Synthesis and characterization of nanomaterials Mn, Ce and C doped zno and evaluation of their photo - Oxidation potential

TheMn - ZnOTN and Ce -ZnOTN synthesis conditions were

investigated by a hydrothermal methods and selected the suitable

conditions. The suitable synthesis conditions of Mn-ZnOTN materials

were the hydrothermal temperature 150oC; mole ratio NaOH/Zn2+ = 3;

volume ratio (ml) of solvent H/R = 75/75; molar ratio Mn2+/Zn22+ = 2%

and the reaction time 24 hours; The suitable synthesis conditions of CeZnOTN materials were: hydrothermal time 24 hours, hydrothermal

temperature 150oC, mole ratio NaOH/Zn2+ = 6, molar ratio Ce3+/Zn2+ = 3%,

solvent volume 150 ml. Mn-ZnOTN and Ce-ZnOTN materials had rodshape, nanosize, hexagonal wurtzitestructure and could absorb visible

light. The photocatalytic activity of them increased following the order of


selected for the synthesis of C, Mn-ZnO materials; C, Ce-ZnO and C,CeZnO/MWCNTs (CZCT).

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l was synthesized - Effects of the temperature: The temperatures of hydrothermal were changed from 110°C to 170°C. - Effects of NaOH concentration: The molar ratios of NaOH/Zn2+were changed 1.5; 3.0 and 6.0. - Effect of solvent: The volume ratio (ml) of water/ethanol (H/R) solution were 150/0, 70/80, 110/40 and 40/110. - Effect of doped Manganese content: The molar ratios were Mn2+/Zn2+ were 1%, 2% and 6%, respectively. - Influence of PVA content: Experiments carried out were 7%, 10% and 15%, respectively. b> Synthesis of C,Ce co-doped ZnO (C, Ce-ZnO). The synthesis of C,Ce-ZnO was prepared similarly to the C,Mn-ZnO synthesis. Salt Mn(CH3COO) 2 was replaced by salt Ce(NO3)3. 2.1.3. Synthesis of C, Ce co-doped ZnO combined with multi-layer carbon nanotube composite materials (C,Ce-ZnO/MWCNTs) a>Preperation and treatment of multi-layer carbon nanotubes (MWCNTs) The mixture of 5 grams of carbon (MWCNTs) was boiled with 500ml by concentrated HNO3 solution in the circulation system about 3 hours. MWCNTs were rinsed by deionized water to pH = 7 and dried at 90oC for 12 hours and continued to boil it by 500ml NaOH 0.5M for 3 hours in the circulation system and cooled and rinsed several times with deionized water to pH approximately 7 and dried at 90oC for 12h. b> Synthesis of C,Ce-ZnO/MWCNTs nanocomposite materials The condition to prepare C,Ce-ZnO/MWCNTs materials was the same as that to prepare C, Ce-ZnO,. The difference in reaction condition is the of weight percentages of MWCNTs/materials of approximately 16.94%; 22.22%; 37.97%; 50.5% and 62.01%, respectively denoted CZCT1, CZCT2, CZCT3, CZCT4 and CZCT5 were added after solution was stirred 60 minutes. 2.2. The methods to study materials. Characteristic properties of materials were investigated using thermogravimetric and diferential themal analysis (DTA-TG), X-ray diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FT- IR), UV-Vis diffuse reflectance spectroscopy (UV-VIS), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray 6 photoelectron spectroscope (XPS), Brunauer-Emmett-Teller (BET)analysis and energy –dispersive x-ray spectroscopy (EDX). 2.3.Evaluation of photocatalytic activities of materials: 2.3.1.Photocatalytic reactions of methylene blue (MB) decomposition of materials under visible light. a >Caribration curve results of MB solution. The caribration curve was created and identified by linear interval of MB solution. b> Perform photocatalytic reactions. 