Heavy Metal Anions Research Articles

PE/PP fibrous adsorbents with bifunctional groups of tertiary amine and phosphate prepared by electron beam induced co-grafting for heavy metal adsorption of both cationic and anionic forms in acidic conditions

A novel fabric adsorbent having bifunctional groups of tertiary amine and phosphate was prepared by co-graft polymerization of 2-diethylaminoethyl methacrylate (NMA) and 2-hydroxyethyl methacrylate phosphate (PMA) onto a polyethylene/polypropylene nonwoven fabric (PE/PP NF) under low-energy electron beam acceleration. The process involved pre-irradiating the fabric and immersing it in the comonomer solution for grafting. The kinetics of radiation-induced graft polymerization at a total dose of 100 kGy was investigated. For pre-irradiation at 100 kGy, the optimum condition offering highest degree of grafting was at 12 wt% of NMA, 8 wt% of PMA and 4 h of reaction time. The adsorption of anions using hydrogen chromate (HCrO4−) or Cr(VI) and cations using lead (Pb(II)), cadmium (Cd(II)) and copper (Cu(II)) in aqueous solution was carried out. The results demonstrated that the bifunctional adsorbent was able to adsorb both heavy metal anionic and cationic ions from water. The co-grafted adsorbents with tertiary amine and phosphate were able to adsorb 85 % Cr(VI) anion and 29 % Pb(II) cations from mixed Cr(VI) and Pb(II) solution at pH 3.0 and 71 % Pb(II), 13 % Cd(II) and 31 % Cu(II) from mixed Pb(II), Cd(II) and Cu(II) solution at pH 5.0. The unique achievement of this study is its hypothesis that a bifunctional adsorbent can be prepared from radiation-induced graft polymerization of two different monomers onto NF, along with proof that the prepared bifunctional adsorbent can actually absorb both cationic or anionic heavy metals forms. Additionally, the adsorbent's preparation offers a rapid and straightforward one-step grafting technique. Therefore, the new bifunctional adsorbents can remove heavy metal ions in aqueous solution, either in the cation or anion form, thus offering highly promising applications in industrial wastewater treatment.

Effective adsorptive removal of heavy metal anion Cr(Ⅵ) and dye cation methylene blue by the novel 2D material TiVCTx MXene

With the increasingly serious industrial pollution, the effective removal of heavy metal ions and organic pollutants from wastewater has become a key issue of environmental protection. In this paper, a new MXene material, TiVCTx, was prepared by in situ etching, and its adsorption capacity of heavy metal anion Cr(Ⅵ) and methylene blue (MB) dye cation was studied. The effect of adsorption time, pH values, temperatures, initial concentrations of adsorbent and adsorbate, interfering ions on the Cr(Ⅵ) and MB adsorption of TiVCTx was systematically investigated. It is found that TiVCTx has excellent Cr(Ⅵ) and MB adsorption property, the adsorption capacity can be as high as 600mg/g and 1430mg/g, respectively. The adsorption experiments revealed that the adsorption process of Cr(Ⅵ) conformed to the Langmuir isotherm model and the Pseudo-second-order kinetic model, which indicated that the Cr(Ⅵ) adsorption was a heat-absorbing monolayer chemisorption. In contrast, the adsorption process of MB is in accordance with the Freundlich isotherm model and the Pseudo-second-order kinetic model, suggesting that the MB adsorption was an exothermic multilayer chemisorption. The results of X-ray electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis further confirmed that the reductive adsorption and electrostatic adsorption can account for the outstanding Cr(VI) and MB adsorption capacity of TiVCTx, respectively.

