Yttrium and aluminum co-doped ZnO were successfully synthesized by the sol-gel method, showing high photocatalytic activity for hydrogen production (5.71 mmol h À1 g À1 ) in the water-lactic acid system under visible-light irradiation for the first time, exhibiting excellent stability and recyclability.As a kind of unique metal oxide, 1,2 because of its excellent optical and electrical properties, zinc oxide (ZnO) is a potential candidate for a variety of practical applications including semiconductors, eld-effect transistors, luminescence, solar cells, gas sensors, photodetectors, UV-blocking and other aspects. [3][4][5][6][7] Besides, ZnO has become a promising photocatalyst, owing to its lower cost, exible preparation method, non-toxicity, high photosensitivity, chemical and thermal stability. 8-12 Thus, more and more scientists are attracted to the intensive research on the photocatalytic H 2 production with ZnO recently. 13,14 While ZnO has a wide band gap of 3.2 eV and responds only to the UV part of the solar spectrum. 15,16 As a result, it is very desirable to enhance the photoactivity of ZnO and extend its light absorption capability into the visible region. 17,18 It is well known that semiconductor coupling, dye sensitization, and metal, non-metal or co-doping have been applied to develop visible light sensitive ZnO. 5,19,20 Among them, many reports on doping of ZnO with metals such as copper (Cu), 21 indium (In) 22 and lanthanum (La) 23 are available, resulting in the modication of their band gap, but there are relatively few using ZnO doped with aluminium (Al), 24 yttrium (Y) 25 or codoped ZnO. Noticeably, Al and Y have been found to be very efficient for visible light induced photocatalysis because they can decrease the energy band gap, promoting the surface segregation and the surface enrichment, and improving the photocatalytic performance. 25,26 Various methods such as the hydrothermal process, sol-gel method and co-precipitation method have been reported for the synthesis of undoped or doped ZnO nanoparticles (NPs). 27 In these approaches, sol-gel is the most effective and facile method to prepare the NPs. 23,28 However, to the best of our knowledge, Al and Y co-doped ZnO has never been synthesized by sol-gel and used for the eld of photocatalytic hydrogen production. Based on our previous research, 29-31 we report a modied sol-gel method to fabricate ZnO NPs embedded by Al and Y, driven by vacuum annealing (see Experimental details in the ESI †). The resulting ZnO NPs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), UV-vis and photoluminescence (PL) spectroscopies. Futhermore, their photocatalytic activities are investigated under visible light irradiation.The purity and crystallinity of the as-synthesized samples were investigated by XRD, and the results are displayed in Fig. 1a and b. Fig. 1a shows the XRD patterns of aluminumdoped zinc oxide (AZO) NPs with different Y doping ratios. All diffraction peaks were in good agreemen...