Adsorption behavior of heavy metal ions on a polymer-immobilized amphoteric biosorbent: Surface interaction assessment

Smart paper-based materials incorporating nitrogen and boron co-doped MXene quantum dots for rapid adsorption and sensitive detection of Cr2O72. J Colloid Interface Sci 2024;679:510-520. [PMID: 39378686 DOI: 10.1016/j.jcis.2024.10.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Dichromate ion (Cr2O72-) is a highly toxic chromium-containing compound that poses significant hazards to the digestive, respiratory systems, skin, and mucous membranes. Currently, the detection and adsorption of Cr2O72- face significant challenges, including the time-consuming and low sensitivity nature of traditional analytical methods. The limited efficiency and capacity of existing adsorbents hinder their practical application in real-time water quality monitoring and environmental remediation. Herein, using polyethyleneimine-functionalized (PEI) pulp fiber paper as the substrate, we developed smart paper-based materials (designated as NB-MQDs@PP) incorporated with nitrogen and boron co-doped MXene quantum dots (NB-MQDs) for rapid adsorption and sensitive detection of Cr2O72-. Compared to undoped MQDs, NB-MQDs exhibited longer excitation wavelength and enhanced oxidation stability. As anticipated, NB-MQDs achieved rapid (response time of 10 s) and sensitive (detection limit of 1.2 μM) recognition of Cr2O72- within a wide pH range with a quenching efficiency of 99.9%. Simultaneously, two on-site detection methods, immersion and cyclic filtration, were constructed based on NB-MQDs@PP. The detection limit of the immersion method was 17.0 nM, while the cyclic filtration method had a detection limit as low as 3.8 nM, surpassing the majority of those reported literatures. Remarkably, NB-MQDs@PP exhibited outstanding enrichment capacity towards Cr2O72-, with an adsorption capacity of up to 162.4 mg/g. This work provides a novel strategy for creating unique paper-based materials with excellent capture and monitoring dual-function, which can be customized according to the requirements of various application scenarios.

Selective adsorption of Cu(II) on amino-modified alginate-based aerogel: As a catalyst for the degradation of organic contaminant

In this study, amino-modified graphene oxide(NGO) was prepared by introducing amino functional groups. Based on the cross-linking between Ca(II) and sodium alginate (SA), associated with dense slit-like pore resulted from the nano-sheet accumulation of NGO and montmorillonite (MMT), composite aerogels (NGM) with stable pore structure were constructed, thus it realized the selective recovery of hydrated copper ions in complex wastewater systems. Raman analysis and density functional theory calculation confirmed the construction of amino-modified defect GO and significantly improved its chemical reactivity, which laid the foundation for the construction of slit pore structure of NGM (SEM can confirm). At the same time, it proposed that the good selective adsorption of Cu(II) on NGM was related to the synergism of strong electrostatic force, ion exchange and complexation based on the characterizations of FT-IR and XPS. In order to realize the value-added utilization of NGM aerogel (NGMC) after adsorbing Cu(II), NGMC was used as a catalyst to degrade organic pollutants in wastewater. Systematic experiments shown that NGMC can degrade organic pollutants with a degradation efficiency >80 %. In summary, NGM had a broad application prospect for selective recovery of Cu(II) from complex wastewater systems without second pollution.

Synthesis and fabrication of magnetically separable phosphate-modified magnetic chitosan composites for lead(II) selective removal from wastewater

To address the urgent need for efficient removal of lead-containing wastewater and reduce the risk of toxicity associated with heavy-metal wastewater contamination, materials with high removal rates and easy separation must be developed. Herein, a novel organic-inorganic hybrid material based on phosphorylated magnetic chitosan (MSCP) was synthesized and applied for the selective removal of lead (II) from wastewater. From the characterization and the experimental results can be obtained that the magnetic saturation strength of MSCP reaches 14.65 emu/g, which can be separated quickly and regenerated readily, and maintains high adsorption performance even after 5 cycles, indicating that the adsorbent possesses good magnetic separation performance and durability. Also, MSCP showed high selective adsorption performance for lead in the multiple metal ions coexistence solutions at pH 6.0 and room temperature, with an adsorption coefficient SPb-MSCP of 78.85%, which was much higher than that of MSC (the SPb-MSC was 11.59%). Additionally, in the single lead system, the sorption characteristics of Pb(II) on MSCP and MCP had obvious pH-responsiveness, and their adsorption capacity increased with the increase of solution pH, reaching the maximal values of 80.19 and 72.68 mg/g, respectively. It is noteworthy that the acid resistance of MSCP with an inert layer coated on the core is significantly improved, with almost no iron leaching from MSCP over the entire acidity range, while MCP has 7.63 mg/g of iron leaching at pH 1.0. Significantly, MSCP exhibited a maximum adsorption capacity of 102.04 mg/g, which matches the Langmuir model at pH 6.0 and 298.15 K, and points to the pseudo-second-order kinetics of the chemisorption process of Pb(II) on MSCP. These findings highlight the great potential of MSCP for Pb(II) removal from aqueous solution, making it a promising solution for Pb(II) contamination in wastewater.

Construction of cellulose-based hybrid hydrogel beads containing carbon dots and their high performance in the adsorption and detection of mercury ions in water

Cellulose-based adsorbents have been extensively developed in heavy metal capture and wastewater treatment. However, most of the reported powder adsorbents suffer from the difficulties in recycling due to their small sizes and limitations in detecting the targets for the lack of sensitive sensor moieties in the structure. Accordingly, carbon dots (CDs) were proposed to be encapsulated in cellulosic hydrogel beads to realize the simultaneous detection and adsorption of Hg (II) in water due to their excellent fluorescence sensing performance. Besides, the molding of cellulose was beneficial to its recycling and further reduced the potential environmental risk generated by secondary pollution caused by adsorbent decomposition. In addition, the detection limit of the hydrogel beads towards Hg (II) reached as low as 8.8 × 10-8 M, which was below the mercury effluent standard declared by WHO, exhibiting excellent practicability in Hg (II) detection and water treatment. The maximum adsorption capacity of CB-50 % for Hg (II) was 290.70 mg/g. Moreover, the adsorbent materials also had preeminent stability that the hydrogel beads could maintain sensitive and selective sensing performance towards Hg (II) after 2 months of storage. Additionally, only 3.3% of the CDs leaked out after 2 weeks of immersion in water, ensuring the accuracy of Hg (II) evaluation. Notably, the adsorbent retained over 80% of its original adsorption capacity after five consecutive regeneration cycles, underscoring its robustness and potential for sustainable environmental applications.

