Development of novel titanate nanotubes reduced graphene oxide composite for the removal of heavy metals from aqueous solution

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURAL AND FORESTRY VU THI HOAI TOPIC TITLE: DEVELOPMENT OF NOVEL TITANATE NANOTUBES/ REDUCED GRAPHENE OXIDE COMPOSITE FOR THE REMOVAL OF HEAVY METALS FROM AQUEOUS SOLUTION BACHELOR THESIS Study Mode: Full-time Major: Environmental Science and Management Faculty: International Training and Development Center Batch: 2010-2015 Thai Nguyen, 15/01/ 2015 DOCUMENTATION PAGE WITH ABSTRACT Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor of environmental Science and Management Student name Vu Thi Hoai Student ID DTN1053110084 Thesis Tiltle Supervisor(s) Development of Novel Titanate Nanotubes/ Reduced Graphene Oxide Composite for the Removal of Heavy Metals from Aqueous Solution Prof Dr Nguyen The Dang, Thai Nguyen University of Agriculture and Forestry, Vietnam Prof Ruey-an Doong, National Tsing Hua University Abstract Graphene oxide (GO), is a two dimensional carbon nano-material which exhibits a great adsorption potential Graphene functionalized composites enhance its adsorption efficiency for toxic heavy-metals from contaminated waste water Titanium nanotubes and GO were assembled in basic medium via microwave-assisted hydrothermal method The strong anchoring of TNT on the surface of GO sheets can be easily observed by TEM (Transmission Electron Microscopy), XRD (X-ray Diffraction) Diffraction on GO sheets confirmed through D-band and G-band ration by Raman Spectroscopy As-synthesized TNT/rGO composite shows high efficiency and high selectivity toward heavy metals in aqueous solution The results indicated that TNT/rGO composite with high adsorption efficiency and fast adsorption equilibrium can be used as a practical adsorbent for heavy metals in aqueous solution Keywords Titanate nanotube, Graphene oxide, composite, hydrothermal, adsorption Number of papers 44 pages Date of submission: 15/01/2015 ACKNOWLEDGEMENTS I am deeply indebted to my research supervisor Prof Ruey-An Doong, whose stimulating motivations and valuable ideas helped me to complete my thesis and I would like to offer my sincere gratitude to prof Dr Nguyen The Dang for his support throughout my thesis with his patience and knowledge whilst allowing me the room to work in my own way I attribute the level of my Bachelor degree to his encouragement and effort I am grateful to Rama Shanker Sahu (PhD) and Yen-Tung Yang (PhD) for their valuable help, advices and constructive comments during all my experiments and writing thesis I would like to thank Duncan, Sammy, Joyce (MS) for their great support in characterizing my samples, YC Ken Tsai (PhD) and Rudy (PhD) for their impressive help in adsorption studies I would also like to thank Khanh, Linh and all FATECOL members, Biomedical Engineering and Environmental Sciences, National Tsing-Hua University, Taiwan, who provided their ongoing support, questions and suggestions Finally, I would like to express my love and gratitude to my beloved parents for their support & endless love VU THI HOAI TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF ABBREVIATIONS PART I INTRODUCTION 1.1 Research rationale 1.2 Research's Objectives PART II LITERATURE REVIEW 2.1 Overview of heavy metals 2.1.1 Definitions and sources of heavy metals 2.1.2 Characteristics of heavy metals .7 2.2 Heavy metal pollution in the world and Vietnam 2.2.1 In estuary, coastal and marine areas 2.2.2 In acid sulfate soil areas 2.3 Characteristics and hazards of some heavy metals 10 2.3.1 Arsenic (As) 10 2.3.2 Cadmium (Cd) 11 2.3.3 Lead (Pb) 12 2.3.4 Copper (Cu) 13 2.4 Effects of heavy metal to environmental and human health 14 2.5 Some of treatment methods for the removal of heavy metals from aqueous solution 15 2.5.1 Carbon materials 15 2.5.2 Phytoremediation 18 2.5.3 Nanomaterials 19 2.5.4 Titanate nanotubes 19 2.6 Overview of handling heavy metals in aqueous solution using Titanate nanotube / reduced graphene oxide composite 20 2.6.1 Scientific Basis of handling heavy metals in aqueous solution by rGO-TNT composite 20 2.6.2 Some research results of absorption of heavy metals in water by rGO-TNT composite 20 2.6.3 Prospects of technological rGO-TNT composite in removal of heavy metals in aqueous solution .21 PART III METHODS 22 3.1 Materal 22 3.1.1 Chemicals .22 3.1.2 Instruments .22 3.2 Methods 23 3.2.1 Synthesis of TNT 23 3.2.2 Synthesis of Graphene oxide 24 3.2.3 Synthesis of rGO-TNT Composite 25 3.2.4 Adsorption Experiment 25 3.2.5 The method of determining the characteristics of the material 27 PART IV RESULTS 32 4.1 Characterization of GO and titanate nanotubes/rGO composite 32 4.2 Morphology of TNT, GO and rGO-TNT composite 35 4.3 Application into removal of heavy metal ions 36 PART V DISCUSSION AND CONCLUSION 39 5.1 Discussion 39 5.2 Conclusion 40 REFERENCES 42 LIST OF FIGURES Figure 3.1 Schematic of TNT synthesis.