Characteristics of amine-crosslinked wheat straw and its adsorption mechanisms for phosphate and chromium (VI) removal from aqueous solution

Insight into the wheat residues-derived adsorbents for the remediation of organic and inorganic aquatic contaminants: A review

Wheat is a major grain crop of the world that provides a stable food for human consumption. Large amounts of by-products/waste materials are produced after the harvesting and processing of wheat crop. Such materials can cause an environmental issue if not disposed of properly. Several studies have shown that wheat residues can be efficient precursors for adsorbents because of their availability, renewability, lignocellulosic composition, and surface active groups enriched structure. In the literature, there are few review articles that address wheat residues-based adsorbents. However, these reviews were specific in terms of adsorbate or adsorbent and did not provide detailed information about the modification, properties, and regeneration of these adsorbents. This article extensively reviews the utilization of wheat biomass/waste including straw, bran, husk, and stalk as precursors for raw or untreated, chemically treated, carbonaceous, and composite adsorbents against various environmental pollutants. The influences of inlet pollutant amount, adsorbent dose, pH, temperature, and time on the performance of adsorbents against pollutants were considered. The maximum uptakes, equilibrium time, and adsorption nature were identified from isotherms, kinetic, and thermodynamic studies. The highest adsorbed amounts of most tested contaminants were 448.20, 322.58, and 578.13 mg/g for lead, chromium, and copper, 1374.6 and 1449.4 mg/g for methylene blue and malachite green, and 854.75, 179.21, and 107.77 mg/g for tetracycline, phosphate, and nitrate, respectively. For the studied adsorbate/adsorbent systems the adsorption mechanism and regeneration were also discussed. Significant results and future directions are finally presented.

Removal of inorganic toxic contaminants from wastewater using sustainable biomass: A review

Lignocellulosic biomass is most abundant, ecofriendly and sustainable material on this green planet which has received great attention due to exhaustion of petroleum reserves and various environmental complications. Due to its abundance and sustainability, it has been opted in number of advanced applications i.e. synthesis of green chemicals, biofuels, paper, packaging, biocomposite and for discharge of toxic contaminants from wastewaters. Utilization of sustainable biomass for removal of toxic pollutants from wastewater is robust technique due to its low-cost and easy availability. In this review, we have summarized removal of inorganic pollutants by sustainable lignocellulosic biomass in their natural as well as in chemically functionalized form. Various techniques for modification of sustainable biomass have been discussed and it was found that modified biomass showed better biosorption ability as compared to natural biomass. We conclude that modified biomass biosorbents are useful for removal of toxic inorganic pollutants to deficient levels. Several modification strategies can improve the qualities of biosorbent, however grafting is the most successful among them, as demonstrated in this work. The numerous grafting methods using a free radical grafting process are also summarized in this review article. This review also gathers studies comparing sorption capabilities with and without modification using modified and unmodified biosorbents. Chemically modified cellulosic biomass is favoured over untreated biomass because it has a higher adsorption efficiency, which is favoured by a large number of reactive binding sites, improved ion-exchange characteristics, and more functional groups available after modification.

Recent developments in alginate-based adsorbents for removing phosphate ions from wastewater: a review

The huge development of the industrial sector has resulted in the release of large quantities of phosphate anions which adversely affect the environment, human health, and aquatic ecosystems. Naturally occurring biopolymers have attracted considerable attention as efficient adsorbents for phosphate anions due to their biocompatibility, biodegradability, environmentally-friendly nature, low-cost production, availability in nature, and ease of modification. Amongst them, alginate-based adsorbents are considered one of the most effective adsorbents for removing various types of pollutants from industrial wastewater. The presence of active COOH and OH^- groups along the alginate backbone facilitate its physical and chemical modifications and participate in various possible adsorption mechanisms of phosphate anions. Herein, we focus our attention on presenting a comprehensive overview of recent advances in phosphate removal by alginate-based adsorbents. Modification of alginate by various materials, including clays, magnetic materials, layered double hydroxides, carbon materials, and multivalent metals, is addressed. The adsorption potentials of these modified forms for removing phosphate anions, in addition to their adsorption mechanisms are clearly discussed. It is concluded that ion exchange, complexation, precipitation, Lewis acid-base interaction and electrostatic interaction are the most common adsorption mechanisms of phosphate removal by alginate-based adsorbents. Pseudo-2^nd order and Freundlich isotherms were figured out to be the major kinetic and isotherm models for the removal process of phosphate. The research findings revealed that some issues, including the high cost of production, leaching, and low efficiency of recyclability of alginate-based adsorbents still need to be resolved. Future trends that could inspire further studies to find the best solutions for removing phosphate anions from aquatic systems are also elaborated, such as the synthesis of magnetic-based alginate and various-shaped alginate nanocomposites that are capable of preventing the leaching of the active materials.

