Heavy Metal Adsorption Capacity Research Articles

A review of hydroxyapatite synthesis for heavy metal adsorption assisted by machine learning.

Heavy metals (HMs) represent a persistent and significant threat to aquatic ecosystems. Hydroxyapatite (HAp) has emerged as a utilized material in the remediation of environmental HMs, owing to its exceptionally high porosity, expansive surface area, and the presence of three-dimensional ordered channels. An in-depth study of the synthesis strategy of HAp and its adsorption properties can help reduce the cost of remediating HMs in aquatic environments and alleviate the water shortage. In this paper, we reviewed 466 works of literature on the adsorption of heavy metals by HAp based on the Web of Science database between 2013 and 2023 that focused on the adsorption of heavy metals by HAp. We meticulously synthesized the findings related to the synthesis conditions-namely precipitation, hydrothermal, and calcination-as well as the characterization parameters and the adsorption capacity of HAp for heavy metals such as Pb2+, Cd2+, Cu2+, Zn2+, and Ni2+. Synthesizing advanced materials by reducing the number of experiments is essential to accelerate material development. Machine learning (ML) holds significant promise in material discovery and performance enhancement. We have consolidated the qualitative and quantitative relationships between HAp synthesis conditions, characterization parameters, and heavy metal adsorption capacity across previous studies, utilizing both the Statistical Package for Social Sciences (SPSS) and ML techniques. Building on the most recognized heavy metal adsorption mechanisms, we have evaluated the influence of characterization parameters on adsorption performance. We have outlined the optimal synthetic conditions for enhancing the adsorption of Pb2+, Cd2+, Cu2+, Zn2+, and Ni2+ through precipitation, hydrothermal, and calcination methods, offering a practical guide for the targeted synthesis of HAp tailored to specific heavy metal adsorption capacities.

Structural Characterization and Antioxidant Activity of Exopolysaccharide Produced from Beet Waste Residue by Leuconostoc pseudomesenteroides

Lactic acid bacteria exopolysaccharide (EPS) is a large molecular polymer produced during the growth and metabolism of lactic acid bacteria. EPS has multiple biological functions and is widely used in fields such as food and medicine. However, the low yield and high production cost of EPS derived from lactic acid bacteria limit its widespread application. In this study, we used beet waste residue as a substrate to produce EPS by fermentation with Leuconostoc pseudomesenteroides to improve the utilization rate of agricultural waste and reduce the production cost of lactic acid bacterial EPS. After purification, the molecular weight (Mw) of EPS was determined to be 417 kDa using high-performance size exclusion chromatography (HPSEC). High-performance liquid chromatography (HPLC), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy revealed that the EPS was composed of glucose subunits with α-1,6 glycosidic linkages. The thermal analysis and heavy metal adsorption capacity revealed a relatively high degradation temperature of 315.54 °C and that the material could effectively adsorb Cu2+. Additionally, the findings indicated that the EPS exhibited a significant ability to neutralize free radicals, a property that was found to be concentration dependent. Furthermore, the results of the intracellular study showed the protective effect of freshly isolated EPS on tBHP-induced cellular oxidative stress at a concentration of 50 µg/mL. These results suggest that the EPS from L. pseudomesenteroides may be developed as antioxidant agents for functional food products and pharmaceutical applications due to its capacity to scavenge free radicals.

Manganese-modified biochar for sediment remediation: Effect, microbial community response, and mechanism