Enhanced adsorption of dye wastewater by low-temperature combined NaOH/urea pretreated hydrochar: Fabrication, performance, and mechanism

The highly stable biomass structure formed by cellulose, hemicellulose, and lignin results in incomplete conversion and carbonization under hydrothermal conditions. In this study, pretreated corn straw hydrochar (PCS-HC) was prepared using a low-temperature alkali/urea combination pretreatment method. The Mass loss rate of cellulose, hemicellulose, and lignin from pretreated biomass, as well as the effects of the pretreatment method on the physicochemical properties of PCS-HC and the adsorption performance of PCS-HC for alkaline dyes (rhodamine B and methylene blue), were investigated. The results showed that the low-temperature NaOH/urea pretreatment effectively disrupted the stable structure formed by cellulose, hemicellulose, and lignin. NaOH played a dominant role in solubilizing cellulose and the combination of low temperature and urea enhanced the ability of NaOH to remove cellulose, hemicellulose, and lignin. Compared to the untreated hydrochar, PCS-HC exhibited a rougher surface, a more abundant pore structure, and a larger specific surface area. The unpretreated hydrochar exhibited an adsorption capacity of 64.8% for rhodamine B and 66.32% for methylene blue. However, the removal of rhodamine B and methylene blue by PCS-BC increased to 89.12% and 90.71%, respectively, under the optimal pretreatment conditions. The PCS-HC exhibited a favorable adsorption capacity within the pH range of 6-9. However, the presence of co-existing anions such as Cl-, SO42-, CO32-, and NO3- hindered the adsorption capacity of PCS-HC. Among these anions, CO32- exhibited the highest level of inhibition. Chemisorption, including complexation, electrostatic attraction, and hydrogen bonding, were the primary mechanism for dye adsorption by PCS-HC. This study provides an efficient method for utilizing agricultural waste and treating dye wastewater.

Highly selective detection and removal of mercury ions in the aquatic environment based on magnetic ZIF-71 multifunctional composites with sufficient chlorine functional groups

The development of both detection and removal technologies for heavy metal ions is of great importance. Most of the existing adsorbents that contain oxygen, nitrogen or sulfur functional groups can remove heavy metals, but achieving both selective detection and removal of a single metal ion is difficult because they bind to a wide range of heavy metal ions. Herein, we selected zeolite imidazolium hydrochloride framework-71 (ZIF-71) with sufficient chlorine functional groups to fabricate magnetic ZIF-71 multifunctional composites (M-ZIF-71). M-ZIF-71 had a large specific surface area, excellent water stability, and good magnetic properties, which made M-ZIF-71 conducive to the separation and recovery of adsorbents and the assembly of electrodes. M-ZIF-71 exhibited high selectivity, wide linear range (1-500 μg/L), and low detection limit (0.32 μg/L) for electrochemical detection of mercury ions (Hg2+). Meanwhile, M-ZIF-71 demonstrated rapid Hg2+ adsorption with a high capacity of 571.2 mg/g and excellent recyclability. The high selectivity for Hg2+ was attributed to the powerful affinity of highly electronegative chlorine and Hg2+. Moreover, XPS spectra demonstrated the interaction between chlorine and Hg2+. This work provides a new inspiration for applications in the targeted monitoring and removal of heavy metal pollution.

"Green" electrostatic droplet-assisted forming cellulose microspheres with excellent structural controllability and stability for efficient Cr(VI) removal

This study presents a novel and environmentally friendly method for producing cellulose microspheres (CM) with controllable morphology and size using electrostatic droplets. The traditional droplet method for CM production requires complex equipment and harmful reagents. In contrast, the proposed method offers a simple electrostatic droplet approach to fabricate CM10 at 10 kV, which exhibited a smaller volume, linear microscopic morphology, and a larger specific surface area, with a 36.60 % improvement compared to CM0 (prepared at 0 kV). CM10 also demonstrated excellent underwater structural stability, recovering in just 0.5 s, and exhibited the highest adsorption capacity for Cr(VI) at 190.16 mg/g, a 72.15 % improvement over CM0. This enhanced adsorption capacity can be attributed to the unique structure of CM10 and the introduction of more amino groups. Moreover, CM10 displayed good cyclic adsorption capacity and high dynamic adsorption efficiency, making it highly suitable for practical applications. CM10 exhibited remarkable adsorption capacity, stability, and practical value in treating Cr(VI) wastewater. This work proposes a simple and eco-friendly method for producing CM with excellent structural controllability and stability, providing an effective route for wastewater treatment.

Nano‑selenium functionalized chitosan gel beads for Hg(II) removal from apple juice

The presence of potentially toxic elements and compounds poses threats to the quality and safety of fruit juices. Among these, Hg(II) is considered as one of the most poisonous heavy metals to human health. Traditional chitosan-based and selenide-based adsorbents face challenges such as poor adsorption capacity and inconvenient separation in juice applications. In this study, we prepared nano‑selenium functionalized chitosan gel beads (nanoSe@CBs) and illustrated the synergistic promotions between chitosan and nanoSe in removing Hg(II) from apple juice. The preparation conditions, adsorption behaviors, and adsorption mechanism of nanoSe@CBs were systematically investigated. The results revealed that the adsorption process was primarily controlled by chemical adsorption. At the 0.1 % dosage, the adsorbent exhibited high uptake, and the maximum adsorption capacity from the Langmuir isotherm model could reach 376.5 mg/g at room temperature. The adsorbent maintained high adsorption efficiency (> 90 %) across a wide range of Hg(II) concentrations (0.01 to 10 mg/L) and was unaffected by organic acids present in apple juice. Additionally, nanoSe@CBs showed negligible effects on the quality of apple juice. Overall, nanoSe@CBs open up possibilities to be used as a safe, low-cost and highly-efficient adsorbent for the removal of Hg(II) from juices and other liquid foods.

