Photocatalysts composed of graphitic carbon nitride (g-CN) and TiO₂ were efficiently prepared by thermolysis of the MIL-125(Ti) metal organic framework deposited on g-CN. The heterojunction between the 12 nm-sized TiO₂ nanoparticles and g-CN was well established and the highest photocatalytic activity was observed for the g-CN/TiO₂ (3:1) material. The g-CN/TiO₂ (3:1) composite exhibits high visible light performances both for the degradation of pollutants like the Orange II dye or tetracycline but also for the production of hydrogen (hydrogen evolution rate (HER) up to 1330 μmolh⁻¹g⁻¹ and apparent quantum yield of 0.22% using NiS as a cocatalyst). The improved visible light performances originate from the high specific surface area of the photocatalyst (86 m²g⁻¹) and from the efficient charge carriers separation as demonstrated by photoluminescence, photocurrent measurements, and electrochemical impedance spectroscopy. The synthetic process developed in this work is based on the thermal decomposition of metal organic framework deposited on a graphitic material and holds huge promise for the preparation of porous heterostructured photocatalysts.

In this work, novel heterostructured photocatalysts associating graphitic carbon nitride (g-CN) and SmFeO ₃ were prepared via a mixing-ultrasonication process. Structural, optical and morphological characterizations demonstrate that the interfacial junction between g-CN and SmFeO ₃ is well established for all g-CN/SmFeO ₃ composites prepared with g-CN:SmFeO ₃ weight ratio of 20:80, 50:50 and 80:20. The g-CN/SmFeO ₃ (80:20) composite exhibits the highest photocatalytic activity for the degradation of pollutants like the Orange II dye and the tetracycline hydrochloride antibiotic under visible light irradiation. This high photocatalytic activity originates from the enhanced light absorption over the whole visible region compared to pure g-CN and from the improved separation and transfer of photogenerated electron/hole pairs as demonstrated by photoluminescence and photocurrent measurements. A Z-scheme charge carrier transfer mechanism was demonstrated for the photocatalytic reactions. The g-CN/SmFeO ₃ (80:20) catalyst was also demonstrated to be stable and can be reused up to six times without significant alteration of the activity.

I–III–VI₂ group quantum dots (QDs) have attracted high attention in photoelectronic conversion applications, especially for QD-sensitized solar cells (QDSSCs). This group of QDs has become the mainstream light-harvesting material in QDSSCs due to the ability to tune their electronic properties through size, shape, and composition and the ability to assemble the nanocrystals on the surface of TiO₂. Moreover, these nanocrystals can be produced relatively easily via cost-effective solution-based synthetic methods and are composed of low-toxicity elements, which favors their integration into the market. This review describes the methods developed to prepare I-III-VI₂ QDs (AgInS₂ and CuInS₂ were excluded) and control their optoelectronic properties to favor their integration into QDSSCs. Strategies developed to broaden the optoelectronic response and decrease the surface-defect states of QDs in order to promote the fast electron injection from QDs into TiO₂ and achieve highly efficient QDSSCs will be described. Results show that heterostructures obtained after the sensitization of TiO₂ with I-III-VI₂ QDs could outperform those of other QDSSCs. The highest power-conversion efficiency (15.2%) was obtained for quinary Cu-In-Zn-Se-S QDs, along with a short-circuit density (J_SC) of 26.30 mA·cm⁻², an open-circuit voltage (V_OC) of 802 mV and a fill factor (FF) of 71%.

Ternary ZnS/ZnO/graphitic carbon nitride (gCN) photocatalysts were prepared by coupling gCN sheets with ZnO nanorods under solvothermal conditions followed by sulfurization using Na₂S. SEM and TEM analyses show that small-sized ZnS particles (ca. 7.2 nm) deposit homogeneously on the surface of ZnO/gCN nanohybrids. Photoluminescence and electrochemical impedance spectroscopy show that ZnS allows for an enhanced charge separation efficiency as well as prolonged lifetime of photogenerated charge carriers, leading to improved hydrogen photoproduction under UV light irradiation compared to ZnO/gCN. Moreover, the deposition of ZnS nanoparticles improves the photostability of the ZnS/ZnO/gCN catalyst for hydrogen production. A double Z-scheme mechanism is proposed for hydrogen photoproduction using the ZnS/ZnO/gCN heterojunction.