Noble Metal Deposition Research Articles

Deciphering NonCubic Phases in Au Microcrystallites via Under Potential Cu Deposition and Selective Growth of Noble Metal and Sulfide Overlayers

Deciphering <i>NonCubic</i> Phases in Au Microcrystallites via Under Potential Cu Deposition and Selective Growth of Noble Metal and Sulfide Overlayers

Development of Modified TiO2 for Photocatalytic Hydrogen Production

AbstractTiO2 has advantages such as excellent photocatalytic performance, high chemical stability, low price, and not easy to produce secondary pollution. Therefore, the photocatalytic hydrogen production over TiO2 catalyst was an effective way to achieve hydrogen production from solar energy with low energy consumption and low cost. However, the TiO2 catalyst responds only to UV light due to its wide forbidden band, and the electrons and holes were prone to recombination, resulting in the decrease in photocatalytic activity and quantum efficiency. In recent years, researchers have conducted a series of modifications on TiO2 to improve its visible light response, reduce the rate of carrier recombination, and thereby enhance the efficiency of photocatalytic hydrogen production. This paper reviews several main modification methods of TiO2 including morphology regulation, ion doping, semiconductor recombination, noble metal deposition, dye sensitization and their research progress in the field of photocatalytic hydrogen production. Finally, the modification of TiO2 photocatalyst in the future was predicted.

Photocatalytic activity enhancement by noble metal deposition on faceted F-TiO2 synthesised by microwave assisted method. A study of selective oxidation of gas-phase ethanol in a FBPR reactor

In the present work, fluorinated titanium dioxide (TiO2-F) with high exposition of facet {001} was prepared by following a facile and high yield hydrothermal method assisted by microwave. This faceted TiO2 was then modified by Au or Ag deposition at two different metal loadings (0.125 and 0.25 wt%). A wide physicochemical characterisation of the materials was performed. X-ray difractograms showed high {001} facet exposition in all materials. By X-ray fluorescence it was found that the different samples contained about 5% of fluor. All samples presented high surface area and high uniformity and homogeneity of particles, which highlights the good properties that can be achieved by the microwave synthesis method compared to conventional hydrothermal methods. Oxidation state of the noble metals was studied by XPS. On the other side, TiO2-F and the metallised titania powders were immobilised on polystyrene pellets (PS) for evaluating their gas photocatalytic activity in volatile organic compounds (VOCs) decontamination by following the reaction of photoxidation of ethanol in gas phase. It was found that activity was considerably improved by the addition of noble metals, obtaining high conversion and selectivity to CO2. It is remarkable that the selectivity to CO is almost zero. The highest efficiency was found for the faceted TiO2-F sample with the lowest Au loading (0.125 wt%) immobilised on PS where 91% ethanol conversion and 100% CO2 selectivity were achieved. Different reaction variables were also studied.

Research Progress of and Perspectives of BiOCl Photocatalytic Materials

BiOCl is considered as a candidate to effectively separate photogenerated carriers due to its strong internal electronic field, thus being regarded as a new type of photocatalyst. We interpret BiOCl from the crystal structure, photocatalytic mechanism, synthetic method and influence factors of photocatalytic performance. In view of the shortages of inherent wide band-gap and high recombination probability photo-generated carrier for BiOCl, researches on how to improve the photocatalytic ability were summarized by the modification methods such as ion doping, noble metal deposition, heterojunction construction, morphology control and oxygen vacancy engineering during synthesis. Finally, the future development trend of BiOCl was prospected.

