Amine-Functionalized Titanosilicates Prepared by the Sol−Gel Process as Adsorbents of the Azo-Dye Orange II

Preparation and potential application of amino-functionalized titanosilicates to removal of Th(IV) in aqueous solutions: optimization using response surface methodology (RSM)

Mesoporous titanosilicates (TiSil) with a size of almost 25 nm were prepared by an alkali-assisted hydro-thermal route, as an choice for developing efficient adsorbents of Th(IV) ions. TiSil were functionalized with the amino functional group (-NH2) from 3-aminopropyltriethoxysilane (APTES) by post-preparation method. The obtained amino-grafted titanosilicates (TiSilNH2) were characterized by Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), X-ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR) techniques. Adsorption of Th(IV) ions on TiSilNH2 was examined in aqueous solution. Response surface methodology (RSM) based on central composite design (CCD) was applied to optimize the four essential process variables namely initial pH and initial concentration of Th(IV) ions of aqueous solution, amount of adsorbent, and adsorption process temperature for the Th(IV) removal. The adequacy of the model was investigated, and it was deemed to be statistically significant. The optimal predicted adsorption capacity of TiSilNH2 for Th(IV) ions was 83.04 mg/g and the actual value was 84.8 mg/g. The equilibrium adsorption data were fitted to Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models. The equi-librium data were best re-presented by Langmuir isotherm model, showing maximum monolayer adsorption capacity of 87.71 mg/g. The thermodynamic parameters indicated that the Th(IV) adsorption on the TiSilNH2 was a spontaneous, and endo-thermic process at the studied temperatures and occurred via physisorption. Adsorbent recovery by using 0.5 M HNO3 solution for adsorbent reuse indicated that the adsorbent was regenerable and could be employed frequently.

Cross-Linked Ionic Liquid Polymer for the Effective Removal of Ionic Dyes from Aqueous Systems: Investigation of Kinetics and Adsorption Isotherms

In the current study, we have synthesized an imidazolium based cross-linked polymer, namely, 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide (poly[veim][Tf2N]-TRIM) using trimethylolpropane trimethacrylate as cross linker, and demonstrated its efficiency for the removal of two extensively used ionic dyes—methylene blue and orange-II—from aqueous systems. The detailed characterization of the synthesized poly[veim][Tf2N]-TRIM was performed with the help of 1H NMR, TGA, FT-IR and FE-SEM analysis. The concentration of dyes in aqueous samples before and after the adsorption process was measured using an UV-vis spectrophotometer. The process parameters were optimised, and highest adsorption was obtained at a solution pH of 7.0, adsorbent dosage of 0.75 g/L, contact time of 7 h and dye concentrations of 100 mg/L and 5.0 mg/L for methylene blue and orange-II, respectively. The adsorption kinetics for orange-II and methylene blue were well described by pseudo-first-order and pseudo−second-order models, respectively. Meanwhile, the process of adsorption was best depicted by Langmuir isotherms for both the dyes. The highest monolayer adsorption capacities for methylene blue and orange-II were found to be 1212 mg/g and 126 mg/g, respectively. Overall, the synthesized cross-linked poly[veim][Tf2N]-TRIM effectively removed the selected ionic dyes from aqueous samples and provided >90% of adsorption efficiency after four cycles of adsorption. A possible adsorption mechanism between the synthesised polymeric adsorbent and proposed dyes is presented. It is further suggested that the proposed ionic liquid polymer adsorbent could effectively remove other ionic dyes and pollutants from contaminated aqueous systems.

A comprehensive review of anionic azo dyes adsorption on surface-functionalised silicas

Surface -functionalised silica networks are advanced adsorbents. They have been given much attention for treating wastewater using the adsorption technique due to the silanol reactivity, resulting in strong binding affinities towards many pollutants. This review discusses the removal of anionic azo dyes utilising various functional groups such as amines, surfactants, polymers, macrocyclic, and other chelating groups functionalised on silica's surface. This review also reveals the steadily increasing interest in surface-functionalised silicas as adsorbents, emphasising the scholarly advancements in this field as a platform for future research. For that, adsorption capacities with different experimental conditions have been compared. The possible adsorption mechanisms, rate-limiting step, and factors affecting the anionic azo dye adsorption process have been comprehensively discussed. This review discloses that adsorbent characteristics such as porosity and functional groups, besides structural properties of an anionic azo dye, significantly affect adsorption. The adsorption process followed the Langmuir isotherm and pseudo-second-order models, with a predominantly spontaneous and endothermic nature. Multiple interactions, including electrostatic interaction, π-π interactions, and hydrogen bonding, are observed between dyes and functionalised silicas, indicating the adsorption process's complexity. Regeneration and cost-economic analysis are also presented to provide a roadmap for sustainable improvements. Chemical and biological regeneration techniques restore > 80% of the spent functionalised silicas. There is a significant opportunity to improve their efficiencies and regenerability, resulting in surface-functionalised silicas being used commercially instead of only in the laboratory. Finally, future research has been proposed by identifying current research gaps, particularly concerning the application of functionalised silicas in wastewater treatment.

