Progress in layered double hydroxides (LDHs): Synthesis and application in adsorption, catalysis and photoreduction.

Layered double hydroxides (LDHs), also known as anionic clays, have attracted significant attention in energy and environmental applications due to their exceptional physicochemical properties. These materials possess a unique structure with surface hydroxyl groups, tunable properties, and high stability, making them highly desirable. In this review, the synthesis and functionalization of LDHs have been explored including co-precipitation and hydrothermal methods. Furthermore, extensive research on LDH application in toxic pollutant removal has shown that modifying or functionalizing LDHs using materials such as activated carbon, polymers, and inorganics is crucial for achieving efficient pollutant adsorption, improved cyclic performance, as well as effective catalytic oxidation of organics and photoreduction. This study offers a comprehensive overview of the progress made in the field of LDHs and LDH-based composites for water and wastewater treatment. It critically discusses and explains both direct and indirect synthesis and modification techniques, highlighting their advantages and disadvantages. Additionally, this review critically discusses and explains the potential of LDH-based composites as absorbents. Importantly, it focuses on the capability of LDH and LDH-based composites in heterogeneous catalysis, including the Fenton reaction, Fenton-like reactions, photocatalysis, and photoreduction, for the removal of organic dyes, organic micropollutants, and heavy metals. The mechanisms involved in pollutant removal, such as adsorption, electrostatic interaction, complexation, and degradation, are thoroughly explained. Finally, this study outlines future research directions in the field.

A review on the effectiveness of nanocomposites for the treatment and recovery of oil spill.

The introduction of unintended oil spills into the marine ecosystem has a significant impact on aquatic life and raises important environmental concerns. The present review summarizes the recent studies where nanocomposites are applied to treat oil spills. The review deals with the techniques used to fabricate nanocomposites and identify the characteristics of nanocomposites beneficial for efficient recovery and treatment of oil spills. It classifies the nanocomposites into four categories, namely bio-based materials, polymeric materials, inorganic-inorganic nanocomposites, and carbon-based nanocomposites, and provides an insight into understanding the interactions of these nanocomposites with different types of oils. Among nanocomposites, bio-based nanocomposites are the most cost-effective and environmentally friendly. The grafting or modification of magnetic nanoparticles with polymers or other organic materials is preferred to avoid oxidation in wet conditions. The method of synthesizing magnetic nanocomposites and functionalization polymer is essential as it influences saturation magnetization. Notably, the inorganic polymer-based nanocomposite is very less developed and studied for oil spill treatment. Also, the review covers some practical considerations for treating oil spills with nanocomposites. Finally, some aspects of future developments are discussed. The terms "Environmentally friendly," "cost-effective," and "low cost" are often used, but most of the studies lack a critical analysis of the cost and environmental damage caused by chemical alteration techniques. However, the oil and gas industry will considerably benefit from the stimulation of ideas and scientific discoveries in this field.

Metal-organic framework-based materials for the abatement of air pollution and decontamination of wastewater.

Developing new and efficient technologies for environmental remediation is becoming significant due to the increase in global concerns such as climate change, severe epidemics, and energy crises. Air pollution, primarily due to increased levels of H2S, SOx, NH3, NOx, CO, volatile organic compounds (VOC), and particulate matter (PM) in the atmosphere, has a significant impact on public health, and exhaust gases harm the natural sulfur, nitrogen, and carbon cycles. Similarly, wastewater discharged to the environment with metal ions, herbicides, pharmaceuticals, personal care products, dyes, and aromatics/organic compounds is a risk for health since it may lead to an outbreak of waterborne pathogens and increase the exposure to endocrine-disrupting agents. Therefore, developing new and efficient air and water quality management systems is critical. Metal-organic frameworks (MOFs) are novel materials for which the main application areas include gas storage and separation, water harvesting from the atmosphere, chemical sensing, power storage, drug delivery, and food preservation. Due to their versatile structural motifs that can be modified during synthesis, MOFs also have a great promise for green applications including air and water pollution remediation. The motivation to use MOFs for environmental applications prompted the modification of their structures via the addition of metal and functional groups, as well as the creation of heterostructures by mixing MOFs with other nanomaterials, to effectively remove hazardous contaminants from wastewater and the atmosphere. In this review, we focus on the state-of-the-art environmental applications of MOFs, particularly for water treatment and air pollution, by highlighting the groundbreaking studies in which MOFs have been used as adsorbents, membranes, and photocatalysts for the abatement of air and water pollution. We finally address the opportunities and challenges for the environmental applications of MOFs.

Iron-based metal-organic framework: Synthesis, structure and current technologies for water reclamation with deep insight into framework integrity.

