Two zinc(ii) coordination polymers based on flexible co-ligands featuring assembly imparted sensing abilities for Cr2O72− and o-NP

Two new Zn(ii) coordination complexes, formulated as [Zn(opda)(pbib)] (1) and [Zn(ppda)(pbib)(H₂O)] (2), (H₂opda = 1,2-phenylenediacetic acid, H₂ppda = 1,4-phenylene-diacetic acid, pbib = 1,4-bis(1-imidazoly)benzene), have been synthesized. The opda ligands extend a 1D chain containing (Zn-pbib) polymer chains into a 2D layer in 1. In 2, the ppda ligands link Zn(ii) atoms to form a 2D network, then the rigid bis(imidazole) ligands give rise to the 3D structure. The fluorescence property application and mechanisms of two complexes for detecting Cr₂O₇²⁻ and o-NP have been researched. For two complexes, the high quenching percentage in low concentration aqueous solution are 95.75% (Cr₂O₇²⁻, 1), 95.28% (Cr₂O₇²⁻, 2) and 97.56% (o-NP, 1), 96.59% (o-NP, 2). Compared with 2, complex 1 has higher quenching percentage, this could be because 1 is a 3D supramolecular with a large hole. The detection limits have been measured to be 2.992 × 10⁻⁷ M (Cr₂O₇²⁻, 1), and 4.372 × 10⁻⁷ M (Cr₂O₇²⁻, 2), 2.103 × 10⁻⁷ M (o-NP, 1), 1.862 × 10⁻⁷ M (o-NP, 2), respectively. The emissions of two complexes could be effectively and selectively quenched by o-NP and Cr₂O₇²⁻, showing their potential as multi-responsive luminescent sensors.

Two zinc(ii) complexes exhibit the different architectures, and they have been shown to be excellent discriminative probe for the highly selective and sensitive detection of Cr₂O₇²⁻ and o-NP based on their sensitive fluorescence quenching.     

A dipodal molecular probe for naked eye detection of trivalent cations (Al3+, Fe3+and Cr3+) in aqueous medium and its applications in real sample analysis and molecular logic gates

A simple and low cost multifunctional colorimetric receptor L has been designed, synthesized and characterized by ¹H-NMR, IR spectroscopy, ESI-MS spectrometry and elemental analysis. The chemosensor L can selectively detect three biologically and environmentally important trivalent metal ions (Al³⁺, Fe³⁺and Cr³⁺) both visually and spectrophotometrically in CH₃CN–H₂O (1 : 1, v/v) solution in the presence of other biologically relevant metal ions. The Job''s plot analyses indicate the 2 : 2 binding stereochemistry for Al³⁺, Fe³⁺ and Cr³⁺ ions with L, which was further confirmed by ¹H-NMR and ESI-MS studies. The binding constant values were found to be 2.9 × 10⁴ M⁻¹ for Al³⁺, 1.079 × 10⁵ M⁻¹ for Fe³⁺ and 1.366 × 10⁵ M⁻¹ for Cr³⁺ respectively. The detections limits of the sensor for Al³⁺ (2.8 × 10⁻⁷ M), Fe³⁺ (1.9 × 10⁻⁷ M) and Cr³⁺ (2.5 × 10⁻⁷ M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Moreover, colorimetric test kits for rapid detection of Al³⁺, Fe³⁺, and Cr³⁺ could be successively applied for all practical purposes, indicating its potential use in environmental samples. It has also been used in building molecular logic gates.

A dipodal reversible colorimetric trivalent metal ion chemosensor (L) has been designed and synthesized. The chemosensor L successfully detects Al³⁺, Fe³⁺ and Cr³⁺ based on binding site-signaling approach and it has practical application.     

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO42−, Cr2O72− and MnO4−

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)₂]_n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4′-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn₄(modbc)₄ units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb³⁺ in Zn-CP, the as-obtained fluorescent functionalized Tb³⁺@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻, and MnO₄⁻ with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

A composite, Tb³⁺@Zn-CP, for sensing Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and MnO₄⁻ with fast response times was reported.     

