Silica based inorganic–organic hybrid materials for the adsorptive removal of chromium

We employed polymer functionalized silica gel as an adsorbent for the removal of Cr(vi) from water. The chains of 2-aminoethyl methacrylate hydrochloride (AEMA·HCl) polymer were grown from the surface of silica gel via surface-initiated conventional radical polymerization and the resulting hybrid material exhibited high affinity for chromium(vi). To investigate the adsorption behavior of Cr(vi) on diverse polymer based hybrid materials, the removal capacity of (SG-AEMH) was compared with our previously reported branched polyamine functionalized mesoporous silica (MS-PEI). The adsorption capacities of polymer based materials were also compared with their respective monolayer based platforms comprising a 3-aminopropyltriethoxysilane (APTES) functionalized silica gel (SG-APTES) and mesoporous silica (MS-APTES). The polymer based systems showed excellent Cr(vi) adsorption efficiencies compared to monolayer counterparts. The structural characteristics and surface modification of these adsorbents were examined by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The experimental data were analyzed using the Langmuir and Freundlich models. Correlation coefficients were determined by analyzing each isotherm. The kinetic data of adsorption reactions were described by pseudo-first-order and pseudo-second-order equations. Thermodynamic parameters, i.e., change in the free energy (ΔG°), the enthalpy (ΔH°), and the entropy (ΔS°), were also evaluated. The synthesized hybrid materials exhibited a high adsorption capacity for chromium ions. Furthermore, they could be regenerated and recycled effectively.

We employed and compared polymer functionalized silica gel and mesoporous silica as adsorbents for the removal of Cr(vi) from water.

Environmental pollution has become one of the most severe problems, which is harmful to human health and ecological systems. According to recent reports, heavy metals have been considered as the most chronic and acute contaminants globally.^1,2 Various industries such as printed board manufacturing, semiconductor manufacturing, electroplating, leather tanning, mining, steel making, textile dyes and pigments are the major sources of aquatic pollution. Industrial effluent contains different harmful heavy metals such as chromium, copper, lead, mercury.³ Chromium is considered highly alarming for human, animals and plants life. In wastewater, chromium exists in two stable states i.e., Cr(vi) and Cr(iii). Cr(vi) is more lethal due to its solubility within almost the whole pH range and greater mobility in the waterbed.⁴ Various methods such as chemical precipitation, membrane filtration, ion exchange, electrochemical processes, chemical coagulation and adsorption have been utilized to remove heavy metals from wastewater.⁵ Among these methods, adsorption is known to be the most efficient method. A large number of natural and synthetic materials have been used for the adsorption-based removal of heavy metals from wastewater.^6–9 These materials include zeolites, clays, biosorbents, resins, activated carbon magnetic particles and silica. Simple and low cost adsorbents have been synthesized by several researchers for an effective removal of heavy metals including Cr(vi) even at low concentration.^10–17 Li et al., demonstrated the preparation of chitosan nanofibers with an average diameter of 75 nm and cross linked with glutaraldehyde for the removal of Cr(vi).¹⁸ Aboutorabi et al., employed TMU-30 based metal–organic framework (MOF) containing isonicotinate N-oxide as adsorptive sites for the adsorption of Cr(vi) from aqueous solution.¹⁹ Recently, Dong et al., prepared the ionic liquid functionalized cellulose (ILFC) through the grafting of glycidyl methacrylate onto cellulose microsphere followed by reaction with ionic liquid 1-aminopropyl-3-methyl imidazolium nitrate for the adsorptive removal of Cr(vi).²⁰vi).Comparison of adsorption capacities of different adsorbents for Cr(vi) removal

Sr. no	Adsorbents	Adsorption capacity qmax (mg g−1)	Time (min)	pH	References
1	Carbon/boehmite (AlOOH) composite	25.6	360	2.0	51
2	Titanium oxide-Ag composite	25.7	720	2.0	52
3	Polydopamine coated maghemite NPS (MNP@PDA)	38.6	240	3.0	53
4	Fe3O4@NiO nanocomposite	6.9	40	5–10	54
5	MnFe2O4@SiO2-CTAB	25.0	30	3.0	55
6	ZnO/biochar	43.5	120	Natural pH	56
7	γ-AlOOH/PVA granules	35.9	200	5.5	57
8	Yarrowia lipolytica	5.2	120	1.0	58
9	β-Cyclodextrin ionic liquid polyurethane modified magnetic NPs (Fe3O4-CDI-IL MNPs)	2.6	180	3.0	59
10	Blends of henna with chitosan microparticles	17.4	66.21	3.8	60
11	Silver-triazolate MOF	37.0	240	6	61
12	p-Toluidine formaldehyde resin (PTFR) on silica	43.5	300	1.0	62
13	SG-AEMH	63.3	30	4.0	Current study
14	MS-PEI	50.26	30	4.0	Current study

