National Laboratory of Solid State Microstructures, College of Engineering and Applied Science, Ecomaterials and Renewable Energy Research CenterERERC), Nanjing University, No. 22 Hankou Road, Nanjing 210093, People’s Republic of ChinaSchool of Chemistry and Chemical Engineering, University of Jinan, People’s Republic of China
r t i c l e i n f o
rticle history:eceived 11 October 2013eceived in revised form 1 January 2014ccepted 3 January 2014vailable online 11 January 2014
a b s t r a c t
Porous g-C3N4 (pm-g-C3N4) samples were prepared by sintering protonated melamine. Photocatalyticactivities for H2 production over the g-C3N4 samples were evaluated under visible-light irradiation. Spe-cific surface areas and condensation degree of the g-C3N4 samples prepared from protonated melamineturn larger as the calcination temperatures increase (400 ◦C, 450 ◦C, 500 ◦C, 550 ◦C, and 580 ◦C for 1 h).Also, their bandgaps are narrowed and PL peak red shifts, and thus their photocatalytic activities are
enhanced. Compared with the reference g-C3N4 samples synthesized by sintering melamine without anyprotonation (m-g-C3N4), the pm-g-C3N4 samples exhibit better photocatalytic performances, owing tolarger specific surface area, less recombination of photogenerated carriers and higher degree of conden-sation. By optimizing the preparation parameters and the amount of Pt cocatalyst, the highest hydrogenevolution rate of 417 �mol h−1 g−1 was achieved over the pm-g-C3N4 samples synthesized at 550 ◦C for
00-W
ondensation degree 2 h, when irradiated by 3
. Introduction
Photocatalytic hydrogen production by sunlight has been anmportant issue for several decades on account of green and renew-ble energy [1–5]. It is expected that photocatalysts should exhibithe merits of stability, earth-abundance, non-toxicity, and visible-ight absorbance [6–11]. Graphitic carbon nitride (g-C3N4) happenso be one of a few photocatalysts that meet these requirements
entioned above, thus attracting intensive attention since Wangt al. have reported its photocatalytic ability to produce hydrogenrom a methanol aqueous solution under visible-light irradiation12].
In general, g-C3N4 photocatalysts have been synthesized fromirect pyrolysis of cyanamide, dicyandiamide, and melamine. Theses-prepared g-C3N4 samples reveal irregular large particles withpecific surface areas below 10 m2 g−1 [13,14], thus exhibitingmall amount of active sites and weakening their photocatalyticctivity. For this reason, numerous efforts have been made to syn-hesize porous g-C3N4, aiming to provide more reaction sites. In
articular, template methods are versatile to produce porous g-3N4. Hard templates [15–17] for example silica microspheresnd soft templates [18,19] using surfactants are widely utilized to
fabricate the porous structures of g-C3N4. However, these pro-cesses are tedious due to the removal of the sacrificial templatesand unintentional doping caused by the templates. Therefore, it isstill a challenge to explore a facile strategy for synthesizing porousg-C3N4.
Protonation has been of particular interest for modifying g-C3N4in recent years. Mixing g-C3N4 with HCl provides a way to adjustthe electronic bandgap and ionic conductivity of g-C3N4 [20]. Onthe other hand, deprotonation by basic solution improves the cat-alytic activity of g-C3N4 in the Knoevenagel condensation reactions[21]. Dong and Zhang have reported that g-C3N4 prepared from HClprotonated melamine exhibits a porous platelet-like structure [22].Moreover, our group have synthesized a tube-like g-C3N4 by heat-ing HNO3 protonated melamine at 350 ◦C, which offered a reliableand facile strategy to shape g-C3N4 samples [23]. Inspired by theseworks, we envision that the protonation method could influencethe H2 production activity of g-C3N4, which very limited attentionhas paid to in the past literatures.
