Recent advances in miniaturized electrochemical sensors based on carbon nanomaterials for heavy metals in aqueous environments: Nanoarchitectonics and application challenges

Tree bark is among the widely available and low-cost sorbents for metal adsorption in aqueous environments. A state-of-the-art review is compiled carrying out a comprehensive literature search on the biosorption of heavy metals in solution onto different bark species, including a characterization of bark structure and chemistry. The results indicate that biosorption has been gaining importance for bark valorization purposes. Promising heavy metal uptake values have already been attained using different bark species. These values are comparable to those obtained with commercial activated carbons. Bark has a cost advantage over activated carbon and can be used without any pretreatment. Thus, bark offers a green alternative to remove heavy metals from industrial waters. A brief survey of the chemical composition and structure of different bark species is presented. Suggestions are made to improve screening of bark species for specific heavy metal ions sorption.

The relentless paceof industrialization has significantly exacerbatedenvironmental pollution, with heavy-metal ions (HMIs) emerging assome of the most persistent and toxic pollutants in natural ecosystems.Growing concerns over environmental pollution have created a needfor advanced sensing technologies that offer superior sensing sensitivity,selectivity, and reliability. This work reports the development ofan electrochemical sensor based on a UiO-66-NH2(Zr) metal–organicframework (MOF)/graphene oxide (GO) nanocomposite for the simultaneousdetection of HMIs in aqueous environments. Using one-pot hydrothermalsynthesis, MOFs and conductive GO materials were integrated into asingle nanostructure via in situ growth of the UiO-66-NH2(Zr) MOF on the GO matrix, resulting in the formation of astable MOF/GO nanocomposite with enhanced conductivity and increasednumber of effective reaction sites. The amino groups (−NH2) on UiO-66-NH2(Zr) porous materials serve as adsorptionsites to capture HMIs. The morphological, structural, and electrochemicalproperties of the UiO-66-NH2(Zr)-GO nanocomposite wereexamined by using scanning electron microscopy/energy-dispersive spectroscopy(SEM/EDS), powder X-ray diffraction (PXRD), Fourier transform infrared(FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemicalimpedance spectroscopy (EIS). Differential pulse anodic strippingvoltammetry (DPASV) was subsequently employed for the detection ofheavy-metal ions over nanomolar to micromolar concentration rangesusing a UiO-66-NH2(Zr)-GO-modified glassy carbon (GC) electrode.The electrochemical sensor developed in this study was successfullyutilized for the selective and concurrent detection of multiple HMIs,namely, copper ion (Cu2+), cadmium ion (Cd2+), and lead ion (Pb2+) in electrolyte solution. The sensordemonstrated achieving high selectivity and sensitivity (1.30 μAμM–1 for Cu2+, 0.50 μA μM–1 for Cd2+, and 12.38 μA μM–1 for Pb2+) with low limit of detection(LOD) (0.59 ng/mL for Cu2+, 0.84 ng/mL for Cd2+, and 2.9 ng/mL for Pb2+), and observed ≥85% reproducibility.The sensor demonstrated excellent long-term stability and operatedeffectively within a temperature range of 283–313 K, enablingthe simultaneous detection of multiple heavy-metal ions from smallsample volumes. The developed electrochemical method can equally beemployed to detect HMIs at trace (parts-per-billion (ppb)) levelsin diverse environmental matrices such as lake, river, tap water,river sediments, and wastewater.

Research trends of heavy metal removal from aqueous environments

Metal–organic frameworks (MOFs) have emerged as versatile materials for wastewater treatment owing to their high surface area, tunable porosity, and multifunctional active sites. However, the instability of pristine MOFs in aqueous environments and the leaching of metal or ligand species remain critical barriers to their practical application. This review focuses on advanced hybrid MOF composites designed for the removal of organic dyes and heavy metal ions, highlighting their structural features, removal mechanisms, and performance. The focus is made on the recent developments in composite design and functionalization approaches that improve water stability and reusability. The article also examines isotherm and kinetic models, as well as adsorption mechanisms, that govern MOF performance. Special focus is placed on the degradation processes of MOFs in water and the effects that can be reduced by hybridisation. Integrating the state-of-the-art results, this review presents a critical framework that connects synthesis, structure, performance, and reusability, providing guidelines for the rational construction of robust MOF-based adsorbents and photocatalysts to showcase an integrated approach to wastewater remediation. • Recent advances in MOF-based composites in wastewater treatment were reviewed. • MOFs and MOF-based composites design methods were summarized. • MOF-based composites are powerful adsorbents for dyes and metal ions removal. • Possible interaction mechanisms were summarized. • MOF-based composites are cost-effective with recycling and reuse potential. • The challenges and recommendations for future research hotspots were proposed.

