硫脲热解制备G-C3N4分解NO如何获得更佳G-C3N4

E ?cient and Durable Visible Light Photocatalytic Performance of Porous Carbon Nitride Nanosheets for Air Puri ?cation

Fan Dong,*,?Meiya Ou,?Yanke Jiang,?Sen Guo,?and Zhongbiao Wu ?

?Chongqing Key Laboratory of Catalysis and Functional Organic Molecules,College of Environmental and Biological Engineering,Chongqing Technology and Business University,Chongqing 400067,China

?Department of Environmental Engineering,Zhejiang University,Hangzhou,Zhejiang 310027,China

*Supporting Information

The development of visible light driven photocatalysts has been the focus of considerable worldwide attention as photocatalysis technology is intensively applied in several important areas,including especially environmental pollution control and solar energy conversion.1?5In general,most of the photocatalysts are metal-containing,such as metal oxide,metal sul ?de,tungstates,niobates,tantalates,and vandates.6?8Until recently,a new kind of conjugated polymer semi-conductor (graphitic carbon nitride,g-C 3N 4)has been discovered as a fascinating metal-free organic photocatalyst working under visible light.9?13Graphite-like covalent g-C 3N 4is constructed by poly(heptazine)heterocyclic planes packed closely in a way similar to graphite.9The g-C 3N 4is multifunctional with broad applications (energy conversion and storage,contaminants degradation,carbon dioxide storage and reduction,catalysis,solar cells,and sensing)owing to its high stability,appealing electronic structure,and medium band gap.14,15The g-C 3N 4can be facilely prepared by pyrolysis of nitrogen-rich precursors via polycondensation.9?15The texture,electronic structure,and performance of g-C 3N 4are largely depended on the condensation conditions and the types of precursor.14,15The precursors employed for synthesis of g-C 3N 4include cyanamide,dicyandiamide,trithiocyanuric acid,melamine,triazine,heptazine derivatives,and more recently discovered urea and thiourea.16?23The texture and band structure of g-C 3N 4can also be tuned by templating,doping,heterostrucutre design,and postfunctionalization in order to enhance the reactivity in photocatalysis,selective synthesis,and CO 2reduction.24?29increase of surface

areas could improve the photocatalytic activity of materials.30,31The former factor is favorable for the reduction of defects and inhibiting charge carriers recombina-tion,while the later one could provide more active sites for

adsorption and reaction.30,31However,high crystallinity and

large surface areas are contradictory in most of the cases.In another word,the synthesis of catalytic materials with high crystallinity can be normally realized at the expense of large surface areas.Thermal treatment is the most common way to

enhance crystallinity of the catalytic materials.For example,by

increasing the annealing temperature and prolonging the annealing time during synthesis of TiO

2and other inorganic photocatalysts,the crystallinity could be enhanced,which however inevitably resulted in the decrease of surface areas.30,31It is highly desirable that high crystallinity and large surface areas for a catalyst can be achieved simultaneously.In spite of the advances made on the synthesis of g-C

3N 4as a photocatalyst for hydrogen evolution and aqueous pollutant degradation,the micro/nanostructures

of g-C 3N 4need to be improved for better photocatalysis.16?23Moreover,the photo-catalytic treatment e ?ciency of g-C

3N 4for gaseous air pollutants has seldom

been reported.Previously,we have synthesized g-C

3N 4by pyrolysis of urea and found that the pyrolysis conditions have signi ?cant e ?ects on the microstructure and photocatalytic activity of g-C 3N 4.16,22Received:November 11,2013Revised:January 21,2014

Accepted:January 23,2014Published:January 23,2014

In the present work,we develop a simple method to engineer the micro/nanostructures of g-C 3N 4from pyrolysis of thiourea and apply the as-prepared g-C 3N 4in visible light photocatalytic air puri ?cation.The easily available thiourea is a superior precursor because it is nontoxic,low-cost,and earth-abundant.A layer-by-layer coupled with layer-splitting process was proposed for the gradual reduction of layer thickness and size of g-C 3N 4obtained at elevated temperature and prolonged time.The formation mechanism of g-C 3N 4from thiourea was also revealed.Interestingly and importantly,we ?nd that both the crystallinity and the surface areas of g-C 3N 4increase spontaneously with elevated pyrolysis temperature and prolonged pyrolysis time,which is very important to enhance the activity of g-C 3N 4.The morphology and band structure of g-C 3N 4can also be simply engineered by variation of pyrolysis conditions.The optimized g-C 3N 4nanosheets exhibit e ?cient and durable visible light photocatalytic performance in NO removal.This unique ?nding will shed new light on synthesis and engineering of organic photocatalysts for large-scale environmental applications.2.EXPERIMENTAL SECTION 2.1.Synthesis of g-C 3N 4from Thiourea.All chemicals

used in this study were analytical grade and were used without further puri ?cation.In a typical synthesis,10g of thiourea powder was put into an alumina crucible with a cover.The crucible was heated to 550°C at a heating rate of 15°C/min in a tube furnace in air and maintained for 120min.The released air products during thermal treatment were absorbed by dilute NaOH solution of 0.05M.The resulted ?nal yellow powder was ground and collected for use without further treatment.In order to investigate the e ?ects of pyrolysis temperature,g-C 3N 4was synthesized at 500,525,550,575,and 600°C for 120min,respectively.The resulted samples were labeled as CN-500°C,CN-525°C,CN-550°C,CN-575°C,and CN-600°C.In order to investigate the e ?ects of pyrolysis time,g-C 3N 4was synthesized at 550°C for 0,15,30,60,120,and 240min,respectively.The resulted samples were labeled as CN-0min,CN-15min,CN-30min,CN-60min,CN-120min,and CN-240min.Note that the pyrolysis time does not include the time the furnace spent to raise the temperature to 550°C.2.2.Characterization Methods.The crystal phase was analyzed by X-ray di ?raction with Cu K αradiation (XRD:model D/max RA,Japan).The scan rate was 0.02deg/s.The accelerating voltage and the emission current were 40kV and 40mA,respectively.FT-IR spectra were recorded on a Nicolet Nexus spectrometer on samples embedded in KBr pellets.To perform the thermogravimetric-di ?erential scanning calorim-etry analysis (TG-DSC:NETZSCH STA 409PC/PG,

