Nitrogen-rich silicon quantum dots: facile synthesis and application as a fluorescent 'on-off-on' probe for sensitive detection of Hg2+ and cyanide ions.

The sensitive and reliable detection of Hg2+ and CN- as harsh environmental contaminants are of great importance. In view of this, a novel 'on-off-on' fluorescent probe based on nitrogen-rich silicon quantum dots (NR-SiQDs) has been designed for sensitive detection of Hg2+ and CN- ions in aqueous medium. NR-SiQDs were synthesized using a facile, one-step, and environment friendly procedure in the presence of 3-aminopropyl trimethoxysilane (APTMS) and ascorbic acid (AA) as precursors, with l-asparagine as a nitrogen source for surface modification. The NR-SiQDs exhibited strong fluorescence emission at 450 nm with 42.34% quantum yield, satisfactory salt tolerance, and superior photostability and pH stability. The fluorescence emission was effectively quenched using Hg2+ (turn-off) due to the formation of a nonfluorescent stable NR-SiQDs/Hg2+ complex, whereas after the addition of cyanide ions (CN- ), Hg2+ ions could be leached from the surface of the NR-SiQDs and the fluorescence emission intensity of the quenched NR-SiQDs fully recovered (turn-on) due to the formation of highly stable [Hg(CN)4 ]2- species. After optimizing the response conditions, the obtained limits of detection were found to be 53 nM and 0.46 µM for Hg2+ and CN- , respectively. Finally, the NR-SiQD-based fluorescence probe was utilized to detect Hg2+ and CN- ions in water samples and satisfactory results were obtained, suggesting its potential application for environmental monitoring.

Determination of cyanide based on a dual-emission ratiometric nanoprobe using silver sulfide quantum dots and silicon nanoparticles.

A novel ratiometric fluorescent nanoprobe was designed for the sensitive determination of cyanide anion (CN-) by the electrostatic attraction between positively charged silicon nanoparticles (Si NPs) and negatively charged silver sulfide quantum dots (Ag2S QDs). The nanoprobe exhibited two well-resolved emission peaks at 446 nm and 540 nm under a single excitation wavelength (360 nm). In the presence of CN-, the fluorescence of Ag2S QDs at 540 nm was remarkably quenched, while the fluorescence of the Si NPs at 446 nm remained constant, establishing the desired conditions for ratiometric fluorescence detection. Under optimal conditions, the ratiometric fluorescence assay showed good linearity (R2 = 0.9921) within the range 0.05-15 µM, and the limit of detection was calculated to be 56 nM (at an S/N ratio of 3). The proposed Ag2S QD/Si NP nanoprobe has been successfully used to determine CN- in water and sprouting potato samples with satisfactory recoveries in the range 97-110.5%.

Functionalized CMK-3 mesoporous carbon with 2-amino-5-mercapto-1,3,4-thiadiazole for Hg(II) removal from aqueous media.

Ordered mesoporous carbon (CMK-3) was synthesized and functionalized with 2-amino-5-mercapto-1,3,4-thiadiazole groups (AMT-OCMK-3) for Hg(II) removal from aqueous solution. The modified CMK-3 was characterized by X-ray diffraction, N2 adsorption-desorption isotherm, scanning electron microscopy and Fourier transform infrared spectroscopy. The effects of solution pH, contact time, initial Hg(II) concentration and matrix effect were studied. The adsorption data were successfully fitted with the Langmuir model, exhibiting high adsorption capacity of 450.45 mg/g of AMT-OCMK-3. In the solid-phase extraction system a series of experimental parameters such as sample flow rate, sample volume, eluent volume and concentration of the eluent solution have been investigated and established for preconcentration of Hg(II) in aqueous solution. The results showed that the enrichment factor for Hg(II) was 250, the precision (relative standard deviation (RSD), %) for six replicate measurements was 2.05% and the limit of detection for Hg(II) was achieved at 0.17 µg/L.

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review.

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

Preparation of superhydrophobic, green, and eco-friendly modified polylactic acid foams for separation oil from water.

Developing a facile and green strategy to fabricate polymer foams with super hydrophobicity and eco-friendliness for large-scale oil-water separation remains a challenge. In this study, biocompatible polylactic acid polymer foam modified by nanochitosan and stearic acid was used to remove petroleum and organic contaminants in water. All three materials used to prepare and modify this foam are green and inexpensive. F4d foam (prepared by solvent displacement method) and F8d foam (prepared by freeze dryer) can selectively remove oil pollutants in water with a contact angle of 164.01° and 168.51°, respectively. The maximum absorption capacity of oil pollutants by F4d and F8d are related to chloroform with values of 32.7 g/g and 48.51 g/g, respectively. Also, the minimum absorption capacity is related to n-hexane with values of 24.83 g/g and 32.06 g/g. The absorption percentage range of F4d and F8d foams after 15 cycles of absorption-desorption for chloroform is 82.56 % and 87.81 %, respectively, and for n-hexane, is 77.28 % and 85.99 %, respectively. During the continuous water-oil pumping test, the efficiency of foam can be maintained for >15 h, which shows promising hope for large-scale oil pollution cleaning.

