Function integrated chitosan-based beads with throughout sorption sites and inherent diffusion network for efficient phosphate removal

Municipal sludge biochar skeletal sodium alginate beads for phosphate removal

A novel Fe/La decorative biochar filled in sodium alginate beads (SA-KBC-Fe/La) was prepared by a simple sol-gel method and applied to adsorb phosphate (P) efficiently from water in this study. The morphology, structure and chemical component of the hydrogel beads were characterized in detail. And the synthesized bead exhibited easy separation and high P uptake of 46.65 mg/g when the Fe: La was of 1: 2 at 298 K with initial P of 100 mg/L, which was much higher than SA gel bead. The adsorption showed that the optimal pH was 6, and the adsorption was met with pseudo-second-order kinetics and Langmuir isothermal models, indicating a chemical adsorption process. The adsorption capacity remained 82 % after 5 cycles of adsorption. The adsorption mechanism of P was mainly of ligand exchange and electrostatic attraction. Compared with other reported adsorbents, the modification of Fe/La could enhance the mechanical property of SA-KBC-Fe/La beads with increasing active sites. Additionally, the involved biochar could lead to excellent thermal stability and hierarchical porous structure of beads with larger specific surface area (54.22 m2/g). The study could provide new ideas for P removal and strategy for the final disposal of municipal sludge.

Efficient adsorption of phosphorus by macroscopic MOF/chitosan composites and preliminary investigation of subsequent phosphorus recovery through electrochemically-driven struvite precipitation

The proper management of phosphorus (P) from wastewater is crucial for sustainable development consideration. Herein, we developed a strategy which combines adsorption via tailored adsorbents and electrochemically-driven struvite precipitation (ESP) for P recovery. Novel polydopamine-modified Ce-MOF/chitosan composite beads (PDA@Ce-MOF-CS) were prepared by a facile in situ growth of Ce-MOF crystals incorporated natural polymers and PDA coating. The physicochemical properties of PDA@Ce-MOF-CS were characterized. Both batch and fixed-bed column experiments were conducted to evaluate its adsorption performances. Representatively, PDA@Ce-MOF-CS performed good selectivity for P removal and exhibited a maximum adsorption capacity of 161.13 mg P/g at pH 3 and 318 K. Meanwhile, the developed adsorbent showed great reusability after ten regeneration cycles as well as good adsorption stability. The dominant mechanism for efficient P adsorption included electrostatic attraction, surface precipitation and ligand exchange. Interestingly, PDA@Ce-MOF-CS exhibited a remarkable adsorption capacity of 92.86 mg P/g by treating real P-rich electroplating wastewater, and the desorbed P in the eluate could be effectively recovered and converted into a solid fertilizer as struvite via ESP. Overall, this work provided a new research direction for P recovery from wastewater as struvite by combined technologies with the help of macroscopic MOF architectures.

Synthesis of porous calcium-guar gum benzoate nano-biohybrids for sorptive removal of congo red and phosphates from water

This work aims to develop an eco-sound nano-bio-hybrid sorbent using sustainable materials for sorptive elimination of congo red and phosphates from aquatic environment. An amphipathic biopolymer derivative, high DS guar gum benzoate (GGBN) was used for entrapment of as synthesized calcium carbonate nanoparticles using solvent diffusion nano-precipitation technique. Designer nano-biohybrids were developed upon experimenting with various materials stoichiometry. SEM, XRD and EDX studies confirmed near-uniform impregnation of rhombohedral calcium carbonate crystals throughout the biopolymer matrix. Average pore size distribution and surface area of final product Ca-GGBNC, were estimated from NDLFT and BET methods respectively. Analysis of adsorption findings acquired at study temperature 27 ± 2 °C showed that the maximum adsorption capacity of Ca-GGBNC recorded qmax, 333.33 mg/g for congo red azo dye and that for phosphate was at 500 mg/g. Adsorptive removal was noted and both components followed pseudo second order kinetics. Intra-particle diffusion kinetics investigation disclosed that the boundary layer effect was prominent and the adsorption rates were not solely directed by the diffusion stage. Activation energy, Ea was to be estimated using Arrhenius equation at 56.136 and 47.015 KJ/mol for congo red and phosphates respectively. The calculated thermodynamic parameters(ΔG°, ΔH°, and ΔS°) revealed the spontaneous, feasible and endothermic sorption process. Owing to active surface area, spherical size, functional moiety and porous network, antibacterial properties of nanobiohybrid were persistent and MIC against E. coli and S. aureus were recorded at 200 μg/mL and 350 μg/mL respectively.

