Photo-assisted Method Research Articles

Abundant Exterior/Interior Active Sites Enable Three-Dimensional PdPtBiTe Dumbbells C-C Cleavage Electrocatalysts for Actual Alcohol Fuel Cells.

Developing high-activity electrocatalysts is of great significance for the commercialization of direct alcohol fuel cells (DAFCs), but it still faces challenges. Herein, three-dimensional (3D) porous PdPtBiTe dumbbells (DBs) were successfully fabricated via the visible photoassisted method. The alloying effect, defect-rich surface/interface and nanoscale cavity, and open pores make the 3D PdPtBiTe DBs a comprehensive and remarkable electrocatalyst for the C1-C3 alcohol (ethanol, ethylene glycol, glycerol, and methanol) oxidation reaction (EOR, EGOR, GOR, and MOR, respectively) in an alkaline electrolyte, and the results of in situ Fourier transform infrared spectra revealed a superior C-C bond cleavage ability. The 3D PdPtBiTe DBs exhibit ultrahigh EOR, EGOR, GOR, and MOR mass activities of 25.4, 23.2, 16.8, and 18.3 A mgPd + Pt-1, respectively, considerably surpassing those of the commercial Pt/C and Pd/C. Moreover, the mass peak power densities of 3D PdPtBiTe DBs in actual ethanol, ethylene glycol, glycerol, or methanol fuel cells increase to 409.5, 501.5, 558.0, or 601.3 mW mgPd + Pt-1 in O2, respectively. This study provides a new class of multimetallic nanomaterials as state-of-the-art multifunctional anode electrocatalysts for actual DAFCs.

Synergistic engineering of infiltration–coating strategy and interfacial interaction boosts pseudocapacitive kinetics for zinc-ion capacitor

Effective adjustment of structure and interface charge transfer ability of composite electrode materials are the key to improve the electrochemical performance of the zinc-ion capacitor. Herein, a novel 3D birdcage-like architecture composed of interactive carbon nanotube (CNT) network confining ZIF-67 is prepared though the infiltration–coating strategy, followed by a photo-assisted method to reinforce the coupling interaction between ZIF-67 and CNTs, which is directly used as an cathode of zinc-ion capacitors (ZICs). In terms of this composite, the birdcage-like structure with abundant voids facilitates the ionic/electrolyte transport and buffers the shrinkage/expansion of pseudocapacitive ZIF-67 during intercalation–conversion–deintercalation reactions. Moreover, the robust connection between the ZIF-67 and CNTs can effectively prevent structural deterioration and ensure the ion/electron transport between ZIF-67 and CNTs, thus resulting in a high Zn ion diffusion coefficient, which synergistically guarantees the rate capability and cyclic stability of ZICs. Consequently, the ZICs exhibit a high specific capacitance of 142.33F g−1 (0.5 A/g) and a high energy density of 44.5 Wh kg−1 (375 W kg−1). Furthermore, the ZICs shows excellent cycling stability (92.5% capacitance retention after 5000 cycles at a current density of 0.5 A/g). Our work provides a novel design tactic to enhance the storage properties of zinc ions.

Bio-inspired high-efficiency photosystem by synergistic effects of core-shell structured Au@CdS nanoparticles and their engineered location on {001} facets of SrTiO3 nanocrystals

Natural photosynthesis, which provides a green and high-efficiency energy conversion path by spatial separation of photogenerated carriers through combined actions of molecules ingeniously arranged in an efficient solar nanospace, highlights the importance of rational nanostructure design to realize artificial high-efficiency photosystem. Inspired by these unique features, we constructed a high-efficiency ternary photosystem by selectively decorating the {001} facets of 18-facet SrTiO 3 with Au@CdS photosensitizers via a green photo-assisted method. Benefiting from the dual-facilitated charge carriers transportation in core-shell structured Au@CdS heterojunction and well-faceted 18-facet SrTiO 3 nanocrystal, such a photocatalyst could realize the effective spatial separation of photogenerated electrons and holes. As expected, the 18-facet SrTiO 3 /Au@CdS photocatalyst exhibits superior activity in visible-light-driven photocatalytic hydrogen evolution (4.61 mmol h −1 g −1 ), 166% improvement in comparison with randomly deposited Au@CdS (1.73 mmol h −1 g −1 ). This work offers new insight into the development of green and high-efficiency photocatalytic systems based on the rational nanostructure design by crystal facet engineering.

