3D macropore carbon-vacancy g-C3N4 constructed using polymethylmethacrylate spheres for enhanced photocatalytic H2 evolution and CO2 reduction

Metal-free g-C_3N_4 is widely used in photocatalytic reactions owing to its suitable band structure.However, it has low specific surface area and insufficient absorbance for visible light, and its photoexcited carriers have high recombination rates. In this study, the 3 D macropore C-vacancy g-C_3N_4 was prepared through a facile one-step route. Polymethylmethacrylate is used as a template to increase the surface reaction sites of g-C_3N_4 and extend its visible-light range. Compared to unmodified g-C_3N_4, the H2 production and CO_2 reduction rates of the fabricated g-C_3N_4 significantly improved. The special pore structure significantly improved the light utilization efficiency of g-C_3N_4 and increased the number of surface-active sites. The introduction of C-vacancy extended the absorption band of visible-light and suppressed the carrier recombination. The newly developed synthesis strategy can improve solar energy conversion efficiency and potentially modifies g-C_3N_4.     

Functional groups to modify g-C_3N_4 for improved photocatalytic activity of hydrogen evolution from water splitting

Rational modification by functional groups was regarded as one of efficient methods to improve the photocatalytic performance of graphitic carbon nitride(g-C_3 N_4).Herein,g-C_3 N_4 with yellow(Y-GCN) and brown(C-GCN) were prepared by using the fresh urea and the urea kept for five years,respectively,for the first time.Experimental results show that the H2 production rate of the C-GCN is 39.06 μmol/h,which is about 5 times of the Y-GCN.Meantime,in terms of apparent quantum efficiency(AQ.E) at 420 nm,C-GCN has a value of 6.3% and nearly 7.3 times higher than that of Y-GCN(0.86%).The results of XRD,IR,DRS,and NMR show,different from Y-GCN,a new kind of functional group of —N=CH— was firstly in-situ introduced into the C-GCN,resulting in good visible light absorption,and then markedly improving the photocatalytic performance.DFT calculation also confirms the effect of the —N=CH— group band structure of g-C_3N_4.Furthermore,XPS results demonstrate that the existence of —N=CH— groups in C-GCN results in tight interaction between C-GCN and Pt nanoparticles,and then improves the charge separation and photocatalytic performance.The present work demonstrates a good example of "defect engineering" to modify the intrinsic molecular structure of g-C_3N_4 and provides a new avenue to enhance the photocatalytic activity of g-C_3N_4 via facile and environmental-friendly method.     

Preparation of ZnO/GO composite material with highly photocatalytic performance via an improved two-step method

ZnO/graphene oxide(ZnO/GO) composite material,in which ZnO nanoparticles were densely coated on the GO nanosheets,was successfully prepared by an improved two-step method and characterized by IR, XRD,TEM,and UV-vis techniques.The improved photocatalytic property of the ZnO/GO composite material,evaluated by the photocatalytic degradation of methyl orange(MO) under UV irradiation,is ascribed to the intimate contact between ZnO and GO,the enhanced adsorption of MO,the quick electron transfer from excited ZnO particles to GO sheets and the activation of MO molecules viaπ-πinteraction between MO and GO.     

In-situ hydrothermal synthesized γ-Al_2O_3/O-g-C_3N_4 heterojunctions with enhanced visible-light photocatalytic activity in water splitting for hydrogen

In this work,γ-Al_2O_3 and hydrogen peroxide treated g-C_3N_4(O-g-C_3N_4) were combined through a novel in-situ hydrothermal method to form heterojunction structured photocatalysts.These photocatalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy(PL).FT-IR results indicate that oxygen functional groups can be grafted on the surface of O-g-C_3N_4 by hydrogen peroxide treatment.The visible light photocatalytic hydrogen evolution rate was investigated in 10 vol% TEOA aqueous solution.The optimal Al_2O_3 mass content is set to be 20 wt% and the corresponding hydrogen evolution rate is 1288 μmol/h/g which is approximately 6,3 folds that of pristine g-C_3N_4 and O-g-C_3N_4 respectively and 1.6 folds that of mechanical mixed composite with the same Al_2O_3 mass content.The photocurrent density–time curves were carried out under visible light illumination for four on–off cycles.The electrochemical impedance spectroscopy(EIS) measurements verified the enhanced separation efficiency of electron–hole pairs.This work raised a new method to form the heterojunction structured photocatalysts and achieved a remarkable improvement of the photocatalytic activity in water splitting for hydrogen under visible light irradiation.     

