A highly efficient and noble metal-free photocatalytic system using NixB/CdS as photocatalyst for visible light H2 production from aqueous solution

Photocatalytic H₂ production from water is one of the most attractive issues for the conversion of solar energy into chemical energy. In this study, the Ni_xB/CdS photocatalyst was firstly used for photocatalytic H₂-evolution reaction and showed efficient visible-light photocatalytic activity and good stability for H₂-evolution from aqueous solution. The optimal Ni_xB loading content was determined to be 0.8 wt.%, and the corresponding H₂-production rate reached up to 4.8 mmol·h^− 1·g^− 1 after a 10 h visible light irradiation. It is proposed that the loading of Ni_xB on the surface of CdS could effectively increase the separation of photo-generated electrons and holes and greatly enhance the photocatalytic activity.     

Integration of tailored reduced graphene oxide nanosheets and electrospun polyamide-66 nanofabrics for a flexible supercapacitor with high-volume- and high-area-specific capacitance

Nanofiber fabric is firstly introduced to replace common microfiber fabrics as the platform for flexible supercapacitors. Nanofiber and microfiber electrodes can be simply fabricated using a dipping process that impregnates reduced graphene oxide (RGO) nanosheets into electrospun polyamide-66 (PA66) nanofiber and microfiber fabrics. RGO nanosheets are tailored to various sizes and only RGO with a medium diameter of 250–450 nm (denoted as M-RGO) can effectively penetrate the pores of nanofiber fabrics for constructing smooth conductive paths within PA66 nanofiber fabrics. The synergistic effect between suitable sizes of RGO nanosheets and nanofiber fabrics with a high specific area provides a symmetric supercapacitor composed of M-RGO/PA66 nanofiber fabric electrodes with high-volume and high-area specific capacitance (C_S,V and C_S,A, equal to 38.79 F cm⁻³ and 0.931 F cm⁻² at 0.5 A g⁻¹, respectively), which are much larger than that of a symmetric supercapacitor composed of RGO/PA66 microfiber fabric electrodes (8.52 F cm⁻³ and 0.213 F cm⁻² at 0.5 A g⁻¹). The effect of impregnating nanofiber fabrics with suitably sized RGO to promote C_S,V and C_S,A of flexible supercapacitors has been demonstrated.     

Novel Ag2S/ZnS/carbon nanofiber ternary nanocomposite for highly efficient photocatalytic hydrogen production

Novel Ag₂S/ZnS/carbon nanofiber (CNF) ternary nanocomposite with high photocatalytic H₂ production performance was synthesized by combination of an in-situ solid-state process and a cation-exchange reaction, using organic–inorganic layered zinc hydroxide nanofibers as precursor. Moreover, the loading amount of Ag₂S nanocrystals can be readily regulated by changing the AgNO₃ concentration, and the optimized H₂ production rate was 224.9 μmol h^− 1, significantly higher than that of the reported ZnS-based composite photocatalysts. The synergistic effect of CNF and Ag₂S as water reduction and oxidation cocatalyst, respectively, can greatly suppress the charge recombination thus resulting in high photocatalytic H₂ production activity.     

A novel noble metal-free ZnS–WS2/CdS composite photocatalyst for H2 evolution under visible light irradiation

A novel ZnS–WS₂/CdS composite photocatalyst for H₂ evolution under visible light irradiation has been successfully synthesized. The loading amounts of WS₂ and ZnS on the CdS surface were optimized. A H₂ evolution rate up to 1224 μmol·h^− 1 has been achieved for the 9.6 mol% ZnS–1 mol% WS₂/CdS photocatalyst. The enhancement of the photocatalytic activity is attributed to the synergistic effect of WS₂ as co-catalyst and ZnS as passivation layer.     

