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NANOSYSTEMS:
PHYSICS, CHEMISTRY, MATHEMATICS
Kharina S.N., et al. Nanosystems: Phys. Chem. Math., 2024,15 (3), 388-397.
http://nanojournal.ifmo.ru
Original article
DOI 10.17586/2220-8054-2024-15-3-388-397
Copper-modified g-C3N4/TiO2 nanostructured photocatalysts for H2 evolution from glucose aqueous solution
Sofiya N. Kharina", Anna Yu. Kurenkova6, Andrey A. Saraevc, Evgeny Yu. Gerasimovd, Ekaterina A. Kozlovae
Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia
[email protected], [email protected],[email protected], [email protected], [email protected]
Corresponding author: Sofiya N. Kharina, [email protected]
Abstract Two strategies for synthesis of copper-modified composite photocatalysts based on graphitic carbon nitride and titanium dioxide for hydrogen evolution reaction are presented. The first one is based on the mechanical dispersion of separately prepared g-C 3N4 and commercial TiO2 (Evonik P25), modified with copper. Another approach is co-calcination of melamine and commercial TiO2 with subsequent modification by copper. The samples were characterized using X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The synthesized photocatalysts were tested in hydrogen evolution from glucose aqueous solution under visible light irradiation (440 nm). The largest photocatalytic activities met 235 and 259 ^mol g-1h-1, corresponding to the first and the second photocatalyst series, respectively. The most active photocatalyst from the first series 1 wt.% g-C3N4/1 wt.% CuOn/TiO2 maintained its hydrogen production rate during a 6-hour cyclic stability test.
Keywords photocatalysis, photocatalytic H2 production, biomass photoreforming, glucose photoconversion, composite photocatalysts, titanium dioxide, graphitic carbon nitride, visible light irradiation Acknowledgements This study was supported by Russian Science Foundation, project No. 23-73-01161. Authors thank to A. V. Zhurenok for UV-Vis spectra measurements and D. D. Mishchenko for XRD analysis. For citation Kharina S.N., Kurenkova A.Yu., Saraev A.A., Gerasimov E.Yu., Kozlova E.A. Copper-modified g-C3N4/TiO2 nanostructured photocatalysts for H2 evolution from glucose aqueous solution. Nanosystems: Phys. Chem. Math., 2024,15 (3), 388-397.
1. Introduction
To overcome the energy shortage and ensure the sustainable development of mankind, the use of hydrogen as an energy carrier rather than traditional fuels is considered to be the most reasonable trend. Despite the fact that hydrogen is mainly produced from non-renewable sources such as coal and natural gas, more attention must be paid to the use of renewable energy sources. The promising approach is the photoreforming of biomass. Its key advantages are simplicity, low operating cost, non-requirement of high pressure and temperature during the treatment and wide variety of catalysts [1,2]. Moreover, this technique is not only based on solar energy inputs and inexhaustible biomass substrates, but could use the byproducts from industrial biomass conversion, e.g. alcohols (methanol, ethanol, glycerol, isopropanol), carboxylic acids (lactic, formic, acetic) mono-, di- and polysaccharides [3-11]. Although biomass-derived products have long been utilized as an energy source, they are often used for hydrogen production through high-energy consuming thermochemical or low-efficiency biorefinery processes. Therefore, developing an effective photoreforming process does remain of the great demand.
Titanium dioxide being one of the best n-type semiconducting and widely studied photocatalysts has been employed for various applications [12-14]. Providing its strong oxidizing and moderate reducing abilities, the band structure of TiO2 limits its activity within the UV range. To shift its light absorption edge to a greater wavelength region, the use is made of visible light sensitive semiconductors. This helpful strategy is to obtain the heterostructure, which contains TiO2 and some narrow-band gap semiconducting material intimately connected. The formation of heterojunction between two
semiconductors leads to increased charge separation and, therefore, to higher light absorption efficiency [15-17].