Open in a separate windowSilica based porous materials are considered as promising adsorbents for water remediation due to their high surface area, well defined tunable pore size and high adsorption capacity.^21,22 Owing to their economic feasibility, high thermal and mechanical stabilities, they can be utilized as inorganic solid matrixes in the inorganic–organic hybrid materials.^23,24 Several researchers have contributed in the development of functionalized silica based adsorbents for the removal of heavy metals.^25–31 Fan et al., prepared the Schiff base functionalized Pb(ii) imprinted silica-supported organic–inorganic hybrid adsorbent for the selective removal of Pb(ii) from aqueous solution.³² Radi et al., reported the synthesis of chelate β-ketoenol furan functionalized silica particles (SiNFn) for the selective adsorption of Cd(ii).³³ More Recently, Qihui et al., demonstrated the fabrication of thiol functionalized silica microspheres doped with CdTe quantum dots (CQDSMs) for the efficient adsorption of Ag⁺.³⁴ The surface of silica can be tailored with different functional groups to enhance their selectivity towards specific pollutants.^35,36 Modification can be achieved via post-synthesis grafting and co-condensation.³⁷ Post-synthesis grafting offers a facile avenue to controlling surface properties of materials and facilitates the functionalization of the internal pores of porous materials, ultimately helping in developing material with optimized bulk and interfacial properties.³⁸ Numerous organic functional groups such as amine, thiol, carboxylate, alkyl chloride, and aromatic functional groups have been incorporated through post-synthesis grafting strategy.^39–44 In case of silica based materials, the silanol groups present on the surface assist the covalent introduction of a wide range of functional groups, which act as stable and efficient chelating moieties towards a variety of metal ions. The excellent metal adsorption property of these functionalized silica materials are attributed to the presence of electron donor heteroatoms such as O, S and N in the incorporated functional groups.^45,46 The surface functionalization can be either monolayer or polymer based. The polymer based surface functionalization results in a higher surface functional group density that ultimately improves the absorption capacity of the functionalized material. Despite obvious advantages of the polymer based surface functionalization, majority of the efforts in the field of developing materials for water remediation have been focused on monolayer based surface functionalizations.Herein, we demonstrated the potential of polymer functionalized silica based inorganic–organic hybrid materials for Cr(vi) adsorption (Scheme 1). The chains of 2-aminoethyl methacrylate hydrochloride were grafted on the surface of silica gel via surface-initiated conventional radical polymerization (SI-cRP) approach. We have also compared the adsorption capacity of SG-AEMH with polyamine functionalized MCM-41 mesoporous silica (MS-PEI).⁴⁷ The APTES derived monolayer based amine functionalized silica gel (SG-APTES) and mesoporous silica (MS-APTES) were also examined and compared with polymer grafted silica materials. Our results show that SG-AEMH and MS-PEI were more effective for chromium adsorption. Furthermore, the experimental data were fitted to different adsorption models, and the corresponding parameters were determined. In addition, kinetic and thermodynamic analyses were performed to understand the mechanism of the adsorption processes.Open in a separate windowScheme 1Schematic illustration of (a) synthesis of APTES based monolayer (SG-APTES) and AEMH based polymer functionalized silica gel (SG-AEMH), (b) polyamine functionalized mesoporous silica (MS-PEI).     

Two Ln-based metal–organic frameworks based on the 5-(1H-1,2,4-triazol-1-yl)-1,3-benzenedicarboxylic acid ligand: syntheses,structures, and photocatalytic properties

Two new metal–organic frameworks (MOFs) having the formula [Ln₂(H₂O)₃(L)₃·3H₂O]_n (Ln = Sm for MOF-Sm and Tb for MOF-Tb) have been synthesized solvothermally by reacting LnCl₃·6H₂O with 5-(1H-1,2,4-triazol-1-yl)-1,3-benzenedicarboxylic acid (H₂L) and characterized. Single crystal X-ray analyses for MOF-Sm and MOF-Tb revealed that both MOFs are isostructural and display a (6,8)-connected 3D structure with a point symbol of (3⁵·4⁴·6⁶)(3⁵·4⁶·5¹⁷). The natures of weak interactions existing in both MOFs have been assessed using Hirshfeld surface analyses and fingerprint plots. The utility of MOF-Sm as a photocatalyst for the safe photodegradation of the model aromatic dye methyl violet (MV) is also checked. The photocatalysis results showed that MOF-Sm offers reasonable photocatalytic degradation of this dye. The plausible photocatalytic mechanism of MOF-Sm aided photocatalysis has been explained with the help of band gap calculations using density of states (DOS) and partial DOS plots.

Two new 3D Ln-based complexes showing (6,8)-connected topology were synthesized and the photocatalytic activity of the Sm(iii)-based MOF towards the degradation of methyl violet (MV) in water explored.     

Correction: Two Ln-based metal–organic frameworks based on the 5-(1H-1,2,4-triazol-1-yl)-1,3-benzenedicarboxylic acid ligand: syntheses,structures, and photocatalytic properties

Correction for ‘Two Ln-based metal–organic frameworks based on the 5-(1H-1,2,4-triazol-1-yl)-1,3-benzenedicarboxylic acid ligand: syntheses, structures, and photocatalytic properties’ by Fei Yuan et al., RSC Adv., 2020, 10, 39771–39778, DOI: 10.1039/D0RA07159E.

The authors regret that in the Graphical Abstract of the original article, incorrect figures were included. The Graphical Abstract online has been replaced with an updated version.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Synthesis of 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides and their tautomerism

Two complementary pathways for the preparation of N-substituted 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides (5) were proposed and successfully realized in the synthesis of 20 representative examples. These methods use the same types of starting materials viz. succinic anhydride, aminoguanidine hydrochloride, and a variety of amines. The choice of the pathway and sequence of the introduction of reagents to the reaction depended on the amine nucleophilicity. The first pathway started with the preparation of N-guanidinosuccinimide, which then reacted with amines under microwave irradiation to afford 5. The desired products were successfully obtained in the reaction with aliphatic amines (primary and secondary) via a nucleophilic opening of the succinimide ring and the subsequent recyclization of the 1,2,4-triazole ring. This approach however failed when less nucleophilic aromatic amines were used. Therefore, an alternative pathway, with the initial preparation of N-arylsuccinimides and their subsequent reaction with aminoguanidine hydrochloride under microwave irradiation, was applied. The annular prototropic tautomerism in the prepared 1,2,4-triazoles 5 was studied using NMR spectroscopy and X-ray crystallography.

Two complementary pathways for the preparation of N-substituted 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides were proposed and successfully realized in the synthesis of 20 representative examples.     