In situ photodeposition of nickel oxides on CdS for highly efficient hydrogen production via visible-light-driven photocatalysis

Low-cost photocatalysts of CdS combined with nickel oxides were prepared by a simple in situ photodeposition method. The activity of photocatalytic hydrogen evolution under visible-light (λ > 400 nm) on CdS was enhanced significantly by loading nickel oxides, and reached to the maximum rate of 445.6 μmol h^− 1, being about 41 times and 1.9 times of the H₂ evolution on pure CdS and CdS loaded with 1.5 wt.% Pt, respectively. The characterizations of X-ray photoelectron spectroscopy and transmission electron microscopy with energy dispersive spectrometer indicated that the nickel oxides were loaded on CdS particles in the formation of Ni₂O₃ species, which acted as electron traps and facilitated the charge separation.     

A novel TiO2 − xNx/BN composite photocatalyst: Synthesis,characterization and enhanced photocatalytic activity for Rhodamine B degradation under visible light

A novel TiO_2 − xN_x/BN composite photocatalyst was prepared via a facile method using melamine–boron acid adducts (M·2B) and tetrabutyl titanate as reactants. The morphological results confirmed that nitrogen-doped TiO₂ nanoparticles were uniformly coated on the surface of porous BN fibers. A red shift of absorption edge from 400 nm (pure TiO₂) to 520 nm (TiO_2 − xN_x/BN composites) was observed in their UV–Vis light absorption spectra. The TiO_2 − xN_x/BN photocatalysts exhibited enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) and the highest photocatalytic degradation efficiency reached 97.8% under visible light irradiation for 40 min. The mechanism of enhanced photocatalytic activity was finally proposed.     

A new polymorph telluridoindate [In(en)3][In5Te9(en)2] with photocatalytic properties

A new polymorph telluridoindate [In(en)₃][In₅Te₉(en)₂] (denoted as β-type, en = ethylenediamine) has been solvothermally synthesized and characterized. The crystal data for the β-type are listed as follows: monoclinic, space group Cc (No. 9), a = 11.642(2), b = 20.421(4), c = 17.577(4) Å, β = 92.20(3)°, V = 4175.7(14) Å³, Z = 4. The β-type contains organic-decorated [In₄Te₉(en)]^6 − supertetrahedral cluster and [InTe₃(en)]^3 − tetrahedron, which are interconnected to form an organic-decorated 2-D telluridoindate layer of [In₅Te₉(en)₂^3 −]_n with 9-membered rings. Two relevant conformers of telluridoindates are compared with each other. The β-type indicates absorption edge at 2.23 eV and exhibits photocatalytic activity for degradation of methyl orange (MO).     

Synthesis,structure and photocatalytic hydrogen evolution of a silver-linked hexaniobate Lindqvist chain

By using a combination of hydrothermal and diffusional strategies, a one-dimensional polyoxoniobate K₅[H₂AgNb₆O₁₉]·11H₂O (1) has been synthesized. The structure was characterized by single-crystal X-ray diffraction, UV spectroscopy, TG analysis, PXRD and IR spectrum. 1 crystallizes in the hexagonal P63/mmc space group with a = 9.8171(2) Å, c = 16.5442(6) Å, and V = 1380.84(6) Å³. It is the first Ag-containing polyoxoniobate, which consists of [H₂AgNb₆O₁₉]^5 − polyoxoanion and potassium ions. In addition, 1 exhibits the photocatalytic H₂ evolution activity.     

Structural and optical characterization of Zn0.95−xMg0.05AlxO nanoparticles

The structural and optical properties of ZnO nanoparticles doped simultaneously with Mg and Al were investigated. XRD results revealed the hexagonal wurtzite crystalline structure of ZnO. The FE-SEM study confirmed the formation of nano-sized homogeneous grains whose sizes decreased monotonously with increasing doping concentrations of Mg and Al. The absorption spectra showed that band gap increased from 3.20 to 3.31 eV with Mg doping. As the Al concentration changed from x=0.01 to x=0.06 mol% at constant Mg concentration the band gap observed to be decreased. Particle sizes estimated from effective mass approximation using absorption data and these values are in good agreement with the crystallite sizes calculated from XRD data. Raman spectra of ZnO showed a characteristic peak at 436 cm⁻¹ correspond to a non-polar optical phonon E₂ (high). With increase of the Al doping concentrations, E₂ (high) phonon frequency shifted to 439 cm⁻¹ from to 436 cm⁻¹. The origin of E₂ (high) peak shift in ZnO nanoparticles is attributed to optical phonon confinement effects or the presence of intrinsic defects on the nanoparticles. PL spectra indicated that with increase of Al co-doping along with Mg into ZnO, intensity of the peak positioned at 395 nm was initially increased at x=0 and then decreased with increase of the Al concentrations from x=0.01 to x=0.06 mol%.     

