Co-doped Carbon Quantum Dots Research Articles

Embedded iron and nitrogen co-doped carbon quantum dots within g-C3N4 as an exceptional PMS photocatalytic activator for sulfamethoxazole degradation: The key role of Fe[sbnd]N bridge

The covalent modification of graphite-phase carbon nitride (g-C3N4) by carbon quantum dots (CQDs) is a promising way to improve its photocatalytic performance. Although CQDs can act as charge mediator for electrons storage and transfer, it is crucial to construct efficient interfaces, which serves as active sites for tight connect with g-C3N4 and fast release of electrons. Herein, a novel iron and nitrogen co-doped carbon quantum dots (Fe, N-CQDs) assembled g-C3N4 composite (FNCCN) was constructed via FeN bridge by hydrothermal and thermal polymerization methods. The FNCNN rivaled popular nitrogen-doped carbon quantum dots (N-CQDs) combined with g-C3N4 composites for peroxymonosulfate (PMS) activation and degradation of sulfamethoxazole (SMX). The SMX degradation rate (0.0963 min−1) is 5.38 and 3.15 times higher than that of g-C3N4 and N-CQDs/g-C3N4. The characterization and DFT calculation results suggest that Fe, N-CQDs was successfully incorporated into carbon matrix of g-C3N4 via FeN covalent bond, which joints the two counterparts closely and creates electron transport channels for higher electrons transfer efficiency. The FeN coordinated structure promotes PMS reduction on Fe2+ of FeN sites for HO and SO4- production and expedited photo carries separation through Fe3+/Fe2+ cycling. In addition, the degradation efficiency, ROS identification, EPR test and degradation pathway of SMX was determined, and the intermediate toxicity of degradation products was predicted. This work constructed a tight atomic-level connection between hydrophobic g-C3N4 and hydrophilic CQDs, which improved an effective strategy for accelerating electron transport and efficient photocatalytic activation of PMS.

Photoelectrochemical quenching-recovery biosensor based on NSCQDs/Fe2O3@Bi2S3 for the detection of trypsin

BackgroundThe content of trypsin will change when pancreatic diseases occur, therefore developing a high-performance method for trypsin detection is of great significance for guiding patients on medication plans and improving their prognosis. Photoelectrochemical (PEC) analysis techniques have emerged as a solution to apply for bioassays. ResultsHerein, the Fe2O3@Bi2S3 and Nitrogen and sulfur co-doped carbon quantum dots (NSCQDs) were successfully synthesized by a hydrothermal method. Subsequently, NSCQDs/Fe2O3@Bi2S3 with a photocurrent amplification effect covered on fluorine-doped tin oxide (FTO) electrode as the substrate material and apoferritin (APO) as a bio-recognition element to quench the photocurrent of the substrate material which can be excited with light. Due to the decomposition specifically between APO and trypsin, the photocurrent response increased. The linear range for trypsin detection showed satisfied results from 2 to 1000 ng mL−1 under optimal conditions, with a detection limit of 0.42 ng mL−1 and a recovery rate of 97.41 %–103.02 %, enabling efficient quantitative analysis of trypsin. SignificanceIn this experiment, a PEC biosensor with simple operation, low detection limit, excellent selectivity and strong stability was successfully prepared, enabling quantitative analysis of trypsin in human serum samples through the quenching-recovery mechanism. It holds great significance for diagnosis and serves as a practical method for the detection of trypsin in the future.

Optimization, Kinetics, and Thermodynamics Study on the Degradation of RhB by ZnO Modified with Nitrogen and Sulfur Co-Doped Carbon Quantum Dots

Optimization, Kinetics, and Thermodynamics Study on the Degradation of RhB by ZnO Modified with Nitrogen and Sulfur Co-Doped Carbon Quantum Dots

Enhancing photocatalytic destruction of lignin via cellulose derived carbon quantum dots/g-C3N4 heterojunctions

