The photocatalytic hydrogen production performance of porous titanium dioxide , a derivative of Mil-125 (Ti), was improved by using lignin-based carbon quantum

The photocatalytic hydrogen production performance of porous titanium dioxide , a derivative of Mil-125 (Ti), was improved by using lignin-based carbon quantum | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The photocatalytic hydrogen production performance of porous titanium dioxide , a derivative of Mil-125 (Ti), was improved by using lignin-based carbon quantum Kai Zhang, XuDong Zhu, Hong Yan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5121593/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 11 Dec, 2024 Read the published version in Research on Chemical Intermediates → Version 1 posted 11 You are reading this latest preprint version Abstract Carbon points in lignin were prepared by hydrothermal method at 180 ℃ for 12 h. Carbon points with diameters of 1-5 nm were observed by transmission electron microscopy. The prepared lignin carbon point solution was put into the synthesis system of Mil-125(Ti) derivative porous titanium dioxide (M-TiO 2 ) with 10, 15 and 20 mL, respectively, at 150 ℃ and 48 h to obtain CQDs/M-TiO 2 composite photocatalyst series. Through a series of characterization and analysis of its structure and morphology, it is proved that the carbon point is successfully recombined with Mil-125(Ti) derivative porous titanium dioxide (M-TiO 2 ). Through ultraviolet-visible-near-infrared diffuse reflection and flat band potential analysis, we determined that CQDs can improve the light absorption range of porous titanium dioxide (M-TiO 2 ), a derivative of Mil-125(Ti), and calculated the band structure of the material. It is proved that CQDs and Mil-125(Ti) derivative porous titanium dioxide(M-TiO 2 ) constitute a type Ⅰ heterojunction. Photoelectrochemical analysis shows that CQDs/M-TiO 2 composite catalyst has better separation and transport efficiency than M-TiO 2 photogenerated electrons and holes. The photocatalytic hydrogen production activity test at a wavelength of > 380 nm showed that the hydrogen production rate of CQDs-15/M-TiO 2 composite reached 6715 umol/h·g, which was 5.6 times that of M-TiO 2 alone (1200 μmol/h·g). lignin lignin carbon dots metal organic framework heterojunction photocatalytic hydrogen production Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction The rapid growth of global energy demand makes it extremely urgent to develop and make full use of renewable energy sources and promote the diversified transformation of the energy system [ 1 ] . Hydrogen energy (H 2 ), as a green, efficient and sustainable energy source, is considered to be an ideal renewable energy solution [ 2 ] . In particular, the method of producing hydrogen by water cracking using solar energy has attracted more and more attention due to its abundant resources and pollution-free characteristics. In order to realize the effective conversion of solar energy, it is urgent to develop new, efficient and stable photocatalysts. Researchers have been looking for inexpensive, environmentally friendly, and renewable resources as ideal photocatalyst materials [ 3 , 4 ] . As a newly emerging photocatalytic material in recent years, metal-organic framework materials (MOFs) are famous for their high specific surface area, abundant catalytic active sites, diverse pore structures and adjustable pore surfaces [ 5 – 8 ] . At present, MOFs show great development potential in the fields of gas adsorption and separation, energy storage and conversion, optics, catalysis, chemical sensing and biomedicine [ 9 ] . MOFs exhibit unique advantages in photolysis of water to produce hydrogen, the optical properties of MOFs materials can be effectively adjusted through precise adjustment of metal centers and organic ligands [ 10 ] ; Its unique pore structure not only facilitates the smooth introduction of guest molecules, but also significantly reduces the distance of charge transport. In addition, the abundant unsaturated metal sites in MOFs act as active centers, which play a positive role in promoting the catalytic reaction. MOFs have a wide range of applications in photolysis water reactions. It plays a catalytic role in promoting the oxidation-reduction process; It can also be used as a sensitizer that is generated and transferred after light energy is inhaled; It can even act as a photocatalyst, catalyzing light. A new class of composite functional materials, such as porous carbon and metal oxides, can be derived from MOFs through pyrolysis reactions at high temperatures. Du et al. [ 11 ] obtained nanometer ZnO material with good catalytic performance by sintering ZIF-8 at atmospheric pressure, and studied the effect of this material on the catalytic performance of methylene blue. Kumar et al. [ 12 ] innovatively combined MOFS-derived Ni 2 P with CdS to construct a new class of materials for the decomposition of aquatic hydrogen. In addition, Li et al. [ 13 ] also achieved remarkable results by successfully synthesizing TiO 2 derived from MIL-125(Ti), which showed more excellent photocatalytic performance. These studies not only broaden the application scope of MOFs materials, but also provide new inspiration and ideas for the progress of photocatalysis technology. MOFs form heterojunction with semiconductor materials of different energy levels, which can effectively improve the separation of photogenerated charge and hole, and greatly improve the light utilization rate.Hu et al. [ 14 ] synthesized CdS/MIL-53(Fe) complex by solution thermal method, and realized efficient degradation of Rhodamine B through photocatalysis. Among various Ti-based MOF photocatalysts, NH 2 -MIL-125(Ti) is a typical Ti-based MOF, which is assembled from cyclic Ti 8 O 8 (OH) 4 octamer and 2-amino-terephthalic acid, and has been reported as a potential photocatalyst for H 2 production by water decomposition. NH 2 -MIL-125(Ti) has a narrow band gap of 2.5 eV and absorbs light in the visible region [ 15 , 16 ] .The amino group in the organic ligand absorbs sunlight to produce electron-hole pairs, and the electrons are then separated and transferred to the Ti 4+ active site on the Ti-oxygen cluster for further reduction reactions. Guo et al. [ 17 ] demonstrated that the crystal face of nanoscale MIL-125-NH 2 (Ti) relies on photocatalysis for hydrogen production. Inspired by density functional theory (DFT) calculations, it is found that MIL-125-NH 2 (Ti) with controlled surfaces has varying activity, Where MIL-125-NH 2 (Ti) with {110} crystal faces has the highest H 2 yield (60.8 µmol/h·g) and apparent quantum yield (3.60% at 420 nm) about three times higher than those with dominant {111} crystal faces. Xiao et al. [ 18 ] constructed Pt@MIL-125/Au and Pt/MIL-125/Au by integrating the plasma effect of Au nanords and the Schottky association with PtNPs into the semiconductor MOF MIL-125. By forming the interface of the two metal MOFs, a wide range of light absorption and fast charge separation can be achieved. At this position, Au-MOF interface is established, plasma hot electrons are injected into LUMO of MOF to construct PT-MOF interface, forming Schottky barrier as electron "pump", guiding one-way electron flow to be captured by the Pt active site on the interface. The results show that the spatial separation of Pt and Au by MOF greatly promotes the charge migration and separation. Therefore, Pt@MIL-125/Au and Pt dispersed outside MOF and MOF exhibited an unusually high photocatalytic hydrogen production rate (1743.0 µmol/h·g) under visible light irradiation. Much better than Pt/MIL-125/Au (161.3 µmol/h·g) and MIL-125/Au (10.2 µmol/h·g), as well as other pairs with similar Pt or Au content. This work highlights the important role of the Au plasma effect in enlarging light absorption, as well as the important role of the location of Pt in water cracking photocatalysis for hydrogen production. High energy ultraviolet and short wavelength visible light in sunlight will adversely affect organic synthesis. CQDs has the ability to utilize long wavelength light and exchange energy with solution, which provides convenient conditions for its use as photocatalyst in organic synthesis [ 19 ] . Recent studies have found that 1–4 nm CQDs has excellent near-infrared photocatalytic performance for selective oxidation of alcohols to benzaldehyde, with a conversion rate of 92% and a selectivity of 100%. Its excellent performance is due to the electron transport property of CQDs for H 2 O 2 excitation in the near infrared region [ 20 ] . At the same time, Liu et al. [ 21 ] reported the unique photochemical properties of Au/ carbon quantum dots (AuNP-CQDs), and developed a new material with high efficiency and selectivity for cyclohexane oxidation reaction. On this basis, the synthesis of cyclohexanone was achieved by using visible light and H 2 O 2 synergistic catalysis. Li et al. [ 22 ] successfully combined carbon quantum dots (CQDs) with TiO 2 to form nanocomposites through band-gap engineering modification, aiming to improve the utilization efficiency of full-spectrum sunlight. Studies have shown that this TIO 2 -CQDs can completely degrade methylene blue (MB) within 25 min, while the degradation efficiency of pure TiO 2 is only 5%. In addition, other metal oxides and nanocomposites formed by metal phosphates and CQDs also show good photocatalytic properties. In recent years, renewable biomass resources, represented by lignin, have attracted increasing attention. Lignin is a kind of aromatic polymer compound commonly found in plants. In the process of pulping and papermaking, a large amount of lignin-rich waste liquid is inevitably generated. These waste liquids are discharged randomly, and only a few of them are used as low value-added products [ 23 , 24 ] . If it can be properly developed, it can not only solve the current problem of energy shortage, but also reduce environmental pollution. At present, lignin has been widely used as a stabilizer, feed additive and plant growth regulator in industry, agriculture and other fields, but the utilization of lignin is very limited, and the high-value utilization of lignin remains to be studied. In recent years, semiconductor quantum dots (CQDs) have attracted much attention for their excellent fluorescence emission, multi-exciton generation, light collection and photochemical properties, and have been applied in biosensing, imaging and photocatalysis. However, at present, the preparation materials of semiconductor quantum dots are restricted their application and development [ 23 – 25 ] . In view of this, carbon quantum dots (CQDs) have become a potential substitute material for semiconductor quantum dots due to their low toxicity, biocompatibility, low cost, chemical inertness, and similar fluorescence and photocatalytic properties [ 26 ] . Therefore, the conversion of lignin into products with high added value, such as the preparation of lignin carbon point composite catalysts and their application in photocatalytic hydrolysis to hydrogen production, has become a key research target. In this way, it can not only improve the utilization value of lignin, but also provide new solutions to solve energy and environmental problems. 