A series of Ln4III clusters: Dy4 single molecule magnet and Tb4 multi-responsive luminescent sensor for Fe3+, CrO42−/Cr2O72− and 4-nitroaniline

Five tetranuclear lanthanide clusters of compositions [Ln₄L₄(NO₃)₂(Piv)₂]·2CH₃OH (Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5); H₂L = 2-(((2-hydroxy-3-methoxybenzyl)imino)methyl)-6-methoxyphenol; Piv = pivalic acid) were synthesized under solvothermal conditions. The structures of 1–5 were characterized by single-crystal X-ray crystallography. Complexes 1–5 possess a zig-zag topology with [Ln₄O₆] cores being formed by the fusion of oxygen atom-bridged two [Ln₂O₂] moieties. Direct-current magnetic susceptibility studied in the 2–300 K range revealed weak antiferromagnetic interactions in 1, 2, 4, 5 and ferromagnetic interactions in 3. Complex 3 exhibits single molecule magnet (SMM) behavior. The luminescence studies indicated that complex 2 can serve as highly sensitive and selective luminescent materials for Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and 4-nitroaniline (4-NA), demonstrating that complex 2 should be a potential candidate for multi-responsive luminescent sensor.

Five tetranuclear lanthanide clusters were synthesized. Dy₄ complex exhibits single molecule magnet (SMM) behavior and Tb₄ compound shows sensing properties towards Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and 4-nitroaniline (4-NA).     

Fluorescence detection of malachite green and cations (Cr3+, Fe3+ and Cu2+) by a europium-based coordination polymer

Due to remarkable fluorescence characteristics, lanthanide coordination polymers (CP) have been widely employed in fluorescence detection, but it is rarely reported that they act as multifunctional luminescent probes dedicated to detecting malachite green (MG) and various metal ions. A europium-based CP fluorescent probe, Eu(PDCA)₂(H₂O)₆ (PDCA = 2,6-pyridinedicarboxylic acid), has been synthesized and exhibited excellent recognition ability for malachite green and metal cations (Cr³⁺, Fe³⁺ and Cu²⁺) among 11 metal cations, 13 anions and six other compounds. The recognition was achieved by fluorescence quenching when MG, Cr³⁺, Fe³⁺ and Cu²⁺ were added to a suspension of Eu(PDCA)₂(H₂O)₆ respectively. Eu(PDCA)₂(H₂O)₆ is a multifunctional luminescent probe, and displayed high quenching efficiencies K_sv (2.10 × 10⁶ M⁻¹ for MG; 1.46 × 10⁵ M⁻¹ for Cr³⁺; 7.26 × 10⁵ M⁻¹ for Fe³⁺; 3.64 × 10⁵ M⁻¹ for Cu²⁺), and low detection limits (MG: 0.039 μM; Cr³⁺: 0.539 μM; Fe³⁺: 0.490 μM; Cu²⁺: 0.654 μM), presenting excellent selectivity and sensitivity, especially for MG. In addition, Eu(PDCA)₂(H₂O)₆ was also made into fluorescent test strips, which can rapidly and effectively examine trace amounts of MG, Cr³⁺, Fe³⁺ and Cu²⁺ in aqueous solutions. This work provides a new perspective for detecting malachite green in fish ponds and heavy metal ions in waste water.

A europium-based CP fluorescent sensor was synthesized and exhibited excellent recognition ability for malachite green (MG) and metal cations (Cr³⁺, Fe³⁺ and Cu²⁺).     

Zn2+ removal from the aqueous environment using a polydopamine/hydroxyapatite/Fe3O4 magnetic composite under ultrasonic waves

