硅藻土_g_C3N4复合材料的制备及其可见光增强活性_王丹军

第31卷 第8期 无 机 材 料 学 报

V ol. 31

No. 8

2016年8月

Journal of Inorganic Materials Aug., 2016

Received date: 2016-01-06; Modified date: 2016-01-22

Foundation item: National Natural Science Foundation of China (21373159); Project of Science & Technology Office of Shananxi Province

Article ID: 1000-324X(2016)08-0881-09 DOI: 10.15541/jim20160015

Synthesis of Diatomite/g-C 3N 4 Composite with Enhanced

Visible-light-responsive Photocatalytic Activity

WANG Dan-Jun 1, SHEN Hui-Dong 1, GUO Li 1, 2, HE Xiao-Mei 1, ZHANG Jie 1, FU Feng 1

(1. School of Chemistry & Chemical Engineering, Shaanxi Key Laboratory of Chemical Reaction Engineering, Yan’an University, Yan’an 716000, China; 2. School of Materials Science & Engineering, Shaanxi Normal University, Xi’an 710119, China)

Abstract: Novel visible-light-responsive diatomite/g-C 3N 4 composite was successfully synthesized via a facile im-pregnation-calcination method. The sample was characterized by TG, XRD, FE-SEM, HR-TEM, FT-IR, XPS, UV-Vis-DRS, and PL spectra. The photocatalytic activities of samples were evaluated by degradation of RhB under visible light irradiation. Experimental results indicated that 2.32wt% diatomite/g-C 3N 4 composite exhibits high effi-ciency for the degradation of RhB. The photoreaction kinetics constant value is about 1.9 times as high as that of g-C 3N 4 under visible light irradiation. The radical trap experiments indicate that ·O 2- serves as the main active species for the photodegradation of RhB over 2.32wt% diatomite/g-C 3N 4 under visible light irradiation. The enhanced photo-activity is mainly attributed to the electrostatic interaction between g-C 3N 4 and negatively charged diatomite, synergis-tic effect lead to the efficient migration of the photogenerated electrons and holes of g-C 3N 4.

Key words: diatomite/g-C 3N 4 composite; impregnation-calcination method; visible-light-irradiation; electrostatic in-teraction

Up to now, it is still a difficult problem to treat dyes

wastewater due to its high stability and complicated com-positions. The conventional treatment methods, such as absorption, ultrafiltration, reverse osmosis, coagulation, etc . are ineffective for its decolorization and mineraliza-tion [1]. In order to cope with the growing environmental problems, new efficient environment purification tech-nologies have been developed, such as advanced oxidation processes [2]

. Photocatalytic technology is an efficient means which is applicable on completely degrading or-ganic pollutants in waste water but very challenging proc-ess to convert solar energy into chemical energy [3]. So, it is urgent and indispensable to utilize sunlight efficiently, development of more efficient, sustainable, visible-light- responsive photocatalytic materials. Recently, graphitic carbon nitride (g-C 3N 4) which is a metal-free polymeric photocatalyst, have attracted exten-sive attention because of its good photocatalytic perform-ance for hydrogen or oxygen production via water split-ting under visible light irradiation [4]. In general, the prepa-ration of g-C 3N 4 obtained by heating low-cost melamine

was investigated by Zou’s group [5]. The metal free g-C 3N 4

photocatalyst possesses very high thermal, optical, chemical

stability and exceptional electronic as well as biocompati-ble properties [6], which make it valuable for photocatalytic applications. However, the photocatalytic performance of

g-C 3N 4 has been restricted due to its optical moderate band gap (E g =2.7 eV) and the high recombination rate of

photogenerated electron hole pairs [7]. Therefore, scientists have made significant efforts to improve the photocata-lytic activity of g-C 3N 4. To this end, various strategies

have been developed, such as doping with metal/nonmetal

elements [8-11], formation of heterosjunction (e.g. CdS/g- C 3N 4[12], SmVO 4/g-C 3N 4[13], N-TiO 2/g-C 3N 4[14], g-C 3N 4/

Ag 3PO 4 [15], DyVO 4/g-C 3N 4[16], etc.), isotype heterostruc-ture and noble metal modification [17-18]. Up to now, it is still a challenge to construct g-C 3N 4 based photocatalyst with efficient utilization of visible light, suitable band edges for targeted reactions, high stability, environmental

friendliness, and low cost materials to modify g-C 3N 4. Diatomite is a naturally formed non-metallic siliceous

sedimentary material [19]. Due to its high porosity, specific

surface area, high adsorption capability, cheap, abundant, non-toxic and environmental friendly, diatomite represents an attractive substrate for immobilization of variety of photocatalysts [20-22]. Compared with other clay, it has 网络出版时间：2016-11-29 13:21:14

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882 无机材料学报第31卷

natural ordered micro-/macroporous structures, high ad-sorption capacity and possesses abundant adsorption sites. These advantages make diatomites to be one of the most promising adsorption materials in processing wastewa-ter[23-25]. Furthermore, studies have confirmed that diato-mites is a good matrix for synthesizing composite photo-catalysts with higher photocatalytic activity, such as TiO2/diatomite[26-27],(PEG)/diatomite[28], Ce-TiO2/diato-mite[29], and PCM/diatomite[30].

Recently, Wang and co-worked reported that MoS2 with layered structure can promote the photocatalytic activity of g-C3N4[31]. Very recently, Li et al[32] reported the ben-tonite/g-C3N4, which exhibited a significantly enhance-ment photocatalytic activity, Si–OH on the surface of lay-ered bentonite can form strong forces with g-C3N4, which allow the prompt migration of light-induced charge. Herein, in view of the similar structure and composition of diatomite and bentonite, a impregnation-calcination route was employed to synthesize the novel visible-light- responsive diatomite/g-C3N4 composite. The photodegra-dation experiments were performed and the possible mechanisms of enhancement of diatomite/g-C3N4 compos-ite were also investigated.

