Toxic Heavy Metal Ions Research Articles

Locally resonant porous phononic crystal sensor for heavy metals detection: A new approach of highly sensitive liquid sensors

In this research, a novel and highly sensitive phononic crystal (PnC) sensor is presented for the detection of CdBr2 concentrations at a low scale (ppm) which is considered a highly toxic heavy metal ion in freshwater. The proposed sensor is composed of two thin layers of rubber covering both the top and bottom surfaces of a one-dimensional ternary porous silicon (PSi) PnC. As a result, the whole designed structure is arranged as {rubber/[PSi1/PSi2/PSi3]N/rubber}. The appearance of local resonant modes is due to the presence of two thin rubber layers as a cap layer of the PnC design. In particular, the spectral position of the modes is significantly tuned when filling the PSi layers with CdBr2 ions. It is worth mentioning that the novelty of this work is mainly focused on three axes. The first one is the use of locally resonant PnCs (not conventional defective ones) as highly sensitive biosensors. The second one, the liquid of interest here is considered a dangerous aqueous solution with a very low scale (ppm). The last promising point, we proposed the pores inside Si layers are filled with a liquid material in contrast to most of the micromechanics methods of composite materials that supposed the pores are empty (just voids are inside). To realize the best performance of this sensor, an optimization strategy of some related parameters such as the rubber layer thickness, the geometry of the PnC, and the unit cell number was conducted. In this regard, the proposed sensor provides promising values of sensitivity, quality factor, detection limit, and damping rate of 47.25 Hz/ppm, 2756.2, 82 ppm, and 0.00018, respectively. Therefore, the present design could be of serious contribution to liquid sensors and bio-sensing applications due to its simplicity, novelty, and high performance.

Simultaneous Quantitation of Lead and Cadmium on an EDTA-Reduced Graphene Oxide-Modified Glassy Carbon Electrode.

Cadmium (Cd) and lead (Pb) are classified as category one toxicants. The provisional guideline values, according to the World Health Organization (WHO), for Cd and Pb are 3 and 10 ppb, respectively. An easy, quick, and cheap analytical technique is in demand for the determination of these toxic heavy metals in water. Hence, a novel electrochemical sensing platform is developed by modifying the glassy carbon electrode with ethylenediaminetetraacetic acid (EDTA)-functionalized reduced graphene oxide (ErGO) for the low-cost simultaneous quantitation of toxic heavy-metal ions, lead and cadmium, in real water samples. EDTA is grafted to the surface of graphene oxide, via amine linkage, and the oxygen functionality is reduced by a green agent, tyrosine. Various physical and electrochemical characterizations of the as-prepared electrocatalytic material were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), ζ-potential, ultraviolet diffuse reflectance spectroscopy (UV-DRS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc. The glassy carbon electrode (GCE) is modified with ErGO by a simple drop-casting method for simultaneous metal-ion quantitation by differential pulse voltammetry (DPV). EDTA functionalization of graphene oxide and its further reduction using the green agent enhance the stability and sensitivity of the electrode substrate. The limits of detection for cadmium and lead ions calculated for ErGO/GCE are 1.02 and 2.52 ppb, while the limits of quantification for lead and cadmium ions are 3.41 and 8.4 ppb, and their sensitivities are 0.8 and 0.6 nA/ppb, respectively. Real river water contains 200.2 ± 0.38 ppb of Pb2+ ions (mean ± stdev, n = 3) by the DPV technique, which is validated by ICP-OES analysis.

Highly efficient and simultaneous remediation of heavy metal ions (Pb(II), Hg(II), As(V), As(III) and Cr(VI)) from water using Ce intercalated and ceria decorated titanate nanotubes