In this study, an easily magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was suitably synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution, and its structural properties were thoroughly examined using different analytical techniques. The effect of multiple parameters like pH, ultrasonic power, ultrasonic time, adsorbent dose, and initial Zn²⁺ concentration on the adsorption efficiency was assessed using RSM-CCD. According to the acquired results, by increasing the adsorbent quantity, ultrasonic power, ultrasonic time, and pH, the Zn²⁺ adsorption efficiency increased and the interaction between the variables of ultrasonic power/Zn²⁺ concentration, pH/Zn²⁺ concentration, pH/absorbent dose, and ultrasonic time/adsorbent dose has a vital role in the Zn²⁺ adsorption. The uptake process of Zn²⁺ onto PDA/HAp/Fe₃O₄ followed Freundlich and pseudo-second order kinetic models. The maximum capacity of Zn²⁺ adsorption (q_m) obtained by PDA/HAp/Fe₃O₄, HAp/Fe₃O₄, and HAp was determined as 46.37 mg g⁻¹, 40.07 mg g⁻¹, and 37.57 mg g⁻¹, respectively. Due to its good performance and recoverability (ten times), the HAp/Fe₃O₄/PDA magnetic composite can be proposed as a good candidate to eliminate Zn²⁺ ions from a water solution.

A magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution and the structural properties were examined.     

Metal–organic framework bearing new viologen ligand for ammonia and Cr2O72− sensing

Three anionic metal–organic frameworks (MOFs) {[Zn₃(BTEC)₂(H₂O)(4-BCBPY)]·(H₂O)}_n (1–3) (BTEC⁴⁻ = 1,2,4,5-benzenetetracarboxylic acid anion, 4-BCBPY²⁺ = 1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium dication) were synthesized in the reaction of 1,2,4,5-benzenetetracarboxylic acid with different metal salts such as ZnNO₃, ZnCl₂, and ZnSO₄, under solvothermal conditions in the presence of 1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium chloride. Single crystal X-ray diffraction analysis shows that compounds 1, 2 and 3 have MOF structures based on binuclear metal building units, which are connected by two protonated BTEC⁴⁻ ligands and three zinc ions, and the viologen cation 4-BCBPY²⁺ is located in the channel to achieve charge balance. Compounds 1, 2 and 3 have good photosensitivity, respond to sunlight, UV light and blue ray, and turn blue. The D–A distance and π–π stacking distance of the discolored samples (1P, 2P and 3P) changed. In addition, the three compounds showed visible color changes to ammonia vapor, rapidly changing from white to blue. At the same time, the three compounds exhibited fluorescence quenching to ammonia vapor and Cr₂O₇²⁻. It is further proved that compounds 1, 2 and 3 are fluorescent sensors with a low detection limit (for Cr₂O₇²⁻: 10⁻⁵ M) and high sensitivity for ammonia vapor and Cr₂O₇²⁻. It was found that photochromic behavior, ammonia sensing properties can be tuned by the nature of metal salts.

Three MOFs based on different metal salts were synthesized, and metal salts were found to play a key role in regulating the performance of MOFs.     

Extraction and preconcentration of Ni(ii), Pb(ii), and Cd(ii) ions using a nanocomposite of the type Fe3O4@SiO2@polypyrrole-polyaniline

In this study, the application of Fe₃O₄@SiO₂@polypyrrole-polyaniline magnetic nanocomposite was studied for Ni(ii), Cd(ii), and Pb(ii) ions preconcentration extraction. In this regard, the silica layer prevents the Fe₃O₄ nanoparticles (NPs) from aggregating over a broad pH range value and simultaneously improves chemical stability and hydrophilicity. By using a Box–Behnken design, the effect of various parameters affecting the preconcentration was studied. FAAS was employed to quantify the eluted analytes. The detection limits are 0.09, 1.1, and 0.3 ng mL⁻¹ for Ni(ii), Cd(ii) and Pb(ii), ions, respectively. The relative standard deviations (RSDs%) were calculated for determining the method''s precision, lower than 7.5%. The capacities of sorption are 75, 84, and 98 mg g⁻¹, respectively. With the usage of a certified reference material, the developed method was validated. After that, the validated method was employed to rapidly extract trace target ions from food samples and gave satisfactory results.

In this study, the application of Fe₃O₄@SiO₂@polypyrrole-polyaniline magnetic nanocomposite was studied for Ni(ii), Cd(ii), and Pb(ii) ions preconcentration extraction.     

