A biocompatible and novelly-defined Al-HAP adsorption membrane for highly effective removal of fluoride from drinking water

Performance and mechanism of La-Fe metal-organic framework as a highly efficient adsorbent for fluoride removal from mine water

Water fluoride pollution has caused non-negligible harm to the environment and humans, and thus it is crucial to find a suitable treatment technology. In this study, La-Fe@PTA adsorbent was synthesized for the defluoridation of mine water. The results showed that the optimum conditions for defluoridation by La-Fe@PTA were pH close to 7.0, the initial F- concentration of 10 mg/L, the dosage of 0.5 g/L and the adsorption time of 240 min. Compared with SO42‒, Cl‒, NO3‒, Ca2+ and Mg2+, CO32‒ and HCO3‒ presented severer inhibition on fluoride uptake by La-Fe@PTA. The adsorption process fits well with the pseudo-second-order kinetic model and Freundlich model, and the maximum adsorption capacity of Langmuir model was 95 mg/g. Fixed-bed adsorption results indicated that fluoride in practical fluorinated mine water could be effectively removed from 3.6 mg/L to less than 1.5 mg/L within 130 bed volume (BV) by using 1.5 g La-Fe@PTA. Furthermore, the adsorbent still had good adsorption capacity after regeneration, which confirms the great application potential of La-Fe@PTA as a fluoride ion adsorbent. The mechanism analysis showed that La-Fe@PTA adsorption of fluorine ions is a physicochemical reaction driven by electrostatic attraction and ion exchange.

Investigation on Applying Biodegradable Material for Removal of Various Substances (Fluorides, Nitrates and Lead) from Water

Sapropel was used as a biodegradable material for water treatment. Sapropel is a sedimentary layer of a mix of organic and inorganic substances accumulated in the bottoms of lakes for thousands of years. It is a jelly-like homogeneous mass and has properties of sorption. Sapropel is used as a biosorbent and an environment-friendly fertiliser, and it is used in building materials and in the beauty industry as well. In water, there are abundant various solutes that may cause a risk to human health. Such substances include fluorides, nitrates and lead in different sources of water. The goal of this investigation is to explore and compare the efficiencies of removal of different pollutants (fluorides, nitrates and lead) from aqueous solutions upon using sapropel as a sorbent. In this research, various doses of sapropel (0.1, 0.5, 1, 5, 10, 20, 50, 100 and 200 g/L) and various mixing times (15, 30, 60, 90 and 120 min) were used for removal of fluorides, nitrates and lead from aqueous solutions. It was found that the maximum efficiency (up to 98.57%) of lead removal from aqueous solutions by sapropel was achieved when the minimum doses of it (0.1 and 0.5 g/L) were used. The most efficient removal of fluorides (64.67%) was achieved by using 200 g/L of sapropel and mixing for 120 min. However, sapropel does not adsorb nitrates from aqueous solutions.

Preparation of MOF/polypyrrole and flower-like MnO2 electrodes by electrodeposition: High-performance materials for hybrid capacitive deionization defluorination

Fluorine pollution has become a global public health problem due to its adverse health effects. Adsorption is the primary method for removing fluoride from drinking water. However, the adsorption method has disadvantages such as difficulty in recovering the adsorbent, and the need to add additional chemicals for regeneration, thereby causing secondary pollution, which limits further industrial applications. Capacitive deionization (CDI), as an emerging water treatment technology, has attracted widespread attention due to its advantages of simple operation, low energy consumption and less environmental impact. In this study, a polypyrrole (PPy) film was prepared on a graphite substrate by electrodeposition, and then metal-organic framework Ce/Zn-BDC-NH₂ (CZBN) was deposited on the PPy film by electrophoretic deposition to obtain CZBN/PPy electrode was obtained. The CZBN/PPy anode was then coupled with the MnO₂ cathode for capacitive removal of fluoride in a CDI cell. Both CZBN/PPy and MnO₂ electrodes exhibit pseudocapacitive behavior, which can selectively and reversibly intercalate F^- (CZBN/PPy) and Na⁺ (MnO₂) ions. As expected, the CZBN/PPy-MnO₂ system exhibits excellent fluorine removal performance. In 1.2 V, 100 mg/L F^- solution, the F^- removal capacity can reach 55.12 mg/g. It has high F^- selectivity in the presence of some common anions, and can maintain high F^- removal ability even after five adsorption regeneration processes. The mechanism of F^- removal was studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). F^- was mainly removed by electrostatic interaction and ion exchange with hydroxyl. The excellent defluorination performance of the CZBN/PPy-MnO₂ system makes it have good practical application prospects.