Among the vary of prospective narrow band semiconductors [18,19], graphitic carbon nitride g-C3N4 is believed to be a promising candidate. Its narrow band gap (2.7 eV) and the strongly negative conduction band position (-1.3 eV vs. NHE) make g-C3N4 an effective material for proton reduction with hydrogen formation under visible light [20-22]. In comparison with traditional photocatalysts being active under visible radiation - metal chalcogenides, the important advantages of g-C3N4 are non-toxicity and outstanding chemical and thermal stability (up to 600 °C) [23]. As many other
© Kharina S.N., Kurenkova A.Yu., Saraev A.A., Gerasimov E.Yu., Kozlova E.A., 2024
pristine semiconductors g-C3N4 suffers from the fast charge-carrier recombination, which restrains its application. To increase the life time of photogenerated charge carriers, a lot of efforts has been made to synthesize the composites based on g-C3N4 and wide bandgap semiconductors such as TiO2. Such strategy allows one to promote the charge separation and increase their lifetime.
There are multiple photocatalytic applications where g-C3N4/TiO2 is utilized [24], with H2 production being among them. For instance, Hongjian [16] fabricated g-C3N4/TiO2 by ball-milling, after than 0.5 wt.% Pt cocatalyst was pho-todeposited on the composite. The photocatalyst 50 % g-C3N4/TiO2 has demonstrated the greatest H2 production rate (22.4 molh-1), which is twice as higher as unmodified g-C3N4. Another effective technique to modify semiconductor photocatalyst and increase the life time of photogenerated electrons and holes is the deposition of metal particles, such as Pt, Ni, Cu, etc., which act as electron mediators between two semiconductors. Bo Chai and colleagues [15] have developed g-C3N4/Pt/TiO2 nanocomposite via a facile chemical adsorption followed by a calcination process. As a sacrificial agent the use was made of triethanolamine (TEOA) - one of the most effective electron donors for g-C3N4-based photocatalysts. The results have revealed the H2 production rate rising with the increasing of g-C3N4 content and the activity reaching the maximum - 178 ^mol h-1 for the photocatalyst, which contains 30 % g-C3N4 loaded on Pt/TiO2. A comprehensive study [17] has been carried out on ternary CdS/TiO2/g-C3N4 composites applied both in H2 evolution and dye degradation processes. The authors have reported that the system accomplishes an S-scheme heterojunction, which leads to enhanced photocatalyst activity compared to the individual components.
Despite the examples mentioned above, there is still insufficient information on studies that aim to expand the application area of g-C3N4 and its activation for photocatalytic H2 production from biomass components. The article presented compares two different synthetic approaches for composite photocatalysts based on g-C3N4 and TiO2 for H2 generation from glucose aqueous solutions under visible light irradiation (440 nm). The main purpose of this work is to determine the effect of g-C3N4 loading on the photocatalytic activity of TiO2 under visible light. Additionally, two synthetic strategies are proposed and their comparison is discussed herein. In our previous study [25] the influence of copper cocatalyst particles dispersed on TiO2 was comprehensively discussed and it was found that CuOn (n = 0.5 - 1) enhanced the photocatalytic H2 evolution rate over TiO2-based photocatalysts. In the present work, the CuOn cocatalyst was used as well. Two series of nanostructured composites have been synthesized. The first one has been made through the mechanical dispersion of g-C3N4 and copper-modified TiO2. To compare, the second series has been obtained by calcining melamine and TiO2 mechanical mixture followed by copper deposition.
2. Experimental section
2.1. Photocatalyst characterization
The photocatalysts were analyzed by X-ray diffraction (XRD), UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM).
