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Photocatalytic hydrogen production under solar light irradiation is an attractive and appealing technology to produce green and renewable hydrogen fuel to reduce CO2 emission and air pollution. Due to its special physicochemical properties, TiO2 photocatalysts have been commonly used as a promising photocatalyst for hydrogen production. However, its wide bandgap energy, which can be only activated under UV-light and fast charge carriers recombination restricts their photocatalytic applications. Nevertheless, several approaches have been proposed to reduce its bandgap energy for visible light activity. Among them, the doping TiO2 with a dopant can be regarded as an effective method not only to cause a shift of the light absorption toward the visible region but also to diminish the charge recombination. This review concentrated on the influence of different types of dopants on the enhancement of the photocatalytic activity of TiO2. Furthermore, the methods of synthesis and the characterization techniques used for doped-TiO2 were carefully checked. Importantly, this review examined that the photocatalytic hydrogen production activity of the doped-TiO2 depends heavily on the type and concentration of the dopants. Furthermore, a metal-like Cu, noble metals like Au and Pt are the most widely studied dopants for TiO2 due to their superior work function. In addition, nitrogen was also widely used as a nonmetal owing to its ability to reduce the bandgap energy of TiO2. The findings also showed that the sol-gel method is still widely used in the preparation of doped-TiO2 photocatalysts due to the high crystallinity and surface area of the obtained nanoparticles.

The g-C3N4/NaNbO3 photocatalyst was synthesized by simply calcining the mixture of NaNbO3 and melamine. The synthesized composite exhibits high photocatalytic performance in the selective oxidation of 5-Hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) when using water as solvent. The structure and composition of g-C3N4/NaNbO3 photocatalysts were characterized by TG, XRD, SEM, UV–Vis, FT-IR, and XPS methods, and the optical and electrochemical properties were investigated by EIS, PC, and PL techniques. O2− was inferred to be the primary active species in this process based on the active species trapping experiment. Heterostructure formation of g-C3N4/NaNbO3 composites efficiently promoted the separation of photo-generated electron-hole pairs and accelerated the electron transfer rate, thus reduced the formation of OH, and sequentially improved the selectivity of FFCA. The highest HMF conversion of 35.8% with FFCA selectivity of 87.4% was achieved on C/N-59.6 photocatalyst under the irradiation of visible light. The possible mechanism and reaction route were also proposed.

In recent years, graphitic carbon nitride (g-C3N4) has shown promising performance as a metal-free conjugated polymer containing graphitic stacking of C3N4 layers, which are constructed from tri-s-triazine units connected by planar amino groups. Pure g-C3N4 with a band gap energy of 2.7 eV (460 nm) makes it an applicable and efficient visible-active photocatalyst for energy conversion and environmental applications. This is because of its appropriate electronic band structures, efficient optical absorption, and extraordinary thermal and chemical stability. Currently, the major focus in photocatalysis research is on the design and development of visible-light-driven photocatalysts that are stable and highly efficient for practical applications. In this current mini-review, a comprehensive survey is conducted on graphitic carbon nitride (g-C3N4) as a metal-free novel visible-light photocatalyst and the progress in the synthesis and design of high-efficiency g-C3N4-based nanomaterial photocatalysts with controllable structures and morphologies is discussed in detail. Various approaches for modifying the electronic band structure and visible-light harvesting, including metal (cation), non-metal (anion) doping, noble metal loading, and composite formation with other semiconductors are discussed in detail. Photocatalytic applications of g-C3N4 as metal-free catalysts in photocatalytic water splitting for hydrogen production, CO2 photoreduction, organic pollutant degradation, and bacterial disinfections are introduced and discussed in detail. Finally, this critical mini-review summarizes some outlooks on the ongoing challenges in the development of efficient and low cost metal-free g-C3N4 systems, which provide a good complement to the literature on g-C3N4 based metal-free nanomaterial photocatalysts.

