Fluorescent sensing platform for the detection of p-nitrophenol based on Cu-doped carbon dots

Optical Materials 97 (2019) 109396

Contents lists available at ScienceDirect

Optical Materials journal homepage: www.elsevier.com/locate/optmat

Fluorescent sensing platform for the detection of p-nitrophenol based on Cudoped carbon dots

T

Jing Fanga, Shujuan Zhuoa,b,∗, Changqing Zhua,∗∗ a

Anhui Laboratory of Molecule-Based Materials, Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Key Laboratory of Chemo-Biosensing, School of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, PR China b Anhui Meijia New Materials Company Limited, Wuhu, 241000, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: Cu-doped carbon dots p-Nitrophenol Inner filter effect Fluorescence detection

In this study, we presented a facile strategy to synthesis Cu-doped carbon dots (Cu-CDs) through one-step hydrothermal approach using CuCl2·2H2O and ethanediamine as reaction precursor. Interestingly, the fluorescence of Cu-CDs can be quenched greatly in the presence of p-nitrophenol. Thus, a high selectivity and sensitivity fluorescent sensing platform is constructed for the detection of p-nitrophenol on account of the inner filter effect. Under the optimal condition, the linear detection range is 0.5–50 μM with the detection limit of 0.08 μM (S/ N = 3). This method is successfully applied in quantification of p-nitrophenol in lake water samples, which exhibits potential application prospect.

1. Introduction p-Nitrophenol (p-NP) is a kind of compound widely utilized in fine chemicals. It is used as a raw material or additive for various chemicals, such as pesticides, medicines, dyes, rubber additives, photosensitive materials, and vulcanized materials [1]. However, p-NP can be absorbed by the skin, simultaneously, long-term exposure can stimulate and inhibit the central nervous system and vagal nerve endings, and induce various diseases [2]. Thus, US Environmental Protection Agency (EPA) lists it as a priority pollutant control list [3]. Since p-NP contaminants can cause severe harm to the health of human beings and environment, establishing a rapid, simple, low-cost and sensitive protocol for examining of trace p-NP in environmental samples is of considerable significance [4]. So far, various tools have been developed for the detection of p-NP, including electrochemical [5], phosphorimetric [6], electrocatalytic [7], and colorimetric method [8]. Due to these methods have some defects, such as the preparation process is complex and expensive, which limits their broad use. In contrast, fluorescence analysis displays superiority on account of simplicity, sensitivity and rapidity [9,10]. Consequently, some fluorescent probes or chemosensors have been reported for p-NP assay [11–14]. Carbon dots (CDs) have been widely applied in various fields, for example, energy conversion and storage [15], anticounterfeiting and energyption [16], vivo bioimaging and theranostics [17], neuronal

manipulations [18], sensing [19], fingerprint imaging [20] and photocatalysis [21], owing to unique performance including high stability, good biocompatibility, small sizes, and fascinating photophysi/chemi properties [22]. Although CDs have many excellent properties, their functionality and low fluorescence quantum yield still pose serious challenges [23]. Heteroatom doped carbon and/or other materials have become prevalent means to enhance the performance of these materials [24–34]. Accordingly, heteroatom doping is also a good strategy to improve the fluorescence quantum yield, alter electronic characteristics and endow novel functionalities to the CDs [35,36]. Particularly, metaldoped carbon dots have become a current research focus in virtue of their exceptional optical properties [37–40]. So far, many methods are explored to produce nanomaterials [41–43], including hydrothermal route [44,45], microwave synthesis [46,47], solvothermal reaction [48,49] and high-temperature calcination [50]. Among them, the hydrothermal method has been the most extensively used for its simplicity and environmental friendliness [51]. Simultaneously, the nanomaterials have been widely applied in many fields [52–55], including heavy removal or extract [56–60], supercapacitor [61,62], electromagnetic interference shielding [63], photovoltaic devices [64], anticorrosion [65] and sensing/sensor [66–71]. Herein, we synthesized metal Cu-doped carbon dots (Cu-CDs) via single-step hydrothermal route and designed a simple but effective method to detect p-NP based on Cu-CDs (Scheme 1). This analysis

∗

Corresponding author. Anhui Laboratory of Molecule-Based Materials, Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Key Laboratory of Chemo-Biosensing, School of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, PR China ∗∗ Corresponding author. E-mail addresses: [email protected] (S. Zhuo), [email protected] (C. Zhu). https://doi.org/10.1016/j.optmat.2019.109396 Received 28 July 2019; Received in revised form 14 September 2019; Accepted 18 September 2019 0925-3467/ © 2019 Elsevier B.V. All rights reserved.

Optical Materials 97 (2019) 109396

J. Fang, et al.

Then the solution was diluted to 2 mL with ultrapure water and incubated at room temperature for 2 min to react completely. Afterwards, the fluorescence intensities were measured with the following settings of the spectrofluorimeter: photomultiplier tube voltage, 900 V; excitation and emission band-passes, 10 nm. 2.5. Assay of p-NP in lake water The performance of this probe for assay p-NP in real water samples was studied using the standard addition method. Besides, lake water samples obtained from the lake of Anhui Normal University, and samples were treated according to the previous report [72]. Firstly, the lake water samples were treated by filtration to remove impurities. Then, the lake water samples (10 mL) were centrifuged at 10000 rpm for 20 min to remove the precipitation, and the supernatant was transferred to the filter through a 0.22 μm membrane to further remove impurity substance. Next, 200 μL of the Cu-CDs solutions, 1 mL PBS buffer and different amounts of p-NP were added into volumetric tube sequentially, then 100 μL lake water samples were added. And the mixture was diluted to 2 mL with ultrapure water. After equilibrium for 2 min, the obtained mixture was used for fluorescence determination.

Scheme 1. Preparation of Cu-CDs and the proposed sensing mechanism schematic for p-NP detection.

system exhibited rapid response to p-NP within 2 min. Significantly, the sensing mechanism was proposed that the possible reason was attributed to the inner filter effect (IFE) induced fluorescence quenching of pNP towards Cu-CDs. Notably, the developed method was successfully used for p-NP assay in lake water samples, demonstrating that as-obtained Cu-CDs have great potential for practical application in environmental field. 2. Experimental section 2.1. Chemical and materials

3. Results and discussion

p-Nitrophenol (99%), ethanediamine, lysine (Lys) and glutamic acid (Glc) were obtained from Macklin Biochemical Co. Ltd (Shanghai, China). Copper (II) chloride dihydrate (CuCl2·2H2O) (99%), potassium chloride (KCl), zinc chloride (ZnCl2), ferric chloride (FeCl3) and glucose (Glu) were purchased from Sinopharm (Shanghai, China). Hydroquinone (H2Q), resorcinol, o-aminophenol (OAP), uric acid (UA) and catechol were acquired from Aladdin (Shanghai, China). Phosphate buffer (PBS, 0.1 M) was prepared by mixing solutions of Na2HPO4·12H2O and NaH2PO4·2H2O. All other reagents were of analytical grade and no need to be further purification when using. Ultrapure water (18.2 MΩ cm) was used throughout.