0.1 g of material were reacted in 100 ml of MB solution under visible light (from Osram and Ace glassphotochemical equipment- sunlight simulated photocatalytic device). First, the mixture was stirred in the dark until the solution was in absorptive balance. 3 or 4 ml of MB solution was centrifuged to extract the solids and measure the optical density (time t = 0, optical density Ao). The solution was illuminated and stirredcontinuosly. For each period of time, 4 ml of sample were centrifuged and measured density (At) until the solution was discolored. Decompositon efficiency MB was calculated with the formula: 𝐻 = 𝐶𝑜− 𝐶𝑡 𝐶𝑜 × 100 = 𝐴0−𝐴𝑡 𝐴0 × 100 In which: Ao: initial optical density, At: optical density at that time, H: decomposition efficiency of MB solution. 2.3.2. Determination of photodynamic kinetics. Langmuir - Hinshelwood model were used to test the photocatalytic kinetic reactions. The kinetic equation is ln (Co/Ct) = kapp.t. Where Co and Ct are the reactant concentrations at times t = 0 and t = t respectively, kappis constant of speed of reactions. 2.3.3. Measurement method of chemical oxygen demand (COD) TCVN 6491: 1999. COD was determined by accordance with TCVN 6491: 1999 (ISO 6060: 1989) and SMEWW 5220 standardized methods for analysis water and waste water. CHAPTER 3: RESULTS AND DISCUSSIONS 3.1. The synthesis of Mn doped ZnO and Ce doped ZnO materials. In this section, Mn doped ZnO and Ce doped ZnO materials were synthesized by two different methods: combustion and hydrothermal method. The effects of factors on the structure, phase composition and average crystal size of the materials were investigated by using X-ray diffraction (XRD) method. The characterized properties and photocatalytic activity of representative materials (materials that had been synthesized at 7 the best conditions within the scope of the thesis review) were studied by using modern physic-chemical methods. 3.1.1. X-ray diffraction (XRD) results. Fig 3.1. The XRD paterns of (a) Mn-ZnOĐC, (b) Ce-ZnO ĐC, (c) Mn-ZnOTN and (d) Ce-ZnOTN with the different doping content of Mn and Ce. (b) (a) (d) (c) 8 The effects of doped Mn and Ce on the structure, crystal phase composition of the synthesized materials were focused. The Mn doped ZnO and Ce doped ZnO materials synthesized by the combustion and hydrothermal method were signed by Mn-ZnOĐC,Ce-ZnOĐC and Mn- ZnOTN, Ce-ZnOTN. The results of XRD (fig. 3.1a, 3.1c, 3.1d) were shown that all of the Mn-ZnOĐC, Mn-ZnO-TN and Ce-ZnOTN materials and the samples with the mole ratio Ce3+/Zn2+ ≤ 2(fig. 3.1b) had hexagonal wurtzitesingle phase structure of ZnO. However, the XRD patterns of Ce-ZnOĐC with the molar ratio of Ce3+/Zn2+ ≥ 3 (Fig. 3.1b) were shown that there were a cubic phase of Ce or CeO2. It was remarkable that the XRD diffraction peaks of these materials were shift slightly towards smaller 2 theta diffraction angle as compared to XRD patern of ZnO synthesized at the same condition. It was suggested that Mn and Ce were doped into ZnO due to interstitial incorpration of Ce ions in ZnO matrix or replaced by Zn ions with Mn ions in ZnO crystal lattice. Ion Zn2+ and ion Mn2+ had the same charge and their radius were not significantly different (Zn2+: 0.74Ao, Mn2+: 0.8Ao). Therefore, Mn2+ions can be subtituted Zn2+ ions or occupied defects during the synthesis process. Radius of Ce ions (Ce4+: 0.92Ao, Ce3+: 1.03Ao) were bigger and more different that of Zn ions so Ce ions can be successfully intergrated into the Zn ions sites.Cerium ions were easily reduced or oxidized to form Ce and CeO2 because of the short reaction time (2 hours) and high heating temperature (550oC)(XRD patern 3.1b). 