Nano for Air, Water and Land Pollution

Transcription

1 Nano for Air, Water and Land Pollution 1 2 Water Treatment Liquid Phase The Good, the Bad & the Ugly Improving Air Quality Gas Phase Environment Nanotechnology Soil Remediation Solid Phase 3 4 1

2 The Ugly The Bad Nature of nanoparticles themselves Characteristics of the products made Manufacturing processes involved. As nano xyz is manufactured, what materials are used? What waste is produced? Are toxic substances used in the manufacturing of nanoxyz? What happens when nano xyz gets into the air, soil, water, or biota? 5 6 The Good Nanotechnology has the potential to substantially benefit environmental quality and sustainability through Pollution prevention Treatment Remediation Information Air 7 8 2

3 Treatment and Remediation There are three major ways in which nanotechnology is being used to treat and reduce the different air pollutants; 1. adsorption by nano absorptive materials, 2. degradation by nanocatalysis, and 3. filteration/separation by nanofilters. 1. Adsorption by nano adsorptive materials Carbon nanostructures average pore diameter, pore volume, and surface area making them significant for industrial application as nanoadsorbents with high selectivity, affinity, and capacity. Highly reactive surface sites or structures bonds can also play an important role in the adsorption (attaching useful molecules Degradation by Nanocatalysts Can use semiconductor materials photocatalytic properties Reaction occurs at surface, nano large surface areas TiO 2 nanoparticles (self cleaning coatings are capable to depollution atmospheric contaminants such as nitrogen oxides, VOCs and other pollutants into less toxic species (Shen et al., 2015)

4 CNT s & Graphene Bismuth oxybromide (BiOBr) nanoplate microspheres catalyst Widely used for increasing the photocatalytic efficiency of TiO 2 Composite of TiO 2 CNTs the electrons can be easily transferred through the CNTs and retard the electron hole recombination (Low et al., 2017). The conduction band of CNTs lies at a more positive level compared to that of TiO 2, hence the electrons can be moved from TiO 2 to CNTs (Figure) (a) SEM images at low magnification, (b) high magnification of the BiOBr nanocatalyst and (c) the decrease in NO concentration by BiOBr nanocatalyst under UV-visible light irradiation (Source: Ai et al., 2015) Metal oxide nanocatalysts Nanofibres of silver, iron, gold and manganese oxide are some of the recently used nanoscale metals and metal oxides can be used in environmental control to remove several volatile organic compounds from industrial smokestacks Other examples Nanogold can eliminate carbon monoxide from indoor air at room temperature. Au Pt co catalyst was found to be 100 times more active than that made of a conventional material for trichloroethylene (TCE) decomposition. As a concept, ZnO photocatalyst is currently being developed and is expected to have two functions to detect and reduce contaminants (Yadavet al., 2017)

5 3. Filtration/separation by Nanofilters Photos and SEM images of the MOFilter (metal organic) before and after PM capture The MOFilters show high removal efficiencies for PM2.5 and PM10 Nanofibre coated filter media air filtration (e.g. dust removal) at industrial plants for filtration of the inlet air for gas turbines (Muralikrishnanet al., 2014). In particulate, nano structured membranes are suitable for several VOCs vapors (Scholtenet al., 2011). (Source:Zhanget al., 2016) Others: Silver nanoparticles and copper nanoparticles filters are widely used in the air filtration technology as antimicrobial materials to remove bioaerosols through air conditional processes. One of the most environmental challenges is the removing of particulate matter (PM) which causes serious harm to public health. Metal organic frameworks (MOFs) are crystalline materials with high porosity, tunable pore size, and rich functionalities, holding the promise for contaminant capture (Zhanget al., 2016). Here, nanocrystals of four unique MOF structures are processed into nanofibrous filters. These MOFilters can also be effective and selective to adsorb toxic gases such as SO 2 when exposed in a stream of SO 2 /N 2 mixture

