Development of a robust method for Cd(II) ions analysis using CeO2- and CeO2-Cu-BTC-based electrochemical sensors

Simple and sensitive electrochemical sensors were fabricated from cerium oxide (CeO2) and copper-benzene tricarboxylic acid-modified cerium oxide (CeO2-Cu-BTC) materials for differential pulse voltammetric analysis of toxic cadmium (Cd) ions in aqueous solutions. The materials were prepared by hydrothermal method and structurally characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray (SEM-EDX), thermogravimetric analysis (TGA), and X-ray diffraction analysis (XRD). The CeO2-modified carbon paste electrode (CeCPE) and the CeO2-Cu-BTC-modified carbon paste electrode (CeBCPE) were electrochemically characterized by their cyclic voltammetry and electrochemical impedance study in standard K3[Fe(CN)6] single-electron redox process. Their electrochemical surface areas, electrode surface coverages, and charge transfer resistances were calculated to be 1.46 cm2, 2.338 × 10-5 mol∙cm-2, and 2790 Ω and 5.48 cm2, 2.476 × 10-5 mol∙cm-2, and 1254.65 Ω for CeCPE and CeBCPE, respectively. These fabricated electrodes were used as electrochemical sensors for cadmium ion estimation by optimizing the experimental parameters through differential pulse voltammetry. The optimized conditions included 10% modifier for CeCPE and 5% modifier for CeBCPE in 0.12 M HCl solution of pH 5 as supporting electrolyte at - 1.2 V deposition for 30 s in 0.01 to 10 mg L-1 linear cadmium solution range. Under these conditions, the limit of quantification (LOQ) of 0.368 mg L-1 and 0.005 mg L-1 was calculated for CeCPE and CeBCPE electrodes, respectively. The limit of detection (LOD) was calculated to be 0.121 mg L-1 and 0.002 mg L-1 for CeCPE and CeBCPE, respectively. All the experimental results indicated that electrodes fabricated from CeO2-Cu-BTC show better performance as compared to CeO2-based electrodes. Both these types of electrochemical sensors presented good repeatability and performance in the presence of interfering ions as well. From these findings, it can also be inferred that these electrochemical sensors can provide a simple and very sensitive method for approximation of toxic cadmium ions in aqueous solutions.

An "off-on" fluorescent nanosensor for the detection of cadmium ions based on APDC-etched CdTe/CdS/SiO2 quantum dots

In this study, we have developed a novel fluorescent "OFF-ON" quantum dots (QDs) sensor based on CdTe/CdS/SiO2 cores. Ammonium pyrrolidine dithiocarbamate (APDC), ethylenediamine tetraacetic acid (EDTA), and 1,10-phenanthroline (Phen) served as potential chemical etchants. Among these three etchants, APDC exhibited the most pronounced quenching effect (94.06%). The APDC-etched CdTe/CdS/SiO2 QDs demonstrated excellent optical properties: the fluorescence of the APDC-etched CdTe/CdS/SiO2 QDs system (excitation wavelength: 365 nm and emission wavelength: 622 nm) was significantly and selectively restored upon the addition of cadmium ions (Cd2+) (89.22%), compared to 15 other metal ions. The linear response of the APDC-etched CdTe/CdS/SiO2 QDs was observed within the cadmium ion (Cd2+) concentration ranges of 0-20 μmol L-1 and 20-160 μmol L-1 under optimized conditions (APDC: 300 μmol L-1, pH: 7.0, reaction time: 10 min). The detection limit (LOD) of the APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ was 0.3451 μmol L-1 in the range of 0-20 μmol L-1. The LOD achieved by the QDs in this study surpasses that of the majority of previously reported nanomaterials. The feasibility of using APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ detection in seawater, freshwater, and milk samples was verified, with average recoveries of 95.27%-110.68%, 92%-106.47%, and 90.73%-111.60%, respectively, demonstrating satisfactory analytical precision (RSD ≤ 8.26).

