Advances in poly(heptazine imide)/poly(triazine imide) photocatalyst

Polymeric carbon nitride(PCN)has garnered increasing attention as a metal-free photocatalyst with a suitable band gap.In efforts to enhance its photocatalytic performance,researchers have examined various PCN materials,including poly(heptazine imide)(PHI)and poly(triazine imide)(PTI),two isomers within the PCN family that exhibit distinct and superior photocatalytic activity compared to other forms.The challenge,however,lies in the common practice among researchers to categorize PHI and PTI along with other PCN types under the overarching term“g-C_(3)N_(4),”which significantly impedes optimization efforts.The objective of this review is to provide comprehensive insights into the structural features,photoelectrochemical properties,and effective characterization methods employed for distinguishing between PHI and PTI materials.The review also summarizes various optimization strategies,such as crystallinity adjustments,defect engineering,morphology control,constructing heterojunction,and atomic-level metal loading dispersion,to elevate the photocatalytic activity of PHI and PTI,in addition to summarizing the history of carbon nitride development.Furthermore,this review highlights the primary applications of PHI and PTI,encompassing nitrogen fixation,biomass conversion,organic synthesis,CO_(2)reduction,pollutant degradation,H_(2)O_(2)production,and photocatalytic water splitting.Lastly,the prospects and challenges associated with further advancing PHI and PTI are thoroughly examined.

S-scheme heterojunction/Schottky junction tandem synergistic effect promotes visible-light-driven catalytic activity

Designing photocatalysts with high light utilization and efficient photogenerated carrier separation for pollutant degradation is one of the important topics for sustainable development.In this study,hierarchical core–shell materialα-Fe_(2)O_(3)@ZnIn_(2)S_(4)with a step-scheme(S-scheme)heterojunction is synthesized by in situ growth technique,and MXene Ti_(3)C_(2)quantum dots(QDs)are introduced to construct a double-heterojunction tandem mechanism.The photodegradation efficiency ofα-Fe_(2)O_(3)@ZnIn_(2)S_(4)/Ti_(3)C_(2)QDs to bisphenol A is 96.1%and its reaction rate constant attained 0.02595 min^(−1),which is 12.3 times that of pureα-Fe_(2)O_(3).Meanwhile,a series of characterizations analyze the reasons for the enhanced photocatalytic activity,and the charge transport path of the S-scheme heterojunction/Schottky junction tandem is investigated.The construction of the S-scheme heterojunction enables the photo-generated electrons ofα-Fe_(2)O_(3)and the holes of ZnIn2S4 to transfer and combine under the action of the reverse built-in electric field.Due to the metallic conductivity of Ti_(3)C_(2)QDs,the photogenerated electrons of ZnIn_(2)S_(4)are further transferred to Ti_(3)C_(2)QDs to form a Schottky junction,which in turn forms a double-heterojunction tandem mechanism,showing a remarkable charge separation efficiency.This work provides a new opinion for the construction of tandem double heterojunctions to degrade harmful pollutants.

Fully conversing and highly selective oxidation of benzene to phenol based on MOFs-derived CuO@CN photocatalyst

Developing highly efficient photocatalysts for selective oxidation of benzene to phenol is of great significance. However, it is still challenging to simultaneously achieve high conversion rate and selectivity.Herein, we demonstrate 99.9% of benzene photoconversion and 99.1% of phenol selectivity under the illumination of AM 1.5 for 12 h. For this purpose, an advanced CuO@CN photocatalyst has been fabricated by loading tubular carbon nitride(CN) with CuO nanoparticles thermally polymerized from Cu-based metal-organic frameworks(MOFs). The sluggish photocharge carrier recombination rate and the excellent stability indicate that the as-prepared nanocomposite is an ideal photocatalyst for benzene oxidation application. This work paves a new avenue for designing novel photocatalyst based on MOFs and carbon nitride materials.

Engineering of SnO_(2)/TiO_(2) heterojunction compact interface with efficient charge transfer pathway for photocatalytic hydrogen evolution

Fabricating an efficient charge transfer pathway at the compact interface between two kinds of semiconductors is an important strategy for designing hydrogen production heterojunction photocatalysts.In this work,we prepared a compact,stable and oxygen vacancy-rich photocatalyst(SnO_(2)/TiO_(2) heterostructure)via a simple and reasonable in-situ synthesis method.Briefly,SnCl_(2)–2H_(2)O is hydrolyzed on the TiO_(2) precursor.After the pyrolysis process,SnO_(2) nanoparticles(5 nm)were dispersed on the surface of ultrathin TiO_(2) nanosheets uniformly.Herein,the heterojunction system can offer abundant oxygen vacancies,which can act as active sites for catalytic reactions.Meanwhile,the interfacial contact of SnO_(2)/TiO_(2) grading semiconductor oxide is uniform and tight,which can promote the separation and migration of photogenerated carriers.As shown in the experimental results,the hydrogen production rate of SnO_(2)/TiO_(2) is 16.7 mmol h^(-1)g^(-1)(4.4 times higher than that of TiO_(2)),which is owing to its good dynamical properties.This work demonstrates an efficient strategy of tight combining SnO_(2)/TiO_(2) with abundant oxygen vacancies to improve catalytic efficiency.

