Presentation on theme: "1. Advanced layered double hydroxides and its applications by Dr. P. SANGEETHA Assistant Professor Materials Chemistry Division School of Advanced Sciences."— Presentation transcript:
1. Advanced layered double hydroxides and its applications by Dr. P. SANGEETHA Assistant Professor Materials Chemistry Division School of Advanced Sciences VIT, Vellore
Hydrotalcite synthesis via co-precipitation reactions using MgO and Al(OH) 3 precursors Potential applications, such as clinic anti-acid, catalyst support, adsorptive flotation, flame retardant, acid scavengers in polymer composites and as a raw material for high temperature insulating porous ceramics. This compound is usually produced by controlled chemical equilibrium shifting processes (such as co-precipitation) that requires various other purification steps and careful drying (freeze drying or ultrafiltration). A novel route to synthesize hydrotalcite is presented, based on the hydration, dissolution and co-precipitation reactions carried out almost simultaneously in aqueous suspension containing reactive magnesium oxide and aluminum hydroxide
A Route for MAH Co-precipitation
Concomitant synthesis of highly crystalline Zn–Al layered double hydroxide and ZnO: Phase interconversion and enhanced photocatalytic activity Metal oxide/hydroxide with hierarchical nanostructures has emerged as one of the most promising materials for their unique, attractive properties and feasibility of applications in various fields. A concomitant synthesis of crystalline zinc aluminum layered double hydroxide (ZnAl-LDH) nanostructure and ZnO is presented using Al substrate as template. Studies on interconversion of ZnO to LDH phase in bulk solution under hydrothermal conditions produced Al-doped ZnO (AZO) in one case, and in other, it improves the crystallinity of LDH film templated on Al substrate.
(a) SEM images of plate LDH sample of experiment 1. Inset is the photographic image of 2 cm 2 cm Al plate fabricated with ZnAl-LDH assembles, (b) XRD pattern of ZnO sample precipitated in bulk solution (experiment 1), and (c) SEM images of bulk ZnO sample Representation: Simultaneous synthesis of crystalline LDH and ZnO Ref: Journal of Colloid and Interface Science 366 (2012) 28–36
Mg–Al hydrotalcite catalysts for transesterification of vegetable oils Mg–Al hydrotalcites rehydrated after calcination are promising catalysts for the methanolysis of vegetable oils. To gain insight into the basis of their catalytic action, the adsorption of methanol over some commercial Mg–Al hydrotalcites was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Different species formed after methanol adsorption were identified, being the total quantity of methoxy species related to the basic character of the sample.
Heteropoly blue-intercalated layered double hydroxides for cationic dye removal from aqueous media
Heteropoly blue-intercalated layered double hydroxide (HB- LDH) was obtained by aqueous ion exchange of a Zn–Al LDH precursor in nitrate form with the reduced polyoxometalate anions [PW10Mo2O40]5−. The HB-LDH has been used for the removal of cationic dye methylene blue (MB) from aqueous solutions via adsorption. The intercalation of large cluster anion [PW10Mo2O40]5− into LDH could induce the adsorption to cationic dye of MB, obviously. The HB-LDH shows much higher cationic dye adsorption capacity than pure LDH and the maximum adsorption capacity Qmax of MB onto ZnAl–PW10Mo2 is mg/g.
Complexing agent assisted synthesis of high aspect ratio Fe 3+/ Mg 2+ layered double hydroxides A new, facile synthesis for Fe 3+ /Mg 2+ LDHs is developed and the crucial feature of the synthesis is the usage of a complexing agent (diethylenetriamine, DETA) to increase the solubility of iron phases precipitated intermediately. The optimized synthesis route yields high aspect ratio Fe 3+ /Mg 2+ LDHs which are expected to be interesting filler materials for flame retardant nanocomposites.
Direct synthesis of a chloride-form of pyroaurite (Fe 3 + /Mg 2 + LDH) ► Usage of a complexing agent prevents FeOOH precipitation ► Synthesis yields high crystallinity and high aspect ratio LDHs.
Synthesis Of Glycerol Carbonates By Transesterification Of Glycerol - Using Supported Hydrotalcites As Catalysts
Proposal of mechanism of hydrotalcite-catalyzed transesterification of glycerol with DEC.
