Ultrasound assisted synthesis of Mg-Mn-Zr impregnated activated carbon for effective fluoride adsorption from water

Advances and future perspectives of water defluoridation by adsorption technology: A review

Fluoride contamination in water sources poses a significant challenge to human health and the environment. In recent years, adsorption technology has emerged as a promising approach for water defluoridation due to its efficiency and cost-effectiveness. This review article comprehensively explores the advances in water defluoridation through adsorption processes. Various adsorbents, including natural and synthetic materials, have been investigated for their efficacy in removing fluoride ions from water. The mechanisms underlying adsorption interactions are elucidated, shedding light on the factors influencing defluoridation efficiency. Moreover, the review outlines the current state of technology, highlighting successful case studies and field applications. Future perspectives in the field of water defluoridation by adsorption are discussed, emphasizing the need for sustainable and scalable solutions. The integration of novel materials, process optimization, and the development of hybrid technologies are proposed as pathways to address existing challenges and enhance the overall efficacy of water defluoridation. This comprehensive assessment of the advances and future directions in adsorption-based water defluoridation provides valuable insights for researchers, policymakers, and practitioners working towards ensuring safe and accessible drinking water for all.

Kinetics, isotherm, mechanism, and recyclability of novel nano-sized Ce4+-doped Ni-Al layered double hydroxide for defluoridation of aqueous solutions

Excessive fluoride removal from aqueous solutions is of utmost importance as it has an adverse impact on human health. This study investigates the defluoridation efficiency of a novel nano-sized Ce+4-doped Ni/Al layered double hydroxide (Ni-Al-Ce LDH) for aqueous solutions. The synthesized Ni-Al-Ce LDH exhibited a well-defined nanoscale plate-like morphology and a high surface area with an average size of 11.51 nm, which contributed to its enhanced fluoride adsorption capacity. XRD, SEM, HRTEM, and BET studies confirmed these characteristics. XPS analysis confirmed the presence of Ce4+ ions within the Ni-Al LDH. The experimental results indicated that the process of defluoridation followed a pseudo-second-order model of kinetics, suggesting a chemisorption mechanism. The fluoride adsorption isotherms demonstrated well fits to the Freundlich, Langmuir, and Jovanovic models, indicating both monolayer and multilayer fluoride adsorption on the Ce-doped Ni-Al LDH. The maximum adsorption capacity was found to be 238.27 mg/g (Langmuir) and 130.73 mg/g (Jovanovic) at pH 6.0 and 25 °C. The proposed mechanisms for fluoride adsorption on the LDH include ion exchange, surface complexation, hydrogen bonding, and ligand exchange. The Ni-Al-Ce LDH nanomaterial exhibited good recyclability, maintaining 71% of the fluoride adsorption efficiency even after four consecutive cycles. This study highlights the significant role of Ce doping in improving the performance of Ni-Al LDH as a defluoridation adsorbent.

3D flower-like zirconium magnesium oxide nanocomposite for efficient fluoride removal

A 3D flower-shaped bimetallic nanocomposite zirconium magnesium oxide (ZMO) was prepared first time by the controlled solution combustion method using triethanolamine (TEA) as a fuel and chelating agent. The composite material was used to remove excess fluoride via adsorption. The thermal stability of the adsorbent was characterized by thermogravimetric analysis (TGA). Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) were used to characterize the adsorbent. The surface charge of the nano adsorbent was determined by Zeta Sizer. The surface area and pore volume of the adsorbent were determined by Brunauer-Emmett-Teller (BET) isotherm and Barrett-Joyner-Halenda (BJH) methods. The adsorption behavior of fluoride was studied systematically varying the pH, contact time, adsorbent dose, and initial fluoride concentration. The adsorption followed the Langmuir isotherm model with a maximum adsorption capacity of 42.14 mg/g. The pseudo-second-order kinetic model was confirmed by the adsorption study. The maximum adsorption efficiency was in the 6-10 pH range. The reaction mechanism was mainly based on ion exchange between hydroxy and fluoride ions which was proven by X-ray photoelectron spectroscopy (XPS). Real water tests indicated that ZMO could be used as a potential defluoridation agent for fluoride containing groundwater treatment.

