Highly efficient adsorption of Pb(II) from aqueous solution using amino-functionalized SBA-15/calcium alginate microspheres as adsorbent

A comprehensive review on preparation and functional application of the wood aerogel with natural cellulose framework

As the traditional aerogel has defects such as poor mechanical properties, complicated preparation process, high energy consumption and non-renewable, wood aerogel as a new generation of aerogel shows unique advantages. With a natural cellulose framework, wood aerogel is a novel nano-porous material exhibiting exceptional properties such as light weight, high porosity, large specific surface area, and low thermal conductivity. Furthermore, its adaptability to further functionalization enables versatile applications across diverse fields. Driven by the imperative for sustainable development, wood aerogel as a renewable and eco-friendly material, has garnered significant attention from researchers. This review introduces preparation methods of wood aerogel based on the top-down strategy and analyzes the factors influencing their key properties intending to obtain wood aerogels with desirable properties. Avenues for realizing its functionality are also explored, and research progress across various domains are surveyed, including oil-water separation, conductivity and energy storage, as well as photothermal conversion. Finally, potential challenges associated with wood aerogel exploitation and utilization are addressed, alongside discussions on future prospects and research directions. The results emphasize the broad research value and future prospects of wood aerogels, which are poised to drive high-value utilization of wood and foster the development of green multifunctional aerogels.

Visualized adsorption and enhanced photocatalytic removal of Cr6+ by carbon dots-incorporated fluorescent nanocellulose aerogels

In this study, carbon dots (CDs) and titanate nanofibers (TNs) were mixed with TEMPO-oxidized nanocellulose (TOCNC) to prepare fluorescent nanocellulose aerogels (FNAs) by a Schiff base reaction. The resulting FNA can detect the adsorption of Cr6+ through the fluorescence quenching in CDs and promote the removal of Cr6+ through the synergistic effect of CDs in photocatalysis. The optimized FNA has a maximum adsorption capacity of 543.38 mg/g, higher than most reported Cr6+ adsorbents. This excellent performance is due to the porous structure of the aerogel, which gives it a high specific surface area of 20.53 m2/g and provides abundant adsorption sites. Simultaneously, CDs can enhance the amino-induced Cr6+ adsorption, improve the photocatalytic performance of TNs, and expose more adsorption sites through electrostatic adsorption of amino-induced reduction products (Cr3+). This study explores the preparation of visualized nanosorbents with enhanced photocatalytic removal of Cr6+ and provides a new direction for nanoscale photocatalysts.

Efficient removal of Cu2+ and methylene blue pollutants from an aqueous solution by applying a new hybrid adsorbent based on alginate-chitosan and HAP derived from Moroccan rock phosphate

Alginate-chitosan/hydroxyapatite (Alg-Cs/HAP) beads were prepared as adsorbent to remove methylene blue (MB) and copper ions from an aqueous solution using a batch system. FTIR, TGA, point of zero charge (pHpzc), SEM, XRD, and BET analysis were used to characterize the elaborated material. The effect of several parameters such as initial pH value, adsorbent dose, temperature, contact time, and initial pollutant concentration were also investigated. The obtained results showed that Alg-Cs/HAP exhibit excellent adsorption properties for Cu (II) and MB removal, with high adsorption capacities of copper ions (208.34 mg/g) and methylene blue (454.54 mg/g). The kinetic of the adsorption process is correlated with the pseudo-first-order for methylene blue and the pseudo-second-order for copper ions. The equilibrium data for MB dye fitted the Freundlich isotherm model, thus implying that the adsorption process consists of multilayer adsorption as well as interactions between the adsorbate and the adsorbent. The equilibrium data for copper ions corresponds closely with the Langmuir model which suggests that the adsorbed molecules occur over a monolayer. Various thermodynamic parameters such as the standard Gibbs energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were calculated. All results indicated that Alg-Cs/HAP material has a good potential for the treatment of wastewater.