3.1. Characterization of the Cu-CDs The Cu-CDs can be obtained through a one-pot hydrothermal route. As shown in Fig. 1a, transmission electron microscopy (TEM) image confirmed the morphology of the Cu-CDs. It indicates that the shape of the as-prepared Cu-CDs is spherical and reveals that the Cu-CDs possess a good monodispersity and narrow size distribution, the diameter of the obtained Cu-CDs ranged between 1 and 3 nm, with an average diameter of 1.8 nm (Fig. 1b). The high resolution TEM (HRTEM) image (inset in Fig. 1a) displays an interplanar spacing of about 0.23 nm, which is similar to that of (100) lattice plane of graphitic carbon, indicating the crystalline nature of Cu-CDs. The effects of pH, ionic strengths and UV exposure on the stability of the Cu-CDs were measured and presented in Fig. 2. The fluorescence intensity of Cu-CDs gradually increase with pH increment from 5 to 12 (Fig. 2a), while the intensity displays negligible change after irradiated under UV light (365 nm) for 60 min (Fig. 2b), indicating their excellent photo-stability. Additionally, Cu-CDs maintain stable fluorescence intensities even the concentration of NaCl reaching as high as 1 M (Fig. 2c). The chemical composition and structure were further characterized by FTIR spectrum. As can be seen from Fig. 3a, the characteristic absorption peak around 3448 cm−1 is attributed to the stretching vibration of O–H group. The peak located at 2861 cm−1 is ascribed to the stretching vibration of C–H bond. The peak centered at 1595 cm−1 stems from the C]C stretching vibration. The peak appeared at 1454 and 1361 cm−1 could be identified as C–N and C–O groups [73], indicating that nitrogen and oxygen-containing groups are presence on the surface of CDs, which imparts high water-solubility to CDs.

2.2. Instruments Fluorescence study was conducted on a FS5 Fluorescence Spectrophotometer. X-ray photoelectron spectroscopy (XPS) data were collected using an ESCALAB 250XI electron spectrometer (Thermo, USA). Transmission electron microscopy (TEM) was carried out on a HT-7700 (Tokyo, Japan). Fourier transform infrared (FTIR) spectrum was recorded using a PerkinElmer FTIR spectrophotometer (PE-983, USA) using KBr pellet at room temperature. UV–Vis absorption spectra were measured from a U-2910 spectrophotometer (Hitachi, Japan). 2.3. Preparation of Cu-doped CDs The Cu-CDs were prepared by one-step hydrothermal treatment of ethanediamine and CuCl2·2H2O as reaction precursor. Briefly, 1 mL ethanediamine and 0.1 g CuCl2·2H2O were dissolved in 29 mL of ultrapure water under bath sonication for 5 min. Following the mixture solution was transferred into a 50 mL Teflon-equipped stainless steel autoclave, the reaction system was sealed and heated at 180 °C for 10 h. After the obtained solution was cooled down to room temperature naturally, the products were collected by centrifuging. Finally, the obtained Cu-CDs solution was purified using a dialysis bag (MWCO 1000) for 24 h to remove the impurities. After purification, the Cu-CDs aqueous solution was stored at 4 °C before use. 2.4. Fluorescence analysis of p-NP A fluorescence assay for p-NP under the following procedures. Briefly, 200 μL of the Cu-CDs solutions was put into 1 mL of PBS (0.1 M, pH 11), followed by the addition of different concentrations of p-NP.

Fig. 1. (a) TEM and HRTEM (inset) images of the Cu-CDs. (b) The corresponding particles size distribution. 2

Optical Materials 97 (2019) 109396

J. Fang, et al.

Fig. 2. Fluorescence intensity variations of the Cu-CDs as a function of (a) pH, (b) UV exposure and (c) concentration of NaCl.

The full XPS survey spectrum of the Cu-CDs clearly shows four peaks at 285.1, 401, 532.1 and 935.1 eV (Fig. 3b), which are attributed to C 1s, N 1s, O 1s and Cu 2p, respectively. And the corresponding content of each element is C 50.56%, N 11.73%, O 36.2% and Cu 1.51% (At%). The appearance of the C 1s peak (Fig. 4a) at 284.6, 285.1 and 285.9 eV, are ascribed to C–C/C]C, C–N and C–O [74], respectively. Additionally, the N 1s spectrum exhibits three peaks at 399.5, 400.1 and 406.6 eV (Fig. 4b) that may be assigned to C–N–C, C–N/N–H and NO3 groups [75,76]. The high resolution O 1s spectrum in Fig. 4c could be deconvoluted into two peaks, locating at 531.9 and 532.6 eV, which are belong to C–O and C]O/N]O groups [77]. The Cu 2p spectrum (Fig. 4d) displays that the metal copper doped into CDs successfully. There exists two main peaks at 934.8 and 954.7 eV, which is likely classified to Cu 2p3/2 and Cu 2p1/2 bonding orbitals [78]. 3.2. Optical properties of Cu-CDs The UV–Vis absorption and fluorescence spectra of Cu-CDs were depicted in Fig. 5a. The absorption spectrum of the Cu-CDs exhibited two absorption peaks around at 227 and 318 nm, which may be assigned to the π-π* transition of aromatic sp2 domain and n-π* transition of C]O [79]. Meanwhile, the Cu-CDs show a maximum emission at 380 nm with excitation wavelength at 320 nm. Moreover, excitationdependent behavior of Cu-CDs was also observed (Fig. 5b), which likely attributed to the existence of different-size nanodots and considerable of emissive traps sites on the Cu-CDs surface [80]. The fluorescence quantum yield of the Cu-CDs is 7.8% (quinine sulfate as a reference).

Fig. 4. High-resolution XPS spectra of (a) C 1s, (b) N 1s, (c) O 1s and (d) Cu 2p of the Cu-CDs.

at higher pH. The experimental results show that pH 11 was the optimum value. Therefore, pH 11 was selected for sensing system. The incubation time was optimized in Fig. 6b. Upon the addition of p-NP, the fluorescence intensity of Cu-CDs decreased rapidly with time and become slowly after 2 min. Thus, 2 min was chosen for the sensing.