XRD pattern of the g-C3N4 was obtained using a D8 ADVANCE diffractometer equipped with a LYNXEYE linear detector (Bruker AXS GmbH, Karlsruhe, Germany) at room temperature in the 20 of 10 - 60° with a step of 0.05° with Ni-filtered CuKa radiation (A = 1.5418 A). Diffuse reflectance UV-vis spectra were recorded using a UV-2501 PC spectrophotometer with an ISR-240A diffuse reflectance unit (Shimadzu, Kyoto, Japan). The morphology of the photocatalysts was studied by HRTEM using a ThemisZ electron microscope (Thermo Fisher Scientific, Waltham, MA, USA) at an accelerating voltage of 200 kV. The study of the chemical composition of the photocatalysts was carried out by XPS on an electronic spectrometer SPECS SurfaceNanoAnalysis GmbH (Germany). The spectrometer was equipped with a PHOIBOS-150-MCD-9 hemispherical analyzer, an XR-50 characteristic X-ray source with a double Al/Mg anode. Non-monochromatic MgKa radiation (hv = 1253.6 eV) was used to record the spectra. To take into account the effect of charging the samples, we used the position of the peak corresponding to titanium dioxide (E(Ti2p3/2) = 458.7 eV).
2.2. Synthesis of the photocatalysts
In order to synthesize the photocatalysts, all chemicals were taken in analytical grade without any additional purification.
2.2.1. TiO2 pretreatment. TiO2 samples were obtained using commercially available Evonik P25. Evonik P25 (0.500 g) was placed in a crucible and calcined at 600 - 750 °C for 3 h at a heating rate of 3 °Cmin-1. The resulting powder was then collected and ground thoroughly in a ceramic mortar.
2.2.2. g-C3N4 synthesis. Melamine was used as a precursor for graphitic carbon nitride formation via thermal condensation process. 20 g of melamine to be loaded in a covered crucible was heated to 600 °C at a rate of 10 °Cmin-1 and held for 2 h. The yellow powder was ground in mortar for the further usage.
2.2.3. 1st series of composite photocatalysts. The first series of photocatalysts were obtained by copper deposition on the TiO2 surface and subsequent dispersing it with g-C3N4. Copper loading (1 and 5 wt.%) was carried out via chemical precipitation route. A 0.1 M Cu(NO3)2 aqueous solution was added to proper amounts (495 and 475 g) of calcined or pristine TiO2 and stirred for 1 hour. An excess of NaBH4 aqueous solution was appended and the mixture was stirred for 1.5 hours followed by washing with deionized water and centrifugation. The damp precipitate was then dried at 60 ° C in air during 12 hours. The samples containing 1 wt.% of CuOn (n = 0.5 - 1) and TiO2 calcined at different temperatures were separated off to investigate their photocatalytic properties. Further, 1 and 5 wt.% of g-C3N4 was mixed with 1 or 5 wt. % CuOn/TiO2-750 in acetone and kept under constant stirring at 50 °C for 60 minutes to obtain particles distributed homogeneously. Then the suspension was heated on a water bath until acetone evaporated and dried at 60 °C in air for 12 hours. The first series of composites was referred to as X-CN/Y-Cu/TiO2-750 (where X and Y represent weight content of g-C3N4 and CuOn respectively).
2.2.4. 2st series of composite photocatalysts. To obtain the second photocatalyst series, melamine and TiO2-750 were mixed and ground in a mortar with mass ratios (wt. %) melamine : TiO2 ranging from 10 : 90 to 50 : 50. The mixture was calcined under the same thermal treatment conditions as described above. Following the calcination, 1 wt. % of copper was deposited on the composite surface using the method mentioned in the previous paragraph. The composites were labelled as 1-Cu/X-M/TiO2-750, where X represents the weight percentage of melamine.
2.3. Photocatalytic experiments
The photocatalytic activity tests were carried out in a glass reactor containing the quartz window and the sampler to analyze the gas phase (Fig. 1). The reaction mixture was obtained by suspending 50 mg of the photocatalyst in 100 ml 0.1 M glucose aqueous solution. Prior to each experiment, the reactor was purged with argon for 20 minutes to remove oxygen in the gas phase. The use was made of the commercially available visible light LED (440 nm, 580 mWcm-2) placed on a distance of 1 cm away from the quartz window. Also, the rate of H2 evolution on the most active photocatalyst was studied under AM1.5G illumination using a sunlight simulator "Pico" (G2V Optics, Canada). Gas phase analysis was carried out using a gas chromatograph CHROMOS GC-1000 equipped with a thermal conductivity detector and a NaX zeolite column to determine the amount of H2 evolved quantitatively.
