Chemical Bonding and Crystal Structure Schemes in Atomic/Molecular Layer Deposited Fe-Terephthalate Thin Films

Advanced deposition routes are vital for the growth of functional metal-organic thin films. The gas-phase atomic/molecular layer deposition (ALD/MLD) technique provides solvent-free and uniform nanoscale thin films with unprecedented thickness control and allows straightforward device integration. Most excitingly, the ALD/MLD technique can enable the in situ growth of novel crystalline metal-organic materials. An exquisite example is iron-terephthalate (Fe-BDC), which is one of the most appealing metal-organic framework (MOF) type materials and thus widely studied in bulk form owing to its attractive potential in photocatalysis, biomedicine, and beyond. Resolving the chemistry and structural features of new thin film materials requires an extended selection of characterization and modeling techniques. Here we demonstrate how the unique features of the ALD/MLD grown in situ crystalline Fe-BDC thin films, different from the bulk Fe-BDC MOFs, can be resolved through techniques such as synchrotron grazing-incidence X-ray diffraction (GIXRD), Mössbauer spectroscopy, and resonant inelastic X-ray scattering (RIXS) and crystal structure predictions. The investigations of the Fe-BDC thin films, containing both trivalent and divalent iron, converge toward a novel crystalline Fe(III)-BDC monoclinic phase with space group C2/c and an amorphous Fe(II)-BDC phase. Finally, we demonstrate the excellent thermal stability of our Fe-BDC thin films.

Geopolymer-Based Materials for the Removal of Ibuprofen: A Preliminary Study

Every year, new compounds contained in consumer products, such as detergents, paints, products for personal hygiene, and drugs for human and veterinary use, are identified in wastewater and are added to the list of molecules that need monitoring. These compounds are indicated with the term emerging contaminants (or Contaminants of Emerging Concern, CECs) since they are potentially dangerous for the environment and human health. To date, among the most widely used methodologies for the removal of CECs from the aquatic environment, adsorption processes play a role of primary importance, as they have proven to be characterized by high removal efficiency, low operating and management costs, and an absence of undesirable by-products. In this paper, the adsorption of ibuprofen (IBU), a nonsteroidal anti-inflammatory drug widely used for treating inflammation or pain, was performed for the first time using two different types of geopolymer-based materials, i.e., a metakaolin-based (GMK) and an organic-inorganic hybrid (GMK-S) geopolymer. The proposed adsorbing matrices are characterized by a low environmental footprint and have been easily obtained as powders or as highly porous filters by direct foaming operated directly into the adsorption column. Preliminary results demonstrated that these materials can be effectively used for the removal of ibuprofen from contaminated water (showing a concentration decrease of IBU up to about 29% in batch, while an IBU removal percentage of about 90% has been reached in continuous), thus suggesting their potential practical application.

Interfacial Engineering Boosting the Activity and Stability of MIL-53(Fe) toward Electrocatalytic Nitrogen Reduction

The electrochemical nitrogen reduction reaction (eNRR) has emerged as a promising strategy for green ammonia synthesis. However, it suffers unsatisfactory reaction performance owing to the low aqueous solubility of N2 in aqueous solution, the high dissociation energy of N≡N, and the unavoidable competing hydrogen evolution reaction (HER). Herein, a MIL-53(Fe)@TiO2 catalyst is designed and synthesized for highly efficient eNRR. Relative to simple MIL-53(Fe), MIL-53(Fe)@TiO2 achieves a 2-fold enhancement in the Faradaic efficiency (FE) with an improved ammonia yield rate by 76.5% at -0.1 V versus reversible hydrogen electrode (RHE). After four cycles of electrocatalysis, MIL-53(Fe)@TiO2 can maintain a good catalytic activity, while MIL-53(Fe) exhibits a significant decrease in the NH3 yield rate and FE by 79.8 and 82.3%, respectively. Benefiting from the synergetic effect between TiO2 and MIL-53(Fe) in the composites, Fe3+ ions can be greatly stabilized in MIL-53(Fe) during the eNRR process, which greatly hinders the catalyst deactivation caused by the electrochemical reduction of Fe3+ ions. Further, the charge transfer ability in the interface of composites can be improved, and thus, the eNRR activity is significantly boosted. These findings provide a promising insight into the preparation of efficient composite electrocatalysts.

