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Article

The Preparation of Amorphous Aluminum Oxide Modified g-C3N4 to Improve Photocatalytic Performance in Contaminant Degradation Applications

by
Yining Zheng
,
Congcong Wang
,
Wenjing Fu
,
Qi An
,
Cundi Wei
and
Lina Li
*
Key Laboratory of Automobile Materials of Ministry of Education, Solid Waste Recycling Engineering Research Center of Jilin, School of Materials Science and Engineering, State Key laboratory of Inorganic Synthesis & Preparative Chemistry, Jilin University, Changchun 130022, China
*
Author to whom correspondence should be addressed.
Catalysts 2020, 10(9), 1036; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091036
Submission received: 5 August 2020 / Revised: 21 August 2020 / Accepted: 3 September 2020 / Published: 9 September 2020
(This article belongs to the Special Issue Porous Materials and Catalysts)
Browse Figures
Review Reports Versions Notes

Abstract

:
For the first time, aluminum alloy was used as the main source to prepare aluminum oxide-modified carbon nitride with a melamine–cyanuric acid supramolecular complex. The introduction of amorphous aluminum oxide confers macroporosity to the skeletons of g-C3N4-AlOx. Its surface area increased to 75.5 m2g−1, about 1.5 times that of single g-C3N4. After modification, the visible light response range was expanded, especially at 450~500 nm, while the band structure could be adjusted. Compared with g-C3N4, g-C3N4-AlOx has better photocatalytic performance, the adsorption rate for the dye rhodamine B (RhB) is about 2.1 times that of g-C3N4, and the RhB removal rate is 1.2 times that of g-C3N4.

Graphical Abstract

1. Introduction

The rapid development of global industrialization and growth of population have led to increasing demand for energy. With non-renewable energy sources being increasingly consumed and rapidly depleted, the effective utilization and development of renewable energy sources has become extremely urgent and received wide attention [1,2,3].
As an important part of renewable energy, solar energy has competitive advantages, such as wide distribution, large energy reserves, cleanliness and safety [3,4]. In order to promote the usage of solar energy, research on photocatalytic materials with good stability and high activity becomes a key topic in material science [5,6,7,8,9]. Among all the materials, g-C3N4 is eye-catching because of its low cost, low toxicity and wide light response range [10,11,12]. Since the first report about its use in water splitting in 2009 [13], related reports have continued. Compared with the classic photocatalyst TiO2, g-C3N4 not only exhibits satisfying photocatalytic activity under ultraviolet light but also can be activated by part-visible light [5,14,15,16]. This property makes g-C3N4 appealing, as visible light accounts for about 43% of the solar spectrum [4,17,18]. To date, its application in photocatalysis includes water splitting [13,19], organic matter degradation [20,21], CO2 reduction [22,23,24] and photocatalytic organic reactions [24,25].
However, g-C3N4 still presents several disadvantages, such as its low specific surface area, low charge mobility, high excitation dissociation energy, high electron hole recombination rate and inappropriate valence electron positions [19,26,27,28]. These limitations result in the low quantum efficiency of g-C3N4 at an irradiation wavelength of 420–460 nm [13,29]. A lot of research on g-C3N4 modification has been carried out to improve its catalytic efficiency, including acid treatment [30], noble metal deposition [31,32], anchoring dye sensitization [33], morphological modification [34,35], etc. In addition, doping is also an effective way to introduce impurities into the g-C3N4 matrix to change the electronic structure and energy band configuration, such as non-metallic element doping and metal oxide semiconductor coupling with g-C3N4 to form heterojunctions (Cu2O, TiO2, ZnO, etc.) [6,36,37,38,39]. In fact, the formation of a heterojunction between metal oxide and g-C3N4 can effectively shorten the distance of the electron transport path, inhibit the rapid recombination of photo-generated electron holes and provide more sites for g-C3N4 to bind to the reaction substrate in the photocatalytic process [40].
Al2O3, as a cheap, non-toxic material, can combine with g-C3N4 to enhance the photocatalytic activity of g-C3N4. Compared with other metal oxides, aluminum oxide has the advantages of abundant reserves, a low cost, no pollution, good chemical inertia, good thermal stability, a large specific surface area and so on [4]. Its photoelectron defects can effectively inhibit the fast recombination of photoexcited carriers in Al2O3/g-C3N4 material, so the material has better photocatalytic activity. Previous studies have reported that although alumina does not have photocatalytic activity, amorphous alumina indeed helped with Al2O3/g-C3N4’s photocatalytic performance. That is owing to the defect sites of Al2O3, which can accept electrons from g-C3N4 in the Al2O3/g-C3N4 composite and inhibit the fast recombination of photoexcited carriers [4,41]. Currently, effective coupling methods include ultrasonic dispersion, chemical adsorption, in situ thermal polymerization and so on. [20] In order to achieve better performance, new strategies for preparation should be explored to expand the possible material scope. Herein, a better preparation method that can combine aluminum oxide with g-C3N4 is explored. In this protocol, aluminum alloy was directly used as an Al source to form g-C3N4-AlOx with melamine (M) and cyanic acid (CA). Using this method, g-C3N4-AlOx was well mixed with a homogeneous element distribution, and its specific surface area was about 1.5 times that of g-C3N4. The photocatalytic performance of g-C3N4-AlOx was significantly improved compared with that of g-C3N4 in rhodamine B (RhB) degradation experiments.