German),20mg of dry sample was sealed in an Al 2O

3crucible

with a lid and scanned at a rate of 20°C/min.A scanning

electron microscope (SEM,JEOL model JSM-6490,Japan)was used to characterize the morphology of the samples.The morphology and structure were examined by transmission

electron microscopy (TEM:JEM-2010,Japan).The UV ?vis

di ?use re ?ection spectra were obtained for the dry-pressed disk

samples using a Scan UV ?vis spectrophotometer (UV ?vis DRS:UV-2450,Shimadzu,Japan)equipped with an integrating sphere assembly,using BaSO

4as re ?ectance sample.Nitrogen

adsorption ?desorption isotherms were obtained on a nitrogen adsorption apparatus (ASAP 2020,USA)with all samples

degassed at 150°C prior to measurements.

2.3.Visible Light Photocatalytic Performance for NO Puri ?cation.The photocatalytic activity was investigated by removal of NO at ppb levels in a continuous ?ow reactor as shown in Figure 1(Figure S1shows the photo of the reactor

system).The volume of the rectangular reactor,made of

stainless steel and covered with Saint-Glass,was 4.5L (30cm ×

15cm ×10cm).A 150W commercial tungsten halogen lamp

was vertically placed outside the reactor.A UV cuto ??lter (420nm)was adopted to remove UV light in the light beam.Photocatalyst (0.2g)was coated onto a dish with a diameter of 12.0cm.The coated dish was then pretreated at 70°C to remove water in the suspension.The catalyst adhesion on the dish was ?rm enough to avoid the erosion (or removal)of the catalyst during air ?owing.

The NO gas was acquired from a compressed gas cylinder at a concentration of 100ppm of NO (N

2balance,BOC gas).

The initial concentration of NO was diluted to about 600ppb

by the air stream.The desired relative humidity (RH)level of the NO ?ow was controlled at 50%by passing the zero air streams through a humidi ?cation chamber.The gas streams

were premixed completely by a gas blender,and the ?ow rate was controlled at 2.4L/min by a mass ?ow controller.After the adsorption ?desorption equilibrium was achieved,the lamp was turned on.The concentration of NO was continuously measured by a chemiluminescence NO analyzer (Thermo

Environmental Instruments Inc.,42i-TL),which monitors NO,NO 2,and NO x (NO x represents NO +NO

2)with a sampling

rate of 1.0L/min.The removal ratio (η)of NO was calculated

as η(%)=(1?C /C

0)×100%,where C and C

0are

concentrations of NO in the outlet stream

and the feeding stream,

respectively.

Figure 1.Schematic ?ow diagram of the reactor system.

3.RESULTS AND DISCUSSION 3.1.Phase Structure and Transformation.Figure 2a shows the XRD patterns of the prepared g-C 3N 4samples

treated under di ?erent temperatures in the range of 500?600°C.All of the g-C 3N 4samples in Figure 2a have similar

di ?raction patterns,suggesting that all samples are similar in crystal structure.A typical (002)peak around 27.5°is observed,which indicates the graphite-like stacking of the conjugated aromatic units of CN with an interlayer distance of 0.33nm.9A typical (100)di ?raction peak around 13.0°corresponding to a distance of 0.68nm could be assigned to the in-plane repeated units.9Further observation on an enlarged view of (002)peak in Figure 2b shows that the di ?raction angle 2θof (002)peak increases from 27.31°for the CN-500°C sample to 27.73°for the CN-600°C sample when the pyrolysis temperature increases from 500to 600°C.This result implies that g-C 3N 4becomes more compact when thiourea is treated at a

higher pyrolysis temperature.Figure 2c shows the XRD patterns of the prepared g-C 3N

4treated at 550°C for di ?erent

times in the range of 0?240min.The two peaks at around 27.5°and 13°can be observed for all the as-prepared samples in Figure 2c.From Figure 2d,we can see that the di ?raction angle 2θof (002)peak increases from 27.24°for CN-0min to 27.66°for CN-240min when the pyrolysis time increases from 0to 240min (Figure 2d).This result suggests that the interlayer distance of g-C 3N 4decreases with prolonged

pyrolysis time,which is similar to the e ?ects of pyrolysis temperature on the crystal structure.Figure 2also illustrates that the di ?raction peak intensity become stronger when the pyrolysis temperature is increased and pyrolysis time is prolonged.This fact implies that the crystallinity of g-C 3N 4is improved

with the elevated pyrolysis temperature and prolonged pyrolysis time.

