Metal Electrocatalysts for Hydrogen Production in Water Splitting.

The rising demand for fossil fuels and the resulting pollution have raised environmental concerns about energy production. Undoubtedly, hydrogen is the best candidate for producing clean and sustainable energy now and in the future. Water splitting is a promising and efficient process for hydrogen production, where catalysts play a key role in the hydrogen evolution reaction (HER). HER electrocatalysis can be well performed by Pt with a low overpotential close to zero and a Tafel slope of about 30 mV dec-1. However, the main challenge in expanding the hydrogen production process is using efficient and inexpensive catalysts. Due to electrocatalytic activity and electrochemical stability, transition metal compounds are the best options for HER electrocatalysts. This study will focus on analyzing the current situation and recent advances in the design and development of nanostructured electrocatalysts for noble and non-noble metals in HER electrocatalysis. In general, strategies including doping, crystallization control, structural engineering, carbon nanomaterials, and increasing active sites by changing morphology are helpful to improve HER performance. Finally, the challenges and future perspectives in designing functional and stable electrocatalysts for HER in efficient hydrogen production from water-splitting electrolysis will be described.

Enhanced CO2 capture potential of UiO-66-NH2 synthesized by sonochemical method: experimental findings and performance evaluation.

The excessive release of greenhouse gases, especially carbon dioxide (CO2) pollution, has resulted in significant environmental problems all over the world. CO2 capture technologies offer a very effective means of combating global warming, climate change, and promoting sustainable economic growth. In this work, UiO-66-NH2 was synthesized by the novel sonochemical method in only one hour. This material was characterized through PXRD, FT-IR, FE-SEM, EDX, BET, and TGA methods. The CO2 capture potential of the presented material was investigated through the analysis of gas isotherms under varying pressure conditions, encompassing both low and high-pressure regions. Remarkably, this adsorbent manifested a notable augmentation in CO2 adsorption capacity (3.2 mmol/g), achieving an approximate enhancement of 0.9 mmol/g, when compared to conventional solvothermal techniques (2.3 mmol/g) at 25 °C and 1 bar. To accurately represent the experimental findings, three isotherm, and kinetic models were used to fit the experimental data in which the Langmuir model and the Elovich model exhibited the best fit with R2 values of 0.999 and 0.981, respectively. Isosteric heat evaluation showed values higher than 80 kJ/mol which indicates chemisorption between the adsorbent surface and the adsorbate. Furthermore, the selectivity of the adsorbent was examined using the Ideal Adsorbed Solution Theory (IAST), which showed a high value of 202 towards CO2 adsorption under simulated flue gas conditions. To evaluate the durability and performance of the material over consecutive adsorption-desorption processes, cyclic tests were conducted. Interestingly, these tests demonstrated only 0.6 mmol/g capacity decrease for sonochemical UiO-66-NH2 throughout 8 consecutive cycles.

MIL-101(Cr), an Efficient Heterogeneous Catalyst for One Pot Synthesis of 2,4,5-tri Substituted Imidazoles under Solvent Free Conditions.

A chromium-containing metal-organic framework (MOF), MIL-101 (Chromium(III) benzene-1,4-dicarboxylate), was used to catalyze the one pot, three component synthesis of some 2,4,5-trisubstituted imidazoles under solvent-free conditions. The advantages of using this heterogeneous catalyst include short reaction time, high yields, easy and quick isolation of catalyst and products, low amount of catalyst needed, and that the addition of solvent, salt, and additives are not needed. This catalyst is highly efficient and can be recovered at least 5 times with a slight loss of efficiency. The structure of the metal-organic frameworks (MOF) was confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (HNMR) were performed to confirm some of the synthesized products. Experimental data indicated that the optimum amount of catalyst was 5 mg for benzil (1 mmol), 4-chlorobenzaldehyde (1 mmol), and ammonium acetate (2.5 mmol), and the synthetic route to the various imidazoles is performed in 10 min by 95% yield, an acceptable result rivalling those of other catalysts.

Adsorption of Lead Ions by a Green AC/HKUST-1 Nanocomposite.

