Microplastics (MPs) are an emerging threat to terrestrial ecosystems and have attracted global attention. In this study, durian shell was used as biochar raw material to provide magnetism, and then it was modified with chitosan to make chitosan-modified magnetic biochar (CMBC). The prepared CMBC was used to simulate the adsorption of MPs in sewage. Experimental results showed that the amount of CMBC was 0.1 g, pH was 10, the concentration of 160 mg/L had the optimal adsorption effect, the adsorption rate reached up to 97.22 %, and the adsorption capacity was 15.56 mg/g. According to the adsorption kinetic analysis, the adsorption process conformed to be the Freundlich model. The removal rate of MPs still remained at 76.41 % when CMBC, a green environmentally friendly adsorption material, was recycled for five times. This research broadens the understanding for the evaluation of magnetic biochar effectiveness in the adsorption of MPs pollution.

Chitosan (CS)/SiO2 composites film were synthesized by the sol-gel method in the moderate environment. The polymer composites were characterized by FTIR, UV-Visible, SEM, TEM and DSC techniques. SiO2 nanoparticles were dispersed homogeneously within the sphericity. Significantly, the resultant CS/SiO2 composites film showed the specific fluorescence response to Al3+ over than other metal ions. CS/SiO2 gel sensor exhibits a detection range from 0 mg/L to 8.82 × 10−4 mg/L (LOD=1.4 ×10−5 mg/L). The gel sensor was successfully used for the detection of Al3+ in water samples. Therefore, the gel sensor had a broad application prospect in other promising applications such as environmental quality and food safety monitoring.

Novel nanostructured materials are expected to revive materials for chemiresistive sensor applications. MoS2-based gas sensor is widely studied, however, which usually is capable of detecting gas at ppm level. Here, owing to the two-dimensional layered structure that facilitated the surface reaction, sulfur nanosheets (S-NSs) was first designed to composite with MoS2 to improve the sensing performance. Because of the unique electronic and physical properties of S-NSs, the developed chemiresistive sensor based on MoS2@S-NSs nanocomposite demonstrated to realize ultrasensitive detection of NH3 at 0.1 ppt level with a response signal of 68%, and which also showed fast response and recover (9/8.7seconds respectively) at room temperature in air. Except for the good electrical conductivity and the large adsorption site of MoS2, the excellent sensing property of S-NSs itself made the most important contribution to this appealing high sensitivity to NH3. Additionally, this study has also put forth comprehensive gas sensing mechanisms based on experimental results. In essence, this research offers an innovative materials system tailored for the highly efficient detection of NH3.

The N–C QDs@MIP from wheat straw was synthesized by a gel-sol method and it could be used as a sensor for penicillin. The study paves an avenue to develop highly efficient sensor for the detection of antibiotics.

Sulfur nanosheets (S-NSs) have received increasing attention in biochemistry fielded due to adequate inherent antibacterial, antifungal activities, outstanding stability and reusability. The electron transfer between the iron ions (Fe3+) and S-NSs brings S-NSs aggregation lead to the fluorescence intensity of S-NSs decreases in a wide linear concentration range from 12 to 108 mu M. More interestingly, the quenched fluorescence of S-NSs/Fe3+ could be recovered by salicylic acid (SA) in a linear range of 8-80 mu M because of a stable complex could be form between SA and Fe3+and the proposed sensor for SA showed the outstanding advantages of simplicity, specificity, and fast. The method included environmentally friendly, low-cost, convenient, and wide linear range, which makes it a novel method for routine applications for Fe3+ and SA detection.

Magnetized pitaya peel bio-based carbon aerogel (MCA) was prepared by hydrothermal and freeze-drying methods; then, magnetized bio-based carbon aerogel (MCKEA) was obtained by the surface functionalization of MCA with 3-amino-1, 2-propylene glycol and KH-550. MCA and MCKEA were characterized by SEM, FT-IR, and XRD. The adsorption properties of MCA and MCKEA for dyes were investigated. It showed that the adsorption capacity of MCKEA for dyes was greater than that of MCA, especially for acid chromium blue K. The adsorption of acid chromium blue K by MCKEA conforms to the pseudo-second-order kinetic model and Langmuir adsorption model. The reusability experimental results showed that MCKEA can be reused for nine times. So MCKEA is a kind of adsorbent with high efficiency, high reusability, and low cost, which has broad application prospect.