Utilization of KOH-modified fly ash for elimination from aqueous solutions of potentially toxic metal ions

Long-term accumulation of toxic heavy metals in the environment was a potential hidden danger. High energy consumption, complicated operation and low adsorption capacity were the disadvantages of most current adsorbents. This study used one-step modification of fly ash (FA) by low-temperature melting method with KOH as the activator to generate modified fly ash (KFA) with high adsorption capacity to remove heavy metals from aqueous solutions. Various characterization results revealed a destruction that occurred on the surface structure of adsorbent, 12 times increase in specific surface area, and metal ions were successfully adsorbed onto KFA surface. Furthermore, adsorption proceeded most favorably at pH of 5, the presence of ionic strength and co-existing cations significantly influenced the adsorption effects. The description of adsorption data was more suitable by pseudo-second-order kinetics and Langmuir isotherm models. And in single system at 25 °C, for Pb(II), Cu(II), and Cd (II), the q_m were 337.41, 310.09 and 125.00 mg·g^-1. However, in ternary system, the q_m decreased for all three ions in the order Pb(II) > Cu(II) > Cd(II), which was different from the law in single system, and the Pb(II) adsorption was found to have a significant inhibited effect on adsorption of Cd(II) and Cu(II). The adsorption mechanisms including ion exchange, electrostatic attraction and complexation were revealed. And by exploring the bioaccessibility of absorbed heavy metals in four simulated digestive fluids, it was found that KFA could load heavy metal ions and enable their release in organisms and other aquatic environments, which provided the possibility for subsequent related studies. Therefore, KFA with low energy consumption and high adsorption capacity is equipped a prospective development space on removing heavy metals from wastewater.

Fabrication, Characterization and Adsorption Investigation of Nano Zinc Oxide–Sodium Alginate Beads for Effective Removal of Chromium (VI) from Aqueous Solution

Alginate–zinc oxide (Alg–ZnO) biocomposite was synthesized and tested as a chromium ions Cr(VI) adsorbent for environmental applications. Alg–ZnO biocomposite was prepared by the interaction between sodium alginate biopolymer and zinc oxide nanoparticles (ZnO–NPs), prepared by modified wet chemical method. The solid adsorption characteristics of the synthesized Alg–ZnO biocomposite were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–Vis spectroscopy. Adsorption isotherms of chromium ions on the prepared Alg–ZnO biocomposite were investigated with varying the initial concentration of Cr(VI) under different application conditions such as pH, contact time, adsorbent dosage, and temperature. Adsorption of Cr(VI) was investigated by different isotherm models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. Maximum adsorption capacities (31.09 and 34.63 mg/g) were achieved by ZnO–NPs and Alg–ZnO, respectively at 25 °C. The results of isotherm models indicate the perfect applicability of Langmuir and Dubinin–Radushkevich models, revealing the dominance of monolayer and the physisorption of chromium ions onto the studied adsorbents.

Biomimetic Polylactic Acid Electrospun Fibers Grafted with Polyethyleneimine for Highly Efficient Methyl Orange and Cr(VI) Removal

The rapid growth of industrialization has resulted in the release of large quantities of pollutants into the environment, especially dyes and heavy metals, which are environmentally hazardous for humans and animals. It is considered as the most promising and environmentally friendly route to develop green materials by using the green modification method, which has no negative impact on the environment. In this work, the green material of polylactic acid (PLA) was used as the substrate material, and a novel modification method of polydopamine (PDA)-assisted polyethyleneimine (PEI) grafting was developed. The electrospun PLA fibers are mainly composed of stereocomplex crystallites, which were achieved via the electrospinning of poly(l-lactic acid) and poly(d-lactic acid). The water-soluble PEI was grafted onto the PDA-modified PLA fibers through the glutaraldehyde-assisted cross-linking reaction. The prepared composite fibers can be degraded, which is environmentally friendly and meets the requirements of sustainable development. The potential application of such PLA composite fibers in wastewater treatment was intensively evaluated. The results show that at appropriate fabrication conditions (PDA concentration of 3 g·L^-1 and a PEI molecular weight of 70,000 g·mol^-1), the composite fibers exhibit the maximum adsorption capacities of 612 and 398.41 mg·g^-1 for methyl orange (MO) and hexavalent chromium [Cr(VI)], respectively. Simultaneously, about 64.79% of Cr(VI) adsorbed on the composite fibers was reduced to Cr(III). The above results show that the PLA composite fibers have a good development prospect in the field of wastewater treatment.