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

Flexible fabrication chitosan-polyamidoamine aerogels by one-step method for efficient adsorption and separation of anionic dyes

Chitosan in situ grown polyamidoamine (CTS-Gx PAMAM (x = 0, 1, 2, 3)) aerogels were fabricated by a facile one-step freeze-drying method, with glutaraldehyde serving as a crosslinker. The three-dimensional skeletal structure of aerogel provided numerous adsorption sites and accelerated the effective mass transfer of pollutants. The adsorption kinetics and isotherm studies of the two anionic dyes were consistent with the pseudo-second-order and Langmuir models, indicating that the removal of rose bengal (RB) and sunset yellow (SY) was a monolayer chemisorption process. The maximum adsorption capacity of RB and SY reached 370.28 mg/g and 343.31 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacities of the two anionic dyes reached 81.10% and 84.06% of the initial adsorption capacities, respectively. The major mechanism between the aerogels and dyes was systematically investigated based on using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy analyses, confirming that electrostatic interaction, hydrogen bonding and van der Waals interactions were the main driving forces for the superior adsorption performance. Furthermore, the CTS-G2 PAMAM aerogel exhibited good filtration and separation performance. Overall, the novel aerogel adsorbent possesses excellent theoretical guidance and practical application potential for the purification of anionic dyes.

Fabrication of chitosan/phenylboronic acid/SiO2 hydrogel composite silk fabrics for enhanced adsorption and controllable release on luteolin

Due to the growing demand for self-health and safety, eco-friendly health textile products with natural colors and pharmacological functionalities have gained considerable popularity. Rapid adsorption and controlled release of active molecules are important issues for functional health textiles. In this study, a functionalized chitosan-based hydrogel composite silk fabric was prepared using chitosan, 3-carboxyphenylboronic acid, and 3-(2, 3-epoxypropyl oxygen) propyl silane by dip-pad and vacuum freeze-drying techniques. The results showed that the incorporation of chitosan/phenylboronic/SiO2 hydrogel into silk fibers improved the UV protection capacity, mechanical properties, and adsorption properties of silk fabrics. The effects of various parameters on the luteolin adsorption properties of silk fabrics were discussed, including metal salt types, salt dosage, pH value, dyeing temperature, initial luteolin concentration, and dyeing time. Under the dyeing temperature of 60 °C and pH of 6.8, the luteolin exhaustion of the composite silk was more than that of the untreated silk, and the adsorption process followed the quasi-second-order kinetic model and the Langmuir adsorption isotherm model. Furthermore, the luteolin-dyed composite silk materials exhibited strong antioxidant activity and controllable release behavior with various pH levels. The as-prepared chitosan-hydrogel composite silk could be a promising material for the sustained release of drugs in medical and healthcare textiles.

A dual-cycle regeneration to recover high-value and high-purity FePO4 from real wastewater for Li-battery application

The recovery of high-purity and high-value FePO4 raw materials from wastewater has great prospects in LiFePO4 battery industry due to the huge demand for new energy vehicle. However, the conventional in-situ FePO4 precipitation, as well as ex-situ PO43- adsorption-alkali regeneration, was incapable of efficiently obtaining high-purity products. To solve these problems, a dual-cycle regeneration method of Fe-NH2-polyacrylonitrile (PAN) adsorbent and H2SO4 desorbing solution was proposed to ex-situ FePO4 recovery from wastewater for Li-battery application. Benefitted from coordination interaction and electrostatic attraction, the maximum PO43- adsorption capacity of Fe-NH2-PAN reached 73.1 ± 0.4 mg/g. The average PO43- removal rate of continuous flow devices were 88.5% and 91.3% when treating low-P-concentration (0.22 mg/L) municipal wastewater (MW) and high-P-concentration (48.9 mg/L) slaughterhouse wastewater (SW) respectively. Furthermore, high-purity FePO4 analyzed by XRD spectra was achieved from the desorption solution at pH ∼1.6, resulting in the ultrahigh P recovery efficiencies of 91.4 ± 3.2%-96.3 ± 2.5% for SW and 82.7 ± 3.5% for MW. Besides, the LiFePO4/C electrodes made of recycled FePO4 exhibited a better discharge capacity (37.3 - 55.8 mAh/g) than that of commercial FePO4 agent (32.2 - 35.1 mAh/g) from 80 to 132 cycles, which showed the promising feasibility of recovering FePO4 from wastewater for Li-battery application.

Synthesis of co-pyrolyzed biochar using red mud and peanut shell for removing phosphate from pickling wastewater: Performance and mechanism

Iron (Fe)/iron oxide-modified biochar has practicable adsorption capability for phosphorus (P), but it is expensive. In this study, we synthesized novel low-cost and eco-friendly adsorbents co-pyrolyzed biochars using Fe-rich red mud (RM) and peanut shell (PS) wastes via a one-step pyrolysis process for removing P from pickling wastewater. The preparation conditions (heating rate, pyrolysis temperature, and feedstock ratio) and P adsorption behaviors were systematically investigated. In addition, a series of characterization and approximate site energy distribution (ASED) analyses were conducted to understand the P adsorption mechanisms. The magnetic biochar (BR7P3) with m (RM):m (PS) of 7:3 prepared at 900°C and 10 °C/min had a high surface area (164.43 m2/g) and different abundant ions (including Fe3+, and Al3+). In addition, BR7P3 exhibited the best P removal capability (142.6 mg/g). The Fe2O3 from RM was successfully reduced to Fe0, which was easily oxidized as Fe3+ to precipitate with H2PO4-. The electrostatic effect, Fe-O-P bonding, and surface precipitation were the main mechanisms of P removal. ASED analyses revealed that high distribution frequency and solution temperature led to a high P adsorption rate of the adsorbent. Therefore, this study provides new insight into the waste-to-wealth strategy by transforming PS and RM into mineral-biomass biochar with excellent P adsorption capability and environmental adaptability.

