Photodeposition Method Research Articles

Photocatalytic Overall Water Splitting Reaction Feature on Photodeposited NixP/γ-Ga2O3Nanosheets

Solar light-driven overall water splitting for hydrogen production is an ideal solution to climate warming and energy shortage issues. Obtaining a highly efficient and stable photocatalyst remains a major challenge at present. Herein, NixP/γ-Ga2O3 nanosheets, which were synthesized from NiCl2, NaH2PO2, and home-made γ-Ga2O3 nanosheets by the photodeposition method under 254 UV irradiation for 30 min, are found as a highly active and durable photocatalyst for pure water splitting into H2 and O2 without a sacrificial reagent. The H2 production rate is as high as 5.5 mmol·g–1·h–1 under 125 W high-pressure mercury lamp irradiation, which is 3.4 and 2.5 times higher than that on the pristine γ-Ga2O3 nanosheets and Pt/γ-Ga2O3 nanosheets, respectively, and is 2.0 times higher than that on the 0.5 wt % Ni2P/γ-Ga2O3 reported previously. However, the O2 evolution rate is much less than the H2 evolution rate in the initial reaction stage. On prolonging the irradiation time, H2 evolution declines, while O2 evolution increases until it reaches its stoichiometric value corresponding to H2. The reason for the photocatalytic behavior of NixP/γ-Ga2O3 is studied and the corresponding mechanism is suggested. The absent or low oxygen evolution in the initial reaction stage is because the dioxygen generated from water oxidation by the photogenerated holes is wholly or partially captured by the surface oxygen vacancies to form the surface peroxide bonds (−O–O−). Once the oxygen vacancies are eliminated by the photogenerated O2, the overall water splitting reaction would reach the steady state. Thereafter, H2 production decreases from 5.5 to 2.0 mmol·g–1·h–1, but the O2 evolution gradually approaches the corresponding stoichiometric value, especially for the photocatalyst treated with H2O2 for 24 h.

Enhanced photocatalytic ammonia oxidation activity and nitrogen selectivity over Ag/AgCl/N-TiO2 photocatalyst

The removal of ammonia (NH3) emitted from agricultural and industrial activities is of great significance to protect human health and ecological environment. Photocatalytic NH3 oxidation to N2 under mild conditions is a promising strategy. However, developing visible light photocatalysts for NH3 oxidation is still in its infancy. Here, we fabricate N-TiO2 and Ag/AgCl/N-TiO2 photocatalysts by sol-gel and photodeposition methods, respectively. The introduction of N not only endows TiO2 with visible light response (absorption edge at 460 nm) but also results in the formation of heterophase junction (anatase and rutile). Thus, N-TiO2 shows 2.0 and 1.8 times higher than those over anatase TiO2 and commercial TiO2 for NH3 oxidation under full spectrum irradiation. Meanwhile, surface modification of Ag can simultaneously enhance visible light absorption (generating localized surface plasmon resonance effect) and charge separation efficiency. Therefore, the photocatalytic activity of Ag/AgCl/N-TiO2 is further improved. Furthermore, the presence of N and Ag also enhances the selectivity of N2 product owing to the change of reaction pathway. This work simultaneously regulates photocatalytic conversion efficiency and product selectivity, providing some guidance for developing highly efficient photocatalysts for NH3 elimination.

Gallium Oxide Assisting Ag-Loaded Calcium Titanate Photocatalyst for Carbon Dioxide Reduction with Water

