A fluorimetric and colorimetric dual-mode sensor based on N, S co-doped carbon dots functionalized silver nanoparticles for glucose detection.

A fluorescent-colorimetric dual-signal platform, N, S co-doped carbon dots functionalized silver nanoparticles (NS-CDs-AgNPs), was designed in situ by reducing AgNO3 in the presence of N, S co-doped carbon dots (NS-CDs) under the assistance of microwave irradiation for glucose determination. With the formation of silver nanoparticles (AgNPs), the intrinsic fluorescence of NS-CDs was quenched, showing the fluorescence state was off. Whereas the fluorescence of NS-CDs can be switched on when a trace amount of H2O2 was added. Based on this novel phenomenon, the peroxidase-like activity of NS-CDs-AgNPs by using 3,3',5,5'-tetramethylbenzidine (TMB) chromogen and H2O2 as substrates was evaluated. The Km values of the prepared probe for H2O2 and TMB were 0.84 mM and 0.01 mM with the Vm of 6.65 × 10-8 M S-1 and 3.01 × 10-8 M S-1, respectively. The results showed that NS-CDs-AgNPs had good peroxidase-like activity and strong affinity to TMB and H2O2. It confirmed that there is a redox interaction between AgNPs and H2O2, and H2O2 can oxidize Ag to produce Ag+, which is the main reason that the fluorescence of NS-CDs-AgNPs can be activated by H2O2. The hydroxyl radical (·OH) was formed in the process of reaction, which can further oxidize TMB for color reaction. Meanwhile, glucose can be oxidized to produce H2O2 in the presence of glucose oxidase (GOx). Based on the phenomenon, a fluorimetric and colorimetric dual-mode sensor for glucose detection was established. Satisfactory results were obtained with the linear range of 0.1-80 µM for fluorimetric mode and 0.5-5 µM for colorimetric mode, respectively. Additionally, the LOD was below 0.32 µM and 0.21 µM, respectively. The method was successfully applied to determine the glucose in human serum with satisfactory recovery and RSD.

Microwave-assisted preparation of yellow fluorescent graphitic carbon nitride quantum dots for trace tetracycline-specific detection.

Tetracycline (TC) is extensively utilized in livestock breeding, aquaculture, and medical industry. TC residues seriously harm food security, the environment, and human health. There is an urgent need to exploit a highly efficient and sensitive testing method to monitor TC residue levels in aquatic environments. In this study, graphitic carbon nitride quantum dots (g-CNQDs) were successfully synthesized by a one-step microwave-assisted method using citric acid and urea as precursors. The as-prepared g-CNQDs with size of 1.25-3.75 nm exhibited bright yellow fluorescence at 523 nm when excited at 397 nm. Interestingly, this characteristic fluorescence emission of g-CNQDs could be selectively and efficiently quenched by TC. Based on this phenomenon, for TC detection was successfully explored and applied in real water samples. Wide linear scope of 7-100 µM, low detection limit (LOD) of 0.48 µM, satisfactory recovery of 97.77%-103.4%, and good relative standard deviation (RSD) of 1.05-5.87% were obtained. Mechanism investigations revealed that the static quenching and the inner filter effect (IFE) were responsible for this fluorescence quenching between g-CNQDs and TC. This work not only provided a facile approach for g-CNQDs synthesis but also constructed a g-CNQDs-based fluorescent sensor platform for the highly sensitive and selective detection of TC in aquatic environments.

A colorimetric and fluorometric dual-mode probe for Cu2+detection based on functionalized silver nanoparticles.

A novel colorimetric/fluorescent probe (AgNPs-GSH-Rh6G2) was prepared by linking silver nanoparticles (AgNPs) with rhodamine 6G derivative (Rh6G2) using glutathione (GSH) as a linker molecule. The prepared probe showed obvious fluorescence change and colorimetric response after adding copper ions. Based on this phenomenon, a colorimetric/fluorescence dual-mode detection method was constructed to recognize copper ions. The linear ranges of fluorescence detection and colorimetric detection were 0.10 to 0.45 mM and 0.15 to 0.65 mM, respectively, and the limit of detection were 0.18 µM and 24.90 µΜ. In addition, the dual-mode probe has achieved satisfactory results in the detection of copper ions in sediment samples. The successful construction of AgNPs-GSH-Rh6G2 not only provide a reliable tool for the detection of copper ions, but also shed light on a new idea for the multi-mode development of the detection platform.

Magnetic Fe3O4/bamboo-based activated carbon/UiO-66 composite as an environmentally friendly and effective adsorbent for removal of Bisphenol A.

