References
  -  G. Boix, J. Troyano, L. Garzón-Tovar, C. Camur, N. Bermejo,
    A. Yazdi, J. Piella, N.G. Bastus, V.F. Puntes, I. Imaz, D. Maspoch,
    MOF-Beads containing inorganic nanoparticles for the
    simultaneous removal of multiple heavy metals from water,
    ACS Appl. Mater. Interfaces, 12 (2020) 10554–10562. 
-  L. Zhang, D. Peng, R.-P. Liang, J.-D. Qiu, Graphene-based
    optical nanosensors for detection of heavy metal ions, TrAC,
    Trends Anal. Chem., 102 (2018) 280–289. 
-  X. Qu, P.J.J. Alvarez, Q. Li, Applications of nanotechnology
    in water and wastewater treatment, Water Res., 47 (2013)
    3931–3946. 
-  Jumina, Y. Priastomo, H.R. Setiawan, Mutmainah,
    Y.S. Kurniawan, K. Ohto, Simultaneous removal of lead(II),
    chromium(III), and copper(II) heavy metal ions through an
    adsorption process using C-phenylcalix[4]pyrogallolarene
  material, J. Environ. Chem. Eng., 8 (2020) 103971, doi:10.1016/j.jece.2020.103971. 
-  J. Wang, D. Zhang, S. Liu, C. Wang, Enhanced removal of
    chromium(III) for aqueous solution by EDTA modified
    attapulgite: adsorption performance and mechanism, Sci. Total
    Environ., 720 (2020) 137391, 
 doi: 10.1016/j.scitotenv.2020.137391.
-  T.A. Saleh, Nanocomposite of carbon nanotubes/silica
    nanoparticles and their use for adsorption of Pb(II): from
    surface properties to sorption mechanism, Desal. Water Treat.,
    57 (2015) 10730–10744. 
-  M.F. Hamza, S. Lu, K.A.M. Salih, H. Mira, A.S. Dhmees,
    T. Fujita, Y. Wei, T. Vincent, E. Guibal, As(V) sorption from
    aqueous solutions using quaternized algal/polyethyleneimine
    composite beads, Sci. Total Environ., 719 (2020) 137396,
    doi: 10.1016/j.scitotenv.2020.137396. 
-  X. Fang, J. Li, X. Li, S. Pan, X. Zhang, X. Sun, J. Shen,
    W. Han, L. Wang, Internal pore decoration with polydopamine
    nanoparticle on polymeric ultrafiltration membrane for
    enhanced heavy metal removal, Chem. Eng. J., 314 (2017) 38–49. 
-  W.A. Khanday, M. Asif, B.H. Hameed, Cross-linked beads
    of activated oil palm ash zeolite/chitosan composite as a bioadsorbent
    for the removal of methylene blue and acid blue 29
    dyes, Int. J. Biol. Macromol., 95 (2017) 895–902. 
-  K. Varaprasad, T. Jayaramudu, E.R. Sadiku, Removal of dye
    by carboxymethyl cellulose, acrylamide and graphene oxide
    via a free radical polymerization process, Carbohydr. Polym.,
    164 (2017) 186–194. 
-  Z. Yang, H. Yang, Z. Jiang, T. Cai, H. Li, H. Li, A. Li, R. Cheng,
    Flocculation of both anionic and cationic dyes in aqueous
    solutions by the amphoteric grafting flocculant carboxymethyl
    chitosan-graft-polyacrylamide, J. Hazard. Mater.,
    254–255 (2013) 36–45. 
-  B. Xiang, D. Ling, H. Lou, H. Gu, 3D hierarchical flower-like
    nickel ferrite/manganese dioxide toward lead(II) removal from
    aqueous water, J. Hazard. Mater., 325 (2017) 178–188. 
-  Y. Zhou, Y. He, Y. Xiang, S. Meng, X. Liu, J. Yu, J. Yang,
    J. Zhang, P. Qin, L. Luo, Single and simultaneous adsorption of
    pefloxacin and Cu(II) ions from aqueous solutions by oxidized
    multiwalled carbon nanotube, Sci. Total Environ., 646 (2019)
    29–36. 
-  E. Erdem, N. Karapinar, R. Donat, The removal of heavy metal
    cations by natural zeolites, J. Colloid Interface Sci., 280 (2004)
    309–314. 