Synthesis and biological evaluation of 4-(1H-1,2,4-triazol-1-yl)benzoic acid hybrids as anticancer agents

A series of 4-(1H-1,2,4-triazol-1-yl)benzoic acid hybrids (1–17) was successfully synthesized and their structures were established by NMR and MS analysis. In vitro cytotoxic evaluation indicated that some of the hybrids exhibited potent inhibitory activities against MCF-7 and HCT-116 cancer cell lines, with IC₅₀ values ranging from 15.6 to 23.9 µM, compared with reference drug doxorubicin (19.7 and 22.6 µM, respectively). Notably, the most potent compounds, 2, 5, 14, and 15, not only exhibited an obvious improvement in IC₅₀ values, but demonstrated very weak cytotoxic effects toward normal cells (RPE-1) compared with doxorubicin. A further investigation showed that compounds 2 and 14 clearly inhibited the proliferation of MCF-7 cancer cells by inducing apoptosis. In addition, these hybrids showed acceptable correlation with bioassay results in regression plots generated by 2D QSAR models. Our results indicated that 1,2,4-triazole benzoic acid hybrids could be used as a structural optimization platform for the design and development of more selective and potent anticancer molecules.

A series of 4-(1H-1,2,4-triazol-1-yl)benzoic acid hybrids (1–17) was successfully synthesized and their structures were established by NMR and MS analysis. Their anticancer activity against HCT-116, MCF-7 and normal human RPE-1 cells were examined.     

Characterization and simulation study of organic solar cells based on donor–acceptor (D–π–A) molecular materials

In this study, the analysis of microelectronic and photonic structure in a one dimension program [AMPS-1D] has been successfully used to study organic solar cells. The program was used to optimize the performance of organic solar cells based on (carbazole-methylthiophene), benzothiadiazole and thiophene [(Cbz-Mth)-B-T]2 as electron donors, and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as an electron acceptor. The optoelectronic properties of these dyes were investigated by using the Density Functional Theory DFT/B3LYP/6-31G(d,p) method. We studied the influence of the variation of the thickness of the active layer, the temperature, and the density of the effective states of the electrons and the holes in the conduction and valence bands respectively on the performance of the solar cells based on [(Cbz-Mth)-BT]2–PCBM as a photoactive material, sandwiched between a transparent indium tin oxide (ITO) and an aluminum (Al) electrode. The addition of other thiophene units in the copolymer or the deposition of a layer of PEDOT between the anode (ITO) and the active layer, improves the performances of the cell, especially resulting in a remarkable increase in the value of the power conversion efficiency (PCE).

The solar cell ITO/PEDOT/[(Cbz-Mth)-B-DT]2-A:PCBM/Al under study and the results obtained, including a power conversion efficiency of 11%. The impact of several parameters on the performance has been studied to obtain the optimal device architecture.     

Syntheses,characterization and properties of three coordination polymers with interpenetrating structures comprising 4,4′-(1H-1,2,4-triazol-1-yl)methylene-bis(benzonic acid)

Three new coordination polymers (CPs), {[Pb(tmdb)](H₂O)}_n (1), {[Zn(tmdb)(bimb)_0.5]}_n (2) and {[Zn₃(tmdb)₃(bpmb)_1.5](H₂O)₆}_n (3) (H₂tmdb = 4,4′-(1H-1,2,4-triazol-1-yl)methylene-bis(benzonic acid), where bpmb = 1,4-bis(pyridin-4-ylmethoxy)benzene and bimb = 1,4-bis(imidazoly-1-yl)benzene), have been solvothermally or hydrothermally synthesized. Compound 1 is a 2D network with the point symbol (4·6·8)(4·6²) and compound 2 is a 4-fold interpenetrating 3D network with spiral chains. The topological type of 2 is dmc (topos&RCSR.ttd) with the point symbol (4·8²)(4·8⁵). Compound 3 is a 3-fold interpenetrating 3D network with the point symbol (6³)₂(8·6⁵)₂(10·6²)(8·10·6⁴). The electrochemiluminescence (ECL) behaviors of 2 and 3 were studied. The applications of CP 2 and 3 in detecting ions were explored, and the results show that they can be used as fluorescent probes to selectively detect and identify Fe³⁺ ions in water. In addition, the applications of CP 2 and 3 in the adsorption and separation of dyes were researched. Furthermore, the gas adsorption of 3 was studied.

The synthesis and characterization of three compounds with H₂tmdb ligands is reported. The polymers were analyzed using PXRD, IR, TGA and fluorescence spectrometry.     

Three new coordination polymers based on bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane: syntheses,structures, multiresponsive luminescent sensitive detection for antibiotics and pesticides,and antitumor activities

Three novel coordination polymers (CPs), namely, {[Ag₂(L)₂(Mo₄O₁₃)·(CH₃CN)]}_n (1), {[Zn(L)(1,4-bdc)₂·2(1,4-H₂bdc)]}_n (2), {[Cd(L)(1,4-bdc)_0.5]}_n (3) have been synthesized under solvothermal conditions by the reaction of bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane (L) and varied metal salts. Their structures are determined by single X-ray crystal diffraction, and further characterized by elemental analysis, IR, TGA and PXRD. CP 1 with ammonium molybdate as a secondary ligand displays a 2D network with (2,3,3,3,4)-connected net topology and the point symbol of {4·8²}₆{4·8⁴·10}₂{8}, CP 2 and CP 3 with 1,4-H₂bdc as a secondary ligand demonstrate 3D structures with different topologies. CP 2 exhibits high sensibility and low detection limit in the recognition of antibiotics (NZF, NFT and FZD) and pesticide (DCN) identification. CP 1 demonstrates good anti-tumor activity toward the tested glioma cells. The possible luminescent sensitivity and anti-tumor mechanisms are also discussed.

Three novel coordination polymers (CPs) have been synthesized under solvothermal conditions by the reaction of bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane (L) and varied metal salts.     