3.3. Optimization of experimental conditions 3.4. Fluorescence assay for p-NP

To obtain excellent sensing performance of Cu-CDs, we evaluated critical analytical parameters, including pH and reaction time. As we all known, pH values of the buffer is a key factor for the reacting system. As presented in Fig. 6a, the fluorescence intensity of Cu-CDs progressively raise in selected pH range. Addition of p-NP led to fluorescence quenching in the whole pH range and quenching extent was enhanced

Cu-CDs are expected to be ideal candidate to detect p-NP under the optimum conditions. When adding different amounts p-NP into Cu-CDs solution, the response of Cu-CDs fluorescence was illustrated in Fig. 7a. As can be seen that the fluorescence intensity of Cu-CDs decreases

Fig. 3. (a) FT-IR spectrum and (b) XPS full scan of Cu-CDs. 3

Optical Materials 97 (2019) 109396

J. Fang, et al.

Fig. 5. (a) UV–Vis absorption and fluorescence spectra of Cu-CDs. (b) Excitation-dependent emission of Cu-CDs.

Fig. 6. (a) Fluorescence response of the proposed method at different pH values. (b) Time-dependent fluorescence response of the sensing system. The concentration of p-NP is 50 μM. The error bar represents the standard deviation for three determinations. Fig. 7. (a) The fluorescence emission spectra with increasing p-NP concentration, p-NP concentration was 0, 0.5, 1, 5, 10, 20, 45 and 50 μM (from top to bottom), respectively. (b) The calibration curve of pNP obtained with Cu-CDs. F0 and F are the intensity of the Cu-CDs in the absence and presence of p-NP. The error bars mean the standard deviation of three assays.

3.5. Possible sensing mechanism of Cu-CDs to p-NP

Table 1 Comparison of analytical performance for p-NP sensing using fluorescent methods. Materials

Linear range (μM)

LOD (μM)

Refs.

MIP-capped CdTe QDs B,N-CDs Cr-CDs NCDs Amine-CQDs@UiO-66 PCDs Cu-CDs

1–30 0.5–60 0.8–150 0.1–100 0.01–20 0.5–60 0.5–50

0.04 0.2 0.27 0.017 0.0035 0.26 0.08

[81] [82] [83] [84] [85] [86] This work

Fig. 8a reveals that there is a substantial wide overlap between the absorption spectrum of p-NP and the emission spectrum of the Cu-CDs. The result indicates the possibility of IFE process occurred between the Cu-CDs and p-NP. Moreover, Fig. 8b shows the fluorescence lifetime profiles of the Cu-CDs alone and mixture of the Cu-CDs and p-NP. We can see that the fluorescence lifetime is almost unchanged with the addition of p-NP. To further explore the detection mechanism for p-NP, the UV–Vis absorption spectra of Cu-CDs, p-NP and Cu-CDs + p-NP system were measured. As described in Fig. 8c, compared with the absorption spectrum of p-NP alone, no new absorption peak appeared upon addition of Cu-CDs, indicating that no ground state complexes are formed between Cu-CDs and p-NP. By combination of larger spectral overlap and invariant fluorescence lifetime, the possible quenching mechanism of p-NP towards Cu-CDs was ascribed to IFE [87,88].

gradually with increment of p-NP. The linear detection range is 0.5–50 μM with the limit of detection (LOD) as low as 0.08 μM (R2 = 0.998, Fig. 7b). Additionally, the sensing performance is comparable to those of other fluorescent analytical methods, as summarized in Table 1.

4

Optical Materials 97 (2019) 109396

J. Fang, et al.

Fig. 8. (a) The UV–Vis absorption spectrum of p-NP and the fluorescence emission spectrum for Cu-CDs. (b) The fluorescence decay curves of Cu-CDs in the absence and presence of p-NP. (c) UV–Vis absorption spectra of Cu-CDs, p-NP and Cu-CDs + p-NP system.

4. Conclusions In summary, a facile and green synthesis route has developed for preparation of fluorescent Cu-CDs. Moreover, a high selectivity and sensitivity sensing platform was constructed to detection p-NP based on Cu-CDs probe. The possible mechanism for the fluorescence sensing was attributed to inner filter effect of p-NP towards Cu-CDs. Importantly, the proposed sensing strategy is successfully applied to the detection of pNP in lake water samples, demonstrating potential application in environmental monitoring. Declaration of competing interest Fig. 9. The fluorescence response of the Cu-CDs in the presence of 40 μM different species. F0 and F are the intensity of the Cu-CDs in the absence and presence of interferent.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Table 2 Detection of p-NP in lake water samples. Samples

1

2

3

Acknowledgments

Spiked (μM)

Found (μM)

Recovery (%)

3 3 3 20 20 20 45 45 45

2.94 3.07 3.08 20.96 20.4 19.8 46.8 45.9 44.5

98 102 103 105 102 99 104 102 98.9

RSD (%)

2.6

This work was supported by Anhui Laboratory of Molecule-Based Materials Open Fund (No. fzj19006) and National Natural Science Foundation of China (Nos. 21303003 and 21375003).

2.8

References [1] T. Shu, J.X. Wang, X.F. Lin, Z.P. Zhou, F. Liang, L. Su, X.J. Zhang, Dual-emissive gold nanoclusters for label-free and separation-free ratiometric fluorescence sensing of 4-nitrophenol based on the inner filter effect, J. Mater. Chem. C 6 (2018) 5033–5038 https://doi.org/10.1039/c8tc00448j. [2] B. Dinesh, R. Saraswathi, Electrochemical synthesis of nanostructured copper-curcumin complex and its electrocatalytic application towards reduction of 4-nitrophenol, Sens. Actuators B 253 (2017) 502–512 https://doi.org/10.1016/j.snb. 2017.06.149. [3] J. Bjerketorp, W.F.M. Röling, X.M. Feng, A.H. Garcia, H.J. Heipieper, S. Håkansson, Formulation and stabilization of an Arthrobacter strain with good storage stability and 4-chlorophenol-degradation activity for bioremediation, Appl. Microbiol. Biotechnol. 102 (2018) 2031–2040 https://doi.org/10.1007/s00253-017-8706-6. [4] H. Yuan, J. Yu, S.L. Feng, Y.J. Gong, Highly photoluminescent pH-independent nitrogen-doped carbon dots for sensitive and selective sensing of p-nitrophenol, RSC Adv. 6 (2016) 15192–15200 https://doi.org/10.1039/c5ra26870b. [5] J.I. Colades, M.D.G. de Luna, M.F.N. Secondes, C.P. Huang, Electrochemical in-situ hydrogen peroxide generation in a packed-bed reactor for Fenton oxidation of pnitrophenol in aqueous solution, Process Saf. Environ. Prot. 123 (2019) 161–168 https://doi.org/10.1016/j.psep.2018.10.014. [6] S.Q. Luo, Y.M. Miao, J.P. Guo, X.J. Sun, G.Q. Yan, Phosphorimetric determination of 4-nitrophenol using mesoporous molecular imprinting polymers containing manganese (II)-doped ZnS quantum dots, Microchim. Acta 186 (2019) 249 https:// doi.org/10.1007/s00604-019-3362-4. [7] P. Balasubramanian, T.S.T. Balamurugan, S.M. Chen, T.W. Chen, Simplistic synthesis of ultrafine CoMnO3 nanosheets: an excellent electrocatalyst for highly sensitive detection of toxic 4-nitrophenol in environmental water samples, J. Hazard Mater. 361 (2019) 123–133 https://doi.org/10.1016/j.jhazmat.2018.08.070. [8] S. Scarano, P. Palladino, E. Pascale, A. Brittoli, M. Minunni, Colorimetric determination of p-nitrophenol by using ELISA microwells modified with an adhesive polydopamine nanofilm containing catalytically active gold nanoparticles, Microchim. Acta 186 (2019) 146 https://doi.org/10.1007/s00604-019-3259-2. [9] T.F. Hao, X. Wei, Y.J. Nie, Y.Q. Xu, Y.S. Yan, Z.P. Zhou, An eco-friendly molecularly imprinted fluorescence composite material based on carbon dots for fluorescent detection of 4-nitrophenol, Microchim. Acta 183 (2016) 2197–2203 https://doi. org/10.1007/s00604-016-1851-2.

