SnO2 Composite Films for Enhanced Photocatalytic Activities

Synthesis and preparation of acid capped CdSe nanocrystals as successful adsorbent and photocatalyst for the removal of dyes from water and its statistical physics analysis

In this study, mercaptosuccinic acid capped CdSe nanocrystals were successfully synthesized and used as photocatalyst for the effective removal of methylene blue (MB) inaqueous solution under visible light and sunlight irradiations including its analysis with statistical physics theory. Dye adsorption properties of these nanocrystals were investigated via experimental kinetics and equilibrium studies. These experimental data were modeled via the application of statistical physics theory to explain the corresponding adsorption mechanism and to characterize the steric and energetic parameters involved in the dye removal. A maximum adsorption capacity of 27.07 mg g^-1 (80% of dye removal) was observed in 10 min using an initial concentration of 30 mg L^-1. Statistical physics calculations indicated that the adsorption energy was lower than 40 kJ mol^-1. It was also established that the dye adsorption was associated to the electrostatic interactions and hydrogen bonding where dye aggregation and multi-molecular adsorption were expected. Overall, the dye removal was a spontaneous, feasible and exothermic. It was concluded that adsorption properties of CdSe-MSA nanocrystals improved the dye photo-catalytic degradation efficiency under visible light thus achieving up to 80% degradation efficiency in 60 min. The synergic effect of adsorption and photo-catalytic degradation performance was mainly due to the surface area (136.43 m² g^-1), small size (3.7 nm), and structural defects (selenium vacancies S_e, interstitial of cadmium I_Cd) of CdSe nanocrystals, which enhanced both the response of these nanomaterials to visible light and their photo-catalytic activity. In summary, these nanocrystals are promising materials to be used in wastewater treatment under sunlight for the removal of organic compounds like dyes.

Synthesis and characterization of pristine and strontium-doped zinc oxide nanoparticles for methyl green photo-degradation application

Herein we describe an effective route for the degradation of methyl green (MG) dye under visible light illumination by pristine and strontium (Sr)-doped zinc oxide (ZnO) photocatalysts (synthesized by the simple chemical precipitation method). The x-ray diffraction structural analysis has confirmed that both photocatalysts exhibit the hexagonal wurtzite structure; without any additional phase formation in Sr-doped ZnO, in particular. The optical properties of the synthesized photocatalysts have been investigated using UV-vis absorption spectroscopy in the wavelength range of 250-800 nm. Through Tauc's plot, the slight decrease from 3.3 to 3.2 eV in band gap energy has been elucidated (in the case of Sr-doped ZnO), which has been further confirmed by the quenching in the intensity of Photoluminescence (PL) emission spectrum. This may be due to sub-band level formation between valence and conduction band, caused by the impregnation of Sr²⁺ions into ZnO host. The morphological study has also been performed using Field Emission Scanning Electron Microscope, which indicates nanoparticles (NPs) based surface texture for both photocatalysts. During the photocatalytic activity study, after 30 min irradiation of visible light, ∼65.7% and ∼84.8% photocatalytic degradation of MG dye has been achieved for pristine and Sr-doped (2 wt%) ZnO photocatalysts, respectively. The rate of photocatalytic reaction (K) has been observed to be ∼0.06399 min^-1for Sr-doped (2 wt%), whereas nearly half magnitude ∼0.03403 min^-1has been observed for pristine ZnO, respectively. The significantly improved photodegradation activity may be ascribed to the relatively broader optical absorption capability, surface defects and the enhanced charge separation efficiency of the Sr-doped ZnO photocatalyst.

The Influence of Synthesis Methods and Experimental Conditions on the Photocatalytic Properties of SnO2: A Review

Semiconductors based on transition metal oxides represent an important class of materials used in emerging technologies. For this, the performance of these materials strongly depends on the size and morphology of particles, surface charge characteristics, and the presence of bulk and surface defects that are influenced by the synthesis method and the experimental conditions the materials are prepared. In this context, the present review aims to report the importance of choosing the synthesis methods and experimental conditions to modify structural, morphological, and electronic characteristics of semiconductors, more specifically, tin oxide (SnO2), since these parameters may be a determinant for better performance in various applications, including photocatalysis. SnO2 is an n-type semiconductor with a band gap between 3.6 and 4.0 eV, whose intrinsic characteristics are responsible for its electrical conductivity, good optical characteristics, high thermal stability, and other qualities. Such characteristics have provided excellent results in advanced oxidative processes, i.e., heterogeneous photocatalysis applications. This process involves semiconductors in the production of hydroxyl radicals via activation by light absorption, and it is considered as an emerging and promising technology for domestic-industrial wastewater treatment. In our review article, we focused on the photodegradation of different organic dyes and types of persistent organic pollutants using SnO2-based photocatalysts, and how the efficiency of these materials can be impacted by synthesis methods and experimental conditions employed to prepare them.

