Preparation and lead ion removal property of hydroxyapatite/polyacrylamide composite hydrogels

Hydroxyapatite and its composite in heavy metal decontamination: Adsorption mechanisms, challenges, and future perspective

Nanohydroxyapatite (n-HAP), recognized by its peculiar crystal architecture and distinctive attributes showcased the underlying potential in adsorbing heavy metal ions (HMI). In this paper, the intrinsic mechanism of HMI adsorption by n-HAP was first revealed. Subsequently, the selectivity and competitiveness of n-HAP for HMI in a variety of environments containing various interferences from cations, anions, and organic molecules are elucidated. Next, n-HAP was further categorized according to its morphological dimensions, and its adsorption properties and intrinsic mechanisms were investigated based on these different morphologies. It was shown that although n-HAP has excellent adsorption capacity and cost-effectiveness, its application is often challenging to realize due to its inherent fragility and agglomeration, the technical problems required for its handling, and the difficulty of recycling. Finally, to address these issues, this paper discusses the tendency of n-HAP and its hybridized/modified materials to adsorb HMI as well as the limitations of their applications. By summarizing the limitations and future directions of hybridization/modification HAP in the field of HMI contamination abatement, this paper provides insightful perspectives for its gradual improvement and rational application.

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.

Development of cellulose/hydroxyapatite/TiO2 scaffolds for efficient removal of lead (II) ions pollution: Characterization, kinetic analysis, and artificial neural network modeling

The utilization of nano-biodegradable composites for removing pollutants and heavy metals in aquatic environments has been widespread. This study focuses on synthesizing cellulose/hydroxyapatite nanocomposites with titanium dioxide (TiO2) via the freeze-drying method for the adsorption of lead ions in aquatic environments. The physical and chemical properties of the nanocomposites, including structure, morphology, and mechanical properties, were analyzed through FTIR, XRD, SEM, and EDS. In addition, parameters affecting the adsorption capacity, such as time, temperature, pH, and initial concentration, were determined. The nanocomposite exhibited a maximum adsorption capacity of 1012 mg⸱g-1, and the second-order kinetic model was found to govern the adsorption process. Additionally, an artificial neural network (ANN) was created using weight percentages (wt%) of nanoparticles included in the scaffold to predict the mechanical behavior, porosity, and desorption of the scaffolds at various weight percentages of hydroxyapatite (nHAP) and TiO2. The results of the ANN indicated that the incorporation of both single and hybrid nanoparticles into the scaffolds improved their mechanical behavior and desorption, as well as increased their porosity.

Reduced Graphene Oxide-Zinc Sulfide Nanocomposite Decorated with Silver Nanoparticles for Wastewater Treatment by Adsorption, Photocatalysis and Antimicrobial Action

Reduced graphene oxide nanosheets decorated with ZnS and ZnS-Ag nanoparticles are successfully prepared via a facile one-step chemical approach consisting of reducing the metal precursors on a rGO surface. Prepared rGO-ZnS nanocomposite is employed as an adsorbent material against two model dyes: malachite green (MG) and ethyl violet (EV). The adsorptive behavior of the nanocomposite was tuned by monitoring some parameters, such as the time of contact between the dye and the adsorbent, and the adsorbent dose. Experimental data were also simulated with kinetic models to evaluate the adsorption behavior, and the results confirmed that the adsorption of both dyes followed a pseudo 2nd order kinetic mode. Moreover, the adsorbent was also regenerated in a suitable media for both dyes (HCl for MG and ethanol for EV), without any significant loss in removal efficiency. Ag doped rGO-ZnS nanocomposite was also utilized as a photocatalyst for the degradation of the selected organic contaminant, resorcinol. The complete degradation of the phenolic compound was achieved after 60 min with 200 mg of rGO-ZnS-Ag nanocomposite under natural sunlight irradiation. The photocatalytic activity was studied considering some parameters, such as the initial phenol concentration, the photocatalyst loading, and the pH of the solution. The degradation kinetics of resorcinol was carefully studied and found to follow a linear Langmuir-Hinshelwood model. An additional advantage of rGO-ZnS and rGO-ZnS-Ag nanocomposites was antibacterial activity against Gram-negative bacterium, E. coli, and the results confirmed the significant performance of the nanocomposites in destroying harmful pathogens.

