•CDs/g-C3N4/ZnO composites were synthesized by a facile impregnation-thermal method.•CDs/g-C3N4/ZnO samples were characterized by various characterization technologies.•CDs/g-C3N4/ZnO samples showed high visible-light-induced photocatalytic performance.Tetracycline (TC) in the water environment always brings negative impacts on human health and ecosystem equilibrium. Here we report that the carbon dots (CDs)/g-C3N4/ZnO nanocomposite prepared by a facile impregnation-thermal method exhibits outstanding photocatalytic activities for the total photodegradation of TC. Notably, the 30 wt% g-C3N4/ZnO with introducing 4 mL CDs solution (500 mg/L) photocatalyst displays the best photocatalytic activity in the degradation of TC (100 mL, 10 mg/L; 100% degradation within 30 min) under very weak visible irradiation (λ > 420 nm, 18 mW/cm2). In present system, CDs deposited on the surfaces of g-C3N4/ZnO heterojunction not only increases the visible-light response, but also promotes the efficiency of electron-hole pairs separation due to its electrons transfer property. Experiments further confirm that the superoxide radical (O2−) and hydroxyl radical (OH) formed on the surface of the photocatalyst are in charge of the degradation of TC.

•CDs/Ag/AgBr samples were prepared by a facile precipitation-photoreduction method.•CDs/Ag/AgBr samples were characterized by various characterization technologies.•CDs/Ag/AgBr samples showed outstanding NIR-induced photocatalytic performance.Ever-increasing environmental concerns have stimulated great progresses in photocatalytic technology in collection with the environmental remediation and solar energy utilization. In this study, carbon dots (CDs)/Ag/AgBr nanocomposites were prepared via a facile precipitation-photoreduction method. Moreover, CDs/Ag/AgBr nanocomposites show a strong absorbance in the full solar spectrum due to the interaction of Ag nanoparticles (Ag-NPs) and CDs. Meanwhile, compared with pristine AgBr and Ag/AgBr nanoparticles, a dramatic enhancement in the degradation of tetracycline under near-infrared light irradiation is observed over the CDs/Ag/AgBr nanocomposites. Significantly, the extraordinary photocatalytic performance is attributed to the extended absorption in the full spectrum, effective charge separation, and synergistic enhancement induced by surface plasmon resonance of Ag-NPs and the photogenerated change transfer properties of CDs in the complex nanocomposites.

•CDs/Znln2S4 microspheres with high photocatalytic activity were successfully synthesized by one-step hydrothermal method.•CDs/Znln2S4 samples were characterized by various characterization technologies.•CDs/Znln2S4 complex photocatalysts presented outstanding visible-light-induced photocatalytic performance.To design highly-effective photocatalysts including various fascinating properties of eco-friendly, visible-light response and good durability has been strongly desired in photocatalysis field. Here, we synthetised a series of different proportions of carbon dots (CDs) as an ideal cocatalyst to enhance the photocatalytic activity of ZnIn2S4 microspheres in the range of visible light. Simultaneously, CDs(5)/ZnIn2S4 hybrid photocatalyst exhibits the highest photocatalytic activity for degradating methyl orange (MO) (10 mg/L; 100% degradation within 40 min), which is 2.34 times higher than that of ZnIn2S4 alone. Additionally, the crystalline phases, structure, specific surface area and optical properties of as-prepared samples were characterized. The mechanism of enhanced photocatalytic activity of CDs/ZnIn2S4 composite was also discussed.

Stable bioimaging with nanomaterials in living cells has been a great challenge and of great importance for understanding intracellular events and elucidating various biological phenomena. Herein, we demonstrate that N,S co-doped carbon dots (N,S-CDs) produced by one-pot reflux treatment of C3N3S3 with ethane diamine at a relatively low temperature (80 °C) exhibit a high fluorescence quantum yield of about 30.4%, favorable biocompatibility, low-toxicity, strong resistance to photobleaching and good stability. The N,S-CDs as an effective temperature indicator exhibit good temperature-dependent fluorescence with a sensational linear response from 20 to 80 °C. In addition, the obtained N,S-CDs facilitate high selectivity detection of tetracycline (TC) with a detection limit as low as 3 × 10−10 M and a wide linear range from 1.39 × 10−5 to 1.39 × 10−9 M. More importantly, the N,S-CDs display an unambiguous bioimaging ability in the detection of intracellular temperature and TC with satisfactory results.

•CDs were applied to combine with CdS for visible light overall water splitting the first time.•CDs-CdS can work without any sacrificial agents.•The stoichiometric ratio of produced H2/O2 can adjust from 9:1 to 2:1 by changing CDs content.•CDs can stabilize CdS as oxidation site in low CDs concentration.•CDs can stabilize CdS as both oxidation and reduction sites with the high CDs concentration.Cadmium sulfide (CdS) has long time been one of the most promising inorganic photocatalysts for hydrogen production driven by visible light. However, the photocorrosion of CdS is the most serious problem which constrains its development. Here, we report the design and fabrication of a carbon dots-cadmium sulfide (CDs-CdS) nanocomposite, showing significant photocatalytic water splitting properties with impressive stability without requirement for any sacrificial agents or cocatalysts. The highest hydrogen production rate was obtained for about 2.55 μmol h−1, with an oxygen evolution rate for about 0.52 μmol h−1, when the concentration of CDs in the sample is 0.03 gCDs/gcatalyst. Even the produced H2 and O2 are not equal to the stoichiometric ratio of 2:1 (H2:O2), the CDs-CdS nanocomposite shows greater stability (8-time repetitive catalytic experiments) than the CdS catalysts reported up to now (without sacrificial agents or cocatalysts). It is also inspiring that when we increased the concentration of CDs in the catalysts, the produced H2 and O2 were gradually adjusted to meet the stoichiometric ratio of 2:1 in spite of low hydrogen production rate (0.13 μmol h−1).We report the design and fabrication of carbon dots-cadmium sulfide (CDs-CdS) nanocomposite, showing significant photocatalytic water splitting properties with impressive stability without requirement for any sacrificial agents under visible light. The CDs can stabilize CdS due to its function as oxidation site in low CDs concentration, and it can work as both oxidation and reduction sites when the CDs concentration is high.Download high-res image (167KB)Download full-size image

