The behavior of [Fe(2)(CO)(4)(κ(2)-PNP(R))(μ-pdt)] (PNP(R) =(Ph(2)PCH(2))(2)NR, R=Me (1), Ph (2); pdt=S(CH(2))(3)S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3)SO(3)H or CH(3)SO(3)H; the cation with a bridging hydride ligand, 1 μH(+) (R=Me) or 2 μH(+) (R=Ph) is obtained rapidly. Only 1 μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4)·Et(2)O or CF(3)SO(3)H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2)-H(2) species in the Fe(I)Fe(II) state. When R=Ph, the bridging hydride cation 2 μH(+) cannot be protonated at the amine function by HBF(4)·Et(2)O or CF(3)SO(3)H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH(+). The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7 s(-1)) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.
Fouling has been widely recognized as the Achilles’ heel of membrane processes and the growing perception about the relevance of this critical issue has driven the development of advanced antifouling strategies. Herein, novel fouling-resistant ultrafiltration (UF) membranes for Cadmium (Cd) remediation were developed via a blending method by combining the flexibility of cellulose acetate (CA) with the complex properties of poly(acrylic acid) (PAA). A systematic characterization, based on differential scanning calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR), confirmed the homogeneity of the blend favored by hydrogen interconnections between CA and PAA polymeric chains. The concentration of PAA with respect to CA played a key role in tuning the morphology and the hydrophilic character of the novel UF membranes prepared via non-solvent-induced phase separation (NIPS). UF experiments revealed the tremendous advantages of the blend since CA/PAA membranes showed superior performance with respect to the neat CA membrane in terms of (i) water permeability; (ii) Cd rejection; and (iii) antifouling resistance to humic acid (HA). Concisely, the increasing of the concentration of PAA in the casting solution was found to be beneficial to improve the flux recovery ratio (FRR) coupled with the decline of the total fouling ratio (Rt). Overall, PAA is an effective additive to prepare CA membranes with enhanced antifouling properties exploitable for the remediation of water bodies contaminated by heavy metals via UF process.
The presence of heavy metals in wastewater has become a serious issue and a global concern for the environment and public health with rapid progress of modern textile industry. To minimize the health risks of heavy metals their complexation to a chelating agent constitute a promising process using membrane separation. We highlight for the first time the use of Keggin type-polyoxometalates (PW12) as complexing agent to eliminate heavy metals from synthetic textile wastewater. Indeed, Filtration experiments were performed through the ultrafiltration organic regenerated cellulose membrane (3KDa). Effects of pressure (1–2.5 bar), PW12 concentration (10–50 mg·L−1), salt concentration (10−4–2 M) and pH value (2–12) on cadmium (Cd) and copper (Cu) removal were regularly explored. Experimental data showed that the addition of PW12 improves metal removal efficiency (up to 90%). The addition of NaCl salt decrease significantly the metals retention until 42%. The retention drop probably due to the competition between Na+ and metals on complexation same negative sites of the PW12 and to the electric double-layer compressing. 24 full factorial design has been used to evaluate the most influencing parameters. Results obtained revealed that the maximum metal retention was 99% for both Cd and Cu.
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