Pure and Antimony-doped Tin Oxide Nanoparticles for Fluorescence Sensing and Dye Degradation Applications

Luminescent antimony doped tin oxide nanoparticles have drawn tremendous attention from researchers due to its low cost, chemical inertness and stability. Herein, a quick, facile and economic hydrothermal/solvothermal method was utilized for the preparation of antimony doped (1%, 3%, 5%, 7% and 10%) tin oxide nanoparticles. The antimony doping in a reasonable range can change the properties of SnO2. As such, a lattice distortion increases with increase in doping, which is evidenced through crystallographic studies. It was found that the highest photocatalytic degradation efficiency of malachite green (MG) dye of about 80.86% was achieved with 10% Sb-doped SnO2 in aqueous media due to small particle size. Moreover, 10% Sb-doped SnO2 also showed the highest fluorescence quenching efficiency of about 27% for Cd2+ of concentration 0.11 µg/ml in the drinking water. The limit of detection (LOD) comes out as 0.0152 µg/ml. This sample selectively detected the cadmium ion even in the presence of other heavy metal ions. Notably, 10% Sb-doped SnO2 could appeared as a promising sensor for fast analysis of Cd2+ ions in real samples.

RSM optimization studies for cadmium ions adsorption onto pristine and acid-modified kaolinite clay

Clay has been reported as an active absorbent for the removal of toxic heavy metals from aqueous medium. In this study, pristine and acid modified kaolinite clays (PKC and AMKC) were prepared, characterized using various analyses, and tested for Cd2+ ion adsorption from textile industry wastewater. After acid modification, the specific surface area of clay increased from 84.2 to 389.4 m2/g. Adsorption isotherm, kinetics and thermodynamics behaviour process were examined. The pH at (pHpzc) of 8.5 indicate that AMKC surface is positively charged for pH below the pHpzc attracting anions. Response surface methodology was used to investigate the effect of adsorption process factors on Cd2+ ion removal uptake. At the optimum process conditions of 45.3 °C temperature, 0.63 g/L adsorbent dosage, and 120.9 min contact time, the percentages of Cd2+ adsorbed by PKC and AMKC were 77.82% and 99.19%, respectively. Various models were employed to analyzed the kinetic and equilibrium data. The Pseudo-first order, Pseudo-second order and Intra-particle diffusion were used to evaluate the kinetic data, while the Langmuir, Freundlich and Temkin isotherm models were applied to analyzed the equilibrium data. The sorption kinetics was found to be best described by Pseudo-second order considering the high correlation coefficient (R2), smaller Chi-square (ᵪ2) and sum of square error (SSE). The Freundlich model was the most accurate in describing the equilibrium data followed by Langmuir and Temkin respectively. The thermodynamic reveal that the reaction is spontaneous and endothermic in nature, and increase in randomness between the adsorbent and adsorbate. The obtained activation energy (Ea) value suggest that the adsorption mechanism of Cd(II) is a physisorption dominated.

Interaction between mitophagy, cadmium and zinc

Mitophagy is the selective degradation of mitochondria by autophagy. This process is considered to be one of the stages of mitochondrial quality control, as a result of which damaged depolarized mitochondria are eliminated, thus limiting the formation of reactive oxygen species and the release of apoptogenic factors. Selective degradation of mitochondria by autophagy is one of the main ways to protect cells from cadmium toxicity, which results in dysfunction of the mitochondrial electron transport chain, leading to electron leakage, production of reactive oxygen species and cells death. However, excessive autophagy can be dangerous for cells. Currently, the participation of cadmium ions in normal physiological processes has not been detected. Zn²⁺, unlike Cd²⁺, regulate the activity of a large number of functionally important proteins, including transcription factors, enzymes, and adapters. It has been shown that Zn²⁺ not only participate in autophagy, but are also crucial for basal or induced autophagy. It is likely that zinc drugs can be used to reduce the cadmium toxicity and in the regulation of mithophagy.

Facile synthesis and characterization of Fe3O4/analcime nanocomposite for the efficient removal of Cu(II) and Cd(II) ions from aqueous media

In the water purification field, heavy metal pollution is a problem that causes severe risk aversion. This study aimed to examine the disposal of cadmium and copper ions from aqueous solutions by a novel Fe3O4/analcime nanocomposite. A field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction were used to characterize the synthesized products. The FE-SEM images showed that the analcime and Fe3O4 samples consist of polyhedral and quasi-spherical shapes with average diameters of 923.28 and 28.57 nm, respectively. Besides, the Fe3O4/analcime nanocomposite consists of polyhedral and quasi-spherical shapes with average diameters of 1100.00 nm. The greatest uptake capability of the Fe3O4/analcime nanocomposite toward the copper and cadmium ions is 176.68 and 203.67 mg/g, respectively. The pseudo-second-order kinetic model and Langmuir equilibrium isotherm best describe the uptake of copper and cadmium ions using the Fe3O4/analcime nanocomposite. The uptake of copper and cadmium ions using the Fe3O4/analcime nanocomposite is exothermic and chemical in nature.