………………………… .…24 Figure 3.2 Schematic of GO synthesis…… ……………………… …… …… 25 Figure 3.3 Adsorption experiment of Copper by TNT and rGO-TNT ………………27 Figure 3.4 Atomic adsorption spectroscopy (AAS)…………………… … …… 28 Figure 3.5 Raman spectroscopy…………………………………………………… 30 Figure 3.6 Schematic of TEM …………………………….…………… .…… 31 Figure .7 The process TEM characterization…… ………………………… ….32 Figure 4.1 Raman spectra of GO, rGO-TNT materials…………….…………… …33 Figure 4.2 XRD patterns of GO……………………………………………… 34 Figure 4.3 XRD patterns of TNT and rGO-TNT composite…………… …… .35 Figure 4.5 TEM images of the synthesis TNT and rGO-TNT composite………… 36 Figure 4.6 The adsorption of Cu(II) by TNT at pH=5 in aqueous solution at room temperature.……………………………………………………………….… … 37 Figure 4.7 The adsorption of Cu(II) by rGO /TNT composite in aqueous solution at room temperature.………………………… ……….… 38 LIST OF TABLES Table 4.1 The results of Cu (II) adsorption experiment by TNT, was observed by Atomic adsorption spectroscopy (AAS) ……………………………………………37 Table 4.2 The results of Cu (II) adsorption experiment by rGO-TNT, was observed by Atomic adsorption spectroscopy (AAS)…………………………………………… 38 LIST OF ABBREVIATIONS Abbreviations Full text content TNT Titanate nanotube GO Graphene oxide TNT-rGO Titanate nanotube and reduced graphene oxide XRD X-Ray Diffraction TEM Transmission Electron Microscopy AAS Atomic adsorption spectroscopy PART I INTRODUCTION 1.1 Research rationale Pollution of air, water and soil is a worldwide issue for the eco-environment and human society Most of the earth's surface is covered by water, and most of the human body is composed of water These are the two facts illustrating the critical linkages between water, health and ecosystems It can be seen that, water is the most essential compound on the earth for the human activities Providing clean water is the prime requirement of the human being for their better health Since the fast growing sector of industries, expansion of population, and urbanization have largely contributed to the severe contamination of water, air and soil Chemical and fertilizers use in domestic and agricultural activities leads to the lifetime threatening diseases Intense use of heavy metals in industries for dyeing, paint etc is becoming one of the most serious environment problems globally Its presence in low concentration of heavy metals in various water resources could be harmful to human health The treatment of heavy metals is so important due to their persistence in the environment In order to remove the heavy metals, various techniques have been developed The traditional treatment processes for heavy metals include chemical precipitation, electrolysis, adsorption, and ion exchange Among these methods, adsorption is an efficient technology, which has been widely used for the removal of metal ions in aqueous solutions A wide variety of adsorbents including activated carbon, water treatment sludge, zeolite, fly ash, and biomass have been reported to effectively adsorb metal ions, showing varying extent of effectiveness in removing the toxic pollutants from air, water and soil More recently, one-dimensional (1-D) titanate nanotube (TNT) have been reported to be an attractive adsorbent to effectively adsorb a wide variety of metal ions including Cu, Pb, Cd, and Zn because of their large specific surface areas and layered structures TNT is considered as a modified structure in photo catalysis owing to its special electronic and mechanical properties, high photo catalytic activity, large specific surface area and high pore volume, a potential material for removal of metal ions in the aqueous solution Besides, in the past few years, Graphene