Possible adsorption mechanisms of the removal of tetracycline from water by La-doped Zn-Fe-layered double hydroxide

All-in-one spot test method for tetracycline using molecularly imprinted polymer-coated paper integrated into a portable 3D printed platform with smartphone-based fluorescent detection

A molecularly imprinted polymer (MIP) has been synthetized, characterized, impregnated on paper, and integrated into a 3D printed platform with smartphone-based fluorescent detection for the determination of tetracycline in water samples. The MIP synthesis was performed by precipitation polymerization, which was subsequently deposited onto a glass microfiber paper. The synthesized polymer and the MIP@paper have been characterized by FTIR spectroscopy, scanning electron microscopy, and EDS spectroscopy. Afterward, a 3D printed detection platform that houses monochromatic LED strips as radiation source and a smartphone as detector have been used for determination of tetracycline. Digital image processing was based on the RGB colour model using image J software and the red intensity channel was used as analytical signal due to its higher sensitivity. Several factors that affect the adsorption capacity and fluorescent detection have been optimized. Under optimum conditions, detection limit of 0.04 mg L-1 and good linearity up 5 mg L-1 (r = 0.998), were achieved. The intra- and inter-day precision of 4.9 and 7.2 %, respectively, expressed as relative standard deviation (%RSD) were obtained, showing the good precision of the proposed methodology. Satisfactory recoveries between 87 and 98 % were obtained spiking real water sample matrices at different concentrations (0.1-0.3 mg L-1). The portable 3D platform with smartphone-based fluorescent detection exploiting all-in-one spot test method for tetracycline using MIP@paper was evaluated with AGREE and GAPI metrics, evidencing its environmentally friendly approach. Furthermore, the BAGI tool demonstrated the practicality of the method, in terms of functionality and applicability compared to previous HPLC and spectrofluorometric methods.

Actinobacterium-Mediated Green Synthesis of CuO/Zn-Al LDH Nanocomposite Using Micromonospora sp. ISP-2 27: A Synergistic Study that Enhances Antimicrobial Activity

Bacterial resistance to conventional antibiotics has created an urgent need to develop enhanced alternatives. Nanocomposites combined with promising antibacterial nanomaterials can show improved antimicrobial activity compared to that of their components. In this work, green synthesized CuO nanoparticles (NPs) supported on an anionic clay with a hydrotalcite-like structure such as Zn-Al layered double hydroxide (LDH) nanocomposite were investigated as antimicrobial agents. This nanocomposite was synthesized using Micromonospora sp. ISP-2 27 cell-free supernatant to form CuO NPs on the surface of previously synthesized LDH. The prepared samples were characterized using UV-Vis spectrophotometry, XRD, FTIR, Field emission scanning electron microscopy with EDX, zeta potential, and hydrodynamic particle size. UV-vis spectral analysis of the biosynthesized CuO NPs revealed a maximum peak at 300 nm, indicating their successful synthesis. The synthesized CuO NPs had a flower-like morphology with a size range of 43-78 nm, while the LDH support had a typical hexagonal layered structure. The zeta potentials of the CuO NPs, Zn-Al LDH, and CuO NPs/LDH nanocomposite were -21.4, 22.3, and 30.8 mV, respectively, while the average hydrodynamic sizes were 687, 735, and 528 nm, respectively. The antimicrobial activity of the produced samples was tested against several microbes. The results demonstrated that the nanocomposite displayed superior antimicrobial properties compared to those of its components. Among the microbes tested, Listeria monocytogenes ATCC 7644 was more sensitive (30 ± 0.34) to the biosynthesized nanocomposite than to CuO NPs (25 ± 0.05) and Zn-Al LDH (22 ± 0.011). In summary, the use of nanocomposites with superior antimicrobial properties has the potential to offer innovative solutions to the global challenge of antibiotic resistance by providing alternative treatments, reducing the reliance on traditional antibiotics, and contributing to the development of more effective and targeted therapeutic approaches.

