Covalent organic frameworks (COFs) usually have weak emission because of π–π stacking between layers, linkage bond rotation, or photoinduced electron transfer (PET) between monomer parts, which gives a chance to prepare “off–on” fluorescent sensors based on these weakly emissive COFs. Here, nitrogen-doped carbon dots (NCDs) encapsulated in COFTAPT-TT (NCCOFTAPT-TT) are successfully prepared by a one-pot method, in which COFTAPT-TT is synthesized by ammonaldehyde condensation between 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and thieno[3,2-b]thiophene-2,5-dicarboxaldehyde (TT) in the presence of NCDs. NCCOFTAPT-TT emits a strong NCD peak at 445 nm and a weak peak of COFTAPT-TT at 337 nm due to PET between electron-deficient TAPT and electron-rich TT. The NCDs lead spherical stacked COFTAPT-TT to self-exfoliate into NCCOFTAPT-TT nanosheets, which greatly improves the dispersion and stability of NCCOFTAPT-TT. In the presence of Cu2+ (0–10.0 μM), the fluorescence of NCDs is quenched but the fluorescence of COFTAPT-TT remains unchanged. The linear range is 51.9 nM to 0.75 μM, and the detection limit is 17.3 nM. Then, Cu2+ inhibits the PET process to result in an enhancement of COFTAPT-TT fluorescence and the fluorescence of NCDs remains unchanged, thus realizing a Cu2+ off–on ratiometric fluorescent sensor with high sensitivity, good selectivity, and good stability. This off–on fluorescent sensor has a linear range of 18–26 μM. This work provides a new idea for application of COFs with weak emission to construct off–on fluorescent sensors. 

Self-Exfoliating Double-Emission N-Doped Carbon Dots in Covalent Organic Frameworks for Ratiometric Fluorescence “Off–On” Cu2+ Detection

Empirical parameters of solvents describing their hydrogen-bond (HB) acidity (e.g., the Kamlet–Taft α parameter) are often difficult to determine for new solvents because they are not directly related to a single definition process. Here, we propose a simple method based on one probe, the betaine dye 30, and one reference process, the solvatochromism of this dye, measured by its first electronic transition energy, ET(30). These ET(30) values are calculated within the time-dependent density functional theory framework, using a polarizable continuum solvent model (PCM). The part of ET(30) values that is not included in the PCM calculation is taken as the HB component of the measured ET(30) values, allowing us to deduce a solvent HB acidity parameter α₁. The validity of this simple model is assessed by good linear correlations between α₁ and a variety of solute properties mainly depending on the solvent’s HB acidity. The quality of fit observed with α₁ is at least comparable with that obtained by previous solvent HB acidity scales. The simplicity of our method is illustrated by the determination of α₁ and of its companion, the electrostatic solvent parameter ES, for some new green solvents derived from glycerol.

Determination of a Solvent Hydrogen-Bond Acidity Scale by Means of the Solvatochromism of Pyridinium-N-phenolate Betaine Dye 30 and PCM-TD-DFT Calculations B

Lubrication behavior of fluorescent graphene quantum dots hybrid polyethylene glycol lubricant

DFT study of common anions adsorption at graphene surface due to anion-π interaction

Fluorescence Quenching and Highly Selective Adsorption of Ag+ Using N-Doped Graphene Quantum Dots/Poly(vinyl alcohol) Composite Membrane

"On-off-on" fluorescence switch of graphene quantum dots: A cationic control strategy

Lithium plays an increasingly important role in scientific and industrial processes, and it is extremely important to extract lithium from a high Mg2+/Li+ mass ratio brine or to recover lithium from the leachate of spent lithium-ion batteries. Conventional wisdom shows that Li+ with low valence states has a much weaker adsorption (and absorption energy) with graphene than multivalent ions such as Mg2+. Here, we show the selective adsorption of Li+ in thermally reduced graphene oxide (rGO) membranes over other metal ions such as Mg2+, Co2+, Mn2+, Ni2+, or Fe2+. Interestingly, the adsorption strength of Li+ reaches up to 5 times the adsorption strength of Mg2+, and the mass ratio of a mixed Mg2+/Li+ solution at a very high value of 500 : 1 can be effectively reduced to 0.7 : 1 within only six experimental treatment cycles, demonstrating the excellent applicability of the rGO membranes in the Mg2+/Li+ separation. A theoretical analysis indicates that this unexpected selectivity is attributed to the competition between cation–π interaction and steric exclusion when hydrated cations enter the confined space of the rGO membranes.

Unexpected Selective Absorption of Lithium in Thermally Reduced Graphene Oxide Membranes

At ambient conditions, potassium dihydrogen phosphate (KDP) usually exists in tetragonal structure, and only transforms to monoclinic structure at a temperature around 503 K. In this study, stable monoclinic KDP is developed at room temperature using a mixture of graphene oxides and unsaturated KDP solution. Furthermore, a reversible phase transition between monoclinic and tetragonal structure is observed by tuning the distance between graphene oxide layers. The first-principles calculation suggests that the tetragonal structure is more energetically favorable when KDP is sandwiched by two graphitic surfaces with a large interlayer distance, whereas the monoclinic structure is more stable with a small interlayer distance. This is attributed to the interaction between ${\mathrm{K}}^{+}$ cations and \ensuremath{\pi} electrons in the graphitic surface, which distorts the local structural configurations. The increase of interaction strength with decreasing interlayer distance not only reduces the crystal-liquid interfacial free energy, which promotes the formation of the monoclinic structure in unsaturated solution, but also stimulates transformation of existing tetragonal KDP to monoclinic structure. The observations shed light on the nucleation mechanism for crystal structure that is usually infeasible and unstable at ambient conditions, and provide an avenue to tune crystal structures for a wide range of metal salts.

Tuning crystal structure of potassium dihydrogen phosphate at ambient conditions

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Ruobing Yi

Author Tools

Chat about Author

Papers

"On-off-on" fluorescence switch of graphene quantum dots: A cationic control strategy

Unexpected Selective Absorption of Lithium in Thermally Reduced Graphene Oxide Membranes

Tuning crystal structure of potassium dihydrogen phosphate at ambient conditions