Currently, the realization of rationally designed architectures based on polyoxometalates (POMs) with designed functions has mostly been achieved through the preparation of functional films. However, the traditional approaches suffer from the drawbacks such as time-consuming processes, ill-defined structure and quality, random orientation of the POM molecules, and unsatisfactory performance. In this study, microcrystals of Ag9[EuW10O36]·36H2O (denoted as Ag9[EuW10O36]) were synthesized via a titration method by treating Na9[EuW10O36]·32H2O (denoted as Na9[EuW10O36]), selected as a prototype, with Ag+, leading to the formation of a water-insoluble crystalline powder with a uniform hexagonal platelet morphology. After this, a simple yet efficient manual assembly method was used to rapidly manufacture Ag9EuW10O36 microcrystal thin films on a glass substrate with high coverage, high crystallinity, and highly preferential orientation. Note that the as-prepared films emit orange polarized fluorescence with an anisotropy value of about 0.21, which places them among the materials of largest anisotropy. It is expected that the manual assembly approach can be generally adopted for the fabrication of many other kinds of polyoxometalate-based materials on various substrates for practical applications.

Composite films with alternating layers (PAH/PSS)3(AB/POM)n (PAH = polyallylamine hydrochloride, PSS = polystyrene sulfonate) derived from Alcian Blue-tetrakis(methyl-pyridinium) chloride (abbreviated as AB) and Keggin type polyoxometalates (POM = H4SiW12O40, H3PW12O40, H3PMo12O40, H5PMo10V2O40) have been fabricated and characterized. Under laser irradiation at 532 nm with a pulse duration of 6–7 ns, a repetition rate of 10 Hz and the intensity of the light at focus E0 being 10 μJ, the composite films exhibit self-defocusing behavior and saturated absorption effects, and the nonlinear optical absorption coefficient β (m W−1) and refractive index n2 (m2 W−1) of the films are 4–5 times larger than those of pure AB solution in view of their magnitude. Interestingly, it is found that third-order NLO susceptibilities χ(3) of films are in the order of χ(3)(AB/PSS) < χ(3)(AB/SiW12) < χ(3)(AB/PW12) < χ(3)(AB/PMo12) < χ(3)(AB/PMo10V2), which is reversed to the order of ELUMO(SiW12) > ELUMO(PW12) > ELUMO(PMo12) > ELUMO(PMo10V2), affirming that the incorporation of different Keggin type POMs of a lower LUMO energy level with phthalocyanine molecules into multilayers could tune the NLO responses of phthalocyanine films. It is concluded that the lower LUMO level of POM than that of the phthalocyanine can stimulate the easier transformation of excited electrons from AB to the POM within the donor–acceptor system (phthalocyanine molecules acted as an electron donor while POMs as an electron acceptor in the composite films) when flashed with the laser, which is thought to be accountable for the profound third-order optical nonlinearity of the composite films.

HKUST-1 was impregnated effectively on millimeter-sized mesoporous γ-Al2O3 beads under hydrothermal conditions, resulting in formation of a composite material HKUST-1@γ-Al2O3 that features high specific surface area, remarkable enhanced mechanical strength, chemical and thermal stability, and low cost. The composite material exhibited excellent performance with the adsorptive desulfurization capacity of 59.7 mg S/g MOF (versus 49.1 mg S/g MOF for bare HKUST-1) for a model oil composed of dibenzothiophene (with the initial S-content being 1000 ppmwS) and n-octane. Experimental results also revealed that HKUST-1@γ-Al2O3 could reduce 35 ppmwS sulfur content of the model oil lower than 9.6 ppmwS at a ratio of HKUST-1@γ-Al2O3 to oil over 30 wt %, indicating effectiveness for deep adsorptive desulfurization. The Gibbs free energy for DBT adsorption by HKUST-1@γ-Al2O3 was found smaller than that by HKUST-1 due to efficient utilization of active centers, shorter diffusion channels and larger specific surface area of nanosized HKUST-1 particles formed under confined environment of γ-Al2O3 channels/pores. Remarkably, the used HKUST-1@γ-Al2O3 beads can easily be regenerated by acetone washing and the adsorptive desulfurization capacity just slightly decreased after experiencing five recycles. The results indicate that the as-synthesized HKUST-1@γ-Al2O3 beads have great potential as an adsorbent for adsorptive desulfurization in practical applications.

