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Abstract Under strong oxidative environment of vanadium redox flow batteries (VRFB), membrane instability is a serious challenge. Anion exchange membranes (AEMs) are expected to reduce vanadium ion permeability due to Donnan exclusion. Herein, we report long alkyl chain grafted quaternized graphene oxide bonded poly(ether sulfone) by 1,4-diazabicyclo[2,2,2]octane (DABCO) coupling, which provides plenty of amine groups. This helps to improve the ionic conductivity. Whereas, long alkyl chain (C16) grafted quaternized graphene oxide causes well phase separation (hydrophilic-hydrophobic) and decent ionic pathway for ionic transportation. The reported AEMs showed good stabilities under harassed acidic/oxidative conditions due to the bulky nature of chemically grafted QG with the main polymer backbone. This results steric hindrance to resist the attack of oxidative species. Suitably optimized PS-DTQG-5 AEM, showed 32.46% water uptake, 2.14 meq/g ion exchange capacity, 6.06 × 10−2 S/cm ionic conductivity, and 18.93 × 105 S min cm−3 selectivity for VRFB. The VRFB assembled with PS-DTQG-5 AEM, displayed extremely good efficiencies (coulombic (98.06%), energy (76.4%), and voltage (78.0%)) at 60 mA cm−2, higher than those for Nafion 117 membrane. Further, stabilities under ex-situ oxidation conditions and in-situ cycle test (approx. 80) in VRFB operating environment make PS-DTQG-5 AEM as an attractive candidate. Graphical abstract fx1 Highlights • Grafting of quaternized graphene oxide containing C16 chain by DABCO coupling. • Acid/oxidative stable AEMs based on poly(ether sulfone) with plenty of amine groups. • AEMs with good conductivity and impervious for vanadium ion due to Donnan exclusion. • Well-architected PS-DTQG-5 membrane with good efficiencies and durability for VRFB. [ABSTRACT FROM AUTHOR]

Abstract Sulfonated poly(ether ether ketone) (SPK)/imidized graphene oxide (IGO) composite cation exchange membrane (CEM) with varied composition was prepared and assessed as a promising candidate for water desalination by electrodialysis (ED). Incorporation of multi-functionalized (SO 3 H and COOH) IGO in SPK matrix leads a high performance CEM with improved electrochemical and physicochemical properties (conductivity, permselectivity, water content and ion-exchange capacity), stabilities (thermal, mechanical, and chemical) essential for diversified electro-membrane processes. Due to the presence of multi-functional oxygenated groups, strong hydrogen bonding between IGO and SPK led suitable hydrophobic–hydrophilic architecture and formation of ionic clusters responsible for ion conducting channels. Well optimized SPK/IGO-8 composite CEM exhibited good water uptake (32.56%), ion-exchange capacity (2.16 meq·g−1), high permselectivity (0.87), and conductivity (5.40 × 10−2 S cm−1) due to high molality of sulphonic acid groups. Relatively high limiting current density (I lim) value for SPK/IGO-8 composite CEM provide a broad window for applying high current density across the electrodialyser to achieve fast water desalination without any unwanted water splitting. Further, low frictional coefficient between counter-ion and membrane matrix plus good electrodialysis performance of SPK/IGO-8 composite CEM revealed its potential candidate for water desalination. Graphical abstract Unlabelled Image Highlights • Multi-functional cation-exchange membrane (CEM) for water desalination by electrodialysis • High performance sulfonated poly(ether ether ketone)/imidized graphene oxide composite CEM • High limiting current density responsible for fast desalination under high current density • Low energy consumption and high current efficiency of CEM for water desalination [ABSTRACT FROM AUTHOR]

Sulphonated imidized graphene oxide (SIGO) (graphene oxide (GO) tethered sulphonated polyimide) has been successfully synthesized by polycondensation reaction using dianhydride and sulphonated diamine. Polymer electrolyte membranes (PEMs) are prepared by using SIGO (different wt%) and sulphonated poly(imide) (SPI). Resultant SPI/SIGO composite PEMs exhibit improved stabilities (thermal, mechanical and oxidative) and good water-retention properties (high bound water content responsible for proton conduction at high temperature by internal self-humidification). Incorporation of covalent bonded SIGO into SPI matrix results hydrophobic−hydrophilic phase separation and facile architecture of proton conducting path. Well optimized sulphonated poly(imide)/sulphonated imidized graphene oxide (15 wt%) (SPI/SIGO-15) composite membrane shows 2.24 meq g −1 ion-exchange capacity (IEC); 11.38 × 10 −2 S cm −1 proton conductivity; 5.12% bound water content; and 10.52 × 10 −7 cm 2 s −1 methanol permeability. Maximum power density for pristine SPI membrane (57.12 mW cm −2 ) improves to 78.53 mW cm −2 for SPI/SIGO-15 membrane, in single-cell direct methanol fuel cell (DMFC) test at 70 °C using 2 M methanol fuel. Under similar experimental conditions, Nafion 117 membrane exhibits 62.40 mW cm −2 maximum power density. Reported strategy for the preparation of PEMs, offers a useful protocol for grafting of functionalized inorganic materials with in organic polymer chain by imidization. [ABSTRACT FROM AUTHOR]