The model and mechanism of adsorptive technologies for wastewater containing fluoride: A review

With the continuous development of society, industrialization, and human activities have been producing more and more pollutants. Fluoride discharge is one of the main causes of water pollution. This review summarizes various commonly used and effective fluoride removal technologies, including ion exchange technology, electrochemical technology, coagulation technology, membrane treatment, and adsorption technology, and points out the outstanding advantages of adsorption technology. Various commonly used fluoride removal techniques as well as typical adsorbent materials have been discussed in published papers, however, the relationship between different adsorbent materials and adsorption models has rarely been explored, therefore, this paper categorizes and summarizes the various models involved in static adsorption, dynamic adsorption, and electrosorption fluoride removal processes, such as pseudo-first-order and pseudo-second-order kinetic models, Langmuir and Freundlich isotherm models, Thomas and Clark dynamic adsorption models, including the mathematical equations of the corresponding models and the significance of the models are also comprehensively summarized. Furthermore, this comprehensive discussion delves into the fundamental adsorption mechanisms, quantification of maximum adsorption capacity, evaluation of resistance to anion interference, and assessment of adsorption regeneration performance exhibited by diverse adsorption materials. The selection of the best adsorption model not only predicts the adsorption performance of the adsorbent but also provides a better description and understanding of the details of each part of the adsorption process, which facilitates the adjustment of experimental conditions to optimize the adsorption process. This review may provide some guidance for the development of more cost-effective adsorbent materials and adsorption processes in the future.

Synthesis of Composites for the Removal of F- Anions

This work presents the synthesis of amine and ferrihydrite functionalized graphene oxide for the removal of fluoride from water. The synthesis of the graphene oxide and the modified with amine groups is developed by following the modified Hummer's method. Fourier transform infrared spectrometry, X-ray, Raman spectroscopy, thermogravimetric analysis, surface charge distribution, specific surface area and porosity, adsorption isotherms, and the van't Hoff equation are used for the characterization of the synthesized materials. Results show that the addition of amines with ferrihydrite generates wrinkles on the surface layers, suggesting a successful incorporation of nitrogen onto the graphene oxide; and as a consequence, the adsorption capacity per unit area of the materials is increased.

Controllable Doping of Mn into Ni0.075-xMnxAl0.025(OH)2(CO3)0.0125·yH2O for Efficient Adsorption of Fluoride Ions

Here, the structural, optical, and adsorptive behaviors of Ni_0.075-xMn_xAl_0.025(OH)₂(CO₃)_0.0125·yH₂O (Ni-Mn/Al) layered double hydroxides (LDHs) are investigated to capture fluoride from aqueous media. The 2D mesoporous plate-like Ni-Mn/Al LDHs are successfully prepared via a co-precipitation method. The molar ratio of divalent to trivalent cations is maintained at 3:1 and the pH at 10. The X-ray diffraction (XRD) results confirm that the samples consist of pure LDH phases with a basal spacing of 7.66 to 7.72 Å, corresponding to the (003) planes at 2θ of 11.47^o and the average crystallite sizes of 4.13 to 8.67 nm. The plate-like Mn-doped Ni-Al LDH consists of many superimposed nanosheets with a size of 9.99 nm. Energy-dispersive X-ray and X-ray photoelectron spectroscopies confirm the incorporation of Mn²⁺ into the Ni-Al LDH. UV-vis diffuse reflectance spectroscopy results indicate that incorporating Mn²⁺ into LDH enhances its interaction with light. The experimental data from the batch fluoride adsorption studies are subjected to kinetic models such as pseudo-first order and pseudo-second order. The kinetics of fluoride retention on Ni-Mn/Al LDH obey the pseudo-second-order model. The Temkin equation well describes the equilibrium adsorption of fluoride. The results from the thermodynamic studies also indicate that fluoride adsorption is exothermic and spontaneous.