Noble metal nanoparticles and nanodiamond modified strontium titanate photocatalysts for room temperature CO production from direct hydrogenation of CO2

The activation and conversion of CO2 can be achieved on multifunctional catalytic sites at the metal/oxide interface by taking advantage of the synergy between noble metal nanoparticles and supports. Herein, sequential deposition of noble metals (Ru, Rh, and Pt) and nanodiamonds (NDs) was carried out on the surface of strontium titanates (STO). The noble metals and NDs were deposited in either 1 wt% or 10 wt%. The samples were characterized with in-situ as well as ex-situ spectroscopic and microscopic techniques and tested towards photocatalytic CO2 hydrogenation. The sequential deposition of the noble metals and NDs enhanced light absorption properties, which also led to higher photocatalytic activity. The STO-ND-Ru sample had the highest photocatalytic CO2 hydrogenation efficiency (47.5%) and showed improved selectivity for CH4 (14.5%). Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies showed that the hydrogenation of CO2 to CO and CH4 followed different mechanisms for pristine STO and STO-ND-Ru.

In-situ preparation of N-doped Bi0/OVs-BiVO4 photocatalysts with enhanced photocatalytic properties

Elemental doping, noble metal deposition and defect engineering have proven to be effective strategies to enhance the photogenerated charge pairs separation behavior of semiconductor materials and ameliorate their photocatalytic performance. In this study, N-doped Bi0/OVs-BiVO4 photocatalysts were constructed in-situ by calcining BiVO4 precursors under a hydrogen/nitrogen atmosphere. The experimental results demonstrate the successful reduction and loading of Bi0 onto the BiVO4 surface and the introduction of N doing and oxygen vacancies (OVs). The optical absorption range of BiVO4 is broadened by the synergistic effect of the surface plasmon resonance (SPR) effect of Bi0, N-doping and OVs, inducing enhanced separation efficiency of the photoinduced carriers. The photocatalytic degradation rate constant of Rhodamine B (RhB) on samples treated with a hydrogen/nitrogen atmosphere for 10 min under simulated sunlight irradiation is 4.8 times better than that on the blank BiVO4. The enhanced photocatalytic performance of N-doped Bi0/OVs-BiVO4 originates from the synergistic effect of SPR effect of Bi0, N-doping and OVs. This work highlights that the improvement of BiVO4 photocatalytic property can be achieved by calcining BiVO4 under a hydrogen/nitrogen mixed atmosphere.

Development of a Simple Electroless Method for Depositing Metallic Pt-Pd Nanoparticles over Wire Gauge Support for Removal of Hydrogen in a Nuclear Reactor.

Electroless noble metal deposition on the conducting substrate is widely used to obtain the desired film or coating on the substrate of interest. Wire-gauge-based Pt/Pd/Pt-Pd (individually, sequentially, and simultaneously deposited) catalysts have been developed using formaldehyde and sodium formate as reducing agents. Various surface pretreatment methods like SnCl2 + PdCl2 seeding, oxalic acid etching, and HCl activation (etching) have been employed to obtain the desired noble metal coating. Minimum time duration was observed for simultaneously deposited catalysts using formaldehyde as a reducing agent. Prepared catalysts were characterized for noble metal deposition, coating kinetics, surface morphology, and binding energy. The catalyst was found to be active for H2 and O2 recombination reactions for hydrogen mitigation applications in nuclear reactors.

Research progress of vanadium pentoxide photocatalytic materials.

Photocatalytic reactions convert solar energy into chemical energy through a clean and green reaction process. Photocatalytic technology based on semiconductor materials provides us with a new idea in energy utilization and environmental governance. It was found that vanadium pentoxide (V2O5) has a narrow band gap, wide response range in the visible region, high oxygen density in the V2O5 lattice, high oxidation state of V5+, small energy requirement, and superior catalytic activity in partial oxidation. Therefore, the utilization rate of sunlight and photocatalytic oxidation can be greatly improved using V2O5 materials. However, the narrow band gap of V2O5 also makes it easier for the photogenerated electrons and holes to recombine in the excited state, and the stored energy is instantly consumed by carrier recombination. Therefore, how to promote the carrier separation of V2O5 and improve the photocatalytic efficiency are the key problems to be solved. Herein, several methods to improve the photocatalytic performance of V2O5 are reviewed, including metallic ion doping, non-metallic ion doping, semiconductor recombination, and noble metal deposition. Finally, it is suggested that future research directions should focus on a variety of modification methods simultaneously to promote photocatalytic efficiency and lower the cost, which will enable V2O5 to have a broad development prospect in the field of photocatalysis.

