Photodeposition Process Research Articles

An Ultrasensitive, Disposable, and “Plug and Play” Surface-Enhanced Raman Scattering Substrate for the In Situ Detection of Trace Thiram in Water

In this work, TiO2 nanotube arrays were fabricated on Ti meshes via anodic oxidation and decorated with Ag nanoparticles by a photodeposition process. Then the surface-enhanced Raman scattering (SERS) effect of the as-prepared samples for trace thiram was directly investigated in a thiram aqueous solution. The stability and selectivity of our substrates were also explored. In addition, for practical purposes, we further studied the SERS of trace thiram in tap water using the as-prepared sample as a SERS substrate. At last, the surface-enhanced mechanism was discussed preliminarily. It can be found that the Ag-nanoparticle-decorated TiO2 nanotube array on a Ti mesh is an ultrasensitive SERS substrate for trace thiram in water. The detection limits are up to 1 × 10–9 mol L–1 in deionized water and 1 × 10–7 mol L–1 in tap water, respectively. Moreover, this substrate possesses dramatic signal uniformity [relative standard deviation <6% (spot-to-spot)], excellent reproducibility [relative standard deviation <...

Photochemical Synthesis of Radiate Titanium Oxide Microrods Arrays Supporting Platinum Nanoparticles for Photoassisted Electrooxidation of Methanol

AbstractPhotoassisted catalysis is recently adopted to accelerate the kinetics of the methanol oxidation, which allows the photocatalysis and electrocatalysis simultaneously occur on the catalyst surface and even on interior region. The rational design of highly efficient photoassisted electrocatalysts is highly desirable, however, it is very challenging. In this study, architectures of radiate TiO2 microrods arrays support Pt nanoparticles (Pt NPs/TiO2 MRs) are developed, via the combination of first hydrothermal and subsequent photodeposition process. Benefited from the synergetic effect of photocatalytic acceleration and the radiate architectures, the mass activity of Pt NPs/TiO2 MRs for methanol electrooxidation, under UV irradiation (wavelength: 365 nm), is 2.77 and 6.1 times as high as those of Pt NPs/TiO2 MRs without irradiation and commercial Pt/C, respectively. Moreover, under UV irradiation, both the CO tolerance and durability of the Pt NPs/TiO2 MRs catalysts are significantly improved. Notably, in both acidic and alkaline media, the Pt NPs/TiO2 MRs catalysts show improved electrocatalytic performance for photoassisted electrooxidation of methanol. This study provides a building art toward 3D architectures of radiate semiconductor MRs arrays supporting metallic NPs, and offers an effective way to improve the electrochemical activity of methanol oxidation utilizing the synergistic combination of photocatalysis and electrocatalysis.

Chloride ion: A promising hole scavenger for photocatalytic hydrogen generation

The investigation pertains to elucidation of promising role of in-situ chloride ions generated during the photoreduction of HAuCl4 as an internal sacrificial donor for photocatalytic hydrogen generation. The hydrogen evolution rate (HER) observed was 4.16 mmol h−1 using in-situ route of photocatalyst formation which is significantly higher than the conventional route of formation of recovered photocatalyst. This unreported and unprecedented enhancement is explained on the basis of role of chloride ions released from the gold precursor. Experimental data inferring the effect of chloride ions on photocatalytic hydrogen generation using AuTiO2 are also briefly explained. The role of anionic sacrificial donors suggests several potential possibilities for their applications in photocatalysis considering their presence in wastewater as well as their low cost and abundant availability. The work also introduces one-step photodeposition and hydrogen generation process against traditional recovered photocatalyst, wherein the catalysts were prepared first by normal route of photodeposition, recovered and then employed for hydrogen generation.