A new nanocomposite consisting of activated carbon (AC) from the Cortaderia selloana flower and copper-based metal-organic framework (HKUST-1) was synthesized through a single-step solvothermal method and applied for the removal of lead ions from aqueous solution through adsorption. The nanocomposite, AC/HKUST-1, was characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDX) methods. The SEM images of both HKUST-1 and AC/HKUST-1 contain octahedral crystals. Different factors affecting adsorption processes, such as solution pH, contact time, adsorbent dose, and initial metal pollution concentration, were studied. The adsorption isotherm was evaluated with Freundlich and Langmuir models, and the latter was fitted with the experimental data on adsorption of lead ion. The adsorption capacity was 249.4 mg g-1 for 15 min at pH 6.1, which is an excellent result rivalling previously reported lead adsorbents considering the conditions. These nanocomposites show considerable potential for use as a functional material in the ink formulation of lead sensors.

Fabrication of nanocomposite photocatalyst CuBi2O4/Bi3ClO4 for removal of acid brown 14 as water pollutant under visible light irradiation.

In the present study, CuBi2O4/Bi3ClO4 nanocomposites have been fabricated via an improved Pechini sol-gel process using the mixtures of various gelling agents and polybasic acids. This work shows that by controlling the reaction conditions such as kind of polybasic acids, gelling agents, pH and mole ratio of polybasic acid to total metals, the CuBi2O4/Bi3ClO4 nanocomposites with ultrafine sphere-like, irregular polyhedral-like, plate-like and cubic-like morphologies were prepared. The phase, elemental composition, morphology and optical characteristics of as-synthesized CuBi2O4/Bi3ClO4 nanostructures were analyzed utilizing UV-Vis, FESEM, TEM, HRTEM, FT-IR, XRD, TOC and EDS techniques. Furthermore, the CuBi2O4/Bi3ClO4 nanocomposites exhibited excellent TOC removal (75%) and photocatalytic activity (92%) to photodegradation of acid brown 14 azo dye as water pollutants under visible light irradiation. The excellent degradation activity of CuBi2O4/Bi3ClO4 photocatalyst can be attributed to the strong visible light absorption, high charge separation efficiency, fine particle size distribution and proper band gap of the nanocomposite. In addition, the reliable photocatalytic mechanism was discussed on the basis of the radical trapping study, which revealed the h+ and O2- radicals were the prevailing active species in the photocatalytic process.

Design of a remote-control drug delivery implantable chip for cancer local on demand therapy using ionic polymer metal composite actuator.

Since the local, on demand, cancer therapy is a challenging clinical issue today, this paper presents the design, fabrication and characterization of a remotely controlled single reservoir drug delivery chip using Ionic Polymer Metal Composite (IPMC) actuator. Here, Drug release was externally programmed and controlled wirelessly on demand by a communication circuit. The transmitter and receiver circuits were designed to control the release/sealed status remotely even from 7 cm distance while the transmitter and receiver were coupled magnetically. IPMC here was used as the moving cap of the reservoir, that in release mode, lets the drug out on demand with a low received power of 20 mW. The novel simple design could release the whole content of the drug which is remarkable in comparison with the designs which need complicated optimizations of diffuser, nuzzle and IPMC diaphragm pump, leading to an incomplete release. To make sure that there is no leakage in the sealed mode, IPMC was attached to a polydimethylsiloxane (PDMS) support film. Biocompatibility of all the components of the chip were tested by 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay.

Piperazine-1,4-diium pyridine-2,3-dicarboxyl-ate methanol monosolvate.

The title solvated molecular salt, C(4)H(12)N(2) (2+)·C(7)H(3)NO(4) (2-)·CH(3)OH or (pipzH(2))(py-2,3-dc)·MeOH, was prepared by the reaction of pyridine-2,3-dicarb-oxy-lic acid (py-2,3-dcH(2)) and piperazine (pipz) in methanol (MeOH) as solvent. One of the two carboxylate groups of the acid fragment is nearly perpendicular to the pyridine ring and the other is almost in its plane [C-C-C-O torsion angles = -85.50 (11) and 88.07 (11)° and N-C-C-O torsion angles = -176.31 (8) and 5.41 (13)°]. In the crystal, the components are linked by O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, generating a three-dimensional network.