Heavy metal sediment pollution has become an increasingly serious problem associated with industrial development, so extensive studies have been conducted concerning their removal. Biochar has recently shown good potential for in-situ remediation of heavy metal-contaminated sediments. The heavy metal adsorption capacity of inexpensive biochar can be improved by loading it with metal oxides. In this study, manganese-modified biochar (MBC) was prepared by KMnO4-modified waste-activated sludge biochar and applied to immobilize Pb and Cd in sediments. Its effects on the sediment microbial community were also investigated. The Results showed that manganese modification of the biochar made it more conducive to the adsorption of heavy metals, owing to its higher specific surface area and graphitization structure, more active sites and oxygen-containing groups, and the presence of Mn2O3 crystal structure on the surface. The maximum adsorption capacities of this material for Pb2+ and Cd2+ in solution were 176.9 mg/g and 44.0 mg/g, respectively. The application of MBC to the remediation of heavy metal-contaminated sediments transformed Pb and Cd in the sediments from exchangeable to residual state. The F4 content of Pb in the sediments increased from 40.52%-42.36% to 49.11%–51.14% after application of 1% MBC, and to 63.94%–64.49% after application of 5% MBC. Correspondingly, the F1 content of Pb in the sediments decreased from 29.09%-30.68% to 17.43%–17.69% after the application of 5% MBC. Furthermore, MBC efficiently enriched the microbial biodiversity and affected the microbial population structure within 60 days. The relative abundance of uncultured f Symbiobacteraceae and Fonticella communities significantly increased after incubation. The results may provide empirical support for the combination of metal oxides and biochar for the remediation of heavy metal-contaminated sediments.

Cost-Effective Synthesis of MXene Cadmium Sulfide (CdS) for Heavy Metal Removal.

Background Environmental contamination resulting from the release of untreated industrial wastewater has emerged as a critical worldwide issue. These effluents frequently have high levels of heavy metals and antibiotics, which are bad for aquatic ecosystems and human health. Oftentimes, conventional wastewater treatment techniques fall short of effectively eliminating these pollutants. Innovative materials that may efficiently absorb or break down contaminants from contaminated water sources are, therefore, desperately needed. Hydrothermally produced MXene cadmium sulfide (CdS) composites have shown great promise as an adsorbent material because of their special qualities, which include high surface area, chemical stability, and customizable surface functions that improve their adsorption capacity for heavy metals and antibiotics alike. Aim The aim of this study is to produce MXene-CdS nanoparticles in a cost-effective method for the simultaneous removal of heavy metals from aqueous contaminants for water pollution control. Methods and materials MXenes were synthesized by selectively etching Ti3AlC2 MAX-phase ceramics using aqueous HF. CdS nanoparticles were synthesized separately and integrated with MXenes via a hydrothermal process. The resulting MXene CdS nanocomposites were characterized using scanning electron microscopy (SEM) for morphology, energy dispersion spectrum (EDS) for elemental composition, X-ray diffraction(XRD) study for phase identification, and removal of heavy metals viaMXene CdS. Results Consistent distribution of CdS nanoparticles on the MXene surface and the creation of MXene CdS nanomembranes with a well-defined shape were observed by SEM analysis. Ti, C, Cd, and S elements, indiciaries of a successful composite formation, were confirmed to be present by EDS. The crystalline structure of both the MXene and CdS phases was confirmed by the distinctive peaks seen in the XRD patterns. MXene-CdS composites facilitate the effective removal of chromium ions from contaminated water. The excellent hydrophilicity of the produced nanomembrane allowed for effective interaction with watery contaminants. Conclusion This study showcases the successful synthesis and characterization of MXene-CdS nanocomposites for environmental remediation, particularly in removing toxic metals like chromium from industrial effluents. SEM analysis confirmed the uniform distribution of CdS nanoparticles on the MXene surface, while elemental composition validated their integration. XRD analysis confirmed the crystalline structures of both components. The nanocomposite exhibited excellent hydrophilicity, enhancing the efficient adsorption of heavy metals. Its large surface area and chemical stability contribute to high adsorption efficiency, making it ideal for wastewater treatment. The scalable synthesis process supports practical applications. This research highlights MXene-CdS nanocomposites as a cost-effective, sustainable solution for water pollution control.

Optimization of extracellular polysaccharides (EPS) production by Stenotrophomonas rhizophila JC1 and its protective effect on alfalfa under Pb2+ stress

