Synthesis of cadmium sulfide nanosheets for smart photocatalytic and sensing applications

Herein, we report the synthesis, characterizations, photocatalytic and sensing applications of ultra-wide cadmium sulfide (CdS) nanosheets. The CdS nanosheets were prepared by a simple solution process at low-temperature using cetyltrimethyl ammonium bromide (CTAB) as a stabilizing agent. The synthesized CdS nanosheets were characterized by several techniques which confirmed large-scale growth, well-crystallinity and hexagonal crystal phase of the prepared nanosheets. The synthesized nanosheets were used as effective photocatalyst for the photocatalytic degradation of harmful toxic dye, i.e. methyl orange. The photocatalytic activities were evaluated by measuring the photodegradation rate of MO in presence of CdS nanosheets under UV light irradiation. Interestingly, over 90% degradation of MO dye was achieved in 75 min using 0.15 g of photocatalyst, i.e. CdS nanosheets. Further, the synthesized nanosheets were used as efficient scaffold to fabricate highly sensitive, selective and reproducible fluorescent sensor for the detection of Picric Acid (PA). The observed detection of limit for the fabricated sensor was ~2.46 μM. Moreover, the interfering studies confirmed that the developed sensor possesses very good selectivity towards PA as it detect selectively even in the presence of several other coexisting aromatic compounds such as phenol, benzaldehyde, benzoic acid and aniline.     

Characterization and photocatalytic activity in aqueous medium of TiO2 and Ag-TiO2 coatings on quartz

In the present study, TiO₂ and Ag-TiO₂ catalysts have been supported in the form of thin layers by a dip-coating procedure on quartz substrate. The resulting materials have been characterized by SEM/EDX, XRD, XPS and UV-vis absorption spectroscopy. The immobilized catalysts were tested in the photocatalytic degradation of malic acid. For this reaction, the presence of metallic silver does not produce an intrinsic increase in photocatalytic activity in comparison with pure titania. The apparent increase observed in activity is principally due to the increase in the exposed surface due to the textural characteristics of the Ag-TiO₂ layer in comparison with TiO₂. In addition, the presence of metallic silver always produces an increase in activity in comparison with oxidized Ag⁺ ions. This can be explained by the increase in the electron-hole pair-separation efficiency induced by trapping of electrons by metallic silver.     

Nanostructured CeO2 microspheres synthesized by a novel surfactant-free emulsion

Nanostructured CeO₂ microspheres with an average diameter of 11 μm were prepared by a novel surfactant-free emulsion for the first time. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET) measurements were used to characterize the products. The images of SEM showed that the CeO₂ microspheres consisted of petal-like nanostructures with petal thickness in a range of 60 nm to 100 nm. The BET measurements showed the specific surface area of the CeO₂ microspheres exceeded 43 m²/g. The XRD analysis indicated the nanostructured CeO₂ microspheres were of cubic lattice. A possible mechanism of an interfacial precipitation reaction with the droplets of solid-stabilized emulsion as templates was proposed.     

Structural,photocatalytic, biological and catalytic properties of SnO2/TiO2 nanoparticles

TiO₂ and SnO₂/TiO₂ nanoparticles with different SnO₂ contents (0–20 wt%) were synthesized via surfactant-assisted sol-gel method using a cationic surfactant (cetyltrimethylammonium bromide, CTAB). The effects of SnO₂ content on the structural, optical, and catalytic activity of TiO₂ have been studied by X-ray diffraction (XRD), Transmission electron microscope (TEM), Scanning electron microscope (SEM), Fourier transformer infrared (FTIR) and UV–vis diffuse reflection spectroscopy (DRS). The total surface acidity of the prepared samples was measured by nonaqueous titration of n-butylamine in acetonitrile and the types of Brönsted and Lewis acid sites were distinguish using FTIR spectra of chemisorbed pyridine. XRD patterns analysis indicates that the crystallite size reduced remarkably and the transformation of anatase-to-rutile phase accelerated greatly with increasing the SnO₂ content. TEM images exhibit a spherical shape with an average particle size varying in the range 10–24 nm and high-resolution TEM images (HRTEM) show lattice fringes with interplanar spacing 0.35 nm and 0.32 nm which corresponding to anatase and rutile phases, respectively. SEM images show the amount of SnO₂ on the TiO₂ surface increases with increasing the SnO₂ content and the particles of SnO₂ were aggregated on TiO₂ surface with increasing SnO₂ content to 20% wt. The catalytic activity was tested by various applications: Photodegradation of Methylene Blue (MB) and Rhodamine B (RhB) under UV–vis irradiations and synthesis of xanthene (14-phenyl-14H-dibenzo [a,j] xanthene). Antibacterial and antioxidant activities were also studied. The antibacterial property test was carried out via agar disc diffusion method, and the results indicated that the prepared catalysts showed moderate antibacterial activity.     