Effects and mechanism on cadmium adsorption removal by CaCl2-modified biochar from selenium-rich straw

As every-one knows, cadmium contamination poses a significant and permanent threat to people and aquatic life. Therefore, research on how to remove cadmium from wastewater is essential to protect the natural environment. In this study, agricultural and forestry waste straw sprayed with selenium-enriched foliar fertilizer was prepared as biochar, which was altered by calcium chloride (CaCl₂) to remove Cd²⁺ from water. The outcomes demonstrated that biochar generated by pyrolysis at 700 °C (BC700) had the best adsorption effect. Secondly, pseudo-second-order kinetics and Langmuir adsorption models were used to predict the Cd²⁺ adsorption. Finally, electrostatic adsorption, ion exchange, and complexation of oxygen functional groups (OFGs) were demonstratedto be the main adsorption mechanisms. These conclusions indicate that selenium-rich straw biochar is a novel adsorbent for agroforestry waste recovery. Meanwhile, this work will offer a promising strategy for the overall utilization of rice straw.

Highly sensitive biosensor based on aptamer and hybridization chain reaction for detection of cadmium ions

In this work, a highly sensitive biosensor for detecting cadmium ions (Cd²⁺ ) was developed based on Cd²⁺ -specific DNA aptamer and hybridization chain reaction (HCR). The Cd²⁺ -aptamer (named S0) was used to recognize Cd²⁺ and trigger HCR reaction. Without Cd²⁺ , S0 initiated the HCR to form long nicked dsDNA structures to quench the fluorescence. Then, Cd²⁺ can bind with S0 to block HCR to recover fluorescence. This biosensor had high sensitivity with the detection limit of 0.36 nM and a linear range from 0 to 10 nM. Moreover, it showed a satisfactory selectivity and recovery rates.

Mercapto-functionalized ordered mesoporous silica-modified PVDF membrane for efficiently scavenging Cd2+ from water

In this study, (3-mercaptopropyl) triethoxysilane (MPTMS)-modified ordered mesoporous silica (OMS) materials were prepared using a post-grifting method, with MPTMS as the organic functionalized reagent. The OMS materials were analyzed by FT-IR spectra, N₂ sorption, and small angle X-ray scattering to evaluate their potential for scavenging Cd²⁺ from water. Moreover, a (3-mercaptopropyl) triethoxysilane-functionalized ordered mesoporous silica modified polyvinylidene fluoride (MPTMS-OMS/PVDF) membrane was synthesized using the solvent phase inversion method to remediate wastewater containing heavy metal ions. The MPTMS-OMS was characterized by a maximum specific surface area of 422 m²/g, high surface hydrophilicity, and high pure water flux. The MPTMS-OMS/PVDF exhibited a dynamic adsorption capacity for Cd²⁺ in water. At an MPTMS-OMS content of 5 wt%, the Cd²⁺ removal efficiency was 90%, whereas the pure PVDF showed no Cd²⁺ adsorption capacity. These results highlight the potential of the MPTMS-OMS/PVDF membrane to eliminate Cd²⁺ during the decontamination of aqueous streams containing low-concentrations of contaminants.

Synthesis of polystyrene-based hyper-cross-linked polymers for Cd(II) ions removal from aqueous solutions: Experimental and RSM modeling

The hyper-cross-linked polymers (HCPs) based on the polystyrene was synthesized during the Friedel-Craft reaction in various situations. The HCPs synthesis were carried out in various operating conditions including reaction time in the range of 3-23 h, the ratio of cross-linker to monomer in range of 1-5 at temperature of 80 ℃. In addition, the cadmium adsorption process was carried out at a temperature in the range of 25-85 ℃ and initial cadmium concentration in the range of 10-100 mg/L. The response surface methodology (RSM) has been applied for optimizing the process using synthesis and adsorption parameters. The optimized synthesis conditions were obtained 3.32, 11.26 h, 80 ℃, in ratio, synthesis time, and temperature, respectively. Also, the optimized adsorption conditions were obtained 80 mg/L and 35 ℃, initial cadmium ion concentration, and temperature, respectively. The surface area and thermal stability were obtained at 853.89 m²/g and 450 ℃, respectively. The maximum adsorption capacity and removal efficiency had been obtained 950 mg/g and 92% at a temperature of 20 ℃, after 80 min, respectively. The maximum adsorption capacity and removal efficiency were observed in the initial concentration of 120 mg/L and 10 mg/L, respectively. The adsorption process behavior was surveyed using isotherm, kinetic and thermodynamic models. The isotherm results showed that the adsorption of cadmium by HCPs is multi-layer and heterogeneous. The thermodynamic parameters showed that the process is exothermic and spontaneous. Finally, the kinetic results showed that the process occurred physically and slowly as the temperature raised.

