An excellent multifunctional photocatalyst cooperated by polyoxometalate-viologen framework for CEES oxidation, Cr(VI) reduction and dyes decolorization under different light regimes

Photocatalytic detoxification of highly toxic agents is a promising approach to protect ecological environment and human health, and the key problem lies in the development of novel efficient photocatalysts. Herein,...

A Sm-MOF/GO nanocomposite membrane for efficient organic dye removal from wastewater

The instability of graphene oxide (GO) membranes in aqueous solutions restricts their application in wastewater treatment through the membrane separation technology. In this work, a nanocomposite membrane (Sm-MOF/GO) composed of samarium metal–organic frameworks (Sm-MOFs) and GO nanosheets was successfully fabricated via the filtration of the corresponding Sm-MOF/GO dispersions. The in situ growth of Sm-MOF with aqueous stability on the GO sheets prevented the adjacent GO layers from expanding in aqueous solutions, thus endowing the prepared Sm-MOF/GO membrane with a stable membrane skeleton structure. Besides, the successful loading of Sm-MOF enlarged the layer space of the composite membrane, which was beneficial for higher permeance. The optimization of the Sm-MOF loading contents was also investigated to prepare M-X (where X represents the mass ratio of the MOF raw material to the total mass of the reactants). Subsequently, the fabricated M-0.31 possessed a high permeance of 26 L m⁻² h⁻¹ bar⁻¹, which was 3 times higher than that of a pure GO membrane; moreover, high rejections (>91%) to rhodamine B and methylene blue were obtained. After continuous 5.5 h filtration, the excellent rejection was still maintained as expected, indicating the long-term stability of M-0.31.

A nanocomposite membrane composed of samarium metal-organic frameworks and graphene oxide nanosheets was fabricated for organic dye removal.

A novel photochromic metal-organic framework with good anion and amine sensing

A novel metal-organic hybrid photochromic compound [Zn (CV) (L2)]·2H2O (1) (CV = N,N'-4,4'-bipyridiniodipropionate, H2L2 = isophthalic acid) has been synthesized solvothermally. Compound 1 features a two-dimensional (2D) framework structure, exhibiting photochromic properties under sunlight and UV irradiation with an obvious color change from colorless to dark blue. Meanwhile, the luminescence properties of 1 were investigated, and the results suggested that 1 has good properties of detecting dichromate ions. Furthermore, compound 1 shows different color changes when exposed to different alkyl-amines, and 1 can also be deposited into paper to use as portable test strips. This work can be applied to practical applications as a multifunctional detector against light and chemicals.

A series of host–guest coordination polymers containing viologens: syntheses, crystal structures, thermo/photochromism and factors influencing their thermo/photochromic behaviors

Some viologen-containing compounds displaying thermo/photochromic behaviors which can be used as inkless print media and anti-counterfeiting materials have been reported.

Photochromic and photomodulated luminescence properties of two metal–viologen complexes constructed by a tetracarboxylate-anchored bipyridinium-based ligand

Photochromic and photomodulated luminescence properties of two metal–viologen complexes constructed using a tetracarboxylate-anchored bipyridinium-based ligand are reported.

Photochromism, photoluminescence modulation and selective recognition of small molecules of two highly stable dynamic metal–organic frameworks

Two highly stable dynamic Ln-MOFs show photochromism, tunable photoluminescence, and selective recognition of small molecules.

Piezochromism and hydrochromism through electron transfer: new stories for viologen materials

A pyridinium-carboxylate compound undergoes reversible color change under pressure owing to the formation of radicals via electron transfer; dehydration and hydration can also trigger electron transfer.

While viologen derivatives have long been known for electrochromism and photochromism, here we demonstrated that a viologen-carboxylate zwitterionic molecule in the crystalline state exhibits piezochromic and hydrochromic behaviors. The yellow crystal undergoes a reversible color change to red under high pressure, to green after decompression, and finally back to yellow upon standing at ambient pressure. Ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance X-ray diffraction and DFT calculations suggested that the piezochromism is due to the formation of radicals via pressure-induced electron transfer from carboxylate to pyridinium, without a crystallographic phase transition. It was proposed that electron transfer is induced by pressure-forced reduction of intermolecular donor–acceptor contacts. The electron transfer can also be induced by dehydration, which gives a stable green anhydrous radical phase. The color change is reversible upon reabsorption of water, which triggers reverse electron transfer. The compound not only demonstrates new chromic phenomena for viologen compounds, but also represents the first example of organic mechanochromism and hydrochromism associated with radical formation via electron transfer.

The structural diversity and properties of nine new viologen based zwitterionic metal–organic frameworks

A viologen based ligand has been explored as a functional building block to synthesize a series of nine new zwitterionic metal–organic frameworks with this contribution reporting on their structural, thermal and photochromic properties.

A fluorescent, photochromic and thermochromic trifunctional material based on a layered metal–viologen complex

A 2D layered viologen-based zinc complex exhibits the rare discolored function of reversible photochromism and thermochromism. Interestingly, its fluorescence can be switched by visible light irradiation and heating in air.