In this present study, HNO3-protonated melamine was used tosynthesize the g-C3N4 samples. The as-prepared g-C3N4 photocata-lysts exhibited a higher hydrogen production activity, comparedwith the reference sample which was obtained by direct heating
the melamine [14]. The present study proves that the one-dimensional porous structure and the increased condensationdegree of g-C3N4 lead to the better photocatalytic performance forproducing H2.
Fig. 1. XRD patterns of pm-g-C3N4 samples at 400 ◦C for 1 h (a), 450 ◦C for 1 h (b),◦ ◦ ◦ ◦ ◦
tri-s-triazine units lie at about 810 cm−1 [26]. The other band in the1250–1650 cm−1 region is due to the skeletal stretching vibrationsof the CN heterocycles [27].
54 Y. Zhong et al. / Applied Sur
. Experimental
.1. Preparation of g-C3N4
All the chemicals used were analytical-grade reagents with-ut further purification. In a typical experiment, 5 mmol ofelamine powder was dissolved into 50 mL of ethylene glycol.
hen 0.6 M HNO3 solution (50 mL) was added dropwise into thebove solution while stirring at room temperature. White precipi-ates were collected and washed by ethanol for three times. Afterried at 60 ◦C for 6 h, the precursor of protonated melamine wasbtained, and then it was placed in an alumina boat. The g-C3N4amples were obtained by heating the precursor under variousemperatures in a muffle furnace. For comparison, a reference g-3N4 sample was prepared by directly heating melamine at 500 ◦Cor 2 h, followed by at 520 ◦C for another 2 h [14]. In this study,-C3N4 samples prepared by heating melamine and HNO3 pro-onated melamine are represented as m-g-C3N4 and pm-g-C3N4,espectively.
.2. Characterization
The crystal structures of g-C3N4 samples were characterizedy a powder X-ray diffractometer (XRD, Ultima III, Rigaku Corp.,apan) using Cu-K� radiation (� = 1.54178 A, 40 kV, 40 mA). Thehermal stabilities of the products were measured using a thermalnalyzer (DSC/DTA-TG, STA 449 F3 Jupiter, Germany). The chemi-al states were verified by X-ray photoelectron spectroscopy (XPS,hermo ESCALAB 250 spectrometer) using monochromated Al K�1486.6 eV) source. Fourier transformed infrared (FTIR) spectraere obtained with an FTIR spectrometer (IRprestige-21, Shimadzuorp., Japan). The field-emission scanning electron microscope (FE-EM, Nova NanoSEM 230, FEI, USA) and transmission electronicroscopy (TEM, JEM-2100, JEOL, Japan) were used to investigate
he surface morphologies. The specific surface area was collectedhrough Brumauer–Emmett–Teller (BET) method by N2 adsorptionTriStar-3000, Micromeritics, USA). UV–vis diffuse reflection spec-ra were operated on a UV–vis spectrophotometer (UV-2500PC,himadzu Corp., Japan). Photoluminescence (PL) spectra wereecorded by a Cary Eclipse spectrophotometer with a Xe lamp ashe excitation source (Cary Eclipse, VARIAN, USA).
.3. Photocatalytic activity test
Photocatalytic activity of g-C3N4 was evaluated by H2 produc-ion from aqueous solutions in a closed gas cyclic system. Thevolved gas was measured with TCD gas chromatograph (Shi-adzu, GC-8A, MS-5A column, TCD, Ar carrier), connecting to a
as circulating line. Pt cocatalyst was loaded by an in situ photore-uction method using H2PtCl6 solution and triethanolamine (TEA)as employed as a sacrificial electron donor. In a typical proce-ure, 0.1 g of a g-C3N4 photocatalyst was suspended in 243 mL ofater containing an appropriate amount of H2PtCl6 and 10 vol% of
riethanolamine. A 300-W Xe lamp (16.1 mW cm−2) with a cutofflter (� ≥ 420 nm) was used to provide visible light.
