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In this work, titanium dioxide nanotubes (TNTs) were first synthesized via hydrothermal method at 110 °C. To reduce hydrophilicity, the synthesized TNTs were annealed at 350 °C and then aged in air at ambient temperature. Subsequently, polyvinylidene fluoride (PVDF) mixed matrix membranes (MMMs) containing the modified TNTs were prepared by phase inversion method. Performance of the prepared PVDF/TNTs MMMs was evaluated in vacuum membrane distillation (VMD) process. Effects of polymer concentration and content of the modified TNTs on the fabricated membrane performance in the VMD process were investigated. Hydrophilicity reduction of the synthesized TNTs after annealing and aging was confirmed by FTIR analysis. It was found that the modified TNTs with partial hydrophilicity could improve the VMD performance of the fabricated MMMs. The results showed that the modified TNTs improve the membrane porosity, finger-like cavities, thermal and mechanical properties without having a significant negative effect on the hydrophobicity of the PVDF membrane. Compared to the neat PVDF membrane, water flux and salt rejection of the MMM containing 2 wt% of the modified TNTs were improved by 38.7% and 47.0%, respectively. Response surface methodology (RSM) was used to study the effects of operating parameters of VMD process such as feed flow rate, feed temperature and feed concentration on the membrane performance. The obtained optimum conditions are: flow rate of 36.99 LPH, temperature of 77.79 °C and concentration of 10.18 g/l. Under optimum conditions, water flux and salt rejection were maximized as 92.55 L/m2.h and 99.9%, respectively. The prepared PVDF/TNTs MMMs with improved properties can be used in MD applications successfully.

In this work, metal-organic framework derived porous carbon (MOFDPC) nanoparticles (NPs) were synthesized and incorporated into cellulose acetate (CA) polymeric matrix to prepare biodegradable CA/MOFDPC adsorptive membranes via phase inversion method. Polyethylene glycol (PEG) was used as pore former agent. Performance of the prepared membranes was evaluated in methylene blue (MB) removal from aqueous solution via continuous adsorption experiments. The physicochemical properties of the fabricated membranes were characterized by contact angle measurement, SEM, FTIR, AFM, TGA and tensile strength analysis. At first, the effects of PEG concentration and MOFDPC NPs loading were investigated. It was found that the best performance is obtained for the prepared membrane containing 15 wt% PEG and 2 wt% of MOFDPC NPs as the optimal adsorptive membrane. Then, the effects of solution pH, initial MB concentration and operating pressure on the MB removal capability of the prepared optimal adsorptive membrane were investigated. Reusability of the optimal adsorptive membrane was studied via subsequent adsorption/desorption cycles. Its long-term behavior was also studied. The obtained results showed that the prepared biodegradable CA/MOFDPC adsorptive membrane with MB removal percentage of 98.2% and permeate flux of 76.03 LMH and excellent reusability and long-term behavior can be potentially utilized for wastewater treatment applications especially MB removal.

In this study, graphene oxide/iron oxide (GO/Fe3O4) nanohybrids were successfully synthesized through bonding (3-Aminopropyl) triethoxysilane(APTES)-functionalized Fe3O4 with GO nanosheets and then incorporated into polyethersulfone (PES) polymer matrix to fabricate ultrafiltration (UF) mixed matrix membrane (MMM) (GO/Fe3O4/PES) via phase inversion method. A magnetic field of about 0.1 Tesla was induced during the casting process of the membrane solution to fabricate the magnetized GO/Fe3O4/PES membrane (M-GO/Fe3O4/PES) and the magnetic field effect on the membrane characteristics was studied. For better comparison, the Fe3O4/PES membranes with and without induction of magnetic field were also fabricated and compared. It was found that the M-GO/Fe3O4/PES membrane with permeance of 252 L/m2.h.bar and water contact angle (WCA) of 53.9° shows the best performance. As compared with the neat PES membrane, WCA of the M-GO/Fe3O4/PES membrane decreased by 35.0% and its pure water flux (PWF) increased up to 76.2%. The M-GO/Fe3O4/PES membrane showed high rejection towards bovine serum albumin (BSA) of about 92.0% and flux recovery ratio (FRR) of about 87.9%. The reduction in total fouling from 84.35% for the neat PES membrane to 41.50% for the M-GO/Fe3O4/PES membrane showed the effectiveness of the proposed membrane fabrication method. This membrane can be used as support for high quality nanofiltration (NF) and reverse osmosis (RO) membranes, effectively.