In order to understand the phase transformation during pyrolysis of thiourea,TG-DSC was carried out.The range of temperature is from room temperature to 800°C at a heating

rate of 20°C/min.An alumina crucible with a cover was used during thermal analysis to simulate the actual thermal environment of thiourea pyrolysis.The DSC and TG thermograms for thiourea (Figure 3)clearly show that several phase transformations can be observed in the semiclosed system.An endothermic peak at 190°C is the melting point of thiourea.The strongest endothermic peak appears in the temperature range 210?295°C,and the weight of the sample decreased rapidly by 70.5%.The peak at 236°C (overlapped by

the strong peak)indicates the reaction of thiourea into cyanamide.Cyanamide is a common precursor to synthesize g-C 3N 4.The sharp peak at 266°C implies that the thermal condensation of cyanamide into melamine occurred in this temperature range.The weak endothermic peak at 312°C corresponds to the further condensation process

where

Figure 2.XRD pattern of g-C 3N 4treated under di ?erent temperatures (a)and enlarged view of (002)peak (b),XRD pattern of g-C 3N 4treated for

di ?erent times (c)and enlarged view of (002)peak (d).

melamine is transformed to melem.The weight loss in this temperature range is about 10.4%.The further weight loss (about 6.4%)with an endothermic peak at 422°C can be ascribed to the phase formation from melem to graphitic carbon nitride.Finally,the endothermic peak at 707°C with a weight loss of 12.7%can be attributed to the sublimation of carbon nitride.The TG-DSC results imply the mechanistic transformation process of carbon nitride from pyrolysis of thiourea.93.2.Chemical Composition.The FT-IR spectra of all the samples are shown in Figure 4.We can observe the absorption band at 801cm ?1corresponding to a breathing mode of triazine,the absorption bands in the range of 1200?1600cm ?1attributing to stretching mode of C ?N heterocycles,and the broad bands in the range of the 3000?3700cm ?1region attributing to the adsorbed H 2O molecules and N ?H vibration.22For the samples treated under lower temperature and for shorter time,the incomplete condensation of thiourea results in the weak vibration of the C 6N 7units.This poor condensation can be improved by increasing the pyrolysis temperature and time to promote the formation process of g-C 3N 4.3.3.Morphology and Nanostructure Formation Mechanism.The typical SEM images of the as-prepared samples are illustrated in Figure 5.Figure 5a shows that the CN-500°C sample is composed of thick layers attached with some agglomerated particles.Figure 5b demonstrates that the CN-550°C sample is mainly composed of interconnected thin layers with some pores that may result from the gas bubbles during pyrolysis of thiourea.In the case of the CN-600°C sample,as shown in Figure 5c,a large number of small thin layers with abundant pores can be observed.The gas bubbles play a key role in the formation of porous structure.Figure 5d demonstrates that the CN-0min sample is composed of large irregular particles with some layered structure.For the CN-30min sample as shown in Figure 5e,thick plates with some particles can be observed.Increasing the pyrolysis time to 240min,the thickness of the sample is signi ?cantly reduced,and porous structure is generated at the same time (Figure 5f).By summarizing the above observations,we can conclude that

elevating the pyrolysis temperature and prolonging the pyrolysis time could make the resulted g-C 3N 4samples possess small size,thin layers,and porous structure.This is a facile way to tune the microstructures of g-C

3N 4.The EDX elemental mapping of the typical CN-120min sample (Figure 5g)is shown in Figures 5h,5i,and 5j.It can be seen that the C 3N 4sample prepared from thiourea was composed of C,N,and O elements,indicating S was released from the pyrolysis.The microstructure was further investigated by TEM.Figure 6a shows that the CN-500°C sample has a bulk structure composing of large particles with a layer structure.When the pyrolysis temperature was increased to 550°C,the resulted g-

C 3N 4sample was of a sheetlike structure with reduced thickness (Figure 6b).When the pyrolysis temperature was further raised up to 600°C,the resulted g-C 3N

4sample was composed of a thinner sheetlike porous structure due to the successful introduction of mesopores of several tens of nanometers in the CN-600°C sample (Figure 6c).Further observation in Figure 6a and Figure 6c implies that the average size of the sheets are decreased with increasing temperature probably because the large layers are split into smaller ones under higher temperature.

For the g-C

3N 4samples prepared at 550°C for di ?erent times,Figure 6d shows that the CN-0min sample consists of large particles with irregular shape.A thick and smooth

sheetlike structure is clearly observed for the CN-60min in Figure 6e.The morphology of the CN-240min sample

was Figure 3.TG-DSC thermograms for heating

thiourea.Figure 4.FT-IR spectra of g-C 3N 4treated under di ?erent temperatures (a)and g-C 3N 4treated for di ?erent times (b).

quite di ?erent,and many thin ?at sheets and some mesopores can be clearly seen in Figure 6f.This typical sheetlike morphology imparts CN-240min with a large speci ?c surface https://www.wendangku.net/doc/3b1449160.html,bining the SEM and TEM results,we can ?nd that the thickness and the size of the g-C 3N 4sheetlike nanostructures

were reduced simultaneously when the pyrolysis temperature was increased and the pyrolysis time was prolonged.Such variation in structure would lead to the formation of g-C 3N

4

with high surface areas and large pore volumes,which is bene ?cial for enhancing the photocatalytic activity.The mass of g-C

3N 4products obtained under di ?erent

temperatures and times with the same amount of thiourea was

measured.The weight of g-C 3N 4products was decreased

with

Figure 5.SEM images of CN-500°C (a),CN-550°C or CN-120min (b),CN-600°C (c),CN-0min (d),CN-30min (e),CN-240min (f),SEM image (g),and EDX elemental maping of C,N,and O (h,i,j)in image (g).

