In situ One-Pot Fabrication of MoO3-x Clusters Modified Polymer Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution

Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production.In this work,molybdenum oxides(MoO3-x)were in situ loaded on polymer carbon nitride(PCN)via a simple one-pot impregnation-calcination approach.Different from post-impregnation method,intimate coupling interface between high-dispersed ultra-small MoO3-xnanocrystal and PCN was successfully formed during the in situ growth process.The MoO3-x-PCN-X(X=1,2,3,4)photocatalyst without noble platinum(Pt)finally exhibited enhanced photocatalytic hydrogen performance under visible light irradiation(λ>420 nm),with the highest hydrogen evolution rate of 15.6μmol/h,which was more than 3 times that of bulk PCN.Detailed structure-performance revealed that such improvement in visible-light hydrogen production activity originated from the intimate interfacial interaction between high-dispersed ultra-small MoO3-xnanocrystal and polymer carbon nitride as well as efficient charge carriers transfer brought by Schottky junction formed.

Electron-Deficient Zn-N_(6) Configuration Enabling Polymeric Carbon Nitride for Visible-Light Photocatalytic Overall Water Splitting

Despite of suitable band structures for harvesting solar light and driving water redox reactions,polymeric carbon nitride(PCN)has suffered from poor charge transfer ability and sluggish surface reaction kinetics,which limit its photocatalytic activity for water splitting.Herein,atomically dispersed Zn-coordinated three-dimensional(3D)sponge-like PCN(Zn-PCN)is synthesized through a novel intermediate coordination strategy.Advanced characterizations and theoretical calculations well evidence that Zn single atoms are coordinated and stabilized on PCN in the form of Zn-N_(6) configura-tion featured with an electron-deficient state.Such an electronic configuration has been demonstrated contributive to promoted electron excitation,accelerated charge separation and transfer as well as reduced water redox barriers.Further benefited from the abundant surface active sites derived from the 3D porous structure,Zn-PCN realizes visible-light photocatalysis for overall water splitting with H_(2) and O_(2) simultaneously evolved at a stoichiometric ratio of 2:1.This work brings new insights into the design of novel single-atom photocatalysts by deepening the understanding of electronic configurations and reactive sites favorable to excellent photocatalysis for water splitting and related solar energy conversion reactions.

Improved Plasmonic Hot‑Electron Capture in Au Nanoparticle/Polymeric Carbon Nitride by Pt Single Atoms for Broad‑Spectrum Photocatalytic H_(2)Evolution

ABSTRACT Rationally designing broad-spectrum photocatalysts to harvest whole visible-light region photons and enhance solar energy conversion is a“holy grail”for researchers,but is still a challenging issue.Herein,based on the common polymeric carbon nitride(PCN),a hybrid co-catalysts system comprising plasmonic Au nanoparticles(NPs)and atomically dispersed Pt single atoms(PtSAs)with different functions was constructed to address this challenge.For the dual co-catalysts decorated PCN(PtSAs–Au_(2.5)/PCN),the PCN is photoexcited to generate electrons under UV and short-wavelength visible light,and the synergetic Au NPs and PtSAs not only accelerate charge separation and transfer though Schottky junctions and metal-support bond but also act as the co-catalysts for H_(2) evolution.Furthermore,the Au NPs absorb long-wavelength visible light owing to its localized surface plasmon resonance,and the adjacent PtSAs trap the plasmonic hot-electrons for H_(2) evolution via direct electron transfer effect.Consequently,the PtSAs–Au_(2.5)/PCN exhibits excellent broad-spectrum photocatalytic H_(2) evolution activity with the H_(2) evolution rate of 8.8 mmol g^(−1) h^(−1) at 420 nm and 264μmol g^(−1) h^(−1) at 550 nm,much higher than that of Au_(2.5)/PCN and PtSAs–PCN,respectively.This work provides a new strategy to design broad-spectrum photocatalysts for energy conversion reaction.

