High-performance Visible-light Photocatalysts Research Articles

Hybrid NiCo2O4-BiOCOOH heterostructure nanocomposite impregnated porous polymer monolith as high-performance visible light photocatalyst for the decontamination of antimicrobial pollutants

We report a first-of-its-kind preparation of a NiCo2O4-BiOCOOH heterostructure as visible light-responsive nanocomposites (NCs) for the fast decontamination of moxifloxacin drug molecules, with longer persistence and non-biodegradability nature that could promote gene-resistance bacteria in aqueous medium. Further, a reusable/recoverable photocatalyst is fabricated through the uniform decoration of NiCo2O4(15 %)-BiOCOOH(85 %), i.e., NB-15 NCs across a tailor-made poly(EGDMA) monolith (PEM) that serves as the host template for the photoactive NCs. The electron microscopy, optical spectroscopy, diffraction, and surface analysis techniques confirm the photocatalyst's superior structural morphology, surface topography, and porosity features that assist in high-performance photocatalysis. The inorganic-organic hybrid photocatalyst exhibits a narrow energy bandgap that promotes ample generation of reactive oxygen species upon visible light irradiation, as confirmed by the electrochemical and spectroscopic analysis. The BET/BJH plot for the photocatalyst reveals a large surface area of 345 m2/g, with voluminous pore distributions (2–80 nm), indicating the coexistence of mesopores-infused macroporous framework that offers better contact/equilibration of the pollutant molecules with the abundantly dispersed photoactive sites. The optimized parameters reveal ≥99.2 % drug dissipation in ≤0.33 h and drug mineralization in ≤2.0 h, using a mere 50 mg of photocatalyst irradiated with a 150 W/cm2 tungsten lamp. The synthesized photocatalyst has a simple/cost-saving procedure that can transform into scalable, cheaper, and eco-friendly products for the real-time monitoring of toxic pollutants. Besides, the photocatalyst exhibits excellent stability and reusability characteristics for efficiently decontaminating organic pollutants, thus highlighting an innovative approach for fabricating high-performance photocatalysts.

Novel CuBi2O4-BiOCl/rGO heterostructure nanocomposite as high-performance visible light photocatalyst for the disintegration of persistent antimicrobials in aquatic environment

The article highlights the fabrication of a novel CuBi2O4-BiOCl/rGO heterojunction nanocomposite as a renewable visible light photocatalyst for the quick disintegration of a persistent fluoroquinolone-based antimicrobial drug, i.e., enrofloxacin (ENF) in aquatics. CuBi2O4-BiOCl (CBO-BOC) nanocomposites (NCs) of varying BOC stoichiometric ratios were synthesized, of which CBO-(30%) BOC NC (CB-30) revealed top photocatalytic traits, which was analogously dispersed onto reduced graphene oxide (rGO) nanosheets, to serve as the visible light photon responsive materials. The electron microscopic and spectroscopic techniques were deployed to understand the CB-30/rGO heterostructure's surface topography and structural morphology. The FE-SEM, HR-TEM and XPS analysis confirmed the dispersion of CBO nanospheres onto the BOC nanoflakes and further confirmed the successful imbuement of CB-30 NCs onto the rGO nanosheets. The CB-30/rGO photocatalyst revealed excellent porosity and surface area for the fast dissipation of pharmaceutical pollutants. The impact of various operating parameters, such as solution pH, drug concentration, CBO-BOC stoichiometry, CB-30/rGO dosage, photosensitizers/electron acceptors, light intensity and matrix tolerance limits, were augmented to enhance the photocatalytic efficiency of the proposed new-age photocatalyst. Under optimized conditions, complete drug mineralization was achieved in ≤0.33 h for complete mineralization of 30 ppm of ENF, using 0.075 g of photocatalyst. The time-dependent profiling of photoproducts/intermediates derived from the photocatalytic degradation of ENF was monitored by HR-MS analysis. The acute and chronic toxicity effects of ENF and its organic intermediate were predicted using the ECOSAR model for selected aquatic life forms. The photocatalyst exhibited reusability up to seven cycles, with excellent thermal/chemical stability, for pollutant decontamination from industrial effluents and environmental samples.

