Showing papers in "Applied Surface Science in 2019"

Green tea extract mediated biogenic synthesis of silver nanoparticles: Characterization, cytotoxicity evaluation and antibacterial activity

Abstract: Silver nanoparticles (AgNPs) are widely used in biomedical fields because of their potent antimicrobial activity. Biogenic synthesis of nanoparticles has gained considerable attention due to its simplicity, low cost and absence of organic solvents. This work describes the one-pot one-minute biogenic synthesis of AgNPs with a commercial green tea extract (Camellia sinensis). The tea polyphenols acted as reducing and stabilizing agents for the nanoparticles. The surface of the biogenic AgNPs was further coated with polyethylene glycol (PEG) to enhance their dispersion and biocompatibility. The obtained nanoparticles were extensively characterized by ultraviolet-visible spectroscopy (UV–vis), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), electronic and atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), dynamic light scattering and inductively coupled plasma mass spectrometry (ICP-MS). The results demonstrated the formation of spherical nanoparticles of pure Ag° coated with tea polyphenols, at the nanoscale and with moderate polydispersity. The nanoparticles did not exhibit significant toxicity to human keratinocyte (HaCaT) cells. The antimicrobial efficacy of the biogenic nanoparticles was demonstrated against gram-positive Staphylococcus aureus (ATCC 29213), gram-negative Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (ATCC 700603), Escherichia coli (ATCC 25922) and Salmonella enterica (ATCC 14028) bacterial strains. Salmonella enterica was found to be the most sensitive strain to the nanoparticles, with a minimum inhibitory concentration and minimum bactericidal concentration of 7 and 15 µg/mL, respectively. Interestingly, at the concentration range in which the AgNPs showed an antibacterial effect, they were not toxic to HaCaT mammalian cells. Thus, green tea synthesized AgNPs could find important biomedical applications in the combat of pathogenic bacteria with low cytotoxicity to normal cells.

Towards Oxide Electronics: a Roadmap

Abstract: At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore’s law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics.

A novel α-Fe2O3@g-C3N4 catalyst: Synthesis derived from Fe-based MOF and its superior photo-Fenton performance

Abstract: Fabricating heterojunction catalysts is a promising strategy for improving the performance in heterogeneous photo-Fenton reaction (PFR). Herein, a Z-scheme heterostructured α-Fe2O3@g-C3N4 catalyst was successfully synthesized through the co-calcination of melamine and Fe-based MOF. The characterization results demonstrated that α-Fe2O3 nanoparticles anchored on the surface of g-C3N4 successfully. The degradation of tetracycline (TC) in visible-light/H2O2 system was adopted to evaluate the photo-Fenton activity of the catalysts. About 92% of TC was degraded by the optimum composite FOCN-0.45 in 60 min; the degradation rate (0.042 min−1) of TC by the FOCN-0.45 is 6, 7 and 14 times higher than that by pristine MIL-53 (Fe) (0.007 min−1), α-Fe2O3 (0.006 min−1) and g-C3N4 (0.003 min−1), respectively. The prepared FOCN-0.45 composite exhibited excellent performance and high stability in a wide range of pH value. The promoted photo-Fenton catalytic efficiency benefited from the Z-scheme heterojunctions of α-Fe2O3@g-C3N4, which enhanced the separation ability of photo-generated charge carriers and increased the electrons that participated in Fe2+/Fe3+ cycle. The boosting OH radicals degraded organic pollutants as main reactive radicals. This work presents a feasible path to design and synthesize heterogeneous photo-Fenton catalysts for the removal of organic pollutants.

Novel and efficient synthesis of Ag-ZnO nanoparticles for the sunlight-induced photocatalytic degradation

Abstract: Plasmonic metal-semiconductor nanostructures endow them with an enormous potential application in photocatalysis, however, the uniform deposition of metal NPs as small as a few nanometers remains a challenge. Here, we demonstrate the effectiveness of two-step polymer-network gel process in the synthesis of Ag-ZnO nanocatalyst with superior photocatalytic properties. Because of uniform distributed Ag NPs, large specific surface area and abundant surface oxygen vacancies, the Ag-ZnO nanoparticles exhibit a super high photocatalytic efficiency in comparison to pure ZnO nanoparticles. The efficiency can be further improved by optimizing the external factors, such as catalyst dosage, ambient temperature and initial solution pH. Good stability and practicability indicate its potential application in environmental purification. Our work does not only provide a feasible strategy for the synthesis of high property Ag-ZnO nanophotocatalysts, but also enriches the understanding of metal-metal oxide nanostructures.

