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An environment friendly, economic and maneuverable hydrothermal method was proposed for fabrication of nitrogen and chlorine co-doped carbon quantum dots (N,Cl-CQDs). D-Glucosamine hydrochloride as the only precursor offered source of carbon, nitrogen and chlorine. As a consequent N,Cl-CQDs can emit blue luminescence and detect Fe${}^{3+}$ by fluorescence response with high selectivity and sensitivity. There is a linear semilogarithmic correlation between the quenching efficiency $F_0∕F$ and the concentration of Fe${}^{3+}$ with a detection limit of 0.167 $\mu$M. The N,Cl-CQDs exhibit a high quantum yield of 16.8% along with the fluorescence lifetime of 2.2ns. It is worth noting that the prepared N,Cl-CQDs show excellent biocompatibility and they are promising materials for sensing and biology.

Nonhazardous and value-added utilization of biomass tar remains a great challenge in biomass gasification development. Herein, both model compounds and real biomass tar were for the first time tested as the carbon source for carbon quantum dots, where the resultants demonstrated excellent monodispersibility and strong fluorescence, quantum efficiency up to 53% and 43% were achieved. Moreover, the real tar-derived CQDs further revealed as a highly selective and sensitive probe for Fe${}^{3+}$, indicating its great potential ion sensing. It is expected that this work would open up a new strategy for biomass tar valorization.

Herein, carbon quantum dots (CQDs) and gold nanoparticles (Au NPs) were synthesized and deposited on the surface of Polysulfone (PSF) membrane using polydopamine as the sublayer, resulting in excellent antibacterial property and photocatalytic activity for degradation of organic dyes. Water contact angle (WCA) of the membrane before and after surface modification dropped from $93.9^{\circ }$ to $58.4^{\circ }$, due to outstanding hydrophilicity of CQDs. The antibacterial test against $E$. $coli$ found that the CQDs/Au NPs were beneficial to improve the antibacterial property of the membrane, and the antibacterial rate could reach 90%, effectively prolonging the service life of the membrane. In addition, the adsorption of bovine serum albumin (BSA) molecules on the membrane was significantly reduced, and the irreversible fouling ratio also decreased from 41.3% to 10.7%. On the other hand, the CQDs/Au NPs layer was used as a photocatalytic material for degradation of methylene blue.

Double element co-doped carbon quantum dots (CQDs) have unique electron properties and broad prospects in photocatalysis. In this paper, the phosphorus and nitrogen co-doped CQDs (PNCQDs) were loaded on TiO₂ nanosheets by in-situ synthesis method. Physical structure and chemical composition of samples were analyzed by XRD, FT-IR, XPS, SEM and TEM. UV–Vis spectra show the donor–acceptor coupling between PNCQDs and TiO₂ and enhanced strong UV light absorption. Photoluminescence spectra indicate that PNCQDs effectively promote charge separation, which is different from nitrogen doped CQDs. The sample 1-PNCT with the optimal phosphorus doping amount has the highest kinetic constant for photodegradation of Methylene Blue (MB), which is 3.4 times pure TiO₂. A possible Z-scheme photodegradation mechanism is proposed according to the active species scavenge experiment results in which PNCQDs can not only accept but also localize photogenerated electrons to dopant sites due to the quantum wells created by P and N doping energy barriers.

In this paper, we prepared a fluorescent sensor based on carbon quantum dots (CDs) and molecularly imprinted technology (MIT) that was successfully synthesized and applied to the detection of aspirin (Asp) residues in biological and pharmaceutical samples. The molecularly imprinted fluorescence sensor had the high sensitivity of quantum dots and the high selectivity of molecularly imprinted polymers (MIPs). Nitrogen-doped carbon quantum dots (N-CDs) with high fluorescence intensity were prepared and then was coated with silicon by the reverse microemulsion method. Finally, 3-aminopropyltriethoxysilane (APTES) was used as the functional monomer and Asp as the template molecule, molecularly imprinted layers were formed around the N-CDs. Under the best experimental conditions, the detection limit of the sensor was 0.198mgL${}^{-1}$. Between 0.9–9.0mgL${}^{-1}$, this fluorescence sensor had a good linear relationship with the concentration of Asp. To test the practicability of the sensor, we used this fluorescent sensor to detect Asp in human urine and saliva. Satisfied recovery rate between 101.1–105.1% and 102.1–106.0% were obtained, respectively.

Willow, a common tree species, is mainly distributed in temperate regions of the Northern Hemisphere. Catkins are the seeds of willow. In addition to propagating new willows, it is of great significance to study its application in other areas. Carbon quantum dots (CQDs) have attracted extensive attention owing to their excellent luminescence properties, low toxicity and water solubility. The use of CQDs for accurate measurement of pH is of great significance in environmental, medical and other fields. Based on this, blue-emission fluorescent CQDs with 4.93% quantum yield (Q.Y.) are prepared via natural product catkins as the only raw material by one-step hydrothermal method. The prepared CQDs exhibit excellent water solubility, narrow particle size distribution, excitation-dependent photoluminescence properties and sensitive pH response behavior. The fluorescence intensity of CQDs has a good linear relationship with pH in the range of 6–12, and the correlation coefficient is 0.994. In addition, the CQDs have good stability, and the response to pH displays excellent reversibility, which can be developed as a pH sensor to quantitatively monitor the pH values in real water samples. Thereby, the potential practical application is promising.

