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The work reports a facile synthesis of high thermally stable nanocrystalline anatase TiO2 nanoparticles (NPs) doped with different atomic concentrations (0.5, 1.0, 3.0, and 6.0%) of Gd3+ and Nd3+ ions by a template-free and one-step solvothermal process, using titanium(IV) butoxide as a titanium precursor and dimethyl sulfoxide (DMSO) as a solvent. The structure and morphology of the Gd3+, Nd3+, and 0.5%Gd3+-0.5%Nd3+/doped TiO2 NPs have been characterized by using various analytical techniques. The Gd3+/ and Nd3+/TiO2 molar ratios were found to have a pronounced impact on the crystalline structure, size, and morphology of TiO2 NPs. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed the proper substitution of Ti4+ by Gd3+ and Nd3+ ions in the TiO2 host lattice. The as-prepared Gdx/TiO2, Ndx/TiO2, and Gd1.0/Ndx/TiO2 bimetallic NPs, x = 0.5, 1.0, 3.0, and 6%, have been investigated as electrocatalysts for hydrogen evolution reaction (HER) in 1.0 M KOH solution using a variety of electrochemical techniques. At any doping percentage, the Gd1.0/Ndx/TiO2 bimetallic NPs showed higher HER catalytic performance than their corresponding counterparts, i.e., Gdx/TiO2 and Ndx/TiO2. Upon increasing the Nd content from 0.5 to 6.0%, the HER catalytic performance of the Gd1.0/Ndx/TiO2 bimetallic NPs was generally enhanced. Among the studied materials, the bimetallic Gd1.0/Nd6.0/TiO2 NPs emerged as the most promising catalyst with an onset potential of −22 mV vs. RHE, a Tafel slope of 109 mV dec−1, and an exchange current density of 0.72 mA cm−2. Such HER electrochemical kinetic parameters are close to those recorded by the commercial Pt/C (onset potential: −15 mV, Tafel slope: 106 mV dec−1, and exchange current density: 0.80 mA cm−2), and also comparable with those measured by the most active electrocatalysts reported in the literature. The synergistic interaction of Gd and Nd is thought to be the major cause of the bimetallic catalyst's activity. [ABSTRACT FROM AUTHOR]

Fly ash (FA) is a waste product generated in huge amounts by coal-fired electric and steam-generating plants. As a result, the use of FA alone or in conjunction with other materials is an intriguing study topic worth exploring. Herein, we used FA waste in conjunction with titanium oxide (TiO2) to create (FA-TiO2) nanocomposites. For the first time, a cathodic polarization pre-treatment regime was applied to such nanocomposites to efficiently produce hydrogen from an alkaline solution. The FA-TiO2 hybrid nanocomposites were prepared by a straightforward solvothermal approach in which the FA raw material was mixed with titanium precursor in dimethyl sulfoxide (DMSO) and refluxed during a given time. The obtained FA-TiO2 hybrid nanocomposites were fully characterized using various tools and displayed a cenosphere-like shape. The synthesized materials were tested as electrocatalysts for the hydrogen evolution reaction (HER) in 0.1 M KOH solution in the dark, employing various electrochemical techniques. The as-prepared (unactivated) FA-TiO2 exhibited a considerable HER electrocatalytic activity, with an onset potential (EHER) value of −144 mV vs. RHE, a Tafel slope (−bc) value of 124 mV dec−1 and an exchange current density (jo) of ~0.07 mA cm−2. The FA-TiO2′s HER catalytic performance was significantly enhanced upon cathodic activation (24 h of chronoamperometry measurements performed at a high cathodic potential of −1.0 V vs. RHE). The cathodically activated FA-TiO2 recorded HER electrochemical kinetic parameters of EHER = −28 mV, −bc = 115 mV dec−1, jo = 0.65 mA cm−2, and an overpotential η10 = 125 mV to yield a current density of 10 mA cm−2. Such parameters were comparable to those measured here for the commercial Pt/C under the same experimental conditions (EHER = −10 mV, −bc = 113 mV dec−1, jo = 0.88 mA cm−2, η10 = 110 mV), as well as to the most active electrocatalysts for H2 generation from aqueous alkaline electrolytes. [ABSTRACT FROM AUTHOR]

