Malaysian Journal of Analytical Sciences, Vol 28 No 5 (2024): 1150 - 1168

 

SODIUM ALGINATE/β-CYCLODEXTRIN AS SUPRAMOLECULAR HYDROGEL FOR ADSORPTION OF PERFLUOROOCTANE SULFONATE

 

(Natrium Alginat/β-Siklodekstrin Sebagai Hidrogel Supramolekul untuk Penjerapan Perfluorooktana Sulfonat)

 

Aiza Farhani Zakaria1, Norizah Abdul Rahman1, Noorfatimah Yahaya3, Wan Nazihah Wan Ibrahim4,

Saw Hong Loh5, Dyia Syaleyana Md Shukri6 and Sazlinda Kamaruzaman1,2*

 

1Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400, UPM Serdang Selangor, Malaysia

2Natural Medicines and Product Research Laboratory (NaturMeds), Institute of Bioscience (IBS), Universiti Putra Malaysia, 43400, UPM Serdang Selangor, Malaysia

3Integrative Medicine Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, 13200 Kepala Batas, Penang, Malaysia

4Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

5Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia

6Faculty Applied Sciences, Universiti Teknologi MARA Cawangan Perlis, Kampus Arau, 02600 Arau, Perlis.

*Corresponding author: sazlinda@upm.edu.my

 

 

Received: 1 September 2023; Accepted: 24 July 2024; Published:  27 October 2024

 

 

Abstract

Perfluorooctane sulfonate (PFOS) has been classified as a persistent organic pollutant that contributes to water pollution due to its slow environmental degradation properties.  Due to the need for effective removal of PFOS from polluted water bodies, a supramolecular hydrogel incorporating sodium alginate and β-cyclodextrin (SA-β-CD hydrogel) was developed to facilitate the entrapment of PFOS. The adsorption study has been utilised to remove PFOS via batch experiment procedure on several adsorptive parameters such as pH, contact time and initial concentration. The optimum conditions with a dose of 1280 mg of SA-β-CD hydrogels beads were applied at 70°C, contact time of 30 minutes, pH of 5.5, 10 mL of 10.0 ppm of PFOS solution, and 250 rpm of stirring rate were reported. The adsorption capacity and efficiency removal of PFOS by SA-β-CD hydrogel beads has achieved up to 0.0764 mg/g and 84.72%, respectively.  Based on the data obtained, the adsorption kinetic study, which follows a pseudo-second-order model, was fitted to illustrate the adsorption of PFOS by SA-β-CD hydrogel beads, with an R² value of 0.990. The adsorption isotherm study showed that the adsorption of PFOS by SA-β-CD hydrogel beads fits the Langmuir isotherm model, with an R² value of 0.987. The adsorption of PFOS occurs as a monolayer/single layer and involves chemisorption to the hydrogel beads. Therefore, this work demonstrates that SA-β-CD hydrogel beads may be useful in controlling environmental water pollution.

 

Keywords: water pollution, persistent organic pollutant, perfluorooctane sulfonate, hydrogel

 

Abstrak

Perfluorooktana sulfonat (PFOS) telah diklasifikasikan sebagai bahan pencemar organik berterusan yang menyumbang kepada pencemaran air disebabkan oleh sifat degradasi alam sekitar yang perlahan. Oleh sebab itu, hidrogel supramolekul yang menggabungkan natrium alginat dan β-siklodekstrin (hidrogel SA-β-CD) telah dibangunkan untuk membantu memerangkap PFOS daripada badan air yang tercemar. Kajian penjerapan telah digunakan untuk mengeluarkan PFOS melalui prosedur eksperimen kelompok pada beberapa parameter penjerapan seperti pH, masa sentuhan dan kepekatan awal. Keadaan optimum dengan dos 1280 mg manik hidrogel SA-β-CD digunakan pada 70°C, masa sentuhan 30 minit, pH 5.5, 10 mL larutan PFOS 10.0 ppm, dan 250 rpm kadar kacau dilaporkan. Kapasiti penjerapan dan penyingkiran kecekapan PFOS oleh manik hidrogel SA-β-CD telah mencapai sehingga 0.0764 mg/g dan 84.72%, masing-masing. Berdasarkan data yang diperoleh, kajian kinetik penjerapan yang merupakan model  pseudo-tertib dua telah digunakan untuk menggambarkan penjerapan PFOS oleh manik hidrogel SA-β-CD dengan nilai R2 yang diperolehi ialah 0.990. Manakala kajian penjerapan isoterma, penjerapan PFOS oleh manik hidrogel SA-β-CD telah digunakan pada model Langmuir isoterma dengan nilai R2 yang diperolehi ialah 0.987. Penjerapan PFOS berlaku sebagai lapisan tunggal/satu lapisan dengan penjerapan kimia kepada manik hidrogel. Oleh itu, kerja ini menunjukkan bahawa manik hidrogel SA-β-CD boleh membantu sebagai inisiatif untuk mengawal pencemaran air di alam sekitar.