Lignocellulosic biomass exhibits a promising potential for production of carbon materials. Nitrogen and phosphorus co-doped carbon quantum dots (N,P-CQDs) were fabricated via (NH4)2HPO4 assisted hydrothermal treatment of cellulose pulp fibers. The as-prepared N,P-CQDs were characterized by HRTEM, FTIR, fluorescence and UV–vis, and then incorporated into g-C3N4 (CN) through sonication and liquid deposition, forming N,P-CQDs/sonication treated g-C3N4 (C-SCN) composites, which were then explored as photocatalysts. The photocatalytic ability of C-SCN towards model lignin was further analyzed. The results showed that, the fluorescence intensity and photoluminescence performance of N,P-CQDs were much higher than that of CQDs; the heterojunction was successfully constructed between the composites of N,P-CQDs and SCN; the incorporation of N,P-CQDs enhanced the visible light absorption, but reduced the band gap of the composite heterojunction; the resultant photocatalysts exhibited a good photocatalytic ability of model lignin via catalyze the fracture of β–O–4′ ether bond and CC bond, i.e., the photocatalytic degradation ratio reached up to 95.5 %; and the photocatalytic reaction generated some valuable organics such as phenyl formate, benzaldehyde, and benzoic acid. This study would promote the high value-added utilization of lignocellulosic resources especially in the transformation of lignin, conforming the concept of sustainable development.

Preparation of carbon quantum dots and their application in the detection of vitamin B2.

A novel metal-doped carbon quantum dot, zinc-chlorine co-doped carbon quantum dots (Zn/Cl-CQDs), has been developed for the fluorescent probe detection of vitamin B2 and the analysis of the correlation properties of this carbon quantum dot and vitamin B2. Stability experiments demonstrate that Zn/Cl-CQDs possess good fluorescence properties under alkaline conditions. However, when vitamin B2 is added into Zn/Cl-CQDs, the fluorescence intensity decreases sharply, indicating that the fluorescence sensor shows rapid and sensitive detection of vitamin B2 under the static quenching. Lastly, the use of Zn/Cl-CQDs in the detection of vitamin B2 tablets and vitamin B2-rich fruits resulted in recovery rates of 98.2% and 100.6%, respectively. Therefore, this method can be well applied to the detection and analysis of vitamin B2, and has great development prospects in the pharmaceutical industry and food monitoring fields.

Effective construction of Cu, S-CQDs/BiVO4 composites through a facile and efficient route

Monoclinic bismuth vanadate (m-BiVO4) is a well-known photocatalytic material. However, its poor charge transport and photogenerated electron hole rapid recombination limit the application of m-BiVO4. In this paper, we successfully constructed a novel copper-sulfur co-doped carbon quantum dots (Cu, S-CQDs)/BiVO4 nanocomposite through a facile and efficient route, which significantly improved the photocatalytic performance of BiVO4. The physicochemical properties of Cu, S-CQDs and Cu, S-CQDs/BiVO4 samples were studied by various characterization. It was concluded from the degradation experiments that the photocatalytic degradation rate of rhodamine B reaches 99% in 60 min under natural light. The degradation curve compounds the quasi-primary kinetic model, and the kinetic coefficient of degradation is 0.07831 min−1, which is 5.37 times than that of pure BiVO4. Moreover, the free radical scavenging experiments reveal that the hole and superoxide radicals play a major role in the photocatalysis process. After four cycles, the activity of photocatalyst exhibits high stability, which is extremely important for the photocatalytic process. In the summery, the prepared Cu, S-CQDs/BiVO4has many advantages, such as environmental-friendly, low cost and a wide range of applications.

Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe3+, Ascorbic Acid and Alkaline Phosphatase Activities

Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe3+, Ascorbic Acid and Alkaline Phosphatase Activities

Enhancing the visible light absorption of MOF-808 by surface decoration with sulfur and nitrogen co-doped carbon quantum dots: Highly efficient photocatalyst for improved photocatalytic water remediation