•The Ni3(C3N3S3)2 coordination polymer was firstly synthesized by a simple wet-chemical method.•The as-prepared Ni3(C3N3S3)2 exhibited excellent photocatcalytic H2-producing activity from the half-reaction of water splitting.•The photostability of Ni3(C3N3S3)2 was effectively improved by means of triethanolamine.Sparked by the increasing energy crisis, much research has been focused on seeking board spectrum-driven photocatalysts for water splitting. Herein, the Ni3(C3N3S3)2 coordination polymer was firstly synthesized by a simple wet-chemical method, as a novel board spectrum-driven photocatalyst for water splitting. The as-prepared Ni3(C3N3S3)2 exhibited excellent photocatcalytic H2-producing activity from the half-reaction of water splitting without the help of any sacrificial agents or cocatalysts, and the amounts of H2 production are 65.3, 53.9 and 16.3 μmol corresponding to UV (λ < 400 nm), visible (400 ≤ λ ≤ 760 nm) and near-infrared (λ > 760 nm) irradiation after 24 h, respectively. Another valuable finding is that after adding triethanolamine as a sacrificial donor, the average H2 evolution efficiencies on Ni3(C3N3S3)2 were efficaciously increased by around 2-fold with the H2 production value of 112.6, 93.3 and 30.1 μmol for 24 h under the UV light, visible light and near-infrared light exposure, respectively. More importantly, the stability of Ni3(C3N3S3)2 was effectively improved by means of triethanolamine. The results facilitate the increasing attention of narrow band gap non-noble metal coordination polymers treated as board spectrum-driven photocatalysts for expanding the utilization of solar light.Download high-res image (188KB)Download full-size imageWe have successfully synthesized a novel Ni3(C3N3S3)2 coordination polymer by a facile wet-chemical rout for the first time. Specifically, the as-prepared Ni3(C3N3S3)2 possessed UV–vis-NIR broad spectrum absorption and can be acted as a board spectrum-driven photocatalyst for water splitting into hydrogen. As expected, the H2 production performance from pure water over Ni3(C3N3S3)2 was realized through from UV (λ < 400 nm) to Vis (400 ≤ λ ≤ 760 nm) and NIR (λ > 760 nm) without any sacrificial agents or cocatalysts, and the amounts of H2 production are 65.3, 53.9 and 16.3 μmol corresponding to UV, Vis and NIR irradiation after 24 h, respectively. Significantly, the efficiency of H2 production and the stability over the Ni3(C3N3S3)2 could be improved with the assistance of triethanolamine. And the average H2 evolution efficiencies on Ni3(C3N3S3)2 were efficaciously increased by around 2-fold with the H2 production value of 112.6, 93.3 and 30.1 μmol for 24 h under the UV, Vis and NIR light exposure, respectively.

Since the misuse and overuse of tetracycline (TC) increase the pollution of aqueous solution, it is highly desirable to develop highly effective, stable, eco-friendly, economical, and facile photocatalysts for the photocatalytic degradation of TC in an aqueous solution. Herein, we designed and synthesized a highly efficient CoO/g-C3N4 p–n heterojunction via a facile solvothermal method. The experimental results demonstrated that after the coupling of CoO with g-C3N4, CoO nanoparticles were uniformly distributed on the surface of wrinkled g-C3N4 layers not only to readily form a p–n heterjunction, but also to avert the aggregation; and the CoO/g-C3N4 p–n heterojunction photocatalysts exhibited superior visible-light photocatalytic activity and stability for the removal of TC. The high photocatalytic activity could be attributed to the generation of an internal electric field induced by the p–n heterojunctions, effectively promoting the separation of photoinduced charge.

Electrochemical reduction of carbon dioxide (CO2) to methanol (CH3OH) catalyzed by transition metals has been proved feasible and effective in aqueous electrolytes. In this work, we introduce a FeS2/NiS nanocomposite electrocatalyst synthesized by traditional hydrothermal method, which selectively reduces CO2 to CH3OH with an unprecedented overpotential of 280 mV and a high faradaic efficiency up to 64% at the potential of −0.6 V vs. reversible hydrogen electrode (RHE). The FeS2/NiS nanocomposite electrocatalyst exhibits a stable current density of 3.1 mA cm−2 over a 4 hour stability test. The high selectivity towards CO2 electroreduction to CH3OH may be attributed to the special ladder structure of the FeS2/NiS nanocomposite. The active sites are located at the interface between FeS2 and NiS which can effectively suppress the side reaction hydrogen evolution reaction and facilitate the CO2 reduction reaction.

Photocatalytic overall water splitting using particulate semiconductors is a potential means of storing solar energy in using the intermittency of sunlight as a primary source of power and zero emission of carbon dioxide. Herein, we constructed a composite material with carbon dots (CDs) anchored on the surface of octahedral CoO as a highly efficient and long-term stable photocatalyst for overall water splitting under visible light irradiation (λ > 400 nm). The structure and morphology of the CDs/CoO composite were investigated by a series of characterization methods. The obtained CDs/CoO composites exhibit more-efficient visible light absorption than pure CoO, leading to higher photocatalytic activity for overall water splitting. The optimized photocatalytic H2 and O2 production was achieved for the CDs/CoO composite with a content of 5 wt% CDs (5% CDs/CoO), showing a H2 (O2) evolution rate of 1.67 μmol h−1 (0.91 μmol h−1) with an expected 2 : 1 stoichiometry, which is up to 6 times as high as that of pristine CoO. Additionally, the 5% CDs/CoO composite also shows outstanding photocatalytic stability for over 15 cycling experiments. This enhanced photocatalytic activity and outstanding stability in CDs/CoO composites could be ascribed to several merits of CDs that not only improved charge separation efficiency and visible-light absorption but also effectively conducted heat generated by the photo-thermal effect of CoO.