1 Materials and methods

1.1 Sample preparation

All reagents were of analytical purity and were used without further purification. In a typical procedure, 1.0 g of diatomite was placed in a plastic beaker and mixed with 20 mL of 2.0 mol/L NaOH solution under magnetic stir-ring. After reaction for 12 h at ambient temperature, the sample was collected and washed until achieving pH of the solution was 7.0, then dried at 80℃ overnight, and ground into a powder in a mortar. The obtained product was denoted treated diatomite.

Synthesis of diatomite/g-C3N4. Firstly, in order to ob-tain well dispersed diatomite sheets, a certain amount of diatomite (0.01 g, 0.02 g, 0.04 g, 0.10 g, 0.20 g) was dis-persed in 30 mL methyl alcohol with 30 min continuous ultrasonic at room temperature. Subsequently, 4.0 g me-lamine was added to the diatomite suspension with stirring at 25 for 4 h. Then, the mixture was dried at 70

℃℃ for 6 h and the resulting dried mixtures were calcinated at 550℃for 4 h in a muffle furnace. The obtained products are grayish yellow, which were obtained from six reactant systems. According to thermogravimetric analysis (TG) results, the weight contents of diatomite in diatomite/g- C3N4 composites were estimated to be 1.22wt%, 2.32wt%, 5.46wt%, 13.88wt% and 25.21wt%, respectively. Bulk g-C3N4 was also prepared according to the similar above process. Based on the TG result of 2.32wt%diatomite/g-C3N4 composite, diatomite and g-C3N4 mechanical mixture were prepared by mixing diatomite (0.01 g) with g-C3N4 (0.55 g), which was de-noted as diatomite/g-C3N4 mixture. In addition, diato-mite/g-C3N4 (2.32wt%)sample was also prepared by using diatomite without alkali treated as material, and the resulted sample was denoted as untreateddiatomite/g-C3N4 (2.32wt%).

1.2 Characteration

The crystalline phases of diatomite/g-C3N4 composites were analyzed by XRD using a Shimadzu XRD-7000

X-ray diffractometer (CuKα, 0.15418 nm). The mor-phologies and structure of the obtained samples were ex-amined by FE-SEM (JSM-6700F) and HR-TEM (JEM-2100). FT-IR spectra of samples were recorded on a Nicolet Avatar-370 spectrometer at room temperature. The UV-Vis diffuse reflection spectra (UV-Vis-DRS) of the samples were measured using a Shimadzu UV-2550 UV-Vis spectrophotometer. BaSO4 was used as the re-flectance standard. X-ray photoelectron spectroscopy (XPS) analysis was performed on an ESCA Lab MKII

X-ray photoelectron spectrometer. TG analysis was done

on STA-449C Jupiter (NETZSCH Corporation, Germany). 1.3 Photocatalytic experiment

The photocatalytic activities of diatomite/g-C3N4 were evaluated by using RhB as a model pollutant under irra-diation of a 400 W metal halide lamp with an optical filter to cut off the light below 420 nm. In a typical process, 200 mg of photocatalyst and 200 mL RhB solu-tion was stirred in dark for 1.0 h to establish an adsorp-tion/desorption equilibrium. At interval of 10 min, 10 mL solution was sampled and centrifuged to remove the catalyst particles. The concentration was analyzed by measuring the maximum absorbance at 554 nm for RhB using a Shimadzu UV-2550 spectrophotometer. In order

to further investigate the active species involved in the photocatalytic process, a series of quenching tests have been performed. EDTA-2Na (ethylenediamine tetraacetic acid disodium salt), IPA (isopropanol), BQ (p-benzoquinone) was used as a quencher for holes (h+), hydroxyl radicals (·OH) and superoxide radical (·O2-), respectively[33]. The concentration of quencher is 1 mmol/L in the solution.

2 Results and discussion

2.1 XRD, XPS and TG analysis

Fig. 1 shows the powder XRD patterns of raw diatomite, alkali treatment diatomite, g-C3N4 and various diato-mite/g-C3N4 composites. As can be seen from Fig. 1(a), two marked peaks can be ascribed to (100) and (002)

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WANG Dan-Jun, et al : Synthesis of Diatomite/g-C 3N 4 Composite with Enhanced Visible-light-responsive (883)

characteristic diffraction planes of the g-C 3N 4[5-6]. For the

diatomite clay, the XRD pattern of raw diatomite revealed that the main phase of non-crystalline opal-A with the characteristic broad peak centered at the peak of 21.8°[24]. The XRD pattern of alkali treatment diatomite was similar to that of raw diatomite, indicating that the NaOH etching did not alter the diatomite mineral structure. In the case of diatomite/g-C 3N 4 composites, crystalline diatomite is not obviously observed with low diatomite loadings. However, in the enlarged Fig. 1(b) from 25°to 30°, the as-prepared diatomite/g-C 3N 4 composites with higher diatomite load-

ings (>2.32%), the peak intensity corresponding to (002) lattice plane decreased. This result suggested that the di-atomite/g-C 3N 4 composites are constituted by g -C 3N 4 and diatomite.

To investigate the valence states of various species, the diatomite/g-C 3N 4 (2.32wt%) was studied by X-ray photo-electron spectroscopy (XPS). XPS results indicate the presence elements of Si, C, N and O in the diato-mite/g-C 3N 4 (2.32wt%) composite (Fig. 2(a)). The C1s characteristic peaks at 288.08 eV and 284.58 eV , as shown in Fig. 2(b), are assigned to C–N–C coordination and the adventitious carbon, respectively [9]. Fig. 2(c) shows the N1s binding energy of g-C 3N 4 at 398.78 eV, which is assigned to nitrogen element of sample [9]. Both C1s and N1s binding energies of 2.32wt% diatomite/g-C 3N 4 show minor negative shifts compared to pure g-C 3N 4, indicating there exist the interaction force between di-atomite and g-C 3N 4.

