Band Engineering and Morphology Control of Oxygen‑Incorporated Graphitic Carbon Nitride Porous Nanosheets for Highly Efficient Photocatalytic Hydrogen Evolution

Graphitic carbon nitride(g-C3N4)-based photocatalysts have shown great potential in the splitting of water.However,the intrinsic drawbacks of g-C3N4,such as low surface area,poor diffusion,and charge separation efficiency,remain as the bottleneck to achieve highly efficient hydrogen evolution.Here,a hollow oxygen-incorporated g-C3N4 nanosheet(OCN)with an improved surface area of 148.5 m2 g^−1 is fabricated by the multiple thermal treatments under the N2/O2 atmosphere,wherein the C–O bonds are formed through two ways of physical adsorption and doping.The physical characterization and theoretical calculation indicate that the O-adsorption can promote the generation of defects,leading to the formation of hollow morphology,while the O-doping results in reduced band gap of g-C3N4.The optimized OCN shows an excellent photocatalytic hydrogen evolution activity of 3519.6μmol g^−1 h^−1 for~20 h,which is over four times higher than that of g-C3N4(850.1μmol g^−1 h^−1)and outperforms most of the reported g-C3N4 catalysts.     

Confined reaction inside nanotubes: New approach to mesoporous g-C3N4 photocatalysts

Mesoporous g-C3N4 nanorods (NRs) are synthesized through the nano-confined thermal condensation of cyanamide in silica nanotubes (NTs) with porous shells.The gas bubbles retained during condensation and the limited cyanamide precursor inside the silica NTs lead to the formation of mesoporous g-C3N4.This nano-confined reaction is an alternative method to the traditional templating process for the synthesis of mesoporous materials.The as-prepared mesoporous g-C3N4 NRs exhibit remarkably improved photocatalytic activity and high stability in water splitting and degradation of Rhodamine B compared with bulk g-C3N4.     

g-C3N4 encapsulated ZrO2 nanofibrous membrane decorated with CdS quantum dots: A hierarchically structured,self-supported electrocatalyst toward synergistic NH3 synthesis

The advancement of electrocatalytic N2 reduction reaction (NRR) toward ambient NH3 synthesis lies in the development of more affordable electrocatalysts than noble metals. Recently, various nanostructures of transition metal compounds have been proposed as effective electrocatalysts;however, they exist in the form of loose powders, which have to be immobilized on a matrix before serving as the electrode for electrolysis. The matrix, being it carbon paper, carbon cloth or metal foam, is electrocatalytically inactive, whose introduction inevitably raises the invalid weight while sacrificing the active sites of the electrode. Herein, we report on the fabrication of a flexible ZrO2 nanofibrous membrane as a novel, self-supported electrocatalyst. The heteroatom doping can not only endow the nanofibrous membrane with excellent flexibility, but also induce oxygen vacancies which are responsible for easier adsorption of N2 on the ZrO2 surface. To improve the electrocatalytic activity, a facile SILAR approach is employed to decorate it with CdS quantum dots (QDs), thereby tuning its Fermi level. To improve the conductivity, a g-C3N4 nanolayer is further deposited which is both conductive and active. The resulting hierarchically structured, self-supported electrocatalyst, consisting of g-C3N4 encapsulated ZrO2 nanofibrous membrane decorated with CdS QDs, integrates the merits of the three components, and exhibits a remarkable synergy toward NRR. Excellent NH3 yield of 6.32 × 10?10 mol·s?1cm?2 (?0.6 V vs. RHE) and Faradaic efficiency of 12.9% (?0.4 V vs. RHE) are attained in 0.1 M Na2SO4.     

Sulfur-doped g-C_3N_4/rGO porous nanosheets for highly efficient photocatalytic degradation of refractory contaminants

Graphitic carbon nitride(g-C_3N_4, CN) has attracted increasing interests in the field of photocatalysis due to its high visible-light-response. However, its photocatalytic activity is still lower for degradation of refractory contaminants such as Cr(Ⅵ) and Rhodamine B(RhB) etc. Herein, we report a facile method to synthesize a novel sulfur(S)-doped CN/reduced graphene oxide(rGO) porous nanosheet(S-CN/rGO PNs)via a supramolecular self-assembling followed by a solvothermal treatment. The as-prepared porous SCN/rGO PNs are stable with high specific surface area ～188.5 m~2 g~(-1) and exhibit a significantly enhanced photocatalytic activity of ～17-fold and 15-fold higher than that of bulk CN for the degradation of RhB and Cr(Ⅵ) under visible light irradiation, respectively. Typically, 50 mL of 15 mg/mL RhB can be degraded within 20 min by 10 mg S-CN/rGO PNs. The mechanism can be explained by the synergistic effect of S doping and porous structure which can effectively reduce the band gap of CN and increase the specific surface area to promote the separation and transfer of photo-generated charge carriers. The results have provided a new way to significantly enhance the photocatalytic activity of g-C_3N_4 for degradation of refractory contaminants.     