2.5

3.6. Selectivity detection for p-NP The selectivity of method is an vital parameter. So, various common substances, including several substances with similar structure to p-NP, amino acids, and different ions were investigated. As described in Fig. 9, the fluorescence of the Cu-CDs was quenched significantly on the addition of p-NP compared with other interfering species, namely, other substance have little effect on the fluorescence of the Cu-CDs at the same concentration, indicating that Cu-CDs possess excellent selectivity for assay of p-NP.

3.7. Application of the p-NP detection method in water samples To evaluate the potential application of the Cu-CDs, we used the CuCDs based fluorescence sensing platform for detection of p-NP quantitatively in real lake water samples. As displayed in Table 2, it was found that the observed values were consistent with those of the added p-NP with relative standard deviation (RSD) within 2.5–2.8%. In addition, the satisfactory recoveries of the real samples were 98–105%. These results show that the method has a good application prospect in the field of environmental assessment. 5

Optical Materials 97 (2019) 109396

J. Fang, et al. [10] S. Geng, S.M. Lin, S.G. Liu, N.B. Li, H.Q. Luo, A new fluorescent sensor for detecting p-nitrophenol based on β-cyclodextrin-capped ZnO quantum dots, RSC Adv. 6 (2016) 86061–86067 https://doi.org/10.1039/c6ra17378k. [11] M. Tian, Y.M. Liu, Y.T. Wang, Y. Zhang, Yellow-emitting carbon dots for selective detecting 4-NP in aqueous media and living biological imaging, Spectrochim. Acta, Part A 220 (2019) 117117 https://doi.org/10.1016/j.saa.2019.05.022. [12] G.H.G. Ahmed, R.B. Laíño, J.A.G. Calzón, M.E.D. García, Highly fluorescent carbon dots as nanoprobes for sensitive and selective determination of 4-nitrophenol in surface waters, Microchim. Acta 182 (2015) 51–59 https://doi.org/10.1007/ s00604-014-1302-x. [13] X. Wei, Z.P. Zhou, T.F. Hao, H.J. Li, Y.Z. Zhu, L. Gao, Y.S. Yan, A novel molecularly imprinted polymer thin film at surface of ZnO nanorods for selective fluorescence detection of para-nitrophenol, RSC Adv. 5 (2015) 44088–44095 https://doi.org/10. 1039/c5ra05093f. [14] M. Mao, C. Deng, Y. He, Y.L. Ge, G.W. Song, Fluorescence detection of p-nitrophenol in water using bovine serum albumin capped ag nanoclusters, J. Fluoresc. 27 (2017) 1421–1426 https://doi.org/10.1007/s10895-017-2080-8. [15] C. Hu, M.Y. Li, J.S. Qiu, Y.P. Sun, Design and fabrication of carbon dots for energy conversion and storage, Chem. Soc. Rev. 48 (2019) 2315–2337 https://doi.org/10. 1039/c8cs0075k. [16] H.Y. Yang, Y.L. Liu, Z.Y. Guo, B.F. Lei, J.L. Zhuang, X.J. Zhang, Z.M. Liu, C.F. Hu, Hydrophobic carbon dots with blue dispersed emission and red aggregation-induced emission, Nat. Commun. 10 (2019) 1789 https://doi.org/10.1038/s41467019-09830-6. [17] J.J. Du, N. Xu, J.L. Fan, X.J. Peng, Carbon Dots for in Vivo Bioimaging and Theranostics, Small (2019) 1805087 https://doi.org/10.1002/small.201805087. [18] V.B. Kumar, R. Kumar, A. Gedanken, O. Shefi, Fluorescent metal-doped carbon dots for neuronal manipulations, Ultrason. Sonochem. 52 (2019) 205–213 https://doi. org/10.1016/j.ultsonch.2018.11.017. [19] D. Gu, P.B. Zhang, L. Zhang, H. Liu, Z.B. Pu, S.M. Shang, Nitrogen and phosphorus co-doped carbon dots derived from lily bulbs for copper ion sensing and cell imaging, Opt. Mater. 83 (2018) 272–278 https://doi.org/10.1016/j.optmat.2018.06. 