STUDY ON SYNTHESIS AND CHARACTERIZATION OF NEW MATERIALS BASED NANOSTRUCTURES OF GRAPHENE APPLIED IN ENVIRONMENTAL TREATMENT

VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY …… ….***………… HA QUANG ANH STUDY ON SYNTHESIS AND CHARACTERIZATION OF NEW MATERIALS BASED NANOSTRUCTURES OF GRAPHENE APPLIED IN ENVIRONMENTAL TREATMENT Major: Theoretical chemistry and physical chemistry Code: 62.44.01.19 SUMMARY OF CHEMICAL DOCTORAL THESIS Hanoi – 2016 INTRODUCTION The urgency of the thesis While industry dramatically develops, agriculture also pays the main role in the expansion of national economy However, as a consequence of expanding ecomomy, water resouces are effected by the toxic agents coming from planting and feeding These poisons can be biologicallly deposited in the water, which leads to harm the life of uder water creatures as well as the human life Therefore, not only heightenned the environment protection attitude, Government should find the way to remove the contaminants (heavy metal ions, dye, pesticide…) from aqueus solution In recent years, carbon materials and the carbon based materials are widely used as effficient adsorbent because of high specific surface, stabilization and resistance to chemical and thermal agent Moreover, this type of material is easy modified, which leads to create the new chemical and physical properites such as decomposating the dye and heavy metal ions Further more, the modified material can increase the adsorption capacity and selectivity for removal of the toxic agents in the waste The nano structured carbon materials, such as carbon nano tubes, are familiar with people Because of the high cost in producing, it is limited for the application So, investigation of new adsorbents based on carbon material has received a great of interest Graphene and Graphene based material are the answers Actually, graphene is introduced in 2004 but it received a Nobel price for this material in 2010 This material is more and more popular and it is used in the various field: Electronics, photo electronics, electrical chemistry, mechanics and optics are examples The graphene is a new carbon material Basically, it is defined as one carbon atomic or several carbon layers with sp2 bonding which forms the crystallization type like honey bee Thank to their unique physical and chemical properties, graphene and GO (grapahene oxide) have many applications, including adsorption area Although many studies on synthesis and application ability of graphene based material are reported The studies of the modifed graphene still less focused and investigated Moreover, the technique which produced and modifies GO from graphene oxide layer by using microwave and the reduction from GO to rGO by using thermal reduction still less reported Thus, regarding the reasons mentionned above, we choose the subject of the thesis: “Study on synthesis and characterization of new materials based nanostructures of graphene applied in environmental treatment” Objectives of the thesis Synthesis and characterization of the GO (exfoliation by using the microwave (GOVS) and ultrasonic (GOSA) technigues), rGO, Fe3O4-GO, Fe-Fe3O4-GO and evaluation of these adsorbents for removal of activated dyes, asenic and heavy metal ions Main contents of the thesis - The parameters affect on the GO synthesis by using microwave and ultrasonication; reduction GO to rGO Characterizing the sythesized GO, rGO and Graphite oxide - The factors affect on the synthesis Fe3O4-GOVS material such as pH, concentration ratio Fe3+/Fe2+, temperature and stir speed - Synthesi of Fe-Fe3O4-GOVS - Characterization of Fe3O4-GOVS and Fe-Fe3O4-GOVS by using XRD, XPS, FTIR, HR-TEM, etc - Studying adsorption isotherm, adsorption kinetic of dye and heavy metal ions by the adsorbents: GOVS, rGO, Fe3O4-GOVS and Fe-Fe3O4-GOVS Thesis Layout The thesis consits of 150 pages, 93 pictures and diagrams, 50 tables and 143 references In detail: Preface Chapter 1: Overview Chapter 2:: Investigating method and experiment Chapter 3: Results and Dicussions Conclusion List of works has been published New findings of the thesis References Appendix CHAPTER 1: OVERVIEW This chapter has 35 pages which briefly introduce the carbon based material Moreover, this part also clearly shows the structure of Graphene, Graphene oxide; adsorptive sites and the graphene, graphene oxide synthesis methods; preparing magnetic composite from graphene, graphene oxide and ion oxides The ability of these materials in the treatment of dye, asenic and heavy metal ions in water are included CHAPTER 2: EXPERIMENT AND INVESTIGATION METHOD There are 22 pages in this chapter which consist of: 