2. Result and Discussion

2.1. Characterization of As-Prepared Samples

X-ray diffraction was used in order to reveal the structure and crystallinity variation of materials before and after the calcination process. As shown in Figure 1a, under the condition of continuous stirring, cyanuric acid and melamine would form a cyanuric acid–melamine (CM) supramolecular complex with a characteristic peak at around 27.9°. The AlOxHy colloid prepared in this protocol shows no specific XRD patterns, revealing its amorphous nature. With the addition of AlOxHy colloids, the main peaks of CM-AlOxHy remained similar to those of CM, illustrating that the main skeleton of the composite was still CM. The intensity of these peaks decreased compared with those of the CM complex, which shows the successful introduction of the AlOxHy colloid. After calcination, it could be found that the CM turned to g-C3N4, with a specific peak at 27.4°, representing its two dimensional structure. The XRD pattern of g-C3N4-AlOx is basically consistent with that of single g-C3N4, suggesting that the main composition of g-C3N4-AlOx is g-C3N4. The characteristic peak at 27.3° is marked as g-C3N4 (JCPDS #87-1526), and the (002) plane of the aromatic segment is stacked between the planes [42,43]. The refined lattice parameters of g-C3N4 and composite material g-C3N4-AlOx obtained by using the Scherer formula [44,45] are a = 398 (340) Å and a = 52 (5) Å, respectively. This shows that compounding the materials can effectively reduce the grain size of g-C3N4.
The surface area, porosity of g-C3N4, composite g-C3N4-AlOx and amorphous aluminum oxide were studied with the nitrogen adsorption–desorption method at 77 K. All samples were treated under vacuum at 423 K for 4 h prior to these measurements. It can be observed from Figure 2a that the N2 adsorption isotherms of g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide increase slowly at low relative pressure and sharply at high relative pressure. These materials present type IV isotherms with hysteresis loops of type 3 (H3), revealing the samples are all mesoporous materials. Based on this information, the specific surface areas were calculated with the BET model. The BET surfaces area of g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide were evaluated to be 51.1, 75.5 and 189.2 m2g−1, respectively. The surface area of g-C3N4-AlOx was higher than that of g-C3N4, which would be helpful in catalysis. Its surface area is between that of g-C3N4 and that of amorphous aluminum oxide, suggesting the successful combination of the two components in the new material. The pore size distributions of the samples were calculated with the Nonlocal Density Functional Theory (NLDFT) method, as shown in Figure 2b. Compared with that of g-C3N4 and amorphous aluminum oxide, the porosity of g-C3N4-AlOx includes not only the mesoporous part but also macroporosity (60–130 nm). The appearance of new porosity displays a new structure in g-C3N4-AlOx, which means that the CM complex and AlOxHy colloid are not simply mixed together in the g-C3N4-AlOx but they form new material. This proves that the new preparation strategy is valuable for achieving new materials and expanding the material scope. Additionally, the material in this method very likely possesses A heterojunction structure, which is usually preferred in semiconductor catalysis.
The morphology of g-C3N4-AlOx was investigated with SEM as shown in Figure 3. The SEM photos show that single g-C3N4 displays tubular structures, with a diameter of about 500 nm, and a relatively smooth surface (Figure 3a). For amorphous aluminum oxide-decorated g-C3N4, the morphology changes greatly into an irregular “coralloid” structure with a rough surface (Figure 3b,c). Importantly, a large number of pores appear in the “coralloid” structure, whose existence is consistent with the results of the N2 adsorption–desorption measurements discussed above. The morphology variation intuitively proves the change in material structure and influence of Al colloids. In order to reveal the element composition, g-C3N4-AlOx was analyzed with energy dispersive X-ray energy spectroscopy (EDS). The EDS mapping images (Figure 3d) suggest that the four main elements Al, C, N and O are extensively distributed in g-C3N4-AlOx. This even existence of amorphous aluminum oxide is probably the reason for the increased in surface area, in that they act as template agents during the skeleton formation process. It also shows that the method of mixing AlOxHy colloid with supramolecular complex CM is so effective that the amorphous alumina keeps close contact with g-C3N4. The close combination of two materials provides the possibility of a heterojunction structure, which may be good for further catalysis applications. The selected area in Figure 3b was analyzed, and the corresponding EDX results are given in Table 1. The EDX results reveal that the amorphous aluminum oxide makes up about 5.10 wt% of g-C3N4-AlOx (here, X is defaulted to 1.5).