Robust and Multifunctional 3D Graphene-Based Aerogels Reinforced by Hydroxyapatite Nanowires for Highly Efficient Organic Solvent Adsorption and Fluoride Removal

In view of the serious perniciousness and complex diversity of actual wastewater systems, exploiting a robust and multifunctional adsorbent material featuring high sorption efficiency, broad-spectrum applicability, and excellent recyclability in treating multifarious pollutants in water (such as oils and fluoride ions) is highly required; however, it is still a daunting goal to pursue to date. In this work, novel mechanically robust and exceptional graphene oxide/hydroxyapatite nanowire (GO/HAPNW) aerogels (RGHAs/polydopamine (PDA)@RGHAs) with adjustable surface wettability were developed through a facile sol-gel self-assembly technology and subsequently optional bioinspired hydrophilic modification. Thanks to the reinforcing effect of HAPNWs with higher aspect ratio, a remarkably improved mechanical robustness (including superior compressibility and superelasticity) was acquired for the resulting aerogels. Based on the cooperative effect of the favorable selective wetting properties (i.e., hydrophobic/oleophilic for RGHAs) and the excellent mechanic stability, the aerogels displayed an outstanding sorption performance for diverse oils/organic solvents accompanied with a prominent recyclability. Specifically, a fairly high adsorption capacity of as high as 191 times of its own mass (for pump oil) was achieved based on a fast adsorption kinetic process. More importantly, superamphiphilic three-dimensional (3D) PDA@RGHAs revealed an extraordinary removal capability for water-soluble fluoride ions, exhibiting a superior equilibrium adsorption capacity (q_e, 9.93 mg/g), which is distinctly superior to those of low-dimensional fluorine adsorbent materials recently reported. Accordingly, the as-prepared 3D aerogels combining both superior oil/organic solvent adsorption and excellent defluorination capability reveal a competitive application prospect toward effective intricate oily wastewater purification.

Zr-Based Biocomposite Materials as an Alternative for Fluoride Removal, Preparation and Characteristics

The development of biocomposite materials used as adsorbents to remove ions in aqueous media has become an attractive option. The biomasses (base materials) are chemically treated and impregnated with metal cations, becoming competitive for fluoride-capture capacity. In this research, Valence orange (Citrus sinensis) and Red Delicious apple (Malus Domestica) peels were modified by alkaline treatment, carboxylation, and impregnation with zirconium (Zr). These materials were characterized morphologically and structurally to understand the modifications in the treated biomasses and the mechanism of fluoride adsorption. The results show changes in surface area and composition, most notably, an increment in roughness and Zr impregnation of the bioadsorbents. After batch experimentation, the maximum capacity of the materials was determined to be 4.854 and 5.627 mg/g for the orange and apple peel bioadsorbent, respectively, at pH 3.5. The experimental data fitted the Langmuir model, suggesting that chemisorption occurs in monolayers. Finally, the characterization of the bioadsorbents in contact with fluoride allowed the replacement of OH species by fluoride or the formation of hydrogen bonds between them as an adsorption mechanism. Therefore, these bioadsorbents are considered viable and can be studied in a continuous system.

Fluoride ions sorption using functionalized magnetic metal oxides nanocomposites: a review

Fluoride is an anionic pollutant found superfluous in surface or groundwater as a result of anthropogenic actions from improper disposal of industrial effluents. In drinking water, superfluous fluoride has been revealed to trigger severe health problems in humans. Hence, developing a comprehensive wastewater decontamination process for the effective management and preservation of water contaminated with fluoride is desirable, as clean water demand is anticipated to intensify considerably over the upcoming years. In this regard, there have been increased efforts by researchers to create novel magnetic metal oxide nanocomposites which are functionalized for the remediation of wastewater owing to their biocompatibility, cost-effectiveness, relative ease to recover and reuse, non-noxiousness, and ease to separate from solutions using a magnetic field. This review makes an all-inclusive effort to assess the effects of experimental factors on the sorption of fluoride employing magnetic metal oxide nanosorbents. The removal efficiency of fluoride ions onto magnetic metal oxides nanocomposites were largely influenced by the solution pH and ions co-existing with fluoride. Overall, it was noticed from the reviewed researches that the maximum sorption capacity using various metal oxides for fluoride sorption was in the order of aluminium oxides >cerium oxides > iron oxides > magnesium oxides> titanium oxides, and most sorption of fluoride ions was inhibited by the existence of phosphate trailed by sulphate. The mechanism of fluoride sorption onto various sorbents was due to ion exchange, electrostatic attraction, and complexation mechanism.