Value-added application of cattle manure bottom ash for phosphorus recovery from water and replenishment in soil

This study addresses ways to circulate the flow of phosphorus (P) from water to soil to improve water quality and provide a sustainable supply of P into soil. Here, bottom ash (BA_CCM), the byproduct of the combustion of cattle manure, which is performed for obtaining energy, was used to remove P in wastewater. Next, the P-captured BA_CCM was used as P fertilizer for rice growth. BA_CCM was primarily composed of Ca (49.4%), C (24.0%), and P (9.9%), and the crystalline phases of Ca were calcium carbonate (CaCO₃) and hydroxyapatite (Ca₅(PO₄)₃OH). The mechanism of P removal by BA_CCM involves the formation of hydroxyapatite by reacting Ca²⁺ with PO₄^3-. A reaction time of 3 h was required to achieve P adsorption to BA_CCM, and the maximum P adsorption capacity of BA_CCM was 45.46 mg/g. The increase in solution pH reduced P adsorption. However, at pH > 5, the P adsorption amount was maintained regardless of the pH increase. The presence of 10 mM SO₄^2- and CO₃^2- reduced P adsorption by 28.4% and 21.5%, respectively, and the impact of the presence of Cl^- and NO₃^- was less than 10%. The feasibility of BA_CCM was tested using real wastewater, and 3.33 g/L of BA_CCM dose achieved a P removal ratio of 99.8% and a residual concentration of <0.02 mg/L. The toxicity unit of BA_CCM determined for Daphnia magna (D. magna) was 5.1; however, the BA_CCM after P adsorption (P-BA_CCM) did not show any toxicity to D. magna. BA_CCM after P adsorption was used as an alternative to commercial P fertilizer. Rice fertilized with a medium level of P-BA_CCM showed better agronomic values for most agronomic traits, except root length, than that seen with the commercial P fertilizer. This study suggests that BA_CCM can be used as a value-added product to address environmental issues.

Recovery of Phosphate(V) Ions from Water and Wastewater Using Chitosan-Based Sorbents Modified-A Literature Review

Over the past two decades, there has been increasing interest in the use of low-cost and effective sorbents in water treatment. Hybrid chitosan sorbents are potential materials for the adsorptive removal of phosphorus, which occurs in natural waters mainly in the form of orthophosphate(V). Even though there are numerous publications on this topic, the use of such sorbents in industrial water treatment and purification is limited and controversial. However, due to the explosive human population growth, the ever-increasing global demand for food has contributed to the consumption of phosphorus compounds and other biogenic elements (such as nitrogen, potassium, or sodium) in plant cultivation and animal husbandry. Therefore, the recovery and reuse of phosphorus compounds is an important issue to investigate for the development and maintenance of a circular economy. This paper characterizes the problem of the presence of excess phosphorus in water reservoirs and presents methods for the adsorptive removal of phosphate(V) from water matrices using chitosan composites. Additionally, we compare the impact of modifications, structure, and form of chitosan composites on the efficiency of phosphate ion removal and adsorption capacity. The state of knowledge regarding the mechanism of adsorption is detailed, and the results of research on the desorption of phosphates are described.

Titanium dioxide nanoparticles functionalized chitosan toward bio-based antibacterial adsorbent for enhanced phosphate capture

Developing an eco-friendly, sustainable and antibacterial adsorbent is significant for actual water treatment. Herein, a new bio-based antibacterial adsorbent based on titanium dioxide (TiO₂) nanoparticles functionalized chitosan (CS) was prepared through an in-situ hydrolysis strategy using titanium oxysulfate as the source of TiO₂. The as-obtained CS/TiO₂ nanocomposite was characterized by a variety of analytical techniques. According to the Langmuir mode, the adsorption capacity of CS/TiO₂ reached 23.64 mg P g^-1, almost 8 times higher than that of CS. In addition, the normalized adsorption capacity (adsorption value per Ti) of CS/TiO₂ was calculated to be 102.68 mg P g^-1 Ti^-1, much higher than pure TiO₂ (60.11 mg P g^-1 Ti^-1). Moreover, CS/TiO₂ exhibited a highly selective capacity for phosphate removal in the presence of competing anions, and showed high stability in a wide pH range of 3.0-9.0. When the phosphate concentration was 2.0 mg P L^-1, the removal efficiency of phosphate reached 99.5 % and the residual concentration was only 10 μg P L^-1, which meets the USEPA standards for eutrophication prevention and control. In addition, after treatment by CS/TiO₂, the phosphate concentration of two sewage water samples decreased from 1.50 and 1.0 mg P L^-1 to <0.010 mg P L^-1, meeting the standard of level II water based on the Environmental Quality Standard of China (GB3838-2002). Ligand exchange and electrostatic interactions are mainly responsible for phosphate adsorption by CS/TiO₂. Furthermore, the CS/TiO₂ nanocomposites exhibited excellent antibacterial activity, which could avoid biofouling contamination caused by microorganisms. Benefiting from the above advantages, the as-designed CS/TiO₂ nanocomposite has great potential as a bio-based antibacterial adsorbent for phosphate removal or capture from wastewater.