2.1 Experiment - Synthesis of Graphene oxide by Hummers modified method using H2SO4 (98%) and KMnO4 as oxidant agents - Exfoliation of Graphite oxide by microwave and ultrasonic technique - Synthesizing rGO by thermal reduction method using GO as starting material in N2 gas flow - Synthesizing magnetic composite from Fe3O4 – GO by co-precipitation method using FeCl3 and FeCl2 as Fe-sources and NH4OH as precipitation agent - Synthesizing Fe-Fe3O4-GO by chemical reduction method by using NaBH4 as reducing agent - Eveluation of the adsorption ability of synthesized materials for RR195, Cd(II), Cu(II) and As(V) Adsorption by Langmuir and Feundlich model - In order to investigate the kinetics of adsorption based on the pseudo-first-order and pseudo-second-order equations 2.2 Characterization methods - Chemical determination composition: EDX, XPS, UV-Vis, AAS - Characterizing material method: XRD, TEM, HR-TEM, BET, FTIR, XPS, FE-SEM, VMS (vibration magnetometer system) CHAPTER 3: RESULTS AND DISCUSSION This chapter contains 72 pages The details are: 3.1 The factors affect on the synthesis of GO and rGO 3.1.1 XRD results of Graphite before and after oxidation The XRD results show that for Graphite-Sigma Aldrich the peak 2θ = 26,5o is existed, characterizing the Graphite material Moreover, the peak 2θ = 11o is the evidence of the oxygen bonding formation between Graphite layers, which leads to the formation of GO structure 3.1.2 The factors affect on the exfoliation of GO by microwave and ultrasonic technique * The effect of microwave time: 1,2,3 and minutes Conditions: microwave power 700 W, graphite oxide weight 1g Basing on the recovery efficiency and XRD results of all samples, the suitable microwave time is minutes * The effect of microwave power: 216, 700, 1000 and 1200 W Conditions: graphite oxide weight 1g, microwave time: minutes with different microwave powers The results of XRD, FTIR show that the microwave power is 700 W * The effect of ultrasonic time on the GOSA process from graphite oxide: 30, 60 and 120 minutes On this investigation, the ratio Graphite oxide/H2O at mg/mL, the graphite oxide weight at 0,1 g and power 40 W are fixed According to the XRD and HR-TEM results, the suitable ultrasonic time is 60 minutes 3.1.4 The effect of temperature on the reduction of GOVS to rGO The thermal reduction performed at 400, 600, 800 and 1000 oC with heating rate 20 oC/minute and N2 gas flow 15-20 mL/minute Combining with the purpose of saving energy, the results of XRD and FTIR give 600 oC as the best temperature for reduction The yield of this process is in the range of 50 - 60% 3.2 The characterization of synthesized GO and rGO 3.2.1 X-ray Diffraction methods (XRD) Cuong (tuy chon) Cường độ (a.u) GOSA GOVS 10 rGO 20 30 Goc22Theta thetha(độ) Góc 40 50 Figure 3.8 XRD Patterns of GOSA, GOVS and rGO after synthesizing In the XRD patterns of GOVS and GOSA there are characteristic peaks at 2 = 11,5o and 11,2o, respectively, while for rGO it show a peak at 2 = 25,8o, which confirm the structure of GO and rGO 3.2.2 Fourier transform infrared spectroscopy (FTIR) Figure 3.9 FT-IR spectra of GOSA, GOVS and rGO Thank to these spectroscopies, there is the carbony group – C=O (in range 1700 -1730 cm-1) in the samples Beside the carbony group, there are other groups existed in these samples C–O in the range of 1200-1250 cm-1, C=C in aromatic compound in the range of 1500-1600 cm-1 and C-O-C in the range of 1060 cm-1 are examples Moreover, beacause of the peak from 3400 – 3850 cm-1, OH group is existed, which is slightly changed to the range of 3460 – 3500 cm-1 after supersonic process Moreover, the peak of other groups are also undergone the change within this process More detail is C=C at 1633 cm-1, C-O at 1168 cm-1 and carbonyl at 1728 cm-1 It is interesting that, after thermal reduction, the FTIR result of rGO does not contain the characterized peaks of GO (fig 3.9) which demonstrates the loss of huge amount of the functional group on GO surface 3.2.3 High Resolution Transmission Electron Microscope (HR – TEM) The calculation from HR-TEM indicates that the number of layers of GOSA, GOSV and rGO are 10, 7-8 and 5-6, respectively Moreover, the gap between each layer is about 0,4 nm for rGO, 0,6 nm 3.2.4 N2 adsorption–desorption isotherms (BET) This method determines the specific area, pore size, volume and the pore distribution of material The BET results of synthesized material are in table 3.3 Table 3.3 The parameters of GOSA, GOVS and rGO Parameters GOSA Specific area (m2/g) Micro-capillary volume (cm3/g) Total capillary volume (cm3/g) Average of capillary diameter (nm) GOVS rGO 56 331 300 0,0004 0,0015 