Gamma irradiation synthesis of pectin- based biohydrogels for removal of lead cations from simulated solutions

Bio-based hydrogels (denoted as PC-PAAc/GA) comprised of Pectin (PC) and polyacrylic acid (PAAc) reinforced with different ratios of gallic acid (GA) were prepared by gamma radiation at irradiation dose 20 kGy. The prepared hydrogels were investigated by different analytical tools. The swelling performance was studied versus time, pH of the medium and gallic acid content. The experimental data depicted that the swelling increases with pH of medium until the equilibrium of swelling after 350 min. The maximum swelling was attained at pH10 for both PC-PAAc and PC-PAA/GA1.5. Also, the data reveal that the incorporation of GA in the hydrogel matrix enhanced the swelling performance of the hydrogel up to an optimum value of GA, i.e. PC-PAA/GA1.5. Further increase in GA concentration leads to formation of a highly crosslinked structure with reduced swelling. The results demonstrated that the prepared hydrogels displayed excellent antibacterial activity against gram + ve bacteria (E.coli) and gram-ve bacteria (S.aureus). This potent antimicrobial activity is mainly originated from GA which was proved as a strong antibacterial agent. Moreover, the removal performance of the investigated hydrogels was verified towards Pb+2 cation as one of the most poisonous heavy metals. The data revealed that the maximum removal percentage of Pb (II) was attained by PC-PAAc/GA1.5 hydrogel (90 mg g−1). The correlation coefficients of the Langmuir model are too higher than that of the Freundlich model that assumed the adsorption of lead cations is mainly a chemical process.

Highly efficient and selective heterogeneous catalytic reduction of 2-nitroaniline by cerium oxide nanocatalyst under microwave irradiation

Efficient nanocatalyst with incredible performance is highly demanding in a heterogeneous catalysis system. Herein, we report the facile fabrication of uniform and highly stable Cerium Oxide nanoparticles (CeO₂ NPs), through chemical precipitation method using sodium hydroxide as reducing agent. The synthesized material is characterized through highly sophisticated techniques including UV-Visible, FT-IR, SEM, AFM, XRD, and Zeta Sizer- Potential to check the particle formation, surface morphology, topography, crystalline nature, size, and surface potential. The heterogeneous catalytic performance of CeO₂ NPs has been accomplished for the reduction of 2-nitroaniline from the aqueous media. The CeO₂ nanocatalyst displayed excellent reusability, while the reduction in several repetitive catalytic cycles against 2-nitroaniline under optimized conditions. The CeO₂ nanocatalyst shows 99.12% efficiency within 60s reaction time under a greener source of microwave radiation.

Use of superabsorbent polymer in soil-cement subsurface barriers for enhanced heavy metal sorption and self-healing

Conventional subsurface barrier materials for contamination containment deteriorate in aggressive environments and only have a limited exchange/adsorption capacity for heavy metals. This study focused on the potential use of superabsorbent polymer (SAP) in soil-cement subsurface barriers for enhanced heavy metal sorption and self-healing. The SAP adsorption results for lead, copper, zinc and nickel were well fitted by the Langmuir model. The SAP had the highest adsorption capacity for lead at 175 mg/g, and plays a key role in the removal of the heavy metals in an acidic environment. In addition, the incorporation of SAP in soil-cement increased the ductility and had negligible adverse effects on mechanical and permeability properties. When cracks propagate in the matrix, the SAP is exposed to the ingress of water and swells, and this swelling reaction seals the cracks. The SAP-containing soil-cement demonstrated enhanced self-healing performance in terms of the recovery of permeability. The uniform dispersion and the 3D network of the SAP were observed using micro-CT scanning, and good bonding and self-healing mechanism were confirmed by SEM-EDX analysis. The results suggest the significant potential for the SAP-based approach for the development of more resilient subsurface barriers with enhanced heavy metal sorption and self-healing.

Hydrogel-Based Adsorbent Material for the Effective Removal of Heavy Metals from Wastewater: A Comprehensive Review

Water is a vital resource that is required for social and economic development. A rapid increase in industrialization and numerous anthropogenic activities have resulted in severe water contamination. In particular, the contamination caused by heavy metal discharge has a negative impact on human health and the aquatic environment due to the non-biodegradability, toxicity, and carcinogenic effects of heavy metals. Thus, there is an immediate need to recycle wastewater before releasing heavy metals into water bodies. Hydrogels, as potent adsorbent materials, are a good contenders for treating toxic heavy metals in wastewater. Hydrogels are a soft matter formed via the cross-linking of natural or synthetic polymers to develop a three-dimensional mesh structure. The inherent properties of hydrogels, such as biodegradability, swell-ability, and functionalization, have made them superior applications for heavy metal removal. In this review, we have emphasized the recent development in the synthesis of hydrogel-based adsorbent materials. The review starts with a discussion on the methods used for recycling wastewater. The discussion then shifts to properties, classification based on various criteria, and surface functionality. In addition, the synthesis and adsorption mechanisms are explained in detail with the understanding of the regeneration, recovery, and reuse of hydrogel-based adsorbent materials. Therefore, the cost-effective, facile, easy to modify and biodegradable hydrogel may provide a long-term solution for heavy metal removal.

