Metal Ions Cd Research Articles

ADSORPTION CAPACITY OF CARBONIZED TITONIA DIVERSIFOLIA TOWARDS Cd2+ AND CU2+ UNDER DIFFERENT pH, ADSORPTION CAPACITY AND CONCENTRATION

Adsorption studies were performed to investigate the adsorption capacity of carbonized Tithonia diversifolia towards heavy metal ions (Cd2+ and Cu2+) under different pH, contact time, concentration and temperature conditions. Cadmium metal concentrations at; 25 ppm, 50 ppm, 75 ppm, 100 ppm, 150 ppm and 200 ppm of metal solutions were prepared and the pH was adjusted to 5. The uptake of copper (II) increases as the pH of the solution increases; at pH 1, pH 2, pH 3, pH 4 and pH 5, percentage metal bound were 20.59, 48.47, 94.26 and 94.08% respectively, at pH 5 and pH 6, percentage metal bound dropped to 93.26, 92.62% respectively. The increase in the removal of copper as pH increases is attributed to the decrease in competition between proton and Cu2+ ion for the surface site. Cadmium study showed that the optimum binding pH is 5 while at pH 1, pH 2, pH 3, pH4 and pH 6, percentage bound were 25.59, 59.12, 96.76, 96.14 and 98.31% respectively. The percentage removal for cadmium (II) ion is low at pH 1 and remains high and almost constant at pH 6. The high binding power of cadmium (II) ion at the initial stage is attributed to the biomass having maximum binding sites available for interaction. Our findings showed that the amount of Cu+2 and Cd2+ adsorbed was found to vary with the initial solution pH, adsorbent dosage and concentration.

Graphene oxide-based sorbents modified with waste orange peel biochar for Cd(II) removal from aqueous waste streams

ABSTRACT Living organisms are at great risk from the highly toxic metal cadmium (II). It is not allowed to be in industrial effluent or drinking water that is dumped into cadmium-containing water bodies. It has been classified as a carcinogen by the IARC and the US EPA. Thus, it is essential to discover a practical and economical technique for removing cadmium from an aqueous solution. In the present work, a novel and easy-to-prepare component of graphene oxide/orange peel/chitosan composite (GO-OP-CS) was prepared and examined using various analytical techniques as a hybrid product with improved physicochemical properties and metal ion Cd(II) adsorption capabilities. The results showed that Cd (II) ion adsorption occurred initially fairly fast and that a pH of 6 was optimal for both adsorption and removal of Cd (II) ions. The thermodynamic analysis revealed that the adsorption of Cd(II) is spontaneous and exothermic. The experimental results showed that the functional groups present on the adsorbent surfaces (such as hydroxyl, carboxyl, epoxy, amine, and so on) led to the improvement of the Cd(II) metal’s ability to absorb. This novel composite exhibited a high adsorption capacity (qmax) of 537.63 mg/g. The results of the toxic Cd(II) sorption using the synthesized composite showed that its adsorption kinetics and sorption isotherm confirmed the pseudo-second-order and Langmuir models, respectively. The proposed method is also reliable for Cd(II) sorption for preconcentration and remediation before Cd testing from genuine samples, such as wastewater, digested tobacco, and e-battery samples.

Reusable polymer-based fluorescent sensor nanoprobe for selective detection of Cd2+ ions in real water sources

Fabrication of a polymer based QD–4AT fluorescence sensor nanoprobe for the detection of target heavy metal ions (Cd2+) in real water sources.

Dual-Function Sensing Platform for Hg2+ Based on a Redox-Active Thiosemicarbazone Receptor