Presence of heavy metal ionic contaminants in water is a matter of global concern, owing to their disastrous impact on human health and environment. Cerium intercalated, ceria decorated titanate nanotubes (CCTNT) was developed for efficient adsorption of toxic heavy metal ions: Pb(II),Hg(II),As(V),As(III) and Cr(VI) from water. The phase and structure of the material was confirmed using XRD, FTIR and Raman analysis. The TEM images established the morphology. The chemical properties of the surface were confirmed using the EDS and XPS analysis. The surface area was measured using the BET method. The adsorptive properties of CCTNT were evaluated in the batch mode. It was observed that CCTNT, with wide pH window for adsorption of heavy metal ions, is applicable for both groundwater and wastewater remediation. In addition, it exhibited ultrafast adsorption of all five contaminants using a low adsorbent dosage. The Langmuir adsorption capacities of the adsorbent were calculated to be 66.76, 97.18, 189.59, 199.80, 288.23 mg/g respectively for the removal of Cr(VI),Pb(II),As(V), Hg(II) and As(III) from water. CCTNT is further suitable for highly efficient and simultaneous removal of all five heavy metal ions water. These attractive properties make CCTNT a superior material for adsorption of heavy metal ions from water.

Batch Adsorption Studies of Natural Composite Hydrogel for Removal of Co(II) Ions

Innovative methods for handling industrial wastewater containing heavy metals has been receiving significant attention from researchers in recent years. Proper treatment of wastewater is compulsory to avoid the release of toxic heavy metal ions into water bodies. In this study, we developed a new adsorptive material, i.e., orange peel/acrylamide composite hydrogel for the removal of Co(II) ions from aqueous solution. The results showed that the adsorption of Co(II) by our hydrogen was well-fitted with the pseudo-second-order model. Its adsorption rate against Co(II) ions could reach up to 56 mg/g at pH 6. Further investigations are still needed to maximize the adsorption capacity of orange peel/acrylamide composite hydrogel.

Methylmercury bioaccumulation in water flea Daphnia carinata by AIEgen

Mercury ion (Hg2+) is a toxic heavy metal ion and Hg2+ is convertible to methylmercury (MeHg) by many aquatic microorganisms, leading to bioaccumulation and biomagnification in aquatic organisms, which can interfere with brain development and function in humans. This study employs a newly developed AIEgen (Aggregation-induced emission fluorogen) to quantify and visualise the process of MeHg bioaccumulation in vivo on the species of water flea Daphnia carinata. Two approaches to MeHg absorption were taken, either by direct incubation in a MeHg solution or by indirect consumption of algae contaminated with MeHg. We analysed the relationship between the ratio of photoluminescence (PL) intensities (I585/I480) and MeHg concentration (CMeHg) and generated a master curve for determining MeHg concentration based on the measurement of PL intensities. Fluorescent image analysis showed the occurrence of MeHg in D. carinata to be mainly in the compound eyes, optic nerve and carapace. This study indicates that MeHg absorption can be quantified and visualised in the body of zooplankton, and the MeHg transfer to zooplankton is more likely through direct exposure than via indirect food intake. The accumulation of MeHg in the eye and the nervous system could be the cause of the high mortality of D. carinata exposed to MeHg in water.

Novel adsorbents for the removal of toxic cadmium ions from polluted water

Cadmium is one of the most toxic heavy metal ions found in wastewaters and its remedial methods are globally investigated. Removal methods based on biomaterials as adsorbents are proving to be simple, effective and eco-friendly. In the present investigation, bio-adsorbents derived from Cochlospermum regium plant stems (CRSP) and its active carbon (CRAC) are observed to have good adsorption for toxic cadmium ions. Hence, extraction conditions are optimized for maximum Cd-extraction: 55.0% with ‘CRSP’ and 70.0% with ‘CRAC’, from Cd2+ solutions of concentration: 25.0 mg/L. The adsorption capacities are 6.9 mg/g with CRSP and 12.6 mg/g with ‘CRAC’. When ‘CRAC’ is impregnated with nano-CeO2 (CRAC.nCeO2) and is used as adsorbent, the percentage of Cd-extraction is increased to 90.0% and adsorption capacity to 22.5 mg/g at the optimized extraction conditions. To overcome the agglomeration of nanoparticles, the ‘CRAC.nCeO2’ is immobilized in Zr-alginate beads and thus obtained beads are investigated as adsorbent. With beads (CRAC.nCeO2–Zr.alg), the percentage of Cd-adsorption is enhanced to 95.0% and adsorption capacity to 24.6 mg/g. The adsorbents are characterized by adopting XRD and FTIR techniques. The adsorption mechanism is assessed by evaluating thermodynamic parameters, isotherm and kinetic models. The thermodynamic parameters and FTIR spectral characteristics indicate the formation of ‘surface complex’ between Cd2+ and adsorbent’s functional groups. The adsorption follows Freundlich isotherm and pseudo-second order model. Many co-ions have not effected the percentage of extraction and interestingly, the presence of some cations (Al3+ and Fe3+) have synergistically enhanced the Cd-extraction. Spent sorbents can be regenerated and reused with marginal loss of adsorption capacity. The adsorbents developed are successfully used to treat real Cd-polluted wastewater. The novelty of the present investigation is that the effective, eco-friendly, renewable and robust sorbents with high sorption capacities are developed for Cd-remediation of water.

