AgBr Surface Research Articles

Electron-buffer-mediated dual Z-scheme ZnSe/Ag2Se/AgBr heterojunction for efficient CO2 photocatalytic reduction

Design of photocatalysts with high-efficiency for sunlight utilization is one of the prerequisites for CO2 photoreduction. Besides, modulating a stable electron-donating environment to meet the energy barrier for CO2 reduction to CO is crucial. In this work, the ZnSe/Ag2Se/AgBr (ZAA) heterojunction was fabricated by growing the ZnSe on the AgBr surface accompanied by in-situ generation of Ag2Se between the two components by hydrothermal process. Results showed that the ZAA exhibited excellent light response ability over the full wavelength range. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) demonstrated that the charge transfer of the ZAA conformed to dual Z-scheme mechanism, with the Ag2Se acting as an electron transfer bridge, which in turn acted as an electron reservoir to accelerate electron transfer, facilitating carriers’ separation. The highest CO yield of 54.14 µmol/g/h was obtained from the optimal ZAA-2, which was 11.76 and 10.44 times of pure ZnSe and Ag2Se, respectively. This work demonstrated the feasibility of a dual Z-scheme heterostructure with full spectrum response for offering stable electron-donating environment and improving electron transfer for enhanced photocatalytic activity.

Boosting the photocatalytic properties of NaTaO3 by coupling with AgBr

AgBr/NaTaO3 composites, with different molar % of NaTaO3 (Br/NTO(X%)), have been synthesized by simple precipitation methods; bare NaTaO3 was synthesized by hydrothermal procedure, while AgBr was synthesized by a precipitation procedure using cetyl-tri-methyl-ammonium bromide (CTAB) and AgNO3. Samples have been characterized by X-ray diffraction (XRD), N2 adsorption, UV–vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of the as-prepared photo-catalysts was evaluated through photocatalytic degradation of rhodamine B (RhB), methyl orange (MO) and caffeic acid (CAFA) under UV and visible illumination. Single AgBr material and Br/NTO(X%) composites displayed the ability to absorb light in the visible region, while NaTaO3 is only photoactive under UV irradiation. Based on the position of conduction and valence bands of AgBr and NaTaO3, the heterojunction between these two photo-catalysts corresponds to a type II junction. In the case of photocatalytic degradation of RhB and CAFA, Br/NTO(x%) composites have highest photocatalytic activity than that obtained by both parental materials under the same operational conditions. AgBr and Br/NTO(x%) composites achieve a fast degradation of MO, together with a considerable adsorption capacity, attributed to the presence of a remaining amount of residual CTAB on the AgBr surface. In summary, coupling AgBr with NaTaO3 improves the photocatalytic activity under both UV and visible illumination with respect to the parental components, but the performance of the composites is highly dependent on the type of substrate to be degraded and the illumination conditions.

Synthesis and characterization of Bi2SiO5-coated Ag/AgBr photocatalyst with highly efficient decontamination of organic pollutants

In this work, a novel nanoscale leaf-like ternary Bi2SiO5/Ag/AgBr photocatalyst was synthesized by means of the hydrothermal reaction together with an in situ photoreduction procedure. The ternary Bi2SiO5/Ag/AgBr composites possessed a neoteric heterostructure, in which the surface of AgBr was wrapped with nano-sheet Bi2SiO5. Through the coating of Bi2SiO5, the growth of AgBr nanoparticles was hindered, thereby inhibiting the agglomeration. In ternary composites, the particle size of Ag/AgBr obviously decreased, which reduced from 5 um to 0.6 um, approximately. The above effects of Bi2SiO5 on the morphology of Ag/AgBr were conducive to increasing the chance of contact between the active center and the reactant, thus promoting photocatalytic activity. Systematic researches showed that the BA 1–5 (the composite with a Bi2SiO5/Ag/AgBr molar ratio of 1:5) exhibited the optimal removal efficiency for RhB degradation, which was 5.97 times and 3.28 times that of Ag/AgBr and Bi2SiO5, respectively. Co-effect of the surface plasmon resonance (SPR) induced by Ag0 as well as formed heterojunction composed of Bi2SiO5, AgBr and Ag also contributed a lot in the splendid light absorption of ternary composites. H2-TPR analysis indicated that the reduction ability of Ag/AgBr was further enhanced, comparing with that of bare Ag/AgBr. This present work can provide an original approach to devise and manufacture the Ag/AgBr-based photocatalysts.