Goethite/montmorillonite adsorption coupled with electrocoagulation for improving fluoride removal from aqueous solutions

A new material GMS is produced as electrodes in the electrocoagulation (EC) process for F− removing from aqueous environments. The removal rate reaches 99.47% through the EC/GMS. Adsorption and co-precipitation are the main F− removal pathways.

Structure-Activity Relationship of Lanthanide-Incorporated Nano-Hydroxyapatite for the Adsorption of Fluoride and Lead

The growing demand for water purification provided the initial momentum to produce lanthanide-incorporated nano-hydroxyapatite (HAP) such as HAP·CeO2, HAP·CeO2·La(OH)3 (2:1), and HAP·CeO2·La(OH)3 (3:2). These materials open avenues to remove fluoride and lead ions from contaminated water bodies effectively. Composites of HAP containing CeO2 and La(OH)3 were prepared using in situ wet precipitation of HAP, followed by the addition of Ce(SO4)2 and La(NO3)3 into the same reaction mixture. The resultant solids were tested for the removal of fluoride and lead ions from contaminated water. It was found that the composite HAP·CeO2 shows fluoride and lead ion removal capacities of 185 and 416 mg/g, respectively. The fluoride removal capacity of the composite was improved when La(OH)3 was incorporated and it was observed that the composite HAP·CeO2·La(OH)3 (3:2) has the highest recorded fluoride removal capacity of 625 mg/g. The materials were characterized using scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) spectrometry, Fourier transform infrared (FT-IR) spectrometry, X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area analysis. Analysis of results showed that Ce and La are incorporated in the HAP matrix. Results of kinetic and leaching analyses indicated a chemisorptive behavior during fluoride and lead ion adsorption by the composites; meanwhile, the thermodynamic profile shows a high degree of feasibility for fluoride and lead adsorption.

Preparation, characterization serpentine-loaded hydroxyapatite and its simultaneous removal performance for fluoride, iron and manganese

Aiming at the problem of excessive fluorine, iron, and manganese pollution in groundwater in mining areas, a serpentine-loaded hydroxyapatite (Srp/HAP) composite adsorbent was prepared by wet chemical coprecipitation. The preparation conditions of the Srp/HAP composite adsorbent were explored, Srp/HAP was microscopically characterized, and the adsorption performance and adsorption mechanism of the Srp/HAP composite adsorbent for F⁻, Fe²⁺ and Mn²⁺ were analyzed. The results showed that the optimal preparation conditions for the composite particles were as follows: solid–liquid ratio of Srp to calcium nitrate solution 20%, aging time 20 h, calcination temperature 180 °C, and calcination time 90 min. Compact Srp/HAP composite adsorbent particles were successfully prepared, and both the lamellar crimp structure of the Srp surface and the problem of HAP surface agglomeration were resolved. After loading, the specific surface area and pore volume of the particles significantly increased, and the surface pore structure improved, which is conducive to the simultaneous adsorption and removal of fluorine, iron and manganese. The optimal reaction conditions for Srp/HAP treatment of composite water samples with F⁻, Fe²⁺ and Mn²⁺ mass concentrations of 5 mg L⁻¹, 20 mg L⁻¹ and 5 mg L⁻¹, respectively, are as follows: dosage of Srp/HAP 3 g L⁻¹, pH 7, temperature 35 °C, and reaction time 150 min. Under these conditions, the removal rates of F⁻, Fe²⁺ and Mn²⁺ were 98.6%, 99.9% and 99.8%, respectively. The quasi-second-order kinetic model and Langmuir isothermal adsorption model described the adsorption process of F⁻, Fe²⁺ and Mn²⁺ by the composite particles well. The adsorption process includes both surface physical adsorption and chemical adsorption. Chemical adsorption is mainly characterized by ion exchange and surface complexation. The Srp/HAP composite particles can be used as an excellent adsorbent for the treatment of groundwater containing fluorine, iron and manganese ions in mining areas.

A new adsorbent Srp/HAP for simultaneous removal of fluoride, iron and manganese was prepared, characterized and analyzed.