oxide (GO) have attracted tremendous interest in the world Graphene is a two-dimensional carbon nanomaterial with single layer of sp2 hybridized carbon atoms arranged in six membered rings Graphene has strong mechanical, thermal, and electrical properties with a theoretical value of specific surface area at 2630 m2/g GO is a functionalized graphene with varying oxygen containing groups Several views have been reported on applications of GO in different areas such as physics, chemistry, biology, and material science In particular, graphene based materials are used as adsorbents for pollutants removal since graphene oxide possesses several functional groups and has strong acidity, exhibiting high adsorption for basic compounds and cations Graphene also has a hydrophobic surface and presents high adsorption to chemicals due to strong π–π interaction Among several physical, chemical and biological treatment techniques, the adsorption is one of the simplest, fastest and most efficient processes or the removal of heavy metals Considering all aspects and issues mentioned above, I have paid attention to the preparation of titanate nanotube/reduced graphene oxide composite and subsequently used them as adsorbents electrons and therefore have a smaller electron mean free path than lighter atoms) (Roson Ct Ste Ksan Diego) Successful imaging of materials using TEM depends on the contrast of the sample relative to the background Samples are prepared for imaging by drying on a copper grid that is coated with a thin layer of carbon Materials with electron densities that are significantly higher than amorphous carbon are easily imaged Figure The process TEM characterization 31 PART IV RESULTS 4.1 Characterization of GO and titanate nanotubes/rGO composite The presence of rGO component in the rGO-TNT composite and the structural properties are confirmed by Raman spectroscopy and X-Ray diffraction technique Figure 4.1 Raman spectra of GO, rGO-TNT materials Figure 4.1 shows the Raman spectra of Graphene Oxide and rGO-TNT composite The Raman active 98 cm-1, 138 cm-1, 190cm-1, 228 cm-1, 276 cm-1, 396 cm-1, 664 cm-1 and 865 cm-1 modes for the composites match with titanate structure (Habashi 2009 and Liu et al, 2005) In addition, the peaks of the composite are broader and significantly shifted 98 cm-1 to 228 cm-1 The peak blue shift and broadening of the Raman spectra were analyzed using the most intense in this stage (228 cm-1 peak) The peak position and broadening of Raman spectrum is mainly affected by the size of the nanomaterial as well as defects and temperature 32 Raman spectroscopy is also widely used for the characterization of the electronic structure of carbon products A change in Raman band intensity and blue shifts provide information on the nature of carbon- carbon bonds and defects The Raman spectra in Figure 4.1 show the characteristic D and G bands at 1346 cm-1 and 1589 cm1 found in GO and the composite The D band is common feature for sp defects in carbon, and the G band provides information on plane vibrations of sp bonded carbons The intensity ratio of the D band to the G band usually reflects the order of defects in GO or graphene Compared to GO, rGO-TNT composites show two differences in the Raman spectra First, the calculated ID/IG of the rGO-TNT samples were lower than that of GO, indicating a lower density of defects present in rGO Second, the G band shifts by ~ 5cm−1 in the rGO-TNT Therefore, both the change in Raman band intensity and the blue shift of the G band provide clear evidence for the presence of graphene in the composite) Intensity (a.u.) GO 10 20 30 40 50 60 theta Figure 4.2 XRD patterns of GO 33 X-ray diffraction can also provide information on the crystal structure of the GO, TNTs and rGO-TNT Figure 4.2 shows a XRD pattern of GO with a sharp peak at about 2θ = 10.5o corresponding to (002) reflection was observed, giving an interlayer spacing of 0.9 nm Intensity (a.u.) rGO-TNT TNT 10 20 30 40 50 60 70 80 theta Figure 4.3 XRD patterns of TNT and rGO-TNT composite The crystal structures of as-prepared TNT and RGO–TNT electrodes were analyzed by XRD, as shown in Figure 4.3 The peaks present clearly represent the formation of titanate nanostructures, derived from microwave-assisted hydrothermal conditions, can be assigned as NaxH2-xTi3O7 in our