Ag/AgBr/Graphene Oxide Nanocomposite Synthesized via Oil/Water and Water/Oil Microemulsions: A Comparison of Sunlight Energized Plasmonic Photocatalytic Activity

In this article, we report that Ag/AgBr nanostructures and the corresponding graphene oxide (GO) hybridized nanocomposite, Ag/AgBr/GO, could be facilely synthesized by means of a surfactant-assisted assembly protocol, where an oil/water microemulsion is used as the synthesis medium. We show that thus-produced nanomaterials could be used as highly efficient and stable plasmonic photocatalysts for the photodegradation of methyl orange (MO) pollutant under sunlight irradiation. Compared with the bare Ag/AgBr nanospecies, Ag/AgBr/GO displays distinctly enhanced photocatalytic activity. More importantly, the as-prepared nanostructures exhibit higher photocatalytic activity than that of the corresponding Ag/AgBr-based nanomaterials synthesized via<i> </i>a water/oil microemulsion and than that of the corresponding Ag/AgCl-based nanospecies synthesized by an oil/water microemulsion. An explanation has been proposed for these interesting findings. Our results suggest that thus-manufactured Ag/AgBr/GO plasmonic photocatalysts are promising alternatives to the traditional UV light or visible-light driven photocatalysts

P‑Type Cu-Doped Zn_0.3Cd_0.7S/Graphene Photocathode for Efficient Water Splitting in a Photoelectrochemical Tandem Cell

By doping Cu­(I) ions in Zn_0.3Cd_0.7S, a novel p-type Cu doped Zn_0.3Cd_0.7S modified graphene (Zn_0.3Cd_0.7S (Cu)/GR) film photocathode was prepared. The as-prepared p-type Zn_0.3Cd_0.7S (Cu)/GR photocathode and an n-type WO₃/graphene (WO₃/GR) photoanode were used to assemble a photoelectrochemical tandem cell. Through examination of the optoelectronic and photoelectrochemical properties of Zn_0.3Cd_0.7S (Cu)/GR and WO₃/GR photoelectrode, we evaluate the feasibility of the tandem cell for overall water splitting under UV–vis light irradiation. The optimal Cu doping in Zn_0.3Cd_0.7S photocathode concentration was found to be 6%. The rates of hydrogen and oxygen evolved from this tandem cell with the optimal electrodes were 65.6 and 12.3 μmol g^–1 h^–1 (80.5 and 15.1 μmol cm^–2 h^–1), respectively. This study suggests a promising method for constructing an efficient photoelectrochemical tandem device for overall water splitting

CuI as Hole-Transport Channel for Enhancing Photoelectrocatalytic Activity by Constructing CuI/BiOI Heterojunction

In this paper, CuI, as a typical hole-transport channel, was used to construct a high-performance visible-light-driven CuI/BiOI heterostructure for photoelectrocatalytic applications. The heterostructure combines the broad visible absorption of BiOI and high hole mobility of CuI. Compared to pure BiOI, the CuI/BiOI heterostructure exhibited distinctly enhanced photoelectrocatalytic performance for the oxidation of methanol and organic pollutants under visible-light irradiation. The photogenerated electron–hole pairs of the excited BiOI can be separated efficiently through CuI, in which the CuI acts as a superior hole-transport channel to improve photoelectrocatalytic oxidization of methanol and organic pollutants. The outstanding photoelectrocatalytic activity shows that the p-type CuI works as a promising hole-transport channel to improve the photocatalytic performance of traditional semiconductors

Template-Free Synthesis of Cube-like Ag/AgCl Nanostructures via a Direct-Precipitation Protocol: Highly Efficient Sunlight-Driven Plasmonic Photocatalysts

In this paper, we report that cube-like Ag/AgCl nanostructures could be facilely fabricated in a one-pot manner through a direct-precipitation protocol under ambient conditions, wherein no additional issues such as external energy (e.g., high temperature or high pressure), surfactants, or reducing agents are required. In terms of using sodium chloride (NaCl) as chlorine source and silver acetate (CH₃COOAg) as silver source, it is disclosed that simply by adding an aqueous solution of NaCl into an aqueous solution of CH₃COOAg, Ag/AgCl nanostructures with a cube-like geometry, could be successfully formulated. We show that thus-formulated cube-like Ag/AgCl nanospecies could be used as high-performance yet durable visible-light-driven or sunlight-driven plasmonic photocatalysts for the photodegradation of methyl orange (MO) and 4-chlorophenol (4–CP) pollutants. Compared with the commercially available P25–TiO₂, and the Ag/AgCl nanospheres previously fabricated via a surfactant-assisted method, our current cube-like Ag/AgCl nanostructures could exhibit much higher photocatalytic performance. Our template free protocol might open up new and varied opportunities for an easy synthesis of cube-like Ag/AgCl-based high-performance sunlight-driven plasmonic photocatalysts for organic pollutant elimination