YFeO3/g-C3N4 composites with varying weight ratios were prepared following three different methods The optimum weight ratio and the method of preparation for enhanced visible photocatalytic activity towards the degradation of organic contaminants were identified. The successful formation of the composites was proven by XRD and IR measurements. XPS analysis shows that the inactive Y2O3 passive layer on the hexagonal YFeO3 (h-YFeO3) disappeared during the composite formation, resulting in a direct and intimate contact of h-YFeO3/g-C3N4 which is crucial for the photocatalytic activities. The loading of h-YFeO3 varied from 1 to 20% and the highest activity was achieved at 2.4%. At the optimum loading 80% degradation of methyl orange (MO) was obtained under 5 h visible light illumination. The composite photocatalyst shows also modest activity for the photodegrading of 4-chlorophenol (4-CP). Additionally the synthesized composites were characterized by high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflection UV–vis spectroscopy (DR-UV–vis). In order to determine the relative band positions of the composite photocatalysts their flat band potentials were estimated from Mott-Schottky analysis. Improved charge separation in the composite is mainly responsible for the enhanced photoactivity and supported by photoluminescence experiments.

Photocatalytic hydrogen generation via water splitting is a sustainable, renewable, and promising technology to produce green and clean hydrogen fuel by disassociating water into H2 and O2 using TiO2 photocatalyst, and sunlight with negligible impact on the environment, which can fulfill the future requirements of energy. TiO2-based photocatalysts are one of the most effective and widely used photocatalysts for photocatalytic hydrogen production due to their high photostability, abundance, high efficiency, non-toxicity, and low cost. However, TiO2 as a common photocatalyst cannot be easily applied to photocatalysis due to its wide bandgap energy that can only be activated under UV light, which occupies around 2–5% of the solar spectrum and the higher recombination rate of the photogenerated charge carriers before migrating to the surface to split water that restricted its photocatalytic performance. For that, factors such as surface area, particle size, and calcination temperature that affect the photocatalytic activity of TiO2 were highlighted. Additionally, the rational strategies such as doping, composite structure, dyes sensitization, defects engineering, and others that are used in enhancing their activities are described in detail. Importantly, the investigation showed that various parameters such as pH, sacrificial reagent, light intensity, catalyst, cocatalyst loading and catalyst deactivation, have great effects on photocatalytic hydrogen production over TiO2-based photocatalysts. Through reviewing the important state-of-the-art advances on this topic, this comprehensive review may provide new opportunities for designing and constructing highly effective TiO2-based photocatalysts for other applications in photocatalysis.

Ferrites have been widely known as excellent photocatalysts thanks to their excellent properties such as relatively narrow bandgaps, chemical, and thermal stability, excellent magnetic property, and low-cost. They have recently been explored for their visible-light activity for various photocatalysis applications. In this review, the classification of ferrites according to their crystalline structure is discussed. Several ferrites synthesis approaches have been reviewed including the citric acid-assisted sol-gel method, hydrothermal methods, coprecipitation, and solid-state reactions. Besides, optical, structural, electronic, and morphological properties of ferrites were characterized using several physical and analytical methods are highlighted. A comprehensive survey on their photocatalytic applications with more emphasis on their novelties is briefly reviewed. These applications not only include the degradation of organic and inorganic pollutants and bacterial disinfection, but also on hydrogen production via water splitting, and CO2 photoreduction. In this review, we summarize the latest developments in designing and developing highly efficient ferrite photocatalysts. We conclude with an overview and some observations on challenges and future directions in the exploration as a photocatalyst of ferrite-based materials.

In recent years, heterogeneous photocatalysis using semiconductor and solar energy has gained a lot of attention owing to its potential applications in many fields such as the generation of renewable and sustainable hydrogen fuel, degradation of organic pollutants, and CO2 photoreduction. Due to its photochemical stability, fascinating electronic band structures, and effective light harvesting accompanied by suitable bandgap energy of 2.7 eV, graphitic carbon nitride (g-C3N4) has been considered as a promising metal-free photocatalyst for solving the energy crisis and environmental problems. Nevertheless, due to the low-charge carrier mobility, and low surface area, its photocatalytic efficiency is limited. Because of its unique band structure, coupling it with a large bandgap semiconductor to produce a heterojunction composite offers a promising way to improve the charge separation, expand the surface area, and boost light absorption. For that, g-C3N4 as a robust photocatalyst together with numerous synthesis methods has been highlighted. Three primary systems of g-C3N4-based nanocomposites have been classified and summarized: namely metal oxides, sulfides, and ferrites. We have summarized the latest applications of g-C3N4/nanocomposites in solar energy conversion and environmental remediation. This review ends with an overview and several insights on the problems and future avenues in investigating advanced nanomaterials based on g-C3N4.