Characterization of the micro-interfacial interactions of heterogeneous particulate matter (fine-grained sediment and microplastics) with copper ions

Providing safe drinking water and clean water is becoming a more challenging task all around the world. Although some critical issues and limits remain unsolved, implementing ecologically sustainable nanomaterials (NMs) with unique features, e.g., highly efficient and selective, earth-abundance, renewability, low-cost manufacturing procedures, and stability, has become a priority. Carbon nanoparticles (NPs) offer tremendous promise in the sectors of energy and the environment. However, a series of far more ecologically friendly synthesis techniques based on natural, renewable, and less expensive waste resources must be explored. This will reduce greenhouse gas emissions and harmful material extraction and assist the development of green technologies. The progress achieved in the previous 10 years in the fabrication of novel carbon-based NMs utilizing waste materials as well as natural precursors is reviewed in this article. Research on carbon-based NPs and their production using naturally occurring precursors and waste materials focuses on this review research. Water treatment and purification using carbon NMs, notably for industrial and pharmaceutical wastes, has shown significant potential. Research in this area focuses on enhanced carbonaceous NMs, methods, and novel nano-sorbents for wastewater, drinking water, groundwater treatment, as well as ionic metal removal from aqueous environments. Discussed are the latest developments and challenges in environmentally friendly carbon and graphene quantum dot NMs.

A large amount of pollutants discharged into water bodies and which has significantly affect the quality of aquatic environments. The removal of pollutants from water bodies is highly desirable for the safe aquatic lives and human activities. Recently, the development of green and environmentally friendly adsorbent with favorable properties for adsorption of pollutants has gained high attention. Chitosan, the second most abundant polymer in nature, derived from aquatic media, has a high potential in many applications, including wastewater treatment. The presence of amino and hydroxyl groups in chitosan’s structure not only serve as active sites for pollutants attachment, but ease for structural modification. Modification of pure chitosan into chitosan composites have gained attention as a promising approach for removing various classes of pollutants such as dyes, heavy metals and pharmaceuticals from aqueous environment. This chap uniquely highlights the type of chitosan composites, along with their application in aquatic environment. There is also a list of common modifying agents and biomaterials used in the creation of superior chitosan composites. This work is valuable as it gives insight into the development of green and efficient wastewater treatment technology using chitosan-based adsorbent.

Microplastics, as emerging pollutants, have received great attention in the past few decades due to its adverse effects on the environment. Microplastics are ubiquitous in the atmosphere, soil, and water bodies, and mostly reported in aqueous environment. This paper summarizes the abundance and types of microplastics in different aqueous environments and discusses the interactions of microplastics with other contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), antibiotics, and heavy metals. The toxicity of microplastics to aquatic organisms and microorganisms is addressed. Particularly, the combined toxic effects of microplastics and other pollutants are discussed, demonstrating either synergetic or antagonistic effects. Future prospectives should be focused on the characterization of different types and shapes of microplastics, the standardization of microplastic units, exploring the interaction and toxicity of microplastics with other pollutants, and the degradation of microplastics, for a better understanding of the ecological risks of microplastics.

Modification of chitosan macromolecule and its mechanism for the removal of Pb(II) ions from aqueous environment

The removal of toxic heavy metal ions from water resources is crucial for environmental protection and public health. In this study, we address this challenge by developing a surface functionalization technique for the selective adsorption of these contaminants. Our approach involves atomic layer deposition (ALD) followed by vapor-phase silanization of porous substrates. We utilized porous silica gel powder (∼100 μm particles, 89 m2/g surface area, ∼30 nm pores) as an initial substrate. This powder was first coated with ∼0.5 nm ALD Al2O3, followed by vapor-phase grafting of a thiol-functional silane. The modified powder, particularly in acidic conditions (pH = 4), showed high selectivity in adsorbing Cd(II), As(V), Pb(II), Hg(II), and Cu(II) heavy metal ions in mixed ion solutions over common benign ions (e.g., Na, K, Ca, and Mg). Langmuir adsorption isotherms and breakthrough adsorption studies were conducted to assess heavy metal binding affinity and revealed the order of Cd(II) < Pb(II) < Cu(II) < As(V) < Hg(II), with a significantly higher affinity for As(V) and Hg(II) ions. Time-dependent uptake studies demonstrated rapid removal of heavy metal ions from aqueous environments, with Hg(II) exhibiting the fastest adsorption kinetics on thiol-modified surfaces. These findings highlight the potential of ALD and vapor-phase silanization to create effective adsorbents for the targeted removal of hazardous contaminants from water.