Role of Substituents in the Removal of Emerging Fluorinated Liquid Crystal Monomer Pollutants under the UV/Peroxydisulfate Treatment

Fluorinated liquid crystal monomers (LCMs) have been identified as emerging persistent and bioaccumulative chemicals with non-negligible environmental concentrations. Herein, 12 fluorinated LCMs including highly detected 4-ethoxy-2,3-difluoro-4′-(trans-4-propylcyclohexyl)biphenyl (EDPB) were selected as target fluorinated LCMs to investigate their structure–reactivity relationships by the ultraviolet/peroxydisulfate (UV/PDS) treatment. EDPB with biphenyl and ethoxy showed the highest first-order degradation rate constant of 1.93 h–1, while that of fluorinated LCMs with ethoxy (1.10–1.26 h–1) and biphenyl (0.45–0.56 h–1) and without biphenyl or ethoxy (0.27–0.30 h–1) decreased sequentially. HO• and SO4•– were identified as the main oxidative species in the UV/PDS treatment. Theoretical calculation suggested that biphenyl and ethoxy can significantly alter the electron distribution of LCM molecules, providing more attackable sites for HO• and SO4•– on LCMs with biphenyl or ethoxy. Oxalic acid, cyclohexane, and bicyclohexane were the main degradation products of fluorinated LCMs even though their degradation pathways were determined by their different molecular structures. Toxicity estimation revealed that fluorinated LCMs with high acute toxicity and developmental toxicity could be decomposed into some final products with less toxicity. This study is expected to fill knowledge gaps in the structure–activity relationships of fluorinated LCMs by the UV/PDS treatment

Phase Effect of Ni_<i>x</i>P_<i>y</i> Hybridized with g‑C₃N₄ for Photocatalytic Hydrogen Generation

The use of noble metal-free nickel phosphides (Ni_<i>x</i>P_<i>y</i>) as suitable cocatalysts in photocatalytic hydrogen (H₂) generation has gained a lot of interest. In this paper, for the first time, three different crystalline phases of nickel phosphides, Ni₂P, Ni₁₂P₅, and Ni₃P, were synthesized and then hybridized with g-C₃N₄ to investigate the phase effect of Ni_<i>x</i>P_<i>y</i> on photocatalytic H₂ generation. It has been found that all three phases of Ni_<i>x</i>P_<i>y</i> work as effective cocatalysts for the enhancement of visible light H₂ generation with g-C₃N₄. The effective charge transfer between g-C₃N₄ and Ni_<i>x</i>P_<i>y</i>, demonstrated by photoelectrochemical properties, photoluminescence, and time-resolved diffused reflectance, contributes to the enhanced photocatalytic H₂ generation performance. Interestingly, Ni₂P/g-C₃N₄ showed the highest photocatalytic activity among the three Ni_<i>x</i>P_<i>y</i>/g-C₃N₄. Ni_<i>x</i>P_<i>y</i> with a higher ratio of phosphorus (Ni₂P) can accelerate charge transfer and provide more Ni–P bonds, leading to a preferable H₂ generation performance

Surfactant Assistance in Improvement of Photocatalytic Hydrogen Production with the Porphyrin Noncovalently Functionalized Graphene Nanocomposite