2. Experiments 2.1 Materials and Methods 2.1.1 Reagents used Ethylenediamine, basic lignin, terephthalic acid, N, N-dimethylformamide (DMF), tetrabutyl titanate, methanol, anhydrous ethanol, distilled water. 2.2 Catalyst and cost 2.2.1 Synthesis of lignin carbon quantum dots 0.5 g alkaline lignin was dissolved in 47 mL deionized water, dispersed by ultrasound at 200 W for 10 min, then the solution was magnetically stirred at 500 r/min for 30 min, and 3 mL ethylenediamine (EDA) was gradually added during the process. Then the mixed solution was transferred to 100 mL polytetrafluoroethylene lined reactor and heated at 180 ℃ for 12 h. After the reaction was finished and cooled to room temperature, the mixture was iltered with 0.22 µm microporous membrane to remove impurities. Subsequently, the supernatant was dialyzed with a dialysis bag (molecular weight: 3000 Da) for 1 week. The well-dialyzed filtrate is CQDs. 20 mL of CQDs was freeze-dried for subsequent characterization tests. The remaining CQDs was refrigerated at 4 ℃ for subsequent composite photocatalyst synthesis 2.2.3 Synthesis of M-TiO 2 Firstly, 2.2 g terephthalic acid was dissolved in a mixed solution of 36 mL DMF and 4 mL methanol for continuous ultrasonic dispersion for 30 min, then 2.4 mL tetrabutyl titanate was added to the solution for ultrasonic dispersion for 10 min, followed by magnetic stirring for 1 h. The stirred mixture was transferred to a 100 mL reaction kettle lined with polytetrafluoroethylene and heated at 150 ℃ for 48 h. After the reaction was finished and cooled to room temperature, the mixture was centrifuged at 8000 r/min for 8 min and washed with methanol, DMF and anhydrous ethanol three times each. Finally, the mixture was dried in vacuum at 80 ℃ for 12 h to obtain pure M-TiO 2 . 2.2.4 Synthesis of CQDs/M-TiO 2 composite photocatalyst First, 10, 15 and 20 mL lignin carbon point solution was added to 42.4 mL M-TiO 2 synthesis precursor, ultrasonic for 10 min, and then the solution was stirred at 500 r/min magnetic force for 30 min, and then added to 100 mL reaction kettle with polytetrafluoroethylene lining after homogenization. The mixture was heated at 150 ℃ for 48 h, and after the reaction was finished and cooled to room temperature, the mixture was centrifuged at 6000 r/min for 8 min, and washed with methanol, DMF and ethanol three times each. Finally, the composite photocatalyst was obtained by vacuum drying at 80 ℃ for 12 h, and was denoted as CQDs-X/M-TiO 2 (X is the amount of CQDs added). 2.3 Evaluation of photocatalytic activity In this study, an online photocatalytic test system and a gas chromatograph were used to test the photocatalyst. The 300 W xenon lamp simulated sunlight was used as the reaction light source, and the H 2 was detected by gas chromatograph. The photocatalytic reaction vessel was 100 mL quartz reactor. First, 45 mL distilled water, 5 mg photocatalyst to be measured and 5 mL triethanolamine were added to the photocatalytic reactor successively, and the mixture was homogenized by ultrasound for 30 min. 0.1 mL chloroplatinic acid was added. The reactor was installed on the photocatalytic hydrogen production system device, and the whole test device was an online device. The on-line system was vacuumed with a vacuum pump, and the vacuum condition was maintained for continuous light reaction for 6 h. Sampling test was conducted every 1 hour. 3. Results and Discussion Using xenon lamp as light source (λ ≥ 380 nm), 5 mg composite photocatalyst CQDs-X/M-TiO 2 , 5 mL triethanolamine as sacrificial agent and 45 mL water as reaction system, the hydrogen production efficiency of CQDs-X/M-TiO 2 composite photocatalyst was evaluated by adding 3%precious metal Pt. As shown in Fig. 1 (a)and(b), the hydrogen production rate of M-TiO 2 was 1200 µmol/h·g, and the hydrogen production efficiency was significantly improved after the introduction of lignin carbon points (CQDs). The hydrogen production rate of CQDs-10/M-TiO 2 was 3480 µmol/h·g; The hydrogen production rate of CQDs-15/M-TiO 2 composite was maximized, reaching 6715 µmol/h·g, about 5.6 times of pure M-TiO 2 . When the dosage of CQDs was 20 mL, the hydrogen production rate of CQDs-20/M-TiO 2 was only 4083 µmol/h·g, so 15 mL was determined to be the best addition amount of CQDs. Moreover, by observing the yield line chart of composite photocatalysts with different CQDs addition amounts, it can be clearly seen that the yield increase is very stable, and there is no surge or excitation decline, indicating that the catalytic process is very peaceful and stable. Through the measurement of hydrogen production efficiency, we know that the hydrogen production efficiency of M-TiO 2 supported by CQDs can be improved, especially the hydrogen production efficiency of CQDs-15/M-TiO 2 is the most excellent. Therefore, CQDs-15/M-TiO 2 was selected as the object of further study, and all aspects of its characteristics were studied to clarify the composite situation of CQDs and M-TiO 2 . Figure 2 (a) shows the XRD pattern of CQDs, and Fig. 2 (b) shows the powder X-ray diffraction (XRD) pattern of CQDs-X/M-TiO 2 . It can be seen that the prepared CQDs is relatively pure, and the carbon source in the lignin has been successfully converted to CQDs and is amorphous. It can be seen from Fig. 2 (b) that the prepared M-TiO 2 is anatase phase TiO 2 (JCPDS No. 21-1272). The diffraction peaks of (101), (004), (200), (211) and (204) crystal planes are 25.38°, 37.88°, 48.28°, 55.34° and 62.83°, respectively. After CODs composite, the crystal phase, crystal form and crystallization degree of M-TiO 2 are almost not affected, and the characteristic diffraction peak attributed to CQDs is not detected, which is due to the low concentration of CODs, which is difficult to detect. At the same time, it can be seen that the introduction of CODs with different composite proportions has almost no effect on the crystal structure of CQDs-X/M-TiO 2 composites. Figure 3 shows the SEM image and TEM image of the catalyst. It can be clearly observed from Fig. 3 (a) that M-TiO 2 presents an irregular sphere-shaped structure with a size of 2–3 µm and a thickness of about 1 µm. As can be seen from the SEM of CQDs-15/M-TiO 2 in Fig. 3 (b), the composite photocatalyst presents a similar morphology and structure to M-TiO 2 without much change, and no CQDs nanoparticles can be observed on its surface, and a porous structure can be observed at 200 nm by magnification of the CQDs-15/M-TiO 2 image. However, at the size of 100 nm, it can be observed that there is a plush-needle structure under the porous structure, which indicates that it has an excellent specific surface area. By comparing before and after Fig. 3 (c) and (d), it can be clearly seen that the lignin carbon point is supported on M-TiO 2 , indicating that CQDs-15/M-TiO 2 has been successfully synthesized. The particle size and distribution of CQDs were observed in detail by transmission electron microscopy (TEM). As shown in Fig. 2 (e), the nanoparticles in the CQDs sample were well dispersed and mainly showed a round and spherical structure. In addition, a few large particles with darker colors were also observed. Due to the small particle size of the carbon point of these large particles, their specific surface area is relatively large, which leads to high surface energy, unstable energy state, prone to aggregation phenomenon, the so-called "agglomeration" phenomenon. In order to further quantify the particle size distribution of carbon points, statistical analysis was carried out using Image J software, and the results were shown in Fig. 3 (h). The particle size of carbon points is mainly distributed in the range of 1–5 nm, especially in the range of 1.5-4 nm. By comparing before and after Fig. 3 (f) and (g), it can be clearly seen that lignin carbon points are supported on M-TiO 2 , indicating that CQDs-15/M-TiO 2 has been successfully synthesized. Figure 4 shows the infrared spectra of CQDs, M-TiO 2 and CQDs-X/M-TiO 2 composite photocatalysts. In the Figs. 1631 and 1350 cm − 1 are the characteristic peaks of CQDs, representing the C = O and C-N functional groups respectively. The peaks of 1710 and 1116 cm − 1 are the characteristic peaks of M-TiO 2 .The characteristic peaks of CQDs and M-TiO 2 can be seen from the infrared spectra of CQDs-X/M-TiO 2 composite photocatalyst, which indicates that CQDs is successfully synthesized on M-TiO 2 . At the same time, the curve bending after 1000 cm − 1 shows that the structure of M-TiO 2 is not destroyed after the composite of CQDs and M-TiO 2 . In addition, it can be seen that the peak of CQDs-15/M-TiO 2 is the most obvious at 1350 cm − 1 , indicating that CQDs combines better with M-TiO 2 at this addition level. Figure 5 (a) shows the DRS test results of CQDs, M-TiO 2 and CQDs-X/M-TiO 2 composite photocatalyst. CQDs belongs to the full absorption wavelength, and the optical absorption capacity of M-TiO 2 decreases sharply after 300 nm. However, M-TiO 2 composite with CQDs increased its absorption wavelength to 380 nm and then began to decline, and did not return to zero at 800 nm. By comparing the absorption values under the same wavelength conditions, it can be seen that CQDs-15/M-TiO 2 has the strongest optical absorption capacity. Figure 5 (b) shows the results of the bandgap energy calculation of the sample by using the Tauc plot method. The band gaps of CQDs, M-TiO 2 , CQDs-10/M-TiO 2 , CQDs-15/M-TiO 2 and CQDs-20/M-TiO 2 are 1.9, 3.32, 3.08, 2.92 and 3.17 