Photocatalytic activity of novel AgBr/WO3 composite photocatalyst under visible light irradiation for methyl orange degradation

The coupled WO3-AgBr nanocatalyst, part II: Synthesis, characterization, and the boosted photocatalytic activity towards metronidazole in an aqueous solution

The AgBr and WO3 nanoparticles (NPs) were synthesized and coupled, and the coupled AgBr-WO3 binary catalyst, as well as the individual AgBr and WO3 NPs, were then characterized by XRD, FTIR, DRS, and SEM-EDX. XRD results showed the formation of orthorhombic WO3 cubic AgBr crystals. The crystallite sizes of 45, 28, and 45 nm were estimated by the Scherrer formula for the as-prepared AgBr, WO3, and AgBr-WO3 catalysts, respectively. The DRS study estimated band gap energies using both absorption edge wavelengths and the Kubelka-Munk model. The band gap energies of 2.72, 3.06, and 2.92 eV were obtained for the direct electronic transitions of AgBr, WO3, and AgBr-WO3. The ECB (potential position) of AgBr and WO3 were estimated to be 0.01 and 0.52 V, while their EVB values were 2.60 and 3.55 V, respectively. Typical FTIR absorption bands of W‒OH, the W‒O‒W, and AgBr bonds have appeared at 1637 cm-1, 823 (and 766) cm-1, and 1384 cm-1, respectively. The pHpzc of 4 was estimated for the individual and coupled catalysts. In studying the photocatalytic activity of the catalysts in the photodegradation of metronidazole (MNZ) a boosted activity was achieved for the coupled system. This increased activity depends on the maximum AgBr:WO3 mole ratio in a 1:3 mol ratio. Grinding time applied to prepare the coupled catalyst has also varied the photocatalytic activity.

High-Efficient Visible-Light Photocatalysis Performance and Light-Corrosion Resistance of Ag3PO4 Constructed by double-Z System Composites

Novel visible-light-driven Ag₃PO₄/AgBr/AgI photocatalysts were prepared via a simple self-assembly strategy combined with in-situ anion-exchanging process. The photocatalytic activity of Ag₃PO₄ was significantly improved by constructing double-Z system. Specifically, the obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy (DRS). Under visible light irradiation (λ > 420 nm), the Ag₃PO₄/AgBr/AgI photocatalysts showed much higher photocatalytic activity than bulk Ag₃PO₄ for the degradation of formaldehyde (HCHO), and 100% HCHO degradation could be obtained within 28 min. The degradation efficiency could be maintained in five cycles. Further electron paramagnetic resonance (ESR) tests demonstrated that both •OH and •O₂^- generated in the system. This study provides new insights into the fabrication of highly efficient visible-light-driven photocatalysts and facilitates their practical application in emerging environment issues.

Photocatalytic degradation of organic dye and tetracycline by ternary Ag2O/AgBr-CeO2 photocatalyst under visible-light irradiation

In this work, CeO2 nanosheets decorated with Ag2O and AgBr are successfully fabricated via a simple sediment-precipitation method. The as-prepared ternary Ag2O/AgBr-CeO2 composite with double Z-scheme construction was analyzed by various analytical techniques. Ag nanoparticles (NPs) used as the electron medium could reduce the recombination of photoelectrons and holes, thus leading to the improvement of photocatalytic performance of these catalysts. Due to the unique structure and composite advantages, the optimal Ag2O/AgBr-CeO2 photocatalysts exhibit the superior tetracycline (TC) degradation efficiency of 93.23% and favorable stability with near-initial capacity under visible light irradiation. This ternary Z-scheme structure materials will be the well-promising photocatalysts or the purification of antibiotic wastewater.

A redox-active support for the synthesis of Au@SnO2 core-shell nanostructure and SnO2 quantum dots with efficient photoactivities

A defect pyrochlore-type Sn1.06Nb2O5.59F0.97 (SnNbOF) nano-octahedron is used as a redox-active support for fabricating Au@SnO2 core-shell and SnO2 quantum dots at room temperature without the use of organic species or foreign reducing reagents. Gold (Au) and SnO2 components were obtained through an in situ redox reaction between the HAuCl4 and reductive Sn2+ ions incorporated in SnNbOF. The composition and morphology of the resulting nanocomposites (denoted as Au-SnNbOF) could be controlled by adjusting the Au/SnNbOF ratio. The Au-SnNbOF nanocomposites exhibited efficient photoactivities for methyl orange (MO) degradation under the visible light irradiation (λ > 420 nm), during which the MO was almost completely degraded within 8 min. Among all the samples, the 5wt% Au-SnNbOF nanocomposite had the highest rate constant (0.43 min-1), which was 40 times higher than that of the blank SnNbOF.