Syntheses,structures, and magnetic properties of mixed-ligand complexes based on 3,6-bis(benzimidazol-1-yl)pyridazine

Six new metal–organic coordination polymers (CPs) [Ni(L)(2,5-TDC)(H₂O)]_n(1), [Ni(L)(1,3-BDC)(H₂O)]_n (2), [Ni(L)(1,4-BDC)(H₂O)]_n (3), [Mn(L)(2,5-TDC)(H₂O)]_n (4), [Mn(L)(2,6-PYDC)(H₂O)]_n (5) and [Mn(L)(1,4-NDC)]_n (6) were achieved by reactions of the corresponding metal salt with mixed organic ligands (L = 3,6-bis(benzimidazol-1-yl)pyridazine, 2,5-H₂TDC = thiophene-2,5-dicarboxylic acid, 1,3-H₂BDC = isophthalic acid, 1,4-H₂BDC = terephthalic acid, 2,6-H₂PYDC = pyridine-2,6-dicarboxylic acid, 1,4-H₂NDC = naphthalene-1,4-dicarboxylic acid) under solvothermal condition. CPs 1–6 were characterized by single-crystal X-ray diffraction, IR, TG, XRD and elemental analyses. Their structures range from the intricate 3D CPs 1, 3, 4 and 6 to the 2D coordination polymer 2 and the infinite 1D chain 5. The CPs 1–4 and 6 underlying networks were classified from the topological viewpoint, disclosing the distinct sql (in 1), pcu (in 3 and 6), new topology (in 2), and dia (in 4) topological nets. Moreover, analysis of thermal stability shows that they had good thermal stability. Finally, magnetic properties of CPs 1–6 have been studied, the results showed that complex 2 had ferromagnetic coupling and complexes 1, 3–6 were antiferromagnetic.

Six new metal–organic coordination polymers were prepared by reactions of the corresponding metal salt with mixed organic ligands under solvothermal conditions. The compounds were structurally, magnetically and catalytically characterized.     

Efficient full-colour organic light-emitting diodes based on donor–acceptor electroluminescent materials with a reduced singlet–triplet splitting energy gap

A series of efficient blue-emitting materials, namely, Cz-DPVI, Cz-DMPVI, Cz-DEPVI and TPA-DEPVI, possessing a donor–acceptor architecture with dual carrier transport properties and small singlet–triplet splitting is reported. These compounds exhibit excellent thermal properties with a very high glass-transition temperature (T_g), and thus, a stable uniform thin film was formed during device fabrication. Among the weak donor compounds, specifically, Cz-DPVI, Cz-DMPVI and Cz-DEPVI, the Cz-DEPVI-based device showed the maximum efficiencies (L: 13 955 cd m⁻², η_ex: 4.90%, η_c: 6.0 cd A⁻¹, and η_p: 5.4 lm W⁻¹) with CIE coordinates of (0.15, 0.06) at 2.8 V. The electroluminescent efficiencies of Cz-DEPVI were higher than that of the strong donor TPA-DEPVI-based device (L: 13 856 cd m⁻², η_ex: 4.70%, η_c: 5.7 cd A⁻¹, and η_p: 5.2 lm W⁻¹). Furthermore, these blue emissive materials were used as hosts to construct efficient green and red phosphorescent OLEDs. The green device based on Cz-DEPVI:Ir(ppy)₃ exhibited the maximum L of 8891 cd m⁻², η_ex of 19.3%, η_c of 27.9 cd A⁻¹ and η_p of 33.4 lm W⁻¹ with CIE coordinates of (0.31, 0.60) and the red device based on Cz-DEPVI:Ir(MQ)₂(acac) exhibited the maximum L of 40 565 cd m⁻², η_ex of 19.9%, η_c of 26.0 cd A⁻¹ and η_p of 27.0 lm W⁻¹ with CIE coordinates of (0.64, 0.37).

The Cz-DEPVI device showed high efficiencies of L: 13955 cd m⁻², η_ex: 4.90%, η_c: 6.0 cd A⁻¹, η_p: 5.4 lm W⁻¹ and CIE coordinates of (0.15, 0.06) at 2.8 V.     

A series of new polyoxometalate-based metal–organic complexes with different rigid pyridyl-bis(triazole) ligands: assembly,structures and electrochemical properties

Five new polyoxometalate (POM)-based metal–organic complexes (MOCs) with different rigid pyridyl-bis(triazole) ligands, namely, H{Co₂(Hpyttz-I)₂(H₂O)₆[CrMo₆(OH)₆O₁₈]}·8H₂O (1), {Co₂(H₂pyttz-I)₂(H₂O)₄[TeMo₆O₂₄]}[Co(H₂O)₆]·3H₂O (2), {Co₃(Hpyttz-II)₂(H₂O)₆[γ-Mo₈O₂₆]}·10H₂O (3), {Ni₃(Hpyttz-II)₂(H₂O)₆[γ-Mo₈O₂₆]}·10H₂O (4), {Ni₃(Hpyttz-III)₂(H₂O)₈[γ-Mo₈O₂₆]}·10H₂O (5) (H₂pyttz-I = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H₂pyttz-II = 3-(pyrid-3-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H₂pyttz -III = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), were successfully synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Complex 1 is a two-dimensional (2D) supramolecular network based on the binuclear complex unit: [Co₂(Hpyttz-I)₂(H₂O)₆ [CrMo₆(OH)₆O₁₈]]. Complex 2 is a 1D supramolecular chain derived from the binuclear cobalt complex: {Co₂(H₂pyttz-I)₂(H₂O)₄[TeMo₆O₂₄]}²⁻, the discrete [Co(H₂O)₆]²⁺ units act as counter cations. Complexes 3 and 4 are isostructural with different center metals (M = Co or Ni), the adjacent γ-Mo₈O₂₆⁴⁻ anions are linked by the M^II ions to form a 1D M-γ-Mo₈O₂₆ inorganic chain. Then 1D M-γ-Mo₈O₂₆ inorganic chains are linked together by the 1D metal–organic M-(Hpyttz-II) chains to form a 3D framework. In complex 5, γ-Mo₈O₂₆⁴⁻ anions are bridged by the Ni^II ions to give a 1D Ni-γ-Mo₈O₂₆ inorganic chain, the adjacent 1D Ni-γ-Mo₈O₂₆ chains are connected through [Ni(Hpyttz-III)₂] units to form a 2D layer. The effect of POM type and coordination site of the ligands on the structures of the title complexes were discussed. The title complexes 1, 2 and 5 exhibit excellent bifunctional electrocatalytic activities toward the reduction of bromate/hydrogen peroxide and the oxidation of ascorbic acid. In addition, the redox potentials of complexes 1, 2 and 5 are highly sensitive to pH and may be used as a kind of potential pH sensor.