A review on adsorptive separation of toxic metals from aquatic system using biochar produced from agro-waste

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

Enhanced degradation of phenol by a novel biomaterial through the immobilization of bacteria on cationic straw

As phenol possesses a threat to human health, there is a great demand to search for fast and efficient methods for it to be discharged. In this study, a novel biomaterial was prepared by the immobilization of bacteria on a cationic straw carrier, and the remediation ability of the biomaterial on phenol-containing wastewater was investigated. The free bacteria could degrade 1,000 mg/L phenol within 240 h, while the prepared biomaterial was 192 h, shortening by 48 h that of free bacteria. In addition, the degradation tolerance of biomaterial increased from 1,000 mg/L to 1,200 mg/L than the free bacteria, within 216 h, which shortened by 24 h the degradation time of 1,000 mg/L phenol by free bacteria (240 h). Further, under different pH conditions, the degradation efficiency of phenol by prepared biomaterial was much higher than that of free bacteria. Especially for the lower pH 5, the degradation efficiency of biomaterial was nearly twice that of the free bacteria. This investigation demonstrates that this biomaterial has great potential in the field of remediation of organic pollution.

Facile synthesis of Fe3O4 anchored polyaniline intercalated graphene oxide as an effective adsorbent for the removal of hexavalent chromium and phosphate ions

Adsorption media of hybrid composites is a promising candidate to eliminate the toxic contaminants from an aqueous environment, and good regeneration ability has received considerable interest to be utilized in water and wastewater treatment. Herein, we synthesized Fe₃O₄ anchored polyaniline intercalated graphene oxide (Fe₃O₄x%-PANI@GO, where x = 10, 20 and 50% of Fe₃O₄ particles) hybrid composites by co-precipitation and modified Hummers' method, followed by in-situ polymerization. The as-synthesized Fe₃O₄x%-PANI@GO acts as a potential host in welcoming the guest ions such as anionic contaminants with different interactions in this work. Besides, the advantages of easy separation by the external magnetic field, the Fe₃O₄x%-PANI@GO hybrid composite also achieve a great adsorption efficiency of 143.54 and 135.67 mg/g for Cr(VI) and phosphate ions, respectively, than the other adsorbents reported in the literature. The as-synthesized adsorbents were characterized by different analytical techniques and influencing parameters such as contact time, co-existing anions, solution pH, adsorption isotherms, and kinetics were studied in detail. The adsorption system of Fe₃O₄50%-PANI@GO hybrid composite follows the Langmuir isotherm and pseudo-second-order kinetic model for the elimination of Cr(VI) and phosphate ions from aqueous solutions. The feasible removal mechanism of Cr(VI) and phosphate ions was explored by FTIR and XPS techniques for anionic pollutants. Moreover, the selectivity and recyclability tests showed that the Fe₃O₄50%-PANI@GO hybrid composites demonstrated a high adsorption capacity towards the anionic ions from the aqueous environment. Therefore, the present investigation suggested that the Fe₃O₄50%-PANI@GO hybrid composites is an effective adsorbent for the elimination of Cr(VI) and phosphate ions from wastewater.

Capture and Release Recyclable Dimethylaminomethyl-Calixarene Functional Cloths for Point-of-Use Removal of Highly Toxic Chromium Water Pollutants

Chromium(VI) contamination of drinking water arises from industrial activity wherever there is a lack of environmental legislation enforcement regarding the removal of such pollutants. Although it is possible to remove such harmful metal ions from drinking water through large-scale facilities, there currently exists no safe and simple way to filter chromium(VI) oxoanions at the point of use (which is potentially safer and necessary in remote locations or humanitarian scenarios). High-surface-area cloth substrates have been functionalized with calixarene molecules for the selective capture of aqueous chromium(VI) oxoanions in the presence of structurally similar anions. This is accomplished by pulsed plasmachemical deposition of a linker layer and subsequent functionalization with dimethylaminomethyl-calixarene (5,11,17,23-tetrakis[(dimethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene). Chromium(VI) oxoanions are captured by simply passing polluted water through the functionalized cloth, while other ions not harmful/beneficial to human health remain in the water. These cloth filters are simple to use, highly selective, and easily recyclable-thus making them attractive for point-of-use application in geographic regions lacking appropriate wastewater treatment plants or flawed environmental monitoring systems. Chromium(VI) pollutants have been successfully removed from real-world contaminated industrial wastewater streams using the dimethylaminomethyl-calixarene functionalized cloths.

