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    Topic review

    Sol-Gel Technology

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    The commercial availability of inorganic/organic precursors for sol-gel formulations is very high and increases day by day. In textile applications, the precursor-synthesized sol-gels along with functional chemicals can be deposited onto textile fabrics in one step by rolling, padding, dip-coating, spraying or spin coating. By using this technology, it is possible to provide fabrics with functional/multi-functional characteristics including flame retardant, anti-mosquito, water- repellent, oil-repellent, anti-bacterial, anti-wrinkle, ultraviolet (UV) protection and self-cleaning properties. These surface properties are discussed, describing the history, basic chemistry, factors affecting the sol-gel synthesis, progress in sol-gel technology along with various parameters controlling sol-gel technology. Additionally, this review deals with the recent progress of sol-gel technology in textiles in addressing fabric finishing, water repellent textiles, oil/water separation, flame retardant, UV protection and self-cleaning, self-sterilizing, wrinkle resistance, heat storage, photochromic and thermochromic color changes and the improvement of the durability and wear resistance properties.

    1. Introduction

    Textile wet processing consists of three important processes, namely pretreatment, coloration (dyeing or printing) and finishing [1][2]. Pretreatment (i.e. scouring, bleaching) is done first to prepare the textiles for the subsequent process called coloration [3][4]. After coloration, the textiles are subjected to the finishing process according to the end-use or consumer requirements [1][2][5][6]. As mentioned, the finishing process is the last chance to provide added value [7]. The finishing process provides special functional properties to the textiles such as flame-retardancy, water-repellency, water-proof, antimicrobial, soil/stain resistance, etc. [8]. Textile finishing can be classified according to different factors based on durability (durable or semi-durable), chemical (wet processing), mechanical (dry or physical treatments such as brushing, shearing, raising), aesthetic (modify the hand/ drape) and functional finishes. Generally, chemical finishing involves the addition of different chemicals based on the intended textile end-use [7]. Among the different finishing techniques, chemical finishing has been widely studied due to the current trends together with the customer requirements for high-tech or high-performance applications [9][10][11][12]. In the past two decades, sol-gel- assisted textile finishing has played a vital role in the development of novel applications to improve the basic properties of textiles. Generally, sol-gel-based textile finishing has more advantages to overcome the shortcomings of conventional finishing techniques [13][14][15][16][17]. The main advantages are eco-friendliness, less chemical utilization, low-temperature treatment, low toxicity to human health, protection of the inherent properties of textile materials, and the possibility to adjust the thickness of the coating and long-lasting properties of finished fabrics. Some types of sol-gel systems also have bacteriostatic or antibacterial effects [16][17][18][19][20][21][22]. These systems are anatase-modified photoactive TiO2 coatings and sol-gel coatings with colloidal metals or metal compounds embedded in them, such as silver, silver salt, copper compound, zinc or quaternary ammonium salt [18], so sol-gel technology can be applied to textiles to develop various functional finishes with antibacterial [23][24][25][26][27][28][29][30][31][32], water repellent [33][34][35][36][37][38], superhydrophobic [39][40][41][42][43][44], oil/water separations [45][46][47][48][49][50][51][52][53], flame-retardant [54][55][56][57][58][59][60][61][62] multi-functional [63][64][65][66][67][68], ultraviolet (UV) protection [69][70], self-cleaning as well as soil-repellency [18][71][72], photocatalytic [73][74], wear & abrasion resistance properties [75]. The main aim of this review paper is to describe the history, synthesis, application and progress of sol-gel finishing in the textile industry. The various applications of sol-gel techniques in textile finishing are summarized in Figure 1.

    Figure 1. Various applications of sol-gel finishing on textile fabrics.

