Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat organic compounds and bacteria in biological treatment system outflow

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In this article, we present a process to synthesize new material using urea modified nitrogen TiO2 nano using the hydrometallurgical method. A solution that was a mixture of TiCl4, (NH2)2CO, NH4NO3 and PVA was hydrolyzed at a „suitable‟ temperature and stirring speed and then calcined at 600 oC in 3 hours

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Nội dung Text: Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat organic compounds and bacteria in biological treatment system outflow

JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2015-00082 Chemical and Biological Sci. 2015, Vol. 60, No. 9, pp. 83-90 This paper is available online at http://stdb.hnue.edu.vn CREATING NITROGEN MODIFIED TiO2 NANO MATERIAL BY UREA COVERED ON LATERITE IN ORDER TO TREAT ORGANIC COMPOUNDS AND BACTERIA IN BIOLOGICAL TREATMENT SYSTEM OUTFLOW Nguyen Hoang Nam1, Nguyen Hoang Hiep2, Tran Thi Hong Van3 and Nguyen Thi Thanh Huong4 1 Faculty of Environment, Hanoi University of Mining and Geology 2 Department of Environment, Tampere University Finland 3 Faculty of Chemistry, Hanoi National University of Education 4 Faculty of Chemistry, Military Medical University Abstract. In this article, we present a process to synthesize new material using urea modified nitrogen TiO2 nano using the hydrometallurgical method. A solution that was a mixture of TiCl4, (NH2)2CO, NH4NO3 and PVA was hydrolyzed at a „suitable‟ temperature and stirring speed and then calcined at 600 oC in 3 hours. The obtained product has the diameter in range 20 - 30 nm nanometers, and the organic removal efficiency of this material is high. Using about 30 minutes of sunlight, the COD value at the inflow was about 300 - 500 mg/L while at the outflow it was 0 mg/L, and the bacteria in the outflow was 20 CFU/100mL. Covering TiO2 nano on laterite saved in material, also save amount of money needed to separate the material from water. Keywords: TiO2 nano, urea, treat, COD, organic compound. 1. Introduction Organic pollutants in water is a major problem in Vietnam and elsewhere around the globe. A variety of organic treatment methods have been provided and chemical, biological and physical methods have been used in waste treatment. Choice of method depends on factors such as flow rate, degree of contamination, weather conditions, economical feasibility, availability of treatment materials and the object to be treated. Received October 16, 2015. Accepted December 30, 2015. Contact Tran Thi Hong Van, e-mail address: hongvan0505@yahoo.com 83
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van and Nguyen Thi Thanh Huong Nowadays, nanotechnologies are commonly applied to treat water containing organic compounds because they are economically beneficial and environmentally friendly. However, an adequate amount of light is required for photochemical reactions to occur efficiently, effectively and economically. Starting from above demand, it appear: TiO2 is a semiconductor material, has wide forbidden zone. Pure TiO2 is effective only in the ultraviolet zone of < 380 nm. Ultraviolet radiation portion from the sun to earth's surface only account for nearly 4% so using this radiation for environmental treatment and TiO2 catalyst purposes is reduced. Therefore, to use sun radiation in visible light zone in photo-catalyst reaction require reducing forbidden zone energy of TiO2. Previously, a good deal of research has been done on modifying TiO2 such as using Cr, Zr, etc., especially modify by nitrogen to new structure which achieve higher photo-catalysis ability [1]. In the presence of sunlight, TiO2 nano becomes a stronger oxidizer, 1.5 times stronger than O3 and twice that of Cl2, two of the most common substances used in environmental treatment. TiO2 nano can decompose sustainable organic compounds and highly toxic such as such as dioxin and benzene, as well as some viruses and disease microorganisms, more efficiently than others methods [2]. Thus, to recover catalyst materials economically, the catalyst must remain on a carrier which has a large surface area such as active carbon, crystal, silica gel, polymer materials, zeolite, cotton and