Application of common nano-materials for removal of selected metallic species from water and wastewaters: A critical review

Removal mechanism of Pb(ii) from soil by biochar-supported nanoscale zero-valent iron composite materials

As an adsorbent, biochar has a highly porous structure and strong adsorption capacity, and can effectively purify the environment. In response to the increasingly serious problem of heavy metal pollution in water, this study used nano zero valent iron and rice husk biochar to prepare a new type of magnetic sheet-like biochar loaded nano zero valent iron (BC-nZVI) composite material through rheological phase reaction, showing remarkable advantages such as low cost, easy preparation, and superior environmental remediation effect. The physical and chemical properties and structure of the material were extensively characterized using various methods such as HRTEM, XPS, FESEM, EDS, XRD, FTIR, and RAMAN. Concurrently, batch experiments were undertaken to assess the removal efficiency of Pb(ii) by BC-nZVI, with investigations into the influence of pH value, temperature, soil water ratio, and initial concentration of heavy metal ion solution on its removal efficiency. The results indicate that the removal of Pb(ii) by BC-nZVI reaches an equilibrium state after around 120 minutes. Under the conditions of pH 6, temperature 20 °C, soil water ratio 1 : 5, and BC-nZVI dosage of 1 g L-1, BC-nZVI can reduce the Pb(ii) content in wastewater with an initial concentration of 30 mg L-1 to trace levels, and the treatment time is about 120 minutes. The analysis of adsorption kinetics and isotherms indicates that the adsorption process of Pb(ii) by BC-nZVI adheres to the quasi-second-order kinetic model and Langmuir model, suggesting a chemical adsorption process. Thermodynamic findings reveal that the adsorption of Pb(ii) by BC-nZVI is spontaneous. Furthermore, BC-nZVI primarily accumulates Pb(ii) through adsorption co-precipitation. BC-nZVI serves as an eco-friendly, cost-effective, and highly efficient adsorbent, showing promising capabilities in mitigating Pb(ii) heavy metal pollution. Its recoverability and reusability facilitated by an external magnetic field make it advantageous for remediating and treating lead-contaminated sites.

Chitosan-Modified Biochars to Advance Research on Heavy Metal Ion Removal: Roles, Mechanism and Perspectives

The chitosan-modified biochars BC-CS 1-1, BC-CS 2-1 and BC-CS 4-1 were subjected to the synthetic application of biochar from agriculture waste and chitosan for the adsorption of Cu(II), Cd(II), Zn(II), Co(II) and Pb(II) ions from aqueous media. The results displayed a heterogeneous, well-developed surface. Additionally, the surface functional groups carboxyl, hydroxyl and phenol, determining the sorption mechanism and confirming the thermal stability of the materials, were present. The sorption evaluation was carried out as a function of the sorbent dose, pH, phase contact time, initial concentration of the solution and temperature. The maximum value of q_t for Pb(II)-BC-CS 4-1, 32.23 mg/g (C₀ 200 mg/L, mass 0.1 g, pH 5, 360 min), was identified. Nitric acid was applied for the sorbent regeneration with a yield of 99.13% for Pb(II)-BC-CS 2-1. The produced sorbents can be used for the decontamination of water by means of the cost-effective and high-performance method.

Facile Preparation and Analytical Utility of ZnO/Date Palm Fiber Nanocomposites in Lead Removal from Environmental Water Samples