Nanomaterials-based gas sensors are conducive to online, real-time monitoring and large-scale production due to their simplicity, low energy consumption and miniaturization. Conventional nanomaterial-based (metal oxide semiconductor or two-dimensional nanomaterials) gas sensors are less sensitive (ppm-ppb level). So, it is significantly meaningful to develop new gas-sensing materials. Herein, Ag@sulfur nanosheets (S-NSs) nanocomposite-based sensor is explored for ultrasensitive detection of NH3 in dry air at room temperature at parts per trillion (ppt) level. Introducing Ag nanoparticles (NPs) on S-NSs, improved electrical conductivity and created more effective adsorption sites, leading to a high response rate of 1.92 for 3 ppt NH3. The developed Ag@ S-NSs sensor showed a linear response to NH3 in the range of 3-70 ppt with correlation coefficient of 0.996. Moreover, the developed Ag@S-NSs sensor showed fast response and recovery time (28/7 s) to NH3. The probable sensing mechanism is supposed that the polarization-induction of NH3 changed of electronic energy level of Ag@S-NSs, and the changed energy is at approximately the same energy level of the Ag@S-NSs itself. Thus, a response signal caused by NH3 with low concentration can also be felt by Ag@S-NSs sensing materials itself.

An updated organic solvation-assisted intercalation and collection (OAIC) strategy was developed to prepare high-quality 2D transition metal carbon/nitride (MXene) and evaluate its effects on the structure and properties of polylactide (PLA). Then, PLA composites with different MXene contents were prepared by solution casting method. Transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, UV–visible spectrometry, x-ray diffraction, differential scanning calorimetry, polarized optical microscopy and mechanical tests were used to characterize the MXene/PLA composites. Also, physical models were established to describe the modification mechanism of MXene on PLA. The results show that our updated OAIC strategy successfully prepared single-layered, large-sized MXene nanosheets, which can disperse in both aqueous phase and organic solvent uniformly and stably. MXene and PLA are physically blended in the resultant composites, since PLA shows the typical spherulite morphology. Crystallite size of PLA was refined by the as-synthesized MXene nanosheets. The MXene/PLA composites illustrated prominent UV shielding effect: its UV shielding performance is very close to 100

In this paper, NC QDs were obtained from agricultural waste (wheat straw), functionalized by 4,5-imidazole dicarboxylic acid and used to detect gentamicin in aqueous solution. The NC QDs were characterized by HRTEM, XPS, UV-Vis, etc. The fluorescence properties of the functionalized NC QDs for GEN detection were studied at λem = 385 nm. The fluorescence intensity showed a good linear relationship with the GEN concentration of samples (I = 343.10 + 30.07C, R2 = 0.9896) for GEN concentrations ranging from 0 to 2.9 × 10-4 mol/L. The sensing mechanism was found to be fluorescence resonance energy transfer (FRET) between the functionalized NC QDs and GEN. The results indicated that the method had good repeatability for GEN detection. The technology could be extended to biological detection.

The sensitive, rapid and selective detection of nitroaromatic explosives was very important because they were harmful to public safety. Methods selectively to detect p-nitrophenol (PNP) were few. In this work, graphitic carbon nitride (g-C3N4) nanosheets were used as sensors to detect PNP in aqueous solution. g-C3N4 nanosheets were found to have significantly decreased fluorescence intensity when PNPs were introduced into the system. The concentration of PNP was from 7.782 × 10–6 to 7.273 × 10−5 mol/L. The feasibility of the proposed sensor in the samples was further studied, and the satisfactory results were obtained. Overall, a novel and efficient sensor for PNP detection through a combined static-and-dynamic quenching mechanism was developed. The strategy paved the way to meet the requirements of public safety.