Recently, our group developed a platform for adsorptive stripping voltammetric analysis of heavy metals based on electrodes modified with “clickable” thiosemicarbazone ligands, achieving detection limits for Hg2+ in the nM range1. Here, we present an extension of our previous results towards obtaining an innovative, dual-function sensing platform suitable for both rapid screening and accurate quantitation of mercury. For this purpose, we designed a novel ferrocene-based redox-active thiosemicarbazone receptor having an intramolecular signalling pathway between the binding site and redox-active center, a prerequisite for obtaining efficient redox-active receptors3. The metalloligand, which also contains an azido functional group, was synthesized by reacting 4-(6-azidohexyl)-3-thiosemicarbazide1 with ferrocenealdehyde. The binding properties of the ligand towards several heavy metal ions (Cd2+, Cu2+, Hg2+, Ni2+, Pb2+, Zn2+) were evaluated by UV-VIS spectroscopy, ESI-MS and cyclic voltammetry. Notably, the voltammograms recorded in the presence of sub-stoechiometric amounts of Hg2+ displayed a “two-wave” behavior4 for the Fc/Fc+ redox couple (ΔEp~100 mV), suggesting a high binding constant for this particular ion. Next, modified electrodes were prepared by grafting glassy carbon substrates with triisopropylsilyl-protected phenylethynyl groups through the electrochemical reduction of the corresponding diazonium salt5, followed by deprotection of the alkyne groups and „click” immobilization of the thiosemicarbazone receptor. The electrode surface functionalization was further assessed using electrochemical techniques and X-ray photoelectron spectroscopy, and the complexation behavior of the modified electrodes in the presence of heavy metal ions was investigated using Osteryoung square-wave voltammetry6. As expected, the Fc/Fc+ couple from the surface-immobilized ligand displayed the same voltammetric behavior as in solution, and the appearance of a new voltammetric wave shifted by ~100 mV allows the rapid qualitative screening of Hg2+. Furthermore, the modified electrodes were employed for the accurate quantitation of Hg2+ ions using the accumulation at open circuit-anodic stripping voltammetry technique, achieving a LOD of 5.0 nM. Finally, we demonstrate that electrodes modified with the thiosemicarbazone metalloligand have a very good reproducibility, reusability and stability. Acknowledgements This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-III-P1-1.1-TE-2021-1163, within PNCDI III.

Evaluating the Potential of Multi-Walled Carbon Nanotube-Modified Clay as a Landfill Liner Material.

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress-strain curve, peak deviation stress, shear strength parameters (internal friction angle and cohesion), microstructures, and adsorption performance of the clay were analyzed. The results showed that the optimum moisture content (OMC) increased from 16.15% to 18.89%, and the maximum dry density (MDD) decreased from 1.79 g/cm3 to 1.72 g/cm3 with the increase in MWCNTs. The permeability coefficients firstly fell and then gradually rose as the MWCNTs increased; the minimum permeability coefficient was 8.62 × 10-9 cm/s. The MWCNTs can also effectively increase the peak deviation stress of the clay, and at the maximum level, the peak deviation stress was increased by 286%. SEM images were processed using the Pore and Crack Analysis System (PCAS), and the results showed that the appropriate amount of MWCNTs could fill the pores and strengthen the clay structure. The effect of the MWCNT-modified clay on the adsorption performance of common heavy metal ions Cd2+, Mn2+ and Cu2+ in landfill leachate was analyzed by batch adsorption tests. The maximum adsorption capacities (Qmax) of Cu2+, Cd2+ and Mn2+ in the 2% MWCNT-modified clay were, respectively, 41.67 mg/g, 18.69 mg/g, and 4.97 mg/g. Compared with the clay samples without MWCNTs, the adsorption properties of Cu2+, Cd2+, and Mn2+ were increased by 228%, 124%, and 202%, respectively. Overall, the results suggest that MWCNT-modified clays have the potential to be suitable barrier materials for the construction of landfills.

A selective and sensitive probes of chalcone derivative as a fluorescent chemosensor for the detection of Cr3+ ion

A new chalcone based chemosensor like 6-cinnamoylthiochroman-4-one (AZAN), has been designed and synthesized from 6-chlorothiochroman-4-one and cinnamaldehyde via keto ethylenic linkage. Its amino derivatives were synthesized by using urea (AZANU), thiourea (AZANTU) and 2,6-diamino pyridine (AZANPy) respectively and its metal ion sensing properties were investigated. The sensors can selectively recognize and sense the metal cations by showing different fluorescent characteristics at different concentrations. The fluorescence intensity shows remarkable enhancement by Cr3+ over other common metal ions (Cd2+, Hg2+ and Pb2+). The proposed mechanism can be confirmed by UV–Vis and emission titration. The newly synthesized receptor can sense the metal ions even in nano molar level. The binding or association constant and detection limit of chemosensor to Cr3+ are 1.684 × 105 M−1 and 0.2245 × 10−9 M respectively. A computation using the density functional theory was done to gain detailed insights into the electronic structures of the ligand and its derivatives. B3LYP function and 6-31G(d,p) basis set were used to optimize the ground-state geometry of the chemical and its derivatives.

