Sugarcane Bagasse Hydrolysis by Metal Ions Mediated Synthesis of

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Sugarcane Bagasse Hydrolysis by Metal Ions Mediated Synthesis of Perovskite LaCoO3 and the Photocatalytic Performance for Hydrogen from Formaldehyde Solution under Visible Light Minghui Wu, Mingping Luo, Minxue Guo, and Lishan Jia* Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian China ABSTRACT: Perovskite LaCoO3 was successfully synthesized using natural sugarcane bagasse with tunable oxygen vacancy. The preparation process was studied to elucidate the interaction between sugarcane bagasse and metal ions. And the prepared catalysts were characterized by XRD, SEM, XPS, DRS, and PL. The results indicated that bagasse was partly hydrolyzed by metal nitrate solution, and the gel was formed by adsorption and complexation between rich organic groups and metal ions, differing from citric acid complexation with metal ions. The bagasse fragments mediation in the process could modulate the amount of oxygen vacancy. An appropriate oxygen vacancy may act as the defect energy level above the valence band of LaCoO3 to adjust the band gap and accelerate charge transfer, resulting in high photocatalytic performance. Photocatalytic tests in formaldehyde aqueous solution under visible light demonstrated that LaCoO3 prepared by sugarcane bagasse exhibited higher hydrogen production than that prepared by conventional citric acid method. KEYWORDS: Sugarcane bagasse, Hydrolysis, Perovskite, Oxygen vacancy, Photocatalysis

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INTRODUCTION The development of clean hydrogen fuels is one of the concerns of current research, which can effectively resolve the unsustainable fossil fuels resulting in environmental pollution problems.1,2 In many processes, photocatalytic water splitting to hydrogen has always been a promising clean and green technology.3,4 For commercial applications, further enhancement of the visible light absorption and water splitting hydrogen release performance of photocatalysts has been a concern.5 In recent decades, most photocatalytic studies are focused on the development of novel catalyst such as non-metal (C, S, N) doped metal oxide,6−8 heterojunction structure composite,9,10 and noble metal surface modified semiconductor11−13 with high photocatalytic performance. In general, the photocatalyst, especially containing lattice defects and oxygen vacancies, exhibits good photocatalytic properties,14−16 which can be attributed to the formation of moderate impurity levels to promote the narrowing of the band gap and to suppress the photogenerated electron−hole recombination.17 Among many preparation methods for obtaining such structure photocatalysts, the formation of sol−gel by metal ion and complex organic reagent is an effective method for various defect materials, because the precursors can be mixed on the molecular level to guarantee a good chemical homogeneity of the system.18 However, it is limited in practical applications due to the complexity of the process and the high cost of reagents.19 Many studies have used soluble biomass as complexing agent to synthesize composite catalysts by sol−gel method.20,21 © 2017 American Chemical Society

Natural biomass could not only replace the conventional chemical reagents because of the advantages of being green, environmental, and low cost but also provide abundant functional groups to interact with the metal ions leading to change in the surface properties, and even form a unique structure of the synthesized photocatalysts, which could bring lattice defects and tune the amount of oxygen vacancy.22 In our previous studies, biomass extracts as complexing agents were formed by sol−gel with metal ions, and the perovskite containing defects and oxygen vacancies was obtained for photocatalytic hydrogen production with high performance.23,24 However, this has been rarely reported in which insoluble natural biomass was directly utilized for the synthesis of composite oxides, because natural polymer molecules make it difficult to form uniformly dispersed metal ions in a sol−gel. Recently, there are many reports that metal ions hydrolyze cellulose and other insoluble biomass macromolecules to make them into soluble biomass small molecules to further synthesize silver nanoparticles.25,26 It is known that sugarcane bagasse is mainly composed of hemicellulose, cellulose, and lignin, which can be hydrolyzed, breaking the macromolecule into small molecular units.27−29 The rich functional groups such as carboxyl and hydroxyl could provide binding sites and play a dominant role in complexing and interaction with metal ions, Received: August 19, 2017 Revised: September 23, 2017 Published: October 8, 2017 11558