Understanding the Plasmonic Effect of Enhanced Photodegradation with Au Nanoparticle Decorated ZnO Nanosheet Arrays under Visible Light Irradiation.

Plasmonic-enhanced photocatalysis using visible light is considered a promising strategy for pollution photodegradation. However, there is still a lack of comprehensive and quantitative understanding of the underlying mechanisms and interactions involved. In this study, we employed a two-step process to fabricate arrays of ZnO nanosheets decorated with Au nanoparticles (Au-ZnO NS). Various characterization techniques were used to examine the morphological, structural, and chemical properties of the fabricated Au-ZnO NS array. Furthermore, we systematically investigated the photocatalytic degradation of methyl orange under visible light irradiation using Au-ZnO NS arrays prepared with varying numbers of photochemical reduction cycles. The results indicated that as the number of photochemical reduction cycles increased, the photodegradation efficiency initially increased but subsequently decreased. Under visible light irradiation, the Au-ZnO NS array obtained via four cycles of photochemical reduction exhibits the highest photocatalytic degradation rate of methyl orange 0.00926 min-1, which is six times higher than that of the ZnO NS array. To gain a better understanding of the plasmonic effect on photodegradation performance, we utilized electromagnetic simulations to quantitatively investigate the enhancement of electric fields in the Au-ZnO NS array. The simulations clearly presented the nonlinear dependencies of electric field intensity on the distribution of Au nanoparticles and the wavelength of radiation light, leading to a nonlinear enhancement of hot electron injection and eventual plasmonic photodegradation. The simulated model, corresponding to four cycles of photochemical reduction, exhibits the highest electric field intensity at 550 nm, which can be attributed to its strong plasmonic effect. This work provides mechanistic insights into plasmonic photocatalysts for utilizing visible light and represents a promising strategy for the rational design of high-performance visible light photocatalysts.

High-Performance Visible-Light Photocatalysts for H2 Production: Rod-Shaped Co3O4/CoO/Co2P Heterojunction Derived from Co-MOF-74

Photocatalyst systems generally consist of catalysts and cocatalysts to realize light capture, charge carrier migration, and surface redox reactions. Developing a single photocatalyst that performs all functions while minimizing efficiency loss is extremely challenging. Herein, rod-shaped photocatalysts Co3O4/CoO/Co2P are designed and prepared using Co-MOF-74 as a template, which displays an outstanding H2 generation rate of 6.00 mmol·g−1·h−1 when exposed to visible light irradiation. It is 12.8 times higher than pure Co3O4. Under light excitation, the photoinduced electrons migrate from the catalysts of Co3O4 and CoO to the cocatalyst Co2P. The trapped electrons can subsequently undergo a reduction reaction to produce H2 on the surface. Density functional theory calculations and spectroscopic measurements reveal that enhanced performance results from the extended lifetime of photogenerated carriers and higher charge transfer efficiency. The ingenious structure and interface design presented in this study may guide the general synthesis of metal oxide/metal phosphide homometallic composites for photocatalysis.

Development of a new high-performance visible-light photocatalyst by modifying tin disulfide with cyclized polyacrylonitrile

Tin disulfide (SnS2) coupled with cyclized polyacrylonitrile (CPAN) was prepared via a hydrothermal synthesis-mixing in the solution-solvent evaporation-thermal cyclization method from inexpensive SnCl4·5H2O, thioacetamide and polyacrylonitrile (PAN). The as-synthesized SnS2/CPAN exhibited not only a substantially increased photocatalytic activity (2.1 times that of bare SnS2), but also a fair stability in the visible-light (λ > 420 nm)-induced reduction of aqueous Cr(VI). The modification with CPAN is capable of enlarging the specific surface area, enhancing the transfer and separation of photogenerated charge carriers, and increasing the Cr(VI)-adsorbing capacity of SnS2, leading to the improved photocatalytic activity of SnS2/CPAN. This study is instructive to exploit PAN to make SnS2-based and other semiconductor-based new efficient visible-light photocatalysts. Moreover, the method employed for preparing SnS2/CPAN nanocomposite is simple, economical, and practical for producing various semiconductor/CPAN composite materials for photocatalytic and even other applications.

