Pt-grafted, hierarchical mesoporous carbon nanofibers (Pt/MPCNFs) electrocatalysts have been developed using electrospinning for high-performance PEM fuel cells. The morphological analysis of Pt/MPCNFs revealed uniformly dispersed Pt nanoparticles (2–3 nm) strongly grafted onto the hierarchical nanochannels of mesoporous carbon nanofibers (MPCNFs). Pyridinic and pyrrolic nitrogen species formed in the sp² graphitic structure during the carbonization process of the MPCNFs have been found to play a major role in augmentation of the triple phase boundaries in the catalyst support materials. Pt/MPCNFs exhibited outstanding electrocatalytic performance towards the oxygen reduction reaction (ORR) with a positively shifted onset potential (54 mV), half-wave potential (78 mV) and high limiting current density (4.75 mA cm⁻² at 0.4 V) compared to state-of-the-art Pt/C electrocatalysts in acidic medium and they exhibited superior long-term stability (89.8% retention after 30 000 s and less change in activity after 10 000 potential sweeps). Pt/MPCNFs as a cathode catalyst yielded a maximum power density of 428.6 mW cm⁻² during single cell testing, which is 2.08 times higher than a commercial Pt/C electrocatalyst. The electrochemical performance evaluation clearly implied that the unique combination of ultrathin nanofibers with a three-dimensional mesoporous structure, high electrical conductivity, enhanced specific surface area, homogeneous dispersion of Pt nanocatalysts and the presence of optimal nitrogen doping offers superior electrocatalytic activity via a favorable four-electron pathway and long-term operating stability during repeated cycles. Performance analysis in a single PEM fuel cell shows twice the power density (428 mW cm⁻²) with Pt/MPCNFs compared to commercial electrocatalyst membranes due to the effective enhancement in the triple phase boundaries, indicating that Pt/MPCNFs are potential candidates for high-performance, durable PEMFCs.

Immobilizing enzymes onto nanomaterials is a promising approach for increasing the efficiency of industrial biotransformation processes. Nanomaterials have large surface areas and unique physicochemical characteristics, they increase enzyme stability and catalytic efficiency, and they can be reused multiple times, making them favorable over free enzymes. Various nanomaterials, including carbon-based materials, metal and metal oxide nanoparticles, and polymeric nanoparticles, have been explored for immobilizing enzymes. Immobilized enzymes are more reusable than free enzymes, which are suitable for industrial applications such as in pharmaceuticals, as drug intermediates, and for synthesizing fine chemicals. Using immobilized enzymes multiple times enables numerous catalytic reactions, substantially increasing product yield and minimizing enzyme consumption, thus optimizing process efficiency and cost-effectiveness of manufacturing processes. This review explores recent developments in nanomaterials for immobilizing enzymes and biotransformation.

In the present investigation, an ecofriendly magnetic inorganic-protein hybrid system-based enzyme immobilization was developed using partially purified laccase from Trametes versicolor (TvLac), Fe₃O₄ nanoparticles, and manganese (Mn), and was successfully applied for synthetic dye decolorization in the presence of enzyme inhibitors. After the partial purification of crude TvLac, the specific enzyme activity reached 212 U∙mg total protein⁻¹. The synthesized Fe₃O₄/Mn₃(PO₄)₂-laccase (Fe₃O₄/Mn-TvLac) and Mn₃(PO₄)₂-laccase (Mn-TvLac) nanoflowers (NFs) exhibited encapsulation yields of 85.5% and 90.3%, respectively, with relative activities of 245% and 260%, respectively, compared with those of free TvLac. One-pot synthesized Fe₃O₄/Mn-TvLac exhibited significant improvements in catalytic properties and stability compared to those of the free enzyme. Fe₃O₄/Mn-TvLac retained a significantly higher residual activity of 96.8% over that of Mn-TvLac (47.1%) after 10 reuse cycles. The NFs showed potential for the efficient decolorization of synthetic dyes in the presence of enzyme inhibitors. For up to five reuse cycles, Fe₃O₄/Mn-TvLac retained a decolorization potential of 81.1% and 86.3% for Coomassie Brilliant Blue R-250 and xylene cyanol, respectively. The synthesized Fe₃O₄/Mn-TvLac showed a lower acute toxicity towards Vibrio fischeri than pure Fe₃O₄ nanoparticles did. This is the first report of the one-pot synthesis of biofriendly magnetic protein-inorganic hybrids using partially purified TvLac and Mn.

The total rate of plastic production is anticipated to surpass 1.1 billion tons per year by 2050. Plastic waste is non-biodegradable and accumulates in natural ecosystems. In 2020, the total amount of plastic waste was estimated to be 367 million metric tons, leading to unmanageable waste disposal and environmental pollution issues. Plastics are produced from petroleum and natural gases. Given the limited fossil fuel reserves and the need to circumvent pollution problems, the focus has shifted to biodegradable biopolymers, such as polyhydroxyalkanoates (PHAs), polylactic acid, and polycaprolactone. PHAs are gaining importance because diverse bacteria can produce them as intracellular inclusion bodies using biowastes as feed. A critical component in PHA production is the downstream processing procedures of recovery and purification. In this review, different bioengineering approaches targeted at modifying the cell morphology and synchronizing cell lysis with the biosynthetic cycle are presented for product separation and extraction. Complementing genetic engineering strategies with conventional downstream processes, these approaches are expected to produce PHA sustainably.

Multi-enzymatic strategies have shown improvement in bioconversion during cofactor regeneration. In this study, purified l-arabinitol 4-dehydrogenase (LAD) and nicotinamide adenine dinucleotide oxidase (Nox) were immobilized via individual, mixed, and sequential co-immobilization approaches on magnetic nanoparticles, and were evaluated to enhance the conversion of l-arabinitol to l-xylulose. Initially, the immobilization of LAD or Nox on the nanoparticles resulted in a maximum immobilization yield and relative activity of 91.4% and 98.8%, respectively. The immobilized enzymes showed better pH and temperature profiles than the corresponding free enzymes. Furthermore, co-immobilization of these enzymes via mixed and sequential methods resulted in high loadings of 114 and 122 mg/g of support, respectively. Sequential co-immobilization of these enzymes proved more beneficial for higher conversion than mixed co-immobilization because of better retaining Nox residual activity. Sequentially co-immobilized enzymes showed a high relative conversion yield with broader pH, temperature, and storage stability profiles than the controls, along with high reusability. To the best of our knowledge, this is the first report on the mixed or sequential co-immobilization of LAD and Nox on magnetic nanoparticles for l-xylulose production. This finding suggests that selecting a sequential co-immobilization strategy is more beneficial than using individual or mixed co-immobilized enzymes on magnetic nanoparticles for enhancing conversion applications.