Biswa Nath Bhadra

Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities

Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as –OH and –NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of –OH and –(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water.

Adsorption of benzotriazole and benzimidazole from water over a Co-based metal azolate framework MAF-5(Co)

Benzotriazole (BTA) and benzimidazole (BZI) are regarded as water pollutants because of their extensive uses in industry and appreciable water solubility. The adsorption of both BTA and BZI from water over a newly synthesized metal-organic framework, MAF-5(Co), was investigated and compared with zeolitic imidazole frameworks (ZIFs), such as ZIF-8(Zn) and ZIF-67(Co), as well as commercial activated carbon. MAF-5(Co) had the highest adsorption capacities for both BTA and BZI. The maximum adsorption capacities of MAF-5(Co) for BTA and BZI were 389 and 175mgg-1, respectively. Hydrophobic and π-π interactions between the aromatic adsorbate BTA and MAF-5(Co) were suggested as a plausible mechanism. Based on the zeta potential of MAF-5(Co) and effects of pH on the BTA adsorption, electrostatic interactions between the MAF-5(Co) and BTA species might also affect the adsorption of BTA over MAF-5(Co). MAF-5(Co) can be recycled for adsorptive removal of BTA by simple ethanol washing. Therefore, MAF-5(Co) is suggested as a promising adsorbent for the removal of BTA and BZI from water.

Selective Adsorption of n-Alkanes from n-Octane on Metal-Organic Frameworks: Length Selectivity

The liquid-phase adsorption of n-alkanes (from n-octane (C8) solvent) with different chain lengths was carried out over three metal-organic frameworks (MOFs), viz., metal-azolate framework-6 (MAF-6), copper-benzenetricarboxylate (Cu-BTC), and iron-benzenetricarboxylate (MIL-100(Fe)), and a conventional adsorbent activated carbon (AC). MAF-6 and Cu-BTC were found to have significant selectivity for the adsorption of n-dodecane (C12) and n-heptane (C7), respectively, from C8. Selectivity for C12 on MAF-6 was also observed in competitive adsorption from binary adsorbate systems. To understand the selective adsorption of C12 on MAF-6 more, the adsorption of C12 from C8 over MAF-6 was investigated in detail and compared with that over AC. The obtained selectivities over MAF-6 and Cu-BTC for C12 and C7, respectively, might be explained by the similarity between cavity size of adsorbents and molecular length of n-alkanes. In the case of AC and MIL-100(Fe), no specific adsorption selectivity was observed because the cavity sizes of the two adsorbents are larger than the size of the n-alkanes used in this study. The adsorption capacities (qt) of n-alkanes over AC and MIL-100(Fe) decreased and increased, respectively, as the polarity (or length) of the adsorbates increased, probably because of nonpolar and polar interactions between the adsorbents and n-alkanes. On the basis of the results obtained, it can be concluded that matching the cavity size (of adsorbents) with the molecular length (of n-alknaes) is more important parameter than the MOFs hydrophilicity/hydrophobicity for the selective adsorption/separation of alkanes.

A remarkable adsorbent for removal of contaminants of emerging concern from water: Porous carbon derived from metal azolate framework-6

A series of metal-azolate frameworks or MAFs-MAF-4, -5, and -6-were synthesized and pyrolyzed to prepare porous carbons derived from MAFs (CDM-4, -5, -6, respectively). Not only the obtained carbons but also MAFs were characterized and applied for the adsorption of organic contaminants of emerging concern (CECs, including pharmaceuticals and personal care products) such as salicylic acid, clofibric acid, diclofenac sodium, bisphenol-A, and oxybenzone (OXB) from water. CDM-6 was found to be the most remarkable adsorbent among the tested ones (including activated carbon) for all the adsorbates. OXB was taken as a representative adsorbate for detailed adsorption studies as well as understanding the adsorption mechanism. H-bonding (H-acceptor: CDM; H-donor: CECs) was suggested as the principal mechanism for the adsorption of tested adsorbates. Finally, CDMs, especially CDM-6, were suggested as highly efficient and easily recyclable adsorbents for water purification.

Adsorptive removal of aromatic hydrocarbons from water over metal azolate framework-6-derived carbons

Metal azolate framework-6 (MAF-6) was pyrolyzed at 1000°C to yield MOF-derived carbons (MCs). The obtained MCs were used to eliminate aromatic hydrocarbons, including polyaromatic hydrocarbons (PAHs; e.g., naphthalene (NAP), anthracene (ATC), and pyrene (PRN)) and benzene (BZ) from water via adsorption. The adsorption results over the MCs were compared with that of pristine MAF-6 and commercial activated carbon (AC). MC obtained after 24h (MC-24) exhibited a remarkable adsorption efficiency compared to that of the other MCs (obtained after different durations), MAF-6, and AC. For example, MC-24 led to adsorptions of NAP around 17 and 2.5 times those of pristine MAF-6 and AC, respectively. Or, the maximum adsorption capacities (Q0) of MAF-6, AC and MC-24 for NAP were 14, 104 and 237mg/g, respectively. Moreover, Q0 values of MC-24 for ATC and PRN were also very high of 284 and 307mg/g, respectively. Based on the properties of PAHs and the hydrophobicity of MC-24, hydrophobic interaction was suggested as the main mechanism for the adsorption of PAHs and BZ. In addition, MC-24 can be recycled by washing with acetone with little loss in performance. Therefore, MC-24 is recommended as a competitive adsorbent for aromatic hydrocarbon removal from water.

TiO2-Containing Carbon Derived from a Metal–Organic Framework Composite: A Highly Active Catalyst for Oxidative Desulfurization

A new metal-organic framework (MOF) composite consisting of Ti- and Zn-based MOFs (ZIF-8(x)@H2N-MIL-125; in brief, ZIF(x)@MOF) was designed and synthesized. The pristine MOF [H2N-MIL-125 (MOF)]- and an MOF-composite [ZIF(30)@MOF]-derived mesoporous carbons consisting of TiO2 nanoparticles were prepared by pyrolysis (named MDC-P and MDC-C, respectively). MDC-C showed a higher surface area, larger pore sizes, and larger mesopore volumes than MDC-P. In addition, the TiO2 nanoparticles on MDC-C have more uniform shapes and sizes and are smaller than those of MDC-P. The obtained MDC-C and MDC-P [together with MOF, ZIF(30)@MOF, pure/nanocrystalline TiO2, and activated carbon] were applied in the oxidative desulfurization reaction of dibenzothiophene in a model fuel. The MDC-C, even with a lower TiO2 content than that of MDC-P, showed an outstanding catalytic performance, especially with a very low catalyst dose (i.e., a very high quantity of dibenzothiophene was converted per unit weight of the catalyst), fast kinetics (∼3 times faster than that for MDC-P), and a low activation energy (lower than that for any reported catalyst) for the oxidation of dibenzothiophene. The large mesopores of MDC-C and the well-dispersed/small TiO2 might be the dominant factors for the superior catalytic conversions. The oxidative desulfurization of other sulfur-containing organic compounds with various electron densities was also studied with MDC-C to understand the mechanism of catalysis. Moreover, the MDC-C catalyst can be reused many times in the oxidative desulfurization reaction after a simple washing with acetone. Finally, composing MOFs and subsequent pyrolysis is suggested as an effective way to prepare a catalyst with well-dispersed active sites, large pores, and high mesoporosity.