Binary Biosorption of Cu(II) and Cr(VI) by Naturally Formed Biofilm Matrices

Water pollution poses a significant ecological threat, contributing to the widespread degradation of aquatic ecosystems. Among the pollutants, heavy metals pose severe risks to both organisms and human health, emphasizing the urgent need for effective pollution control technologies. Biosorption presents a promising, cost-effective, and environmentally friendly solution to mitigate heavy metal contamination. Biofilms, consisting of microbial communities, have emerged as potential biosorbents for heavy metals. Since heavy metals can exist as cations and anions concurrently in aquatic environments, understanding their behavior in binary systems is essential for biosorption strategies. This study focuses on the binary biosorption of Cu(II) and Cr(VI), representing cationic and anionic heavy metals. Specific adsorption sites are identified by analyzing adsorption kinetics, isotherms, and IR spectra of biofilms. The results indicate that biofilms, in a binary scenario, demonstrate nearly identical adsorption capacities for Cu(II) and Cr(VI). Moreover, the adsorption process follows the Langmuir adsorption model, emphasizing the potential of biofilms as effective biosorbents for the simultaneous removal of cationic and anionic heavy metals. This study advocates for a sustainable approach to heavy metal remediation through the utilization of biofilms.

Optimal preparation of magnetic diatomite for simultaneous removal of cationic and anionic heavy metal

Magnetic diatomite can remove both cationic and anionic heavy metals. In the study, with crystalline Miyi diatomite with a low purity and a low activity as the carrier, magnetic diatomite was prepared by the co-precipitation method, and the preparation process was further optimized. XRD, SEM, and ICP-OES characterized the prepared composites. The optimized process parameters of magnetic diatomite preparation were determined as follows: n ( Fe 2+ ) / n ( Fe 3+ ) mole ratio of 1:2, 1.0 mol/L Fe 2+ , 2.0 mol/L Fe 3+ , 1.5 mol/L NaOH, and a synthesis temperature of 30 °C. The as-prepared magnetic diatomite was ferromagnetic, negatively charged, easy to recover, and had a specific surface area of 70.5227 m2/g. It realized the good removal effect on a single contaminant ( VO 3 − , Cr 2 O 7 2− or Cd 2+ ). Especially in the complex solution containing the three contaminants, the overall removal rate of VO 3 − , Cr 2 O 7 2− and Cd 2+ was above 85%.

Photochemical Origins of Iron Flocculation in Acid Mine Drainage.

Acid mine drainage (AMD) raises a global environmental concern impacting the iron cycle. Although the formation of Fe(III) minerals in AMD-impacted waters has previously been reported to be regulated by biological processes, the role of abiotic processes remains largely unknown. This study first reported that a photochemical reaction coupled with O2 significantly accelerated the formation of Fe(III) flocculates (i.e., schwertmannite) in the AMD, as evidenced by the comparison of samples from contaminated sites across different natural conditions at latitudes 24-29° N. Combined with experimental and modeling results, it is further discovered that the intramolecular oxidation of photogenerated Fe(II) with a five-coordinative pyramidal configuration (i.e., [(H2O)5Fe]2+) by O2 was the key in enhancing the photooxidation of Fe(II) in the simulated AMD. The in situ attenuated total reflectance-Fourier transform infrared spectrometry (ATR-FTIR), UV-vis spectroscopy, solvent substitution, and quantum yield analyses indicated that, acting as a precursor for flocculation, [(H2O)5Fe]2+ likely originated from both the dissolved and colloidal forms of Fe(III) through homogeneous and surface ligand-to-metal charge transfers. Density functional theory calculations and X-ray absorption spectroscopy results further suggested that the specific oxidation pathways of Fe(II) produced the highly reactive iron species and triggered the hydrolysis and formation of transient dihydroxo dimers. The proposed new pathways of Fe cycle are crucial in controlling the mobility of heavy metal anions in acidic waters and enhance the understanding of complicated iron biochemistry that is related to the fate of contaminants and nutrients.