eV, respectively. Therefore, the successful recombination of CQDs and M-TiO 2 can be proved by the change of light absorption range and band gap. The elemental composition and chemical state of composite photocatalyst CQDs-15/M-TiO 2 were determined by X-ray photoelectron spectroscopy (XPS). Figure 6 shows the full XPS spectrum of CQDs-15/M-TiO 2 . As shown in Fig. 6 , the response peaks of O, N, C, Ti and other elements can be detected in the XPS measurement spectrum of CQDs-15/M-TiO 2 composite photocatalyst, without excess impurity peaks. The content of N element is small, and the spectral peak is not obvious in the full spectrum diagram, and its content mainly exists in the carbon point. In Fig. 7 (a) C1s high-resolution fine spectrum of XPS elements, three distinct peaks of binding energy 284.6, 286 and 288.3 eV can be clearly seen, corresponding to Sp2 hybrid carbon, C-NH 2 and N-C = N bonding, respectively. In Fig. 7 (b) O 1s high resolution fine spectrum of XPS elements, three distinct peaks of binding energy of 529.6, 531.6 and 532.9 eV can be clearly seen, corresponding to Ti-O, C-OH and O-H combination bonds, respectively. In the fine spectrum of XPS elements for N 1s shown in Fig. 7 (c), it can be seen that the fitting peaks at 396.8, 399.7 and 402.5 eV in CQDs-15/M-TiO 2 samples correspond to the characteristic peaks of pyridine nitrogen, amide group and graphitic nitrogen, respectively. Finally, by fitting the fine spectrum of Ti 2p (Fig. 7 (d)), it can be found that the binding energy is 458.5 and 464.3 eV, corresponding to Ti 2p3/2 and Ti 2p1/2, respectively. Therefore, through the analysis of the above results, it is further proved that the preparation of CQDs-15/M-TiO 2 composite photocatalyst is successful. Figure 8 (a) shows the nitrogen adsorption-desorption isotherm curve of M-TiO 2 and CQDs-15/M-TiO 2 composite photocatalyst. It is observed that the curves of the two photocatalysts are consistent with the characteristics of type IV isotherms, indicating that both M-TiO 2 and CQDs-15/M-TiO 2 have the characteristics of mesoporous structure, and the addition of CQDs does not change the original mesoporous characteristics of M-TiO 2 . The adsorption-desorption isotherm curves of both photocatalysts showed H3-type hysteresis rings, which indicated the existence of slit channels formed by particle accumulation in the materials. The specific surface area of M-TiO 2 and CQDs-15/M-TiO 2 are 215.24 and 137.76 m²/g, respectively. The specific surface area of the composite photocatalyst is slightly lower than that of M-TiO 2 , which is mainly due to the introduction of CQDs. In order to explore the effect of CQDs on the photocurrent response of M-TiO 2 , the photocurrent response of CQDs-X/M-TiO 2 composite photocatalyst was tested. As can be seen from Fig. 8 (b), under the illumination condition with wavelength λ > 380 nm, both M-TiO 2 and CQDs-X/M-TiO 2 will be stimulated by light to produce corresponding photocurrent response curves, and it can be clearly observed that CQDs-15/M-TiO 2 has the highest photocurrent response. The second is CQDs-20/M-TiO 2 and CQDs-10/M-TiO 2 , which are higher than M-TiO 2 without composite CQDs, indicating that CQDs-X/M-TiO 2 after composite CQDs shows a better photocurrent response. Among them, the photocurrent response of CQDs-15/M-TiO 2 is about 5 times that of M-TiO 2 , so the photoelectric performance of CQDs-15/M-TiO 2 will be studied. According to the data shown in Fig. 8 (c), it can be seen that the size of the semicircle part in the Nyquist map of the CQDs-15/M-TiO 2 composite photocatalyst is smaller than that of the M-TiO 2 material alone. This phenomenon indicates that M-TiO 2 can absorb specific wavelengths of light released by CQDs while maintaining its original visible light response characteristics. This additional light absorption helps to reduce the interfacial charge transfer impedance of the CQDs-15/M-TiO 2 composite photocatalyst, thereby enhancing its current transfer efficiency. In short, this composite photocatalyst performs better in charge transport than M-TiO 2 alone. Figure 8 (d) shows the photoluminescence spectra (PL) of M-TiO 2 and CQDs-15/M-TiO 2 at 468 nm excitation wavelength. By comparison, it can be found that the emission peak intensity of M-TiO 2 is the highest, indicating that the photogenerated carrier recombination phenomenon is relatively serious. The emission peak of CQDs-15/M-TiO 2 composite photocatalyst is significantly reduced, indicating that the electron transfer situation has been improved. These results indicate that CQDs has great potential in improving the transfer of photogenerated electrons and holes. The above tests and characterization all proved the excellent performance of CQDs-15/M-TiO 2 . In order to explore the stability of hydrogen production efficiency of CQDs-15/M-TiO 2 , a photocatalytic performance cycle test was performed on CQDs-15/M-TiO 2 at λ ≥ 380 nm, as shown in Fig. 9 (a). After 5 consecutive cycles of testing within 30 h, CQDs-15/M-TiO 2 still maintained good photocatalytic activity and stable hydrogen production efficiency. In addition, we conducted crystal analysis of the photocatalyst after 30 h continuous reaction. Figure 9 (b) shows the XRD test of CQDs-15/M-TiO 2 after the reaction. It can be seen from the Figure that the structure of the composite photocatalyst after 30 h photocatalytic reaction is not destroyed. Therefore, it is confirmed that the composite photocatalyst CQDs-15/M-TiO 2 has good stability. Figure 10 shows the M-S test curve, and the test results show that the flat-band potentials of CQDs and M-TiO 2 are − 0.55 and − 0.72 eV respectively (vs. Ag/AgCl). The test curves of these samples all have positive slopes indicating that they are typical N-type semiconductors. According to the characteristics of N-type semiconductors, the conduction band position is more negative than the flat band potential of 0.1 eV, so the CQDs and M-TiO 2 conduction potentials are − 0.45 and − 0.62 eV respectively (vs. NHE, pH 7), which both meet the H + /H 2 REDOX potential (NHE) requirements. The above analysis shows that the composite photocatalyst can meet the thermos dynamic requirements of photocatalytic hydrogen evolution. Based on the above characteristics and the analysis of photocatalytic hydrogen production performance, the mechanism of photocatalytic hydrogen production is obtained. As shown in Fig. 11 , when the composite photocatalyst CQDs-15/M-TiO 2 is irradiated by visible light, the electrons on VB of M-TiO 2 are excited to CB. Because the CB potential of M-TiO 2 (-0.72 eV vs. NHE) is lower than that of CQDs (-0.55 eV vs. NHE), the CB potential of M-TiO 2 (-0.72 eV vs. NHE) can be transferred to the CB of CQDs. With the transfer of photogenerated electrons to the corresponding conduction band, they migrate to Pt, thereby reducing the hydrogen protons in water to hydrogen. In the above process, the introduction of CQDs can improve the absorption and response of the catalyst to light, and make the catalyst produce more electrons and holes. At the same time, CQDs contributes to the transfer and transfer of photogenerated electrons in the system. Due to the presence of sacrificial agents, the photocatalytic hydrogen production rate mainly depends on the electron-hole logarithm of light generation and the electron transport rate. Therefore, the interaction of CQDs and M-TiO 2 in the composite photocatalyst helps to significantly improve the photocatalytic performance of the composite photocatalyst. Based on the above analysis, the photocatalytic hydrogen production performance of some MOF catalysts is listed. As shown in Fig. 12 , the performance of CQDs-X/M-TiO 2 composite photocatalysts prepared in this paper is superior to Ni 2 P@UIO-66-NH 2 , MoO 3 /MIL-125-NH 2 , MIL-125-NH 2 /Co(Ⅱ) and MIL-125-NH/Co(Ⅲ) composite photocatalysts. Through the composite photocatalyst prepared with lignin carbon points, the high-value utilization of lignin is realized, and the hydrogen production efficiency of MOF derivatives photocatalyst is improved, and there is still a lot of room for improvement in the future. 4. Conclusion In this paper, waste lignin was used to prepare lignin carbon points, and MOF derivative M-TiO 2 was selected as the basic photocatalyst. In order to improve the defects of M-TiO 2 , such as narrow light absorption range, wide band gap, easy recombination of e − /h + and limited application range, and achieve high efficiency hydrogen production, CQDs-X/M-TiO 2 composite photocatalyst was designed. And a hydrothermal method was used for synthesis. The optimal amount of CQDs was determined with hydrogen production efficiency as the index, and then the structure, morphology and photoelectric testing of the composite photocatalyst were studied. Meanwhile, the photocatalytic stability of the composite photocatalyst was evaluated and the catalytic mechanism was analyzed. The results are as follows: It was found that the hydrogen production rate of CQDs-X/M-TiO 2 composite photocatalyst was significantly improved by the measurement of photocatalytic hydrogen production efficiency, among which CQDs-15/M-TiO 2 had the best hydrogen production efficiency, up to 6715 µmol/h·g, about 5.6 times that of M-TiO 2 photocatalyst. The crystallinity of CQDs-15/M-TiO 2 composite photocatalyst has no obvious change before and after doping with CQDs. The photoelectric analysis shows that CQDs-15/M-TiO 2 has better photocharge carrier migration rate and wider light absorption range under the condition of illumination. The photocatalytic performance of CQDs-15/M-TiO 2 composite photocatalyst was tested for 5 times in 30 h, and the crystal type test before and after the reaction proved that CQDs-15/M-TiO 2 composite photocatalyst still maintained good photocatalytic activity, and the photocatalytic hydrogen production performance did not change significantly. It shows that the CQDs-15/M-TiO 2 composite photocatalyst has good stability. Based on the above studies and M-S characterization, it is concluded that the hydrogen production mechanism of CQDs-15/M-TiO 2 composite photocatalyst is that the band gap structure of CQDs and M-TiO 2 can build heterojunction, and the heterostructure can promote electron transfer, increase the light absorption and REDOX ability, thus improving the efficiency of photocatalytic hydrogen production and making the lignin obtain high value utilization. Declarations Ethical approval This statement does not apply. Funding:National Natural Science Foundation of China (22278099), National Natural Science Foundation Regional Innovation and Development Joint Fund Key project (U23A20135). Availability of data and materials: The authors confirm that the data supporting the findings of this study are available within the article [and/or its supplementary materials]. Author Contribution All authors reviewed the manuscript. References Tian J, Zhang Y, Du L, et al. Nature Chemistry, 2020, 12(12): 1150-1156. Wang Q, Hisatomi T, Jia Q, et al. Nature Materials, 2016, 15(6): 611-615. Furat Dawood,M. Anda,GM Shafiullah. International Journal of Hydrogen Energy. 