. Results and discussion
.1. XRD analysis
The phase structures of the samples were investigated byRD, the results of which were shown in Fig. 1. All the g-C3N4
amples exhibit a strong peak at 27.4◦ (d = 0.326 nm) correspond-ng to the characteristic inter-layer stacking of (0 0 2) planesd = 0.328 nm) [24], which confirms the formation of a graphitictructure. The m-g-C3N4 sample presents a relatively weak peak
500 C for 1 h (c), 550 C for 1 h (d), 550 C for 2 h (e), 580 C for 1 h (f), 500 C for 2 hand then 520 ◦C for another 2 h (g), and m-g-C3N4 sample at 500 ◦C for 2 h and then520 ◦C for another 2 h (h).
at 13.0◦ (d = 0.679 nm) close to the tri-s-triazine based intra-layerstructural packing motif (2� = 13.08◦, d = 0.68 nm) [25]. Further-more, pm-g-C3N4 sample calcined at 400 ◦C reveals a peak locatedat 17.7◦ (d = 0.49 nm), which is in agreement with the s-triazinebased in-planar structural packing (2� = 17.4◦, d = 0.47 nm) [23].However, when the heating temperature increases, the intra-layerperiodicities of pm-g-C3N4 samples are destroyed, as indicated bythe disappearance of the diffraction peak at 17.7◦.
3.2. FTIR spectra
The graphitic structures of these g-C3N4 samples were furtherdemonstrated by FTIR spectra. As shown in Fig. 2, the broad bandwithin the range of 3100–3500 cm−1 for the precursor is relatedto N–H stretching vibration [16], which disappears after sinteringbecause of the condensation process. As-prepared pm-g-C3N4 sam-ples exhibit two types of vibration. The characteristic peaks of the
Fig. 2. FTIR spectra of the precursor and pm-g-C3N4 samples at 550 ◦C for 1 h and550 ◦C for 2 h.
Y. Zhong et al. / Applied Surface Sc
Fig. 3. (a) XPS spectra of the precursor and pm-g-C3N4 sample at 550 ◦C for 2 h andhs
3
spgtcaCs
photocatalysts and reduce water into H with a low overpotential
igh-resolution XPS spectra of (b) C 1s and (c) N 1s of the as-prepared pm-g-C3N4
ample. The binding energy was calibrated on the reference C 1s at 284.71 eV.
.3. XPS spectra
XPS spectra of the precursor and pm-g-C3N4 sample are pre-ented in Fig. 3. The survey spectrum of precursor reveals theresence of oxygen in the pm-g-C3N4 samples. However, the oxy-en content decreases significantly after sintering process owingo the loss of nitro group (Fig. 3a). Therefore, we infer that the pre-ursor is composed of melamine with protonated amino groups
nd nitrate ions. In the high-resolution C 1s spectra of the pm-g-3N4 sample, the binding energy of 288.10 eV is characteristic forp2-C (Fig. 3b) [26]. Further, the N 1s peak in the high-resolution
ience 295 (2014) 253– 259 255
N 1s spectra can be fitted with three peaks (Fig. 3c). The bondingenergy at 398.6 eV is assigned to sp2-N, while the peaks at 399.5and 400.8 eV are attributed to the tertiary nitrogen N-(C)3 groupsand the remaining amino C–N–H groups, respectively [26].
To evaluate the thermal stabilities of these samples, the precur-sor and pm-g-C3N4 were measured by thermal analysis (Fig. S1).The strong endothermal peak centered at around 315.2 ◦C in Fig.S1a is associated with the weight loss of about 92.8%. It indicatesthat sublimation and condensation process along with the loss ofamino and nitro groups occur in this temperature range. As shownin Fig. S1b, the as-prepared pm-g-C3N4 samples become unstableabove 475.4 ◦C. Moreover, combustion of the g-C3N4 sample takesplace at about 575 ◦C and then its decomposition occurs at 600 ◦C.