Efficient visual adsorption of Pb2+ by nanocellulose/sodium alginate microspheres with fluorescence sensitivity

In this study, carbon dots (CDs) were prepared by a one-pot hydrothermal method using tempo-oxidized cellulose nanocrystals (TOCNC) and polyethylenimine (PEI). The CDs were self-assembled with a microsphere adsorbent prepared using TOCNC and sodium alginate (SA). CDs-TOCNC/SA-an environmentally friendly, fluorescent-sensitive, and recyclable microsphere adsorbent-was obtained. FTIR analysis showed that PEI successfully modified the CDs. In addition, the fluorescence quenching of CDs was observed when the concentration of Pb²⁺ was 0.0001-100 mg/L, indicating that CDs can dynamically monitor Pb²⁺. CDs-TOCNC/SA can produce blue fluorescence under 365 nm UV light and selectively and efficiently adsorb Pb²⁺. When the concentration of Pb²⁺ was 0.0001-100 mg/L, fluorescence quenching of the adsorbent was observed, indicating that CDs-TOCNC/SA could visually adsorb Pb²⁺. The adsorption isotherm and kinetic parameters show that the adsorption process conforms to the Langmuir isotherm model at 298 K, and the maximum adsorption capacity of Pb²⁺ was 190.1 mg/g at pH = 5. Moreover, CDs-TOCNC/SA could still obtain 78.99 % Pb²⁺ after five sorption-desorption cycles. The adsorption mechanism may involve ion exchange, electrostatic attraction, intra-particle diffusion, and chemical complexation.

Calcium alginate/silk fibroin peptide/Bletilla striata polysaccharide blended microspheres loaded with tannic acid for rapid wound healing

Biodegradable natural polymers are receiving increasing attention as potential candidates for wound dressing. In the present study, composite microspheres (mCSB) based on calcium alginate (CA), silk fibroin peptide (SP), and Bletilla striata polysaccharide (BSP) were prepared by the reverse emulsion method. The excellent swelling properties of microspheres enable them to rapidly promote thrombosis. Microspheres can increase the platelet aggregation index to 1.5 and the aggregation rate of red blood cells to as high as 80 %. Furthermore, tannic acid (TA)-loaded microspheres demonstrate a slow-release effect on TA; this allows the microspheres to exhibit good long-lasting antibacterial properties. Due to the synergistic effects of SP and TA, the cell senescence was delayed, with a 126.69 % survival rate of fibroblasts after 3 days of incubation. In addition, TA led to a rapid reduction in inflammation levels, with a wound closure rate of >92.80 % within 7 days. The multifunctional TA-loaded mCSB has great application potential for rapid wound healing and the treatment of wound hemostasis.

A comparative study on selectivity and sensitivity of new chromium and copper electrodes

4-Methylcoumarin-7-yloxy-N-phenyl acetamide and 4-methylcoumarin-7-yloxy-N-4-nitrophenyl acetamide were synthesized and used as new ionophores in the carbon paste matrix to produce two novel potentiometric modified electrodes. The selectivity of the electrode changed from copper (II) to chromium (III) with the addition of a nitro group to the phenyl ring of the ionophore. The ionophores’ tendency to ions was confirmed by UV–visible spectrophotometry. Both electrodes were modified by multi-walled carbon nanotubes (MWCNTs) as an excellent modifier of carbon paste electrode (CPE). The best sensor response in the case of copper (II) selective CPE was obtained by 5% ionophore, 65% graphite powder, 5% MWCNT, and 25% paraffin oil. In addition, in the case of chromium (III) selective CPE, these conditions are 20% ionophore, 50% graphite powder, 5% MWCNT, and 25% paraffin oil. The copper (II) selective CPE showed a Nernstian slope of 32.15 mV/decade within the concentration range of 1.0 × 10^–10–1.0 × 10^–1 mol L⁻¹, while chromium (III) selective CPE showed a Nernstian slope of 19.28 mV/decade over the concentration range of 1.0 × 10^–10–7.0 × 10^–3 mol L⁻¹. The electrodes have short response time of less than 5 s and were used successfully to determine copper (II) in wastewater and to speciation of chromium (III) and chromium (VI).