Влияние связующего и красителей на механизм туннельной люминесепнции микрокристаллов AgBr(I)

It was previously found that in emulsion microcrystals (EMC) AgBr (I) (with silver content corresponding to pBr 4), the centers responsible for tunneling recombination at T = 77 K, with a maximum of luminescence at λmax~ 560 nm when excited from light from the absorption region of AgBr (I) EMCs (λ ~ 450 nm) as a result of temperature quenching, they undergo structural transformation into centers, which, under the same excitation, provide tunneling recombination with a wavelength depending on the binder: for EMC AgBr (I) obtained in water ‒ λmax~ 720 nm, in gelatin ‒ λmax~ 750 nm. In the present work, similar structural transformations of the centers determining tunneling recombination with λmax~ 560 nm, to the centers with luminescence on λmax~ 720 nm were implemented for AgBr (I) EMCs synthesized in polyvinyl alcohol (PVA) with an increase in the content of silver ions in the emulsion (from pBr 4 to 7). Responsible for this transformation, as follows from the obtained results, are mobile interstitial silver ions Agi +, which transform these tunnel recombination centers. The effect of the binder on the recombination processes in EMC AgBr (I) is manifested in changes in the kinetics of the increase in luminescence with λmax~ 560 nm upon excitation by light from the absorption region of AgBr (I) EMC (λ ~ 450 nm) to a stationary level. For a binder whose molecules do not interact with Ag centers Agin+, n = 1, 2 (water, PVA at pBr 4), increase in luminescence with λmax~ 560 nm occurs monotonically from zero to the maximum stationary level. For a binder (in our case, G is gelatin), whose molecules with centers Agin+ (n = 1,2) form complexes (Agin0G+), the kinetics of the increase in luminescence in EMC AgBr (I) to a stationary level at λmax~ 560 nm at pBr 4 is characterized by the presence of “flash flare”. Adsorption on the surface of EMC AgBr (I) (in PVA at pBr 7) of the dye is manifested as follows: if, before the introduction of the dye, the kinetics of the increase in luminescence with λmax~ 560 nm, when excited from light from the absorption region of AgBr (I) EMC (λ ~ 450 nm) to a stationary level, “flare-up” appeared, then after the introduction of the dye, the luminescence increases with λmax~ 560 nm occurs monotonically from zero to the maximum stationary level. Studies of the “flash” of luminescence stimulated by infrared (IR) light, after the termination of the action of exciting light, showed that when the kinetics of the increase in luminescence with λmax~ 560 nm to the stationary level, it exhibits "flare-up", a "flash" stimulated by IR light is not observed at λ ~ 560 nm. In the absence of “flash flare”, a “flash” at λ ~ 560 nm is observed. From our point of view, the results obtained indicate that “flare-up burning” is due to the presence of deep centers of electron localization with a small capture cross section, and not a photochemical reaction stimulated by exciting light. Key words: AgBr (I) microcrystals, emulsions, glow centers, luminescence flare-up.

Facile preparation of visible-light-responsive kaolin-supported Ag@AgBr composites and their enhanced photocatalytic properties

A novel visible light responsive Ag@AgBr/kaolin photocatalyst was synthesized via in-situ deposition-precipitation method. The X-ray diffraction (XRD) and high-resolution transmission electron spectroscopy (HRTEM) analysis proved the formation of Ag@AgBr nanoparticles in the surface of kaolin clay. The phases, chemical compositions and optical properties of the as-prepared Ag@AgBr/kaolin composite were well characterized by X-ray photoelectron spectroscopy (XPS) and UV–visible diffused reflectance spectra. The photocatalytic activity of the Ag@AgBr/kaolin composite was investigated by the degradation of methyl orange (MO) and rhodamine B (RhB) solution under visible light irradiation.The Ag@AgBr/kaolin composite could be effectively applied over a wide range of pH 2.54–10.95 in the degradation of typical dyes and also showed higher stability and reusability capacity even after four cycles. Active radical trapping experiments suggested that the boosting photocatalytic activities was enhanced due to the moreactive sites, large surface area, and surface plasmonic resonance of metallic Ag nanoparticles on the surface of AgBr. This study might provide a newinsight into the design of high-efficiency clay-supported photocatalyst for organic pollutants degradation and environmental remediation.