    2. Sol-Gel Technology: History, Chemistry and Synthesis

    Sol-gel technology has tremendous potential due to the combination of novel materials with a high degree of homogeneity at the molecular level with excellent physical and chemical properties [76][77]. In ancient times in China, tofu was prepared by utilizing this technology and hence it is not a new technology [78][79]. In the mid-19th century, sol-gel technology was used for preparing one-component compounds using sols and gels [80][81]. In the process of making glass, the sol-gel process requires less temperature compared to the conventional high-temperature melting method [82][83]. The method of forming a gel by mixing SiCl4 and ethanol and hydrolysis in humid air was discovered by Ebelmen in 1846 [84][85]. The sol-gel method was successfully used to produce SiO2-B2O3-A12O3-Na2O-K2O multi-component glasses which were analyzed by Dislich [86], thus creating great curiosity towards sol-gel technology. In 1981, the first international workshop on glasses [77][79][81][87] and ceramics from gels was held, which helped to further develop sol-gel technology. Sol-gel technology is being used widely since 1980 in the process of synthesizing superconducting materials [88], functional ceramic materials [89], nonlinear optical materials [90], catalysts and enzyme carriers [91][92], porous glass materials and other materials [93][94]. It was a milestone in the history of materials science in which many papers and patents broadly utilizing surface coating and other aspects were published [95][96]. The solution, sol or gel, solidifies the compounds of metal-organic or inorganic (precursor) to form a sol or gel state, followed by the development of an oxide by heat treatment. The polycondensation reaction transforms Si-OR- and Si-OH-comprising species into siloxane compounds which is the basic chemical principle of sol-gel treatment of silica-based materials. Corner sharing connects this to SiO4 tetrahedra (or RSiO3 tetrahedra in hybrid materials) from a structural point of view. In order to achieve a stable gel, it is essential to maximize the number of siloxane bonds (-Si-O-Si-) and subsequently minimize the number of silanol (Si-OH) and alkoxo (Si-OR) groups [18][97][98][99].

    3. Future Trends and Challenges of Sol-Gel Finishing in Textiles

    Over a past few decades, the development of innovative multi-disciplinary approaches in textile research and development has brought about unceasing functional changes in the textile and clothing industry. Sol-gel based textile finishing is one among them. The thin-coat finishing of textiles carried out by the sol-gel methods is gaining greater and greater importance owing to its suitability for the versatile functionalization of textiles to impart properties that are difficult and even impossible to obtain with the use of conventional finishing methods. Since the 1960s, sol-gel coating methods for substrates such as metals, glass, and ceramics have been extensively studied. In the past few decades, research on sol-gel technology has focused on making the functionality of textile materials an alternative to conventional textile finishing. The sol-gel technology can improve the water and oil repellency, flame retardancy, UV resistance, antibacterial property and anti-wrinkle properties of textiles, and the method has the characteristics of simple process, excellent functionality, environmental friendliness and long-lasting functionality.

    Globally the textile market is mainly dependent on the revolution in high-performance textile products, among them one of the prominent driving forces is sol-gel assisted textile finishing, allowing high-performance textiles to stay ahead of the competition. Market volatility and world-wide competition are the two major factors influencing the textile industry. Henceforth, there arises an urge to boost the ability to produce and merchandize supreme quality and in enriching the products. Even though there are optimistic characteristics features in sol-gel based textile finishing, there are still a lot of items that should be considered. The foremost issue is cost, which has the capacity to limit the expansion of sol-gel based coatings on textiles and mass production. Stated differently, sol-gel coating methods provide functional finished products that seem to be overpriced and require R&D spending in the textile industry. In spite of the fact the long lasting properties of the products finished using these methods are noteworthy, in order to achieve the goal of reaching the common man as well as to a particular community it is expected that the forthcoming technology on textile finishing process must be inexpensive. As a result of the enormous economic potential, besides scientists and researchers, businesses are also attracted to the unique and new properties of sol-gel materials.

    The entry is from 10.3390/ma13081838


    1. Schindler, W.D.; Hauser, P.J. Introduction to chemical finishing. In Chemical Finishing of Textiles; Woodhead Publishing Ltd.: Cambridge, UK, 2004; pp. 1–6.
    2. Schindler, W.D.; Hauser, P.J. Chemical finishing processes. In Chemical Finishing of Textiles; Woodhead Publishing Ltd.: Cambridge, UK, 2004; pp. 7–28.