Structural and compositional diversity of biosurfactants produced by a novel strain of Sporosarcina luteola ME44 from oil reservoir.

The urealytically active microorganism Sporosarcina luteola induces the precipitation of metals, which has attracted attention in biomineralization, bioremediation, and industrial waste recycling. Herein, we report a novel biosurfactant-producing strain of S. luteola ME44 isolated from Chinese Oilfield. The structure, composition, and surface activity of the biosurfactants produced by S. luteola ME44 were investigated by using a combination of the high-performance liquid chromatography, time-of-flight mass spectrometry, and surface tensiometer. The biosurfactant extracted by strain ME44 was identified as surfactin with five variants and the yield was 1010±60mg⋅L-1 . This is the first report on the structural composition and surface activity of biosurfactants isolated from the S. luteola. It extended our knowledge about the role of the species S. luteola in the ecosystem of extreme natural environments such as oil reservoir. In addition, S. luteola ME44 showed bioprecipitation properties for metal ions Cd(II), Cu(II), Zn(II), and Ag(I), which indicated the application potential of S. luteola in the field of bioremediation.

Synthesis and Characterization of Adsorbent Materials Magnetite Mercaptosilicate Ion Imprinted Polymer as Cadmium Ion Adsorbent

Cadmium (Cd) is a toxic heavy metal with the active property of reacting with other components so that cadmium residues can quickly enter the food chain and cause cardiovascular, kidney, and cancer diseases. The purpose was to synthesize the magnetite mercaptosilicate ion imprinted polymer adsorbent material by forming Ion-Imprinted Polymer as a template, to analyze the characterization results using XRD and SEM-EDS, and to determine the adsorption test results for Cd metal ions. The results of the characterization of XRD show that there is a broad peak at a diffraction angle of 2θ= 20-220 with an amorphous structure, which is silica, and there is a high peak at a diffraction angle of 2θ= 35.55140 which indicates magnetite. The results of SEM analysis with magnifications of 500x, 1000x, and 5000x showed that the surface morphology of the particles was not uniform. For the EDS results, it can be seen that the components of the magnetite mercaptosilicate ion imprinted polymer material are elements C, O, Si, S, and Fe, with a mass percentage of 25.0%; 41.2%; 29.9%; 3.28% and 0.8%. The results of the adsorption test for the Magnetite-IIP-Mercaptosilika Material were able to adsorb Cd ions with the highest adsorption capacity of 10.536 mg/g at a concentration of 100 mg/L. Then the selectivity coefficient value of the Ion Cd metal ion is 2.32 greater than 1, indicating that the selectivity of the magnetite mercaptosilicate ion imprinted polymer material is much higher for Ion Cd metal ions than for Cu and Cr ions with a selectivity coefficient of 0.1 and 0.26.

Synthesis of Binary Metal Doped CuO Nanoarchitecture for Congo red dye Removal: Synergistic Effects of Adsorption and Mineralization Techniques

Herein, a microwave-assisted fabrication technique has been practiced for the generation of pristine CuO and Cd/Zn co-doped CuO (Cu0.94Cd0.03Zn0.03O) nanopowders with the identical weight ratio of cadmium and zinc metals. The structure, chemical nature, shape, and optical response of CuO and Cu0.94Cd0.03Zn0.03O were assessed by PXRD, FESEM, FTIR, and UV–vis analytical techniques. PXRD results affirmed that CuO and Cu0.94Cd0.03Zn0.03O have developed in a single monoclinic phase; other extra phases are absent. The crystallite sizes of CuO and Cu0.94Cd0.03Zn0.03O were identified as 18.5 nm and 14.39 nm. The FESEM image of the Cu0.94Cd0.03Zn0.03O sample demonstrated a nanosheet-like morphology that was developed after the co-doping of Zn and Cd metal ions. FTIR graphs established the occurrence of Cu–O main bonds in both fabricated nanopowders. The UV–vis examination demonstrated that Cd and Zn co-doping has substantially reduced the energy gap of pristine CuO from 2.0 eV to 1.54 eV. This massive reduction in CuO bandgap assists it in catching extra photons to stimulate valence-band electrons and hence boosts the activity of the catalyst under sunlight irradiations. Moreover, including Cd and Zn has also effectively hindered the e−/h+ recombination in CuO throughout the photocatalysis process. The photocatalytic activities of pristine CuO and Cu0.94Cd0.03Zn0.03O nanosheets were probed against Congo-red (CR) pollutants under sunlight irradiations. The mineralization efficiency was detected as maximum (∼87.88%) for Cu0.94Cd0.03Zn0.03O nanosheets in contrast to pristine CuO nanostructures. Cu0.94Cd0.03Zn0.03O nanosheets, due to their astonishing properties, could be an economical alternative in creating intelligent strategies for mineralizing organic pollutants in industrial effluents.