The samples were characterized by Fourier transform infrared spectroscopy (FTIR), as shown in Figure 4. g-C3N4-AlOx possesses the peaks most characteristic of g-C3N4 in the FTIR spectrum. This shows that its main structure is similar to that of g-C3N4, which is a connected hepazine ring. The peak band around 3000–3450 cm−1 is attributed to the stretching vibration of N-H and hydroxyl (O-H) groups, and is derived from the process of supramolecular dehydration while forming g-C3N4. Compared with the peak band in the box of g-C3N4, the peak band of g-C3N4-AlOx near 3000–3450 cm−1 is broadened and the peak strength is slightly increased, indicating that there were more hydroxyl groups on the surface of g-C3N4-AlOx. This is possibly because AlOxHy colloid joins the supramolecular formation and changes the surface structure of the original g-C3N4. It is worth noting that g-C3N4-AlOx has an absorption peak near 2200 cm−1, which is not shown in the graphs of single g-C3N4 and amorphous aluminum oxide. This absorption peak is attributed to the peak characteristic of C≡N. The appearance of this new peak again illustrates that AlOxHy colloid affects the supramolecular formation and, later, the g-C3N4-AlOx synthesis. In the presence of AlOxHy, some triazine rings in the supramolecular formation do not condense into heptazine rings completely but result in C≡N on the surface of the material. Overall, this is consistent with the previous analysis showing that g-C3N4-AlOx is a new material from g-C3N4 surface decoration.
The details of g-C3N4-AlOx regarding the chemical composition and local connectivity motifs were revealed by X-ray photoelectron spectroscopy (XPS, Figure 5). In the C1s curve of single g-C3N4, the main signal peak appears at 288.3 eV, which is attributed to sp2C in triazine rings (N–C=N2). (The other peak around 284.8 eV is recognized as adventitious carbon from impurities.) After the decoration of AlOx colloids, the C1s peak in g-C3N4-AlOx becomes shifted to a higher binding energy area (288.4 eV), indicating its chemical environment has changed and there is close interaction between amorphous aluminum oxide and g-C3N4 (Figure 5a). The N1s spectrum of g-C3N4-AlOx was similar to that of g-C3N4, which shows that the main framework of g-C3N4-AlOx is still g-C3N4 (Figure 5b). Compared with those for amorphous aluminum oxide, the positions of the O1s peak and Al2p peak also exhibit variation in g-C3N4-AlOx. In amorphous aluminum oxide, the positions of O1s and Al2p locate at 531.3 and 74.4 eV, which are shifted to 532.1 and 74.7 eV in g-C3N4-AlOx (Figure 5b,c). This change illustrates strong chemical interaction between the two components, which suggests the successful preparation of g-C3N4-AlOx with an interactive interface.
The g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide were studied with solid UV-vis absorption spectroscopy. As shown in Figure 6a, pristine g-C3N4 exhibits a light absorption range from ultraviolet light to visible light, and its absorption edge wavelength is at around 450 nm. After decoration with AlOxHy colloid, the absorption edge of g-C3N4-AlOx was redshifted to around 500 nm, which is an improvement for wider solar light spectrum absorption. The redshift of adsorption usually comes from the enlargement of conjugations. Here, the variation of adsorption may imply that amorphous aluminum oxide takes part in the conjugations in the new system. In the g-C3N4-AlOx, the conjugation may contain p–π conjugation, instead of only π-π conjugation from g-C3N4. As amorphous aluminum oxide only responds to ultraviolet light, the better light response performance of g-C3N4-AlOx is indeed due to the decoration effect of aluminum oxide on g-C3N4, instead of simple mixing. The band gap of those materials can be calculated with the Tauc plot method. The bandgap of g-C3N4-AlOx is calculated to be 2.51 eV, which is a little narrower than that of g-C3N4, at around 2.66 eV. One possible reason for this result is that the addition of AlOxHy colloid leads to lower crystallinity (Figure 1b) and more crystal defects in g-C3N4-AlOx. In addition, in Figure 6, it is also clear that g-C3N4-AlOx has two components in its absorbance edge, which implies that the sample is not monodisperse in size. In this protocol, amorphous aluminum oxide was successfully doped but probably not evenly dispersed. To further determine the valence band level, g-C3N4-AlOx samples were characterized by ultraviolet photoelectron spectroscopy (UPS, Figure 6c). The maximum values of the g-C3N4 and g-C3N4-AlOx valence bands were −5.96 and −5.36 eV vs. vacuum or 1.46 and 0.86 eV vs. NHE (Normal Hydrogen Electrode); E (eV) = −4.5 − ENHE (V) [37]. Considering the width of the forbidden band, the minimum values of the corresponding conduction band are calculated to be −1.20 and −1.65 V vs. NHE, respectively. This result proves this method is effective in band structure adjustment, which provides g-C3N4-AlOx with completely different possibilities in photocatalysis.