Removal of Pb2+ from synthetic aqueous solution using hydroxyapatite and hydroxyapatite@AD37 composite materials

In this paper, a simple method was proposed to obtain hydroxyapatite (HA) and hydroxyapatite/partially hydrolysed polyacrylamide (HA/AD37) composite materials which where applied to lead retention from aqueous solution by means of the batch method. The characterization of the materials verified that the presence of AD37 created interconnected porosity in the composite HA/AD37 giving it a good swelling properties that conducted to an easy separation of the material from aqueous solutions. Retention experiments carried out by varying the dose of lead and the contact time between adsorbent and adsorbate showed that the maximum adsorption capacity (Qmax) obtained for 2072.2 mg/L as initial concentration of Pb2 + was equal to 984.63 mg/g for HA and 924.50 mg/g for HA/AD37. Furthermore, AD37 used alone cannot retain Pb2 + ions. Indeed, the calculated Qmax of AD37 part of the composite was of 806.57 mg/g. The obtained Qmax values was elevated more than the reported values in many literatures. Based on the correlation coefficient, the kinetic study proved that pseudo-second order model agrees well with the obtained experimental data for Pb2+ retention by both HA and HA/AD37. Also, isotherm study explored that adsorption of lead was best fitted by Langmuir model for HA and Temkin model for HA/AD37. At last, the mechanism of retention was probed by characterizing the adsorbents after contact with lead ions by XRD and SEM. The results showed the transformation of calcium-hydroxyapatite to different structures of lead hydroxyapatite confirming the presence of ion exchange mechanism between Ca2+ and Pb2+.

Lignin grafted hydroxyapatite entrapped in polyacrylamide: Characterization and adsorptive features for Th4+ and bovine serum albumin

Water-soluble sulfolignin (SL) was grafted onto hydroxyapatite (Hap) by using epichlorohydrin. SLgHap was then entrapped in cross-linked polyacrylamide by in situ polymerizations of acrylamide and N, N'-methylenebisacrylamide to obtain the composite of PSLgHap. The composite was characterized by FT-IR, BET- porosity, XRD, EDXRF, SEM-EDX, TGA-DTG, PZC, CEC, and swelling tests. The adsorptive features of PSLgHAP were investigated for Th⁴⁺ and BSA in view of its dependence on pH, ionic intensity, concentration, temperature, and time. The results of characterization tests confirmed the formation of PSLgHap. The grafting efficiency concerning sulfur contents of PSLgHap was 96% by EDXRF. The isotherms were best represented by the Sips model, Langmuir adsorption capacities were 369 and 390 mg g_SLgHap^-1 for BSA and Th⁴⁺. The enthalpy and entropy changes were positive whilst Gibbs energy was negative by entropy controlled. The adsorption kinetics of both species was obeyed to pseudo second-order model, whereas it was first-order for BSA and hybrid-order for Th⁴⁺ of Langmuir model.

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.

Synthesis, characteristics, and applications of modified starch nanoparticles: A review

Nowadays, starch nanoparticles (SNPs) are drawing attention to the scientific community due to their versatility and wide range of applications. Although several works have extensively addressed the SNP production routes, not much is discussed about the SNPs modification techniques, as well as the use of modified SNPs in typical and unconventional applications. Here, we focused on the SNP modification strategies and characteristics and performance of the resulting products, as well as their practical applications, while pointing out the main limitations and recommendations. We aim to guide researchers by identifying the next steps in this emerging line of research. SNPs esterification and oxidation are preferred chemical modifications, which result in changes in the functional groups. Moreover, additional polymers are incorporated into the SNP surface through copolymer grafting. Physical modification of starch has demonstrated similar changes in the functional groups without the need for toxic chemicals. Modified SNPs rendered differentiated properties, such as size, shape, crystallinity, hydrophobicity, and Zeta-potential. For multiple applications, tailoring the aforementioned properties is key to the performance of nanoparticle-based systems. However, the number of studies focusing on emerging applications is fairly limited, while their applications as drug delivery systems lack in vivo studies. The main challenges and prospects were discussed.

The removal of Cu(II) and Pb(II) ions from aqueous solutions by temperature-sensitive hydrogels based on N-isopropylacrylamide and itaconic acid

This study deals with the potential use of poly(N-isopropylacrylamide-co-itaconic acid) temperature-sensitive hydrogels as an adsorbent for the removal of Cu(II) and Pb(II) ions from aqueous solutions. For this aim, the adsorption properties of hydrogels were examined by adsorption capacities, adsorption isotherm, and adsorption kinetics experiments. To describe the adsorption characteristics of hydrogels, the obtained experimental data were evaluated by Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich isotherm models. Adsorption kinetics experiments were carried out not only in single systems but also in binary systems where both ions were at equal initial concentrations for competitive adsorption studies. To predict the behaviors of the competitive and non-competitive adsorption process of ions onto hydrogels, the experimental adsorption data were analyzed by the pseudo-first-order model and the pseudo-second-order model. According to non-competitive ion removal findings, the adsorption capacities followed order Cu(II) > Pb(II) for all hydrogels, and the pseudo-second-order kinetic model explained the adsorption properties of the hydrogels. Competitive ion removal studies showed that all hydrogels were selective to Cu(II) ion. Furthermore, in the case of comparative investigations both of competitive Cu(II) and competitive Pb(II) removal by hydrogels, the metal ion removal capacity of N10 hydrogel was found as a bit higher than that of N7.5 and N5 in 48 h. That is, as the acidic group content increased in the hydrogel network, the adsorption capacity values also increased. In addition, the reusability of temperature-sensitive hydrogels seems possible without regeneration or after regenerating with acid, in case the temperature is increased above the LCST. Furthermore, even if it cannot be reused, these hydrogels that retain metal ions reach very small volumes by shrinking when the LSCT is exceeded, and thus they can be eliminated more easily than other conventional gels due to their small size. As a result, this temperature-sensitive hydrogel may propose as an alternative environmentally friendly adsorbent candidate for can be used for water purification and wastewater treatment.