First-principles insight into Ni-doped InN monolayer as a noxious gases scavenger

Abstract: Using first-principles theory, we theoretically investigate the most stable doping site of Ni atom on pristine InN monolayer and adsorption behavior of Ni-doped InN (Ni-InN) monolayer upon four noxious gases (NO, CO2, H2S and NH3). Electron localization function (ELF), electron deformation density (EDD) as well as density of state (DOS) are considered to further understand the adsorption behavior of Ni-InN monolayer towards gas molecules. For possible application of our proposed material, work function and band structure of the isolated and gas adsorbed Ni-InN monolayer are analyzed as well. It is found that the Ni dopant prefers to be adsorbed on the pristine InN monolayer at the TN site with the lowest biding force (Eb) of −3.02 eV. Four gases could be stably adsorbed on the Ni-InN monolayer surface wherein the chemisorption is identified due to the large adsorption energy (Ead) and charge transfer (QT). ELF, EDD and DOS analyses corroborate the strong chemical interaction between Ni dopant and activated atoms in gas molecules. The band structure analysis provides the sensing mechanism of Ni-InN based resistance-type chemical sensor for detection of such four gaseous species. Our calculations can supply some guidance to explore promising novel gas sensors using group III-V nitrides in the gas-sensing field and environmental monitoring fields.

Pd-doped MoS2 monolayer: A promising candidate for DGA in transformer oil based on DFT method

Abstract: Density functional theory (DFT) method was carried out to simulate the adsorption of three dissolved gases on Pd-doped MOS2 (Pd-MoS2) monolayer. We initially studied the possible structures of Pd-MoS2 monolayer and found that the Pd dopant preferred to be adsorbed onto the surface by TMo site. The adsorption and desorption performance, along with the sensing principle of Pd-MoS2 towards three typical gases, including H2, CH4 and C2H2, were analyzed. These analysis indicated that Pd-MoS2 could be a satisfied material for C2H2 and H2 sensing at specific condition; while it is unsuitable for detection of CH4 due to the weak interaction and extremely short recovery time. All these give a first insight into the application of Pd-MoS2 for DGA, evaluating the working operation of the transformer through sensitive detection of H2 and C2H2. We are hopeful that this work would support informative knowledge for experimentalists to realize the potential of Pd-MoS2 in the field of electrical engineering in the near future.

Synthesis of Ti3C2/Fe3O4/PANI hierarchical architecture composite as an efficient wide-band electromagnetic absorber

Abstract: A hierarchical architecture of Ti3C2/Fe3O4/PANI composite as a high-efficiency microwave absorber was synthesized using HF etching, coprecipitation and in-situ polymerization route. Layered Ti3C2 was used as a matrix material with high surface area and a network offering more paths of electron transfer. The adding of PANI and Fe3O4 can generate an outstanding microwave absorption property because of enhanced interfacial polarization, strong attenuation loss and excellent impedance matching. The hierarchical Ti3C2/Fe3O4/PANI ternary composite shows a strongest reflection loss (RL) of −40.3 dB at 15.3 GHz, which is higher than those of Fe3O4 and Ti3C2/Fe3O4. Furthermore, it also displays broad absorption frequency band, possessing the efficient absorption bandwidth (

Environment friendly chemical mechanical polishing of copper

Abstract: Chemical mechanical polishing slurry of copper usually contains more than four compositions, in which strong acids, alkalis or hazardous chemicals are normally employed. With these slurries, surface roughness less than 1 nm is difficult to obtain on the surface of copper after chemical mechanical polishing. It is a challenge to develop a kind of novel chemical mechanical polishing slurry for copper including three environment friendly compositions. In this study, a kind of novel chemical mechanical polishing slurry is developed consisting of silica, hydrogen peroxide and chitosan oligosaccharide, where all the three compositions are environment friendly. After chemical mechanical polishing, surface roughness Ra and peak-to-valley values are 0.444 and 5.468 nm respectively. Chemical mechanical polishing mechanism is elucidated by infrared and X-ray photoelectron spectra and electrochemical measurements. Firstly, Cu surface is oxidized by hydrogen peroxide, forming CuO and Cu(OH)2. Then, CuO and Cu(OH)2 are dissolved by H+ ions released by the ionization of chitosan oligosaccharide. Subsequently, Cu2+ ions are chelated by chitosan oligosaccharide molecules. Finally, the adsorbed layer is removed by silica nanospheres, generating ultra-smooth surface of copper. The findings propose a new route for fabrication devices of copper and other transition metals used in integrated circuits, graphene, transformers, batteries and electronics industries.