This study reports a facile approach for preparing low-cost, eco-friendly nanocomposites of ZnO nanoparticles (NPs) and date palm tree fiber (DPF) as a biomass sorbent. The hypothesis of this research work is the formation of an outstanding adsorbent based on the date palm fiber and ZnO nanoparticles. ZnO NP/DPF nanocomposites were synthesized by mixing the synthesized ZnO NPs and DPF in different mass ratios and evaluating their efficacy in adsorbing Pb2+ from aqueous solutions. The structure and surface morphology of the developed ZnO NP/DPF nanocomposite were critically characterized by XRD, FESEM, and TEM techniques. Compared to ZnO NPs, the ZnO NP/DPF nanocomposites displayed significantly enhanced Pb2+ uptake. Pb2+ adsorption was confirmed via various isotherm and kinetic models and thermodynamics. The computed Langmuir sorption capacity (qm) was found to be 88.76 mg/g (R2 > 0.998), and the pseudo-second-order R2 > 0.999 model was most appropriate for describing Pb2+ adsorption. Impregnating the biomass with ZnO NPs enhanced the spontaneity of the process, and the value (−56.55 kJ/mol) of ΔH displayed the exothermic characteristics of Pb2+ retention. Only the loaded ZnO NP/DPF achieved the removal of a high percentage (84.92%) of Pb2+ from the environmental water sample (seawater). This finding suggests the use of ZnO NP/DPF nanocomposites for removing heavy metals from environmental water samples to purify the samples.

Removal of Ni(II) Ions by Poly(Vinyl Alcohol)/Al2O3 Nanocomposite Film via Laser Ablation in Liquid

Al₂O₃-poly(vinyl alcohol) nanocomposite (Al₂O₃-PVA nanocomposite) was generated in a single step using an eco-friendly method based on the pulsed laser ablation approach immersed in PVA solution to be applicable for the removal of Ni(II) from aqueous solution, followed by making a physicochemical characterization by SEM, XRD, FT-IR, and EDX. After that, the effect of adsorption parameters, such as pH, contact time, initial concentration of Ni(II), and medium temperature, were investigated for removal Ni(II) ions. The results showed that the adsorption was increased when pH was 5.3, and the process was initially relatively quick, with maximum adsorption detected within 90 min of contact time with the endothermic sorption process. Moreover, the pseudo-second-order rate kinetics (k₂ = 9.9 × 10⁻⁴ g mg⁻¹ min⁻¹) exhibited greater agreement than that of the pseudo-first-order. For that, the Ni(II) was effectively collected by Al₂O₃-PVA nanocomposite prepared by an eco-friendly and simple method for the production of clean water to protect public health.

Functionalization of MXene-based nanomaterials for the treatment of micropollutants in aquatic system: A review

The increased industrialization and urbanization generate a larger quantity of effluent that is discharged into the environment regularly. Based on the effluent composition produced from various industries, the number of hazardous substances such as heavy metals, hydrocarbons, volatile organic compounds, organic chemicals, microorganisms introduced into the aquatic systems vary. The conventional wastewater treatment systems do not meet the effluent standards before discharge and require a different treatment system before reuse. Adsorption is an eco-friendly technique that uses selective adsorbents to remove hazardous pollutants even at microscale levels. MXene, a 2-Dimensional nanomaterial with resplendent properties like conductivity, hydrophilicity, stability, and functionalized surface characteristics, is found as a potential candidate for pollutant removal systems. This review discusses the fabrication, characterization, and application of MXene based nanoparticles to remove many pollutants in water treatment systems. The improvement in surface properties and adsorption capacity of MXene based NPs, when modified using different modification agents, has also been discussed. Their feasibility in terms of economic and environmental aspects has been evaluated to understand their scope for practical application in large-scale industries. The challenges towards the synthesis and toxicity's importance have been discussed, with the appropriate recommendations.

Alginate-based nano-adsorbent materials - Bioinspired solution to mitigate hazardous environmental pollutants

Population growth and industrialization is associated with the elevation of hazardous pollutants, including heavy metals, biomedical wastes, personal-care products, endocrine-disrupters, pharmaceutically active compounds, and colorants in the environment. The scientific focus has been devoted to developing novel adsorbents to mitigate hazardous pollutants by constructing hybrids of different polymers and nano-structured materials for improved workability and physicochemical attributes. Recently, much attention has been devoted to nanomaterials in environmental remediation, owning to their exceptional characteristics including novel electrical/chemical features, quantum size effects, tunable functionalization, high scalability, and surface-area-to-volume ratio. Target-specific designing of nanocomposites impart high functionality. The cost-effective and eco-friendly synthesis of bioadsorbent materials is increasing for the removal of hazardous pollutants. Due to biocompatible, biodegradable, and eco-friendly nature, sodium alginate has been widely reported for the preparation of bioadsorbent materials to remove different inorganic/organic pollutants. In this review, the potentialities of alginate-based nanocomposites have been described for environmental remediation purposes. Different nanomaterials, including silica, metallic oxide, graphene oxide, hybrid inorganic-organic, non-magnetic-magnetic, carbon nanorods, nanotubes, polymeric nanocarriers, and several other materials have been described in combination with alginate biopolymer for environmental remediation.