Optimization of preparation parameters for environmentally friendly attapulgite functionalized by chitosan and its adsorption properties for Cd2

This work focused on using attapulgite and chitosan as raw materials to improve the adsorption capacity of Cd²⁺ from the aqueous phase by optimizing the preparation experimental parameters. The modification parameters (attapulgite-chitosan mass ratio, calcination temperature, and time) were specifically studied and optimized. The results indicated that the mass ratio of attapulgite to chitosan was 1:4, the calcination temperature was 300 °C, and the calcination time was 1 h. Both raw and functionalized attapulgite samples were characterized by nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and zeta potential analysis. A series of adsorption experiments showed that the pseudo-second-order kinetic model and Langmuir adsorption isotherm better corresponded with the adsorption characteristics of the newly prepared adsorbent, and the maximum adsorption amount of Cd²⁺ was 109.30 mg/g. Moreover, the effects of the pH value and coexisting cations on the Cd²⁺ adsorption in aqueous solution were investigated. Adsorption mechanism of Cd²⁺ on adsorbent might attribute to complexation, ion exchange reaction, and self-polarization.

A phosphorescence resonance energy transfer-based "off-on" long afterglow aptasensor for cadmium detection in food samples

Cadmium contamination is a severe food safety risk for human health. Herein, a long afterglow "off-on" phosphorescent aptasensor was developed based on phosphorescence resonance energy transfer (PRET) for the detection of Cd²⁺ in complex samples which minimizes the interference of background fluorescence. In this scheme, initially the phosphorescence of Cd²⁺-binding aptamer conjugated long afterglow nanoparticles (Zn₂GeO₄:Mn) was quenched by black hole quencher 1 (BHQ₁) modified complementary DNA. Upon encountering of Cd²⁺, the aptamer interacted with Cd²⁺ and the complementary DNA with BHQ₁ was released, leading to phosphorescence recovery. The content of Cd²⁺ could be quantified by the intensity of phosphorescence recovery with 100 μs gate time (which eliminated the sample autofluorescence) with a linear relationship between 0.5 and 50 μg L^-1 and a limit of detection (LOD) of 0.35 μg L^-1. This method was successfully demonstrated for Cd²⁺ detection in drinking water and yesso scallop samples. The "off-on" phosphorescent aptasensor based on PRET of long afterglow nanomaterials could be an effective tool for Cd²⁺ detection in food samples.

Rapid detection of cadmium ions in meat by a multi-walled carbon nanotubes enhanced metal-organic framework modified electrochemical sensor

This work presents an electrochemical device based on a composite modification of amine functionalized Zr(IV) metal-organic framework (UiO-66-NH2) and multi-walled carbon nanotubes (MWCNTs) for voltammetry determination of cadmium ions (Cd2+). The UiO-66-NH2@MWCNTs composites were prepared by one-pot hydrothermal reaction. The prepared sensor performs excellent performance, which was attributed to the synergism between UiO-66-NH2 with a special octahedral structure and enlarged surface area and MWCNTs with outstanding conductivity. Under optimal experiment condition, the fabricated sensor showed good linear relationship from 0.5 to 170 μg/L, with a detection limit of 0.2 μg/L. Finally, the sensor was successfully applied to detect Cd2+ in meat samples (N = 21) with relative standard deviation (RSD) lower than 4.5% and recovery of 95.1-107.5%, and the results were compared with certified method, there was no statistical significance difference between the developed sensor and certified method at a 95% confidence level.

A colorimetric aptamer-based method for detection of cadmium using the enhanced peroxidase-like activity of Au-MoS2 nanocomposites

In this work, a colorimetric aptamer-based method for detection of cadmium using gold nanoparticles modified MoS₂ nanocomposites as enzyme mimic is established. In short, biotinylated Cd²⁺ aptamers are immobilized by biotin-avidin binding on the bottoms of the microplate, the complementary strands of Cd²⁺ aptamers are connected to the Au-MoS₂ nanocomposites which have the function of enhanced peroxidase-like activity. The csDNA-Au-MoS₂ signal probe and target Cd²⁺ compete for binding Cd²⁺ aptamer, the color change can be observed by addition of chromogenic substrate, thereby realizing visual detection of Cd²⁺. The absorbance of the solution at 450 nm has a clear linear relationship with the Cd²⁺ concentration. The linear range is 1-500 ng/mL, and the limit of detection is 0.7 ng/mL. The assay was used to test white wine samples, the results are consistent with those of atomic absorption spectrometry; which prove that this method can be used for detection of Cd²⁺ in real samples.