Fig. 3 shows the weight loss of diatomite is negligible, which indicating very few residual water and organic impurities exist in diatomite, and the dehydroxylation of aluminosilicate is slightly. As for diatomite/g-C 3N 4 composites, they have no obvious difference in the ther-mal stability. The initial decomposition temperature of diatomite/g-C 3N 4 composites is at about 545℃, which is lower than that of g-C 3N 4 at 550℃. The reason may be attributed to the existence of fluffy sheets of g-C 3N 4 in the composites. However, the complete decomposition temperature of diatomite/g-C 3N 4 composites is at about 710℃, which is almost equal to that of g-C 3N 4. The quality score of diatomite was almost close to the theo-retical calculated value of diatomite/g-C 3N 4, for example (Table 1).

Fig. 1 XRD patterns of samples

(a) XRD patterns of diatomite, g -C 3N 4 and diatomite/g-C 3N 4 composite; (b) Enlarged XRD pattern of diatomite g-C 3N 4

and diatomite/g-C 3N 4 composites from 25° to 30°

The peaks marked by (●) in (a) are the characteristic of the Quartz impurity in the diatomite sample

Fig. 2 XPS spectra of g-C 3N 4 and diatomite/g-C 3N 4(2.32wt%)

(a) Survey spectra; (b) C1s; (c) N1s

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Table 1 Content in diatomite/g-C 3N 4 by TG curves analysis

Samples

Diatomite theoretical content /wt%

Diatomite experimental/wt%

Diatomite/g-C 3N 4 (1.22wt%)

1.79

1.22

Diatomite/g-C 3N 4 (2.32wt%) 3.56 2.32

Diatomite/g-C 3N 4 (5.46wt%) 6.78 5.46

Diatomite/g-C 3N 4 (13.88wt%) 15.38 13.88

Diatomite/g-C 3N 4 (25.21wt%) 26.67 25.21

Fig. 3 TG curves for heating diatomite, g-C 3N 4 and diato-mite/g-C 3N 4 composites

2.2 Morphology and structure analysis

Fig. 4 shows the size and morphology of g-C 3N 4, raw diatomite, alkali treatment diatomite and diatomite/g-C 3N 4 composites. It can be seen that diatomite sample has disk-like and highly developed macroporous structure. After NaOH washing, the morphology of raw diatomite

was preserved, while the size of the central macropores increased (Fig. 4(a)-(b)). After diatomite loading onto the surface of layered g-C 3N 4, the diatomite/g-C 3N 4 composite can be observed with abundant fluffy sheets (Fig. 4(c)). Fig. 4(d) is the TEM image of 2.32wt%diatomite/g-C 3N 4. It can be clearly observed that some diatomite particles was loaded on the surface of layered structure g-C 3N 4. In HR-TEM image(Fig. 4(f)), the border of diatomite and g-C 3N 4 can be observed clearly, suggesting diatomite lay-ers combining well with g-C 3N 4.

Fig. 5 shows the FT-IR spectra of diatomite, g-C 3N 4, and diatomite/g-C 3N 4 composites. As can be seen from Fig. 5, the intense peaks in the FTIR spectrum at 1629 cm -1, 1105 cm -1, 796 cm -1 and 467 cm -1 are observed for the raw diatomite, which are related to the structure of diatomite, the peak at 1105 cm -1 is due to vibration siloxane linkages Si–O–Si [34]. The band at 1629 cm -1 reflects H–O–H bonding vibration of structured water molecules of silica. The peaks ob-served at 796 cm -1 is assigned to vibration in the silica structure of the symmetric external Si–O bond [35]. Ac-cording to Elze and Rice’s report [36], occurrence of the band with a maximum at 467 cm -1 is characteristic of the

Fig. 4 FE-SEM and TEM images of samples

(a) FE-SEM image of diatomite; (b) FE-SEM image of alkali washed diatomite; (c) FE-SEM image of diatomite/g-C 3N 4 composite; (d) TEM of diato-mite/g-C 3N 4 composite; (e) SEAD pattern of g-C 3N 4; (f) Conjunction edge between flake-like g-C 3N 4 and diatomite particles

第8期 WANG Dan-Jun, et al: Synthesis of Diatomite/g-C3N4 Composite with Enhanced Visible-light-responsive (885)

Fig. 5 FT-IR spectra of diatomite, g-C3N4 and diatomite/g- C3N4 composites

Si–O bonds in silica minerals such as tridymite and cris-tobalite. All these characteristic peaks suggest that diato-mite is mainly composed of SiO2. For the g-C3N4 sample, peaks positions between 1200 and 1650 cm-1 regions are related to the stretching modes of CN heterocycles[37]. The peaks at 1642 cm-1 and 1561 cm-1 ascribed to the C≡N stretching vibrations modes[38], while the peaks at 1241 cm-1, 1322 cm-1 and 1405 cm-1 to the aromatic C–N strechings[39]. The peak located at 808 cm-1 was related to the characteristic breathing mode of triazine units[40]. In the case of diatomite/g-C3N4 composites, the wide band with intense absorption observed at 467 cm-1 is character-istic of the Si–O bonds in silica minerals. The FT-IR re-sults indicate that this diatomite/g-C3N4 composites con-tains two fundamental components of diatomite and g-C3N4 and that no appreciable chemical reaction occurred between diatomite and g-C3N4.