Bioinspired Strategy for Efficient TiO2/Au/CdS Photocatalysts Based On Mesocrystal Superstructures in Biominerals and Charge-Transfer Pathway in Natural Photosynthesis.

Natural photosynthesis involves an efficient charge-transfer pathway through exquisitely arranged photosystems and electron transport intermediates, which separate photogenerated carriers to realize high quantum efficiency. It inspires a rational design construction of artificial photosynthesis systems and the architectures of semiconductors are essential to achieve optimal performance. Of note, biomineralization processes could form various mesocrystals with well-ordered superstructures for unique optical applications. Inspired by both natural photosynthesis and biomineralization, we construct a ternary superstructure-based mesocrystal TiO2 (meso-TiO2)/Au/CdS artificial photosynthesis system by a green photo-assisted method. The well-ordered superstructure of meso-TiO2 and efficient charge-transfer pathway among the three components are crucial for retarding charge recombination. As a result, the meso-TiO2/Au/CdS photocatalyst displays enhanced visible light-driven photocatalytic hydrogen evolution (4.60 mmol h-1 g-1), which is 3.2 times higher than that of commercial TiO2 (P25)/Au/CdS with disordered TiO2 nanocrystal aggregates (1.41 mmol h-1 g-1). This work provides a promising bioinspired design strategy for photocatalysts with an improved solar conversion efficiency.

The Graphitic Carbon Nitride (g-C3N4): A Promising Material for Photocatalytic CO2 Reduction

The excess use of fossil fuel and rapid industrialization increase of CO2 level in the atmosphere. Efficient conversion of CO2 to value added chemicals and fuels are the best method to reduce CO2 level as well as to maintain sustainability. To overcome the kinetic and thermodynamic barrier in CO2, a suitable heterostructure composite is necessary. Among different types of materials carbon based materials and their composites are shown their suitability electrochemical, thermal and photo-assisted method of CO2 conversion. Among different carbon based materials, graphitic carbon nitrite (g-C3N4) is a sustainable, inexpensive photocatalyst for CO2 conversion. This present article tries to summarize recent works based on conversion of CO2 in presence of solar light using g-C3N4 based composites. This provides an outlook for the future development of new catalysts to reduce CO2 effectively and save our earth from CO2 pollution.

Holey graphene anchoring of the monodispersed nano-sulfur with covalently-grafted polyaniline for lithium sulfur batteries

The homogeneous distribution of nano-sulfur onto 3D structures for the development of high-performance Li-S batteries (LSBs) is a top concern to solve the low utilization of sulfur, sluggish redox kinetics, and lithium polysulfide (LiPS) shuttle effect. Herein, a novel “egg tray” hierarchical architecture of confining and uniformly distributing nano-sulfur into a 3D holey graphene (HG) framework with polyaniline crosslinking (3DHG/NS/CPANI) via photo-assisted method was designed for high-mass-loading LSB cathode. Notably, HG contains both conductive skeletons as electron transfer paths and abundant void spaces in favor of homogenous sulfur anchoring. This configuration improves the contact between nano-sulfur and graphene for effective charge transportation and provides buffering space for volume variations during electrochemical processes. Moreover, a facile photo-assisted method was developed to cross link HG with polyaniline to act as an efficient polysulfide adsorbent, allowing nano-sulfur (NS) to be firmly embedded into the holes of graphene through physical and chemical effects, thus prohibiting the dissolution and shuttle effect of polysulfide. Considering these advantages, the prepared 3DHG/NS/CPANI electrode exhibited excellent performance with high sulfur utilization and specific capacity, resulting in specific discharge capacities at 0.5 and 1C of 1082 and 921 mA h −1, respectively, and small capacity decay of 0.04% per cycle over 500 cycles at 1C. The strategy in this work, which synergistically combines morphology control, nano-sulfur positioning, and structural engineering to enhance the electrochemical performance for Li−S batteries, will offer a valuable reference to energy storage and conversion advances.

Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions.

Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. The aim of this study is to evaluate the control that such a photoassisted method can exert on the properties of ruthenium nanoparticles supported on TiO2 by means of the variation of the incident irradiance and hence of the photodeposition rate. For that purpose, different Ru/TiO2 systems with the same metal load have been prepared under varying irradiance and characterized by means of elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the so-obtained materials has been evaluated by using the degradation of formic acid in water under UV-A light. Particles with size around or below one nanometer were obtained, depending on the irradiance employed in the synthesis, with narrow size distribution and homogeneous dispersion over the titania support. The relation between neutral and positive oxidation states of ruthenium could also be controlled by the variation of the irradiance. The obtained photocatalytic activities for formic acid oxidation were in all cases higher than that of undecorated titania, with the sample obtained with the lowest irradiation giving rise to the highest oxidation rate. According to the catalysts characterization, photocatalytic activity is influenced by both Ru size and Ru0/Ruδ+ ratio.

Analysis of the Spatial-Frequency Characteristics of the Photo-Assisted Method of a Quartz Rough Surface Nano-Polishing

The relationship between the spatial-frequency parameters of a rough surface with a random profile, which has a Gaussian form of the correlation function, and the amplitude-frequency characteristics of the electric field created by this surface is determined. The numerical determination of the evanescent field optimal configuration formed near the quartz rough surface in the gaseous medium saturated with chlorine molecules when illuminated from the quartz side has been considered. The finite-element approach is used to solve the Helmholtz two-dimensional vector equation. It was found that at the initial stage of photochemical polishing different electrodynamic conditions are created for the etching process depending on the profile height standard deviation value. In particular, when the standard deviation is less than 1 nm, all surface protrusions, for which the spatial spectrum harmonics of the profile are located in the region of the maximum slope of the spectral function, are most actively etched. This leads to a decrease in the effective width of the spatial spectrum of a rough quartz surface and an increase in its correlation length. Therefore, simultaneously with decreasing the height of the protrusions, the surface becomes flatter. The paper shows the different character of quartz surface nano-polishing process conditions depending on the initial standard deviation of the profile height.

Holey Graphene Anchoring of the Monodispersed Nano-Sulfur with Covalently-Grafted Polyaniline for Lithium Sulfur Batteries

A novel “egg tray” hierarchical architecture of confining and distributing nano-sulfur into a 3D holey graphene (HG) framework with polyaniline crosslinking (3DHG/NS/CPANI) via photo-assisted method was designed for high-mass-loading Li−S batteries cathode. Notably, HG contains both conductive skeletons as electron transfer paths and abundant void spaces in favor of homogenous sulfur anchoring. This configuration improves the contact between nano-sulfur and graphene for effective charge transportation and provides buffering space for volume variations during electrochemical processes. Moreover, a facile photo-assisted method was developed to cross link HG with polyaniline to act as an efficient polysulfide adsorbent, allowing nano-sulfur (NS) to be firmly embedded into the holes of graphene through physical and chemical effects, thus prohibiting the dissolution and shuttle effect of polysulfide. Considering these advantages, the prepared 3DHG/NS/CPANI electrode exhibited excellent performance with high sulfur utilization and specific capacity, resulting in specific discharge capacities at 0.5 and 1C of 1082 and 921 mAh-1 , respectively, and small capacity decay of 0.04% per cycle over 500 cycles at 1C. The strategy in this work, which synergistically combines morphology control, nano-sulfur positioning, and structural engineering to enhance the electrochemical performance for LSB, will offer a valuable reference to energy storage and conversion advances.

