Amphiphilic PA-induced three-dimensional graphene macrostructure with enhanced removal of heavy metal ions

Sequential removal of phosphate and copper(II) ions using sustainable chitosan biosorbent

Although adsorbents are good candidates for removing phosphorus and heavy metals from wastewater, the use of biosorbents for the sequential treatment of phosphorus and copper has not yet been studied. Porous chitosan (CS)-based biosorbents (CGBs) were developed to adsorb phytic acid (PA), a major form of organic phosphate. This first adsorbate (PA) further served as an additional ligand (P-type ligand) for the CGBs (N-type ligand) to form a complex with the second adsorbate (copper). After the adsorption of PA (the first adsorbate), the spent CGBs were recycled and used as a new adsorbent to adsorb Cu(II) ions (the second adsorbate), which was expected to have a dual coordination effect through P, N-ligand complexation with copper. The interactions and complexation between CS, PA and Cu(II) ions on the PA-adsorbed CGBs (PACGBs) were investigated by performing FTIR, XPS, XRD, and SEM-EDS analyses. The PACGBs exhibited fast and enhanced adsorption of Cu(II) ions, owing to the synergistic effect of the amino groups of CS (the original ligand, N-type) and the phosphate groups of PA (an additional ligand, P-type) on the adsorption of Cu(II) ions. This is the first time that sequential removal of phosphorus and heavy metals by biosorbents has been performed using biosorbents.

Polymeric biomolecules based nanomaterials: Production strategies and pollutant mitigation as an emerging tool for environmental application

The ever-exploding global population coupled with its anthropogenic impact has imparted unparalleled detrimental effects on the environment and mitigating them has emerged as the prime challenge and focus of the current century. The niche of nanotechnology empowered by composites of biopolymers in the handling of xenobiotics and environmental clean-up has an unlimited scope. The appositeness of biopolymer-nanoparticles (Bp-NPs) for environmental contaminant mitigation has received unique consideration due to its exclusive combination of physicochemical characteristics and other attributes. The current review furnishes exhaustive scrutiny of the current accomplishments in the development of Bp-NPs and biopolymer nanomaterials (Bp-NMs) from various polymeric biomolecules. Special attention was provided for polymeric biomolecules such as cellulose, lignin, starch, chitin, and chitosan, whereas limited consideration on gelatin, alginate, and gum for the development of Bp-NPs and Bp-NMs; together with coverage of literature. Promising applications of tailored biopolymer hybrids such as Bp-NPs and Bp-NMs on environmentally hazardous xenobiotics handling and pollution management are discussed as to their notable environmental applications.

Water-stable metal organic framework-199@polyaniline with high-performance removal of copper II

Metal organic frameworks (MOFs)-based adsorbents for copper ion (Cu²⁺) generally have the disadvantages of instability in water, low adsorption capacity, and selectivity. Aimed at such problems, we fabricated MOF-199 coated with polyaniline (MOF-199@PANI, core@shell) composite for specific adsorption of Cu²⁺ in water efficiently. Combined with the characterization by SEM, XRD, and FT-IR, the comprehensively excellent performance probably derived from porous structures of MOF-199, as well as the complexation between Cu²⁺ and the N atoms of imine moieties in PANI. In addition, the coating process by PANI perfectly protected the MOF skeleton. The isothermal data fitted well to Langmuir isotherm model, of which the calculated adsorption capacity reached 7831.34 mg/g. It was one or two orders of magnitude higher than some other new absorbent for Cu²⁺ including some carbon-based or organic adsorbents. On the basis of the optimization including pH value, temperature, and ratio of raw materials, the fabricated composite has realized the removal of the spiked Cu²⁺ in actual fresh water and industrial wastewater samples.

