Opposite regulation effects of Al3+ on different types of carbon quantum dots and potential applications in information encryption.

Regulating the photoluminescence (PL) of carbon quantum dots (CQDs) through ion modification is a well-established and effective approach. Herein, we report the opposite regulation effects of Al3+ ions on the PL properties of two distinct types of CQDs (graphene quantum dots, GQDs, and nitrogen-doped carbon quantum dots of 2,3-diaminophenazine, DAP), and elucidate the underlying mechanism of the binding of Al3+ ions to different PL sites on CQDs by employing ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. Specifically, Al3+ ions are primarily situated around the oxygen-containing groups, which do not impact the π-π regions of GQDs. However, Al3+ ions are preferentially adsorbed on the top of pyridine nitrogen in the phenazine rings of DAP, thus reducing the PL regions of DAP. Based on the opposite PL effects of Al3+ on GQDs and DAP, we explore potential applications of information encryption and successfully realize multi-level information encryption and decryption, which may provide new strategies for CQDs in information security.

Information security scheme using deep learning-assisted single-pixel imaging and orthogonal coding.

Providing secure and efficient transmission for multiple optical images has been an important issue in the field of information security. Here we present a hybrid image compression, encryption and reconstruction scheme based on deep learning-assisted single-pixel imaging (SPI) and orthogonal coding. In the optical SPI-based encryption, two-dimensional images are encrypted into one-dimensional bucket signals, which will be further compressed by a binarization operation. By overlaying orthogonal coding on the compressed signals, we obtain the ciphertext that allows multiple users to access with the same privileges. The ciphertext can be decoded back to the binarized bucket signals with the help of orthogonal keys. To enhance reconstruction efficiency and quality, a deep learning framework based on DenseNet is employed to retrieve the original optical images. Numerical and experimental results have been presented to verify the feasibility and effectiveness of the proposed scheme.

Unexpectedly efficient ion desorption of graphene-based materials.

Ion desorption is extremely challenging for adsorbents with superior performance, and widely used conventional desorption methods involve high acid or base concentrations and large consumption of reagents. Here, we experimentally demonstrate the rapid and efficient desorption of ions on magnetite-graphene oxide (M-GO) by adding low amounts of Al3+. The corresponding concentration of Al3+ used is reduced by at least a factor 250 compared to conventional desorption method. The desorption rate reaches ~97.0% for the typical radioactive and bivalent ions Co2+, Mn2+, and Sr2+ within ~1 min. We achieve effective enrichment of radioactive 60Co and reduce the volume of concentrated 60Co solution by approximately 10 times compared to the initial solution. The M-GO can be recycled and reused easily without compromising its adsorption efficiency and magnetic performance, based on the unique hydration anionic species of Al3+ under alkaline conditions. Density functional theory calculations show that the interaction of graphene with Al3+ is stronger than with divalent ions, and that the adsorption probability of Al3+ is superior than that of Co2+, Mn2+, and Sr2+ ions. This suggests that the proposed method could be used to enrich a wider range of ions in the fields of energy, biology, environmental technology, and materials science.

Comparison of water desalination performance of porous graphene and MoS2 nanosheets.

Following graphene and its derivatives, molybdenum disulfide (MoS2) has become a research hotspot in two-dimensional materials. Both graphene and MoS2 exhibit great potential in water treatment. A variety of nanoporous graphene or MoS2 membranes have been designed for water desalination. In this work, we compared the water flux and ion rejection of MoS2 and graphene nanopores, using molecular dynamics simulations. The simulation results demonstrate that monolayer nanopores have higher water fluxes than bilayer nanopores with lower ion rejection rates. MoS2 nanopores perform better than graphene in terms of water permeability. Exploration of the underlying mechanism indicates that the water molecules in the MoS2 pores have faster velocity and higher mass density than those in the graphene pores, due to the outer hydrophobic and inner hydrophilic edges of MoS2 pores. In addition, increasing the polarity of the pore edge causes a decrease in water flux while enhancement of ion rejection. Our findings may provide theoretical guidance for the design of MoS2 membranes in water purification.

Experimental optical encryption based on random mask encoding and deep learning.