Effect of sacrificial agents on the dispersion of metal cocatalysts for photocatalytic hydrogen evolution

Surface photodeposition of noble metal cocatalyst has been regarded as an effective approach to facilitate the separation of charge carriers and reduce the over-potential of water reduction, thus to enhance the photocatalytic H2-production activities of semiconductor photocatalyst. Herein, the influences of sacrificial agents used in the photodeposition process on the dispersion of noble metal nanoparticles are investigated, via a series of technique of photocatalytic hydrogen evolution test, microstructure analysis and photoelectrochemical measurement. As a result, the sacrificial agents are found to show large impact on the loading amount, particle size and distribution of different metals on the surface of g-C3N4. The real loading amount of Pt and Au is higher in methanol solution than that in triethanolamine solution. Better distribution and smaller size of Pt nanoparticles are achieved in the presence of methanol; while better distribution and smaller size of Au nanoparticles are achieved in the presence of triethanolamine. As a result, quite different charge transfer ability is achieved for the synthesized Pt and Au decorated g-C3N4, which subsequently leads to disparate photocatalytic activities of the same g-C3N4 photocatalyst under various conditions. The finding in this work indicates that the valid deposition content, particle size and distribution of metal cocatalysts should be carefully taken into account when comparing the photocatalytic activities among various samples.

Influence on the saturable absorption of the induced losses by photodeposition of zinc nanoparticles in an optical fiber.

In this work, the influence of induced losses on the saturable absorption by zinc nanoparticles photodeposited onto the core of an optical fiber end is reported. Samples with different losses were obtained by the photodeposition technique using a continuous wave laser at 1550 nm. The nonlinear absorption of the saturable absorber was characterized by the P-scan technique using a high-gain pulsed erbium-doped fiber amplifier. The results have demonstrated that for optical fibers with variable induced losses by deposited nanoparticles, the modulation depth increases proportionally based on the nonlinear absorption coefficient. With induced losses fixed at 3 dB, it was demonstrated that the modulation depth increased as a function of the optical power used in the photodeposition process. The saturation intensity of the saturable absorber presents small shifts for higher intensities.

Visible-light-driven Ag/Bi3O4Cl nanocomposite photocatalyst with enhanced photocatalytic activity for degradation of tetracycline

In this study, a novel Ag/Bi3O4Cl photocatalyst has been synthesized by a facile photodeposition process. Its photocatalytic performance was evaluated from the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). The 1.0 wt% Ag/Bi3O4Cl photocatalyst could significantly enhance the degradation of TC compared with pure Bi3O4Cl, with the degradation level reaching 94.2% in 120 minutes. The enhancement of photocatalytic activity could be attributed to the synergetic effect of the photogenerated electrons (e−) of Bi3O4Cl and the surface plasmon resonance (SPR) caused by Ag nanoparticles, which could improve the absorption capacity of visible light and facilitate the separation of photogenerated electron–hole pairs. In addition, electron spin resonance (ESR) analysis and trapping experiments demonstrated that the superoxide radicals (˙O2−), hydroxyl radicals (˙OH) and holes (h+) played crucial roles in the photocatalytic process of TC degradation. The present work provides a promising approach for the development of highly efficient photocatalysts to address current environmental pollution, energy issues and other related areas.

ZnO and Pt-ZnO photocatalysts: Characterization and photocatalytic activity assessing by means of three substrates

ZnO nanoparticles have been previously synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without the addition of a template. The as-prepared ZnO material was anealed at 400°C in air for 2h. The Pt-ZnO catalysts (0.5 or 1.0 Pt wt.%) were obtained by photochemical deposition method on the surface of the prepared ZnO sample, using hexachloroplatinic acid (H2PtCl6). It has been shown that Zn2+ is lost from the photocatalyst to the medium and a replacement of the cationic vacancies of Zn2+ by Pt4+ cations occurs during the platinization process of the ZnO samples, regardless of whether the platinum metal photodeposition process. The as-prepared catalysts were characterized by XRD, BET, FE-SEM, TEM, XPS and diffuse reflectance spectroscopy (DRS). Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination: Methyl Orange and Rhodamine B were chosen as dye substrates and Phenol as a transparent substrate. High conversion values (ca. 100%) and a total organic carbon (TOC) removal of 90–96%, were obtained over these photocatalysts after 160min of UV illumination. In general, it was observed that the presence of Pt on ZnO affects the lattice parameters and the crystallite size. Although ZnO can completely degrade RhB, MO and Phenol totally in ca. 60min, the process is more efficient for Pt–ZnO photocatalysts.