Stenotrophomonas rhizophila JC1 and its extracellular polysaccharides (EPS) have been shown to effectively adsorb heavy metals in previous studies. The fermentation conditions of EPS by S. rhizophila JC1 were optimized using the Box-Behnken design (BBD). The composition, structural characteristics, and heavy metal adsorption capacity of EPS were systematically evaluated. The alleviation mechanism of Pb2+ stress on alfalfa was investigated through EPS inoculation. The maximum EPS yield reached 0.313 %. EPS consisted of glucose, glucosamine, galactose, and mannose in a molar ratio of 12.20:1:22.29:1.68. EPS also contained four distinct polymers with molecular weights of 623,683.71 Da, 144,072.27 Da, 105,892.21 Da, and 51,094.79 Da. The adsorption processes conformed to the pseudo-second-order model and Langmuir isotherm model. High Pb2+ concentrations significantly reduced germination percentage, germinative force, root length, fresh weight, and soluble protein, inhibited photosynthesis, exacerbated oxidative stress, and caused damage to the antioxidant system, thereby inhibiting seedling growth. EPS at low concentrations can promote alfalfa seed germination and mitigate Pb2+ stress by reducing the aforementioned damage. This study highlights the potential of EPS in soil remediation and enhancing plant resistance to heavy metal stress.

Insight into biochar as sustainable biomass: Production methods, characteristics, and environmental remediation

Industrialization has contributed significantly to the advancement and sustenance of human civilization. However, it has also posed serious challenges to environmental sustainability, notably through heavy metal pollution, which has severely impacted ecological systems. Recent studies have explored the use of biochar for the removal of heavy metals from aqueous solutions. This review underscores the diverse physicochemical and structural characteristics of biochar, derived from various biomass sources through different pyrolysis processes, and their varying adsorption efficiencies. The review aims to investigate current biochar production technologies, their unique properties, and their maximum removal efficiency and adsorption capacity for heavy metals. The primary adsorption mechanisms, adsorption isotherms, and kinetic models have been identified. Furthermore, the study confirms that optimal conditions—such as the choice of precursors, pyrolysis temperature, and an understanding of the advantages and limitations—are crucial for designing biochar with superior structural and physicochemical properties. This review provides an updated overview of biochar-based heavy metal treatment in aquatic systems, highlighting existing research gaps and suggesting future research directions.

Synthesis and characterization of chitosan Schiff base grafted with formaldehyde and aminoethanol: As an effective adsorbent for removal of Pb(II), Hg(II), and Cu(II) ions from aqueous media

Grafted chitosan materials show the characteristics of high stability, easy separation and recovery, and good heavy metal adsorption capacity, and have received much attention in the adsorption process. Therefore, in this work, novel grafted chitosan-based adsorbent CS-EHBSB@F-AE was prepared by a one-pot reaction of chitosan (CS), 3-ethoxy-4-hydroxybenzaldehyde (EHB), formaldehyde (F) and aminoethanol (F). The microstructure and morphology of the as-prepared composite CS-EHBSB@F-AE were characterized by FT-IR, TGA, DSC, FE-SEM, and BET analyses. The adsorption performance of the as-prepared CS-EHBSB@F-AE composite on Pb(II), Hg(II), and Cu(II) ions from aqueous was investigated using batch experiment and the effects of the initial pH of the solution, contact time, and initial metal ions concentration and temperature on the adsorption efficiency were investigated and discussed. At the best conditions, CS-EHBSB@F-AE exhibited remarkable adsorption capacity of 246.7 mg/g, 203.9 mg/g, and 234.4 mg/g in absorbing Pb(II), Hg(II), and Cu(II), respectively. The adsorption equilibrium and the kinetic studies confirmed that the ions adsorption process fits well with the Langmuir isotherm and pseudo-second-order (PSO) models. Additionally, the adsorption efficiency of Pb(II), Hg(II), and Cu(II) metal ions by the composite CS-EHBSB@F-AE was reduced by increasing the temperature from 298 K to 318 K. In addition, after the sixth ads/des cycles, the as-prepared adsorbent still exhibited high removal efficiency with a decrease in adsorption efficiency of Pb(II) (5.53 %), Hg(II) (15.43 %) and Cu(II) (8.27 %). Finally, we proposed that the ions adsorption by CS-EHBSB@F-AE has happened using the coordination of active groups containing nitrogen and oxygen atoms on the surface of the adsorbent with the Pb(II), Hg(II), and Cu(II) metal ions.

