Polybenzimidazole/Nafion hybrid membrane with improved chemical stability for vanadium redox flow battery application

In order to increase the chemical stability of polybenzimidazole (PBI) membrane against the highly oxidizing environment of a vanadium redox flow battery (VRFB), PBI/Nafion hybrid membrane was developed by spray coating a Nafion ionomer onto one surface of the PBI membrane. The acid–base interaction between the sulfonic acid of the Nafion and the benzimidazole of the PBI created a stable interfacial adhesion between the Nafion layer and the PBI layer. The hybrid membrane showed an area resistance of 0.269 Ω cm² and a very low vanadium permeability of 1.95 × 10⁻⁹ cm² min⁻¹. The Nafion layer protected the PBI from chemical degradation under accelerated oxidizing conditions of 1 M VO₂⁺/5 M H₂SO₄, and this was subsequently examined in spectroscopic analysis. In the VRFB single cell performance test, the cell with the hybrid membrane showed better energy efficiency than the Nafion cell with 92.66% at 40 mA cm⁻² and 78.1% at 100 mA cm⁻² with no delamination observed between the Nafion layer and the PBI layer after the test was completed.

Novel polybenzimidazole (PBI)/Nafion hybrid membranes for the VRFB are made by spray coating a Nafion layer to protect PBI from chemical degradation.     

Enhanced phosphate removal by zero valent iron activated through oxidants from water: batch and breakthrough experiments

In this study, oxidants including hydrogen peroxide (H₂O₂), hypochlorite (ClO⁻) and persulfate (S₂O₈²⁻) were employed to promote zero-valent iron (ZVI) corrosion and enhance phosphate (P) removal from water through batch and breakthrough experiments. Characterization results indicated that the addition of oxidant can cause large-scale corrosion of the iron surface. This subsequently generates more iron ions and active minerals, resulting in a large number of reaction-adsorption sites for P removal. Therefore, compared with the ZVI alone system (29.4%), the removal efficiency of P by oxidant/ZVI system (H₂O₂ : ClO⁻ : S₂O₈²⁻ = 33.2% : 54% : 67.1%) was improved. For the oxidant/ZVI system, H₂O₂ can promote the corrosion of ZVI to a certain extent. However, the solution pH could be increased during the corrosion process. This leads to inhibition of P removal performance by the H₂O₂/ZVI system, which only increased by 12.9% to 33.2%. The reaction between NaClO and ZVI consumes less H⁺, and the reaction product Cl⁻ can pierce the passivation layer on the surface of the ZVI through the pitting effect. As such, the NaClO/ZVI system attained a 54% P removal rate. Compared with H₂O₂ and NaClO, a better P removal effect of about 67.1% can be achieved by using Na₂S₂O₈, since the oxidation corrosion process of Na₂S₂O₈ does not consume H⁺, and it also has the strongest oxidizing properties. Furthermore, an appropriate increase in oxidant dosing (0.1–2 mM) could improve the efficiency at which of P is removed. Five batch cycle experiments showed that the oxidant/ZVI system has a higher removal capacity and longer life-span. In the long-term column running, the P removal capacity and operation life of the NaClO/ZVI column are 9.6 times and 3.2 times higher than that of the ZVI column, respectively. This work demonstrates that an oxidant/ZVI system can be an efficient method for P removal in water, which also provides a new idea for solving the problem of ZVI corrosion passivation.

This model is used to illustrate the enhanced P removal by oxidant stimulated ZVI.     

