In the past two decades, dynamic covalent chemistry has been greatly developed, which is mainly reflected in two aspects: 1. new dynamic covalent bonds (DCBs) are continuously discovered; 2. various ...DCBs have been introduced into polymer materials for different functions. These functional polymer materials have brought new opportunities for sustainable development. In this review, we provide an overview of various functions endowed by DCBs in polymer materials, including self-healing, chemical recycling, and shape controlling. Particularly, we pay much attention to the three-dimensional (3D) shape reconfiguration/programming, surface patterning, and reversible actuation. In addition, we also give the current issues, challenges, and opportunities on DCBs-containing materials and point out its developing directions in the future.
Solution-processed films of colloidal aliovalent niobium-doped anatase TiO2 nanocrystals exhibit modulation of optical transmittance in two spectral regionsnear-infrared (NIR) and visible lightas ...they undergo progressive and reversible charging in an electrochemical cell. The Nb-TiO2 nanocrystal film supports a localized surface plasmon resonance in the NIR, which can be dynamically modulated via capacitive charging. When the nanocrystals are charged by insertion of lithium ions, inducing a well-known structural phase transition of the anatase lattice, strong modulation of visible transmittance is observed. Based on X-ray absorption near-edge spectroscopy, the conduction electrons localize only upon lithium ion insertion, thus rationalizing the two modes of optical switching observed in a single material. These multimodal electrochromic properties show promise for application in dynamic optical filters or smart windows.
We report the growth and structural, electrical, and optical characterization of vertically oriented single-crystalline iron pyrite (FeS2) nanowires synthesized via thermal sulfidation of steel foil ...for the first time. The pyrite nanowires have diameters of 4–10 nm and lengths greater than 2 μm. Their crystal phase was identified as cubic iron pyrite using high-resolution transmission electron microscopy, Raman spectroscopy, and powder X-ray diffraction. Electrical transport measurements showed the pyrite nanowires to be highly p-doped, with an average resistivity of 0.18 ± 0.09 Ω cm and carrier concentrations on the order of 1021 cm–3. These pyrite nanowires could provide a platform to further study and improve the physical properties of pyrite nanostructures toward solar energy conversion.
X-ray photoelectron spectroscopy (XPS) is a nearly universal method for quantitative characterization of both organic and inorganic layers on surfaces. When applied to nanoparticles, the analysis is ...complicated by the strong curvature of the surface and by the fact that the electron attenuation length can be comparable to the diameter of the nanoparticles, making it necessary to explicitly include the shape of the nanoparticle to achieve quantitative analysis. We describe a combined experimental and computational analysis of XPS data for molecular ligands on gold nanoparticles. The analysis includes scattering in both Au core and organic shells and is valid even for nanoparticles having diameters comparable to the electron attenuation length (EAL). To test this model, we show experimentally how varying particle diameter from 1.3 to 6.3 nm leads to a change in the measured A C/A Au peak area ratio, changing by a factor of 15. By analyzing the data in a simple computational model, we demonstrate that ligand densities can be obtained, and, moreover, that the actual ligand densities for these nanoparticles are a constant value of 3.9 ± 0.2 molecules nm–2. This model can be easily extended to a wide range of core–shell nanoparticles, providing a simple pathway to extend XPS quantitative analysis to a broader range of nanomaterials.
Chalcogenide nanocrystals or quantum dots (QDs) such as CdSe and PbSe have great potential as absorbers for QD-sensitized solar cells, but their practical utility is limited by fast degradation when ...exposed to ambient environments. Here we present results showing that small organic molecules acting as hole-accepting ligands can be very effective in reducing photooxidation of CdSe QDs. The aromatic amine, 4-dimethylaminothiophenol (DMATP), is shown to be especially effective in enhancing stability of CdSe QDs when illuminated in air or in aqueous environments. Using photoluminescence and density functional theory (DFT) calculations, we show that the enhanced stability results from hole transfer from the QD to the ligand and delocalization of the resulting positive charge on the aromatic ring and amino group instead of the sulfur atom that links the molecule to the CdSe.
While ZnO has excellent electrical properties, it has not been widely used for dye-sensitized solar cells, in part because ZnO is chemically less stable than widely used TiO2. The functional groups ...typically used for surface passivation and for attaching dye molecules either bind weakly or etch the ZnO surface. We have compared the formation of molecular layers from alkane molecules with terminal carboxylic acid, alcohol, amine, phosphonic acid, or thiol functional groups on single-crystal zinc oxide (101̅0) surfaces. Atomic force microscopy (AFM) images show that alkyl carboxylic acids etch the surface whereas alkyl amine and alkyl alcohols bind only weakly on the ZnO(101̅0) surface. Phosphonic acid-terminated molecules were found to bind to the surface in a heterogeneous manner, forming clusters of molecules. Alkanethiols were found to bind to the surface, forming highly uniform monolayers with some etching detected after long immersion times in an alkanethiol solution. Monolayers of hexadecylphosphonic acid and octadecanethiol were further analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. AFM scratching shows that thiols were bound strongly to the ZnO surface, suggesting the formation of strong Zn–S covalent bonds. Surprisingly, the tridentate phosphonic acids adhered much more weakly than the monodentate thiol. The influence of organic grafting on the charge transfer to ZnO was studied by time-resolved surface photovoltage measurements and electrochemical impedance measurements. Our results show that the grafting of thiols to ZnO leads to robust surfaces and reduces the surface band bending due to midgap surface states.
