The separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been a research focus. In this paper, the composite g-C 3 N 4 -WO 3 photocatalysts with different main parts of C 3 N 4 or WO 3 were prepared by ball milling and heat treatment methods. The photocatalytic performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) methods. The separation mechanisms of photogenerated electrons and holes of the g-C 3 N 4 -WO 3 photocatalysts were investigated by electron spin resonance technology (ESR), photoluminescence technique (PL), and determination of reactive species in the photocatalytic reactions. When the main part of the g-C 3 N 4 -WO 3 photocatalyst is WO 3 (namely g-C 3 N 4 /WO 3 ), the transport process of the photogenerated electrons and holes adopts the generic band–band transfer. Meanwhile, g-C 3 N 4 is covered by WO 3 powder, and the role of g-C 3 N 4 can not be played fully. The photocatalytic activity of the photocatalyst is not obviously increased. However, when the primary part of the WO 3 -g-C 3 N 4 photocatalyst is g-C 3 N 4 (namely WO 3 /g-C 3 N 4 ), the migration of photogenerated electrons and holes exhibits a typical characteristic of Z-scheme photocatalyst, and the photocatalytic activity of the photocatalyst is increased greatly.

Study on the separation mechanisms of photogenerated electrons and holes for composite photocatalysts g-C3N4-WO3

Porous graphitic carbon nitride (g-C3N4) was prepared by a simple pyrolysis of urea, and then a g-C3N4–Pt-TiO2 nanocomposite was fabricated via a facile chemical adsorption followed by a calcination process. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance absorption spectra, and electron microscopy. It is found that the visible-light-induced photocatalytic hydrogen evolution rate can be remarkably enhanced by coupling TiO2 with the above g-C3N4, and the g-C3N4–Pt-TiO2 composite with a mass ratio of 70 : 30 has the maximum photoactivity and excellent photostability for hydrogen production under visible-light irradiation, and the stable photocurrent of g-C3N4–TiO2 is about 1.5 times higher than that of the bare g-C3N4. The above experimental results show that the photogenerated electrons of g-C3N4 can directionally migrate to Pt-TiO2 due to the close interfacial connections and the synergistic effect existing between Pt-TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently separated in space, which is beneficial for retarding the charge recombination and improving the photoactivity.

Graphitic carbon nitride (g-C3N4)–Pt-TiO2 nanocomposite as an efficient photocatalyst for hydrogen production under visible light irradiation

Novel plasmonic Bi nanoparticles deposited in situ in (BiO)2CO3 microspheres (Bi/BOC) were fabricated via a one-pot hydrothermal treatment of bismuth citrate, sodium carbonate, and thiourea. Different characterization techniques, including XRD, SEM, TEM, XPS, UV–vis DRS, PL, time-resolved fluorescence spectra, and photocurrent generation, were performed to investigate the structural and optical properties of the as-prepared samples. The results indicated that the Bi nanoparticles were generated on the surface of (BiO)2CO3 microspheres via the in situ reduction of Bi3+ by thiourea. The Bi nanoparticle deposited (BiO)2CO3 microspheres were employed for the photocatalytic removal of NO in air under visible light irradiation, and the sample exhibited a drastically enhanced photocatalytic activity and oxidation ability. The highly enhanced activity was attributed to the cooperative contribution of the surface plasmon resonance (SPR) effect, the efficient separation of electron–hole pairs, and the prolonged lif...

Noble metal-like behavior of plasmonic Bi particles as a cocatalyst deposited on (BiO)2CO3 microspheres for efficient visible light photocatalysis

