MOFs for water purification

A new strategy to construct MOF-on-MOF derivatives for the removal of tetracycline hydrochloride from water by activation of peroxymonosulfate

A MOF-on-MOF composite derivative material named ZIF-67@Ce-MOF-600 was designed and synthesized. The preparation of ZIF-67@Ce-MOF-600 was optimized from the aspects of the ratio of metal and ligand, heat-treatment temperature. It was demonstrated by XRD, FT-IR, SEM-EDS and TEM. The optimum conditions for the activation of PMS by ZIF-67@Ce-MOF-600 for the degradation of tetracycline (TC) were investigated by adjusting the catalyst dosage, TC, pH, peoxymonosulfate (PMS) concentration, and different kinds of water, co-existing anions and pollution. Under optimal conditions (20 mg catalysts and 50 mg PMS added) in 100 mL of tetracyclines (TC) solvent (20 mg TC/L), the removal rate could reach up to 99.2% and after five cycles was 70.5%. The EPR results indicated the presence of free radicals and non-free radical, among which free radicals intended to play a major role in the degradation process. Its possible degradation pathways and attack sites were analyzed by liquid-phase mass spectrometry and DFT analysis.

Application of manganese oxide-based materials for arsenic removal: A review

In the context of growing arsenic (As) contamination in the world, there is an urgent need for an effective treatment approach to remove As from the environment. Industrial wastewater is one of the primary sources of As contamination, which poses significant risks to both microorganisms and human health, as the presence of As can disrupt the vital processes and synthesis of crucial macromolecules in living organisms. The global apprehension regarding As presence in aquatic environments persists as a key environmental issue. This review summarizes the recent advances and progress in the design, strategy, and synthesis method of various manganese-based adsorbent materials for As removal. Occurrence, removal, oxidation mechanism of As(III), As adsorption on manganese oxide (MnOx)-based materials, and influence of co-existing solutes are also discussed. Furthermore, the existing knowledge gaps of MnOx-based adsorbent materials and future research directions are proposed. This review provides a reference for the application of MnOx-based adsorbent materials to As removal.

Enhanced adsorption and co-adsorption of heavy metals using highly hydrophilicity amine-functionalized magnetic hydrochar supported MIL-53(Fe)-NH2: performance, kinetics, and mechanism studies

It is a "kill two birds with one stone" method to convert invasive plants into hydrochar via hydrothermal carbonization as well as coinciding with 3R rules (reduction, recycling, and reuse). In this work, a series of hydrochars (pristine, modified, and composite) derived from invasive plants Alternanthera philoxeroides (AP) were prepared and applied to the adsorption and co-adsorption of heavy metals (HMs) such as Pb(II), Cr(VI), Cu(II), Cd(II), Zn(II), and Ni(II). The results show that MIL-53(Fe)-NH₂- magnetic hydrochar composite (M-HBAP) displayed a strong affinity for HMs, which the maximum adsorption capacities for HMs were 153.80 (Pb(II)), 144.77 (Cr(VI)), 80.58 (Cd(II)), 78.62 (Cu(II)), 50.39 (Zn(II)), and 52.83(Ni(II)) mg/g (c₀ = 200 mg/L, t = 24 h, T = 25 ℃, pH = 5,2,6,4,6,5). This may be because the doping of MIL-53(Fe)-NH₂ enhanced the surface hydrophilicity of hydrochar, which allows hydrochar to disperse in the water within 0.12 s and possessed excellent dispersibility compared with pristine hydrochar (BAP) and amine-functionalized magnetic modified hydrochar (HBAP). Furthermore, the BET surface area of BAP was improved from 5.63 to 64.10 m²/g after doing MIL-53(Fe)-NH₂. M-HBAP shows a strong adsorption effect on the single HMs system (52-153 mg/g), while it decreased significantly (17-62 mg/g) in the mixed HMs system due to the competitive adsorption. Cr(VI) can produce strong electrostatic interaction with M-HBAP, Pb(II) can react with CaC₂O₄ on the surface of M-HBAP for chemical precipitation, and other HMs can react with functional groups on the surface of M-HBAP for complexation and ion exchange. In addition, five adsorption-desorption cycle experiments and vibrating sample magnetometry (VSM) curves also proved the feasibility of the M-HBAP application.

