Nanotubular halloysite clay as efficient water filtration system for ...
Nanotubular halloysite clay as efficient water filtration system for cationic and anionic dyes removal Yafei Zhao, Elshad Abdullayev and Yuri Lvov Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71270
Abstract
Results and Discussion
Halloysite clay has chemical structure similar to kaolinite but it is rolled in tubes with diameter of 50 nm and length of ca. 1000 nm. Halloysite exhibits higher adsorption capacity for both cationic and anionic dyes because it has negative SiO2 outermost and positive Al2O3 inner lumen surface. An adsorption study using cationic Rhodamine 6G and anionic Chrome azurol S has shown approximately two times better dye removal for halloysite as compared to kaolin. Halloysite filters have been effectively regenerated up to 50 times by burning the adsorbed dyes. Overall removal efficiency of anionic Chrome azurol S exceeded 99.9% after 5th regeneration cycle of halloysite. Chrome azurol S adsorption capacity decreases with the increase of ionic strength, temperature and pH. For cationic Rhodamine 6G, higher ionic strength, temperature and initial solution concentration were favorable to enhanced adsorption with optimal pH 8. The equilibrium adsorption data were described by Langmuir and Freundlich isotherms.
ζ-potential of halloysite and kaolinite at different pH
Adsorption of Rhodamine 6G and Chrome azurol S onto halloysite and kaolinite
Effect of halloysite adsorbent dose (a) and temperature (b) and on dye adsorption
Comparison of isotherm models for dyes adsorption onto halloysite and kaolinite Halloysite
Halloysite and Kaolinite Halloysite is a naturally occurring 1:1 dioctahedral aluminosilicate clay mineral chemically similar to kaolinite. Halloysite nanotubes with ca. 50 nm diameter, 10 nm lumen and 1 µm length are formed by rolling kaolinite sheets during natural hydrothermal process. Halloysite tubes have multilayer walls with negatively charged Si-OH on the outer surface and positively charged Al-OH on the inner surface (at pH between 4 and 9) and does not require exfoliation, contrary to the kaolinite plate-like morphology. This unique bivalent morphology with spatially separated negative and positive surfaces makes halloysite tube a promising absorbent for variety of pollutants, both positive and negative.
Models
Rhodamine 6G
qm KL R RL
43.6 0.27 0.998 0.07-0.40
1/n KF R
0.23 10.3 0.945
Kaolinite
Chrome azurol S
Rhodamine 6G
Chromeazurol S
21.4 0.27 0.999 0.01-0.07
36.7 0.0078 0.949 0.2-0.7
0.09 12.6 0.707
0.45 1.96 0.950
Langmuir model
Adsorption of Rhodamine 6G (a), Chrome azurol S (b) on pristine and modified halloysite
38.7 0.52 0.994 0.1-0.5 Freundlich model 0.33 5.05 0.969
Dye removal efficiency (%) of filters made from halloysite and kaolinite during 5 reuse cycles Sample Halloysit e TEM images of halloysite empty lumen and multilayer walls (a-b), SEM images of submicron halloysite tubes (c) and of 2-7 µm kaolinite plates (d)
Tubule halloysite and platy kaolinite structures Demonstration of the water filters prepared by one grams of halloysite and kaolinite clays, tested on Chrome azurol S (a) and Rhodamine 6G solutions with 300 mg/L concentration. UV spectra of the filtered water samples are demonstrated on right for clear presentation of the unfiltered dye (b).
Experimental methods The batch experiments were carried out in 2 mL centrifuge tubes containing 1 mL of dye solutions and 2 mg adsorbent clay (except for the effect of adsorbent dose). The tubes were kept static at 20-60 °C. On reaching equilibrium the tubes were centrifuged for 5 min at 14000 rpm and the concentration of supernatant was determined using UV-Vis Spectrophotometer (Agilent, 8453). One gram of adsorbent clay was added to the water filter and cellucotton was used to block the adsorbent powder. The system was kept at 20 °C. 300 mg/L Rhodamine 6G and Chrome azurol S dyes solution were studied in the system and dyes concentration were determined after filtration, respectively. In order to study the reusability of halloysite, the used adsorbents were dried under 60 °C in the oven and burned at 300 °C. After that, the burned samples were reused as adsorbents in the water filter system and dyes concentration were measured again after filtration. The adsorption-burningadsorption cycle were repeated for five times.
For further information contact [email protected]
Dye filtration from 2nd generation kaolinite and halloysite filters: Chrome azurol S (a) and Rhodamine 6G (b) solution passed from halloysite filters; Chrome azurol S (c) and Rhodamine 6G (d) solution passed from kaolinite filters. Concentrations of dyes were 300 mg/L in all the cases.