cellulose. * Reaction mechanism Heterogeneous photo-catalysis process can occurs in gas phase or liquid phase. Similar to other heterogeneous catalyst processes, the heterogeneous photo-catalysis process is divided in 6 steps: - Diffuse react substances from liquid or gas phase to catalyst surface. - Absorb react substances on catalyst surface. - Adsorb light photons, moleculesshift from basic stage to electron stimulation stage. - Photochemical reaction. - Desorb products. - Defuse products into gas or liquid phase. * Conditions for a substance to have photo-catalysis ability - Having photo-activity. - Having suitable forbidden zone energy to adsorb ultraviolet or visible light. hυ + (SC) → e- + h+ A(ads) + e- → A- (ads)D(ads) + h+ → D+ (ads) Ion A (ads) and D+ (ads) after formed will react together through a series of - mediatereactions and then form the final products. Figure 1. Photochemical reaction mechanism [5] 84
Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat... Therefore, the photons adsorption process is the beginning step for the whole reaction series. In the photo-catalysis process, quantum efficiency can be reduced by the recombination of electrons and holes. e- + h+ → (SC) + E In which (SC) is neutralizing semiconductor center and E is the energy released in the form of electromagnet radiation ( hυ’ ≤ hυ ) or heat. In the presence of light, TiO2 nano become hydrophobic or hydrophilic depending on manufacture technology. This ability is applied to create self-cleaning without chemical compound surface and mechanical impact or freezing device without electricity. The powerful photo-catalysis ability of TiO2 nano remains being researched and applied in fuel battery and treating CO2 causing greenhouse effect. TiO2 nano operates in the catalysis mechanism so it doesn't reduce, meaning its use involves a once time investment and long term use. 2. Content 2.1. Materials and methods * Chemicals PVA, (NH2)2CO, NH4NO3, TiCl4, NH2OH.HCl, C2H5OH, methylene blue: produced by Merck Germany. Triple times distilled water: Produced in our laboratory. Dispense TiCl4 3M (produced by mixing TiCl4 in cold water then diluting it to a 0.5 M solution by adding cold water). * Analytical methods Instruments used to perform the experiments were: - COD was determined with Optizen 2120 UV/Shimadzu. - Nano particle size was determined using a Scanning Electron Microscope (SEM) Jeol 5410 LV produced in Japan and TEM LIBRA120 produced in Germany. - Drying cabinet (produced in Germany), oven (Carbolite model AAF-11/7 produced in England). - Ultra-distilled water * Produce TiO2 nano TiO2 nano production - Mix chemicals in exact volume ratio then stir, heatìg it to 70 oC in 24 hours. - Then raise the temperature to 90 oC in 12 hours. - Dry at 120 oC in 12 hours. - Calcine at 250 oC in 8 hours. - Calcine at 600 oC in 3 hours. * Cover TiO2 material on laterite carrier The process of covering material on laterite occurs in the steps below: First, calcine crushed laterite and sieve to a particle diameter of 1mm at 1000 oC over 3 hours with a heat acceleration velocity of 10 oC/min. After that, wash it with 1 time distilled water till clear, then continue to wash with triple distilled water. Dry at 120 oC in 8 hours. Produce solgel solution add to laterite and continue to stir using a stirrer with wings, keep at 90 oC for 24 hours. Dry products, combust solgel at 250 oC, continue to calcine at 600 oC over 3 hours with a heat acceleration rateof 10 oC/min. 85
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van and Nguyen Thi Thanh Huong * Testing material activity Photo-activity To ensure that these materials have photochemical ability require testing their photo- activity property using methylene blue. The steps: - Add 100 mL standard methylene blue to 0.1 g material. - Test ability to remove material in the sunlight, ultraviolet and dark. - Sampling times are: 30', 60‟, 90‟, 120‟, 150´, 180'. - Measure optical absorption of methylene blue at a wavelength of 664 nm 2.2. Resuls and discussion 2.2.1. Produce TiO2 nano The preparation nano TiO2 was conducted according to the composition and volume ratio of the material is shown in Table 1. Table 1. Composition and volume rate of substances for the preparation of nano-TiO2 PVA (4%) TiCl4 (0.5M) (NH2)2CO NH4NO3(1M) (1M) 180 60 450 60 Faculty