Seed-mediated photodeposition route to Ag-decorated SiO2@TiO2 microspheres with ideal core-shell structure and enhanced photocatalytic activity

Ag-decorated SiO2@TiO2 microspheres (SiO2@TiO2-Ag) with ideal core-shell structure and enhanced photocatalytic activity were successfully fabricated by combining both coating anatase TiO2 on the surface of SiO2 spheres and subsequent depositing face-centered cubic Ag nanoparticles (NPs) on the coated TiO2 surface via novel sol-gel method and Ag-seed-mediated photodeposition (PD) route, respectively. The morphology, structure, composition and optical properties of the resulting composites were characterized in detail. The results reveal that the monodisperse SiO2 spheres of ∼260 nm were covered uniformly and perfectly by the TiO2 nanoparticle coating layer with the thickness of ca. 55 nm by the novel sol-gel method. Further, homogeneously and highly dispersed Ag NPs with an average size of 8 ± 1.5 nm were strongly anchored onto the TiO2 surface in SiO2@TiO2 core-shell spheres by the modified PD process (Ag-seed-mediated PD route), whereas polydispersed Ag aggregates and detached Ag NPs were irregularly deposited over the TiO2 surface in previous works, which is the inherent problem and has not been effectively solved for depositing noble metal NPs such as Au, Ag, Pt, Pd on TiO2 surface by conventional PD method. The formation mechanism of small and uniformly dispersed Ag NPs with narrow size distribution via the modified PD method is tentatively explained by both nucleation kinetics and growth kinetics. The key reason is that the pre-deposited seeds firmly tethered on SiO2@TiO2 spheres served as nucleation sites and anchoring points for the further nucleation and subsequent growth of Ag via photoreduction of Ag+.

Photochemical synthesis and enhanced photocatalytic activity of MnOx/BiPO4 heterojunction

Monoclinic BiPO4 with rod-like shape was prepared via a CTAB-assisted hydrothermal route. MnOx nanoparticles were loaded on the surfaces of BiPO4 rods by a photo-deposition process to form MnOx/BiPO4 heterojunctions. The as-prepared samples were characterized by XRD, SEM, TEM, XPS, FL, and UV-Vis diffuse reflectance measurements. The results showed that MnOx nanoparticles were strongly anchored to the surfaces of BiPO4 rods when the mole ratio of Mn to Bi was controlled at a low level, forming MnOx/BiPO4 heterojunctions with effective and sound interfaces. The MnOx/BiPO4 heterojunctions exhibited higher photoactivity than pristine BiPO4 for photodegradation of methyl blue under UV irradiation, which could be attributed to the efficient charge transfer at the heterojunction interfaces. The higher light absorption ability of MnOx/BiPO4 in the range of 300–420 nm compared with pristine BiPO4 was also responsible for the enhanced photocatalytic activities of MnOx/BiPO4 heterojunctions.

2D Arrays of Hexagonal Plasmonic Necklaces for Enhanced Second Harmonic Generation.

Hexagonal plasmonic necklaces of silver nanoparticles organized in 2D superlattices on functional ferroelectric templates are fabricated in large-scale spatial regions by using a surfactant-free photo-deposition process. The plasmonic necklaces support broad radiative plasmonic resonances allowing the enhancement of second harmonic generation (SHG) at the ferroelectric domain boundaries. A 400-fold SHG enhancement is achieved at the near-UV spectral region with subsequent interest for technological applications.

Anodic Ag/TiO2 nanotube array formation in NaOH/fluoride/ethylene glycol electrolyte as a photoanode for dye-sensitized solar cells

Self-organized, 23 μm-thick anodic TiO2 nanotube (TNT) arrays were formed in sodium hydroxide/fluoride/ethylene glycol (EG) electrolyte at 60 V for 60 min. The presence of sodium hydroxide (NaOH) in the fluoride/EG electrolyte accelerates the formation of the TiO2 nanotube arrays. The anodic film was then decorated with silver nanoparticles (Ag NPs) by the photodeposition process and used as a photoanode in a rear-side-illuminated dye-sensitized solar cell. The Ag NPs decorated TNT arrays, with the former having diameters of 10–30 nm formed from 0.2 M of Ag-precursor solution and exhibiting the highest photoconversion efficiency (η) of 3.7% and a short-circuit current density of 12.2 mA cm−2 compared to η = 3% and short-circuit current density of 9.1 mA cm−2 for a sample without Ag NPs. The increase in η is thought to be due to the surface plasmon resonance and excess electrons from the nanoparticles.