Advancements in heavy metals removal from effluents employing nano-adsorbents: Way towards cleaner production

Due to the development in science field which gives not only benefit but also introducesundesirable pollution to the environment. This pollution is due to poor discharge activities of industrial effluents into the soil and water bodies, surface run off from fields of agricultural lands, dumping of untreated wastes by municipalities, and mining activites, which deteriorates the cardinal virtue of our environment and causes menace to human health and life. Heavy metal(s), a natural constituent on earth's crust and economic important mineral, due to its recalcitrant effects creates heavy metal pollution which affects food chain and also reduces the quality of water. For this, many researchers have performed studies to find efficient methods for wastewater remediation. One of the most promising methods from economic point of view is adsorption, which is simple in design, but leads to use of a wide range of adsorbents and ease of operations. Due to advances in nanotechnology, many nanomaterials were used as adsorbents for wastewater remediation, because of their efficiency. Many researchers have reported that nanoadsorbents are unmitigatedly a fruitful solution to address this world's problem. This review presents a potent view on various classes of nanoadsorbents and their application to wastewater treatment. It provides a bird's eye view of the suitability of different types of nanomaterials for remediation of wastewater and Backspace gives up-to-date information about polymer based and silica-based nanoadsorbents.

Fly ash-based geopolymers: an emerging sustainable solution for heavy metal remediation from aqueous medium

Background

The water supplies are hindered because aquatic resources have constrained with natural and man-made pollution activities in terms of releasing huge amounts of contaminants from different point and non-point sources across the globe. The industries like metal plating, batteries, paint, fertilizers, tanneries, textile industries, dyeing industries, mining operations, and paper industries discharge their effluents into the environment directly or indirectly, and hence, they are considered as the key sources of heavy metals contamination in water resources. Heavy metals are inorganic, non-biodegradable, persistent, and having a tendency to get accumulated in biotic and abiotic components of environment as compared to organic pollutants. Some heavy metal cations, for example, mercury, arsenic, cadmium, zinc, lead, nickel, copper, and chromium, are carcinogenic in nature and so, lethal. There are growing health concerns due to toxic impacts of heavy metals on every genre of ecosystem. To deal with the bottleneck situation, it is highly imperative to search a feasible solution for heavy metal remediation in water in context of preventing amalgamation of noxious contaminants in food web. Different methods are exercised for the remediation of such impurities from its solutions. One method, i.e. adsorption is found to be the simplest, economical, efficient, and eco-friendly in this context.

Main body

Geopolymers exhibit heterogeneous amorphous microstructure and wide surface area. The compatibility for depollution and the performance of these materials mainly depend upon their preparation methods, composition, and microstructure. Fly ash-based geopolymer may serve as a better alternate to various cost-effective adsorbents and it will be a proven environmentally viable, waste to money solution by consuming heaps of fly ash waste for the adsorbent modified by using fly ash. The possible utilization of wastes from several industries is a matter of concerned sustainability benefits. This study shows that fly ash-based geopolymers have the potential to cope up with the problems and risk factors associated with the fly ash waste management and it would be the utmost scientific panacea in the field of removing toxins from aqueous medium and maintain environmental health in the future.

Short conclusions

The literature available in different databases is very limited pertaining to heavy metal remediation using fly ash-based geopolymers. Keeping all the factors in mind, this article is an attempt to summarize relevant informations related to work done on fly ash-based geopolymers for treating aqueous solutions comprising heavy metals.