of Chemistry, HUS, VNU, D8 ADVANCE-Bruker - Sample TiO2 500 d=3.515 400 300 Lin (Cps) 200 d=1.891 d=2.376 d=1.668 d=1.699 d=1.481 100 d=2.332 d=2.430 d=1.365 0 20 30 40 50 60 70 2-Theta - Scale File: Dung mau TiO2.raw - Type: 2Th/Th locked - Start: 20.000 ° - End: 70.010 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 17 s - 2-Theta: 20.000 ° - Theta: 10.000 ° - Chi: 0.00 ° - 1) Left Angle: 24.200 ° - Right Angle: 26.660 ° - Left Int.: 27.4 Cps - Right Int.: 25.6 Cps - Obs. Max: 25.314 ° - d (Obs. Max): 3.516 - Max Int.: 394 Cps - Net Height: 368 Cps - FWHM: 0.423 ° - Chord Mid.: 2 01-078-2486 (C) - Anatase, syn - TiO2 - Y: 95.69 % - d x by: 1. - WL: 1.5406 - Tetragonal - a 3.78450 - b 3.78450 - c 9.51430 - alpha 90.000 - beta 90.000 - gamma 90.000 - Body-centered - I41/amd (141) - Figure 2. Schematic X-ray of nano TiO2 Schematic X-ray diffraction (XRD) showed that the peaks are sharp demonstrate the material's purity TiO2 modulation is high. The characteristic peak structure in the form of Anatase TiO2 at positions 2θ = 25.3º, 37.8º, 48º, 53.90º, 55º, 62.52º appear. Thus, in the form of Anatase TiO2 structure was confirmed. After modulation, pictures were taken of produced materials SEM and TEM. Results from SEM and TEM images have illustrated that the size of the TiO2 particles is to nano size which is approximately 20 - 30 nm. Mechanisms that proceeded material modulation are: at from 70 to 90 oC, urea is hydrolyzed gradually to form NH3 and CO2, NH3 continues to be hydrolyzed to form NH4+ and OH-, providing OH- for Ti4+ precipitation process to form Ti(OH)4. The gradual hydrolysisofurea have created suitable condition for hydroxide precipitation to have tiny particles and avoid to be localized precipitation. 86
Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat... Figure 3. SEM image of TiO2 prepared by solgel method Figure 4. TEM image of TiO2 prepared by solgel method Polyvinyl alcohol (PVA) is used to reduce localized titanium hydroxide particles. In a solution containing Ti4+ and PVA it occurs reaction that creates complex of Ti4+ ions with OH- in polymer network. Ti4+ ions break the space circuit in the organic polymer. When particles reach the limit stage, very small titaniumoxide particles are formed beside network [3]. Ammonia and nitrate ions were taken to system which play the role of avoiding flocculation, simultaneously modifying material [4]. According to results of Luu Minh Dai, calcination temperature of 600 oC and a retention time of 3 hours would be most efficient. With longer calcination times, the materials‟ particle structure will alter unexpectedly [4]. 2.2.2. Photochemical ability of TiO2 nano The test of photo-catalysis activity of material is very important because it decides whether the material have the ability to provide electrons and holes in the presence of light. Table 2. Results of testing the photo-activity of TiO2 using methylene blue Sample/Time (min) 30 60 90 120 Efficiency (%) 34.7% 62.6% 86.6% 97.0% 87
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van and Nguyen Thi Thanh Huong Results have shown that photochemical ability of the material is highly effected and reached an efficiency of 97% after 120 minutes. This means that when TiO2 is in a material, it can become a photo-catalyst. The processes occurs as presented below [2, 5]: TiO2 + hv → TiO2 (h+ + e-) TiO2(h+) + H2O →∙OH + H+ + TiO2 TiO2(h+) + OH- →∙OH + TiO2 TiO2 (h+) + R → R∙ + TiO2 TiO2(e-) + O2 → O2-∙ + TiO2 TiO2(e-) + H2O2 → OH- + ∙OH + TiO2 O2-∙ + H+ → HO2∙ HO2∙ → O2 + H2O2 H2O2 + O2 → O2 + OH- + ∙OH These activated products have strong oxidizing properties, oxidizing organic compounds to CO2 and H2O. The results above confirm that TiO2 nano modulated have very good photochemical ability. 2.2.3. Efficiency of COD removal by laterite and laterite covered by TiO2 Research on COD removal efficiency has been done using as a sample the outflow of a system's filtration columns on two materials: treated laterite and laterite covered by TiO 2 under various conditions. Next, testing is done to determine whether it was organic compounds and microorganisms that were absorbed or removed. Figure 5 indicates the results of COD removal on laterite and laterite covered by TiO 2 in dark, sunlight and ultraviolet light conditions. The results illustrate that the amount of COD at the inflow is 180 mg, and after 1 hour of treatment, COD removal by TiO2 material in the presence of sunlight is most efficient. Outflow is at only 20 mg. Meanwhile, in the presence of ultraviolet light, the amount of outflow COD is at 120 mg, and in dark conditions reached 60 mg. As the retention time increased to 2 hours, it was found that in sunlight as well as ultraviolet light, the amount of COD was insignificant. Results also indicate that even in dark condition, TiO2 material can absorb organic compound very well after 2.5 hours. Figure 5. COD removal in various conditions 88
Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat... Compared to just laterite, in similar conditions and amount of time, their removal efficiency is lower (Figure 5). However, laterite absorption ability was significant and it can remove COD completely after 3 hours under all research conditions. As we can see, nitrogen modified TiO2 material covered on laterite shows absorption ability and it can remove organic compounds through photochemical reaction. Therefore, this material is highly efficiency in organic removal in a short retention time. 2.2.4. Bacteria removal efficiency by laterite and laterite covered by TiO2 Research has been done on bacteria removal efficiency using samples from the outflow of a filter column in a treatment system on laterite covered by TiO2 in various conditions. Figure 6 illustrates the results of bacteria removal by laterite covered by TiO2 nano in conditions of darkness, natural light and ultraviolet light. Research has indicated that the amount of coliform bacteria in the inflow is 350 mg and, after 1 hour of treatment, the removal efficiency of sunlight and ultraviolet light are relatively high with an outflow of 70 microorganisms/100 mL. Meanwhile, the amount of bacteria is 150 individuals/100 mL. As the retention time extends to 2 hours, it was found that in the presence of sunlight or ultraviolet light, the amount of bacteria in the outflow was about 40 individuals/100 mL. Results also indicate that TiO2 material has the ability to absorb bacteria very well after 2 hours. Figure 6. Bacteria removal process in various conditions As can be seen, nitrogen modified TiO2 material covered on laterite, besides having absorption ability, can remove bacteria through photochemical reactions. Therefore, this material provides highly efficient bacteria removal even with a short retention time and can be useful for domestic water regulation. 3. Conclusion Nitrogen modified TiO2 material covered on laterite is a new photo-catalyst material that can be used in visible light effectively and can efficiently treat organic compounds as well as bacteria. Saving material and without centrifugalization to separate materials after treatment, money is saved in the treatment processes. Acknowledgment. This work was funded by the German Federal Ministry of Education and Research (BMBF), grant number 02WB0957 and 02WB0958. The authors would like to thank P. Kuschk, J. Richter, K. Puschendorf, C. Pietsch, I. Mäusezahl, J. Mattusch, J. Steffen, and U. Kappelmeyer for their technical assistance and support. 89
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van and Nguyen Thi Thanh Huong REFERENCES [1] Trang, T. N. T. T., 2011. Research preparation, surveys structure, photocatalytic activity of titanium dioxide nano powder from TiCl4 and amines. University of Science, VNU, Hanoi (in Vietnamese). [2] Khataee A. R. and M. B. Kasiri, 2010. Review Photocatalytic degradation of organic dyes in the presence of nanostructured titanium dioxide: Influence of the chemical structure of dyes. Journal of Molecular Catalysis A: Chemical, 328: pp. 8-26. [3] Loan, B. T. P. and M. V. Trinh, 2011. Introducing some natural mineral materials (Bentonite; Laterite) capable of use as absorbent materials Arsenic in drinking water. Toxicology Journal No. 20, p. 20 (in Vietnamese) [4] Dai L. M. and N. N. T. T. Loan, 2009. Synthesis of Fe2O3 nanometer size by gel combustion method and research on arsenic adsorption capacity, manganese, iron. Journal of Chemistry 47 (6A): 260-264 (in Vietnamese). [5] http://luanvan.net.vn/luan-van/thuc-trang-o-nhiem-asen-trong-moi-truong-nuoc-o-cac- thanh-pho-lon-hien-nay-45251/Nano TiO2 - Nano TiO2 - material interest, Hoahocngaynay.com/Vusta. 90