An efficient and highly selective photocatalytic conversion of carbon dioxide (CO2) into valuable chemicals such as carbon monoxide (CO) using water (H2O) as an electron donor has been much attractive and deeply desired, which requires the development of advanced photocatalysts based on a functional design. As the Ag-loaded calcium titanate (CaTiO3, CTO) photocatalyst showed a high selectivity to CO2 reduction in aqueous solution and the Ag-loaded gallium oxide (Ga2O3) photocatalyst showed a higher activity for both H2O splitting and CO2 reduction, herein, a series of composite photocatalyst samples consisting of Ga2O3 and CTO were simply fabricated by calcination of the physical mixtures, followed by loading of a Ag cocatalyst with a photodeposition method. The optimized sample with the Ag cocatalyst exhibited both a high CO formation rate of 56.9 μmol h–1 (higher than that of Ag/Ga2O3) and a high selectivity of 95.0% (comparable to Ag/CTO) in the photocatalytic CO2 reduction with H2O. In this composite photocatalyst, most of the electrons generated in the photoexcited Ga2O3 part migrated to the minor CTO particles to contribute to the selective CO2 reduction reaction, which was evidenced by the selective photodeposition of Ag species on the CTO part. The selective CO formation originates from the property of Ag-loaded CTO photocatalyst as the active part in the composite photocatalyst. The Ga2O3 part functions as an antenna to receive the light and donate the photoexcited electrons to the much decorated Ag/CTO part, where the concentrated electrons would promote CO2 reduction with high efficiency.

Nano Pt/TiO2 photocatalyst for ultrafast production of sulfamic acid derivatives using 4-nitroacetanilides as nitrogen precursor in continuous flow reactors

The design of reactors based on high performance photocatalysts is an important research in catalytic hydrogenation. In this work, modification of titanium dioxide nanoparticles (TiO2 NPs) was achieved by preparation of Pt/TiO2 nanocomposites (NCs) through photo-deposition method. Both nanocatalysts were used for the photocatalytic removal of SOx from the flue gas at room temperature in the presence of hydrogen peroxide, water, and nitroacetanilide derivatives under visible light irradiation. In this approach, chemical deSOx was achieved along with protection of the nanocatalyst from sulfur poising through the interaction of the released SOx from SOx-Pt/TiO2 surface with p-nitroacetanilide derivatives to produce simultaneous aromatic sulfonic acids. Pt/TiO2 NCs have a bandgap of 2.64 eV in visible light range, which is lower than the bandgap of TiO2 NPs, whereas TiO2 NPs have a mean size of 4 nm and a high specific surface area of 226 m2/g. Pt/TiO2 NCs showed high photocatalytic sulfonation of some phenolic compounds using SO2 as a sulfonating agent along with the existence of p-nitroactanilide derivatives. The conversion of p-nitroacetanilide followed the combination processes of adsorption and catalytic oxidation–reduction reactions. Construction of an online continuous flow reactor–high-resolution time-of-flight mass spectrometry system had been investigated, realizing real-time and automatic monitoring of completion the reaction. 4-nitroacetanilide derivatives (1a-1e) was converted to its corresponding sulfamic acid derivatives (2a–2e) in 93–99% isolated yields of within 60 s. It is expected to offer a great opportunity for ultrafast detection of pharmacophores.

NiS Protective Layer for Repelling Chloride Ion Effectively for Water Oxidation on Photocatalytic Seawater Splitting

Due to the increase of global power use, the shortage of energy supply and global warming have become the main obstacles to social and economic development. Today’s society is gradually developing cleaner and greener energy represented by solar energy to alleviate the current energy shortage. Among them, semiconductor photocatalytic water splitting technology is one of the most important methods. However, global freshwater resources are in short supply; the design and synthesis of proper photocatalysts for seawater splitting has been regarded as one of the most powerful approaches solving the dilemma of a shortage of freshwater resources and utilization of solar energy. Based on that, the quaternion Pt/Co3O4–NiS/STO composites for photocatalytic water splitting in a seawater system were successfully synthesized by a simple hydrothermal method and photodeposition method. Noticeably, the loading of Pt and Co3O4 cocatalysts greatly improved the separation efficiency of photogenerated electrons and holes. At the same time, the surface modification of NiS made the photocatalysts able to resist the toxicity of a large number of chloride ions in seawater. The oxygen yield for seawater splitting was nearly twice that of untreated samples and about half of the amount of that in pure water. Our work introduced an ideal modification material structure to demonstrate the feasibility of seawater splitting, which would guide other photocatalytic seawater splitting systems in the future.