Two novel Anderson-type and three octamolybdate (γ-Mo₈O₂₆) polyoxometalate-based metal–organic complexes were synthesized and structurally characterized. The electrochemical and bifunctional electrocatalytic behaviors of the title compounds have been investigated in detail.     

Efficient and chromaticity-stable flexible white organic light-emitting devices based on organic–inorganic hybrid color-conversion electrodes

We have developed a novel organic–inorganic hybrid color conversion electrode composed of Ag NWs/poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) via a solution process, which is the first report on a color conversion electrode for applications in flexible optoelectronics. Using the Ag NWs/MEH-PPV composite film as the anode on polyethylene terephthalate substrate and combined with a blue organic light emitting devices (OLEDs) unit employing bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(iii)) (Flrpic) in 1,3-bis(carbazol-9-yl)benzene (mCP) as the emitting layer, a highly efficient and chromaticity-stable color-conversion flexible white OLEDs (WOLEDs) is achieved with a maximum current efficiency of 20.5 cd A⁻¹. To the best of our knowledge, this is the highest efficiency reported for color-conversion based flexible WOLEDs. Our work provides an approach to achieving high-performance flexible WOLEDs devices and demonstrates great potential for lighting and display applications.

We have developed a novel color conversion electrode composed of Ag NWs/MEH-PPV via a solution process, which is the first report on a color conversion electrode for applications in flexible optoelectronics.     

Photocatalytic degradation of organic pollutants through conjugated poly(azomethine) networks based on terthiophene–naphthalimide assemblies

A conjugated poly(azomethine) network based on ambipolar terthiophene–naphthalimide assemblies has been synthesized and its electrochemical and UV-vis absorption properties have been investigated. The network has been found to be a promising candidate for the photocatalytic degradation of organic pollutants in aqueous media.

A conjugated two-dimensional poly(azomethine) network based on ambipolar terthiophene–naphthalimide assemblies has been synthesized and its electrochemical and UV-vis absorption properties have been investigated.