Green Synthesis of MnO Nanoparticles Using Abutilon indicum Leaf Extract for Biological, Photocatalytic, and Adsorption Activities

We report the synthesis of MnO nanoparticles (AI-MnO NAPs) using biological molecules of Abutilon indicum leaf extract. Further, they were evaluated for antibacterial and cytotoxicity activity against different pathogenic microbes (Escherichia coli, Bordetella bronchiseptica, Staphylococcus aureus, and Bacillus subtilis) and HeLa cancerous cells. Synthesized NAPs were also investigated for photocatalytic dye degradation potential against methylene blue (MB), and adsorption activity against Cr(VI) was also determined. Results from Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Energy-dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR) confirmed the successful synthesis of NAPs with spherical morphology and crystalline nature. Biological activity results demonstrated that synthesized AI-MnO NAPs exhibited significant antibacterial and cytotoxicity propensities against pathogenic microbes and cancerous cells, respectively, compared with plant extract. Moreover, synthesized AI-MnO NAPs demonstrated the comparable biological activities results to standard drugs. These excellent biological activities results are attributed to the existence of the plant’s biological molecules on their surfaces and small particle size (synergetic effect). Synthesized NAPs displayed better MB-photocatalyzing properties under sunlight than an ultraviolet lamp. The Cr(VI) adsorption result showed that synthesized NAPs efficiently adsorbed more Cr(VI) at higher acidic pH than at basic pH. Hence, the current findings suggest that Abutilon indicum is a valuable source for tailoring the potential of NAPs toward various enhanced biological, photocatalytic, and adsorption activities. Consequently, the plant’s biological molecule-mediated synthesized AI-MnO NAPs could be excellent contenders for future therapeutic applications.

Adsorption of Fluorides in Drinking Water by Palm Residues

Fluorides represent a significant problem in low- and middle-income countries (LMICs). In fact, this ion is essential for human health but, if taken in excess, it can cause dental and skeletal fluorosis. In LMICs, the pollution of groundwater from fluorides is of natural origin. Therefore, if providing alternative sources for drinking water (DW) supply is not possible, the use of specific processes for the removal of fluorides becomes essential. The adsorption on alternative materials, such as agro-food residues, can be a valid treatment for the removal of fluorides in the LMIC considering: (i) their optimal removal yields, (ii) the high availability, and (iii) the low cost. In recent years, the interest on the use of palm residues (PRs) becomes significant. Optimal pH, temperature, adsorbent dosage, and possible combination with metals to increase adsorption performances were deeply investigated. The activated PRs also present two other advantages: (i) very high surface area, and (ii) very low reduction in uptake capacity when regenerated. However, all tests were conducted with synthetic waters in laboratory-scale reactors while application on real-scale are absent. This makes other studies on this type of alternative adsorbent material still necessary.

Wheat Straws and Corn Straws as Adsorbents for the Removal of Cr(VI) and Cr(III) from Aqueous Solution: Kinetics, Isotherm, and Mechanism

In this paper, the adsorption properties of wheat straw (WS) and corn straw (CS) for Cr(VI) and Cr(III) in solution were studied. The effects of adsorption time, pH of the solution, temperature, and initial concentration of metal ions on adsorption capacity were investigated. The adsorption mechanism was discussed. The results showed that the adsorption isotherms of WS and CS for Cr(VI) and Cr(III) satisfied the Langmuir equation. By fitting the Langmuir equation, the saturated adsorption capacity of WS for Cr(VI) and Cr(III) can reach 125.6 and 68.9 mg g^-1, and that of CS for Cr(VI) and Cr(III) can reach 87.4 and 62.3 mg g^-1 , respectively. The adsorption kinetics conformed to the pseudo-second-order kinetic equation. The effect of temperature on the adsorption capacity was not significant. Physical diffusion and chemical adsorption coexist in the process of adsorption of metal ions by straws, and chemical adsorption is dominant, and the effect of physical diffusion on the chemical adsorption rate can be neglected. It can be seen from the experimental results that the treatment of chromium-containing wastewater by using cheap and easily available wheat straw and corn straw had a remarkable effect. The adsorbed straw could be completely desorbed and had excellent recyclability, indicating that the straws are ideal adsorbents.

