References
  -  W. Kong, F. Zhao, H. Guan, Y. Zhao, H. Zhang, B. Zhang,
    Highly adsorptive mesoporous carbon from biomass using
    molten-salt route, J. Mater. Sci., 51 (2016) 6793–6800. 
-  Y.H. Magdy, H. Altaher, Kinetic analysis of the adsorption of
    dyes from high strength wastewater on cement kiln dust, J.
    Environ. Chem. Eng., 6 (2018) 834–841. 
-  N. Mokhtar, E.A. Aziz, A. Aris, W.F.W. Ishak, N.S.M. Ali,
    Biosorption of azo-dye using marine macro-alga of Euchema
    Spinosum, J. Environ. Chem. Eng., 5 (2017) 5721–5731. 
-  M. Bounaas, A. Bouguettoucha, D. Chebli, A. Reffas, I. Harizi,
    F. Rouabah, A. Amrane, High efficiency of methylene blue
    removal using a novel low-cost acid treated forest wastes,
    Cupressus semperirens cones: experimental results and modeling,
    Part. Sci. Technol., 6351 (2018) 1–10. 
-  M.T. Yagub, T.K. Sen, S. Afroze, H.M. Ang, Dye and its removal
    from aqueous solution by adsorption: a review, Adv. Colloid
    Interface Sci., 209 (2014) 172–184. 
-  T. Ngulube, J.R. Gumbo, V. Masindi, A. Maity, An update on
    synthetic dyes adsorption onto clay based minerals: a state-ofart
    review, J. Environ. Manage., 191 (2017) 35–57. 
-  G. Liu, Z. Hu, R. Guan, Y. Zhao, H. Zhang, B. Zhang, Efficient
    removal of methylene blue in aqueous solution by freeze-dried
    calcium alginate beads, Korean J. Chem. Eng., 33 (2016)
    3141–3148. 
-  Y. Lu, H. Shang, H. Guan, Y. Zhao, H. Zhang, B. Zhang, Enhanced
	  visible-light photocatalytic activity of BiVO4 microstructures via
  annealing process, Superlattices Microstruct., 88 (2015) 591–599. 
-  R.A. Reza, M. Ahmaruzzaman, Comparative study of waste
    derived adsorbents for sequestering methylene blue from
    aquatic environment, J. Environ. Chem. Eng., 3 (2015) 395–404. 
-  P. Luo, B. Zhang, Y. Zhao, J. Wang, H. Zhang, J. Liu, Removal
    of methylene blue from aqueous solutions by adsorption onto
    chemically activated halloysite nanotubes, Korean J. Chem.
    Eng., 28 (2011) 800–807. 
-  V.K. Gupta, D. Pathania, S. Agarwal, S. Sharma, De-coloration
    of hazardous dye from water system using chemically modified
    Ficus carica adsorbent, J. Mol. Liq., 174 (2012) 86–94. 
-  M. Ahmaruzzaman, A review on the utilization of fly ash, Prog.
    Energy Combust. Sci., 36 (2010) 327–363. 
-  A.Y.W. Sham, S.M. Notley, Adsorption of organic dyes from
    aqueous solutions using surfactant exfoliated graphene, J.
    Environ. Chem. Eng., 6 (2018) 495–504. 
-  C.F. Carolin, P.S. Kumar, A. Saravanan, G.J. Joshiba, Mu.
    Naushad, Efficient techniques for the removal of toxic heavy
    metals from aquatic environment: a review, J. Environ. Chem.
    Eng., 5 (2017) 2782–2799. 
-  L. Mouni, L. Belkhiri, J.-C. Bollinger, A. Bouzaza, A. Assadi,
    A. Tirri, F. Dahmoune, K. Madani, H. Remini, Removal of
    Methylene Blue from aqueous solutions by adsorption on
    kaolin: kinetic and equilibrium studies, Appl. Clay Sci., 153
    (2018) 38–45. 
-  M.S.U. Rehman, M. Munir, M. Ashfaq, N. Rashid, M.F. Nazar,
    M. Danish, J.-I. Han, Adsorption of Brilliant Green dye from
    aqueous solution onto red clay, Chem. Eng. J., 228 (2013) 54–62. 
-  L.-G. Yan, L.-L Qin, H.-Q. Yu, S. Li, R.-R. Shan, B. Du,
    Adsorption of acid dyes from aqueous solution by CTMAB
    modified bentonite: kinetic and isotherm modeling, J. Mol. Liq.,
    211 (2015) 1074–1081. 
-  ENVIS Centre on Fly Ash GOI, 2017. Availabe at:
    http://cbrienvis.nic.in/summaryof fly ash.html 
-  H. Cho, D. Oh, K. Kim, A study on removal characteristics
    of heavy metals from aqueous solution by fly ash, J. Hazard.
    Mater., 127 (2005) 187–195. 
-  K. Rastogi, J.N. Sahu, B.C. Meikap, M.N. Biswas, Removal of
    methylene blue from wastewater using fly ash as an adsorbent
    by hydrocyclone, J. Hazard. Mater., 158 (2008) 531–540. 