Review on manganese dioxide for catalytic oxidation of airborne formaldehyde

Abstract: Indoor formaldehyde (HCHO) pollution is becoming an important issue with the increase of space confinement. Manganese dioxide (MnO2) has attracted great attention due to its high catalytic activity, thermal stability, facile synthesis with low-cost materials and availability in various crystal morphologies. This review covers recent progress on MnO2-based materials for catalytic oxidation of HCHO, with a particular emphasis on the enhancement of the catalytic activity at low temperature. According to different modification strategies, MnO2 catalysts are divided into three categories, namely, single MnO2 (generally showing tunneled or layered structures), doped or composite MnO2, and supported MnO2 catalysts. Specifically, modification of single MnO2, especially layered MnO2, is deeply discussed in terms of morphology control, and defect engineering, aiming at regulating surface active species; doping or composite MnO2 could alter the properties of the catalysts and facilitate the entire reaction process (i.e., adsorption, reaction and desorption), favoring the rate-limiting step from the thermodynamic and kinetic points of view; supporting MnO2 on carriers is necessary for practical application. Moreover, reaction mechanism of HCHO oxidation by single or composite MnO2 is also reviewed. Finally, perspective on the challenges and opportunities for exploring advanced MnO2-based catalysts is presented.

Corrosion inhibition of mild steel in 1 M HCl solution by ethanolic extract of eco-friendly Mangifera indica (mango) leaves: Electrochemical, molecular dynamics, Monte Carlo and ab initio study

Abstract: The mild steel corrosion inhibition in 1 M HCl solution containing Mangifera indica (mango) (M. indica) leaves extract was examined by electrochemical and surface studies. The presence of many active components with aromatic and oxygen containing functional groups in the extract of M. indica was shown by transform infrared spectroscopy (FT-IR) and ultraviolet-visible spectrophotometry (UV–Vis). Results revealed that with increasing inhibitor concentration and immersion time the inhibition efficiency increased and reached the maximum value of 92% after 24 h in the presence of 1000 ppm inhibitor. It was shown that in the presence of M. indica extract both iron anodic dissolution rate and cathodic hydrogen evolution reaction rate efficiently decreased reflecting a mixed inhibition action. The inhibitor adsorption on mild steel followed a Langmuir isotherm. Surface studies revealed the inhibitor film formation on the iron surface resulting in the surface damage decline and increase of hydrophobicity. Also, the theoretical results confirmed the inhibitor adsorption on the steel surface through its reactive sites.

Graphene oxide spontaneous reduction and self-assembly on the zinc metal surface enabling a dendrite-free anode for long-life zinc rechargeable aqueous batteries

Abstract: Rechargeable aqueous Zn-based batteries are one of the most promising large-scale energy storage devices, benefiting from their eco-friendliness, low cost, high power/energy densities, and safety advantages without using flammable and poisonous organic liquid electrolytes. However, various challenges, such as infinite volume change and growth of dendrites during the electrostripping/electroplating process, lead to low cycling stability (cell shorting) and hinders the application of Zn-based batteries. Herein, a facile and effective approach to reduce graphene oxide (GO) spontaneously by zinc metal is developed and subsequently, the reduced graphene oxide (rGO) is self-assembled to create a layer-by-layer film on the Zn foil surface. This self-assembled, layered rGO on a Zn surface provides a large electroactive area and a soft substrate for Zn electrodeposition, which significantly mitigates Zn dendritic growth by eliminating its driving force. Compared with bare Zn, this composite anode exhibits much lower overpotential (~20 mV at 1 mA cm−2) and excellent long-life cyclability. A full-device with active carbon demonstrates good rate capacity and superior cycling stability. This well-designed anode also provides a useful solution and the possibility of constructing a dendrite-free advanced zinc anode. This is very important to all the zinc-based batteries for grid-scale storage.