Integrating polyoxometalates into porphyrin moieties via covalent bond is expected to be a new approach to tune and enhance the nonlinear optical responses of porphyrins. The effectiveness and efficiency of this proposal has been examined and witnessed by studying two new hybrid compounds as a prototype, namely, (Bu4N)4K2[{C52H32N5O2Zn}HNC(CH2O)3P2V3W15O59]·2(C4H9NO) (1) and (Bu4N)4K2[{C52H34N5O2}HNC(CH2O)3P2V3W15O59]·3(C4H9NO) (2), in which porphyrins acting as electron donor and Dawson type polyoxometalate acting as electron acceptor are connected via short tether through covalent bond. The new compounds are systematically characterized by means of elemental analyses, FT-IR, 1H NMR, ESI-MS, TG/DTA, UV–vis, fluorescence emission spectra, and cyclic voltammetry measurement. Remarkably, great enhancement in reverse saturation absorption is achieved in 1 and 2 which is ca. 1 order of magnitude greater than their individual reactants. Additionally, optical-limiting thresholds are obtained being 0.484 J/cm2 for 1 and 0.501 J/cm2 for 2, respectively, implying their high potential as low-power optical-limiting materials.

A family of covalently bonded hybrid compounds composed of Anderson type polyoxometalate (POM) moiety and porphyrin moiety have been synthesized and thoroughly characterized. The compounds all show remarkable nonlinear reverse saturable absorption and self-defocusing effect at 532 nm with a pulse duration τ = 6 ns, rendering them promising candidate materials for device applications in photonics and optoelectronics. More importantly, it is found that the hybrid wherein POM is coupled covalently to porphyrin through shorter bridge has an NLO response superior to the hybrid wherein POM is bonded via longer bridge to porphyrin, and the hybrid having two porphyrins connected to POM shows more enhancement than the hybrid having single porphyrin fused to POM. Disclosure of the inherent structure–property relationship is expected to be instructive for exploration of new porphyrin-POM based NLO materials. Meantime, the hybrid compounds have optical-limiting thresholds lower than 1.0 J/cm2, implying their high potential as lower power OL materials.

A series of uniform and smooth (TCPP/LDH)n films and (TCPP/P5W30/LDH)n films were fabricated with meso-tetrakis(p-carboxyphenyl)porphyrin (TCPP), Preyssler-type polyoxometalate K12.5Na1.5[NaP5W30O110]·15H2O (P5W30), and exfoliated Mg2Al–NO3 layered double hydroxide (LDH) monolayer nanaosheets by layer-by-layer assembly technique. The resulting films were characterized by UV–visible spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and fluorescence spectroscopy. Their third-order nonlinear optical properties were studied by Z-scan measurement with laser pulse duration of 6–7 ns at a wavelength of 532 nm. The (TCPP/LDH)n films exhibit notable self-defocusing effect and saturated absorption effect which is different from TCPP solution. The optical nonlinearity of films becomes larger with the increase of the number of bilayers. The third-order nonlinear optical coefficient χ(3) of (LDH/TCPP)50/LDH is calculated to be (6.4 ± 0.18) × 10–11 esu. Remarkably, experimental results showed that the (LDH/P5W30/LDH/TCPP)n/LDH films exhibit much larger nonlinearity than that of the (LDH/TCPP)n/LDH films when n is the same, which is thought to result from the interlayered charge/energy transfer between porphyrin and polyoxometalate although the LDH sheet is electron-inert material.

