还原石墨/氧化锌复合薄膜的制备及其光电转换性能

本工作研究不同过程还原的氧化石墨rGO/ZnO(reduced graphiteoxide/ZnO)复合膜的可见光激发光电转换性能。氧化石墨(GO)经KOH还原处理或NaBH4还原处理后,和氧化锌溶胶混合,通过旋涂法和热处理在F掺杂SnO2薄膜导电玻璃(FTO)衬底上形成复合薄膜。采用XRD、FTIR、FE-SEM、XPS、UV-Vis等方法对复合薄膜的晶相结构、微观形貌等进行表征,并测试了复合薄膜在可见光照射下的光电转换性能。GO的预处理过程对复合薄膜的结构影响显著,采用NaBH4对GO处理更有利于形成均匀薄膜。光电流测试结果表明不同复合薄膜均能实现可见光照射下产生光电流,其原理为rGO的光激发电子跃迁到ZnO,而空穴在rGO中迁移,在rGO与ZnO界面实现光生载流子分离。其中NaBH4处理后的rGO/ZnO复合薄膜光电流密度最大,达6×10-7A·cm-2。     

Near‐Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping

Phase‐stable CsSn_xPb_1?xI₃ perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near‐infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra‐low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X‐ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I^? and Sn²⁺ ions upon Na doping, which potentially helps to stabilize Sn²⁺ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na‐doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.     

Synthesis and Catalytic Reactions of Nanoparticles formed by Electrospray Ionization of Coinage Metals

Noble metals can be ionized by electrochemical corrosion and transported by electrospray ionization. Mass spectrometry (MS) showed solvated metal ions as the main ionic constituent of the sprayed droplets. Collection of the electrospray plume on a surface yielded noble metal nanoparticles (NPs) under ambient conditions. The NPs were characterized by several techniques. Under typical conditions, capped‐nanoparticle sizes averaged 2.2 nm for gold and 6.5 nm for silver. The gold nanoparticles showed high catalytic activity in the reduction of p‐nitrophenol by NaBH₄. Efficient catalysis was also observed by simply directing the spray of solvated Au⁺ onto the surface of an aqueous p‐nitrophenol/NaBH₄ mixture. Organometallic ions were generated by spiking ligands into the spray solvent: for example, Cu^I bipyridine cations dominated the spray during Cu electrocorrosion in acetonitrile containing bipyridine. This organometallic reagent was shown to be effective in the radical polymerization of styrene.     

Synthesis of gold/polydopamine composite surfaces on glass substrates for localized surface plasmon resonance and catalysis

Composite materials of polydopamine (PDA) and gold nanoparticles on glass substrates (Au/PDA@slide) were obtained via a simple chemical process. First, PDA films (PDA@slide) were formed by immersing slides in 20 mg ml⁻¹ dopamine aqueous solution at pH = 8.5 for 1 h. Then, PDA@slide was dipped in 0.02 M chloroauric acid (HAuCl₄) aqueous solution for a certain time, Au/PDA@slide being formed. Gold nanoparticles were obtained by the reductive properties of PDA. The morphology and chemical composition of the composite material were characterized using scanning electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy. The catalytic properties of Au/PDA@slide were evaluated using the reduction of 4‐nitrophenol (4‐NP) in the presence of sodium borohydride (NaBH₄) aqueous solution at room temperature. The catalytic activity of the optimal Au/PDA@slide was so satisfactory that the reduction of 4‐NP was completed within 10 min. Moreover, the Au/PDA@slide composite material was stable up to five cycles without significant loss of its catalytic activity. In addition, Au/PDA@slide also exhibited photocatalytic ability, photodegrading 2.5 ml of 17.5 mg l⁻¹ methyl orange in 100 min. By measuring the UV–visible absorption bands of Au/PDA@slide, it was proved that the condition of the strongest surface plasmon resonance of Au/PDA@slide was the optimal condition for catalytic reduction of 4‐NP.     

