To get the optimization of reaction conditions, we used N-methylaniline (1a) as a model substrate to explore photocatalytic selective N-methylation of amines using carbon dioxide (Table ). Rare product can be obtained in the absence of catalyst or in the presence of catalyst but in a dark atmosphere (entry 1, 10, 13). Interestingly, commercial TiO2 gives a half conversion under the identical conditions (in CH3CN at 450nm and 12 h, entry 12), which unambiguously indicates that photocatalytic is suitable for for this process but TiO2 behave as the best catalytic activity in UV region. Besides, trace product is surprisingly detectable in other solvents with commonly used methylation, such as DMF and dioxane (entry 7-8). It is delighted to find that the enough NaBH4 is excellent for high selective formation of N, N-dimethyl aniline (3a) (entry 1, 14). It is noteworthy that the temperature of the reaction system increased on light irradiation because of the photothermal effect. In sharp contrast experiments show that less 3a formation in thermocatalytic system was observed with the 30  yield of 3a and 10  yield of 2a at refluxed temperature 80 C (entry 15), indicating that the N-methylation of amines using carbon dioxide is not driven by heat. The NH2-MIL-125 (Ti), obtained by a simple solvothermal reaction, was synthesized following our previous reported procedure. In brief, 2-aminoterephthalic acid (H2ATA) (2.178 g, 12 mmol), 18 mL of N,Ndimethyformamide (DMF) and 2 mL of MeOH wwere added to a Teflon liner with a magneton, and Ti(OC4H9)4 (1 ml, 3 mmol) was added drop by drop. Then, the above mixture was stirred for 30 min, and magneton was removed.