3.4. SEM and TEM observation
Fig. 4 depicts the typical SEM images of the precursor, m-g-C3N4 and pm-g-C3N4 samples at the same magnification. As canbe seen, the protonated melamine exhibits a one-dimensional rod-like structure which has a length up to dozens of microns. Forthe formation of protonated melamine, melamine is dissolved intoethylene glycol and then white precipitate forms since HNO3 solu-tion decreases its solubility. During the precipitating process, theprotonated melamine undergoes self-assembly to a rod-like struc-ture [23], as shown in Fig. 4a. After sintering, the pm-g-C3N4samples reveal porosity originating from the loss of amino andnitro groups. Higher sintering temperature causes partial struc-ture collapse of pm-g-C3N4 while the one-dimensional porousstructure remains. In contrast to pm-g-C3N4 samples (Fig. 4b–h),m-g-C3N4 sample reveals irregular bulk particles (Fig. 4i). Given theattractive advantages of large specific surface area to provide suf-ficient reaction sites, the improved charge transfer and separationof photogenerated charge carriers by the reduced particle size, theone-dimensional porous architectures are beneficial to the photo-catalytic reaction. In addition, the nitrogen adsorption–desorptionisotherms (Fig. S2) for the as-prepared samples prepared fromprotonated melamine at 550 ◦C for 1 h, 550 ◦C for 2 h, and 580 ◦Cfor 1 h, respectively, feature type IV properties, which suggestedthe presence of the porous (mesoporous and macroporous) struc-tures. Therefore, the one-dimensional porous mp-g-C3N4 samplesare suitable for photocatalytic application. Since the pm-g-C3N4samples become unstable above 475.4 ◦C, the porous structure isunobvious in the pm-g-C3N4 samples prepared at 500 ◦C for 2 hand then 520 ◦C for 2 h (Fig. S2). Further morphology details weregiven by TEM observation. As shown in Fig. 5, m-g-C3N4 samplesat 550 ◦C for 1 h, 550 ◦C for 2 h, 580 ◦C for 1 h and 500 ◦C for 2 hand then 520 ◦C for 2 h reveal typical porous structures. Mesoporesand macropores (dozes of nanometers in size) are covering g-C3N4samples, which is consistent with SEM and BET results.
3.5. Photocatalytic activity
With one-dimensional porous structure, stable chemical andthermal activity at ambient conditions, as-prepared pm-g-C3N4may be a suitable candidate for photocatalytic H2 production. Thephotocatalytic activities for H2 production over the as-preparedsamples were tested under visible-light irradiation (� ≥ 420 nm).As shown in Fig. S4, after loading 3.0 wt.% of Pt and a dwell time of9 h, the photocatalytic H2 production over Pt-loaded pm-g-C3N4is enhanced by a factor of ∼12, in comparison with that overpm-g-C3N4 without any cocatalyst. The photogenerated electronstransfer to the Pt cocatalyst loaded on the surface of pm-g-C3N4
2on Pt cocatalyst, thereby suppressing the recombination of pho-toinduced carries [28]. As a result, the photocatalytic performanceof pm-g-C3N4 samples is enhanced by depositing Pt cocatalyst.
256 Y. Zhong et al. / Applied Surface Science 295 (2014) 253– 259
Fig. 4. SEM images for the precursor (a), pm-g-C3N4 samples at 400 ◦C for 1 h (b), 450 ◦C for 1 h (c), 500 ◦C for 1 h (d), 550 ◦C for 1 h (e), 550 ◦C for 2 h (f), 580 ◦C for 1 h (g),500 ◦C for 2 h and then 520 ◦C for 2 h (h) and m-g-C3N4 sample at 500 ◦C for 2 h and then 520 ◦C for 2 h (i).
Fig. 5. TEM images for pm-g-C3N4 samples at 550 ◦C for 1 h (a), 550 ◦C for 2 h (b), 580 ◦C for 1 h (c) and 500 ◦C for 2 h and then 520 ◦C for 2 h (d).