Protein interactions with nanosized hydrotalcites of different composition Nanosized hydrotalcite-like compounds (HTlc) with different chemical composition were prepared and used to study protein adsorption. Two soft proteins, myoglobin (Mb) and bovine serum albumin (BSA), were chosen to investigate the nature of the forces controlling the adsorption and how these depend on the chemical composition of the support
Synthesis of hydrotalcite by neutralization of bauxite residue mud leachate with acidic saline drainage water Co-disposal of alkaline bauxite residue leachate with acidic deep drainage waters. Co-disposal can generate a neutral pH solution and hydrotalcite precipitate. Hydrotalcite formation aids removal of alkalinity and salt from solution.
Coupling reaction Combining two industrially important reactions, viz., an exothermic hydrogenation and endothermic dehydrogenation on one catalyst is a challenging task in the area of catalysis. Coupling of two contradictory chemical transformations over a single catalyst bed has several advantages : operational simplicity mitigation of thermodynamic limitations eco-friendly and enhanced product selectivities An exothermic reaction and endothermic reaction has been coupled. Tuning of coupling reaction with respect to mass balance and thermal balance.
Coupling reaction 1. Endothermic reaction: Dehydrogenation of 1,4 butanediol to Gamma Butyrolactone 2. Exothermic reaction : Hydrogenation of Nitrobenzene to aniline 3. Coupling reaction: An Endothermic and Exothermic reaction is coupled.
Finds promising applications in areas such as: catalysis, medicine, additives in polymer. Practical applications include, solar cells and gas sensors. Inorganic materials such as LDHs must be fabricated into well-oriented continuous supported thin films or self-supporting membranes, and this step can be at least as challenging as the synthesis of the material itself is in a powdered form Advanced layered double hydroxides
LDHs display great potential as precursors/supports to prepare catalysts. The catalytic sites can be preferentially orientated, highly dispersed, and firmly stabilized to afford excellent catalytic performance and recyclability. The approaches to prepare catalysts based on LDH materials include, but are not limited to, exfoliation of the brucite-like layers, lattice orientation/lattice confinement by the brucite-like layers, and intercalation 24 ….contd
25 2. Bio- porous carbon materials for water purification One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water-rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment.
Importance of water Over 75% of the Earths surface is covered in water 97.5% of this water is salt water, leaving only 2.5% as fresh water Nearly 70% of that fresh water is frozen in the icecaps of Antarctica and Greenland; most of the remainder is present as soil moisture, or lies in deep underground aquifers as groundwater not accessible to human use.
Access to water ≠ Safe drinking water
Clean water Disinfection Decontamination Re-use and reclamationDesalination Shannon etal. Nature 452(2009) Science and technology for water quality management
Current Purification Methods Chemical – Activated Carbon – Chlorination – UV light Biological – Bacteria to decompose waste – Oxidation of chemicals Mechanical – Settling – Sand or similar screening material This water must of course be first purified to be fit for human consumption The methods used for this are:
Integrated Solution CONVENTIONAL WASTE WATER TREATMENT Process Raw Water Water Treatment Plant Treated Water Effluent Treatment Plant Effluent Discharge WASTE WATER MANAGEMENT USING MEMBRANE PROCESSES Process Raw Water Water Treatment Plant Treated Water Product Recovery Plant (NF) Effluent Partially treated effluent Water Recovery & Recycle Plant (RO) Recycled Water Recovered Product Minimal Discharge Source Reduction Product Recovery Water Reuse Waste Minimisation Industrial Waste Water Management (any capacity KLD to MLD)
Nano-material Contaminants Removal Metal nanoparticles & Bimetallic nanoparticles (effective redox media) Organic & inorganic pollutants Metal oxide like TiO2 (effective photocatayst) Organics like Chloro-alkanes and inorganic pollutants like heavy metals Metal oxides like MgO and Ag nanoparticles Bacteria removal Carbon Nanotubes (Nanosorbents) Heavy metals like Pb, Cd, Cu etc.; organics like dioxin, anions like arsenate, fluoride etc ; bacteria like E. Coli and polio virus Nanotube/ nanoparticle embedded membrane (Nanocomposite membrane) Removal of wide range of contaminants from water with high flux, high selectivity, less fouling characteristics Activated carbon fibers (nanosorbents) Organics like benzene, toulene etc. Nano-materials of Interest for Water Purification
Selected nanomaterials currently being evaluated as functional materials for water purification Dendrimer (repeatedly branched polymeric species) Zeolite (microporous aluminosilicate materials) Carbon Nano-TubeMetal Oxide
Nanotechnology in Water Purification Bacteria removal Anions removal (Arsenite, Arsenate etc.) Organic contaminants removal Heavy Metals Removal (Lead, Cadmium etc.)