(Invited) Water Splitting and Carbon Dioxide Conversion By Mixed-Anion Materials

Mixed-anion materials that consist more than one anionic species in a single-phase have attracted attention for various applications. Oxynitrides containing d0- or d10-metal cations are typical example of visible-light-driven photocatalysts for water splitting and CO2conversion. In this presentation, recent progress on the development of mixed-anion materials for water splitting and CO2 conversion made by our group will be given. While two-dimensional (2D) undoped layered oxynitrides are potential candidates as high performance visible-light photocatalysts, synthesis of 2D layered oxynitrides is generally difficult because most of them are metastable phases and are not chemically very stable. We found an exceptional example of a 2D layered oxynitride, K2LaTa2O6N (more specifically, K2LaTa2O6N·1.6H2O), which is a Ruddlesden-Popper phase two-layer perovskite analogous to Li2LaTa2O6N and has a band gap of 2.5 eV. This material undergoes in situH+/K+ exchange in aqueous solution while keeping its visible light absorption capability. The protonated, Ir-modified K2LaTa2O6N exhibited photocatalytic activity for H2 evolution from aqueous NaI solution under visible light, outperforming Pt/ZrO2/TaON and Pt/SrTiO3:Rh, which are one of the best-performing oxynitride and oxide photocatalysts for H2 evolution, respectively. The use of mixed-anion materials is of interest not only for photocatalysts but also for catalysts promoting water oxidation and CO2reduction. For example, we found that certain oxyfluorides work as electrocatalysts for water oxidation. A 2D perovskite oxyfluoride Pb3Fe2O5F2 exhibits activity for electrochemical water oxidation to O2, which is 8 times more active than a 3D bulk PbFeO2F.

MXene-derived C-doped TiO2/Ti3C2 heterojunction as a high-performance visible-light photocatalyst

Fabrication TiO2 with conductive two-dimensional materials is an effective strategy to improve its photocatalytic activity. Herein, a well-defined carbon-doped TiO2/Ti3C2 heterojunction is constructed via in situ controllable oxidation of Ti3C2 MXene in carbon dioxide. The formed C-doped TiO2 nanoparticles as the photocatalyst uniformly disperse on the surface of Ti3C2 MXene and generate electrons and holes under irradiation. The two-dimensional Ti3C2 MXene, owing to its excellent conductivity, acts as the electron transport channels and accelerates the separation of photogenerated electrons and holes. Meanwhile, due to its large specific surface area and good solubility, Ti3C2 MXene may facilitate to enhance the adsorption of pollutant on the photocatalyst as well as the absorption of photocatalyst for visible light. Therefore, the unique merits of TiO2 and Ti3C2 MXene are integrated to deliver the composites high photocatalytic activity. The proper content of Ti3C2 MXene and TiO2 in the composite is crucial for enhancing the photocatalytic performance, which can be effectively tuned by varying the oxidation temperature. In this work, C-doped TiO2/Ti3C2 oxidized at 400 °C presents the optimum photocatalytic performance.

High-performance visible light photocatalyst antibacterial applications of ZnO and plasmonic-decorated ZnO nanoparticles

High-performance visible light photocatalyst antibacterial applications of ZnO and plasmonic-decorated ZnO nanoparticles

ZrO2–Ag2O nanocomposites encrusted porous polymer monoliths as high-performance visible light photocatalysts for the fast degradation of pharmaceutical pollutants

This work reports a unique ZrO2-Ag2O heterojunction nanocomposite uniformly dispersed on a macro-/meso-porous polymer monolithic template to serve as simple and effective visible light-driven heterogeneous plasmonic photocatalysts for water decontamination. The monolithic photocatalysts' structural properties and surface morphology are characterized using various surface and structural characterization techniques. The photocatalytic performance of the proposed photocatalysts is evaluated by optimizing multiple operational parameters. The photocatalytic properties of the fabricated monolithic nanocomposite are monitored through time-dependent photocatalytic disintegration of norfloxacin drug, a widely employed antimicrobial, with considerable aquatic persistence. The analytical results conclude that a (60:40) ZrO2-Ag2O nanocomposite embedded polymer monolith exhibits superior photocatalytic activity for the complete mineralization of norfloxacin molecules under optimized conditions of solution pH (3.0), photocatalyst quantity (100mg), pollutant concentration (15mg/L), photosensitizers (2.0mM KBrO3), visible light intensity (300W/cm2 tungsten lamp) and irradiation time (≤ 1h). The proposed new-age inorganic-organic hybrid visible light photo-catalysts with superior structural and surface properties exhibit brilliant performance and fast responsiveness for water decontamination applications, in addition to their excellent chemical stability, high durability, multi-reusability, and cost-effectiveness.