2.2. Photocatalytic Activity

The photocatalytic activity of g-C3N4-AlOx was investigated with a rhodamine B (RhB) degradation experiment under visible light irradiation. In a typical degradation test, 5.0 mg of powder was added as a catalyst in 10.0 mL of RhB aqueous solution (10 mgL−1). After 30 mins of stirring in the dark, the whole system was subjected to white light illumination (380–840 nm). During the whole degradation process, the remaining RhB concentration was tested every 20 min by obtaining UV-vis spectra at the wavelength of 554 nm as shown in Figure 7. Amorphous aluminum oxide can absorb a small amount of dyes in the dark but can hardly degrade dyes in visible light. g-C3N4-AlOx displays better photocatalytic performance than g-C3N4, successfully eliminating 92.77% of the RhB within 80 min (Figure 7a). For better intuitiveness, the RhB degradation performance of g-C3N4-AlOx and single g-C3N4 is compared in terms of photodegradation first order profiles in Figure 7b. Those curves are in good agreement with the pseudo-first-order correlation of kinetics:
ln(C0/Ct) = kt + ln(C0/C1),
C0: initial concentration of the dye; Ct: instantaneous concentration of the dye; C1: the dye concentration after 30 min of adsorption; ln(C0/C1): the adsorption efficiency of the photocatalyst for RhB; ln(C0/C): the degradation efficiency of the photocatalyst for RhB.
The calculated pseudo-first-order rate constant K and correlation coefficient R are shown in Table 2. According to the value of the intercept ln(C0/C1) on the vertical axis of the dynamic curve, it can be found that the adsorption rate of g-C3N4-AlOx for RhB is about 2.1 times higher than that of g-C3N4 for RhB. This reveals that the amorphous aluminum oxide indeed helps with the promotion of photocatalytic performance. Amorphous aluminum oxide provides more sites for g-C3N4 electrons to combine, promotes electron-hole separation and improves photocatalytic activity. Besides, g-C3N4-AlOx possesses a large number of macroporous structures, in which incident light is more prone to multiple scattering, increasing the light utilization rate of the material. The doping of amorphous alumina confers a smaller grain size and larger porosity to the final composite material.

