We report an anion exchange composite material based on a protonated amine-functionalized metal–organic framework, denoted Metal Organic Resin-1 (MOR-1), and alginic acid (HA). MOR-1–HA material shows an exceptional capability to rapidly and selectively sorb Cr(VI) under a variety of conditions and in the presence of several competitive ions. The selectivity of MOR-1–HA for Cr(VI) is shown to be the result of strong O₃Cr^VI⋯NH₂ interactions. The composite sorbent can be successfully utilized in an ion-exchange column, in contrast to pristine MOR-1 which forms fine suspensions in water passing through the column. Remarkably, an ion exchange column with only 1% wt MOR-1–HA and 99% wt sand (an inert and inexpensive material) is capable of reducing moderate and trace Cr(VI) concentrations to well below the acceptable safety limits for water. The relatively low cost of MOR-1–HA/sand column and its high regeneration capability and reusability make it particularly attractive for application in the remediation of Cr(VI)-bearing industrial waste.

In this review we approach the emerging field of sensors based on luminescent metal–organic frameworks from the perspective of the most commonly encountered pitfalls and we suggest best practices so that they can be avoided.

UiO-66-NH₂ type materials show excellent capability for removal of Cr(vi) from industrial waste.

We recently discovered that a Ca²⁺ two-dimensional framework, namely [Ca(H₄L)(DMA)₂]·2DMA (Ca-MOF), was capable of exchanging the Ca²⁺ ions with Cu²⁺ almost quantitatively in a matter of seconds in aqueous solution. Herein, we report that Ca-MOF exhibits the capability of both removal and voltammetric determination of heavy metal ions in aqueous media. Ca-MOF shows one of the highest Pb²⁺ sorption capacities (∼522 mg g⁻¹) reported for MOFs. More importantly, a column filled with Ca-MOF (1% wt) particles dispersed in silica sand (99% wt) can quantitatively remove traces of Pb²⁺ (∼100 ppb) from a relatively large volume of a wastewater simulant solution (containing a large excess of competitive ions). Ca-MOF is also highly efficient for sorption of Cd²⁺, Ni²⁺ and Zn²⁺, even in the presence of several competitive cations. Actually, the Cd²⁺ sorption capacity (∼220 mg g⁻¹) of Ca-MOF is one of the largest reported for MOFs. Furthermore, detailed Ni²⁺ and Zn²⁺ sorption studies of MOFs have not been described prior to this work. The mechanism of the M²⁺ (M²⁺ = Pb²⁺, Cd²⁺, Ni²⁺, Zn²⁺) exchange process was elucidated based on a series of spectroscopic, analytical and X-ray diffraction methods. In addition, a simple ready-to-use electrochemical sensor based on modified graphite paste with Ca-MOF was fabricated and successfully utilized for the determination of Pb²⁺, Cd²⁺, Cu²⁺ and Zn²⁺ at μg L⁻¹ levels in aqueous solutions by anodic stripping voltammetry (ASV). Overall, this work demonstrates, for the first time, a dual function of a MOF as a sorbent and as an electrochemical sensor for heavy metal ions, thus opening a new window for materials with application in both environmental remediation and monitoring.