-  S. Banerjee, G.C. Sharma, M.C. Chattopadhyaya, Y.C. Sharma,
    Kinetic and equilibrium modeling for the adsorptive removal of
    methylene blue from aqueous solutions on of activated fly ash
    (AFSH), J. Environ. Chem. Eng., 2 (2014) 1870–1880. 
-  Z. Liu, Y. Liu, Structure and properties of forming adsorbents
    prepared from different particle sizes of coal fly ash, Chin. J.
    Chem. Eng., 23 (2015) 290–295. 
-  L.D. Lin, Y. Lin, C.J. Li, D.Y. Wu, H.N. Kong, Synthesis of
    zeolite/hydrous metal oxide composites from coal fly ash as
    efficient adsorbents for removal of methylene blue from water,
    Int. J. Miner. Process., 148 (2016) 32–40. 
-  L. Li, S. Wang, Z. Zhu, Geopolymeric adsorbents from fly ash
    for dye removal from aqueous solution, J. Colloid Interface Sci.,
    300 (2006) 52–59. 
-  J. Davidovits, Geopolymers and geopolymeric material, J.
    Therm. Anal., 35 (1989) 429–441. 
-  R.S. Blissett, N.A. Rowson, A review of the multi-component
    utilisation of coal fly ash, Fuel, 97 (2012) 1–23. 
-  N.-U. Amin, A multi-directional utilization of different ashes,
    RSC Adv., 4 (2014) 62769–62788. 
-  K. Al-Zboon, M.S. Al-Harahsheh, F.B. Hani, Fly ash-based
    geopolymer for Pb removal from aqueous solution, J. Hazard.
    Mater., 188 (2011) 414–421. 
-  M.N. Mužek, S. Svilović, J. Zelić, Kinetic studies of cobalt
    ion removal from aqueous solutions using fly ash-based
    geopolymer and zeolite NaX as sorbents, Sep. Sci. Technol., 51
    (2016) 2868–2875. 
-  Y. Zhang, L. Liu, Fly ash-based geopolymer as a novel
    photocatalyst for degradation of dye from wastewater,
    Particuology, 11 (2013) 353–358. 
-  M.I. Khan, T.K. Min, A.K. Azizli, S. Sufian, H. Ullah, Z.
    Man, Effective removal of methylene blue from water using
    phosphoric acid based geopolymers: synthesis, characterizations
    and adsorption studies, RSC Adv., 5 (2015) 61410–61420. 
-  J. Chen, Y. Wang, S. Zhou, X. Lei, Reduction/immobilization
    processes of hexavalent chromium using metakaolin-based
    geopolymer, J. Environ. Chem. Eng., 5 (2017) 373–380. 
-  T. Luukkonen, H. Runtti, M. Niskanen, E.T. Tolonen, M.
    Sarkkinen, K. Kemppainen, J. Rämö, U. Lassi, Simultaneous
    removal of Ni(II), As(III), and Sb(III) from spiked mine effluent
    with metakaolin and blast-furnace-slag geopolymers, J.
    Environ. Manage., 166 (2016) 579–588. 
-  S.S. Amritphale, D. Mishra, M. Mudgal, R.K. Chouhan, N.
    Chandra, A novel green approach for making hybrid inorganicorganic
    geopolymeric cementitious material utilizing fly ash
    and rice husk, J. Environ. Chem. Eng., 4 (2016) 3856–3865. 
-  U.E.ul Haq, S.P. Kunjalukkal, A. Licciulli, Synthesis and
    characteristics of fly ash and bottom ash based geopolymers—a
    comparative study, Ceram. Int., 40 (2013) 2965–2971. 
-  M.S. Al-Harahsheh, K. Al Zboon, L. Al-Makhadmeh, M.
    Hararah, M. Mahasneh, Fly ash based geopolymer for heavy
    metal removal: a case study on copper removal, J. Environ.
    Chem. Eng., 3 (2015) 1669–1677. 
-  H. Singh, G. Chauhan, A.K. Jain, S.K. Sharma, Adsorptive
    potential of agricultural wastes for removal of dyes from
    aqueous solutions, J. Environ. Chem. Eng., 5 (2017) 122–135. 
-  J. Liu, Y. Wang, Y. Fang, T. Mwamulima, S. Song, C. Peng,
    Removal of crystal violet and methylene blue from aqueous
    solutions using the fly ash-based adsorbent material-supported
    zero-valent iron, J. Mol. Liq., 250 (2018) 468–476. 
-  S. Kuai, Z. Nan, Formation of sandwich structured
	  ZnCe0.03Fe1.97O4@nSiO2@SBA-15 and adsorptive removal of
    methylene blue from aqueous solution, Chem. Eng. J., 244
  (2014) 273–281. 
-  E.I. El-Shafey, S.N.F. Ali, S. Al-Busafi, H.A.J.Al-Lawati,
    Preparation and characterization of surface functionalized
    activated carbons from date palm leaflets and application
    for methylene blue removal, J. Environ. Chem. Eng., 4 (2016)
    2713–2724. 
