Ultrathin dodecyl-sulfate-intercalated Mg-Al layered double hydroxide nanosheets with high adsorption capability for dye pollution

Precise control of photogenerated carrier behavior of zinc oxide through band reconstruction to enhance photocatalytic treatment of dye wastewater

In the field of photocatalytic treatment of dye wastewater, zinc oxide (ZnO) is a typical semiconductor photocatalyst, but it has some disadvantages such as wide band gap, low carrier yield and easy recombination. In this study, Cr-ZnO/N-CQDs catalyst was synthesised using the strategy of p-type doping and construction of Z-scheme heterojunction. The results showed that the removal rate of Cr-ZnO/N-CQDs for MB dye was 97.42 %, which was 70.56 % higher than that of ZnO, and was still 92.16 % after 5 cycles, and the TOC removal rate of methylene blue wastewater was 88.60 %. The reason for the enhanced photocatalytic activity of Cr-ZnO/N-CQDs is that the π* electron (e-) in the N-CQDs interact with the 3d orbitals of Cr-ZnO, so that e- is more easily transferred from the valence band of Cr-ZnO to the conduction band of N-CQDs. The band gap of p-type Cr-ZnO is narrowed, which makes its photogenerated carrier yield increase, hole concentration raise, and the adsorption capacity of H2O molecules reduce by 1.04 eV. The density functional theory calculation shows that the maximum Gibbs free energy of Cr-ZnO for the production of hydroxyl radical is 0.05 eV lower than that of ZnO. This study lays theoretical and practical foundation for the photocatalytic treatment of dye wastewater with ZnO.

The Electronic Properties and Adsorption Performance of LDH/Graphene, and LDH/g-C3N4 for the Removal of Pharmaceutical Contaminants: A Molecular Dynamics Simulation

Water shortages and pharmaceutical pollution are two interconnected crises that pose severe threats to global health, environmental sustainability, and economic stability. Pharmaceutical pollution is widespread and has reached potentially toxic levels in over 258 rivers in 104 countries. So far, more interest has been paid towards efficient water treatment processes in recent years. In this study, we explore the efficacy of layered double hydroxide (LDH) nanocomposites with graphene and graphitic carbon nitride (g-C3N4) as promising adsorbents of pharmaceutical contaminants. The LDH nanocomposite has been designed and simulated for the first time, consisting of two layers of sodium hydroxide with a layer of graphene and g-C3N4. We investigated the adsorption performance of LDH, specifically LDH/graphene and LDH/g-C3N4, for the removal of pharmaceutical contaminants including acetaminophen (AC), caffeine (CAF), and sulfamethoxazole (SMZ). Through comprehensive molecular dynamics simulations using the reactive forcefield (ReaxFF) software, we investigated the adsorption mechanisms, kinetics, and adsorption capacity of pharmaceutical contaminants onto these nanocomposite surfaces. Our findings showed that the combination of LDH/graphene had a higher adsorption capacity for the removal of pharmaceutical contaminants than LDH/g-C3N4. At 70 Picoseconds (Ps), 124, 129, and 142 molecules of each of the pharmaceutical contaminants AC, CAF and SMZ, respectively, had been adsorbed by LDH/graphene, with a higher exothermic energy equating to -1111, -1015, and -1150 × 103 kJ/mol, respectively. On the other hand, for LDH/g-C3N4 at 70 Ps, 108, 110, and 120 molecules of AC, CAF and SMZ, respectively, had been adsorbed, with exothermic energy equating to -978, -948, and -1173 × 103 kJ/mol, respectively. Finally, we calculated the electronic properties, including the band gap and density of state of the nanocomposite materials, to check their effect on the adsorption process. In addition, the results showed that the adsorption kinetics followed a pseudo-first-order model, while the adsorption isotherms for AC, CAF and SMZ adhered to the Langmuir model.

Enhanced dispersion of prussian blue via intercalation into layered double hydroxides for efficient solar seawater evaporation

Prussian blue (PB) is favored for its photothermal absorption capability in solar vapor generation applications. However, the photothermal conversion efficiency of current PB-based devices is limited by the material's poor dispersion. Herein, we report a method of incorporating PB in the interlayers of layered double hydroxides (LDHs) to prevent its aggregation. The dispersion is further enhanced and stabilized by the addition of sodium dodecyl sulfate (SDS). The thermal and water stability of PB is improved due to the rigid structure of LDHs and interactions between layers and anions. Elemental analysis confirms that with the increase of molar ratio of Mg/Al and the introduction of SDS, concentrations of PB are decreased accordingly. As a result, the rate of solar vapor generation is increased by 35.9% for powders containing 50 mg of equivalent PB. Of note, converting this material into a three-dimensional structure of high rebound foam further enhances solar water evaporation rate, from 0.79 kg m-2 h-1 to 0.98 kg m-2 h-1, with only 20 mg of equivalent PB, increasing the corresponding photothermal conversion efficiency from 53.8% to 66.3%.