Microwave awakening the n-π^(*) electronic transition in highly crystalline polymeric carbon nitride nanosheets for photocatalytic hydrogen generation

The n-π^(*) electronic transition in polymeric carbon nitride(PCN)can remarkably harvest visible light,which thus potentially promotes the photocatalytic hydrogen H2 generation.However,awaking the n-π^(*) lectronic transition has proven to be a grand challenge.Herein,we reported on the awakening of n-π^(*) electronic transition by microwave thermolysis of urea pellet,which yielded the PCN with absorption edge of 600 nm,near 140 nm red-shift from 460 nm of pristine PCN.The n-π^(*) electronic transition endows PCN with an increased photocata lytic H_(2) generation,with a highest H_(2) rate of 61.7μmol h^(-1) under visible light exposure,which is near 6 times higher than that by using the PCN from the thermolysis of urea pellets in an electric furnace(10.6μmol h^(-1)).Furthermore,the n-π^(*) transition in PCN leads to the longest wavelength of 535 nm that can initiate H2 generation,remarkably longer than the absorption edge of pristine PCN(460 nm).This work manifests the advantages of microwave sintering route to awaken the n-π^(*) electronic transition in PCN for an increased photocata lytic performance.

Two birds with one stone: Engineering polymeric carbon nitride with n-π^(*) electronic transition for extending light absorption and reducing charge recombination

The weak visible light harvesting and high charge recombination are two main problems that lead to a low photocatalytic H2 generation of polymeric carbon nitride(p-CN).To date,the approaches that are extensively invoked to address this problem mainly rely on heteroatom-doping and heterostructures,and it remains a grand challenge in regulating dopant-free p-CN for increasing H2 generation.Here,we report utilizing the inherent n-π^(*)electronic transition to simultaneously realize extended light absorption and reduced charge recombination on pCN nanosheets.Such n-π^(*)electronic transition yields a new absorption peak of 490 nm,which extends the light absorption edge of p-CN to approximately 590 nm.Meanwhile,as revealed by the photoluminescence(PL)spectra of p-CN at the single-particle level,the n-π*electronic transition gives rise to an almost quenched PL signal at room temperature,unravelling a dramatically reduced charge recombination.As a consequence,a remarkably improved photocatalytic performance is realized under visible light irradiation,with a H2 generation rate of 5553μmol g^(-1)·h^(-1),~12 times higher than that of pristine p-CN(460μmol·g^(-1)·h^(-1))in the absence of the n-π^(*)transition.This work illustrates the highlights of using the inherent n-π^(*)electronic transition to improve the photocatalytic performance of dopant-free carbon nitrides.

Enhanced photocatalytic performance of polymeric C_3N_4 doped with theobromine composed of an imidazole ring and a pyrimidine ring

Molecular doping has been proven to be an effective approach to adjusting the electronic structure of polymeric carbon nitride(PCN)and thus improving its optical properties and photocatalytic activity.Herein,theobromine,a compound composed of an imidazole ring and a pyrimidine ring,was first copolymerized with urea to prepared doped PCN.Experimental investigations and theoretical calculations indicate that,a narrowing in band gap and a positive shift in valence band positon happened to the theobromine doped PCN,owing to the synergistic effect between the pyrimidine ring and the imidazole ring in the theobromine molecule.Moreover,it is shown that the doping with theobromine at a suitable mass fraction makes the obtained sample exhibit decreased photoluminescent emission,enhanced photocurrent density,and reduced charge-transport resistance.Consequently,an enhancement in the photocatalytic activity for water oxidation is found for the sample,which oxygen evolution rate is 4.43 times higher than that of the undoped PCN.This work sheds light on the choice of the molecular dopants for PCN to improve its photocatalytic performance.

Two-dimensional polymeric carbon nitride: structural engineering for optimizing photocatalysis

As a two-dimensional(2D) material, polymeric carbon nitride(g-C_3N_4) nanosheet holds great potentials in environmental purification and solar energy conversion. In this review, we summarized latest progress in the optimization of photocatalytic performance in 2D g-C_3N_4. Some of the latest structural engineering methods were summed up, where the relevant influences on the behaviors of photoinduced species were emphasized. Furthermore, the construction strategies for band structure modulation and charge separation promotion were then discussed in detail. A brief discussion on the opportunity and challenge of 2D g-C_3N_4-based photocatalysis are presented as the conclusion of this review.

