Addressing the Trade-Off between Crystallinity and Yield in Single-Walled Carbon Nanotube Forest Synthesis Using Machine Learning.

Synthetic trade-offs exist in the synthesis of single-walled carbon nanotube (SWCNT) forests, as growing certain desired properties can often come at the expense of other desirable characteristics such as the case of crystallinity and growth efficiency. Simultaneously achieving mutually exclusive properties in the growth of SWCNT forests is a significant accomplishment, as it requires overcoming these trade-offs and balancing competing mechanisms. To address this, we trained a machine-learning regression model with a set of 585 "real" experimental synthesis data, which were taken using an automatic synthesis reactor. Subsequently, 16000 exploratory "virtual" experiments were performed by our trained model to examine potential routes toward addressing the current crystallinity-height trade-off limitation, and suggestions on growth conditions were predicted. Importantly, additional validation using "real" experimental syntheses showed good agreement with the predictions as well as a 48% increase in growth efficiency while maintaining the high crystallinity (G/D-ratio). This highlighted the effectiveness and accuracy of the predictive capability of our machine-learning model, which achieved improved results in less than 50 validation tests. Furthermore, the trained model revealed the surprising importance of the nature of the carbon feedstock, particularly the reactivity and concentration, as a route for overcoming the trade-off between the SWCNT crystallinity and growth efficiency. These results of the high-efficiency synthesis of highly crystalline SWCNT forests represent a significant advance in overcoming synthetic trade-off barriers for complex multivariable systems.

Electrolyte and Interphase Engineering of Aqueous Batteries Beyond "Water-in-Salt" Strategy.

Aqueous batteries are promising alternatives to non-aqueous lithium-ion batteries due to their safety, environmental impact, and cost-effectiveness. However, their energy density is limited by the narrow electrochemical stability window (ESW) of water. The "Water-in-salts" (WIS) strategy is an effective method to broaden the ESW by reducing the "free water" in the electrolyte, but the drawbacks (high cost, high viscosity, poor low-temperature performance, etc.) also compromise these inherent superiorities. In this review, electrolyte and interphase engineering of aqueous batteries to overcome the drawbacks of the WIS strategy are summarized, including the developments of electrolytes, electrode-electrolyte interphases, and electrodes. First, the main challenges of aqueous batteries and the problems of the WIS strategy are comprehensively introduced. Second, the electrochemical functions of various electrolyte components (e.g., additives and solvents) are summarized and compared. Gel electrolytes are also investigated as a special form of electrolyte. Third, the formation and modification of the electrolyte-induced interphase on the electrode are discussed. Specifically, the modification and contribution of electrode materials toward improving the WIS strategy are also introduced. Finally, the challenges of aqueous batteries and the prospects of electrolyte and interphase engineering beyond the WIS strategy are outlined for the practical applications of aqueous batteries.

A Microwave-Assisted, Solvent-Free Approach for the Versatile Functionalization of Carbon Nanotubes.

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.

Bacterial-based cancer therapy: An emerging toolbox for targeted drug/gene delivery.

Precise targeting and high therapeutic efficiency are the major requisites of personalized cancer treatment. However, some unique features of the tumor microenvironment (TME) such as hypoxia, low pH and elevated interstitial fluid pressure cause cancer cells resistant to most therapies. Bacteria are increasingly being considered for targeted tumor therapy owing to their intrinsic tumor tropism, high motility as well as the ability to rapidly colonize in the favorable TME. Compared to other nano-strategies using peptides, aptamers, and other biomolecules, tumor-targeting bacteria are largely unaffected by the tumor cells and microenvironment. On the contrary, the hypoxic TME is highly conducive to the growth of facultative anaerobes and obligate anaerobes. Live bacteria can be further integrated with anti-cancer drugs and nanomaterials to increase the latter's targeted delivery and accumulation in the tumors. Furthermore, anaerobic and facultatively anaerobic bacteria have also been combined with other anti-cancer therapies to enhance therapeutic effects. In this review, we have summarized the applications and advantages of using bacteria for targeted tumor therapy (Scheme 1) in order to aid in the design of novel intelligent drug delivery systems. The current challenges and future prospects of tumor-targeting bacterial nanocarriers have also been discussed.

Growth of Homogeneous High-Density Horizontal SWNT Arrays on Sapphire through a Magnesium-Assisted Catalyst Anchoring Strategy.

In-situ growth of high-density single-walled carbon nanotube (SWNT) arrays with homogeneity is highly desirable for integrated circuits. However, disastrous migration and aggregation of catalyst nanoparticles on substrate has greatly limited the area of as-grown SWNT arrays. Herein, we develop a magnesium-assisted catalyst anchoring strategy to restrain catalyst nanoparticles sintering on substrate. Magnesium modification ameliorates sapphire surface by high temperature solid reaction and thus provides a stronger metal-support interaction (SMSI). Hereby, we realize the direct growth of high-density SWNT arrays that fully cover an entire 10×10 mm2 substrate with the local highest density of ≈110 tubes µm-1 using iron as catalyst. This strategy was also proven universal when employing solid carbide catalysts.

Growth of Semiconducting Single-Walled Carbon Nanotubes Array by Precisely Inhibiting Metallic Tubes Using ZrO2 Nanoparticles.

Synthesis of high-quality single-walled carbon nanotubes arrays with pure semiconducting type is crucial for the fabrication of integrated circuits in nanoscale. However, the naturally grown carbon nanotubes usually have diverse structures and properties. Here the bicomponent catalyst using Au and ZrO2 is designed and prepared. The Au nanoparticle serves as the catalysts for carbon feedstock cracking and facilitating the nucleation of carbon nanotubes, whereas the close-connected ZrO2 forms a localized etching zone around Au by releasing lattice oxygen and to inhibit the nucleation of metallic carbon nanotubes precisely. The obtained single-walled carbon nanotubes array show a high semiconducting content of >96%, on the basis of good performance of field-effect transistor devices. And such building of localized etching zone is compatible with other catalyst systems as a universal and efficient method for the scalable production of semiconducting carbon nanotubes.