MoS2/CdS rod-like nanocomposites as high-performance visible light photocatalyst for water splitting photocatalytic hydrogen production

This study demonstrates a high-performance visible-light-driven photocatalyst for water splitting H 2 production. CdS nanorods (30 nm in diameters) with shorter radial transfer paths and fewer defects were prepared by a solvothermal method. To mitigate the recombination of electrons and holes, MoS 2 nanosheets with rich active sites were modified on the surface of CdS nanorods by a room-temperature sonication treatment. The photocatalytic water splitting tests show that the MoS 2 /CdS nanocomposites exhibit excellent H 2 evolution rates. The highest H 2 evolution rates (63.71 and 71.24 mmol g −1 h −1 in visible light and simulated solar light irradiation) was found at the 6% MoS 2 /CdS nanocomposites, which was 14.61 times and 13.39 times higher than those of the corresponding pristine CdS nanorods in visible light and simulate solar light irradiation, respectively. The apparent quantum efficiency (AQE) of the 6% MoS 2 /CdS nanocomposites at 420 nm was calculated to be 33.62%. The electrochemistry tests reveal that the enhanced photocatalytic activity is a result of extra photogenerated charge carries, greatly enhanced charge separation and transfer ability of the MoS 2 /CdS composites. This study may give new insights for the rational design and facile synthesis of high-performance and cost-effective bimetallic sulfide photocatalysts for solar-hydrogen energy conversion. • CdS/MoS 2 composites were prepared by a room-temperature sonication method. • This material shows excellent photocatalytic H 2 production performance. • The decoration of MoS 2 nanosheets enables to effectively reduce photo-corrosion. • The performance is due to good separation and transfer ability.

Mixed-dimensional 1D CdS/2D MoSe2 heterostructures for high-performance photocatalytic hydrogen production

Rationally designing heterojunction photocatalysts with well-defined nanostructures and intimate interfacial contact is highly significant for improving the photocatalytic hydrogen evolution reaction (HER) activity. Here, we report on the fabrication of one-dimensional (1D) CdS/two-dimensional (2D) MoSe2 heterostructure for efficient photocatalytic hydrogen production. It is revealed that layered MoSe2 nanosheets are randomly anchored on CdS nanorods via an in-situ solvothermal process. When the loading content was kept at 10 wt%, the mix-dimensional nanohybrids exhibited a highly improved hydrogen-evolving rate up to 25.8 mmol g −1 h −1, which is 4 times higher than that of pristine CdS nanorods. The apparent quantum efficiency (AQE) of the optimized hybrid catalyst CM-10 is determined to be around 30% at 420 nm. The enhancement of photocatalytic HER activity can be attributed to the synergistic effect between 1D CdS nanorods and 2D MoSe2 nanosheets, which enables the accelerated electron-hole separation and more efficient interfacial charge transport. The findings in this study imply that, through morphology control and interfacial engineering, the efficiency and long-term stability of heterojunction photocatalysts toward hydrogen production from water splitting can be effectively tuned, providing new insights into the development of robust and high-performance visible light photocatalysts.

Electrophoretic deposition and characterization of self-doped SrTiO3 thin films.

Herein, titanium (Ti3+) self-doped strontium titanate (SrTiO3), so-called blue SrTiO3, with a bandgap of 2.6 eV and favorable photocatalytic characteristics was fabricated through a facile and effective method. For electrochemical investigations, the electrophoretic deposition was applied to produce SrTiO3 thin films on (fluorine-doped tin oxide) FTO conductive substrates. The electrophoretic voltage of 20 V and a process duration of 10 min were optimized to reach transparent and uniform coatings on FTO. The blue SrTiO3 reveals lower resistance (charge transfer resistance of 6.38 Ω cm-2) and higher electron mobility (current density value of 0.25 mA cm-2) compared to a pure SrTiO3 electrode. These findings may provide new insights for developing high-performance visible light photocatalysts.