Summary: A new bipyridine‐containing manganese (II) complex, namely [(BPy)2MnCl2]·0.5H2O (MnC), was synthesized and characterized. Spectral and X‐ray structural features revealed that MnC has an octahedral environment around Mn(II). Graphene oxide (GO) was noncovalently functionalized with the MnC. MnC‐ and (MnC/GO)‐modified glassy carbon (GC) interfaces with different loading densities (0.2, 0.4, 0.8, and 1.0 mg cm−2) were tested as electrocatalysts for efficient generation of H2 in 0.1 M KOH solution. The GC‐MnC catalysts exhibited high electrocatalytic activity for the HER, which enhances upon increasing the catalyst's loading density. The GC‐MnC catalyst's HER activity, at any tested loading density, was found to further increase upon supporting MnC on GO. The best performing electrocatalyst, namely GC‐(MnC/GO) with a loading density of 1.0 mg cm−2, exhibited high HER catalytic activity with a low onset potential value of −22 mV vs. reference hydrogen electrode (RHE) and a high exchange current density of 0.75 mA cm−2. It delivered a current density of 10 mA cm−2 at an overpotential value of 119 mV. In addition, it recorded a Tafel slope value of −114 mV dec−1. These HER electrochemical kinetic parameters approached those measured here for the commercial Pt/C under the same operating conditions (−10 mV vs. RHE, 0.88 mA cm−2, 113 mV dec−1, and 110 mV to yield a current density of 10 mA cm−2) and also comparable to the most active molecular electrocatalysts for H2 generation from aqueous alkaline electrolytes published in the literature. The long‐term stability of the best performing electrocatalyst, namely GC‐MnC (1.0 mg cm−2)/GO, was evaluated using cyclic voltammetry (repetitive cycling up to 5000 cycles) and chronoamperometry (48 hours) techniques, and the obtained results revealed its promising stability. A plausible mechanism for the interaction of MnC with GO was proposed based on density functional theory (DFT) calculations. DFT calculations confirmed the catalytic role of the supporting material (GO) on the fabricated metal complex in catalyzing the HER. [ABSTRACT FROM AUTHOR]

Three mononuclear 2-picolylamine-containing zinc(III) complexes viz [(2-PA)2ZnCl]2(ZnCl4)] (Zn1), [(2-PA)2Zn(H2O)](NO3)2] (Zn2) and [Zn(2-PA)2(OH)]NO3] (Zn3) were synthesized and fully characterized. Spectral and X-ray structural characteristics showed that the Zn1 complex has a square-pyramidal coordination environment around a zinc(II) core. The hydroxide complex Zn3 was non-covalently functionalized with few layers of graphene oxide (GO) sheets, formed by exfoliation of GO in water. The resulting Zn3/GO hybrid material was characterized by FT-IR, TGA-DSC, SEM-EDX and X-ray powder diffraction. The way of interaction of Zn3 with GO has been established through density functional theory (DFT) calculations. Both experimental and theoretical findings indicate that, on the surface of GO, the complex Zn3 forms a complete double-sided adsorption layer. Zn3 and its hybrid form Zn3/GO have been individually investigated as electrocatalysts for the hydrogen evolution reaction. The hybrid heterogenized form Zn3/GO was supported on glassy carbon (GC) with variable loading densities of Zn3 (0.2, 0.4 and 0.8 mg cm−2) to form electrodes. These electrodes have been tested as molecular electrocatalysts for the hydrogen evolution reaction (HER) using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 0.1 M KOH. Results showed that both GC-Zn3 and GC-Zn3/GO catalysts for the HER are highly active, and with increase of the catalyst's loading density, this catalytic activity enhances. The high catalytic activity of HER with a low onset potential of −140 mV vs. RHE and a high exchange current density of 0.22 mA cm−2 is achieved with the highest loading density of Zn3 (0.8 mg cm−2). To achieve a current density of 10 mA cm−2, an overpotential of 240 mV was needed. [ABSTRACT FROM AUTHOR]