    3. Hauser, P. Fabric Finishing: Pretreatment/Textile wet processing. In Textiles and Fashion; Woodhead Publishing Ltd.: Cambridge, UK, 2015; pp. 459–473.
    4. Richards, P.R. Fabric Finishing: Dyeing and Colouring. In Textiles and Fashion: Materials, Design and Technology; Elsevier: Cambridge, UK, 2014; pp. 475–505. ISBN 9780857095619.
    5. Periyasamy, A.P.; Venkatesan, H. Eco-Materials in Textile Finishing; Springer: Cham/Basel, Switzerland, 2019; Volume 3, ISBN 9783319682556.
    6. Periyasamy, A.P.; Ramamoorthy, S.K.; Lavate, S.S. Eco-Friendly Denim Processing; Springer: Cham/Basel, Switzerland, 2019; Volume 3, ISBN 9783319682556.
    7. Routte, H.K. Encyclopedia of Textile Finishing; Woodhead Publishing Limited: Cambridge, UK, 1995; ISBN 9781845690663.
    8. Schindler, W.D.; Hauser, P.J. Repellent finishes. In Chemical Finishing of Textiles; Woodhead Publishing Ltd.: Cambridge, UK, 2004; pp. 74–86.
    9. Shabbir, M.; Sheikh, J.N. Introduction to Textiles and Finishing Materials. In Frontiers of Textile Materials; Wiley: Hoboken, NJ, USA, 2020; pp. 1–11.
    10. Bashari, A.; Shakeri, M.; Shirvan, A.R.; Najafabadi, S.A.N. Functional Finishing of Textiles via Nanomaterials. In Nanomaterials in the Wet Processing of Textiles; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2018; pp. 1–70.
    11. Mittal, K.L.; Bahners, T. (Eds.) Textile Finishing; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2017; ISBN 9781119426790.
    12. Periyasamy, A.P.; Rwahwire, S.; Zhao, Y. Environmental Friendly Textile Processing. In Handbook of Ecomaterials; Springer: Cham/Basel, Switzerland, 2019; Volume 3, ISBN 9783319682556.
    13. Panitz, J.-C.; Geiger, F. Leaching of the Anthraquinone Dye Solvent Blue 59 Incorporated into Organically Modified Silica Xerogels. J. Sol Gel Sci. Technol. 1998, 13, 473–477.
    14. Hsu, W.P.; Yu, R.; Matijević, E. Well-defined colloidal pigments. ii: Monodispersed inorganic spherical particles containing organic dyes. Dyes Pigments 1992, 19, 179–201.
    15. Shibuichi, S.; Yamamoto, T.; Onda, T.; Tsujii, K. Super Water- and Oil-Repellent Surfaces Resulting from Fractal Structure. J. Colloid Interface Sci. 1998, 208, 287–294.
    16. Trepte, J.; Böttcher, H. Improvement in the Leaching Behavior of Dye-Doped Modified Silica Layers Coated onto Paper or Textiles. J. Sol Gel Sci. Technol. 2000, 19, 691–694.
    17. Mahltig, B.; Knittel, D.; Schollmeyer, E.; Böttcher, H. Incorporation of Triarylmethane Dyes into Sol-Gel Matrices Deposited on Textiles. J. Sol Gel Sci. Technol. 2004, 31, 293–297.
    18. Mahltig, B.; Haufe, H.; Böttcher, H. Functionalisation of textiles by inorganic sol–gel coatings. J. Mater. Chem. 2005, 15, 4385–4398.
    19. Mahltig, B.; Audenaert, F.; Böttcher, H. Hydrophobic silica sol coatings on textiles-the influence of solvent and sol concentration. J. Sol Gel Sci. Technol. 2005, 34, 103–109.
    20. Maghimaa, M.; Alharbi, S.A. Green synthesis of silver nanoparticles from Curcuma longa L. and coating on the cotton fabrics for antimicrobial applications and wound healing activity. J. Photochem. Photobiol. B Biol. 2020, 204, 111806.