A simple technique to prepare g-C3N4/Fe3O4 nanocomposites by electrostatic interaction has been demonstrated by carboxyl g-C3N4 nanosheets and Fe3O4 nanoparticles which contain amino groups. The nanocomposites were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The emission of the g-C3N4/Fe3O4 nanocomposites was quenching when Cu2+ was detected and recovering after adding the EDTA solution. At the optimum conditions, the fluorescence intensity is proportional to the concentration of Cu2+ in the range of 0–8 × 10−5 mol/L. The linear regression equation is Y = − 16.87X + 0.6209, and the correlation coefficient is 0.998. The sensing system has good reproducibility when it is used to detect Cu2+. This sensor would be a common platform for detecting Cu2+ in the aqueous system.

A novel film consisting of ZnCdS/ZnS quantum dots (QDs) and g-C3N4 nanosheets conjugated with carboxymethyl chitosan (CMCS) chains via weak bonds was built. The Mn2+ in contact with the composite film forced the chitosan to undergo conformational changes, resulting in the intermolecular complex R-COO-(Mn-2(+))-NH2-R, which enhanced the fluorescence. The film was developed for trace Mn-2(+) determination according to the fluorescence resonance energy transfer mechanism by the enhancement effect of the film. The sensor exhibited a good linearity (F = 2.0852C + 168.667) for Mn-2(+) at a concentration of 1.961 x 10(-6)-1.667 x 10(-5) mol/L under certain conditions with a correlation coefficient of 0.9981. The film was successfully used to determine Mn-2(+) with recoveries in the range of 90%-107% in the real water samples. The proposed method provides a simple, facile, sensitive, and fast detection method for Mn-2(+).

Abstract A solid fluorescence sensor composed of g-C3N4 nanosheets and chitosan solid film was fabricated by electrostatic interaction. The g-C3N4 nanosheet/chitosan solid film showed selectivity and sensitivity to Cu2+ which was higher than that of other metal ions in common use. Cu2+ ions were found to efficiently bind and quench the fluorescence of the g-C3N4 nanosheet/chitosan solid film. The absorption band of the g-C3N4 nanosheet/chitosan solid film was at 240 nm in the presence of Cu2+, and the maximum emission peak was at 380 nm. Copper ion concentrations were between 0 and 3.1 × 10−5 mol/L at pH 7, the detection limit is 5 nM, compared with previous reports, it was much lower than before. Good linear relationships existed between the metal ion concentration and fluorescence intensity of g-C3N4 nanosheets in the quenching and recovering processes. This is the first study to report on the detection of Cu2+ by utilizing g-C3N4 nanosheet/chitosan composite film. The as-prepared films were conveniently prepared, easy to operate, and recyclable, as well as sensitive and selective to detect Cu2+ in water. All these features indicate the sensor’s potential application in disease diagnosis.

A 0D/2D (0-dimensional/2-dimensional) nanostructure was designed by self-assembly of N–C QDs and carboxylated g-C 3 N 4 nanosheets and used as a fluorescence resonance energy transfer (FRET) fluorescent sensor. The N–C QDs/g-C 3 N 4 nanosheets were synthesized via the amino group on the N–C QD surface and the –COOH of the carboxylated g-C 3 N 4 nanosheets. The mechanism of detection of metronidazole (MNZ) by N–C QDs/g-C 3 N 4 nanocomposites is based on FRET between negatively charged N–QDs and positively charged carboxylated g-C 3 N 4 nanoparticles. N–C QDs/g-C 3 N 4 nanostructures displayed good responses for the detection of MNZ at normal temperature and pressure. The decrease in the fluorescence intensity showed a good linear relationship to MNZ concentration within 0–2.6 × 10 −5 mol/L, and the detection limit was 0.66 μM. The novel FRET sensor will have a great potential in clinical analysis and biological studies. Graphical Abstract

A ratio fluorescent probe to detect Ag+ using arginine-naphthalene imide (AN) had been elaborately designed and synthesized. The structure of AN was characterized by 1HNMR and FTIR. The optical properties of AN were investigated by ultraviolet and fluorescence spectroscopy. The results indicated that the fluorescent intensity of AN was enhanced gradually with the increase of Ag+ concentration, which was hardly affected by other metal ions such as Bi3+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Hg2+, Pb2+, K+ and Na+. A good linear correlation was displayed between the concentration of Ag+ (ranging from 4.30 to 11.40 μmol L−1) and the fluorescence intensity (R2 = 0.9985). The detection limit was 0.1883 μmol L−1. The mechanism of the sensor may be based on the principle of intramolecular charge transfer. It was expected that this novel ratio sensor could be used for the detection of silver ions in water.