Enhanced photo-Fenton activity and stability for sulfamethoxazole degradation by FeS2@TiO2 heterojunction derived from MIL-125

FT-x composites with core-shell structure (FT = FeS₂@TiO₂, x represents the mass ratio of the used FeCl₃·6H₂O to MIL-125) were fabricated by a hydrothermal method using MIL-125(Ti) as a self-sacrificing template. Both the photo-Fenton activity and stability of the FT-1 were improved greatly in comparison with its counterparts due to the unique core-shell structure and synergistic effect between FeS₂ and TiO₂. Especially, the Fe leaching concentration of FT-1 was approximately 1/10 of the individual FeS₂, benefiting from the protection effect of TiO₂ shell. Under dark condition, the formed FeOOH occupied active sites and inhibited iron cycle as well as H₂O₂ decomposition, leading to the inactivation of FT-1. UV light irradiation not only boosted the catalytic activity but also prevented the FT-1 from reactivity decline owning to the regeneration of Fe²⁺ by photogenerated electrons and continuous generation of ·OH. Experimental and DFT calculation results indicated that a type-II heterojunction was formed, in which photogenerated electrons were transferred from FeS₂ core to TiO₂ shell, accelerating charge separation and further boosting sulfamethoxazole (SMX) degradation. FT-1 displayed outstanding photo-Fenton activity in wide pH ranged from 2 to 6 and good anti-interfering ability toward impurities in water matrix. Besides, the reusability of FT-1 was good, in which 90% SMX degradation was maintained even after 5 runs. Noteworthy, the photo-Fenton activity was recovered via a revulcanization process, in which FeOOH was completely transformed into FeS₂. This founding provided insights for the design and construction of heterojunction with both excellent photo-Fenton activity and stability.

Structure-performance correlation guided cerium-based metal-organic frameworks: Superior adsorbents for fluoride removal in water

Fluoride in the hydrosphere exceeds the standard, which could be critically hazardous to human health and the natural environment. The adsorption method is a mature and effective way to remove pollutants in water, including fluoride. In this study, we synthesized three kinds of cerium-based metal-organic frameworks (Ce-MOFs) with different structures and properties by modulating the organic ligands (i.e., trimesic acid (BTC), 1,2,4,5-benzenetetracarboxylic acid (PMA), and terephthalic acid (BDC)) via the solvothermal method. The adsorption kinetics of Ce-MOFs on fluoride well fit the pseudo second order model, and their adsorption isotherms also conform to Langmuir isothermal model. The thermodynamic study reveals that the adsorption process is a spontaneous endothermic reaction. The maximum saturated adsorption capacities of Ce-BTC, Ce-PMA, and Ce-BDC are 70.7, 159.6, and 139.5 mg g^-1, respectively. Ce-MOFs have stable and excellent adsorption capacity at pH = 3-9. Coexisting anions (Cl^-, SO₄^2-, and NO₃^-) do not affect the performance of Ce-MOFs for fluoride removal. Moreover, Ce-MOFs also show their broad prospect as superior fluoride adsorbents because of their excellent performance and reusability in real water samples. Organic ligands have a remarkable influence on the defluoridation performance of Ce-MOFs. This work will provide a feasible idea for designing MOFs as superiors adsorbents for defluoridation.

A micron-sized Co-MOF sheet to activate peroxymonosulfate for efficient organic pollutant degradation

A Co-MOF with a 2D morphology (BUC-92) was prepared, which exhibited outstanding rhodamine B (RhB) degradation performance via peroxymonosulfate (PMS) activation.