Composites of small Ag clusters confined in the channels of well-ordered mesoporous anatase TiO2 and their excellent solar-light-driven photocatalytic performance

Small Ag clusters confined in the channels of ordered mesoporous anatase TiO2 have been fabricated via a vacuum-assisted wet-impregnation method, utilizing well-ordered mesoporous anatase TiO2 with high thermal stability as the host. The composites have been characterized in detail by X-ray diffraction, X-ray photoelectron spectroscopy X-ray absorption fine structure （XAFS） spectroscopy, N2 adsorption, UV-visible diffuse reflectance spectroscopy and transmission electron microscopy. The results indicate that small Ag clusters are formed and uniformly confined in the channels of mesoporous TiO2 with an obvious confinement effect. The presence of strong AgO interactions involving the Ag clusters in intimate contact with the pore walls of mesoporous TiO2 is confirmed by XAFS analysis, and favors the separation of photogenerated electron-hole pairs, as shown by steady-state surface photovoltage spectroscopy and transient-state surface photovoltage measurements. The ordered mesoporous Ag/TiO2 composites exhibit excellent solar-light-driven photocatalytic performance for the degradation of phenol. This is attributed to the synergistic effects between the small Ag clusters acting as traps to effectively capture the photogenerated electrons, and the surface plasmon resonance of the Ag clusters promoting the absorption of visible light. This study clearly demonstrates the high-efficiency utilization of noble metals in the fabrication of high-performance solar-light-driven photocatalysts.

Nitrogen-doped graphene supported Pd@PdO core- shell clusters for C-C coupling reactions

The introduction of nitrogen significantly decreases the metal particle size and improves the performance of metal-based graphene-supported catalysts. In this work, the density functional theory is used to understand the interaction between nitrogen-doped graphene and Pd@PdO clusters. Experiments show that small size Pd@PdO clusters （1-2 nm） can be grown uniformly on nitrogen-doped graphene sheets by a facile oxidation-reduction method. The nanoscale interaction relationship between nitrogen-doped graphene and Pd@PdO clusters is investigated through X-ray photoelectron spectroscopy （XPS） and X-ray absorption spectra （XAS）. The composite catalysts are applied in Suzuki-Miyaura reactions giving high yields and good structural stability. These results have potential impact in design and optimization of future high performance catalyst materials for cross coupling reactions.

Synergetic enhancement of surface reactions and charge separation over holey C_(3)N_(4)/TiO_(2)2D heterojunctions

Efficient charge separation and rapid interfacial reaction kinetics are crucial factors that determine the efficiency of photocatalytic hydrogen evolution.Herein,a fascinating 2D heterojunction photocatalyst with superior photocatalytic hydrogen evolution performance–holey C_(3)N_(4)nanosheets nested with TiO_(2)nanocrystals(denoted as HCN/TiO_(2))–is designed and fabricated via an in situ exfoliation and conversion strategy.The HCN/TiO_(2)is found to exhibit an ultrathin 2D heteroarchitecture with intimate interfacial contact,highly porous structures and ultrasmall TiO_(2)nanocrystals,leading to drastically improved charge carrier separation,maximized active sites and the promotion of mass transport for photocatalysis.Consequently,the HCN/TiO_(2)delivers an impressive hydrogen production rate of 282.3 lmol h^(-1)per10 mg under AM 1.5 illumination and an apparent quantum efficiency of 13.4%at a wavelength of 420 nm due to the synergetic enhancement of surface reactions and charge separation.The present work provides a promising strategy for developing high-performance 2D heterojunctions for clean energy applications.