5
I
Fig. 1. Scheme of set-up for photocatalytic activity test. 1 - magnetic stirrer, 2 - stir bar, 3 - reaction suspension, 4 - glass reactor, 5 - sampler, 6 - quartz window, 7 - LED, 8 - power supply.
3. Results and discussions 3.1. Catalysts characterization
The photocatalyst synthesized were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM).
The X-ray diffraction pattern of the synthesized g-C3N4 shown in Fig. 2a demonstrates two characteristic peaks at 20 = 12.8° and 27.8°, which corresponds to the (210) and (002) crystal planes, respectively. The signal attributed to periodic stacking of triazine units is indicated as (210), thus suggesting that g-C3N4 forms a rhombic structure rather than a hexagonal structure.
Fig. 2. a) XRD patterns of g-C3N4; b) Cu2p core-level spectra of photocatalysts. The spectra are normalized to the integral intensity of the corresponding Ti2p spectra.
The state and relative concentrations of elements in the surface layer of photocatalysts were analyzed by XPS (Table 1). At the survey spectra of the catalysts, peaks corresponding to Cu, Ti, N, C and O were found. The peaks related to g-C3N4 cannot be identified in the spectrum of C1s carbon due to the low concentration of g-C3N4 in the photocatalysts studied and the presence of carbon impurities from the atmosphere. The g-C3N4 content was estimated based on analysis of the N1s spectrum. It is worth noting that the near-surface layer of the photocatalyst 1-CN/1-Cu/TiO2-750 contains a larger amount of nitrogen compared to the sample 1-Cu/25-M/TiO2-750. At the same time, the concentration of copper on the surface, on the contrary, is higher in the case of 1-Cu/25-M/TiO2-750. The g-C3N4 concentration in these photocata-lysts may indeed differ due to different syntheses, however, since copper is deposited using the same method, its content in the volume of photocatalysts should be the same. It can be concluded that, in the case of the 1-CN/1-Cu/TiO2-750 sample, the copper particles are partially shielded by g-C3N4; while in the 1-Cu/25-M/TiO2-750 photocatalyst, copper is predominantly located on the surface of the photocatalyst.
Table 1. Relative atomic concentrations of elements in the surface area of the photocatalysts and N1s, Cu2p3/2, and Ti2p3/2 binding energies
Photocatalysts [N]/[Ti] [Cu]/[Ti] Cu0/1+, % Nls CU2P3/2 Ti2p3/2
C-N=C (C)3-N N-H Cu0/1+ Cu2+ TiO2
1-CN/1-Cu/TiO2 -750 1-Cu/25-M/TiO2 -750 0.11 0.04 0.07 0.22 50 20 398.7 398.7 400.0 400.0 401.1 401.1 932.7 932.7 934.5 934.5 458.7 458.7
The Cu2p spectra demonstrates the presence of copper in the Cu2+, Cu+, and/or Cu0 states (Fig. 2b). The Cu2p core-level spectrum of both shows two intense Cu2p3/2 and Cu2p1/2 peaks at 932.7 and 952.7 eV and corresponding core-level satellite peaks at 941.1 - 943.8 eV and 962.1 eV, respectively. The presence of satellite peaks is observed for Cu2+ state, while Cu2p spectrum of Cu0/1+ does not have the satellite peaks [26,27]. The Cu2p3/2 peak at 932.7 eV corresponds to copper in the metallic and/or Cu1+ state. Due to the close binding energies of the corresponding Cu2p3/2 peaks, it is quite difficult to distinguish the Cu0 and Cu1+ state by XPS technique [26,28].