The magnetic Fe3O4/bamboo-based activated carbon/Zr-based metal-organic frameworks composite (Fe3O4/BAC/UiO-66) was prepared by hydrothermal method. The as-prepared material was analyzed via TEM, XRD, FT-IR, BET-BJH, VSM and XPS techniques, the results showed that it had good dispersion and magnetic separation capacity (Ms = 44.06 emu∙g-1). Then, the adsorption properties of materials for bisphenol A (BPA) were studied. The results revealed that the removal efficiency of 50 mg·L-1 BPA by 0.1 g of adsorbent can reach 87.18-95% in a wide pH range. Langmuir isotherm model and pseudo-second-order kinetic well fitted the adsorption data. The thermodynamic data indicated that the adsorption process was spontaneous and endothermic. Moreover, BAC as a supporter and UiO-66 as the functional part in the ternary composite may have a synergistic effect, which was beneficial for the removal of contaminants. The Fe3O4/BAC/UiO-66 can be simply separated from the water using its strong magnetism after finish adsorption process, which effectively avoids secondary contamination.

A novel colorimetric/fluorescent dual-signal probe based on silver nanoparticles functionalized with L-cysteine and rhodamine 6G derivatives for copper ion detection and cell imaging.

The dual-signal probe utilizing functionalized silver nanoparticles (AgNPs) is a promising sensing tool. Herein, a novel colorimetric/fluorescent dual-signal probe (AgNPs-L-Cys-Rh6G2) was fabricated for copper ion (Cu2+) detection and cell imaging by using L-cysteine as a "bridge" to connect AgNPs and rhodamine 6G derivatives. The AgNPs-L-Cys-Rh6G2 probe exhibits a dual-signal response to Cu2+ due to Rh6G2 hydrolysis, resulting in a high fluorescence response and a significant change in color from light yellow to pink under sunlight. The linear detection ranges of the AgNPs-L-Cys-Rh6G2 probe for Cu2+ were 100-450 µM and 150-650 µM using fluorescent and colorimetry methods, respectively. The detection limits were as low as 0.169 µM and 1.36 µM, respectively. Meanwhile, the proposed probe was applied to detect Cu2+ in the actual sediment with satisfactory recovery and low relative standard deviation. Furthermore, the probe was further employed for fluorescence imaging in HeLa cells. In brief, the developed AgNPs-L-Cys-Rh6G2 sensing platform can be used for simultaneous Cu2+ determination and cell imaging.

Optimization of adsorption performance of cerium-loaded intercalated bentonite by CCD-RSM and GA-BPNN and its application in simultaneous removal of phosphorus and ammonia nitrogen.

Excessive phosphorus (P) and ammonia nitrogen (NH3-N) in water bodies can lead to eutrophication of the aquatic environment. Therefore, it is important to develop a technology that can efficiently remove P and NH3-N from water. Here, the adsorption performance of cerium-loaded intercalated bentonite (Ce-bentonite) was optimized based on single-factor experiments using central composite design-response surface methodology (CCD-RSM) and genetic algorithm-back propagation neural network (GA-BPNN) models. Based on the determination coefficient (R2), mean absolute error (MAE), mean square error (MSE), mean absolute percentage error (MAPE), and root mean square error (RMSE), the GA-BPNN model was found to be more accurate in predicting adsorption conditions than the CCD-RSM model. The validation results showed that the removal efficiency of P and NH3-N by Ce-bentonite under optimal adsorption conditions (adsorbent dosage = 1.0 g, adsorption time = 60 min, pH = 8, initial concentration = 30 mg/L) reached 95.70% and 65.93%. Furthermore, based on the application of these optimal conditions in simultaneous removal of P and NH3-N by Ce-bentonite, pseudo-second order and Freundlich models were able to better analyze adsorption kinetics and isotherms. It is concluded that the optimization of experimental conditions by GA-BPNN has some guidance and provides a new approach to explore adsorption performance after optimizing the conditions.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater.

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400 °C for 2 h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00 mg L-1 by the DTCA-Na was more than 80% when the contact time was 60 min, pH was 6-10, the dosage of adsorbent was 1.00 g, and the temperature was 25 °C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.

Fixed-bed column dynamics of ultrasound and Na-functionalized diatomite to remove phosphate from water.

A continuous fixed-bed column study was used to evaluate phosphate adsorption performance of U-D-Na which was functionalized by the cheap NaCl reagent after simple ultrasonic purification of diatomite. In this work, various effect factors, including flow rate, initial phosphate concentration, and the bed height, on breakthrough performance of fixed column were investigated. Experimental results demonstrated that the breakthrough time declined with the increase of inlet phosphate concentration and feed rate, whereas the increase of bed height turned out to significantly extend the breakthrough time. The dynamic adsorption process could be well fitted by the Thomas model, with a correlation coefficient R2 > 0.9000 under main operating conditions. A thrice loop of effective regeneration was achieved with 0.1 M hydrochloric acid eluent and deionized water. The maximum removal rate for phosphate was more than 95% in the column adsorption process. The results proved that U-D-Na could be used as a better alternative phosphate adsorbent for wastewater in a continuous column sorption process.