Direct oxidation of methane to methanol using CuMoO4

Upgrading methane into methanol or other high value-added chemicals is not only beneficial to mitigate the greenhouse effect, but also provides basic raw materials for industrial production. Nowadays, most research is limited to zeolite systems, and it is a considerable challenge to extend the support to metal oxides while achieving a high yield of methanol. In this paper, we take advantage of impregnation methods to synthesise a novel Cu/MoO₃ catalyst, which can convert methane to methanol in the gaseous phase. At 600 °C, the Cu(2)/MoO₃ catalyst can achieve a maximum STY_CH3OH of 47.2 μmol (g⁻¹ h⁻¹) with a molar ratio CH₄ : O₂ : H₂O = 5 : 1.4 : 10. Consequences of SEM, TEM, HRTEM and XRD substantiate that Cu is incorporated into the lattice of MoO₃ to form CuMoO₄. And transmission infrared spectroscopy, Raman spectroscopy together with XPS characterization techniques confirm the generation of CuMoO₄, which is the main active site provider. This work provides a new support platform for Cu-based catalyst research in the methane-to-methanol system.

Upgrading methane into methanol or other high value-added chemicals is not only beneficial to mitigate the greenhouse effect, but also provides basic raw materials for industrial production.     

Effect of H2SO4/H2O2 pre-treatment on electrochemical properties of exfoliated graphite prepared by an electro-exfoliation method

The effect of pre-treating graphite sheets in a H₂SO₄/H₂O₂ solution before electro-exfoliation is reported. It was revealed that the volume fraction of H₂SO₄ to H₂O₂ during pre-treatment could control the degree of exfoliation of the resulting exfoliated graphite (EG). X-ray diffraction (XRD), Raman, and Fourier transform infrared (FTIR) spectroscopy analyses have suggested that EG produced by first pre-treating the graphite sheet in H₂SO₄/H₂O₂ solution with the H₂SO₄ : H₂O₂ volume fraction of 95 : 5 demonstrates the highest exfoliation degree. This sample also demonstrated excellent electrochemical properties with good electrical conductivity (36.22 S cm⁻¹) and relatively low charge transfer resistance (R_ct) of 21.35 Ω. This sample also showed the highest specific capacitance of all samples, i.e., 71.95 F g⁻¹ at 1 mV s⁻¹ when measured at a voltage range of −0.9 to 0 V. Further measurement at an extended potential window down to −1.4 V revealed the superior specific capacitance value of 150.69 F g⁻¹. The superior morphology characteristics and the excellent electrical properties of the obtained EG are several reasons behind its exceptional properties. The pre-treatment of graphite sheets in H₂SO₄/H₂O₂ solution allegedly leads to easier and faster exfoliation. The faster exfoliation is allegedly able to prevent massive oxidation, which frequently induces the formation of graphite/graphene oxide (GO) in a prolonged process. However, too large H₂O₂ volume fraction involved during pre-treatment seems to cause excessive expansion and frail structure of the graphite sheets, which leads to an early breakdown of the structure during electrochemical exfoliation and prohibits layer by layer exfoliation.

Early expansion of graphite after H₂SO₄/H₂O₂ pre-treatment and cyclic voltammograms of exfoliated graphite (EG) prepared with various volume fractions of H₂O₂.     

Fe-MOFs prepared with the DBD plasma method for efficient Fenton catalysis

Fe-MOFs were successfully synthesized with the dielectric barrier discharge (DBD) plasma method, and applied for degradation of methyl orange by the Fenton process. Fe-MOFs were characterized by XRD, SEM, EDS, BET and FT-IR. A systematic study was carried out to optimize the synthesis conditions, taking into account the Fenton capacity performance for degradation of methyl orange. The optimal synthesis conditions were a discharge time of 100 min, discharge voltage of 18 kV, reactant concentration of 14 g L⁻¹ and reactant mass ratio (TA : FeCl₃·6H₂O) of 1 : 5, with influence on the crystallization, morphologies and particle size. The degradation rate of methyl orange could reach 85% within 40 min with the MO concentration of 50 mg L⁻¹, Fe-MOF dosage of 0.12 g L⁻¹, pH of 5 and H₂O₂ at 1 mL L⁻¹. Meanwhile, the Fenton catalytic process was conducted covering a range of catalyst concentrations, initial MO concentrations, pH and H₂O₂ amounts. Higher catalyst concentration, lower MO initial concentration, pH of 3 and H₂O₂ amount of 1 mL L⁻¹ were conducive to the degradation efficiency.