6 Soil Possibilities nanoscale iron is in use in full scale projects with encouraging success. particles such as self assembled monolayers on mesoporous supports (SAMMS ), dendrimers, carbon nanotubes, and metalloporphyrinogens Advantages of nanoparticles Highly reactive due to large surface area to volume ratio, providing a greater number of reactive sites This allows for increased contact with contaminants, thereby resulting in rapid reduction of contaminant concentrations. Nanoparticles may pervade very small spaces in the subsurface and remain suspended in groundwater, which would allow the particles to travel farther than macro sized particles and achieve wider distribution. However, bare iron nanoparticle may not travel very far from injection site. Bimetallic Nanoparticles (BNP s) Good for contaminants in soil and groundwater. BNPs consist of particles of elemental iron or other metals in conjunction with a metal catalyst, such as platinum (Pt), gold (Au), nickel (Ni), and palladium. combination of metals increases the kinetics of the oxidation reduction (redox) reaction, thereby catalyzing the reaction. Palladium and iron BNPs are commercially available and currently the most common. In bench scale tests, BNPs of iron combined with palladium showed contaminant degradation two orders of magnitude greater than microscale iron particles alone (Zhang, 2006b). These particles were 99.9 percent iron and less than 0.1 percent palladium Schematic of Pd/Au BNPs idealized as clusters, with a 4-nm Au core and variable Pd surface coverage from 0 to 100 percent (with corresponding Pd content). (Nutt, 2006) 6

7 ezvi (zero valent iron) Remediation of chlorinated hydrocarbons The product consists of ZVI surrounded by an oil liquid membrane that facilitates the treatment of chlorinated hydrocarbons. ezvi is made from food grade surfactant, biodegradable oil, water Outer layer is hydrophobic, as are the contaminants Structure of an ezvi particle (modified from O Hara, 2006) Zero valent, or elemental, iron (ZVI) In the presence of an oxidizing agent, Fe0 becomes oxidized to ferrous ions (Fe 2+ ), and the two released electrons become available to reduce other compounds. aerobic conditions, 2Fe 0 + 4H + + O 2 2Fe H 2 O OR 2Fe 0 + 2H 2 O 2Fe 2+ + H 2 + 2OH In addition to the above reactions, ZVI can also react with contaminants. The figure illustrates a reaction that shows the reducing ability of elemental iron with a chlorinated hydrocarbon: The Fe0 (in the form of a BNP) transforms TCE to ethane, releasing Fe 2+ ions and chloride ions. Scanning electron microscope image of titanium dioxide nanotubes (Chen, 2005) Nanosized titanium dioxide Photocatalysis to mineralize a variety of herbicides, insecticides, and pesticides via photocatalysis and can convert other contaminants to less toxic compounds (Konstantinou, 2003). When aqueous titanium dioxide suspensions are irradiated with light energy greater than 3.2 ev, electrons are generated according to the equation below: TiO 2 + hν e + h + The electrons can reduce specific contaminants directly. May also react with dissolved oxygen or the oxygen adsorbed on the surface of the titanium dioxide, reducing it to a superoxide radical anion that can oxidize specific contaminants Schematic of functionalized nano-sized pore within a SAMMS particle (modified from Mattigod, 2004) SAMMS Self Assembled Monolayers on mesoporous supports Nanoporous ceramic substrate coated with a monolayer of functional groups tailored to preferentially bind to the target contaminant. The functional molecules covalently bond to the silica surface, leaving the other end group available to bind to a variety of contaminants Can be cleaned and re used Contaminants successfully sorbed to SAMMS particles include radionuclides, mercury, chromate, arsenate, pertechnetate, and selenite 7

