Design of metal-organic frameworks(MOFs)-based photocatalyst for solar fuel production and photo-degradation of pollutants

Metal organic frameworks(MOFs)is a research hotspot in the solar fuel production and photo-degradation of pollutants field due to high surface area,rich metal/organic species,large pore volume,and adjustability of structures and compositions.Therefore,in this review,we first summarized the design factors of photocatalytic materials based on MOF from the perspective of"star"MOF.The modification strategies of MOFs-based photocatalysts were discussed to improve its photocatalytic activity and specific applications were summarized as well,including photocatalytic CO_(2)reduction,photocatalytic water splitting and photo-degradation of pollutants.Finally,the advantages and disadvantages of MOFs-based photocatalysts were discussed,the current challenges were highlighted,and suggestions for future research directions were proposed.

CdBiO2Br nanosheets in situ strong coupling to carbonized polymer dots and improved photocatalytic activity for organic pollutants degradation

Carbonized polymer dots(CPDs)modified layer-structured CdBiO_(2)Br(CPDs/CdBiO_(2)Br)Z-scheme heterojunction hybrid material has been synthesized via simple solvothermal method.The hybrid material with Z-scheme heterojunction can effectively maintain the original highly oxidizing holes of CdBiO_(2)Br and the highly reducing electrons of CPDs.In addition,the construction of heterostructure is beneficial to the migration and separation of photogenerated carriers.Under visible light irradiation,6 wt%CPDs/CdBiO_(2)Br showed the best catalytic activity for degradation of organic pollutants.Free radical capture experiments and ESR analysis confirmed that the main active species are·O_(2)^(-)and h^(+).The decomposition process of organic pollutants was analyzed by LC-MS.Finally,the probable visible light mechanism performance of CPDs/CdBiO_(2)Br as direct Z-scheme heterojunction photocatalytic materials was proposed.

Terpyridine-based metallo-cuboctahedron nanomaterials for efficient photocatalytic degradation of persistent organic pollutants

Metal–organic cage photocatalysts with nanoscale dimensions have received wide attention in the field of photocatalytic environmental pollutant treatment due to their large cavities,easy modification,high tunability,and enriched active sites.Herein,we prepared a series of dihydroanthracene-cored terpyridine-based metallo-cuboctahedron nanomaterials through a selfassembly method,which exhibited satisfactory degradation performance for persistent organic pollutants under visible light irradiation.In particular,under light conditions,S1-Zn,one of the prepared nanomaterials,produced photogenerated holes oxidizing water molecules to∙OH,which attacked ibuprofen(IBU)for up to 95% degradation.Simultaneously,the corresponding photogenerated electrons reduced the dissolved oxygen in water,producing 66.2μmol/L hydrogen peroxide.The obtained supramolecular photocatalytic materials have a stable structure with non-precious metals and do not require a sacrificial agent.The metal sites of metallo-cuboctahedrons adsorb pollutants and transfer captured holes to them,accelerating degradation and promoting simultaneous H_(2)O_(2) production.This work not only proposes a simple and efficient synthesis method for supramolecular photocatalysts but also opens up opportunities for efficient,low-cost,and multifunctional materials for environmental persistent organic pollutants treatment.

One-step preparation of Fe_xO_y/N-GN/CNTs heterojunctions as a peroxymonosulfate activator for relatively highly-efficient methylene blue degradation

Persulfate decontamination technologies utilizing radical‐driven processes are powerful tools for the treatment of a broad range of impurities.However,the design of high‐performance catalytic activators with multi‐functionality remains a great challenge.Therefore,in this study,three‐dimensional multifunctional FexOy/N‐GN/CNTs(N‐GN:nitrogen‐doped graphene,CNTs:carbon nanotubes)heterojunctions,which can be employed as microwave absorbers and catalysts,were synthesized via a solvothermal method and applied to activate peroxymonosulfate for the degradation of methylene blue(MB).X‐ray diffraction(XRD),Fourier transform infrared spectrometer(FTIR),scanning electron microscope(SEM),and X‐ray photoelectron microscopy(XPS)analyses revealed that the FexOy were anchored in‐situ onto the N‐GN network.Using MB as the model organic dye,various factors,such as degradation systems,PMS loading,initial organic pollutant concentration,and catalyst dosage were optimized.The results revealed that the remarkable efficiency was attributable to the synergistic effects of carbon,nitrogen,and iron‐based species.The oxidation system corresponded to the pseudo‐first‐order kinetic with a k value of^0.33 min^-1.It was demonstrated that both SO4^-and OH^-were the predominant reactive species through quenching experiments.Because these heterojunctions were employed as microwave absorbers and have a semiconductor‐like texture,the Fe/N co‐rich hierarchical porous carbon skeleton favored electron transport and storage.These heterojunctions increase the options for transitional metal catalysts and highlights the importance of designing other heterojunctions for specific applications,such as supercapacitors,energy storage,CO2 capture,and oxygen reduction electrocatalysts.