As the misuse and overuse of tetracycline (TC) contribute to water pollution, it is imperative to explore an efficient and cost-effective approach for the removal of TC in aqueous solution. Photocatalysis is a green and sustainable chemical technique because of its utilization of solar energy. From the view of practical application, it is significant to design a highly efficient, stable, eco-friendly and economical photocatalyst. In this work, CuBi2O4/g-C3N4 p–n heterojunctions with different CuBi2O4 content (10–90 wt%) were prepared via a facile calcining method. The CuBi2O4/g-C3N4 heterojunctions exhibit superior photocatalytic activity in the degradation of TC, compared with pristine CuBi2O4 and g-C3N4. The optimum photoactivity of 70 wt% CuBi2O4/g-C3N4 is up to 4 and 6 times higher than that of CuBi2O4 and g-C3N4, respectively. The enhanced photocatalytic activity can be attributed to p–n junction photocatalytic systems, which effectively promote charge carrier separation and transfer. It is anticipated that the design of CuBi2O4/g-C3N4 could offer the insight needed to construct inexpensive and highly efficient g-C3N4-based heterojunction photocatalysts, to relieve urgent environmental deterioration.

We present a simple hydrothermal method to fabricate multifunctional modified carbon dots (with –COOH, –OH, –SH, and –NH2 groups, named NS-Cdots) using citric acid and L-cysteine as raw materials. The functional NS-Cdots exhibit high fluorescent quantum yield (38.9%), low cytotoxicity and good biocompatibility. A reasonable photoluminescence mechanism of the NS-Cdots was proposed in which the pyridine derivatives serve as conjugating units and dominate the main emission behavior. The NS-Cdots can also be used as excellent fluorescent probes for cell imaging in vitro and as effective thermometers with a wide temperature detection range from 20 °C to 95 °C.

In recent years, carbon dots (C-dots) have become a rising star for a spectrum of environmental and energy applications, ranging from chemical catalysis, to photocatalysis, electrocatalysis and energy storage, such as batteries and capacitors, due to their unique physicochemical, optical and electrical properties. This review discusses the up-to-date progress on carbon dots, with an emphasis on their environmental and energy applications along with some discussion on the challenges and promises in this exciting and promising field.

Highly efficient electrocatalysts remain huge challenges in direct methanol fuel cells (DMFCs). Here, a Pt–Co3O4–CDs/C composite was fabricated as an anode electrocatalyst with low Pt content (12 wt%) by using carbon dots (CDs) and Co3O4 nanoparticles as building blocks. The Pt–Co3O4–CDs/C composite catalyst shows a significantly enhanced electrocatalytic activity (1393.3 mA mg−1 Pt), durability (over 4000 s) and CO-poisoning tolerance. The superior catalytic activity should be attributed to the synergistic effect of CDs, Pt and Co3O4. Furthermore, the Pt–Co3O4–CDs/C catalyst was integrated into a single cell, which exhibits a maximum power density of 45.6 mW cm−2, 1.7 times the cell based on the commercial 20 wt% Pt/C catalyst.

Hydrogen is an ideal energy carrier for renewable energy, but a high overpotential is required to achieve reasonable H2 evolution, which makes the design of highly active electrocatalysts for hydrogen evolution reaction (HER) urgent. Here, we report a nitrogen, sulfur co-doped carbon dots (NSCDs)/CoS hybrid with a three-dimensional mesoporous sponge-like nanostructure, fabricated via heat-treatment, which as electrocatalyst exhibits the desired electrocatalytic activity for electrochemical HER. A series of NSCDs/CoS hybrids with different contents of NSCDs were prepared by adjusting the concentration of NSCDs, of which the NSCDs/CoS hybrid with 20 mg L−1 NSCDs exhibits the best electrocatalytic activity towards HER with an onset potential of 0.095 V, an overpotential at 10 mA cm−2 of 165 mV, a small Tafel slope of 56 mV per decade, and a good stability in 0.5 M H2SO4. The excellent electrocatalytic activity of NSCDs/CoS for HER is attributed to synergetic effects of NSCDs and CoS, in which the NSCDs could protect the CoS from dissolution/agglomeration under acidic conditions, and the increased surface area of the NSCDs/CoS hybrid and the high charge transfer efficiency between NSCDs and CoS via Co–S–C bonding enhanced the HER performance.

Using photocatalysts to split water into hydrogen and oxygen is a promising way to produce renewable energy. Efficient and stable photocatalysts are desired for overall water splitting under visible light. We demonstrate that the cobalt(II) oxide (CoO)/graphitic carbon nitride (CoO/g-C3N4) composites synthesized by a one-step thermal decomposition method exhibit enhanced photocatalytic efficiency for overall water splitting without sacrificial reagents. 10%CoO/g-C3N4 exhibits optimal photocatalytic performance, where H2 and O2 evolution rates are, respectively, 0.46 μmol h−1 and 0.21 μmol h−1 under visible light irradiation without any sacrificial reagents. It is worth mentioning that the H2 and O2 production almost approaches the stoichiometric ratio 2 : 1. The enhanced photocatalytic activity of CoO/g-C3N4 may be ascribed to the efficient charge separation and fast decomposition of H2O2 by CoO.

