Hierarchical ZnO/Ag nanocomposites for plasmon-enhanced visible-light photocatalytic performance

Surface plasmon resonance (SPR) of the noble metals improve the photocatalytic activity of semiconductor metal oxides in the visible light region. This work reports the facile preparation of SPR induced visible light active hierarchical ZnO/Ag nanocomposite photocatalysts by using environmental friendly two-step method. The prepared nanocomposites analyzed by using various techniques such as powder-XRD, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, photoluminescence spectroscopy, and photocurrent measurements. The results indicate the formation of hierarchical ZnO/Ag nanocomposites, which shows surface plasmon absorbance and enhanced photocurrent responses. Because of the SPR effect, the nanocomposites show improved visible light photocatalytic activity by enhancing the electron-hole pair separation in Rhodamine B degradation system.     

Preparation of WO3-reduced graphene oxide nanocomposites with enhanced photocatalytic property

In this work, WO₃-reduced graphene oxide (RGO) nanocomposite was synthesized via a simple one-pot hydrothermal method. The synthesized nanocomposite was characterized by SEM, XRD, EDX, UV–vis spectroscopy, N₂ adsorption/desorption, photocurrent response, electrochemical impedance spectroscopy and Raman spectroscopy. The superior contact between WO₃ and RGO sheets in the nanocomposite facilitates the photocatalytic degradation of methylene blue and evolution of oxygen. The cause of the enhanced photocatalytic performance could ascribe to the highly facilitated electron transport by the synergistic effect between WO₃ and RGO sheets, as well as suppressing the electron hole pair recombination in the nanocomposite.     

Carbon-based TiO2-x heterostructure nanocomposites for enhanced photocatalytic degradation of dye molecules

Application of brown titanium dioxide (TiO_2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO_2-x nanoparticles with g-C₃N₄, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO_2-x nanocomposite with high rate constants of 0.075 min^?1_, 0.083 min^?1 and 0.093 min^?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO_2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e^?)/hole (h⁺) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO_2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO_2-x is carried out.     

Pulsed laser ablation in liquid synthesis of ZnO/TiO2 nanocomposite catalyst with enhanced photovoltaic and photocatalytic performance

In this work, we employed an impurity-free nanoparticle synthesis technique, known as pulsed laser ablation in liquid (PLAL), to integrate titanium dioxide nanoparticles (TiO₂ NPs) into zinc oxide nanorods (ZnO NRs) with varying relative proportions. The main objective of this integration was to enhance the charge carrier separation of photo-generated electron hole pairs during solar irradiation. For the synthesis process, an Nd:YAG laser at 532 nm wavelength was applied as an ablation source, along with deionized water as a solvent medium in which the precursor materials were dispersed prior to laser irradiation. The nanocomposites were characterized by X-ray diffraction (XRD), UV–vis absorption and in-situ Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM). The synthesized nanocomposites were primarily utilised in two applications: firstly, as a catalyst in the degradation of methyl orange (MO) and secondly, as photo-anode in dye sensitized solar cell (DSSC). Our research has demonstrated that optimal performance was obtained for the nanocomposite containing 10% and 90% (by weight) TiO₂ NPs and ZnO respectively, which we define as the ideal nanocomposite. Relative to pure ZnO, the photo-conversion efficiency of the ideal composite was improved substantially by 63.73%, whilst the photo-degradation rate was enhanced by 3 fold. The oxidation state and the microstructural of the segregated ideal nanocomposite confirms that oxygen vacancy defects were created when perfect surface integration occurs between TiO₂ and ZnO. Nonetheless, we believe that the performance enhancement is predominantly due to the excellent charge carrier separation and fast interfacial electron flow in this nanocomposite.     

Fabrication and characterization of CdS/BiVO4 nanocomposites with efficient visible light driven photocatalytic activities

Novel CdS/BiVO₄ nanocomposites were synthesized by simple solvothermal method. The as-prepared samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman spectroscopy, UV–vis diffuse reflectance spectra (DRS), Fourier transform infrared spectra (FT-IR) and photoluminescence (PL). In the nanocomposites, CdS particles were deposited on the surface of the BiVO₄. The photocatalytic tests showed that the CdS/BiVO₄ nanocomposites possessed a higher rate for degradation of malachite green (MG) than the pure BiVO₄ under visible light irradiation. The 1.5-CdS/BiVO₄ nanocomposite photocatalyst was found to degrade 98.3% of MG under visible light irradiation. Moreover, the photocatalytic mechanism of CdS/BiVO₄ nanocomposites was also discussed. The results showed that the nanocomposite construction between CdS and BiVO₄ played a very important role in their photocatalytic properties, which has the potential application in solving environmental pollution issues utilizing solar energy effectively.     