The Degradation and Pollution of Soils on the Territory of the Kovykta Gas Condensate Field

In this paper, research results from the time interval 2002-2012 are used to give an account of the chemical composition of soils on the territory of the Kovykta gas condensate field. The findings presented provide a better understanding of the ecological state of soil cover, its resilience to anthropogenic impacts, and its possible disturbance caused by the drilling pad construction activity, and by the laying of geophysical profiles. An analysis of soil pollution for the study territory generally showed that the soils are polluted with chemical elements which refer to toxicity classes： Pb, Cu, Ni, Cr, Ba and Mn. High levels ofoil products were detected near boreholes. Strong mineralization was recorded in the soil near borehole. It has a chloride-sodium chemical composition. As a result of the construction of foundation pits, recesses, ditches and earth embankments, the soil is totally destroyed, and rock outcrops show up. Disturbances of the sod cover due to road construction or even by all-terrain vehicles in these extreme conditions entail an accelerated development of linear erosion to form scours and gullies. Elimination of the canopy layer leads to an increase in surface heating, and to an acceleration of permafrost thawing. Swamping is accelerated on negative relief forms due to the increased entry of melt waters.

Self-adaptive bulk/surface engineering of Bi_(x)O_(y)Br_(z) towards enhanced photocatalysis:Current status and future challenges

The bulk/surface states of semiconductor photocatalysts are imperative parameters to maneuver their performance by significantly affecting the key processes of photocatalysis including light absorption,separation of charge carrier,and surface site reaction.Recent years have witnessed the encouraging progress of self-adaptive bulk/surface engineered Bi_(x)O_(y)Br_(z) for photocatalytic applications spanning various fields.However,despite the maturity of current research,the interaction between the bulk/surface state and the performance of Bi_(x)O_(y)Br_(z) has not yet been fully understood and highlighted.In this regard,a timely tutorial overview is quite urgent to summarize the most recent key progress and outline developing obstacles in this exciting area.Herein,the structural characteristics and fundamental principles of Bi_(x)O_(y)Br_(z)for driving photocatalytic reaction as well as related key issues are firstly reviewed.Then,we for the first time summarized different self-adaptive engineering processes over Bi_(x)O_(y)Br_(z)followed by a classification of the generation approaches towards diverse Bi_(x)O_(y)Br_(z)materials.The features of different strategies,the up-to-date characterization techniques to detect bulk/surface states,and the effect of bulk/surface states on improving the photoactivity of Bi_(x)O_(y)Br_(z)in expanded applications are further discussed.Finally,the present research status,challenges,and future research opportunities of self-adaptive bulk/surface engineered Bi_(x)O_(y)Br_(z)are prospected.It is anticipated that this critical review can trigger deeper investigations and attract upcoming innovative ideas on the rational design of Bi_(x)O_(y)Br_(z)-based photocatalysts.

Hetero-Janus Nanofibers as an Ideal Framework for Promoting Water-pollutant Photoreforming Hydrogen Evolution

Photoreforming hydrogen evolution(Pr-HE)of a water-pollutant system could simultaneously achieve efficient hydrogen production and pollutant degradation.It provides a new way to solve energy and environmental issues,but the poor internal charge separation still limits its performance.This work designed hetero-Janus nanofibers(HJNFs)with ordered electric field distribution and separated redox surfaces to promote Pr-HE of the water-pollutant system.Taking ZnO/NiO heterojunction as an example,the hetero-Janus structures were prepared via"Dual-channel"electrospinning and further confirmed by the element morphology analysis and asymmetric distribution of the XPS spectra.The theoretical simulation showed that Janus structures could effectively inhibit the electron trap and hole trap generation,then accelerate the directional carrier migration to the surface.Experimental investigations also confirmed that Janus structures could effectively suppress internal exciton luminescence and accelerate surface charge transfer.The Pr-HE amount and the corresponding propranolol(PRO)degradation rate of HJNFs were 7.9 and 1.5 times higher than hetero-mixed nanofibers(HMNFs).The enhancement factor of Pr-HE in water-PRO to pure water was about 3.1,but nearly zero for HMNFs.This prominent synergistic effect was due to the enhancement of charge separation and the inhibition of cascade side reaction from hetero-Janus structures.Furthermore,the synchronous Pr-HE and degradation reactions were significantly promoted by selective introducing Ag nanoparticles in one side of the HJNFs for enlarging the interfacial Fermi energy level difference.The hetero-Janus strategy offers a new perspective on designing efficient photoreforming photocatalysts for energy and environment applications.

