Enhanced Selective Electrosorption of Nitrate from Wastewater by Controllably Doping Nitrogen into Porous Carbon with Micropores.

The biological NO3- removal process might be accompanied by high CO2 emissions and operation costs. Capacitive deionization (CDI) has been widely studied as a very efficient method to purify water. Here, a porous carbon material with a tunable nitrogen configuration was developed. Characterization and density functional theory calculation show that nitrogenous functional groups have a higher NO3- binding energy than Cl-, SO42-, and H2PO4-. In addition, the selectivity of NO3- is improved after the introduction of micropores by using the pore template. The NO3- ion removal and selectivity of MN-C-12 are 4.57 and 3.46-5.42 times that of activated carbon (AC), respectively. The high NO3- selectivity and electrosorption properties of MN-C-12 (the highest N content and micropore area) are due to the synergistic effect of the affinity of nitrogen functional groups to NO3- and microporous ion screening. A CDI unit for the removal of nitrogen from municipal wastewater was constructed and applied to treat wastewater meeting higher discharge standards of A (N: 15 mg L-1) and B (N: 20 mg L-1) ((GB18918-2002), China). This work provides new insights into enhanced carbon materials for the selective electrosorption of wastewater by CDI technology.

MOF-Derived Ni/ZIF-8/ZnO Arrays on Carbon Fiber Cloth for Efficient Adsorption-Catalytic Oxidation.

The catalytic oxidation of toxic organic pollutants in water requires enhanced efficiency for commercial applications. A ZnO nanorod array grown on a carbon fiber cloth (CFC) serves as the zinc source to ensure that the Ni/ZIF-8/ZnO nanoreactor is constructed. The Ni/ZIF-8/ZnO/CFC nanoreactor efficiently activates peroxymonosulfate (PMS) for bisphenol A (BPA) degradation owing to its high density of active sites, high adsorbability, and dispersibility structure, which concentrates catalytic and adsorptive sites within a confined space. Experimental and theoretical calculations clearly show that the introduction of Ni is beneficial for improving the adsorption of BPA and the activation of PMS. The synergistic mechanism of BPA adsorption-PMS activation is also investigated, and the degradation pathway of BPA is examined. Moreover, a filter catalytic unit is constructed using Ni/ZIF-8/ZnO/CFC to achieve a continuous zero discharge of BPA, which is convenient for nanocatalyst recycling. This study aims to develop a new strategy for the removal of emerging organic pollutants from water using a system with strong adsorption and catalytic capabilities.

Renewable Adsorbents for Selective Phosphorus Removal: Co(OH)2-Derived ZIF-67 on Anion Exchange Resin.

Metal organic framework (MOF)-based adsorbents are appealing for removing low-concentration phosphates with interfering ions in wastewater purification, a new strategy developed to maintain the good activity of metal sites. Here, ZIF-67 was immobilized onto the porous surface of anion exchange resin (D-201) with a high loading amount of 22.0 wt % by a modifiable Co(OH)2 template. We observed that the removal rate of low-concentration phosphate (2 mg P/L) by ZIF-67/D-201 nanocomposites was 98.6%, and more than 90% phosphate adsorption capacity was still maintained, with 5 times molar concentration of interfering ions in the solution. Moreover, after six times of regeneration by solvothermal reaction in the ligand solution, the structure of ZIF-67 was better preserved in D-201 with more than 90% phosphate removal rate. ZIF-67/D-201 could be employed effectively in fixed-bed adsorption runs. By the analysis of experiment and characterization, we found that during the adsorption-regeneration process of ZIF-67/D-201 for phosphate, reversible structural transformation of ZIF-67 and Co3(PO4)2 occurred in D-201. In general, the study reported a new method to develop MOF adsorbents for wastewater treatment.

Sustainable and ultrafast antibiotics removal, self-cleaning and disinfection with electroactive metal-organic frameworks/carbon nanotubes membrane.

Although conventional nanofiltration (NF) membrane is widely applied in water treatment, it faces the challenges of insufficient selectivity toward emerging contaminants, low permeability and non-sustainable fouling control. Herein, a novel electroactive metal-organic frameworks/carbon nanotubes membrane was constructed by facile and green nanobubbles-mediated non-solvent-induced phase separation (NIPS) strategy for ultrafast antibiotics removal. It presented 3-fold to 100-fold higher permeability (101.3-105.7 L·h-1·m-2·bar-1) without compromising rejection (71.8 %-99.3 %) of common antibiotics (tetracycline, norfloxacin, sulfamethoxazole, sulfamethazine) than most commercial and state-of-the-art NF membranes. The separation mechanism was due to the synergy of loose selective layer with three-dimensional interconnected networks and UiO-66/CNTs with unique pore sieving and charge property. It also presented excellent antibiotics selectivity with high NaCl/tetracycline separation factor of 194 and CuCl2/tetracycline separation factor of 316 for remediation of antibiotics and heavy metal combined pollution. Meanwhile, it possessed efficient anti-fouling, antibacterial and electro-driven self-cleaning ability, which enabled sustainable fouling control and disinfection with short process, low energy and chemical consumption. Furthermore, potential application of UiO-66/CNTs membrane in wastewater reclamation was demonstrated by stable antibiotics rejection, efficient flux recovery and long-term stability over 260 h. This study would provide useful insights into removal of emerging contaminants from water by advanced NF membrane.