Hierarchical porous Ni/Co-LDH hollow dodecahedron with excellent adsorption property for Congo red and Cr(VI) ions

Abstract: High-performance adsorption toward Congo red and Cr(VI) depends on the design of hierarchical nanostructures. Herein, hierarchical porous Ni/Co-layered double hydroxide (NiCo-LDH) hollow dodecahedra were synthesised by etching zeolitic imidazolate framework-67 (ZIF-67) as a self-sacrificing template with Ni(NO3)2. The synthesised NiCo-LDH showed better adsorption property for adsorbing Congo red and Cr(VI) ions (Cr2O72−) than NiCo2O4-NiO, which was obtained by calcining NiCo-LDH at 350 °C. The adsorption processes of Congo red and Cr(VI) ions very well fitted the pseudo-second-order model. The Langmuir model was more suitable than the Freundlich model in describing the adsorption isotherm, and the theoretical maximum adsorption capacities of Congo red and Cr(VI) ions were 909.2 and 99.9 mg g−1 at 30 °C, respectively. Furthermore, the synthesised NiCo-LDH was recyclable and could selectively adsorb anionic dyes. This work can serve as a basis for designing and manufacturing excellent adsorbents for water treatment.

Fabrication of p-n CuBi2O4/MoS2 heterojunction with nanosheets-on-microrods structure for enhanced photocatalytic activity towards tetracycline degradation

Abstract: Semiconductor-based photocatalytic oxidation technology represents a promising strategy for clean, low-cost, and environmental friendly to solve the water pollution problems by utilizing solar energy. Herein, p-CuBi2O4/n-MoS2 as a noble-metal-free efficient visible-light driven composite was successfully synthesized via a simply one-pot hydrothermal method, which possessed the unique nanosheets-on-microrods heterostructure. Based on the experimental data analysis, with the assistance of MoS2, the absorption band of the prepared heterojunction becomes broader and covers the entire visible region. And the highest photocatalytic activity for the degradation of tetracycline was achieved when introducing ~5% weight ratio of MoS2 in the composite (76%, 120 min), which is about 2.79 and 2.96 times than that of MoS2 and CuBi2O4, respectively. And the improvement of the photocatalytic activity of the p-CuBi2O4/n-MoS2 derives from the energy band matching and the formation of the built-in electric field. This work will open opportunities for designing the high-efficient CuBi2O4-based p-n heterojunction photocatalysts and would be of great significance to satisfy ever-increasing environmental demands in the future.

Review on noble metal-based catalysts for formaldehyde oxidation at room temperature

Abstract: Formaldehyde (HCHO) is a ubiquitous indoor air pollutant that can cause a variety of adverse health effects; therefore, it is of paramount importance to remove HCHO from indoor air. Catalytic HCHO oxidation at room temperature is the most promising technique for indoor HCHO removal, which entails the development of high-efficiency HCHO oxidation catalysts. In this review, we comprehensively summarize the significant and recent advances in room-temperature HCHO oxidation over noble metal-based catalysts, which contain platinum (Pt), gold (Au), palladium (Pd), silver (Ag), and/or rhodium (Rh) as the essential ingredient. In particular, we focus on the relationship between the chemical and structural properties of the catalysts and their HCHO oxidation performance, as well as the catalytic reaction mechanisms, as revealed by sophisticated in-situ spectroscopic techniques and theoretical calculations. Through the past decade of research efforts, highly efficient HCHO oxidation can be achieved at ambient temperature over well-designed catalysts with minimal noble metal content (e.g.,

Selective adsorption of organic dyes on graphene oxide: Theoretical and experimental analysis

Abstract: The adsorption behaviors of methylene blue, rhodamine B, and methyl orange over graphene oxide were studied both experimentally and theoretically. From the experimental results and characterizations of fresh graphene oxide and graphene oxide after adsorption, selective adsorption of positive dye occurred via electrostatic interactions between the N+H group (positive dipole from dye molecules, MB) and oxygen functional group of GO (negative dipole), as identified in the zeta potential, FT-IR, and XPS analyses. The selectivity for positive dye was rapid and quantitative where removal efficiencies of 97% and 88% were obtained for the positive dyes methylene blue and rhodamine B, respectively, within 15 min; the negative dye, methyl orange, was not adsorbed. The most probable arrangement of dyes on graphene oxide was evaluated using Ab initio molecular dynamics, and the adsorption energy was calculated. The most favorable adsorption configuration was found at 2298 fs for methyl orange and 2290 fs for methylene blue. Our results demonstrate that methylene blue is more strongly (−2.25 eV/molecule) adsorbed on the GO surface than methyl orange (−1.45 eV/molecule).