A chiral 3D polymer with right- and left-helices based on 2,2′-biimidazole: Synthesis,crystal structure and fluorescent property

A novel three-dimensional (3D) polymer [Cd₂(Hbiim)₄]_n (H₂biim = 2,2′-biimidazole) 1 was obtained through hydrothermal reaction and characterized by single crystal X-ray diffraction, and the fluorescent property was also determined. Compound 1 crystallizes in a monoclinic chiral space group P2₁ and contains two types of helical chains. Hbiim⁻ partially deprotonated of H₂biim exhibits two different coordination modes, which contributes greatly to the formation of the 3D chiral framework. Compound 1 exhibits blue fluorescence at 488 nm in the solid-state upon excitation at 430 nm.     

A novel 3D POMOF based on dinuclear copper (II)-oxalate complexes and Keggin polyoxoanions with excellent photocatalytic activity

A novel coordination polymer, [Cu₂(btx)₂(C₂O₄)][H₂SiW₁₂O₄₀]·12H₂O (btx = 1,4-bis(triazol-1-ylmethyl)benzene)] (1) has been synthesized by hydrothermal reaction, and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction. Compound 1 is composed of α-Keggin type [SiW₁₂O₄₀]^4 − polyoxoanions and dinuclear copper (II)-btx complexes. The dinuclear copper (II)-btx complex is a three-dimensional (3D) porous framework, in which the [SiW₁₂O₄₀]^4 − as 4-coordinating guests are encapsulated, forming a novel 3D POMOF with two kinds of open channels along both a and b axes. Additionally, compound 1 shows excellent photocatalytic properties for the degradation of methylene blue (MB) under both visible and ultraviolet (UV) light. The molecular design of 1 not only generates a new POMOF, but also opens a new avenue to produce photocatalytic materials.     

Facile fabrication of pseudo-microspherical ZnO/CdS core-shell photocatalysts for solar hydrogen production by water splitting

Photocatalytic hydrogen production attracts great attention due to its clean energy conversion and renewable usage. In order to achieve efficient charge separations in photocatalysts, pseudo-microspherical ZnO/CdS core-shell structures were fabricated by precipitation method. ZnO pseudo-microspheres of about 2 µm diameter were uniformly synthesized, and they were used as core materials covered with various amounts of CdS shell nanoparticles. The highest hydrogen production rate from as-prepared photocatalysts was 146 μmol g⁻¹ h⁻¹ at 63 wt% CdS content under one sun irradiation condition. After thermal treatments, it was much improved to 241.2 μmol g⁻¹ h⁻¹ at the same CdS content possibly due to the increased crystallinity and efficient charge flows with an aid of additional CdO component. Reproducibility of hydrogen production revealed stable mode of operation for three consecutive runs. Therefore, ZnO/CdS/CdO ternary photocatalyst systems provide efficient charge separations and electron flows for improving solar hydrogen production by suppressing electron-hole recombinations.     

Enhancement of Lipase-catalyzed Synthesis of Caffeic Acid Phenethyl Ester in Ionic Liquid with DMSO Co-solvent

Caffeic acid phenethyl ester (CAPE) is a natural and rare ingredient with several biological activities, but its industrial production using lipase-catalyzed esterification of caffeic acid (CA) and 2-phenylethanol (PE) in ionic liquids (ILs) is hindered by low substrate concentrations and long reaction time. To set up a high-efficiency bioprocess for production of CAPE, a novel dimethyl sulfoxide (DMSO)–IL co-solvent system was established in this study. The 2% (by volume) DMSO–[Bmim][Tf₂N] system was found to be the best medium with higher substrate solubility and conversion of CA. Under the optimum conditions, the substrate concentration of CA was raised 8-fold, the reaction time was reduced by half, and the conversion reached 96.23%. The kinetics follows a ping-pong bi-bi mechanism with inhibition by PE, with kinetic parameters as follows: V_max = 0.89 mmol · min^− 1 · g^− 1, K_m,CA = 42.9 mmol · L^− 1, K_m,PE = 165.7 mmol · L^− 1, and K_i,PE = 146.2 mmol · L^− 1. The results suggest that the DMSO co-solvent effect has great potential to enhance the enzymatic synthesis efficiency of CAPE in ILs.     