•Spherical millimeter-sized mesoporous γ-Al2O3 beads are selected as catalyst carrier.•Surface of the beads is functionalized with amino groups.•Phosphotungstic acid is stably anchored on the beads via electrostatic interaction.•The obtained materials show excellent oxidative desulfurization for DBT.•Remarkable advantages are witnessed for the obtained materials.The composite material HPW/NH2–Al2O3 was successfully prepared by immobilization of phosphotungstic acid H3PW12O40 (HPW) on the surface of amino functionalized spherical millimeter-sized mesoporous γ-Al2O3 beads (NH2–Al2O3), that featured high specific surface area, remarkable enhanced mechanical strength, chemical stability and low cost. This composite material was characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Brunner−Emmet−Teller (BET) and mechanical strength measurements. The experimental results showed that introduction of NH2 group in between HPW and Al2O3 surface not only provide strong binding sites for catalytic centers HPW to get high dispersion on the carrier surface but also prevent HPW from structural decomposition. As a consequence, the prepared HPW/NH2–Al2O3 exhibited excellent catalytic performance in the oxidative desulfurization of model oil composed of dibenzothiophene (DBT) and n-octane. The 350 ppmwS of sulfur content in 20 mL of n-octane can be dropped down to 2.8 ppmwS in 2 h using 60 mg of HPW/NH2–Al2O3 catalyst under the optimal conditions. Remarkably, the catalyst can be conveniently recycled by simple decantation method. After 10 times recycling, the oxidation desulfurization efficiency just dropped down slightly from 99.2% to 98.6%. The results indicate that synthesized HPW/NH2–Al2O3 beads have great potential as a catalyst in oxidative desulfurization for special practical applications.Phosphotungstic acid immobilized on amino functionalized spherical millimeter-sized mesoporous γ-Al2O3 beads possesses high potentials for practical oxidative desulfurization of dibenzothiophene.

A series of 3D coordination polymers {[Ln2(bdcd)(ox)2(H2O)3]·4H2O}n (Ln = Eu (1), Tb (2), Sm (3), Dy (4), and Gd (5)), which crystallize in the triclinic space group P with Z = 2, have been synthesized successfully based on the versatile ligands 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide (H2bdcd) and oxalic acid (H2ox). The compounds were characterized by means of IR spectroscopy, elemental analysis, TG, and powder X-Ray diffraction, whereby compounds 1 and 2 were structurally characterized. All of the compounds are isomorphous and have a 3D open framework in which ox2− ligands bridge Ln3+ ions through their carboxylate groups resulting in the formation of a 1D Ln–ox infinite chain in the ac plane. The adjacent 1D Ln–ox infinite chains are then connected to each other through coordination interactions between Ln3+ ions and the carboxylate groups and N-oxide atoms of bdcd2− ligands resulting in a 3D (7,8)-connected open framework with a (38·49·54) (37·49·511·6) topology possessing 1D channels with lattice water molecules as residents. The photoluminescence properties of compounds 1, 2 and 4 were investigated in detail.

Composite films derived from the water-soluble Keplerate-type polyoxometalate (NH4)42[Mo132O372(CH3COO)30(H2O)72]·ca. 300H2O·ca. 10CH3COONH4 (denoted (NH4)42{Mo132}) and chloroform-soluble tetraphenylporphyrin perchlorate [H2TPP](ClO4)2 are successfully fabricated by a layer-by-layer self-assembly method and characterized by UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The structure of the {Mo132} and [H2TPP]2+ in the films remain intact in light of the results of UV-vis spectroscopy and XPS. UV-vis spectra measurements reveal that the amounts of deposition of {Mo132} and [H2TPP]2+ remain constant in every adsorption cycle in the composite films assembly process. Nonlinear optical properties of the composite films have been investigated by using the Z-scan technique at a wavelength of 532 nm and pulse width of 7 ns. The results show that the composite films have notable nonlinear saturated absorption and self-defocusing effects. The combination of {Mo132} with [H2TPP]2+ can result in composite films with remarkably enhanced optical nonlinearities. The interfacial charge transfer induced by laser from porphyrin to POM in the films is thought to play a key role in the enhancement of NLO response. The third-order NLO susceptibility χ(3) of the composite films increases with the increase of film thickness.

