Evaluation of sterilization possibility in water environment of activated nano mno2 coated on calcined laterite

Evaluation of sterilization possibility in water Abstract: The TEM images of solution clearly reveal the presence of a large quantity of nanomanganese dioxide particles with lozenge sha

Evaluation of sterilization possibility in water

Abstract: The TEM images of solution clearly reveal the presence of a large

quantity of nanomanganese dioxide particles with lozenge shape and barked sphere with diameters around 30nm The SEM images of material’s surface shows the distribution of barked sphere shape nano MnO2 all over laterite surface

- Investigation sterilizing possibilities in static condition and dynamic condition

- Manganese has affect in sterilizing capabilities of BRM It reacts with MnO2

to create semi-product [MnO2.Mn].nO2 which plays as strong sterilization substances

Keywords: Quản lý chất thải; Xử lý ô nhiễm; Hóa học môi trường

Content

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 are used in order to improve the productivity in agricultural production, which also causes the scarcity of clean resources [1]

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]

of the negative aspects of chlorination [6]

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 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:

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

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

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 900oC 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

2.2.2 Research methods

2.2.2.1 Synthesis of nano MnO 2 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 MnO2solution 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, interacting with the specimen as it passes through An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor [25]

Surface analysis was done using Scanning Electron Microscope (SEM) The SEM uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens The signals that derive from electron-sample interactions reveal information about the sample [26]

2.2.2.3 Investigation of sterilizing capability of nano MnO 2 adsorbents

The routine monitoring of the bacteriological quality of drinking water relies on

the use of the indicator organisms Escherichia coli (E coli) and coliforms which

are used to indicate fecal contamination or other water quality problems such as failures of disinfection, bacterial regrowth within the distribution system or ingress

The most commonly employed technique for the detection of these organisms in water is membrane filtration Normally, water (100ml) is concentrated by membrane filtration and the membranes placed onto a selective and differential medium such as Endo agar [27] which inhibits the growth of gram positive bacteria Appropriately diluted (10-2) sample (100mL in volume) volumes were filtered through 0.45µm membrane filters Plates were then incubated for 24h at

37oC on endo agar for total coliform

The bacteria number was determined in initial water sample and followed the time of sterilizing process

The experiments were performed in the static condition as well as the dynamic condition to estimate the sterilizing capability of MnO2 nanoparticles Specifically, contact time and the ratio between material and water sample were chosen as fundamental parameters Therefore, other parameters which affect the alteration of contact time and the ratio between material and polluted water sample, such as the column height, the flow rate, etc in the dynamic condition, were taken into consideration

2.2.2.4 Examine the mechanism of sterilization of MnO 2 coated on calcined laterite in water

There are two main purposes in this part: One is to examine whether the mechanism of sterilization of MnO2 coated on calcined laterite is influenced by the high oxidation potential of MnO2 The other is to survey the effects of Mn2+

on sterilizing process of MnO2 by changing the concentration of Mn2+

Chapter 3

RESULTS AND DISCUSSION 3.1 Synthesis of nano MnO 2 adsorbents

The coating process was carried out as shown in Figure 3

Figure 1: Coating process

The TEM images of MnO2 nanoparticles solution clearly reveal the presence of a large quantity of nanoparticles and assemble to form barbed sphere shape with the diameter approximately 30nm (as shown in Figure 4-6)

Figure 2: MnO 2 nanoparticles with the magnification of 100000 times

A: Before coating B: After coating Figure 7: Creation of adsorbent coating by nano MnO 2 particles (100k)

Figure 3: Creation of adsorbent coating by nano MnO 2 particles (200k)

On SEM images in the same scale, it is easy to recognize different surface pictures of the material before and after coating MnO2 nanoparticles Before coating, the surface of laterite was quite smooth; but after coating there were nanoparticles of MnO2 in barbed sphere shape distributed tight all over laterite surface

The clinging of MnO2 nanoparticles on calcined laterite surface was recognized for application purpose, but the essence of this phenomenon was not determined

so far There may were any chemical bond, what was binding energy, was there