0,018 0,283 1,719 1,596 9,6 - 21,4 7,8 - 21,2 8,8 - 22,5 From the Table 3.3, the GOVS and rGO have the high specific area and these are times higher than that of GOSA 3.2.5 X-ray photoelectron spectroscopy (XPS) As the results of XPS: - There are huge amount of oxygen in the functional group existing on GOSV and GOSA and the number of these group is dramatically decreased in rGO - The thermal reduction from GO to rGO are clearly demonstrated by the peak of π→π* in the aromatic compound at 291,5 eV - On the thermal reduction process from GO to rGO, the ratio of C/O increases from 2,32 (GOSA) and 2,98 (GOVS) to 6,15 and 10,89, respectively The composition of elements in GOVS, GOSA and rGO is in table 3.4 Table 3.4 The composition of elements in GOVS, GOSA and rGO (%At) Sample/elements C O C/O rGO GOVS GOSA rGO (from thermal reduction GOSA) 91,59 73,92 69,88 7,41 25,08 30,12 10,89 2,98 2,32 86,02 13,98 6,15 3.3 The factors effect on the Fe3O4-GOVS synthesizing In this part, we focus on synthesizing and evaluating the properties of Fe3O4-GOVS synthesized by co-participation method By this way, the products have the small particle size, fine distribution and easy to recover by the external magnetic field 3.3.1 The effect of co-participation reaction temperature For clearly showing the effect of co-participation reaction temperature on the morphology, phase change and size of Fe3O4GOVS Nano, the samples are made under the various temperature: 30 o C (GF1), 50 oC (GF2) and 80 oC (GF3) The characterized methods are used: XRD, XPS and TEM While the XRD shows the increase of particle size Fe3O4 nano on GOVS with increasing temperature, XPS results demonstrate that there is only Fe3O4 on GOVS (without γFe2O3) Therefore, in the reaction temperature range from 30 to 80 oC, the synthesized materials are purity (only phase Fe3O4 on GOVS) TEMs of GF1, GF2 and GF3 give the shape of Fe3O4 on GOVS This shape is spherical and it is fine distribution, especially the sample at 80 o C The particle size of GF1, GF2 and GF3 has the increasing trend with nm for GF1, 13 nm for GF2 and 15 nm for GF3 The XPS also conclude that the sample with 80 oC acheives the highest Fe concentraion (17,23%) In brielfly, 80 oC is chosen 3.3.2 The effect of precursor concentration Making samples with the different concentration ratios Fe3+/Fe2+: N (0,01M/0,005M), GF3 (0,1M/0,05M), N1 (1M/0,5M) N2 (2M/1M), with the reaction temperature at 80 oC, pH = 10 and stir speed 500 rpm The particle size increases with the rise of concentration ratio, basing on the XRD results The particle size is determined with Scheerer equation which is collected in Table 3.7 Tabke 3.7 Paticle size of Fe3O4-GOVS synthesizing Sample N GF3 N1 N2 dXRD (nm) 7,3 13,4 18,2 36,1 When comparing the TEM results of all sample, we see that it easily distinguishes the change in particle size For example, the particle size in N, GF3, N1 and N2 is nm, 15 nm, 25 nm and 40 nm, respectively Moreover, Fe3O4 is in the spherical shape, fine distribution and posited at the space between each layer However, for high recovery efficiency, we need the high saturated sample Two sample GF3 and N1 belong to the highest group So, the choice is GF3 the range 500-1000 rpm, there is a slight decrease in particle size Therefore, we choose the stir speed 500 rpm 3.4 Synthesizing Fe3O4-GOVS and Fe-Fe3O4-GOVS material - Procedure for synthesizing Fe3O4-GOVS Figure 3.24 The procedue for synthesizing Fe3O4 - GOVS Basing on the above results, after geting Fe3O4-GOVS, we will make the Feo nano on this surface by using NaBH4 as a reducer agent and Fe3+ from (FeCl3.6H2O) The nitrogen is blown on this system (fig 2.5) By this method, the percentage of Feo on Fe3O4-GOVS surface is about 10% in weight Figure 2.5 Procedure for synthesizing Fe-Fe3O4-GOVS 11 3.5 Characterization of Fe3O4-GOVS and Fe-Fe3O4-GOVS 3.5.1 X-ray diffraction (XRD) Intensity (a.u) M * 440 M 422 400 M 511 220 M 311 *: Feo 111 M: Fe3 O4 M M M * Fe3O4-GO Fe-Fe3O4-GO 10 20 30 40 50 60 70 Thetha Scale Figure 3.25 XRD patterns of Fe3O4-GOVS and Fe-Fe3O4-GOVS XRD results show that there are the formation of Fe0 and Fe3O4 on the samples, which is the cause of existing the peaks 2θ at 45° and 68° These peaks are characterized for Feo 3.5.2 TEM and HR-TEM Spectroscopy (a) (b) (c) Figure 3.26 The TEM of Fe3O4-GOVS (a) and Fe-Fe3O4-GOVS (b,c) 12 As the results of TEM and HR-TEM Spectroscopy (Figure 3.26), the particle size of Fe3O4 nano is about 12-17 nm However, there are some clusters of Fe3O4 having the particle size with 20 nm In contrasting, the particle size of Feo nano is slightly small (about 5-10 mm) 3.5.3 FTIR Spectroscopy Intensity (a.u) According to FTIR results, there is Fe3O4 nano on the surface of GOSV, which leads to the existance of peak at 578,2 cm-1 This is the characterized peak for Fe-O bonding in Fe3O4, Fe-Fe3O4 and GOVS While the peaks at 1230 Wavenumber (cm ) cm-1 and 1576 cm-1 are C=O and C-O, the peak Figure 3.27 FTIR spectra of Fe-Fe3O4-GO at 2342 cm-1 are the and Fe3O4-GO bonding of CO2 with Fe3O4-GOVS and Fe-Fe3O4-GOVS Furthermore, there is the formation of Feo nano on the Fe3O4-GOVS because of the characterized peak at 1048,5cm-1 -1 3.5.4 EDX Spectroscopy of Fe-Fe3O4-GOVS and Fe3O4-GOVS EDX Spectroscopy results in Table 3.8 Table 3.8 The element composition in Fe3O4-GOVS and Fe-Fe3O4-GOVS Fe3O4-GOVS Fe-Fe3O4-GOVS Element % weight % atom % weight % atom C 35,97 74,46 29,96 57,98 O 15,44 19,98 12,36 17,97 Fe 48,59 17,96 57,68 24,05 Total (%) 100 100 100 100 13 From Table 3.8, the percentage of Fe in Fe3O4-GOVS is about 48,59% in weight and 18% in atom, which is close to the initial calculation ( 50% in weight and 20 % in atom) After adding to Feo with 10% in weight on the Fe3O4-GOVS, the percentage of Fe in weight reaches to 57,68% (~ 9.1% in weight) It is close to the initial calculation 3.5.5 N2 adsorption–desorption isotherms (BET) of Fe-Fe3O4-GOVS and Fe3O4-GOVS The BET results show that these materials belong to the layer structure form From Table 3.9, Fe-Fe3O4-GO has a high specific area and high pore volumn and these are higher than that of Fe3O4-GOVS Moreover, these two material belongs to average capillary system (average capillary system is 99%, while the micro capillary system is about 1%) The capillary diameter is in the range from 8-13 nm Table 3.9 Textual characteristics of Fe-Fe3O4-GOVS and Fe3O4-GOVS Parameters Fe3O4-GOVS Fe-Fe3O4-GOVS 169 177 Micro-capillary volume (cm3/g) 0,0033 0,0043 Total capillary volume (cm3/g) 0,499 0,523 Average of capillary diameter (nm) 8,8 - 12,1 8,9 - 12,3 Specific area (m2/g) 3.5.6 XPS spectra of Fe-Fe3O4-GOVS and Fe3O4-GOVS XPS spectroscopy results (Fig 3.30) demonstrate the purity of Fe3O4 on the GO because there are the characterized peaks at 711 eV and 725 eV For Fe-Fe3O4-GOVS, beside the peaks of Fe3O4, two other peaks at 719 and 733 eV are existed It can be explained by the reaction between Feo and Fe3O4-GOVS, which is conduct to the formation of Fe2O3, FeOOH Moreover, because of the peak at 706 eV, the particle size of Feo nano is predicted about less than 10 nm Although these XPS 14 spectroscopies not contain the peaks of -Fe2O3, the: C-C, C-O, OC=O, C=O, Fe-O and π-π* are still remained Fe 2p1/2 725 eV Fe2p3/2 711 eV Fe3+ 733eV Intensyty (a.u) Intensity (a.u) C1s Fe- Fe3O4-GO O1s Fe2p Na1s Fe3 O4 -GO Fe0 706 eV 740 1300 1100 Fe3+ 719 eV Fe-Fe3 O4 -GO Fe3O4-GO 900 700 500 300 735 730 725 720 715 710 705 700 Binding Energy (eV) 100 Binding Energy (E) C-C 284.8 eV C-O 535 eV Intensity (a.u) Intensity (a.u) Fe-O 529.9 eV C=O 531.5 eV -C=O 288.3 eV C-O 285.5 eV 291.5 ev 540 538 536 534 532 530 528 296 526 294 292 290 288 286 284 282 280 Binding Energy (eV) Binding Energy (eV) Figure 3.30 XPS spectra of Fe-Fe3O4-GOVS and Fe3O4-GOVS 3.5.7 Magnetic property of Fe-Fe3O4-GOVS and Fe3O4-GOVS Using VSM to study the magnetic property of these sample, the results show that the coercive force is close to zore for both two samples Moreover, the staturated magnetization of Fe3O4-GOVS is 35 emu/g Similarly, that value of Fe-Fe3O4-GOVS is 29 emu/g 3.6 Adsorption ability of GOSA, GOVS and rGO material The next part is the adsoprtion ability of GOSA, GOVS and rGO material for the die RR195 For Fe3O4-GOVS and Fe-Fe3O4GOVS, beside RR195, we also investigate the adsorption ability for some metallic ions such as: Cu(II), Cd(II) and As(V) 15 3.6.1 The adsorption ability of GOVS, GOSA and rGO for RR195 3.6.1.1 The effect of pH The effect of pH on the adsoprtion capacity of these materials for RR195 is illustrated in picture 3.32 Basing on this picture, the effect of pH on adsoprtion ability of rGO is not so much On the other hand, the Figure 3.32 The effect of pH on the higher pH is, the lower adsorption of GO and rGO for RR195 adsorption capacity of GOVS and GOSA are The pH = 5.5 is chosen because of the real application 3.6.1.2 Estimating the adsorption ability of GOVS, GOSA and rGO for RR195 The experiment is carried out with the below conditions: temperature fixed at 30 oC, pH fixed at 5.5, stir speed fixed at 150 rpm and RR195 concentration changed from 100 mg/L to 500 mg/L Figure 3.33 The adsorption capacity GO and rGO for RR195 (200 mg/L) with time (a) and the isotherm adsorption curve for RR195 (b) According to Figure 3.33a, the adsorption ability for RR195 of these