Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention aspotentially efficient, environmentally friendly and low cost methods for water/air purification as well as forrenewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies havebeen found due to the fast recombination of the charge carriers. Development of heterostucture photocatalystsby depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable bandedge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw newprospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor(SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor(NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition,texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Ramanspectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, asuitable combination of UV–visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy(XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for eachsystem. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen.Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %)and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen.These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPSmeasurements along with their good textural and structural properties. This concept of semiconductingheterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future toremove undesirable organics from the environment and to produce renewable hydrogen.
Abstract The 4-NPHyd (4-nitrophenylhydrazine) electrochemical sensor assembled using wet-chemically prepared ZnO/SnO 2 nanoparticle (NPs) decorated a glassy carbon electrode (GCE) with conductive Nafion binder. The synthesized NPs characterized by XPS, ESEM, EDS, and XRD analysis. The calibration of the proposed sensor obtained from current versus concentration of 4-NPHyd found linear over a concentration (0.1nM~0.01mM) of 4-NPHyd, which denoted as the dynamic range (LDR) for detection of 4-NPHyd. The 4-NPHyd sensor sensitivity calculated using the LDR slope considering the active surface of GCE (0.0316 cm2), which is equal to be 7.6930 µAµM-1cm-2, an appreciable value. The detection limit (LOD) at signal/noise (S/N=3) estimated, and outstanding lower value at 94.63±4.73 pM perceived. The analytical parameters such as reproducibility, long-term performing ability and response time are found as appreciable. Finally, the projected sensor shows exceptional performances in the detection of 4-NPHyd in environmental samples.
In this study, activated carbon (AC) was prepared from peanut shell by activation with potassium hydroxide.The process parameters to prepare (AC) were optimized with respect to time, temperature and impregnation ration.The prepared AC was characterized by N 2 adsorptiondesorption isotherms Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy and scanning electron microscopy.The maximum BET surface area achieved was found to be 716 m 2 /g.The AC exhibited excellent adsorption performance to methylene blue (MB).The Langmuir isotherm model was fitted well to describe the equilibrium adsorption data and the maximum adsorption capacity was achieved to be 1,388 mg/g.The adsorption followed the pseudo-second-order kinetic model.The thermodynamic study showed that the MB adsorption onto AC was exothermic and spontaneous.Considering high adsorption capacity, AC derived from peanut shells can be used as a promising adsorbent for efficient treatment of textile wastewaters.
Nanoporous SnO2–ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO2 particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO2 particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption analyses, transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy. The SnO2–ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO2 nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV–visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO2–ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO2, that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO2–ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO2–ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO2 and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO2–ZnO photocatalyst because of the energy difference between the conduction band edges of SnO2 and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO2–ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.
The present study aims to prepare waste water caltrop (Trapanatans L.) epicarp (WCS)-based adsorbents such as raw WCS (WCS-Raw), citric acid-grafted WCS (WCS-CA), acrylamide-grafted WCS (WCS-AM), and calcined WCS (WCS–Si) for Ni(II) removal from aqueous solution in batch adsorption process. The physical and chemical properties of the prepared adsorbents were investigated by different characterization techniques such as scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, nitrogen adsorption-desorption analyses, and pH at the Point of Zero Charge (pHpzc) in order to assess the suitability and effectiveness of the adsorbents for the removal of Ni(II) by understanding their surface morphology, chemical composition, porosity, and surface charge properties. The experimental Ni(II) adsorption data followed both the Langmuir isotherm and the pseudo-second-order kinetic model suggesting the adsorption process on the prepared adsorbents is well-described by these models. The modified adsorbents WCS-CA, WCS-AM, and WCS-Si exhibited a maximum adsorption capacity of 52.08, 40.32, and 158.73 mg/g, respectively, while WCS-Raw had a capacity of 29.06 mg/g. The thermodynamic study revealed that the adsorption process was feasible, spontaneous, and endothermic. The desorption study demonstrated that the adsorbents could be reused for multiple cycles with minimal loss of activity. The present work evidenced the potential practical applicability and sustainability of the WCS -based adsorbents as promising adsorbents in treating and removing Ni(II) from wastewater.
Highly sensitive and selective uric acid sensor was fabricated using facile wet-chemically prepared ternary doped ZnO/Ag2O/Co3O4nanoparticles onto glassy carbon electrode by electrochemical approach, which introduced a prospective and reliable route to the future development of enzyme-free sensor by doped nanomaterials in broad scales.
Abstract This study deals with the analysis of Cure rate estimation based on Type 1 censoring. Here we consider both known and unknown form of survival function to estimate the cure parameter. Cure models have been proposed for cure rate estimation. We have tried to estimate the cure parameter by using Maximum Likelihood Estimation (MLE) and Non-Parametric Maximum Likelihood Estimation (NPMLE) method. The analysis showed that cute rate estimator is to be obtained from the analytic solution of the estimating equation when the survival function of the cure model is known. The analysis also showed that the cure rate estimator may be obtained from the numerical solution of the estimating equation when survival function is unknown.
Abstract This study deals with the analysis of estimation of cure rate. Mixture models have been proposed for cure rate estimation. In this paper we have tried to estimate the cure parameter by considering censored data specifically for Type 2 censoring from mixture model. We have used parametric Maximum likelihood estimation (PMLE) method and non parametric maximum likelihood (NPMLE) method to estimate the parameter. From the analysis we have found an explicit solution for the parameter of cure rate model based on Type 2 censoring for known distribution function. On the other hand when the distribution function are unknown, we have found a non-parametric estimating equations for on based on Type 2 censoring scheme.