Removing Heavy Metals: Cutting-Edge Strategies and Advancements in Biosorption Technology

This article explores recent advancements and innovative strategies in biosorption technology, with a particular focus on the removal of heavy metals, such as Cu(II), Pb(II), Cr(III), Cr(VI), Zn(II), and Ni(II), and a metalloid, As(V), from various sources. Detailed information on biosorbents, including their composition, structure, and performance metrics in heavy metal sorption, is presented. Specific attention is given to the numerical values of the adsorption capacities for each metal, showcasing the efficacy of biosorbents in removing Cu (up to 96.4%), Pb (up to 95%), Cr (up to 99.9%), Zn (up to 99%), Ni (up to 93.8%), and As (up to 92.9%) from wastewater and industrial effluents. In addition, the issue of biosorbent deactivation and failure over time is highlighted as it is crucial for the successful implementation of adsorption in practical applications. Such phenomena as blockage by other cations or chemical decomposition are reported, and chemical, thermal, and microwave treatments are indicated as effective regeneration techniques. Ongoing research should focus on the development of more resilient biosorbent materials, optimizing regeneration techniques, and exploring innovative approaches to improve the long-term performance and sustainability of biosorption technologies. The analysis showed that biosorption emerges as a promising strategy for alleviating pollutants in wastewater and industrial effluents, offering a sustainable and environmentally friendly approach to addressing water pollution challenges.

Superassembled MXene-carboxymethyl chitosan nanochannels for the highly sensitive recognition and detection of copper ions

Copper ions (Cu2+), as a crucial trace element, play a vital role in living organisms. Thus, the detection of Cu2+ is of great significance for disease prevention and diagnosis. Nanochannel devices with an excellent nanoconfinement effect show great potential in recognizing and detecting Cu2+ ions. However, these devices often require complicated modification and treatment, which not only damages the membrane structure, but also induces nonspecific, low-sensitivity and non-repeatable detection. Herein, a 2D MXene-carboxymethyl chitosan (MXene/CMC) freestanding membrane with ordered lamellar channels was developed by a super-assembly strategy. The introduction of CMC provides abundant space charges, improving the nanoconfinement effect of the nanochannel. Importantly, the CMC can chelate with Cu2+ ions, endowing the MXene/CMC with the ability to detect Cu2+. The formation of CMC-Cu2+ complexes decreases the space charges, leading to a discernible variation in the current signal. Therefore, MXene/CMC can achieve highly sensitive and stable Cu2+ detection based on the characteristics of nanochannel composition. The linear response range for Cu2+ detection is 10-9 to 10-5 M with a low detection limit of 0.095 nM. Notably, MXene/CMC was successfully applied for Cu2+ detection in real water and fetal bovine serum samples. This work provides a simple, highly sensitive and stable detection platform based on the properties of the nanochannel composition.

Novel α-amino acid-like structure decorated biochar for heavy metal remediation in acid soil

Neither chemical nor physical adsorption play well in heavy metals remediation in acid soil due to the competing behavior of abundant protons, where stable chelators that can be reused are of significant demand. Herein, biochar with abundant nitro and carboxyl groups is prepared, which can be assembled into self-supporting electrode. Under the catalyzation of electricity, the surface decorated -NO2 on the biochar can be in situ transformed into -NH2. Combined with the carboxyl group that attached on the same carbon atom, a special α-amino acid-like structure modified biochar (α-AC@BC) can be successfully constructed. Due to the strong affinity between the α-amino acid-like ligand and heavy metals, this α-AC@BC exhibits high removal efficiencies of 83.41%, 80.94%, 92.54% and 77.05% for available copper, cadmium, lead and zinc respectively, even in a strong acid soil with low pH of 4. After four adsorption-desorption cycles, the α-AC@BC could still eliminate 83.88% of copper. The high adsorption energy among -NH2, -COOH and heavy metals (-2.99 eV for copper, -1.90 eV for lead, -1.30 eV for zinc and -0.91 eV for cadmium) could form steady coordination structure to guarantee a highly practical application potential of α-AC@BC in strong acid soil. This study provides a novel concept for the decontamination of multiple heavy metal polluted acid soil.

Simultaneous Cr(VI) reduction and Cr(III) sequestration in a wide pH range by using magnetic chitosan-based biopolymer

The simultaneous reduction of Cr(VI) and sequestration of the resulting Cr(III) in one process is highly desirable as a cost-effective and environmental-friendly approach for the decontamination of Cr(VI)-polluted wastewater. However, most of the existing adsorptive materials are only effective in low pH environments (pH = 1-3), severely restricting the adsorption efficiency and cost effectiveness. Herein, we proposed a chitosan-based magnetic porous microsphere (PPy@PMCS) for simultaneous Cr(VI) reduction and Cr(III) sequestration in a wide pH range. Benefiting from its abundant interaction sites, Cr(VI) was effectively adsorbed on the surface and then immediately reduced to Cr(III) with much lower toxicity. Most importantly, the resulting Cr(III) was in-situ sequestrated by the complexation of chitosan matrix. As a result, PPy@PMCS exhibited a maximum Cr(VI) adsorption capacity of 330.42 mg/g at pH 2.0 and an adsorption capacity of 167.82 mg/g even at near neutral pH (6.0), which is superior to most reported adsorbents. Furthermore, the exhausted PPy@PMCS can be rapidly separated from solutions under an external magnetic field and facilely regenerated. The proposed novel biopolymer-based material shows great application potentials in wastewater treatment.

Effect mechanism of iron conversion on adsorption performance of hydrochar derived from coking sludge

In this study, Fe conversion during hydrothermal carbonization (HTC) of coking sludge were investigated, and the effect mechanism of Fe component on the adsorption performance of coking sludge hydrochar (CHC) was explored. The results showed that after HTC treatment, more than 95 % of Fe remained in the CHC. Fe3+ was reduced to Fe2+ by sugar and amino acids. Fe was stabilized during the HTC process and was still predominantly in the Fe manganese oxidation state. The CHC prepared at 270 °C exhibited excellent adsorption capacities for Congo red (CR), tetracycline (TC), and Cr (VI). Their maximum adsorption capacities were 140.85, 147.06, and 19.92 mg/g, respectively. Quantitative adsorption mechanism experiments, XRD and VSM characterization revealed that Fe component played a significant role in adsorption, and CHC with more Fe3O4 exhibited better adsorption capacity. The results of the XPS characterization of CHC before and after adsorption showed that Fe3O4 provided rich Fe adsorption sites on the surface of CHC to strengthen the adsorption efficiency of pollutants through Fe3+/Fe2+ reduction and complexation of Fe-O/N. In addition, the formed Fe3O4 also imparted CHC with magnetic properties (Ms = 4.12 emu/g) to facilitate the subsequent separation and recovery. These results demonstrated that the prepared CHC has great potential for treating actual wastewater containing CR and TC.