8 Nano for soil Agricultural Nanobiotechnology: Modern Agriculture for a Sustainable Future edited by Fernando López Valdez, Fabián Fernández Luqueño From Table 7.1 it can be seen the removal of metal ions is one of the most common problems addressed using nanomaterials ( particularly nanoparticles) Zerovalent iron (ZVI) on if the most frequently cited used in different forms in permeable barriers or treatment in situ of soil for removal of a wide variety of contaminants Treatment & Remediation End-of-pipe management and cleanup of pollution Iron Treatment Walls Used in groundwater treatment for many years. Iron chemically reduces organic and inorganic environmental contaminants. Currently involves granular or microscale iron ( 50 m or 50,000 nm). and Nanotechnology Nanosized iron enhances the reaction. Enhanced further by coupling with other metals (Fe/Pd)* on the nanoscale. Nano Fe 0 is more reactive and effective than the microscale. Smaller size makes it more flexible -- penetrates difficult to access areas. Many other examples: Using gold nanoparticles embedded in a porous manganese oxide as a room temperature catalyst to breakdown volatile organic compounds in air. Using crystals containing nano sized pores to trap carbon dioxide. Using a to remove nitrogen oxide from smokestacksnanocatalyst containing cobalt and platinum Reducing the amount of platinum used in catalytic converters. Converting carbon dioxide to methanol; which can be used to power fuel cells. Reducing emissions from power plants by converting carbon dioxide into nanotubes. Removal of carbon dioxide from industrial smoke stacks using: Carbon nanotube based membranes Nanostructured membranes Genetically engineered enzymes * Elliot and Zhang ES&T 2001, 35,

9 Magnetic nanoparticles Non ZVI particles Magnetic nanoparticles have large surface areas relative to their volume and can easily bind with chemicals. Surface modified, they can be used to bind with contaminants such as arsenic or oil and then be removed using a magnet Mat of potassium manganese nanowires. A group of researchers at the Massachusetts Institute of Technology (MIT) have developed a paper towel for oil spills that is comprised of this membrane The nanowire membrane selectively absorbs oil with high efficiency. Former sponges absorb water as well Cannot be heated to high temps to remove oil The oil can be recovered by heating the mat, which can then be reused. My note: where does the burnt hydrocarbons go? nzvi, bi metallic nanoscale particle (BNemulsified zero valent iron (ezvi) May chemically reduce the following contaminants effectively: perchloroethylene (PCE) TCE, ci1, 2 dichloroethylene (c DCE), vinyl chloride (VC), and tetrachloroethane (TCA), along with, polychlorinated biphenyls (PCBs), halogenated aromatics, nitroaromatics, and metals such as arsenic or chromium

10 Getting them in there Usually site specific, dependent on the geology found and the form in which the nanoparticles will be injected. Direct route of injection existing monitoring wells, piezometers, or injection wells. Recirculation involving injecting nanoparticles in upgradient wells while downgradient wells extract groundwater. The extracted groundwater is mixed with additional nanoparticles and reinjected in the injection well. The wells keep the water in the aquifer in contact with the nzvi, and also prevent the larger agglomerated iron particles from settling out, allowing continuous contact with the contaminant. Additional methods direct push, pressure pulse technology, liquid atomization injection, pneumatic fracturing, and hydraulic fracturing. The direct push method involves driving direct push rods, similar to small drilling augers, progressively deeper into the ground. Schematic of two methods of groundwater remediation using nano iron Water Many of the techniques mentioned can be used for water treatment as well e.g. ZVI, membranes etc

11 Slide of nanotec water purifier Made of carbon nanotubes. Pore size: μm. Can remove virus, bacteria, suspended solids, large multivalent ions, dissolved organics, herbiscides, pesticides etc. Greater efficiency compared to microfilters and ultrafilters. Energy usage Low. 1. Nanofilters: Nanofilter. Developed by Argonne National Laboratory [3] Nanosorbents: Used majorly in water remediation. For removing inorganic and organic pollutants, from contaminated water. Nanoparticles used as sorbents. Nanoparticles can be functionalized with various chemical groups to increase their affinity towards target compounds. Nanocrystalline zeolites can remediate water containing cationic species such as ammonium and heavy metals. As well chemicals like 137 Cs and 90 Sr. [5]. Magnetic nanoparticles bind with contaminants, such as oil and arsenic and removed using a magnet. 3. Nanocatalysts & redox active nanoparticles: Nanoparticles serve as catalysts. Chemically degrade pollutants. Scientists from IISc, Bangalore India are evaluating immobilized nano titanium dioxide particles for degrading organic as well inorganic pollutants. [6] Nanoscale zerovalent Fe 0 & bimetallic Fe 0 detoxify organic & inorganic pollutants in aqueous solutions. Fe 0, Fe 0 /Pt 0, Fe 0 /Pd 0, Fe 0 /Ag 0, Fe 0 /Ni 0, Fe 0 /Co 0 can reduce chlorinated alkanes, alkenes, chlorinated benzenes, pesticides, organic dyes, nitro aromatics, nitrates to less toxic and recalcitrant byproducts. [7]

