Preparation of Layered Double Hydroxides toward Precisely Designed Hierarchical Organization (original) (raw)
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Layered Double Hydroxides (LDHs): Versatile and Powerful Hosts for Different Applications
Layered double hydroxides are an emerging and intriguing class of materials having unique structural properties that allow their application in very different fields, such as catalysis, pollution control, agriculture, electronic, nanomedicine and drugs delivery. They are constituted by a sheets structure with formula [M2+1-x M3+x (OH)2](An-)x/n yH2O (M2+= Zn, Mg, Fe, Ni, Co..; M3+=Al, Ga, Fe…; An- = nitrates, carbonates, chloride). The exchange of these counterions with others inorganic/organic species, producing hybrid nanocomposites, makes these systems ideal candidates for many application. The goal is to find the right cationic ratio and the proper experimental conditions (pH, temperature, time, concentrations) to make the exchange process rapid and with high yield. A large number of synthetic processes for the nanocomposites production are theoretically disposable: coprecipitation, ionic exchange, reconstruction, hydrothermal or sol-gel synthesis. We will briefly describe the structural features of LDHs and the most widespread synthetic procedures.
Inorganics
Layered double hydroxides (LDHs), a type of synthetic clay with assorted potential applications, are deliberated upon in view of their specific properties, such as adsorbent-specific behavior, biocompatibility, fire-retardant capacity, and catalytic and anion exchange properties, among others. LDHs are materials with two-dimensional morphology, high porosity, and exceptionally tunable and exchangeable anionic particles with sensible interlayer spaces. The remarkable feature of LDHs is their flexibility in maintaining the interlayer spaces endowing them with the capacity to accommodate a variety of ionic species, suitable for many applications. Herein, some synthetic methodologies, general characterizations, and applications of LDHs are summarized, encompassing their broader appliances as a remarkable material to serve society and address several problems viz. removal of pollutants and fabrication of sensors and materials with multifaceted useful applications in the medical, electroc...
Chemistry of Materials, 2009
A simple, economical, and environmentally friendly method for the production of layered double hydroxides (LDHs) is presented. The synthesis procedure is based on dispersing insoluble metal oxides, adjusting the pH by adding an optimum amount of metal nitrates, and dispersing and aging the product for a short time (6-8 h). The final product does not require washing, opposite to the traditional coprecipitation synthesis procedure. A dissolution-precipitation-recrystallization mechanism is proposed for the formation of LDHs, based on particle size measurements, XRD analyses, radial distribution functions, and 27 Al MAS NMR studies. Solids were characterized by XRD, N 2 physisorption, TGA-DTA, SEM, and TEM, revealing that both LDHs and their calcination products have very similar properties to those prepared by conventional procedures. Pure LDH phase is obtained after 6-8 h; a large, uniform particle size that would usually require prolonged hydrothermal treatments is attained. Surface areas ranged from 32 to 93 m 2 g -1 and from 140 to 230 m 2 g -1 for fresh and calcined samples, respectively. This new method is intended to satisfy the growing demand of LDHs in large-scale applications as catalysts, SO x adsorbents, PVC additives, etc.
Chemistry of …, 2009
A simple, economical, and environmentally friendly method for the production of layered double hydroxides (LDHs) is presented. The synthesis procedure is based on dispersing insoluble metal oxides, adjusting the pH by adding an optimum amount of metal nitrates, and dispersing and aging the product for a short time (6-8 h). The final product does not require washing, opposite to the traditional coprecipitation synthesis procedure. A dissolution-precipitation-recrystallization mechanism is proposed for the formation of LDHs, based on particle size measurements, XRD analyses, radial distribution functions, and 27 Al MAS NMR studies. Solids were characterized by XRD, N 2 physisorption, TGA-DTA, SEM, and TEM, revealing that both LDHs and their calcination products have very similar properties to those prepared by conventional procedures. Pure LDH phase is obtained after 6-8 h; a large, uniform particle size that would usually require prolonged hydrothermal treatments is attained. Surface areas ranged from 32 to 93 m 2 g -1 and from 140 to 230 m 2 g -1 for fresh and calcined samples, respectively. This new method is intended to satisfy the growing demand of LDHs in large-scale applications as catalysts, SO x adsorbents, PVC additives, etc.
Layered double hydroxides: A review
Combination of two-dimensional layered materials and intercalation technique offers a new area for developing nanohybrids with desired functionality. Layered double hydroxides (LDHs) are mineral and synthetic materials with positively charged brucite type layers of mixed metal hydroxides. Exchangeable anions located in interlayer spaces compensate for positive charge of brucite type layer. Since most biomolecules are negatively charged, can be incorporated between LDHs. A number of cardiovascular, anti-inflammatory agents are either carboxylic acids or carboxylic derivatives and could be ion exchanged with LDHs to have controlled release. LDHs have technological importance in catalysis, separation technology, medical science and nanocomposite material engineering.