Progress in modifications of 3D graphene-based adsorbents for environmental applications

3D graphene-based materials are promising adsorbents for environmental applications. Furthermore, increasing attention has been paid to the improvement of 3D graphene adsorbents for removing pollutants. In this article, the progress in the modification of 3D graphene materials and their performance for removing pollutants were reviewed. The modification strategies, which were classified as (1) the activation with CO₂ (steam and other oxidants) and (2) the surface functionalization with polymers (metals, and metal oxides), were evaluated. The performances of modified 3D graphene materials were assessed for the removal of waste gases (such as CO₂), refractory organics, and heavy metals. The challenges and future research directions were discussed for the environmental applications of 3D graphene materials.

New Polymer Inclusion Membranes in the Separation of Palladium, Zinc and Nickel Ions from Aqueous Solutions

The new polymer inclusion membrane (PIM) with a 1-alkyltriazole matrix was used to separate palladium(II) ions from aqueous chloride solutions containing a mixture of Zn-Pd-Ni ions. The effective conditions for transport studies by PIMs were determined based on solvent extraction (SX) studies. Furthermore, the values of the stability constants and partition coefficients of M(II)-alkyltriazole complexes were determined. The values of both constants increase with the growing hydrophobicity of the 1-alkyltriazole molecule and have the highest values for the Pd(II) complexes. The initial fluxes, selectivity coefficients, and recovery factors values of for Pd, Zn and Ni were determined on the basis of membrane transport studies. The transport selectivity of PIMs were: Pd(II) > Zn(II) > Ni(II). The initial metal ion fluxes for all the cations increased with the elongation of the alkyl chain in the 1-alkyltriazole, but the selectivity coefficients decreased. The highest values of the initial fluxes at pH = 4.0 were found for Pd(II) ions. The best selectivity coefficients Pd(II)/Zn(II) and Pd(II)/Ni(II) equal to 4.0 and 13.4, respectively, were found for 1-pentyl-triazole. It was shown that the microstructure of the polymer membrane surface influences the kinetics of metal ion transport. Based on the conducted research, it was shown that the new PIMs with 1-alkyltriazole can be successfully used in an acidic medium to separate a mixture containing Pd(II), Zn(II) and Ni(II) ions.

Adsorption of impurities from nickel-plating baths using commercial sorbents to reduce wastewater discharges

The presence of moderate concentrations of impurities in the nickel-plating baths generates failures on the coated pieces. This situation entails the necessity of replacing the electroplating bath, which implies the generation of large volumes of wastewater with metallic species and high quantity of sludge. For this reason, the adsorption of the principal impurities of nickel-plating baths of an industry was analyzed in this work. Particularly, the removal of Zn²⁺ was studied in more detail since the presence of this metal in the baths generates black spots on the coated pieces. Different commercial materials were used as adsorbents and Zn²⁺ adsorption studies were carried out using both standard solutions and industrial water from the nickel-plating baths. All the adsorption tests were performed in batch systems under constant agitation and the quantification of the impurities was made by ICP-MS analysis. The bone char (BC) was an efficient adsorbent for the removal of the principal impurities of nickel-plating baths. The use of molecular simulation tools helped to understand the preferences of the hydroxyapatite (the principal component of bone char) for different metallic ions present in the industrial waters. According to both the experimental adsorption and molecular simulation results, hydroxyl and phosphate groups of bone char are responsible of the adsorption of impurities of nickel-plating baths.

One-step synthesis of cake-like biosorbents from plant biomass for the effective removal and recovery heavy metals: Effect of plant species and roles of xanthation