Characteristics of catechin loading rice porous starch/chitosan functional microsphere and its adsorption towards Pb2+

In this paper, we explore the adsorption potential of catechin (CT) loaded composite microspheres and provide a new micron scale carrier of functional factor. Chitosan (CS) modified rice porous starch (RPS/CS) was used as a CT adsorption carrier to prepare bioactive CT-loaded composite microspheres (CT@RPS/CS). The adsorption kinetics, storage characteristics, and biological activity maintenance of CT@RPS/CS were studied in an aqueous solution, and the sustained-release characteristics of CT@RPS/CS were studied in vitro during simulated gastrointestinal digestion. An aqueous solution further studied the removal characteristics of adsorbed heavy metal ion Pb²⁺. RPS/CS can significantly improve the ability to adsorb CT. RPS/CS can also significantly improve CT's storage stability, antioxidant stress, and slow-release characteristics, and the sustained release effect in gastric and intestinal juice. CT@RPS/CS can be removed Pb²⁺ by adsorbing in the solution, and their adsorption was physical adsorption and chemisorption, but the primary interaction is chemisorption. CT@RPS/CS can be used as a micron carrier of new food functional factors, which has potential space for improving and expanding the functional characteristics of its loaded functional factors and the endowing of new functions.

A post-functional Ti-based MOFs composite for selective removal of Pb (II) from water

Lead ions in water have notorious effects on humans and environment. It is important to design an adsorbent with high adsorption capacity and reproducibility for efficiently removing Pb (II)ions from polluted water. Here, a novel Ti-based MOFs material (BDB-MIL-125(Ti)@Fe₃O₄) was prepared by modifying NH₂-MIL-125(Ti) with sulfhydryl and amino groups. Due to the large number of active sites, the maximum Pb (II) adsorption capacity of BDB-MIL-125(Ti)@Fe₃O₄ was 710.79 mg/g at 25 °C and pH = 6 within 120 min corresponding to a maximum removal rate of 95.68%. The adsorbent also has extremely high selectivity and good cycling adsorption performance. The adsorption isotherms and kinetics agree with the Langmuir and the pseudo-second-order models, indicating that the process was chemisorption. Thermodynamic studies prove that spontaneous processes enhance Pb (II) adsorption at higher temperatures. DFT and FMOs calculations were used to discuss the adsorption mechanism. The sulfhydryl groups on the surface of organic ligands have a stronger affinity for Pb (II).

Fabrication of novel bio-adsorbent and its application for the removal of Cu(II) from aqueous solution

As eco-friendly adsorption material, hydroxyapatite (Ca₅(PO₄)₃OH, HA) has been extensively applied to the removal of heavy metal ions. However, separating and recovering of HA powder after the adsorption process limits their application. Alginate-based composite beads (HCA) encapsulated with HA and cellulose were designed to remove Cu(II) from aqueous solution. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used for characteristic analysis. An extensive discussion in terms of HCA adsorption capacity, effect of various Cu(II) concentration, and analysis of the involved mechanisms of Cu(II) removal on the biosorption. HCA beads showed that the maximum adsorption capacity for Cu(II) of 64.14 mg/g at pH = 5 with 8 h contact time. The Langmuir adsorption isotherm and second-order kinetic model gave the closest fit. HCA beads display good regeneration ability after four cycles and offer potentiality for practical application.