Machine learning and statistical physics modeling of tetracycline adsorption using activated carbon derived from Cynometra ramiflora fruit biomass

The current investigation reports the usage of adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN), the two recognized machine learning techniques in modelling tetracycline (TC) adsorption onto Cynometra ramiflora fruit biomass derived activated carbon (AC). Many characterization methods utilized, confirmed the porous structure of synthesized AC. ANN and ANFIS models utilized pH, dose, initial TC concentration, mixing speed, time duration, and temperature as input parameters, whereas TC removal percentage was designated as the output parameter. The optimized configuration for the ANN model was determined as 6-8-1, while the ANFIS model employed trimf input and linear output membership functions. The obtained results showed a strong correlation, indicated by high R2 values (ANNR2: 0.9939 & ANFISR2: 0.9906) and low RMSE values (ANNRMSE: 0.0393 & ANFISRMSE: 0.0503). Apart from traditional isotherms, the dataset was fitted to statistical physics models wherein, the double-layer with a single energy satisfactorily explained the physisorption mechanism of TC adsorption. The sorption energy was 21.06 kJ/mol, and the number of TC moieties bound per site (n) was found to be 0.42, conclusive of parallel binding of TC molecules to the adsorbent surface. The adsorption capacity at saturation (Qsat) was estimated to be 466.86 mg/g - appreciably more than previously reported values. These findings collectively demonstrate that the AC derived from C. ramiflora fruit holds great potential for efficient removal of TC from a given system, and machine learning approaches can effectively model the adsorption processes.

Synthesis and characterization of new composite from modified silica-coated MnFe2O4 nanoparticles for removal of tetracycline from aqueous solution

In this study, a new composite from silica coated MnFe2O4 nanoparticles, diethylenetriamine, 3-chloropropyl trimethoxysilane and Mg-Al Layered Double Hydroxide (Mg-Al LDH/DETA/CPTMS/SCNPs) composite was synthesized. The Mg-Al LDH/DETA/CPTMS/SCNPs composite was examined by Fourier transform infrared spectrometer (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDS), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA) and Vibrating Sample Magnetometry (VSM). The synthesized composite exhibited magnetic property with a saturation magnetization of 0.40 emu g-1. The Mg-Al LDH/DETA/CPTMS/SCNPs composite was utilized as a successful adsorbent for removal of tetracycline from aqueous solutions. The effect of various operation factors such as initial drug concentration, adsorbent dosage, pH and contact time were investigated. The optimized variable conditions such as adsorbent dose of 60 mg L-1, drug concentration of 100 mg L-1, pH = 7 and contact time 30 min were obtained. For describing the adsorption isotherms, the Langmuir, Freundlich and Temkin adsorption models were utilized. The results indicated that the adsorption isotherm is in good agreement with Langmuir model. According to the Langmuir analysis, the maximum adsorption capacity (qm) of the Mg-Al LDH/DETA/CPTMS/SCNPs composite for tetracycline was obtained to be 40.16 mg g-1. The kinetic studies revealed that the adsorption in all cases to be a pseudo second-order process. The negative value of ΔG° and the positive value of ΔH° showed the adsorption process to be spontaneous and endothermic.

Porous Fe-Porphyrin as an Efficient Adsorbent for the Removal of Ciprofloxacin from Water

Antibiotics are widely used in medicine, but they are not fully metabolized in the body and can end up in wastewater. Conventional wastewater treatment methods fail to completely remove antibiotic residues, which can then enter rivers and streams. Adsorption is a promising technique for removing antibiotics from wastewater, even at low concentrations. The successful one-pot synthesis of an adsorbent, iron-containing porphyrin-based porous organic polymer (Fe-POP), was achieved through the reaction of pyrrole groups and terephthalaldehyde in the presence of FeCl3. Characterized by a substantial BET surface area of 597 m2 g-1, Fe-POP was systematically investigated for its adsorption potential in the removal of the antibiotic Ciprofloxacin (CIP) from aqueous solutions. By systematic variation of key parameters, including pH, adsorbent loading, and CIP concentration, the adsorption conditions were optimized. Under the optimal conditions at pH = 3, CIP concentration of 5 ppm, and 25 mg of Fe-POP, the maximum adsorption capacity reached an impressive 263 mg g-1. The robust adsorption behavior was elucidated through the fitting of experimental data to the Langmuir adsorption isotherm (R2 = 0.962) and the pseudo-second-order kinetic model (R2 = 0.999) with lower error values. These models suggested that the adsorption process predominantly involved chemical interactions between CIP molecules and the Fe-POP surface. Fe-POP exhibited a robust structure with a high adsorption capacity, showcasing its efficacy in removing CIP contaminants from water. Therefore, Fe-POP can be considered a valuable adsorbent for water treatment applications, specifically for antibiotic removal.