Multienzymes activity of metals and metal oxide nanomaterials: applications from biotechnology to medicine and environmental engineering

With the rapid advancement and progress of nanotechnology, nanomaterials with enzyme-like catalytic activity have fascinated the remarkable attention of researchers, due to their low cost, high operational stability, adjustable catalytic activity, and ease of recycling and reuse. Nanozymes can catalyze the same reactions as performed by enzymes in nature. In contrast the intrinsic shortcomings of natural enzymes such as high manufacturing cost, low operational stability, production complexity, harsh catalytic conditions and difficulties of recycling, did not limit their wide applications. The broad interest in enzymatic nanomaterial relies on their outstanding properties such as stability, high activity, and rigidity to harsh environments, long-term storage and easy preparation, which make them a convenient substitute instead of the native enzyme. These abilities make the nanozymes suitable for multiple applications in sensing and imaging, tissue engineering, environmental protection, satisfactory tumor diagnostic and therapeutic, because of distinguished properties compared with other artificial enzymes such as high biocompatibility, low toxicity, size dependent catalytic activities, large surface area for further bioconjugation or modification and also smart response to external stimuli. This review summarizes and highlights latest progress in applications of metal and metal oxide nanomaterials with enzyme/multienzyme mimicking activities. We cover the applications of sensing, cancer therapy, water treatment and anti-bacterial efficacy. We also put forward the current challenges and prospects in this research area, hoping to extension of this emerging field. In addition to therapeutic potential of nanozymes for disease prevention, their practical effects in diagnostics, to monitor the presence of SARS-CoV-2 and related biomarkers for future pandemics will be predicted.

Simultaneous Elimination of Dyes and Antibiotic with a Hydrothermally Generated NiAlTi Layered Double Hydroxide Adsorbent

In this study, a hydrothermal route was used to design a novel NiAlTi layered double hydroxide. The material so-obtained was characterized using various physiochemical techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis for structural analysis, scanning electron microscopy, transmission electron microscopy for morphological analysis, and so on. The material so-obtained was further applied for wastewater remediation and was found to be an efficient, cost-effective, and reusable adsorbent. Organic contaminants such as dyes and antibiotics were used as pollutants to carry out the removal study. NiAlTi LDH was found to be an excellent adsorbent for the removal of anionic dyes and antibiotics. Excellent performance was shown by NiAlTi LDH at a broad pH range from 4 to 10 for anionic dyes (orange II and methyl orange), but tetracycline removal was predominantly maximum at pH = 9. Further, the kinetic studies also revealed that the adsorption process of both organic contaminants obeyed a pseudo-second-order model. In addition, the Langmuir isotherm adsorption model fitted the experimental results for both types of pollutants very well. The attained maximum adsorption capacity was superb for both organic dyes and antibiotics (1250 mg/g for MO, 2000 mg/g for OII, and 238.09 mg/g for TC). NiAlTi LDH was also capable of simultaneous elimination from a mixture of antibiotics and dyes. Further, NiAlTi LDH also showed outstanding stability and reusability, making it one of the most promising materials for large-scale wastewater remediation contaminated by dyes and antibiotics.

Polyethylene Glycol-Modified Layered Double Hydroxides: Synthesis, Characterization, and Study on Adsorption Characteristics for Removal of Acid Orange II from Aqueous Solution

The present study aimed to improve the adsorption characteristics of the pristine layered double hydroxide (LDH) by physicochemical modification using polyethylene glycol (PEG₄₀₀), a nontoxic hydrophilic polymer. With this objective, LDH was synthesized and modified with different concentrations of PEG₄₀₀. The PEG-modified LDHs (LDH/PEGs) were characterized using X-ray diffraction, thermogravimetric analysis, Brunauer-Emmett-Teller surface area and porosity measurement, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and zeta potential measurements. The adsorption properties of the pristine LDH (PLDH) and the LDH/PEGs were studied for the removal of Acid Orange II from water, and the results were compared. The PLDH treated with 15% PEG solution showed ∼30% increase in adsorption capacity as compared to the PLDH. The adsorption isotherm data were analyzed using Langmuir, Freundlich, and Temkin isotherm models. The values of thermodynamic parameters such as ΔS and ΔH showed the spontaneous and endothermic nature of the adsorption process. The adsorption kinetics data for both PLDH and the LDH/PEG adsorbents presented a good fit to the pseudo-second-order kinetic model.

Synthesis of hydrophobic and hydrophilic TiO2 nanofluids for transformable surface wettability and photoactive coating

TiO₂ nanofluids, possessing a highly dispersed TiO₂ core and an organic shell, have been used for the fabrication of coatings with transformable wettability.