In this research, a novel biodegradable cellulose acetate (CA)-based nanocomposite adsorbent filled with metal-organic framework-derived porous carbon (MOF-DPC) nanoparticles was fabricated through the phase inversion method for methylene blue (MB) removal from aqueous solution. The MOF-DPC nanoparticles were synthesized via one-step carbonization of MOF-5 at 1000 ​°C under an argon environment. The synthesized MOF-DPC nanoparticles were characterized by HR-TEM, SEM, BET, XRD, Raman, and FTIR analyses, while the fabricated CA/MOF-DPC adsorbent by FTIR and TGA analyses. The effects of various parameters such as MOF-DPC loading (0–2 ​wt%), solution pH (3–11), initial MB concentration (5–200 ​mg ​L−1), solution temperature (25–65 ​°C), and contact time (0–960 ​min) on decolorization behavior of the fabricated CA/MOF-DPC adsorbent were investigated. A high removal efficiency (87.72%) and an acceptable adsorption capacity (41.36 ​mg ​g−1) were achieved at the optimum conditions (2 ​wt% MOF-DPC loading, pH value of 11, MB concentration of 50 ​mg ​L−1, temperature of 65 ​°C and contact time of 6 ​h). The kinetic and equilibrium data were fitted well by the pseudo-second-order kinetic model (R2 ​= ​0.9945) and the Freundlich adsorption isotherm model (R2 ​= ​0.9886), respectively. The thermodynamic investigations confirmed that the adsorption is endothermic and spontaneous at higher temperatures. This study has recommended the fabricated CA/MOF-DPC nanocomposite as a promising adsorbent for the treatment of wastewaters.

In this study, charcoal-based carbon nanomaterial (CNM) was used to modify thin film composite (TFC) membranes for forward osmosis (FO) process. Different amounts of CNM were incorporated into polyethersulfone (PES) and the effects of CNM addition on hydrophilicity, roughness, and morphology of the prepared substrates were investigated. To fabricate the TFC-FO membranes, m-phenylenediamine (MPD) and trimesoyl chloride (TMC) were used for polyamide (PA) layer formation on the substrate surface. FO performance of the prepared TFC membranes was evaluated in both FO and pressure retarded osmosis (PRO) modes using deionized (DI) water as feed solution (FS) and 1 M NaCl solution as draw solution (DS). Also, to study the TFC membranes capability for desalination purposes, the Caspian Seawater was used as FS. It was found that incorporation of CNM into the TFC membrane substrate leads to the reduced structural parameter (S), significantly. The membrane containing 0.5 wt% CNM showed the best performance with water flux of 12.08 and 32.25 L.m−2.h−1 (LMH) in FO and PRO modes, respectively (approximately 3 times higher than that for the neat membrane). Also, Js/Jw value significantly reduced from 1.40 to 0.25 g/L. This research demonstrated that charcoal-based CNM is a proper candidate for modification of the TFC-FO membranes to achieve high water flux and selectivity.