012. [20] I. Milenkovic, M. Algarra, C. Alcoholado, M. Cifuentes, J.M. Lázaro-Martínez, E. Rodríguez-Castellón, D. Mutavdžić, K. Radotić, T.J. Bandosz, Fingerprint imaging using N-doped carbon dots, Carbon 144 (2019) 791–797 https://doi.org/10.1016/j. carbon.2018.12.102. [21] S.J. Zhuo, M.W. Shao, S.T. Lee, Upconversion and downconversion fluorescent graphene quantum dots: ultrasonic preparation and photocatalysis, ACS Nano 6 (2012) 1059–1064 https://doi.org/10.1021/nn2040395. [22] F.S. Wu, M.Q. Yang, H. Zhang, S.Z. Zhu, X.J. Zhu, K. Wang, Facile synthesis of sulfur-doped carbon quantum dots from vitamin B1 for highly selective detection of Fe3+ ion, Opt. Mater. 77 (2018) 258–263 https://doi.org/10.1016/j.optmat.2018. 01.048. [23] P.G. Luo, S. Sahu, S.T. Yang, S.K. Sonkar, J.P. Wang, H.F. Wang, G.E. LeCroy, L. C, Y.P. Sun, Carbon “quantum” dots for optical bioimaging, J. Mater. Chem. B 1 (2013) 2116–2127 https://doi.org/10.1039/c3tb00018d. [24] S.Z. Xu, Y.L. Lv, X.F. Zeng, D.P. Cao, ZIF-derived nitrogen-doped porous carbons as highly efficient adsorbents for removal of organic compounds from wastewater, Chem. Eng. J. 323 (2017) 502–511 https://doi.org/10.1016/j.cej.2017.04.093. [25] Y.J. Zhai, J. Wang, Q. Gao, Y.Q. Fan, C.X. Hou, Y. Hou, H. Liu, Q. Shao, S.D. Wu, L.L. Zhao, T. Ding, F. Dang, Z.H. Guo, Highly efficient cobalt nanoparticles anchored porous N-doped carbon nanosheets electrocatalysts for Li-O2 batteries, J. Catal. 377 (2019) 534–542 https://doi.org/10.1016/j.jcat.2019.07.055. [26] C.X. Hou, J. Wang, W. Du, J.C. Wang, Y. Du, C.T. Liu, J.X. Zhang, H. Hou, F. Dang, L.L. Zhao, Z.H. Guo, One-pot synthesized molybdenum dioxide-molybdenum carbide heterostructures coupled with 3D holey carbon nanosheets for highly efficient and ultrastable cycling lithium-ion storage, J. Mater. Chem. 7 (2019) 13460–13472 https://doi.org/10.1039/c9ta03551f. [27] M. Idrees, S. Batool, J. Kong, Q. Zhuang, H. Liu, Q. Shao, N. Lu, Y.N. Feng, E.K. Wujcik, Q. Gao, T. Ding, R.B. Wei, Polyborosilazane derived ceramics-nitrogen sulfur dual doped graphene nanocomposite anode for enhanced lithium ion batteries, Electrochim. Acta 296 (2019) 925–937 https://doi.org/10.1016/j.electacta. 2018.11.088. [28] W. Du, X.N. Wang, J. Zhan, X.Q. Sun, L.T. Kang, F.Y. Jiang, X.Y. Zhang, Q. Shao, M.Y. Dong, H. Liu, V. Murugadoss, Z.H. Guo, Biological cell template synthesis of nitrogen-doped porous hollow carbon spheres/MnO2 composites for high-performance asymmetric supercapacitors, Electrochim. Acta 296 (2019) 907–915 https:// doi.org/10.1016/j.electacta.2018.11.074. [29] H.J. Qi, M. Teng, M. Liu, S.X. Liu, J. Li, H.P. Yu, C.B. Teng, Z.H. Huang, H. Liu, Q. Shao, A. Umar, T. Ding, Q. Gao, Z.H. Guo, Biomass-derived nitrogen-doped carbon quantum dots: highly selective fluorescent probe for detecting Fe3+ ions and tetracyclines, J. Colloid Interface Sci. 539 (2019) 332–341 https://doi.org/10. 1016/j.jcis.2018.12.047. [30] M. Zhang, J. Meng, Q.Y. Liu, S.Y. Gu, L. Zhao, M.Y. Dong, J.X. Zhang, H. Hou, Z.H. Guo, Corn stover-derived biochar for efficient adsorption of oxytetracycline from wastewater, J. Mater. Res. (2019) 1–11 https://doi.org/10.1557/jmr.2019. 198. [31] H.L. Shindume, Z.Y. Zhao, N. Wang, H. Liu, A. Umar, J.X. Zhang, T.T. Wu, Z.H. Guo, Enhanced photocatalytic activity of B, N-codoped TiO2 by a new molten nitrate process, J. Nanosci. Nanotechnol. 19 (2019) 839–849 https://doi:10.1166/jnn. 2019.15745. [32] W.Y. Deng, T.H. Kang, H. Liu, J.X. Zhang, N. Wang, N. Lu, Y. Ma, A. Umar, Z.H. Guo, Potassium hydroxide activated and nitrogen doped graphene with enhanced supercapacitive behavior, Sci. Adv. Mater. 10 (2018) 937–949 https://doi. org/10.1166/sam.2018.3279.

