• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Heteropolyacids-Immobilized Graphitic Carbon Nitride: Highly Efficient Photo-Oxidation of Benzyl Alcohol in the Aqueous Phase

    2021-06-04 10:02:56LifuWuSaiAnYuFeiSong
    Engineering 2021年1期

    Lifu Wu, Sai An*, Yu-Fei Song*

    State Key Laboratory of Chemical Resource Engineering, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology,Beijing 100029, China

    Keywords:Photocatalysis Heteropolyacids Graphitic carbon nitride Benzaldehyde

    ABSTRACT Benzaldehyde is a highly desirable chemical due to its extensive application in medicine, chemical synthesis and food sector among others.However,its production generally involves hazardous solvents such as trifluorotoluene or acetonitrile, and its conversion, especially selectivity in the aqueous phase, is still not up to expectations. Hence, developing an environmentally benign, synthetic process for benzaldehyde production is of paramount importance. Herein, we report the preparation of a photocatalyst(PW12-P-UCNS,where PW12 is H3PW12O40·xH2O and P-UCNS is phosphoric acid-modified unstack graphitic carbon nitride) by incorporating phosphotungstic acid on phosphoric acid-functionalised graphitic carbon nitride(g-C3N4) nanosheets. The performance of PW12-P-UCNS was tested using the benzyl alcohol photo-oxidation reaction to produce benzaldehyde in H2O, at room temperature (20°C). The asprepared PW12-P-UCNS photocatalyst showed excellent photocatalytic performance with 58.3% conversion and 99.5%selectivity within 2 h.Moreover,the catalyst could be reused for at least five times without significant activity loss. Most importantly, a proposed Z-scheme mechanism of the PW12-P-UCNScatalysed model reaction was revealed.We carefully investigated its transient photocurrent and electrochemical impedance,and identified superoxide radicals and photogenerated holes as the main active species through electron spin-resonance spectroscopy and scavenger experiments. Results show that the designed PW12-P-UCNS photocatalyst is a highly promising candidate for benzaldehyde production through the photo-oxidation reaction in aqueous phase, under mild conditions.

    1. Introduction

    Aromatic aldehydes such as benzaldehydes are essential and highly desirable fine chemicals due to their wide applicability[1].Industrially,benzaldehyde can be obtained by the chlorination of toluene and subsequent saponification [2]. This, synthetic process generally employs the use of potent oxidants like CrVI, ClO-,Br2,or peroxy acids,leading to the over-oxidation of target product and thereby its poor selectivity. Nowadays, with the increasingly prominent environmental and energy problems, and the continuous requests for improvement of industrial processes with energy-extensive consumption,laborious post-treatment and difficult separation, such as benzaldehyde production, there is an urgent need to develop environmentally-benign, synthetic processes.

    Recently, photocatalysis, which is considered a promising and green strategy, has drawn the attention of researchers towards driving chemical reactions to produce valuable compounds [3,4].Compared with traditional heating treatment, the utilisation of solar power can be a potential energy-source for industrial production processes, as it allows for energy conservation and environmental protection. Therefore, based on the principles of green and sustainable chemistry,the selective conversion process of benzyl alcohol to produce benzaldehyde using semiconductors,can be considered as one of the most promising ways.So far,multifarious semiconductors (i.e., metal oxides, nitrides, sulfides, etc.) have been used for the oxidation reaction of benzyl alcohol [1,4-8].Unfortunately, most of them suffer from high production cost,environmentally hostile production processes,and poor selectivity.As such, it is highly challenging to design a novel and economical photocatalyst for efficient synthesis of benzaldehyde in aqueous phase. Graphitic carbon nitride (g-C3N4) has excellent characteristics, such as stable physicochemical properties, nontoxicity, and a suitable band gap (2.7 eV) for the absorption of ultraviolet (UV)-visible light. Moreover, it can be obtained from various abundant and inexpensive feedstocks, such as cyanamide, urea, melamine,and thiourea. However, significant decrease of photocatalytic activity is usually reported for g-C3N4due to the rapid recombination of photogenerated electrons and holes (eCB-and hV+B), which significantly decreases the photocatalytic efficiency.The aforementioned drawback can be effectively settled by coupling with various semiconductors [9].

    Polyoxometalates (POMs) are composite of transition metal oxide clusters, which are a huge and rapidly expanding family.Due to POMs’unique chemical structures and numerous characteristics in accordance with semiconductor metal oxide clusters,they are generally regarded as the analogs of the latter and exhibit excellent photochemical performance in various chemical reactions [5]. Upon irradiation with light energy, the surface of photocatalyst can trap the photogenerated electrons and holes, and thereby the reactive oxygen species ofor/and ·OH radicals are formed to facilitate the photocatalytic reaction. Since the photocatalytic oxidation reaction of benzyl alcohol under solar light irradiation was reported using a POMs catalyst ([S2W18O62]4-)[10], the unique charms of POMs in photocatalytic synthesis of chemicals with high added value, especially aromatic aldehydes,were discovered [5,11].

    Herein, we report for the first time the fabrication of a heterogeneous photocatalyst (PW12-P-UCNS; where PW12is H3PW12O40·xH2O and P-UCNS is phosphoric acid-modified unstack g-C3N4) by immobilising phosphotungstic acid onto a g-C3N4surface modified with phosphoric acid. This photocatalyst is applied in a green photocatalytic reaction system, for selective photo-oxidation to produce benzaldehyde in aqueous phase. The as-prepared PW12-P-UCNS exerted outstanding photocatalytic oxidation performance, attributed to three factors. Firstly, the incorporated POMs acted as superior electron acceptors to curb the recombination of photogenerated electrons and holes.Secondly, the P-UCNS with phosphoric acid-modified surface improved the absorption of O2to generate more active species(radicals). Thirdly, the interfacial photogenerated electrons within PW12-P-UCNS followed a Z-scheme mechanism, which obtained an efficient charge separation by the fast transfer pathway. Moreover, the high oxidation activity and reusability of the PW12-P-UCNS photocatalyst revealed a broad and promising application prospects.

    2. Experimental section

    2.1. Chemicals and reagents

    All solvents and chemicals were provided from Energy Chemical(China), were of analytical grade, and were used without further treatment.