Fe-MOFs were successfully synthesized with the dielectric barrier discharge (DBD) plasma method, and applied for degradation of methyl orange by the Fenton process.     

Synthesis and anion recognition studies of new oligomethylene bis(nitrophenylureylbenzamide) receptors

A new series of oligomethylene bis(nitrophenylureylbenzamide) receptors were synthesized varying the relative position of the urea and amide groups (ortho4 and meta8) and the length of the oligomethylene chain (C₂ to C₈). An anion recognition study was performed with TBAX salts (X = AcO⁻, BzO⁻, F⁻, H₂PO₄⁻, and HP₂O₇³⁻) by UV-vis and ¹H NMR. The flexibility of these receptors allows a cooperative effect of both ureylbenzamide units in the receptors. Noteworthy, the ortho position favored the 1 : 1 stoichiometry in the complexes with the carboxylates. The formation of 2 : 1 receptor–anion complexes with both types of receptors 4 and 8 and with hydrogen pyrophosphate and high log K values obtained were very significant in this work. The NMR studies evidenced the formation of supramolecular complexes, even in a competitive solvent, such as DMSO.

Synthesis and supramolecular interaction of new oligomethylene bis(4-nitrophenylureylbenzamide) receptors with different anions.     

TiO2–Au composite nanofibers for photocatalytic hydrogen evolution

TiO₂-based materials for photocatalytic hydrogen (H₂) evolution have attracted much interest as a renewable approach for clean energy applications. TiO₂–Au composite nanofibers (NFs) with an average fiber diameter of ∼160 nm have been fabricated by electrospinning combined with calcination treatment. In situ reduced gold nanoparticles (NPs) with uniform size (∼10 nm) are found to disperse homogenously in the TiO₂ NF matrix. The TiO₂–Au composite NFs catalyst can significantly enhance the photocatalytic H₂ generation with an extremely high rate of 12 440 μmol g⁻¹ h⁻¹, corresponding to an adequate apparent quantum yield of 5.11% at 400 nm, which is 25 times and 10 times those of P25 (584 μmol g⁻¹ h⁻¹) and pure TiO₂ NFs (1254 μmol g⁻¹ h⁻¹), respectively. Furthermore, detailed studies indicate that the H₂ evolution efficiency of the TiO₂–Au composite NF catalyst is highly dependent on the gold content. This work provides a strategy to develop highly efficient catalysts for H₂ evolution.

The H₂ production rate of TiO₂–Au nanofibers is dramatically improved to 12 440 μmol g⁻¹ h⁻¹, 10 times that of pure TiO₂.     

Nitrogen-doped hierarchical porous carbon derived from a chitosan/polyethylene glycol blend for high performance supercapacitors

Nitrogen-doped hierarchical porous carbon (NHPC) materials were synthesized by using a chitosan/polyethylene glycol (PEG) blend as raw material through a facile carbonization–activation process. In this method, chitosan was used as a nitrogen-containing carbon precursor, low cost and large-scale commercial PEG was employed as a porogen. The physical and electrochemical properties of the resultant NHPC were affected by the ratio of chitosan and PEG. The sample obtained by the ratio of 3 : 2 exhibits a high specific surface area (2269 m² g⁻¹), moderate nitrogen doping (3.22 at%) and optimized pore structure. It exhibits a high specific capacitance of 356 F g⁻¹ in 1 M H₂SO₄ and 271 F g⁻¹ in 2 M KOH at a current density of 1 A g⁻¹, and over 230 F g⁻¹ can be still retained at a high current density of 20 A g⁻¹ in both electrolytes. Additionally, the assembled symmetric supercapacitors show an excellent cycling stability with 94% (in 1 M H₂SO₄) and 97% (in 2 M KOH) retention after 10 000 cycles at 1 A g⁻¹. These results indicate that the chitosan/PEG blend can act as a novel and appropriate precursor to prepare low-cost NHPC materials for high-performance supercapacitors.

NHPC was prepared from a low cost chitosan/PEG blend by a facile method for high performance supercapacitors.     