Mechanism on Carbon Vacancies in Polymeric Carbon Nitride for CO2 Photoreduction

Defect engineering has being regarded as one of the effective ways to regulate chemical and electronic structure of semiconductors.Recently,our collaborative work has shown experimentally that carbon vacancy on polymeric carbon nitride(CV)can greatly improve the CO2 to CO conversion with a 45-fold improvement over the polymeric carbon nitride(Angew.Chem.Int.Ed.,2019,58,1134).In order to clarify the detailed mechanism of promotion,we have systematically studied the electronic properties of CV and hydrogenated CV(CV+H)as well as the effective CO2 reduction reaction through density functional theory calculations.We found that it is the synergistic effect for the CO2 reduction reaction in the CV systems,as the onset potentials of several CVs are much lower than that of the polymeric carbon nitride.In particular,the onset potentials of CV1,CV2,and CV2+H are around 0.9~1.5 eV with a strong chemisorbed CO2 on them.Combined with the analysis of the electronic properties,our results confirm that defect engineering increases the lifetime of photo-generated charges,improves photocatalytic activity,and promotes the CO2 reduction reaction on the defected polymeric carbon nitrides.

Cationic surface polarization centers on ionic carbon nitride for efficient solar-driven H_(2)O_(2) production and pollutant abatement

Solar-driven H_(2)O_(2)production and emerging organic pollutants(EOPs)elimination are of great significance from the perspective of environmental sustainability.The efficiency of the photocatalytic reaction system is the key challenge to be addressed.In this work,the strategy of constructing surface ionic local polarization centers to enhance the exciton dissociation of the polymeric photocatalytic is demonstrated.Selected bipyridinium cation(TMAP)is complexed on a K^(+)-incorporated carbon nitride(CNK)framework,and the combination of local polarization centers both on the surface(bipyridinium cation)and bulk(K+cation)contributes to a superior photocatalytic H_(2)O_(2)production performance,affording a remarkable H_(2)O_(2)generation rate of 46.8μmol h^(-1)mg^(-1)and a high apparent quantum yield(AQY)value of 77.5%under irradiation of 405 nm photons.As substantiated experimentally by steady state/transient spectroscopy techniques,the surface local polarization centers increase the population of the long-lived trapped electrons,and thereby promote the interfacial charge transfer process for chemical conversion reaction.The strategy is potentially applicable to the design of a wide range of efficient solar-to-chemical conversion systems.

Semi-heterogeneous photo-Cu-dual-catalytic cross-coupling reactions using polymeric carbon nitrides

A merger of copper catalysis and semiconductor photocatalysis using polymeric carbon nitride(PCN)for multi-type cross-coupling reactions was developed.This dual-catalytic system enables mild C-H arylation,chalcogenation,and C-N cross-coupling reactions under visible light irradiation with a broad substrate scope.Good-to-excellent yields were obtained with appreciable site selectivity and functional group tolerance.Metal-free and low-cost PCN photocatalyst can easily be recovered and reused several times.

A facile method to introduce a donor-acceptor system into polymeric carbon nitride for efficient photocatalytic overall water splitting

It is a prospective strategy to produce sustainable energy by photocatalytic overall water splitting(POWS).This work aims to develop a simple method for integrating a donor-acceptor system into polymeric car-bon nitride(PCN)structure,which could accelerate the charge separation significantly.In the as-prepared photocatalyst(COCNT),carbon and oxygen were successfully incorporated into the framework of PCN,and the chemical environment of C and O was well probed by X-ray absorption near-edge structure(XANES)and X-ray photoelectron spectroscopy(XPS).It showed that the C-containing and O-containing segments of COCNT played the role of a donor,while the heptazine part played the role of an acceptor.In addition,Density-functional-theory(DFT)calculations confirmed the spatial split of the highest occupied molec-ular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)for promoting charge separation.Impressively,COCNT could efficiently split pure water to generate hydrogen and oxygen.And,the photo-catalytic hydrogen evolution rate over COCNT(1550.9μmol g^(-1)h^(-1))is about 17-fold higher than that of PCN.Finally,we proposed a possible photocatalytic mechanism to explain the above results.

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO_(2) Reduction to C1 Products

Photocatalytic CO_(2)reduction to C1 fuels is considered to be an important way for alleviating increasingly serious energy crisis and environmental pollution.Due to the environment-friendly,simple preparation,easy formation of highly-stable metal-nitrogen(M-Nx)coordination bonds,and suitable band structure,polymeric carbon nitride-based single-atom catalysts(C_(3)N_(4)-based SACs)are expected to become a potential for CO_(2)reduction under visible-light irradiation.In this review,we summarize the recent advancement on C_(3)N_(4)-based SACs for photocatalytic CO_(2)reduction to C1 products,including the reaction mechanism for photocatalytic CO_(2)reduction to C1 products,the structure and synthesis methods of C_(3)N_(4)-based SACs and their applications toward photocatalytic CO_(2)reduction reaction(CO_(2)RR)for C1 production.The current challenges and future opportunities of C_(3)N_(4)-based SACs for photoreduction of CO_(2)are also discussed.