Remediation of Arsenic and Heavy Metals and Soil Stabilization by Waste Chitosan based Biochar

Objectives : This study aims to evaluate the feasibility of converting waste chitosan adsorbents, laden with microalgae, into biochar for application as a stabilizing agent to remediate heavy metal-contaminated soil and improve soil quality.Methods : Waste chitosan adsorbents were converted into biochar through two processes: dry thermal carbonization at 400°C to produce pyrochar and hydrothermal carbonization at 200°C to produce hydrochar. The elemental compositions, surface functional groups, morphologies of the biochars were evaluated by elemental analyzer, FT-IR spectrometer, and SEM analysis. The arsenic and heavy metal adsorption characteristics of the produced biochars were assessed. Additionally, the produced biochars were applied as stabilizing agents to arsenic and heavy metal-contaminated soil with varying mixing ratios of 2, 5 and 10 wt%. After a one-week soil stabilization experiment, soil properties and TCLP(Toxicity Characteristic Leaching Procedure) leaching tests were conducted.Results and Discussion : The pyrochar produced from waste chitosan exhibited a porous structure with high pH (pH 10) and minimal surface functional groups. The hydrochar consisted of spherical particles with functional groups such as hydroxyl and amine groups on the surface, exhibiting a slightly acidic pH of 5.8. Pyrochar has a higher adsorption capacity for cationic heavy metals compared to hydrochar due to its porous structure and high pH. On the other hand, when applied to soil, hydrochar demonstrated superior stabilization efficiency for arsenic and heavy metals. This is attributed to the diverse surface functional groups containing oxygen on the hydrochar. The stabilization efficiency was influenced by the biochar mixing ratio, with a 5% hydrochar application resulting in 10-64% stabilization efficiency for all elements.Conclusion : This study confirmed that biochar produced from waste chitosan effectively stabilizes arsenic and heavy metals in soils. Additionally, the quantity of biochar used can impact its effectiveness in stabilization.

Adsorption behavior of heavy metals onto microplastics derived from conventional and biodegradable commercial plastic products

This study extensively explored the adsorption behavior of heavy metals (Pb+2, Ni+2, Cu+2, Zn+2, and Cd+2) onto microplastics (MPs). The particle sizes of MPs ranged from 0.149 to 0.25 mm. The microplastics were generated from commercial products manufactured from both conventional (polyethylene (PE) bottle, polystyrene (PS) spoon, and polyethylene terephthalate (PET) egg carton) and biodegradable (polylactic acid (PLA) spoon, and polylactic acid (PLA) egg carton) plastics. The study also considered the influence of solution pH on the adsorption capacity of heavy metals. Regarding the adsorption potential for Cu+2, the ranking was as follows: PLA-egg (1408 μg·g−1) > PLA-spoon (735 μg·g−1) > PE-bottle (315 μg·g−1) > PET-egg (283 μg·g−1) > PS-spoon (237 μg·g−1). PLA MPs showed the highest adsorption capacity due to the lower thermal stability and higher presence of surface oxygen functional groups. Moreover, the adsorption capacities of the five metals onto PLA-spoon and PLA-egg decreased in the following order: Pb (1785 μg·g−1) > Zn (1267 μg·g−1) > Cd (748 μg·g−1) > Cu (735 μg·g−1) > Ni (722 μg·g−1), and Pb (1520 μg·g−1) > Ni (1412 μg·g−1) > Cu (1408 μg·g−1) > Zn (1118 μg·g−1) > Cd (423 μg·g−1), respectively. The SEM-EDS, FTIR and XPS results demonstrated that surface oxygen-containing functional groups play an important role during the adsorption process. This study extended its analysis to quantify the metal content of the post-adsorption MPs, revealing uneven adsorption of heavy metals onto the MPs. This implies that the diversity of commercial plastic products may result in significant variations in their ability to adsorb heavy metals, underscoring the importance of effectively managing discarded commercial plastic products.