Manufacturing of Photoactive β-Bismuth Oxide by Flame Spray Oxidation

Photoactive tetragonal bismuth oxide powder with different semiconducting characteristics was synthesized from Bi-pellets by flame spray oxidation. The effect of feedstock particle size and standoff distance (SOD) on the physical properties of β-Bi2O3 keeping constant the fuel/oxygen ratio is here reported. The flame spray oxidized powder was collected either from evaporated or in-flight particles quenched in water. The combination of flame spray processing parameters led to different β-Bi2O3 phase contents, oxidation characteristics, size distribution (nanometric and micrometric sized), morphology, and optical properties of the sprayed powder. The highest micrometric β-Bi2O3 content quenched in water was obtained at a SOD of 30 cm using a particle size distribution of 12-60 μm of Bi-feedstock. The obtained powder from in-flight particles collected in water allowed us to analyze the oxidation characteristics of bismuth. Micrometric powder shows the synthesis of snowman-like Bi/β-Bi2O3 Janus particles. The nanometric sized Bi2O3 powder was continuously obtained by spray oxidation, where its collection efficiency depends on processing parameters and showed spherical morphology and a highly pure tetragonal phase with narrow visible light absorbance (Eg = 2.26 eV). These optical characteristics indicate that the obtained β-Bi2O3 powder is suitable for high-performance visible-light photocatalyst.

Trimesoyl Chloride-Melamine Copolymer-TiO2 Nanocomposites as High-Performance Visible-Light Photocatalysts for Volatile Organic Compound Degradation

Benzene is a typical volatile organic compound (VOC) and is found widely in industrial waste gases. In this study, trimesoyl chloride-melamine copolymer (TMP)-TiO2 nanocomposites with excellent photocatalytic efficiency in visible-light degradation of gas-phase benzene were synthesized via an in situ hydrothermal synthesis. The optimal conditions for TMP-TiO2 nanocomposite synthesis were determined by orthogonal experiments. The structural, physiochemical, and optoelectronic properties of the samples were studied by various analytical techniques. Ultraviolet-visible diffuse reflectance spectroscopy and surface photovoltage spectra showed that the positions of the light-absorbance edges of the TMP-TiO2 nanocomposites were sharply red-shifted to the visible region relative to those of unmodified TiO2. The most efficient TMP-TiO2 nanocomposite was used for photocatalytic oxidative degradation of gas-phase benzene (initial concentration 230 mg m−3) under visible-light irradiation (380–800 nm); the degradation rate was 100% within 180 min. Under the same reaction conditions, the degradation rates of unmodified TiO2 (hydrothermally synthesized TiO2) and commercial material Degussa P25 were 19% and 23.6%, respectively. This is because the Ti–O–N and Ti–O–C bonds in TMP-modified TiO2 reduce the band gap of TMP-TiO2. The amide bonds in the TMP decrease the TiO2 nanoparticle size and thus increased the specific surface area. The conjugated structures in the TMP provide abundant active sites for trapping photogenerated electrons and promote the separation and transfer of photogenerated electrons and holes.

Magnetically recoverable MgFe2O4/conjugated polyvinyl chloride derivative nanocomposite with higher visible-light photocatalytic activity for treating Cr(VI)-polluted water

A facile three-step method was adopted to synthesize MgFe2O4/conjugated polyvinyl chloride (CPVC) nanocomposite. XRD, Raman, XPS, SEM, EDX, element mapping, and HRTEM analyses confirmed the formation of MgFe2O4/CPVC nanocomposite. The optical and magnetic properties of the obtained MgFe2O4/CPVC nanocomposite were measured using UV–Vis spectrophotometer and vibrating sample magnetometer, respectively. Through photocatalytic reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation, it can be noticed that MgFe2O4/CPVC nanocomposite had both improved visible-light photocatalytic activity (about 2.1 times that of MgFe2O4 nanoparticles) and good photocatalytic stability. Moreover, MgFe2O4/CPVC nanocomposite can also be easily recovered by use of a magnet. Based on electrochemical impedance, transient photocurrent response and Mott-Schottky measurement, the mechanism responsible for the enhanced photocatalytic activity of MgFe2O4/CPVC nanocomposite was proposed. Finally, MgFe2O4/CPVC nanocomposite was applied to photocatalytic treatment of the diluted black chromium electroplating solution at different pH. Results showed that MgFe2O4/CPVC nanocomposite had significant visible-light photocatalytic activity in treating the diluted black chromium electroplating solution over a wide pH range (1.4–10.3), and its treatment efficiency increased with the decrease of solution pH. Thus, MgFe2O4/CPVC nanocomposite has the potential to be a new magnetically recoverable, high-performance visible-light photocatalyst for treating Cr(VI)-polluted water.