Enhancing both selectivity and coking-resistance of a single-atom Pd<Subscript>1</Subscript>/C<Subscript>3</Subscript>N<Subscript>4</Subscript> catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading,where Pd-based catalysts are widely used because of their high hydrogenation activities.However,poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns.In this work,atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation.During selective hydrogenation of acetylene in excess ethylene,the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/A12O3 and Pd/SiO2 catalysts.In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement.More impressively,the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance.Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.     

Active {010} facet-exposed Cu2MoS4 nanotube as high-efficiency photocatalyst

Rational design and facet-engineering of nanocrystal is an effective strategy to optimize the catalytic performance of abundant and economic semiconductorbased photocatalysts.In this study,we demonstrate a novel ternary Cu2MoS4 nanotube with the {010} facet exposed,synthesized via a hydrothermal method.Compared with two-dimensional Cu2MoS4 nanosheet with the {001} facet exposed,this one-dimensional nanotube exhibits highly enhanced performance of photodegradation and water splitting.Both theoretical calculations and experimental results suggest that the conduction band minimum (CBM) of the {010} facet crystal shows lower potential than that of the {001} facet.In particular,the up-shifted CBM in Cu2MoS4 nanotube is significantly beneficial for the absorption of dye molecules and reduction of H+ to H2.These results may open a new route for realizing high-efficiency photocatalysts based on Cu2MX4 by facet engineering.     

β-Cyclodextrin polymer networks stabilized gold nanoparticle with superior catalytic activities

Support materials play a significant role in heterogeneous nanocatalysis.In this work,β-cyclodextrin(β-CD)was used directly as a monomer to construct polymer networks for gold nanoparticles(Au NPs)immobilization.Using the simple nucleophilic substitution reaction,β-CD based polymer networks(β-CDP-N andβ-CDP-C)were successfully prepared.Compared toβ-CDP-C,the hydroxyl groups and N atoms inβ-CDP-N played a synergistic role in immobilizing smaller Au NPs,thus leading to high catalytic activities.Notably,the apparent rate constant(Kapp)value for Au@β-CDP-N in the reduction of 4-nitrophenol to 4-aminophenol is 14.15×10^-2s^-1,which shows a significant improvement over all previously reported Au NPs with solid supports under similar conditions.Considering the negligible porosity of theβ-CDP-N support,we purposed a"capture-catalysis-release"model to explain the high catalytic activity of Au@β-CDP-N.This explanation is supported by the guest-responsive properties ofβ-CDP-N.Moreover,the Au@β-CDP-N is easily recycled and maintained its high catalytic efficiency after seven successful cycles.     

The Pattern Growth of Carbon Nanotubes by Self-assembled Monolayers Techniques

The well controllable selective growth of carbon nanotubes (CNTs)on the desired area is an important issue for their future applications. In this study, a novel method for selective growth of CNTs was proposed by using the technology of self-assembly monolayers (SAMs) and the Fe-assisted CNTs growth. The Si wafers with the a ： Si/Si3N4 layer patterns were first prepared by low pressure chemical vapor deposition (LPCVD)and lithography techniques to act as the substrates for selective deposition of SAMs. The selectivity of SAMs from APTMS solution (N-(2-aminoethyl)-3-aminopropyltrimethoxsilane) is based on its greater reactivity of head group on a-Si than Si3N4 films. The areas of pattern with SAMs will first chelate the Fe3 ions by their diamine-terminated group. The Fe^3 ions were then consolidated to become Fe-hydroxides in sodium boron hydride solution to form the Fe-hydroxides pattern. Finally, the Fe-hydroxides pattern was pretreated in H plasma to become a well-distributed Fe nano-particles on the surface, and followed by CNTs deposition using Fe as catalyst in a microwave plasma-chemical vapor deposition (MP-CVD) system to become the CNTs pattern. The products in each processing step, including microstructures and lattice images of CNTs, were characterized by contact angle measurements, scanning electron microscopy (SEM), XPS, Auger spectroscopy, transmission electron microscopy (TEM) and high resolution TEM (HRTEM) deposition. The results show that the main process parameters include the surface activation process and its atmosphere, consolidation time and temperature, H plasma pretreatment. The function of each processing step will be discussed.     