    21. Mahltig, B.; Böttcher, H. Modified silica sol coatings for water-repellent textiles. J. Sol Gel Sci. Technol. 2003, 27, 43–52.
    22. Mahltig, B.; Fiedler, D.; Böttcher, H. Antimicrobial sol-gel coatings. J. Sol Gel Sci. Technol. 2004, 32, 219–222.
    23. Mahltig, B.; Textor, T. Silver containing sol-gel coatings on polyamide fabrics as antimicrobial finish-description of a technical application process for wash permanent antimicrobial effect. Fibers Polym. 2010, 11, 1152–1158.
    24. Dadvar, S.; Tavanai, H.; Dadvar, H.; Morshed, M.; Ghodsi, F.E. UV-protection and photocatalytic properties of electrospun polyacrylonitrile nanofibrous mats coated with TiO2 nanofilm via sol-gel. J. Sol Gel Sci. Technol. 2011, 59, 269–275.
    25. Mahltig, B.; Fiedler, D.; Simon, P. Silver-containing sol-gel coatings on textiles: Antimicrobial effect as a function of curing treatment. J. Text. Inst. 2011, 102, 739–745.
    26. Mahltig, B.; Fiedler, D.; Fischer, A.; Simon, P. Antimicrobial coatings on textiles-modification of sol-gel layers with organic and inorganic biocides. J. Sol Gel Sci. Technol. 2010, 55, 269–277.
    27. Vihodceva, S.; Kukle, S.; Muter, O. Antimicrobial Properties of the Modified Cotton Textiles by the Sol-Gel Technology. Adv. Mater. Res. 2015, 1117, 213–216.
    28. Ren, Y.; Zhang, Y.; Zhao, J.; Wang, X.; Zeng, Q.; Gu, Y. Phosphorus-doped organic-inorganic hybrid silicon coating for improving fire retardancy of polyacrylonitrile fabric. J. Sol Gel Sci. Technol. 2017.
    29. Rivero, P.J.; Goicoechea, J. Sol-gel technology for antimicrobial textiles. In Antimicrobial Textiles; Sun, G., Ed.; Woodhead Publishing: Sawston, UK, 2016; pp. 47–72. ISBN 9780081005859.
    30. Trovato, V.; Teblum, E.; Kostikov, Y.; Pedrana, A.; Re, V.; Nessim, G.D.; Rosace, G. Sol-gel approach to incorporate millimeter-long carbon nanotubes into fabrics for the development of electrical-conductive textiles. Mater. Chem. Phys. 2020, 240, 122218.
    31. Mahltig, B.; Grethe, T.; Haase, H. Antimicrobial coatings obtained by sol-gel method. In Handbook of Sol-Gel Science and Technology: Processing, Characterization and Applications; Klein, L., Aparicio, M., Jitianu, A., Eds.; Springer: Cham, Switzerland, 2018; pp. 3461–3487. ISBN 9783319321011.
    32. Plutino, M.R.; Colleoni, C.; Donelli, I.; Freddi, G.; Guido, E.; Maschi, O.; Mezzi, A.; Rosace, G. Sol-gel 3-glycidoxypropyltriethoxysilane finishing on different fabrics: The role of precursor concentration and catalyst on the textile performances and cytotoxic activity. J. Colloid Interface Sci. 2017, 506, 504–517.
    33. Shen, K.; Yu, M.; Li, Q.; Sun, W.; Zhang, X.; Quan, M.; Liu, Z.; Shi, S.; Gong, Y. Synthesis of a fluorine-free polymeric water-repellent agent for creation of superhydrophobic fabrics. Appl. Surf. Sci. 2017, 426, 694–703.
    34. Yang, M.; Liu, W.; Jiang, C.; He, S.; Xie, Y.; Wang, Z. Fabrication of superhydrophobic cotton fabric with fluorinated TiO2 sol by a green and one-step sol-gel process. Carbohydr. Polym. 2018, 197, 75–82.