materials undergoes a decrease trend with detail: rGO > GOVS > GOSA While the optimum time for adsorption process of rGO and GOVS is in the range of 0-6 h, that time of GOSA is from to h And h is the requirement time for the adsorption equilibrium 16 3.6.1.3 The isotherm adsorption This experiment is carried out at pH = 5,5 and the various initial concentration of RR195 The results of this adsorption process is suitable with the Langmuir equation The detail is collected in Table 3.21 Table 3.21 The summry of isotherm adsorption of GO amd rGO for RR195 under Langmuir and Freundlich equation Langmuir Freundlich Absorbent Qmax KL R2 KF 1/n R2 GOVS GOSA rGO 212,7 58,8 250 0,022 0,040 0,025 0,999 0,994 0,997 4,36 3,74 5,38 0,346 0,208 0,279 0,976 0,876 0,989 3.6.2 Kinetic adsorption of GOVS and rGO for RR195 We see that the adsorption capacity Qmax of GOSV and rGO for RR195 are from 3,6 to 4,3 times higher than that of GOSA (according to Table 3.12) So, this thesis focuses on the kinetic adsorption of GOSV and rGO for RR195 The results demonstrate that this process obeys the quadric equation More details are in Table 3.19 Table 3.19 Parameters of quadric kinetic equation (for RR195) Material GOVS rGO Equations t Qt t Qt R22 = 0,0077 + 0,0071.t 0,999 = 0,0018 + 0,994 k2 (g/mg.h) Qe, exp (mg/g) Qe, cal (mg/g) 0,0065 140,01 140,84 0,0206 160,16 163,93 0,0061.t Qe, cal: adsorption capacity equilibrium calculate by kinetic equation Qe, exp: adsorption capacity equilibrium calculated by experiment From the Table 3.19, the adsorption rate of rGO for RR195 with concentration 200 mg/L is 0,0206 g/mg.h which is higher than that of GOVS (0,0065 g/mg.h) 17 3.7 Estimating the adsorption ability of Fe3O4-GOVS and Fe-Fe3O4GOVS 3.7.1 The adsoprtion ability of Fe3O4-GOVS and Fe-Fe3O4-GOVS for RR195 In order to estimate the adsorption ability of Fe3O4-GOVS and Fe-Fe3O4-GOVS for RR195, we use the GOVS, GOSA and rGO as the references For the same adsorption reaction conditions: temperature 30 oC, m/V = g/L, initial concentration RR195 = 100 mg/L and constant pH, the adsorption ability of these samples has the decreasing trend like this: rGO > GOVS > Fe-Fe3O4-GOVS > Fe3O4GOVS > GOSA 3.7.2 The adsorption ability for heavy metal ions: Cu(II) and Cd(II) 3.7.2.1 Point of zero charge of Fe3O4-GOVS and Fe-Fe3O4-GOVS ∆pH= (pH đầu- pH cuối) a 2 10 11 12 ∆pH= (pH đầu- pH cuối) 4 b 2 10 11 12 -1 -1 pH ban đầu -2 -2 pH ban đầu Picture 3.41 Pooint of zero charge (pHpzc) of Fe3O4-GOVS (a) and Fe-Fe3O4-GOVS (b) From above pictures, the point of zero charge of Fe3O4-GOVS is appropiate 5.2 Siminally, the Fe-Fe3O4-GOVS has the point of zero charge about 5.4 In addition that, the chosen pH for this experiment is 3.7.2.2 Isotherm adsorption of GOVS and Fe3O4-GOVS for Cu(II) and Cd(II) 18 Table 3.25 Langmuir and Freundlich isotherm constants for Cd(II) and Cu(II) adsorption of Fe3O4-GOVS and GOVS Isotherm Langmuir Qmax (mg/g) KL (l/mg) R2 RL Freundlich 1/n KF[(mg/g)(L/ mg)1/n] R2 Fe3O4GOVS Adsorpt ion Cd(II) 52,63 1,27 0,998 0,15 Material, pH=6 Fe3O4GOVS GOVS GOVS Adsorption Cd(II) Adsorption Cu(II) Adsorption Cu(II) 29,41 0,28 0,998 0,067 30,3 0,83 0,992 0,24 22,73 0,13 0,998 0,13 0,440 0,339 0,188 0,444 21,33 9,09 15,92 4,12 0,899 0,978 0,963 0,955 According to the Table 3.25, the adsorption of Fe3O4-GOVS and GOVS for Cu(II) and Cd(II) obeys the Langmuir equation The maximum adsorption capacity of Fe3O4-GOVS and GOVS for Cd(II) are 52,63 mg/g and 29,41 mg/g, respectively In comparison, this value for Cu(II) are about 30,3 mg/g and 22,73 mg/g 3.7.2.3 The isotherm adsorption of Fe-Fe3O4-GOVS for Cu(II) and Cd(II) Table 3.28 Langmuir and Freundlich isotherm constants for Cd(II) adsorption of Fe- Fe3O4-GOVS Langmuir and Fe-Fe3O4-GOVS, Fe-Fe3O4-GOVS, Freundlich isotherm pH = 6, Cu(II) pH = 6, Cd(II) Langmuir Qmax (mg/g) 90,9 108,6 KL (L/mg) 0,282 0,375 R2 0,996 0,987 RL 0,034 0,026 Freundlich 1/n 0,401 0,473 KF [(mg/g)(L/mg)1/n] 23,068 29,507 R2 0,975 0,972 19 Basing on those results, the adsorption process belongs to Langmuir model In these, maximum adsorption capacity of FeFe3O4-GOVS for Cd(II) and Cu(II) is 108,6 mg/g and 90,9 mg/g, respectively, which is higher than that of Fe3O4-GOVS (with (52 mg/g and 30,3 mg/g) at the pH at That is the evidence for forming new absorbing centers (Feo, Fe2O3, FeOOH) on the Fe-Fe3O4-GOVS surface Thank to these centers, the adsorption capacity significantly increase 3.7.2.4 The kinetic adsortion of Fe-Fe3O4-GOVS for Cd(II) After deeply observing the adsorption of Fe-Fe3O4-GOVS for Cd(II), we find that this process has the adsorption equation obeying the quadric equation The detail results show in Table 