Electrostatic Complexation Research Articles

Construction of magnetic particles sprayed hydroxyapatite based bio-ceramic beads for selective fluoride removal

The current study concentrates on the fabrication of hydroxyapatite in an exploitable bead form with enhance defluoridation capacity (DC) and quick separation. Hence, magnetic iron oxide/alginate-gelatin/hydroxyapatite/β-cyclodextrin based beads (MAGHC bio-ceramic beads) were prepared and constructively utilized for fluoride retention from water. The responsible parameter for fluoride removal was performed by batch mode. The physic-chemical properties of the developed MAGHC bio-ceramic beads were characterized with different sophisticated instrumental methods namely EDAX, SEM and FTIR studies. The different adsorption kinetic and isotherms studies were carried out to fit experimental data of fluoride adsorption onto MAGHC bio-ceramic beads. The fluoride adsorption method was thermodynamically feasible and endothermic nature. Defluoridation by MAGHC bio-ceramic beads was majorly governed by electrostatic interaction and complexation. The reusable and actual real water sample test also investigated using developed MAGHC bio-ceramic beads. The results revealed that MAGHC bio-ceramic beads could reusable and efficiently remove fluoride from drinking water at field condition.

Wet-Process-Modified Blue-Green Algae Biochar by K2FeO4 for the Efficient Adsorption of Cr(VI) from Water

Iron-modified biochar adsorbent shows its promise for removing Cr(VI) from water. However, the traditional dry-grinding modification methods to prepare iron-modified biochar (DFeBC) usually result in the aggregation of iron oxide particles, thus impeding the adsorption capacity. Herein, blue-green algae waste derived biochar modified in a wet process by K2FeO4 (WFeBC) was developed, and it showed well-distributed iron oxide on the surface of the biochar. As a result, WFeBC displayed a larger theoretical adsorption capacity of 66.22 mg/g than that of DFeBC (48.54 mg/g). It was found that the uniform-distributed iron oxide and abundant oxygen functional groups of WFeBC played an important role in the removal process of Cr(VI). In the adsorption process, the reduction of Cr(VI) to Cr(III) by Fe(II) promoted the removal of hexavalent chromium. The Cr(VI) will be attracted by protonated oxygen functional groups through electrostatic interaction and complexation in an acid environment. All the results show that the wet modification of biochar by K2FeO4 can effectively improve the removal ability of WFeBC to Cr(VI).

Addition of gelatin increased the spray drying performance of the Pickering emulsion stabilized by the ovalbumin – gum Arabic electrostatic complex

Gelatin was added to the perilla seed oil (PSO) Pickering emulsion stabilized by the ovalbumin (OVA) – gum Arabic (GA) electrostatic complex to increase its spray drying performance. The results indicated that the addition of gelatin to the primary PSO Pickering emulsion in mass ratio to the OVA – GA complex 1:1 before high-pressure homogenization could increase the total solid concentration of the feed to 20% and decrease the surface oil content of the resultant powder to 9.90% without compromising its total oil content (77.84%) and powder yield (76.08%) compared with that in the absence of gelatin. Characterization of the Pickering emulsions revealed that gelatin adsorbed to the surface of the primary emulsion droplets through electrostatic interaction and the subsequent high-pressure homogenization caused composition and structure rearrangement in the emulsion interface, leading to reduced particle size and viscosity of the secondary emulsion. The optimized PSO powder possessed excellent structural integrity according to scanning electron microscope observation as well as good flowability and water dispersibility. Hence, the addition of gelatin is an effective strategy to improve the economy for producing powders with ultra-high oil contents by spray drying Pickering emulsions stabilized by the OVA – GA electrostatic complex.

A novel green synthesized magnetic biochar from white tea residue for the removal of Pb(II) and Cd(II) from aqueous solution: Regeneration and sorption mechanism