Cotton functionalized with nanostructured TiO2-Ag-AgBr layer for solar photocatalytic degradation of dyes and toxic organophosphates.

The functionalization of cotton fabric with photoactive TiO2-Ag-AgBr nanostructured layer has been successfully developed using a low temperature non-aqueous sol-gel route and aqueous suspension of AgBr. Evidence for the growth of TiO2 layer and the immobilization of AgBr nanoparticles have been confirmed by Raman, XRD and XPS. GSDR analysis revealed a strong absorption in the visible region brought by surface Plasmon resonance (SPR) of Ag nanocrystals generated at the surface of AgBr. The XPS evidenced the presence of Ag+, Ag0 and bromine, suggesting that Ag0 formed a shell around the deposited AgBr. The immobilized TiO2-Ag-AgBr heterostructured layer imparts a strong photocatalytic activity under visible light for the degradation of dyes in aqueous solution as well as of dimethyl methylphosphonate (DMMP), a chemical warfare agent simulant. These new catalytically active functionalized fabrics, with self-detoxification properties, have great potential for application in chemical protective clothes and might offer new opportunities for the design of functional materials for toxic chemical protection.

First principles study of the Ag nanoclusters adsorption effect on the photocatalytic properties of AgBr(1 1 0) surface

The electronic structures and photocatalytic performance of Agn/AgBr(110)(n = 7–13) are studied using density functional theory (DFT). The adsorption of Agn (n = 7–13) nanoclusters on AgBr(110) surface induces a new metal-induced gap band (MIGB) located between the valence band (VB) and the conduction band (CB), the variety of the electronic characters of AgBr(110) favor the visible and infrared light absorption, which improves the sunlight utilization. The dominant localization of the photo-excited electrons on the Agn clusters of Agn/AgBr(110)(n = 7–13) facilitates the oxidation-reduction reactions occurring on the surface and also effectively reduces the photolysis of AgBr under the sunlight irradiation. The overpotentials of the CB and VB edges indicate that photocatalytic conversion of CO2 with H2O to methanol is possible on AgBr(110) deposited with the Agn nanoclusters, which has been realized experimentally (An et al., 2012). The substantial strengthening of visible and infrared light absorption and the free energy profiles for the conversion of CO2 with H2O to methanol indicate that Ag13/AgBr(110) surface can be expected to be the excellent photocatalysts.

A novel in-situ synthesis and enhanced photocatalytic performance of Ag/AgI/AgBr/Sulfonated polystyrene heterostructure photocatalyst

Ag/AgI/AgBr/Sulfonated polystyrene heterostructure photocatalyst was synthesised through in-situ ion exchange followed by calcination and light reduction. Field emission scanning electron microscopy, UV–Vis diffuse reflectance spectra and X-ray diffraction were utilized to characterize the morphology, optical absorption property and phase structure of the as-prepared photocatalyst, respectively. By degradation of Rhodamine B under visible light, the Ag/AgI/AgBr/SPs microspheres exhibited a significant enhancement in photocatalytic activity compared with Ag/AgBr and Ag/AgI. Furthermore, the heterojunction formed between AgI and AgBr, and the remarkable visible light absorption attributed to Ag nanoparticles on the surface of AgBr and AgI were considered as the main reasons of the enhancement.

