Enhanced visible light photocatalytic activities of template free mesoporous nitrogen doped reduced graphene oxide/titania composite catalysts

Rapid Microwave-Assisted Synthesis of N/TiO2/rGO Nanoparticles for the Photocatalytic Degradation of Pharmaceuticals

Nanocomposites comprising nitrogen-doped TiO₂ and reduced graphene oxide (N/TiO₂/rGO), with different rGO loading qualities, were prepared by a cost-effective microwave-assisted synthesis method. The synthesized materials were broadly characterized by Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (FTIR), photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Anatase was the only crystalline phase observed for all synthesized materials. The rGO loading did not affect the morphological properties, but it positively influenced the photocatalytic activity of the nanocomposite materials, especially at low rGO loading. Photocatalysts were evaluated via the degradation of specific organic micropollutant (OMP) pharmaceuticals: ciprofloxacin (CIP), diclofenac (DCF), and salicylic acid (SA), under different radiation sources: ultraviolet A (UVA), solar light simulator (SLS), blue visible light (BVL) and cold visible light (CVL). CIP and SA were removed effectively via the synergy of adsorption and photocatalysis, while DCF degradation was achieved solely by photocatalysis. After implementing scavenger agents, photocatalytic degradation processes mainly depended on the specific pollutant type, while irradiation sources barely defined the photocatalytic mechanism. On the other hand, changes in irradiation intensity significantly influenced the photolysis process, while photocatalysis was slightly affected, indicating that irradiation spectra are more relevant than intensity.

Layered KTO/BiOCl nanostructures for the efficient visible light photocatalytic degradation of harmful dyes

Novel KTO/BiOCl nanostructured photocatalysts with various weight proportions were synthesized using a simple hydrothermal process. The as-prepared nanostructured composite catalysts were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis diffused reflectance spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy with high resolution, X-ray photoelectron spectroscopy, and photoluminescence (PL). The photocatalytic activity of prepared catalysts was examined using Rhodamine B (RhB) and Congo Red (CR) as the aimed pollutants. BiOCl nanoparticles were distributed uniformly on the surface of the K₂Ti₄O₉ nanobelts. The optical properties showed that the layered titanate with BiOCl nanostructured photocatalyst displayed improved photoresponsivity due to the narrowed bandgap. The PL results showed that the greater inhibition of the electron-hole recombination process and KTO/BiOCl with a mass proportion of 20% revealed the most favorable photocatalytic behavior. The rate constant of RhB and CR degradation was five times as high as that of the bare BiOCl and titanate. The superior photocatalytic performance was attributed to the advancement of heterojunction between the KTO nanobelt and BiOCl. The KTO/BiOCl nanostructure is a promising visible, active photocatalyst, and the photocatalytic mechanism is discussed using the possible band structures of BiOCl and KTO.

Degradation of Harmful Organics Using Visible Light Driven N-TiO₂/rGO Nanocomposite

Nitrogen doped titania over reduced form of graphene oxide (N-TiO₂/rGO) catalysts were synthesized by adopting single step hydrothermal route. All the prepared photocatalysts were thoroughly characterized by using different analytical tools such as XRD, Raman, UV-DRS, FE-SEM and HRTEM. The photocatalytic activities of bare and composite catalysts were evaluated towards the photocatalytic decolourisation/degradation of Methylene blue dye (MB) and Metronidazole antibiotic (MTZ) under visible electromagnetic radiation. Among all the synthesized catalysts, N-TiO₂/rGO composite catalyst showed the highest decolourisation/degradation activity towards both the dye and the antibiotic. The most active catalyst was also tested under UV and solar light irradiations which showed promising results. The stability of the most active catalyst (N-TiO₂/rGO) was examined by recyclability test. The possible photocatalytic mechanism was proposed for the composite catalyst.