Metal-organic frameworks (MOFs) have aroused growing attention in the domain of photocatalysis. However, the photocatalytic performance of MOFs has been severely restricted by their fast recombination of photo-generated electrons and low utilization of solar energy. Combining MOFs with narrow-gap semiconductors can help to overcome their functional shortcomings. In this work, MOF-808 and sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were synthesized using a simple solvothermal technique. Then, novel MOF-808/S,N-CQDs(x) (MS-x) composites were fabricated through a simple solvent-deposition technique to decorate various amounts of S,N-CQDs on the surface of MOF-808. The morphology of MOF-808 and MS-0.5 composite, along with the lattice spacing, and size distribution of decorated S,N-CQDs on MOF-808 surface were investigated by SEM and HR-TEM analyses. According to the UV–Vis DRS and Tauc plots findings, MOF-808 was not photo-active in visible light region because of its large band gap energy (3.85 eV). In contrast, the photocatalytic performance of the prepared composites in Rhodamine B (RhB) degradation was significantly enhanced compared with MOF-808 under visible light irradiation. The results confirmed that S,N-CQDs play a key role in enhancing the visible light absorption efficiency. MS-0.5 composite exhibited the highest photocatalytic activity among the other composites and demonstrated high RhB photodegradation up to 89 % under visible light and 95 % under sunlight irradiation in optimal conditions. According to the kinetic studies, MS-0.5 composite had the highest rate constant, 29.67 and 6.93 times greater than S,N-CQDs and MOF-808, respectively. The scavenger tests revealed that h+ and OH radicals were the main active intermediates in the photocatalytic reaction. In addition, MS-0.5 composite exhibited excellent reusability because only a minor loss of photoactivity was observed after four reaction cycles.

Multi-component determination based on high quantum yield “on-off-on” carbon quantum dots sensor

The nitrogen(N)-sulfur(S)-sodium(Na(I)) co-doped carbon quantum dots (CQDs) were synthesized via a one-step hydrothermal method, which exhibited a remarkably high fluorescence quantum yield (24.58%) and exceptional optical properties. The fluorescence “on-off-on” sensor was constructed. The fluorescence of CQDs was rapidly quenched with Fe(III) and the fluorescence recovered by ascorbic acid (Asc) partially and arginine (Arg)/histidine (His) completely. The CQDs fluorescence sensor demonstrated rapid response, exceptional sensitivity, excellent stability, remarkable selectivity, and robust anti-interference performance, which was feasible to simultaneously determine the concentrations of multiple analytes in the sample with satisfactory recovery rates. The “on-off-on” fluorescence mechanism of CQDs was investigated, revealing the significant potential of carbon nano-functionalized materials in the field of drug detection through fluorescence sensing.

Transfer, transportation, and adsorption of UV-B by Mg-N co doped carbon quantum dots: Response of growth indicators, antioxidant effect and mechanism explanation

Mg and N co-doped carbon quantum dots (Mg-N-CQDs) were synthesized and applied to alleviate oxygen toxicity by UV-B radiation and enhance antioxidative responses to wheat seedlings. It showed that Mg-N-CQDs pre-treatment attenuated the UV-B stress effects in a dose-dependent manner, as indicated by enhancing the characteristics of seed germination and early seedling growth parameters. Meanwhile, Mg-N-CQDs can be applied in plant nutrient solutions with nitrogen, phosphorus, potassium, and other fertilizers to promote the growth of seedlings. Furthermore, efficient antioxidant systems, chlorophyll content, and stability of fluorescence intensity were activated by Mg-N-CQDs pre-treatment, which effectively increased the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and eliminate the contents of malondialdehyde (MDA) and hydrogen peroxide, and the production rate of superoxide anion radical in the roots and germs, thereby preventing oxidative damage from UV-B stress. Notably, Mg-N-CQDs pre-treatment significantly increased the expression of related genes to improve the antioxidant capacity of roots and germs, resulting in an increased level of ATPS, CS, and GS. The mechanism study indicated that amino and hydroxyl groups and Mg, N modified CQDs could broaden the light absorption range of CQDs and improve the ability to convert blue light and ultraviolet rays to visible light, which was the main reason why Mg-N-CQDs could relieve wheat seedlings from ultraviolet stress. Therefore, Mg-N-CQDs could serve as a regulator to reduce the damage of UV-B, laying the foundation for their application in environmental protection and agricultural production.

