Enhancing multifunctional photocatalysis with acetate-assisted cesium doping and unlocking the potential of Z-scheme solar water splitting

Graphitic carbon nitride(g-C_(3)N_(4))has been extensively doped with alkali metals to enlarge photocatalytic output,in which cesium(Cs)doping is predicted to be the most efficient.Nevertheless,the sluggish diffusion and doping kinetics of precursors with high melting points,along with imprecise regulation,have raised the debate on whether Cs doping could make sense.For this matter,we attempt to confirm the positive effects of Cs doping on multifunctional photocatalysis by first using cesium acetate with the character of easy manipulation.The optimized Csdoped g-C_(3)N_(4)(CCN)shows a 41.6-fold increase in visible-light-driven hydrogen evolution reaction(HER)compared to pure g-C_(3)N_(4) and impressive degradation capability,especially with 77%refractory tetracycline and almost 100%rhodamine B degradedwithin an hour.The penetration ofCs+is demonstrated to be a mode of interlayer doping,and Cs–N bonds(especially with sp^(2) pyridine N in C═N–C),along with robust chemical interaction and electron exchange,are fabricated.This atomic configuration triggers the broadened spectral response,the improved charge migration,and the activated photocatalytic capacity.Furthermore,we evaluate the CCN/cadmium sulfide hybrid as a Z-scheme configuration,promoting the visible HER yield to 9.02 mmol g^(−1) h^(−1),which is the highest ever reported among all CCN systems.This work adds to the rapidly expanding field of manipulation strategies and supports further development of mediating served for photocatalysis.

Engineering g-C_(3)N_(4)based materials for advanced photocatalysis:Recent advances

Photocatalysis driven by abundant yet intermittent solar energy has considerable potential in renewable energy generation and environmental remediation.The outstanding electronic structure and physicochemical properties of graphitic carbon nitride(g-C_(3)N_(4)),together with unique metal-free characteristic,make them ideal candidates for advanced photocatalysts construction.This review summarizes the up-to-date advances on g-C_(3)N_(4)based photocatalysts from ingenious-design strategies and diversified photocatalytic applications.Notably,the advantages,fabrication methods and limitations of each design strategy are systemically analyzed.In order to deeply comprehend the inner connection of theory–structure–performance upon g-C_(3)N_(4)based photocatalysts,structure/composition designs,corresponding photocatalytic activities and reaction mechanisms are jointly discussed,associated with introducing their photocatalytic applications toward water splitting,carbon dioxide/nitrogen reduction and pollutants degradation,etc.Finally,the current challenges and future perspectives for g-C_(3)N_(4)based materials for photocatalysis are briefly proposed.These design strategies and limitations are also instructive for constructing g-C_(3)N_(4) based materials in other energy and environment-related applications.

Core-Shell Semiconductor-Graphene Nanoarchitectures for Efficient Photocatalysis:State of the Art and Perspectives

Semiconductor photocatalysis holds great promise for renewable energy generation and environment remediation,but generally suffers from the serious drawbacks on light absorption,charge generation and transport,and structural stability that limit the performance.The core-shell semiconductorgraphene(CSSG)nanoarchitectures may address these issues due to their unique structures with exceptional physical and chemical properties.This review explores recent advances of the CSSG nanoarchitectures in the photocatalytic performance.It starts with the classification of the CSSG nanoarchitectures by the dimensionality.Then,the construction methods under internal and external driving forces were introduced and compared with each other.Afterward,the physicochemical properties and photocatalytic applications of these nanoarchitectures were discussed,with a focus on their role in photocatalysis.It ends with a summary and some perspectives on future development of the CSSG nanoarchitectures toward highly efficient photocatalysts with extensive application.By harnessing the synergistic capabilities of the CSSG architectures,we aim to address pressing environmental and energy challenges and drive scientific progress in these fields.

From the perspective of experimental practice: High-throughput computational screening in photocatalysis

Photocatalysis,a critical strategy for harvesting sunlight to address energy demand and environmental concerns,is underpinned by the discovery of high-performance photocatalysts,thereby how to design photocatalysts is now generating widespread interest in boosting the conversion effi-ciency of solar energy.In the past decade,computational technologies and theoretical simulations have led to a major leap in the development of high-throughput computational screening strategies for novel high-efficiency photocatalysts.In this viewpoint,we started with introducing the challenges of photocatalysis from the view of experimental practice,especially the inefficiency of the traditional“trial and error”method.Sub-sequently,a cross-sectional comparison between experimental and high-throughput computational screening for photocatalysis is presented and discussed in detail.On the basis of the current experimental progress in photocatalysis,we also exemplified the various challenges associated with high-throughput computational screening strategies.Finally,we offered a preferred high-throughput computational screening procedure for pho-tocatalysts from an experimental practice perspective(model construction and screening,standardized experiments,assessment and revision),with the aim of a better correlation of high-throughput simulations and experimental practices,motivating to search for better descriptors.

