Synthesis and Characterization of N-Doped Porous TiO₂ Hollow Spheres and Their Photocatalytic and Optical Properties

The effect of cetyltrimethylammonium bromide (CTAB) addition on green synthesis of porous N-doped TiO2 for photoreduction of heavy metal ion Cr(vi)

In this study, porous TiO2 photocatalysts modified by nitrogen (NCT) were successfully synthesized using a combination of green synthesis methods by utilizing Aloe vera (L.) Burm. f. peel and hydrothermal method. In addition, TiO2 was modified by increasing the active surface area using Cetyltrimethylammonium Bromide (CTAB). The X-ray Diffraction (XRD) results indicated that the anatase phase was formed. The result of the Diffuse Reflectance Spectroscopy UV-Vis (DRS UV-Vis) using the Tauc-plot method showed that all porous N-doped TiO2 samples experienced a decrease in the energy gap. This indicates the successful modification of TiO2 by nitrogen, as confirmed by the Fourier Transform Infra-Red (FTIR) result. Field Emission Scanning Electron Microscopy (FESEM) result showed that the synthesized TiO2 had a spherical morphology of 10-30 nm diameter. The Braunauer, Emmett, and Teller (BET) result indicated that the type IV isotherm curve with a mesoporous structure was formed. The NCT0.75 sample had a surface area and pore size of 95.02 m2 g-1 and 8.021 nm, respectively, while the NTi0.75 sample had a surface area and pore size of 90.97 m2 g-1 and 5.161 nm, respectively. The photocatalytic activity of the porous N-doped TiO2 was tested on photoreduction of metal pollutant model Cr(vi). The result demonstrated that the NCT0.75 sample had the most optimal photocatalytic activity by reducing 89.42% of Cr(vi) metal ions.

Hierarchically ordered macroporous TiO2 architecture via self-assembled strategy for environmental remediation

Hierarchical orderd macroporous TiO₂ architecture (HOMTA) was prepared with aid of ethylenediamine (EDA) and investigated the impact of amine molecules on the properties of TiO₂ architecture. The different variation of amine molecules (EDA) leads to tunning the morphology under hydrothermal approach which is confirmed by FESEM and TEM analysis. The XRD and Raman studies confirms the crystal structure of anatase and brookite phase of TiO₂. The surface of the architecture strongly depended on the concentration of EDA which plays a vital role in surface area which is revealed by Brunauer Emmett-Teller (BET) analysis. The obtained HOMTA was employed as photocatalyst and active photoanode in the dye sensitized solar cells (DSSC). The DSSC device exhibits excellent efficiency (η) of 5.27% for the EDA capped TiO₂ (S5) which had high surface area (167.11 m²/g) for better dye loading, whereas the lower concentration of EDA capped TiO₂ (S1, S2, S3 and S4) resulted the efficiency of 2.14, 3.90, 3.25 and 4.37%, respectively. The efficiency of photocatlysis degradation of the prepared samples (S1, S2, S3, S4 and S5) was 94.8, 90.47, 91.41, 91.32 and 93.75% under light source. The excellent photocatalysis property was achieved by S5 within 6 min due to high surface area which inducing more active site.

N-Doped Yellow TiO2 Hollow Sphere-Mediated Visible-Light-Driven Efficient Esterification of Alcohol and N-Hydroxyimides to Active Esters

Herein we report a simple synthetic protocol for N-doped yellow TiO₂ (N-TiO₂ ) hollow spheres as an efficient visible-light-active photocatalyst using aqueous titanium peroxocarbonate complex (TPCC) solution as precursor and NH₄ OH. In the developed strategy, the ammonium ion of TPCC and NH₄ OH acts as nitrogen source and structure-directing agent. The synthesized N-TiO₂ hollow spheres are capable of promoting the synthesis of active esters of N-hydroxyimide and alcohol through simultaneous selective oxidation of alcohol to aldehyde followed by cross-dehydrogenative coupling (CDC) under ambient conditions upon irradiation of visible light. It is possible to develop a novel and cost-effective one-pot strategy for the synthesis of important esters and amides on gram scale using the developed strategy. The catalytic activity of N-TiO₂ hollow spheres is much superior to that of other reported N-TiO₂ samples as well as TiO₂ with varying morphology.

Carbon Wrapped Ni₃S₂ Nanocrystals Anchored on Graphene Sheets as Anode Materials for Lithium-Ion Battery and the Study on Their Capacity Evolution

Ni₃S₂ nanocrystals wrapped by thin carbon layer and anchored on the sheets of reduced graphene oxide (Ni₃S₂@C/RGO) have been synthesized by a spray-coagulation assisted hydrothermal method and combined with a calcination process. Cellulose, dissolved in Thiourea/NaOH aqueous solution is chosen as carbon sources and mixed with graphene oxide via a spray-coagulation method using graphene suspension as coagulation bath. The resulted cellulose/graphene suspension is utilized as solvent for dissolving of Ni(NO₃)₂ and then used as raw materials for hydrothermal preparation of the Ni₃S₂@C/RGO composites. The structure of the composites has been investigated and their electrochemical properties are evaluated as anode material for lithium-ion batteries. The Ni₃S₂@C/RGO sample exhibits increasing reversible capacities upon cycles and shows a superior rate performance as well. Such kinds of promising performance have been ascribed to the wrapping effect of carbon layer which confines the dislocation of the polycrystals formed upon cycles and the enhanced conductivity as the integration of RGO conductive substrate. Discharge capacities up to 850 and 630 mAh·g⁻¹ at current densities of 200 and 5000 mA·g⁻¹, respectively, are obtained. The evolution of electrochemical performance of the composites with structure variation of the encapsulated Ni₃S₂ nanocrystals has been revealed by ex-situ TEM and XRD measurements.

Spray-Drying-Induced Assembly of Skeleton-Structured SnO2/Graphene Composite Spheres as Superior Anode Materials for High-Performance Lithium-Ion Batteries

Three-dimensional skeleton-structured assemblies of graphene sheets decorated with SnO₂ nanocrystals are fabricated via a facile and large-scalable spray-drying-induced assembly process with commercial graphene oxide and SnO₂ sol as precursors. The influences of different parameters on the morphology, composition, structure, and electrochemical performances of the skeleton-structured SnO₂/graphene composite spheres are studied by XRD, TGA, SEM, TEM, Raman spectroscopy, and N₂ adsorption-desorption techniques. Electrochemical properties of the composite spheres as the anode electrode for lithium-ion batteries are evaluated. After 120 cycles under a current density of 100 mA g^-1, the skeleton-structured SnO₂/graphene spheres still display a specific discharge capacity of 1140 mAh g^-1. It is roughly 9.5 times larger than that of bare SnO₂ clusters. It could still retain a stable specific capacity of 775 mAh g^-1 after 50 cycles under a high current density of 2000 mA g^-1, exhibiting extraordinary rate ability. The superconductivity of the graphene skeleton provides the pathway for electron transportation. The large pore volume deduced from the skeleton structure of the SnO₂/graphene composite spheres increases the penetration of electrolyte and the diffusion of lithium ions and also significantly enhances the structural integrity by acting as a mechanical buffer.