-  J.C.Y. Ng, W.H. Cheung, G. McKay, Equilibrium studies of the
    sorption of Cu(II) ions onto chitosan, J. Colloid Interface Sci.,
    255 (2002) 64–74. 
-  R. Celis, M.C. HermosÍn, J. Cornejo, Heavy metal adsorption by
    functionalized clays, Environ. Sci. Technol., 34 (2000) 4593–4599. 
-  D. Sud, G. Mahajan, M.P. Kaur, Agricultural waste material as
    potential adsorbent for sequestering heavy metal ions from
    aqueous solutions – a review, Bioresour. Technol., 99 (2008)
    6017–6027. 
-  M. Hua, S. Zhang, B. Pan, W. Zhang, L. Lv, Q. Zhang, Heavy
    metal removal from water/wastewater by nanosized metal
    oxides: a review, J. Hazard. Mater., 211–212 (2012) 317–331. 
-  I.S. Sayan Bhattacharya, A. Mukhopadhyay, D. Chattopadhyay,
    U.C. Ghosh, D. Chatterjee, Role of nanotechnology in water
    treatment and purification: potential applications implications,
    Int. J. Chem. Sci. Technol., 3 (2013) 59–64. 
-  S. Zafar, M.I. Khan, H. Rehman, J. Fernandez-Garcia, S. Shahida,
    P. Prapamonthon, M. Khraisheh, A. Rehman, H.B. Ahmad,
    M.L. Mirza, N. Khalid, M.H. Lashari, Kinetic, equilibrium,
    and thermodynamic studies for adsorptive removal of cobalt
    ions by rice husk from aqueous solution, Desal. Water Treat.,
    204 (2020) 285–296. 
-  G. Zhao, J. Li, X. Ren, C. Chen, X. Wang, Few-layered graphene
    oxide nanosheets as superior sorbents for heavy metal ion
    pollution management, Environ. Sci. Technol., 45 (2011)
    10454–10462. 
-  O.S. Bello, O.M. Atoyebi, K.A. Adegoke, E.O. Fehintola,
    A.O. Ojo, Removal of toxicant chromium(VI) from aqueous
    solution using different adsorbents, J. Chem. Soc. Pak., 37 (2015)
    190–206. 
-  U. Khalil, M.B. Shakoor, S. Ali, S.R. Ahmad, M. Rizwan,
    A.A. Alsahli, M.N. Alyemeni, Selective removal of hexavalent
    chromium from wastewater by rice husk: kinetic, isotherm and
    spectroscopic investigation, Water, 13 (2021) 263, doi: 10.3390/
    w13030263. 
-  R.K. Vempati, S.C. Musthyala, M.Y.A. Mollah, D.L. Cocke,
    Surface analyses of pyrolysed rice husk using scanning force
    microscopy, Fuel, 74 (1995) 1722–1725. 
-  S. Zafar, M.I. Khan, M. Khraisheh, S. Shahida,T. Javed,
    M.L. Mirza, N. Khalid, Use of rice husk as an efective sorbent
    for the removal of cerium ions from aqueous solution: kinetic,
    equilibrium and thermodynamic studies, Desal. Water Treat.,
    150 (2019) 124–135. 
-  S. Zafar, M.I. Khan, M. Khraisheh, S. Shahida, N. Khalid,
    M. Latif Mirza, Effective removal of lanthanum ions from
    aqueous solution using rice husk: impact of experimental
    variables, Desal. Water Treat., 132 (2019) 263–273. 
-  S. Zafar, M.I. Khan, M. Khraisheh, M.H. Lashari, S. Shahida,
    M.F. Azhar, P. Prapamonthon, M.L. Mirza, N. Khalid, Kinetic,
    equilibrium and thermodynamic studies for adsorption of
    nickel ions onto husk of Oryza sativa, Desal. Water Treat.,
    167 (2019) 277–290. 
-  S. Zafar, M.I. Khan, W. Hassan, S. Mubeen, T. Javed,
    S. Shahida, S. Manzoor, A. Shanableh, A. Rehman, M.L. Mirza,
    
 N. Khalid, M.H. Lashari, Application of NaOH-treated rice
    husk for adsorptive discharge of cobalt ions from wastewater,
    Desal. Water Treat., 226 (2021) 328–338.