Removal of arsenic by metal organic framework/chitosan/carbon nanocomposites: Modeling, optimization, and adsorption studies.

In this work removal of the arsenic (As) spiked in water through adsorption using synthesized nanocomposites as a adsorbent. The Zn-BDC@chitosan/carbon nanotube (Zn-BDC@CT/CNT) and Zn-BDC@chitosan/graphene oxide (Zn-BDC@CT/GO) were synthesized from metal organic framework, carbon nanotube/graphene oxide and natural polysaccharide. Results of adsorption experiments showed that the Zn-BDC@CT/GO possessed a higher adsorption capacity than that of the Zn-BDC@CT/CNT. A study on the adsorption of As onto Zn-BDC@CT/GO was conducted and the process parameters were optimized by response surface methodology (RSM). A five-level, four-factor central composite design (CCD) has been used to determine the effect of various process parameters on As uptake from aqueous solution. By using this design a total of 20 adsorption experimental data were fitted. The regression analysis showed good fit of the experimental data to the second-order polynomial model with coefficient of determination (R2) value of 0.9997 and model F-value of 1099.97. The adsorption matched with the pseudo-second-order model and the Freundlich model. The thermodynamic parameters revealed that the nature of adsorption was feasible, spontaneous and endothermic process. Adsorption of As in the presence of other competitive ions was not significantly affected The effective adsorption performance also sustained even after ten adsorption-desorption cycles, indicating favorable reusability.

Enhanced adsorption properties of zirconium modified chitosan-zeolite nanocomposites for vanadium ion removal.

The novel hybrid adsorbents, which were composed of nanozeolite and nanochitosan (NZ@NCT) and nanozeolite-multi walled carbon nanotube and nanochitosan (CNZ@NCT) were produced by simple method. The adsorption capacity of synthesized nanocomposites towards vanadium (V) was compared with that of a clinoptilolite-nanochitosan nanocomposite (CPL@NCT) obtained from natural zeolite. Zirconium (Zr) was employed to modify prepared nanocomposites because Zr (IV) has a strong affinity towards oxyanions such as V. Zr-modified nanocomposites and their pristine nanocomposites were comparatively characterized by different techniques. Batch experiments were conducted to find out the influence of different experimental factors. The adsorption capacities of all prepared materials towards V ions decreased with temperature increasing from 298 to 348 K. The calculated values of the thermodynamic parameters ΔH and ΔG demonstrated that the adsorption was exothermic and spontaneous. The adsorption process was described by the Freundlich isotherm and pseudo-second order model. The V species loaded nanocomposites could be regenerated by 0.5 M HCl-1.0 M thiourea solution. The adsorption performance was not considerably influenced by the coexistence of the nickel ( Ni2+) but nitrate (NO3-) and sulfate (SO42-) revealed slightly greater negative effects. The as-prepared nanocomposites can be used in three adsorption cycles without specific changing its adsorption efficiency.

Characterization of functionalized chitosan-clinoptilolite nanocomposites for nitrate removal from aqueous media.

The nanochitosan/clinoptilolite (Nano-CS/Clino) composite, Nano-CS/Clino activated by hydrochloric acid (Nano-CS/Clino@H) and Nano-CS/Clino functionalization with pentaethylenehexamine (Nano-CS/Clino@PEHA) has been used to removal of nitrate ions from aqueous media. The textural properties of the Nano-CS/Clino nanocomposites were studied by various characterization techniques. The Nano-CS was synthesized by ionic gelation technique that using tripolyphosphate as cross-linking agent. The BET specific surface area of chitosan and Nano-CS is 0.9774 and 52.8850 m2/g. The effects of different parameters on the removal of nitrate were measured in detail. The prepared Nano-CS/Clino@PEHA composite possess enhanced nitrate adsorption capacity of 277.77 mg/g than Nano-CS/Clino@H and Nano-CS/Clino were found to be 227.27 and 185.18 mg/g. The Dubinin-Radushkevich, Freundlich and Langmuir adsorption models were applied to describe the equilibrium isotherms. The experimental data were also analyzed by first- and second-order and intra particle diffusion. Thermodynamic parameters studies revealed that the nature of adsorption nitrate by nanocomposites synthesized is spontaneous and exothermic. The overall adsorption tendency of synthesized nanocomposites toward nitrate (NO3-) in the presence of CO32-, SO42- and Cl- under competitive conditions, followed the order: NO3- > CO32-> Cl-> SO42-. Desorption process was carried out with NaOH and proven it was an effective agent in the discharge of nitrate.