Graphitized Cu-β-cyclodextrin polymer driving an efficient dual-reaction-center Fenton-like process by utilizing electrons of pollutants for water purification

Excessive consumption of energy and resources is a major challenge in wastewater treatment.Here,a novel heterogeneous Fenton-like catalyst consisting of Cu-doped graphenelike catalysts (Cu-GCD NSs) was first synthesized by an enhanced carbothermal reduction of β-cyclodextrin (β-CD).The catalyst exhibits excellent Fenton-like catalytic activity for the degradation of various pollutants under neutral conditions,accompanied by low H_(2)O_(2)consumption.The results of structural characterization and theoretical calculations confirmed that the dual reaction centers (DRCs) were constructed on Cu-GCD NSs surface through C-O-Cu bonds supported on zero-valent copper species,which play a significant role in the high-performance Fenton-like reaction.The pollutants that served as electron donors were decomposed in the electron-poor carbon centers,whereas H_(2)O_(2)and dissolved oxygen obtained these electrons in the electron-rich Cu centers through C-O-Cu bonds,thereby producing more active species.This study demonstrates that the electrons of pollutants can be efficiently utilized in Fenton-like reactions by DRCs on the catalyst surface,which provides an effective strategy to improve Fenton-like reactivity and reduce H_(2)O_(2)consumption.

Bicarbonate activation of hydrogen peroxide: A new emerging technology for wastewater treatment

The serious limitations of available technologies for decontamination of wastewater have compelled researchers to search for alternative solutions. Catalytic treatment with hydrogen peroxide, which appears to be one of the most efficient treatment systems, is able to degrade various organics with the help of powerful ·OH radicals. This review focuses on recent progress in the use of bicarbonate activated hydrogen peroxide for wastewater treatment. The introduction of bicarbonate to pollutant treatment has led to appreciable improvements, not only in process efficiency, but also in process stability. This review describes in detail the applications of this process in homogeneous and heterogeneous systems. The enhanced degradation, limited or lack of leaching during heterogeneous degradation, and prolonged catalysts stability during degradation are salient features of this system. This review provides readers with new knowledge regarding bicarbonate, including the fact that it does not always harm pollutant degradation, and can significantly benefit degradation under some conditions.

Heterojunction between anodic TiO_2/g-C_3N_4 and cathodic WO_3/W nano-catalysts for coupled pollutant removal in a self-biased system

An anodic TiO2/g-C3N4 hetero-junction and cathodic WO3/W were used to build a self-sustained catalytic fuel cell system for oxidizing rhodamine B or triclosan and reducing NO3^--N to N2 simultaneously.The WO3 nano-catalyst was formed in situ by heating and oxidizing a tungsten wire in air.Cyclic voltammetry and current-time curves were used to characterize the electrochemical properties of the electrodes and system.Aeration and activation of molecular oxygen by self-biased TiO2/g-C3N4 led to the formation of reactive oxidizing species in the fuel cell.The mechanism of simultaneous anodic oxidation of pollutants and cathodic reduction of nitrate was proposed.The spontaneously formed circuit and tiny current were used simultaneously in treating two kinds of wastewater in the reactor chambers,even without light illumination or an external applied voltage.This new catalytic pollution control route can lower energy consumption and degrade many other kinds of pollutants.

Interfacial engineering of graphitic carbon nitride(g-C_3N_4)-based metal sulfide heterojunction photocatalysts for energy conversion: A review

As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C3N4) has become research hotspots in the community. However, g-C3N4 photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C3N4-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C3N4-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C3N4,(2) modification strategies of g-C3N4,(3) design principles of TMS-modified g-C3N4 heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories:(1) Type I heterojunction,(2) Type II heterojunction,(3) p-n heterojunction,(4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C3N4-based heterostructured photocatalysts in H2 evolution, CO2 reduction, N2 fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C3N4-based heterostructured photocatalysts toward practical benefits for a sustainable future.