Preparation and Characterization of an Invasive Plant-Derived Biochar-Supported Nano-Sized Lanthanum Composite and Its Application in Phosphate Capture from Aqueous Media

Invasive plants pose a great threat to natural ecosystems owing to their rapid propagation and spreading ability in nature. Herein, a typical invasive plant, Solidago canadensis, was chosen as a novel feedstock for the preparation of nano-sized lanthanum-loaded S. canadensis-derived biochar (SCBC-La), and its adsorption performance for phosphate removal was evaluated by batch adsorption experiment. The composite was characterized by multiple techniques. Effects of parameters, such as the initial concentration of phosphate, time, pH, coexisting ions, and ionic strength, were studied on the phosphate removal. Adsorption kinetics and isotherms showed that SCBC-La shows a faster adsorption rate at a low concentration and SCBC-La exhibits good La utilization efficiency than some of the reported La-modified adsorbents. Phosphate can be effectively removed over a relatively wide pH of 3-9 because of the high pH _pzc of SCBC-La. Furthermore, the SCBC-La shows a strong anti-interference capability in terms of pH value, coexisting ions, and ionic strength, exhibiting a highly selective capacity for phosphate removal. Additionally, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements reveal that hydroxyl groups on the surface of SCBC-La were replaced by phosphate and manifest the reversible transformation between La(OH)₃ and LaPO₄. Considering its high adsorption capacity and excellent selectivity, SCBC-La is a promising material for preventing eutrophication. This work gives a new method of pollution control with waste treatment since the invasive plant (S. canadensis) is converted into biochar-based nanocomposite for effective removal of phosphate to mitigate eutrophication.

Synthesis of FeOOH-Loaded Aminated Polyacrylonitrile Fiber for Simultaneous Removal of Phenylphosphonic Acid and Phosphate from Aqueous Solution

Phosphorus is one of the important metabolic elements for living organisms, but excess phosphorus in water can lead to eutrophication. At present, the removal of phosphorus in water bodies mainly focuses on inorganic phosphorus, while there is still a lack of research on the removal of organic phosphorus (OP). Therefore, the degradation of OP and synchronous recovery of the produced inorganic phosphorus has important significance for the reuse of OP resources and the prevention of water eutrophication. Herein, a novel FeOOH-loaded aminated polyacrylonitrile fiber (PAN_AF-FeOOH) was constructed to enhance the removal of OP and phosphate. Taking phenylphosphonic acid (PPOA) as an example, the results indicated that modification of the aminated fiber was beneficial to FeOOH fixation, and the PAN_AF-FeOOH prepared with 0.3 mol L^-1 Fe(OH)₃ colloid had the best performance for OP degradation. The PAN_AF-FeOOH efficiently activated peroxydisulfate (PDS) for the degradation of PPOA with a removal efficiency of 99%. Moreover, the PAN_AF-FeOOH maintained high removal capacity for OP over five cycles as well as strong anti-interference in a coexisting ion system. In addition, the removal mechanism of PPOA by the PAN_AF-FeOOH was mainly attributed to the enrichment effect of PPOA adsorption on the fiber surface's special microenvironment, which was more conducive to contact with SO₄•^- and •OH generated by PDS activation. Furthermore, the PAN_AF-FeOOH prepared with 0.2 mol L^-1 Fe(OH)₃ colloid possessed excellent phosphate removal capacity with a maximal adsorption quantity of 9.92 mg P g^-1. The adsorption kinetics and isotherms of the PAN_AF-FeOOH for phosphate were best depicted by pseudo-quadratic kinetics and a Langmuir isotherm model, showing a monolayer chemisorption procedure. Additionally, the phosphate removal mechanism was mainly due to the strong binding force of iron and the electrostatic force of protonated amine on the PAN_AF-FeOOH. In conclusion, this study provides evidence for PAN_AF-FeOOH as a potential material for the degradation of OP and simultaneous recovery of phosphate.