Effects of Gamma-Synthesized Chitosan on Morphological, Thermal, Mechanical, and Heavy-Metal Removal Properties in Natural Rubber Foam as Sustainable and Eco-Friendly Heavy Metal Sorbents

The properties of natural rubber foam (NRF) containing gamma-synthesized chitosan (CS) powder were investigated to address the growing demand for efficient methods to treat industrial wastewater contaminated with heavy metals. The CS powder was prepared by irradiating chitin (CT) powder with varying doses of gamma rays (0–100 kGy), followed by deacetylation using 40% sodium hydroxide (NaOH) at 100 °C for 1 h. The resulting CS powders were then mixed with natural rubber latex (NRL) at different contents (0, 3, 6, and 9 parts per hundred parts of rubber by weight; phr) and processed using Dunlop techniques to prepare the foam samples. The experimental findings indicated that the degree of deacetylation (%DD) of the CS powder increased initially with gamma doses up to 60 kGy but then decreased at 80 and 100 kGy. In addition, when the CS powder was incorporated into the NRF samples, there were increases in total surface area, density, compression set, and hardness (shore OO), with increasing gamma doses and CS contents. Furthermore, the determination of heavy metal adsorption properties for Cu, Pb, Zn, and Cd showed that the developed NRF sample exhibited high adsorption capacities. For instance, their removal efficiencies reached 94.9%, 82.5%, 91.4%, and 97.0%, respectively, in NRF containing 9 phr of 60 kGy CS. Notably, all adsorption measurements were determined using 3 cm × 3 cm × 2.5 cm specimens submerged in respective metal solutions, with an initial concentration of 25 mg/L. However, the removal capacity per unit mass of the sample (mg/g) showed less dependencies on CS contents, probably due to the higher density of CS/NRF composites in comparison to pristine NRF, resulting in a smaller volume of the former being submerged in the solution, subsequently suppressing the effects from CS in the adsorption. Lastly, tests on the reusability of the developed NRF indicated that the samples could be reused for up to three cycles, with the Cu removal capacity remaining relatively high (83%) in the sample containing 9 phr of 60 kGy CS. The overall outcomes implied that the developed NRF with the addition of gamma-synthesized CS not only offered effective and eco-friendly heavy metal adsorption capacity to improve public health safety and the environment from industrial wastewater but also promoted greener and safer procedures for the synthesis/modification of similar substances through radiation technologies.

Competitive sequestration behavior and mechanism of Cd2+, Pb2+and Ni2+ ions from single, binary and ternary metal laden solution by Hevea brasiliensis wood sawdust (HBS)

HeveaBrasiliensis wood sawdust (HBS), a lignocellulosic material, was employed for the eradication of Cd(II), Pb(II), and Ni(II) from synthetic single and multi-metalsystem. In the realm of multimetal adsorption, HBS exhibited the most substantial adsorption capacities for heavy metals, in the order: Pb(II) > Cd(II) > Ni(II). Experiments involving batch process were carried out to explore the rolesofpH, contact duration, HBS quantity, and preliminary metal concentrations on the adsorption capacity. Optimal conditions for biosorption of metal ions were determined as pH 5.0, dosage of 7 gL−1, and an equilibrium time of 90 min. The pseudo-second-order kinetics andLangmuirisotherm had a favorable alignment with the biosorption of all individual metal ions. Adsorption capacity was 8.45, 13.01 and 6.04 mg g− 1 for Cd, Pb and Ni respectively in single metal system. In binary and ternary system the capacity and adsorption percentages decreases significantly due the presence of competitive metal ions. HBS demonstrated effectiveness in treating real wastewater containing Cd2+, Pb2+and Ni2+ ionsin both single and mixed metal solutions, highlighting the necessity of thoroughly considering the impact of competitive adsorption. SEM with EDS results indicated single metal fixing in a multi-ion solution followed complex mechanisms. The surface area and functional group studies were conducted utilizing BET and a FTIR Spectrometer. Electrostatic attraction and complexation mechanisms were identified as responsible factor for capturing metal ions to the active surfaces of the bio sorbent. Cost analysis reflected the adsorbent cost was $0.021 per liter of mixed contaminated ternary effluent (30 mg L−1).

