Qizhao Wang

Photochemical preparation of Cd/CdS photocatalysts and their efficient photocatalytic hydrogen production under visible light irradiation

Metal Cd can serve as an analogue of cocatalysts loaded on CdS to separate electrons and holes to significantly enhance the efficiency of CdS photocatalytic hydrogen production. A series of Cd/CdS photocatalysts were synthesized at various molar ratios of CdSO4 and Na2S2O3·5H2O in the presence of simulated solar irradiation. Superior photocatalytic activities relative to that of pure CdS were observed on the Cd/CdS photocatalysts. When the optimal molar ratio R of Na2S2O3·5H2O to cadmium salt is 7, it results in a high average H2-production rate of 1753 μmol h−1. Possible mechanisms for both the formation and the enhanced photocatalytic activity of Cd/CdS were proposed on the basis of theoretical speculation and experimental observations. Most of all, this work highlights that (i) Cd/CdS leads to an improvement in the photocatalytic activity for H2 generation; and (ii) adding Na2S2O3·5H2O into the solution containing cadmium ions to prepare Cd/CdS can effectively remove cadmium ions.

CNx-modified Fe3O4 as Pt nanoparticle support for the oxygen reduction reaction

A novel electrocatalyst support material, nitrogen-doped carbon (CNx)-modified Fe3O4 (Fe3O4-CNx), was synthesized through carbonizing a polypyrrole-Fe3O4 hybridized precursor. Subsequently, Fe3O4-CNx-supported Pt (Pt/Fe3O4-CNx) nanocomposites were prepared by reducing Pt precursor in ethylene glycol solution and evaluated for the oxygen reduction reaction (ORR). The Pt/Fe3O4-CNx catalysts were characterized by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrocatalytic activity and stability of the as-prepared electrocatalysts toward ORR were studied by cyclic voltammetry and steady-state polarization measurements. The results showed that Pt/Fe3O4-CNx catalysts exhibited superior catalytic performance for ORR to the conventional Pt/C and Pt/C-CNx catalysts.

Highly Efficient Photocatalytic Hydrogen Production of Flower-like Cadmium Sulfide Decorated by Histidine

Morphology-controlled synthesis of CdS can significantly enhance the efficiency of its photocatalytic hydrogen production. In this study, a novel three-dimensional (3D) flower-like CdS is synthesized via a facile template-free hydrothermal process using Cd(NO3)2•4H2O and thiourea as precursors and L-Histidine as a chelating agent. The morphology, crystal phase, and photoelectrochemical performance of the flower-like CdS and pure CdS nanocrystals are carefully investigated via various characterizations. Superior photocatalytic activity relative to that of pure CdS is observed on the flower-like CdS photocatalyst under visible light irradiation, which is nearly 13 times of pure CdS. On the basis of the results from SEM studies and our analysis, a growth mechanism of flower-like CdS is proposed by capturing the shape evolution. The imidazole ring of L-Histidine captures the Cd ions from the solution, and prevents the growth of the CdS nanoparticles. Furthermore, the photocatalytic contrast experiments illustrate that the as-synthesized flower-like CdS with L-Histidine is more stable than CdS without L-Histidine in the hydrogen generation.

Fabricating a g-C3N4/CuOx heterostructure with tunable valence transition for enhanced photocatalytic activity

Heterostructured g-C3N4/CuOx nanocomposites were successfully prepared with varying the content of g-C3N4 via a mixed solvent-thermal method. Organic ammonia ethanolamine was used as the reductant to adjust the valence of CuOx. Meanwhile, the bulk g-C3N4 was efficiently exfoliated into ultrathin nanoplates during the synthesis process. It is found that the different contents of g-C3N4 can effectively accelerate the valence transition of Cu in the nanocrystals. That is, the successive appearance of CuO and Cu2O with the enhancement of g-C3N4 content. These heterostructured composites were characterized for structural, morphological, elemental distribution, optical properties, specific surface area and photo-generated carrier separation efficiency by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectrum. The photocatalytic performance investigations indicate that the CN5–CuOx is stable enough and shows a remarkable photocatalytic efficiency for degrading methyl orange (MO) under simulated sunlight irradiation, compared with the pure CuOx nanocrystals. The enhanced photocatalytic performance can be attributed to the enlarged surface area, beneficial heterojunction among Cu2O@g-C3N4 and efficient carrier separation efficiency. The abundant Cu substrate in the CuOx nanocrystals functions as a rapid electron/hole pair transfer avenue and inhibits their recombination. Thus the photocatalytic efficiency is tremendously enhanced.

Carbon-supported platinum-decorated nickel nanoparticles for enhanced methanol oxidation in acid media

Carbon-supported platinum-decorated nickel nanoparticles (denoted as Pt-Ni/C) with intimate contact of Pt and Ni are prepared by a galvanic displacement reaction between Ni/C nanoparticles and PtCl62− in aqueous solution. It demonstrates a higher mass activity and stability to methanol oxidation reaction than conventional Pt/C and PtRu/C catalysts by a rotating disk electrode in acid solution, which could be attributed to the modified electronic structure of the Pt-Ni/C nanoparticles.

