Zhengxin Ding

An Amine-Functionalized Titanium Metal–Organic Framework Photocatalyst with Visible-Light-Induced Activity for CO2 Reduction†

Let your light shine: the photocatalytic reduction of carbon dioxide to the formate anion under visible light irradiation is for the first time realized over a photoactive Ti-containing metal-organic framework, NH(2)-MIL-125(Ti), which is fabricated by a facile substitution of ligands in the UV-responsive MIL-125(Ti) material.

Metal-free activation of H2O2 by g-C3N4 under visible light irradiation for the degradation of organic pollutants

Semiconducting carbon nitride materials were successfully prepared via a thermal poly-condensation of dicyandiamide as a precursor at >500 °C. The resulting materials were investigated as metal-free catalysts for the activation of H(2)O(2) with visible light under mild conditions, using the decomposition of Rhodamine B (RhB) in aqueous solution as a model reaction. Results revealed that carbon nitride catalysts can activate H(2)O(2) to generate reactive oxy-radicals under visible light irradiation without employment of any metal additives, leading to the mineralization of the dye. Factors affecting the degradation of organic compounds are pH values and the concentration of H(2)O(2). Recycling of the catalyst indicated no obvious deactivation during the entire catalytic reaction, indicating good (photo)chemical stability of metal-free polymeric carbon nitride photocatalysts for environmental purification. This study demonstrated a promising approach for the activation of green oxidant, hydrogen peroxide, by the newly-developed polymer photocatalysts for environmental remediation and oxidation catalysis.

Cobalt Imidazolate Metal-Organic Frameworks Photosplit CO 2 under Mild Reaction Conditions**

Metal-organic frameworks (MOFs) have shown great promise for CO2 capture and storage. However, the operation of chemical redox functions of framework substances and organic CO2 -trapping entities which are spatially linked together to catalyze CO2 conversion has had much less attention. Reported herein is a cobalt-containing zeolitic imidazolate framework (Co-ZIF-9) which serves as a robust MOF cocatalyst to reduce CO2 by cooperating with a ruthenium-based photosensitizer. The catalytic turnover number of Co-ZIF-9 was about 450 within 2.5 hours under mild reaction conditions, while still keeping its original reactivity during prolonged operation.

Synthesis of transition metal-modified carbon nitride polymers for selective hydrocarbon oxidation.

Modification of graphitic carbon nitride (g-C(3)N(4)) photocatalyst with transition metals was achieved with a simple soft-chemical approach using dicyandiamide monomer and metal chloride as precursors, in combination with a thermal-induced polycondensation at 600 °C under nitrogen atmosphere. The resultant organic-inorganic hybrid materials were thoroughly characterized by a variety of techniques, including X-ray diffraction (XRD), UV/Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), N(2)-sorption, transmission electron microscopy (TEM), photoluminescence (PL), and FTIR. Benzene hydroxylation and styrene epoxidation reactions were employed to evaluate the catalytic/photocatalytic activity of the synthesized g-C(3)N(4)-based catalysts. Results showed that Fe- and Cu-modified g-C(3)N(4) were active for the hydroxylation of benzene to phenol using H(2)O(2) under mild conditions. It was also found that g-C(3)N(4) could promote the catalytic epoxidation of styrene using molecular oxygen as the primary oxidant; after modification with Co and Fe, the catalytic performance for styrene epoxidation with O(2) could be significantly improved, especially when coupled with visible-light irradiation.

N-Doped SiO2/TiO2 mesoporous nanoparticles with enhanced photocatalytic activity under visible-light irradiation

Mesoporous nanocrystalline N-doped SiO2/TiO2 visible-light photocatalysts were prepared by treating SiO2/TiO2 xerogels in a flow of nitrogen gas bubbled through concentrated ammonia solution. Structural characterization and performance analysis results revealed that the addition of SiO2 remarkably altered the phase composition, specific surface area, microstructure, as well as the photocatalytic activity of N-doped TiO2. The presence of SiO2 in N-doped TiO2 particles suppressed the formation of rutile phase and the crystal growth of N-doped TiO2 particles during thermal calcinations. When weight ratio of SiO2/TiO2 was in 0.05-0.20, the N-doped SiO2/TiO2 exhibited higher photocatalytic activity than the N-doped TiO2, and optimum ratio was found to be 0.05. The enhanced photocatalytic activity could be attributed to the higher specific area, larger pore volume, and more surface hydroxyl groups in the catalyst.