Fixed-bed adsorption studies of endocrine-disrupting compounds from water by using novel calcium-based metal-organic frameworks

The presence of emerging water pollutants such as endocrine-disrupting compounds (EDCs), including 17-ethynylestradiol (EE2), bisphenol A (BPA), and perfluorooctanoic acid (PFOA), in contaminated water sources poses significant environmental and health challenges. This study aims to address this issue by investigating the efficiency of novel calcium-based metal-organic frameworks, known as mixed-linker calcium-based metal-organic frameworks (Ca-MIX), in adsorbing these endocrine-disrupting compounds. This study analyzed the influence of influent concentration, bed height, and flow rate on pollutant removal, with bed height emerging as a crucial factor. From the breakthrough curves, it was determined that the column maximum adsorption capacities followed the order of 17-ethynylestradiol (101.52 μg/g; 40%) > bisphenol A (99.07 μg/g; 39%) > perfluorooctanoic acid (81.28 μg/g; 32%). Three models were used to predict the adsorption process, with the Yan model outperforming the other models. This suggests the potential of mixed-linker calcium-based metal-organic frameworks for removing endocrine-disrupting compounds from water, using the Yan model as an effective predictor. Overall, this study provides valuable insights for the development of effective water treatment methods using mixed-linker calcium-based metal-organic frameworks to remove endocrine-disrupting compounds from contaminated water sources.

Growth Control of Metal-Organic Framework Films on Marine Biological Carbon and Their Potential-Dependent Dopamine Sensing

Ever-evolving advancements in films have fueled many of the developments in the field of electrochemical sensors. For biosensor application platforms, the fabrication of metal-organic framework (MOF) films on microscopically structured substrates is of tremendous importance. However, fabrication of MOF film-based electrodes always exhibits unsatisfactory performance, and the mechanisms of the fabrication and sensing application of the corresponding composites also need to be explored. Here, we report the fabrication of conformal MIL-53 (Fe) films on carbonized natural seaweed with the assistance of an oxide nanomembrane and a potential-dependent electrochemical dopamine (DA) sensor. The geometry and structure of the composite can be conveniently tuned by the experimental parameters, while the sensing performance is significantly influenced by the applied potential. The obtained sensor demonstrates ultrahigh sensitivity, a wide linear range, a low limit of detection, and a good distinction between DA and ascorbic acid at an optimized potential of 0.3 V. The underneath mechanism is investigated in detail with the help of theoretical calculations. This work bridges the natural material and MOF films and is promising for future biosensing applications.

Modified gelatin/iron- based metal-organic framework nanocomposite hydrogel as wound dressing: Synthesis, antibacterial activity, and Camellia sinensis release

A new kind of Camellia sinensis-loaded nanocomposite hydrogel based on modified gelatin/iron-metal-organic framework was developed as an antibacterial wound dressing. Gelatin as a biocompatible natural polymer was modified with methacrylate anhydride to produce gelatin methacrylate. Thereafter, acrylic acid and acrylamide were grafted on gelatin methacrylate during an aqueous polymerization process. To enhance the porosity, mechanical strength, and drug loading capability of the hydrogel and reduce its toxicity, iron- based metal-organic framework was incorporated within the hydrogel. To add more functionality to the final wound dressing, Camellia sinensis, an antibacterial herbal drug was loaded on the hydrogel. The structural and chemical properties of prepared nanocomposite hydrogel were investigated by FTIR, XRD, SEM, and TGA techniques. The incorporation of iron-based metal-organic framework within the hydrogel matrix led to an increase in its water absorption value from 400.10 to 547.96 (g/g). The release study of Camellia sinensis (CS) extract from the prepared nanocomposite hydrogel exhibited a sustained release manner. The antibacterial test revealed the nanocomposite hydrogel contain extract has an effective antibacterial function against "Bacillus serous", "Staphylococcus aureus", "Streptococcus mutans"," Escherichia coli", "Klebsiella pneumoniae", and "Pseudomonas aeruginosa" bacteria. Therefore, the synthesized nanocomposite is a good candidate as an antibacterial hydrogel wound dressing. .

Recent Progress in the Removal of Legacy and Emerging Organic Contaminants from Wastewater Using Metal-Organic Frameworks: An Overview on Adsorption and Catalysis Processes

Water covers about 70% of the Earth’s surface, but the amount of freshwater available for human use is only 2.5% and, although it is continuously replenished via the water cycle, freshwater is a finite and limited resource. The Earth’s water is affected by pollution and while water quality is an issue of global concern, the specific regulations on contaminants of emerging concern (CECs) are limited. In order to achieve the goals set by EU regulations, the treatment of wastewater is a scientifically and technologically challenging issue. Metal–organic frameworks (MOFs) are promising materials used for the removal of priority and emerging contaminants from wastewater, since they can mitigate those contaminants via both adsorption as well as catalysis processes. MOFs can offer selective adsorption of CECs by various adsorption mechanisms. The catalytic removal of priority and emerging organic contaminants from wastewater using MOFs implies Fenton, electro-Fenton, and photo-Fenton processes. Overall, MOFs can be considered as promising materials for the elimination of priority and emerging organic contaminants from various wastewater types, but the involved processes must be studied in detail for a larger number of compounds.