Photodegradation of Rhodamine B over a novel photocatalyst of feather keratin decorated CdS under visible light irradiation

A novel photocatalyst of feather keratin (FK)-decorated CdS was synthesized by a simple co-precipitation method. Scanning electron microscopy (SEM) showed that the particle sizes of FK/CdS nanocomposites were smaller than pure CdS. The coexistence of FK and CdS in the photocatalysts was further confirmed by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results of photocatalytic experiments demonstrated that the FK/CdS composites exhibit significantly enhanced photocatalytic activity for the photocatalytic degradation of RhB compared with pure CdS under visible light irradiation. The enhanced photocatalytic activity of the FK/CdS composites can be attributed to the similar affinity between FK and RhB, which can effectively separate the photogenerated electron–hole pairs. This method not only improves the photocatalytic activity of CdS, but also reduces the environmental pollution of waste feathers. In addition, the possible degradation mechanism of RhB is proposed.

Designed C3N4/CdS–CdWO4 core–shell heterostructure with excellent photocatalytic activity

C3N4/CdS–CdWO4 core–shell heterostructure photocatalysts were prepared via a facile solvent volatilization method. High-resolution transmission electron microscopy (HRTEM) analysis demonstrated that an interfacial structure was present between the C3N4 shell and the CdS–CdWO4 core, and the specific function of the modification of C3N4 was investigated by room-temperature photoluminescence spectroscopy and transient photocurrent measurement. The heterostructure photocatalysts displayed enhanced photocatalytic activity in the degradation of RhB dye than that of the single components and binary composites. Among the as-prepared samples, the best photocatalytic performance was achieved by 10 wt% C3N4/CdS–CdWO4, which was about 5.7 and 14.6 times that of CdS–CdWO4 and C3N4, respectively, under UV-visible light irradiation. Owing to the formation of a C3N4/CdS–CdWO4 ternary heterostructure, its efficient pollutant-removing ability and stability can be attributed to the improved separation of photogenerated carriers and transfer efficiency for the intensive built-in electric field intensity. Radical trapping experiments proved that h+ and ˙O2− play crucial roles in the photocatalytic process.

Microwave synthesis of three-dimensional nickel cobalt sulfide nanosheets grown on nickel foam for high-performance asymmetric supercapacitors

A facile and cost-effective microwave method is developed to prepare ternary nickel cobalt sulfide (NiCo2S4) interconnected nanosheet arrays on nickel foam (NF). When acting as an electrochemical supercapacitor electrode material, the as-prepared NiCo2S4/NF shows a high specific capacitance of 1502 F g-1 at a current density of 1 A g-1, and outstanding cycling stability of 91% capacitance retention after 8000 cycles. In addition, a asymmetric supercapacitor (ASC) is composed of NiCo2S4/NF as positive electrode and activated carbon as negative electrode, which exhibits a high energy density of 34.7 W h kg-1 at a power density of 750 W kg-1 and long-term cyclic stability (83.7% capacity retention after 8000 cycles). Even at a high power density of 15 kW kg-1, it still remains an energy density of 17.9 W h kg-1, which is able to light up a light-emitting diode. These findings provide a new and facile approach to fabricate high-performance electrode for supercapacitors.

Preparing ZnWO4–CdS composite with excellent visible light photocatalytic activity under mild conditions

AbstractZnWO4–CdS composite was designed and synthesized via a surface functionalized route under mild conditions. In this composite, CdS nanoparticle was successfully anchored on ZnWO4 nanorod with addition of citric acid. The formed composite was characterized by X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller, photoluminescence and transient photocurrent response. Besides, a possible nucleation-growth mechanism was proposed. To explore the photocatalytic performance of as-prepared ZnWO4–CdS composite, methylene blue and ciprofloxacin were chosen as the representative to systematically assess the degradation ability of as-prepared composite under visible light irradiation. The obtained results indicate that the ZnWO4–CdS3 composite photocatalyst is more efficient to methylene blue and ciprofloxacin than others under same conditions. The greatly enhanced photocatalytic performance of ZnWO4–CdS composite can be attributed to larger specific surface area, wider photo adsorption range and higher photo-induced carriers separation efficiency. A reasonable mechanism of the enhanced photocatalytic activity was confirmed and demonstrated by a series of characterization methods.Graphical Abstract The formation of n-n heterojunction between ZnWO4 and CdS can effectively promote the separation and transfer efficiency of photo-generated carriers and enhance the photocatalytic performance of composite.

Preparation of visible-light-driven BiOBr composites with heteropolyacids (H3PW12O40) encapsulated by a zeolite for the photo-degradation of methyl orange

BiOBr composites with heteropolyacids (H3PW12O40, PTA) were encapsulated within a zeolite using the impregnation method. The samples were characterized by Fourier transform infrared spectrophotometry (FT-IR), X-ray diffractometry (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectra, and N2 physisorption, and their photocatalytic activity was investigated by photocatalytic degradation of methyl orange, whose results indicate that zeolite (SBA-15)-modified BiOBr composites with immobilized phosphotungstic acid exhibit excellent photocatalytic properties.