DOI: 10.1021/acssuschemeng.7b02884 ACS Sustainable Chem. Eng. 2017, 5, 11558−11565

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Figure 1. X-ray diffractograms of sugarcane bagasse samples and prepared catalysts. (A) SB, SB-1, and SB-6; (B) SB-8; (C) (a) LaCoO3−CA, (b) LaCoO3−SB1.5, (c) LaCoO3−SB1.0, (d) LaCoO3−SB0.5, (e) LaCoO3−SB0.3, and (f) LaCo; (D) corresponding XRD patterns in the 32.0−34.5° 2θ range of spectra a−d od panel C. (Open diamonds) LaCoO3, (filled diamonds) La(OH)3, and (filled clubs) Co3O4.

which are beneficial to the synthesis of composite catalysts.30,31 Perovskite oxide LaCoO3 as a typical photocatalyst has been extensively investigated because of its interesting physicochemical properties.32,33 As reported, the structure and property of this material are closely correlative to the synthesis of precursor and/or dopant,34−36 which could bring lattice defects and tune the amount of oxygen vacancy. A certain number of oxygen vacancies acting as a defect level could narrow the band gap and retard the recombination of photogenerated electrons and holes effectively on the surface of the photocatalyst so as to affect the material properties.37−39 Therefore, how to efficiently synthesize LaCoO3 with promising performance through constructing oxygen vacancy is taken into consideration. Hence, our work tends to directly use various quantities of natural sugarcane bagasse because of the aforementioned specific characteristics to interact with metal ions and synthesize perovskite LaCoO3. The bagasse is characterized to elucidate the interaction with metal ions and its role in the

preparation process. Besides, the relationship between the amount of oxygen vacancy on the perovskite induced by biomass and the performance of photocatalytic hydrogen production is investigated.

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EXPERIMENTAL SECTION

Materials. The sugarcane bagasse was harvested from Fujian Province in China. It was put into a drying oven until water removal was completed. The dried bagasse was ground into fragments and sieved to particles of sizes below 200 μm. La(NO3)3·6H2O, Co(NO3)2·6H2O, and citric acid (C6H8O7·3H2O) were of analytical reagent grade, purchased from Sinopharm Chemical Reagent Co. Ltd. Sample Preparation. La(NO3)3·6H2O and Co(NO3)2·6H2O with a La/Co molar ratio of 1/1 were dissolved in deionized water under manual stirring to obtain a 100 mL aliquot of 0.4 mol·L−1 metal nitrate solution. And sugarcane bagasse (1.0 g dry weigh) was added and stirred, and then the mixture was put into a drying oven at 80 °C. To investigate the interaction between bagasse and metal ions, the mixture was impregnated in the metal nitrate solution for 1, 6, and 8 h and 11559

DOI: 10.1021/acssuschemeng.7b02884 ACS Sustainable Chem. Eng. 2017, 5, 11558−11565