Defective MOFs-based electrocatalytic self-cleaning membrane for wastewater reclamation: Enhanced antibiotics removal, membrane fouling control and mechanisms.

In order to resolve the poor antibiotics rejection and serious fouling of ultrafiltration (UF) membrane during municipal wastewater reclamation, a novel anodic membrane (defective UiO-66 (D-UiO-66)/Graphite/Polyvinylidene fluoride (PVDF)) with high pure water flux (596.1 L•h - 1•m - 2•bar-1) was fabricated by incorporating defective zirconium based metal-organic framework (D-UiO-66) and conductive graphite particles into PVDF matrix and applied in the coupling of electro-oxidation and membrane filtration process. Compared to the other anodic membranes (i.e., Graphite/PVDF and UiO-66/Graphite/PVDF), D-UiO-66/Graphite/PVDF possesses superior anti-fouling and self-cleaning abilities (flux recovery=100%, model foulant: bovine serum albumin) in both intermittent and continuous supply of electric field under current density of 0.01 mA/cm2; moreover, efficient antibiotics (tetracycline, norfloxacin, tylosin and sulfamethoxazole) removal (> 96.6%) and bactericidal efficiency against E. coli and S. aureus (100%) were achieved simultaneously without the addition of chemical reagents due to the higher electrocatalytic activity of anodic membrane for oxidation of pollutants by •OH and •O2- free radicals. Three degradation pathways of antibiotics were proposed and the self-cleaning mechanism of membrane was dominated by the synergy of the partial mineralization and the reduced fouling potential of foulants after oxidation as revealed by the increase in hydrophilicity, and decrease in negative charge and molecular weight. The fabricated membrane also presents excellent electrochemical stability, separation and self-cleaning performance for treatment of municipal secondary effluent during long-term filtration with low electric energy consumption, which is promising in wastewater reclamation.

Pre-ozonation for the mitigation of reverse osmosis (RO) membrane fouling by biopolymer: The roles of Ca2+ and Mg2.

Despite plenty of literatures focused on the application of pre-ozonation prior to membrane, it was still unclear about the role of divalent cations (Ca2+ and Mg2+) in reverse osmosis (RO) membrane fouling mitigation. In this study, ozone pre-treatment (0.10, 0.25 and 0.50 mg O3/mg DOC (dissolved organic carbon)) was employed to oxidize model biopolymer, which was represented by bovine serum albumin (BSA) and sodium alginate (SA) in the presence of Ca2+ and Mg2+ (0.5, 1.0 and 2.0 mM). Cross-flow filtration was conducted to investigate RO membrane fouling by concentration mode. The results showed that at appropriate ozone dose there were measurable changes in physicochemical properties of BSA and SA, including increases in particle size, hydrophilicity, density of negative charge and carboxylic groups. Pre-ozonation markedly alleviated RO fouling by BSA at ozone dose of 0.25 mg O3/mg DOC when Ca2+ and Mg2+ concentrations raised from 0.5 to 2.0 mM since the increase in electrostatic (EL) repulsion and decrease in hydrophobic (HP) interaction compensated the increase in divalent cation bridging. Similar results were obtained for SA fouling in the presence of Mg2+. In contrast, the effect of pre-ozonation on SA fouling strongly depended on the concentration of Ca2+. In brief, it mitigated SA fouling at 0.5 mM Ca2+, whereas accelerated irreversible fouling at higher Ca2+ concentration (1.0 and 2.0 mM) due to the overwhelming effect of divalent cation bridging compared to EL and HP interactions, as revealed by adsorption experiments (in-situ streaming potential measurement). Pre-ozonation shifted the fouling layer from compact to porous and weakened the adhesion forces between foulants and membrane (foulants) except for SA containing 1.0 and 2.0 mM Ca2+. This study may provide the guidance for the application of pre-ozonation prior to RO filtration.

Influence of surface properties of RO membrane on membrane fouling for treating textile secondary effluent.

Reverse osmosis (RO) is a promising technology for treating and reusing textile secondary effluent (SE). To better understand the effect of membrane surface properties on membrane fouling, the performances of three commercial polyamide thin-film composite RO membranes (BW30-4040, CPA2-4040, and RE-4040-FEN) with different roughness and hydrophilicity were investigated for treating textile SE. The RO membranes were characterized by ATR-FTIR, SEM, AFM, and contact angle, respectively. The results showed that the flux increased with an increase in the surface hydrophilicity of membrane. CPA2-4040 had the highest hydrophilic surface and thus the largest initial flux. There was a strong correlation between the membrane fouling and the surface roughness; the fouling increased with an increase in the surface roughness. The roughest surface of CPA2-4040 led to the most significantly flux decline. However, the fouling reversibility was not related directly to surface roughness. BW30-4040 with the secondary roughness and the most hydrophobic surface had the highest fouling reversibility. This was mainly due to the primary hydrophilicity of textile SE in nature. Fluorescence excitation-emission matrix (EEM) showed that hydrophilic neutral protein-like matters and soluble microbial products (SMP) were the main foulants, thus stronger affinity with hydrophilic surface of membrane. Graphical abstract ᅟ.