Dispersive liquid-liquid microextraction combined with gas chromatography-flame photometric detection. Very simple, rapid and sensitive method for the determination of organophosphorus pesticides in water.

A new method was used for the extraction of organophosphorus pesticides (OPPs) from water samples: dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-flame photometric detection (GC-FPD). In this extraction method, a mixture of 12.0 microL chlorobenzene (extraction solvent) and 1.00 mL acetone (disperser solvent) is rapidly injected into the 5.00 mL water sample by syringe. Thereby, a cloudy solution is formed. In fact, the cloudy state is because of the formation of fine droplets of chlorobenzene, which has been dispersed among the sample solution. In this step, the OPPs in water sample are extracted into the fine droplets of chlorobenzene. After centrifuging (2 min at 5000 rpm), the fine droplets of chlorobenzene are sedimented in the bottom of the conical test tube (5.0+/-0.3 microL). Sedimented phase (0.50 microl) is injected into the GC for separation and determination of OPPs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, temperature and salt effect were investigated. Under the optimum conditions, the enrichment factors and extraction recoveries were high and ranged between 789-1070 and 78.9-107%, respectively. The linear range was wide (10-100,000 pg/mL, four orders of magnitude) and limit of detections were very low and were between 3 to 20 pg/mL for most of the analytes. The relative standard deviations (RSDs) for 2.00 microg/L of OPPs in water with internal standard were in the range of 1.2-5.6% (n=5) and without internal standard were in the range of 4.6-6.5%. The relative recoveries of OPPs from river, well and farm water at spiking levels of 50, 500 and 5000 pg/mL were 84-125, 88-123 and 93-118%, respectively. The performance of proposed method was compared with solid-phase microextraction (SPME) and single drop microextraction. DLLME is a very simple and rapid (less than 3 min) method, which requires low volume of sample (5 mL). It also has high enrichment factor and recoveries for extraction of OPPs from water.

Taguchi optimization approach for Pb(II) and Hg(II) removal from aqueous solutions using modified mesoporous carbon.

Using the Taguchi method, this study presents a systematic optimization approach for removal of lead (Pb) and mercury (Hg) by a nanostructure, zinc oxide-modified mesoporous carbon CMK-3 denoted as Zn-OCMK-3. CMK-3 was synthesized by using SBA-15 and then oxidized by nitric acid. The zinc oxide was loaded to the modified CMK-3 by the equilibrium adsorption of Zn(II) ions from aqueous solution followed by calcination to convert zinc nitrate to zinc oxide. The CMK-3 had porous structure and high specific surface area which can accommodate zinc oxide in a spreading manner, the zinc oxide connects to the carbon surface via oxygen atoms. The controllable factors such as agitation time, initial concentration, temperature, dose and pH of solution have been optimized. Under optimum conditions, the pollutant removal efficiency (PRE) was 97.25% for Pb(II) and 99% for Hg(II). The percentage contribution of each controllable factor was also determined. The initial concentration of pollutant is the most influential factor, and its value of percentage contribution is up to 31% and 43% for Pb and Hg, respectively. Our results show that the Zn-OCMK-3 is an effective nanoadsorbent for lead and mercury pollution remediation. Langmuir and Freundlich adsorption isotherms were used to model the equilibrium adsorption data for Pb(II) and Hg(II).

Fast and efficient mesoporous adsorbents for the separation of toxic compounds from aqueous media.

The effect of cationic template on the adsorption of chromium (VI), furfural and copperphthalocyanine-3,4',4'',4'''-tetrasulfonic acid tetrasodium salt (CuPc) in MCM-41 and MCM-48 mesoporous materials was investigated in this work. We used cetyltrimethylammonium bromide (CTAB) as the cationic template and sodiummetasilicate (for MCM-41) and tetraethyl-orthosilicon (for MCM-48) as the silica source for the synthesis of mesoporous materials. The properties of synthesized samples were characterized with XRD-low angle, SEM, N(2) adsorption-desorption and TG-DT analysis. The extent of adsorption was investigated as a function of solution pH, shaking speed, contact time, analyte concentration, reaction temperature and supporting electrolyte (sodium chloride) concentration. Langmuir and Freundlich isotherms were used to model the adsorption equilibrium data. The as-synthesized mesoporous samples showed very high adsorption capacity for the analytes and adsorption uptakes were rapid on the adsorbents reaching equilibrium in less than 2 h. The materials without surfactant did not show significant affinity for the analytes.