**4. Recent development of novel membranes for desalination**

In commercial RO membranes, almost the majority of materials that are used are dominated by thin-film composite (TFC) polyamide and its derivatives. At these membranes, we are faced with critical challenges like relatively low water permeability, high fouling tendency and low selectivity [39]. For example, in commercial TFC RO membranes the typical water permeability for seawater reverse osmosis (SWRO) and brackish water reverse osmosis (BWRO) is range from <sup>1</sup>2Lm<sup>2</sup> <sup>h</sup><sup>1</sup> bar<sup>1</sup> and <sup>2</sup>–8Lm<sup>2</sup> <sup>h</sup><sup>1</sup> bar<sup>1</sup> , respectively [40]. One of the fields in desalination that is been focus on it, is synthesizing novel membranes with better antifouling performance and improved separation properties.

Much of the exciting progresses are fueled by the recent emergence of promising novel materials for desalination. Among them, the most notable examples include aquaporin (AQP) proteins [11, 41, 42] and some carbon-based materials such as carbon nanotubes (CNTs) [43] and graphene-based materials [44]. At the moment, in RO membranes, the old asymmetric cellulose acetate largely replaced with TFC polyamide membranes [45, 46]. New TFC polyamide membranes compared to the former membranes, have been shown better performance in water permeability and salt rejection (e.g., in SWRO rejection of NaCl is >99.9%), pH tolerance (1–11) and wider operating temperature range (0–45°C) [11].

#### **4.1 Novel materials and methods for synthesizing desalination membranes**

## *4.1.1 Carbon-based materials*

Because of exceptional water transport properties of Carbon based materials (CBMs), e.g., nanoporous graphene (NPG) [47, 48], carbon nanotubes (CNTs) [49, 50], and graphene oxide (GO) [11, 51] have been raised hopes of improvement in the membrane processes (**Tables 5** and **6**). In these materials, the characteristic of water channel dimensions as well as chemical modifications (e.g., the presence of carboxyl, amine and other groups) determines the rejection properties [11, 56, 75]. The characteristic of the channel dimensions in NPG and CNTs are sorted by their respective pore sizes [51]. In CNTs and NPG, the channel sizes determined by their synthesis conditions, but, in GO the characteristic channel size is highly dependent


**Table 5.** *Material properties of polyamide,*

 *AqpZ, CNT, NPG and graphene oxide [11].*
