Phosphate or arsenate modified UiO-66-NO2: Amorphous mesoporous matrix

Metal-organic frameworks for food contaminant adsorption and detection

Metal-organic framework materials (MOFs) have been widely used in food contamination adsorption and detection due to their large specific surface area, specific pore structure and flexible post-modification. MOFs with specific pore size can be targeted for selective adsorption of some contaminants and can be used as pretreatment and pre-concentration steps to purify samples and enrich target analytes for food contamination detection to improve the detection efficiency. In addition, MOFs, as a new functional material, play an important role in developing new rapid detection methods that are simple, portable, inexpensive and with high sensitivity and accuracy. The aim of this paper is to summarize the latest and insightful research results on MOFs for the adsorption and detection of food contaminants. By summarizing Zn-based, Cu-based and Zr-based MOFs with low cost, easily available raw materials and convenient synthesis conditions, we describe their principles and discuss their applications in chemical and biological contaminant adsorption and sensing detection in terms of stability, adsorption capacity and sensitivity. Finally, we present the limitations and challenges of MOFs in food detection, hoping to provide some ideas for future development.

Chitosan-assisted MOFs dispersion via covalent bonding interaction toward highly efficient removal of heavy metal ions from wastewater

Metal organic frameworks (MOFs) have been considered to be robust adsorbent for the removing heavy metal ions from wastewater due to their unique properties such as large active sites, high specific surface area and high porosity, etc., however, their practical engineering application faces the problem of serious agglomeration. In this work, a new strategy of chitosan (CS) assisting MOF dispersion was proposed to develop the new generation of MOF-based adsorbents, namely, CS grafted UiO-66-NH₂ composite materials (CGUNCM). The UiO-66-NH₂ was selected and it was grafted onto the main chains of CS through covalent bonding interaction with the aid of glutaraldehyde, which was totally different from the common method that grafting molecular chains on the surface of MOFs resulting in the dramatic reduction of active adsorption sites. The results show that grafting MOFs onto CS main chains not only greatly improves the dispersion of MOFs but also reserves the morphology of MOFs as much as possible. The adsorption performances toward Cu(II) and Pb(II) were intensively studied by varying adsorbate concentration, ionic strength, the contact time, adsorption temperature and pH value of solution. The results show that the composite adsorbent exhibits high adsorption efficiency and the adsorption equilibrium can be reached within 45 min, and the maximum adsorption capacity toward Cu(II) and Pb(II) achieve 364.96 mg/g and 555.56 mg/g, respectively. Furthermore, the composite adsorbent shows good reusability. This work provides a new method of fabricating the MOF-based adsorbent and paves the way for the practical application of such adsorbents in wastewater treatment.

Amorphous mesoporous matrix from metal-organic framework UiO-66 template with strong nucleophile substitution

The metal-organic framework (MOF) UiO-66 is made of zirconium clusters coordinated with 1,4-benzenedicarboxylate linkers that is stable in water and is highly tolerant to extremely acidic or basic environments. Conversely, the zirconium clusters are affine to nucleophiles so the crystalline structures of UiO-66 can be converted into amorphous derivatives. In a mineral acid solution both protons and coordinating nucleophile are present. This study for the first time revealed that it is the strong nucleophile instead of proton deteriorate the crystalline structures of UiO-66. Also, the so-produced amorphous mesoporous matrix, if not totally dissolved, can be applied as an efficient adsorbent. The noted adsorption capabilities of Cu(II) and nucleophiles by these amorphous mesoporous matrix did not correlate with the structural crystallinity or the internal surface area; conversely, the doped nucleophiles were noted to contribute to the adsorption tendencies towards Cu(II) and phosphate species via electrostatic interactions and hydrogen bonding, respectively. Conversion of sacrificing UiO-66 template to amorphous matrix can be applied as an effective way to fabricate specific adsorbent with resistance to extreme pH and strong nucleophile challenges.

Metal–organic frameworks vs. buffers: case study of UiO-66 stability

The combination of zirconium-based MOF UiO-66 with buffered environment leads to UiO-66 decomposition.

Excess adsorption of phosphoric acid from extremely acidic solutions by covalent organic framework EB-COF:Br

The industrial waste streams with excess phosphorus acid (H₃PO₄) was generated in semiconductor industries that has extremely low pH rendering commercial adsorbents unfit for adsorption recycling of valuable materials. This study for the first time use covalent organic framework EB-COF:Br to adsorb phosphoric acid from extremely acidic H₃PO₄ solutions at pH ranging 0.86 to -0.65. The EB-COF:Br could maintain structural stability with these extremely acidic solutions. At 25 °C, 95% adsorption could be completed within 10 min of contact; while the adsorption capacities of EB-COF:Br from 75% H₃PO₄ solution ranged 6520‒6980 mg-H₃PO₄/g during 25-45 °C. The adsorption is regarded isoenthalpic with no heat effects. Water washing is efficient for H₃PO₄ desorption, and the washed COF can be reused as an efficient adsorbent under extremely acidic environment. The interactions between (‒N⁺=) and (‒CO) groups, and part of the (‒NH‒) groups participated in the adsorption process with adsorbed H₃PO₄ molecules. The adsorbed H₃PO₄ molecules then formed H-bonding to trap the excess free H₃PO₄ molecules to the internal cavity of the COF.