3.30 Table 3.30 Some parameters of the apparent kinetic Pseudo-first order equation and Pseudo-second order equation FePseudo-first order Fe3O4equation GOVS 50 mg/L Ln(Qe-Qt) = 2,647 - 0,094.t 100 mg/L Ln(Qe-Qt) = 2,615 - 0,057.t FePseudo-second order Fe3O4equation GOVS 50 mg/L t/Qt = 0,021.t + 0,023 100 mg/L t/Qt = 0,011.t + 0,008 k1 (minute1 ) 0,094 0,057 47,296 11,107 88,980 13,663 R22 k2(g/mg minute) Qe, exp (mg/g) Qe, cal (mg/g) 0,999 0,999 0,019 0,015 47,296 88,980 47,619 90,909 R12 0,935 0,705 Qe, exp (mg/g) Qe, cal (mg/g) 3.7.3 The adsorption of GOVS, Fe3O4-GOVS and Fe-Fe3O4-GOVS for As(V) 3.7.3.1 The effect of pH After investigating the effect of pH on the adsorption of Fe3O4GOVS and Fe-Fe3O4-GOVS for As(V), we see that pH has much effect on this process which the surface of Fe3O4-GOVS contaning positive charge when pH < pHpzc (pHpzc ~ 5,2) Because of consisting 20 of the positive charge on the surface and complex formation, this material is a high adsorption ability In contrast, if pH is higher than pHpzc, the surface of Fe3O4-GOVS will charge the nagetive, which results in the dramatic decrease of adsorption ability Similarly, for Fe-Fe3O4-GO with pHpzc ~ 5,4, the adsorption ability for As(V) also significantly decrease when the pH is higher than 5,4 Therefore, we choose the pH at for As(V) adsorption In comparison, with pH = 5, the adsorption efficient of GOVS for As(V) is low, about 10% at concentration mg/L (Qmax =1,75 mg/g) 3.7.3.2 The isotherm adsorption The adsorption process of Fe-Fe3O4-GOVS and Fe3O4-GOVS for As(V) obeys the Langmuir equation The maximum adsorption capacities of Fe3O4-GOVS and Fe-Fe3O4-GOVS at pH = for As(V) are 25 mg/g and 43,47 mg/g, respectively The details are shown in Table 3.32 Table 3.32 Parameters of isotherm adsorption process of Fe3O4GOVS and Fe-Fe3O4-GOVS for As(V) Langmuir and Freundlich isotherm Langmuir isotherm Qmax (mg/g) KL (l/mg) R2 RL Freundlich isotherm 1/n KF [(mg/g)(L/mg)1/n] R2 Materials Fe3O4-GOVS, Fe-Fe3O4-GOVS, pH = pH = 25 0,406 0,981 0,058 43,47 0,451 0,996 0,053 0,284 2,737 0,788 0,421 6,410 0,940 3.7.3.3 The kinetics adsorption of Fe3O4-GOVS and Fe-Fe3O4GOVS for As(V) 21 The study results showed that the apparent kinetic equation pseudo-second order equation matching process adsorption of As(V) on the Fe-Fe3O4-GOVS and Fe3O4-GOVS Synthesis of the parameters of the apparent kinetic equation are shown in Table 3.37 Table 3.37 Rate adsorption constants and As(V) adsorption capacities calculated according to pseudo-second order equation Absorbent R22 Equations t = 0,004 + 0,030.t Qt t = 0,014 + 0,047.t Fe3O4-GOVS Qt Fe-Fe3O4GOVS k2 Qe, exp Qe, cal (g/mg.h) (mg/g) (mg/g) 0,999 0,220 32,905 33,333 0,999 0,150 20,743 21,276 Basing on this table, the adsorption rate of Fe-Fe3O4-GOVS for As(V) (20 mg/L) is 1,5 times higher than that of Fe3O4-GOVS The details are 0,22 g/mg.h and 0,15 g/mg.h, respectively These results reconfirm the above conclusion that: the adsorption rate of Fe-Fe3O4-GOVS for As(V) is higher than that of Fe3O4-GOVS 3.8 Desorption and reusability From the above results, the adsorption capacity of Fe-Fe3O4GOVS for dye and heavy metal ions (Cu(II), Cd(II) and As(V)) is higher than that of Fe3O4-GOVS Thus, Fe-Fe3O4-GOVS is chosen for the reuse experiment with the cycles number After each time of adsorption process, the absorbent is desorbed In case of adsorbing the die, the desorption substances are water and the mixture of ethanol and methanol Similiarly, the desorption substance is HCl 0,1M at pH ~ for metallic ion adsorption The experiment results after the 3rd cycle show that the time life of Fe-Fe3O4-GOVS is really good The adsoprtion efficiencies of this material for RR195 at 100 mg/L after the 3rd cycle is 50,0%, 48,9% and 45,5% Furthermore, for Cd(II) (10 mg/L), the adsoprtion efficiencies of Fe-Fe3O4-GOVS After the fourth cycle are higher than that of RR195 That is 98,6%, 95,7% and 93,1% 22 CONCLUSION - GO and rGO were successfully synthesized from natural graphite by the modified Hummers’ method using H2SO4 and KMnO4 as oxidant agents Exfoliation of GO by using microwave and ultrasonic technique as well as thermal reduction of GO to rGO in N2 gas at 600 o C The products (GO and rGO) have the structure of several atomic carbon layers The ratio C/O changes from 2.32 to 10.89, which related to GO and rGO There are fuctional groups on the GO and rGO surfaces, such as: -OH, C=O, C-O, COO- and the strength of these groups on GO and rGO surfaces increase with this trend: rGO < GOVS < GOSA rGO and GOVS have the high specific surface and much higher than that of GOSA (about times) - Nano composite Fe3O4-GOVS was successfully