The continuous production of plant wastes and heavy metal pollution of waters have become widespread unavoidable challenges. Reutilization of plant wastes to treat toxic metal-contaminated water is an eco-friendly way to simultaneously solve these problems. Herein, three cake-like biosorbents were synthesized from tea waste, trimmed lawn grass and Nephrolepis cordifolia leaves through a one-step xanthation modification method combined with lyophilization, respectively. The plant species affected the appearance, structure and mechanical strength of the biosorbents due to the different contents of hydrocarbons and inorganic substances, which influenced the gel-like degree and thus the ability of the particles to pack between water molecules. The maximum adsorption capacities of the modified materials for Pb(II), Cu(II) and Cd(II) were 247.20, 85.80 and 265.31 mg/g, respectively, far higher than those of the original wastes, and the adsorption was selective. These results were mainly attributed to newly introduced -(CS)-S-Na groups, which triggered ion exchange, complexation and microprecipitation between heavy metal ions and functional groups. As-prepared biosorbents owned an excellent regenerability, which contributed to recovery heavy metals. The physicochemical properties and adsorption performances of the modified materials indicated that xanthation is a universal modification method suited to different plant biomasses with great potential to purify heavy metal-contaminated water. These biosorbents with excellent separability and regenerability might be promising for continuous-flow sewage treatment.

As(V) adsorption by a novel core-shell magnetic nanoparticles prepared with Iron-containing water treatment residuals

A novel core-shell magnetic nanoparticle was synthesized through heterogeneous nucleation technique and utilized to remove As(V) from water. Both the magnetic core and the coating material, amorphous FeOOH shell, were prepared with iron-containing water treatment residuals (WTRs), also called iron sludge. The bare magnetic nanoparticles (MNPs) and coated magnetic nanoparticles (c-MNPs) were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Brunauer-Emmett -Teller analysis (BET), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The c-MNPs, mainly consisting of maghemite (γ-Fe₂O₃) as the magnetic core and amorphous FeOOH as the coating material, could be easily separated from water through a hand-held magnet, the saturation magnetization of which is 36.4 emu/g. Freundlich adsorption isotherm model could better described the As(V) adsorption behavior of c-MNPs than Langmuir model, and kinetic data could be described well by the pseudo-second order model. The maximum As(V) adsorption capacity of c-MNPs (26.05 mg/g) was more than twice that of MNPs (12.74 mg/g). At 25 °C, 0.2 g/L of the c-MNPs could reduce the As(V) from 400 μg/L to below the maximum contaminant level (MCL) of 10 μg/L over a broad pH ranging from 4 to 8. The c-MNPs still exhibited effective adsorption in the presence of co-existing anions including nitrate, chloride, carbonate, and sulfate, whereas, silicate and phosphate had a negative influence on the As(V) adsorption. Throughout five consecutive cycles, the adsorbents could still maintain high As(V) adsorption capacity.

Kinetics and Thermodynamics Studies for Cadmium (II) Adsorption onto Functionalized Chitosan with Hexa-Decyl-Trimethyl-Ammonium Chloride

A new adsorbent material was obtained by functionalization of chitosan with hexa-decyl-trimethyl-ammonium chloride and tested as an adsorbent for Cd(II) ions. Functionalization is due to the desire to improve the adsorbent properties of the biopolymer used for removal of metallic ions. Obtained material was characterized by FTIR (Fourier Transform InfraRed spectroscopy), SEM (Scanning Electron Microscopy) and EDX (Energy dispersive X-ray Spectroscopy). To prove the Cd(II) adsorption mechanism, we performed adsorption tests determining influence of biopolymer ratio, pH, contact time, temperature and Cd(II) initial concentration. Obtained experimental data were modeled using two kinetics models: pseudo-first-order and pseudo-second-order models. Cd(II) adsorption kinetics was better described by pseudo-second-order model. Further, experimental data were fitted using three different adsorption isotherms: Langmuir, Freundlich and Sips. The studied adsorption process is well described by the Sips adsorption isotherm, when the maximum adsorption capacity value is near the experimental one. Likewise, we evaluated the values of thermodynamic parameters which indicate that the studied process is an endothermic and spontaneous one, being a physical adsorption. Prepared adsorbent materials have a maximum adsorption capacity of 204.3 mg Cd²⁺ per gram at pH > 4.0 and 298 K. In addition, this material was reused for Cd²⁺ recovery for 20 times.