Synthesis of graphene quantum dots for their supramolecular polymorphic architectures

How to regulate the supramolecular structures in the assembly of graphene quantum dots(GQDs)is still a great challenge to be overcome.Herein,the GQDs of 1-3 layers with high quality are synthesized from the new precursor m-trihydroxybenzene in a green method.More importantly,a strategy for designing the supramolecular structures of GQDs is demonstrated,and the novel supramolecular morphologies of GQDs have been constructed for the first time.Moreover,the supramolecular morphologies of GQDs can be well controlled by regulating the preparation conditions,and the formation mechanism of the branch-like supramolecular structure has been explained by the the diffusion-limited aggregation(DLA)model.This work not only develops a new precoursor to synthesize GQDs,but also opens up an effective route toform the polymorphic supermolecules,thus greatly facilitating their potential applications.     

Effects of morphology and concentration of CuS nanoparticles on alignment and electro-optic properties of nematic liquid crystal

Nanopartides (NPs) with flower-like and frame morphologies were synthesized from CuS,a remarkable transition-metal sulfide.We introduced two kinds of CuS NPs into a nematic liquid crystal (LC) 4-cyano-4'-n-pentylbiphenyl (5CB) and investigated the morphology-and concentration-dependent alignment and electro-optic (E-O) effects of CuS NPs on 5CB.A trace amount of flower-like CuS NPs induced a uniform homeotropic orientation of LC molecules;this is attributable to the obtained desirable compact nanosheet structure.Moreover,both flower-like and frame CuS NPs induced a remarkable improvement in the E-O properties of 5CB,and the flower-like CuS/5CB system exhibited a better performance.The doped CuS NPs in the LC host suppressed the shielding effect and strengthened the electric field,resulting in outstanding E-O properties.At a doping concentration of 0.05 wt.％,CuS NPs were well-dispersed and achieved the optimum E-O performance.This study provides a novel method for inducing a uniform orientation and enhanced E-O properties of LC molecules by doping with extraordinary CuS NPs,leading to potential applications in establishing flexible LC displays.     

N-Graphene Nanowalls via Plasma Nitrogen Incorporation and Substitution: The Experimental Evidence

Incorporating nitrogen(N)atom in graphene is considered a key technique for tuning its electrical properties.However,this is still a great challenge,and it is unclear how to build N-graphene with desired nitrogen configurations.There is a lack of experimental evidence to explain the influence and mechanism of structural defects for nitrogen incorporation into graphene compared to the derived DFT theories.Herein,this gap is bridged through a systematic study of different nitrogen-containing gaseous plasma post-treatments on graphene nanowalls(CNWs)to produce N-CNWs with incorporated and substituted nitrogen.The structural and morphological analyses describe a remarkable difference in the plasma–surface interaction,nitrogen concentration and nitrogen incorporation mechanism in CNWs by using different nitrogen-containing plasma.Electrical conductivity measurements revealed that the conductivity of the N-graphene is strongly influenced by the position and concentration of C–N bonding configurations.These findings open up a new pathway for the synthesis of N-graphene using plasma post-treatment to control the concentration and configuration of incorporated nitrogen for application-specific properties.     

Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

Crystalline Fe/MnO@C core–shell nanocapsules inlaid in porous amorphous carbon matrix(FMCA)was synthesized successfully with a novel confinement strategy.The heterogeneous Fe/MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2–18 GHz.The addition of MnO2 confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon.The heterogeneous materials composed of crystalline–amorphous structures disperse evenly and its density is significantly reduced on account of porous properties.Meanwhile,adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network.The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption.The optimal reflection loss(RL)is up to−45 dB,and the effective bandwidth(RL<−10 dB)is 5.0 GHz with 2.0 mm thickness.The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber,but also offers a general duty synthesis method for heterogeneous crystalline–amorphous composites with tunable composition in other fields.     