Mechanistic insight into the photocatalytic N-alkylation of piperazine with alcohols over TiO2 supported Pd catalysts

N-alkylated piperazines can be synthesized by the thermal catalytic alkylation of piperazine with alkyl halides or alcohols in the presence of supported metal catalysts. However, these processes either discharge large amounts of waste or require harsh conditions. Here, we report the results of N-alkylation of piperazine with lower alcohols (methanol, ethanol, and propanol) without external hydrogen addition at room temperature in the presence of a TiO2-supported Pd catalyst (Pd/TiO2-P) prepared by photodeposition method. Compared with the catalysts prepared by the conventional chemical reduction or hydrogen reduction, the Pd/TiO2-P catalyst showed the highest conversion of piperazine and the best selectivity to N-alkypiperazines. The mechanistic studies indicated that this phenomenon occurs via tandem photocatalytic reactions involving alcohol dehydrgenation to aldehyde, aldehyde condensation with piperazine to enamine, and enamine hydrogenation to N-alkylated piperazines. Considering the experimental results of methanol isotope kinetics, the α-C–H cleavage of methanol to form hydroxymethyl radical (·CH2OH) was proven to be the rate-determining step in the N-alkylation reaction of piperazine with low carbon alcohols. The characterization and control experiments revealed that the size of Pd nanoparticles and the valence of Pd species were vital to the reaction. The Pd/TiO2-P catalyst with an average of 2.5 ± 0.5 nm Pd particles and approximately 68% Pd0 species on surfaces presented the highest activity for the photocatalytic tandem reactions of methanol dehydrogenation and enamine hydrogenation.

Confined Space and Heterojunction Dual Modulation of ZnO/ZnS for Boosting Photocatalytic CO2 Reduction

The reduction of CO2 to chemical fuel driven by solar energy can not only meet the growing demand for renewable energy, but also balance the carbon cycle in nature. However, the current photocatalysts have low CO2 conversion due to their poor light capture ability, narrow light response range, and high recombination probability of photogenerated carriers. Herein, a heterogeneous photocatalyst of hollow structured ZnO/ZnS decorated with Pt nanoparticles is synthesized through the hydrothermal process and photodeposition method, showing excellent photocatalytic activity for CO2 reduction in long‐time stability and ≈100% CO selectivity, which can mainly contribute to natural enhanced light‐capture ability of the hollow confined space due to multiple reflection and scattering of light in the cavity, thus improving separation efficiency of photogenerated charge carriers due to the type II junction constructed between ZnO and ZnS and the additional reaction active sites after decorating Pt nanoparticles in the surface of the hollow structure.

Amorphous Mixed-Vanadium-Tungsten Oxide Films as Optically Passive Ion Storage Materials for Solid-State Near-Infrared Electrochromic Devices.

Near infrared (NIR) electrochromic (EC) devices that selectively modulate the NIR light without affecting the daylight represent a promising window technology for saving energy consumption of buildings. Current research efforts have been focused on developing NIR-EC materials, while little attention has been directed to the optically passive ion storage materials that are crucial for balancing charges in a full NIR-EC device. Herein, we report that amorphous phase mixed-vanadium-tungsten oxide films exhibit minimum optical change with high ion storage capacity, which enables the usage of the mixed-metal oxides as optically passive counter electrode materials for NIR-EC devices. The mixed-vanadium-tungsten oxide films are synthesized by a room-temperature solution-based photodeposition method that allows us to precisely engineer the metal compositions and thicknesses of the mixed-metal oxide films, thus optimizing their optical inertness and ion storage capability. A solid-state NIR-EC device assembled with the mixed-vanadium-tungsten oxide film as an ion storage layer and the amorphous tungsten oxide hydrate as the NIR-EC layer shows fast response speed with cycling stability up to 10,000 cycles, proving the outstanding charge balancing capability of mixed-metal oxide. Our work provides an efficient strategy for developing optically passive ion storage films with high ion storage capability for high-performance EC devices.