Biomimetic high-flux proton pump constructed with asymmetric polymeric carbon nitride membrane

Biological proton pumps ferry protons in an active manner and have a high flux(a few to 10 protons/(s·nm^(2))).Integrating these features in an artificial membrane may open the way for a wide range of applications but it remains challenging.In this work,we employed a structural engineering strategy to construct an asymmetric photonic polymeric carbon nitride(C3N4)membrane that exhibited photo-driven high flux proton pumping performance.The ion transport path through the membrane is reminiscent of that in the high-flux asymmetric biological ion channel.In addition,it has a photonic structure that mimics the mosquito compound eyes with improved light adsorption.Finally,the asymmetric structure constitutes an isotype(n-n)heterojunction that enhances the separation of the light-induced electron-hole pairs.As a result,the membrane shows a flux of 89μA/cm^(2)under 100 mW/cm^(2)white light illumination(approximately one sun),the highest ever reported.This translates to a pumping rate of~6 proton/(s·nm^(2)),comparable to the biological counterpart.This work highlights the potential of multi-level structural engineering to construct high-performance bionic devices,and may find applications in solar energy harvesting and solar powered membrane process.

Promoting condensation kinetics of polymeric carbon nitride for enhanced photocatalytic activities

Polymeric carbon nitride(CN)semiconductor by thermal condensation of N-rich precursors has attracted much attention for its capability ranging from photocatalytic and photoelectrochemical energy conversion to biosensing.However,the influence of condensation process on the final structure of CN was rarely studied,making the condensation kinetic far from be fully optimized.Herein,we report the preparation of CN by a simple condensation kinetics modulation using a faster ramping rate during the polymerization process.The modified condensation recipe was even simpler than the conventional one,but led to an improved photocatalytic H2 evolution up to 3 times without any additional chemicals or other complements.Detailed mechanism studies revealed the increase of crystallinity and surface area due to the rapid condensation played the key roles.This work would offer a more facile and effective way to prepare bulk CN for large-scale industrial applications of bulk CN with higher photocatalytic actives for sustainable energy,environmental and biosensing.

Anchoring Single Nickel Atoms on Carbon-vacant Carbon Nitride Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Polymeric carbon nitride(PCN)has emerged as a promising candidate for photocatalytic hydrogen evolution,but its dependence on scarce and high-cost noble metal co-catalysts severely limits its extensive application.It will be of great promise to develop non-noble metal single-atom co-catalysts with low-cost and high atom utilization to improve the photocatalytic performance over PCN.Herein,single Ni atoms are successfully anchored onto carbon-vacant PCN nanosheets(CCN-SANi)via a two-step ammonia thermal treatment and photo-deposition process.Theoretical calculations and experimental results demonstrate that the optical absorption property and the charge transfer ability of CCN-SANi have been significantly improved with the introduction of single Ni atoms to form Ni-N3 sites.In comparison to carbon-vacant PCN(CCN)loaded with Ni clusters,the obtained CCN-SANi exhibits 11.4 times increased photocatalytic performance,with the highest hydrogen evolution rate reaching 511μmol/(g·h),which is even 1.7 times higher than that of CCN loaded with Pt clusters.This research proposes an inspiring and reliable strategy to design novel single-atom semiconducting polymers with electronic structures manipulated for efficient photocatalysis.