Hydrothermal synthesis of Mg/Al-layered double hydroxide modified water hyacinth hydrochar for remediation of wastewater containing mordant brown dye

A high-performance dye adsorbent of Mg/Al-layered double hydroxide modified water hyacinth hydrochar (MgAl@WH) was synthesized by a simple hydrothermal method. The surface functional groups, elemental composition, crystalline structure, and surface morphology of the prepared (MgAl@WH) were determined using different analytical techniques. The characterization results revealed that the (MgAl@WH) hydrochar surface offered more active adsorption sites, facilitating the mordant brown (anionic dye) adsorption, leading to its superior performance with much higher uptake capability (311.0 mg g-1 at 298 K) than Mg/Al double hydroxide nanosheets (MgAl DLHs, 80.2 mg g-1 at 298 K) and dried water hyacinth (WH, 10.0 mg g-1 at 298 K). The adsorption behavior of MgAL@WH follows the pseudo second order kinetic model (R2 = 0.999) and Langmuir isotherm model (R2 = 0.999). Moreover, MgAl@WH bonded efficiently with mordant brown dye via hydrogen bonding and interlayer anion exchange with monolayer formation. Additionally, the recycling tests revealed that the MgAl@WH can be reused over 10 cycles without significant change in the removal efficiency. Based on the obtained findings, Mg/Al-layered double hydroxide modified water hyacinth hydrochar (MgAl@WH), for its economic and environmental benefits, has recently been used as an efficient adsorbent to remediate industrial wastewater containing anionic dyes.

A Self-Healing Gel with an Organic-Inorganic Network Structure for Mitigating Circulation Loss

Lost circulation control remains a challenge in drilling operations. Self-healing gels, capable of self-healing in fractures and forming entire gel block, exhibit excellent resilience and erosion resistance, thus finding extensive studies in lost circulation control. In this study, layered double hydroxide, Acrylic acid, 2-Acrylamido-2-methylpropane sulfonic acid, and CaCl2 were employed to synthesize organic-inorganic nanocomposite gel with self-healing properties. The chemical properties of nanocomposite gels were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy and thermogravimetric analysis. layered double hydroxide could be dispersed and exfoliated in the mixed solution of Acrylic acid and 2-Acrylamido-2-methylpropane sulfonic acid, and the swelling behavior, self-healing time, rheological properties, and mechanical performance of the nanocomposite gels were influenced by the addition of layered double hydroxide and Ca2+. Optimized nanocomposite gel AC6L3, at 90 °C, exhibits only a self-healing time of 3.5 h in bentonite mud, with a storage modulus of 4176 Pa, tensile strength of 6.02 kPa, and adhesive strength of 1.94 kPa. In comparison to conventional gel, the nanocomposite gel with self-healing capabilities demonstrated superior pressure-bearing capacity. Based on these characteristics, the nanocomposite gel proposed in this work hold promise as a candidate lost circulation material.

Biomimetic mineralization of nacre-inspired multiple crosslinked PVA/CaAlg/SiO2 membrane with simultaneously enhanced mechanical and separation properties

Inspired by the natural nacre structure, we propose a new strategy to fabricate mineralized, multiple crosslinked hydrogel membranes with the "rigid silica in soft polymer" nacre-like structure. In-situ SiO₂ nanoparticles (NPs) and polyvinyl alcohol/sodium alginate (PVA/NaAlg) are used to simulate the rigid "bricks" and soft "mortar" compositions of nacre, respectively. The nacre-like mineralized (PVA/CaAlg/SiO₂) membrane showed a higher tensile strength of 4.1 ± 0.08 MPa, excellent pure water flux of 170 ± 3 L/m²h, and an oil/water rejection rate of 99 %. The interwoven hierarchal structure, similar to nacre, was determined by SEM analysis. In addition, incorporating SiO₂ NPs increases the anti-swelling, roughness, and hydrophilicity of the membranes. PVA/CaAlg/SiO₂ membrane exhibited excellent superhydrophilicity (WCA value was 0°) and superoleophobicity underwater (OCA value was 162°). PVA/CaAlg/SiO₂ membrane also showed excellent separation performance for water-soluble organic pollutants and can be used for dye separation with rejection efficiencies of 99.5 %, 99.1 %, and 98.3 % for Congo red (CR), Alizarin red (AR), and Sunset yellow (SY), respectively. Moreover, PVA/CaAlg/SiO₂ membrane had outstanding long-term filtration and antifouling performance. The biomineralization-inspired structure provides a promising technique that can be used to prepare high-performance organic-inorganic membranes with great promise for wastewater separation application.

