Visible-Light-Driven Photocatalytic Activity of SnO2-ZnO Quantum Dots Anchored on g-C3N4 Nanosheets for Photocatalytic Pollutant Degradation and H-2 Production

A zero-dimensional/two-dimensional heterostructure consists of binary SnO2-ZnO quantum dots (QDs) deposited on the surface of graphitic carbon nitride (g-C3N4) nanosheets. The so-called SnO2-ZnO QDs/g-C3N4 hybrid was successfully synthesized via an in situ co-pyrolysis approach to achieve efficient photoactivity for the degradation of pollutants and production of hydrogen (H-2) under visible-light irradiation. High-resolution transmission electron microscopy images show the close contacts between SnO2-ZnO QDs with the g-C3N4 in the ternary SnO2-ZnO QDs/g-C3N4 hybrid. The optimized hybrid shows excellent photocatalytic efficiency, achieving 99% rhodamine B dye degradation in 60 min under visible-light irradiation. The enriched charge-carrier separation and transportation in the SnO2-ZnO QDs/g-C3N4 hybrid was determined based on electrochemical impedance and photocurrent analyses. This remarkable photoactivity is ascribed to the "smart" heterostructure, which yields numerous benefits, such as visible-light-driven fast electron and hole transfer, due to the strong interaction between the SnO2-ZnO QDs with the g-C3N4 matrix. In addition, the SnO2-ZnO QDs/g-C3N4 hybrid demonstrated a high rate of hydrogen production (13 673.61 mu mol g(-1)), which is 1.06 and 2.27 times higher than that of the binary ZnO/g-C3N4 hybrid (12 785.54 mu mol g(-1)) and pristine g-C3N4 photocatalyst (6017.72 mu mol g(-1)). The synergistic effect of increased visible absorption and diminished recombination results in enhanced performance of the as-synthesized tin oxide-and zinc oxide-modified g-C3N4. We conclude that the present ternary SnO2-ZnO QDs/g-C3N4 hybrid is a promising electrode material for H-2 production and photoelectrochemical cells

Tiny MoO3 nanocrystals self-assembled on folded molybdenum disulfide nanosheets via a hydrothermal method for supercapacitor

Coupling of two active semiconductors can easily lead to a deterioration of their intrinsic properties. In this work, tiny MoO3 nanocrystals were deposited on 3D MoS2 frameworks via a hydrothermal reaction, with heterostructures forming by oxygen-bonding interactions at their interface. When tested as a supercapacitor electrode, the MoS2/MoO3 heterostructure exhibited a high specific capacitance of 287.7 F g(-1) at a current density of 1 A g(-1), and a remarkable cycling stability after 1000 cycles at 1 A g(-1) in an aqueous solution compared to pristine MoS2. The results thus reveal the superior properties of the MoS2/MoO3 heterostructure for supercapacitor electrode

Removal of Phosphorus by Ferric Ion-Rich Solutions Prepared Using Various Fe(III)-Containing Minerals

Various biological, chemical, and physical technologies have been studied to effectively remove total phosphorus (T-P) from wastewater. Among them, some mineral suspensions and cations in the aqueous phase have shown great potential for promoting phosphorus removal via chemical precipitation. Herein, we investigated the efficiency of T-P removal using various chemical-based cations (Fe2+, Fe3+, Mg2+, and Al3+); ferric ions (Fe3+) showed the highest T-P-removal efficiency (33.1%), regardless of the type of anion (Cl−, NO3−, and SO42−). To prepare natural Fe3+-rich solutions, three different Fe(III)-rich minerals (hematite, lepidocrocite, and magnetite) were treated with various HCl concentrations to maximize the dissolved Fe3+ amounts. Lepidocrocite in 2 N HCl showed the most effective Fe3+-leaching ability (L-Fe dissolved solution). Almost no significant difference in Fe3+ leaching was observed between HCl and H2SO4, whereas lepidocrocite-2 N H2SO4 showed the highest T-P-removal ability (91.5%), with the formation of amorphous Fe(III)-P precipitates. The L-Fe dissolved solution exhibited a higher T-P-removal efficiency than polyammonium chloride under real wastewater conditions. Our results can provide fundamental knowledge about the effect of cations on T-P removal in wastewater treatment and the feasibility of using the Fe3+ leaching solution prepared from Fe(III)-containing minerals for efficient T-P removal via chemical precipitation