Experimental Determination of Velocity-Field Characteristic of Holes in GaN

This study presents a photo-assisted method to measure the drift velocity of carriers in semiconductors, and successfully used to determine the drift velocity of holes in GaN. A p-i-n diode with a buried p-type layer was designed and fabricated on a free-standing GaN substrate. By reverse-biasing the p-i-n diode and illuminating the cathode layer using an ultraviolet light simultaneously, photo-generated holes were injected into the depletion region and accelerated by the electric field to reach the saturation velocity. The drift velocity ( $\text{v}_{\text {d}}$ )–electric field (E) characteristic can be obtained from the photocurrent induced by photo-generated holes. The measured hole drift velocity can be written as $v_{\text {d}}=\mu _{\text {LF}}E /[1+(\mu _{\text {LF}}E/v_{{\mathrm {sat}}})^{{\beta }}]^{{1}/\beta }$ , where $\mu _{\text {LF}}\,\,=17$ cm2/Vs is the low-field hole mobility, $v_{\text {sat}}= 6.63\times 10^{{6}}$ cm/s is the saturation velocity, $\beta =1.75$ is the fitting parameter. The method presented in this study is a unique way of determining the saturation drift velocity of holes in GaN.

Green synthesis of silver nanostructures with amino acid-modified Pluronic F127 for antibacterial applications

The aim of this work was to evaluate the use of amino acid-functionalized Pluronic F127 derivatives in the synthesis of silver nanostructures (SNS), such as nanoparticles (SNP) and nanoclusters (SNC). Herein, glycine, L-alanine, and DL-alanine were used to functionalize poly(ethylene oxide) (PEO) end groups from the polymer chain via an esterification pathway. The esterified polymers were used for reducing and stabilizing SNS by a hydrothermal or a photo-assisted route (using a UVA light). The functionalized polymers were characterized by FTIR and the obtained SNS were characterized by UV–vis spectroscopy and TEM, which showed that the SNS obtained by the hydrothermal route are predominantly spherical, whereas those obtained by photo-assisted method give rise to rods and prisms. Kinetic studies showed that alanine and glycine form particles with different rates and that the different enantiomers (L and DL) influence the size and shape of SNS. The nanoparticles obtained by the two routes had their antibacterial efficiency tested against S. aureus by the Agar well diffusion method.

Enhanced Production of γ‐Valerolactone with an Internal Source of Hydrogen on Ca‐Modified TiO2 Supported Ru Catalysts

Calcium-modified titania supported Ru catalysts were synthesized and evaluated for the hydrogenation of levulinic acid with formic acid as an internal hydrogen source and water as a green solvent. A new elegant photoassisted method was developed for the synthesis of uniform-size and evenly distributed Ru particles on the titania surface. Compared with the counterpart catalysts prepared by classical wet impregnation, enhanced levulinic acid conversion and γ-valerolactone yield were obtained and further improved through modification of the support by introduction of calcium into the titania support. This synthesis approach resulted in a change of the surface and bulk properties of the support, namely a decrease in the anatase crystallite size and the formation of a new calcium titanate phase. As a consequence, the properties of the catalysts were modified, and smaller ruthenium particles that had stronger interactions with the support were obtained. This affected the strength of the CO adsorption on the catalyst surface and facilitated the reaction performance. The optimum size of Ru particles that allowed for most efficient levulinic acid conversion was established.

Biodegradable and active nanocomposite pouches reinforced with silver nanoparticles for improved packaging of chicken sausages

Abstract This study reports the development of biodegradable PVA-montmorillonite K10 clay nanocomposite blend films with in situ generated ginger extract mediated silver nanoparticles. Photo-assisted method using sunlight irradiation was adopted for the rapid and eco-friendly in situ generation of ginger extract mediated silver nanoparticles in the composite. FTIR, XRD and SEM analysis were conducted to confirm the generation of AgNPs. The nanocomposite blend film had clear antimicrobial activity against common food borne pathogens S. Typhimurium and S. aureus. It also had superior mechanical properties, water resistivity and light barrier ability compared to control films. Indoor soil burial test revealed the nanocomposite blend would degrade completely within 110 days. The nanocomposite blend film was then fabricated into novel packaging pouches and found to be highly efficient in reducing the microbial burden in chicken sausage samples, compared to control polyethylene pouches, signifying its potentiality in extending the shelf life of chicken meat products.