High-performance hydrophobic magnetic hydrotalcite for selective treatment of oily wastewater

Oil emulsified in water is one of the most difficult mixtures to treat due to the good stability of emulsions, so there is a growing demand for more efficient methods for separating immiscible oil/water mixtures. In this context, the focus of this study was to obtain an adsorbent for the selective treatment of a simulated oily wastewater. To this aim, a modified hydrotalcite sample with hydrophobic and magnetic characteristics was prepared and characterized. Initially, the effect of sodium dodecyl sulfate (SDS) amount on the adsorbent characteristics was evaluated (266-800 mg_SDS g^-1_LDH). The hydrophobic hydrotalcite (LDH-SDS) containing 533 mg_SDS g^-1_LDH (LDH-SDS2) presented a higher interlayer space where the surfactant molecules were arranged perpendicular to the lamellae, allowing better access to the hydrotalcite pores and facilitating the selective adsorption of oil compounds. Moreover, the synergistic association of hydrophobic properties with super-wetting and effective adhesion oil to Fe₃O₄ favoured the selective adsorption of the simulated oily wastewater onto the hydrophobic and magnetic hydrotalcite (LDH-MSDS), facilitating the post-treatment separation. The kinetic analysis demonstrated that the adsorption equilibrium was attained in 120 min and the pseudo-second order model was the most suitable for predicting the removal of total organic carbon (TOC) from the simulated oily wastewater. The Langmuir model described very well the equilibrium experimental data, with a maximum adsorption capacity for TOC removal using LDH-MSDS of 659.9 mg g^-1. Therefore, the modified hydrotalcite prepared in this study showed intrinsic characteristics that make it a promising adsorbent for the selective treatment of oily wastewaters.

Adsorption of polycyclic aromatic hydrocarbons over CuZnFeAl–LDH modified by sodium dodecyl sulfate

Polycyclic aromatic hydrocarbons (PAHs) have received extensive attention due to being highly toxic, mutagenic, and carcinogenic organic pollutants. As a result, a series of adsorbents have been designed and developed to solve the problem. In this paper, CuZnFeAl–S has been explored as a highly efficient adsorbent for PAHs. First, CuZnFeAl–LDH was prepared using a coprecipitation method and then calcined at 500 °C to obtain CuZnFeAlO. Finally, CuZnFeAl–S was prepared by modifying CuZnFeAlO with sodium dodecyl sulfate (SDS). The physical and chemical properties of the adsorbents were characterized by XRD, N₂ adsorption–desorption, SEM, ICP, FT-IR, TG-DSC, and IGC; subsequently their adsorption performance was investigated. The results show that the surface properties of CuZnFeAl–S changed from hydrophilic to hydrophobic after SDS modification, which enhanced the adsorption of PAHs obviously. The removal of naphthalene and phenanthrene on CuZnFeAl–S reached 97.3% and 90.3%, respectively. And the adsorption process of naphthalene and phenanthrene conforms to Langmuir adsorption and Freundlich adsorption, respectively. Besides, the adsorption thermodynamics indicate that the adsorption of PAHs was a spontaneous exothermic reaction. The highly efficient PAH adsorption performance of CuZnFeAl–S is the synergistic result of various molecule interactions, such as hydrogen bonding, π–π interactions, and electrostatic attraction.

CuZnFeAl–S improves the adsorption of polycyclic aromatic hydrocarbons, which has a profound impact on environmental treatment.

