The rising burden on the issue of water scarcity necessitates a cost-effective, efficient water treatment technology in order to provide high-quality clean water and meet global water demand. Membrane distillation (MD) is a relatively new alternative separation method that may be utilized for desalination. This technology is promising to replace currently dominating pressure driven membranes-based desalination methods. However, most of current studies aim at improving the MD membrane in terms of cost, durability and salt rejection. This work attempts to address some of the bottlenecks concerning the commercialization of these membranes in the desalination industry by focusing on the utilization of cheap raw materials for the synthesis of nanoparticles and the membrane. Functionalized Carbon Nanotubes (f-CNTs) were derived from local waste biomass and utilized as an additive to improve the efficacy of the membrane used in an MD unit configuration. Local waste date palm stems (Phoenix dactylifera) were used to prepare activated carbon (AC) using KOH and two metal chloride salts (NaCl and ZnCl2) as activation agents. The carbonization was conducted at 600 oC for 2hr under nitrogen flow, followed by activation at 750 oC for 2 hr under carbon dioxide gas flow. AC was characterized using a scanning electron microscope (SEM), Attenuated total reflectance Fourier transform infrared (ATR FT-IR), Thermogravimetric analysis (TGA). In addition, surface morphology was characterized by Iodine adsorption and Brunauer-Emmett-Teller (BET), at different carbon-to-activation-agent-ratios. FTIR spectra results showed a reduction in AC-NaCl bands compared to other AC, which indicates less functional surface groups. At 750 oC, the TGA analysis showed that carbon yield as AC-ZnCl2 > AC-NaCl > AC-KOH. However, among all samples, AC NaCl at 1:2 ratio was the best in terms of iodine removal. This treated AC sample exhibited about 18.3 % maximum iodine removal, which indicates the high surface area and porosity with 550.44 m2 /g, 348.74 m2 /g, and 201.69 m2 /g BET, micropores and mesopores surface areas, respectively. In conclusion, the local Omani date palm waste stems can be used for AC production with a well porous structure using cheap and environmentally friendly salts as activation agents. Furthermore, the produced AC attained better adsorption characteristics among other alternatives. The current work addresses the utilization of AC as a supporting substrate combined with NaCl as a novel green catalyst for the synthesis of carbon nanotubes (CNTs) via a catalyzed chemical vapor deposition (cCVD) method. The effect of different AC NaCl ratios on CNT growth was investigated. The nano-particle yield was estimated and samples were characterized by BET, Electron microscopy (SEM and TEM), XRD, FTIR, and TGA analyses. The asymmetrical porous structure and high surface area of the AC clearly offer excellent uniform NaCl dispersion properties on the surface, resulting in a high catalyst-transition metal free-yield of CNTs forest growth. The results showed higher mass yield in the order AC-NaCl 1:2 > AC-NaCl 1:1 > AC NaCl 1:3 ratios. AC and NaCl are excellent choices as substrate and catalyst combinations for the synthesis of metal-free MWCNTs as they are cost-effective and environmentally friendly. Acid functionalization was conducted using an acid mixture of H2SO4:HNO3 at different volume ratios to improve the CNTs dispersity and to eliminate contaminants from their surfaces. Functionalized carbon nanotubes (f-CNTs) were then employed to prepare composite membranes for saline water desalination via direct contact membrane distillation (DCMD). Different f-CNT loadings were tested. All produced membranes were subjected to various characterization tests including porosity, SEM, ATR-FTIR, TGA, Contact Angle (CA) and Tensile strength tests. The results showed that the inclusion of f-CNT structure could improve hydrophilicity, porosity, thermal stability, and mechanical strength of the composite membranes. The DCMD process was also improved using f-CNTs compared to other membranes as the f-CNTs offered additional pathways for water vapor transport. In the DCMD experiments, the highest permeate flux reached was 19.6 kg/m2 .hr and > 99% salt rejection at 80 oC feed and 20 oC permeate temperature. This was achieved with 78.8o contact angle, 56% porosity and thermal stability higher by more that to 11 °C compared to pristine PVDF. Overall, the results show that PVDF-f-CNTs membranes offer a potential and encouraging alternative to existing membranes. Central composite design (CCD) was applied to analyze and optimize the performance of PVDF-f-CNT 0.03% membrane. CCD is the most common design used in response surface method (RSM). The MD performance was modeled using the quadratic regression model as a function of the operating conditions (feed temperature, flow rate and concentration) was studied. Feed temperature had higher x impact on vapor flux for DCMD compared with the other variables as it was the most significant factor (p-value < 0.05) followed by feed flow rate (p-value =0.0830). On the other hand, feed concentration had the least effect on the flux (p-value =0.1683). Increasing feed temperature improves the evaporation rate in the feed side which consequently creates higher vapor pressure difference, therefore, improving MD flux. Optimization of operating conditions was conducted to maximize permeate flux within the range. A desirability of 0.776 was achieved at a feed temperature of 80 oC, feed flow rate of 75mL/min and 0.4 M feed concentration in which a flux of 19.472 kg/m2 .hr was obtained. Another optimization study was conducted at wider ranges and maximum flux of 31.078 kg/m2 .hr could be found at 90 oC feed temperature, 80mL/min flow and 0.4 M NaCl feed concentration. A permeate flux of 29.7 kg/m2 .hr was achieved by the validation experiments, which indicates the reasonable accuracy of the predicting model. The inclusion of waste-biomass-based carboxylated CNTs increased the MD process performance by enhancing the interactions between water and the membrane and boosting vapor permeability while preventing liquid from penetrating the membrane pores. This work contributes in paving the way for enhancing the MD process performance and promoting its commercial application potential.