Y. Zhong et al. / Applied Surface Science 295 (2014) 253– 259 257
Fig. 6. Time courses of H2 evolution under 300 W Xe lamp with a cutoff filter(420 nm) and triethanolamine (10 vol%) on 3.0 wt.% Pt-loaded pm-g-C3N4 samplesa ◦ ◦ ◦ ◦ ◦
(a
PbwmaaFatTttaatai
3
mphpbbtavtt
oiaosbti
t 400 C for 1 h (a), 450 C for 1 h (b), 500 C for 1 h (c), 550 C 1 h (d), 550 C for 2 he), 580 ◦C for 1 h (f), 500 ◦C for 2 h and then 520 ◦C for 2 h (g), and m-g-C3N4 samplet 500 ◦C for 2 h and then 520 ◦C for 2 h (h).
Fig. 6 shows the time courses of H2 evolution over 3.0 wt.%t-loaded g-C3N4 samples sintered at various conditions. It cane clearly seen that, the H2 evolution activities are improvedith higher calcination temperatures, when heating protonatedelamine at various temperatures (400 ◦C, 450 ◦C, 500 ◦C, 550 ◦C,
nd 580 ◦C) for 1 h, respectively. The calculated BET specific surfacereas from nitrogen adsorption–desorption isotherms are shown inig. S3. In the case of the mp-g-C3N4 samples, the specific surfacereas of the mp-g-C3N4 samples prepared at the various tempera-ures for 1 h are 9.74, 13.0, 14.1, 59.3 and 73.6 m2 g−1, respectively.he specific surface areas turn larger as the calcination tempera-ures increases from 400 to 580 ◦C. This result demonstrates thathe larger surface areas contribute to improved photocatalyticctivity. The specific surface area of mp-g-C3N4 samples preparedt 550 ◦C for 2 h reaches 86.4 m2 g−1, which is the largest among allhe g-C3N4 samples. This sample exhibits the best photocatalyticctivity for H2 evolution (284 �mol h−1 g−1) under visible-lightrradiation.
.6. PL spectra and UV–vis absorption spectra
Fig. 7 displayed the PL spectra of the g-C3N4 samples. The nor-alized PL spectra (Fig. 7a) are acquired from the pm-g-C3N4
owders using an excitation wavelength of 350 nm. Obviously, theigher sintering temperature, the longer wavelength does the PLeak centered at and consequently the lower energy the opticalandgap shifts toward. Since the bandgap of g-C3N4 can be reducedy adjusting the degree of condensation to a larger extent [29,30],he narrowed optical bandgap reveals that as the sintering temper-ture increases, the condensation degree of pm-g-C3N4 is enlarged,ia the release of more and more NH3 molecules. In this regard, elec-ron transition from �–�* needs lower excitation energy and thushe light harvesting extends to longer wavelength.
UV–vis diffuse reflection spectra were used to investigate theptical properties of the g-C3N4 samples. As shown in Fig. 8, anncrease in calcination temperatures results in a redshift of thebsorption edge in pm-g-C3N4 samples and the pm-g-C3N4 samplebtained at 580 ◦C exhibits two absorption bands due to decompo-
ition. Note that remarkable redshifts of the absorption edges cane observed when the calcination temperature increases from 400o 450 ◦C, which are in good agreement with the PL spectra shownn Fig. 7a. The corresponding bandgaps calculated from Tauc plots
Fig. 7. (a) Normalized PL spectra of pm-g-C3N4 samples at various temperatures for1 h. (b) PL spectra for pm-g-C3N4 and m-g-C3N4 (sintering at 500 ◦C for 2 h and then520 ◦C for 2 h). (c) PL spectra for pm-g-C3N4 samples at 550 ◦C for different hours.
are 2.90, 2.71, 2.68, 2.65 and 2.58 eV for the pm-g-C3N4 samples cal-cined at 400, 450, 500, 550 and 580 ◦C for 1 h, respectively, as shownin the inset of Fig. 8. This calculation also suggests the indirectbandgaps of the as-obtained g-C3N4 samples, which is consistent
with the result based on density functional theory [31]. Therefore,together with the PL spectra, higher sintering temperature inducedbetter light absorbance may also contribute to better photocatalyticperformance.