Novel magnetically separable anhydride-functionalized Fe3O4@SiO2@PEI-NTDA nanoparticles as effective adsorbents: synthesis,stability and recyclable adsorption performance for heavy metal ions

In this paper, a novel adsorbent, Fe₃O₄@SiO₂@PEI-NTDA, was first prepared by the immobilization of an amine and anhydride onto magnetic Fe₃O₄@SiO₂ nanoparticles with polyethylenimine (PEI) and 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTDA) for the removal of heavy metal ions from aqueous solutions. The structure of Fe₃O₄@SiO₂@PEI-NTDA was systematically investigated; the results confirmed that amine and anhydride groups were successfully covalently grafted onto the surface of Fe₃O₄@SiO₂, which showed a homogenous core–shell structure with three layers of about 300 nm diameter (Fe₃O₄ core: 200 nm, nSiO₂ layer: 20 nm, and PEI-NTDA layer: 20 nm). The adsorption performance of Fe₃O₄@SiO₂@PEI-NTDA NPs was evaluated for single Pb²⁺ and coexisting Cd²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions in an aqueous solution in a batch system. The amine and anhydride groups may have a synergistic effect on Pb²⁺ removal through electrostatic interactions and chelation; Fe₃O₄@SiO₂@PEI-NTDA NPs exhibited preferable removal of Pb²⁺ with maximum adsorption capacity of 285.3 mg g⁻¹ for Pb²⁺ at a solution pH of 6.0, adsorbent dosage of 0.5 g L⁻¹, initial Pb²⁺ concentration of 200 mg L⁻¹ and contact time of 3 h. The adsorption mechanism conformed well to the Langmuir isotherm model, and the adsorption kinetic data were found to fit the pseudo-second order model. Fe₃O₄@SiO₂@PEI-NTDA NPs could be recovered easily from their dispersion by an external magnetic field and demonstrated good recyclability and reusability for at least 6 cycles with a high adsorption capacity above 204.5 mg g⁻¹. The magnetic adsorbents showed high stability with a weight loss below 0.65% in the acid leaching treatment by 2 M HCl solution for 144 h. This study indicates that Fe₃O₄@SiO₂@PEI-NTDA NPs are new promising adsorbents for the effective removal of Pb²⁺ in wastewater treatment.

A magnetically separable adsorbent, anhydride-functionalized Fe₃O₄@SiO₂@PEI-NTDA, was successfully constructed for removal of heavy metal ions from aqueous solution.     

Two rare {M2(MoO4)2}n chain-containing molybdate-based metal–organic complexes with a bis-pyrazole-bis-amide ligand: fluorescent sensing and photocatalysis performance

By introducing a bis-pyrazole-bis-amide ligand, N,N′-bis(1H-pyrazole-4-carboxamide)-1,4-benzene (L), two molybdate-based metal–organic complexes containing {M₂(MoO₄)₂}_n (M = Co, Zn), [Co₂L₂(MoO₄)₂]·H₂O (1), [Zn₂L₂(MoO₄)₂]·H₂O (2), have been prepared under hydrothermal/solvothermal conditions. X-ray diffraction analyses reveal that both 1 and 2 are isostructural. An interesting structural feature is that a kind of {M₂(MoO₄)₂}_n chain could be found in 1 and 2, although different raw materials [Mo₇O₂₄]⁶⁻ and [PMo₁₂O₄₀]³⁻ anions were utilized. Then these chains are further linked by L ligands into a two dimensional (2D) structure. The title complexes represent the first examples containing {MoO₄} units and pyrazole-/or amide-derivative ligands. Complexes 1 and 2 exhibit distinct performances due to different metal centers, with 2 acting as a fluorescent sensor for Fe³⁺, MnO₄⁻, CrO₄²⁻ and Cr₂O₇²⁻, but 1 being a better photocatalyst towards degradation of cationic dyes methylene blue (MB) and neutral red (NR).

Two molybdate-based complexes containing {M₂(MoO₄)₂}_n (M = Co or Zn) chains were obtained, which demonstrated different properties: excellent photocatalytic degradation performance of cationic dyes for 1 and fluorescence sensing behavior for 2.     