Comparison of Cd2+ adsorption onto amphoteric, amphoteric-cationic and amphoteric-anionic modified magnetic bentonites

Organic-magnetic bentonites (OMBts), i.e., amphoteric modified MBt (BS-MBt), amphoteric-cationic modified MBt (BS-CT-MBt) and amphoteric-anionic modified MBt (BS-SDS-MBt), obtained by modifying magnetic bentonite (MBt) with amphoteric surfactant (BS), cationic surfactant (CT) and anionic surfactant (SDS) were investigated with the aim to remove cadmium (Cd²⁺). The modifier contents, surface charge and Cd²⁺ adsorption performances of OMBts were compared, and the influences of pH, temperature and ionic strength on Cd²⁺ removal were evaluated. Results showed that modifier contents of OMBts increased in the order: BS-CT-MBt > BS-MBt > BS-SDS-MBt. Although CEC of adsorbents increased in the order: MBt > BS-MBt > BS-SDS-MBt > BS-CT-MBt. The BS-MBt exhibited the highest Cd²⁺ adsorption capacity (233.19 mmol kg^-1) than other adsorbents. The adsorption isotherms could be well described by Langmuir model. The Cd²⁺ adsorption capacities on MBt and OMBts increased with an increase in pH, temperature and with a decrease of ionic strength. According to characterizations (FT-IR and XPS) and experiments, Cd²⁺ adsorption on MBt and OMBts most possibly involved electrostatic interaction, ion exchange, and surface complexation. Furthermore, the adsorption of Cd²⁺ on BS-MBt was also attributed to the chelation. The amidocyanogen group of BS-CT-MBt inhibited adsorption of Cd²⁺ due to electrostatic repulsion, while Cd²⁺ was adsorbed on BS-SDS-MBt through electrostatic attraction induced by the sulfo group.

Applications of carbon quantum dots to alleviate Cd2+ phytotoxicity in Citrus maxima seedlings

Heavy metal pollution may affect plant growth. The focus of this study was to explore remediation agents that alleviate cadmium toxicity in plants. The Citrus maxima (grapefruit) seedlings were cultivated for 10 days under hydroponic conditions amended with different concentrations of Cd²⁺ (50 and 200 mg/L) and CDs (600 and 900 mg/L). Our observations on roots and leaves showed that, the plant exposed to 200 mg/L Cd²⁺ alone was damaged, supported by the changes in anthocyanin contents, activity of antioxidant enzymes and cell membrane peroxidation damage (up to 35.8-45%). However, the physiological properties of the plant were improved upon exposed to 200 mg/L Cd²⁺ plus 900 mg/L CDs; it can be ascribed to Cd²⁺ sorption to the co-exposed CDs which reduced its freely dissolved concentration by more than 22.5%, thus significantly reducing the amount of Cd²⁺ entered the plant roots by 50.7-89.4%. Due to the oxidative stress induced by Cd²⁺ exposure at 200 mg/L, expression of glutathione-producing genes was up-regulated by 30-360% relative to the control, while the genes expression upon exposure to 200 mg/L Cd²⁺ and 900 mg/L CDs was reduced by 48.4-91.5% relative to that exposed to 200 mg/L Cd²⁺ alone. However, detoxification of CDs on plant leaves at 600 mg/L was insignificant, because a portion of Cd²⁺ taken up by roots can be transported to leaves associated with the internalized CDs. Therefore, CDs can be utilized as a repair agent to mitigate toxicity of Cd²⁺ to plant especially at a high amendment level (900 mg/L).

