Surface functionalization and modification including the grafting process are effective approaches to improve and enhance the reverse osmosis (RO) membrane performance. This work is aimed to synthesize grafted/crosslinked cellulose acetate (CA)/cellulose triacetate (CTA) blend RO membranes using N‐isopropylacrylamide (N‐IPAAm) as a monomer and N,N‐methylene bisacrylamide (MBAAm) as a crosslinker. The morphology of these membranes was analyzed by scanning electron microscopy and their surface roughness was characterized by atomic force microscopy. The performance of these membranes was evaluated through measuring two major parameters of salt rejection and water flux using RO unit at variable operating pressures. It was noted that the surface average roughness obviously decreased from 148 nm for the pure CA/CTA blend membrane with 2.5% CTA to 110 nm and 87 nm for the grafted N‐IPAAm and grafted/crosslinked N‐IPAAM/MBAAm/CA/CTA‐RO membranes, respectively. Moreover, the contact angle decreased from 51.98° to 47.6° and 43.8° after the grafting and crosslinking process. The salt rejection of the grafted CA/CTA‐RO membrane by 0.1% N‐IPAAm produced the highest value of 98.12% and the water flux was 3.29 L/m2h at 10 bar.

Shaker ebrahim 2 ✉ this work aims to prepare new types of grafted and crosslinked cellulose acetate (cA) reverse osmosis (Ro) membranes by phase inversion technique. the grafting and/or crosslinking processes of the pristine cA-Ro membrane were conducted using N-isopropylacrylamide (n-ipAAm) and N,Nmethylene bisacrylamide (MBAAm), respectively. the grafting/crosslinking mechanism onto the cA-Ro membrane surface was proposed. Atomic force microscope (AfM) images of the pure cA-Ro and 0.1 wt% N-IPAAm-grafted CA-RO membranes revealed that the surface roughness was 42.99 nm and 11.6 nm, respectively. Scanning electron microscopy (SEM) images of the 0.1 wt% grafted/crosslinked membrane indicated the finger-like macrovoids structure. It was observed that the contact angle of the pristine CA-RO membrane was 66.28° and declined to 49.7° for 0.1 wt % N-IPAAm-grafted CA-RO membrane. The salt rejection of the pristine CA-RO membrane was 93.7% and increased to 98.9% for the grafted 0.1 wt % N-IPAAm/CA-RO membrane. The optimum grafted/crosslinked composition was 0.1 wt %/ 0.013 wt % which produced the salt rejection and water flux of 94% and 3.2 L/m 2 h at low pressure, respectively. it was concluded that both the grafting and crosslinking processes enhanced the performance of the cA-Ro membranes. The RO membranes process is one of the most reliable, efficient and cost-effective water desalination techniques to meet the demand and indigence of the fresh water 1-3. The most common polymeric materials used in RO membrane manufacture are either cellulose acetate (CA) or polysulfone coated with dense layer of polyamide thin film 4-7. Surface functionalization enables the RO membranes to have a better water quality, stability and permeability and consequently reducing RO operational costs and energy consumption. The surface properties of RO membranes, including hydrophilicity, water permeability, salt rejection, water flux, and surface roughness are the main parameters which determine water affinity and the interactions mechanism with salts 8. Surface modification techniques such as grafting by hydrophilic molecules have been made to improve the membrane performance 9,10. Different types of the graft polymerization of monomers onto cellulose were carried out by radical, ionic and ring opening or living radical polymerizations 11-15. The modification of the membrane surfaces can be carried out by "grafting-from" and "grafting to" approaches. In the grafting-to method end-functionalized polymer molecules bind with complementary functional groups located on the surface to produce tethered chains. However, this method is rarely to be used in the membrane modification because of the low density of grafted polymer chains. The grafting from technique uses the polymerization initiated from the substrate surface by attached initiating groups. Molecules of a monomer penetrate through the already grafted polymer layer easily and significant grafted amounts can be reached. This technique is commonly used for the preparation of thick grafted l...