Kaolinite
Reuse cycle 1 2 3 4 5 1 2 3 4 5
Chromeazuro Rhodamine lS 6G 99.999 99.999 99.995 99.996 99.993 99.991 99.995 99.984 99.983 99.965
99.757 99.218 98.358 96.317 96.609 99.236 97.630 97.803 95.511 95.990
Conclusions (1) Halloysite is a promising nanoadsorbent to remove both positive and negative organic dyes from wastewater. Presence of positively charged lumen and negatively charge outer surface gives HNTs advantages over flat kaolinite in adsorption both positive and negative species. (2) Halloysite is novel nanomaterial which can be used in water filter system. The removal efficiency of halloysite is higher than most of conventional adsorbents. (3) Halloysite can be regenerated by burning after adsorption and be reused. Dye removal efficiency exceeded 99.9% after 5 reuse cycles for negative Chrome azurol S and 95% for positive Rhodamine 6G. (4) Optimal pH for Rhodamine 6G adsorption was in the range of 8 and 9 while acidic solutions were favorable for Chrome azurol S adsorption. Higher temperatures favor Rhodamine 6G adsorption.
Reference Diagram of water filter system
[1] Y.M. Lvov, D.G. Shchukin, H. Möhwald, R.R. Price, ACS Nano. 2 (2008), 814-820. [2] E. Abdullayev, K. Sakakibara, K. Okamoto, W. Wei, K. Ariga, Y. Lvov, ACS Appl. Mater. Interface 3 (2011), 4040-4046. [3] Y. Zhao, B. Zhang, Y. Zhang, J. Wang, J. Liu, R. Chen. Sep. Sci. Technol. 45 (2010), 1066-1075. [4] Y. Zhao, B. Zhang, X. Zhang, J. Wang, J. Liu, R. Chen. Water Sci. Technol. 62 (2010), 937-946. [5] W.O. Yah, A. Takahara, Y.M. Lvov, J. Am. Chem. Soc. 134 (2012), 1853-1859. [6] E. Abdullayev, Y. Lvov, J. Mater. Chem. 20 (2010), 6681-6687. [7] P. Luo, Y. Zhao, B. Zhang, J. Liu, Y. Yang, J. Liu, Water Res. 44 (2010), 1489-1497. [8] Y. Zhao, B. Zhang, X. Zhang, J. Wang, J. Liu, R. Chen. J. Hazard. Mater. 178 (2010), 658-664. [9] P. Luo, J. Zhang, B. Zhang, J. Wang, Y. Zhao, J. Liu, Ind. Eng. Chem. Res. 50 (2011), 10246-10252.
Acknowledgements Support with NSF-1029147 and NSFEPS1003897 grants are acknowledged. Authors are thankful to Applied Minerals Inc., USA for providing halloysite samples.
Abstract
Results and Discussion
Halloysite clay has chemical structure similar to kaolinite but it is rolled in tubes with diameter of 50 nm and length of ca. 1000 nm. Halloysite exhibits higher adsorption capacity for both cationic and anionic dyes because it has negative SiO2 outermost and positive Al2O3 inner lumen surface. An adsorption study using cationic Rhodamine 6G and anionic Chrome azurol S has shown approximately two times better dye removal for halloysite as compared to kaolin. Halloysite filters have been effectively regenerated up to 50 times by burning the adsorbed dyes. Overall removal efficiency of anionic Chrome azurol S exceeded 99.9% after 5th regeneration cycle of halloysite. Chrome azurol S adsorption capacity decreases with the increase of ionic strength, temperature and pH. For cationic Rhodamine 6G, higher ionic strength, temperature and initial solution concentration were favorable to enhanced adsorption with optimal pH 8. The equilibrium adsorption data were described by Langmuir and Freundlich isotherms.
ζ-potential of halloysite and kaolinite at different pH
Adsorption of Rhodamine 6G and Chrome azurol S onto halloysite and kaolinite
Effect of halloysite adsorbent dose (a) and temperature (b) and on dye adsorption
Comparison of isotherm models for dyes adsorption onto halloysite and kaolinite Halloysite
Halloysite and Kaolinite Halloysite is a naturally occurring 1:1 dioctahedral aluminosilicate clay mineral chemically similar to kaolinite. Halloysite nanotubes with ca. 50 nm diameter, 10 nm lumen and 1 µm length are formed by rolling kaolinite sheets during natural hydrothermal process. Halloysite tubes have multilayer walls with negatively charged Si-OH on the outer surface and positively charged Al-OH on the inner surface (at pH between 4 and 9) and does not require exfoliation, contrary to the kaolinite plate-like morphology. This unique bivalent morphology with spatially separated negative and positive surfaces makes halloysite tube a promising absorbent for variety of pollutants, both positive and negative.