Construction of electrochemical sensing interface towards Cd(II) based on activated g-C3N4 nanosheets: considering the effects of exfoliation and protonation treatment

There is an urgent need to construct highly selective low-cost sensors for fast detection of toxic metal ions such as cadmium. When compared with 3D bulk materials, 2D layered materials after activation treatments show superior performances for electrochemical metal ion detection. The bulk graphitic carbon nitride (hereafter b-g-C₃N₄) was prepared by thermal polymerization with urea as a precursor; it was then activated through ultrasonic liquid exfoliation and protonation which resulted in successful fabrication of activated ultrathin g-C₃N₄ nanosheets (hereafter a-g-C₃N₄). The a-g-C₃N₄-modified glassy carbon electrode demonstrates excellent electrochemical performances for Cd²⁺ detection with 22.668 μA/μM sensitivity and 3.9 nM LOD (S/N = 3) due to high specific surface area and active sites created on the 2D layered structure. The chemical interference of Pb²⁺, Cu²⁺, and Hg²⁺ on Cd²⁺ detection was minimal. We have also measured Cd²⁺ in natural water and rice samples using the newly developed a-g-C₃N₄-modified electrode with high spike recoveries. Our results demonstrate the potential applications of newly developed a-g-C₃N₄-modified electrode for rapid detection of toxic metal ions in different sample matrixes. Graphical Abstract The activated g-C₃N₄ nanosheets (a-g-C₃N₄) were synthesized and used to construct electrochemical sensors with high sensitivity and anti-interference performance.

The cytotoxicities in prokaryote and eukaryote varied for CdSe and CdSe/ZnS quantum dots and differed from cadmium ions

The present study focused on the bioaccumulation and cytotoxicities of Cd²⁺, CdSe quantum dots (QDs) and CdSe/ZnS QDs in Escherichia coli (E. coli, represents prokaryotic system) and Phanerochaete chrysosporium (P. chrysosporium, represents eukaryotic system), respectively. Two types of QDs were characterized by transmission electron microscopy (TEM) and dynamic light scattering. The inductively coupled plasma optical emission spectrometer results showed that the bioaccumulation amounts of CdSe QDs by E. coli and P. chrysosporium were larger than those of CdSe/ZnS QDs due to the smaller particle size and less negative surface charges of CdSe QDs. Confocal microscopy and TEM results showed that there was an interaction between QDs and cells, and QDs have entered into the cells eventually, leading to the change of cell morphology. Plasma membrane fluidities and membrane H⁺-ATPase activities of E. coli and P. chrysosporium decreased gradually with the increasing concentrations of Cd²⁺, CdSe and CdSe/ZnS QDs. Results of the cell viabilities and intracellular reactive oxygen species levels indicated that the induced cytotoxicities were decreased as follows: CdSe QDs > CdSe/ZnS QDs > Cd²⁺. These findings suggested that the cytotoxicity of QDs was not only attributed to their heavy metal components, but also related to their nanosize effects which could induce particle-specific toxicity. The above results offer valuable information for exploring the cytotoxicity mechanism of QDs in prokaryote and eukaryote.

Cytotoxicity of CdTe quantum dots with different surface coatings against yeast Saccharomyces cerevisiae

Cadmium (Cd)-based QDs are well studied owing to their excellent optical properties. The applications of Cd-based QDs in biomedical filed, however, is hindered by its inherent toxicity. In this study, to overcome the inherent toxicity of heavy metals, CdTe QDs were encapsulated with different shells (NAC, MPA and GSH) to reduce the leakage of Cd from the core. We studied the cytotoxicity of the three kinds of CdTe QDs on S. cerevisiae by spectroscopic, electrochemical, microscopic methods and microcalorimetric technique. Results showed that toxicity of CdTe QDs increased with the augment of QD concentration. According to the values of IC₅₀ ((GSH-CdTe QDs (15.3 nmol/L) < MPA-CdTe QDs (56.2 nmol/L) < NAC-CdTe QDs (89.8 nmol/L)), the most toxic one is GSH-CdTe QDs, followed by MPA-CdTe QDs, then NAC-CdTe QDs. The coatings have contribution to their toxicity. The three kinds of QDs with the similar shape (sphere) can enter the cell by the clathrin-mediated endocytosis and lead to the different impairments. The mechanism of cytotoxicity is due to the release of Cd²⁺ leading elevation of intracellular reactive oxygen species (ROS), which damage mitochondria. The clathrin-mediated endocytosis is a significant factor in determining the toxicity of CdTe QDs.

