Hollow carbon spheres derived from self-assembled chitosan/poly(γ-glutamic acid) nanoparticles for oil-in-water emulsion separation

With the rapid science and technology advancement, the oil-water separation in oily wastewater has become an urgent problem, especially the emulsified oil-water mixtures. Hollow carbon spheres (HCSs) have tremendous potential in separating oil-water emulsions due to their rich porous channels and high surface-to-volume ratio. In this work, as-prepared chitosan/poly(γ-glutamic acid) nanoparticles crosslinked by Ni2+ (Ni2+/CS/γ-PGA NPs) were used as carbon precursor to fabricate HCSs. This strategy separated the formation process of the biomolecular microspheres and the carbonization process. Especially, the Ni2+/CS/γ-PGA NPs were fabricated from the self-assembly of chitosan and γ-PGA in aqueous solution and the crosslinking of Ni2+ via the electrostatic interactions, facilitating the formation of biomolecular microspheres and making the usable of biomolecule-based carbon precursors diversity. After lyophilization, Ni2+/CS/γ-PGA NPs powder was obtained, which was then carbonized in a tube furnace under N2 atmosphere. During the carbonization process, the nickel species aggregated together to form the core of nickel@carbon nanoparticles, and carbon formed the shell. At last, nickel nanoparticles were removed from the carbon framework by hydrochloric acid, obtaining HCSs with super-hydrophobicity and lipophilicity. The as-prepared HCSs exhibited excellent separation performance in oil-in-water emulsions.

Confined synthesis of ternary FeCoMn single-atom nanozyme in N-doped hollow mesoporous carbon nanospheres for synergistic chemotherapy and chemodynamic cancer therapy

Recently, nanozymes show increasing biological applications and promising possibilities for therapeutic intervention, while their mediated therapeutic outcomes are severely compromised due to their insufficient catalytic activity and specificity. Herein, ternary FeCoMn single atoms were incorporated into N-doped hollow mesoporous carbon nanospheres by in situ confinement pyrolysis at 800 °C as high-efficiency nanozyme. The confinement strategy endows the as-prepared nanozyme with the enhanced catalase- and oxidase-like activities. Specifically, the FeCoMn TSAs/N-HCSs nanozyme can decompose intracellular H2O2 to generate O2 and subsequently convert O2 to cytotoxic superoxide radicals (O2∙-), which can initiate cascade enzymatic reactions in tumor microenvironment (TME) for chemodynamic therapy (CDT). Moreover, the cancer therapy was largely enhanced by loading with doxorubicin (DOX). Impressively, the FeCoMn TSAs/N-HCSs nanozyme-mediated CDT and the DOX-induced chemotherapy endow the DOX@FeCoMn TSAs/N-HCSs with effective tumor inhibition, showing the superior therapeutic efficacy.

Hollow nitrogen-doped carbon nanospheres as cathode catalysts to enhance oxygen reduction reaction in microbial fuel cells treating wastewater

Hollow nanospheres play a pivotal role in the electro-catalytic oxygen reduction reaction (ORR), which is a crucial step in microbial fuel cell (MFC) device. Herein, the hollow nitrogen-doped carbon nanospheres (HNCNS) were synthesized with the sacrifice of silica coated carbon nanospheres (CNS@SiO₂) as template. HNCNS remarkably enhanced the ORR activity compared to the solid carbon and solid silica spheres. By tuning calcination temperature (800-1100 °C), the surface chemistry properties of HNCNS were effectively regulated. The optimal HNCNS-1000 catalyst which was calcined at 1000 °C exhibited the highest ORR activity in neutral media with the onset potential of 0.255 V and half-wave potential of -0.006 V (vs. Ag/AgCl). Single chamber MFC (SCMFC) assembled with HNCNS-1000 cathode unveiled comparable activity to a conventional Pt/C reference. It showed the highest maximum power density of 1307 ± 26 mW/m², excellent output stability of 5.8% decline within 680 h, chemical oxygen demand (COD) removal of 94.0 ± 0.3% and coulombic efficiency (CE) of 7.9 ± 0.9%. These excellent results were attributed to a cooperative effect of the optimized surface properties (e.g., structural defects, relative content of pyrrolic nitrogen and specific surface area) and the formation of hollow nanosphere structure. Furthermore, the positive linear relationship of the structural defects and pyrrolic nitrogen species with the maximum power generation in SCMFC were clearly elucidated. This study demonstrated that the cost effective HNCNS-1000 was a promising alternative to commercial Pt/C catalyst for practical application in MFCs treating wastewater. Our result revealed the effectiveness of MFC fabricated with HNCNS-1000 cathode catalyst in terms of power generation and wastewater treatment.