The UV-vis diffuse reflection spectra and Tauc plots of the photocatalysts are shown in Fig. 3. To plot the absorption spectra in Tauc coordinates the adsorption coefficient F(R) was found from the DRS data using the Kubelka-Munk equation [25] (1):
f ^^, (1)
where R is the reflection coefficient of the sample. When comparing the spectra of 1 % CuOn/TiO2 and pure TiO2 (Fig. 3a), it is evident that the absorption edge of 1 % CuOn/TiO2 has shifted to the long-wavelength region and the reflection decreases within the 500 - 800 nm. Such effect suggests that the separation of photogenerated electron-hole pairs in the CuOn/TiO2 heterojunction has been effectively improved [29-31]. Notably, there is almost no difference observed between 1-CN/1-Cu/TiO2 and 1-Cu/25-M/TiO2. The composites reflectance spectra are characterized by a
Wavelength, nm E, eV
Fig. 3. (a) UV-VIS spectrafor theTiO2, g-CsN^ 1 % CuO„/TiO2,1-CN/1-Cu/TiO2-750 and 1-Cu/25-M/TiQ2-750 and (b) Tauc plots for the TiO2 and g-C3N4
greater redshift compared with 1 % CuOn/TiO2. The results obtained consider, that modifying TiO2 with a small amount (1 - 2 wt.%) of narrow band semiconductors enhances light harvesting and promotes photocatalytic activity under visible light irradiation.
The study of morphology of the 1-CN/1-Cu/TiO2 -750 photocatalyst showed that the composite consists of well-crystallized TiO2 polyhedrons covered with copper nanoparticles and 2D nanosheets of g-C3N4 (Fig. 4a,b). Due to the fact that copper deposition has been followed by composite synthesis, g-C3N4 surface is copper-free. The size of TiO2 particles is in the range of 20 - 200 nm, while copper particles have a narrow particle size distribution not exceeding the value of 5 nm (Fig. 4c). The photocatalyst microstructure was investigated in details using EDS elemental mapping. Despite the tendency of g-C3N4 layers to stick together, the EDS analysis (Fig. 4d,e,f) shows that the elements are uniformly distributed across the entire catalyst surface.
Fig. 4. TEM images and HAADF analysis with EDS of 1-CN/1-Cu/Ti02-750
Although, different synthetic processes have been applied, the morphology of 1-Cu/10-M/Ti02-750 (as shown in Fig. 5) resembles one for 1-CN/1-Cu/Ti02-750. As the sample discussed previously, 1-Cu/25-M/Ti02-750 has well-distinguished particles with an average diameter from 20 to 200 nm. The TEM image (Fig. 5c) displays some Cu0n nanoparticles (with average diameter of less than 5 nm) adsorbed onto the photocatalyst surface. Due to visually unresolved crystal structure in the Fig. 5c, the photocatalyst surface is believed to consist of Ti02 in intimate contact with g-C3N4 and Cu0n hemispheres on top. Moreover, g-C3N4 is clearly seen to have extended nanosheet morphology as
Fig. 5. TEM images and HAADF analysis with EDS of 1-Cu/25-M/TiO2-750
presented in Fig. 5b. Finally, HAADF analysis with elemental mapping demonstrates uniformly distribution of CuOn and g-C3N4 particles on the TiO2 surface.
3.2. Photocatalytic activity
At the beginning, synergistic effect of TiO2 modification with g-C3N4 and copper cocatalyst was investigated. The activities of unmodified TiO2,1 wt.% Cu/TiO2, 1 wt.% g-C3^/TiO2, and 1 wt.% g-C3 N4/1 wt.% Cu/TiO2 photocatalysts were tested in the H2 evolution reaction from glucose solution under visible light irradiation (440 nm). The deposition of g-C3N4 and copper leads to a decrease in the rate of H2 evolution compared to unmodified TiO2, probably due to a decrease in the adsorption of glucose on the surface of the photocatalyst (Fig. 6a). However, the co-deposition of both g-C3N4 and CuOn on the TiO2 surface promotes the rate of H2 evolution. This synergistic effect is caused by an increase in light absorption by the composite photocatalyst and an increase in the lifetime of photogenerated charge carriers.
In the previous works, we studied the effect of calcination of TiO2 on photocatalytic activity and showed that heat treatment in some cases leads to an increase in the activity of the photocatalyst [32]. Therefore, further for the synthesis of composite photocatalysts, TiO2 was calcined at 750 °C.