Bithiophene-based COFs for silver ions detection and removal

Covalent organic frameworks (COFs) are promising in the detection and removal of toxic heavy metal ions from water. However, achieving detection and removal functions requires systematic control of stability, porosity, pore environment, and luminescence properties, which remains a challenge for most COFs materials. Herein, we develop a bithiophene-based stable COF, TAPA-BTDC, with dual functions of simultaneous detection and removal of silver ions from aqueous solution through elaborate structural design and control of the pore environment. The obtained TAPA-BTDC has good thermal stability and chemical stability, possesses high crystallinity and moderate specific surface area (396.83 m2/g), and contains dense bithiophene-S chelating sites on the pore walls. These characteristics work together to give TAPA-BTDC the dual function of selective detection and effective removal of silver ions from aqueous solution. This dual function can be attributed to the π-complexation between bithiophene-S chelating sites and silver ions, as verified by X-ray photoelectron spectroscopy. The charge transfer between bithiophene-S and silver ions alters the weak fluorescence emission caused by the π−π layered structure, enabling TAPA-BTDC to selectively detect silver ions through fluorescence enhancement, and even trace amounts of Ag+ (2.4 × 10−4 mmol/L) can cause observable fluorescence emission. Meanwhile, these bithiophene-S scattered across the pore wall also provide a large number of accessible chelating sites for TAPA-BTDC, enabling it to effectively remove Ag+ with a maximum adsorption capacity up to 398.61 mg/g, and TAPA-BTDC can be easily regenerated five times without loss of performance. The results of this study reveal the exceptional potential of COFs with reasonably tailor-made structure in dealing with heavy metal ion contamination.

N, S co-doped carbon quantum dots/TiO2 composite for visible-light-driven photocatalytic reduction of Cr (VI)

A novel carbon quantum dots (CQDs) sensitized TiO2 (N, S-CQDs/TiO2) composite was prepared and used as a visible-light-active photocatalyst for the reduction of Cr (VI), one of the most toxic heavy metal ions. Experimental results from the batch reaction process indicated that the composite was able to completely reduce Cr (VI) to Cr (III) at pH 2.0 after 3 h′ exposure to visible light with the initial Cr (VI) concentration being 20.0 mg/L and a catalyst dosage of 1.0 g/L. It was also found that lower pH and lower initial concentration of Cr (VI) led to high reduction efficiency. Compare with pure TiO2, a four-fold increase in reduction efficiency of Cr (VI) was achieved by the N, S-CQDs/TiO2 composite under the same reaction conditions. The prepared composite also demonstrated good reusability and stable photocatalytic performance in real water samples. Results from this study confirm that sensitization of TiO2 with CQDs is efficient in broadening the light absorption range of TiO2, expanding its application in visible-light-driven photocatalysis.

Existence of a novel heavy metal-tolerant Pseudomonas aeruginosa strain Zambia SZK-17 Kabwe 1: the potential bioremediation agent in the heavy metal-contaminated area.