TNT nanostructures However, no apparent peaks for graphene were observed in the rGO–TNT sample Similar results were also reported by others However, the existence of graphene in our rGO–TNT electrode can be clearly elucidated by the above Raman analysis and following TEM, SEM images 34 4.2 Morphology of TNT, GO and rGO-TNT composite The morphological evolution of titanate in rGO-TNT composite was observed by TEM (transmission electron microscopy) images Figure 4.5 TEM images of the synthesis TNT and rGO-TNT composite Figure 4.5a show the TEM image of TNT before the attachment of rGO The titanate nanotube showed tubular structures with lengths around 200-250 nm And, the TEM observation in Figure 4.5b reveals numerous overlapped layers with high transparency, implying very thin sheet- like structure No trace of spherical titanate nanotubes precursors was found in hybrid materials, implying the successful interaction of Ti species in between carbonaceous layers and subsequent transform to sheet-like structure In addition, Raman spectra detected on large area showed the presence of dominant Ti and O species together with small amount of C It can be obviously three components were well distributed in the hybrid material as shown in the mapping in 35 Figure 4.5c Such characteristics demonstrate that the rGO sheets were assembled on the titanate nanotubes 4.3 Application into removal of heavy metal ions The absorption capacity of Copper ion by the TNT and rGO/TNT composite were examined Table 4.1 The results of Cu (II) adsorption experiment by TNT, was observed by Atomic adsorption spectroscopy (AAS) Cont.(mg/L) 10 20 0.317 0.332 0.383 0.447 0.591 10 0.303 0.303 0.304 0.306 0.31 30 0.303 0.304 0.305 0.31 0.306 60 0.303 0.303 0.306 0.306 0.306 180 0.301 0.301 0.302 0.305 0.303 Time(min) 1.0 TNT ppm ppm ppm 10 ppm 20 ppm 0.8 0.6 C/C0 0.4 0.2 0.0 -0.2 -0.4 30 60 90 120 Time (min) 150 180 Figure 4.6 The adsorption of Cu(II) by TNT at pH=5 in aqueous solutionat room temperature 36 Figure 4.6 shows the absorbed amounts of Cu(II) ion by different concentration of TNT including 1ppm, 2ppm, 5ppm, 10 and 20ppm, and different absorption time (10, 30 or 180 minutes) The adsorption of copper ion by titanate nanotubes increased rapidly with the increase in the equilibrium Cu (II) concentration The higher is the concentration, more stronger is the adsorption capacity The amount of heavy metal has reduced from 0.591 mg/L to 0.31 mg/L at the concentration is 20 ppm and mitigation under the next period Table 4.2 The results of Cu (II) adsorption experiment by rGO-TNT, was observed by Atomic adsorption spectroscopy (AAS) Cont.(mg/L) 10 20 0.317 0.332 0.383 0.447 0.591 10 0.303 0.303 0.302 0.306 0.305 30 0.303 0.303 0.303 0.304 0.304 60 0.304 0.303 0.303 0.304 0.303 180 0.301 0.301 0.301 0.301 0.302 Time(min) rGO-TNT 1.0 ppm ppm ppm 10 ppm 20 ppm 0.8 C/C0 0.6 0.4 0.2 0.0 -0.2 -0.4 30 60 90 120 Time (min) 150 180 Figure 4.7 The adsorption of Cu(II) by rGO /TNT composite in aqueous solution at room temperature 37 When using the TNT / rGO composite, the ability to effectively absorb higher is shown in Figure 4.7 The absorbed amounts of Cu(II) ion are also by different concentration of TNT including 1ppm, 2ppm, 5ppm, 10 and 20ppm, and different absorption time( 10, 30 or 180 minute) The adsorption of copper ion by titanate nanotubes/reduced graphene oxide increased rapidly with the increase in the equilibrium Cu(II) concentration In the concentration of ppm, the ability to absorb copper after 10 minutes was 0.015 mg /L and was slightly increased from 0.001 to 0.003 mg/L at 180 minutes When increasing the concentration to 20 ppm, the beginning adsorption with no adsorbent was 0.591 mg/L and with 10 mg of TNT/rGO composite in 10 minutes, the adsorption capacity was 0.305 mg/L and it was 0.302 mg/L, 180 minutes When compared with TNT, the adsorption capacities of the rGO/TNT composite reached higher than TNT It is well known that adsorption strongly depend on the pore structure and surface area as well as surface functionality of rGO/TNT 38 PART V DISCUSSION AND CONCLUSION 5.1 Discussion To summary, the study has developed a graphene-based nano composite for the removal of toxic heavy metals from aqueous solution Graphene has unique morphology, chemical structure, and electronic properties