Photo-Assisted Chemical Mechanical Polishing of Si Wafer Using Phosphorescent Particles as a Luminescent Agent

Chemical mechanical polishing (CMP) is used for fabricating semiconductor wafer surfaces because it produces smooth and damage-free surfaces. Polishing efficiency is a key factor to decrease fabrication costs. Photo-assisted CMP—a promising method to improve polishing efficiency—requires a special setup allowing the material surface to be directly illuminated by the excitation light, which increases initial setup costs. Thus, a photo-assisted method that improves polishing efficiency without a special setup is strongly desired. We report a photo-assisted CMP method that employs phosphorescent particles (PhPs). X-ray analysis demonstrates that the Si surface is oxidized by photo-chemical treatment using PhPs. Further, photo-assisted CMP using PhPs added into a polishing slurry improves the material removal rate for Si under UV irradiation on the polishing pad; however, large and blocky PhPs generate defects on the polished surface. A double-layered polishing pad (abrasive layer partly stacked on the phosphorescent layer) is proposed to obtain smooth and defect-free surfaces. Compared with conventional CMP, photo-assisted CMP using the double-layered pad achieves higher polishing efficiency and smoother (0.19 nm Ra) surfaces without generating defects under optimal polishing conditions; thus, this method has potential applications to achieve semiconductor wafer fabrication with a simple polishing setup.

Facet-Selective Deposition of Metal (M=Au, Pt, Pd) Nanoparticles on Co3 O4 Crystals: Magnetically Separable Photocatalyst with Improved Catalytic Performance.

Depositing noble metals on specific facets of semiconductors can improve the separation of photoexcited hole-electron pairs during the photocatalytic reaction, resulting in enhanced photocatalytic performance. This work describes the selective deposition of noble metal nanoparticles (Au, Pt, Pd) on some specific facets of p-type Co3 O4 through a simple and facile photoassisted method. The deposition of Au nanoparticles (NPs) on {111} facets of Co3 O4 nanocrystals (NCs) can remarkably improve their photocatalytic activity towards water oxidation, which can be attributed to enhanced charge spatial separation. Moreover, the magnetically separated photocatalysts are good examples of new designed photocatalysts that can be recovered easily.

Precise control of branch-length of light irradiated gold nanostars and associated thermal performance

Gold nanostars are multi-branched nanoparticles with tip structures. Nanostars have excellent photoelectric properties, which make them able to be used in a variety of optoelectronics devices. Moreover, these stars have good biocompatibility and low toxicity, which opens broad application prospect in the biomedical field. Gold nanostars with admirable optical as well as thermal properties, are thought as a good candidate in cancer treatment that is a hot research topic in recent years. Gold nanostars with different branch-lengths were prepared by the photo-assisted method, and the effect of light was well studied in relation with gold nanostar branch-length. In the solution system, HEPES was used as the reducing agent, stable agent and shape-inducing agent. Under light irradiation, a certain amount of chloroauric acid solution (HAuCl4) was added to the HEPES solution. After a period of time, gold nanostars were prepared. Different wavelengths of irradiating light were selected in this experiment. The wavelength has different effects on the growth of branches associated with gold nanostars. The transmission electron microscope and the ultraviolet-visible-near infrared spectrophotometer were used to analyze the morphology and absorption spectra of gold nanostars. Meanwhile, a nano-measurer software was used to determine branch-lengths of gold nanostars under light irradiation of different wavelengths. The results indicate that the branches of the nanostars under irradiation were shorter than those of nanostars without irradiation. Different branch lengths correspond to different irradiation wavelengths. Based on these results, the physical process of shortening nanostars branches was analyzed, and a theoretical model of changing branch-length in the process of light-induced nanostars growth was proposed. The model indicates that there are two steps when the branch-length is changing. Firstly, the branch-length grows longer with the overall growth of the nanostar. Secondly, the nanostar becomes shorter because of the insatiability of HEPES molecules that are adsorbed on the nanostar surface with the increasing solution temperature. Through a photothermal measurement, a xenon lamp (wavelength 670 nm) was used as a light source to measure the temperature change within 30 min, and then the photothermal conversion efficiency of the gold nanostars was calculated. The results show that the branch-length of gold nanostars can be precisely controlled by light irradiation with slight variation in wavelength. The photothermal conversion efficiency of gold nanostars can also be regulated.