Visible light induced methylene blue dye degradation photo-catalyzed by WO3/graphene nanocomposites and the mechanism

Graphene incorporated WO₃ nanocomposites with different graphene contents were synthesized in the present study using the hydrothermal approach. The results showed nano-structured WO₃ sticks were uniformly dispersed within the graphene sheets. The incorporation of the graphene significantly decreased the band gap energy of the pristine WO₃. Due to this reason, the prepared WO₃/Graphene nanocomposites had much higher photodegradation efficiency to the methylene blue dye than the pristine WO₃. More importantly, it was found that the prepared nanocomposites could initiate dye degradation with a very desirable efficiency under visible light, and the methylene blue molecules could be converted to some small molecules during this process. This study provides an effective photocatalyst which can initiate dyestuff degradation in the wastewater under visible light.     

Direct microwave synthesis of graphitic C3N4 with improved visible-light photocatalytic activity

The graphitic carbon nitride (g-C₃N₄) was rapidly synthesized via direct high-energy microwave heating approach. During the preparation process, only low-cost melamine and artificial graphite powders were used, without any metal catalysts or inert protective gas. The microstructure was investigated by using X-ray diffraction (XRD), Flourier transformed infrared (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). The spectra of XRD and HRTEM indicated that the obtained g-C₃N₄ had a high crystallinity. The optical spectra covering Photoluminescence (PL) and Ultraviolet-visible (UV–vis) were also measured at room temperature. PL peak and UV–vis absorption edge of the g-C₃N₄ were shown at 455 nm and 469 nm, respectively, indicating visible-light photocatalytic property. Finally, the photocatalytic activity of g-C₃N₄ was investigated and evaluated as photocatalyst for the photo-degradation of Rhodamine B (RhB) and Methyl Orange (MO) in aqueous solution under visible-light (λ>420 nm) irradiation, respectively. Results indicated that the g-C₃N₄ sample displayed an excellent performance of removing of RhB and MO due to the improved crystallinity and large surface area of 126 m²/g. After the visible-light photocatalytic reaction for 40 min, the decolorization ratios of RhB and MO reached up to 100% and 94.2%, respectively.     

Novel photocatalytic performance of magnetically recoverable MnFe2O4/BiVO4 for polluted antibiotics degradation

In the study, we successfully decorated MnFe₂O₄ on BiVO₄ to highly improve its photocatalytic activity for degradation of tetracycline as well as its magnetically recovery. The decoration of MnFe₂O₄ on BiVO₄ led to formation of MnFe₂O₄/BiVO₄ Z scheme heterojunction to effectively prevent the charge recombination in each material. Upon visible light, the MnFe₂O₄/BiVO₄ heterojunction produced significant available amounts of e^? and h⁺ existing in the conduction band of the MnFe₂O₄ and the valence band of the BiVO₄, respectively. These produced e^? on the conduction band of the MnFe₂O₄, which reduction potential was approximately ?0.41 eV, exhibited strong reduction potential reducing oxygen to produce ^?O_2^? radicals while h⁺ on the valence band of the BiVO₄, which oxidation potential was 2.77 eV, showed strong oxidation potential oxidizing water and hydroxyl groups to produce ^?OH radicals. These generated active oxygen radicals effectively degraded TC in water (~92%). The used photocatalysts were easily recovered from photocatalytic suspension using an external magnet due to high magnetically activity of the MnFe₂O₄, which tightly bonded with BiVO₄ in the MnFe₂O₄/BiVO₄ heterojunction. Finally, the recovered MnFe₂O₄/BiVO₄ heterojunction was very active and stable for tetracycline degradation in long-term process.     