Kraft paper industries perform causticization (NaOH production) by fresh lime (CaO) addition in green liquor (rich in sodium carbonate) resulting calcium carbonate (CaCO 3) as precipitate, which is washed, dried and calcined at ~900 °C to regain CaO, making the process energy intensive and environmentally polluting. Current investigation reports electro-electrodialysis (EED) based conversion of green liquor to NaOH using alkali resistant composite membrane made from graphene oxide (GO) and SPK [sulfonated poly (ether ether ketone)]. Using optimized process parameters: current density (60 mA·cm−2), flow rate (2.0 L·h−1), 25 °C, and batch recirculation of 0.5 L of green liquor through EED set up (66 cm2), resulted 0.5 L (2.35 mol·L−1). Corresponding current efficiency and energy consumption estimates were ~67.9% and ~0.126 kW·h·mol−1 respectively. After thirty batches of experiment, the performance of NaOH production and its energy consumption remains unaltered. Performance in house membrane was compared with commercial (FKB-PK-130). Cost estimation based on lab-scale data for treatment of 50,000 L/day of green liquor through conventional and EED technique showed ~$2050 per day without solid waste generation and environmental pollution. [Display omitted] • One-step NaOH production from green liquor without solid/liquid waste generation. • GO loaded sulfonated polyether ether ketone membrane used for electro-electrodialysis. • Adequate alkaline stability of SPK/GO-5 could electrolyze industrial green liquor. • Optimized current density and flow rate are used for maximum NaOH production. • Caustic production from electro-electrodialysis is cost efficient compared to conventional process. [ABSTRACT FROM AUTHOR]

The layer-by-layer casting technique was adopted to fabricate bipolar membranes (BPMs) comprising a cation-exchange layer (CEL), an interfacial layer (IL, phosphorylated graphene oxide (PGO) and/or quaternized graphene oxide (QGO)), and an anion-exchange layer (AEL). Under applied dc potential gradient, water molecules dissociate at the IL and generate H+ and OH-. The effect of the IL nature (PGO, QGO, and mixed PGO/QGO) on the water splitting performance of the BPM was thoroughly studied. Well optimized BPM-PGO/QGO exhibited high current efficiency (CE) and low energy consumption and was assessed to be superior in comparison with different commercial BPMs. The reported BPM showed improved water splitting performance, significant reduction in resistance, and high permselectivity (low co-ion leakage) for over 10 experimental cycles. Relatively stable performance of BPM-PGO/QGO made it industrially viable for water splitting. [ABSTRACT FROM AUTHOR]

To achieve efficient water desalination/waste water treatment at high temperature, highly stable aliphatic/aromatic sulphonated poly(imide) (SPI)-phosphorylated graphene oxide (PGO) based temperature resistant cation exchange membranes (CEMs) were architected. The structural features: aliphatic connector between terminal end groups, direct grafting of sulfonic acid groups on aromatic rings, were responsible for their improved performance and stabilities. Data for Pristine (SPI) and composite (SPI/PGO) membranes suggested that membrane performance and stabilities were significantly improved with incorporation of PGO in the SPI matrix. Incorporation of PGO in the membrane matrix contributed towards mechanical, thermal and oxidative resistant nature, while presence of multi-ionic clusters (–SO 3 H & –PO 3 H 2 ) was responsible for hydrophilic ion conducting channels. Most suitable SPI/PGO-8 composite CEM (IEC: 2.37 mequiv g −1 ) exhibited 6.8×10 − 2 S cm −1 ionic conductivity and 0.96 t + m value and found to be promising candidate for electrodialytic water desalination. Further, significantly improved process performances (energy consumption and current efficiency) for water desalination by electrodialysis (ED) provides sustainable and feasible alternative for applying ED for salt separation in aqueous media at high temperature. [ABSTRACT FROM AUTHOR]