Photocatalytic reduction of Cr(VI) using Mg-doped WO3 nanoparticles

The hydrothermal synthesis method was employed for the fabrication of pristine tungsten trioxide (WO₃) and that of varying dopant percentages (1, 3 and 5% m/m) of magnesium (Mg-WO₃). The optical and structural properties of the synthesized materials were characterized using DRS, XRD, FTIR, TEM, BET, FESEM, XPS, PL, and Raman. Rectangular shaped nanostructures were observed through FESEM, wherein confirmed as monoclinic with the aid of XRD, FTIR and Raman analysis. Visualization of the doping was carried out using HRTEM imagery, which was also confirmed by a slight increase (0.0069 nm) of d spacing. As a consequence, band gaps were diminished and band edge positions were shifted. Band edge position shifts were confirmed via XPS analysis (0.08 eV). The point of zero charge was observed to shift towards positive upon doping at working pH 1 and 3.75 pH was the highest recorded. The rate of recombination was greatly reduced upon doping was observed through PL analysis. This was supported by DFT calculations, in which case the reduction of the rate of recombination was attributed to the introduction of Mg orbital. An improved efficiency was observed via the photo reduction of Cr(VI) metal ion in waste water, in which case, 97% reduction was attained.

A Review on Synthesis and Characterization of Ag2O Nanoparticles for Photocatalytic Applications

Even though the photocatalytic processes are a good technology for treatment of toxic organic pollutants, the majority of current photocatalysts cannot utilize sunlight sufficiently to realize the decomposition of these organic pollutants. As stated by various researchers, metal oxide nanoparticles have a significant photocatalytic performance under visible light source. Among various chemical and physical methods used to synthesize nanostructured silver oxide, green synthetic route is a cheaper and environmental friendly method. To confirm the optimum production of Ag2O NPs, effect of pH, extract concentration, metal ion concentration, and contact time were optimized. The structure, morphology, crystallinity, size, purity, elemental composition, and optical properties of obtained Ag2O NPs were characterized by different techniques, such as scanning electron microscopy (SEM), transmission electron microscope (HRTEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and UV-visible spectrophotometer accordingly as revealed by our literature review. The photocatalytic performance of the synthesized nanocrystalline Ag2O by photocatalytic degradation of organic dyes under visible light irradiation has been discussed thoroughly in this review. Many past studies revealed that organic dyes and pollutants are decomposed completely by green synthesized Ag2O NPs under irradiation of visible light.

Facile fabrication of silver iodide/graphitic carbon nitride nanocomposites by notable photo-catalytic performance through sunlight and antimicrobial activity

Silver iodide/graphitic carbon nitride nanocomposites have been successfully fabricated through sonication-assisted deposition-precipitation route at room temperature and hydrothermal method. Varied mass ratios and preparation processes can modify the structure, purity, shape, and scale of specimens. The purity of the product was confirmed by Energy Dispersive X-Ray Spectroscopy (EDS) and X-ray crystallography. The morphology and size of specimens could be observed with transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The bandgap was evaluated around 2.82 eV for pure g-C₃N₄. The bandgap has reduced to 2.70 eV by increasing the quantity of silver iodide in the nanocomposites. The photocatalytic activity of AgI/C₃N₄ has been studied over the destruction of rhodamine B (RhB) and methyl orange (MO) through visible radiation due to their suitable bandgap. The as-prepared AgI/C₃N₄ nanocomposites photocatalyst revealed better photocatalytic behavior than the genuine AgI and C₃N₄ which ascribed to synergic impacts at the interconnection of C₃N₄ and AgI. Furthermore, these nanocomposites have great potential for being a great antibacterial agent.

Co3O4-Ag photocatalysts for the efficient degradation of methyl orange

In this paper, a series of Co3O4-Ag photocatalysts with different Ag loadings were synthesized by facile hydrothermal and in situ photoreduction methods and fully characterized by XRD, SEM, TEM, FTIR spectroscopy, XPS, UV-vis and PL techniques. The catalysts were used for the degradation of methyl orange (MO). Compared with the pure Co3O4 catalyst, the Co3O4-Ag catalysts showed better activity; among these, the Co3O4-Ag-0.3 catalyst demonstrated the most efficient activity with 96.4% degradation efficiency after 30 h UV light irradiation and high degradation efficiency of 99.1% after 6 h visible light irradiation. According to the corresponding dynamics study under UV light irradiation, the photocatalytic efficiency of Co3O4-Ag-0.3 was 2.72 times higher than that of Co3O4 under identical reaction conditions. The excellent photocatalytic activity of Co3O4-Ag can be attributed to the synergistic effect of strong absorption under UV and visible light, reduced photoelectron and hole recombination rate, and decreased band gap due to Ag doping. Additionally, a possible reaction mechanism over the Co3O4-Ag photocatalysts was proposed and explained.