Mechanism and degradation pathways insight of photocatalytic oxidation antibiotics by geometrical Ag/AgNbO3/BiVO4 plasmon Z-type heterojunction

Three-dimensions geometry-like plasmon Ag/AgNbO3/BiVO4 (Ag/ANO/BVO) Z-type heterojunction photocatalyst was synthesized by electrostatic self-assembly and photo-deposition method. Levofloxacin hydrochloride (LEF) became the target degradation object to evaluate photocatalytic activity. The 3-Ag/ANO/BVO showed the best photocatalytic properties compared with other as-synthesized catalysts. The apparent rate constant of 3-Ag/ANO/BVO was 0.0235 min−1, which separately was 47.00, 5.22, and 1.85 times higher than that of AgNbO3 (ANO), BiVO4 (BVO), and 40%-AgNbO3/BiVO4 (40-ANO/BVO). Several reaction parameters including catalyst dosage, initial LEF concentration, and reaction pH values were filtrated to investigate optimal photocatalytic reaction conditions of the 3-Ag/ANO/BVO composite. The elevated photocatalytic activity can be attributed to the effective migration and separation of photo-induced carriers on the contact interface due to the formation of Z-type heterojunction and broadened visible light absorption range by localized surface plasmon resonance (LSPR) in 3-Ag/ANO/BVO composite. Furthermore, formed intermediates during the photocatalytic oxidation of LEF molecules were detected via high-performance liquid chromatography-mass spectrometry (HPLC-MS). Ultimately, a plasmonic Z-type photocatalytic mechanism was verified through a variety of characterization tests and simulations method (finite difference time domain, FDTD).

A Comparison of Photodeposited RuOx for Alkaline Water Electrolysis

The storage of renewable energy is a pressing challenge to overcome in the transition toward a power grid based on plentiful, yet intermittent energy supplies. The renewables-driven electrolysis of water to form hydrogen fuel is an attractive avenue, but requires better oxygen-evolution reaction (OER) catalysts to be feasible at scale. RuO2 is touted as one of the superior OER catalysts but only under acidic conditions; RuO2 electrocatalysts suffer from poor stability under alkaline conditions. In this work, we evaluate three photodeposited RuOx OER electrocatalysts, all prepared via a scalable photodeposition method. Based on electrochemical and spectroscopic studies (X-ray photoelectron spectroscopy and X-ray absorption spectroscopy), our main findings are that nanocrystalline RuOx catalysts outperform their amorphous counterpart and are more stable under alkaline (0.1 M KOH) conditions. This works thus lifts a major hurdle toward the use of RuOx for alkaline water electrolysis.

Preparation of NaNbO3 microcube with abundant oxygen vacancies and its high photocatalytic N2 fixation activity in the help of Pt nanoparticles

In this study, the photocatalytic N2 immobilization performance of NaNbO3 is enhanced via oxygen vacancy introduction and Pt loading. The designed Pt-loaded NaNbO3 with rich oxygen defects (Pt/O-NaNbO3) is synthesized by combining ion-exchange and photodeposition methods. Characterization result indicates that the O-NaNbO3 has hollow microcube morphology and higher surface area than NaNbO3. The introduced oxygen defects greatly affect the energy band structure. The band gap is slightly narrowed and the conduction band is raised, allowing O-NaNbO3 to generate electrons with strong reducibility. Moreover, the oxygen defects reduced the work function of NaNbO3, leading to increased charge separation in the bulk phase. The loaded Pt nanoparticles can further increase the surface charge separation via the formed Schottky barriers between Pt and O-NaNbO3, which was thought to be the primary cause of the increased photocatalytic activity. Additionally, the oxygen vacancies and metal Pt also contribute to the adsorption and activation of N2. Under the combined effect of the above changes, Pt/O-NaNbO3 presents much higher photoactivity than NaNbO3. The optimized NH3 production rate reaches 293.3 μmol/L g-1h−1 under simulated solar light, which is approximately 2.2 and 20.2 times higher than that of O-NaNbO3 and NaNbO3, respectively. This research offers a successful illustration of how to improve photocatalytic N2 fixation and may shed some light on how to design and construct efficient photocatalysts by combining several techniques.