Co-monomer polymer anion exchange resin for removing Cr(VI) contaminants: Adsorption kinetics, mechanism and performance

Modified anion exchange resin (EDE-D301) was synthesized by mixing monomers: epichlorohydrin (ECH), dimethylamine (DMA), ethylenediamine (EDA) with the weakly alkaline anion exchange resin D301 through in-situ polymerization method. Adsorption performance of EDE-D301 for removing Cr(VI) contaminants was investigated in batch and column systems. Physicochemical properties of the anion exchange resins were characterized to determine the adsorption mechanism and regeneration ability. Characteristic results revealed that EDE-D301 showed enhanced surface area, positive charge and contents of N and Cl elements, indicating that the modifying reagents of monomers were successfully polymerized in the resin. The experimental adsorption data fitted well to the pseudo-second-order kinetic model and the Langmuir isotherm model. The fixed-bed experiments showed that the exhaustion time increased with increasing the bed depth, and decreased with increasing the flowrate and influent concentration. Adsorption capacity for Cr(VI) onto EDE-D301 was determined at a maximum level of 298 mg·g^-1, and remained at 93% after four consecutive cycles. FTIR and XPS analysis indicated that the ion exchange and complexation were responsible for the Cr(VI) adsorption.

Selective and efficient sequestration of phosphate from waters using reusable nano-Zr(IV) oxide impregnated agricultural residue anion exchanger

There is an urgent need to develop low-cost and effective adsorbents for enhanced removal of phosphate from contaminated waters. In this study, nanosized Zr(IV) oxide particles were immobilized on the amino modified corn staw (MCS) to fabricate a novel nanocomposite (Zr@MCS) with superior application capability. Compared with the widely used commercial anion exchangers in previous studies, the modified agricultural residue was empolyed as the host to avoid the high costs and secondary pollution in the preparation. Zr@MCS displayed remarkable selective removal of phosphate from water even in the presence of coexisting anions (Cl^-, SO₄^2-, NO₃^-) at high levels, as well as with a high adsorption capacity, fast adsorption kinetics and high availability in the wide range of pH 2-8 toward phosphate. The excellent adsorption performance of Zr@MCS is attributed to the synergistic effect of the electrostatic attraction of the quaternary ammonium groups fixed on the host skeleton and the specific adsorption of phosphate derived from the hydroxyl functional groups of Zr(IV) oxide. The exhausted Zr@MCS can be effectively regenerated by 5% NaOH-NaCl solution for sustainably utilized, and phosphorus in the desorption effluent could be recovered as high-quality struvite by a simple struvite recovery process. Furthermore, the considerable treatment volume for the synthetic solution and real wastewater in a fixed-bed flow system indicated that Zr@MCS is of great potential for phosphate removal in practice.

Enhanced adsorption of nitrate from water by modified wheat straw: equilibrium, kinetic and thermodynamic studies

This study represents the first attempt to chemically modify wheat straw (WS) using 3-chloropropyltrimethoxysilane (CPTMS) and (1,4-diazabicyclo[2.2.2]octane) (DABCO). Field emission scanning electron micrographs (FESEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectra confirmed the successful morphological and structural modification of WS and the thermal stability of the modified WS (MWS). The MWS was used to remove nitrate from water. The optimum conditions of nitrate adsorption onto MWS were examined by conducting batch experiments. The results indicated that 85% of nitrate was removed under the conditions of initial nitrate concentration = 20 mg L^-1, initial solution pH = 7, contact time = 10 min, MWS dosage = 2 g L^-1 and temperature ≈ 25 °C. The kinetic adsorption data were best fitted to the general order model and the adsorption process occurred in three distinct stages. The equilibrium adsorption data were well described by the Langmuir isotherm. Additionally, separation factor values were smaller than 1, implying that the adsorption process was favorable. The presence of competing anions impeded the nitrate adsorption in the order of sulfate > chloride > bicarbonate> phosphate. Thermodynamic parameters suggested that the adsorption process was exothermic, feasible and spontaneous in nature. Overall, the MWS could achieve efficient removal of nitrate under the simplest operating conditions.