2.3 UV-Vis-DRS analysis

Fig. 6 shows the UV-Vis-DRS spectra of pure g-C3N4 and diatomite/g-C3N4 composites. In Fig. 6(a), the absorp-tion edge of pure g-C3N4

exhibited a strong absorption ability in the visible-light region. It can also be clearly seen that diatomite/g-C3N4 composites with different diatomite contents show differ-ent absorption abilities as compared with pure g-C3N4, indicating that there may be some interaction between diatomite and g-C3N4. In previous TEM analysis, the di-atomite/g-C3N4 composites show enlarged much fluffy layer structure. In view of the partly imperfect poly-mer-like structure of g-C3N4[41], the g-C3N4 in diato-mite/g-C3N4 might have more defects compared with the pure g-C3N4, which improves the utilization of light energy. The band gap energy (E g) of samples can be estimated from the plots of (αhν)1/2vs photon energy (Fig. 6(b)). Therefore, the visible light responses of diatomite/g-C3N4 composites are significant improved. 2.4 Photocatalytic activity

Fig. 7(A) shows the photocatalytic activity of samples for the degradation of RhB under visible light irradiation. It was found that RhB self-degradation was negligible, diatomite/g-C3N4 (2.32wt%) and diatomite/g-C3N4 (5.46wt%) exhibited higher photocatalytic activity than that of g-C3N4. After irradiation for 30 min, the photocatalytic degradation rate of RhB was 98.94% and 91.00% for for diatomite/g-C3N4 (2.32wt%) and pure g-C3N4, respectively. The photocatalytic activity of diatomite/g-C3N4 improved with increasing diatomite content, and the optimal di-atomite content was 2.32wt%. The photocatalytic activ-ity of diatomite/g-C3N4 mixture, untreated and treated diatomite/g-C3N4 (2.32wt%) was compared and listed in Fig. 7(B). It was clearly observed that diatomite/g-C3N4 (2.32wt%) sample exhibited the highest degradation. It may be ascribed to two reasons: firstly, alkali treatment can improve the specific surface area of diatomite, which is beneficial to absorb the RhB; secondly, alkali treatment can enhance the electrostatic interaction of g-C3N4 and diatomite. When g-C3N4/diatomite is dispersed in water, Na+ diffused away from the solid surface and left the negative charges on the diatomite surface. The negatively charged of diatomite can promote the immigration of elec-trons and holes, thus suppress the charge recombination. The alkali treated diatomite possesses more Na+ than that of untreated diatomite, which results in the treated diato-mite/g-C3N4 showing higher degradation than that of un-treated one.

Fig. 7(C) showed that the pseudo first order rate constant (k) for RhB degradation with g-C3N4 was 0.07618 min-1. For diatomite/g-C3N4 composites with diatomite contents of 1.22wt%, 2.32wt%, 5.46wt%, 13.88wt%, 25.21wt% and diatomite/g-C3N4 mixture, the corresponding k value were calculated to be 0.07758, 0.14239, 0.10701, 0.03183, 0.02353, and 0.06089 min-1, respectively. In the diato-mite/g-C3N4 composites, the k value of diatomite/g-C3N4 (2.32wt%) is 1.9 times as high as that of the pure g-C3N4. However, further increasing the proportion of diatomite, the k value shows a slight decrease due to the shading ef-fect. Therefore, excess loading of diatomite could prevent g-C3N4 from absorbing the light and result in a deceasing of catalytic activity. It can be seen from Fig. 7(D) that the absorptive property of diatomite/g-C3N4 increase re-markably with increasing diatomite content. However, the adsorption capacity of diatomite/g-C3N4 composites is not superior to that of diatomite and g-C3N4 mixture. It is ob-vious that the enhanced photocatalytic activity of diato-mite/g-C3N4 composites is not ascribed to the adsorption capability. The significant differences in the interface of the composite is responsible for the enhanced photocata-

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lytic activity of diatomite/g-C 3N 4 composite [32].

Fig. 7(E) shows temporal evolution of the spectral changes during photocatalytic degradation of RhB over diatomite/g-C 3N 4 (2.32wt%) composite. It can be seen that the intensity of the absorption peak decrease drastically within 30 min. On the other hand, from the viewpoint of practical application, it is important to evaluate the stabil-ity of the diatomite/g-C 3N 4 catalyst. The repeated experi-

ment results indicated that the photocatalytic activity of 2.32wt%diatomite/g-C 3N 4 composite showed negligible decreasing after five cycles and the crystal structure didn’t not change after the photocatalytic reaction(Fig. 7(F)).

2.5 Photocatalytic mechanism

Generally speaking, PL spectra analysis was a reliable method to investigate the fate of photogenerated electrons and holes [42]

. Therefore, in present study, PL spectrum was

Fig. 6 (a) UV-Vis spectra and (b) plot of (αh ν)1/2 vs energy (h ν) for the band gap energy of g-C 3N 4

and diatomite/g-C 3N 4 composites

Fig. 7 Photocatalytic activity of the samples

(A) Photocatalytic degradation efficiency of RhB by g-C 3N 4 and diatomite/g-C 3N 4 composites; (B) Comparison of mixted, treated and untreated diato-mite/g-C 3N 4(2.32wt%); (C) Kinetic fit for the degradation of RhB with g-C 3N 4 and diatomite/g-C 3N 4 composites (a, blank; b, g-C 3N 4; c, diatomite/g-C 3N 4 (1.22wt%); d, diatomite/g-C 3N 4 (2.32wt%); e, diatomite/g -C 3N 4 (5.46wt%); f, diatomite/g-C 3N 4 (13.88wt%); g, diatomite/g-C 3N 4 (25.21wt%); h, diato-mite/g- C 3N 4 mixture (2.32wt%); i, diatomite); (D) Adsorption percentage and rate constants; (E) Absorption spectral changes of RhB under visible

light irradiation using diatomite/g-C 3N 4 (2.32wt%) as photocatalyst; (F) XRD patterns of diatomite/g-C 3N 4 before and after being used