Judd–Ofelt parameters and X-ray irradiation results of MNb2O6:Eu3+ (M = Sr,Cd, Ni) phosphors synthesized via a molten salt method

Trivalent Eu-activated MNb₂O₆ (M = Sr, Cd, Ni) ceramic phosphors were produced using the molten salt route, which involves a low sintering temperature and provides improved homogeneity. The photoluminescence (PL) and radioluminescence (RL) spectra of phosphors exhibited characteristic Eu³⁺ emissions with ⁵F₀ → ⁷F_j transitions, and strong peaks occurred at the ⁵D₀ → ⁷F₂ transition. The PL and RL emissions of SrNb₂O₆:Eu³⁺ decreased over 3 mol%, while both emissions for CdNb₂O₆:Eu³⁺ and NiNb₂O₆:Eu³⁺ increased with increasing Eu³⁺ concentration. The spectral properties of phosphors were evaluated by determining Judd–Ofelt intensity parameters (Ω₂, Ω₄) from the PL emission spectrum. The quantum efficiencies (η_QE%) of MNb₂O₆:Eu³⁺ (M = Sr, Cd, Ni) phosphors with the highest emission were found as 61.87%, 41.89%, and 11.87% respectively. Bandwidths (σ_e × Δλ_eff) and optical gains (σ_e × τ) of MNb₂O₆:Eu³⁺ (M = Sr, Cd, Ni) phosphors with highest emissions were found as follows; 24.182 × 10⁻²⁸, 28.674 × 10⁻²⁸, 38.647 × 10⁻²⁸ cm³ and 20.441 × 10⁻²⁵, 13.790 × 10⁻²⁵, 3.987 × 10⁻²⁵ cm² s, respectively, corresponding to the ⁵D₀ → ⁷F₂ transition.

SEM micrographs and PL–RL emissions of MNb₂O₆: Eu³⁺ (M = Sr, Cd, Ni) phosphors.     

Synthesis of Fe3O4@PVBC–TMT nanoparticles for the efficient removal of heavy metals ions

Core–shell magnetic Fe₃O₄@PVBC–TMT (Fe₃O₄@polyvinylbenzyl chloride–trithiocyanuric acid) nanoparticles containing trithiocyanuric acid groups were fabricated and employed for the fast removal of heavy metals from an aquatic environment. The morphology, structure and properties of Fe₃O₄@PVBC–TMT nanoparticles were characterized by a series of modern analytical tools. The adsorption behavior of the Fe₃O₄@PVBC–TMT nanoparticles for heavy metals ions in aqueous solutions was investigated by batch experiments. The maximum removal capacities of the Fe₃O₄@PVBC–TMT nanoparticles toward Mn²⁺, Ni²⁺, Cu²⁺, Cd²⁺ and Pb²⁺ ions were 127.4, 146.6, 180.5, 311.5, and 528.8 mg g⁻¹, respectively. Importantly, it is found that Pb²⁺ ions can be completely and quickly removed by the Fe₃O₄@PVBC–TMT nanoparticles. The equilibrium was established within 6 min, and the removal efficiencies were found to be 99.9%, 99.8% and 99.5% for Pb²⁺ ions at the initial concentrations of 100 mg L⁻¹, 200 mg L⁻¹ and 300 mg L⁻¹, respectively. It is hoped that the core–shell magnetic Fe₃O₄@PVBC–TMT nanoparticles may find application in wastewater treatment.

Core–shell Fe₃O₄@PVBC–TMT nanoparticles were fabricated and served as a valid magnetic adsorbent for the removal of heavy metals ions.     