A Review on Catalytic Nanomaterials for Volatile Organic Compounds VOC Removal and Their Applications for Healthy Buildings

In order to improve the indoor air quality, volatile organic compounds (VOCs) can be removed via an efficient approach by using catalysts. This review proposed a comprehensive summary of various nanomaterials for thermal/photo-catalytic removal of VOCs. These representative materials are mainly categorized as carbon-based and metallic oxides materials, and their morphologies, synthesis techniques, and performances have been explained in detail. To improve the indoor and outdoor air quality, the catalytic nanomaterials can be utilized for emerging building applications such as VOC-reduction coatings, paints, air filters, and construction materials. Due to the characteristics of low cost, non-toxic and high chemical stability, metallic oxides such as TiO₂ and ZnO have been widely investigated for decades and dominate the application market of VOC-removal catalyst in buildings. Since other catalysts also showed brilliant performance and have been theoretically researched, they can be potential candidates for applications in future healthy buildings. This review will contribute to further knowledge and greater potential applications of promising VOC-reducing catalytic nanomaterials on healthier buildings for a better indoor and outdoor environment well-being.

Degradation of antibiotics in multi-component systems with novel ternary AgBr/Ag3PO4@natural hematite heterojunction photocatalyst under simulated solar light

Abatement of antibiotics from aquatic systems is of great importance but remains a challenge. Herein, we prepared ternary AgBr/Ag₃PO₄@natural hematite (AgBr/Ag₃PO₄@NH) heterojunction composite via a simple route for the photocatalytic degradation of antibiotic pollutants. By adjusting the dose of Ag species, four products with different Ag content (denoted as Ag_0.5BrPFe, Ag₁BrPFe, Ag_1.5BrPFe, and Ag₂BrPFe) were developed. Among them, Ag_1.5BrPFe exhibited the best photocatalytic activity. Four antibiotics (i.e. ciprofloxacin (CIP), norfloxacin (NOR), sulfadiazine (SDZ), and tetracycline (TTC)) could be degraded with synthesized Ag_1.5BrPFe in multi-component systems. Water matrix indexes including solution pH, coexisting anions, humic acids exhibited distinct effects on the degradation process. The results revealed that the degradation process was accelerated at acidic conditions while depressed at basic conditions. Superoxide radical and hole were detected by in situ electron spin resonance technique and played the dominant roles. The degradation pathway TTC was tentatively established followed with the identification of the degradation intermediates and computational analysis. This work would shed light on the photocatalytic degradation mechanism of organic pollutants by the AgBr/Ag₃PO₄@NH composite.

Visible-Light-Driven Photocatalytic Activity of Magnetic BiOBr/SrFe12O19 Nanosheets

Magnetic BiOBr/SrFe₁₂O₁₉ nanosheets were successfully synthesized using the hydrothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and UV-visible diffused reflectance spectra (UV-DRS), and the magnetic properties were tested using a vibration sample magnetometer (VSM). The as-produced composite with an irregular flaky-shaped aggregate possesses a good anti-demagnetization ability (Hc = 861.04 G) and a high photocatalytic efficiency. Under visible light (λ > 420 nm) and UV light-emitting diode (LED) irradiation, the photodegradation rates of Rhodamine B (RhB) using BiOBr/SrFe₁₂O₁₉ (5 wt %) (BOB/SFO-5) after 30 min of reaction were 97% and 98%, respectively, which were higher than that using BiOBr (87%). The degradation rate of RhB using the recovered BiOBr/5 wt % SrFe₁₂O₁₉ (marked as BOB/SFO-5) was still more than 85% in the fifth cycle, indicating the high stability of the composite catalyst. Meanwhile, after five cycles, the magnetic properties were still as stable as before. The radical-capture experiments proved that superoxide radicals and holes were main active species in the photocatalytic degradation of RhB.