Chiral nanostructures have attracted extensive interest as components for chiral applications. Carbon quantum dots (CQDs) with superior properties, including low toxicity and good biocompatibility, can render the field of QDs with more potential biological applications in bioimaging, biosensors, and drug delivery. Herein, we report the fabrication of nitrogen and sulfur co-doped chiral CQDs (L-/D-CQDs) with strong symmetrical circular dichroism (CD) signals at about 212 and 240 nm. These chiral CQDs exhibit strong photoluminescence (PL) emission (at 460 nm) and outstanding enantioselective electrochemical recognition ability. A series of experiments further confirms that these chiral CQDs possess independent PL and chiral properties. With a temperature increase, PL is quenched with a good linear correlation of 0.992, whereas the CD signals remain almost the same. On the other hand, the PL of L- or D-CQDs shows no difference towards small chiral molecules detection with right or opposite configuration. In addition, the L- or D-CQDs excited with circularly polarized light (CPL) show similar PL properties regardless of their right or left configuration.

•BiVO4/CDs/CdS Z-scheme photocatalyst with CDs as solid-state electron mediator was designed.•BCC50 shows the best photocatalytic activity with stoichiometric ratio of H2/O2 evolution.•BiVO4/CDs/CdS photocatalyst could efficiently photocatalytic overall water splitting.Z-scheme photocatalytic system is an efficient way to achieve high efficiency photocatalytic overall water splitting. However, the acquisition of efficient Z-scheme visible-light photocatalysts is still a huge challenge at present due to the inactive visible light-active component and various low-band-gap for semiconductors. Herein, we constructed the BiVO4/CDs/CdS Z-scheme photocatalyst with carbon dots (CDs) as solid-state electron mediator, which exhibits excellent photocatalytic activity and stability for photocatalytic overall water splitting under visible light. The BCC50 (BiVO4/CDs/CdS with the mass ratio of BiVO4/CdS = 50%) as photocatalyst shows the best photocatalytic activity with stoichiometric ratio of H2 evolution rate of 1.24 μmol/h and O2 evolution rate of about 0.61 μmol/h. The enhanced photocatalytic activity of the Z-scheme photocatalyst can be attributed to high efficiencies for separation and transport of photogenerated charge carriers and extended the lifetime of electrons and holes.We constructed the BiVO4/CDs/CdS Z-scheme photocatalyst with carbon dots (CDs) as solid-state electron mediator, exhibiting excellent photocatalytic activity and stability for photocatalytic overall water splitting under visible light. The BCC50 (BiVO4/CDs/CdS with the mass ratio of BiVO4/CdS = 50%) as photocatalyst shows the best photocatalytic activity with stoichiometric ratio of H2 evolution rate of 1.24 μmol/h and O2 evolution rate of about 0.61 μmol/h. The enhanced photocatalytic activity of the Z-scheme photocatalyst can be attributed to high efficiencies for separation and transport of photogenerated charge carriers and extended the lifetime of electrons and holes.Download high-res image (107KB)Download full-size image

•CDs-CoO composites were firstly synthesized by one-step solvothermal method.•CDs as co-catalyst modified and stabilized the (111) facets of CoO octahedrons.•CDs-CoO composites exhibited outstanding photocatalytic activity and stability.Octahedral CoO with exposed high-reactive (111) facets holds a promising noble-metal-free material in the photocatalysis. However, the (111) facet is usually unstable and easily deactivated during the photocatalytic process as the result of its poloar catastrophe. In this work, carbon dots (CDs) as co-catalyst modified and stabilized the (111) facets of CoO octahedrons (CDs-CoO) were prepared by one-step solvothermal method. The desired CDs-CoO shows the excellent photocatalytic activity and well stability. Meanwhile, the CDs-CoO (5 wt.%) composite exhibits the highest photocatalytic activity for degradation of tetracycline (87%, 60 min), and presents remarkable photostability after five successive cycles (5 h). This enhanced photocatalytic activity and outstanding stability in CDs-CoO composites could be ascribed to several merits of CDs that not only improve charge separation efficiency but also strengthen the interaction between CDs and high-reactive (111) facets of CoO octahedrons.Carbon dots (CDs) as co-catalyst modified and stabilized the (111) facets of CoO octahedrons (CDs-CoO) were prepared by one-step solvothermal method. Meanwhile, the CDs-CoO composite not only exhibits excellent photocatalytic activity, but also presents remarkable photostability. This enhanced photocatalytic activity and outstanding stability in CDs-CoO composites could be ascribed to CDs not only improve charge separation efficiency but also strengthen the interaction between CDs and high-reactive (111) facets of CoO octahedrons.Download high-res image (103KB)Download full-size image

•Surface functionalized carbon dots were synthesized by hydrothermal method.•NS-CDs can be applied in a variety of detection applications.•NS-CDs always have a satisfactory behavior to quantitative detection of molecules.The surface functionalization will introduce additional functional groups on carbon dots (CDs) surface and then enrich the properties of CDs. Here, we show the various surface functionalized CDs (-COOH, -OH, -SH, -NH2, etc, named as NS-CDs) were synthesized with fascinating features, including high quantum efficiency (38.9%), long-term stability and good biocompatibility. Notably, it can serve as multifunction fluorescent probe in sensing system, including label-free detections in hydrogen peroxide (H2O2) with a wide linear range (1.20 × 10−3 – 8.80 × 10–12 M) and a low limit of detection (LOD, 1.00 × 10–12 M); and glutathione, covering a concentration range of 2.00 × 10−3 – 1.00 × 10−7 M and LOD of 1.00 × 10−7 M. In addition, the NS-CDs as fluorescent probe could selectively detect metal ions (such as, Hg2+, 1.00 × 10−8 − 1.50 × 10−3 M, 1.00 × 10−7 M), antibiotics (tetracycline, 1.00 ×10−10 − 2.50 × 10−5 M, 1.00 ×10−10 M) and toxic pollutant (nitrobenzene, 5.00 × 10−7 to 1.00 × 10−3 g L−1, 5.00 × 10−7 g L−1) with wide linear range and satisfactory detection limits.We show various surface functionalized CDs (-COOH, -OH, -SH, -NH, etc) with fascinating features can be label-free detection in hydrogen peroxide, glutathione, heavy metal ions (Hg2+/Ag+), antibiotics and toxic pollutant with satisfactory detection limits and range.Download high-res image (375KB)Download full-size image