Microwave-enhanced catalytic degradation of phenol over nickel oxide

A mix-valenced nickel oxide, NiO_x, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiO_x by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196 °C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiO_x (>+2 and S_BET = 201 m² g⁻¹) ≫ C300 (+2 and S_BET = 104 m² g⁻¹) > C400 (+2 and S_BET = 52 m² g⁻¹) > C500 (+2 and S_BET = 27 m² g⁻¹). The introduction of microwave irradiation could greatly shorten the time of phenol degradation.     

Hidden value in low-cost inorganic pigments as potentially valuable magnetic materials

Inorganic pigments are substances that develop colour in organic solids such as ceramics and glazes, and are usually a complex mixture of oxides, and relatively low-cost. Their chromatic properties have been extensively studied, yet surprisingly the magnetic and electrical properties of these economic and common materials have been neglected, despite the fact many are based on ferrite spinels. Therefore, we investigated these properties in commercial black and brown pigments, to assess their potential as magnetic materials. The brown and black pigments were found to be spinel ferrites, with estimated formulas of Fe_1.34Cr_0.62Mn_0.66Zn_0.22Ni_0.10Co_0.06O₄ and Fe_1.02Cr_0.97Co_0.57Mn_0.23Ni_0.21O₄, respectively. The brown pigment also contained a higher amount of SiO₂ compared to the black pigment (~7 mol% vs. ~2 mol%), which appeared as a second phase of crystalline quartz, and adversely affected its porosity, magnetisation and electrical ac conductivity, compared to the black pigment. However, both were very magnetic and very soft ferrites. The brown pigment had M_s=11.7 A m² kg⁻¹ and H_c of 1.5 kA m⁻¹, with a high electrical conductivity (σ) of 4×10⁻⁴−7×10⁻³ Ω⁻¹ m⁻¹ between 100 Hz and 1 MHz. The black pigment was equally magnetically soft, but had a much greater magnetisation and lower electrical conductivity, with M_s=18.7 A m² kg⁻¹, H_c=2.4 kA m⁻¹, and σ=5×10⁻⁶−8×10⁻⁵ Ω⁻¹ m⁻¹ between 100 Hz and 1 MHz.This work has revealed the potential hidden value of low-cost commercial inorganic pigments based on spinel ferrites as magnetic materials. This demonstrates their potential at low-cost alternative materials for applications such as in power supply transformers, switching materials and sensors, where soft magnetisation is especially important.     

Synthesis of bimetallic PtPd nanocubes on graphene with N,N-dimethylformamide and their direct use for methanol electrocatalytic oxidation

Bimetallic PtPd nanocubes supported on graphene nanosheets (PtPdNCs/GNs) were prepared by a rapid, one-pot and surfactant-free method, in which N,N-dimethylformamide (DMF) was used as a bi-functional solvent for the reduction of both metal precursors and graphene oxide (GO) and for the surface confining growth of PtPdNCs. The morphology, structure and composition of the thus-prepared PtPdNCs/GNs were characterized by transmission electron microscopy (TEM), high resolution TEM, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Because no surfactant or halide ions were involved in the proposed synthesis, the prepared PtPdNCs/GNs were directly modified onto a glassy carbon electrode and showed high electrocatalytic activity for methanol oxidation in cyclic voltammetry without any pretreatments. Moreover, with the synergetic effects of Pt and Pd and the enhanced electron transfer by graphene, the PtPdNCs/GNs composites exhibited higher electrocatalytic activity (j_p = 0.48 A mg⁻¹) and better tolerance to carbon monoxide poisoning (I_f/I_b = 1.27) compared with PtPd nanoparticles supported on carbon black (PtPdNPs/C) (j_p = 0.28 A mg⁻¹; I_f/I_b = 1.01) and PtNPs/GNs (j_p = 0.33 A mg⁻¹; I_f/I_b = 0.95). This approach demonstrates that the use of DMF as a solvent with heating is really useful for reducing GO and metal precursors concurrently for preparing clean metal–graphene composites.     