A new class of thin-film nanocomposite (TFN) nanofiltration (NF) membrane was synthesized successfully by incorporation of carbon nanomaterials (oxidized multi-walled carbon nanotube (O-MWCNT) and graphene oxide (GO)) into polyethersulfone (PES) substrate via phase inversion method, substrate surface coating with polyvinyl alcohol (PVA) and then cross-linking with glutaraldehyde (GA). For better comparison, thin-film composite (TFC) membranes (without carbon nanomaterials incorporation into PES substrate) were also synthesized and the optimum concentrations of PVA and GA solutions were obtained. The fabricated TFC and TFN (TFN/O-MWCNTs and TFN/GO) membranes were characterized by SEM, AFM, ATR-IR spectroscopy and contact angle measurements. It was found that incorporation of O-MWCNTs and GO into the PES substrate results in more elongated finger-like pores and larger macrovoids in the substrate and also reduced thickness of the thin skin layer and roughness of the membrane surface. The optimum TFC membrane showed pure water flux of about 13.2 LMH and Na2SO4 rejection of 84 % at 4 bar, while the TFN/O-MWCNTs and TFN/GO membranes showed 54 % and 35 % improvement in water permeability, respectively, without immolating Na2SO4 rejection. The rejection sequence was obtained as R (Na2SO4) > R (MgSO4) > R (NaCl) that confirms the membranes surface has negatively charge.

In this work, Mg-Al layer double hydroxide (Mg-Al LDH) nanoparticles were synthesized through co-precipitation technique. Then, a novel polyvinylidene fluoride (PVDF) mixed-matrix ultrafiltration (UF) membrane containing the synthesized Mg-Al LDH nanoparticles was fabricated via the phase inversion technique. The nanoparticle and membrane were characterized by Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FESEM), X-Ray diffraction (XRD), Water contact angle (WCA), and Atomic force microscopy (AFM). The effects of polymer, pore-former, and nanofiller contents were studied to find the optimum membrane by the stepwise procedure. The obtained results showed that with increasing the content of Mg-Al LDH nanoparticles up to an optimum value (0.5 wt%), surface hydrophilicity, average pore size, porosity, roughness, and antifouling properties of the fabricated mixed-matrix membranes considerably improve. The pure water flux, BSA rejection, and the flux recovery ratio of 213 L/m2 h, 98.8%, and 94.8%, were achieved, respectively. Finally, the simulation of concentration, velocity, and pressure profiles on the optimum membrane was performed, which covered the experimental results with 0.2% discrepancy.

In this study, hydrophilic zirconium 1,4-dicarboxybenzene (UiO-66) and chromium (III) terephthalate (MIL-101) metal-organic frameworks (MOFs) and faujasite (FAU) zeolite nanocrystals were synthesized successfully and incorporated into polyvinylidene fluoride (PVDF) matrix as nanofillers to fabricate mixed matrix membranes (MMMs) via non-solvent induced phase separation (NIPS) process. The effects of casting solution temperature and casting speed as two important factors in membrane fabrication via phase inversion method on performance and structure of the neat PVDF membrane were investigated. Then, various contents of the synthesized nanofillers were loaded into the PVDF matrix and the effects of the synthesized nanofillers on hydrophilicity, pure water flux (PWF), morphology and antifouling properties of the fabricated MMMs were explored. Antifouling studies were also performed using Bovine serum albumin (BSA). The obtained results demonstrated that incorporation of the synthesized nanofillers into the PVDF membrane has positive effect on performance and structure of the fabricated MMMs and the MMM containing 0.1 wt% MIL-101 showed the best performance with water flux of 360 LMH, BSA rejection of 100%, irreversible fouling of 22.2% and flux recovery ratio of 77.7%. This work highlighted the potential application of the MOFs as effective nanofillers for MMM fabrication.