Rationally designed and hierarchically structured functionalized aluminium organic frameworks incorporated chitosan hybrid beads for defluoridation of water

In this present investigation, aluminium (Al³⁺) fabricated 2-aminobenzene-1,4-dicarboxylic acid (ABDC) namely Al@ABDC metal organic frameworks (MOFs) was developed for defluoridation studies. The unique advantages of developed MOFs possess high selectivity, high porosity and enhanced surface area but the developed powder form of Al@ABDC MOFs has several limitations in field applications like slow filtration and column blockage. To prevail over these troubles, biopolymer namely chitosan (CS) supported Al@ABDC MOFs namely Al@ABDC-CS beads were developed for effective fluoride adsorption from water. The synthesized Al@ABDC-CS beads were employed for the retention of fluoride in batch level. The defluoridation capacities (DCs) of Al@ABDC MOFs and Al@ABDC-CS beads were found to be 4880 and 4900 mgF^- kg^-1 respectively. The influencing parameters of adsorption method namely agitation time, adsorbent dosage, initial fluoride concentration, pH, co-existing anions and temperature were exploit to get utmost defluoridation capacity (DC) of Al@ABDC-CS beads. The experimental data of Al@ABDC-CS beads have been evaluated utilizing Langmuir, Fruendlich and Dubinin-Radushkevich (D-R) isotherms. The defluoridation nature of Al@ABDC-CS beads was determined by the thermodynamic parameters. The order of reaction of Al@ABDC-CS beads was studied using various kinetic models. The regeneration and field water studies of Al@ABDC-CS beads were also carried out to check their reusability and suitability at field conditions.

Novel Application of Tagua Shell (Phytelephas aequatorialis) as Adsorbent Material for the Removal of Pb(II) Ions: Kinetics, Equilibrium, and Thermodynamics of the Process

Tagua shell is a material generated in the handcrafted jewelry industry, which is discarded since it does not have a specific use. The present study evaluates this material as an adsorbent for the removal of lead (II) in aqueous media. The adsorbent was characterized through the point of zero charge technique, X-ray microanalysis, scanning electron microscopy, and Fourier-transform infrared spectroscopy. Tests were carried out in a static system using a lead (II) solution of 100 mg·L−1 to establish the process conditions, setting a pH of 5, an adsorbent dose of 1.8 g/100 mL, and a contact time of 60 min. The kinetic study performed showed that the experimental data had a better fit with the pseudo-second order model. The experimental equilibrium data were correlated using the Langmuir, Freundlich, Toth, Redlich–Peterson, and Sips models, of which the Langmuir and Sips models proved to be the best to represent the adsorption process due to the high coefficient of determination they presented at the different temperatures, being between 0.9629–0.9899 and 0.9819–0.9900, respectively. The maximum amount of lead adsorbed was 22.0348 mg·g−1 at a temperature of 298 K. Finally, the thermodynamics study indicated that the process is endothermic, spontaneous, and thermodynamically stable.

Application of hybrid MOF composite in extraction of f-block elements: Experimental and computational investigation

An attempt was made to understand the sorption behaviour of UO₂²⁺, Th⁴⁺ and Eu³⁺ on novel hybrid metal-organic framework composites, FeBDC@CoBDC. The XRD pattern revealed the composite nature of the hybrid MOF materials, while FTIR and Raman spectroscopic analyses evidenced the presence of different functional moieties. The thermal stability of the hybrid MOF composites was investigated through thermogravimetric analysis. The sorption predominantly followed Langmuir isotherm with sorption capacity of 189 mg g^-1, 224 mg g^-1 and 205 mg g^-1 for UO₂²⁺, Th⁴⁺ and Eu³⁺ respectively. The sorption proceeded through chemisorption following pseudo 2^nd order rate kinetics. The processes were found to be thermodynamically favourable and endothermic in nature. However, they were entropically driven. Multiple contacts of complexing agents were necessary for quantitative elution of f-elements from loaded MOF. The MOF showed moderate stability towards radiation exposure. DFT calculation was used for the optimization of structures, estimation of bond length and estimation of binding energy. In hybrid MOF composites, the Fe atom was having six coordination with 4 O atoms of BDC moieties and 2 O atoms of -OH groups. The O atoms of BDC and -OH groups were coordinated to Eu, Th and U atoms during their sorption.