3.1.2. FT-IR spectra results Table 3.1. Wavenumber and vibration of the bonds. Ocillated bonding Wavenumber (cm-1) Mn- ZnOĐC Ce- ZnOĐC Mn- ZnOTN Ce- ZnOTN ZnO δH-O-H 1587 1593 1651 1599 1629-1645 νO-H 3425 3415 3448 3448 3440-3462 νO-C=O 2360 2362 - - 2364-2366 𝛎𝐍𝐎𝟑− 1406 1406 - - 1384 𝛎𝐂𝐎𝐎− - - 1550 1550 - νZn-O-M 445 457 509 524 431-443 9 Hình 3.2. FT-IR spectra of Mn-ZnOĐC, Ce-ZnOĐC, Mn-ZnOTN and Ce-ZnOTN. The results of the FT-IR spectra (Figure 3.2 and Table 3.1) of the synthesized materials were confirmed the presence of the bonds in the samples. Especially, the Zn-O-Mn and Zn-O-Ce bonds and wavenumbers of Mn-ZnO and Ce-ZnO materials were shifted toward larger wavenumber compared with Zn-O bond in ZnO material that was synthesized at the same condition. 3.1.3. The results of SEM, TEM The TEM images of Mn-ZnOĐC and Ce-ZnOĐC were shown that the Mn-ZnOĐC and Ce-ZnOĐC materials which synthesized by the combustion method were uniform nanosphere particles. Mn-ZnOĐC particles were aggregated together. The SEM images of Mn-ZnOTN and Ce-ZnOTN were shown that the particles were uniform nanorods. The Mn- ZnO material was short nanorods and the Ce-ZnO was long nanorods. 10 Fig. 3.3.SEM images of Mn-ZnOĐC, Ce-ZnOĐC, Mn-ZnOTN and Ce- ZnOTN 3.1.4. The UV-VIS results: Fig 3.4.Band gap of Mn-ZnO Mn-ZnOĐC, Ce-ZnOĐC, Mn-ZnOTN and Ce-ZnOTN. The UV-VIS results (Fig 3.4) were demonstrated the successful doping of Mn and Ce into ZnO matrix. As a result, ZnO band gap was narowed Mn-ZnO ĐC Ce-ZnO ĐC Mn-ZnOTN Ce-ZnOTN 11 after doping with Mn or Ce compared with the undoped ZnO. Band gaps of Mn-ZnOĐC, Ce-ZnOĐC, Mn-ZnOTN and Ce-ZnOTN were 2.97; 3.0; 3,0 and 3,03 eV respectively coresponded with the optical absorption wavelengths ≤ 418; ≤414; ≤414 and ≤410 nm respectively. Therefore, the results of the study and characteristics were shown that Mn doped ZnO and Ce doped ZnO were successfully synthesized by combustion and hydrothermal methods. Materials were in nanometer size and had the ability to absorb visible light. 3.1.5. Photocatalytic activity of Mn-ZnO and Ce-ZnO The MB decomposition abilities of the materials under the visible light were increased by following order: Mn-ZnO-ĐC <Ce-ZnO-ĐC <Mn- ZnO-TN<Ce-ZnO-TN (Fig 3.5). The efficiency of MB decomposition were 58.5%; 73.7%; 88.4% and 98.1% respectively under visible light after 90 minutes (Fig 3.6). Fig 3.5. The efficiencies of MB under visibe light of (a) ZnOĐC, Mn- ZnOĐC, Ce-ZnOĐC; (b)ZnOTN, Mn-ZnOTN and Ce-ZnOTN. Fig 3.6.The efficiencies of MB decomposition after 90 minutes under visibe light of Mn-ZnOĐC, Ce-ZnOĐC, Mn-ZnOTN and Ce-ZnOTN. 3.1.6. The kinetics of MB decomposition reactions of Mn-ZnO and Ce- ZnO under visible light synthesized by two different methods. (a) (b) 12 Fig 3.7. Relationship between ln (Co / Ct) and time for photocatalytic degradation of MB under visible light with Mn-ZnOĐC, Ce-ZnOĐC, Mn-ZnOTN and Ce-ZnOTN. The kinetics of MB decomposition reactions of the materials were complied the Langmuir-Hinshelwood model and a first - order reaction. The constant rate k increased in the order: Mn-ZnOĐC<Ce-ZnOĐC<Mn- ZnOTN <Ce-ZnOTN. The rate constant of the MB decomposition reaction under the visible light of Ce-ZnOTN was the biggest that of MB decomposition coresponded to the fact. The speed of MB decomposition reaction of Ce-ZnOTN is the fastest. Based on the results of the studies about the characteristics and preliminary evaluation of photocatalytic activity of the representative materials, the hydrothermal method was chosen for the