2020;45 (7):3847-3869. Qi Zhang,Wenmiao Chen,Liping Wen. Sustainable Production and Consumption. 2022;33 (0):890-902. Shi Y, Yang A F, Cao C S, et al. Coordination Chemistry Reviews, 2019, 390: 50-75. Guo X, Liu L, Zhao Y, et al. Coordination Chemistry Reviews, 2021, 435:213785. Wu Q, Zhang C, Sun K, et al. Acta Chimica Sinica, 2020, 78(7): 688. Yap M H, Fow K L, Chen G Z. Green Energy&Environment, 2017, 2(3): 218-245. Zhang X, Wang X, Fan W, et al. Chinese Journal of Chemistry, 2020, 38(5): 509-524. Kampouri S, Ebrahim F M, Fumanal M, et al. ACS Applied Materials&Interfaces, 2021, 13(12): 14239-14247. Du Y, Chen R Z, Yao J F, et al. Journal of Alloys and Compounds, 2013, 551: 125-130. Kumar D P, Choi J, Hong S, et al. ACS Sustainable Chemistry&Engineering, 2016, 4(12): 7158-7166. Li J, Xu X, Liu X, et al. Journal of Alloys and Compounds, 2017, 690: 640-646. Hu L, Deng G, Lu W, et al. Applied Surface Science, 2017, 410: 401-413. Horiuchi Y, Toyao T, Saito M, et al. The Journal of Physical Chemistry C,2012,116(39): 20848-20853. Kampouri S, Nguyen T N, Spodaryk M, et al. Advanced Functional Materials, 2018, 28(52): 1806368. Guo F, Guo J H, Wang P, et al. Chemical science,2019,10(18):4834-4838. Han L, Luo J, et al. Angewandte Chemie International Edition, 2018, 57(4): 1103-1107. Kumar A S, Ye T, Takami T, et al. Nano Letters, 2008, 8(6): 1644-1648. Zhang X, Huang H, Liu J, et al. Journal of Materials Chemistry A, 2013, 1(38): 11529-11533. Han Y, Huang H, Zhang H, et al. Acs Catalysis, 2014, 4(3): 781-787. Li H T, He X D, Kang Z H, et al. Angew. Chem, 2010, 122: 4532-4536. Wang X, Cao L, Lu F, et al. Chemical Communications, 2009, (25): 3774-3776. Larson D R, Zipfel W R, Williams R M, et al. Science, 2003, 300(5624): 1434-1436. Geys J, Nemmar A, Verbeken E, et al. Environmental Health Perspectives, 2008, 116(12): 1607-1613. Lin P, Chen J W, Chang L W, et al. Environmental Science & Technology, 2008, 42(16): 6264-6270. Sun, K. et al. Angew Chem Int Ed 59, 2020, 22749-22755. Zhang, C. et al. Angewandte Chemie. 2022, 134(28): e202204108. Li Z, Jiang H L. ACS Catal. 2016, 5359–5365. Nasalevich M A, Becker R, Ramos-Fernandez E V, et al. Energy Environ. 2015, 364-375. Hao X, Cui Z, Zhou J, et al. Nano Energy. 2018 105–116. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 11 Dec, 2024 Read the published version in Research on Chemical Intermediates → Version 1 posted Editorial decision: Revision requested 23 Oct, 2024 Reviews received at journal 23 Oct, 2024 Reviewers agreed at journal 22 Oct, 2024 Reviewers agreed at journal 13 Oct, 2024 Reviews received at journal 11 Oct, 2024 Reviewers agreed at journal 07 Oct, 2024 Reviewers agreed at journal 06 Oct, 2024 Reviewers invited by journal 06 Oct, 2024 Editor assigned by journal 21 Sep, 2024 Submission checks completed at journal 21 Sep, 2024 First submitted to journal 20 Sep, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5121593","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":369746932,"identity":"16597b81-f2aa-4bc7-8391-d8ab427c4c63","order_by":0,"name":"Kai Zhang","email":"","orcid":"","institution":"Harbin University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Kai","middleName":"","lastName":"Zhang","suffix":""},{"id":369746933,"identity":"03052004-1119-4fa8-95c2-9483127443d8","order_by":1,"name":"XuDong Zhu","email":"","orcid":"","institution":"Harbin University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"XuDong","middleName":"","lastName":"Zhu","suffix":""},{"id":369746934,"identity":"999f4064-be4e-4c7f-8c90-ccc1ad4e098a","order_by":2,"name":"Hong Yan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCklEQVRIie2PMUvDQBTHXyjcdDaOF5S2H+GKcC7FL+JyR0CX6CiCsQ0I52cIiJ/BKTieHFyWk67ZjItTBrvpVhOXLtdmFLzf8B48/r/3eAAez98EtWWEQL/U/BoOUV/lKAxMTGsLuLci8jvLoncJeGeelq+mXj3fBk/GcCIeT/CQJKyGdHbqVOzl+TS35YBaragoYoxIckzBnF1kLkUl7GBPGkQrw7koBq3CSJBpt7JsOgXTt4Yq8bDooVTdlZREmZ1mItO7lahqWJRLRUMwMXBTYoQ/rgjf8stw+bNzJecLCbr8/kpvRuP7uCCf6cypTFTX9MZonwNwR7xl/LtrvjEK1Za8x+Px/EfWoM9eq1PBhbsAAAAASUVORK5CYII=","orcid":"","institution":"Harbin University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Hong","middleName":"","lastName":"Yan","suffix":""}],"badges":[],"createdAt":"2024-09-20 07:36:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5121593/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5121593/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11164-024-05467-3","type":"published","date":"2024-12-11T15:57:31+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":69349264,"identity":"e53558a3-1745-4fd9-8feb-91ff437f7fe2","added_by":"auto","created_at":"2024-11-19 12:50:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":73127,"visible":true,"origin":"","legend":"\u003cp\u003eThe cumulative H\u003csub\u003e2\u003c/sub\u003e yield and yield of CQD-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst with different amounts of\u003c/p\u003e\n\u003cp\u003eCQDs in 6 h reaction\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/26897226089dfda5373f8da4.png"},{"id":69347928,"identity":"c1569266-fe44-498f-aa26-2a85edf079fd","added_by":"auto","created_at":"2024-11-19 12:34:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":74614,"visible":true,"origin":"","legend":"\u003cp\u003eThe XRD patterns of CQDs, CQDs-X/M-TiO2\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/922cb4f60b4f1a9e4cd30618.png"},{"id":69349067,"identity":"3c61d1cc-e5dc-4606-89b5-910f1b01a5cb","added_by":"auto","created_at":"2024-11-19 12:42:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":222866,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e and TEM image of CQDs、M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs/M-TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/3bbf87f09ff0f1c80bacf36b.png"},{"id":69347939,"identity":"69d7a75e-ffbf-478f-88f4-5183c2122ea8","added_by":"auto","created_at":"2024-11-19 12:34:45","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":75152,"visible":true,"origin":"","legend":"\u003cp\u003eThe FT-IR Spectra of CQDs-X/M-TiO2\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/2b2cdaf6ab8621bffd4abe1b.png"},{"id":69349267,"identity":"7e0eda04-5d13-48cb-9956-9cd863bd93c9","added_by":"auto","created_at":"2024-11-19 12:50:45","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":65621,"visible":true,"origin":"","legend":"\u003cp\u003eUV-vis-IR absorption spectra of CQDs, M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-X /M-TiO\u003csub\u003e2\u003c/sub\u003e (a) and (b) Bandgap energy diagram\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/c742d31437a69133a4a9146d.png"},{"id":69351055,"identity":"27eea916-1aea-49f4-85c2-b7abf5a82319","added_by":"auto","created_at":"2024-11-19 13:06:45","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":31785,"visible":true,"origin":"","legend":"\u003cp\u003eXPS survey spectrum of CQDs-15/M-TiO2\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/4aef51b2d64bfcebd6a74eea.png"},{"id":69350172,"identity":"f504d9e2-3fed-4af7-911b-d6db4c945b75","added_by":"auto","created_at":"2024-11-19 12:58:45","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":112957,"visible":true,"origin":"","legend":"\u003cp\u003eElement Fine Spectrum of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e(a) C 1s (b), O 1s (c), N 1s (d) Ti 2p .\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/0d835613d62d05b9934ae9ce.png"},{"id":69349068,"identity":"80d9bc47-53be-4129-8a9d-250a5f7f83ac","added_by":"auto","created_at":"2024-11-19 12:42:45","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":166537,"visible":true,"origin":"","legend":"\u003cp\u003e(a)N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms ,(b)Photocurrent response curves,(c)Ac imped\u003c/p\u003e\n\u003cp\u003eance diagram,(d)Photoluminescence spectra\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/642a6c5fe4638711da58e8e9.png"},{"id":69347930,"identity":"52db2c3a-ccf6-4560-becb-5b513520146b","added_by":"auto","created_at":"2024-11-19 12:34:44","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":70911,"visible":true,"origin":"","legend":"\u003cp\u003e(a) CQDs-15/M-TiO2 Hydrogen Production cycle test diagram and (b)XRD pattern before and after the reaction\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/0126d41a94abc425dc63c537.png"},{"id":69347934,"identity":"aa5f2f35-b143-4aeb-8c16-3664844864fa","added_by":"auto","created_at":"2024-11-19 12:34:45","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":25951,"visible":true,"origin":"","legend":"\u003cp\u003eMott-Schottky plot of CQDs and M-TiO2\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/180ab8b0d11f68237efcf473.png"},{"id":69350174,"identity":"9ece6523-0b22-48e6-a502-f72756b5a204","added_by":"auto","created_at":"2024-11-19 12:58:45","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":108728,"visible":true,"origin":"","legend":"\u003cp\u003ePhotocatalytic hydrogen production mechanism of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite phot\u003c/p\u003e\n\u003cp\u003eocatalyst\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/b2c0c90f53f46a0a45271088.png"},{"id":69349074,"identity":"32a0b86d-97f6-432c-baa6-dd6c618f140c","added_by":"auto","created_at":"2024-11-19 12:42:45","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":59675,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of hydrogen production performance of MOF catalysts [27-31]\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/a9909694b297b422f66012f1.png"},{"id":71552530,"identity":"8a73bbec-13b1-4ad1-acde-ddb1efb87d17","added_by":"auto","created_at":"2024-12-16 