Biopolymer-Based Nanohydroxyapatite Composites for the Removal of Fluoride, Lead, Cadmium, and Arsenic from Water

In this study, hydroxyapatite (HAP) nanocomposites were prepared with chitosan (HAP-CTS), carboxymethyl cellulose (HAP-CMC), alginate (HAP-ALG), and gelatin (HAP-GEL) using a simple wet chemical in situ precipitation method. The synthesized materials were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, and thermogravimetric analysis. This revealed the successful synthesis of composites with varied morphologies. The adsorption abilities of the materials toward Pb(II), Cd(II), F-, and As(V) were explored, and HAP-CTS was found to have versatile adsorption properties for all of the ions, across a wide range of concentrations and pH values, and in the presence of common ions found in groundwater. Additionally, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy confirmed the affinity of HAP-CTS toward multi-ion mixture containing all four ions. HAP-CTS was hence engineered into a more user-friendly form, which can be used to form filters through its combination with cotton and granular activated carbon. A gravity filtration study indicates that the powder form of HAP-CTS is the best sorbent, with the highest breakthrough capacity of 3000, 3000, 2600, and 2000 mL/g for Pb(II), Cd(II), As(V), and F-, respectively. Hence, we propose that HAP-CTS could be a versatile sorbent material for use in water purification.

Activated mineral adsorbent for the efficient removal of Pb(II) and Cd(II) from aqueous solution: adsorption performance and mechanism studies

Activated mineral adsorbent (AMA) was prepared via double salts (Na₂SO₄ and CaCO₃) heat treatment activation of solid-state potassium feldspar. Adsorption performance of AMA for Cd(II) and Pb(II) was investigated by batch mode and factors affecting adsorption including pH value, initial concentration of adsorbate, contact time, adsorbent dosage and temperature on adsorption performance for Cd(II) and Pb(II) were studied. The results indicated that the adsorption process was pH dependent, endothermic and spontaneous. When the adsorption process of Cd(II) and Pb(II) on AMA reached equilibrium, the maximum saturated adsorption capacities were 263.16 and 303.03 mg/g for Cd(II) and Pb(II) ions, respectively, showing higher adsorption removal efficiency. The Langmuir adsorption isotherm and pseudo second kinetic equation could well fit the adsorption process of Cd(II) and Pb(II) by AMA. Besides, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were also performed to further reveal the adsorption mechanism. The results indicated that ion exchange, precipitation and adsorption played an important role in adsorption process. From the investigation, it was concluded that AMA was an excellent adsorbent with the advantages of environment-friendly, inexpensive, facile preparation and higher adsorption capacity of toxic Cd(II) and Pb(II) ions.

MOFs for the treatment of arsenic, fluoride and iron contaminated drinking water: A review

Over the last few decades, the global pollution of surface and groundwater poses a serious threat not only to human beings but also towards aquatic lives due to the presence of emerging contaminants. Among the others, the presence of arsenic, fluoride, and iron are considered as the most common toxic pollutants in water bodies. The emergence of metal organic frameworks (MOFs) with high porosity and surface area is represented as significant inclusion into the era of entrapping contaminants present in drinking water. In the present review article, an in-depth insight is provided on the recent developments in the removal of arsenic, fluoride, and iron from drinking water using MOFs. Various aspects related to the synthesis, latest technologies adopted for the modifications in the synthesis process and advanced applications of MOFs for the removal of such contaminants are explicitly discussed. A detailed insight was provided to understand the mechanism of various interactions of MOFs with arsenic and fluoride. With respect to arsenic, fluoride, and iron removal the ultrastructural morphology of MOFs is assessed based on different molecular arrangements. Further, commercial aspects of various MOFs are presented in order to highlight the process feasibility. Finally, various perspectives and challenges involved in process scale up are comprehensively narrated with an aspiration of futuristic developments. The paper will be beneficial to the readers for acquiring a piece of in-depth knowledge on MOFs and its various synthesis approaches along with remarkable achievements for the removal of arsenic, fluoride, and iron from contaminated drinking water.

A simple chemical method for the synthesis of Cu2+ engrafted MgAl2O4 nanoparticles: Efficient fluoride adsorbents, photocatalyst and latent fingerprint detection