elevated pyrolysis temperature and prolonged pyrolysis time,resulting from gradual decomposition of solid g-C 3N

4due to

thermal oxidation in air.The conjugated layered g-C 3N 4is

constructed by the hydrogen bonding between aromatic CN units.The energy of the hydrogen bond is weak and can be destroyed by thermal oxidation.As a result,the layer of CN units would be gradually oxidized and removed in a layer-by-layer way during thermal treatment.16Subsequently,the thickness of g-C 3N 4samples would be decreased with elevated pyrolysis temperature and prolonged pyrolysis time (Figures 5and 6).Meanwhile,large g-C 3N 4layers were split into smaller layers to reduce surface energy (Figures 5and 6).16On this basis,a layer-by-layer coupled with layer-splitting process can be proposed for the explanation of reduction of layer thickness and size of g-C 3N 4samples obtained at elevated temperature

and prolonged time.3.4.Texture Property.The nitrogen adsorption ?desorp-tion isotherms and Barrett ?Joyner ?Halenda (BJH)pore-size distribution of selected samples are displayed in Figure 7.Figures 7a and 7b show that the CN-500°C sample exhibits nonporous structure.When the pyrolysis temperature exceeds 550°C,signi ?cant enlargement of surface areas and the

generation of nanopores (mesopores)can be observed (Figure

7b and Table 1).The CN-600°C sample is type IV (Brunauer,Deming,Deming,and Teller,BDDT classi ?cation)with a hysteresis loop at high relative pressure between 0.5and 1.0,suggesting the presence of mesopores (2?50nm)and macropores (>50nm).32There are type H3hysteresis loops at 0.45

0<1.00in the isotherms of the optimized samples

(CN-600°C and CN-240min),which are often observed on

the aggregates of platelike particles giving rise to slit-shaped pores which agrees well with the nanosheet-like morphology (Figures 5c and 5f).32It can be seen from Figure 7a and Table 1that increasing the condensation temperature from 500to 600°C causes a great enhancement of surface area and pore volume from 5

m 2/g and 0.029cm 3/g for the CN-500°C sample to 36m 2/g and 0.25cm 3/g for the CN-600°C sample.The creation of a porous structure can also be observed directly from SEM images (Figures 5a-5c).The e ?ects of pyrolysis time on the texture property of the as-prepared g-C 3N 4samples

are

Figure 6.TEM images for CN-500°C (a),CN-550°C or CN-120min (b),CN-600°C (c),CN-0min (d),CN-60min (e),and CN-240min (f).

similar.With increasing thermal treating time,the hysteresis loops shift to the region of lower relative pressure,and the areas of the hysteresis loops gradually become large.Prolonging the pyrolysis time from 0to 240min leads to signi ?cant enlargement of surface area from 6m 2/g for the CN-0min sample to 71m 2/g for the CN-240min sample,together with pore volume from 0.036to 0.35cm 3/g (Figures 8a and 8b and Table 1).The change of peak pore size with pyrolysis time also con ?rms the introduction of mesopores in the CN-240min sample treated for a longer time (Table 1).The high surface area and large pore volume of CN-600°C and CN-240min samples can be attributed to the reduced layer thickness and size.This interesting result is consistent with SEM and TEM observations (Figures 5and 6).

The crystallinity and the surface areas of g-C 3N 4organic photocatalyst can be enhanced with elevated pyrolysis temper-ature and prolonged pyrolysis time (Figures 2and 8).This thermal behavior of g-C 3N 4is contrary to most porous inorganic photocatalysts,which typically undergo structure deformation/pore collapse with decreased surface area upon increasing the heating temperature in order to improve the crystallinity,as it is known that the creation of porous structures with high surface area in g-C

3N 4relied largely on

templates (for example SiO 2,zeolite,and Triton X-100)followed by etching of the templates.33?36Such a process is relatively tedious and thus prevents the large scale applications.

This drawback can be overcome by our remarkable observation in this research.The porous nanostructure of g-C 3N 4can be self-generated by a facilely optimized thermal treatment.Porous g-C

3N 4with high surface area has been readily synthesized by a template-free method though treating thiourea at higher temperature for a longer time.The creation of porous nanostructure could facilitate catalytic sorption and promote the localization of light-induced electrons in the

conjugated

Figure 7.N 2adsorption ?desorption isotherms of CN-500°C,CN-550°C,and CN-600°C (a)and the corresponding pore-size distribution curves (b),N 2adsorption ?desorption isotherms of CN-0min,CN-30min,CN-60min,CN-120min,and CN-240min (c)and corresponding pore-size distribution curves (d).Table 1.S BET ,Pore Volume,Peak Pore Size,and NO Removal Ratio for Selected g-C 3N 4Samples a sample name S BET (m 2/g)total pore volume (cm 3/g)peak pore size (nm)η(NO)(%)CN-500°C 50.029nonporous 10.2CN-550°C 270.142 2.6/4.122.0CN-600°C 360.25 2.6/3.8/32.632.7CN-0min 60.036 3.87.7CN-30min 100.060 3.814.1CN-60min 120.073 3.817.6CN-120min 270.142 2.6/4.122.0CN-240min 710.35 2.8/3.8/31.132.3C-doped TiO 2451230.25 3.521.8

BiOI 5060.027 3.7/18.314.9a The data for C-doped TiO 2and BiOI were collected from references.