Promoting near-infrared photocatalytic activity of carbon-doped carbon nitride via solid alkali activation

Ultrabroad spectral absorption is required for semiconductor photocatalysts utilized for solar-to-chemical energy conversion.The light response range can be extended by element doping,but the photocatalytic performance is generally not enhanced correspondingly.Here we present a solid alkali activation strategy to synthesize near-infrared(NIR)light-activated carbon-doped polymeric carbon nitride(A-cPCN)by combining the copolymerization of melamine and 1,3,5-trimesic acid.The prepared A-cPCN is highly crystalline with a narrowed bandgap and enhanced efficiency in the separation of photogenerated electrons and holes.Under irradiation with NIR light(780 nm≥λ≥700 nm),A-cPCN shows an excellent photocatalytic activity for H_(2)generation from water with rate of 165µmol g^(−1)h^(−1),and the photo-redox activity for H_(2)O_(2)production(109µmol g^(−1)h^(−1))from H_(2)O and O_(2),whereas no observed photocatalytic activity over pure PCN.The NIR photocatalytic activity is due to carbon doping,which leads to the formation of an interband level,and the alkali activation that achieved shrinking the transfer distance of photocarriers.The current synergistic strategy may open insights to fabricate other carbon-nitrogen-based photocatalysts for enhanced solar energy capture and conversion.

Water Molecule-Triggered Anisotropic Deformation of Carbon Nitride Nanoribbons Enabling Contactless Respiratory Inspection

The exploitation of the interaction between nanostructured matter and small molecules,such as H_(2)O at interfaces via dynamic hydrogen bonding,is essentially the key for smart,responsive nanodevices but remains challenging.Herein,the authors report that the carbon nitride nanoribbons(CNNRs)with an anisotropic intraplanar and interplanar molecular arrangement underwent a deformation by H_(2)O triggering.Both experiments of bulk samples and single nanoribbons disclosed that the reversible formation of a hydrogen-bonded H_(2)O adsorption layer was the source of the CNNRs deformation,reminiscent of the hydration-triggered twist of natural bean pods in seeding.Nonetheless,CNNRs had a more balanced H_(2)O affinity,enabling a superior response and recovery time.By coupling with carbon nanotubes,the authors also converted the deformation of CNNRs into more straightforward electrical readouts with record-fast response time.Further applied to capture fluctuations in humidity in real-time respiration,a higher detection sensitivity was obtained in a contactless mode,which compared favorably with the clinical breath-testing station.Given the carbon nitride family with various C/N ratios,surface properties,and topography,this finding that CNNRs are an outstanding H_(2)O transducer would significantly pave the way for the H_(2)O-triggered smart devices in broad prospective applications.

金属原子诱导的微环境调控在聚合氮化碳光催化析氢中的研究

开发高效稳定的半导体光催化剂对光催化技术迈向实际应用至关重要.聚合物氮化碳(CN)因其优异的物理化学性质而被视为最具发展前景的制氢光催化剂之一.在过去几十年中,从热力学或动力学角度开发的一系列改性策略已经显著提升了CN的光催化制氢性能.近期,金属原子修饰策略为CN改性提供了一条新途径,这种策略可以精确调控CN的微环境.本文全面回顾了金属原子修饰的CN光催化剂在光催化分解水制氢领域的最新研究进展,包括金属单原子修饰的CN、金属双原子修饰的CN、金属单原子与团簇共修饰的CN,重点阐述了金属原子对提升光催化性能的关键作用.此外,本文还全面总结了发展先进的金属原子修饰的CN光催化剂所面临的挑战与机遇.

Molecular engineering of C_(x)N_(y):Topologies,electronic structures and multidisciplinary applications

As a class of metal-free two-dimensional(2D)semiconductor materials,polymeric carbon nitrides have attracted wide attention recently due to its facile regulation of the molecular and electronic structures,availability in abundance and high stability.According to the different ratios of C and N atoms in the fra mework,a series of C_(x)N_(y)materials have been successfully synthesized by virtue of various precursors,which further triggers extensive investigations of broad applications ranging from sustainable photocatalytic reactions and highly sensitive optoelectronic biosensing.In view of topological structures on their electronic structures and material properties,the as-reported C_(x)N_(y)could be generally classified into two main categories with three-or six-bond-extending frameworks.Owing to the effective n→π*transition in most C_(x)N_(y)materials,the relative energy level of the lone-pair electrons on N atoms is high,which thus endows the mate rials with the capability of visible light absorption.Meanwhile,the different repeating units,bridging groups and defect sites of these two kinds of C_(x)N_(y)allow them to effectively drive a diverse of promising applications that require specific electronic,inte rfacial and geometric properties.This review paper aims to summarize the recent progress in topological structure design and the relevant electronic band structures and striking properties of C_(x)N_(y)materials,In the final part,we also discuss the existing challenges of C_(x)N_(y)and outlook the prospect possibilities.