Synthesis and Characterization of Porous MgO Nanosheet-Modified Activated Carbon Fiber Felt for Fluoride Adsorption

In the present work, the porous MgO nanosheet-modified activated carbon fiber felt (MgO@ACFF) was prepared for fluoride removal. The MgO@ACFF was characterized by XRD, SEM, TEM, EDS, TG, and BET. The fluoride adsorption performance of MgO@ACFF also has been investigated. The adsorption rate of the MgO@ACFF toward fluoride is fast; more than 90% of the fluoride ions can be adsorbed within 100 min, and the adsorption kinetics of MgO@ACFF can be fitted in a pseudo-second-order model. The adsorption isotherm of MgO@ACFF fitted well in the Freundlich model. Additionally, the fluoride adsorption capacity of MgO@ACFF is larger than 212.2 mg/g at neutral. In a wide pH range of 2-10, the MgO@ACFF can efficiently remove fluoride from water, which is meaningful for practical usage. The effect of co-existing anions on the fluoride removal efficiency of the MgO@ACFF also has been studied. Furthermore, the fluoride adsorption mechanism of the MgO@ACFF was studied by the FTIR and XPS, and the results reveal a hydroxyl and carbonate co-exchange mechanism. The column test of the MgO@ACFF also has been investigated; 505-bed volumes of 5 mg/L fluoride solution can be treated with effluent under 1.0 mg/L. It is believed that the MgO@ACFF is a potential candidate for a fluoride adsorbent.

Role of tailing colloid from vanadium-titanium magnetite in the adsorption and cotransport with vanadium

The geochemical cycling of vanadium (V) in mining areas has attracted much attention. However, little knowledge was about the effects of tailing colloids on the fate and transport of vanadium in tailing reservoirs which was ignored before. This study investigated the interactions of tailing colloids from vanadium-titanium magnetite with vanadium. Colloid characterization, tailing leaching, adsorption, and column experiments of single and cotransport of tailing colloid with V were conducted. Results show that 98.08% V in the vanadium-titanium magnetite tailing was in the residual state with limited leachable V under various conditions. The adsorption of V to the tailing colloid was via electrostatic attraction and surface complexation on the heterogeneously distributed sorption sites on the colloid surface. The adsorption control step was the diffusion of V into the tailing colloid pores. The increase in pH and the decrease in ionic strength (IS) promoted the single transport of tailing colloid and V in quartz sand columns. In cotransport scenarios, V promoted the transport of tailing colloids via the surface coating effect. In contrast, the transport of V was retarded by the adsorbed tailing colloid on the quartz sand surface. The pre-adsorbed V in the column enhanced the subsequent transport of tailing colloids by electrical repulsion, while the pre-adsorbed tailing colloids facilitated the subsequent transport of V via cotransport of the released colloids with V. The high mobility of the tailing colloid and V and their cotransport in the porous media highly demonstrated the potential V pollution pathways that need to be taken into account.

One-pot solution combustion synthesis of porous spherical-shaped magnesium zinc binary oxide for efficient fluoride removal and photocatalytic degradation of methylene blue and Congo red dye

A novel porous spherical-shaped magnesium zinc binary oxide (MZO) was successfully prepared for the first time using a chemical process for fluoride removal and photocatalytic methylene blue (MB) and Congo red (CR) dye degradation. XRD, FESEM, and TEM were studied for phase formation, topographic, crystallographic, and detailed structural information. The surface charge and optical properties of the adsorbent were studied by zeta potential and photoluminescence spectra. The synthesized nano-adsorbents showed high fluoride removal capacity (43.10 mg/g) and photocatalytic activity with a degradation efficiency of 97.83% and 78.40% for MB and CR, respectively. The adsorption was strongly pH-dependent and worked well in the range 6-9. The kinetic studies were performed for both fluoride removal and dye degradation and were found to follow pseudo-second-order and first-order rate law, respectively. The samples were found to be extremely reusable and selective for fluoride removal in presence of co-ions such as NO₃^-, SO₄^2-, and Cl^-. The basic fluoride adsorption process of the samples can be related to ion exchange and electrostatic interactions, according to XPS and FTIR data. The detailed mechanistic study of photocatalytic dye degradation showed that the reaction occurred via OH radicals. Thus, MZO could be considered an effective and quick adsorbent for water purification in fluoride-containing groundwater and industrial dye wastewater.

