Detection Of Mercury Research Articles

Construction of mercury ion fluorescence system in water samples and art materials and fluorescence detection method for rhodamine B derivatives

Abstract At present, the research on fluorescent molecular probe has become a hot topic in the field of environmental science, chemical materials, medicine, and other fields. Therefore, the detection of industrial mercury-containing wastewater (Hg2+) is of great significance. In this article, the fluorescent probe is used to detect mercury ions, and when compared with the traditional detection method, the fluorescent probe has the advantage of operation such as the effect of simplicity is evident. The experiments first synthesized rhodamine B derivatives and then the synthesized rhodamine B derivative fluorescent molecular probes were constructed and used to detect the mercury ions in water sample and oil paints. It was demonstrated that rhodamine B-derived probes have been constructed by UV and fluorescence spectroscopy. The different metal ions and rhodamine B-derived fluorescent molecular probes were compounded, resulting in the appearance of fluorescence peak centered at 583 nm only after the addition of metallic mercury ions with almost no response from other ions. The mercury ion rhodamine B derivative is more responsive to metallic mercury ions.

Fluorogenic detection of mercury ion in aqueous environment using hydrogel‐based AIE sensing films

AbstractA “turn‐on” fluorescent sensing strategy was developed for ultrasensitive detection of heavy metal mercury ion (Hg2+) directly in water. It utilized an aqueous soluble aggregation‐induced emission (AIE)‐active probe, named 1,1,2,2‐tetrakis(4‐(1H‐tetrazol‐5‐yl)phenyl)ethene (TPE‐4TA), composing of a luminescent tetraphenylene core and multiple anionic tetrazolate spawns. The probe retained dark when molecularly dissolved in water. However, mercury ions can ligate with multiple tetrazolate groups to form infinite coordination polymer particles spontaneously, thus inducing a fluorogenic AIE response for in situ analysis. Moreover, by embedding this AIE sensing molecules in a hydrophilic polyvinyl alcohol substrate, the resulting hydrogel film allowed in situ detection of Hg2+ on a laser‐induced fluorescence analysis setup in aqueous environment. This strategy worked effectively in common aqueous environments with pH from 4 to 7.5 and showed high sensitivity (limit of detection down to 0.38 ppb/1.9 nM), good selectivity and a wide linearity range for quantification. This work may lead to a reliable and promising platform for on‐site environmental water analysis.

Novel highly selective fluorescence sensing strategy for Mercury(Ⅱ) in water based on nitrogen-doped carbon quantum dots

In this work, a fluorescent signal-closing probe of nitrogen-doped carbon quantum dots (NCQDs) was developed for quantitative detection of mercury ions (Hg2+). In this detection system, the NCQDs with high quantum yield (QY, 63.80 %) were synthesized via simple hydrothermal method with Methyl Glycine Diacetic acid Trisodium Salt (MGDA) and m-phenylenediamine (MPD) as carbon and nitrogen sources. The NCQDs have a typical surface structure and exceptional fluorescence stability, and their fluorescence zones are centered on excitation wavelengths of 440 nm and emission wavelengths of 510 nm. Under optimal conditions, the NCQDs have outstanding anti-interference ability to various ions and high selectivity to mercury ions. The fluorescence intensity of the detection system is weakened due to the generation of non-fluorescent groups caused by the static quenching effect. The fluorescence quenching efficiency shows a fascinating linear relationship with Hg2+ ions at 0–100 μM (y = 0.0051x-0.015, R2 = 0.9943), and the detection limit is 0.9 μM. Acute toxicity test shows that NCQDs have low toxicity and little harm to environment. The detection system can be used for the quantification of mercury ions in environmental water samples, and the recovery rate is between 99.64 % and 103.43 %, indicating that it is a simple and economical fluorescence detection method.