Synthesis of polystyrene-based hyper-cross-linked polymers for Cd(II) ions removal from aqueous solutions: Experimental and RSM modeling

The hyper-cross-linked polymers (HCPs) based on the polystyrene was synthesized during the Friedel-Craft reaction in various situations. The HCPs synthesis were carried out in various operating conditions including reaction time in the range of 3-23 h, the ratio of cross-linker to monomer in range of 1-5 at temperature of 80 ℃. In addition, the cadmium adsorption process was carried out at a temperature in the range of 25-85 ℃ and initial cadmium concentration in the range of 10-100 mg/L. The response surface methodology (RSM) has been applied for optimizing the process using synthesis and adsorption parameters. The optimized synthesis conditions were obtained 3.32, 11.26 h, 80 ℃, in ratio, synthesis time, and temperature, respectively. Also, the optimized adsorption conditions were obtained 80 mg/L and 35 ℃, initial cadmium ion concentration, and temperature, respectively. The surface area and thermal stability were obtained at 853.89 m²/g and 450 ℃, respectively. The maximum adsorption capacity and removal efficiency had been obtained 950 mg/g and 92% at a temperature of 20 ℃, after 80 min, respectively. The maximum adsorption capacity and removal efficiency were observed in the initial concentration of 120 mg/L and 10 mg/L, respectively. The adsorption process behavior was surveyed using isotherm, kinetic and thermodynamic models. The isotherm results showed that the adsorption of cadmium by HCPs is multi-layer and heterogeneous. The thermodynamic parameters showed that the process is exothermic and spontaneous. Finally, the kinetic results showed that the process occurred physically and slowly as the temperature raised.

Role of surface functional groups of hydrogels in metal adsorption: From performance to mechanism

Hydrogels have been studied quite intensively in recent decades regarding whether their metal adsorption abilities may be modified or even enhanced via functionalization (i.e., functionalizing the surfaces of hydrogels with specific functional groups). Studies have found that functionalizing hydrogels can in fact give them higher adsorptive power. This enhanced adsorptive performance is articulated in this paper through critically reviewing more than 120 research articles in such terms as the various techniques of synthesizing functionalized hydrogels, the roles that specific functional groups play on adsorption performance, selectivity, reusability, as well as on adsorption mechanism. Moreover, this critical review offers insight into future designs of functionalized hydrogels with specific metal adsorption capabilities.

Adsorption affinity of Zn (II) ions for nanostructured zirconium phosphate/silica or titania composites

The paper presents the kinetics of Zn (II) ions adsorption as well as its dependence as a function of pH on nanostructured zirconium phosphate and its composites with silica and titania. The nanostructured zirconium phosphate-containing composites were obtained by mechanical processing in the Pulverisette-7 (Fritsch Gmbh) mill. The obtained composites were characterized by a heterogeneous surface coverage of silica gel or titanium oxides. Zinc ions adsorption studies on these adsorbents showed practically complete removal of Zn (II) from aqueous solutions with an initial concentration of < 0.0001 mol/dm3 and a pH > 4 within 10 min.

Graphene-Based Macromolecular Assemblies for Scavenging Heavy Metals

The integration of graphene or graphene oxide nanosheets into three-dimensional (3D) graphene-based macromolecular assemblies (GMAs), in the form of sponges, beads, fibres, films, and crumpled nanosheets, has greatly advanced their environmental remediation applications. This is attributed to the outstanding physicochemical characteristics and superlative mechanical features of 3D GMAs, including precise and physically linked permeable networks, enormous surface area, profound porosity, and high-class sturdiness, amongst others. In this review, the recent advancements towards the exploration of 3D GMAs as an exciting new class of high-performance adsorbents, for eliminating toxic heavy metal ions from both wastewater and freshwater, are systematically summarized and discussed, from both fundamental and applied perspectives. In particular, the numerous surface modification techniques that are actively pursued to enrich the metal adsorption capacity of 3D GMAs, are comprehensively examined. Additionally, associated challenges are pointed out and tactical research strategies and improvements are proposed, with an eye on the conceivable future.