Zinc(ii) and cadmium(ii) amorphous metal–organic frameworks (aMOFs): study of activation process and high-pressure adsorption of greenhouse gases

Two novel amorphous metal–organic frameworks (aMOFs) with chemical composition {[Zn₂(MTA)]·4H₂O·3DMF}_n (UPJS-13) and {[Cd₂(MTA)]·5H₂O·4DMF}_n (UPJS-14) built from Zn(ii) and Cd(ii) ions and extended tetrahedral tetraazo-tetracarboxylic acid (H₄MTA) as a linker were prepared and characterised. Nitrogen adsorption measurements were performed on as-synthesized (AS), ethanol exchanged (EX) and freeze-dried (FD) materials at different activation temperatures of 60, 80, 100, 120, 150 and 200 °C to obtain the best textural properties. The largest surface areas of 830 m² g⁻¹ for UPJS-13 (FD) and 1057 m² g⁻¹ for UPJS-14 (FD) were calculated from the nitrogen adsorption isotherms for freeze-dried materials activated at mild activation temperature (80 °C). Subsequently, the prepared compounds were tested as adsorbents of greenhouse gases, carbon dioxide and methane, measured at high pressures. The maximal adsorption capacities were 30.01 wt% CO₂ and 4.84 wt% CH₄ for UPJS-13 (FD) and 24.56 wt% CO₂ and 6.38 wt% CH₄ for UPJS-14 (FD) at 20 bar and 30 °C.

Two novel amorphous metal–organic frameworks UPJS-13 and UPJS-14, constructed of Zn(ii)/Cd(ii) ions and extended tetrahedral linker were prepared, characterised and applied as adsorbents for carbon dioxide and methane.     

A novel catalytic kinetic method for the determination of mercury(ii) in water samples

Mercury(ii) ions act as catalyst in the substitution of cyanide ion in hexacyanoruthenate(ii) by pyrazine (Pz) in an acidic medium. This property of Hg(ii) has been utilized for its determination in aqueous solutions. The progress of reaction was followed spectrophotometrically by measuring the increase in absorbance of the yellow colour product, [Ru(CN)₅Pz]³⁻ at 370 nm (λ_max, ε = 4.2 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 5.0 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 7.5 × 10⁻⁴ M [Pz], pH 4.00 ± 0.02, ionic strength (I) = 0.05 M (KCl) and temp. 45.0 ± 0.1 °C. The proposed method is based on the fixed time procedure under optimum reaction conditions. The linear regression (calibration) equations between the absorbance at fixed times (t = 15, 20 and 25 min) and [Hg(ii)] were established in the range of 1.0 to 30.0 × 10⁻⁶ M. The detection limit was found to be 1.5 × 10⁻⁷ M of Hg(ii). The effect of various foreign ions on the proposed method was also studied and discussed. The method was applied for the determination of Hg(ii) in different wastewater samples. The present method is simple, rapid and sensitive for the determination of Hg(ii) in trace amount in the environmental samples.

Mercury(ii) ions act as catalyst in the substitution of cyanide ion in hexacyanoruthenate(ii) by pyrazine (Pz) in an acidic medium.     

Cu(i) substituted wurtzite ZnO: a novel room temperature lead free ferroelectric and high-κ giant dielectric

Semiconducting wurtzite ZnO, with the highest incipient piezoelectricity is an attractive alternative choice with doping transition metal ions in the host lattice to develop novel binary ferroelectric materials that can be easily fabricated in any device architecture. Up to 8% Cu⁺ ion substitution on Zn²⁺ sites in the ZnO lattice was achieved by careful selection of raw material and adaptation of a low temperature sol–gel synthesis route for the preparation of bulk material. Phase purity and substitution of Cu⁺ ions in the ZnO lattice along with oxide-ion vacancy formation was confirmed using Powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray analysis (EDX), X-ray Photoelectron Spectroscopy (XPS) and Magnetic property measurement system (MPMS) studies. A giant dielectric constant (∼6300) was observed at 600 °C for Zn_0.95Cu_0.05O_1−δ pellets at 100 kHz frequency. Bulk Zn_0.95Cu_0.05O_1−δ also exhibits ferroelectricity at room temperature with remnant polarization P_r and V_c equal to 9.60 × 10⁻³ μC cm⁻² and 3.83 × 10² V cm⁻¹ respectively.

Cu⁺ ion substituted ZnO, Zn_1−xCu_xO_1−δ have shown high dielectric constant (∼6300) at 600 °C at 100 kHz frequency and ferroelectricity at room temperature than for bulk Zn_0.95Cu_0.05O_1−δ samples.     