A novel biochar-based magnetic nanocomposite (GSMB) was prepared from white tea waste via green synthesis method. The sorption properties and regeneration of GSMB were studied using Pb(II) and Cd(II) to better understand its ability in heavy metal recovery. The adsorption kinetics data were modelled using pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models, while Pb(II) and Cd(II) isotherms were modelled with Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models. Results showed that Pb(II) adsorption was well described by pseudo-second order while the Elovich model best described the Cd(II) adsorption trend, indicating the sorption of Pb(II) and Cd(II) onto GSMB were dominated by chemisoprtion rather than physisorption. Langmuir model gave the best fit to Pb(II) sorption, and the Cd(II) adsorption was well described by Temkin model. The maximum adsorption capacity of Pb(II) and Cd(II) onto GSMB were 81.6 mg/g and 38.6 mg/g, respectively. Scanning electron microscope coupled with energy dispersive x-ray, X-ray diffraction and Fourier transform infrared spectroscopy analyses revealed that iron oxides played a key role during adsorption process and the adsorption mechanisms include surface electrostatic attraction and surface complexation for both metals. Among the five regenerating agents studied, 0.1 M EDTA-2Na was favoured for the desorption of Pb(II) onto GMSB. The findings from the regeneration studies revealed ∼54% of Pb(II) adsorption capacity remained after three sorption-desorption cycles implying the adsorbent could potentially be further reused.

Synergistic effect and mechanism of Cd(II) and As(III) adsorption by biochar supported sulfide nanoscale zero-valent iron

Biochar derived from bamboo was used to support sulfide nanoscale zero-valent iron (S-nZVI@BC) for simultaneous removal of Cd(II) and As (III) from aqueous media. Scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) characterization confirmed the successful synthesis of the S-nZVI@BC. Adsorption kinetics and isotherms indicated that co-adsorption of Cd(II) and As(III) onto S-nZVI@BC was well represented by pseudo-second-order model (R2Cd(II) = 0.990, R2As(III) = 0.995) and Langmuir model (R2Cd(II) = 0.954, R2As(III) = 0.936). The maximum adsorption was 162.365 and 276.133 mg/g for Cd(II) and As(III), respectively, in a co-adsorption system, which was significantly higher than that in a single adsorption system (103.195 and 223.736 mg/g, respectively). Batch experiments showed that the Cd(II)-to-As(III) concentration ratio significantly affected the co-adsorption with the optimal ratio of 1:2. Ca2+ and Mg2+ significantly inhibited Cd(II) removal. In contrast, phosphate and humic acid significantly inhibited As(III) removal. Electrochemical analysis indicated S-nZVI@BC had a lower corrosion potential and resistance than nZVI@BC, making it more conducive to electron transfer and chemical reaction. Electrostatic adsorption, complexation, co-precipitation, and redox were the primary mechanisms for Cd(II) and As(III) removal. Overall, the present study provides new insights into the synergistic removal of Cd(II) and As(III) by S-nZVI@BC, which is a very promising adsorbent for the effective removal of Cd(II) and As(III) from contaminated wastewater.

Fe-modified fly ash/cotton stalk biochar composites for efficient removal of phosphate in water: mechanisms and green-reuse potential.

Excessive phosphate content input into natural water can lead to the waste of resource and eutrophication. Biochar is a kind of low-cost adsorbent. However, its adsorption capacity for phosphate is low. In order to solve this problem, Fe compound-modified fly ash/cotton stalk biochar composites (Fe-FBC) were prepared through co-pyrolyzed fly ash and cotton stalk at 800℃, followed by infiltration of FeSO4 solution. The samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, and zeta potential. After modification, the hydrophilicity and polarity of Fe-FBC increased. In addition, the pore volume, specific surface area, and surface functional groups were significantly improved. The adsorption behavior of Fe-FBC for the removal of phosphate from water can be well fitted by the pseudo-second-order kinetic and Sips isotherm adsorption model, with a maximum adsorption capacity of 47.91mg/g. Fe-FBC maintained a high adsorption capacity in the pH range of 3-10. The coexisting anions (NO3-, SO42-, and Cl-) had negligible effects on phosphate adsorption. The adsorption mechanisms of Fe-FBC include electrostatic attraction, ligand exchange, surface complexation, ion exchange, chemical precipitation, and hydrogen bonding. Moreover, the desorption process of phosphate was investigated, indicating that the phosphate-saturated Fe-FBC could use as slow-release phosphate fertilizer. This study proposed a potentially environmental protection and recycling economy approach, which consists of recycling resources and treating wastes with wastes.