Surface and interface engineering of hierarchical photocatalysts

Abstract: In developing efficient heterogeneous photocatalysts, the design and fabrication of hierarchical semiconductors at the micro/nanometer scales have received much attention during the past decade due to their unique advantages in addressing the critical problems during photocatalysis. However, there are still many challenges in designing and constructing highly efficient hierarchical photocatalysts. Thus, in this review, we first systematically summarize and discusse the fundamentals and important interface engineering strategies of designing hierarchical photocatalysts, such as fabricating Z-Scheme heterojunctions, constructing Schottky-based heterojunctions, creating carbon-based heterojunctions and designing multicomponent heterojunctions. Then, especially, the different surface modification approaches of hierarchical porous photocatalysts, including loading cocatalysts, exposing the reactive facets, introducing defects/heteroatoms, adding photosensitizers, are highlighted. Finally, the major conclusions are made regarding this promising class of heterogeneous photocatalysts, and some perspectives are given on its future development. Through studying the important advances on this topic, it may pave a new avenue for fabricating highly effective hierarchical semiconductors for various applications in photocatalysis, electrocatalysis, thermal catalysis and other fields.

Hierarchically CdS–Ag2S nanocomposites for efficient photocatalytic H2 production

Abstract: Hierarchically nanostructured CdS composed of 4.7 nm-thick self-assembled ultrathin nanosheets was synthesised through a microwave-assisted solvothermal method. Ag2S nanoparticles (NPs) were deposited at the edge of the CdS nanosheets by an in situ ion exchange strategy. The hierarchically CdS–Ag2S nanocomposites exhibited a high visible light photocatalytic H2 evolution rate of 375.6 μmol h−1 g−1, which was 11.5 times higher than that of pure CdS. Given the difference in work functions between CdS and Ag2S, electrons diffused from the CdS side to the Ag2S side until the Fermi levels align after their contact. When the CdS–Ag2S was illuminated, the photogenerated electrons on the conduction band of the CdS further migrated to Ag2S. Considering the lower overpotential of Ag2S, the electrons more easily participated in the reduction of protons. Meanwhile, the holes on the valence band of CdS reacted with the hole sacrificial agent (triethanolamine). In this process, the photogenerated electron–hole pairs realised effective separation. The introduction of Ag2S also enhanced the utilisation of infrared light and increased the temperature of CdS surface.

Co, Mn-LDH nanoneedle arrays grown on Ni foam for high performance supercapacitors

Abstract: To solve the agglomeration of layered double hydroxides (LDH) for improving their supercapacitor performances, Co, Mn-LDH nanoneedle arrays grown on Ni foam (Co, Mn-LDH@NF hybrid) was fabricated via a one-step hydrothermal strategy. The Ni foam served as the skeleton frame for anchoring Co, Mn-LDH nanoneedles to form three dimensional net structures, and open spaces among Co, Mn-LDH nanoneedles. When Co, Mn-LDH@NF hybrid was used as binder-free electrodes for supercapacitors, it displayed outstanding supercapacitor performances with a high specific capacitance of 2422 F g−1 at 1 A g−1, and superior cyclic stability for maintaining a capacitance of 2096 F g−1 after 3000 cycles, which was only 13.5% capacity loss ratio. The excellent supercapacitor performances were ascribed to three dimensional net structure and LDH nanoneedle structure, which provided abundant electrochemical active sites, alleviated volume expansion, and had good electrical conductivity.

Sol-gel synthesized hexagonal boron nitride/titania nanocomposites with enhanced photocatalytic activity

Abstract: Hexagonal boron nitride (H-BN)/titania (TiO2) nanocomposites photocatalysts were synthesized by a facile sol-gel method The structure was verified by comprehensive analysis from X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope and transmission electron microscope The degradation of organic dyes such as rhodamine B (RhB) and methylene blue (MB) under UV light irradiation was used to measure the photocatalytic activity of the h-BN/TiO2 nanocomposites The photocatalytic performance and the stability of H-BN/TiO2 nanocomposites in the degradation of dyes (MB and RhB) significantly outperformed pure TiO2 nanoparticles The formed B O Ti bond in H-BN/TiO2 gave rise to a strong link between h-BN sheets and TiO2 nanoparticles, and thus the charge transportation rate was improved and the recombination of electrons and holes was suppressed in the photocatalytic processes The degradation percentage for RhB and MB reached 98% and 92% within 50 min irradiation The degradation rate (k) of first-order linear value of h-BN/TiO2 nanocomposites (005952 and 00498) for RhB and MB degradation was 364 and 422 times higher than that of pure TiO2 (001637 and 00118) The enhanced photocatalytic property of the nanocomposites was attributed to the reduction in charge recombination and the adsorption interaction between organic dyes and h-BN Consequently, h-BN sheets hold a great promise to enhance the photocatalytic activity of semiconductive materials