Enhanced adsorption of phenol from aqueous solution by KOH combined Fe-Zn bimetallic oxide co-pyrolysis biochar: Fabrication, performance, and mechanism

In this study, impregnation combined with KOH activation with different mixing methods was used to prepare magnetic biochar. The effects of synthetic method on biochar physicochemical properties and adsorption performance were explored. The results showed that treatment of a Fe-Zn oxide with KOH activation provided excellent adsorption properties with adsorption capacity of 458.90 mg/g due to well-developed microporous structure and rich-in O-containing functional groups as well as exposed oxidizing functional groups (Fe2O3 and FeOOH). Langmuir-Freundlich and pseudo-second-order models accurately fit phenol adsorption. Neutral conditions (pH = 6) and lower ionic strengths were beneficial to phenol removal. Additionally, the predominant adsorption processes were physisorption and chemisorption. Correlation analyses and characterization data confirmed that pore filling, π-π interactions and surface complexation were the dominant driving forces for phenol adsorption. This research provides an environmentally friendly method for utilizing agricultural wastes for the removal of a variety of pollutions from aquatic environment.

Facile synthesis of chitosan-tartaric acid biosorbents for removal of Cu(II) and Cd(II) from water and tea beverages

Consumption of water and tea beverages leads to the intake of heavy metals by humans. Development of technology for decontamination greatly reduces the risks of the heavy metal exposure. In this study, environment-friendly chitosan-tartaric acid biosorbents (CTBs) were synthesized by a facile one-step cross-linking strategy to mitigate the Cu(II) and Cd(II) contamination in water and tea beverages. The cross linkage of tartaric acid and chitosan endowed CTBs with excellent properties in aspects of surface roughness, mechanical strength, and acid resistance. Adsorption performance and mechanism of CTBs were studied, and the Langmuir isotherm model and pseudo-second-order kinetic model were adhered during adsorption. Up to 90 % removal efficiencies of Cu(II) and Cd(II) from water and tea beverages by CTBs were achieved. Moreover, the adsorption showed only a slight reduction in the quality of tea beverages. This study offers a new insight for reduction of heavy metals-pollution in beverages.

H2O2 modified peanut shell-derived biochar/alginate composite beads as a green adsorbent for removal of Cu(II) from aqueous solution

In this study, a novel composite bead (MPB-ALG) was prepared by encapsulating H₂O₂ modified peanut shell-derived biochar (MPB) into alginate matrix through a facile method. The structure and properties of prepared materials were characterized using FTIR, BET, SEM, and XPS. Batch adsorption experiments were performed to compare Cu(II) adsorption performance of MPB, plain alginate beads (ALG) and MPB-ALG. The effect parameters of the components, solution pH, contact time, initial concentration and coexisting ions were studied systematically. The results showed that the maximum adsorption capacity of the optimized MPB-ALG-1 (MPB/alginate = 1:1 w/w%) was 117.4 mg g^-1 at pH 5, which was much higher than that of MPB (37.4 mg g^-1). The adsorption kinetics and isotherms data of Cu(II) on MPB-ALG-1 were well described by Elovich kinetic model and Freundlich adsorption isotherm. Compared with plain ALG beads, MPB-ALG-1 exhibited better reusability and anti-interference of coexisting ions. Finally, the adsorption mechanisms of Cu(II) on MPB-ALG-1 beads were revealed by FTIR and XPS analysis. The experimental results demonstrated that MPB-ALG-1 beads can be used as an environmentally friendly and efficient adsorbent for the removal of Cu(II) from wastewater.

Preparation of esterified biomass waste hydrogels and their removal of Pb2+, Cu2+ and Cd2+ from aqueous solution

The treatment of polluted water is a serious environmental problem in the world. Biomass is easily modified and can be prepared into adsorbent materials, which is expected to solve the problem of heavy metal ion adsorption in sewage. In this paper, esterified tobacco straw based hydrogels (ETS-PAA) were synthesized from waste tobacco straw biomass. The structure and thermal stability of these hydrogels were characterized by FTIR, SEM, EDS, XPS and TG. The adsorption of metal ions by the hydrogel was measured by ICP-MS. The effects of initial ion concentration, adsorption time, pH, and temperature on the heavy metal adsorption were investigated. The results showed that ETS-PAA possessed more pores, which led to a better adsorption capacity. The maximum adsorption amounts of Pb²⁺, Cu²⁺ and Cd²⁺ were 2.41 mmol·g^-1, 1.93 mmol·g^-1 and 1.77 mmol·g^-1, respectively. Finally, the adsorption mechanism and kinetics were analyzed. The adsorption was mainly accomplished by ion exchange of -COOK on the monomer chain with heavy metal ions, coordination of -OH and -CONH with heavy metal ions and interaction of ester bond, -COOH with heavy metal ions. The adsorption process was in accordance with the pseudo-second-order kinetic model and Freundlich model. The adsorption process belonged to multilayer chemisorption. This work shows that ETS-PAA was a promising material for the removal of heavy metal pollutants from aqueous solution.

Preparation of sludge-cyanobacteria composite carbon for synergistically enhanced co-removal of Cu(II) and Cr(VI)

Traditional sludge disposal is currently restricted by the risk of secondary pollution. Sludge carbon material has gained widespread attention because of its low cost and environmentally sustainable properties. However, owing to the high ash content and low-energy density of sludge, sludge pyrolysis alone has certain limitations, and the performance of carbon materials needs to be improved. Herein, a sludge-cyanobacteria composite carbon (SCC) was easily synthesized, and the adsorption process of Cu(II) and Cr(VI) by SCC was examined. SCC-700-2-50% exhibited a high S_BET (1047.54 m²/g) and developed pore structure rich in functional groups (such as -NH, -OH, and C-O). The combination of pore structure and functional groups improved the adsorption performance of SCC. The adsorption processes exhibited a synergistic effect in a binary system: the q_m of Cu(II) and Cr(VI) were 386 mg/g and 341 mg/g, respectively, and the selectivity of Cu(II) adsorption by SCC was greater than Cr(VI). The adsorption process, examined by SEM-EDS, FTIR, and XPS analysis, indicated that Cu(II) as a cationic interface strengthens Cr(VI) adsorption through electrostatic interaction, and the anion Cr(VI) created a valid electrostatic shield against the electrostatic repulsion between H⁺ and Cu(II), facilitating Cu(II) adsorption. SCC had great reusability: Cu(II) and Cr(VI) adsorption capacity were 90% and 84%, of the initial adsorption capacity, respectively, after six cycles. This study demonstrates the prospect of SCC as a valid adsorbent for multiple heavy metal contaminations removal.