Optimizing 2D MoS2 for removal of anionic heavy metals from water: insights from density functional theory study

Optimizing 2D MoS2 for removal of anionic heavy metals from water: insights from density functional theory study

Construction of polyaniline/MXene/graphene oxide ternary nanohybrid for sequestration and reduction of hypertoxic Cr(VI) in water

The anionic heavy metal contaminant chromium (Cr) is highly mobile, oxidizing, and carcinogenic, predisposing it to a range of biological health and environmental issue. Herein, polyaniline/MXene/graphene oxide ternary nanohybrid (PMG) with multiple types of functional groups and high efficiency of electron transfer capacity was synthesized by electrostatic self-assembly of polyaniline (PANI)-assisted MXene and graphene oxide (GO) two-dimensional nanoplates for the adsorption of hazardous Cr(VI). The charge transfer process promoted the polymerization of aniline on the surface of MXene, and the generation of PANI induced MXene and GO to intercalate with each other and ultimately ameliorated the over-negative potential of the MXene and GO composites. The adsorbent PMG exhibited the optimum adsorption effectiveness of 156.2 mg/g for Cr(VI) at pH = 2 and a sample dosage of 1 g/L. Isotherm and kinetic exploration experiments, combined with the findings of zeta potential, XPS, and first-principles calculations, indicated that approximately 89.3% of Cr(VI) was transformed into Cr(III) and anchored by PMG, revealing the adsorption mechanism to be probably a multilayered chemisorption involving redox reactions, electrostatic interactions, and complexation. The anti-interference experiments and cycling tests further confirmed the prominent application potential of PMG. This study provides feasible insights for remediating water contaminated with hexavalent chromium.

Ionized acrylamide-based copolymer / terpolymer hydrogels for recovery of positive and negative heavy metal ions.

In this study, we explored the effective capture of both cations and anions onto a single adsorbent. Acrylamide (AAm) served as the polymer backbone, onto which co-monomers sodium p-styrenesulfonate (SS) and N,N-dimethylaminopropyl acrylamide (DMAPAA) were grafted, creating ionized polymer hydrogel adsorbents. These adsorbents were engineered for the synergistic separation and recovery of heavy metal cations and anions from concentrated solutions, focusing specifically on industrially significant ions such as Ni2+-, Cu2+, Zn2+ and (Cr2O7)2-. The adsorption and desorption behaviors of the AAm terpolymer hydrogels were investigated across various pH solutions, considering the competition and concentrations of these specific metal ions. Moreover, the study delved into the effects of the internal pH environment within the hydrogel adsorbents, determining its impact on the type of metal adsorbed and the adsorption capacity. Our findings indicated that the adsorption of cations was enhanced with a higher proportion of SS relative to DMAPAA in the hydrogel. In contrast, significant anion capture occurred when the concentration of DMAPAA exceeded that of SS. However, equal ratios of SS and DMAPAA led to a noticeable reduction in the adsorption of both types of substrates, attributed to the counteractive nature of these co-monomers. To enhance the adsorption efficiency, it may be necessary to consider methods for micro-scale separation of the two types of monomers. Additionally, the adsorption capacity was observed to be directly proportional to the swelling capacity of the hydrogels. For complete desorption and separation of the cations and anions from the adsorbent, the application of concentrated NaOH solutions followed by HNO3 was found to be essential. Given the varying concentrations of cation and anion pollutants, often present in heavy metal factory effluents, it is crucial to fine-tune the ratios of DMAPAA and SS during the synthesis process. This adjustment ensures optimized efficiency in the decontamination and recovery of these significant heavy metal ions.

Advances in mechanism for the microbial transformation of heavy metals: implications for bioremediation strategies.