An adaptable, energy efficient chemical process is employed to synthesize Cu²⁺ engrafted MgAl₂O₄ nanoparticles (Mg_1-xCu_xAl₂O₄, x=0, 0.1, 0.3, 0.5 abbreviated as MCA0, MCA1, MCA3, and MCA5 respectively), using chelating ligand and the calcination temperature was determined by the thermogravimetric analysis of the precursor mass. They acted as good fluoride adsorbent in the presence of co-ions, different pH (2-11) via chemisorption revealed from Fourier-transform infrared spectroscopy (FTIR) and photodegraded Methylene Blue (MB). The satisfactory results were for MCA1 (specific surface area 25.05m²/g) with 97% fluoride removal at pH7.0 for the 10mg/L initial fluoride concentration for 1.5g/L adsorbent dose with 45min contact time obeying the Langmuir isotherm model with negative thermodynamic parameters and 4mmol of MCA3 with 98.51% photodegradation for 10^-5mol/LMB solution obeying pseudo-second-order and pseudo-first-order kinetics respectively. The proposed photodegradation mechanism of MB was established by the FTIR and high-performance liquid chromatography (HPLC) analysis. The nanoparticles are cubic, estimated through X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The band gap energies, grain size, and the effective working pH were estimated by diffuse reflectance spectra (DRS), scanning electron microscope (SEM), and zero-point potential analysis respectively. A soil candle with MCA1 also fabricated for the household purpose and tested with some fluorinated field samples. The MCA3 was able to enhance the latent fingerprint on smooth surfaces.

Mg-Al Mixed Oxide Adsorbent Synthesized Using FCT Template for Fluoride Removal from Drinking Water

To make full use of natural waste, a novel Mg-Al mixed oxide adsorbent was synthesized by the dip-calcination method using the fluff of the chinar tree (FCT) and an Mg(II) and Al(III) chloride solution as raw materials. The adsorbents were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The effects of the Mg/Al molar ratio and calcination temperature on the performance of the novel Mg-Al mixed oxide adsorbent were investigated. The optimized Mg-Al mixed oxide adsorbent had a Langmuir adsorption capacity of 53 mg/g. This adsorption capacity was higher than that of the separate Mg oxide and Al oxide. The synergy between Mg and Al is beneficial to the adsorption performance of the material. The fluoride adsorption capacity of the optimized Mg-Al mixed oxide adsorbent is only slightly affected by ions such as Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, and K⁺ and is excellent for use in recycling and real water. The hydroxyl groups on the surface of the Mg-Al mixed oxide adsorbent play a key role in the adsorption of fluorine. The as-obtained novel Mg-Al mixed oxide adsorbent is an efficient and environmentally friendly agent for fluoride removal from drinking water.

Bone-derived biochar and magnetic biochar for effective removal of fluoride in groundwater: Effects of synthesis method and coexisting chromium

The presence of fluoride in groundwater in excess of 1.5 mg L^-1 is a major environmental health concern, and biochar is a promising low-cost adsorbent for the treatment of such water. In the present study, pristine and magnetic biochars were synthesized by peanut hull and bovine bone for the adsorption of fluoride. The biochars were systematically characterized by SEM-EDS, BET, XRD, VSM, FT-IR, and XPS. The experiment results showed that the magnetic biochar prepared by soaking biomass in FeCl₃ solution and then pyrolyzing ("prepyrolysis") had a higher adsorption capacity than that prepared by mixing pristine biochar with Fe²⁺ /Fe³⁺ solution and then treating with NaOH ("postpyrolysis"). The bone-derived biochar and magnetic biochar exhibited high adsorption capacity of fluoride (>5 mg g^-1 ) due to the presence of hydroxyapatite (HAP) and γ-Fe₂ O₃ . The 0.1 M NaOH solution could be optimal desorption agent, and the adsorption-desorption experiments indicated the bone biochars maintained the reasonable adsorption capacity after several cycles. Moreover, the coexisting Cr(VI) and fluoride could be removed simultaneously by bone-derived biochars. It is suggested that bovine bone-derived pristine and magnetic biochars can be used as preferential adsorbents for fluoride removal from contaminated groundwater. PRACTITIONER POINTS: Bone-derived pristine and magnetic biochars exhibit high adsorption capacity for fluoride in weakly alkaline solution. The presence of hydroxyapatite and γ-Fe₂ O₃ in bone-derived biochars plays an important role for fluoride adsorption. Magnetic biochars prepared by soaking biomass in FeCl₃ solution and then pyrolyzing ("prepyrolysis") perform better. The coexisting Cr(VI) and fluoride can be simultaneously removed in groundwater by bone biochars.