A study on the reduction of heavy metal ions (Cd2+ and Cr3+) in waste water from chemistry laboratory by Pericopsis elata adsorbent

This research was aimed the at preparation and application of Pericopsis elata adsorbent in reducing the concentration of heavy metal ions present in waste water obtained from chemistry laboratory. Atomic Absorption Spectroscopy (AAS) was used to determine the concentration of heavy metal ions (Cd2+ and Cr3+) in laboratory waste water. The concentration of Cd and Cr were 155 and 122 mg/L. At a dosage of 0.25, 0.5 and 0.75 g the concentration ranged from 21.55 25.65 mg/L for Cr and 12.90 14.32 mg/L for Cd. At pH value of 2, 7 and 11, the concentration were 11.30, 20.33 and 39.50 mg/L for Cr and 15.30, 28.20 and 24.80 mg/L for Cd respectively. The concentration of Cr and Cd on adsorption increases with an increase in contact time of the adsorbate. At contact time of 20, 40 and 60, the adsorption concentration were 16.60, 19.30 and 29.40 (mg/L) for Cr and 10.50, 20.40, 48.10 (mg/L) for Cd. The results indicate that as the pH, contact time and temperature increases, the percentage removal of Cr and Cd also increases. As adsorbent dosage increased the percentage removal of Cr and Cd also increased. The result of the morphology showed a porous, rough and irregular surface with crystalline structure which indicated more macro pores for adsorption. It can be deduced that the Pericopsis elata adsorbent provides an external surface of porous and more reactive sites, which enhanced its adsorption capacity.

Adsorpsi Logam Cd Menggunakan α-Selulosa dari Kulit Buah Nanas

Pineapple fruit is widely consumed that impact on the waste produced. One of which is pineapple peel has a high cellulose content of around 69.5-71%. In this research, the synthesis of α-cellulose from pineapple peel was tings in order produce an adsorbent for Cd2+ metal ions. The prepared pineapple peel powder was delignified using 2% NaOH to remove lignin, were delignified again using 18% NaOH. The α-cellulose formed was bleached using 3.5% NaOCl. α-cellulose was hydrolyzed using H2SO4 with various concentrations of 2, 3 and 4%. The goal is to determine the optimum absorption of the adsorbent. Based on this research, it was found that the maximum adsorption capacity was obtained at 4% H2SO4 variation which is 108 mg/g and an efficiency of 54%. The adsorption isotherm model on cellulose meets the assumptions of chemical, and physical adsorption as shown by the R2 value of 0.999. Chemical adsorption (Langmuir isotherm) is indicated by the reaction of the OH group with the metal ion Cd2+. Physical adsorption (Freundlich isotherm) that occurs at heterogeneous adsorption sites supported by changes in surface area (BET) values.

Characterization of Fiber Optic Biosensors Based on Chitinase Immobilization on Chitosan Film-Tofu Solid Waste: Metal Ions Monitoring in Water