Heavy metals are extensively discharged through various anthropogenic activities, resulting in an environmental risk on a global scale. In this case, microorganisms can survive in an extreme heavy metal-contaminated environment via detoxification or resistance, playing a pivotal role in the speciation, bioavailability, and mobility of heavy metals. Therefore, studies on the mechanism for the microbial transformation of heavy metals are of great importance and can provide guidance for heavy metal bioremediation. Current research studies on the microbial transformation of heavy metals mainly focus on the single oxidation, reduction and methylation pathways. However, complex microbial transformation processes and corresponding bioremediation strategies have never been clarified, which may involve the inherent physicochemical properties of heavy metals. To uncover the underlying mechanism, we reclassified heavy metals into three categories based on their biological transformation pathways, namely, metals that can be chelated, reduced or oxidized, and methylated. Firstly, we comprehensively characterized the difference in transmembrane pathways between heavy metal cations and anions. Further, biotransformation based on chelation by low-molecular-weight organic complexes is thoroughly discussed. Moreover, the progress and knowledge gaps in the microbial redox and (de)methylation mechanisms are discussed to establish a connection linking theoretical advancements with solutions to the heavy metal contamination problem. Finally, several efficient bioremediation strategies for heavy metals and the limitations of bioremediation are proposed. This review presents a solid contribution to the design of efficient microbial remediation strategies applied in the real environment.

Engineering a sustainable cadmium sulfide/polyethyleneimine-functionalized biochar/chitosan composite for effective chromium adsorption: optimization, co-interfering anions, and mechanisms.

A novel eco-friendly adsorbent was fabricated by mixing mushroom-derived cadmium sulfide and polyethyleneimine-functionalized biochar that was fabricated from coffee waste with a chitosan biopolymer. The green-synthesized CdS/PEI-BC/CTS composite was analyzed using several characterization methods to identify its morphological, compositional, and structural characteristics. In addition, the adsorption property of the composite was investigated for hexavalent chromium as a model for anionic heavy metals. The best adsorption conditions to efficiently adsorb Cr(vi) onto CdS/PEI-BC/CTS were scrutinized in the batch mode. The experimental results elucidated that the higher adsorption efficacy for Cr(vi) was 97.89% at pH = 3, Cr(vi) concentration = 50 mg L-1, CdS/PEI-BC/CTS dose = 0.01 g, and temperature = 20 °C. The impact of co-interfering anionic species on Cr(vi) adsorption was identified in simulated wastewater. The recycling property of the CdS/PEI-BC/CTS composite was assessed for ten runs to ensure the applicability of the green composite. The adsorption mechanism and interaction types were proposed on the basis of kinetic and isotherm studies, along with analysis tools. The mechanistic study proposed that the Cr(vi) adsorption onto CdS/PEI-BC/CTS occurred via chemical and physical pathways, including protonation, electrostatic interactions, reduction, and coordination bonds.

Codisposal of landfill leachate concentrate and antimony mine soils using a one-part geopolymer system for cationic and anionic heavy metals immobilization

Geopolymer solidification/stabilization technology has developed rapidly in the remediation field of heavy metal-contaminated soil. However, geopolymers exhibit low anionic heavy metal immobilization efficiency due to their electronegativity and alkali activation characteristics. This study constructed a one-part blast furnace slag-based geopolymer system using landfill leachate concentrate (LLC) as chlorine and humic acid sources and achieved the solidification/stabilization of cations (Cd, Cu, Hg, and Pb) and anions (Sb and As) in the antimony mine soils (AMS). The LLC addition increased the Sb and As fixation rates from 92%∼94% and 82∼86%, respectively, to over 99%, reducing the leaching concentration of all heavy metal ions to the ppb level. LLC improved the chemical stability and physical encapsulation of Sb/As in three ways: inducing a Friedel’s salt (FS) formation, enhancing humic acid complexation/chelation, and promoting geopolymerization. Wet curing was more conducive to FS formation in the geopolymer than dry curing and increased the 28-day compressive strength by 38.5%. Due to the SiO2 skeleton support effect in AMS, a 30 wt% AMS addition was beneficial for geopolymer strength development. Our study provided a harmless method for the codisposal of LLC and AMS and improved the efficiency of geopolymer fixation of complex heavy metal cations and anions.