3D-printed monolithic biofilters based on a polylactic acid (PLA) - hydroxyapatite (HAp) composite for heavy metal removal from an aqueous medium

High flux, monolithic water purification filters based on polylactic acid (PLA) functionalised with fish scale extracted hydroxyapatite (HAp) were prepared by solvent-assisted blending and thermally induced phase separation (TIPS), followed by twin-screw extrusion into filaments and processed via three-dimensional (3D) printing. The printed filters with consistent pore geometry and channel interconnectivity as well as homogenous distribution of HAp in the PLA matrix showed adsorption capabilities towards heavy metals i.e. cadmium (Cd) and lead (Pb) with maximum adsorption capacity of 112.1 mg g_HAp⁻¹ and 360.5 mg g_HAp⁻¹ for the metal salt of Pb and Cd, respectively. The adsorption was found to be driven by a combination of ion exchange, dissolution and precipitation on HAp and surface complexation.

Water purification filters based on polylactic acid functionalised with hydroxyapatite were prepared by solvent-assisted blending and thermally induced phase separation (TIPS), extruded into filaments and processed via three-dimensional (3D) printing.

Natural Drug-Loaded Bimetal-Substituted Hydroxyapatite-Polymeric Composite for Osteosarcoma-Affected Bone Repair

Repairing segmental bone deformities after resection of dangerous bone tumors is a long-standing clinical issue. The study's main objective is to synthesize a natural bioactive compound-loaded bimetal-substituted hydroxyapatite (BM-HA)-based composite for bone regeneration. The bimetal (copper and cadmium)-substituted HAs were prepared by the sol-gel method and reinforced with biocompatible polyacrylamide (BM-HA/PAA). Umbelliferone (UMB) drug was added to the BM-HA/PAA composite to enhance anticancer activity further. The composite's formation was confirmed by various physicochemical investigations, such as FT-IR, XRD, SEM, EDAX, and HR-TEM techniques. The bioactivity was assessed by immersing the sample in simulated body fluid for 1, 3, and 7 days. The zeta potential values of BM-HA/PAA and BM-HA/PAA/UMB are -36.4 mV and -49.4 mV, respectively. The in vitro viability of the prepared composites was examined in mesenchymal stem cells (MSCs). It shows the ability of the composite to produce osteogenic bone regeneration without any adverse effects. From the gene expression and PCR results, the final UMB-loaded composite induced osteogenic markers, such as Runx, OCN, and VEFG. The prepared bimetal substituted polyacrylamide reinforced HA composite loaded with UMB drug has the ability for bone repair/regenerations.

Recycling of biogenic hydroxyapatite (HAP) for cleaning of lead from wastewater: performance and mechanism

In China, the utilization and recycling of chicken waste have become a significant environmental issue. In this study, we investigate the efficacy of biogenic hydroxyapatite (HAP) materials, recycled from chicken waste, for Pb(II) sequestration from wastewater. The results from batch experiments indicate that biogenic HAP could effectively remove Pb(II) from an aqueous solution. The maximum removal efficiency of Pb (more than > 99%) was observed under the following operational conditions: initial pH of 3.0, initial Pb(II) concentrations of 208 mg/L, and 1 g/L of HAP adsorbents. The presence of coexisting divalent ions, including Ca2+, Mg2+, and Mn2+, had no significant influence on Pb(II) removal. Spectroscopic analysis suggests that the dissolution-precipitation mechanism was mainly responsible for Pb(II) sequestration under acidic conditions (pH ≤ 3.0). Our findings indicate that biogenic HAP recycled from biowaste can be used as an efficient adsorbent for cleaning Pb(II) from wastewater.

A 3D porous fluorescent hydrogel based on amino-modified carbon dots with excellent sorption and sensing abilities for environmentally hazardous Cr(VI)

To effectively detect and remove environmentally hazardous Cr(VI), a novel 3D porous fluorescent hydrogel was synthesised using amino-modified carbon dots and cellulose nanofibers. The synthesised fluorescent hydrogel was characterized to determine its morphology, crystalline structure, chemical composition and optical property using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy and photoluminescence spectroscopy. The sorption properties of the synthesised fluorescent hydrogel were further analyzed. The maximum sorption capacity for Cr(VI) reached 534.4 mg/g, the adsorption isotherm was well fitted using Langmuir model, and the adsorption kinetics were well fitted using a pseudo-second-order model. The sensing ability of the synthesized hydrogel for Cr(VI) was also determined. Furthermore, the mechanism of Cr(VI) sorption and sensing was determined. Accordingly, this novel 3D porous fluorescent hydrogel was identified to be a promising sorbent with advantages of excellent sorption and sensing abilities for environmentally hazardous Cr(VI).

