Tài liệu Evaluation of sterilization possibility in water environment of activated nano Mno2 coated on calcined laterite

ĐẠI HỌC QUỐC GIA HÀ NỘI TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN --------------------------- Cao Việt EVALUATION OF STERILIZATION POSSIBILITY IN WATER ENVIRONMENT OF ACTIVATED NANO MnO2 COATED ON CALCINED LATERITE CHUYÊN NGÀNH: QUẢN LÝ CHẤT THẢI VÀ XỬ LÝ VÙNG Ô NHIỄM (CHƯƠNG TRÌNH ĐÀO TẠO QUỐC TẾ) LUẬN VĂN THẠC SĨ KHOA HỌC GIÁO VIÊN HƯỚNG DẪN: PGS.TS. TRẦN HỒNG CÔN Hà Nội - 2011 Table of contents Abbreviation ....................................................................................................................i List of Figures ................................................................................................................ ii List of Tables ................................................................................................................ iii Chapter 1......................................................................................................................... 1 INTRODUCTION .......................................................................................................... 1 1.1 Water situation in general ...................................................................................... 1 1.2 Water sterilization .................................................................................................. 3 1.2.1 Boiling ............................................................................................................. 4 1.2.2 Chlorine ........................................................................................................... 5 1.2.3. Ozone ............................................................................................................. 5 1.2.4 Ultraviolet light ............................................................................................... 6 1.2.5 Hydrogen peroxide .......................................................................................... 7 1.2.6 Solar disinfection ............................................................................................ 7 1.2.7 Photocatalysis on semiconductors .................................................................. 7 1.2.8 High speed water sterilization using one-dimensional nanostructures ........... 7 1.3 Nanotechnology ..................................................................................................... 8 1.4 Manganese dioxide............................................................................................... 10 1.5 Laterite ................................................................................................................. 11 Chapter 2....................................................................................................................... 13 OBJECTIVES AND RESEARCH METHODS ........................................................ 13 2.1 Objectives ............................................................................................................. 13 2.2 Materials and Research methods.......................................................................... 13 2.2.1 Material and instruments ............................................................................... 13 2.2.2 Research methods ......................................................................................... 14 2.2.2.1 Synthesis of nano MnO2 adsorbents .......................................................... 14 2.2.2.3 Investigation of sterilizing capability of nano MnO2 adsorbents............... 15 Chapter 3....................................................................................................................... 17 RESULTS AND DISCUSSION .................................................................................. 17 3.1 Synthesis of nano MnO2 adsorbents .................................................................... 17 3.2 Investigation of sterilizing capability of nano manganese dioxide ...................... 23 3.2.1 Investigation in static condition .................................................................... 24 3.2.2 Investigation in dynamic condition ............................................................... 28 3.3 Mechanism of sterilization of MnO2 coated on calcined laterite in water ........... 33 3.3.1 Investigation the influence of Mn2+ in sterilizing capability ........................ 33 3.3.2 Examine the mechanism of sterilization of MnO2 ........................................ 35 Chapter 4....................................................................................................................... 38 CONCLUSION ............................................................................................................. 38 REFERENCES ............................................................................................................. 40 Abbreviation MD Manganese Dioxide UV Ultraviolet DNA Deoxyribonucleic Acid SODIS Solar Disinfection CNT Carbon Nanotube AgNWs Silver Nanowires‟ TEM Transmission Electron Microscopy SEM Scanning Electron Microscope EPA Environmental Protection Agency E. coli Escherichia coli BRM Bacteria removing material MPN Most probable number EBCT Empty Batch Contact Time i List of Figures Figure 1: Nanoscale materials ........................................................................................ 10 Figure 3: Coating process............................................................................................... 18 Figure 4: MnO2 nanoparticles with the magnification of 40000 times .......................... 19 Figure 5: MnO2 nanoparticles with the magnification of 60000 times .......................... 