A fiber-optic biosensor based on the immobilization of chitinase enzyme on chitosan-solid waste tofu film has been proven to be effective for analyzing the presence of Cd (II) ions in the coastal area of Makassar. The working mechanism of the fiber optic biosensor is based on the inhibitory properties of the chitinase enzyme by the metal ion Cd (II). Research objectives determine the optimization of chitosan film by using solid waste tofu immobilized chitinase, characterization of chitosan film - solid waste tofu immobilized kiinase, the characterization of fiber optic biosensors includes inhibition percentage and measurement concentration range, detection limit value, selectivity and reproducibility. The results showed the optimum conditions for chitosan film-solid waste tofu at a concentration ratio of 55%: 45% with an intensity of 32.01, tensile strength of film (tensile strength) of 36.01. The characterization of the biosensor which includes the percentage of inhibition, and the measurement concentration range of Cd (II) ion was obtained at a percentage of 27.126% with a measurement concentration range of 1.0 x 10-5 – 1 x 10-8 M or equivalent to 0.0083 – 8.30 ppm (103 Cd (II) 83.0 ppm). The detection limit value is 6.1 or equivalent to 5.9 x 10-6 M (0.00076 ppm). The fiber optic biosensor is selective for Co (II), Cd (II) and Zn (II) ions with a biosensor reproducibility of 0.1592 + 0.0562. The measurement results for the concentration of metal ion Cd (II) at 4 (four) locations were in the range of 0.1446 – 0.270, the lowest was at the Losari Beach location at 0.1446 ppm while the highest was obtained at the Soekarno Hatta Port location at 0.2194 ppm. The fiber optic biosensor measurement did not differ significantly from the SSA

Copper oxide nanocomposite particles supported on sodium alginate-g-polyallylamine based reduced graphene oxide: An efficient electrochemical sensor for sensitive detection of cadmium ions in water

A highly sensitive and selective electrochemical sensor, sodium alginate-g-polyallylamine/reducedgrapheneoxide/CuO nanocomposite particles (SAGPMRGO@CuO NPs) has been synthesized for the detection of Cd2+ ions in the aqueous environment. The graft copolymer/reduced graphene oxide supported CuO nanocomposite particles are prepared through bioreduction of graphene oxide by a novel synthesized graft copolymer sodium alginate-g-PAAM (SAG-g-PAAM) to reduced graphene oxide (SAGPMRGO) followed by using it as both a reductant and a stabilizing agent to obtain SAGPMRGO@CuO hybrid nanocomposite particles. The graft copolymer is prepared via free radical solution phase graft copolymerization technique. The graphene oxide (GO) is prepared by the oxidation of graphite using modified Hummer's method. The prepared nanocomposite particles are characterized by UV-VIS, FTIR and Raman spectroscopy, powder X-ray diffraction (PXRD), HRTEM-EDS, FESEM, XPS and DLS analysis with zeta potential measurement in colloidal suspension. The prepared graft copolymer is characterized by 1H and 13C NMR spectroscopy, PXRD and FESEM analysis and the SAMPGRGO is characterized by UV-VIS and Raman spectroscopy, PXRD and FESEM analysis. The CuO nanocomposite particles are spindle shaped with an average particle size ranges from 15.6 nm to 32.1 nm and are well polydispersed. Metal ion (Cd2+) sensing is carried out by cyclic voltammetry (CV) and chronoamperometry (CA) analysis under optimum conditions. The limit of detection (LOD) and limit of quantitation (LOQ) is found to be 1.27 nM and 4.24 nM respectively which is lower than some other reported works. The reproducibility and stability properties of the developed sensor are examined where the results are found to be satisfactory. The selective detection of Cd2+ ions in a river water sample is also evaluated with an excellent performance.

Two unique 2D metal-organic frameworks based on various metal-oxygen chains for high sensitivity sensing of Fe(III) and Cr(VI) in aqueous media

Two new 2D MOFs, namely, {[Cd2(HL)(H2O)(DMF)2]·(H2O)·(DMF)}n (1), {[Co2(HL)(H2O)(DMF)2]·(H2O)·(DMF)}n (2) were constructed under the solvothermal conditions by using 2,4-di(2′,5′-dicarboxylphenyl)benzoic acid and d10 metal ion Cd(Ⅱ) and Co(Ⅱ). Because the diversity of ligands leads to two different coordination patterns in complexes 1–2, resulting in 1 and 2 with multiple structures. Both 1 and 2 exhibit a 3D supramolecular framework, which based on different metal-oxygen chains. The chains form a 2D layered structure through the carboxyl oxygen atoms in the ligand. The solid-state luminescence spectra of 1 at room temperature showed that the maximum emission peak is 458 nm (λex = 346 nm). At the same time, 1 showed high fluorescence selectivity and low detection limit for Fe3+ cations, Cr2O72− and CrO42− anions in aqueous solution, and can be used as a potential multifunctional material for the detection of these substances. In addition, the fluorescence sensing properties and quenching mechanism of the above ions are discussed in detail.