Structural color materials with reversible stimuli‐responsiveness to external environment have been widely used in sensors, encryption, display, and other fields. Compared with other stimuli, visible ...light is highly controllable both temporally and spatially with less damage to materials, which is more suitable for structural color patterning. Herein, a new diselenide‐containing shape memory material is prepared and used for creating patterns via visible light stimulus. In this system, the structural color originates from birefringence of stretched materials, whose shapes can be fixed while maintaining the mechanical stress. The fixed stress can be released by diselenide metathesis under visible light irradiation. By regulating the wavelength or irradiation time with a commercial projector, the pattern with tunable structural colors is realized and the structural color pattern can be erased and rewritten arbitrarily. During the patterning process, the optical signal is first stored as mechanical signal and then transformed back to optical signal. It is a new method for preparing visible‐light‐responsive structural color material and has great potential in display devices, anticounterfeiting labels, and data storage.
Microregions with various structural colors in a diselenide‐containing shape memory material are achieved under the irradiation of different wavelengths of light. By combining the visible‐light‐induced stress relaxation and birefringence, a tunable structural color pattern appears in the chromatic polarization system. The structural color material with visible light responsiveness can serve as a tool for optical data storage.
Metal oxides play a key role in many emerging applications in renewable energy, such as dye-sensitized solar cells and photocatalysts. Because the separation of charge can often be facilitated at ...junctions between different materials, there is great interest in the formation of heterojunctions between metal oxides. Here, we demonstrate use of the copper-catalyzed azide–alkyne cycloaddition reaction, widely referred to as “click” chemistry, to chemically assemble photoactive heterojunctions between metal oxide nanoparticles, using WO3 and TiO2 as a model system. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy verify the nature and selectivity of the chemical linkages, while scanning electron microscopy reveals that the TiO2 nanoparticles form a high-density, conformal coating on the larger WO3 nanoparticles. Time-resolved surface photoresponse measurements show that the resulting dyadic structures support photoactivated charge transfer, while measurements of the photocatalytic degradation of methylene blue show that chemical grafting of TiO2 nanoparticles to WO3 increases the photocatalytic activity compared with the bare WO3 film.
Programming 2D sheets to form 3D shapes is significant for flexible electronics, soft robots, and biomedical devices. Stress regulation is one of the most used methods, during which external force is ...usually needed to keep the stress, leading to complex processing setups. Here, by introducing dynamic diselenide bonds into shape‐memory materials, unconstrained shape programming with light is achieved. The material could hold and release internal stress by themselves through the shape‐memory effect, simplifying programming setups. The fixed stress could be relaxed by light to form stress gradients, leading to out‐of‐plane deformations through asymmetric contractions. Benefiting from the variability of light irradiation, complex 3D configurations can be obtained conveniently from 2D polymer sheets. Besides, remotely controlled “4D assembly” and actuation, including object transportation and self‐lifting, can be achieved by sequential deformation. Taking advantage of the high spatial resolution of light, this material can also produce 3D microscopic patterns. The light‐induced stress gradients significantly simplify 3D shape programming procedures with improved resolution and complexity and have great potential in soft robots, smart actuators, and anti‐counterfeiting techniques.
Through introducing light‐responsive diselenide bonds into polymer films, homogeneous stress fixed by shape‐memory effect can be relaxed to form a stress gradient. Once the stress gradient is activated, various deformations, including bending, folding, twisting, and helix, can be realized through the asymmetric contraction, which can be further combined for 3D shape programming, sequential deformation, and microscopic optical patterning.
NK cell-based immunotherapy and pemetrexed (Pem)-based chemotherapy have broad application prospects in cancer treatment. However, the over-expressed NK cell inhibitory receptor on the surface of ...cancer cells and the low cell internalization efficiency of Pem greatly limit their clinical application. Herein, we construct a series of selenium-containing nanoparticles to synergistically enhance Pem-based chemotherapy and NK cell-based immunotherapy. The nanoparticles could deliver Pem to tumor sites and strengthen the chemotherapy efficiency of Pem by seleninic acid, which is produced by the oxidation of β-seleno ester. Moreover, seleninic acid can block the expression of inhibitory receptors against NK cells, thereby activating the immunocompetence of NK cells. The in vitro and in vivo experiments reveal the potential chemo-enhancing and immune-activating mechanism of seleninic acid, emphasizing the promising prospects of this strategy in effective chemoimmunotherapy.
