Qingchun Ge

Polyelectrolyte-Promoted Forward Osmosis–Membrane Distillation (FO–MD) Hybrid Process for Dye Wastewater Treatment

Polyelectrolytes have proven their advantages as draw solutes in forward osmosis process in terms of high water flux, minimum reverse flux, and ease of recovery. In this work, the concept of a polyelectrolyte-promoted forward osmosis-membrane distillation (FO-MD) hybrid system was demonstrated and applied to recycle the wastewater containing an acid dye. A poly(acrylic acid) sodium (PAA-Na) salt was used as the draw solute of the FO to dehydrate the wastewater, while the MD was employed to reconcentrate the PAA-Na draw solution. With the integration of these two processes, a continuous wastewater treatment process was established. To optimize the FO-MD hybrid process, the effects of PAA-Na concentration, experimental duration, and temperature were investigated. Almost a complete rejection of PAA-Na solute was observed by both FO and MD membranes. Under the conditions of 0.48 g mL(-1) PAA-Na and 66 °C, the wastewater was most efficiently dehydrated yet with a stabilized PAA-Na concentration around 0.48 g mL(-1). The practicality of PAA-Na-promoted FO-MD hybrid technology demonstrates not only its suitability in wastewater reclamation, but also its potential in other membrane-based separations, such as protein or pharmaceutical product enrichment. This study may provide the insights of exploring novel draw solutes and their applications in FO related processes.

Hydroacid complexes: a new class of draw solutes to promote forward osmosis (FO) processes

A new class of draw solutes from hydroacid complexes is presented. With hydroacid complexes as draw solutes in FO, superior performance is achieved in terms of high water fluxes and negligible reverse solute fluxes. The characteristics of expanded configurations, abundant hydrophilic groups and ionic species are essential for hydroacid complexes as competent draw solutes.

Effective As(III) Removal by A Multi-Charged Hydroacid Complex Draw Solute Facilitated Forward Osmosis-Membrane Distillation (FO-MD) Processes

Effective removal of As(III) from water by an oxalic acid complex with the formula of Na3[Cr(C2O4)3] (Na-Cr-OA) is demonstrated via an forward osmosis-membrane distillation (FO-MD) hybrid system in this study. Na-Cr-OA first proved its superiority as a draw solute with high water fluxes and negligible reverse fluxes in FO, then a systematic investigation of the Na-Cr-OA promoted FO process was conducted to ascertain the factors in As(III) removal. Relatively high water fluxes of 28 LMH under the FO mode and 74 LMH under the pressure retarded osmosis (PRO) mode were achieved when using a 1000 ppm As(III) solution as the feed and 1.0 M Na-Cr-OA as the draw solution at 60 °C. As(III) removal with a water recovery up to 21.6% (FO mode) and 48.3% (PRO mode) were also achieved in 2 h. An outstanding As(III) rejection with 30-3000 μg/L As(III) in the permeate was accomplished when As(III) feed solutions varied from 5 × 10(4) to 1 × 10(6) μg/L, superior to the best FO performance reported for As(III) removal. Incorporating MD into FO not only makes As(III) removal sustainable by reconcentrating the Na-Cr-OA solution simultaneously, but also reduces the As(III) concentration below 10 μg/L in the product water, meeting the WHO standard.

The different roles of metal ions and water molecules in the recognition and catalyzed hydrolysis of ATP by phenanthroline-containing polyamines

The phenanthroline bridging polyaza ligands L1, L2 and L3 can selectively and strongly bind nucleotides at physiological pH, and hence accelerate the hydrolysis rate of the bound ATP. It is interesting that a phosphoramidate intermediate at 2.88 ppm (should be added 5.63 ppm when compared with other models) was found in the hydrolysis process of L/ATP. By introduction of metal ions (critical Zn(2+) or hard Mg(2+), Ca(2+)) to the L/ATP system, recognition of the anionic substrates by the protonated ligands was greatly promoted. However, due to the different affinities of metal ions to the receptor and the substrate, ATP hydrolysis in Zn(2+)/L/ATP system and Mg(2+)(Ca(2+))/L/ATP system occurs through different mechanisms. By comparison with the M/ATP (M=Zn(2+), Mg(2+), Ca(2+)) system, the rates of ATP-hydrolysis in the Mg(2+)Ca(2+)/L/ATP system and the Zn(2+)/L/ATP system were enhanced and retarded, respectively. Moreover, the reasons contributing to large rate range of the L/ATP systems and M(2+)/L/ATP systems were given. The results show that metal ions vertically regulate the recognition and hydrolysis of ATP. On the other hand, water molecule participates in the hydrolysis reactions at different steps with different functions in the L/ATP systems and M(Zn(2+), Mg(2+), Ca(2+))L/ATP systems.

Thermodynamic studies on supramolecular interactions of metal ions with nucleotides/tripods ligands

Abstract Four closely related polyamino tripodal ligands 1,3,5-tri(n-2′,5′-diaminohexane)-benzene (L1), 1,3,5-tri(n-2′,5′-diaminoheptane)-benzene (L2), 1,3,5-tri(n-2′,5′-diaminooctane)-benzene (L3) and 1,3,5-tri(n-2′,5′-diaminononane)-benzene (L4) were synthesized and characterized. Each tripodal ligand forms six protonated species in solution. The binding of these tripodal ligands to the nucleotide anions ATP, ADP and AMP are described in detail, with equilibrium constants given for each species formed. The strength of binding increases with the number of protons, corresponding to an increase in the number of hydrogen bonds and to an increase in the coulombic attractive forces. Moreover, the existence of a benzene spacer takes π-stacking interactions with the nucleobase residue of the nucleotides. At the same time, the coordination properties of the ternary complexes formed from the above tripods and Zn(II) and ATP were studied. The metal complexes of tripods recognize the nucleotides via multiple interactions that are similar to those occurring in the center of enzymes.