Carbon supported ternary layered double hydroxide nanocomposite for Fluoxetine removal and subsequent utilization of spent adsorbent as antidepressant

Fluoxetine (FLX) is one of the most persistent pharmaceuticals found in wastewater due to increased use of antidepressant drugs in recent decades. In this study, a nanocomposite of ternary ZnCoAl layered double hydroxide supported on activated carbon (LAC) was used as an adsorbent for FLX in wastewater effluents. The nanocomposite was characterized using Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and surface area analysis (BET). The adsorption investigations showed that the maximum removal capacity was achieved at pH 10, with a 0.1 g/L adsorbent dose, 50 mL volume of solution, and at a temperature of 25 °C. The FLX adsorption process followed the Langmuir-Freundlich model with a maximum adsorption capacity of 450.92 mg/g at FLX concentration of 50 µg/mL. Density functional theory (DFT) computations were used to study the adsorption mechanism of FLX and its protonated species. The safety and toxicity of the nanocomposite formed from the adsorption of FLX onto LAC (FLX-LAC) was investigated in male albino rats. Acute toxicity was evaluated using probit analysis after 2, 6, and 24 h to determine LD50 and LD100 values in a rat model. The FLX-LAC (20 mg/kg) significantly increased and lengthened the sleep time of the rats, which is important, especially with commonly used antidepressants, compared to the pure standard FLX (7 mg/kg), regular thiopental sodium medicine (30 mg/kg), and LAC alone (9 mg/kg). This study demonstrated the safety and longer sleeping duration in insomniac patients after single-dose therapy with FLX-LAC. Selective serotonin reuptake inhibitors (SSRIs) like FLX were found to have decreased side effects and were considered the first-line mood disorder therapies.

Precursor-oriented design of nano-alumina for efficient removal of antibiotics

Rapid and efficient removal of environmental antibiotics is vital to curb bacterial resistance. Through rational precursors-oriented design, we attain the best Al2O3 absorbent by 500 °C calcination of ammonium aluminium carbonate hydroxide (AACH) precursor from NH4HCO3 route (AACH-NH4HCO3-500) for fast and efficient removal of tetracycline (TC) and other antibiotics from environmental waters including high-salinity wastewater. AACH-NH4HCO3-500 (0.25 g·L-1) can remove (69.92 ± 1.78)% of aqueous TC (0.025 g·L-1) within 5 min and (97.62 ± 2.75)% within 2 h, and the adsorption capacity is 444.4 mg·g-1, which is the highest qmax of TC for the 2 h-adsorptions among numerous adsorbents. AACH-NH4HCO3-500 has fine tolerance to the coexisting substances, and can be easily regenerated and reused, and has no harm even discarded. The relations among the synthetic methods, the structural features, and the adsorption functions of Al2O3 are disclosed through a systematic comparison of the commercial Al2O3 and different Al2O3 nanomaterials attained from three precursors produced by five different routes. The reasons behind the exceptional adsorption performance are discussed throughout. Our findings would facilitate the development of excellent adsorbents for removal of other pollutants.

Study on the behavior and mechanism of NiFe-LDHs used for the degradation of tetracycline in the photo-Fenton process

An environment-friendly 3D NiFe-LDHs photocatalyst was fabricated via a simple hydrothermal method and characterized by means of SEM, XRD, BET, XPS and FT-IR. It is a highly efficient heterogeneous photo-Fenton catalyst for the degradation of TC-HCl under visible light irradiation. After exploring the effects of catalyst dosage, initial concentration of TC-HCl, solution pH and H2O2 concentrations, the optimal reaction conditions were determined. The experiment results showed that the degradation efficiency can reach 99.11% through adding H2O2 to constitute a photo-Fenton system after adsorption for 30 min and visible light for 60 min. After four cycles, the degradation rate decay is controlled within 21.2%, indicating that NiFe-LDHs have excellent reusable performance. The experimental results of environmental factors indicate that Fe2+ and Ca2+ promoted the degradation of TC-HCl, both Cl- and CO32- inhibited the degradation of TC-HCl. Two other antibiotics (OTC and FT) were selected for research and found to be effectively removed in this system, achieving effective degradation of a variety of typical new pollutants. The radical trapping tests and ESR detection showed that ·OH and ·O2- were the main active substances for TC degradation in the photo-Fenton system. By further measuring the intermediate products of photodegradation, the degradation pathway of TC-HCl was inferred. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in this system. This study provides a theoretical and practical basis for the removal of TC in aquatic environments.