Hydrothermal Synthesis, Characterization and Exploration of Photocatalytic Activities of Polyoxometalate: Ni-CoWO4 Nanoparticles

This study demonstrated the hydrothermal synthesis of bimetallic nickel-cobalt tungstate nanostructures, Ni-CoWO4 (NCW-NPs), and their phase structure, morphology, porosity, and optical properties were examined using X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy- energy dispersive X-ray spectroscopy (SEM-EDS), high resolution Transmission electron microscopy (HR-TEM), Brunauer-Emmett-Teller (BET) and Raman instruments. It was found that as-calcined NCW-NPs have a monoclinic phase with crystal size ~50–60 nm and is mesoporous. It possessed smooth, spherical, and cubic shape microstructures with defined fringe distance (~0.342 nm). The photocatalytic degradation of methylene blue (MB) and rose bengal (RB) dye in the presence of NCW-NPs was evaluated, and about 49.85% of MB in 150 min and 92.28% of RB in 90 min degraded under visible light. In addition, based on the scavenger’s study, the mechanism for photocatalytic reactions is proposed.

Nanoporous metal oxide composite materials: A journey from the past, present to future

Along with the progress of porous metal oxides, the development of multi-metal oxide composite materials have received a significant attention in the last few decades owing to the interesting physical and chemical properties of the hybrid oxide nanostructures. Consequently, a large number of national and international articles, communications etc. related to these oxide composites have come to light. This review conveys a comprehensive overview of those nanoporous metal oxide composites, illustrating various synthetic pathways and formation mechanisms for composite oxides based on template and non-templated routes. Also, characteristic properties of the synthesized materials analyzed using various techniques have been discussed systematically here. Moreover, the current review will also focus on a thorough literature survey of significant potential applications of these oxide composites in different fields including catalysis, biosensing, adsorption, energy conversion, toxic chemical removal, solar cell etc. demonstrating the impact of the metal compositions, nanostructures on the performances of the materials. Finally, a brief perspective is mentioned indicating the future prospects of these porous composites. Though, the scope of this review is limited to porous metal oxide composites, the information presented here can be helpful for any researchers working in other emerging fields.

Tuning the type of nitrogen on N-RGO supported on N-TiO2 under ultrasonication/hydrothermal treatment for efficient hydrogen evolution - A mechanistic overview

Efficient hydrogen production through water splitting has been the challenging task to be achieved in the present context of energy crisis. Among the various catalysts employed, nitrogen doped Titanium dioxide/Reduced graphene oxide (N-TiO₂/RGO) nanocomposite has been established to be a promising photocatalytic material for this purpose. However, nuances of doping nitrogen on TiO₂ and the type of nitrogen (pyridinic, pyrrolic and graphitic) stabilized on RGO responsible for facilitating the H₂ production has not yet been addressed mechanistically. In the present investigation, an attempt has been made to synthesise N-Titanium dioxide/N-Reduced graphene oxide (NTNG) nanocomposite under ultrasonication followed by hydrothermal treatment. A stainlesssteel ultrasonic bath, of 6.5 L tank size (LxBxH) 300 × 150 × 150 mm, was used for ultrasonic treatments. The transducers located at the bottom of the ultrasonic bath generate a frequency of 40 kHz with maximum power of 200 W. A mechanism has been proposed including the nuances of formation and the stabilisation of each type of nitrogen on N-RGO as a function of ultrasonication time. The present work supports the stabilization of a given type of nitrogen on RGO through keto enol tautomerism. XPS and FTIR studies have been undertaken to identify the different types of nitrogen doping and the presence of functional groups respectively. XRD, UV-Vis DRS and PL investigations have been made to establish morphological profile and band gap structure of the nanocomposite. It was observed that pyrrolic type nitrogen stabilized on N-RGO augments the efficiency of photocatalytic activity through hydrogen production by water splitting.

Photocatalytic performance of visible active boron nitride supported ZnFe2O4 (ZnFe2O4/BN) nanocomposites for the removal of aqueous organic pollutants

ZnFe₂O₄/BN nanocomposites were synthesized using  solvothermal method. The microscopic images revealed uniform dispersion of ZnFe₂O₄ nanospheres on the surface of BN nanosheets. PL studies showed lower e⁻/h⁺ pair recombination.  ZnFe₂O₄/9.3% BN showed outstanding photocatalytic activity.