A review on TiO_2-based Z-scheme photocatalysts

TiO2‐based Z‐scheme photocatalysts have attracted considerable attention because of the low recombination rate of their photogenerated electron–hole pairs and their high photocatalytic efficiency.In this review,the reaction mechanism of Z‐scheme photocatalysts,recent research progress in the application of TiO2‐based Z‐scheme photocatalysts,and improved methods for photocatalytic performance enhancement are explored.Their applications,including water splitting,CO2reduction,decomposition of volatile organic compounds,and degradation of organic pollutants,are also described.The main factors affecting the photocatalytic performance of TiO2‐based Z‐scheme photocatalysts,such as pH,conductive medium,cocatalyst,architecture,and mass ratio,are discussed.Concluding remarks are presented,and some suggestions for the future development of TiO2‐based Z‐scheme photocatalysts are highlighted.

Two-Dimensional Transition Metal Oxide and Chalcogenide-Based Photocatalysts

Two-dimensional(2D) transition metal oxide and chalcogenide(TMO&C)-based photocatalysts have recently attracted significant attention for addressing the current worldwide challenges of energy shortage and environmental pollution. The ultrahigh surface area and unconventional physiochemical, electronic and optical properties of 2D TMO&Cs have been demonstrated to facilitate photocatalytic applications. This review provides a concise overview of properties, synthesis methods and applications of 2D TMO&C-based photocatalysts. Particular attention is paid on the emerging strategies to improve the abilities of light harvesting and photoinduced charge separation for enhancing photocatalytic performances,which include elemental doping, surface functionalization as well as heterojunctions with semiconducting and conductive materials. The future opportunities regarding the research pathways of 2D TMO&C-based photocatalysts are also presented.

SYNTHESIS OF HYDROPHILIC ZnS NANOCRYSTALS AND THEIR APPLICATION IN PHOTOCATALYTIC DEGRADATION OF DYE POLLUTANTS

Hydrophilic ZnS nanocrystals with narrow size distribution were synthesized via homogeneous precipita- tion using EDTA as stabilizer. The as-synthesized products were characterized with XRD, TEM, HRTEM and UV-Vis spectrum. UV-Vis spectra showed that ZnS nanocrystals exhibited strong quantum-confined effect with a blue shift in the band gap of light absorbance. The photocatalytic activity of these nanocrystals was also investigated for the liquid phase photocatalytic degradation of Basic Violet 5BN (BV5) dye under UV irradiation. It was found that the ZnS nanocrystals had good catalytic activity for photodegradation of BV5.

Hydrogen producing water treatment through mesoporous TiO2 nanofibers with oriented nanocrystals

The development of well-defined TiO2 nanoarchitectures is a versatile strategy to achieve high-efficiency photocatalytic performance.In this study,mesoporous TiO2 nanofibers consisting of oriented nanocrystals were fabricated by a facile vapothermal-assisted topochemical transformation of preformed H-titanate nanobelts.The vapothermal temperature is crucial in tuning the microstructures and photocatalytic redox properties of the resulting mesoporous TiO2 nanofibers.The microstructures were characterized with XRD,TEM,XPS and nitrogen adsorption-desorption isotherms,etc.The photocatalytic activities were evaluated by photocatalytic oxidation of organic pollutant(Rhodamine B as an example)as well as photocatalytic reduction of water to generate hydrogen(H2).The nanofibers vapothermally treated at 150°C showed the highest photocatalytic activity in both oxidation and reduction reactions,2 times higher than that of P25.The oriented alignment and suitable mesoporosity in the resulting nanofiber architecture were crucial for enhancing photocatalytic performances.The oriented alignment of anisotropic anatase nanocrystals shall facilitate faster vectorial charge transportation along the nanofibers architecture.And,the suitable mesoporosity and high surface area would also effectively enhance the mass exchange during photocatalytic reactions.We also demonstrate that efficient energy-recovering photocatalytic water treatments could be accomplished by a cascading oxic-anoxic process where the dye is degraded in the oxic phase and hydrogen is generated in the successive anoxic phase.This study showcases a novel and facile method to fabricate mesoporous TiO2 nanofibers with high photocatalytic activity for both clean energy production and environmental purification.

Metal‐organic framework‐derived multifunctional photocatalysts

Metal‐organic framework(MOF)‐derived nanomaterials have attracted widespread attention,because the excellent features,such as high surface area,porosity and tunable properties are inherited from MOFs.Moreover,the derivatives avoid the poor conductivity and stability of MOFs.MOF‐derived nanomaterials can easily be regulated by a specific selection of metal nodes and organic linkers,resulting in multifunctionality in photocatalysis.MOF derivatives can be used not only as semiconductor photocatalysts,but also as co‐catalysts for photocatalytic hydrogen evolution,CO_(2) reduction,pollutants degradation,etc.This review focuses on the multifunctional applications of MOF derivatives in the field of photocatalysis.The researches in recent years are analyzed and summarized from the aspects of preparation,modification and application of MOF derivatives.At the end of the review,the development and challenges of MOF derivatives applied in photocatalysis in the future are put forward,in order to provide more references for further research in this field and bring new inspiration.