Glutathione assisting the waste tobacco leaf to synthesize versatile biomass-based carbon dots for simultaneous detection and efficient removal of mercury ions

High-efficient conversion of the waste biomass into eco-friendly novel bifunctional materials for selective monitoring and effective removal of mercury ions (Hg2+) is of great significance to achieve the environment sustainable development, but has not attracted enough attention. Herein, we exploited glutathione (GSH) assisting waste tobacco leaf as the biomass-related precursors to successfully yield a novel red fluorescence emission biomass-based carbon nanodots (CDs) with a remarkably large Stokes shift of ∼ 232 nm through one-pot hydrothermal method. Owing to the synergistic Hg-S bond and the coordination effects of the Hg2+ to the abundant –COOH, –NH2 and –OH groups on the surface of CDs, this proposed biomass-based CDs showed a red fluorescence decrease response for Hg2+ with a high selectivity and a lower detection limit of 0.45 μM in environmental water samples. Furthermore, this binding endowed this proposed biomass-based CDs possessed a high removal efficiency of above 99.4% for Hg2+ as well. This work showed a novel insight into recycling the waste tobacco leaf into novel, economic, efficient, reliable, and eco-friendly biomass-based CDs for simultaneously precise traceability and high-efficient removal of Hg2+ pollution in environmental matrices.

A FRET-based ratiometric fluorescent probe for Hg2+ detection in aqueous solution and bioimaging in multiple samples

Mercury ion, as a metal cation with great toxic effect, is widely present in various production and living environments. It seriously threatens human health and environmental safety. It is of great significance to develop convenient and effective methods for mercury ion detection. Here, we designed and synthesized a new ratiometric fluorescent probe (namely APS-NA) for the detection of mercury ions in the environment and multiple biological samples. The probe is constructed by covalently connecting two fluorophores with lipolic acid to achieve fluorescence resonance energy transfer (FRET). In the molecular structure of APS-NA, acridone is used as an energy donor, 1,8-naphthalimide is used as an energy acceptor, and a dithioacetal group is used as the reaction site for Hg2+. The intact APS-NA mainly shows the green fluorescence from the acceptor moiety 1,8-naphthalimide; the presence of Hg2+ ions would break the dithioacetal linkage between acridone and 1,8-naphthalimide; the defunctionalization of FRET would lead to bright blue fluorescence emission of acridone; thus ratiometric fluorescent detection of Hg2+ can be achieved by this recognition process. The probe not only has a large Stokes shift (Δλ = 110 nm), but also has high selectivity, high sensitivity (low detection limit 30 nM) and naked eye visualization. In addition, we have successfully used this probe for the detection Hg2+ of actual samples and imaging of a variety of organisms. These results indicate that the probe has broad application prospects.

Low-Tech Test for Mercury Detection: A New Option for Water Quality Assessment

Mercury pollution is a global environmental problem, especially in low-resource areas where artisanal iron mining is taking place and industrialization is on the rise. Therefore, there is a demand for simple methods for the determination of toxic metals at low. In this study, an on-field membrane lateral flow test system for sensitive and specific detection of Hg2+ in natural waters matrix is proposed. For this purpose, mercaptosuccinic acid (MSA) conjugated with protein-carrier (bovine serum albumin) was pre-impregnated in the test zone of the strip and used as a capping agent for mercury complexation. Quantitative evaluation of the analyte was provided by the use of gold nanoparticles stabilized with Tween-20 as a detecting agent. The sensing principle relies on the formation of Au–Hg nanoalloy during the migration of a solution containing Hg2+ along the strip, followed by capture in the test zone with the formation of a colored complex. Under optimum conditions, the proposed lateral flow test exhibited the linear correlation between color intensity in the test zone from the concentration of Hg2+ in the range of 0.04–25 ng/mL. The total analysis time was 11 min, without the need for the usage of additional instrumentation. The detection limit was estimated to be 0.13 ng/mL, which is 45 times lower than the WHO guidelines. The applicability of the proposed lateral flow test was confirmed by the analysis of natural waters, with the recoveries ranging from 70 to 120%. Due to the high affinity of Au to Hg and the use of a capping agent for mercury complexing, the developed system demonstrates high selectivity toward Hg2+. Compared to existing analytical methods, the proposed approach can be easily implemented and is characterized by economy and high analytical performance.