Application of Cerebellar Model Articulation Controller （CMAC） with a Modified Algorithm in Monitoring Machine Performance Degradation

On the basis of CMAC-PDM (Pattern Discrimination Model) , a novel algorithm of CMAC for monitoring machine degradation is proposed in this paper. The output of CMAC with the novel algorithm represents the state of a machine and PDM is not needed. The principle was explained by analyzing the modified mapping process of CMAC. The novel CMAC is applied to a tool condition monitoring system and two methodologies (novel CMAC and CMAC-PDM) are compared. The results prove that the novel algorithm is feasible and its computational complexity is reduced significantly.     

Orientation controlled preparation of nanoporous carbon nitride fibers and related composite for gas sensing under ambient conditions

Creating pores in suprastructures of two-dimensional (2D) materials while controlling the orientation of the 2D building blocks is important in achieving large specific surface areas and tuning the anisotropic properties of the obtained functional hierarchical structures.In this contribution,we report that arranging graphitic carbon nitride (g-C3N4) nanosheets into one-dimensional (1D) architectures with controlled orientation has been achieved by using 1D oriented melem hydrate fibers as the synthetic precursor via a polycondensation process,during which the removal of water molecules and release of ammonia gas led to the creation of pores without destroying the 1D morphology of the oriented structures.The resulting porous g-C3N4 fibers with both meso-and micro-sized pores and largely exposed edges exhibited good sensing sensitivity and selectivity towards NO2.The sensing performance was further improved by hybridization of the porous fibers with Au nanoparticles (Au NPs),leading to a detection limit of 60 ppb under ambient conditions.Our results suggest that the highly porous g-C3N4 fibers and the related hybrid structures with largely exposed graphitic layer edges are excellent sensing platforms and may also show promise in other electronic and electrochemical applications.     

Tribotronic transistor sensor for enhanced hydrogen detection

Hydrogen detection with a high sensitivity is necessary for preventing potential explosions and fire.In this study,a novel ZnO tribotronic transistor is developed by coupling a ZnO field effect transistor (FET) and triboelectric nanogenerator in free-standing mode and is used as a sensor for hydrogen detection at room temperature.Tribotronic modulated performances of the hydrogen sensor are demonstrated by investigating its output characteristics at different sliding distances and hydrogen concentrations.By applying an external mechanical force to the device for sliding electrification,the detection sensitivity of the ZnO tribotronic transistor sensor is improved,with a significant enhancement achieved in output current by 62 times at 500 ppm hydrogen and 1 V bias voltage.This study demonstrates an extension of the applications of emerging tribotronics for gas detection and a prospective approach to improve the performance of the hydrogen sensor via human-interfacing.     

Single step fabrication of N-doped graphene/Si3N4/SiC heterostructures

In-plane heteroatom substitution of graphene is a promising strategy to modify its properties. The ability to dope graphene with electron-donor nitrogen heteroatoms is highly important for modulating electrical properties of graphene. Here we demonstrate a transfer-free method to directly grow large area quasi free-standing N-doped graphene bilayers on an insulating substrate （Si3N4）. Electron-bombardment heating under nitrogen flux results in simultaneous growth of N-doped graphene and a Si3N4 layer on the SiC surface. The decoupling of N-doped graphene from the substrate and the presence of Si3N4 are identified by X-ray photoemission spectroscopy and low-energy electron diffraction. The substitution of nitrogen atoms in the graphene planes was confirmed using high resolution X-ray photoemission spectroscopy which reveals several atomic configurations for the nitrogen atoms： Graphitic-like, pyridine-like, and pyrrolic- like. Furthermore, we demonstrated for the first time that N-doped graphene could be used to efficiently probe oxygen molecules via nitrogen atom defects.     

YN<Subscript>2</Subscript> monolayer: Novel p-state Dirac half metal for high-speed spintronics

In spintronics,it is highly desirable to find new materials that can simultaneously possess complete spin-polarization,high-speed conduction electrons,large Curie temperature,and robust ferromagnetic ground states.Using first-principles calculations,we demonstrate that the stable YN2 monolayer with octahedral coordination is a novel p-state Dirac half metal (DHM),which not only has a fully spin-polarized Dirac state,but also the highest Fermi velocity (3.74 x 105 m/s) of the DHMs reported to date.In addition,its half-metallic gap of 1.53 eV is large enough to prevent the spin-flip transition.Because of the strong nonlocal p orbitals of N atoms (N-p) direct exchange interaction,the Curie temperature reaches over 332 K.Moreover,its ferromagnetic ground state can be well preserved under carrier doping or external strain.Therefore,the YN2 monolayer is a promising DHM for high-speed spintronic devices and would lead to new opportunities in designing other p-state DHMs.     