Keggin-type polyoxoanion PW12O403−-containing one-dimensional nano-tubular arrays, with the structure polyethylenimine/polystyrenesulfonate/(poly(allylammonium)/polystyrenesulfonate)3(poly(allylammonium)/PW12O403−)8, were fabricated as a prototype using a layer-by-layer deposition technique in porous anodic aluminum oxide and polycarbonate templates with a pore diameter of 200 nm, and characterized by IR, UV-vis and SEM. The resulting nano-tubes have a uniform diameter of 180 ± 20 nm and a uniform wall thickness of 30 ± 5 nm. These arrays have shown superior performance in the UV light irradiated photo-degradation of Rhodamine B (selected as a representative dye) under mild conditions with respect to both the catalytic efficiency and operating convenience due to the confinement within the nano-tubes both in the latitudinal and radial direction. Remarkably, the catalytic activity of the nano-tubular arrays could be recovered by means of simple immersion in the polyoxoanion solution when the catalytic reactivity became reduced, which is vital in view of practical applications. The total organic carbon content changes and GC-MS measurements were conducted to identify the degradation products. The hydroxyl radical mechanism was found to be adopted by the photo-degradation reaction.

A new family of silver(I)–lanthanide(III) heterometallic-organic frameworks having the formula [AgLn(bpdc)2] (Ln = Eu (1), Tb (2), Sm (3), Dy (4), Y (5), Yb (6), Er (7), Ho (8); H2bpdc = 2,2′-bipyridine-3,3′-dicarboxylic acid), each of which crystallizes in the monoclinic space group C2/c with Z = 4, has been hydrothermally synthesized. The compounds were characterized by means of IR, elemental analysis, thermogravimetric-differential thermal analysis, and powder X-ray diffraction (XRD), wherein compounds 1, 2, and 4–8 were structurally characterized. The powder XRD and single-crystal structures of the title compounds indicate that all the compounds are isostructural and feature a three-dimensional (3-D) open framework. In the structures of the compounds, bpdc2– ligands link Ln3+ through their carboxylic groups, resulting in the formation of a one-dimensional {Ln(bpdc)2}n infinite chain along the c direction. The adjacent chains are then connected to each other through the coordination interaction between Ag+ and the pyridyl N atoms of bpdc2– ligands from the chains, resulting in a 3-D (2,4,6)-connected open framework with (411·64)(43·82·10)(8)2 topology. The compounds show remarkable good thermally stability up to 370 °C because neither aquo ligands nor lattice water molecules exist in the composition of the compounds. The photoluminescent properties of compounds 1 and 2 were studied in detail. The energy level of the triplet states of the ligand H2bpdc 21 505 cm–1 (465 nm) was determined based on the 77 K emission spectrum of the compound [Gd2(bpdc)3(phen)2(H2O)2]·6H2O 9. The 5D0 and 5D4 emission lifetimes (1.58 and 1.76 ms) and the overall quantum yields (21% and 22%) were determined for the compounds 1 and 2, respectively.

Three new supramolecular compounds [H2TPP]1.5[SW11VO40]·5CH3CN·4H2O 1, [H2TPP]2[SW10V2O40]·4CH3CN·3H2O 2, and [H2TPP][SW12O40]·4H2O 3 composed of [H2TPP]2+ cation and vanadium substituted Keggin-type polyoxometalate (POM) anion [SW12−nVnO40](2+n)− (n = 0–2) were prepared and characterized. The third-order nonlinear optical (NLO) and optical limiting (OL) properties of resulting hybrids were studied by using an Nd:YAG laser at 532 nm with a pulse duration of τ = 7 ns. The results demonstrate that all of these supramolecular compounds have significant nonlinear reverse saturated absorption, self-defocusing behavior, and good OL performance, especially for compound 1, which has a second hyperpolarizability γ value of 7.05 × 10−29 (esu) and exhibits a comparable OL performance with the most well-known OL materials such as In(Pc*)Cl indicating that they are potentially excellent NLO materials. Remarkably, it was also observed that the degree of vanadium substitution in POM anions corresponding to different onset of reduction potential influences the NLO and OL properties of the resulting compounds: third-order NLO and OL properties of compound 2 are inferior to those of compound 1, and are better than those of compound 3. Both their second hyperpolarizability γ values and the OL performance were observed to be inversely proportional to the HOMO–LUMO gaps of the resulting compounds. The excited charge transfer from porphyrin to POM anions in the supramolecular compounds when exposed to laser irradiation is thought to play key role in the enhancement of NLO and OL response.