Self-templated microwave-assisted hydrothermal synthesis of two-dimensional holey hydroxyapatite nanosheets for efficient heavy metal removal

Heavy metals have caused serious environmental problems and threat to human health. Ultrathin and holey two-dimensional (2D) nanosheets have recently drawn significant attention as superb adsorbent material to remove heavy metal ions due to their unique physicochemical properties. Herein, we report a self-template-directed ultrafast reaction route to synthesis porous hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanosheets via a microwave-assisted hydrothermal method using poly(allylamine hydrochloride) as an additive. The resulting hydroxyapatite nanosheets showed a high specific surface area (92.9 m² g^-1) and excellent adsorption performance for various heavy metal ions including Pb(II), Cu(II), and Cd(II), with maximum adsorption capacities of 210.5, 31.6, and 24.9 mg g^-1, respectively. The adsorption kinetics fitted well with the pseudo-second-order equation and the equilibrium data showed a high correlation coefficient with the Langmuir model. Based on the experimental results and analysis, we can conclude that the sorption of heavy metal ions with the hydroxyapatite nanosheets mainly attributes to surface complexation and cation exchange. The present synthetic strategy allows the fast and massive production of porous hydroxyapatite ultrathin nanosheets and may also potentially be applicable to the fabrication of other metal phosphates with assembled or hierarchical porous structures towards various applications such as water purification.

Biocompatible HA@Fe3 O4 @N-CDs hybrids for detecting and absorbing lead ion

The trinary hydroxyapatite@Fe₃ O₄ @N-doped carbon dots (HA@Fe₃ O₄ @N-CDs) hybrids were prepared by one-pot hydrothermal approach and utilized to detect and remove lead ion from aqueous solution. The structures and morphologies of as-obtained nanorod-like HA@Fe₃ O₄ @N-CDs hybrids were characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy measurements. These HA@Fe₃ O₄ @N-CDs hybrids possess good magnetism by magnetic hysteresis test and multi-colored fluorescence by the CLSM measurement. Furthermore, the as-obtained hybrids display excellent biocompatibility by MTT assay. Importantly, the trinary magnetic HA@Fe₃ O₄ @N-CDs hybrids as a green detector and adsorbent of Pb²⁺ were investigated. The influence of the different pH, the concentration of heavy metal, and the maximum adsorption capacity on removal efficiency was measured in detail. The maximum Pb²⁺ adsorption capacity on HA@Fe₃ O₄ @N-CDs hybrids is 450 mg/g. The kinetic mechanism was a pseudo-second order model, and the isotherm data was fitted well by the Langmuir isotherm and Freundlich model. Hence, the nanorod-like HA@Fe₃ O₄ @N-CDs hybrids could be a multifunctional material with significant potential applications in heavy metal detection and adsorption, bone tissue regeneration, magnetic therapy, and biomedicine. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Carboxymethyl cellulose/polyacrylamide composite hydrogel for cascaded treatment/reuse of heavy metal ions in wastewater

A new bio-based bilateral hydrogel containing carboxymethyl cellulose (CMC) and polyacrylamide (PAM) was prepared for the wastewater remediation. The obtained CMC/PAM composite hydrogel reveals a strong single-ion affinity for copper (Cu^II), lead (Pb^II) and cadmium (Cd^II) ions, as well as multi-ion absorbability with its equilibrium data following the Langmuir adsorption model and its adsorption process abiding by a pseudo-second-order kinetics. To demonstrate its recycled use for the metal ions, the adsorbed Cu^II ions in the hydrogel were reduced in situ to form homogeneously dispersed Cu nanoparticles (NPs), leading to the Cu NPs-loaded CMC/PAM hydrogel. Reduction of 4-nitrophenol to 4-aminophenol with high efficiency was successfully achieved by this Cu NPs-loaded CMC/PAM hydrogel, verifying the hydrogel's dual functionalities towards the wastewater treatment and catalytic application.