16:07:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1507023,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5121593/v1/b82faae9-75f7-4581-aea4-4620da4d1d0c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The photocatalytic hydrogen production performance of porous titanium dioxide , a derivative of Mil-125 (Ti), was improved by using lignin-based carbon quantum","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe rapid growth of global energy demand makes it extremely urgent to develop and make full use of renewable energy sources and promote the diversified transformation of the energy system\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. Hydrogen energy (H\u003csub\u003e2\u003c/sub\u003e), as a green, efficient and sustainable energy source, is considered to be an ideal renewable energy solution\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. In particular, the method of producing hydrogen by water cracking using solar energy has attracted more and more attention due to its abundant resources and pollution-free characteristics. In order to realize the effective conversion of solar energy, it is urgent to develop new, efficient and stable photocatalysts. Researchers have been looking for inexpensive, environmentally friendly, and renewable resources as ideal photocatalyst materials\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. As a newly emerging photocatalytic material in recent years, metal-organic framework materials (MOFs) are famous for their high specific surface area, abundant catalytic active sites, diverse pore structures and adjustable pore surfaces\u003csup\u003e[\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. At present, MOFs show great development potential in the fields of gas adsorption and separation, energy storage and conversion, optics, catalysis, chemical sensing and biomedicine\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. MOFs exhibit unique advantages in photolysis of water to produce hydrogen, the optical properties of MOFs materials can be effectively adjusted through precise adjustment of metal centers and organic ligands\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e; Its unique pore structure not only facilitates the smooth introduction of guest molecules, but also significantly reduces the distance of charge transport. In addition, the abundant unsaturated metal sites in MOFs act as active centers, which play a positive role in promoting the catalytic reaction. MOFs have a wide range of applications in photolysis water reactions. It plays a catalytic role in promoting the oxidation-reduction process; It can also be used as a sensitizer that is generated and transferred after light energy is inhaled; It can even act as a photocatalyst, catalyzing light.\u003c/p\u003e \u003cp\u003eA new class of composite functional materials, such as porous carbon and metal oxides, can be derived from MOFs through pyrolysis reactions at high temperatures. Du et al.\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e obtained nanometer ZnO material with good catalytic performance by sintering ZIF-8 at atmospheric pressure, and studied the effect of this material on the catalytic performance of methylene blue. Kumar et al.\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e innovatively combined MOFS-derived Ni\u003csub\u003e2\u003c/sub\u003eP with CdS to construct a new class of materials for the decomposition of aquatic hydrogen. In addition, Li et al. \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e also achieved remarkable results by successfully synthesizing TiO\u003csub\u003e2\u003c/sub\u003e derived from MIL-125(Ti), which showed more excellent photocatalytic performance. These studies not only broaden the application scope of MOFs materials, but also provide new inspiration and ideas for the progress of photocatalysis technology. MOFs form heterojunction with semiconductor materials of different energy levels, which can effectively improve the\u003c/p\u003e \u003cp\u003eseparation of photogenerated charge and hole, and greatly improve the light utilization rate.Hu et al.\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e synthesized CdS/MIL-53(Fe) complex by solution thermal method, and realized efficient degradation of Rhodamine B through photocatalysis. Among various Ti-based MOF photocatalysts, NH\u003csub\u003e2\u003c/sub\u003e-MIL-125(Ti) is a typical Ti-based MOF, which is assembled from cyclic Ti\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e(OH)\u003csub\u003e4\u003c/sub\u003e octamer and 2-amino-terephthalic acid, and has been reported as a potential photocatalyst for H\u003csub\u003e2\u003c/sub\u003e production by water decomposition. NH\u003csub\u003e2\u003c/sub\u003e-MIL-125(Ti) has a narrow band gap of 2.5 eV and absorbs light in the visible region\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e.The amino group in the organic ligand absorbs sunlight to produce electron-hole pairs, and the electrons are then separated and transferred to the Ti\u003csup\u003e4+\u003c/sup\u003e active site on the Ti-oxygen cluster for further reduction reactions. Guo et al.\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e demonstrated that the crystal face of nanoscale MIL-125-NH\u003csub\u003e2\u003c/sub\u003e(Ti) relies on photocatalysis for hydrogen production. Inspired by density functional theory (DFT) calculations, it is found that MIL-125-NH\u003csub\u003e2\u003c/sub\u003e(Ti) with controlled surfaces has varying activity, Where MIL-125-NH\u003csub\u003e2\u003c/sub\u003e(Ti) with {110} crystal faces has the highest H\u003csub\u003e2\u003c/sub\u003e yield (60.8 \u0026micro;mol/h\u0026middot;g) and apparent quantum yield (3.60% at 420 nm) about three times higher than those with dominant {111} crystal faces. Xiao et al.\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e constructed Pt@MIL-125/Au and Pt/MIL-125/Au by integrating the plasma effect of Au nanords and the Schottky association with PtNPs into the semiconductor MOF MIL-125. By forming the interface of the two metal MOFs, a wide range of light absorption and fast charge separation can be achieved. At this position, Au-MOF interface is established, plasma hot electrons are injected into LUMO of MOF to construct PT-MOF interface, forming Schottky barrier as electron \"pump\", guiding one-way electron flow to be captured by the Pt active site on the interface. The results show that the spatial separation of Pt and Au by MOF greatly promotes the charge migration and separation. Therefore, Pt@MIL-125/Au and Pt dispersed outside MOF and MOF exhibited an unusually high photocatalytic hydrogen production rate (1743.0 \u0026micro;mol/h\u0026middot;g) under visible light irradiation. Much better than Pt/MIL-125/Au (161.3 \u0026micro;mol/h\u0026middot;g) and MIL-125/Au (10.2 \u0026micro;mol/h\u0026middot;g), as well as other pairs with similar Pt or Au content. This work highlights the important role of the Au plasma effect in enlarging light absorption, as well as the important role of the location of Pt in water cracking photocatalysis for hydrogen production.\u003c/p\u003e \u003cp\u003eHigh energy ultraviolet and short wavelength visible light in sunlight will adversely affect organic synthesis. CQDs has the ability to utilize long wavelength light and exchange energy with solution, which provides convenient conditions for its use as photocatalyst in organic synthesis\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Recent studies have found that 1\u0026ndash;4 nm CQDs has excellent near-infrared photocatalytic performance for selective oxidation of alcohols to benzaldehyde, with a conversion rate of 92% and a selectivity of 100%. Its excellent performance is due to the electron transport property of CQDs for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e excitation in the near infrared region\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. At the same time, Liu et al.\u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e reported the unique photochemical properties of Au/ carbon quantum dots (AuNP-CQDs), and developed a new material with high efficiency and selectivity for cyclohexane oxidation reaction. On this basis, the synthesis of cyclohexanone was achieved by using visible light and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e synergistic catalysis. Li et al.\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e successfully combined carbon quantum dots (CQDs) with TiO\u003csub\u003e2\u003c/sub\u003e to form nanocomposites through band-gap engineering modification, aiming to improve the utilization efficiency of full-spectrum sunlight. Studies have shown that this TIO\u003csub\u003e2\u003c/sub\u003e-CQDs can completely degrade methylene blue (MB) within 25 min, while the degradation efficiency of pure TiO\u003csub\u003e2\u003c/sub\u003e is only 5%. In addition, other metal oxides and nanocomposites formed by metal phosphates and CQDs also show good photocatalytic properties.\u003c/p\u003e \u003cp\u003eIn recent years, renewable biomass resources, represented by lignin, have attracted increasing attention. Lignin is a kind of aromatic polymer compound commonly found in plants. In the process of pulping and papermaking, a large amount of lignin-rich waste liquid is inevitably generated. These waste liquids are discharged randomly, and only a few of them are used as low value-added products\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. If it can be properly developed, it can not only solve the current problem of energy shortage, but also reduce environmental pollution. At present, lignin has been widely used as a stabilizer, feed additive and plant growth regulator in industry, agriculture and other fields, but the utilization of lignin is very limited, and the high-value utilization of lignin remains to be studied. In recent years, semiconductor quantum dots (CQDs) have attracted much attention for their excellent fluorescence emission, multi-exciton generation, light collection and photochemical properties, and have been applied in biosensing, imaging and photocatalysis. However, at present, the preparation materials of semiconductor quantum dots are restricted their application and development\u003csup\u003e[\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. In view of this, carbon quantum dots (CQDs) have become a potential substitute material for semiconductor quantum dots due to their low toxicity, biocompatibility, low cost, chemical inertness, and similar fluorescence and photocatalytic properties\u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. Therefore, the conversion of lignin into products with high added value, such as the preparation of lignin carbon point composite catalysts and their application in photocatalytic hydrolysis to hydrogen production, has become a key research target. In this way, it can not only improve the utilization value of lignin, but also provide new solutions to solve energy and environmental problems.