Optimization of Removal of Phosphate from Water by Adsorption Using Biopolymer Chitosan Beads

The need for clean water is the most basic human right. Water scarcity will be one important environmental problem of all countries in the future. Phosphate is a harmful matter for public health and the environment. In this study, the removal of phosphate from water by chitosan, which is an environmentally friendly material, was investigated. Chitosan adsorbent spheres were prepared for phosphate separation from water by adsorption, which is a feasible method. The effects of phosphate concentration, adsorbent dosage, and operation time on the removal were investigated. The removal increased with acid concentration and adsorbent amount. The maximum adsorption capacity of chitosan beads is 87.26 mg/g. Adsorption behavior of the chitosan beads were examined by Langmuir and Freundlich isotherms and pseudo-first and second-order kinetic models. The adsorption process was optimized by the response surface method (RSM). Trial version of Design Expert® 12.0 was used in the study. It has been understood as a result of the RSM statistical analysis that higher phosphate removal values would be obtained by increasing the amount of adsorbent. ANOVA analysis showed that adsorbent dosage had the biggest effect on removal of phosphate using chitosan beads prepared for adsorption.

Adsorptive removal of anionic azo dye by Al3+-modified magnetic biochar obtained from low pyrolysis temperatures of chitosan

Magnetic γ-Fe₂O₃/Al³⁺@chitosan-derived biochar (m-Fe₂O₃/Al³⁺@CB) was prepared by introducing magnetic maghemite (γ-Fe₂O₃) nanoparticles and aluminum sulfate [Al₂(SO₄)₃] into chitosan-derived biochar (CB) obtained at low pyrolysis temperatures. m-Fe₂O₃/Al³⁺@CB was used to remove typical anionic azo dye (Congo red, CR). Effects of initial CR concentration, contact time, initial pH value, background electrolytes, and temperature on CR adsorption by m-Fe₂O₃/Al³⁺@CB were studied. Compared with magnetic chitosan-derived biochar (m-Fe₂O₃@CB), m-Fe₂O₃/Al³⁺@CB exhibited excellent performance for a wider range of pH values (pH 1-7) and in the presence of background electrolyte. The introduction of Al³⁺ is an effective method for improving the properties of magnetic chitosan-derived biochar. High CR adsorption capacity (636.94 mg g^-1) of m-Fe₂O₃/Al³⁺@CB could result from collaborative effect of flocculation/coagulation and electrostatic attraction. These results demonstrated that m-Fe₂O₃/Al³⁺@CB is a potential adsorbent for effective removal of organic dyes from aqueous solution due to its high adsorption capacity and convenient magnetic recovery and stronger anti-interference ability against coexisting anions in wastewater.

Chitosan-Based Polymer Nanocomposites for Environmental Remediation of Mercury Pollution

Mercury is a well-known heavy metal pollutant of global importance, typically found in effluents (lakes, oceans, and sewage) and released into the atmosphere. It is highly toxic to humans, animals and plants. Therefore, the current challenge is to develop efficient materials and techniques that can be used to remediate mercury pollution in water and the atmosphere, even in low concentrations. The paper aims to review the chitosan-based polymer nanocomposite materials that have been used for the environmental remediation of mercury pollution since they possess multifunctional properties, beneficial for the adsorption of various kinds of pollutants from wastewater and the atmosphere. In addition, these chitosan-based polymer nanocomposites are made of non-toxic materials that are environmentally friendly, highly porous, biocompatible, biodegradable, and recyclable; they have a high number of surface active sites, are earth-abundant, have minimal surface defects, and are metal-free. Advances in the modification of the chitosan, mainly with nanomaterials such as multi-walled carbon nanotube and nanoparticles (Ag, TiO₂, S, and ZnO), and its use for mercury uptake by batch adsorption and passive sampler methods are discussed.

Lanthanum-modified polydopamine loaded Acinetobacter lwoffii DNS32 for phosphate and atrazine removal: Insights into co-adsorption and biodegradation mechanisms

A novel biobased composite was developed for the removal of phosphate (P) and atrazine from agricultural wastewater. A composite with strong P affinity and good biocompatibility, synthesized from La³⁺ and polydopamine (PDA), was immobilized onto an atrazine-degrading bacterium Acinetobacter lwoffii DNS32 (La/PDA/DNS32). Following Box-Behnken design optimization, the maximum removal rate of P (500 mg L^-1) and atrazine (100 mg L^-1) by La/PDA/DNS32 reached 28 % and 100 %, respectively. Density functional theory calculations revealed that La/PDA had more negative adsorption energy (-5.90 eV) than PDA alone and exhibited prominent electrophilic sites. Additionally, La/PDA-induced sorption of atrazine improved transmembrane transport and enhanced expression of degradation-associated genes in strain DNS32. La/PDA nanoparticles surrounding strain DNS32 provided a shielding effect and exhibited desirable biostability, thermal stability, and acid-alkaline resistance under contamination stress. This study demonstrates the promising potential of La/PDA/DNS32 in reducing the P and atrazine pollution caused by agricultural production.