Properties of complexes of whey protein isolate fibrils (WPIF) and octenyl succinate starch (OSS) and their applications in emulsion stabilization and custard cream

Emulsifying properties of octenyl succinate starch (OSS), an emulsifier widely used in the food industry, need to be improved further. This work aimed to improve the emulsification properties of OSS based on its complexation with whey protein isolate fibrils (WPIF). The zeta-potential and turbidity results indicated that WPIF and OSS formed soluble electrostatic complexes at a low mixing ratio (r (WPIF/OSS) = 0.10–0.50) and pH 3.0–5.0. According to the FTIR and TEM results of WPIF/OSS complexes, molecular interactions existed between WPIF and OSS. The oil-in-water emulsion with WPIF/OSS complexes as emulsifiers were constructed, and the optimum condition was searched by controlling the pH value of 3.0–7.0, r of 0.10–10.00, and complexes concentration of 0.25–3.00 wt%. The emulsification properties of the WPIF, OSS and WPIF/OSS complexes were evaluated by comparing the particle size, zeta-potential and visual appearance of fresh and stored emulsions. WPIF/OSS complex at r = 0.10, pH = 3.0, and 1.00 wt% total concentration exhibited the best emulsification properties and the best resistance to high salt (200 mM) and high temperature (90 °C). The addition of WPIF/OSS significantly improved the quality of the custard cream. This work used the novel nano-material of WPIF to improve the emulsifying properties of OSS and expanded the application of OSS in food products.

Delamination of multilayer Ti3C2Tx MXene alters its adsorpiton and reduction of heavy metals in water

MXenes are considered as an emerging class of two-dimensional (2D) adsorbent for various environmental applications. In this work, two different morphologies of Ti3C2Tx MXene (multilayer (ML-Ti3C2Tx) and delaminated titanium carbide (DL-Ti3C2Tx)) were prepared through mild in situ HF etching and further delamination. The structural differences between the two were explored with a focus on their effects on the performance and mechanism of removing heavy metals from water. In comparison to ML-Ti3C2Tx, DL-Ti3C2Tx had more oxygen-containing functional groups, higher specific surface area (19.713 vs. 8.243 m2/g), larger pore volume (0.135 vs. 0.040 cm3/g), higher maximum Pb(II) adsorption capacity (77.0 vs. 56.68 mg/g), but lower maximum Cu(II) adsorption capacity (23.08 vs. 55.46 mg/g). Further investigation revealed that the removal of Pb(II) by the MXenes was mainly controlled through electrostatic attraction and surface complexation mechanisms, while Cu(II) was removed mainly through surface reduction by Ti-related groups. Because delamination of ML-Ti3C2Tx increased the surface area and surface functional groups, DL-Ti3C2Tx became a better sorbent for Pb(II) in water. During sonication, however, delamination inevitably led to partial oxidation of Ti3C2Tx nanosheets and thus weakened the reducing ability of DL-Ti3C2Tx for Cu(II) in water. Nevertheless, both ML- and DL-Ti3C2Tx not only exhibited excellent heavy metal adsorption capacity under different solution conditions, but also showed good reusability. Findings of this study indicate that Ti3C2Tx MXenes are promising adsorbents for treating heavy metal pollutants in water.

Investigating the electrostatic complexation of BCNO nanoparticles with a stimuli-responsive double hydrophilic graft copolymer

The co-assembly of nanoparticles within double hydrophilic block copolymers (DHBC) via electrostatic complexation is a novel approach for the development of stimuli-responsive nanodrugs with improved bioavailability, biocompatibility, intracellular uptake, and therapeutic efficacy. This study investigated the co-assembly of boron carbon oxynitride (BCNO) nanoparticles within an acid-labile polyethylene glycol-graft-polyethyleneimine (PEG-g-PEI) DHGC as a promising boron nanodrug for boron neutron capture therapy (BNCT). First, BCNO nanoassemblies are prepared by mixing the charged-neutral graft copolymer of PEG-g-PEI into a dispersion of negatively charged BCNO nanoparticles. The BCNO nanoparticles and DHGC complex were characterized using various techniques, including dynamic light scattering, zeta potential, and transmission electron microscopy (TEM). Additionally, this study investigated the change in the hydrodynamic size and zeta potential of the DHGC/BCNO nanoparticle complexation over a wide range of mixing ratios (VBCNO/VDHGC). The results revealed that the BCNO nanoassemblies formed a stable aqueous dispersion at all mixing ratios investigated in this work. In addition, the size and surface charge of the BCNO nanoassemblies can be systematically modulated by adjusting the mixing ratio, molecular weight of the charged segment, ionic strength, and pH of the solution. TEM analysis revealed that the BCNO nanoassemblies formed at a high mixing ratio exhibited polydispersed size and irregular morphologies. With decreasing mixing ratio, the size of the BCNO nanoassemblies decreased, and the cluster exhibited a spherical morphology. In addition, an increase in the molecular weight of the charged PEI segment (10,000, 60,000, and 270,000 g/mole) of the DHGC resulted in the formation of larger BCNO aggregates. Lastly, the stability and pH-responsive behavior of the BCNO nanoassemblies were investigated at pH of 6.9, 6.0, and 5.0. Under mildly acidic conditions, the Schiff base bond cleaved, which resulted in the disassembly of the BCNO aggregates into smaller clusters with a spherical morphology. The DHGC@BCNO nanoassemblies exhibited an exceptional intracellular boron uptake of 627 ng-B/104 cells in MDA-MB-231 triple-negative breast cancer cells. In comparison, cells treated with bare BCNO nanoparticles and [10B]BPA small molecular boron drug demonstrated intracellular boron uptake of only 125 ng-B/104 cells and 17 ng-B/104 cells, respectively. The study highlights the potential of electrostatic colloidal co-assembly as a synthetic tool for developing hybrid nanomaterials with remarkable intracellular boron loading. This represents a significant step towards the development of an efficacious boron drug for boron neutron capture therapy (BNCT).