Template assisted synthesis of Ag/AgBr/AgCl hollow microspheres with heterojunction structure as highly activity and stability photocatalyst

Ag/AgBr/AgCl hollow microspheres were synthesised through template assisted synthesis method followed by calcination and light reduction method. Field emission scanning electron microscopy, UV–Vis absorption spectra and X-ray diffraction were utilized to characterize the morphology, optical absorption property and phase structure of the as-prepared photocatalyst, respectively. By degradation of Rhodamine B under visible light, the Ag/AgBr/AgCl hollow microspheres exhibited a significant enhancement in photocatalytic activity compared with Ag/AgCl and Ag/AgBr. Furthermore, the heterojunction formed between AgCl and AgBr, the remarkable visible light absorption attributed to Ag nanoparticles on the surface of AgBr are considered as the main reasons of the enhancement.

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

This study reports an easy synthesis protocol of a novel bimetallic silver halide (Au/AgBr-Ag) plasmonic heterostructure as a visible light induced photocatalyst. In this process, first CTAB capped Au NPs were coated with AgBr, and then Ag nanoparticles were formed on the surface of AgBr by photoreduction, while exposing to daylight at room temperature. The presence of Au and Ag improves the visible absorption ability of NPs and avoids charge recombination of the semiconductor AgBr during photoexcitation, which in turn enhances 16 and 8.9 fold the photocatalytic efficiency of Rhodamine B dye degradation under visible light irradiation compared to that of pure AgBr and AgBr/Ag, respectively. The recycling tests of the photocatalyst show only ∼8.7% decrease in efficiency after the 5th cycle of reuse without changing the morphology. During the photocatalytic process, active superoxide radicals (O2˙-) play a major role, proved through scavenger trapping and photoluminescence experiments. The presence of two plasmonic metals (Au and Ag) in the heterostructure helps to improve visible light absorption as well as avoid charge recombination of the semiconductor AgBr to act as a better photocatalyst. Since this heteronanostructure can be easily synthesized by a one-step method, this study could provide a new approach for the development of efficient bimetallic/semiconductor halide plasmonic photocatalysts with enhanced visible absorption and better charge separation.

The synthesis, activity, stability and the charge transfer identification of Ag:AgBr/γ-Al2O3 photocatalyst for organic pollutant decomposition in water

Highly stable Ag:AgBr/γ-Al2O3 photo-catalyst was obtained by dispersing AgBr sol on hollow γ-Al2O3 microsphere. Metallic Ag nanoparticles were in situ generated on AgBr crystals by a photo-reduction method. The activity of catalyst was characterized by MO and phenol decomposition. The light irradiation response, the life times of the photo-induced charges, and the charge separation and transition were determined by the UV–vis diffuse reflection spectra, open circuit voltage decay spectra and transient photocurrent responses. The as-prepared Ag:AgBr/γ-Al2O3 catalyst can response to visible light irradiation. Charge separation was clarified to correlate with electrons transferring from Ag to AgBr surface and the consequent reaction with ads-O2 to generate O2− species. It was found that the O2− rather than OH played a dominant role in the photocatalytic oxidation of MO and phenol in water. However, the electrons trended to transfer from AgBr to Ag intrinsically without light irradiation. Therefore, the electron transfer between Ag and AgBr reaching the dynamic equilibrium was the key factor for obtaining a high stable Ag/AgBr catalyst which can be obtained by optimizing the Ag:AgBr ratio. Loading amount of Ag:AgBr on γ-Al2O3 was optimized to 30wt.% and the metallic Ag content was stabilized at 9wt.% of Ag:AgBr catalyst.

Super-high photocatalytic activity, stability and improved photocatalytic mechanism of monodisperse AgBr doped with In

Monodisperse In3+ doped AgBr (In-AgBr) nanoparticles were synthesized by a hydrothermal route. The pure AgBr and In-AgBr samples were investigated by X-ray powder diffraction, transmission electron microscopy, ultraviolet-visible absorption spectroscopy, X-ray photoelectron spectroscopy, measurement of total organic carbon, and electron paramagnetic resonance spectrometry. In-AgBr was more photocatalytically active than pure AgBr in photodegradation of 20mg/L methyl orange under visible light irradiation (λ>420nm). The 0.05mol/L In-AgBr sample showed the highest photodegradation efficiency and high stability. The doped In3+ expanded the light absorption range, reduced the band gap of AgBr and improved the utilization of photons. The additional In3+ can inhibit the formation of Ag particles on the surface of AgBr, which can further stabilize AgBr. The doped In3+ in AgBr served as a temporary site for trapping of photoinduced electrons, and thereby obviously restrained the recombination of photoinduced electron-hole pairs on the surface of AgBr. The enhanced photocatalytic ability of In-AgBr may be mainly attributed to the improved separation efficiency of photogenerated charges.