Due to the rapid growth of urbanization and intensive industrialization, pollution has evolved into a serious concern that produces a great negative impact on human health and the environment.^1,2 Therefore, many efforts are currently devoted to addressing environmental remediation through the degradation and removal of hazardous contaminants.^3–5 In this regard, photocatalysis has been identified as a suitable approach for environmental remediation given that it is an energy efficient technique that does not require chemical input and does not produce sludge residue.⁶ In recent years, organic semiconducting polymers have evolved into a new type of metal-free and heterogeneous photocatalyst suitable for solar-energy utilization.⁷ The modularity of organic polymers allows the efficient tunning of their electronic and optical properties by bottom-up organic synthesis through the choice of suitable monomeric building blocks.^8–10 Within this context, there is a growing demand for new organic polymeric semiconductors carefully designed to have suitable energy levels of the frontier orbitals, an appropriate bandgap and good intrinsic charge mobility.¹¹For the design of suitable polymeric semiconductors for photocatalysis, it is not only important that the photocatalysts absorb light in the visible light range but also an efficient dissociation of the photogenerated charge carriers is required. The combination of electron-poor acceptor (A) and electron-rich donor (D) moieties in the polymer structure may prevent a fast recombination process following photoexcitation.¹² In addition, it has been found that polymers networks bearing conjugated moieties may exhibit π-stacked columns that can facilitate charge transport.¹³In this respect, molecular and polymeric materials based on the combination of oligothiophene^14,15 and naphthalimide moieties^16,17 connected through conjugated linkers have shown to be very effective in order to efficiently tune their frontier orbital levels and produce tunable organic semiconductors with good charge transport properties.^18–24 As an example, in Fig. 1 is depicted the structure of NIP-3T, an ambipolar organic semiconductor, for which the one-electron HOMO–LUMO excitation consists of the displacement of the electron density from the HOMO, primarily localized on the oligothiophene fragment, to the LUMO, localized on the naphthalimide unit.²⁵Open in a separate windowFig. 1(a) Monomer containing an electron donor terthiophene system directly conjugated with an electron acceptor naphthalimide moiety through a conjugated pyrazine linker (NIP-3T). (b) HOMO and (c) LUMO computed orbital topologies for NIP-3T.²⁵Among conjugated polymers, poly(azomethine)s have found application as organic semiconductors in heterogeneous photocatalysis because of their π-conjugated system and suitable band levels matching the redox window of water.²⁶ The incorporation of D–A monomeric assemblies into poly(azomethine) networks represents an efficient strategy to obtain ambipolar polymeric networks with tunable frontier orbital levels for photocatalytic applications. Thus, in this communication we report the synthesis of a novel donor–acceptor poly(azomethine) network (NIP3T-ANW, Scheme 1) based on NIP-3T monomers. The potential of this system as photodegrading agent for the elimination of contaminant organic dyes in aqueous media is also explored.Open in a separate windowScheme 1Schematic representation of the synthesis of NIP3T-ANW.The synthesis of the macromolecular poly(azomethine) network NIP3T-ANW is acomplished through Schiff-base reactions between trigonal monomers endowed with amine functionalities (TAPB,²⁷Scheme 1) and linear naphthalimide–thiophene-based monomers endowed with complementary aldehyde functional groups (NIP3T2CHO,²⁴Scheme 1). Typically, both monomers were dissolved in an o-dichlorobenzene/n-butanol/acetic acid (1 : 1 : 0.1) mixture, which was then heated at 120 °C under solvothermal reaction conditions for 72 h. A black solid was obtained which was insoluble in common solvents such as water, acetone, THF, toluene or chlorinated solvents like dichloromethane or chloroform. The obtained solid was washed several times with THF to remove the starting materials and low-molecular weight by-products. After drying under vacuum, a black solid was obtained. The yield, as determined by weight, was 98%.To investigate the chemical nature of the material, as well as to determine the conversion of the functional groups after the reaction, we have employed attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy (Fig. 2). The bands arising from the NH₂ stretching (3000–3400 cm⁻¹) and NH₂ deformation (1650 cm⁻¹) vibrations of the primary amine group of TAPB and the signals from the aldehyde groups of NIP3T2CHO around 2870 (C–H stretching) and 1663 cm⁻¹ (C O stretching) are virtually absent in the NIP3T-ANW spectrum. In addition, a prominent new band is found at 1573 cm⁻¹, which can be assigned to the C N stretching vibration of the imine linkages within the newly formed poly(azomethine) network.^28–30Open in a separate windowFig. 2(a) IR spectra of NIP3T2CHO (blue), TAPB (red) and NIP3T-ANW (black). (b) Solid-state ¹³C CP-MAS NMR spectrum of NIP3T-ANW.Solid-state ¹³C cross-polarization magic angle spinning NMR (¹³C CP-MAS NMR) spectrum (Fig. 2) reveals the characteristic imide signals of the 1,8-naphthalimide moiety at 164.4 ppm, as well as the signal corresponding to the imine carbon at 154 ppm and a signal at 148 ppm which can be assigned to the aromatic carbon neighbouring the nitrogen of the C N group. The absence of the sp² carbons from the NIP3T2CHO ²⁴ aldehyde functionalities above 180 ppm satisfactorily confirms the condensation between the aldehyde and the amine derivatives.Due to the rigidity and geometry of the building blocks, the imine linkers could be ideally generated in such a way that result in a canonical layered hexagonal structure³¹ as predicted by theoretical calculations (Fig. S1 and S2^†). However, in the actual framework, X-ray diffraction (XRD) measurements indicate that the material is mainly amorphous with only some ordered regions, as indicated by the good agreement between the weak and broad diffraction peaks observed at 2θ values larger than 3 and those predicted by calculations for the ideal canonical layered hexagonal structure (Fig. S3^†). In this regard, NIP3T-ANW was submitted to an exfoliation process following a previously described protocol³² for the exfoliation of two-dimensional polymers (see ESI^† for details). The exfoliated material was analysed by dynamic light scattering (DLS) showing a monomodal size distribution of ca. 400 nm (Fig. S4^†) and transmission electron microscopy (TEM) reveals a sheet-like structural aspect (Fig. S5^†).Thermogravimetric analysis of the poly(azomethine) network NIP3T-ANW shows that the degradation starts at around 450 °C and only 40% weight loss is observed at 700 °C (Fig. S6^†). This thermal stability is significantly higher than that observed for NIP3T (Fig. 1), the analogous molecular system based on terthiophene connected with naphthalimide through pyrazine for which the degradation starts at 200 °C (Fig. S6^†).^22,25In photocatalysis mediated by semiconductors, electron–hole pairs (excitons) are generated after light absorption and afterwards dissociate into free charge carriers that can be utilized for redox reactions^33,34 such as CO₂ fixation,³⁵ water splitting³⁶ or organic mineralization.