    2.2. Fabrication of UCNS

    Bulk g-C3N4was synthesised according to Ref. [12]. A quantity of 0.9 g of bulk g-C3N4was dispersed into 150 mL HCl solution(14.8 wt%) followed by sonicating for 1 h and stirring for another 24 h. Subsequently, it was subjected hydrothermal treatment at 110°C.After 5 h,the suspension was centrifuged,filtrated,washed with water,and finally dried at 80°C overnight,leading to the formation of unstack g-C3N4nanosheets (UCNS).

    2.3. Fabrication of PW12-P-UCNS

    As shown in Fig. 1, 0.1 g UCNS was scattered in 100 mL of 0.3 mol·L-1H3PO4solution and the above was stirred for 5 h to allow for adsorption of phosphoric acid on the surface of UCNS.The P-UCNS was collected by centrifugation. After heating at 60 °C in an oven for 180 min, it underwent heat-treatment at 300 °C for 90 min. P-UCNS was washed using distilled water and then dried, in order to remove weakly bound phosphoric acid anions from its surface[13].Subsequently,predetermined quantity of H3PW12O40(PW12)was placed in a 20 mL P-UCNS suspension of anhydrous ethanol,followed by stirring.After drying overnight,the PW12-P-UCNS photocatalyst was finally obtained.

    2.4. Characterisation

    Transmission electron microscopy (TEM) was performed using a HT7700 machine. A Shimadzu XRD-6000 diffractometer was used to collect the X-ray diffraction (XRD) patterns within the range of 3°-70°. A Bruker Vector 22 infrared spectrometer was employed to collect Fourier transform infrared spectroscopy (FTIR) spectra within the range of 400-4000 cm-1. Thermogravimetric analysis (TGA) was conducted using a TGA/DSC 1 machine with small furnace (SF; temperature range to 1100 °C)from METTLER TOLEDO, USA, under nitrogen atmosphere. X-ray photoelectron spectroscopy(XPS)was conducted using a Quantera SXM machine from ULVAC-PHI Inc., Japan. High-resolution transmission electron microscopy(HRTEM)was carried out using a JEM-2010 electron microscope(JEOL Ltd.,Japan).Porosimetry analysis was conducted using a ASAP 2020M machine (Micromeritics Instrument Corporation, USA).

    Fig. 1. Illustrated representation of the synthetic process for the PW12-P-UCNS.

    2.5. Performance tests

    The photocatalytic performance of as-prepared PW12-P-UCNS was systematically investigated using benzyl alcohol photooxidation as a model reaction to synthesis benzaldehyde under Xe light (300 W) at room temperature. Firstly, 20 mg of the prepared catalyst was scattered into 10 mL reactants solution(10 mmol·L-1). Before light illumination, the reactive system was placed in the dark for 30 min with continuous stirring, in order to reach the adsorption-desorption equilibrium between reactants and the catalyst. Subsequently, oxygen was bubbled into the mixture and sustained for 2 h. After irradiation, an 1 mL mixture was taken out,followed by centrifugation and filtration to separate the photocatalyst. Gas chromatography was employed using GC-2010 Pro (with HP-5 chromatographic column: inner diameter=0.25 mm,length=30 m;Shimadzu Corporation,Japan),to analyse and identify the products, using cyclooctane as an internal standard,and thus calculate the benzyl alcohol conversion and benzaldehyde selectivity.

    2.6. Photoelectrochemical tests

    Experiments were conducted on a typical CHI 760E electrochemical workstation (CH Instruments, Inc., USA), using a 300 W Xe lamp as a light source. Photocurrent analysis was conducted in Na2SO4solution (0.1 mol·L-1) by selecting Ag/AgCl and Pt wire as the reference and counter electrode,respectively.Working electrodes were prepared as follows: 5 mg catalyst was suspended in 1 mL of ethanol solution using ultrasonication. A volume of 80 μL of the above slurry was coated on an ITO substrate and left to dry. The cyclic voltammogram (CV) plot and Mott-Schottky measurements were conducted as shown in previous work [1,12].

    3. Results and discussion

    3.1. Synthesis of catalysts

    As shown in Fig. 1, the PW12-P-UCNS was successfully fabricated using hydrothermal treatment and an immersion process.Briefly, bulk g-C3N4was obtained by firstly treating it with urea at 550 °C. Then, g-C3N4was exfoliated via a HCl-assisted hydrothermal treatment and sonication. The above powder was further modified by phosphoric acid and PW12-P-UCNS was finally prepared after the incorporation of PW12.During the preparation of the PW12-P-UCNS,the-NH2groups from the edges of P-UCNS were protonated by the acid to form[-NH3+][H2PW12O40-]species at the interface between PW12and P-UCNS. The leakage of the Keggin units can be avoided due to the strong bonding of PW12and P-UCNS via acid-base and electrostatic interaction. Moreover, the incorporation of PW12accelerates the transfer and separation of charge carriers.

    3.2. Compositional and structural information

    As shown in Fig.2,the XRD patterns can be used to characterise the chemical structure of bulk g-C3N4, UCNS, P-UCNS, PW12, and PW12-P-UCNS. The two broad peaks positioned at 27.5° and 13.0°, on the bulk g-C3N4spectra are matched to (002) and (100)of the graphitic carbon materials, respectively [12,14]. The slight shift of (002) peak for the UCNS and P-UCNS compared with bulk g-C3N4is attributed to the protonation of heterocyclic N atoms(C-N=C) [15-17]. Moreover, it can be seen that the shifts of PUCNS in higher 2θ angles are due to the lower extent of stacking between nanosheets [18,19]. For as-prepared PW12-P-UCNS, it shows that the characteristic peaks of the Keggin structure (2θ of 8°-11° and 18°-30°) and P-UCNS (at 2θ of 14° and 28.2°) in the XRD diagram, indicating that the structures of Keggin units and P-UCNS supports are remained after the incorporation of PW12.