N-doped porous carbons derived from Zn-porphyrin-MOF

N-doped porous metal–organic framework (MOF)-derived carbons (MDCs) were directly synthesized from a new Zn-DpyDtolP-MOF (ZnDpyDtolP·1/2DMF, H₂DpyDtolP = 5,15-di(4-pyridyl)-10,20-di(4-methylphenyl)porphyrin) containing a 3D hexagonal network through a self-templated carbonization method. KOH-activated MDC derivatives denoted as MDC-700-nKOH were also prepared with different weight ratios of KOH activator to MDC (MDC : KOH = 1 : n, where n = 1, 2). Compared to bare MDC, MDC-700-nKOH showed effective improvements of both gas sorption and electrochemical capacitive properties. More developed microporosity by KOH activation might induce great enhancement of high operating capacitive performances. The N-doped MDC-700-2KOH had high maximum gravimetric specific capacitance (555.6 F g⁻¹) and specific energy (40.4 W h kg⁻¹) at 0.1 A g⁻¹ in 1 M H₂SO₄. Even at a high current density of 190 A g⁻¹ in 6 M KOH, it exhibited high capacitive performance with a large specific power of 80 423 W kg⁻¹. MDC-700-nKOH electrodes also showed good recycling properties of electrochemical capacitance up to 30 000 cycles.

The porphyrin-based Zn-MOF is directly carbonized and activated by KOH for the generation of N-doped porous carbons acting as high performance supercapacitor electrode materials.     

A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3−

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu²⁺ and HSO₃⁻ in a CH₃OH/H₂O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor ML showed an obvious “on–off” fluorescence quenching response toward Cu²⁺ and the ML-Cu²⁺ complex showed an “off–on” fluorescence enhancement response toward HSO₃⁻. The detection limit of the sensor ML was 0.36 μM to Cu²⁺ and 1.4 μM to HSO₃⁻. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu²⁺ and the recovery rate of ML-Cu²⁺ complex identifying HSO₃⁻ could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4–8.

A highly selective chemosensor based on a BODIPY chromophore for sequential recognition of Cu²⁺ and HSO₃⁻.     

Fabrication of high performance TFN membrane containing NH2-SWCNTs via interfacial regulation

A high-flux thin film nanocomposite (TFN) nanofiltration (NF) membrane for low pressure operation (3.5 bar) was fabricated by blending purified amino-functionalized single-walled carbon nanotubes (NH₂-SWCNTs) with piperazine (PIP) as aqueous phase monomers through interfacial polymerization (IP). The surface properties and structures of the polyamide (PA) active layer were suitably tailored by introducing different amounts of NH₂-SWCNTs into the PA layer. It was found that the homogeneous incorporation of NH₂-SWCNTs facilitated a more integral PA layer along with improved roughness, hydrophilicity, and surface charge of the modified membranes, which could be validated by membrane characterisation including SEM, AFM, ATR-FTIR, XPS, zeta potential and water contact angle measurements. Based on cross-flow NF tests, the optimized ultra-thin NH₂-SWCNT-TFN membranes with 0.002 wt% of NH₂-SWCNTs exhibited outstanding water permeability of up to 17.8 L m⁻² h⁻¹ bar⁻¹, 71.1% higher than that of the pristine membrane, along with high MgSO₄ rejection of 91.0% and Na₂SO₄ rejection of 96.34%. Meanwhile, NH₂-SWCNT-TFN membranes also showed excellent long-term stability and antifouling ability. This work demonstrates a facile strategy to fabricate a scalable, low-pressure and ultra-thin TFN membrane with excellent performance.

The surface properties and structures of the polyamide (PA) active layer were suitably tailored by introducing different amounts of NH₂-SWCNTs into the PA layer.     