20 Figure 6: MnO2 nanoparticles with the magnification of 100000 times ........................ 21 Figure 7: Creation of adsorbent coating by nano MnO2 particles (100k) ...................... 22 Figure 8: Creation of adsorbent coating by nano MnO2 particles (200k) ...................... 22 Figure 9: Shaking equipment for static condition investigation .................................... 23 Figure 10: Column device for dynamic condition investigation ................................... 24 Figure 11: Samples in contact time‟s influence experiment .......................................... 25 Figure 13: Samples in BRM/water ratio‟s influence experiment .................................. 27 Figure 14: Samples in BRM/water ratio‟s influence experiment .................................. 28 Figure 15: Model of column device ............................................................................... 29 Figure 16: Samples in flow rate in BRM column‟s influence experiments ................... 30 Figure 17: Influence of flow rate on bacteria sterilizing in BRM column..................... 30 Figure 18: Samples in the experiments .......................................................................... 32 Figure 19: Influence of column height on bacteria sterilizing in BRM column ............ 32 Figure 21: Influence of Mn2+ in sterilizing capabilities ................................................. 35 ii List of Tables Table 1: Influence of contact time on bacteria sterilizing .............................................. 24 Table 2: Influence of the ratio of BRM and water on bacteria sterilizing ..................... 27 Table 3: Influence of flow rate on bacteria sterilizing in BRM column ........................ 29 Table 4: Influence of column height on bacteria sterilizing in BRM column ............... 31 Table 5: Influence of Mn2+ in sterilizing capabilities .................................................... 34 iii Chapter 1: Introduction Chapter 1 INTRODUCTION 1.1 Water situation in general Water is one of the world‟s most essential demands for human life, and the origin of all animal and plant life on the planet. Civilization would be impossible without steady supply of fresh and pure water and it has been considered a plentiful natural resource because the sensitive hydrosphere covers about 75% of the Earth's surface. Its total water content is distributed among the main components of the atmosphere, the biosphere, oceans and continents. However, 97% of the Earth's water is salty ocean water, which is unusable for most human activities. Much of the remaining 3% of the total global water resource, which is fresh-water, is locked away in glaciers and icebergs. Approximately 20% of the freshwater resources are found as groundwater, and only 1% is thought to be easily accessible surface water located in biomass, rivers, lakes, soil moisture, and distributed in the atmosphere as water vapor. [1] In the process of rapid development of science and technology, the demand for pure water is increasing to serve multifarious purposes in different types of industries. Global water consumption raised six folds in the past century, double the rate of population growth. In addition, the boom in world‟s population during recent decades, has contributed to the dramatically rising demand of pure water usage for both household and industrial purposes. The high population density and industrialization speed have triggered the hydrosphere to be polluted with inorganic and organic matters at a considerable rate. Moreover, to satisfy the food demand, a number of harmful chemicals such as pesticides and herbicides 1 Chapter 1: Introduction are used in order to improve the productivity in agricultural production, which also causes the scarcity of clean resources. [1] The contamination of ground water (mostly by toxic metal ions due to both natural and anthropogenic reasons) is also one of concerning issues on clean water. It is necessary to assess the quality of water used in industry, household activities and drinking purpose. Understanding of the importance of clean water in human life, many countries has gradually adjusted their environmental regulations more stringently to reserve clean water resources. With the purpose of overcoming the water pollution problems, and to meet the stricter environmental regulations, scientists and researchers have focused on improving exist water purification processes and approaching to alternative water treatment technologies as well, so as to increase the efficiency of those decontamination methods. It is surveyed that human awareness about the seriousness of water pollution has enhanced over the world. People have also started realizing that water is not an unlimited resource, hence it needs to be protected and smartly used. An ideal water treatment process should have the capability to mineralize completely all the toxic organic components without leaving behind any harmful by-products and to recover all toxic metals from wastewater. In broader classification, biological, mechanical, thermal, chemical or physical treatments, or their combinations may be applied to purify contaminated water. The choice of the proper water treatment processes depend on the nature of the pollutants presenting in water, and on the acceptable contamination level in treated water. There are two main purposes of water treatment study – the reduction of contaminant level in the discharged stream to meet environmental standards, and 2 Chapter 1: Introduction the purification of water to ultrapure water in order to be able to use in semiconductor, microelectronic and pharmaceutical industries. Moreover, the cost or effectiveness of