The different roles of metal ions and water molecule in the hydrolysis of ATP catalyzed by phenanthroline-based polyamines

Abstract The phenanthroline (Phen)-based polyaza ligands can efficiently recognize nucleotides and significantly enhance the rate of ATP hydrolysis under the regulation of metal ions, which act as “messenger” between the substrates and the receptors. The water molecule (or –OH) participates in the catalytic hydrolysis of ATP in different steps with different functions.

Forward osmosis for oily wastewater reclamation: Multi-charged oxalic acid complexes as draw solutes

Forward osmosis (FO) has demonstrated its merits in hybrid FO seawater desalination. However, FO may have a potential for other applications if suitable draw solutes are available. In this study, a series of novel draw solutes based on oxalic acid (OA)-transitional metal complexes are presented. Influential factors of FO performance have been systematically investigated by varying the transitional metals, cations of the complex draw solutes as well as the experimental conditions. Compared to NaCl and other recently synthesized draw solutes, the OA complexes show superior FO performance in terms of high water fluxes up to 27.5 and 89.1 LMH under the respective FO and PRO (pressure retarded osmosis) modes, both with negligible reverse solute fluxes. The features of octahedral geometry, abundant hydrophilic groups and ionic species are crucial for the OA complexes as appropriate draw solutes with satisfactory FO performance. Among the synthesized OA complexes, the ammonium salt of chromic complex (NH4-Cr-OA) outperforms others due to the presence of more ionic species in its complex system. NH4-Cr-OA also performs better than the typical NaCl draw solute in FO oily wastewater treatment with higher water recovery and negligible reverse fluxes. Dilute solutions of OA complexes have been reconcentrated through membrane distillation (MD) and reused to new round of FO processes. The OA complexes have demonstrated their suitability and superiority as a novel class of draw solutes for the FO process in this study.

Synthesis, characterization and thermodynamic properties of metal complexes of a phenanthroline-bridging macrocyclic ligand

A macrocyclic ligand incorporating phenanthroline has been synthesized by the reaction of 2,9-dichloromethyl-1,10-phenanthroline with dioxo[13]aneN4(dioxo[13]aneN4 = 1,4,7,11-tetraazacyclotridecane-8,10-dione). The stability constants of its Cu2+, Co2+, Hg2+ and Pd2+ metal complexes have been measured by potentiometric pH titration technique. It was found that a π-dp electrostatic interaction between Cu2+ and the phenanthroline moiety does exist in the binary systems. Stability constants of ternary systems containing Cu2+, ligand L(L1) and α-amino acids (AA, L2) in aqueous solution were also determined. Linear free energy relationships (LFER) exist in the ternary systems.

A Novel Multi-Charged Draw Solute That Removes Organic Arsenicals from Water in a Hybrid Membrane Process

The potential of forward osmosis for water treatment can only be maximized with suitable draw solutes. Here a three-dimensional, multicharge draw solute of decasodium phytate (Na10-phytate) is designed and synthesized for removing organic arsenicals from water using a hybrid forward osmosis (FO) - membrane distillation (MD) process. Efficient water recovery is achieved using Na10-phytate as a draw solute with a water flux of 20.0 LMH and negligible reverse solute diffusion when 1000 ppm organic arsenicals as the feed and operated under ambient conditions with FO mode. At 50 °C, the novel draw solute increases water flux by more than 30% with water fluxes higher than 26.0 LMH on the FO side, drastically enhancing water recovery efficiency. By combining the FO and MD processes into a single hybrid process, a 100% recovery of Na10-phytate draw solute was achieved. Crucially, organic arsenicals or Na10-phytate draw solutes are both rejected 100% and not detected in the permeate of the hybrid process. The complete rejection of both organic arsenicals and draw solutes using hybrid membrane processes is unprecedented; creating a new application for membrane separations.

The role of copper(II) ion in regulating H-bonding and coulombic interactions in copper(II)/tripod/polyphosphate systems

The tripodal ligands L, 1,3,5-tri(5-R-2,5-diazapentyl)benzene (R = Me, L1; Et, L2, n-Pr, L3; n-Bu, L4), when protonated, bind strongly and selectively with polyphosphates (Ph) such as orthophosphate (PO), pyrophosphate (PP) and tri-phosphate (tP) respectively in aqueous solution. The results are consistent with the hypothesis that the formation of hydrogen bonds as well as the coulombic interactions plays an important role in the supramolecular interactions between Ph and polyammonium receptors. Moreover, the stability constants of the ternary systems containing the CuII, tripod and polyphosphate were determined by the pH-metric method. Recognition of the polyphosphate anions by the protonated tripods was promoted by the introduction of CuII. Thus the bound metal ion can act as a ‘messenger’ to regulate the H-bonding and electrostatic interactions of the counter-part of the molecular complexes. Fundamental knowledge gained from such studies may then provide valuable insights into the relationship between the structure and reactivity and how the enzymes themselves function.