Fabrication of a high-adsorption N–TiO2/Bi2MoO6 composite photocatalyst with a hierarchical heterostructure for boosted weak-visible-light photocatalytic degradation of tetracycline

TiO₂ hierarchical heterostructure photocatalyst was successfully fabricated through the in situ growth of Bi₂MoO₆ nanosheets on rough N–TiO₂ nanorods with a bark-like surface. The structure–property relationship of this composite material were researched.

N-Doped Carbon-Coated ZnS with Sulfur-Vacancy Defect for Enhanced Photocatalytic Activity in the Visible Light Region

In this work, N-doped carbon-coated ZnS with a sulfur-vacancy defect (ZnS@N-C) was performed for the visible-light-driven photodegradation of tetracycline hydrochloride (TCH). The obtained ZnS@N-C exhibited enhanced photocatalytic activity compared with ZnS for TCH removal. Among these ZnS@N-C composites, ZnS@N-C-3 with N-doped content of 3.01% (100 nm) presented the best visible-light photocatalytic activity and superior long-term photocatalytic stability after five cycle times for TCH removal in the visible light region. This may be ascribed to the interface between the N-doped carbon shell and ZnS with a sulfur-vacancy defect for efficient charge transfer and the restrained recombination of charge carriers. Electron spin resonance (ESR) results indicate that the ·O₂^‒ radical plays a crucial role in the enhanced photocatalytic activity of ZnS@N-C-3.

Ultrasonically aided selective stabilization of pyrrolic type nitrogen by one pot nitrogen doped and hydrothermally reduced Graphene oxide/Titania nanocomposite (N-TiO2/N-RGO) for H2 production

Herein, we report the simultaneous doping of nitrogen on TiO₂ and reduced graphene oxide (N-TiO₂/N-RGO) with exclusive stabilization of pyrrolic type nitrogen on RGO network by ultrasonic conditions followed by hydrothermal method for efficient photocatalytic H₂ production. Interestingly, during synthesis of N-TiO₂/N-RGO composite, pyrrolic type nitrogen in RGO has been exclusively stabilized as confirmed by XPS analysis. The exclusive stabilization of pyrrolic nitrogen changed the optical and electronic properties of N-TiO₂/N-RGO nanocomposites by giving two π-electrons to the system for extended conjugation, which enhanced the optical absorption and charge carrier separation efficiency as confirmed by UV-Vis DRS and PL studies. Notably, N-TiO₂/N-RGO nanocomposite demonstrated. This enhanced photocatalytic activity can be ascribed to synergetic action of N-TiO₂ and N-RGO in optical and photogenerated charge carrier separation. Moreover, the plausible mechanism for exclusive stabilization of pyrrolic type nitrogen and enhanced photocatalytic activity were also proposed.

BiVO4 /N-rGO nano composites as highly efficient visible active photocatalyst for the degradation of dyes and antibiotics in eco system

Herein, we report the synthesis of novel nitrogen doped reduced graphene oxide/ BiVO₄ photo catalyst by single step hydrothermal method. The physicochemical properties of the catalysts were characterized using XRD, N₂ adsorption-desorption, Raman, XPS, SEM TEM, DRS-UV and EIS techniques. The synthesized catalysts were tested for their catalytic activity in the photo degradation of some harmful textile dyes (methylene blue & congo red) and antibiotics (metronidazole and chloramphenicol) under visible light irradiation. Reduced charge recombination and enhanced photocatalytic activity were observed due to the concerted effect between BiVO₄ and nitrogen-rGO. The degradation efficiency of BiVO₄/N-rGO in the degradation of CR and MB was remarkably high i.e 95% and 98% under visible light irradiation. Similarly 95% of MTZ and 93% of CAP were degraded under visible light irradiation. HPLC studies implied that both the dyes and antibiotics were degraded to the maximum extent. The plausible photocatalytic mechanism on the basis of experimental results was suggested.

Preparation and enhanced photocatalytic hydrogen-evolution activity of ZnGa2O4/N-rGO heterostructures

Schematic diagram of photocatalytic hydrogen-evolution of ZnGa₂O₄/N-rGO illustrating that N-rGO acted as a catalyst support and electron sink for promoting charge separation and transfer.