Magnetically Separable Fe3O 4/AgBr Hybrid Materials: Highly Efficient Photocatalytic Activity and Good Stability.

Magnetically separable Fe3O4/AgBr hybrid materials with highly efficient photocatalytic activity were prepared by the precipitation method. All of them exhibited much higher photocatalytic activity than the pure AgBr in photodegradation of methyl orange (MO) under visible light irradiation. When the loading amount of Fe3O4 was 0.5 %, the hybrid materials displayed the highest photocatalytic activity, and the degradation yield of MO reached 85 % within 12 min. Silver halide often suffers serious photo-corrosion, while the stability of the Fe3O4/AgBr hybrid materials improved apparently than the pure AgBr. Furthermore, depositing Fe3O4 onto the surface of AgBr could facilitate the electron transfer and thereby leading to the elevated photocatalytic activity. The morphology, phase structure, and optical properties of the composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–visible diffuse reflectance spectra (UV–vis DRS), and photoluminescence (PL) techniques.

A facile way to synthesize Ag@AgBr cubic cages with efficient visible-light-induced photocatalytic activity

The novel cubic cage Ag@AgBr plasmonic photocatalysts were first synthesized via a water soluble sacrificial salt-crystal-template (SCT) process. This is achieved by the photo-reduction process was used to produce Ag nanoparticles on the surface of AgBr. The physical and photophysical properties of the as-prepared Ag@AgBr cubic cages were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and photoluminescence spectroscopy (PL). The results showed that Ag@AgBr cubic cages have excellent photocatalytic performance under visible light illumination, since the methyl orange (MO) dyes were completely degraded within 80s over Ag@AgBr photocatalysts and the photocatalytic activity maintains a high level after 7 cycles. A possible catalytic mechanism for Ag@AgBr cubic cages is proposed which is attributed to the surface plasmon resonance (SPR) effect from Ag and hybrid effect from AgBr.

In-situ anion exchange synthesis of AgBr/Ag2CO3 hybrids with enhanced visible light photocatalytic activity and improved stability

AgBr/Ag2CO3 hybrids were synthesized via an in situ anion-exchange reaction between Ag2CO3 and NaBr. The obtained hybrids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), UV–vis diffuse reflectance spectroscopy (DRS) and terepthalic acid-photo luminescence (TA-PL) technique. The as prepared AgBr/Ag2CO3 hybrids exhibited wide absorption in the visible light region and displayed efficient and higher photocatalytic activities towards the degradation of dye molecules (Ponceau BS) as compared to pure AgBr and Ag2CO3 samples under visible light irradiation (λ>400nm). The enhanced photocatalytic activity of AgBr/Ag2CO3 was related to the efficient separation of electron–hole pairs derived from matching band potentials between AgBr and Ag2CO3, as well as the good electron trapping role of Ag° nanoparticles in situ formed on the surface of AgBr and Ag2CO3 particles during photocatalytic oxidation process. The quenching effect of different scavengers of reactive species suggested that OH and h+ play major role in the degradation of PBS. The enhanced stability of the hybrid was attributed to the trapping of photogenerated electrons from the surface of catalyst by Ag° nanoparticles which suppress the photocorrosion.

Fabrication of Ag-coated AgBr nanoparticles and their plasmonic photocatalytic applications

Ag-coated AgBr nanoparticles (Ag@AgBr) were fabricated via an aqueous, one-pot route. In this system, poly(vinyl alcohol) (PVA) acted as a stabilizer for the formation of nanoscale AgBr composites through interaction with Ag ions and their hydroxyl (–OH) groups. The mild reducing agent L-arginine was used for partial reduction of AgBr to form metallic Ag nanoparticles on the AgBr surface. The metallic Ag nanoparticles enhanced light absorption in the visible region due to surface plasmon resonance (SPR). The size of the synthesized nanoparticles was controlled by varying the reaction temperature, and was found to influence the light absorption of Ag@AgBr nanocomposites. The prepared nano-photocatalysts exhibited excellent photocatalytic activities under both visible light and direct sunlight.