prepared by coprecipitaion method in base solution (NH3) and composite Fe-Fe3O4GOVS by chemical reducion method using NaBH4 as a reducer agent The cheracterization results shows the co-existence of both Fe3O4 and Feo on the surface of GOVS, which has Fe-O bonding The formation of Fe3O4 on GOVS surface is uniform under room temperature and the particle size depends on the temperature, pH, concentration and stirring speed According to XRD and TEM, the particle size of Fe3O4 on GOVS is about 15 nm and the particle size of Feo is less than 10 nm Both Fe3O4-GOVS and Fe-Fe3O4-GOVS have the magnetic property and high saturated magnetization (35 emu/g and 29 emu/g) respectively and they are easily recoved by applying the external magnetic field - All five materials GOVS, GOSA, rGO, Fe3O4-GOVS and FeFe3O4-GOVS show high adsorption capacity of the reactive dyes RR195 with the maximum adsorption capacity of 300 mg/g for rGO The order of adsorption ability is the following: GOSA < Fe3O4GOVS < Fe-Fe3O4-GOVS < GOVS < rGO - GOVS, Fe3O4-GOVS and Fe-Fe3O4-GOVS can adsorp selectively heavy metal ions such as Cu(II), Cd(II) and As(V) The order of adsorption ability is the following: GOhVS < Fe3O4-GOVS < FeFe3O4-GOVS It is interesting that with content 10% Feo in mass on the surface; Fe- Fe3O4-GOVS exhibited higher adsorption capacity 23 for heavy metal ions: Cu(II), Cd(II) and As(V) as compared to that of the Fe3O4-GOVS In detail, Fe3O4-GOVS has Qmax of Cu(II), Cd(II) As(V): 30,3 mg/g; 52,03 mg/g and 25 mg/g, respectively, while Fe-Fe3O4-GOVS is 90,9 mg/g; 108,6 mg/g and 43,47 mg/g - According to the adsorption isotherm and adsorption kinetic, the adsoprtion of GOVS, GOSA, rGO for RR195 and the adsoption of Fe3O4-GOVS and Fe-Fe3O4-GOVS for Cd(II), Cu(II), As(V) obey to Langmuir model and second order kinetic equation Reaction rate constant and adsorption capacity of Cd(II), Cu(II) and As(V) on FeFe3O4-GOVS is 1.5 time higher than that of Fe3O4-GOVS NEW FINDINGS OF THE THESIS GO and rGO with several atomic carbon layers (< 8) were successfully synthesized by the oxidation chemical wet method from natural graphite and exfoliation of GO by using microwave rGO is produced by thermal reduction method from GO The synthesized GO and rGO have high specific surface, with high adsoprtion capacity of dyes and heavy metal ions Nano composite Fe3O4-GOVS was successfully prepared by coprecipitaion method (In situ) and composite Fe-Fe3O4-GOVS by chemical reducion method using NaBH4 as a reducer agent The products have the particle size in nano scale (10-20 nm) and uniform distribution on the GO and rGO surface Fe-Fe3O4-GOVS exhibited a high adsoprtion capacity for Cd(II), Cu(II), As(V) and it is much higher than that of published result using similar material This leads to remove more efficiently the contaminants such as asenic and heavy metal ions from aqueus solution Isotherm adsorption and adsorption kinetic of Fe-Fe3O4-GOVS with metallic ions (Cd(II) and As(V)) obeys Langmuir model and second order kinetic equation 24 LIST OF WORKS HAS BEEN PUBLISHED Giang Ha Le, Anh Quang Ha, Quang Ke Nguyen, Quyet Tien Ngo, Binh Quang Ngo, Canh Đuc Đao, Kien Trung Nguyen, Phuong Tuyet Dang, Hoa T Kim Tran, Ngo Đinh Vu and Tuan Anh Vu, Synthesis, charaterization and ability of arsenic removal by graphene oxide and Fe3O4/GO nanocomposite, Journal of Chemistry, 2014, 6A-52, 143-148 Anh Quang Ha, Giang Ha Le, Quang Ke Nguyen, Trang T Thu Quan, Ngo Đinh Vu and Tuan Anh Vu, Study arsenic removal ability of Fe3O4/GO Fe/Fe3O4/GO nano composite, Journal of Chemistry, 2015, T.53 (3E12), 285-291 Anh Quang Ha, Giang Ha Le, Quang Ke Nguyen, Ngo Đinh Vu and Tuan Anh Vu, Synthesis and ability for Cu(II), Cd(II) removal of graphene oxide (GO) and Fe3O4/GO nanocomposite, Journal of Chemistry, 2015, T.53 (3E12), 279-285 Anh Quang Ha, Giang Ha Le, Quang Ke Nguyen, Quan T Thu Trang, Ngo Đinh Vu and Tuan Anh Vu, Study on Cd(II) adsorpion ability from aqueous solution by Fe/Fe3O4/GO nanocomposite, Journal of catalysis and adsorption, 2015, T.4, N02, 132-138 Anh Quang Ha, Lê Thị Mai Hoa, Giang Ha Le, Quang Ke Nguyen, Canh Đuc Đao, Kien Trung Nguyen, Hoa T Kim Tran, Phuong Tuyet Dang and Tuan Anh Vu, Adsorption of Rodamin B from aqueous by graphene oxide and graphene, Journal of catalysis and adsorption, 2015, T.4, N02, 160-168 Anh Quang Ha, Lê Thị Mai Hoa, Giang Ha Le, Quang Ke Nguyen, Quyet Tiến Ngo, Canh Đuc Đao, Kien Trung Nguyen, Phuong Tuyet Dang, Hoa T Kim Tranvà Tuan Anh Vu, Study on synthesis, characterization and ability of dye adsorption by graphene and graphene oxide from natural graphite, Journal of catalysis and adsorption, 2015, T.4, N04B, Anh Quang Ha, Hoa Thị Mai Le, Giang Ha Le, Quang Ke Nguyen, Ngo Đinh Vu and Tuan Anh Vu, Study on dye reactive RR195 adsorption ability from aqueous solution by graphene oxide and graphene, Journal of Analytical Sciences; 2015, T20-4, 20-27 Le Ha Giang, Le Thi Mai Hoa, Ha Quang Anh, Nguyen Ke Quang, Dao Duc Canh, Nguyen Thi Phuong, Tran Thi Kim Hoa, Dang Tuyet Phuong and Vu Anh Tuan, Fe-Fe3O4/GO COMPOSITE AS NOVEL AND HIGHLY EFFICIENT PHOTOCATALYST IN REACTIVE DYE DEGRADATION, Proceeding of IWNA 2015, 11-14 November 2015, Vung Tau, Viet Nam pp.638-642 25 [...]