Biochar-layered double hydroxide composites for the adsorption of tetracycline from water: synthesis, process modeling, and mechanism

Antibiotic-contaminated water is a crucial issue worldwide. Thus, in this study, the MgFeCa-layered double hydroxides were supported in date palm-derived biochar (B) using co-precipitation, hydrothermal, and co-pyrolysis methods. It closes gaps in composite design for pharmaceutical pollutant removal, advances eco-friendly adsorbents, and advances targeted water cleanup by investigating synthesis methodologies and gaining new insights into adsorption. The prepared B-MgFeCa composites were investigated for tetracycline (TC) adsorption from an aqueous solution. The B-MgFeCa composites synthesized through co-precipitation and hydrothermal methods exhibited better crystallinity, functional groups, and well-developed LDH structure within the biochar matrix. However, the co-pyrolysis method resulted in the LDH structure breakage, leading to the low crystalline composite material. The maximum adsorption of TC onto all B-MgFeCa was obtained at an acidic pH range (4-5). The B-MgFeCa composites produced via hydrothermal and co-pyrolysis methods showed higher and faster TC adsorption than the co-precipitation method. The kinetic results can be better described by Langmuir kinetic and mixed order models at low and high TC concentrations, indicating that the rate-limiting step is mainly associated with active binding sites adsorption. The Sip and Freundlich models showed better fitting with the equilibrium data. The TC removal by B-MgFeCa composites prepared via hydrothermal, the highest estimated uptake which is around 639.76 mg.g-1 according to the Sips model at ambient conditions, and co-pyrolysis was mainly dominated by physical and chemical interactions. The composite obtained via the co-precipitation method adsorbed TC through chemical bonding between surface functional groups with anionic species of TC molecule. The B-MgFeCa composite showed excellent reusability performance for up to five cycles with only a 30% decrease in TC removal efficiency. The results demonstrated that B-MgFeCa composites could be used as promising adsorbent materials for effective wastewater treatment.

Functionally-designed floatable amino-modified ZnLa layered double hydroxides/cellulose acetate beads for tetracycline removal: Performance and mechanism

The over-reliance on tetracycline antibiotics (TC) in the animal husbandry and medical field has seriously affected the safety of the ecological environment. Therefore, how to effectively treat tetracycline wastewater has always been a long-term global challenge. Here, we developed a novel polyethyleneimine (PEI)/Zn-La layered double hydroxides (LDH)/cellulose acetate (CA) beads with cellular interconnected channels to strengthen the TC removal. The results of the exploration on its adsorption properties illustrated that the adsorption process exhibited a favorable correlation with the Langmuir model and the pseudo-second-order kinetic model, namely monolayer chemisorption. Among the many candidates, the maximum adsorption capacity of TC by 10 %PEI-0.8LDH/CA beads was 316.76 mg/g. Apart from that, the effects of pH, interfering species, actual water matrix and recycling on the adsorption of TC by PEI-LDH/CA beads were also analyzed to verify their superior removal capability. The potential for industrial-scale applications was expanded through fixed-bed column experiments. The proven adsorption mechanisms mainly included electrostatic interaction, complexation, hydrogen bonding, n-π EDA effect and cation-π interaction. The self-floating high-performance PEI-LDH/CA beads exploited in this work provided fundamental support for the practical application of antibiotic-based wastewater treatment.

Facile Hydrothermal Synthesis of Cu2MoS4 and FeMoS4 for Efficient Adsorption of Chlortetracycline

Contamination of antibiotics in an aqueous environment has attracted wide attention. Developing high-efficiency adsorbents for antibiotics removal is urgent. In this work, two kinds of ternary transition metal chalcogenides—Cu2MoS4 and FeMoS4 with superior adsorption performance were prepared by a facile hydrothermal synthesis method. The microstructure and physicochemical properties of the adsorbents were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The as-prepared Cu2MoS4 and FeMoS4 were found to have dramatic potential for the adsorption of chlortetracycline (CTC) in an aqueous solution with an extremely high adsorption capacity. The Langmuir maximum adsorption capacity of Cu2MoS4 and FeMoS4 to CTC can reach 1203.81 and 2169.19 mg/g, respectively, which goes far beyond the common adsorbents as reported. Moreover, the adsorption kinetics, thermodynamics as well as adsorption mechanism were examined in detail by a batch of adsorption experiments.