synthesis of subsequent materials. Table 3.2. Reaction rate constant k, R2 coefficient and linear regression equation for MB degradation. Materials Linear regression equation R2 k (phút-1) Mn-ZnOĐC Y = 0,0111x - 0,0289 0,9999 0,011 Ce-ZnOĐC Y = 0,0141x – 0,0987 0,9983 0,012 Mn-ZnOTN Y = 0,0280x - 0,2157 0,9950 0,025 Ce-ZnOTN Y = 0,0315x – 0,1426 0,9995 0,029 3.2. The synthesis of Mn, C codoped ZnO (C, Mn-ZnO) and ZnO Ce, C codoped ZnO (C, Ce-ZnO). As presented by the experimental section in 2.1.2, C, Mn-ZnO and C, Ce-ZnO materials were synthesized by hydrothermal method at different conditions with precursors of zinc acetate, manganese acetate, nitrate, PVA 13 and the solvents such as ethanol and distilled water. In which, PVA and ethanol were considered as carbon sources in the synthesis of materials. 3.2.1. X-ray diffraction (XRD) resultsof C, Mn-ZnO and C, Ce-ZnO The effects of Mn and C doping as well as of Ce and C doping to the structure and crystal phase components of ZnO were discussed. The XRD paterns of C,Mn-ZnO and C,Ce-ZnO (Fig 3.8 and 3.9) were shown that all samples had a single hexagonal structure of ZnO. No phase of Mn, Ce, C as well as their compounds were appeared. Notably, the diffraction peak positions of these materials were slightly shifted towards the larger 2θ angles compared with the undoped ZnO which was synthesized in the same condition. This was different from Mn doped ZnO, Ce doped ZnO or C doped ZnO which their diffraction peak positions were shifted towards the lower 2θ angles. Therefore, it was shown that manganese and carbon as well as Ce and C were successfully co-doped into crystal lattice without altering the structure of ZnO. Manganese and cerium were presented by the precursors of manganese acetate and nitrate nitrate, while carbon could be produced by PVA and ethanol in the hydrothermal process. It was precise by the hydrothermal process with high spontaneous pressure, manganese, cerium and carbon can be doped into the ZnO matrix. Fig 3.8. XRD paterns of C,Mn-ZnO at (a) different molar ratios of Mn2+/Zn2+and (b) different molar ratios of PVA/Zn2+. (a) (b) 14 Fig 3.9. XRD paterns of C,Ce-ZnO at (a) different molar ratios of Ce3+/Zn2+ and (b) different molar ratios of PVA/Zn2+. 3.2.2. Infrared spectrum results of C, Mn-ZnO and C, Ce-ZnO. The results of the FT-IR spectra of C, Mn-ZnO and C, Ce-ZnO (Fig. 3.10) were shown that the shifts of wavenumber of the Zn-O bonding absorption in Mn-ZnO and C, Mn-ZnO as well as in Ce-ZnO and C, Ce- ZnO towards the large wavenumber compared with ZnO. However, these shifts in C, Mn codoped ZnO and C, Ce codoped ZnO were shorter than those in Mn doped ZnO and Ce doped ZnO. It was suggested that manganese and carbon as well as cerium and carbon were successfully co- doped into ZnO matrix and formed the Zn-O-Mn and Zn-O-Ce bonds. Fig 3.10. The FT-IR spectra of (a) C, Mn-ZnO; (b) C, Ce-ZnO. 3.2.3. SEM and UV-VIS results of C, Mn-ZnO and C, Ce-ZnO (a) (b) (a) (b) 15 The SEM images of C, Mn-ZnO and C, Ce-ZnO (Figure 3.11) were shown that the particles were ellipsoids, fair uniform, sharpness and nanometer-size. Their surfaces were sponge. Fig 3.11. SEM images of (a) C,Mn-ZnO; (b) C,Ce-ZnO. The UV-VIS spectra of C, Mn-ZnO and C, Ce-ZnO (Figure 3.12) were demonstrated the successful co-doping of Mn and C as well as C and Ce into ZnO by hydrothermal method with their smaller narrow band gap. Band gaps of C,Mn-ZnO, and Ce,C-ZnO were determined 2.86 eV and 2.95 eV respectively, corresponded by the wavelengths less than of 434 nm and 421 nm. These