第8期 WANG Dan-Jun, et al: Synthesis of Diatomite/g-C3N4 Composite with Enhanced Visible-light-responsive (887)

employed to further verify the interfacial charge transfer dynamics between the hetero-geneous interface of pure g-C3N4 and the diatomite/g-C3N4 composites. As can be seen in Fig. 8, for the pure g-C3N4, one main emission peak appears at about 470 nm, which is attributed to the inner band gap of g-C3N4[4]. After introducing diatomite onto g-C3N4, the intensities of the PL signal for the diato-mite/g-C3N4 composites are lower than that of g-C3N4, indicating that the composites have a lower recombination rate of electrons and holes under visible-light irradiation. As a consequence, it is reasonable to conclude that diato-

mite loading can enhance photocatalytic activity of g-C3N4.

In addition, BQ, EDTA-2Na, and IPA were used as quenchers for ·O2- , holes (h+), and ·OH scavengers, re-spectively[43-44]. Fig. 9 shows the active species trapping experiment in photocatalytic process of diatomite/g-C3N4 (2.32wt%) composite. The experimental results indicated that the photodegradation of RhB was almost not affected by adding EDTA-2Na as quencher of h+, respectively. While IPA slightly suppressed the photocatalytic degrada-tion of RhB. Nevertheless, the activity of the diatomite/ g-C3N4 (2.32wt%) composite was largely suppressed by the addition of BQ. Thus, it could be inferred that ·O2-serve as the main active species for the photodegradation of RhB over diatomite/g-C3N4 (2.32wt%) under visible light irradiations, and the reaction was partly driven by the action of ·OH radicals. Considering the above re-sults, ·OH, ·O2-were established as the main reactive spe-cies for RhB degradation, as depicted in the following formule:

diatomite/g-C3N4+hγ→diatomite/g-C3N4(e-+h+) (1)

e- + O2→ O2–(2) 2e– + O2– + 2H+→ ·OH + OH–(3)

RhB + .O2– /.OH/ → CO2 + H2O+ (4)

As discussed above, three main reasons for the increase in the photocatalytic efficiency of coupled g-C3N4/diato-mite composites are: (i) the absorption edges of Fig. 8 PL spectra of g-C3N4 and diatomite/ g-C3N4 composites Fig. 9 Trapping experiment of active species during photocata-lytic degradation of RhB over diatomite/g-C3N4 (2.32wt%) under visible light irradiation

diatomite/g-C3N4 composites shift significantly to longer wavelengths compared with the pure g-C3N4, which indi-cates the composites can be excited by more visible light photons; (ii) the improved adsorptive activity of diato-mite/g-C3N4 composites compared with that of g-C3N4; (iii) the electrostatic interaction, the negatively charged of di-atomite can promote the immigration of electrons and holes, thus suppresses the charge recombination.

When g-C3N4/diatomite is dispersed in water, Na+ dif-fused away from the solid surface the exchangeable cations and left the negative charges on the diatomite sur-face. Under visible light irradiation, only g-C3N4 can be activated, the e-/h+ pairs of g-C3N4 should present on the g-C3N4 surface. The excited electrons and holes of g-C3N4 should be driven to migrate efficiently due to electrostatic interaction between g-C3N4 and the negatively charged diatomite. Thus, the charge recombination could be easily suppressed, leaving more charge carriers and enhancing the photocatalytic activity. Driven by the calcinations process, the layers of diatomite and g-C3N4 are splitted into many fluffy and thin sheets and a tight contact of di-atomite with g-C3N4 can be achieved[45-46]. Therefore, the high photoactivity of diatomite/g-C3N4 composite arises from the synergistic effects between diatomite and g-C3N4 interfaces.

3 Conclusions

A novel visible-light-responsive diatomite/g-C3N4 composite was successfully synthesized via a facile im-pregnation-calcination method. Photocatalytic experimen-tal result indicated that diatomite/g-C3N4 composites ex-hibited higher photocatalytic activity than pure g-C3N4 in the degradation of RhB. The radical trap experiments showed that the degradation of Rh

B was driven mainly by

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the ·O 2-, and partly by the action of ·OH radicals. The sig-nificant enhancement in the photocatalytic performance of diatomite/g-C 3N 4 composites is ascribed not only to its adsorptivity but also to the interaction between g-C 3N 4 and diatomite, this can promote the efficient migration of the photogenerated electrons and holes of g-C 3N 4 and conse-quently improves the photocatalytic activity. This strategy is expected to be extended to other g-C 3N 4 loaded materi-als, which might have potential applications in removing pollutant.

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WANG Dan-Jun, et al : Synthesis of Diatomite/g-C 3N 4 Composite with Enhanced Visible-light-responsive (889)

Solar Cells, 2011, 95: 1647–1653.

[29] LIANG X H, FU X Y . Effect of the Ce-TiO 2/diatomite on the pho-to-catalysis degradation of MB. Mater. Sci. Forum., 2014, 789: 44–47.

[30] JEONG S G, JEON J, LEE J H, et al . Optimal preparation of

PCM/diatomite composites for enhancing thermal properties. Int. J. Heat Mass Trans., 2013, 62: 711–717.

[31] GUO S F, SHI L. Synthesis of succinic anhydride from maleic an-hydride on Ni/diatomite catalysts. Catal. Today , 2013, 212: 137–141.