In this paper, a 5,10,15,20-tetrakis­(4-(hydroxyl)­phenyl) porphyrin (TPPH) noncovalently functionalized reduced graphene oxide (RGO) nanohybrid has been facilely synthesized by immobilizing TPPH on RGO nanosheets. This nanohybrid was characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), and UV–vis spectra, which demonstrated that the TPPH molecule was attached on the surface of the graphene nanosheet. The results of fluorescence quenching and photocurrent enhancement of TPPH–RGO exhibit that the fast electrons transfer from photoexcited TPPH molecules to RGO sheets. Compared with bare TPPH or RGO functional Pt nanoparticles, the TPPH-sensitized RGO loaded with Pt nanoparticles shows remarkable enhanced photocatalytic activity under UV–vis light irradiation. The superior electron-accepting and electron-transporting properties of graphene greatly accelerate the electron transfer from excited TPPH to Pt catalysts, which promote the photocatalytic activity for hydrogen evolution. More importantly, with the assistance of cetyltrimethylammonium bromide (CTAB) surfactant, the catalytic activity and stability is further improved owing to aggregation prevention of TPPH–RGO nanocomposites. Our investigation might not only initiate new opportunities for the development of a facile synthesis yet highly efficient photoinduced hydrogen evolution system (composed of organic dye functionalized graphene) but also pave a new avenue for constructing graphene-based matericals with enhanced catalytic performance and stability under surfactant assistance

Silver Iodide Microstructures of a Uniform Towerlike Shape: Morphology Purification via a Chemical Dissolution, Simultaneously Boosted Catalytic Durability, and Enhanced Catalytic Performances

The fabrication of microstructures/nanostructures of a uniform yet well-defined morphology has attracted broad interest from a variety of fields of advanced functional materials, especially catalysts. Most of the conventional methods generally suffer from harsh synthesis conditions, requirement of bulky apparatus, or incapability of scalable production, etc. To meet these formidable challenges, it is strongly desired to develop a facile, cost-effective, scalable method to fulfill a morphology purification. By a precipitation reaction between AgNO₃ and KI, we report that irregular AgI structures, or their mixture with towerlike AgI architectures could be fabricated. Compared to the former, the mixed structures exhibit enhanced catalytic reactivity toward the photodegradation of Methyl Orange pollutant. However, its catalytic durability, which is one of the most crucial criteria that are required by superior catalysts, is poor. We further show that the irregular structures could be facilely removed from the mixture via a KI-assisted chemical dissolution, producing AgI of a uniform towerlike morphology. Excitingly, after such simple morphology purification, our towerlike AgI displays not only a boosted catalytic durability but also an enhanced catalytic reactivity. Our chemical dissolution-based morphology purification protocol might be extended to other systems, wherein high-quality advanced functional materials of desired properties might be developed

Metal-Free Photocatalyst for H₂ Evolution in Visible to Near-Infrared Region: Black Phosphorus/Graphitic Carbon Nitride

In the drive toward green and sustainable chemistry, exploring efficient and stable metal-free photocatalysts with broadband solar absorption from the UV to near-infrared region for the photoreduction of water to H₂ remains a big challenge. To this end, a binary nanohybrid (BP/CN) of two-dimensional (2D) black phosphorus (BP) and graphitic carbon nitride (CN) was designed and used as a metal-free photocatalyst for the first time. During irradiation of BP/CN in water with >420 and >780 nm light, solid H₂ gas was generated, respectively. Owing to the interfacial interaction between BP and CN, efficient charge transfer occurred, thereby enhancing the photocatalytic performance. The efficient charge-trapping and transfer processes were thoroughly investigated with time-resolved diffuse reflectance spectroscopic measurement. The present results show that BP/CN is a metal-free photocatalyst for artificial photosynthesis and renewable energy conversion

Visible-Light-Assisted Electrocatalytic Oxidation of Methanol Using Reduced Graphene Oxide Modified Pt Nanoflowers-TiO₂ Nanotube Arrays

In this work, Pt nanoflowers deposited on highly ordered TiO₂ nanotube arrays (TNTs) by modification of reduced graphene oxide (RGO) nanostructures have been synthesized. The ternary complex (Pt-TNTs/RGO) displays efficient electrocatalytic performance toward methanol oxidation in alkaline medium. The electrochemical impedance spectroscopy (EIS) and responsive photocurrent results indicate that the presence of graphene could effectively promote charge separation during electrocatalytic process. Interestingly, with assistance of visible light illumination, the electrocatalytic activity and stability of the ternary complex electrode toward methanol oxidation are distinctly improved. Both electro- and photo-catalytic processes for methanol oxidation contribute to the enhanced catalytic performance and stability. Moreover, the ternary electrode also displays efficient photoelectrocatalytic degradation of methylene blue (MB) under visible light illumination. The present work sheds light on developing highly efficient and long-term stability catalysts for methanol oxidation with assistance of visible-light illumination