## 1 Introduction
MD technologies include DCMD (Direct Contact Membrane Distillation) [26], where the membrane on the permeate side and the liquid on the cold side are in direct contact; AGMD (Air Gap Membrane Distillation) [27; 28], where, on the permeate side, the air gap serves as a condensing surface; SGMD (Sweeping Gas Membrane Distillation), wherein the evaporation of less volatile molecules is aided when the gas is driven through a gap on the permeable side; and VMD (Vacuum Membrane Distillation), where vacuum has an impact on the gap channel's structure [29], owing to DCMD's lack of a need for an additional condenser, which has led to it attracting increasing amounts of attention for being better suited to water applications. In terms of MD configuration, DCMD is the most straightforward method as high-permeate flux can be obtained under simple operating circumstances despite the fact that DCMD has a low thermal efficiency, and a low effective drive due to evaporator proximity to condenser surface [30]. AGMD has high heat utilization efficiency and a low permeate flux. Additionally, SGMD has remarkable thermal efficiency; however, achieving a high permeate flux demands a large flow rate of swept gas. VMD has a greater permeate flux and thermal efficiency. As with the DCMD, by raising the temperature of the feed and flow rate, the VMD's efficiency can be enhanced. However, the VMD setup process is quite complex, mainly due to the need for vacuum and an external condenser [31; 32]. This is a serious flaw in VMD; because of this drawback, one of the least researched desalination MD configurations is VMD. In addition, compared to DCMD, a higher productivity at cooler temperatures is not constantly ensured by the VMD's configuration complexity. Because of its simple structure, DCMD can be used at low temperatures and its permeate flux is superior to that of VMD [33]. VMD only has advantages when temperatures or flow rates are higher. In addition, unlike DCMD, VMD does not directly control the permeate-side temperature, and vacuum pressure can also only be realized using vacuum pumps. In VMD, due to the application of vacuum, membrane surfaces may also show significant high-pressure changes; ultimately, the membrane may be wetted or become less hydrophobic. Therefore, DCMD is the most suitable choice for desalination research. In the DCMD, on both surfaces of the hydrophobic membrane, the liquid flows with various temperatures [34; 35]. As seen in Figure 1, the liquid is in direct contact with the hydrophobic membrane. Liquid on the feed side does not flow across the membrane surface. The driving force is the disparity in vapor pressure brought on by the temperature disparity, causing the volatile substances in the hot solution on the feed side to undergo a phase transition. The gas phase volatile components enter the permeate side through the membrane pores, and the low temperature solution on the permeate side then condenses the gas phase volatile components passed through the membrane pores to dissolve them in the receiving solution [36]. Membrane material selection is an important factor in determining DCMD efficiency. Since the variety of DCMD uses, examples include the treatment of factory water, the ground, the ocean, sewage, retrieved water, toxic water, condensation water, and furnace effluent. The total achievement of DCMD processes depends more and more on membranes [37]. Therefore, according to the goal contaminants present in particular uses, the most suitable hydrophobic membrane should be selected accordingly. The most suitable membranes for MD uses include low surface energy, a high degree of porosity (small average size of pore, narrow size of pores spread), and low thermal conductivity. This is because the lower the thermal conductivity of the MD membrane, the less heat can be lost through the membrane. It is helpful to select appropriate membranes to increase the permeate flux. In their investigation of various membranes, [PERSON] et al.