Facile synthesis of graphene oxide-silver nanocomposite for decontamination of water from multiple pollutants by adsorption, catalysis and antibacterial activity

Here in, we presented a facile one-step method for the synthesis of Graphene oxide-silver (GO-Ag) nanocomposite and its applications as a sorbent for the elimination of some toxic pollutants from aqueous medium, as an efficient catalyst in the individual as well as simultaneous reduction reactions of multiple compounds, and as an antibacterial agent for the destruction of some harmful microorganisms existent in wastewater. GO was prepared using a modified Hummers method and Ag nanoparticles were integrated on GO sheets by chemical reduction of Ag⁺ ions on the surfaces of GO sheets. The composition and morphology of the nanocomposite was extensively characterized with elemental dispersive X-ray analysis (EDX), Fourier transform infra-red (FT-IR) spectroscopy, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). The GO-Ag nanocomposite demonstrated remarkable adsorption capacities and recyclability for malachite green (MG) and ethyl violet (EV) dyes. Various experimental parameters affecting adsorptive behavior of nanocomposite like temperature, pH, time of contact between dye and adsorbent, and adsorbent dose were evaluated thoroughly. Experimental data was simulated with different adsorption isotherms and kinetic models to evaluate adsorption behavior of both dyes and results confirmed the adsorption of both the dyes to be followed by pseudo 2nd order kinetic model and Langmuir adsorption model. Moreover, adsorbent was regenerated in suitable media for both dyes without any loss in removal efficiency. The catalytic performance for the 2-nitroaniline (2-NA) reduction was investigated in detail. Most importantly, the prepared nanocomposite was found to have potential to adsorb multiple pollutants all together as well as to catalyze the simultaneous reduction of a mixture of dyes (MG, MO, and EV) and 2-NA. An additional advantage of the GO-Ag nanocomposite was its antibacterial activity acquired to the presence of Ag nanoparticles. Two bacterial strains (Gram-negative bacterium, E. coli and the Gram-positive bacterium, S. aureus) were used to test antibacterial activity of composite and the results confirmed the remarkable performance of the nanocomposite in destroying harmful pathogens.

Optimization of flocculation conditions for soluble cadmium removal using the composite flocculant of green anion polyacrylamide and PAC by response surface methodology

In this work, we describe a flocculation performance evaluation of a novel anionic polyacrylamide (APAM) synthesized using low dose γ-ray initiation. The APAM structure and morphology were characterized using Fourier transform-infrared spectroscopy (FTIR), High performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. In comparison to commercially purchased APAM (Mw = 1.0 × 10⁷), γ-ray initiation was demonstrated to be a more effective method to increase molecular weight, decrease the residual acrylamide monomer, and improve thermal stability. Flocculant performance was evaluated by assessing their ability to remove Cd(II) from water. We utilized the Plackett-Burman (PB), steepest ascent, and response surface methodology (RSM) experimental design to identify the optimal flocculating conditions for the removal of soluble Cd(II). Under optimal conditions [26.84 mg L^-1 CaO, 71.28 mg L^-1 polyaluminium chloride (PAC) and 2.87 mg L^-1 APAM], the maximum percent removal of Cd(II) was observed to reach 93.65%. A potential flocculation mechanism for the Cd(II) removal from water was further studied by evaluating the colloid Zeta potential. Results from these studies demonstrated that PAC had a greater capability to change the Zeta potential of collide under alkaline conditions, while APAM played a critical role in the bridging, enmeshment, and sweeping effect. The composite of two types of predominance makes considerable sense in regards to enhancing flocculating efficiency, decreasing secondary pollution, and reducing flocculant cost.

Nano-hydroxyapatite polymeric hydrogels for dye removal

Herein, two kinds of nano-hydroxyapatite were synthesized from Clam and Magellan shell by wet chemical precipitation method. Mainly, carboxymethyl cellulose/acrylamide/nano-hydroxyapatite composite hydrogels were developed via a free-radical polymerization process and investigated as a sorbent for Acid Blue 113 (AB) from aqueous AB solution. The swelled and kinetic behaviours of hydrogels were investigated using a gravimetric method. The swelling properties of the CMC-AM-hydrogels were influenced by the calcium electrolytes (Ca²⁺) content in nano-hydroxyapatites. The diffusion coefficient value increased with the increase of nano-hydroxyapatite content in the CMC-AM/nHA-CS (0.22353–0.27681 cm² s⁻¹) and CMC-AM/nHA-MS (0.22377–0.29737 cm² s⁻¹) hydrogels. The mechanism of water diffusion was found to be anomalous transport. The CMC-AM/nHA-MS hydrogels showed high AB absorption efficiency and adsorption capacities. These results explained that the nano-hydroxyapatites of Magellan shells based hydrogels are attractive nanocomposite hydrogels for the adsorption of dye in the water purification applications.

Schematic diagram of nHA and nHA based hydrogels development via wet chemical and free-radical polymerization process and absorbent process of nHA hydrogel.

A novel method to prepare a magnetic carbon-based adsorbent with sugar-containing water as the carbon source and DETA as the modifying reagent

A novel magnetic heavy metal adsorbent was prepared via diethylenetriamine (DETA) modification on magnetic hydrothermal carbon, with glucose and sugar-containing waste water as the carbon source. The prepared materials were characterized by FT-IR, SEM, TEM, EDXRF, TGA, elemental analysis, XPS, and magnetic moment determination. In this paper, the adsorption mechanism of the modified and unmodified adsorbents was well discussed. Four kinds of waste water (watermelon juice, expired sprite, sugar-pressing waste water, and confectionary waste water) were employed to produce heavy metal ion adsorbents; the chemical properties of hydrothermal carbon derived from the proposed sources were analyzed as well. The maximum uptake capacity for Cu²⁺, Pb²⁺, and Cd²⁺ of the adsorbent produced from glucose was 26.88, 103.09, and 25.38 mg g^-1, respectively. After 5 cycles, the adsorption ability was still well preserved. This work represents an efficient new direction for the treatment of heavy metal ions in water and the reuse of sugar-containing waste water. Graphical abstract The schemetic of DETA-modified magnetic carbon preparing from sugar-containing wastewater.