We present an experimental scheme for optical encryption using random mask encoding and deep learning technique. A phase image is encrypted into a speckle pattern by a random amplitude modulation in the optical transmission. Before decryption processing, a neural network model is used to learn the mapping relationship between the pure-phase object and the speckle image rather than characterizing the filter film used in the scheme explicitly or parametrically. The random binary mask is made by a polyethylene terephthalate film and 2500 object-speckle pairs are used for training. The experimental results demonstrate that the proposed scheme based on deep learning could be successfully used as a random binary mask encrypted image processor, which can quickly output the primary image with high quality from the cyphertext.

A Facile Preparation of Multicolor Carbon Dots.

Carbon dots (CDs) have raised broad interest because of their great potential in the fluorescence related fields, such as photocatalysis and bioimaging. CDs exhibit different optical properties when dissolved in various solvents. However, the effects of solvents during the process of preparation on the fluorescence emission of CDs are still unclear. In this work, CDs were prepared by a simple one-pot solvothermal route. Typical critic acid and thiourea were used as precursors. Through changing the volume ratio of water to N,N-dimethylformamide (DMF), we have obtained color tunable CDs, with the emission wavelength from 450 to 640 nm. TEM images, Raman and XPS spectra indicate that the particle size of CDs and the content of surface functional groups (C-N/C-S and C≡N bonds) increase with the increasing ratio of DMF to water, which results in the optimal emission wavelength red-shifted. The prepared multicolor CDs may have prospects in the lighting applications.

Effects of interlayer spacing and oxidation degree of graphene oxide nanosheets on water permeation: a molecular dynamics study.

Graphene oxide (GO) membranes have shown great potential in the applications of water filtration and desalination. The flow behavior and structural properties of water molecules through GO nanochannels are still under debate. In this work, molecular dynamics simulations were performed to explore the effects of interlayer spacing and oxidation degree of GO nanochannels on water transport. The results show that GO nanosheets have strong adsorption capacity. The adsorbed layer of water molecules on GO surface is thermodynamically stable and not easy to flow. When the interlayer spacing falls into the range of 0.6 ~ 1.0 nm, water molecules form into single or double adsorbed layers between two GO nanosheets. When the interlayer spacing is bigger than 1.2 nm, the other water layers in the middle of nanochannel become disordered. Taking the separation performance based on size exclusion into consideration, the most suitable interlayer spacing for water nanofiltration is approximate 1.2 nm, which has one flowing layer of water molecules. Oxygen-containing groups are unfavorable for water permeation, as more and more hydrogen bonds prevent water flowing on GO surface with the increasing oxidation degree. Our simulation results may help to improve the design of GO nanofiltration membranes for water treatment.

On Demand Attachment and Detachment of rac-2-Br-DMNPA Tailoring to Facilitate Chemical Protein Synthesis.

Herein, we developed a bifunctional reagent rac-2-Br-DMNPA 2 for the late-stage protection of peptide cysteine. Through the identification of its t-Bu ester 1 as a more competent form under ligation conditions, facile N-terminal and side-chain caging for the model peptide and protein were accomplished. Building upon this, a one-pot ligation and photolysis strategy was applied in the synthesis of the mini-protein chlorotoxin. More importantly, we extended the utility of 2 as a bifunctional linker for traceless solid-phase chemical ligation.

Ultrahigh water permeance of a reduced graphene oxide nanofiltration membrane for multivalent metal ion rejection.

We develop a kind of pure rGO membrane using amino-hydrothermal reduction that exhibits an ultrahigh water permeance of 142.5 L m-2 h-1 bar-1 while still maintaining a high rejection rate of 91.6% for multivalent metal ions. The prepared rGO membranes have two types of spacing: larger hydrophilic spacing and smaller hydrophobic spacing, resulting in superior filtration performance. This provides a new avenue for multivalent metal ion separation using pure rGO membranes.

Fullerene-intercalated graphene nanocontainers for gas storage and sustained release.