Water is a supreme requirement for the existence of life, the contamination from the point and non-point sources are creating a great threat to the water ecosystem. Advance tools and techniques are required to restore the water quality and metal-organic framework (MOFs) with a tunable porous structure, striking physical and chemical properties are an excellent candidate for it. Fe-based MOFs, which developed rapidly in recent years, are foreseen as most promising to overcome the disadvantages of traditional water depolluting practices. Fe-MOFs with low toxicity and preferable stability possess excellent performance potential for almost all water remedying techniques in contrast to other MOF structures, especially visible light photocatalysis, Fenton, and Fenton-like heterogeneous catalysis. Fe-MOFs become essential tool for water treatment due to their high catalytic activity, abundant active site and pollutant-specific adsorption. However, the structural degradation under external chemical, photolytic, mechanical, and thermal stimuli is impeding Fe-MOFs from further improvement in activity and their commercialization. Understanding the shortcomings of structural integrity is crucial for large-scale synthesis and commercial implementation of Fe-MOFs-based water treatment techniques. Herein we summarize the synthesis, structure and recent advancements in water remediation methods using Fe-MOFs in particular more attention is paid for adsorption, heterogeneous catalysis and photocatalysis with clear insight into the mechanisms involved. For ease of analysis, the pollutants have been classified into two major classes; inorganic pollutants and organic pollutants. In this review, we present for the first time a detailed insight into the challenges in employing Fe-MOFs for water remediation due to structural instability.

An overview on non-spherical semiconductors for heterogeneous photocatalytic degradation of organic water contaminants.

Because of their carcinogenicity and mutagenicity, the elimination of organic contaminants from surface and subsurface water is a subject of environmental significance. Conventional water decontamination approaches such as membrane separation, ultrafiltration, adsorption, reverse osmosis, coagulation, etc., have relatively higher operating costs and can generate highly toxic secondary contaminants. On the other hand, heterogeneous photocatalysis, an advanced oxidation process (AOP), is considered a clean and cost-effective process for organic pollutants degradation. Owing to their distinctive structure and physicochemical properties non-spherical semiconductors have gained considerable limelight in the photocatalytic degradation of organic contaminants. The current review briefly introduces a wide range of organic water contaminants. Recent advances in non-spherical semiconductor assembly and their photocatalytic degradation applications are highlighted. The underlying mechanism, fundamentals of photocatalytic reactions, and the factors affecting the degradation performance are also alluded including the current challenges and future research perspectives.

Ionic liquid-based antimicrobial materials for water treatment, air filtration, food packaging and anticorrosion coatings.

Efforts to widen the scope of ionic liquids applications across diverse research areas have flourished in the last two decades with developments in understanding and tailoring their physical, chemical, and biological properties. The promising applications of ionic liquids-based materials as antimicrobial systems is due to their ability and flexibility to be tailored in varying sizes, morphologies, and surface charges. Ionic liquids are also considered as greener materials. Common methods for the preparation of ionic liquid-based materials include crosslinking, loading, grafting, and combination of ionic liquids with other polymeric materials. Recent research focuses on the tuning of the biological properties to design novel ionic liquids-based antimicrobial materials. Here, the properties, synthesis and applications of ionic liquids and ionic liquids-based materials are reviewed with focus on antimicrobial activities applied to water treatment, air filtration, food packaging, and anticorrosion.

Characterization and physicochemical aspects of novel cellulose-based layered double hydroxide nanocomposite for removal of antimony and fluoride from aqueous solution.

A series of novel adsorbents composed of cellulose (CL) with Ca/Al layered double hydroxide (CCxA; where x represent the Ca/Al molar ratio) were prepared for the adsorption of antimony (Sb(V)) and fluoride (F-) ions from aqueous solutions. The CCxA was characterized by Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), elemental analysis (CHNS/O), thermogravimetric analysis (TGA-DTA), zeta potential, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis. The effects of varying parameters such as dose, pH, contact time, temperature and initial concentration on the adsorption process were investigated. According to the obtained results, the adsorption processes were described by a pseudo-second-order kinetic model. Langmuir adsorption isotherm model provided the best fit for the experimental data and was used to describe isotherm constants. The maximum adsorption capacity was found to be 77.2 and 63.1 mg/g for Sb(V) and F-, respectively by CC3A (experimental conditions: pH 5.5, time 60 min, dose 15 mg/10 mL, temperature 298 K). The CC3A nanocomposite was able to reduce the Sb(V) and F- ions concentration in synthetic solution to lower than 6 µg/L and 1.5 mg/L, respectively, which are maximum contaminant levels of these elements in drinking water according to WHO guidelines.

Cytotoxic aquatic pollutants and their removal by nanocomposite-based sorbents.