 

Kata kunci: pencemaran air, pencemar organik berterusan, perfluorooktana sulfonat, hidrogel

References

1.      Xiao, F., Simcik, M. F., and Gulliver, J. S. (2013). Mechanisms for removal of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) from drinking water by conventional and enhanced coagulation. Water Research, 47(1): 49-56.

2.      Franke, V., McCleaf, P., Lindegren, K., and Ahrens, L. (2019). Efficient removal of per- and polyfluoroalkyl substances (PFASs) in drinking water treatment: Nanofiltration combined with active carbon or anion exchange. Environmental Science: Water Research and Technology, 5(11): 1836-1843.

3.      Wang, Y., and Zhu, H. (2014). Detection of PFOS and copper (II) ions based on complexation induced fluorescence quenching of porphyrin molecules. Analytical Methods, 6(7): 2379-2383.

4.      Zhao, Y. G., Wong, C. K. C., and Wong, M. H. (2012). Environmental contamination, human exposure and body loadings of perfluorooctane sulfonate (PFOS), focusing on Asian countries. Chemosphere, 89(4): 355-368.

5.      Buck, R. C., Franklin, J., Berger, U., Conder, J. M., Cousins, I. T., De Voogt, P., ... and van Leeuwen, S. P. (2011). Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins. Integrated Environmental Assessment and Management, 7(4): 513-541.

6.      Li, X., Chen, S., Quan, X., and Zhang, Y. (2011). Enhanced adsorption of PFOA and PFOS on multiwalled carbon nanotubes under electrochemical assistance. Environmental Science and Technology, 45(19): 8498-8505.

7.      Yan, T., Chen, H., Jiang, F., and Wang, X. (2014). Adsorption of perfluorooctane sulfonate and perfluorooctanoic acid on magnetic mesoporous carbon nitride. Journal of Chemical & Engineering Data, 59(2): 508-515. 

8.      Van Tran, V., Park, D., and Lee, Y. C. (2018). Hydrogel applications for adsorption of contaminants in water and wastewater treatment. Environmental Science and Pollution Research, 25(25): 24569-24599.

9.      Alves, A. V., Tsianou, M., and Alexandridis, P. (2020). Fluorinated surfactant adsorption on mineral surfaces: Implications for PFAS fate and transport in the environment. Surfaces, 3(4): 516-566. 

10.   Lee, P., and Rogers, M. A. (2012). Effect of calcium source and exposure-time on basic caviar spherification using sodium alginate. International Journal of Gastronomy and Food Science, 1(2): 96-100.

11.   Puscaselu, R. G., Lobiuc, A., Dimian, M., and Covasa, M. (2020). Alginate: from food industry to biomedical applications and management of metabolic disorders. Polymers, 12(10): 2417. 

12.   Sánchez-Fernández, J., Presbítero-Espinosa, G., Peña-Parás, L., Pizaña, E. I. R., Galván, K. P. V., Vopalensky, M., Kumpová, I., and Elizalde-Herrera, L. E. (2021). Characterization of sodium alginate hydrogels reinforced with nanoparticles of hydroxyapatite for biomedical applications. Polymers, 13(17): 2927.

13.   Gidwani, B., and Vyas, A. (2014). Synthesis, characterization and application of epichlorohydrin-β-cyclodextrin polymer. Colloids and Surfaces B: Biointerfaces, 114: 130-137.