    Further, structural information of as-prepared PW12-P-UCNS was obtained through FT-IR measurement.Typically,g-C3N4shows peaks centered at 890 and 810 cm-1, attributed to the breathing mode of the heptazine ring (Fig. 2(b)) [20]. The signals centered at 1637, 1570, and 1463 cm-1can be attributed to the υC-N, while the peaks observed at 1416 cm-1can be assigned to υC=N[21,22].Moreover, the signals appearing at 1248 and 1327 cm-1can be assigned to the υC-NH-Cor υC-N(-C)-C[17,23]. The broad peaks centered at the range of 3000 to 3500 cm-1can be assigned to the υO(shè)-Hand υN-H,[24,25]. For UCNS and P-UCNS, the signals at 1463 and 1637 cm-1(assigned to C=N and C-N, respectively) shift to 1466 and 1639 cm-1,respectively.In addition,the peak positioned at 1570 cm-1, ascribed to C=N in the CN heterocycles, becomes inconspicuous, implying that g-C3N4were protonated successfully[15,26,27]. The new signal observed at 985 cm-1in the P-UCNS spectrum, corresponds to the phosphoric acid groups [28]. The FT-IR spectrum of PW12shows characteristic vibration peaks at 1080, 984, 890, and 798 cm-1, respectively [29]. All of the characteristic peaks for PW12and P-UCNS mentioned so far can also be observed in the spectrum of PW12-P-UCNS. Therefore, the above results indicate that ① the g-C3N4successfully transforms to P-UCNS after exfoliating,protonating,and modifying by phosphoric acid; ②PW12is successfully incorporated on the P-UCNS surface;③the primary Keggin structure of PW12remains intact after immobilisation.

    Fig. 2. The (a) XRD and (b) FT-IR for different specimens (UCNS, P-UCNS, bulk g-C3N4, PW12, and PW12-P-UCNS). JCPDS: Joint Committee on Powder Diffraction Standards.

    The PW12-P-UCNS photocatalyst was also analysed using XPS.Peaks for P, O, N, W, and C elements are clearly detected for PW12-P-UCNS (Fig. 3(a)). The C 1s XPS spectrum of the PW12-PUCNS (Fig. 3(b)), can be divided into four signals centered at 289.2, 288.0, 286.0, and 284.8 eV. The peaks centered at 288 and 284.8 eV are attributed to the N=C(-N)2unit and reference C species,respectively[16,30,31].The peaks originated from C species of C-O and C-NH2groups can be found at 289.2 and 286.0 eV. In the N 1s spectrum (Fig. 3(c)), the four peaks located at 404.0, 400.2,399.1, and 398.2 eV are attributed to the C-NH+=C, C-N-H or N-H2groups, N-(C)3, and sp2hybridised C-N=C groups, respectively [32-35]. Moreover, it is clear that the N 1s and C 1s spectra of PW12-P-UCNS show an obvious shift, compared with UCNS and P-UCNS due to the protonation and strong electrostatic interaction of the PW12species [13,17,29]. The W 4f XPS spectrum of the PW12-P-UCNS (Fig. 3(d)) shows that it is divided into two signals centered at 37.4 and 35.3 eV, ascribing to the W 4f5/2and W 4f7/2spin-orbit components accordingly, indicating the WVIspecies of the incorporated PW12[36]. Moreover, the negative shifts of the binding energy that can be observed compared with the PW12spectrum (W 4f5/2of 37.9 eV and W 4f7/2of 35.8 eV), can be explained through the chemical interaction between P-UCNS and the Keggin units [37].

    3.3. Morphological characteristics and textural properties

    The morphology of PW12-P-UCNS was investigated using TEM and was compared with g-C3N4, UCNS, and P-UCNS. As shown in Fig. 4, all the prepared materials show layered nanostructures.Compared with g-C3N4, which shows thick and blocky nanostructure (~29 nm for thickness, in Appendix A Fig. S1), the as-prepared PW12-P-UCNS exhibits extremely thin nanosheets(~12 nm for thickness, Fig. S1). The open-up surface provides abundant active sites and shorter diffusion distances, is conducive to accelerate charge separation and mass transfer, and thereby leads to enhanced photo-oxidation activity of PW12-P-UCNS [38].Moreover, it can be seen that the thickness of UCNS rapidly decreases to 10 nm following the hydrothermal treatment of g-C3N4,and it almost remains after the incorporation of phosphoric acid and POMs. This observation is consistent with the result obtained from atomic force microscopy (AFM). Closer inspection of the HRTEM images (Fig. S2 in Appendix A) shows that the prepared PW12-P-UCNS is well-defined with uniformly dispersed black spots. This is in agreement with the dimensions of the PW12clusters, and suggests that the clusters are uniformly incorporated on P-UCNS. Furthermore, the as-prepared UCNS, P-UCNS,and PW12-P-UCNS exhibit porous nanostructures, as revealed by the measurement of porosity (Fig. S3 in Appendix A).

    3.4. Optical absorption properties

    Fig.3. (a)XPS survey of different samples(PW12-P-UCNS,g-C3N4,and UCNS);XPS spectra of the(b)C 1s,(c)N 1s of UCNS,P-UCNS,and PW12-P-UCNS,and(d)W 4f for PW12 and PW12-P-UCNS.

    Fig. 4. TEM of (a) PW12-P-UCNS, (b) P-UCNS, (c) UCNS, and (d) bulk g-C3N4.

    Fig. 5. UV-Vis/DRS plots of different samples (g-C3N4, UCNS, P-UCNS, PW12, and PW12-P-UCNS).

    3.5. Performance studies

    In order to test the performance of PW12-P-UCNS,the oxidation reaction of benzyl alcohol under Xe lamp illumination was chosen.For comparison, PW12, P-UCNS, and PW12-P-UCNS with varying PW12loading were also tested(the corresponding characterization results can be seen in Figs. S5-S7).