systems,which are bene ?cial for photocatalysis by carbon nitride.113.5.Variation of Band Gap.The relationship between optical property and pyrolysis conditions is investigated by UV ?vis DRS,as shown in Figure 9.An absorption edge located in a visible light region is observed for all the samples,which originates from band gap transitions from valence band to conduction band.The absorption edges of g-C 3N 4samples change with the variation of pyrolysis temperature and time.The band gap energy can be estimated from the intercept of the

tangents to the plots of (αh ν)1/2vs photon energy,as shown in Figures 9b and 9d.Figures 9a and 9b indicate that when the temperature increases from 400to 550°C,slight reduction band gap energy from 2.49to 2.42eV can be detected.This bathochromic shift in band gap is ascribed to the enhanced structural connections with enhanced van der Waals

interaction

Figure 8.The correlation between S BET and the pyrolysis temperature and time for selected samples (a)and the correlation between pore volume and the pyrolysis temperature and time for selected samples

(b).Figure 9.UV ?vis DRS (a,c)and plots of (αh ν)1/2vs photon energy (b,d)of g-C 3N 4samples treated under di ?erent temperatures and treated for di ?erent

times.

between the tri-s-triazine cores as higher pyrolysis temperature results in a higher degree of polymerization and a denser packing of the tri-s-triazine units (Figure 2).37This,in turn,leads to a stronger overlapping of molecular orbitals of the aromatic sheet stacks.Further increasing the temperature from 550to 600°C leads to the hypsochromic shift of the absorption edges from 2.42eV for CN-550°C to 2.57eV for CN-600°C due to the quantum con ?nement e ?ects induced by nanozised particles as high temperatures could signi ?cantly reduce the size of g-C 3N 4through layer-by-layer oxidation coupled with layer splitting (Figures 5and 6).38Figures 9c and 9d imply that prolonging the pyrolysis time from 0to 240min causes the band gap energy of g-C 3N 4samples to increase from 2.37to 2.90eV obviously.The relationship between band gap energy of g-C 3N 4and pyrolysis conditions can be found in Figure 9.Recently,Wang et al.developed a novel comonomer strategy to tentatively modify the texture and band structure of g-C 3N 4by chemical incorporation of monomer building blocks into the conjugated polymeric network of g-C 3N 4.39In this research,we can ?nd a simple approach to control the microstructure and band gap of g-C 3N 4by tuning the pyrolysis temperature and time,being a potentially valuable way to alter the physical and chemical properties of polymeric semiconductors.3.6.Visible Light Photocatalytic Activity and Stability for NO Removal.3.6.1.Photocatalytic Removal of NO and Monitoring of Reaction Intermediates.The as-prepared g-C 3N 4samples were applied for gaseous NO degradation under visible light irradiation in a continuous reactor in order to demonstrate their potential ability for air puri ?cation.Figures 10a and 10b show the variation of NO concentration (C /C 0%)with irradiation time over g-C 3N 4samples treated under di ?erent temperatures.Here,C 0is the initial concentration of NO,and C is the concentration of NO after photocatalytic reaction at time t .Previous investigation indicated that NO could not be photolyzed under light irradiation.40It can be found in Figure 10a that NO could not be degraded without photocatalyst under light irradiation or with photocatalyst (CN-600°C)for lack of light irradiation.In the presence of photocatalyst,the NO reacted with the photogenerated reactive radicals to produce the ?nal product of HNO 3.Because g-C 3N 4has a suitable band gap that can be directly excited by visible light,all g-C 3N 4samples treated under di ?erent temperatures and for di ?erent times show decent visible light photocatalytic activity toward NO removal,as shown in Figure 10.Figure 10a indicates that the NO removal ratio of g-C 3N 4samples increases from 10.2%to 32.7%when the pyrolysis temperatures increase from 500to 600°C after 45min irradiation.Figure 10b implies that the NO removal ratio of g-C 3N 4samples increases from 7.7%to as high as 32.3%when the pyrolysis time increases from 0to 240min (Table 1).The visible light activity of CN-600°C and CN-240min samples exceeds that of C-doped TiO 2(21.8%)and BiOI (14.9%),suggesting

that

Figure 10.Visible light photocatalytic activities of g-C 3N 4samples treated under di ?erent temperatures (a)and g-C 3N 4samples treated for di ?erent times (b)for removal NO in air (continuous reactor,NO concentration:600ppb).Monitoring of the fraction of NO 2intermediate over g-C 3N 4

samples treated under di ?erent temperatures (c)and g-C 3N 4samples treated for di ?erent times (d)

during photocatalytic reaction.

variation of thermal treatment conditions is an e ?ective approach to enhance the activity of g-C 3N 4.Under the optimized thermal conditions,the photocatalytic activity of g-C 3N 4from thiourea is higher than that of the sample from urea,demonstrating the advantage of thiourea as precursor.16The reaction intermediate of NO 2during photocatalytic oxidation of NO is monitored online as shown in Figures 10c and 10d.The fraction of NO 2generated over g-C 3N 4samples during irradiation decreases with increased pyrolysis temper-ature and prolonged pyrolysis time,which can be ascribed to the fact that the surface areas and pore volumes are increased accordingly.The di ?usion rate of reaction intermediate over g-C 3N 4samples with high surface areas and large pore volume is faster,thus promoting the oxidation of intermediate NO 2to