Synthesis and characterization of graphene oxide sheets integrated with gold nanoparticles and their applications to adsorptive removal and catalytic reduction of water contaminants

Here, we report the facile synthesis of graphene oxide–gold (GO–Au) nanocomposites and their use as adsorbents for the removal of toxic industrial dyes from water and as catalysts for the individual and simultaneous reduction of a dye and a nitro compound in aqueous medium. GO sheets were prepared using a modified Hummers method while Au nanoparticles were integrated on GO sheets by reducing Au(iii) ions on the surfaces of GO sheets using sodium citrate as a reducing agent. The prepared composite was characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), elemental dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy and thermal gravimetric analysis (TGA). The GO–Au nanocomposite demonstrated efficient adsorption capacities and recyclability for malachite green (MG) and ethyl violet (EV) dyes. The effects of various experimental parameters including temperature, pH, contact time, and adsorbent dose were studied. From the simulation of experimental data with different adsorption isotherms and kinetic models it was found that the adsorption of both the dyes followed the Freundlich adsorption model and a pseudo-second order kinetic model, respectively. Moreover, the adsorbent showed better recyclability for both dyes without any compromise on the removal efficiency. Similarly, the catalytic performance for the reduction of 2-nitroaniline (2-NA) has been investigated in detail by using the prepared nanocomposite as a catalyst. Most importantly, we reported the simultaneous adsorption of cationic and anionic dyes from water using the prepared nanocomposite as well as the simultaneous catalytic reduction of a mixture of EV and 2-NA. So, considering the facile synthesis process and the efficient removal of a variety of dyes and the catalytic performance this work opens up a tremendous opportunity to bring GO based nanocomposites from experimental research to practically applied materials for wastewater treatment.

Preparation of graphene oxide–gold (GO–Au) nanocomposites as adsorbents and catalysts for decontamination of water.

Biomineralization of Pb(II) into Pb-hydroxyapatite induced by Bacillus cereus 12-2 isolated from Lead-Zinc mine tailings

The remediation of Pb(II) through biomineralization is rergarded as a promising technique as well as an interesting phenomenon for transforming heavy metals from mobile species into very stable minerals in the environment. Studies are well needed for in-depth understanding the mechanism of Pb(II) immobilized by bacteria. In the present study, we investigated the uptake and biomineralization of Pb(II) using Bacillus cereus 12-2 isolated from lead-zinc mine tailings. The maximum Pb(II) uptake capacity of B. cereus 12-2 was 340 mg/g at pH 3.0. Zeta potential analyses and selective passivation experiments demonstrated that electrostatic attraction was the main force driving the uptake of Pb(II), while the carboxyl, amide and phosphate functional groups of the bacteria provided the binding sites for immobilizing Pb(II). XRD and TEM investigation revealed that the Pb(II) loaded on bacteria could be stepwise transformed into rod-shaped Ca2.5Pb7.5(OH)2(PO4)6 nanocrystal. Combined with protein denaturalization experiments, we proposed that the biomineralization of Pb(II) possibly consisted of two steps: (1) Rapid biosorption of Pb(II) on B. cereus 12-2 through the synergy of electrostatic attraction, ionic exchange and chelating activity of functional groups; (2) enzyme-mediated mineral transformation from amorphous precipitate to rod-shaped crystalline minerals happening gradually inside the bacteria.

Hydrothermal-assisted biomimetic synthesis of a brush-like Hap/PAN composite and its application for decontaminating metal ions

A novel and functional ‘brush-like’ Hap/PAN composite was synthesized by a two-step method for the first time.

Mesoporous carbonated hydroxyapatite/chitosan porous materials for removal of Pb(ii) ions under flow conditions

Mesoporous carbonated hydroxyapatite/chitosan porous materials are fabricated for the first time, which show good adsorption properties for Pb(ii) ions even under flow conditions.