Carbon quantum dot with co-doped nitrogen and phosphorus for tazettine ratiometric fluorescent sensing

An overdose of tazettine (TZ) has toxic side effects, which makes it extremely important to rapidly and subtly determine the TZ. In this study, double-emitting, nitrogen–phosphorus co-doped carbon quantum dots (N,P-CQDs) were prepared using cis-butenedioic acid, phosphoric acid, and p-phenylenediamine. An effective inner filter effect (IFE) can occur between TZ and N,P-CQDs, resulting in their fluorescence quench. Therefore, a ratio fluorescent probe was constructed for detecting the TZ was constructed. After optimizing the experimental conditions, the quenching efficiency showed a strong linear connection with the TZ concentration in the range of 0.01–30 µmol/L, with the detection limit of 0.002 µmol/L. This method could be satisfactorily applied to detect TZ in mouse plasma samples.

Rapid environmentally benign label free detection of heparin using highly fluorescent N,S-CDs sensing probe through a turn-on mechanism

Heparin (HEP) is one of the oldest anticoagulant drugs that currently still in widespread clinical use. It lacks chromophore and not easily derivatized due to its hydrophilic nature. In this work we developed a green, selective, and sensitive fluorescence sensor for detection of HEP in its injection dosage forms. The sensor is composed of nitrogen and sulfur co-doped carbon quantum dots (N,S-CDs) semi quenched by Fe3+. The N,S-CDs were prepared using microwave assisted pyrolysis in 3.5 min and exhibited high emission at 425 nm after excitation at 350 nm with high quantum yield of 96%. Owing to the anionic nature of HEP, it could compete with N,S-CDs for Fe3+ complexation resulting in turning-on the quenched fluorescence. This fluorescence enhancement was linear over a concentration range between 6 and 20 μg/mL (R2 = 0.99) with a limit of detection of 1.41 µg/ml. The accuracy and precision of the proposed sensor were indicated by percentage recovery values between 98% −102% and %RSD less than 2, respectively. Furthermore, the proposed sensor was successfully applied for determination of HEP in injection dosage form. The developed sensor showed excellent greenness on analytical eco-scale (score 93%) and GAPI scale.

Nitrogen and sulfur co-doped coal-based carbon quantum dots enhance the photocatalytic hydrogen evolution of Co-Fe-P derived from MOF

In order to explore the functional application of coal and realize the high-value application of low-quality coal. Therefore, low-cost coal as a carbon source into environmental protection, high-value coal-based carbon quantum dots (CQDs). This study employed high-sulfur coal as the carbon source and urea as the nitrogen source to successfully synthesize nitrogen and sulfur co-doped coal-based carbon quantum dots (NSCQDs) via a one-pot hydrothermal method. These NSCQDs were utilized as co-catalysts to assist the photocatalytic water splitting and hydrogen evolution of metal phosphides (Co-P and Fe-P). The obtained catalysts were subjected to systematic structural and property analyses, and the photocatalytic hydrogen evolution activity and stability were investigated, along with an analysis of the photocatalytic mechanism. The results revealed that the novel composite photocatalyst exhibited high hydrogen evolution activity, with a maximum hydrogen evolution rate of 28.41 mmol·g−1·h−1 at pH 10. Under a wavelength of 520 nm, the apparent quantum efficiency (AQE) reached 4.93%, and the solar-to-hydrogen (STH) conversion efficiency reached 0.46%. The semiconductor type (n-type) of the monophasic catalyst was determined through Mott-Schottky analysis, and the band structure was analyzed accordingly. The conduction and valence band positions for Co-P were determined to be -0.44 eV and 1.31 eV, respectively, while those for Fe-P were found to be -0.51 eV and 1.17 eV, respectively. Based on these results, it is inferred that an S-type heterojunction is formed between Co-P and Fe-P, and NSCQDs enhanced photocatalytic hydrogen evolution as an auxiliary catalyst. This research advances the synthesis of coal-based carbon quantum dots and provides the key information for the photocatalytic decomposition of water and hydrogen evolution using coal-based CQDs.