³⁷ Some of the crucial factors that make the photocatalytic process favourable are the levels of conduction and valence as well as the width of the band gap.^38–40 Thus, in order to characterize these parameters, the electrochemical and optical properties of NIP3T-ANW have been analysed.The electrochemical properties of NIP3T and NIP3T-ANW were studied by cyclic voltammetry (Fig. 3). Both materials show ambipolar redox behaviour in which the reversible reduction processes are characteristic of the naphthalimide unit, while the oxidation processes can be ascribed to the conjugated oligothiophene moiety.^19–22,24 For NIP3T-ANW, the first reversible reduction wave (−1.29 V) is shifted to less negative values in comparison with NIP-3T (−1.41 V). On the other hand, the first oxidation half wave potential for NIP3T is observed at +0.41 V and for NIP3T-ANW at +0.44 V. These shifts agree with the electron acceptor ability of the imine linker.Open in a separate windowFig. 3(a) The UV-vis DRS spectra of NIP3T and NIP3T-ANW. (b) Cyclic voltammetry of the NIP3T monomer and the corresponding polymer.The absorption spectrum of NIP3T-ANW as determined by UV-vis diffuse reflectance spectroscopy (UV-vis DRS, Fig. 3) shows a strong absorption in all the UV-vis range, extending even to the near infrared. This broad absorption is red-shifted in comparison with the one observed for NIP3T (Fig. 3), which reflects the formation of the new polymer network with an extended conjugation through the alpha positions of the terthiophenes.Using the corresponding cut-off wavelengths, the optical band gaps E_g found for NIP3T and NIP3T-ANW are 1.59 and 1.42 eV respectively. This optical result suggests that the incorporation of the NIP3T core into an extended conjugated system efficiently harvests photons from the visible range, even extending into the near IR region.To shed some light into the degree of crystallinity of the synthesized NIP3T-ANW network, we have carried out a battery of density functional theory (DFT)-based calculations with the QUANTUM ESPRESSO plane-wave DFT simulation code⁴¹ (see details in ESI^†). We have considered periodic boundary conditions to obtain a fully-relaxed ground-state crystal structure. Optimization of the cell-shape and size, simultaneously to the relaxation of the structure, reveals a hexagonal 2D lattice with an optimized parameter of 48.46 Å. Different interlayer stacking fashions have been tested, with only one yielding a good agreement with the experimental diffractogram from 2θ values >3°. The most favourable stacking predicted by theory consists in an intermediate configuration between the perfectly eclipsed and staggered configurations, with an interlayer distance of 3.42 Å, and permits an adequate accommodation of the layers profiting adjacent pores. Details on the structure can be found in the ESI.^†Additionally, we have computed the electronic band diagram of the obtained crystal structure along the high-symmetry k-path Γ → K → M → Γ, revealing a wide-gap (1.91 eV) semiconducting character, with rather dispersive valence and conduction bands, mainly resembling the molecular HOMO and LUMO of the molecular building blocks (see Fig. S7^†). Besides, computed time-dependent DFT (TDDFT) UV-vis spectrum manifests an excellent agreement with the experimental UV-vis spectra (Fig. S8^†). A broad and pronounced peak-feature is obtained between 600 and 800 nm, centred at around 720 nm (1.7 eV), which agrees with the optical gap of 1.6 eV found for NIP3T from Fig. 3a. This feature corresponds to electronic transitions between the valence and conduction bands, with an energy difference of around 0.2 eV between the optical and the electronic gap, which indicates that charge relaxation in excited states is not much significative. The good agreement between theoretical predictions on the canonically periodic computed system and the experimental evidences seems to justify the presence of some high-crystallinity regions from the synthesis.The band gap of a semiconductor material and the reduction and oxidation potentials are key parameters which determine its light-harvesting properties and types of reaction that can be conducted and therefore the overall photo-catalytic activity. A shift in the adsorption edge of a semiconductor towards longer wavelengths implies a narrower band gap and the efficient harvesting of a wider photons range.⁴²NIP3T-ANW seems to be an appealing material to be utilized as photocatalyst given (i) the optimal light harvesting properties as shown by the optical characterization, (ii) the efficient generation of electron–hole pairs owing to the insertion of terthiophene moieties, and (iii) the right energy band positions for the material.⁷ We therefore evaluated the photocatalytic activity of NIP3T-ANW under white light for the degradation of a model organic pollutant (Rhodamine B dye, RhB) in aqueous solution.⁴³ In the absence of catalyst, RhB remains stable in solution under illumination (Fig. 4a and S9^†). However, in presence of NIP3T-ANW nearly 90% of RhB in an aqueous solution is degraded after 120 min, showing the enhanced catalytic activity of the material (Fig. 4a and S10^†). Furthermore, a good stability is shown upon 4 straight catalytic cycles (Fig. 4b, S11 and S12^†). In contrast, in the presence of the NIP3T moiety, only a 55% degradation of RhB is observed in the same timeframe (Fig. 4a and S11^†).Open in a separate windowFig. 4RhB degradation curves. (a) Comparison between the degradation effect of NIP3T, NIP3T-ANW and without catalyst. (b) NIP3T-ANW stability after four recycling cycles.In the photocatalytic degradation of organic pollutants, they are typically broken down through the attack of superoxide and hydroxyl species, formed when atmospheric oxygen reacts with photogenerated electrons or when water or OH ions are oxidized by holes, respectively.⁴⁴ Additionally, electron–hole pairs (or excitons) can directly reduce or oxidize organic pollutants in aqueous environments. Consequently, the evaluation of the photodegradation mechanism of organic pollutants, despite challenging, can provide meaningful insights about the nature of a semiconductor photocatalyst.⁴⁵ With the aim of evaluating the photodegradation mechanism we performed the measurements in the presence of different scavengers, namely an aqueous solution of AgNO₃ (100 mg L⁻¹), which captures photogenerated electrons, or triethanolamine (TEOA), which traps photogenerated holes (Fig. S13^†).^46,47 In the presence of Ag⁺ we could observe that the photocatalytic efficiency is enhanced, while the addition of TEOA quenched the performance, therefore suggesting that holes are the active specie in the photodegradation mechanism (Fig. S14^†).In summary, we have presented an approach towards the incorporation of D–A π-conjugated monomeric assemblies into poly(azomethine) networks to yield a purely organic semiconductor for the photocatalytic degradation of organic pollutants in aqueous media. The poly(azomethine) network benefits from a straightforward poly(condensation) approach which favourably competes with the elaborate high-temperature protocols applied for the preparation of inorganic materials. This work enriches the family of donor–acceptor organic semiconductor networks and, given its modular nature, paves the way for the development of a promising family of materials for photocatalytic applications.     