Synthesis, characterization, and application of graphene oxide/layered double hydroxide /poly acrylic acid nanocomposite (LDH-rGO-PAA NC) for tetracycline removal: A comprehensive chemometric study

Tetracycline (TC), as the second produced and used antibiotic worldwide, is difficult to be entirely metabolized not only in the body, but also in the treatment processes of water and/or wastewater. Therefore, special attention needs to be paid on defining or developing new options for removing such contaminant. Herein, a reduced graphene oxide (GO) was integrated with Ni-Al layered double hydroxide (LDH) as well poly acrylic acid (LDH-rGO-PAA) and examined to reduce TC -as a model antibiotic-in water media under different operational parameters of TC initial concentration, pH, NC dose, and time. The governed behaviour in the adsorption process was investigated using three model methods of response surface methodology (RSM), artificial neural networks (ANN), and general regression neural network (GRNN) after confirming the physico-chemical properties of LDH-rGO-PAA nanocomposite (NC) using different techniques. The LDH-rGO-PAA NC displayed a good performance as either removal efficiency (R = 94.87 ± 0.25%) or adsorption capacity (q_e = 887.5 mg/g) with the respective values of 110 mg/L, 6.3, 20 mg, and 18.50 min for the mentioned factors (TC initial concentration, pH, NC dose, and time, respectively), which was higher than that of reported for the similar adsorbents until now.

Peroxydisulfate-assisted sonocatalytic degradation of metribuzin by La-doped ZnFe layered double hydroxide

Metribuzin is an herbicide that easily contaminates ground and surface water. Herein, La-doped ZnFe layered double hydroxide (LDH) was synthesized for the first time and used for the degradation of metribuzin via ultrasonic (US) assisted peroxydisulfate (PDS) activation. The synthesized LDH had a lamellar structure, an average thickness of 26 nm, and showed mesoporous characteristics, including specific surface area 110.93 m2 g-1, pore volume 0.27 cm3 g-1, and pore diameter 9.67 nm. The degradation efficiency of the US/La-doped ZnFe LDH/PDS process (79.1 %) was much greater than those of the sole processes, and the synergy factor was calculated as 3.73. The impact of the reactive species on the sonocatalytic process was evaluated using different scavengers. After four consecutive cycles, 10.8 % loss occurred in the sonocatalytic activity of the La-doped LDH. Moreover, the efficiency of the US/La-doped LDH/PDS process was studied with respect to the degradation of metribuzin in a wastewater matrix. According to GC-MS analysis, six by-products were detected during the degradation of metribuzin. Our results indicate that the US/La-doped ZnFe LDH/PDS process has great potential for efficient degradation of metribuzin-contaminated water and wastewater.

Insights into the Synergistic Removal of Copper(II), Cadmium(II), and Chromium(III) Ions Using Modified Chitosan Based on Schiff Bases-g-poly(acrylonitrile)

Chitosan has received broad consideration as an adsorbent for all pollutants because of its low cost and great adsorption potential. However, its shortcomings, including sensitivity to pH, poor thermal stability, and poor mechanical strength, limit its use. The functional groups of chitosan can be modified to enhance its performance by the grafting technique and Schiff base modification. The grafting process used acrylonitrile (Ch-g-PAN) as a monomer and potassium persulfate as an initiator. After that, the modification via preparation of the Schiff base reaction using salicylaldehyde (Ch-g-Sch I) and P-anisaldehyde (Ch-g-Sch II) was carried out. The synthesized copolymers were detailed and characterized through several spectroscopic and microscopic techniques including infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. In addition, Ch-g-Sch I and Ch-g-Sch II were applied in the removal of different metal ions such as Cu²⁺, Cd²⁺, and Cr³⁺. The maximum adsorption capacity of Ch-g-Sch I for Cd²⁺ was 183.7 mg g^-1 in 24 h, while in the case of Ch-g-Sch II, the maximum adsorption capacity for Cd²⁺ was improved to 322.9 mg g^-1 for the same time. Moreover, adsorption thermodynamic analysis displays that the all ion adsorption process was not random and the pseudo-second-order model fitted with experimental results. Finally, Ch-g-Sch I and Ch-g-Sch II were applied as designs for industrial wastewater treatment with significant efficiency.

Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

Valorization of spent double substituted Co-Ni-Zn-Fe LDH wastewater nanoadsorbent as methanol electro-oxidation catalyst

Finding suitable non-expensive electrocatalyst materials for methanol oxidation is a significant challenge. Waste valorization of spent wastewater nanoadsorbents is a promising route toward achieving circular economy guidelines. In this study, the residual of layered double hydroxide (LDH) can be used as an electrocatalyst in direct methanol fuel cells as a novel approach. The Co-Ni-Zn-Fe LDH was prepared by the co-precipitation method followed by the adsorption of methyl orange (MO). Moreover, the spent adsorbent was calcined at different temperatures (200, 400, and 600 °C) to be converted to the corresponding mixed metal oxides (MMO). The prepared samples were characterized using XRD, FTIR, HRTEM, zeta potential, and hydrodynamic size measurements. The spent adsorbent was tested as an electro-catalyst for direct methanol electro-oxidation. The spent LDH/MO adsorbent showed a maximum current density of 6.66 mA/cm² at a 50 mV/s scan rate and a 1 M methanol concentration. The spent MMO/MO adsorbent showed a maximum current density of 8.40 mA/cm² at a 200 °C calcination temperature, 50 mV/s scan rate, and a 3 M methanol concentration. Both samples show reasonable stability over time, as indicated by the chronoamperometric response. Further nanoengineering of used nanoadsorbents could be a promising path to repurposing these wastes as electro-oxidation catalysts.

La/LaF3 co-modified MIL-53(Cr) as an efficient adsorbent for the removal of tetracycline

Chromium based metal-organic framework (MIL-53(Cr)) has enormous potential in the removal of organic contaminants from aqueous solutions due to its outstanding water stability, whereas its poor adsorption capacity limits the application. In this study, La/LaF₃-MIL-53(Cr) was successfully synthesized by taking the advantages of La doping and LaF₃ encapsulation with one-step hydrothermal method. Diverse analysis tools were utilized to verify that La not only existed in the framework, but also was loaded in the pores in the form of LaF₃. The adsorption experiment results demonstrated that 0.3-La/LaF₃-MIL-53(Cr) exhibited significantly improved adsorption capacity by four times compared with the pristine MIL-53(Cr) material. XPS and FTIR revealed that the affinity of La to tetracycline was significantly stronger than that of Cr and the excellent dispersion of LaF₃ in the material may also be the cause of the increase in adsorption capacity. This study described a simple method to combine two different forms of modification and the modified material was potential for tetracycline adsorption.

LDH Nanocubes Synthesized with Zeolite Templates and Their High Performance as Adsorbents

In this work, the efficiency of the adsorptive removal of the organic cationic dye methylene blue (MB) from polluted water was examined using three materials: natural clay (zeolite), Zn-Fe layered double hydroxide (LDH), and zeolite/LDH composite. These materials were characterized via X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) diffraction (XRF), low-temperature N2 adsorption, pore volume and average pore size distribution and field emission scanning electron microscopy (FE-SEM). The properties of the applied nanomaterials regarding the adsorption of MB were investigated by determining various experimental parameters, such as the contact time, initial dye concentration, and solution pH. In addition, the adsorption isotherm model was estimated using the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models. The Langmuir model was the best-fitting for all applied nanomaterials. In addition, the kinetics were analyzed by using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, and the pseudo-second-order model was an apparent fit for all three applied nanomaterials. The maximum Adsorption capacity toward MB obtained from the materials was in the order zeolite/LDH composite > zeolites > Zn-Fe LDH. Thus, the zeolite/LDH composite is an excellent adsorbent for the removal of MB from polluted water.

Photocatalytic Degradation of Antibiotics by Superparamagnetic Iron Oxide Nanoparticles. Tetracycline Case

The challenges associated with the uncontrolled presence of antibiotics such as tetracycline in the environment have necessitated their removal through different techniques. Tetracycline is hard to degrade in living organisms and can even be converted to more toxic substances. In view of this, we synthesized iron oxide nanoparticles with good magnetization (70 emu g−1) and 15 nm particle size for the adsorption and photocatalytic degradation of tetracycline. Characterization carried out on the synthesized iron oxides revealed a bandgap of 1.83 eV and an isoelectric point at pH 6.8. The results also showed that the pH of the solution does not directly influence the adsorption of tetracycline. The adsorption isotherm was consistent with the model proposed by Langmuir, having 97 mg g−1 adsorption capacity. Combined with the superparamagnetic behavior, this capacity is advantageous for the magnetic extraction of tetracycline from wastewater. The mechanisms of adsorption were proposed to be hydrogen bonding and n-π interactions. Photocatalytic degradation studies showed that approximately 40% of tetracycline degraded within 60 min of irradiation time with UV/vis light. The kinetics of photodegradation of tetracycline followed the pseudo-first-order mechanism, proceeding through hydroxyl radicals generated under illumination. Moreover, the photogenerated hydrogen peroxide could lead to heterogeneous photo-Fenton processes on the surface of iron oxide nanoparticles, additionally generating hydroxyl and hydroperoxyl radicals and facilitating photodegradation of tetracycline.