14.   Păduraru, D. N., Niculescu, A. G., Bolocan, A., Andronic, O., Grumezescu, A. M., and Bîrlă, R. (2022). An updated overview of cyclodextrin-based drug delivery systems for cancer therapy. Pharmaceutics, 14(8):1748.

15.   Yadav, V. R., Suresh, S., Devi, K., and Yadav, S. (2009). Effect of cyclodextrin complexation of curcumin on its solubility and antiangiogenic and anti-inflammatory activity in rat colitis model. AAPS PharmSciTech, 10(3): 752-62.

16.   Qin, X., Bai, L., Tan, Y., Li, L., Song, F., and Wang, Y. (2019). β-Cyclodextrin-crosslinked polymeric adsorbent for simultaneous removal and stepwise recovery of organic dyes and heavy metal ions: Fabrication, performance and mechanisms. Chemical Engineering Journal, 372: 1007-1018.

17.   Belenguer-Sapiña, C., Pellicer-Castell, E., Mauri-Aucejo, A. R., Simó-Alfonso, E. F., and Amorós, P. (2020). Cyclodextrins as a key piece in nanostructured materials: Quantitation and remediation of pollutants. Nanomaterials, 11(1): 7. 

18.   Yadav, S., Asthana, A., Singh, A. K., Chakraborty, R., Vidya, S. S., Susan, M. A. B. H., and Carabineiro, S. A. C. (2021). Adsorption of cationic dyes, drugs and metal from aqueous solutions using a polymer composite of magnetic/β-cyclodextrin/activated charcoal/Na alginate: Isotherm, kinetics and regeneration studies. Journal of Hazardous Materials, 409(8):124840.

19.   Liu, Z., Sun, Y., Xu, X., Qu, J., and Qu, B. (2020). Adsorption of Hg(II) in an aqueous solution by activated carbon prepared from rice husk using KOH activation. ACS Omega, 5(45): 29231-29242.

20.   Chen, A. H., Liu, S. C., Chen, C. Y., and Chen, C. Y. (2008). Comparative adsorption of Cu(II), Zn(II), and Pb(II) ions in aqueous solution on the crosslinked chitosan with epichlorohydrin. Journal of Hazardous Materials, 154(1–3): 184-191.

21.   Melo, B. C., Paulino, F. A. A., Cardoso, V. A., Pereira, A. G. B., Fajardo, A. R., and Rodrigues, F. H. A. (2018). Cellulose nanowhiskers improve the methylene blue adsorption capacity of chitosan-g-poly(acrylic acid) hydrogel. Carbohydrate Polymers, 181: 358-367.

22.   Zulfiqar, M., Lee, S. Y., Mafize, A. A., Kahar, N. A. M. A., Johari, K., and Rabat, N. E. (2020). Efficient removal of Pb (II) from aqueous solutions by using oil palm bio-waste/MWCNTs reinforced PVA hydrogel composites: kinetic, isotherm and thermodynamic modeling. Polymers, 12(2): 430.

23.   Elanchezhiyan, S., Muthu Prabhu, S., Han, J., Kim, Y. M., Yoon, Y., and Park, C. M. (2020). Synthesis and characterization of novel magnetic Zr-MnFe2O4@rGO nanohybrid for efficient removal of PFOA and PFOS from aqueous solutions. Applied Surface Science, 528:146579.

24.   Wang, B., Gao, B., Zimmerman, A. R., and Lee, X. (2018). Impregnation of multiwall carbon nanotubes in alginate beads dramatically enhances their adsorptive ability to aqueous methylene blue. Chemical Engineering Research and Design, 133: 235-242.

25.   Badruddoza, A. Z. M., Bhattarai, B., and Suri, R. P. S. (2017). Environmentally friendly β-cyclodextrin–ionic liquid polyurethane-modified magnetic sorbent for the removal of PFOA, PFOS, and Cr(VI) from water. ACS Sustainable Chemistry & Engineering, 5(10): 9223-9232.

26.   Rahimi, Z., Zinatizadeh, A. A., Zinadini, S., and van Loosdrecht, M. C. M. (2020). β-cyclodextrin functionalized MWCNTs as a promising antifouling agent in fabrication of composite nanofiltration membranes. Separation and Purification Technology, 247(10): 116979.