Synthesis of porous CeO2-SnO2 nanosheets gas sensors with enhanced sensitivity

Two-dimension (2D) CeO₂-SnO₂ nanosheets with uniform size and small rhombus nanopores were synthesized by the hydrothermal method. The structure of CeO₂-SnO₂ nanosheets was confirmed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The gas sensing behaviors of the fabricated sensors were systematically investigated. Under optimum operating temperature (340 °C), the response to 100 ppm ethanol of the CeO₂-SnO₂ sensor was 44, which was 2 times larger than that of the SnO₂ sensor (about 19). The response and recovery time of the CeO₂-SnO₂ sensor were 25 s and 6 s, while that of the SnO₂ sensor were 29 s and 7 s, respectively. The results revealed that porous CeO₂-SnO₂ nanosheets enhanced the gas sensing properties and shortened the response/recovery time, which were attributed to the porous structure and the effect of the CeO₂-doping. In addition, the ethanol sensing mechanism was carefully discussed.     

Synthesis of Bi2O3/TiO2 nanostructured films for photocatalytic applications

Dendritic growth of bismuth oxide nanostructured films was accomplished by reactive magnetron sputtering. The deposition of the Bi₂O₃ template layers was adapted to abide a vapour-liquid-solid mechanism in order to develop a 3D growth morphology with high surface area templates for photocatalytic applications. TiO₂ photocatalytic thin films were deposited at a later stage onto Bi₂O₃ layers. The obtained heterostructured films were characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy. Additionally, the photocatalytic efficiency was assessed by conducting an assay using methylene blue dye as testing pollutant under a UV-A illumination. The photocatalytic tests revealed that the Bi₂O₃ layers functionalized with TiO₂ thin films are more efficient at degrading the pollutant, by a factor of 6, when compared with the individual layered films.     

Local structure and photocatalytic activity of B2O3–SiO2/TiO2 ternary mixed oxides prepared by sol–gel method

The local structure and the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides (SiO₂ content was fixed as 30 at.% with respect to TiO₂) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing Ti---O---Si with Si---O---B or Ti---O---B bonds. Also, paramagnetic species such as O⁻ and Ti³⁺ defects were formed by the boron incorporation. In SiO₂/TiO₂ mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B₂O₃–SiO₂/TiO₂ samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m² l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti³⁺ sites are responsible for the deterioration in the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase.     

Preparations and photocatalytic properties of magnetically separable nitrogen-doped TiO2 supported on nickel ferrite

A magnetically separable nitrogen-doped photocatalyst TiO_2−xN_x/SiO₂/NiFe₂O₄ (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO₂/NiFe₂O₄ (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO_2−xN_x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO₂/NiFe₂O₄ (SN) nanoparticles adhere to the surface of TiO_2−xN_x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO₂ coating round the surface of NiFe₂O₄ nanoparticles prevents effectively the injection of charges from TiO₂ particles to NiFe₂O₄, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity.     