The first series of photocatalysts was tested in the photocatalytic H2 production from glucose aqueous solution. The results obtained are summarized in the Fig. 6b and Table 2. The maximum activity of 235 ^mol-h-1-g-1 is achieved for 1-CN/1-Cu/TiO2-750, considering the variation of g-C3N4 content. Further increasing the g-C3N4 loading up to 5 wt.% causes a decline in activity to 174 ^mol-h-1 -g-1. Additionally, an increase in copper loading results in a decrease in the H2 production rate, consistent with the earlier study [25]. However, the activity of all composite photocatalysts significantly exceeds the activity of commercial TiO2.
Fig. 6. Photocatalytic activity of the first photocatalyst series depending on copper and g-C3N4 amount
To investigate the impact of the synthetic method on photocatalyst activity, we examined the second series of composites under the same conditions (Fig. 7). Starting with the equal melamine: TiO2 ratio, the H2 production rate increases from 172 up to 259 ^mobh-1-g-1 (Table 2) for 1-Cu/50-M/Ti02 and 1-Cu/25-M/TiO2, respectively. However, decreasing the melamine content may slightly depress the photocatalytic activity. The trend involved is observed for the previous photocatalyst as well. When g-C3N4 content raised, it covers the large portion of Ti02 surface and impedes the glucose adsorption due to low affinity. The samples, corresponding to 10 and 25 wt.% melamine content before calcination, exhibit 243 and 259 ^mobh-1-g-1, respectively. These values are comparable to each other and indicate that the samples are among the most prominent photocatalysts in the series concerned.
350 300
10:90 20:80 25:75 30:70 35:65 50:50 melamine : Tif), ratio, wt.%
Fig. 7. Photocatalytic activity of the second photocatalyst series depending on melamine: TiO2 mass ratio. Photocatalysts: 1-Cu/X-M/TiO2-750.
The rate of H2 evolution under the solar light was determined using the most active photocatalyst 1-Cu/25-M/TiO2-750 (Table 3). Its activity is on par with other data in the literature and is inferior only to data obtained using a more powerful light source. In addition, it is worth noting that this photocatalyst does not contain expensive platinum group metals and can be synthesized from available precursors. The synthetic approach proposed in the work can significantly reduce the cost of the generated H2 solar fuel.
3.3. Photocatalytic stability test
In our previous work, it has been established for CuOn/TiO2 photoactivity that it is fluctuant and dramatically decreases under long-term light irradiation [38]. To test the impact of g-C3N4 loading on the catalyst stability, we are to screen the 1-CN/1-Cu/TiO2-750 in cyclic experiments. As shown in Fig. 8, the H2 amount on 1-CN/1-Cu/TiO2-750 does not lower significantly after each cycle and the rate of H2 evolution is the same within the experimental error. It is worth mentioning that the addition of g-C3N4 allows increasing the stability of copper-modified TiO2, if compare to the previous study. Thus, this fact suggests composite heterostructure with g-C3N4 being responsible for enhanced reusability of the catalyst.