-  T.A. Saleh, Isotherm, kinetic, and thermodynamic studies on
    Hg(II) adsorption from aqueous solution 
 by silica-multiwall
    carbon nanotubes, Environ. Sci. Pollut. Res. Int., 22 (2015)
    16721–16731.
-  V.K. Gupta, T.A. Saleh, Characterization of the chemical
    bonding between Al2O3 and nanotube in MWCNT/Al2O3
    nanocomposite, Curr. Nanosci., 8 (2012) 739–743. 
-  U.C. Abubakar, K.R. Alhooshani, T.A. Saleh, Effect of
    ultrasonication and chelating agents on the dispersion of NiMo
    catalysts on carbon for hydrodesulphurization, J. Environ.
    Chem. Eng., 8 (2020) 103811, doi: 10.1016/j.jece.2020.103811. 
-  T.A. Saleh, Simultaneous adsorptive desulfurization of diesel
    fuel over bimetallic nanoparticles loaded on activated carbon,
    J. Cleaner Prod., 172 (2018) 2123–2132. 
-  T.A. Saleh, The influence of treatment temperature on the
    acidity of MWCNT oxidized by HNO3 or a mixture of HNO3/H2SO4, Appl. Surf. Sci., 257 (2011) 7746–7751. 
-  A. Rana, M.K. Arfaj, A.S. Yami, T.A. Saleh,
    Cetyltrimethylammonium modified graphene as a clean
    swelling inhibitor in water-based oil-well drilling mud,
    J. Environ. Chem. Eng., 8 (2020) 103802, doi: 10.1016/j.jece.2020.103802. 
-  V.C. Srivastaa, I.D. Mall, I.M. Mishra, Characterization of
    mesoporous rice husk ash (RHA) and adsorption kinetics of
    metal ions from aqueous solution onto RHA, J. Hazard. Mater.,
    134 (2006) 257–267. 
-  S. Kazy, K. Sar, P. Sen, A.K. Singh, F.D.S.S., Extracellular
    polysaccharides of a copper-sensitive and a copper-resistant
    Pseudomonas aeruginosa stain: synthesis, chemical nature and
    copper binding, World J. Microbiol. Biotechnol., 18 (2002)
    583–588. 
-  S.K. Kazy, S. D’Souza, P. Sar, Uranium and thorium
    sequestration by a Pseudomonas sp.: mechanism and chemical
    characterization, J. Hazard. Mater., 163 (2009) 65–72. 
-  X. Ying-Mei, Q. Ji, H. De-Min, W. Dong-Mei, C. Hui-Ying,
    G. Jun, Z. Qiu-Min, Preparation of amorphous silica from oil
    shale residue and surface modification by silane coupling
    agent, Oil Shale, 27 (2010) 37–46. 
-  L. Ludueña, D. Fasce, V.A. Alvarez, P.M. Stefani, Nanocellulose
    from rice husk following alkaline treatment to remove silica,
    BioResources, 6 (2011) 1440–1453. 
-  S. Larous, A.-H. Meniai, M.B. Lehocine, Experimental study of
    the removal of copper from aqueous solutions by adsorption
    using sawdust, Desalination, 185 (2005) 483–490. 
-  A. Özer, D. Özer, A. Özer, The adsorption of copper(II) ions
    on to dehydrated wheat bran (DWB): determination of the
    equilibrium and thermodynamic parameters, Process Biochem.,
    39 (2004) 2183–2191. 
-  J. Egila, B. Dauda, T. Jimoh, Biosorptive removal of cobalt(II)
    ions from aqueous solution by Amaranthus hydridus L. stalk
    wastes, Afr. J. Biotechnol., 9 (2010) 8192–8198. 
-  M. Malakootian, A. Almasi, H. Hossaini, Pb and Co removal
    from paint industries effluent using wood ash, Int. J. Environ.
    Sci. Technol., 5 (2008) 217–222. 
-  B. Subramanyam, A. Das, Linearized and non-linearized
    isotherm models comparative study on adsorption of aqueous
    phenol solution in soil, Int. J. Environ. Sci. Technol., 6 (2009)
  633–640.