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ACS Sustainable Chemistry & Engineering then filtrated and dried to get sugarcane bagasse residue, marked as SB-1, SB-6, and SB-8, respectively. The original sugarcane bagasse without impregnation in metal nitrate solution was denoted as SB. The above mixture dried in the oven for more than 12 h could obtain a gellike product, noted as SB-gel. The gel prepared by citric acid was signed as CA-gel for comparison. The gel-like product, after roasting by heating mantle and grinding with an agate mortar, was calcined at 700 °C for 2 h to form a perovskite phase, defined as LaCoO3−SB1.0. The added amount of sugarcane bagasse was surveyed. For the dosages of 0.3, 0.5, and 1.5 g of sugarcane bagasse, the resultants were labeled LaCoO3−SB0.3, LaCoO3−SB0.5, and LaCoO3−SB1.5, respectively. Conventional LaCoO3 photocatalyst prepared by citric acid40 (the molar ratio of metal cations/citric acid, 2:0.6) was named as LaCoO3− CA. And the one with no added complexing reagent was named after LaCo. All the catalysts were prepared by the same process except the complexing reagent. Characterization. X-ray diffraction (XRD) patterns were gained on a PANalytical X-pert spathic powder diffractometer with Cu Kα radiation source. Scanning electron microscopy (SEM) analysis was obtained using a LEO 1530 scanning electron microscope, with which energy dispersive spectrometer (EDS) analysis was taken. Fourier transform infrared spectroscopy (FTIR) was conducted using a Nicolet Avatar 330 Fourier transform spectrometer with KBr as dispersant. X-ray photoelectron spectroscopy (XPS) was carried out on a PHI Quantum 2000 scanning ESCA microprobe with a monochromatized microfocused Al X-ray source. Ultraviolet−visible diffuse reflection spectroscopy (UV−vis DRS) was measured with a Varian Cary 5000 UV−vis spectrophotometer. Photoluminescence spectrum (PL) was recorded at room temperature with a Hitachi F7000 spectrophotometer using Xe lamp as the excitation source. The process of gelation for utilizing sugarcane bagasse to synthesize perovskite LaCoO3 was investigated by XRD, EDS, and FTIR to integratedly clarify the interaction between bagasse and metal ions. Thereinto, the crystallinity index (CI) was obtained from the ratio between the intensity of the 002 peak (I002) and the minimum dip (Iam) between the 002 and the 101 peaks according to27,28

CI = (I002 − Iam)/I002 × 100

Table 1. Crystallinity of Sugarcane Bagasse Samples sample

crystallinity index (%)

SB SB-1 SB-6

42 25 22

groups such as hydroxyl and enhance interaction between bagasse and metal ions contributing to adsorption and complexation with metal ions. With the increase of time, the crystalline structure of bagasse is extremely destroyed in SB-8. In Figure 1B, the diffractogram shows no cellulose diffraction peaks but is well matched with the characteristic diffraction peaks of La2Co3(NO3)12·24H2O (JCPDS Card No. 29-0746). The result implies that the mixture of metal (La, Co) nitrate ions may react with biological fragments and form a complex net-like structure and further produce a gel. As shown in Figure 1C for the catalysts, with the increasing amount of sugarcane bagasse, the X-ray diffraction peaks tend to form perovskite LaCoO3. The characteristic diffraction peaks confirm that LaCoO3−CA, LaCoO3−SB1.5, LaCoO3−SB1.0, and LaCoO3−SB0.5 form a perovskite structure corresponding to the standard diffraction pattern given in the XRD data card (JCPDS Card No. 84-0848). Conversely, LaCoO3−SB0.3 and LaCo are identified as LaCoO3 (JCPDS Card No. 84-0848), La(OH)3 (JCPDS Card No. 83-2034), and Co3O4 (JCPDS Card No. 80-1532), suggesting moderate sugarcane bagasse benefits the formation of perovskite structure. Figure 1D presents the main peaks of LaCoO3−CA, LaCoO3−SB1.5, LaCoO3−SB1.0, and LaCoO3- SB0.5 in the 32.0−34.5° 2θ range. A shift toward higher 2θ angles is observed in LaCoO3 prepared by sugarcane bagasse, suggesting distortion of the crystal lattice of LaCoO3, which is possibly caused by the interaction between bagasse and metal ions in the process of forming perovskite. EDS Characterization. EDS analysis (Table 2) confirms the interaction of metal ions and sugarcane bagasse. In original