    Fig.6(a)shows the activity of PW12,P-UCNS,and PW12-P-UCNS towards the selective benzyl alcohol oxidation under Xe lamp illumination.A blank experiment without photocatalyst was also performed under the same conditions,and the results showed that the reaction without PW12-P-UCNS, under irradiation, for 2 h, barely proceeds. The adsorption of reactants on as-prepared photocatalysts was also considered, by initially leaving the catalytic system in the dark, under stirring, for 0.5 h. After illumination for 2 h,the order of photo-oxidation activity follows the order of PW12-P-UCNS >P-UCNS >PW12. Obviously, the as-prepared PW12-PUCNS photocatalyst exhibits the highest photocatalytic oxidation activity,reaching benzyl alcohol conversion of 58.3%and benzaldehyde selectivity of 99.5%.The influence of PW12loading of PW12-PUCNS on photocatalytic oxidation activity was also researched. As shown in Fig.6(b), increasing PW12loading leads to an increase of the conversion to benzyl alcohol,while the selectivity to benzaldehyde markedly decreases. In order to obtain high conversion to benzyl alcohol and selectivity to benzaldehyde,PW12-P-UCNS with 34.8 wt%PW12loading was selected for subsequent photocatalytic tests with comprehensive consideration of conversion-to-benzyl alcohol and selectivity-to-benzaldehyde (Fig. S8). Moreover, the oxidation activity of as-prepared PW12-P-UCNS was compared with the reported value in literature and exhibited excellent catalytic performance (Table S1). The prepared PW12-P-UCNS shows the following competitive advantages: ①The solvent of catalytic system is water, making the process green, eco-friendly, and sustainable;②high target product selectivity and reactant conversion obtained under mild reaction conditions (short reaction time and low reaction temperature); ③high stability and inexpensive production compared to noble metals.

    3.6. Photocatalyst reusability

    Fig. 6. The catalytic performance of (a) various photocatalysts and (b) PW12-P-UCNS with different PW12 loading towards the benzyl alcohol conversion and benzaldehyde selectivity in deionized water. PW12-P-UCNS 1, PW12-P-UCNS 2, PW12-P-UCNS, and PW12-P-UCNS 3 represent PW12 loading of 13.7%, 22.6%, 34.8%, and 46.2%, respectively.Reaction conditions: 20 mg catalysts, 10 mL deionized water, 0.1 mmol benzyl alcohol, and 2 h Xe lamp irradiation.

    The regeneration and reusability of photocatalysts are considered as two key issues to evaluate catalytic performance. Herein,the reusability of as-prepared PW12-P-UCNS was evaluated by catalysing the oxidation of benzyl alcohol for five consecutive cycles.As shown in Fig.7(a),after five consecutive cycles,the benzaldehyde selectivity is retained almost as high as in the original performance, whereas the benzyl alcohol conversion shows a slight decrease after three cycles. In order to investigate the cause of activity loss, we initially performed inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis using the reaction liquid after separating the photocatalyst,to identify whether PW12is leaching in the catalytic system.Based on tungsten content results, it can be confirmed that leaching of PW12species hardly occurs in the examined reaction system. Furthermore, structural and morphological information of the used PW12-P-UCNS catalyst was obtained using FT-IR, XRD, and TEM. As can be seen in Fig. 7(b), the used PW12-P-UCNS catalyst exhibits thin flaky nanostructure. Moreover, the characteristic signals ascribed to the Keggin units of PW12can still be found and there is no obvious structural change in Fig. 7(d). These results suggest that the activity loss of PW12-P-UCNS after five consecutive cycles could be attributed to the mass loss of photocatalyst during recycling,although for at least five consecutive cycles, the as-prepared PW12-P-UCNS does not show any morphological or structural change.

    3.7. Photocatalytic mechanism

    Fig. 7. (a) Reusability; (b) the image of TEM; (c) spectra of FT-IR; and (d) spectra of XRD towards fresh and used PW12-P-UCNS photocatalyst. Reaction conditions: 20 mg catalysts, 10 mL deionized water, 0.1 mmol benzyl alcohol, and 2 h Xe lamp irradiation.

    The behaviors of photogenerated electron-hole pairs can be monitored by testing their photoelectrochemical properties [4].Initially, the separation and transfer efficiency of the photogenerated charge carriers towards the as-prepared P-UCNS and PW12-P-UCNS photocatalysts was evaluated using transient photocurrent measurement.As shown in Fig.8(a),the photocurrent responses of P-UCNS and PW12-P-UCNS can be reproduced and are stable over a period of five illumination cycles. It was found that PW12-P-UCNS(2.52 μA) showed a 3.8-fold enhancement in the photocurrent intensity compared with P-UCNS (0.66 μA). This indicates the much-improved separation and transfer efficiency for photogenerated electrons and holes, attributed to the incorporation of PW12species. The incorporated PW12functions as superior electron acceptors, restricting the recombination of photogenerated electrons and holes.Moreover,the intensity of the photoluminescence(PL) spectra emission spectra indicates the recombination rate of photogenerated electron-hole pairs. As shown in Fig. S9, the asprepared PW12-P-UCNS exhibited the lowest radiation recombination rate of photogenerated carriers compared with g-C3N4, UCNS and P-UCNS, which was consistent with the results obtained from transient photocurrent measurement.

    Subsequently, the separation efficiency of the photogenerated electrons and holes was investigated using electrochemical impedance spectroscopy (EIS) measurements [2]. The high-frequency semicircle in the Nyquist plot represents the charge-transfer procedure, whose radius reflects the charge-transfer resistance[42,43]. The smaller radius of semicircle indicates the smaller charge-transfer resistance. The as-prepared PW12-P-UCNS showed smaller radius of curvature compared with P-UCNS, implying higher charge separation efficiency (Fig. 8(b)). The above results show that the charge separation efficiency and resistance of charge transfer of photocatalyst were greatly improved after the incorporation of PW12.

    In order to investigate the potential mechanism of PW12-PUCNS nanocomposite for selective alcohol oxidation,we examined the main active species in the reaction by the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin-trapping electron spin resonance(ESR) measurements. As shown in Fig. 9(a), there was no obvious signal without light irradiation.Under solar light and the presence of PW12-P-UCNS photocatalyst, there were characteristic signals with 1:1:1:1 of intensity ratio in methanol dispersion, which can be assigned to the DMPO-·adduct [44]. This indicates that ·can be formed in the photocatalytic course upon irradiation.

    The effect of different active species on the model reaction was carefully investigated by using potassium persulfate (K2S2O8) as electron scavengers, oxalic acid (C2H2O4) as hole scavengers, 1,4-benzoquinone (BQ) as ·O-2 scavengers, and tertbutyl alcohol(TBA) asscavengers [1,2,5,45]. As shown in Fig. 9(b), when C2H2O4or BQ was introduced, the conversion of benzyl alcohol rapidly declined, demonstrating thatand holes were important active moieties in the current oxidation system. Meanwhile,the decrease of conversion-to-benzyl alcohol in the TBA-added photocatalytic system was negligible, implying that ·OH radicals showed no vital role during the current photocatalytic reaction process.Furthermore,it was found that conversion-to-benzyl alcohol increased slightly after adding K2S2O8. This suggested that the addition of electron scavenger increased greatly the consumption of electrons, thus increasing the amount of active holes on PW12-P-UCNS and improving the indirect hole oxidation of benzyl alcohol on the surface [1].