Application of three dimensional porous aerogels as adsorbent for removal of heavy metal ions from water/wastewater: A review study

Nowadays, by rapid development of economies and industries, water contamination through the heavy metal ions (toxic, non-toxic and radioactive) is a great concern and an important environmental problem. Currently, numerous techniques such as chemical precipitation, coagulation, ion-exchange, filtration, reverse osmosis, biological treatment and physical adsorption are presented by researchers for removing and recycling heavy metal ions from wastewater. Among these methods, adsorption approach is one of the most efficient techniques for the elimination of heavy metal ions from aqueous solutions. There are a number of low cost absorbent such as agricultural and industrial solid waste such as lingo-cellulosic materials, wheat bran, peanut shell, moss peat, fly ash, bagasse, tree fern, gram husk, nanostructures (such as TiO₂, SiO₂, SnO₂, ZnO, etc.), 3D porous structures (aerogels), etc. which have been developed and tested to efficient removal of heavy metal ions from wastewater. In this study, a critical review of the applications of aerogels in water and sewage purifications is performed. For this reason, different kinds of aerogel namely organic, inorganic and organic-inorganic hybrid aerogels are investigated. It is concluded that the most applicable aerogels used in these studies are graphene-based aerogels due to more porous structure as well as simplification of their modification. Also, in this review paper, for the first time we summarized and highlighted the recent literature information about heavy metal ions and theirs removal methods from aqueous pollutants and wastewater/water, adsorption kinetics, isotherms and thermodynamics models by different type of three dimensional (3D) porous structure. In additional, in this review article, the influence of various parameters such as pH solution, temperature, initial concentration of heavy metal ions, composition, contact time, coexisting ions and adsorbent dosage on the adsorption process of heavy metal ions were investigated.

A sulfur, nitrogen dual-doped porous graphene nanohybrid for ultraselective Hg(ii) separation over Pb(ii) and Cu(ii)

Two-dimensional (2D) porous graphene is attractive as a high-permeability membrane for ionic and molecular separation. Here, we propose a sulfur, nitrogen dual-doped 2D porous graphene (SNPG) nanohybrid by adopting a facile one-step process. The resulting sandwich-like porous nanohybrid features uniform ion-gated nanopores for efficient transport of target heavy metal ions while blocking undesired ions, as well as abundant multi-binding ligands for selectively chelating permeated heavy metal ions. We show from systematic experiments that this SNPG nanohybrid exhibits outstanding selectivity and ability to separate Hg(ii) ions in mixtures with eight other metal ions. An excellent uptake capability (803 mg g^-1) and high removal ability (>99%) within the entire pH range of 2-10 can be obtained. Given the specific 2D porous nanostructure and specific binding ligands, SNPG exhibits an ultrahigh separation factor towards Hg(ii) that is up to four orders of magnitude higher than those of Pb(ii), Cd(ii) and Cu(ii) ions, significantly higher than those of most reported adsorbents. These findings provide a new opportunity to develop selective materials and devices for applications such as efficient recognition, extraction and separation of target metal ions in complex aqueous environments.

Recent Advances in Applications of Hybrid Graphene Materials for Metals Removal from Wastewater

The presence of traces of heavy metals in wastewater causes adverse health effects on humans and the ecosystem. Adsorption is a low cost and eco-friendly method for the removal of low concentrations of heavy metals from wastewater streams. Over the past several years, graphene-based materials have been researched as exceptional adsorbents. In this review, the applications of graphene oxide (GO), reduce graphene oxide (rGO), and graphene-based nanocomposites (GNCs) for the removal of various metals are analyzed. Firstly, the common synthesis routes for GO, rGO, and GNCs are discussed. Secondly, the available literature on the adsorption of heavy metals including arsenic, lead, cadmium, nickel, mercury, chromium and copper using graphene-based materials are reviewed and analyzed. The adsorption isotherms, kinetics, capacity, and removal efficiency for each metal on different graphene materials, as well as the effects of the synthesis method and the adsorption process conditions on the recyclability of the graphene materials, are discussed. Finally, future perspectives and trends in the field are also highlighted.