Single/co-adsorption and mechanism of methylene blue and lead by β-cyclodextrin modified magnetic alginate/biochar

Due to the high biological toxicity, the concurrent elimination of lead (Pb (II)) and methylene blue (MB) has become a challenging problem. Therefore, a newly β-cyclodextrin (β-CD) modified magnetic alginate/biochar (β-CD@MBCP) material was developed. Comprehensive characterizations proved the successful coating of β-CD onto MBCP surface by microwave-aided fabrication. The β-CD@MBCP achieved high-efficiency uptake for contaminants under a wide pH scope. In the dual system, Pb (II) elimination was facilitated with the presence of MB, due to the active sites provided by MB. In the presence of Pb (II), MB uptake was inhibited due to the electrostatic repulsion between positively charged MB and Pb (II). Electrostatic attraction and complexation contributed to capturing Pb (II), while π-π interactions, host–guest effect, and H-bonding were important in MB elimination. After four cycles, β-CD@MBCP maintained comparatively good renewability. Findings demonstrated that β-CD@MBCP could be an effective remediation material for Pb (II)/MB adsorption from aqueous environments.

Multifunctional sustainable films of bacterial cellulose nanocrystal-based, three-phase pickering nanoemulsions: A promising active food packaging for cheese

Owing to increasing plastic pollution and concerns about food safety, extensive research attention has been paid to biodegradable active packaging. Herein, we developed bacterial cellulose nanocrystal (BCN)-based three-phase Pickering nanoemulsion gelatin (GL) films. In detail, bacterial cellulose was obtained using Acetobacter xylinum, which was then hydrolyzed using sulfuric acid to prepare BCNs. Carnosic acid (CA) and ε-polylysine (εPL) were incorporated into the BCN matrix through electrostatic complexation and the matrix was ultrasonically triggered as an emulsification self-assembly strategy, forming the multifunctional BCN-based three-phase O/W Pickering nanoemulsions (CA-εPL PEs). Furthermore, a novel active packaging film (GL-CA-εPL PEs) was designed via intermolecular hydrogen bonding and dehydration condensation by introducing CA-εPL PEs into the 3D network structures of a GL matrix; both phases showed good interaction and compatibility, along with excellent antioxidant, antibacterial, UV-shielding, good mechanical, heat-sealing, sustainable release, and biodegradable properties. Additionally, fresh (acid-coagulated) and mozzarella cheese were packed in the GL-CA-εPL100 PE film, and their shelf life was extended due to delayed lipid peroxidation and inhibition of the growth of spoilage microorganisms. Sensorial and flavored (GC-IMS) analyses showed no significant differences between the samples packed in the GL-CA-εPL100 PE active film and the unpacked samples. This study provides scientific insights for designing BCN-based O/W multifunctional three-phase Pickering nanoemulsion delivery systems for active food packaging; the proposed method can be promising for reducing the environmental impact of plastic pollution.