Phosphorene-Based Heterostructured Photocatalysts

Semiconductor photocatalysis is a potential pathway to solve the problems of global energy shortage and environmental pollution.Black phosphorus(BP)has been widely used in the field of photocatalysis owing to its features of high hole mobility,adjustable bandgap,and wide optical absorption range.Nevertheless,pristine BP still exhibits unsatisfactory photocatalytic activity due to the low separation efficiency of photoinduced charge carriers.In recent years,the construction of heterostructured photocatalysts based on BP has become a research hotspot in photocatalysis with the remarkable improvement of photoexcited charge-separation efficiency.Herein,progress on the design,synthesis,properties,and applications of BP and its corresponding heterostructured photocatalysts is summarized.Furthermore,the photocatalytic applications of BP-based heterostructured photocatalysts in water splitting,pollutant degradation,carbon dioxide reduction,nitrogen fixation,bacterial disinfection,and organic synthesis are reviewed.Opportunities and challenges for the exploration of advanced BP-based heterostructured photocatalysts are presented.This review will promote the development and applications of BP-based heterostructured photocatalysts in energy conversion and environmental remediation.

Recent Progress,Challenges,and Prospects in Two‑Dimensional Photo‑Catalyst Materials and Environmental Remediation

The successful photo-catalyst library gives significant information on feature that affects photo-catalytic performance and proposes new materials.Competency is considerably significant to form multi-functional photo-catalysts with flexible characteristics.Since recently,two-dimensional materials(2DMs)gained much attention from researchers,due to their unique thickness-dependent uses,mainly for photo-catalytic,outstanding chemical and physical properties.Photo-catalytic water splitting and hydrogen(H2)evolution by plentiful compounds as electron(e−)donors is estimated to participate in constructing clean method for solar H2-formation.Heterogeneous photocatalysis received much research attention caused by their applications to tackle numerous energy and environmental issues.This broad review explains progress regarding 2DMs,significance in structure,and catalytic results.We will discuss in detail current progresses of approaches for adjusting 2DMs-based photo-catalysts to assess their photo-activity including doping,hetero-structure scheme,and functional formation assembly.Suggested plans,e.g.,doping and sensitization of semiconducting 2DMs,increasing electrical conductance,improving catalytic active sites,strengthening interface coupling in semiconductors(SCs)2DMs,forming nano-structures,building multi-junction nano-composites,increasing photo-stability of SCs,and using combined results of adapted approaches,are summed up.Hence,to further improve 2DMs photo-catalyst properties,hetero-structure design-based 2DMs’photo-catalyst basic mechanism is also reviewed.

Effect of dye-metal complexation on photocatalytic decomposition of the dyes on TiO_2 under visible irradiation

The photocatalytic degradation of dyes （Acid Chrome Blue K （ACBK） and Alizarin Red （AR）） with strong complexation ability was investigated in the presence of metal ions under visible light irradiation. It was found that, at low dye-metal ratio, the photodegradation of ACBK was markedly inhibited by the addition of high oxidative potential Cu2＋. However, at high dye-metal ratio, the presence of Cu2＋ enhanced the photodegradation of ACBK. The negtive effect of Cu2＋ on the photodegradation of AR was observed for all dyemetal ratios. The relative chemical inert Zn2＋ tended to enhance the photodegradation of both anionic dyes. The mechanism underlying the different effect of Cu2＋ was discussed from the different roles of surface-adsorbed and dye-coordinated Cu2＋ in the photodegradation of dyes.

Thermal catalysis under dark ambient conditions in environmental remediation:Fundamental principles, development, and challenges

Thermal catalytic degradation of organic pollutants conducted in the dark at room temperature under atmospheric pressure without the need of external chemicals and energy sources has attracted a lot of attention over the last two decades. It provides unparalleled advantages over other advanced oxidation processes (AOPs) in treating domestic and industrial contaminated wastewater from the viewpoint of energy/chemical conservation and ease of operation. Rich knowledge has been accumulated in terms of the synthesis and application of thermal catalysts though controversies remain regarding their underlying mechanisms. This review sheds light on the proposed thermo- catalysis mechanism for the first time and presents the development of thermal catalysts under dark ambient conditions with a focus on catalyst materials, catalytic activity, and mechanism. The present review aims to provide mechanistic insights into the rational design of novel and efficient catalysts, and their underlying mechanisms as well as the emerging challenges and perspectives in thermo-catalysis under dark ambient conditions used for the practical and efficient treatment of contaminated wastewater.