In the present work, bare TiO2 and different molar concentrations of iron (Fe3+)-doped TiO2 photocatalysts (0.05−1 mol % Fe) were prepared by a simple precipitation method for photocatalytic hydrogen production and degradation of organic pollutants (MO and 4-CP) under light irradiation of λ ≥ 320 nm. XRD revealed the presence of anatase phase for both bare TiO2 and Fe doped titania. Based on the XPS results, Fe3+ ions are hardly seen may be attributed to the location of iron inside the titania matrix rather than their appearance at the surface. UV–vis-DRS of the doped titania demonstrated a redshift toward visible region owing to the reduced bandgap energy. N2 adsorption results showed that the doped materials have higher surface area compared to bare TiO2 due to decrease particle size. Importantly, electrochemical experiments (electrochemical impedance spectroscopy (EIS), photocurrent (PC), and photoluminescence (PL)) revealed that higher photogenerated charge carrier separation efficiency of iron-doped titania. Results showed that the 0.1 mol % Fe doped TiO2 exhibited the highest photocatalytic activity for both degradation and H2 evolution reactions. Furthermore, high surface area, small particle size and enhanced visible-light absorption as well as improved charge transfer and separation are believed to be responsible for the improvement of photocatalytic activity of the doped materials.

In the present work, ZnO/g-C3N4 photocatalysts were synthesized via a simple calcination method. The physical properties of the obtained ZnO/g-C3N4 nanocomposites were characterized by various physicochemical techniques. The photocatalytic activity of the photocatalysts was investigated by the degradation of methyl orange (MO) and 4-chlorophenol (4-CP) under visible light irradiation. Especially, the photocatalytic efficiency was the highest when the percentage of ZnO was 10%. However, an increase of the photocatalytic activities was related to the interfacial transfer of photogenerated electrons and holes, leading to the effective charge separation. More importantly, the nanocomposite showed no activity toward hydrogen.

This study is investigating the direct growth of graphene on a membrane filter and a copper surface by injecting ethanol vapor into an inductively coupled plasma (ICP) at atmospheric pressure. Low temperature (

By injecting ethanol molecules into the argon plasma environment graphene sheets can be produced [1]. From this motivation the atmospheric pressure 2.45 GHz microwave plasma source was built. The argon and helium discharges with ethanol were obtained in a quartz tube which placed in a rectangular cavity. The discharge environment will be analyzed by optical emission method. The synthesized graphene sheets will be analyzed by scanning electron microscopy, x-ray diffraction method and Raman spectroscopy. The plasma power, gas flow rate and temperature effect on graphene sheets will be given.

Hexagonal perovskite YFeO3 was synthesized by a complex-assisted sol-gel technique allowing crystallization at calcination temperatures below 700 °C. As determined by diffuse reflectance spectroscopy (DRS) and Tauc plots, the hexagonal YFeO3 exhibits a lower optical band gap (1.81 eV) than the orthorhombic structure (about 2.1 eV or even higher) being typically obtained at elevated temperatures (>700 °C), and thus enables higher visible light photocatalysis activity. Structure and morphology of the synthesized YFeO3 perovskites were analyzed by powder X-ray diffraction (XRD) and nitrogen adsorption, proving that significantly smaller crystallite sizes and higher surface areas are obtained for YFeO3 with a hexagonal phase. The photocatalytic activity of the different YFeO3 phases was deduced via the degradation of the model pollutants methyl orange and 4-chlorophenol. Experiments under illumination with light of different wavelengths, in the presence of different trapping elements, as well as photoelectrochemical tests allow conclusions regarding band positions of YFeO3 and the photocatalytic degradation mechanism. X-ray photoelectron spectroscopy indicates that a very thin layer of Y2O3 might support the photocatalysis by improving the separation of photogenerated charge carriers.