Photo-reduction of bromate in drinking water by metallic Ag and reduced graphene oxide (RGO) jointly modified BiVO4 under visible light irradiation

Bromate (BrO3−), an oxyhalide disinfection by-product (DBP) in drinking water, has been demonstrated to be carcinogenic and genotoxic. In the current work, metallic Ag and reduced graphene oxide (RGO) co-modified BiVO4 was successfully synthesized by a stepwise chemical method coupling with a photo-deposition process and applied in the photo-reduction of BrO3− under visible light irradiation. In this composite, metallic Ag acted as an electron donor or mediator and RGO enhanced the BrO3− adsorption onto the surface of catalysts as well as an electron acceptor to restrict the recombination of photo-generated electron-hole pairs. The Ag@BiVO4@RGO composite exhibited greater photo-reduction BrO3− performance than pure BiVO4, Ag@BiVO4 and RGO@BiVO4 under identical experimental conditions: initial BrO3− concentration 150 μg/L, catalyst dosage 0.5 g/L, pH 7.0 and visible light (λ > 420 nm). The photoluminescence spectra (PL), electron-spin resonance (ESR), photocurrent density (PC) and electrochemical impedance spectroscopy (EIS) measurements indicated that the modified BiVO4 enhanced the photo-generated electrons and separated the electron-hole pairs. The photocatalytic reduction efficiency for BrO3− removal decreased with the addition of electron quencher K2S2O8, suggesting that electrons were the primary factor in this photo-reduction process. The declining photo-reduction efficiency of BrO3− in tap water should attribute to the consumption of photo-generated electrons by coexisting anions and the adsorption of dissolved organic matter (DOM) on graphene surface. The overall results indicate a promising application potential for photo-reduction in the DBPs removal from drinking water.

XAFS study on a photodeposition process of Pt nanoparticles on TiO2 photocatalyst

A photodeposition process of Pt metal particles on anatase TiO2 in the aqueous solution of H2PtCl6 (precursor) and methanol (reductant) was studied using transmission electron microscopy, UV-vis spectroscopy and X-ray absorption fine structure spectroscopy. These analyses proposed the photodeposition mechanism of Pt on TiO2 by the photogenerated electrons: the photo-assisted adsorption of Pt4+ complexes on TiO2 through the ligand exchange at the initial stage, followed by the successive rapid reduction of Pt4+ to Pt0 to grow the Pt metal particles, which gives small and almost uniform size of Pt metal nanoparticles.

Enhanced activity of Ag[sbnd]MgO[sbnd]TiO2 catalyst for photocatalytic conversion of CO2 and H2O into CH4

Using solar energy to recycle carbon dioxide (CO2) offers a brand new opportunity for simultaneous mitigation of the global climate change effect and production of energy-bearing compounds. Silver (Ag) and magnesium oxide (MgO) co-modified titania (TiO2) (AgMgTi) synthesized through a combined impregnation and photo-deposition process. The catalysts were characterized through surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence spectrum (PL). The TEM and XPS analysis demonstrated the presence of Ag nanoparticles (NPs) on the AgMgTi catalyst. The synergistic activities of Ag NPs and MgO significantly contributed to CO2 photoreduction to methane (CH4). CH4 yield over the AgMgTi catalyst was 20 times higher than over P25 TiO2, and was higher than over single modified catalysts (MgOTiO2 or AgTiO2) under either ultraviolet (UV) or UV–vis irradiation. MgO on the surface of TiO2 enhanced the chemisorption of CO2 and/or initiated the CO2 reduction process, and hence facilitated the conversion of CO2 to CH4. Under UV light excitation, the deposited Ag NPs facilitated the separation of electron–hole due to the formation of Schottky barriers on the metal-semiconductor interface. Visible light in the solar spectrum improved the energy of trapped electrons on Ag NPs through enhanced localized electric field attributed to the Ag surface plasmon resonance (SPR) effect. Abundant electrons with higher energy facilitated CH4 formation. Therefore, more CH4 was obtained under UV–vis irradiation comparing to that under UV irradiation. This study demonstrated that the AgMgTi catalyst can effectively utilize full spectrum solar energy for simultaneous reduction of CO2 and production of energy-bearing compounds.