?nal NO 3?,as shown in the following reactions.40The ?nal oxidation products (nitric acid or nitrate ions)can be simply washed away by water wash.Note that as the photocatalytic reaction was going on,the NO concentration in the outlet was decreased gradually due to the conversion of NO to NO 3?.The NO concentration would reach minima until the photocatalytic reaction reached equilibrium.The slight rising of NO concentration was due to the accumulation of NO 3?product on the catalyst surface.40,44After long-term irradiation,the NO concentration in the outlet would reach a steady state.+?→+NO 2OH NO H O 22(1)+?→+?+NO OH NO H 23(2)++→NO NO H O 2HNO 222(3)+?→??NO O NO 23(4)Thermal treatment is a general process employed to crystallize catalytic materials.The e ?ects of thermal treatment conditions on the microstructure and photocatalytic activity of di ?erent types of photocatalysts have been widely inves-tigated.23,30,31,41?43Yu et al.studied the e ?ects of calcination temperature on the photocatalytic activity of TiO 2from titanate and found that activity of TiO 2deceased with an increase in calcination temperature in the range of 400to 900°C due to the sintering and crystallite growth and decrease of surface areas and pore volume.41In most cases,there was a medium calcination temperature (not too high and not too low)to make a balance between the surface areas and crystallinity in order to optimize the activity of photocatalysts.For example,Zaleska et al.42found that the optimal preparation temperature for boron-doped TiO 2with the highest activity was 400°C in the range of 300?600°C.However,in our case,the activity of the g-C 3N 4sample is enhanced progressively with continuous elevated temperature and prolonged pyrolysis time (Table 1).

This unique variation of the activity should be related to the

unusual change of texture property and band gap of g-C 3N

4

with di ?erent thermal treatment conditions (Figures 5,6,8,and 9).

The remarkably improved photocatalytic activities of the g-C 3N 4samples with respect to elevated temperature and prolonged pyrolysis time demonstrated above can be explained as the synergistic e ?ects of enhanced crystallinity,nanosheet-like morphology,large surface area,large pore volume,and increased band gap.First,for the g-C 3N 4sample treated at high temperature and for a long time,the enhancement of crystallization (Figure 2)is advantageous to reduce the recombination rate of photogenerated electrons and holes due to a decrease in the number of the defects.43Second,the

nanosheet-like structure (Figures 5and 6)enhances the

transport of photogenerated electrons along the nanosheet,thus lowering the hole ?electron recombination.44?47Third,the thin thickness and porous character result in a large surface area for pollutant adsorption.48,49Fourthly,large pore volume (Figure 8)provides more active site for quick reactant

di ?usion.31,49,50Lastly and importantly,the increase in the

band gap increases the redox ability of charge carriers generated

under irradiation (Figure 9).46All these favorable factors

cocontribute to the signi ?cantly improved photocatalytic activities of g-C 3N 4samples synthesized at elevated temper-

ature (600°C)and treated for a long time (240min).

3.6.2.Photochemical Stability with Multiple Runs.To further test the stability of the optimized CN-600°C and CN-240min samples for practical application,repeated reaction tests were carried out.The sample after one run was used

directly without further treatment for the next photocatalytic

reaction run.As shown in Figure 11,the NO removal ratios of

CN-600°C and CN-240min samples could be well maintained

after ?ve cycles under visible light irradiation.Except for a slight drop in the activity during the third running,no further decrease in activity in the following runs can be observed.These results clearly demonstrate that nanostructured porous g-C

3N 4photocatalysts with enhanced and durable activity can

be successfully synthesized and applied for e ?cient air

puri ?

cation.

Figure 11.Multiple photocatalytic reaction over the CN-600°C sample (a)and the CN-240min sample (b)for removal of NO in air.

The stability of CN-600°C and CN-240min samples is further con ?rmed by XRD and FT-IR spectra after repeated reaction runs,as shown in Figure 12.It can be seen in Figure 12a that the crystal structure of CN-600°C and CN-240min samples were almost identical to the fresh samples (Figure 2),indicating their good phase stability.All the absorption bands for both samples are identical to the FT-IR spectra of fresh samples (Figure 4).The reaction intermediates and reaction products during photocatalytic oxidation of NO (such as NO 2

and HNO 2)cannot be observed.These results indicate that the reaction intermediates and products could di ?use rapidly owing to the bene ?cial porous nanostructures (Figures 6c and 6f).42For the ?rst time,we have discovered the unique e ?ects of pyrolysis temperature and time on the texture property,band gap structure,and visible light photocatalytic activity of g-C 3N 4

derived from thiourea.By facile variation of the pyrolysis conditions,we can engineer the nanostructures of g-C 3N 4and make them possess e ?cient and durable visible light photo-catalytic performance for air pollutant puri ?cation.The as-prepared g-C 3N 4nanostructures can also be applied in other related areas such as solar energy conversion,photosynthesis,and catalyst support.4.CONCLUSION Conjugated g-C 3N 4nanostructures were synthesized by direct pyrolysis of thiourea in air.The formation of g-C 3N 4from thiourea involved multiple processes under thermal treatment.The unique e ?ects of pyrolysis temperature and time on the microstructure and photocatalytic activity of g-C 3N 4were investigated and revealed.The crystallinity,morphology,surface area,pore structures,band gap structure,and photo-catalytic activity of g-C 3N 4was strongly dependent on the pyrolysis temperature and time.For the g-C 3N 4samples obtained at elevated temperature and prolonged time,the layer thickness and size of g-C 3N 4were reduced through a layer-by-layer coupled with layer-splitting process.When the pyrolysis temperature was increased from 500to 600°C and the pyrolysis time was prolonged from 0to 240min,the visible light photocatalytic activity of porous g-C 3N 4nanosheets toward gaseous NO puri ?cation was signi ?cantly enhanced,exceeding that of C-doped TiO 2and BiOI.The activity enhancement of porous g-C 3N 4nanostructures can be ascribed to the synergistic contributions of enhanced crystallinity,nanosheet-like morphology,large surface area,large pore volume,and enlarged band gap.The optimized CN-600°C and CN-240min nanosheets samples can be used multiplely without obvious deactivation,demonstrating their high stability under repeated light irradiation.The present work demon-strated that the nanostructures of conjugated carbon nitride derived from thiourea can be facilely engineered and improved by facile thermal treatment for e ?cient visible light photo-catalytic

air puri ?cation.■ASSOCIATED CONTENT *Supporting Information

The photo of the reactor system (Figure S1).This material is available free of charge via the Internet at https://www.wendangku.net/doc/3b1449160.html,.■AUTHOR INFORMATION Corresponding