Three-dimensional mesoporous calcium carbonate–silica frameworks thermally activated from porous fossil bryophyte: adsorption studies for heavy metal uptake

In this paper, three-dimensional mesoporous calcium carbonate–silica frameworks have been created from the straw tufa (ST) originating from porous fossil bryophyte by a thermal activation technique. A batch of adsorption kinetic and thermodynamic experiments were used to investigate the adsorption capacity of Cd(ii) onto the samples. The ST after thermal activation has shown a significant ability for the uptake of heavy metals. It exhibited maximum adsorption capacities of 12.76 mg g⁻¹, 14.09 mg g⁻¹, 17.00 mg g⁻¹, and 33.81 mg g⁻¹ for Cd(ii) at the activation temperature of 300, 450, 600 and 750 °C, respectively. Through competitive adsorption for Cd(ii)and Pb(ii), the ST thermally activated at 750 °C exhibited maximum equilibrium adsorption capacities of 24.65 mg g⁻¹, 25.91 mg g⁻¹, and 30.94 mg g⁻¹ for Cd(ii) uptake at 298.1 K, 308.1 K and 318.1 K, respectively, whereas it exhibited values of 91.59 mg g⁻¹, 101.32 mg g⁻¹, and 112.19 mg g⁻¹ for Pb(ii) removal. The adsorption capacities of Cd(ii) and Pb(ii) both decrease with the addition of the other heavy metal cations, indicating that the adsorption is hindered by the competitive adsorption and the adsorption active sites on the mineral surface are readily exchangeable. The adsorption of Cd(ii) and Pb(ii) followed the pseudo-second order kinetics model well. In addition, the Langmuir model could accurately describe the adsorption isotherms. Based on the results of characterization with TEM, XRD and XPS, the adsorption mechanisms could be primarily explained as formation of Cd(OH)₂ and CdCO₃ as well as Cd(HCO₃)₂ precipitation on the surface of ST. These characteristics of ion-exchange and the adsorptive property for ST modified allow it to be widely used in artificial wetland landfill and environmental protection.

Three-dimensional mesoporous calcium carbonate–silica frameworks have been created and have shown excellent adsorption capacities for Cd(ii) and Pb(ii).     

Selective fluorescent sensing of LMOFs constructed from tri(4-pyridylphenyl)amine ligand

Three new luminescent metal–organic frameworks (LMOFs), [Zn(tppa)(ndc)]_n (1), [Cd(tppa)(oba)]_n (2), [Zn₂(tppa)(bpdc)₂]_n (3) (tppa = tri(4-pyridylphenyl)amine, ndc = 1,4-naphthalenedicarboxylic acid, oba = 4,4′-oxydibenzoic acid, bpdc = 4,4′-biphenyldicarboxylic acid) have been synthesized by solvothermal method. Complexes 1 and 2 are 2-D two-fold interpenetrating structures, aligning into a 3-D structure through C–H⋯π stacking interactions, while 3 is a 5-fold interpenetrating three-dimensional structure. The internal quantum yields (IQYs) of complexes 1–3 are 32.7%, 45.7% and 24.0% (λ_ex = 365 nm), separately. Furthermore, all the complexes show different luminescence signal changes towards aromatic volatile organic compounds (AVOCs). Complex 1 exhibits a high sensitivity in the detection of both Fe³⁺ and Cr³⁺ with large quenching coefficients of K_sv 2.57 × 10⁴ M⁻¹ and 2.96 × 10⁴ M⁻¹, respectively. All these results demonstrated potential applications in chemical sensing.

Three new LMOFs, complexes 1–3, have been solvothermally synthesized. 1 and 2 are 2-D structures, whiles 3 is a 3-D structure. And 1 exhibits in detecting Fe³⁺ and Cr³⁺. All of them have potential applications in chemical sensing.     