Role of emerging chitosan and zeolite-modified adsorbents in the removal of nitrate and phosphate from an aqueous medium: A comprehensive perspective

Due to industrialization and population growth, freshwater supplies are diminishing and becoming impure with high organic pollutant concentrations such as nitrate and phosphate, which shows a high adverse impact on aquatic and human lives. In drinking water sources, particularly groundwater, nitrate is considered as one of the major pollutants which causes methemoglobinemia (in newborn infants), carcinogenic activities and diabetes. Excess concentration of phosphate leads to eutrophication and death of aquatic species due to reduced dissolved oxygen content. Therefore, all countries must implement highly effective technologies for treating wastewater. Chitosan and zeolite are naturally occurring and cost-effective adsorbent materials with a higher surface area that exhibit greater nitrate and phosphate adsorption. Surface modification of chitosan and zeolite increases the adsorption capacity of adsorbents for the removal of both anions selectively. This paper reviews the current development of modified chitosan and zeolite adsorbents for anion adsorption, with an emphasis on modification by zero and multivalent metals and metal oxides, different surfactants, biomass-derived carbon, and natural and synthetic polymers. Multiple adsorption parameters, optimum adsorption condition, adsorption mechanism, regeneration study, research gap and future aspects have been explained for further research work.

Chitosan-Modified Biochars to Advance Research on Heavy Metal Ion Removal: Roles, Mechanism and Perspectives

The chitosan-modified biochars BC-CS 1-1, BC-CS 2-1 and BC-CS 4-1 were subjected to the synthetic application of biochar from agriculture waste and chitosan for the adsorption of Cu(II), Cd(II), Zn(II), Co(II) and Pb(II) ions from aqueous media. The results displayed a heterogeneous, well-developed surface. Additionally, the surface functional groups carboxyl, hydroxyl and phenol, determining the sorption mechanism and confirming the thermal stability of the materials, were present. The sorption evaluation was carried out as a function of the sorbent dose, pH, phase contact time, initial concentration of the solution and temperature. The maximum value of q_t for Pb(II)-BC-CS 4-1, 32.23 mg/g (C₀ 200 mg/L, mass 0.1 g, pH 5, 360 min), was identified. Nitric acid was applied for the sorbent regeneration with a yield of 99.13% for Pb(II)-BC-CS 2-1. The produced sorbents can be used for the decontamination of water by means of the cost-effective and high-performance method.

Phosphate removal and recovery by lanthanum-based adsorbents: A review for current advances

Controlling eutrophication and recovering phosphate from water bodies are hot issues in the 21st century. Adsorption is considered to be the best method for phosphate removal because of its high adsorption efficiency and fast removal rate. Among the many adsorbents, lanthanum (La)-based adsorbents have been paid more and more attention due to their strong affinity to phosphorus. This paper reviews research of phosphate adsorption on La-based adsorbents in different La forms, including lanthanum oxide/hydroxide, lanthanum mixed metal oxide/hydroxide, lanthanum carbonate, La³⁺, La-based metal-organic framework (La-MOF) and La-MOF derivatives. The La-based adsorbents can be loaded on many carriers, such as carbon material, clay minerals, porous silica, polymers, industrial wastes, and others. We find that lanthanum oxide/hydroxide and La³⁺ adsorbents are mostly studied, while those in the forms of lanthanum carbonate, La-MOF, and La-MOF derivatives are relatively few. The kinetic process of most phosphate adsorption is pseudo-second-order and the isotherm process is in accordance with the Langmuir model. The cost of La-based and other traditional adsorbents was compared. The adsorption mechanisms are categorized as electrostatic attraction, ligand exchange, Lewis acid-base interaction, ion exchange and surface precipitation. Besides, regeneration methods of La-based adsorbents are mainly acid, alkali, and salt-alkali. In addition, the La-based adsorbents after absorbing phosphate can be directly used as a slow-release fertilizer. This review provides a basis for the research on phosphate adsorption by La-based adsorbents. It should be carried out to further develop La-based materials with high adsorption capacity and good regeneration ability. Meanwhile, studies have been conducted on the reuse of phosphate after desorption, which needs more attention in future research.

Biochar/Mg-Al spinel carboxymethyl cellulose-La hydrogels with cationic polymeric layers for selective phosphate capture

Recently, biochar-related phosphate sorbents have been extensively investigated and achieved significant progress; however, there is still much room for enhancement on capturing performance and recovery of powdery ones after sorption. Herein, a new kind of adsorbent, in which biochar/Mg-Al spinel encapsulated in carboxymethyl cellulose-La hydrogels with cationic polymeric layers, was fabricated, aiming for integrating multi-advantages of each component for enhanced phosphate capture. Batch static experiments were correlated to the phosphate adsorption performance of the adsorbent. The maximum phosphate adsorption capacity of the adsorbent was 89.65 mg P/g at pH = 3. The Langmuir isotherm model and the pseudo-second-order kinetic model fitted well with the adsorption behavior of the adsorbent. More importantly, this composite adsorbent that integrated with biochar, Mg-Al spinel, cationic polymeric components exhibited favorable selectivity over coexisting anions (Cl^-, SO₄^2-, HCO₃^- and NO₃^-) and performed good reusability after five consecutive cycles. By virtue of the bead-like feature, fixed-bed column experiments demonstrated that the Thomas model fitted the breakthrough curves well under varied experimental conditions. The adsorption mechanism of phosphate on the designed composite adsorbent with multi-components could be described as the electrostatic attraction, ligand exchange and inner-sphere complexation, which might account for the efficient phosphate capturing performance.

