Nickel-Doped Decatungstate as a Robust Photocatalyst for Violet Light-Triggered Redox Coupling Conversion of Alcohol and Water to Aldehyde/Ketone and Hydrogen.

The effective coupling of photoinduced alcohol oxidation and water reduction may economically produce hydrogen (H2) from water, which is of great significance in solving the current energy crisis. This study discloses that decatungstate (DT) and especially Ni2+ions-doped DTs are active for the photoreaction of benzyl alcohol with H2O, and under 48 h of violet light illumination, the best 1%Ni-DT yields ca. 86.1% benzoic acid and a 4.65 h-1 H2 generation efficiency (turnover frequency, TOF). Also, 1%Ni-DT is efficient for the photoredox coupling reaction of aliphatic and especially aromatic primary/secondary alcohols with water. A series of characterizations support that the doubled-reduced H2DT produced from the photoreaction plays a key role in water reduction to H2, which is accelerated by the doped Ni2+. In particular, it and the derived Ni3+ may construct a Z-type catalyst for water overall splitting, thereby hoisting the acid yield and H2 amount in the later stage of the photoreaction.

Highly efficient and tunable visible-light-catalytic synthesis of 2,5-diformylfuran using HBr and molecular oxygen.

This paper discloses that inexpensive hydrobromic acid (HBr) is active and highly selective to the photo-oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) with dioxygen (O2) or even with water under visible light illumination, which can achieve the highest 89.1% DFF yield in DMSO at 80 °C under pure O2 atmosphere. More importantly, under bifunctional acid-photooxidation catalysis of HBr, fructose can be directly converted to DFF and its two-step cascade conversion in DMSO provides a far higher DFF yield (80.2%) than the one-step cascade conversion in MeCN (42.1%). The results of HMF photooxidation catalyzed by hydrohalic acids, free radical quenching tests and EPR spectrum support that the Br atom and superoxide (O2 -˙) anion radicals generated by HBr photolysis in O2 are active species for the oxidation of HMF to DFF and their activities are adjusted by the reaction medium. This photo-synthetic protocol is very simple and practical, especially with low operating costs, showing a good industrial application prospect.

Hybridizing Engineering Strategy of Decatungstate. 2. Regulated Effect of Doping Transition Metal Ions on Photocatalytic Oxidation Performance of (nBu4N)4W10O32.

This paper discloses a simple and productive hybridizing engineering (HE) strategy for the 3d transition-metal-ion (Mn+ = Fe3+, Fe2+, Co2+, Ni2+)-doped (nBu4N)4W10O32 (Mn+-TBADT) compounds as highly efficient visible-light catalysts. Ultraviolet visible (UV-vis), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectra, and cyclic voltammetry (CV) characterizations indicate that the synthetic quality, redox capacity, and visible light harvesting efficiency of TBADT, especially the separation efficiency of its photogenerated electron-hole pairs, are regulated by the metal ion dopants and gradually improved with a change of the dopant from Fe3+, Fe2+, and Co2+ to Ni2+, along with a continuous and significant enhancement of its photocatalytic efficiency in the visible-light-triggered selective oxidation of ethylbenzene with dioxygens in acetonitrile. The best 0.5 mol % Ni2+-doped TBADT can achieve a ca. 55% conversion under optimal reaction conditions and also exhibits much higher photocatalytic activity for the photo-oxidation of toluene, cyclohexane, and benzyl alcohol compared to pure TBADT. This HE strategy showcases great potential in improving the photocatalysis performance of TBADT.

Visible-Light-Triggered Quantitative Oxidation of 9,10-Dihydroanthracene to Anthraquinone by O2 under Mild Conditions.

The development of mild and efficient processes for the selective oxygenation of organic compounds by molecular oxygen (O2 ) is key for the synthesis of oxygenates. This paper discloses an atom-efficient synthesis protocol for the photo-oxygenation of 9,10-dihydroanthracene (DHA) by O2 to anthraquinone (AQ), which could achieve quantitative AQ yield (100 %) without any extra catalysts or additives under ambient temperature and pressure. A yield of 86.4 % AQ was obtained even in an air atmosphere. Furthermore, this protocol showed good compatibility for the photo-oxidation of several other compounds with similar structures to DHA. From a series of control experiments, free-radical quenching, and electron paramagnetic resonance spin-trapping results, the photo-oxygenation of DHA was probably initiated by its photoexcited state DHA*, and the latter could activate O2 to a superoxide anion radical (O2 .- ) through the transfer of its electron. Subsequently, this photo-oxidation was gradually dominated by the oxygenated product AQ as an active photocatalyst obtained from the oxidation of DHA by O2 .- , and was accelerated with the rapid accumulation of AQ. The present photo-oxidation protocol is a good example of selective oxygenation based on the photoexcited substrate self-activated O2 , which complies well with green chemistry ideals.

A novel green process for tannic acid hydrolysis using an internally sulfonated hollow polystyrene sphere as catalyst.

A polystyrene-hollow sphere catalyst was prepared by treating polystyrene-encapsulated calcium carbonate particles with concentrated hydrochloric acid. This catalyst was characterized using TGA, FT-IR, optical microscope, SEM-EDX and XPS. Evidences from SEM-EDX and XPS analyses indicated that the sulfonate groups were on the inner surface of the polystyrene hollow sphere. The polystyrene hollow spheres were used as catalyst in the hydrolysis of tannic acid. Reaction conditions including the reaction temperature and time, loading of catalyst, ratio of tannic acid to H2O and number of recycles were optimized. A high yield of gallic acid was obtained as the reaction performed under the following conditions: a temperature of 80 °C, a molar ratio of tannic acid to H2O of 1 : 3, and a catalyst loading of 7% w/w (based on the mass of tannic acid). This catalyst showed excellent catalytic performance, easy separation, high stability and good reusability. This work provides a new strategy for the controllable synthesis of polystyrene hollow structures with sulfonic groups on the inner surface and an excellent and prospective catalyst for the production of gallic acid through hydrolysis of tannic acid.