Minfang Zhang

Microbial fuel cells (MFCs) enable simultaneous energy generation and organic waste treatment; however, their performance is often limited by inefficient electron transfer at the microbe–electrode interface. Carbon nanotubes (CNTs) have been widely investigated as anode materials owing to their high electrical conductivity and large specific surface area, yet how surface area and electrical conductivity jointly influence anode performance under thermophilic conditions remain unclear. In this study, two types of single-walled CNTs, super-growth CNTs (SG-CNTs), which possess high surface area, and enhanced direct injection pyrolytic synthesis CNTs (eDIPS-CNTs), which possess high electrical conductivity, were used to fabricate anodes individually and in controlled mixtures on stainless-steel mesh substrates. The anodes were evaluated in thermophilic MFCs inoculated with compost-derived microbial communities at 55 °C. All CNT-based anodes exhibited enhanced redox activity relative to CNT-free controls, with distinct redox features observed at −0.55 to −0.60 V vs Ag/AgCl. Notably, the SG-CNT/eDIPS-CNT anode prepared at a 1:1 (w/w) ratio delivered the highest current response and achieved approximately one order of magnitude higher relative electrical output than the CNT-free control. Gas evolution and microbial community analyses further suggest that CNT composition influences anaerobic microbial electron utilization without markedly inhibiting microbial activity. These findings highlight the importance of the nanoscale CNT-network architecture in optimizing electron transfer in thermophilic MFCs.

Carbon nanotubes (CNTs) have shown promise for biological and medical applications due to their biocompatibility, superior electrical conductivity, unique optical properties, and chemical modifiability. For instance, our research group has developed bright near-infrared imaging probe by using oxygen-doped CNTs, so far [1-3]. On the other hand, the adverse effects of CNTs on the environment and human health have recently become a concern. Since CNTs are made of stable graphite, their potential for accumulation in the environment and in living organisms has been discussed. Elucidation of the biodegradation properties of CNTs is thus an essential issue in discussing their long-term safety. In recent years, there have been several reports on the biodegradability of CNTs, but the results differ from report to report, and many details are still unknown. Under these circumstances, we used a technique to measure the amount of CNTs taken up into cells using the near-infrared absorption property of CNTs, and clarified the biodegradation of CNTs in immune cells [4]. The rate of CNT biodegradation was directly proportional to the amount of reactive oxygen species generated, indicating that the biodegradation of CNTs in immune cells was due to reactive oxygen species [5]. Furthermore, the biodegradation mechanism of CNTs is thought to involve oxidation by hypochlorous acid generated during the enzymatic reaction. When hypochlorous acid compounds were mixed with CNT dispersion, we found that the CNT dispersion easily became transparent [5]. This degradation method is applicable to single-walled carbon nanotubes, multi-walled carbon nanotubes, and even graphene [6,7]. We are currently working on international standardization activities for this method. [1] Y. Iizumi, M. Yudasaka, J. Kim, H. Sakakita, T. Takeuchi, T. Okazaki, Oxygen-doped carbon nanotubes for near-infrared fluorescent labels and imaging probes, Sci. Rep., 8, 6272 (2018). [2] T. Takeuchi, Y. Iizumi, M. Yudasaka, S. K. Kondoh, T. Okazaki, Characterization and biodistribution analysis of oxygen-doped single-walled carbon nanotubes used as in vivo fluorescence imaging probes, Bioconjugate Chem., 30, 1323−1330 (2019). (Cover Article) [3] K. Kojima, Y. Iizumi, M. Zhang, T. Okazaki, Streptavidin-conjugated oxygen-doped single-walled carbon nanotubes as near-infrared labels for immunoassays, Langmuir, 38, 1509-1513 (2022). [4] M. Yang, M. Zhang, H. Nakajima, M. Yudasaka, S. Iijima, T. Okazaki, Time-Dependent Degradation of Carbon Nanotubes Correlates with Decreased Reactive Oxygen Species Generation In Macrophages, Int. J. Nanomedicine, 14, 2797-2807 (2019). [5] M. Zhang, Y. Deng, M. Yang, H. Nakajima, M. Yudasaka, S. Iijima, T. Okazaki, A Simple Method for Removal of Carbon Nanomaterials from Wastewater Using Hypochlorite, Sci. Rep. 9, 1284 (2019). [6] M. Zhang, M. Yang, H. Nakajima, M. Yudasaka, S. Iijima, T. Okazaki, Diameter-Dependent Degradation of 11 Types of Carbon Nanotubes: Safety Implications, ACS Appl. Nano Mater., 2, 4293-4301 (2019). [7] M. Zhang, M. Yang, Y. Okigawa, T. Yamada, H. Nakajima, Y. Iizumi, T. Okazaki, Patterning of graphene using wet etching with hypochlorite and UV light, Sci. Rep., 12, 1541 (2022).