[33] J.K. Zhao, S.S. Ge, D. Pan, Q. Shao, J. Lin, Z.K. Wang, Z. Hu, T.T. Wu, Z.H. Guo, Solvothermal synthesis, characterization and photocatalytic property of zirconium dioxide doped titanium dioxide spinous hollow microspheres with sunflower pollen as bio-templates, J. Colloid Interface Sci. 529 (2018) 111–121 https://doi.org/10. 1016/j.jcis.2018.05.091. [34] B.Q. Zhao, Q. Shao, L.H. Hao, L. Zhang, Z. Liu, B. Zhang, S.S. Ge, Z.H. Guo, Yeasttemplate synthesized Fe-doped cerium oxide hollow microspheres for visible photodegradation of acid orange, J. Colloid Interface Sci. 511 (2018) 39–47 https:// doi.org/10.1016/j.jcis.2017.09.077. [35] Y.Q. Dong, H.C. Pang, H.B. Yang, C.X. Guo, J.W. Shao, Y.W. Chi, C.M. Li, T. Yu, Carbon-based dots co-doped with nitrogen and sulfur for high quantum yield and excitation-independent emission, Angew. Chem. Int. Ed. 52 (2013) 7800–7804 https://doi.org/10.1002/anie.201301114. [36] Q. Xu, J.F. Wei, J.L. Wang, Y. Liu, N. Li, Y.S. Chen, C. Gao, W.W. Zhang, T.S. Sreeprased, Facile synthesis of copper doped carbon dots and their application as a “turn-off” fluorescent probe in the detection of Fe3+ ions, RSC Adv. 6 (2016) 28745–28750 https://doi.org/10.1039/c5ra27658f. [37] S.J. Zhuo, L.L. Gao, P. Zhang, J.Y. Du, C.Q. Zhu, Living cell imaging and sensing of hydrogen sulfide using high-efficiency fluorescent Cu-doped carbon quantum dots, New J. Chem. 42 (2018) 19659–19664 https://doi.org/10.1039/c8nj03654c. [38] H.H. Fan, G.Q. Xiang, Y.L. Wang, H. Zhang, K.K. Ning, J.Y. Duan, L.J. He, X.M. Jiang, W.J. Zhao, Manganese-doped carbon quantum dots-based fluorescent probe for selective and sensitive sensing of 2,4,6-trinitrophenol via an inner filtering effect, Spectrochim. Acta, Part A 205 (2018) 221–226 https://doi.org/10. 1016/j.saa.2018.07.006. [39] Z. Mu, J.H. Hua, S.A. Feng, Y.L. Yang, A ratiometric fluorescence and light scattering sensing platform based on Cu-doped carbon dots for tryptophan and Fe(III), Spectrochim. Acta, Part A 219 (2019) 248–256 https://doi.org/10.1016/j.saa. 2019.04.065. [40] S.K. Tammina, D.Z. Yang, X. Li, S. Koppala, Y.L. Yang, High photoluminescent nitrogen and zinc doped carbon dots for sensing Fe3+ ions and temperature, Spectrochim. Acta, Part A 222 (2019) 117141 https://doi.org/10.1016/j.saa.2019. 117141. [41] X.L. Luo, Z. Pan, F. Pei, Z.P. Jin, K.K. Miao, P.F. Yang, H.M. Qian, Q. Chen, G.D. Feng, In situ growth of hollow Cu2O spheres using anionic vesicles as soft templates, J. Ind. Eng. Chem. 59 (2018) 410–415 https://doi.org/10.1016/j.jiec. 2017.10.052. [42] M.K. Liu, Y.Q. Liu, Y. Yan, F.S. Wang, J.H. Liu, T.X. Liu, A highly conductive carbon-sulfur film with interconnected mesopores as an advanced cathode for lithium-sulfur batteries, Chem. Commun. 53 (2017) 9097–9100 https://doi.org/10. 1039/c7cc04523a. [43] Z.P. Lin, B. Lin, Z.P. Wang, S.G. Chen, C.W. Wang, M.Y. Dong, Q. Gao, Q. Shao, T. Ding, H. Liu, S.D. Wu, Z.H. Guo, Facile preparation of 1T/2H-Mo(S1-xSex)2 nanoparticles for boosting hydrogen evolution reaction, ChemCatChem 11 (2019) 2217–2222 https://doi.org/10.1002/cctc.201900095. [44] Y.X. He, Q.Y. Chen, H. Liu, L. Zhang, D.Y. Wu, C. Lu, W.Q. Yang, D.F. Jiang, M.F. Wu, J.X. Zhang, Y.C. Li, J.C. Fan, C.T. Liu, Z.H. Guo, Friction and wear of MoO3/graphene oxide modified glass fiber reinforced epoxy nanocomposites, Macromol. Mater. Eng. 304 (2019) 1900166 https://doi.org/10.1002/mame. 201900166. [45] H.Y. Sun, Z.Q. Yang, Y.N. Pu, W.W. Dou, C.Y. Wang, W.H. Wang, X.P. Hao, S.G. Chen, Q. Shao, M.Y. Dong, S.D. Wu, T. Ding, Z.H. Guo, Zinc oxide/vanadium pentoxide heterostructures with enhanced day-night antibacterial activities, J. Colloid Interface Sci. 547 (2019) 40–49 https://doi.org/10.1016/j.jcis.2019.03. 061. [46] X.L. Luo, F. Pei, W. Wang, H.M. Qian, K.K. Miao, Z. Pan, Y.S. Chen, G.D. Feng, Microwave synthesis of hierarchical porous materials with various structures by controllable desilication and recrystallization, Microporous Mesoporous Mater. 262 (2018) 148–153 https://doi.org/10.1016/j.micromeso.2017.11.037. [47] J.Y. Tian, Q. Shao, J.K. Zhao, D. Pan, M.Y. Dong, C.X.Z. Jia, T. Ding, T.T. Wu, Z.H. Guo, Microwave solvothermal carboxymethyl chitosan templated synthesis of TiO2/ZrO2 composites toward enhanced photocatalytic degradation of Rhodamine B, J. Colloid Interface Sci. 541 (2019) 18–29 https://doi.org/10.1016/j.jcis.2019. 01.069. [48] B. Lin, Z.P. Lin, S.G. Chen, M.Y. Yu, W. Li, Q. Gao, M.Y. Dong, Q. Shao, S.D. Wu, T. Ding, Z.H. Guo, Surface intercalated spherical MoS2xSe2(1−x) nanocatalysts for highly efficient and durable hydrogen evolution reactions, Dalton Trans. 48 (2019) 8279–8287 https://doi.org/10.1039/c9dt01218d. [49] K. Le, Z. Wang, F.L. Wang, Q. Wang, Q. Shao, V. Murugadoss, S.D. Wu, W. Liu, J. R Liu, Q. Gao, Z.H. Guo, Sandwich-like NiCo layered double hydroxide/reduced graphene oxide nanocomposite cathodes for high energy density asymmetric supercapacitors, Dalton Trans. 48 (2019) 5193–5202 https://doi.org/10.1039/ c9dt00615j. [50] D. Pan, S.S. Ge, J.K. Zhao, J.Y. Tian, Q. Shao, L. Guo, X.M. Mai, T.T. Wu, V. Murugadoss, H. Liu, T. Ding, S. Angaiah, Z.H. Guo, Synthesis and characterization of ZnNiIn layered double hydroxides derived mixed metal oxides with highly efficient photoelectrocatalytic activities, Ind. Eng. Chem. Res. 58 (2019) 836–848, https://doi.org/10.1021/acs.iecr.8b04829. [51] Y.Q. Guo, X.T. Yang, K.P. Ruan, J. Kong, M.Y. Dong, J.X. Zhang, J.W. Gu, Z.H. Guo, Reduced graphene oxide heterostructured silver nanoparticles significantly enhanced thermal conductivities in hot-pressed electrospun polyimide nanocomposites, ACS Appl. Mater. Interfaces 11 (2019) 25465–25473, https://doi.org/10. 1021/acsami.9b10161. [52] P. Yang, L.J. Yang, Q. Gao, Q. Luo, X.C. Zhao, X.M. Mai, Q.L. Fu, M.Y. Dong, J.C. Wang, Y.W. Hao, R.Z. Yang, X.C. Lai, S.D. Wu, Q. Shao, T. Ding, J. Lin, Z.H. Guo, Anchoring carbon nanotubes and post-hydroxylation treatment enhanced