    35. Yu, M.; Li, P.; Feng, Y.; Li, Q.; Sun, W.; Quan, M.; Liu, Z.; Sun, J.; Shi, S.; Gong, Y. Positive effect of polymeric silane-based water repellent agents on the durability of superhydrophobic fabrics. Appl. Surf. Sci. 2018, 450, 492–501.
    36. Zhou, H.; Zhao, Y.; Wang, H.; Lin, T. Recent Development in Durable Super-Liquid-Repellent Fabrics. Adv. Mater. Interfaces 2016, 3, 1600402.
    37. Zahid, M.; Mazzon, G.; Athanassiou, A.; Bayer, I.S. Environmentally benign non-wettable textile treatments: A review of recent state-of-the-art. Adv. Colloid Interface Sci. 2019, 270, 216–250.
    38. Textor, T.; Mahltig, B. A sol-gel based surface treatment for preparation of water repellent antistatic textiles. Appl. Surf. Sci. 2010, 256, 1668–1674.
    39. Pan, C.; Shen, L.; Shang, S.; Xing, Y. Preparation of superhydrophobic and UV blocking cotton fabric via sol-gel method and self-assembly. Appl. Surf. Sci. 2012.
    40. Zhao, Q.; Wu, L.Y.L.; Huang, H.; Liu, Y. Ambient-curable superhydrophobic fabric coating prepared by water-based non-fluorinated formulation. Mater. Des. 2016.
    41. Zhang, J.; Li, B.; Wu, L.; Wang, A. Facile preparation of durable and robust superhydrophobic textiles by dip coating in nanocomposite solution of organosilanes. Chem. Commun. 2013.
    42. Xue, C.H.; Li, M.; Guo, X.J.; Li, X.; An, Q.F.; Jia, S.T. Fabrication of superhydrophobic textiles with high water pressure resistance. Surf. Coatings Technol. 2017.
    43. Teli, M.D.; Annaldewar, B.N. Superhydrophobic and ultraviolet protective nylon fabrics by modified nano silica coating. J. Text. Inst. 2017.
    44. Xue, C.H.; Jia, S.T.; Chen, H.Z.; Wang, M. Superhydrophobic cotton fabrics prepared by sol-gel coating of TiO2 and surface hydrophobization. Sci. Technol. Adv. Mater. 2008.
    45. Gao, X.; Wen, G.; Guo, Z. Durable superhydrophobic and underwater superoleophobic cotton fabrics growing zinc oxide nanoarrays for application in separation of heavy/light oil and water mixtures as need. Colloids Surf. A Physicochem. Eng. Asp. 2018, 559, 115–126.
    46. Cao, N.; Lyu, Q.; Li, J.; Wang, Y.; Yang, B.; Szunerits, S.; Boukherroub, R. Facile synthesis of fluorinated polydopamine/chitosan/reduced graphene oxide composite aerogel for efficient oil/water separation. Chem. Eng. J. 2017, 326, 17–28.
    47. Lei, S.; Shi, Z.; Ou, J.; Wang, F.; Xue, M.; Li, W.; Qiao, G.; Guan, X.; Zhang, J. Durable superhydrophobic cotton fabric for oil/water separation. Colloids Surf. A Physicochem. Eng. Asp. 2017, 533, 249–254.
    48. Li, K.; Zeng, X.; Li, H.; Lai, X.; Xie, H. Facile fabrication of superhydrophobic filtration fabric with honeycomb structures for the separation of water and oil. Mater. Lett. 2014, 120, 255–258.
    49. Zhu, X.; Tu, W.; Wee, K.-H.; Bai, R. Effective and low fouling oil/water separation by a novel hollow fiber membrane with both hydrophilic and oleophobic surface properties. J. Memb. Sci. 2014, 466, 36–44.
    50. Cheng, Q.-Y.; Zhao, X.-L.; Li, Y.-D.; Weng, Y.-X.; Zeng, J.-B. Robust and nanoparticle-free superhydrophobic cotton fabric fabricated from all biological resources for oil/water separation. Int. J. Biol. Macromol. 2019, 140, 1175–1182.