Enhancement of pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics by La doping

Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La³⁺ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (T_d) decreases. p is 7.24 × 10⁻⁴C m⁻² °C⁻¹ at RT at x = 0.5% and 105.4 × 10⁻⁴C.m^−2 °C⁻¹ at T_d at x = 0.2%. F_i and F_v show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 ⁻¹⁰ m v⁻¹) (x = 0.5%) and from 0.021 to 0.048 (m².C⁻¹) respectively. F_i and F_v show a huge increase to 37.6 × 10⁻¹⁰ m v⁻¹ and 0.56 m² C⁻¹ respectively at T_d at x = 0.2%. F_C shows values of 2.10, 2.89, and 2.98 (x10⁻⁹C cm⁻² °C⁻¹) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications.     

Sol-gel synthesis of new TiO2/activated carbon photocatalyst and its application for degradation of tetracycline

A new efficient photocatalyst consisting of TiO₂-activated carbon composite (TiO₂/AC) was synthesized by sol-gel process and applied to decomposition of tetracycline (TC). Its properties and catalytic activity were evaluated in comparison with bare TiO₂ and P25, based on several characterization techniques and TC photodegradation kinetic studies. The results showed TiO₂/AC has better structural and electronic features for photocatalysis; S_BET of 129 m² g^–1, exclusively anatase phase, crystal size of 8.53 nm and band gap energy of 3.04 eV. The catalytic activity of the material was evaluated based on photodegradation kinetic studies of TC from aqueous solution (with initial concentration=50 mg L⁻¹ and catalyst dosage=1.0 g L⁻¹). Non-linear kinetic model of pseudo-first order were fitted to the resulting experimental data. The apparent first-order rate constant (k_app=42.9×10^–3 min^–1) and half-life time (t_1/2=16.1 min) determined for TiO₂/AC were better than those for P25 and bare TiO₂. TC degradation by-products were investigated by HPLC-MS, showing TC was completely degraded after 75 min, producing fragments with m/z smaller than 150.     

Structure and magnetism of novel dinuclear cobalt(II) complexes

Two dinuclear cobalt(II) complexes of the formula [Co₂X₄(isonia)₄] have been synthesized and structurally characterized; isonia is unidentate neutral iso-nicotinamide and X are furan-3- or furan-2-carboxylate ligands. The chromophore {CoO₄N₂} is formed of two iso-nicotinamide ligands and three furancarboxylate ligands where two of them bear a bridging function and one is a terminal-bidentate ligand. The magnetic data confirm a weak exchange interaction (J / hc = − 2 cm^− 1) and a high single-ion zero-field splitting (D / hc = 63 and 33 cm^− 1, respectively).     

A novel transition-metal-linked hexaniobate cluster with photocatalytic H2 evolution activity

A novel transition-metal (TM) complex based on Lindqvist polyoxoniobate K₁₀[(Nb₆O₁₉)Cr^III(H₂O)₂]₂·28H₂O (1) has been synthesized by a new two-pot synthesis strategy and structurally characterized by single crystal X-ray diffraction analysis, IR spectrum, UV–vis spectroscopy, XRPD and TG analysis. Compound 1 crystallizes in the C2/m space group with a = 32.143(19) Å, b = 10.030(6) Å, c = 12.878(8) Å, β = 110.611(9)°, and V = 3886(4) ų. X-ray structure analysis reveals that polyanion [(Nb₆O₁₉)Cr^III(H₂O)₂]₂^10 − (1a) represents the first example of two nuclear dimeric polyoxoniobate, in which two Lindqvist anions [Nb₆O₁₉]⁸ are sandwiched by two {Cr^III(H₂O)₂} groups. Further, 1 exhibits photocatalytic H₂ evolution activity.