Microwave-enforced green synthesis of novel magnetic nano composite adsorbents based on functionalization of wood sawdust for fast removal of calcium hardness from water samples

Developing new generation of adsorbents for water treatment to reduce calcium hardness and producing high quality water is important and continuous trend. This manuscript is devoted with this direction. Thus, two novel magnetic nanocomposite adsorbents were synthesized by covalently binding of tartaric acid (TA) and citric acid (CA) to wood sawdust coated magnetic nanoparticles (WSD@Fe₃ O₄ NPs) using green microwave solvent-less technique. The adsorbents thus prepared WSD@Fe₃ O₄ NPs-TA and WSD@Fe₃ O₄ NPs-CA were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Preliminary batch experiments were performed to evaluate percentage of Ca(II) adsorbed by the bare WSD@Fe₃ O₄ NPs and its functionalized forms by TA and CA, as a function of pH (initial concentration 80 mg/L), indicated 59.5%, 84.70%, and 99.29%, respectively, at pH 7 as optimal value. To attain maximum adsorption capacity, effect of adsorbent dosage and contact time were also optimized for the two modified adsorbents. Accordingly, Ca(II) adsorption capacity was determined to be 18.4 mg/g as exhibited by WSD@Fe₃ O₄ NPs-TA. However, WSD@Fe₃ O₄ NPs-CA showed higher capacity value recorded to be 27.2 mg/g. The novel adsorbents were successfully applied for fast reduction of calcium hardness from real water samples, during 15-20 min and via two consecutive in situ batch operations. PRACTITIONER POINTS: This manuscript aims to minimize Ca(II) hardness in aqueous solutions by performing magnetic separation under external magnetic field. WSD was magnetized using Fe₃ O₄ then modified by using safe organic modifiers using of the benefits of solvent-less microwave radiation technique for adsorbent synthesis and functionalization. Two novel environmentally magnetic nanocomposites WSD@Fe₃ O₄ NPs-TA and WSD@Fe₃ O₄ NPs-CA were checked on real water samples.

Removal of heavy metals and radionuclides from water using nanomaterials: current scenario and future prospects

There is an increase in concern about the hazardous effects of radioactivity due to the presence of undesirable radioactive substances in our vicinity. Nuclear accidents such as Chernobyl (1986) and Fukushima (2011) have further raised concerns towards such incidents which have led to contamination of water bodies. Conventional methods of water purification are less efficient in decontamination of radioisotopes. They are usually neither cost-effective nor environmentally friendly. However, nanotechnology can play a vital role in providing practical solutions to this problem. Nano-engineered materials like metal oxides, metallic organic frameworks, and nanoparticle-impregnated membranes have proven to be highly efficient in treating contaminated water. Their unique characteristics such as high adsorption capacity, large specific surface area, high tensile strength, and excellent biocompatibility properties make them useful in the field of water purification. This review explores the present status and future prospects of nanomaterials as the next-generation water purification systems that can play an important role in the removal of heavy metals and radioactive contaminants from aqueous solutions.

Multifunctional Magnetic Oxide Nanoparticle (MNP) Core-Shell: Review of Synthesis, Structural Studies and Application for Wastewater Treatment

The demand for water is predicted to increase significantly over the coming decades; thus, there is a need to develop an inclusive wastewater decontaminator for the effective management and conservation of water. Magnetic oxide nanocomposites have great potentials as global and novel remediators for wastewater treatment, with robust environmental and economic gains. Environment-responsive nanocomposites would offer wide flexibility to harvest and utilize massive untapped natural energy sources to drive a green economy in tandem with the United Nations Sustainable Development Goals. Recent attempts to engineer smart magnetic oxide nanocomposites for wastewater treatment has been reported by several researchers. However, the magnetic properties of superparamagnetic nanocomposite materials and their adsorption properties nexus as fundamental to the design of recyclable nanomaterials are desirable for industrial application. The potentials of facile magnetic recovery, ease of functionalization, reusability, solar responsiveness, biocompatibility and ergonomic design promote the application of magnetic oxide nanocomposites in wastewater treatment. The review makes a holistic attempt to explore magnetic oxide nanocomposites for wastewater treatment; futuristic smart magnetic oxides as an elixir to global water scarcity is expounded. Desirable adsorption parameters and properties of magnetic oxides nanocomposites are explored while considering their fate in biological and environmental media.