Novel hybrid nanostructures or nanocomposites are receiving increasing attention due to their newly evolved properties. In this work, α-Fe 2 O 3 anchored to graphene oxide (GO) nanosheet (α-Fe 2 O 3 @GO) was synthesized through a facile hydrolysis process and its photo-catalytic performances and durability in heterogeneous Fenton system were fully evaluated. The decolorization rates of methylene blue in α-Fe 2 O 3 @GO + H 2 O 2  + UV system within a wide pH range were approximately 2.9-fold that of classical Degussa P25 TiO 2  + UV and 2.4-fold that of α-Fe 2 O 3  + H 2 O 2  + UV. This enhanced decolorization of methylene blue (MB) in α-Fe 2 O 3 @GO + H 2 O 2  + UV system were attributed to the unique incorporation of GO into the catalyst which not only mediated the morphology of active sites α-Fe 2 O 3 nanoparticles but also offered high electron conductivity and electrostatic attraction between negatively charged GO with positively charged MB. High efficiencies of degradation were achieved on various surface charged organic pollutants (around 96–100%), such as cationic compounds of MB and rhodamine B (RhB), anionic compound Orange II (OII) and Orange G (OG), neutral compounds of phenol, 2-nitrophenol (2-NP) and endocrine disrupting compound 17β-estradiol (E2). The dominant reactive oxygen species (ROS) responsible for decolorization, such as hydroxyl radicals ( OH) and superoxide anion radicals (O 2 − ) generated by activation of H 2 O 2 on the surface of α-Fe 2 O 3 @GO were detected and quantified by free radical quenching methods. The possible degradation mechanism of MB involved the rupture of phenothiazine ring by desulfurization and the rupture of phenyl ring due to the attack of ROS, which was analyzed by LC/MS/MS. The reduction of MB and its intermediates was consistent with the decreasing trend of the acute toxicity towards luminous bacteria with the increasing irradiation time. The results lay a foundation for highly effective and durable photo-Fenton technologies for organic wastewater within wider pH ranges than the conventional photo-Fenton reaction.

Enhanced catalytic degradation of methylene blue by α-Fe2O3/graphene oxide via heterogeneous photo-Fenton reactions

Efficient generation of active oxygen-related radicals plays an essential role in boosting advanced oxidation process. To promote photocatalytic oxidation for gaseous pollutant over g-C3N4, a solid–gas interfacial Fenton reaction is coupled into alkalinized g-C3N4-based photocatalyst to effectively convert photocatalytic generation of H2O2 into oxygen-related radicals. This system includes light energy as power, alkalinized g-C3N4-based photocatalyst as an in situ and robust H2O2 generator, and surface-decorated Fe3+ as a trigger of H2O2 conversion, which attains highly efficient and universal activity for photodegradation of volatile organic compounds (VOCs). Taking the photooxidation of isopropanol as model reaction, this system achieves a photoactivity of 2–3 orders of magnitude higher than that of pristine g-C3N4, which corresponds to a high apparent quantum yield of 49% at around 420 nm. In-situ electron spin resonance (ESR) spectroscopy and sacrificial-reagent incorporated photocatalytic characteriz...

Constructing Solid–Gas-Interfacial Fenton Reaction over Alkalinized-C3N4 Photocatalyst To Achieve Apparent Quantum Yield of 49% at 420 nm

The polyaniline (PANI)/TiO2 nanocomposites have been successfully synthesized via a hydrothermal method and followed by a low-temperature calcination treatment process. We find that such a PANI/TiO2 nanocomposite exhibits higher photocatalytic activity and stability than bare TiO2 and TiO2-xNx toward the liquid-phase degradation of methyl orange (MO) under both UV and visible light (420 nm < λ < 800 nm) irradiation. More noteworthy, the PANI/TiO2 photocatalyst still perform good activity toward MO and 4-chlorophenol (4-CP) under the longer wavelength of light (550 nm < λ < 800 nm). The total organic carbon (TOC) tests show that the mineralization rate of MO and 4-CP over PANI/TiO2 are apparently higher than bare TiO2 under the irradiation of both UV and visible light. The presence of synergic effect between PANI and TiO2 is believed to play an essential role in affecting the photoreactivity. At last, the roles of active species in the photocatalytic process are compared by using different types of active ...

Highly Efficient Photocatalytic Degradation of Organic Pollutants by PANI-Modified TiO2 Composite

In the present paper, we propose a new type of catalyst, Pt/LaVO4/TiO2 (PLVT), which combines the use of UV and visible light for photocatalysis on LaVO4/TiO2 (LVT) and the heating effect of infrared light for low-temperature thermocatalysis on Pt. Under simulated solar light, benzene as an objective pollutant can be 100% eliminated and converted into CO2 and H2O on PLVT at 70 °C with an obvious synergetic effect of photocatalysis and thermocatalysis. The photothermocatalytic activity at 70 °C is about three times the sum of the photocatalytic activity and thermocatalytic activity. The stable performance of PLVT in a 60 hour durability test also indicates its applicable potential. The roles of Pt and LVT in the synergetic effect are discussed by comparing PLVT with control samples regarding the interaction between Pt and LVT under photothermocatalytic conditions. On the basis of the above experimental results, a possible mechanism of the synergetic effect is proposed.