Molecular dynamics simulations are performed to investigate the storage capacity and sustained release of nitrogen (N2) in the graphene-based nanocontainers. Sandwiched graphene-fullerene composites (SGFC) composed of two parallel graphene sheets and intercalated fullerenes are constructed. The simulation results show that the mass density of N2 at the first layer is extremely high, due to the strong adsorption ability of graphene sheets. And N2 molecules at this adsorbed layer are thermodynamically stable. Furthermore, we analyze the storage efficiency of SGFC. In general, the gravimetric and volumetric capacities decrease with the increasing number of intercalated fullerenes. On the contrary, the stability of SGFC is enhanced by more intercalated fullerenes. We therefore make a compromise and propose that 1 fullerene per 5 nm2 graphene to build a SGFC, which is much effective to storage N2. We also verify the reversibility that N2 can sustainably release from the SGFC. Our results may provide insights into the design of graphene-based nanocomposites for gas storage and sustained release with excellent structural stability and high storage capacity. Graphical abstract.

Molecular insights into the dispersion stability of graphene oxide in mixed solvents: Theoretical simulations and experimental verification.

HYPOTHESIS: Improving the dispersion stability of graphene oxide (GO) suspensions is of great importance in many potential applications of GO, such as GO-based laminated membranes used for separation, printable electronics, and aqueous liquid crystals. EXPERIMENTS: Molecular dynamics (MD) simulations and quantum chemistry (QC) calculations along with complementary experiments were performed to study the dispersion stability of GO in the mixtures of water and polar organic solvents (dimethyl sulfoxide (DMSO), ethanol, and acetone). FINDINGS: GO exhibits better dispersion stability in a solvent mixture than in pure water. The MD simulations uncover the underlying mechanism that mixed solvent layers are formed steadily on the surface of GO sheets and screen the interactions between them. QC calculations reveal that both DMSO and water form hydrogen bonds with the oxidized regions of GO. X-ray diffraction experiments confirm that the GO sheets are intercalated by DMSO and water molecules. Furthermore, the optimal ratio of the organic solvent to water is determined to achieve the best dispersion stability of GO through MD simulations. And such ratio is also verified by ultraviolet absorption spectral experiments. Thus, our findings provide a facile method to prepare GO suspensions with high dispersion stability.

Molecular dynamics simulations of loading and unloading of drug molecule bortezomib on graphene nanosheets.

Graphene has been regarded as one of the most hopeful candidates for transporting drugs to target cells because of its huge surface area and high cellular uptake. In this work, we performed molecular dynamics simulations to investigate the potential application of graphene as a substrate to carry and deliver drug molecules. Bortezomib (BOR) was selected as a model drug, as its atomic structure and polarity are suitable to be adsorbed on pristine graphene (PG) and graphene oxide (GO). First, BOR molecules are loaded on graphene surface to form graphene-BOR complexes, then these complexes readily enter the lipid bilayer and finally BOR releases from graphene surface into the membrane. The entry of graphene-BOR complexes into the membrane is mainly driven by the hydrophobic interactions between lipid tails and the basal plane of nanosheets, while the electrostatic interaction between the polar groups of BOR and lipid headgroups contributes to the release of BOR from graphene into the membrane. Different from PG, BOR molecules are hard to remove from GO surface after the complex enters the lipid bilayer. The electrostatic attraction from the oxygen-containing groups enhances the binding of BOR on GO. Potential of mean force calculations confirm that BOR on GO has lower free energy than it adsorbed on PG surface. The results indicate that the adsorption intensity and release rate of graphene nanosheets can be tuned by oxidation and electrification, and graphene served as substrate to transport and release particular drug molecules is feasible.

Ultrahigh permeance of a chemical cross-linked graphene oxide nanofiltration membrane enhanced by cation-π interaction.

Cross-linking with large flexible molecules is a common method to improve the stability and control the interlayer spacing of graphene oxide (GO) membranes, but it still suffers from the limitation of low water flux. Herein, a novel high flux GO membrane was fabricated using a pressure-assisted filtration method, which involved a synergistic chemical cross-linking of divalent magnesium ions and 1,6-hexanediamine (HDA) on a polyethersulfone (PES) support. The membrane cross-linked with magnesium ions and HDA (GOHDA-Mg2+ ) exhibited a high water flux up to 144 L m-2 h-1 bar-1, about 7 times more than that of cross-linked GO membranes without adding magnesium ions (GOHDA), while keeping excellent rejection performance. The GOHDA-Mg2+ membrane also showed an outstanding stability in water for a long time. The effects of magnesium ions on the GOHDA-Mg2+ membrane were analyzed using several characterization methods, including Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results indicated that magnesium ions not only promoted reasonable cross-linking, but also improved the stacking of GO sheets to give lower mass transfer resistance channels for water transport in the membranes, resulting in the ultrahigh permeance of the GO membranes.