Cs0.33WO3/(t-m)-BiVO4 double Z-type heterojunction photothermal synergistic enhanced full-spectrum degradation of antibiotics

The Cs0.33WO3/(t-m)-BiVO4 double-Z heterojunction photocatalysts were prepared with photodeposition method and Cs0.33WO3 photothermal effect. After 180 min of reaction to Visible/NIR light, the dual Z-type heterojunction photocatalyst degraded 40 mg/L TC at the rates of 90.49 % and 91.94 %, respectively. The TOC removal rates were 73.41 % and 75.85 %, respectively. Moreover, the double Z-type heterojunction photocatalyst has good degradation stability and broad-spectrum degradability in the full spectral range. The presence of small polariton leap effects in Cs0.33WO3 crystals radiates energy in the form of phonons and raises the temperature of the liquid-phase reaction system, and the photothermal-photocatalytic synergy accelerates and enhances the degradation catalytic activity of the heterojunction. The synergistic contribution of photothermal effect-photocatalysis applied to environmental purification is presented in this study as a novel and practical research proposal.

Synthesis of TiO2/MoSx/Ag nanocomposites via photodeposition for enhanced photocatalysis and membrane fouling mitigation

In this research, to improve photocatalytic organic pollutant removal, we synthesized amorphous MoSx (a-MoSx) and Ag on TiO2 via a two-step photodeposition method. The As-synthesized TiO2/a-MoSx/Ag (TMA) photocatalyst exhibited a highly enhanced photocatalytic degradation performance of methylene blue which showed 3.6 times higher reaction rate constant than that of TiO2 photocatalyst. Furthermore, TMA photocatalyst was applied to the ultrafiltration (UF) membrane to mitigate fouling of the membrane. To realize a stable immobilization of photocatalyst on the membrane surface, polydopamine (PDA), which is a biocompatible mussel-inspired adhesive material, was utilized to form an adhesive layer. After PDA coating, TMA photocatalyst was stably deposited on the UF membrane, resulting to increased hydrophilicity. Fouling was successfully mitigated by photocatalytic self-cleaning property of TMA deposited UF membrane and flux recovery ratio was improved by 28% under irradiation. Owing to the simple and easy approach of both photodeposition-based heterostructure photocatalyst synthesis and post-processing of photocatalyst coating on the membrane, we present that our strategy for membrane fouling mitigation is suitable for future membrane technology.

Advances in photochemical deposition for controllable synthesis of heterogeneous catalysts.

Photochemical deposition has been attracting increasing attention for preparing nano-catalysts due to its mild reaction conditions, simplicity, green and safe characteristics, and potential for various applications in photocatalysis, thermal catalysis, and electrocatalysis. In this review, we provide an overview of recent advances in photochemical deposition methods for fabricating heterogeneous catalysts, and summarize the factors that influence the nucleation and growth of metal nanoparticles during the photochemical process. Specifically, we focus on the various factors including surface defects, crystal facets, surface properties and the surface plasmon effect on the size, morphology and distribution control of metal and metal oxide nanoparticles on semiconductors. The control of the photogenerated charges and the triggered photochemical reactions have been proved to be significant in the photochemical deposition process. Besides, the applications of the obtained catalytic materials in thermal catalysis and electrocatalysis is highlighted, considering that many reviews have covered photocatalysis applications. We first introduce the principle of photodeposition, nucleation and growth theory, and factors affecting photodeposition. Then, we introduce photodeposition methods that can achieve "controlled" photodeposition from a strategic perspective. Finally, we summarize the fruitful results of controlled photodeposition and provide future prospects for the development of controlled photodeposition technologies and methods, as well as the deepening and expansion of applications.

Well-dispersed Au co-catalyst deposited on a rutile TiO2 photocatalyst via electron traps.

We deposited Au nanoparticles as a co-catalyst onto a TiO2 photocatalyst by reducing [AuCl4]- using electrons trapped in the oxygen vacancies of TiO2. The dispersibility and hydrogen production ability of the Au co-catalyst are higher than those prepared using the conventional photodeposition method.

Ruthenium and palladium bimetallic nanoparticles achieving functional parity with a rhodium cocatalyst for TiO2-photocatalyzed ring hydrogenation of benzoic acid.