Modification of Hydroxyapatite with Ion-Selective Complexants: 1-Hydroxyethane-1,1-diphosphonic Acid

Hydroxyapatite (HAP) was modified with 1-hydroxyethane-1,1-diphosphonic acid (HEDP), and its effect on divalent metal ion binding was determined. HAP was synthesized from calcium hydroxide and phosphoric acid. After calcination, it was modified with HEDP, and the influence of time and temperature on the modification was investigated. HEDP incorporation increased as its initial solution concentration increased from 0.01 to 0.50 M. Unmodified and modified HAP were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and specific surface area analysis. Ca/P ratios, acid capacities, and phosphorus elemental analyses gave the effect of modification on composition and surface characteristics. A high reaction temperature produced new phosphonate bands at 993, 1082, and 1144 cm-1 that indicated the presence of HEDP. HAP modification at a high temperature-long reaction time had the highest HEDP loading and gave the sharpest XRD peaks. The emergence of new HAP-HEDP strands was observed in SEM images for treated samples while EDS showed high phosphorus contents in these strands. Modified HAP had a high acid capacity from the additional P-OH groups in HEDP. The P(O)OH groups maintain their ability to bind metal ions within the HAP matrix: contacting the modified HAP with 10-4 N nitrate solutions of five transition metal ions gives an affinity sequence of Pb(II) > Cd(II) > Zn(II) > Ni(II) > Cu(II). This result is comparable to that of commercially available di(2-ethylhexyl)phosphoric acid, a common solvent extractant, and the trend is consistent with the Misono softness parameter of metal ion polarizabilities.

Fabrication of hydroxyapatite/chitosan porous materials for Pb(ii) removal from aqueous solution

Hydroxyapatite/chitosan porous materials are fabricated by a freeze-drying method for Pb(ii) removal from aqueous solution.

Synthesis of linear low-density polyethylene-g-poly (acrylic acid)-co-starch/organo-montmorillonite hydrogel composite as an adsorbent for removal of Pb(ΙΙ) from aqueous solutions

The purpose of this work is to remove Pb(II) from the aqueous solution using a type of hydrogel composite. A hydrogel composite consisting of waste linear low density polyethylene, acrylic acid, starch, and organo-montmorillonite was prepared through emulsion polymerization method. Fourier transform infrared spectroscopy (FTIR), Solid carbon nuclear magnetic resonance spectroscopy (CNMR)), silicon(-29) nuclear magnetic resonance spectroscopy (Si NMR)), and X-ray diffraction spectroscope ((XRD) were applied to characterize the hydrogel composite. The hydrogel composite was then employed as an adsorbent for the removal of Pb(II) from the aqueous solution. The Pb(II)-loaded hydrogel composite was characterized using Fourier transform infrared spectroscopy (FTIR)), scanning electron microscopy (SEM)), and X-ray photoelectron spectroscopy ((XPS)). From XPS results, it was found that the carboxyl and hydroxyl groups of the hydrogel composite participated in the removal of Pb(II). Kinetic studies indicated that the adsorption of Pb(II) followed the pseudo-second-order equation. It was also found that the Langmuir model described the adsorption isotherm better than the Freundlich isotherm. The maximum removal capacity of the hydrogel composite for Pb(II) ions was 430mg/g. Thus, the waste linear low-density polyethylene-g-poly (acrylic acid)-co-starch/organo-montmorillonite hydrogel composite could be a promising Pb(II) adsorbent.

Magnetic Co–Fe bimetallic nanoparticle containing modifiable microgels for the removal of heavy metal ions, organic dyes and herbicides from aqueous media

Poly(methacrylic-co-acrylonitrile) (p(MAc-co-AN)) microgels were prepared and nitrile groups were converted to amidoxime groups by chemical modification.

Bioinspired fabrication and lead adsorption property of nano-hydroxyapatite/chitosan porous materials

Nano-hydroxyapatite/chitosan porous materials possess great applications for removal of Pb²⁺ ions from environmental and industrial wastes.

Characterization, Dissolution, and Solubility of Lead Hydroxypyromorphite [Pb5(PO4)3OH] at 25–45°C

Dissolution of the hydroxypyromorphite [lead hydroxyapatite, Pb5(PO4)3OH] in HNO3solution (pH = 2.00), ultrapure water (pH = 5.60), and NaOH solution (pH = 9.00) was experimentally studied at 25°C, 35°C, and 45°C. The XRD, FT-IR, and FE-SEM analyses indicated that the hydroxypyromorphite solids were observed to have indistinguishable change during dissolution. For the hydroxypyromorphite dissolution in aqueous acidic media at initial pH 2.00 and 25°C, the aqueous phosphate concentrations rose quickly and reached the peak values after 1 h dissolution, while the aqueous lead concentrations rose slowly and reached the peak values after 1440 h. The solution Pb/P molar ratio increased constantly from 1.10 to 1.65 near the stoichiometric ratio of 1.67 to 209.85~597.72 and then decreased to 74.76~237.26 for the dissolution at initial pH 2.00 and 25°C~45°C. The averageKspvalues for Pb5(PO4)3OH were determined to be 10−80.77(10−80.57−10−80.96) at 25°C, 10−80.65(10−80.38−10−80.99) at 35°C, and 10−79.96(10−79.38−10−80.71) at 45°C. From the obtained solubility data for the dissolution at initial pH 2.00 and 25°C, the Gibbs free energy of formation [ΔGfo] for Pb5(PO4)3OH was calculated to be −3796.71 kJ/mol (−3795.55~−3797.78 kJ/mol).