Understanding the adsorption and anticorrosive mechanism of DNA inhibitor for copper in sulfuric acid

Abstract: Deoxyribonucleic acid (DNA) was investigated for suppressing copper corrosion in 0.5 M H2SO4 through electrochemical measurement, microscopic surface observation, X-ray photoelectron spectroscopy (XPS) analysis and molecular dynamics (MD) simulation. Results indicate that DNA acts as an effective cathodic-type inhibitor that mainly suppresses cathodic reaction by forming anchored DNA-adsorption film. The film shows active blocking effect, obeys the Langmuir adsorption model and involves physisorption and chemisorption. The MD simulation gives the new insights at molecular level and indicates the formation of an interesting double barrier of DNA molecule on the Cu (111) surface due to its unique twist structure.

Electronic and optical properties of van der Waals heterostructures of g-GaN and transition metal dichalcogenides

Abstract: Based on first-principles calculations, we systematically investigate the electronic and optical properties of van der Waals (vdW) heterostructures composed of graphene-like gallium nitride (g-GaN) and transition metal dichalcogenides (TMDs). The investigated vdW heterostructures (g-GaN/MoS2, g-GaN/WS2, g-GaN/MoSe2, and g-GaN/WSe2) are all semiconductors with direct bandgap. In particular, both the g-GaN/MoS2 and g-GaN/WS2 vdW heterostructures possess type-II band alignment, which will facilitate the separation of photogenerated carriers, and enhance their lifetime. Furthermore, band edge positions of these two heterostructures satisfied both water oxidation and reduction energy requirements, suggesting the potential in photocatalysts for water splitting. In addition, both g-GaN/MoS2 and g-GaN/WS2 vdW heterostructures exhibit a high electron mobility, which ensure that the redox reactions for water splitting will be effectively proceeded. More importantly, they show significant absorption peaks in the visible light region, leading to highly efficient utilization of the solar energy. These fascinating properties render the g-GaN/MoS2 and g-GaN/WS2 vdW heterostructures high-efficiency photocatalysts for water splitting.

Novel g-C3N4/g-C3N4 S-scheme isotype heterojunction for improved photocatalytic hydrogen generation

Abstract: Rationally designing heterostructure is a promising way to promote the charge carrier separation of intrinsic photocatalysts, thus contributes the improvement of solar to chemical energy conversion. Herein, a novel isotype heterojunction consisted of MCN and UCN, respectively derived from hydrothermally-treated melamine and urea, was synthesized. Owing to the well compatibility and matched band structure, an S-scheme charge transfer mechanism is confirmed for working on MCN/UCN isotype heterojunction, thus endowing strong redox ability, efficient charge carrier separation efficiency and prolonged lifetime. As a result, MCN/UCN exhibits improved photocatalytic water splitting activity under visible light irradiation, which displays approximately 5.5 and 1.8-fold enhancement as compared to the pure MCN and UCN, respectively. The rationally synthesized S-scheme isotype heterojunction will pave the way for developing highly efficient g-C3N4-based photocatalysts.

Enhanced visible-light photocatalytic CO2 reduction performance of Znln2S4 microspheres by using CeO2 as cocatalyst

Abstract: ZnIn2S4 flower-like microspheres decorated with CeO2 as cocatalyst have been successfully fabricated through a microwave-assisted hydrothermal method for visible-light carbon dioxide (CO2) photoreduction to produce methanol (CH3OH) All the composite photocatalysts exhibited a more excellent photocatalytic performance than bare CeO2 and ZIS, and reached the highest with a CH3OH evolution rate of 0542 µmol g−1 h−1 when the content of CeO2 was 5 wt% In the composites, the CeO2 with oxygen vacancies acted as a significant cocatalyst to efficiently trap the photogenerated electrons from ZIS and thus boosted the separation of photoinduced charge carriers, while the unique 3D structure of ZIS made it with a relatively large specific area, which could provide abundant active reaction sites and render the reactants and products diffuse more easily This study verified the CeO2 as one of the ideal cocatalyst candidates for ZnIn2S4 in the application of photocatalytic CO2 reduction, and gave rise to an increasing interest in expanding potential applications of ZnIn2S4 based materials in the field of energy conversion