Chitosan-assisted MOFs dispersion via covalent bonding interaction toward highly efficient removal of heavy metal ions from wastewater

Metal organic frameworks (MOFs) have been considered to be robust adsorbent for the removing heavy metal ions from wastewater due to their unique properties such as large active sites, high specific surface area and high porosity, etc., however, their practical engineering application faces the problem of serious agglomeration. In this work, a new strategy of chitosan (CS) assisting MOF dispersion was proposed to develop the new generation of MOF-based adsorbents, namely, CS grafted UiO-66-NH₂ composite materials (CGUNCM). The UiO-66-NH₂ was selected and it was grafted onto the main chains of CS through covalent bonding interaction with the aid of glutaraldehyde, which was totally different from the common method that grafting molecular chains on the surface of MOFs resulting in the dramatic reduction of active adsorption sites. The results show that grafting MOFs onto CS main chains not only greatly improves the dispersion of MOFs but also reserves the morphology of MOFs as much as possible. The adsorption performances toward Cu(II) and Pb(II) were intensively studied by varying adsorbate concentration, ionic strength, the contact time, adsorption temperature and pH value of solution. The results show that the composite adsorbent exhibits high adsorption efficiency and the adsorption equilibrium can be reached within 45 min, and the maximum adsorption capacity toward Cu(II) and Pb(II) achieve 364.96 mg/g and 555.56 mg/g, respectively. Furthermore, the composite adsorbent shows good reusability. This work provides a new method of fabricating the MOF-based adsorbent and paves the way for the practical application of such adsorbents in wastewater treatment.

Behavior and mechanism of the adsorption of lead by an eco-friendly porous double-network hydrogel derived from keratin

In this study, a novel eco-friendly porous double-network keratin/polyacrylic acid (keratin-PAA) hydrogel was prepared using the one-pot method to improve the adsorption performance of the hydrogel toward Pb(II). The obtained porous keratin-PAA hydrogel was then characterized using nitrogen adsorption-desorption isotherms, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The interaction mechanism of Pb(II) and the keratin-PAA hydrogel was further investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that keratin-PAA hydrogel was successfully synthesized, with a specific surface area of 49.35 m²/g and a uniform pore distribution of 6.20 nm. The synthesized keratin-PAA hydrogel only took 6 min to adsorb nearly 70% of Pb(II) from the solution because of the interconnected porous network. The keratin-PAA hydrogel also showed a maximal adsorption amount of 234.6 mg/g, and satisfactory selectivity toward Pb(II). The adsorption kinetics of the keratin-PAA hydrogel binding to Pb(II) could be better described by the pseudo-second-order model, whereas the adsorption isotherms could be fitted using the Langmuir equation; this suggested that chemisorption was the main rate-limiting step. The XPS and FT-IR analysis results indicated that the sulfur-, nitrogen- and oxygen-containing groups in the keratin-PAA hydrogel were the main binding sites for Pb(II). In real aqueous samples, the keratin-PAA hydrogel could remove 93-104% of Pb(II). It is clear that the keratin-PAA hydrogel is an outstanding adsorbent material for the removal of Pb(II) from aqueous samples.

Exploring the role of mesoporous silica nanoparticle in the development of novel drug delivery systems

The biocompatible nature of mesoporous silica nanoparticles (MSN) attracted researchers' attention to deliver therapeutic agents in the treatment of various diseases, where their porous nature, high drug loading efficiency, and suitability to functionalize with a specific ligand of MSN helped to obtain the desired outcome. The application of MSN has been extended to deliver small chemicals to large-sized peptides or proteins to fight against complex diseases. Recently, formulation researches with MSN have been progressed for various non-conventional drug delivery systems, including liposome, microsphere, oro-dispersible film, 3D-printed formulation, and microneedle. Low bulk density, retaining mesoporous structure during downstream processing, and lack of sufficient in vivo studies are some of the important issues towards the success of mesoporous silica-based advanced drug delivery systems. The present review has aimed to evaluate the application of MSN in advanced drug delivery systems to critically analyze the role of MSN in the respective formulation over other functionalized polymers. Finally, an outlook on the future direction of MSN-based advanced drug delivery systems has been drawn against the existing challenges with this platform.