    Therefore,it was proven that hV+Band·O-2were the main active moieties for the examined oxidation system under solar light illumination.

    Fig. 8. Profiles of (a) photocurrent-time and (b) electrochemical impedance spectroscopy (EIS) measurement. -Z′′: negative imaginary impedance; Z′: real impedance.

    Fig.9. (a)The DMPO spin-trapping ESR spectra of PW12-P-UCNS.I:DMPO in dark;II:PW12-P-UCNS in dark;III:DMPO-Xe lamp;IV:PW12-P-UCNS-Xe lamp.(b)The results of different scavengers in the PW12-P-UCNS-photocatalytic benzyl alcohol oxidation. 1G = 1 × 10-4 T.

    In order to estimate the relative positions of CB and VB of PW12and P-UCNS,we calculated the optical band gap,CV,and measured the flat band potential (Fig. S10). Based on the above results, the conventional type II-heterojunction and direct Z-scheme mechanism can be used to describe the current catalytic system.

    Fig. 10. The proposed mechanism for the PW12-P-UCNS-catalysed benzyl alcohol photo-oxidation under the current catalytic system.

    On the other hand,as-prepared PW12-P-UCNS photocatalyst can act as the H-bonding acceptor because of the C-N-H, C-OH, and POMs species present on the surface. Accordingly, the surface of PW12-P-UCNS photocatalysts prefers to adsorb the reactants via H-bonding or electrostatic interaction, leading to the high benzyl alcohol conversion.Meanwhile,the weak interaction between benzaldehyde and PW12-P-UCNS makes the former desorb quickly from the surface,avoiding the over-oxidation of the target product and thereby obtaining high selectivity of benzaldehyde. Such a Z-scheme-driven photocatalysedoxidation reaction shows excellent benzyl alcohol conversion and benzaldehyde selectivity attributed to the sharp separation of photogenerated electron-hole pairs and abundance of active species of ·radicals. Based on the aforementioned results, as-prepared PW12-P-UCNS can be used as an effective and environmentally benign photocatalyst for the chosen oxidation reaction.

    4. Conclusion

    To summarise, an efficient and environmentally friendly photocatalyst (PW12-P-UCNS) was successfully constructed by immobilising PW12on g-C3N4nanosheets modified using phosphoric acid. The as-prepared PW12-P-UCNS photocatalyst showed excellent photocatalytic performance including its activity and stability in selective benzyl alcohol oxidation to produce benzaldehyde, that is, 58.3% conversion of benzyl alcohol and 99.5%selectivity to benzaldehyde within 2 h.Careful investigation of the photoelectrochemical properties, including photocurrent,scavenger experiments, and ESR measurement, such a Z-schemedriven catalytic performance can be assigned to the following facts.Firstly, the incorporated Keggin units facilitate the spontaneous migration of electrons, and thereby accelerate interfacial charge carrier separation; secondly, more abundant ·O2-radicals (the detected main active species during the current selective photooxidation reaction process)are generated,which is beneficial from the improvement of O2adsorption on the surface of P-UCNS.Based on the aforementioned results and observations,the PW12-P-UCNS photocatalysts show great potential for driving chemical oxidation reactions using sunlight.

    Acknowledgements

    This research was supported by the National Nature Science Foundation of China (21625101, 21521005, and 21808011), the National Key Research and Development Program of China(2017YFB0307303), Beijing Natural Science Foundation(2202039) and the Fundamental Research Funds for the Central Universities (XK1802-6, XK1902, and 12060093063).

    Compliance with ethics guidelines

    Lifu Wu,Sai An,and Yu-Fei Song declare that they have no conflict of interest or financial conflicts to disclose.

    Appendix A. Supplementary data

    Supplementary data to this article can be found online at https://doi.org/10.1016/j.eng.2020.07.025.