Facile oxalic acid-assisted construction of laminated porous N-deficient graphitic carbon nitride: Highly efficient visible-light-driven hydrogen evolution photocatalyst

The laminated porous N-deficient g-C_3N_4(CN–H)is successfully synthesized by a facile two-step hydrothermal calcination method using oxalic acid-assisted melamine as the precursor.Compared with pristine g-C_3N_4(224μmol g~(-1)h~(-1)),the CN–H shows superior photocatalytic hydrogen production activity(up to 728μmol g~(-1)h~(-1)),which is three times higher than the unmodified counterpart.To draw out the multifaceted influences of oxalic acid modification on the visible-light-induced photocatalytic activity,various techniques are utilized to investigate the formation mechanism,structural characteristics and photoelectrical properties of CN–H.The results indicate that the addition of a trace amount of oxalic acid to the precursor melamine results in a g-C_3N_4 structure possessing the advantage of both nitrogen defects and laminated porosity.These properties can enlarge specific surface areas of g-C_3N_4,enhance an efficient separating of photogenerated electron-hole pairs and extend the range of spectral response,all contributing to the enhancement of the visible-light-induced photocatalytic activity.     

Reduced Ti-MOFs encapsulated black phosphorus with high stability and enhanced photocatalytic activity

The generation of green hydrogen(H_2) energy is of great significance to solve worldwide energy and environmental issues. Reduced Ti based photocatalyst has recently attracted intensive attention due to its excellent photocatalytic activity, while the synthesis of reduced Ti based photocatalysts with high stability is still a great challenge. Here, we report a facile method for synthesis of reduced Ti metal organic frameworks(small amounts of Pt incorporated) encapsulated BP(BP/R-Ti-MOFs/Pt) hybrid nanomaterial with enhanced photocatalytic activity. The strong interaction between Ti and P reduces the valence state of the binding Ti⁴⁺on the BP surface, forming abundant reduced Ti⁴⁺within R-Ti-MOFs/BP. Such reduced Ti⁴⁺render R-Ti-MOFs/BP efficient charge transfer and excellent light absorption capability, thus promote the photocatalytic H_2 production efficiency. Furthermore, the Ti-P interaction stabilizes both reduced Ti⁴⁺and BP during the photocatalytic reaction, which greatly enhanced the stability of the obtained BP/R-TiMOFs/Pt photocatalyst.     

A comparison of H+-restacked nanosheets and nano-scrolls derived from K4Nb6O17for visible-light degra-dation of dyes

H＋-restacked nanosheets and nanoscrolls peeled from K4Nb6O17 display different structures and surface characters. The two restacked samples with increased surface areas have an amazing visible-light response for the photodegradation of dyes, which is superior to commercial TiO2 （P25） and Nb205. By comparison, H＋/nanosheets have a relatively faster photodegradation rate originated from large and smooth basal plane. The work reveals that dye adsorbed on the unfolded nanosheets can effectively harvest sunlight. Due to facile preparation, low-cost and high photocatalytic efficiency, H＋/nanosheets and H＋/nanoscrolls might be used for the visible light-driven degradation of organic dyes as a substitute for TiO2 in industry.     

Wavelength-sensitive photocatalytic H_2 evolution from H_2S splitting over g-C_3N_4 with S,N-codoped carbon dots as the photosensitizer

Photocatalytic splitting of hydrogen sulfide(H2S) for hydrogen evolution is a promising method to solve the energy and environmental issues.In this work,S,N-codoped carbon dots(S,N-CDs)/graphitic carbon nitride(g-C3N4) nanosheet is synthesized by hydrothermal method as an efficient photocatalyst for the decomposition of H2S.In addition to the characterization of the morphology and structure,chemical state,optical and electrochemical performances of S,N-CDs/g-C3N4,hydrogen evolution tests show that the activity of g-C3N4 is improved by introducing S,N-CDs,and the enhancement depends strongly on the wavelength of incident light.The photocatalytic hydrogen production rate of S,N-CDs/g-C3N4 composite reaches 832 μmol g-1h-1, which is 38 times to that of g-C3N4 under irradiation at 460 nm.Density functional theory calculations and electron paramagnetic resonance as well as photoluminescence technologies have altogether authenticated that the unique wavelength-dependent photosensitization of S,N-CDs on g-C3N4;meanwhile,a good match between the energy level of S,N-CDs and g-C3N4 is pivotal for the effective photocatalytic activity.Our work has unveiled the detailed mechanism of the photocatalytic activity enhancement in S,N-CDs/g-C3N4 composite and showed its potential in photocatalytic splitting of H2S for hydrogen evolution.     