CuO and CuO-ZnO catalysts supported on CeO2 and CeO2-LaO3 for low temperature water-gas shift reaction

This paper describes an investigation on CuO and CuO-ZnO catalysts supported on CeO₂ and CeO₂-La₂O₃ oxides, which were designed for the low temperature water-gas shift reaction (WGSR). Bulk catalysts were prepared by co-precipitation of metal nitrates and characterized by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), surface area (by the BET method), X-ray photoelectron spectroscopy (XPS), and in situ X-ray absorption near edge structure (XANES). The catalysts' activities were tested in the forward WGSR, and the CuO/CeO₂ catalyst presented the best catalytic performance. The reasons for this are twofold: (1) the presence of Zn inhibits the interaction between Cu and Ce ions, and (2) lanthanum oxide forms a solid solution with cerium oxide, which will cause a decrease in the surface area of the catalysts. Also the CuO/CeO₂ catalyst presented the highest Cu content on the surface, which could influence its catalytic behavior. Additionally, the Cu⁰ and Cu¹⁺ species could influence the catalytic activity via a reduction-oxidation mechanism, corroborating to the best catalytic performance of the Cu/Ce catalyst.     

The preparation,characterization and photocatalytic activity of radical-shaped CeO2/ZnO microstructures

This paper uses a wet-chemical precipitation route to prepare radical-shaped ZnO microprisms and to deposit Cerium oxide (CeO₂) on the surface of ZnO, to form CeO₂/ZnO microstructures. The samples are characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy. Their catalytic activity is also evaluated using methylene blue (MB) as a detection reagent. CeO₂/ZnO systems exhibit higher UV absorption and transparency in the visible region. The experimental results show that the deposition of CeO₂ nanospecies is successful and that the radical-shaped microstructures of ZnO are well maintained. The CeO₂/ZnO microstructures exhibit a much greater intensity of UV-light absorptivity and much higher photocatalytic activity than those of radical-shaped ZnO microprisms.     

Preparation of egg-shell type Al2O3-supported CdS photocatalysts for reduction of H2O to H2

Alumina-supported cadmium sulfide photocatalysts were prepared for the photocatalytic reduction of water to hydrogen using visible light. The activity depends on the nature of interaction between alumina and cadmium and also on the distribution of CdS on the support. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen desorption and temperature-programmed oxidation. The impregnation of alumina hydrogel with an ammoniacal solution results into a chemical interaction between cadmium sulfide and alumina and also yields a preferential distribution of cadmium sulfide on the surface which give a better activity to the photocatalyst. The possible role of ammonia in causing the solute segregation to the surface during the drying stage of the catalyst preparation has been explained.     

Visible light induced photocatalytic activity of Nb2O5/carbon cluster/Cr2O3 composite materials

Nano-sized Nb₂O₅/carbon cluster/Cr₂O₃ composite material was prepared by the calcination of NbCl₅/chromium acetylacetonate/epoxy resin complex under an argon atmosphere. The Pt-loaded Nb₂O₅/carbon cluster/Cr₂O₃ composite material shows the photocatalytic activity under visible light irradiation. The composite material successfully decomposed the water into H₂ and O₂ in the [H₂]/[O₂] ratio of 2. Electron spin resonance spectral examination suggests a two-step electron transfer in the process of Nb₂O₅ → carbon cluster → Cr₂O₃ → Pt.     

Synthesis and electrochemiluminescence of the CeO2/TiO2 composite

CeO₂/TiO₂ composite with kernel–shell structure was synthesized by a sol–gel process. The characterization results show that the composite is made up of anatase phase TiO₂ and cubic system CeO₂. The electrochemiluminescence (ECL) behavior of the CeO₂/TiO₂ composite was studied by a cyclic voltammetry in the presence of persulfate, and the effect factors on ECL emission were discussed. Based on a series of experiments, it is proposed that the strong dual ECL emission produced by the CeO₂/TiO₂ composite resulted from the benefit ECL effect of interface heterojunction in composite.     

Synthesis, characterization and photocatalytic activity of N-doped TiO2 modified by platinum chloride

Structures and photocatalytic performance of N-doped TiO₂ modified by platinum chloride (PtCl_x/N-TiO₂) was investigated. It was found that the PtCl_x/N-TiO₂ forms anatase structure of TiO₂ involving nitrogen, chloride species and platinum ions (+IV) as major species, and it exhibits higher photocatalytic activity than either N-TiO₂ or PtCl_x/TiO₂ for the decomposition of acetic acid or acetaldehyde in aqueous solutions under visible light irradiation (λ > 420 nm). An enhancement of the photocatalytic activity on PtCl_x/N-TiO₂ has been proposed as a Z-scheme mechanism for charge separation between platinum chloride and N-TiO₂.     