In this study, thin film composite (TFC) membranes were modified using carbon nanofibers (CNFs) for forward osmosis (FO) applications. Carboxyl functionalization of CNFs was performed to increase their surface hydrophilicity and dispersion in a polysulfone (PSF) matrix as the membrane substrate. Different concentrations of both carboxyl functionalized CNFs (f-CNFs) (0.1, 0.3, and 0.5 wt%,) and raw CNFs (0.3 wt%) were incorporated in the polymer matrix and hydrophilicity, porosity, surface roughness, tensile strength and morphology of the nanocomposite substrates were characterized. The optimal membrane was achieved based on the best performance (higher water flux and lower reverse solute flux). Thereby, the TFC membrane containing 0.3 wt% of the f-CNFs was selected as the optimal membrane. The FO water flux of this membrane was almost 2 times higher than the neat TFC membrane in both FO (active layer facing FS) and PRO (active layer facing DS) modes of operation. Water flux of 13.08 L m− 2 h− 1 and specific reverse solute flux of 0.24 g L− 1 were achieved when 1 M NaCl was used as the draw solution (DS) and Deionized (DI) water was used as the feed solution (FS) under the FO mode. Furthermore, incorporation of the f-CNFs decreased the structural parameter (S) of the TFC membranes leading to lower internal concentration polarization (ICP). From the results, it was concluded that the f-CNFs is a suitable candidate for TFC-FO membranes modification to achieve high membrane performance.

There is a knowledge gap for the application of one-dimensional graphene in the adsorption process. Our hypothesis was based on the fact that graphene oxide nanoribbons (GONRs) as one-dimensional graphene with more desired edges and specific surface area than other carbonaceous nanomaterials have more oxygen containing functional groups (active sites) on their edges and basal planes and therefore are more capable in adsorption of pollutants. In this regard, we synthesized GONRs by unzipping of multi-walled carbon nanotubes (MWCNTs) and investigated the adsorption behavior of GONRs by ultrasonic-assisted adsorptive removal of As(V) and Hg(II) ions from aqueous solution. The obtained results showed that As(V) ions are more favorably adsorbed onto the GONRs than Hg(II) ions and with increasing initial As(V) and Hg(II) ions concentration to 300 ppm, the equilibrium adsorption uptake of the synthesized GONRs increases to 155.61 and 33.02 mg/g for As(V) and Hg(II) ions, respectively through a rapid separation process in just 12 min. Also, three kinetic models and Freundlich and Langmuir adsorption isotherms were applied to evaluate the obtained experimental results. Our findings highlight the potential application of GONRs as one-dimensional graphene adsorbent with more desired edges than MWCNTs and graphene oxide (GO) and high adsorption capacity for selective removal of heavy metals.

In this work, new types of positively charged thin-film nanocomposite (TFN) membranes were prepared by assembling hyperbranched polyethyleneimine (HPEI) followed by chemical cross-linking using glutaraldehyde (GA) onto hydrolyzed polyacrylonitrile (PAN) support layer containing functionalized multi-walled carbon nanotubes (f-MWNTs) or graphene oxide (GO). The effects of HPEI concentration, deposition time and HPEI solution pH on the thin-film composite (TFC) membrane performance were evaluated in details. TFN membranes were synthesized using the optimized conditions in terms of HPEI deposition parameters. The effect of f-MWNTs or GO incorporation in the support layer of the prepared TFN membranes on membrane water permeability and salt rejection was also investigated. The obtained results demonstrated that pure water permeability of the prepared TFN-CNT and TFN-GO membranes enhanced by 38% and 64%, respectively, compared to the TFC membrane. Moreover, the TFN membranes overcame the trade-off between rejection and permeability. The rejections of the TFC and both TFN membranes for salts decreased in an order of R (MgCl2) > R (MgSO4) > R (NaCl) > R (Na2SO4) confirming positively charge of the membrane surface. This indicated that the rejection mechanism of the salts is mainly the Donnan exclusion.