Synthesis of crystalline g-C_(3)N_(4) with rock/molten salts for efficient photocatalysis and piezocatalysis

Graphitic carbon nitride(g-C_(3)N_(4))is emerging as a promising visible-light photocatalyst while the low crystallinity with sluggish charge separation/migration dynamics significantly restricts its practical applications.Currently,synthesizing highly crystalline g-C_(3)N_(4) with sufficient surface activities still remains challenging.Herein,different from using alkali molten salts which is commonly reported,we propose an approach for synthesis of highly crystalline g-C_(3)N_(4) with FeCl3/KCl rock/molten mixed salts.The rock salt can serve as the structure-directing template while molten salt provides the required liquid medium for re-condensation.Intriguingly,the synthesized photocatalyst showed further enhanced crystallinity and improved surface area along with high p/p*excitation compared with crystalline C_(3)N_(4) prepared from conventional molten-salt methods.These catalytically advantageous features lead to its superior photocatalytic and piezocatalytic activities with a high reactivity for overall water splitting that is not commonly reported for C_(3)N_(4).This work provides an effective strategy for structural optimization of organic semiconductor based materials and may inspire new ideas for the design of advanced photocatalysts.

Atomic Ni directional-substitution on ZnIn_(2)S_(4) nanosheet to achieve the equilibrium of elevated redox capacity and efficient carrier-kinetics performance in photocatalysis

It is a challenge to coordinate carrier-kinetics performance and the redox capacity of photogenerated charges synchronously at the atomic level for boosting photocatalytic activity.Herein,the atomic Ni was introduced into the lattice of hexagonal ZnIn_(2)S_(4) nanosheets(Ni/ZnIn_(2)S_(4))via directionalsubstituting Zn atom with the facile hydrothermal method.The electronic structure calculations indicate that the introduction of Ni atom effectively extracts more electrons and acts as active site for subsequent reduction reaction.Besides the optimized light absorption range,the elevation of Efand ECBendows Ni/ZnIn_(2)S_(4) photocatalyst with the increased electron concentration and the enhanced reduction ability for surface reaction.Moreover,ultrafast transient absorption spectroscopy,as well as a series of electrochemical tests,demonstrates that Ni/ZnIn_(2)S_(4) possesses 2.15 times longer lifetime of the excited charge carriers and an order of magnitude increase for carrier mobility and separation efficiency compared with pristine ZnIn_(2)S_(4).These efficient kinetics performances of charge carriers and enhanced redox capacity synergistically boost photocatalytic activity,in which a 3-times higher conversion efficiency of nitrobenzene reduction was achieved upon Ni/ZnIn_(2)S_(4).Our study not only provides in-depth insights into the effect of atomic directional-substitution on the kinetic behavior of photogenerated charges,but also opens an avenue to the synchronous optimization of redox capacity and carrier-kinetics performance for efficient solar energy conversion.

Rational design of photofunctional dyes BODIPYs/aza-BODIPYs and applications for photocatalysis, photoelectric conversion and thermochromic materials

4,4-Difluoro-4-bora-3a,4a-diaza-sindacene (BODIPY) is a sort of photofunctional dye which possesses advantages including strong light-capturing property, high photon-resistance, etc. Meso-N substituted aza-BODIPY is a crucial derivative of BODIPY scaffold that has the favorable optical properties and a significant spectral redshift. The photophysical properties can be tuned by molecular design, and the attenuation path of the excited state energy release of absorbed light energy can be well controlled via structural modifications, enabling tailored application. It has been extensively employed in life medicine fields including fluorescence imaging diagnosis, photodynamic therapy photosensitizer and photothermal therapy reagent and so forth. Extensive research and review have been performed in these areas. However, BODIPYs/aza-BODIPYs have a significant role in energy, catalysis, optoelectronics, photo-responsive materials and other fields. Nevertheless, there are relatively few studies and reviews in these fields on the modification and application based on BODIPY/aza-BODIPY scaffold. Herein, in this review we summarized the application of BODIPY/aza-BODIPY in the aforementioned fields, with the molecular regulation of dye as the foundation and the utilization in the above fields as the objective, in the intention of providing inspiration for the exploration of innovative BODIPY/aza-BODIPY research in the field of light resource conversion and functional materials.