The Functional Fe3O4@SiO2@AuNPs SERS Nanomaterials for Rapid Enrichment and Detection of Mercury Ions in Licorice

There has been an increasing demand for rapid and sensitive techniques for the detection of heavy metal ions that are harmful to the human body in traditional Chinese medicine (TCM). However, the complex chemical composition of TCM makes the quantitative detection of heavy metal ions difficult. In this study, the magnetic Fe3O4@SiO2@AuNPs nanoparticles combined with a probe molecule DMcT were used for the specific enrichment and detection of Hg2+ in the complex system of licorice. The core of Fe3O4 was bonded with SiO2 to increase its stability. A layer of AuNPs was deposited to produce a “core–shell” Raman substrate with high surface-enhanced Raman spectroscopy (SERS) activity, which was surface modified by DMcT probe molecules with sulfhydryl groups. In the presence of Hg2+, Hg2+ binds to N on the amino group of DMcT to form N-Hg2+-N complexes, which induces Fe3O4@SiO2@AuNPs-DMcT clustering to enhance SERS signal. The Raman probe molecule DMcT showed an excellent linear relationship (R2 = 0.9709) between the SERS signal at 1416 cm−1 and the Hg2+ concentration (0.5~100 ng/mL). This method achieved a good recovery (89.10~111.00%) for the practical application of detection of Hg2+ in licorice extracts. The results demonstrated that the functional Fe3O4@SiO2@AuNPs-DMcT performed effective enrichment and showed high sensitivity and accurate detection of heavy metal ions from the analytes.

Efficient Synthesis of Highly Photo‐stable N‐doped Carbon Quantum Dots and their Applications in Detection and Cellular Imaging of Mercury Ions

AbstractIn this work, the nitrogen doped carbon quantum dots (N‐CQDs) were synthesized by a simple microwave hydrothermal method using citric acid (carbon source) and urea (dopant) and optimized the preparation conditions by orthogonal tests. The synthesized N‐CQDs emitted a bright blue fluorescence with specific selectivity for Hg2+. The study revealed a static quenching mechanism of Hg2+ on the N‐CQDs. The N‐CQDs showed good linear correlation in the range of 0–120 μM for the detection of Hg2+ with a low detection limit of 22.50 nM. We also demonstrated the suitability of the N‐CQDs for the detection of Hg2+ in tap water and industrial wastewater with spiked recoveries of 97.56 %–103.58 %. In addition, the synthesized N‐CQDs with high fluorescence intensity, good optical stability and biocompatibility were successfully applied to fluorescent inks and imaging of Hela cells. This indicated that the synthesized N‐CQDs have promising applications in Hg2+ detection, bioimaging, and fluorescence anti‐counterfeiting.

One-step synthesis of highly fluorescent carbon dots as fluorescence sensors for the parallel detection of cadmium and mercury ions.

Cadmium (Cd2+) and mercury ions (Hg2+) are essential for the quality control of food samples because of their serious toxicity to human health, but the effective and simple strategy for their parallel detection remains challenging. In this paper, a rapid and simple parallel detection method for Cd2+ and Hg2+ was developed using carbon dots (CDs) as fluorescent sensors. A one-step hydrothermal method with a single precursor l-arginine as both the carbon and nitrogen sources was employed to prepare nitrogen-doped CDs (N-CDs). N-CDs exhibited a uniform particle size and excitation-independent fluorescence emission. The maximum emission wavelength of N-CDs was observed at 354 nm with the excitation wavelength at 295 nm. The quantum yield of N-CDs reached as high as 71.6% in water. By using sodium diphosphate and phytic acid as masking agents, the fluorescent sensor can be quenched by Cd2+ and Hg2+ in the linear range of 0–26.8 μM and 0–49.9 μM within 5 min. Other common ions in farm products showed no significant effect on the fluorescence intensity of the sensing system. The results demonstrated that the sensing system had good selectivity and sensitivity for Cd2+ and Hg2+. The detection limits for Cd2+ and Hg2+ were 0.20 and 0.188 μM, respectively. In addition, the fluorescent sensor had been successfully applied for the detection of Cd2+ and Hg2+ in fruits and vegetables, and the recoveries were 86.44–109.40% and 86.62–115.32%, respectively. The proposed fluorescent sensor provides a rapid, simple, and sensitive detection method for Cd2+ and Hg2+ in food samples and thus a novel quantitative detection method for heavy metal ions in foods.

A smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor for visual detection of mercury ions and l-penicillamine

Establishment of a rapid, sensitive, visual, accurate and low-cost fluorescence detection system to detect multiple targets was of great significance in food safety evaluation, ecological environment monitoring and human health monitoring. In this work, a smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor was proposed based on metal-organic framework (NH2-MIL-101(Fe)) and CdTe quantum dots (CdTe QDs) for visual detection of mercury ions (Hg2+) and L-penicillamine (L-PA), in which NH2-MIL-101(Fe) was used as the reference signal and CdTe QDs was used as the response signal. The down-conversion fluorescence system at excitation wavelength of 300 nm (ex: 330 nm) was used to detect Hg2+ and L-PA, in which the detection limit of Hg2+ was 0.053 nM with the fluorescence color changed from green to blue, and the detection limit of L-PA was 1.10 nM with the fluorescence color changed from blue to green. Meanwhile, the up-conversion fluorescence system at excitation wavelength of 700 nm (ex: 700 nm) was used to detect Hg2+ and L-PA. The detection limits of Hg2+ and L-PA were 0.11 nM and 2.93 nM, respectively. The detection of Hg2+ and L-PA were also carried out based on the color extraction RGB values identified by the smartphone with a detection limit of 0.091 nM for Hg2+ and 8.97 nM for L-PA. In addition, the concentrations of Hg2+ and L-PA were evaluated by three-dimensional dynamic analysis in complex environments. The smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor system provides a new strategy for detection Hg2+ and L-PA in food safety evaluation, environmental monitoring and human health monitoring.

Portable and miniature mercury analyzer using direct sampling inbuilt-metal ceramic electrothermal vaporization

In this work, a small-size inbuilt-metal ceramic heater (IMCH) was for the first time utilized as a solid sampling electrothermal vaporizer (ETV), and then a novel direct sampling mercury analyzer coupled with a miniature atomic absorption spectrometer was thereby fabricated for sensitive determination of mercury in soil. The mercury analyzer is mainly composed of an IMCH-ETV, a catalytic pyrolysis furnace (CPF) using Al2O3 particles as a new filler, an atomic absorption spectrometer (AAS) and a miniature air pump for carrier gas; herein, the mostly used gold amalgamation was canceled. The IMCH with 30 W heating fulfills the 100% vaporization of mercury from up to 80 mg soil samples using 0.1 L min−1 air carrier. Under the optimized conditions, the method detection limit (LOD) was 0.4 ng g−1 for a 50 mg sample and the RSD of 11 repeated measurements of GSS-3a soil certified reference material (CRM) was 4%. Furthermore, the measured Hg values in various soil CRMs and real soil samples were within their certified values and consistent with that using the Chinese standard method (solid sampling catalytic pyrolysis AAS with gold amalgamation); and the recoveries were 85–113%, which proved favorable analytical accuracy and precision. This fabricated instrumentation only occupies 5 kg and 200 W power consumption vs. more than 25 kg and 1000 W for the traditional Hg analyzer. Therefore, the proposed IMCH-ETV-AAS method is very suitable for portable and rapid detection of mercury in soil.

High-performance detection of trace Hg2+ concentration enhanced by a functionalized optic-microfiber sensor

The monitoring of heavy metal ions content has positive significance for water resources quality monitoring and environmental protection. Herein, a tapered microfiber sensor functionalized polydopamine/4-mercaptopyridine (PDA/4-MPY) film for detection of trace mercury ion (Hg2+) concentration in water is proposed and demonstrated. The microfiber interferometer has excellent sensing performance including a refractive index (RI) sensitivity response of 1146 nm/RIU and a low-cross temperature response of −0.03 nm/℃. Hg2+ heavy metal ion is captured by the surface functional film to affect the RI of the microfiber surface, which lead to the wavelength shift of the interference spectrum. Experiments demonstrate that the sensor has an obvious regular response to Hg2+ in the range of 0–100 nM, in which the sensitivity reaches 1.015 nm/nM in the range of 0–10 nM with a high reliability (R2 = 0.99). This sensor has high sensitivity response and strong specific recognition to trace Hg2+ concentration under the advantages of simple fabrication and low cost. Furthermore, the success of the proposed sensor also indicates that the combination of microfiber and nanomaterial has a bright prospect in the field of optical detection.