Facile Synthesis of Tin Dioxide Nanoparticles for Photocatalytic Degradation of Congo Red Dye in Aqueous Solution

This research work reports an approach used to prepare a SnO2 photocatalyst by precipitation and calcination pathways and describes an investigation of the effects of preparation parameters on SnO2 yield. The SnO2 photocatalyst was further used for the photocatalytic degradation of Congo red (CR) dye, and the removal efficiency was optimized using response surface methodology. The results indicate that the SnO2 photocatalyst yield was the highest in 0.05 M of the precursor, stannous chloride and 28 wt % ammonia as the precipitant, pH 10, at 30 °C. The transmission electron microscopy results of the SnO2 photocatalyst illustrate that the average particle size was mainly around 30–50 nm and had a solid spherical shape. The X-ray diffraction results reveal that the prepared sample had a highly crystalline SnO2 rutile crystal structure. The prediction and experimental results of the Response surface methodology (RSM) indicate that, when the reaction time was 97 min, the operating temperature was 47 °C, the photocatalyst dosage was 751 mg/L, and the optimal degradation rate of the CR dye was 100%. After five consecutive photodegradation reactions, the degradation rate remained at 100%. The results demonstrated that the SnO2 photocatalyst prepared in this study possesses excellent reusability.

Microwave-assisted rapid degradation of DDT using nanohybrids of PANI with SnO2 derived from Psidium Guajava extract

The present work reports microwave-assisted synthesis of SnO₂ nanoparticles via green route using Psidium Guajava extract. For the enhancement of catalytic activity, nanohybrids of SnO₂ were formulated using different ratios of polyaniline (PANI) via ultrasound-assisted chemical polymerization. Formation of nanohybrids was confirmed via IR and XPS studies. The UV-vis DRS spectra of PANI/SnO₂ revealed significant reduction in the optical band gap upon nanohybrid formation. Microwave-assisted catalytic efficiency of pure SnO₂, PANI, PANI/SnO₂ nanohybrids was investigated using DDT as a model persistent organic pollutant. The degradation efficiency of PANI/SnO₂ was found to increase with the increase in the loading of PANI. Around 87% of DDT degradation was achieved within a very short period of 12 min under microwave irradiation using PANI/SnO₂-50/50 as catalyst. The effect of DDT concentration was explored and the degradation efficiency of PANI/SnO₂-50/50 catalyst was noticed to be as high as 82% in presence of 100 mg/L of DDT. The effect of microwave power on the degradation efficiency revealed 79% degradation using the same nanohybrid when exposed to microwave irradiation for 5 min under 1110 W microwave power. Scavenging studies confirmed the generation of OH, O₂^- radicals. The fragments with m/z values as low as 86 and 70 were confirmed by LCMS analysis. Recyclability tests showed that PANI/SnO₂-50/50 nanohybrid exhibited 81% degradation of DDT (500 mg/L) even after the third cycle, which reflected high catalytic efficiency as well as remarkable stability of the catalyst. This green nanohybrid could therefore be effectively utilized for the rapid degradation of persistent organic pollutants.

Eco-friendly Synthesis of CRGO and CRGO/SnO2 Nanocomposite for Photocatalytic Degradation of Methylene Green Dye

Reduced graphene oxide (rGO) was synthesized from a simple, cost-effective, and eco-friendly method by using Capsicum annuum (CA) as reducing agent. The rGO was mixed with SnO₂ to synthesize a nanocomposite. The synthesized materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and UV-visible spectroscopy techniques. The SnO₂-C. annuum reduced graphene oxide (CRGO) nanocomposite exhibited a photodegradation efficiency of 97.4% when employed to remove methylene green (MG) dye. The synthesized nanocomposite showed improved photodegradation ability due to its high charge transfer and separation and owing to the presence of the large surface area of the CRGO network system. Degraded water was used in the plant and animal survival study, in which the dye solution treated with CRGO nanocomposite exhibited better growth compared to that of untreated MG solution. Likewise, in the ecotoxicity study, Artemia salina and zebra fish (Danio rerio) survival was found to be enhanced with CRGO nanocomposite-treated dye solution. This finding supports the effectiveness of CRGO/SnO₂ nanocomposite for the treatment of MG dye-contaminated effluent samples.

Tridoped TiO2 Composite Films for Improved Photocatalytic Activities

The Fe/B/F tridoped TiO2-ZnO composite films attached to glass substrates were prepared via a simple sol–gel method. We appraised all samples’ photocatalytic activities by the degradation of methyl green and formaldehyde solutions. The samples were characterized by photoluminescence (PL) spectra, UV-Vis diffraction reflectance absorption spectra (DRS), X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy (EDS), and Brunner–Emmet–Teller (BET) measurements. According to the results of DRS and PL spectroscopy, the multi-modification could not only enhance visible light absorption intensity, but also decrease the recombination rate of photo-generated electron-hole pairs. XRD results revealed that the sample was mainly in anatase crystal type. FE-SEM results shown that the sample had fewer particle aggregates and almost no cracks. The specific surface area of the Fe/B/F tridoped TiO2-ZnO was 104.9 m2·g−1, while that of the pure TiO2 was 84.0 m2·g−1. Compared to pure TiO2 and TiO2-ZnO, the Fe/B/F tridoped TiO2-ZnO composite film had the highest photocatalytic activity due to their synergies.

Synthesis of SnO2, Zn-doped SnO2 and Zn2SnO4 nanostructure-based hierarchical architectures by using deep eutectic precursors and their photocatalytic application

Synthesis of Zn containing SnO₂ nanostructure-based hierarchical architectures by using deep eutectic precursors and their application for methyl orange degradation.