Summary A newly synthesized zinc(II) complex, namely tert‐butyl N‐(2 mercaptoethyl)carbamatozinc(II) complex [Zn(Boc‐S)2] (Boc = tert‐butyl N‐[2‐mercaptoethyl]carbamate), has been used as an organozinc precursor for the production of crystalline ZnO and ZnO/TiO2 nanoparticles. The synthesized complex and the obtained nanomaterials were fully characterized using various spectroscopic and surface analysis techniques. Their surface morphology, chemical purity and stoichiometry have been investigated by scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDX) as well as X‐ray fluorescence. The synthesized Zn(II) molecular complex, ZnO and ZnO/TiO2 nanomaterials have been tested in alkaline aqueous solution (1.0 MNaOH) for the hydrogen evolution reaction (HER) using various electrochemical techniques. The results revealed high HER catalytic performance of ZnO and ZnO/TiO2 cathode materials, with the latter exhibiting higher catalytic activity recording an exchange current density (jo) of 0.3 mA cm−2. This current value, which approaches that of Pt wire (0.5 mA cm−2), cross‐sectional area ~0.008 cm2, is about 11 and 100 times greater than those measured for ZnO alone (0.028 mA cm−2) and TiO2 alone (0.0032 mA cm−2), respectively. Moderate catalytic activity was recorded for the complex catalyst, namely GC‐Zn(Boc‐S)2 with jo value of (0.01 mA cm−2). Tafel slope values of 130 and 122 mV dec−1 were calculated for ZnO and ZnO/TiO2, respectively. Such Tafel slope values, which are close to that of the Pt wire (120 mV dec−1), referred to a Volmer‐controlled HER kinetics. Other important electrochemical parameters describing the kinetics of the HER, such as roughness factor (Rf) and turnover frequency (TOF) were also estimated and discussed. The high numerical values of the various HER kinetic parameters recorded for the ZnO/TiO2 catalyst, in addition to its high stability and durability (stable for up to 10 000 continuous cathodic polarization cycles), besides maintaining its morphology and chemical composition after stability test (confirmed from SEM/EDX and XRD examinations), located it in a privileged position among the most efficient HER electrocatalysts reported in the literature. [ABSTRACT FROM AUTHOR]

Summary: In this work, PdO/TiO2 and Eu2O3/TiO2 nanocomposites (NCs) were synthesized using a new facile, template‐free, and one‐step solvothermal approach and characterized by several instrumentation techniques. X‐ray photoelectron spectroscopy studies revealed the presence of oxidized form of the Pd and Eu nanoparticles within the NC materials (PdO and Eu2O3). The two catalysts exhibited remarkable activity for the hydrogen evaluation reaction (HER) in a strong alkaline solution (4.0 M NaOH) with PdO/TiO2 catalyst being the best, which recorded an exchange current density (jo) of 0.26 mA cm−2 and a Tafel slope (βc) of 125 mV dec−1. Such parameters are not far from those recorded for a commercial Pt/C catalyst (0.71 mA cm−2 and 120 mV dec−1) performed here under the same operating conditions. Eu2O3/TiO2 catalyst recorded jo and βc values of 0.05 mA cm−2 and 135 mV dec−1. The Tafel slopes 125 and 135 mV dec−1 calculated on the PdO/TiO2 and Eu2O3/TiO2 catalysts suggest a HER kinetics controlled by the Volmer step. PdO/TiO2 catalyzed the HER with a high turnover frequency of 2.3 H2/s at 0.2 V versus the reversible hydrogen electrode, while Eu2O3/TiO2 catalyst only measured a turnover frequency value of 1.25 H2/s at the same overpotential. The two catalysts exhibited excellent stability and durability after 10 000 cycles and 72 hours of controlled potential electrolysis at a high cathodic overpotential, reflecting their practical applicability. Scanning electron microscope and X‐ray photoelectron spectroscopy examinations revealed that the morphology and chemistry of both catalysts were not altered as a result of the performed long‐term stability and durability tests. [ABSTRACT FROM AUTHOR]