Removal of binary dyes mixtures with opposite and similar charges by adsorption, coagulation/flocculation and catalytic oxidation in the presence of CeO2/H2O2 Fenton-like system

In this study, the removal of binary mixtures of dyes with similar (Orange II/Acid Green 25) or opposite charges (Orange II/Malachite Green) was investigated either by simple adsorption on ceria or by the heterogeneous Fenton reaction in presence of H₂O₂. First, the CeO₂ nanocatalyst with high specific surface area (269 m²/g) and small crystal size (5 nm) was characterized using XRD, Raman spectroscopy and N₂ physisorption at 77 K. The adsorption of single dyes was studied either from thermodynamic and kinetic viewpoints. It is shown that the adsorption of dyes on ceria surface is highly pH-dependent and followed a pseudo-second order kinetic model. Adsorption isotherms fit well the Langmuir model with a complete monolayer coverage and higher affinity towards Orange II at pH 3, compared to other dyes. For the (Orange II/Acid Green 25) mixture, both the amounts of dyes adsorbed on ceria surface and discoloration rates measured from Fenton experiments were decreased by comparison with single dyes. This is due to the adsorption competition existing onto the same surface Ce^x+ sites and the reaction competition with hydroxyl radicals, respectively. The behavior of the (Orange II/Malachite Green) mixture is markedly different. Dyes with opposite charges undergo paired adsorption on ceria as well as homogeneous and heterogeneous coagulation/flocculation processes, but can also be removed by heterogeneous Fenton process.

Cr-Doped ZnO Nanoparticles: Synthesis, Characterization, Adsorption Property, and Recyclability

In this paper, a mild solvothermal method has been employed to successfully synthesize a series of Cr-doped ZnO nanoparticles (NPs) with different Cr(3+) contents, which is a kind of novel and high-efficiency absorbent for the removal of acid dye methyl orange (MO) from aqueous solution. The as-prepared products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Brunauer, Emmet, and Teller (BET), and Zeta potential measurements. In accordance with the adsorption capacity of the products, the obtained optimal Cr/Zn molar ratio is 6%. The adsorption process of MO on Cr-doped ZnO was investigated by kinetics, thermodynamics, and isotherm technologies, which, respectively, indicated that the adsorption was fast (adsorption reached equilibrium in 2 h) and followed a pseudo-second-order model, that the adsorption process was spontaneous and endothermic, and that it agreed well with the Langmuir isotherm with a maximum adsorption capacity of 310.56 mg g(-1). Moreover, a reasonable mechanism was proposed to elucidate the reasons for their adsorption behavior. In addition, a simple and low-cost chemical method was developed to separate and recycle ZnO and MO from the used adsorbent, effectively avoiding the secondary pollution. This work can not only describe efficient experimental approaches for obtaining novel adsorbents and recycling them but also offer valuable clues for the preparation and property study of other semiconductor adsorbents.

Adsorption of Azo-Dye Orange II from Aqueous Solutions Using a Metal-Organic Framework Material: Iron- Benzenetricarboxylate

A Metal-Organic Framework (MOF), iron-benzenetricarboxylate (Fe(BTC)), has been studied for the adsorptive removal of azo-dye Orange II from aqueous solutions, where the effect of various parameters was tested and isotherm and kinetic models were suggested. The adsorption capacities of Fe(BTC) were much higher than those of an activated carbon. The experimental data can be best described by the Langmuir isotherm model (R² > 0.997) and revealed the ability of Fe(BTC) to adsorb 435 mg of Orange II per gram of adsorbent at the optimal conditions. The kinetics of Orange II adsorption followed a pseudo-second-order kinetic model, indicating the coexistence of physisorption and chemisorption, with intra-particle diffusion being the rate controlling step. The thermodynamic study revealed that the adsorption of Orange II was feasible, spontaneous and exothermic process (−25.53 kJ·mol⁻¹). The high recovery of the dye showed that Fe(BTC) can be employed as an effective and reusable adsorbent for the removal of Orange II from aqueous solutions and showed the economic interest of this adsorbent material for environmental purposes.

Preparation, characterization and application of magnetic Fe3O4-CS for the adsorption of orange I from aqueous solutions

Fe₃O₄ (Fe₃O₄-CS) coated with magnetic chitosan was prepared as an adsorbent for the removal of Orange I from aqueous solutions and characterized by FTIR, XRD, SEM, TEM and TGA measurements. The effects of pH, initial concentration and contact time on the adsorption of Orange I from aqueous solutions were investigated. The decoloration rate was higher than 94% in the initial concentration range of 50–150 mg L⁻¹ at pH 2.0. The maximum adsorption amount was 183.2 mg g⁻¹ and was obtained at an initial concentration of 400 mg L⁻¹ at pH 2.0. The adsorption equilibrium was reached in 30 minutes, demonstrating that the obtained adsorbent has the potential for practical application. The equilibrium adsorption isotherm was analyzed by the Freundlich and Langmuir models, and the adsorption kinetics were analyzed by the pseudo-first-order and pseudo-second-order kinetic models. The higher linear correlation coefficients showed that the Langmuir model (R² = 0.9995) and pseudo-second-order model (R² = 0.9561) offered the better fits.