band gap levels were smaller than Mn-ZnOTN (3.0 eV) and Ce-ZnO (3.03 eV) respectively. There, simultaneous co-dopings of carbon and manganese, carbon and cerium enhanced the optical properties of ZnO in the visible light. Fig 3.12. Band gap of (a) C,Mn-ZnO; (b) C,Ce-ZnO. 3.2.4. The XPS spectra of C,Mn-ZnO and C,Mn-ZnO. The XPS spectra of C, Mn-ZnO (Fig. 3.13a) confirmed the presence of elements in sample such as Zn, Mn, C and O as well as their chemical states. On this spectral image, the peaks at 1022.2 and 1045.38 characterized the bond energies of Zn2p3/2 and Zn2p1/2, respectively. In the bonding energy region of the O1s, two peaks were observed. one of them was high intensity peak at 531 eV and low intensity peak at 533.01 eV. The high intensity peak was corresponded to O-2 in Zn-O bond of the ZnO cryticle lattice. The low intensity could be contributed to C-O bond (a) (b) (b) (a) 16 that could be formed by doping carbon into the ZnO matrix. Notably, the C1s states were appeared at 285,64 and 289,58 eV corresponded to the C- OH and O- (C = O) bonds, respectively. Here, these peaks were related to the C-O and O- (C = O) bonds in the ZnO matrix. This could be predicted that Zn was linked to C-O and C-OH. Otherwise, the energy levels at 641.2 and 655.3 eV were corresponded to Mn2p3/2 and Mn2p1/2. This was confirmed that manganeses were existed in the representative sample and the successfully doped into the ZnO crystal lattice. Ions of Mn2+ and Zn2+ had the same ion charge and their radius were not much different., Therefore, the Mn2+ ions could be easily replaced the Zn2+ ion sites or occupied into cation holes in ZnO lattice. From the XPS results, the atomic percentages of C1s, O1s, Zn2p and Mn2P in C, Mn-ZnO samples were determined 16.4%; 49.63%; 32.49% and 1.48% respectively. Therefore, the XPS spectra of C, Mn-ZnO were confirmed the successful doping of carbon and manganese into ZnO matrix. Fig 3.13. XPS spectra of (a) C,Mn-ZnO and (b) C,Ce-ZnO. (a) (b) 17 The XPS spectrum of C, Ce-ZnO (Fig. 3.13b) were shown that the peaks at 1021.3 eV and 1044.2 eV were corresponded to Zn2p3/2 and Zn2p1/2 respectively. The wide peak at 530.25 eV was assigned to O1s. It was noted that the C1s orbital with bond energy displayed at respective peaks at 282.3 eV, 285.4 and 289.6. The first peak was attributed to carbon in the Zn-C bond due to carbon replacing oxygen in ZnO lattice. The second peak was corresponded to referential C of the measurement. The third peak was revealed O-(C=O) bond. Particularly, there were presence of two spin-orbital sets of Ce3d3/2 and Ce3d5/2. The peaks at 881.9 eV; 885,18 eV; 897,88 eV; 900.2 eV belongedto Ce3d3/2 and the peaks at 903.2 eV; 907.08 eV and 916.28 eV belonged to Ce3d5/2. The peaks at 881.9 eV; 897,88 eV; 900.2 eV; 907.08 eV and 916.28 eV were assigned to +4 oxidation of Ce. The two remaining peaks which were weak at 885.18 eV and 903.2 eV were characterised for cerium with +3 oxidation state. Therefore, cerium existed with two oxidation states, +3 and +4. The +4 oxidation state was major. From the XPS spectrum of C, Ce-ZnO, the atomic percentages of Zn2p, O1s, Ce3d and C1s were determined to be 22.32%; 52.15%; 1.95% and 23.58%, respectively. In conclusion, the results of XRD, IR, SEM, XPS and UV-VIS study were shown that C, Mn-ZnO materials were successfully synthesized by hydrothermal method. Materials were in the hexagonal wurtzite structure, nanometer size, elliptical shape (nanoelipsoid). C, Mn-ZnO and C, Ce-ZnO materials could be absorbed goodvisible light. 