Terra Rossa Soil as an Adsorbent to Remove Hexavalent Chromium in Aqueous Solutions

Kaolinite is a phyllosilicate clay of type 1:1 which is usually associated with iron oxides in nature. The clay is abundant in Terra Rossa soils which is located in the Gunungkidul, karst area. Based on the structure and nature of it’s the charge, it has the potential to adsorb anionic heavy metals, especially hexavalent chromium. Heavy metal chromium in the form of hexavalent is very dangerous for human health and the metal is mostly produced from the waste of leather tanning factories that are widely available in Yogyakarta. The purpose of this study was to investigate the possibility of using Terra Rossa soil as an adsorbent to remove heavy metal Cr (VI) from aqueous solution. The experiment was carried out by mixing the adsorbent with a dose of: 1 – 4.5 grams of fine soil, Φ 0.5 mm into a 50 ml solution containing 10 ppm chromium with pH 5 and 3. Stirred at 200 rpm for 2 hours, then centrifuged 3500 rpm for 20 minutes. The filtrate was given phosphoric acid and diphenyl carbazide and then measured using a spectrophotometer with a wavelength of 540 nm. The results showed that the average percentage of chromium removal at pH 5 = 30%, while pH 3 = 49%. The adsorbent absorption (mg/g) decreased in line with increasing adsorbent dose. Absorption graphs of Freundlich and Langmuir models in pH3 solution show R2=0.9264 and 0.9361 respectively, while in pH5 solution the R2 values are 0.3752 and 0.3461, respectively. Adsorption capacity according to Freundlich = 1.7331 mg/g, while according to Langmuir = 5.28 mg/g with adsorption site affinity 0.1894 L/mol.

Removal of Cationic and Anionic Heavy Metal Ions From Aqueous Phase by a HGMS and Magnetized Zeolite

A magnetic separation study was conducted employing magnetized zeolite and a high gradient magnetic separation system (HGMS) for removal of both cationic and anionic heavy metals. Magnetized zeolite Y was prepared with variable iron contents ranged from 1.2-22.8% based on surface concentration. The magnetized zeolite showed decreased adsorption capacity for cations while the adsorption capacity of the adsorbent for anion increased and the adsorption capacity was proportional to the iron contents. The captured rate of dispersed adsorbents after use for removal of contaminants is a very important factor in water treatment processes. The magnetic separation system recovered more than 98% of magnetized zeolite at 3 T of magnetic field. Current result indicates the combination of magnetized zeolite and HGMS separation could be an efficient alternative for simultaneous removal of cationic and anionic heavy metal from water phase.

Autonomous enrichment and deep removal of heavy metals by salt-tolerant gradient polyelectrolyte hydrogels

The integration of nanostructured materials into hydrogel matrix with chemical gradient holds great promise in gathering the pollutants and enhancing their adsorption or photocatalytic performance. However, the electric potentials rooting in the common gradient polyelectrolyte hydrogel are almost completely shielded by the co-existing counter-ions. In this study, a salt-tolerant gradient polycationic electrolyte hydrogel was fabricated by free radical copolymerization under the induction of unilateral UV illumination, which was used as nanofillers matrix. The cation-π interactions between the adjacent cations and aromatic rings endow the gradient polycationic electrolyte hydrogels deserving the salt-tolerant properties. Thus, the build-in electric potentials are still reactive on enrichment of the anionic heavy metals in highly concentrated salt solutions, altering the defects of the common gradient polyelectrolyte hydrogel. Using Sb(V) adsorption and Cr(VI) photocatalytic reduction as target reactions, the gradient composite hydrogels always display fast and high removal capacities towards these anionic pollutants in the saline solutions of 500 mM, as well as good stability and reusability. This salt-tolerant hydrogel matrix provides a smart material platform with self-driven forces in the fields of pollutant enrichment and removal.