Author *

Phone:+862362769785605.Fax:+862362769785605.E-

mail:dfctbu@https://www.wendangku.net/doc/3b1449160.html,.Author Contributions

All authors have seen and given approval to the ?nal version of the manuscript.

Notes

The authors declare no competing ?nancial interest.■ACKNOWLEDGMENTS

This research is ?nancially supported by the National Natural Science Foundation of China (51108487),the Natural Science Foundation Project of CQ CSTC (cstc2013jcyjA20018,cstc2013yykfB50008),the Science and Technology Project from Chongqing Education Commission (KJ130725),the Innovative Research Team Development Program in University of Chongqing (KJTD201314),and the Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education

(LZJ1204).■REFERENCES (1)Chen,C.C.;Ma,W.H.;Zhao,J.C.Semiconductor-Mediated Photodegradation of Pollutants under Visible-Light Irradiation.Chem.

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生产车间各岗位操作规程

生产车间安全操作规程 为保证操作工人的人身安全以及财产不受损失，根据《危险化学品安全条例》，操作工人必须按照以下操作规程进行操作。 一、操作工人必须掌握化学物品的特性（物理、化学性能），熟悉操作工艺。 二、操作工必须持证上岗，有高度的安全意识。 严格做好双人领料、双人投料制度。 三、在化学危险品操作过程中必须佩带防护用品，对接触化学危险品的容器，要及时进行加工处理。 四、操作工必须对防护用品及急救用品进行检查，定期更换，确保防护用品及急救用品能有效使用。 五、不允许将化学危险品以及其有关的物品带出车间。 六、严禁在车间内进食、喝茶、娱乐等与工作无关的行为。 七、化学危险品工作区域内除持证人员外，其他工作人员及闲杂人员等不得进入。 八、对违规操作以及发生的大小事故将追究各级责任人的责任。 称量工序操作规程 设备：台秤、捕尘设施 状态标志：已清洁、正在运行、清场合格证、生产证； 记录填写：批生产记录；所需容器具准备齐全；所用物料确认无

误。 操作： ? 1 操作人员根据称量配料的数量到净桶存放室领取洁净的桶和舀子等器具，将其用小车运至称量配料间，并用75%酒精擦拭消毒。 ? 2 操作人员依据“生产指令”和限额领料单到中间站领取所需物料，核对其名称、规格、编号、数量等，并在交接单和物料进出记录上签字确认领用，用小车运至称量配料室。 ? 3 在QA人员监控下，按照制剂指令的规定比例，称量各物料的单锅数量。 ? 4 物料按比例称重后及时悬挂标示牌，填写称量配料记录，将所配物料递交下一工序。 ? 5 称量配料结束后取下“生产证”，换上“待清洁”标示牌。 ?清场 制粒工序操作规程 设备：摇摆式颗粒机 状态标志：已清洁、正在运行、清场合格证、生产证； 记录填写：设备运行和维护保养记录、批生产记录；所需容器具准备齐全；所用物料确认无误。

2氨基硫脲的合成

化学通报990311
Page 1 of 4
化学通报
CHEMISTRY 1999年 第3期 No.3 1999
1，3-二氨基硫脲的合成研究
孙晓红 关键词 二氨基硫脲 合成 催化 刘源发
1，3-二氨基硫脲(简称TCH)是一种重要的有机合成中间体，在一些杂环类医药、 农药的合成中有广泛的用途，同时它的一些金属衍生物也具有较大的应用价值。关于 其合成方法文献已有报道［1］，且一直受到研究工作者的重视。在几种不同的合成方 法中，通常采用的是以二硫化碳和水合肼为原料，经两步反应制得TCH，以反应式表示 如下：
从原料来源及工艺条件来看，这是一条合理的工艺路线，二硫化碳与水合肼在较 低温度下反应，先生成二硫代肼基甲酸钅 井(简称HDTC)，后者经加热分解，放出硫 化氢，冷却后过滤，即可得到TCH。但此种方法早期文献报道收率一般低于70%［2,3］, 如加热温度控制不当，反应剧烈，难以控制，TCH的收率会更低，且不安全，目前国内 有关生产厂家仍采用此工艺路线。后有一些文献报道了有关此方法的改进研究，发现 过量的水合肼存在可提高收率［4］，加入水及一些低烷基醇有利于反应进行，但并不 增加反应收率；一些胺或强碱如四亚甲基二胺、氢氧化钠存在下可增加TCH的收率 ［5］；在巯基乙醇存在下，二硫化碳与过量水合肼反应不仅可提高收率，同时可减少 副产物生成，可使水合肼循环套用次数增加，TCH的平均收率～90%［6］。但是以上方 法存在反应时间过长，一般需20h左右及催化剂巯基乙醇价格贵，来源困难的问题。 我们在文献［6］的基础上，对此方法进行了改进研究，研究成功以氯乙醇等卤代 醇代替巯基乙醇，并适当提高脱硫化氢的反应温度，使反应时间大为缩短，在10h以内 即可完成反应，过量的水合肼可循环套用的工艺条件，TCH的收率一般均在90%以上。
1 实验部分
1.1 主要原料及规格 二硫化碳，化学纯； 80%水合肼，化学纯； 2-氯乙醇，分析纯； 1，3-氯-2丙醇，自制； 巯基乙醇，化学纯。 1.2 实验步骤 1.2.1 操作方法 在装有搅拌器、温度计、滴液漏斗及冷凝器(上口连有尾气导出管) 的四口烧瓶中加入80%水合肼3mol及适量水，2-氯乙醇12g，冰水浴冷却至15℃左右， 搅拌下滴加二硫化碳1mol，约1h加完，然后在室温下搅拌30min，此时有黄色结晶HDTC 析出。加入6g氢氧化钠，加热升温并控制反应温度在75～85℃之间反应10h，所放出的 硫化氢气体经导气管用稀氢氧化钠吸收。冷却至室温，过滤析出的白色颗粒状TCH。用 150mL甲醇洗涤，干燥，得产物重97.5g,收率92%。 将过滤所得母液及甲醇洗涤液合并，加入反应瓶，搅拌下于15℃左右，30min之 内，滴加0.52mol二硫化碳，继续在此温度下反应1h。冷却至0℃，30min后，过滤析出 https://www.wendangku.net/doc/3b1449160.html,/web/chemistry/2000/https://www.wendangku.net/doc/3b1449160.html,/col/1999/hxtb/hxtb9903/... 2011-10-27