Vinyl substituted triphenylamine based turn-off fluorescent probe for selective and sensitive detection of mercury (II) in water and live cells

Here, we report vinyl substituted triphenylamine (TPA-alk) fluorescent probe for the rapid and efficient detection of mercury ion (Hg2+) in water and biological environment. TPA-alk detects Hg2+ selectively over a wide range of competitive metal ions with a blue shift of 43 nm in the UV absorbance spectrum. The detection limit is found to be 0.146 µM (29.2 ppb) with high selectivity over a wide range of competitive metal ions. DFT study explains the blue shift in the UV–vis absorption band of the optical probe upon the addition of Hg2+. Cell viability assay illustrates that the probe is biocompatible and it has low cytotoxicity even at its higher concentration. Cell imaging studies demonstrate the efficiency of the TPA-alk probe for the micromolar detection of mercury (II) in live BMG1 cells.

Phosphorus-doped oligomeric carbon nitride for selective fluorescence detection of mercury (II) ions

Selective and sensitive analysis of mercury (II) ions is a challenging topic in fluorescent sensors. Herein, we obtained a new selective mercury (II) ion fluorescence sensor by converting microscale hollow-tube-structured phosphorus-doped polymeric carbon nitride into phosphorus-doped carbon nitride oligomers with needle-like nanostructures by a hydrothermal reaction. The unique oligomeric microstructure and surface-rich terminal amino and hydroxyl functional groups of the fluorescence sensor synergistically endow it with selective quenching of mercury (II) ions. This phosphor-doped carbon nitride oligomer-based mercury (II) ion-selective fluorescence sensor achieves a minimum detection limit of 0.35 nmol L−1 in the range from 1–100 nmol L−1 (correlation coefficient of 0.9976) and a quantum yield of 16.6%. The detection of mercury (II) ions in actual shrimp samples demonstrated the sensitivity and accuracy of this fluorescence sensor. This work provides a new possibility for developing green and inexpensive mercury (II) ion-selective fluorescent sensors.

Electrochemical sensor applying ZrO2/nitrogen-doped three-dimensional porous carbon nanocomposite for efficient detection of ultra-trace Hg2+ ions

In this study, a ZrO2/nitrogen-doped three-dimensional porous carbon (ZrO2/N-3DPC) nanocomposite was manufactured to fabricate an effective electrochemical sensor for the detection of ultra-trace mercury ion (Hg2+). The synthesized N-3DPC had an open pore structure, large specific surface area and enough continuous mass transfer channels, which can facilitate the diffusion and transmission of electrons and ions at the sensing interface, providing an effective adhesion platform for electrochemical deposition of ZrO2 nanoparticles. Benefiting from the synergistic effect of ZrO2 and N-3DPC, the developed electrochemical sensor had good adsorption and catalytic performance for Hg2+ with a wider linear range of 0.1–220 μg L−1 and a lower detection limit of 0.062 μg L−1. Meanwhile, the sensor exhibited remarkable repeatability, reproducibility, stability and anti-interference, and was further applied to detect Hg2+ in seafood and tap water with satisfactory recoveries (97.1–103.1%) and lower relative standard deviation (≤4.3%). The proposed strategy of electrochemical sensing detection of Hg2+ provides a new idea and direction for the research of ZrO2/N-3DPC nanocomposite in the field of analysis and detection, which is also of great significance to ensure foods, environmental safety and human health.

Ultrasensitive detection of Hg(II) by small-sized Mn3O4 loaded on g-C3N4 nanosheets: Heterojunction facilitates electron transfer and Mn(II)/Mn(III)/Mn(IV) cycle

