Fullerene-based low-dimensional (LD) heterostructures have emerged as excellent energy conversion materials. We constructed van der Waals 1T-MoS2/C60 0D-2D heterostructures via a one-pot synthetic approach for catalytic hydrogen generation. The interfacial 1T-MoS2–C60 and C60–C60 interactions as well as their electrocatalytic properties were finely controlled by varying the weight percentages of the fullerenes. 1T-MoS2 platforms provided a novel template for the formation of C60 nanosheets (NSs) within a very narrow fullerene concentration range. The heterostructure domains of 1T-MoS2 and C60 NSs exhibited excellent hydrogen evolution reaction (HER) performances, with one of the lowest onset potentials and ΔG H* values for LD non-precious nanomaterials reported to date.

We report the structural chemistry and optical properties of tin (Sn)mixed gallium oxide (Ga 2 O 3 ) compounds, where the interfacial phase modulationinduced structural distortion in turn induces variations in the band gap and nonlinear optical activity. The Sn incorporation into Ga 2 O 3 causes significant reduction in the band gap and induces nonlinear optical activity upon chemical composition tuning. Detailed investigation performed on the structural chemistry, phase stabilization, surface morphology, and optical and electrochemical properties of Sn-mixed Ga 2 O 3 compounds (Ga 2−2x Sn x O 3 , 0.00 ≤ x ≤ 0.3, Ga-Sn-O) indicates that the Sn-incorporation-induced effects are significant. To produce Ga-Sn-O materials of high structural and chemical quality, we adopted a simple solid-state chemical reaction route involving first calcining and then sintering the material at higher temperatures. Structural chemistry analyses of sintered Ga-Sn-O compounds by X-ray diffraction (XRD) showed solid solution formation at lower Sn concentrations (x ≤ 0.10). The XRD analyses indicate the SnO 2 secondary phase formation at higher (x > 0.10) Sn concentrations. Surface morphology analysis using scanning electron microscopy (SEM) also showed a positive relationship between phase separation and Sn concentration. Optical absorption spectra showed a substantial redshift in the band gap (E g ), which would allow Ga-Sn-O compounds to have wide spectral selectivity. At higher Sn concentrations (x = 0.25−0.30), corroborating with structural/chemical analyses, an additional lower-energy sub-band transition that explicitly corresponds to SnO 2 appears in the optical absorption data. Importantly, the evidence of nonlinear optical activity in Ga-Sn-O, which is otherwise not traditionally known for such an activity, as well as dipolar-and quadrupolar-shaped dependence of activity with the polarization angle of the excitation source was detected. At higher concentrations (x ≥ 0.15), Sn was found to be insoluble, which can be attributed to Ga 2 O 3 and SnO 2 possessing different formation enthalpies and cation (Ga 3+ and Sn 4+ ) chemistries. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and optical and electrochemical properties could be useful to optimize Ga-Sn-O inorganic compounds for optical, optoelectronic, and photocatalytic device applications.

This work for the first time unfurls the fundamental mechanisms and sets the stage for an approach to derive electrocatalytic activity, which is otherwise not possible, in a traditionally known wide band-gap oxide material. Specifically, we report on the tunable optical properties, in terms of wide spectral selectivity and red-shifted band gap, and electrocatalytic behavior of iron (Fe)-doped gallium oxide (β-Ga2O3) model system. X-ray diffraction (XRD) studies of sintered Ga2–x Fe x O3 (GFO) (0.0 ≤ x ≤ 0.3) compounds provide evidence for the Fe3+ substitution at Ga3+ site without any secondary phase formation. Rietveld refinement of XRD patterns reveals that the GFO compounds crystallize in monoclinic crystal symmetry with a C2/m space group. The electronic structure of the GFO compounds probed using X-ray photoelectron spectroscopy data reveals that at lower concentrations, Fe exhibits mixed chemical valence states (Fe3+, Fe2+), whereas single chemical valence state (Fe3+) is evident for higher Fe content (x = 0.20–0.30). The optical absorption spectra reveal a significant red shift in the optical band gap with Fe doping. The origin of the significant red shift even at low concentrations of Fe (x = 0.05) is attributed to the strong sp–d exchange interaction originated from the 3d5 electrons of Fe3+. The optical absorption edge observed at ≈450 nm with lower intensity is the characteristic of Fe-doped compounds associated with Fe3+–Fe3+ double-excitation process. Coupled with an optical band-gap red shift, electrocatalytic studies of GFO compounds reveal that, interestingly, Fe-doped Ga2O3 compound exhibits electrocatalytic activity in contrast to intrinsic Ga2O3. Fe-doped samples (GFO) demonstrated appreciable electrocatalytic activity toward the generation of H2 through electrocatalytic water splitting. An onset potential and Tafel slope of GFO compounds include ∼900 mV, ∼210 mV dec–1 (x = 0.15) and ∼1036 mV, ∼290 mV dec–1 (x = 0.30), respectively. The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms such as doping resulting in new catalytic centers, enhanced conductivity, and electron mobility. Hence, in this report, for the first time, we explored a new pathway; the electrocatalytic behavior of Fe-doped Ga2O3 resulted due to Fe chemical states and red shift in the optical band gap. The implications derived from this work may be applicable to a large class of compounds, and further options may be available to design functional materials for electrocatalytic energy production.

