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In this paper, commercially available graphene oxide (GO) was used as nanomaterials to modify polyamide reverse osmosis (RO) membrane surface. After functionalization, the membrane surface properties were improved as the water contact angle was reduced from 41.7 ± 4.5⁰ to 26.9 ± 0.9⁰ demonstrating improvement in hydrophilic properties besides decreasing membrane surface roughness. Membrane scaling tests were done in the presence of CaSO 4 solution at 20 mM concentration as feedwater showed that the modified membranes (GO@RO) had superior anti-scaling properties. Results indicated that the permeate flux was reduced by only 15% at the end of the scaling experiment as opposed to the bared RO membrane which faced up to 22% decline in flux. The results of scanning electron microscopy, Fourier transform infrared, and X-ray diffraction confirmed that the bared RO membrane was extensively scaled by the CaSO 4 precipitates. The results of antibacterial tests showed that GO functionalization caused an inhibition of bacterial growth by 81.7% as compared to the unmodified RO membrane. Moreover, experiments were also performed to investigate microbially induced calcium sulfate precipitation on membranes. Overall, it was found that GO functionalization not only reduces biofouling but can also inhibit mineral scaling and microbially induced mineral formation. Image 1 [ABSTRACT FROM AUTHOR]

The polyamide reverse osmosis (RO) membrane was modified with graphene oxide (GO), followed by polymerization of acrylic acid (used as an antiscalant) for the reduction of both biofouling and mineral scaling. After functionalization, the water contact angle reduced from 41.7 ± 4.5° for unmodified RO membrane to 24.4 ± 1.3° for the modified RO membranes, which showed that membrane hydrophilicity was significantly enhanced, in addition to the improvement in surface smoothness. The modified membranes were tested for their anti-scaling and anti-biofouling characteristics. When the mineral scaling test was performed using CaSO 4 solution as feedwater, the permeate flux was reduced by only 3% as compared to the unmodified RO membrane which encountered up to 22% decline in flux by the end of the experiment. After the scaling test, the membrane surface was characterized by Scanning electron microscopy – energy-dispersive X-ray spectroscopy, Fourier transform infrared, and X-ray diffraction techniques. The results showed that the unmodified RO membrane was fully covered with gypsum precipitates. Whereas, the precipitates were detected only at the highly saturated zones of the water channel i.e. towards the exit of water flow. Additionally, the anti-bacterial test was performed through bacteriostasis rate determination, which showed that the modified membranes inhibited the growth of nearly 95% of the bacterial cells. Further experiments were also performed to investigate the inhibition of both scaling and biofouling by modified RO membranes. Thus, it was found that the polymer-modified GO coated RO membranes were able to diminish both gypsum scaling and biofilm formation demonstrating their potential to control different types of membrane fouling. Unlabelled Image • The reverse osmosis membrane was modified with graphene oxide and polyacrylic acid. • The surface smoothness and hydrophilicity of the modified membranes were improved. • The permeate flux was reduced by only 3% as compared to unmodified RO membrane. • The modified membranes inhibited the growth of nearly 97% of the bacterial cells. • The modified membranes were able to diminish both gypsum scaling and biofouling. [ABSTRACT FROM AUTHOR]

• Membrane fouling is major hurdle for the widespread use of membrane technology. • Increase in temperature can affect CaSO 4 scaling intensity, and morphology. • At higher temperature, crystal morphology changes from rod shape to rosette structures. • Using PCA, membrane's permeate flux can be differentiated at different conditions. • FTIR results showed the involvement of OH, COOH and NH 2 groups in membrane scaling. Membrane fouling is one of the major hurdles in widespread use of seawater reverse osmosis (SWRO) in desalination industry. There are various factors that affect the inorganic fouling or scaling of Reverse osmosis (RO) membranes. In this research, the effect of temperature on scaling of RO and Graphene oxide (GO) coated RO membrane by calcium sulfate was investigated. It was found that the increase in temperature enhanced the membrane scaling which was evident by the severe flux decline over time leading to increase in mass of crystals precipitated (M t) and thickness of the scale layer. There was strong positive correlation (R2 ≥ 0.97) noted between M t and the temperature. The results of SEM-EDX and XRD confirmed that the crystals formed under the experimental conditions are gypsum. Results of this research showed that there was no significant difference in terms of crystal morphology, scaling intensity and mechanism after modifying RO membrane with GO. It was noted that the morphology of the crystals varied from rod shaped to rosette structures under the influence of temperature. Furthermore, the results of FTIR helped to understand the mechanism of interaction between the membranes and the gypsum. The hydrophilicity of the scaled membrane was also measured to investigate the changes in the properties of the membrane after scaling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Positively charged PEI improved deposition and orientation of GO on PSf. • Synergic effects of PEI-modification and GO govern the formation of PA. • A thin but rough PA is formed on the surface of PEI-modified PSf substrate. • PEI-interlayer TFN membrane showed greater water flux without affecting rejection. In this work, the polyethyleneimine (PEI)-interlayered thin film nanocomposite (iTFN) membranes were developed by establishing graphene oxide (GO)-incorporated polyamide (PA) layer atop PEI-coated polysulfone (PSf) substrate for reverse osmosis process. The effects of PEI layer sandwiched between selective layer and substrate were studied by varying several main parameters of the PEI coating process, i.e., PEI concentration (0.005–0.2 wt/v%), drying time (0–120 min), and coating layer number (1–3 layers). The positively charged PEI interlayer was found to alter not only the hydrophilicity and pore structure of the substrate but also improve the orientation and distribution of deposited GO through electrostatic interaction. Synergic effects of GO and PEI, including enhanced substrate surface hydrophilicity and increased amine content, eventually formed a rough but thin PA layer. As a result, almost all iTFN membranes exhibited higher NaCl rejection and water permeability than the control TFN membrane (without PEI intermediate layer). This experiment revealed that PSf substrate modified with a single layer of 0.05 wt/v% PEI followed by 60-min drying yielded the TFN membrane (i.e., iTFN-C0.05-T60-L1) with the best desalination performances (96.66% NaCl rejection and 2.24 L/m2·h·bar). The control TFN membrane meanwhile showed lower performance, i.e., 95.61% NaCl rejection and 1.69 L/m2·h·bar. [ABSTRACT FROM AUTHOR]