Chiral Polymer Dots Show Unexpected Versatility of Highly Ordered Self-Assembly into Chiroptical Liquid Crystals, Ultra-Thin Films, and Long-Ribbons.

Compared to the organic counterparts, chiral self-assembly of nanomaterials shows persistency to kinetic factors such as solvent environments, and consequently, dynamic modulation of self-assembly and functions remains major challenge. Here, it is shown that alkylated, chiral polymer dots (c-PDs) give highly ordered self-assemblies with amplified chirality adaptive to solvent environments, and one-to-many hierarchical aggregation can be realized. The c-PDs tended to self-assemble into nanohelices with cubic packing in the solid state, which, thanks to the thermo-responsiveness, transformed into thermic liquid crystals upon heating. Cotton effects and circularly polarized luminescence evidenced the chirality transfer from central chirality to supramolecular chirality. At the air-water interface, the c-PDs are self-assembled into monolayers, which further stack into multiple layers with chirality transfer and highly ordered packing. In addition, undergoing a good/poor solvent exchange, the c-PDs afforded ultra-long microribbons up to a length scale of millimeters, which are constituted by the bilayer lamellar stacking. The versatile chiral self-assembly modalities with long-range ordered packing arrays of carbonized c-PDs via solvent strategy are realized. This feature is comparable to the organic species, although the c-PDs have no atomic precise structures. This work would surely expand the applications of quantum dot ordered self-assembly with adaptiveness to kinetic factors.

Carbon Dot-Based Hydrogels: Preparations, Properties, and Applications.

Hydrogels have extremely high moisture content, which makes it very soft and excellently biocompatible. They have become an important soft material and have a wide range of applications in various fields such as biomedicine, bionic smart material, and electrochemistry. Carbon dot (CD)-based hydrogels are based on carbon dots (CDs) and auxiliary substances, forming a gel material with comprehensive properties of individual components. CDs embedding in hydrogels could not only solve their aggregation-caused quenching (ACQ) effect, but also manipulate the properties of hydrogels and even bring some novel properties, achieving a win-win situation. In this review, the preparation methods, formation mechanism, and properties of CD-based hydrogels, and their applications in biomedicine, sensing, adsorption, energy storage, and catalysis -are summarized. Finally, a brief discussion on future research directions of CD-based hydrogels will be given.

Self-Assembly of Cholesteryl Carbon Dots with Circularly Polarized Luminescence in Solution and Solvent-Free Phases.

Incorporating carbon dots (CDs) into chiral self-assemblies will endow the system with intriguing optoelectronic, catalytic, and chiroptical activities. Utilization of chiral substituents to rationally manipulate chiral self-assembly of the CDs, however, remains a major challenge. In this work, cholesteryl monoprotected ethylene diamine was used as a precursor to synthesize CDs with a cholesteryl periphery. The rigid, apolar, and chiral cholesteryl facilitates the polarity-sensitive self-assembly of CDs in organic solvents, showing circularly polarized luminescence (CPL) with dissymmetry g-factor at 10-3 grade. Temperature-variable characterizations suggested the formation of thermotropic liquid crystals within a wide temperature range driven by the interdigitation of cholesteryl segments, which further anchor the graphitic CD cores into tetragonal and cubic arrays. Self-assembly in a solvent-free state arouses sufficient chirality transfer and boosted the g-factors to 10-2 order of magnitude. This work unveils multiple and chiral self-assembly of CDs controlled by the cholesteryl substituents, exhibiting variable architectures and tunable CPL.

Supramolecular structures from structurally persistent and surface active carbon dots in water.

Carbon dots (CDs) have developed into an important class of nanomaterials that have attracted increasing attention during the past decades. Despite numerous types of CDs reported to date, research on their self-assembly is still limited. Herein, we report for the first time the self-assembly of CDs in water, which show concentration-dependent aggregation behavior. The CDs used have a structural motif of a fully carbonized core surrounded by a highly condensed, polymeric network, to which triethylene glycol monomethyl ether (TGME) chains are grafted. When dissolved in water, they show a low critical aggregation concentration (cac) of 0.07 mg mL-1 with the lowest surface tension of ∼37 mN m-1. Above this cac, nanoclusters and vesicles are observed at relatively low and high concentrations, respectively. At an intermediate concentration, polymorphism is noticed where nanotubes coexist with nanorods. At an elevated temperature, the CDs become more hydrophobic due to the dehydration of peripheral TGME, which decreases the cac and triggers phase transfer from water to toluene. These surface active CDs were used to disperse and stabilize multi-walled carbon nanotubes in water, which showed much better performance than that of both traditional ionic and nonionic surfactants. Our work indicates that with a careful structural design, CDs can be developed into a new type of amphiphiles with properties superior to those of traditional surfactants in specific aspects.

Photoluminescent, Ferromagnetic, and Hydrophobic Sponges for Oil-Water Separation.

To find a facile way to produce a hydrophobic sponge that can effectively absorb oils is urgent to resolve the environmental pollution and ecological disaster caused by oil spillage. Here, alkylated carbon dots (C dots) were prepared from pyrolysis of a mixture of dodecylamine and citric acid followed by purification through silica gel column chromatography. Polyurethane sponge was modified by alkylated C dots by a simple dip-coating method, which endows the photoluminescent and hydrophobic sponge with good absorption capacities for various oils and nonpolar organic solvents with high recyclability. The water contact angle of the modified sponge can reach 138.8°. Interestingly, the sponge enables visual absorption under UV irradiation in the dark, which has not been achieved by other carbon-based adsorbents. The sponge was further made ferromagnetic by introducing alkylated Fe3O4 nanoparticles into its structure, which allowed controllable oil-water separation.