258 Y. Zhong et al. / Applied Surface Sc
Fig. 8. Normalized UV–vis diffuse reflection spectra for pm-g-C3N4 samples at var-iab
3
scltapPsips(1nTsPSefiTtbdprp
Sgo
ous temperatures for 1 h. The diffuse reflectance spectra were transformed to thebsorbance by the Kubelka–Munk relationship. Tauc plots evaluating the opticalandgaps are shown in the inset.
.7. Effects of the protonation on the photocatalytic activity
Up to now, the sharply improved activity over the pm-g-C3N4ample obtained at higher sintering temperature is attributed to beombinational effects of increased specific surface area and betteright absorbance. In order to clarify the effects of the protonation onhe improved photocatalytic activity over the pm-g-C3N4 sample,dditional investigation is needed. The same sintering process waserformed on protonated melamine and melamine, respectively.hotocatalytic H2 production over the pm-g-C3N4 and m-g-C3N4amples calcined at 500 ◦C for 2 h and then 520 ◦C for 2 h are shownn Fig. 6(g and h). The pm-g-C3N4 sample is found to exhibit higherhotocatalytic activity than the m-g-C3N4 samples. The calculatedpecific surface areas for the pm-g-C3N4 and m-g-C3N4 samplesprepared by sintering at 500 ◦C for 2 h and then 520 ◦C for 2 h) are9.4 and 16.6 m2 g−1, respectively, which suggests that the proto-ation plays a minor role in increasing their specific surface areas.he comparison of PL spectra between these two samples is pre-ented in Fig. 7b. The pm-g-C3N4 sample exhibits a relatively weakL intensity, which is only about 30% of that of m-g-C3N4 sample.ince a PL peak is aroused by the recombination of photoinducedlectron–hole pairs [25,27], a relatively strong PL intensity signi-es fast recombination rate of photogenerated electron–hole pairs.he weaker PL emission intensity of pm-g-C3N4 sample indicateshe improved charge separation of photoinduced charge carriersecause of the porous structure (see Scheme 1) [32]. The photoin-uced electrons migrate to the surface of Pt particles, while the
hotoinduced holes migrate to the pores. Since the oxidation andeduction reaction occur on the separated sites, recombination ofhotoinduced carriers was inhibited. On the other hand, 12.2 nm
cheme 1. A schematic diagram for photocatalytic H2 evolution process on a porous-C3N4 sample. The oxidation and reduction reaction occur on the separated sitesf the porous structure, leading to less recombination of photoinduced carriers.
ience 295 (2014) 253– 259
of redshift can be notably observed in the pm-g-C3N4 sample,compared with m-g-C3N4 sample. These results indicate that pro-tonation of the melamine results in higher degree of condensationand less recombination of photoinduced carriers, which help to ahigher H2 evolution activity over the pm-g-C3N4 sample. One possi-ble explanation for the higher condensation induced by protonationmay be that protonation of melamine facilitates the release of NH3molecules. As a result, the protonation treatment of melamine pre-cursor plays an essential role in enhancing the light absorbance ofthe pm-g-C3N4 samples.
3.8. Optimization of photocatalytic activities
Next, we optimize the sintering condition of the pm-g-C3N4samples. The results show that the H2 evolution activity (Fig. 6e)increases further when sintering process is extended by another1 h at 550 ◦C, compared with Fig. 6d. Other sintering conditionslike 600 ◦C for 1 h, 580 ◦C for 2 h and 550 ◦C for 3 h led very lowyield owing to the unstability of the pm-g-C3N4 samples abovethe temperature of 475.4 ◦C. The calculated specific surface areaof the mp-g-C3N4 sample increases from 59.3 to 86.4 m2 g−1. Alsothe comparison of PL spectra between pm-g-C3N4 samples cal-cined at 550 ◦C for 1 h and 550 ◦C for 2 h is presented in Fig. 7c. Byextending the sintering time from 1 h to 2 h, no obvious redshiftappears which suggests the similar light absorption properties.However, the PL emission intensity turns weaker. That is becausethe increased surface area provides more reaction sites and finallyleads to less recombination of photogenerated carriers. Thus, theincreased specific surface area induced by further sintering and lessrecombination of photogenerated carriers now make major contri-bution to the higher activity for photocatalytic H2 production, whileextending calcination time induced better light absorbance on thepm-g-C3N4 sample calcinated at 550 ◦C for 2 h imposes relativelysmall effect.