Grape pomace as a biosorbent for fluoride removal from groundwater

This study presents a new type of biomass material for defluoridation from water; the material was prepared by loading tetravalent zirconium ions onto grape pomace produced from grape juicing and wine factories. Experiments showed that the optimum pH of defluoridation is around 3.0, and the fluorine removal efficiency could reach 96.13% for one-time contact. In batchwise adsorption tests, it was very interesting to find that even at pH values near 10, at which traditional adsorbents usually do not function for defluoridation, the removal efficiency of fluoride was still more than 90% for the Zr(iv)-loaded grape pomace (Zr(iv)-GP) biosorbent; proton release from Zr(iv)-GP was confirmed to cause an automatic decrease of the pH, which can save additional acid consumption in the case of one-time use and render the defluoridation more convenient and efficient. The maximum adsorption capacity of Zr(iv)-GP was 7.54 mg g-1; as a comparison, the maximum adsorption capacities of zirconium-loaded strongly acidic ion exchange resin D001 and zirconium-loaded weakly acidic ion exchange resin D113 were evaluated to be 4.85 mg g-1 and 1.14 mg g-1, respectively. The effects of coexisting anions, such as Cl-, NO3-, SO4 2-, CO3 2- and HPO4 2-, on the fluorine removal efficiency were also examined; it was found that CO3 2- and HPO4 2- anions had drastically adverse effects on defluoridation, while Cl-, NO3-, and SO4 2- appeared not to interfere. Real groundwater containing 1.8 mg L-1 fluoride sampled from Guanzhuang Village in Haixing County of Hebei Province was used for defluoridation through a continuous column adsorption process; it was found that pre-adjusting the groundwater pH affected the purification efficiency drastically, i.e., the time of the breakthrough point for the inlet groundwater pH at 3.0 was about 8 times longer than that at the original pH of 8.18. In addition, the Zr(iv)-GP adsorbent retained good adsorption capacity even after 3 cycles of adsorption-desorption-adsorption operations, indicating that the synthesized zirconium-loaded grape pomace is a very promising new fluorine-removing material for groundwater purification.

Nanosorbent of hydroxyapatite for atrazine: A new approach for combating agricultural runoffs

The attention of current work was on the fabrication of effective nanoadsorbent of hydroxyapatite (HAp) for the controlled release of atrazine (ATZ) formulation. The ATZ-HAp complex (ATZ@HAp) was able to inhibit the growth of Brassica sp. under in situ conditions. This developed methodology aspires to cease the agricultural runoffs of ATZ applied with the HAp adjuvant and ensure their effective functioning. The efficacy of the protocol was mainly accomplished by adsorbing ATZ over the surface of HAp NPs that restricted its premature runoff and promoted the prolonged herbicidal efficiency. The influence of fundamental parameters i.e., HAp dose, ATZ dose and initial pH on the adsorption process was investigated systematically. The suitability of ATZ@HAp complex for real world application was adjudged after proofing its toxicological behaviour and its role in Zea mays plantations. The complex was found to be non-toxic and nurturing due to its phosphate rich nature. Further investigations of ATZ@HAp complex and its effect on the non-target species will help in establishing an effective framework for their commercial use in agricultural practices.

Ultralong Hydroxyapatite Nanowire-Based Filter Paper for High-Performance Water Purification

A new kind of environmentally friendly filter paper based on ultralong hydroxyapatite nanowires (HAPNWs) and cellulose fibers (CFs) with excellent filtration and adsorption properties has been developed for the application in high-performance water purification. The use of polyamidoamine-epichlorohydrin (PAE) resin increases the wet mechanical strength of the as-prepared HAPNW/CF filter paper. The addition of CFs enhances the mechanical strength of the HAPNW/CF filter paper. Owing to the porous structure and superhydrophilicity of the as-prepared HAPNW/CF filter paper, the pure water flux is as high as 287.28 L m^-2 h^-1 bar^-1 under cross-flow conditions, which is about 3200 times higher than that of the cellulose fiber paper with addition of PAE. More importantly, the as-prepared HAPNW/CF filter paper shows superior performance in the removal of TiO₂ nanoparticles (>98.61%) and bacteria (up to 100%) in water by the size exclusion and blocking effect. In addition, the HAPNW/CF filter paper also exhibits high adsorption capacities for methyl blue (273.97 mg g^-1) and Pb²⁺ ions (508.16 mg g^-1). The adsorption mechanism of the HAPNW/CF filter paper is investigated. The as-prepared environmentally friendly HAPNW/CF filter paper with both excellent filtration and adsorption properties has promising application in high-performance water purification to tackle the worldwide water scarcity problem.