Facile Functionalization of Natural Peach Gum Polysaccharide with Multiple Amine Groups for Highly Efficient Removal of Toxic Hexavalent Chromium (Cr(VI)) Ions from Water

The development of low-cost adsorbent with excellent adsorption property remains a big challenge. Herein, the functionalization of natural peach gum polysaccharide (PGP) with multiple amine groups for the removal of toxic Cr(VI) ions from water was studied. The obtained PGP-NH₂ gel exhibited high-removal efficiency (>99.5%) toward Cr(VI) ions, especially with relatively low initial concentration of Cr(VI) ions (≤250 mg/L). The influences of pH, ionic strength, contact time, initial concentration, and temperature on the adsorption of Cr(VI) ions were systematically investigated. The PGP-NH₂ gel showed rapid adsorption rate and could reach adsorption equilibrium within about 40 min. The Cr(VI) ion uptake process could be described by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of PGP-NH₂ gel could reach 188.32 mg/g. Thermodynamic investigation results indicated the spontaneous and exothermic characteristic of the uptake process. Moreover, the PGP-NH₂ gel also exhibited favorable reusability, and 135.52 mg/g of adsorption capacity was retained even after being reused for five times. Considering its low cost and superior uptake property, the PGP-NH₂ gel holds a great promise for employing as an adsorbent to treat Cr(VI) ion-containing wastewater.

Synthesis of S-ligand tethered cellulose nanofibers for efficient removal of Pb(II) and Cd(II) ions from synthetic and industrial wastewater

Cellulose nanofibers (CNFs) tethered with sulphur as anionic ligand were synthesized from medical absorbent cotton by dissolution with NaOH, CO(NH₂)₂ followed by mechanical intrusion of sulphur from SC(NH₂)₂ at an elevated temperature. The solid-phase CNFs embedded with sulphur complexes possessed negative sites which were used to remove cationic metals viz., Pb(II) and Cd(II) from synthetic and industrial wastewater. The physicochemical properties of the CNFs were analyzed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), pH at point of zero charge (pH_pzc) and X-ray photoelectron spectroscopy (XPS). Batch adsorption studies were conducted with synthetic wastewater to optimize the conditions for Pb(II) and Cd(II) removal by CNFs. Different adsorption kinetic models were applied to assess and define the adsorption mechanism. The maximum Langmuir adsorption capacity was found to be 1.16 and 0.82 mmol g^-1 for Pb(II) and Cd(II) ions, respectively. Regeneration studies showed that the CNFs can be reused using 0.1 M NaOH as eluent. The percentage removal efficiency of different cationic metals by CNFs from untreated industrial wastewater ranged from ca. 90-98%.

Research on adsorption of Cr(Ⅵ) by Poly-epichlorohydrin-dimethylamine (EPIDMA) modified weakly basic anion exchange resin D301

A novel composite, EPIDMA/D301, with high adsorption capacity and particular affinity toward Cr(Ⅵ) was well prepared utilizing cationic polyelectrolyte poly-epichlorohydrin-dimethylamine (EPIDMA) impregnated in the networking pores of the styrene macroporous weak basic anion exchange resin D301. The physicochemical characteristics of EPIDMA/D301 were characterized by the Brunauer-Emmett-Teller (BET), zeta potential, FTIR, SEM-Mapping and XPS. The adsorption properties were researched via the influence of the concentration of EPIDMA, adsorbent dose, pH, the initial concentration of Cr(Ⅵ) solution, contact time and temperature. Results presented that the weakly basic anion exchange resin supported cationic polymer showed the excellent potential of removing Cr(VI) ions primarily due to the nonspecific Cr(VI) adsorption resulted from the polymeric host D301, the electrostatic attraction of amino groups fixed on the D301 matrix and the embedded EPIDMA with Cr(VI) ions and the ion exchange by the displacement of Cl^- mainly derived from EPIDMA with Cr(VI) ions. The kinetic data were best fitted by the pseudo-second-order kinetic model. The batch equilibrium data followed Langmuir isotherm model well with the maximum adsorption capacity of 194 mg g^-1 at 25 °C, which demonstrated that the styrene anion exchange resin modified with EPIDMA might be an efficient approach to eliminate potentially toxic metals.

Enhanced adsorption of anionic toxic contaminant Congo Red by activated carbon with electropositive amine modification

Anionic ionizable toxic organic contaminants, such as pesticides, herbicides, pharmaceuticals and dyestuffs, are widely detected in aqueous and can exert specific toxicity in organisms. They are hard removed by traditional adsorbents with negative surface charges and hydrophilic property. To solve that bottleneck problem, this study synthesized a carbon-based electropositive absorbent via surface activation and radical impregnation. The monolayer adsorption capacity and favorability of the novel adsorbent increased 4.2 and 16 times compared with activated carbon, evaluated by Congo Red. The adsorption kinetics could be described by pseudo-second-order equation, dominated by chemisorption and shortened 75% equilibrium time. The excellent adsorption behavior of synthesized material was attributed to created and bridged electropositive quaternary ammonium structure onto activated carbon, identified with XPS and FT-IR. Additionally, the abundant mesoporous structures of modified carbon provide more tunnels and facilitate adsorption of Congo Red, identified by AutoSorb-iQ. With the batch experiments of pH and ion strength influence, the absorbent behaved well in acidic low ion strength conditions and attenuated by coexisting cations. The study provides a high efficiency, large capacity and low cost materials to remove anionic ionizable organic contaminants in aqueous.