Ultrathin porous amine-based solid adsorbent incorporated zeolitic imidazolate framework-8 membrane for gas separation

A novel gas separation approach is proposed in this work by combining an amine-based solid adsorbent with a zeolitic imidazolate framework-8 (ZIF-8) membrane. This was achieved by incorporating the amine-based solid adsorbent during the fabrication of the ZIF-8 membrane on a macroporous substrate. An amine-based solid adsorbent was prepared using porous ZIF-8-3-isocyanatopropyltrimethoxysilane (IPTMS) and N-[(3-trimethoxysilyl)propyl]diethylenetriamine (3N-APS) amine compounds. The as-prepared porous amine-based solid adsorbent (denoted as ZIF-8-IPTMS-3N-APS) possessed excellent adsorptive CO₂/N₂ and CO₂/CH₄ separation performances. As the adsorbent needs to be regenerated, this could indicate that the CO₂ adsorption separation process cannot be continuously operated. In this work, an amine-based solid adsorbent was applied during the preparation of the ZIF-8 membranes owing to the following reasons: (i) gas separation by the membrane can be operated continuously; (ii) the amino group provides a heterogeneous nucleation site for ZIF-8 to grow; and (iii) the reparation of surface defects on the macroporous substrate can be performed prior to the growth of the ZIF-8 membrane. Herein, the ZIF-8 membrane was successfully fabricated, and it possessed excellent CO₂/CH₄, CO₂/N₂, and H₂/CH₄ separation performances. The 0.6 μm ultrathin ZIF-8 membrane demonstrated a high CO₂ permeance of 4.75 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 35 °C and 0.1 MPa, and ideal CO₂/N₂ and CO₂/CH₄ selectivities of 4.67 and 6.02, respectively. Furthermore, at 35 °C and 0.1 MPa, the ideal H₂/CH₄ selectivity of the ZIF-8 membrane reached 31.2, and a significantly high H₂ permeance of 2.45 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹.

The amine-based solid adsorbent was innovatively incorporated during the fabrication of the ZIF-8 membrane for gas separation.     

Three-channel capillary NF membrane with PAMAM-MWCNT-embedded inner polyamide skin layer for heavy metals removal

Nanofiltration (NF) membranes with simultaneous high rejection of divalent cations and anions and high water permeation were designed and fabricated via interfacial polymerization (IP) on three-channel capillary ultrafiltration (UF) membranes. MWCNTs-COOH were modified with poly(amidoamine) (PAMAM) and the as-synthesized MWCNTs-PAMAM were embedded into the inner polyamide skin-layer of the NF membranes by incorporating them into a piperazine (PIP) aqueous solution, followed by IP with trimesoyl chloride (TMC). The rigid MWCNTs and the dendrimer PAMAM molecules endow the as-fabricated NF membranes with high porosity and good hydrophilicity. Additionally, the –NH₂ groups of PAMAM introduce some positive sites into the polyamide layer. The as-prepared NF membranes with incorporated MWCNTs-PAMAM exhibit a pure water flux of 48.7 L m⁻² h⁻¹ and 92.6% and 88.5% rejection for Na₂SO₄ and MgCl₂, respectively, at 4 bar. Moreover, the NF membranes display high rejection for sulfates and metal cations, including heavy metal ions. The practicability of the membranes for mine-wastewater treatment was tested, and the membranes showed above 80% rejection of heavy metals and solution flux of about 30 L m⁻² h⁻¹. In addition, their separation performance and stability were satisfactory during the long-term run. The high rejection of the membranes for metal cations is ascribed to the positive sites offered by MWCNTs-PAMAM and the narrow membrane pores since both electrostatic repulsion and size exclusion play a role during membrane filtration. The good separation performance of the membranes for multivalent anions and heavy metal cations illustrates their potential for applications in heavy metal wastewater treatment.

MWCNTs-PAMAM were incorporated into the polyamide layer of NF membranes and the prepared membranes showed good permeation and rejection performances.     