Amino-functionalized graphene oxide for Cr(VI), Cu(II), Pb(II) and Cd(II) removal from industrial wastewater

Amino-functionalized graphene oxide (GO-NH2) was synthesized by grafting (3-aminopropyl) triethoxysilane on the graphene oxide (GO) surface. The GO-NH2 with high surface area and numerous active sites can efficiently adsorb Cr(VI), Cu(II), Pb(II) and Cd(II) ions. The maximum adsorption capacities of GO-NH2 for Cr(VI), Cu(II), Pb(II) and Cd(II) were 280.11, 26.25, 71.89 and 10.04 mg g−1, respectively. The pseudo-first-order and pseudo-second-order kinetic models were employed to describe the kinetic processes. The experimental data agreed well with the pseudo-second-order kinetic equation, and the adsorption of heavy metals onto GO-NH2 occurs via chemical adsorption. The characteristics of Cr(VI), Cu(II), Pb(II) and Cd(II) in the GO-NH2 adsorption processes were analyzed using the Langmuir and Freundlich isotherm models. The adsorption processes of Pb(II) and Cd(II) on GO-NH2 were fit by the Langmuir model. The Freundlich isotherm model was well correlated to Cr(VI) and Cu(II). The GO-NH2 is a promising material for the removal of heavy metal ions from industrial wastewater. This study provides an effective pathway to process industrial wastewater, and the GO-NH2 has a good adsorption effect for the treatment of heavy metals in industrial wastewater.

Cadmium removal from rice protein via synergistic treatment of rhamnolipids and F127/PAA hydrogels

Heavy metal ions can accumulate in the area's crop harvest, such as rice, via a tight binding with protein. Such binding paves great difficulties to remove heavy metal ions. This study aims to remove cadmium from contaminated rice protein using rhamnolipid biosurfactant together with Pluronic F127/poly (acrylic acid) (i.e., F127/PAA) hydrogels. The two-step consequential washing removed 92% of cadmium in rice protein, making the residual cadmium content below the safety level (<0.2 mg/kg) without impairing the main components and structure of rice protein. Interestingly, the washing by either rhamnolipids or hydrogels failed to effectively remove cadmium, indicating the synergistic effect of the two materials. Mechanistically, rhamnolipids with higher Cd²⁺ binding constant compete with protein on binding with cadmium and then deliver it to F127/PAA hydrogels that present highest Cd²⁺ adsorptive capability for immobilization. In considering that the F127/PAA hydrogels are reusable, this treatment is low-cost, safe and effective for removal of cadmium from polluted rice products.

Crumpled graphene balls as rapid and efficient adsorbents for removal of copper ions

A novel, three-dimensional (3D), self-supporting material-the crumpled graphene ball-was developed using an aerosol capillary approach. The resultant crumpled-graphene-ball architecture showed a self-supporting, 3D network microstructure with plenty of ridges and wrinkles. Due to their unique structural characteristics, the 3D balls exhibited a rapid adsorption rate and superior adsorption capacity toward the copper ion (Cu²⁺). It was noted that the adsorption capacity for Cu²⁺ reached about 224.56 mg/g within 2 min. A high adsorption capacity, fast adsorption kinetics, excellent regeneration and reusability characteristics, and the ease of materials processing make these crumpled graphene balls ideal candidates for heavy metal ion decontamination in practical application.