The pressing challenge of heavy metal pollution in water sources demands innovative and sustainable solutions. This project explored recent advancements in heavy metal remediation techniques, focusing on the utilization of cellulose–silica composites and tailored surface modification techniques. The synthesis strategies and properties of cellulose–silica adsorbents highlight their enhanced adsorption capacities and structural robustness for removing heavy metal pollutants from aqueous environments. The study investigated various surface modification approaches, including thiol functionalization, amino acid grafting, and silane coupling agents, for optimizing the surface chemistry and morphology of cellulose–silica composites. Mechanistic insights into the adsorption processes and kinetics of modified adsorbents were studied, along with considerations for optimizing adsorption performance under different environmental conditions. The adsorption method for hexavalent chromium (Cr (VI) removal from domestic and industrial wastewater is widely desirable due to public health concerns about the heavy metal. The study aimed to investigate the adsorption of Cr (VI) using a novel adsorbent: an amine-functionalized cellulose-silica composite derived from banana pseudo-stem. The in-situ sol-gel method was used to create cellulose-silica silane functionalized composites and analyzed them through different characterization techniques such as attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), Scanning Electron Microscopy (SEM), and transmission electron microscopy (TEM) techniques. ATR-FTIR depicted key organic constituents in raw banana pseudo-stem fibers (BF) and the formation of Si–O bonds in Bleached Cellulose-Silica (BC–SiO2) composite and further enhanced by the grafting of N-[3- (trimethoxysilyl)propyl]ethylenediamine (DAPTMS) onto the BC-SiO2 surface in BC-SiO2- DAPTMS. Functionalization with varying DAPTMS concentrations (2, 4, and 10%) was employed to enhance the composites' adsorption capacity, binding affinity, and thermal stability. Comprehensive characterization using ATR-FTIR, XRD, TGA, BET, SEM, and TEM revealed structural and thermal modifications, with higher DAPTMS concentrations improving adsorption performance. The modifications of BC with SiO2 followed by DAPTMS result in the BC-SiO2-DAPTMS composite, which has reduced crystallinity as shown by XRD and enhanced thermal stability as demonstrated by TGA, while BET analysis showed altered surface area and pore characteristics in BC-SiO2-DAPTMS (2%). The SEM and TEM imaging provided visual evidence of structural modifications and improved dispersion in BC-SiO2-DAPTMS composites. The effects of initial Cr (VI) concentration, adsorbent weight dosage, contact time, and pH on the removal efficiency of Cr (VI) using amine-functionalized cellulose–silica composites were also investigated. The results highlighted significant differences in adsorption performance based on the composite formulation and operating conditions. The initial Cr (VI) concentration effect revealed that BCSiO₂-DAPTMS (4%) consistently achieved the highest removal efficiencies, peaking at 97.14% at 0.3 mg/L. BC-SiO₂-DAPTMS (10%) followed closely, with efficiency stabilizing around 95.53% at higher concentrations. BC-SiO₂-DAPTMS (2%) exhibited lower but improving performance with increasing concentrations. Adsorbent weight dosage experiments demonstrated that increasing weight enhanced removal efficiency, with BC-SiO₂-DAPTMS (10%) achieving optimal performance (95.46%) at 1 g, though benefits plateaued beyond this weight. The impact of contact time showed BC-SiO₂-DAPTMS (10%) achieving equilibrium after 50 minutes, with a maximum removal efficiency of 91.29%. BC-SiO₂-DAPTMS (4%) exhibited a similar trend, but with a slightly lower maximum efficiency of 84.30%. The pH study indicated that acidic conditions (pH 1–4) were most favourable for Cr (VI) removal, with BC-SiO₂- DAPTMS (10%) reaching the highest removal efficiency (89.27% at pH 3) and maintaining superior performance across all pH levels. Overall, BC-SiO₂-DAPTMS (10%) demonstrated the best performance across all conditions, followed by BC-SiO₂-DAPTMS (4%), underscoring the importance of higher DAPTMS functionalization for enhanced Cr (VI) adsorption. These findings offer valuable insights into optimizing composite design and operational parameters for effective Cr(VI) remediation in contaminated water systems. The kinetic modelling followed the pseudosecond order (PSO) model, while the Freundlich and Langmuir isotherms provided insights into the adsorption mechanisms. The overall results demonstrated that the BC-SiO₂-DAPTMS composites, particularly at 4% and 10% DAPTMS concentrations, are effective, scalable, and sustainable adsorbents for Cr (VI) remediation, offering significant potential for practical water treatment applications. The study offered valuable insights into the development of effective adsorbent materials for sustainable heavy metal remediation applications.