Synergistic antimicrobial effects of photodynamic antimicrobial chemotherapy and gentamicin on Staphylococcus aureus and multidrug-resistant Staphylococcus aureus.

BACKGROUND: Bacterial resistance to antibiotics is generally increasing, which has become a great challenge for treating infectious diseases caused by microbes. Photodynamic antibacterial chemotherapy (PACT) has been considered as a promising method for inactivating bacteria. The combination of antimicrobial agent with PACT may provide efficient way against drug-resistant microbe. This study aims to investigate the synergistic effects of PACT mediated by toluidine blue (TB), combined with gentamicin (GEN) on common pathogens Staphylococcus aureus (S. aureus) and multidrug-resistant S. aureus (MDR S. aureus). METHODS: Alkaline lysis was used to detect the uptake of TB by S. aureus and MDR S. aureus. Plate counting was applied to evaluate the inhibition efficiency of GEN alone, TB-PACT alone, and work together. Flow cytometry and fluorescence microscopy were performed to examine the permeability of bacterial membranes after different treatments. Intracellular and extracellular reactive oxygen species (ROS) were assessed with the assist of H2DCF-DA and SOSG probes. RESULTS: TB-PACT combined with GEN led to more pronounced antibacterial effects in S. aureus and MDR S. aureus, as compared with either alone. TB-PACT treatment permeabilized the bacterial membranes, promoted GEN cellular accumulation and augmented the antibacterial efficiency. The intracellular ROS generation by the combination of TB-PACT and GEN was much higher than that of single treatment groups. CONCLUSIONS: TB-PACT decreased the GEN cytotoxic threshold and usage, and the synergy of them significantly enhanced the sterilization of S. aureus and MDR S. aureus.

Growth of Single-Walled Carbon Nanotubes with Different Chirality on Same Solid Cobalt Catalysts at Low Temperature.

Currently, designing solid catalysts at high temperature is the main strategy to realize single-walled carbon nanotubes (SWNTs) with specific chirality, meaning it is very hard and challenging to create new catalysts or faces to fit new chirality. However, low temperatures make most catalysts solid, and developing solid catalysts at low temperature is desired to realize chirality control of SWNTs. A rational approach to grow SWNTs array with different chiralities on same solid Co catalysts at low temperature (650 °C) is herein put forward. Using solid Co catalysts, near-armchair (10, 9) tubes horizontal array with ≈75% selectivity and (12, 6) tubes array with ≈82% are realized by adopting a small amount of ethanol and large amount of CO respectively. (10, 9) tubes are enriched for thermodynamic stability and (12, 6) tubes for kinetics growth rate. Both kinds of tubes show a similar symmetry to the Co (1 1 1) face with threefold symmetry for the symmetry matching nucleation mechanism proposed earlier. This method provides a new strategy to study the nucleation mechanism and more possibilities for preparing new solid catalysts to control the structure of SWNTs.

Carburization of Fe/Ni Catalyst for Efficient Growth of Single-Walled Carbon Nanotubes.

Scale-up production of single-walled carbon nanotubes (SWNTs) with high quality and purity is in pursuit, since the subsequent post purification treatment of residual metal or amorphous carbon is complicated and restricts further applications. Here, a compatible method to efficiently synthesize pure SWNTs on various supporters by using the precarburized Fe/Ni catalysts is reported. The preparation of catalysts is achieved by gas phase deposition together with CO gas at proper temperature, and the carburization of metal particles occurring simultaneously contributes to the size limitation of catalysts. By using micro-quartz sand as a recyclable supporter, high-quality SWNTs with a yield of 50 mg h-1 are prepared with 60% metal precursor utilization, 81% carbon source utilization, and only 0.12% (m/m) metal residues. Taking advantage of carburized Fe/Ni catalysts and appropriate supports makes it possible to balance the quantity, purity, and quality among SWNTs growth. Furthermore, this method provides a straightforward pathway to strongly combine SWNTs and diverse composite materials for further potential applications.

Microwave-Assisted Regeneration of Single-Walled Carbon Nanotubes from Carbon Fragments.

Direct growth of chirality-controlled single-walled carbon nanotubes (SWNTs) with metal catalyst free strategy, like cloning or epitaxial growth, has suffered from the low efficiency. The underlying problem is the activation of seed edge. Here an unexpectedly efficient microwave-assisted pathway to regenerate SWNTs from carbon fragments on SiO2 /Si substrate is demonstrated via Raman spectroscopy and atomic force microscope (AFM) characterization. In this attempt, microwave irradiation provides fast heating to remove polar groups bonded to carbon nanotubes and reduce the spontaneous closure of tubes' open ends. The survived SWNT and carbon fragments connected to it after plasma treatment are simply microwaved and then they serve as the template for regeneration. Scanning electron microscope and AFM characterizations indicate that the efficiency of the regeneration can reach 100%. And the regenerated SWNT has been proved without any change in chirality compared to the original SWNT. Electrical measurements on regenerated carbon nanotube films indicate 1 and 2 times increase in on/off ratio and on-state current respectively than original carbon nanotube films obtained from solution-phase separation, confirming the improvement of SWNT's quality. The microwave-assisted regeneration is found to be highly effective and would be applied to improve the cloning efficiency of carbon nanotubes potentially.