The direct determination Mn2+ using carboxymethyl chitosan crosslinked with cyclodextrin containing hydrogen-bonded N-C QDs (N-C QD/CCSCD nanocomposites). The probable mechanism of the N-C QD/CCSCD nanocomposites' fluorescence was quenched by Mn2+ could be interpreted as acyclic crown ether chelation. Mn2+ induced the N-C QD/CCSCD clusters assembly to form large aggregates, which resulted in aggregation caused quenching. The linear detection (I = 479.93-15.94C (R-2 = 0.9954)) can be established at Mn2+ concentrations from 0 to 21.11 x 10(-6) mol/L. Common metal ions, except iron and magnesium, showed minimal effect on detection. It could satisfy the standard range of Mn2+ in actual water samples. The method which using chelating assembly mechanism to build a novel sensor would provide a new model for the application of polymer materials in this field, but the precise assembly of polymer is an unsolved challenge.

A 0D/2D (0-dimensional/2-dimensional) nanostructure was designed by self-assembly of N-C QDs and carboxylated g-C3N4 nanosheets and used as a fluorescence resonance energy transfer (FRET) fluorescent sensor. The N-C QDs/g-C3N4 nanosheets were synthesized via the amino group on the N-C QD surface and the -COOH of the carboxylated g-C3N4 nanosheets. The mechanism of detection of metronidazole (MNZ) by N-C QDs/g-C3N4 nanocomposites is based on FRET between negatively charged N-QDs and positively charged carboxylated g-C3N4 nanoparticles. N-C QDs/g-C3N4 nanostructures displayed good responses for the detection of MNZ at normal temperature and pressure. The decrease in the fluorescence intensity showed a good linear relationship to MNZ concentration within 0-2.6 × 10-5 mol/L, and the detection limit was 0.66 μM. The novel FRET sensor will have a great potential in clinical analysis and biological studies.

A novel fluorescence probe was built by using graphitic carbon nitride (g-C3N4) nanosheets. Fluorescence of the g-C3N4 nanosheet solution was effectively quenched by Fe3+ via photoinduced electron transfer (PET). Moreover, the linear detection range for Fe3+ was 0-43.33 nM with a limit of detection of 4 nM. Fluorescence recovery of g-C3N4 was observed upon addition of ascorbic acid (AA) to the g-C3N4 nanosheet-Fe3+ system, and the paramagnetic Fe3+ was reduced to diamagnetic Fe2+ by blocking PET. An "on-off-on" fluorescence response was observed through the oxidation-reduction between Fe3+ and AA. Furthermore, a wide linear detection range for AA was found in 0-26.67 nM. Thus, this system can play a dual role in the selective and sensitive detection of Fe3+ and AA in aqueous media via "on-off-on" fluorescence response. (C) 2018 Elsevier B.V. All rights reserved.

A novel sensor based on Ag2S/chitosan films was prepared via a coordination-driven self-assembled method. Experiments demonstrated that Ag2S was inert to chitosan film. Structural, and sensing property studies were realized by FTIR, DSC, SEM, and fluorescence analysis. DSC showed good crystallization after manipulation, showing that the Ag2S QDs were uniformly distributed in the film, leading to a good fluorescence property. The fluorescence of the films was selective to benzaldehyde. The linear detection on benzaldehyde concentration by the fluorescence method can be established was from 0 to 10(8) mg/L. The films could be quenched because of the electron transfer between benzaldehyde and Ag2S QDs. It would therefore be developed as an optical sensor.

Sulfur nanomaterials exceed carbon nanomaterials in terms of the antimicrobial or antifungal properties. A novel S QDs which were prepared by “top-down” methodology to detect Co2+and norfloxacin was constructed for the first time. S QDs can play a dual role for detection of Co2+as well as norfloxacin in aqueous media as a fluorescent switch.