In this work, for the first time a new carbon nanomaterial (CNM) with was synthesized from charcoal and characterized using SEM, TEM, EDX, CHNS, FTIR, XRD and Raman analysis. The obtained characterization results showed that the synthesized CNM has two-dimentional morphology (layer structure with nanometeric thickness), high oxygen and nitrogen contents (with carbon to oxygen atomic ratio of about 2.11) and interlayer spacing of about 0.8 nm. The synthesized CNM was used to prepare a positively charged membrane via vacuum-filtration method for removal of divalent heavy metal ions from contaminated water. Hyperbranched polyethyleneimine (HPEI) was used as crosslinking agent. Structure and properties of the prepared membranes without and with HPEI crosslinking were characterized using SEM and WCA analysis. The WCA of the prepared membranes without and with HPEI crosslinking is about 51° and 60°, respectively. Performance and separation mechanism of the prepared membranes were investigated. The prepared HPEI crosslinked membrane with positively charged surface showed superior performance for removal of divalent heavy metal ions from aqueous solutions with rejection sequence of R (Zn2+: 95.65%) > R (Cd2+: 94.10%) > R (Cu2+: 92.56%) > R (Ni2+: 92.34%) > R (Pb2+: 90.51%). The obtained results showed that performance of the prepared HPEI crosslinked membrane is based on steric hindrance and Donnan electrostatic exclusion. Performance of the prepared crosslinked membrane during four cycles of regeneration was also evaluated. The prepared membrane with high structural stability and durability can be employed repeatedly for divalent heavy metal ions removal from contaminated water.

Carbon nanotubes–mullite composite was synthesized by direct growth of carbon nanotubes on mullite particles via chemical vapor deposition method using cyclohexanol and ferrocene as carbon precursor and catalyst, respectively. The carbon nanotubes–mullite composite was oxidized with concentrated nitric acid and functionalized with chitosan and then used as a novel adsorbent for copper ions removal from water. The results demonstrated that modification with concentrated nitric acid and chitosan improves copper ions adsorption capacity of the prepared composite, significantly. Langmuir and Freundlich isotherms and two kinetic models were applied to fit the experimental data. The carbon nanotubes growth on mullite particles to form the carbon nanotubes–mullite composite with further modification is an inherently safe approach for many promising environmental applications to avoid some concerns regarding environment, health and safety. It was found that the modified carbon nanotubes–mullite composite can be considered as an excellent adsorbent for copper ions removal from water.

In this study, chemical vapor deposition (CVD) method (with two proposed synthesis processes) was used for inducting two different morphologies of CNTs in mullite pore channels as a novel adsorptive membrane for nickel ions (Ni 2+ ) removal from water. Cyclohexanol and ferrocene were used as carbon source and catalyst, respectively. The first proposed synthesis process involves coevaporation and pyrolysis of a mixed solution composed of cyclohexanol and ferrocene in a neutral atmosphere and the second involves sublimation and decomposition of ferrocene in a reactor individually and subsequently introduction of cyclohexanol as vapor to the reactor by a carrier gas during the reaction. Effects of synthesis parameters such as reaction time, catalyst content and reactor pressure on growth process, and structure and properties of the induced CNTs in pore channels of the mullite substrate were also investigated. Finally the optimized CNTs growth conditions for achieving a uniform distribution of the CNTs in the mullite pore channels were reported. The CNTs–mullite composite membranes prepared under the optimum conditions were oxidized with nitric acid and then successfully used as adsorptive membranes for nickel ions removal from water. Moreover, Langmuir and Freundlich isotherm models were used to describe adsorption behavior of nickel ions by the prepared adsorptive membrane.

A novel cross-linked graphene oxide (GO) membrane was prepared by vacuum filtration using a two-step method, including activation of GO carboxyl groups by a mixture of 1-Ethyl-3- (3-dimethylaminopropyl) carbodiimide (EDC) and N -Hydroxysuccinimide (NHS) and then cross-linking with polyethyleneimine (PEI). In the cross-linking process, the activated carboxyl groups of GO react with amine groups of PEI through a simple and efficient method. GO cross-linking with PEI significantly improves membrane dimensional stability and salt rejection. The rejection of the cross-linked GO membrane was evaluated by NaCl, Na2SO4 and MgCl2 solutions, and the obtained results followed the order of R (MgCl2) > R (NaCl) > R (Na2SO4). The prepared cross-linked GO membrane was characterized by FTIR, XRD, SEM, FESEM, EDS, WCA, AFM and BET analysis. Also, the effects of operating parameters such as N2 pressure, feed temperature and pH on the cross-linked GO membrane performance were investigated.