Removal of Cr(VI) from tanning wastewater using chitosan-SDS complexes in PEUF: Optimization and analysis via response surface methodology

In this study, we addressed the removal of hexavalent chromium (Cr(VI)), a highly toxic and soluble anionic heavy metal, using enhanced ultrafiltration (UF). The objective was to eliminate Cr(VI) species with molecular weights beyond the retention capability of standard UF membranes and achieve their retention through the incorporation of polymers and polymer-surfactant complexes within the UF membrane. Chitosan, a cationic polymer, and sodium lauryl sulfate (SDS), an anionic surfactant, were used in this context. The Cr(VI) solution was subjected to ultrafiltration in a laboratory-scale membrane cell, and its removal was assessed spectrophotometrically. Polymer and surfactant structures were characterized using turbidity, electrical conductivity, SEM-EDX, and FTIR analyses. Experimental studies were conducted using the face-centered central composite design (CCD) of the response surface methodology (RSM) to determine optimal removal and permeate flux values, as well as to unveil the relationships between the studied factors and the resulting responses.The results revealed that 100 % of the Cr(VI) species were removed from wastewater in the chitosan-based polymer-enhanced ultrafiltration (PEUF) study. With the chitosan-SDS complex, a removal efficiency of 98.33 % was achieved in synthetic wastewater. The PEUF study employing chitosan and the chitosan-SDS complex yielded permeate flux values of 30.73 L/h/m2 and 53.89 L/h/m2, respectively. The optimized conditions obtained from the models were then applied to real wastewater obtained from a leather industry tanning process. In the case of chitosan and the chitosan-SDS complex, the Cr(VI) removal efficiencies in the real wastewater were 4.40 % and 98.33 %, respectively.

Plasmonic nanoparticle's anti-aggregation application in sensor development for water and wastewater analysis.

Colorimetric sensors have emerged as a powerful tool in the detection of water pollutants. Plasmonic nanoparticles use localized surface plasmon resonance (LSPR)-based colorimetric sensing. LSPR-based sensing can be accomplished through different strategies such as etching, growth, aggregation, and anti-aggregation. Based on these strategies, various sensors have been developed. This review focuses on the newly developed anti-aggregation-based strategy of plasmonic nanoparticles. Sensors based on this strategy have attracted increasing interest because of their exciting properties of high sensitivity, selectivity, and applicability. This review highlights LSPR-based anti-aggregation sensors, their classification, and role of plasmonic nanoparticles in these sensors for the detection of water pollutants. The anti-aggregation based sensing of major water pollutants such as heavy metal ions, anions, and small organic molecules has been summarized herein. This review also provides some personal insights into current challenges associated with anti-aggregation strategy of LSPR-based colorimetric sensors and proposes future research directions.

Removal of Heavy Metal Ions Using Pristine and Functionalized Natural Zeolites

Heavy metal ions have attracted significant concern regarding their toxicity in living organisms. Concurrently, the removal of heavy metals by the adsorption method is also under the spotlight because it is effective, less cost-demanding, and easy to operate. To date, natural zeolites become one of the most used adsorbents for it is low cost, abundant in reserve, and has high selectivity towards heavy metal. Zeolites possess negatively charged three-dimensional frameworks built by SiO4 and AlO4 tetrahedra, which are balanced by counter-cations. The cations within zeolite frameworks can be exchanged with the heavy metal cations in an aqueous environment. This review comprehensively reports the adsorption capacity of heavy metal ions using pristine and modified natural zeolite. The important aspects, including the physicochemical properties of pristine and modified natural zeolites, heavy metal ion adsorption isotherms, kinetics, and thermodynamics, are discussed in detail. It is imperative to note that the physicochemical properties of natural zeolites greatly determine the adsorption capability. Furthermore, natural zeolites could be modified with various molecules such as surfactants and polymers to improve the adsorption capacity and adsorb heavy metal anions. Ultimately, this review is concluded with prospects for future improvement.

Removal Performance of KOH-Modified Biochar from Tropical Biomass on Tetracycline and Cr(VI).