12 4. Bioactive nanoparticles: Nano Ag Being evaluated to decrease use of chemical reagents used for disinfection. MgO nanoparticles effective against Gram positive and Gram negative bacteria. [8] Silver nanoparticles found effective against both Gram positive and negative. Especially, Staphylococcus aureus, E.coli, Klebsiella pneumoniae and Pseudomonas aeruginosa [9] Product How it works Importance Developers Nanorust to remove arscenic Magnetic nanoparticles of iron India, Bangladesh and other developing Rice University, United States. oxide suspended in water bind arsenic, which is then removed with a magnet countries suffer thousands of cases of arsenic poisoning each year, linked to poisoning of wells. Desalination membrane A combination of polymers and nanoparticles that draws in water ions and repels dissolved salts. Already in the market, this membrane enables desalination with lower energy costs than reverse osmosis. University of California, Los Angeles and NanoH 2 O Product How it works Importance Developers Nanofiltration Membrane Membrane made up of polymers with a pore Field tested to treat drinking water in China Sachen Industries, Korea. size ranging from nm and desalinate water in Iran. Using this membrane requires less enrgy than reverse osmosis. Nanomesh waterstick A straw like filtration The waterstick cleans the Seldon Laboratories device that uses carbon water as it is drunk., United States. nanotubes plaed on a flexible, porous material. Doctors in Africa are using a prototype and the final product is said to be available at an affordable cost in developing countries

13 Product How it works Importance Developers World Filter Filter using a Designed specifically for KX Industries, US nanofibre layer, made the household or up of polymers, resins, ceramics and other materials that remove contaminants. community level use in developing countries. The filters are effective, easy to use and require no maintenance. Pesticide Filter Filter using Pesticides are often found in Indian Institute of nanosilver to adsorb the developing countries Technology, and then degrade water supply. This pesticide Chennai, India and three pesticides filter can provide a typical Eureka Forbes commonly found in the Indian water supplies. Indian household with 6000 Limited, India. liters of clean water in one year. Nanotec After the 2011 BKK floods 6 filtration steps one of which is the antimicrobial nanocoating ceramic filtration unit. Long lasting and no traces of silver particles are detected in the drinking water. Can be setup and operated using solar energy within minutes Detection Nanotechnology can also detect water borne Contaminants like heavy metals. A new type of nanomaterial called nanostructured silica has been found to detect heavy metals It has large surface area and regular pores, has the capability of being able to extract heavy metals from wastewaters. Electrodes are separated with a small atomic gap so a few ions can be detect. Sensors Used for Process control, compliance and ecosystem monitoring, and data/information interfaces. Need to be Low cost, rapid, precise, and ultra sensitive. Operated remotely and continuously, in situ, and in real time. Single Molecule Detection Molecules adsorb on surface of nano or micro cantilever, causes a change in surface stress, cantilever bends. Used to detect chemicals using either a specific reaction between analyte and sensor layer or chem/physisorption processes. Applications to bio-toxins as well. IBM--Berger et al., Science 1997 June 27; 276:

14 Sense and Shoot Approach to Pollution Treatment Dual role of ZnO semicondouctor film as a sensor and photocatalyst >300 nm UV Kamat, P.V, et al. J.Phys.Chem. B 2002, 106, Nanosized zinc oxide (ZnO) senses organic pollutants indicated by change in visible emission signal. The ZnO shoots the pollutants via photocatalytic oxidation to form more environmentally benign compounds. Sensing capability means that the energy-consuming oxidation stage only occurs when the pollutants present. Multifunctionality and smartness is highly desirable for environmental applications. Potential health and environmental risks. Integration of nanomaterials into existing water purification systems. Availability and cost Nanotechnology a cautionary note Risk toxicity and exposure Nanoexposure studies only on inhalation Aquatic environment? Time lag (see also DDT history) Safe particles 55 14