Hexa-kis-(dimethyl sulfoxide-κO)thallium(III) trinitrate.

The title compound, [Tl(C(2)H(6)OS)(6)](NO(3))(3), consists of six dimethyl sulfoxide (DMSO) mol-ecules coordinated to a Tl(III) atom, which lies on a axis, and three nitrate anions (3. symmetry) to neutralize the charge. The coordination polyhedron around the Tl(III) atom is octa-hedral, defined by six O atoms of the DMSO mol-ecules. In the crystal structure, C-H⋯O hydrogen bonds are observed. One of the nitrate groups exhibits half-occupation.

Hexaaqua-nickel(II) tetra-aqua-bis-(µ-pyridine-2,6-dicarboxyl-ato)bis-(pyridine-2,6-dicarboxyl-ato)trinickelate(II) octa-hydrate.

The title compound, [Ni(H(2)O)(6)][Ni(3)(C(7)H(3)NO(4))(4)(H(2)O)(4)]·8H(2)O, was obtained by the reaction of nickel(II) nitrate hexa-hydrate with pyridine-2,6-dicarb-oxy-lic acid (pydcH(2)) and 1,10-phenanothroline (phen) in an aqueous solution. The latter ligand is not involved in formation of the title complex. There are three different Ni(II) atoms in the asymmetric unit, two of which are located on inversion centers, and thus the [Ni(H(2)O)(6)](2+) cation and the trinuclear {[Ni(pydc)(2)](2)-µ-Ni(H(2)O)(4)}(2-) anion are centrosymmetric. All Ni(II) atoms exhibit an octa-hedral coordination geometry. Various inter-actions, including numerous O-H⋯O and C-H⋯O hydrogen bonds and C-O⋯π stacking of the pyridine and carboxyl-ate groups [3.570 (1), 3.758 (1) and 3.609 (1) Å], are observed in the crystal structure.

(Propane-1,3-diammonium) bis-(4-hydroxy-pyridine-2,6-dicarboxyl-ato-κO,N,O)zinc(II) 3.5-hydrate.

The asymmetric unit of the title compound, (C(3)H(12)N(2))[Zn(C(7)H(3)NO(5))(2)]·3.5H(2)O, contains two formula units. The compound consists of an anionic complex, a doubly protonated propane-1,3-diamine as a counter-ion and 3.5 uncoord-inated water mol-ecules. The coordination polyhedron around the Zn(II )atom is distorted octa-hedral, defined by four O atoms and two N atoms from two Hchel (H(3)chel = 4-hydroxy-pyridine-2,6-dicarboxylic acid) ligands. In the crystal structure, O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds along with π-π stacking inter-actions [centroid-centroid distance = 3.473 (2) Å] are observed to reinforce the crystal cohesion.

(2,9-Dimethyl-1,10-phenanthroline)(4-hydroxy-pyridine-2,6-dicarboxyl-ato)copper(II) trihydrate.

In the title complex, [Cu(C(7)H(3)NO(5))(C(14)H(12)N(2))]·3H(2)O, there are two independent neutral mol-ecules of the Cu complex along with six mol-ecules of water of hydration in the asymmetric unit. The Cu(II )atoms in each complex adopt a distorted square-pyramidal coordination geometry being penta-coordinated by one N and two O atoms of 4-hydroxy-pyridine-2,6-dicarboxyl-ate anions and two N atoms of 2,9-dimethyl-1,10-phenanthroline (dmp) molecules. In the crystal structure, there are O-H⋯O and C-H⋯O hydrogen bonds and five π-π stacking inter-actions with centroid-centroid distances in the range 3.620 (1)-3.712 (1) Å. In addition, a C-H⋯π inter-action between a heterocyclic ring of dmp is observed to reinforce the crystal cohesion.

Bis(2,4,6-triamino-1,3,5-triazin-1-ium) tris-(pyridine-2,6-dicarboxyl-ato)-zirconate(IV) tetra-hydrate.