Transition metal oxides are widely used in electrochemical detection because of the promotion of redox of heavy metal ions (HMIs) by valence change behavior. However, it is challenging to favorably promote the valence change to achieve the improvement of detection sensitivity. Herein, a Mn3O4/g-C3N4 composite (named as MO-CN) with small-sized of Mn3O4 and high proportion of Mn(II) and Mn(III) was prepared, which reveals an excellent performance on detecting mercury ion (Hg(II)). It is discovered that Mn3O4 becomes small in size and well disperses on g-C3N4, which solves the adverse effect of agglomeration and also lead to a good conductivity. And g-C3N4 can provide more adsorption sites to enhance the adsorption on Hg(II). Heterojunction is proved to form in MO-CN and thus accelerates electrons to flow from g-C3N4 to Mn3O4. This results in transforming Mn(IV) to Mn(II) and Mn(III) in Mn3O4, thereby promoting the cycle of Mn(II)/Mn(III)/Mn(IV) and furthermore facilitating the redox of Hg(II). Simultaneously, the obtained sensitivity (473.43 μA μM−1 cm−2) and limit of detection (LOD, 0.003 μM) are as expected. The nanocomposites and heterojunction based on transition metal oxide and 2D nanomaterials is promising to boost the detection of HMIs.

Rational design of a water-soluble TICT-AIEE-active fluorescent probe for mercury ion detection

Considering that mercury ions (Hg2+) have long been a threat to human health and the environment due to their persistence, mobility and bioenrichment, the detection and removal of Hg2+ is of great significance. Therefore, a simple water-soluble naphthalimide derived fluorescent dye with AIEE characteristics was reasonably constructed based on twisted intramolecular charge transfer (TICT) mechanism, a series of probes were synthesized to demonstrate this mechanism. The probe NIDEA (naphthalimide-diethanolamine) bonding Hg2+ through the specific combination of the N-unsubstituted naphthalimide group and Hg2+ to form a classic “imide-Hg-imide” structure. Moreover, the introduction of diethanolamine moiety enhanced the water-solubility of the probe, and also made the dye molecule possess the feature of AIEE. The fluorescence titration experiment showed that there were two good linear relationships between the fluorescence intensity of the probe NIDEA and the concentration of Hg2+ in the range of 0–2.5 μM and 2.5–7.5 μM, and the limit of detection was 46.7 nM. Also, the probe could detect Hg2+ in aqueous solution sensitively, ensuring its application in the actual water sample in the environment and living cells. At the same time, NIDEA can be used to detect Hg2+ by Tyndall effect (TE) without limitation of instrument and technology, the limit of detection was 20.9 nM. Furthermore, this paradigm by introduction of the highly effective TICT structure supports a promising methodology for the construction of simple water-soluble AIE/AIEE-active probes.

Interface engineering of MoS2 nanopetal grown on carbon nanofibers for the electrocatalytic sensing of mercury (II) and efficient hydrogen evolution

Deep concerns about the hazards to human health posed by the misuse of Hg2+ constitute a considerable scientific challenge. To address these concerns, we coated electrospun carbon nanofibers (CNFs) with petal-like MoS2 grown and followed this with a facile hydrothermal treatment using thiourea (TA), thioacetamide (TAA), or l-cysteine (L-Cys) as sulfur precursors. The proposed MoS2-TA-CNF screen-printed carbon electrode (SPE) showed excellent electrocatalytic performance for the electrochemical detection of mercury ions (Hg2+) and hydrogen evolution reaction (HER) applications in acidic medium. Interestingly, MoS2-TA-CNFs have inherent electrocatalytic behavior and lower charge transfer kinetics (Rct = 46 Ω), higher anodic signal intensities, and lower anodic signal potentials than MoS2-L-Cys–CNF–SPEs or MoS2-TAA–CNF–SPEs. The proposed electrocatalyst had an ultra-low detection limit (0.16 nM) and a linear range of 5–125 nM with excellent sensitivity (4.152 μA nM-1 cm-2) for the one-step detection of Hg2+. Furthermore, square wave voltammetry (SWV) showed the anodic peak of Hg2+ was at 0.04 V (vs. Ag/AgCl). The practicability of the designed sensor was confirmed by on-site Hg2+ monitoring in samples of river, sea, and industrial water and provided satisfactory recoveries from 86.6% to 110.9% with RSDs below 5% as determined by ICP-OES. Furthermore, optimized MoS2-TA–CNF–SPEs had a low overpotential of only 146 mV and achieved at10 mA/cm2, a Tafel slope of 72.4 mV/dec, and better electron transfer resistance in HER than MoS2-L-Cys-CNF or MoS2-TAA–CNF–SPEs in acidic media over 25 h. The devised bifunctional electrocatalyst provides a unique novel means of rapidly monitoring Hg2+ concentrations in water and conducting hydrogen evolution reactions as alternatives to noble metal-based electrocatalysts.