Highly efficient and rapid Pb(ii) removal from acidic wastewater using superhydrophilic polystyrene phosphate resin

Novel superhydrophilic polystyrene phosphate resin was synthesized for efficient and rapid Pb(ii) removal from acidic wastewater.

Possibility of Removing Pb and Cd from Polluted Water by Modified Fly Ash

In this study, fly ash (FA) was modified by sodium hydroxide to prepare a new adsorption material (IP) and treat Pb2+- and Cd2+-polluted wastewater. The effect of preparation parameters (mass ratio of FA/NaOH and modification temperature) on IP adsorption performance was investigated. The results indicated that the IP4 showed the highest adsorption capacity prepared at the FA/NaOH mass ratio of 1 : 2 and the roasting temperature of 250°C. The IP4 was characterized by SEM, EDX, XRD, and FTIR analyses. The results showed that the surface morphology and microstructure of FA were significantly changed. Furthermore, in order to study the adsorption performance of Pb2+ and Cd2+ on IP4, the different initial concentrations of Pb2+ and Cd2+, pH, and contact time were analyzed, and the results indicated that IP4 has excellent adsorption capacity for heavy metals. In addition, kinetic model results demonstrated that the adsorption behavior of Pb2+ and Cd2+ on IP4 was better described by a pseudo-second-order model.

Ninhydrin-functionalized chitosan for selective removal of Pb(II) ions: Characterization and adsorption performance

A chitosan-based adsorbents (CS-Ninhydrin) was prepared by grafting ninhydrin for Pb(II) ions adsorption. SEM-EDS, XRD and FTIR analysis were used to characterize the synthesized CS-Ninhydrin. The static adsorption experiments showed that CS-Ninhydrin had a good removal rate for Pb(II) ions in a wide range of pH 3 to 7, quickly reached equilibrium (120 min) and had a higher adsorption capacity (196 mg/g). Pseudo second-order and Langmuir models showed that the adsorption process of Pb(II) by CS-Ninhydrin was a single-layer chemical adsorption. Temperature experiments showed that the reaction was a spontaneous exothermic process. In the wastewater experiment, CS-Ninhydrin showed an excellent selectivity to Pb(II) ions. The reusability of CS-Ninhydrin was perfect after five adsorption-desorption cycles. The main adsorption mechanism was the chelating and electrostatic action between N and O groups in CS-Ninhydrin and Pb(II) ions. Therefore, the new adsorbent CS-Ninhydrin was expected to promote the wide application of chitosan in Pb(II) adsorption.

Synthesis of amino-functionalized biochar/spinel ferrite magnetic composites for low-cost and efficient elimination of Ni(II) from wastewater

Novel amino-modified rice bran biochar/MgFeAlO₄ (RB@MgFeAlO₄-NH₂) magnetic composites were synthesized via a simple one-step solvothermal approach and applied for removing toxic Ni(II) from wastewater. The elimination process and sorption performance of Ni(II) on RB@MgFeAlO₄-NH₂ were analyzed by combining batch experiments and spectral techniques. The sorption isotherms and kinetic data indicated that Ni(II) sorption on RB@MgFeAlO₄-NH₂ was monolayer and rapid. The experimental results confirmed that the obtained RB@MgFeAlO₄-NH₂ magnetic composite had high sorption capacity for Ni(II). The maximum sorption capacity of Ni(II) on RB@MgFeAlO₄-NH₂ was 201.62 mg g^-1. The researches based on the sorption mechanism showed that the ion exchange mechanism accounted for 76.51% of Ni(II) sorption. In addition, the amino, carboxyl and hydroxyl functional groups were also involved in the complexation with Ni(II). In view of its multiple advantages of environmental friendliness, low cost, easy magnetic separation and high sorption capacity, RB@MgFeAlO₄-NH₂ will be an excellent adsorbent for low-cost and efficient elimination of Ni(II) from aqueous solutions.