(1)

where I002 is the intensity of plane 002 at around 22° and Iam is related to the amorphous structure at around 18°. And the prepared catalysts were characterized by XRD, XPS, DRS, and PL. Photocatalytic Reaction. Photocatalytic production reaction of H2 was estimated in a self-made quartz inner reaction vessel. The photocatalyst (0.2 g) was suspended with a magnetic stirrer in aqueous formaldehyde solution (1.5 M) for a total solution volume of 160 mL. And a jacket between the lamp and reaction chamber to keep the reactor temperature constant at 50 °C was filled with 2 mol·L−1 NaNO2 solution, serving as an internal circulation cooling medium to eliminate UV light (cutoff < 400 nm). Before irradiation, the solution was sostenuto bubbled with N2 at a rate of 60 mL·min−1 for 30 min. Then the gas content was checked by GC to confirm that no oxygen was present. A 125 W xenon lamp was used as light source. And the evolution gas was gathered and analyzed by GC (TCD, molecular sieve 5 Å column and Ar carrier).

Table 2. EDS Analysis Results of Sugarcane Bagasse Samples atomic ratio (%)

C

O

SB SB-1 SB-6 SB-8

62.25 61.43 59.36 33.06

37.76 38.30 39.95 50.16

N

La

Co

14.61

0.15 0.38 1.20

0.12 0.31 0.97

sugarcane bagasse (SB), C and O are determined to be the main elements. After being treated with metal nitrate solution, La and Co elements appear, the amount of which grows with increasing impregnation time. There are N elements appearing and the highest percent of oxygen in SB-8 among all the samples. It is ascribed to the adsorption of nitrate ions, in agreement with the XRD analysis, which demonstrates the formation of La2Co3(NO3)12·24H2O, development into biological fragments, and creation of a gel. FTIR Characterization. FTIR spectra of different sugarcane bagasse samples and gels are shown in Figure 2A. As can be seen, SB, SB-1, and SB-6 show similar spectrum curves, corresponding to the characteristic vibrations of sugarcane bagasse.27,28 And the bands of SB-8 resemble those of SB-gel and CA-gel, which suggests that, in the SB-8 sample, abundant metal ions have been incorporated into the sugarcane bagasse and formed a xerogel after drying.

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RESULTS AND DISCUSSION XRD Characterization. Figure 1 shows XRD patterns of sugarcane bagasse samples and the prepared catalysts. As can be seen in Figure 1A, SB, SB-1, and SB-6 display typical cellulose diffraction peaks, where the highest peak at around 22° corresponds to the (002) crystallographic planes. Obviously, the peaks of sugarcane bagasse impregnated with metal nitrate solution are weaker compared to SB. The crystallinity index of sugarcane bagasse samples is calculated according to eq 1 and summarized in Table 1. SB, SB-1, and SB-6 show 42%, 25%, and 22% crystallinity, respectively. The result indicates that the cellulose chain of bagasse may be partially destroyed, due to the hydrolysis by metal ions. It may improve the exposure of active 11560

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Figure 2. (A) Infrared spectra (FTIR) of sugarcane bagasse samples and gels. The corresponding FTIR spectra of (B) SB, SB-1, and SB-6 from 2000 to 800 cm−1 and (C) SB-8, SB-gel, and CA-gel from 1250 to 500 cm−1 (SB, original sugarcane bagasse; SB-1, SB-6, and SB-8: sugarcane bagasse impregnated with 0.1 mol·L−1 metal nitrate solution for 1, 6, and 8 h, respectively; SB-gel, gel prepared by sugarcane bagasse; CA-gel, gel prepared by citric acid).

Figure 3. (A) O 1s and (B) Co 2p XPS spectra of (a) LaCoO3−CA, (b) LaCoO3−SB1.5, (c) LaCoO3−SB1.0, and (d) LaCoO3−SB0.5.