Using a solution technique, poly (allylamine hydrochloride)-wrapped multiwalled carbon nanotubes (MWNT–PAH) incorporated poly (vinyl alcohol) (PVA) membranes were prepared. Multiwalled carbon nanotubes (MWNTs) were synthesized via the CVD method using cyclohexanol and ferrocene as the carbon precursor and catalyst, respectively. The prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The prepared membranes were subjected to pervaporation (PV) dehydration of isopropanol (IPA). MWNTs wrapped with PAH were well dispersed in the polymer matrix in comparison with prepared MWNTs. Degree of swelling (DS) of the prepared membranes decreased by addition of MWNT–PAH into the PVA matrix. Furthermore, PV results revealed that incorporation of modified carbon nanotubes (CNTs) into the PVA matrix increases water selectivity significantly due to rigidification of the polymer chains. The nanocomposite membrane containing 1 wt% of MWNT–PAH exhibited excellent PV properties. Permeation flux and separation factor were .229 kg/m2 h and 141.2 for the raw PVA and .207 kg/m2 h and 948.4 for the membrane prepared with 1 wt% of MWNT–PAH respectively. Separation factor decreased significantly by further addition of MWNT–PAH due to its agglomeration in the PVA matrix.

Carbon nanotube (CNT) sheets were synthesized via chemical vapor deposition of cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, functionalized using concentrated nitric acid and liquid ammonia and employed as adsorbents to study their nitrate adsorption characteristics. The results demonstrated that functionalization with nitrogen-containing groups improves nitrate adsorption capacity of the oxidized CNT sheets, significantly. Various isotherms and kinetic models were applied to fit the experimental data. Effects of contact time, initial nitrate concentration and adsorbent dosage were also investigated. Regeneration performance for the first time was also studied. For comparison, a similar study was performed with commercial activated carbon (AC). It was found out that the functionalized CNT sheets with higher nitrate adsorption capacity, shorter equilibrium time and better regeneration performance than AC, can be considered as potential adsorbents for nitrate removal from water in domestic applications.

Carbon nanotubes (CNTs) were synthesized by chemical vapor deposition of cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, and purified by thermal oxidation and acid treatment. Desalination using purified CNTs as adsorbent was performed. Effects of purification (treatment with HNO 3 (8 M), HNO 3 /H 2 SO 4 (1/1) and HNO 3 /H 2 SO 4 (1/3)), initial salt concentration (10,000, 20,000 and 30,000 mg/l), temperature (25, 35 and 45 °C) and initial pH (3, 7 and 11) on adsorption uptake (mg/g) of the purified CNTs in desalination process were investigated using Taguchi experimental design (L 9 orthogonal array). Optimum conditions were predicted, and confirmed by carrying out some new experiments. Relative importance of the effects of various factors was evaluated using analysis of variance (ANOVA). Langmuir and Freundlich isotherm models were applied to fit the experimental data.

Carbon nanotubes (CNTs) were synthesized by CVD method using cyclohexanol and ferrocene as carbon precursor and catalyst, respectively. Nitric acid was used for purification and functionalization of CNTs. TEM image of CNTs before and after purification revealed that acid treatment could remove encapsulated catalyst particles. Afterward, highly pure and functionalized CNTs were incorporated in poly (vinyl alcohol) (PVA) to synthesize PVA–CNTs nanocomposite membranes. FESEM characterization was carried out to investigate dispersion of different CNTs loading in PVA matrix. The results showed that 2 wt.% CNTs loading is better dispersed in the polymer and increasing CNTs loading more than 2 wt.% agglomerates CNTs. Degree of swelling results for nanocomposite membranes showed that present of CNTs in the PVA membranes reduce the degree of swelling. Furthermore, pervaporation (PV) results revealed that incorporating of CNTs in PVA matrix increases significantly water selectivity due to rigidification of the polymer chains. The water selectivities for the pristine PVA and 2 wt.% CNTs loading nanocomposite membranes were evaluated as 119 and 1794, respectively.

