Solid state engineering of Bi2S3/rGO nanostrips: an excellent electrode material for energy storage applications.

The study presents a novel, one-pot, and scalable solid-state reaction scheme to prepare bismuth sulphide (Bi2S3)-reduced graphene oxide (rGO) nanocomposites using bismuth oxide (Bi2O3), thiourea (TU), and graphene oxide (GO) as starting materials for energy storage applications. The impact of GO loading concentration on the electrochemical performance of the nanocomposites was investigated. The reaction follows a diffusion substitution pathway, gradually transforming Bi2O3 powder into Bi2S3 nanostrips, concurrently converting GO into rGO. Enhanced specific capacitances were observed across all nanocomposite samples, with the Bi2S3@0.2rGO exhibiting the highest specific capacitance of 705 F g-1 at a current density of 1 A g-1 and maintaining a capacitance retention of 82% after 1000 cycles. The superior specific capacitance is attributed to the excellent homogeneity and synergistic relation between rGO and Bi2S3 nanostrips. This methodology holds promise for extending the synthesis of other chalcogenides-rGO nanocomposites.

In situ synthesis of g-C3N4/Ti3C2Tx nano-heterostructures for enhanced photocatalytic H2 generation via water splitting.

Herein, we demonstrated the in situ synthesis of g-C3N4/Ti3C2Tx nano-heterostructures for hydrogen generation under UV visible light irradiation. The formation of the g-C3N4/Ti3C2Tx nano-heterostructures was confirmed via powder X-ray diffraction and supported by XPS. The FE-SEM images indicated the formation of layered structures of MXene and g-C3N4. HR-TEM images and SAED patterns confirmed the presence of g-C3N4 together with Ti3C2Tx nanosheets, i.e., the formation of nano-heterostructures of g-C3N4/Ti3C2Tx. The absorption spectra clearly showed the distinct band gaps of g-C3N4 and Ti3C2Tx in the nano-heterostructure. The increase in PL intensity and broadening of the peak with an increase in g-C3N4 indicated the suppression of electron-hole recombination. Furthermore, the nano-heterostructure was used as a photocatalyst for H2 generation from water and methylene blue dye degradation. The highest H2 evolution (1912.25 µmol/0.1 g) with good apparent quantum yield (3.1%) and an efficient degradation of MB were obtained for gCT-0.75, which was much higher compared to that of the pristine materials. The gCT-0.75 nano-heterostructure possessed a high surface area and abundant vacancy defects, facilitating the separation of charge carriers, which was ultimately responsible for this high photocatalytic activity. Additionally, TRPL clearly showed a higher decay time, which supports the enhancement in the photocatalytic activity of the gCT-0.75 nano-heterostructure. The nano-heterostructure with the optimum concentration of g-C3N4 formed a hetero-junction with the linked catalytic system, which facilitated efficient charge carrier separation also responsible for the enhanced photocatalytic activity.

Highly crystalline anatase TiO2 nanocuboids as an efficient photocatalyst for hydrogen generation.

Highly crystalline anatase titanium dioxide (TiO2) nanocuboids were synthesized via a hydrothermal method using ethylenediamine tetraacetic acid as a capping agent. The structural study revealed the nanocrystalline nature of anatase TiO2 nanocuboids. Morphological study indicates the formation of cuboid shaped particles with thickness of ∼5 nm and size in the range of 10-40 nm. The UV-visible absorbance spectra of TiO2 nanocuboids showed a broad absorption with a tail in the visible-light region which is attributed to the incorporation of nitrogen atoms into the interstitial positions of the TiO2 lattice as well as the formation of carbonaceous and carbonate species on the surface of TiO2 nanocuboids. The specific surface areas of prepared TiO2 nanocuboids were found to be in the range of 85.7-122.9 m2 g-1. The formation mechanism of the TiO2 nanocuboids has also been investigated. Furthermore, the photocatalytic activities of the as-prepared TiO2 nanocuboids were evaluated for H2 generation via water splitting under UV-vis light irradiation and compared with the commercial anatase TiO2. TiO2 nanocuboids obtained at 200 °C after 48 h exhibited higher photocatalytic activity (3866.44 µmol h-1 g-1) than that of commercial anatase TiO2 (831.30 µmol h-1 g-1). The enhanced photoactivity of TiO2 nanocuboids may be due to the high specific surface area, good crystallinity, extended light absorption in the visible region and efficient charge separation.