Manipulate the nano-structure of layered double hydroxides via calcination for enhancing immobilization of anionic dyes on collagen fibers

In this work, we present an effective approach for promoting the immobilization of anionic dyes on the collagen fibers of the leather matrix via introducing layered double oxide (LDO), which is obtained by calcining layered double hydroxides (LDH), inspired by incorporating their memory effect and charge effect. The results indicate that the calcination increases specific surface area, oxygen vacancies, and Al³⁺ defects of LDH nanosheets, and the structure of LDH nanosheets can be reconstructed by rehydration. Diffusion behavior of both LDH and LDO nanosheets into the collagen fibers follows the Langmuir model. The LDO nanosheets can penetrate into the collagen fibers more easily and evenly than that of the LDH nanosheets. Moreover, the formation of ionic bonds, hydrogen bonds, and coordination bonds between the nanosheets and the collagen stabilizing the collagen microstructures can endow the collagen fibers with improved thermal stability. Increased porosity of the collagen fibers results in enhanced adsorption and immobilization capacity for anionic dyes on the collagen fibers of the leather matrix in leather post-tanning process. Furthermore, adsorption behavior of anionic dye on the collagen fibers can be well accorded with pseudo-second-order and Langmuir model, exhibiting a monolayer adsorption process. This established cooperative approach will be helpful to extend the application of clay for improving the dyeing performance of leather matrix towards eco-leather manufacture and effectively reduce emission of dyes from the source in leather manufacturing.

Application of ZnO-Nd Nano-Photocatalyst for the Reactive Red 198 Dye Decolorization in the Falling-Film Photocatalytic Reactor

A large amount of Reactive red 198 (RR198) is released yearly into the environment. RR198 is toxic for human and aquatic creatures; therefore, it should be removed from wastewater before releasing into the environment. In this study, the nano ZnO-Nd -photo-catalyst for the first time was synthesized by the combustion method. First, the physical characteristics of the generated nano photocatalyst were evaluated using FESEM, XRD, Bandgap calculation, and FTIR analysis. Then, the ZnO-Nd nano-photocatalyst was suspended into the contaminated water with RR198 dye in a falling-film photocatalytic reactor. The effects of parameters such as the amount of H2O2, catalyst dose, pH, and initial concentration of dye were investigated during the experiments. Finally, the decolorization process with the falling-film photocatalytic reactor was optimized using response surface methodology (RSM). The physical characteristics showed that the average particle size of the synthesized ZnO-Nd was 40 nm. Doping ZnO with Nd reduced the photocatalyst energy bandgap by 14%. The results indicated that the optimum amount of catalyst dose and pH level was 0.1 g/L and 5, respectively. The simultaneous usage of H2O2 and ZnO-Nd with an H2O2/dye ratio of two increased dye removal performance by 90%. The results demonstrated that the developed equations can be applied to predict the performance of the falling-film photoreactor. This study showed that using the nano ZnO-Nd photocatalyst in a falling-film photocatalytic reactor under optimum operating conditions is an appropriate way to remove RR198 from water.

Recent progress in the synthesis of Layered Double Hydroxides and their application for the adsorptive removal of dyes: A review

Layered double hydroxides (LDHs), also known as anionic clays, are lamellar inorganic solids with a brucite-like structure and consist of positively charged metal hydroxide sheets intercalated by anions and water molecules. Choice of LDH is beneficial as it displays properties like simple synthesis procedures, adjustable structure, stability, large surface area, homogeneous positive charge distribution over the surface, interplanar spacing, and versatility to synthesize a variety of composites. Due to these properties LDHs act as efficient adsorbents for wastewater treatment. This review presents a detailed overview of the removal of hazardous organic dyes using different LDHs and LDH-hybrids/composites. The review also incorporates methods of synthesis of various LDHs and composites and the effect of their morphology on dye removal capacity. The effects of adsorption variables such as pH, adsorbent dosage, initial concentration of dye, contact time on the adsorption of these materials are also explained along with adsorption isotherms, kinetics and operative mechanisms. This article incorporates 156 references, majority of which have been taken from the available literature of last 5 years.

