demonstrate the TE conversion, five BC/Ag2Se paper pieces were connected in series to construct a TE module. The module is very flexible and can be curved to attach to any arbitrary shape of the hot/cold surfaces. In addition, the process for fabricating the BC/Ag2Se paper is scalable without any use of advanced or expensive instruments. This makes it a very attractive choice as a flexible TE generator.

Flexible thermoelectric (FTE) devices have become attractive in recent years since they can be utilized as a power generator for wearable and portable electronics. This work fabricated FTE nanocomposites from bacterial cellulose (BC) and Ag2Se via an easy and inexpensive method. The blended BC was thoroughly mixed with Ag2Se powders before casting onto a filter paper via vacuum filtration, followed by oven-drying and hot-pressing. Phase formation of Ag2Se in the BC nanofiber network was confirmed by x-ray diffraction and energy dispersive spectroscopy. SEM images revealed the distribution of Ag2Se particles in the BC matrix. The Ag2Se particles were densely packed for large Ag2Se concentrations in the BC/Ag2Se nanocomposite. Thermoelectric measurements found that the electrical conductivity (σ) and Seebeck coefficient (S) varied with the Ag2Se proportion due to the changes in the carrier concentration and carrier mobility. The maximum σ of 5.7 × 104 S/m and S of −80 μV/K were observed at room temperature (RT), yielding the power factor (PF) of ∼300 μW/mK2. This PF value is comparable to other FTE materials, but the process used in this research is much simpler. The thermal conductivity was 0.56 W/mK at RT. Moreover, the BC/Ag2Se nanocomposites were highly flexible and could be attached to curved surfaces. In addition, the FTE module was constructed from BC/Ag2Se uni-leg elements, which could generate an output power of 0.28 μW. In addition, the simple fabrication process makes the BC/Ag2Se nanocomposite readily expandable to an industrial scale for modern FTE devices.

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