Nanomaterials in speciation analysis of metals and metalloids

Nanomaterials have draw extensive attention from the scientists in recent years mainly due to their unique and attractive thermal, mechanical and electronic properties, as well as high surface to volume ratio and the possibility for surface functionalization. Whereas mono functional nanomaterials providing a single function, the preparation of core/shell nanoparticles allows different properties to be combined in one material. Their properties have been extensively exploited in different extraction techniques to improve the efficiency of separation and preconcentration, analytical selectivity and method reliability. The aim of this paper is to provide an updated revision of the most important features and application of nanomaterials (metallic, silica, polymeric and carbon-based) for solid phase extraction and microextraction techniques in speciation analysis of some metals and metalloids (As, Cr, Sb, Se). Emphasis will be placed on the presentation of the most representative works published in the last five years (2015-2019).

Nanotechnology-based sorption and membrane technologies for the treatment of petroleum-based pollutants in natural ecosystems and wastewater streams

Petroleum processing wastewater (PPW) is a complex mixture of free, soluble, and emulsive hydrocarbons that often contain heavy metals and/or solid particles. As these hazardous constituents can accumulate in human beings and the environment, exposure to the PPW can have harmful effects in various respects. The use of environmental nanotechnologies (E-Nano) is considered an attractive option to resolve the problems associated with PPW. Among different treatment technologies, E-Nano-based sorption (adsorption/absorption) and membrane filtration approaches have been proven to have outstanding efficacy in remediation of PPW pollutants. It is, however, crucial to determine the appropriate technological option (e.g., low-cost operational conditions) for the practical application of such technologies. In this review, the potential of E-Nano-based sorption and membrane technologies in the treatment of various PPW pollutants is discussed based on their performances in comparison to traditional technologies. Their suitability is evaluated further in relation to their merits/disadvantages and economic feasibility with the goal of constructing a perspective map to efficiently implement the E-Nano technologies.

Polymeric ion exchanger supported ferric oxide nanoparticles as adsorbents for toxic metal ions from aqueous solutions and acid mine drainage

BACKGROUND

Acid mine drainage (AMD) is a worldwide industrial pollution of grave concern. AMD pollutes both water sources and the environment at large with dissolved toxic metals which are detrimental to human health. This paper reports on the preparation of polymeric ion exchange resins decorated with hydrated iron oxides and their application for the ecological removal of toxic metals ions from AMD.

METHODS

The hydrated iron oxide particles were incorporated within commercial chelating ion exchange resins using the precipitation method. The synthesised hybrid resins were then characterized using appropriate spectroscopic and solid-state techniques. The metal ion levels were measured using the inductively coupled plasma-optical emission spectrometer (ICP-OES). The optimization of contact time, pH, and adsorbent dosage were conducted to enhance the efficiency of adsorption of toxic metals onto the hybrid organic/inorganic nanosorbents. Kinetics and adsorption isotherms were constructed to study the adsorption mechanisms of the adsorbents.

RESULTS

The results showed that the dispersed Fe-O is hydrated and amorphous within the hybrid materials. The adsorption kinetics followed the pseudo-second-order shown by the high R² values. The hybrid adsorbents were finally tested on environmental AMD samples and were able to remove toxic metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn at various removal degrees.

CONCLUSION

Solution pH played a crucial role in the adsorption of toxic metals on hybrid iron oxide adsorbents. The hybrid TP-260 HFO had higher affinity for toxic metals than other prepared adsorbents thus has a potential for acidic mine water pollution remediation. The adsorbed Al(III) can be recovered using NaCl-NaOH binary solution from the loaded resins.