Characterization of self-standing Ti-containing porous silica thin films and their reactivity for the photocatalytic reduction of CO2 with H2O

Self-standing porous silica thin films with different pore structures were synthesized by a solvent evaporation method and used as photocatalysts for the photocatalytic reduction of CO₂ with H₂O at 323 K. UV irradiation of these Ti-containing porous silica thin films in the presence of CO₂ and H₂O led to the formation of CH₄ and CH₃OH as well as CO and O₂ as minor products. Such thin films having hexagonal pore structure exhibited higher photocatalytic reactivity than the Ti-MCM-41 powder catalyst even with the same pore structure. From FTIR investigations, it was found that these Ti-containing porous silica thin films had different concentrations of surface OH groups and showed different adsorption properties for the H₂O molecules toward the catalyst surface. Furthermore, the concentration of the surface OH groups was found to play a role in the selectivity for the formation of CH₃OH.     

Reaction of carboxylic acids on CeO2(111) and CeO2(100)

The reactions of HCOOH and CH₃COOH on CeO₂(111) and CeO₂(100) were studied using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The carboxylic acids were found to dissociate on both surfaces to form carboxylates. Adsorbed formates and acetates decomposed near 600 K to produce primarily the dehydration products CO and CH₂CO, respectively. This result is consistent with previous studies which have indicated that the ease of reduction of the oxide is the primary factor in determining the selectivity for dehydration versus dehydrogenation during carboxylate decomposition. In addition to CO and CO₂, small amounts of formaldehyde were produced during formate decomposition on both CeO₂(111) and CeO₂(100). In contrast, acetone was observed as a product during acetate decomposition only on the CeO₂(111) surface.     

Role of CeO2 in Ni/CeO2–Al2O3 catalysts for carbon dioxide reforming of methane

Ni catalysts supported on γ-Al₂O₃, CeO₂ and CeO₂–Al₂O₃ systems were tested for catalytic CO₂ reforming of methane into synthesis gas. Ni/CeO₂–Al₂O₃ catalysts showed much better catalytic performance than either CeO₂- or γ-Al₂O₃-supported Ni catalysts. CeO₂ as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO₂ had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al₂O₃ catalysts for this reaction. A weight loading of 1–5 wt% CeO₂ was found to be the optimum. Ni catalysts with CeO₂ promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO₂-promoted catalysts are attributed to the oxidative properties of CeO₂.     

Preparation and photocatalytic activity of Keggin-ion tungstate and TiO2 hybrid layer-by-layer film composites

Keggin ions (PW₁₂O₄₀³⁻ (PW₁₂), SiW₁₂O₄₀⁴⁻ (SiW₁₂), H₂W₁₂O₄₀⁶⁻ (H₂W₁₂)) and TiO₂ hybrid thin films were prepared using the layer-by-layer method. Their photocatalytic activities were investigated using gaseous 2-propanol decomposition. All films were transparent in the visible wavelength range. For 2-propanol decomposition, H₂W₁₂ was the most effective for the combination with TiO₂ despite having the smallest TiO₂ deposition amount. The photocatalytic activity of the PW₁₂–TiO₂ hybrid film was increased 2.3 times by visible light with UV illumination. This increase was less remarkable for hybrid films of other Keggin ions, suggesting that the visible light excitation of reduced PW₁₂ plays an important role in the enhancement of 2-propanol decomposition.     

Microporous high-surface area layered CeO2

A simple procedure for the obtaining of microporous high-surface area layered ceria is described. The synthesis consists of the formation of cerium hydroxide by precipitation of cerium (III) chloride with ammonium carbonate followed by a calcination step. The samples obtained were calcined at temperatures from 150 °C to 350 °C. The effects of calcination temperature on the crystalline phase, particle size, anisotropy, surface area and the textural, morphological and reducibility properties have been studied by powder X-ray diffraction, BET, scanning electron microscopy and temperature-programmed reduction techniques. The anisotropic effects on the particle growth were studied by means of a Williamson–Hall plot.