Since the cocatalyst can enhance the catalytic performance, wehave checked the effects of Pt-loading amount on the photocat-alytic H2 production. According to the curves in Fig. S5, the activityfor H2 evolution improves firstly with an increase in the Pt con-tent and then decreases gradually. The results give the maximumH2 evolution rate with 4.0 wt.% of loaded Pt, which is as high as417 �mol h−1 g−1. It is reasonable to conclude that cocatalyst doesimprove the efficiency of photocatalytic water splitting, however,excessive loading of Pt will affect the light absorption by the pm-g-C3N4 samples and lead to poor activity [28].
4. Conclusion
In summary, we have investigated the effects of protonationon the photocatalytic performances of the g-C3N4 samples dur-ing their preparation. The g-C3N4 samples (pm-g-C3N4) exhibit aporous structure due to the decomposition of self-assembled rod-like protonated melamine, which may exhibit less recombination ofphotogenerated charge carriers. Since the release of NH3 moleculesis facilitated by the protonation treatment of melamine, the pm-g-C3N4 samples may exhibit higher degree of condensation andtherefore better light absorbance, compared with m-g-C3N4 sam-ples prepared by heating melamine. These factors led to betterphotocatalytic activities for H2 evolution over the pm-g-C3N4 sam-ples under visible-light irradiation. Upon increasing the sinteringtemperature, the pm-g-C3N4 sample exhibited increased specificsurface area and better light absorbance. After optimizing the cal-
cination temperature of protonated melamine (550 ◦C for 2 h) andthe amount of Pt cocatalyst (4 wt.%), the highest hydrogen evolutionrate of 417 �mol h−1 g−1 was achieved over the pm-g-C3N4 sam-ple under visible-light irradiation of 300-W Xe lamp (� ≥ 420 nm).
face Sc
Tooc
A
CoI15L
A
i0
R
[[
[
[
[[[
[
[[[
[[[[
[[[[
Y. Zhong et al. / Applied Sur
he present synthesis method for g-C3N4 holds great advantagesn increasing light absorption and decreasing the recombinationf photogenerated electron–hole pairs, which are pivotal in photo-atalytic performance.
cknowledgements
This work is supported by National Basic Research Program ofhina (973 Program, 2013CB632404), a Project Funded by the Pri-rity Academic Program Development of Jiangsu Higher Educationnstitutions, New Century Excellent Talents in University (NCET-2-0268), the National Natural Science Foundation of China (Nos.1272102 and 21103070), and the Open Research Fund of State Keyaboratory of Bioelectronics, Southeast University.
ppendix A. Supplementary data
Supplementary material related to this article can be found,n the online version, at http://dx.doi.org/10.1016/j.apsusc.2014.1.008.
eferences
[1] T.S. Teets, D.G. Nocera, Chem. Commun. 47 (2011) 9268.
[2] X.B. Chen, S.H. Shen, L.J. Guo, S.S. Mao, Chem. Rev. 110 (2010) 6503.[3] B. Yue, Q. Li, H. Iwai, T. Kako, J. Ye, Sci. Technol. Adv. Mater. 12 (2011) 275.[4] Z.S. Li, T. Yu, Z.G. Zou, J.H. Ye, Appl. Phys. Lett. 88 (2006) 071917.[5] J.Y. Feng, Z.Q. Wang, J.J. Wang, L.J. Wan, S.C. Yan, Z.S. Li, Z.G. Zou, Eur. J. Inorg.