3.2.5. Photocatalytic activities of ZnO-Mn, C and ZnO-Ce, C Photocatalytic activities of C, Mn-ZnO and C, Ce-ZnO Fig 3.14. The MB decomposition efficiencies of (a) ZnO, Mn-ZnO and C,Mn-ZnO; (b) ZnO,Ce-ZnO and C,Ce-ZnO. Figure 3.14 was shown that the MB decomposition efficiencies increased in the order of ZnO <Mn-ZnO <C, Mn-ZnO and ZnO <Ce-ZnO < C,Ce- (a) (b) 18 ZnO. The MB decomposition efficiency of C, Mn-ZnO was 92.8% after 90 mins while that of C,Ce-ZnO was approximate 100% after 75 mins under visible light. Kinetics of MB decomposition reaction of C,Mn-ZnO and C,Ce- ZnO. The results of Table 3.3 and Figure 3.15 were shown that kinetic of MB decomposition reaction of the materials under the visible light was followed the Langmuir-Hinshelwood model and the first-order reaction. The reaction rate constant k increased following the order: ZnOTN <Mn- ZnOTN <Ce-ZnOTN <C,Mn-ZnO <C, Ce-ZnO. In which , the reaction rate constant of the C,Ce-ZnO photocatalyst was 2.4 times faster than that of the C,Mn-ZnO photocatalyst,2.5 times faster than that of the Ce-ZnO photocatalyst and, especially 3.6 times faster than that of the ZnO photocatalyst. Fig 3.15. Linear plots of ln(Co/Ct) versus time for MB degradation of Mn-ZnO; Ce-ZnO; C, Ce-ZnO and C, Mn-ZnO in aqueous solution under visible light. Table 3.3. Reaction rate constant k, R2 coefficient and linear regression equation for MB degradation. Materials Linear regression equation R2 k (phút-1) C,Mn-ZnO Y=0,032x-0,194 0,9968 0,028 Mn-ZnOTN1 Y=0,0235x-0,1615 0,9991 0,021 ZnOTN1 Y=0,019x-0,0535 0,9972 0,018 C,Ce-ZnO Y=0,0695x-0,0863 0,999 0,068 Ce-ZnOTN2 Y=0,0231x+0,1143 0,998 0,027 ZnOTN2 Y=0,0198x-0,0229 0,9981 0,019 19 Conclusion: Properties and assessments of doping role of Mn, C and Ce, C to optical properties and photocatalytic activity of ZnO were investigated. The final result of co-doped C and Mn as well as C and Ce into ZnO had strongly enhanced photocatalytic activity of material. C,Mn- ZnO and C,Ce-ZnO materials exhibited excellent photocatalytic activity under visible light and especial C,Ce-ZnO material. Thus, C,Ce-ZnO material was selected to synthese nanocomposite materials based on combination with multi-layered carbon nanotubes. 3.3. The synthesis of composite material Ce,C-ZnO/MWCNTs. 3.3.1. The characteristic study on Ce,C-ZnO/MWCNTs (CZCT) materials. Fig 3.16. (a) DTA-TG curve of CZCT2; (b) XRD paterns of CZCTs. The DTA-TG results of the CZCT2 material (Fig. 3.16a) were shown that weight loss of 21.978% occurred only at a temperature range 300°C - 600°C with a great exothermal peak at 567.76°C attributed by the carbon oxidation of materials (MWCNTs). Above 600oC, the TG curve was almost stable and no more thermal effect on the DTA. It was evident that the CZCT2 composite material obtained was stable and did not treat further processing. The XRD results of the composite materials with different MWCNTs content (Fig. 3.16b) were shown presence of two phases: the first phase was wurtzite hexagonal structure with 9 diffraction peaks at 2 theta angle, 86°; 34,45°; 36.32°; 47.72°; 56.70°; 62.94°; 66.65°; 68.03° and 69.22° corresponding to planes (100), (002), (101), (102), (110), (103), (200), (112) and (201) (This result was good agreement with the wurtzite hexagonal ZnO structure corresponded to JCPDS 00-036-1451 standard card); the second phase was graphite carbon with weakly intensity diffraction peaks at 2 theta angle 26 and18° characterised by the (002) plane of graphite carbon. The higher intensity of peak ,the higher the MWCNTs content in the