Preparation of nitrogen-doped hollow carbon nanosphere/graphene composite aerogel for efficient removal of quinoline from wastewater

The deep removal of quinoline from coking wastewater is a prerequisite for reducing its potential threat to environmental safety. Therefore, it is urgent to develop advanced materials for efficient removal of quinoline in wastewater. In this work, a nitrogen-doped hollow carbon nanosphere/graphene composite aerogel (HCNS/NGA) was prepared by in-situ reduction self-assembly strategy, in which HCNS prevents the agglomeration of graphene oxide (GO) nanosheets, and a special sphere-sheet mutual support structure is formed to ensure the structural stability. As-prepared HCNS/NGA exhibits large specific surface area, hierarchical pore structure, and excellent conductivity. Large cavity inside and hierarchically porous structure that primarily consists of micropores, resulting in high quinoline adsorption performance (138.37 ± 2.58 mg g^-1 at 298 K). Furthermore, in a fixed-bed column adsorption system, the partition coefficient at 10% breakthrough reaches up to 35.19 mg g^-1 μM^-1. More importantly, HCNS/NGA, as a conductive monolithic sorbent, can realize easy solid-liquid separation, as well as efficient regeneration in situ by electrochemically assisted regeneration. After ten regeneration cycles, the adsorption capacity retention is 91.54%. In short, as an efficient adsorbent, HCNS/NGA has an enormous application potential in wastewater treatment.

NIR-II-activated biocompatible hollow nanocarbons for cancer photothermal therapy

Photothermal therapy has attracted extensive attentions in cancer treatment due to its precise spatial-temporal controllability, minimal invasiveness, and negligible side effects. However, two major deficiencies, unsatisfactory heat conversion efficiency and limited tissue penetration depth, hugely impeded its clinical application. In this work, hollow carbon nanosphere modified with polyethylene glycol-graft-polyethylenimine (HPP) was elaborately synthesized. The synthesized HPP owns outstanding physical properties as a photothermal agent, such as uniform core-shell structure, good biocompatibility and excellent heat conversion efficiency. Upon NIR-II laser irradiation, the intracellular HPP shows excellent photothermal activity towards cancer cell killing. In addition, depending on the large internal cavity of HPP, the extended biomedical application as drug carrier was also demonstrated. In general, the synthesized HPP holds a great potential in NIR-II laser-activated cancer photothermal therapy.

Cu2+-modified hollow carbon nanospheres: an unusual nanozyme with enhanced peroxidase-like activity

A Cu²⁺-modified carboxylated hollow carbon nanospheres (Cu²⁺-HCNSs-COOH) was designed with enhanced peroxidase-like activity for the detection of hydrogen peroxide (H₂O₂) and degradation of methylene blue (MB). Hollow polymer nanospheres were fabricated from aniline, pyrrole, Triton-100, and ammonium persulfate via confined interfacial copolymerization reaction, which can be pyrolyzed to create HCNSs with the hollow gap diameter of about 20 nm under high temperature. Combining the synergistic effect of coordination and electrostatic interaction, Cu²⁺-HCNSs-COOH was constructed by anchoring Cu²⁺ on the surface of HCNSs-COOH. Furthermore, Cu²⁺-HCNSs-COOH has higher affinity for 3,3',5,5'-tetramethylbenzidine and H₂O₂ of 0.20 mM and 0.88 mM, respectively. Based on the rapid response of Cu²⁺-HCNSs-COOH to H₂O₂, we constructed a colorimetric sensing platform by detecting the absorbance of the 3,3',5,5'-tetramethylbenzidine-H₂O₂ system at 652 nm for quantifying H₂O₂, which holds good linear relationship between 1 and 150 μM and has a detection limit of 0.61 μM. We also investigated the degradation of MB in the presence of Cu²⁺-HCNSs-COOH and H₂O₂, which can degrade 80.7% pollutants within 30 min. This research developed an unusual nanozyme for bioassays and water pollution treatment, which broadened the way for the rapid development of clinical diagnostics and water pollution treatment.

Nanohollow Carbon for Rechargeable Batteries: Ongoing Progresses and Challenges

Among the various morphologies of carbon-based materials, hollow carbon nanostructures are of particular interest for energy storage. They have been widely investigated as electrode materials in different types of rechargeable batteries, owing to their high surface areas in association with the high surface-to-volume ratios, controllable pores and pore size distribution, high electrical conductivity, and excellent chemical and mechanical stability, which are beneficial for providing active sites, accelerating electrons/ions transfer, interacting with electrolytes, and giving rise to high specific capacity, rate capability, cycling ability, and overall electrochemical performance. In this overview, we look into the ongoing progresses that are being made with the nanohollow carbon materials, including nanospheres, nanopolyhedrons, and nanofibers, in relation to their applications in the main types of rechargeable batteries. The design and synthesis strategies for them and their electrochemical performance in rechargeable batteries, including lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, and lithium-sulfur batteries are comprehensively reviewed and discussed, together with the challenges being faced and perspectives for them.

Interface-mediated fabrication of bowl-like and deflated ballon-like hollow carbon nanospheres

In our work, two kinds of hollow carbon nanospheres with controlled morphologies have been successfully prepared from low-cost and nontoxic glucose as the sole carbon precursor under neutral aqueous medium via a simple hydrothermal route. During the process, sodium dodecylbenzene sulfonate (SDBS) and triblock copolymer P123 ((EO)20(PO)70(EO)20) was skillfully selected as the structure-directing agent, respectively. SEM, TEM and AFM results revealed that the two products showed bowl-like and deflated-balloon-like morphology with uniform particle sizes, respectively. Based on the experimental observations, a possible formation mechanism was also discussed, in which the growth of the carbon nanospheres involved an interface-medicated assembly process. The present method was easy, green and mild. Apart from the unique nanostructure, the obtained bowl-like hollow carbon nanospheres exhibited excellent biocompatibility. In particular, it should be mentioned that the open window formed by the bowl-like morphology can facilitate ion transport, thus improving their performances.