Biosorption and retention of orthophosphate onto Ca(OH)2-pretreated biomass of Phragmites sp

The biosorption of phosphorus in the form of orthophosphate (Po) from wastewater using biomass as the sorbent is of potential importance because the Po-loaded biomass could be applied in the agricultural sector as fertilizer and soil conditioner. However, biomass generally displays a very low affinity for Po sorption and therefore biomass surface modification is required. In the present study, the biomass (as model grinded leaves of Phragmites sp. were used) was pretreated with Ca(OH)2 to enhance Po biosorption capacity (qe). The results indicate that the alkaline pretreatment resulted in a modification of surface functional groups. It was concluded that the main sorption mechanisms were ligand exchange and electrostatic attraction. A series of experiments were conducted to investigate the performance of the pretreated biomass for Po uptake under various conditions. Isotherm and thermodynamic studies were also applied and analyzed. The biosorption process was best described by the pseudo-second order kinetic model and Langmuir isotherm, which gave a qmax of 12.27mgP/g at 25°C and pH7. The Ca(OH)2 treated Phragmites biomass applied in this study for Po recovery may present some potential advantages in terms of costs and environmental impact.

Removal of phosphate and chromium(vi) from liquids by an amine-crosslinked nano-Fe3O4 biosorbent derived from corn straw

A magnetic biocomposite based bio-sorbent (corn straw) was prepared after in situ co-precipitation with Fe²⁺ and Fe³⁺ solutions and amine functionalization.

Adsorption of phosphate on surface of magnetic reed: characteristics, kinetic, isotherm, desorption, competitive and mechanistic studies

A magnetic biocomposite was prepared by Fe₃O₄in situ co-precipitation and amine functionalization processes by using virgin reed as starting material.

Flower-, wire-, and sheet-like MnO2-deposited diatomites: Highly efficient absorbents for the removal of Cr(VI)

Flower-, wire-, and sheet-like MnO2-deposited diatomites have been prepared using a hydrothermal method with Mn(Ac)2, KMnO4 and/or MnSO4 as Mn source and diatomite as support. Physical properties of the materials were characterized by means of numerous analytical techniques, and their behaviors in the adsorption of chromium(VI) were evaluated. It is shown that the MnO2-deposited diatomite samples with different morphologies possessed high surface areas and abundant surface hydroxyl groups (especially the wire-like MnO2/diatomite sample). The wire-like MnO2/diatomite sample showed the best performance in the removal of Cr(VI), giving the maximum Cr(VI) adsorption capacity of 101 mg/g.

Zr(IV) loaded cross-linked chitosan beads with enhanced surface area for the removal of nitrate and phosphate

In this work, a new method namely silica dissolution method, has been adapted to increase the surface area of the cross-linked chitosan beads. Zr(IV) was loaded in the cross-linked chitosan beads in order to make it selective for the nitrate and phosphate anions from aqueous solutions. Zr(IV) loaded cross-linked chitosan beads prepared by normal method (ZrCB) and silica dissolution method (SD-ZrCB) were characterised using N2 adsorption/desorption studies, SEM, EDAX, XRD, FTIR, TGA, DTA and water regain property. The SD-ZrCB exhibited higher N2 adsorption, water regain property as well as anion adsorption capacity than ZrCB. Batch method was adapted for the adsorption studies. The nitrate and phosphate adsorbed SD-ZrCB was regenerated using 0.025M NaCl solution. There was not much drop in adsorption capacities up to 10th regeneration cycle. Freundlich adsorption isotherm was the best fit adsorption isotherm among Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms which have been used to fit the nitrate and phosphate adsorption data. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of adsorption process.

Preparation of an organic–inorganic polyurethane–Al2O3 anion exchange fibrous composite and its application in the development of a membrane electrode for the determination of chromium(vi) in water

An ion-selective electrode was developed using a polyurethane–Al₂O₃ organic–inorganic fibrous composite for the determination of Cr(vi) in water.