Abstract We report here a facile, template-free and one-step solvothermal approach for the synthesis of high-temperature stable gold/titania nanocomposite (NCs), providing a new, simple, quick and inexpensive wet-chemical route. Our approach is based on the assembly of gold salt and titanium butoxide in dimethyl sulfoxide (DMSO). Also, we present here, for the first time, a cathodically activated Au/TiO 2 catalyst with Pt/C activity for the hydrogen evolution reaction (HER) in 0.5 M H 2 SO 4 in the dark. The as-prepared (unactivated) Au/TiO 2 NCs exhibits considerable electrocatalytic activity for H 2 generation in the dark, with a low onset potential (E HER) of −64 mV vs. RHE, a Tafel slope (- b c) of 60 mV dec−1 and an exchange current density (j o) of 0.12 mA cm−2. Long-term stability and durability tests in 0.5 M H 2 SO 4 , employing cyclic voltammetry technique (10,000 of repetitive cycling) and 72 h of chronoamperometry measurements at a high cathodic potential (cathodic activation), reveal that the electrocatalyst activates during such aging processes yielding an activated Au/TiO 2 catalyst with Pt/C-like activity for H 2 generation (E HER -3 mV, - b c : 35 mV dec−1, and j o : 0.95 mA cm−2). The outstanding HER activity of the activated catalyst is discussed. [ABSTRACT FROM AUTHOR]

Numerous clean energy systems rely on the oxygen evolution process (OER), which takes place during water splitting reaction. For this purpose, transition-metal oxides have garnered considerable attentions as a prominent OER electrocatalysts. In present study, we fabricate the nanosheet arrays of metal oxide/carbon (MOx/C; M = Fe, Ag, and Mn) fabricated via hydrothermal route. As templates, this approach employs the covered 2-dimensional (2D) metal-organic frameworks (2D-MOFs), and these MOx/C arrays made from 2D MOFs exhibit significant electrocatalytic activity and durability. Among all, Ag 2 O/C showed the overpotentials of 270 mV at a current density (j) of 10 mA cm−2, while the tafel slope is 45 mV dec−1, that is lower than other metal oxide-based catalysts like MnO/C, and Fe 2 O 3 /C. It also shows 48 h high stability due to the conductive nature, larger surface area and the presence of carbon cage for easy transfer of electrons. The conceptual framework and synthetic strategy employed in this study can be applied to create more multi-metal oxide anchoring Ag 2 O carbon matrix-based electrocatalysts that are extremely efficient, affordable, and perform significantly better in OER and other future applications. [ABSTRACT FROM AUTHOR]

Water is a vital ingredient in all life forms and crucial for their survival. Yet, contamination of water by toxic effluents from various sources makes it lethal, posing a threat to the environment and health of living beings. Therefore, an effective and efficient method for the treatment of these effluents is the need of the hour. In continuation to our recent investigations into the application of heterogeneous catalytic systems in treating environmental contaminants , herein we report the design and synthesis of palladium(0) nanoparticles immobilized graphitic-carbon nitride (g-C 3 N 4 -Si@Pd) as a nanocatalyst in a facile four-step synthesis. The g-C 3 N 4 -Si@Pd nanocatalyst was characterized by various spectroscopic and microscopic techniques such as FT-IR, FE-SEM, EDS, ICP-OES, TEM, BET, TGA and p -XRD to confirm its structure and morphology. It was then successfully explored for its catalytic activity in the reduction of various environmental contaminants, such as 4-nitrophenol, chromium(VI), methyl orange and rhodamine B. Being heterogeneous in nature, the nanocatalyst was easily recovered from the reaction mass by simple centrifugation. The g-C 3 N 4 -Si@Pd nanocatalyst is economical, facile, requires mild reaction conditions and produce non-toxic byproducts. Also, the g-C 3 N 4 -Si@Pd nanocatalyst exhibited high electrocatalytic activity and high electronic conductivity in hydrogen evolution reaction. [Display omitted] • New g-C 3 N 4 -Si@Pd nanocatalyst was developed by immobilization of palladium nanoparticles on graphitic carbon nitride. • The prepared g-C 3 N 4 -Si@Pd nanocatalyst was characterized by various spectroscopic and microscopic techniques. • g-C 3 N 4 -Si@Pd nanocatalyst was studied for the catalytic reduction of 4-NP, Cr(VI), MO and RB. • g-C 3 N 4 -Si@Pd nanocatalyst could be easily recovered by simple centrifugation and reused at least 5 times without any major loss of activity. • The g-C 3 N 4 -Si@Pd nanocatalyst also exhibited high electrocatalytic activity and high electronic conductivity in hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]