A new series of four isostructural mononuclear lanthanide complexes Ln(HPDH)3(H2O)3·H2O (Ln = Sm(III) 1, Eu(III) 2, Tb(III) 3 and Dy(III) 4; H2PDH = 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione) has been prepared and characterized by IR, elemental analysis, XRD and TG-DTA methods. Single crystal X-ray diffraction analysis of both complexes 1 and 3 revealed that the mononuclear discrete complexes form 3-D supramolecular networks via hydrogen bonds and offset stacking (–H⋯π) interactions. The photoluminescence study of the title complexes revealed the photoluminescent potential of the antenna ligand (H2PDH) toward the concerned lanthanide cations. The luminescence based sensing ability of the partially dehydrated complex Tb(HPDH)3(H2O)33a towards small solvent molecules, along with its reusability, has been studied. Isopropyl alcohol was found to be an excellent sensitizer, while tetrahydrofuran was a highly quenching solvent with a first order behavior towards the photoluminescence intensity. The photoluminescence intensity was found to decrease with the increase of the dielectric constant and normalized Dimroth–Reichardt ET parameter values for protic solvents, while reverse behavior was observed for dipolar aprotic solvents.

By reacting the unique Keplerate type molybdenum-oxide based polyoxometalate (NH4)42·[Mo132O372·(CH3COO)30(H2O)72]·ca.300H2O·ca.10CH3COONH4(1) with tetramethylammonium bromide, a new derivative (NH4)26[TMA]16{Mo132O372(H2O)72(CH3COO)30}·ca.7NH4CH3COO·ca.189H2O(2, TMA=tetramethylammonium) was prepared. Compound 2 was characterized by Fourier transform infrared spectroscopy(FTIR), UV-Vis, elemental and thermogravimetric analyses. By the well-established Z-scan technique, investigations on the nonlinear optical(NLO) properties of the series of compounds derived from the Keplerate type molybdenum-oxide-based poly-oxometalate, namely, the newly prepared compound 2, the three previously reported compounds, included compound 1, (NH4)18(TBA)24{Mo132O372(H2O)72(CH3COO)30}·ca.7NH4CH3COO·ca.173H2O(3, TBA=tetrabutylammonium) and (DODA)40(NH4)2[(H2O)nMo132O372(CH3COO)30(H2O)72](4, DODA=dimethyldioctadecylammonium), reveal that the third-order nonlinearity[χ(3)] values of compounds 1, 2 and 3 in the DMF/H2O solution and compound 4 in chloroform are almost the same, which indicates that the counter cations with different length of alkyl chains show ignorable impacts on the NLO susceptibility. In other words, the remarkable third-order nonlinearities[χ(3)≈10−19 m2/V2] mainly come from the [Mo132O372(CH3COO)30(H2O)72]42− anions. This fact reveals that the applications of the NLO active polyoxometalates in various environments(such as hydrophilic, hydrophobic, polar, apolar, etc.) can be achieved by simply varying cations to meet the demands in the design of diverse devices.

Hydrothermal reactions of lanthanide nitrates with glyphosate have resulted three new isostructural 3D lanthanide–organic frameworks, Ln(NO3)(H2L) [Ln = Eu (1), Tb (2), Gd (3); H4L = 2,5-dioxo-1,4-piperazinylbis(methylphosphonic) acid], with good yields, where H4L as a new ligand was formed via in situ cyclodehydration of original ligand glyphosates during the hydrothermal reaction. The compounds were thoroughly characterized by IR, UV–vis, elemental analysis, single-crystal X-ray diffraction analysis, powder X-ray diffraction analysis, and thermogravimetric/differential thermal analysis (TG-DTA). Three compounds display 3D 6,6-connected open frameworks with 413·62 topology possessing 1D channels in which NO3– anions act as troglodytes by chelating Ln3+ centers. The TG-DTA study of the compounds showed remarkable thermal stability up to 380 °C. Under room temperature UV-light irradiation, the Eu3+ and Tb3+ compounds showed the corresponding characteristic Ln3+ intra 4fn emission peaks. The triplet energy level (21882 cm–1) of the ligand (H4L) was determined from the emission spectrum of its Gd3+ compound at 77 K. The emission lifetimes (1.54 ms of 5D0 for compound 1 and 1.98 ms of 5D4 for compound 2) and absolute emission quantum yields (10.1% for compound 1 and 5.9% for compound 2) were also determined.