Mesoporous-rich calcium and potassium-activated carbons prepared from degreased spent coffee grounds for efficient removal of MnO42− in aqueous media

Commercial ACs typically possess high surface areas and high microporosity. However, ACs with appreciable mesoporosity are growing in consideration and demand because they are beneficial for the adsorption of large species, such as heavy metal ions. Thus, in this study, degreased coffee grounds (DCG) were used as precursors for the production of ACs by means of chemical activation at 600 °C for the efficient removal of manganese in the form of MnO₄²⁻. One of the most common activating agents, ZnCl₂, is replaced by benign and sustainable CaCl₂ and K₂CO₃. Three ratios 1 : 1, 1 : 0.5 and 1 : 0.1 of precursor-to-activating agent (g g⁻¹) were investigated. Porosimetry indicates 1 : 1 CaCl₂ DCGAC is highly mesoporous (mesopore volume 0.469 cm³ g⁻¹). CaCl₂ DCGAC and K₂CO₃ DCGAC shows high adsorption capacities of 0.494 g g⁻¹ and 0.423 g g⁻¹, respectively for the uptake of MnO₄²⁻ in aqueous media. The adsorption process follows pseudo-second order kinetics inline with the Freundlich isotherm (R² > 0.9). Thermodynamic data revealed negative values of ΔG (approx −0.1751 kJ mol⁻¹) demonstrating that the adsorption process on 1 : 1 CaCl₂DCGAC was spontaneous.

Spent coffee grounds are an interesting high volume renewable resource for valorisation. Activation with CaCl₂ produces mesoporous carbons with high capacity for removal of MnO₄²⁻.     

Removal of As(iii) and As(v) from water using green,silica-based ceramic hollow fibre membranes via direct contact membrane distillation

Arsenite [As(iii)] and arsenate [As(v)] removal by direct contact membrane distillation (DCMD) using novel hydrophobic green, silica-based ceramic hollow fibre membranes derived from agricultural rice husk was investigated in this work. The green ceramic hollow fibre membranes were prepared from amorphous (ASHFM) and crystalline (CSHFM) silica-based rice husk ash and modified to be hydrophobic via immersion fluoroalkylsilane (FAS) grafting of 1H,1H,2H,2H-perfluorodecyltriethoxysilane. Superhydrophobic contact angle values up to 157° and 161° were obtained for ASHFM and CSHFM, respectively. Remarkably, the membrane surface morphology mimicked a look-alike lotus-leaf structure with decrement in pore size after grafting via the silane agent for both membranes. The effect of arsenic pH (3–11), arsenic concentration (1–1000 ppm) and feed temperature (50–80 °C) were studied and it was found that feed temperature had a significant effect on the permeate flux. The hydrophobic CSHFM, with a flux of 50.4 kg m⁻² h⁻¹ for As(iii) and 51.3 kg m⁻² h⁻¹ for As(v), was found to be the best of the tested membranes. In fact, this membrane can reject arsenic to the maximum contaminant level (MCL) limit of 10 ppb under any conditions, and no swelling mechanism of the membranes was observed after testing for 4 hours.

Arsenite [As(iii)] and arsenate [As(v)] removal by direct contact membrane distillation (DCMD) using novel hydrophobic green, silica-based ceramic hollow fibre membranes derived from agricultural rice husk was investigated in this work.     

Binuclear and tetranuclear Zn(ii) complexes with thiosemicarbazones: synthesis,X-ray crystal structures,ATP-sensing,DNA-binding,phosphatase activity and theoretical calculations