Palladium supported on mixed-metal–organic framework (Co–Mn-MOF-74) for efficient catalytic oxidation of CO

Successful monometallic and bimetallic metal–organic frameworks with different Co/Mn ratios have been synthesized under solvothermal conditions. The as-synthesized MOFs followed by deposition of Pd nanoparticles with 0.5 to 7 wt%. The XRD, BET, SEM, TEM, EDAX and FT-IR characterization results reveal that bimetallic MOFs and Pd nanoparticles were finely dispersed on the prepared MOFs surfaces. XRD results confirm the formation of the desire MOFs and show the high degree of dispersion of Pd nanoparticles. TEM images show that Pd nanoparticles are nano-sized with almost uniform shape. EDAX shows that Pd nanoparticles successfully loaded on Co_0.5–Mn_0.5-MOF-74 catalyst. CO oxidation as a model reaction was then used to assess the catalytic performance of the prepared catalysts. The catalytic activity results show enhancement in the catalytic activities of monometallic MOFs after introducing another metal in the same framework and show an excellent improvement in CO conversion after loading with Pd nanoparticles. Furthermore, the samples that contain Pd nanoparticles exhibits higher catalytic activities which raised with increasing the content of Pd nanoparticles.

Pd nanoparticles were loaded on Co_x–Mn_(1−x)-MOF-74. 5 wt% Pd@Co_0.5–Mn_0.5-MOF-74 was the most effective catalyst for CO oxidation. The prepared catalysts displayed excellent stability during CO oxidation without significant decrease in catalytic performance.     

Metal–organic frameworks (MOFs) based nanofiber architectures for the removal of heavy metal ions

Environmental heavy metal ions (HMIs) accumulate in living organisms and cause various diseases. Metal–organic frameworks (MOFs) have proven to be promising and effective materials for removing heavy metal ions from contaminated water because of their high porosity, remarkable physical and chemical properties, and high specific surface area. MOFs are self-assembling metal ions or clusters with organic linkers. Metals are used as dowel pins to build two-dimensional or three-dimensional frameworks, and organic linkers serve as carriers. Modern research has mainly focused on designing MOFs-based materials with improved adsorption and separation properties. In this review, for the first time, an in-depth look at the use of MOFs nanofiber materials for HMIs removal applications is provided. This review will focus on the synthesis, properties, and recent advances and provide an understanding of the opportunities and challenges that will arise in the synthesis of future MOFs–nanofiber composites in this area. MOFs decorated on nanofibers possess rapid adsorption kinetics, a high adsorption capacity, excellent selectivity, and good reusability. In addition, the substantial adsorption capacities are mainly due to interactions between the target ions and functional binding groups on the MOFs–nanofiber composites and the highly ordered porous structure.

Metal–organic frameworks (MOFs) are promising and effective materials for removing heavy metal ions from contaminated water owing to their high porosity, remarkable physical and chemical properties, and high specific surface area.     

Modeling rapid and selective capture of nNOS–PSD-95 uncouplers from Sanhuang Xiexin decoction by novel molecularly imprinted polymers based on metal–organic frameworks

Novel and highly selective molecularly imprinted polymers based on the surface of metal–organic frameworks, NH₂-MIL-101(Cr) (MIL@MIP_S), were successfully fabricated to capture neuronal nitric oxide synthase–postsynaptic density protein-95 (nNOS–PSD-95) uncouplers from Sanhuang Xiexin Decoction (SXD) for stroke treatment. The resultant polymers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction. The performance tests revealed that MIL@MIPs had a large binding capacity, fast kinetics, and excellent selectivity. Then the obtained polymers were satisfactorily applied to solid-phase extraction coupled with high-performance liquid chromatography to selectively capture nNOS–PSD-95 uncouplers from SXD. Furthermore, the biological activities of components obtained from SXD were evaluated in vivo and in vitro. As a consequence, the components showed a potent neuroprotective effect from the MTS assay and uncoupling activity from the co-immunoprecipitation experiment. In addition, the anti-ischemic stroke assay in vivo was further investigated to determine the effect of reducing infarct size and ameliorating neurological deficit by the active components. Therefore, this present study contributes a valuable new method and new tendency to selectively capture active components for stroke treatment from SXD and other natural medicines.

Novel MIL@MIPs were prepared to rapidly capture nNOS–PSD-95 uncouplers from Sanhuang Xiexin decoction, coupled with SPE and HPLC.     

A Zn(ii) metal–organic framework based on bimetallic paddle wheels as a luminescence indicator for carcinogenic organic pollutants: phthalate esters

Based on the multifunctional ligand 3-(1H-1,2,4-triazol-1-yl)isophthalic acid (H₂TIA), a three-dimensional coordination polymer, namely {[Zn(TIA)]·DMA}_n (Zn-1) was synthesized solvothermally. Single-crystal X-ray diffraction analyses confirmed that Zn-1 is a 3D framework composed of binuclear Zn₂ paddle wheels with one-dimensional channels long the a direction. Further topological analyses revealed that MOF Zn-1 existed as a (3,6)-connected rtl binodal net {4·6²}²{4²·6¹⁰·8³}. Furthermore, the luminescence explorations indicate that complex Zn-1 is the first MOF for luminescent probing of phthalate esters (carcinogenic organic pollutants) with a high quenching-efficiency constant and low fluorescence-detection limit.

A three-dimensional coordination polymer {[Zn(TIA)]·DMA}_n (Zn-1) with rtl binodal topology has been synthesized. In addition, Zn-1 is the first MOF for luminescent probing of phthalate esters.     

Synthesis and photoluminescence properties of hybrid 1D core–shell structured nanocomposites based on ZnO/polydopamine

In the present work, we report on the modelling of processes at the zinc oxide and polydopamine (ZnO/PDA) interface. The PDA layer was deposited onto ZnO nanorods (NRs) via chemical bath deposition. The defect concentrations in ZnO before and after PDA deposition were calculated and analysed. The ZnONRs/PDA core–shell nanostructures were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and Fourier-transform infrared (FTIR) spectroscopy, photoluminescence (PL) measurements, and diffuse reflectance spectroscopy. The TEM and electron energy loss spectroscopy (EELS) measurements confirmed the conformal coating of PDA, while the PL emission from ZnO and ZnONRs/PDA samples showed a reduction of intensity after the PDA deposition. The decrease of defect concentration participating in PL and quantum efficiency explains the PL reduction. Finally, the observed decrease of activation energies and a shift of the PL peaks are attributed to the formation of an additional local electrical field between the PDA and ZnO nanostructures.

The results shown in this study provide a unique insight into the optical and electronic processes of the ZnO/PDA interface.