Synergistic Fluoride Adsorption by Composite Adsorbents Synthesized From Different Types of Materials—A Review

The reduction of fluoride concentrations in water is one of many concerns. Adsorption is the most widely used technology for fluoride removal and the center to development of adsorption technology is the improvement of adsorbents. This review classifies the typical fluoride removal adsorbents into four types: metal oxides/hydroxides, biopolymers, carbon-based, and other adsorbents. The exploitation of new materials and the synthesis of composite materials are two ways of developing new adsorbents. In comparison to the discovery of novel adsorbents for fluoride adsorption, research into the composite synthesis of different types of conventional adsorbents has proliferated in recent years. The traditional adsorbents used the earliest, metal oxides, can act as active centers in a wide range of applications for modifying and compounding with other types of adsorbents. This study emphasizes reviewing the research on fluoride removal by composite adsorbents synthesized from different types of metal-modified materials. Seven factors were compared in terms of material characterization, initial fluoride concentration, adsorbent dose, pH, temperature, reaction time, and maximum adsorption capacity. The modification of composite adsorbents is facile and the synergistic effect of the different types of adsorbents significantly improves fluoride adsorption capacity. Metal composite adsorbents are synthesized by facile coprecipitation, hydrothermal, or impregnation modification methods. The adsorption mechanisms involve electrostatic attraction, ion exchange, complexation, and hydrogen bonding. The fluoride adsorption capacity of composite adsorbents has generally improved, indicating that most modifications are successful and have application prospects. However, to achieve significant breakthroughs in practical applications, numerous issues such as cost, separation/regeneration performance, and safety still need to be considered.

Optimization of fluoride removal by Al doped ZnO nanoparticles using response surface methodology from groundwater

The current novel work presents the optimization of factors affecting defluoridation by Al doped ZnO nanoparticles using response surface methodology (RSM). Al doped ZnO nanoparticles were synthesized by the sol-gel method and validated by FTIR, XRD, TEM/EDS, TGA, BET, and particle size analysis. Moreover, a central composite design (CCD) was developed for the experimental study to know the interaction between Al doped ZnO adsorbent dosage, initial concentration of fluoride, and contact time on fluoride removal efficiency (response) and optimization of the process. Analysis of variance (ANOVA) was achieved to discover the importance of the individual and the effect of variables on the response. The model predicted that the response significantly correlated with the experimental response (R² = 0.97). Among the factors, the effect of adsorbent dose and contact time was considered to have more influence on the response than the concentration. The optimized process parameters by RSM presented the adsorbent dosage: 0.005 g, initial concentration of fluoride: 1.5 g/L, and contact time: 5 min, respectively. Kinetic, isotherm, and thermodynamic studies were also investigated. The co-existing ions were also studied. These results demonstrated that Al doped ZnO could be a promising adsorbent for effective defluoridation for water.

Study on antibacterial and fluoride-releasing properties of a novel composite resin with fluorine-doped nano-zirconia fillers

OBJECTIVE

A novel composite resin (CR) with fluorine-doped nano-zirconia (F-ZrO₂) fillers was developed as an antibacterial restorative material. This article described the synthesis and investigated the fluoride release, antibacterial property and cytotoxicity of the novel CR.

METHODS

F-ZrO₂ powders with different fluorine contents (0% F-ZrO₂, 5% F-ZrO₂, 10% F-ZrO₂ or 20% F-ZrO₂) were synthesized by chemical precipitation method and characterized by XRD, SEM and TEM-EDS. The content and release of fluoride were also determined. 20% F-ZrO₂ powers were selected to develop the novel CRs (FZ-25, FZ-50, and FZ-75). The fluoride release from the novel CRs during 28 days was recorded. The antibacterial property of the novel CRs was investigated with direct contact test (DCT) and metabolic activity test (CCK8). The cytotoxicity of the CRs was also evaluated here.

RESULTS

F-ZrO₂ powders with different fluorine contents were obtained. The fluoride release increased with increasing of the fluoride content. Through the antibacterial performance evaluation, 20% F-ZrO₂ powders, which exhibiting the best antibacterial property, were selected as the fillers for preparing the novel CR. The novel CR with F-ZrO₂ fillers exhibited an effective antibacterial effect. Compared with the control group, the antibacterial rates of FZ-25, FZ-50 and FZ-75 were 51.65%, 54.14% and 66.80% (p<0.05), respectively. No obvious cytotoxicity of the novel CR was detected in this study.

CLINICAL SIGNIFICANCE

The novel CR with continuous fluoride release and proper antibacterial property is expected to be used as an antibacterial material to reduce secondary caries.