Preparation,characterization and photocatalytic properties of BiOBr/ZnO composites

BiOBr/ZnO composite photocatalysts were prepared by a simple hydrothermal method. The as-prepared samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), high-resolution transmission electron microscopy(HRTEM), UV–Vis diffusion reflectance spectroscopy(DRS) and photoluminescence(PL) spectroscopy, respectively. The photocatalytic activities were evaluated by the degradation of methyl blue(MB) under the simulated sunlight irradiation. Among all the samples, the BiOBr/ZnO composite with a mole ratio of 3:1(Bi:Zn) exhibited the best photocatalytic activity. The improvement of photocatalytic activity was mainly attributed to the low recombination ratio of photo-induced electron-hole pairs. The possible photocatalytic mechanism was discussed on the basis of the band structures of BiOBr and ZnO.     

Reinforced polysulfide barrier by g-C_3N_4/CNT composite towards superior lithium-sulfur batteries

The notorious shuttle effect has long been obstructing lithium-sulfur(Li-S) batteries from yielding the expected high energy density and long lifespan.Herein,we develop a multifunctional polysulfide barrier reinforced by the graphitic carbon nitride/carbon nanotube(g-C_3 N_4/CNT) composite toward inhibited shuttling behavior and improved battery performance.The obtained g-C_3 N_4 delivers a unique spongelike architecture with massive ion transfer pathways and fully exposed active interfaces,while the abundant C-N heteroatomic structures impose strong chemical immobilization toward lithium polysulfides.Combined with the highly conductive agent,the g-C_3 N_4/CNT reinforced separator is endowed with great capability of confining and reutilizing the active sulfur within the cathode,thus contributing to an efficient and stable sulfur electrochemistry.Benefiting from these synergistic attributes,Li-S cells based on g-C_3 N_4/CNT separator exhibit an excellent cyclability with a minimum decay rate of 0.03% per cycle over 500 cycles and decent rate capability up to 2 C.Moreover,a high areal capacity of 7.69 mAh cm^-2can be achieved under a raised sulfur loading up to 10.1 mg cm^-2.demonstrating a facile and efficient pathway toward superior Li-S batteries.     

Ultrathin zinc selenide nanosheet-based intercalation hybrid coupled with CdSe quantum dots showing enhanced photocatalytic CO_2 reduction

Fabrication of well-designed heterojunctions is an extraordinarily attractive pathway for boosting the photocatalytic activity toward CO_2 photoreduction.Herein,a novel kind of na nosheet-based intercalation hybrid coupled with CdSe quantum dots(QDs) was successfully fabricated by a facile solvothermal method and served as photocatalyst for full-spectrum-light-driven CO_2 reduction.Ultra-small CdSe QDs were rationally in-situ introduced and coupled with lamellar ZnSe-intercalation hybrid nanosheet,resulting in the formation of CdSe Q.Ds/ZnSe hybrid heterojunction.Significantly,the concentration of Cd~(2+) could change directly the crystallinity and micromorphology of ZnSe intercalation hybrid,which in turn would impact on the photocatalysis activity.The optimized CdSe QDs/ZnSe hybrid-5 composite demonstrated a considerable CO yield rate of the 25.6 μmol g~(-1) h~(-1) without any additional cocatalysts or sacrificial agents assisting,making it one of the best reported performance toward CO_2 photoreduction under full-spectrum light.The elevated CO_2 photoreduction activity could be attributed to the special surface heterojunction,leading to improving the ability of light absorption and promoting the separation/transfer of photogenerated carriers.This present study developed a new strategy for designing inorganic-organic heterojunctions with enhanced photocatalyst for CO_2 photoreduction and provided an available way to simultaneously mitigate the greenhouse effect and alleviate energy shortage pressure.     