Size effect of Pt co-catalyst on photocatalytic efficiency of g-C3N4 for hydrogen evolution

Abstract: Graphitic carbon nitride (g-C3N4) with Pt co-catalyst was synthesized by in-situ photoreduction and used as a visible light photocatalyst. The size of Pt co-catalyst can be controlled form single atoms to nano-clusters by the induced amount of Pt precursor. The results indicated that compared with nano-clusters, the Pt0.1-CN (with 0.1 wt% Pt loading amount) which is characterized as single-atom Pt exhibits a pronounced photocatalytic hydrogen evolution capability. For Pt0.1-CN with single-atom Pt as co-catalyst, the H2 generation is up to 473.82 µmol mg−1pt under visible light irradiation (λ > 420 nm). The enhanced photocatalytic performance is mainly attributed to the synergistic effect of high light adsorption efficiency, effective charge separation, and high dispersed active sites of Pt atoms. The results of this work highlighted that loading g-C3N4 with Pt single atoms will achieve a maximum utilization efficiency of Pt atoms and an improvement photocatalytic performance.

A Z-scheme mechanism of N-ZnO/g-C3N4 for enhanced H2 evolution and photocatalytic degradation

Abstract: The N-ZnO/g-C3N4 composites prepared by high temperature calcination exhibited excellent performance in both the photocatalytic H2 evolution and photocatalytic degradation of Methylene blue (MB). It can be seen that the absorption range of ZnO extends from ultraviolet light to UV–visible light after N dopant. The combination with g-C3N4 further enhances the absorption range of N-ZnO, thereby increasing the utilization of light. A Z-scheme photocatalytic system mechanism of N-ZnO/g-C3N4 has been proposed for the enhanced H2 evolution and photocatalytic degradation rate. The proper bands position of N-ZnO facilitates the formation of Z-scheme mechanism. The electrons on CB of N-ZnO would migrate to VB of g-C3N4, which can effectively prevent the recombination of electrons and holes. The generation of electrons in CB of g-C3N4 and accumulation of holes in VB of N-ZnO can improve the photocatalytic efficiency.

Cu2−xSe/CdS composite photocatalyst with enhanced visible light photocatalysis activity

Abstract: To design efficient photocatalysis system, the recombination of electron-hole pairs in photocatalysts should be suppressed. Herein, p type Cu2−xSe/n type CdS composite photocatalyst was proposed for the first time to improve photocatalysis performance for Rhodamine B (RhB) degradation. Among the various ratio composites, 10 wt% Cu2−xSe/CdS shows the best photocatalysis performance, the degradation rate of RhB was enhanced 7.8 times than that of pristine CdS. The enhanced photocatalysis performance was mainly ascribed to the formation of Cu2−xSe/CdS p-n junction, which will lead to effective charge separation in the composite photocatalyst.

First-principle study of electronic and optical properties of two-dimensional materials-based heterostructures based on transition metal dichalcogenides and boron phosphide

Abstract: Van der Waals (vdW) heterostructure can improve the performance of the 2D materials and provide more applications. Based on density functional theory (DFT) calculations, the properties of vertical heterostructures formed by transition metal dichalcogenides (TMDs) MX2 (M = Mo, W; X = S, Se) and boron nitride (BP) were addressed. In particular, the vdW interaction exist in all these heterostructures instead of covalent bonding. The MoSe2/BP and WSe2/BP vdW heterostructures possess direct bandgap characterized by type-II band alignment and powerful built-in electric field across the interface, which can effectively separate the photogenerated-charge. Meanwhile, the MoS2/BP and WS2/BP vdW heterostructures also have the direct bandgap and intrinsic type-I band alignment. Furthermore, all heterostructures exhibit excellent optical absorption in the visible and near-infrared regions. Our investigation shows an effective method to design new vdW heterostructures based on TMDs and explores their applications for photocatalytic, photovoltaic, and optical devices.