In situ growth of metallic MoO 2 films on fluorinedoped tin oxide (FTO) and MoO 2 powderi ns olution was achieved simultaneously by as imple hydrothermal process employing citric acid as the surfactant. The growth mechanism of MoO 2 nanostructures (NSs) at the heterogeneousi nterface and in homogeneous mediumproceeds in adifferent manner in which seeds grow in ap referred orientation on FTO, whereas they propagate in all directions in solution. The high lattice matching of FTO and MoO 2 favours the film growth whichc ould not be obtainedo no ther conventional substrates. The disc morphologyo fM oO 2 nanostructures was changed to other diversem orphologyb yv arying the synthesis conditions, particularly by the addition of nitric acid. Ac ompetitive effect of nitric acid and citric acid on the structure direction produced various shapes.T he electrochemicalw ater activation studies showt hat hydrogen-an-nealedM oO 2 is an excellent hydrogen evolution reaction (HER) catalyst with good stability.H -MoO 2 film/FTO displays al ow onset overpotential of72 mV with aT afel slope of 84.1 mV dec À1 ,w hereas the powder form exhibits an onset overpotential of 46 mV with aT afel slope of 71.6 mV dec À1 . The large active surface area, exposure of fringe facets of (110) and the lesser electrochemical charge-transferr esistance offered by the hydrogen-annealed MoO 2 NSsp laya major role in the enhanced HERa ctivity.[a] Dr.

Tailoring the optical and electronic properties of wide band gap β-Ga2O3 has been of tremendous importance to utilize the full potential of the material in current and emerging technological applications in electronics, optics, and optoelectronics. In the present work, we report the effect of Ti-dopant insolubility driven chemical inhomogeneity on the structural, morphological, chemical bonding, electronic structure, and band gap red shift characteristics in Ga2O3 polycrystalline compounds. Ga2–2x Ti x O3 (GTO; 0 ≤ x ≤ 0.20) compounds were synthesized using a conventional high-temperature solid state reaction route under variable calcination temperatures (1050–1250 °C) while sintering was performed at 1350 °C. X-ray diffraction analysis of GTO samples reveals that the formation of single-phase compounds occurs only at a very low concentration of Ti doping (<5 at. %), whereas higher Ti doping results in composite formation with a significant undissolved TiO2 rutile phase. However, in sintered samples, fraction of undissolved rutile phase transformed into monoclinic TiO2. Rietveld refinement of intrinsic Ga2O3 and single-phase Ti-doped compound (x = 0.05) confirms that samples are stabilized in monoclinic symmetry with C2/m space group. Surface morphologies of samples reveal that intrinsic Ga2O3 exhibits rod shaped morphology, while Ti-doped compounds exhibit spherical morphology. Moreover, in doped compounds with abnormal grain growth, lattice twinning induced striations were noted in contrast to intrinsic Ga2O3. High-resolution X-ray photoelectron spectroscopic analysis of Ga 2p shows a positive shift compared to metallic Ga due to interaction between the electron cloud of adjacent ions. Ti 2p1/2 spectra show anomalous broadening due to the Coster–Kronig effect. First-principles calculations using hybrid density functional theory show that Ti preferentially substitutes on octahedral Ga sites and that it behaves as a deep donor in Ga2O3. From the optical absorption spectra, a red shift in the optical band gap is observed. Absorption within the band gap of Ga2O3 is attributed to the inclusion of undissolved TiO2, as TiO2 has a type I alignment within the gap of Ga2O3. In addition, the electrocatalytic behavior of GTO compounds was examined. From electrocatalytic studies it is evident that doped compounds exhibit appreciable electrocatalytic activity in contrast to intrinsic Ga2O3.