Synergistic remediation of lead pollution by biochar combined with phosphate solubilizing bacteria

Pb(II) is extreme toxic to biological cells, which limits the restoration of Pb(II) by functional strains. This study examined a Pb(II)-tolerant phosphate solubilizing bacteria(PSB) Ochrobactrum sp. J023 combined with corn stover biochar to enhance the immobilization of Pb(II). The results showed that the removal rate of Pb(II) by biochar combined with phosphate-solubilizing bacteria was as high as 71.30 %. SEM-EDS showed that more disordered crystals appeared on the surface of biochar treated with bacteria. XRD analysis indicated that the mineralization products of Pb(II) in biochar combined strain system were mainly in Pb₅(PO₄)₃OH and Pb₅(PO₄)₃Cl. FT-IR analysis revealed that there were more phosphate groups involved in the mineralization process when biochar was added. XPS verified the formation of PbO or lead-containing precipitates in this system, and the amount of lead precipitates was larger. The mechanism of lead fixation by strain combined with biochar can be regarded that the strain regulates the microenvironment of the biochar surface, enhances the release of phosphate and promotes the generation of stable pyroxite. Moreover, biochar composition and porous structure not only provide nutrient elements for strains, but also protect and promote the metabolism of strains. Biochar adsorption also reduces the loss of available phosphorus, which helps PSB to fix Pb sustainably and effectively. This suggests that the synergistic effect of PSB-biochar can not only effectively reduce the mobility and bioavailability of Pb(II), but also increase the sustainability of remediation. Therefore, the combination of phosphate solubilizing bacteria and biochar is a promising approach to the remediation of heavy metal pollution.

A novel biosorbent functionalized pillar[5]arene: Synthesis, characterization and effective biosorption of Cr(VI)

Among toxic chemicals, hexavalent chromium (Cr(VI)) is one of the most carcinogenic and toxic pollutants that hostiles to the health of both humans and other living things. Therefore, the removal of Cr(VI) is of great importance to keep our environment clean and tidy. In this study, an easy-make, inexpensive, and natural biosorbent material (Sp-P[5]) was prepared to preserve our environment using a pillar[5]arene based-on sporopollenin microcapsule. The prepared biosorbent was successfully characterized by some techniques such as FTIR, XRD, and SEM. The biosorbent, Sp-P[5], exhibited an open mesoporous structure richly decorated with multi-amine-containing moieties resulting in enhanced Cr(VI) sorption. The sorption behavior of Cr(VI) ions is satisfactorily adapted from the sorption kinetics pseudo-second-order law and the isotherm models to the Langmuir model at different temperatures. The Langmuir model fits at different temperatures (298-328 K) and the maximum sorption capacities of the Cr(VI) ion ranged from 106.38 to 117.26 mg/g. The thermodynamic calculations reveal that the sorption of Cr(VI) ions on the Sp-P[5] is entropy-driven, endothermic, and spontaneous. The prepared biosorbent was also applied to the natural wastewater samples and different ions (chromate and dichromate). The sorption and desorption experiments showed that the sorption efficiency for Cr(VI) ions of the Sp-P[5] decreased to 70.88 % after 8 cycles. As result, the synthesized biosorbent, Sp-P[5], has outstanding potential in the removal of Cr(VI) ions from water bodies and natural wastewater systems.

Selective removal of Hg(II) by UiO-66-NH2 modified by 4-quinolinecarboxaldehyde: from experiment to mechanism

In wastewater, heavy metal Hg causes serious harm to ecology, so it needs to be removed. In this paper, a novel MOF adsorbent (UiO-66-QU) was prepared by modifying UiO-66-NH₂ with 4-quinolinecarboxaldehyde, which was used to selectively remove Hg(II) from water. The adsorbent was characterized using Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), zeta potentiometer, and X-ray photoelectron spectroscopy (XPS). In order to investigate the Hg(II) adsorption performance of UiO-66-QU, the effect of time, initial concentration, pH, and temperature were carried out. Langmuir model fitting shows that the maximum adsorption capacity of UiO-66-QU for Hg(II) is 556 mg/g at 298 K. The experimental results show that UiO-66-QU has better Hg(II) adsorption capacity than UiO-66-NH₂. The isotherm is in accordance with pseudo-second-order models. It is indicated that the adsorption process is mainly monolayer chemical adsorption. The thermodynamic parameters also indicate that the adsorption process is spontaneous and endothermic. It has excellent reusability and selectivity. XPS and the zeta potential showed that the adsorption mechanism was the complex reaction of Hg(II) with nitrogenous group. Therefore, the adsorbent has potential application prospects in removal of Hg(II) from wastewater.

Recovering rare earth elements via immobilized red algae from ammonium-rich wastewater

Biotreatment of acidic rare earth mining wastewater via acidophilic living organisms is a promising approach owing to their high tolerance to high concentrations of rare earth elements (REEs); however, simultaneous removal of both REEs and ammonium is generally hindered since most acidophilic organisms are positively charged. Accordingly, immobilization of acidophilic Galdieria sulphuraria (G. sulphuraria) by calcium alginate to improve its affinity to positively charged REEs has been used for simultaneous bioremoval of REEs and ammonium. The results indicate that 97.19%, 96.19%, and 98.87% of La, Y, and Sm, respectively, are removed by G. sulphuraria beads (GS-BDs). The adsorption of REEs by calcium alginate beads (BDs) and GS-BDs is well fitted by both pseudo first-order (PFO) and pseudo second-order (PSO) kinetic models, implying that adsorption of REEs involves both physical adsorption caused by affinity of functional groups such as -COO- and -OH and chemical adsorption based on ion exchange of Ca²⁺ with REEs. Notably, GS-BDs exhibit high tolerance to La, Y, and Sm with maximum removal efficiencies of 97.9%, 96.6%, and 99.1%, respectively. Furthermore, the ammonium removal efficiency of GS-BDs is higher than that of free G. sulphuraria cells at an initial ammonium concentration of 100 mg L^-1, while the efficiency decreases when initial concentration of ammonium is higher than 150 mg L^-1. Last, small size of GS-BDs favors ammonium removal because of their lower mass transfer resistance. This study achieves simultaneous removal of REEs and ammonium from acidic mining drainage, providing a potential strategy for biotreatment of REE tailing wastewater.