Nanostructured N doped TiO2 efficient stable catalyst for Kabachnik-Fields reaction under microwave irradiation.

Herein, we report nitrogen-doped TiO2 (N-TiO2) solid-acid nanocatalysts with heterogeneous structure employed for the solvent-free synthesis of α-aminophosphonates through Kabachnik-Fields reaction. N-TiO2 were synthesized by direct amination using triethylamine as a source of nitrogen at low temperature and optimized by varying the volume ratios of TiCl4, methanol, water, and triethylamine, under identical conditions. An X-ray diffraction (XRD) study showed the formation of a rutile phase and the crystalline size is 10 nm. The nanostructural features of N-TiO2 were examined by HR-TEM analysis, which showed they had rod-like morphology with a diameter of ∼7 to 10 nm. Diffuse reflectance spectra show the extended absorbance in the visible region with a narrowing in the band gap of 2.85 eV, and the high resolution XPS spectrum of the N 1s region confirmed successful doping of N in the TiO2 lattice. More significantly, we found that as-synthesized N-TiO2 showed significantly higher catalytic activity than commercially available TiO2 for the synthesis of a novel series of α-amino phosphonates via Kabachnik-Fields reaction under microwave irradiation conditions. The improved catalytic activity is due to the presence of strong and Bronsted acid sites on a porous nanorod surface. This work signifies N-TiO2 is an efficient stable catalyst for the synthesis of α-aminophosphonate derivatives.

Synthesis of silver-loaded ZnO nanorods and their enhanced photocatalytic activity and photoconductivity study.

Herein, we synthesized ZnO nanorods using a solvothermal reaction technique at 200 °C for 24 h, and the prepared ZnO nanorods were decorated with silver (Ag) nanoparticles to enhance their photocatalytic activity. The Ag nanoparticles were photochemically deposited on the ZnO rods with varying molar concentrations (from 0.5 to 10 mol%), and their various physicochemical properties were studied. The prepared material was characterised using different spectroscopic techniques. XRD revealed the formation of a highly crystalline hexagonal phase of ZnO. For a higher silver loading (>5 mol%), separate peaks corresponding to cubic silver were observed in the XRD pattern. The photoluminescence spectra of the Ag/ZnO nanostructures show two distinct peaks at 390 and 500 nm; interestingly, the PL intensity of the ZnO emission peak at 500 nm decreases with an increase in the silver concentration. The diffuse reflectance spectra of Ag/ZnO indicate absorbance at 380 nm due to ZnO and a slight hump at 440 nm that corresponds to silver nanoparticles. The FE-SEM and TEM analysis indicates the formation of a hexagonal rod-like morphology, with the lengths of the rods ranging from around 50 to 200 nm and a diameter of around 30 nm. TEM also confirms the presence of Ag nanoparticles with sizes in the range of 20 to 30 nm on the surface of the ZnO nanorods. The photocatalytic activity of the Ag/ZnO nanostructures was evaluated by following the degradation of methylene blue (MB) dye under a 400 W mercury vapour lamp. ZnO with 10 mol% Ag loading shows the highest photocatalytic activity as compared to the 0.5, 1 & 5 mol% Ag-ZnO catalysts. The observed apparent rate constant for the photocatalytic MB degradation using 10 mol% Ag-ZnO (Kapp = 6.01 × 10-2 min-1) was six times that of pure ZnO (Kapp = 1.09 × 10-2 min-1). A gradual increase in the photocatalytic activity of Ag/ZnO was observed with an increase in the silver concentration. The photocurrent response of the prepared Ag-ZnO nanostructures was examined by a photoconductivity study. Moreover, the photocatalytic performance of the sample was correlated with the photoconductivity of the samples. The photoconductivity of the samples was stable, and the photoconductivity of 10 mol% Ag-ZnO was almost 20 times that of pure ZnO, resulting in a higher photocatalytic activity.

ZnCl2 loaded TiO2 nanomaterial: an efficient green catalyst to one-pot solvent-free synthesis of propargylamines.