[32] HOU Y , LAURSEN A B, ZHANG J, et al . Layered nanojunctions

[33] [34] [35] [36] [37] [38] lytic activity of Bi 2WO 6 hybridized with graphite-like C 3N 4. J. Mater. Chem ., 2012, 22(23): 11568–11573.

[39] ZIMMERMAN J L, WILLIAMS R, KHABASHESKU V N, et al .

Synthesis of spherical carbon nitride nanostructures. Nano Lett ., 2001, 1: 731–734.

[40] JIANG L, CHEN L L, ZHU J J, et al . Novel p-n heterojunction

photocatalyst constructed by porous graphite-like C 3N 4 and nanos-tructured BiOI: facile synthesis and enhanced photocatalytic activ-ity. Dalton Trans., 2013, 42(44): 15726–15734.

[41] ZHANG Y , THOMAS A, ANTONIETTI M, et al . Activation of

carbon nitride solids by protonation: morphology changes, en-院, 西安710119)

摘 要: 采用浸渍-焙烧法制备了具有可见光响应活性的硅藻土/g-C 3N 4复合光催化材料。利用TG 、XRD 、FE-SEM 、HR-TEM 、FT-IR 、XPS 、UV-Vis-DRS 和 PL 谱等手段对其物相组成、形貌和光吸收特性进行表征。以RhB 的光催化降解为探针反应评价催化剂的活性。光催化结果表明, 2.32wt%硅藻土/g-C 3N 4复合材料对RhB 有较高的催化活性, 光催化降解的速率常数是纯g-C 3N 4的1.9倍。自由基捕获实验表明, ·O 2–是RhB 在硅藻土/g-C 3N 4复合材料上光催化降解的主要活性物种。光催化活性提高的主要原因在于硅藻土和g-C 3N 4之间静电作用有利于光生电子-空穴在g-C 3N 4表面的迁移, 进而提高g-C 3N 4的光催化活性。

关 键 词: 硅藻土/g-C 3N 4复合材料; 浸渍-焙烧法; 可见光照射; 静电作用 中图分类号: TB321 文献标识码: A

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感应器的预制体外表面是温度最高的区域，碳的沉积由此开始，向径向发展。 温度梯度法的设备如下图：

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4金属基复合材料制备方法及应用

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浅谈中职学校就业方向英语教学 摘要：中职学校英语教学具有很强的挑战性和灵活性，老师不但要具有深厚的专业知识，更需要根据中职学生与普通中学学生性质的不同而有针对性地进行英语教学。中职英语老师需要有针对性的备课，灵活多变的课堂组织教学，以及不可忽略的课后教学。 关键词：中职学生就业方向英语教学 中图分类号： g718 文献标识码： c 文章编号：1672-1578（2011)11-0215-02 许多中等职业学校的教师都认为教学就是把自己所学知识倾囊 相授，这些年教学实践使笔者明白中职英语教学具有很强的挑战性和灵活性，老师不但要具有深厚的专业知识，更需要根据中职学生与普通中学学生的性质不同，而有针对性地进行英语教学。下面笔者主要针对就业方向的中职学生浅谈一下英语教学应该注意的几点： 1 有针对性地备课 中等职业学校学生的文化知识一般比较差，英语老师在教学前是否认真的有针对性的备课是教学是否成功的首要条件，备课时教师要熟悉大纲和教材，把握教学内容；分析教学任务，明确教学目标；研究学生特点和性质以及学生的知识基础，选择教学方法；设计教学过程，编写教学计划，从而为上课做好充分的准备。中等职业学校就业方向的英语教学应以“适用”为备课原则，以求学生能掌握一些基础英语知识以及能说一些日常生活适用的英语，很多属于高

考的英语知识点或难点则可以选择不予讲解。 2 进行有效的课堂组织教学 2.1激发学习英语的激情与兴趣 每个教师都明白学习兴趣对于教学的重要性，而在中职学校教学过程中这一点显得尤为重要，中职学生在中学的文化课已经相对薄弱，这严重导致了他们缺乏对文化课的学习兴趣，进入中职学校还要学习文化课，他们显然没有任何的学习兴趣，尤其是英语这一学科，一些学生甚至连26个英语字母都在中学时没能掌握，不能准确的针对国际音标发音，怎能还有学习兴趣？所以作为一名中职学校的英语教师，怎样唤醒中职学生的英语学习兴趣是一个教学过程中的一个重点也是难点，培养中职学生学习英语的激情与兴趣应该从两点出发：首先，要从教师本身出发。我们很多人都认为老师一般都需要在学生面前建立自己的威信，这点的确需要，但是往往很多老师过于严肃，让学生产生了相当大的畏惧心理，再加上教学内容全是枯燥的英语语法知识，中职学生怎能对英语学习充满学习兴趣？其实老师上英语课应该一改严肃的教学风格，上课可以带上丰富的肢体语言，英语语言可以抑扬顿挫，面部表情可以根据授课内容而变化，同时老师面对学生要少一点架子，多一点的尊重和真诚，少一点尖酸刻薄，多一点赏识和信赖，少一些冷漠，多一点的热情和交流.师生之间只有互相了解，互相沟通，互相平等，学生才会喜欢你，才会爱你，到那时候，“亲其师而信其道”，一名这样的英语教师在学生喜欢的环境下教学必定充满了教学乐趣，学生同时也

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纳米复合材料制备

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纳米复合材料制备文件管理序列号：[K8UY-K9IO69-O6M243-OL889-F88688]

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Ti基复合材料及其制备技术研究进展评述

先进材料制备科学与技术课题报告 ——Ti基复合材料及其制备技术研究进展报告 学院：材料科学与工程学院 学号：SY1401210 姓名：刘正武 2014年12月24日