Ternary Ag/AgCl/BiOIO_3 composites for enhanced visible-light-driven photocatalysis

Ternary Ag/AgC l/BiO IO3 composite photocatalysts are prepared by a facile method. Enhanced visible-light absorption and charge carrier separation are achieved after the introduction of Ag/AgC l particles into BiO IO3 systems,as revealed by ultraviolet-visible diffuse-reflectance spectrometry,photocurrent response and electrochemical impedance spectroscopy. The Ag/AgC l/BiO IO3 composites are applied to the visible-light photocatalytic oxidization of NO in air and exhibit an enhanced activity for NO removal in comparison with Ag/AgC l and pure BiO IO3. A possible photocatalytic mechanism for Ag/AgC l/BiO IO3 is proposed,which is related to the surface plasmon resonance effects of Ag metal and the effective carrier separation ability of BiO IO3. This work provides insight into the design and preparation of BiO IO3-based materials with enhanced visible-light photocatalysis ability.

Photocatalysis of TiO2 Sheets Prepared by Templating Filter Paper

Titanium dioxide sheet photocatalysts composed of interwoven microstrips were successfully synthesized using filter paper as templates. The synthesized samples were characterized by means of Fourier transform infrared spectroscopy, surface area analyzer, thermogravimetric analysis, powder X-ray diffraction, and scanning electron microscopy. The photocatalytic activities of the samples were evaluated by the degradation of methyl orange in an aqueous solution under UV-illumination. The results demonstrated that the paper-like TiO2 sheets with the optimum proportion of anatase/rutile （10/1） had the highest photoactivity. And the presence of the filter paper fiber can improve the crystallinity, raise the anatase-rutile transformation temperature and contribute to the formation of being paper-like. A detailed formation mechanism for TiO2 sheets is proposed.

Hydrogenation and Ammoniation of SrTiO3 for an Enhanced Visible-light Photocatalysis

Hydrogenation and ammoniation of SrTiOa （STO）, a normal ultraviolet photocatalyst, were performed by annealing STO（100） in Hz：N2=5%：95% and NH3, respectively, at various temperatures T. It was found that hydrogenation at T≥900℃ remarkably enhanced the UV photocatalytic ability of STO, but the visible-light photocatalysis was still unavailable, while ammoniation at T≥800℃ introduced the N doping, resulting in visible-light photocat- alytie activity. Furthermore, when a hydrogenated STO was subjected to ammoniation, the visible-light photocatalytie ability was nearly the same as that of the ammoniated one; but the hydrogenation of an ammoniated one significantly enhanced visible-light photoeatalysis, indicating a synergetic effect of hydrogenation and ammoniation. Discussions and identifications have been made to analyze these results.

Thermal nitridation of triazine motifs to heptazine-based carbon nitride frameworks for use in visible light photocatalysis

A thermal nitridation route for the assembly and polymerization of molecular triazine units to heptazine-based covalent frameworks has been successfully established. The obtained conjugated carbon nitride polymers feature nanostructures that show enhanced photocatalytic reactivity for hydrogen production under visible light irradiation.

Fabrication of a β-Bi_2O_3/BiOI heterojunction and its efficient photocatalysis for organic dye removal

To improve β-Bi2O3 photocatalysis,we couple β-Bi2O3 with BiO I to form β-Bi2O3/BiO I heterojunctions through an in-situ treatment with hydriodic acid. The prepared heterojunctions are characterized with X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy,ultra violet-diffuse reflectance spectroscopy,and X-ray photoelectron spectroscopy. Upon visible-light irradiation（λ 420 nm）,the β-Bi2O3/BiO I heterojunctions,especially with the molar ratio of HI to β-Bi2O3 at 0.4,exhibit much higher photocatalytic activity than pure β-Bi2O3 and BiO I for the degradation of methyl orange. The efficient separation of photogenerated electron-hole pairs across the interface of the heterojunction between β-Bi2O3 and BiO I would be responsible for the enhanced photocatalytic performances.