Photo and Chemical Reduction of Copper onto Anatase‐Type TiO2 Nanoparticles with Enhanced Surface Hydroxyl Groups as Efficient Visible Light Photocatalysts

In this study, the photocatalytic efficiency of anatase‐type TiO₂ nanoparticles synthesized using the sol–gel low‐temperature method, were enhanced by a combined process of copper reduction and surface hydroxyl groups enhancement. UV–light‐assisted photo and NaBH₄‐assisted chemical reduction methods were used for deposition of copper onto TiO₂. The surface hydroxyl groups of TiO₂ were enhanced with the assistance of NaOH modification. The prepared catalysts were immobilized on glass plates and used as the fixed‐bed systems for the removal of phenazopyridine as a model drug contaminant under visible light irradiation. NaOH‐modified Cu/TiO₂ nanoparticles demonstrated higher photocatalytic efficiency than that of pure TiO₂ due to the extending of the charge carriers lifetime and enhancement of the adsorption capacity of TiO₂ toward phenazopyridine. The relationship of structure and performance of prepared nanoparticles has been established by using various techniques, such as XRD, XPS, TEM, EDX, XRF, TGA, DRS and PL. The effects of preparation variables, including copper content, reducing agents rate (NaBH₄ concentration and UV light intensity) and NaOH concentration were investigated on the photocatalytic efficiency of NaOH‐modified Cu/TiO₂ nanoparticles.     

Surface hydroxylation of poly(vinylidene fluoride) (PVDF) film

The surface of PVDF film was selectively modified by wet chemistry. Treatment with aqueous LiOH produced HF-elimination and the emergence of an oxygen-containing functionality. The XPS analysis clearly indicated the presence of ketone-, ether(epoxide)-, and alcohol motifs. The percentage of alcohols could be significantly increased by reduction of the ketones with NaBH₄ in 2-propanol, followed by reduction of the epoxides with DIBAL-H in hexane. Thus, the full treatment led to a PVDF surface displaying 7 to 16% of oxygen-containing units, of which about 60% consisted in alcohol motifs. The reactvity of the surface-displayed hydroxyl functions was assayed by radiolabeling with [³H]-Ac₂O. © 1997 John Wiley & Sons, Inc. J. Polym Sci A: Polym Chem 35: 1227–1235, 1997     

Synthesis,characterization of SiO2 supported-industrial phosphoric acid catalyst for hydrolysis of NaBH4 solution

Abstract

Tunisian industrial phosphoric acid H₃PO₄ was supported on silica gel SiO₂ (SIPA) to catalyze the hydrolysis reaction of aqueous alkaline sodium borohydride (NaBH₄). The SiO₂ was produced from purified quartz sand using alkali fusion-acidification chemical process. The BET surface area results indicate that the prepared silica gel could reach a specific surface area up to 585 m²/g. The addition of PO₃H₂ functional groups resulted in an increase of surface acidity of SiO₂ catalyst as shown by FT-IR and DTA-DTG spectra. The total acidity of SIPA catalyst was determined by titration to be 2.8?mmol H⁺/g. SEM/EDS maps reveal the distribution of heavy metals on the silica surface. The effect of supported PO₃H₂ functional groups and heavy metals on the NaBH₄ hydrolysis reaction was studied for different ratios of SIPA catalyst to NaBH₄. The sample 12SIPA/NaBH₄ leads to a very high hydrogen generation rate (up to 90%). The activation energy of hydrogen generation by NaBH₄ hydrolysis was 25.7?kJ mol^?1.     

Electrochemical Response of Cobalt(II) in the Presence of Ammonia

The electrochemical oxidation of cobalt(II) at gold, boron‐doped diamond, basal and edge plane pyrolytic graphite, and highly oriented pyrolytic graphite electrodes in aqueous solutions containing NH₃ has been studied using cyclic voltammetry, with subsequent chemical and electrochemical processes explained in detail. Furthermore, the electro‐reduction of [Co(NH₃)₆]³⁺ in the presence of different electrolytes has also been studied to obtain a better understanding of the oxidation pathway of the Co(II)‐ammine complexes. In aqueous solution the mechanism can be described by the following scheme:     

Homogeneous Palladium Nanoparticles Surface Hosts Catalyzed Reduction of the Chromophoric Azo (–N=N–) Group of Dye,Acid Orange 7 by Borohydride in Alkaline Media

In alkaline media, well‐characterized gelatin‐stabilized palladium (GPd) nanoparticles catalyze the reduction of the azo group containing pollutant dye, Acid Orange 7 (AO7) by sodium borohydride (NaBH₄) to 1‐amino‐2‐napthol and sulfanilic acid. Kinetic observations and detailed FTIR studies suggests that the reaction follows Langmuir–Hinshelwood kinetic model, where during the reaction both AO7 and borohydride are adsorbed on the GPd surface. Plots of lnk_o versus ln[AO7] or ln[NaBH₄] show that the order of reaction with respect to AO7 and NaBH₄ remains almost same over different molar ratios of [NaBH₄]/[AO7]. The catalyzed reaction shows an initial induction period (t₀) due to a surface‐restructuring process of GPd nanoparticles, and (1/t₀) can be defined as the rate of surface restructuring. The activation energy of the catalyzed reaction and energy of the surface‐restructuring process of GPd are estimated as 22 ± 3 and 25 ± 7 kJ M^?1, respectively.     