Coverage control of CdSe quantum dots in the photodeposition on TiO2 for the photoelectrochemical solar hydrogen generation

CdSe quantum dots (QDs) have successfully been formed on the TiO2 surface by the photodeposition of Se QDs and their subsequent transformation into CdSe QDs (CdSe/TiO2) (Fujishima et al., 2014). The addition of mercaptoacetic acid (MAA) in the second step of the two-step photodeposition process significantly decreases the CdSe particle size and the contact angle against the TiO2 surface to increase the TiO2-surface coverage by CdSe QDs with the particle size distribution sharpened. X-ray photoelectron and Raman spectroscopy measurements indicated that MAA is densely chemisorbed on the surface of CdSe QDs through CdS bond, whereas sparsely adsorbed on the TiO2 surface. Photoelectrochemical (PEC) cells using CdSe/TiO2 as the photoanode for hydrogen (H2) generation from aqueous sulfide solution were fabricated. The rate of H2 generation strongly depends on the concentration of MAA (C) added in the photoanode preparation, and the photoanode prepared at C=0.04mM affords a maximum solar-to-hydrogen conversion efficiency of 0.028%.

Photochemical synthesis of SnO2/TiO2 composite nanotube arrays with enhanced lithium storage performance

Nanostructured SnO2/TiO2 hybrid materials can be promising anode materials for lithium ion batteries (LIBs). We herein report a novel and energy-saving photodeposition approach to fabricate SnO2/TiO2 composite nanotubes. In the photodeposition process, Sn2+ ions are oxidized to SnO2 by the photogenerated holes, thus SnO2 nanoparticles are deposited onto both the inner and outer walls of TiO2 nanotubes. This results in the formation of the SnO2/TiO2 composite nanotubes with a hierarchically porous architecture. The existence of the positive bias can enhance the photooxidation of Sn2+ ions by decreasing the hole–electron recombination, leading to the deposition of more SnO2 nanoparticles on the walls of TiO2 nanotubes. The SnO2/TiO2 composite film electrode fabricated by the photodeposition at the positive bias shows much higher lithium storage capacity than the corresponding controllable electrodes during the electrochemical cycling at a current density of 100 μA cm−2. The specific capacity of SnO2 in the composite film electrode photodeposited at the positive bias is estimated to be 766 mAh g−1 after 100 cycles at a current density of 100 μA cm−2, demonstrating its prominent lithium storage performance. The as-constructed facile and energy-saving photodeposition method can be used as an efficient route to prepare other composite materials with controlled morphologies and dimensions.

Au/BiOCl heterojunction within mesoporous silica shell as stable plasmonic photocatalyst for efficient organic pollutants decomposition under visible light

A new mesoporous silica protected plasmonic photocatalyst, Au/BiOCl@mSiO2, was prepared by a modified AcHE method and a subsequent UV light induced photodeposition process. The surfactant-free heterojunction allows the electrons spontaneously flow from Au to nearby BiOCl surface, leading to the accumulation of positive charges on Au surface, and negative charges on Bi species under visible light. Au/BiOCl@mSiO2 exhibits high visible light photocatalytic efficiency in complete oxidation of aqueous formaldehyde and Rhodamin B. We showed that a positive relationship exists between the LSPR effect and rate enhancements, and leads to a hypothesis that the metallic Au LSPR enhances the photocatalytic rates on nearby semiconductors by transferring energetic electrons to BiOCl and increasing the steady-state concentration of active OH species by a multi-electron reduction of molecular oxygen. The OH species is the main oxidant in photocatalytic transformations, whose intensity is greatly enhanced in the dye-involving systems due to the synergetic effect between LSPR and dye sensitization processes. In addition, the mesoporous SiO2 shell not only inhibits the over growth of BiOCl nanocrystals within the silica frameworks, but also protects the dissolution of chloride or Au species into aqueous solution, which ultimately makes the Au/BiOCl@mSiO2 catalysts rather stable during photocatalysis.