\u003c/p\u003e"},{"header":"2. Experiments","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and Methods\u003c/h2\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003e2.1.1 Reagents used\u003c/h2\u003e \u003cp\u003eEthylenediamine, basic lignin, terephthalic acid, N, N-dimethylformamide (DMF), tetrabutyl titanate, methanol, anhydrous ethanol, distilled water.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Catalyst and cost\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Synthesis of lignin carbon quantum dots\u003c/h2\u003e \u003cp\u003e0.5 g alkaline lignin was dissolved in 47 mL deionized water, dispersed by ultrasound at 200 W for 10 min, then the solution was magnetically stirred at 500 r/min for 30 min, and 3 mL ethylenediamine (EDA) was gradually added during the process. Then the mixed solution was transferred to 100 mL polytetrafluoroethylene lined reactor and heated at 180 ℃ for 12 h. After the reaction was finished and cooled to room temperature, the mixture was iltered with 0.22 \u0026micro;m microporous membrane to remove impurities. Subsequently, the supernatant was dialyzed with a dialysis bag (molecular weight: 3000 Da) for 1 week. The well-dialyzed filtrate is CQDs. 20 mL of CQDs was\u003c/p\u003e \u003cp\u003efreeze-dried for subsequent characterization tests. The remaining CQDs was refrigerated at 4 ℃ for subsequent composite photocatalyst synthesis\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Synthesis of M-TiO\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eFirstly, 2.2 g terephthalic acid was dissolved in a mixed solution of 36 mL DMF and 4 mL methanol for continuous ultrasonic dispersion for 30 min, then 2.4 mL tetrabutyl titanate was added to the solution for ultrasonic dispersion for 10 min, followed by magnetic stirring for 1 h. The stirred mixture was transferred to a 100 mL reaction kettle lined with polytetrafluoroethylene and heated at 150 ℃ for 48 h. After the reaction was finished and cooled to room temperature, the mixture was centrifuged at 8000 r/min for 8 min and washed with methanol, DMF and anhydrous ethanol three times each. Finally, the mixture was dried in vacuum at 80 ℃ for 12 h to obtain pure M-TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4 Synthesis of CQDs/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst\u003c/h2\u003e \u003cp\u003eFirst, 10, 15 and 20 mL lignin carbon point solution was added to 42.4 mL M-TiO\u003csub\u003e2\u003c/sub\u003e synthesis precursor, ultrasonic for 10 min, and then the solution was stirred at 500 r/min magnetic force for 30 min, and then added to 100 mL reaction kettle with polytetrafluoroethylene lining after homogenization. The mixture was heated at 150 ℃ for 48 h, and after the reaction was finished and cooled to room temperature, the mixture was centrifuged at 6000 r/min for 8 min, and washed with methanol, DMF and ethanol three times each. Finally, the composite photocatalyst was obtained by vacuum drying at 80 ℃ for 12 h, and was denoted as CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e (X is the amount of CQDs added).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Evaluation of photocatalytic activity\u003c/h2\u003e \u003cp\u003eIn this study, an online photocatalytic test system and a gas chromatograph were used to test the photocatalyst. The 300 W xenon lamp simulated sunlight was used as the reaction light source, and the H\u003csub\u003e2\u003c/sub\u003e was detected by gas chromatograph. The photocatalytic reaction vessel was 100 mL quartz reactor. First, 45 mL distilled water, 5 mg photocatalyst to be measured and 5 mL triethanolamine were added to the photocatalytic reactor successively, and the mixture was homogenized by ultrasound for 30 min. 0.1 mL chloroplatinic acid was added. The reactor was installed on the photocatalytic hydrogen production system device, and the whole test device was an online device. The on-line system was vacuumed with a vacuum pump, and the vacuum condition was maintained for continuous light reaction for 6 h. Sampling test was conducted every 1 hour.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eUsing xenon lamp as light source (λ\u0026thinsp;\u0026ge;\u0026thinsp;380 nm), 5 mg composite photocatalyst CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e, 5 mL triethanolamine as sacrificial agent and 45 mL water as reaction system, the hydrogen production efficiency of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst was evaluated by adding 3%precious metal Pt. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a)and(b), the hydrogen production rate of M-TiO\u003csub\u003e2\u003c/sub\u003e was 1200 \u0026micro;mol/h\u0026middot;g, and the hydrogen production efficiency was significantly improved after the introduction of lignin carbon points (CQDs). The hydrogen production rate of CQDs-10/M-TiO\u003csub\u003e2\u003c/sub\u003e was 3480 \u0026micro;mol/h\u0026middot;g; The hydrogen production rate of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite was maximized, reaching 6715 \u0026micro;mol/h\u0026middot;g, about 5.6 times of pure M-TiO\u003csub\u003e2\u003c/sub\u003e. When the dosage of CQDs was 20 mL, the hydrogen production rate of CQDs-20/M-TiO\u003csub\u003e2\u003c/sub\u003e was only 4083 \u0026micro;mol/h\u0026middot;g, so 15 mL was determined to be the best addition amount of CQDs. Moreover, by observing the yield line chart of composite photocatalysts with different CQDs addition amounts, it can be clearly seen that the yield increase is very stable, and there is no surge or excitation decline, indicating that the catalytic process is very peaceful and stable. Through the measurement of hydrogen production efficiency, we know that the hydrogen production efficiency of M-TiO\u003csub\u003e2\u003c/sub\u003e supported by CQDs can be improved, especially the hydrogen production efficiency of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e is the most excellent. Therefore, CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e was selected as the object of further study, and all aspects of its characteristics were studied to clarify the composite situation of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a) shows the XRD pattern of CQDs, and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (b) shows the powder X-ray diffraction (XRD) pattern of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e. It can be seen that the prepared CQDs is relatively pure, and the carbon source in the lignin has been successfully converted to CQDs and is amorphous. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) that the prepared M-TiO\u003csub\u003e2\u003c/sub\u003e is anatase phase TiO\u003csub\u003e2\u003c/sub\u003e (JCPDS No. 21-1272). The diffraction peaks of (101), (004), (200), (211) and (204) crystal planes are 25.38\u0026deg;, 37.88\u0026deg;, 48.28\u0026deg;, 55.34\u0026deg; and 62.83\u0026deg;, respectively. After CODs composite, the crystal phase, crystal form and crystallization degree of M-TiO\u003csub\u003e2\u003c/sub\u003e are almost not affected, and the characteristic diffraction peak attributed to CQDs is not detected, which is due to the low concentration of CODs, which is difficult to detect. At the same time, it can be seen that the introduction of CODs with different composite proportions has almost no effect on the crystal structure of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composites.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the SEM image and TEM image of the catalyst. It can be clearly observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) that M-TiO\u003csub\u003e2\u003c/sub\u003e presents an irregular sphere-shaped structure with a size of 2\u0026ndash;3 \u0026micro;m and a thickness of about 1 \u0026micro;m. As can be seen from the SEM of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b), the composite photocatalyst presents a similar morphology and structure to M-TiO\u003csub\u003e2\u003c/sub\u003e without much change, and no CQDs nanoparticles can be observed on its surface, and a porous structure can be observed at 200 nm by magnification of the CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e image. However, at the size of 100 nm, it can be observed that there is a plush-needle structure under the porous structure, which indicates that it has an excellent specific surface area. By comparing before and after Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) and (d), it can be clearly seen that the lignin carbon point is supported on M-TiO\u003csub\u003e2\u003c/sub\u003e, indicating that CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e has been successfully synthesized. The particle size and distribution of CQDs were observed in detail by transmission electron microscopy (TEM). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(e), the nanoparticles in the CQDs sample were well dispersed and mainly showed a round and spherical structure. In addition, a few large particles with darker colors were also observed. Due to the small particle size of the carbon point of these large particles, their specific surface area is relatively large, which leads to high surface energy, unstable energy state, prone to aggregation phenomenon, the so-called \"agglomeration\" phenomenon. In order to further quantify the particle size distribution of carbon points, statistical analysis was carried out using Image J software, and the results were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(h). The particle size of carbon points is mainly distributed in the range of 1\u0026ndash;5 nm, especially in the range of 1.5-4 nm. By comparing before and after Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(f) and (g), it can be clearly seen that lignin carbon points are supported on M-TiO\u003csub\u003e2\u003c/sub\u003e, indicating that CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e has been successfully synthesized.