Facile synthesis of nitrogen, sulfur co-doped carbon quantum dots for selective detection of mercury (II)

Facile synthesis of nitrogen, sulfur co-doped carbon quantum dots for selective detection of mercury (II)

N,P co-doped carbon quantum dots bridge g-C3N4 and SnO2: Accelerating charge transport in S-scheme heterojunction for enhanced photocatalytic hydrogen production

The preparation of photocatalysts with efficient electron-hole separation efficiency is the key to achieving sustainable utilization of solar energy. Herein, a three-phase composite of N,P co-doped carbon dots (NPCDs), SnO2 nanowires, and g-C3N4 nanotubes (CNNT) is synthesized, forming an S-scheme SnO2/NPCDs/CNNT heterojunction. The construction of S-scheme heterojunction not only improves the reduction ability due to band bending, but also promotes the separation of carriers. The conductive NPCDs are located between SnO2 and CNNT and formed as a unique charge transfer channel that accelerates carriers transfer between S-scheme heterojunction interfaces. Additionally, NPCDs serves as electron acceptors to receive electrons from the conduction band of CNNT, thereby further facilitating the carrier separation. This synergistically boosts the photocatalytic hydrogen production activity of SnO2/NPCDs/CNNT three-phase catalysts, leading to a high H2 yield (10.73 mmol·g−1·h−1) and outstanding cyclic stability. This study offers a strategy for designing heterostructure photocatalysts that enhanced charge separation through interface engineering.

Lanthanum nitrogen Co-doped carbon quantum dots as optical and smartphone sensors for serotonin detection

A simple bottom up approach using hydrothermal technique was applied to prepare lanthanum and nitrogen Co-doped carbon quantum dots and were characterized by XRD, EDS, TEM, SEM FT-IR, XPS, fluorescence and UV-VIS spectroscopy to study their crystal structure, elemental and chemical composition, particle size, morphology and optical properties. It was found that morphology was spherical and particle size was 3–4 nm. EDS and XPS helps to prove the successful doping of lanthanum and nitrogen to carbon quantum dots with excitation and emission wavelengths 340 and 445 nm respectively. The intense blue color of fluorescent QDs were quenched with addition of serotonin due to the electrostatic interactions, π-π stacking interaction and may be due to complex formation between La,N-CQDs/Ser and the static quenching mechanism with inner filter effect has been observed. These La,N-CQDs were used as fluorescent probes for sensitive and selective detection of serotonin in a good linear range of 0–38 nM with low limit of detection 7.4 nM.The smartphone based portable detection was also developed for detection of serotonin providing the reliable information for analysis of color change and real sample analysis studies were also carried out. The uniqueness, high sensitivity and accuracy of the optical probe that was constructed are confirmed and this method's LOD is also highly competitive.

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots (NSCQDs) nanoparticles on the surface of sheet cobalt-based metal-organic framework (Co-MOF) and graphitic carbon nitride (g-C3N4, CN). The structure and properties of the obtained catalysts were systematically analyzed. NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region. The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254 μmol/(g·h) at pH = 9. At the same time, NSCQDs synergy Co-MOF/CN composites have good stability. After four cycles of hydrogen production, the performance remains relatively stable. The transient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts. The semiconductor type (n-type semiconductor) of the single-phase catalyst was determined by the Mott–Schottky test, and the band structure was analyzed. The conductive and valence bands of CN are −0.99 and 1.72 eV, respectively, and the conduction and valence bands of Co-MOF are −1.85 and 1.33 eV, respectively. The mechanism of the photocatalytic reaction can be inferred, that is, Z-type heterojunction is formed between CN and Co-MOF, and NSCQDs was used as cocatalyst.

Facile synthesis of NS-doped carbon dots as sensitive “ON-OFF-ON” fluorescent sensor for Cu2+ and GSH detection

In this paper, a novel nitrogen and sulfur co-doped carbon quantum dots (NS-CQDs) were successfully prepared by a dehydration exothermic carbonization method. The NS-CQDs exhibited uniform size distribution, splendid photostability, and bright fluorescence emission with a fluorescence quantum yield of 24.1 %. It was found that Cu2+ could quench the fluorescence at 467 nm based on the static quenching effect when Cu2+ was added to the NS-CQDs. At this time, the fluorescence sensor changed from the “ON” state to the “OFF” state. When glutathione (GSH) was further introduced into the NS-CQDs/Cu2+ system, the fluorescence intensity of NS-CQDs was amazingly restored through the coordination reaction between GSH and Cu2+. The fluorescence sensor changed from the “OFF” state to the “ON” state. Therefore, NS-CQDs as an “ON-OFF-ON” fluorescence sensor was designed for sequential detection of Cu2+ and GSH. Furthermore, this study successfully demonstrated the sensor’s ability to selectively detect Cu2+ and GSH within a wide concentration range. Specifically, the detection range for Cu2+ was 0.1 μM−200.0 μM with a detection limit of 0.07 μM, while the range for GSH was 0.6 μM−180.0 μM with a detection limit of 0.1 μM. Most importantly, the NS-CQDs nanosensor could reliably monitor Cu2+ and GSH levels in human serum samples, with significant potential for practical applications.