Nanoceria as an Electron Reservoir: Spontaneous Deposition of Metal Nanoparticles on Oxides and Their Anti-inflammatory Activities.

Designing metal-metal oxide heteronanostructures with synergistic and superior activities (unattainable in the case of a single entity) is of great interest for a wide range of technological applications. Traditional synthetic strategies typically require reducing agents, stabilizing ligands, or high temperature reductive treatment to produce oxide-supported metals. Herein, a facile noble metal deposition strategy is developed to produce silver, gold, and platinum nanocrystals on the surface of hollow mesoporous cerium oxide nanospheres without any pretreatment. Unlike the galvanic replacement reaction, the developed protocol employs the innate reductive potential of CeO2 to produce a high density of ultrafine noble metal nanocrystals homogeneously immobilized onto the surface of CeO2 nanospheres. The multienzyme-like activities (i.e., superoxide dismutase-like and catalase-like) of CeO2@metal nanostructures, originating from CeO2 and metal nanoparticles, were effectively utilized for anti-inflammatory therapies in two in vivo models. This oxygen vacancy-mediated reduction strategy can be generalized to produce diverse metal-metal oxide nanostructures for a wide range of applications.

Noble Metals Deposited LaMnO3 Nanocomposites for Photocatalytic H2 Production.

Due to the growing demand for hydrogen, the photocatalytic hydrogen production from alcohols present an intriguing prospect as a potential source of low-cost renewable energy. The noble metals (Ag, Au, Pd and Pt) deposited LaMnO3 nanocomposites were synthesized by a non-conventional green bio-reduction method using aqueous lemon peel extract, which acts as both reducing and capping agent. The successful deposition of the noble metals on the surface of LaMnO3 was verified by using powder XRD, FTIR, TEM, N2-physisorption, DR UV-vis spectroscopy, and XPS techniques. The photocatalytic activity of the synthesized nanocomposites was tested for photocatalytic H2 production under visible light irradiation. Different photocatalytic reaction parameters such as reaction time, pH, catalyst mass and reaction temperature were investigated to optimize the reaction conditions for synthesized nanocomposites. Among the synthesized noble metal deposited LaMnO3 nanocomposites, the Pt-LaMnO3 nanocomposite offered superior activity for H2 production. The enhanced photocatalytic activity of the Pt-LaMnO3 was found as a result from low bandgap energy, high photoelectrons generation and enhanced charge separation due to deposition of Pt nanoparticles. The effective noble metal deposition delivers a new route for the development of plasmonic noble metal-LaMnO3 nanocomposites for photocatalytic reforming of aqueous methanol to hydrogen.

Significantly enhanced photocatalytic activity by surface acid corrosion treatment and Au nanoparticles decoration on the surface of SnFe2O4 nano-octahedron