Physical and Optical Properties of N,S-Codoped Carbon Quantum Dots Derived from Cigarette Butts for Mercury Ions Detection

The accumulation of mercury metal ion (Hg2+) in polluted river water is a problem in the emergence of various diseases in humans, because it is accumulated in drinks and food eaten every day. Therefore, the development of an accurate, sensitive, efficient and convenient method is very important to detect the content of metal mercury ions in polluted water. In this study, Carbon Quantum Dots (CQDs) was made simultaneously doped with Nitrogen (N) and Sulphur (S) atoms, so called N,-S codoped CQDs for the application of mercury metal ion sensors in polluted water. CQDs were prepared from wasted cigarette butts, which contain cellulose acetate as a source of carbon and nicotine as N-atoms source. The preparation of carbon solutions precursors were made by two ways of treatments namely put wasted cigarette filters/butts with water for 6-12 months (precursor I) and atomic S doping was done by adding sulfuric acid (H2SO4) with a volume-percentage of 0, 10% and 20% in water. The second treatment was carried out through the washing of wasted cigarette filter with sulfuric acid solution with a volume percentage of 20% sulfuric acid in water (precursor II). CQDs were prepared by use of hydrothermal method at 180°C for 6 hours. The synthesized solution was neutralized with sodium carbonate (Na2CO3). The solution was then centrifuged at 10,000 rpm for 15 minutes and filtered with a 0.22 µm microsyringe filter. The result of solution is a transparent and turns into blue when irradiated by a 365 nm UV laser, which indicates that CQDs has been formed. The FTIR results of the CQDs solution without S doping showed the presence of groups containing N atoms, namely at wave numbers 1417 cm-1 (C–N), 1540 cm-1 (CON–H), 1650 cm-1 (C=N/C=O). This means that N-doped CQDs have been formed. The C–S functional group was identified at a wave number of 1361 cm-1 in the S atom-doped CQDs. The HR-TEM images showed that the CQDs had a size less than 10 nm, and the distance between graphene crystals plane is in the range of 0.22-0.28 nm. The absorption spectra of the CQDs are ranging from 200 nm to 350 nm. S atom doping does not affect the absorbance spectrum significantly. The CQDs without S-atom doping has a PL spectrum from 300 nm to 800 nm with an emission peak of 417 nm. While, the N,-S codoped CQDs have a PL emission peak at 404 nm. The addition of doping from 10% to 20% did not change the peak emission wavelength. The CQDs sizes, optical properties and FTIR spectra of N, S-codoped CQDs show no significant difference when were prepared from precursor I and precursor II. This shows that the preparation of N, S co-doped CQDs can be produced much faster by washing cigarette butts directly with sulfuric acid prior to hydrothermal process as compared to precursor I which needs 6-12 months.

A High Efficient Electrocatalytic Activity of Metal‐organic Frameworks ZnO/Ag/ZIF‐8 Nanocomposite for Electrochemical Detection of Toxic Heavy Metal Ions

AbstractA novel electrochemical sensor on ZIF‐8 nanocomposites (Ag/ZnO/ZIF‐8) was developed to analyze the mercury ions (Hg2+). The ZIF‐8 materials are one of the 3‐dimensional porous metal‐organic frameworks with highly accessible pores and great surface area. The ZIF‐8 nanocomposites were prepared through simple sol‐gel methods and their physio‐chemical properties were characterized via different analytical analyses. As a result of cyclic voltammetry, Ag/ZnO/ZIF‐8 exhibited a better electrocatalytic behavior towards the detection of mercury ions (Hg2+). Furthermore, the composite modified electrode was then inspected as a sensor for DPV detection of mercury ions. The nanocomposite sensor performed a wide linear range from 0.5 μM to 140 μM with a low detection limit of 40 nM, and high sensitivity of 56.06 μA μM−1 cm−2. Moreover, the ZIF‐8 composite sensor showed a higher selectivity toward the detection of mercury ions (Hg2+). The real‐time applications of the ZIF‐8 composites sensor were inspected in various samples with good sensitivity.