Ever growing populations in cities are associated with a major increase in road vehicles and air pollution. The overall high levels of urban air pollution have been shown to be of a significant risk to city dwellers. However, the impacts of very high but temporally and spatially restricted pollution, and thus exposure, are still poorly understood. Conventional approaches to air quality monitoring are based on networks of static and sparse measurement stations. However, these are prohibitively expensive to capture tempo-spatial heterogeneity and identify pollution hotspots, which is required for the development of robust real-time strategies for exposure control. Current progress in developing low-cost micro-scale sensing technology is radically changing the conventional approach to allow real-time information in a capillary form. But the question remains whether there is value in the less accurate data they generate. This article illustrates the drivers behind current rises in the use of low-cost sensors for air pollution management in cities, whilst addressing the major challenges for their effective implementation.

The rise of low-cost sensing for managing air pollution in cities

Inorganic-organic hybrid white light phosphors.

Lanthanide coordination polymers constructed from the asymmetrical N-heterocyclic rigid carboxylate: Synthesis, crystal structures, luminescence properties and magnetic properties

A zinc-based anionic metal–organic framework, [HDMA]2[Zn2(BDC)3(DMA)]·6DMF (HDMA+: dimethylammonium, BDC2−: 1,4-benzenedicarboxilate, DMA: dimethylamine and DMF: N,N′-dimethylformamide) has been solvothermally synthesized. And its cations, HDMA+, are exchanged by various lanthanides to form the hybrid systems via a post-synthetic process. These lanthanide(III)-loaded materials have shown different luminescent behaviors, indicating that this kind of anionic MOF could effectively sensitive lanthanides and be used as a potential luminescent probe towards different lanthanide ions. Besides, this system exhibits selective adsorption ability to cationic dyes, such as Rhodamine B, Basic Red 2 and Methylene Blue. RhB@1 has a fastest selection and realizes the probing of various organic solvent molecules as well as volatile organic benzenes (VOBs), especially for sensing acetone and aniline.

Anionic metal–organic framework hybrids: functionalization with lanthanide ions or cationic dyes and fluorescence sensing of small molecules

Metal-organic frameworks (MOFs) have attracted extensive research interest because of their high specific surface area, tunable microporosity, low skeleton density and good stability, and they are seen as ideal functional materials for the detection and removal of metal ions. Current research is mainly focused on the trade-off between the permeability and selectivity, and the development of MOFs composites with superior performance to obtain satisfactory adsorption and separation capacity, such as MOFs membranes. In this review, we first summarize the various design and synthesis strategies for MOFs and MOF membrane materials, including with/without solvent, the mechanochemical method, the primary growth method and the secondary growth method. The recent advances in MOFs and MOFs membranes for the adsorption and removal of different types of metal ions are then highlighted. Finally, the opportunities and challenges for the future development of MOFs and MOFs membranes are proposed. This review aims to provide a deep understanding of the rational design and application research of MOFs and MOF membranes and promote development and progress in MOF hybrid materials.

Recent advances in metal-organic frameworks/membranes for adsorption and removal of metal ions

White-light emission by selectively encapsulating single lanthanide metal ions into alkaline earth metal-organic coordination polymers

A low-cost and convenient fluorescent indicator of alkaline earth metal–organic coordination polymer Sr(H2ABTC)(DMF)(H2O) (1) (ABTC = 3,3,5,5-azobenzenetetracarboxylic acid) was designed and synthesized by using a flexible ligand ABTC and alkaline earth metal ion Sr2+ for sensing trace amine gases in the air. The complex 1 was characterized by X-ray single crystal measurement, mainly composed of conjugated fluorophore and uncoordinated carboxyl groups. A series of detailed experiments confirmed the dramatic change of fluorescence color under ultraviolet. When the complex 1 interacted with amine gases, its fluorescence emission intensity is enhanced and emission peak redshift greatly. Of most important, convenient fluorescence detection for amine gases was realized by a homemade indicator box, which was reusable and allowed to detect the concentration of amine gases down to 10 ppb (parts per billion) upon real-time (3 min). The sensing mechanisms were analyzed through the closed-loop stiffening effect and the enhanced conjugate effect.

Xu-Gang Chen

Papers

White-light emission by selectively encapsulating single lanthanide metal ions into alkaline earth metal-organic coordination polymers

An UV equipped box for photoactivation with a fluorescent coordination polymer for recognizing amine gases by “turn-color” in air