Layered double hydroxides: a gleam on their synthetic routes with biomedical applications
Layered double hydroxides: a gleam on their synthetic routes with biomedical applications, 2023
sustainability perspective. The reduction of waste and utilization or recyclization of waste with the exploration of sustainable and cost-effective materials and treatment methods are becoming the fascinating aspect of science and technology [1, 2]. Sustainable research is generally based on the green chemistry concept which requires the need for environmental, economic and social aspects to be assimilated. It involves the use of various materials that are facile synthesized from easily available and low-cost precursors with no hazardous effluents. These materials have been widely used for the energy-saving, waste reduction, recycling of plastics, water treatment, etc. Catalysis and adsorption are important tools for the processing and production of various chemicals or fuels through environmental sustainability and remediation [3-5]. Recently, the pertinence of layered double hydroxide (LDHs) or Hydrotalcite-type anionic clays (HTs) in various fields has gained considerable attention into their environmental remediation and sustainable development. These clays have been studied and recently investigated in catalysis and adsorption processes. Furthermore, these clay materials can also be produced by the facile and ease of synthesis pathways from easily available chemicals with less hazardous effluents. These materials are quite stable, cost-effective
Towards understanding, control and application of layered double hydroxide chemistry
Journal of Materials Chemistry, 2006
Layered double hydroxides (LDHs) have a vast number of potential applications in fields as diverse as separation chemistry, polymer additives and catalysis. They are facile and cheap to prepare, and are environmentally friendly. In this paper, some of the most exciting recent developments in LDH chemistry are discussed, with an emphasis on how we can control their chemistry and how in situ techniques can provide enhanced understanding of the nanoscopic processes involved in intercalation reactions.
Synthesis of layered double hydroxides through continuous flow processes: A review
Chemical Engineering Journal, 2019
Different continuous flow processes allow the production of LDHs particles with controlled size and morphology or individual nanosheets, and of LDH-based hybrids and nanocomposites. Continuous flow method Microreactor Static method Metal salt solution Alkaline solution Batch LDH particle diameter Volume (%) LDH particle diameter Volume (%) Metal salt solution Alkaline solution Synthesis of layered double hydroxides through continuous flow processes: A review
A B S T R A C T This work is the first report that critically reviews the properties of layered double hydroxides (LDHs) on the level of speciation in the context of water treatment application and dynamic adsorption conditions, as well as the first report to associate these properties with the synthetic methods used for LDH preparation. Increasingly stronger maximum allowable concentrations (MAC) of various contaminants in drinking water and liquid foodstuffs require regular upgrades of purification technologies, which might also be useful in the extraction of valuable substances for reuse in accordance with modern sustainability strategies. Adsorption is the main separation technology that allows the selective extraction of target substances from multicomponent solutions. Inorganic anion exchangers arrived in the water business relatively recently to achieve the newly approved standards for arsenic levels in drinking water. LDHs (or hydrotalcites, HTs) are theoretically the best anion exchangers due to their potential to host anions in their interlayer space, which increases their anion removal capacity considerably. This potential of the interlayer space to host additional amounts of target aqueous anions makes the LDHs superior to bulk anion exchanger. The other unique advantage of these layered materials is the flexibility of the chemical composition of the metal oxide-based layers and the interlayer anions. However, until now, this group of " classical " anion exchangers has not found its industrial application in adsorption and cat-alysis at the industrial scale. To accelerate application of LDHs in water treatment on the industrial scale, the authors critically reviewed recent scientific and technological knowledge on the properties and adsorptive removal of LDHs from water on the fundamental science level. This also includes review of the research tools useful to reveal the adsorption mechanism and the material properties beyond the nanoscale. Further, these properties are considered in association with the synthetic methods by which the LDHs were produced. Special attention is paid to the LDH properties that are particularly relevant to water treatment, such as exchangeability ease of the interlayer anions and the LDH stability at the solid-water interface. Notably, the LDH properties (e.g., rich speciation, hydration, and the exchangeability ease of the interlayer anions with aqueous anions) are considered in the synthetic strategy context applied to the material preparation. One such promising synthetic method has been developed by the authors who supported their opinions by the unpublished data in addition to reviewing the literature. The reviewing approach allowed for establishing regularities between the parameters: the LDH synthetic method―structure/surface/interlayer―removal―suitability for water treatment. Specifically, this approach allowed for a conclusion about either the unsuitability or promising potential of some synthetic methods (or the removal approaches) used for the preparation of LDHs for water purification at larger scales. The overall reviewing approach undertaken by the authors in this work mainly complements the other reviews on LDHs (published over the past seven to eight years) and for the first time compares the properties of these materials beyond the nanoscale.
Synthesis, characterization and applications of layered double hydroxides containing organic guests
New Journal of Chemistry, 1998
A new resin is prepared by coupling amberlite XAD-4 with salicylic acid through an azo spacer. Then the polymer support was coupled with cystein. The resulting sorbent has been characterized by FT-IR and elemental analysis and studied for adsorption and kinetic behavior of aspartic acid on the modified amberlite XAD-4. The optimum pH value for sorption of the amino acid was 8.5. The sorption capacity was found to be 5.31 mmol g −1 of resin for aspartic acid. The modified resin can be reused for 20 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 99 % was obtained for the aspartic acid with 0.5 M nitric acid as eluting agent. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The rate constants of pseudo-first-order, pseudosecond-order adsorption and intra-particular diffusion were found 1.68 × 10 −2 min −1 , 1.14 × 10 −5 min −1 mg −1 g and 59.62 mg g −1 min −1/2 , respectively.