Structural comparison of a new compound [(bpp)3H6]Fe2IIIFe2IIMo24V(H2PO4)8(HPO4)4(PO4)4O48(OH)12· (H2O)4·2H2O(1)[bpp=1,3-di(4-pyridyl)propane] with our previously reported two compounds [(bpy)3FeII]3sdFe2IIIFe2IIMo24V(H2PO4)8(HPO4)4(PO4)4O48(OH)12(H2O)4·12H2O(2) and [(bpy)3FeII]2FeIIFeIIIMo12V(H2PO4)2(H2−xPO4)·(H1+xPO4)(HPO4)2(PO4)2O24(OH)6(H2O)2·9H2O(x=0-21)(3)(bpy=2,2′-bipyridine), which all exhibit one-dimensional mixed-valence iron molybdophosphate anionic chains constructed by alternating connection of FeIII ions and magic [FeII(Mo6P4O31)2] units, reveals that the non-hydrogen atomic ratios of Mo:Fe:P:O within the polymeric anionic chains are the same for all the three compounds, while the polymeric anionic chains of the different compounds bear different numbers of negative charges. And therefore there exist different numbers of counter cations per {Fe2III[Fe2II(P16Mo24VO124)]} unit found in the titled compounds. It discloses that not only are the spatial assembling of counter cations and polymeric inorganic chains of three compounds quite different, but also the O—FeIII—O bond angles and FeIII—O bond lengths of the three different inorganic chains exhibit small differences. What is more important is that such small changes in bond length and bond angle in the assemblage of FeIII—O bonds lead to the considerable fluctuations of inorganic chains in their structural conformation within the three compounds, reflecting an interesting phenomenon of “flexibility” in the pure inorganic one dimensional mixed-valence iron molybdophosphate chains.

Currently, the realization of rationally designed architectures based on polyoxometalates (POMs) with designed functions has mostly been achieved through the preparation of functional films. However, the traditional approaches suffer from the drawbacks such as time-consuming processes, ill-defined structure and quality, random orientation of the POM molecules, and unsatisfactory performance. In this study, microcrystals of Ag9[EuW10O36]·36H2O (denoted as Ag9[EuW10O36]) were synthesized via a titration method by treating Na9[EuW10O36]·32H2O (denoted as Na9[EuW10O36]), selected as a prototype, with Ag+, leading to the formation of a water-insoluble crystalline powder with a uniform hexagonal platelet morphology. After this, a simple yet efficient manual assembly method was used to rapidly manufacture Ag9EuW10O36 microcrystal thin films on a glass substrate with high coverage, high crystallinity, and highly preferential orientation. Note that the as-prepared films emit orange polarized fluorescence with an anisotropy value of about 0.21, which places them among the materials of largest anisotropy. It is expected that the manual assembly approach can be generally adopted for the fabrication of many other kinds of polyoxometalate-based materials on various substrates for practical applications.

Composite films derived from the water-soluble Keplerate-type polyoxometalate (NH4)42[Mo132O372(CH3COO)30(H2O)72]·ca. 300H2O·ca. 10CH3COONH4 (denoted (NH4)42{Mo132}) and chloroform-soluble tetraphenylporphyrin perchlorate [H2TPP](ClO4)2 are successfully fabricated by a layer-by-layer self-assembly method and characterized by UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The structure of the {Mo132} and [H2TPP]2+ in the films remain intact in light of the results of UV-vis spectroscopy and XPS. UV-vis spectra measurements reveal that the amounts of deposition of {Mo132} and [H2TPP]2+ remain constant in every adsorption cycle in the composite films assembly process. Nonlinear optical properties of the composite films have been investigated by using the Z-scan technique at a wavelength of 532 nm and pulse width of 7 ns. The results show that the composite films have notable nonlinear saturated absorption and self-defocusing effects. The combination of {Mo132} with [H2TPP]2+ can result in composite films with remarkably enhanced optical nonlinearities. The interfacial charge transfer induced by laser from porphyrin to POM in the films is thought to play a key role in the enhancement of NLO response. The third-order NLO susceptibility χ(3) of the composite films increases with the increase of film thickness.