Our previous study showed that a rhodium (Rh) cocatalyst is indispensable for ring hydrogenation of benzoic acid over a titanium(IV) oxide (TiO2) photocatalyst. In this study, we explored ring hydrogenation under an Rh-free condition by using two kinds of cocatalyst that were inactive for this reaction when used solely. Cyclohexanecarboxylic acid as the ring hydrogenation product was successfully obtained when ruthenium (Ru) and palladium (Pd) were simultaneously loaded on TiO2, indicating that this bimetallic system can be used in place of an Rh cocatalyst in ring hydrogenation. The state and distribution of Ru and Pd in particles loaded on TiO2 were investigated by transmission electron microscopy, X-ray photon spectroscopy, and X-ray absorption near edge structure analysis. The functions of Ru and Pd as cocatalysts are discussed on the basis of results of characterization and activity tests. The effects of different contents of Ru and Pd in Ru-Pd/TiO2 prepared by a two-step photodeposition method on catalytic activity and the features of the reaction system were investigated in detail.

Accurate modulation of NiS cocatalysts on the photoelectron transfer sites of BiVO4 for photocatalytic H2O2 generation

A sulfur-mediated photodeposition method is used to accurate modulate NiS cocatalyst at photoelectron transfer sites of BiVO4, which markedly boosts photocatalytic activity of interfacial O2 reduction to H2O2 for BiVO4.

Insight into the photocatalytic reduction of hexavalent chromium using photodeposited metal nanoparticle-TiO2 photocatalysis.

Hexavalent chromium (Cr(VI)) is carcinogenic to organisms. It is widely used in several industries. In this work, we investigated the Cr(VI) photocatalytic reaction with a scavenger on Pt and Cu-TiO2 photocatalysts. Metal-deposited TiO2 was successfully synthesized by a photodeposition method. TEM-EDX, XRD, and UV-DR were analyzed to study the changes in morphology, crystallinity, and the electronic properties of photocatalysts. The rate of charge recombination during reduction and photoluminescence (PL) spectroscopy was used to examine the catalysts in depth. Cu-TiO2 demonstrates the highest photocatalytic activity for 63.74% of Cr(VI) removal. To understand the photoreduction of Cr(VI), the fate transformation of Cr species during the adsorption and reaction was investigated using in situ XANES. The results demonstrated that the Cr(III) was noticeably main component adsorbed over the catalyst, particularly in Cu-TiO2. The presence of humic acid can boost the Cr(VI) removal efficiency and enhanced the Cr(VI) reduction to Cr(III). We believe that the extensive research on Cr(VI) photoreduction on metal-TiO2 heterojunction will provide a comprehensive understanding of catalytic behaviors, paving the way for rationally designed novel Cr reduction catalysts.

Fabrication of Nano-Ag Encapsulated on ZnO/Fe2V4O13 Hybrid-Heterojunction for Photodecomposition of Methyl Orange

Novel silver encapsulated nanocomposite zinc oxide/iron tetra-poly-vanadate (Ag-ZnO/Fe2V4O13) was synthesized with various wt% of silver (1.0–2.5 wt% of Ag) by cost-effective photo-deposition method under the irradiation of ultraviolet-A (UV-A) light. The nanostructure of the Ag-ZnO/Fe2V4O13 was explored by various characterization techniques. The surface functionalities were confirmed by Fourier transform infrared spectra and the crystalline nature of the material was revealed by X-ray diffraction patterns. Furthermore, the surface morphology and the optical properties of the composites were analyzed by scanning electron microscopy, energy dispersive X-ray–elemental color mapping (ECM), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence. The crystallite size of Ag-ZnO/Fe2V4O13 was 28.5 nm which was consistent with HRTEM analysis. The photocatalytic activity was tested against aqueous methyl orange degradation under UV-A light irradiation. In all five runs, the stability of the catalyst was confirmed by reusability measurements and almost 98% of degradation was achieved. A suitable degradation pathway was proposed based on intermediates obtained during the degradation analyzed by gas chromatography–mass spectrometry. Trapping experiments confirmed that the superoxide radical anion (O2•−) was considered as the most active species for this degradation process. Complete mineralization was confirmed by the measurements of chemical oxygen demand.

Integration of the straightforward and environmentally friendly sol–gel/solvothermal and photodeposition methods as a way to prepare highly photoactive Au/S-TiO2 and Cu/S-TiO2 materials

Integration of the straightforward and environmentally friendly sol–gel/solvothermal and photodeposition methods as a way to prepare highly photoactive Au/S-TiO2 and Cu/S-TiO2 materials