The title compound, (C(3)H(7)N(6))(2)[Zr(C(7)H(3)NO(4))(3)]·4H(2)O or (tataH)(2)[Zr(pydc)(3)]·4H(2)O (tata is 2,4,6-triamino-1,3,5-triazine and pydcH(2) is pyridine-2,6-dicarboxylic acid), was obtained by reaction between pydcH(2), tata and zirconyl chloride octa-hydrate in aqueous solution. In the structure, the Zr(IV )atom is nine-coordinated by three (pydc)(2-) groups, resulting in an anionic complex which is balanced by two (tataH)(+) cations. One of the NH(2) groups shows positional disorder, with site occupation factors of 0.60 and 0.40. There are four uncoordinated water mol-ecules (one of which is disordered with occupation factors of 0.70 and 0.30) in the crystal structure. Several inter-molecular inter-actions, including O-H⋯O, O-H⋯N, N-H⋯O, N-H⋯N, C-H⋯O and C-H⋯N hydrogen bonds, a C-O⋯π inter-action [O⋯Cg 3.89, C⋯Cg 4.068 (3) Å; C-O⋯Cg 89° where Cg is the centroid of the triamine ring], and π-π stacking [with centroid-centroid distances of 3.694 (2) and 3.802 (2) Å] are also present.

catena-Poly[[[aqua-cadmium(II)]bis-(µ-4-hydroxy-pyridine-2,6-dicarboxyl-ato)[aqua-cadmium(II)]di-µ-aqua] tetra-hydrate].

The title polymeric compound, {[Cd(2)(C(7)H(3)NO(5))(2)(H(2)O)(4)]·4H(2)O}(n) or {[Cd(2)(hypydc)(2)(H(2)O)(4)]·4H(2)O}(n) (where hypydcH(2) is 4-hydroxy-pyridine-2,6-dicarboxylic acid), was synthesized by the reaction of cadmium(II) nitrate hexa-hydrate with 4-hydroxy-pyridine-2,6-dicarboxylic acid and propane-1,3-diamine, in a 1:2:2 molar ratio in aqueous solution. The compound is a seven-coordinate binuclear polymeric complex with distorted penta-gonal bipyramidal geometry around Cd(II) [Cd-O = 2.247 (4)-2.474 (3) Å]. In the binuclear monomeric units, the central atoms join together by O atoms of two bridging tridentate (hypydc)(2-) ligands, and the polymer propagates via two bridging water mol-ecules that link each Cd(II )centre of one monomer to the adjacent neighbour. Propane-1,3-diamine (pn) does not appear in the product but plays a role as a base. Inter-molecular O-H⋯O and C-H⋯O hydrogen bonds, and π-π stacking inter-actions, with distances of 3.725 (3) and 3.766 (3) Å, connect the various components.

catena-Poly[[triaqua-cadmium(II)]-µ-pyridine-2,3-dicarboxyl-ato-κN,O:O].

The title polymeric compound, [Cd(C(7)H(3)NO(4))(H(2)O)(3)](n) or [Cd(py-2,3-dc)(H(2)O)(3)](n), where py-2,3-dcH(2) is pyridine-2,3-dicarboxylic acid, was obtained by the reaction of cadmium(II) nitrate hexa-hydrate with (pipzH(2))(py-2,3-dc) as a proton-transfer compound in aqueous solution (pipz is piperazine). The mol-ecular structure shows that only the anionic fragment of the starting proton-transfer compound is present in the complex, while the (pipzH(2))(2+) dication has been lost. Each (py-2,3-dc)(2-) ligand bridges two Cd(II) atoms in two different coordination modes, i.e. one end acts as a monodentate and the other end as a bidentate ligand. The three remaining coordination sites on the metal center are occupied by water mol-ecules. The geometric arrangement of the six donor atoms around the Cd(II) atom is distorted octa-hedral. In the crystal structure, O-H⋯O and C-H⋯O hydrogen bonds play an important role in stabilizing the supra-molecular structure.

Guanidinium (aqua-2κO)(4-hydr-oxy-6-carboxy-pyridine-2-carboxyl-ato-2κO,N,O)(µ-4-hydroxy-pyridine-2,6-dicarboxyl-ato-1:2κO,N,O:O)(4-hydroxy-pyridine-2,6-dicarboxyl-ato-1κO,N,O)dizincate(II) dihydrate.