Theoretical insights into interfacial and electronic structures of NiO_x/SrTiO_3 photocatalyst for overall water splitting

SrTiO_3 is a promising candidate photocatalyst for overall water splitting.Loading suitable cocatalysts,such as NiO_x,the mixture of Ni and NiO,remarkably improve the photocatalytic activity.However,spatial locations and functions of components in NiO_x/SrTiO_3 are under debate.Here,using first-principles density functional theory(DFT)calculations,we investigate the initial growth of Ni_n(n=1–4)and(NiO)_n(n=1,2 and 4)clusters on stoichiometric(100)surfaces of SrTiO_3,and explore interfacial and electronic structures of composite photocatalysts.It is found that Ni_n clusters are easier to undergo aggregation on SrO-termination than on TiO_2-termination.The adsorption of Ni_ncluster on(100)surfaces elevates the Fermi level towards the conduction band,which may benefit the occurrence of hydrogen evolution reaction.The structural similarity between(NiO)_n cluster and surface has an essential effect on the most stable adsorption configuration.For(NiO)_n/SrTiO_3 systems,the occupied states of(NiO)_n cluster well overlap with those of(100)surfaces in the valence band maximum,which is in favor of the separation of photogenerated electrons and holes to SrTiO_3 support and(NiO)_n cluster,respectively.The detailed DFT analysis provides important insights into the growth of NiO_x on surfaces of SrTiO_3and presents an explanation on the different models of NiO_x/SrTiO_3 photocatalyst proposed by experimental groups.Our calculations build a basis for further investigations on the mechanism of photocatalytic water-splitting reaction in NiO_x/SrTiO_3composite system.     

Magnetically recoverable Cu2O/Fe3O4 composite photocatalysts：Fabrication and photocatalytic activity

A magnetically separable Cu2O/Fe3O4 magnetic composite photocatalyst was synthesized in large quantities by a fast and simple route. The as-prepared photocatalysts were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）. Furthermore, the Cu2O/Fe3O4 composite photocatalysts were tested using methyl orange （MO） degradation reaction under visible light irradiation （100 mW/cm2） and demonstrated to have a high photocatalytic efficiency toward the decomposition of MO under visible light irradiation with good recyclability.     

Role of transition metal oxides in g-C3N4-based heterojunctions for photocatalysis and supercapacitors

g-C₃ N₄ emerges as a star 2 D photocatalyst due to its unique layered structure,suitable band structure and low cost.However,its photocatalytic application is limited by the fast charge recombination and low photoabsorption.Rationally designing g-C₃ N_4-based heterojunction is promising for improving photocatalytic activity.Besides,g-C₃ N₄ exhibits great potentials in electrochemical energy storage,In view of the excellent performa...     

Fabrication of macroporous polystyrene/graphene oxide composite monolith and its adsorption property for tetracycline

Macroporous polystyrene microsphere/graphene oxide(PS/GO) composite monolith was first prepared using Pickering emulsion droplets as the soft template. The Pickering emulsion was stabilized by PS/GO composite particles in-situ formed in an acidic water phase. With the evaporation of water and the oil phase(octane), the Pickering emulsion droplets agglomerated and combined with each other, forming a three-dimensional macroporous PS/GO composite matrix with excellent mechanical strength. The size of the macrospores ranged from 4 mm to 20 mm. The macroporous PS/GO composite monolith exhibited high adsorption capacity for tetracycline(TC) in an aqueous solution at p H 4–6. The maximum adsorption capacity reached 197.9 mg g 1at p H 6. The adsorption behaviour of TC fitted well with the Langmuir model and pseudo-second-order kinetic model. This work offers a simple and efficient approach to fabricate macroporous GO-based monolith with high strength and adsorption ability for organic pollutants.     

Synergistic impact of cocatalysts and hole scavenger for promoted photocatalytic H_2 evolution in mesoporous TiO_2–NiS_x hybrid

Photocatalytic solar energy conversion to hydrogen is sustainable and attractive for addressing the global energy and environmental issue. Herein, a novel photocatalytic system(NiS/Ni_3S_4 cocatalysts modified mesoporous TiO_2) with superior photocatalytic hydrogen evolution capability through the synergistic impact of NiS/Ni_3S_4(NiS_x) cocatalyst and efficient hole scavenger has been demonstrated. The photocatalytic hydrogen evolution of TiO_2–Ni Sxhybrids with the different content of Ni Sxand upon different organic hole scavengers was both investigated. The hybrid of TiO_2 decorated with 3%(mole ratio of Ni~(2+)) Ni Sxcocatalyst in methanol solution showed the optimal photocatalytic hydrogen evolution rate of 981.59 μmol h~(-1)g~(-1) which was about 20 times higher than that of bare mesoporous TiO2. Our results suggested that the boosted hydrogen production performance is attributed to both the improved photoinduced electrons migration between NiS and Ni_3S_4 in cocatalyst and the high hole captured efficiency by hole scavengers of methanol.     