Investigation of an eco-friendly aerogel as a substrate for the immobilization of MoS2 nanoflowers for removal of mercury species from aqueous solutions

An adsorbent that exhibits high affinity for inorganic mercury (Hg²⁺) with a high removal efficiency of methylmercury (MeHg⁺) has been developed. The adsorbent demonstrates a symbiotic relationship between its two components, molybdenum disulphide nanoflowers (MoS₂NFs) and a poly (vinyl alcohol) (PVA) aerogel. Furthermore, we modified the distribution and loading of the MoS₂NFs, which was possible due to the stable porous support, and investigated the biocompatibility of the aerogel-support adsorbent. The performance of the optimized material exhibited a distribution coefficient of 9.71 × 10⁷ mL g^-1. In addition, the adsorbent was effective over a wide pH range and could efficiently purify both contaminated lake and sea water. The key motivation for using an aerogel support was to stabilise the MoS₂NFs during purification of the water (resulting in improved performance compared to using freestanding MoS₂NFs) and the ability to regenerate the used adsorbent. In addition, animal tests confirmed an extremely low toxicity of the adsorbent to fish, along with the excellent purification results.

Synthesis of mesoporous silica-calcium phosphate hybrid nanoparticles and their potential as efficient adsorbent for cadmium ions removal from aqueous solution

Since adsorption and nanomaterials had been respectively found to be the most promising technique and the preferred adsorbents for heavy metal ions removal, in this study, novel mesoporous silica-calcium phosphate (MS-CP) hybrid nanoparticles were synthesized by a facile one-pot method, and subsequently assessed as adsorbent for Cd²⁺ removal from aqueous solution. MS-CP were characterized by scanning and transmission electron microscopies, etc. The influences of initial Cd²⁺ concentration, contact time, solution temperature and solution pH on removal efficiency of Cd²⁺ were investigated in detail. The results revealed that MS-CP were nanospheres of ∼20 nm and presented a bimodal pore distribution (3.82 nm and 12.40 nm), a high surface area (314.56 m²/g) and a large pore volume (1.21 cm³/g). The Cd²⁺ removal experiments demonstrated that MS-CP had a high adsorption capacity due to electrostatic interaction between Cd²⁺ and silanol groups on MS-CP surface, as well as ion-exchange between Cd²⁺ and calcium in MS-CP. Additionally, removal efficiency of Cd²⁺ increased with increasing contact time and solution temperature, while decreased as initial Cd²⁺ concentration increased. The maximum adsorption capacity of Cd²⁺ by MS-CP was above 153 mg/L. These results suggested that the as-synthesized MS-CP could be promising adsorbent for Cd²⁺ removal from aqueous solution.

Determination of six organophosphorus pesticides in water samples by three-dimensional graphene aerogel-based solid-phase extraction combined with gas chromatography/mass spectrometry

In the present study, a three-dimensional graphene aerogel (3D-GA), synthesised by chemical reduction of an aqueous solution of graphene oxides (GOs) with ethylenediaminethermal by a simple water bath method followed by freeze-drying treatment, was used for the solid-phase extraction (SPE) of six organophosphorus pesticides (OPPs) (i.e. trichlorfon, dimethoate, ethoprophos, parathion, fenitrothion and fenthion) from water samples. The target analytes were extracted using packed SPE cartridges and then eluted with tetrahydrofuran. The eluate was collected and dried with high-purity nitrogen gas at room temperature. After redissolving in acetone, the residue was analysed using gas chromatography/mass spectrometry (GC/MS). The proposed method demonstrated a good linearity between 0.5 and 500 μg L-1 with the correlation coefficient of 0.9990-0.9998. The limits of detection (LODs) (S/N = 3) and the limits of quantification (LOQs) (S/N = 10) for the six OPPs pesticides were in the range of 0.12-0.58 μg L-1 and 0.41-1.96 μg L-1, respectively. The accuracy of the present method was evaluated by measuring the recovery of the spiked samples, which ranged from 93.8% to 104.2% with relative standard deviations (RSDs) of 1.1-5.6%. The established method was successfully applied to the determination of the target analytes in environmental water samples including tap water, river water, drinking water and lake water, demonstrating its great potential for the determination of OPPs in water.