Fabrication of Ultrathin Nanosheets of Graphitic Carbon Nitride Heterojunction with Spherical Shaped Bi2O3 Nanoparticles for High Performance Visible Light Photocatalyst

A combined microwave-calcinations approach is developed to synthesize of β-Bi2O3/g-C3N4 hybrid nanocomposite and methodically investigated their structural, optical and photocatalytic properties. XRD and TEM results divulge that tetragonal structure and the individual spherical shaped nanoparticles 35–40 nm were uniformly scattered over the g-C3N4 sheets. The formation of g-C3N4 and β-Bi2O3 can develop the light absorption ability and separation of photogenerated carriers of β-Bi2O3, which is confirmed through photoluminescence and UV–Vis DRS analysis. The photocatalytic degradation of congo-red (CR) and malachite green (MG) dyes were evaluated under visible light irradiation. The β-Bi2O3/g-C3N4 heterojunction exhibited higher photocatalytic activity towards MG dye such as high photodegradation efficiency (94.8%) and good stability (92%) than bare β-Bi2O3. This could be due to the high surface area and synergic effect between the β-Bi2O3 and g-C3N4 p–n junctions. This work provides an efficient β-Bi2O3/g-C3N4 hybrid for removal of toxic pollutants and waste water treatments.

D35-TiO2 nano-crystalline film as a high performance visible-light photocatalyst towards the degradation of bis-phenol A

Dye-sensitized photocatalytic suspension system for wastewater treatment is still limited in practice due to particle aggregation, fast charge carrier recombination, poor stability and recycling issue. In this study, we combine TiO2 nano-crystalline film with D35 organic dye to fabricate a new visible-light photocatalyst D35-TiO2, which exhibits excellent visible light absorption. Its transient photocurrent is almost 10 times higher than pure TiO2 under visible light illumination (λ > 420 nm). Besides the well characterizations of the D35-TiO2 film, e.g., SEM, EDS, TEM, XRD, UV–Vis DRS, XPS, PL and I-T, degradation of bis-phenol A (BPA) is performed as the model reaction to test its photocatalytic activity. Meanwhile, we employ external bias in the reaction system to further enhance the photogenerated charge carrier separation, and improve the photocatalytic efficiency. Under the better experimental conditions of initial BPA concentration (5 mg/L), initial pH (pH 7), external bias (0.25 V) and sensitizer concentration (0.1 mM), BPA is almost completely degraded in 300 min, and the four intermediates are gradually mineralized. The ecotoxicity of BPA also decreases significantly after the photodegradation. During the reaction, O2− plays a dominant role, meanwhile ·OH and h+D35 also contribute to the BPA degradation. After five cycles, the D35-TiO2 film still maintain the normal photocatalytic activity. Due to the high stability and recyclability, the D35-TiO2 nano-crystalline film provides a sustainable way for degrading micropollutants in wastewater.

Novel Ag@AgCl@AgBr heterostructured nanotubes as high-performance visible-light photocatalysts for decomposition of dyes

Recently, AgX (X = Cl, Br, I) materials have been demonstrated as novel and efficient visible-light photocatalysts for the decomposition of various organic compounds and dyes. Herein, heterostructured Ag@AgCl@AgBr nanotubes were prepared by an anion-exchange reaction between Ag@AgCl nanotubes and Br− anions, and their photocatalytic activities towards the decomposition of organic pollutants were studied. The as-synthesized photocatalysts were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE–SEM), high-resolution transmission electron microscopy combined with energy-dispersive X-ray spectroscopy (HR–TEM/EDS), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The structure characterization studies confirmed that the photocatalysts had nanotubular morphology. Compared to polyhedral Ag@AgBr nanoparticles, the incorporation of Br− ions into the Ag@AgCl framework remarkably enhanced the photocatalytic activities. The as-prepared Ag@AgCl@AgBr nanotubes can also be reused due to their high stability. Under visible light irradiation, >98.5% of Rhodamine B (RhB) and 90.3% of Red Acid I (RAI) were decomposed within 45 min using the catalyst AB–2 (Cl−/Br- = 1:1). The catalyst AB–2 displayed higher photocatalytic activity due to its enhanced surface area and photoelectron transfer, attributed to its novel heterostructured configuration.