A series of novel carbohydrate-based carbon adsorbents were synthesized by self-propagating combustion for tetracycline removal

Herein, a series of novel adsorbents derived from glucose, maltose, and starch zinc oxide (ZnO) loaded carbohydrate-based carbon materials (Zn-Cs) were synthesized by a fast and efficient self-propagating combustion synthesis method (SCS). The experimental results show that Zn-Cs exhibits excellent adsorption performance (>375 mg/g) to tetracycline, and the pseudo-second-order model and Freundlich model can better describe the adsorption data. The adsorption capacities of Zn-Cs were over 300 mg/g throughout the wide pH range (6-9), while various coexisting ions in the concentration range of 0-10 mg/L and the presence of humic acid had nearly no impact on the adsorption of tetracycline. Moreover, the adsorption experiment of simulated hospital wastewater shows that the adsorption capacity of Zn-Cs for tetracycline exceeds 185 mg/g. The adsorption mechanism of tetracycline are H-bond, complexation, and conjugation effect. This work provides an efficient, excellent versatility and time-saving strategy for preparing high-performance carbohydrate-based carbon materials for adsorbents.

Fabrication of Manganese-Supported Activated Alumina Adsorbent for Defluoridation of Water: A Kinetics and Thermodynamics Study

Fluoride pollution frequently occurs in many underground drinking water sources due to discrepancies in the geological environment. To address this problem, a manganese-supported activated alumina (MnOOH-supported AA) adsorbent was proposed in the present study. The adsorbent was prepared with an impregnation method, then the morphology and microstructure were systematically characterized. Further, the adsorption kinetics and thermodynamics were systematically explored through static experiments to confirm the adsorption mechanism. The results showed that MnOOH was successfully loaded on the activated alumina (AA), and irregular and convex spinous structures were formed on the surface of particles. Compared with the AA, MnOOH-supported AA exhibited a significantly higher defluoridation rate, which has been doubled. The kinetic behavior of fluoride adsorption on MnOOH-supported AA was governed by the quasi-second-order kinetics model with regression coefficients of 0.9862, 0.9978 and 0.9956, respectively. The adsorption rate was mainly ascribed to the intra-particle diffusion. Additionally, the Freundlich isotherm equation fitted the adsorption thermodynamic process reasonably well compared with the Langmuir adsorption model. Specifically, the correlation coefficients were 0.9614, 0.9383 and 0.9852 at 25 °C, 35 °C and 45 °C, respectively. The adsorption–desorption isotherm plot was similar to the Type V isotherm. The whole fluoride adsorption was a spontaneous endothermic reaction, and controlled by chemical adsorption. These results demonstrated that MnOOH-supported AA as an alternative to the conventional AA showed promising potential for defluoridation in drinking water treatment.

The adsorption of fluoride from aqueous solutions by Fe, Mn, and Fe/Mn modified natural clinoptilolite and optimization using response surface methodology

Natural clinoptilolite was modified using iron, manganese, or iron-manganese for adsorption of fluoride from aqueous solutions. Natural and modified clinoptilolite samples were characterized by X-ray fluorescence spectrometry, scanning electron microscope, X-ray diffraction, and Brunauer-Emmett-Teller. For all modified clinoptilolite samples, the time required to reach equilibrium was determined as 5 hr. The effects of adsorbent dose, pH, and initial fluoride concentration for fluoride adsorption were determined using the Box-Behnken Design. Maximum fluoride removal efficiency was 80.23% at the solution pH of 11, iron-modified clinoptilolite amount of 1.08 g/50 ml and at the initial fluoride concentration of 2 mg/L. Fluoride adsorption on iron-modified clinoptilolite showed good compatibility with the Freundlich isotherm and the pseudo-second-order kinetic model. The adsorption capacity of iron-modified clinoptilolite was found to be 1.72 mg/g for the initial fluoride concentration of 50 mg/L. This study has shown that BBD is an effective and dependable method in determining the optimum conditions for fluoride adsorption. PRACTITIONER POINTS: Response surface methodology is effective in determining the optimum conditions for fluoride adsorption using modified clinoptilolite. Fluoride adsorption on iron-modified clinoptilolite is well described Freundlich isotherm and follows pseudo-second-order kinetic model. Fluoride removal percentage not only depends on the adsorbent dose, but also depends on the initial fluoride concentrations. Regeneration process using acid solution is not very effective for desorption of iron-modified zeolite. The natural clinoptilolite is an effective and economical adsorbent for adsorption of fluoride.