the water treatment processes also plays a significant role in choosing a particular one. Biodegradation, adsorption in activated carbon, air stripping, incineration, ion-exchange, coagulation-precipitation, membrane separation, thermal and catalytic oxidation, oxidation by permanganate, chlorine, ozone and hydrogen peroxide are widely applied in conventional water treatment processes for organic and inorganic pollutant containing water. Besides advantages, each process has their own shortcomings which are being improved gradually via new technologies. [1, 2] 1.2 Water sterilization Water sterilization technology is useful in various ways for our daily life. For example, it is used in water and sewerage systems treatment. Methods commonly used for sterilization include chemicals, heat, ultraviolet (UV) radiation, and ozone. Chemicals (chlorine, peroxide, etc.) are utilized extensively for sterilization because of their simplicity; however, they probably form unexpected effects, such as modifying the quality of the target. In addition, sterilization by chlorine usually generates odorous substances and bio-hazardous materials. [2] It is not totally accurate to assess whether water is of an appropriate quality only by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that maybe present in water from an unknown source. Even natural spring water – considered safe for all practical purposes in the 1800s – must now be tested before determining what kind of treatment, if any, is needed. Chemical 3 Chapter 1: Introduction analysis, while expensive, is the only way to obtain the information necessary for deciding on the appropriate method of purification. [3] Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in safe containers could save a huge number of lives each year. Sterilization is accomplished both by filtering out harmful microbes by and also adding disinfectant chemicals in the last step in purifying drinking water. Water is disinfected to kill any pathogens which pass through the filters. Possible pathogens include viruses, bacteria, including Escherichia coli, Campylobacter and Shigella, and protozoa, including Giardia lamblia and other cryptosporidia. In most developed countries, public water supplies are required to maintain a residual disinfecting agent throughout the distribution system, in which water may remain for days before reaching the consumer. Following the introduction of any chemical disinfecting agent, water is usually held in temporary storage often called a contact tank or clear well to allow the disinfecting action to complete. [4] 1.2.1 Boiling Boiling is an easy, cheap and common way to eliminate contaminations and microorganisms in developing countries, but this method is only practical for small amounts. When the water has boiled for 5 – 10 min all the pathogens have been killed and the water is safe to drink. [2] The main disadvantage of this method is that it requires a continuous source of heat and appropriate equipment. 4 Chapter 1: Introduction 1.2.2 Chlorine Chlorine is most effective against pathogens and not as much for turbidity; it will function relatively effectively up to 20 NTU [2]. If chlorine were combined with other methods such as rapid sand filtration the turbidity would decrease. Chlorine Bleach can be used to purify water with the dosage of 1 part of bleach and 10 parts of water and wait for 30 min, or longer if the solution still looks cloudy [3]. It is important to note that chlorine bleach does not kill Cryptosporidium and may not kill Giardia, a pathogen and a parasite that both give diarrheal diseases [5]. It is difficult to determine the correct chlorine dosage, too much gives an unpleasant taste and people will be reluctant to drink it, but a too small dosage will not kill the germs [4]. The drawback of this method is that it the storage of chlorine and its use must need careful handling, large chlorine residual may cause bad taste. 1.2.3. Ozone Ozone (O3) is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe. It is an effective method to inactivate harmful protozoa that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and added to the water by bubble contact. Some of the advantages of ozone include the production of fewer dangerous by-products (in comparison to chlorination) and the lack of taste and odor produced by ozonization. Although fewer by-products are formed by ozonation, it has been discovered that the use of ozone produces a small amount 5 Chapter 1: Introduction of the suspected carcinogen bromate, although little bromine should be present in treated water. Another of the main disadvantages of ozone is that it leaves no disinfectant residual in the water. Ozone has been used in drinking water plants since 1906 where the first industrial ozonation plant was built in Nice, France. The U.S. Food and Drug Administration has accepted ozone as being safe; and it is applied as an anti-microbiological agent for the treatment, storage, and processing of foods. [6] The disadvantage of this method is the high cost for operation. 1.2.4 Ultraviolet light Ultraviolet light is very effective at inactivating cysts, as long as the water has a low level of colour so the UV can pass through without being absorbed. Ultraviolet light works against viruses, bacteria, pathogens and other potentially harmful particles by modifying and even destroying their nucleic acids and disrupting their deoxyribonucleic acid (DNA). When employed in a UV filter, UV light can have two effects on these microorganisms. It can either eliminate their ability to reproduce, or can kill them outright, a more desirable outcome where water purification is concerned. The main disadvantage to the use of UV radiation is that, like ozone treatment, it leaves no residual disinfectant in the water. Because neither ozone nor UV radiation leaves a residual disinfectant in the water, it is sometimes necessary to add a residual disinfectant after they are used. This is often done through the addition of chloramines, discussed above as a primary disinfectant. When used in this manner, chloramines provide an effective residual disinfectant with very few of the negative aspects of chlorination. [6] 6 Chapter 1: Introduction The main disadvantages of this methods is the low efficiency and the dependent on water turbidity. 