27.   Ragavan, K., and Rastogi, N. K. (2017). β-Cyclodextrin capped graphene-magnetite nanocomposite for selective adsorption of Bisphenol-A. Carbohydrate Polymers, 168: 129-137. 

28.   Qian, Z. J., Zhang, J., Xu, W. R., and Zhang, Y. C. (2022). Development of active packaging films based on liquefied shrimp shell chitin and polyvinyl alcohol containing β-cyclodextrin/cinnamaldehyde inclusion. International Journal of Biological Macromolecules, 214(3): 67-76.

29.   Verma, A., Thakur, S., Mamba, G., Prateek, Gupta, R. K., Thakur, P., and Thakur, V. K. (2020). Graphite modified sodium alginate hydrogel composite for efficient removal of malachite green dye. International Journal of Biological Macromolecules, 148: 1130-1139.

30.   Zhijiang, C., Cong, Z., Ping, X., Jie, G., and Kongyin, Z. (2018). Calcium alginate-coated electrospun polyhydroxybutyrate/carbon nanotubes composite nanofibers as nanofiltration membrane for dye removal. Journal of Materials Science, 53(20): 14801-14820.

31.   Thakur, S., and Arotiba, O. (2018). Synthesis, characterization and adsorption studies of an acrylic acid-grafted sodium alginate-based TiO2 hydrogel nanocomposite. Adsorption Science and Technology, 36(1–2): 458-477.

32.   Wu, Y., Qi, H., Shi, C., Ma, R., Liu, S., and Huang, Z. (2017). Preparation and adsorption behaviors of sodium alginate-based adsorbent-immobilized β-cyclodextrin and graphene oxide. RSC Advances, 7(50): 31549-31557.

33.   Darini, A., Eslaminejad, T., Nematollahi Mahani, S. N., and Ansari, M. (2019). Magnetogel nanospheres composed of cisplatin-loaded alginate/β-cyclodextrinas controlled release drug delivery. Advanced Pharmaceutical Bulletin, 9(4): 571-577.

34.   Godiya, C. B., Xiao, Y., and Lu, X. (2020). Amine functionalized sodium alginate hydrogel for efficient and rapid removal of methyl blue in water. International Journal of Biological Macromolecules, 144: 671-681.

35.   Yang, J.-S, Han, S.-Y, Yang, L., and Zheng, H.-C. (2014). Synthesis of beta-cyclodextrin-grafted-alginate and its application for removing methylene blue from water solution. Journal of Chemical Technology & Biotechnology, 91(3): 618-623.

36.   Shen, Y., Niu, L., Yu, Z., Wang, M., Shang, Z., and Yang, Y. (2018). Sodium alginate-grafted β-cyclodextrins as a matrix for immobilized Arthrobacter simplex for cortisone acetate biotransfromation. Applied Surface Science, 444: 42-47.

37.   Shen, L., Jin, Z., Wang, D., Wang, Y., and Lu, Y. (2018). Enhance wastewater biological treatment through the bacteria induced graphene oxide hydrogel. Chemosphere, 190: 201-210.

38.   Cataldo, S., Muratore, N., Orecchio, S., and Pettignano, A. (2015). Enhancement of adsorption ability of calcium alginate gel beads towards Pd(II) ion. A kinetic and equilibrium study on hybrid Laponite and Montmorillonite–alginate gel beads. Applied Clay Science, 118: 162-170.

39.   Kurwadkar, S., Dane, J., Kanel, S. R., Nadagouda, M. N., Cawdrey, R. W., Ambade, B., Struckhoff, G. C., & Wilkin, R. T. (2022). Per- and polyfluoroalkyl substances in water and wastewater: A critical review of their global occurrence and distribution. Science of the Total Environment, 809: 151003.

40.   Barton, K., Starling, A. P., Higgins, C. P., McDonough, C. A., Calafat, A. M., and Adgate, J. L. (2020). Sociodemographic and behavioral determinants of serum concentrations of per- and polyfluoroalkyl substances in a community highly exposed to aqueous film-forming foam contaminants in drinking water. International Journal of Hygiene and Environmental Health, 223(1): 256-266. 

41.   Asadi, S., Eris, S., and Azizian, S. (2018). Alginate-based hydrogel beads as a biocompatible and efficient adsorbent for dye removal from aqueous solutions. ACS Omega, 3(11): 15140-15148.