Rare earth metal Gd influenced defect sites in N doped TiO2: Defect mediated improved charge transfer for enhanced photocatalytic hydrogen production

In this experimental studies, we report the synthesis of TiO2 co-doped by both cationic and anionic sites by simple sol-gel based method. All the prepared samples exhibit the anatase crystalline morphology however, showed lattice distortion caused by the displacement of Ti4+ sites by Gd3+. The improved visible absorption is witnessed by the Gd and N co-doping with an assured redshift in the absorption edge. The N and Gd displacement inside TiO2 lattice accompanied by the creation of O-Ti-N and Gd-O-Ti bonds are characterized by the X-ray photoelectron spectra. The strong resonance signal by Gd4f electrons in the electron paramagnetic resonance spectroscopy further substantiate the displacement of lattice cites of TiO2 by Gd3+ ions. The longevity of the photo produced charges observed in fluorescence spectra of Gd and N co-doped TiO2 is because of the effective transfer of charges to the defect sites. The aforementioned catalysts are tested for their capacity for the H-2 production from water splitting. The 2 wt% gadolinium and nitrogen co-doped TiO2 has shown 10764 mu mol g(-1) H-2 production which is 26 times higher than the commercial Degussa P-25 catalyst. The enhanced activity for hydrogen production can be attributed to factors such as increased absorptivity under visible light and effective charge carrier separation

Removal of Phosphorus by Ferric Ion-Rich Solutions Prepared Using Various Fe(III)-Containing Minerals

Various biological, chemical, and physical technologies have been studied to effectively remove total phosphorus (T-P) from wastewater. Among them, some mineral suspensions and cations in the aqueous phase have shown great potential for promoting phosphorus removal via chemical precipitation. Herein, we investigated the efficiency of T-P removal using various chemical-based cations (Fe2+, Fe3+, Mg2+, and Al3+); ferric ions (Fe3+) showed the highest T-P-removal efficiency (33.1%), regardless of the type of anion (Cl−, NO3−, and SO42−). To prepare natural Fe3+-rich solutions, three different Fe(III)-rich minerals (hematite, lepidocrocite, and magnetite) were treated with various HCl concentrations to maximize the dissolved Fe3+ amounts. Lepidocrocite in 2 N HCl showed the most effective Fe3+-leaching ability (L-Fe dissolved solution). Almost no significant difference in Fe3+ leaching was observed between HCl and H2SO4, whereas lepidocrocite-2 N H2SO4 showed the highest T-P-removal ability (91.5%), with the formation of amorphous Fe(III)-P precipitates. The L-Fe dissolved solution exhibited a higher T-P-removal efficiency than polyammonium chloride under real wastewater conditions. Our results can provide fundamental knowledge about the effect of cations on T-P removal in wastewater treatment and the feasibility of using the Fe3+ leaching solution prepared from Fe(III)-containing minerals for efficient T-P removal via chemical precipitation

Eco-friendly, hydrogen fluoride-free, morphology-oriented synthesis of TiO2 with exposed (001) facets