Cost-effective phosphorus removal from aqueous solution by a chitosan/lanthanum hydrogel bead: Material development, characterization of uptake process and investigation of mechanisms

Excessive phosphorus is one of the main reasons leading to eutrophication that causes severe ecosystem imbalance and negative human health impacts. In this study, several chitosan (CS)/lanthanum (La) hydrogel beads were first synthesized and tested for phosphorus removal. The stable cross-linked CS/La hydrogel bead prepared with the optimized conditions of 10 wt% La/CS and 1.5 mL of 5% glutaraldehyde demonstrated exceptional performance in the removal. It removed phosphate effectively from an aqueous solution in the pH range from 2 to 7. The complete phosphate uptake was achieved at contact time of 6 h under the completely mixing batch condition. The experimental maximum adsorption capacity of 107.7 mg g^-1 was observed at solution pH 4. The phosphate adsorption was well described by the Freundlich isotherm and the intraparticle surface diffusion model. Furthermore, the adsorbent was effectively regenerated and reused in a five-cycle adsorption-desorption operation. The removal of phosphate can be attributed to electrostatic attraction and ion exchange. Moreover, the bead was capable of removing heavy metals: copper, zinc and lead. This adsorbent may be served as a cost-effective material for the treatment of phosphorus-contaminated water so as to minimize the occurrence of eutrophication.

Preparation of resin-based composites containing Ce and cationic polymers with abundant promotional affinity sites for phosphate capture

A new type of composite, D301-Ce+, for efficient and selective phosphate removal.

Multifunctional Fe3O4/TiO2/NH2-UiO-66 with integrated interfacial features for favorable phosphate adsorption

Excessive use and discharge of phosphate are the decisive factors leading to water eutrophication, and adsorption is deemed among the most effective methods in phosphorus capture. This study prepared the...

Rapid and selective harvest of low-concentration phosphate by La(OH)3 loaded magnetic cationic hydrogel from aqueous solution: Surface migration of phosphate from -N+(CH3)3 to La(OH)3

Phosphate is an important factor for the occurrence of surface water eutrophication, and is also a non-renewable resource which faces a potential depletion crisis. In this study, La(OH)₃ loaded magnetic cationic hydrogel composite MCH-La(OH)₃-EW was used to absorb low strength phosphate in simulated water and real water. The adsorption amount of MCH-La(OH)₃-EW was 39.14 ± 0.31 mg P/g and the equilibrium time was 120 min at the initial phosphate concentration of 2.0 mg P/L. The adsorption process was a spontaneous endothermic reaction. MCH-La(OH)₃-EW exhibited a high selectivity towards phosphate within pH of 4.0-10.0 or in the presence of co-existing ions (including Cl^-, SO₄^2-, NO₃^-, HCO₃^-, SiO₃^2-) and humic acid. After 10 cycles of adsorption-desorption, the adsorption amount of regenerated MCH-La(OH)₃-EW still remained at 63.4% of its maximum value. For the real water sample with phosphate concentration of 2.0 mg P/L, the phosphate removal efficiency could achieve 97.65-98.90% and the effluent turbidity was 2.10-4.27 NTU at the MCH-La(OH)₃-EW dosage of 0.04 g/L. The adsorption mechanism analysis showed that both quaternary amine groups (-N⁺(CH₃)₃) and La(OH)₃ of MCH-La(OH)₃-EW were involved in the process of phosphate adsorption. The electrostatic interaction between phosphate and -N⁺(CH₃)₃ rapidly occurred at the initial stage of adsorption process, then the electrostatic absorbed phosphate migrated to La(OH)₃ on the surface of MCH-La(OH)₃-EW via ligand exchange to form inner-sphere complex. This phenomenon was conducive to phosphate adsorption kinetics by MCH-La(OH)₃-EW.