t, min Run number
Fig. 8. Photocatalytic stability test: the kinetic curves of H2 production (a), the dependence of H2 generation rate on cycle number (b)
Table 2. Activities of the photocatalysts synthesized
Photocatalyst
Designation
i i,-i
W(H2 ), Mmolg-1h
TiO2 unmodified
28
1st series of photocatalysts
1 % g-C3N4 |1 % CuOn |TiO2 -750 1-CN/1-Cu/TiO2-750 235
5 % g-C3N4 |1 % CuOn |TiO2 -750 5-CN/1-Cu/TiO2-750 174
1 % g-C3N4 |5 % CuOn |TiO2 -750 1-CN/5-Cu/TiO2-750 172
5 % g-C3N4 |5 % CuOn |TiO2 -750 5-CN/5-Cu/TiO2 -750 166
2st series of photocatalysts
1 % CuO„ |g-C3N4 (melamine : TiO2 = 1 % CuO„ |g-CsN4 (melamine : TiO2 = 1 % CuO„ |g-C3N4 (melamine : TiO2 = 1 % CuO„ |g-C3N4 (melamine : TiO2 = 1 % CuO„ |g-C3N4 (melamine : TiO2 = 1 % CuO„ |g-C3N4 (melamine : TiO2 =
TiO2-750 10 : 90) TiO2-750 20 : 80) TiO2-750 25 : 75) TiO2-750 30 : 70) TiO2-750 35 : 50) TiO2-750 50 : 50)
1-Cu/10-M/TiO2-750 1-Cu/20-M/TiO2-750 1-Cu/25-M/TiO2-750 1-Cu/30-M/TiO2-750 1-Cu/35-M/TiO2-750 1-Cu/50-M/TiO2-750
243 222 259 202 181 172
Table 3. The comparison of activity values of the photocatalysts based on g-C3N4 and TiO2 with previously published data on H2 photogeneration from a glucose solution
No. Photocatalyst Conditions W(H2), ^molg-1h-1 Article
C0 (glucose) C(catalyst), gL-1 Light source
1 1-Cu/25-M/TiO2-750 0.1 M 0.5 Simulated solar light (AM1.5G, 100 mW/cm2) 295 Present work
2 3 wt. % Pt/O-g-C3N4 0.1 M 0.25 Simulated solar light (500 W/m2) 870 [33]
3 0.5 wt. % Pd/TiO2 0.5 gL-1 0.5 LED, 375 - 380 nm, 1.5 W/m2 590 [34]
4 2 wt. % PtAu/g- C3N4 0.16 M (pH = 13) 0.3 Xenon lamp (350 - 800 nm, 170 mW/cm2) 2370 [35]
5 W- and N-doped Pt-TiO2 1 mM 1.0 Natural solar irradiation 1000 [36]
6 Cd0.8Zn0.2S/Au/g-C3N4 0.1 M 0.5 Xenon lamp (A > 420 nm) 123 [37]
4. Conclusion
This work proposed and investigated new photocatalysts based on TiO2 and g-C3N4 for H2 production from glucose aqueous solution under visible radiation (440 nm) and solar light (AM1.5G). Two series of photocatalysts were synthesized: one by mechanically dispersing g-C3N4 with TiO2 and the other by co-calcinating melamine and TiO2. The structure and properties of photocatalysts were established using the complex of physicochemical methods. The deposition of CuOn and g-C3N4 particles on the TiO2 surface was shown to alter its optical properties, resulting in a redshift of the absorption edge. Photocatalytic experiments were conducted to test the H2 evolution rate over the samples obtained. The first series had a maximum rate of 235 ^mol h-1g-1, while the second series -259 ^mol h-1g-1 (440 nm), corresponding to 1-CN/1-Cu/TiO2-750 and 1-Cu/25-M/TiO2-750, respectively. The cyclic stability tests of the 1-CN/1-Cu/TiO2-750 showed the rate of photocatalytic H2 evolution kept the same during 4 cycle of experiments. Thus, in this work, active and stable photocatalysts were proposed for the production of H2 under the solar light. It is worth noting that these photocatalysts could be obtained from inexpensive and available precursors such melamine, copper nitrate, and commercial TiO2.
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Submitted 18 April 2024; revised 9 May 2024; accepted 10 May 2024
Information about the authors:
Sofiya N. Kharina - Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave, 5, Novosibirsk, 630090, Russia; ORCID 0009-0000-9399-0231; [email protected]
Anna Yu. Kurenkova - Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave, 5, Novosibirsk, 630090, Russia; ORCID 0000-0002-4150-7049; [email protected]
AndreyA. Saraev - Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave, 5, Novosibirsk, 630090, Russia; ORCID 0000-0001-9610-9921; [email protected]
Evgeny Yu. Gerasimov - Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave, 5, Novosibirsk, 630090, Russia; ORCID 0000-0002-3230-3335; [email protected]
Ekaterina A. Kozlova - Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave, 5, Novosibirsk, 630090, Russia; ORCID 0000-0001-8944-7666; [email protected]
Conflict of interest: the authors declare no conflict of interest.