Mechanism of Biological Transport and Transformation of Copper, Cadmium, and Zinc in Water by Chlorella

This study investigates the effectiveness of Chlorella vulgaris in treating copper, cadmium, and zinc in aqueous solutions; the aim of this study was to examine the effects of various factors on the adsorption capacity of Chlorella in water. This study explored the intra- and extracellular adsorption and accumulation patterns of copper (Cu(II)), cadmium (Cd(II)), and zinc (Zn(II)), revealing their molecular response mechanisms under the most suitable conditions. The adsorption capacity of Chlorella to Cu(II), Cd(II), and Zn(II) in water was 93.63%, 73.45%, and 85.41%, respectively. The adsorption mechanism for heavy metals is governed by both intracellular and extracellular diffusion, with intracellular absorption serving as a supplement and external uptake predominating. XRD, XPS, FTIR, SEM-EDX, and TEM-EDX analyses showed that there would be the formation of precipitates such as Cu2S, CuS2, CdS, and ZnSO4. The adsorption of Cu(II) involves its simultaneous reduction to Cu(I). Moreover, specific functional groups present on the cellular surface, such as amino, carboxyl, aldehyde, and ether groups, interact with heavy metal ions. In view of its efficient heavy metal adsorption capacity and biosafety, this study recommends Chlorella as a potential biosorbent for the bioremediation and environmental treatment of heavy metal contaminated water in the future.

Montmorillonite Clay as an Adsorbent for the Remediation of Cd (II) Ions in Aqueous Solutions: A Comparison With Pb (II) Ions

ABSTRACTHeavy metal ions are hazardous to both human health and the environment. Montmorillonite (MMT) clay has recently piqued interest for its adsorption capacity of heavy metals and its use in controlling contaminants, in particular in surface and waste waters. This research sheds light on the possibility of the application of natural Albanian MMT clay from the Prrenjas Region of Albania as an adsorbent of Cd (II) ions in aqueous solutions, making a comparison with the capacity of such clay for the adsorption of Pb (II) ions. The set of variables studied included concentrations of metal ions, amount of clay pH, time, and temperature of interaction and adsorption process (all of them following batch technique), and optimal conditions have been determined. The adsorption capacity of natural clay for Cd (II) ions was 6.735 mg/g, as compared to 17.9 mg/g for Pb (II) ions. Langmuir and Freundlich isotherms were applied to evaluate the mode of adsorption with results showing that all isotherms are linear and the Langmuir model fitted better with the experimental data. It is determined that the adsorption of Cd (II), similar to that of Pb (II), is well‐fitted by the second‐order reaction kinetic following the Lagergen model. The results demonstrate good potentiality for Prrenjas MMT as a low‐cost adsorbent to remove Cd (II) from aqueous systems, in particular, for wastewater treatment.

Hydrochar Production Methods: Comparative Insights into Hydrothermal and Microwave Processes

This study compares hydrochar production from agricultural waste using conventional hydrothermal carbonization (HTC) and microwave-assisted carbonization methods. Wheat straw (HWS), rice straw (HRS), and bagasse (HBG) were used as feedstocks. Microwave-assisted carbonization resulted in higher yields and distinct chemical structures compared to conventional HTC. Microwave hydrochars (m-HWS, m-HRS, mHBG) showed lower surface areas but increased pore volumes and thermal stability. They also exhibited enhanced heavy metal adsorption capacities, particularly at higher pH levels. These findings highlight the advantages of microwave-assisted carbonization for producing hydrochar with superior properties, offering insights for optimizing production processes and expanding applications.

Synthesis of CS-Fe3O4/GO nanocomposite for adsorption of heavy metal in aqueous environment

In this study, magnetic material based on graphene oxide (GO) was developed for enhanced adsorption capacity for heavy metals. The Fe3O4 nanoparticles were combined with the GO material using a chitosan (CS) binder to obtain the CS-Fe3O4/GO nanocomposite. The adsorption capacity of this nanocomposite was evaluated by removing heavy metals including Ni2+ ions. When GO was composed with Fe3O4 and CS, the GO films were densely covered with ferromagnetic particles, which were bound and densely distributed on the GO film surface due to the interaction between GO and CS. The optimal conditions for the complexation of Ni2+ and 4-(2-pyridyl azo)-rezoxine (PAR) are 1 ml Ni2+, 2 ml PAR 100 mg l−1, pH = 6 (adjusted with 0.7 ml of the 0.1 M K2HPO4 solution) and a complexation time of 20 min. After 50 min of adsorption, the Ni2+ removal efficiency of the CS-Fe3O4/GO nanocomposite reached 81.21% and the corresponding adsorption capacity was 2.03 mg g−1 . The Ni2+ removal process followed the first-order model and Freundlich isotherm. This process was spontaneous (ΔG o < 0) and an exothermic process (ΔH o = −1128.875 J·mol−1). In addition, the factors affecting this process were investigated, including the pH solution, the dosage of the CS-Fe3O4/GO nanocomposite and the initial Ni2+ concentration. The CS-Fe3O4/GO nanocomposite showed a potential adsorption capacity in removing Ni2+ at low concentrations from wastewater.