Genetically modified metallothionein/cellulose composite material as an efficient and environmentally friendly biosorbent for Cd2+ removal

Metallothioneins (MTs) are a class of cysteine-rich metal-binding proteins. Cadmium (Cd) is one of the toxic heavy metal pollutants. In our previous research, the full-length cDNA of MT (Cd specificity) from freshwater crab (Sinopotamon henanense) (ShMT) was cloned and genetically modified to ShMT3 by site-directed mutagenesis to enhance the tolerance for Cd²⁺, however, it was limited in actual Cd²⁺ adsorption due to instability. Here, ShMT3-CBM, a novel recombinant fusion protein, was prepared. CBM is a carbohydrate binding module that can specifically bind cellulose while ShMT3 can effectively chelate Cd²⁺. The biosorbent Cellulose1-ShMT3-CBM was obtained by screening suitable cellulose materials. The selective adsorption experiments showed that Cellulose1-ShMT3-CBM had a preference for Cd²⁺. In low-concentration Cd²⁺ solutions, the removal efficiency was >99 %, and the adsorption equilibrium was reached within 15 min. The saturated adsorption capacity of Cellulose1-ShMT3-CBM for Cd²⁺ is 180.35 ± 4.67 mg/g (Dry Weight). Regeneration experiments showed that adsorption efficiency was maintained after six cycles. The MTT experiment showed that Cellulose1-ShMT3-CBM had low cytotoxicity. Meanwhile, Cellulose1-ShMT3-CBM can preferentially remove Cd²⁺ in actual water samples and boiler sewage. In this study, an environmentally friendly biosorbent which can adsorb Cd²⁺ efficiently and quickly was prepared for actual water treatment.

Facile fabrication of highly dispersed Pd catalyst on nanoporous chitosan and its application in environmental catalysis

With the development of society, the problem of environmental pollution is becoming increasingly serious, such as the typical pollution of nitro compounds or dyes in wastewater. An effective strategy to remove these organic pollutants is catalytic conversion, including converting them into more chemically valuable compounds. Herein, a nanoporous chitosan microsphere derived from seafood waste resources of chitin was constructed via sol-gel method, which was used as supports to successfully fabricate a highly dispersed Pd nano-catalyst (mean diameter ~ 1.8 nm) via a facile way based on its interconnected nanoporous structure and rich functional -OH/-NH₂ groups. The synthetic catalyst was applied to the hydrogenation of toxic nitro compounds, which could efficiently and selectively catalyze the conversion of nitro compounds. The catalyst was also used for the degradation of some representative dyes, which also showed good activity and stability, suggesting potential of applications in green environmental governance.

Removal of Cd2+ from water containing Ca2+ and Mg2+ using titanate nanotubes modified by carbon

Calcium and magnesium ions usually exist in natural water. When Cd²⁺ is removed from water by adsorption, it will be inhibited by these two ions. Titanate nanotubes (TNTs) have an effective adsorption capacity for Cd²⁺ due to extraordinary ion exchange property. However, TNTs also adsorb Ca²⁺ and Mg²⁺ in water. In this study, carbon-modified TNT (TNT/C) and TNT/C further treated with acid (TNT/HC) were synthesized by hydrothermal synthesis. The transmission electron microscope (TEM) images show that TNT/C or TNT/HC still keep nanotube morphology. The experimental results show the order of adsorption amount to Cd²⁺ is TNT (171.56 mg/g) > TNT/C (166 mg/g) > TNT/HC (159.88 mg/g) when there is no Ca²⁺ or Mg²⁺. But when there is 0.1 M Ca²⁺ or Mg²⁺ in the water, the order of Cd²⁺ adsorption capacity becomes TNT/HC (44.28, 49.04 mg/g) > TNT/C (58.84, 69.32 mg/g) > TNT (65.52, 70.6 mg/g). It indicates that the surface carbon modification can alleviate the hindrance of Ca²⁺ or Mg²⁺ to Cd²⁺ removal. This is because the carbon on the surface of TNT captured part of Ca²⁺ or Mg²⁺; it made more Cd²⁺ be successfully absorbed by TNT through ion exchange. This mechanism was confirmed by the X-ray photoelectron spectroscopy (XPS) spectra analysis. The results of this paper can provide ideas for the adsorption and removal of Cd²⁺ in water in the presence of Ca²⁺ or Mg²⁺.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Single and binary adsorption of lead and cadmium ions in aqueous solutions and river water by butylamine functionalized vermiculite: performance and mechanism

Lead and cadmium are toxic to human, animal, and plant health; they enhance oxidative stress indirectly while simultaneously acting through other toxicodynamic mechanisms. In this study, pristine vermiculite (VER) was functionalized with butylamine (BUT) and a novel organoclay (BUT-VER) adsorbent material was produced for simultaneous removal of Pb(II) and Cd(II) in aquatic medium. The adsorbents were characterized by spectroscopic, microscopic, spectrometric, and potentiometric techniques. The adsorption affecting parameters, including pH, time, initial concentration, temperature, and co-existing cations were investigated and optimized. The kinetic data results were in better agreement with pseudo-second-order (PSO) model (R² > 0.992). Multiple isotherm models were used to study the adsorption system and results showed that adsorption was monolayer. The BUT-VER showed an improvement in adsorption capacity in a single system (Pb(II): from 134.2 to 160.6 mg g^-1) and (Cd(II): from 51.1 to 58.9 mg g^-1) while in binary system (Pb(II): from 107.3 to 114.5 mg g^-1) and (Cd(II): from 33.7 to 39.7 mg g^-1), respectively. Furthermore, BUT-VER was tested in real river water and removed efficiency of >99% was achieved in just 1 h. The dominant mechanisms were electrostatic attraction and complexation. BUT-VER was regenerated for five consecutive cycles and showed >90% removal efficiency. These findings suggest that the proposed inexpensive adsorbent has the potential for practical applications of toxic metals removal from water.

Mixed bacteria-loaded biochar for the immobilization of arsenic, lead, and cadmium in a polluted soil system: Effects and mechanisms

The present study explored the immobilization of mixed bacteria-loaded biochar on As, Pb, and Cd was explored. Physisorption and sodium alginate encapsulation were used to synthesize two kinds of mixed bacteria-loaded biochars, referred to as BCM and BCB. The observations of Scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy distinctly demonstrated the colonization of mixed bacteria on biochar. Besides, the addition of BCM and BCB could increase soil pH with increasing incubation time. The residual fraction of heavy metals and soil dehydrogenase activities were also enhanced after 28 days of incubation. Pb was mainly immobilized by co-precipitation, which meant that Pb could be converted into a consistent crystalline form such as Pb₅(PO₄)₃OH. The X-ray photoelectron spectroscopy and X-ray diffraction analyses of materials identified the formation of Ca₂As₂O₇ and the presence of oxidation from trivalent arsenic to pentavalent arsenic. Cd was adsorbed by forming precipitations (CdCO₃) and exchanging ions with the BCM and BCB. Synergistic reactions between anions and cations also contributed to the immobilization of heavy metals, such as the formation of PbAs₂O₆ and Cd₃(AsO₄)₂. These results confirmed that mixed bacteria-loaded biochar was a feasible technology for the remediation of heavy metals contamination in site soils.