To investigate the interaction between sugarcane bagasse and metal ions, the enlargement spectrogram of SB, SB-1, and SB-6 is carefully examined, shown in Figure 2B. On the infrared spectra of original sugarcane bagasse (SB), the absorption bands at 1733, 1604, 1513, and 1250 cm−1 are features of the functional groups in lignin. To be specific, the bands at 1733 and 1604 cm−1 are ascribed to CO and C−Ph, respectively. The 1513 cm−1 peak can be identified as benzene ring vibration mode, and the peak at 1250 cm−1 is due to C−O stretching of phenols.28,41,42 The band at 1328 cm−1 corresponds to C−H stretching mode in cellulose.41 Then the band at 1048 cm−1 is due to the C−O stretching vibration in hemicellulose and cellulose.43 These peaks of close position can also be observed on curves for SB-1 and SB-6, indicating that sugarcane bagasse treated with metal nitrate solution keeps the main organic functional groups, which are a benefit to complexing with metal

ions. Meanwhile, it deserves notice that the bands mentioned above are distinctly reduced with some slight red shift in the spectra of SB-1 and SB-6, due to the binging of metal ions.44 Bands at 1162 and 1108 cm−1 are assigned to glycosidic C−O− C bonds,27,45 and the intensity decrease after being treated with metal nitrate solution, illustrating the degradation of cellulose chains. It is also verified by the XRD results (Figure 1). And the peak at 1376 cm−1 attributed to O−H vibration of phenolic group28 shifts to 1384 cm−1 with intensity being increased, revealing the existence of N−O adsorption.38 It can be concluded that the disruption of sugarcane bagasse may be due to the interaction and hydrolysis of metal nitrate solution. Confirmed by the similar FTIR spectra of SB-gel and CA-gel in Figure 2A, it is considered that both sugarcane bagasse and citric acid can be used as complexing agents in preparing LaCoO3 perovskite. For comparison, Figure 2C presents the 11561

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component is usually affected by its surrounding chemical environment.48 Coupling with XRD measurements, the different proportion of sugarcane bagasse hydrolyzate and metal (La, Co) nitrate ions can produce different structural complex precursor, which may lead to formation of corresponding oxygen vacancies and surface defects on the perovskite surface after the heat treatment process. It can be concluded that sugarcane bagasse interacts with metal ions to change the structure and surface properties of catalysts. UV−Vis DRS Characterization. As can be seen in Figure 4A, all photocatalysts have similar diffuse reflection curves. And it is apparent that, at the wavelength range from 200 to 800 nm, LaCoO3 prepared by sugarcane bagasse presents higher absorbance than LaCoO3−CA, especially in the visible light region. From the spectra in the UV−vis region, the positions of the absorption edges are determined by the interception of the straight line fitted through the low-energy side of the curve [F(R)hν]2 versus hν, where F(R) is the Kubelka−Munk function and hν is the energy of the incident photon.49 The corresponding transformed diffuse reflectance spectra are shown in Figure 4B, and the band gap energy is evaluated by the extrapolation method50 summarized in Table 4. The optical

infrared spectrograms of SB-8, SB-gel, and CA-gel with wavenumbers ranging from 1250 to 500 cm−1. The bands at 1159 and 1105 cm−1 from SB-8 and SB-gel attract attention. These two bands are both attributed to C−O−C stretching of glycosidic bonds (original sugarcane bagasse (SB) at 1162 and 1108 cm−1). Hence it can be inferred that metal ions developed into bagasse fragments to form a special gel, different from that produced by conventional chemical complexing reagents. The existence of varisized biomass fragments mediates the formation of perovskite, which may affect the structure and surface properties of catalysts. XPS Characterization. Figure 3A presents the O 1s XPS spectra of LaCoO3−CA, LaCoO3−SB1.5, LaCoO3−SB1.0, and LaCoO3−SB0.5. The binding energies around 528.6 and 531.3 eV are attributed to surface lattice oxygen and absorbed oxygen species, respectively.46 And the ratio of adsorbed oxygen to surface lattice oxygen is shown in Table 3. As can be seen, the Table 3. Ratio of Adsorbed Oxygen to Surface Lattice Oxygen for Photocatalysts binding energy (eV)

catalyst

adsorbed oxygen

surface lattice oxygen

ratio of adsorbed oxygen to surface lattice oxygen

LaCoO3−CA LaCoO3−SB1.5 LaCoO3−SB1.0 LaCoO3−SB0.5

531.4 531.1 531.0 531.1

528.8 528.7 528.8 528.6

1.29 1.44 1.50 3.16

Table 4. Band Gap Energy of Photocatalysts photocatalysts

value (eV)

photocatalysts

value (eV)