Photocatalytic degradation of herbicides under visible light using Pd-WO3 nanorods

A hydrothermal method was used to prepare a tungsten trioxide (WO3) nanorod, and a photo-assisted method was used to deposit palladium metal onto its surface. Various techniques were used to characterize the WO3 and Pd-WO3 nanorods. The results reveal tungsten trioxide to have a nanorod shape and that palladium was deposited as dots on the tungsten trioxide surface. Additionally, we noticed that the form of palladium on the surface of WO3 nanorods is metallic palladium and that palladium is well dispersed over the WO3 nanorod surface. To measure the photocatalytic activity of WO3 and Pd-WO3 nanorods, the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under visible light was studied. The photocatalytic activity of the Pd-WO3 nanorods was higher than that of the WO3 nanorods. In addition, the photocatalytic activity of Pd-WO3 nanorods increased with an increasing weight percentage of doped palladium. The highest photocatalytic activity, lowest band gap energy and lowest electron-hole recombination time were measured for 0.15wt% Pd-WO3 nanorods. Finally, the photocatalytic stability of 0.15wt% Pd-WO3 nanorods allowed their reuse for the degradation of 2,4-D five times without loss of activity.

Photoassisted Deposition of Palladium Nanoparticles on Carbon Nitride for Efficient Oxygen Reduction

One of the major challenges associated with fuel cells is the design of highly efficient electrocatalysts to reduce the high overpotential of the oxygen reduction reaction (ORR). In this study, a facile photoassisted method was employed for the direct deposition of palladium nanoparticles (Pd NPs) onto graphitic carbon nitride (g-C3N4) for efficient oxygen reduction. The fabricated catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Fourier transmission infrared (FTIR) spectroscopy. The electrocatalytic activity of the prepared catalysts was examined using cyclic voltammetry (CV), linear scan voltammetry (LSV), and chronoamperometry (CA). Our studies have shown that the synthesized Pd-g-C3N4 nanocomposite exhibited robust electrocatalytic behavior toward the ORR in 0.1 M KOH solution, where the desirable f...

Improvement of interaction in and properties of PMMA-MWNT nanocomposites through microwave assisted acid treatment of MWNT

Soluble derivatives of multi-walled carbon nanotubes (MWNT) embedded in a poly(methylmethacrylate) (PMMA) matrix forming thick, homogeneous and transparent nanocomposites, were prepared and characterized. A new photo-assisted method using microwaves, to purify the MWNTs from amorphous carbon and synthesis catalyst clusters, was tested in a sulphonitric mix. This method shortened the processing time compared to other methods. Pristine and functionalized MWNTs were introduced into the MMA, then in situ photo-polymerized. Transmission electron microscopy (TEM) and X-ray diffractometry (XRD), as well as Fourier-transform infrared (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy were used to monitor the effects of the treatment on the different components. The thermal properties of the composites were determined through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The short, microwave treated and polyethylene glycol (PEG) functionalized MWNTs showed the best dispersion in and interaction with PMMA, and had the most significant influence on the thermal properties of this polymer.

Photoassisted Magnetization of Fullerene C60 with Magnetic-Field Trapped Raman Scattering

We report a photoassisted method to magnetize microcrystal fullerene C(60) at room temperature by exciting it to triplet states via a proper laser radiation and then trapping the spin-polarized states under a strong magnetic field. Novel changes on Raman scattering of the C(60) microcrystals were observed in the presence and absence of the magnetic field. In particular, the Raman spectra were found to exhibit a "hysteresis" phenomenon when the external magnetic field was removed. In light of this, we propose magnetic-field-trapped Raman spectroscopy (MFTRS) and employ first-principle calculations to reproduce the Raman activities of C(60) at different states. Further, MFTRS of the fullerene is demonstrated to originate from its photoassisted magnetization (PAM). The PAM strategy enables the magnetization of materials which consist of only light elements; meanwhile, the MFTRS investigation may open a new research field in Raman spectroscopy.