BackgroundThe introduction of pendent bulky groups along the polymer backbone results in a less ordered polymer matrix and increases the solubility characteristics without affecting thermal properties. The inclusion of chromogenic chemical moieties in the chains can give rise to the luminescent converter material which permits the preparation of materials with potential applications. Aromatic polymers containing heterocyclic rings in the main chain are known for their high thermal resistance, good hydrolytic stability, low dielectric and tough mechanical properties. There is currently much research directed towards the discovery of new blue light-emitting polymers, with characteristics of high efficiency and high reliability. Herein, we describe the preparation of aromatic polyamides and poly (1,3,4-oxadiazole-amide)s nanoparticles with pendant structures comprised of m- and p-acetoxybenzamide groups, where the acetoxybenzamide groups act as signaling units due to their fluorescent and chromogenic characteristics.ResultsAromatic polyamides and poly(1,3,4-oxadiazole-amide)s nanoparticles with pendant structures comprised of m- and p-acetoxybenzamide groups were successfully prepared and characterized using different analytical methods. Most polyamides were obtained as well-separated spherical nanoparticles while aramide containing pyridine produced aggregated particles attributed to the molecular self assembly via H-bond directed organization of molecular precursors. The thermal behavior of all polymers exhibited two major thermal decompositions due to the subsequent breakage of the acetoxy group in the lateral chain and cleavage of the main amide bonds. Photoluminescence studies revealed that the blue emissions for the polyamide derived from benzidine were blue-shifted (shifted to a lower wavelength) compared to that of polyamides containing flexible linkages.ConclusionsWe report the synthesis of aromatic polyamides and poly(1,3,4-oxadiazole-amide)s nanoparticles with pendant structures comprised of m- and p-acetoxybenzamide groups. The thermal behavior of all polymers exhibited two major decompositions due to breakage of the acetoxy group in the lateral chain and cleavage of the main amide bonds. Structure- photoluminescence correlation demonstrated an interesting connection between structural modification and optical properties. The blue emissions for the polyamide derived from benzidine, attributed to the highly conjugation system, was blue shifted with the introduction of flexible linkages. The prepared polymers dissolved in warm polar aprotic solvents. Further investigations to obtain films with reasonably good mechanical properties for different applications are in progress.

Polyindole is considered an excellent conducting polymer with interested properties for different applications. A novel polyindole (PIn)/CuInS (CIS)/ZnS quantum dots (QDs) nanocomposite was synthesized via in situ polymerization of PIn in presence of CIS/ZnS QDs. By investigating the effect of CIS/ZnS QDs on optical properties of PIn, it was found that the optical band gaps of PIn, CIS/ZnS QDs, and PIn/CIS/ZnS QDs nanocomposite were 3.24 eV, 4.68 eV and 3.44 eV, respectively. From the luminance spectra, it was observed that emission peaks of PIn at 442 and 468 nm are independent of the excitation wavelength with the highest intensity at excitation wavelength of 380 nm. However, the luminance spectrum of PIn/CIS/ZnS QDs nanocomposite exhibited a quenching peak for CIS/ZnS QDs while the intensity of PIn peak was enhanced. High resolution of transmission electron microscope image of CIS/ZnS QDs revealed nanocrystals with a size of 3–4.5 nm and lattice space of 0.2 nm. PIn/CIS/ZnS QDs nanocomposite as the fluorescent probe was employed for sensing different concentrations of Pb2+ from 5 to 50 ppb. The reaction between PIn/CIS/ZnS QDs and Pb2+ was slightly quenched and fixed after 90 min. The emission peak was reduced gradually with increasing concentration of lead via photo-induced electron transfer or ion exchange mechanism. The value of correlation coefficient (R2) was 0.99, the sensitivity was 0.0041 ppb−1 and limit of detection value was 4.48 ppb.

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