... According to the adsorption isotherm and adsorption kinetic, the adsoprtion of GOVS, GOSA, rGO for RR195 and the adsoption of Fe3O4-GOVS and Fe-Fe3O4-GOVS for Cd(II), Cu(II), As(V) obey to Langmuir model and second order kinetic equation Reaction rate constant and adsorption capacity of Cd(II), Cu(II) and As(V) on FeFe3O4-GOVS is 1.5 time higher than that of Fe3O4-GOVS NEW FINDINGS OF THE THESIS 1 GO and. .. we also investigate the adsorption ability for some metallic ions such as: Cu(II), Cd(II) and As(V) 15 3.6.1 The adsorption ability of GOVS, GOSA and rGO for RR195 3.6.1.1 The effect of pH The effect of pH on the adsoprtion capacity of these materials for RR195 is illustrated in picture 3.32 Basing on this picture, the effect of pH on adsoprtion ability of rGO is not so much On the other hand, the... Phuong Tuyet Dang and Tuan Anh Vu, Adsorption of Rodamin B from aqueous by graphene oxide and graphene, Journal of catalysis and adsorption, 2015, T.4, N02, 160-168 Anh Quang Ha, Lê Thị Mai Hoa, Giang Ha Le, Quang Ke Nguyen, Quyet Tiến Ngo, Canh Đuc Đao, Kien Trung Nguyen, Phuong Tuyet Dang, Hoa T Kim Tranvà Tuan Anh Vu, Study on synthesis, characterization and ability of dye adsorption by graphene and. .. investigating the effect of pH on the adsorption of Fe3O4GOVS and Fe-Fe3O4-GOVS for As(V), we see that pH has much effect on this process which the surface of Fe3O4-GOVS contaning positive charge when pH < pHpzc (pHpzc ~ 5,2) Because of consisting 20 of the positive charge on the surface and complex formation, this material is a high adsorption ability In contrast, if pH is higher than pHpzc, the surface of. .. Kinetic adsorption of GOVS and rGO for RR195 We see that the adsorption capacity Qmax of GOSV and rGO for RR195 are from 3,6 to 4,3 times higher than that of GOSA (according to Table 3.12) So, this thesis focuses on the kinetic adsorption of GOSV and rGO for RR195 The results demonstrate that this process obeys the quadric equation More details are in Table 3.19 Table 3.19 Parameters of quadric kinetic... effect of pH on the higher pH is, the lower adsorption of GO and rGO for RR195 adsorption capacity of GOVS and GOSA are The pH = 5.5 is chosen because of the real application 3.6.1.2 Estimating the adsorption ability of GOVS, GOSA and rGO for RR195 The experiment is carried out with the below conditions: temperature fixed at 30 oC, pH fixed at 5.5, stir speed fixed at 150 rpm and RR195 concentration changed... R2 Materials Fe3O4-GOVS, Fe-Fe3O4-GOVS, pH = 5 pH = 5 25 0,406 0,981 0,058 43,47 0,451 0,996 0,053 0,284 2,737 0,788 0,421 6,410 0,940 3.7.3.3 The kinetics adsorption of Fe3O4-GOVS and Fe-Fe3O4GOVS for As(V) 21 The study results showed that the apparent kinetic equation pseudo-second order equation matching process adsorption of As(V) on the Fe-Fe3O4-GOVS and Fe3O4-GOVS Synthesis of the parameters of. .. specific surface and much higher than that of GOSA (about 5 times) - Nano composite Fe3O4-GOVS was successfully prepared by coprecipitaion method in base solution (NH3) and composite Fe-Fe3O4GOVS by chemical reducion method using NaBH4 as a reducer agent The cheracterization results shows the co-existence of both Fe3O4 and Feo on the surface of GOVS, which has Fe-O bonding The formation of Fe3O4 on GOVS surface... temperature and the particle size depends on the temperature, pH, concentration and stirring speed According to XRD and TEM, the particle size of Fe3O4 on GOVS is about 15 nm and the particle size of Feo is less than 10 nm Both Fe3O4-GOVS and Fe-Fe3O4-GOVS have the magnetic property and high saturated magnetization (35 emu/g and 29 emu/g) respectively and they are easily recoved by applying the external... 3.41 Pooint of zero charge (pHpzc) of Fe3O4-GOVS (a) and Fe-Fe3O4-GOVS (b) From above pictures, the point of zero charge of Fe3O4-GOVS is appropiate 5.2 Siminally, the Fe-Fe3O4-GOVS has the point of zero charge about 5.4 In addition that, the chosen pH for this experiment is 6 3.7.2.2 Isotherm adsorption of GOVS and Fe3O4-GOVS for Cu(II) and Cd(II) 18 Table 3.25 Langmuir and Freundlich isotherm constants