34 Contd… Earlier nanomaterials has been used extensively for purification of water. Recently, porous carbon materials, which are bio based, has got considerable scope towards pure water. Removal of contaminants and recycling of the purified water would provide significant reductions in cost, time, and labor to industry and result in improved environmental stewardship. The world is facing formidable challenges in meeting rising demands of clean water as the available supplies of freshwater are decreasing due to: ….. extended droughts, ….. population growth, …..more stringent health-based regulations, and ….. competing demands from a variety of users
Carbon Nano-Tubes (CNT) Graphitic sheets rolled into seamless tubes have diameters ranging from tubes have diameters ranging from about a nanometer to tens of nanometers about a nanometer to tens of nanometers with lengths up to centimeters have unique electrical, thermal, hydrodynamic and mechanical properties properties SWNT-A single graphite sheet rolled MWNT-Multiple graphitic sheets rolled 1. Soumitra Kar, R.C. Bindal, S. Prabhakar, P.K. Tewari, 'Potential of Carbon Nano-Tubes in Water Purification: an Approach towards Development of an Integrated Membrane System', International J. of Nuclear Desalination, Vol.3, No.2, 2008, pp K. Dasgupta, Soumitra Kar, Ramani Venugopal, R.C. Bindal, S. Prabhakar, P.K. Tewari, Self-standing Geometry of Aligned Carbon Nano-Tubes with High Surface Area, Materials Letters, Vol. 62, 2008 pp
Advanced types of Mechanical Filtration Some methods of mechanical filtering are actually capable of doing so on the nano-metre scale: i.e. Diatom filtration Reverse Osmosis
Diatom Filtration SEM micrographs of diatoms Diatoms are small single-celled marine algae that use silica to form hard shells. They have small pores that allow the flow of nutrients. a-d Examples of diatom morphologies (scale 10μm) e Valve openings (scale 1μm) Due to their small size and hard shells they can be packed together to form compact filters capable of filtering objects on the micron scale Unfortunately due to the relatively large size of their pores they are incapable of removing chemical impurities
Reverse Osmosis Pressure is applied across a membrane, driving pure water across while leaving concentrate behind Drawbacks: Most of the water wasted ~87% High pressures are needed to maintain flow Membrane rapidly loses efficacy
Nanotube filters The Use of Carbon Nano-tubes as filtering devices a. Schematic of the process b. Photograph of the bulk tube. c. SEM image of the aligned tubes with radial symmetry resulting in hollow cylindrical structure (scale 1 mm).
Views of the Filter 1.SEM picture of filter cartridge a.SEM of wall of cartridge (scale 100µm ) b.Same (scale 10µm) c.Lattice of Carbon Nanotubes can be seen (5µm)
How the Filter Works The nano-tubes act as a kind of molecular filter, allowing smaller molecules (such as water) to pass through the tubes, while contaminants are too large to pass through. Due to their electronic configuration smaller ions that would otherwise pass through are also blocked
Removal of bacteria using nanotube filter a, The unfiltered water containing E. coli bacteria b, The E. coli bacteria (marked by arrows) grown by the culture of the polluted water c, The filtration experiment d, The water filtered through nanotube filter e, The filtrate after culture showing the absence of the bacterial
A schematic of how iron nano-particles can be used for the selective removal of groundwater contaminants. Field tests have shown that they can remove up to 98% of contaminants
Domestic Water Purifier Contaminated water pure water Ultra-Filtration (UF) based domestic and community level water purification technologies Removal of bacteria and virus from the contaminated water Works without electricity.