•g-C3N4/ZnIn2S4 samples were prepared by a one-step hydrothermal method for the sake of degrading TC.•g-C3N4/ZnIn2S4 samples were characterized by various characterization technologies.•g-C3N4/ZnIn2S4 samples showed outstanding photocatalytic activity compared with the pure g-C3N4 and ZnIn2S4.It is a widespread concern to address the antibiotics in water with low-cost and eco-friendly photocatalysts that could efficiently harvest solar light. Herein, we designed an efficient photocatalyst by integrating the lamellar g-C3N4 into Znln2S4 microflowers through a one-step hydrothermal method. The as-synthesized g-C3N4/Znln2S4 heterojunction photocatalysts exhibited evidently enhancement on the photocatalytic activities for the degradation of tetracycline (100 mL, 20 mg/L) compared with pristine g-C3N4 and Znln2S4. Significantly, g-C3N4/Znln2S4 composite with loading 50 wt.% g-C3N4 showed the highest photocatalytic performance (almost 100% degradation within 120 min), which was around 40 and 22.8 times higher than that of g-C3N4 and Znln2S4, respectively. This enhanced photocatalytic activity of g-C3N4/Znln2S4 is mainly attributed to the formation of heterostructure that can efficiently promote the transfer of photoinduced electrons and holes between g-C3N4 and ZnIn2S4, restricting the recombination of electron-hole pairs. In addition, a possible mechanism was also proposed.

Monitoring of bacterial viability is crucial for food safety and human health. Fluorescence staining with dyes is one of the simple and fast methods to assess bacterial viability. However, obtaining stable and non-poisonous dyes is still a huge challenge. Herein, we demonstrate that nitrogen, phosphorus and sulfur co-doped carbon dots (NPSCDs) can selectively stain dead bacteria rather than live ones because they possess a highly negative ζ potential (−41.9 mV), indicating that NPSCDs could serve as an efficient dye for bacterial viability evaluation. The NPSCDs were synthesized by one-step hydrothermal carbonization of a yeast extract, and exhibit favorable photoluminescence (PL) with high quantum yield (QY, 32%), excellent photostability (under acid/alkaline and strong ionic strength), good biocompatibility and low toxicity. Moreover, the designed NPSCDs show a precise response to temperature within the range from 30 °C to 90 °C, in which the fluorescence of the NPSCDs decreased linearly with an increase in temperature and recovered with a decrease in temperature. More importantly, when the live bacteria were incubated with NPSCDs, as the temperature increases, the NPSCDs could selectively stain dead bacteria in real time along with a decrease in fluorescence intensity simultaneously, showing a significant reduction in bacterial viability from 80% to 15% upon heating at 60 °C for more time. The development of NPSCDs paves a new way for the synthesis of a sensitive fluorescent probe that can be used in real-time monitoring of bacterial viability.

Ag3PW12O40/C3N4 nanocomposites were successfully synthesized by loading Ag3PW12O40 into C3N4, in which case Ag3PW12O40 is gained through reaction between AgNO3 and H3PW12O40 at room temperature. The obtained nanocomposites show efficient and light-operated catalytic activity for hydrocarbon selective oxidation (selective oxidation of cyclooctene and cyclohexane) without adding any oxidant at 60 °C. For cyclooctene, the conversion based on cyclooctene is 41.26%, and the selectivity of selective oxidation to epoxycyclooctane can be up to 77.2%. The nanocomposite catalyst yielded oxidation of cyclohexane to cyclohexanone with 8.62% efficiency and >99.0% selectivity. In the catalytic system, the oxidant (H2O2) in the catalysis process can be produced by the irradiation of C3N4 and then decomposed into HO· with the help of Ag3PW12O40. The observed improvement in the activities of photo-induced oxidation of cyclooctene and cyclohexane is mainly attributed to the high BET surface area of C3N4. With the synergistic effect of Ag3PW12O40 and C3N4, the nanocomposite displays considerable catalytic activity, which sheds light on the catalyst design applied in the selective oxidation of hydrocarbon.

Developing highly efficient and low cost hydrogen evolution reaction (HER) electrocatalysts is still a huge challenge. In this study, we demonstrate a facile method to fabricate a nitrogen, phosphorus co-doped carbon dots/CoS2 (NPCDs/CoS2) hybrid as an electrocatalyst for HER with desirable electrocatalytic activities (low overpotential ∼78 mV and small Tafel slope ∼76 mV dec−1) and long-term stability (after 1000 CV cycles with negligible current loss ∼1 mA cm−2) in acidic media.

It is highly desired for the development of efficient bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in renewable energy technologies. In this work, cobalt, nitrogen-codoped carbon was prepared by a facile one-step method and demonstrated to exhibit good electrocatalytic performance for ORR and OER via a complete four-electron process. Besides, the catalyst prepared at 900 °C also displayed excellent stability for both ORR and OER. Furthermore, the origin of catalytic activity was also explored, which was attributed to the synergistic effects of metallic Co and quaternary N.发展可再生新能源技术迫切需要寻找既可以在氧还原反应(ORR)中起到催化作用,又具有催化氧析出反应(OER)的双功能催化剂。本文利用900°C热分解方法一步合成制备出钴、氮共掺的碳材料。实验结果表明,它具有较好的ORR和OER催化能力;同时,钴、氮共掺的碳材料对ORR和OER催化反应都是四电子反应过程。

The C3N4-tyrosinase (TYR) hybrid is a highly accurate, sensitive and simple fluorescent probe for the detection of dopamine (DOPA). Under optimized conditions, the relative fluorescence intensity of C3N4-TYR is proportional to the DOPA concentration in the range from 1 × 10−3 to 3 × 10−8 mol L−1 with a correlation coefficient of 0.995. In the present system, the detection limit achieved is as low as 3 × 10−8 mol L−1. Notably, these quantitative detection results for clinical samples are comparable to those of high performance liquid chromatography. Moreover, the enzyme-encapsulated C3N4 sensing arrays on both glass slide and test paper were evaluated, which revealed sensitive detection and excellent stability. The results reported here provide a new approach for the design of a multifunctional nanosensor for the detection of bio-molecules.