Green “turn-off” luminescent nanosensors for the sensitive determination of desperately fluorescent antibacterial antiviral agent and its metabolite in various matrices

Nitazoxanide (NTX) is an antimicrobial drug that was used for the treatment of various protozoa. However, during the coronavirus pandemic, NTX has been redirected for the treatment of such virus that primarily infect the respiratory tract system. NTX is now used as a broad-spectrum antiviral agent. In this study, a highly sensitive and green spectrofluorometric method was developed to detect NTX in various dosage forms and its metabolite, tizoxanide (TX), in human plasma samples using nitrogen and sulfur co-doped carbon quantum dots nanosensors (C-dots). A simple and eco-friendly hydrothermal method was used to synthetize water soluble C-dots from citric acid and l-cysteine. After excitation at 345 nm, the luminescence intensity was measured at 416 nm. Quenching of C-dots luminescence occurred upon the addition of NTX and was proportional to NTX concentration. Assessment of the quenching mechanism was performed to prove that inner filter effect is the underlying molecular mechanism of NTX quenching accomplished. After optimizing all experimental parameters, the analytical procedure was evaluated and validated using the ICH guidelines. The method linearity, detection and quantification limits of NTX were 15 × 10–3–15.00 µg/mL, 56.00 × 10–4 and 15 × 10–3 µg/mL, respectively. The proposed method was applied for the determination of NTX in its commercial pharmaceutical products; Nanazoxid® oral suspension and tablets. The obtained % recovery, relative standard deviation and % relative error were satisfactory. Comparison with other reported spectrofluorimetric methods revealed the superior sensitivity of the proposed method. Such high sensitivity permitted the selective determination of TX, the main metabolite of NTX, in human plasma samples making this study the first spectrofluorimetric method in literature that determine TX in human plasma samples. Moreover, the method greenness was assessed using both Eco-Scale and AGREE approaches to prove the superiority of the proposed method greenness over other previously published spectrofluorimetric methods for the analysis of NTX and its metabolite, TX, in various dosage forms and in human plasma samples.

Integration of N, P-doped carbon quantum dots with hydrogel as a solid-phase fluorescent probe for adsorption and detection of Fe3+

In this work, a novel nitrogen-phosphorus co-doped carbon quantum dots (N, P-CQDs) hydrogel was developed utilizing the as-synthesized N, P-CQDs and acrylamide (AM) with the existence of ammonium persulfate and N, N′-methylene bisacrylamide (N-MBA). In consistent with pure N, P-CQDs, the N, P-CQDs hydrogel also shows a dramatic fluorescence property with maximum emission wavelength of 440 nm, which can also be quenched after adsorbing iron ions (Fe3+). When the concentration of Fe3+ is 0–6 mmol l−1, a better linear relationship between Fe3+ concentration and the fluorescence intensities can be easily obtained. Additionally, the N, P-CQDs hydrogel exhibits better recyclability. This confirms that the N, P-CQDs hydrogel can be used for adsorbing and detecting Fe3+ in aqueous with on–off–on mode. The fluorescence quenching mainly involves three procedures including the adsorption of Fe3+ by hydrogel, integration of Fe3+ with N, P-CQDs and the transportation of conjugate electrons in N, P-CQDs to the vacant orbits of Fe3+ and the adsorption process follows a pseudo-second-order kinetic model confirmed in the Freundlich isotherm model. In conclusion, this work provides a novel route for synchronously removing and detecting the metal ions in aqueous by integrating N, P-CQDs with hydrogel with better recyclability.