Experimental and modeling studies for adsorbing different species of fluoride using lanthanum-aluminum perovskite

The function of doping nitrogen on removing fluoride with decomposing La-MOF-NH2: Density functional theory calculation and experiments

Fluoride is an important pollutant in wastewater, and adsorption is an effective way to remove fluoride. Because nitrogen plays an important role in adsorbent materials, computational models were developed to understand the changes in work function resulting from nitrogen doping. La-N-C-800°C, was prepared by pyrolyzing La-MOF-NH2 to verify the influence on the performance of removing fluoride by electrosorption. Material and electrochemical performance tests were performed to characterize La-N-C-800°C. Adsorption kinetics, adsorption thermodynamics, initial concentrations, pH, and ions competition were investigated using La-N-C-800°C for fluoride removal. In addition, density functional theory was applied to evaluate the function of nitrogen. When nitrogen atoms were added, the density of states, partial density of states, populations, and different orbits of charge were calculated to discover deep changes. Nitrogen strengthened the carbon structure and La2O3 structure to remove fluoride. In addition, nitrogen can also act as an adsorption site in the carbon structure. These results provide design ideas for improving the performance of adsorbent materials by doping elements.

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.

Preparation of aluminium-hydroxide-modified diatomite and its fluoride adsorption mechanism

As the current excessive accumulation of fluoride (F^-) in the environment can be hazardous to human health, it is essential to remove fluoride from wastewater. In this study, diatomite (DA) was used as a raw material and modified using aluminum hydroxide (Al-DA) for use in the adsorption of F^- from water bodies. SEM, EDS, XRD, FTIR, and Zeta potential characterization analyses were carried out; adsorption tests and kinetic fitting were performed, and the effects of pH, dosing quantity, and presence of interfering ions on the adsorption of F^- by the materials were investigated. The results show that the Freundlich model effectively describes the adsorption process of F^- on DA, which therefore involves adsorption-complexation interactions; however, the Langmuir model effectively describes the adsorption process of F^- on Al-DA, corresponding to unimolecular layer adsorption mainly via ion-exchange interactions, that is, adsorption is dominated by chemisorption. Aluminum hydroxide was shown to be the main species involved in F^- adsorption. The efficiency of F^- removal by DA and Al-DA was over 91% and 97% for 2 h, and the adsorption kinetics were effectively fit by the quasi-secondary model, suggesting that chemical interactions between the absorbents and F^- control the adsorption process. The adsorption of F^- was highly dependent on the pH of the system, and the maximum adsorption performance was obtained at pH 6 and 4. The optimal dosage of DA and Al-DA was 4 g/L. Even in the presence of interfering ions, the removal of F^- on Al-DA reached 89%, showing good selectivity. XRD and FTIR studies showed that the mechanism of F^- adsorption on Al-DA involved ion exchange and the formation of F-Al bonds.

Research progresses on the application of perovskite in adsorption and photocatalytic removal of water pollutants

The problem of global water pollution and scarcity of water resources is becoming increasingly serious. Multifunctional perovskites can well drive adsorption and photocatalytic reactions to remove water pollutants. There are many advantages of perovskites, such as abundant oxygen vacancies, easily tunable structural morphology, stable crystal state, highly active metal sites, and a wide photo response range. However, there are few reviews on the simultaneous application of perovskite to adsorption and photocatalytic removal of water pollutants. Thus, this paper discusses the preparation methods of perovskite, the factors affecting the adsorption of water environmental pollutants by perovskite, and the factors affecting perovskite photocatalytic water pollutants. The particle size, specific surface area, oxygen vacancies, electron-hole trapping agents, potentials of the valence band, and conduction band in perovskites are significant influencing factors for adsorption and photocatalysis. Strategies for improving the performance of perovskites in the fields of adsorption and photocatalysis are discussed. The adsorption behaviors and catalytic mechanisms are also investigated, including adsorption kinetics and thermodynamics, electrostatic interaction, ion exchange, chemical bonding, and photocatalytic mechanism. It summarizes the removal of water pollutants by using perovskites. It provides the design of perovskites as high-efficiency adsorbents and catalysts for developing new technologies.

Fluoride remediation from on-site wastewater using optimized bauxite nanocomposite (Bx-Ce-La@500): Synthesis maximization, and mechanism of F─ removal

Bauxite is a widely available Al-O-rich mineral with great potential for abating fluoride. However, low adsorption capacity, a narrow workable pH range, and a lack of clarity on the best removal mechanism hinder its application. In this work, a highly efficient bauxite nanocomposite (Bx-Ce-La@500) was synthesized via doping and pyrolysis, and its fluoride adsorption in industrial wastewater was examined. Doping Ce/La synergistically improved the fluoride adsorption affinity of the composite (from pH_PZC 8.0 ~ 10.0) and enhanced the •OH. The materials were characterized by SEM-EDS, BET, XRD, and TGA while XPS, FTIR, and DFT were used to investigate the mechanism of fluoride sorption. Results show that Bx-Ce-La@ 500 has a positive zeta potential of 26.3-23.1 mV from pH 1~ 10. The Langmuir model was the best fit with a maximum adsorption capacity of 88.13 mg/g and removal efficiency up to 100% in 50 ppm F^- solution. The high F^- removal was attributed to the enhanced surface affinity and the formation of adequate •OH on the material. Except for carbonate and phosphate ions, other ions exhibited negligible effects and the selective removal of F^- in real wastewater was high. The main mechanism of adsorption was the ligand/ion exchange and electrostatic attraction.