Water is an extremely essential compound for human life and, hence, accessing drinking water is very important all over the world. Nowadays, due to the urbanization and industrialization, several noxious pollutants are discharged into water. Water pollution by various cytotoxic contaminants, e.g. heavy metal ions, drugs, pesticides, dyes, residues a drastic public health issue for human beings; hence, this topic has been receiving much attention for the specific approaches and technologies to remove hazardous contaminants from water and wastewater. In the current review, the cytotoxicity of different sorts of aquatic pollutants for mammalian is presented. In addition, we will overview the recent advances in various nanocomposite-based adsorbents and different approaches of pollutants removal from water/wastewater with several examples to provide a backdrop for future research.

Synthesis of novel adsorbent by intercalation of biopolymer in LDH for the removal of arsenic from synthetic and natural water.

This study focuses on the synthesis of nanocomposites named CCA and CZA that were prepared by the incorporation of cellulose (CL) in the Ca/Al and Zn/Al layered double hydroxide (LDH), respectively. These materials were then used for the uptake of As(III) and As(V) from aqueous medium. Characterization of both nanocomposites (CCA and CZA) was done using FTIR and Raman analysis to identify the functional groups, N2 adsorption-desorption isotherms to determine the specific surface area and pore geometry and XPS analysis to obtain the surface atomic composition. Some other characters were investigated using simultaneous TGA and DTA and elemental chemical analysis (CHNS/O). The crystallinity of the prepared nanocomposites was displayed by XRD patterns. Furthermore, the sheet-like structure of the LDHs and the irregularity of surface morphology with porous structure were observed by TEM and SEM microphotographs. Optimization of maximum adsorption capacity was adjusted using different parameters including pH, contact time and adsorbent dosage. The pseudo-second-order model was in good fitting with kinetics results. The adsorption isotherm results showed that CZA exhibits better adsorption capacity for As(III) than CCA and the Langmuir isotherm model described the data well for both nanocomposites. Thermodynamic studies illustrated the endothermic nature of CCA and exothermic nature on CZA, as well as the fact that the adsorption process is spontaneous. A real water sample collected from well located in Gabes (Tunisia), has also been treated. The obtained experimental results were confirmed that these sorbents are efficient for the treatment of hazardous toxic species such as.

Application of zinc-aluminium layered double hydroxides for adsorptive removal of phosphate and sulfate: Equilibrium, kinetic and thermodynamic.

In this study, a series of layered double hydroxide (ZxAy LDH) material was synthesized with different molar ratios and calcination temperatures to remove phosphate and sulfate ions from synthetic solution. ZxAy LDH was characterized by XRD, FTIR, BET and SEM analysis. The highest removal was obtained by Z3A200 LDH that is LDH with a Zn-Al molar ratio of 3 and calcined at 200 °C. The leaching of Zn and Al was more under highly acidic pH compared to pH 5 and 8. Adsorption isotherms data had a good fit with Langmuir model and maximum adsorption under optimum conditions led to 2.6-2.72 and 1.02-1.31 mmol/g for phosphate and sulfate, respectively. Kinetic studies have been performed by applying reaction based models and diffusion-based models, which indicated the chemisorption interaction for Z3A200 by a controlling step of the macro-pore and micro-pore diffusion for phosphate and sulfate adsorption process onto Z3A200, respectively. Thermodynamic studies showed that adsorption process onto Z3A200 was endothermic and spontaneous. Thus, phosphate and sulfate adsorption by using optimized Zn-Al LDH appears to be a promising adsorbent for their removal.

Fabrication of novel metal ion imprinted xanthan gum-layered double hydroxide nanocomposite for adsorption of rare earth elements.

The work focus to enhance the properties of xanthan gum (XG) by anchoring metal ions (Fe, Zr) and encapsulating inorganic matrix (M@XG-ZA). The fabricated nanocomposite was characterized by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR), surface area (BET) and zeta potential analysis. The adsorption of Sc, Nd, Tm and Yb was investigated after screening of synthesized materials in detail to understand the influence of pH, contact time, temperature and initial REE (rare earth element) concentration both in single and multicomponent system via batch adsorption. The adsorption mechanism was verified by FTIR, SEM and elemental mapping. The SEM images of Zr@XG-ZA demonstrate scutes structure, which disappeared after adsorption of REEs. The maximum adsorption capacities were 132.30, 14.01, 18.15 and 25.73 mg/g for Sc, Nd, Tm and Yb, respectively. The adsorption efficiency over Zr@XG-ZA in multicomponent system was higher than single system and the REEs followed the order: Sc > Yb > Tm > Nd. The Zr@XG-ZA demonstrate good adsorption behavior for REEs up to five cycles and then it can be used as photocatalyst for the degradation of tetracycline. Thus, the work adds a new insight to design and preparation of efficient bifunctional adsorbents from sustainable materials for water purification.