Biomaterial functionalized cerium nanocomposite for removal of fluoride using central composite design optimization study

Excess fluoride concentration in drinking water is a global issue, as this has an adverse effect on human health. Several adsorbents have been synthesized from natural raw material to remove fluoride from water. Reported adsorbents have some problems with the leaching of metal ions, fewer adsorption sites, and low adsorption capacity. Therefore, to address this, an effective biomaterial derived from the Luffa cylindrica (LC), containing many active sites, was integrated with a nano form of cerium oxide to form a robust, biocompatible, highly porous, and reusable LC-Ce adsorbent. This synthesized biosorbent offers better interaction between the active sites of LC-Ce and fluoride, resulting in higher adsorption capacity. Several factors, influence the adsorption process, were studied by a central composite design (CCD) model of statistical analysis. Langmuir's and Freundlich's models well describe the adsorption and kinetics governed by the pseudo-second-order model. The maximum monolayer adsorption capacity was found to be 212 and 52.63 mg/g for LC-Ce and LC, respectively determined by the Langmuir model. Detailed XPS and FTIR analyses revealed the underlying mechanism of fluoride adsorption via ion-exchange, electrostatic interaction, H-bonding, and ion-pair formation. All the results indicate that LC-Ce could serve as a suitable adsorbent for efficient fluoride removal (80-85%).

The adsorption characteristics of fluoride on commercial activated carbon treated with quaternary ammonium salts (Quats)

Commercial activated carbon was treated with six quaternary ammonium salts (Quats), namely, hexyltrimethylammonium (HTMA), octyltrimethylammonium (OTMA), decyltrimethylammonium (DCTMA), dodecyltrimethylammonium (DDTMA), Tetradecyltrimethylammonium (TDTMA), and hexadecyltrimethylammoium (HDTMA) as to enhance the fluoride adsorption capacity. In batch mode experiments, fluoride adsorption onto the Quats-treated activated carbon decreased dramatically with increase in solution pH. Fluoride removal by the Quats-treated activated carbons was closely related to the Quats chain length at less-than critical micelle concentration (CMC). Multi-site adsorption isotherm described fluoride adsorption characteristics well. Results showed that activated carbon treated with DDTMA exhibited the best fluoride adsorption density among all Quats investigated. DDTMA-treated activated carbons exhibited two-fold increase in the fluoride adsorption capacity compared to the untreated activated carbon. Results of regeneration, by alkaline desorption and/or Quats re-loading, showed fluoride-laden activated carbons have high reusability. DDTMA increased the positive surface charge of the activated carbon that enhanced fluoride adsorption. DDTMA-treated activated carbon was promising for fluoride removal from water with much enhanced removal capacity.

Precipitation Methods Using Calcium-Containing Ores for Fluoride Removal in Wastewater

F-containing wastewater does great harm to human health and the ecological environment and thus needs to be treated efficiently. In this paper, the new calcium-containing precipitant calcite and aided precipitant fluorite were adopted to purify F-containing wastewater. Relevant reaction conditions, such as reaction time, oscillation rate, dosage of hydrochloric acid, calcite dosage and the assisting sedimentation performance of fluorite, and action mechanism are analyzed. The experiment showed that the removal rate of fluoride in simulated wastewater reached 96.20%, when the reaction time, the dosage of calcite, the dosage of 5% dilute hydrochloric acid, and the oscillation rate was 30 min, 2 g/L, 21.76 g/L, and 160 r/min, respectively. Moreover, the removal rate of fluoride in the actual F-containing smelting wastewater reaches approximately 95% under the optimum condition of calcite dosage of 12 g/L, reaction time of 30 min, and oscillation rate of 160 r/min. The addition of fluorite significantly improves the sedimentation performance of the reactive precipitates. The experimental results showed that calcite and fluorite can effectively reduce the concentration of fluoride ions in F-containing wastewater and solve the problem of slow sedimentation of reactive precipitates.