Effect of Nitrogen-Doped Carbon Dots (NCDs) on the Characteristics of NCD/MIL-53(Fe) Composite and Its Photocatalytic Performance for Methylene Blue Degradation under Visible Light

Metal-organic framework composites, which are combined from metal-organic framework and advanced carbon material, have drawn great attention in many fields of application such as environmental remediation and catalysts. Within this paper, the carbon/MIL-53(Fe) composite was fabricated via an in situ synthesis, in which N-containing carbon dots (NCDs) were mixed with MOF precursors’ solutions under various ratios before going through the solvothermal stage. It was showed that the introduction of a certain amount of NCDs would affect characteristic features and improve the photocatalytic performance of final products. The optimal doping content of NCDs in NCD/MIL-53(Fe) composite was determined. SEM images showed that the M-140 appeared as hexagonal bipyramid-shaped crystals with an average size of 700 nm. Compared with pristine MIL-53(Fe), the M-140 was more visibly light-responsive, and its calculated band gap energy was approximately 2.3 eV. In addition, M-140 catalyst also displayed more excellent photocatalytic activity for Methylene Blue degradation in a pH range from 5 to 7. Under optimal conditions, MB was achieved within 60 minutes and the removal rate was nearly 100% after 5 cycles. The photocatalytic mechanism of the obtained NCD/MIL-53(Fe) composite was discussed.

Removal of ibuprofen from aqueous media by adsorption: A comprehensive review

Ibuprofen (IBP) is a non-steroidal anti-inflammatory drug released into the environment through hospital and medical effluents, pharmaceutical wastewater and veterinary use. The aim of this paper is to review the empirical findings on the adsorption of IBP from aqueous media. A preliminary ecotoxicological assessment confirmed the environmental risk of IBP in the aqueous environment. Open literature works considered in this review were for the past decade (2010-2020). Carbon-based adsorbents are the best class of adsorbent for the uptake of IBP and the highest reported maximum adsorption capacity (q_max) for IBP is 496.1 mg/g by SWCNTs. The range of adsorption capacities for IBP uptake in this review is between 0.0496 and 496.1 mg/g. The mechanism of uptake is majorly by hydrophobic interactions, π - π stacking, hydrogen bonds, electrostatic interactions and dipole-dipole interaction. IBP uptake was best fit to a wide variety of isotherm models but was well suited to the pseudo-second order kinetics model. The thermodynamics of IBP uptake depends majorly on the nature of the adsorbent and desorption from the solid phase is based on an appropriate choice of the eluent. Knowledge gaps were observed in used adsorbent disposal and process improvement. In the future, interest would increase in scale-up, industrial applications and practical utilisation of the research findings which would help in sustainable water resource management.

A binary MOF of iron and copper for treating ciprofloxacin-contaminated waste water by an integrated technique of adsorption and photocatalytic degradation

A novel MIL 53(Fe–Cu) was synthesized by a solvothermal process. This binary metal organic framework removed ciprofloxacin from waste water.

Metal-Organic Framework MIL-53(Fe): Synthesis, Electrochemical Characterization, and Application in Development of a Novel and Sensitive Electrochemical Sensor for Detection of Cadmium Ions in Aqueous Solutions

A metal-organic framework MIL-53(Fe) was successfully synthesized by a simple hydrothermal method. A synthesized MIL-53(Fe) sample was characterized, and results indicated that the formed MIL-53(Fe) was a single phase with small particle size of 0.8 μm and homogeneous particle size distribution was obtained. The synthesized MIL-53(Fe) has been used to modify a glassy carbon electrode (GCE) by a drop-casting technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements of the MIL-53(Fe)-modified GCE showed that the MIL-53(Fe) was successfully immobilized onto the GCE electrode surface and the electrochemical behavior of the GCE/MIL-53(Fe) electrode was stable. In addition, several electrochemical parameters of MIL-53(Fe)-modified GCE (GCE/MIL-53(Fe)) including the heterogeneous standard rate constant ( $k^0$ ) and the electrochemically effective surface area ( $A$ ) were calculated. Obtained results demonstrated that the synthesized MIL-53(Fe) with the small particle size, highly homogeneous particle size, and high electrochemically effective surface area was able to significantly enhance the electrochemical response signal of the working electrode. Therefore, the GCE/MIL-53(Fe) electrode has been used as a highly sensitive electrochemical sensor for cadmium ion (Cd(II)) monitoring in aqueous solution using differential pulse voltammetry (DPV) technique. The response signal of the electrochemical sensor increased linearly in the Cd(II) ion concentration range from 150 nM to 450 nM with the limit of detection (LOD) of 16 nM.