Bacterial biomass may serve as an important environmental cleaning agent to toxic heavy metal ions at the expense of chemical processes which are not environmentally friendly. This study aimed at characterizing bacterial agents which could serve as a potential in situ bioremediation agent at the site of isolation. The characterization was performed using both phenotypic and molecular approaches. A novel Pseudomonas aeruginosa strain Pseudomonas aeruginosa Zambia SZK17 Kabwe1 was successfully isolated, identified, and characterized. The strain showed a promising tolerance to heavy metals such as copper (2mM), zinc, nickel (2mM), cobalt (1mM), and cadmium (0.5mM) at the laboratory level. The bacterium has shown the bioaccumulation of at least 60% of copper (II) sulfate (0.3655mg/l) with R = 69.75%, cadmium (II) chloride (0.0241mg/l) with R = 69.98%, zinc (II) chloride (0.1389mg/l) with R = 69.91%, nickel (II) chloride (0.1155mg/l) with R = 69.92%, and cobalt (II) chloride (0.593mg/l) with R = 69.92%. The highest bioaccumulation has been observed in heavy metals cadmium, zinc, nickel, and cobalt. Characterization of the bacterium on pH has revealed that at a very high pH (≥ 9) and lower (≤ 5.5) pH, the bacterium tended to have reduced growth with optimum growth at pH 8. The high temperature at around 40°C had a negative effect on the growth performance of the bacterium while optimum growth was observed at 28°C. This novel P. aeruginosa strain has shown the phenotypic attributes to become a potential bioremediation agent; however, further investigation needs to be done to understand the genes and or molecular mechanisms that drive their tolerance to multiple heavy metals.

Cu Nanoparticle-Based Solution and Paper Strips for Colorimetric and Visual Detection of Heavy Metal Ions.

The intrinsic toxicity of heavy metal ions to human health or other species calls for the need to develop an analytical tool for the easy and rapid detection of these ions based on inexpensive and stable nanomaterials. This article describes the potential utility of stable Cu nanoparticles (CuNPs) in the detection of toxic metal ions by solution and paper strip-based methods. For this, first, a dodecyl sulfate ion-stabilized CuNP (DS-CuNP) colloid was synthesized by a chemical reduction method. This was followed by treating the dispersion with heavy metal ions and monitoring the spectral change by spectrophotometric and colorimetric techniques. Among a host of metal ions, Hg2+, Cd2+, and Pb2+ have been found to significantly affect the surface plasmon resonance band of CuNPs by concomitantly altering the color of its solution. Notably, the brownish color of CuNP solution changed readily to milky white in the presence of Hg2+. Furthermore, the fabricated brownish-yellow test paper strips containing DS-CuNPs transformed to a prominent white color in the presence of a few drops of Hg2+ solution. This change in color of the paper strips could be visually detected by the naked eye. The experiments involving the detection of the various ions were carried out by optimizing the experimental conditions qualitatively as well as quantitatively. The limit of detection of the analytes (metal ions) has been found to be 10 μM. Routine analytical techniques like UV–vis spectroscopy, dynamic light scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy formed part of the experiments.

Preparation and Performance of PU/Cpsf Blend Ultrafiltration Membranes for Removal of Heavy Metal Ion Rejection Studies

The performance of membranes for a specific application can be determined with the help of structural properties such as molecular weight cut-off (MWCO), morphology, and pore statistics. Heavy metal ions from aqueous streams can be separated with the help of ultrafiltration membranes. In the presence and absence of the various components of the additive poly (ethylene glycol) 600, MWCOs and pore statistics of polyurethane (PU) and carboxylated polysulfone (CPSf) blend ultrafiltration (Total Polymer Concentration = 17.5 wt %) were studied with the help of dextran of different molecular weights ranging from 19 kDa to 150 kDa. The derived pore size, porosity, and the number of pores have a remarkable relationship with the MWCO, morphology, and the flux performance of the membranes. The blend membranes rejected certain toxic divalent heavy metal ions such as copper, cadmium, nickel, and zinc by complexing them into a polymeric ligand, poly(ethyleneimine) (PEI). The effect of polymer blend compositions and additive concentrations on metal ions' rejection and permeate flux are discussed

Poly(N-isopropylmethacrylamide-co-4-acrylamidobenzo-18-crown-6) microgels with expanded networks for excellent adsorption of lead(II) ions