    亚洲av成人精品一区久久| 日韩成人伦理影院| 黑人猛操日本美女一级片| 免费人妻精品一区二区三区视频| 亚洲欧美日韩东京热| 国产午夜精品一二区理论片| 亚洲国产最新在线播放| 少妇丰满av| 国产一区二区三区综合在线观看 | 久久毛片免费看一区二区三区| 国产一区有黄有色的免费视频| 我要看黄色一级片免费的| 精品一区在线观看国产| 久久人人爽人人爽人人片va| 少妇的逼好多水| 一级毛片电影观看| 成人18禁高潮啪啪吃奶动态图 | a 毛片基地| 国产精品国产三级国产av玫瑰| 一级,二级,三级黄色视频| 我的老师免费观看完整版| 国产精品久久久久久久电影| 日本免费在线观看一区| 日本-黄色视频高清免费观看| 国产精品不卡视频一区二区| 妹子高潮喷水视频| 韩国高清视频一区二区三区| 麻豆成人午夜福利视频| 日韩av免费高清视频| 亚洲自偷自拍三级| 成人国产av品久久久| 少妇精品久久久久久久| 精品99又大又爽又粗少妇毛片| 国产无遮挡羞羞视频在线观看| 免费看av在线观看网站| 青春草亚洲视频在线观看| 蜜臀久久99精品久久宅男| 日本黄色日本黄色录像| 新久久久久国产一级毛片| 亚洲精品日本国产第一区| 日韩成人av中文字幕在线观看| 一级毛片 在线播放| av在线观看视频网站免费| 女人久久www免费人成看片| 在线观看人妻少妇| 三级国产精品片| 简卡轻食公司| 一本色道久久久久久精品综合| 在线观看av片永久免费下载| 伦精品一区二区三区| 国产在线一区二区三区精| 亚洲国产色片| 啦啦啦中文免费视频观看日本| 少妇人妻 视频| 天天操日日干夜夜撸| 日本黄色日本黄色录像| 日本欧美视频一区| 三级国产精品片| 能在线免费看毛片的网站| 狂野欧美激情性xxxx在线观看| 欧美bdsm另类| 国内少妇人妻偷人精品xxx网站| 亚洲性久久影院| 99久久人妻综合| 久久人人爽人人片av| 毛片一级片免费看久久久久| 在线观看国产h片| 日日撸夜夜添| av网站免费在线观看视频| 观看av在线不卡| 国产一区二区在线观看av| 日本猛色少妇xxxxx猛交久久| 日韩伦理黄色片| 亚洲欧美日韩东京热| 18+在线观看网站| 欧美老熟妇乱子伦牲交| 成人免费观看视频高清| 亚洲成人av在线免费| 中文天堂在线官网| 亚洲图色成人| 青春草国产在线视频| 亚洲欧美中文字幕日韩二区| 一级毛片我不卡| 最近的中文字幕免费完整| 国产一级毛片在线| 日日啪夜夜爽| 赤兔流量卡办理| 国产精品99久久久久久久久| 久久狼人影院| 免费在线观看成人毛片| 日韩欧美精品免费久久| 午夜免费鲁丝| 黄色毛片三级朝国网站 | 亚洲精品一二三| 99久久精品一区二区三区| 成人综合一区亚洲| 亚洲,欧美,日韩| 黄色配什么色好看| 精品一品国产午夜福利视频| av专区在线播放| 国产精品国产av在线观看| 人妻一区二区av| 伊人久久精品亚洲午夜| 人人妻人人爽人人添夜夜欢视频 | 国产免费又黄又爽又色| 久久毛片免费看一区二区三区| av有码第一页| 日本免费在线观看一区| 高清午夜精品一区二区三区| 中文字幕久久专区| 亚洲国产成人一精品久久久| 少妇熟女欧美另类| 国产片特级美女逼逼视频| av卡一久久| 久久精品久久精品一区二区三区| 亚洲欧洲日产国产| 中国三级夫妇交换| 免费播放大片免费观看视频在线观看| 国产真实伦视频高清在线观看| av在线观看视频网站免费| 国产精品国产三级专区第一集| 边亲边吃奶的免费视频| 肉色欧美久久久久久久蜜桃| 久久久国产精品麻豆| 免费大片黄手机在线观看| 亚洲欧美日韩东京热| 成人综合一区亚洲| 91成人精品电影| 国产深夜福利视频在线观看| 一级av片app| 国产 精品1| 五月天丁香电影| 精品久久久精品久久久| 校园人妻丝袜中文字幕| 国国产精品蜜臀av免费| 成人国产av品久久久| 亚洲av成人精品一区久久| 日韩欧美一区视频在线观看 | av又黄又爽大尺度在线免费看| 视频区图区小说| 成人毛片a级毛片在线播放| 全区人妻精品视频| 亚洲电影在线观看av| 国产极品天堂在线| 日本wwww免费看| 亚洲内射少妇av| 啦啦啦中文免费视频观看日本| 男人和女人高潮做爰伦理| 国产精品女同一区二区软件| 国产精品久久久久久av不卡| 五月天丁香电影| 免费看av在线观看网站| 亚洲三级黄色毛片| 人妻制服诱惑在线中文字幕| 午夜视频国产福利| 嘟嘟电影网在线观看| 亚洲欧美中文字幕日韩二区| 国产精品99久久99久久久不卡 | 成人黄色视频免费在线看| 亚洲一区二区三区欧美精品| 日韩人妻高清精品专区| 亚洲国产精品专区欧美| 噜噜噜噜噜久久久久久91| 六月丁香七月| 日韩欧美精品免费久久| 欧美 亚洲 国产 日韩一| 免费黄色在线免费观看| 丝袜喷水一区| 亚洲久久久国产精品| 久久久亚洲精品成人影院| 日韩在线高清观看一区二区三区| 精品一品国产午夜福利视频| 日本黄色日本黄色录像| 国产免费福利视频在线观看| 国产一区二区三区av在线| 久久久精品94久久精品| 国产精品久久久久成人av| 在线观看www视频免费| 亚洲成人一二三区av| 大又大粗又爽又黄少妇毛片口| 日韩,欧美,国产一区二区三区| 边亲边吃奶的免费视频| 亚洲国产欧美在线一区| 国模一区二区三区四区视频| 久久精品夜色国产| 看十八女毛片水多多多| 少妇的逼好多水| 国产精品熟女久久久久浪| 特大巨黑吊av在线直播| 久久精品熟女亚洲av麻豆精品| 国产高清国产精品国产三级| 国产有黄有色有爽视频| 色网站视频免费| 婷婷色综合大香蕉| 国产成人精品婷婷| 一二三四中文在线观看免费高清| 久久久久国产精品人妻一区二区| 中文字幕人妻熟人妻熟丝袜美| 国产精品国产av在线观看| 我的老师免费观看完整版| 久久久久精品久久久久真实原创| 一边亲一边摸免费视频| 亚洲高清免费不卡视频| 秋霞在线观看毛片| 成人美女网站在线观看视频| 