Kinetics, Isotherm, Thermodynamics, and Recyclability of Exfoliated Graphene-Decorated MnFe2O4 Nanocomposite Towards Congo Red Dye

Herein, we described the use of exfoliated graphene- (EG-) decorated magnetic MnFe2O4 nanocomposite (EG@MnFe2O4) for the removal and adsorption of Congo red (CR) dye from wastewater. Firstly, the precursors (EG, MnFe2O4) and EG@MnFe2O4 were fabricated, characterized using several physical analytical techniques such as X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and N2adsorption/desorption isotherm measurement. For the adsorption experiments, the effect of contact time (0–240 min), concentration (10–60 mg/L), solution pH (2–10), adsorbent dosage (0.03–0.07 g), and temperature (283–313 K) was rigorously studied. To elucidate the adsorption mechanism and behaviour of CR over EG@MnFe2O4 and MnFe2O4 adsorbents, the kinetic models (pseudo-first-order, pseudo-second-order, Elovich, and Bangham) and isotherm models (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) have been adopted. The kinetic results indicated that models adhered to the pseudo-second-order equation, exhibiting the chemisorption mechanism in heterogeneous phrase. Meanwhile, the isotherm results revealed the adsorption of CR over EG@MnFe2O4 obeyed the monolayer behaviour (Langmuir model) rather than multilayer behaviour (Freundlich equation) over MnFe2O4. The thermodynamic study also suggested that such adsorption was an endothermic and spontaneous process. With high maximum adsorption capacity (71.79 mg/g) and good recyclability (at least 4 times), EG@MnFe2O4 can be a potential alternative for the adsorptive removal of CR dye from water.

Process Optimization by a Response Surface Methodology for Adsorption of Congo Red Dye onto Exfoliated Graphite-Decorated MnFe2O4 Nanocomposite: The Pivotal Role of Surface Chemistry

Natural graphite, a locally available, eco-friendly, and low-cost carbonaceous source, can be easily transformed into exfoliated graphite (EG) with many surface functional groups via a chemical oxidation route. Combination between EG and magnetic MnFe2O4 is a promising strategy to create a hybrid kind of nanocomposite (EG@MnFe2O4) for the efficient adsorptive removal of Congo red (CR) dye from water. Here, we reported the facile synthesis and characterization of chemical bonds of EG@MnFe2O4 using several techniques such as Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). In particular, the quantity method by Boehm titration was employed to identify the content of functional groups: Carboxylic acid (0.044 mmol/g), phenol (0.032 mmol/g), lactone (0.020 mmol/g), and total base (0.0156 mmol/g) on the surface of EG@MnFe2O4. Through the response surface methodology-optimized models, we found a clear difference in the adsorption capacity between EG-decorated MnFe2O4 (62.0 mg/g) and MnFe2O4 without EG decoration (11.1 mg/g). This result was also interpreted via a proposed mechanism to elucidate the contribution of surface functional groups of EG@MnFe2O4 to adsorption efficiency towards CR dye.

A hollow mesoporous carbon from metal-organic framework for robust adsorbability of ibuprofen drug in water

Herein, we described a tunable method for synthesis of novel hollow mesoporous carbon (MPC) via direct pyrolysis (800^oC) of MIL-53 (Fe) as a self-sacrificed template. The structural characterization revealed a hollow, amorphous, defective and mesoporous MPC along with high surface area (approx. 200 m² g^-1). For the experiments of ibuprofen adsorption onto MPC, effects of contact time, MPC dosage, ionic strength, concentration and temperature were systematically investigated. The optimal conditions consisted of pH = 3, concentration 10 mg l^-1 and dose of 0.1 g l^-1 for the highest ibuprofen removal efficiency up to 88.3% after 4 h. Moreover, adsorption behaviour, whereby chemisorption and monolayer controlled the uptake of ibuprofen over MPC, were assumed. Adsorption mechanisms including H-bonding, π-π interaction, metal-oxygen, electrostatic attraction were rigorously proposed. In comparison to several studies, the MPC nanocomposite in this work obtained the outstanding maximum adsorption capacity (206.5 mg g^-1) and good reusability (5 cycles); thus, it can be used as a feasible alternative for decontamination of ibuprofen anti-inflammatory drug from water.