One-step fabrication of dual functional Tb3+ coordinated polymeric micro/nano-structures for Cr(VI) adsorption and detection

Hexavalent chromium Cr(VI) has been considered as one of the most hazardous heavy metals because of its strong and persistent toxicity to the ecosystem and human beings. Herein, we have synthesized a double hydrophilic block co-polyarylene ether nitriles (abbreviated as dhPEN) bearing aromatic backbone as well as pendent carboxyl and sulfonate groups. Afterward, the synthesized dhPEN has been co-assembled with the lanthanide Tb³⁺ via a one-step solvent exchange protocol, leading to generation of Tb³⁺ coordinated dhPEN (Tb-dhPEN) micro/nano-structures that exhibit good adsorption capacity and detection sensitivity towards Cr(VI). More specifically, the direct self-assembly of dhPEN and Tb³⁺ in mixed H₂O/DMF solvents resulted to Tb-dhPEN microparticles with lamellar structures, which exhibited a high Cr(VI) adsorption capacity approaching to 402 mg/g. The detailed characterization confirm that Cr(VI) is adsorbed and partially reduced to Cr(III) by the Tb-dhPEN microparticles via chemical interaction. Furthermore, the self-assembly of dhPEN with Tb³⁺ in the H₂O/DMF mixed solvents containing NaOH contributed to the generation of spherical nanoparticles showing green emission at 545 nm, which can be selectively quenched by the Cr(VI), leading to the specific detection of trace concentration of Cr(VI) down to 0.12 nM as well as reliable determination of Cr(VI) presented in real environmental samples.

Structural and Optical Characterizations of Cadmium Chalcogenide Layers on Polyamide Formed Using Monotelluropentathionic Acid

Mixed cadmium tellurides–cadmium sulfide thin layers were formed on the polyamide PA 6. Monotelluropentathionic acid (H₂TeS₄O₆) was used as a precursor of tellurium and sulfur. A low-temperature, nontoxic, and cost-effective SILAR method was applied. Cadmium telluride (CdTe) and sulfide (CdS) layers were formed through the consecutive reactions of sorbed/diffused chalcogens species from telluropentathionate anion (TeS₄O₆²⁻) with functional groups of polyamide and alkaline cadmium sulfate. The pseudo-second-order rate and Elovich kinetic models were the best fit to quantify an uptake of chalcogens and cadmium on PA 6. The effects of chalcogens and Cd on the structure and optical properties of PA 6 were characterized using UV-Vis and IR spectra. The clear changes of these properties depended on the concentration and exposure time in the precursor solutions. Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were applied in order to evaluate the effect of the chalcogen species on the changes in structure of polyamide 6 films, depending on the exposure time in the solution of the chalcogens precursor and its concentration. The optical bandgap energy of the formed layers was found to be in the order of 1.52–2.36 eV. Studies by scanning electron microscopy and atomic force microscopy reveal that the diameter of the average grain is approximately 30 nm. The grains are conical in shape and unevenly distributed all over the surface of the substrate.

Reduction and removal of Cr(VI) in water using biosynthesized palladium nanoparticles loaded Shewanella oneidensis MR-1

In materials science, "green" synthesis has gotten a lot of interest as a reliable, long-lasting, and ecofriendly way to make a variety of materials/nanomaterials, including metal/metal oxide nanomaterials. To accommodate various biological materials, green synthesis of metallic nanoparticles has been used (e.g., bacteria, fungi, algae, and plant extracts). In this work, Shewanella oneidensis MR-1 was used to biosynthesize palladium nanoparticles (bioPd) under aerobic conditions for the Cr(VI) bio-reduction. The size and distribution of bio-Pd are controlled by adjusting the ratio of microbial biomass and palladium precursors. The high cell: Pd ratio has the smallest average particle size of 6.33 ± 1.69 nm. And it has the lowest electrocatalytic potential (-0.132 V) for the oxidation of formic acid, which is 0.158 V lower than commercial Pd/C (5%). Our results revealed that the small size and uniformly distributed extracellular bio-Pd could achieve completely catalytic reduction of 200 mg/L Cr(VI) solution within 10 min, while the commercial Pd/C (5%) need at least 45 min. The bio-Pd materials maintain a high reduction during five cycles. Microorganisms play an important role in the whole process, which can fully disperse palladium nanoparticles, completely reduce Cr(VI), and effectively adsorb Cr(III). This work expands our understanding and provides a reference for the design and development of efficient and green bio-Pd catalysts for environmental pollution control under simple and mild conditions.

Mechanism analysis of the immobilization of heavy metal ions with the water-soluble polymer: The influence of resin structure and the further adsorption of chelate

Polymer materials have become one of the potential materials for remediation of heavy metal (HM) contamination in water and soil. However, the specific advantages of polymers are rarely studied. Water-soluble thiourea formaldehyde resin (WTF) is one of the effective polymer amendments. Through leaching experiments, WTF can stabilize 93.0% of Cd²⁺ and 99.7% of Cu²⁺. The results of HM morphology analysis show that after adding WTF, most of the HMs have been transformed into a relatively stable state. For example, in the process of remediation of 6 mg/kg Cd contaminated soil, the proportion of acid-soluble Cd decreased from 56.5% to 12.8%, and the residual state increased from 13.5% to 45.4%. Compared with the resin-free structure, the three-dimensional structure of the resin plays an important role, but the efficiency of precipitation with HMs is doubled. According to the simulation of the adsorption process by Materials Studio, the characterization of the scanning electron microscope-energy dispersive instrument and the results of the adsorption experiment, in the solution, the precipitate formed by WTF and Cd²⁺ has multilayer adsorption of HMs, and can further adsorb HM by -OH. Soil enzyme activity experiments proved that the risk of secondary pollution by adding WTF is rare, and even WTF can achieve the effect of slow-release nitrogen fertilizer. In the WTF remediation process, the biological toxicity reduction of HMs is result from, on the one hand, the complexation of functional group of WTF; on the other hand, the resin structure of WTF; in addition, multi-layer adsorption and adsorption of end groups in the precipitation formed by WTF and HM. This work provides a theoretical basis for the potential capabilities of water-soluble resins and is beneficial to the design and development of subsequent amendments.