Previously, we showed that the anti-osteoclast effect of zoledronate (ZOL), a type of bisphosphonate, is enhanced when it is used as a nanocomposite comprising ZOL, an “oxidized single-walled carbon nanohorn (OxCNH) with a spherical shape” and calcium phosphate (CaP). This nanocomposite, termed OxCNH-CaP-ZOL, is a potential therapeutic agent for patients with bone fragility associated with metastatic bone cancer. Because OxCNH-CaP-ZOL contains by-products that comprise CaP–ZOL nanocomposites, the aim of this study was to prepare more sophisticated nanocomposites lacking such by-products; it was achieved by reducing the availability of calcium and phosphate ions during the preparation process. In this new nanocomposite, ZOL loading onto OxCNH was mediated by Ca, and therefore it is referred to as OxCNH-Ca-ZOL. Because the amount of ZOL in OxCNH-Ca-ZOL was about half that in OxCNH-CaP-ZOL and murine macrophages (RAW264.7 cells) took up less OxCNH-Ca-ZOL than OxCNH-CaP-ZOL, the amount of ZOL inside RAW264.7 cells exposed to OxCNH-Ca-ZOL was less than that inside cells exposed to OxCNH-CaP-ZOL. Despite this drawback, OxCNH-Ca-ZOL had suppressive effects similar to OxCNH-CaP-ZOL on the viability of RAW264.7 cells. The reason for these phenomena is not clear; however, it could be due to the differences in the ZOL release rate between OxCNH-Ca-ZOL and OxCNH-CaP-ZOL. In addition, receptor activator of nuclear factor kappa-B ligand (RANKL)-induced differentiation of RAW264.7 cells into osteoclasts was suppressed by co-administration of RANKL with OxCNH-Ca-ZOL as effectively as with OxCNH-CaP-ZOL, and indeed, their effects were greater than those of free ZOL.

Carbon nanotubes (CNTs) are increasingly being used in industrial applications, but their toxicological data in animals and humans are still sparse. To assess the toxicological dose-response of CNTs and to evaluate their pulmonary biopersistence, their quantification in tissues, especially lungs, is crucial. There are currently no reference methods or reference materials for low levels of CNTs in organic matter. Among existing analytical methods, few have been fully and properly validated. To remedy this, we undertook an inter-laboratory comparison on samples of freeze-dried pig lung, ground and doped with CNTs. Eight laboratories were enrolled to analyze 3 types of CNTs at 2 concentration levels each in this organic matrix. Associated with the different analysis techniques used (specific to each laboratory), sample preparation may or may not have involved prior digestion of the matrix, depending on the analysis technique and the material being analyzed. Overall, even challenging, laboratories' ability to quantify CNT levels in organic matter is demonstrated. However, CNT quantification is often overestimated. Trueness analysis identified effective methods, but systematic errors persisted for some. Choosing the assigned value proved complex. Indirect analysis methods, despite added steps, outperform direct methods. The study emphasizes the need for reference materials, enhanced precision, and organized comparisons.

Carbon nanotubes (CNTs) stand out for their exceptional electrical, thermal, and mechanical attributes, making them highly promising materials for cutting-edge, lightweight, and flexible thermoelectric applications. However, realizing the full potential of advanced thermoelectric CNTs requires precise management of their electrical and thermal characteristics. This study, through interface optimization, demonstrates the feasibility of reducing the thermal conductivity while preserving robust electrical conductivity in single-walled CNT films. Our findings reveal that blending two functionalized CNTs offers a versatile method of tailoring the structural and electronic properties of CNT films. Moreover, the modified interface exerts a substantial influence over thermal and electrical transfer, effectively suppressing heat dissipation and facilitating thermoelectric power generation within CNT films. As a result, we have successfully produced both p- and n-type thermoelectric CNTs, attaining impressive power factors of 507 and 171 μW/mK² at room temperature, respectively. These results provide valuable insights into the fabrication of high-performance thermoelectric CNT films.

Low toxicity in both in vitro and in vivo settings for carbon nanohorns modified with polyamidoamine was observed, and their complexation with insulin is accomplished.

While the functionalization of carbon nanotubes (CNTs) has attracted extensive interest for a wide range of applications, a facial and versatile strategy remains in demand. Here, we report a microwave-assisted, solvent-free approach to directly functionalize CNTs both in raw form and in arbitrary macroscopic assemblies. Rapid microwave irradiation was applied to generate active sites on the CNTs while not inducing excessive damage to the graphitic network, and a gas-phase deposition afforded controllable grafting for thorough or regioselective functionalization. Using methyl methacrylate (MMA) as a model functional group and a CNT sponge as a model assembly, homogeneous grafting was exhibited by the increased robust hydrophobicity (contact angle increase from 30 to 140°) and improved structural stability (compressive modulus increased by 135%). Therefore, when our MMA-functionalized CNTs served as a solar absorber for saline distillation, high operating stability with a superior water evaporation rate of ∼2.6 kg m^-2 h^-1 was observed. Finally, to highlight the efficacy and versatility of this functionalization approach, we fabricated asymmetrically hydrophobic CNT sponges by regioselective functionalization to serve as a moisture-driven generator, which demonstrated a stable open-circuit voltage of 0.6 mV. This versatile, solvent-free approach can complement conventional solution-based techniques in the design and fabrication of multifunctional nanocarbon-based materials.

In the process of bone metastasis, tumor cells spread to the bones to activate osteoclasts, which cause pathological bone resorption and destruction. Bisphosphonates (BPs) inhibit osteoclast activation to resorb bone, reducing bone pain and fracture. We previously developed a nanocomposite for potential localized treatment of bone metastasis by loading a BP compound, ibandronate, onto oxidized carbon nanohorns (OxCNHs), a next-generation drug carrier, using calcium phosphates (CaPs) as mediators to generate OxCNH-CaP-BP nanocomposites. The objective of the present study was to determine nanocomposite formation and biological properties of nanocomposites constructed from two BPs, zoledronate and pamidronate. In vitro tests using murine macrophages (RAW264.7 cells) and osteoclasts differentiated from RAW264.7 cells revealed that the resulting OxCNH-CaP-BP nanocomposites suppressed cell viability in a BP type-dependent manner and more effectively than OxCNHs or BPs alone. The mechanism for the potent and BP type-dependent suppression of cell viability by OxCNH-CaP-BP nanocomposites, based on their relative cellular uptake and reactive oxygen species generation, is also discussed. The present study supports the conclusions that BPs can be loaded onto OxCNHs using CaPs as mediators, and that OxCNH-CaP-BP nanocomposites are putative medicines for localized treatment of metastatic bone destruction.