Synthesis of reduced graphene oxide and its application for the removal of anaionic dye TURQUOISE GN

Although graphene oxide (GO) and its derivatives showed excellent adsorption capacities for dyes and heavy metals, its application is limited to cationic and commercially used dyes. In this article reduced graphene oxide (RGO) was prepared and applied for the adsorption of a commercially used anionic dye. GO was prepared from graphite powder by modified Hummer’s method and reduced to RGO by hydrazine hydrate. Characterization of prepared RGO was carried out by Raman spectroscopy, ESEM, XRD, elemental analysis and the surface charge was determined by zeta potential analysis. An anionic dye TURQUOISE GN (TGN) was used to investigate the adsorption capacity of prepared RGO. To know the adsorption properties of RGO, the effects of solution pH, dosage of adsorbent, concentration of the dye, adsorption time and temperature on adsorption capacity of RGO were also studied. The distribution of the adsorbate on the RGO surface was studied with both Langmuir and Freundlich isotherm models and it was found that it preferably followed Langmuir model. The theoretical maximum adsorption capacity was found to be 588.24 mg/g at pH 7. To find out the mechanism of the adsorption of TGN on RGO pseudo-first-order and pseudo-second order kinetic models were applied and the results fitted perfectly with the second-order kinetic model. The exhausted RGO was regenerated by treating with 2 % HCl followed by washing with demineralized water and showed moderate adsorption capacity.

Study on Adsorption of Cd in Solution and Soil by Modified Biochar-Calcium Alginate Hydrogel.

Contamination with cadmium (Cd) is a prominent issue in agricultural non-point source pollution in China. With the deposition and activation of numerous Cd metal elements in farmland, the problem of excessive pollution of agricultural produce can no longer be disregarded. Considering the issue of Cd pollution in farmland, this study proposes the utilization of cross-linked modified biochar (prepared from pine wood) and calcium alginate hydrogels to fabricate a composite material which is called MB-CA for short. The aim is to investigate the adsorption and passivation mechanism of soil Cd by this innovative composite. The MB-CA exhibits a higher heavy metal adsorption capacity compared to traditional biochar and hydrogel due to its increased oxygen-containing functional groups and heavy metal adsorption sites. In the Cd solution adsorption experiment, the highest Cd2+ removal rate reached 85.48%. In addition, it was found that the material also has an excellent pH improvement effect. Through the adsorption kinetics experiment and the soil culture experiments, it was determined that MB-CA adheres to the quasi-second-order kinetic model and is capable of adsorbing 35.94% of Cd2+ in soil. This study validates the efficacy of MB-CA in the adsorption and passivation of Cd in soil, offering a novel approach for managing Cd-contaminated cultivated land.

Enhanced heavy metal adsorption capacity of surface-functionalized Philippine natural zeolite in simulated wastewater