We report a sustainable strategy for fabricating thermal-resistance anti-fouling cation exchange membrane (CEM), using sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (SPPO), and phosphorylated graphene oxide (FGO). The GO was phosphorylated, and different CEMs (3.0–7.0 % weight ratio of FGO) were prepared to investigate their electrodialysis (ED) performance. Structural features of SPPO-FGO composite CEMs such as ̴ 21.51 % degree of sulphonation (SPPO), bi-functional (-SO 3 H, and -PO 3 H 2) nature, and balanced hydrophobic-hydrophilic segments, etc., were attributed for thermal-resistance and anti-fouling membrane nature of the membrane. The presence of FGO in the SPPO polymer matrix significantly improved mechanical, thermal, oxidative stabilities, ionic conductivity (κ m ), and counter-ion transport number (t m +). Suitable optimized SPPO-FGO/7 % (7.0 % of FGO) showed excellent physicochemical properties (14.1 % water uptake, 3.2 % swelling ratio, and 1.76 m eq./g ion exchange capacity), along with 10.92 × 10−2 S cm−1 conductivity, and 0.95 counter-ion transport number at 30 °C. Improved i - V curves and ED performance at 60 °C, showed relatively low energy consumption (0.72 k W hr/kg of NaCl removed), and high current efficiency (99.0 %) for SPPO-FGO/7 % CEM revealed, its potential candidature for electrodialytic water desalination. Further, CEM also avoids any significant deterioration in ED performance due to the presence of cationic, anionic and zwitterionic foulants. [Display omitted] • Architecting of thermal-resistance anti-fouling bi-functional CEM for the electrodialysis applications. • Balanced hydrophobic-hydrophilic phase in the membrane matrix for improved stabilities and performance. • Improved thermal-resistance and ionic conductivity of the SPPO-FGO composite CEM due to presence of bi-functional groups. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyaniline encapsulated sulphonated graphene oxide doped high conducting membrane. • Specific mono-valent selective high performance cation exchange membrane. • Mono- and bi-valent ions separation by electrodialysis. • Sustainable and alternative process for salt separation/recovery. Polyaniline encapsulated sulphonated graphene oxide (SGO-PANI) was prepared by ion exchange process. The SGO-PANI was incorporated in sulphonated poly(ether ether ketone) (SPEEK) matrix to fabricate the mono-valent selective cation exchange membrane. The structural morphology of SGO-PANI was studied by FTIR, XPS, SEM and XRD spectra. Resultant SPEEK@SGO-PANI membrane exhibited excellent stabilities and physicochemical and electrochemical properties suitable for electrodialysis (ED) applications. Encapsulation of strong acid with a weak base seems to improve electrostatic repulsion between membrane surfaces and of bi-valent ions, which are responsible for significant flux reduction. Chronopotentiometric and current–voltage responses of SPEEK@SGO-PANI membrane confirmed its ion-conducting nature along with 3.32 mA cm−2 limiting current density (I lim). Reported SPEEK@SGO-PANI membrane showed a high electrodialytic flux of Na+ compared to bi-valent ions (Mg2+, Ca2+, and Cd2+). Extremely low energy consumption and high current efficiency (81.18%) at 6.0 V applied voltage for Na+ (0.10 M) revealed the promising nature of the reported membrane. Observed mono-valent ion selectivity aroused due to improved electrostatic repulsion of bi-valent ions with the membrane surface. [ABSTRACT FROM AUTHOR]

In the context of many applications, such as polymer composites, energy-related materials, sensors, ‘paper’-like materials, field-effect transistors (FET), and biomedical applications, chemically modified graphene was broadly studied during the last decade, due to its excellent electrical, mechanical, and thermal properties. The presence of reactive oxygen functional groups in the grapheme oxide (GO) responsible for chemical functionalization makes it a good candidate for diversified applications. The main objectives for developing a GO based nanohybrid proton exchange membrane (PEM) include: improved self-humidification (water retention ability), reduced fuel crossover (electro-osmotic drag), improved stabilities (mechanical, thermal, and chemical), enhanced proton conductivity, and processability for the preparation of membrane-electrode assembly. Research carried on this topic may be divided into protocols for covalent grafting of functional groups on GO matrix, preparation of free-standing PEM or choice of suitable polymer matrix, covalent or hydrogen bonding between GO and polymer matrix etc. Herein, we present a brief literature survey on GO based nano-hybrid PEM for fuel cell applications. Different protocols were adopted to produce functionalized GO based materials and prepare their free-standing film or disperse these materials in various polymer matrices with suitable interactions. This review article critically discussed the suitability of these PEMs for fuel cell applications in terms of the dependency of the intrinsic properties of nanohybrid PEMs. Potential applications of these nanohybrid PEMs, and current challenges are also provided along with future guidelines for developing GO based nanohybrid PEMs as promising materials for fuel cell applications. [ABSTRACT FROM AUTHOR]

