*3.1.6 Surface modified NPs*

Although, the addition of the NPs into polymer matrix by simple blending method offers superior advantageous in terms of rejection, antifouling, and permeability, the tendency of NPs to agglomeration due to high surface free energy and high affinity to water molecules during phase separation on one hand, and the possibly release of NPs into filtrate due to weak interactions between NPs and polymer chains on the other hand, makes surface modification of NPs mandatory to obtain a hybrid membrane with well dispersed, stable, and compatable NPs. Modifications are based on either chemical treatment of NPs or grafting of functional polymers on hydroxyl groups available in NPs. Oxidation, for example, could be the desired pathway through acid treatment to create carboxyl and hydroxyl functional groups on carbon nanotubes. Different surfactants have also been proposed to be grafted on NPs surfaces to mitigate the agglomeration and their mechanisms have been reviewed detailed in the literature [87]. Besides the improvement of homogenous dispersivity, stability, and compatibility, the functionalization of NPs increases the membrane antifouling property as they offer higher surface charge density, which is useful for the rejection of the foulants. Ayyaru and Ahn studied with the PES nanocomposite membranes blended with surface modified TiO2 NPs (anatase, 20–25 nm in size) for fouling mitigation [88]. The TiO2 nanoparticles were sulfonated by replacing the surface hydroxyl groups with –SO3H group and the loading effect of sTiO2 NPs was investigated. Surface roughness, porosity, and pore size of the modified membranes exhibited notable enhancement compared to the PES membrane. Increasing porosity revealed a good distribution of sTiO2 NPs in the dope solution. The improved properties of sTiO2 blended membranes such as high hydrophilicity permeability, anti-fouling performance, and improved BSA rejection were attributed


#### *Promising Techniques for Wastewater Treatment and Water Quality Assessment*


*Filtration performances and physical characteristics of the hybrid membranes prepared by blending method.*