Enhancing the sensitivity of a surface plasmon resonance-based optical sensor for zinc ion detection by the modification of a gold thin film

Surface plasmon resonance (SPR) sensors as novel optical sensors for the detection of a variety of analytes have been receiving increasing attention and their sensitivity has become the research hotspot recently. In this study, the sensitivity of an SPR optical sensor was enhanced by modifying a gold thin film with a nanocrystalline cellulose (NCC)-based material for zinc ion (Zn²⁺) detection that exists in the environment due to industrial processing. By replacing the gold thin film with a novel modified-gold thin film, Zn²⁺ can be detected from the range of 0 to 10 ppm using SPR. It is believed that the Zn²⁺ may interact with the negative charge molecules that exist on the modified-gold thin film, and this was confirmed via X-ray photoelectron spectroscopy (XPS). Moreover, this modified-gold-SPR has a high sensitivity of 1.892° ppm⁻¹ up to 0.1 ppm with an enhanced detection of Zn²⁺ as low as 0.01 ppm. The SPR results also followed the Langmuir isotherm model with a binding affinity of 1.927 × 10³ M⁻¹, which further confirmed the sensitivity of the SPR sensor. In addition, using the modified-gold thin film, SPR has a higher affinity towards Zn²⁺ compared to other metal ions, i.e. Ni²⁺, Fe²⁺, Cr²⁺, Mn²⁺, and Co²⁺.

This work focus on sensitivity enhancement of surface plasmon resonance (SPR) optical sensor by modifying the gold thin film with nanocrystalline cellulose (NCC) based material for zinc ion (Zn²⁺) detection.     

A multifunctional composite Fe3O4/MOF/l-cysteine for removal,magnetic solid phase extraction and fluorescence sensing of Cd(ii)

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater. The adsorption kinetics and isotherms were investigated, and the results indicated that the adsorption obeyed the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity was calculated to be 248.24 mg g⁻¹. Fe₃O₄/MOF/l-cysteine was further applied to determine trace amounts of Cd(ii) in real water samples using ICP-AES (inductively coupled plasma-atomic emission spectroscopy) based on magnetic solid-phase extraction (MSPE). The determination limit was 10.6 ng mL⁻¹. Additionally, Fe₃O₄/MOF/l-cysteine can also be used as a fluorescent sensor for “turn-off” detection of Cd(ii), and the detection limit was 0.94 ng mL⁻¹.

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater.     

Alkaline earth metal ion coordination increases the radical scavenging efficiency of kaempferol

Flavonoids are used as natural additives and antioxidants in foods, and after coordination to metal ions, as drug candidates, depending on the flavonoid structure. The rate of radical scavenging of the ubiquitous plant flavonoid kaempferol (3,5,7,4′-tetrahydroxyflavone, Kaem) was found to be significantly enhanced by coordination of Mg(ii), Ca(ii), Sr(ii), and Ba(ii) ions, whereas the radical scavenging rate of apigenin (5,7,4′-trihydroxyflavone, Api) was almost unaffected by alkaline earth metal (AEM) ions, as studied for short-lived β-carotene radical cations (β-Car˙⁺) formed by laser flash photolysis in chloroform/ethanol (7 : 3) and for the semi-stable 2,2-diphenyl-1-picrylhydrazyl radical, DPPH˙, in ethanol at 25 °C. A 1 : 1 Mg(ii)–Kaem complex was found to be in equilibrium with a 1 : 2 Mg(ii)–Kaem₂ complex, while for Ca(ii), Sr(ii) and Ba(ii), only 1 : 2 AEM(ii)–Kaem complexes were detected, where all complexes showed 3-hydroxyl and 4-carbonyl coordination and stability constants of higher than 10⁹ L² mol⁻². The 1 : 2 Ca(ii)–Kaem₂ complex had the highest second order rate constant for both β-Car˙⁺ (5 × 10⁸ L mol⁻¹ s⁻¹) and DPPH˙ radical (3 × 10⁵ L mol⁻¹ s⁻¹) scavenging, which can be attributed to the optimal combination of the stronger electron withdrawing capability of the (n − 1)d orbital in the heavier AEM ions and their spatially asymmetrical structures in 1 : 2 AEM–Kaem complexes with metal ion coordination of the least steric hindrance of two perpendicular flavone backbones as ligands in the Ca(ii) complex, as shown by density functional theory calculations.

Radical scavenging activity of kaempferol is notably enhanced by Ca(ii) binding.