A combustion flame method is developed for the convenient and scalable fabrication of single- and dual-doped carbon quantum dots (CQDs) (N-CQDs, B-CQDs, P-CQDs, and S-CQDs and dual-doped B,N-CQDs, P,N-CQDs, and S,N-CQDs), and the doping contents can be easily adjusted by simply changing the concentrations of precursors in ethanol. These single/dual-doped CQDs, especially B,N-CQDs, show high catalytic activities for the oxygen reduction reaction.

High-intensity fluorescent carbon dots (CDs) coupled with tyrosinase (TYR) yielded hybrids, as a fluorescent probe, which were efficient, fast, stable and sensitive in the detection of levodopa (L-DOPA). The detection limit of L-DOPA was as low as 9.0 × 10−8 mol L−1 with a wide linear range from 3.17 × 10−4 mol L−1 to 3.11 × 10−7 mol L−1. The efficient selective detection of L-DOPA can be attributed to the CDs that are excellent electron acceptors/donors and exhibit high adsorption capacity of H+. It is worth mentioning that TYR does not require modification and immobilization, and the test results could be read as soon as the probe–sample incubation was completed. Moreover, the test results are comparable to those of the present clinical fluorescence and high performance liquid chromatography (HPLC) methods. Our experimental results indicated that CDs possess great potential in the development of various enzyme-based biosensors.

Nanocomposites based on transition metal oxides (Co3O4, etc.) and carbon nanostructures with low-cost, high activity and good stability are promising catalysts toward electrochemical water oxidation, which is desirable but remains challenging. Here, we report the design and synthesis of nanocomposite based on carbon quantum dots (CQDs), SnO2 and Co3O4 (CQDs/SnO2–Co3O4) as the electrocatalyst for highly efficient oxygen evolution reaction (OER). In alkaline media, the complex exhibited high electrocatalytic activity and long-term stability, which was better than either pristine Co3O4 or SnO2–Co3O4 composite. Moreover, the CQDs/SnO2–Co3O4 with a molar ratio of Sn:Co at 1:3 revealed the highest catalytic activity toward OER among different molar ratios of CQDs/SnO2–Co3O4 composites. Experimental results indicated that the Co atoms were considered as the active centre, the nano-sized SnO2 enhanced electronic conductivity and the insoluble CQDs layer on the surface effectively protected the catalyst, thus the composite structure resulted in the excellent electrocatalytic activity and high stability.

Due to methanol being a cheap and widely available fuel, much effort has been devoted to the study of platinum-based catalysts for methanol oxidation. In addition to the development of efficient electro-catalysts, another approach to improve fuel cell performance is to develop alternative catalyst supports. Here, we report mesoporous carbon nanoparticles as a catalyst support which could greatly improve the catalytic activity of the catalyst for methanol oxidation, which can not only promote the formation of a larger electrochemically active surface area (801.038 m2 g−1) to afford more active sites for electrochemical reactions, but also facilitate effective electron transfer through the electrode surface. The mesoporous carbon nanoparticles were synthesized through a simple hydrothermal method using glucose as the precursor and modification with ionic liquids. The Pt nanoparticles deposited onto the resulting mesoporous carbon nanoparticles, as the catalyst, exhibited excellent electrochemical activity compared with commercial Pt/C catalyst and Pt nanoparticles.

We demonstrate the fabrication of phosphate functionalized activated carbon by a facile heating method, as a metal-free electrocatalyst, which exhibits excellent electrocatalytic activity for the oxygen reduction reaction in an alkaline medium, it also enhances the durability and tolerance for methanol crossover effects. The improvement of the oxygen reduction reaction activity was closely related to the large specific surface area (976.4 m2 g−1) and high phosphorus content (1.88%) of the electrocatalyst. The newly-developed material represents a promising step towards replacing Pt/C catalysts and could potentially lead to commercial-scale fuel cell production.

We demonstrate that the semi-carbonized nanostructures of carbohydrate (cellulose and glucose as precursors) show high performance as photocatalysts directly for selective oxidation of cis-cyclooctene with air as an oxidant. Three dimensionally macroporous carbon spheres (3DMPCS) prepared from cellulose carbonized at 500 °C yielded the highest conversion of cis-cyclooctene (32.6%) and a high selectivity of 2-hydroxycyclooctanone (90.4%) after 24 h reaction, while cellulose carbonized at lower heat treatment temperatures (HTTs) (0–400 °C) or higher (600–900 °C) gave lower cis-cyclooctene conversion. The 3DMPCS synthesized from glucose carbonized at 600 °C shows higher performance in selective oxidation of cis-cyclooctene (12.2% conversion of cis-cyclooctene and 75.4% selectivity of 2-hydroxycyclooctanone) than glucose carbonized at other HTTs (200–500 °C and 700–900 °C) as catalysts. The results indicate that the semi-carbonized nanostructures of carbohydrates are highly efficient photocatalysts.