1.2.5 Hydrogen peroxide Hydrogen peroxide (H2O2) works in a similar way to ozone. Activators such as formic acid are often added to increase the efficacy of disinfection. It has the disadvantages that it is slow-working, phytotoxic in high dosage, and decreases the pH of the water it purifies. [6] 1.2.6 Solar disinfection One low-cost method of disinfecting water that can often be implemented with locally available materials is solar disinfection (SODIS). It partially relies on the ultraviolet radiation that is part of sunlight. Unlike methods that rely on firewood, it has low impact on the environment. [6] 1.2.7 Photocatalysis on semiconductors The processes of heterogeneous photocatalysis on semiconductors, developed during the last twenty years, were firstly regarded as potential methods for hydrogen photoproduction from water. However, even at the very beginning of their development, some papers appeared which dealt with photooxidation of organic and some inorganic (e.g. CN- ions) compounds. For more than ten years the interest of scientists has turned into application of the heterogeneous photocatalytic methods to water detoxification. [6] 1.2.8 High speed water sterilization using one-dimensional nanostructures One-dimensional nanostructures have been extensively explored for a variety of applications in electronics, energy and photonics. Most of these applications involve coating or growing the nanostructures on flat substrates with architectures inspired by thin film devices. It is possible, however, to make 7 Chapter 1: Introduction complicated three-dimensional mats and coatings of metallic and semiconducting nanowires, as has been recently demonstrated in the cases of superwetting nanowire membranes and carbon nanotube (CNT) treated textiles and filters. Silver nanowires‟ (AgNWs) and CNTs‟ have unique ability to form complex multiscale coatings on cotton to produce an electrically conducting and high surface area device for the active, high-throughput inactivation of bacteria in water. [6] 1.3 Nanotechnology Nanotechnology is the science of the small; the very small. It is the use and manipulation of matter at a tiny scale. At this size, atoms and molecules work differently, and provide a variety of surprising and interesting uses. The prefix of nanotechnology derives from „nanos‟ – the Greek word for dwarf. A nanometer is a billionth of a meter, or to put it comparatively, about 1/80,000 of the diameter of a human hair. Nanotechnology should not be viewed as a single technique that only affects specific areas. It is more of a „catch-all‟ term for a science which is benefiting a whole array of areas, from the environment, to healthcare, to hundreds of commercial products. Although often referred to as the 'tiny science', nanotechnology does not simply mean very small structures and products. Nanoscale features are often incorporated into bulk materials and large surfaces. Nanotechnology is already in many of the everyday objects around us, but this is only the start. It will allow limitations in many existing technologies to be overcome and thus has the potential to be part of every industry: Health and medicine - With advances in diagnostic technologies, doctors will be able to give patients complete health checks quickly and routinely. If any 8 Chapter 1: Introduction medication is required this will be tailored specifically to the individual based on their genetic makeup, thus preventing unwanted side-effects. As a result, the health system will become preventative rather than curative. Society and the environment - Renewable energy will become the norm. For example, solar cells based on quantum dots could be as much as 85% efficient. Wind, wave, and geothermal energy will also be tapped more effectively using new materials and stored or delivered more efficiently through advances in batteries and hydrogen fuel cells. New ambient sensor systems will allow us to monitor our effect on the environment and take immediate action, rather than “waiting to see”. Nanotechnology will also help us clean up existing pollution and make better use of the resources available to us. New materials - Nanomaterials such as quantum dots, carbon nanotubes and fullerenes will have applications in many different sectors because of their new properties. So quantum dots can be used in solar cells, but also in optoelectronics, and as imaging agents in medical diagnostics. Carbon nanotubes can be used in displays, as electronic connectors, as strengthening materials for polymer composites, and even as nanoscale drug dispensors. Fullerenes can be used in cosmetics, as “containers” for the delivery of drugs, in medical diagnostics, and even as nanoscale lubricants. 9 Chapter 1: Introduction Figure 1: Nanoscale materials Nanoscale materials and devices hold great promise for advanced diagnostics, sensors, targeted drug delivery, smart drugs, screening and novel cellular therapies. [7] The future of nanotechnology has great potential. However, it also has the potential to change society more than the industrial revolution. It will affect everyone and so should be developed for everyone. 