A Literature Review of Modelling and Experimental Studies of Water Treatment by Adsorption Processes on Nanomaterials

A significant growth in the future demand for water resources is expected. Hence researchers have focused on finding new technologies to develop water filtration systems by using experimental and simulation methods. These developments were mainly on membrane-based separation technology, and photocatalytic degradation of organic pollutants which play an important role in wastewater treatment by means of adsorption technology. In this work, we provide valuable critical review of the latest experimental and simulation methods on wastewater treatment by adsorption on nanomaterials for the removal of pollutants. First, we review the wastewater treatment processes that were carried out using membranes and nanoparticles. These processes are highlighted and discussed in detail according to the rate of pollutant expulsion, the adsorption capacity, and the effect of adsorption on nanoscale surfaces. Then we review the role of the adsorption process in the photocatalytic degradation of pollutants in wastewater. We summarise the comparison based on decomposition ratios and degradation efficiency of pollutants. Therefore, the present article gives an evidence-based review of the rapid development of experimental and theoretical studies on wastewater treatment by adsorption processes. Lastly, the future direction of adsorption methods on water filtration processes is indicated.

Antimicrobial nanocomposite adsorbent based on poly(meta-phenylenediamine) for remediation of lead (II) from water medium

In this study, poly(m-phenylenediamine)@ZnO (PmPDA@ZnO) nanocomposite was fabricated by in-situ chemical oxidative polymerization for the effective lead(II) removal from aqueous solutions. PmPDA@ZnO was characterized by several instrumental methods like FTIR, XRD, EDX, TGA, FESEM, TEM, zeta potential, and BET. The TEM images showed a core–shell-like structure for the PmPDA@ZnO nanocomposite. TGA results showed that the thermal stability of the PmPDA@ZnO nanocomposite was higher than the PmPDA. The maximum adsorption of lead (II) onto PmPDA@ZnO nanocomposite was obtained at pH 6, adsorbent dosage 60 mg, lead(II) ion concentration 90 mg/L, and agitation time 90 min. Langmuir and Freundlich's isotherm models were evaluated to simulate the lead(II) sorption via empirical data. Langmuir's model was in good agreement with empirical data with a maximum adsorption capacity (Q_max) of 77.51 mg/g. The kinetic data adsorption fitted best the pseudo-second-order model. The values of thermodynamic parameters of ΔS° and ΔH° were obtained 0.272 J/mol K, and 71.35 kJ/mol, respectively. The spontaneous and endothermic behavior of the adsorption process was confirmed by the negative and positive response of ΔG° and ΔH°, respectively. Moreover, the addition of coexisting cations e.g. cobalt (II), nickel (II), calcium (II), and copper (II) had no significant effect on the removal efficiency of lead(II). Adsorption–desorption studies showed that the PmPDA@ZnO nanocomposite can be remarkably regenerated and reused after three sequential runs without a significant decline in its adsorption performance. The antimicrobial activities of PmPDA@ZnO nanocomposite were evaluated against Escherichia coli and Staphylococcus aureus bacteria species. These results confirmed that the PmPDA@ZnO nanocomposite could be a good candidate for water decontamination.

Highly efficient fluoride removal from water using 2D metal-organic frameworks MIL-53(Al) with rich Al and O adsorptive centers

In this study, metal-organic framework MIL-53(Al) was synthesized and studied to understand the different mechanisms between normal MIL-53(Al) and 2D metal-organic framework MIL-53(Al) for removing fluoride. Comparatively, the 2D MIL-53(Al) had two-dimensional linear morphology rather than block shape, indicating more expose adsorptive sites than normal MIL-53(Al). The batch adsorption experiments were applied to investigate the performance of 2D MIL-53(Al), including pH, adsorption kinetics, and thermodynamics. The 2D MIL-53(Al) (75.50 mg/g) showed better adsorption capacity than normal MIL-53(Al) (35.63 mg/g). The adsorption process of 2D MIL-53(Al) followed the pseudo-first-order model and Langmuir model. The adsorption mechanism of this material was further studied by using experimental characterization and density functional theory calculations in detail. The main adsorptive sites were Al and O in the 2D MIL-53(Al), and the relationship between fluoride binding with Al and O was HF₂ ^- > HF > F^-. The species of fluoride were HF₂ ^-, HF, F at different pH and concentrations. Hence, this study provides a significant way on the application of two-dimensional materials for removing fluoride.

Nanomaterials in Water Applications: Adsorbing Materials for Fluoride Removal

Fluoride is an important pollutant in many countries, such as China, India, Australia, the United States, Ethiopia, etc [...].

Removal of fluoride from industrial wastewater by using different adsorbents: A review

Many industries such as iron and steel metallurgy, copper and zinc smelting, the battery industry, and cement manufacturing industries discharge high concentrations of fluoride-containing wastewater into the environment. Subsequently, the discharge of high fluoride effluent serves as a threat to human life as well as the ecological ability to sustain life. This article analyses the advantages and drawbacks of some fluoride remediation technologies such as precipitation and flocculation, membrane technology, ion exchange technology, and adsorption technology. Among them, adsorption technology is considered the obvious choice and the best applicable technology. As such, several adsorbents with high fluoride adsorption capacity such as modified alumina, metal oxides, biomass, carbon-based materials, metal-organic frameworks, and other adsorption materials including their characteristics have been comprehensively summarized. Additionally, different adsorption conditions of the various adsorbents, such as pH, temperature, initial fluoride concentration, and contact time have been discussed in detail. The study found out that the composite synergy between different materials, morphological and structural control, and the strengthening of their functional groups can effectively improve the ability of the adsorbents for removing fluoride. This study has prospected the direction of various adsorbents for removing fluoride in wastewater, which would serve as guiding significance for future research in the field.