Understanding the factors affecting the adsorption of Lanthanum using different adsorbents: A critical review.

Over the past few decades, removal and recovery of Lanthanum (La) have received great attention due to its significance in different industrial processes. In this review, the application of various adsorbents viz. biosorbents, commercial and hybrid materials, nanoparticles, nanocomposites etc. have been summarized in terms of the removal and recovery of La. The influence of various operating parameters including pH, dosage, contact time, temperature, coexisting ions, adsorption kinetics, isotherm and thermodynamics were investigated. Statistical analysis of the obtained data revealed that 60% and 70% of the authors reported an optimum pH of 4-6 and a dose of 1-2 g/L, respectively. It can be concluded on the basis of an extensive literature survey that the adsorbent materials (especially hybrids nanocomposites) containing carboxyl, hydroxyl and amine groups offered efficient La removal over a wide range of pH with higher adsorption capacity as compared to other adsorbents (e.g., biosorbents and magnetic adsorbents). Also, in most cases, equilibrium and kinetics were followed by Langmuir and pseudo second-order model and adsorption was endothermic in nature. To evaluate the adsorption efficiency of several adsorbents towards La, desorption and regeneration of adsorbents should be given due consideration. The main objective of the review is to provide an insight into the important factors that may affect the recovery of La using various adsorbents.

Dry and wet ozonation of denim: Degradation products, reaction mechanism, toxicity and cytotoxicity assessment.

The study aims to identify the denim ozonation by-products under different operating conditions and investigate the chemical toxicity of these compounds via the inhibitory effect of the sample on the light emission of bioluminescent bacteria (Vibriofischeri) and on human health using the HepG2 human hepatoma cell line. Various by-products in treated denim extract were detected w gas chromatography-mass spectrometry (GC-MS) analysis. The results revealed that the main oxidation by-product was isatin (1H-indole-2,3-dione), which formed in excess amounts on wet ozonated denim. It was observed that this compound showed more toxicity when high ozone concentrations were used, especially in the presence of moisture. It exhibited a considerable antibacterial activity. EC20 and EC50 average values of 5.55% and 13.47% were obtained with a wet ozonation rinse bath at 48 g/N·m3, which makes it hazardous to aquatic environments.

N- and O- ligand doped mesoporous silica-chitosan hybrid beads for the efficient, sustainable and selective recovery of rare earth elements (REE) from acid mine drainage (AMD): Understanding the significance of physical modification and conditioning of the polymer.

Silica-chitosan hybrid beads were synthesized via three different methods to investigate the selective recovery of REE from AMD. The influence of amino/non-amino silanes, high molecular weight/high viscous chitosan and N-/O- based ligands were studied and their effects on REE removal efficiencies were analyzed. The adsorption efficiencies of three various groups of modified beads were inspected with respect to feed pH, in a single and a multi-component system, and their affinities towards the light and heavy rare earth elements (LREE/ HREEs) were interpreted to understand the intra-series REE separation behavior. The focus of the study was mainly directed towards utilizing these fabricated beads for the recovery of valuable REEs from the real AMD obtained at three different sampling depths which was found rich in iron, sulfur and aluminum. Moreover, the selectivity of the beads towards REEs improved with silanized and ligand immobilized gels and their impacts on REE recovery in the presence of competing ions were successfully presented in this paper. Also, the synthesized beads showed rapid REE adsorption and recovery within a process time of 5 min. Group II adsorbents, synthesized by forming silica-chitosan hybrid beads followed by PAN/acac modifications, showed superiority over the other groups of adsorbents.

Influence of relaxation modes on membrane fouling in submerged membrane bioreactor for domestic wastewater treatment.

Relaxation and backwashing have become an integral part of membrane bioreactor (MBR) operations for fouling control. This study was carried out on real municipal wastewater to evaluate the influence of different operational strategies on membrane fouling at equivalent water yield. Four relaxation modes (MBR10+0, MBR10+1, MBR10+1.5 and MBR10+2) were tested to analyze membrane fouling behavior. For the optimization of relaxation modes, fouling rate in terms of trans-membrane pressure, hydraulic resistances and characteristics of fouling fractions were analyzed. It has been observed that cake layer resistance was minimum in MBR10+1.5 but pore blockage resistance was increased in all relaxation modes. Moreover, high instantaneous flux contributed significantly to fouling rate at the initial stage of MBR operations. Relaxation modes were also efficient in removing irreversible fouling to some extent. Under all relaxation modes, COD removal efficiency ranged from 92 to 96.5%. Ammonium and TP removal were on the lower side due to the short solids and hydraulic retention time.