Despite tremendous efforts devoted to the study of new nanocatalysts, obtaining effective nanocatalysts for the oxidation of cyclohexane under mild conditions is still a great challenge. The silver modified carbon quantum dots were synthesized by a simple chemistry method and demonstrated to exhibit excellent catalytic ability for cyclohexane oxidation (conversion based on cyclohexane reached about 58.9% and selectivity to cyclohexanone reached about 84.6%) under visible light, which can be attributed to the synergistic catalysis of Ag nanoparticles and carbon quantum dots. Besides, the carbon quantum dots can stabilize Ag nanoparticles for the prevention of aggregation. Moreover, the silver modified carbon quantum dots showed good reusability, being reused after ten consecutive runs. Based on a series of experiments, it can be concluded that the silver modified carbon quantum dots are green and efficient nanocatalysts for the oxidation of cyclohexane.

Carbon quantum dots (CQDs) obtained from polyethylene glycol were demonstrated to be easy-to-use photoluminescence probes for the detection of glucose. Here, the photoluminescence of CQDs was significantly enhanced by H2O2 produced from glucose oxidase-catalyzed oxidation of glucose. Moreover, CQDs showed an ultrasensitive detection of glucose, with a detection limit of up to 1 nM.

To develop green catalysts for cyclohexane oxidation with high efficiency and high selectivity is a trend in nanotechnology and nanocatalysis. In this work, we demonstrate that copper nanoparticles/carbon quantum dots (Cu/CQDs) hybrid as photocatalyst exhibits excellent catalytic activity in the oxidation of cyclohexane (conversion based on cyclohexane of 50.2% and selectivity to cyclohexanone of about 78.3%) under a low temperature with tert-butyl hydroperoxide as oxidant. It is worth mentioning that the Cu/CQDs hybrid photocatalyst can be implemented in efficient catalytic oxidation of cyclohexane under a mild condition (60 °C), which may provide a cogent pathway for the development of high-performance catalysts for C–H oxidation.

We describe the preparation of carbon dots (CDs) from glucose that possess high stability, a quantum yield of 0.32, and low toxicity (according to an MTT assay). They were used, in combination with the fluorogenic zinc(II) probe quercetin to establish a fluorescence resonance energy transfer (FRET) system for the determination of Zn(II). The CDs are acting as the donor, and the quercetin-Zn(II) complex as the acceptor. This is possible because of the strong overlap between the fluorescence spectrum of CDs and the absorption spectrum of the complex. The method enables Zn(II) to be determined in the 2 to 100 μM concentration range, with a 2 μM detection limit. The method was applied to image the distribution of Zn(II) ions in HeLa cells.

The phosphorus-doped macroporous carbon spheres (PMCS) with a high specific surface area (574.68 m2 g−1) were synthesized by a template method. A series of catalytic experiments showed that the PMCS possessed excellent catalytic ability for the selective oxidation of cyclooctene (conversion based on cyclooctene was 50.69% and the selectivity to epoxycyclooctane was 88.47%).

A carbon dots/tyrosinase (CDs/TYR) hybrid as a low-cost fluorescent probe for the detection of dopamine exhibits high sensitivity, stability, and precision. The detection limit of dopamine is as low as 6.0 × 10−8 mol L−1, and the wide detection range is from 1.318 × 10−4 mol L−1 to 2.06 × 10−7 mol L−1. This kind of fluorescent probe did not need enzyme immobilization and modification, and the experiment results could be revealed as soon as the probe–sample incubation was completed. More importantly, these test results are comparable to that of the present clinical fluorescence detection and high-performance liquid chromatography (HPLC), and the results show that the three methods agreed well with each other.

•Controllable assembly of unique metal–organic units•Manipulating metal–organic units to construct expectant architectures•CV behavior of the two title compoundsTwo hybrid materials based on Keggin-type polyoxometalate, [Ag4(mtrz)4(H2O)2(SiW12O40)] (1), [Ag4(mtez)5(SiW12O40)]·H2O (2), (mtrz = 1-methyl-1,2,4-triazole, mtez = 1-methyl-1,2,3,4-tetrazole), have been hydrothermally synthesized and structurally characterized. Through the use of the azole ligands mtrz and mtez, compounds 1 and 2 with totally different metal–organic units are obtained. In 1, the mtrz ligands with N atoms in meta-positions induced the formation of chain-like metal–organic units, while in 2, the mtez ligands with adjacent N atoms induced the assembly of tetranuclear units. The SiW12 anions act as bridging linkers to evolve the structural dimensionality of the two title compounds into 2D network and 3D framework, respectively.Coordination site induced different unique metal–organic units.

It is highly desired for the development of efficient bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in renewable energy technologies. In this work, cobalt, nitrogen-codoped carbon was prepared by a facile one-step method and demonstrated to exhibit good electrocatalytic performance for ORR and OER via a complete four-electron process. Besides, the catalyst prepared at 900 °C also displayed excellent stability for both ORR and OER. Furthermore, the origin of catalytic activity was also explored, which was attributed to the synergistic effects of metallic Co and quaternary N.

High-intensity fluorescent carbon dots (CDs) coupled with tyrosinase (TYR) yielded hybrids, as a fluorescent probe, which were efficient, fast, stable and sensitive in the detection of levodopa (L-DOPA). The detection limit of L-DOPA was as low as 9.0 × 10−8 mol L−1 with a wide linear range from 3.17 × 10−4 mol L−1 to 3.11 × 10−7 mol L−1. The efficient selective detection of L-DOPA can be attributed to the CDs that are excellent electron acceptors/donors and exhibit high adsorption capacity of H+. It is worth mentioning that TYR does not require modification and immobilization, and the test results could be read as soon as the probe–sample incubation was completed. Moreover, the test results are comparable to those of the present clinical fluorescence and high performance liquid chromatography (HPLC) methods. Our experimental results indicated that CDs possess great potential in the development of various enzyme-based biosensors.