This work reports a simple, low cost and eco-friendly one-step hydrothermal method to obtain Si- and N-doped carbon quantum dots (Si-N-CQDs) using only citric acid and (3-aminopropyl) trimethoxysilane. These codoped Si-N-CQDs demonstrated 0D spherical morphology and an average size of $\sim$2.54 nm as well as good solubility in water and high quantum yield equal to 14.3%. Fluorescence emission of these Si-N-CQDs was quenched selectively under the presence of ${\mathrm{\text{Fe}}}^{3+}$. Based on this property, we developed a very sensitive sensor capable of detecting ${\mathrm{\text{Fe}}}^{3+}$ up to 400 $\mu$M concentration with a 3.14 $\mu$M detection limit. This sensor was used for ${\mathrm{\text{Fe}}}^{3+}$ detection in real tap and lake water and demonstrated satisfactory recovery equal to 102.3–108.0% and 103.5–108.5%, respectively. Photocatalytic activity of our Si-N-CQDs was demonstrated using methylene blue (MB) organic dye. The degradation rate of MB under visible light irradiation increased 2.7 times under the presence of Si-N-CQDs within 60 min. Such excellent performance was attributed to very efficient light absorption of Si-N-CQDs as well as excellent electron transfer and separation of photogenerated charge carriers.

Mesoporous g-C₃N₄ is prepared by a hard template method and is then decorated by carbon quantum dots (CQDs) and TiO₂ nanoparticles through an impregnation route followed by a hydrothermal method. The synthesized hybrids possess higher specific surface area up to 131cm²/g and show effective absorption of visible light range and improved instantaneous photocurrent response, which reveals the enhanced photo-generated carrier separation efficiency. The first-order kinetic reaction rate constant of photocatalytic degradation of gaseous benzene by TCPCN-2 is 5.5 times of the bulk g-C₃N₄. Its degradation rate is up to 96.08% with good photocatalytic stability. Thus, the TiO₂ nanoparticles and CQDs co-decorated g-C₃N₄ hybrids are promising photocatalysts.

We have demonstrated that variation of the precursor concentration during hydrothermal synthesis of carbon nanodots is an efficient mean to tune the yield of the products keeping their optical properties the same. Moreover, we found that the nature of the precursor determined the sensitivity and selectivity of detection of metal ions in the solution via quenching the fluorescence.

Keggin-type polyoxometalates is a kind of promising photocatalyst with adjustable light absorption range. However, the high recombination rate of photogenerated charge carriers hampered its photocatalytic efficiency. To solve this weakness, novel carbon quantum dots (CQDs) modified Cs₄PW₁₁O₃₉Fe(III)(H₂O) photocatalysts (CQDs/Cs₄PW₁₁Fe) have been synthesized via a hydrothermal process. Phase structure, morphology, optical and electronic properties of the as prepared photocatalysts were systematically characterized by XRD, SEM, TEM, DRS and surface photovoltage tests. It could be found that CQDs was well deposited on the surface of Cs₄PW₁₁Fe, which has broadened the light absorption of Cs₄PW₁₁Fe. The photodegradation efficiencies of the CQDs/Cs₄PW₁₁Fe composite photocatalysts for RhB under visible light irradiation were clearly enhanced. Trapping experiments were carried out to detect the photocatalytic mechanisms. The charge transfer and separation efficiencies of the samples were confirmed by electrochemical impedance spectroscopy tests.

A facile strategy is reported to synthesize nitrogen-doped carbon quantum dots (N-CQDs) with fluorescence emission by a one-step hydrothermal treatment under different temperatures with dicyanodiamide and citric acid as precursor materials of nitrogen and carbon sources, respectively. The as-produced N-CQDs display green or blue fluorescence under the ultraviolet lamp was controlled by the reaction temperature. Consequently, the as-prepared sample reacted at 200${}^{\circ }$C (N-CQDs-200), within the range of 3 nm, exhibits blue fluorescence excited at 365 nm irradiation with the maximum quantum yield (QY) of ca. 30.6%. Moreover, the N-CQDs possess rich functional groups such as nitrous groups and multiple oxygenated groups, which result in a favorable solubility in most hydrophilic solvents. From the characterization and discussion of TEM, HRTEM, FT-IR, XPS, Raman and UV-Vis, it is illustrated that the fluorescence performance was largely related to the nanomorphology, nitrogen concentration, multi-surface emission sites and various forms of transitions derived from the nitrogen doping. With the excellent fluorescence performance and the favorable solubility in solvents, the products are potentially suitable for monitoring organics.

Amine modified carbon quantum dots was synthesized by the acid oxidation method and hydrothermal route from coal in Barkol coalmine area and amine water. The features and properties of the product were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Photoluminescence Spectra (PL), UV-visible Spectroscopy (UV/vis), Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD). The results indicated that the GQDs have bright aquamarine with high water solubility, good photostability.