composite was. (a) (b) 20 The FT-IR spectra of CZCT4 (Fig. 3.17a) was shown that the peaks were revealed to the bonds of the CZCT4 compositmaterial. The peaks with high intensity at about 3448 cm-1 indicated successful introducing of O-H bonds into the surface of MWCNTs. Peak at 1077 cm-1was coresponded by C = C bond of the carbon atom (MWCNTs). Peak at 468 cm-1 was contributed by Zn-O-Ce bond. This "cohesiveness" and interaction of surface electrons of MWCNTs and C,Ce-ZnO in the composite material were shifted the optical absorption wavelength of the CZCT to visible light region. Thus, its band gap energy obtained was 2.4 eV narrower than of C, Ce-ZnO (2.95 eV). Fig 17. (a) FT-IR spectrum of CZCT4; (b) Band gap energy of CZCT4. The SEM images (Figure 3.18) were shown the existence and combination of MWCNTs and C, Ce-ZnO components in composite materials. In which, the C, Ce-ZnO nanoparticles with elliptical shape were attached into the surface of multi-layer carbone nanotubes. The C, Ce-ZnO nanoparticles were distributed evenly into the MWCNTs surface and there had a relatively "tight" surface cohension among them. Fig 3.18.SEM images of (a) MWCNTs, (b) CZCT4. The XPS spectra (Figure 3.19) of CZCT4 were shown the surface chemistry states of the composite nanocomposite synthesized. This spectra confirmed the presence of peaks with binding energies corresponded to the (a) (b) (a) (b) 21 orbital Zn2p, Ce3d, O1s and C1s as well as their chemical states. Comparision of peak intensity of Ce3d and C1s in CZCT material and in C,Ce-ZnO materials and shift of the binding energy of the peaks were confirmed the cohesion and surface interaction of the MWCNTs and C,Ce- ZnO in composite materials. Fig 3.19. XPS spectra of CZCT4 and C,Ce-ZnO. Summaryly, the finding of the study on the properties of CZCT nanocomposite material demonstrated the successful synthesis of CZCT materials by hydrothermal method. The CZCT material could absorp visible light well. 3.3.2. The photocatalytic activity of CZCT. Effect of MWCNTs content on photocatalytic activity of CZCT material. The results of MB decomposition (Figure 3.20) were shown that the catalytic samples exhibited good photocatalytic efficiency under visible light (after the MB solution was obtained adsorption equilibrium). Comparision of the MB decomposition efficiency of the samples indicated that the CZCT4 material was the best MB decomposision after illuminated 120 minutes. 22 Fig 3.20. The MB decomposition efficiences of the CZCT material with different MWCNTs content after 120 min. Effect of catalytic amount on photocatalytic activity of CZCT material. Fig 3.21. The MB photodegradation efficience of CZCT4 with the different catalysis amount. Table 3.4. The rate constant of photocatalytic reactions with the different catalysis amount. Amount (gram) Reaction rate (min- 1) 0,01 3,575.10-3 0,05 17,5.10-3 0,1 29,8.10-3 Figure 3.21 and table 3.4 were shown that MB solution were not decayed under visible light without photocatalysts. When increased the catalytic mass from 0.01 to 0.1 grams, the MB decomposition efficiencies were increased gradually and the MB decomposition efficiency of 0.1 grams of catalysts was the fastest. When increased the catalyst mass from 0.01 to 0.05 g, the reaction rate were increased nearly 5 times. However, when continued to increase the catalyst mass to 0.1 grams, the reaction rate was increased approximately 1.7 times. This showed that the excessive catalysts of nanoparticles were coverred the

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