LaCoO3−CA LaCoO3−SB1.0

2.65 2.32

LaCoO3−SB1.5 LaCoO3−SB0.5

2.49 2.43

absorption threshold of LaCoO3−CA is calculated to be 468 nm, corresponding to the band gap energy of 2.65 eV, whereas LaCoO3−SB1.0 shows a red shift of the absorption edge, which is 534 nm, corresponding to the narrowest band gap energy of 2.32 eV. A narrow band gap energy is a benefit in the light harvesting process,40 which may well be caused by the existence of the defect level for oxygen vacancy. PL Characterization. Photoluminescence (PL) emission spectra of as-prepared photocatalysts are shown in Figure 5. From the spectra of LaCoO3−SB1.5, LaCoO3−SB1.0, and LaCoO3−SB0.5, PL intensity changes with the added amount of sugarcane bagasse, and LaCoO3−SB1.0 exhibits the lowest PL signal, whereas LaCoO3−CA presents the highest PL intensity. PL emission is the result of the recombination of excited

ratio value of LaCoO3 prepared by sugarcane bagasse decreases with the increasing amount of bagasse, but is still above 1.29 for LaCoO3−CA. The results manifest that sugarcane bagasse could play a part in adjusting the amount of oxygen vacancy. An appropriate amount of oxygen vacancy may become a defect level and then reduce the band gap and enhance charge transfer to improve photocatalytic activity.37,40,47 Figure 3B shows the Co 2p core level spectra. There are two characteristic peaks located at around 780 and 796 eV, corresponding to 2p3/2 and 2p1/2 spin−orbit doublet peaks, respectively.32 It is noticed that peaks of LaCoO3−SB0.5 apparently shift to lower binding energies, consistent with the O 1s XPS analysis, in which LaCoO3−SB0.5 presents the highest ratio (3.16) of adsorbed oxygen to surface lattice oxygen. The binding energy of a

Figure 4. (A) UV−vis DRS patterns and (B) the plots of [F(R)hν]2 versus hν of LaCoO3−CA, LaCoO3−SB1.5, LaCoO3−SB1.0, and LaCoO3−SB0.5. 11562

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pyrolysis. Sugarcane bagasse mediation in the preparation process helps produce a special gel to form the perovskite structure and adjust the number of oxygen vacancies to improve photocatalytic activity simultaneously. Photocatalytic Activity. Figure 7 shows the photocatalytic activity of prepared photocatalysts in hydrogen production

Figure 5. PL spectra of LaCoO3−CA, LaCoO3−SB1.5, LaCoO3−SB1.0, and LaCoO3−SB0.5 (excitation wavelength at 295 nm).

electrons and holes. As reported, the lower PL intensity of the samples demonstrates a lower recombination rate.51 It is reasonable to assume that sugarcane bagasse could interact with metal ions to affect the surface structure of LaCoO3, and the formation of appropriate oxygen vacancy can trap electrons to retard the recombination of photogenerated electron−holes, with the benefit of promoting the photocatalytic activity. Conceivable Formation Mechanism. Through the above analysis of sugarcane bagasse in the preparation process and the characterization of prepared catalysts, we put forward a probable formation mechanism of LaCoO3 prepared by sugarcane bagasse and try illuminating the synthesis process and the role of sugarcane bagasse. As a reference, Figure 6 shows the schematic diagram of the preparation process for LaCoO3−SB1.0. First, sugarcane bagasse is hydrolyzed with the interaction of metal ions and then disintegrated into small fragments as interaction is enhanced. Those bagasse fragments provide special structure and abundant organic functional groups to adsorb and chelate with metal ions to form a network-like gel, which is different from the conventional citric acid complexation with metal ions. For roasting and calcination proceeding, the perovskite phase forms with nitrates and sugarcane bagasse