    51. Yan, L.; Li, J.; Li, W.; Zha, F.; Feng, H.; Hu, D. A photo-induced ZnO coated mesh for on-demand oil/water separation based on switchable wettability. Mater. Lett. 2016, 163, 247–249.
    52. Shang, Q.; Liu, C.; Zhou, Y. One-pot fabrication of robust hydrophobia and superoleophilic cotton fabrics for effective oil-water separation. J. Coat. Technol. Res. 2018, 15, 65–75.
    53. Stolz, A.; Le Floch, S.; Reinert, L.; Ramos, S.M.M.; Tuaillon-Combes, J.; Soneda, Y.; Chaudet, P.; Baillis, D.; Blanchard, N.; Duclaux, L.; et al. Melamine-derived carbon sponges for oil-water separation. Carbon N. Y. 2016, 107, 198–208.
    54. Liang, S.; Neisius, N.M.; Gaan, S. Recent developments in flame retardant polymeric coatings. Prog. Org. Coat. 2013, 76, 1642–1665.
    55. Colleoni, C.; Donelli, I.; Freddi, G.; Guido, E.; Migani, V.; Rosace, G. A novel sol-gel multi-layer approach for cotton fabric finishing by tetraethoxysilane precursor. Surf. Coat. Technol. 2013, 235, 192–203.
    56. Guido, E.; Alongi, J.; Colleoni, C.; Di Blasio, A.; Carosio, F.; Verelst, M.; Malucelli, G.; Rosace, G. Thermal stability and flame retardancy of polyester fabrics sol-gel treated in the presence of boehmite nanoparticles. Polym. Degrad. Stab. 2013, 98, 1609–1616.
    57. Alongi, J.; Ciobanu, M.; Malucelli, G. Sol-gel treatments on cotton fabrics for improving thermal and flame stability: Effect of the structure of the alkoxysilane precursor. Carbohydr. Polym. 2012, 87, 627–635.
    58. Alongi, J.; Ciobanu, M.; Malucelli, G. Thermal stability, flame retardancy and mechanical properties of cotton fabrics treated with inorganic coatings synthesized through sol–gel processes. Carbohydr. Polym. 2012, 87, 2093–2099.
    59. Selvakumar, N.; Azhagurajan, A.; Natarajan, T.S.; Mohideen Abdul Khadir, M. Flame-retardant fabric systems based on electrospun polyamide/boric acid nanocomposite fibers. J. Appl. Polym. Sci. 2012, 126, 614–619.
    60. Alongi, J.; Ciobanu, M.; Tata, J.; Carosio, F.; Malucelli, G. Thermal stability and flame retardancy of polyester, cotton, and relative blend textile fabrics subjected to sol–gel treatments. J. Appl. Polym. Sci. 2011, 119, 1961–1969.
    61. Jiang, Z.; Wang, C.; Fang, S.; Ji, P.; Wang, H.; Ji, C. Durable flame-retardant and antidroplet finishing of polyester fabrics with flexible polysiloxane and phytic acid through layer-by-layer assembly and sol-gel process. J. Appl. Polym. Sci. 2018, 135, 46414.
    62. Horrocks, A.R. Flame Retardant Textile Finishes. In Textile Finishing: Recent Developments and Future Trends; Wiley: Hoboken, NJ, USA, 2017; pp. 69–127.
    63. Zhang, D.; Williams, B.L.; Shrestha, S.B.; Nasir, Z.; Becher, E.M.; Lofink, B.J.; Santos, V.H.; Patel, H.; Peng, X.; Sun, L. Flame retardant and hydrophobic coatings on cotton fabrics via sol-gel and self-assembly techniques. J. Colloid Interface Sci. 2017, 505, 892–899.
    64. Ouadil, B.; Amadine, O.; Essamlali, Y.; Cherkaoui, O.; Zahouily, M. A new route for the preparation of hydrophobic and antibacterial textiles fabrics using Ag-loaded graphene nanocomposite. Colloids Surf. A Physicochem. Eng. Asp. 2019, 579, 123713.