国产av码专区亚洲av| 色吧在线观看| 嘟嘟电影网在线观看| 九九在线视频观看精品| 久久精品久久精品一区二区三区| 男女无遮挡免费网站观看| 欧美精品一区二区免费开放| 在现免费观看毛片| 看十八女毛片水多多多| 人人澡人人妻人| 又爽又黄a免费视频| 男的添女的下面高潮视频| 美女xxoo啪啪120秒动态图| 久久精品国产a三级三级三级| 两个人的视频大全免费| 日日爽夜夜爽网站| a级一级毛片免费在线观看| 26uuu在线亚洲综合色| 我要看黄色一级片免费的| 人妻一区二区av| 七月丁香在线播放| 91精品国产九色| 亚洲欧美精品自产自拍| 亚洲国产精品一区三区| 久久国产精品男人的天堂亚洲 | 大又大粗又爽又黄少妇毛片口| 国产午夜精品久久久久久一区二区三区| 99九九在线精品视频 | 99九九线精品视频在线观看视频| 狂野欧美激情性bbbbbb| 涩涩av久久男人的天堂| 午夜91福利影院| 丝袜在线中文字幕| 黄色日韩在线| a级毛片在线看网站| 日日撸夜夜添| 精品一区在线观看国产| 欧美丝袜亚洲另类| 国产欧美日韩精品一区二区| 日本免费在线观看一区| 日韩制服骚丝袜av| 在现免费观看毛片| 大又大粗又爽又黄少妇毛片口| 免费高清在线观看视频在线观看| 日韩av免费高清视频| 丰满饥渴人妻一区二区三| 中国美白少妇内射xxxbb| 欧美亚洲 丝袜 人妻 在线| 男女国产视频网站| 男人和女人高潮做爰伦理| 涩涩av久久男人的天堂| 久久久久国产网址| 久久99精品国语久久久| 国产亚洲91精品色在线| 国语对白做爰xxxⅹ性视频网站| 成年av动漫网址| h日本视频在线播放| 国产真实伦视频高清在线观看| 黑人猛操日本美女一级片| 黄色视频在线播放观看不卡| 国产在线男女| 午夜福利在线观看免费完整高清在| 五月伊人婷婷丁香| 校园人妻丝袜中文字幕| 在线观看www视频免费| 中文资源天堂在线| 最新的欧美精品一区二区| 最后的刺客免费高清国语| 久久亚洲国产成人精品v| 亚洲自偷自拍三级| 国产乱人偷精品视频| 日本av免费视频播放| 一本一本综合久久| 你懂的网址亚洲精品在线观看| 国产日韩一区二区三区精品不卡 | 国产欧美日韩一区二区三区在线 | 一级片'在线观看视频| 久久久久久久大尺度免费视频| 男的添女的下面高潮视频| 偷拍熟女少妇极品色| 亚洲国产成人一精品久久久| 日韩视频在线欧美| 亚洲,一卡二卡三卡| 有码 亚洲区| 王馨瑶露胸无遮挡在线观看| 国产精品一二三区在线看| 日韩精品免费视频一区二区三区 | 天天操日日干夜夜撸| 久久久久久伊人网av| 久久久久人妻精品一区果冻| 18禁在线无遮挡免费观看视频| 欧美丝袜亚洲另类| 人人妻人人爽人人添夜夜欢视频 | 久久久久久久久大av| 少妇猛男粗大的猛烈进出视频| 熟女人妻精品中文字幕| 午夜影院在线不卡| 免费观看av网站的网址| 国产成人免费观看mmmm| 亚洲综合精品二区| 成年av动漫网址| 黄色配什么色好看| 亚洲精品日韩av片在线观看| 日日摸夜夜添夜夜爱| 欧美日韩亚洲高清精品| 亚洲电影在线观看av| 亚洲av福利一区| 99久久精品国产国产毛片| 在线观看一区二区三区激情| 免费观看av网站的网址| 亚洲内射少妇av| 日韩 亚洲 欧美在线| 久久婷婷青草| 久久久午夜欧美精品| 亚洲精品久久午夜乱码| 97在线人人人人妻| 在线看a的网站| 成人特级av手机在线观看| 久热久热在线精品观看| 免费人妻精品一区二区三区视频| 简卡轻食公司| 我的老师免费观看完整版| 亚洲va在线va天堂va国产| 免费大片黄手机在线观看| 国产精品女同一区二区软件| 欧美高清成人免费视频www| 国产男女内射视频| 大又大粗又爽又黄少妇毛片口| 日日撸夜夜添| 日日啪夜夜爽| 草草在线视频免费看| 91精品国产九色| 汤姆久久久久久久影院中文字幕| 美女内射精品一级片tv| av在线app专区| 亚洲精品国产av成人精品| 日韩精品免费视频一区二区三区 | 成人国产麻豆网| 在现免费观看毛片| 91精品一卡2卡3卡4卡| 99久久精品热视频| a 毛片基地| 一个人看视频在线观看www免费| 亚洲一级一片aⅴ在线观看| 亚洲精品456在线播放app| 高清午夜精品一区二区三区| 搡老乐熟女国产| 日本91视频免费播放| 精品人妻偷拍中文字幕| 国产av国产精品国产| 丝袜喷水一区| 国产黄色免费在线视频| 免费观看性生交大片5| 九九爱精品视频在线观看| 日韩人妻高清精品专区| 日日爽夜夜爽网站| 亚洲国产毛片av蜜桃av| 高清黄色对白视频在线免费看 | 高清在线视频一区二区三区| 边亲边吃奶的免费视频| 人人澡人人妻人| 亚洲国产成人一精品久久久| 国产有黄有色有爽视频| 视频区图区小说| 最近手机中文字幕大全| 国产淫语在线视频| 如日韩欧美国产精品一区二区三区 | 日韩成人av中文字幕在线观看| 精品国产乱码久久久久久小说| 中文字幕av电影在线播放| 中文字幕制服av| 波野结衣二区三区在线| 99久久中文字幕三级久久日本| 91精品伊人久久大香线蕉| 免费黄网站久久成人精品| 免费看不卡的av| 看非洲黑人一级黄片| 国产精品久久久久久精品电影小说| 欧美+日韩+精品| 日本vs欧美在线观看视频 | 黄色配什么色好看| 国国产精品蜜臀av免费| 成年av动漫网址| a级毛片在线看网站| 卡戴珊不雅视频在线播放| 另类亚洲欧美激情| 国产成人91sexporn| 久久精品国产亚洲网站| 黄色日韩在线| 嫩草影院新地址| 亚洲丝袜综合中文字幕| 国产精品秋霞免费鲁丝片| 少妇熟女欧美另类| 一级,二级,三级黄色视频| 国产淫片久久久久久久久| 成年美女黄网站色视频大全免费 | 午夜影院在线不卡| 午夜激情久久久久久久| 国产精品国产av在线观看| 亚洲精品色激情综合| 欧美日韩亚洲高清精品| 如何舔出高潮| 18+在线观看网站| 精品人妻偷拍中文字幕| 