Magnetic aminated lignin/CeO2/Fe3O4 composites with tailored interfacial chemistry and affinity for selective phosphate removal

Phosphorus (P) has brought a series of environmental problems while benefiting mankind. To reclaim phosphorus from wastewater efficiently and conveniently, a novel magnetic adsorbent with aminated lignin/CeO₂/Fe₃O₄ composites (AL-NH₂@Fe₃O₄-Ce) possessing a high affinity to phosphate and easily separated from aqueous solutions was developed in this work. The characterization results revealed that Fe and Ce elements have been doped into the aminated lignin successfully. Batch experiment results convinced that the maximum phosphate adsorption capacity of AL-NH₂@Fe₃O₄-Ce was 183.72 mg P/g at pH = 3, which was roughly 4.5 times greater than aminated lignin and 8.5 times greater than cerium oxide, respectively. The adsorption isotherm was fitted well by the Langmuir model, and the adsorption kinetics was in line with the pseudo-second-order model. The adsorption thermodynamics indicated the adsorption process was spontaneous and naturally exothermic. Additionally, AL-NH₂@Fe₃O₄-Ce exhibited high selectivity towards phosphate over common coexisting anions (Cl^-, NO₃^-, HCO₃^-, SO₄^2- and F^-). After five consecutive cycles, the adsorption performance of AL-NH₂@Fe₃O₄-Ce decreased by only 16% compared with the fresh adsorbent, indicating that AL-NH₂@Fe₃O₄-Ce exhibited excellent recycling ability. The results of XPS analysis and batch experiments showed that the possible mechanisms were electrostatic attraction and inner-sphere complexation. The tailored interfacial chemistry affinity to phosphate as well as endowed magnetic property reveled AL-NH₂@Fe₃O₄-Ce could be adopted as an up and coming adsorbent in phosphate removal process.

Chitosan based adsorbents for the removal of phosphate and nitrate: A critical review

The tremendous development in the industrial sector leads to discharging of the several types of effluents containing detrimental contaminants into water sources. Lately, the proliferation of toxic anions particularly phosphates and nitrates onto aquatic systems certainly depreciates the ecological system and causes a deadly serious problem. Chitosan (Cs) is one of the most auspicious biopolymer adsorbents that are being daily developed for removing of various contaminants from polluted water. This is due to its unparalleled benefits involving biocompatibility, non-toxicity, facile modifications and low-cost production. Nevertheless, chitosan displays considerable drawbacks including low adsorption capacity, low surface area and lack of reusability. Therefore, few findings have been established regarding the aptitude of modified chitosan-based adsorbents towards phosphate and nitrate anions. This review elaborates an overview for the current advances of modified chitosan based-adsorbent for phosphate and nitrate removal, in specific multivalent metals-modified chitosan, clays and zeolite-modified chitosan, magnetic chitosan and carbon materials-modified chitosan. The efforts that have been executed for enriching their adsorption characteristics as well as their possible adsorption mechanisms and reusability were well addressed. Besides, the research conclusions for the optimum adsorption conditions were also discussed, along with emphasizing the foremost research gaps and future potential trends that could motivate further research and innovation to find best solutions for water treatment problems facing the world.

Recovery of phosphorus as soluble phosphates from aqueous solutions using chitosan hydrogel sorbents

This manuscript presents new method of phosphorus recovery from aqueous solutions in a convenient form of readily-soluble phosphates using chitosan hydrogels. Non-modified chitosan hydrogel granules (CHs) and chitosan hydrogel granules crosslinked with epichlorohydrin (CHs-ECH) served as orthophosphate ion carriers. The developed method was based on cyclic sorption/desorption of orthophosphates, with desorption performed in each cycle to the same solution (the concentrate). The concentrations of orthophosphates obtained in the concentrates depended on, i.a., sorbent type, sorption pH, source solution concentration, and desorption pH. Phosphorus concentrations in the concentrates were even 30 times higher than these in the source solutions. The maximum concentrate concentrations reached 332.0 mg P-PO₄/L for CHs and 971.6 mg P-PO₄/L for CHs-ECH. The experimental series with CHs-ECH were characterized by higher concentrations of the obtained concentrate, however the concentrates were also more contaminated with Cl⁻ and Na⁺ ions compared to series with CHs. The high content of chlorine and sodium ions in the concentrates was also favored by the low pH of sorption (pH < 4) and very high pH of desorption (pH > 12) in the cycles. After concentrate evaporation, phosphorus content in the sediment ranged from 17.81 to 19.83% for CHs and from 16.04 to 17.74% for CHs-ECH.

Network interior and surface engineering of alginate-based beads using sorption affinity component for enhanced phosphate capture

In order to alleviate the environmental problems caused by excessive discharge of phosphate, an environmental friendly and highly efficient bio-sorbent (SA-La@PEI) for phosphate was fabricated by combing strategies of sorption affinity component mediated and poly(ethylenimine) surface engineering of alginate beads. Various characterization methods like SEM, FTIR, XRD and XPS were adopted to examine the morphology and functional group composition of SA-La@PEI. Through detailed tests, SA-La@PEI exhibited excellent adsorption performance of 121.2 mg/g, which was better than most published materials. More importantly, the outstanding phosphate selectivity of SA-La@PEI was exposed when NO₃^-, HCO₃^-, SO₄^2- and Cl^- were added to the phosphate solution. Considering the integrated components in composites, both chemical precipitation and electrostatic attraction can be considered as the dominant mechanisms of phosphate adsorption. Totally, as-prepared SA-La@PEI beads might be a promising sorbent for the decontamination of excessive phosphate because of its low-cost, excellent adsorption performance and mechanical strength.