Synergistic effects in N‐K_2Ti_4O_9/UiO‐66‐NH_2 composites and their photocatalysis degradation of cationic dyes

N-K2Ti4O9/UiO-66-NH2 composites synthesized by a facile solvothermal method have a core-shell structure with UiO-66-NH2 forming the shell around a N-K2Ti4O9 core.Their photocatalytic activities in the degradation of dyes under visible light irradiation were investigated.The N-K2Ti4O9/UiO-66-NH2 composites exhibited higher photocatalytic activity than the pure components.This synergistic effect was due to the high adsorption capacity of UiO-66-NH2 and that the two components together induced an enhanced separation efficiency of photogenerated electron-hole pairs.The mass ratio of N-K2Ti4O9 to ZrCl4 of 3：7 in the composite exhibited the highest photocatalytic activity.Due to the electrostatic attraction between the negatively charged backbone of UiO-66-NH2with the positively charged groups of cationic dyes,the composites were more photocatalytically active for cationic dyes than for anionic dyes.

Rare earth ion modified TiO_2 sols for photocatalysis application under visible light excitation

TiO_2 sols modified by rare earth (RE) ions (Ce^(4+), Eu^(3+), or Nd^(3+))were prepared by coprecipitation-peptization method. The photocatalysis activity was studied byinvestigating the photodegradation effects of active brilliant red dye X-3B. It is found that TiO_2sols modified by Ce^(4+), Eu^(3+), or Nd^(3+) have the anatase crystalline structure, which areprepared at 70℃. All RE^(n+)-TiO_2 sol samples have uniform nanoparticles with similar morphology,which are homogenously distributed in aqueous colloidal systems. The particle sizes are 10, 8, and12 nm for Nd^(3+)-TiO_2, Eu^(3+)-TiO_2, and Ce^(4+)-TiO_2, respectively. The character of ultrafineand positive charge sol particles contributes to the good adsorption of X-3B dye molecule on thesurface of titania (about 30% X-3B adsorption amount). Experimental results exhibit thatRE^(n+)-TiO_2 sol photocatalysts have the capability to photodegrade X-3B under visible lightirradiation. Nd^(3+)-TiO_2 and Eu^(3+)-TiO_2 show higher photocatalytic activity than Ce^(4+)-TiO_2,which is due to the difference of standard redox potential of RE^(n+)/RE^((n-1)+). RE^(n+)-TiO_2sols demonstrate more excellent interfacial adsorption and photodegradation effects to X-3B thanP_(25) TiO_2 crystallites. Moreover, the degradation mechanism of X-3B is proposed as dyephotosensitization and electron scavenging by rare earth ions.

Multifarious roles of carbon quantum dots in heterogeneous photocatalysis

As a new member of carbon material family, carbon quantum dots (CQDs) have attracted tremendous attentions for their potentials in the heterogeneous photocatalysis applications. Due to the unique microstructure and optical properties, the roles of CQDs played in the CQDs-based photocatalytic systems have been found to be diverse with the continuous researches in this regard. Herein, we provide a concise minireview to elaborate the multifarious roles of CQDs in photocatalysis, including photoelectron mediator and acceptor, photosensitizer, photocatalyst, reducing agent for metal salt, enhancing adsorption capacity and spectral converter. In addition, the perspectives on future research trends and challenges are proposed, which are anticipated to stimulate further research into this promising field on designing a variety of efficient CQDs-based photocatalysts for solar energy conversion. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

2D MXenes as Co-catalysts in Photocatalysis:Synthetic Methods

Since their seminal discovery in 2011,two-dimensional(2D)transition metal carbides/nitrides known as MXenes,that constitute a large family of 2D materials,have been targeted toward various applications due to their outstanding electronic properties.MXenes functioning as co-catalyst in combination with certain photocatalysts have been applied in photocatalytic systems to enhance photogenerated charge separation,suppress rapid charge recombination,and convert solar energy into chemical energy or use it in the degradation of organic compounds.The photocatalytic performance greatly depends on the composition and morphology of the photocatalyst,which,in turn,are determined by the method of preparation used.Here,we review the four different synthesis methods(mechanical mixing,self-assembly,in situ decoration,and oxidation)reported for MXenes in view of their application as co-catalyst in photocatalysis.In addition,the working mechanism for MXenes application in photocatalysis is discussed and an outlook for future research is also provided.

Differences and Similarities of Photocatalysis and Electrocatalysis in Two-Dimensional Nanomaterials:Strategies,Traps,Applications and Challenges

Photocatalysis and electrocatalysis have been essential parts of electrochemical processes for over half a century.Recent progress in the controllable synthesis of 2D nanomaterials has exhibited enhanced catalytic performance compared to bulk materials.This has led to significant interest in the exploitation of 2D nanomaterials for catalysis.There have been a variety of excellent reviews on 2D nanomaterials for catalysis,but related issues of differences and similarities between photocatalysis and electrocatalysis in 2D nanomaterials are still vacant.Here,we provide a comprehensive overview on the differences and similarities of photocatalysis and electrocatalysis in the latest 2D nanomaterials.Strategies and traps for performance enhancement of 2D nanocatalysts are highlighted,which point out the differences and similarities of series issues for photocatalysis and electrocatalysis.In addition,2D nanocatalysts and their catalytic applications are discussed.Finally,opportunities,challenges and development directions for 2D nanocatalysts are described.The intention of this review is to inspire and direct interest in this research realm for the creation of future 2D nanomaterials for photocatalysis and electrocatalysis.