Molecular-level investigation on removal mechanisms of aqueous hexavalent chromium by pine needle biochar

Pine needle biochar produced via oxygen-limited pyrolysis at 800 °C for 2 h was used for removing aqueous hexavalent chromium [Cr(VI)] from water. The optimality of the pseudo-second order kinetic model indicated the chemisorption dominated the removal process. Strong acid environment (pH = 2.0) was more conductive to Cr(VI) removal. The functional groups (C–O, O–C–O, C = O) on biochar contributed to Cr(VI) elimination from aqueous solution. The governing removal mechanisms involved electrostatic attraction, reduction, and complexation. Especially, confocal micro-X-ray fluorescence (μ-XRF) mapping indicated that Cr ions and functional groups were primarily distributed on the surface of biochar. This study firstly provided a deep interpretation of Cr speciation and spatial distribution on pine needle biochar, which provided important information on removal mechanisms of Cr(VI) by pine needle biochar.

Synthesis of novel magnetic activated carbon for effective Cr(VI) removal via synergistic adsorption and chemical reduction

The removal of a toxic contaminant like Cr(VI) from the water via green adsorbents like biochar and activated carbon is an eco-friendly technique. In this paper, using commercial activated carbon as a raw material, magnetic ferric oxide/activated carbon (Fe3O4@AC) was prepared by the chemical co-precipitation method, and Cr(VI) adsorption in water was applied. The synthesized materials were characterized by advanced characterization techniques including XRD, BET, FT-IR, and XPS. The effects of initial Cr(VI) concentration, temperature, and adsorption time on the adsorption effect of Cr(VI) were evaluated. Results illustrated that the maximum Cr(VI) adsorption achieved by Fe3O4@AC was 45.3 mg/g, with a removal rate of 88.8% at the optimum pH of 2.0 and an adsorption time of 12 h. Under these conditions, Cr(VI) adsorption by Fe3O4@AC fits the pseudo-second-order kinetic model (PSO) and Langmuir isotherm model and is a spontaneous, endothermic, and irreversible process. The results of BET, XRD, FT-IR, and XPS characterization analysis of Cr(VI) before and after adsorption suggested that the adsorption mechanism of Fe3O4@AC is mainly based on chemisorption, supplemented by physical adsorption, accompanied by electrostatic attraction and complexation.

Competitive adsorption behavior and mechanisms of coexisting EDTA-Cu(Ⅱ) and EDTA-Cr(Ⅲ) on ferrihydrite

EDTA-complexed heavy metals (EDTA-CHMs), one of the typical contaminants in industrial effluents, present challenges for wastewater purification because of their stability and high solubility over a wide pH range. Selective adsorption of various EDTA-CHMs coexisting in industrial wastewater is crucial for the recovery of heavy metal resources. Hence, investigating the competitive behavior and selective adsorption mechanisms of coexisting EDTA-CHMs during the effluent removal process is worthwhile. In this study, we chose Ferrihydrite (Fh) as the adsorbent and focused on the competitive adsorption behavior of two common EDTA-CHMs (EDTA-Cu(Ⅱ) and EDTA-Cr(Ⅲ)) on the Fh surface, as well as their removal mechanisms. For binary systems (EDTA-Cu(Ⅱ) and EDTA-Cr(Ⅲ)), the maximum adsorption capacity of Fh for EDTA-Cu(Ⅱ) was 17.32 mg/g, but because of the coexisting EDTA-Cu(Ⅱ), adsorption of EDTA-Cr(Ⅲ) by Fh was severely inhibited. In a competition experiment with binary contaminants of different EDTA complexes, Fh consistently exhibited stronger adsorption performance on EDTA-Cu(Ⅱ) when the ratio and addition order of EDTA-Cu(Ⅱ) and EDTA-Cr(Ⅲ) in the coexisting system was changed, and the valence state of the EDTA-CHMs was the key factor. The adsorption mechanism indicated that Fh could directly adsorb EDTA-CHMs through electrostatic interaction and surface complexation. The recycling rate of EDTA-Cu(Ⅱ) was still approximately 70.63% after five cycles of treatment with Na2SO4 solution. This study provides new insights into the adsorption behavior of coexisting EDTA-CHMs on adsorbents and the selective removal of related pollutants.