摘要 钛基复合材料(TMCS)以其高的比强度、比刚度和良好的抗高温、耐腐蚀性能,在航空航天、汽车等领域有着广阔的应用前景,引起了材料研究者的广泛兴趣。国外对钛基复合材料的研究已有近40年的历史,发展相当迅速,开发出来的原位合成工艺、纤维涂层等制备技术已经成功用于制备高性能钦基复合材料。国内TMCS研究起步较晚,虽取得了一定成绩,但与国外相 比还有一定差距。 本文主要从钛基复合材料的研究背景，强化原理，以及存在的主要问题方面做了总结，并对国内外的研究现状作了简要评述。钛合金本身具有较高的室温和高温比强度、低密度、高弹性模量。加入增强相，又进一步提高比弹性模量、比强度和抗蠕变能力。颗粒增强钛基复合材料(PTMCS)与纤维增强钛基复合材料(FTMCS)相比，具有制备工艺较简单，成本较低，无各向异性，可得到近净型零件等优点，是很有前途的复合材料。自生钛基复合材料基体将由纯钛基体向Ti6Al转化，并加入其它的合金元素，会得到实际应用。 关键词：钛基复合材料；性能；制备；研究进展

目录 第1章前言 ----------------------------------------------------------------------------------------------------------------------------- 4 1.1研究背景及原理-------------------------------------------------------------------------------------------------------------- 4 1.2 主要问题 ---------------------------------------------------------------------------------------------------------------------- 5 第2章国内外研究进展及评述 ---------------------------------------------------------------------------------------------------- 6 2.1 Ti基复合材料增强体的种类---------------------------------------------------------------------------------------------- 6 2.2陶瓷颗粒增强钛基复合材料 ---------------------------------------------------------------------------------------------- 7 2.2 自生钛基复合材料--------------------------------------------------------------------------------------------------------- 11 第3章结论 --------------------------------------------------------------------------------------------------------------------------- 13 参考文献 -------------------------------------------------------------------------------------------------------------------------------- 14

铝基复合材料的研究发展现状与发展前景

铝基复合材料的研究发展现状与发展前景摘要：铝基复合材料具有很高的比强度、比模量和较低的热膨胀系数，兼具结构材料和功能材料的特点。介绍了铝基复合材料的分类、制造工艺、性能及应用等几个方面，最后对铝基复合材料的研究状况及其发展趋势。做了简单的介绍。 关键词：铝基复合材料，制造工艺，性能，应用 Abstract:Aluminum matrix composite was in capacity of structure materials and function materials for its high specific strength and high specific modulus and low coefficient of thermal expansion.The classification of aluminum matrix composite were introduced and the preparation process、properties and application of aluminum matrix composite was expounded,and then the domestic research status and future development trends of the composite were summed up. Key words:aluminum matrix composites，preparation process，properties，application. 1.发展历史 1.1概述 复合材料是由两种或两种以上物理和化学性质不同的材料通过先进的材料制备技术组合而成的一种多相固体材料。根据基体材料不同，复合材料包括三类:聚合物基复合材料(PMC)、金属基复合材料(MMC)和陶瓷基复合材料(CMC)[1]。金属基复合材料在20世纪60年代末才有较快的发展，是复合材料的一个新分支，其以高比强、高比模和耐磨蚀等优异的综合性能，在航空、航天、先进武器系统和汽车等领域有广泛的应用，已成为国内外十分重视发展的先进复合材料。 在金属基复合材料中，铝基复合材料具有密度低、基体合金选择范围广、可热处理性好、制备工艺灵活、比基体更高的比强度、比模量和低的热膨胀系数，尤其是弥散增强的铝基复合材料，不仅具有各向同性特征，而且具有可加工性和价格低廉的优点，更加引起人们的注意[2]。铝基复合材料具有很大的应用潜力，并且已有部分铝基复合材料成功地进入了商业化生产阶段。 铝基复合材料是以金属铝及其合金为基体，以金属或非金属颗粒、晶须或纤维为增强相的非均质混合物。按照增强体的不同，铝基复合材料可分为纤维增强铝基复合材料和颗粒增强铝基复合材料。纤维增强铝基复合材料具有比强度、比模量高，尺寸稳定性好等一系列优异性能，但价格昂贵，目前主要用于航天领域，作为航天飞机、人造卫星、空间站等的结构材料。颗粒增强铝基复合材料可用来制造卫星及航天用结构材料、飞机零部件、金属镜光学系统、汽车零部件；此外还可以用来制造微波电路插件、惯性导航系统的精密零件、涡轮增压推进器、电子封装器件等[3]。 然而不管增强物的类型和形状尺寸如何，大多数铝基复台材料具有以优点： ①重量轻、比强度、比刚度高。 ②具有高的剪切强度。 ③热膨胀系数低，热稳定性高，并有良好的导热性和导电性。 ④具有卓越的抗磨耐磨性。 ⑤能耐有机液体，如燃料和溶剂的侵蚀。 ⑥可用常规工艺和设备进行成型和处理。 1.2分类