A review on heterogeneous photocatalysis for environmental remediation:From semiconductors to modification strategies

Heterogeneous photocatalysis,an advanced oxidation process,has garnered extensive attention in the field of environmental remediation because it involves the direct utilization of solar energy for the removal of numerous pollutants.However,the application of heterogeneous photocatalysis in environmental remediation has not achieved the expected consequences due to enormous challenges such as low photocatalytic efficiencies and high costs of heterogeneous photocatalysts in large-scale practical applications.Furthermore,pollutants in the natural environment,including water,air,and solid phases,are diverse and complex.Therefore,extensive efforts should be made to better understand and apply heterogeneous photocatalysis for environmental remediation.Herein,the fundamentals of heterogeneous photocatalysis for environmental remediation are introduced.Then,potential semiconductors and their modification strategies for environmental photocatalysis are systematically presented.Finally,conclusions and prospects are briefly summarized,and the direction for the future development of environmental photocatalysis is explored.This review may provide reference directions toward understanding,researching,and designing photocatalytic remediation systems for various environmental pollutants.

Heterostructured ZnFe_2O_4/Fe_2TiO_5/TiO_2 Composite Nanotube Arrays with an Improved Photocatalysis Degradation Efficiency Under Simulated Sunlight Irradiation

To improve the visible light absorption and photocatalytic activity of titanium dioxide nanotube arrays(TONTAs), ZnFe_2O_4(ZFO) nanocrystals were perfused into pristine TONTA pipelines using a novel bias voltageassisted perfusion method. ZFO nanocrystals were well anchored on the inner walls of the pristine TONTAs when the ZFO suspensions(0.025 mg m L^(-1)) were kept under a60 V bias voltage for 1 h. After annealing at 750 °C for2 h, the heterostructured ZFO/Fe_2 TiO_5(FTO)/TiO_2 composite nanotube arrays were successfully obtained. Furthermore, Fe^(3+)was reduced to Fe^(2+)when solid solution reactions occurred at the interface of ZFO and the pristine TONTAs. Introducing ZFO significantly enhanced thevisible light absorption of the ZFO/FTO/TONTAs relative to that of the annealed TONTAs. The coexistence of type I and staggered type II band alignment in the ZFO/FTO/TONTAs facilitated the separation of photogenerated electrons and holes, thereby improving the efficiency of the ZFO/FTO/TONTAs for photocatalytic degradation of methylene blue when irradiated with simulated sunlight.

Photocatalytic nitrogen fixation: An attractive approach for artificial photocatalysis

Ammonia synthesis via the Haber-Bosch process, which has been heralded as the most important invention of the 20 th century, consumes massive amounts of energy, around 1%–2% of the world’s annual energy consumption. Developing green and sustainable strategies for NH3 synthesis under ambient conditions, using renewable energy, is strongly desired, by both industrial and sci-entific researchers. Artificial photosynthesis for ammonia synthesis, which has recently attracted significant attention, directly produces NH3 from sunlight, and N2 and H2O via photocatalysis. This has been regarded as an ideal, energy-saving and environmentally-benign process for NH3 produc-tion because it can be performed under normal temperature and atmospheric pressure using re-newable solar energy. Although sustainable developments have been achieved since the pioneering work in 1977, many challenging issues（e.g., adsorption and activation of nitrogen molecules on the surface of photocatalysts under mild conditions） have still not been well solved and the photocata-lytic activities are generally low. In this miniature review, I summarize the most recent progress of photocatalytic N2 fixation for ammonia synthesis, focusing specifically on two attractive aspects for adsorption and activation of nitrogen molecules： one is engineering of oxygen vacancies, and the other is mimicking natural nitrogenase for constructing artificial systems for N2 fixation. Several representative works focusing on these aspects in artificial systems have been reported recently, and it has been demonstrated that both factors play more significant roles in photocatalytic N2 re-duction and fixation under ambient conditions. At the end of the review, I also give some remarks and perspective on the existing challenges and future directions in this field.