CO₂-甲苯光催化转化制高值化学品是实现CO₂与甲苯协同转化，提高CO₂光催化转化效率的有效途径之一。CO₂-甲苯光催化反应体系仍面临催化剂可见光利用率、光生载流子复合效率和苯甲醛产量及选择性较低的技术瓶颈。因此，本文提出ZnTi-LDH和ZnTi-LDH/g-C₃N₄构筑及光催化O₂/CO₂氧化甲苯新策略，首先采用尿素水热法，通过Zn²⁺/Ti⁴⁺比例调变，探讨了ZnTi-LDH形貌特征和光电化学性能调控机制，并明晰了ZnTi-LDH组成和O₂/CO₂比例变化对光催化甲苯氧化性能的影响，阐明了该反应体系的反应机理；为进一步提升ZnTi-LDH光催化性能，采用静电自组装法，制备了一系列形貌结构不同的ZnTi-LDH/g-C₃N₄催化剂，探讨了复合比例和g-C₃N₄形貌对ZnTi-LDH/g-C₃N₄催化剂结构和催化性能的影响规律，揭示了该复合光催化剂高选择性催化氧化甲苯的反应机理。主要研究结果如下：

（1）采用尿素水热法合成了Zn²⁺/Ti⁴⁺比例不同的系列ZnTi-LDH，采用XRD、FT-IR、SEM、XPS等分析手段，研究了Zn²⁺/Ti⁴⁺比例变化对ZnTi-LDH形貌结构、光电性质的影响规律；在光催化加压反应釜装置上，于50℃、1 MPa，300 W氙灯光照射反应12 h条件下，探究了ZnTi-LDH组成变化对光催化CO₂氧化甲苯反应性能的影响规律。结果表明，Zn²⁺/Ti⁴⁺比例为3:1的ZnTi-LDH（ZT-3/1）具有较高的比表面积、适宜的孔隙结构和丰富的羟基基团，并且其光催化活性最高，光催化反应产物CO和苯甲醛产量分别为32.92和261.32 μmol·g^-1·h^-1，选择性分别达到89%和49%。

（2）在光催化加压反应釜装置上，于50℃、1 MPa，300 W氙灯光照射反应12 h条件下，以ZT-3/1为光催化剂，研究了O₂/CO₂比例变化对甲苯氧化反应性能的影响规律，同时探讨了催化剂的循环反应活性和稳定性。结果表明，当O₂:CO₂=2:8时，CO和苯甲醛的产量最高分别达到121.37和947.89 μmol·g^-1·h^-1，选择性分别提高到96%和60%，相比CO₂-甲苯反应分别提升了7%和11%。O₂/CO₂-甲苯反应的总产量达到1716.57 μmol·g^-1·h^-1，是CO₂-甲苯反应的3.02倍。该催化剂在5次循环测试中表现出良好的可重复使用性。连续反应12小时后，该催化剂的甲苯氧化产物的总产量呈增加趋势，但苯甲醛的选择性有所降低。

（3）采用自由基猝灭实验、同位素标记实验、EPR、GC-MS、原位红外等手段探究了光催化O₂/CO₂-甲苯反应机理。结果表明，甲苯首先与光生空穴作用生成苄基自由基；苄基自由基与不同活性物种（·O₂^-和·OH）反应，依次生成苄基过氧化物和苯甲醇；苄基过氧化物和苯甲醇分别通过脱水反应和h⁺及·OH反应生成目标产物苯甲醛,这两条反应路径协同作用保障了苯甲醛的高效生成。O₂和CO₂的协同作用拓展了自由基反应的路径、提高了载流子利用效率，从而显著提升了光催化转化效率。

（4）采用静电自组装法制备了一系列的ZnTi-LDH/g-C₃N₄复合光催化剂，采用XRD、FT-IR、SEM、UV-Vis等分析手段，研究了g-C₃N₄形貌变化对ZnTi-LDH/g-C₃N₄形貌结构、光电化学性能的影响规律。在光催化加压反应釜装置上，于50℃、1 MPa，300 W氙灯光照射反应12 h条件下，探究了ZnTi-LDH/g-C₃N₄组成变化和形貌变化对光催化甲苯氧化性能的影响规律。结果表明，ZT-3/1与纳米管状g-C₃N₄（G-CN）以3:1的质量比复合形成ZT/G-CN，其光催化O₂/CO₂-甲苯反应性能最佳，CO和苯甲醛的产量分别达到141.72和1088.09 μmol·g^-1·h^-1，其选择性分别为96%和64%。相比ZT-3/1，苯甲醛的选择性提高了4%。