Facile one-step synthesis of CuZn-HDS/alginate hydrogel beads for highly efficient and selective removal of methyl orange

Hydroxy double salts (HDSs) have shown enormous potential for removing dyes from wastewater. However, the powder form of HDSs limits their potential in commercial applications. Herein, we proposed a facile one-step route to incorporate CuZn-HDS into the copper alginate matrix for methyl orange removal. This strategy could not only shape CuZn-HDS to beads but also significantly enhance the adsorption ability of the matrix. The obtained composite hydrogel beads displayed high water stability and excellent adsorption performance for MO, with more than 98% of MO being removed by CuZn-HDS/Alg-0.5. The maximum adsorption capacity of CuZn-HDS/Alg-0.5 for MO was 763.3 mg·g−1 at 298 K. Besides, the adsorption process matched the pseudo-second-order kinetic model and fitted well with the Freundlich model, suggesting that the adsorption of MO onto CuZn-HDS/Alg-0.5 was a multilayer chemical adsorption process. More importantly, CuZn-HDS/Alg-0.5 could selectively adsorb MO from MO & RhB (Rhodamine B) and MO & MB (Methylene blue) mixed solution. Mechanism studies indicated that the removal of MO was attributed to the electrostatic interaction, complexation interaction and ion exchange interaction between MO and CuZn-HDS/Alg-0.5. This work opens a new route for developing eco-friendly and efficient adsorbents to remove dyes from wastewater.

A Photochemical Study of Photo-Induced Electron Transfer from DNAs to a Cationic Phthalocyanine Derivative.

Water-soluble cationic gallium(III)-Pc complex (GaPc) is capable of photogenerating ROSs but does not exhibit photocytotoxicity in vivo. GaPc binds selectively, through a π-π stacking interaction, to the 5'-terminal G-quartet of a G-quadruplex DNA. The photo-excited state of GaPc of the complex is effectively quenched through electron transfer (ET) from the ground state of DNA guanine (G) bases to the photo-excited state of GaPc (ET(G-GaPc)). Hence the loss of the photocytotoxicity of GaPc in vivo is most likely to be due to the effective quenching of its photo-excited state through ET(G-GaPc). In this study, we investigated the photochemical properties of GaPc in the presence of duplex DNAs formed from a series of sequences to elucidate the nature of ET(G-GaPc). We found that ET(G-GaPc) is allowed in electrostatic complexes between GaPc and G-containing duplex DNAs and that the rate of ET(G-GaPc) (kET(G-GaPc)) can be reasonably interpreted in terms of the distance between Pc moiety of GaPc and DNA G base in the complex. We also found that the quantum yields of singlet oxygen (1O2) generation (ΦΔs) determined for the GaPc-duplex DNA complexes were similar to the value reported for free GaPc (Fujishiro R, Sonoyama H, Ide Y, et al (2019) J Inorg Biochem 192:7-16), indicating that ET(G-GaPc) in the complex is rather limited. These results clearly demonstrated that photocytotoxicity of GaPc is crucially affected by ET(G-GaPc). Thus elucidation of interaction of a photosensitizer with biomolecules, i.e., an initial process in PDT, would be helpful to understand its subsequent photochemical processes.

“One-can” strategy for the synthesis of hydrothermal biochar modified with phosphate groups and efficient removal of uranium(VI)

Significant selectivity, reasonable surface modification and increased structural porosity were three key factors to improve the competitiveness of biochar in the adsorption field. In this study, a hydrothermal bamboo-derived biochar modified with phosphate groups (HPBC) was synthesized using “one-can” strategy. BET showed that this method could effectively increase the specific surface area (137.32 m2 g−1) and simulation of wastewater experiments indicated HPBC had an excellent selectivity for U(VI) (70.35%), which was conducive to removal of U(VI) in real and complex environments. The accurate matchings of pseudo-second-order kinetic model, thermodynamic model and Langmuir isotherm showed that at 298 K, pH = 4.0, the adsorption process dominated by chemical complexation and monolayer adsorption was spontaneous, endothermic and disordered. Saturated adsorption capacity of HPBC could reach 781.02 mg g−1 within 2 h. The introduction of phosphoric acid and citric acid by “one-can” method not only provided abundant -PO4 to assist adsorption, but also activated oxygen-containing groups on the surface of the bamboo matrix. Results showed that adsorption mechanism of U(VI) by HPBC included electrostatic action and chemical complexation involving P–O, PO and ample oxygen-containing functional groups. Therefore, HPBC with high phosphorus content, outstanding adsorption performance, excellent regeneration, remarkable selectivity and green value provided a novel solution for the field of radioactive wastewater treatment.