The title compound, (CH(6)N(3))[Zn(2)(C(7)H(3)NO(5))(2)(C(7)H(4)NO(5))(H(2)O)]·2H(2)O, has an anionic binuclear complex of Zn(II) balanced with a guanidinium cation. There are two uncoord-inated water mol-ecules in the structure. The asymmetric unit of the compound has two different coordination types (the coordination of Zn1 is distorted trigonal-bipyramidal, while that of Zn2 is distorted octahedral) of Zn(II) in the crystal structure that are bridged to each other via one hypydc(2-) group (hypydcH(2) is 4-hydroxy-pyridine-2,6-dicarboxylic acid). A variety of inter-molecular O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds involving water mol-ecules, cations and anions, and also a weak π-π inter-action [3.798 (1) Å], are responsible for extending the structure into a three-dimensional network.

Bis(piperazinediium) benzene-1,2,4,5-tetra-carboxyl-ate hexa-hydrate.

The title compound, 2C(4)H(12)N(2) (2+)·C(10)H(2)O(8) (4-)·6H(2)O or (pipzH(2))(2)(btc)·6H(2)O, was formed from the reaction between benzene-1,2,4,5-tetra-carboxylic acid (btcH(4)) as a proton donor and piperazine (pipz) as a proton acceptor. A variety of O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, as well as C-H⋯π inter-actions, are present in the crystal structure. Two water O atoms are each disordered over two positions; for both the site occupany factors are ca 0.66 and 0.34.

Poly[ethyl-enediaminium [di-µ-aqua-(µ(6)-benzene-1,2,4,5-tetra-carboxyl-ato-κO,O:O,O:O:O,O:O:O,O)dithallium(I)]].

The title compound, {(C(2)H(10)N(2))[Tl(2)(C(10)H(2)O(8))(H(2)O)(2))]}(n), was prepared using (enH(2))(2)(btc)·2H(2)O and thallium(I) nitrate (en = ethyl-enediamine and btcH(4) = benzene-1,2,4,5-tetra-carboxylic acid). The enH(2) cation and btc ligand are each located on an inversion centre. The Tl(I) atom is seven-coordinated by three btc ligands and two water mol-ecules in an irregular geometry due to the stereochemically active lone pair on the Tl centre. The water mol-ecule and btc ligand are bonded to the Tl atoms in µ- and µ(6)-forms, respectively, leading to a three-dimensional structure. The crystal structure involves O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, and also a Tl⋯π inter-action of 3.537 (1) Å.

4,4'-Bipyridinium bis-(2-carboxy-pyridine-3-carboxyl-ate).

The title salt, C(10)H(10)N(2) (2+)·2C(7)H(4)NO(4) (-) or (4,4'-bpyH(2))(py-2,3-dcH)(2), prepared by the reaction between pyridine-2,3-dicarboxylic acid (py-2,3-dcH(2)) and 4,4'-bipyridine (4,4'-bpy), consists of two anions and one centrosymmetric dication. In the crystal, there are two strong O-H⋯O hydrogen bonds involving the two carboxyl-ate groups, with an O⋯O distance of 2.478 (1) Å, and an N-H⋯N hydrogen bond between the anion and cation, with an N⋯N distance of 2.743 (1) Å. These inter-actions, along with other O-H⋯O and C-H⋯O hydrogen bonds, π-π stacking [centroid-centroid distances 3.621 (7) and 3.612 (7) Å] and ion pairing, lead to the formation of the three-dimensional structure.

Piperazinediium bis-(2-carboxy-pyridine-3-carboxyl-ate).

The asymmetric unit of the title salt, C(4)H(12)N(2) (2+)·2C(7)H(4)NO(4) (-) or pipzH(2) (2+)·2(py-2,3-dcH(-)), prepared by a reaction between pyridine-2,3-dicarboxylic acid (py-2,3-dcH(2)) and piperazine (pipz), contains a monoanion and half of a centrosymmetric dication. The anionic fragment individually has two intra-molecular hydrogen bonds, an almost linear O-H⋯O bond between two carboxyl-ate groups and a C-H⋯O bond between the aromatic ring and carboxyl-ate group. Other O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds are responsible for three-dimensional expansion of the structure.