Unusual photocatalytic materials with UV-VIS-NIR spectral response: deciphering the photothermocatalytic synergetic effect of Pt/LaVO4/TiO2

Two facile and green methods without any templates, catalysts, surfactants or organic solvents were applied to synthesize ZnSn(OH)6 nanoparticles, i.e. homogeneous precipitation (HP) and hydrothermal (HT). The photocatalytic activities were evaluated on the degradation of organic pollutants under ultraviolet light illumination. Compared to commercial P25, the photoactivity of ZnSn(OH)6 was remarkably improved. The conversion and mineralization ratio of the photocatalytic degradation of benzene by the ZnSn(OH)6-HP were up to 75% and 68%, which is about 20 and 2 times higher than that of P25. The ZnSn(OH)6 has also exhibited high performance toward other persistent organic compounds as well as methyl orange in suspended solution. The order of photodegradation efficiencies of different catalysts was ZnSn(OH)6-HP > P25 > ZnSn(OH)6-HT. Based on the characterization results and the detection of active species, the possible mechanism of the high photocatalytic activity of ZnSn(OH)6-HP was discussed. The simplified synthesis of zinc hydroxystannate with outstanding activity could be promisingly used in the future photocatalytic application.

High photocatalytic performance of zinc hydroxystannate toward benzene and methyl orange

The rose-flower-like BaSb2O6 (R-BaSb2O6) and marigold-flower-like BaSb2O6 (M-BaSb2O6) have been successfully prepared by a simple hydrothermal method avoiding high temperature, templates, catalysts, surfactants, or organic solvents. Their structures and morphologies have been investigated by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and selected-area electron diffraction. Ba/Sb molar ratio and pH values in the precursor play significant roles in building two kinds of flower-like BaSb2O6. Time dependent experiments reveal the possible formation mechanisms of the BaSb2O6 microstructures. When used as a photocatalyst, the M-BaSb2O6 exhibits the best photocatalytic activity among R-BaSb2O6, M-BaSb2O6 and BaSb2O6 synthesized by solid state reaction. The morphology of M-BaSb2O6 results in the large BET specific surface area and unique light propagation mode, which greatly improve the interaction among photons, organic compounds and photocatalyst, and thus enhance photocatalytic activity. The photocatalytic stability experiments demonstrate the sufficient stability of M-BaSb2O6 during the photocatalytic process.

One-step template-free synthesis of BaSb2O6 micro-flowers and their associated photocatalytic activity

The invention discloses a catalyst with an optothermal coupling effect and a preparation method thereof. The method comprises the following steps of: 1) preparing titanium oxide sol by using a sol-gel method; 2) preparing LaVO4 nano powder by using a hydrothermal method; 3) adding the prepared LaVO4 nano powder into the titanium oxide sol, fully mixing, drying, and performing high-temperature heat treatment to prepare a LaVO4/TiO2 nano heterojunction composite material; and 4) impregnating the prepared LaVO4/TiO2 nano heterojunction composite material into solution of chloroplatinic acid, drying and performing high-temperature heat treatment, and reducing, washing and drying to obtain a Pt/LaVO4/TiO2 catalyst through excessive solution of sodium borohydride. Compared with Pt/TiO2 and Pt/gamma-Al2O3 catalysts, the Pt/LaVO4/TiO2 catalyst has higher activity and stability on the organic pollutants such as benzene, toluene, dimethylbenzene, cyclohexane and acetone under the same reaction conditions; and moreover, the catalyst has high optothermal coupling performance, the benzene in the organic exhaust gas can be efficiently degraded under illumination conditions when the heating temperature reaches 70 to 90 DEG C, the benzene conversion rate is 99 percent, and the mineralization rate is 95 percent.

Junhua Hu

Papers

Highly Efficient Photocatalytic Degradation of Organic Pollutants by PANI-Modified TiO2 Composite

Unusual photocatalytic materials with UV-VIS-NIR spectral response: deciphering the photothermocatalytic synergetic effect of Pt/LaVO4/TiO2

High photocatalytic performance of zinc hydroxystannate toward benzene and methyl orange

One-step template-free synthesis of BaSb2O6 micro-flowers and their associated photocatalytic activity

Catalyst with optothermal coupling effect and preparation method thereof