Low-temperature transformations of sodium sulfate and sodium selenite in the presence of pre-reduced palladium modifier in graphite furnaces for electrothermal atomic absorption spectrometry

The low-temperature interaction (up to 550°C) of a pre-reduced palladium modifier with sodium sulfate and sodium selenite on the pyrolytic graphite platform was studied using X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis. The equipment applied allowed the introduction of samples heated in an argon flow into the analytical chamber of the XPS spectrometer without contact with the air. Electron microprobe analysis showed that palladium and sulfur preferably occupy different areas on the platform surface. On the contrary, selenium from sodium selenite tends to occupy areas of the graphite surface covered with palladium. The most probable reason for this is the chemisorption of selenium (IV) on the palladium surface at the drying stage. No changes in the XPS spectra of metallic Pd and S⁶⁺ were observed when Na₂SO₄ and Pd were heated together on the graphite platform in the range 100–550°C. The reduction of sodium selenite on the graphite surface already starts during drying. Pre-reduced palladium intensifies this process. The rate of the reduction is proportional to the amount of palladium, and in the presence of palladium at an atomic ratio of Pd/Se=7.5, the transformation of Se⁴⁺ into Se⁰ completes at 250°C.     

Electrochemical Behaviour of HOPG and CVD‐Grown Graphene Electrodes Modified with Thick Anthraquinone Films by Diazonium Reduction

Highly oriented pyrolytic graphite (HOPG) and graphene grown on Ni (Ni‐Gra) or Cu (Cu‐Gra) by chemical vapour deposition were modified with thick anthraquinone (AQ) films (7?60 nm) by redox grafting of the pertinent diazonium salt. Glassy carbon (GC) electrodes were used for comparison. The AQ‐modified GC electrodes showed excellent blocking properties towards the Fe(CN)₆^3?/4? redox probe, although it was noted that in the case of Ni‐Gra and Cu‐Gra, the blocking ability depended strongly on the underlying substrate. Oxygen reduction studies revealed good electrocatalytic activity of AQ‐modified HOPG, Ni‐Gra, and Cu‐Gra, compared with the bare electrodes.     

Multi‐shaped Amorphous Alloy Ni‐B: Ultrasonically Aided Complexing‐reduction Preparation,Catalytic Ability for NaBH4 Hydrolysis Yielding H2 Gas

The multi‐shaped amorphous alloy (Ni‐B) powders were prepared by complexing reduction route using sodium borohydride (NaBH₄) as reductant with assistance of ultrasonic wave. The selected complexants, i.e. water, ammonia, salicylic acid, and ethylene diamine tetraacetic acid (EDTA) possess sequentially escalating complexation ability. The chemical composition and shapes of the product samples obtained under different conditions were characterized by X‐ray powder differaction, selected area electron diffraction, and transmission electron microscope. The influence of reaction conditions such as the types of Ni‐B, temperatures, NaBH₄ concentrations, and sodium hydroxide (NaOH) content on the hydrogen generation rate of hydrolysis of NaBH₄ solution were investigated in detail. The results show that the as‐prepared Ni‐B powders all belong to amorphous alloy with variable element contents, and the Ni‐B sample prepared from EDTA complexation, possessing the best fineness and dispersity, has the strongest catalytic activity. The mean apparent activation energy of the hydrolysis reaction is 64.90 kJ · mol^–1. The NaBH₄ concentration has little impact on hydrogen generation rate, implying that the catalytic hydrolysis of NaBH₄ solution should be the pseudo zero‐order reaction. Keeping the NaOH content at below 5 % could inhibit the hydrolysis of NaBH₄ solution, but the NaOH contents from 10 % to 15 % will significantly promote the hydrolysis rate of NaBH₄. The hydrolysis reaction mechanisms, especially the effect of NaOH content on the hydrolysis reaction were also analyzed.     