The main advantages of this removal procedure include simplicity, cost effectiveness, rapidity, and higher removal efficiency of TNT/rGO In this study we have synthesized titanate nanotubes by hydrothermal method, graphene oxide by Hummer method and titanate nanotubes/reduced graphene oxide composite by hydrothermal method, and their adsorption capacity was evaluated XRD, TEM, and Raman spectroscopy studies revealed the structural morphology of the synthesized material and confirmed the formation of titanate nanotube of lengths 200-250 nm The presence of rGO component in the rGO-TNT composite and the structural properties were confirmed by Raman spectroscopy and X-Ray diffraction Experimental results obtained in this study clearly demonstrate that TNT/rGO composite are an effective adsorbent for heavy metals The amount of heavy metal has reduced from 0.591 mg/L to 0.304 mg/L at the concentration was 20 ppm in 30 minutes and mitigation under the next period The experiment also compared the absorption capacity between rGP/TNT and TNT, the results shows that the absorption capacitie of the rGO/TNT was higher than TNT; it depends on the pore structure and surface area as well as surface functionality of rGO/TNT Thus, it is suggested that TNT/rGO prepared here could be a promising candidate sorbent material for removing heavy metal ions from aqueous solutions beyond the ordinary use of adsorbents The 39 outstanding physicochemical properties of the TNT/rGO materials will play a very important role in environmental pollution management in the future 5.2 Conclusion In conclusion, results shown in the thesis clearly indicate the morphology of TNT and rGO by SEM and TEM The adsorption of Cu ions by TNT/rGO composites was examined and analyzed The TNT/GO nanocomposites showed excellent adsorption capacity toward Cu (II) adsorption and the adsorption can be complete within 30 This finding is interest and can be extended to remove other toxic chemicals in waters and soils * There still lies a necessity in continuing the research on the adsorption of titanate nanotube/reduced graphene oxide on the other materials such as metals (Pb, As, Hg, ) * Researching the adsorption of heavy metal ions of TNT/rGO to large scale that may have high practical applicability * Significant tests regarding the ability to remove other ions on TNT/rGO to be used for a variety of different contaminated water environment Although every attempt has been made to make the review work presented in Section2 as up-to-date as possible, unintentional omission of important references if any, is regretted In this report, Graphene oxide (GO) was prepared from graphite powder according to the modified Hummer method The present study may be extended to other methods for high quality Graphene oxide In the present experiment, Cu(II) was adsorbed by TNT and rGO-TNT, we have done only single metal (Cu) adsorbent However in future we can with different heavy metals removal experiment 40 Nanocomposite based other materials may be explored for its deployment in removal of toxic heavy metals from aqueous solution 41 REFERENCES Alkorta, I., Hernández-Allica, J., & Garbisu, C (2004) Plants against the global epidemic of arsenic poisoning Environment international, 30(7), 949-951 Åström, M., & Björklund, A (1995) Impact of acid sulfate soils on stream water geochemistry in western Finland Journal of Geochemical Exploration, 55(1), 163-170 Bissen, M., & Frimmel, F H (2003) Arsenic—a review Part I: occurrence, toxicity, speciation, mobility Acta hydrochimica et hydrobiologica, 31(1), 9-18 Bryan, G W., & Langston, W J (1992) Bioavailability, accumulation and effects of heavy metals in sediments with special reference to United Kingdom estuaries: a review Environmental Pollution, 76(2), 89-131 Chandra, V., Park, J., Chun, Y., Lee, J W., Hwang, I C., & Kim, K S ( 2010) Waterdispersible magnetite-reduced graphene oxide composites for arsenic removal ACS nano, 4(7), 3979-3986 Clark, D B., Pollock, N., Bukstein, O G., Mezzich, A C., Bromberger, J T., & Donovan, J E (1997) Gender and comorbid psychopathology in adolescents with alcohol dependence Journal of the American Academy of Child & Adolescent Psychiatry, 36(9), 1195-1203 Doong, R A., Chang, S M., & Tsai, C W ( 2013) Enhanced photoactivity of Cudeposited titanate