Simultaneous extraction of Cu2+ and Cd2+ ions in water, wastewater, and food samples using solvent-terminated dispersive liquid-liquid microextraction: optimization by multiobjective evolutionary algorithm based on decomposition

Solvent-terminated dispersive liquid-liquid microextraction (ST-DLLME) as a simple, fast, and low-cost technique was developed for simultaneous extraction of Cd²⁺ and Cu²⁺ ions in aqueous solutions. Multiobjective evolutionary algorithm based on decomposition with the aid of artificial neural networks (ANN-MOEA/D) was used for the first time in chemistry, environment, and food sciences to optimize several independent variables affecting the extraction efficiency, including disperser volume and extraction solvent volume, pH, and salt addition. To perform the ST-DLLME operations, xylene, methanol, and dithizone were utilized as an extraction solvent, disperser solvent, and chelating agent, respectively. Non-dominated sorting genetic algorithm versions II and III (NSGA II and NSGA III) as multiobjective metaheuristic algorithms and in addition central composite design (CCD) were studied as comparable optimization methods. A comparison of results from these techniques revealed that ANN-MOEA/D model was the best optimization technique owing to its highest efficiency (97.6% for Cd²⁺ and 98.3% for Cu²⁺). Under optimal conditions obtained by ANN-MOEAD, the detection limit (S/N = 3), the quantitation limit(S/N = 10), and the linear range for Cu²⁺ were 0.05, 0.15, and 0.15-1000 μg L^-1, respectively, and for Cd²⁺ were 0.07, 0.21, and 0.21-750 μg L^-1, respectively. The real sample recoveries at a spiking level of 0.05, 0.1, and 0.3 mg L^-1 of Cu²⁺ and Cd²⁺ ions under the optimal conditions obtained by ANN-MOEA/D ranged from 94.8 to 105%.

Fluorescence turn-on sensing of trace cadmium ions based on EDTA-etched CdTe@CdS quantum dot

Cadmium-caused environmental pollution and diseases have always been worldwide problems. Thus it is extremely urgent to establish a cheap, rapid, simple and selective detection method for trace cadmium in drinking water. In this study, a fluorescence "turn-on" method based on ethylene diamine tetraacetic acid (EDTA)-etched CdTe@CdS quantum dots (QDs) was designed to detect Cd²⁺. High resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) were utilized for chemical and structural characterization of the as-prepared QDs. Based on chemical etching of EDTA on the surface of CdTe@CdS QDs, specific Cd²⁺ recognition sites were produced, and then results in fluorescence quenching. The introduction of Cd²⁺ could identify these sites and restore the fluorescence of the EDTA-QDs system. Under the optimum conditions, the nanoprobe shows a linear response range from 0.05 to 9 μM with a very low detection limit of 0.032 μM. In addition, the reported fluorescence probe in this work displays a good selectivity for trace Cd²⁺ over other metal ions and an admirable practicability in real water samples.

Adsorption of cadmium ions using the bioadsorbent of Pichia kudriavzevii YB5 immobilized by polyurethane foam and alginate gels

Pichia kudriavzevii YB5, mutated from Pichia kudriavzevii A16 with a strong ability to remove cadmium ions, was immobilized by polyurethane foam and alginate gels in this work. The immobilization conditions were optimized as follows: sodium alginate concentration of 2% (w/v), calcium chloride concentration of 2% (w/v), biomass dose of 1 × 10⁹ cell/mL, and cross-linking time for 4 h. Then, the results of batch adsorption experiments showed that the removal capacity of prepared bioadsorbent was significantly affected by the pH of media, contact time, and the initial Cd(II) concentration, and a suitable adsorption conditions of Cd(II) could be achieved with a pH value of 6.0 at 20 °C for 90 min. Kinetic and isothermal results indicated the behavior of Cd(II) adsorption onto immobilized P. kudriavzevii YB5 fitted to the pseudo-second-order kinetic equation and the Langmuir adsorption model. Thermodynamic results showed that the Cd(II) adsorption process was endothermic and spontaneous in nature. Besides, the Cd(II) removing capacity of the prepared bioadsorbent was also tested in the oyster hydrolysates, showing an average removal rate of 54.35%. Thus, the immobilized P. kudriavzevii YB5 adsorbent had great potential for application in aquatic products to ensure the food safety.