Remediation of azo-dyes based toxicity by agro-waste cotton boll peels mediated palladium nanoparticles

The present study reports an environmental benign route for the synthesis of palladium nanoparticles (Pd NPs) using agro-waste empty cotton boll peels aqueous extract for the first time. Surface Plasmon Resonance (SPR) band in absorption spectrum of Pd NPs at 275 nm confirmed the formation of Pd NPs by using UV–Vis spectroscopy. Crystalline nature of Pd NPs was confirmed by powder XRD analysis. Size and morphology was studied by transmission electron microscopy (TEM). The cotton peels extract acted as a source of phytochemicals which primarily reduced Pd⁺² to Pd⁰ nanoparticles (Pd NPs) and imparted stability of Pd NPs by surface capping. The characteristic functional groups of phytochemicals in extract and capped Pd NPs surfaces were identified by FT-IR analysis. Catalytic activity of the synthesised Pd NPs was checked against reduction of hazardous azo-dyes such as Congo red, Methyl orange, Sunset yellow and Tartrazine with NaBH₄ as electron donors. Pd NPs catalysed reduction of all azo-dyes by NaBH₄ in aqueous medium was monitored by UV–visible spectroscopy where Pd NPs mediated transfer of electrons from NaBH₄ to azo-dyes as carrier. The synthesized Pd NPs acted as a good catalyst and could be a promising material in degrading toxic azo-dyes from industrial effluents and wastewater.     

Uniformly dispersed copper nanoparticles onto the modified magnetically recoverable nanocatalyst for aqueous synthesis of primary amides

Magnetically recoverable and environmentally friendly Cu‐based heterogeneous catalyst has been synthesized for the one‐pot conversion of aldehydes to their corresponding primary amides. The Fe₃O₄@SiO₂ nanocomposites were prepared by synthesis of Fe₃O₄ magnetic nanoparticles (MNPs) which was then coated with a silica shell via Stöber method. Bi‐functional cysteine amino acid was covalently bonded onto the siliceous shell of nanocatalyst. The Cu^II ions were then loaded onto the modified surface of nanocatalyst. Finally, uniformly dispersed copper nanoparticles were achieved by reduction of Cu^II ions with NaBH₄. Amidation reaction of aryl halides with electron‐withdrawing or electron‐donating groups and hydroxylamine hydrochloride catalyzed with Fe₃O₄@SiO₂@Cysteine‐copper (FSC‐Cu) MNPs in aqueous condition gave an excellent yield of products. The FSC‐Cu MNPs could be easily isolated from the reaction mixture with an external magnet and reused at least 8 times without significant loss in activity.     

Ultra‐low‐loading palladium nanoparticles stabilized on nanocrystalline Polyaniline (Pd@PANI): A efficient,green, and recyclable catalyst for the reduction of nitroarenes

Ultra‐low‐loading Pd@PANI nanocomposites (0.048 w.t% Pd) were synthesized via a method that combined interfacial polymerization and in situ composite with camphor sulfonic acid ((+)‐CSA) as a dopant. Transmission electron microscopy (TEM), X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, and X‐ray photoelectron spectroscopy (XPS) were performed to characterize the structures. It can be used as an efficient catalyst for the reduction of nitroarenes in aqueous solution by using a smaller amount of NaBH₄ (2.5 equiv.) at room temperature with high activity (TON = 3.4 × 10³), good stability (cycled eight times), as well as wide applicability (27 substrates). The catalyst also showed a marvelous activity in the gram‐level reaction (yield = 92%). UV–Visible spectrophotometry was used to investigate the reaction kinetics for the reduction of 4‐nitrophenol to 4‐aminophenol, and the results reconfirmed the excellent performance of the catalyst. The unique properties and superior performance of the prepared ultra‐low‐loading Pd@PANI nanocomposites lead it be an attractive alternative catalyst for conventional organic catalytic applications.     

Preparation and characterization of polypyrrole with dispersed metallic rhodium particles

Polypyrrole (PPy) with dispersed metallic Rh particles has been prepared by all‐chemical route, i.e. reduction of Rh³⁺ ions existing in RhCl₃ aqueous solutions with sodium borohydride (NaBH₄) carried out in the presence of the previously obtained PPy doped with chloride ions (PPyCl). PPy–Rh composites thus formed have been characterized using X‐ray diffraction (XRD), scanning and transmission electron microscopies (SEM, TEM) combined with energy dispersive X‐ray (EDX) microanalysis, Rh3d X‐ray photoelectron (XPS), and IR spectroscopies. This has made it possible to find out that metallic Rh nanoparticles, mainly of sizes below 10 nm, have been present in the composites. Agglomerates, with sizes up to 0.7 µm, have been formed in the systems containing higher amounts of Rh. PPy serving as the matrix in the composites has been doped. However, its doping level has been lower than that of the starting PPyCl. This has been explained by partial reduction of the polymer occurring during preparation of the composites. Catalytic properties of the PPy–Rh systems have been investigated using isopropyl alcohol conversion as a test reaction. It has been established that the composites are active redox catalysts. This makes them promising materials for applications as catalysts of various redox processes. Copyright © 2010 John Wiley & Sons, Ltd.     