Combination of sonochemical and freeze-drying methods for synthesis of graphene/Ag-doped TiO2 nanocomposite: A strategy to boost the photocatalytic performance via well distribution of nanoparticles between graphene sheets

Preparation of visible-light active photocatalysts for efficient degradation of pollutants from the industrial wastewater has received considerable attention in recent decades. The present study introduces a new sonochemical route for the preparation of graphene/TiO₂/Ag nanocomposite for visible-light photocatalytic degradation of X6G (C.I. Reactive Yellow 2), a commonly used textile azo-dye. The obtained graphene/TiO₂/Ag nanocomposite is extracted from the reaction solution by two drying methods: (1) conventional centrifuging and drying, and (2) freeze drying. Both of the dried samples are calcinated at 500 °C. The TEM images reveal that distribution of TiO₂/Ag nanoparticles within the graphene sheets in the freeze dried nanocomposite is better than the conventional dried sample. Furthermore, the freeze dried nanocomposite has higher photocatalytic activity than the other nanocomposite. In conventional centrifuging and drying method, some of the TiO₂/Ag nanoparticles are gradually pushed out from the graphene sheets during the drying process and graphene layers are stacked, therefore the dispersion effect of sonication is destroyed. However, in the freeze dried nanocomposite, because of the fast freezing of the sonicated sample by liquid N₂, the TiO₂/Ag nanoparticles are kept between the graphene sheets and calcination process attached and fixed them to the graphene, preserving the dispersion effect of sonication.     

Solvothermal synthesis of porous MnCo2O4.5 spindle-like microstructures as high-performance electrode materials for supercapacitors

This study presents the facile preparation of novel MnCo₂O_4.5 microspindles (MSs) for the first time through a rapid solvothermal method combined with subsequent calcination of the precursor at 450 °C for 4 h in air. The MnCo₂O_4.5 MSs have an average length of 4–5 µm and diameter of 2–4 µm, respectively, achieving a specific surface area as high as 83.3 m² g⁻¹. In addition, the size and morphology of the MnCo₂O_4.5 microstructures could be easily tuned by some parameters including reaction time, volume ratio of ethanol to water, and dosage of urea. The electrochemical performance was further evaluated in three-electrode system, detailed electrochemical characterizations revealed that such MnCo₂O_4.5 MSs exhibited both high specific capacitance of 343 F g⁻¹ at a current density of 0.5 A g⁻¹ and excellent cycling performance of 81.3% capacitance retention after 5000 cycles at a current density of 4 A g⁻¹ in 2 M of KOH electrolyte, which made it a potential electrode material for an advanced supercapacitor. Furthermore, the present synthetic method is simple and can be extended to the synthesis of other electrode materials based on transition metal oxides.     

Insight into the adsorption and photocatalytic properties of in-situ synthesized g-C3N4/SnS2 nanocomposite

In this paper, a novel g-C₃N₄/2 wt% SnS₂ nanocomposite was successfully synthesized using an in-situ growth of SnS₂ on g-C₃N₄. X-ray diffraction (XRD), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET) method, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectrometer were used to characterize the photocatalysts. Exploring adsorption behavior, as an importatnt stage during photocatalytic reactions, is of great importance. Hence, both adsorption and photocatalytic performance of the synthesized photocatalysts have been investigated in detail. The adsorption isotherm fittings exhibited that Freundlich and Langmuir-Freundlich models can be applied to the methylene blue (MB) adsorption on the photocatalysts, indicating surface heterogeneity should be considered. A pseudo-second-order model was fitted to explore the adsorption kinetics. According to the observed redshift in the Fourier transform infrared spectroscopy (FTIR) result of g-C₃N₄/SnS₂ nanocomposite, π-π interaction was dominant during MB adsorption. Also, a slight redshift and significant PL intensity reduction in g-C₃N₄/SnS₂ nanocomposite led to 96% photocatalytic efficiency after 180 min under visible light radiation. The kinetics of photodegradation over g-C₃N₄/SnS₂ was about 9 and 3 times higher than those of g-C₃N₄ and SnS₂ photocatalysts, respectively. The superoxide and hydroxyl radicals were the main reactive species in the photocatalytic degradation with a Z-scheme charge transfer mechanism. The g-C₃N₄/SnS₂ nanocomposite was found to be remarkably stable after three consecutive cycles of MB degradation.     