Molecular Dynamics Simulations of the Permeation of Bisphenol A and Pore Formation in a Lipid Membrane.

Bisphenol A (BPA) is particularly considered as one of the most suspicious endocrine disruptors. Exposure to BPA may bring about possible human toxicities, such as cancerous tumors, birth defects and neoteny. One of the key issues to understand its toxicities is how BPA enters cells. In this paper, we perform molecular dynamics simulations to explore the interactions between BPA and a phospholipid membrane (dipalmitoylphosphatidylcholine, DPPC bilayer). The simulation results show that BPA can easily enter the membrane from the aqueous phase. With the increasing concentrations of BPA in the membrane, BPA tends to aggregate and form into cluster. Meanwhile, several DPPC lipids are pulled out from each leaflet and adsorbed on the cluster surface, leading to pore formation. Detailed observations indicate that the lipid extraction results mainly from the dispersion interactions between BPA cluster and lipid tails, as well as weak electrostatic attractions between lipid headgroups and the two hydroxyl groups on BPA. The lipid extraction and pore formation may cause cell membrane damage and are of great importance to uncover BPA's cytotoxicity.

Molecular simulations of conformation change and aggregation of HIV-1 Vpr13-33 on graphene oxide.

Recent experiments have reported that the fragment of viral protein R (Vpr), Vpr13-33, can assemble and change its conformation after adsorbed on graphene oxide (GO) and then reduce its cytotoxicity. This discovery is of great importance, since the mutation of Vpr13-33 can decrease the viral replication, viral load and delay the disease progression. However, the interactions between Vpr13-33 and GO at atomic level are still unclear. In this study, we performed molecular dynamics simulation to investigate the dynamic process of the adsorption of Vpr13-33 onto GO and the conformation change after aggregating on GO surface. We found that Vpr13-33 was adsorbed on GO surface very quickly and lost its secondary structure. The conformation of peptides-GO complex was highly stable because of π-π stacking and electrostatic interactions. When two peptides aggregated on GO, they did not dimerize, since the interactions between the two peptides were much weaker than those between each peptide and GO.

Exploring the Effects on Lipid Bilayer Induced by Noble Gases via Molecular Dynamics Simulations.

Noble gases seem to have no significant effect on the anesthetic targets due to their simple, spherical shape. However, xenon has strong narcotic efficacy and can be used clinically, while other noble gases cannot. The mechanism remains unclear. Here, we performed molecular dynamics simulations on phospholipid bilayers with four kinds of noble gases to elucidate the difference of their effects on the membrane. Our results showed that the sequence of effects on membrane exerted by noble gases from weak to strong was Ne, Ar, Kr and Xe, the same order as their relative narcotic potencies as well as their lipid/water partition percentages. Compared with the other three kinds of noble gases, more xenon molecules were distributed between the lipid tails and headgroups, resulting in membrane's lateral expansion and lipid tail disorder. It may contribute to xenon's strong anesthetic potency. The results are well consistent with the membrane mediated mechanism of general anesthesia.

Effects on lipid bilayer and nitrogen distribution induced by lateral pressure.

The lateral pressure exerted on cell membrane is of great importance to signal transduction. Here, we perform molecular dynamics simulation to explore how lateral pressure affects the biophysical properties of lipid bilayer as well as nitrogen distribution in the membrane. Our results show that both physical properties of cell membrane and nitrogen distribution are highly sensitive to the lateral pressure. With the increasing lateral pressure, area per lipid drops and thickness of membrane increases obviously, while nitrogen molecules are more congested in the center of lipid bilayer than those under lower lateral pressure. These results suggest that the mechanism of nitrogen narcosis may be related to the lateral pressure.