Оценка возможности использования отходов железо-магниевого производства для очистки сточных вод от тяжелых металлов (Cd2+, Zn2+, Co2+, Cu2+)

Relevant problems associated with treatment of industrial wastewater from heavy metal ions are considered. Due to industrial development, the amount of wastewater increases as well as the risks of heavy metals getting into surface and groundwater, accumulating in water bodies and becoming aggressive environmental pollutants, which affect the animal and human organisms. To assess the possibility of extracting metal ions (Cd2+, Zn2+, Co2+, Cu2+) from industrial wastewater and their further treatment, studies were carried out on redistribution of heavy metals in the “wastewater – waste” system using iron-magnesium production waste. Samples of the investigated waste weighing 0.1; 0.2; 0.5; 1; 1.5; 2 g were taken for wastewater volume of 50 ml per each subsample. Contact time varied from 5 to 180 min, waste fraction was 1 mm. The interaction process showed that the waste efficiently removes metal ions (Cd2+, Zn2+, Co2+, Cu2+) from industrial wastewater. The efficiency of removing a pollutant from the solution depends on the weight of the waste subsample, initial concentration of metal ions, and contact time.

First-principle study on the stability of Cd passivates in soil

The stable existence of heavy metals in soil under natural conditions is the core issue in heavy metal pollution solidification and remediation technology. However, the existing research is limited to soil passivation tests of different materials or biochar adsorption tests and cannot reveal the internal mechanism of functional groups of different compounds in soil passivation. This paper takes the common heavy metal ion Cd2+ as an example to analyze the stability of the combination of heavy metal ions and common ion groups in soil. The stability and existing form of Cd are analyzed by using first-principle calculations, and the free energy, band structure, and partial density of states of CdCO3, CdSO4, CdCl2, and CdSiO3 are computed. The stability of Cd binding to common anions in soil is determined. Results show the descending order of structural stability of cadmium compounds is CdSiO3, CdSO4, CdCO3, and CdCl2. SO42− and SiO32− can be used as preferred functional groups for cadmium pollution passivation. Anhydrous sodium sulfate and sodium silicate are promising passivators.

Magnetic Fe3O4 nanoparticles decorated phosphorus-doped biochar-attapulgite/bismuth film electrode for smartphone-operated wireless portable sensing of ultra-trace multiple heavy metal ions.

Pollution caused by both forestry wastes and heavy metals has increasingly drawn attention owing to environmental safety concerns. After essential oil is extracted from Cinnamomum camphoras (L.), the branches are used as forestry wastes to prepare a phosphorus-doped biochar-attapulgite/bismuth film electrode decorated with magnetic Fe3O4 nanoparticles (MBA-BiFE). The smartphone-operated wireless portable sensor is employed for the simultaneous ultratrace voltammetric detection of multiple heavy metal ions (Cd2+, Pb2+, and Hg2+). Cd2+, Pb2+, and Hg2+ exhibit excellent electrochemical responses in linear ranges of 0.1nM-5μM, 0.01nM-7μM, and 0.1nM-3μM with limits of detection equal to 0.036, 0.003, and 0.011nM, respectively. The recoveries of MBA-BiFE for Cd2+, Pb2+, and Hg2+ are 93.6-109.9%, 86.0-107.5%, and 94.8-104.6%, respectively, and the RSD values for repeated measurements of Cd2+, Pb2+, and Hg2+ are 4.2%, 2.8%, and 3.3%, respectively. A machine learning model based on an artificial neural network algorithm is constructed to enable a smart determination of ultratrace hazardous multiple metal ions. The portable sensor based on the screen-printed integrated three-electrode sensor modified using MBA-BiFE demonstrates advantages and practicability in outdoor detection, compared with conventional sensors based on MBA-BiFE. This study provides a smartphone-operated wireless portable sensing technique for high-potential applications in environmetallomics or agrometallomics using forestry waste-derived biochar as substrate for electrode preparation. HIGHLIGHTS: • Fe3O4 decorated phosphorus-doped biochar-attapulgite/bismuth film electrode. • A smartphone-operated sensor for analysis of multiple heavy metal ions. • An Artificial neural network model for smart analysis of Cd2+, Pb2+, and Hg2+.

Elaboration and Characterization of a New Heavy Metal Sensor Functionalized by Extracellular Polymeric Substances Isolated from a Tunisian Thermophilic Microalga Strain Graesiella sp.