Carbon nitride for the selective oxidation of aromatic alcohols in water under visible light.

The selective oxidation of aromatic alcohols in water is achieved by using a carbon nitride (CN) catalyst, dioxygen, and visible light. The unique electronic structure of CN avoids the direct formation of hydroxyl radicals, which typically cause the total oxidation of organics. The chemical stability of CN allows several chemical protocols for photoredox catalysis in water, as exemplified by cooperative catalysis involving Brønsted acids. This leads to a new, green pathway for diverse organic transformations using sunlight and water.

Photochemical synthesis of submicron- and nano-scale Cu2O particles.

Submicron- and nano-scale cuprous oxide particles derived from copper acetate and copper gluconate complexes were synthesized via a photochemical route in polar media without further reducing agents. The morphology, composition, and phase structure of as-prepared Cu(2)O were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). Factors affecting the morphology and size of the Cu(2)O products have been examined in detail to determine the optimum parameters to achieve a controllable synthesis. The results show that solvent is the most key factor in size- and shape-control of the Cu(2)O products. Water induces the formation of submicron particles, while alcohol results in nanoscale particles. The photochemical growth of Cu(2)O particles can be fine tuned by varying the parameters of the reaction procedure, e.g. solvent, precursor ligand, and additive. The IR results indicate that these Cu(2)O particles result from the photoinduced intramolecular electron transfer between metal and ligand. The method can be easily controlled and is expected to be applicable for the preparation of cuprous oxide supported catalysts.

Photocatalytic Oxidation of CO on TiO2: Chemisorption of O2, CO, and H2

On the surface: Adsorption of O(2) at the surface oxygen vacancy (SOV) sites of TiO(2) reconstructs the lattice oxygen (healing SOVs), resulting in a decrease of the photocatalytic activity of oxidizing CO over vacuum-pretreated TiO(2) with increasing temperature (see scheme). Adsorption of H(2) produces new SOVs at the TiO(2) surface and stabilizes the photocatalytic activity. Photocatalytic oxidation of CO over vacuum-pretreated TiO(2) is performed in a series of systems with the introduction of O(2), CO, and H(2) in different orders. The photocatalytic oxidation of CO is dependent on the order of introduction of O(2), CO, or H(2), and introducing O(2) prior to CO promotes the oxidation of CO. Moreover, an increase of reaction temperature suppresses the oxidation of CO, but the preintroduction of H(2) reduces this suppression effect. The results of the chemisorption of O(2), CO, and H(2) at the TiO(2) surface reveal that the adsorbed O(2) heals the surface oxygen vacancy (SOV) sites of TiO(2), while the adsorbed CO and H(2) promote the formation of new SOVs. It is proposed that changes in the amounts of adsorbed O(2) and SOVs are mainly responsible for the differences of CO conversion in different systems.

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS, PL, and EPR

The electronic structure and photoactivation process in N-doped TiO(2) is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat- and photoinduced N-doped TiO(2) catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti(3+) states are formed to enhance the optical absorption in the visible-light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N-doped TiO(2), the DRS absorption and PL emission in the visible spectral region of 450-700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N(s)·, oxygen vacancies with one electron (V(o)·), and Ti(3+) ions are produced with light irradiation and the intensity of N(s)· species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO(2) corresponding to the main absorption band at 410 nm of N-doped TiO(2), but oxygen vacancies and Ti(3+) states as defects contribute to the visible-light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N-doped TiO(2) is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen-vacancy-related defects leads to quenching of paramagnetic N(s)· species but they stabilize the active nitrogen species N(s)(-).

A general templated method to homogeneous and composition-tunable hybrid TiO2 nanocomposite fibers

Sequential impregnations of metal ions and titanium tetraisopropoxide (TTIP) into activated carbon fibers (ACF) followed by a solvothermal treatment has been found to be a general method in the preparations of homogeneous and composition-tunable hybrid TiO(2) hierarchical nanocomposite fibers like WO(3)/TiO(2), Fe(2)O(3)/TiO(2) and SnO(2)/TiO(2).