Solid‐State Carbon Dots with Efficient Cyan Emission towards White Light‐Emitting Diodes

Efficient cyan‐emitting solid carbon dots (CDs) were synthesized via a one‐pot hydrothermal method. The obtained solid CDs show a broad absorption from 270–460 nm with a maximum around 400 nm, and emit intense cyan light around 500 nm with an internal photoluminescence quantum efficiency of 34.1 % under 400 nm excitation. The emission maximum of the solid CDs remains unchanged under 320–400 nm excitations. Compared with dilute aqueous of CDs (2.5 mg mL^?1), the emission of solid CDs shows an obvious red‐shift of 50 nm. The red‐shift is caused by resonant energy transfer due to larger spectral overlap and smaller interparticle distance, together with a new surface state caused by aggregation in solid CDs. A lamp with white LEDs was fabricated by dropping a mixture of solid CDs, CaAlSiN₃:Eu²⁺ and silicon resin on the top of a near‐ultraviolet LED chip. Under an operating current of 20 mA, the as‐fabricated white LED generates a high‐quality, warm white light with a color rendering index of 86.1, a color temperature of 4340 K, and a luminescence efficiency of 31.3 lm W^?1.     

Near-Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping

Phase-stable CsSn_xPb_1−xI₃ perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near-infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra-low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X-ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I⁻ and Sn²⁺ ions upon Na doping, which potentially helps to stabilize Sn²⁺ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na-doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.     

Influence of the preparation conditions of Pd‐ZrO2 and AuPd‐ZrO2 nanoparticle–decorated functionalised MWCNTs: Electron spectroscopy study aided with the QUASES

The Pd, AuPd, and ZrO₂ nanoparticle–decorated functionalised multiwalled carbon nanotubes (f‐MWCNTs) were reported as efficient catalysts of formic acid (FA) electro‐oxidation. Different preparation conditions influence their chemical and structural properties analysed by X‐ray photoelectron spectroscopy aided with the quantitative analysis of surfaces by electron spectroscopy. Different reduction procedures such as NaBH₄, a polyol microwave‐assisted method (PMWA), and a high pressure microwave reactor (HPMWR) were applied for decorating ZrO₂/f‐MWCNTs with Pd and AuPd nanoparticles. The ZrO₂ nanoparticles are attached through oxygen groups to the surface of f‐MWCNTs. In NaBH₄ and HPMWR procedures, Pd nanoparticles precipitate predominantly on ZrO₂ of nearly nominal stoichiometry, whereas in PMWA procedure, Pd and AuPd nanoparticles precipitate predominantly on the surface of f‐MWCNTs, bridging with oxygen groups and ZrO_x (x < 2) and leading to Pd‐O‐Zr phase formation. Strong reducing procedures (NaBH₄ and FA) led to smaller Pd nanoparticle size, Pd oxide content, and PdO_x overlayer thickness in contrary to weak reduction procedures (HPMWR and PMWA). The highest content of Pd‐O‐Zr phase appeared for Pd predominant precipitation on ZrO₂ nanoparticles (HPMWR) in contrary to Pd and AuPd predominant precipitation on surface of f‐MWCNTs (NaBH₄ ~ FA > PMWA). Larger content of Pd‐O‐Zr phase in AuPd‐decorated ZrO₂/f‐MWCNTs in contrary to Pd‐decorated sample (PMWA) could be justified by different electronic properties of nanoparticles. The FA treatment of Pd and AuPd‐ZrO₂/f‐MWCNTs samples provided decreasing Pd oxide content, overlayer thickness, nanoparticle size, increasing nanoparticle surface coverage and density, amount of Pd‐O‐Zr, what results from reduction of oxygen groups bridging with Pd and ZrO_x nanoparticles, also through Pd‐O‐Zr phase.     

Cucurbit[7]uril as a Tool in the Green Synthesis of Gold Nanoparticles

A simple, green, one‐pot synthesis of gold nanoparticles was achieved through the reaction of an aqueous mixture of potassium tetrachloroaurate(III) and the macrocycle cucurbit[7]uril in the presence of sodium hydroxide at room temperature without introducing any kind of traditional reducing agents and/or external energy. The as‐prepared gold nanoparticles showed catalytic activity for the reduction reaction of 4‐nitrophenol in the presence of NaBH₄, which has been established by visual inspection and UV/Vis spectroscopy. This report is the first for the preparation of gold nanoparticles using cucurbit[7]uril in aqueous media through chemical reduction without employing conventional reducing agents and/or external energy.