The effects of carbon disulfide driven functionalization on graphene oxide for enhanced Pb(II) adsorption: Investigation of adsorption mechanism

The surface properties of graphene oxide (GO) have been identified as the key effects on the adsorption of Pb(II) from aqueous solutions in this study. This study reveals the effect of the surface reactivity of GO via Carbon Disulfide (CS₂) functionalization for Pb(II) adsorption. After successfully preparing CS₂ functionalized GO (GOCS), the specific techniques were applied to investigate Pb(II) adsorption onto GOCS. Results indicated that the new sulfur-containing functional groups incorporated onto GOCS significantly enhanced Pb(II) adsorption capacity on GOCS than that of GO, achieving an improvement of 31% in maximum adsorption capacity increasing from 292.8 to 383.4 mg g^-1. The equilibrium adsorption capacity for GOCS was 280.2 mg g^-1 having an improvement of 83.2% over that of 152.97 mg g^-1 for GO at the same initial concentration of 150 mg L^-1 under the optimal pH of 5.7. Moreover, the results of adsorption experiments showed an excellent fit to the Langmuir and Pseudo-Second-Order models indicating the monolayer and chemical adsorption, respectively. The mechanism for Pb(II) adsorption on GOCS was proposed as the coordination, electrostatic interactions, cation-pi interactions, and Lewis acid-base interactions. The regeneration study showed that GOCS had an appreciable reusability for Pb(II) adsorption with the adsorption capacity of 208.92 mg g^-1 after five regeneration cycles. In summary, GOCS has been proved to be a novel, useful, and potentially economic adsorbent for the high-efficiency removal of Pb(II) from aqueous solutions.

Preparation of Fe3O4@SiO2@ P(AANa-co-AM) Composites and Their Adsorption for Pb(II)

A series of magnetic composites of sodium polyacrylate and polyacrylamide copolymer [Fe₃O₄@SiO₂@P(AANa-co-AM)] were prepared. The investigation showed that the adsorption efficiency of Pb(II) was the best when the acrylamide/acrylic acid (AM/AA) mass ratio of composites was 5:5. Therefore, the composite of this ratio was selected as the adsorbent to systematically adsorb Pb(II) in aqueous solution. Static adsorption of Pb(II) to the magnetic composites in aqueous solutions was investigated by varying the solution pH and the concentration of Pb(II). The adsorption kinetics and isotherms model of Pb(II) on the Fe₃O₄@SiO₂@P(AANa-co-AM) composites followed a pseudo-second-order model and the Langmuir isotherm model, respectively. When the temperatures were 298.15, 308.15, and 318.15 K, the maximum adsorption capacities of Fe₃O₄@SiO₂@P(AANa-co-AM) composites were 237.53, 248.14, and 255.10 mg/g, respectively. The thermodynamic study of adsorption showed that the adsorption of Pb(II) on Fe₃O₄@SiO₂@P(AANa-co-AM) composites was a spontaneous endothermic process. The X-ray photoelectron spectroscopy (XPS) analysis showed that the adsorption of Pb(II) was due to the chelation between -COO^- and Pb(II). After four adsorption-desorption cycles, the adsorbent can still maintain a high adsorption capacity.

Development and application of magnetic solid phase extraction in tandem with liquid-liquid extraction method for determination of four tetracyclines by HPLC with UV detection

A novel HPLC-UV method was developed for the determination of four tetracyclines based on magnetic solid phase extraction in tandem with liquid-liquid extraction. The water-soluble amino functionalized magnetite nanoparticle (MNP-NH₂) was used as an adsorbent for extraction/preconcentration of tetracycline, oxytetracycline, chlortetracycline, and doxycycline from bovine milk samples. Fourier transform infrared spectrometer, transmission electron microscope, X-ray diffraction, and elemental analyze techniques were used to characterize the material. Some key parameters which influence liquid-liquid extraction and magnetic dispersive solid-phase extraction procedure, including volume of extraction solvent, the amount of adsorbent, the pH, extraction and desorption time, the composition of the eluent, and elution frequency were investigated. The proposed method exhibited a linear range of 50.0-2500.0 μg L^-1 (r² = 0.9941) with and good reproducibility (RSD < 2.2%, n = 3). The limit of detection and quantification were 40.0 and 50.0 μg L^-1. This method was verified using milk sample spiked with four tetracyclines (100.0-200.0 μg L^-1), and accuracies of 87.8-107.5%, which confirmed its applicability in real-sample analysis. The proposed method also shows potential application prospects for other water-soluble adsorbents.