Polyaspartate extraction of cadmium ions from contaminated soil: Evaluation and optimization using central composite design

The occurrences of heavy metal contaminated sites and soils and the need for devising environmentally friendly solutions have become global issues of serious concern. In this study, polyaspartate (a highly biodegradable agent) was synthesized using L-Aspartic acid via a new modified thermal procedure and employed for extraction of cadmium ions (Cd) from contaminated soil. Response surface methodology approach using 3⁵ full faced centered central composite design was employed for modeling, evaluating and optimizing the influence of polyaspartate concentration (36-145mM), polyaspartate/soil ratio (5-25), initial heavy metal concentration (100-500mg/kg), initial pH (3-6) and extraction time (6-24h) on Cd ions extracted into the polyaspartate solution and its residual concentration in the treated soil. The Cd extraction efficacy obtained reached up to 98.8%. Increase in Cd extraction efficiency was associated with increase in the polyaspartate and Cd concentration coupled with lower polyaspertate/soil ratio and initial pH. Under the optimal conditions characterized with minimal utilization of the polyaspartate and high Cd ions removal, the extractible Cd in the polyaspartate solution reached up to 84.4mg/L which yielded 85% Cd extraction efficacy. This study demonstrates the suitability of using polyaspartate as an effective environmentally friendly chelating agent for Cd extraction from contaminated soils.

Effects of Cd(II) on the stability of humic acid-coated nano-TiO2 particles in aquatic environments

The stability of nanoparticles (NPs) in aquatic environments is important to evaluate their adverse effects on aquatic ecosystems and human health. Nanoparticle stability is known to be influenced by coexisting ions and dissolved organic matter. This study was designed to investigate the effects of coexisting low-level Cd(II) on the stability of humic acid-coated nano-TiO₂ (HA-TiO₂) particles in aquatic environments by measuring their aggregation kinetics through time-resolved dynamic light scattering (DLS) and monitoring suspended HA-TiO₂ concentrations via optical absorbance changes over time. The particles exhibited aggregation behavior consistent with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The results showed that Cd(II) concentration, pH, and ionic strength had various effects on the aggregation kinetics of the HA-TiO₂ NPs. The HA-TiO₂ particles aggregated faster as the Cd(II) concentration increased whereas the stability of the nanoparticles increased as the solution pH increased or ionic strength decreased regardless of the Cd(II) concentration. At the fixed pH and ionic strength conditions, the addition of Cd(II) promoted aggregation of nanoparticles, leading to higher attachment efficiencies. The enhanced aggregation of the HA-TiO₂ NPs in the presence of coexisting cadmium ions in aqueous solutions indicated that the fate and transport of nanoparticles could be greatly affected by heavy metals in aquatic environments.

Integrated ion imprinted polymers-paper composites for selective and sensitive detection of Cd(II) ions

Paper-based sensor is a new alternative technology to develop a portable, low-cost, and rapid analysis system in environmental chemistry. In this study, ion imprinted polymers (IIPs) using cadmium ions as the template were directly grafted on the surface of low-cost print paper based on the reversible addition-fragmentation chain transfer polymerization. It can be applied as a recognition element to selectively capture the target ions in the complex samples. The maximum adsorption capacity of IIPs composites was 155.2mgg^-1 and the imprinted factor was more than 3.0. Then, IIPs-paper platform could be also applied as a detection element for highly selective and sensitive detection of Cd(II) ions without complex sample pretreatment and expensive instrument, due to the selective recognition, formation of dithizone-cadmium complexes and light transmission ability. Under the optimized condition, the linear range was changed from 1 to 100ngmL^-1 and the limit of detection was 0.4ngmL^-1. The results were in good agreement with the classic ICP-MS method. Furthermore, the proposed method can also be developed for detection of other heavy metals by designing of new IIPs.

Biodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by Phanerochaete chrysosporium in the presence of Cd2

Aerobic biodegradation of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) by Phanerochaete chrysosporium in the presence of Cd²⁺ was investigated in this study. The results showed that P. chrysosporium could effectively degrade BDE-47, and its extracellular enzyme played an important role in the process of decomposition. BDE-47 biodegradation by fungi was more tolerant than extracellular enzyme in the presence of Cd²⁺. Also, both of the activity of two typical enzymes, MnP and LiP, descended with ascended Cd²⁺ concentration. Based on the four mono-hydroxylated PBDEs (5-OH-BDE-47, 4'-OH-BDE-17, 6-OH-BDE-47, and 2'-OH-BDE-28) and two bromophenols (2,4-DBP, 4-BP) detected, three possible degradation pathways were proposed, inferring that BDE-47 was more easily to transform via hydroxylation. With addition of Cd²⁺, the types of degradation products did not change, merely a variation of the content of these products observed. Meanwhile, the major metabolites of BDE-47, bromophenol compounds, have been found to be transformed or even mineralized by P. chrysosporium quickly, which also helped better explain why the amounts of BDE-47 decomposed did not match with that of the metabolites detected.