Figure 7. Photocatalytic activity of different photocatalysts from formaldehyde aqueous solution under xenon-lamp irradiation (catalyst concentration = 1.25 g·L−1; HCHO concentration = 1.5 M; reaction time = 120 min; reaction temperature = 50 °C).

from formaldehyde solution under visible light irradiation for 120 min. In the figure, LaCo, prepared with no complexing agent, has no photocatalytic activity. The hydrogen evolution rate improves with the increasing amount of sugarcane bagasse, which facilitates the formation of the perovskite structure. LaCoO3−SB1.0 presents the optimum photocatalytic performance, of which the hydrogen evolution rate eaches 106 μmol· h−1·g−1, much higher than that of LaCoO3−CA (62 μmol·h−1· g−1). Moreover, all samples prepared by sugarcane bagasse reveal an advantage in harvesting visible light over that produced by citric acid. The photocatalytic activity changes with the oxygen vacancy content. These results demonstrate that photocatalytic activity is closely related to the perovskite

Figure 6. (A) Proposed formation mechanism of LaCoO3−SB1.0, (B) Photograph of sugarcane bagasse and metal nitrate solution mixture, (C) photograph of SB-gel, (D) SEM micrographs of LaCoO3−SB1.0, and (E) structural representation of LaCoO3−SB1.0. 11563

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ACS Sustainable Chemistry & Engineering Table 5. H2 Evolution Rate of Photocatalysts Based on Oxide and Noble Metal Doped Oxide photocatalyst Nb−Fe-co-doped La2Ti2O7 Fe3O4@SiO2@Bi2WO6@g-C3N4 Bi2O3/ZrO2 LaCoO3−SB1.0

light source 500 350 125 125

W W W W

xenon lamp xenon lamp mercury lamp xenon lamp

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CONCLUSION Hydrolysis of bagasse by metal ions mediated the synthesis of perovskite. With the interaction of metal nitrate solution, the sugarcane bagasse was transformed into small biomass fragments with rich organic functional groups. The adsorption and complexation of metal ions with organic groups such as hydroxyl and carboxyl groups on the biomass fragments formed the gel, further helping develop the structure and crystal of perovskite. Simultaneously, the interaction between biomass fragments and metal ions could produce appropriate oxygen vacancy on the perovskite. The prepared perovskite had excellent photocatalytic performance in hydrogen production from formaldehyde solution under visible light irradiation. This work presents a simple, cheap, and green method to prepare perovskite oxides with higher photocatalytic activity. AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 0592 2188283. Fax: +86 0592 2184822. E-mail: [email protected]. ORCID

Lishan Jia: 0000-0003-0632-5546 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by a general program of the National Natural Science Foundation of China (Grant No. 21176203). And we thank the Analysis and Testing Center of Xiamen University for analysis and equipment support in this study.

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structure of LaCoO3. An appropriate oxygen vacancy as a defect level can narrow the band gap and favor the transfer of charge carriers to efficiently affect photocatalytic activity. The comparison of the H2 evolution rate of related literaturereported photocatalysts is shown in Table 5. The result shows that LaCoO3−SB1.0 has a relatively high activity among composite metal oxide photocatalysts. This indicates that the preparation of perovskite by biomass hydrolysis is not only a green process but also a unique method for perovskite structure of LaCoO3, which contributes to the photocatalytic hydrogen production system.

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highest H2 production (μmol·gcat−1·h−1)

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DOI: 10.1021/acssuschemeng.7b02884 ACS Sustainable Chem. Eng. 2017, 5, 11558−11565