A label-free aptamer-based cytosensor for specific cervical cancer HeLa cell recognition through a g-C3N4-AgI/ITO photoelectrode

Facile and efficient detection of cancer cells in the early phases of the disease is one of the main challenges in cancer diagnostics. It has been found that photoactive materials and bio-recognition elements are two key factors in the development of promising photoelectrochemical (PEC) biosensors for cancer cell detection, which can play significant roles for realizing early cancer diagnostics with high sensitivity and selectivity. In this study, we designed a novel label-free PEC aptamer-based cytosensor for the specific detection of cancer cells such as HeLa cells by using water-dispersible g-C₃N₄-AgI nanocomposites as visible light-sensitive materials and anti-CEM/PTK7 aptamer as the bio-recognition element. It was observed that when a suitable amount of AgI nanoparticles was doped in two-dimensional graphite-like carbon nitride nano-sheets (g-C₃N₄ NSs), the visible light photocurrent response could be significantly improved. The PEC response of the as-prepared biosensor based on the g-C₃N₄-AgI/ITO photoelectrode was linearly proportional to the relevant cancer cells such as HeLa cells at concentrations ranging from 10 to 10⁶ cells per mL with a limit of detection of 5 cells per mL. In addition, the g-C₃N₄-AgI/ITO photoelectrode and the fabricated cytosensor exhibited long-term stability, good reproducibility, excellent selectivity, and high sensitivity, demonstrating the successful conjugation of g-C₃N₄-AgI NSs with the aptamer and target cancer cells in the high performance PEC cytosensor.

Application of Ag/AgBr/GdVO4 composite photocatalyst in wastewater treatment

Ag/AgBr/GdVO₄ composite photocatalysts were designed and synthesized in this paper. The physical and chemical structures, as well as optical properties of the synthesized composite were investigated via XRD, XPS, TEM, and UV-vis. It is found that the composite showed a ternary heterojunction structure of Ag, AgBr and GdVO₄. Meanwhile, it has a high intensity of light current, indicating its high separation efficiency of electron and hole. Photocatalytic oxidation of rhodamine B (RhB) under visible light irradiation was performed to investigate the activity of the Ag/AgBr/GdVO₄ composite. Result indicates that it shows excellent photocatalytic activity. Under visible light irradiation for 12min, about 80% of RhB (30μmol/L) was degraded. The degradation rate is estimated to be 0.253 min-1, which is three times higher than that of pure AgBr. The high photoactivity can be ascribed to the synergetic effect of AgBr, GdVO₄, and Ag nanoparticle in separation of electron-hole pairs.

Self-assembly of metal/semiconductor heterostructures via ligand engineering: unravelling the synergistic dual roles of metal nanocrystals toward plasmonic photoredox catalysis

Metal nanocrystals (NCs) have been recognized as an important class of nanomaterials by virtue of their unique surface plasmon resonance (SPR) effect and pivotal roles as electron traps in photocatalysis. Nevertheless, it is still challenging to unambiguously unravel and simultaneously harness the dual synergistic roles of metal NCs in a single photocatalytic system for solar-to-chemical energy conversion. Herein, an efficient ligand-triggered electrostatic self-assembly strategy was developed to achieve the spontaneous and monodispersed attachment of Au NCs onto 1D WO₃ nanorods (NRs) via pronounced electrostatic attractive interaction, in which tailor-made positively charged Au NCs were closely integrated with negatively charged WO₃ NRs. The intimate integration of Au NCs with WO₃ NRs at the nanoscale could significantly benefit the extraction, separation, and migration of plasmon-induced energetic hot carriers over Au NCs and promote the separation of photogenerated charge carriers over the WO₃ substrate. Such a cooperative synergy stemming from SPR and the electron-withdrawal effects of the Au NCs resulted in distinctly enhanced photoredox catalytic performances for plasmonic photocatalysis under both simulated solar and visible light irradiation. Our study highlights the significance of utilizing a rational interface design between metal NCs and semiconductors for excavating the multifarious roles of metal NCs in substantial solar energy conversion.

Fabrication of novel visible-light-driven AgI/g-C(3)N(4) composites with enhanced visible-light photocatalytic activity for diclofenac degradation

A visible-light-driven heterostructured AgI/g-C₃N₄ was prepared by a deposition-precipitation method. The composition, structure, morphology, and optical properties of the photocatalyst were characterized by Brunauer-Emmett-Teller method (BET), X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscope (SEM), UV-vis diffused reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), photocurrent, and electrochemical impedance spectroscopy (EIS), respectively. AgI/g-C₃N₄ composite photocatalysts exhibited higher photocatalytic activities than those of AgI nanoparticles and g-C₃N₄ in the degradation of diclofenac (a model anti-inflammatory medicine) under visible light irradiation (λ≥400nm). When the mass molar ratio of AgI was 45% in AgI/g-C₃N₄, the reaction rate constant of diclofenac degradation reached 0.561min^-1, which was almost 12.5 and 43.2 times higher than that achieved by AgI (0.045min^-1) and g-C₃N₄ (0.013min^-1). The h⁺ and O₂^- were pinpointed as the main reactive species in the photocatalytic reaction using their obligate radical scavengers. Diclofenac was completely degraded and partly mineralized during the photodegradation. The main intermediates were determined by liquid chromatograph mass spectrometer (LC-MS), and toxicological assessments were carried out to evaluate the change of toxicity in the degradation process. In addition, the photocatalysts showed excellent stability over multiple reaction cycles. Finally, a possible photocatalytic and charge separation mechanism was proposed.