Lead(II) (Pb2+) ions are toxic heavy metal ions that can accumulate in the human body through water and cause severe health problems, including neurotoxicity, nephrotoxicity, hematological toxicity and even genotoxicity effects. To remove Pb2+ selectively and effectively from aqueous solutions, we develop a novel type of Pb2+-recognizable microgels with excellent adsorption capacity to Pb2+, which are fabricated from 4-acrylamidobenzo-18-crown-6 (B18C6Am) and N-isopropylmethacrylamide (NIPMAM) monomers by precipitation copolymerization method. The prepared poly(N-isopropylmethacrylamide-co-4-acrylamidobenzo-18-crown-6) (PNMB) microgels exhibit expanded structures, because the electron-donating methyl groups at α-carbon could descend the polarity of CO in the NIPMAM monomers and thus weaken the polymer segment···segment interactions. The expanded structures of PNMB microgels are beneficial for adsorption of Pb2+ due to the low steric hindrance in the polymeric networks. The Pb2+ adsorption isotherms of PNMB microgels are consistent with the Langmuir model for monolayer adsorption. The results indicate that the prepared Pb2+-recognizable PNMB microgels are highly promising for the selective removal of lead(II) ions from aqueous solutions.

Enhanced selective electrosorption of Pb2+ from complex water on covalent organic framework-reduced graphene oxide nanocomposite

Selective capture of the toxic and ubiquitous heavy metal ions is crucially desired yet still significant challenge for water purification. Herein, a covalent organic framework-reduced graphene oxide nanocomposite (TpPa@rGO) was developed and employed as cathode for the first time to selectively remove Pb2+ from complex water via an electrosorption process. Specifically, the rGO provides the electrical conductivity and induces the electric double layer capacitance to attract cations approaching to the electrode surface, while the TpPa endows abundant highly selective redox-active sites to capture Pb2+. Thanks to the ingenious synergy of capacitive rGO and redox-active TpPa, more than 99.6% of Pb2+ can be effectively removed by the TpPa@rGO electrode in a mixed solution containing Pb(NO3)2 (50 mg L−1) and multicomponent nitrates (100 mg L−1 for each), as well as good cycling stability. Interestingly, the interfering ions can serve as additional electrolytes to accelerate the accumulation of Pb2+ around the TpPa@rGO electrode instead of competing for active sites, thereby increasing the absolute adsorption capacity of Pb2+ from 94.6 mg g−1 in single Pb(NO3)2 solution to 129.8 mg g−1 in the multicomponent solution. The enhanced selective electrosorption mechanism on Pb2+ removal by TpPa@rGO and their recyclability were also investigated. The capacitive matrix and additional electrolytes accelerate the ion transfer and enhance ion accessibility to the electrode, thereby anchoring the Pb2+ on the N/O groups of TpPa. This study may put forward a promising method for the selective capture of heavy metal ions in complex water.

Cotton fabric functionalized with nanostructured MoS2: Efficient adsorbent for removal of Pb, Hg, Cd and Cr from water

In the present work, nanostructured Molybdenum disulphide (MoS2), supported on a cotton fabric, was prepared in situ via a hydrothermal approach using ammonium heptamolybdate and thiourea as precursors, combining the mechanical strength and flexibility of cotton textile with the outstanding adsorption performance of layered MoS2. Evidence for the in situ generation of crystalline MoS2 at the cotton fibres surface was obtained by XRD, Raman and XPS spectroscopies and the morphology of the appended MoS2 layer was analysed by FESEM microscopy, revealing a flower-like structure uniformly grown onto the cotton fibres. Batch adsorption experiments have demonstrated the effective adsorption of Hg(II), Pb(II), Cd(II) and Cr(VI) from aqueous solutions within a short time (less than 15 min) and with adsorption capacities between 300 and 1200 mg/g, depending on the metal ion. A distribution coefficient (Kd) exceeding 104 was achieved for Hg, Pb and Cd, confirming the exceptional adsorption efficiency of the hybrid structure, made of cotton and MoS2 (Cot-MoS2), for these classes of highly toxic heavy metal ions. A Langmuir model was fitted to kinetics experimental results through a non-linear least square fitting with good correlation values. Isotherm studies showed that the adsorption process, while well described by a Langmuir model, was better described by a Sips equation mixing Langmuir and Freundlich adsorption models, the exponent α, being not very different from 1, confirms that the dispersion of energy adsorption is not very large.As a proof-of-concept for the potential applicability of the hybrid structure Cot-MoS2 for the in-flow water decontamination from toxic heavy metal ions, a column filled with Cot-MoS2 was tested under continuous filtration conditions, achieving a removal efficiency of more than 99%.