The synergy effect of surface modifications using acid treatment and noble metal (Au) deposition on the efficiency of SnFe2O4 (SFO) nano-octahedron photocatalyst has been investigated. Inorganic acids (H2SO4 and HNO3) were employed to compare the effects of different acids. It has been found that after corrosion treatment using H2SO4 and deposition of Au nanoparticles, SnFe2O4 nano-octahedron (Au-S-SFO) showed significantly enhanced photocatalytic activity under simulated light irradiation. Au-S-SFO was characterized by XRD, XPS, EDS, FTIR, Uv–vis-DRS, SEM, PL and EIS analysis. The mechanism for the photocatalytic chlortetracycline (CTC) degradation and CO2 reduction was investigated by the scavenger tests. The stability of Au-S-SFO was confirmed by continuously repeated tests followed by XRD and TEM analysis. The surface corrosion treatment of SFO octahedron with H2SO4 could produce hydroxyl group (–OH) and sulfonic acid group (-SO3H) as reaction sites. These active sites not only enhanced the Au nanoparticles deposition to the acid treated SFO surface, but also acted as the Brønsted acid sites which enhance the water adsorption and provide protons for CTC degradation and CO2 reduction. These effects improved the carrier separation and transfer efficiency. In addition, the photocatalytic efficiency was further enhanced by the surface plasmon resonance (SPR) effect of Au nanoparticles deposited on the surface of acid treated SFO. As a result of the synergy effect of both acid treatment and SPR effect from the Au NPs, Au-S-SFO exhibited >2.5 times higher photocatalytic CTC degradation efficiency than pure SFO. Furthermore, Au-S-SFO displayed the highest CO2 reduction activity with 2.81, 1.92, and 2.69 times higher evolution rate for CO, CH4 and H2, respectively, than that of pure SFO.

Recyclable visible-light photocatalytic composite materials based on tubular Au/TiO2/SiO2 ternary nanocomposites for removal of organic pollutants from water

The highly active free radicals generated by semiconductor materials in the photocatalytic technology can achieve efficient degradation of organic pollutants. Tubular Au/TiO2/SiO2 ternary nanocomposite is fabricated under high-temperature ablation via the sacrificial template and noble metal deposition. SiO2 is deposited to inhibit the growth of grain size of TiO2. The tubular structure can effectively increase the scattering times and improve the utilization of visible-light. Au nanoparticles (Au NPs) absorb visible-light and promote the formation of photogeneration-hole pairs. Besides, Au NPs can also be used as an electron acceptor to delay the recombination rate of photogeneration electron-hole pairs, and improve the photocatalytic activity. Furthermore, the polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) gel was used to load and immobilize TiO2-based catalytic materials, and the composite gel still has a good photocatalytic activity with favorable cyclability. This work opens up a new opportunity for designing the photocatalytic composite material with long-term catalytic stability and excellent reusability.

Noble metal nanoparticles (Mx = Ag, Au, Pd) decorated graphitic carbon nitride nanosheets for ultrafast catalytic reduction of anthropogenic pollutant, 4-nitrophenol

We report an effective facile immobilization of noble nanoparticles (Mx = Ag, Au and Pd) assembled on g-C3N4 (g-CN) prepared via a simple ultra-sonication strategy. The Mx assembled g-CN nanocomposites were applied for the effective conversion of 4-nitrophenol (4-NP). As prepared nanocomposites were characterized by techniques of XRD, SEM-EDS, TEM, XPS, and FT-IR analysis to gain crystallographic structural, and morphological insights. The Pd@g-C3N4 (Pd@g-CN) nanocomposite exhibited best catalytic performance (kapp = 1.141 min−1) toward the conversion of 4-NP to 4-aminophenol (4-AP), almost 100% within 4 min using aqueous sodium borohydride (NaBH4). The higher catalytic efficiency of Pd@g-CN could be attributed to the surface electron density on the Pd and rapid electron transfer capacity. Interestingly, g-CN not only role as a stabilizer but also provided compatibility for noble metal deposition, which improves the chemical and morphological stability of noble metal nanoparticles. Different reaction parameters including concentrations of 4-NP, and catalyst amount were studied. These unique combinations make noble metal nanoparticles anchored g-CN nanosheets an ideal platform for catalysis applications and environmental remediation.