国产精品久久久久久av不卡| 亚洲三级黄色毛片| 亚洲欧美精品专区久久| 99久久精品国产国产毛片| 99re6热这里在线精品视频| 丰满人妻一区二区三区视频av| 久久国内精品自在自线图片| 久久鲁丝午夜福利片| 精品午夜福利在线看| 欧美成人精品欧美一级黄| 亚洲精品aⅴ在线观看| 久久青草综合色| 成人美女网站在线观看视频| 国产精品无大码| 亚洲国产精品成人久久小说| 大香蕉久久网| √禁漫天堂资源中文www| 久久久久久久久久久丰满| 男人舔奶头视频| 老司机影院成人| 成人免费观看视频高清| 99re6热这里在线精品视频| 大片电影免费在线观看免费| 亚洲成人一二三区av| 国产免费一级a男人的天堂| 国语对白做爰xxxⅹ性视频网站| 内射极品少妇av片p| 欧美少妇被猛烈插入视频| 在线观看人妻少妇| 日本色播在线视频| 久久韩国三级中文字幕| 亚洲人成网站在线观看播放| 免费观看a级毛片全部| 国产亚洲精品久久久com| 内射极品少妇av片p| 亚洲经典国产精华液单| 精品人妻熟女av久视频| 亚洲欧美成人精品一区二区| 极品人妻少妇av视频| 亚洲欧美中文字幕日韩二区| 看十八女毛片水多多多| 亚洲精品国产色婷婷电影| videos熟女内射| 亚洲精品,欧美精品| 国内精品宾馆在线| 制服丝袜香蕉在线| 51国产日韩欧美| 日产精品乱码卡一卡2卡三| 欧美成人精品欧美一级黄| 国产精品秋霞免费鲁丝片| 一个人免费看片子| 久久久精品94久久精品| 不卡视频在线观看欧美| 亚洲va在线va天堂va国产| 国产成人精品无人区| 国产精品国产三级国产专区5o| 亚洲天堂av无毛| 精品亚洲乱码少妇综合久久| 久久久国产一区二区| 99久久精品一区二区三区| xxx大片免费视频| 国产高清三级在线| 中文字幕久久专区| 久久国产乱子免费精品| 国产精品一区www在线观看| 久久国产精品大桥未久av | 精品少妇内射三级| 日韩一区二区视频免费看| 一区二区av电影网| 在线 av 中文字幕| 三级经典国产精品| av一本久久久久| videos熟女内射| 街头女战士在线观看网站| 美女cb高潮喷水在线观看| 女性生殖器流出的白浆| 国产男女内射视频| 国产精品麻豆人妻色哟哟久久| 男女啪啪激烈高潮av片| 好男人视频免费观看在线| 男人添女人高潮全过程视频| 各种免费的搞黄视频| 精品99又大又爽又粗少妇毛片| 全区人妻精品视频| 亚洲国产精品一区三区| 午夜影院在线不卡| 国产一区二区在线观看av| 18禁动态无遮挡网站| 亚洲av国产av综合av卡| 日韩亚洲欧美综合| 精品国产露脸久久av麻豆| 精品少妇久久久久久888优播| 午夜免费男女啪啪视频观看| 有码 亚洲区| 久久这里有精品视频免费| 大码成人一级视频| 丝袜喷水一区| 亚洲怡红院男人天堂| 91精品国产九色| 91午夜精品亚洲一区二区三区| 欧美性感艳星| 国产成人精品一,二区| 成人黄色视频免费在线看| a 毛片基地| 天天操日日干夜夜撸| 丰满少妇做爰视频| 高清视频免费观看一区二区| 亚洲av男天堂| 成年av动漫网址| 国产黄频视频在线观看| 精品国产国语对白av| 欧美日本中文国产一区发布| 国产精品一区二区在线不卡| 日韩精品免费视频一区二区三区 | 一级a做视频免费观看| 日韩一区二区三区影片| 边亲边吃奶的免费视频| 女性被躁到高潮视频| 精品熟女少妇av免费看| 我要看黄色一级片免费的| 九九在线视频观看精品| 色视频在线一区二区三区| 久热这里只有精品99| 18禁裸乳无遮挡动漫免费视频| 欧美成人精品欧美一级黄| 日产精品乱码卡一卡2卡三| 国产精品一区www在线观看| 交换朋友夫妻互换小说| 老司机亚洲免费影院| 国产成人一区二区在线| 狂野欧美激情性xxxx在线观看| 人妻 亚洲 视频| 亚洲内射少妇av| 国产免费又黄又爽又色| 亚洲情色 制服丝袜| 少妇熟女欧美另类| 国产精品无大码| 国产日韩欧美在线精品| 日本爱情动作片www.在线观看| 亚洲国产精品一区二区三区在线| 另类精品久久| 欧美精品国产亚洲| 少妇高潮的动态图| 国产美女午夜福利| 搡女人真爽免费视频火全软件| 久久婷婷青草| 久久青草综合色| 国产亚洲午夜精品一区二区久久| 简卡轻食公司| 国产极品天堂在线| 99热这里只有精品一区| 色哟哟·www| 性高湖久久久久久久久免费观看| 国产精品久久久久久精品电影小说| av免费观看日本| 大又大粗又爽又黄少妇毛片口| 一二三四中文在线观看免费高清| 亚洲av欧美aⅴ国产| 内地一区二区视频在线| 免费av中文字幕在线| av有码第一页| 国产中年淑女户外野战色| 九九久久精品国产亚洲av麻豆| 97超碰精品成人国产| 精品卡一卡二卡四卡免费| 免费人妻精品一区二区三区视频| 中文在线观看免费www的网站| 少妇裸体淫交视频免费看高清| 日本-黄色视频高清免费观看| 国产精品伦人一区二区| 色哟哟·www| 亚洲av二区三区四区| 国产成人aa在线观看| 国产伦精品一区二区三区视频9| kizo精华| 国产精品久久久久成人av| 久久精品国产自在天天线| 99久久精品一区二区三区| 欧美日韩国产mv在线观看视频| 婷婷色麻豆天堂久久| 在线观看人妻少妇| 午夜免费鲁丝| 日韩人妻高清精品专区| 十八禁高潮呻吟视频 | 黄色欧美视频在线观看| 一区二区三区四区激情视频| 午夜福利网站1000一区二区三区| 老熟女久久久| 欧美性感艳星| 成人毛片a级毛片在线播放| 国产爽快片一区二区三区| 我要看日韩黄色一级片| 久久人妻熟女aⅴ| 精品99又大又爽又粗少妇毛片| av一本久久久久| 天堂中文最新版在线下载| 久久久久久人妻| av天堂久久9| 久久99一区二区三区| 高清毛片免费看| 一级毛片久久久久久久久女| 久久99一区二区三区| 亚洲国产精品国产精品| 久久久久人妻精品一区果冻| 亚洲国产精品一区二区三区在线| 自线自在国产av|