Effective and reusable nano-silica synthesized from barley and wheat grass for the removal of nickel from agricultural wastewater

In the present study, a comparative analysis was performed on the extraction of nickel ions (Ni²⁺) from agricultural wastewater using nanosilica (NS) synthesized from barley (NS-B) and wheat (NS-W) grass waste with a yield of 92.4%. The experimental procedure was conducted on barley and wheat waste to obtain an 85% pure NS that served as the adsorbent for nickel extraction in wastewater. The NS was characterized and studied using X-ray fluorescence (XRF), which demonstrated that NS synthesized from barley contained 94.2% SiO₂, while NS synthesized from wheat contained 93.0% SiO₂. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to determine the surface morphology of the nanoparticles. The energy-dispersive X-ray (EDX) analysis and Fourier transform infrared (FTIR) analysis were used to determine the elements and functional groups of the synthesized particles, respectively. Lastly, particle size and surface area analyses were performed using the Brunauer-Emmett-Teller (BET) method, which determined that the nanoparticles were 70 and 102 nm for NS-B and NS-W, respectively. The adsorption of nickel ions from agricultural wastewater was studied at various concentrations (10-200 mg/L). The kinetic models indicate that sorption equilibrium time was 65 min and that the reaction followed the pseudo-first-order kinetics model with a regression coefficient (R²) of 0.9289. Corresponding studies indicated that the Freundlich isotherms best describe the sorption reaction with an R² value of 0.9958, which indicates the multilayer adsorption of nickel on the adsorbent. In their standard and real states, the samples indicated that NS-B and NS-W provided high levels of nickel (Ni²⁺) removal at 95 and 90%, respectively.

Efficient removal of Cd(II), Cu(II), Pb(II), and Zn(II) from wastewater and natural water using submersible device

In this study, a simple submersible device was tested to remove and recover Cd(II), Cu(II), Pb(II), and Zn(II) from model wastewater and real natural water. To obtain this device, fine particles (< 0.1 mm) of a new hybrid adsorbent based on the mesoporous carbon and Fenton-modified humic acids were fixed onto a highly porous polymeric matrix. The hybrid adsorbent was characterized by various methods. The main mechanism for Cd(II), Cu(II), Pb(II), and Zn(II) adsorption by the hybrid adsorbent is chemosorption by surface functional groups, the total concentration of which was found to be 1.56 mmol g^-1. The adsorption capacity depends on pH, and at pH 6.0, it has the following order (mmol g^-1): Cu(II) (1.14) > Pb(II) (0.86) > Zn(II) (0.59) > Cd(II) (0.50). The possibility of applying a submersible device for the removal and recovery of these metals from multi-metal wastewaters and reservoirs was studied. A high efficiency of metal removal (95-99.9%) and recovery (85-99%) from wastewater remained in at least six consecutive adsorption-desorption cycles. Effective removal of metals from the water of a contaminated reservoir contributed to the rapid restoration of the phytoplankton organisms after their oppression by metals. Thus, the use of a submerged device with the new hybrid adsorbent can be an effective way of remediating wastewaters and natural waters contaminated with metals.

Nanomaterials as versatile adsorbents for heavy metal ions in water: a review

Over the years, heavy metal pollution has become a very serious environmental problem worldwide. Even though anthropogenic sources are believed to be the major cause of heavy metal pollution, they can also be introduced into the environment from natural geogenic sources. Heavy metals, because of their toxicity and carcinogenicity, are considered to be the most harmful contaminants of groundwater as well as surface water, a serious threat to both human and aquatic life. Nanomaterials due to their size and higher surface area to volume ratio show some unique properties compared to their bulk counterpart and have drawn significant attention of the scientific community in the last few decades. This large surface area can make these materials as effective adsorbents in pollution remediation studies. In this review, an attempt has been made to focus on the applicability of different types of nanomaterials, such as clay-nanocomposites, metal oxide-based nanomaterials, carbon nanotubes, and various polymeric nanocomposites as adsorbents for removal of variety of heavy metals, such as As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, U, V, and Zn, from water as reported during the last few years. This work tries to analyze the metal-nanomaterial interactions, the mechanism of adsorption, the adsorption capacities of the nanomaterials, and the kinetics of adsorption under various experimental conditions. The review brings forward the relation between the physicochemical properties of the nanomaterials and heavy metal adsorption on them.