Electroless plating Ni-P cocatalyst decorated g-C3N4 with enhanced photocatalytic water splitting for H2 generation

Abstract: This work reports the nickel-phosphorus (Ni-P) cocatalyst decorated graphitic C3N4 (g-C3N4/Ni-P) for photocatalytic water splitting to H2 generation. The g-C3N4/Ni-P composite is prepared through two steps, first step is thermal decomposition of urea to produce g-C3N4 and the second step is electroless plating to coast Ni-P on the g-C3N4 surface, resulting in the noticeable increase of the photocatalytic activity of g-C3N4. Among these as-prepared samples reported in this work, the highest photocatalytic activity is detected at 3 wt% (g-C3N4/Ni-P-3%), in which H2 production rate is 1051 μmol g−1 h−1. However, higher than 3 wt% Pt modification the g-C3N4 generates only 841 μmol g−1 h−1 of H2, and almost no generation of H2 by pure g-C3N4 has been determined. Based on photoluminescence and photocurrent measurements, a photocatalytic mechanism for pure g-C3N4 and g-C3N4/Ni-P-3% has been suggested, that is, the loading of Ni-P NPs accelerates the separation of photogenerated e−-h+ pairs and relaying photogenrated e− via Ni-P particles to react with H2O, and thus improves photocatalytic performance of g-C3N4 for water splitting into H2 generation.

Novel solvothermal preparation and enhanced microwave absorption properties of Ti3C2Tx MXene modified by in situ coated Fe3O4 nanoparticles

Abstract: Two-dimensional transition metal carbide/nitrides, typically represented by Ti3C2Tx, have been believed as a potential novel microwave absorption material because of their unique two-dimensional (2D) laminated structure, native defects and abundant surface chemistry. However, its intrinsic single dielectric loss mechanism limits the future improvement of microwave absorption properties. Herein, we report a simple solvothermal route for in situ heterogeneous nucleation and growth of Fe3O4 magnetic nanoparticles on the Ti3C2Tx MXene surface and interlayer, which is denoted as Fe3O4@Ti3C2Tx nanocomposites, thus balancing the impedance matching, introducing more loss mechanism and enhancing microwave absorption performance. Interestingly, the solvothermal process provides a reducing environment which protects Ti3C2Tx MXene from oxidation at temperature up to 200 °C, endowing Ti3C2Tx MXene a high stability compared with hydrothermal process. The sample containing 25 wt% Fe3O4 exhibits an impressive microwave absorption performance, the minimum RL of −57.2 dB at 15.7 GHz and an effective absorption bandwidth of 1.4 GHz (thickness 4.2 mm), which is mainly attributed to the suitable impedance matching, enhanced interface polarization and Debye relaxation caused by unique laminated heterointerface structure of Fe3O4@Ti3C2Tx. This work provides a simple and novel strategy for the modification of MXene and the development of high performance MXene based microwave absorbing materials.

Bio-based magnetic metal-organic framework nanocomposite: Ultrasound-assisted synthesis and pollutant (heavy metal and dye) removal from aqueous media

Abstract: In the recent decade, Metal-Organic Frameworks (MOFs) and their most popular subclasses (zeolitic imidazolate frameworks (ZIFs)) are widely studied for removing contaminants from the effluent. Herein, the magnetic bionanocomposite (eggshell membrane-zeolitic imidazolate framework) was synthesized using a facile, efficient, and green ultrasound-assisted method. Zeolitic imidazolate frameworks-67 (ZIF-67) crystals were stabilized on the surface of magnetic eggshell membrane (Fe3O4@ESM) support to prepare the ZIF-67@ Fe3O4@ESM composite as a novel adsorbent with the high surface area (1263.9 m2/g). Several analyses such as XRD, FTIR, SEM/EDS/Mapping, VSM, and BET were used to confirm the characterization and structural changes of ZIF-67 crystals before and after the composition process. Thereafter, copper cation (Cu2+) capture and dye (Basic Red 18: BR18) adsorption process were designed and thoroughly studied using the prepared adsorbents. It was found that the adsorption rate and removal percentage of the ZIF-67@Fe3O4@ESM composite are faster and higher than that of the pure ZIF-67 for both types of contaminants. Moreover, the magnetic feature of the composite adsorbent caused to a facile separation from liquid media. The results showed that the Langmuir adsorption isotherm well explained the obtained equilibrium data with a maximum adsorption capacity of 344.82 and 250.81 mg/g for Cu2+ and BR18, respectively. Kinetic studies showed that the pseudo-second order model was capable to fit the experimental data of the simultaneous removal of heavy metal ion and dye molecule.