Constructing Pd-N interactions in Pd/g-C_(3)N_(4)to improve the charge dynamics for efficient photocatalytic hydrogen evolution

The formation of chemical bonds between metal ions and their supports is an effective strategy to achieve good catalytic activity.However,both the synthesis of active metal species on a support and control of their coordination environment are still challenging.Here,we show the use of an organic compound to produce tubular carbon nitride(TCN)as a support for Pd nanoparticles(NPs),creating a composite material(NP-Pd-TCN).It was found that Pd ions preferentially bind with the electron-rich N atoms of TCN,leading to strong metal-support interactions that benefit charge transfer from g-C_(3)N_(4)to Pd.X-ray absorption spectroscopy further revealed that the metal-support interactions resulted in the formation of Pd-N bonds,which are responsible for the improvement in the charge dynamics as evidenced by the results from various techniques including photoluminescence(PL)spectroscopy,photocurrent measurements,and electrochemical impedance spectroscopy(EIS).Owing to the good dynamical properties,NP-Pd-TCN was used for photocatalytic hydrogen evolution under visible-light irradiation(λ>420 nm)and an excellent evolution rate of~381μmol·h^(-1)(0.02 g of the photocatalyst)was attained.This work aims to promote a strategy to synthesize efficient photocatalysts for hydrogen production by controllably introducing metal nanoparticles on a support and in the meantime forming chemical bonds to achieve intimate metal-support contact.

Creation of Mo active sites on indium oxide microrods for photocatalytic amino acid production

As an n-type semiconductor, In_(2)O_(3)is considered a promising photocatalyst for producing amino acids using biomass derivatives as precursors. However, similar to other intrinsic semiconductors, In_(2)O_(3)suffers from poor charge dynamics. Herein, we show the synthesis of Mo-doped In_(2)O_(3)(Mo-In_(2)O_(3)) with a porous rod-shaped structure through a onestep solvothermal reaction followed by calcination. Under visible-light irradiation, Mo-In_(2)O_(3)achieves a high conversion rate of 81% for the reaction that transforms lactic acid into alanine with a selectivity of 91%. Spectroscopic techniques and density functional theory calculations reveal that Mo doping introduces defect states slightly below the conduction band of In_(2)O_(3), which improves the separation of photogenerated electron-hole pairs. In addition, Mo atoms on the surface form extra adsorption and reaction centers that greatly enhance the reaction rate. This work provides insights into the development of transition metal-doped semiconductor photocatalysts to produce amino acids.

Supramolecular precursor derived loofah sponge-like Fe_(2)O_(x)/C for effective synergistic reaction of Fenton and photocatalysis

Fenton or photocatalytic degradations of organic contaminants are recognized as promising approaches to address the increasing environmental pollution issues.Herein,we develop the effective synergistic catalysis reaction of Fenton and photocatalysis based on a loofah sponge-like Fe_(2)O_(x)/C nanocomposite,which exhibits excellent nitrobenzene photocatalytic degradation property.It is noted that Fe2O3 nanoparticles with surface Fe^(2+) species were encapsulated with an ultrathin carbon layer(denoted as Fe_(2)O_(x)/C)via a supramolecular self-sacrificing template and following thermal treatment process.The experimental results indicated that the thin layer carbon coating not only inhibited the Fe iron leaching from the Fe_(2)O_(x)but also prompted the separation and transferring of electrons–hole pairs.The introduction of Fe_(2)O_(x)/C enables the Fenton reaction to induce a rapid Fe^(2+)/Fe^(3+)cycle,and meanwhile,together with the photocatalytic reaction to produce continuous active substances for the subsequent degradation catalytic reaction without successive H2O2,resulting in the inexpensive and the effective photocatalytic procedure.As a result,100%nitrobenzene(100 mg/L)was degraded and 97%of the organic carbon was mineralized in 90 min using the Fe_(2)O_(x)/C(0.1 g/L)at a low H_(2)O_(2) dosage(0.50 mM),under air mass(AM)1.5 irradiation.Theoretical calculations confirmed that the Fe_(2)O_(x)/C-600 with thin carbon layer promoted the dissociation of H2O2 and the·OH desorption.The synergistic catalysis of this work may provide new ideas for low-cost and more efficient treatment of pollutants.

A facile solution phase synthesis of directly ordering monodisperse FePt nanoparticles

The ordered Pt-based intermetallic nanoparticles(NPs)with small size show superior magnetic or catalytic properties,but the synthesis of these NPs still remains a great challenge due to the requirement of high temperature annealing for the formation of the ordered phase,which usually leads to sintering of the NPs.Here,we report a simple approach to directly synthesize monodisperse ordered L1_(0)-FePt NPs with average size 10.7 nm without further annealing or doping the third metal atoms,in which hexadecyltrimethylammonium chloride(CTAC)was found to be the key inducing agent for the thermodynamic growth of the Fe and Pt atoms into the ordered intermetallic structure in the synthetic process.In particular,10.7 nm L1_(0)-FePt NPs synthesized by the proper amount of CTAC show a coercivity of 3.15 kOe and saturation magnetization of 45 emu/g at room temperature.The current CTAC-assisted synthetic strategy makes it possible to deeply understand the formation of the ordered Pt-based intermetallic NP in solution phase synthesis.