Two Zinc(ii) complexes [Zn₄(L¹)₄]·2H₂O (1) and [Zn₂(L²)₂]·2H₂O (2) of pyruvaldehydethiosemicarbazone ligands are reported. The complexes were characterized by elemental analysis, IR, NMR, UV-vis spectroscopy and by single-crystal X-ray crystallography. X-ray crystal structure determinations of the complexes show that though Zn : ligand stoichiometry is 1 : 1 in both the complexes, the molecular unit is tetranuclear for 1 and binuclear for 2. Both the complexes show selective sensing of ATP at pH 7.4 (0.01 M HEPES) in CH₃CN–H₂O (9 : 1) medium in the presence of other anions like AcO⁻, NO₃⁻, F⁻, Cl⁻, H₂PO₄⁻, HPO₄²⁻ and P₂O₇²⁻. The UV-titration experiments of complexes 1 and 2 with ATP results in binding constants of 2.0(±0.07) × 10⁴ M⁻¹ and 7.1(±0.05) × 10³ M⁻¹ respectively. The calculated detection limits of 6.7 μM and 1.7 μM for 1 and 2 respectively suggest that the complexes are sensitive detectors of ATP. High selectivity of the complexes is confirmed by the addition of ATP in presence of an excess of other anions. DFT studies confirm that the ATP complexes are more favorable than those with the other inorganic phosphate anions, in agreement with the experimental results. Phosphatase like activity of both complexes is investigated spectrophotometrically using 4-nitrophenylphosphate (NPP) as a substrate, indicating the complexes possess significant phosphate ester hydrolytic efficiency. The kinetics for the hydrolysis of the substrate NPP was studied by the initial rate method at 25 °C. Michaelis–Menten derived kinetic parameters indicate that rate of hydrolysis of the P–O bond by complex 1 is much greater than that of complex 2, the k_cat values being 212(±5) and 38(±2) h⁻¹ respectively. The DNA binding studies of the complexes were investigated using electronic absorption spectroscopy and fluorescence quenching. The absorption spectral titrations of the complexes with DNA indicate that the CT-DNA binding affinity (K_b) of complex 1 (2.10(±0.07) × 10⁶ M⁻¹) is slightly greater than that of 2 (1.11(±0.04) × 10⁶ M⁻¹). From fluorescence spectra the apparent binding constant (K_app) values were calculated and they are found to be 5.41(±0.01) × 10⁵ M⁻¹ for 1 and 3.93(±0.02) × 10⁵ M⁻¹ for 2. The molecular dynamics simulation demonstrates that the Zn(ii) complex 1 is a good intercalator of DNA.

A binuclear and a tetranuclear zinc(ii) of pyruvaldehyde thiosemicarbazone show selective sensing of ATP at pH 7.4 (0.01 M HEPES) in CH₃CN–H₂O (9 : 1) medium. The DNA binding and phosphatase activities of the complexes are also reported.     

A novel nanofiltration membrane inspired by an asymmetric porous membrane for selective fractionation of monovalent anions in electrodialysis

The present study describes the synthesis of new nanofiltration membranes inspired by asymmetric porous membranes used as monovalent anion selective membranes for electro-membrane separation. The membrane surface was firstly modified, by deposition of a mussel-inspired “bio-glue” polydopamine (PDA) layer, and subsequently a compact polyamide layer was polymerized on the surface of the membrane''s active layer. The chemical constitution and structure of these modified porous membranes were explored by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The surface roughness and hydrophilicity of the membranes were explored by atomic force microscopy (AFM) and water contact angle measurements, respectively. In addition, the electrochemical properties of the surface of the modified membranes were analyzed in terms of membrane surface resistance and zeta potential values. As for the performance of these modified porous membranes, this was investigated by measuring the permselectivity of a Cl⁻/SO₄²⁻ system. The obtained results show that the new membranes exhibit an enhanced monovalent anion permselectivity, which is in agreement with the improved membrane surface properties. Furthermore, membranes modified by the addition of a PDA layer and a dense polyamide active layer lead to a significant improvement in selectivity , compared with a conventional interfacial polymerization modified membrane . The excellent performance can be ascribed to the synergistic effect of the compact PDA layer and negatively charged interfacial polymerization layer, dependent on the sieving and electrostatic repulsion, respectively. Thus, this process is promising for the further development of porous monovalent selective anion exchange membranes.

The present study describes the synthesis of new nanofiltration membranes inspired by asymmetric porous membranes used as monovalent anion selective membranes for electro-membrane separation.     