    65. Kowalczyk, D.; Brzeziński, S.; Kamińska, I. Multifunctional bioactive and improving the performance durability nanocoatings for finishing PET/CO woven fabrics by the sol-gel method. J. Alloys Compd. 2015, 649, 387–393.
    66. Foksowicz-Flaczyk, J.; Walentowska, J.; Przybylak, M.; Maciejewski, H. Multifunctional durable properties of textile materials modified by biocidal agents in the sol-gel process. Surf. Coat. Technol. 2016, 304, 160–166.
    67. Malucelli, G. Sol-Gel Flame Retardant and/or Antimicrobial Finishings for Cellulosic Textiles. In Handbook of Renewable Materials for Coloration and Finishing; Scrivener Publishing: Beverly, MA, USA, 2018; pp. 501–519.
    68. Vasiljević, J.; Tomšič, B.; Jerman, I.; Orel, B.; Jakša, G.; Kovač, J.; Simončič, B. Multifunctional superhydrophobic/oleophobic and flame-retardant cellulose fibres with improved ice-releasing properties and passive antibacterial activity prepared via the sol-gel method. J. Sol Gel Sci. Technol. 2014, 70, 385–399.
    69. Vihodceva, S.; Kukle, S. Improvement of UV Protection Properties of the Textile from Natural Fibres by the Sol-gel Method. IOP Conf. Ser. Mater. Sci. Eng. 2013, 49, 12022.
    70. Paul, R.; Bautista, L.; De la Varga, M.; Botet, J.M.; Casals, E.; Puntes, V.; Marsal, F. Nano-cotton Fabrics with High Ultraviolet Protection. Text. Res. J. 2009, 80, 454–462.
    71. Mishra, A.; Butola, B.S. Development of Cotton Fabrics with Durable UV Protective and Self-cleaning Property by Deposition of Low TiO2 Levels through Sol-gel Process. Photochem. Photobiol. 2018, 94, 503–511.
    72. Jhatial, A.K.; Khatri, A.; Ali, S.; Babar, A.A. Sol-gel finishing of bamboo fabric with nanoparticles for water repellency, soil release and UV resistant characteristics. Cellulose 2019, 26, 6365–6378.
    73. Jang, I.; Leong, H.J.; Noh, H.; Kang, T.; Kong, S.; Oh, S.G. Preparation of N-functionalized TiO2 particles using one-step sol-gel method and their photocatalytic activity. J. Ind. Eng. Chem. 2016, 37, 380–389.
    74. Liang, H.; Liu, K.; Ni, Y. Synthesis of mesoporous α-Fe2O3 via sol-gel methods using cellulose nano-crystals (CNC) as template and its photo-catalytic properties. Mater. Lett. 2015, 159, 218–220.
    75. Brzeziński, S.; Kowalczyk, D.; Borak, B.; Jasiorski, M.; Tracz, A. Nanocoat finishing of polyester/cotton fabrics by the sol-gel method to improve their wear resistance. Fibres Text. East. Eur. 2011, 6, 83–88.
    76. Pierre, A.C. General Introduction. In Introduction to Sol-Gel Processing; Pierre, A.C., Ed.; Springer: Boston, MA, USA, 1998; pp. 1–9. ISBN 978-1-4615-5659-6.
    77. Sakka, S.; Kamiya, K. The sol-gel transition in the hydrolysis of metal alkoxides in relation to the formation of glass fibers and films. J. Non. Cryst. Solids 1982, 48, 31–46.
    78. Ye, C.-Q. Sol-Gel Processes of Functional Powders and Films. In Chemical Reactions in Inorganic Chemistry; InTech: London, UK, 2018.
    79. Dislich, H.; Hinz, P. History and principles of the sol-gel process, and some new multicomponent oxide coatings. J. Non.-Cryst. Solids 1982, 48, 11–16.
    80. Danks, A.E.; Hall, S.R.; Schnepp, Z. The evolution of ‘sol–gel’ chemistry as a technique for materials synthesis. Mater. Horizons 2016, 3, 91–112.