Colloidal magnesium hydroxide Nanoflake: One-Step Surfactant-Assisted preparation and Paper-Based relics protection with Long-Term Anti-Acidification and Flame-Retardancy

Enhancing the interfacial dispersion and suspension stability is crucial for magnesium hydroxide (Mg(OH)₂) nanomaterials in the long-term deacidification of paper-based cultural relics. However, because of the low specific surface area and the poor solvent compatibility of as-prepared large-sized Mg(OH)₂, it often tends to agglomerate and settle down during the usage and storage, that is harmful for paper protection due to its unevenly deacidification and nonuniformly distribution on paper cellulose. Herein, we propose a feasible preparation of colloidal Mg(OH)₂ ultrathin nanoflakes with high dispersion stability via a simple one-step surfactant-assisted strategy. The surfactant acts as both a structure-direct agent to confine the growth of Mg(OH)₂ with rich active sites and a surface modifier to enhance its solvent adaptability and dispersion stability, avoiding the common fussy procedure with additional steric stabilizer. Owing to the evenly interaction with free acid species therein and the uniformly distribution on the paper fiber as alkaline reserve, the as-obtained Mg(OH)₂ presents the superior paper protection performance characterized by its safer pH of 7.29 for the original aged paper (pH = 5.03) and the excellent long-term anti-acidification effect with competitive pH of 5.47 after accelerated-aging at 105 °C for 5 months. Furthermore, Mg(OH)₂ nanoflakes with surfactant-modified structure also endue them as an improved flame retardant for multifunctional paper protection. The protection with Mg(OH)₂ has little effect on the paper surface properties and cellulose crystallinity, in line with the principle of least intervention. This work will put forward a feasible way toward colloidal Mg(OH)₂ nanoflakes with excellent paper protection performance, shedding light on the development of emerging protection materials for paper-based cultural relics.

Enhanced adsorption properties of organic ZnCr-LDH synthesized by soft template method for anionic dyes

Organic ZnCr-LDH (ST-LDH) was synthesized by a facile one-step hydrothermal technique using methyl orange (MO) as a soft template agent, which can efficiently remove methyl orange (MO), Congo red (CR), and orange II (OII) from aqueous solution. The microstructure of ST-LDH by modifying changed obviously, from the cellular structure to the stacking structure formed by the face-face contact of hydrotalcite nanosheets, which resulted in much more exchangeable nitrate ions to remain in the interlayer space. The pre-insertion of benzene sulfonate as a pillar expanded the interlayer gallery, which facilitated the pollutant anions (MO, CR, and OII) into the interlayer of LDH in the subsequent adsorption process. The maximum adsorption capacity of ST-LDH for MO, CR, and OII was 4200.8 mg/g, 1252.0 mg/g, and 1670.6 mg/g, respectively, which is approximately 1.86 times, 1.8 times, and 2.32 times that of the pristine NO₃-LDH, respectively. The removal mechanism of anionic dyes was determined as anion exchange between NO₃^- anions and dye molecules. The adsorption behavior for MO and OII is multilayer adsorption, while the adsorption behavior for CR is monolayer adsorption. The adsorption process mainly was controlled by the chemical bonding between the dye molecules and adsorbent active sites. The LDH can be effectively regenerated by photocatalysis after MO adsorption. The ST-LDH has a great potential to be used as a high-efficient adsorbent to remove anionic dyes from aqueous solution. The schematic illustration of the synthetic process of soft template agent modified and unmodified hydrotalcites by one-pot hydrothermal method and the adsorption process of MO by ST-LDH were shown in Fig. 12. Modified hydrotalcite (ST-LDH) was prepared using methyl orange (MO) as a soft template agent. Compared with unmodified hydrotalcite (NO₃-LDH), the insertion of benzene sulfonate anions into the hydrotalcite layer resulted in the increase of the interlayer spacing from 8.269 to 8.654Å. The LDH host structure pre-intercalated by benzene sulfonate anions evolved into pillared materials in interlayer; benzene sulfonate anions as a column expanded the interlayer spacing of (003) base plane, which facilitated the pollutant anions (MO, CR, and OII) into the interlayer of ST-LDH and exchanged with NO₃^- anion in the subsequent adsorption process. It can be inferred that in the process of modification hydrotalcite by benzene sulfonate, a small amount of benzene sulfonate anions pre-inserted into the gallery of hydrotalcite with a monolayer model in the process of hydrotalcite modification, and its inclination angle is calculated to be about 29.1°. After ST-LDH sample adsorbed the MO molecules, dye molecules intercalated into the LDH host, and successful exchange with NO₃^- anions, the d₀₀₃ value increased to 24.78 Å. A large amount of MO^- anions were intercalated into the gallery of ST-LDH with a bilayer model according to the Freundlich isotherm model, and the tilting angle increases to 53.6°. The adsorption capacity of MO by ST-LDH was significantly enhanced to 4200.8 mg/g, which was much higher than that of NO₃-LDH (2252.8 mg/g). Schematic illustration of the synthetic process of LDH materials and adsorption process of MO by ST-LDH.