42.   Deng, S., Zhang, Q., Nie, Y., Wei, H., Wang, B., Huang, J., … Xing, B. (2012). Sorption mechanisms of perfluorinated compounds on carbon nanotubes. Environmental Pollution, 168: 138-144.

43.   Taka, A. L., Fosso-Kankeu, E., Pillay, K., and Mbianda, X. Y. (2018). Removal of cobalt and lead ions from wastewater samples using an insoluble nanosponge biopolymer composite: adsorption isotherm, kinetic, thermodynamic, and regeneration studies. Environmental Science and Pollution Research, 25(22), 21752-21767.

44.   Guo, W., Huo, S., Feng, J., & Lu, X. (2017). Adsorption of perfluorooctane sulfonate (PFOS) on corn straw-derived biochar prepared at different pyrolytic temperatures. Journal of the Taiwan Institute of Chemical Engineers, 78: 265-271.

45.   Wang, F., & Shih, K. (2011). Adsorption of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) on alumina: Influence of solution pH and cations. Water Research, 45(9): 2925-2930.

46.   Guo, W., Huo, S., Feng, J., and Lu, X. (2017). Adsorption of perfluorooctane sulfonate (PFOS) on corn straw-derived biochar prepared at different pyrolytic temperatures. Journal of the Taiwan Institute of Chemical Engineers, 78: 265-271.

47.   Yan, T., Chen, H., Jiang, F., and Wang, X. (2014). Adsorption of perfluorooctane sulfonate and perfluorooctanoic acid on magnetic mesoporous carbon nitride. Journal of Chemical and Engineering Data, 59(2): 508-515.

48.   Gagliano, E., Sgroi, M., Falciglia, P. P., Vagliasindi, F. G. A., and Roccaro, P. (2020). Removal of poly- and perfluoroalkyl substances (PFAS) from water by adsorption: Role of PFAS chain length, effect of organic matter and challenges in adsorbent regeneration. Water Research, 171: 115381.

49.   Khan, S. A., Siddiqui, M. F., and Khan, T. A. (2020). Synthesis of poly(methacrylic acid)/montmorillonite hydrogel nanocomposite for efficient adsorption of amoxicillin and diclofenac from aqueous environment: kinetic, isotherm, reusability, and thermodynamic investigations. ACS Omega, 2020: 361.

50.   Bei, Y., Deng, S., Du, Z., Wang, B., Huang, J., and Yu, G. (2014). Adsorption of perfluorooctane sulfonate on carbon nanotubes: Influence of pH and competitive ions. Water Science and Technology, 69(7): 1489-1495.

51.   Gutierrez, A. M., Frazar, E. M., Klaus, V., Paul, P., and Hilt, J. Z. (2021). Hydrogels and hydrogel nanocomposites: Enhancing healthcare through human and environmental treatment. Advanced Healthcare Materials, 11(7): 2101820.

52.   Huang, Z., Liu, S., Zhang, B., and Wu, Q. (2014). Preparation and swelling behavior of a novel self-assembled β-cyclodextrin/acrylic acid/sodium alginate hydrogel. Carbohydrate Polymers, 113: 430-437.

53.   Liu, Z., Sun, Y., Xu, X., Qu, J., and Qu, B. (2020). Adsorption of Hg(II) in an aqueous solution by activated carbon prepared from rice husk using KOH activation. ACS Omega, 5(45): 29231-29242.

54.   Al-Harby, N. F., Albahly, E. F., and Mohamed, N. A. (2021). Kinetics, isotherm and thermodynamic studies for efficient adsorption of congo red dye from aqueous solution onto novel cyanoguanidine-modified chitosan adsorbent. Polymers, 13(24): 4446. 

55.   Elanchezhiyan, S., Muthu Prabhu, S., Han, J., Kim, Y. M., Yoon, Y., and Park, C. M. (2020). Synthesis and characterization of novel magnetic Zr-MnFe2O4@rGO nanohybrid for efficient removal of PFOA and PFOS from aqueous solutions. Applied Surface Science, 528: 146579.