    81. Zarzycki, J. Gel→glass transformation. J. Non.-Cryst. Solids 1982, 48, 105–116.
    82. Pierre, A.C. Gelation. In Introduction to Sol-Gel Processing; Pierre, A.C., Ed.; Springer: Boston, MA, USA, 1998; pp. 169–204. ISBN 978-1-4615-5659-6.
    83. Pierre, A.C. The Chemistry of Precursors Solutions. In Introduction to Sol-Gel Processing; Pierre, A.C., Ed.; Springer: Boston, MA, USA, 1998; pp. 11–89. ISBN 978-1-4615-5659-6.
    84. Kursawe, M.; Hilarius, V.; Pfaff, G.; Anselmann, R. Sol-gel Coating Processes. In Modern Surface Technology; John Wiley & Sons: Hoboken, NJ, USA, 2006; pp. 205–220. ISBN 3527315322.
    85. Baccile, N.; Babonneau, F.; Thomas, B.; Coradin, T. Introducing ecodesign in silica sol-gel materials. J. Mater. Chem. 2009, 19, 8537–8559.
    86. Dislich, H. New Routes to Multicomponent Oxide Glasses. Angew. Chem. Int. Ed. Engl. 1971.
    87. Klein, L.C.; Garvey, G.J. Monolithic dried gels. J. Non.-Cryst. Solids 1982, 48, 97–104.
    88. Kordas, G. Sol-gel processing of ceramic superconductors. J. Non.-Cryst. Solids 1990, 121, 436–442.
    89. Vincenzini, P. High Performance Ceramic Films and Coatings; North-Holland Publishing, Co.: Amsterdam, The Netherlands, 1991; ISBN 978-0444890580.
    90. Kim, H.K.; Kang, S.-J.; Choi, S.-K.; Min, Y.-H.; Yoon, C.-S. Highly Efficient Organic/Inorganic Hybrid Nonlinear Optic Materials via Sol-Gel Process: Synthesis, Optical Properties, and Photobleaching for Channel Waveguides. Chem. Mater. 1999, 11, 779–788.
    91. Owens, G.J.; Singh, R.K.; Foroutan, F.; Alqaysi, M.; Han, C.-M.; Mahapatra, C.; Kim, H.-W.; Knowles, J.C. Sol-gel based materials for biomedical applications. Prog. Mater. Sci. 2016, 77, 1–79.
    92. Avnir, D.; Braun, S.; Lev, O.; Ottolenghi, M. Enzymes and Other Proteins Entrapped in Sol-Gel Materials. Chem. Mater. 1994, 6, 1605–1614.
    93. Inayat, A.; Reinhardt, B.; Herwig, J.; Küster, C.; Uhlig, H.; Krenkel, S.; Raedlein, E.; Enke, D. Recent advances in the synthesis of hierarchically porous silica materials on the basis of porous glasses. New J. Chem. 2016, 40, 4095–4114.
    94. Feinle, A.; Elsaesser, M.S.; Hüsing, N. Sol-gel synthesis of monolithic materials with hierarchical porosity. Chem. Soc. Rev. 2016, 45, 3377–3399.
    95. Livage, J. Inorganic Materials, Sol-Gel Synthesis of. In Encyclopedia of Materials: Science and Technology; Buschow, K.H.J., Cahn, R.W., Flemings, M.C., Ilschner, B., Kramer, E.J., Mahajan, S., Veyssière, P.B., Eds.; Elsevier: Oxford, UK, 2001; pp. 4105–4107. ISBN 978-0-08-043152-9.
    96. Handbook of sol-gel science and technology: Processing, characterization, and applications. Choice Rev. Online 2013.
    97. Hench, L.L.; West, J.K. The Sol-Gel Process. Chem. Rev. 1990.
    98. Brinker, C.J.; Frye, G.C.; Hurd, A.J.; Ashley, C.S. Fundamentals of sol-gel dip coating. Thin Solid Films 1991, 201, 97–108.
    99. Brinker, C.J.; Scherer, G.W. Particulate Sols and Gels. In Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing; Elsevier: Amsterdam, The Netherlands, 1990; ISBN 9780080571034.