3. Materials and Methods

3.1. Materials

Al-Ga-In ternary alloy (99% aluminum), melamine (C3N3(NH2)3), cyanic acid (C3H3N3O3), methanol (CH3OH) and AlCl3·6H2O were all purchased from Aladdin (Shanghai, China) and used without further purification.

3.2. Preparation of Photocatalyst

First, melamine (1.5 g) and cyanic acid (1.5 g) were mixed in deionized water for 6 h at room temperature to form a supramolecular complex, cyanuric acid–melamine (CM). Then, the CM was ultrasonically dispersed in 100 mL of methanol for 30 min to obtain Part 1. AlCl3·6H2O was used to prepare an AlCl3 solution (0.7 mol L−1, 100 mL) and heated to 90 °C. At the same temperature (90 °C), 1 g of Al-Ga-In ternary alloy was added into the solution and stirred for 3 h until the reaction was completed. It is cooled to room temperature to form a colloid, and the liquid metal (Ga-In alloy liquid metal ball) present at the bottom was sucked out. Then, after removing the unreacted metal, 100 mL of methanol was added to the colloid and stirred for 2 h to obtain Part 2. The two parts activated by methanol were mixed and stirred for 2 h. Then, they were dried in a vacuum drying oven (80 °C). After grinding, the dried samples were heated to 600 °C in an argon atmosphere in a tube furnace for 4.5 h. The final product g-C3N4-AlOx was obtained. In addition, the part 1 and the part 2 of the different substance quantities were synthesized and tested, and the data were presented in the supplementary material.

4. Conclusions

In this article, a new preparation strategy was proposed for amorphous aluminum oxide-modified carbon nitride with aluminum alloy as an aluminum source. The introduction of amorphous aluminum oxide confers macroporosity to the skeletons of g-C3N4-AlOx. The material prepared by this method shows a smaller grain size, larger specific surface area, wider light response range, better photocatalytic performance and different band structure in comparison with g-C3N4. These changes help with the improvement of its photocatalytic performance.

Supplementary Materials

The following are available online at https://0-www-mdpi-com.brum.beds.ac.uk/2073-4344/10/9/1036/s1. Figure S1: XRD pattern of each synthetic sample: (a,b) before roasting and (c,d) after roasting; Figure S2: (a,c) N2 adsorption–desorption isotherm and (b,d) pore size distribution of samples; Figure S3: TEM images of g-C3N4-AlOx; Figure S4: FTIR absorption spectra of the samples; Figure S5: The XPS survey spectra of the samples; Figure S6: UV–vis absorption spectra of the samples; Figure S7: (a,c) photocatalytic activity comparison for RhB photodegradation by the samples under visible light irradiation, and (b,d) first order profiles of photodegradation of RhB by the samples.

Author Contributions

Formal analysis, investigation, writing—original draft, and writing—review and editing, Y.Z.; methodology and conceptualization, L.L. and C.W. (Cundi Wei); project administration, Q.A.; validation, C.W. (Congcong Wang) and W.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Jilin University Key Laboratory of Automobile Materials of the Ministry of Education (45119031B028), the State Key laboratory of Inorganic Synthesis & Preparative Chemistry (2020-39), the National Natural Science Foundation of China (grant No. 41472035), and the Province/Jilin University co-construction project funds for new materials (SXGJSF 2017-3).