Improved nanocomposite of montmorillonite and hydroxyapatite for defluoridation of water

A novel hydroxyapatite montmorillonite (HAP-MMT) nanocomposite system was synthesized using a simple wet chemical in situ precipitation method. Neat nano hydroxyapatite (HAP) was also synthesized for comparison. The characterization of the materials was carried out using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) isotherms to study the functional groups, morphology, crystallinity and the surface area respectively. Batch adsorption studies and kinetic studies on fluoride adsorption were conducted for the HAP-MMT system and for neat HAP. The effect of parameters such as contact time, pH, initial concentration, temperature, and thermodynamic parameters and the effect of coexisting ions on fluoride adsorption by HAP-MMT were studied. Results of the isotherm experiments were fitted to four adsorption isotherm models namely Langmuir, Freundlich, Temkin and Dubinin Radushkevich. Fluoride adsorption over HAP-MMT fitted to the Freundlich adsorption isotherm model and showed more than two-fold improved adsorption capacity (16.7 mg g⁻¹) compared to neat HAP. The best-fitting kinetic model for both adsorbents was found to be pseudo second order. Calculated thermodynamic parameters indicated that the fluoride adsorption by HAP-MMT is more favorable compared to that on HAP within the temperature range of 27 °C–60 °C. Improved fluoride adsorption by HAP-MMT is attributed to the exfoliated nature of HAP-MMT. Gravity filtration studies carried out using a 1.5 ppm fluoride solution, which is closer to the ground water fluoride concentrations of Chronic Kidney Disease of unknown etiology (CKDu) affected areas in Sri Lanka, resulted in a 1600 ml g⁻¹ break through volume indicating the potential of HAP-MMT to be used in real applications.

A novel hydroxyapatite montmorillonite (HAP-MMT) nanocomposite was synthesized using a simple wet chemical in situ precipitation method. This nanocomposite showed improved adsorption properties towards fluoride ions in water.

Zn(II), Pb(II), and Cd(II) adsorption from aqueous solution by magnetic silica gel: preparation, characterization, and adsorption

A novel magnetic silica gel adsorbent (Fe₃O₄-Si-COOH) was successfully prepared by introducing carboxyl group in situ to improve the performance for Pb(II), Zn(II), and Cd(II) adsorption. Infrared spectroscopy (IR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermo-gravimetric analyzer (TGA), the Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) characterizations suggested that Fe₃O₄-Si-COOH has been successfully prepared. The adsorption performance was evaluated by batch experiments with different initial concentrations, ionic strength, contact time, and pH. The adsorption kinetics data followed pseudo-second-order model and exhibited a three-stage intraparticle diffusion mode. Isothermal adsorption equilibrium data were best fitted by the Freundlich model and the adsorption capacity were 155, 110, and 93 mg/g (initial concentration 210 mg/L) for Pb(II), Zn(II), and Cd(II), respectively. The result of X-ray photoelectron spectroscopy (XPS) survey spectrum suggested that the main adsorption mechanism is that the H⁺ of carboxyl groups exchanged with heavy metal ions in the adsorption processes. In addition, the adsorbed Fe₃O₄-Si-COOH could be regenerated and the adsorption capacity of reused Fe₃O₄-Si-COOH could maintain 80.3% after five cycles. Hence, the Fe₃O₄-Si-COOH could be a kind of potential material for removing Pb(II), Zn(II), and Cd(II) from wastewater. Graphical abstract.

Removal of fluoride by carbohydrate-based material embedded with hydrous zirconium oxide nanoparticles

Herein, we fabricated a novel carbohydrate-based adsorbent by using the pomelo peel (PP) as the biocarrier. The virgin PP was embedded with hydrous zirconium oxide (HZO) nanoparticle, forming the HZO-PP composites for highly efficient fluoride adsorption. Characteristics of HZO-PP were determined by TEM, SEM, XPS, XRD, BET surface area, and FTIR. The result showed that HZO nanoparticles have been successfully anchored onto the inner pore of PPs, which play a significant role in defluorination. It is favorable for fluoride uptake with more acidic solution, which greatly enhanced the interfacial reaction between the fluoride ions and protonated HZO through electrostatic interaction or electro-dipole interaction. No significant Zr leaching and organic dissolution were observed within pH 3.0-11.0; this indicated the strong interfacial reaction between the biocarrier and HZO, which illustrated the high stability of the HZO-PP for use. Competing tests indicated that fluoride uptake by HZO-PP still retained about 76-88% as the concentrations of coexisting NO₃^- or SO₄^2- was 25 times higher than that of F^-. The HZO-PP in column after six adsorption-regeneration cycles still retained 94% of adsorption capacity (15.4 mg/g). All these results implied that biomaterials anchored with multivalent metal oxides represented the potential nanocomposites for fluoride removal.