Preparation of a new gel-type lignin-based cationic adsorption resin for efficient removal of Ca2+ from aqueous solutions

Presently, most studies on modified lignin focused on the adsorption to heavy metal cations, but rarely to Ca2+ in hard water. Therefore, this work prepared a new gel-type lignin-based cationic adsorption resin (E-LSAF) through the crosslinking and curing of alkali lignin grafted by sodium sulfite sulfonated acetone to remove Ca2+ in water. Under the determined optimum synthesis conditions, E-LSAF with a highest sulfonic group content of 1.99 mmol/g was obtained. Structural and physicochemical measuring results showed E-LSAF was a gel-type resin, owning strong hydrophilicity, high mechanical strength, excellent thermal stability and acid-alkaline resistance. Adsorption results indicated the adsorption of E-LSAF to Ca2+ was well-fitted by Langmuir model, and the maximum adsorption capacity reached 45.8 mg/g. Pseudo-second-order model can describe this adsorption process well, suggesting it a chemisorption process. Dynamic column adsorption results showed E-LSAF could transform hard water into soft or even very soft water. The regeneration efficiency still maintained 80 % after 5 cycles. The adsorption mechanism was attributed to electrostatic attraction, ion exchange and complexation. This work provided a high-performance lignin-based cationic adsorption material with high adsorption capacity to Ca2+ and excellent acid-alkaline resistance, which filled the research gap of using modified sulfonated lignin to remove Ca2+ from water.

Efficient cadmium immobilization by organic loaded Na-montmorillonite in a contaminated soil

Clay minerals are effective sorbents for toxic metal immobilization in contaminated soils and waters. However, their Cd immobilization efficiency is unclear when they are loaded with organics. In this study, sodium montmorillonite (Na-M) was successfully loaded with potassium humate, chitosan, and glycine to adsorb Cd(II) in solution. Potassium humate loaded Na-M (Na-M-HA), which had the highest specific surface area and cation exchange capacity (CEC), showed the highest Cd(II) adsorption capacity (73.7 mg g−1), 22.5 % and 81.8 % higher than that of chitosan loaded Na-M (Na-M-CTS) and glycine loaded Na-M (Na-M-G), respectively. The pseudo-second-order kinetic model best described (R2 > 0.98) the adsorption kinetics of Cd(II) on the three Na-Ms, indicating that the adsorption processes were of chemisorption nature. The adsorption isotherm of Cd(II) on Na-M-HA was of the Freundlich type, suggesting multilayer adsorption. In contrast, the isothermal adsorption of Cd(II) on Na-M-CTS (R2 = 0.99) and Na-M-G (R2 = 0.89) was better described by the Langmuir model, suggesting the dominance of monolayer adsorption in the adsorption process. High temperature, high pH, low background ionic strength, and low valence competing cations favored Cd(II) adsorption on Na-M-HA. The underlying mechanisms of Cd(II) sorption on Na-M-HA were electrostatic attraction, ion exchange and complexation. Na-M-HA was applied to a Cd polluted soil planted with lettuce (Lactuca sativa L.). in a pot experiment. Compared to the control with no adsorbent application, Na-M-HA application at 2 % effectively reduced the available Cd content in soil and Cd accumulation in plant by 36.0 % and 56.8 %, respectively. This work demonstrated that Na-M-HA is a green, low-cost and excellent adsorbent for Cd stabilization, and that its application in Cd-polluted soils can efficiently reduce Cd bioavailability and thereby Cd transfer along the food chain and eventually reduce the threat of Cd pollution to human health.

Facile production of highly active rice straw bioadsorbent to remove Cu in wastewater

A bioadsorbent with a high specific surface area and high content of oxygen-containing functional groups was prepared from silica depleted rice straw ash (SDRSA). The starting material was a by-product of rice straw after alkoxysilane extraction. The maximum adsorption capacity of SDRSA for copper ions was 26.7 mg/g, which was higher than previously reported biomass adsorbents. The effects of adsorbent dose, pH, contact time, and other conditions on the adsorption performance of SDRSA on Cu2+ were investigated. The adsorption process of Cu2+ on SDRSA was well fitted by the Langmuir isotherm model and the pseudo-second-order kinetic model. The physicochemical properties and adsorption mechanism of SDRSA were investigated by specific surface area testing (BET), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Boehm titration methods. Electrostatic interaction, complexation, ion exchange, and precipitation are the possible Cu2+ removal mechanisms. The preparation method requires only simple washing and drying, and the alcohol can be distilled and recycled. Thus, SDRSA is very low cost and convenient to prepare in large quantities. This work presents a novel approach to optimize adsorbent production to mitigate heavy metal pollution.