6

Optical Materials 97 (2019) 109396

J. Fang, et al.

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

[67]

[68]

[69]

[70]

Ni nanofiber catalysts towards efficient hydrous hydrazine decomposition for effective hydrogen generation, Chem. Commun. 55 (2019) 9011–9014 https://doi. org/10.1039/c9cc04559g. H.B. Gu, X.L. Xu, M.Y. Dong, P.T. Xie, Q. Shao, R.H. Fan, C.T. Liu, S.D. Wu, R.B. Wei, Z.H. Guo, Carbon nanospheres induced high negative permittivity in nanosilver-polydopamine metacomposites, Carbon 147 (2019) 550–558 https:// doi.org/10.1016/j.carbon.2019.03.028. J.X. Zhang, P.P. Li, Z.Z. Zhang, X.J. Wang, J.J. Tang, H. Liu, Q. Shao, T. Ding, A. Umar, Z.H. Guo, Solvent-free graphene liquids: promising candidates for lubricants without the base oil, J. Colloid Interface Sci. 542 (2019) 159–167 https:// doi.org/10.1016/j.jcis.2019.01.135. N.N. Wu, D.M. Xu, Z. Wang, F.L. Wang, J.R. Liu, W. Liu, Q. Shao, H. Liu, Q. Gao, Z.H. Guo, Achieving superior electromagnetic wave absorbers through the novel metal-organic frameworks derived magnetic porous carbon nanorods, Carbon 145 (2019) 433–444 https://doi.org/10.1016/j.carbon.2019.01.028. D. Pan, S.S. Ge, J.Y. Tian, Q. Shao, L. Guo, H. Liu, S.D. Wu, T. Ding, Z.H. Guo, Research progress in the field of adsorption and catalytic degradation of sewage by hydrotalcite-derived materials, Chem. Rec. 19 (2019) 1–16 https://doi.org/10. 1002/tcr.201900046. Y.H. Yuan, Q.H. Yu, J. Wen, C.Y. Li, Z.H. Guo, X.L. Wang, N. Wang, Ultrafast and highly selective uranium extraction from seawater by hydrogel-like spidroin-based protein fiber, Angew. Chem. Int. Ed. 58 (2019) 11785–11790 https://doi.org/10. 1002/anie.201906191. S.L. Zhao, Y.H. Yuan, Q.H. Yu, B.Y. Niu, J.H. Liao, Z.H. Guo, N. Wang, S. Zhao, Y. Yuan, Q. Yu, B. Niu, N. Wang, Dual-surface amidoximated halloysite nanotube for high-efficient and economical uranium extraction from seawater, Angew. Chem. Int. Ed. (2019), https://doi.org/10.1002/anie.201908762. Y.X. Qian, Y.H. Yuan, H.L. Wang, H. Liu, J.X. Zhang, S. Shi, Z.H. Guo, N. Wang, Highly efficient uranium adsorption by salicylaldoxime/polydopamine graphene oxide nanocomposites, J. Mater. Chem. 6 (2018) 24676–24685 https://doi.org/10. 1039/c8ta09486a. S.W. Li, P.P. Yang, X.H. Liu, J.X. Zhang, W. Xie, C. Wang, C.T. Liu, Z.H. Guo, Graphene oxide based dopamine mussel-like cross-linked polyethylene imine nanocomposite coating with enhanced hexavalent uranium adsorption, J. Mater. Chem. 7 (2019) 16902–16911 https://doi.org/10.1039/c9ta04562g. Y. Ma, C.P. Hou, H.P. Zhang, Q.Y. Zhang, H. Liu, S.D. Wu, Z.H. Guo, Three-dimensional core-shell Fe3O4/Polyaniline coaxial heterogeneous nanonets: preparation and high performance supercapacitor electrodes, Electrochim. Acta 315 (2019) 114–123 https://doi.org/10.1016/j.electacta.2019.05.073. B. Kirubasankar, V. Murugadoss, J. Lin, T. Ding, M.Y. Dong, H. Liu, J.X. Zhang, T.X. Li, N. Wang, Z.H. Guo, S. Angaiah, In situ grown nickel selenide on graphene nanohybrid electrodes for high energy density asymmetric supercapacitors, Nanoscale 10 (2018) 20414–20425 https://doi.org/10.1039/c8nr06345a. D.W. Jiang, V. Murugadoss, Y. Wang, J. Lin, T. Ding, Z.C. Wang, Q. Shao, C. Wang, H. Liu, N. Lu, R.B. Wei, A. Subramania, Z.H. Guo, Electromagnetic interference shielding polymers and nanocomposites-a review, Polym. Rev. 59 (2019) 280–337 https://doi.org/10.1080/15583724.2018.1546737. J. Ren, Q. Luo, Q.Z. Hou, H. Chen, T. Liu, H.C. He, J.S. Wang, Q. Shao, M.Y. Dong, S.D. Wu, N. Wang, J. Lin, Z.H. Guo, Suppressing charge recombination and ultraviolet light degradation of perovskite solar cells using silicon oxide passivation, Chemelectrochem 6 (2019) 3167–3174 https://doi.org/10.1002/celc.201900688. G.Y. Zhu, X.K. Cui, Y. Zhang, S.G. Chen, M.Y. Dong, H. Liu, Q. Shao, T. Ding, S.D. Wu, Z.H. Guo, Poly (vinyl butyral)/graphene oxide/poly (methylhydrosiloxane) nanocomposite coating for improved aluminum alloy anticorrosion, Polymer 172 (2019) 415–422 https://doi.org/10.1016/j.polymer.2019.03.056. C.Q. Lou, T. Jing, J.Z. Tian, Y.J. Zheng, J.X. Zhang, M.Y. Dong, C. Wang, C.X. Hou, J.C. Fan, Z.H. Guo, 3-Dimensional graphene/Cu/Fe3O4 composites: immobilized laccase electrodes for detecting bisphenol A, J. Mater. Res. (2019) 1–12 https://doi. org/10.1557/jmr.2019.248. C. Shi, H.J. Qi, R.X. Ma, Z. Sun, L.D. Xiao, G.B. Wei, Z.H. Huang, S.X. Liu, J. Li, M.Y. Dong, J.C. Fan, Z.H. Guo, N, S-self-doped carbon quantum dots from fungus fibers for sensing tetracyclines and for bioimaging cancer cells, Mater. Sci. Eng. C 105 (2019) 110132 https://doi.org/10.1016/j.msec.2019.110132. H.B. Gu, H.Y. Zhang, C. Ma, H.L. Sun, C.T. Liu, K. Dai, J.X. Zhang, R.B. Wei, T. Ding, Z.H. Guo, Smart strain sensing organic–inorganic hybrid hydrogels with nano barium ferrite as the cross-linker, J. Mater. Chem. C 7 (2019) 2353–2360 https:// doi.org/10.1039/c8tc05448g. D.W. Jiang, Y. Wang, B. Li, C.Y. Sun, Z.J. Wu, H. Yan, L.X. Xing, S.L. Qi, Y.C. Li, H. Liu, W. Xie, X.J. Wang, T. Ding, Z.H. Guo, Flexible sandwich structural strain sensor based on silver nanowires decorated with self-healing substrate, Macromol. Mater. Eng. 304 (2019) 1900074 https://doi.org/10.1002/mame.201900074. H. Liu, Q.M. Li, S.D. Zhang, R. Yin, X.H. Liu, Y.X. He, K. Dai, C.X. Shan, J. Guo,

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[79]

[80]

[81]

[82]

[83]

[84]

[85]

[86]

[87]

[88]