ZnO-CNTs纳米复合材料的制备及性能表征

物理化学学报(Wuli Huaxue Xuebao) October Acta Phys.?Chim.Sin.,2006,22(10)：1175~1180 ZnO?CNTs纳米复合材料的制备及性能表征朱路平1,2黄文娅3马丽丽4傅绍云1,*余颖4贾志杰4 (1中国科学院理化技术研究所,北京100080；2中国科学院研究生院,北京100049； 3武汉耀华玻璃有限公司,武汉430010；4华中师范大学纳米科技研究院,武汉430079)摘要以醋酸锌(Zn(CH3COO)2·2H2O)和经硝酸处理过的碳纳米管(CNTs)为原料,一缩二乙二醇(DEG)为溶剂, 采用溶胶法制备得到ZnO?CNTs纳米复合材料,并通过XRD、TEM、SEM、IR、PL等手段对样品进行了表征, TEM及SEM结果显示,负载在碳纳米管上的氧化锌纳米颗粒的尺寸小于25nm.讨论了反应时间、反应温度等 因素对产品形貌的影响,并对复合材料的光致发光效应及其形成机理进行了初步的探讨.PL结果表明,相对于 纯ZnO,ZnO?CNTs纳米复合材料的近紫外发射峰峰位发生了明显的蓝移. 关键词：溶胶法,ZnO?CNTs,纳米复合材料,红外吸收,光致发光光谱 中图分类号：O648 Synthesis and Characteristics of ZnO?CNTs Nanocomposites ZHU,Lu?Ping1,2HUANG,Wen?Ya3MA,Li?Li4FU,Shao?Yun1,*YU,Ying4JIA,Zhi?Jie4 (1Technical Institute of Physics and Chemistry,Chinese Academy of Sciences,Beijing100080,P.R.China；2Graduate School of the Chinese Academy of Sciences,Beijing100049,P.R.China；3Wuhan Yaohua Pilkington Safety Glass Co.Ltd.,Wuhan 430010,P.R.China；4Institute of Nano?Science and Technology,Central China Normal University,Wuhan430079,P.R.China) Abstract ZnO?CNTs nanocomposites were successfully synthesized by sol method using Zn(CH3COO)2·2H2O and treated multiwalled carbon nanotubes(CNTs)as raw materials and diethyleneglycol(DEG)as regent.The samples were determined by means of X?ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),infrared(IR)absorbence,and photoluminescence(PL)spectrum.TEM and SEM images indicated that the coating layer was composed of ZnO nanoparticles with size less than25nm.The effects of various experimental conditions,such as reaction duration and reaction temperature on the obtained composites were investigated as well.Finally,PL function and possible formation mechanism of ZnO?CNTs nanocomposites were proposed.The PL spectra of ZnO?CNTs nanocomposites showed obvious blue?shifts compared with that of pure ZnO nanomaterial. Keywords：Sol method,ZnO?CNTs,Nanocomposite,IR absorbence,PL spectrum 碳纳米管(CNTs)自从1991年[1]被发现以来,由于其独特的结构、纳米级的尺寸、高的有效比表面积和可呈现导体的性质,使其在工程材料的纳米增强相和半导体材料等方面很受关注.同时,由于其具有极大的比表面积和化学稳定性,以及独特的电子结构、孔腔结构和吸附性能,也被认为是一种良好的载体[2?6].近几年来,由于碳纳米管管壁的官能化的发展,加之其优良的电子传导性,对反应物种和反应产物的特殊吸附及脱附性能,特殊的孔腔空间立体选择性,碳与金属催化剂的金属?载体强相互作用以及碳纳米管的量子效应而导致的特异性催化和光催化性质,使其越来越多地用作催化剂载体[7].目前 [Article]https://www.wendangku.net/doc/b512294701.html, Received:March22,2006;Revised:April14,2006.*Correspondent,E?mail:lpzhu@https://www.wendangku.net/doc/b512294701.html, or syfu@https://www.wendangku.net/doc/b512294701.html,;Tel/Fax:010?82543752.国家自然科学基金(20207002)资助项目 鬁Editorial office of Acta Physico?Chimica Sinica 1175

复合材料的制备方法

聚合物/粘土纳米复合材料的插层制备方法 刘京京 河北联合大学轻工学院11材1，唐山063000 【摘要】：介绍了插层制备聚合物/粘土纳米复合材料的主要方法:剥离—吸附法、原位聚合插层法、熔融插层法和模板合成法;对插层法制备聚合物今后的研究方向提出一些建议。 【关键词】：纳米复合材料粘土聚合物插层 0引言 “纳米材料”作为一种新材料类别的概念是在20世纪80年代早期提出来的，从其一诞生，就因广阔的商业前景而被美国材料学会誉为“21世纪最有前途的材料”。 目前，聚合物纳米复合材料的制备方法主要有：原子分散法、溶胶-凝胶法、分子复合材料形成法、插层复合法等①。 插层复合法师制备高性能聚合物基纳米复合材料的一种重要方法②，它是将单体或聚合物插入粘土片层间，破坏粘土的片层结构，使其以厚度为1nm左右的片层分散于聚合物中，形成聚合物纳米复合材料。

1插层制备聚合物/粘土纳米复合材料的方法插层制备聚合物/粘土纳米复合材料的方法主要有如下4中： 1.1剥离—吸附法 选用一种溶剂将粘土剥离成单层，其中聚合物是可溶的。由于所有粘土中使层结合在一起的作用力较弱，所有容易被分散在一种液态溶剂中，然后在剥离的片层上吸附聚合物，溶剂挥发或混合物沉淀时，片层重组形成三明治状的聚合物。最佳状态下可形成一种有序多层结构，在此过程中，也可通过乳液聚合得到纳米复合材料，其中粘土分散在水相中。 (1)聚合物溶液的剥离—吸附法 此方法广泛采用水溶性的聚合物，如聚乙烯醇（PVOH），聚环氧乙烷(PEO)，聚乙烯基吡咯烷酮或聚丙烯酸，制备纳米复合材料。将聚合物水状溶液加入到完全剥离的钠基粘土分散相中，在水溶液宏观大分子和粘土层间所存在的强相互作用力，往往有暖气层面重新聚集。这种状态正对应一种真正的纳米复合材料杂化物的生成。 (2)预聚物溶液的剥离—吸附法 Toyota研究小组③第一个用此法制备聚酰亚胺纳米复合材料，其中聚酰亚胺的前驱体是由4,4—二胺二苯醚与苯均二酐逐步