Simple solid-state synthesis and improved performance of Ni(OH)2-TiO2 nanocomposites for photocatalytic H2 production

To reduce the cost of the traditional noble metal-loaded photocatalysts for H₂ production, low-cost Ni(OH)₂-TiO₂ nanocomposites were designed and synthesized by a simple room-temperature solid-state chemical method (RSCM), which is a facile, low-cost and eco-friendly manipulation. Various testing methods and tools were used to characterize the crystal structure, elemental composition, morphology, light absorption ability, fluorescent performance, photocurrent density, and photocatalytic activity of the obtained nanocomposites. The results indicated that RSCM can be used to synthesize Ni(OH)₂-TiO₂ nanocomposites with a small size (50 nm) and good dispersity. Compared to pure TiO₂, the obtained nanocomposites displayed excellent photocatalytic performance for H₂ production by photocatalytic water-splitting. The amount of hydrogen needed for the optional nanocomposite NOT-1 was 9180 μmol/g, which is 29 times that of the commercial P25. The reason for the improved performance for photocatalytic hydrogen production is that the existing Ni(OH)₂ in nanocomposites promoted the separation between the photogenerated electron and holes.     

Synthesis of novel Cd2P2O7/Ag3PO4 photocatalyst with enhanced visible-light photocatalytic performance and the enhancement mechanism

Novel Cd₂P₂O₇/Ag₃PO₄ photocatalysts containing different mass fractions of Cd₂P₂O₇ were synthesized by a hydrothermal method. The photocatalysts were characterized by X-ray diffractometry, transmission electron microscopy, X-ray photoelectron spectroscopy, Electron spin resonance (ESR), Fourier transform infrared spectrometry, ultraviolet–visible absorption spectroscopy and photoluminescence spectroscopy. Photocatalytic activity was decided by the effective separation and low recombination rate of photogenerated electron-hole pairs. During the experiments, the Cd₂P₂O₇/Ag₃PO₄ composites possessed fierce electron- hole separation capacity. In particular, the 1 wt% Cd₂P₂O₇/Ag₃PO₄ catalyst displayed higher photocatalytic performance than pure Ag₃PO₄ under visible-light irradiation (λ>420 nm). The ESR spectrum showed the main active species during the methyl orange degradation were ·OH and ·O₂⁻.     

Ternary Ag@SrTiO3@CNT plasmonic nanocomposites for the efficient photodegradation of organic dyes under the visible light irradiation

In this research, carbon nanotube (CNT)-modified plasmonic silver-strontium titanate (Ag@ SrTiO₃) nanocomposites for the degradation of the organic dye were prepared by the sol-gel method. The characterization of all products was carried out using the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption test (BET), field emission-scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), and transient photocurrent (TPC) studies. It was found that the incorporation of Ag in and introducing CNT into the SrTiO₃ nanoparticles reduced the crystallite size to 21 nm and the band gap energy to 2.7 eV. The Reduced PL peak intensity, increased photocurrent value, and reduced charge transfer resistance approved that the Ag@SrTiO₃@CNT nanocomposite had a greater charge transfer efficiency than other samples. The optimal dosage of the photocatalyst, for the complete degradation of 5 ppm of the methylene blue (MB) solution after 30 min of the visible light irradiation, was decided as 0.5 g/L. Besides, in the experimental environment, the Ag@SrTiO₃@CNT sample illustrated the most significant photocatalytic performance of the degradation of methyl orange (MO) and Rhodamine B (RhB) dyes. The detailed mechanism and kinetics of the degradation procedure were clarified. Finally, the prepared system displayed increased stability and reusability in the entire cyclic degradation experiment.     

Investigation of g-C3N4/ZnAl2O4 and ZnO/ZnAl2O4 nanocomposites: From synthesis to photocatalytic activity of pollutant dye model

The fabrication of nanocomposite photocatalytsts with excellent photocatalytic activity is an important step in the improved degradation of organic dyes. A series of nanocomposite photocatalysts was synthesized with g-C₃N₄ and ZnO loading contents of 10, 20 and 30%. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The optical band gaps of g-C₃N₄, ZnO and ZnAl₂O₄ were about 2.79, 3.21 and 3.55 eV, respectively. Methylene blue (MB) was degraded over the prepared photocatalysts under UV irradiation. Photocatalytic activity was about 9.1 and 9.6 times higher, respectively, on 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts than on pure ZnAl₂O₄ spinel powders. Recycling experiments showed that 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts exhibited good stability after five cycles of use.     

Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites

CoFe₂O₄ (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. For preparation of magnetic polymeric films, CoFe₂O₄ nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Magnetic properties of the samples were investigated using an alternating gradient force magnetometer (AGFM). CoFe₂O₄ nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe₂O₄ (10%) nanocomposites is higher than that obtained for PS/CoFe₂O₄ (30%).     