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 10 01036 g001 550
Figure 1. XRD patterns of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide before (a) and after calcination (b).
Figure 1. XRD patterns of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide before (a) and after calcination (b).
Catalysts 10 01036 g001
Catalysts 10 01036 g002 550
Figure 2. (a) N2 adsorption–desorption isotherm, and (b) pore size distribution diagram of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide.
Figure 2. (a) N2 adsorption–desorption isotherm, and (b) pore size distribution diagram of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide.
Catalysts 10 01036 g002
Catalysts 10 01036 g003 550
Figure 3. SEM images of (a) single g-C3N4; (b and c) g-C3N4-AlOx; and (d) energy-dispersive X-ray (EDX) mapping of g-C3N4-AlOx.
Figure 3. SEM images of (a) single g-C3N4; (b and c) g-C3N4-AlOx; and (d) energy-dispersive X-ray (EDX) mapping of g-C3N4-AlOx.
Catalysts 10 01036 g003
Catalysts 10 01036 g004 550
Figure 4. FTIR absorption spectra of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide.
Figure 4. FTIR absorption spectra of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide.
Catalysts 10 01036 g004
Catalysts 10 01036 g005 550
Figure 5. High resolution XPS spectra of the (a) C1s, (b) N1s, (c) O1s and (d) Al2p peaks of the samples.
Figure 5. High resolution XPS spectra of the (a) C1s, (b) N1s, (c) O1s and (d) Al2p peaks of the samples.
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Catalysts 10 01036 g006 550
Figure 6. (a) UV–vis absorption spectra, (b) Tauc’s plot, (c) ultraviolet photoelectron spectra (UPS) and (d) band structures of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide.
Figure 6. (a) UV–vis absorption spectra, (b) Tauc’s plot, (c) ultraviolet photoelectron spectra (UPS) and (d) band structures of single g-C3N4, g-C3N4-AlOx and amorphous aluminum oxide.
Catalysts 10 01036 g006
Catalysts 10 01036 g007 550
Figure 7. (a) Photocatalytic activity comparison for rhodamine B (RhB) photodegradation by the samples under visible light irradiation, and (b) first order profiles of photodegradation of RhB by the samples.
Figure 7. (a) Photocatalytic activity comparison for rhodamine B (RhB) photodegradation by the samples under visible light irradiation, and (b) first order profiles of photodegradation of RhB by the samples.
Catalysts 10 01036 g007
Table
Table 1. The element content distribution according to EDS mapping analysis of g-C3N4-AlOx for a selected area.
Table 1. The element content distribution according to EDS mapping analysis of g-C3N4-AlOx for a selected area.
ElementWeight%Atomic%
C39.6144.19
N51.5249.30
Al2.681.33
Table
Table 2. Kinetic fitting equation, quasi-first-order rate constant k and correlation coefficient in the process of the degradation of RhB by each sample prepared.
Table 2. Kinetic fitting equation, quasi-first-order rate constant k and correlation coefficient in the process of the degradation of RhB by each sample prepared.
SampleFitted Equationk
(min−1)		Correlation
Coefficient R
no catalystln(C0/Ct) = 1.96 × 10−4t + 3.37 × 10−41.96 × 10−49.89 × 10−1
g-C3N4ln(C0/Ct) = 1.42 × 10−2t − 5.39 × 10−21.42 × 10−29.94 × 10−1
g-C3N4-AlOxln(C0/Ct) = 2.92 × 10−2t − 1.10 × 10−12.92 × 10−29.94 × 10−1
g-C3N4-AlOx-adsorptionln(C0/Ct) = 1.01 × 10−3t + 3.52 × 10−11.01 × 10−39.97 × 10−1
amorphous aluminum oxideln(C0/Ct) = 4.89 × 10−4t + 3.34 × 10−24.89 × 10−49.92 × 10−1

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Zheng, Y.; Wang, C.; Fu, W.; An, Q.; Wei, C.; Li, L. The Preparation of Amorphous Aluminum Oxide Modified g-C3N4 to Improve Photocatalytic Performance in Contaminant Degradation Applications. Catalysts 2020, 10, 1036. https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091036

AMA Style

Zheng Y, Wang C, Fu W, An Q, Wei C, Li L. The Preparation of Amorphous Aluminum Oxide Modified g-C3N4 to Improve Photocatalytic Performance in Contaminant Degradation Applications. Catalysts. 2020; 10(9):1036. https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091036

Chicago/Turabian Style

Zheng, Yining, Congcong Wang, Wenjing Fu, Qi An, Cundi Wei, and Lina Li. 2020. "The Preparation of Amorphous Aluminum Oxide Modified g-C3N4 to Improve Photocatalytic Performance in Contaminant Degradation Applications" Catalysts 10, no. 9: 1036. https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091036

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