Chromium Distribution, Leachability and Speciation in a Chrome Plating Site

Hexavalent chromium (Cr(VI)) waste produced by chrome plating activities pollutes the surrounding environment and harms human health. However, information about the chromium (Cr) pollution characteristics of actual electroplating sites is still lacking. In this study, the concentration, leachability and speciation of Cr in soils from a typical chrome plating site were analyzed. Our results showed that this site was severely contaminated by Cr (7.2 to 7735.2 mg/kg) and Cr(VI) reached the mean concentration of 138.7 mg/kg. The spatial distribution of Cr(VI) was related to the plating processes. Chrome plating and sewage treatment areas could be considered as the hot spots of contaminated sites. The vertical distribution of Cr(VI) was mainly affected by soil properties, where the loam layer retained and reduced a large amount of Cr(VI) due to its high content of iron minerals and finer particle fractions. Additionally, the chemical extraction results showed that Cr was mainly in non-residual fractions and the existence of Cr(VI) led to a high leaching toxicity based on the toxicity characteristic leaching procedure (TCLP) results. Moreover, X-ray photoelectron spectroscopy (XPS) results revealed the speciation of Cr in the long-term contaminated soils. A large amount of Cr(VI) was reduced into Cr(III) and mainly existed as Cr(OH)3 and Cr2O3. Furthermore, Cr(VI) tended to precipitate as CaCrO4 and persisted in soils. Therefore, it is necessary to find appropriate strategies to remediate these contaminated soils. Overall, these findings strengthen our understanding of Cr(VI) behaviors and lay a foundation for the future pollution investigation, ecological remediation and risk assessment of sites contaminated by electroplating.

Phosphate-crosslinked β-cyclodextrin polymer for highly efficient removal of Pb(ii) from acidic wastewater

Novel phosphate-crosslinked β-cyclodextrin polymer was synthesized for highly efficient Pb(ii) removal from acidic wastewater.

Removal of emulsified oil from water by using recyclable chitosan based covalently bonded composite magnetic flocculant: Performance and mechanism

In this work, a novel recyclable covalently bonded magnetic flocculant (FS-MC) was successfully prepared by combining chitosan-based modified polymers (MCS) with Fe₃O₄@SiO₂ through a silane coupling agent. The covalent bond Fe-O-Si-O-C and the core-shell structure of FS-MC were confirmed through several characterization methods. The emulsified oily wastewater flocculation performance and mechanism by using FS-MC were evaluated and studied. Results showed that 94.47%, 93.95%, and 92.98% of emulsified oil could be removed by using FS-MC1, FS-MC2 and FS-MC3 at dosages of 2.0, 2.5, and 2.0 mg/L, respectively. Furthermore, FS-MC exhibited an excellent behavior on the removal of organic compounds with molecular weight > 10 kDa, including long chain alkanes, cycloalkanes, and aromatic hydrocarbon compounds. In addition, triple-phase separation of oil, water and flocculants was achieved by using magnetic FS-MC. Due to the introduction of cationic and hydrophobic groups in FS-MC, charge neutralization, compression double electric-layer action, hydrophobic interaction, interfacial adsorption bridging and sweep-flocculation synergistically contributed and enhanced the removal of emulsified oil. Recycling experiments also showed that no obvious decrease of oil removal rate was observed by using magnetic FS-MC flocculants in five cycles.

Thiol-methyl-modified magnetic microspheres for effective cadmium (II) removal from polluted water

For effective removal of cadmium (II) (Cd(II)) from polluted water, a magnetic adsorbent of Fe₃O₄@SiO₂ core-shell microspheres modified with methyl-protected thiol groups (Fe₃O₄@SiO₂-SH-Protected) was synthesized and characterized by scanning electron, transmission electron, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopies, as well as X-ray diffraction, Raman spectroscopy, and magnetic measurements. Characterization results showed that thiol groups on the surface of Fe₃O₄@SiO₂ material were protected to avoid disulfide formation. Batch adsorption experiments were conducted by varying the contact time, initial pH, solid-liquid ratio, temperature, Cd(II) concentrations, and interfering cations. Fe₃O₄@SiO₂-SH-Protected material exhibited much higher adsorption capacity than Unprotected forms and other adsorbents due to methyl group protection. The maximum adsorption capacity calculated from the Langmuir fitting was 27.5 mg·g^-1 (pH 7, 25 °C), and the adsorption kinetics followed a pseudo-second-order model, and adsorption mainly dominated by film diffusion processes. Thermodynamic parameters indicated that the adsorption process was a spontaneous, endothermic, and positive entropic process. Cd(II)-loaded on the adsorbent was easily desorbed with 0.1 M HCl and the adsorbent stable in 0.1 M HCl for long times, showing good reusability and stability.

Laboratory and simulation study on the Cd(Ⅱ) adsorption by lake sediment: Mechanism and influencing factors

Sediments are the major sinks for Cd(Ⅱ) in the aquatic environment. Here, the detailed binding mechanisms and effects of environmental factors on Cd(Ⅱ) adsorption onto lake sediment were tested by a batch of adsorption and characteristic experiments. Sediment samples and sediment-Cd complexes were characterized using Scanning electron microscopy, Energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction spectral analyses. The interactive and main effect of parameters such as pH, flow velocity, Cd(II) concentration, sediment particle size, humic acid, fulvic acid and adsorption time involved in the adsorption process were determined using two models based on response surface methodology (RSM) and a back-propagation neural network with genetic algorithm (GABP). Results showed that Cd(II) adsorption onto sediment was mainly achieved through surface complexation with O-containing groups and precipitation with carbonate and sulfide. RSM was favorable for modeling Cd(II) adsorption in lake systems because it intuitively reflected the influence of the factors and had a good fitting precision (R² = 0.8838, RSME = 2.5496) close to that of the GABP model (R² = 0.8959, RSME = 2.5410). pH, sediment particle size, and humic acid exerted strong influences on Cd(II) immobilized by the sediment. Overall, our findings facilitate a better understanding of Cd(II) mobility in lakes and provide a reference for controlling heavy metals derived from both aqueous and sediment sources.

Efficient removal of Pb(ii) and Cr(vi) from acidic wastewater using porous thiophosphoryl polyethyleneimine

A porous thiophosphoryl polyethyleneimine was synthesized to remove Pb(ii) and Cr(vi) from acidic wastewater.