Magnetic and Biocompatible Fullerenol/Fe(III) Microcapsules with Antioxidant Activities.

Fullerene C60 (refers to C60 hereafter) has a unique three-dimensional architecture and intriguing physicochemical properties. It has great potential applications in materials chemistry and life science. However, a big obstacle for the widespread application of C60 lies in the limited strategies to make supramolecular structures with diverse morphologies and functions. Herein, we report a strategy to prepare C60-based, magnetic microcapsules which can be used as external antioxidants to effectively attenuate oxidative stress. The microcapsules are composed of fullerenol, a highly water-soluble C60 multiadduct, and iron ions (Fe3+) released from a rusty nail. They can be easily obtained through coordination between the hydrophilic functional groups in fullerenol and Fe3+ with polystyrene microspheres as templates. The fullerenol/Fe3+ microcapsules have good colloidal stability both in water and serum. Their biocompatibility has been confirmed by in vitro tests on HEK293 and Hela cells. Electron spin resonance measurements indicate that the fullerenol/Fe3+ microcapsules can effectively scavenge hydroxyl radicals (OH·-) produced by H2O2, which greatly improves the living environment of the cells. The fullerenol/Fe3+ microcapsules exhibit ferromagnetic properties and can respond to the external magnetic field, enabling magnetic manipulation, and/or separation in practical applications.

Fullerene-Directed Synthesis of Flowerlike Cu3(PO4)2 Crystals for Efficient Photocatalytic Degradation of Dyes.

Biomineralization is a typical methodology developed by nature to produce calcium-based materials. A method mimicking this process has nowadays become popular for the preparation of artificial organic-inorganic hybrids. Here, Cu3(PO4)2 crystals with a flowerlike morphology have been prepared using water-soluble derivatives of fullerene C60 as templates. In a typical system, flowerlike crystals of Cu3(PO4)2 (denoted FLCs-Cu) were obtained by simply dropping an aqueous solution of CuSO4 into phosphate-buffered saline (PBS) containing a highly water-soluble multiadduct of C60 (fullerenol). The best condition for the preparation of FLCs-Cu appeared at 0.20 mg·mL-1 fullerenol and 0.10 mol·L-1 PBS. During the formation of FLCs-Cu, fullerenol acts as a template and its content in FLCs-Cu is trace (less than 5% by atom) as confirmed by scanning electron microscopy mapping and thermogravimetric analysis. This feature makes fullerenol reusable, and the FLCs-Cu can be prepared repeatedly using the same fullerenol aqueous solution at least 10 times without a noticeable change in the morphology. The N2 adsorption/desorption isotherm showed that the doping of fullerenol increased the specific surface area of the Cu3(PO4)2 crystal. When fullerenol was replaced by C60 monoadducts that are cofunctionalized with a pyrrolidine cation and oligo(poly(ethylene oxide)) chains, FLCs-Cu can form as well, indicating that the strategy of using water-soluble C60 derivative as a template to get FLCs-Cu is universal. As a typical example of practical applications, the photocatalytic activity of the FLCs-Cu was investigated toward the degradation of dyes including rhodamine B and rhodamine 6G. In both cases, efficient photodegradation has been confirmed.

Improving the Power Conversion Efficiency of Carbon Quantum Dot-Sensitized Solar Cells by Growing the Dots on a TiO2 Photoanode In Situ.

Dye-sensitized solar cells (DSSCs) are highly promising since they can potentially solve global energy issues. The development of new photosensitizers is the key to fully realizing perspectives proposed to DSSCs. Being cheap and nontoxic, carbon quantum dots (CQDs) have emerged as attractive candidates for this purpose. However, current methodologies to build up CQD-sensitized solar cells (CQDSCs) result in an imperfect apparatus with extremely low power conversion efficiencies (PCEs). Herein, we present a simple strategy of growing carbon quantum dots (CQDs) onto TiO2 surfaces in situ. The CQDs/TiO2 hybridized photoanode was then used to construct solar cell with an improved PCE of 0.87%, which is higher than all of the reported CQDSCs adopting the simple post-adsorption method. This result indicates that an in situ growing strategy has great advantages in terms of optimizing the performance of CQDSCs. In addition, we have also found that the mechanisms dominating the performance of CQDSCs are different from those behind the solar cells using inorganic semiconductor quantum dots (ISQDs) as the photosensitizers, which re-confirms the conclusion that the characteristics of CQDs differ from those of ISQDs.

Fluorescent vesicles formed by simple surfactants induced by oppositely-charged carbon quantum dots.

We show for the first time that stable fluorescent vesicles can be constructed by mixing oppositely-charged carbon quantum dots (CQDs) and simple surfactants in water, and can be potentially used as a new generation of biomarkers and drug delivery vehicles.

Correction: Fluorescent vesicles formed by simple surfactants induced by oppositely-charged carbon quantum dots.

Correction for 'Fluorescent vesicles formed by simple surfactants induced by oppositely-charged carbon quantum dots' by Xiaofeng Sun et al., Chem. Commun., 2016, 52, 12024-12027.