A new trick on an old support: Zr in situ defects-created carbon nitride for efficient electrochemical nitrogen fixation

Electrochemical nitrogen reduction reaction(NRR) to produce ammonia under ambient conditions is considered as a promising approach to tackle the energy-intensive Haber-Bosch process,but the low Faradaic efficiency and yield of NH_3 are still a challenge.Herein,a carbon-vacancies enriched mesoporous g-C_3 N_4 is developed by an in situ Zr doping strategy.The in situ mesoporous-forming mechanism is deeply understood by TPSR to reveal the functions of Zr dopant that pulls C from the precursor of C_3 N_4,resulting the formation of homogeneous mesopores with about 57% of the one C-defective s-triazine ring in C_3 N_4.Due to the defect sites obtained in metal doping synthesis,the RuAu bimetallic supported catalyst(RuAu_3/0.3 Zr-C_3 N_4) exhibits effective NRR performance with a Faraday efficiency of 11.54% and an NH_3 yield of 5.28 μg h^-1 mg_cat ^-1.at-0.1 V(RHE),which is nearly 10 times higher than that of RuAu_3/C_3 N_4 catalyst.This work proposes a simple and template-free preparation method for the high defect density mesoporous C_3 N_4,and provides new possibilities of a wide application of mesopore g-C3 N4.     

Why the hydrothermal fluorinated method can improve photocatalytic activity of carbon nitride

Carbon nitride(CN) photocatalysts have attracted much attention due to their excellent photocatalytic properties.And hydrothermal fluorination is a common method to improve the photocatalytic effect of CN photocatalyst.Here,the influence of the band gap was first revealed of fluorination and hydroxylation of CN photocatalyst based on the first theoretical principle.Here,the effect of fluorination and hydroxylation on the CN band gap was discussed for the first time using the first theoretical principle.With F atoms and OH doping,the band gap of CN was significantly improved,conduction band and valence band moved up.Then,F-CN photocatalyst with F atoms and OH was successfully synthesized by a hydrothermal fluorinated method.Next,the reasons why F-CN photocatalyst was more effective than that of traditional CN photocatalyst were fully discussed.From the photocatalytic effect of photocatalyst(12,593.2 μmolg^-1 h^-1to the morphology(super-small nanosheets),structure(homojunctions),composition(metal-free),specific surface area(54.1 m²/g),visible light absorption response(AQE is10.9% at 420 nm) and photo-induced carrier life(14.13 ns).Therefore,this work has a great guiding effect on the development of CN photocatalyst.     

Preparation and characterization of highly photoactive nanocrystalline TiO_2 powders by solvent evaporation- induced crystallization method

Highly photoactive bi-phase nanocrystalline TiO2 photocatalyst was prepared by a solvent evaporation-induced crystallization (SEIC) method, and calcined at different temperatures. The obtained TiO2 photocatalyst was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results show that solvent evaporation can promote the crystallization and phase transformation of TiO2 at 100℃. When calcination temperatures are below 600℃, the prepared TiO2 powders show bimodal pore size distributions in the mesoporous region. At 700℃, the pore size distributions exhibit monomodal distribution of the inter-aggregated pores due to the collapse of the intra-aggregated pores. At 100℃, the obtained TiO2 photocatalyst by this method shows good photocatalytic activity, and at 400℃, its photocatalytic activity exceeds that of Degussa P25. This may be attributed to the fact t     

A 3D MIL-101@rGO composite as catalyst for efficient conversion of straw cellulose into valuable organic acid

Efficient conversion of straw cellulose to chemicals or fuels is an attracting topic today for the utilization of biomass to substitute for fossil resources. The development of catalysts is of vital importance.In this work, a composite catalyst metal-organic frameworks(MOFs) immobilized on three-dimensional reduced graphene oxide(3D-r GO) were synthesized by in situ growth of the MIL-101(Cr) within the 3Dr GO matrix. The supporting of 3D-r GO guaranteed the dispersion and acid site density of MI...