56.   Hasani, N., Selimi, T., Mele, A., Thaçi, V., Halili, J., Berisha, A., and Sadiku, M. (2022). Theoretical, equilibrium, kinetics and thermodynamic investigations of methylene blue adsorption onto lignite coal. Molecules, 27(6): 1856.

57.   Sahara, T., Wongsawaeng, D., Ngaosuwan, K., Kiatkittipong, W., Hosemann, P., and Assabumrungrat, S. (2023). Highly effective removal of perfluorooctanoic acid (PFOA) in water with DBD-plasma-enhanced rice husks. Scientific Reports, 13(1): 40197.

58.   Khamizov, R. Kh. (2020). A pseudo-second order kinetic equation for sorption processes. Russian Journal of Physical Chemistry A, 94(1): 171-176.

59.   León, G., Hidalgo, A., Martínez, A., Guzmán, M. A., and Miguel, B. (2023). Methylparaben adsorption onto activated carbon and activated olive stones: comparative analysis of efficiency, equilibrium, kinetics and effect of graphene-based nanomaterials addition. Applied Sciences, 13(16): 9147. 

60.   Hassan, M., Liu, Y., Naidu, R., Du, J., and Qi, F. (2020). Adsorption of perfluorooctane sulfonate (PFOS) onto metal oxides modified biochar. Environmental Technology and Innovation, 19: 100816.

61.   Chen, W., Zhang, X., Mamadiev, M., and Wang, Z. (2017). Sorption of perfluorooctane sulfonate and perfluorooctanoate on polyacrylonitrile fiber-derived activated carbon fibers: In comparison with activated carbon. RSC Advances, 7(2): 927-938.

62.   Shen, Y., Niu, L., Yu, Z., Wang, M., Shang, Z., and Yang, Y. (2018). Sodium alginate-grafted β-cyclodextrins as a matrix for immobilized Arthrobacter simplex for cortisone acetate biotransfromation. Applied Surface Science, 444: 42-47.

63.   Niu, B., Yang, S., Li, Y., Zang, K., Sun, C., Yu, M., … Zheng, Y. (2020). Regenerable magnetic carbonized Calotropis gigantea fiber for hydrophobic-driven fast removal of perfluoroalkyl pollutants. Cellulose, 27(10): 5893-5905.

64.   Zaggia, A., Conte, L., Falletti, L., Fant, M., Chiorboli, A. (2016). Use of strong anion exchange resins for the removal of perfluoroalkylated substances from contaminated drinking water in batch and continuous pilot plants. Water Research, 91: 137-146.

65.   McCleaf, P., Englund, S., Oestlund, A., Lindegren, K., Wiberg, K., Ahrens, L. (2017). Removal efficiency of multiple poly- and perfluoroalkyl substances (PFASs) in drinking water using granular activated carbon (GAC) and anion exchange (AE) column tests. Water Research, 120: 77e87.

66.   Rahman, M. F., Peldszus, S., Anderson, W. B., (2014). Behaviour and fate of per- fluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water treatment: a review. Water Research, 50: 318-340.

67.   Appleman, T. D., Higgins, C. P., Quin~ones, O., Vanderford, B. J., Kolstad, C., Zeigler- Holady, J. C., Dickenson, E. R. V. (2014). Treatment of poly- and perfluoroalkyl substances in U.S. full-scale water treatment systems. Water Research, 51: 246-255.

68.   Xiao, F., Zhang, X., Penn, L., Gulliver, J. S. and Simcik, M. F. (2011). Effects of monovalent cations on the competitive adsorption of perfluoroalkyl acids by kaolinite: experimental studies and modeling. Environmental Science Technology, 45: 10028-10035.

69.   Campos-Pereira, H., Kleja, D. B., Sjöstedt, C., Ahrens, L., Klysubun, W., and Gustafsson, J. P. (2020). The adsorption of per- and polyfluoroalkyl substances (PFASs) onto ferrihydrite is governed by surface charge. Environmental Science & Technology, 54(24): 15722-15730.

70.   Zhan, W., Gao, L., Fu, X., Siyal, S. H., Sui, G., and Yang, X. (2019). Green synthesis of amino-functionalized carbon nanotube-graphene hybrid aerogels for high performance heavy metal ions removal. Applied Surface Science, 467-468: 1122-1133.