Hydrophilic and organophilic pervaporation of industrially important α,β and α,ω-diols

The distillation-based purification of α,β and α,ω-diols is energy and resource intensive, as well as time consuming. Pervaporation separation is considered to be a remarkable energy efficient membrane technology for purification of diols. Thus, as a core pervaporation process, hydrophilic polyvinyl alcohol (PVA) membranes for the removal of water from 1,2-hexanediol (1,2-HDO) and organophilic polydimethylsiloxane–polysulfone (PDMS–PSF) membranes for the removal of isopropanol from 1,5 pentanediol (1,5-PDO) were employed. For 1,2-HDO/water separation using a feed having a 1 : 4 weight ratio of 1,2-HDO/water, the membrane prepared using 4 vol% glutaraldehyde (GA4) showed the best performance, yielding a flux of 0.59 kg m⁻² h⁻¹ and a separation factor of 175 at 40 °C. In the organophilic pervaporation separation of the 1,5-PDO/IPA feed having a 9 : 1 weight ratio of components, the PDMS membrane prepared with a molar ratio of TEOS alkoxy groups to PDMS hydroxyl groups of 70 yielded a flux of 0.12 kg m⁻² h⁻¹ and separation factor of 17 638 at 40 °C. Long term stability analysis found that both hydrophilic (PVA) and organophilic (PDMS) membranes retained excellent pervaporation output over 18 days'' continuous exposure to the feed. Both the hydrophilic and organophilic membranes exhibited promising separation performance at elevated operating conditions, showing their great potential for purification of α,β and α,ω-diols.

The distillation-based purification of α,β and α,ω-diols is energy and resource intensive, as well as time consuming.     

Preparation and photocatalytic performance of tungstovanadophosphoric heteropoly acid salts

Tungstovanadophosphoric heteropoly acid H₅PW₁₀V₂O₄₀·5.76H₂O (HPWV) has been synthesized via stepwise acidification and gradual addition of elements. Some metals like Fe, Al and Cu were introduced into the heteropoly acid (HPA) in the molar ratio of 10 : 6, 10 : 6 and 10 : 4 respectively. The prepared catalysts were characterized by UV, FTIR, TG/DTA and XRD. The results indicated that HPWV and its metal salts all contain Keggin units, which are the primary structures of the heteropoly acids. The homogeneous photocatalytic degradation of phenol by heteropoly acid salts was studied in detail under artificial UV irradiation and addition of hydrogen peroxide (H₂O₂), and the effects of initial phenol and H₂O₂ concentrations on the rate of photocatalytic phenol degradation were examined. The results suggested that the heteropoly acid salts showed good catalytic activities for phenol degradation via the ·OH radical mechanism. Under irradiation with a 10 W Hg lamp, 96% phenol was degraded within less than 60 min in the solution containing 50 mg L⁻¹ phenol + 2 μmol L⁻¹ Fe₅(PW₁₀V₂O₄₀)₃ + 4 μmol L⁻¹ H₂O₂, with the performance of the catalysts in order FePWV > AlPWV > CuPWV > HPWV. This work demonstrated that the photo-Fenton reaction catalyzed by the heteropoly acid salts was a promising advanced oxidation tool for the treatment of phenol-containing wastewater.

Tungstovanadophosphoric heteropoly acid H₅PW₁₀V₂O₄₀·5.76H₂O (HPWV) has been synthesized via stepwise acidification and gradual addition of elements.     

Sulfonated graphene oxide/Nafion composite membranes for high temperature and low humidity proton exchange membrane fuel cells

Iron oxide (Fe₃O₄) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe₃O₄–SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe₃O₄ nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe₃O₄–SGO composite membranes. Nafion/Fe₃O₄–SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe₃O₄–SGO (3 wt%) composite membrane at 120 °C under 20% relative humidity (RH) was 11.62 mS cm⁻¹, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe₃O₄–SGO composite membrane delivered a peak power density of 258.82 mW cm⁻² at a load current density of 640.73 mA cm⁻² while operating at 120 °C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm⁻² was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm⁻². Thus, Nafion/Fe₃O₄–SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.

Preparation process of Nafion/Fe₃O₄–SGO composite membranes.