Adsorption of cadmium (Cd) and lead (Pb) using powdered activated carbon derived from Cocos Nucifera waste: A kinetics and equilibrium study for long-term sustainability

In this research, the activated carbon was prepared using burnt Coconut (Cocos Nucifera) shell and was used as an adsorbent in the removal of toxic heavy metal ions of lead (Pb) and cadmium (Cd) from the aqueous solution using batch adsorption study. Cocos Nucifera was initially collected in the forming shell and then it was crushed in the form of granular. The carbon shell's surface has been modified with an oxidizing agent such as sulphuric acid or nitric acid to increase the shell's adsorption capacity. The effect contact time, pH, temperature, initial concentration, and adsorbent dosage level were analyzed. The result shows that the optimum pH was 6, and the capacity of adsorption was affected by the temperature. The efficiency of the adsorption rises with an increment in temperature. In addition, the characteristics of the adsorbents were studied by making use of SEM, FT-IR, and Energy Dispersive X-ray Analysis (EDX). The adsorption isotherm study was carried out using Langmuir and Freundlich isotherm model, and it shows the charcoal/carbon shell adsorption followed the Langmuir isotherm model. The modeling result of the kinetic model study indicates that the adsorption mechanism of lead (Pb) and cadmium (Cd) process of adsorption were fitted with a pseudo-second-order equation.

Formaldehyde-modified NH2-UiO-66 for specific sensing and simultaneous removal of mercury ions

Herein, a formaldehyde-modified metal-organic framework, FA/NH 2 -UiO-66 is facilely synthesized via one-pot solvothermal reaction. Under excitation of 365 nm UV light, the drastic fluorescence enhancement triggered by Hg 2+ ions and the un-interfered signal by the coexisting metal ions renders a sensitive and specific fluorescent detection of Hg 2+ ions. A low detection limit (0.0885 nM, M refers to mol L −1 ) and a wide linear range (0.1 nM∼40 μM) are obtained based on calculation of the fluorescence intensity versus the concentration of Hg 2 ions. The mechanism of fluorescence enhancement is ascribed to the intermolecular cyclization when Hg 2+ is trapped by imino group on FA/NH 2 -UiO-66. Moreover, the target- directed adsorption by FA/NH 2 -UiO-66 leads to an effective mercury separation from contaminative system, which exhibits a satisfactory adsorption efficiency of 95.42% within 50 minutes. This work thus delivers a dual-functional MOFs-based platform for visual and hypersensitive Hg 2+ tracking and effective removal of the toxic heavy metal ions, showing promise in tackling the environmental problems with monitoring and remediation synchronously.

Sensitive, Selective and Simultaneous Monitor of Multiple Heavy Metals in Environment Using a Low-Cost MIL-53(Fe)/Ag2CrO4 Modified GCE Sensor

Due to the strong toxicity of heavy metal ions to public health and the environment, it is a great challenge to develop a method for ultra sensitive capture and determination of heavy metal ions effectively. Herein, a novel heterostructure composite (MIL-53(Fe)/Ag2CrO4, named MA(1:x)) was prepared by a simple method successfully. MA(1:x) modified GCE was applied to detect heavy metals ions simultaneously. Significantly, the designed MA(1:1)/GCE sensors performed outstanding detection performances. The wide ranges of 7.49 ∼ 320.00 μmol l−1 and 7.49 ∼ 320.04 μmol l−1 are obtained for Pb(II) and Cu(II) ions, respectively. The LOD of the MA(1:1)/GCE sensor was determined to be 27.40 nmol l−1 (5.68 ppb) for Pb(II) and 86.96 nmol l−1 (5.52 ppb) for Cu(II) ion simultaneously, which are lower than the allowable level of drinking water stipulated by the World Health Organization (WHO). Possible detection mechanism by the MA(1:1)/GCE was discussed. The MA(1:1)/GCE was successfully applied to monitor heavy metal ions locate in tap and river water. The recoveries are in the range of 93.86%–104.4%, which further proves the potential in analyzing real samples. Moreover, the MA(1:1)/GCE also showed excellent stability, selectivity, reproducibility. A novel method was provided to construct sensitive sensors for simultaneous analysis of different metal ions.