Noble metal modified (002)-oriented ZnO hollow spheres for the degradation of a broad range of pollutants

Zinc oxide hollow spheres were fabricated by applying sucrose-derived carbon spheres as templates that were eliminated through calcination. For this purpose, two synthesis methods were examined and compared, chemical impregnation and solvothermal method. The most suitable ZnO hollow structure was selected for noble metal deposition (Au and Pt at 1 wt%) to further increase the photocatalytic activity. The photocatalytic activity was examined by the decomposition of three different model pollutants (phenol, Na-ibuprofen and diuron) under UV irradiation. The as-synthesized hollow sphere structures and its noble metal composites were further examined by XRD, SEM, IR, DRS, PL. The templates did not modify the structure of ZnO only the morphology and contributed to the preservation of the original structure during calcination. The structural, optical and photocatalytic activity was correlated with both the application of carbon sphere template, and noble metal deposition respective their role in the improvement of the photocatalytic activity.

Ag3PO4-based photocatalysts and their application in organic-polluted wastewater treatment.

Semiconductor photocatalysis technology has shown great potential in the field of organic pollutant removal, as it can use clean and pollution-free solar energy as driving force. The discovery of silver phosphate (Ag3PO4) is a major breakthrough in the field of visible light responsive semiconductor photocatalysis due to its robust capacity to absorb visible light < 520nm. Furthermore, the holes produced in Ag3PO4 under light excitation possess a strong oxidation ability. However, the strong oxidation activity of Ag3PO4 is only achieved in the presence of electron sacrifice agents. Otherwise, photocorrosion would greatly reduce the reuse efficiency of Ag3PO4. This review thus focuses on the structural characteristics and preparation methods of Ag3PO4. Particularly, the recent advances in noble metal deposition, ion doping, and semiconductor coupling, as well as methods of magnetic composite modification for the improvement of catalytic activity and recycling efficiency of Ag3PO4-based catalysts, were also discussed, and all of these measures could enhance the catalytic performance of Ag3PO4 toward organic pollutants degradation. Additionally, some potential modification methods for Ag3PO4 were also proposed. This review thus provides insights into the advantages and disadvantages of the application of Ag3PO4 in the field of photocatalysis, clarifies the photocorrosion essence of Ag3PO4, and reveals the means to improve photocatalytic activity and stability of Ag3PO4. Furthermore, it provides a theoretical and methodological basis for studying Ag3PO4-based photocatalyst and also compiles valuable information regarding the photocatalytic treatment of organic polluted wastewater.

RuS2-modified NiW/Al2O3 catalysts for refractory 4,6-dimethyl-dibenzothiophene hydrodesulfurization

Al2O3-supported noble metal (NM)-modified hydrodesulfurization (HDS) catalysts (W 15.8 wt% and Ni 3.5 wt%) were applied in refractory 4.6-dimethyl-dibenzothiophene elimination. Corresponding Ru-doped (0.5 and 0.7 wt%) materials were either dried (120 °C) or dried followed by calcining (400 °C) after NM deposition prior to activation (400 °C, 15/85H2S/H2 mixture). In solid at 0.5 wt% NM calcined after Ru deposition ruthenium was less dispersed (XRD and TPR) than over corresponding just dried one. Also, WS2 had higher dispersion (HR-TEM) on the latter. However, “NiWS” phase was enhanced (XPS) on the former material. NM-doped catalysts annealed before activation showed significantly enhanced activity (x2.4 and x1.6, solids with 0.5 and 0.7 wt% Ru, respectively) in refractory dibenzothiophene (DBT) HDS, as to that of pristine NiW/Al2O3. Enhanced hydrogenating properties of the former materials improved S elimination from sterically-hindered DBT. Conversely, Ru-doping was detrimental on NiW/alumina when non-annealed prior to activation. Unreduced Run+ and decreased pyrite-like RuS2 species (XPS) on those catalysts could be related to their strongly diminished HDS activity.