Polymer dots grafted TiO2 nanohybrids as high performance visible light photocatalysts

As a new member of carbon dots (CDs), Polymer dots (PDs) prepared by hydrothermal treatment of polymers, usually consist of the carbon core and the connected partially degraded polymer chains. This type of CDs might possess aqueous solubility, non-toxicity, excellent stability against photo-bleaching and high visible light activity. In this research, PDs were prepared by a moderate hydrothermal treatment of polyvinyl alcohol, and PDs grafted TiO2 (PDs-TiO2) nanohybrids with TiOC bonds were prepared by a facile in-situ hydrothermal treatment of PDs and Ti (SO4)2. Under visible light irradiation, the PDs-TiO2 demonstrate excellent photocatalytic activity for methyl orange degradation, and the photocatalytic rate constant of PDs-TiO2 is 3.6 and 9.5 times higher than that of pure TiO2 and commercial P25, respectively. In addition, the PDs-TiO2 exhibit good recycle stability under UV–Vis light irradiation. The interfacial TiOC bonds and the π-conjugated structures in PDs-TiO2 can act as the pathways to quickly transfer the excited electrons between PDs and TiO2, therefore contribute to the excellent photocatalytic activity.

The reaction mechanism of plasmonic photocatalytic NO oxidation on Bi-metal/BiPO<sub>4</sub>

With the rapid development of economy, factories and vehicles make the air pollution became a worldwide focused issue. As one of the major air pollutants, nitric oxide (NO) would lead to serious atmospheric problems such as acid rain, haze, and photochemical smog. However, low concentration nitric oxide is hard to be removed by the way of industrialization. Photocatalysis, as a green and effective technology, has become one of the most promising technologies for solving air pollution problems and that works on low concentration air pollutant. As one of the typical photocatalyst, BiPO4 consists of alternating layers of [Bi2O2]2+ and PO43− groups and has the better UV-light photocatalysis performance when compare with TiO2, emerging as an attractive photocatalyst. At present, the study to enable BiPO4 respond visible light which comes up with many ways, such as element doping, build heterojunction and surface hybridization. The recent investigation shows that metal Bi possess the property of surface plasmon resonance (SPR) as well as noble metal like gold could enhance the photocatalysis activity by increasing light absorption and raising the separation efficiency of photogenerated electron-hole pair. In this study, Bi/BiPO4 composite photocatalyst was synthesized via a two steps method. Firstly, the hexagonal phase BiPO4 was prepared by a precipitation method. And then, the metal Bi was deposited on the surface of BiPO4 in the presence of NaBH4. The as-prepared photocatalyst was applied to the photocatalytic removal of low concentration of NO in air. The microstructures of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), UV-visible diffuse-reflectance spectrum (UV-vis DRS) and electron spin-resonance spectroscopy (ESR). The in situ FT-IR was used to analyze the reaction intermediates of photocatalytic NO oxidation under visible light irradiation. On the basis of free radicals capture from ESR, the reaction mechanism was proposed. The results show that the surface plasmon resonance of Bi metal promoted the visible light absorption and separation of photogenerated charge on BiPO4. The DFT calculation results indicated that the presence of oxygen defects induced the formation of the intermediate energy level between the valence band and the conduction band of the bismuth phosphate, which is beneficial to the electron transition from valence band. The results of electronic structure calculations manifest that the metal Bi also plays a role of storing and transferring electrons from the conduction band of BiPO4. The generation and rapid transfer of photogenerated carriers could decrease the photogenerated electron-hole pair recombination rate. As a result, the BiPO4 can be converted into a high performance visible light photocatalyst. The present work could provide new insights into the understanding of the Bi-based plasmonic photocatalyst and the mechanism of gas-phase photocatalytic reaction.