Owing to its excellent properties, TiO2 is considered as a wonder material and has been studied extensively in various fields of research. Furthermore, because of its morphology-oriented properties, anatase TiO2 synthesized with controllable morphology and exposed (001) facets has been a subject of interest in recent times. In this perspective, herein, we report the controlled synthesis of anatase TiO2 with different morphologies by an ecofriendly method. Samples of anatase TiO2 with various morphologies were prepared with sodium titanates and urea as the starting materials under a one-pot hydrothermal method. Their morphologies were simply controlled by varying the concentration of urea in the aqueous solutions. From the FESEM and TEM images, changes in the morphologies, such as the presence of rods, rhombohedral, square bi-pyramidal, and truncated square bi-pyramidal structures, were observed. The growth mechanism of different morphologies of TiO2 was established by considering the changes in the FTIR, Raman and TG-DTA patterns of the samples. These studies confirmed that the ammonium and carbonate ions formed during the hydrothermal conditions adsorbed on some crystal planes and hindered the growth of that plane, which resulted in TiO2 with various morphologies. The UV-Vis DRS of the prepared samples showed intense absorption with a band gap of 3.2 eV, which confirmed the optical properties of TiO2. The photocatalytic activity of the as-synthesized samples was tested through methylene blue degradation. Optimum activity was seen for the TiO2 with a truncated square bi-pyramidal morphology. The highly reactive exposed (001) facets of the truncated square bi-pyramidal morphology were responsible for the enhanced photocatalytic activit

Single-step hydrothermal synthesis of wrinkled graphene wrapped TiO2 nanotubes for photocatalytic hydrogen production and supercapacitor applications

Herein, we discuss the synthesis of reduced graphene oxide and TiO2 (rGO-TiO2) nanocomposites with varying ratios of rGO to TiO2 by hydrothermal method. Photocatalytic ability of the nanocomposites was assessed for H2 production under natural sunlight. At 5 wt% GO loading, the rGO-TiO2 exhibited 24,880 ??mol/g/h H2, 12.9 times to commercial P25-TiO2 (1920 ??mol/g/h). The symmetric supercapacitor device fabricated using rGO-TiO2 demonstrated 160 F/g specific capacitance with 99% retention. The efficient charge carrier separation and transportation between TiO2 nanotubes and rGO resulted high photocatalytic activity. The synergistic double layer pseudo capacitor behavior of rGO-TiO2 is the reason for improved specific capacitance

Hydrothermally synthesized Na2Ti3O7 nanotube-V2O5 heterostructures with improved visible photocatalytic degradation and hydrogen evolution - Its photocorrosion suppression

There is still a need to prepare heterostructure photocatalysts with high activity and recyclability but without using precious metals to reduce the cost of photocatalysts. Thus, a facile and simple method for the synthesis of a Na2Ti3O7 nanotube-V2O5 heterostructure photocatalyst via hydrothermal synthesis is reported herein. The chemical composition, morphology, and structural features of the photocatalyst were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N-2 adsorption-desorption specific surface area analysis (BET), and diffuse reflectance absorption (DRS) methods. It was observed that the specific surface area of the Na2Ti3O7 nanotube-V2O5 heterostructure photocatalyst increased with the incorporation of V2O5. The Na2Ti3O7 nanotube-V2O5 heterostructure photocatalyst was then used for the removal of rhodamine B (RhB) under simulated solar light irradiation. The Na2Ti3O7 nanotube-V2O5 heterostructure photocatalyst revealed excellent photocatalytic activity and photodegradation kinetics as compared to pristine Na2Ti3O7 nanotubes and V2O5 photocatalysts. Furthermore, both the photoactivity and long-term stability of the Na2Ti3O7 nanotube-V2O5 heterostructure photocatalyst were superior to those of the pristine Na2Ti3O7 nanotubes and V2O5 photocatalysts. The excellent photocatalytic performance of the Na2Ti3O7 nanotube-V2O5 heterostructure photocatalyst can be ascribed to its high specific surface area (283.71 m(2)g(-1)), mesoporous structure, highly dispersed V2O5 nanoparticles, and hindrance of electron-hole pair recombination of Na2Ti3O7 due to the V2O5 incorporation, which is proven by the photoelectrochemical results, including photocurrent and electron impendence spectroscopy results. In addition, during the study of photocatalytic hydrogen evolution, the hydrogen yield of the Na2Ti3O7/V2O5 nanocomposite was 1.83 times that of pristine Na2Ti3O7, which also exhibited excellent photocatalytic activity