Research Progress of Noble Metal Deposition in Vitrification of High-Level Liquid Wastes

Research Progress of Noble Metal Deposition in Vitrification of High-Level Liquid Wastes

Photocatalytic Degradation of Pharmaceutically Active Compounds with Nano-TiO2: Recent Advances and Future Trends

As an emerging contaminant in water environments, pharmaceutically active compounds (PhACs) can be traced in pharmaceuticals, domestic wastewater and waste disposal, and biological metabolism etc. However, there are technical deficiencies in terms of removing PhACs in traditional wastewater treatment plants. Photocatalytic degradation of PhACs with nano-TiO2has proved to be an effective means to solve these problems, but there are two intrinsic drawbacks: low visible-light utilization and easily-recombined electron-holes. The paper introduces five modification methods of nano-TiO2: metal ion doping, non-metal doping, noble metal deposition, composite of semiconductor materials and immobilization. Then, the literature review summarizes the recent advances and breakthroughs made in nano-TiO2for PhACs’ removal, with an emphasis on the modifications for enhancing the efficiency of treatment methods using nano-TiO2. Finally, it proposes a number of possible further research orientations.

High‐performance photocatalyst containing noble metals selectively deposited inside mesopore

AbstractWe describe a general photoelectrical deposition process for the priority deposition of noble metals inside surface mesopores, which are selectively formed in the interstitial regions between crystal arrays composed of sintered photoactive nanocrystals. The basis of our approach is to prepare continuous coherent bonds between photoactive nanocrystals aligned toward the surface accompanied by the formation of interstices (2–20 nm) filled with a heterogeneous insulator phase between the crystal arrays; the subsequent removal of part of the heterogeneous phase creates surface mesopores. The coherent crystalline structure causes a smooth electron flow from the outside to the inside of the array through the coherent boundaries of the nanocrystals during photodeposition using an ultraviolet lamp, accompanied by outside‐hole consumption and noble metal deposition in the recesses of the surface mesopores. The size and morphology of the deposited noble metals are restricted to the shape of the formed mesopores, which can be easily controlled. This approach is applicable to a wide range of functional materials and is expected to be applicable to the preparation of excellent photocatalysts, redox catalysts, and photochromic materials. Using our new process, we also achieved a remarkable increase in the photocatalytic activity of the obtained Pd‐deposited TiO2/SiO2 photocatalytic fiber.

Versatile Hollow ZSM-5 Nanoreactors Loaded with Tailorable Metal Catalysts for Selective Hydrogenation Reactions.

Zeolites are one of the most commonly used materials in the chemical industry, acting as catalysts or catalyst supports in different applications. Recently, the synthesis and functionalization of hollow zeolites have attracted many research interests, owing to the unique advantages of their hollow morphology. In the development of more sustainable processes, the hollow zeolites are often endowed with additional stability, selectivity, and activity. Herein, we present a stepwise synthetic protocol to prepare a range of complex hollow ZSM-5 catalysts with catalytic nanoparticles. Solid ZSM-5 crystals were first synthesized from Stöber silica spheres. This solid ZSM-5 sample was then loaded with transition metals via the impregnation method. A subsequent hollowing process was carried out in hydrothermal conditions in which hollow ZSM-5 crystals with confined transition metals inside were synthesized. More specifically, after the encapsulation of transition metals inside hollow ZSM-5, two different approaches have been further devised to allow the deposition of noble metals into the interior cavities or onto the exterior surfaces of the hollow ZSM-5. The deposition of Pt on the exterior surface was carried out by mixing the hollow ZSM-5 sample with presynthesized Pt nanoparticles. Loading of Pd in the interior was achieved by the galvanic replacement reaction between the Pd ions and embedded transition metals inside the hollow ZSM-5 sample. The catalytic performance of these reactor-like nanocatalysts has been evaluated with hydrogenation reactions in both liquid and gas phases, and their compositional and structural merits have been illustrated. For the hollow ZSM-5 sample with Pd loaded inside, liquid-phase selective hydrogenation of styrene over 4-vinylbiphenyl has been achieved with the ZSM-5 shell acting as a molecular sieve. The deposition of Pt on the exterior has improved the C2-C4 product yield when tested for the gas-phase CO2 hydrogenation reaction.