An Au/AgBr–Ag heterostructure plasmonic photocatalyst with enhanced catalytic activity under visible light

An efficient bimetallic–semiconductor (Au/AgBr–Ag) plasmonic heterostructure with plasmon enhanced absorption and plasmonic sensitization for visible light induced photocatalysis.

Facile synthesis of AgI/BiOI-Bi2O3 multi-heterojunctions with high visible light activity for Cr(VI) reduction

AgI sensitized BiOI-Bi2O3 composite (AgI/BiOI-Bi2O3) with multi-heterojunctions was prepared using simple etching-deposition process. Different characterization techniques were performed to investigate the structural, optical and electrical properties of the as-prepared photocatalysts. It was found that the ternary AgI/BiOI-Bi2O3 composite exhibited: (1) improved photocurrent response, (2) smaller band gap, (3) greatly reduced charge transfer resistance and (4) negative shift of flat band potential, which finally led to easier generation and more efficient separation of photo-generated electron-hole pairs at the hetero-interfaces. Thus, for the reduction of Cr(VI), AgI/BiOI-Bi2O3 exhibited excellent photocatalytic activity under visible light irradiation at near neutral pH. AgI/BiOI-Bi2O3 was optimized when the initial molar ratio of KI to Bi2O3 and AgNO3 to Bi2O3 was 1:1 and 10%, respectively. The estimated kCr(VI) on optimized AgI/BiOI-Bi2O3 was about 16 times that on pure Bi2O3. Good stability was also observed in cyclic runs, indicating that the current multi-heterostructured photocatalyst is highly desirable for the remediation of Cr(VI)-containing wastewater.

Environmental manipulation to promote stem cell survival in vivo: use of aggregation, oxygen carrier, and BMP-2 co-delivery strategies

While mesenchymal stem cell (MSC)-based strategies for critically-sized bone defect repair hold promise, poor cell survival in vivo remains a significant barrier to the translation of these therapeutics.

The role of Sn in enhancing the visible-light photocatalytic activity of hollow hierarchical microspheres of the Bi/BiOBr heterojunction

The synergistic effect of oxygen vacancies and the Bi/BiOBr heterojunction broadens the light absorption range and promotes the charge separation efficiency.

Universal degradation performance of a high-efficiency AgBr/Ag2CO3 photocatalyst under visible light and an insight into the reaction mechanism

A AgBr/Ag₂CO₃ photocatalyst exhibited excellent photocatalytic activity and stability under visible light and a two-stage photocatalytic mechanism was proposed.

Synthesis of Mo-doped WO3 nanosheets with enhanced visible-light-driven photocatalytic properties

Ion doping provides a powerful means for the fabrication of a functionalized photocatalyst that is both active and stable.

Selective construction of junctions on different facets of BiVO4 for enhancing photo-activity

The combination of p–n and m–s junctions over BiVO₄ results in an additional effect for improving photo-activity.

Advanced nanoarchitectures of silver/silver compound composites for photochemical reactions

Silver/silver compound (SSC) composites have received much attention as a type of potential materials in photochemical reactions due to their high efficiency, facile syntheses and availability of raw materials. This article reviews the state-of-the-art progress on the advanced nanoarchitectures of SSC composites. We begin with a survey on the general synthetic strategies for SSC composites, and then step into relatively detailed methods for size and morphology tunable two-component and more delicate multi-component SSC nanostructures. In addition, the electronic structure-related mechanisms of such materials and the recent studies on their stability are summarized. This review also highlights some perspectives on challenges related to the SSC composites and the possible research in the future.

Catalytic activity of MnOx/WO3 nanoparticles: synthesis, structure characterization and oxidative degradation of methylene blue

MnO_x/WO₃ nanoparticles were found to be an effective catalyst for the degradation of methylene blue, an important industrial dye and a problematic pollutant.

La2Ti2O7 nanoplates decorated with Cu2ZnSnS4 nanoparticles for enhanced visible-light-driven photocatalytic activity

Novel Cu₂ZnSnS₄/La₂Ti₂O₇ hetero-junction photocatalysts with high visible-light-driven photocatalytic activities were achieved by a green process.