-  P. Duxson, J.L. Provis, G.C. Lukey, S.W. Mallicoat, W.M. Kriven,
    J.S.J. van Deventer, Understanding the relationship between
    geopolymer composition, microstructure and mechanical
    properties, Colloids Surf., A, 269 (2005) 47–58. 
-  U. Rattanasak, P. Chindaprasirt, Influence of NaOH solution
    on the synthesis of fly ash geopolymer, Miner. Eng., 22 (2009)
    1073–1078. 
-  S. Saha, C. Rajasekaran, Enhancement of the properties of fly ash
    based geopolymer paste by incorporating ground granulated
    blast furnace slag, Constr. Build. Mater., 146 (2017) 615–620. 
-  J. Davidovits, Geopolymer, Green Chemistry and Sustainable
    Development Solutions, Geopolymer Proceedings, 2005, p. 10. 
-  J. Ojima, Determining of crystalline silica in respirable dust
    samples by infrared spectrophotometry in the presence of
    interferences, J. Occup. Health, 45 (2003) 94–103. 
-  M.N. Mužek, J. Zelić, D. Jozić, Microstructural characteristics of
    geopolymers based on alkali-activated fly ash, Chem. Biochem.
    Eng. Q., 26 (2012) 89–95. 
-  T. Bakharev, Resistance of geopolymer materials to acid attack,
    Cem. Concr. Res., 35 (2005) 658–670. 
-  K. Somna, C. Jaturapitakkul, P. Kajitvichyanukul, P.
    Chindaprasirt, NaOH-activated ground fly ash geopolymer
    cured at ambient temperature, Fuel, 90 (2011) 2118–2124. 
-  S. Shakoor, A. Nasar, Groundwater for sustainable development
    adsorptive treatment of hazardous methylene blue dye from
    artificially contaminated water using Cucumis sativus peel
    waste as a low-cost adsorbent, Groundwater Sustainable Dev.,
    5 (2017) 152–159. 
-  R.K. Gautam, A. Mudhoo, M.C. Chattopadhyaya, Kinetic,
    equilibrium, thermodynamic studies and spectroscopic analysis
    of Alizarin Red S removal by mustard husk, J. Environ. Chem.
    Eng., 1 (2013) 1283–1291. 
-  N.A. Oladoja, Y.D. Aliu, Snail shell as coagulant aid in the alum
    precipitation of malachite green from aqua system, J. Hazard.
    Mater., 164 (2009) 1496–1502. 
-  M.K. Dahri, M.R.R. Kooh, L.B.L. Lim, Application of Casuarina
    equisetifolia needle for the removal of methylene blue and
    malachite green dyes from aqueous solution, Alexandria Eng.
    J., 54 (2015) 1253–1263. 
-  M.F. Elkady, A.M. Ibrahim, M.M.A. El-Latif, Assessment of
    the adsorption kinetics, equilibrium and thermodynamic
    for the potential removal of reactive red dye using eggshell
    biocomposite beads, Desalination, 278 (2011) 412–423. 
-  K.B. Fontana, E.S. Chaves, J.D.S. Sanchez, E.R.L.R. Watanabe,
    J.M.T.A. Pietrobelli, G.G. Lenzi, Textile dye removal from
    aqueous solutions by malt bagasse: isotherm, kinetic and
    thermodynamic studies, Ecotoxicol. Environ. Saf., 124 (2016)
    329–336. 
-  S. Tunali, A.S. Özcan, A. Özcan, T. Gedikbey, Kinetics and
    equilibrium studies for the adsorption of Acid Red 57 from
    aqueous solutions onto calcined-alunite, J. Hazard. Mater., 135
    (2006) 141–148. 
-  P. Patnukao, A. Kongsuwan, P. Pavasant, Batch studies of
    adsorption of copper and lead on activated carbon from
    Eucalyptus camaldulensis Dehn bark, J. Environ. Sci., 20 (2008)
    1028–1034. 
-  J.-Q. Jiang, C. Cooper, S. Ouki, Comparison of modified
    montmorillonite adsorbents: Part I: preparation, characterization
    and phenol adsorption, Chemosphere, 47 (2002) 711–716. 
-  M. Diab, A.Z. El-Sonbati, A.A. El-Bindary, K.S. Mohamed, A.A.
    Al-Sarawy and M.A. Farid, Removal of hazardous azocoumarin
    dye from aqueous solutions using activated carbon prepared
    from rice straw, Desal. Wat. Treat., 57 (2016) 19391–19401. 
-  R.M. Novais, G. Ascensão, D.M. Tobaldi, M.P. Seabra, J.A.
    Labrincha, Biomass fly ash geopolymer monoliths for effective
    methylene blue removal from wastewaters, J. Cleaner Prod., 171
    (2018) 783–794. 
-  Y. Liu, C. Yan, Z. Zhang, Y. Gong, H. Wang, X. Qiu, A facile
    method for preparation of floatable and permeable fly ashbased
    geopolymer block, Mater. Lett., 185 (2016) 370–373. 
-  Y. Liu, Y.-J. Liu, Biosorption isotherms, kinetics and
    thermodynamics, Sep. Purif. Technol., 61 (2008) 229–242.