Hydrophilic ZnO Nanoparticles@Calcium Alginate Composite for Water Purification

Herein, hydrophilic ZnO nanoparticles@calcium alginate composite has been prepared by embedding hydrophilic ZnO nanoparticles (NPs) into calcium alginate. The hydrophilic ZnO NPs within the composites can act as a killer of bacteria, while calcium alginate can remove the organic impurities due to its adsorption capacity, thus realizing the purification of water via sterilization and removal of organics. A water purifier based on the composite has been demonstrated, the aerobic bacterial counts of the contaminated water can be decreased from 2240 to 9 cfu mL^-1, and the turbidity of the water is decreased to 0.51 NTU, which is below the maximum permissible of Guidelines for Drinking-water Quality designed by the World Health Organization. Sterilization mechanism studies show that the ZnO NPs can cause excessive oxidative stress in cells, inducing bacteria to produce large amounts of intracellular reactive oxygen species (ROS), which leads to the apoptosis of the bacteria.

PEI-modified core-shell/bead-like amino silica enhanced poly (vinyl alcohol)/chitosan for diclofenac sodium efficient adsorption

Residual diclofenac sodium (DS) in water is a potential hazard. The electrostatic attraction between amino group of adsorbents and carboxyl group of DS under acidic conditions can effectively remove DS from water. Herein, a novel core-shell adsorbent of poly(vinyl alcohol)/chitosan/amino-grafted silica@polyethylenimine (PVA/CS/SAP@PEI) gel bead was prepared to efficiently uptake DS from wastewater. In this study, the gel bead was characterized using FTIR, XPS, SEM, EDS, and ¹³C NMR. The experimental data shows that there is a strong correlation between adsorption capacity. The adsorption data fitted well with the Freundlich isotherm model and the pseudo-second-order model. The results of thermodynamics show that the adsorption process is spontaneous, endothermic, and increases entropy. The maximum adsorption capacity for DS was calculated as 493.81 mg/g at pH 5 (308 K). The adsorbent still exhibited excellent adsorption capacity after recycling five times, showing it has excellent potential for practical applications.

Facile synthesis of amino-functional large-size mesoporous silica sphere and its application for Pb2+ removal

Amino-functional large-size mesoporous silica spheres (LMS-AP) were successfully synthesized through a one-step method with (3-aminopropyl) triethoxysilane (APTES) addition during the pseudomorphic transformation process. LMS-AP were characterized using thermogravimetry-differential thermal analysis, Nitrogen adsorption-desorption measurement, infrared spectroscopy, and X-ray photoelectron spectroscopy. The study found that -NH₂ was grafted into LMS, and the LMS-AP had a better thermal stability than other samples. The Pb²⁺ removal properties of LMS-AP were investigated using the static and dynamic experiments in simulated and real wastewater solutions. The kinetic and equilibrium experiments indicated that the adsorption process of LMS-AP fitted the Langmuir adsorption model and the pseudo-second-order kinetics model (R² > 0.98), respectively. The maximum Q_e (mg/g) was about 100 mg/g in the static adsorption condition. The adsorption mechanism of removal of Pb²⁺ was also investigated. In fix bed column experiments, LMS-AP exhibited excellent Pb²⁺ adsorption ability for simulated wastewater, with the maximum q_e (mg/g) of 48.7 mg/g for particle size under 1-3 mm. Meanwhile in actual industrial wastewater treatment process, LMS-AP had a better Pb²⁺, Zn²⁺ and Cr (VI) removal efficiency of 80% and As (V) of 30-40% removal efficiency at initial pH 4, suggesting selective adsorption property for different heavy metal ions.