The selective deposition of silver nanoparticles onto {1 0 1} facets of TiO2 nanocrystals with co-exposed {0 0 1}/{1 0 1} facets, and their enhanced photocatalytic reduction of aqueous nitrate under simulated solar illumination

Highly efficient photocatalytic reduction of environmental pollutants requires the enrichment of photogenerated electrons on the photocatalyst’s surface. Thus, proper material design and modification are needed to efficiently separate photogenerated electron/hole pairs and achieve their oriented migrations for the enrichment of photogenerated electrons on their surface. In this work, a modified photo-deposition process was developed which successfully deposited silver nanoparticles selectively on {101} facets of TiO2 nanocrystals with co-exposed {001}/{101} facets. The synergistic effect of crystal facet engineering and the selective deposition of silver nanoparticles on {101} facets largely enhanced the separation of photogenerated carriers and enriched the presence of photo-generated electrons onto the surface of TiO2 to a net negative-charged surface. A strong photocatalytic reduction capability of the sample was demonstrated by its superior photocatalytic reduction activity on aqueous nitrate under a simulated solar illumination. The removal ratio of aqueous nitrate reached ∼95%, and most of the reduction product was the desirable N2 with the selectivity over 90%. These TiO2 nanocrystal with co-exposed {001}/{101} facets and silver modification on {101} facets could also effectively remove both nitrate and various organic pollutants from water simultaneously.

M@MIL-100(Fe) (M = Au, Pd, Pt) nanocomposites fabricated by a facile photodeposition process: Efficient visible-light photocatalysts for redox reactions in water

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed noble-metal nanoparticles (Au, Pd, Pt) were immobilized on MIL-100(Fe) (denoted M@MIL-100(Fe)) using a facile room-temperature photodeposition technique. The resulting M@MIL-100(Fe) (M = Au, Pd, and Pt) nanocomposites exhibited enhanced photoactivities toward photocatalytic degradation of methyl orange (MO) and reduction of heavy-metal Cr(VI) ions under visible-light irradiation (λ ≥ 420 nm) compared with blank-MIL-100(Fe). Combining these results with photoelectrochemical analyses revealed that noble-metal deposition can effectively improve the charge-separation efficiency of MIL-100(Fe) under visible-light irradiation. This phenomenon in turn leads to the enhancement of visible-light-driven photoactivity of M@MIL-100(Fe) toward photocatalytic redox reactions. In particular, the Pt@MIL-100(Fe) with an average Pt particle size of 2 nm exhibited remarkably enhanced photoactivities compared with those of M@MIL-100(Fe) (M = Au and Pd), which can be attributed to the integrative effect of the enhanced light absorption intensity and more efficient separation of the photogenerated charge carrier. In addition, possible photocatalytic reaction mechanisms are also proposed.

Controllable synthesis and photocatalytic activity of Ag/BiOI based on the morphology effect of BiOI substrate

Two series of morphology-dependent Ag/BiOI composites were successfully synthesized by using a facile photodeposition method. The typical BiOI 2D plate and 3D flower with exposed (001) facets were applied as substrates. The morphology effects of BiOI on the growth of Ag quantum dots and the photocatalytic activity of Ag/BiOI were discussed. During the photodeposition process, weak separation efficiency of BiOI 2D plate facilitated the formation of larger sized Ag quantum dots which displayed higher electron trapping efficiency and resulted in higher photocatalytic activity than those with smaller size on BiOI 3D flower. The pseudo-first-order rate constants kapp of BiOI plate and BiOI flower were 0.32 and 0.85h−1 while the corresponding activities of Ag/BiOI were further increased 3.25 and 1.11 times for degrading methyl orange. It is a promising way to regulate the activity of Ag/BiOI even the universal noble metal/semiconductor composite through controlling the morphology of semiconductor substrate.