Preparation, characterization, and photocatalytic activity of porous AgBr@Ag and AgBrI@Ag plasmonic photocatalysts

Porous AgBr@Ag and AgBrI@Ag plasmonic photocatalysts were synthesized by a multistep route, including a dealloying method to prepare porous Ag, a transformation from Ag to AgBr and AgBrI, and a photo-reduction process to form Ag nanoparticles on the surface of AgBr and AgBrI. It was found that the porous structure kept unchanged during Ag was transferred into AgBr, AgBrI, AgBr@Ag, and AgBrI@Ag. Both porous AgBr@Ag and porous AgBrI@Ag showed much higher visible-light photocatalytic activity than cubic AgBr@Ag for the degradation of methyl orange, which is because the interconnected pore channels not only provide more reactive sites but also favor the transportation of photo-generated electrons and holes. For AgBrI@Ag, AgBrI solid solution formed at the interface of AgBr and AgI, and the phase junction can effectively separate the photo-generated electrons and holes, favorable to the improvement of photocatalytic activity. The optimal I content for obtaining the highest activity is ∼10at.%.

Controllable synthesis of plasmonic Ag/AgBr photocatalysts by a facile one-pot solvothermal route

Plasmonic photocatalysts Ag/AgBr composites were synthesized by a facile one-step solvothermal route. Unlike the traditional photoreduction method, metallic Ag in the present work was in situ anchored on the surface of AgBr by reducing radicals created through the thermal process. The structures (e.g., particle size, composition, and dispersion) of metallic Ag nanoparticles could be well controlled by simply changing the reaction temperature and solvent. The as-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectra (DRS). The as-prepared Ag/AgBr composites exhibited excellent photocatalytic efficiency for the degradation of azo dye methyl orange (MO), phenol, and 2-chlorophenol under visible light irradiation. It was found that the activity was highly dependent on the particle size, composition and the dispersing extent of Ag nanoparticles. The photocatalytic mechanism was studied by radical-trapping experiments and the photoluminescence (PL) technique with terephthalic acid, and the results indicated that O2- and h+ played great roles in the rapid degradation of organic pollutants under visible light irradiation.

Silver halide/silver iodide@silver composite with excellent visible light photocatalytic activity for methyl orange degradation

AgBr/AgI@Ag composite photocatalyst was prepared by a handy multistep route, including controllable double-jet precipitation to synthesize cubic AgBr microcrystals, ion exchange to form AgI on AgBr surface, and visible light reduction to generate Ag nanoparticles. UV–Vis diffuse reflectance and electrochemical impedance spectra demonstrated that AgBr/AgI composite structure not only favors forming more silver nanoparticles to harvest visible light but also facilitates the transfer of charge carriers when compared with pure AgBr. Beneficial from the synergistic effect of highly effective visible light harvest and electron–hole separation, AgBr/AgI@Ag shows higher photocatalytic activity for the degradation of methyl orange (MO) than AgBr, AgBr@Ag, and AgBr/AgBr.

AgBr@Ag/TiO2 core–shell composite with excellent visible light photocatalytic activity and hydrothermal stability

[email protected]/TiO2 core–shell photocatalysts were fabricated by a facile green route. TiO2 was uniformly coated on the surface of cubic AgBr, making [email protected]/TiO2 core–shell photocatalyst show excellent hydrothermal stability. Beneficial from that Ag nanoparticles and AgBr can respond to visible light and core–shell structure can effectively separate the photogenerated electrons and holes, [email protected]/TiO2 core–shell composites exhibited outstanding visible light photocatalytic activity for the degradation of acid orange 7. The activity of [email protected]/TiO2 is related to the thickness of TiO2 shell, and the optimal shell thickness for obtaining the highest activity is 10 nm.