Models
Rhodamine 6G
qm KL R RL
43.6 0.27 0.998 0.07-0.40
1/n KF R
0.23 10.3 0.945
Kaolinite
Chrome azurol S
Rhodamine 6G
Chromeazurol S
21.4 0.27 0.999 0.01-0.07
36.7 0.0078 0.949 0.2-0.7
0.09 12.6 0.707
0.45 1.96 0.950
Langmuir model
Adsorption of Rhodamine 6G (a), Chrome azurol S (b) on pristine and modified halloysite
38.7 0.52 0.994 0.1-0.5 Freundlich model 0.33 5.05 0.969
Dye removal efficiency (%) of filters made from halloysite and kaolinite during 5 reuse cycles Sample Halloysit e TEM images of halloysite empty lumen and multilayer walls (a-b), SEM images of submicron halloysite tubes (c) and of 2-7 µm kaolinite plates (d)
Tubule halloysite and platy kaolinite structures Demonstration of the water filters prepared by one grams of halloysite and kaolinite clays, tested on Chrome azurol S (a) and Rhodamine 6G solutions with 300 mg/L concentration. UV spectra of the filtered water samples are demonstrated on right for clear presentation of the unfiltered dye (b).
Experimental methods The batch experiments were carried out in 2 mL centrifuge tubes containing 1 mL of dye solutions and 2 mg adsorbent clay (except for the effect of adsorbent dose). The tubes were kept static at 20-60 °C. On reaching equilibrium the tubes were centrifuged for 5 min at 14000 rpm and the concentration of supernatant was determined using UV-Vis Spectrophotometer (Agilent, 8453). One gram of adsorbent clay was added to the water filter and cellucotton was used to block the adsorbent powder. The system was kept at 20 °C. 300 mg/L Rhodamine 6G and Chrome azurol S dyes solution were studied in the system and dyes concentration were determined after filtration, respectively. In order to study the reusability of halloysite, the used adsorbents were dried under 60 °C in the oven and burned at 300 °C. After that, the burned samples were reused as adsorbents in the water filter system and dyes concentration were measured again after filtration. The adsorption-burningadsorption cycle were repeated for five times.
For further information contact [email protected]
Dye filtration from 2nd generation kaolinite and halloysite filters: Chrome azurol S (a) and Rhodamine 6G (b) solution passed from halloysite filters; Chrome azurol S (c) and Rhodamine 6G (d) solution passed from kaolinite filters. Concentrations of dyes were 300 mg/L in all the cases.
Kaolinite
Reuse cycle 1 2 3 4 5 1 2 3 4 5
Chromeazuro Rhodamine lS 6G 99.999 99.999 99.995 99.996 99.993 99.991 99.995 99.984 99.983 99.965
99.757 99.218 98.358 96.317 96.609 99.236 97.630 97.803 95.511 95.990
Conclusions (1) Halloysite is a promising nanoadsorbent to remove both positive and negative organic dyes from wastewater. Presence of positively charged lumen and negatively charge outer surface gives HNTs advantages over flat kaolinite in adsorption both positive and negative species. (2) Halloysite is novel nanomaterial which can be used in water filter system. The removal efficiency of halloysite is higher than most of conventional adsorbents. (3) Halloysite can be regenerated by burning after adsorption and be reused. Dye removal efficiency exceeded 99.9% after 5 reuse cycles for negative Chrome azurol S and 95% for positive Rhodamine 6G. (4) Optimal pH for Rhodamine 6G adsorption was in the range of 8 and 9 while acidic solutions were favorable for Chrome azurol S adsorption. Higher temperatures favor Rhodamine 6G adsorption.
Reference Diagram of water filter system
[1] Y.M. Lvov, D.G. Shchukin, H. Möhwald, R.R. Price, ACS Nano. 2 (2008), 814-820. [2] E. Abdullayev, K. Sakakibara, K. Okamoto, W. Wei, K. Ariga, Y. Lvov, ACS Appl. Mater. Interface 3 (2011), 4040-4046. [3] Y. Zhao, B. Zhang, Y. Zhang, J. Wang, J. Liu, R. Chen. Sep. Sci. Technol. 45 (2010), 1066-1075. [4] Y. Zhao, B. Zhang, X. Zhang, J. Wang, J. Liu, R. Chen. Water Sci. Technol. 62 (2010), 937-946. [5] W.O. Yah, A. Takahara, Y.M. Lvov, J. Am. Chem. Soc. 134 (2012), 1853-1859. [6] E. Abdullayev, Y. Lvov, J. Mater. Chem. 20 (2010), 6681-6687. [7] P. Luo, Y. Zhao, B. Zhang, J. Liu, Y. Yang, J. Liu, Water Res. 44 (2010), 1489-1497. [8] Y. Zhao, B. Zhang, X. Zhang, J. Wang, J. Liu, R. Chen. J. Hazard. Mater. 178 (2010), 658-664. [9] P. Luo, J. Zhang, B. Zhang, J. Wang, Y. Zhao, J. Liu, Ind. Eng. Chem. Res. 50 (2011), 10246-10252.
Acknowledgements Support with NSF-1029147 and NSFEPS1003897 grants are acknowledged. Authors are thankful to Applied Minerals Inc., USA for providing halloysite samples.