The present study aimed to develop and characterize new heavy metal sensors functionalized by extracellular polymeric substances (EPSs) isolated from a Tunisian thermophilic microalga strain Graesiella sp. The elaborated sensor showed a highly homogeneous character and revealed a microstructural lamellar arrangement, high crystalline nature, and several functional groups. Electrochemical impedance spectroscopy (EIS) and acoustic wave sensing were used as sensing techniques to explore the ability of microalgae-EPS-functionalized sensors to detect cadmium and mercury as heavy metals. For impedimetric measurements, a two-dipole circuit was adopted and showed good-fitted results with a low total error. The acoustic sensor platforms showed good compatibility with EPS in adjacent water. For both EPS-functionalized sensors, metal ions (Cd2+, Hg2+) were successfully detected in the concentration range from 10-10 M to 10-4 M. Impedimetric sensor was more sensitive to Cd2+ at low concentrations before saturation at 10-7 M, while the acoustic sensor exhibited more sensitivity to Hg2+ over the full range. The results highlight a new potential alternative to use microalgae EPSs as a sensitive coating material for the detection of heavy metals. However, its use in a real liquid medium requires further investigation of its selectivity in the presence of other compounds.

Graphene Quantum Dots Doped with Sulfur and Nitrogen as Versatile Electrochemical Sensors for Heavy Metal Ions Cd(II), Pb(II), and Hg(II)

A sulfur co-doped nitrogen-graphene quantum dot (S,N-GQD) was synthesized from polyaniline using sulfuric acid as an acid catalyst and S-doping agent. Thus, through a simple hydrothermal synthesis method, we could achieve nanosized (∼4 nm) highly crystalline and aromatic S,N-GQDs. The S,N-GQDs, for the first time, exhibited simultaneous sensing toward three of the top 10 toxic metal ions: Cd(II), Pb(II), and Hg(II) with highly sharp peaks and adequate peak-to-peak separation, while the control N-GQD (no S co-doping) exhibited current response only for Cd(II) and the current response of Cd(II) on S,N-GQD was ∼7-fold higher than that of on N-GQD. The detection limit values were lowest hitherto for Cd(II), Pb(II), and Hg(II) on S,N-GQD with 1, 10, and 1 pM, respectively, for the simultaneous sensing of the metal ions. The significantly enhanced sensitivity compared to that of N-GQD for Cd(II) and the versatile simultaneous sensing capability of S,N-GQD is assigned to the co-doping with S, which enabled the sensing of Pb(II) and Hg(II) through the M(II)–S interactions and the enhanced electronic properties, respectively. The sensing characteristics were effectively stretched to actual environmental water samples such as groundwater, seawater, and wastewater, spiked with Cd(II), Pb(II), and Hg(II), and accomplished ∼100% recovery in all the tested samples with a relative standard deviation of ≤0.5%.

Impact of Self-Fabricated Graphene–Metal Oxide Composite Anodes on Metal Degradation and Energy Generation via a Microbial Fuel Cell

Microbial fuel cells (MFCs) are thought to be ecologically friendly, despite electron transport and generation challenges. In order to address this, the efficiency of MFCs was investigated using two different anode electrodes made from biomass: graphene oxide (GO) and graphene oxide-metal oxide (GO-MO) (GO-ZnO). After 18 days of operation, the maximum power density for GO was 0.69 mW/m2, whereas the maximum power density for GO-ZnO was 1.05 mW/m2. Furthermore, the ability of MFCs to transform the soluble metal ions (Cd2+, Cr3+, Pb2+, and Ni2+) into an insoluble state was investigated, which is a secondary use of MFCs with significant benefits. In the soluble state of metal ion transformation into an insoluble state, the rate of GO-ZnO was higher (92.71%) than that of GO (81.20%). The outcomes of material, analytical, and biological tests undertaken to validate the efficiency of anodes are presented. It has been shown that using innovative materials as electrodes in MFCs is a potential method for improving electron transport. Furthermore, as an organic substrate, food waste seems to be a viable alternative to more traditional options. In light of these discoveries, we investigate various unanswered issues and possibilities for MFCs. Organic substrate evaluation trials were also included in the present results to demonstrate that organic waste may be a reliable source of MFC performance. This article also has a thorough discussion of food waste oxidation, as well as challenges and future recommendations.