Chem. 2013 (2013) 4142.
[[[[
ience 295 (2014) 253– 259 259
[6] Z.G. Zou, J.H. Ye, K. Sayama, H. Arakawa, Nature 414 (2001) 625.[7] Z.G. Zou, H. Arakawa, J. Photochem. Photobiol. A 158 (2003) 145.[8] H. Yu, S.X. Ouyang, S.C. Yan, Z.S. Li, T. Yu, Z.G. Zou, J. Mater. Chem. 21 (2011)
11347.[9] J. Zhang, S. Yan, S.L. Zhao, Q. Xu, C. Li, Appl. Surf. Sci. 280 (2013) 304.10] D.-N. Bui, J. Mu, L. Wang, S.-Z. Kang, X.Q. Li, Appl. Surf. Sci. 274 (2013) 328.11] C. Wang, Q.Q. Hu, J.Q. Huang, L. Wu, Z.H. Deng, Z.G. Liu, Y. Liu, Y.G. Cao, Appl.
Surf. Sci. 283 (2013) 188.12] X.C. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J.M. Carlsson, K. Domen,
M. Antonietti, Nat. Mater. 8 (2009) 76.13] A. Thomas, A. Fischer, F. Goettmann, M. Antonietti, J. Muller, R. Schlogl, J.M.
Carlsson, J. Mater. Chem. 18 (2008) 4893.14] S.C. Yan, Z.S. Li, Z.G. Zou, Langmuir 25 (2009) 10397.15] X.H. Li, X.C. Wang, M. Antonietti, Chem. Sci. 3 (2012) 2170.16] J. Xu, H.T. Wu, X. Wang, B. Xue, Y.X. Li, Y. Cao, Phys. Chem. Chem. Phys. 15 (2013)
4510.17] F. Goettmann, A. Fischer, M. Antonietti, A. Thomas, Angew. Chem. Int. Ed. 45
(2006) 4467.18] H.J. Yan, Chem. Commun. 48 (2012) 3430.19] Y. Wang, X.C. Wang, M. Antonietti, Y.J. Zhang, ChemSusChem 3 (2010) 435.20] Y.J. Zhang, A. Thomas, M. Antonietti, X.C. Wang, J. Am. Chem. Soc. 131 (2009)
50.21] F.Z. Su, M. Antonietti, X.C. Wang, Catal. Sci. Technol. 2 (2012) 1005.22] G.H. Dong, L.Z. Zhang, J. Mater. Chem. 22 (2012) 1160.23] J. Gao, Y. Zhou, Z.S. Li, S.C. Yan, N.Y. Wang, Z.G. Zou, Nanoscale 4 (2012) 3687.24] F. Dong, L.W. Wu, Y.J. Sun, M. Fu, Z.B. Wu, S.C. Lee, J. Mater. Chem. 21 (2011)
15171.25] S.C. Yan, Z.S. Li, Z.G. Zou, Langmuir 26 (2010) 3894.26] Q.J. Xiang, J.G. Yu, M. Jaroniec, J. Phys. Chem. C 115 (2011) 7355.27] S.X. Min, G.X. Lu, J. Phys. Chem. C 116 (2012) 19644.28] P. Zhou, Z.S. Li, Z.G. Zou, Curr. Inorg. Chem. 2 (2012) 184.
29] W. Wei, T. Jacob, Phys. Rev. B 87 (2013) 085292.30] Y. Zhang, T. Mori, J. Ye, Sci. Adv. Mater. 4 (2012) 282.31] Y. Xu, S.P. Gao, Int. J. Hydrogen Energy 37 (2012) 11072.32] X.Y. Chen, T. Yu, X.X. Fan, H.T. Zhang, Z.S. Li, J.H. Ye, Z.G. Zou, Appl. Surf. Sci. 253