For a sustainable ecosystem and the benefit of mankind, knowledge of environmental pollution with a health impact is crucial.Industrial waste and sewage sources contaminate the Ganga River's water.Freshwater algae have a well-known ability to bioaccumulate heavy metals.We investigated the ability of the green algae Hydrodictyon reticulatum and Rhizoclonium sp. to biologically accumulate heavy metals in an aqueous environment as a response to the increasing environmental contamination associated with heavy metals.We analysed the heavy metals Cd, Cr, Pb, and Fe.We collected algal biomass and Ganga water samples from Prayagraj, Uttar Pradesh, in March 2022 to study heavy metals.Heavy metals were analyzed using a spectrophotometric technique and an atomic absorption spectrometer (Perkin Elmer A-700).Green algae can highly accumulate heavy metals.We examined heavy metals in algal and Ganga water samples.We found the concentrations of heavy metals in Ganga water in the following order: Cd > Cr > Pb > Fe.In Hydrodictyon reticulatum, the bioaccumulation factor was 169.16 for Fe, 27.5 for Pb, 22.14 for Cr, and 2.58 for Cd.In Rhizoclonium sp., it was 352.5 for Fe, 34.74 for Pb, 27.63 for Cr, and 3.13 for Cd.

Heavy metal industries pose a serious threat to the environment. Conventional methods used for heavy metal removal are generally not always low-cost and environmentally friendly. So, researchers focused to investigate alternative biosorbents for the uptake of heavy metal. In this study, Laurus nobilis leaves (LNL) were used as a biosorbent for the uptake of toxic metals such as Pb2+ and Cd2+ from aqueous solutions. Batch biosorption experiments under varied conditions, such as biosorbent dosage, solution pH, heavy metal concentration, biosorption time, ionic strength, humic acid effect and competitive metal ions (Cd(II), Pb(II), Cu(II) and Zn(II)) were performed. The biomass was characterized using FT-IR spectra and SEM images. The nonlinearized and linearized isotherm models were compared and discussed. A single-stage batch bioreactor system for each heavy metal based on the best fit nonlinear isotherm model also has been presented. The biosorption of Pb(II) on LNL fitted better in the Langmuir model and Cd(II) biosorption fitted better in the Freundlich model by nonlinearized equations. The LNL exhibited the maximum monolayer biosorption capacities (qmax) of 7.1 and 32.5 mg/g for cadmium and lead, respectively. LNL showed great potential especially in Pb(II) uptake. LNL may be promising for heavy metal removal from aqueous environment.

Author response for "An overview of sensors and sensing materials for heavy metals in aqueous environments"

The growth of bacteria on stainless steel wires was used as a model to investigate which properties of SnF2 produced anti-bacterial effects against S. mutans. Wire-adherent bacteria were exposed for one min, twice a day, to various fluoride or control compounds having similar ions, pH, valence, or atomic weights. After two days, the thickness of adherent bacteria was scored visually, and the decrease in pH of the growth medium was determined. Bacteria from each wire were then dried, weighed, and analyzed for metal content. Electron microscopy and electron microprobe were used to identify the location of heavy metal deposits in the bacteria. Only SnF2 dramatically altered S. mutans growth and metabolism, and this anti-bacterial effect was associated with a large uptake of tin into the bacterial cells. The fluoride salts of sodium, lead, zinc, and copper had little influence on S. mutans growth in this test system. The pH of the various fluoride salts or controls generally had no effect on the activity of the test compounds, except for the noted inactivation of SnF2 at elevated pH's. Since SnF4 did not alter the growth or metabolism of S. mutans, a unique property of SnF2--possibly the reactivity in an aqueous environment--may be responsible for its anti-bacterial properties.