1.4 Manganese dioxide Manganese dioxide (MnO2) occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. In the past decades, Manganese dioxide have been exploited for heavy metal removal from aqueous media, i.e., heavy metal ions [8], arsenate [9], and phosphate [10] from natural water has attracted considerable attention, because it would significantly mediate the fate and the mobility of the target pollutants in water [11, 12]. For example, Kanungo et al. [12] and Kanungo et al. [13] studied 10 Chapter 1: Introduction the sorption of Co(II), Ni(II), Cu(II), and Zn(II) ions on manganese dioxide particles in the presence of different electrolytes. They found that these toxic metals can be effectively trapped by manganese dioxide through electrostatic forces and formation of inner-sphere complexes. The specific properties of manganese dioxide render it a potential sorbent for heavy metal ion removal from contaminated water. Manganese dioxide has high oxidation potential so it can disrupt the integrity of the bacterial cell envelope through oxidation (similar with Ozone, Chlorine…). 1.5 Laterite Laterites are residual products, which are formed during prolonged mechanical and chemical weathering of ultramafic bedrocks at the surface of the earth [14]. It was found that laterite‟s profiles depend on the conditions of weathering intensities, geotectonic zones and the parent rock‟s compositions. Laterite is used to describe soils, ferruginous materials, weathering profiles, and chemical compositions, which are based on SiO2, Al2O3, and Fe2O3 [15]. Laterite is categorized as soil which contains up to 60.3% iron [16] and is available in many tropical regions, such as India, Vietnam, Philippines and China [17-19]. Furthermore, laterite adsorbs other ion and heavy metals, such as fluoride (F), cesium (Cs), mercury (Hg II) and lead (Pb) [20-22]; in water treatment, laterite has been found to be effective and feasible as an adsorbent in removing some heavy metals in contaminated groundwater. When laterite heated to 420-900oC, the removal capacity is even better. Expanded laterite has special properties such as high porosity (and consequently, low density), it is chemically rather inert, non-toxic, thus it can be used as excellent filter aid and as a filler in various processes and materials. 11 Chapter 1: Introduction Because of it low specific surface area and acidic surface, expanded laterite was found to be of limited use as an adsorbent for bacterial removal on its own, but it can be utilized as an appropriate carrier material. On the other hand, nanoparticles MnO2 have a large surface area and high oxidation potential which make them excellent candidates for the bacterial removal in general. 12 Chapter 2: Objectives and Methodology Chapter 2 OBJECTIVES AND RESEARCH METHODS 2.1 Objectives When materials possess nanoparticle size, they will have special properties in chemical, physical, adsorption and electrode, etc. Therefore, the research objectives are addressed as follows: - To synthesize MnO2 nanoparticles coated on calcined laterite; - Analyzing of MnO2 nanoparticles formation portion and its physical structure; - To investigate the sterilization possibilities of created material; - To examine the mechanism of sterilization of MnO2 coated on calcined laterite in water. 2.2 Materials and Research methods 2.2.1 Material and instruments All chemicals were reagent grade and they were used without further purification. Laterite ore was taken from coal and baked at 900 oC. Potassium permanganate (KMnO4), ethanol, sodium hydroxide (NaOH, 98%), and hydrogen peroxide (H2O2) were made in China. Agar was purchased from Ha Long company, endo agar from Merck. Petri disks, distilled water and others instruments which were used in the experiment, taken from Faculty of Chemistry lab equipment. For structural characterization, the samples were taken to use Transmission Electron Microscopy (TEM) operated at 80kV. Surface analysis was done using Scanning Electron Microscope (SEM) (Hitachi S-4800) in National Institute of Hygiene and Epidemiology. 13 Chapter 2: Objectives and Methodology 2.2.2 Research methods 2.2.2.1 Synthesis of nano MnO2 adsorbents According to Environmental Protection Agency (EPA) [23], particles are classified regarding to size: in term of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are size between 2,500 and 100 nanometers. Ultrafine particles, or nanoparticles are sized between 100 and 1 nanometers. Therefore, our goal is to create particles which have the size between 100 and 1 nanometers. The MnO2 nanoparticles were synthesized using potassium permanganate (KMnO4) as a precursor using a slight modification of method [24] in the following way: stirring vigorously a 100ml water:ethanol (1:1, v/v) solution using magnetic stirrer at room temperature for 10 min, and then the solution was added 5ml of KMnO4 0.05M, stirring steady then put slowly H2O2 until brown black color appears (around 10ml H2O2 10%). Finally, colloidal nano MnO2 solution was taken for analyzing of nanoparticles formation portion and coating on calcined laterite. To synthesize laterite/MnO2, the dried calcined laterite, which was grained with size of 0.1 – 0.5 mm diameter, was poured into MnO2 nanoparticles solution with the volumetric portion of solid and liquid was 1/1. The soaking time was 8 to 24 hours. Then the liquid phase was drained off. Solid phase was washed out of dissolved ions and dried to get bacterial removing material (BRM). 2.2.2.2 Structural characterization For structural characterization, the samples were taken to use Transmission Electron Microscopy (TEM) operated at 80kV. TEM is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, 14