nanotubes for removal of bisphenol A Applied Catalysis B: Environmental, 129, 48-55 42 Doong, R A., Tsai, C W., & Liao, C I ( 2012) Coupled removal of bisphenol A and copper ion by titanate nanotubes fabricated at different calcination temperatures Separation and Purification Technology, 91, 81-88 Foulkes, W D., Stefansson, I M., Chappuis, P O., Bégin, L R., Goffin, J R., Wong, N., & Akslen, L A (2000) Germline BRCA1 mutations and a basal epithelial phenotype in breast cancer Journal of the National Cancer Institute, 95(19), 1482-1485 Hanno zur Loye (2013) X-Ray Diffraction-How it works Retrieved from: http://www.chem.sc.edu/faculty/zurloye/xrdtutorial_2013.pdf (accessed 10 December 2014) He, F., Fan, J., Ma, D., Zhang, L., Leung, C., & Chan, H L ( 2010) The attachment of Fe< sub> 3 O< sub> 4 nanoparticles to graphene oxide by covalent bonding Carbon, 48(11), 3139-3144 Horiba Scientific (2013) Understanding Physical Parameters of Hard Carbon Films Using Raman Spectra Retrieved from: http://www.azom.com/article.aspx?ArticleID=10105 (accessed on 10 December 2014) Hummers Jr, W S., & Offeman, R E (1958) Preparation of graphitic oxide.Journal of the American Chemical Society, 80(6), 1339-1339 Kudin, K N., Ozbas, B., Schniepp, H C., Prud'Homme, R K., Aksay, I A., & Car, R (2008) Raman spectra of graphite oxide and functionalized graphene sheets Nano letters, 8(1), 36-41 43 Lee, Y C., & Yang, J W (2012) Self-assembled flower-like TiO< sub> 2 on exfoliated graphite oxide for heavy metal removal Journal of Industrial and Engineering Chemistry, 18(3), 1178-1185 Liu, X Y., & Coville, N J (2005) A Raman study of titanate nanotubes South African Journal of Chemistry, 58, p-110 Matschullat, J (2000) Arsenic in the geosphere—a review Science of the Total Environment, 249(1), 297-312 Nguyen-Phan, T D., Pham, V H., Kim, E J., Oh, E S., Hur, S H., Chung, J S., & Shin, E W (2012) Reduced graphene oxide–titanate hybrids: Morphologic evolution by alkali-solvothermal treatment and applications in water purification Applied Surface Science, 258(10), 4551-4557 Perera, S D., Mariano, R G., Vu, K., Nour, N., Seitz, O., Chabal, Y., & Balkus Jr, K J (2012) Hydrothermal synthesis of graphene-TiO2 nanotube composites with enhanced photocatalytic activity Acs Catalysis, 2(6), 949-956 Rahman, M A., & Hasegawa, H (2011) Aquatic arsenic: phytoremediation using floating macrophytes Chemosphere, 83(5), 633-646 Sreeprasad, T S., Maliyekkal, S M., Lisha, K P., & Pradeep, T (2011) Reduced graphene oxide–metal/metal oxide composites: facile synthesis and application in water purification Journal of hazardous materials, 186(1), 921-931 Tam, N F Y., & Wong, Y S (1996) Retention and distribution of heavy metals in mangrove soils receiving wastewater Environmental Pollution, 94(3), 283-291 Yang, S T., Chang, Y., Wang, H., Liu, G., Chen, S., Wang, Y., & Cao, A (2010) Folding/aggregation of graphene oxide and its application in Cu< sup> 2+ removal Journal of colloid and interface science, 351(1), 122-127 Yifei, G (2012) Nanomaterials as sorbents to remove heavy metal ions in wastewater treatment Journal of Environmental & Analytical Toxicology 44 Zhang, Y., Chen, B., Zhang, L., Huang, J., Chen, F., Yang, Z., & Zhang, Z (2011) Controlled assembly of Fe O magnetic nanoparticles on graphene oxide Nanoscale, 3(4), 1446-1450 Zhao, G., Li, J., Ren, X., Chen, C., & Wang, X (2011) Few-layered graphene oxide nanosheets as superior sorbents for heavy metal ion pollution management Environmental science & technology, 45(24), 10454-10462 Zheng, W., & Lin, P (1995) Accumulation and distribution of Cu, Pb, Zn and Cd in Avicennia marina mangrove community of Futian in Shenzhen.Oceanologia et Limnologia Sinica, 27(4), 388-393 45 ... of Novel Titanate Nanotubes/ Reduced Graphene Oxide Composite for the Removal of Heavy Metals from Aqueous Solution Prof Dr Nguyen The Dang, Thai Nguyen University of Agriculture and Forestry,... Overview of handling heavy metals in aqueous solution using Titanate nanotube / reduced graphene oxide composite 2.6.1 Scientific Basis of handling heavy metals in aqueous solution by rGO-TNT composite. .. 2.6.2 Some research results of absorption of heavy metals in water by rGO-TNT composite Graphene based nano composite for the removal of toxic heavy metals from aqueous solution was studied very