Solvothermal preparation and characterization of ordered-mesoporous ZrO2/TiO2 composites for photocatalytic degradation of organic dyes

ZrO₂/TiO₂ composites with an ink-bottle mesoporous structure were synthesized by a mild solvothermal method without high-temperature calcination. Many caves in this ink-bottle structure can adsorb organic groups, making them suitable for catalytic materials. The effects of ZrO₂ additions and particle size on the morphology and catalytic performance of composite powders were investigated. Comparative experiments on changing the particle size and the content of ZrO₂ show that the TiO₂-10 wt% ZrO₂ composite has outstanding photocatalytic performance under simulated sunlight, especially when the particle size of as-prepared ZrO₂ is on the submicron scale. By mixing two different n-type semiconductors of ZrO₂ and TiO₂, a new heterostructure is formed to hinder the autonomous recombination of excited electron-hole pairs, improving photocatalytic activity.     

Promoting the photocatalytic reduction of CO2 and dye degradation via multi metallic Smx modified CuCo2O4 Reverse spinel hybrid catalyst

Structuring a multi-functional photocatalyst of which enable high visible light harnessing so as to address the environmental pollution issues is the need of the hour. In view of this, a combination of catalytically active Cu, Co with enhanced adsorption capacity and Sm dopant that can enrich the catalyst with the defect centres would result in a tailor-made photocatalyst. Samarium (Sm) (1–12 wt %) doped CuCo₂O₄ were synthesized by simple precipitation route. The synergistic influence of Sm, Cu and Co on the photocatalytic ability has been ascertained by optical, structural and morphological methods like XRD, BET, SEM, XPS, Photocurrent, PL, ESR, fluorescence quenching, NMR methods. Thus prepared catalyst was utilized for the photo-catalytic mineralization of methylene blue and reaction was optimized and also it has been proven robust for the photo-reduction of CO₂ into value added products, which are identified by NMR spectral analysis. A comprehensive mechanism has been suggested based on the experimental results. The present research provides the concept of multi-functional photo-catalyst for effluent decontamination and CO₂ reduction.     

Nanostructured CeO2 for selective-sensing and smart photocatalytic applications

Well crystalline CeO₂ nanoparticles have been successfully synthesized via solution combustion synthesis (SCS) using (NH₄)₂[Ce(NO₃)₆] and C₄H₆O₆ as oxidizer and fuel. The structural characteristics of as-synthesized material were investigated in terms of FESEM, HRTEM, EDS, XRD, FTIR and UV–Vis spectroscopy techniques. The surface area of synthesized CeO₂ nanoscale material was obtained from BET plot. Results showed a pure, well-crystallized, flake-like mesoporous material to be formed with crystallite size of 18.86?nm. The focus of this study was to investigate the application of as-synthesized CeO₂ nanomaterial for sensing and photocatalytic degradation of picric acid (PA) in its aqueous solution. It was found to be highly selective for PA detection in aqueous solution when compared with other aromatic compounds. Detection limit (0.52?µM) for PA when compared with earlier studies was found to be much better. In addition, 0.05?gm of as-synthesized CeO₂ nanomaterial is found to be optimum amount ensuring maximum catalytic photodegradation of 10?ppm PA in aqueous solution. These experimental findings point out that as-synthesized CeO₂ nanomaterial can be efficiently used as an effective chemical sensor and photocatalyst.     

Build-in electric field induced step-scheme TiO2/W18O49 heterojunction for enhanced photocatalytic activity under visible-light irradiation

Artificial Z-scheme heterostructure photocatalysts, inspired by the natural photosynthesis, have been explored for water contamination owing to the efficiency of charge carriers separation and enhanced redox capacity. Herein, a novel step-scheme TiO₂/W₁₈O₄₉ heterojunction integrating TiO₂ nanosheets and spindle-like W₁₈O₄₉ was prepared via a two-step solvothermal method. The TiO₂/W₁₈O₄₉ heterojunction with the optimum ratio exhibited excellent photodegradation of RhB higher by a factor of 2.26 and TC degradation higher by a factor of 3.32 than the pristine TiO₂ when exposed to visible light. The reactive free radical trapping experiment indicated •O₂⁻ was determined to the dominant reactive species. Furthermore, XPS analysis and •O₂⁻ quantification measurements confirmed a build-in electric field induced step-scheme structure in TiO₂/W₁₈O₄₉ composites, which effectively enhanced the separation of carriers, thus improved photocatalytic activity. The present study will offer a new perception related to the formation of step-scheme heterostructure for photocatalytic degradation.