**4. Conclusion and outlook**

[100] owing to its exceptional optical properties, nontoxicity, low cost, and high stability toward photo and chemical corrosion [101]. However, the major limitation of some of the metal oxide– based photocatalyst materials for potential applications includes the fast recombination of the charge carriers due to the low quantum yield and wide band gap limitation in harvesting a wider portion of the solar energy [102]. Hence, the design of metal oxide–based photocatalyst materials for the degradation of contaminants, which are of high photostability, visible light active, and photoactivity are of considerable interest to provide a fundamental insight into the underlying mechanism of photocatalysis as well as designing a more efficient and easily tunable metal oxide–based photocatalyst materials. To address these restrictions, metal oxides are normally immobilized with polymers. The incorporation of metal oxide into a polymeric material with appropriate energy levels enhances the charge migration between the inorganic metal oxide and polymer to reduce the recombination of the charge carriers [103]. Recently, nanocomposites of several conductive polymers and metal oxide nanoparticles have been fabricated with improved photocatalytic responses in the visible region. Polymeric materials are currently been applied in water treatment due to their pore size distribution, perfect mechanical rigidity, tunable, and large surface area [104]. For example, some organic nanofiber membranes, such as cellulose, polyacrylonitrile, polyvinylpyrrolidone, polytetrafluoroethylene, and polyvinyl acetate are considered as an excellent catalyst supports owing to their high porosity, high permeability, large surface area and good flexibility [105]. The improvements in the fabrication approach employed for designing materials, the characterization and computational techniques have facilitated the fine-tuning of compositional and structural characteristics of materials. The

novel porous polytetrafluoroethylene nanofiber membrane with Fe<sup>2</sup>

ciency of >99% after 80 min. TiO<sup>2</sup>

186 Descriptive Inorganic Chemistry Researches of Metal Compounds

polysulfone/carbon-covered alumina/TiO<sup>2</sup>

polyaniline-TiO<sup>2</sup>

a three-step method [105]. Under simulated UV light irradiation, the porous nanocomposite displayed superior photocatalytic degradation toward Acid Red dye with a degradation effi-

superb photocatalytic performance toward pollutants degradation [106]. The photocatalytic performance of a transition metal coordination polymer(TMCP)/polyoxometalate nanocomposite was enhanced by immobilizing polypyrrole into the TMCP surface *via* a superficial *in situ* chemical oxidation polymerization method [107]. Under simulated visible light irradiation, the as-prepared nanocomposite displayed better photocatalytic performance toward the degradation of Rhodamine B (RhB) dye. Transition metal ions were incorporated into TiO<sup>2</sup>

fly-ash cenospheres with poly(o-phenylenediamine) through ion imprinting technology [108]. The results demonstrated that the as-prepared nanocomposite effectively photodegrades the tetracycline with a photodegradation rate of 71.7%. A silica nanohybrid with different Ru(II) polypyridyl nanocomposites exhibited improved photocatalytic degradation with respect to Rhodamine 6G dye compared to the functionalized silica nanohybrid [109]. Hydrothermal and electrospinning route was used to prepare polyvinylidene fluoride/titanium dioxide nanocomposite with different compositions of anatase, brookite, and rutile and the nanocomposite displayed a relatively high photocatalytic degradation toward phenol [110]. The two types of

activity toward RhB dye under visible light irradiation was tested [111]. The results displayed that the nanocomposite without a fabric membrane degraded 78.7% of RhB, while the nanocomposite with fabric membrane degraded 82.4% of RhB after 300 min. Polysulfone-based

with a hollow fiber membrane was synthesized through a dry-wet spinning

O3

membranes were successfully prepared and their

/polypropylene nanocomposite has been reported to show

was prepared through

/

Metal oxide polymer nanocomposites offer great prospects to revolutionize water treatment owing to their unique properties. In this chapter, we have comprehensively reviewed the various synthesis and characterization technique of nanomaterials, unique properties of nanocomposites and progress in water treatment using polymer/inorganic metal oxide nanocomposites. The fundamentals and unique features of metal oxide, as well as the underlying mechanism of the visible light response metal oxide–based photocatalyst, have been deliberated. The polymer/inorganic metal oxide nanocomposite has been extensively used for the photodegradation of pollutants, ion exchanger, adsorbent, membrane, and photocatalytic disinfection in water treatment. For instance, polymer-based nanocomposites have several intrinsic importance such as high mechanical strength, long-term stability, and low-cost fabrication process, while the inorganic metal oxide possesses superior optical, electronic, magnetic, and catalytic properties. Thus, the hybridization of polymers and metal oxide could enhance several properties of the resultant nanocomposites. In conclusion, the polymer/metal oxide nanocomposite reviewed in this book chapter possesses superior photodegradation activity toward pollutants under simulated light irradiation owing to the large expose area of the nanocomposite, effective migration and separation of charge carriers as well as the strong electrostatic interaction between the catalyst and the pollutants. Moreover, the nanocomposite, exhibit high antibacterial activity, strong affinity toward ions owing to the strong electrostatic interactions between the positively charged ions of the inorganic metal oxide and the lone pair of the organic polymers, excellent regeneration, and adsorption performances, better antifouling property, excellent hydrophilicity due to porosity, larger surface pore size, less microvoids as well as good ion-exchange capacity. Though this book chapter is not a comprehensive, but can give a basic idea about polymer nanocomposites in the various water treatment approaches.

Though considerable development in water treatment using metal oxide and polymer nanocomposite has been accomplished, studies in this area are still at the primary stage and additional advancement is essential. The design and fabrication of materials for water treatment process, particular visible light-response polymer/metal oxide–based photocatalyst materials are significant, but several reports briefly consider only the technical hurdles, high operating cost, and environmental risks. In future, to enhance the practicability of visible light response polymer/metal oxide–based photocatalyst materials in water treatment, several key issues, such as improving the photostability and efficiency of the photocatalyst materials need to be addressed. Moreover, the usage of photocatalytic materials in the photodegradation of pollutants is still a major issue considering the degradation and dissolution of the pollutants, which can hinder their photocatalytic performances. Hence, care should be taken when designing a functional polymer/metal oxide–based material with suitable physicochemical properties. Developing a suitable immobilization approach with cost-effective solid-liquid separation is also important. Currently, an exhausting catalyst during the photocatalysis process will endanger the regeneration of the catalysts and impacts severe effects on the environment as a result of catalysts outflow. To acquire an improved photodegradation efficiency, incorporating different techniques is essential. The accumulation of an enormous amount of theoretical study is also significant to prove an in-depth understanding of the preparation, performances, optimisation, and properties of polymer/metal oxide–based photocatalysts for water treatment.