Monitoring of bacterial viability is crucial for food safety and human health. Fluorescence staining with dyes is one of the simple and fast methods to assess bacterial viability. However, obtaining stable and non-poisonous dyes is still a huge challenge. Herein, we demonstrate that nitrogen, phosphorus and sulfur co-doped carbon dots (NPSCDs) can selectively stain dead bacteria rather than live ones because they possess a highly negative ζ potential (−41.9 mV), indicating that NPSCDs could serve as an efficient dye for bacterial viability evaluation. The NPSCDs were synthesized by one-step hydrothermal carbonization of a yeast extract, and exhibit favorable photoluminescence (PL) with high quantum yield (QY, 32%), excellent photostability (under acid/alkaline and strong ionic strength), good biocompatibility and low toxicity. Moreover, the designed NPSCDs show a precise response to temperature within the range from 30 °C to 90 °C, in which the fluorescence of the NPSCDs decreased linearly with an increase in temperature and recovered with a decrease in temperature. More importantly, when the live bacteria were incubated with NPSCDs, as the temperature increases, the NPSCDs could selectively stain dead bacteria in real time along with a decrease in fluorescence intensity simultaneously, showing a significant reduction in bacterial viability from 80% to 15% upon heating at 60 °C for more time. The development of NPSCDs paves a new way for the synthesis of a sensitive fluorescent probe that can be used in real-time monitoring of bacterial viability.

Since the misuse and overuse of tetracycline (TC) increase the pollution of aqueous solution, it is highly desirable to develop highly effective, stable, eco-friendly, economical, and facile photocatalysts for the photocatalytic degradation of TC in an aqueous solution. Herein, we designed and synthesized a highly efficient CoO/g-C3N4 p–n heterojunction via a facile solvothermal method. The experimental results demonstrated that after the coupling of CoO with g-C3N4, CoO nanoparticles were uniformly distributed on the surface of wrinkled g-C3N4 layers not only to readily form a p–n heterjunction, but also to avert the aggregation; and the CoO/g-C3N4 p–n heterojunction photocatalysts exhibited superior visible-light photocatalytic activity and stability for the removal of TC. The high photocatalytic activity could be attributed to the generation of an internal electric field induced by the p–n heterojunctions, effectively promoting the separation of photoinduced charge.

Chiral nanostructures have attracted extensive interest as components for chiral applications. Carbon quantum dots (CQDs) with superior properties, including low toxicity and good biocompatibility, can render the field of QDs with more potential biological applications in bioimaging, biosensors, and drug delivery. Herein, we report the fabrication of nitrogen and sulfur co-doped chiral CQDs (L-/D-CQDs) with strong symmetrical circular dichroism (CD) signals at about 212 and 240 nm. These chiral CQDs exhibit strong photoluminescence (PL) emission (at 460 nm) and outstanding enantioselective electrochemical recognition ability. A series of experiments further confirms that these chiral CQDs possess independent PL and chiral properties. With a temperature increase, PL is quenched with a good linear correlation of 0.992, whereas the CD signals remain almost the same. On the other hand, the PL of L- or D-CQDs shows no difference towards small chiral molecules detection with right or opposite configuration. In addition, the L- or D-CQDs excited with circularly polarized light (CPL) show similar PL properties regardless of their right or left configuration.

We present a simple hydrothermal method to fabricate multifunctional modified carbon dots (with –COOH, –OH, –SH, and –NH2 groups, named NS-Cdots) using citric acid and L-cysteine as raw materials. The functional NS-Cdots exhibit high fluorescent quantum yield (38.9%), low cytotoxicity and good biocompatibility. A reasonable photoluminescence mechanism of the NS-Cdots was proposed in which the pyridine derivatives serve as conjugating units and dominate the main emission behavior. The NS-Cdots can also be used as excellent fluorescent probes for cell imaging in vitro and as effective thermometers with a wide temperature detection range from 20 °C to 95 °C.

Hydrogen is an ideal energy carrier for renewable energy, but a high overpotential is required to achieve reasonable H2 evolution, which makes the design of highly active electrocatalysts for hydrogen evolution reaction (HER) urgent. Here, we report a nitrogen, sulfur co-doped carbon dots (NSCDs)/CoS hybrid with a three-dimensional mesoporous sponge-like nanostructure, fabricated via heat-treatment, which as electrocatalyst exhibits the desired electrocatalytic activity for electrochemical HER. A series of NSCDs/CoS hybrids with different contents of NSCDs were prepared by adjusting the concentration of NSCDs, of which the NSCDs/CoS hybrid with 20 mg L−1 NSCDs exhibits the best electrocatalytic activity towards HER with an onset potential of 0.095 V, an overpotential at 10 mA cm−2 of 165 mV, a small Tafel slope of 56 mV per decade, and a good stability in 0.5 M H2SO4. The excellent electrocatalytic activity of NSCDs/CoS for HER is attributed to synergetic effects of NSCDs and CoS, in which the NSCDs could protect the CoS from dissolution/agglomeration under acidic conditions, and the increased surface area of the NSCDs/CoS hybrid and the high charge transfer efficiency between NSCDs and CoS via Co–S–C bonding enhanced the HER performance.

Stable bioimaging with nanomaterials in living cells has been a great challenge and of great importance for understanding intracellular events and elucidating various biological phenomena. Herein, we demonstrate that N,S co-doped carbon dots (N,S-CDs) produced by one-pot reflux treatment of C3N3S3 with ethane diamine at a relatively low temperature (80 °C) exhibit a high fluorescence quantum yield of about 30.4%, favorable biocompatibility, low-toxicity, strong resistance to photobleaching and good stability. The N,S-CDs as an effective temperature indicator exhibit good temperature-dependent fluorescence with a sensational linear response from 20 to 80 °C. In addition, the obtained N,S-CDs facilitate high selectivity detection of tetracycline (TC) with a detection limit as low as 3 × 10−10 M and a wide linear range from 1.39 × 10−5 to 1.39 × 10−9 M. More importantly, the N,S-CDs display an unambiguous bioimaging ability in the detection of intracellular temperature and TC with satisfactory results.