One-pot green synthesis of propargylamines using ZnCl2 loaded TiO2 nanomaterial under solvent-free conditions has been effectively accomplished. The aromatic aldehydes, amines, and phenylacetylene were reacted at 100 °C in the presence of the resultant catalyst to form propargylamines. The nanocrystalline TiO2 was initially synthesized by a sol-gel method from titanium(iv) isopropoxide (TTIP) and further subjected to ZnCl2 loading by a wet impregnation method. X-ray diffraction (XRD) patterns revealed the formation of crystalline anatase phase TiO2. Field emission scanning electron microscopy (FESEM) showed the formation of agglomerated spheroid shaped particles having a size in the range of 25-45 nm. Transmission electron microscopy (TEM) validates cubical faceted and nanospheroid-like morphological features with clear faceted edges for the pure TiO2 sample. Surface loading of ZnCl2 on spheroid TiO2 nanoparticles is evident in the case of the ZnCl2 loaded TiO2 sample. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti4+ and Zn2+ species in the ZnCl2 loaded TiO2 catalyst. Energy-dispersive X-ray (EDS) spectroscopy also confirmed the existence of Ti, O, Zn and Cl elements in the nanostructured catalyst. 15% ZnCl2 loaded TiO2 afforded the highest 97% yield for 3-(1-morpholino-3-phenylprop-2-ynyl)phenol, 2-(1-morpholino-3-phenylprop-2-ynyl)phenol and 4-(1,3-diphenylprop-2-ynyl)morpholine under solvent-free and aerobic conditions. The proposed nanostructure-based heterogeneous catalytic reaction protocol is sustainable, environment-friendly and offers economic viability in terms of recyclability of the catalyst.

Nanostructured N-doped orthorhombic Nb2O5 as an efficient stable photocatalyst for hydrogen generation under visible light.

The synthesis of orthorhombic nitrogen-doped niobium oxide (Nb2O5-xNx) nanostructures was performed and a photocatalytic study carried out in their use in the conversion of toxic H2S and water into hydrogen under UV-Visible light. Nanostructured orthorhombic Nb2O5-xNx was synthesized by a simple solid-state combustion reaction (SSCR). The nanostructural features of Nb2O5-xNx were examined by FESEM and HRTEM, which showed they had a porous chain-like structure, with chains interlocked with each other and with nanoparticles sized less than 10 nm. Diffuse reflectance spectra depicted their extended absorbance in the visible region with a band gap of 2.4 eV. The substitution of nitrogen in place of oxygen atoms as well as Nb-N bond formation were confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. A computational study (DFT) of Nb2O5-xNx was also performed for investigation and conformation of the crystal and electronic structure. N-Substitution clearly showed a narrowing of the band gap due to N 2p bands cascading above the O 2p band. Considering the band gap in the visible region, Nb2O5-xNx exhibited enhanced photocatalytic activity toward hydrogen evolution (3010 µmol h-1 g-1) for water splitting and (9358 µmol h-1 g-1) for H2S splitting under visible light. The enhanced photocatalytic activity of Nb2O5-xNx was attributed to its extended absorbance in the visible region due to its electronic structure being modified upon doping, which in turn generates more electron-hole pairs, which are responsible for higher H2 generation. More significantly, the mesoporous nanostructure accelerated the supression of electron and hole recombination, which also contributed to the enhancement of its activity.

Novel functionality of organic 6,13-Pentacenequinone as a photocatalyst for hydrogen production under solar light.

6,13-Pentacenequinone (PQ), an intermediate for an organic semiconductor pentacene, was synthesized by single step solvent free solid state reaction at room temperature under ambient conditions which is hitherto unattempted. The phase purity has been confirmed by XRD and NMR. Optical study showed the absorption at 390 and 412 nm attributed to the π-π* and n-π* transitions, respectively. Cyclic voltammetry indicates the semiconducting nature of PQ having a band gap of 3 eV. The photoluminescence study revealed emissions at 408 and 432 nm. Considering the good thermal stability and absorption well within visible region, wisely, PQ has been used as a photocatalyst for the hydrogen production under solar light. Surprisingly we observed the utmost hydrogen evolution i.e. 4848 µmol/h/0.1 g (quantum efficiency 6.8%). The repeatability and reusability study confirmed the stability of the photocatalyst. The confirmation of the photocatalytic effect was also confirmed using methylene blue (MB) dye degradation under natural sunlight. The observed rate constant (Kapp) for photocatalytic MB degradation was 1.60 × 10(-2) min(-1). The use of an organic photocatalyst for hydrogen production has been demonstrated for the first time. This novel organic photocatalyst can also be explored for water splitting.