难处理金矿提金的现状及发展趋势

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急性毒性经口：类别4 生殖毒性：类别2 对水环境危害-急性：类别2 对水环境危害-慢性：类别2 标签要素： 象形图： 警示词：警告 危险性说明：吞咽有害（经口）。怀疑损害生育能力或胎儿。对水生生物有毒。对水生生物有毒并且有长期持续影响。 防范说明： 预防措施： —密闭操作，注意通风。 —操作尽可能机械化、自动化。 —操作人员必须经过专门培训，严格遵守操作规程。 —建议操作人员配戴自吸过滤式防毒面具（半面罩），戴橡胶耐酸碱手套。—远离火种、热源，工作场所严禁吸烟。 —使用防爆型通风系统和设备，防止粉尘泄漏到工作场所空气中。—避免与氧化剂、酸类接触。 —搬运时轻装轻卸，防止包装损坏； —配备相应品种和数量的消防器材，泄漏时，建议佩戴过滤式防毒面具（半面罩）。 —紧急事态抢救或撤离时，应佩戴空气呼吸器。 —作业场所不得进食、饮水、吸烟。 —禁止让该产品进入周围环境中。 事故响应： —如食入：饮足量温水，催吐。立即就医。 产品名称: 硫脲 SDS编号：2013080502 修订日期： 2013年8月5日

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信阳师范学院本科学生毕业论文（设计）开题报告

信阳师范学院本科学生毕业论文（设计）中期检查表

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间、班组三级人员组成。 3.2 公司实行机安全生产大检查制度，厂部每周要检查一次，车间每天要检查一次，班组要经常检查，对检查出的事故隐患必须整改。 3.3 公司建立窑长统一指挥下的看火操作责任制，实行“三班保一窑”的煅烧管理措施和单窑考核产量、质量的办法，以利于稳定机立窑热工制度。 程序 4.1 开窑操作 4.1.1 填窑及烘窑 A. 在填窑前必须对卸料篦子进行细致检查，严禁金属物等其它硬性异物遗留而造成卸料故障。 B. 填窑前必须进行全系统机电设备负荷运转20-30分钟，确认运转正常，仪表、信号等可靠，才能进行填窑和开窑生产。

有些金矿为什么难浸出

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8、确保巡检路线畅通、安全。 9、确认电路开关位置是否处于备妥状态。 10、检查各阀板完好，阀门动作是否灵活。 11、检查破碎机轴承传动轴是否完好，确认运行良好。 12、检查注油泵是否工作正常，各油路是否畅通、完好，确认冷却水管理路畅通、阀门打开、水量充足。 13、检查板喂机各托辊是否运行正常，链板、轨道是否完好。 14、确认电机、减速机能正常运转。 15、确认破碎机内给料辊、锤头、板击板、篦条完好，排铁门工作正常。 16、确认收尘器的滤袋、反吹机构、卸灰机构工作正常。 17、检查风机轴承是否完好，轴是否弯曲，确认工作

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班组长安全职责 1、认真执行上级政府和公司有关安全生产的各项规定，模范遵守安全操作规程，对本班组员工在生产中的安全和职业健康负责。 2、对新调入的员工进行班组级安全教育，并在熟悉工作前指定专人负责其安全。 3、组织本班组人员学习安全生产规程，检查执行情况，教育员工在任何情况下不违章蛮干。发现违章作业，立即制止。 4、经常进行安全检查，发现问题及时解决。对班组不能解决的问题，要采取临时防范措施，并及时上报。 5、认真执行交接班制度，遇到不安全问题，未能在本班内予以排除的，交接班时应交待清楚，并做好交接班记录。 6、发生各类事故，要保护现场，立即上报，详细记录，并组织全班员工认真分析，吸取教训，提出防范措施。 7、参加本部门、车间组织的安全生产活动，认真履行安全职责。