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the infrared spectra of CQDs, M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalysts. In the Figs.\u0026nbsp;1631 and 1350 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the characteristic peaks of CQDs, representing the C\u0026thinsp;=\u0026thinsp;O and C-N functional groups respectively. The peaks of 1710 and 1116 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the characteristic peaks of M-TiO\u003csub\u003e2\u003c/sub\u003e.The characteristic peaks of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e can be seen from the infrared spectra of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst, which indicates that CQDs is successfully synthesized on M-TiO\u003csub\u003e2\u003c/sub\u003e. At the same time, the curve bending after 1000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e shows that the structure of M-TiO\u003csub\u003e2\u003c/sub\u003e is not destroyed after the composite of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e. In addition, it can be seen that the peak of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e is the most obvious at 1350 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating that CQDs combines better with M-TiO\u003csub\u003e2\u003c/sub\u003e at this addition level.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) shows the DRS test results of CQDs, M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst. CQDs belongs to the full absorption wavelength, and the optical absorption capacity of M-TiO\u003csub\u003e2\u003c/sub\u003e decreases sharply after 300 nm. However, M-TiO\u003csub\u003e2\u003c/sub\u003e composite with CQDs increased its absorption wavelength to 380 nm and then began to decline, and did not return to zero at 800 nm. By comparing the absorption values under the same wavelength conditions, it can be seen that CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e has the strongest optical absorption capacity. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b) shows the results of the bandgap energy calculation of the sample by using the Tauc plot method. The band gaps of CQDs, M-TiO\u003csub\u003e2\u003c/sub\u003e, CQDs-10/M-TiO\u003csub\u003e2\u003c/sub\u003e, CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-20/M-TiO\u003csub\u003e2\u003c/sub\u003e are 1.9, 3.32, 3.08, 2.92 and 3.17 eV, respectively. Therefore, the successful recombination of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e can be proved by the change of light absorption range and band gap.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe elemental composition and chemical state of composite photocatalyst CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e were determined by X-ray photoelectron spectroscopy (XPS). Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the full XPS spectrum of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the response peaks of O, N, C, Ti and other elements can be detected in the XPS measurement spectrum of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst, without excess impurity peaks. The content of N element is small, and the spectral peak is not obvious in the full spectrum diagram, and its content mainly exists in the carbon point. In Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) C1s high-resolution fine spectrum of XPS elements, three distinct peaks of binding energy 284.6, 286 and 288.3 eV can be clearly seen, corresponding to Sp2 hybrid carbon, C-NH\u003csub\u003e2\u003c/sub\u003e and N-C\u0026thinsp;=\u0026thinsp;N bonding, respectively. In Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b) O 1s high resolution fine spectrum of XPS elements, three distinct peaks of binding energy of 529.6, 531.6 and 532.9 eV can be clearly seen, corresponding to Ti-O, C-OH and O-H combination bonds, respectively. In the fine spectrum of XPS elements for N 1s shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c), it can be seen that the fitting peaks at 396.8, 399.7 and 402.5 eV in CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e samples correspond to the characteristic peaks of pyridine nitrogen, amide group and graphitic nitrogen, respectively. Finally, by fitting the fine spectrum of Ti 2p (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(d)), it can be found that the binding energy is 458.5 and 464.3 eV, corresponding to Ti 2p3/2 and Ti 2p1/2, respectively. Therefore, through the analysis of the above results, it is further proved that the preparation of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst is successful.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a) shows the nitrogen adsorption-desorption isotherm curve of M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst. It is observed that the curves of the two photocatalysts are consistent with the characteristics of type IV isotherms, indicating that both M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e have the characteristics of mesoporous structure, and the addition of CQDs does not change the original mesoporous characteristics of M-TiO\u003csub\u003e2\u003c/sub\u003e. The adsorption-desorption isotherm curves of both photocatalysts showed H3-type hysteresis rings, which indicated the existence of slit channels formed by particle accumulation in the materials. The specific surface area of M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e are 215.24 and 137.76 m\u0026sup2;/g, respectively. The specific surface area of the composite photocatalyst is slightly lower than that of M-TiO\u003csub\u003e2\u003c/sub\u003e, which is mainly due to the introduction of CQDs. In order to explore the effect of CQDs on the photocurrent response of M-TiO\u003csub\u003e2\u003c/sub\u003e, the photocurrent response of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst was tested. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b), under the illumination condition with wavelength λ\u0026thinsp;\u0026gt;\u0026thinsp;380 nm, both M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e will be stimulated by light to produce corresponding photocurrent response curves, and it can be clearly observed that CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e has the highest photocurrent response. The second is CQDs-20/M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-10/M-TiO\u003csub\u003e2\u003c/sub\u003e, which are higher than M-TiO\u003csub\u003e2\u003c/sub\u003e without composite CQDs, indicating that CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e after composite CQDs shows a better photocurrent response. Among them, the photocurrent response of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e is about 5 times that of M-TiO\u003csub\u003e2\u003c/sub\u003e, so the photoelectric performance of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e will be studied. According to the data shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(c), it can be seen that the size of the semicircle part in the Nyquist map of the CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst is smaller than that of the M-TiO\u003csub\u003e2\u003c/sub\u003e material alone. This phenomenon indicates that M-TiO\u003csub\u003e2\u003c/sub\u003e can absorb specific wavelengths of light released by CQDs while maintaining its original visible light response characteristics. This additional light absorption helps to reduce the interfacial charge transfer impedance of the CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst, thereby enhancing its current transfer efficiency. In short, this composite photocatalyst performs better in charge transport than M-TiO\u003csub\u003e2\u003c/sub\u003e alone. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(d) shows the photoluminescence spectra (PL) of M-TiO\u003csub\u003e2\u003c/sub\u003e and CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e at 468 nm excitation wavelength. By comparison, it can be found that the emission peak intensity of M-TiO\u003csub\u003e2\u003c/sub\u003e is the highest, indicating that the photogenerated carrier recombination phenomenon is relatively serious. The emission peak of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst is significantly reduced, indicating that the electron transfer situation has been improved. These results indicate that CQDs has great potential in improving the transfer of photogenerated electrons and holes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe above tests and characterization all proved the excellent performance of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e. In order to explore the stability of hydrogen production efficiency of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e, a photocatalytic performance cycle test was performed on CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e at λ\u0026thinsp;\u0026ge;\u0026thinsp;380 nm, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a). After 5 consecutive cycles of testing within 30 h, CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e still maintained good photocatalytic activity and stable hydrogen production efficiency. In addition, we conducted crystal analysis of the photocatalyst after 30 h continuous reaction. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b) shows the XRD test of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e after the reaction. It can be seen from the Figure that the structure of the composite photocatalyst after 30 h photocatalytic reaction is not destroyed. Therefore, it is confirmed that the composite photocatalyst CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e has good stability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the M-S test curve, and the test results show that the flat-band potentials of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e are \u0026minus;\u0026thinsp;0.55 and \u0026minus;\u0026thinsp;0.72 eV respectively (vs. Ag/AgCl). The test curves of these samples all have positive slopes indicating that they are typical N-type semiconductors. According to the characteristics of N-type semiconductors, the conduction band position is more negative than the flat band potential of 0.1 eV, so the CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e conduction potentials are \u0026minus;\u0026thinsp;0.45 and \u0026minus;\u0026thinsp;0.62 eV respectively (vs. NHE, pH 7), which both meet the H\u003csup\u003e+\u003c/sup\u003e/H\u003csub\u003e2\u003c/sub\u003e REDOX potential (NHE) requirements. The above analysis shows that the composite photocatalyst can meet the thermos dynamic requirements of photocatalytic hydrogen evolution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the above characteristics and the analysis of photocatalytic hydrogen production performance, the mechanism of photocatalytic hydrogen production is obtained. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, when the composite photocatalyst CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e is irradiated by visible light, the electrons on VB of M-TiO\u003csub\u003e2\u003c/sub\u003e are excited to CB. Because the CB potential of M-TiO\u003csub\u003e2\u003c/sub\u003e(-0.72 eV vs. NHE) is lower than that of CQDs (-0.55 eV vs. NHE), the CB potential of M-TiO\u003csub\u003e2\u003c/sub\u003e (-0.72 eV vs. NHE) can be transferred to the CB of CQDs. With the transfer of photogenerated electrons to the corresponding conduction band, they migrate to Pt, thereby reducing the hydrogen protons in water to hydrogen. In the above process, the introduction of CQDs can improve the absorption and response of the catalyst to light, and make the catalyst produce more electrons and holes. At the same time, CQDs contributes to the transfer and transfer of photogenerated electrons in the system. Due to the presence of sacrificial agents, the photocatalytic hydrogen production rate mainly depends on the electron-hole logarithm of light generation and the electron transport rate. Therefore, the interaction of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e in the composite photocatalyst helps to significantly improve the photocatalytic performance of the composite photocatalyst.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the above analysis, the photocatalytic hydrogen production performance of some MOF catalysts is listed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, the performance of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalysts prepared in this paper is superior to Ni\u003csub\u003e2\u003c/sub\u003eP@UIO-66-NH\u003csub\u003e2\u003c/sub\u003e, MoO\u003csub\u003e3\u003c/sub\u003e/MIL-125-NH\u003csub\u003e2\u003c/sub\u003e, MIL-125-NH\u003csub\u003e2\u003c/sub\u003e/Co(Ⅱ) and MIL-125-NH/Co(Ⅲ) composite photocatalysts. Through the composite photocatalyst prepared with lignin carbon points, the high-value utilization of lignin is realized, and the hydrogen production efficiency of MOF derivatives photocatalyst is improved, and there is still a lot of room for improvement in the future.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this paper, waste lignin was used to prepare lignin carbon points, and MOF derivative M-TiO\u003csub\u003e2\u003c/sub\u003e was selected as the basic photocatalyst. In order to improve the defects of M-TiO\u003csub\u003e2\u003c/sub\u003e, such as narrow light absorption range, wide band gap, easy recombination of e\u003csup\u003e\u0026minus;\u003c/sup\u003e/h\u003csup\u003e+\u003c/sup\u003e and limited application range, and achieve high efficiency hydrogen production, CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst was designed. And a hydrothermal method was used for synthesis. The optimal amount of CQDs was determined with hydrogen production efficiency as the index, and then the structure, morphology and photoelectric testing of the composite photocatalyst were studied. Meanwhile, the photocatalytic stability of the composite photocatalyst was evaluated and the catalytic mechanism was analyzed. The results are as follows:\u003c/p\u003e \u003cp\u003eIt was found that the hydrogen production rate of CQDs-X/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst was significantly improved by the measurement of photocatalytic hydrogen production efficiency, among which CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e had the best hydrogen production efficiency, up to 6715 \u0026micro;mol/h\u0026middot;g, about 5.6 times that of M-TiO\u003csub\u003e2\u003c/sub\u003e photocatalyst. The crystallinity of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst has no obvious change before and after doping with CQDs. The photoelectric analysis shows that CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e has better photocharge carrier migration rate and wider light absorption range under the condition of illumination. The photocatalytic performance of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst was tested for 5 times in 30 h, and the crystal type test before and after the reaction proved that CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst still maintained good photocatalytic activity, and the photocatalytic hydrogen production performance did not change significantly. It shows that the CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst has good stability. Based on the above studies and M-S characterization, it is concluded that the hydrogen production mechanism of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst is that the band gap structure of CQDs and M-TiO\u003csub\u003e2\u003c/sub\u003e can build heterojunction, and the heterostructure can promote electron transfer, increase the light absorption and REDOX ability, thus improving the efficiency of photocatalytic hydrogen production and making the lignin obtain high value utilization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthical approval This statement does not apply.\u003c/p\u003e\n\u003cp\u003eFunding:National Natural Science Foundation of China (22278099), National Natural Science Foundation Regional Innovation and Development Joint Fund Key project (U23A20135).\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials: The authors confirm that the data supporting the findings of this study are available within the article [and/or its supplementary materials].\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eTian J, Zhang Y, Du L, et al. 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Nano Energy. 2018 105\u0026ndash;116.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"lignin, lignin carbon dots, metal organic framework, heterojunction, photocatalytic hydrogen production","lastPublishedDoi":"10.21203/rs.3.rs-5121593/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5121593/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCarbon points in lignin were prepared by hydrothermal method at 180 ℃ for 12 h. Carbon points with diameters of 1-5 nm were observed by transmission electron microscopy. The prepared lignin carbon point solution was put into the synthesis system of Mil-125(Ti) derivative porous titanium dioxide (M-TiO\u003csub\u003e2\u003c/sub\u003e) with 10, 15 and 20 mL, respectively, at 150 ℃ and 48 h to obtain CQDs/M-TiO\u003csub\u003e2\u003c/sub\u003e composite photocatalyst series. Through a series of characterization and analysis of its structure and morphology, it is proved that the carbon point is successfully recombined with Mil-125(Ti) derivative porous titanium dioxide (M-TiO\u003csub\u003e2\u003c/sub\u003e). Through ultraviolet-visible-near-infrared diffuse reflection and flat band potential analysis, we determined that CQDs can improve the light absorption range of porous titanium dioxide (M-TiO\u003csub\u003e2\u003c/sub\u003e), a derivative of Mil-125(Ti), and calculated the band structure of the material. It is proved that CQDs and Mil-125(Ti) derivative porous titanium dioxide(M-TiO\u003csub\u003e2\u003c/sub\u003e) constitute a type Ⅰ heterojunction. Photoelectrochemical analysis shows that CQDs/M-TiO\u003csub\u003e2\u003c/sub\u003e composite catalyst has better separation and transport efficiency than M-TiO\u003csub\u003e2\u003c/sub\u003e photogenerated electrons and holes. The photocatalytic hydrogen production activity test at a wavelength of \u0026gt; 380 nm showed that the hydrogen production rate of CQDs-15/M-TiO\u003csub\u003e2\u003c/sub\u003e composite reached 6715 umol/h·g, which was 5.6 times that of M-TiO\u003csub\u003e2\u003c/sub\u003e alone (1200 μmol/h·g).\u003c/p\u003e","manuscriptTitle":"The photocatalytic hydrogen production performance of porous titanium dioxide , a derivative of Mil-125 (Ti), was improved by using lignin-based carbon quantum","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-19 12:34:40","doi":"10.21203/rs.3.rs-5121593/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-10-24T01:55:21+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-23T10:28:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"150468443367982353672475990656037788478","date":"2024-10-23T03:48:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"206601801505969749313251757828107118842","date":"2024-10-13T17:36:21+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-11T04:16:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"278870236787763487608245327535064516552","date":"2024-10-07T22:26:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"123847777676237291979112660288152485250","date":"2024-10-07T03:44:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-07T03:18:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-09-21T12:35:03+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-09-21T12:34:02+00:00","index":"","fulltext":""},{"type":"submitted","content":"Research on Chemical Intermediates","date":"2024-09-20T07:34:57+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b5764d14-bba4-435c-bf99-fa674f95aaf7","owner":[],"postedDate":"November 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-16T16:04:37+00:00","versionOfRecord":{"articleIdentity":"rs-5121593","link":"https://doi.org/10.1007/s11164-024-05467-3","journal":{"identity":"research-on-chemical-intermediates","isVorOnly":false,"title":"Research on Chemical Intermediates"},"publishedOn":"2024-12-11 15:57:31","publishedOnDateReadable":"December 11th, 2024"},"versionCreatedAt":"2024-11-19 12:34:40","video":"","vorDoi":"10.1007/s11164-024-05467-3","vorDoiUrl":"https://doi.org/10.1007/s11164-024-05467-3","workflowStages":[]},"version":"v1","identity":"rs-5121593","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5121593","identity":"rs-5121593","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}