7

C.T. Liu, C.Y. Shen, X.J. Wang, N. Wang, Z.C. Wang, R.B. Wei, Z.H. Guo, Electrically conductive polymer composites for smart flexible strain sensors: a critical review, J. Mater. Chem. C 6 (2018) 12121–12141 https://doi.org/10.1039/c8tc04079f. Q.M. Li, H. Liu, S.D. Zhang, D.B. Zhang, X.H. Liu, Y.X. He, L.W. Mi, J.X. Zhang, C.T. Liu, C.Y. Shen, Z.H. Guo, Superhydrophobic electrically conductive paper for ultrasensitive strain sensor with excellent anti-corrosion and self-cleaning property, ACS Appl. Mater. Interfaces 11 (2019) 21904–21914 https://doi.org/10.1021/ acsami.9b03421. J.L. Yu, X.Y. Wang, Q. Kang, J.H. Li, D.Z. Shen, L.X. Chen, One-pot synthesis of a quantum dot-based molecular imprinting nanosensor for highly selective and sensitive fluorescence detection of 4-nitrophenol in environmental waters, Environ. Sci. Nano 4 (2017) 493–502 https://doi.org/10.1039/c6en00395h. S.J. Zhuo, Y.Y. Guan, H. Li, J. Fang, P. Zhang, J.Y. Du, C.Q. Zhu, Facile fabrication of fluorescent Fe-doped carbon quantum dots for dopamine sensing and bioimaging application, Analyst 144 (2019) 656–662 https://doi.org/10.1039/c8an01741g. H. Liu, Q.S. Zhao, J.Y. Liu, X. Ma, Y. Rao, X.D. Shao, Z.T. Li, W.T. Wu, H. Ning, M.B. Wu, Synergistically enhanced activity of nitrogen-doped carbon dots/graphene composites for oxygen reduction reaction, Appl. Surf. Sci. 423 (2017) 909–916 https://doi.org/10.1016/j.apsusc.2017.06.225. S. Sun, Y. Wang, L.N. Wang, T. Guo, X.R. Yuan, D.X. Zhang, Z.H. Xue, X.B. Zhou, X.Q. Lu, Synthesis of Au@nitrogen-doped carbon quantum dots@Pt core-shell structure nanoparticles for enhanced methanol electrooxidation, J. Alloy. Comp. 793 (2019) 635–645 https://doi.org/10.1016/j.jallcom.2019.04.212. Y.F. Hsu, Y.H. Chen, C.W. Chang, The spectral heterogeneity and size distribution of the carbon dots derived from time-resolved fluorescence studies, Phys. Chem. Chem. Phys. 18 (2016) 30086–30092 https://doi.org/10.1039/c6cp05813b. J.Y. Du, Y. Zhao, J. Chen, P. Zhang, L.L. Gao, M.Q. Wang, C. Cao, W. Wen, C.Q. Zhu, Difunctional Cu-doped carbon dots: catalytic activity and fluorescence indication for the reduction reaction of p-nitrophenol, RSC Adv. 7 (2017) 33929–33936 https://doi.org/10.1039/c7ra05383e. Z.P. Li, Y.W. Zhang, H. Xia, Y. Mu, X.M. Liu, A robust and luminescent covalent organic framework as a highly sensitive and selective sensor for the detection of Cu2+ ions, Chem. Commun. 52 (2016) 6613–6616 https://doi.org/10.1039/ c6cc01476c. Z. Yang, M.H. Xu, Y. Liu, F.J. He, F. Gao, Y.J. Su, H. Wei, Nitrogen-doped, carbonrich, highly photoluminescent carbon dots from ammonium citrate, Nanoscale 6 (2014) 1890–1895 https://doi.org/10.1039/c3nr05380f. S.K. Kailasa, S. Ha, S.H. Baek, L.M.T. Phan, S. Kim, K. Kwak, T.J. Park, Tuning of carbon dots emission color for sensing of Fe3+ ion and bioimaging applications, Mater. Sci. Eng. C 98 (2019) 834–842 https://doi.org/10.1016/j.msec.2019.01. 002. L.Y. Jiang, H.J. Liu, M. Li, Y. Xing, X.Q. Ren, Surface molecular imprinting on CdTe quantum dots for fluorescence sensing of 4-nitrophenol, Anal. Methods 8 (2016) 2226–2232 https://doi.org/10.1039/c5ay03160e. N. Xiao, S.G. Liu, S. Mo, N. Li, Y.J. Ju, Y. Ling, N.B. Li, H.Q. Luo, Highly selective detection of p-nitrophenol using fluorescence assay based on boron, nitrogen codoped carbon dots, Talanta 184 (2018) 184–192 https://doi.org/10.1016/j.talanta. 2018.02.114. C.M. Li, Y.K. Zheng, H.W. Ding, H. Jiang, X.M. Wang, Chromium(III)-doped carbon dots: fluorometric detection of p-nitrophenol via inner filter effect quenching, Microchim. Acta 186 (2019) 384 https://doi.org/10.1007/s00604-019-3444-3. D.K. Dang, C. Sundaram, Y.L.T. Ngo, W.M. Choi, J.S. Chung, E.J. Kim, S.H. Hur, Pyromellitic acid-derived highly fluorescent N-doped carbon dots for the sensitive and selective determination of 4-nitrophenol, Dyes Pigments 165 (2019) 327–334 https://doi.org/10.1016/j.dyepig.2019.02.029. J.M. Yang, X.W. Hu, Y.X. Liu, W. Zhang, Fabrication of a carbon quantum dotsimmobilized zirconium-based metal-organic framework composite fluorescence sensor for highly sensitive detection of 4-nitrophenol, Microporous Mesoporous Mater. 274 (2019) 149–154 https://doi.org/10.1016/j.micromeso.2018.07.042. L. Han, S.G. Liu, J.Y. Liang, Y.J. Ju, N.B. Li, H.Q. Luo, pH-mediated reversible fluorescence nanoswitch based on inner filter effect induced fluorescence quenching for selective and visual detection of 4-nitrophenol, J. Hazard Mater. 362 (2019) 45–52 https://doi.org/10.1016/j.jhazmat.2018.09.025. G.L. Li, H.L. Fu, X.J. Chen, P.W. Gong, G. Chen, L. Xia, H. Wang, J.M. You, Y.N. Wu, Facile and sensitive fluorescence sensing of alkaline phosphatase activity with photoluminescent carbon dots based on inner filter effect, Anal. Chem. 88 (2016) 2720–2726 https://doi.org/10.1021/acs.analchem.5b04193. J.C. Wei, Y. Yang, J.Y. Dong, S.P. Wang, P. Li, Fluorometric determination of pesticides and organophosphates using nanoceria as a phosphatase mimic and an inner filter effect on carbon nanodots, Microchim. Acta 186 (2019) 66 https://doi.org/10. 1007/s00604-018-3175-x.