Quality assessment of graphene: Continuity,uniformity, and accuracy of mobility measurements

With the increasing availability of large-area graphene,the ability to rapidly and accurately assess the quality of the electrical properties has become critically important.For practical applications,spatial variability in carrier density and carrier mobility must be controlled and minimized.We present a simple framework for assessing the quality and homogeneity of large-area graphene devices.The field effect in both exfoliated graphene devices encapsulated in hexagonal boron nitride and chemical vapor-deposited (CVD) devices was measured in dual current-voltage configurations and used to derive a single,gate-dependent effective shape factor,β,for each device.β is a sensitive indicator of spatial homogeneity that can be obtained from samples of arbitrary shape.All 50 devices investigated in this study show a variation (up to tenfold) inβ as a function of the gate bias.Finite element simulations suggest that spatial doping inhomogeneity,rather than mobility inhomogeneity,is the primary cause of the gate dependence ofβ,and that measurable variations ofβ can be caused by doping variations as small as 1010 cm-2.Our results suggest that local variations in the position of the Dirac point alter the current flow and thus the effective sample shape as a function of the gate bias.We also found that such variations lead to systematic errors in carrier mobility calculations,which can be revealed by inspecting the correspondingβ factor.     

Experimental and DFT Studies of Au Deposition Over WO3/g-C3N4 Z-Scheme Heterojunction

A typical Z-scheme system is composed of two photocatalysts which generate two sets of charge carriers and split water into H2 and O2 at different locations.Scientists are struggling to enhance the efficiencies of these systems by maximizing their light absorption,engineering more stable redox couples,and discovering new O2 and H2 evolutions co-catalysts.In this work,Au decorated WO3/g-C3N4 Z-scheme nanocomposites are fabricated via wet-chemical and photo-deposition methods.The nanocomposites are utilized in photocatalysis for H2 production and 2,4-dichlorophenol(2,4-DCP)degradation.It is investigated that the optimized 4Au/6%WO3/CN nanocomposite is highly efficient for production of 69.9 and 307.3μmol h−1 g−1 H2 gas,respectively,under visible-light(λ>420 nm)and UV–visible illumination.Further,the fabricated 4Au/6%WO3/CN nanocomposite is significant(i.e.,100%degradation in 2 h)for 2,4-DCP degradation under visible light and highly stable in photocatalysis.A significant 4.17%quantum efficiency is recorded for H2 production at wavelength 420 nm.This enhanced performance is attributed to the improved charge separation and the surface plasmon resonance effect of Au nanoparticles.Solid-state density functional theory simulations are performed to countercheck and validate our experimental data.Positive surface formation energy,high charge transfer,and strong non-bonding interaction via electrostatic forces confirm the stability of 4Au/6%WO3/CN interface.     

Uniform assembly of gold nanoparticles on S-doped g-C_3N_4 nanocomposite for effective conversion of 4-nitrophenol by catalytic reduction

In this work, a simple synthesis of sulfur doped graphitic carbon nitride(S-g-C_3N_4) act as a support cum stabilizers for gold nanoparticles(Au) and its was characterized by UV–vis and XRD to measure the absorbance and crystallinity, respectively. The functional group and morphology of the samples were identified using FT-IR and TEM. Finally, the Au@S-g-C_3N_4 nanocatalyst exhibits good catalytic performance and stability in the reduction of hazardous 4-nitrophenol(NP) compared to S-g-C_3N_4 using Na BH4.Moreover, the Au@S-g-C_3N_4 nanocomposite holds a good catalytic efficiency(near 100%) achieved by within 5 min. The highest catalytic reduction of NP is due to the synergistic effect of Au nanoparticles decorated on S-g-C_3N_4. The fast electron transfer reduction mechanism was elucidated and discussed.Excellent reusability and stability of the developed nanocomposites were also observed in consecutive reduction experiments. The filtering and catalyzing device was used for the direct conversion of NP polluted water. This method can open a new avenue for the metal nanoparticles based carbon materials heterogeneous catalyst and its reduction of toxic contaminants.