The photocatalytic transformation of CO₂ and toluene into high-value chemicals represents one of the effective strategies for enhancing the efficiency of CO₂ utilization via tandem conversion. However, the current CO₂-toluene photocatalytic system still faces several critical challenges, including low visible-light utilization efficiency, severe recombination of photogenerated charge carriers, and limited yield and selectivity of benzaldehyde. To address these issues, this study proposes a novel photocatalytic strategy involving the construction of ZnTi-LDH and ZnTi-LDH/g-C₃N₄ composite catalysts for O₂/CO₂-assisted selective oxidation of toluene. Initially, ZnTi-LDH were synthesized via a urea-assisted hydrothermal method, and the influence of Zn²⁺/Ti⁴⁺ ratios on the morphology and photoelectrochemical properties of ZnTi-LDH was systematically investigated. The effects of catalyst composition and the O₂/CO₂ ratio on the photocatalytic oxidation of toluene were also studied to elucidate the underlying reaction mechanism. To further enhance photocatalytic performance, a series of ZnTi-LDH/g-C₃N₄ composites with varied morphologies and compositions were prepared via electrostatic self-assembly. The impact of composite ratios and the structural characteristics of g-C₃N₄ on the catalyst properties and photocatalytic behavior was analyzed. The results provide insights into the mechanism of highly selective photocatalytic oxidation of toluene over ZnTi-LDH/g-C₃N₄, offering a promising strategy for efficient CO₂ valorization. The main research findings are summarized as follows:

A series of ZnTi-LDH with varying Zn²⁺/Ti⁴⁺ ratios were synthesized via the urea hydrothermal method. The influence of the Zn²⁺/Ti⁴⁺ ratio on the morphology, structure, and photoelectric properties of ZnTi-LDH was systematically investigated using XRD, FT-IR, SEM, and XPS. The photocatalytic performance of ZnTi-LDH in the oxidation of toluene under CO₂ conditions was evaluated in a photocatalytic pressurized reactor at 50℃, 1 MPa, and under 300 W xenon lamp irradiation for 12 hours. The results demonstrated that ZnTi-LDH with a Zn²⁺/Ti⁴⁺ ratio of 3:1 (denoted as ZT-3/1) exhibited a high specific surface area, an appropriate pore structure, and abundant hydroxyl groups, leading to the highest photocatalytic activity. The yields of CO and benzaldehyde were 32.92 μmol·g^-1·h^-1 and 261.32 μmol·g^-1·h^-1, respectively, with selectivities of 89% and 49%, respectively.

(2) This study investigated the effect of varying O₂/CO₂ ratios on the photocatalytic oxidation performance of toluene using ZT-3/1 as a catalyst in a pressurized reactor under the conditions of 50℃, 1 MPa, and 300 W xenon lamp irradiation for 12 hours. Additionally, the cyclic reactivity and stability of the catalyst were evaluated. The results show that when O₂:CO₂=2:8, the yields of CO and benzaldehyde reach up to 121.37 and 947.89 μmol·g^-1·h^-1 respectively, and the selectivity increases to 96% and 60% respectively. Compared with the CO₂-toluene reaction, they increase by 7% and 11% respectively. The total yield of the O₂/CO₂-toluene reaction reached 1716.57 μmol·g^-1·h^-1, which was 3.02 times higher than that of the CO₂-toluene reaction. The catalyst exhibited excellent reusability over five cycles of testing. After 12 hours of continuous reaction, the total production of toluene oxidation products increased, but the selectivity of benzaldehyde decreased.

(3) The mechanism of the photocatalytic O₂/CO₂-toluene reaction was explored through free radical quenching experiments, isotope labeling experiments, EPR analysis, GC-MS detection, and in-situ infrared spectroscopy. The results revealed that toluene initially reacts with photogenerated holes to form benzyl radicals. These benzyl radicals subsequently react with different active species (·O₂^- and ·OH) to produce benzyl peroxides and benzyl alcohol, respectively. Benzyl peroxides and benzyl alcohol generate benzaldehyde through dehydration reactions and h⁺/·OH reactions, respectively. The synergistic effect of these two reaction pathways ensures the efficient formation of benzaldehyde. The cooperative action of O₂ and CO₂ expands the pathways of free radical reactions and enhances carrier utilization efficiency, thereby significantly improving photocatalytic conversion efficiency.

(4) A series of ZnTi-LDH/g-C₃N₄ composite photocatalysts were prepared using the electrostatic self-assembly method. The effects of g-C₃N₄ morphology changes on the morphology, structure, and photoelectrochemical properties of ZnTi-LDH/g-C₃N₄ composites were comprehensively analyzed using XRD, FT-IR, SEM, and UV-Vis spectroscopy. The effects of the composition and morphology of ZnTi-LDH/g-C₃N₄ on the oxidative performance of toluene were evaluated in a photocatalytic pressurized reactor under conditions of 50°C, 1 MPa, and 300 W xenon lamp irradiation for 12 hours. The results show that the combination of ZT-3/1 and nanotubular g-C₃N₄ (G-CN) in a mass ratio of 3:1 to form ZT/G-CN exhibits superior photocatalytic performance for the O₂/CO₂-toluene reaction. The production rates of CO and benzaldehyde were 141.72 and 1088.09 μmol·g^-1·h^-1, respectively, with selectivities of 96% and 64%, respectively. Compared to ZT-3/1, the selectivity of benzaldehyde increased by 4%.