Di-quaternized graphene oxide based multi-cationic cross-linked monovalent selective anion exchange membrane for electrodialysis. [Display omitted] • Di-quaternized graphene oxide as a nano cross-linker. • The moderate amount of QGO loading for cross-linked anion exchange membrane. • Cross-linked nanocomposite membranes for monovalent anion separation. • Monovalent selective cross-linked membranes outperform with pristine membrane. A series of monovalent anion selective membranes were synthesized by crosslinking of chloromethylated polysulfone with 1,4-diazabicyclo [2.2.2] octane functionalized graphene oxide (QGO). Cross-linking of QGO provides dense polymer matrix as well as additional functional sites to the membrane. The effect of QGO on physicochemical and electrochemical properties was studied in detail. The best optimized membrane, CrPSf-3 (3 wt% of nano cross-linker) showed 2.01 mmol·g−1 ion exchange capacity, 9.90% swelling ratio, 31.20% water uptake, 72 mS·cm−1 chloride ion conductivity and 0.95 counter ion transport number along with good mechanical and thermal stability. Electrodialysis performance of membrane permselectivity between Cl− and SO 4 2− was studied in mixed salt solution of 0.05 mol·L-1 (NaCl + Na 2 SO 4). The CrPSf-3 membrane showed 5.7 separation factor (SF) for Cl−/SO 4 2− which is higher than pristine QPSf (1.7) and commercial FAB-PK-130 membrane (2.01). Furthermore, higher Cl− flux (2.97 mol·m-2h−1) was observed for CrPSf-3 membrane as compare to pristine QPSf (1.45 mol·m-2h−1) and commercial membrane (1.6 mol·m−2·h−1). To achieve monovalent anion selectivity, effective cross-linking is facile approach to control compactness of the membrane and ion transport channels. Reported cross-linked membrane possesses a potential candidate for water desalination, wastewater treatment, or other monovalent selective separation processes. [ABSTRACT FROM AUTHOR]

Cross-linked brominated poly phenylene oxide-functionalized graphene oxide nanocomposite anion exchange membrane. • Amine ended functionalized graphene oxide by condensation reaction. • Cross-linked nanocomposite anion exchange membranes for electrodialysis. • Temperature resistant cross-linked nanocomposite AEMs for water desalination. • Suitably optimized PPO/AGO-8 AEM with improved electrodialytic performance. A new age strategic route to synthesize cross-linked nanocomposite anion exchange membranes (AEMs) from functionalized graphene oxide was reported here. Nanocomposite crosslinking networks were formed by reacting aminopropylsilane graphene oxide (AGO) with brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO). Amine ended functionalized graphene oxide; AGO was synthesized by condensation reaction between graphene oxide and 3-aminopropyltrimethoxysilane. A variety of nano cross-linker; AGO loading was introduced into membrane casting solution and the prepared membranes were explored based on physicochemical and electrochemical properties. The best optimized AEM; PPO/AGO-8 showed ion exchange capacity 2.2 mmol·g−1, water uptake 37.91%, swelling ratio 9.8%, conductivity 8.38 × 10−2 S·cm−1, counter ion transport number (0.97) and 108 A·m−2 limiting current density (I lim) with maintaining good thermo-mechanical stability due to covalent interaction between polymer and nanofiller. Desalination performances were evaluated on the basis of removal ratio (RR NaCl), current efficiency (η) and energy consumption (EC) over a whole range of temperatures (25 °C to 55 °C). On being applied in ED, the PPO/AGO-8 membrane showed slightly higher RR NaCl (47.23%), η (86.0%) and lower EC (2.85 kWh·kg−1 NaCl) than commercial Fumatech FAB-PK-130 membrane (RR NaCl : 43.8%, η: 82.34% and EC: 3.21 kWh·kg−1 NaCl) under same temperature (55 °C). The superior ED performance of synthesized cross-linked nanocomposite AEM is suggested to be a promising candidate for electrodialytic desalination and temperature based separation and purification processes for industrial applications. [ABSTRACT FROM AUTHOR]