Cyclohexanol and xylene were used as carbon precursors, for synthesis of multiwall carbon nanotubes (MWCNTs) arrays in a CVD system at temperature of 750 °C, using nitrogen as carrier gas and ferrocene as catalyst. Different characterization methods were employed to compare the MWCNTs structure synthesized by these two precursors. All scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and Raman spectroscopy results illustrated that using cyclohexanol could significantly reduce formation of amorphous carbon and catalyst particles in the as-grown CNTs. The less amorphous carbon can be attributed to in situ oxidation in presence of oxygen atom of cyclohexanol. Characterizations showed that MWCNTs with high purity could be obtained using cyclohexanol as carbon precursor. The as-grown MWCNTs were purified by oxidation and acid treatment. Characterization of the purified MWCNTs using HNO3/H2SO4 (1/3 or 1/1), 8 M HCl or 8 M HNO3 was carried out. The results showed that 8 M HNO3 could be considered as the best chemical to obtain more pure MWCNTs, less amorphous and metal particles and less damaged MWCNTs. The Raman spectroscopy results demonstrated that HNO3/H2SO4 (1/3) treatment could more disorder the MWCNTs structure and this was attributed to the bigger destroying effect of this acid treatment. Furthermore, the TEM analysis of MWCNTs before and after acid treatment revealed that acid treatment could remove encapsulated catalyst particles. The FTIR analysis illustrated that purification of the MWCNTs with nitric acid could connect the functional groups onto the outer surface of MWCNTs and this resulted in more dispersion of the MWCNTs in water.

Carbon nanotube (CNT) film was synthesized directly on macroporous surface of α-alumina support by chemical vapor deposition (CVD) of cyclohexanol and ferrocene in nitrogen atmosphere at 650 °C, and oxidized using HNO 3 and H 2 SO 4 and then employed as membrane in desalination process (sodium chloride removal from water). In order to enhance the performance of the oxidized CNTs membrane, effects of operating parameters on the yield of desalinated water (separation percent and permeate flux) were studied. Four parameters at three levels were selected: feed concentration (10,000, 20,000 and 30,000 ppm), temperature (25, 35 and 45 °C), pressure (4, 7 and 10 bar) and flow rate (200, 350 and 500 l/h). Taguchi method was used to plan a minimum number of experiments and to find the optimal conditions. The results showed that increasing feed concentration, temperature and flow rate as well as decreasing pressure optimize the performance of the oxidized CNTs membrane (separation percent and permeate flux). Analysis of variance (ANOVA) was applied and it was found that temperature is the most influential factor on the oxidized CNTs membrane performance (its contribution percentage was calculated to be about 60%).

Permanent hard water softening using oxidized carbon nanotube (CNT) sheets was performed. CNT sheets were synthesized by chemical vapor deposition of cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, and oxidized with concentrated nitric acid at room temperature and then employed as adsorbent for permanent hard water softening. Various isotherms and kinetic models were applied to fit the experimental data. It was found out that the adsorption behavior of hard mineral ions by oxidized CNT sheets match well with the Freundlich isotherm and the pseudo-second-order kinetic model. The results demonstrated that the oxidized CNT sheets can be used as an effective adsorbent for hard water softening due to their high adsorption capacity. Also, using the oxidized CNT sheets, hard water softening without CNT leakage into water is economically feasible.

Desalination using carbon nanotube (CNT) sheets was performed. Carbon nanotube sheets were synthesized by chemical vapor deposition using cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, and oxidized with concentrated nitric acid at room temperature and then employed as adsorbent for salty water desalination (sodium chloride removal from water). Effects of adsorption time and initial salt concentration on performance of the oxidized CNT sheets were investigated. It was found out that both Langmuir and Freundlich isotherm models match the experimental data very well. The results demonstrated that the oxidized CNT sheets can be used as an effective adsorbent for salty water desalination due to their very high adsorption capacity. Also, using the oxidized CNT sheets, desalination without CNT leakage into water is economically feasible.