The adsorption efficiency of surface-functionalized Philippine natural zeolite (PNZ) for heavy metal uptake from single and mixed metal ion-simulated wastewater solution is reported in this work. Atomic adsorption spectroscopy (AAS) findings revealed that NaCl-modified PNZ (MPNZ) exhibited the highest zinc ion adsorption of 99.96 % while PNZ yielded an adsorption of 95.61 %. The adsorption isotherms of raw PNZ and MPNZ both show similar shapes that reflect Type IV adsorption-desorption isotherms with Type H2 hysteresis loop which can be observed for micro-mesoporous materials (pore containing 2–50 nm). An increase in PNZ pore size from 10.11 nm to 13.36 nm for NaCl-PNZ and 15.59 for NaOH-PNZ is observed after alkaline treatment. EDS confirmed the decrease in Si/Al ratio from 4.02 to 3.76, indicative of possible higher negative charge in the PNZ framework which is favorable for an enhanced Coulombic or electrostatic interaction with the cationic heavy metals being detected in this study. MPNZ demonstrated an adsorption capacity of 99.96 % for copper in mixed-ion solution while 88.49 % and 86.67 % were obtained for zinc and nickel, respectively. These values are higher compared to PNZ having only 32.21 % uptake for zinc and 38.00 % for nickel. A hierarchy of the average metal adsorption capacity showed the order: copper > nickel > zinc. Rapid adsorption at the first hour of the adsorption reaction was attained in all solutions while samples with pH 9 exhibited the highest Ni2+ and Zn2+ percent removal. Moreover, the increase in initial solution concentration led to lower adsorption efficiency and the maximum uptake was attained at 100 ppm. The equilibrium data of adsorption and mechanism were suitably described by Langmuir isotherm model. With these, surface functionalization of PNZ has further enhanced its cationic adsorption capacity on heavy metals in both single and mixed-ion solution having promising potential for wastewater remediation.

Application and mechanism of carbonate material in the treatment of heavy metal pollution: a review.

Among the many heavy metal pollution treatment agents, carbonate materials show strong flexibility and versatility by virtue of their high adsorption capacity for heavy metals and the characteristics of multiple and simple modification methods. It shows good potential for development. This review summarizes the application of carbonate materials in the treatment of heavy metal pollution according to the research of other scholars. It mainly relates to the application of surface-modified, activated, and nano-sized carbonate materials in the treatment of heavy metal pollution in water. Natural carbonate minerals and composite carbonate minerals solidify and stabilize heavy metals in soil. Solidification of heavy metals in hazardous waste solids is by MICP. There are four aspects of calcium carbonate oligomers curing heavy metals in fly ash from waste incineration. The mechanism of treating heavy metals by carbonate in different media was discussed. However, in the complex environment where multiple types of pollutants coexist, questions on how to maintain the efficient processing capacity of carbonate materials and how to use MICP to integrate heavy metal fixation and seepage prevention in solid waste base under complex and changeable natural environment deserve our further consideration. In addition, the use of carbonate materials for the purification of trace radioactive wastewater and the safe treatment of trace radioactive solid waste are also worthy of further exploration.

Mesoporous Mg–Al–Ti composite oxide incorporated mixed matrix ultrafiltration membrane with superior multi-heavy metal removal capacity, anti-fouling & anti-microbial property

Mesoporous Mg–Al–Ti ternary composite oxide nano-adsorbents have demonstrated an exceptional performance to remove multiple heavy metals (As, Pb, Cd, Cr). Incorporation of these nanoparticles (NPs) in polysulfone membrane created a multifunctional mixed matrix membrane (MMM) with heavy metal adsorption capacity (both cationic and anionic species), enhanced hydrophilicity, anti-fouling property, and anti-microbial activity. The best heavy metal removal performance was shown by the membrane incorporated with 0.8 wt% NPs. Hydrophilicity improvement was studied through the decrease in water contact angle from 71° to 57° and surface probing using atomic force microscopy (AFM). With a maximum As(III) adsorption capacity of 256.6 mg/g, the membrane had a breakthrough volume of 25L and could provide safe drinking water for 19 h from a real Arsenic (As) contaminated groundwater sample with a flux of 48 l/m2-h. Beyond that, >90 % removal of Cd, Pb & Cr was also observed with maximum adsorption capacity of 652.9 mg/g, 332.5 mg/g, and 89.4 mg/g respectively. 92.5 % flux recovery after filtering a 1000 ppm bovine serum albumin showed the anti-fouling property. Successful inhibition of both gram-positive and gram-negative bacterial growth, and >99.99 % removal of colony forming units (CFU/ml) in the filtration process confirmed the anti-microbial resistance. With its multifunctionality, these membranes hold great potential for practical water treatment applications.