Enhanced Defluoridation Capacity From Aqueous Media via Hydroxyapatite Decorated With Carbon Nanotube

In this work, the potential of a novel hydroxyapatite decorated with carbon nanotube composite (CNT-HAP) for fluoride removal was investigated. The synthesized CNT-HAP composite was systematically characterized by X-ray diffraction(XRD), Fourier Transform infrared spectroscopy(FTIR), scanning electron microscope (SEM) and Brunauer–Emmett–Teller(BET). Batch adsorption experiments were conducted to investigate the defluorination capacity of CNT-HAP. The CNT-HAP composite has a maximum adsorption capacity of 11.05 mg·g⁻¹ for fluoride, and the isothermal adsorption data were fitted by the Freundlich model to calculate the thermodynamic parameters. Thermodynamic analysis implies that the adsorption of fluoride on CNT-HAP is a spontaneous process. Furthermore, the adsorption of fluoride follows pseudo-second-order model. The effects of solution pH, co-existing anions and reaction temperature on defluorination efficiency were examined to optimize the operation conditions for fluoride adsorption. It is found that the optimized pH-value for fluoride removal by CNT-HAP composite is 6. In addition, among five common anions studied in this work, the presence of HCO3- and PO43- could considerably affect the fluoride removal by CNT-HPA in aqueous media. Finally, the underlying mechanism for the fluoride removal by CNT-HAP is analyzed, and an anion exchange process is proposed.

A Comparative Study on Removal of Hazardous Anions from Water by Adsorption: A Review

This paper presents a comparative review of arsenite (As(III)), arsenate (As(V)), and fluoride (F−) for a better understanding of the conditions and factors during their adsorption with focus on (i) the isotherm adsorption models, (ii) effects of pH, (iii) effects of ionic strength, and (iv) effects of coexisting substances such as anions, cations, and natural organics matter. It provides an in-depth analysis of various methods of arsenite (As(III)), arsenate (As(V)), and fluoride (F-) removal by adsorption and the anions’ characteristics during the adsorption process. The surface area of the adsorbents does not contribute to the adsorption capacity of these anions but rather a combination of other physical and chemical properties. The adsorption capacity for the anions depends on the combination of all the factors: pH, ionic strength, coexisting substances, pore volume and particles size, surface modification, pretreatment of the adsorbents, and so forth. Extreme higher adsorption capacity can be obtained by the modification of the adsorbents. In general, pH has a greater influence on adsorption capacity at large, since it affects the ionic strength, coexisting anions such as bicarbonate, sulfate, and silica, the surface charges of the adsorbents, and the ionic species which can be present in the solution.

Characterization and adsorption properties of cross-linked yeast/β-cyclodextrin polymers for Pb(ii) and Cd(ii) adsorption

A cross-linked yeast/β-cyclodextrin polymer (Y–β-CDP) was synthesized to remove Pb(ii) and Cd(ii) from aqueous solution.

Study on the removal of organic micropollutants from aqueous and ethanol solutions by HAP membranes with tunable hydrophilicity and hydrophobicity

A biocompatible and uniquely defined hydroxyapatite (HAP) adsorption membrane with a sandwich structure was developed for the removal of organic micropollutants for the first time. Both the adsorption and membrane technique were used for the removal of organic micropollutants. The hydrophilicity and hydrophobicity of the HAP adsorbent and membrane were tunable by controlling the surface structure of HAP. The adsorption of organic micropollutants on the HAP adsorbent was studied in batch experiments. The adsorption process was fit with the Freundlich model, while the adsorption kinetics followed the pseudo-second-order model. The HAP membrane could remove organic micropollutants effectively by dynamic adsorption in both aqueous and ethanol solutions. The removal efficiencies of organic micropollutants depended on the solution composition, membrane thickness and hydrophilicity, flow rate, and the initial concentration of organic micropollutants. The adsorption capacities of the HAP membrane with a sandwich structure (membrane thickness was 0.3 mm) were 6700, 6510, 6310, 5960, 5490, 5230, 4980 and 4360 L m-2 for 1-naphthyl amine, 2-naphthol, bisphenol S, propranolol hydrochloride, metolachlor, ethinyl oestradiol, 2,4-dichlorophenol and bisphenol A, respectively, when the initial concentration was 3.0 mg L-1. The biocompatible HAP adsorption membrane can be easily regenerated by methanol and was thus demonstrated to be a novel concept for the removal of organic micropollutants from both aqueous and organic solutions.

Adsorptive removal of aqueous bezafibrate by magnetic ferrite modified carbon nanotubes

MFe₂O₄/CNTs were synthesized and successfully applied for the removal of aqueous bezafibrate. The adsorption behavior and mechanism were elucidated in detail.