Highlighting the Importance of Characterization Techniques Employed in Adsorption Using Metal-Organic Frameworks for Water Treatment.

The accumulation of toxic heavy metal ions continues to be a global concern due to their adverse effects on the health of human beings and animals. Adsorption technology has always been a preferred method for the removal of these pollutants from wastewater due to its cost-effectiveness and simplicity. Hence, the development of highly efficient adsorbents as a result of the advent of novel materials with interesting structural properties remains to be the ultimate objective to improve the adsorption efficiencies of this method. As such, advanced materials such as metal–organic frameworks (MOFs) that are highly porous crystalline materials have been explored as potential adsorbents for capturing metal ions. However, due to their diverse structures and tuneable surface functionalities, there is a need to find efficient characterization techniques to study their atomic arrangements for a better understanding of their adsorption capabilities on heavy metal ions. Moreover, the existence of various species of heavy metal ions and their ability to form complexes have triggered the need to qualitatively and quantitatively determine their concentrations in the environment. Hence, it is crucial to employ techniques that can provide insight into the structural arrangements in MOF composites as well as their possible interactions with heavy metal ions, to achieve high removal efficiency and adsorption capacities. Thus, this work provides an extensive review and discussion of various techniques such as X-ray diffraction, Brunauer–Emmett–Teller theory, scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectroscopy, and X-ray photoelectron spectroscopy employed for the characterization of MOF composites before and after their interaction with toxic metal ions. The review further looks into the analytical methods (i.e., inductively coupled plasma mass spectroscopy, ultraviolet-visible spectroscopy, and atomic absorption spectroscopy) used for the quantification of heavy metal ions present in wastewater treatment.

MicroRNAs: Key Players in Plant Response to Metal Toxicity.

Environmental metal pollution is a common problem threatening sustainable and safe crop production. Heavy metals (HMs) cause toxicity by targeting key molecules and life processes in plant cells. Plants counteract excess metals in the environment by enhancing defense responses, such as metal chelation, isolation to vacuoles, regulating metal intake through transporters, and strengthening antioxidant mechanisms. In recent years, microRNAs (miRNAs), as a small non-coding RNA, have become the central regulator of a variety of abiotic stresses, including HMs. With the introduction of the latest technologies such as next-generation sequencing (NGS), more and more miRNAs have been widely recognized in several plants due to their diverse roles. Metal-regulated miRNAs and their target genes are part of a complex regulatory network. Known miRNAs coordinate plant responses to metal stress through antioxidant functions, root growth, hormone signals, transcription factors (TF), and metal transporters. This article reviews the research progress of miRNAs in the stress response of plants to the accumulation of HMs, such as Cu, Cd, Hg, Cr, and Al, and the toxicity of heavy metal ions.

Surface state dominated and carbon core coordinated red-emitting carbon dots for the detection of Cr2O72- and cell imaging

Cr(VI) as a toxic heavy metal ion can easily enter into the body through drinking or eating and cause liver and kidney diseases as well as cancer. Considering its high biological toxicity and adverse effects on human body, it is desirable to develop a probe to monitor its level in the environment. Herein, a high-efficiency fluorescent nanoprobe based on red emissive carbon dots (R-CDs) was established through a convenient solvothermal strategy. The as-prepared CDs with excitation-independency had the fixed emission wavelength at 627 nm when the excitation wavelength was 560 nm. Further study manifested that the new surface state formed by nitrogen and sulfur doping and the increased conjugated system established through dehydration and carbonization were the main reasons for the fluorescence redshift. In this system, these R-CDs as a fluorescent probe exhibited high specificity and sensitivity to Cr2O72- with the linear range of 4–40 μΜ and the limit of detection could reach 80.00 nM. The quenching of these CDs by Cr2O72- was efficiently induced through a static quenching process. Meanwhile, the obtained CDs could enter into HeLa cells through endocytosis and exhibit bright red fluorescence in cells under a confocal laser scanning microscope. Thus, this work provided a promising probe not only for detecting Cr(VI) in natural environment but also for imaging in cells.