Biochar can be used to address the excessive use of tetracycline and micronutrient chromium (Cr) in wastewater that potentially threatens human health. However, there is little information about how the biochar, made from different tropical biomass, facilitates tetracycline and hexavalent chromium (Cr(VI)) removal from aqueous solution. In this study, biochar was prepared from cassava stalk, rubber wood and sugarcane bagasse, then further modified with KOH to remove tetracycline and Cr(VI). Results showed that pore characteristics and redox capacity of biochar were improved after modification. KOH-modified rubber wood biochar had the highest removal of tetracycline and Cr(VI), 1.85 times and 6 times higher than unmodified biochar. Tetracycline and Cr(VI) can be removed by electrostatic adsorption, reduction reaction, π-π stacking interaction, hydrogen bonding, pore filling effect and surface complexation. These observations will improve the understanding of the simultaneous removal of tetracycline and anionic heavy metals from wastewater.

Efficiency and mechanism in preparation and heavy metal cation/anion adsorption of amphoteric adsorbents modified from various plant straws

Cellulose can be modified for the loading of functional groups such as amino groups, sulfydryl groups, and carboxyl groups. Cellulose-modified adsorbents generally have specific adsorption capacities for either heavy metal anions or cations, and possess the advantages of wide raw material source, high modification efficiency, high adsorbent recyclability, and great convenience in recovery of the adsorbed heavy metals. At present, preparation of amphoteric heavy metal adsorbents from lignocellulose has attracted great attention. However, the difference in efficiency of preparing heavy metal adsorbents by modification of various plant straw materials and mechanism for the difference remain to be further explored. In this study, three plant straws, including Eichhornia crassipes (EC), sugarcane bagasse (SB) and metasequoia sawdust (MS), were sequentially modified by tetraethylene-pentamine (TEPA) and biscarboxymethyl trithiocarbonate (BCTTC) to obtain amphoteric cellulosic adsorbents (EC-TB, SB-TB and MS-TB, respectively), which can simultaneously adsorb heavy metal cations or anions. The heavy metal adsorption properties and mechanism before and after modification were compared. Pb(II) and Cr(VI) removal rates by the three adsorbents were 2.2–4.3 folds and 3.0–13.0 folds of those before modification, respectively, following the order of MS-TB > EC-TB > SB-TB. In the five-cycle adsorption-regeneration test, the Pb(II) and Cr(VI) removal rate by MS-TB decreased by 58.1 % and 21.5 %, respectively. Among the three plant straws, MS possessed the most abundant hydroxyl groups and the largest specific surface area (SSA), and accordingly MS-TB had the highest load of adsorption functional groups [(C)NH, (S)CS and (HO)CO] and also the largest SSA among the three adsorbents, which contribute to its highest modification and adsorption efficiency. This study is of great significance for screening suitable raw plant materials to prepare amphoteric heavy metal adsorbents with superior adsorption performance.

An ultralight and flexible nanofibrillated cellulose/chitosan aerogel for efficient chromium removal: Adsorption-reduction process and mechanism

Heavy metals in water are critical global environmental problems. In particular, the anionic heavy metal chromium (Cr) has carcinogenic and genotoxic risks on human health. To this end, an ultralight and flexible nanofibrillated cellulose (NFC)/chitosan (CS) aerogel was developed only by freeze-drying combined with physical thermal cross-linking for efficient one step co-removal of Cr(VI) and Cr(III). The maximum adsorption capacity of Cr(VI) and total Cr calculated according to the Langmuir model was 197.33 and 134.12 mg/g, respectively. Even in the presence of competing soluble organics, anions and oil contaminants, the resulting NFC/CS-5 aerogels showed excellent selectivity. The aerogel exhibited outstanding mechanical integrity, remaining intact after 17 compressions in air and underwater. Meanwhile, after 5 adsorption-desorption cycles, the aerogel was easy to regenerate and maintained a high regeneration efficiency of 80.25%. Importantly, self-assembled NFC/CS-5 aerogel filter connected with the peristaltic pump could purify 752 mL of industrial wastewater with Cr(VI) pre-concentration capacity of 49.71 mg/g. XPS and FT-IR verified that electrostatic interactions, reduction and complexation acted as the main driving forces for the adsorption process. Moreover, such aerogel possessed broad application prospects for alleviating heavy metal pollution in agriculture.